Cationic Redox Reactions Research Articles

Mitigating Strain Accumulation in Li2RuO3 via Fluorine Doping.

Lithium ruthenium oxide (Li2RuO3) is an archetypal lithium rich cathode material (LRCM) with both cation and anion redox reactions (ARRs). Commonly, the instability of oxygen redox activities has been regarded as the root cause of its performance degradation in long-term operation. However, we find that not triggering ARRs does not improve and even worsens its cyclability due to the detrimental strain accumulation induced by Ru redox activities. To solve this problem, we demonstrate that F-doping in Li2RuO3 can alter its preferential orientation and buffer interlayer repulsion upon Ru redox, both of which can mitigate the strain accumulation along the c-axis and improve its structural stability. This work highlights the importance of optimizing cation redox reactions in LRCMs and provides a new perspective for their rational design.

Perspective on High-Stability Single-Crystal Li-Rich Cathode Materials for Li-Ion Batteries.

Benefiting from anionic and cationic redox reactions, Li-rich materials have been regarded as next-generation cathodes to overcome the bottleneck of energy density. However, they always suffer from cracking of polycrystalline (PC) secondary particles and lattice oxygen release, resulting in severe structural deterioration and capacity decay upon cycling. Single-crystal (SC) design has been proven as an effective strategy to relieve these issues in traditional Li-rich cathodes with PC morphology. Herein, we first reviewed the main synthesis routes of SC Li-rich materials including solid-state reaction, molten salt-assisted, and hydrothermal/solvothermal methods, in which the differences in grain morphology, electrochemical behaviors, and other properties induced by various routes were analyzed and discussed. Furthermore, the distinct characteristics were compared between SC and PC cathodes from the aspects of irreversible capacity, structural stability, capacity/voltage degradation, and gas release. Besides, recent advances in layered SC Li-rich oxide cathodes were summarized in detail, where the unique structural designs and modification strategies could greatly promote their structural/electrochemical stability. At last, challenges and perspectives for the emerging SC Li-rich cathodes were proposed, which provided an exceptional opportunity to achieve high-energy-density and high-stability Li-ion/metal batteries.

Improved Performance of High‐Entropy Disordered Rocksalt Oxyfluoride Cathode by Atomic Layer Deposition Coating for Li‐Ion Batteries

Lithium‐excess cation‐disordered rocksalt materials are a promising class of transition metal‐based cathodes that exhibit high specific capacity and energy density. The exceptional performance is achieved through participation of anionic redox in addition to cationic redox reactions in the electrochemistry. However, anionic redox reactions accompanied by oxygen evolution, accelerated electrolyte breakdown, and structural evolution lead to voltage hysteresis and low initial Coulombic efficiency. Herein, an Al2O3 layer with varying thickness has been coated onto a high‐entropy disordered rocksalt oxyfluoride cathode through atomic layer deposition to enhance battery performance. The results indicate that the utilization of a uniform Al2O3 coating improves the capacity retention and rate capability of the cathode, with the performance being strongly dependent on the layer thickness. Further investigation into cathode–electrolyte interfacial reactions reveals that the thin protecting Al2O3 coating can reduce the decomposition of electrolyte on the cathode surface but cannot prevent bulk phase degradation during prolonged cycling. These findings highlight the need for optimized coating design on the disordered rocksalt cathode to improve battery performance.

Investigation on the Origin of Sluggish Anionic Redox Kinetics in Cation-Disordered Cathode

Cation-disordered rock salt (DRX) cathodes exhibit high specific capacity due to the simultaneous use of anionic and cationic redox reactions. However, DRX systems face severe challenges that limit their practical applications; a most important challenge is their poor rate performance. In this work, the structure and morphology of Li1.17Ti0.58Ni0.25O2 (LTNO) were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), etc. In combination with various electrochemical characterizations, we found that the sluggish kinetics of anionic redox within LTNO can be the key reason for the inferior rate performance. By sample relaxation at moderate temperature and X-ray absorption near edge structure (XANES), the ligand-to-metal charge transfer process is verified to occur between O and Ni and exhibits a prolonged characteristic time of 113.8 min. This time-consuming charge transfer process is verified to be the very fundamental origin of the slow kinetics of oxygen oxidation and reduction. This claim is further supported by the galvanostatic intermittent titration technique (GITT) at different temperatures. These findings provide essential guidance for understanding and further optimizing cathodes with anion redox reactions not only in the context of DRX cathodes but also conventional Li-rich cathodes.

