Low-Temperature Structural Battery Electrolytes Produced by Polymerization-Induced Phase Separation

Structural battery electrolytes (SBEs) possess both high ionic conductivity and high mechanical strength and stiffness. These emerging materials are critical components in load-bearing structural batteries, which offer mass and volume savings beneficial to electrified transportation and aerospace applications. However, in extreme cold (< −40 °C), conventional liquid electrolytes freeze or become too viscous to conduct ions. Further, liquid electrolytes alone are unsuitable for structural batteries because liquids cannot bear structural loads. Here, we report a two-phase solid–liquid structural battery electrolyte capable of conducting ions in extreme cold. Specifically, the structural battery electrolyte consists of a bicontinuous solid, cross-linked bisphenol A-ethoxylated dimethacrylate resin and a lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI)/fluoroethylene carbonate (FEC)-diglyme-based liquid electrolyte. The relative liquid/solid content was varied, and ionic conductivities of 1.62 × 10–4 S/cm at −10 °C and 7.44 × 10–6 S/cm at −40 °C were obtained for the case of 90 wt % liquid/10 wt % solid. When the liquid content of the structural battery electrolyte was increased from 50 to 90 wt %, the modulus decreased from 0.910 GPa to 8.13 × 10–4 GPa at 25 °C, and ultimate tensile strength (UTS) decreased from 14.9 to 0.0582 MPa. These findings culminated in the application of the structural electrolyte to a graphite vs lithium metal half-cell battery operated at 0.1 C-rate where it exhibited a charging capacity of 353 mAh g–1 (∼95% of graphite’s theoretical capacity). Taken together, these results have immediate relevance to the electrification of automobiles, aircraft, and spacecraft.