Lithium-rich Transition-metal Oxides Research Articles

Nanomaterial coating for layered lithium rich transition metal oxide cathode for lithium-ion battery

Nanomaterial coating for layered lithium rich transition metal oxide cathode for lithium-ion battery

Doping Strategy to Improve the Electrochemical Behavior of Lithium Rich Transition Metal Oxides As Cathodes for Lithium-Ion Batteries

Lithium-rich transition metal oxides are considered a promising cathodic solutions in Li-ion batteries to meet the growing energetic demand, thanks to their high specific capacity and operational voltage [1-2]. Li-rich layered materials have a general stoichiometry Li1+xTM1-xO2, in which TM is a blend of transition metals, as Ni, Mn, Co [2]. They stand out due to their high lithium concentration and specific capacity [1-2]. The higher capacity of Lithium-Rich can be attributed to the specific anionic redox reaction in the bulk at above 4.5 V. Nevertheless, large irreversible capacity loss in the first cycle, poor rate capability, mean working potential decay upon cycling and cobalt content are still major drawbacks that are hindering commercialization. In order to make these materials up scalable to industrial production, it is important to consider the reduction of costs and the toxicity of raw materials, in particular cobalt. Cobalt reduction has been identified as major driver to improve the environmental benignity of batteries and the sustainability of the overall production-consumption-recycling lifecycle. Several efforts to reduce these problems have been made, including the development of different synthetic strategies, doping and surface modification. The most, widely explored, chemical strategy to mitigate the voltage decay and structural degradation in Lithium Rich cathodes is the doping. Elemental doping can be divided into cation and anion doping. As an example, incorporation of redox inactive metals, such as Al, Zr, Ti, has been proposed in order to stabilize the lattice as well as the partial replacement of lithium ions with other alkali cations, e.g. K and Na; or doping the oxygen anion sublattice. In this communication, we present our doping approaches. In particular, the simultaneous replacement of cobalt in the layered structure with aluminum and lithium (over-lithiation). Moreover, we present over-lithiated Co-free materials where the introduction of different amount of iron has been investigated. The characterization of these novel layered materials is reported in terms of composition, structure, morphology and electrochemical performances. These approaches can be applied as a strategy to mitigate the voltage decay and reduce the Cobalt content.[1] Ji, X. et al. Journal of Power Sources 487, (2021).[2] Zhao, S. et al. Angewandte Chemie - International Edition 60, 2208–2220 (2021).

Entropic Stabilization in Lithium Rich Transition Metal Oxide Cathodes

It is well known that lithium rich transition metal oxide cathodes (LRM) experience voltage fade and capacity loss over the course of cycling, and it is generally known that these are a result of the LRM materials’ general instability 1–7. However, the mechanisms behind these losses are still unknown, due in large part to the structural ambiguity and controversy associated with the LRM material structure. In this perspective we consider the role entropy plays in LRM materials’ structural stability and electrochemical properties. With this mind set we argue that due to their metastability LRM cathodes’ structure and properties are not synthesis agnostic, and therefore establishment of consistent synthetic procedures is of paramount importance. We also propose that LRM materials could be categorized as entropically stabilized oxides through exploring their configurational entropies, phase behaviors, and thermal responses. The entropic stabilization of LRM materials is also found to be consistent with the ordering behaviors of LRM cathode transitional metal layers, with this ordering presenting both compositional, thermal, and electrochemical dependencies. The impact of these behaviors on the redox and electrochemical structure and activation of LRM materials is also explored. Finally, we seek to put these findings into the context of the wider battery field. Fell, C. R. et al. Correlation Between Oxygen Vacancy, Microstrain, and Cation Distribution in Lithium-Excess Layered Oxides During the First Electrochemical Cycle. Chem. Mater. 1621–1629 (2013) doi:10.1021/cm4000119.Lu, Z., Beaulieu, L. Y., Donaberger, R. A., Thomas, C. L. & Dahn, J. R. Synthesis, Structure, and Electrochemical Behavior of Li [Ni x Li(1/2-2x/3) Mn(2/3-x/3)]O2. J. Electrochem. Soc. 149, A778–A791 (2002).Wu, Y. & Manthiram, A. High Capacity, Surface-Modified Layered Li†Li„1−x.../3Mn„2−x.../3Nix/3Cox/3‡O2 Cathodes with Low Irreversible Capacity Loss. Electrochem. Solid-State Lett. 9, A221–A224 (2006).Dupré, N., Cuisinier, M., Legall, E., War, D. & Guyomard, D. Contribution of the oxygen extracted from overlithiated layered oxides at high potential to the formation of the interphase. J. Power Sources 299, 231–240 (2015).Jarvis, K. A. et al. Formation and effect of orientation domains in layered oxide cathodes of lithium-ion batteries. Acta Mater. 108, 264–270 (2016).Jiang, M., Key, B., Meng, Y. S. & Grey, C. P. Electrochemical and Structural Study of the Layered, ‘Li-Excess’; Lithium-Ion Battery Electrode Material Li[Li 1/9 Ni 1/3 Mn 5/9 ]O 2. Chem. Mater. 21, 2733–2745 (2009).Hy, S. et al. Performance and design considerations for lithium excess layered oxide positive electrode materials for lithium ion batteries. Energy Environ. Sci. 9, 1931–1954 (2016).

