Electrochemical Reaction of Lithium with Nanostructured Silicon Anodes: A Study by In‐Situ Synchrotron X‐Ray Diffraction and Electron Energy‐Loss Spectroscopy

Silicon‐based anodes are an appealing alternative to graphite for lithium‐ion batteries because of their extremely high capacity. However, poor cycling stability and slow kinetics continue to limit the widespread use of silicon in commercial batteries. Performance improvement has been often demonstrated in nanostructured silicon electrodes, but the reaction mechanisms involved in the electrochemical lithiation of nanoscale silicon are not well understood. Here, in‐situ synchrotron X‐ray diffraction is used to monitor the subtle structural changes occurring in Si nanoparticles in a Si‐C composite electrode during lithiation. Local analysis by electron energy‐loss spectroscopy and transmission electron microscopy is performed to interrogate the nanoscale morphological changes and phase evolution of Si particles at different depths of discharge. It is shown that upon lithiation, Si nanoparticles behave quite differently than their micrometer‐sized counterparts. Although both undergo an electrochemical amorphization, the micrometer‐sized silicon exhibits a linear transformation during lithiation, while a two‐step process occurs in the nanoscale Si. In the first half of the discharge, lithium reacts with surfaces, grain boundaries and planar defects. As the reaction proceeds and the cell voltage drops, lithium consumes the crystalline core transforming it into amorphous Li_xSi with a primary particle size of just a few nanometers. Unlike the bulk silicon electrode, no Li₁₅Si₄ or other crystalline Li_xSi phases were formed in nanoscale Si at the fully‐lithiated state.     

All‐Solid‐State Lithium‐Ion Microbatteries Using Silicon Nanofilm Anodes: High Performance and Memory Effect

All‐solid‐state thin film lithium batteries are promising devices to power the next generations of autonomous microsystems. Nevertheless, some industrial constraints such as the resistance to reflow soldering (260 °C) and to short‐circuiting necessitate the replacement of the lithium anode. In this study, a 2 V lithium‐ion system based on amorphous silicon nanofilm anodes (50–200 nm thick), a LiPON electrolyte, and a new lithiated titanium oxysulfide cathode Li_1.2TiO_0.5S_2.1 is prepared by sputtering. The determination of the electrochemical behavior of each active material and of whole systems with different configurations allows the highlighting of the particular behavior of the Li_xSi electrode and the understanding of its consequences on the performance of Li‐ion cells. Lithium‐ion microbatteries processed with industrial tools and embedded in microelectronic packages exhibit particularly high cycle life (?0.006% cycle^?1), ultrafast charge (80% capacity in 1 min), and tolerate both short‐circuiting and reflow soldering. Moreover, the perfect stability of the system allows the assignment of some modifications of the voltage curve and a slow and reversible capacity fade occurring in specific conditions, to the formation of Li₁₅Si₄ and to the expression of a “memory effect.” These new findings will help to optimize the design of future Li‐ion systems using nanosized silicon anodes.     

Synthesis,Characterization, and Structural Modeling of High‐Capacity,Dual Functioning MnO2 Electrode/Electrocatalysts for Li‐O2 Cells

