Welding surface epitaxial layer enables high-loading sulfide all-solid-state batteries

Ultrahigh-Ni layered oxide cathodes suffer from high surface reactivity and severe strain propagation in sulfide all-solid-state batteries. Herein, we propose an in situ transformation strategy employing indium oxide to "capture" residual lithium impurities on the ultrahigh-Ni LiNi_0.9Co_0.05Mn_0.05O₂ (NCM90) cathode. Simultaneously, the near-surface structure is reconstructed and forms a conformal epitaxial layer via residual alkali "welding". The reconstructed layer effectively suppresses spontaneous side reactions at the cathode-electrolyte interface and then prevents the structural fatigue in the bulk phase. The sulfide all-solid-state lithium batteries (ASSLBs) deliver a high reversible capacity of ∼2 mAh cm^-2 (>190 mAh g^-1, 0. 069 mA cm^-2), long cycling stability, and a good rate capability with a cathode loading of 9 mg cm^-2. Coupling synchrotron X-ray tomography (micro-/nano-CT) and X-ray absorption near-edge structure (XANES), the multi-scale observations from the particle level to the electrode levels reveal greatly alleviated interfacial instability and chemo-mechanical disintegration. We highlight the importance of surface engineering in stabilizing Ni-rich layered cathodes toward high-energy sulfide ASSLBs.