Cathode Material For Zn-ion Batteries Research Articles

Polar organic molecules assisting Mo-based cathode materials for enhanced zinc-ion transfer kinetics

The Mo-based oxides/sulfides are promising cathode materials for Zn-ion batteries (ZIBs). However, the volume expansion and poor intrinsic electronic conductivity limit their electrochemical performance. Herein, a strategy of introducing active organic small molecule (ethylenediamine) into the interlayer of the Mo-based oxides/sulfides (MoOS) is reported to solve these shortcomings. The experimental analysis reveals that ethylenediamine (EDA) can regulate the composition ratio of MoO3/MoS2 for its reduction ability, which can improve the electronic conductivity of the EDA-intercalated MoOS (MoOS-EDA). Besides, EDA can efficiently decrease the Zn2+ insertion energy for its strong coordinated ability with Zn2+, in combination with the enhanced interlayer spacing and the strong repulsion with Zn2+ from the non-polar group –CH2CH2 in EDA, leading to enhanced ionic transferring kinetics and Zn2+ storage ability. The theoretical and experimental analysis have confirmed the organic guest and inorganic skeleton all participate in the Zn2+ storage process. As a result, compared with the MoOS cathode, the MoOS-EDA exhibits improved specific capacity (203 vs. 88 mAh/g at 0.1 A/g) and prolonged cycle stability. Moreover, the soft-package cell based on MoOS-EDA cathode also delivers an impressive electrochemical performance. This work provides a strategy to improve the Zn2+ transfer kinetics in MoS2 cathode material towards high-performance ZIBs.

Poly(3,4-ethylenedioxythiophene) encapsulation/intercalation boosting stability and zinc ion storage properties of vanadyl phosphates

The electrochemical properties of vanadyl phosphates as cathode materials for Zn-ion batteries have been severely hindered by their inherent poor electronic conductivity, unavoidable dissolution in aqueous solutions, and sluggish reaction kinetics. In this study, poly(3,4-ethylenedioxythiophene) (PEDOT) is introduced in vanadyl phosphates (PEDOT-VOP) through the in situ polymerization as interlayer guest species and surface coating layer, along with the generation of oxygen vacancies. The intercalated PEDOT develops strong interaction with the host layer, which can maintain its structural integrity. In addition, the PEDOT coating shell can enhance electronic conductivity together with oxygen vacancies to promote efficient electron transfer and prevent dissolution of active materials to stabilize the vanadyl phosphate core. As a result, the PEDOT-VOP electrode demonstrates a high discharge capacity of 180 mA h g−1 at 0.1 A/g with good rate performance (128 mA h g−1 at 2 A/g) and enhanced cycling stability (a capacity retention of 88.6 % after 2000 cycles at 1 A/g). The reversible Zn2+ insertion/extraction mechanism is further validated by diverse ex situ tests.

Low-strain layered Zn0.56VOPO4∙2H2O as a high-voltage and long-lifespan cathode material for Zn-ion batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) have been regarded as a potential competitor in grid-scale energy storage scenarios due to the merits of high safety, easy manufacturing and cost-efficiency. However, the lack of suitable robust hosts to accommodate Zn2+ with high electrostatic repulsion remains the major obstacle to the development of ZIBs. The exploration of low-strain Zn-storage cathode materials is a critical strategy to address the challenges. In this work, we developed a layered phyllo-oxovanadophosphate Zn0.56VOPO4∙2H2O as a structurally stable cathode material for the first time. Benefiting from the "inductive effect" of strong P–O covalent bonds and the single-phase reaction mechanism with tiny lattice volume distortion of 1.9%, the Zn0.56VOPO4∙2H2O cathode manifests a high operating voltage of 1.46 V and ultralong cycle life (capacity retention of 70.5% after 8000 cycles). Importantly, the versatility and practicability of this layered cathode is verified in both "rocking-chair" ZIBs and anode-free ZIBs, all of which demonstrate outstanding cycling performance. The low-strain structural superiority and prominent electrochemical performance are expected to inspire more efforts in the research of Zn-storage polyanionic cathode materials and revitalize the development of rechargeable ZIBs towards energy storage applications.

