Thermal stability and reduction mechanism of LiNi0.8Co0.1Mn0.1O2 and LiNi0.5Co0.2Mn0.3O2 cathode materials studied by a Temperature Programmed Reduction

The temperature Programmed Reduction method was applied to analyze the structural and thermal behavior of LiNixCoyMnzO2 (x = 0.5 and 0.8). All reduction phases of LiNi0.5Co0.2Mn0.3O2 powder were transitioned above 843 K. For LiNi0.8Co0.1Mn0.1O2 powder, three reduction steps are starting at 661 K. It contributes to the transition to Ni2+, Co2+, Ni-0, and Co-0 phases, respectively. It was consistent with the reduction mechanism of LiNiO2 and LiCoO2. In delithiated NCM523, only a structural change from H1 to M is observed, which does not significantly affect thermal stability. For delithiated NCM811, the TPR result was sharply reduced to 536 K in the H2-H3 structural transition. When charged to 4.4 V, it decomposes into a NiO-like phase at 507 K. The reducing phase was verified through X-ray diffraction after all decomposition steps of the TPR results. As a result, the TPR method can confirm the reduction mechanism and thermal stability of the cathode material.