Stepwise optimization of single-ion conducting polymer electrolytes for high-performance lithium-metal batteries

Single-ion conducting polymer electrolytes(SIPEs) are promising candidates for high-energy and highsafety lithium-metal batteries(LMBs). However, their insufficient ionic conductivity and electrochemical stability hinder their practical application. Herein, three new SIPEs, i.e., poly(1,4-phenylene ether ether sulfone)-Li(PEES-Li), polysulfone-Li(PSF-Li), and hexafluoropolysulfone-Li(6FPSF-Li), all containing covalently tethered perfluorinated ionic side chains, have been designed, synthesized, and compared to investigate the influence of the backbone chemistry and the concentration of the ionic group on their electrochemical properties and cell performance. Especially, the trifluoromethyl group in the backbone and the concentration of the ionic function appear to play an essential role for the charge transport and stability towards oxidation, and the combination of both yields the best-performing SIPE with high ionic conductivity of ca. 2.5 × 10-4S cm-1, anodic stability of more than 4.8 V, and the by far highest capacity retention in Li‖LiNi0.6Co0.2Mn0.2O2cells.