Complete Electrochemical Characterization and Limiting Current of Polyacetal Electrolytes

Abstract

We investigate a polyacetal-based electrolyte, poly(1,3,6-trioxocane) (P(2EO-MO)) mixed with lithium bis (trifluoromethanesulfonyl)imide (LiTFSI) salt, and report full electrochemical characterization of the transport parameters and a thermodynamic property in comparison to the previously reported poly(ethylene oxide) (PEO) electrolyte data [D. Gribble et al., J. Electrochem. Soc. , 166, A3228 (2019)]. While the steady-state current fraction ( ρ + ) of P(2EO-MO) electrolyte is greater than that of PEO electrolyte in the entire salt concentration window we explored, the rigorously defined transference number using Newman’s concentrated solution theory ( t + 0 ) appears to be similar to that of PEO electrolyte. On the basis of full electrochemical characterization, we calculate the salt concentration profile as a function of position in the cell and predict limiting current density ( i L L ) as a function of salt concentration. Experimental data were compared to the predicted values. The non-monotonic behaviors were observed both in prediction and experimental results with offset peak positions. We find that the limiting current density of P(2EO-MO) electrolyte is systematically lower than that of PEO electrolyte in most of the salt concentrations with the exception of r av = 0.05. It is noteworthy that even though one measure of electrolyte efficacy ( κρ + ) is superior in P(2EO-MO) electrolyte, the limiting current density, which is another metric of electrolyte efficacy at high currents, is not greater in P(2EO-MO).