Effect of sintering temperature on Li/Ni mixing and electrochemical performance in high-nickel LiNi0.8Co0.1Mn0.1O2 cathodes

Abstract

High-nickel layered oxide LiNi_xCo_yMn_zO₂ (where x + y + z = 1 and x ≥ 0.6) has emerged as a primary focus in research on power battery cathode materials, owing to its high energy density and cost-effectiveness. However, high-nickel cathodes are prone to Li/Ni mixing during synthesis, which can potentially affect the discharge specific capacity, rate, and cycling stability of the battery. In high-nickel cathode materials, the degree of Li/Ni mixing is significantly influenced by the sintering temperature. In this study, we comprehensively investigated sintering temperature to achieve high capacity and cycling stability in LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode materials. We identified the optimal sintering temperature and investigated the mechanism behind performance degradation caused by over-sintering. This study concludes that the NCM811 cathode material synthesized at 760 °C exhibits minimal Li/Ni mixing and demonstrates superior electrochemical performance, with a capacity retention of 89.0% after 100 cycles at 1.0 C and a low polarization voltage of 0.045 V. A series of chemical and structural characterizations reveal a correlation between over-sintering, Li/Ni mixing and capacity decay. Specifically, the over-sintering temperature during synthesis of the NCM811 cathode material exhibits a linear positive correlation with Li/Ni mixing, leading to structural degradation that impedes lithium-ion diffusion pathways. Increased surface reactivity contributes to the formation of unstable cathode–electrolyte interfaces, while elevated interfacial reaction by-products deplete active material, resulting in higher capacity loss. Additionally, the pronounced, steeper two-phase irreversible H2 → H3 phase transition triggered by over-sintering accelerates the layered structure degradation, leading to the rapid decay of capacity.