Oxygen Vacancy Modulation of Bimetallic Oxynitride Anodes toward Advanced Li‐Ion Capacitors

Binary metal oxides (such as NiCo₂O₄) are regarded as attractive electrode materials for advanced energy storage devices since they offer more electrochemical activity and higher capacity than monometal oxide. However, the volume expansion and low electronic conductivity are the main bottleneck seriously hindering their application. To overcome these barriers, a novel strategy that introduces a bimetallic oxynitride layer (NiCoON) with oxygen vacancy to the surface of NiCo₂O₄ nanowires as an anode for Li‐ion capacitors (LICs) is proposed. The oxygen vacancy on the surface and the modulation of multiple valence states are investigated by the electron paramagnetic resonance, X‐ray photoelectron spectroscopy characterization, and first‐principles calculation. Benefiting from the merits of substantially improved electrical conductivity and increased concentration of active sites, the optimized NiCoON electrode delivers remarkable capacity (1855 mAh g^?1 at 0.2 A g^?1) and rate performance. The LIC device assembled by NiCoON anodes and N‐doped carbon nanowire cathodes delivers excellent rate capability, high energy density (148.5 Wh kg^?1), and outstanding power density (30 kW kg^?1). This study provides a new pathway for developing bimetallic oxides with an improved performance in electrochemical energy storage, conversion fields, and beyond.     

High Reversible Pseudocapacity in Mesoporous Yolk–Shell Anatase TiO2/TiO2(B) Microspheres Used as Anodes for Li‐Ion Batteries

As an anode material for lithium‐ion batteries, titanium dioxide (TiO₂) shows good gravimetric performance (336 mAh g^?1 for LiTiO₂) and excellent cyclability. To address the poor rate behavior, slow lithium‐ion (Li⁺) diffusion, and high irreversible capacity decay, TiO₂ nanomaterials with tuned phase compositions and morphologies are being investigated. Here, a promising material is prepared that comprises a mesoporous “yolk–shell” spherical morphology in which the core is anatase TiO₂ and the shell is TiO₂(B). The preparation employs a NaCl‐assisted solvothermal process and the electrochemical results indicate that the mesoporous yolk–shell microspheres have high specific reversible capacity at moderate current (330.0 mAh g^?1 at C/5), excellent rate performance (181.8 mAh g^?1 at 40C), and impressive cyclability (98% capacity retention after 500 cycles). The superior properties are attributed to the TiO₂(B) nanosheet shell, which provides additional active area to stabilize the pseudocapacity. In addition, the open mesoporous morphology improves diffusion of electrolyte throughout the electrode, thereby contributing directly to greatly improved rate capacity.     

A New Strategy to Effectively Suppress the Initial Capacity Fading of Iron Oxides by Reacting with LiBH4

In this work, a new facile and scalable strategy to effectively suppress the initial capacity fading of iron oxides is demonstrated by reacting with lithium borohydride (LiBH₄) to form a B‐containing nanocomposite. Multielement, multiphase B‐containing iron oxide nanocomposites are successfully prepared by ball‐milling Fe₂O₃ with LiBH₄, followed by a thermochemical reaction at 25–350 °C. The resulting products exhibit a remarkably superior electrochemical performance as anode materials for Li‐ion batteries (LIBs), including a high reversible capacity, good rate capability, and long cycling durability. When cycling is conducted at 100 mA g^?1, the sample prepared from Fe₂O₃–0.2LiBH₄ delivers an initial discharge capacity of 1387 mAh g^?1. After 200 cycles, the reversible capacity remains at 1148 mAh g^?1, which is significantly higher than that of pristine Fe₂O₃ (525 mAh g^?1) and Fe₃O₄ (552 mAh g^?1). At 2000 mA g^?1, a reversible capacity as high as 660 mAh g^?1 is obtained for the B‐containing nanocomposite. The remarkably improved electrochemical lithium storage performance can mainly be attributed to the enhanced surface reactivity, increased Li⁺ ion diffusivity, stabilized solid‐electrolyte interphase (SEI) film, and depressed particle pulverization and fracture, as measured by a series of compositional, structural, and electrochemical techniques.     

