No abstract

Calcium batteries are an emerging, next generation energy storage technology undergoing intense research toward viable operation. A key aspect in their development is plating and stripping of a calcium metal anode in suitable electrolytes. Herein, we report that calcium can be plated and stripped at room temperature in an ionic-liquid-based electrolyte. Thick continuous deposits (∼20 μm) of crystalline calcium are plated and stripped over 10 cycles to areal capacities of 2.2 mAh cm −2 at a current density of 0.56 mA/cm 2 . This work presents ionic liquids as viable electrolytes for calcium anodes to enable redox activity for calcium 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/ Ca 2+ , 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.

Solid networks are produced from polytetrahydrofuran (PTHF) and 3,4-epoxycyclohexylmethyl-3′,4′epoxycyclohexane carboxylate through visible-light-initiated photo-cross-linking. The networks were loaded with different quantities of calcium nitrate to create solid polymer electrolytes (SPEs). The ion conductivity was determined by impedance spectroscopy, and the thermal properties were determined by thermogravimetric analysis and differential scanning calorimetry. All samples were rubber-like and stable over a temperature range of 30−120 °C. With greater salt loading, the ion conductivity of the electrolytes first increases and then decreases. A sample with a molar O:Ca ratio of 1.9 yielded the highest conductivity of 1.14 × 10 −4 S/cm at room temperature and transference number of 0.359 at 70 °C. The response of conductivity to temperature is modeled with both VTF and Arrhenius equations. This copolymer system provides an approach to calcium ion solid electrolytes for solid-state calcium ion batteries.

No abstract