Preparation and Electrochemical Investigation of Na and Cl Co-Doped LiNi_0.5Co_0.2Mn_0.3O₂ Cathode Materials

Abstract—LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode materials are susceptible to irreversible phase changes and surface side reactions between electrode materials and electrolyte during charging and discharging, which represent a severe danger to the safety and electrochemical performance of batteries. Li$_{{1.06--x}}$Na_xNi_0.5Co_0.2Mn_0.3O$_{{2--y}}$Cl_y cathode materials co-doped with Na⁺ and Cl^– were prepared by a simple co-precipitation method. The effects of crystal structure, morphology and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and charge-discharge performance tests. The results show that the doping of Na⁺ and Cl^– reduces the mixing of cations and expands the diffusion channels of Li⁺. Currently, the doped 1%-NCM has a high charge-discharge capacity and the best cycling performance (187.56 mA h g^–1 at 1 C with the highest capacity retention at 76.29% after the first cycle). After 50 cycles, the specific capacity retention was 138.33 mA h g^–1, which increased the capacity retention by 18.58% compared with the unmodified material, indicating that the co-doping of anions and cations improved the Li⁺ de-embedding ability as well as the specific capacity.