Study On Controlled Synthesis Of Vanadium-Based Cathode Materials By Liquid Phase And Zinc Storage Properties Of Aqueous Zinc-Ion Batteries

Aqueous zinc ion batteries are considered to be the most promising candidate materials due to their environmentally friendly,safe and low toxicity.However,the practical application of vanadium-based oxides as cathode materials is limited due to their low conductivity and poor structural stability under fast and deep discharge conditions.Starting from optimizing the structure of vanadium-based materials,this paper first designs and implements a single optimization strategy.On this basis,a variety of optimization strategies are used to improve the performance of vanadium-based materials,aiming to develop electrode materials with high performance and improve the electrochemical performance of aqueous zinc ion batteries.The details are as follows:（1）Herein,surface-oxidized vanadium nitride（O-VN）is synthesized by a one-step hydrothermal method without multi-step reactions,which is applied as cathode material for aqueous zinc ion batteries.After in-situ electrochemical activation,it turns into Zn₃（OH）₂V₂O₇·2H₂O with copious oxygen vacancies/defects.The electrochemical phase transition and in-situ defect induction can provide abundant active sites for the storage of Zn²⁺,thus increasing the energy storage performance of electrode materials.As expected,the Zn₃（OH）₂V₂O₇·2H₂O with oxygen defects holds on good structural and morphological stability during cycling,which exhibits excellent specific capacity(510 m Ah g^-1at 0.1 A g^-1and 199 m Ah g^-1at 10 A g^-1)and superior cycle stability(72.6%capacity retention after 3000 cycles at 20 A g^-1).（2）（NH₄）₂（S（（S₂）Mo（S₂））₃）/vanadium oxide/graphene oxide composite is obtained by hydrothermal method,which is used as the cathode material for aqueous zinc ion batteries.After the first charging/discharging process,a novel vanadium-based cathode based on molybdenum ion doped and graphene oxide supported heterostructured material is formed by an efficient electrochemically reconstructed strategy,which exhibits excellent electrochemical properties.The cathode material owns a high discharge capacity of 545 m Ah g^-1at the current density of 0.1 A g^-1.At the current density of 10.0 A g^-1,it can register a high reversible discharge capacity of 102 m Ah g^-1,and the specific capacity remains at 92 m Ah g^-1and the capacity retention is 90.2%after 8,000 cycles.The electrochemical performance is obviously superior to other materials without adding molybdenum ions or graphene oxide.The excellent performance should result from the synergistic effect of molybdenum ion doping and graphene oxide supporting.This study provides a novel idea for the optimization strategy of vanadium-based materials.