Substantial Doping Engineering in Layered LiNi0.5+xCo0.2−xMn0.3O2 Materials for Lithium-Ion Batteries

Abstract

To reduce cost while maintaining the specific capacity of LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode, we systematically explore the effect of Ni substitution for Co on the structure, electrochemical performance, and thermal stability of NCM523, LiNi0.55Co0.15Mn0.3O2 (NCM5.5:1.5:3), and LiNi0.6Co0.1Mn0.3O2 (NCM613) cathodes in this study. These materials were investigated by scanning electron microscopy, particle-size analysis, Rietveld refinement of X-ray diffraction, inductively coupled plasma-atomic emission spectroscopy, X-ray photoelectron spectroscopy, charge-discharge testing, electrochemical impedance spectroscopy, the galvanostatic intermittent titration technique, and differential scanning calorimetry. The results indicate that a decrease in the Co content of NCM523 lead to an increase in the voltage platform and discharge capacity, which contributes to the improvement of the energy density. However, the initial efficiency, cycle performance, rate capability, and low-temperature performance was found to slightly decrease. This behavior can be attributed to the lower Co content yielding higher degrees of Li+/Ni2+ disordering, higher resistance, lower Li+ diffusivity, and higher activation energy (E a ). Moreover, as the Co content decreased, the thermal stability of NCM523 was slightly decreased. Considering both cost and performance, NCM5.5:1.5:3 and NCM613 materials deserve to be considered as the preferred next-generation materials.