关键词: 高镍三元材料, 单颗粒微电极, 交流阻抗, 锂离子扩散系数

Abstract:

Electrochemical performances such as capacity, rate, cycle and thermal stability of the nickel (Ni), cobalt (Co) and manganese (Mn) ternary cathode material, LiNi_xCo_yMn_zO₂ (x + y + z = 1), are significantly influenced by the proportion of Ni, Co, and Mn elements. To obtain higher specific capacity, LiNi_0.6Co_0.2Mn _0.2O₂ (NCM622) and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) with high amounts of Ni element were employed for the lithium ion batteries. By now, many studies have been focusing on the thermal and cycling stabilities of NCM622 and NCM811. However, there is lack of reports on the intrinsic kinetic properties of these two cathode materials. In this work, single particle microelectrode has been employed to investigate the intrinsic kinetic properties of NCM622 and NCM811 without the influences of binder, conductive agent, and electrode structure. Charge-discharge test, electrochemical impedance spectroscopy (EIS), and potentiostatic intermittent titration (PITT) methods were used for the evaluation of the kinetic properties of NCM622 and NCM811. Due to the increased Ni²⁺/Ni³⁺ and decreased Mn⁴⁺ amounts, the NCM811 material presented better kinetics properties and higher columbic efficiency compared with NCM622. The discharge capacity retention of NCM811 was above 80.8% at 20C compared to 0.5C, which is much higher than that of NCM622 with 68.6%.

Key words: ternary material, single particle microelectrode, electrochemical impedance spectroscopy, Li⁺ diffusion coefficient