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Three-dimensional conductive network formed by carbon nanotubes in aqueous processed NMC electrode
Abstract
Aqueous processing of lithium nickel manganese cobalt oxide (LiNi0.5Mn0.3Co0.2O2, NMC 532) cathodes was investigated by incorporating carbon nanotubes (CNTs) as the conductive additive. Morphology observation showed CNTs evenly disperse across the electrode, uniformly covering each primary particle, and form three-dimensional electronic pathways. A resistance measurement indicated the CNTs can improve the electronic conductivity of the composite electrode by an order of magnitude compared to carbon black. CNTs based electrodes showed higher rate performance, lower hysteresis, and better cycling performance with 99.4% capacity retention after 200 cycles in full pouch cells compared to 94.6% for carbon black based electrode. Meanwhile, the content of active materials in the electrode was increased from 90 wt% to 96 wt% and the energy density was increased by 11.7%. This research demonstrates an effective combined approach for achieving aqueous processed cathodes with enhanced durability while simultaneously achieving higher energy density by reducing the content of inactive components.
... Also, the conductive layer offers diffusion channels, which enable rapid Li + ion diffusion, resulting in accelerated and facilitated transport of Li + ions. 22,24,25 However, these coatings are less effective in maintaining the structure of cathode materials. An intelligent solution for improving all of the properties at once could be the use of a combination of two coating materials, in which one component improves the structural stability and the other one boosts the ion/electrical conductivity. ...
... 42 Higher discharge capacity of the rGO−ZrO 2 -coated cathode in the first cycle can be due to an increase in the electronic conductivity between NCM811 particles and reduction in electrode resistance and also accelerated and facilitated transport of Li + ion through diffusion channels provided by the rGO sheets. 22,24,25 After 100 cycles, the ZrO 2 -coated cathode shows discharge capacities of 142.1 and 137.3 mA h g −1 , which are significantly higher than 124.3 and 105.2 mA h g −1 of the pristine sample at 25 and 55°C and 1C. This can be explained by the reduction in the contact surface of the cathode by the ZrO 2 coating, which prevents unwanted side reactions and cathode degradation. ...
... 42,43 Among all of the samples, the rGO−ZrO 2coated sample delivers the highest discharge capacity (171.8 and 172.3 mA h g −1 ), which can be explained by the barrier effect of ZrO 2 NPs that prevents the performance degradation during cycling and the effect of rGO sheets in increasing the electronic conductivity and Li + ion diffusion. 24,25,42,43 As shown in Table S1, Columbic efficiency (CE) values, a measure of the reversibility of electrochemical reaction, are as follows: CE rGO-ZrO 2 -coated > CE ZrO 2 -coated > CE pristine . In an ideal cell with no side reactions on the electrodes, the flow of Li + or electrons should be entirely from reversible electrochemical reactions and the CE is equal to 100%. ...
LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) has been considered as a promising cathode for Li-ion batteries (LIBs) due to its high electrochemical capacity and low cost; however, poor cycling stability is one of the main restricting factors in industrial applications of the NCM811 cathode material. Notably, the capacity fading and low structural stability of NCM811 are intensified at elevated temperatures. ZrO 2-and composite rGO−ZrO 2-coated NCM811 were fabricated by a facile wet chemical method and evaluated at 25 and 55°C to overcome these impediments. The ZrO 2 coating provides superior cycling and thermal stability and perfectly protects the cathode active material from deleterious side reactions, and HF attacks by suppressing the direct contact of NCM811 particles and electrolytes. Despite these advantages, the discharge capacity of the ZrO 2-coated cathode material (166.3, 187.7 mAh g −1) is slightly lower than that of the pristine cathode (171.7, 193.0 mAh g −1) due to the insulative nature of ZrO 2 NPs, after one cycle at ambient and elevated temperatures. The first cycle discharge capacity increased to 185.9 and 206.7 mAh g −1 at 25 and 55°C, respectively, with the rGO−ZrO 2-coated cathode material. The capacity retention reached 92.4 and 83.3%, showing high capacities of 171.8 and 172.3 mAh g −1 at 1C after 100 cycles at 25 and 55°C , whereas the pristine cathode material exhibited low retention values of 72.4 and 54.5% with discharge capacities of 124.3 and 105.2 mAh g −1 under the same conditions, respectively. The incorporation of rGO into the coating can make up for the ZrO 2 coating imperfection and, at the same time, can enhance the ion/electron conductivity of the electrode by providing a conductive network on the surface of the cathode material. In light of the fact that ZrO 2-and composite rGO−ZrO 2-coated NCM811 cathode materials exhibit superior performance; they can pave the way for industrial applications of high-energy-density lithium-ion batteries.
... The D-band corresponds to a hybridized vibrational mode associated with grain edges, indicating a disorder in the structure. The G-band is related to an in-plane vibrational mode of bond stretching between two atoms in a graphene unit cell [47]. However, no band peaks were observed for the bare LMP electrode. ...
... A higher capacity of ~6.2 mAh cm − 2 was obtained for the CNT-LMP electrode compared to ~5.6 mAh cm − 2 for the bare LMP electrode, even though the bare and CNT-LMP electrodes have theoretical capacities of 7.0 mAh cm − 2 and 6.5 mAh cm − 2 , respectively. This improvement can be attributed to the increased electronic contact between the individual LMP particles because of the addition of the CNT conductive agent, whose role has already been demonstrated in forming a three-dimensional (3D) conductive network within the composite electrode [47]. The cells were disassembled, and a post-mortem SEM analysis was carried out to confirm the enhanced practical capacity of the CNT-LMP electrode. ...
Enlarging the surface area in the Li metal electrode is practically attractive for increasing long-term cycle life. In this regard, Li metal powders (LMPs) have a larger surface area, which is very beneficial for controlling dendrites and fast charging compared to planar Li metal foil. However, there is the need to increase nucleation sites in LMP electrodes for faster charging and suppress unavoidable dead Li formation caused by an electrical disconnection between individual LMPs and current collector for their commercial application. Herein, we present a 40 μm-thick, carbon nanotube-embedded LMP (CNT-LMP) electrode. The CNTs improve the LMP inter-particle contact and the contact with the Cu current collector and provide additional Li nucleation sites. As a result, the Li/Li symmetric cell with the CNT-LMP electrode exhibited a stable cycling and a longer cycle life (over 1000 h) than the bare LMP electrode (680 h). Furthermore, a full cell of LiNi0.6Mn0.2Co0.2O2/CNT-LMP could achieve a longer and more stable cycle performance of up to 600 cycles under practical current conditions (0.5 C/2 C, Charge/Discharge). In comparison, the bare cell without CNT decayed suddenly after 300 cycles.
... Compared to 0D carbon black, 1D carbon nanotubes (CNTs) can provide conductivity by forming a 3D network. Such a network can increase the conductivity by one order of magnitude compared to normal carbon black electrodes [17]. In addition, higher conductivity is not the only benefit from such a 3D network as the formed structure also provides mechanical reinforcement. ...
... To enhance the performance of NMC622 electrodes, replacement of conventional conducting carbon black by SWCNT with excellent conductivity and (electro)chemical stability is investigated [17]. Conventional carbon black and SWCNTs conductive additives have different morphologies, which is expected to affect the electrode structure. ...
Enhancing lithium-ion batteries (LiBs) cycle life is essential from both economic and sustainability perspective. In addition, to make their application in electric vehicles (EVs) even more feasible, the energy and power density have to be enhanced as well. Improvement in the electrical conductivity of battery electrodes can lead to an augmentation in power density and this can be achieved by using highly conductive carbon nanomaterials in the electrode fabrication. On the other hand, cycle life of LiBs is affected by dilation of both positive and negative electrodes during lithium ion (de)-insertion, and this can be also tailored by electrode design. In this work, ozonated long single walled carbon nanotubes (SWCNTs) are utilized to improve electrical conductivity of a LiNi0.6Mn0.2Co0.2O2 (NMC622) positive electrode along with enhancement of the mechanical strength. The enhancement effect of the ozone-treated SWCNTs on the NMC622 positive electrodes is demonstrated by means of electrochemical impedance spectroscopy and in-situ dilatometry. Compared to a conventional conductive carbon containing electrode, the presence of SWCNTs in an NMC622 electrode decreases irreversible height change occurring during a formation cycle from 276 nm to 86 nm and decreases overall electrode height change ∼5.5 times. Furthermore, coulombic and energy efficiencies of the Ozonated SWCNT NMC622 electrodes are improved by 1.2 % and 6.4 %, respectively, compared to the reference NMC622 electrode after 250 cycles in a three-electrode assembly, showing great potential for SWCNTs to be used in LiBs. Hence, addition of optimized amount of modified SWCNTs is capable of enhancing both power density and cycling stability of LiBs simultaneously.
... The effective carbon content that can contribute to enhance the electrochemical behavior of the sample mainly depends on the graphitized carbon or the crystallized content of carbon within the active sample. 26,27 The crystallized carbon contents of all the samples have been calculated using the integral area within the D and G bands of Raman spectra using the relation crystalline carbon content (in %) = A(G)/(A(G) + A(D)), where A(D) and A(G) are the integral areas within the D and G bands, respectively [ Figure 1(ii)(a−e)]. The calculated crystalline percentages of carbon for all the samples are tabulated in Table S2. ...
... A welldispersed conductive additive and an effective carbon content are highly important to proliferate the electronic conductivity. 26 LFTS/C@5MWCNT exhibits a higher graphitized carbon content than the other samples, which significantly improved the electrochemical activity of the sample. However, Energy & Fuels pubs.acs.org/EF ...
... [1][2][3][4] Many researchers have been concentrated on improving material natures to inherently enhance the performance of lithium ion batteries. For instance, researchers have attempted to introduce new components such as nanophase carbon [5][6][7][8] and silicon [9][10][11][12] to cathode and anode materials, respectively, for improving electrical and physical properties, which resulted in the enhancement of electrochemical performance. Some researchers have chosen to modify electrode material via physical and chemical methods, such as quenching or doping LiFePO 4 cathode, [13][14][15] treating xLi 2 MnO 3 •(1-x)Li(NiMnCo)O 2 cathode with ammonia, 16,17 and varying the atomic composition of Li(NiMnCo)O 2 , [18][19][20] to accomplish high electrochemical performance. ...
... The crystal aligned LiNi 0.5 Mn 0.3 Co 0.2 O 2 electrode was experimentally confirmed to record superior capability of lithium ion transport to a pristine LiNi 0.5 Mn 0.3 Co 0.2 O 2 electrode. Because the kinetics of lithium ion transport in LiNi x Mn y Co 1-(x+y) O 2 intrinsically occurs along the (00 l) plane direction, the aligned LiNi 0. 5 20 mmol) were added to deionized water and precipitated by using NaOH. The precipitate was recovered and dried in a vacuum oven at 120°C overnight. ...
The crystal alignment technology of lithium nickel manganese oxide (LiNi0.5Mn0.3Co0.2O2) is proposed using its magnetic properties. The crystalline LiNi0.5Mn0.3Co0.2O2 exhibits the paramagnetic behavior at room temperature as well as the magnetic anisotropy originated from its crystallographic anisotropy. If the crystalline LiNi0.5Mn0.3Co0.2O2 is exposed to a magnetic field, it can tend to rotate to an angle minimizing its system energy due to spontaneous magnetization. Taking these magnetic natures into account, the vector quantity of an external magnetic field (i.e., magnetic flux density and field direction) is adjusted to apply to a viscous LiNi0.5Mn0.3Co0.2O2 slurry coated onto a current collector; thus, the crystal aligned LiNi0.5Mn0.3Co0.2O2 electrode is obtained, in which the (00 l) plane is notably oriented perpendicular to the surface of a current collector. The aligned LiNi0.5Mn0.3Co0.2O2 electrode consistently records superior electrochemical performance to a pristine LiNi0.5Mn0.3Co0.2O2 electrode because the former demonstrates an improved capability of lithium ion transport during the charge/discharge process in a lithium ion battery. The aligned LiNi0.5Mn0.3Co0.2O2 is considered to have the improved transport capability because the kinetics of lithium ion transport in LiNixMnyCo1-(x+y)O2 intrinsically occurs along the (00 l) plane. © 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.