Possibilities and Challenges of Cathode Materials for Zn-Ion Batteries

The demand for energy storage solutions has been steadily rising with the increasing prevalence of renewable energy sources and the widespread use of portable electronic devices. In this context, zinc-ion...

Carbon enhanced nucleophilicity of Na3V2(PO4)3: A general approach for dendrite-free zinc metal anodes

Zincophilic property and high electrical conductivity are both very important parameters to design novel Zn anode for aqueous Zn-ion batteries (AZIBs). However, single material is difficult to exhibit zincophilic property and high electrical conductivity at the same time. Herein, originating from theoretical calculation, a zincophilic particle regulation strategy is proposed to address these limitations and carbon coated Na3V2(PO4)3 is taken as an example to be a protective layer on zinc metal (NVPC@Zn). Na3V2(PO4)3 (NVP) is a common cathode material for Zn-ion batteries, which is zincophilic. Carbon materials not only offer an electron pathway to help Zn deposition onto NVPC surface, but also enhance the zinc nucleophilicity of Na3V2(PO4)3. Hence, this hybrid coating layer can tune zinc deposition and resist side reactions such as hydrogen generation and Zn metal corrosion. Experimentally, a symmetrical battery with NVPC@Zn electrode displays highly reversible plating/stripping behavior with a long cycle lifespan over 1800 h at 2 mA cm−2, much better than carbon and Na3V2(PO4)3 solely modified Zn electrodes. When the Na3V2(PO4)3 is replaced with zincophobic Al2O3 or zincophilic V2O3, the stability of the modified zinc anodes is also prolonged. This strategy expands the option of zincophilic materials and provides a general and effective way to stabilize the Zn electrode.

Bi-layered calcium vanadium oxide as a cathode material for wet organic electrolyte-based rechargeable Zn-ion batteries

Zn-ion batteries attract considerable attention as a promising option for large-scale energy storage owing to their many benefits, including safety, high abundance of zinc, low fabrication costs, and ease of handling in air. However, to improve their effectiveness, three key technical challenges must be overcome: low electrolyte performance, metal dendrite formation, and a limited choice of host materials. This study introduces a new cathode material for Zn-ion batteries — double-layered Ca0.26V2O5·H2O — that exhibits outstanding performance in a wet organic electrolyte. The cathode material demonstrates an initial discharge capacity of 268.76 mAh g−1 at a rate of 0.2C and average operating voltage of 0.82 V (vs. Zn2+/Zn) with excellent capacity retention. A reversible Zn intercalation/crystal water extraction reaction is confirmed by conducting elemental and structural analyses, including powder X-ray diffraction. Furthermore, the results of bond valence sum calculations support the formation of a two-dimensional network of Zn-ion conduction pathways along the a-axis and b-axis, illustrating the electrochemical zinc intercalation into the wet organic electrolyte. Overall, this study not only introduces double-layered Ca0.26V2O5·H2O as a new cathode material for Zn-ion batteries but also provides valuable insights into the electrochemical zinc intercalation/crystal water extraction in wet organic electrolytes.

Dimerizing Lawsone into Bis-lawsone to Counter Solubility and Attain Facile Zn2+ Ion Diffusion for Stable Capacity in Aqueous Zinc-Ion Batteries

