Preparation And Performance Study Of Vanadium-based Zinc Ion Battery Cathode Materials

Aqueous zinc ion batteries are the next generation of power sources due to their high theoretical capacity,low redox potential,abundant reserves,safety and environmental protection.Vanadium-based materials with multiple oxidation states,multiple structures and high abundance are becoming widely used as positive electrode materials.Wearable flexible smart electronics are gradually developing into a necessity of life.Based on the above background,this study proposes to use cationic intercalation of vanadium oxide in different valence states.Reduced acidified carbon nanotubes were used as a substrate to prepare adhesive-free self-supporting thin film electrodes.On the one hand,this solution can improve the electrochemical properties of vanadate.And on the other hand,it can be applied to aqueous flexible zinc ion batteries.In this study,CuV₂O₆,K₂V₆O₁₆·2.7H₂O and(NH₄)₂V₆O₁₆·1.5H₂O,respectively,were prepared by hydrothermal method using divalent and monovalent metal ions Cu²⁺,K⁺,and non-metal ions NH₄⁺intercalated vanadium oxide,which were made into flexible and strong thin film electrodes by vacuum filtration method.The main research in this paper is in three parts as follows.(1)Preparation and electrochemical properties of CuV₂O₆/RCNTs freestanding films:CuV₂O₆ nanorods were synthesized by hydrothermal method;Self-supporting composite films without adhesive of CuV₂O₆ and reductive acidified carbon nanotubes(CuV₂O₆/reductive acidified carbon nanotubes,CVO/RCNTs)were synthesized by vacuum filtration.Through testing and characterization,it was concluded that the self-supporting electrode scheme had greatly improved the electrochemical performance of CuV₂O₆.The film electrode showed a high reversible capacity of 353 mAh/g at 0.1 A/g.The CVO/RCNTs composite membrane was prepared into flexible gel batteries,which showed stable electrochemical performance under different bending degrees.(2)Preparation and electrochemical properties of K₂V₆O₁₆·2.7H₂O/RCNTs films:K₂V₆O₁₆·2.7H₂O nanowires were synthesized by hydrothermal method,and K₂V₆O₁₆·2.7H₂O/RCNTs freestanding composite films were synthesized by vacuum filtration.The characterization and test results showed that the specific capacity of K₂V₆O₁₆·2.7H₂O was greatly improved by the self-supporting electrode film scheme.For instance,the initial specific capacity was 309.3 mAh/g at the current density of 2A/g and it admirably remained 267.6mAh/g after 200 cycles,which showed a capacity retention rate of 86.5%.(3)Preparation and electrochemical performance of(NH₄)₂V₆O₁₆·1.5H₂O/RCNTs:(NH₄)₂V₆O₁₆·1.5H₂O nanowires were synthesized by hydrothermal method,and(NH₄)₂V₆O₁₆·1.5H₂O/RCNTs freestanding composite membrane was prepared by vacuum filtration.After characterization and test,it was concluded that the self-supporting film scheme had a slight improvement on the electrochemical performance of(NH₄)₂V₆O₁₆·1.5H₂O.In this regard,the initial specific capacity of the electrode was147.2 mAh/g and it could remain 203.8 mAh/g after 200 cycles(at the current density of 2 A/g).