Lithium Transition Metal Oxide Cathodes Research Articles

Origins and Importance of Intragranular Cracking in Layered Lithium Transition Metal Oxide Cathodes.

Li-ion batteries have a pivotal role in the transition toward electric transportation. Ni-rich layered transition metal oxide (LTMO) cathode materials promise high specific capacity and lower cost but exhibit faster degradation compared with lower Ni alternatives. Here, we employ high-resolution electron microscopy and spectroscopy techniques to investigate the nanoscale origins and impact on performance of intragranular cracking (within primary crystals) in Ni-rich LTMOs. We find that intragranular cracking is widespread in charged specimens early in cycle life but uncommon in discharged samples even after cycling. The distribution of intragranular cracking is highly inhomogeneous. We conclude that intragranular cracking is caused by local stresses that can have several independent sources: neighboring particle anisotropic expansion/contraction, Li- and TM-inhomogeneities at the primary and secondary particle levels, and interfacing of electrochemically active and inactive phases. Our results suggest that intragranular cracks can manifest at different points of life of the cathode and can potentially lead to capacity fade and impedance rise of LTMO cathodes through plane gliding and particle detachment that lead to exposure of additional surfaces to the electrolyte and loss of electrical contact.

Is Transition Metal Dissolution a Major Degradation Process in Commercial Li-Ion Cells? Application of Impedance with Extended Sub-mHz Low-Frequency Range

Transition metal dissolution is a well-known degradation process in Li-ion batteries correlated with capacity fade1. Transition metals from a lithium transition metal oxide cathode can dissolve which causes structural changes in the crystal structure leading to deterioration of the material. Additionally, dissolved transition metals can migrate to the anode and reduce on the surface, impacting the surface activity of the anode composite and increasing its impedance.It is generally known that electrochemical performance of a Li-ion insertion battery electrode is primarily defined by the active material chemistry, further it is strongly impacted by the material and electrode-level engineering (particle size and aggregation, electrode porosity and tortuosity, electrolyte amount and properties, conductive additive and binder choice and their distribution in electrode composite). Furthermore, impedance response of an insertion electrode exhibits a strong dependence upon lithiation level (x). The specific dependence of impedance of an electrode upon x should allow to help in separating the two individual contributions of the two electrodes in a full cathode-anode battery cell. Thus, not surprisingly, Electrochemical Impedance Spectroscopy (EIS) is a common electrochemical technique of choice for degradation studies of Li-ion batteries2. Typically, EIS spectra of batteries are measured in frequency spans from MHz (laboratory cells) or kHz (commercial cells) down to mHz ranges. However, impedance measurements down to lower minimal frequencies (below 1 mHz) are often avoided from the practical reasons due to the inevitably longer measurement times being required.In the present work cylindrical commercial 18650-size high-energy NMC-Graphite(+Si) cells were electrochemically (galvanostatically) cycled at various conditions. In the constant temperature regime (10°C, 23°C, 35°C or 45°C) the tested cells were systematically cycled within various depth of discharge (DoD) ranges to observe the effect of the voltage range on the evolution (decline) of cell capacity. EIS responses were measured at different selected states of charge (SoC), with the aim to help to resolve the individual contributions of cathode and anode. State of health (SoH) of a battery was determined by current integrated capacity measurement and was periodically monitored after specific number of cycles and correlated with the impedance growth. EIS measurements down to conventional 10 mHz as well as to very low frequencies (0.1 mHz) were performed and compared to determine what additional information and insights for developing of a physics-based battery cell model and degradation modes can be obtained by including the extended low-frequency range (down to 0.1 mHz). We systematically investigated evolution (increase) of impedance of commercial Li-ion cells including the extended low-frequency range.After completion of the cycling test, post-mortem analysis of the cell components was performed on selected cells. Cells were disassembled, electrodes carefully removed, properly washed and SEM-EDX and ICP-MS analysis was performed on the cathode and anode samples. The amount of transition metals in both cathode and anode was determined.We thoroughly confirmed that the impedance of the commercial (full cells) in general increases during the decrease of capacity at all the tested conditions. Importantly, EIS spectra measured down to very low frequencies show that in addition to the (expected) increase of the real component (Re(Z)) simultaneously also the imaginary component (Im(Z)) significantly increases. We provide novel physics-based explanation of the underlying phenomena. Electrochemical characterization of the half cells prepared from the harvested electrodes in general showed a decrease in capacity and increase in voltage hysteresis for both cathode and anode – the actual changes showing strong dependence upon conditions during cycling. EDX and ICP-MS analysis revealed that the composition of the cathode active material remained practically unchanged and that the amount of the transition metals (TMs) deposited on the anode did not increase greatly with the cycling – the total amount of detected TMs remaining well below 300 ppm (relative to the amount of TMs in pristine cathode). Gilbert, J. A., Shkrob, I. A. & Abraham, D. P. Transition Metal Dissolution, Ion Migration, Electrocatalytic Reduction and Capacity Loss in Lithium-Ion Full Cells. J. Electrochem. Soc. 164, A389–A399 (2017).Meddings, N. et al. Application of electrochemical impedance spectroscopy to commercial Li-ion cells: A review. J. Power Sources 480, 228742 (2020). Figure 1. a) Typical examples of EIS response of 811-NMC-Graphite(+Si) full cells measured at SoC = 0.5 (3.705 V) down to 1 mHz (dark colors) and down to 0.1 mHz (lighter dolors) for pristine cell (black/grey), cell cycled at 23°C (blue), and cell cycled at 45°C (red). The corresponding SoH values were: 1, 0.39, and 0.39, respectively. b) Comparison of capacity of the half-cells prepared with the cathodes and anodes harvested from the initial commercial cells (panel a). Figure 1

