Article

A Kinetic Indicator of Ultrafast Nickel-Rich Layered Oxide Cathodes

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Abstract

Elucidating high-rate cycling-induced nonequilibrium electrode reactions is crucial for developing extreme fast charging (XFC) batteries. Herein, we unveiled the distinct rate capabilities of a series of Ni-rich layered oxide (NRLO) cathodes by quantitatively establishing their dynamic structure–kinetics relationships. Contrary to conventional views, we discovered electrode kinetic properties obtained ex-situ near equilibrium states failed to assess the effective rate capability of NRLOs at ultrafast C rates. Further, the kinetic phase heterogeneity, characterized by the dynamic separations in in-situ X-ray diffraction patterns and deviations in NRLO c-axis lattice parameters, exclusively correlated with the capacity reduction under XFC and became an effective indicator of the NRLO rate capability. Enhancing the cycling temperature boosted the rate capability of studied NRLOs by ∼10%, which was further verified to mitigate the kinetic phase heterogeneity during XFC. Overall, this study lays the groundwork for tuning the kinetic phase heterogeneity of electrodes to develop ultrafast batteries.

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... Accordingly, the voltage curves in the asymptotic limit of extremely slow rates should converge towards the true thermodynamic equilibrium curve. 28 Ni-rich NMC cathode materials are assumed to have a solid solution nature-i.e. at low cycling rates, they behave as a single-phase material 29 in most of the compositional range, while the small voltage plateau between about 4.15 and 4.2 V vs Li + /Li°is due to the coexistence of two phases (H2 and H3) with limited lithium solubility. 30 On the other hand, it has been suggested that a kinetic two-phase coexistence is formed at high lithiation degrees during charging. ...
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In PART-1 of this paper, we present a generally applicable experimental methodology and a preliminary analysis strategy that can help researchers in the field of batteries to perform relevant measurements and a simple initial check of the self-consistency of the obtained impedance data of lithium-ion insertion electrodes. Using a model system based on a Ni-rich NMC active material, we demonstrate the necessary experimental steps to perform reliable and accurate impedance measurements of active electrodes (cells) and the characterization techniques required for a meaningful analysis of the obtained impedance data. We demonstrate the practical application of a simple preliminary analysis in which mass normalization of impedance spectra together with the assumption of ideal capacitive behavior allows access to the total (chemical) insertion capacitance, Ctotal , of the studied active material in an electrode. Furthermore, we show for the first time that there is an exact quantitative relationship (equality) between Ctotal , and the differential capacitance, Cd , of porous insertion electrodes. A series of impedance data obtained by systematically varying the NMC cathode mass (thickness) is further analyzed step by step in PART-2. Therein, we explain in detail the approach of analyzing impedance spectra using an advanced physics-based Transmission Line Model (TLM) and demonstrate the practical applicability of the scaling methodology. The main objective of PART-1 is to provide experimenters with directly applicable tools and skills to develop a basic intuition for exploring and explaining the key phenomena observed in the impedance responses of porous Li-ion insertion cathodes. PART-2 will highlight the major advantages of analyzing impedance data using physics-based models. Any model that is based on elements with physical meaning and is correct should pass the “consistency test” included in the scaling relations.
... Another possibility taken into consideration is that it is not the intrinsic phase evolution process of NCM811, i.e., a kineticinduced two-phase-like behavior is accounted for the splitting of reflections, which is mostly reported under fast charging conditions. 40,41 But some studies have also pointed out that the two-phase-like phenomenon can also occur in the cases without kinetic limitations, e.g., at low charging rates or in a relaxation state. 42,43 In this work, the latter case is in line with our observation. ...
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Fast-charging batteries typically use electrodes capable of accommodating lithium continuously by means of solid-solution transformation because they have few kinetic barriers apart from ionic diffusion. One exception is lithium titanate (Li4Ti5O12), an anode exhibiting extraordinary rate capability apparently inconsistent with its two-phase reaction and slow Li diffusion in both phases. Through real-time tracking of Li+ migration using operando electron energy-loss spectroscopy, we reveal that facile transport in Li4+ x Ti5O12 is enabled by kinetic pathways comprising distorted Li polyhedra in metastable intermediates along two-phase boundaries. Our work demonstrates that high-rate capability may be enabled by accessing the energy landscape above the ground state, which may have fundamentally different kinetic mechanisms from the ground-state macroscopic phases. This insight should present new opportunities in searching for high-rate electrode materials.
