Probing the Self‐Boosting Catalysis of LiCoO2 in Li–O2 Battery with Multiple In Situ/Operando Techniques

Designing high‐activity catalysts and revealing the in‐depth structure–property relationship is particularly important for Li–O₂ batteries. Herein, the self‐boosting catalysis of LiCoO₂ as an electrocatalyst for Li–O₂ batteries and the investigation of its self‐adjustment mechanism using in situ X‐ray absorption spectroscopy and other operando characterization techniques is reported. The intercalation/extraction of Li⁺ in LiCoO₂ not only induces the change in Co valence and modulates the electronic/crystal structure but also tunes the surface disorder degree, lattice strain, and local symmetry, which all affect the catalysis activity. In a discharge, highly ordered LiCoO₂ acts as a catalyst to boost oxygen reduction reaction. During charging, the initial extraction of Li⁺ from LiCoO₂ induces Li/oxygen vacancy and Co⁴⁺, which deforms CoO₆ octahedron as well as lowers the symmetry, and accordingly promotes oxygen evolution reaction. This article offers insights into tuning the activity of catalysts for Li–O₂ batteries with the intercalation/extraction of alkali metal ions in traditional cathodes.     

Tuning Anionic Redox Activity and Reversibility for a High‐Capacity Li‐Rich Mn‐Based Oxide Cathode via an Integrated Strategy

When fabricating Li‐rich layered oxide cathode materials, anionic redox chemistry plays a critical role in achieving a large specific capacity. Unfortunately, the release of lattice oxygen at the surface impedes the reversibility of the anionic redox reaction, which induces a large irreversible capacity loss, inferior thermal stability, and voltage decay. Therefore, methods for improving the anionic redox constitute a major challenge for the application of high‐energy‐density Li‐rich Mn‐based cathode materials. Herein, to enhance the oxygen redox activity and reversibility in Co‐free Li‐rich Mn‐based Li_1.2Mn_0.6Ni_0.2O₂ cathode materials by using an integrated strategy of Li₂SnO₃ coating‐induced Sn doping and spinel phase formation during synchronous lithiation is proposed. As an Li⁺ conductor, a Li₂SnO₃ nanocoating layer protects the lattice oxygen from exposure at the surface, thereby avoiding irreversible oxidation. The synergy of the formed spinel phase and Sn dopant not only improves the anionic redox activity, reversibility, and Li⁺ migration rate but also decreases Li/Ni mixing. The 1% Li₂SnO₃‐coated Li_1.2Mn_0.6Ni_0.2O₂ delivers a capacity of more than 300 mAh g^?1 with 92% Coulombic efficiency. Moreover, improved thermal stability and voltage retention are also observed. This synergic strategy may provide insights for understanding and designing new high‐performance materials with enhanced reversible anionic redox and stabilized surface lattice oxygen.     

Faster Activation and Slower Capacity/Voltage Fading: A Bifunctional Urea Treatment on Lithium‐Rich Cathode Materials

Li‐rich layered oxides are promising cathode materials for next‐generation Li‐ion batteries because of their extraordinary specific capacity. However, the activation process of the key active component Li₂MnO₃ in Li‐rich materials is kinetically slow, and the complex phase transformation with electrode/electrolyte side reactions causes fast capacity/voltage fading. Herein, a simple thermal treatment strategy is reported to simultaneously tackle these challenges. The introduction of a urea thermal treatment on Li‐rich material Li_1.87Mn_0.94Ni_0.19O₃ leads to oxygen deficiencies and partially reduced Mn ions on the oxide surface for activating the Li‐rich phase. In situ synchrotron study confirms that the urea‐treated cathode shows much faster Li extraction from both Li and transition metal layers with less oxygen evolution upon charging than that of untreated counterparts. Moreover, the decomposition products of urea during thermal treatment subsequently deposit on the surface of cathode material, leading to a unique passivation layer against side reactions between electrode and electrolyte. Soft X‐ray absorption spectroscopy reveals the structural evolution mechanism with a significantly suppressed dissolution of Mn species over cycling measurement. The urea‐treated Li_1.87Mn_0.94Ni_0.19O₃ shows accelerated activation kinetics to reach high capacity of 270 mA h g^–1 and demonstrates excellent capacity retention of 98.49% over 300 cycles with slower voltage decay.     