Given the higher volumetric capacity of Zn (5853 mAh cm−3), aqueous zinc-ion batteries can be considered as alternatives to lithium-ion batteries for energy storage applications. Here we focus on redox-active, non-toxic, and eco-friendly organic materials with quinone moiety, i.e., Lawsone (LS) and its dimer Bis-lawsone (BL), as a cathode material for Zn-ion batteries. The reversibility of LS and BL is confirmed by cyclic voltammetry between 0.3 and 1.6 V in zinc sulfate and zinc triflate electrolytes. The electrochemical performance of BL in the zinc triflate electrolyte is improved by the reduction in the solubility of BL in the electrolyte and improvement in Zn2+ diffusion in the BL matrix. Besides, it is known that Zn electrodes passivate better in zinc triflates, which contributes to improved plating/stripping of Zn. The dimerization strategy counteracts solubility and facilitates the diffusion of Zn2+, resulting in a stable charge–discharge with a specific capacity of 200 mAh g–1. The cell attained 77% of the theoretical capacity at a current density of 100 mA g–1. Zn-BL cells show fast kinetics and reversibility for up to 760 cycles retaining 85% of initial capacity despite the partial solubility of BL in electrolytes. In addition, the Nafion-212 membrane is introduced as a separator instead of a traditional glass fiber separator. The negatively charged backbone of Nafion helps eliminate the crossover problem by coulostatic repulsion with negatively charged BL and LS.

Sodium-Ion Substituted Water Molecule in Layered Vanadyl Phosphate Enhancing Electrochemical Kinetics and Stability of Zinc Ion Storage.

Vanadyl phosphate (VOPO4 ·2H2 O) has been regarded as one of the most promising cathode materials for aqueous Zn-ion batteries due to its distinct layered structure. However, VOPO4 ·2H2 O has not yet demonstrated the exceptional Zn ion storage performance owing to the structural deterioration during repeated charging/discharging process and poor intrinsic conductivity. In this work, 2D sodium vanadyl phosphate (NaVOPO4 ·0.83H2 O, denoted as NaVOP) is designed as a cathode material for Zn-ion batteries, in which sodium ions are preinserted into the interlayer, replacing part of water. Benefiting from the in situ surface oxidization, improved electronic conductivity, and increased hydrophobicity, the NaVOP electrode exhibits a high discharge capacity of 187 mAh g-1 at 0.1 A g-1 after activation, excellent rate capability and enhanced cycling performance with 85% capacity retention after 1500 cycles at 1 A g-1 . The energy storage mechanism of the NaVOP nanoflakes based on the rapid Zn2+ and H+ intercalation pseudocapacitance are investigated via multiple ex situ characterizations.

Porous V2O3/C composite electrodes derived from V-MOF with advanced performance for Zn-ion battery

Vanadium oxides are promising cathode materials for Zn-ion batteries. However, they are always suffered from inferior performance because of intrinsic sluggish kinetics, poor conductivity and surface elements dissolution. In this work, porous composite of V2O3 nanoparticles embedded in carbon framework is fabricated by pyrolysis of a Vanadium-base MOF. Attributing to the abundant pores, high specific area and conductive carbon framework, the obtained hierarchical composite delivers a high specific capacity of 240 mAh g−1 at 0.5 A g−1 although the content of carbon is up to 50%, and exhibits a good rate performance with 86.6% retention when the current densities increased from 0.5 to 4 A g−1. Moreover, the cycling performance of the composite is much better than that of commercial V2O3.

Mechanically Improved Zn-Ion Battery Cathodes Based on Branched Aramid Nanofibers

Zinc-ion batteries address common environmental and safety concerns by using nontoxic and abundant metals in conjunction with aqueous electrolytes. Nonetheless, for applications such as structural energy storage, where a multifunctional system aims to replace both the structural and energy storage subsystems of an electric vehicle, safe but mechanically strong components are desired. MnO2, a typical cathode material for Zn-ion batteries, however, exhibits poor mechanical performance. Therefore, a lack of knowledge remains for mechanically strong cathodes for safe, structural Zn-ion batteries. Here, we combine branched aramid nanofibers (BANFs) with MnO2 particles and reduced graphene oxide (rGO) to fabricate mechanically improved cathodes for Zn-ion batteries. The addition of BANFs allows for an increase in the MnO2 loading and significantly improved electrochemical properties (up to 190% increase of capacity). Additionally, hydrogen bonding between BANFs and rGO notably improved the mechanical properties (up to 51% increase in ultimate tensile strength and up to 593% increase in ultimate strain). Electrochemo-mechanical tests were also performed to assess coupling, showing that applied strain decreases the capacity, but no measurable internal stresses develop during electrochemical cycling. This work combines the multifunctionality of structural electrodes with the inherent safety of Zn-ion batteries.