Engineering of surface oxygen vacancies in Co-free concentration-gradient Li-rich cathodes for high-capacity batteries

Li-rich layered oxides (LLOs) are the most promising high-capacity materials in the Li-ion batteries owing to their cumulative oxygen anionic and cationic redox reactions. However, irreversible oxygen evolution and transition-metal migration aggravate structural rearrangement and capacity fading. Although Co-containing LLO possesses practical capacity and stability for commercial purposes, it suffers from scarcity, toxicity, and high cost of cobalt. To ameliorate these bottlenecks, we improved the reversibility of anionic and cationic redox in Co-free concentration-gradient LLO by integrating oxygen vacancies and high Ni/Mn ratio on LLO's surface. We found that surface oxygen vacancies suppress oxygen release from the surface, reduce the interfacial resistance that arises from electrolyte decomposition, and increase the ionic diffusion; thereby, enhancing the cathode's capacity. Concentration-gradient LLO cathode with an appropriate Mn/Ni ratio improved cation migration's structural stability and reversibility in the layered and spinel-layered Li-rich materials. As a result, the charge transfer and interfacial resistance decreased during the gradual de-lithiation and Ni redox reaction. The Co-free LLO with surface Mn/Ni∼1.5 delivered a reversible capacity of 250 mAh/g, with 99% capacity retention after 85 cycles at 0.1 C. This work provided a practical approach for resolving the capacity decay of the Co-free LLOs by engineering the cathode/electrolyte interface and structure.

Investigating Mixed Cationic and Anionic Redox Chemistry in Chalcogen Based Cathodes for Li-Ion Batteries

Current state-of-the-art Li-ion batteries are reaching their theoretical limit with respect to the capacity, a property largely limited by cathode materials that have so far relied solely on cationic-redox of transition-metal ions (e.g., M3+/4+ in LiMO2 where M is Co, Ni, and Mn) for driving the electrochemical reactions. Recently, the introduction of new anion-redox cathode materials can lead to a doubling of capacity by accommodating multielectron redox chemistries that have gained research interest. (1) However, current anion-redox cathode materials based on Li-rich layered oxides (represented by the formula Li1+xM1-xO2 where M is Co, Ni, and Mn) suffer from voltage fade, large hysteresis, and sluggish kinetics, which originate mysteriously from the anionic redox activity of oxygen ligand itself. (2) It is widely accepted that the covalency between transition metal – oxygen ligand in traditional cathode materials needs to be altered to take advantage of anion redox chemistry. Here, we present an alternative approach of incorporating improved metal – ligand covalency by less electronegative chalcogen sulfur ligands in the cathode structural framework where the metal d-band penetration into ligand p-band thereby utilizing mixed anionic and cationic redox chemistry. (3) Through this design strategy, we investigated anion redox activity in layered cathode material based on Li2SnS3, and their lithiation/delithiation properties were evaluated through in-depth electrochemical analysis. Further, the charge contributors during electrochemical reactions were identified by spectroscopy analysis, and morphological evolution due to mixed anionic and cationic redox reactions were evaluated using high-resolution transmission electron microscopy(HR-TEM) and high annular dark field-scanning transmission electron microscopy(HAADF) investigations.The results reveal the multi redox induced structural modifications and its surface amorphization with nanopore formation during cycling. Findings from this research will inspire Ni and Co free chalcogen cathode design and various functional materials in the pursuit of next generation cathode materials.References J. R. Croy, M. Balasubramanian, K. G. Gallagher, A. K. Burrell, Review of the US Department of Energy’s “Deep Dive” effort to understand voltage fade in Li-and Mn-rich cathodes. Accounts of chemical research 48, 2813-2821 (2015). G. Assat, J. M. Tarascon, Fundamental understanding and practical challenges of anionic redox activity in Li-ion batteries. Nature Energy 3, 373-386 (2018). S. Nagarajan, S. Hwang, M. Balasubramanian, N. K. Thangavel, L. M. R. Arava, Mixed Cationic and Anionic Redox in Ni and Co Free Chalcogen-Based Cathode Chemistry for Li-Ion Batteries. Journal of the American Chemical Society 143, 15732-15744 (2021).