Application of high energy X-ray diffraction and Rietveld refinement in layered lithium transition metal oxide cathode materials

Application of high energy X-ray diffraction and Rietveld refinement in layered lithium transition metal oxide cathode materials

Tailoring electrolyte solvation to push the capacity limit of layered oxide cathodes via polarized ferroelectric polymers

The critical challenges for full lithium utilization in nickel-rich lithium transition metal oxide cathodes are the capacity loss and power fading, which stem from irreversibly structural transition and unstable cathode-electrolyte interface upon excessive delithiation at high charge voltages. Here we discover a novel electrochemical phenomenon that the local solvation structure of the electrolyte can be regulated by well-polarized ferroelectric polymer and demonstrate its potential in pushing the capacity limit of Ni-rich lithium layered oxide cathodes without sacrificing their structural integrity. This polarized configuration in the ferroelectric polyvinylidene fluoride (PVDF) coating tailors the local solvation structure by repelling the electrolyte anions and promoting the aggregation of lithium-ions at the cathode-electrolyte interface, which significantly boost the (de)lithiation kinetics, redox reversibility and structural integrity of the cathodes. The LiNi0.8Co0.1Mn0.1O2 cathode with polarized PVDF displays an exceptionally high capacity of 232 mAh g−1 with a high initial Coulombic efficiency of 92.5%, and the NCM811/graphite pouch cell with polarized-PVDF/PP separator shows a higher capacity retention rate of 88.6% after 200 cycles at 55 °C.

Study on the Structural Degradation of the Polyaniline(PANi) Coated LiNi0.90Co0.85Mn0.15o Particles

