双包覆法改善高压钴酸锂正极材料的电化学性能

通过结合固相和液相包覆在Al掺杂LiCoO₂表面共包覆了钛酸锂（Li₄Ti₅O₁₂）和聚吡咯（PPy）。这种双包覆方法不仅稳定了高电压下LiCoO₂的表面，还增强了材料的离子和电子电导率。电化学测试表明，当活性物质、导电剂和黏结剂的质量比为80∶ 10∶10时，在0.5C （1C=180 mA·g^-1）电流下，循环300周后的容量保持率为76.9%，且在5C电流密度下可逆比容量为150 mAh· g^-1；由于双包覆后LiCoO₂电子电导率大幅提高，当活性物质、导电剂和黏结剂的质量比为90∶3∶7时，在0.5C电流下，循环200周后的容量保持率为82.8%，且在5C电流密度下可逆比容量为130 mAh·g^-1。X射线光电子能谱测试表明，包覆层可以在循环中保持稳定且能抑制LiCoO₂材料在高电压下的表面副反应。

Boosting the Electrochemical Performance of High-Voltage LiCoO2 Cathode by a Dual-Coating Strategy

In this study, by using the solid and liquid coating method, LiCoO₂ was dual-coated by lithium titanate (Li₄Ti₅O₁₂) and polypyrrole (PPy). The coating layers not only protect the surface of LiCoO₂ at high voltage but also increase its ion conductivity and electronic conductivity. According to the result of the electrochemistry test, when the mass ratio of active material, conductive agent, and binder was 80:10:10, the capacity retention of the modified material after 300 cycles at 0.5C (1C=180 mA·g^-1) was 76.9%. Its reversible capacity was 150 mAh·g^-1 at 5C current density. Due to the improvement of electric conductive of dual-coated LiCoO₂, when this mass ratio was 90:3:7, the capacity retention after 200 cycles at 0.5C was 82.8%. Its reversible capacity was 130 mAh·g^-1 at 5C current density. As shown in X-ray photoelectron spectra, the coating layers can keep stability during cycling and prevent side reactions on the surface.