Interfacial Stabilization of Li2O-Based Cathodes by Malonic-Acid-Functionalized Fullerenes as a Superoxo-Radical Scavenger for Suppressing Parasitic Reactions.

The utilization of an anionic redox reaction as an innovative strategy for overcoming the limitations of cathode capacity in lithium-ion batteries has recently been the focus of intensive research. Li2O-based materials using the anionic (oxygen) redox reaction have the potential to deliver a much higher capacity than commercial cathodes using cationic redox reactions based on transition-metal ions. However, parasitic reactions attributed to the superoxo species (such as LiO2), derived from the Li2O active material of the cathode, deteriorate the stability of the interface between the cathode and electrolyte, which has limited the commercialization of Li2O-based cathodes. To address this issue, malonic-acid-functionalized fullerenes (MC60) were applied in the electrolyte as an additive for scavenging the superoxo radicals (O21- in LiO2) that trigger parasitic reactions. MC60 can efficiently capture superoxo radicals using the π-conjugated surface and the malonate functionality on the surface. As a result, MC60 considerably enhanced the available capacity and cycling performance of the Li2O-based cathodes, decreased the interfacial layer formed on the cathode surface, and hindered the generation of byproducts, such as Li2CO3, CO2, and C-F3, derived from parasitic reactions. In addition, the loss of Li2O from the cathode surface during cycling was also suppressed, validating the ability of MC60 to capture superoxo radicals. This result confirms that the introduction of MC60 can effectively alleviate the parasitic reactions at the cathode/electrolyte interface and improve the electrochemical performance of Li2O-based cathodes by scavenging the superoxo species.

Anionic Redox Chemistry for Sodium-Ion Batteries: Mechanisms, Advances, and Challenges

The increasing reliance on energy demands has called for continual improvement of sodium-ion batteries (SIBs) due to the abundant Na resources and low cost. Na-based layered transition metal oxides (TMOs) are promising cathode materials due to their unique structural characteristics that provide two-dimensional (2D) ion diffusion channels and maintain structural integrity during the extraction and insertion of Na-ions. However, the energy density of conventional TMO cathodes is mainly limited by cationic redox reactions. Activating anionic redox (O2–/On–) for additional capacity in TMO cathodes is promising to improve the energy density of SIBs, though the chemistry of anionic redox reaction (ARR) is still unclear. This overview focuses on the underlying science, development, and latest advances of ARR in SIBs. The challenges and possible approaches are discussed in light of ARR reversibility and voltage hysteresis. This review will provide insights on improving the energy density of advanced TMOs cathodes with ARR activity.

Enabling Anionic Redox Stability of P2-Na5/6 Li1/4 Mn3/4 O2 by Mg Substitution.

Oxygen-based anionic redox reactions have recently emerged as a lever to increase the capacity of Mn-rich layered oxide cathodes in addition to the charge compensation based on cationic redox reactions for sodium-ion batteries. Unfortunately, the irreversibility of anionic redox often aggravates irreversible structure change and poor cycling performance. Here, a stable anionic redox is achieved through substituting Na ions by Mg ions in P2-type Na0.83 Li0.25 Mn0.75 O2 . Density functional theory (DFT) calculations reveal that Mg substitution effectively decreases the oxygen chemical potential, causing an improvement in lattice oxygen stability. Moreover, at a highly desodiated state, Mg ions that remain in the lattice and interact with O 2p orbitals can decrease the undercoordinated oxygen and the nonbonded, electron-deficient O 2p states, facilitating the reversibility of oxygen redox. When cycled in the voltage range of 2.6-4.5V where only anionic redox occurs for charge compensation, Na0.773 Mg0.03 Li0.25 Mn0.75 O2 presents a much better reversibility, giving a 4 times better cycle stability than that of Na0.83 Li0.25 Mn0.75 O2 . Experimentally, Na0.773 Mg0.03 Li0.25 Mn0.75 O2 exhibits a ≈1.1% volume expansion during sodium insertion/extraction, suggestive of a "zero-strain" cathode. Overall, the work opens a new avenue for enhancing anionic reversibility of oxygen-related Mn-rich cathodes.