Anionic Redox in Alkali-Rich Chalcogenides for Energy-Dense, Lithium-Ion Batteries

Lithium-rich transition-metal oxides and chalcogenides exhibit reversible charge-storage reactions centered at anionic sites (e.g., O2–, S2–, or Se2–), augmenting well-established metal cation-sited redox reactions to increase the energy density of lithium-ion or sodium-ion batteries by up to 100%.1 Despite these promising characteristics, the structure–property relationships that govern cation- and anion-coupled redox reactions in chalcogenides remain poorly understood. We deconvolve the cation/anion redox mechanisms of Li+-insertion in alkali-rich chalcogenides by modulating the transition metal–sulfide electronic band structure via systematic metal substitution for iron in Li2Fe1–xMxS2. Key electrochemical characteristics (cation/anion redox potential, Li+-insertion capacity, reversibility) will be correlated with electronic and structural properties as a function of chalcogenide composition using such techniques as X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering. Experimental results will be compared with density functional theory (DFT) calculations of analogous model systems. Understanding the relationship between band structure and reversible charge-storage will guide the design of alkali-rich chalcogenides that are candidates to transition into commercial Li-ion batteries. Due to the absence of oxygen in the chalcogenide crystal structure, batteries that use these as cathode materials will be inherently safer to operate at elevated temperatures and challenging charge–discharge duty cycles. C.J. Hansen, J.J. Zak, A.J. Martinolich, N.H. Bashian, F. Kaboudvand, A. Van der Ven, B.C. Melot, J.N. Welker, and K.A. See. Multielectron, Cation and Anion Redox in Lithium-Rich Iron Sulfide Cathodes. J. Am. Chem. Soc. 142 (2020) 6737–6749.

Sulfuration of Li‐Rich Mn‐Based Cathode Materials for Multianionic Redox and Stabilized Coordination Environment

Lithium-rich transition metal oxides (LLOs) can deliver high specific capacity over 250 mAh g-1 , stemming from additional contribution of oxygen redox. However, the formation of O(2- n )- (0 < n< 2) species and even oxygen gas during the deep oxidation stage leads to progressive structural transformation that cause voltage decay/hysteresis, sluggish kinetics, and poor thermostability, preventing real-world application of LLOs. Therefore, the substantive key relies on enhancing the anionic redox stability in LLOs. Here, a sulfuration procedure of LLOs (S-LLOs) is proposed, in which sulfur anions are incorporated into oxygen sites in the lattice structure and form polyanions on the surface. Proved by structural characterizations and density functional theory (DFT) calculations, sulfur anions in the interior lattice can reversibly participate in the redox process and enhance the integral coordination stability by mitigating undesired oxygen redox. Moreover, S polyanions at the surface form a protecting layer for interfacial stability. The electrochemical measurements indicate that S-LLO demonstrates a high discharge capacity of 307.8 mAh g-1 , an outstanding capacity retention rate of 91.5% after 200 cycles, along with excellent voltage maintenance, rate capability, and thermostability. The sulfuration process of LLOs with multianionic redox mechanism highlights a promising strategy to design novel high-energy-density cathode materials with superior cycling performance.