... Many different carbon materials have been used as conductive additives in the cathode, such as Ketjen black [21], Super P (SP) [22], onion-like carbon [8,23], carbon nanotubes (CNTs) [11,24], vaporgrown carbon fiber [22], and graphene [10,25,26]. Carbon blacks, like SP, are zero-dimensional (0D) particles that are extensively used due to their high conductivity and low cost. ...
... The presence of a considerable amount of CeC in CNHs is one of the reasons for the strong D-band [36]. The G band is due to the sp 3 bond vibration in graphitic carbon, while the 2D band is related to the graphitization degree [23,24,27]. The ID/IG value was calculated to study the degree of disorder of these nanocarbon materials. ...
... Therefore, an ideal strategy involves the creation of a robust protective coating for NMC without sacrificing lithium or introducing new materials. Since the conductive additive cannot protect NMC, [14] the key of the matter arises if an aqueous-based binder can generate a functional coating layer on NMC particles during the electrode fabrication process. ...
Nickel‐rich LiNi0.8Co0.1Mn0.1O2 (NMC 811) cathode offers high voltage and high specific capacity, making it promising for high energy density batteries. However, large‐scale manufacturing of aqueous‐processed NMC 811 electrodes remains challenging due to proton exchange causing material decomposition and capacity loss. This work addresses this issue by constructing an in situ nanocellulose protective layer for NMC 811 particles via electrostatic interactions during the slurry preparation. For the first time, the interatomic spacing between inter‐chains of nanocellulose is measured through wide‐angle X‐ray scattering and demonstrate the ability to effectively confine interlayer water using atomistic simulations. Moreover, this nanocellulose coverage simultaneously minimizes Li⁺ surface segregation and mitigates water infiltration. Owing to less material decomposition during the aqueous processing, nanocellulose‐protected NMC electrodes exhibit higher initial coulombic efficiency (83% vs 62% at 0.1C) and capacity (133 vs 59 mAh g⁻¹ at 6C) than unprotected electrodes. Additionally, optimized aqueous‐processed NMC electrodes offer comparable or even superior electrochemical properties compared to the electrodes fabricated using the conventional toxic organic solvent, N‐methyl‐2‐pyrrolidone. Consequently, the developed approach enables affordable, sustainable aqueous processing for Nickel‐rich NMC 811 cathodes with excellent electrochemical performances.
... The parameterization of the financial model regarding material prices is therefore also mainly based on public sources from 2021 [73] and the BatPac v5.0 release from July 2022 [72]. A few values were taken from slightly older sources from 2018 [74,75]. All values that were initially given in EUR were converted to $ with an average exchange rate of 1.18 $ EUR −1 for the H. Pegel et al. year 2021 [76]. ...
The cost saving potential of large-format tabless cylindrical lithium-ion cells has been widely recognized since Tesla announced their plans to produce and BMW has confirmed to adopt this type of cells due to economic benefits among other reasons. However, a quantification and deep analysis of the cost reduction emerging from enlarged dimensions and further innovations such as different housing materials has not been reported in scientific literature so far. In this study, the process steps of manufacturing a large-format tabless cylindrical cell are examined and published in detail for the first time. A model is established that incorporates all manufacturing steps as a function of cell dimensions and choice of housing material. It was found that enlarging the dimensions from the conventional 2170 to the 4680 format achieved a cost reduction of 10.9% for two main reasons. First, the manufacturing cost per kWh decreases due to certain manufacturing steps being directly dependent on the number of cells produced. Second, the cells volumetric energy density itself increases due to a better volume efficiency of the active material share which further decreases the number of cells required. Introducing aluminum housings offers additional cost saving potential of as much as 2.5% of the total cost of 4680 cells due to an efficient backwards impact extrusion manufacturing process and lower cost of the aluminum raw material compared to nickel-plated steel.
... Location of gigafactory Germany [52] Annual output in GWh year −1 40 [52] Number of shifts per day 3 [53] Working hours per day 8 [53] Working days per year 300 [53] Machine availability in % 90 [18] 3.5 Financial model the BatPac v5.0 release from July 2022 [55]. A few values were taken from slightly older sources from 2018 [57,58]. ...
... Leaching can be compensated with novel cell architectures such as the reserve LIBs [13]. With respect to the slurry, while the pH can be easily controlled and lowered below the Al corrosion threshold through the addition of acids [14][15][16], coping with the high surface tension of water, due to being an intrinsic property, requires more effort in finding the right inactive slurry components (i.e., type of conductive carbon [11,17], binder [18][19][20][21][22][23][24], co-solvents such as alcohols [12,18], etc.) and slurry formulation (i.e., ratio and amount of the slurry components [18,20,22,25]), which results in a homogeneous, flexible and defect-free coating with good electrochemical properties. ...
The aqueous processing of cathode materials for lithium-ion batteries (LIBs) has both environmental and cost benefits. However, high-loading, water-based electrodes from the layered oxides (e.g., NMC) typically exhibit worse electrochemical performance than NMP-based electrodes. In this work, primary, binary, and ternary binder mixtures of aqueous binders such as CMC, PAA, PEO, SBR, and Na alginate, in combination with bare and C-coated Al current collectors, were explored, aiming to improve the rate capability performance of NMC811 electrodes with high areal capacity (≥4 mAh cm−2) and low binder content (3 wt.%). Electrodes with a ternary binder composition (CMC:PAA:SBR) have the best performance with bare Al current collectors, attaining a specific capacity of 150 mAh g−1 at 1C. Using carbon-coated Al current collectors results in improved performance for both water- and NMP-based electrodes. This is further accentuated for Na-Alg and CMC:PAA binder compositions. These electrodes show specific capacities of 170 and 80 mAh g−1 at 1C and 2C, respectively. Although the specific capacities at 1C are comparable to those for NMP-PVDF electrodes, they are approximately 50% higher at the 2C rate. This study aims to contribute to the development of sustainably processed NMC electrodes for high energy density LIBs using water as solvent.
... [51] Hence, the use of various types of CNTs as a conductive additive has been investigated by several research groups. [52][53][54][55] ...
The aim of this work is to answer the question: how to realize high energy and high‐power lithium‐ion batteries. Lithium‐metal and graphite anodes with nickel manganese cobalt (NMC) cathodes of varying thickness are investigated with finite element modelling. The overpotential analysis is performed to pinpoint the source of losses and the possible ways to decrease them. The electrolyte overpotential, resulting from the salt concentration gradient and leading to saturation and depletion of lithium in parts of the cell is identified as the main factor causing poor specific capacity at high discharge/charge currents. The influence of various parameters, including concentration and transference number of lithium salt in the electrolyte, NMC particle size, electrolyte conductivity and the exchange current density, on the galvanostatic response of modelled battery cells is discussed. The increase of the transference number would improve the performance as this would decrease the electrolyte salt concentration gradient. Lithium depletion effect can be also minimized by elevating the initial electrolyte salt concentration, as well as by increasing the porosity of the cathode, particularly at the cathode/separator boundary.
... However, water-based processing introduces materials compatibility, dispersion, and formulation challenges that require careful consideration [13][14][15][16][17][18][19][20]. Although it is widely used for graphite anodes [11,21], aqueous processing has not been adopted for cathodes due to concerns about adverse effects of water on the active material. ...
Despite recent advances in lithium-ion battery technology, further energy density improvements and cost reductions are necessary to achieve widespread adoption of electric vehicles. Nickel-rich formulations of lithium nickel manganese cobalt oxide (NMC) have been developed as promising high-energy, high-voltage cathode materials capable of significantly increasing the energy density of lithium-ion batteries. Aqueous processing of these cathodes offers significant environmental benefits and lower production expenses compared to traditional processing using N- methylpyrrolidone (NMP). However, Ni-rich NMC materials can react with water during electrode preparation, and with electrolyte during battery assembly and cycling, resulting in metal leaching that can cause structural changes and performance degradation. We investigated the effect of aqueous processing on the structure and electrochemical behavior of these cathode materials by exposing four NMC powders with varying nickel contents (NMC 333, NMC 532, NMC 622, NMC 811) to water and electrolyte for different time durations meant to simulate electrode processing and battery assembly conditions. The resulting metal dissolution was then measured using inductively coupled plasma mass spectrometry (ICP-MS). Since the pH of aqueous slurries can differ depending on composition, and pH variation may lead to additional reactions, the effect of pH was also explored.
We found that lithium dissolution increases with increasing nickel content at all pH values, and slurries made with all four powders become basic during typical processing times. Dissolution of Ni, Mn, and Co in water was minimal for all formulations. In order to gain a better fundamental understanding of the structural changes taking place during these reactions, a subset of the NMC powders was characterized by SEM and X-ray photoelectron spectroscopy (XPS) before and after exposure to water and electrolyte. In addition, the effect of aqueous processing on battery performance was evaluated by comparing the rate performance of pouch cells made using cathodes processed with different water exposure durations. Correlating processing conditions with performance could lead to the design of new approaches to mitigate metal leaching from Ni-rich NMC materials and enable the use of these cathodes for high energy density lithium-ion batteries.
Acknowledgment
This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (VTO) (Deputy Director: David Howell) Applied Battery Research subprogram (Program Manager: Peter Faguy).
Figure 1
... However, it is not uncommon to find a reduction in overpotentials from coating carbon on NMC, [22][23][24][25][26][27][28][29][30][31] NCA, [32][33][34][35] or even LCO particles. [36,37] Increased loading of conductive additives is also commonly associated with overpotential reduction, [9,10,[38][39][40][41][42][43][44] which is generally attributed to enhanced electron percolation and reduced requirements for conduction in the active material. These observations are puzzling for several reasons. ...
Electronic resistance in lithium‐ion battery positive electrodes is typically attributed to the bulk resistance of the active material and the network resistance of the carbon additive. Expected overpotentials from these bulk components are minimal relative to that from charge‐transfer resistance. However, literature reports show that cell overpotentials are often much more sensitive to conductive additives than the expected level from bulk or percolating‐network transport. This discrepancy motivated a detailed examination of the contact resistance between the active material and conductive additive. The contact and bulk resistances are simultaneously measured using dense bar samples of lithium‐layered oxides (LixNi1 /3Mn1/3Co1/3O2 and LixNi0.5Mn0.3Co0.2O2) in contact with carbon black. It is found that the contact resistance dominates the overall electronic resistance when the length scale is smaller than millimeters; after correcting for contact effects, bulk conductivity of layered oxides is determined to be orders‐of‐magnitude higher than previously reported. In porous electrodes, it is found from three‐electrode electrochemical impedance spectroscopy that the carbon content most heavily influences the low‐frequency regime (≈0.01 Hz), as opposed to the high frequency (>10³ Hz) regime expected from electronic percolating properties. Constriction effects within the layered oxide are identified as the dominant mechanism for contact resistance and its implication is investigated for porous electrodes.
... Particulate carbon (carbon black, acetylene black, graphite powder) is the conventional conductive additive of choice for LIBs. Alternative conductive additives exist in terms of metal powders [43], metal fibres [44], vapour grown carbon fibres [45], carbon nanotubes [20,46,47], graphene [48][49][50], and conducting polymers [47,51,52]. ...
