A gel single ion conducting polymer electrolyte enables durable and safe lithium ion batteries via graft polymerization

Abstract

Concentration polarization issues and lithium dendrite formation, which associate inherently with the commercial dual-ion electrolytes, restrict the performance of lithium ion batteries. Single ion conducting polymer electrolytes (SIPEs) with high lithium ion transference numbers (t₊ ≈ 1) are being intensively studied to circumvent these issues. Herein, poly(ethylene-co-vinyl alcohol) (EVOH) is chosen as the backbone and then grafted with lithium 3-chloropropanesulfonyl(trifluoromethanesulfonyl)imide (LiCPSI) via Williamson's reaction, resulting in a side-chain-grafted single ion polymer conductor (EVOH-graft-LiCPSI). The ionomer is further blended with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) by solution casting for practical use. The SIPE membrane with ethylene carbonate and dimethyl carbonate (EC/DMC = 1 : 1, v/v) as plasticizer (i.e., gel SIPE) exhibits an ionic conductivity of 5.7 × 10⁻⁵ S cm⁻¹, a lithium ion transference number of 0.88, a wide electrochemical window of 4.8 V (vs. Li/Li⁺) and adequate mechanical strength. Finally, the gel SIPE is applied in a lithium ion battery as the electrolyte as well as the separator, delivering an initial discharge capacity of 100 mA h g⁻¹ at 1C which remains at 95 mA h g⁻¹ after 500 cycles.