Structural and Electrochemical Properties of Low-Cobalt-Content LiNi0.6+xCo0.2–xMn0.2O2 (0.0 ≤ x ≤ 0.1) Cathodes for Lithium-Ion Batteries

The layered oxides LiNi_0.6+xCo_0.2-xMn_0.2O₂ are promising cathode materials for Li-ion batteries (LIBs) owing to their moderate energy densities and structure stabilities. In this study, we systematically investigate the effects of substitution of Co by Ni on the structures, morphologies, and electrochemical properties of LiNi_0.6+xCo_0.2-xMn_0.2O₂ (0.0 ≤ x ≤ 0.1). The physical characteristics of these materials are studied by particle size analysis, scanning electron microscopy, inductively coupled plasma-atomic emission spectroscopy, Rietveld refinement of X-ray diffraction data, and X-ray photoelectron spectroscopy. The electrochemical properties are investigated by charge-discharge cycling, galvanostatic intermittent titration, and electrochemical impedance spectroscopy. As the Co content decreases and the Ni content increases, the discharge capacity and voltage platform are slightly improved, while the initial efficiency, cycling performance, rate capability, and thermal stability gradually decrease. The decreased kinetic performance is attributed to the increased degree of cation mixing and resistance, which decreases the Li⁺ diffusivity. Moreover, the activation energy gradually increases with the decrease in the Co content, which decreases the low-temperature performance. Considering its cost, energy density, cycling lifetime, kinetic performance, and safety properties, LiNi_0.65Co_0.15Mn_0.2O₂ is a promising cathode candidate for use in LIBs.