Cost-effective low-toxicity hydrogel quasi-solid polymer electrolyte (QSPE) with a PEO-based hyperbranched polymer host

The drive for safer and longer-lasting power storage devices has centered on the development of solid electrolytes. Our group has developed a PEO-based quasi-solid polymer electrolyte (QSPE) that utilizes a hyperbranched polymer host, generated by in situ polymerization, that imparts mechanical strength while maintaining the amorphous character required for electrolyte conductivity. In this report, a LiCl-in-H₂O QSPE was prepared and characterized. By replacing the traditional QSPE carbonate plasticizer with water, the use of lower-cost, reduced-toxicity electrolytic salts is realized, leading to a safer hydrogel electrolyte. The LiCl-in-H₂O QSPE exhibited competitive room-temperature bulk conductivity (5.5 × 10⁻⁴ S/cm), with mechanical strength (0.40 MPa shear storage modulus) suitable for flexible electronics. Notably, the LiCl-in-H₂O QSPE has a lower cost ($0.60 per g) and acute toxicity estimate (2120 mg/kg) relative to traditional formulations. In structural supercapacitors, the hydrogel QSPE enables specific capacitance 23.11 mF/g of and energy density of 2.05 × 10⁻³ Wh/kg. This work validates the combination of a hyperbranched polymer host with an aqueous lithium salt as a promising and cost-effective strategy for development of safer, next-generation lithium-based energy storage devices.