Interlayer Pre-intercalation,Multiphase Composite And Its Performance Improvement Of Vanadium-based Cathode Materials For Aqueous Zinc Ion Batteries

In recent years,the surge in the demand cost of unrenewable resources such as fossil oil has been affected by the instability of the situation in the Middle East.It is particularly important to maximize the utilization of renewable resources such as solar energy and wind energy.Researchers have paid extensive attention to the conversion of renewable energy into secondary energy storage.The aqueous zinc ion batteries（AZIBs）built on neutral or mild aqueous electrolytes with a zinc plate as the anode,featuring the low cost,good safety and straightforward operation,which became the preferred choice in research.Vanadium has low price,complex valence and diversity of structure.Vanadium-based cathode materials have high theoretical specific capacity and excellent rate performance.They are a kind of cathode materials with widespread application prospects in AZIBs.However,vanadium-based materials arose a series of problems such as unstable material structure,poor conductivity and narrow voltage window in the process of Zn²⁺insertion/extraction,which limits its application in AZIBs.In conclusion,this paper improves the electrochemical stability of the materials by intercalation of metal ions and controllable preparation of composites.The specific contents of research are as follows:（1）（NH₄）₂V₁₀O₂₅·8H₂O material（NVO）was synthesized by hydrothermal method with C₂H₂O₄·2H₂O as reducing agent and NH₄VO₃ as vanadium source.Pre-embedded modification of NVO materials with different Al:V molar ratios（1:3,1:6,1:9）by Al（NO₃）₃·9H₂O as aluminum source.The morphology of Al³⁺pre-embedded materials changed from dense stacked sheet structure to smaller and more dispersed nanosheet structure under the same preparation process.Finely dispersed nanosheets provide fast and convenient diffusion channels for the transmission of Zn²⁺and facilitate the contact between materials and electrolyte.Al-6NVO materials maintains high discharge capacity（252 m Ah/g）after 100 cycles.The discharge capacity of the material can still remain at122.8 m Ah/g after 1200 cycles at 2.0 A/g,and the capacity retention rate is about 94.6%.The diffusion kinetics of Zn²⁺can be effectively improved and the electrochemical performance of the material can be improved due to the synergistic effect of bication NH₄⁺and Al³⁺on the formation of pillar between layers.（2）Na⁺and Ca²⁺co-intercalation V₁₀O₂₄·12H₂O materials（Na,Ca-VOH）were synthesized by hydrothermal method using Na₃VO₄ as vanadium source and anhydrous Ca Cl₂ as calcium source.AZIBs were assembled by using Na,Ca-VOH as anode and commercial zinc foils as cathode.Na⁺(or Ca²⁺)single metal ion pre-embedded V₁₀O₂₄·12H₂O materials were prepared by hydrothermal method.V₁₀O₂₄·12H₂O pure phase materials（VOH）were prepared by aging method.By comparing the electrochemical properties of the four materials,Na,Ca-VOH materials show excellent electrochemical cycle stability.The material maintained a high discharge specific capacity（116.9 m Ah/g）after 500 cycles at a current density of 2.0 A/g,and the capacity retention is about 94.3%.The materials still have 89.0 m Ah/g discharge specific capacity at 5.0 A/g high current density after 1000 cycles,the capacity retention rate is about98.5%.Experiments show that the co-intercalation of Na and Ca metal ions can further expand the layer spacing and improve the stability of the material.The flower structure Na,Ca-VOH material has a large contact area with the electrolyte.The material has a short Zn²⁺diffusion path and effectively improves the diffusion kinetics of Zn²⁺.（3）（NH₄）₂V₆O₁₆·1.5H₂O/Ca V₆O₁₆·3H₂O composites（NVO/CVO materials）were synthesized by hydrothermal method with NH₄VO₃ as vanadium source and Ca（CH₃COO）₂·H₂O as calcium source,and the electrochemical properties ware compared with pure V₂O₅ materials prepared by same method.The NVO/CVO material with short film structure can cycle for 2000 cycles at 2.0 A/g current density,and the specific discharge capacity can still be maintained at 89.8 m Ah/g.The experimental results show that NVO/CVO composites have rich phase interfaces which expand the diffusion channel of zinc ions and effectively improve the diffusion kinetics of Zn²⁺,capacity,rate performance and cycle stability of the materials.