Magnetic Compton Scattering Study of Li-Rich Battery Materials

The redox process in a lithium-ion battery occurs when a conduction electron from the lithium anode is transferred to the redox orbital of the cathode. Understanding the nature of orbitals involved in anionic as well as cationic redox reactions is important for improving the capacity and energy density of Li-ion batteries. In this connection, we have obtained magnetic Compton profiles (MCPs) from the Li-rich cation-disordered rock-salt compound LixTi0.4Mn0.4O2 (LTMO). The MCPs, which involved the scattering of circularly polarized hard X-rays, are given by the momentum density of all the unpaired spins in the material. The net magnetic moment in the ground state can be extracted from the area under the MCP, along with a SQUID measurement. Our analysis gives insight into the role of Mn 3d magnetic electrons and O 2p holes in the magnetic redox properties of LTMO.

Mixing properties of Al2O3(0001)-supported M 2O3 and MM′O3 monolayers (M, M′ = Ti, V, Cr, Fe)

Considering the importance of sub-monolayer transition metal oxides supported on another oxide in many industrial processes, with the help of a DFT + U approach, we provide information on the structural and electronic properties of pure M 2O3 and mixed MM′O3 oxide monolayers (M, M′ = Ti, V, Cr, Fe) supported on an α-Al2O3(0001) support. With their structure in the prolongation of the alumina corundum lattice, the monolayers have non-equivalent surface and interface cations, which leads to two different cation configurations in the mixed oxides. In all cases, the interfacial charge transfer is weak, but strong cation–cation electron redistributions may take place as in TiVO3, TiFeO3, VFeO3, and TiCrO3 in which actual redox processes lead to cation oxidation states different from the expected +3 value. We show that the tendency to mixing relies on the interplay between two very different driving forces. Cation–cation redox reactions, in most cases, strongly stabilise mixed configurations, but preference for a given cation position in the monolayer, because of surface energy reasons, may strengthen, weaken or even block the mixing tendency. By comparison with results obtained in bulk ilmenite, in free-standing monolayers and in MLs deposited on transition metal substrates, we evidence the flexibility of their electronic structure as a function of size, dimensionality and nature of support, as a lever to tune their properties for specific applications.

Electrochemically constructing V-doped BiFeO3 nanoflake network anodes for flexible asymmetric micro-supercapacitors

Bismuth ferrite (BiFeO3) with high specific capacity and wide voltage window, fundamentally stores charge through the reversible redox reactions of cations, but usually suffers from poor rate capability and bad cycling stability, due to its densely-packed crystal structure and multi-electron redox reaction kinetics. We present a novel route to regulate nanoflake network architectures and oxygen vacancy defects of BiFeO3 through V doping and electrochemical induction without annealing. After consecutive charge/discharge process of BiFe0.95V0.05O3 fabricated by electrochemical deposition, the cycled BiFe0.95V0.05O3 (c-BiFe0.95V0.05O3) retains better structural stability and more oxygen vacancies than those of the annealed BiFe0.95V0.05O3, revealing the outstanding superiority of electrochemical induction. The c-BiFe0.95V0.05O3 electrode provides high rate capability and Li+ diffusion coefficient, mainly attributed to its nanoflake network architecture and abundant oxygen vacancies. The first-principle calculation demonstrates V doping and oxygen vacancies can enhance built-in electric field and construct fast ion transport channels for boosting rate capability. Based on the c-BiFe0.95V0.05O3 anode and the PPyHG (polypyrrole hydrogel) cathode, flexible asymmetric micro-supercapacitors can deliver an extremely wide voltage window of 2.3 V and a high areal energy density of 7.33 µWh cm−2 at 63.7 µW cm−2, reflecting its huge potential for flexible energy storage micro-devices.