Nanoflake Arrays of Lithiophilic Metal Oxides for the Ultra‐Stable Anodes of Lithium‐Metal Batteries

A molten lithium infusion strategy has been proposed to prepare stable Li‐metal anodes to overcome the serious issues associated with dendrite formation and infinite volume change during cycling of lithium‐metal batteries. Stable host materials with superior wettability of molten Li are the prerequisite. Here, it is demonstrated that a series of strong oxidizing metal oxides, including MnO₂, Co₃O₄, and SnO₂, show superior lithiophilicity due to their high chemical reactivity with Li. Composite lithium‐metal anodes fabricated via melt infusion of lithium into graphene foams decorated by these metal oxide nanoflake arrays successfully control the formation and growth of Li dendrites and alleviate volume change during cycling. A resulting Li‐Mn/graphene composite anode demonstrates a super‐long and stable lifetime for repeated Li plating/stripping of 800 cycles at 1 mA cm^?2 without voltage fluctuation, which is eight times longer than the normal lifespan of a bare Li foil under the same conditions. Furthermore, excellent rate capability and cyclability are realized in full‐cell batteries with Li‐Mn/graphene composite anodes and LiCoO₂ cathodes. These results show a major advancement in developing a stable Li anode for lithium‐metal batteries.     

Iron Fluoride–Carbon Nanocomposite Nanofibers as Free‐Standing Cathodes for High‐Energy Lithium Batteries

The development of low‐cost, high‐energy cathodes from nontoxic, broadly available resources is a big challenge for the next‐generation rechargeable lithium or lithium‐ion batteries. As a promising alternative to traditional intercalation‐type chemistries, conversion‐type metal fluorides offer much higher theoretical capacity and energy density than conventional cathodes. Unfortunately, these still suffer from irreversible structural degradation and rapid capacity fading upon cycling. To address these challenges, here a versatile and effective strategy is harnessed for the development of metal fluoride–carbon (C) nanocomposite nanofibers as flexible, free‐standing cathodes. By taking iron trifluoride (FeF₃) as a successful example, assembled FeF₃–C/Li cells with a high reversible FeF₃ capacity of 550 mAh g^?1 at 100 mA g^?1 (three times that of traditional cathodes, such as lithium cobalt oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese oxide) and excellent stability (400+ cycles with little‐to‐no degradation) are demonstrated. The promising characteristics can be attributed to the nanoconfinement of FeF₃ nanoparticles, which minimizes the segregation of Fe and LiF upon cycling, the robustness of the electrically conductive C network and the prevention of undesirable reactions between the active material and the liquid electrolyte using the composite design and electrolyte selection.     

A Molecular‐Cage Strategy Enabling Efficient Chemisorption–Electrocatalytic Interface in Nanostructured Li2S Cathode for Li Metal‐Free Rechargeable Cells with High Energy

Using high‐capacity and metallic Li‐free lithium sulfide (Li₂S) cathodes offers an alternative solution to address serious safety risks and performance decay caused by uncontrolled dendrite hazards of Li metal anodes in next‐generation Li metal batteries. Practical applications of such a cathode, however, still suffer from low redox activity, unaffordable cost, and poor processability of infusible and moisture‐sensitive Li₂S. Herein, these difficulties are addressed by developing a molecular cage–engaged strategy that enables low‐cost production and interfacial engineering of Li₂S cathodes for rechargeable Li₂S//Si cells. An efficient chemisorption–electrocatalytic interface is built in extremely nanostructured Li₂S cathodes by harnessing the confinement/separation effect of metal–organic molecular cages on ionic clusters of air‐stable, soluble, and low‐cost Li salt and their chemical transformation. It effectively boosts the redox activity toward Li₂S activation/dissociation and polysulfide chemisorption–conversion in Li‐S batteries, leading to low activation voltage barrier, stable cycle life of 1000 cycles, ultrafast current rate up to 8 C, and high areal capacities of Li₂S cathodes with high mass loading. Encouragingly, this highly active Li₂S cathode can be applied for constructing truly workable Li₂S//Si cells with a high specific energy of 673 Wh kg^?1 and stable performance for 200 cycles at high rates against hollow nanostructured Si anode.     

