Surface to bulk design empowering Ni-rich layered oxide cathode in sulfide-based All-Solid-State batteries

• LLZAO surface coating with bulk Zr doping for NCM811 was constructed. • LLZAO enhances the interfacial kinetics and Zr-doped stabilizes the lattice oxygen. • 2D and 3D distribution of interfacial products were revealed by XPS and TOF-SIMS. • The ASSBs exhibit excellent rate (11C) and long-cycle performance (1000 cycles). All-solid-state batteries (ASSBs) employing sulfide solid electrolytes (SSE) and high-nickel layered oxide cathodes have attracted considerable attention, attributed to their superior safety and great potential for high energy densities. However, the interface compatibility between SSE and nickel-rich oxide cathode remains a challenge. Here, a dual-functional strategy of Li 6.25 La 3 Zr 2 Al 0.25 O 12 surface coating and bulk Zr doping in LiNi 0.8 Co 0.1 Mn 0.1 O 2 was proposed (NCM811@CD-LLZAO), aiming to enhance the interfacial compatibility toward sulfide-based ASSBs. The fabricated ASSBs exhibit an impressive capacity retention rate of 91.1% after 100cycles at 0.1C and can sustain an ultra-long cycling performance over 1000cycles at 1.0C. Remarkably, even at a high rate of 11.0C, the battery still maintains a high capacity, highlighting its excellent rate performance. The distribution of relaxation time (DRT) analysis reveals that the LLZAO buffering layer can enhance the kinetics at the cathode/electrolyte interface. Theoretical calculation further confirms that the strong Zr-O bond formed by Zr doping can stabilize the lattice oxygen and effectively prevent the sulfide solid electrolyte from further electrochemical oxidation, thereby enhancing the interfacial dynamic and stability. These encouraging results provide a new strategy for the practical application of high-energy–density ASSBs, enabling fast charge transfer, extended cycle longevity and enhanced safety.