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Finite element (FE) modeling is a powerful method to investigate the volume change induced by lithium diffusion and the corresponding mechanical degradation for a deeper understanding of (dis)charging process in lithium-ion batteries. However, FE studies on the diffusion-stress interaction taking into consideration the effect of hydrostatic stress gradient in three-dimensional complex structures of electrodes are insufficient and limited. Higher charging rate can cause the high gradient of hydrostatic pressure which affects the diffusion flux in the electrode. Here, we present a fully coupled diffusional-mechanical FE model, which simultaneously solves the equations relevant to the diffusion and the mechanical behavior, by considering the mechanical contact between a tin oxide active layer and the hollow struts of a copper scaffold, as well as the pressure gradient. The numerically computed strains in the copper struts are in good agreement with the experimental strain data, previously measured in operando using X-ray diffraction. Calculations also show that large stresses are induced in the active layer during lithiation, causing elastic tensile strains in the scaffold which displays some residual strains after full discharging. The active layer is predicted to undergo plastic deformation during cyclic (dis)charging, and the amount of which grows significantly with increasing charging rate.
Article
High-nickel layered oxide cathode materials will be at the forefront to enable longer driving-range electric vehicles at more affordable costs with lithium-based batteries. A continued push to higher energy content and less usage of costly raw materials, such as cobalt, while preserving acceptable power, lifetime and safety metrics, calls for a suite of strategic compositional, morphological and microstructural designs and efficient material production processes. In this Perspective, we discuss several important design considerations for high-nickel layered oxide cathodes that will be implemented in the automotive market for the coming decade. We outline various intrinsic restraints of maximizing their energy output and compare current/emerging development roadmaps approaching low-/zero-cobalt chemistry. Materials production is another focus, relevant to driving down costs and addressing the practical challenges of high-nickel layered oxides for demanding vehicle applications. We further assess a series of stabilization techniques on their prospects to fulfill the aggressive targets of vehicle electrification. The development of high-nickel layered oxide cathodes represents an opportunity to realize the full potential of lithium-ion batteries for electric vehicles. Manthiram and colleagues review the materials design strategies and discuss the challenges and solutions for low-cobalt, high-energy-density cathodes.
Article
Extreme fast charging, with a goal of 15 minutes recharge time, is poised to accelerate mass market adoption of electric vehicles, curb greenhouse gas emissions and, in turn, provide nations with greater energy security. However, the realization of such a goal requires research and development across multiple levels, with battery technology being a key technical barrier. The present-day high-energy lithium-ion batteries with graphite anodes and transition metal oxide cathodes in liquid electrolytes are unable to achieve the fast-charging goal without negatively affecting electrochemical performance and safety. Here we discuss the challenges and future research directions towards fast charging at the level of battery materials from mass transport, charge transfer and thermal management perspectives. Moreover, we highlight advanced characterization techniques to fundamentally understand the failure mechanisms of batteries during fast charging, which in turn would inform more rational battery designs. Along with high energy density, fast-charging ability would enable battery-powered electric vehicles. Here Yi Cui and colleagues review battery materials requirements for fast charging and discuss future design strategies.
Article
The nickel-rich layered oxide LiNi0.8Mn0.1Co0.1O2 (NMC811) is a promising future cathode material for lithium-ion batteries in electric vehicles due to its high specific energy density. However, it exhibits fast voltage and capacity fading. In this article, we combine electrochemistry, operando synchrotron X-ray diffraction (XRD), and ex situ solid-state NMR spectroscopy to provide new insights into the structural changes and lithium dynamics of NMC811 during electrochemical charge and discharge, which are essential for a better understanding of its fast degradation. The evolution of the interlayer spacing is tracked by XRD, showing that it gradually increases upon delithiation before collapsing at high state-of-charge (SOC). Importantly, no two-phase O3→O1 transition is observed at high SOC, demonstrating that this cannot be a major cause of degradation. A strong increase of Li dynamics accompanies the increase of the interlayer spacing, which is shown by ⁷Li NMR and electrochemical characterization. At high SOC, Li mobility drops considerably, and Li/vacancy ordering can be observed by NMR. A detailed analysis of ⁷Li NMR spectra at different SOC is provided, demonstrating how Li NMR can be used to extract information on the dynamics of such challenging paramagnetic samples with several hundred different local Li environments. The insights on the evolution of structure and dynamics of NMC811 will further the understanding of its cycling behavior and contribute to the efforts of mitigating its performance fade.
