Highly Reversible Oxygen‐Redox Chemistry at 4.1 V in Na4/7−x[□1/7Mn6/7]O2 (□: Mn Vacancy)

Increasing the energy density of rechargeable batteries is of paramount importance toward achieving a sustainable society. The present limitation of the energy density is owing to the small capacity of cathode materials, in which the (de)intercalation of ions is charge‐compensated by transition‐metal redox reactions. Although additional oxygen‐redox reactions of oxide cathodes have been recognized as an effective way to overcome this capacity limit, irreversible structural changes that occur during charge/discharge cause voltage drops and cycle degradation. Here, a highly reversible oxygen‐redox capacity of Na₂Mn₃O₇ that possesses inherent Mn vacancies in a layered structure is found. The cross validation of theoretical predictions and experimental observations demonstrates that the nonbonding 2p orbitals of oxygens neighboring the Mn vacancies contribute to the oxygen‐redox capacity without making the Mn?O bond labile, highlighting the critical role of transition‐metal vacancies for the design of reversible oxygen‐redox cathodes.     

Synergy Between Metal Oxide Nanofibers and Graphene Nanoribbons for Rechargeable Lithium‐Oxygen Battery Cathodes

The challenges for rechargeable lithium‐oxygen batteries of low practical capacity and poor round‐trip efficiency urgently demand effective cathode materials to overcome the limitations. However, the synergy between the multiple active materials is not well understood. Here, findings of the synergistic effect between electrospun zinc oxide (ZnO) nanofibers and graphene nanoribbons (GNRs) unzipped from carbon nanotubes (CNTs) as cathode materials in rechargeable lithium‐oxygen batteries are described. Furthermore, the overpotentials and discharge capacities are tuned by the surface defect states of ZnO nanofibers and Pt nanocrytals in GNRs. It is observed that the optimized zinc oxide nanofibers hybridized with GNRs achieved a high reversible capacity of 6300 mAh g^‐1_carbon and enhanced stable cyclability under specific 50% of full discharge capacities. This report demonstrates that the ZnO nanofibers with a high degree of defects and hydrophilicity of the surface may be a promising cathode component for rechargeable lithium‐oxygen batteries and the optimum synergy between ZnO nanofibers and GNRs can balance the discharge capacity and cycle life.     

Fused Heteroaromatic Organic Compounds for High‐Power Electrodes of Rechargeable Lithium Batteries

Organic redox compounds are emerging electrode materials for rechargeable lithium batteries. However, their electrically insulating nature plagues efficient charge transport within the electroactive bulk. Alternative to the popular solution of elaborating nanocomposite materials, herein we report on a molecular‐level engineering strategy towards high‐power organic electrode materials with multi‐electron reactions. Systematic comparisons of anthraquinone analogues incorporating fused heteroaromatic structures as cathode materials in rechargeable lithium batteries reveal that the judicious incorporation of heteroaromatics improves the cell performance in terms of specific gravimetric capacity, working potential, rate capability, and cyclability. Combination studies with morphological observation, electrochemical impedance characterization, and theoretical modeling provide insight into the advantage of heteroaromatic building blocks. In particular, benzofuro[5,6‐b]furan‐4,8‐dione ( BFFD ) bearing furan moeities shows a reversible capacity of 181 mAh g^?1 when charged/discharged at 100C, corresponding to a power density of 29.8 kW kg^?1. These results have pointed to a general design route of high‐rate organic electrode materials by rational functionalization of redox compounds with appropriate heteroaromatic units as versatile structural tools.     

K‐Birnessite Electrode Obtained by Ion Exchange for Potassium‐Ion Batteries: Insight into the Concerted Ionic Diffusion and K Storage Mechanism

Novel and low‐cost rechargeable batteries are of considerable interest for application in large‐scale energy storage systems. In this context, K‐Birnessite is synthesized using a facile solid‐state reaction as a promising cathode for potassium‐ion batteries. During synthesis, an ion exchange protocol is applied to increase K content in the K‐Birnessite electrode, which results in a reversible capacity as high as 125 mAh g^?1 at 0.2 C. Upon K⁺ exchange the reversible phase transitions are verified by in situ X‐ray diffraction (XRD) characterization. The underlying mechanism is further revealed to be the concerted K⁺ ion diffusion with quite low activation energies by first‐principle simulations. These new findings provide new insights into electrode process kinetics, and lay a solid foundation for material design and optimization of potassium‐ion batteries for large‐scale energy storage.     

