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Abstract
As a promising cathode material for high performance lithium ion batteries, olivine LiMnxFe1−xPO4(LMFP) combines the high safety of LiFePO4and the high energy density of LiMnPO4. However, there are still obstacles to overcome for achieving higher rate performance, especially its inherent low electronic conductivity and Li⁺diffusion coefficient. Here, the restricting factors for realizing high rate performance LMFP cathode materials are reviewed systematically. The bulk properties that affect the internal ion transport and electronic conduction are thoroughly expounded, particularly the phase transition mechanism, lattice distortion, point defects, element doping, Fe/Mn ratio and particle morphology. Moreover, the effect of utilizing a carbon-based/non-carbon material coating for improving the interface structure on rate performance is discussed comprehensively. A particular emphasis is placed on the design of LMFP-based batteries with high rate capability as well from the aspect of cell preparation technology, including the electrolyte selection and electrode design. Finally, on the basis of state-of-the-art understanding of bulk properties, the interface structure and cell preparation engineering, several technical challenges and research trends in improving the rate performance of LMFP cathode materials are proposed.
... Its main disadvantage is a relatively low specific energy intensity, the theoretical value of which is ~580 W h/kg (for nickelenriched oxide materials this parameter is 700-800 W h/kg), as well as the low density of the material. A partial solution to this problem may be substitution of the Fe 2+ /Fe 3+ redox couple for Mn 2+ /Mn 3+ , the potential of which is 0.7 V higher, which could lead to an increase in the specific energy intensity of the material to 700 W h/kg [3,4]. However, LiMnPO 4 is not used as a cathode material for a number of reasons [2][3][4][5]. ...
... A partial solution to this problem may be substitution of the Fe 2+ /Fe 3+ redox couple for Mn 2+ /Mn 3+ , the potential of which is 0.7 V higher, which could lead to an increase in the specific energy intensity of the material to 700 W h/kg [3,4]. However, LiMnPO 4 is not used as a cathode material for a number of reasons [2][3][4][5]. Firstly, this phosphate has a lower electronic and ionic conductivity than LiFePO 4 , which leads to high overvoltage values during material charging and discharging [6]. ...
... Most authors are inclined to believe that the reason for this behavior is the Jahn-Teller distortion of the Mn 3+ cation [8,9]. Apparently, this distortion is responsible for the greater change in volume during the (de)intercalation of Li + (11%) compared to LiFePO 4 (6.5%), which also negatively affects the electrochemical properties of the material, creating excess voltage at the interfaces of the lithiated and delithiated phases [2][3][4][5][6][7][8][9]. ...
Lithium and transition-metal phosphates are promising cathode materials for lithium-ion batteries. Lithium manganese phosphate LiMnPO4 has a higher specific energy density than LiFePO4 used in practice: theoretical values of 700 and 580 W h/kg, respectively. However, its use is hampered by a number of disadvantages: reduced electronic and ionic conductivity, inferior stability of the structure in the charged form, and large changes in the volume during (de)lithiation. LiMnPO4 and LiMn0.95Ni0.05PO4 samples are synthesized by the solvothermal method and studied using X-ray powder diffraction, low-temperature nitrogen adsorption, scanning electron microscopy, and electrochemical methods. It is shown that a small degree of substitution of Mn for Ni (5 at %) leads to an increase in the capacity and Coulombic efficiency of LiMnPO4, a decrease in charge-transfer resistance, and an increase in Li+ diffusion coefficients.
... Currently, we are at the cusp of the third generation of LiBs where Ni-rich cathode chemistries will be coupled with silicon graphite composites to develop next-generation Li-ion batteries, especially for mobility applications. It has been estimated that in the coming decade high-energy NMC (HE-NMC), high-voltage spinels (HVS) [127], and lithium manganese iron phosphate (LMFP) [128] will transition towards the early stages of commercialization by mitigating their current challenges to satisfy the growing energy density and power density requirements of the EV industry. Figure 21 a shows the timeline for LiB technology development. ...
This review paper presents a comprehensive analysis of the electrode materials used for Li-ion batteries. Key electrode materials for Li-ion batteries have been explored and the associated challenges and advancements have been discussed. Through an extensive literature review, the current state of research and future developments related to Li-ion battery electrodes were identified. The study also covers a wide range of subtopics, including the theoretical aspects of the basic functioning of lithium-ion batteries and the crystal structures of different electrode materials. Additionally, emerging trends and future directions in the development of high-performance commercial battery electrodes have been revealed, providing insights into promising avenues for further research. By synthesizing existing knowledge and analyzing the latest research, this review aims to provide a valuable resource for researchers, practitioners, and stakeholders interested in developing state-of-the-art high-performance Li-ion batteries. The findings and perspectives presented in this paper contribute to a deeper understanding of electrode materials for Li-ion batteries and their advantages and disadvantages, ultimately fostering advancements and innovations in commercial lithium-ion battery (LiB) electrode technology.
... These techniques have almost reached their limit, and a further improvement of the performance requires an increase in the specific energy of LFP itself, for which increasing the mean voltage is the most effective way 15,16 . Among olivine-type cathode materials, LFP has a limited working potential of 3.4 V versus Li/Li + compared with 4.1, 4.8, and 5.2 V for LiMnPO 4 , LiCoPO 4 , and LiNiPO 4 , respectively [17][18][19] . However, these alternative "high-voltage" olivine-type cathodes are far from practical, either because of their poor electrical conductivity or they operate beyond the stable voltage range of the electrolyte. ...
Sustainable battery recycling is essential for achieving resource conservation and alleviating environmental issues. Many open/closed-loop strategies for critical metal recycling or direct recovery aim at a single component, and the reuse of mixed cathode materials is a significant challenge. To address this barrier, here we propose an upcycling strategy for spent LiFePO4 and Mn-rich cathodes by structural design and transition metal replacement, for which uses a green deep eutectic solvent to regenerate a high-voltage polyanionic cathode material. This process ensures the complete recycling of all the elements in mixed cathodes and the deep eutectic solvent can be reused. The regenerated LiFe0.5Mn0.5PO4 has an increased mean voltage (3.68 V versus Li/Li⁺) and energy density (559 Wh kg–1) compared with a commercial LiFePO4 (3.38 V and 524 Wh kg–1). The proposed upcycling strategy can expand at a gram-grade scale and was also applicable for LiFe0.5Mn0.5PO4 recovery, thus achieving a closed-loop recycling between the mixed spent cathodes and the next generation cathode materials. Techno-economic analysis shows that this strategy has potentially high environmental and economic benefits, while providing a sustainable approach for the value-added utilization of waste battery materials.
... Mn is abundant and inexpensive, and the Mn 2+ /Mn 3+ redox occurs at a higher voltage (Fig. 1b). 3,7 This higher voltage plateau potentially gives LMFP superior energy density, shown in Fig. 1a, while remaining low in cost compared to the alternatives. ...
LiMnxFe1−xPO4 is a promising positive electrode material for Li-ion batteries. In order to understand the failure mechanisms of this material, LiMn0.8Fe0.2PO4/graphite pouch cells were cycled at 40 or 55 °C over three voltage ranges: 2.5–3.6 V (Fe plateau), 3.6–4.2 V (Mn plateau), and 2.5–4.2 V (full voltage range). Cells cycled at higher temperature and over the full voltage range had the highest capacity fade. Differential voltage analysis showed that cells cycled over the Mn plateau and full voltage range had the highest Li inventory loss, and there was no active mass loss in any of the cells. Micro X-ray fluorescence spectroscopy showed that cells with higher levels of Mn deposition on the negative electrode had higher Li inventory loss. Constant voltage storage experiments at 55 °C showed rapid capacity loss for cells held at top of charge. Despite having similar Li inventory loss trends to the cycled cells, there was less Mn deposition on the negative electrodes. Thus, the capacity fade mechanisms are different for cells that undergo cycling and storage.
... Due to the similarity of the ions, the properties of LMP and LFP can be combined by partly replacing manganese with iron to form LiMn 1-x -Fe x PO 4 (LMFP) solid solution. [10,11] This way is a better strategy to cope with the Jahn-Teller effect, which make it not only show the high working potential of LMP, but also has the excellent rate performance of LFP. So far, many studies have been published to confirm the idea. ...
The intrinsically low electronic conductivity and slow ion diffusion kinetics limit further development of olivine LiFexMn1‐xPO4 cathode materials. In this paper, with the aim of improving the performance of such materials and alleviating the Jahn‐Taller effect of Mn³⁺ ion, a bimetallic oxalate precursor with gradient distribution of elemental concentration followed with an efficient process is applied to synthesize LiFe0.5Mn0.5PO4 nanocomposite. The results shown that with certain structural modulation of the precursor, the discharge capacity of synthesized LiFe0.5Mn0.5PO4 increased from 149 mAh g⁻¹ to 156 mAh g⁻¹ at 0.1 C, the cycling capacity was also remarkably improved. the Fe0.5Mn0.5C2O4 ⋅ 2H2O‐1 precursor with gradient distribution of elemental concentration effectively restricts the reaction between electrode material and electrolyte, thereby alleviates the dissolution of Mn³⁺ ion, reduces the decay of capacity and improves the stability of the material.
... The cathode material is a crucial component of LIBs. Several types of cathode materials are available, such as layered oxides (LiMO 2 , M = Ni, Co, Mn) [4], spinel oxide (LiM 2 O 4 , M = Mn, Ni, Co) [5], olivine salt (LiMn x Fe 1-x PO 4 ) [6], and lithium-rich manganese-based materials (xLi 2 MnO 3 ·(1-x) LiMO 2 , M = Ni, Co, Mn) [7]. Traditional cathode materials have limitations in terms of capacity and discharge current [8]. ...
In the present study, a novel layered cathodic compound, Li1-xNi0.58Co0.12Mn0.19Fe0.07Cr0.04MgxO2, was synthesized using an economically feasible oxalic acid co-precipitation method. The microstructure, morphology, and electrochemical properties of the synthesized compounds were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), charge–discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Electrochemical test results showed that the sample containing Cr = 0.04 and Mg = 0.02 exhibited the best electrochemical performance with an initial specific capacity of 181.76 mAh·g⁻¹ at 0.1 C, the capacity retention ratios of 88.81% at 200 cycles at 0.5 C. In addition, the 4Cr-2 Mg electrode exhibits superior rate capability with discharge capacities of 182.56, 171.13, 158.51, 133.41, and 121.01 mAh·g⁻¹ at 0.1, 0.2, 0.5, 1, and 2 C, respectively. Replacing Cr can play an essential role in improving maintenance capacity and cycling behavior. Additionally, the diffusibility of lithium-ion batteries (LIBs) was significantly improved as a result of Mg doping, which could be related to the reduction in Li⁺/Ni²⁺ cation mixing and its ionic radius.
