Mn‐Rich P′2‐Na0.67[Ni0.1Fe0.1Mn0.8]O2 as High‐Energy‐Density and Long‐Life Cathode Material for Sodium‐Ion Batteries

Herein, P′2‐type Na_0.67[Ni_0.1Fe_0.1Mn_0.8]O₂ is introduced as a promising new cathode material for sodium‐ion batteries (SIBs) that exhibits remarkable structural stability during repetitive Na⁺ de/intercalation. The O? Ni? O? Mn? O? Fe? O bond in the octahedra of transition‐metal layers is used to suppress the elongation of the Mn? O bond and to improve the electrochemical activity, leading to the highly reversible Na storage mechanism. A high discharge capacity of ≈220 mAh g^?1 (≈605 Wh kg^?1) is delivered at 0.05 C (13 mAg^?1) with a high reversible capacity of ≈140 mAh g^?1 at 3 C and excellent capacity retention of 80% over 200 cycles. This performance is associated with the reversible P′2–OP4 phase transition and small volume change upon charge and discharge (≈3%). The nature of the sodium storage mechanism in a full cell paired with a hard carbon anode reveals an unexpectedly high energy density of ≈542 Wh kg^?1 at 0.2 C and good capacity retention of ≈81% for 500 cycles at 1 C (260 mAg^?1).     

A New P2‐Type Layered Oxide Cathode with Extremely High Energy Density for Sodium‐Ion Batteries

Herein, a new P2‐type layered oxide is proposed as an outstanding intercalation cathode material for high energy density sodium‐ion batteries (SIBs). On the basis of the stoichiometry of sodium and transition metals, the P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂ cathode is synthesized without impurities phase by partially substituting Ni and Fe into the Mn sites. The partial substitution results in a smoothing of the electrochemical charge/discharge profiles and thus greatly improves the battery performance. The P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂ cathode delivers an extremely high discharge capacity of 221.5 mAh g^?1 with a high average potential of ≈2.9 V (vs Na/Na⁺) for SIBs. In addition, the fast Na‐ion transport in the P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂ cathode structure enables good power capability with an extremely high current density of 2400 mA g^?1 (full charge/discharge in 12 min) and long‐term cycling stability with ≈80% capacity retention after 500 cycles at 600 mA g^?1. A combination of electrochemical profiles, in operando synchrotron X‐ray diffraction analysis, and first‐principles calculations are used to understand the overall Na storage mechanism of P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂.     

A Hollow‐Shell Structured V2O5 Electrode‐Based Symmetric Full Li‐Ion Battery with Highest Capacity

The symmetric batteries with an electrode material possessing dual cathodic and anodic properties are regarded as an ideal battery configuration because of their distinctive advantages over the asymmetric batteries in terms of fabrication process, cost, and safety concerns. However, the development of high‐performance symmetric batteries is highly challenging due to the limited availability of suitable symmetric electrode materials with such properties of highly reversible capacity. Herein, a triple‐hollow‐shell structured V₂O₅ (THS‐V₂O₅) symmetric electrode material with a reversible capacity of >400 mAh g^?1 between 1.5 and 4.0 V and >600 mAh g^?1 between 0.1 and 3.0 V, respectively, when used as the cathode and anode, is reported. The THS‐V₂O₅ electrodes assembled symmetric full lithium‐ion battery (LIB) exhibits a reversible capacity of ≈290 mAh g^?1 between 2 and 4.0 V, the best performed symmetric energy storage systems reported to date. The unique triple‐shell structured electrode makes the symmetric LIB possessing very high initial coulombic efficiency (94.2%), outstanding cycling stability (with 94% capacity retained after 1000 cycles), and excellent rate performance (over 140 mAh g^?1 at 1000 mA g^?1). The demonstrated approach in this work leaps forward the symmetric LIB performance and paves a way to develop high‐performance symmetric battery electrode materials.     

