Understanding the role of salts on imine vitrimer electrolyte properties

Covalent adaptable networks (CANs) have emerged as promising materials for recyclability. However, the influence of ionic species on the viscoelastic properties of CANs for electrolyte applications is underexplored. In this work, we study the role of salts with different anions (Br, OTf, TFSI) and cations (Li, Na, K, Im) on the viscoelasticity, morphology, and ionic conductivity of imine vitrimers. Our results show that salts accelerate vitrimer relaxation at elevated temperatures due to the catalytic effect of cations, with larger cations having a stronger impact. However, activation energies vary with ion size, attributed to ion-polymer interactions and salt dissociation energies. Anions act as plasticizers reducing the shear modulus, except bromide due its association with the ethylene oxide backbone. Ionic conductivity increased with larger anions because of lower salt dissociation energies, although ion transport was dominated by segmental dynamics and universal behavior is observed when normalized by Tg. The vitrimers were thermally reprocessable and able to dissolve back to monomer while maintaining mechanical properties and conductivity after recovery. Modulus and ionic conductivity were also investigated with mixed salts and found to be intermediate to pure salt analogs. In conclusion, this work provides insights into tailoring vitrimer properties using various salts for sustainable and safe electrolytes.