It has become clear that cycling lithium‐oxygen cells in carbonate electrolytes is impractical, as electrolyte decomposition, triggered by oxygen reduction products, dominates the cell chemistry. This research shows that employing an α‐MnO₂/ramsdellite‐MnO₂ electrode/electrocatalyst results in the formation of lithium‐oxide‐like discharge products in propylene carbonate, which has been reported to be extremely susceptible to decomposition. X‐ray photoelectron data have shown that what are likely lithium oxides (Li₂O₂ and Li₂O) appear to form and decompose on the air electrode surface, particularly at the MnO₂ surface, while Li₂CO₃ is also formed. By contrast, cells without α‐MnO₂/ramsdellite‐MnO₂ fail rapidly in electrochemical cycling, likely due to the differences in the discharge product. Relatively high electrode capacities, up to 5000 mAh/g (carbon + electrode/electrocatalyst), have been achieved with non‐optimized air electrodes. Insights into reversible insertion reactions of lithium, lithium peroxide (Li₂O₂) and lithium oxide (Li₂O) in the tunnels of α‐MnO₂, and the reaction of lithium with ramsdellite‐MnO₂, as determined by first principles density functional theory calculations, are used to provide a possible explanation for some of the observed results. It is speculated that a Li₂O‐stabilized and partially‐lithiated electrode component, 0.15Li₂O·α‐Li_xMnO₂, that has Mn^4+/3+ character may facilitate the Li₂O₂/Li₂O discharge/charge chemistries providing dual electrode/electrocatalyst functionality.     

Redox Targeting of Anatase TiO2 for Redox Flow Lithium‐Ion Batteries

Anatase TiO₂ is an extensively studied anode material for lithium‐ion batteries because of its superior capability of storing Li⁺ electrochemically. Here reversible lithium storage of TiO₂ is achieved chemically using redox targeting reactions. In the presence of a pair of redox mediators, bis(pentamethylcyclopentadienyl)cobalt (CoCp^* ₂) and cobaltocene (CoCp₂) in an electrolyte, TiO₂ and its lithiated form Li _x TiO₂ can be reduced and oxidized by CoCp^* ₂ and CoCp₂ ⁺, respectively, which accompany Li⁺ insertion and extraction, albeit without attaching the TiO₂ onto the electrode. The reversible chemical lithiation/delithiation and the involved phase transitions are unambiguously confirmed using density functional theory (DFT) calculations, UV‐vis spectroscopy, X‐ray photoelectron spectoscopy (XPS), and Raman spectroscopy. A redox flow lithium‐ion battery (RFLB) half‐cell is assembled and evaluated, which is a critical step towards the development of RFLB full cells.     

Lithium Intercalation Behavior in Multilayer Silicon Electrodes

Next generation lithium battery materials will require a fundamental shift from those based on intercalation to elements or compounds that alloy directly with lithium. Intermetallics, for instance, can electrochemically alloy to Li_4.4M (M = Si, Ge, Sn, etc.), providing order‐of‐magnitude increases in energy density. Unlike the stable crystal structure of intercalation materials, intermetallic‐based electrodes undergo dramatic volume changes that rapidly degrade the performance of the battery. Here, the energy density of silicon is combined with the structural reversibility of an intercalation material using a silicon/metal‐silicide multilayer. In operando X‐ray reflectivity confirms the multilayer's structural reversibility during lithium insertion and extraction, despite an overall 3.3‐fold vertical expansion. The multilayer electrodes also show enhanced long‐term cyclability and rate capabilities relative to a comparable silicon thin film electrode. This intercalation behavior found by dimensionally constraining silicon's lithiation promises applicability to a wide range of conversion reactions.     

Sn‐Alloy Foil Electrode with Mechanical Prelithiation: Full‐Cell Performance up to 200 Cycles

Self‐supporting Sn foil is a promising high‐volumetric‐capacity anode for lithium ion batteries (LIBs), but it suffers from low initial Coulombic efficiency (ICE). Here, mechanical prelithiation is adopted to improve ICE, and it is found that Sn foils with coarser grains are prone to cause electrode damage. To mitigate damage and prepare thinner lithiated electrodes, 3Ag0.5Cu96.5Sn foil is used that has more refined grains (5–10 µm) instead of Sn (50–100 µm), where the abundant grain boundaries (GBs) offer more sliding systems to release stress and reduce deep fractures. Thus, the thickness of Li_x3Ag0.5Cu96.5Sn can be reduced to 50 µm, compared to 100 µm Li_xSn. When the foils contact open air, the Sn‐Li‐O(H) products are more stable than Li‐O(H), thus Li_x3Ag0.5Cu96.5Sn shows outstanding air stability. The as‐prepared 50 µm foil anode achieves stable 200 cycles in LiFePO₄//Li_x3Ag0.5Cu96.5Sn full cell (≈2.65 mAh cm^?2) and the capacity retention is 95%. Even at 5C, the capacity of Li_x3Ag0.5Cu96.5Sn is still up to ≈1.8 mAh cm^?2. The cycle life of NCM523//Li_x3Ag0.5Cu96.5Sn full cell exceeds that of NCM523//Li. Furthermore, 70 µm Li_x3Ag0.5Cu96.5Sn is used as double‐sided anode for a 3 cm × 2.8 cm pouch cell and its actual volumetric capacity density is 674 mAh cm^?3 after 50 cycles.     

