Single-ion conducting poly(ethylene oxide carbonate) as solid polymer electrolyte for lithium batteries

Abstract

Single-ion conducting polymer electrolytes (SIPE) have attracted a lot of interest for application in high energy density lithium metal batteries. SIPEs possess lithium transport numbers close to unity, which does not provoke concentration gradients and holds the promise of limiting lithium dendrite formation. In this article, we have optimized a single-ion polymer incorporating the most successful chemical units in polymer electrolytes, such as ethylene oxide, carbonate and a lithium sulfonimide. This single-ion poly(ethylene oxide carbonate) copolymer was synthesized by polycondensation between polyethylene glycol, dimethyl carbonate and a functional diol including the pendant sulfonamide anionic group and the lithium counter-cation. By playing with the monomer stoichiometry, the crystallinity and ionic conductivity were optimized. The best copolymer showed high ionic conductivity values of 1.2·10-4 S.cm-1 at 70 °C. Lithium interactions and mobility were studied by lithium pulsed field gradient, lithium diffusion, NMR relaxation time measurements and FTIR-ATR analysis. High lithium mobility is observed which is due to the weakly coordinating chemical environment in the polymer and also that the sulfonamide in the SIPE adopts to a greater extent the cis conformation, which is known to promote lithium mobility. Finally, the performance of the singe-ion conducting poly(ethylene oxide carbonate) was compared in lithium symmetric cells versus an analogous conventional salt in polymer electrolyte, showing improved performance in lithium plating and stripping.