Single-Crystal Ni-Rich Layered LiNi0.9Mn0.1O2 Enables Superior Performance of Co-Free Cathodes for Lithium-Ion Batteries

Cobalt-free nickel-rich layered oxides are considered as promising next-generation cathode materials for lithium-ion batteries (LIBs) due to their high capacity and controllable costs. However, the inferior cycling stability makes their application questionable. Herein, polycrystalline LiNi0.9Mn0.1O2 (PC-NM91) and single crystal LiNi0.9Mn0.1O2 (SC-NM91) were prepared by mixing the precursor with LiOH·H2O (and Li2SO4·H2O for SC-NM91). SC-NM91 with complete structure, uniform morphology, and good dispersion was successfully synthesized. The initial discharge capacity and Coulombic efficiency of both samples were similar. However, the capacity retention of SC-NM91 was 85.3% after 300 cycles at 1 C, while PC-NM91 showed only 65.8% under the same conditions. The proposed SC-NM91 cathode has better cycle stability than PC-NM91, especially under severe cycle conditions (4.5 V, 2 C, and 60 °C). The enhanced performance of SC-NM91 can be ascribed to the stronger structure, which prevents intergranular cracks, surface pulverization, disordered phase transition, and interface side reactions. In addition, it has a lower degree of Li+/Ni2+ mixing and fast Li+ diffusivity. This study provides insight into the role of single crystal structure in mitigating the performance degradation of Co-free Ni-rich cathodes and reveals that SC-NM91 can be a commercially available cathode material for high-energy LIBs.