Dendrite‐Free Flexible Fiber‐Shaped Zn Battery with Long Cycle Life in Water and Air

Fiber‐shaped aqueous rechargeable Zn batteries (FARZBs) show flexibility, good reliability, cost‐effectiveness, high energy/power densities, and high safety that have attracted increasing attention as promising energy storage devices for future wearable applications. However, the development of FARZB is limited by its poor cycling life and inferior charge–discharge performance, mainly suffering from zinc dendrite growth and increasing electrode irreversibility. In this work, dendrite‐free fiber‐shaped Zn//Co₃O₄ rechargeable batteries with a long cycle life tested in water and air, are obtained via tuning the surface binding energy of Zn on the anode using the zincophilic N,O‐functional carbon fiber, as well as engineering the Co₃O₄ cathode with a nanowire array structure. The fiber‐shaped Zn//Co₃O₄ full battery demonstrates remarkable long cycle life in water and air with high energy density, impressive flexibility, and excellent waterproof ability (fully immersed and charged/discharged under water for more than 33 h for 3000 cycles with capacity retention of ≈80%). The reversible electrochemical mechanisms of the FARZBs, without obvious zinc dendrite deposits and structural change of Co₃O₄ nanowires, are confirmed by a series of characterizations. These results demonstrate that the FARZBs are promising power sources for emerging wearable electronics.     

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.     

High‐Voltage Oxygen‐Redox‐Based Cathode for Rechargeable Sodium‐Ion Batteries

Recently, anionic‐redox‐based materials have shown promising electrochemical performance as cathode materials for sodium‐ion batteries. However, one of the limiting factors in the development of oxygen‐redox‐based electrodes is their low operating voltage. In this study, the operating voltage of oxygen‐redox‐based electrodes is raised by incorporating nickel into P2‐type Na_2/3[Zn_0.3Mn_0.7]O₂ in such a way that the zinc is partially substituted by nickel. As designed, the resulting P2‐type Na_2/3[(Ni_0.5Zn_0.5)_0.3Mn_0.7]O₂ electrode exhibits an average operating voltage of 3.5 V and retains 95% of its initial capacity after 200 cycles in the voltage range of 2.3–4.6 V at 0.1C (26 mA g^?1). Operando X‐ray diffraction analysis reveals the reversible phase transition: P2 to OP4 phase on charge and recovery to the P2 phase on discharge. Moreover, ex situ X‐ray absorption near edge structure and X‐ray photoelectron spectroscopy studies reveal that the capacity is generated by the combination of Ni²⁺/Ni⁴⁺ and O^2?/O^1? redox pairs, which is supported by first‐principles calculations. It is thought that this kind of high voltage redox species combined with oxygen redox could be an interesting approach to further increase energy density of cathode materials for not only sodium‐based rechargeable batteries, but other alkali‐ion battery systems.     

Rational Construction of Self‐Standing Sulfur‐Doped Fe2O3 Anodes with Promoted Energy Storage Capability for Wearable Aqueous Rechargeable NiCo‐Fe Batteries

Aqueous rechargeable Ni‐Fe batteries featuring an ultra‐flat discharge plateau, low cost, and outstanding safety characteristics show promising prospects for application in wearable energy storage. In particular, fiber‐shaped Ni‐Fe batteries will enable textile‐based energy supply for wearable electronics. However, the development of fiber‐shaped Ni‐Fe batteries is currently challenged by the performance of fibrous Fe‐based anode materials. In this context, this study describes the fabrication of sulfur‐doped Fe₂O₃ nanowire arrays (S‐Fe₂O₃ NWAs) grown on carbon nanotube fibers (CNTFs) as an innovative anode material (S‐Fe₂O₃ NWAs/CNTF). Encouragingly, first‐principle calculations reveal that S‐doping in Fe₂O₃ can dramatically reduce the band gap from 2.34 to 1.18 eV and thus enhance electronic conductivity. The novel developed S‐Fe₂O₃ NWAs/CNTF electrode is further demonstrated to deliver a very high capacity of 0.81 mAh cm^?2 at 4 mA cm^?2. This value is almost sixfold higher than that of the pristine Fe₂O₃ NWAs/CNTF electrode. When a cathode containing zinc‐nickel‐cobalt oxide (ZNCO)@Ni(OH)₂ NWAs heterostructures is used, 0.46 mAh cm^?2 capacity and 67.32 mWh cm^?3 energy density are obtained for quasi‐solid‐state fiber‐shaped NiCo‐Fe batteries, which outperform most state‐of‐the‐art fiber‐shaped aqueous rechargeable batteries. These findings offer an innovative and feasible route to design high‐performance Fe‐based anodes and may inspire new development for the next‐generation wearable Ni‐Fe batteries.     

