Theoretical Specific Capacity Research Articles

A Minireview of Multimetallic Iron‐Based Oxides for Supercapacitive Negative Electrode Materials

The serious mismatch between the positive and negative electrodes of supercapacitors (SCs) makes it imperative to develop high‐performance negative electrode materials. Among them, multimetallic iron‐based oxides (MIBOs) are intensively investigated attributed to their high theoretical specific capacitance, wide operating potential window, copious electrochemical active sites, variable metal oxidation states, and abundant redox centers. This paper briefly introduces some essential information on SCs and the most common synthesis methods of MIBOs. Also, the research progress of several important MIBOs and their composites is discussed. Finally, the existing problems and challenges of MIBOs are summarized and future outlooks are likewise proposed.

Facile synthesis of Cu2O nano-microspheres anode for lithium-ion batteries

Transition metal oxide anode materials exhibit high theoretical specific capacities and can meet the energy density requirements through reasonable design. In this work, a facile wet-chemical method to fabricate Cu2O nano-microspheres anode for lithium-ion batteries with controllable size varied from 0.4 ∼ 1.2 μm is introduced, which basically using copper acetate as copper precursor and ascorbic acid as reducing agent. The solvent composition (DI water only or DI water:Ethanol = 1:1), solution alkalinity (amount of NaOH input), and synthesis temperature are investigated as factors affecting the size and morphology of Cu2O nano-microspheres. The samples are characterized by X-ray diffraction, transmission electron microscope and scanning electron microscope. Nanoparticle cluster structure is observed in the reaction product with the bi-solvent system. With the optimized synthesis condition, the prepared Cu2O anode (size of ∼ 455 ± 41 nm) delivers an initial discharge capacity of 539 mAh/g at a current density of 0.5C, 100 cycles of cyclic discharge at 0.5C with a capacity retention rate of 84.73 %. At the current density of 2C, the specific capacity is 347 mAh/g. Even at a large current density of 5C, the specific capacity is still as high as 219 mAh/g, indicating good rate capability.

“Dead Lithium” Formation and Mitigation Strategies in Anode‐Free Li‐Metal Batteries

AbstractThin lithium‐metal foil is a promising anode material for next‐generation batteries due to its high theoretical specific capacity and low negative potential. However, safety issues linked to dendrite growth, low‐capacity retention, and short cycle life pose significant challenges. Also, it has excess energy that must be minimized in order to reduce the battery costs. To limit excess lithium, practical lithium metal batteries need a negative‐to‐positive electrode ratio as close to 1 : 1 as possible, which can be achieved through limiting excess lithium or using an “anode‐free” metal battery design. However, both designs experience fast capacity fade due to the irreversible loss of active lithium in the cell, caused by the formation of the solid electrolyte interphase (SEI), dendrite formation and “dead lithium,” – refers to lithium that has lost its electronic connection to the anode electrode or current collector. The presence of dead lithium in batteries negatively affects their capacity and lifespan, while also raising internal resistance and generating heat. Additionally, dead lithium encourages the growth of lithium dendrites, which poses significant safety hazards. Within this fundamental review, we thoroughly address the phenomenon of dead lithium formation, assessing its origins, implications on battery performance, and possible strategies for mitigation. The transition towards environmentally friendly and high‐performance metal batteries could be accelerated by effectively tackling the challenge posed by dead lithium.

Modified organic-template synthesis of Co3O4 as high-performance electrode with superior capacitive storage

Electrochemical supercapacitors (ESCs) have great potential in many energy storage technologies because of their outstanding performance. Transition metal oxides with high theoretical specific capacity are promising for ESC electrodes, but their low utilization of capacitive active components and poor cycle stability limit their practical usage. Herein, we have prepared a novel cobalt metal cyanometallic framework (Co-CMF) and further thermally modified it to easily produce a Co3O4 positive electrode with excellent capacitive storage performance. As a result, the electrode exhibits fast, stable and reversible electrochemical performance with a high specific capacity of 241.9 C g−1 and long-term stability with as low as 0.004 % decline per cycle in the 5 M KOH aqueous electrolyte, which are confirmed by in-situ Raman investigation and electrochemical tests, further demonstrating that this modified approach provides a new idea for the development of promising high-capacity electrode materials for large-scale energy storage.