Article
A planar electrochemical cell developed for operando/in situ neutron diffraction experiments at time-of-flight diffractometers was used to study a structural state of LixNi0.8Co0.15Al0.05O2 (NCA) electrodes with different degree of compaction. A two-phase-separated state of the NCA electrodes was observed in the first charge cycle. It was established that stronger compaction of the electrodes partially suppresses the phase separation of the cathode material: reduces a state of charge (SOC) range where two phases coexist, and decreases the difference between structural parameters of the phases. X-ray photoelectron spectroscopy has revealed a presence of Li2CO3 film at the surface of the NCA material in the amount that is unlikely to affect the NCA behavior during the first charge. It was suggested that the phase-separated state is caused by the morphology of the NCA material. This observation could be expanded to layered cathode materials with similar microstructures.
Article
Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air through reaction with atmospheric CO2. This surface impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact versus an eroded Li2CO3 surface-coating. This reaction heterogeneity, with a bimodal distribution of reaction states, has previously been interpreted as a "two-phase" reaction mechanism for NCA, as an activation step that only occurs during the first cycle. Similar surface layers may impact the reaction mechanism observed in other electrode materials using bulk probes such as operando powder XRD.
Article
Using fast time-resolved in situ X-ray diffraction, charge-rate dependent phase transition processes of layer structured cathode material LiNi1/3Mn1/3Co1/3O2 for lithium-ion batteries are studied. During first charge, intermediate phases emerge at high rates of 10C, 30C, and 60C, but not at low rates of 0.1C and 1C. These intermediate phases can be continuously observed during relaxation after the charging current is switched off. After half-way charging at high rate, sample studied by scanning transmission electron microscopy shows Li-rich and Li-poor phases' coexistence with tetrahedral occupation of Li in Li-poor phase. The high rate induced overpotential is thought to be the driving force for the formation of this intermediate Li-poor phase. The in situ quick X-ray absorption results show that the oxidation of Ni accelerates with increasing charging rate and the Ni4+ state can be reached at the end of charge with 30C rate. These results give new insights in the understanding of the layered cathodes during high-rate charging.
Article
Watching batteries fail Rechargeable batteries lose capacity in part because of physical changes in the electrodes caused by electrochemical cycling. Lim et al. track the reaction dynamics of an electrode material, LiFePO 4 , by measuring the relative concentrations of Fe(II) and Fe(III) in it by means of high-resolution x-ray absorption spectrometry (see the Perspective by Schougaard). The exchange current density is then mapped for Li ⁺ insertion and removal. At fast cycling rates, solid solutions form as Li ⁺ is removed and inserted. However, at slow cycling rates, nanoscale phase separation occurs within battery particles, which eventually shortens battery life. Science , this issue p. 566 ; see also p. 543
Article
Using ab initio calculations combined with experiments, we clarified how the kinetics of Li-ion diffusion can be tuned in NMC materials. It is found that Li-ions tend to choose oxygen dumbbell hopping (ODH) at the early stage of charging (delithiation), and tetrahedral site hopping (TSH) begins to dominate when more than 1/3 Li-ions are extracted. In both ODH and TSH, the Li-ions surrounded by nickel (especially with low valence state) are more likely to diffuse with low activation energy and form an advantage path. The Li slab space, which also contributes to the effective diffusion barriers, is found to be closely associated with the delithiation process (Ni oxidation) and the contents of Ni, Co, and Mn.
