Preparation,Composite And Electrochemical Performance Of HNaV₆O₁₆·4H₂O Cathode Material For Aqueous Zinc Ion Batteries

With the development of society,the demand for energy has been increasing,and the development of renewable and pollution-free new energy has become the current priority.As the main energy storage equipment in the current energy market,lithium-ion batteries have the advantages of large capacity,long cycle life and high working voltage,but their disadvantages of high cost,large pollution and low safety limit their further development.At present,the water-based zinc-ion battery,which has the advantages of safety,environmental protection,low manufacturing cost,high current charging and discharging capacity,is considered as a new type of energy storage device that can replace lithium-ion battery.However,the cycle life of the cathode material for zinc ion batteries is still not ideal,and its electrochemical performance needs to be improved.This paper takes HNaV₆O₁₆·4H₂O with high theoretical capacity as the research object,uses a simple one-step hydrothermal method to synthesize the product,and optimizes the hydrothermal temperature and time of HNaV₆O₁₆·4H₂O,and then combines the product with glucose based carbon spheres to obtain the HNaV₆O₁₆·4H₂O cathode material with the best electrochemical performance.The main research contents of this paper are as follows:（1）The effects of hydrothermal temperature and time on the electrochemical properties of HNaV₆O₁₆·4H₂O were studied.Firstly,the phase,morphology and structure of HNaV₆O₁₆·4H₂O prepared under different hydrothermal conditions were characterized by XRD,SEM,TEM and other characterization methods,and then its electrochemical performance was tested by battery tester and electrochemical workstation.The experimental results show that the HNaV₆O₁₆·4H₂O prepared at the hydrothermal temperature of 120℃,160℃,200℃,and the hydrothermal time of 12 h,18 h,and 24 h has the best crystallinity and the smallest grain size.It shows the best electrochemical performance when used as the positive electrode of the aqueous zinc ion battery,and shows a high specific capacity of 508 m Ah·g^-1 at the current density of 0.1 A·g^-1,And it can still maintain 94.4%of the maximum specific capacity after2000 cycles at 2 A·g^-1,reflecting excellent long-term cycle stability.（2）In order to further improve the long cycle performance of HNaV₆O₁₆·4H₂O at high current density,HNaV₆O₁₆·4H₂O was compounded with spherical glucose and a nano carbon layer was constructed on the surface of the cathode material by high temperature heat treatment.The effect of different HNaV₆O₁₆·4H₂O/glucose composite ratio（1:1,1:1.25,1:1.5）on the electrochemical performance of HNaV₆O₁₆·4H₂O was studied and its modification mechanism was explored.The results show that the amorphous nano-thick carbon layer formed on the surface can effectively improve the conductivity of the material,reduce its electrochemical impedance,promote the diffusion of zinc ions,thus improving the high current charge-discharge performance of the material,reduce the direct contact between HNaV₆O₁₆·4H₂O and the electrolyte,effectively inhibit the dissolution and electrochemical reaction of HNaV₆O₁₆·4H₂O in the aqueous electrolyte,and enhance the structural stability of the material in the process of Zn²⁺de-insertion.When the composite ratio is 1:1.25,the composite has the best electrochemical comprehensive performance.It can achieve a specific discharge capacity of 107 m Ah·g^-1 at a high current density of 10 A·g^-1.After 10000 cycles,it still has a high capacity retention rate of 93.8%relative to the stable state,showing excellent long-term cycle stability.