Enhanced high-voltage cycling stability of Ni-rich cathode materials via the self-assembly of Mn-rich shells

Ni-rich layered LiNi1-x-yMnxCoyO2 (NMC, x + y < 0.5) oxides have been demonstrated to be promising cathode materials for high-energy lithium-ion batteries. However, when cycled at high voltages, NMC cathode materials with high Ni content usually show unsatisfactory capacity decay and voltage fading due to side reactions and electrochemical irreversibility during prolonged lithiation/delithiation cycles. Here, we report a Mn-rich Li0.65Mn0.59Ni0.12Co0.13O<delta> (LMNCO) material that consists of layered Li2MnO3 and spinel LiMn1.5Ni0.5O4-type components. LMNCO is a desirable shell material for improving the high-voltage cycling stability of Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode materials. Core-shell-structured NMC811@x% LMNCO materials were fabricated with satisfactory structural conformality via sonofragmentation followed by solvent evaporation-induced self-assembly and post-annealing processes. The optimized NMC811@5% LMNCO cathode material can deliver an initial discharge capacity of 150.0 mA h g(-1) at 5C (1C = 200 mA g(-1)) in a voltage range of 2.7-4.6 V vs. Li+/Li with 83.4% retention for up to 500 cycles, significantly superior to that of the bare NMC811 material (75.6%). The Mn-rich shell also enables the effective stabilization of the Ni-rich cathode materials for long-term cycling at high voltages and 55 degrees C. In addition, this work offers a synthetic prototype for the fabrication of conformal core-shell-structures, which could be adopted for the surface modification of various functional materials to achieve enhanced performance in device applications.