Brominated phosphoric acid tri-p-cresyl ester modified single-crystalline LiNi0.8Co0.1Mn0.1O2 toward enhanced cycling performance

Abstract

High reactivity between single-crystalline high-nickel LiNi_xCo_yMn_1-x-yO₂ cathode materials (Ni-rich SC-NCM) and the electrolyte is considered to be the main cause of fast capacity decay. To prevent direct their direct contact, we utilized a wet coating process to uniformly coat the surface of SC-NCM811 with a layer of brominated phosphoric acid tri-p-cresyl ester (Br-TCP) approximately 6 nm in thickness. X-ray photoelectron spectroscopy analysis of a cycled SC-NCM811 electrode indicates that the Br-TCP coating layer not only plays a key role in reducing interfacial side reactions, but also generates LiBr, a Li-ion conductor, due to reactions with surface lithium sources. The presence of LiBr in the coating layer enhances the lithium-ion dynamics and reduces the impact of coating layer on the lithium-ion diffusion within SC-NCM811. Additionally, the strong ionic bonds of LiBr enable enhanced adhesion between Br-TCP coating layer and SC-NCM811, thereby achieving lasting protection effect. Consequently, the synergistic effects provided by the Br-TCP modification layer are beneficial to delivering excellent electrochemical performance. Specifically, the capacity retention ratio is improved from 8.95 % to 55.28 % over 400 cycles at 1 C. We believe the strategy developed herein can provide valuable guidance in designing advanced surface modified cathodes for high-performance lithium (-ion) batteries.