Ca/Li Synergetic-Doped Na0.67Ni0.33Mn0.67O2 to Realize P2-O2 Phase Transition Suppression for High-Performance Sodium-Ion Batteries.

P2-type layered transition metal oxide Na0.67Ni0.33Mn0.67O2 is considered as a promising cathode for advanced sodium-ion batteries due to its high theoretical specific capacity. However, the P2-type cathode suffers severe P2-O2 phase transition during cycling process, resulting unsatisfactory cyclic stability and rate capability. Herein, a Ca/Li co-doped P2-type Na0.62Ca0.05Ni0.33Mn0.57Li0.10O2 (NCNMLO) cathode material was synthesized through a simple sol-gel method. With the synergistic effect of Ca-doping at Na sites and Li substitution at transition metal (TM) sites, the cathode achieves an excellent electrochemical performance due to the inhibited P2-O2 phase transition and improved ion diffusion with Na+/vacancy disordering arrangement. The NCNMLO cathode exhibits a good cyclic stability with 70.8 % of capacity retention at 1 C after 200 cycles and excellent rate capability with 40.1 mAh g-1 at 20 C. The dual sites doping strategy provides an effective and simple approach for designing high-performance layered oxide cathode materials for sodium-ion batteries.

High-entropy doping for high-voltage LiCoO2 with enhanced electrochemical performances

Lithium cobalt oxide (LiCoO2), as a pioneering layered oxide cathode material for lithium-ion batteries (LIBs), possesses exceptional theoretical specific capacity and cycling stability, positioning it as a leading candidate for commercial LIB applications. Boosting the upper-limit of charge voltage of LiCoO2 is a promising strategy to increase the capacity of batteries, vital for advancing energy storage solutions from portable electronics to electric vehicles. Nevertheless, hybrid redox reactions at high voltages speed up oxygen evolution, electrolyte decomposition, and irreversible phase transitions, ultimately causing rapid capacity fading.To address these challenges, we present a novel approach to enhance the structural stability and electrochemical performances of LiCoO2 cathode via La-Al-Mg-Y high-entropy doping. This strategy significantly improves the high-voltage cycling stability of the cathode material by retaining 72.5 % of its initial capacity after 500 cycles at 5 C under 4.6 V. Furthermore, the structural change caused by the phase transition between the O3 and H1-3 phases is remarkably suppressed. This advancement in LIB cathode technology paves the way for the development of high performance batteries and it is crucial for meeting the growing demand for sustainable energy storage.

Carbonaceous C@FeS Flow Electrode for Electrochemcal Capacitive Deionization Application

FeS has attracted much attention in the field of capacitive deionisation of flow electrodes due to its high theoretical specific capacity and wide range of sources. However, it usually exhibits frustrating performance due to its inherent low conductivity and volume expansion during charging and discharging. Herein, we successfully prepared calcium alginate-coated FeS carbon spheres (C@FeS) with a hollow nanosphere structure by a combination of sol-gel and solid-phase sintering using sodium alginate as a carbon source. This unique hollow structure provides enough space for the expansion of FeS and enhances the stability of the sulfide; meanwhile, the internal “surface-line-surface” structure not only facilitates the migration and charge transfer of ions inside, but also provides more active electrosorption sites. When assembled as the flow electrode of the flow electrode capacitive deionisation (FCDI) system, the desalination capacity of the electrode was improved from 25.32 mg g−1 to 53.12 mg g−1. Therefore, the C@FeS composite is expected to provide a new candidate electrode material for the FCDI system, which will make the future desalination process more cost-effective and efficient.

Inhibiting irreversible Zn2+/H+ co-insertion chemistry in aqueous zinc-MoOx batteries for enhanced capacity stability

