Activating Interfacial Ion Exchange in Composite Electrolytes to Realize High‐Rate and Long‐Cycling Solid‐State Lithium Batteries

Abstract Composite solid electrolytes (CSEs) are promising candidates for solid‐state lithium metal batteries. However, the poor cross‐phase Li + transport restricts the rate performance and cycle life of the batteries. Herein, we revealed the Li + percolation behavior in poly(vinylidene fluoride) (PVDF)‐based CSEs with Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 filler. The de‐coordination barrier from Li + clusters determines interfacial Li + transport capability. We then employed a designed N ‐methyl‐2,2,2‐trifluoroacetamide (NMTFA) ligand to lower the de‐coordination energy and activate interfacial Li + exchange. The ionic conductivity is therefore increased from 3.32 × 10 −4 to 7.30 × 10 −4 S cm −1 . By tracking the 6 Li and 7 Li substitution process, it was identified that the proportion of interfacial Li + transport increases from 11% to 26%. The NMTFA also contributes to the formation of inorganic‐rich interphases with electrodes. As a result, the Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 solid‐state batteries exhibit ultra‐long lifespans of 2400, 3000, and 10 000 times at 2, 5, and 10C, respectively, as well as achieve 1000 cycles at 50 °C and 300 cycles at −30 °C. This work highlights the critical role of interfacial Li + transport for the CSEs with “polymer‐Li + clusters‐filler” configuration to realize high‐rate and long‐cycling solid‐state lithium batteries.