Oxygen Vacancies and Ordering of d‐levels Control Voltage Suppression in Oxide Cathodes: the Case of Spinel LiNi0.5Mn1.5O4‐δ

This study presents a microscopic model for the correlation between the concentration of oxygen vacancies and voltage suppression in high voltage spinel cathodes for Li‐ion batteries. Using first principles simulations, it is shown that neutral oxygen vacancies in LiNi_0.5Mn_1.5O_4‐δ promote substitutional Ni/Mn disorder and the formation of Ni‐rich and Ni‐poor regions. The former trap oxygen vacancies, while the latter trap electrons associated with these vacancies. This leads to the creation of deep and shallow Mn³⁺ states and affects the stability of the lattice Li ions. Together, these two factors result in a characteristic profile of the voltage dependence on Li content. This insight provides guidance for mitigating the voltage suppression in LiNi_0.5Mn_1.5O₄ and other cathodes.     

Interface and Surface Cation Stoichiometry Modified by Oxygen Vacancies in Epitaxial Manganite Films

Perovskite manganites are viewed as one of the key building blocks of oxide spintronics devices due to their attractive physical properties. However, cation off‐stoichiometry at epitaxial interfaces between manganites and other materials can lead to interfacial dead layers, severely reducing the device performance. Here, transmission electron microscopy and synchrotron‐based spectroscopy are used to demonstrate that oxygen vacancies during growth serve as a critical factor for modifying the cation stoichiometry in pulsed laser deposited La_0.8Sr_0.2MnO₃ films. Near the film/substrate (SrTiO₃) interface, A‐site cations (La/Sr) are in excess when oxygen vacancies are induced during film growth, partially substituting Mn. Simultaneously, Sr cations migrate towards the film surface and form a SrO rock‐salt monolayer. Consequentially, a gradient of the Mn nominal valence is observed along the film growth direction, leading to anomalous magnetic properties. The results narrow the selection range of useful oxygen pressures during deposition and demonstrate that accurate cation stoichiometry can only be achieved after oxygen vacancies are eliminated during growth. This finding suggests that the oxygen pressure serves as a tuning parameter for the interfacial dead layers and, hence, for control over device properties.     

A Moisture‐ and Oxygen‐Impermeable Separator for Aprotic Li‐O2 Batteries

Despite the unparalleled theoretical gravimetric energy, Li‐O₂ batteries are still under a research stage because of their insufficient cycle lives. While the reversibility in air‐cathodes has been lately improved significantly by the deepened understanding on the electrode–electrolyte reaction and the integration of diverse catalysts, the stability of the Li metal interface has received relatively much less attention. The destabilization of the Li metal interface by crossover of water and oxygen from the air‐cathode side can indeed cause as fatal degradation for the cycle life as the irreversibility of the air‐cathodes. Here, it is reported that cheap poreless polyurethane separator can effectively suppress this crossover while allowing Li ions to diffuse through selectively. The polyurethane separator also protects Li metal anodes from redox mediators used for enhancing the reversibility of the air‐cathode reaction. Based on the Li metal protection, a persistent capacity of 600 mAh g^?1 is preserved for more than 200 cycles. The current approach can be readily applicable to many other rechargeable batteries that suffer from similar interfacial degradation by side products from the other electrode.     

Quantum‐Chemical Studies on the Geometric and Electronic Structures of Bertholloide Cobalt Oxynitrides

We report electronic structure calculations using density‐functional theory (local density approximation (LDA) and generalized gradient approximation (GGA); plane waves and muffin‐tin orbitals; pseudopotentials and all‐electron approaches) on non‐stoichiometric CoN_xO_1–x oxynitride phases. The preference of the experimentally suggested zinc‐blende structure type over the rock‐salt type is confirmed and explained, on the basis of COHP (crystal orbital Hamilton population) chemical bonding analyses, by reduced Co–Co antibonding interactions in the ZnS structural alternative. A pressure‐induced phase transition into the NaCl type, however, is predicted at approximately 30 GPa. Supercell calculations touching upon the exact composition and local structure of CoN_xO_1–x provide evidence for a broad range of energetically metastable compositions with respect to the zinc‐blende‐type boundary phases CoN and CoO, especially for the more oxygen‐rich phases. All non‐stoichiometric compounds are predicted to be metallic materials which do not exhibit significant magnetic moments. Likewise, there is no indication for anionic ordering such that random anion arrangements are preferred.     