In a drive to increase Li-ion battery energy density, as well as support faster charge discharge speeds, electronic conductivity networks require increasingly efficient transport pathways whilst using ever decreasing proportions of conductive additive. Comprehensive understanding of the complexities of electronic conduction in lithium-ion battery electrodes is lacking in the literature. In this work we show higher electronic conductivities do not necessarily lead to higher capacities at high C-rates due to the complex interrelation between the electronically conducting carbon binder domain (CBD) and the ionic diffusion within electrodes. A wide body of literature is reviewed, encompassing the current maxims of percolation theory and conductive additives as well as the relationships between processing steps at each stage of electrode manufacturing and formation of electronic conduction pathways. The state-of-the-art in electrode characterisation techniques are reviewed in the context of providing a holistic and accurate understanding of electronic conductivity. Literature regarding the simulation of electrode structures and their electronic properties is also reviewed. This review presents the first comprehensive survey of the formation of electronic conductivity networks throughout the CBD in battery electrodes, and demonstrates a lack of understanding regarding the most optimum arrangement of the CBD in the literature. This is further explored in relation to the long-range and short-range electrical contacts within a battery electrode which represent the micron level percolation network and the submicron connection of CBD to active material respectively. A guide to future investigations into CBD including specific characterisation experiments and simulation approaches is suggested. We conclude with suggestions on reporting important metrics such as robust electrical characterisation and the provision of metrics to allow comparison between studies such as aerial current density. Future advances in characterisation, simulation and experimentation will be able to provide a more complete understanding if research can be quantitatively compared.
... However, it is not uncommon to find a reduction in overpotentials from coating carbon on NMC, [22][23][24][25][26][27][28][29][30][31] NCA, [32][33][34][35] or even LCO particles. [36,37] Increased loading of conductive additives is also commonly associated with overpotential reduction, [9,10,[38][39][40][41][42][43][44] which is generally attributed to enhanced electron percolation and reduced requirements for conduction in the active material. These observations are puzzling for several reasons. ...
Electronic resistance in lithium-ion battery positive electrodes is typically attributed to the bulk resistance of the active material and the network resistance of the carbon additive. Expected overpotentials from these bulk components are minimal relative to that from charge-transfer resistance. However, literature reports show that cell overpotentials are often much more sensitive to conductive additives than the expected level from bulk or percolating-network transport. This discrepancy motivates a detailed examination of the contact resistance between the active material and conductive additive. We simultaneously measure contact and bulk resistances using dense bar samples of lithium layered oxides (LixNi1/3Mn1/3Co1/3O2 and LixNi0.5Mn0.3Co0.2O2) in contact with carbon black. We find that the contact resistance dominates the overall electronic resistance when the length scale is smaller than millimeters; after correcting for contact effects, bulk conductivity of layered oxides is determined to be orders-of-magnitude higher than previously reported. In porous electrodes, we find from three-electrode electrochemical impedance spectroscopy that the carbon content most heavily influences the low-frequency regime (around 0.01 Hz), as opposed to the high frequency (>10^3 Hz) regime expected from electronic percolating properties. We identify constriction effects within the layered oxide as the dominant mechanism for contact resistance and investigate its implication for porous electrodes.
... 16,17 The preparation of a suspension of CNTs in a solution of the binder, in which the active material is then dispersed, appeared to be an optimal method of manufacturing electrodes using CNTS as (all or part) conductive additive. 18,19 Furthermore, the price per gram of CNTs, especially multiwall carbon nanotubes MWCNTs has become low enough to favor their utilization in industrial electrodes. 20 The validation of the interest of CNTs as a conductive additive requires their evaluation in highly loaded and dense electrodes, based on conventional active materials to be relevant for EV application. ...
... Generally, the D band refers to the existence of disordered structural and defects, G is associated with the ordered phase, T is attributed to the disordered graphitic lattice or sp 3 -rich phase, D" represents the amorphous sp 2 -bonded forms [34]. It is well known that the value of I D /I G can be adopted for evaluating the microcrystalline structure of carbon materials [35,36]. The I D / I G value of AC-PHC (1.12) is higher than that of AC-PMC (0.93), indicating that there are more defects and disordered structures in AC-PHC, which is highly agree with the XRD results. ...
Activated carbons (ACs) were successfully obtained through direct KOH activation method using pitch coke (PHC) and petroleum coke (PMC) as precursors. The electrochemical properties of Zn-ion hybrid supercapacitors (ZICs) assembled with the prepared ACs as electrodes were further investigated. The results showed that the PHC derived AC displayed suitable oxygen functional groups, sufficient specific surface area and favorable porosity, displaying excellent electrochemical performances with an outstanding specific capacitance of 146.4 mAh/g at 0.1 A/g, a satisfactory rate performance of 58% (from 0.1 to 10 A/g) and a high cycling stability of 95% after 5000 cycles. Furthermore, the as-obtained AC-PHC-based ZICs also delivered prominent energy output of 117 Wh/kg at 160 W/kg and 68 Wh/kg at 15.8 kW/kg.
... 16,17 The preparation of a suspension of CNTs in a solution of the binder, in which the active material is then dispersed, appeared to be an optimal method of manufacturing electrodes using CNTS as (all or part) conductive additive. 18,19 Furthermore, the price per gram of CNTs, especially multiwall carbon nanotubes MWCNTs has become low enough to favor their utilization in industrial electrodes. 20 The validation of the interest of CNTs as a conductive additive requires their evaluation in highly loaded and dense electrodes, based on conventional active materials to be relevant for EV application. ...
The power performance of EV-designed LiNi0.5Mn0.3Co0.2O2 (NMC 532)/PVdF/CB-CNT based electrodes with 25 mg.cm⁻² active mass loading, 3.4 g.cm⁻³ density, 23.5% porosity and 96:1.8:2.2 wt% composition, were measured at 0 °C, 22 °C and 40 °C. The CB/CNTs ratio is 100:0 or 50:50 v%. The polarization resistance and the discharge capacity are improved by using the CB-CNTs blend especially at 0 °C and 40 °C. The shape factor of the CNTs favor the electronic wiring of the active mass at 0 °C by forming conductive bridges over the resistive grain boundaries at the surface of NMC clusters. At 40 °C, the CNTs favor both the electronic and the ionic wirings of the active mass. At this temperature, the swelling of the CB/PVdF domains could be responsible for the degradation of the electrons transfer and ions transport through the electrode. This detrimental phenomenon is mitigated with the CB/CNTs blend likely due to the CNTs shape factor.
... For slurry mixing of state-of-the-art cathode materials based on transition metal layered oxides, conductive additives are essential for the formation of a noninterrupted conductive matrix to support long-range conductivity and short-range electron transfer to the active material surface. [20,73,74] The commonly applied PVdF binder on the cathode side is electrically insulating, but beneficial conductivity is given for clusters formed with conductive additives. [75] In general, CB or graphite derivatives are applied as conductive additives. ...
Despite intensive research activities on lithium ion technology, particularly in the past five decades, the technological background for automotive lithium ion battery mass-production in Europe is rather young, and not yet ready to meet requirements of automobile manufacturers. In light of the strong increase in electromobility, bridging this gap between fundamental research and industrial production is mandatory to keep the value chain of automobile manufacture in European countries. Challenges in know-how transfer from lab-scale to industry-scale arise from different product configurations and objectives. Lab-scale focusses primarily on material development and screening, utilizes small-sized half-cell or single-layered designs with one-side-coated electrodes, and applies manually operated, discontinuous equipment. Whereas industry focusses on optimized trade-offs between throughput, quality and costs. Market-relevant cells contain usually double-side-coated electrodes with comparatively higher areal capacities, assembled into multi-layered configurations. Mass-production is conducted through automated, continuous processes including roll-to-roll manufacturing and consecutive pick-and-place operations. Inevitably, standard laboratory conditions do not allow for prediction of either optimized mass-production process parameters nor physicochemical characteristics of final products. Hence, this review aims to identify challenges in transferring lab-scale results to industry with special focus on pilot-lines as intermediate step between the different technological levels.
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... to reduce the price. For this purpose, NMC 811,31 NMC 532,32 and NMC 442 33 are being developed and applied for commercial usage (particularly for automotive applications). On the other hand, for high-power Li-ion applications with decent safety, spinel LiNi0.5Mn1.5O4 is promising, awaiting advances in electrolyte capable of withstanding its high operating voltage (4.7 V vs. Li/Li + ). ...
The objectives of this thesis are, on the one hand, to develop new electrolytes by the design of new non-hazardous magnesium salts or by the use of aromatic additives such as anthracene and, on the other hand, to synthesize an organic polymer with redox properties suitable for its use as a positive electrode in magnesium batteries. The first methodology was the synthesis of several magnesium salts obtained by the reaction of substituted phenol or thiophenol with the tetrahydroborate anion. The best results were obtained with the salt obtained by the reaction of thiophenol and tetrahydroborate. The impact of this new salt on the improvement of the Mg/electrolyte interface was characterized by chronoamperometry and impedance spectroscopy measurements. In addition, the performance of full cell Mg/Mo6S8 was evaluated, a capacity of 75 mAh/g was obtained after 20 cycles, with a weak polarization of the Mg electrode. The second methodology several π-rich compounds were used. The best promising molecule is the 2-(tert-butyl)anthracene with an improvement in the Mg plating/stripping process reversibility. The second part of this thesis will present the electrochemical performance of organic material using as positive electrode for both lithium and magnesium batteries. Polybenzoquinonedisulfide (PBQDS) was synthesized with very high yield in a green and easy way. After the particle size reduction using ball milling technique, the discharge capacity reaches a stable value of 140 mAh/g at C/20 in sulfolane based electrolyte. In Mg cell, even if similar capacity is obtained in the first cycles, a large capacity fading is observed associated with the trapping of Mg2+ in the active material, due to strong oxygen/Mg2+ interaction. The use of solvation additive (crown ether) in the electrolyte mitigates partially this behaviour, given some interesting leads of improvement.
... to reduce the price. For this purpose, NMC 811,31 NMC 532,32 and NMC 442 33 are being developed and applied for commercial usage (particularly for automotive applications). On the other hand, for high-power Li-ion applications with decent safety, spinel LiNi0.5Mn1.5O4 is promising, awaiting advances in electrolyte capable of withstanding its high operating voltage (4.7 V vs. Li/Li + ). ...
The objectives of this thesis are, on the one hand, to develop new electrolytes by the design of new non-hazardous magnesium salts or by the use of aromatic additives such as anthracene and, on the other hand, to synthesize an organic polymer with redox properties suitable for its use as a positive electrode in magnesium batteries. The first methodology was the synthesis of several magnesium salts obtained by the reaction of substituted phenol or thiophenol with the tetrahydroborate anion. The best results were obtained with the salt obtained by the reaction of thiophenol and tetrahydroborate. The impact of this new salt on the improvement of the Mg/electrolyte interface was characterized by chronoamperometry and impedance spectroscopy measurements. In addition, the performance of full cell Mg/Mo6S8 was evaluated, a capacity of 75 mAh/g was obtained after 20 cycles, with a weak polarization of the Mg electrode. The second methodology several π-rich compounds were used. The best promising molecule is the 2-(tert-butyl)anthracene with an improvement in the Mg plating/stripping process reversibility. The second part of this thesis will present the electrochemical performance of organic material using as positive electrode for both lithium and magnesium batteries. Poly(benzoquinonyldisulfide) (PBQDS) was synthesized with very high yield in a green and easy way. After the particle size reduction using ball milling technique, the discharge capacity reaches a stable value of 140 mAh/g at C/20 in sulfolane based electrolyte. In Mg cell, even if similar capacity is obtained in the first cycles, a large capacity fading is observed associated with the trapping of Mg2+ in the active material, due to strong oxygen/Mg2+ interaction. The use of solvation additive (crown ether) in the electrolyte mitigates partially this behaviour, given some interesting leads of improvement.
... In contrast, most SP particles were sphere-or granule-shaped, with particle sizes ranging between 50 and 100 nm and with a specific area of 61.84 m 2 /g (determined by BET), which was about 40% of that for CNTs. Figure S3 displays the Raman spectra of CNTs and SP. The characteristic peaks located around 1349 cm −1 , 1589 cm −1 , and 2690 cm −1 corresponded to the D band, G band, and 2D band, respectively [30]. An increasing intensity ratio of D band to G band (I D /I G ) indicated that the structure of SP contained more defects [31], which should generally be expected to adversely affect its electrical conductivity. ...