Enhanced Ionic/Electronic Transport in Nano‐TiO2/Sheared CNT Composite Electrode for Na+ Insertion‐based Hybrid Ion‐Capacitors

Ion‐insertion capacitors show promise to bridge the gap between supercapacitors of high power densities and batteries of high energy densities. While research efforts have primarily focused on Li⁺‐based capacitors (LICs), Na⁺‐based capacitors (SICs) are theoretically cheaper and more sustainable. Owing to the larger size of Na⁺ compared to Li⁺, finding high‐rate anode materials for SICs has been challenging. Herein, an SIC anode architecture is reported consisting of TiO₂ nanoparticles anchored on a sheared‐carbon nanotubes backbone (TiO₂/SCNT). The SCNT architecture provides advantages over other carbon architectures commonly used, such as reduced graphene oxide and CNT. In a half‐cell, the TiO₂/SCNT electrode shows a capacity of 267 mAh g^?1 at a 1 C charge/discharge rate and a capacity of 136 mAh g^?1 at 10 C while maintaining 87% of initial capacity over 1000 cycles. When combined with activated carbon (AC) in a full cell, an energy density and power density of 54.9 Wh kg^?1 and 1410 W kg^?1, respectively, are achieved while retaining a 90% capacity retention over 5000 cycles. The favorable rate capability, energy and power density, and durability of the electrode is attributed to the enhanced electronic and Na⁺ conductivity of the TiO₂/SCNT architecture.     

A New Strategy to Build a High‐Performance P′2‐Type Cathode Material through Titanium Doping for Sodium‐Ion Batteries

Herein, Ti⁴⁺ in P′2‐Na_0.67[(Mn_0.78Fe_0.22)_0.9Ti_0.1]O₂ is proposed as a new strategy for optimization of Mn‐based cathode materials for sodium‐ion batteries, which enables a single phase reaction during de‐/sodiation. The approach is to utilize the stronger Ti–O bond in the transition metal layers that can suppress the movements of Mn–O and Fe–O by sharing the oxygen with Ti by the sequence of Mn–O–Ti–O–Fe. It delivers a discharge capacity of ≈180 mAh g^?1 over 200 cycles (86% retention), with S‐shaped smooth charge–discharge curves associated with a small volume change during cycling. The single phase reaction with a small volume change is further confirmed by operando synchrotron X‐ray diffraction. The low activation barrier energy of ≈541 meV for Na⁺ diffusion is predicted using first‐principles calculations. As a result, Na_0.67[(Mn_0.78Fe_0.22)_0.9Ti_0.1]O₂ can deliver a high reversible capacity of ≈153 mAh g^?1 even at 5C (1.3 A g^?1), which corresponds to ≈85% of the capacity at 0.1C (26 mA g^?1). The nature of the sodium storage mechanism governing the ultrahigh electrode performance in a full cell with a hard carbon anode is elucidated, revealing the excellent cyclability and good retention (≈80%) for 500 cycles (111 mAh g^?1) at 5C (1.3 A g^?1).     

Two Birds with One Stone: Metal–Organic Framework Derived Micro‐/Nanostructured Ni2P/Ni Hybrids Embedded in Porous Carbon for Electrocatalysis and Energy Storage