A journey through layered cathode materials for lithium ion cells – From lithium cobalt oxide to lithium-rich transition metal oxides

Lithium ion batteries (LIBs) have emerged as an important power source for various applications including portable electronics, military, space etc. Cathode materials play an important role in deciding the performance of LIBs. Layered transition metal oxides have drawn much attention for application as cathode material in LIBs due to their high specific capacities, high energy densities and good cycle life. LiCoO 2 , LiNi 0.8 Co 0.15 Al 0.05 O 2 and LiMn x Ni y Co z O 2 are the commonly used layered cathode materials in LIBs. In the past two decades, intensive efforts have been made to develop cathode materials with much higher energy densities for meeting the requirements for modern applications. However, several issues and challenges such as their dubious crystal structure, uncertain reaction mechanism, high initial irreversible capacity, fast voltage fading, poor cycle life and poor rate capability must be resolved before they are employed for realistic commercial applications. This review gives an overview of the different layered cathode materials for LIBs starting from the first generation cathode material, LiCoO 2 to the latest Li-rich layered cathode materials. The effect of cathode structure, morphology, role of transition metals and doping of different metal ions on the performance of LIBs are discussed.

Study on Local Chemical Orderings in Li3NbO4-Based Positive Electrode Materials with a Disordered Rock-Salt Structure By a Reverse Monte Carlo Modeling

1. Introduction As a positive electrode material for a lithium-ion battery, lithium-rich transition-metal oxides have drawn much attention due to the high discharge capacity. Among the oxides, we have focused on Li1+xM1-xO2 with a disordered rock-salt structure such as Li3NbO4-based solid solution [1]. It is well known that all the cations occupy a same crystallographic site in the crystals. Due to different ionic radii and electronic states of the cations, however, it can be predicted that local structures (non-periodic structures) around different cation species must be distinguishable, and such hidden strucures must affect Li+ behavior in charge and discharge processes. Therefore, some previous works tried to uncover the local structures [2], but the structures are still under debete. This is because the structures without periodicity do not show prominent Bragg peaks in a diffraction profile.From such background, this work investigated local structures of the Li3NbO4-based materials, which can be also denoted as Li1+x(Nb, M)1-xO2, with the disordered rocksalt structure by a reverse Monte Carlo (RMC) modeling using total scattering data. Especially, we paid special attention on Li1.3Nb0.3Fe0.4O2 and Li1.3Nb0.43Ni0.27O2 as typical materials. Based on the modeling results, we discuss effects of the cation species on the local structures.2. Experimental The Li3NbO4-based materials were synthesized by a conventional solid-state reaction method, according to literature [1]. Metal compositions of the samples were analyzed by an inductively coupled plasma atomic emission spectroscopy, and valences of cations were estimated by X-ray absorption near edge structures (BL14B2, SPring-8). Synchrotron X-ray Bragg profiles were collected with BL19B2 (SPring-8), and the crystal structures (average structures) were refined by a Rietveld method. We also measured neutron and synchrotron X-ray total scattering data at NOVA (J-PARC) and BL04B2 (SPring-8), respectively. By using structure factors S(Q) and reduced pair distribution functions G(r) in addition to the Bragg profiles, we performed the RMC modeling with an RMCProfile software under a bond-valence-sum (BVS) constraint. In the modeling, we optimized cation distributions by swapping the cations.3. Results We made a supercell with 1000 atoms from a refined unit cell, and then performed RMC modeling on Li1.3Nb0.3Fe0.4O2 with the disordered rock-salt structure. As a result, we could obtain an atomic configuration which could reproduce X-ray Bragg profile, neutron G(r), neutron and X-ray S(Q). From the atomic configuration, it was found that a local distortion of NbO6 was larger than those of the others (LiO6 and FeO6) in the material. The large distortion should be induced by a smaller ionic radius of Nb5+ and/or a mismatch of electronic state of Nb5+. Furthermore, it was clarified from a coordination-number analysis that Li tended to be surrounded by Nb considerably in the disordered rock-salt structure. Such a tendency was also observed in an atomic configuration of Li1.3Nb0.43Ni0.27O2. From the results, it can be concluded that Li diffusion is disturbed by a cation with a higher valence in the disordered structure.

Gradient Li-rich oxide cathode particles immunized against oxygen release by a molten salt treatment

