Visualization of Light Elements using 4D STEM: The Layered‐to‐Rock Salt Phase Transition in LiNiO2 Cathode Material

The layered oxide LiNiO₂ (LNO) has been extensively investigated as a cathode active material for lithium‐ion batteries. Despite LNO's high gravimetric capacity, instability issues hinder its commercialization. It suffers from capacity loss during electrochemical cycling and is difficult to synthesize without defects. This is related to poor structural stability, leading to decomposition into the parent rock‐salt‐type oxide. In order to understand such phase transformations and to develop measures to inhibit them, the development of techniques able to image all atoms is crucial. In this study, the use of a fast, pixelated detector and 4D imaging in scanning transmission electron microscopy are explored to tackle this challenge. Selecting specific angular regions in the diffraction patterns and calculating virtual annular bright‐field images significantly enhances the contrast of the lithium atoms, such that all atoms are visible even in realistic samples. The developed technique is applied to image the layered‐to‐rock salt phase transition region. The data show that in this region, nickel atoms are in tetrahedral positions and the oxygen atoms are asymmetrically distributed. Taken together, the results shed light on the phase transformation mechanism at the atomic scale and can guide future research toward stabilizing LNO.     

On the Localized Nature of the Structural Transformations of Li2MnO3 Following Electrochemical Cycling

Although the Li‐excess layered‐oxide Li₂MnO₃ has a high theoretical capacity, structural transformations within the oxide during electrochemical cycling lead to relatively low experimental capacities, hindering its use in practical applications. Here, aberration‐corrected scanning transmission electron microscopy/electron energy loss spectroscopy and high‐resolution X‐ray diffraction are used to characterize the oxide following electrochemical cycling. Microscopy reveals the coexistence of regions with local monoclinic, spinel, and rock‐salt symmetries, indicating localized and inhomogeneous structural evolutions. Crystal structure transformations are observed both at the particle surface and in the bulk. At the surface, these transformed regions resemble spinel Mn₃O₄ or rock‐salt MnO, consistent with oxygen loss. In the bulk, the regions resemble defect spinels, such as the layered‐spinel Li_xMn_4/3O₄, which suggest a partial phase transformation consistent with oxygen retention. Both microscopy and diffraction data of the cycled sample indicate areas of pristine Li₂MnO₃; the presence of such areas, in close proximity to Li_xMn_4/3O₄ areas, suggests that the layered to spinel structure transformation is partially reversible. Spinel, disordered rock salt, and pristine areas are also observed in Li₂MnO₃ samples intentionally damaged by electron beam irradiation. This observation indicates that the dynamic processes resulting in phase transformations can be studied for a variety of oxide systems by a judicious selection of irradiation conditions.     

Spinel‐Layered Core‐Shell Cathode Materials for Li‐Ion Batteries

In an attempt to overcome the problems associated with LiNiO₂, the solid solution series of lithium nickel‐metal oxides, Li[Ni_1–xM_x]O₂ (with M = Co, Mn, Al, Ti, Mg, etc.), have been investigated as favorable cathode materials for high‐energy and high‐power lithium‐ion batteries. However, along with the improvement in the electrochemical properties in Ni‐based cathode materials, the thermal stability has been a great concern, and thus violent reaction of the cathode with the electrolyte needs to be avoided. Here, we report a heterostructured Li[Ni_0.54Co_0.12Mn_0.34]O₂ cathode material which possesses both high energy and safety. The core of the particle is Li[Ni_0.54Co_0.12Mn_0.34]O₂ with a layered phase (R3‐m) and the shell, with a thickness of < 0.5 μm, is a highly stable Li_1+x[CoNi_xMn_2–x]₂O₄ spinel phase (Fd‐3m). The material demonstrates reversible capacity of 200 mAhg‐1 and retains 95% capacity retention under the most severe test condition of 60 °C. In addition, the amount of oxygen evolution from the lattice in the cathode with two heterostructures is reduced by 70%, compared to the reference sample. All these results suggest that the bulk Li[Ni_0.54Co_0.12Mn_0.34]O₂ consisting of two heterostructures satisfy the requirements for hybrid electric vehicles, power tools, and mobile electronics.     