Increasing areal active material loading by thick electrodes is a direct and effective approach to improve the energy density of lithium-ion batteries (LIBs). However, it may also induce large polarization effects and reduce the active material utilization, especially under high charge/discharge current densities. In this work, dual-layered LiNi0.8Co0.15Al0.05O2 (NCA) cathodes with high areal capacity of about 5 mAh/cm2 and gradient porosity are prepared via a layer-by-layer method, in which carbon nanotubes (CNTs) and Super P (SP) carbon are used to build the electron conducting networks as well as to adjust the porosity. It is demonstrated that the CNT-SP cathode, which uses CNTs as the conductive agent in the lower layer (close to the current collector) and SP as the conductive agent in the upper layer (close to the separator), provides the highest areal capacity of 4.81 mAh/cm2 among all configurations studied (CNT-SP, SP-SP, SP-CNT, and CNT-CNT). And it exhibits high capacity retention of 99.5% over 100 cycles in NCA||graphite full pouch cells at current density of 0.2 C rate. The excellent performance of the thick CNT-SP cathode is attributed to the construction of favorable conductive networks which can provide effective and reliable paths for electron transport and Li+ diffusion. Moreover, a thinner electrode/electrolyte interphase layer is found to form in the CNT-SP electrode. This research reveals a viable approach for ameliorating the significant polarization effects and limited active material utilization in thick electrodes through alternate configurations of the conductive agents, which can be easily adopted in state-of-the-art battery manufacturing processes.
... For these reasons, water-based processing is widely used for graphite anodes. On another hand, it is difficult to adopt this process for cathodes, due to adverse effects of water on NCM materials of different compositions [286][287][288][289]. In particular, transition metal oxides produce basic solutions in water [290][291][292][293]. ...
The aim of this article is to examine the progress achieved in the recent years on two advanced cathode materials for EV Li-ion batteries, namely Ni-rich layered oxides LiNi0.8Co0.15Al0.05O2 (NCA) and LiNi0.8Co0.1Mn0.1O2 (NCM811). Both materials have the common layered (two-dimensional) crystal network isostructural with LiCoO2. The performance of these electrode materials are examined, the mitigation of their drawbacks (i.e., antisite defects, microcracks, surface side reactions) are discussed, together with the prospect on a next generation of Li-ion batteries with Co-free Ni-rich Li-ion batteries.
... 13 Materials with a high nickel and low cobalt content have the advantage of relatively low manufacturing costs accompanied with a high theoretical capacity and operation voltage. [13][14][15] Aqueous processing has been investigated for a variety of different layered oxides such as NCM111, 3,[5][6][7]9,10,[16][17][18][19][20][21][22][23][24][25][26][27] NCM424, 28 NCM523, 25,[29][30][31][32][33][34][35] NCM622, 25,27 NCM811, 12,25,[36][37][38] Li-/Mn-rich NCM [39][40][41][42][43][44] and NCA. 6,7,33,[45][46][47][48][49] However, it is often difficult to compare the materials in terms of their processibility in an aqueous environment due to different treatment parameters. ...
Combining the use of nickel-rich layered oxide cathode materials with the implementation of aqueous electrode processing can pave the way to cost-reduced and environmentally friendly electrodes and simultaneously increase the energy density of cells. Herein, LiNi0.33Co0.33Mn0.33O2 (NCM111), LiNi0.6Co0.2Mn0.2O2 (NCM622), LiNi0.8Co0.1Mn0.1O2 (NCM811) and LiNi0.8Co0.15Al0.05O2 (NCA) were evaluated in terms of their response to aqueous processing under the same conditions to facilitate a direct comparison. The results illustrate that mainly nickel driven processes lead to lithium leaching which is combined with the increase of the pH value in the alkaline region. For NCA an additional aluminum-involving lithium leaching mechanism is assumed, which could explain the highest amount of leached lithium and the additional detection of aluminum. Electrochemical tests show a reduced capacity for cells containing water-based electrodes compared to reference cells for the NCM-type materials which increases during the first cycles indicating a reversible Li+/H+-exchange mechanism. In contrast, the NCA cells were completely electrochemically inactive making NCA the most water sensitive material tested in this report. By comparing the cycling performance of cells containing aqueous processed electrodes, a more pronounced capacity fade for nickel-rich cathode materials as compared to their reference cells can be observed.
... Rate capability and energy density also depend on other factors such as the electrode formulation, conductive additive, particle morphology, and cathode materials [48]. Appropriate selection of conductive additive, minimizing the inactive components while maintaining sufficient electronic conductivity, cohesion and adhesion can enhance rate performance [55]. Particle size and morphology is also crucial for the solid electrolyte interface and solid-state diffusion through particles. ...
Extreme fast charging capabilities along with high energy density of Li-ion batteries are the key factors to increase the adoption of electric vehicles while eliminating the problem of range anxiety. The U.S Department of Energy has a goal of <12 min charging time with energy density of >200 Wh kg⁻¹. A combined improvement in the electrode architecture, electrolyte properties, and separator membrane is necessary to achieve this goal. Cells with thin electrodes are capable of extreme fast charging at the expense of low energy density and high cost. Electrode engineering can maximize energy density. Here, the influence of porosity, mass loading and charging protocols on capacity and energy density and electrode kinetics are investigated under extreme fast charging conditions. Increasing the mass loading from 11.5 mg cm⁻² to 25 mg cm⁻² compromises the rate performance due to the mass transport limitation and underutilization of thick electrodes. Reducing the electrode porosity from 50% to 35% improves the rate performance ascribed to shorter Li ion diffusion length. Symmetric cells are cycled to verify the performance of the half cells, suggesting that Li metal plating is the rate limiting step under high current density.
... The D band can be ascribed to defect-induced disordered sp 2 bond vibrations [30], whereas the G band can be attributed to sp 3 vibrations of graphitic carbon. The 2D band can be related to the graphitization degree of carbonaceous materials [31,32]. ...
Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted significant attention due to the distinguishing characteristics of zinc metal, including its low price, abundance in earth, safety and high theoretical specific capacity of 820 mAh g-1. Manganese dioxide (MnO2) is a promising cathode for ZIBs due to high theoretical specific capacity, high discharge voltage plateau, cost-effectiveness and nontoxicity. However, the low electronic conductivity and volumetric changes during electrochemical cycling hinder its practical utilization. Herein, we demonstrate a polyacrylic acid (PAA)-assisted assembling strategy to fabricate freestanding and flexible MnO2/carbon nanotube/PAA (MnO2/CNT/PAA) cathodes for ZIBs. PAA plays an important role in providing excellent mechanical properties to the free-standing electrode. Moreover, the presence of CNT forms an electron conductive network, and the porous structure of MnO2/CNT/PAA electrode accommodates the volumetric variations of MnO2 during charge/discharge cycling. The as-fabricated quasi-solid-state Zn-MnO2/CNT/PAA battery delivers a high charge storage capacity of 302 mAh g-1 at 0.3 A g-1 and retains 82% of the initial capacity after 1000 charge/discharge cycles at 1.5 A g-1. The calculated volumetric energy density of Zn-MnO2/CNT/PAA battery is 8.5 mW h cm-3 (with a thickness of 0.08 cm), which is significantly higher than the reported alkali-ion batteries (1.3 mW h cm-3) and comparable to supercapacitors (6.8 mW h cm-3) and Ni-Zn batteries (7.76 mW h cm-3). The current work demonstrates that free-standing MnO2/CNT/PAA composite is a promising cathode for ZIBs.
... 62 Electronic conduction becomes the limiting factor for power performance in cells with an NMC chemistry, and the addition of conductive additives is used in positive electrode formulations to ameliorate this. 63 In this case, the very low conductivity is expected, as this battery has been manufactured for energy applications where the active material content would have been maximized. Averages were taken, and the values 0.18 S m −1 and 215 S m −1 were used for the positive electrode and negative electrode during simulations. ...
Presented here, is an extensive 35 parameter experimental data set of a cylindrical 21700 commercial cell (LGM50), for an electrochemical pseudo-two-dimensional (P2D) model. The experimental methodologies for tear-down and subsequent chemical, physical, electrochemical kinetics and thermodynamic analysis, and their accuracy and validity are discussed. Chemical analysis of the LGM50 cell shows that it is comprised of a NMC 811 positive electrode and bi-component Graphite-SiOx negative electrode. The thermodynamic open circuit voltages (OCV) and lithium stoichiometry in the electrode are obtained using galvanostatic intermittent titration technique (GITT) in half cell and three-electrode full cell configurations. The activation energy and exchange current coefficient through electrochemical impedance spectroscopy (EIS) measurements. Apparent diffusion coefficients are estimated using the Sand equation on the voltage transient during the current pulse; an expansion factor was applied to the bi-component negative electrode data to reflect the average change in effective surface area during lithiation. The 35 parameters are applied within a P2D model to show the fit to experimental validation LGM50 cell discharge and relaxation voltage profiles at room temperature. The accuracy and validity of the processes and the techniques in the determination of these parameters are discussed, including opportunities for further modelling and data analysis improvements.
... We acknowledge that the optimal electrode composition for physical characteristics and electrical characteristics may not coincide resulting in the large impedance. The role of mixing time, order, and identity of conductive additive all play a role in the electronic performance of the electrodes and will be investigated to optimized to limit the impedance of the battery [50][51][52]. Additionally, future studies cannot discount the influence of other physical characteristics such as adsorption, solubility and chemical structure of the conductive additive to influence the electrochemical performance of the cell. ...
A liquid-to-gel based Leclanché cell has been designed, constructed and characterized for use in implantable medical devices and other applications where battery access is limited. This well-established chemistry will provide reliable electrochemical potential over a wide range of applications and the novel construction provides a solution for the recharging of electrodes in hard to access areas such as an internal pacemaker. The traditional Leclanché cell, comprised of zinc (anode) and manganese dioxide (cathode), conductive carbon powder (acetylene black or graphite), and aqueous electrolyte (NH4Cl and ZnCl2), has been suspended in an agar hydrogel to simplify construction while maintaining electrochemical performance. Agar hydrogel, saturated with electrolyte, serves as the cell support and separator allowing for the discharged battery suspension to be easily replaced once exhausted. Different amounts of active anode/cathode material have been tested and discharge characteristics have been plotted. It has been found that for the same amount of active material, acetylene black batteries have higher energy density compared to graphite batteries. Graphite batteries also discharge faster compared to acetylene black batteries. The results support further development of liquid batteries that can be replaced and refilled upon depletion.
... Carbon Matrixes A novel method to enhance the performance of Ni-rich NMC-based cathodes is to build carbon matrixes containing active material particles. Examples of this method include studies involving graphene nanosheets for NMC811, 141 carbon nanotube conductive networks for NMC532 (Fig. 12d) [201,202], and interwoven carbon fibers for NMC622 [203]. Here, the matrixes chosen are usually highly conductive carbon materials that can enhance charge [126]. ...
The demand for lithium-ion batteries (LIBs) with high mass-specific capacities, high rate capabilities and long-term cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNixMnyCo1−x−yO2, ) cathodes and graphite (LixC6) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid electrolyte interfaces are also reviewed, and trade-offs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions.
Graphic Abstract
The demand for lithium-ion batteries (LIBs) with high mass specific capacities, high rate capabilities and longterm cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNixMnyCo1−x−yO2, x ≥ 0.5) cathodes and graphite (LixC6) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid-electrolyte interfaces (SEIs) are also reviewed and tradeoffs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions. Open image in new window
... However, water-based processing introduces materials compatibility, dispersion, and formulation challenges that require careful consideration [13][14][15][16][17][18][19][20]. Although it is widely used for graphite anodes [11,21], aqueous processing has not been adopted for cathodes due to concerns about adverse effects of water on the active material. ...
