Surface Degradation of Single‐crystalline Ni‐rich Cathode and Regulation Mechanism by Atomic Layer Deposition in Solid‐State Lithium Batteries

Abstract Single‐crystalline Ni‐rich cathode (SC‐NCM) has attracted increasing interest owing to its greater capacity retention in advanced solid‐state lithium batteries (SSLBs), while suffers from severe interfacial instability during cycling. Here, via atomic layer deposition, Li 3 PO 4 is introduced to coat SC‐NCM (L‐NCM), to suppress undesired side reaction and enhance interfacial stability. The dynamic degradation and surface regulation of SC‐NCM are investigated inside a working SSLB by in situ atomic force microscopy (AFM). We directly observe the uneven cathode electrolyte interphase (CEI) and surface defects on pristine SC‐NCM particle. Remarkably, the formed amorphous LiF‐rich CEI on L‐NCM maintains its initial structure upon cycling, and thus endows the battery with improved cycling stability and excellent rate capability. Such on‐site tracking provides deep insights into surface mechanism and structure–reactivity correlation of SC‐NCM, and thus benefits the optimizations of SSLBs.