Model single ion conducting polymer networks for understanding the impact of ion content, crosslink density, and side chain length on Li transport

Single ion conducting polymer networks were designed containing tethered anions of bis(trifluoromethane sulfonamide) (TFSI), an acrylic backbone, and ethylene oxide (EO) side chains and crosslinkers to develop fundamental structure property relationships. The crosslinking density was varied from 1-50 % mol of the starting monomers, while the crosslinker was an EO diacrylate with 11, 22, or 33 atoms between acrylate groups. The Li to EO ratio was set by the density of fixed TFSI sites and spanned 1:20 to 1:100, while the length of EO side chain on non-ionic monomers was 11 or 22 atoms is achieved. By systematically manipulating parameters, a 3 order of magnitude difference in ionic conductivity and a 70 C shift in Tg was observed indicating the importance of design in such networks. Conductivities approaching 10^-5 S/cm are reported in dry, single ion conducting networks which is comparable to the state-of-the art. Adding plasticizer further increases the conductivity. The observed structure-conductivity trends provide insight into the design of single ion conductors for a broad range of energy applications.