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Polymerization via ultraviolet irradiation of LiTFSI21mH2O + PDA liquid mixtures turned most of these liquids into gels or solids. Here, LiTFSI21mH2O denotes a 21 m aqueous solution of lithium bis(trifluoromethanesulfonyl)imide, and PDA stands for a monomer of poly(ethylene glycol) diacrylate of Mn 575. Systematic thermoconductometric measurement on these electrolytes, both before and after the polymerization, showed the gel electrolytes to be considerably more conductive than their precursor liquid mixtures, especially at lower temperatures. A parallel measurement of glass transition temperature, θ g, revealed in these gel electrolytes a unique double glass transition enveloping two sub-transitions each with its own θ g’s. These and a number of other related experimental observations can be consistently and clearly explained based on the existence of a solution and a polymer substructure in the polymerized electrolytes, and on these substructures becoming codominant in the gels. The exceptional conductivity in these gel electrolytes points to a promising direction to formulating a polymer-supported aqueous electrolyte with a set of desirable physical traits and an uncompromising conductivity.

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.

Extensive efforts have been made to seek new battery chemistries based on multivalent working ions, with the aim to replace the mature lithium-ion batteries. These efforts were initially driven by the pursuit of higher capacity/energy, better safety and lower cost, and more recently have significantly intensified with the increasing concerns over the climate change, the limited resources of Co and Ni, and the anxieties over geopolitical as well as ethical risks of the corresponding supply chain. But how far are we from a practical multivalent battery? This talk rigorously examines the achievements made in MV batteries as reported in the current literature, while attempting to explore a pathway through the fog-of-war ahead of us.