Methyl-functionalized hydrangea-like vanadium pentoxide cathode for aqueous zinc ion batteries with high-rate and long-term cycling stability

Vanadium Pentoxide (V 2 O 5 ) is an appealing cathode candidate for Zinc-ion batteries (ZIBs) owing to its modifiable interlayer structure and changeable chemical redox states. However, the extensive practical application is deeply plagued by either poor rate capability or cycling stability performance. Herein, the methyl group decorated V 2 O 5 with hydrangea-like morphology was successfully fabricated by a facile solvothermal method to solve the problem. Such a hydrangea-shaped architecture containing numerous nanosheets is advantageous for the rapid ions/electrons transfer. The extended interlayer distance stemmed from the pillar effect of the methyl-functionalized V 2 O 5 contributes a comparatively steady and rapid Zn 2+ intercalation/deintercalation. When applied in ZIBs, it delivers a superior rate capability (123 mA h g −1 at 4.0 A g −1 ) and an excellent long-life cycling (capacity retention of 112.7 % after 1000 cycles at 4.0 A g −1 ). Electrochemical kinetics investigations of methyl-functionalized V 2 O 5 microsphere show that the capacity is dominantly contributed from pseudocapacitance. As well, mechanism of zinc ion storage has been explored. Such a structural design of electrode materials can be exploited to promote extensive applications of ZIBs in future. Pillaring effect of methyl group in the hydrangea-like V 2 O 5 microsphere ensures the expanded interlayer spacing for advanced Zn storage. • Methyl-functionalized V 2 O 5 is successfully prepared via a simple solvothermal method. • Pillaring effect of methyl group endows the favorable interlayer expansion and structural stability. • Methyl-functionalized V 2 O 5 is a promising cathode material for Zn-ion batteries.

(Invited) Wastewater Derived Cathode Materials for Aqueous Zn-Batteries

While lithium-ion batteries (LIBs) have been widely used for portable devices and electric vehicles, it is highly desirable to develop safer and less expensive batteries as alternative to LIBs. In this regard, zinc (Zn) batteries have attracted much attention because of their excellent safety and low cost. However, one of the challenges is to develop cost-effective and highly efficient cathode materials for Zn-ion batteries (ZIBs) based on transition metal oxides. It would be more economical to recycle transition metals in order to reduce the fabrication cost. Co-precipitation method is widely used for synthesis of LIBs cathode materials, and large amount of wastewater would be produced during co-precipitation and battery production process. In this presentation, we will report a facile and general process for fabrication of cathode materials for aqueous Zn-ion batteries (ZIBs) by reusing wastewater from co-precipitation method. We have selected manganese rich phases with different ratio of nickel to cobalt precursors from co-precipitation wastewater, followed by a simple ball milling process, resulting in metal-hydroxide cathode materials (Mn0.6Ni0.1Co0.3OxHy, Mn0.6Ni0.2Co0.2OxHy, and Mn0.6Ni0.3Co0.1OxHy). Among them, the Mn0.6Ni0.1Co0.3OxHy cathode (with mass loading of 15 mg cm-2) exhibits an initial capacity of 263 mAh g-1 at a current density of 0.1 A g-1, as evaluated in an mixture electrolyte (2M ZnSO4 and 0.1M MnSO4). Furthermore, operando X-ray absorption spectroscopy analysis has revealed the role of each transition metal ions during insertion and desertion of Zn ions. It is found that the ratio of Ni to Co significantly influences ZIBs performances, providing important insight into rational design of more efficient cathode materials for aqueous Zn-ion batteries. Figure 1

