Optimization of Layered Cathode Material with Full Concentration Gradient for Lithium-Ion Batteries

Li[Ni x Co y Mn 1– x – y ]O 2 cathode materials were synthesized with varying concentration gradients of Ni and Co ions from the particle center (0.62–0.74 mol % for Ni and 0.05 mol % for Co) to the surface (0.48–0.62 mol % for Ni and 0.18 mol % for Co), i.e., full concentration gradient (FCG) with fixed Mn concentrations. In particular, the Mn concentration (20, 25, and 33 mol %) was controlled to optimize electrode performance. The average chemical compositions of lithiated products were Li[Ni x Co 0.16 Mn 0.84– x ]O 2 ( x = 0.64, 0.59, 0.51). These cathode materials with concentration gradients followed the general performance trend of conventional layered materials; an increase in Ni content improved the capacity, whereas a higher amount of Mn delivered better capacity retention and thermal properties at the expense of capacity. As a result, we determined an optimal level of Mn concentration among the tested FCG cathodes, which maximized the discharge capacity of 188 mAh g –1 and had an excellent capacity retention of 96% over 100 cycles operated up to 4.3 V at 25 °C, with a composition of FCG Li[Ni 0.59 Co 0.16 Mn 0.25 ]O 2 .