| This article has systematically studied on Li3V2(PO4)3 about its synthesis and performance improvement as lithium battery cathode material,including the introduction of the research on lithium ion battery cathode material, characterization and electrochemical properties study on samples synthesized by different methods, and the performance comparing of synthetic samples before and after modification. Synthetic material were made in to positive electrode ,and assembled into a half-cell with lithium as negative electrode. Using XRD, SEM, TG-DTA analysis and laser particle size analysis to express the characterization of samples, and the electrochemical performance of the system also has been tested with different means, including charge-discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) test.In the experiment, LiOH·H2O and NH4VO3 were used as lithium and vanadium source. Li3V2(PO4)3 cathode material was synthesised by carbothermal reduction method and sol-gel method. Using CTR method to synthesis Li3V2(PO4)3 cathode material, conductive carbon and glucose were used as carbon sources, and sample with glucose as carbon sourse showed better overall performance. Its first discharge capacity was 119.5mAh/g under 0.1C, and retained a discharge capacity as 112.7mAh/g after 20 cycles. In sol-gel method, citric acid was used as chelating agent.We analyzed the effect of precursor pre-calcining, the amount of citric acid(nV:ncitric acid=2:1.5,2:2,2:2.5),calcining degrees(650℃,700℃,750℃) and calcining time (6h,8h,10h,12h) on the electrochemical properties of the material. The results showed that the optimal process for the synthesis of Li3V2(PO4)3 under sol-gel method was listed as follow: the mixture using citric acid as the complex was calcined at 700℃for 8h,and the molar ratio of nLi:nV:nP:ncitric acid was 3.1:2:3:2. The first discharge capacity of the sample was 127.4mAh/g under 0.05C rate.After charged/discharged at 1C rate for 20 cycles,the cathode retained a discharge capacity of 100.9 mAh/g,and this value was more than 90 percent of the first discharge capacity at the same rate.Mg2+,Al3+,Ti4+ and Si4+ were doped in Li3V2(PO4)3 cathode material to synthesize modified materials. The results showed that the performance of samples doping with these four kinds of ion were very different from Li3V2(PO4)3 itself.,and sample doped with Ti4+ formed a new phase-LiTi2(PO4)3. The Mg2+-doped sample with x=0.05 showed the best electrochemical performance, after charged/ discharged at 1C rate for 20 cycles,the cathode retained a discharge capacity of 135 mAh/g,and this value was more than 90 percent of its first discharge capacity at the same rate. The Al3+-doped sample showed the best performance with x=0.05, after charged/ discharged at 0.2C,0.5C and 1C rate for 20 cycles,the sample retained a discharge capacity of 128.9,108.4and 105.0 mAh/g respectively. Si4+-doped sample with x=0.04 showed the best electrochemical performance, after charged/ discharged at 0.05C rate for 30 cycles,the cathode retained a discharge capacity of 132.5 mAh/g, and it remained a discharge capacity for 136.4mAh/g after 30 cycles at 1C rate. Ti4+-doped samples showed the best electrochemical performance at x=0.1, the sample remained a discharge capacity for 120.3mAh/g after 30 cycles at 1C,and doping with Ti4+ can also improve the practical performance of Li3V2(PO4)3 by changing its crystal structure. |
PDF Full Text Request