Rechargeable aqueous Zn-MoOx batteries are promising energy storage devices with high theoretical specific capacity and low cost. However, MoO3 cathodes suffer drastic capacity decay during the initial discharging/charging process in conventional electrolytes, resulting in a short cycle life and challenging the development of Zn-MoOx batteries. Here we comprehensively investigate the dissolution mechanism of MoO3 cathodes and innovatively introduce a polymer to inhibit the irreversible processes. Our findings reveal that this capacity decay originates from the irreversible Zn2+/H+ co-intercalation/extraction process in aqueous electrolytes. Even worse, during Zn2+ intercalation, the formed ZnxMoO3−x intermediate phase with lower valence states (Mo5+/Mo4+) experiences severe dissolution in aqueous environments. To address these challenges, we developed a first instance of coating a polyaniline (PANI) shell around the MoO3 nanorod effectively inhibiting these irreversible processes and protecting structural integrity during long-term cycling. Detailed structural analysis and theoretical calculations indicate that =N– groups in PANI@MoO3−x simultaneously weaken H+ adsorption and enhance Zn2+ adsorption, which endowed the PANI@MoO3−x cathode with reversible Zn2+/H+ intercalation/extraction. Consequently, the obtained PANI@MoO3−x cathode delivers an excellent discharge capacity of 316.86 mA h g−1 at 0.1 A g−1 and prolonged cycling stability of 75.49% capacity retention after 1000 cycles at 5 A g−1. This work addresses the critical issues associated with MoO3 cathodes and significantly advances the understanding of competitive multi-ion energy storage mechanisms in aqueous Zn-MoO3 batteries.

Analysis of interlayer dependency of MoS2/g-C3N4 heterostructure as an anode material for sodium-ion batteries

In this present work, we explore the effectiveness of layered molybdenum disulfide (2H-MoS2) and graphitic carbon nitride (g-C3N4) heterostructure as anode for Sodium-Ion Batteries (SIBs) by using first principles analysis. To study the anode properties, we varied the interlayer distance between 2H-MoS2/g-C3N4 as 3Å, 6Å, 9Å,12 Å, and 14 Å between MoS2 as substrate and g-C3N4 as top layer. The fundamental properties, such as structural stability and electronic structure were analysed for the respective systems. The adsorption kinetics of Na ion on the g-C3N4 layer were analysed by performing molecular dynamics (MD) simulations to understand the adsorption mechanism better. Our results showed that the interlayer distance of 6 Å with formation energy of −4.31 eV, the theoretical specific capacity value of 765.32 mAhg−1, the average electrode potential is between 0.8 and 1.3 V and the adsorption energy of −2.16 eV is suitable for MoS2/g-C3N4 based anodes for Na ion batteries.

Advanced Li-S Battery Configuration Featuring Sulfur-Coated Separator and Interwoven rGO/CNT Fabric Current Collector.

The development of lithium-sulfur batteries (LSBs) marks a crucial milestone in advancing energy storage solutions essential for sustainable energy transitions. With high theoretical specific capacity, cost-effectiveness, and reduced ecological footprint, LSBs promise to enhance electric vehicle ranges, extend portable electronics' operational times, and stabilize grids integrated with renewable energy. However, challenges like complex processing, electrode instability, and poor cycling stability hinder their commercialization. This study introduces a novel battery design that addresses these issues by coating sulfur directly onto the separator instead of the current collector, demonstrating that active sulfur can be effectively utilized without being incorporated into the electrode structure. Using an interwoven substrate made from carbon nanotube (CNT) fabric adorned with reduced graphene oxide (rGO), this setup enhances manufacturing scalability, supports optimal sulfur utilization, and improves battery performance. The rGO decoration provides multiple highly conductive polysulfide trapping sites, enhancing active material reutilization, while the flexibility and mechanical strength of CNT fabric contribute to electrode integrity. This combination boosts electrical conductivity and polysulfide-capturing capability, effectively managing migrating sulfur species during charge-discharge cycles and mitigating sulfur loss and polysulfide shuttling. The results demonstrate superior cycling stability and efficiency, highlighting the potential of this approach in advancing LSB technology.

Spherical NiS2/Ni17S18–C accelerates ion transport and enhances kinetics for lithium-sulfur battery host material

Transition metal sulfides exhibit notable catalytic activity and possess a high theoretical specific capacity as host materials in lithium-sulfur batteries. However, their restricted conductivity and sluggish Li+ transport hinder their broader application. In this research, we developed a Ni-based metal-organic framework (Ni-MOF) using nitrogen-containing benzimidazole and coupled it with a highly conductive carbon nanotube (CNT) to form NixSy (NiS2–Ni17S18)–C/CNT. The N-doped carbon skeleton derived from the MOF enhances the adsorption and chemical anchoring of polysulfides, while the even distribution of NiS2 and Ni17S18 enhances the redox reaction kinetics. Additionally, the conductive CNT networks aid in rapid electron transport, resulting in improved sulfur utilization. Consequently, the NixSy-C/CNT@S electrode demonstrates an impressive initial specific capacity of 1468 mAh g−1 at 0.2C and maintains 904.4 mAh g−1 after 200 cycles. Moreover, NixSy-C/CNT@S displays exceptional cycle stability, with a capacity retention of 76.20 % and a decay rate of only 0.05 % per cycle after 500 cycles at 0.5C. This study paves the way for the development and synthesis of cathode materials with outstanding electrochemical performance in LSBs.