Tungsten Disulfide Catalysts Supported on a Carbon Cloth Interlayer for High Performance Li–S Battery

The capacity limitations of insertion‐compound cathodes has motivated interest in a sulfur cathode for a rechargeable battery cell with a metallic‐lithium anode; but irreversible capacity loss owing to solubility of intermediate Li₂S_x (x = 2–8) polysulfides in the organic‐liquid electrolytes used has prevented practical application. A dual‐function cathode structure consisting of layered tungsten disulfide (WS₂) supported both on the cathode current collector and on a carbon cloth interlayer (CCl) gives excellent performance in a lithium half‐cell by providing strong adsorption of the soluble Li₂S_x on the WS₂ with fast access to electrons from the current collector via a blocking carbon cloth interlayer.     

Si‐Doping Mediated Phase Control from β‐ to γ‐Form Li3VO4 toward Smoothing Li Insertion/Extraction

The γ phase Li₃VO₄ which possesses higher ionic conductivity is more preferable for lithium ion batteries, but it is only stable at high temperature and would convert to low temperature β phase spontaneously when cooling down. Here, the phase control of Li₃VO₄ to stabilize its γ phase in room temperature is successfully mediated by introducing proper Si‐doping, and for the first time the electrochemical performances of γ‐Li₃VO₄ is investigated. It is found that pure γ‐Li₃VO₄ can be obtained in a doping ratio of x = 0.05–0.15 in Li_3+xV_1?xSi_xO₄ with addition of excess Li source in synthesis design. The doping mechanism and the energy changes are investigated in detail by using the first principle calculations, it reveals that an interstitial Li⁺ is formed with doping of Si⁴⁺ in Li₃VO₄ to balance the system charge. When served as an anode, the Si‐doped γ‐Li₃VO₄ shows much smoothed Li⁺ insertion/extraction and enhanced cycle stability with only a single pair of redox peaks, which behaves much different with the complex multicouples of redox peaks in typical β‐Li₃VO₄. These changes in electrochemical performances implies that γ‐Li₃VO₄ can effectively accommodate Li⁺ in an easier and more facile way and relieved structure stress during the charge/discharge process.     

High‐Performance Lithium‐Sulfur Batteries with a Self‐Supported, 3D Li2S‐Doped Graphene Aerogel Cathodes

Lithium‐sulfur (Li‐S) batteries are being considered as the next‐generation high‐energy‐storage system due to their high theoretical energy density. However, the use of a lithium‐metal anode poses serious safety concerns due to lithium dendrite formation, which causes short‐circuiting, and possible explosions of the cell. One feasible way to address this issue is to pair a fully lithiated lithium sulfide (Li₂S) cathode with lithium metal‐free anodes. However, bulk Li₂S particles face the challenges of having a large activation barrier during the initial charge, low active‐material utilization, poor electrical conductivity, and fast capacity fade, preventing their practical utility. Here, the development of a self‐supported, high capacity, long‐life cathode material is presented for Li‐S batteries by coating Li₂S onto doped graphene aerogels via a simple liquid infiltration–evaporation coating method. The resultant cathodes are able to lower the initial charge voltage barrier and attain a high specific capacity, good rate capability, and excellent cycling stability. The improved performance can be attributed to the (i) cross‐linked, porous graphene network enabling fast electron/ion transfer, (ii) coated Li₂S on graphene with high utilization and a reduced energy barrier, and (iii) doped heteroatoms with a strong binding affinity toward Li₂S/lithium polysulfides with reduced polysulfide dissolution based on first‐principles calculations.     