Graphical Abstract
Olivine‐type LiFeyMn1−yPO4 (LFMP) is a promising cathode candidate with high energy density, chemical stability, and cost efficiency. However, an unidentified anomalous lithiation plateau (P II) often emerges between the Mn²⁺/Mn³⁺ and Fe²⁺/Fe³⁺ redox reactions, leading to a decrease in energy density. Herein, it is demonstrated that P II originates from the Mn²⁺/Mn³⁺ couple, yet it differs from the classical Mn³⁺ to Mn²⁺ reaction due to its lower operating voltage. During lithiation, Li⁺ initially accumulates on the particle surface, forming a lithium‐rich phase, while the interior remains a lithium‐poor phase. As lithiation proceeds, the two‐phase boundary experiences local compressive stress due to the counteracting forces during expansion. This stress compresses the boundary lattice, thereby lowering the operating voltage of Mn³⁺ and inducing the formation of P II. Such an effect is exacerbated by increased C‐rates and higher Mn‐content. Interestingly, the compressive stress acts as a double‐edged sword by enhancing Li⁺ diffusion kinetics and mitigating Jahn–Teller distortion, thereby fully unlocking the capacity of Mn³⁺. Furthermore, a particle‐size‐reduction strategy is developed to address the P II, which decreases its contribution from 28.59% to 7.77% at 2 C. These findings deepen the understanding of lithiation mechanisms in LFMP and offer novel insights for developing high‐power/voltage olivine‐type cathodes.
Olivine LiMnxFe1−xPO4 (LMFP) cathodes are gaining attention as a promising alternative to LiFePO4 (LFP) for lithium‐ion batteries (LIBs), offering higher energy density while maintaining lower costs and improved safety compared to traditional layered oxide cathodes. However, their low electronic conductivity remains a challenge. One effective strategy to enhance electrode kinetics is incorporating carbon additives during fabrication. This study examines the role of conductive additive optimization in LiMn0.7Fe0.3PO4 (LMFP73) electrodes and evaluates the impact of refining the electrode manufacturing to improve performance under practical conditions. Electrodes with 0.5 % single‐walled carbon nanotubes (SWCNTs) dispersion demonstrated improved performance. Optimization of mixing protocol, solid content, and coating speed, significantly enhanced the electrode's microstructure, mechanical integrity, and electrochemical response, producing thick electrodes suitable for industrial use. Upscaling to Graphite|LMFP73 single‐layer pouch (SLP) cells with 200 g m⁻² cathode loading resulted in 110 mAh g⁻¹ at C/2, retaining 93 % of the initial capacity after 100 cycles. This work provides practical process parameters to reduce the gap between academic and industrial perspectives in electrode performance assessment under realistic conditions, tackling challenges in performance improvement while taking into account high areal loadings, mechanical properties of the coatings, practical electrode balancing, and electrolyte amount in the cell fabrication process.
The olivine-type Li(Fe, Mn)PO4 positive electrode material is an alternative for LiFePO4 because of its higher energy density. In this study, chemical fluctuations in the Li(Fe, Mn)PO4 single particles were investigated using chemical mapping based on transmission electron microscopy. Spectral imaging based on electron energy-loss spectroscopy revealed the heterogeneous distribution of Mn and Fe in a single particle. The oxidation state of Fe fluctuated significantly in the elemental distribution compared with that of Mn, and Fe³⁺ was preferentially distributed in the Fe-rich domains of the particles. Natural air oxidation generates Fe³⁺ without batteries reactions. The spatial fluctuation of the Fe valence is affected by the local distribution of Mn and Fe.
Olivine-type LiFe1−xMnxPO4 (0 ≤ x < 1) is a high-energy cathode utilized in next-generation power sources. However, its poor electrical/ionic conductivity and Jahn–Teller distortions upon cycling limit its practical behaviors. To overcome these barriers, the use of monovalent Ag+ doping is confirmed to promote all key parameters (e.g., inherent electrical conductivity, cyclic lifespan, rate capability) of LiFe0.5Mn0.5PO4 cathodes. Theoretical calculations predict that this monovalent doping can narrow its bandgap, help shift the density of states toward a higher energy, and raise the electronic state numbers near the Fermi level, guaranteeing the high intrinsic electrical conductivity of the cathode. Four-probe testing solidly confirms that its conductivity can be vastly enhanced by 155.6% after Ag+ doping. In addition, we prove that 1% Ag+ doping is an optimal/economical choice to promote these electrochemical behaviors. Also, in situ x-ray diffraction detections further confirm that our doping can reinforce the lattice structures and inhibit lattice distortions. The assembled cells can output discharge capacity greater than 153.5 mAh g−1 at 0.1 C and achieve a capacity retention rate of 92.5% after 500 cycles, surpassing those of counterpart cases. Our work provides a smart two-birds-with-one-stone strategy to effectively elevate LiFe0.5Mn0.5PO4 cathodes for practical use.
Li‐ion battery performance relies fundamentally on modulation at the microstructure and interface levels of the composite electrodes. Correspondingly, the binder is a crucial component for mechanical integrity of the electrode, serving to interconnect the active material and conductive additive and to firmly attach this composite to the current collector. However, the commonly used poly(vinylidenefluoride) (PVDF) binder presents several limitations, including the use of toxic solvent during processing, a low electrical conductivity which for compensation requires the addition of carbon black, and weak interactions with active materials and collectors. This study investigates Poly(3,4‐ethylenedioxythiophene):poly[(4‐styrenesulfonyl) (trifluoromethylsulfonyl) imide] (PEDOT:PSSTFSI) as an alternative binder and conductive additive, in replacement of both PVDF and carbon black, in Li‐ion batteries with LiFe0.4Mn0.6PO4 at the positive electrode. Complex PEDOT:PSSTFSI significantly improves the electronic conductivity and lithium diffusion coefficient within the electrode, in comparison to standard PVDF binder and carbon black. This enhances significantly the electrochemical performance at high C‐rates and for high active mass loading electrodes. Furthermore, an excellent long‐range cyclability is achieved.
The practical application of LiMn1−xFexPO4 as a cathode material is hindered considerably by its poor electronic conductivity and slow lithium‐ion diffusion. In the present study, a uniform nitrogen‐doped carbon coating on LiMn0.7Fe0.3PO4 (LiMn0.7Fe0.3PO4@NC) was achieved using ethylene diamine tetraacetic acid (EDTA) as a chelating agent and carbon source. The nitrogen‐doped carbon layer enhanced the electronic conductivity and ionic diffusion of the LiMn0.7Fe0.3PO4 cathode. Furthermore, the uniform carbon layer prevented metal ion dissolution and stabilized the crystal structure. The resulting LiMn0.7Fe0.3PO4@NC‐2 sample demonstrated superior performance with a specific capacity of 152.5 mAh g⁻¹ at 0.1 C and preserved 93.7 % of this capacity over 200 cycles at 1 C. Meanwhile, the LiMn0.7Fe0.3PO4@NC‐2 sample demonstrated a high Li⁺ diffusion coefficient (3.98×10⁻¹¹ cm² s⁻¹) and electrical conductivity (1.47×10⁻² S cm⁻¹). This study presents a novel approach to designing high‐performance cathode materials using a cost‐effective and straightforward process.
To improve the ionic conductivity of the LiFePO4 cathode for high-performance solid-state lithium-ion batteries, we incorporated the chemically stable and ion-conductive Li6.75La3Zr1.75Ta0.25O12 (LLZTO) into the cathode. We discovered that the impact of this incorporation on enhancing conductivity was influenced by how well the LLZTO particles were dispersed. A solid-state battery constructed with the LiFePO4 cathode without any LLZTO incorporated exhibited an initial capacity of 146 mAh g−1 at 0.2C, with a retention of 26 % after 100 cycles of charge-discharge. When the cathode was incorporated with LLZTO particles in their original agglomerated state, the initial capacity remained similar to the pristine one, but the retention decreased to <20 %. However, when LLZTO was well-dispersed during incorporation, the initial capacity increased to 160 mAh g−1, and retention improved to over 95 %. The difference in the effectiveness of incorporating dispersed and agglomerated LLZTO on the electrochemical performance has been clarified to be mainly related to the polarization of Li+ during transport in the cathodes. This was elucidated by numerical simulations based on finite element analysis, which revealed that incorporating LLZTO agglomerates leads to a deficiency of Li+ transport in specific regions within the LiFePO4 cathode and non-uniform Li+ transport through LLZTO, resulting in reduced overall cathode conductivity and battery performance.
Ultra‐fast magic‐angle spinning (100+ kHz) has revolutionized solid‐state NMR of biomolecular systems but has so far failed to gain ground for the analysis of paramagnetic organic and inorganic powders, despite the potential rewards from substantially improved spectral resolution. The principal blockages are that the smaller fast‐spinning rotors present significant barriers for sample preparation, particularly for air/moisture‐sensitive systems, and are associated with lower sensitivity from the reduced sample volumes. Here these difficulties are overcome by improvements in rotor ceramics and handling methods that enable the routine use of this setup for repetitive, high‐throughput analysis of sensitive samples. Furthermore, we demonstrate that the sensitivity penalty is less severe than expected for highly paramagnetic solids and is more than offset by the associated improved resolution. While previous approaches employing slower MAS are often unsuccessful in providing sufficient resolution, we show that ultra‐fast 100+ kHz MAS allows site‐specific assignments of all resonances from complex paramagnetic solids. This opens the way to routine characterisation of geometry and electronic structures of functional paramagnetic systems in chemistry, including catalysts and battery materials. We benchmark this approach on a hygroscopic luminescent Tb3+ complex, an air‐sensitive homogeneous high‐spin Fe2+ catalyst, and a series of mixed Fe2+/Mn2+/Mg2+ olivine‐type cathode materials.
Ultra‐fast magic‐angle spinning (100+kHz) has revolutionized solid‐state NMR of biomolecular systems but has so far failed to gain ground for the analysis of paramagnetic organic and inorganic powders, despite the potential rewards from substantially improved spectral resolution. The principal blockages are that the smaller fast‐spinning rotors present significant barriers for sample preparation, particularly for air/moisture‐sensitive systems, and are associated with low sensitivity from the reduced sample volumes. Here, we demonstrate that the sensitivity penalty is less severe than expected for highly paramagnetic solids and is more than offset by the associated improved resolution. While previous approaches employing slower MAS are often unsuccessful in providing sufficient resolution, we show that ultra‐fast 100+kHz MAS allows site‐specific assignments of all resonances from complex paramagnetic solids. Combined with more reliable rotor materials and handling methods, this opens the way to the routine characterization of geometry and electronic structures of functional paramagnetic systems in chemistry, including catalysts and battery materials. We benchmark this approach on a hygroscopic luminescent Tb³⁺ complex, an air‐sensitive homogeneous high‐spin Fe²⁺ catalyst, and a series of mixed Fe²⁺/Mn²⁺/Mg²⁺ olivine‐type cathode materials.