Defect Engineering via Copper Doping on Oxygen‐Deficient Manganese Oxide for Durable Aqueous Zinc‐Ion Battery

Aqueous Zn‐ion batteries (ZIBs) have triggered an astounding research surge because of their high safety, affordability, and impressive electrochemical properties. However, the smooth implementation of this promising technology is hindered by severe structural degradation and sluggish reaction kinetics of the cathode materials. Here, the defect engineering is demonstrated by the substitution doping of Cu2+ in layered δ‐MnO2 to boost the electrochemical reactivity for Zn‐ion storage. Benefited from the nanoscale morphology and oxygen‐deficient structural features, this Zn/MnO2 battery is able to deliver a high reversible capacity of 296.8 mAh g−1 with a capacity retention of 94.9% over 120 cycles (at 0.1 A g−1) and a desirable energy density of 441 Wh kg−1, as well as an ultra‐long cycle life up to 6000 cycles, which is also intensively associated with the facilitated Zn2+ diffusion and charge transfer rates after the Cu2+ dopants, based on the electrochemical kinetics analysis. The effortless but effective defect engineering arising from element doping can provide significant enlightenment to design high‐performance cathode materials for ZIBs.

CTAB controlled electrochemical deposition of manganese dioxide with enhanced performance in aqueous Zn-ion battery

The collapse and dissolution of the structure of the MnO2 positive electrode in the cycle process is mainly caused by the volume expansion during the phase transition process, which leads to the extrusion of the adjacent parts of the electrode and poor cycle performance. To overcome this issue, morphology of MnO2 films were controlled by adding various concentrations of surfactant Hexadecyl trimethyl ammonium Bromide (CTAB) in the electrolytic cell through changing the current distribution characteristics between substrate and solution. The obtained MnO2 nanofilm materials prepared with different concentrations of surfactant were compared from the aspects of surface morphology, specific capacity and cyclic stability. The morphology and structure of the prepared MnO2 were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer Emmett and Teller (BET). As expected, MnO2 with its unique crystal structure exhibited excellent cycling and superior performance (311.2 mAh g−1 at 0.1 A g−1, 177.6 mAh g−1 at 5 A g−1, 125% capacity retention after 4000 cycles at 5 A g−1). This capacity retention was among the highest reported so far for MnO2-based cathode materials for Zn-ion batteries. The excellent electrochemical performance may be due to its unique nanostructure, which provides enough space for the volume expansion and proper structure for the re-deposition of MnO2. This work provides an new sight to develop long-circulation MnO2 electrodes for aqueous Zn ion batteries by designing an advantageous master structure dynamics.

A new Li2Mn3O7 cathode for aqueous Zn-Ion battery with high specific capacity and long cycle life based on the realization of the reversible Li+ and H+ co-extraction/insertion

• Li 2 Mn 3 O 7 is firstly reported as the new cathode for aqueous Zn-ion battery. • Complex storage mechanism is discussed by In-situ XRD and ex-situ XPS. • Excellent performance is related to reversible Li + /H + co-extraction/insertion. • Dynamic mechanism of electrode and reason of capacity variation were pointed. Aqueous Zn-ion batteries (ZIBs) are expected to be used for practical energy storage and grid-scale applications because of their low-cost, high-safety and environmental friendliness. However, it is still a major challenge to achieve a suitable cathode for ZIBs with a high energy density and long cycle life. Herein, we reported a new cathode Li 2 Mn 3 O 7 for aqueous ZIBs and have studied in detail the role of Li + as electrolyte additives in further improving electrochemical performance. The Li + in the additive-contained electrolyte itself not only facilitates the reversible extraction/insertion of Li + in Li 2 Mn 3 O 7 but also effectively reduce the decomposition effect of Li 2 Mn 3 O 7 caused by the charge process through the re-insertion of Li + in subsequent discharge process and thus realizes the reversible deintercalation/intercalation of H + . Owing to the realization of the reversible Li + and H + co-extraction/insertion caused by the use of Li + additive, the Li 2 Mn 3 O 7 electrode exhibits a high reversible specific capacity of 242 mAh g −1 with nearly 100% coulombic efficiency at 200 mA g −1 current density. In particular, due to the enhanced capacitive contribution, Li 2 Mn 3 O 7 electrode presented an impressive life span at high current density 2 A g −1 , and after 1000 cycles, a stable specific capacity greater than 100 mAh g −1 can be maintained, which is significantly better than that of manganese oxide-based cathode materials in ZIBs. Furthermore, by In-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS), we discuss in detail the complex energy storage mechanism of Li 2 Mn 3 O 7 as cathode material for ZIBs with electrolyte containing Li + additive for the first time. Based on the high specific capacity and big current life span, aqueous ZIBs with Li 2 Mn 3 O 7 exbibit a great potential for large scale electrical energy storage.