Silicon Anode with High Initial Coulombic Efficiency by Modulated Trifunctional Binder for High‐Areal‐Capacity Lithium‐Ion Batteries

High‐capacity electrode materials play a vital role for high‐energy‐density lithium‐ion batteries. Silicon (Si) has been regarded as a promising anode material because of its outstanding theoretical capacity, but it suffers from an inherent volume expansion problem. Binders have demonstrated improvements in the electrochemical performance of Si anodes. Achieving ultrahigh‐areal‐capacity Si anodes with rational binder strategies remains a significant challenge. Herein, a binder‐lithiated strategy is proposed for ultrahigh‐areal‐capacity Si anodes. A hard/soft modulated trifunctional network binder (N‐P‐LiPN) is constructed by the partially lithiated hard polyacrylic acid as a framework and partially lithiated soft Nafion as a buffer via the hydrogen binding effect. N‐P‐LiPN has strong adhesion and mechanical properties to accommodate huge volume change of the Si anode. In addition, lithium‐ions are transferred via the lithiated groups of N‐P‐LiPN, which significantly enhances the ionic conductivity of the Si anode. Hence, the Si@N‐P‐LiPN electrodes achieve the highest initial Coulombic efficiency of 93.18% and a stable cycling performance for 500 cycles at 0.2 C. Specially, Si@N‐P‐LiPN electrodes demonstrate an ultrahigh‐areal‐capacity of 49.59 mAh cm^?2. This work offers a new approach for inspiring the battery community to explore novel binders for next‐generation high‐energy‐density storage devices.     

A Li2S‐TiS2‐Electrolyte Composite for Stable Li2S‐Based Lithium–Sulfur Batteries

Li₂S is a fully lithiated sulfur‐based cathode with a high theoretical capacity of 1166 mAh g^?1 that can be coupled with lithium‐free anodes to develop high‐energy‐density lithium–sulfur batteries. Although various approaches have been pursued to obtain a high‐performance Li₂S cathode, there are still formidable challenges with it (e.g., low conductivity, high overpotential, and irreversible polysulfide diffusion) and associated fabrication processes (e.g., insufficient Li₂S, excess electrolyte, and low reversible capacity), which have prevented the realization of high electrochemical utilization and stability. Here, a new cathode design composed of a homogeneous Li₂S‐TiS₂‐electrolyte composite that is prepared by a simple two‐step dry/wet‐mixing process is demonstrated, allowing the liquid electrolyte to wet the powder mixture consisting of insulating Li₂S and conductive TiS₂. The close‐contact, three‐phase boundary of this system improves the Li₂S‐activation efficiency and provides fast redox‐reaction kinetics, enabling the Li₂S‐TiS₂‐electrolyte cathode to attain stable cyclability at C/7 to C/3 rates, superior long‐term cyclability over 500 cycles, and promising high‐rate performance up to 1C rate. More importantly, this improved performance results from a cell design attaining a high Li₂S loading of 6 mg cm^?2, a high Li₂S content of 75 wt%, and a low electrolyte/Li₂S ratio of 6.     