Cobalt content in Li-ion battery cathodes has become a top concern due to its price volatility and limited source availability. Low-cobalt, Ni-rich active materials are promising candidates for next-generation cathodes due to their high capacities, and water-based processing of these materials can further reduce both cost and environmental impact. We systematically evaluated the water compatibility of four different LiNixMn1-x-yCoyO2 (NMC) powders with increasing nickel contents. Comprehensive characterization verified there is no major change to their bulk structures, and only slight surface modifications related to the removal of contaminant species. For the first time, we demonstrate that LiNi0.8Mn0.1Co0.1O2 (NMC 811) cathodes can be formulated in water and cycled 1000 times in full pouch cells with excellent capacity retention (~70% compared to ~76% for NMP-processed cells). When implemented in future battery production lines, aqueous processing of Ni-rich NMC will simultaneously enable cost reductions and higher cell energy densities.
Lithium–sulfur batteries (LSBs) are a promising alternative to lithium-ion batteries because sulfur is highly abundant and exhibits a high theoretical capacity (1675 mA h g⁻¹). However, polysulfide shuttle and other challenges have made it difficult for LSBs to be commercialised. Here, a sulfur/carbon (S/C) composite was synthesised and cathodes were fabricated via scalable melt diffusion and slurry casting methods. Carbon nanoparticles (C65) were used as both sulfur host and electrical additive. Various carbon ratios between the melt-diffusion step and cathode slurry formulation step were investigated. An increased amount of C65 in melt-diffusion led to increased structural heterogeneity in the cathodes, more prominent cracks, and a lower mechanical strength. The best performance was exhibited by a cathode where 10.5 wt% C65 (TC10.5) was melt-diffused and 24.5 wt% C65 was externally added to the slurry. An initial discharge capacity of ∼1500 mA h g⁻¹ at 0.05C and 800 mA h g⁻¹ at 0.1C was obtained with a capacity retention of ∼50% after 100 cycles. The improved electrochemical performance is rationalised as an increased number of C–S bonds in the composite material, optimum surface area, pore size and pore volume, and more homogeneous cathode microstructure in the TC10.5 cathode.
Electrochemical lithium extraction from salt lakes is an effective strategy for obtaining lithium at a low cost. Nevertheless, the elevated Mg : Li ratio and the presence of numerous coexisting ions in salt lake brines give rise to challenges, such as prolonged lithium extraction periods, diminished lithium extraction efficiency, and considerable environmental pollution. In this work, LiFePO4 (LFP) served as the electrode material for electrochemical lithium extraction. The conductive network in the LFP electrode was optimized by adjusting the type of conductive agent. This approach resulted in high lithium extraction efficiency and extended cycle life. When the single conductive agent of acetylene black (AB) or multiwalled carbon nanotubes (MWCNTs) was replaced with the mixed conductive agent of AB/MWCNTs, the average diffusion coefficient of Li+ in the electrode increased from 2.35 × 10−9 or 1.77 × 10−9 to 4.21 × 10−9 cm2·s−1. At the current density of 20 mA·g−1, the average lithium extraction capacity per gram of LFP electrode increased from 30.36 mg with the single conductive agent (AB) to 35.62 mg with the mixed conductive agent (AB/MWCNTs). When the mixed conductive agent was used, the capacity retention of the electrode after 30 cycles reached 82.9%, which was considerably higher than the capacity retention of 65.8% obtained when the single AB was utilized. Meanwhile, the electrode with mixed conductive agent of AB/MWCNTs provided good cycling performance. When the conductive agent content decreased or the loading capacity increased, the electrode containing the mixed conductive agent continued to show excellent electrochemical performance. Furthermore, a self-designed, highly efficient, continuous lithium extraction device was constructed. The electrode utilizing the AB/MWCNT mixed conductive agent maintained excellent adsorption capacity and cycling performance in this device. This work provides a new perspective for the electrochemical extraction of lithium using LFP electrodes.
Due to their low cost, high capacity, mild assembly and testing conditions, as well as environmentally friendly characteristics, rechargeable zinc ion batteries (RZIBs) have attracted more and more attention. RZIBs have a broad development prospect and may partly replace the traditional batteries in the near future. Tremendous efforts have been devoted to developing various of high‐efficient cathode materials for improving comprehensive performances of RZIBs. However, many problems such as poor electron/ion conductivity, weak structural stability and complex energy storage mechanisms still exist in current cathode materials which hinder the practical application of RZIBs. This paper presents a timely review on recent progresses and challenges in cathode materials for rechargeable zinc ion batteries (RZIBs). Various types of reported cathode materials for RZIBs are summarized, their electrochemical performances were compared and their probable working mechanisms are investigated with the association of computational chemistry. Moreover, the existing problems and expected development directions of these materials were further discussed.
Lithium Iron Phosphate (LiFePO4, LFP), as an outstanding energy storage material, plays a crucial role in human society. Its excellent safety, low cost, low toxicity, and reduced dependence on nickel and cobalt have garnered widespread attention, research, and applications. Consequently, it has become a highly competitive, essential, and promising material, driving the advancement of human civilization and scientific technology. The lifecycle and primary research areas of lithium iron phosphate encompass various stages, including synthesis, modification, application, retirement, and recycling. Each of these stages is indispensable and relatively independent, holding significant importance for sustainable development. However, these stages are also closely interconnected, with many similarities in principles and technologies. For example, synthesis and modification are often completed simultaneously, modification and repair serve similar purposes, and the liquid-based synthesis of lithium iron phosphate and its leaching process are essentially reverse processes. The existence of these connections offers the possibility of interdisciplinary cross-fertilization between different stages of research. Therefore, their seamless integration is crucial for sustainable development. This paper provides a comprehensive and holistic perspective. It combines the physical and chemical properties of lithium iron phosphate with its working principles to systematically discuss the current state of research in different stages and their inherent connections. It also explores and evaluates the application prospects of research methods based on their strengths and weaknesses.
Conjugated porous polymers are emerging as sustainable and reliable electrode materials for lithium-ion batteries, owing to their versatile chemical modification, environmental-friendliness, and low cost, but still suffer from insufficient redox-active...
In this paper, we study two factors (carbon additive, N/P ratio) affecting the performance of Li‐ion cells using LiFePO4 (LFP) synthesized via the hydrothermal method. X‐ray diffraction (XRD) results show that the synthesized LFP material is pure and within the single phase of the orthorhombic lattice. The electrochemical properties of synthesized LFP cathode (physically mixed with different carbon C65 and CNTs) were studied by Cyclic voltammetry (CV) and galvanostatically cycling. The diffusion coefficients of LFP‐CNTs and LFP‐C65 were calculated using the Randles‐Sevcik equation and reached 8.350.10‐10 cm2.s‐1 and 1.620.10‐10 cm2.s‐1, respectively. In a rate capability tests, LFP‐CNTs based cell demonstrates an excellent cyclability with a discharge capacity (CapDis) of 147.9 mAh.g‐1 at 0.1C and 84.0 mAh.g‐1 at 5.0C, whereas LFP‐C65 completely lost capacity at 2.0C. In addition, the investigation of negative/positive capacity ratios (N/P ratios) at 1.18 and 1.23 reveals high specific capacity (Capspe), high‐capacity retention, and an excellent charge/discharge efficiency (EC/DC) at different C‐rates.
High-purity NMC111 nanoparticles are obtained by sol–gel synthesis. NMC111/MWCNTs freestanding hybrid composite cathodes are produced by a simple vacuum filtration process without detriment to both the crystalline and morphologic structures of the NMC111 nanoparticles. NMC111/MWCNTs freestanding hybrid composite cathode materials exhibit enhanced cycling stability, long cycle life, and high specific discharge capacity compared with pure NMC111 electrode, which is prepared by the classic slurry method. After 1000 cycles, within 2.5–4.6 V working potential range (at 1 C-rate), the specific discharge capacity of NMC111/MWCNTs freestanding hybrid composite cathode is 118.5 mAh g−1 with a capacity loss rate of 44.2%, considerably higher than the result of pure NMC111 cathode electrode (84.9 mAh g−1 with a capacity loss rate of 59.2%). NMC111/MWCNTs freestanding hybrid cathode has shown lower polarization and good cyclic stability when compared with the pristine NMC111 cathode electrode in the cyclic voltammetry (CV) analysis. MWCNTs in the electrode have high electron conductivity and easies the electron transfer during the electrochemical charge/discharge. Graphite@NMC111/MWCNTs full cells were fabricated to support results acquired with the half cells. To analyze the working of MWCNTs-reinforced freestanding composite cathode in full cell, graphite@NMC111/MWCNTs combination was constituted and obtained a specific discharge capacity of 150.7 mAh g−1 with a capacity loss of 30.4% after 1000 cycles. Extreme cycling and structural stability increased conductivity, and a high cycle number is reached by compressing the NMC111 nanoparticles between MWCNTs. Highly electrical conductive MWCNTs, which are homogeneously dispersed on around the NMC111 nanoparticles, are employed as both structural strengthening components and surface improvers for NMC111 cathode electrodes, not only for enhancing the electrical conductivity but also supplying powerful guarding to the side reactions with the liquid electrolyte. The results have shown that the MWCNTs-based freestanding electrode form can be widely used electrode type for high-level featured lithium-ion batteries.
The presented case study provides mesoscopic insights into the state-of-charge (SOC) distribution of battery electrodes containing layered transition metal oxides with Li(Ni0.5Mn0.3Co0.2)O2 (NMC532). The application of classification-single-particle inductively coupled plasma optical emission spectroscopy (CL-SP-ICP-OES) enables the rapid screening of the lithium content of individual cathode active material (CAM) particles achieving a statistically viable elucidation of the mesoscale SOC distribution between different particles of the electrode. The results reveal the evolution of a persistent mesoscale SOC heterogeneity of the electrode upon delithiation at slow rates and extensive relaxation times as confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The implications of local chemical and structural ramifications of the investigated NMC532 for heterogeneous active material utilization are thoroughly discussed. Furthermore, it is found that the evolved SOC heterogeneity of the electrode is strongly dependent on the current density. The correlation to the decreased capacity utilization is further investigated with a straightforward quantification approach revealing a considerable contribution to capacity fading by persistently inactive lithium in the CAM. The results highlight the importance of the analysis of persistent mesoscale SOC heterogeneity as a potential capacity fade mechanism in layered lithium transition metal oxide-based battery electrodes.
We report on an efficient and practical conducting mode built up by ternary conductive networks for boosting the rate performance of LiFePO4 (LFP) cathodes in lithium-ion batteries (LIBs). The influence on the electrical conductivity, rate capability and continuous ion channels of the resulting electrode are investigated. Carbon nanotubes (CNTs) with long-range electronic conduction are ultimately individually dispersed (mono-dispersed) into an electrode slurry, which connects the short-range conductive regions formed by graphene sheets. Importantly, CNTs provide more open channels for electron and ion transportation, than the blocking function of graphene sheets. Local graphene regions are herein bridged by mono-dispersed long CNTs to construct an efficient conductive network, enabling the composite to have improved fast electron/ion open channels. An efficient and practical conducting mode of "plane-to-line-to-point" is demonstrated to construct both short-/long-range electronic conduction and more open ion channels, while further contributing to conductive points all over the surface area of the LiFePO4 cathode.
Electrode processing plays an important role in advancing lithium-ion battery technologies and has a significant impact on cell energy density, manufacturing cost, and throughput. Compared to the extensive research on materials development, however, there has been much less effort in this area. In this Review, we outline each step in the electrode processing of lithium-ion batteries from materials to cell assembly, summarize the recent progress in individual steps, deconvolute the interplays between those steps, discuss the underlying constraints, and share some prospective technologies. This Review aims to provide an overview of the whole process in lithium-ion battery fabrication from powder to cell formation and bridge the gap between academic development and industrial manufacturing.