Despite the widespread commercialization of LiFePO4 as cathodes in lithium‐ion batteries, the rigid 1D Li‐ion diffusion channel along the [010] direction strongly limits its fast charge and discharge performance. Herein, lattice engineering is developed by the planar triangle BO3³⁻ substitution on tetrahedron PO4³⁻ to induce flexibility in the Li‐ion diffusion channels, which are broadened simultaneously. The planar structure of BO3³⁻ may further provide additional paths between the channels. With these synergetic contributions, LiFe(PO4)0.98(BO3)0.02 shows the best performance, which delivers the high‐rate capacity (66.8 mAh g⁻¹ at 50 C) and long cycle stability (ultra‐low capacity loss of 0.003% every cycle at 10 C) at 25 °C. Furthermore, excellent rate performance (34.0 mAh g⁻¹ at 40 C) and capacity retention (no capacity loss after 2500 cycles at 10 C) at −20 °C are realized.
Environmental impacts and resource availability are significant concerns for the future of lithium-ion batteries. This study focuses on developing novel fluorine-free electrolytes compatible with aqueous-processed cobalt-free cathode materials. The new electrolyte contains lithium 1,1,2,3,3-pentacyanopropenide (LiPCP) salt. After screening various organic carbonates, a mixture of 30:70 wt.% ethylene carbonate and dimethyl carbonate was chosen as the solvent. The optimal salt concentration, yielding the highest conductivity of 9.6 mS·cm−1 at 20 °C, was 0.8 mol·kg−1. Vinylene carbonate was selected as a SEI-stabilizing additive, and the electrolyte demonstrated stability up to 4.4 V vs. Li+/Li. LiFePO4 and LiMn0.6Fe0.4PO4 were identified as suitable cobalt-free cathode materials. They were processed using sodium carboxymethyl cellulose as a binder and water as the solvent. Performance testing of various cathode compositions was conducted using cyclic voltammetry and galvanostatic cycling with the LiPCP-based electrolyte and a standard LiPF6-based one. The optimized cathode compositions, with an 87:10:3 ratio of active material to conductive additive to binder, showed good compatibility and performance with the new electrolyte. Aqueous-processed LiFePO4 and LiMn0.6Fe0.4PO4 achieved capacities of 160 mAh·g−1 and 70 mAh·g−1 at C/10 after 40 cycles, respectively. These findings represent the first stage of investigating LiPCP for the development of greener and more sustainable lithium-ion batteries.
The concerns on the cost of lithium‐ion batteries have created enormous interest on LiFePO4 (LFP) and LiMn1‐xFexPO4 (LMFP) cathodes However, the inclusion of Mn into the olivine structure causes a non‐uniform atomic distribution of Fe and Mn, resulting in a lowering of reversible capacity and hindering their practical application. Herein, a co‐doping of LMFP with Nb and Mg is presented through a co‐precipitation reaction, followed by a spray‐drying process and calcination. It is found that LiNbO3 formed with the aliovalent Nb doping resides mainly on the surface, while the isovalent Mg²⁺ doping occurs into the bulk of the particle. Full cells assembled with the co‐doped LMFP cathode and graphite anode demonstrate superior cycling stability and specific capacity, while maintaining good tap density, compared to the undoped or mono‐doped (only with Nb or Mg). The co‐doped sample exhibits a capacity retention of 99% over 300 cycles at a C/2 rate. The superior performance stems from the enhanced ionic/electronic transport facilitated by Nb coating and the enhanced Mn2+/3+ redox kinetics resulting from bulk Mg doping. Altogether, this work reveals the importance of the synergistic effect of different dopants in enhancing the capacity and cycle stability of LMFP.
Na4Mn1.5Fe1.5(PO4)2P2O7 (NMFPP), with its low cost and high energy density, is essential for accelerating the commercialization of sodium‐ion batteries. However, its practical application is limited by serious voltage hysteresis and detrimental Jahn‐Teller distortions. Herein, a high operating voltage and superior stable Nb‐doped NMFPP with fewer intrinsic anti‐site defects are elaborately designed by the reconstruction of the crystal lattice and electronic distribution. By introducing higher charge density Nb─O bonds, the lengths of Mn‐O bonds are shortened, enhancing lattice stability. As a result, the lattice volume contracted during Na⁺ extraction/insertion is decreased with niobium‐modified Na4(Mn0.5Fe0.5)2.94Nb0.06(PO4)2P2O7, mitigating lattice distortion from the Jahn‐Teller effect and increasing the capacity retention after 1000 cycles from 57.5% to 82.3%. More importantly, the delayed effect of Mn²⁺ involvement in redox reactions is significantly reduced, raising the average operating voltage from 3.32 to 3.64 V and increasing the overall energy density by 13%. This study opens new avenues to develop advanced sodium‐ion battery cathode materials with high energy density and long calendar life for energy storage.
In recent years, batteries have revolutionized electrification projects and accelerated the energy transition. Consequently, battery systems were hugely demanded based on large-scale electrification projects, leading to significant interest in low-cost and more abundant chemistries to meet these requirements in lithium-ion batteries (LIBs). As a result, lithium iron phosphate (LFP) share has increased considerably due to lower cost and higher safety compared to conventional nickel and cobalt-based chemistries. However, their fast-growing share is affected by updated chemistries, where cheaper systems like sodium-ion batteries (SIBs) are becoming more attractive. SIBs also benefited from the greener, more ethical, and evenly distributed elemental resources. SIBs are fast approaching market thanks to mature LIB’s technology and manufacturing scalability using existing Li-ion gigafactories. Additionally, SIBs can be adapted to other emerging technologies, including Li-ion batteries and silicon-based anodes, influencing projections for their broader use. However, despite the lower cost and abundance of sodium chemistries compared to lithium ones, limited manufacturing capacity discourages material suppliers from increasing production, which restricts the supply chain, raises costs, and diminishes Na battery manufacturing. Here, we aim to provide an overview of the progress of SIBs in gaining market share from LIBs. We first reviewed LIB and SIB histories, developments, and market share. Then, we analyzed the offered chemicals in battery components, their resources and supplies, material demand, and supply chain. The commercialization of each system was investigated in addition to the challenges related to energy density, environmental impact, sustainability, and safety. If all these concerns are addressed properly, LIBs and SIBs could potentially offer a more affordable, safer, and sustainable choice for the global energy storage outlook, particularly in short-range electric vehicles and stationary grid storage.
A novel composite consisting of fluorine-doped carbon and graphene double-coated LiMn0.6Fe0.4PO4 (LMFP) nanorods was synthesized via a facile low-temperature solvothermal method that employs a hybrid glucose and polyvinylidene fluoride as carbon and fluorine sources. As revealed by physicochemical characterization, F-doped carbon coating and graphene form a ‘point-to-surface’ conductive network, facilitating rapid electron transport and mitigating electrochemical polarization. Furthermore, the uniform thickness of the F-doped carbon coating alters the growth of nanoparticles and prevents direct contact between the material and the electrolyte, thereby enhancing structural stability. The strongly electronegative F− can inhibit the structural changes in LMFP during charge/discharge, thus reducing the Jahn–Teller effect of Mn3+. The distinctive architecture of the LMFP/C-F/G cathode material exhibits excellent electrochemical properties, exhibiting an initial discharge capacity of 163.1 mAh g−1 at 0.1 C and a constant Coulombic efficiency of 99.7% over 100 cycles. Notably, the LMFP/C-F/G cathode material achieves an impressive energy density of 607.6 Wh kg−1, surpassing that of commercial counterparts. Moreover, it delivers a reversible capacity of 90.3 mAh g−1 at a high current rate of 5 C. The high-capacity capability and energy density of the prepared materials give them great potential for use in next-generation lithium-ion batteries.
Cathode materials are the core components of lithium‐ion batteries owing to the determination of the practical voltage and effective energy of the battery system. However, advanced cathodes have faced challenges related to cation migration and cation intermixing. In this review, the study summarizes the structural failure mechanisms due to the cation mixing of advanced cathodes, including Ni‐rich and Li‐rich layered cathodes, spinel, olivine, and disordered rock‐salt materials. This review starts by discussing the structural degradation mechanisms caused by cation intermixing in different cathodes, focusing on the electronic structure, crystal structure, and electrode structure. Furthermore, the optimization strategies for effective inhibition of cation migration and rational utilization of cation mixing are systematically encapsulated. Last but not least, the remaining challenges and proposed perspectives are highlighted for the future development of advanced cathodes. The accurate analysis of cation migration using advanced characterization, precise control of material synthesis, and multi‐dimensional synergistic modification will be the key research areas for cation migration in cathodes. This review provides a comprehensive understanding of cation migration and intermixing in advanced cathodes. The effective inhibition of cation migration and the rational utilization of cation intermixing will emerge as pivotal and controllable factors for the further development of advanced cathodes.
LiMnxFe1−xPO4 (LMFP) has emerged as a promising cathode material for Li-ion batteries due to its lower cost, better sustainability, and improved thermal and cycling stabilities compared to layered oxide cathodes. The incorporation of Mn in LMFP increases the operating voltage, and therefore the theoretical energy density, compared to LiFePO4. However, with high Mn content, it is difficult to fully utilize the Mn2+/3+ redox due to sluggish kinetics, resulting in a lower practical capacity. Atomic-scale mixing of Mn and Fe is crucial for the optimal electrochemical performance of LMFP, yet the practical scalability and the ease of synthesizing precursor compositions with different Mn contents through co-precipitation reaction remains underexplored. We present here for LMFP manufacturing a novel, scalable precursor (Mn, Fe)5(PO4)2(HPO4)2·4H2O, which is air-stable and is synthesized without the use of ammonia, for the first time. The role of the reactants, pH, and temperature in controlling the phase purity and morphology of the precursor are explored. Particularly, it is found that phase purity is highly sensitive to the Mn : Fe ratio and temperature during co-precipitation. The LMFP cathodes synthesized with the precursor exhibit excellent cycling stability, retaining over 95% capacity after 150 cycles at a C/3 rate. However, while higher Mn content (>60%) increases the average voltage, the specific capacity decreases due to sluggish kinetics, limiting the benefit to energy density. This work presents an industrially scalable method to synthesize mixed precursors for LMFP cathodes with a wide range of Mn contents providing a pathway to fine-tune the Mn content and particle morphology for optimal electrochemical performance.