Polysulfide‐Shuttle Control in Lithium‐Sulfur Batteries with a Chemically/Electrochemically Compatible NaSICON‐Type Solid Electrolyte

A NaSICON‐type Li⁺‐ion conductive membrane with a formula of Li_{1+ x} Y _x Zr_{2? x} (PO₄)₃ (LYZP) (x = 0–0.15) has been explored as a solid‐electrolyte/separator to suppress polysulfide‐crossover in lithium‐sulfur (Li‐S) batteries. The LYZP membrane with a reasonable Li⁺‐ion conductivity shows both favorable chemical compatibility with the lithium polysulfide species and exhibits good electrochemical stability under the operating conditions of the Li‐S batteries. Through an integration of the LYZP solid electrolyte with the liquid electrolyte, the hybrid Li‐S batteries show greatly enhanced cyclability in contrast to the conventional Li‐S batteries with the porous polymer (e.g., Celgard) separator. At a rate of C/5, the hybrid Li ||LYZP|| Li₂S₆ batteries developed in this study (with a Li‐metal anode, a liquid/LYZP hybrid electrolyte, and a dissolved lithium polysulfide cathode) delivers an initial discharge capacity of ≈1000 mA h g^?1 (based on the active sulfur material) and retains ≈90% of the initial capacity after 150 cycles with a low capacity fade‐rate of <0.07% per cycle.     

Tethered Molecular Sorbents: Enabling Metal‐Sulfur Battery Cathodes

A rechargeable battery that uses sulfur at the cathode and a metal (e.g., Li, Na, Mg, or Al) at the anode provides perhaps the most promising path to a solid‐state, rechargeable electrochemical storage device capable of high charge storage capacity. It is understood that solubilization in the electrolyte and loss of sulfur in the form of long‐chain lithium polysulfides (Li₂S_x, 2 < x < 8) has hindered development of the most studied of these devices, the rechargeable Li‐S battery. Beginning with density‐functional calculations of the structure and interactions of a generic lithium polysulfide species with nitrile containing molecules, it is shown that it is possible to design nitrile‐rich molecular sorbents that anchor to other components in a sulfur cathode and which exert high‐enough binding affinity to Li₂S_x to limit its loss to the electrolyte. It is found that sorbents based on amines and imidazolium chloride present barriers to dissolution of long‐chain Li₂S_x and that introduction of as little as 2 wt% of these molecules to a physical sulfur‐carbon blend leads to Li‐S battery cathodes that exhibit stable long‐term cycling behaviors at high and low charge/discharge rates.     

Operando Quantification of (De)Lithiation Behavior of Silicon–Graphite Blended Electrodes for Lithium‐Ion Batteries

Due to the high lithium capacity of silicon, the composite (blended) electrodes containing silicon (Si) and graphite (Gr) particles are attractive alternatives to the all‐Gr electrodes used in conventional lithium‐ion batteries. In this Communication, the lithiation and delithiation in the Si and Gr particles in a 15 wt% Si composite electrode is quantified for each component using energy dispersive X‐ray diffraction. This quantification is important as the components cycle in different potential regimes, and interpretation of cycling behavior is complicated by the potential hysteresis displayed by Si. The lithiation begins with Li alloying with Si; lithiation of Gr occurs at later stages when the potential dips below 0.2 V (all potentials are given vs Li/Li⁺). In the 0.2–0.01 V range, the relative lithiation of Si and Gr is ≈58% and 42%, respectively. During delithiation, Li⁺ ion extraction occurs preferentially from Gr in the 0.01–0.23 V range and from Si in the 0.23–1.0 V range; that is, the delithiation current is carried sequentially, first by Gr and then by Si. These trends can be used for rational selection of electrochemical cycling windows that limits volumetric expansion in Si particles, thereby extending cell life.     

