Surface Modification And Electrochemical Properties Of Vanadium Pentoxide Thin Films

Lithium-ion batteries(LIBs)are excellent power sources for various portable devices because of their environmental friendliness,high output voltage,large capacity,long cycle life and no memory effect.Recently,transition metal oxides such as Ti O₂,Mn O₂ and V₂O₅ with micro-and nanostructures have been investigated as potential candidates for Li-ion battery electrodes.Among these materials,V₂O₅ has a typical two-dimensional layered crystal structure,which improves the storage capacity of lithium ions with a theoretical specific capacity of up to 420 m Ah/g.However,V₂O₅ also suffers from small specific surface area,low electrical conductivity,susceptibility to phase change during charging,poor structural stability,severe performance deterioration,and poor rate capability,which severely limit its application in lithium-ion batteries.It has been shown that the electrochemical performance of V₂O₅ can be improved by doping modification of the V₂O₅material,which can significantly enhance its electrical conductivity and therefore increase the diffusion coefficient of lithium ions in it.Therefore,in this study,we used V₂O₅ thin films as the object of study to modify the surface by doping with silver,copper,and silver-copper co-doping to enhance its electrochemical properties.In this paper,V₂O₅ thin film electrodes with different silver doping amounts were successfully prepared by a combination of sol-gel and electrodeposition methods,and the electrochemical properties of these materials were compared with those before doping.The results show that the appropriate amount of silver ion doping can promote the formation of nanoparticle-like structures on the surface of V₂O₅ thin film,which can effectively increase the specific surface area of V₂O₅thin film electrodes and improve the lithium ion transport in lithium-ion batteries.capacity.In the electrochemical test,the 1 wt.%silver-doped V₂O₅ film electrode showed excellent performance with a specific discharge capacity of 292 m Ah/g,which was 69.5%of the theoretical specific capacity(420 m Ah/g).In order to study the method to further improve the electrochemical performance of V₂O₅ thin film,an efficient copper-doped V₂O₅ thin film was prepared by using analytically pure V₂O₅powder and copper nitrate powder.By analyzing the morphological structure and electrochemical performance,when the mass fraction of copper doping was 1 wt.%,the nano-net-like structure was formed on the surface of the film,and the change of this structure could make the film electrode and electrolyte more This structure change can make the film electrode contact with electrolyte more fully,shorten the diffusion path of lithium ions in V₂O₅ film electrode,and increase the decoupling/embedding channels of lithium ions,which is beneficial to increase the embedded lithium capacity and improve the cycling stability of V₂O₅ film electrode.In addition,on this basis,it is hoped that the structural stability and electrochemical properties of V₂O₅ thin films can be further improved by co-doping with silver and copper to improve the original performance deficiencies.The multi-component materials can draw the advantages of multiple elements and exhibit excellent electrochemical properties.A series of characterization tools and performance analysis show that the appropriate ratio of silver and copper ions co-doping can promote the formation of three-dimensional nanoflower structure,which effectively increases the specific surface area of V₂O₅ thin film electrode,and this structural change can increase the contact area between the film electrode and electrolyte,so that lithium ions can be transported more efficiently in V₂O₅ thin film.The XRD results showed that the Ag⁺and Cu²⁺doping did not affect the crystalline phase structure of the material.The V₂O₅ thin film electrode with the silver to copper doping ratio of 1:1 had the smallest Rct and the largest diffusion coefficient,which played a good role in the transport of lithium ions.