The replacement of Li by Na in an analogue battery to the commercial Li-ion one appears a sustainable strategy to overcome the several concerns triggered by the increased demand for the electrochemical energy storage. However, the apparently simple change of the alkali metal represents a challenging step which requires notable and dedicated studies. Therefore, we investigate herein the features of a NaFe0.6Mn0.4PO4 cathode with triphylite structure achieved from the conversion of a LiFe0.6Mn0.4PO4 olivine for application in Na-ion battery. The work initially characterizes the structure, morphology and performances in sodium cell of NaFe0.6Mn0.4PO4, achieving a maximum capacity exceeding 100 mAh g−1 at a temperature of 55 °C, and adequate rate capability, and suitable retention confirmed by ex-situ measurements. Subsequently, the study compares in parallel key parameters of the NaFe0.6Mn0.4PO4 and LiFe0.6Mn0.4PO4 such as Na+/Li+ ions diffusion, interfacial characteristics, and reaction mechanism in Na/Li cells using various electrochemical techniques. The data reveal that relatively limited modification of NaFe0.6Mn0.4PO4 chemistry, structure and morphology compared to LiFe0.6Mn0.4PO4 greatly impact the reaction mechanism, kinetics and electrochemical features. These changes are ascribed to the different physical and chemical features of the two compounds, the slower mobility of Na+ with respect to Li+ , and a more resistive electrode/electrolyte interphase of sodium compared with lithium. Relevantly, the study reveals analogue trends of the charge transfer resistance and the ion diffusion coefficient in NaFe0.6Mn0.4PO4 and LiFe0.6Mn0.4PO4 during the electrochemical process in half-cell. Hence, the NaFe0.6Mn0.4PO4 achieved herein is suggested as a possible candidate for application in a low-cost, efficient, and environmentally friendly Na-ion battery.
As a successor to LiFePO4, the research interest in LiMn1−yFeyPO4 has been sustained due to its higher working voltage and safety features. However, its further application is limited by the low compaction density caused by uncontrolled particle size. In this study, the high-quality LiMn0.69Co0.01Fe0.3PO4 (LMFP) materials were prepared using the freeze-drying method to process the LMFP precursor synthesized through a solvothermal crystallization method followed by a calcination process at different temperatures (400–550 °C). The results demonstrate that the obtained particles exhibit a spheroidal shape with a low specific surface area after secondary crystallization calcination at 700 °C. The compaction density increased from 1.96 g/cm3 for LMFP precursor (LMFP-M1) to 2.18, 2.27, 2.34, and 2.43 g/cm3 for samples calcined at 400, 450, 500 and 550 °C, respectively, achieving a maximum increase of 24%. The full cell constructed with the high-compaction-density material calcined at 500 °C displayed discharge capacities of 144.1, 143.8, and 142.6 mAh/g at 0.5, 1, and 3 C rates, respectively, with a retention rate of 99% at 3 C rate. After undergoing charging and discharging cycles at a rate of 1 C for up to 800 cycles, the capacity retention rate was found to be 90%, indicating an expected full cell life span exceeding 2500 cycles.
The research strategy of using discarded lithium manganate (LiMn2O4, LMO) and lithium iron phosphate (LiFePO4, LFP) electrode materials to obtain lithium manganese iron phosphate (LiMnxFe1−xPO4, LMFP) materials with high energy density and ionic conductivity is increasingly highlighted as powerful and effective. The study explores a new strategy to prepare high‐performance LMFP materials using high‐temperature sintering based on the successful recovery of LMO and LFP electrode wastes. X‐ray diffraction results show that the LMFP cathode materials are prepared successfully by using discarded LMO and LFP materials. LM0.4F0.6P and LM0.6F0.4P, whose manganese‐to‐iron molar ratio [MR(Mn/Fe)] 4:6 and 6:4, exhibit nano‐sized olivine spheres with lattice diagram corresponding to the (101) crystal planes. The constant current curves show that LM0.6F0.4P has a specific discharge capacity of 154.4 mAh g⁻¹ at 0.2 C. The capacity retention rate is maintained at 96.2% after 100 cycles. The cyclic voltammetry curves show that two distinct pairs of redox potentials appeared for LM0.6F0.4P in the voltage interval located at (3.63 V/3.43 V) and (4.18 V/3.87 V). Thus, the proposed strategy predicts that the discarded LMO and LFP can be used as raw materials to prepare high‐performance LMFP cathode materials, significantly reducing energy consumption and environmental pollution.
The automotive industry aims for the highest possible driving range (highest energy density) in combination with a fast charge ability (highest power density) of electric vehicles. With both targets being intrinsically contradictory, it is important to understand and optimize resistances within lithium-ion battery (LIB) electrodes. In this study, the properties and magnitude of electronic resistance contributions in LiMn0.7Fe0.3PO4 (LMFP)- and LiNixCoyMnzO2 (NCM, x = 0.88~0.90, x + y + z = 1)-based electrodes are comprehensively investigated through the use of different measurement methods. Contact resistance properties are characterized via electrochemical impedance spectroscopy (EIS) on the example of LMFP cathodes. The EIS results are compared to a two-point probe as well as to the results obtained using a novel commercial 46-point probe system. The magnitude and ratio of contact resistance and compound electronic resistance for LMFP- and NCM-based cathodes are discussed on the basis of the 46-point probe measurement results. The results show that the 46-point probe yields significantly lower resistance values than those in EIS studies. Further results show that electronic resistance values in cathodes can vary over several orders of magnitude. Various influence parameters such as electrode porosity, type of current collector and the impact of solvent soaking on electronic resistance are investigated.
LiFe1-xMnxPO4 with elevated energy density is becoming the next-generation olivine-type cathode. However, its long-cyclic stability and delivered capacities are far from perfect, chiefly induced by its intrinsically poor ionic/electrical conductivities,...
Li-ion cells with a LiMnxFe1−xPO4 (LMFP) and LiNi1−x−y−zCoxMnyAlzO2 (NCMA) blending cathode show their benefits of lower cost and higher safety compared to barely NCMA cathode-based cells. However, the rate capability of LMFP material is relatively poor compared to NCMA or even LiFePO4, which is because of the low electronic conductivity of LMFP material and the 1D diffusion channel in its structure. This work discusses the effect on electrochemical performance when blends of various ratios of LMFP are used in an NCMA cathode, with data verified by a 5 Ah pouch cell. This work further investigated the interaction between NCMA and LMFP during charge/discharge. Combining results from experiment and simulation, it evidences that blending more LMFP does not always lead to worse discharge rate but reduces charge rate. Moreover, it is found that, in a constant current discharge/charge process, although the system is under continuous discharge/charge, LMFP works intermittently. This leads to different diffusion polarization states of LMFP in the discharge/charge process and further results in a difference in discharge/charge rate capability. Therefore, to improve rate capability, especially charging rate, using smaller-sized or doped LMFP to improve its diffusion coefficient is an optimized strategy.
We performed an electrochemical investigation of the relaxation process of the LiMn0.75Fe0.25PO4 single-phase reaction after the termination of lithium extraction/insertion for various C rates and lithium contents using the relaxation analysis method. It was found that the lattice constants changed and the unit cell volume increased during the relaxation process. We propose that formation of the lithium defective domain containing the diffusing lithium with a small unit cell volume, through which lithium prefers to diffuse, is kinetically favored during the lithium extraction/insertion process and that the domain separates into the Li-rich phase and the domain without excess lithium during the relaxation process.
The practical application of Li‐rich Mn‐based oxide cathode is predominately retarded by the capacity decline and voltage fading, associated with the structure distortion and anionic redox reactions. Here, a linkage‐functionalized modification approach to tackle these challenges via a synchronous lithium oxidation strategy is reported. The doping of Ce in the bulk phase activates the pseudo‐bonding effect, effectively stabilizing the lattice oxygen evolution and suppressing the structure distortion. Interestingly, it also induces the formation of spinel phase Li4Mn5O12 in the subsurface, which in turn constructs the phase boundaries, thereby arousing the interior self‐built‐in electric field to prevent the outward migration of bulk oxygen anions and boost the charge transfer. Moreover, the formed coating layer Li2CeO3 with oxygen vacancies accelerates Li+ diffusion and mitigates electrolyte cauterization. The corresponding cathode exhibits superior long‐cycle stability after 300 cycles with only a 0.013% capacity drop and 1.76 mV voltage decay per cycle. This work sheds new light on the development of Li‐rich Mn‐based oxide cathodes toward high energy density applications. The practical application of Li‐rich Mn‐based oxide cathodes is limited by the capacity decline and voltage fading, associated with the structure distortion and anionic redox reactions. Here, a linkage‐functionalized modification approach to tackle these challenges via a synchronous lithium oxidation strategy is reported. This work sheds new light on the development of Li‐rich Mn‐based oxide cathodes toward high energy density applications.
The lack of methods to modulate intrinsic textures of carbon cathode has seriously hindered the revelation of in-depth relationship between inherent natures and capacitive behaviors, limiting the advancement of lithium ion capacitors (LICs). Here, an orientated-designed pore size distribution (range from 0.5 to 200 nm) and graphitization engineering strategy of carbon materials through regulating molar ratios of Zn/Co ions has been proposed, which provides an effective platform to deeply evaluate the capacitive behaviors of carbon cathode. Significantly, after the systematical analysis cooperating with experimental result and density functional theory calculation, it is uncovered that the size of solvated PF6− ion is about 1.5 nm. Moreover, the capacitive behaviors of carbon cathode could be enhanced attributed to the controlled pore size of 1.5–3 nm. Triggered with synergistic effect of graphitization and appropriate pore size distribution, optimized carbon cathode (Zn90Co10-APC) displays excellent capacitive performances with a reversible specific capacity of ~ 50 mAh g−1 at a current density of 5 A g−1. Furthermore, the assembly pre-lithiated graphite (PLG)//Zn90Co10-APC LIC could deliver a large energy density of 108 Wh kg−1 and a high power density of 150,000 W kg−1 as well as excellent long-term ability with 10,000 cycles. This elaborate work might shed light on the intensive understanding of the improved capacitive behavior in LiPF6 electrolyte and provide a feasible principle for elaborate fabrication of carbon cathodes for LIC systems.
High‐capacity cathodes and anodes in energy storage area are required for delivering high energy density due to the ever‐increasing demands in the applications of electric vehicles and power grids, which suffer from significant safety concerns and poor cycling stability at the current stage. All‐solid‐state lithium batteries (ASSLBs) have been considered to be particularly promising within the new generation of energy storage, owing to the superiority of safety, wide potential window, and long cycling life. As the key component in ASSLBs, individual solid electrolytes that can meet practical application standards are very rare due to poor performance. To the present day, numerous research efforts have been expended to find applicable solid‐state electrolytes and tremendous progress has been achieved, especially for garnet‐type solid electrolytes. Nevertheless, the garnet‐type solid electrolyte is still facing some crucial dilemmas. Hence, the issues of garnet electrolytes' ionic conductivity, the interfaces between electrodes and garnet solid electrolytes, and application of theoretical calculation on garnet electrolytes are focuses in this review. Furthermore, prospective developments and alternative approaches to the issues are presented, with an aim to improve understanding of garnet electrolytes and promote their practical applications in solid‐state batteries.