Phosphorus-doped lithium- and manganese-rich layered oxide cathode material for fast charging lithium-ion batteries

Owing to their high theoretical specific capacity and low cost, lithium- and manganese-rich layered oxide (LMR) cathode materials are receiving increasing attention for application in lithium-ion batteries. However, poor lithium ion and electron transport kinetics plus side effects of anion and cation redox reactions hamper power performance and stability of the LMRs. In this study, LMR Li1.2Mn0.6Ni0.2O2 was modified by phosphorus (P)-doping to increase Li+ conductivity in the bulk material. This was achieved by increasing the interlayer spacing of the lithium layer, electron transport and structural stability, resulting in improvement of the rate and safety performance. P5+ doping increased the distance between the (003) crystal planes from ~0.474 nm to 0.488 nm and enhanced the structural stability by forming strong covalent bonds with oxygen atoms, resulting in an improved rate performance (capacity retention from 38% to 50% at 0.05 C to 5 C) and thermal stability (50% heat release compared with pristine material). First-principles calculations showed the P-doping makes the transfer of excited electrons from the valence band to conduction band easier and P can form a strong covalent bond helping to stabilize material structure. Furthermore, the solid-state electrolyte modified P5+ doped LMR showed an improved cycle performance for up to 200 cycles with capacity retention of 90.5% and enhanced initial coulombic efficiency from 68.5% (pristine) or 81.7% (P-doped LMR) to 88.7%.

Dual-Site Doping Strategy for Enhancing the Structural Stability of Lithium-Rich Layered Oxides.

Lithium-rich layered oxide (LLO) cathode materials are considered to be one of the most promising next-generation candidates of cathode materials for lithium-ion batteries due to their high specific capacity. However, some inherent defects of LLOs hinder their practical application due to the oxygen loss and structure collapse resulting from intrinsic anion and cation redox reactions, such as poor cycle stability, sluggish Li+ kinetics, and voltage decay. Herein, we put forward a facile synergistic strategy to respond to these shortcomings of LLOs via dual-site doping with cerium (Ce) and boron (B) ions. The doped Ce ions occupy the octahedral sites, which not only enlarge the cell volume but also stabilize the layered framework and introduce abundant oxygen vacancies for LLOs, while B ions occupy the tetrahedral sites in the lattice, which block the migration path of transition metal (TM) ions and reduce the oxygen loss using the strong B-O bond. Based on this dual-site doping effect, after 100 cycles at 1 C, the dual-site doped materials exhibit excellent structural stability with a capacity retention of 91.15% (vs 75.12%) and also greatly suppress the voltage decay in LLOs with a voltage retention of 93.60% (vs 87.83%).

Recent progress in the design of anionic redox in layered oxide electrodes: A mini review

Layered cathode oxides have been attractive for next-generation high-energy-density rechargeable batteries, only that they are approaching the bottleneck of limited specific capacities based on cation redox reactions. Recently, the utilization of anion redox reaction to participate in charge compensation is an important strategy to increase the upper limit of energy density, but it faces issues such as voltage hysteresis and structure decay. In this review, we discuss the anion redox chemistry and the problems faced by such materials. Subsequently, we reviewed the recent research progress from perspectives of transition metal layer design and stacking fault design, hoping to provide a guide for the design of layered oxide cathodes.

Elucidating the Redox Behavior in Different P-type Layered Oxides for Sodium-Ion Batteries.

