A Highly Conductive and Thermally Stable Ionic Liquid Gel Electrolyte for Calcium-Ion Batteries

Calcium-ion batteries are promising alternatives for post-lithium-ion batteries. However, their progress remains limited by challenges associated with the development of stable and effective electrolytes. We report for the first time an ionic liquid polymer gel membrane as both the electrolyte and the separator for use in a calcium-ion battery operating at room temperature. The membrane is prepared via single-step photo-cross-linking of poly(ethylene glycol) diacrylate in the presence of calcium salt dissolved in an ionic liquid and shows room temperature ionic conductivities between 10–4 and 10–3 S/cm, ∼4 V stability vs Ca/Ca2+, a cationic transference number of 0.17, high thermal stability up to ∼300 °C, and full dissociation of the calcium salts in the ionic liquid. A prototype battery demonstrates intercalation-based room-temperature operation, delivering a promising initial discharge capacity of ∼140 mAh/g.