Stabilizing Reversible Oxygen Redox Chemistry in Layered Oxides for Sodium‐Ion Batteries

Triggering oxygen‐related activity is demonstrated as a promising strategy to effectively boost energy density of layered cathodes for sodium‐ion batteries. However, irreversible lattice oxygen loss will induce detrimental structure distortion, resulting in voltage decay and cycle degradation. Herein, a layered structure P2‐type Na_0.66Li_0.22Ru_0.78O₂ cathode is designed, delivering reversible oxygen‐related and Ru‐based redox chemistry simultaneously. Benefiting from the combination of strong Ru 4d‐O 2p covalency and stable Li location within the transition metal layer, reversible anionic/cationic redox chemistry is achieved successfully, which is proved by systematic bulk/surface analysis by in/ex situ spectroscopy (operando Raman and hard X‐ray absorption spectroscopy, etc.). Moreover, the robust structure and reversible phase transition evolution revealed by operando X‐ray diffraction further establish a high degree reversible (de)intercalation processes (≈150 mAh g^?1, reversible capacity) and long‐term cycling (average capacity drop of 0.018%, 500 cycles).     

Amorphous Cobalt Boride (Co2B) as a Highly Efficient Nonprecious Catalyst for Electrochemical Water Splitting: Oxygen and Hydrogen Evolution

It is demonstrated that amorphous cobalt boride (Co₂B) prepared by the chemical reduction of CoCl₂ using NaBH₄ is an exceptionally efficient electrocatalyst for the oxygen evolution reaction (OER) in alkaline electrolytes and is simultaneously active for catalyzing the hydrogen evolution reaction (HER). The catalyst achieves a current density of 10 mA cm^?2 at 1.61 V on an inert support and at 1.59 V when impregnated with nitrogen‐doped graphene. Stable performance is maintained at 10 mA cm^?2 for at least 60 h. The optimized catalyst, Co₂B annealed at 500 °C (Co₂B‐500) evolves oxygen more efficiently than RuO₂ and IrO₂, and its performance matches the best cobalt‐based catalysts reported to date. Co₂B is irreversibly oxidized at OER conditions to form a CoOOH surface layer. The active form of the catalyst is therefore represented as CoOOH/Co₂B. EXAFS observations indicate that boron induces lattice strain in the crystal structure of the metal, which potentially diminishes the thermodynamic and kinetic barrier of the hydroxylation reaction, formation of the OOH* intermediate, a key limiting step in the OER.     

Evolutionary trends in RuBisCO kinetics and their co‐evolution with CO2 concentrating mechanisms

RuBisCO‐catalyzed CO₂ fixation is the main source of organic carbon in the biosphere. This enzyme is present in all domains of life in different forms (III, II, and I) and its origin goes back to 3500 Mya, when the atmosphere was anoxygenic. However, the RuBisCO active site also catalyzes oxygenation of ribulose 1,5‐bisphosphate, therefore, the development of oxygenic photosynthesis and the subsequent oxygen‐rich atmosphere promoted the appearance of CO₂ concentrating mechanisms (CCMs) and/or the evolution of a more CO₂‐specific RuBisCO enzyme. The wide variability in RuBisCO kinetic traits of extant organisms reveals a history of adaptation to the prevailing CO₂/O₂ concentrations and the thermal environment throughout evolution. Notable differences in the kinetic parameters are found among the different forms of RuBisCO, but the differences are also associated with the presence and type of CCMs within each form, indicative of co‐evolution of RuBisCO and CCMs. Trade‐offs between RuBisCO kinetic traits vary among the RuBisCO forms and also among phylogenetic groups within the same form. These results suggest that different biochemical and structural constraints have operated on each type of RuBisCO during evolution, probably reflecting different environmental selective pressures. In a similar way, variations in carbon isotopic fractionation of the enzyme point to significant differences in its relationship to the CO₂ specificity among different RuBisCO forms. A deeper knowledge of the natural variability of RuBisCO catalytic traits and the chemical mechanism of RuBisCO carboxylation and oxygenation reactions raises the possibility of finding unrevealed landscapes in RuBisCO evolution.     

