Lithium Salt Inclusion as a Strategy for Improving the Li + Conductivity of Nafion Membranes in Aprotic Systems

Though popular in polymer electrolyte membrane fuel cells and vanadium redox flow batteries, Nafion membranes are rarely used in lithium batteries because of their poor Li + conductivity in aprotic solvents. The performance of Nafion membranes in aprotic systems can however be improved by the following procedures: H + /Li + exchange, membrane swelling, and contraction in selected aprotic solvents to implant lithium perchlorate (LiClO 4 ) into the membrane interior. A Nafion membrane prepared as such, and containing 7.15 wt% of dispersed LiClO 4 , can have a Li + conductivity as high as 1.22 × 10 −3 S cm −1 in propylene carbonate, and 2.6 × 10 −4 S cm −1 in an ethylene carbonate/dimethyl carbonate mixture at room temperature. The inclusion of LiClO 4 also increases the tensile strength of Nafion 117 membrane by 123.7% and decreases the permeabilities of ferrocene and 1,1′‐dibromoferrocene, the common mediators for redox‐flow Li‐ion batteries, to 9.43 × 10 −7 and 1.50 × 10 −5 cm 2 h −1 , respectively, to deliver a good performance in an experimental flow cell.