The nickel content of the layered lithium transition metal oxide cathodes is proportional to the discharge capacity of energy storage systems. Ni2+ ion, the oxidation state of Ni, moves to the Li sites when Li+ ion is deintercalated during discharge process due to the similar size of ion (Ni2+: 0.069 nm, Li+: 0.076 nm). The spatial transition of Ni2+ ion causes gradual cation mixing and structure degradation of cathode, resulting in the failure of the battery. Also, thick cathode-electrolyte interphase (CEI) is formed on the cathode surface because of the transition metal dissolution, the degradation of electrolyte, and the residual gas such as H2O and CO2.Coating technology is one of the strategies for the physical protection of the cathode surface and the control of CEI layer thickness. Polyaniline(PANi) is a conductive polymer with stable oxidation state. PANi can enhance the electrochemical property and structural stability as a protective layer. In this study, we synthesized PANi material by the oxidative polymereization and coated NCM with the synthesized PANi by sonication method.The PANi-coated NCM(PANi@NCM) has uniform coating layer with 5 nm thickness. PANi@NCM exhibits an initial discharge capacity of 208 mAhg-1 and a capacity retention of 81% after 50 cycles at 45 oC in Figure 1(a) and (b). After the cycling test, pristine and coated cathodes were disassembled for the comparison of the microstructure. Pristine NCM only shows the structural transition from layered structure to structure in the XRD pattern of Figure 1(c). Cross-sectional SEM image of the pristine NCM after cycling test shows micro and macro cracks are distributed from the bulk to the surface of the cathode as shown in Figure 1(d). On the other side, cracks are barely observed on the PANi@NCM particles in Figure 1(e). The layered structure of PANi@NCM is maintained even after cycling test, which are confirmed by TEM analysis with FFT patterns and HAADF images. Figure (f) and (g) show the FFT pattern of the two cathode surfaces after cycling test. Mixed phase is observed on the pristine cathode surface, while the layered structure is maintained on the PANi@NCM surface. Also, the PANi@NCM maintains a thinner passivation layer compared with that of the pristine NCM (6 nm vs 35 nm). In conclusion, the PANi coating layer prevents the degradation of structure and the formation of thick CEI layer. The structural stability enhances the electrochemical performance. Figure 1

(Invited) High-Energy and Safe Lithium-Ion Batteries Using Layered Oxides Cathodes

Ni-rich layered lithium transition metal oxides have been considered as one of the key cathode materials for next-generation lithium-ion batteries for electric vehicle applications due to their high specific capacity of >200 mAh/g and low cost. However, they suffer from crystal and interfacial structural instability under aggressive electrochemical and thermal driving forces, leading to rapid performance degradation and severe safety concerns.In this talk, we will first discuss the fundamental role of Co and Mn in determining the thermal stability of layered cathode materials. By using in situ synchrotron X-ray diffraction and X-ray absorption spectroscopy, we revealed that Co4+ reduces prior to the reduction of Ni4+ and could thus prolong the Ni migration by occupying the tetrahedra sites and, hence, postpone the oxygen release and thermal failure. In contrast, the Mn itself is stable, but barely stabilizes the Ni4+.[1] We will then introduce a transformative approach using an oxidative chemical vapour deposition technique to build a protective conductive polymer (poly(3,4-ethylenedioxythiophene)) skin on layered oxide cathode materials. The ultraconformal poly(3,4-ethylenedioxythiophene) skin facilitates the transport of lithium ions and electrons, significantly suppresses the undesired layered to spinel/rock-salt phase transformation and the associated oxygen loss, mitigates intergranular and intragranular mechanical cracking, and effectively stabilizes the cathode–electrolyte interface. This approach remarkably enhances the capacity and thermal stability under high-voltage operation.[2][1] Building ultraconformal protective layers on both secondary and primary particles of layered lithium transition metal oxide cathodes. Nature Energy, 2019, 4, 484-494.[2] Probing the Thermal-Driven Structural and Chemical Degradation of Ni-rich Layered Cathodes by Co/Mn Exchange J. Am. Chem. Soc. 2020, 142, 19745-19753.