Size-Dependent Reaction Mechanism of λ -MnO 2 Particles as Cathodes in Aqueous Zinc-Ion Batteries

Manganese dioxide (MnO 2 ) with different crystal structures has been widely investigated as the cathode material for Zn-ion batteries, among which spinel λ -MnO 2 is yet rarely reported because Zn-ion intercalation in spinel lattice is speculated to be limited by the narrow three-dimensional tunnels. In this work, we demonstrate that Zn-ion insertion in spinel lattice can be enhanced by reducing particle size and elucidate an intriguing electrochemical reaction mechanism dependent on particle size. Specifically, λ -MnO 2 nanoparticles (NPs, ~80 nm) deliver a high capacity of 250 mAh/g at 20 mA/g due to large surface area and solid-solution type phase transition pathway. Meanwhile, severe water-induced Mn dissolution leads to the poor cycling stability of NPs. In contrast, micron-sized λ -MnO 2 particles (MPs, ~0.9 μ m) unexpectedly undergo an activation process with the capacity continuously increasing over the first 50 cycles, which can be attributed to the formation of amorphous MnO x nanosheets in the open interstitial space of the MP electrode. By adding MnSO 4 to the electrolyte, Mn dissolution can be suppressed, leading to significant improvement in the cycling performance of NPs, with a capacity of 115 mAh/g retained at 1 A/g for over 500 cycles. This work pinpoints the distinctive impacts of the particle size on the reaction mechanism and cathode performance in aqueous Zn-ion batteries.

Ion-intercalation regulation of MXene-derived hydrated vanadates for high-rate and long-life Zn-Ion batteries

Vanadium oxides are promising cathode materials for Zn-ion batteries (ZIBs) because of their high electrochemical performance. However, its low conductivity remains to be the major obstacle for further utilization. Even the conventional introduction of conductive substrate cannot maintain the structural stability of the composite during cycling. Herein, a universal strategy is proposed to fabricate high-rate cathodes by rationally designing the heterostructure through one-step ion intercalation and phase transition of MXene-derived hydrated vanadates. The hydrated vanadate inherits the intrinsic conductivity from MXene, which can promote faster Zn2+ diffusion kinetics. Therefore, Mn2+-intercalated V10O24.nH2O derived from V2CTx as the prototype cathode material shows superior rate capacity and cycling stability (289.6 mAh g−1 at 10 A g−1 after 25,000 cycles with 92.9% retention). Furthermore, the derivatization strategy is extended to Li+ and Al3+ intercalated hydrated vanadates, which also present excellent electrochemical performances. Successful extension indicates that the concept not only presents a blueprint for the development of robust multi-valent ion batteries but also can be generalized to fabricate varied MXene derivatives for wider applications.