Lithium-rich transition metal oxide (Li1+XM1−XO2) cathodes have high energy density above 900 Wh kg−1 due to hybrid anion- and cation-redox (HACR) contributions, but critical issues such as oxygen release and voltage decay during cycling have prevented their application for years. Here we show that a molten molybdate-assisted LiO extraction at 700 °C creates lattice-coherent but depth (r)-dependent Li1+X(r)M1−X(r)O2 particles with a Li-rich (X ≈ 0.2) interior, a Li-poor (X ≈ −0.05) surface and a continuous gradient in between. The gradient Li-rich single crystals eliminate the oxygen release to the electrolyte and, importantly, still allow stable oxygen redox contributions within. Both the metal valence states and the crystal structure are well maintained during cycling. The gradient HACR cathode displays a specific density of 843 Wh kg−1 after 200 cycles at 0.2C and 808 Wh kg−1 after 100 cycles at 1C, with very little oxygen release and consumption of electrolyte. This high-temperature immunization treatment can be generalized to leach other elements to avoid unexpected surface reactions in batteries. Critical issues such as oxygen release during battery cycling plague the development of high-energy Li-rich oxide cathodes. Here the authors report a Li-gradient structure of the oxides, obtained by a selective LiO leaching process via a molten salt treatment, displaying virtually zero oxygen loss.

Low-Dose Aberration-Free Imaging of Li-Rich Cathode Materials at Various States of Charge Using Electron Ptychography

Imaging the complete atomic structure of materials, including light elements, with minimal beam-induced damage of the sample is a long-standing challenge in electron microscopy. Annular bright-field scanning transmission electron microscopy is often used to image elements with low atomic numbers, but due to its low efficiency and high sensitivity to precise imaging parameters it comes at the price of potentially significant beam damage. In this paper, we show that electron ptychography is a powerful technique to retrieve reconstructed phase images that provide the full structure of beam-sensitive materials containing light and heavy elements. Due to its much higher efficiency, we can reduce the beam currents used down to the subpicoampere range. Electron ptychography also allows residual lens aberrations to be corrected at the postprocessing stage, which avoids the need for fine-tuning of the probe that would result in further beam damage and provides aberration-free reconstructed phase images. We have used electron ptychography to obtain structural information from aberration-free reconstructed phase images in the technologically relevant lithium-rich transition metal oxides at different states of charge. We can unambiguously determine the position of the lithium and oxygen atomic columnswhile amorphization of the surface, formation of beam-induced surface reconstruction layers, or migration of transition metals to the alkali layers are drastically reduced.

Architected Macroporous Polyelectrolytes That Suppress Dendrite Formation during High-Rate Lithium Metal Electrodeposition

Batteries assembled with lithium metal anodes and high-capacity cathodes—including air, sulfur, and lithium-rich transition metal oxides—have higher energy density than conventional Li-ion counterparts. Unfortunately, the lifetime of lithium metal cells is typically short, owing to the formation of dendrites on charging, which eventually shorts the cells. Short cycle life is also observed when lithium deposits with a “mossy” morphology; the high surface area of mossy deposits increases the rate of electrolyte degradation, eventually drying out the cells. Here we show that a lithium-ion-conducting, architected macroporous polyelectrolyte (AMP-1) serves as a long-lasting host for uniform and dense lithium–metal electrodeposits. High Coulombic efficiencies indicate the low occurrence of parasitic reactions with the electrolyte. Galvanostatic discharge experiments indicate that AMP-1 suppresses dendrite formation, extending over 2-fold the short-circuit time at high current density. Our success opens new dire...

Effect of Synthetic Condition on Local Chemical Ordering of Li1.2Mn0.6Ni0.2O2 Investigated By Pair Distribution Function Analysis