Review on polymer electrolytes for lithium‐sulfurized polyacrylonitrile batteries

AbstractLithium‐sulfur (Li‐S) batteries are deemed as the next generation of energy storage devices due to high theoretical specific capacity (1675 mAh g−1) and energy density (2600 Wh kg−1). However, the commercial application has always been constrained by lithium polysulfide (LiPSs) shuttling effects and still has a long way to go. Sulfurized polyacrylonitrile (SPAN) is a promising alternative candidate to replace traditional sulfur cathode and is conducive to eliminating LiPSs by realizing “solid‐solid” direct conversion in conventional carbonate electrolytes. However, an over 25% irreversible capacity loss is exhibited inevitably in the first discharge process, the inherent structure of SPAN and the related reaction mechanism remain unclear. In this review, the structure characteristics and electrochemical behaviors of SPAN are summarized for better interpreting current knowledge and favoring the design of high performance materials. In the past few decades, many problems in traditional Li‐S batteries have been solved by improving electrolytes. Polymer electrolytes (PEs) have been widely used due to structural designability, multi‐functionality, exceptional chemical stability, and excellent processability. Surprisingly, the relevant researches on PEs compatible with SPAN remains limited currently. Therefore, the recent modification strategies of gel polymer electrolytes and solid polymer electrolytes in Li‐SPAN batteries are introduced in terms of Li+ transfer and interface engineering, the design principles are concluded, the specific challenges encountered by polymer‐based electrolytes are summarized and the instructive directions for future research on PEs are demonstrated, facilitating the commercialization of Li‐SPAN batteries.

Modification and Functionalization of Separators for High Performance Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSB) have been recognized as a prominent potential next-generation energy storage system, owing to their substantial theoretical specific capacity (1675 mAh g-1) and high energy density (2600 Wh kg-1). In addition, sulfur's abundance, low cost, and environmental friendliness make commercializing LSB feasible. However, challenges such as poor cycling stability and reduced capacity, stemming from the formation and diffusion of lithium polysulfides (LiPSs), hinder LSB's practical application. Introducing functional separators represents an effective strategy to surmount these obstacles and enhance the electrochemical performance of LSBs. Here, we have conducted a comprehensive review of recent advancements in functional separators for LSBs about various (i) carbon and metal compound materials, (ii) polymer materials, and (iii) novel separators in recent years. The detailed preparation process, morphology and performance characterization, and advantages and disadvantages are summarized, aiming to fundamentally understand the mechanisms of improving battery performance. Additionally, the development potential and future prospects of advanced separators are also discussed.

Study on the impact of cutoff voltage on structural and electrochemical stability of sodium-ion layered cathodes

NaNi1/3Fe1/3Mn1/3O2 is recognized for its relatively high theoretical specific capacity and operating voltage, rendering it a sodium-ion cathode material with significant commercial potential. A higher cutoff voltage typically enables more sodium ion deintercalation, thereby achieving higher capacity. However, this increased deintercalation can introduce challenges such as structural instability and side reactions with the electrolyte, leading to electrochemical performance degradation. This study focuses on the migration process of transition metal ions under conditions of high charging cutoff voltage and high sodium removal. At a voltage of 4.3 V, the migration of Ni ions facilitates more charge compensation but is accompanied by irreversible Ni migration, inducing an irreversible phase transition to the O’ phase. Conversely, at a cutoff voltage of 4.1 V, the P3 and O3 phases with high sodium removal demonstrate excellent cycling stability. The specific capacities before and after 150 cycles (at 0.5C) are 142.3 and 113.7 mAh/g, respectively, indicating a tolerable internal structural stress within these high sodium removal phases. This contrasts with the differentiated internal structural stresses generated by the P3, O3, and O’ phases during phase transitions at a cutoff voltage of 4.3 V. The research underscores the importance of regulating reversible crystal phases within the tolerance range of internal stress and avoiding irreversible crystal phases to enhance the cycling stability of cathode materials. These findings provide crucial insights for optimizing NNFMO cathode materials and hold significant implications for the design of high-performance, long-life sodium-ion batteries.