Elevated stability of nickel-rich oxide cathode material with concentration gradient of transition metals via a novel size-controllable calcination method

Consumers are increasingly demanding the range and safety of the electric vehicles. Nickel-rich layered lithium transition-metal oxide cathode material with Ni content exceeding 80% has attracted extensive attention due to its high capacity. To suppress the decrease of cyclic and thermal stability due to the increase of nickel content, LiNi0.87Co0.06Mn0.07O2 particles with transition metal concentration gradient from the interior to the surface are realized. An efficient and low-cost method is proposed involves firstly forming the shell layer with low nickel content by a dry mechanofusion process and subsequently adopting a novel particle size-controllable calcination course. Through which a concentration gradient layer with a thickness of 1 µm is successfully formed, and the particle size of primary particles is effectively controlled at the range of 250–300 nm. The relationship between the calcination conditions, the morphology, particle size of primary particles and the electrochemical performance have been established. Capacity of 211.9 mAh/g and initial coulomb efficiency of 90.29% have been achieved by LiNi0.87Co0.06Mn0.07O2 with superficial transition metal concentration gradient, and the capacity retention rate at 1 C reached 86.1% after 400 cycles in a pouch cell. In addition, the thermal decomposition temperature is elevated from 220 °C to 242 °C, the safety of the Ni-rich material has been also effectively improved.

Communication—Reduction of DC Resistance of Ni-Rich Lithium Transition Metal Oxide Cathode by Atomic Layer Deposition

A coating using Atomic layer deposition (ALD) of Al2O3 was applied to Ni-rich lithium transition metal oxide cathode material. This ALD coating reduces the DC resistance (DCR) and increases the cycling performance of the Ni-rich cathode. The reduced DCR comes from decreased solid electrolyte interphase (SEI) resistance on the anode, which is attributed to reduced transition metal deposition. This is due to the ALD coating preventing the direct contact between the cathode and the electrolyte, and therefore inhibits transition metal dissolution. This study suggests the promise of using ALD coating to reduce the DCR of Ni-rich cathode materials.

Robust Surface Reconstruction Induced by Subsurface Ni/Li Antisites in Ni‐Rich Cathodes

AbstractLoss of active materials is a critical problem of layered oxide cathodes for lithium‐ion batteries and undermines their long‐term electrochemical performance. However, the atomic‐scale outward migration mechanism of transition metals and oxygen remains elusive due to a highly localized environment at surface. Here, the robust surface reconstruction of LiNi0.8Mn0.1Co0.1O2 (NMC811) induced by artificially introduced Ni/Li antisites is reported. Using scanning transmission electron microscopy, the outward co‐migration process of nickel and oxygen ions is directly revealed at the atomic scale, finally resulting in a stable surface structure. The robust nature of this surface structure originates from the strong linear superexchange interaction between subsurface NiLi and surface Ni as supported by first‐principles calculations. An idealized subsurface structure with NiLi is designed to suppress the outward migration of transition metal and oxygen ions and provide a universal lattice‐coherent surface protection strategy for layered lithium transition metal oxide cathodes.

Utilization of electron-beam irradiation under atomic-scale chemical mapping for evaluating the cycling performance of lithium transition metal oxide cathodes

A true chemical information of Ni-rich cathode materials at the atomic scale was obtained.

Challenges and Strategies to Advance High‐Energy Nickel‐Rich Layered Lithium Transition Metal Oxide Cathodes for Harsh Operation

AbstractNickel‐rich layered lithium transition metal oxides (LiNi1−x−yCoxMnyO2 and LiNi1−x−yCoxAlyO2, x + y ≤ 0.2) are the most attractive cathode materials for the next generation lithium‐ion batteries for automotive application. However, they suffer from structural/interfacial instability during repeated charge/discharge, resulting in severe performance degradation and serious safety concerns. This work provides a comprehensive review about challenges and strategies to advance nickel‐rich layered cathodes specifically for harsh (high‐voltage, high‐temperature, and fast charging) operations. Firstly, the degradation pathways of nickel‐rich cathodes including surface/interface degradation, undesired cathode–electrolytes parasitic reactions, gas evolution, inter/intragranular cracking, and electrical/ionic isolation are discussed. Then, recent achievements in stabilizing the structure/interface of nickel‐rich cathodes via surface coating, cation/anion doping, composition tailoring, morphology engineering, and electrolytes optimization are summarized. Moreover, challenges and strategies to improve the performance of Ni‐rich cathodes at the electrode level are discussed. Outlook and perspectives to promote the practical application of nickel‐rich layered cathodes toward automotive application are provided as well.