Confined Fe2VO4⊂Nitrogen‐Doped Carbon Nanowires with Internal Void Space for High‐Rate and Ultrastable Potassium‐Ion Storage

Developing low‐cost, high‐capacity, high‐rate, and robust earth‐abundant electrode materials for energy storage is critical for the practical and scalable application of advanced battery technologies. Herein, the first example of synthesizing 1D peapod‐like bimetallic Fe₂VO₄ nanorods confined in N‐doped carbon porous nanowires with internal void space (Fe₂VO₄?NC nanopeapods) as a high‐capacity and stable anode material for potassium‐ion batteries (KIBs) is reported. The peapod‐like Fe₂VO₄?NC nanopeapod heterostructures with interior void space and external carbon shell efficiently prevent the aggregation of the active materials, facilitate fast transportation of electrons and ions, and accommodate volume variation during the cycling process, which substantially boosts the rate and cycling performance of Fe₂VO₄. The Fe₂VO₄?NC electrode exhibits high reversible specific depotassiation capacity of 380 mAh g^?1 at 100 mA g^?1 after 60 cycles and remarkable rate capability as well as long cycling stability with a high capacity of 196 mAh g^?1 at 4 A g^?1 after 2300 cycles. The first‐principles calculations reveal that Fe₂VO₄?NC nanopeapods have high ionic/electronic conductivity characteristics and low diffusion barriers for K⁺‐intercalation. This study opens up new way for investigating high‐capacity metal oxide as high‐rate and robust electrode materials for KIBs.     

Controlled Oxygen Redox for Excellent Power Capability in Layered Sodium‐Based Compounds

A high‐rate of oxygen redox assisted by cobalt in layered sodium‐based compounds is achieved. The rationally designed Na_0.6[Mg_0.2Mn_0.6Co_0.2]O₂ exhibits outstanding electrode performance, delivering a discharge capacity of 214 mAh g^?1 (26 mA g^?1) with capacity retention of 87% after 100 cycles. High rate performance is also achieved at 7C (1.82 A g^?1) with a capacity of 107 mAh g^?1. Surprisingly, the Na_0.6[Mg_0.2Mn_0.6Co_0.2]O₂ compound is able to deliver capacity for 1000 cycles at 5C (at 1.3 A g^?1), retaining 72% of its initial capacity of 108 mAh g^?1. X‐ray absorption spectroscopy analysis of the O K‐edge indicates the oxygen‐redox species (O^2?/1?) is active during cycling. First‐principles calculations show that the addition of Co reduces the bandgap energy from ≈2.65 to ≈0.61 eV and that overlapping of the Co 3d and O 2p orbitals facilitates facile electron transfer, enabling the long‐term reversibility of the oxygen redox, even at high rates. To the best of the authors' knowledge, this is the first report on high‐rate oxygen redox in sodium‐based cathode materials, and it is believed that the findings will open a new pathway for the use of oxygen‐redox‐based materials for sodium‐ion batteries.     

Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes

Hard carbon (HC) is the state‐of‐the‐art anode material for sodium‐ion batteries (SIBs). However, its performance has been plagued by the limited initial Coulombic efficiency (ICE) and mediocre rate performance. Here, experimental and theoretical studies are combined to demonstrate the application of lithium‐pretreated HC (LPHC) as high‐performance anode materials for SIBs by manipulating the solid electrolyte interphase in tetraglyme (TEGDME)‐based electrolyte. The LPHC in TEGDME can 1) deliver > 92% ICE and ≈220 mAh g^?1 specific capacity, twice of the capacity (≈100 mAh g^?1) in carbonate electrolyte; 2) achieve > 85% capacity retention over 1000 cycles at 1000 mA g^?1 current density (4 C rate, 1 C = 250 mA g^?1) with a specific capacity of ≈150 mAh g^?1, ≈15 times of the capacity (10 mAh g^?1) in carbonate. The full cell of Na₃V₂(PO₄)₃‐LPHC in TEGDME demonstrated close to theoretical specific capacity of ≈98 mAh g^?1 based on Na₃V₂(PO₄)₃ cathode, ≈2.5 times of the value (≈40 mAh g^?1) with nontreated HC. This work provides new perception on the anode development for SIBs.     