Ethylene Carbonate‐Free Electrolytes for High‐Nickel Layered Oxide Cathodes in Lithium‐Ion Batteries

Layered lithium nickel oxide (LiNiO₂) can provide very high energy density among intercalation cathode materials for lithium‐ion batteries, but suffers from poor cycle life and thermal‐abuse tolerance with large lithium utilization. In addition to stabilization of the active cathode material, a concurrent development of electrolyte systems of better compatibility is critical to overcome these limitations for practical applications. Here, with nonaqueous electrolytes based on exclusively aprotic acyclic carbonates free of ethylene carbonate (EC), superior electrochemical and thermal characteristics are obtained with an ultrahigh‐nickel cathode (LiNi_0.94Co_0.06O₂), capable of reaching a 235 mA h g^?1 specific capacity. Pouch‐type graphite|LiNi_0.94Co_0.06O₂ cells in EC‐free electrolytes withstand several hundred charge–discharge cycles with minor degradation at both ambient and elevated temperatures. In thermal‐abuse tests, the cathode at full charge, while reacting aggressively with EC‐based electrolytes below 200 °C, shows suppressed self‐heating without EC. Through 3D chemical and structural analyses, the intriguing impact of EC is visualized in aggravating unwanted surface parasitic reactions and irreversible bulk structural degradation of the cathode at high voltages. These results provide important insights in designing high‐energy electrodes for long‐lasting and reliable lithium‐ion batteries.     

Structural and Chemical Evolution of the Layered Li‐Excess LixMnO3 as a Function of Li Content from First‐Principles Calculations

Li₂MnO₃ is a critical component in the family of “Li‐excess” materials, which are attracting attention as advanced cathode materials for Li‐ion batteries. Here, first‐principle calculations are presented to investigate the electrochemical activity and structural stability of stoichiometric Li_xMnO₃ (0 ≤ x ≤ 2) as a function of Li content. The Li₂MnO₃ structure is electrochemically activated above 4.5 V on delithiation and charge neutrality in the bulk of the material is mainly maintained by the oxidization of a portion of the oxygen ions from O^2? to O^1?. While oxygen vacancy formation is found to be thermodynamically favorable for x < 1, the activation barriers for O^2? and O^1? migration remain high throughout the Li com­position range, impeding oxygen release from the bulk of the compound. Defect layered structures become thermodynamically favorable at lower Li content (x < 1), indicating a tendency towards the spinel‐like structure transformation. A critical phase transformation path for forming nuclei of spinel‐like domains within the matrix of the original layered structure is proposed. Formation of defect layered structures during the first charge is shown to manifest in a depression of the voltage profile on the first discharge, providing one possible explanation for the observed voltage fade of the Li‐excess materials.     

Oxygen Ion Diffusion and Surface Exchange Properties of the α‐ and δ‐phases of Bi2O3

Fast oxide ion conduction is a highly desirable property for materials in a wide range of applications. The fastest reported ionic conductor, representing the current state of the art and an oft‐proposed effective limit of oxide ion conductivity, is the high temperature fluorite‐structured δ phase of Bi₂O₃. Here, the ionic nature of this conduction is, for the first time, directly determined through oxygen tracer diffusion measurements. This phase also presents a remarkably high oxygen surface exchange coefficient, competitive with the highest performance solid oxide fuel cell (SOFC) cathodes yet counterintuitively in a material with negligible electronic conduction. The low temperature α‐Bi₂O₃ polymorph is also investigated, revealing a remarkable drop in diffusivity of over 7 orders of magnitude with a temperature drop of just ≈150 °C. Surprisingly, the diffusion studies also reveal a secondary, significantly faster migration pathway in the α phase. This is attributed to grain boundary conduction and shown to be 3–4 orders of magnitude higher than in the bulk. This previously unobserved property could present an exciting opportunity to tailor ionic conductivity levels through manipulating microstructure down to the nanoscale.     

Oxygen‐Deficient Blue TiO2 for Ultrastable and Fast Lithium Storage

Developing a titanium dioxide (TiO₂)‐based anode with superior high‐rate capability and long‐term cycling stability is important for efficient energy storage. Herein, a simple one‐step approach for fabricating blue TiO₂ nanoparticles with oxygen vacancies is reported. Oxygen vacancies can enlarge lattice spaces, lower charge transfer resistance, and provide more active sites in TiO₂ lattices. As a result, this blue TiO₂ electrode exhibits a highly reversible capacity of 50 mAh g^?1 at 100 C (16 800 mA g^?1) even after 10 000 cycles, which is attributable to the combination of surface capacitive process and remarkable diffusion‐controlled insertion revealed by the kinetic analysis. The strategy of employing oxygen‐deficient nanoparticles may be extended to the design of other robust semiconductor materials as electrodes for energy storage.     

