Interfacial Plasticization Strategy Enabling a Long‐Cycle‐Life Solid‐State Lithium Metal Battery

Abstract The limited ionic conductivity and unstable interface due to poor solid–solid interface pose significant challenges to the stable cycling of solid‐state batteries (SSBs). Herein, an interfacial plasticization strategy is proposed by introducing a succinonitrile (SN)‐based plastic curing agent into the polyacrylonitrile (PAN)‐based composite polymer electrolytes (CPE) interface. The SN at the interface strongly plasticizes the PAN in the CPE, which reduces the crystallinity of the PAN drastically and enables the CPE to obtain a low modulus surface, but it still maintains a high modulus internally. The reduced crystallinity of PAN provides more amorphous regions, which are favorable for Li + transport. The gradient modulus structure not only ensures intimate interfacial contact but also favors the suppression of Li dendrites growth. Consequently, the interfacial plasticized CPE (SF‐CPE) obtains a high ionic conductivity of 4.8 × 10 −4 S cm −1 as well as a high Li + transference number of 0.61. The Li–Li symmetric cell with SF‐CPE can cycle for 1000 h at 0.1 mA cm −2 , the LiFeO 4 (LFP)‐Li full‐cell demonstrates a high capacity retention of 86.1% after 1000 cycles at 1 C, and the LiCoO 2 (LCO)‐Li system also exhibits an excellent cycling performance. This work provides a novel strategy for long‐life solid‐state batteries.