Research Of High Performance V₂O₅·nH₂O Thin Film Electrode For Lithium Ion Battery

Vanadium pentoxide(V2O5·nH2O) has become a very promising cathode material for lithium-ion batteries because of its advantages like good lithium embed performance, high specific capacity, abundant resources, low price and so on. However, the poor structure stability and low conductivity have limited its application in lithium-ion batteries. Here, morphologies and electrochemical performances of V2O5·nH2O thin films prepared by sol-gel method were systematic researched by means of XRD, SEM, XPS and electrochemical measurements.Results from XRD, SEM showed that V2O5·nH2O thin films prepared at low temperature(?250?) have amorphous structure. V2O5·nH2O thin films all have smooth and porous surface characteristics, while V2O5·nH2O thin films with holes on the surface prepared at 150? are most dense and uniform distribution. The diameter of holes is about 50 ~ 90 nm. The large surface is useful to enlarge the contact electrode and electrolyte, short the lithium ion diffusion path and improve specific capacity and cyclic stability.The tests showed the performances of V2O5·nH2O thin film electrode are effected significantly by the annealing temperature. The electrochemical performance of V2O5·nH2O thin film electrode prepared at low temperature(?250 ?) is significantly superior to that of crystalline V2O5 thin films electrode. V2O5·nH2O thin film electrode prepared at 150? showed the best electrochemical performance. The initial discharge specific capacity is 409 mAh/g with the current density of 150 mA/g, while it only decreased by 16.2%(from 277.78 to 232.83 mAh/g) with the increases of current density from 250 to 550 mAh/g(2.2 times). With current density of 550 mA/g, the discharge specific capacity fading rate of V2O5·n H2 O thin film electrode is only 0.14% after charge/discharge 104 cycles, suggesting a nice electrochemical performance and cycle stability. The electron transfer number of the electrode reaction of V2O5·nH2O thin film are 3, and theoretical specific capacity is 441 mAh/g.XPS analysis results showed that the proportion of V4+ in V2O5·nH2O thin film are increased by doping copper, and the structure stability of active material in the electrode and the specific capacity are markedly improved. When Copper doping amount is 1%, the electrochemical performance of V2O5·nH2O thin film electrode is optimal. Under the current density of 250 mA/g, the discharge capacity can reach 344 mAh/g, higher than that of pure V2O5·nH2O by 50 mAh/g, while the fading rate is decreased by 1.1%. Under the current density of 550 mA/g, the discharge capacity of copper-doped V2O5·nH2O thin film is higher than that of pure V2O5·nH2O before 40 cycles, but decreased obviously after 40 cycles, with a higher fading rate and worse stability performance.In conclusion, V2O5·nH2O thin film prepared at 150? has the best morphology and electrochemical performance. Doping copper can not only significantly improved the discharge specific capacity of V2O5·nH2O thin film electrode, but also effectively suppress the capacity attenuation. Therefore both of them could be applied potentially for lithium ion battery.