The construction of bifunctional electrode materials for hydrogen evolution reaction (HER) and lithium‐ion batteries (LIBs) has been a hot topic of research. Herein, metal–organic frameworks (MOFs) derived micro‐/nanostructured Ni₂P/Ni hybrids with a porous carbon coating (denoted as Ni₂P/Ni@C) are prepared using a feasible pyrolysis–phosphidation strategy. On the one hand, the optimal Ni₂P/Ni@C catalyst exhibits superior HER performance with a low overpotential of 149 mV versus a reversible hydrogen electrode (RHE) at 10 mA cm^?2 and excellent durability. The density functional theory computations verify that the strong synergistic effect between Ni₂P and Ni could optimize the electronic structure, thus rendering the enhanced electrocatalytic performance. On the other hand, the Ni₂P/Ni@C electrode displays a reversible capacity of 597 mAh g^?1 after 1000 cycles at 1000 mA g^?1 and improved rate capability as an anode for LIBs, owing to the well‐organized micro‐/nanostructure and conductive Ni core. In addition, the electrochemical reaction mechanism of the Ni₂P/Ni@C electrode upon lithiation/delithiation is investigated in detail via ex situ X‐ray powder diffraction and X‐ray photoelectron spectroscopy methods. It is expected that the facile and controllable approach can be extended to fabricate other MOF‐based metal phosphides/metal hybrids for electrochemical energy storage and conversion systems.     

Heterostructured Nanocube‐Shaped Binary Sulfide (SnCo)S2 Interlaced with S‐Doped Graphene as a High‐Performance Anode for Advanced Na+ Batteries

Heterostructuring electrodes with multiple electroactive and inactive supporting components to simultaneously satisfy electrochemical and structural requirements has recently been identified as a viable pathway to achieve high‐capacity and durable sodium‐ion batteries (SIBs). Here, a new design of heterostructured SIB anode is reported consisting of double metal‐sulfide (SnCo)S₂ nanocubes interlaced with 2D sulfur‐doped graphene (SG) nanosheets. The heterostructured (SnCo)S₂/SG nanocubes exhibit an excellent rate capability (469 mAh g^?1 at 10.0 A g^?1) and durability (5000 cycles, 487 mAh g^?1 at 5.0 A g^?1, 92.6% capacity retention). In situ X‐ray diffraction reveals that the (SnCo)S₂/SG anode undergoes a six‐stage Na⁺ storage mechanism of combined intercalation, conversion, and alloying reactions. The first‐principle density functional theory calculations suggest high concentration of p–n heterojunctions at SnS₂/CoS₂ interfaces responsible for the high rate performance, while in situ transmission electron microscopy unveils that the interlacing and elastic SG nanosheets play a key role in extending the cycle life.     

Watermelon‐Like Structured SiOx–TiO2@C Nanocomposite as a High‐Performance Lithium‐Ion Battery Anode

A unique watermelon‐like structured SiO_x–TiO₂@C nanocomposite is synthesized by a scalable sol–gel method combined with carbon coating process. Ultrafine TiO₂ nanocrystals are uniformly embedded inside SiO_x particles, forming SiO_x–TiO₂ dual‐phase cores, which are coated with outer carbon shells. The incorporation of TiO₂ component can effectively enhance the electronic and lithium ionic conductivities inside the SiO_x particles, release the structure stress caused by alloying/dealloying of Si component and maximize the capacity utilization by modifying the Si–O bond feature and decreasing the O/Si ratio (x‐value). The synergetic combination of these advantages enables the synthesized SiO_x–TiO₂@C nanocomposite to have excellent electrochemical performances, including high specific capacity, excellent rate capability, and stable long‐term cycleability. A stable specific capacity of ≈910 mAh g^?1 is achieved after 200 cycles at the current density of 0.1 A g^?1 and ≈700 mAh g^?1 at 1 A g^?1 for over 600 cycles. These results suggest a great promise of the proposed particle architecture, which may have potential applications in the improvement of various energy storage materials.     

