Surface to bulk synergistic restructuring of ultrahigh nickel-rich LiNi0.96Co0.02Mn0.02O2 cathode for high-performance sulfide-based all-solid-state batteries

The all-solid-state lithium batteries (ASSLBs) based on sulfide solid electrolytes (SSE) and ultrahigh nickel-rich cathode (LiNi_xCo_yMn_1-x-yO₂, where x > 0.9) encounter challenges at the electrolyte-cathode interface, such as oxygen escape and side reactions in a highly delithiated state, resulting in significant structural deterioration and rapid capacity decay. In this study, a novel surface modification strategy that serves multiple functions is proposed to achieve in-situ formation of a Li₂MoO₄ coating layer and bulk doping with Mo element for enhancing the interface compatibility between LiNi_0.96Co_0.02Mn_0.02O₂ (NCM96) and Li₆PS₅Cl (LPSCl) electrolyte. Using thermodynamic/density functional theory calculations, X-ray photoelectron spectroscopy, and in-situ distribution of relaxation times analysis, it is revealed that the incorporated strong MoO bonds in NCM96 and the surficial fast-ionic conductor layer help to stabilize lattice oxygen, and preventing further electrochemical oxidation of the sulfide electrolyte and the formation of oxygenated sulfur and phosphorus species. It is demonstrated that ASSLBs with Mo modified NCM96 as the cathode and LPSCl as the solid electrolyte (SE) exhibit a high discharge capacity of 174.4 mAh g⁻¹ and an excellent cycle retention of 78 % after 200 charge/discharge cycles. This surface-to-bulk synergistic modification strategy provides a new perspective for the design of high-performance sulfide-based ASSLBs.