Article
The lithium (de)-insertion mechanism from LiNi0.80Co0.15Al0.05O2 (NCA) has been investigated by means of combined electrochemical analysis, operando differential electrochemical mass spectrometry (DEMS) experiments, and in situ X-ray diffraction (XRD) experiments during the first three cycles. Qualitative analysis of cyclic voltammetry data illustrated a possible irreversible activation of the material. Operando DEMS and internal cell pressure measurements combined with ex situ XRD and electrochemical impedance spectroscopy demonstrated that Li2CO3 surface film on the NCA electrode degrades on oxidation and reforms on reduction, which has an effect on the lithium (de)-insertion reaction kinetics. In situ XRD studies clearly show mechanistic differences in the reaction pathways between the first and second cycle/following cycles. While the first charge reveals a combination of an irreversible two-phase transition plus a reversible solid solution reaction mechanism, the second charge is mainly dominated by a solid solution process. Such differences have been ascribed to changes in two factors, the electronic conductivity and the Li ion mobility of the NCA electrode.
Article
The absence of a phase transformation involving substantial structural rearrangements and large volume changes is generally considered to be a key characteristic underpinning the high-rate capability of any battery electrode material. In apparent contradiction, nanoparticulate LiFePO4, a commercially important cathode material, displays exceptionally high rates, whereas its lithium-composition phase diagram indicates that it should react via a kinetically limited, two-phase nucleation and growth process. Knowledge concerning the equilibrium phases is therefore insufficient, and direct investigation of the dynamic process is required. Using time-resolved in situ x-ray powder diffraction, we reveal the existence of a continuous metastable solid solution phase during rapid lithium extraction and insertion. This nonequilibrium facile phase transformation route provides a mechanism for realizing high-rate capability of electrode materials that operate via two-phase reactions.
Article
This work attempts to understand the rate capability of layered transition metal oxides LiNiyMnyCo1−2yO2 (0.33 ≤ y ≤ 0.5). The rate capability of LiNiyMnyCo1−2yO2 increase with increasing Co in the compounds and with increasing amount of carbon additives in the electrodes. The lithium diffusion coefficients and electronic conductivities of LixNiyMnyCo1−2yO2 are investigated and compared. The 333 compound has higher diffusivity and electronic conductivity and thus better rate performance than 550. Chemical diffusion coefficients for both delithiation and lithiation of LixNiyMnyCo1−2yO2 investigated by GITT and PITT experiments are calculated to be around 10−10 cm2 s−1, lower than that of LixCoO2. The electronic conductivity of LixNiyMnyCo1−2yO2 is inferior compared to LixCoO2 at same temperature and delithiation stage. However, the LixNiyMnyCo1−2yO2 are able to deliver 55%–80% of theoretical capacity at 5 C with good electronic wiring in the composite electrode that make them very promising candidates for electric propulsion in terms of rate capability.
Article
Nika is an Igor Pro -based package for correction, calibration and reduction of two-dimensional area-detector data into one-dimensional data (`lineouts'). It is free (although the user needs a paid license for Igor Pro ), open source and highly flexible. While typically used for small-angle X-ray scattering (SAXS) data, it can also be used for grazing-incidence SAXS data, wide-angle diffraction data and even small-angle neutron scattering data. It has been widely available to the user community since about 2005, and it is currently used at the SAXS instruments of selected large-scale facilities as their main data reduction package. It is, however, also suitable for desktop instruments when the manufacturer's software is not available or appropriate. Since it is distributed as source code, it can be scrutinized, verified and modified by users to suit their needs.
Article
The rate capability of Li(Ni1/3Mn1/3Co1/3)O-2 (NMC) electrode is studied in this paper at the particle scale. Experimental results obtained on thin electrodes show that NMC is an extremely high-rate material capable of charge and discharge at rates exceeding 100C. The high capacity retention has not been previously reported in the literature. Even higher rate capability was seen on charge. The transport properties of the material were explored by combining experiments on thin electrodes with a continuum model of a single spherical particle. The use of thin electrodes minimized porous electrode effects and allowed the assumption of a uniform current distribution in the electrode. A qualitative estimate of the lithium diffusion coefficient in the NMC particle was obtained by comparing the experimental and simulated potentials during open-circuit relaxation at various states of charge. The fitting results show that the lithium diffusion coefficient increases with increasing state of charge. The value ranges from 10(-16) m(2)/s when completely discharged to 10(-14) m(2)/s when completely charged, suggesting that the use of a varying diffusion coefficient is necessary for studying the transport processes in this material and for further application to the macroscopic porous electrode models.
