Tuning Li₂MnO₃-Like Domain Size and Surface Structure Enables Highly Stabilized Li-Rich Layered Oxide Cathodes

Severe capacity/voltage fading still poses substantial obstacles in the commercial applications of Li-rich layered oxides, which stems from the aggregation of Li₂MnO₃-like domains and unstable surface structure. Here, we report highly stabilized Co-free Li_1.2Ni_0.2Mn_0.6O₂ with uniformly dispersed Li₂MnO₃-like domains and a protective rock-salt structure shell by reducing the oxygen partial pressure during high-temperature calcination. Experimental characterizations and DFT calculations reveal that the uniformly dispersed and small-sized Li₂MnO₃-like domains suppress the peroxidation of lattice oxygen, enabling highly reversible oxygen redox and excellent structural stability. Moreover, the induced rock-salt structure shell significantly restrains lattice oxygen release, TM dissolution, and interfacial side reactions, thereby improving the interfacial stability and facilitating Li⁺ diffusion. Consequently, the obtained Li_1.2Ni_0.2Mn_0.6O₂ which was calcinated under an oxygen partial pressure of 0.1% (LNMO-0.1) delivers a high reversible capacity of 276.5 mAh g^-1 at 0.1 C with superior cycling performance (a capacity retention rate of 85.4% after 300 cycles with a small voltage fading rate of 0.76 mV cycle^-1) and excellent thermal stability. This work links the synthesis conditions with the domain structure and electrochemical performance of Li-rich cathode materials, providing some insights for designing high-performance Li-rich cathodes.