Stepwise Optimization of Single-Ion Conducting Polymer Electrolytes for High-Performance Lithium-Metal Batteries

Abstract

Single-ion conducting polymer electrolytes (SIPEs) are among the most promising candidates for high-energy and high-safety lithium-metal batteries. Nevertheless, their commonly limited ionic conductivity and electrochemical stability hamper their practical application. Herein, three new SIPEs, i.e., poly (1,4-phenylene ether ether sulfone)-Li, polysulfone-Li, and hexafluoropolysulfone-Li, all comprising covalently tethered perfluorinated ionic side chains, were designed, synthesized, and comparatively investigated to unveil the influence of the backbone chemistry and the concentration of the ionic group on their electrochemical properties and the eventual cell performance. In particular, the trifluoromethyl group in the backbone and the concentration of the ionic group turn out to play an important role for the charge transport and electrochemical stability towards oxidation. As a result, the combination of both leads to the best-performing SIPE with a high ionic conductivity of ca. 2.5 × 10-4 S cm-1, an anodic stability of >4.8 V, and the best cycling stability in Li‖LiNi0.6Co0.2Mn0.2O2 cells.