Rambutan‐Like Hybrid Hollow Spheres of Carbon Confined Co3O4 Nanoparticles as Advanced Anode Materials for Sodium‐Ion Batteries

Transition metal oxides, possessing high theoretical specific capacities, are promising anode materials for sodium‐ion batteries. However, the sluggish sodiation/desodiation kinetics and poor structural stability restrict their electrochemical performance. To achieve high and fast Na storage capability, in this work, rambutan‐like hybrid hollow spheres of carbon confined Co₃O₄ nanoparticles are synthesized by a facile one‐pot hydrothermal treatment with postannealing. The hierarchy hollow structure with ultrafine Co₃O₄ nanoparticles embedded in the continuous carbon matrix enables greatly enhanced structural stability and fast electrode kinetics. When tested in sodium‐ion batteries, the hollow structured composite electrode exhibits an outstandingly high reversible specific capacity of 712 mAh g^?1 at a current density of 0.1 A g^?1, and retains a capacity of 223 mAh g^?1 even at a large current density of 5 A g^?1. Besides the superior Na storage capability, good cycle performance is demonstrated for the composite electrode with 74.5% capacity retention after 500 cycles, suggesting promising application in advanced sodium‐ion batteries.     

Copper Thiophosphate (Cu3PS4) as Electrode for Sodium‐Ion Batteries with Ether Electrolyte

Lithium and sodium thiophosphates (and related compounds) have recently attracted attention because of their potential use as solid electrolytes in solid‐state batteries. These compounds, however, exhibit only limited stability in practice as they react with the electrodes. The decomposition products partially remain redox active hence leading to excess capacity. The redox activity of thiophosphates is explicitly used to act as electrode for sodium‐ion batteries. Copper thiophosphate (Cu₃PS₄) is used as a model system. The storage behavior between 0.01 and 2.5 V versus Na⁺/Na is studied in half cells using different electrolytes with 1 m NaPF₆ in diglyme showing the best result. Cu₃PS₄ shows highly reversible charge storage with capacities of about 580 mAh g^?1 for more than 200 cycles @120 mA g^?1 and about 450 mAh g^?1 for 1400 cycles @1 A g^?1. The redox behavior is studied by operando X‐ray diffraction and X‐ray photoelectron spectroscopy. During initial sodiation, Cu₃PS₄ undergoes a conversion reaction including the formation of Cu and Na₂S. During cycling, the redox activity seems dominated by sulfur. Interestingly, the capacity of Cu₃PS₄ for lithium storage is smaller, leading to about 170 mAh g^?1 after 200 cycles. The results demonstrate that thiophosphates can lead to reversible charge storage over several hundred cycles without any notable capacity decay.     

FeP Quantum Dots Confined in Carbon‐Nanotube‐Grafted P‐Doped Carbon Octahedra for High‐Rate Sodium Storage and Full‐Cell Applications

Transition metal phosphides (TMPs) possess high theoretical sodium storage capacities, but suffer from poor rate performance, due to their intrinsic low conductivity and large volume expansion upon sodiation/desodiation. Compositing TMPs with carbon materials or downsizing their feature size are recognized as efficient approaches to address the above issues. Nevertheless the surface‐controlled capacitive behavior is generally dominated, which inevitably compromises the charge/discharge platform, and decreases the operational potential window in full‐cell constructions. In this work, a novel architecture (FeP@OCF) with FeP quantum dots confined in P‐doped 3D octahedral carbon framework/carbon nanotube is rationally designed. Such structure enables a simultaneous enhancement on the diffusion‐controlled capacity in the platform region (2.3 folds), and the surface‐controlled capacity in the slope region (2.9 folds) as compared to that of pure FeP. As a result, an excellent reversible capacity (674 mAh g^?1@ 0.1 A g^?1) and a record high‐rate performance (262 mAh g^?1 @ 20 A g^?1) are achieved. A full‐cell FeP@OCF// Na₃V₂(PO₄)₃ is also constructed showing an outstandingly high energy density of 185 Wh kg^?1 (based on the total mass of active materials in both electrodes), which outperforms the state‐of‐the art TMP‐based sodium‐ion battery full cells.     