A Layered–Tunnel Intergrowth Structure for High‐Performance Sodium‐Ion Oxide Cathode

Delivery of high‐energy density with long cycle life is facing a severe challenge in developing cathode materials for rechargeable sodium‐ion batteries (SIBs). Here a composite Na_0.6MnO₂ with layered–tunnel structure combining intergrowth morphology of nanoplates and nanorods for SIBs, which is clearly confirmed by micro scanning electron microscopy, high‐resolution transmission electron microscopy as well as scanning transmission electron microscopy with atomic resolution is presented. Owing to the integrated advantages of P2 layered structure with high capacity and that of the tunnel structure with excellent cycling stability and superior rate performance, the composite electrode delivers a reversible discharge capacity of 198.2 mAh g^?1 at 0.2C rate, leading to a high‐energy density of 520.4 Wh kg^?1. This intergrowth integration engineering strategy may modulate the physical and chemical properties in oxide cathodes and provide new perspectives on the optimal design of high‐energy density and high‐stable materials for SIBs.     

Suppressing Lithium Dendrite Growth via Sinusoidal Ripple Current Produced by Triboelectric Nanogenerators

Lithium metal as an ultimate anode material of future rechargeable batteries may furnish the highest energy density for its pairing cathode, although preventing the growth of lithium dendrites in liquid electrolytes is a major challenge. This work reports that stable lithium metal anodes can be achieved by charging with high‐frequency sinusoidal ripple current generated by rotating triboelectric nanogenerators (R‐TENGs). Compared with constant DC current charging, sinusoidal ripple current charging by R‐TENG improves the uniformity of lithium deposition during cycling test. Consequently, symmetric Li/Li cells exhibit lower overpotential and better cycling stability. In addition, full cells assembled with lithium metal anodes and LiFePO₄ cathodes show considerably improved capacity retention when charged by R‐TENG's sinusoidal ripple current (99.5%) compared to constant current (78.7%) after 200 cycles. The charging strategy device in this work provides a promising direction toward improving the cycle life of Li metal batteries. In addition, the combination of R‐TENGs with Li metal batteries offers an encouraging solution for achieving stable energy supply in self‐powered systems.     

KTi2(PO4)3 with Large Ion Diffusion Channel for High‐Efficiency Sodium Storage

To accommodate the decreasing lithium resource and ensure continuous development of energy storage industry, sodium‐based batteries are widely studied to inherit the next generation of energy storage devices. In this work, a novel Na super ionic conductor type KTi₂(PO₄)₃/carbon nanocomposite is designed and fabricated as sodium storage electrode materials, which exhibits considerable reversible capacity (104 mAh g^?1 under the rate of 1 C with flat voltage plateaus at ≈2.1 V), high‐rate cycling stability (74.2% capacity retention after 5000 cycles at 20 C), and ultrahigh rate capability (76 mAh g^?1 at 100 C) in sodium ion batteries. Besides, the maximum ability for sodium storage is deeply excavated by further investigations about different voltage windows in half and full sodium ion cells. Meanwhile, as cathode material in sodium‐magnesium hybrid batteries, the KTi₂(PO₄)₃/carbon nanocomposite also displays good electrochemical performances (63 mAh g^?1 at the 230th cycle under the voltage window of 1.0–1.9 V). The results demonstrate that the KTi₂(PO₄)₃/carbon nanocomposite is a promising electrode material for sodium ion storage, and lay theoretical foundations for the development of new type of batteries.     

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.     