Toward Higher Voltage Solid‐State Batteries by Metastability and Kinetic Stability Design

The energy density of battery systems is limited largely by the electrochemical window of the electrolyte. Herein, the combined thermodynamic and kinetic effects of mechanically induced metastability are shown to greatly widen the operational voltage window of solid‐state batteries based on ceramic‐sulfide electrolytes. Solid electrolyte voltage stability up to 10 V is achieved with minimal degradation, far beyond the capability of organic liquid electrolytes. Furthermore, combined experiment, ab initio computation, and theoretical modeling identify the nature of mechanically constrained Li₁₀GeP₂S₁₂ decomposition both within the bulk and at interfaces with cathode materials at very high voltages. Previously unclear kinetic processes are identified that, when properly implemented, can potentially allow solid‐state full cells with remarkably high operational voltages.     

Earth‐Abundant Iron Diboride (FeB2) Nanoparticles as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting

Developing efficient, durable, and earth‐abundant electrocatalysts for both hydrogen and oxygen evolution reactions is important for realizing large‐scale water splitting. The authors report that FeB₂ nanoparticles, prepared by a facile chemical reduction of Fe²⁺ using LiBH₄ in an organic solvent, are a superb bifunctional electrocatalyst for overall water splitting. The FeB₂ electrode delivers a current density of 10 mA cm^?2 at overpotentials of 61 mV for hydrogen evolution reaction (HER) and 296 mV for oxygen evolution reaction (OER) in alkaline electrolyte with Tafel slopes of 87.5 and 52.4 mV dec^?1, respectively. The electrode can sustain the HER at an overpotential of 100 mV for 24 h and OER for 1000 cyclic voltammetry cycles with negligible degradation. Density function theory calculations demonstrate that the boron‐rich surface possesses appropriate binding energy for chemisorption and desorption of hydrogen‐containing intermediates, thus favoring the HER process. The excellent OER activity of FeB₂ is ascribed to the formation of a FeOOH/FeB₂ heterojunction during water oxidation. An alkaline electrolyzer is constructed using two identical FeB₂‐NF electrodes as both anode and cathode, which can achieve a current density of 10 mA cm^?2 at 1.57 V for overall water splitting with a faradaic efficiency of nearly 100%, rivalling the integrated state‐of‐the‐art Pt/C and RuO₂/C.     

Understanding Performance Degradation in Cation‐Disordered Rock‐Salt Oxide Cathodes

The collective redox activities of transition‐metal (TM) cations and oxygen anions have been shown to increase charge storage capacity in both Li‐rich layered and cation‐disordered rock‐salt cathodes. Repeated cycling involving anionic redox is known to trigger TM migration and phase transformation in layered Li‐ and Mn‐rich (LMR) oxides, however, detailed mechanistic understanding on the recently discovered Li‐rich rock‐salt cathodes is largely missing. The present study systematically investigates the effect of oxygen redox on a Li_1.3Nb_0.3Mn_0.4O₂ cathode and demonstrates that performance deterioration is directly correlated to the extent of oxygen redox. It is shown that voltage fade and hysteresis begin only after initiating anionic redox at high voltages, which grows progressively with either deeper oxidation of oxygen at higher potential or extended cycling. In contrast to what is reported on layered LMR oxides, extensive TM reduction is observed but phase transition is not detected in the cycled oxide. A densification/degradation mechanism is proposed accordingly which elucidates how a unique combination of extensive chemical reduction of TM and reduced quality of the Li percolation network in cation‐disordered rock‐salts can lead to performance degradation in these newer cathodes with 3D Li migration pathways. Design strategies to achieve balanced capacity and stability are also discussed.     

