Study On Microwave Synthesis And Modification Of Li₃v₂（po₄）₃ Cathode Materials For Lithium Ion Batteries

Monoclinic lithium vanadium phosphate Li₃V₂（PO₄）₃ is attractive for stable structure, excellent cycle performance and safety. However, their low electronic conductivity impedes their use as electrode materials. In this paper, Li₃V₂（PO₄）₃ was respectively prepared by mechanochemistry method assisted microwave heating route and sol-gel assisted microwave heating rout. The physical properties of Li₃V₂（PO₄）₃ were investigated by XRD and SEM, and their electrochemical performances were investigated by galvanostatic current charge-discharge, cyclic voltammetry, electrochemical impedance spectroscopy. The effects of preparation conditions on the physical properties and electrochemical performances of active materials were investigated.The cathode material Li₃V₂（PO₄）₃ was prepared by mechanochemistry method assisted microwave heating route. The effect of synthesis conditions on the physical performance and electrochemical behavior of Li₃V₂（PO₄）₃ was studied and the synthesis conditions were optimized. The results showed that with the increase of microwave power, the growth of crystal was quickened and the crystal becomes more perfect. It was also found that the morphology of samples affected the specific capacity and cycling performance of Li₃V₂（PO₄）₃ varied with different synthesis conditions, while the charge-discharge curves were similar. The initial charge and discharge capacity of Li₃V₂（PO₄）₃ synthesized on the optimized condition was 132.9m Ah/g at 0.2C rate（3.0-4.3V）, and 111.6m Ah/g at 2C rate.The cathode material Li₃V₂（PO₄）₃ was prepared by sol-gel assisted microwave heating rout. The effect of synthesis conditions on the physical performance and electrochemical behavior of Li₃V₂（PO₄）₃ was studied and the synthesis conditions were optimized. Compared with mechanochemistry method assisted microwave heating route, the method required power reduction, reaction time shorten. The initial charge and discharge capacity of Li₃V₂（PO₄）₃ synthesized on the optimized condition was 122.6m Ah/g at 0.2C rate（3.0-4.3V）.Ni²⁺, Cr³⁺, and Mo⁶⁺were doped in Li₃V₂（PO₄）₃ cathode material to synthesize modified materials by sol-gel assisted microwave heating rout. The results showed that the performance of samples doping with these three kinds of ion were different from Li₃V₂（PO₄）₃ itself. The Ni2+-doped sample with x=0.02 showed the best electrochemical performance; The Cr3+-doped sample with x=0.04 showed the best electrochemical performance; The Mo6+-doped sample with x=0.04 showed the best electrochemical performance. The cathode material Li₃V₂（PO₄）₃ /C+N was preparedby sol-gel method assisted microwave heating route（Melamine as nitrogen source）.The results showed that the addition of nitrogen improved the performance of the material.