Quasi-solid single ion conducting polymer electrolyte membrane containing novel fluorinated poly(arylene ether sulfonimide) for lithium metal batteries

A novel synthesis route for a fluorinated poly (arylene ether sulfonimide) (PAESI) homopolymer with high molecular weight and excellent dispersity was developed. The sulfonimide anion moiety and –C(CF3)2 functional group, located at the polymer backbone, provide for sufficient oxidative stability, single ion conducting (SIC) properties and increased mixability with PVdF-HFP to achieve a co-polymer, which facilitates formation of highly homogeneous and mechanically stable single ion conducting polymer electrolyte (SIPE) membranes in combination with ethylene carbonate (EC):propylene carbonate (PC) (1:1) and EC:dimethyl carbonate (DMC) (1:1) as solvents. Solvent uptake has a major impact on the ionic conductivity of these blend membranes, which was further elucidated by analysis of cation coordination and transport from atomistic molecular dynamic (MD) simulations to gain insight into lithium ion transport. Moreover, the thermal behavior of the novel single ion conducting polymer was investigated before and after lithiation, showing thermal stabilization of the sulfonimide group and the increase of the glass transition temperature (Tg). Dynamic mechanical analysis (DMA) revealed high mechanical strength of the blend membranes and the observations in lithium plating/stripping experiments in Li||Li- and Cu||Li cells implied excellent stability against lithium metal and the penetration by lithium deposits. In lithium iron phosphate (LFP)||Li cells, the SIPE membranes exhibited excellent cycling stability and rate performance.