Ultrahigh dielectric constant is obtained in polymer/MXene composites due to percolation. However, huge dielectric loss is triggered owing to high leakage current. In this work, hybrid filler consisting of Ti2C MXene and ZrO2 was prepared for coordinating high dielectric constant and low dielectric loss in composites. Instead of Ti2C percolation, Ti2C/ZrO2 interface effect mildly increased dielectric constant. Ultrahigh insulation and large aspect ratio of ZrO2 fibers significantly reduced dielectric loss. Binary polymer/Ti2C and ternary polymer/Ti2C-ZrO2 composites were fabricated, and better overall electric traits in ternary system were found. Ti2C/ZrO2 interface effect was studied using density functional theory (DFT) calculations. Ternary composite with 12 wt % filler exhibited high dielectric constant of ~40, low dielectric loss of ~0.09 at 100 Hz and high breakdown strength of ~155 MV m⁻¹. This work might impulse fabrication of MXene-based hybrid fillers for dielectrics.
An attempt has been made to review and analyze the developments made during last few decades on the place of carbon in batteries. First identified as an anode of interest in the form of graphite, carbon has also made a place for itself as conductive agent added during electrode formulation or also as buffer with electrochemical active oxide processing by conversion. The focus is primarily on how to decrease the irreversibility of classical anode materials then how to increase its whole performance through nanostructures, mainly CNTs and graphene. We have identified post-lithium batteries as an opportunity for carbon as anode but also as support to reversible cathode material. Operando measurements may provide several breakthroughs and allow the rational and real design of carbonaceous materials for high power anodes in all types of batteries.
Zn ion batteries (ZIBs) have drawn increasing attentions due to the low cost, high theoretical capacity and excellent safety. Carbon nanotubes (CNTs) as a representative carbon material are widely applied in the design of advanced cathodes and anodes. This review provides a summary of latest developments of CNTs-based electrodes, such as Mn-based and V-based CNTs-containing cathodes and CNTs-modified Zn anodes. Both the preparation and design strategy of the electrodes and the structure-performance relationships are discussed in detail. Finally, a summary of the current progress and future prospects are introduced.
In this study, water-processed LiNi0.5Mn0.3Co0.2O2 cathodes (NMC532) are investigated. Notably, corrosion of
aluminum current collector occurring in aqueous processing owing to alkalinity of NMC slurry is avoided
through addition of phosphoric acid which buffers the slurry pH, or by using a carbon-coated collector. The
impact of small amounts of phosphoric acid on the electrochemical performance is evaluated in half-cells, and
the best formulations are selected to perform further ageing tests in pouch cells. In particular, post mortem
analyses such as electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy are conducted
on the cathodes after long-term cycling in Li-ion cells to fully understand the enhanced cycling stability observed
with H3PO4-containing water-based cathode. These analyses allow to conclude on the influence of the binder, the
current collector, and the aqueous immersion of the NMC532 powder.
In this study, we focus on lateral size effects of graphene nanosheets as conductive additives for LiNi0.5Co0.2Mn0.3O2 (NCM) cathode materials for Li-ion batteries. We used two different lateral sizes of graphene, 13 (GN-13) and 28 µm (GN-28). It can be found that the larger sheet sizes of graphene nanosheets give a poorer rate capability. The electrochemical measurements indicate that GN-13 delivers an average capacity of 189.8 mAh/g at 0.1 C and 114.2 mAh/g at 2 C and GN-28 exhibits an average capacity of 179.4 mAh/g at 0.1 C and only 6 mAh/g at 2 C. Moreover, according to the results of alternating current (AC) impedance, it can be found that the GN-28 sample has much higher resistance than that of GN-13. The reason might be attributed to that GN-28 has a longer diffusion distance of ion transfer and the mismatch of particle size between NCM and GN-28. The corresponding characterization might provide important reference for Li-ion battery applications.
Layered Li[NixCoyMz]O2 (M = Mn or Al, so-called NCM/NCA) ternary cathode materials have attracted a lot of intensive research efforts for high-performance lithium-ion batteries, because of their combined advantages with respect to energy density, production cost and environmental friendliness. However, those ternary metal oxides (especially Ni-rich) suffer from a few electrochemical cycling problems, such as strong capacity fading, severe voltage decay and safety issues. These problems are attributable mainly to the instability/irreversibility of the chemical composition, crystal structure and particle morphology, and the consequent undesirable physical/chemical processes during the synthesis and lithiation/delithiation processes. To circumvent these obstacles, a variety of strategies based on materials, electrode and electrolyte designs are investigated to effectively stabilize the NCM/NCA cathodes and to improve the electrochemical and thermal performance. This review scrutinizes the performance degradation mechanisms of the NCM/NCA materials and summarizes the recent advances in the materials, electrode and electrolyte levels by focusing on the relationships between the composition, structure, morphology, and properties. This paper intends to provide an easy entry for a comprehensive, systematic and deep understanding of the fundamentals, and offer a critical analysis and summary what have been done in the field and what are the challenges or hurdles to overcome.
This paper reports the structural and electrochemical studies of the composite made up of orthorhombic LiMnO2 (o-LiMnO2) and oxidized MWCNTs in various percentages where CNTs replaced the carbon black (CB) as an additive material. X-ray diffraction (XRD) patterns confirmed the formation of distorted orthorhombic phase of the space group with Pmnm. Raman spectra showed eight visible Raman modes of LiMnO2. A blue shift (~7 cm⁻¹) in the Raman mode associated with Mn–O bond of composite materials was observed, which was due to mechanical stresses. The EIS measurement indicated the low charge transfer resistance (105 kΩ) for o-LiMnO2/CNTs composites compared to o-LiMnO2/CB composites (195 kΩ). The CV results confirmed the reduction in potential gap between redox peaks with the addition of CNTs, which decreased from 2.02 V to 1.76 V. CNTs provided a network of conducting channel for Li ions as well as resulted in reduction of polarization of redox potentials.
For advancing lithium-ion battery (LIB) technologies, a detailed understanding of battery degradation mechanisms is important. In this article, experimental observations are provided to elucidate the relation between side reactions, mechanical degradation, and capacity loss in LIBs. Graphite/Li(Ni1/3Mn1/3Co1/3)O2 cells of two very different initial anode/cathode capacity ratios (R, both R > 1) are assembled to investigate the electrochemical behavior. The initial charge capacity of the cathode is observed to be affected by the anode loading, indicating that the electrolyte reactions on the anode affect the electrolyte reactions on the cathode. Additionally, the rate of “marching” of the cathode is found to be affected by the anode loading. These findings attest to the “cross-talk” between the two electrodes. During cycling, the cell with the higher R value display a lower columbic efficiency, yet a lower capacity fade rate as compared to the cell with the smaller R. This supports the notion that columbic efficiency is not a perfect predictor of capacity fade. Capacity loss is attributed to the irreversible production of new solid electrolyte interphase (SEI) facilitated by the mechanical degradation of the SEI. The higher capacity fade in the cell with the lower R is explained with the theory of diffusion-induced stresses (DISs).
Reducing cost and increasing energy density are two barriers for widespread application of lithium-ion batteries in electric vehicles. Although the cost of electric vehicle batteries has been reduced by ~70% from 2008 to 2015, the current battery pack cost (125/kWh). Even though many advancements in cell chemistry have been realized since the lithium-ion battery was first commercialized in 1991, few major breakthroughs have occurred in the past decade. Therefore, future cost reduction will rely on cell manufacturing and broader market acceptance. This article discusses three major aspects for cost reduction: (1) quality control to minimize scrap rate in cell manufacturing; (2) novel electrode processing and engineering to reduce processing cost and increase energy density and throughputs; and (3) material development and optimization for lithium-ion batteries with high-energy density. Insights on increasing energy and power densities of lithium-ion batteries are also addressed. © 2017 The Minerals, Metals & Materials Society (outside the U.S.)
Simple three-electrode pouch cells which can be used in distinguishing the voltage and resistance in individual electrodes of lithium ion batteries have been designed. Baseline (1 mm-staggered alignment, cathode away from a reference electrode) and aligned electrodes to a reference electrode located outside of the anode and cathode were studied to see alignment effects on resistance analysis. Cells composed of A12 graphite anodes, LiNi0.5Mn0.3Co0.2O2 (NMC 532 or NCM 523) cathodes, lithium foil references, microporous tri-layer membranes, and electrolytes, were cycled with cathode cutoff voltages between 3.0 V and 4.3 V for formation cycles or 4.6 V for C-rate performance testing. By applying a hybrid pulse power characterization (HPPC) technique to the cells, resistances of the baseline cells contributed by the anode and cathode were found to be different from those of the aligned cells, although overall resistances were close to ones from aligned cells. Resistances obtained via electrochemical impedance spectroscopy (EIS) and 2D simulation were also compared with those obtained from HPPC.
Processing lithium-ion battery electrode dispersions with water as the solvent during primary drying offers many advantages over NMP. An in-depth analysis of the comparative drying costs of lithium-ion battery electrodes is discussed for both NMP-based and water-based dispersion processing in terms of battery pack 3-6 M savings in associated plant capital equipment (for a plant producing 100,000 10-kWh PHEV batteries) by using water as the electrode solvent. This paper shows a different perspective in that the most important benefits of aqueous electrode processing actually revolve around capital equipment savings and environmental stewardship and not processing cost savings.
The work herein reports on studies aimed at exploring the correlation between electrolyte volume and electrochemical performance of full cell, pouch-cells consisting of graphite/ Li1.02Ni0.50Mn0.29Co0.19O2 (NMC-532) as the electrodes and 1.2 M LiPF6 in ethylene carbonate:ethylmethyl carbonate (EC:EMC) as the electrolyte. It is demonstrated that a minimum electrolyte volume factor of 1.9 times the total pore volume of cell components (cathode, anode, and separator) is needed for long-term cyclability and low impedance. Less electrolyte results in an increase of the measured ohmic resistances. Increased resistance ratios for charge transfer and passivation layers at cathode, relative to initial values, were 1.5–2.0 after 100 cycles. At the cathode, the resistance from charge transfer was 2–3 times higher than for passivation layers. Differential voltage analysis showed that anodes were less delithiated after discharging as the cells were cycled.
Increasing electrode thickness, thus increasing the volume ratio of active materials, is one effective method to enable the development of high energy density Li-ion batteries. In this study, an energy density versus power density optimization of LiNi0.8Co0.15Al0.05O2 (NCA)/graphite cell stack was conducted via mathematical modeling. The energy density was found to have a maximum point versus electrode thickness (critical thickness) at given discharging C rates. The physics-based factors that limit the energy/power density of thick electrodes were found to be increased cell polarization and underutilization of active materials. The latter is affected by Li-ion diffusion in active materials and Li-ion depletion in the electrolyte phase. Based on those findings, possible approaches were derived to surmount the limiting factors. The improvement of the energy–power relationship in an 18,650 cell was used to demonstrate how to optimize the thick electrode parameters in cell engineering.
Graphical Abstract
There is increasing research attention on optimizing the carbon black nanoparticles' structure and loading procedure for improving conductivities and thus, electrochemical performances of cathodes in lithium-ion batteries. Recently, LiNi0.5Co0.2Mn0.3O2(NCM523) has been actively investigated due to its larger specific capacity and lower cost compared to conventional cathode materials. Presented here is a high energy density NCM523 cathode obtained by reducing the carbon content using the state-of-the-art carbon nanoparticles developed at Cabot Corporation. It is the first time that the nonlinear conductivity of NCM523 electrodes has been discovered, which is significantly impacted by the dispersion and surface crystalline quality of carbon black nanoparticles, especially when the loading of carbon black is only 1 wt%. The nonlinear conductivity of the cathodes can dramatically affect their electrochemical performances at high rates (≧3C), which is close to the tunneling saturated current. In addition, there is no discernable difference in terms of the rate and cycle performance of the NCM523 electrodes, when reducing the loading of novel carbon black nanoparticles from 5 wt% to 1 wt% in the cathode. Therefore, the energy density of the electrode can be increased by 9% by using existing commercially available electrode materials.