Anti‐Oxygen Leaking LiCoO2

LiCoO₂ is a prime example of widely used cathodes that suffer from the structural/thermal instability issues that lead to the release of their lattice oxygen under nonequilibrium conditions and safety concerns in Li‐ion batteries. Here, it is shown that an atomically thin layer of reduced graphene oxide can suppress oxygen release from Li_xCoO₂ particles and improve their structural stability. Electrochemical cycling, differential electrochemical mass spectroscopy, differential scanning calorimetry, and in situ heating transmission electron microscopy are performed to characterize the effectiveness of the graphene‐coating on the abusive tolerance of Li_xCoO₂. Electrochemical cycling mass spectroscopy results suggest that oxygen release is hindered at high cutoff voltage cycling when the cathode is coated with reduced graphene oxide. Thermal analysis, in situ heating transmission electron microscopy, and electron energy loss spectroscopy results show that the reduction of Co species from the graphene‐coated samples is delayed when compared with bare cathodes. Finally, density functional theory and ab initio molecular dynamics calculations show that the rGO layers could suppress O₂ formation more effectively due to the strong C? O_cathode bond formation at the interface of rGO/LCO where low coordination oxygens exist. This investigation uncovers a reliable approach for hindering the oxygen release reaction and improving the thermal stability of battery cathodes.     

Synchronous Tailoring Surface Structure and Chemical Composition of Li‐Rich–Layered Oxide for High‐Energy Lithium‐Ion Batteries

Li‐rich–layered oxide is considered to be one of the most promising cathode materials for high‐energy lithium ion batteries. However, it suffers from poor rate capability, capacity loss, and voltage decay upon cycling that limits its utilization in practical applications. Surface properties of Li‐rich–layered oxide play a critical role in the function of batteries. Herein, a novel and successful strategy for synchronous tailoring surface structure and chemical composition of Li‐rich–layered oxide is proposed. Poor nickel content on the surface of carbonate precursor is initially prepared by a facile treatment of NH₃·H₂O, which can retain at a certain low amount on the surface in the final lithiated Li‐rich–layered oxide after a solid‐phase reaction process. Moreover, a phase‐gradient outer layer with “layered‐coexisting phase‐spinel” structure toward to the outside surface is self‐induced and formed synchronously based on poor nickel surface of the precursor. Electrochemical tests reveal this unique surface enables excellent cycling stability, improved rate capability, and slight voltage decay of cathodes. The finding here sheds light on a universal principle both for masterly tailoring surface structure and chemical composition at the same time for improving electrochemical performance of electrode materials.     

Enhanced Cycling Stability of Rechargeable Li–O2 Batteries Using High‐Concentration Electrolytes

The stability of electrolytes against highly reactive, reduced oxygen species is crucial for the development of rechargeable Li–O₂ batteries. In this work, the effect of lithium salt concentration in 1,2‐dimethoxyethane (DME)‐based electrolytes on the cycling stability of Li–O₂ batteries is investigated systematically. Cells with highly concentrated electrolyte demonstrate greatly enhanced cycling stability under both full discharge/charge (2.0–4.5 V vs Li/Li⁺) and the capacity‐limited (at 1000 mAh g^?1) conditions. These cells also exhibit much less reaction residue on the charged air‐electrode surface and much less corrosion of the Li‐metal anode. Density functional theory calculations are used to calculate molecular orbital energies of the electrolyte components and Gibbs activation energy barriers for the superoxide radical anion in the DME solvent and Li⁺–(DME) _n solvates. In a highly concentrated electrolyte, all DME molecules are coordinated with salt cations, and the C–H bond scission of the DME molecule becomes more difficult. Therefore, the decomposition of the highly concentrated electrolyte can be mitigated, and both air cathodes and Li‐metal anodes exhibit much better reversibility, resulting in improved cyclability of Li–O₂ batteries.     

