In Situ Mitigating Cation Mixing of Ni-Rich Cathode at High Voltage Via Li2mno3 Injection

Ni-rich layered oxides (LiNixCoyMnzO2, x≥0.8) have been under intense investigation as cathode materials for high-energy rechargeable lithium ion batteries (LIBs) due to their high capacity and relatively low cost. However, Ni/Li cation mixing, brings about capacity degradation, structure evolution and poor thermal stability, especially at high cut-off voltage. The present work provides an innovative strategy of in-situ mitigating cation mixing for LiNi0.8Co0.1Mn0.1O2 (NCM811) at 4.55V by injecting Li2MnO3 (label as LD-NCM811). The resulting LD-NCM811 exhibits excellent electrochemical property, structural integrity and better thermal stability when compared to conventional NCM811. LD-NCM811 maintains high capacity retention of 93% at 0.3 C after 200 cycles at 25 °C with negligible voltage decay of 40 mV, whereas the NCM811 with a retention of 68% and large voltage decay of 248 mV, with the corresponding cation mixing being mitigated from 13.5% to 7.5%. At the temperature of 45 °C, LD-NCM811 still keeps a considerable capacity retention of 93% at 1 C, significantly superior to the NCM811 with 75%. Characterization and calculation reveal that the excellent performances results from the Li2MnO3 phase with unique superlattice providing lithium voids in transition metal (TM) oxide layers when it is charged above 4.5 V, which is favorable for the mixed Ni ions migrating back to TM layers instead of blocking the lithium channel. This new finding establishes a general strategy for mitigating cation mixing of NCM811 to realize its application in high energy density and safety batteries.