Surface‐to‐Bulk Synergistic Modification of Single Crystal Cathode Enables Stable Cycling of Sulfide‐Based All‐Solid‐State Batteries at 4.4 V

Abstract The interfacial stability between sulfide solid‐state electrolytes (SSEs) and high voltage Ni‐rich oxide cathodes is critical to the electrochemical performances of all‐solid‐state batteries (ASSBs), yet it is challenging to solve the interface issues by surface coating modification. Here, a surface‐to‐bulk synergistic modification is proposed to achieve a highly stable interface through the combination of TiNb 2 O 7 ‐coated and Ti‐doped LiNi 0.6 Mn 0.2 Co 0.2 O 2 single crystals (DC‐TNO@SCNCM). The TiNb 2 O 7 coating layer with thermodynamic/electrochemical stability and electronic insulation avoids the decomposition of SSEs. The strong TiO bond in SCNCM achieved by Ti doping can stabilize lattice oxygen and avoid further electrochemically oxidizing sulfide electrolytes to form oxygenated sulfurous and phosphorous species. The modified DC‐TNO@SCNCM cathode exhibits excellent long‐cycle stability with a capacity retention rate of 92.2% after 140 cycles at a high cut‐off voltage of 4.4 V. This surface‐to‐bulk synergistic modification strategy provides a new perspective for the design of high‐voltage sulfide‐based ASSBs.