Single lithium-ion conducting polymer electrolytes based on poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide] anions

Abstract

New single lithium-ion conducting polymer electrolytes are prepared by a copolymerization of the two monomers, lithium (4-styrenesulfonyl)(trifluoromethanesulfonyl)imide (LiSTFSI) and methoxy-polyethylene glycol acrylate (MPEGA, CH2CHCO2(CH2CH2O)nCH3, n=8) in various monomer ratios. The structures and compositions of the prepared lithium poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide-co-methoxy-polyethylene glycol acrylate] (Li[PSTFSI-co-MPEGA]) copolymers are characterized by 1H and 19F NMR, and gel permeation chromatography (GPC). For comparison, the corresponding blended polymer electrolytes comprising lithium poly[(4-styrenesulfonyl) (trifluoromethanesulfonyl)imide] (LiPSTFSI) and poly(ethylene oxide) (PEO) are also prepared and characterized. The fundamental properties of these two types of lithium-ion conducting polymer electrolytes are comparatively studied, in terms of phase transitions, thermal stability, XRD, ionic conductivities, lithium-ion transference numbers (tLi+), and electrochemical stabilities. Both types of the polymer electrolytes are thermally stable up to 300°C. While both types of polymer electrolytes exhibit single lithium-ion conducting behavior with tLi+>0.9, the solid-state ionic conductivities of the Li[PSTFSI-co-MPEGA] copolymer electrolytes are all higher by 1–3 orders in magnitude than those of the blended ones, irrespective of the concentration of lithium ions. The highest ionic conductivities for the copolymer electrolytes are 7.6×10−6Scm−1 at 25°C and reach 10−4Scm−1 at 60°C, which are obtained at the ethylene oxide (EO) unit/Li+ ratio of 20.5.