Transition-Metal Vacancy Manufacturing and Sodium-Site Doping Enable a High-Performance Layered Oxide Cathode through Cationic and Anionic Redox Chemistry

Triggering the anionic redox chemistry in layered oxide cathodes has emerged as a paradigmatic approach to efficaciously boost the energy density of sodium-ion batteries. However, their practical applications are still plagued by irreversible lattice oxygen release and deleterious structure distortion. Herein, a novel P2-Na_0.76Ca_0.05[Ni_0.23□_0.08Mn_0.69]O₂ cathode material featuring joint cationic and anionic redox activities, where native vacancies are produced in the transition-metal (TM) layers and Ca ions are riveted in the Na layers, is developed. Random vacancies in the TM sites induce the emergence of nonbonding O 2p orbitals to activate anionic redox, which is confirmed by systematic electrochemical measurements, ex situ X-ray photoelectron spectroscopy, in situ X-ray diffraction, and density functional theory computations. Benefiting from the pinned Ca ions in the Na sites, a robust layered structure with the suppressed P2-O2 phase transition and enhanced anionic redox reversibility upon charge/discharge is achieved. Therefore, the electrode displays exceptional rate capability (153.9 mA h g⁻¹ at 0.1 C with 74.6 mA h g⁻¹ at 20 C) and improved cycling life (87.1% capacity retention at 0.1 C after 50 cycles). This study provides new opportunities for designing high-energy-density and high-stability layered sodium oxide cathodes by tuning local chemical environments.     

Unveiling the Anionic Redox Chemistry in Phosphate Cathodes for Sodium-Ion Batteries

Anionic redox chemistry has aroused increasing attention in sodium-ion batteries (SIBs) by virtue of the appealing additional capacity. However, up to now, anionic redox reaction has not been reported in the mainstream phosphate cathodes for SIBs. Herein, the ultrathin VOPO₄ nanosheets are fabricated as promising cathodes for SIBs, where the oxygen redox reaction is first activated accompanied by reversible ClO₄⁻ (from the electrolyte) insertion/extraction. As a result, the VOPO₄ cathode harvests a record-high capacity (168 mAh g⁻¹ at 0.1 C) among its counterparts ever reported. Moreover, the ClO₄⁻ insertion efficiently expands the interlayer spacing of VOPO₄ and accelerates the ion diffusion, enabling an unprecedentedly high rate performance (69 mAh g⁻¹ at 30 C). Via systematic ex situ characterizations and theoretical computations, the anionic redox chemistry and charge storage mechanism upon cycling are thoroughly elucidated. This study opens up a new avenue toward high-energy phosphate cathodes for SIBs by triggering anionic redox reactions.     

High‐Voltage Charging‐Induced Strain,Heterogeneity, and Micro‐Cracks in Secondary Particles of a Nickel‐Rich Layered Cathode Material

Nickel‐rich layered materials LiNi_1‐x‐yMn_xCo_yO₂ are promising candidates for high‐energy‐density lithium‐ion battery cathodes. Unfortunately, they suffer from capacity fading upon cycling, especially with high‐voltage charging. It is critical to have a mechanistic understanding of such fade. Herein, synchrotron‐based techniques (including scattering, spectroscopy, and microcopy) and finite element analysis are utilized to understand the LiNi_0.6Mn_0.2Co_0.2O₂ material from structural, chemical, morphological, and mechanical points of view. The lattice structural changes are shown to be relatively reversible during cycling, even when 4.9 V charging is applied. However, local disorder and strain are induced by high‐voltage charging. Nano‐resolution 3D transmission X‐ray microscopy data analyzed by machine learning methodology reveal that high‐voltage charging induced significant oxidation state inhomogeneities in the cycled particles. Regions at the surface have a rock salt–type structure with lower oxidation state and build up the impedance, while regions with higher oxidization state are scattered in the bulk and are likely deactivated during cycling. In addition, the development of micro‐cracks is highly dependent on the pristine state morphology and cycling conditions. Hollow particles seem to be more robust against stress‐induced cracks than the solid ones, suggesting that morphology engineering can be effective in mitigating the crack problem in these materials.     

Toward Stable Cycling of a Cost-Effective Cation-Disordered Rocksalt Cathode via Fluorination

The recently developed Li-excess cation-disordered rock salts (DRXs) exhibit an excellent chemical diversity for the development of alternative Co/Ni-free high-energy cathodes. Herein, the synthesis of a highly fluorinated DRX cathode, Li_1.2Mn_0.6Ti_0.2O_1.8F_0.2, based on cost-effective and earth-abundant transition metals, via a solid-state reaction, is reported. The fluorinated DRX cathode using ammonium fluoride precursor exhibits more uniform particle size and delivers a specific discharge capacity of 233 mAh g⁻¹ and specific energy of 754 Wh kg⁻¹, with 206 mAh g⁻¹ retained after 200 cycles. The combined synchrotron X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy analysis reveals that the remarkable cycling performance is attributed to the high fluorination and thus enhanced Mn content, enabling the utilization of more Mn redox than the oxide analog. This study demonstrates a great promise to develop next-generation cost-effective DRX cathodes with enhanced capacity retention for high-energy Li-ion batteries.     