A new zinc-ion battery cathode with high-performance: Loofah-like lanthanum manganese perovskite

Due to high safety and excellent rate performance, the aqueous Zn-ion battery is a promising energy storage battery for practical application. However, most manganese-based compounds suffer from poor cycling and rate performance. Herein, a new concept of Zn-ions battery is assembled with the loofah-like LaMnO3 perovskite as a novel cathode, achieving fast ion kinetics through the co-intercalation of Zn2+ and H+ cations. In this work, the Ni-doping strategy is adopted to improve the electrochemical performance of LaMnO3 perovskite as a cathode material for Zn-ion batteries. The resultant LaNixMn1-xO3 (x = 0.2) exhibits a superior capacity of 226 mAh g−1 after 80 cycles at 100 mA g−1 and high working voltages at 1.4 V and 1.26 V vs. Zn2+/Zn in the electrolyte of 2 M ZnSO4 + 0.2 M MnSO4. Even at 500 mA g−1, the new Zn/LaNixMn1-xO3 battery still delivers a discharge capacity of 113 mAh g−1 after 1000 cycles. At medium current density, the electrochemical process of the LaNixMn1-xO3 (x = 0.2) electrode is co-controlled by the solid diffusive and surface-capacitive process with a fast ion diffusion rate. The lanthanum manganese perovskite is a potential cathode material for Zn-ion batteries with long cycle performance and high rate cyclability. This work significantly opens up the way of perovskite materials as new cathodes for high-rate ZIBs.

Zn2+ storage performance and structural change of orthorhombic V2O5 nanowires as the cathode material for rechargeable aqueous zinc-ion batteries

A fundamental understanding of the relationship between electrochemical performance and microstructural variation of electrodes is crucial for developing high-performance electrode materials. In this work, the Zn2+ storage performance and structural evaluation of orthorhombic V2O5 nanowires as a cathode material for Zn-ion batteries in ZnSO4 electrolyte were investigated. At 1000 mA g−1, the orthorhombic V2O5 nanowires exhibited a maximum reversible capacity of 276 mA h g−1 and retained a capacity of 152/95 mA h g−1 after 500/2000 cycles. The cycling performance curve shows three distinct regions: initial capacity increase region (stage I), fast capacity decay region (stage II), and relatively stable capacity region (stage III). The structural evolution of the orthorhombic V2O5 nanowires during cycling was analyzed by ex-situ SEM and XRD characterizations. It demonstrated that upon repeated cycling the orthorhombic V2O5 nanowires experience morphology changes from nanowires to nanofibers and finally interweaved nanofibers; meanwhile, the phase structure transforms from orthorhombic to amorphous phase and accompanied with the formation of Zn3(OH)2V2O7•2H2O phase, which accounts for the capacity change of the electrode during long-term cycling. The pseudocapacitive behavior and Zn2+ diffusion coefficient during discharge/charge processes were analyzed by the sweep voltammetry method and galvanostatic intermittent titration technique, respectively.

Zn-Ion Batteries: Boosting the Rate Capability and Low-temperature Performance by Combining Structure and Morphology Engineering.

Prussian blue analogues (PBAs) have been considered as one kind of the most promising cathode materials for Zn-ion batteries (ZIBs) due to their low cost, high performance, high safety, and high abundance. However, owing to the low conductivity and single electron reaction, it is a great challenge to obtain a PBA cathode material with high reversible capacity, high rate capability, and good temperature adaptability. Here, a cathode material, K1.14(VO)3.33[Fe(CN)6]2·6.8H2O (KVHCF), with a multielectron reaction and double conductive carbon framework (DCCF) is designed and synthesized by combining structure and morphology engineering. With the multielectron reaction and high electronic conductivity simultaneously, the KVHCF@DCCF cathode material delivers a high specific capacity (180 mAh·g-1 @ 400 mA·g-1) and the best rate performance (116 mAh·g-1 @ 8000 mA·g-1) of the reported PBAs. Moreover, KVHCF@DCCF presents a high specific capacity of 132 mAh·g-1 @ 400 mA·g-1 at 0 °C. Even at -10 °C, it still delivers specific capacities of 127 mAh·g-1 @ 40 mA·g-1 and 80 mAh·g-1 @ 400 mA·g-1 with a retention of 86% after 700 cycles. In situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS) are carried out to investigate the charge-discharge electrochemical reaction mechanism.