Building ultraconformal protective layers on both secondary and primary particles of layered lithium transition metal oxide cathodes

Despite their relatively high capacity, layered lithium transition metal oxides suffer from crystal and interfacial structural instability under aggressive electrochemical and thermal driving forces, leading to rapid performance degradation and severe safety concerns. Here we report a transformative approach using an oxidative chemical vapour deposition technique to build a protective conductive polymer (poly(3,4-ethylenedioxythiophene)) skin on layered oxide cathode materials. The ultraconformal poly(3,4-ethylenedioxythiophene) skin facilitates the transport of lithium ions and electrons, significantly suppresses the undesired layered to spinel/rock-salt phase transformation and the associated oxygen loss, mitigates intergranular and intragranular mechanical cracking, and effectively stabilizes the cathode–electrolyte interface. This approach remarkably enhances the capacity and thermal stability under high-voltage operation. Building a protective skin at both secondary and primary particle levels of layered oxides offers a promising design strategy for Ni-rich cathodes towards high-energy, long-life and safe lithium-ion batteries. Intensive research efforts are underway to enable applications of layered lithium transition metal oxides in batteries. Here the authors report an oxidative chemical vapour deposition technique to conformally coat both the primary and the secondary particles of these oxides to unleash potential applications.

A Simple Surface Modification Technique to Improve the Electrochemical Properties of NMC Family Cathode Materials

The facile phosphoric acid (H3PO4) surface modification of layered lithium transition metal oxide cathode materials has been proven to enhance the reversible capacity and rate capability of these materials. Here, we have investigated the effect of this treatment on two NMC cathode materials, Li(Ni1/3Mn1/3Co1/3)O2 (NMC333) and Li(Ni0.5Mn0.3Co0.2)O2 (NMC532). The thin nanolayer of Li3PO4 coating was formed after subjecting the NMCs to H3PO4 solution followed by heating at 500 °C for 5 h under air. The Li3PO4 coating formed is found to be very potent in enhancing the specific capacity of the first discharge as well as the rate capability and capacity retention in the subsequent charge/discharge cycles for both NMCs. The obtained results demonstrate that the H3PO4 treatment is a simple and general method to improve the electrochemical properties of NMCs with different compositions and have the potential for industrial applications.

Hierarchically Structured Core-Shell Design of a Lithium Transition-Metal Oxide Cathode Material for Excellent Electrochemical Performance.

Tuning geometrical parameters of lithium-mixed transition-metal oxide (LiTM) cathode materials is a promising strategy for resource-efficient design of high-performance Li-ion batteries. In this paper, we demonstrate that simple and facile geometrical tailoring of the secondary microstructure of LiTM cathode materials without complex chemical modification or heterostructure engineering can significantly improve overall electrochemical performance of the active cathode materials. An optimized LiTM with a bimodal size distribution of primary particles inside the secondary particles exhibits a 53.8% increase in capacity at a high discharge rate (10 C) compared to a commerciallyavailable reference and comparable rate capability after 100charge/discharge cycles. The key concept of this approach is to maximize the beneficial effects arising from the controlled sizes of primary particles. Multimodal/multiscale microscopic characterizations based on electron tomography and scanning transmission electron microscopy, combined with electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy from the atomic level to the microscale level, were employed to elucidate structural origins of enhanced battery performance. This study paves the way for the resource-efficient microstructure design of LiTM cathode materials to maximize capacity and stability via simple adjustment of processing conditions, which is advantageous for mass-production applications.

Surface and Subsurface Reactions of Lithium Transition Metal Oxide Cathode Materials: An Overview of the Fundamental Origins and Remedying Approaches

AbstractLithium‐ion batteries (LIBs) have become one of the most prevailing techniques for rechargeable batteries. Lithium transition metal oxides are prevalent cathode materials currently, but they face great challenges due to unsatisfactory energy density, chemical/electrochemical instability, and elemental scarcity concerns. Surface/subsurface is the interface where lithium ions cross between the electrolyte and the cathode materials. Its properties and complicated nature are unambiguously regarded as a crucial controlling factor for the overall performance. Tremendous efforts have been made in the exploration of surface modification methods with remarkable progress hitherto. The purpose of this work is to review these surface behaviors in order to understand their fundamental origins and provide a summary of various surface modification methods that can be used to address impeding issues. Finally, a rational method of surface modification is proposed for use in cathode materials.

