Gradient sulfide Ti3(PO4)4 buffer layer enables highly stable NCM811/Li5.3PS4.3Cl1.7 interface for all-solid-state lithium batteries

Abstract

Due to the difference in chemical potential between sulfide solid electrolytes (SSEs) and high-energy nickel-rich layered oxide cathode materials LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811), the space charge layer (SCL) with large impedance is formed at the interface, which severely compromises the electrochemical performance of all-solid-state lithium batteries (ASSLBs). Herein, a gradient sulfide Ti₃(PO₄)₄ coating for NCM811 was designed and prepared. Due to the highly favorable O–S exchange, a gradient sulfide coating with structural and chemical similarity to Li_5.3PS_4.3Cl_1.7 SSE was formed by in situ sulfide Ti₃(PO₄)₄ on the surface of NCM811 using the sulfur-rich phosphorus sulfide molecule P₄S₁₆. The increased sulfur content towards the outer surface of the coating reduces the chemical potential difference between the NCM811 cathode and SSEs, thereby reducing the formation of the SCL and ensuring stable and fast Li⁺ transport at the interface. The full cell with gradient sulfide Ti₃(PO₄)₄-coated NCM811 cathode (PS-NCM811@TiP) exhibited excellent long-cycle stability, with a capacity retention rate of 95.2% after 100 cycles at 0.057 mA cm⁻² and 25 °C. This work provides a new perspective on the surface modification of cathodes for sulfide-based ASSLBs.