INTRODUCTION In the last decade, lithium-rich transition-metal oxides with a monoclinic layered structure have drawn much attention as a cathode of the lithium-ion battery. Among the oxides, Li1.2Mn0.6Ni0.2O2 (LMN) can be regarded as one of promising candidates due to lower cost and environmental load. According to previous works, a synthetic process has much influence on electrochemical properties of LMN and this situation makes the commercial use difficult. In order to uncover an origin of the synthetic-condition effect, it seems that an atomic configuration of LMN must be investigated in detail. As is well known, the Rietveld refinement using the Bragg profile is a typical analytical method, but this technique permits us only to discuss an average structure with periodicity even though a local chemical ordering such as LiMn6cluster is believed to play an important role in a delithiation/lithiation process. In this work, the local chemical orderings of LMN prepared with different synthetic conditions were investigated by the pair distribution function (PDF) analysis, which enables us to discuss longer-range atomic correlation easily than other techniques such as NMR and EXAFS. On the basis of the obtained atomic configurations, an effect of the synthetic condition on the local ordering is discussed. EXPERIMENTAL Li1.2Mn0.6Ni0.2O2was prepared by a co-precipitation method where two kinds of the cooling condition were applied: quenching and slow cooling. The products were characterized by means of X-ray diffraction (XRD) and inductively coupled plasma (ICP) measurements. The average atomic structures (the crystal structures) were refined by the Rietveld method using neutron (SPICA, J-PARC) and synchrotron X-ray (BL02B2 or BL19B2, SPring-8) diffraction patterns. A super cell with 1800 atoms was constructed from the unit cell, and then was used in the Monte Carlo simulation with experimental data, i. e., the reverse Monte Carlo (RMC) modeling. In the modeling, we used simultaneously the Bragg profile, neutron and X-ray structure factors which were obtained by NOVA (J-PARC) and BL04B2 (SPring-8), respectively. We also utilized an inverse Fourier transform of neutron structure factor, which is PDF. The RMC modeling was carried out with the RMCProfile program under the bond-valence-sum (BVS) constraint. RESULTS AND DISCUSSION It was confirmed from XRD and ICP measurements that both the Li1.2Mn0.6Ni0.2O2 had a single phase of the Li2MnO3-type layered structure (S. G.: C2/m) and the analytical metal compositions were almost equal to the nominal value. The Rietveld analysis suggests that a distortion around a Li site is lower in the quenched sample than the other. Such a result is well consistent with the better charge/discharge property of the quenched sample. By using the unit cell refined by the Rietveld analysis, we constructed a super cell and then optimized the atomic configurations on the basis of the RMC algorithm. In the process, neutron and X-ray structure factors were convolved, taking the cell size into account. As an example, Fig. 1 shows neutron D(r) of Li1.2Mn0.6Ni0.2O2 to which the slow cooling process was applied. The obtained atomic configuration snapshot indicates that Li in the transition-metal layer tends to be surrounded by Mn, and Ni at the lithium layer prefer to form a Ni-O domain in the crystal. An effect of the synthetic condition will be discussed. Figure 1

One-Pot Synthesis of Lithium-Rich Cathode Material with Hierarchical Morphology.

Lithium-rich transition metal oxides, Li1+xTM1-xO2 (TM, transition metal), have attracted much attention as potential candidate cathode materials for next generation lithium ion batteries because their high theoretical capacity. Here we present the synthesis of Li[Li0.2Ni0.2Mn0.6]O2 using a facile one-pot resorcinol-formaldehyde method. Structural characterization indicates that the material adopts a hierarchical porous morphology consisting of uniformly distributed small pores and disordered large pore structures. The material exhibits excellent electrochemical cycling stability and a good retention of capacity at high rates. The material has been shown to be both advantageous in terms of gravimetric and volumetric capacities over state of the art commercial cathode materials.

Voltage Variation of Lithium Transition Metal Oxides Caused by the Migration of Cations

In the past decade, major effort has been devoted to understanding the structure and the electrochemical benefit of lithium-rich transition metal oxides for high-energy density lithium-ion batteries because of their potentially high specific capacity of up to 250 mAh g-1 when the materials are electrochemically activated. However, a consensus has not been established yet on the local structure of this class of materials. It has been reported that the excess portion of lithium was homogeneously dissolved in the matrix of the transition metal layer (3b sites of space group 166 or R-3m), forming a solid solution. On the other hand, Thackeray and others believed that the excess lithium on 3b sites has a strong tendency to pair with manganese and segregate to form Li2MnO3 domains. Despite the discrepancy in these researchers’ findings on the local structure, both sides agreed that the excess lithium can be electrochemically activated at a potential above 4.5 V vs. Li+/Li to deliver more reversible specific capacity, offering great opportunity for use of these lithium-rich transition metal oxides as high-capacity cathode materials. However, the structural instability of the material after electrochemical activation causes a continuous decrease in its working potential, a phenomenon which we will call voltage fade, that hinders the commercial deployment of this class of high-capacity cathode materials. The migration mechanism of transition metal in the oxygen framework was investigated here to illustrate the voltage decay of lithium-rich transition metal oxides. For the first time, a voltage increase was observed during the cycling of a lithium manganese oxide spinel within a wide potential window. It was demonstrated that the voltage variation of these lithium transition metal oxides was caused by the continuous migration of transition metal ions, mostly Mn2+ and Co4+, between the octahedral and tetrahedral sites of oxygen framework, resulting in the ration change between the spinel component and layered component. Figure 1

Layered Li2RuO3–LiCoO2 composite as high-performance cathode materials for lithium-ion batteries

Lithium-rich transition metal oxides are attractive cathode materials providing high energy densities for lithium-ion batteries. A layer-structured Li2RuO3-LiCoO2 composite was synthesized by the solid-state reaction method. In the as-prepared composite, Li2RuO3 component not only serves as the electrochemical active phase providing large reversible capacity, but also improves the structural stability of layered LiCoO2 at high potential. Electrochemical measurements show the composite has high reversible specific capacity and good capacity retention. Particularly, the initial discharge specific capacity can reach 240mAh/g at current density of 0.13C between 2.0V and 4.5V. It also exhibits an excellent cycling stability with capacity retention of 75% after 50 cycles. The present work suggests choosing appropriate transition metal M and M′ for Li2MO3-LiM′O2 composite should be an efficient strategy for designing new cathode materials.