Fe3O4 Nanoparticles Embedded in Uniform Mesoporous Carbon Spheres for Superior High‐Rate Battery Applications

Robust composite structures consisting of Fe₃O₄ nanoparticles (～5 nm) embedded in mesoporous carbon spheres with an average size of about 70 nm (IONP@mC) are synthesized by a facile two‐step method: uniform Fe₃O₄ nanoparticles are first synthesized followed by a post‐synthetic low‐temperature hydrothermal step to encapsulate them in mesoporous carbon spheres. Instead of graphene which has been extensively reported for use in high‐rate battery applications as a carbonaceous material combined with metal oxides mesoporous carbon is chosen to enhance the overall performances. The interconnecting pores facilitate the penetration of electrolyte leading to direct contact between electrochemically active Fe₃O₄ and lithium ion‐carrying electrolyte greatly facilitating lithium ion transportation. The interconnecting carbon framework provides continuous 3D electron transportation routes. The anodes fabricated from IONP@mC are cycled under high current densities ranging from 500 to 10 000 mA g^?1. A high reversible capacity of 271 mAh g^?1 is reached at 10 000 mAh g^?1 demonstrating its superior high rate performance.     

Hydrated Layered Vanadium Oxide as a Highly Reversible Cathode for Rechargeable Aqueous Zinc Batteries

Rechargeable aqueous zinc batteries have gained considerable attention for large‐scale energy storage systems because of their low cost and high safety, but they suffer from limitations in cycling stability and energy density with advanced cathode materials. Here, a high‐performance V₅O₁₂·6H₂O (VOH) nanobelt cathode uniformly located on a stainless‐steel substrate via a facile electrodeposition technique is reported. We show that the hydrated layered VOH cathode enables highly reversible and ultrafast Zn²⁺ cation (de)intercalation processes, as confirmed by various electrochemical, X‐ray diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy analyses. It is demonstrated that the binder‐free VOH cathode can deliver a discharge capacity of 354.8 mAh g^?1 at 0.5 A g^?1 with a high initial Coulombic efficiency of 99.5%, a high energy density of 194 Wh kg^?1 at 2100 W kg^?1, and a long cycle life with a capacity retention of 94% over 1000 cycles. In addition, a flexible quasi‐solid‐state Zn–VOH battery is constructed, achieving a reversible capacity of ≈300 mAh g^?1 with a capacity retention of 96% after 50 cycles and displaying excellent electrochemical behaviors under different bending states. This work sheds light on the development of rechargeable aqueous zinc batteries for stationary grid storage applications or flexible energy storage devices.     

Electrochemical Mechanism Investigation of Cu2MoS4 Hollow Nanospheres for Fast and Stable Sodium Ion Storage

Sodium ion batteries (SIBs) are promising alternatives to lithium ion batteries with advantages of cost effectiveness. Metal sulfides as emerging SIB anodes have relatively high electronic conductivity and high theoretical capacity, however, large volume change during electrochemical testing often leads to unsatisfactory electrochemical performance. Herein bimetallic sulfide Cu₂MoS₄ (CMS) with layered crystal structures are prepared with glucose addition (CMS1), resulting in the formation of hollow nanospheres that endow large interlayer spacing, benefitting the rate performance and cycling stability. The electrochemical mechanisms of CMS1 are investigated using ex situ X‐ray photoelectron spectroscopy and in situ X‐ray absorption spectroscopy, revealing the conversion‐based mechanism in carbonate electrolyte and intercalation‐based mechanism in ether‐electrolyte, thus allowing fast and reversible Na⁺ storage. With further introduction of reduced graphene oxide (rGO), CMS1–rGO composites are obtained, maintaining the hollow structure of CMS1. CMS1–rGO delivers excellent rate performance (258 mAh g^?1 at 50 mA g^?1 and 131.9 mAh g^?1 at 5000 mA g^?1) and notably enhanced cycling stability (95.6% after 2000 cycles). A full cell SIB is assembled by coupling CMS1–rGO with Na₃V₂(PO₄)₃‐based cathode, delivering excellent cycling stability (75.5% after 500 cycles). The excellent rate performance and cycling stability emphasize the advantage of CMS1–rGO toward advanced SIB full cells assembly.     

