Electrochemical performance enhancement of LiNi0.6Co0.2Mn0.2O2 at high cut-off voltage by aluminum-doped polypyrrole coating

LiNi0.6Co0.2Mn0.2O2 (NCM622) is a kind of high nickel ternary cathode materials for lithium-ion batteries with high energy density and high discharge platform. However, the insufficient electron/ion conductivities and corrosion of hydrofluoric acid has limited its practical usage. In overcoming the challenges, it is particularly important to find a method that can improve both electronic and ionic conductivities of such a material. In this study, aluminum (Al)-doped polypyrrole (Al@PPy) is used to coat NCM to improve its rate and cycling performance. Compared with the uncoated NCM, Al@PPy-NCM has more electron/ion transport channels and much better cycling stability. It has an initial capacity of 224.3 mAh/g at a current density of 20 mA/g, and a capacity retention rate is 91.6 % after 100 cycles in voltage range of 3.0~4.5 V. At a current density of 200 mA/g, the initial capacity can still be 185.1 mAh/g, and the capacity retention rate can maintain 88.1 % after 200 cycles.