Controllable Synthesis of Mesoporous TiO2 Polymorphs with Tunable Crystal Structure for Enhanced Photocatalytic H2 Production

Multiphasic titanium dioxide (TiO₂) possessing abundant heterophase junctions have been widely used for various photocatalytic applications. Current synthesis of multiphasic TiO₂ mainly involves the process of thermal treatment and multiple steps of rigorous reactions, which is adverse to controlling the crystal phases and phase ratios of multiphasic TiO₂. Meanwhile, the resulting products have relatively low surface area and nonporous structure. Here, a facile polymer‐assisted coordination‐mediated self‐assembly method to synthesize mesoporous TiO₂ polymorphs with controllable heterophase junctions and large surface area by using polyethylenimine as the porogen in an acidic aqueous synthesis system is reported. Using this approach, the crystal phases (triphase, biphase, and monophase) and phase compositions (0–100%) are easily tailored by selecting the suitable acidic media. Furthermore, the specific surface areas (77–228 m² g^?1) and pore sizes (2.9–10.1 nm) are readily tailored by changing the reaction temperature. The photocatalytic activity of mesoporous TiO₂ polymorphs is evaluated by photocatalytic hydrogen evolution. The triphasic TiO₂ exhibits an excellent photocatalytic H₂ generation rate of 3.57 mmol h^?1 g^?1 as compared to other polymorphs, which is attributed to the synergistic effects of heterophase junctions and mesostructure. The band diagram of possible electron transfer pathway for triphasic TiO₂ is also elucidated.     

Regulating the Catalytic Dynamics Through a Crystal Structure Modulation of Bimetallic Catalyst

The surface of solid catalysts is one of the most important factors where the interface with reaction products governs the reaction kinetics. Herein, the crystal phase of palladium–copper nanoparticles (PdCu NPs) is controlled to modulate their surface atomic arrangement, which will govern the growth dynamics of discharge products on their surfaces and thus the catalytic performances in non‐aqueous lithium–oxygen (Li‐O₂) batteries. First‐principles calculations and experimental validations reveal that homogeneous nucleation and distribution of discharge products are observed on the surface of body‐centered cubic PdCu NPs, promoting the oxygen reduction/evolution reaction (ORR/OER) activities in Li‐O₂ batteries. However, the agglomerates formed on the surface of its face‐centered cubic homologue deteriorates ORR/OER activities, which worsen the battery performances. For the first time, this work theoretically and experimentally demonstrates how the crystal phase modulation regulates the nucleation behaviors and growth dynamics of discharge products for ORR/OER.     

Unraveling the Voltage Decay Phenomenon in Li‐Rich Layered Oxide Cathode of No Oxygen Activity

Extensive efforts have been devoted to unraveling the true cause of voltage decay in Li, Mn‐rich layered oxides. An initial consensus was reached on structural rearrangement, then leaned toward the newly discovered lattice oxygen activity. It is challenging to differentiate their explicit roles because these events typically coexist during the electrochemical reaction of most Li‐rich layered oxides. Here, the voltage decay behavior is probed in Li_1.2Ni_0.2Ru_0.6O₂, a structurally and electrochemically relevant compound to Li, Mn‐rich layered oxide, but of no oxygen activity. Such intriguing characteristics allow the explicit decoupling of the contribution of transition metal migration and lattice oxygen activity to voltage decay in Li‐rich layered oxides. The results demonstrate that the microstructural evolution, mainly originating from transition metal migration, is a direct cause of voltage decay, and lattice oxygen activity likely accelerates the decay.     

Probing Dopant Redistribution,Phase Propagation,and Local Chemical Changes in the Synthesis of Layered Oxide Battery Cathodes

Achieving the targeted control of layered oxide properties calls for more fundamental studies to mechanistically probe their evolution during their synthesis. Herein, dopant distribution, phase propagation, and local chemical changes as well as their interplay in multielement-doped LiNiO₂ materials are investigated using spectroscopic, imaging, and scattering techniques. It is shown that dopants undergo dynamic redistribution in the Ni(OH)₂ host lattice at the early stage of calcination (below 300 °C). Such redistribution behavior exhibits strong dopant-dependent characteristics, allowing for targeted surface and bulk doping control. The Ni oxidation process exhibits depth-dependent characteristics and the most rapid Ni oxidation takes place between 300 and 700 °C. Using Ni oxidation state as the proxy for the phase transformation, the buildup of heterogenous phase propagation in the early stage of calcination is shown, especially along the radial direction of secondary particles. The radial heterogenous phase distribution gradually decreases upon completing the calcination. However, a high degree of mosaic-like heterogeneity may still be present in the final product, departing from the perfect layered oxide. The present study offers fundamental insights into manipulating multiscale materials properties during calcination for obtaining stable, high-energy layered oxide cathodes.     