Solid‐State Plastic Crystal Electrolytes: Effective Protection Interlayers for Sulfide‐Based All‐Solid‐State Lithium Metal Batteries

All‐solid‐state lithium metal batteries (ASSLMBs) have attracted significant attention due to their superior safety and high energy density. However, little success has been made in adopting Li metal anodes in sulfide electrolyte (SE)‐based ASSLMBs. The main challenges are the remarkable interfacial reactions and Li dendrite formation between Li metal and SEs. In this work, a solid‐state plastic crystal electrolyte (PCE) is engineered as an interlayer in SE‐based ASSLMBs. It is demonstrated that the PCE interlayer can prevent the interfacial reactions and lithium dendrite formation between SEs and Li metal. As a result, ASSLMBs with LiFePO₄ exhibit a high initial capacity of 148 mAh g^?1 at 0.1 C and 131 mAh g^?1 at 0.5 C (1 C = 170 mA g^?1), which remains at 122 mAh g^?1 after 120 cycles at 0.5 C. All‐solid‐state Li‐S batteries based on the polyacrylonitrile‐sulfur composite are also demonstrated, showing an initial capacity of 1682 mAh g^?1. The second discharge capacity of 890 mAh g^?1 keeps at 775 mAh g^?1 after 100 cycles. This work provides a new avenue to address the interfacial challenges between Li metal and SEs, enabling the successful adoption of Li metal in SE‐based ASSLMBs with high energy density.     

Interfacial Bonding of Metal‐Sulfides with Double Carbon for Improving Reversibility of Advanced Alkali‐Ion Batteries

Engineering interfacial properties of metal‐sulfides toward excellent electrochemical capability is imperative for advanced energy‐storage materials. However, they still suffer from an unclear mechanism of capacity fading, along with ineffective physical–chemical evolution. Herein, a highly‐effective Sb₂S₃ with double carbon is designed with interfacial Sb? C bonds and double carbon, which boosts promoting of ion transferring and alleviates the separation of both active phases (Sb, S). Through “voltage‐cutting” manners, the key elements of capacity improvement about phase transitions are further determined. As expected, even at 5.0 A g^?1, the lithium‐storage capacity remains about 674 mAh g^?1. Utilized as sodium ion battery (SIB) anode, the rate capacity still reaches up to 366 mAh g^?1 at 3.0 A g^?1, much larger than that of Sb₂S₃. Obtaining the full cell of Ni–Fe Prussian blue analog versus M‐Sb₂S₃@DC, the reversible capacity is 330 mAh g^?1 at 0.5 A g^?1. Supported by kinetic analysis, the excellent rate properties are determined by the surface‐controlling behaviors, mainly resulting from the decreased capacitive resistance and improved ion moving. Furthermore, the reassembling evolution of active phases is revealed in detail by ex situ techniques. This work is expected to offer significant insights into interfacial evolutions toward advanced energy‐storage systems.     

Temperature‐Mediated Engineering of Graphdiyne Framework Enabling High‐Performance Potassium Storage

Graphdiyne (GDY), an emerging type of carbon allotropes, possesses fascinating electrical, chemical, and mechanical properties to readily spark energy applications in the realm of Li‐ion and Na‐ion batteries. Nevertheless, rational design of GDY architectures targeting advanced K‐ion storage has rarely been reported to date. Herein, the first example of synthesizing GDY frameworks in a scalable fashion to realize superb potassium storage for high‐performance K‐ion battery (KIB) anodes is showcased. To begin with, first principles calculations provide theoretical guidances for analyzing the intrinsic potassium storage capability of GDY. Meanwhile, the specific capacity is predicted to be as high as 620 mAh g^?1, which is considerably augmented as compared with graphite (278 mAh g^?1). Experimental tests then reveal that prepared GDY framework indeed harvests excellent electrochemical performance as a KIB anode, achieving high specific capacity (≈505 mAh g^?1 at 50 mA g^?1), outstanding rate performance (150 mAh g^?1 at 5000 mA g^?1) and favorable cycling stability (a high capacity retention of over 90% after 2000 cycles at 1000 mA g^?1). Furthermore, kinetic analysis reveals that capacitive effect mainly accounts for the K‐ion storage, with operando Raman spectroscopy/ex situ X‐ray photoelectron spectroscopy identifying good electrochemical reversibility of GDY.     

