Conductivity-modulus-T(g)relationships in solvent-free, single lithium ion conducting network electrolytes

A model system of single-ion conducting network electrolytes with acrylic backbone, ethylene oxide (EO) side chains, tethered fluorinated anions, and mobile Li cations was designed and synthesized to investigate structure-property relationships. By systematically tuning four molecular variables, one at a time, we investigated how crosslinker length, mol% of crosslinker added, Li:EO ratio and side-chain length affect conductivity,T-g, and modulus. Ionic conductivity at 90 degrees C varied by two orders of magnitude (and by three orders of magnitude at room temperature) depending on the molecular details, while a 70 degrees C span in glass transition temperature (T-g) was observed. The range of crosslinking, which can be achieved without impacting conductivity was also elucidated, and the modulus of the electrolyte can be increased by a factor of 8, up to 2.4 MPa, without impacting ion transport. Changes in conductivity due to crosslink density and crosslinker length are fully explained in terms ofT(g)shifts, while comonomer length cannot be accounted for by such a shift. The best performing network exhibited 10(-5)S/cm at high temperature, which is comparable to other single-ion conductors reported in the literature, while the modulus is higher due to crosslinking. Adding 10 wt% propylene carbonate further increased this value to 10(-4)S/cm. This work provides insights into the structure-property relationships of solid-state polymer electrolytes, which retain conductivity but can potentially help suppress dendrites.