A LiMn 0.6 Fe 0.4 PO 4 /CA composite with a high tap density and superior electronic conductivity is synthesized by a combination of wet ball-milling, spray drying, and carbothermal reduction with Carbon aerogel (CA) as a carbon additive. CA is a porous nanomaterial with a very large specific surface area. There are 3D network structure between the primary particles of LiMn 0.6 Fe 0.4 PO 4 when CA is used for carbon coating. This 3D network structure not only is beneficial for the improvement of electronic conductivity but also can absorb a large amount of electrolyte, which helps to improve the Li ⁺ exchange rate between the electrode and electrolyte. More attention, we found that the primary particles of LiMn 0.6 Fe 0.4 PO 4 coated with CA were more compact than those coated without CA, which greatly improved the tap density of the material. Thus the LiMn 0.6 Fe 0.4 PO 4 /CA composite with appropriate amount of CA exhibits a high tap density of 1.6 g cm ⁻³ and excellent electronic conductivity of 8.5 × 10 ⁻² S cm ⁻¹ simultaneously. Resulting in a high volumetric energy density of 856.1 Wh L ⁻¹ at 1 C rate, and discharge capacity of 159.1 mAh g ⁻¹ at 0.2 C.
In pursuit of high‐performance cathode materials for lithium‐ion batteries with high energy and power densities, porous LiFe0.4Mn0.6PO4/CNF free‐standing electrodes have been successfully prepared through a facile ionic liquid (IL) assisted electrospinning method. Owing to the hierarchical porosity and N‐doped carbon layer derived from the ionic liquid, the resulting electrodes exhibited superior electrochemical performances with an improvement of conductivity and pseudocapacitive contribution, delivering a discharge capability of 162.7, 133.5, 114.5, and 102.6 mAh g⁻¹ at the current rates of 0.1, 1, 5, and 10 C, respectively. It is highly expected that this facile IL‐assisted electrospinning method will lead to further developments for other phosphate‐based free‐standing electrodes, which offers a new route in designing polyanionic cathodes for high‐performance Li‐ion batteries.
Carbon-free LiFe0.5Mn0.5PO4 and carbon-coated LiFe0.5Mn0.5PO4/C cathode materials were prepared by the mechanochemically assisted solid-state synthesis. The influence of the carbon coating on the porous structure, morphology, conductivity, and electrochemical characteristics of the cathode materials was analyzed using scanning electron microscopy (SEM), standard contact porosimetry (MSCP), electrochemical impedance spectroscopy (EIS), galvanostatic cycling, and galvanostatic intermittent titration technique (GITT). It has been shown that the specific surface area of LiFe0.5Mn0.5PO4/C is twice as high as that of LiFe0.5Mn0.5PO4 despite the very low content of carbon (3%). This was explained by a non-additive contribution of carbon and the active cathode material to the total specific surface area of the composite due to an introduction of carbon in the pores of the cathode material. Among the two key characteristics of a porous structure—specific surface area and volumetric porosity—specific surface area has the greatest impact on electrochemistry of LiFe0.5Mn0.5PO4/C. Mathematical modeling of the discharge profiles of LiFe0.5Mn0.5PO4/C was carried out and compared with the experiment. The cathode heating at high currents was evidenced. The temperatures and coefficients of solid-state diffusion were estimated at different currents. The calculated diffusion coefficient corresponds to the experimental one obtained by GITT at room temperature.
LiMn0.5Fe0.5PO4 (LMFP)@C and [email protected]2@C nanorods are successfully synthesized by a solvothermal process followed by a calcination at H2/Ar atmosphere. The carbon coating and LiAlO2 coating does not change the morphology and particle size of LMFP, and all samples show nanorod morphology with 50–100 nm in width and 200–300 nm in length. The results show that LiAlO2 coating can offer rapid charge transfer channels with improved intercalation/de-intercalation kinetics of Li ions, which make an outstanding rate capability and cycling stability of as-synthesized [email protected]2@C cathodes. As a result, LiAlO2 coating effectively improves the rate capability and cycling stability of LMFP cathode even at high discharge rates. Hence, [email protected]2 (5 wt%)@C indicates an outstanding rate performance with a reversible discharge capacity of 137.6 and 113.2 mAh g⁻¹ discharged at 0.05 C and 5 C rates, and the composite also shows a good cycle performance with an excellent capacity of 107 mAh g⁻¹ and 86.4% capacity retention rate at 5 C rate after 100 cycles. Therefore, the LiAlO2 coating can be considered as an effective way to improve the electrochemical properties of LMFP.
A composite of olivine lithium manganese iron phosphate (LiMn0.5Fe0.5PO4), external carbon coating and internal embedded carbon flakes, EC-IC-LMFP, is prepared by using phytic acid (PhyA) as phosphorus source via solvothermal process followed by calcination. The composite with improved electronic conductivity and ion diffusivity presents an ultrahigh reversible specific capacity of 193 mAh g−1 at 0.1 C, and an excellent cycling stability of 93% capacity retention after 100 cycles at 1 C when applied as a cathode material for Li-ion batteries (LIBs). Additionally, the composite fine powders exhibit a special microstructure and its volumetric energy density is estimated to reach 1605 Wh L−1, much larger than the commercial LiFePO4.
Three dimensional (3D) nano-LiMn0.6Fe0.4PO4@C/CNT composite was successfully synthesized by an oleylamine-assisted solvothermal method. The prepared composite showed excellent electrochemical performance, especially superior high rate capability. It could deliver a specific discharge capacity of 103.1 mAh/g, even at 80 C. The superior high rate performance of the as-prepared LiMn0.6Fe0.4PO4@C/CNT electrode is attributed to its unique 3D conducting network: (1) the prepared LiMn0.6Fe0.4PO4@C active particles were in nano-scale with a size of 30–50 nm; (2) LiMn0.6Fe0.4PO4 nanoparticles were uniformly coated by amorphous carbon with a thickness of 3 nm; (3) the graphitized conductive CNTs were dispersed homogenously among the LiMn0.6Fe0.4PO4@C active particles. The synergistic effect of the nanoscale amorphous carbon coated LiMn0.6Fe0.4PO4@C active particles and the graphitized CNTs reduces the diffusion path of the lithium ions and benefits the transference ability of electron.
A solid solution of LiMn0.8Fe0.2PO4/Carbon composite has been successfully synthesized by introducing carbon nanotubes (CNT) into the microspheres with porous structure during the spray drying and calcination process. The micro-spherical CNT-embedded LiMn0.8Fe0.2PO4/C composite delivers the features of high voltage, high rate, and cycling stability, which are urgently needed for the development of commercial lithium ion batteries. Benefiting from the subtle porous structure with a moderate specific area, the micro-spherical LiMn0.8Fe0.2PO4/C samples without CNT material exhibits a high reversible capacity (162 mAh g⁻¹ at 0.1 C) and good rate performance. CNT, embedded in the microspheres and entangling with the primary particles, can enhance an interconnected conducting network and optimize the electron transport pathways, resulting in improved lithium ion diffusion coefficient. Therefore, the increased rate capability and cycling performance are obtained. When charged and discharged at 20 C, the composite of LiMn0.8Fe0.2PO4/C microspheres with only 0.5 wt% CNT embedded, still exhibits an obviously higher capacity (128.7 mAh g⁻¹) than those without CNT (120.8 mAh g⁻¹). It also delivers a higher capacity retention of 91.6% up to 500 cycles at 5 C, showing excellent long-term cycle life. Tested in full batteries with Li4Ti5O12 as anode, the CNT-embedded LiMn0.8Fe0.2PO4/C microspheres have shown its promising potential in practice.
LiFe0.4Mn0.6−xCrxPO4/C (x ≤ 0.01) cathode materials with different Cr-doping were synthesized by a nano-milling assisted solid-state method. The experimental results demonstrated that Cr-doping can significantly improve the electrochemical performance of the target material. Among the samples synthesized, the LiFe0.4Mn0.595Cr0.005PO4/C (with 0.5 atm% of Cr) sample exhibited the highest specific capacity and the best rate performance. It delivered initial discharge capacities of 164.0, 156.2, 147.5 and 139.3 mA h g⁻¹ at 0.1C, 0.5C, 2C and 5C, respectively. Moreover, it showed the best cycle stability with capacity retention of 99.2% after 50 cycles at 0.1C. Such enhancement can be ascribed to the improvements in not only the electronic conductivity, but also the Li ion diffusion coefficient. Powder conductivity tests revealed that the conductivity of the powder sample with 0.5% Cr doping presents the highest conductivity of 5.91 × 10⁻⁵ S cm⁻¹, which is almost 5.3 times that of the pristine sample. Calculations of diffusion coefficients using the EIS data also suggested a highest Li ion diffusion coefficient of 4.36 × 10⁻¹⁰ cm² s⁻¹ for the sample with 0.5% Cr doping, which is almost 4.6 times that of the pristine sample. The synthesized LiFe0.4Mn0.595Cr0.005PO4/C with such excellent electrochemical performance showed great potential for application in high-power devices.
A facile co-precipitation approach combined with spray-drying and high-temperature calcinations was developed to synthesize LiMn0.8Fe0.2PO4/C microspheres on a large scale. With an open porous structure, these microspheres are composed of nanoparticles coated with a carbon layer. The electrochemical performances of a LiMn0.8Fe0.2PO4/C cathode were investigated with a water-soluble adhesive, polyacrylic latex (LA133), and compared with the commercial polyvinylidene difluoride (PVDF). The results show that LA133 makes better distribution between the microspheres and acetylene black with a larger and closer contact and stronger adherence. The testing results show that the LiMn0.8Fe0.2PO4/C demonstrates a reversible capacity of 161 mA h g−1. The electrodes with the LA133 adhesive attain higher discharge capacities than the electrodes with PVDF at a large current density, and deliver a long cycle life of 500 cycles at 5C with an excellent capacity retention ratio of 70.5% at room temperature. Even at a low temperature of 0 °C, the LiMn0.8Fe0.2PO4/C electrodes with LA133 retain a capacity of 117 mA h g−1 and stability.
The electrochemical lithiation of the mixed metal olivine LiFe0.75Mn0.25PO4 was followed by operando x-ray absorption spectroscopy (XAS) at both Fe and Mn K edges. XAS data were interpreted using an innovating chemometric approach, allowing the detailed reconstruction of the rather complicated reaction mechanism involving two different metal centres. In this way it was possible to precisely describe the Jahn–Teller effect occurring upon oxidation of the manganese centres. The thorough comprehension of the electrochemical mechanism is of high interest for studying the effect of lithium extraction in the olivine structure in the presence of Mn, which is known to partially hamper the complete lithiation of such mixed metal systems.
