A Solid Polymer Electrolyte from Cross-Linked Polytetrahydrofuran for Calcium Ion Conduction

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.