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

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_6.4La₃Zr_1.4Ta_0.6O₁₂ 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 ⁶Li and ⁷Li 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_0.8Co_0.1Mn_0.1O₂ 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.