Li0.995Nb0.005Mn0.85Fe0.15PO4/C was prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical tests. The results of XRD and XPS show that Nb⁵⁺ and Fe²⁺ are introduced into the lattice of LiMnPO4 to form solid solution and generate a synergistic effect on the shrinkage of lattice and the formation of metal ion-vacancy pairs. When charged/discharged at 1 C, Li0.995Nb0.005Mn0.85Fe0.15PO4/C delivers a discharge capacity of 146 and 161 mAh g⁻¹ with a capacity retention ratio of ∼100 % after 50 cycles at 25 and 60 °C, respectively. Even charged/discharged at 5 C, this sample still gives a discharge capacity of 100 mAh g⁻¹, exhibiting good rate capability and cycling stability. The improved electrochemical performance can be ascribed to the synergistic effect between Nb⁵⁺ and Fe²⁺, which significantly enhances the dynamic stability of the olivine structure, Li⁺ diffusion, and electrochemical kinetics. These results further prove that the electrochemical properties of lithium manganese phosphate can be effectively enhanced by Fe²⁺ and Nb⁵⁺ co-doping.
The practical application of lithium-ion batteries suffers from low energy density and the struggle to satisfy the ever-growing requirements of the energy-storage Internet. Therefore, developing next-generation electrode materials with high energy density is of the utmost significance. There are high expectations with respect to the development of lattice oxygen redox (LOR)-a promising strategy for developing cathode materials as it renders nearly a doubling of the specific capacity. However, challenges have been put forward toward the deep-seated origins of the LOR reaction and if its whole potential could be effectively realized in practical application. In the following Review, the intrinsic science that induces the LOR activity and crystal structure evolution are extensively discussed. Moreover, a variety of characterization techniques for investigating these behaviors are presented. Furthermore, we have highlighted the practical restrictions and outlined the probable approaches of Li-based layered oxide cathodes for improving such materials to meet the practical applications.
Energy storage materials with extreme fast charging (XFC) is currently a crucial technology for lithium-ion batteries (LIBs). However, it is generally believed that attaining both high power density and energy density is a challenging goal in electrochemical systems. Here, we report that Li3V2(PO4)3 can be an XFC cathode for high voltage LIBs. Contrary to conventional belief, Li3V2(PO4)3 at a cut-off voltage of 4.8 V exhibits superior rate performance (a reversible capacity of 119 mAh g−1 was retained at an ultrahigh rate of 100 C) than those at a cut-off voltage of 4.3 V. Empirical characterizations are complemented with first-principles density functional theory (DFT) calculations to uncover the reaction mechanism and the diffusion pathway of the third Li+ in Li3V2(PO4)3. Moreover, the slow capacity decay mechanism of Li3V2(PO4)3 was elucidated by the differential volumetric curves for the first time.
LiMn0·8Fe0·2PO4/C nanocrystal was synthesized by a facile solvothermal reaction. The pH and concentration of lithium ion are changing with the increase of LiOH. The deposition law of precursor ions is investigated, in which Li⁺ exceeds the necessary stoichiometric ratio even in the lowest amount of LiOH. Mn²⁺ and Fe²⁺ possess the similar fixation tendency, and 87.88% Mn²⁺ are deposited at the pH of 3.30. However, nearly all Fe²⁺ are precipitated in a wide pH range (2.96–3.85). The morphology changes from nanosheet to nanoellipsoid under the cooperation of pH and precursor ions. The components of LiMnPO4 and LiFePO4 in LiMn0·8Fe0·2PO4/C are predicted and their contributions to capacity are close to the actual results. Sample S-2.6 delivers the optimum electrochemical performance with a capacity of 150.9, 134.6 and 107.5 mA h·g⁻¹ at 0.05, 1 and 5 C, respectively. It also exhibits high reversibility, low charge transfer resistance (41.2 Ω) and excellent diffusion coefficient (5.38 × 10⁻¹¹ cm² s⁻¹). The capacity retention of sample S-2.6 reaches 96.03% after 200 cycles and it maintains original structure without obvious change according to the ex-situ XRD results. The morphology of the cycled cathode film also maintains its integrity without evident cracks. The low dissolution of Mn²⁺ and Fe²⁺ from LiMn0·8Fe0·2PO4/C shows the enhanced chemical stability.
Graphene has attracted considerable attention as the conductive agent for lithium batteries by providing a superior interfacial contact. However, the wrapping of active materials by the large area of graphene sheets may hinder the transportation of Li⁺ between active particles and electrolyte, especially at a high charge/discharge rates. Herein, holey graphene oxide (h-GO), which is made by a green wet ball-milling of GO in one step without using any catalysts or chemicals, is combined with carbon nanotubes (CNTs) and LiMn0.7Fe0.3PO4 (LMFP) to make a composite cathode for lithium batteries. Results show that after the electrochemical reduction, the LMFP cathode with h-GO/CNT shows remarkedly improved electrochemical performances due to the facilitated Li⁺ transport pathway, compared to that with conventional GO/CNT. For example, LMFP/h-GO/CNT composite cathode can achieve a discharge capacity of 112 mAh g⁻¹ when discharged at 20 C, while LMFP electrode with conventional GO/CNT only shows a discharge capacity of 35 mAh g⁻¹. This study provides a new approach for fabricating holey graphene and can open up new possibilities for applications on power sources.
Olivine-type LiMnPO4 (LMP) cathodes have gained enormous attraction for Li-ion batteries (LIBs) due to high discharge platform, theoretical capacity and thermal stability. However, it is still challenging to achieve encouraging Li-storage behavior owing to the low electronic conductivity and slow Li-ion diffusion rate of LMP. Here, the electrochemical behavior of fibrous LiFexMn1-xPO4@carbon (LFxM1-x[email protected], x = 0, 0.25, 0.5, 0.75, 1) composites with different Fe doping amounts is investigated. Among the composites, LF0.5M0.5[email protected] demonstrates a superior cell performance due to a higher Li-ion diffusion coefficient (DLi), resulting from a proper Fe doping ratio and a more uniform morphology. At a current rate of 0.2 C (1 C = 170 mA g⁻¹), the LF0.5M0.5[email protected] cathode delivers a specific capacity of 150 mAh g⁻¹ up to 500 cycles with a capacity retention of 119%. A longer-term cycling at 5 C for 2000 cycles can be maintained with a reversible capacity exceeding 102 mAh g⁻¹. The fundamental study provides an insightful guidance for future design of cathode materials with high performance.
Compared with nano-sized materials, the long-pathway isolation of the interior part from the electrolyte for bulk electrode materials may result in high ionic diffusion barrier, leading to the poor rate behavior. Either the modification of lattice or construction of porous structure is generally effective to decrease the ion diffusion barrier; however, achieving these multi-scaled modulations simultaneously via a facile approach is still a challenge. Herein, we manipulate a bifunctional dopant to prepare micron-sized Na3V2(PO4)3 with extraordinary synergy of hierarchical architecture and lattice distortion. The cations Zn2+ not only substitutes partial V3+ to enhance the solid-phase ion diffusivity, but also stabilizes the lattice structure due to the pillar effect. Additionally, the anions CH3COO- also participates in the reaction to modulate the porous architecture. The analysis results of GITT, CV and EIS demonstrate that the rational design of morphology and structure compounding lowers the ion diffusion barrier and strengthen the Na+ migration kinetics. When evaluated as the cathode electrode, the optimal composite exhibits improved Na+ ion transport kinetics and superior rate behaviors of 72.2 and 58.7 mAh g-1 at 100 and 200C, respectively.
To overcome the problems faced by the preparation of high-performance LiFe0.5Mn0.5PO4/C cathode material for commercial application in large scale, such as complicated procedures in the synthesis process and/or low volumetric energy density of nanometer-sized sample, herein, micro-agglomerated LiFe0.5Mn0.5PO4/C is prepared by a facile surfactant-assisted solid-state route. A composite carbon source and controllable pre-calcining process are used for achieving the homogenous carbon coating, interconnected pores and uniform particle size distribution. X-ray powder diffraction, Raman spectrum, N2-adsorpotion-desorpotion, scanning/transmission electron microscopy and elemental analysis confirm the microstructure and accurate composition of the as-prepared samples. It is found that the composite source not only increases the homogeneity of the carbon coating layer and the pore-forming ability, but also contributes to inhibiting the size growth of the primary particles. Meanwhile, the suitable pre-calcining time can improve the specific surface area and optimize the carbon content and pore structure, and thus enhance the tap density of the as-prepared material. The typical LiFe0.5Mn0.5PO4/C sample with carbon content of 3.50 wt% displays high reversible capacities and good rate capability, with discharge capacities of 155.0, 141.5 and 120.1 mA h g⁻¹ at 0.1, 1.0 and 5.0 C (1 C = 170 mA g⁻¹), respectively. Furthermore, the sample exhibits superior cycling performance, with a capacity retention above 98% after 200 cycles at 1.0 and 5.0 C. As a result, this LiFe0.5Mn0.5PO4/C exhibits great potential as a cathode material for high power/energy lithium ion batteries because of its easy synthesis, high specific capacity, good rate capability and cycle stability.
Olivine-type LiFe x Mn 1-x PO 4 /C cathode materials are of great interest for lithium-ion batteries because of their higher lithium ion intercalation potential compared with that of LiFePO 4 . Two types of LiFe 0.5 Mn 0.5 PO 4 /C nanorods with different sizes and crystal structures were synthesized through a facile glycol-based solvothermal process with different precursor feeding sequences. The microstructural investigation revealed that the size and structure of the LiFe 0.5 Mn 0.5 PO 4 nanorods can be tuned by nucleation and crystal growth rates of the intermediate precipitates, which can be controlled by precursor feeding sequence. The LiFe 0.5 Mn 0.5 PO 4 nanorods obtained through the first feeding sequence (a solution of transition metal salts was added dropwise into the solution mixture of LiOH and H 3 PO 4 ) exhibited less exposure of the (010) crystal faces and had bigger sizes compared with those of the LiFe 0.5 Mn 0.5 PO 4 nanorods obtained through the second feeding sequence (a LiOH solution was added dropwise into the solution mixture of H 3 PO 4 and transition metal salts). Electrochemical investigations indicated that the LiFe 0.5 Mn 0.5 PO 4 nanorods obtained through the second feeding sequence showed substantially improved electrochemical performance, in which the discharge capacities reached 157 and 119 mAh g ⁻¹ at 0.2 and 5 C, respectively. Furthermore, a capacity retention of 89% was obtained after 500 cycles at 1 C, demonstrating excellent cyclic stability.