3D Hierarchical Porous α‐Fe2O3 Nanosheets for High‐Performance Lithium‐Ion Batteries

To develop a long cycle life and good rate capability electrode, 3D hierarchical porous α‐Fe₂O₃ nanosheets are fabricated on copper foil and directly used as binder‐free anode for lithium‐ion batteries. This electrode exhibits a high reversible capacity and excellent rate capability. A reversible capacity up to 877.7 mAh g^?1 is maintained at 2 C (2.01 A g^?1) after 1000 cycles, and even when the current is increased to 20 C (20.1 A g^?1), a capacity of 433 mA h g^?1 is retained. The unique porous 3D hierarchical nanostructure improves electronic–ionic transport, mitigates the internal mechanical stress induced by the volume variations of the electrode upon cycling, and forms a 3D conductive network during cycling. No addition of any electrochemically inactive conductive agents or polymer binders is required. Therefore, binder‐free electrodes further avoid the uneven distribution of conductive carbon on the current collector due to physical mixing and the addition of an insulator (binder), which has benefits leading to outstanding electrochemical performance.     

Uniform Pomegranate‐Like Nanoclusters Organized by Ultrafine Transition Metal Oxide@Nitrogen‐Doped Carbon Subunits with Enhanced Lithium Storage Properties

Uniform pomegranate‐like nanoclusters (NCs) organized by ultrafine transition metal oxide@nitrogen‐doped carbon (TMO@N–C) subunits (diameter ≈ 4 nm) are prepared on a large scale for the first time through a facile, novel, and one‐pot approach. Taking pomegranate‐like Fe₃O₄@N–C NCs as an example, this unique structure provides short Li⁺/electron diffusion pathways for electrochemical reactions, structural stability during cycling, and high electrical conductivity, leading to superior electrochemical performance. The resulting pomegranate‐like Fe₃O₄@N–C NCs possess a high specific capacity (1204.3 mA h g^?1 at 0.5 A g^?1 over 100 cycles), a stable cycle life (1063.0 mA h g^?1 at 1 A g^?1, 98.4% retention after 1000 cycles), and excellent rate capacities (606.0 mA h g^?1 at 10 A g^?1, 92.0% retention; 417.1 mA h g^?1 at 20 A g^?1, 91.7% retention after 1000 cycles).     

Rechargeable Iron–Sulfur Battery without Polysulfide Shuttling

Sulfur represents one of the most promising cathode materials for next‐generation batteries; however, the widely observed polysulfide dissolution/shuttling phenomenon in metal–sulfur redox chemistries has severely restricted their applications. Here it is demonstrated that when pairing the sulfur electrode with the iron metal anode, the inherent insolubility of iron sulfides renders the shuttling‐free nature of the Fe–S electrochemical reactions. Consequently, the sulfur electrode exhibits promising performance for Fe²⁺ storage, where a high capacity of ≈1050 mAh g^?1, low polarization of ≈0.16 V as well as stable cycling of 150 cycles are realized. The Fe–S redox mechanism is further revealed as an intriguing stepwise conversion of S₈ ? FeS₂ ? Fe₃S₄ ? FeS, where a low volume expansion of ≈32.6% and all‐solid‐state phase transitions facilitate the reaction reversibility. This study suggests an alternative direction to exploit sulfur electrodes in rechargeable transition metal–sulfur batteries.     

Direct Growth of Flower‐Like δ‐MnO2 on Three‐Dimensional Graphene for High‐Performance Rechargeable Li‐O2 Batteries

A challenge still remains to develop high‐performance and cost‐effective air electrode for Li‐O₂ batteries with high capacity, enhanced rate capability and long cycle life (100 times or above) despite recent advances in this field. In this work, a new design of binder‐free air electrode composed of three‐dimensional (3D) graphene (G) and flower‐like δ‐MnO₂ (3D‐G‐MnO₂) has been proposed. In this design, graphene and δ‐MnO₂ grow directly on the skeleton of Ni foam that inherits the interconnected 3D scaffold of Ni foam. Li‐O₂ batteries with 3D‐G‐MnO₂ electrode can yield a high discharge capacity of 3660 mAh g^?1 at 0.083 mA cm^?2. The battery can sustain 132 cycles at a capacity of 492 mAh g^?1 (1000 mAh g_carbon ^?1) with low overpotentials under a high current density of 0.333 mA cm^?2. A high average energy density of 1350 Wh Kg^?1 is maintained over 110 cycles at this high current density. The excellent catalytic activity of 3D‐G‐MnO₂ makes it an attractive air electrode for high‐performance Li‐O₂ batteries.     

