The influence of the voltage plateau on the coulombic efficiency and capacity degradation in LiNi0.5Mn1.5O4 materials

High-voltage LiNi0.5Mn1.5O4 materials with working voltage of 4.7 V vs. Li/Li+ can be used in lithium-ion batteries to meet the demands of high-voltage applications. However, these materials tend to undergo capacity degradation with cycling, and exhibit low coulombic efficiency. The redox reactions of the transition metals in LiNi0.5Mn1.5O4 are related to voltage plateaus, which have an important influence on the electrochemical performance of lithium-ion batteries. In this work, we investigated the effects of two voltage plateaus for LiNi0.5Mn1.5O4 cathode (4.0 V vs. Li+/Li and 4.7 V vs. Li+/Li) on the capacity degradation and coulombic efficiency, through the charging of half-cells to different cut-off potentials. We find that the redox reactions of manganese at the 4.0 V plateau play a negligible role in the capacity loss, while the increase in manganese content in the cathode material can significantly affect the coulombic efficiency. By contrast, when the cell was charged to cut-off potentials ≥4.8 V with a plateau at 4.7 V for nickel, the cell capacity degraded rapidly. Interestingly, when the cells were charged to 5.0 V, the content of P, F, Ni, and Mn increased with the thickness of the SEI film, indicating accelerated decomposition of the electrolyte due to the contribution of nickel. Thus, this work verifies the dependence of the capacity degradation and coulombic efficiency on the voltage plateau, and provides important information for further investigation of the effect of voltage plateaus on the characteristics and behavior of cathode materials.