Graphene oxide, an oxidized derivative of graphene, has many intriguing properties, such as amphiphilicity, negative charge, and easy mass production. However, due to the electronic insulation, graphene oxide cannot be directly used as a conductive agent for lithium batteries before reduction. Here we have demonstrated the enhanced rate and cycle capability of LiMn 0.7 Fe 0.3 PO 4 with in situ electrochemically reduced graphene oxide by starting from discharge to 1.5 V vs. Li ⁺ /Li. For example, LiMn 0.7 Fe 0.3 PO 4 with 2 wt% electrochemically reduced graphene oxide can obtain a high discharge capacity of ∼83 mAh g ⁻¹ at 30C and capacity retention of ∼90% at 1C after 200 cycles, much higher performance than that without graphene oxide (∼10 mAh g ⁻¹ and ∼56%, respectively). Moreover, the cathode with in situ electrochemically reduced graphene oxide also shows better performances than that with the externally reduced graphene oxide. The boosted performance is attributed to the effective conductive network formed by the well-dispersed graphene oxide.
Na ⁺ and Fe ²⁺ were co-doped at the Li and Mn site of LiMnPO 4 /C through a simple solvothermal method. Researches show that Li 1-x Na x Mn 0.8 Fe 0.2 PO 4 /C nanocapsule is generated through the self-assembly without surfactant. The simultaneous successfully doping of Na ⁺ and Fe ²⁺ , which is proved by the EDS and XPS of Li 0.97 Na 0.03 Mn 0.8 Fe 0.2 PO 4 /C (LN-3), does not cause the rearrangement of cation. The particle sizes of nanocapsule decrease gradually with the doping of Na ⁺ . The pyrolytic carbon with excellent conductivity is coated on the surface of nanocapsule. The crystal of LN-3 nanocapsule with regular diffraction lattice is well developed. The doping of Na ⁺ does not change the potential of electrochemical reaction. Cathode LN-3 delivers the maximum electrochemical performance. Its specific capacity at 0.05 C, 1 C and 5 C are improved to 141.7, 125.0 and 89.5 mAh·g ⁻¹ , which is partially resulting from the enhanced diffusion coefficient of lithium ions. The capacity retention ratio in 200 cycles at 0.5 C is 96.65%. The ex-situ XRD patterns after 200 cycles are nearly unchanged and the structure is proved to be very stable. The doping of Na ⁺ can also inhibit the dissolution of Mn ²⁺ and Fe ²⁺ in the electrolyte.
In this work, we develop a facial and high efficient way to synthesize carbon-coated LiMn0.7Fe0.3PO4 (LMFP)/reduced graphene oxide (rGO) sandwich-structured composite, which is fabricated by the direct sonication of LMFP nanoparticles, graphite oxide and carbon source together followed by heat treatment for the formation of carbon coating layer and the reduction of graphene. All the LMFP nanoparticles are founded to prefer to anchor onto the top and bottom surfaces of exfoliated GO homogeneously, forming separately sandwiched structure without agglomeration. The prepared LMFP/rGO@C sandwich-structured composite exhibits an excellent rate capability (discharge capacity of 90 mAh g−1 at 30 C), and good cyclability (discharge capacity of 105 mAh g−1 after 500 cycles). Whereas simply carbon-coated LMFP only shows lower discharge capacity of 13 mAh g−1 at 30 C and 91 mAh g−1 after 500 cycles. This finding paves an efficient way to synthesize graphene-based composite with high performances for lithium-ion batteries.
LiMnxFe1-xPO4 (LMFP) has attracted extensive interest owing to its high safety and appropriate redox potential. Nevertheless, its poor electrochemical kinetics and structural instability, depending on its manganese content, are still limiting its further application. Herein, we realize a concentration-gradient LiMn0.5Fe0.5PO4 hollow sphere cathode material with a carbon coating (HCG-LMFP/C) by a facile and controllable two-step solvothermal approach. On the one hand, the porous hollow architecture can sustain excellent structural stabilization against the volume changes that occur during repeated Li+ intercalation/deintercalation. On the other hand, the unique concentration-gradient structure with its Fe-rich surface can not only relieve interface deterioration and improve the ionic/electric conductivity due to the active nature of LiFePO4, but also guarantees the chemical stability of the LMFP against electrolyte attack and remarkably reduces Mn dissolution, even at elevated temperature. Therefore, the obtained concentration-gradient HCG-LMFP/C cathode shows improved high-rate performance (111 and 78 mAh g-1 at 20 and 60C rates, respectively) and excellent capacity retention (96% after 1000 cycles at the 10C rate) as well as outstanding temperature tolerance (over a temperature range from 40 oC to -10 oC). More importantly, the present gradient strategy opens up a new window for designing high-performance and stable olivine cathodes, which also could be compatible with many other energy-storage materials for various applications.
In this work, heterogeneous carbon/N-doped reduced graphene oxide wrapping LiMn0.8Fe0.2PO4 (LMFP/C/N-rGO) composites were synthesized successfully via a simple solvothermal method coupled with further calcination. The composites were characterized by XRD, SEM, TEM and XPS, and their electrochemical properties were evaluated by CV, EIS and charge-discharge test. The LiMn0.8Fe0.2PO4/C particles were uniformly grown on the surface of three-dimensional N-doped reduced graphene oxide (N-rGO). The interconnected N-rGO among LMFP particles and amorphous carbon coating on LMFP surface build a continuous conductive network which helps the fast transmission of electron. Lithium ion batteries with LMFP/C/N-rGO exhibit superior discharge capacity, rate capability and cycling stability, bringing a broad prospect for the future applications.
Lithium-ion batteries (LIBs) possess many virtues, such as low weight, a high energy density, and a long service life, and are regarded as an essential component of a low-carbon economy. Nowadays, LIBs are widely used in consumer electronics, as well as military and aviation products, and are the focus of significant research in the emerging field of energy materials. The cathode material is one of the most important parts of the LIB; its electrochemical performance plays an important role in the battery voltage, power/energy density, cycle life, and safety. LiFePO4 is a superior cathode material compared to spinel manganite (LiMn2O4) and layered lithium nickel-cobalt-manganese oxide (LiMO2 (M = Mn, Co, Ni)), and LiFePO4 has many advantages, such as excellent thermal stability, cycling performance, economic viability, and environmental friendliness. The theoretical diffusion coefficient of LiFePO4 is 10⁻⁸ cm²·s⁻¹, which is sufficient for Li⁺ de-intercalation in nanoparticles. However, the one-dimensional transport channels are easily blocked by structural defects, resulting in a lower diffusion coefficient and poor rate performance. The electronic conductivity of LiFePO⁴ is about 10⁻⁸ S·cm⁻¹, and this also limits the rate performance. Moreover, the low-temperature performance, low yield, and patent problems are also significant problems facing LiFePO4. In contrast, the stability and cost are not significant limitations to more extensive applications; rather, it is the energy density and power density that must be improved. To meet the above demands, in-depth research on the factors affecting the electrochemical performance of LiFePO4 is required. Many factors affect the electrochemical performance of LiFePO4, such as the synthetic method, particle size, electrolyte environment, electrode structure, and temperature. Based on the current state of research into LiFePO4, we have focused our review on the following three aspects: the characteristics of the nanoparticles, interface environment of the material, and the electrode structure. Finally, we summarize the relationship between the structure and electrochemical performance of LiFePO4 cathode materials: (1) the bulk phase characteristics of the material (phase structure, doping, nanocrystallization, defects, and lithium-ion transport mechanism), (2) interface structure and interface reconstruction under different electrolyte environments, and (3) the electrode structure. Our conclusions have great significance for future research.
Carbon-coated single crystalline nanotubular (NT) and nanoparticular (NP) LiFe1-xMnxPO4 (x = 0, 0.2, and 0.5) cathodes are fabricated to study the effect of compositional and microstructural changes on Li⁺ diffusion and electrochemical properties. Insight in to the compositional effect on Li⁺ diffusion is obtained from DFT facilitated climbing image nudged elastic band (CI-NEB) simulations. NT cathodes exhibit exceptionally good discharge capacities ∼60 (∼165) mAhg⁻¹, ∼32 (∼110) mAhg⁻¹ and ∼22 (∼82) mAhg⁻¹ at 25C (1C) rate for x = 0, 0.2, 0.5, respectively. NP cathodes show capacity <5 mAhg⁻¹ at 5C/2C-rate. The high-rate capability with two orders larger diffusion coefficient in nanotubes is due to improved access to Li⁺ intercalation channels. Whereas, nanoparticles are agglomerated, making b-axis inaccessible. While, Mn substitution affects the discharge capacity, it significantly improves capacity retention from ∼60% (x = 0) to ∼88% (x = 0.2) measured over 1000 cycles at ≥5C. From CI-NEB calculations we infer that Mn increases the activation barrier in its neighbourhood, thereby creating a steep potential hump (∼0.15 eV) for the Li⁺ diffusion. This largely impedes the ion transport and accounts for the steep loss of discharge capacity. We observe, while single crystalline nanotubular LiFePO4 are useful for high power density applications, Mn substitution in small quantities (x∼0.2) is ideal for cathodes with increased cyclic stability at high C-rates.
Li(1−x)Mn0.7Fe0.3PO4 (0.00 ≤ x ≤ 1.0) samples, obtained by electrochemical cycling, were investigated by powder X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The purpose of this work is to map phase transition information for samples at quasi equilibrium i.e. after a long relaxation time. The required high accuracy solid Li⁺ content was determined by atomic emission using the standard addition method. From XRD analysis of the charging cycle samples, the phase diagram was shown to exhibit a solid solution (0 ≤ x ≤ 0.42), followed by a two phases system exhibiting both olivine and heterosite structures (0.42 < x ≤ ~0.91) and finally above x ~ 0.91 the olivine phase is no longer detectable. The same basic pattern was found during the discharge process. Combined analysis of FTIR spectra and XRD data showed a strong correlation, where vibration bands at 690 and 600 cm⁻¹ could be uniquely attributed to the heterosite structure.
