리튬이차전지용 전체 농도 구배형 양극활물질의 조성별 전기화학적 특성 및 열 안정성에 대한 연구

Abstract

Li[NixCoyMn1-x-y]O2 cathode materials were synthesized with varying concentration gradients of Ni and Co ions from the particle center to the surface at a fixed Mn concentration, i.e., full concentration gradient (FCG). In particular, the Mn concentration (20, 25, 30, and 33 mol%) was controlled to optimize electrode performance. The average chemical compositions of lithiated products were Li[NixCo0.16Mn0.84-x]O2 (x= 0.51, 0.54, 0.59, and 0.64). 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 oC, with a composition of FCG Li[Ni0.59Co0.16Mn0.25]O2.