Polymer-Supported Aqueous Electrolytes for Lithium Ion Batteries: I. Application of a Thermoconductometric Method to a LiTFSI + H2O + PDA Electrolyte System

Abstract

A thermoconductometric method, with a uniquely designed sample cell and an in situ polymerization procedure, was applied to a polymer-supported aqueous electrolyte of wPDA + (1−w)LiTFSI21mH2O, where w is in mass fraction, PDA stands for a monomer of poly(ethylene glycol) diacrylate of Mn 575, and LiTFSI21mH2O denotes a 21 m aqueous solution of lithium bis(trifluoromethanesulfonyl)imide. The thermoconductometry curves of temperature differential, Δθ, and conductivity, κ, were collected for these samples in the w range of (0, 0.5) and θ range of (−70, 60) °C. The Δθ curves yielded a partial phase diagram revealing a high degree of compatibility between PDA and LiTFSI21mH2O, and the κ curves formed for the unpolymerized and polymerized electrolytes a pair of data sets which were fitted to yield a pair of κ(w, θ) functions for the definition of a conductivity loss function upon polymerization. This function showed that a significant portion of the conductivity was retained upon polymerization in a large part of the (w, θ) space, where a safe and robust electrolyte with a decent conductivity could be formulated. Molecular and thermodynamic considerations were applied to correlate and discuss the results of the Δθ and κ measurements.