Click Chemistry-Enabled Ionic Monomers for High-Performance Single-Ion Conducting Lithium Battery Electrolytes

Abstract

Single-ion-conducting polymer electrolytes (SICPs) are attractive candidates for all-solid-state lithium-metal batteries because their immobilized anionic groups enable lithium-ion transference numbers approaching unity, thereby suppressing concentration polarization and promoting uniform lithium deposition. However, their widespread application remains limited by insufficient ionic conductivity and the lack of synthetically accessible ionic liquid monomers (ILMs) combining long, flexible spacers with high electrochemical stability. Herein, we report a modular thiol-Michael click strategy for the synthesis of a new family of TFSI-based ILMs incorporating thioether-containing spacers. The proposed approach requires only three reaction steps from readily available starting materials and enables straightforward structural tuning through the selection of commercially available mercapto alcohols. RAFT copolymerization of the resulting ILMs with poly(ethylene glycol) methacrylate, followed by cation exchange, affords a series of SICPs with tunable compositions and properties. The optimized electrolyte exhibits a glass-transition temperature of −45 °C, ionic conductivities of 1.1 × 10−6 and 1.8 × 10−5 S cm−1 at 25 and 70 °C, respectively, a lithium-ion transference number of 0.96, and an anodic stability approaching 5.0 V vs. Li+/Li at 70 °C. Symmetric Li|SICP|Li cells demonstrate stable lithium plating/stripping for more than 1400 h, while all-solid-state Li∥LiFePO4 cells deliver reversible specific capacities of up to 150 and >135 mAh g−1 at C/15 and C/5 rates, with capacity retention over 95% after 200 cycles, and exhibit markedly suppressed lithium dendrite formation compared with previously reported SICPs. These results demonstrate that thioether spacer engineering effectively enhances ion transport while preserving the intrinsic advantages of single-ion conduction, and establish thiol-Michael click chemistry as a simple, scalable platform for next-generation single-ion polymer electrolytes for high-energy lithium-metal batteries.