Conductive Li3.08Cr0.02Si0.09V0.9O4 Anode Material: Novel “Zero‐Strain” Characteristic and Superior Electrochemical Li+ Storage

“Zero‐strain” compounds are ideal energy‐storage materials for long‐term cycling because they present negligible volume change and significantly reduce the mechanically induced deterioration during charging–discharging. However, the explored “zero‐strain” compounds are very limited, and their energy densities are low. Here, γ phase Li_3.08Cr_0.02Si_0.09V_0.9O₄ (γ‐LCSVO) is explored as an anode compound for lithium‐ion batteries, and surprisingly its “zero‐strain” Li⁺ storage during Li⁺ insertion–extraction is found through using various state‐of‐the‐art characterization techniques. Li⁺ sequentially inserts into the 4c(1) and 8d sites of γ‐LCSVO, but its maximum unit‐cell volume variation is only ≈0.18%, the smallest among the explored “zero‐strain” compounds. Its mean strain originating from Li⁺ insertion is only 0.07%. Consequently, both γ‐LCSVO nanowires (γ‐LCSVO‐NW) and micrometer‐sized particles (γ‐LCSVO‐MP) exhibit excellent cycling stability with 90.1% and 95.5% capacity retention after as long as 2000 cycles at 10C, respectively. Moreover, γ‐LCSVO‐NW and γ‐LCSVO‐MP respectively deliver large reversible capacities of 445.7 and 305.8 mAh g^?1 at 0.1C, and retain 251.2 and 78.4 mAh g^?1 at 10C. Additionally, γ‐LCSVO shows a suitably safe operating potential of ≈1.0 V, significantly lower than that of the famous “zero‐strain” Li₄Ti₅O₁₂ (≈1.6 V). These merits demonstrate that γ‐LCSVO can be a practical anode compound for stable, high‐energy, fast‐charging, and safe Li⁺ storage.     

Biomimetic Spider‐Web‐Like Composites for Enhanced Rate Capability and Cycle Life of Lithium Ion Battery Anodes

It is crucial to control the structure and composition of composite anode materials to enhance the cell performance of such anode materials for lithium ion batteries. Herein, a biomimetic strategy is demonstrated for the design of high performance anode materials, inspired by the structural characteristics and working principles of sticky spider‐webs. Hierarchically porous, sticky, spider‐web‐like multiwall carbon nanotube (MWCNT) networks are prepared through a process involving ozonation, ice‐templating assembly, and thermal treatment, thereby integrating the networks with γ‐Fe₂O₃ particles. The spider‐web‐like MWCNT/γ‐Fe₂O₃ composite network not only traps the active γ‐Fe₂O₃ materials tightly but also provides fast charge transport through the 3D internetworked pathways and the mechanical integrity. Consequently, the composite web shows a high capacity of ≈822 mA h g^?1 at 0.05 A g^?1, fast rate capability with ≈72.3% retention at rates from 0.05 to 1 A g^?1, and excellent cycling stability of >88% capacity retention after 310 cycles with a Coulombic efficiency >99%. These remarkable electrochemical performances are attributed to the complementarity of the 3D spider‐web‐like structure with the strong attachment of γ‐Fe₂O₃ particles on the sticky surface. This synthetic strategy offers an environmentally safe, simple, and cost‐effective avenue for the biomimetic design of high performance energy storage materials.     

P2‐K0.75[Ni1/3Mn2/3]O2 Cathode Material for High Power and Long Life Potassium‐Ion Batteries

Rationally designed P2‐K_0.75[Ni_1/3Mn_2/3]O₂ is introduced as a novel cathode material for potassium‐ion batteries (KIBs). P2‐K_0.75[Ni_1/3Mn_2/3]O₂ cathode material designed through electrochemical ion‐exchange from P2‐Na_2/3[Ni_1/3Mn_2/3]O₂ exhibits satisfactory electrode performances; 110 mAh g^?1 (20 mA g^?1) retaining 86% of capacity for 300 cycles and unexpectedly high reversible capacity of about 91 mAh g^?1 (1400 mA g^?1) with excellent capacity retention of 83% over 500 cycles. According to theoretical and experimental investigations, the overall potassium storage mechanism of P2‐K_0.75[Ni_1/3Mn_2/3]O₂ is revealed to be a single‐phase reaction with small lattice change upon charge and discharge, presenting the Ni^4+/2+ redox couple reaction. Such high power capability is possible through the facile K⁺ migration in the K_0.75[Ni_1/3Mn_2/3]O₂ structure with a low activation barrier energy of ≈210 meV. These findings indicate that P2‐K_0.75[Ni_1/3Mn_2/3]O₂ is a promising candidate cathode material for high‐rate and long‐life KIBs.     

