Basicity regulation of Ni-rich layered oxide cathodes for all-solid-state Li-ion batteries

Ni-rich layered oxide cathode materials such as LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811) face poor interfacial stability and serious side reactions with sulfide solid-state electrolytes. This problem is thought to be exacerbated by the gradually accumulated basicity of the surface with the Ni content increasing. Herein, the acidic Li₃PO₄ coating layer on NCM811 particles is introduced by ball-milling approach to neutralize the basicity and aggrandize the interfacial stability. The tailored surface structure and components of NCM811 not only suppress the direct contact of cathode particles with sulfide solid-state electrolyte, but also facilitate electrochemical dynamics by driving the Li⁺ migration across the interface and promoting the electron exchange. Thus, cells with Li₃PO₄ coating layer yield 101.3 mAh g⁻¹ specific capacity at 2.0 C and highly reversed discharging capacity after suffering from harsh work conditions. Additionally, the stable coating layer broadens the electrochemical windows of cells, delivering long cycle stability (>100 cycles 0.5 C). This contribution highlights the importance of basicity regulation of Ni-rich layered oxide cathode and offers a low-cost and effective approach to design the interfacial structures for the development of all solid-state batteries.