Tailoring grain boundary structures and chemistry of Ni-rich layered cathodes for enhanced cycle stability of lithium-ion batteries

A critical challenge for the commercialization of layer-structured nickel-rich lithium transition metal oxide cathodes for battery applications is their capacity and voltage fading, which originate from the disintegration and lattice phase transition of the cathode particles. The general approach of cathode particle surface modification could partially alleviate the degradation associated with surface processes, but it still fails to resolve this critical barrier. Here, we report that infusing the grain boundaries of cathode secondary particles with a solid electrolyte dramatically enhances the capacity retention and voltage stability of the cathode. We find that the solid electrolyte infused in the boundaries not only acts as a fast channel for lithium-ion transport, it also, more importantly, prevents penetration of the liquid electrolyte into the boundaries, and consequently eliminates the detrimental factors, which include cathode–liquid electrolyte interfacial reactions, intergranular cracking and layered-to-spinel phase transformation. This grain-boundary engineering approach provides design ideas for advanced cathodes for batteries. The development of Ni-rich layered lithium transition metal oxides is plagued by their voltage and capacity fading on battery cycling. Here, the authors demonstrate an effective approach to treat these problems by infusing a solid electrolyte into the grain boundaries of the secondary particles of these layered materials.

Oxygen Stability of Disordered, Multi-Lithium Oxide Cathodes for Li-Ion Batteries

Development of high energy density, low-cost, and safe electrode materials is one of the key enablers for advanced batteries for transportation. Currently, one major technical barrier towards development of high energy density lithium-ion batteries is the lack of robust, high-capacity cathodes. Traditional layered LiMO2 (M = Mn, Co, Ni, etc.) cathodes cannot reversibly cycle their entire Li supply (e.g., x ≤ 0.5 in Li1-xCoO2). When charged beyond ~4.3 V vs. Li/Li+, many lithium-transition metal oxide cathodes undergo irreversible structural changes with concomitant oxygen gas evolution, resulting in irreversible capacity loss and voltage fade during cycling.[1-3]Understanding and addressing these structural instabilities is of vital importance to design next-generation cathode materials which can better utilize their Li supply without sacrificing cycle life. The scientific community has largely focused on developing well-ordered cathodes due to the notion that cation mixing reduces the electrode’s reversible capacity. Challenging this widely-held belief, recent work[2, 4-6] has shown that disordered Li-excess cathodes exhibit high capacities and good cycling stability (e.g., Li1.211Mo0.467Cr0.3O2with 266 mAh/g over 10 cycles). The excellent performance of these cathodes has been attributed to anion redox activity and formation of a percolating Li diffusion channel which is not energetically accessible in traditional materials. Motivated by these recent developments, the focus of the present work is to investigate the structural evolution of disordered cathodes during charge/discharge cycling. Multi-lithium cathodes containing transition metals which can access multiple oxidation states during lithium extraction are prepared and characterized. For example, Li2MoO3 (theoretical capacity of 340 mAh/g) can be charged to MoO3 (corresponding to oxidation of Mo4+ to Mo6+) at modest potentials (~2.5 V vs. Li/Li+) that are compatible with standard electrolytes. Furthermore, Li2MoO3 has been shown to have superior oxygen stability compared to Li2MnO3, offering opportunities to prepare composite layered-layered cathodes with the general formula xLi2MoO3•(1-x)LiMO2.[7] In this presentation, results will be presented on disordered, multi-lithium cathodes including Li2MoO3 and Li2MoO3•(1-x)LiMO2. Various synthesis procedures to produce these materials will be discussed, and standard electrochemical half-cell experiments will be coupled with advanced in-situ characterization methods including Raman spectroscopy, mass spectrometry, X-ray absorption spectroscopy (XAS), and X-ray diffraction (XRD) to evaluate the cathodes' oxidative stability. Furthermore, the effects of fluorine doping on cycling stability and oxygen lattice stability will be discussed. Acknowledgements This research has been supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, of the U.S. Department of Energy (DOE) through the Advanced Battery Materials Research (BMR) Program.