Exploiting the Condensation Reactions of Acetophenone to Engineer Carbon‐Encapsulated Nb2O5 Nanocrystals for High‐Performance Li and Na Energy Storage Systems

Efficient synthetic methods to produce high‐performance electrode‐active materials are crucial for developing energy storage devices for large‐scale applications, such as hybrid supercapacitors (HSCs). Here, an effective approach to obtain controllable carbon‐encapsulated T‐Nb₂O₅ nanocrystals (NCs) is presented, based on the solvothermal treatment of NbCl₅ in acetophenone. Two separate condensation reactions of acetophenone generate an intimate and homogeneous mixture of Nb₂O₅ particles and 1,3,5‐triphenylbenzene (TPB), which acts as a unique carbon precursor. The electrochemical performance of the resulting composites as anode electrode materials can be tuned by varying the Nb₂O₅/TPB ratio. Remarkable performances are achieved for Li‐ion and Na‐ion energy storage systems at high charge–discharge rates (specific capacities of ≈90 mAh g^?1 at 100 C rate for lithium and ≈125 mAh g^?1 at 20 C for sodium). High energy and power densities are also achieved with Li‐ and Na‐ion HSC devices constructed by using the Nb₂O₅/C composites as anode and activated carbon (YPF‐50) as cathode, demonstrating the excellent electrochemical properties of the materials synthesized with this approach.     

New Binder‐Free Metal Phosphide–Carbon Felt Composite Anodes for Sodium‐Ion Battery

Metal phosphides are promising anode candidates for sodium‐ion batteries (SIBs) due to their high specific capacity and low operating potential but suffer from poor cycling stability caused by huge volume expansion and poor solid‐state ion transfer rate. Herein, a new strategy to grow a new class of mesoporous metal phosphide nanoarrays on carbon felt (CF) as binder‐free anodes for SIBs is reported. The resultant integrated electrodes demonstrate excellent cycling life up to 1000 times (>90% retention rate) and high rate capability of 535 mAh g^?1 at a current density of 4 A g^?1. Detailed characterization reveals that the synergistic effect of unique mesoporous structure for accommodating huge volume expansion during sodiation/desodiation process, ultrasmall primary particle size (≈10 nm) for providing larger electrode/electrolyte contact area and shorter ion diffusion distance, and 3D conductive networks for facilitating the electrochemical reaction, leads to the extraordinary battery performance. Remarkably, a full SIB using the new CoP₄/CF anode and a Na₃V₂(PO₄)₂F₃ cathode delivers an average operating voltage of ≈3.0 V, a reversible capacity of 553 mAh g^?1, and very high energy density of ≈280 Wh kg^?1 for SIBs. A flexible SIB with outstanding mechanical strength based on this binder‐free new anode is also demonstrated.     

Ultrafine Copper Nanopalm Tree‐Like Framework Decorated with Iron Oxide for Li‐Ion Battery Anodes with Exceptional Rate Capability and Cycling Stability

Ultrafine copper nanopalm tree‐like frameworks conformally decorated with iron oxide (Cu NPF@Fe₂O₃) are prepared by a facile electrodeposition method utilizing bromine ions as unique anisotropic growth catalysts. The formation mechanism and control over Cu growth are comprehensively investigated under various conditions to provide a guideline for fabricating a Cu nanoarchitecture via electrochemical methods. The optimized Cu NPFs exhibit ultrathin (<90 nm) and elongated (2–50 µm) branches with well‐interconnected and entangled features, which result in highly desirable attributes such as a large specific surface area (≈6.97 m² g^?1), free transfer pathway for Li⁺, and high electrical conductivity. The structural advantages of Cu NPF@Fe₂O₃ enhance the electrochemical kinetics, providing large reactivity, fast Li⁺/electron transfer, and structural stability during cycling, that lead to superior electrochemical Li storage performance. The resulting Cu NPF@Fe₂O₃ demonstrates a high specific capacity (919.5 mAh g^–1 at 0.1 C), long‐term stability (801.1 mAh g^–1 at 2 C, ≈120% retention after 500 cycles), and outstanding rate capability (630 mAh g^–1 at 10 C).     

