Accelerated 3D Percolation Network for Ultra‐High Critical Current Density of Composite Solid‐State Electrolyte

Abstract Solid‐state batteries (SSBs) have attracted widespread attention due to their high safety and energy density. However, the sluggish ion transport and interfacial instability of solid‐state electrolytes has emerged as fundamental barriers in practical applications, resulting in the unsatisfied critical current density (CCD< 2 mA cm −2 ). Herein, a high‐flux 3D percolating composite polymer electrolyte (P‐CPE) is proposed, fabricated through in situ polymerization of a localized high‐concentration gel polymer electrolyte (LHCE‐GPE) integrating within a free‐standing porous Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) skeleton. Such P‐CPE electrolyte enables the fast Li + flux along the continuous LATP and LATP/GPE interface to achieve a fantastic conductivity of 1.36 × 10 −3 S cm −1 and LiF‐rich solid electrolyte interphase (SEI) chemistry for robust Li|P‐CPE interfacial stability. Consequently, the as‐assembled Li||Li symmetrical cells demonstrate a recorded CCD exceeding 4.5 mA cm −2 and durable long‐term stability over 3000 h at 0.2 mA cm −2 and as well as stable rate‐cycling even under a larger current density over 3 mA cm −2 , highly surpassing the controlled one (0.5 mA cm −2 ). This work thereby provides a highly promising strategy to high‐flux composite electrolytes designing to boost practical dendrite‐free SSBs.