Suppressing Ni/Li disordering in LiNi0.6Mn0.2Co0.2O2 cathode material for Li-ion batteries by rare earth element doping

The growing demand for efficient lithium-ion batteries to power vehicles and energy storage entails improving cathode material properties. Maintaining the stability of Ni-rich layered structure oxide cathodes is critical for long-term Li-ion battery operation. In this work, a series of LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode materials doped with selected rare earth metal ions (La, Nd, Eu) of various concentrations (0.5-1.5 mol%) was synthesized and systematically studied (XRD, XPS, TEM, STEM-EDX, galvanostatic charge/discharge tests, cyclic voltammetry). The main goal of the research was to suppress the mixing of Ni/Li cations, which influences the electrochemical performance of LiNi0.6Mn0.2Co0.2O2 cathode materials by introducing rare earth elements using co-precipitation. The results showed that the La, Nd, Eu-doped materials exhibit significantly improved electrochemical properties, such as capacity, rate performance, capacity retention and Li+ diffusivity compared to the pristine material. A clear dependence of the doped Ni-rich cathode material capacity on the degree of Ni/Li cation mixing was determined. The presence of a dopant (La, Nd or Eu) with a large radius, the tendency to form strong bonds with oxygen, and electrochemically inactive reduces Ni/Li disordering. It stabilizes the cathode structure, ensuring its better performance. The optimal content of La, Nd and Eu is 1.0, 0.5, and 0.5 mol%, respectively.