Sodium layered transition-metal oxides have attracted great attention for advanced Na-ion batteries (NIBs) because of their rich structural diversity and superior specific capacity provided by not only cation redox reactions but also possible oxygen-related anionic redox reactions. However, they usually undergo severe electrochemical performance fading, especially the voltage retention during the cationic and anionic redox processes. Herein, we design and synthesize a couple of novel sodium lithium magnesium aluminum manganese oxides (Na0.75Li0.2Mg0.05Al0.05Mn0.7O2) with the same Na+ coordination environment but different oxide layer stacking sequences, namely, P2-NLMAMO and P3-NLMAMO. We systematically investigate and compare the voltage decay phenomenon and the cationic/anionic redox processes under different electrochemical cycling windows combined with ex situ hard and soft X-ray absorption spectroscopy techniques. The results clearly indicate that the P2-NLMAMO electrode with a lower extent of Mn redox is prone to deliver a superior capacity retention and rate performance, more importantly, a higher average voltage in contrast to the P3-type counterpart. In addition, negligible change is detected for the average discharge voltage upon extended cycling when increasing the discharge cutoff voltage to 2.5 V for both P2-NLMAMO and P3-NLMAMO. This unique feature work provides an effective strategy for developing high-capacity P-type layered cathodes based on both cationic and anionic redox chemistry under controlled crystal structure arrangement, which could lead to a deeper understanding of the correlation between crystal structure and electrochemical performance for NIBs.

Achieving high structure and voltage stability in cobalt-free Li-rich layered oxide cathodes via selective dual-cation doping

Lithium-rich layered oxides (LLOs) are regarded as one of the most promising cathode materials for next generation Li-ion batteries (LIBs) due to their high energy density. However, the associated oxygen release and structure collapse resulting from the intrinsic anion and cation redox reactions lead to performance degradation, particularly the characteristic voltage fading which has prohibited the commercialization of LLOs for more than a decade. Herein, we have developed a dual-doping technique to overcome the longstanding structure and voltage instabilities of Co-free Li1.2Mn0.533Ni0.267O2, through the concurrent introduction of neodymium (Nd) and aluminum (Al) ions. Selective atomic substitution of Ni/Mn with Nd/Al ions and the preconstructed heteroepitaxial interface significantly enhance the voltage and capacity retention by regulating Ni ion activity and suppressing the phase transformation and Mn dissolution, thereby improving rate performance through tuning the electronic structure and promoting Li+ migration. The dual-doped material exhibits a superior cycling stability, with over 90% voltage retention and 82% capacity retention after 200 cycles, and excellent rate performance (150 mAh g−1 at 10 C).

Tuning anionic/cationic redox chemistry in a P2-type Na0.67Mn0.5Fe0.5O2 cathode material via a synergic strategy

The anionic redox chemistry (O2−→O−) in P2-type sodium-ion battery cathodes has attracted much attention. However, determining how to tune the anionic redox reaction is still a major challenge. Herein, we tune the activity and reversibility of both the anionic and cationic redox reactions of Na0.67Mn0.5Fe0.5O2 though an integrated strategy that combines the advantages of Li2SiO3 coating, Li doping and Si doping, and the initial capacity, rate performance and cycling stability are significantly improved. The in-depth modulation mechanism is revealed by means of neutron diffraction, X-ray absorption spectroscopy, in situ X-ray diffraction, electron paramagnetic resonance spectroscopy, first-principles calculations and so on. The Li2SiO3 coating alleviates the side reactions and enhances the cycling stability. Si4+ doping lowers the Na+ diffusion barrier due to the expanded interlayer spacing. Additionally, Si4+ doping improves the structural stability, oxygen redox activity and reversibility. Li+ doping in Na sites further increases the structure stability. The electron density maps confirm the greater activity of Na and O in the modified sample. Nuclear density maps and bond-valence energy landscapes identify the Na+ migration pathway from Nae site to Naf site (the positions of the Na ions in the crystal structure). The proposed insights into the modulation mechanism of the anionic and cationic redox chemistry are also instructive for designing other oxide-based cathode materials.

Reversible Anionic Redox Activities in Conventional LiNi1/3 Co1/3 Mn1/3 O2 Cathodes.

Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium-excessive layered-oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in LiNi1/3 Co1/3 Mn1/3 O2 . The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high-capacity lithium-ion batteries.

Reversible Anionic Redox Activities in Conventional LiNi1/3Co1/3Mn1/3O2 Cathodes

AbstractRedox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium‐excessive layered‐oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in LiNi1/3Co1/3Mn1/3O2. The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high‐capacity lithium‐ion batteries.