Atomic Structure of Li2MnO3 after Partial Delithiation and Re‐Lithiation

Li₂MnO₃ is the parent compound of the well‐studied Li‐rich Mn‐based cathode materials xLi₂MnO₃·(1‐x)LiMO₂ for high‐energy‐density Li‐ion batteries. Li₂MnO₃ has a very high theoretical capacity of 458 mA h g^?1 for extracting 2 Li. However, the delithiation and lithiation behaviors and the corresponding structure evolution mechanism in both Li₂MnO₃ and Li‐rich Mn‐based cathode materials are still not very clear. In this research, the atomic structures of Li₂MnO₃ before and after partial delithiation and re‐lithiation are observed with spherical aberration‐corrected scanning transmission electron microscopy (STEM). All atoms in Li₂MnO₃ can be visualized directly in annular bright‐field images. It is confirmed accordingly that the lithium can be extracted from the LiMn₂ planes and some manganese atoms can migrate into the Li layer after electrochemical delithiation. In addition, the manganese atoms can move reversibly in the (001) plane when ca. 18.6% lithium is extracted and 12.4% lithium is re‐inserted. LiMnO₂ domains are also observed in some areas in Li_1.63MnO₃ at the first cycle. As for the position and occupancy of oxygen, no significant difference is found between Li_1.63MnO₃ and Li₂MnO₃.     

Freestanding Flexible Li2S Paper Electrode with High Mass and Capacity Loading for High‐Energy Li–S Batteries

Lithium–sulfur (Li–S) batteries are a very appealing power source with extremely high energy density. But the use of a metallic‐Li anode causes serious safety hazards, such as short‐circuiting and explosion of the cells. Replacing a sulfur cathode with a fully‐lithiated lithium sulfide (Li₂S) to pair with metallic‐Li‐free high‐capacity anodes paves a feasible way to address this issue. However, the practical utility of Li₂S cathodes faces the challenges of poor conductivity, sluggish activation process, and high sensitivity to moisture and oxygen that make electrode production more difficult than dealing with sulfur cathodes. Here, an efficient but low‐cost strategy for easy production of freestanding flexible Li₂S‐based paper electrodes with very high mass and capacity loading in terms of in situ carbonthermal reduction of Li₂SO₄ by electrospinning carbon is reported. This chemistry enables high loading but strong affinity of ultrafine Li₂S nanoparticles in a freestanding conductive carbon‐nanofiber network, meanwhile greatly reducing the manufacturing complexity and cost of Li₂S cathodes. Benefiting from enhanced structural stability and reaction kinetics, the areal specific capacities of such cathodes can be significantly boosted with less sacrificing of high‐rate and cycling capability. This unique Li₂S‐cathode design can be directly applied for constructing metallic‐Li‐free or flexible Li–S batteries with high‐energy density.     

Enabling High‐Energy Solid‐State Batteries with Stable Anode Interphase by the Use of Columnar Silicon Anodes

All‐solid‐state batteries (ASSBs) with silicon anodes are promising candidates to overcome energy limitations of conventional lithium‐ion batteries. However, silicon undergoes severe volume changes during cycling leading to rapid degradation. In this study, a columnar silicon anode (col‐Si) fabricated by a scalable physical vapor deposition process (PVD) is integrated in all‐solid‐state batteries based on argyrodite‐type electrolyte (Li₆PS₅Cl, 3 mS cm^?1) and Ni‐rich layered oxide cathodes (LiNi_0.9Co_0.05Mn_0.05O₂, NCM) with a high specific capacity (210 mAh g^?1). The column structure exhibits a 1D breathing mechanism similar to lithium, which preserves the interface toward the electrolyte. Stable cycling is demonstrated for more than 100 cycles with a high coulombic efficiency (CE) of 99.7–99.9% in full cells with industrially relevant areal loadings of 3.5 mAh cm^?2, which is the highest value reported so far for ASSB full cells with silicon anodes. Impedance spectroscopy revealed that anode resistance is drastically reduced after first lithiation, which allows high charging currents of 0.9 mA cm^?2 at room temperature without the occurrence of dendrites and short circuits. Finally, in‐operando monitoring of pouch cells gave valuable insights into the breathing behavior of the solid‐state cell.     

