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

Abstract

Li[NixCoyMn1-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[NixCo1.6Mn0.84-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 degrees C, with a composition of FCG Li[Ni0.59Co0.16Mn0.25]O-2.