Carbon Nanotubes Rooted in Porous Ternary Metal Sulfide@N/S‐Doped Carbon Dodecahedron: Bimetal‐Organic‐Frameworks Derivation and Electrochemical Application for High‐Capacity and Long‐Life Lithium‐Ion Batteries

Lithium ion battery is the predominant power source for portable electronic devices, electrical vehicles, and back‐up electricity storage units for clean and renewable energies. High‐capacity and long‐life electrode materials are essential for the next‐generation Li‐ion battery with high energy density. Here bimetal‐organic‐frameworks synthesis of Co_0.4Zn_0.19S@N and S codoped carbon dodecahedron is shown with rooted carbon nanotubes (Co‐Zn‐S@N‐S‐C‐CNT) for high‐performance Li‐ion battery application. Benefiting from the synergetic effect of two metal sulfide species for Li‐storage at different voltages, mesoporous dodecahedron structure, N and S codoped carbon overlayer and deep‐rooted CNTs network, the product exhibits a larger‐than‐theoretical reversible Li‐storage capacity of 941 mAh g^?1 after 250 cycles at 100 mA g^?1 and excellent high‐rate capability (734, 591, 505 mAh g^?1 after 500 cycles at large current densities of 1, 2, and 5 A g^?1 , respectively).     

Carbon Coated Fe3O4 Nanospindles as a Superior Anode Material for Lithium‐Ion Batteries

Carbon‐coated Fe₃O₄ nanospindles are synthesized by partial reduction of monodispersed hematite nanospindles with carbon coatings, and investigated with scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, and electrochemical experiments. The Fe₃O₄? C nanospindles show high reversible capacity (～745 mA h g^?1 at C/5 and ～600 mA h g^?1 at C/2), high coulombic efficiency in the first cycle, as well as significantly enhanced cycling performance and high rate capability compared with bare hematite spindles and commercial magnetite particles. The improvements can be attributed to the uniform and continuous carbon coating layers, which have several functions, including: i) maintaining the integrity of particles, ii) increasing the electronic conductivity of electrodes leading to the formation of uniform and thin solid electrolyte interphase (SEI) films on the surface, and iii) stabilizing the as‐formed SEI films. The results give clear evidence of the utility of carbon coatings to improve the electrochemical performance of nanostructured transition metal oxides as superior anode materials for lithium‐ion batteries.     

Three Electron Reversible Redox Reaction in Sodium Vanadium Chromium Phosphate as a High‐Energy‐Density Cathode for Sodium‐Ion Batteries

A sodium‐ion battery operating at room temperature is of great interest for large‐scale stationary energy storage because of its intrinsic cost advantage. However, the development of a high capacity cathode with high energy density remains a great challenge. In this work, sodium super ionic conductor‐structured Na₃V_2?xCr_x(PO₄)₃ is achieved through the sol–gel method; Na₃V_1.5Cr_0.5(PO₄)₃ is demonstrated to have a capacity of 150 mAh g^?1 with reversible three‐electron redox reactions after insertion of a Na⁺, consistent with the redox couples of V²⁺/³⁺, V³⁺/⁴⁺, and V⁴⁺/⁵⁺. Moreover, a symmetric sodium‐ion full cell utilizing Na₃V_1.5Cr_0.5(PO₄)₃ as both the cathode and anode exhibits an excellent rate capability and cyclability with a capacity of 70 mAh g^?1 at 1 A g^?1. Ex situ X‐ray diffraction analysis and in situ impedance measurements are performed to reveal the sodium storage mechanism and the structural evolution during cycling.