Single‐Crystalline LiMg Alloy Anode for Deep Cycling All Solid State Lithium Metal Batteries

AbstractAll solid state lithium metal batteries (ASSLMBs) with enhanced energy density has driven the exploration of Li‐alloy anodes such as Li‐Mg alloy owing to its solid‐solution structure and high theoretical specific capacity. But the Li atom diffusion limitation on Li‐Mg electrode surface further leads to sluggish atoms transport dynamics. Herein, single‐crystalline (110)‐oriented Li0.9Mg0.1 (denoted as LiMg(110)) anode is obtained by a tailored melt‐annealing procedure to tackle the above issues. Theoretical analyses and experimental results demonstrate that the crystallographic structural (110) orientation of LiMg anode can facilitate Li atom diffusion and guarantee the electrode stability during deep cycling. As a result, the LiMg(110) electrode exhibits longer cycle life with lower overpotential than polycrystalline LiMg at high current densities and areal capacities in symmetric cells. A critical current density (CCD) at the forefront of 2.5 mA cm−2 is achieved in Li3InCl6 (LIC) solid‐state system. The ASSLMB with high areal capacity (3.8 mAh cm−2), high current density (0.76 mA cm−2), and low negative/positive capacity N/P ratio (2.14) achieves exceptional cyclability over 160 cycles. The outcomes highlight a promising crystallographic regulation strategy toward practical applications of high‐performance lithium metal batteries.

3D Binder-Free Mo@CoO Electrodes Directly Manufactured in One Step via Electric Discharge Machining for In-Plane Microsupercapacitor Application.

Cobalt oxide-based in-plane microsupercapacitors (IPMSCs) stand out as a favorable choice for various applications in energy sources for the Internet of Things (IoT) and other microelectronic devices due to their abundant natural resources and high theoretical specific capacitance. However, the low electronic conductivity of cobalt oxide greatly hinders its further application in energy storage devices. Herein, a new manufacturing method of electric discharging machining (EDM), which is simple, safe, efficient, and environment-friendly, has been developed for synthesizing Mo-doped and oxygen-vacancy-enriched Co-CoO (Mo@Co-CoO) integrated microelectrodes for efficiently constructing Mo@Co-CoO IPMSCs with customized structures in a single step for the first time. The Mo@Co-CoO IPMSCs with three loops (IPMSCs3) exhibited a maximum areal capacitance of 30.4 mF cm-2 at 2 mV s-1. Moreover, the Mo@Co-CoO IPMSCs3 showed good capacitive behavior at a super-high scanning rate of 100 V s-1, which is around 500-1000 times higher than most reported CoO-based electrodes. It is important to note that the IPMSCs were fabricated using a one-step EDM process without any assistance of other material processing techniques, toxic chemicals, low conductivity binders, exceptional current collectors, and conductive fillers. This novel fabrication method developed in this research opens a new avenue to simplify material synthesis, providing a novel way for realizing intelligent, digital, and green manufacturing of various metal oxide materials, microelectrodes, and microdevices.

Very High-Capacity Li/Na-Ion battery anodes Enabled by Blue phosphorene and boron phosphide vdW heterostructure

The fascinating features of van der Waals heterostructure (vdWH) based electrodes and their potential to overcome the limiting properties of single-material systems have sparked a great deal of scientific attention. In this study, we investigate the potential of a blue phosphorene/boron phosphide (Blue-P/BP) vdWH as an anode material for both lithium-ion (Li-ion) and sodium-ion (Na-ion) batteries using first-principles calculations. We suggest that this vdWH could act as an effective anode material for metal-ion batteries, due to their high theoretical capacity and strong binding strength. Intriguingly, the theoretical specific capacity exhibits remarkable values, notably reaching 4510 mAhg−1 for Li and 3849 mAhg−1 for Na, which surpasses all capacities reported in the existing literature. Additionally, electronic structure calculations reveal a significant charge transfer that enhances the metallic characteristics, thereby increasing electrical conductivity. As we delve deeper into the electronic structure and calculate diffusion barriers and pathways, we observe that ionic diffusion (∼0.12/0.11 eV) is notably rapid compared to graphitic anodes (∼0.2 eV). We also found that intercalating Li/Na atoms in the Blue-P/BP vdWH results in low operating potentials of 0.38 V for Li and 0.34 V for Na. This research highlights the substantial enhancement of electrochemical performance of Blue-P/BP vdWH and holds great promise as high-power-density anode materials for Li/Na-ion batteries, facilitating rapid charge and discharge rates.