Article
The present work investigates the effects of cation mixing on electrochemical lithium intercalation involving absorption reaction and diffusion of lithium ion in porous Li1 − δNi1 − yCoyO2 electrodes (0 ≤ δ; y ≤ 1) by using electrochemical impedance spectroscopy (EIS). The measured electrode potential, instantaneous IR drop, lithium absorption resistance and lithium diffusivity have been discussed as functions of lithium content (1 − δ) and cobalt content y with respect to cation mixing between the Ni3+ and Li+ ions in porous Li1 − δNi1 − yCoyO2 electrodes.
Article
electrodes with thicknesses from were coated on Al current collectors. The electrochemical characteristics of these electrodes depend strongly on film thickness, with the largest rate capability for the thinnest film—a electrode can be discharged at a current rate of and still give a capacity of . This shows great promise for high-power applications such as hybrid electrical vehicles. Increasing the amount of carbon in the electrode, decreasing the packing density, or using an electrolyte with lower viscosity and higher ionic conductivity improved the rate performance. This suggests that the thickness effect is caused by a larger electrode resistance and a slower Li-ion conduction through the electrolyte for thicker films. Electrode thickness in turn affects the energy density of a battery, because the percentage of inactive materials increases with decreasing film thickness. An energy density prospect for a 18650-type battery with these electrodes gives a maximum capacity of at rate for a electrode. This corresponds to a volumetric and gravimetric energy density of and , respectively. The effective Li diffusivity in the active material is estimated to be of the order of .
Article
The LiNiO2LiCoO2 system exhibits a complete solid solution. These materials crystallize in the rhombohedral system with a layered structure. They have been used as positive electrode in lithium batteries. Up to 0.5 lithium atom can be reversibly deintercalated in the 3.5 to 4.0 V potential range. The highest specific energy (close to 500 W h/kg) is obtained in the LixNi0.7Co0.3O2 system. Moreover, the very small volume change upon deintercalation increased their interest for application point of view.
Article
The past two decades have shown that the exploration of properties on the nanoscale can lead to substantially new insights regarding fundamental issues, but also to novel technological perspectives. Simultaneously it became so fashionable to decorate activities with the prefix 'nano' that it has become devalued through overuse. Regardless of fashion and prejudice, this article shows that the crystallizing field of 'nanoionics' bears the conceptual and technological potential that justifies comparison with the well-acknowledged area of nanoelectronics. Demonstrating this potential implies both emphasizing the indispensability of electrochemical devices that rely on ion transport and complement the world of electronics, and working out the drastic impact of interfaces and size effects on mass transfer, transport and storage. The benefits for technology are expected to lie essentially in the field of room-temperature devices, and in particular in artificial self-sustaining structures to which both nanoelectronics and nanoionics might contribute synergistically.
Article
New applications such as hybrid electric vehicles and power backup require rechargeable batteries that combine high energy density with high charge and discharge rate capability. Using ab initio computational modeling, we identified useful strategies to design higher rate battery electrodes and tested them on lithium nickel manganese oxide [Li(Ni(0.5)Mn(0.5))O2], a safe, inexpensive material that has been thought to have poor intrinsic rate capability. By modifying its crystal structure, we obtained unexpectedly high rate-capability, considerably better than lithium cobalt oxide (LiCoO2), the current battery electrode material of choice.
Electrochemical Energy Storage Technical Team Roadmap
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Nickel-rich nickel manganese cobalt (NMC622) cathode lithiation mechanism
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Reaction heterogeneity in LiNi0. 8Co0. 15Al0. 05O2 induced by surface layer
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Grenier, A.; et al. Reaction heterogeneity in LiNi0. 8Co0. 15Al0. 05O2 induced by surface layer. Chem. Mater. 2017, 29, 7345− 7352.
High rate capability of Li (Ni1/3Mn1/3Co1
  • S.-L Wu
Wu, S.-L.; et al. High rate capability of Li (Ni1/3Mn1/3Co1/