High Performance Na–CuCl2 Rechargeable Battery toward Room Temperature ZEBRA‐Type Battery

Despite a recent increase in the attention given to sodium rechargeable battery systems, they should be further advanced in terms of their energy density and reliability to successfully penetrate the rechargeable battery market. Here, a new room temperature ZEBRA‐type Na–CuCl₂ rechargeable battery is demonstrated that employs CuCl₂ cathode material and nonflammable inorganic liquid electrolyte. The cathode delivers a high energy density of ≈580 Wh kg^?1 with superior capacity retention over 1000 cycles as well as a high round‐trip efficiency of ≈97%, which has never been obtained in an organic electrolyte system and high‐temperature ZEBRA‐type battery. These excellent electrochemical performances are mainly attributed to the use of the SO₂‐based inorganic electrolyte, which guarantees a reversible conversion reaction between CuCl₂ and CuCl with NaCl. It is also demonstrated that the proposed battery chemistry can be extended to other copper halide materials including CuBr₂ and CuF₂, which also show highly promising battery performances as cathode materials for the Na–Cu halide battery system.     

Realizing Interfacial Electronic Interaction within ZnS Quantum Dots/N‐rGO Heterostructures for Efficient Li–CO2 Batteries

With high theoretical energy density, rechargeable metal–gas batteries (e.g., Li–CO₂ battery) are considered as one of the most promising energy storage devices. However, their practical applications are hindered by the sluggish reaction kinetics and discharge product accumulation during battery cycling. Currently, the solutions focus on exploration of new catalysts while the thorough understanding of their underlying mechanisms is often ignored. Herein, the interfacial electronic interaction within rationally designed catalysts, ZnS quantum dots/nitrogen‐doped reduced graphene oxide (ZnS QDs/N‐rGO) heterostructures, and their effects on transformation and deposition of discharge products in the Li–CO₂ battery are revealed. In this work, the interfacial interaction can both enhance the catalytic activities of ZnS QDs/N‐rGO heterostructures and induce the nucleation of discharge products to form a homogeneous Li₂CO₃/C film with excellent electronic transmission and high electrochemical activities. When the batteries cycle within a cutoff specific capacity of 1000 mAh g^?1 at a current density of 400 mA g^?1, the cycling performance of the Li–CO₂ battery using a ZnS QDs/N‐rGO cathode is over 3 and 9 times than those coupled with a ZnS nanosheets (NST)/N‐rGO cathode and a N‐rGO cathode, respectively. This work provides comprehensive understandings on designing catalysts for Li–CO₂ batteries as well as other rechargeable metal–gas batteries.     

Toward a Reversible Calcium‐Sulfur Battery with a Lithium‐Ion Mediation Approach

Calcium represents a promising anode for the development of high‐energy‐density, low‐cost batteries. However, a lack of suitable electrolytes has restricted the development of rechargeable batteries with a Ca anode. Furthermore, to achieve a high energy density system, sulfur would be an ideal cathode to couple with the Ca anode. Unfortunately, a reversible calcium‐sulfur (Ca‐S) battery has not yet been reported. Herein, a basic study of a reversible nonaqueous room‐temperature Ca‐S battery is presented. The reversibility of the Ca‐S chemistry and high utilization of the sulfur cathode are enabled by employing a Li⁺‐ion‐mediated calcium‐based electrolyte. Mechanistic insights pursued by spectroscopic, electrochemical, microscopic, and theoretical simulation (density functional theory) investigations imply that the Li⁺‐ions in the Ca‐electrolyte stimulate the reactivation of polysulfide/sulfide species. The coordination of lithium to sulfur reduces the formation of sturdy Ca‐S ionic bonds, thus boosting the reversibility of the Ca‐S chemistry. In addition, the presence of Li⁺‐ions facilitates the ionic charge transfer both in the electrolyte and across the solid electrolyte interphase layer, consequently reducing the interfacial and bulk impedance of Ca‐S batteries. As a result, both the utilization of active sulfur in the cathode and the discharge voltage of Ca‐S batteries are significantly improved.     

High‐Performance Reversible Aqueous Zn‐Ion Battery Based on Porous MnOx Nanorods Coated by MOF‐Derived N‐Doped Carbon

