(284c) Investigation of Solvent Composition and Salt Addition in High Transference Number Nonaqueous Polyelectrolyte Solutions

High transference number electrolytes have attracted significant interest for their potential to enable high charge and discharge rates in lithium ion batteries, in addition to minimizing concentration polarization. In particular, nonaqueous polyelectrolyte solutions, in which a lithium neutralized, negatively charged polymer chain is fully dissolved and utilized as the salt, have recently been demonstrated as a promising means of enabling high conductivity, high transference number liquid electrolytes. The majority of polyelectrolyte studies to date have investigated charged polymers in aqueous solution and, as such, there is little understanding of the transport properties of polyelectrolyte solutions in battery relevant carbonate blend solvents. In this work, a polysulfone-based, sulfonated polymer is investigated in dimethylsulfoxide (DMSO) and a blend of ethylene carbonate and dimethyl carbonate (EC/DMC) (2:1 volume ratio) with and without added salt (lithium bis(trifluoromethanesulfonimide), LiTFSI). DMSO has previously been used to solvate polyelectrolytes as it provides high dissociation of the sulfonate anion, yielding conductivity of 1 mS/cm and a Li⁺ transference number greater than 0.8. The polysulfone-based polymer employed here is also fully soluble in EC/DMC, but the resulting solution has significantly lower conductivity despite the mixed solvent having a similar dielectric constant to DMSO. Using pulse field gradient NMR, the diffusion coefficients of the backbone, TFSI, and the lithium ion were tracked. Adding LiTFSI to both polyelectrolyte solutions increases the resulting conductivity, but vastly different transport properties are observed in DMSO versus EC/DMC. These results are discussed in terms of the classic polyelectrolyte theory, and the results clearly demonstrate the importance of considering factors beyond the solvent dielectric constant when designing high transference number nonaqueous polyelectrolyte solutions.