Nanometer-sized LiMn0.8Fe0.2PO4 (nano-LMFP) is one of the most suitable LiMnPO4 derived cathode material to maximize gravimetric capacity and rate capability. However, the poor cycling performance, low volumetric energy density and safety hazard of nano-LMFP limit its large-scale commercialization. To overcome these development bottlenecks, a uniform three-dimensional interconnected conductive carbon network modified LiMn0.8Fe0.2PO4 nanoporous micro-agglomerate (micro-LMFP/C) composite was synthesized via three-step solid-state reaction (3S) combined with three-step carburizing (3C) and two-step pore-forming (2P). The novel design of micro-LMFP/C composite exhibits excellent gravimetric/volumetric reversible capacities, weak electrochemical polarization and high rate capability. Even if increased to 20 C, a satisfactory discharge capacity of 92.5 mAh g⁻¹ (70.2% of the initial value at 0.1 C) and an outstanding discharge plateau of 3.76 V can be observed. More importantly, for the 3S synthetic strategies, the novel 3C2P-assisted synthesis of micro-LMFP/C composite can simultaneously deliver 2.6 and 1.5 times higher volumetric capacity than that of synchronous and stepwise carburizing assisted synthesis of samples, respectively.
Bio-mineralization technology is a feasible and promising route to fabricate phosphate cathode materials with hierarchical nanostructure for high performance lithium-ion batteries. In this work, in order to improve the electrochemical performance of LiMn0.8Fe0.2PO4, hierarchical LiMn0.8Fe0.2PO4/carbon nanospheres are wrapped in-situ with N-doped graphene nanoribbons via bio-mineralization by using yeast cells as nucleating agent, self-assembly template and carbon source. Such LiMn0.8Fe0.2PO4 nanospheres are assembled by more fine nanocrystals with average size of 18.3 nm. Moreover, the preferential crystal orientation along [010] direction and certain anti-site lattice defects can be identified in LiMn0.8Fe0.2PO4 nanocrystals, which promote rapid diffusion of Li ions and generate more active sites for the electrochemical reaction. Moreover, such N-doped-graphene nanoribbon networks, wrapped between LiMn0.8Fe0.2PO4/carbon nanospheres, are beneficial to the fast mobility of electrons and good penetration of electrolyte. As expected, the as-prepared LiMn0.8Fe0.2PO4/carbon multi-composite presents the outstanding electrochemical performance, including the large initial discharge capacity of 168.8 mAh g-1, good rate capability, and excellent long-term cycling stability over 2000 cycles. Therefore, the bio-mineralization method is demonstrated here to be effective to manipulate the microstructure of multi-component phosphate cathode materials based on the requirement of capacity, rate capability and cycle stability for lithium-ion batteries.
Electron transfer and lithium ion diffusion rates are the key factors leading to sluggish electrochemical kinetics of LiMn0.8Fe0.2PO4. In this work, we have successfully synthesized graphene-embedded LiMn0.8Fe0.2PO4 composites via a facile graphene oxide assisted solvothermal route associated with carbonthermal treatment. The effect of graphene on the morphology, crystalline structure as well as electrochemical properties of LiMn0.8Fe0.2PO4 is investigated. It can be found that the introducing graphene can reduce the particle size to form LiMn0.8Fe0.2PO4 nanocrystals without destroying the crystalline structure of LiMn0.8Fe0.2PO4. And the LiMn0.8Fe0.2PO4 nanocrystals dispersed on the graphene sheets which were further cross-linked via the oxygen-containing groups of GO as cross-linking sites, resulting in that graphene sheets embedded in the LiMn0.8Fe0.2PO4 composites. Benefiting from the LiMn0.8Fe0.2PO4 nanocrystal and embedded graphene, the interconnected conducting network referred to electron and lithium ion transport pathways can be improved, resulting in enhanced electrochemical performance. The graphene embedded LiMn0.8Fe0.2PO4 composite displays a high discharge capacity of 163.5, 149.2, 136.0, 120.6, 100.1 and 84.5 mA h g⁻¹ at various rate of 0.1C, 0.5C, 1C, 2C, 5C and 10C, respectively. Meanwhile, it still maintains a reversible capacity of around 120 mA h g⁻¹ after 100 cycles at a rate of 1C.
A Ni‐rich concentration‐gradient Li[Ni0.865Co0.120Al0.015]O2 (NCA) cathode is prepared with a Ni‐rich core to maximize the discharge capacity and a Co‐rich particle surface to provide structural and chemical stability. Compared to the conventional NCA cathode with a uniform composition, the gradient NCA cathode exhibits improved capacity retention and better thermal stability. Even more remarkably, the gradient NCA cathode maintains 90% of its initial capacity after 100 cycles when cycled at 60 °C, whereas the conventional cathode exhibits poor capacity retention and suffers severe structural deterioration. The superior cycling stability of the gradient NCA cathode largely stemmed from the gradient structure combines with the Co‐rich surface, which provides chemical stability against electrolyte attack and reduces the inherent internal strain observed in all Ni‐rich layered cathodes in their charged state, thus providing structural stability against the repeated anisotropic volume changes during cycling. The high discharge capacity of the proposed gradient NCA cathode extends the driving range of electric vehicles and reduces battery costs. Furthermore, its excellent capacity retention guarantees a long battery life. Therefore, gradient NCA cathodes represent one of the best classes of cathode materials for electric vehicle applications that should satisfy the demands of future electric vehicles.
We decorated nano-crystalline LiNbO3 (LN) particles, which played the role of artificial solid electrolyte interfaces (SEIs) on an active material, namely LiCoO2 (LC). Conventional one-step synthesis using metal organic decomposition (MOD) was used initially, but resulted in the presence of an undesired Li-rich compound, Li3NbO4 (L3N), along with a counterpart phase, Co3O4. Hence, we incorporated crystalline LN into the LC matrix via a two-step synthesis method. Treatment at 500–700 °C resulted in single-phase LN-decorated LCs with improved high rate capabilities. The improvement in the rate capability is related to the temperature dependencies of the two most important parameters: 1) the degree of LN crystallinity, which corresponds to the improvement in the polarization, and 2) the density of the triple phase junctions, which act as active Li ion pathways. The optimized capacity, 78 mAh/g at 20 C, of the specimen annealed at 600 °C was 20 C, which is approximately 1.7-fold larger than that of amorphous LN-decorated LC and is 2.6 times higher than that of bare LC. This implied the introduction of a dielectric polarization architecture had a greater impact on the improvement to the rate capability than Li transportation through the amorphous LN.
To improve the kinetic performance of LiMn0.8Fe0.2PO4, a facile and controllable non-stoichiometric one-pot stepwise feeding solvothermal approach is successfully developed for preparing the nickel-doped LiMn0.8Fe0.2PO4 nanosheets. An appropriate particle size, ideal lattice volume, smooth surface morphology and high phase purity of LiMn0.8Fe0.19Ni0.01PO4 nanosheet could be fabricated through trace amount of nickel doping, modest lithium hydroxide deficiency and stepwise feeding mode, which exhibits the optimal cycling performance and rate capability after carbon coating. After 200 charge/discharge cycles at 0.5 C, the LiMn0.8Fe0.19Ni0.01PO4 cathode only slightly decreases to 148 mAh/g, corresponding to the capacity retention of 94.1%. Even if increased to 10 C and 20 C, 75.7% and 65.2%, respectively, initial capacities at 0.1 C can still be maintained. These results demonstrate that a suitable rate of Ni²⁺ contents and a rational synthesized route are helpful to improve electronic conductivity and Li-ion mobility.
Olivine-structured LiMn1-xFexPO4 has become a promising candidate for cathode materials owing to its higher working voltage of 4.1V, and thus larger energy density than that of LiFePO4, which has been used for electric vehicles batteries with the advantage of high safety but disadvantage of low energy density due to its lower working voltage of 3.4V. One drawback of LiMn1-xFexPO4 electrode is its relatively low electronic and Li-ionic conductivity with Li-ion 1D diffusion. Herein, olivine-structured α-LiMn0.5Fe0.5PO4 nanocrystals were synthesized with optimized Li-ion diffusion channels in LiMn1-xFexPO4 nanocrystals by inducing high concentrations of Fe2+-Li+ antisite defects, which showed impressive capacity improvements of approaching 162,127, 73 and 55 mAh g-1 at 0.1C, 10 C, 50 C and 100 C, respectively, and a long-term cycling stability of maintaining about 74% capacity after 1000 cycles at 10 C. By using high-resolution transmission electron microscopy imaging and joint refinement of hard X-ray and neutron powder diffraction patterns, we revealed that the extraordinary high-rate performance could be achieved by suppressing the formation of electrochemically inactive phase (β-LiMn1-xFexPO4, which is firstly reported in this work) embedded in α-LiMn0.5Fe0.5PO4. Owing to the coherent orientation relationship between β and α phases, the β phase embedded would impede the Li+ diffusion along the [100] and/or [001] directions which was activated by the high density of Fe2+-Li+ antisite (4.24%) in α phase. Thus, by optimizing concentrations of Fe2+-Li+ antisite defects and suppressing β-phase-embedded olivine structure, Li-ion diffusion properties in LiMn1-xFexPO4 nanocrystals can be tuned by generating new Li+ tunneling. These findings may provide insights into the design and generation of other advanced electrode materials with improved rate performance.
The kinetic processes during delithiation/lithiation of LixMn0.8Fe0.2PO4 are thoroughly investigated through operando x-ray diffraction and in situ electrochemical impedance spectroscopy combined with galvanostatic intermittent titration technique (GITT), by which new insights on the phase propagation and sluggish kinetics of LiMn0.8Fe0.2PO4 (LMFP) cathode materials are elaborated. In situ analyses on the solvothermally synthesized carbon-coated LMFP mesocrystals reveal that the phase-propagation mechanisms differ during delithiation/lithiation processes, and the sluggish kinetics of LMFP followed by the limitation of achievable (dis)charge capacities originate from the poor apparent Li⁺ diffusivity, which is triggered by Mn redox reaction. Based on the in-depth characterization of the reaction kinetics in LMFP mesocrystals, our work provides fundamental understanding to design high-performance Mn-based olivine cathodes.
A pyrolyzed carbon and reduced graphene oxide co-doped LiMn0.9Fe0.1PO4 (LMFP/C/rGO) is synthesized by a novel and facile amine-assisted coating strategy. The well designed co-doped LiMn0.9Fe0.1PO4 nanoplate (LMFP/C/rGO, 150 nm in length and 20 nm in thickness) is proved to be olivine phase with good crystallinity which is further compared with the sole pyrolyzed carbon coated LiMn0.9Fe0.1PO4 (LMFP/C) from structural and electrochemical points of views. The LMFP/C/rGO exhibits superior electrochemical performances with the specific capacity of 158.0 mAh g⁻¹ at 0.1C and 124.6 mAh g⁻¹ at 20C, which is, to the best of our knowledge, the highest rate capability. Moreover, after 140 cycles at 0.2C rate, around 95% of the initial capacity is still retained. Further analyses disclosed the outstanding electrochemical performances can be ascribed to the collaboration of the uniformly coated pyrolyzed carbon and closely connected rGO with an extraordinary electronic conductivity. Our research shows this effective synthesis strategy is imperative for the improvement of Li-ion battery performance and can be widely used for advanced energy storage.