Rechargeable aqueous zinc‐ion batteries (ZIBs) have been emerging as potential large‐scale energy storage devices due to their high energy density, low cost, high safety, and environmental friendliness. However, the commonly used cathode materials in ZIBs exhibit poor electrochemical performance, such as significant capacity fading during long‐term cycling and poor performance at high current rates, which significantly hinder the further development of ZIBs. Herein, a new and highly reversible Mn‐based cathode material with porous framework and N‐doping (MnO_x@N‐C) is prepared through a metal–organic framework template strategy. Benefiting from the unique porous structure, conductive carbon network, and the synergetic effect of Zn²⁺ and Mn²⁺ in electrolyte, the MnO_x@N‐C shows excellent cycling stability, good rate performance, and high reversibility for aqueous ZIBs. Specifically, it exhibits high capacity of 305 mAh g^?1 after 600 cycles at 500 mA g^?1 and maintains achievable capacity of 100 mAh g^?1 at a quite high rate of 2000 mA g^?1 with long‐term cycling of up to 1600 cycles, which are superior to most reported ZIB cathode materials. Furthermore, insight into the Zn‐storage mechanism in MnO_x@N‐C is systematically studied and discussed via multiple analytical methods. This study opens new opportunities for designing low‐cost and high‐performance rechargeable aqueous ZIBs.     

Sandwich‐Like Reduced Graphene Oxide/Carbon Black/Amorphous Cobalt Borate Nanocomposites as Bifunctional Cathode Electrocatalyst in Rechargeable Zinc‐Air Batteries

The inhibitively high cost of the noble‐metal‐containing materials has become a major obstacle for the large‐scale application of rechargeable zinc‐air batteries (ZABs). To solve this problem in a practical way, a green and scalable method to prepare sandwich‐like reduced graphene oxide /carbon black/amorphous cobalt borate nanocomposites (rGO/CB/Co‐B_i) is reported. These composites are shown to be a highly efficient and robust bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this system, the spontaneous assembly of the GO sheet and CB nanoparticles is demonstrated by noncovalent interactions to build the sandwich‐like structure with hierarchical pore distribution. The impressive ORR and OER activities of the obtained nanocomposite are attributed to the high conductivity, large surface area, and the hierarchically porous channels. With room‐temperature synthesis and significant activities shown in the demonstrative battery test, the prepared nanocomposite can potentially serve as an alternative for noble‐metal‐based rechargeable ZAB cathode materials.     

The Sodium Storage Mechanism in Tunnel‐Type Na0.44MnO2 Cathodes and the Way to Ensure Their Durable Operation

Tunnel‐type sodium manganese oxide is a promising cathode material for aqueous/nonaqueous sodium‐ion batteries, however its storage mechanism is not fully understood, in part due to the complicated sodium intercalation process. In addition, low cyclability due to manganese dissolution has limited its practical application in rechargeable batteries. Here, the intricate sodium intercalation mechanism of Na_0.44MnO₂ is revealed by combination of electrochemical characterization, structure determination from powder X‐ray diffraction data, 3D bond valence difference maps, and barrier‐energy calculations of the sodium diffusion. NaI is proposed as an important electrolyte solution additive. It is shown to form a thin, beneficial, and durable cathode surface film that prevents manganese dissolution. The addition of 0.01 m NaI to electrolyte solutions based on alkyl carbonate solvents and NaClO₄ greatly improves the cycling efficiency, raising the capacity retention from 86% to 96% after 600 cycles. This study determines the core aspects of the sodium intercalation mechanism in tunnel‐type sodium manganese oxide and shows how it can serve as a durable cathode material for rechargeable Na batteries.     

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.     

Native Vacancy Enhanced Oxygen Redox Reversibility and Structural Robustness

Cathode materials with high energy density, long cycle life, and low cost are of top priority for energy storage systems. The Li‐rich transition metal (TM) oxides achieve high specific capacities by redox reactions of both the TM and oxygen ions. However, the poor reversible redox reaction of the anions results in severe fading of the cycling performance. Herein, the vacancy‐containing Na_4/7[Mn_6/7(?_Mn)_1/7]O₂ (?_Mn for vacancies in the Mn? O slab) is presented as a novel cathode material for Na‐ion batteries. The presence of native vacancies endows this material with attractive properties including high structural flexibility and stability upon Na‐ion extraction and insertion and high reversibility of oxygen redox reaction. Synchrotron X‐ray absorption near edge structure and X‐ray photoelectron spectroscopy studies demonstrate that the charge compensation is dominated by the oxygen redox reaction and Mn³⁺/Mn⁴⁺ redox reaction separately. In situ synchrotron X‐ray diffraction exhibits its zero‐strain feature during the cycling. Density functional theory calculations further deepen the understanding of the charge compensation by oxygen and manganese redox reactions and the immobility of the Mn ions in the material. These findings provide new ideas on searching for and designing materials with high capacity and high structural stability for novel energy storage systems.