S/TEM Study of Fading Mechanism of Lithium Transition Metal Oxide Cathode for Lithium Ion Battery

S/TEM Study of Fading Mechanism of Lithium Transition Metal Oxide Cathode for Lithium Ion Battery

Achieving high capacity and rate capability in layered lithium transition metal oxide cathodes for lithium-ion batteries

In this study, we target to find a new composition for a layered mixed metal oxide, which has a high structural stability and a good electrochemical performance. Our strategy is to alter the transition metal composition focusing on the relative amounts of redox active Ni and Co to the inactive Mn, based on highly-stabilized LiNi1/3Co1/3Mn1/3O2. X-ray absorption near-edge structure and X-ray diffraction analyses show that the degree of cation disorder decreases on increasing the ratio of Ni and Co to Mn, by the presence of Ni3+, suggesting that slightly higher Ni and Co contents lead to improved structural stability. Electrochemical studies demonstrate that LiNi0.4Co0.4Mn0.2O2 cathodes exhibit considerable improvements in both the reversible capacity and the rate capabilities at a voltage range of 2.5–4.6 V. In situ XRD measurements reveal that LiNi0.4Co0.4Mn0.2O2 maintains a single-phase and undergoes lesser structural variations compared to controlled compositions during a delithiation process up to 4.6 V, while achieving a high reversible capacity over 200 mAh g−1. As a result, LiNi0.4Co0.4Mn0.2O2 experiences fewer structural degradations during electrochemical cycling, which explains the excellent long-term cycling performance.

Effect of Electrolyte Composition on Capacity Fading of Ni Rich Lithium Transition Metal Oxide Cathode for High Energy Density Lithium Ion Batteries

The lithium-ion battery has been widely employed in mobile applications because of its advantages, such as high energy density, insignificant self-discharge rate, and reasonable price. While it is also the most promising candidate power source for advanced automobiles, it needs further development to meet the specifications of electric vehicles1,2. For example, the driving distance of an electric vehicle on a single charge is becoming more and more important, which requires batteries with ever higher energy density. One of the main strategies to enhance the energy density is to raise the average potential and specific capacity of the cathode materials3. For this purpose, Ni rich lithium transition metal oxides have been developed for promising cathode materials4,5. Nevertheless, there are several limitations that need to be surmounted before the mass production of high energy density batteries containing Ni rich lithium transition metal oxides. In particular, significant capacity fading has been observed with lithium ion battery using Ni rich lithium transition metal oxides6,7. In this study, we found that cathode (Ni-rich LiNi0.8Co0.1Mn0.1O2) surface modification – phase transformation from a layered structure to a cubic phase – exerted a significant influence on battery performance. Such cubic phase hindered ionic and electronic conductivity of cathode particles. The kind of the cubic phase was different by changing the composition of the electrolyte. As a result, the resistance of the cylindrical cells after 300 cycles using different electrolyte showed a large gap, especially on cathode side. [1] B. Scrosati, J. Garche, J. Power Sources, 2010, 195, 2419[2] M. Armand, J.-M. Tarascon, Nature, 2008, 451, 652[3] J. B. Goodenough, Y. Kim, Chem. Mater., 2010, 22, 587[4] W. Liu et al, Angew. Chem. Int. Ed. Engl. 2015, 54, 4440[5] A. Manthiram et al, Adv. Energy Mater, 2016, 6, 1501010[6] D.P. Abraham et al, Electrochem. Comm., 2002, 4, 620[7] S. Watanabe et al, J. Power Sources, 2014, 258, 210