Despite the extensive commercial use of Li1-xNi1-y-zMnzCoyO2 (NMC) as the positive electrode in Li-ion batteries, and its long research history, its fundamental transport properties are poorly understood. These properties are crucial for designing high energy density and high power Li-ion batteries. Here, the transport properties of NMC333 and NMC523 are investigated using impedance spectroscopy and DC polarization and depolarization techniques. The electronic conductivity is found to increase with decreasing Li-content (increasing state-of-charge) from similar to 10(-7) Scm(-1) to similar to 10(-2) Scm(-1) over Li concentrations x = 0.00 to 0.75, corresponding to an upper charge voltage of 4.8 V with respect to Li/Li+. The lithium ion diffusivity is at least one order of magnitude lower, and decreases with increasing x to at x = similar to 0.5. The ionic conductivity and diffusivity obtained from the two measurements techniques (EIS and DC) are in good agreement, and chemical diffusion is limited by lithium transport over a wide state-of-charge range.
Removing residual moisture in lithium-ion battery electrodes is essential for desired electrochemical performance. In this manuscript, the residual moisture in LiNi
0.5
Mn
0.3
Co
0.2
O
2
cathodes produced by conventional solvent-based and aqueous processing is characterized and compared. The electrochemical performance has also been investigated for various residual moisture contents. It has been demonstrated that the residual moisture lowers the first cycle coulombic efficiency, but its effect on short term cycle life is insignificant.
To properly evaluate the prospects for commercially competitive battery electric vehicles (BEV) one must have accurate information on current and predicted cost of battery packs. The literature reveals that costs are coming down, but with large uncertainties on past, current and future costs of the dominating Li-ion technology. This paper presents an original systematic review, analysing over 80 different estimates reported 2007-2014 to systematically trace the costs of Li-ion battery packs for BEV manufacturers. We show that industry-wide cost estimates declined by approximately 14% annually between 2007 and 2014, from above US410 per kWh, and that the cost of battery packs used by market-leading BEV manufacturers are even lower, at US$300 per kWh, and has declined by 8% annually. Learning rate, the cost reduction following a cumulative doubling of production, is found to be between 6 and 9%, in line with earlier studies on vehicle battery technology. We reveal that the costs of Li-ion battery packs continue to decline and that the costs among market leaders are much lower than previously reported. This has significant implications for the assumptions used when modelling future energy and transport systems and permits an optimistic outlook for BEVs contributing to low-carbon transport.
Contemporary methods for dispersion of carbon nanotubes in water and non-aqueous media are discussed. Most attention is paid to ultrasonic and plasma techniques and other physical techniques, as well as to the use of surfactants, functionalizing and debundling agents of distinct nature (elemental substances, metal and organic salts, mineral and organic acids, oxides, inorganic and organic peroxides, organic sulfonates, polymers, dyes, natural products, biomolecules, and coordination compounds). Special studies on CNTs solubilization are examined.
Degradation at the electrode surfaces is one of the major reasons behind capacity fade in well-constructed batteries. The effect of electrolyte additives, in particular vinylene carbonate (VC), is studied extensively for different lithium-ion chemistries and is shown to improve columbic efficiency of some electrodes. We investigate the effect of VC additive in a graphite/NMC333 (lithium-nickel-manganese-cobalt oxide) cell. The addition of VC improves the rate performance, especially, at moderately high rates. A new three-electrode cell design with Li reference electrode was particularly useful in studying the rate performance of each electrode. The rate of side reactions is found to decrease with the addition of VC. Despite these important performance improvements, no significant improvement in the capacity retention is observed. This suggests that the side reactions in graphite/NCM cells consist of two types, (1) repairing cracked solid electrolyte interphase (SEI) on the negative electrode (results in a net consumption of Li from the positive electrode), (2) reforming SEI components that dissolve from the negative electrode and are oxidized at the positive electrode. The VC appears to reduce the second type but have negligible effect on the first. This indicates that columbic efficiency measurements are not a reliable indicator of cell cycle life.
We present changes in the first and second order Raman spectra of multiwalled carbon nanotubes MWNTs functionalized with oxygenated groups. The oxygen groups were introduced onto the nanotube surface through two strong acid purification routes: 1 reflux in concentrated 70% HNO 3 acid for 4 h at 80 ° C and 2 ultrasonification in 3 HNO 3 70% :1H 2 SO 4 98% for 8.5 h. Raman spectroscopy, using two laser excitation wavelengths 514.5 and 632.8 nm, x-ray photoelectron spectroscopy, and thermal gravimetric analysis were employed to study the evolution of the products. All the techniques revealed a higher degree of functionalization for scheme 2 compared to scheme 1. Charge transfer phenomena were manifested by a shift of the C1s core level towards higher binding energies. We found that the intensity of both the D and G energy Raman modes if normalized to the second order mode D * mode follows similar trends upon acid treatments. We interpret this result together with the observed dispersion of G mode as an indication that the G mode in carbon nanotubes is defect induced in a double resonant process. Both acid schemes cause an upshift of D and G Raman modes, due to intercalation of acid molecules, exerting pressure on the sp 2 structure and an electron transfer from the states in MWNTs to the oxygen atoms. © 2006 American Vacuum Society.
Aqueous processing of thick electrodes for Li-ion cells promises to increase energy density due to increased volume fraction of active materials, and to reduce cost due to the elimination of the toxic solvents. This work reports the processing and characterization of aqueous processed electrodes with high areal loading and associated full pouch cell performance. Cracking of the electrode coatings becomes a critical issue for aqueous processing of the positive electrode as areal loading increases above 20–25 mg/cm² (∼4 mAh/cm²). Crack initiation and propagation, which was observed during drying via optical microscopy, is related to the build-up of capillary pressure during the drying process. The surface tension of water was reduced by the addition of isopropyl alcohol (IPA), which led to improved wettability and decreased capillary pressure during drying. The critical thickness (areal loading) without cracking increased gradually with increasing IPA content. The electrochemical performance was evaluated in pouch cells. Electrodes processed with water/IPA (80/20 wt%) mixture exhibited good structural integrity with good rate performance and cycling performance.
Silicon-based electrodes of various areal capacities, from about 1.5 to 15 mAh.cm⁻², were prepared with different conductive additives (carbon black, carbon nanofibers, and carbon nanoplatelets). The sensitivity of the cycling performance to the active mass loading is significant, with a major decrease of the capacity retention with increasing the loading in all cases. There is moreover a critical loading value above which the capacity retention abruptly drops. This critical loading depends on the conductive additive (∼1.75 mg cm⁻² for carbon black, ∼2.25 mg cm⁻² for carbon nanofibers and ∼3 mg cm⁻² for carbon nanoplatelets). The lower capacity retention capability for thicker electrode is attributed to (i) higher mechanical stresses within the electrode films and at the interface with the current collector and to (ii) poorer cohesion of electrodes with higher active silicon loading. Better capacity retention of electrodes with carbon nanoplatelets is attributed to (i) higher initial cohesion of the electrodes and to (ii) good ability of the electrode architecture to reversibly expand/contract upon cycling as shown by in situ electrochemical dilatometry. The efficiency of carbon nanoplatelets as conductive additive allows decreasing its amount in the electrode formulation to 6 wt% without sacrificing cycling performance. Contribution of carbon additives to the mechanical properties of the electrode is as important as their contribution to the electrical properties for silicon.
Successful deployment of electric vehicles requires maturity of the manufacturing process to reduce the cost of the lithium ion battery (LIB) pack. Drying the coated cathode layer and subsequent recovery of the solvent for recycle is a vital step in the lithium ion battery manufacturing plant and offers significant potential for cost reduction. A spreadsheet model of the drying and recovery of the solvent, is used to study the energy demand of this step and its contribution towards the cost of the battery pack. The base case scenario indicates that the drying and recovery process imposes an energy demand of ∼10 kWh per kg of the solvent n-methyl pyrrolidone (NMP), and is almost 45 times the heat needed to vaporize the NMP. For a plant producing 100 K battery packs per year for 10 kWh plug-in hybrid vehicles (PHEV), the energy demand is ∼5900 kW and the process contributes 1.12 per kg of NMP recovered, saving $2.08 per kg in replacement purchase.
Herein, we propose lithium ion batteries (LIBs) without binder or metal foils, based on a three-dimensional carbon nanotube (CNT) current collector. Because metal foils occupy 20–30 wt% of conventional LIBs and the polymer binder has no electrical conductivity, replacing such non-capacitive materials is a valid approach for improving the energy and power density of LIBs. Adding only 1 wt% of few-wall CNTs to the active material enables flexible freestanding sheets to be fabricated by simple dispersion and filtration processes. Coin cell tests are conducted on full cells fabricated from a 99 wt% LiCoO2-1 wt% CNT cathode and 99 wt% graphite-1 wt% CNT anode. Discharge capacities of 353 and 306 mAh ggraphite−1 are obtained at charge–discharge rates of 37.2 and 372 mA ggraphite−1, respectively, with a capacity retention of 65% at the 500th cycle. The suitability of the 1 wt% CNT-based composite electrodes for practical scale devices is demonstrated with laminate cells containing 50 × 50 mm2 electrodes. Use of metal combs instead of metal foils enables charge–discharge operation of the laminate cell without considerable IR drop. Such electrodes will minimize the amount of metal and maximize the amount of active materials contained in LIBs.
This work demonstrates how a very low fraction of graphene greatly enhances the usage efficiency of carbon-based conductive additive in LiCoO2-based lithium ion batteries (LIB) and develops a strategy using binary conductive additive to have a high performance battery, especially with excellent rate performance. With a much lower fraction of carbon additive for a commercial LIB, only 0.2 wt% graphene nanosheet (GN) together with 1 wt% Super-P (SP) constructing an effective conductive network, the prepared battery exhibits outstanding cycling stability (146 mAhg-1 at 1 C with retention of 96.4% after 50 cycles) and rate capability (116.5 mAhg-1 even at 5 C). In this battery, a composite conducting network is formed with a long-range electron pathway formed by a trace amount of GN and the short-range electron pathway by aggregation of SP particles. More interestingly, in micro-sized LiCoO2 system, the GN additive does not present hindrance effect for lithium ion transport even in high rate discharge, which is entirely different from the nano-sized LiFePO4 system. This study further demonstrates commercial potential of GN additive for high performance LIB and more importantly gives a well-designed recipe for its real application.
The electrochemical performance of lithium iron phosphate (LiFePO4) electrodes has been studied to find the optimum content of inactive materials (carbon black + polyvinylidene difluoride [PVDF] polymer binder) and to better understand electrode performance with variation in electrode composition. Trade-offs between inactive material content and electrochemical performance have been characterized in terms of electrical resistance, rate-capability, area-specific impedance (ASI), pulse-power characterization, and energy density calculations. The ASI and electrical conductivity were found to correlate well with ohmic polarization. The results showed that a 80:10:10 (active material: binder: carbon agents) electrode had a higher pulse-power density and energy density at rates above 1C as compared to 90:5:5, 86:7:7 and 70:15:15 formulations, while the 70:15:15 electrode had the highest electrical conductivity of 0.79 S cm−1. A CB/PVDF ratio of ca. 1.22 was found to be the optimum formulation of inactive material when the LiFePO4 composition was 80 wt%.