Solid State NMR Studies of Li2MnO3 and Li-Rich Cathode Materials: Proton Insertion, Local Structure, and Voltage Fade

High energy densities of lithium-rich transition metal oxides cannot be sufficiently maintained on cycling due to high-voltage first-cycle activation and the subsequent structural changes. These changes can be seen as a continuous decrease of the average voltage with cycling, known as voltage fade. Electrochemical and chemical insertion of protons has been reported suggesting that protons generated in the electrolyte could be involved in electrochemical cycling which could play a similar role in the “Li2MnO3 component” of lithium rich transition metal oxides. Here, electrochemical insertion of structural protons, changes in lithium occupancy at various states of charge, and changes in local structure have been investigated via a combination of local probes including solid state NMR, X-ray absorption spectroscopy and first principle calculations. While significant evidence is found for the deposition of non-structural proton-bearing species on electrodes, which accumulate with extensive cycling, structural proton insertion is not found to be a significant process directly effecting voltage fade. The electrochemical activity of disordered Li2MnO3, synthesized at low temperature, is also investigated and its Li removal/insertion properties measured quantitatively with NMR. Major reordering of Li sites and subsequent local structural transitions are observed by NMR and are found to be synchronous with voltage fade.

Degradation and Structural Evolution of xLi2MnO3·(1–x)LiMn1/3Ni1/3Co1/3O2 during Cycling

In the present work, the electrochemical degradation and structural evolution of xLi2MnO3·(1–x)LiMn1/3Ni1/3Co1/3O2 (x = 0.3, 0.5, and 0.7) materials and the role of Li2MnO3 component during electrochemical cycling are systematically studied through careful analysis of electrochemical data, ex-situ XRD, and HR-TEM observations. The materials consisting of higher Li2MnO3 content show better cyclic performance with more significant voltage decay compared to that of xLi2MnO3·(1–x)LiMn1/3Ni1/3Co1/3O2 electrodes with low Li2MnO3 content. The electrochemical degradation of xLi2MnO3·(1–x)LiMn1/3Ni1/3Co1/3O2 electrodes upon cycling not only results from the remarkably increase in impedance caused by the damage of the electrode surface, in particular for low Li2MnO3 content; but also arises from structural rearrangement, especially for high Li2MnO3 content. Upon cycling, high Li2MnO3 content in the crystal structure of lithium-rich transition metal oxides can stabilize the electrode\\electrolyte interface at high potentials, facilitates the rapid formation of cracks and porosity in the cycled electrodes, and promotes the distortions and breakdown of the original well-layered lattice.

Study on High Energy Lithium-Ion Battery with Lithium-Rich Transition Metal Oxides

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Investigation of the Irreversible Capacity Loss in the Lithium-Rich Oxide Li[Li1/5Ni1/5Mn3/5]O2

The lithium-rich transition metal oxides show a larger first charge capacity and larger cycling capacities than the non-lithium-rich transition metal oxides. The disadvantages of the lithium-rich transition metal oxides include relatively poor rate capabilities and relatively large irreversible capacities. In this report, the irreversible capacity loss of the lithium rich oxide Li[Li1/5Ni1/5Mn3/5]O2 was investigated. Stepwise traverse of the oxygen-release plateau increased the cycling capacity of Li/Li[Li1/5Ni1/5Mn3/5]O2 cells and gave evidence that lithium was removed from the transition metal layer at the start of the oxygen release plateau. The irreversible capacity loss was attributed to the diffusion of transition metals into the lithium vacancies in the transition metal layer and the subsequent inability for lithium reinsertion into the transition metal layer. Isothermal calorimetry of Li/Li[Li1/5Ni1/5Mn3/5]O2 cells cycled from 2.5 to 4.4 V (no oxygen loss) supported the view that lithium is not deintercalated from the transition metal layer at the start of charge.