Block Copolymer-Enabled Low-Temperature Structural Battery Electrolytes Produced Using Polymerization-Induced Phase Separation

Structural battery electrolytes (SBEs) require both high ionic conductivity and high mechanical strength and stiffness. However, SBEs produced using the one-pot polymerization-induced phase separation (PIPS) synthesis method suffer from high tortuosity which decreases the effective ionic conductivity. Additionally, conventional liquid electrolytes demonstrate poor performance in low temperatures and are unsuitable for applications in cold climates. Here, we report SBEs generated using PIPS in the presence of an amphiphilic block copolymer (BCP), which modifies the solid-liquid interface that forms during polymerization, resulting in lower tortuosity and improved ionic conductivity. Using a low-temperature liquid electrolyte, the effect of BCP and resin content on the ionic conductivity and mechanical properties is examined. Only 1 wt % of BCP additive is needed to improve the ionic conductivities even at low temperature (2.34 × 10^-3 S/cm at 25 °C and 1.28 × 10^-4 S/cm at -30 °C, which are 78.3% and 99% higher than a similar SBE with no added BCP). The SBE, tested in both lithium iron phosphate and nitroxide radical polymer half-cells, demonstrates good compatibilities with discharge capacities of 145 mAh/g at a C-rate of 0.1 C and 103 mAh/g at a C-rate of 0.2 C, respectively, at 25 °C. At even lower temperatures of -20 °C, these cells retained 30 and 49% of their respective capacities.