Efficient and Stable TiO2:Pt–Cu(In,Ga)Se2 Composite Photoelectrodes for Visible Light Driven Hydrogen Evolution

Novel thin film composite photocathodes based on device‐grade Cu(In,Ga)Se₂ chalcopyrite thin film absorbers and transparent conductive oxide Pt‐implemented TiO₂ layers on top are presented for an efficient and stable solar‐driven hydrogen evolution. Thin films of phase‐pure anatase TiO₂ are implemented with varying Pt‐concentrations in order to optimize simultaneously i) conductivity of the films, ii) electrocatalytic activity, and iii) light‐guidance toward the chalcopyrite. Thereby, high incident‐photon‐to‐current‐efficiencies of more than 80% can be achieved over the full visible light range. In acidic electrolyte (pH 0.3), the most efficient Pt‐implemented TiO₂–Cu(In,Ga)Se₂ composite electrodes reveal i) photocurrent densities up to 38 mA cm^?2 in the saturation region (?0.4 V RHE, reversible hydrogen electrode), ii) 15 mA cm^?2 at the thermodynamic potential for H₂‐evolution (0 V RHE), and iii) an anodic onset potential shift for the hydrogen evolution (+0.23 V RHE). It is shown that the gradual increase of the Pt‐concentration within the TiO₂ layers passes through an efficiency‐ and stability‐maximum of the device (5 vol% of Pt precursor solution). At this maximum, optimized light‐incoupling into the device‐grade chalcopyrite light‐absorber as well as electron conductance properties within the surface layer are achieved while no degradation are observed over more than 24 h of operation.     

Impact of Hydroxylation and Hydration on the Reactivity of α‐Fe2O3 (0001) and (102) Surfaces under Environmental and Electrochemical Conditions

Hematite (α‐Fe₂O₃) is widely used as a catalytic electrode material in photo‐electrochemical water oxidation, where its surface compositions and stabilities can strongly impact the redox reaction process. Here, its surface configurations in environmental or electrochemical conditions are assessed via density functional theory (DFT) calculations conducted at the Perdew, Burke, and Ernzerhof (PBE)+U level. The most energetically favorable surface domains of α‐Fe₂O₃ (0001) and (102) are predicted by constructing the surface phase diagrams in the framework of first‐principle thermodynamics. The relative surface stabilities are investigated as a function of partial pressures of oxygen and water, temperature, solution pH, and electrode potential not only for perfect bulk terminations but also for defect‐containing surfaces having various degrees of hydroxylation and hydration. In order to assess the impact on the redox reactions of the surface planes as well as of the extent of surface hydration/hydroxylation, the thermodynamics of the four‐step oxygen evolution reaction (OER) mechanism are examined in detail for different models of the α‐Fe₂O₃ (0001) and (102) surfaces. Importantly, the results underline that the nature of the surface termination and the degree of near‐surface hydroxylation give rise to significant variations in the OER overpotentials.     

An Open‐Structured Matrix as Oxygen Cathode with High Catalytic Activity and Large Li2O2 Accommodations for Lithium–Oxygen Batteries

The nonaqueous lithium–oxygen (Li–O₂) battery is considered as one of the most promising candidates for next‐generation energy storage systems because of its very high theoretical energy density. However, its development is severely hindered by large overpotential and limited capacity, far less than theory, caused by sluggish oxygen redox kinetics, pore clogging by solid Li₂O₂ deposition, inferior Li₂O₂/cathode contact interface, and difficult oxygen transport. Herein, an open‐structured Co₉S₈ matrix with sisal morphology is reported for the first time as an oxygen cathode for Li–O₂ batteries, in which the catalyzing for oxygen redox, good Li₂O₂/cathode contact interface, favorable oxygen evolution, and a promising Li₂O₂ storage matrix are successfully achieved simultaneously, leading to a significant improvement in the electrochemical performance of Li–O₂ batteries. The intrinsic oxygen‐affinity revealed by density functional theory calculations and superior bifunctional catalytic properties of Co₉S₈ electrode are found to play an important role in the remarkable enhancement in specific capacity and round‐trip efficiency for Li–O₂ batteries. As expected, the Co₉S₈ electrode can deliver a high discharge capacity of ≈6875 mA h g^?1 at 50 mA g^?1 and exhibit a low overpotential of 0.57 V under a cutoff capacity of 1000 mA h g^?1, outperforming most of the current metal‐oxide‐based cathodes.