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.     

Storage Capacity and Cycling Stability in Ge Anodes: Relationship of Anode Structure and Cycling Rate

Operando X‐ray diffraction (XRD) and X‐ray absorption spectroscopy (XAS) studies of Ge anodes are carried out to understand the effect of cycling rate on Ge phase transformation during charge/discharge process and to relate that effect to capacity. It is discovered that the formation of crystalline Li₁₅Ge₄ (c‐Li₁₅Ge₄) during lithiation is suppressed beyond a certain cycling rate. A very stable and reversible high capacity of ≈1800 mAh g^?1 can be attained up to 100 cycles at a slow C‐rate of C/21 when there is complete conversion of Ge anode into c‐Li₁₅Ge₄. When the C‐rate is increased to ≈C/10, the lithiation reaction is more heterogeneous and a relatively high capacity of ≈1000 mAh g^?1 is achieved with poorer electrochemical reversibility. An increase in C‐rate to C/5 and higher reduces the capacity (≈500 mAh g^?1) due to an impeded transformation from amorphous Li_xGe to c‐Li₁₅Ge₄, and yet improves the electrochemical reversibility. A proposed mechanism is presented to explain the C‐rate dependent phase transformations and the relationship of these to capacity fading. The operando XRD and XAS results provide new insights into the relationship between structural changes in Ge and battery capacity, which are important for guiding better design of high‐capacity anodes.     

A Novel α‐MoO3/Single‐Walled Carbon Nanohorns Composite as High‐Performance Anode Material for Fast‐Charging Lithium‐Ion Battery

Orthorhombic α‐MoO₃ is a potential anode material for lithium‐ion batteries due to its high theoretical capacity of 1100 mAh g^?1 and excellent structural stability. However, its intrinsic poor electronic conductivity and high volume expansion during the charge–discharge process impede it from achieving a high practical capacity. A novel composite of α‐MoO₃ nanobelts and single‐walled carbon nanohorns (SWCNHs) is synthesized by a facile microwave hydrothermal technique and demonstrated as a high‐performance anode material for lithium‐ion batteries. The α‐MoO₃/SWCNH composite displays superior electrochemical properties (654 mAh g^?1 at 1 C), excellent rate capability (275 mAh g^?1 at 5 C), and outstanding cycle life (capacity retention of >99% after 3000 cycles at 1 C) without any cracking of the electrode. The presence of SWCNHs in the composite enhances the electrochemical properties of α‐MoO₃ by acting as a lithium storage material, electronic conductive medium, and buffer against pulverization.     

Pseudo‐Zn–Air and Zn‐Ion Intercalation Dual Mechanisms to Realize High‐Areal Capacitance and Long‐Life Energy Storage in Aqueous Zn Battery

Aqueous zinc batteries are considered as promising alternatives to lithium ion batteries owing to their low cost and high safety. However, the developments of state‐of‐the‐art zinc‐ion batteries (ZIB) and zinc–air batteries (ZAB) are limited by the unsatisfied capacities and poor cycling stabilities, respectively. It is of significance in utilizing the long‐cycle life of ZIB and high capacity of ZAB to exploit advanced energy storage systems. Herein, a bulk composite of graphene oxide and vanadium oxide (V₅O₁₂·6H₂O) as cathode material for aqueous Zn batteries in a mild electrolyte is employed. The battery performance is demonstrated to arise from a combination of the reversible cations insertion/extraction in vanadium oxide and especially the electrochemical redox reactions on the surface functional groups of graphene oxide (named as pseudo‐Zn–air mechanism). Along with adjusting the hydroxyl content on the surface of graphene oxide, the specific capacity is significantly increased from 342 mAh g^?1 to a maximum of 496 mAh g^?1 at 100 mA g^?1. The surface‐controlled kinetics occurring in the bulk composite ensure a high areal capacity of 10.6 mAh cm^?2 at a mass loading of 26.5 mg cm^?2, and a capacity retention of 84.7% over 10 000 cycles at a high current density of 10 A g^?1.