Constructing Interfacial Nanolayer Stabilizes 4.3 V High‐Voltage All‐Solid‐State Lithium Batteries with PEO‐Based Solid‐State Electrolyte

Abstract The complicated interfacial problems of poly(ethylene oxide) (PEO)‐based solid polymer electrolytes (SPEs) at high voltages severely hinder its practical applications for high‐energy‐density all‐solid‐state lithium batteries (ASSLBs). Herein, the failure mechanisms of ASSLBs with LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM)‐PEO are studied. It is found that the ASSLBs after charge generates a sharp drop of 0.62 V at the cut‐off voltage of 4.30 V, and induce a high interfacial resistance due to forming an uneven thick cathode electrolyte interface on the NCM surface, as well as cause the destruction of NCM surface structure during storage, leading to serious performance degradation. Constructing the interfacial nanolayer with aromatic polyamide (APA) on the surface of NCM active particles (NCM@APA) can mitigate interfacial side reactions between NCM and SPE. Robust interfacial nanolayers not only effectively protect the crystal structure of NCM but also provide a steady interfacial environment for Li + diffusion kinetics. Accordingly, NCM@APA||SPE||Li ASSLBs exhibit an acceptable voltage drop of 0.27 V after 10 days storage and a substantially improved electrochemical performance with an average coulombic efficiency of 99.1% and capacity retention of 76.7% at 30 mA g −1 after 80 cycles.