Preparation And Performances Of V₂O₅·nH₂O Thin Film Doping K Or Na

Vanadium pentoxide?V₂O₅?has been very promising cathode material of lithium-ion batteries because of its high voltage,high theoretical capacity,abundant and low cost.However its low conductivity and small Li+ diffusion coefficient limit the development of V2O5.Some research have found that doping modification can effectively improve the performance of V2O5.Here,V₂O₅·nH₂O thin films doped by K,Na were prepared with sol-gel method.Furthermore,the effects of doping K or Na on the performance of V₂O₅·nH₂O thin film electrodes had been researched by means of XRD,SEM and electrochemical measurements.Results of XRD,SEM showed that doping K or Na did not alter the structure of V₂O₅·nH₂O thin films,but it increased microcrystalline characteristics.On the other hand,the doping of potassium or sodium had increased the porous structure of V₂O₅·nH₂O,and the aperture was enlarged.The K-doped V₂O₅·nH₂O film was the fluffy,porous structure with aperture of 80-200 nm,while the Na-doped V₂O₅·nH₂O film was the "fishing net" structure with aperture of 300-800 nm.Doping potassium or sodium can increase the specific surface area of V₂O₅·nH₂O film,which leads to the increase of the channel of lithium's de-intercalation and the capacity of V₂O₅·nH₂O film.Doping appropriate K not noly increase the specific capacity but also improve the cycle performance of V₂O₅·nH₂O thin film electrode.The capacities of K-doped V₂O₅·nH₂O thin films were enhanced firstly and then decreased with the increase of the content of K,and the optimum content was 1.25%.The capacities of K-doped V₂O₅·nH₂O thin films electrode decreased with the increase of current density.when the current density was increased from 150 to 2500mA/g?nearly 17 times?,The discharge capacities of the pure and K-doped V₂O₅·nH₂O film electrode were reduced about 40% and 30%.So doping K increased the rate performance of V₂O₅·nH₂O film electrode.Under the current density of 1000 mA/g,the first specific discharge capacity of pure and K-doped V₂O₅·nH₂O thin film electrode were 170 and 223 mAh/g,after 600 cycles,the discharge specific capacity fading rate were 0.11% and 0.073% per cycle.On the other side,under the current density of 2000 mA/g,the first specific discharge capacity were 163 and 187mAh/g.after 600 cycles,the discharge specific capacity fading rate were 0.1% and 0.032% per cycle.Doping appropriate Na not noly increase the specific capacity but also improve the cycle performance of V₂O₅·nH₂O thin film electrode.The capacities of Na-doped V₂O₅·nH₂O thin films were enhanced firstly and then decreased with the increase of the content of Na,and the optimum content was 3%.The capacities of Na-doped V₂O₅·nH₂O thin films electrode decreased with the increase of the current density.when the current density was increased from 500 to 2500mA/g?5 times?,The discharge capacity of the Na-doped V₂O₅·nH₂O film electrode was reduced about 20%.Under the current density of 1000 mA/g and 2000 mA/g,the first specific discharge capacity of Na-doped V₂O₅·nH₂O thin film electrode were 245 and 225 m Ah/g.after 600 cycles,the discharge specific capacity fading rate were 0.082% and 0.07% per cycle.In conclusion,The electrochemical properties of V₂O₅·nH₂O thin film electrode could be improved significantly due to the increase of the surface area and the enhancement of structure stability by doping appropriate amount of K or Na.But the discharge specific capacity of the Na-doped V₂O₅·nH₂O film electrode is higher than the K-doped,so the Na-doped V₂O₅·nH₂O film electrode has superior electrochemical properties.