A Mild Surface Washing Method Using Protonated Polyaniline for Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ Material of Lithium Ion Batteries

The residual lithium compounds on the surface of Ni-rich layered LiNi_xCo_yMn_1-x-yO₂ materials are detrimental to their electrochemical properties. This study reports a mild polyaniline (PANI) washing method to effectively reduce the residual lithium compounds on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ material without any harmful effects on its structural integrity. After the PANI washing process, the rate and cycling performance of LiNi_0.8Co_0.1Mn_0.1O₂ material are significantly enhanced. The as-obtained LiNi_0.8Co_0.1Mn_0.1O₂ material exhibits a discharge capacity of 160.65 mAh g⁻¹ and a capacity retention of 86.95% after 100 cycles at 55 °C and the current rate of 2C, which are much higher than those of pristine material (131.57 mAh g⁻¹ and 74.90%). The performance enhancement mechanism is the reduction of surface residual lithium compounds due to the PANI washing process, leading to the improvement of lithium ions diffusion and electron transport. Furthermore, some PANI can be left and coated on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ material via the washing process, which forms more stable interface film, resulting in even better cycling capability. This study provides a promising strategy for the surface modification of Ni-rich layered oxide materials for lithium ion batteries.