Studies On The Synthesis, Structure And Electrochemical Performance Of Doped Li_1+xV₃O₈ Positive Materials Applied In Lithium-ion Batteries

Layered Li(1+x)V₃O₈ is regarded as a promising cathode material in Li ions battery for its low price, high capacity and other special electrochemical performance. Previous studies show that the structure and the electrochemical performance of Li(1+x)V₃O₈ remarkably depend on the synthesis methods. The material synthesized by the high temperature solid-state reaction has rather low discharge capacity and cycle performance. Although the material synthesized by the liquid-state reaction has higher discharge capacity than that by the high temperature solid-state reaction, it is not practical to synthesize Li(1+x)V₃O₈ with high performance for the complex synthesis process, especially in commercially. In this dissertation, the low temperature solid-state reactions, assisted by dopant and/or microwave post-treatment process, were firstly employed to improve the electrochemical performance of the Li(1+x)V₃O₈ samples.In this dissertation, we have carried out below three study topics.First topic, a fluorion doped lithium vanadium oxide with a theoretical composition of Li(1+x)V₃O_8-yF_0.02 and a real fluorion content of 0.185% prepared by the low temperature solid-state reactions. This Li(1+x)V₃O_8-yF_0.02 with a Li_1.2V₃O₈ phase exhibits a discharge capacity of 269.5mAh/g at the 1st cycle and 219.3 mAh/g at the 40th cycle. The sample stored for 15 days has a discharge capacity of 219.4mAh/g at the 1st cycle and 204.5 mAh/g at the 40th cycle. The sample stored for one month at discharge state possesses a discharge capacity of 118mAh/g at 120th cycle. It shows excellent cycle and storage performance.Second topic, a fluorion and praseodymium ions co-doped lithium vanadium oxide with a theoretical composition of Li(1+x)V₃O_8-y Pr_zF_0.02 firstly prepared by the low temperature solid-state reactions. This sample exhibits a discharge capacity of 208mAh/g at the 1 st cycle, and its capacity increased to 253mAh/g at the 40th cycle.Third topic, a microwave post-treatment process was employed to further improve the electrochemical performance of the fluorion doped lithium vanadium oxide, the experimental results showed that the electrochemical performance of the sample further improved.