The electrochemical potential of cathode materials defines the positive side of the terminal voltage of a battery. Traditionally, cathode materials are the energy-limiting or voltage-limiting electrode. One of the first electrochemical batteries, the voltaic pile invented by Alessandro Volta in 1800 (Phil. Trans. Roy. Soc. 90, 403–431) had a copper-zinc galvanic element with a terminal voltage of 0.76 V. Since then, the research community has increased capacity and voltage for primary (non-rechargeable) batteries and round-trip efficiency for secondary (rechargeable) batteries. Successful secondary batteries have been the lead–acid with
a lead oxide cathode and a terminal voltage of 2.1 V and later the NiCd with a nickel(III) oxide–hydroxide cathode and a 1.2 V terminal voltage. The relatively low voltage of those aqueous systems and the low round-trip efficiency due to activation energies in the conversion reactions limited their use. In 1976, Wittingham (J. Electrochem. Soc., 123, 315) and Besenhard (J. Power Sources 1(3), 267) finally enabled highly reversible redox reactions by intercalation of lithium ions instead of by chemical conversion. In 1980, Goodenough and Mizushima (Mater. Res. Bull. 15, 783–789) demonstrated a high-energy and high-power LiCoO2 cathode, allowing for an increase of terminal voltage far beyond 3 V. Over the past four decades, the international research community has further developed cathode materials of many varieties. Current state-of-the-art cathodes demonstrate voltages beyond any known electrolyte stability window, bringing electrolyte research once again to the forefront of battery research.
A detailed processing cost breakdown is given for lithium-ion battery (LIB) electrodes, which focuses on: 1) elimination of toxic, costly N-methylpyrrolidone (NMP) dispersion chemistry; 2) doubling the thicknesses of the anode and cathode to raise energy density; and 3) reduction of the anode electrolyte wetting and SEI-layer formation time. These processing cost reduction technologies generically adaptable to any anode or cathode cell chemistry and are being implemented at ORNL. This paper shows step by step how these cost savings can be realized in existing or new LIB manufacturing plants using a baseline case of thin (power) electrodes produced with NMP processing and a standard 10-14-day wetting and formation process. In particular, it is shown that aqueous electrode processing can cut the electrode processing cost and energy consumption by an order of magnitude. Doubling the thickness of the electrodes allows for using half of the inactive current collectors and separators, contributing even further to the processing cost savings. Finally wetting and SEI-layer formation cost savings are discussed in the context of a protocol with significantly reduced time. These three benefits collectively offer the possibility of reducing LIB pack cost from 370.3 kWh-1-usable, a savings of $132.5/kWh (or 26.4%).
In lithium-ion battery electrode processing, obtaining good wetting and adhesion of the electrode dispersion to the current collector foil is essential for achieving high capacity and good long-term performance. The surface tension of LiFePO4 aqueous dispersions is much higher than the surface energy of untreated Al foil due to the high surface tension of water (72.8 mN/m), which causes inferior wetting during the coating step. In this work it has been shown that the surface energy of Al foil is significantly increased by corona plasma treatment. Consequently, the wetting and adhesion of the LiFePO4 aqueous dispersion to the Al foil are dramatically improved, as evidenced by contact angle measurements, adhesion energy calculations and interfacial tension calculations. The LiFePO4 cathodes with corona treated Al foil exhibited superior capacity (similar to 20 mAh/g improvement) with no increase in capacity fade at 0.5C/-0.5C cycling compared to an identical electrode without treatment.
This paper describes the development of a thick-film microcathode for use in Li-ion microbatteries in order to provide increased power and energy per area. These cathodes take advantage of a composite porous electrode structure, utilizing carbon nanotubes (CNT) as the conductive filler. The use of carbon nanotubes was found to significantly reduce the measured resistance of the electrodes, increase active material accessibility, and improve electrode performance. In particular, the cycling and power performance of the thick-film cathodes was significantly improved, and the need for compression was eliminated. Cathode thickness and CNT content were optimized to maximize capacity and power performance. Power capability of >50 mW/cm(2) (17 mA/cm(2)) with discharge capacity of >0.17 mAh/cm(2) was demonstrated. The feasibility of fabricating thick-film microcathodes capable of providing the power and capacity needed for use in autonomous microsensor systems was also demonstrated. (C) 2004 The Electrochemical Society.
The preparation of novel composite cathode of LiNi0.7Co 0.3O2 particles and multiwalled carbon nanotubes (MWCNT), was illustrated. The charge-discharge characteristics were examined with CR2032 coin cells and the microstructure of acetylene black and MWCNT was analyzed by high-resolution electron microscopy (HRTEM). The increase of discharge capacity was 39 mAh/g and improvement of cycle efficiency was 3.1% when MWCNTs replaced acetylene black at the same content. The results show that the conductive network formed by the LiNi0.7Co0.3O2 particles which were connected by MWCNT, was effective to improve reversible capacity and cycle efficiency.
Acetylene black, chemical vapor deposit carbon fibers and carbon nanotubes (CNTs) are employed as conductive additives in lithium ion batteries. Among them, carbon nanotubes are proved to be the most effective for decreasing the resistance and improving electrochemical behavior of the composite cathode. Their wire-like shape, crystallinity and nano-size are all considered to be important factors. Their wire-like shape favors developing continuous conductive network and then assures an efficient electronic transport throughout the cathode. Their higher crystalline and nano-size make them show better ability to rapidly transfer electrons and lower percolation threshold in comparison with vapor carbon fiber. Moreover, their higher surface energy guarantees their close contact with the active materials LiCoO2. The results suggest that much conductive additives could be saved by employing CNTs as conducting agents, and the cathode with only a small amount of CNTs conductive additives shows excellent rate capacity. A simplifying model to explain the phenomena is also presented.
The capacity of a lithium‐ion battery decreases during cycling. This capacity loss or fade occurs due to several different
mechanisms which are due to or are associated with unwanted side reactions that occur in these batteries. These reactions
occur during overcharge or overdischarge and cause electrolyte decomposition, passive film formation, active material dissolution,
and other phenomena. These capacity loss mechanisms are not included in the present lithium‐ion battery mathematical models
available in the open literature. Consequently, these models cannot be used to predict cell performance during cycling and
under abuse conditions. This article presents a review of the current literature on capacity fade mechanisms and attempts
to describe the information needed and the directions that may be taken to include these mechanisms in advanced lithium‐ion
battery models.
Single-wall carbon nanotubes pack into crystalline ropes that aggregate into tangled networks due to strong van der Waals attraction. Aggregation acts as an obstacle to most applications, and diminishes the special properties of the individual tubes. We describe a simple procedure for dispersing as-produced nanotubes powder in aqueous solutions of Gum Arabic. In a single step, a stable dispersion of full-length, well separated, individual tubes is formed, apparently due to physical adsorption of the polymer.
Lithium-ion cells being designed for transportation applications must sustain high current pulses under rapid discharge and rapid charge conditions without significant degradation of cell performance. In this article we examine the pulse discharge and charge performance of cells, containing a LiNi0.8Co0.15Al0.05O2-based cathode, a graphite-based anode, and a LiPF6-bearing EC:EMC electrolyte, at current rates ranging from 3 to 25 C. Impedance data indicate that 18650-type cells containing this chemistry can withstand 18 s discharge pulses at rates up to 17 C in the 3.7–4.0 V voltage window. Data from cells containing a LiSn micro-reference electrode show that the positive electrode impedance increases, whereas the negative electrode impedance decreases, with increasing magnitude of the discharge current pulse. The discharge pulse-current that can be sustained by the cell is limited by lithium diffusion into oxide particles of the positive electrode. Copyright © 2009 John Wiley & Sons, Ltd.
Some of the interesting properties when composite structures are formed from nanotubes and a conjugated polymer, poly(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene), are reported. To prepare the composite, multi-walled nanotubes produced in a Kratschmer generator were added to a solution of the polymer in toluene. The suspension was sonicated for 30 min in a low power sonic bath then allowed to settle for 3 days. The suspension was then decanted from the settled solid. This suspension is stable over infinite periods. The suspended material was drop-cast onto carbon grids and examined using transmission electron microscopy.
This paper describes the fabrication and testing of C-LiFePO4/graphite battery with different conductive carbon additives: carbon nanotube (CNT) or carbon black (CB). The discharge capacity, rate capability and cyclic performance of the battery were investigated. Compared with the batteries with CB additive, those with CNT additive show better electrochemical performances with capacity retention ratio of 99.2% after 50 cycles, and the ratio of discharge capacity at 0.1 C rate to that at 1 C rate is 94.6%. The reason for the difference in electrochemical property was studied with cyclic voltammagrams and AC impedance. It was found that, with CNT additive, the polarization voltage was decreased from 0.3 to 0.2 V, and the impedance was decreased from 423.2 to 36.88 Ω. The structures of active materials after cycling were characterized using XRD. The better crystal retaining of LiFePO4 was found in the active materials with CNT added.
Silicon is investigated intensively as a promising anode material for rechargeable lithium-ion batteries. The choice of binder is very important to solve the problem of the large capacity fade observed along cycling. Although carboxymethyl cellulose (CMC) is not an elastomeric binder, it has been shown to vastly improve the cycling performance of Si electrodes. We demonstrate here that the efficiency of CMC can be attributed to its extended conformation in solution that facilitates a networking process of the conductive additive and Si particles during the composite electrode elaboration. Taking advantage of this understanding, we have adjusted the processing conditions and obtained a four times higher reversible capacity of the Si/CMC electrode than that obtained with the same electrode processed with standard conditions.
Multi-walled carbon nanotubes (MWNT) are evaluated as a conducting agent in a high-density cathode for a Li-ion cell. Cathodes of LiCoO2 with a density of up to 4.0 g cm−3 are fabricated using alternate conducting agents of MWNT and conventional carbon black (Super P). An electrode containing MWNT (MWNT-cathode) is superior to one containing Super P (Super P-cathode) in terms of both high-rate (1 C) performance and cycle-life. Results from ac impedance and scanning electron microscopy (SEM) studies indicate that the improved performance of the former electrode is due largely to the resilience of the MWNT aggregates that form conductive bridges between particles of the active material. These resilient bridges maintain intimate contacts between the particles even when the composite expands on cycling. By contrast, similar but rigid bridges of carbon black in the Super P-cathode are broken on cycling. Overall, it is found that MWNT is a good candidate conducting agent to replace Super P and other carbon blacks and hence develop a high-energy Li-ion cell.
Addition of dispersants to aqueous based lithium-ion battery electrode formulations containing LiFePO(4) is critical to obtaining a stable suspension. The resulting colloidal suspensions enable dramatically improved coating deposition when processing electrodes. This research examines the colloidal chemistry modifications based on polyethyleneimine (PEI) addition and dispersion characterization required to produce high quality electrode formulations and coatings for LiFePO(4) active cathode material. The isoelectric point, a key parameter in characterizing colloidal dispersion stability, of LiFePO(4) and super P C45 were determined to be pH = 4.3 and 3.4, respectively. PEI, a cationic surfactant, was found to be an effective dispersant. It is demonstrated that 1.0 wt % and 0.5 wt % PEI were required to stabilize the LiFePO(4) and super P C45 suspension, respectively. LiFePO(4) cathode suspensions with 1.5 wt % PEI demonstrated the best dispersibility of all components, as evidenced by viscosity and agglomerate size of the suspensions and elemental distribution within dry cathodes. The addition of PEI significantly improved the LiFePO(4) performance.
Double coaxial carbon nanotubes with nitrogen (N)-doped and boron (B)-doped multiwalls possess composite Raman characteristics, originating not only from the outer N-doped but also from inner B-doped layers. Both N and B dopings result in substantial shifts of the characteristic D band and G band of sp(2) carbon constituting nanotube walls but in different ways. The downshift of the G band is correlated with the decreases of electrical resistivity of carbon nanotubes regardless of N or B doping.
Characterizing carbon materials with Raman spectroscopy
- Hodkiewicz
J. Hodkiewicz, T.F. Scientific, Characterizing carbon materials with Raman
spectroscopy, Prog. Mater. Sci. 50 (2005) 929e961, https://doi.org/10.1088/
0022-3727/46/12/122001.