天然微晶石墨提纯工艺及可逆储锂性能

Purification Process and Reversible Lithium Storage Performance of Natural Microcrystalline Graphite

天然微晶石墨含量丰富,晶粒微小,表现为各向同性,是制备锂离子电池负极材料的极好原料,但其纯度不高,利用盐酸和氟硅酸对浮选后微晶石墨进行混酸提纯处理。实验结果表明:当液固比为2∶1、HF体积分数为50%、提纯时间为3 h、提纯温度为70℃时固定碳含量最高,达99%;结合XRD、SEM、EDS和Raman分析可知,混酸提纯后微晶石墨纯度提高,层间距变小,结晶度提高;提纯后的微晶石墨首次放电比容量为778. 9 mAh/g,首次库伦效率增加到61. 3%,循环性能、充放电效率和倍率性能均提高,阻抗值均降低。

Natural microcrystalline graphite is rich, and its crystalline grain is tiny, which is used as excellent raw material preparing for lithium ion batteries cathode materials because of its presented isotropic, but its purity is low. Hydrofluoric acid and fluorosilicic acid were used to treat microcrystalline graphite. The experimental results show that when liquid-solid ratio is 2∶ 1, HF volume fraction is 50%, purification time is 3 h, purification temperature is 70 ℃, fixed carbon content is the highest which is 99%. Purity of microcrystalline graphite and crystallinity are increased, interval between layers is decreased combined with XRD, SEM, EDS and Raman analysis. Initial discharge capacity of the purified microcrystalline graphite is 778.9 mAh/g and its initial coulomb efficiency is increased to 61.3%. Cycle performance of purified microcrystalline graphite, charging and discharging efficiency, multiplier performance are improved, and every impedance of lithium ions is decreased.