Electrochemical and Mechanical Behavior in Mechanically Robust Solid Polymer Electrolytes for Use in Multifunctional Structural Batteries

Polymer electrolytes were investigated for potential use in multifunctional structural batteries requiring both mechanical and electrochemical properties. Electrolytes were formulated with a broad range of multifunctional behaviors, spanning continuously from highly conductive and structurally weak materials to poorly conductive and highly structural materials. Solvent-free polymer scaffolds were synthesized from monomers containing poly(ethylene glycol) (PEG) oligomers and one to four vinyl ester groups. The electrolytes were formed by dissolving lithium trifluoromethanesulfonate in the monomers prior to thermal cure. Electrochemical, mechanical, and viscoelastic properties were studied with respect to salt concentration, polymer chemistry, and polymer architecture. The addition of salt was found to have minimal impact on compressive stiffness, whereas it increased T g and significantly influenced ion conductivity, with a maximum conductivity at 9−12% salt w/w PEG. At a constant salt concentration, the homopolymer electrolytes exhibited close to a 1:1 inverse correlation between conductivity and stiffness as monomer composition was changed.