Performance Degradation Mechanism of the Si@N, S-Doped Carbon Anode in Sulfide-Based All-Solid-State Batteries.

Silicon (Si) anode is a promising anode material for all-solid-state lithium batteries with ultra-high theoretical specific capacity and low lithium dendrite risk. However, the inevitable vast volume expansion of Si anode during charge/discharge is recognized as a major limitation preventing its commercial application. Herein, an N, S self-doped amorphous carbon layer coated on porous micron-sized Si (p-mSi@C) is designed to construct an electron/ion conducting network while ensuring structural and interfacial stability. Uneven distribution of von mises stresses during p-mSi lithiation leads to irregular volume expansion and even fragmentation. Meanwhile, the growth of by-products at the interface between p-mSi and electrolyte contact leads to a rapid capacity decay. Compared to p-mSi anode, p-mSi@C reduces the risk of fragmentation thanks to the stress-absorbing effect of amorphous carbon, delivering excellent electrochemical performance (2679.65 mAh g-1 at 0.2 mA cm-2 with initial coulombic efficiency of 84%). More importantly, the chemical failure mechanisms of p-mSi and p-mSi@C composite anodes are revealed through structural characterization, chemical analysis, and simulation, which provides the necessary theoretical guidance for practicalization.

Rational Design of 3D Hierarchical Fe3S4 for Superior Sodium‐Ion Battery Anode Material

AbstractAmong various transition metal sulfides, iron‐based sulfides have attracted wide attention due to their abundant resources, low cost, and non‐toxicity, showing considerable research value in the field of secondary batteries. Thereinto, Fe3S4 has a high theoretical specific capacity of 785 mAh g−1. However, at present, the research related to Fe3S4 anode for sodium‐ion batteries (SIBs) is still in its infancy, and it also suffers from severe volume expansion and limited preparation. Therefore, to further boost its sodium storage potential, the Fe3S4@rGO composite with hierarchical structure and carbonaceous network is proposed in this study. Beneficial from the ingenious hierarchitectures and flexible graphene coating, the Fe3S4@rGO anode exhibits outstanding sodium storage performance, which can deliver a high capacity of 603 mAh g−1 after 1500 cycles with a superior capacity retention of 98%. The micron flower‐like structure composed of 2D nanosheets can provide sufficient active sites and promote the rapid transport of Na+. Meanwhile, the 3D interconnected graphene carbon network makes a crucial contribution to alleviating volume changes and enhancing electrical conductivity. This work reveals the application potential of Fe3S4 as an anode electrode for SIBs and provides available insights for the development of other electrode materials.

Microstructure regulation of WxV1-xO2(B) nanorods with improved electrochemical properties

VO2(B) is regarded as a highly promising cathode material for secondary batteries due to its outstanding theoretical specific capacity and unique expansion tunnel structure, which facilitates reversible insertion and extraction of metal ions. Nonetheless, inherent structural instability, suboptimal ion/electron transport, and constrained capacity resulting from low redox potentials pose challenges to its wider adoption. Hence, in this paper, we proposed a strategy for synthesizing gradient concentration-doped WxV1-xO2(B) nanorods via a one-step hydrothermal method to solve the above problems. The experimental results demonstrated that as the W ion content increased, all fabricated WxV1-xO2(B) nanorods exhibited a monoclinic crystal phase along with noticeable lattice distortion. The positron annihilation lifetime spectra indicated that vacancy clusters were the predominant defect types in WxV1-xO2(B) nanorods. The synergistic effects of grain sizes and vacancy defects contributed to the superior electrochemical performance observed in the W0.01V0.99O2(B) sample. The capacitor retention reached 88.76 % at 0.10 A/g after 1000 charge/discharge cycles. These results had provided experimental foundation for improving electrochemical properties of WxV1-xO2(B) in metal ion secondary batteries.