A Lithium–Sulfur Cell Based on Reversible Lithium Deposition from a Li2S Cathode Host onto a Hostless‐Anode Substrate

The development of lithium–sulfur batteries necessitates a thorough understanding of the lithium‐deposition process. A novel full‐cell configuration comprising an Li₂S cathode and a bare copper foil on the anode side is presented here. The absence of excess lithium allows for the realization of a truly lithium‐limited Li–S battery, which operates by reversible plating and stripping of lithium on the hostless‐anode substrate (copper foil). Its performance is closely tied to the efficiency of lithium deposition, generating valuable insights on the role and dynamic behavior of lithium anode. The Li₂S full cell shows reasonable capacity retention with a Coulombic efficiency of 96% over 100 cycles, which is a tremendous improvement over that of a similar lithium‐plating‐based full cell with LiFePO₄ cathodes. The exceptional robustness of the Li₂S system is attributed to an intrinsic stabilization of the lithium‐deposition process, which is mediated by polysulfide intermediates that form protective Li₂S and Li₂S₂ regions on the deposited lithium. Combined with the large improvements in energy density and safety by the elimination of a metallic lithium anode, the stability and electrochemical performance of the lithium‐plating‐based Li₂S full cell establish it as an important trajectory for Li–S battery research, focusing on practical realization of reversible lithium anodes.     

Operando Lithium Dynamics in the Li‐Rich Layered Oxide Cathode Material via Neutron Diffraction

Neutron diffraction under operando battery cycling is used to study the lithium and oxygen dynamics of high Li‐rich Li(Li_x/3Ni_(3/8‐3x/8)Co_(1/4‐x/4)Mn_(3/8+7x/24)O₂ (x = 0.6, HLR) and low Li‐rich Li(Li_x/3Ni_(1/3‐x/3)Co_(1/3‐x/3)Mn_(1/3+x/3)O₂ (x = 0.24, LLR) compounds that exhibit different degrees of oxygen activation at high voltage. The measured lattice parameter changes and oxygen position show largely contrasting changes for the two cathodes where the LLR exhibits larger movement of oxygen and lattice contractions in comparison to the HLR that maintains relatively constant lattice parameters and oxygen position during the high voltage plateau until the end of charge. Density functional theory calculations show the presence of oxygen vacancy during the high voltage plateau; changes in the lattice parameters and oxygen position are consistent with experimental observations. Lithium migration kinetics for the Li‐rich material is observed under operando conditions for the first time to reveal the rate of lithium extraction from the lithium layer, and transition metal layer is related to the different charge and discharge characteristics. At the beginning of charging, the lithium extraction predominately occurs within the lithium layer. Once the high voltage plateau is reached, the lithium extraction from the lithium layer slows down and extraction from the transition metal layer evolves at a faster rate.     

Structural Changes in Li2MnO3 Cathode Material for Li‐Ion Batteries

Structural changes in Li₂MnO₃ cathode material for rechargeable Li‐ion batteries are investigated during the first and 33^rd cycles. It is found that both the participation of oxygen anions in redox processes and Li⁺‐H⁺ exchange play an important role in the electrochemistry of Li₂MnO₃. During activation, oxygen removal from the material along with Li gives rise to the formation of a layered MnO₂‐type structure, while the presence of protons in the interslab region, as a result of electrolyte oxidation and Li⁺‐H⁺ exchange, alters the stacking sequence of oxygen layers. Li re‐insertion by exchanging already present protons reverts the stacking sequence of oxygen layers. The re‐lithiated structure closely resembles the parent Li₂MnO₃, except that it contains less Li and O. Mn⁴⁺ ions remain electrochemically inactive at all times. Irreversible oxygen release occurs only during activation of the material in the first cycle. During subsequent cycles, electrochemical processes seem to involve unusual redox processes of oxygen anions of active material along with the repetitive, irreversible oxidation of electrolyte species. The deteriorating electrochemical performance of Li₂MnO₃ upon cycling is attributed to the structural degradation caused by repetitive shearing of oxygen layers.