A Targeted Functional Design for Highly Efficient and Stable Cathodes for Rechargeable Li‐Ion Batteries

Despite the great success of Li‐ion batteries (LIBs) up to now, higher demand has been raised with the emergence of the new generation electrics, such as portable devices and electrical vehicles. Even with the improvement on anodes, the cathodes with high capacity and long‐lastingness still remain a challenge. New 3D NiCo₂O₄@V₂O₅ core–shell arrays (CSAs) on carbon cloth as cathodes in LIBs have been reported in this work. The nanodesigned materials realize the theoretical specific capacity of V₂O₅ with high power rate based on the total mass of the framework and amount of active materials. The electrodes achieve superb cycling stability, among the most stable cathodes for LIBs ever reported. From both in situ transmission electron microscopy and quantum level calculations, the 3D NiCo₂O₄ nanosheet frameworks provide high electron conductivity and the skeleton of the robust CSAs without participating in the lithiation/delithiation; the thickness of the layered V₂O₅ plays a key role for Li diffusivity and the capacity contribution of electrodes. The structures herein point to new design concepts for high‐performance nanoarchitectures for LIB cathodes.     

Local Electronic Structure Modulation Enables Fast-Charging Capability for Li-Rich Mn-Based Oxides Cathodes With Reversible Anionic Redox Activity

Anionic and cationic redox chemistries boost ultrahigh specific capacities of Li-rich Mn-based oxides cathodes (LRMO). However, irreversible oxygen evolution and sluggish kinetics result in continuous capacity decay and poor rate performance, restricting the commercial fast-charging cathodes application for lithium ion batteries. Herein, the local electronic structure of LRMO is appropriately modulated to alleviate oxygen release, enhance anionic redox reversibility, and facilitate Li⁺ diffusion via facile surface defect engineering. Concretely, oxygen vacancies integrated on the surface of LRMO reduce the density of states of O 2p band and trigger much delocalized electrons to distribute around the transition metal, resulting in less oxygen release, enhancing reversible anionic redox and the MnO₆ octahedral distortion. Besides, partially reduced Mn and lattice vacancies synchronously stimulate the electrochemical activity and boost the electronic conductivity, Li⁺ diffusion rate, and fast charge transfer. Therefore, the modified LRMO exhibits enhanced cyclic stability and fast-charging capability: a high discharging capacity of 212.6 mAh·g⁻¹ with 86.98% capacity retention after 100 cycles at 1 C is obtained and to charge to its 80%, SOC is shortened to 9.4 min at 5 C charging rate. This work will draw attention to boosting the fast-charging capability of LRMO via the local electronic structure modulation.     

Accessible Li Percolation and Extended Oxygen Oxidation Boundary in Rocksalt-like Cathode Enabled by Initial Li-deficient Nanostructure

Disordered rocksalt cathodes have shown attractive electrochemical performance via oxygen redox, but are limited by a necessary Li-excess level above the percolation threshold (x > 1.09 in Li_xTM_2-xO₂, TM = transition metals) to obtain electrochemical activity. However, a relatively low-Li content is essential to alleviate excessive oxygen charge compensation in rocksalt oxides. Herein, taking the homogeneous Li₂MnO₃ and LiMn₂O₄ as the starting point, disordered rocksalt-like cathodes are prepared with initial Li-deficient nanostructures, cation vacancies, and partial spinel-type structures that provide a solution for the acquisition of fast Li⁺ percolation channels under Li-deficient condition. As a result, the prepared sample exhibits high initial discharge capacity (363 mAh g⁻¹) and energy density (1081 Wh kg⁻¹). Advanced spectroscopy and in situ measurements observe highly reversible charge compensation during electrochemical process and assign coupled Mn- and O-related redox contribution. Theoretical calculations also suggest the novel and chemical reversible trapped molecular O₂ model in the rocksalt structure with vacancies, demonstrating a dual role of Li-deficient structure in promoting cationic oxidation and extending reversible oxygen redox boundary. This work is expected to breakthrough the existing ideas of oxygen oxidation and opens up a higher degree of freedom in the design of disordered rocksalt structures.