Opening the door to liquid-free polymer electrolytes for calcium batteries

This work studies calcium-conducting, solvent-free polymer electrolytes in the framework of today's post-lithium battery strategies. The samples consist of three calcium salts: (i) Ca(CF3SO3)2; (ii) Ca(TFSI)2; and (iii) CaI2 hosted by commercial poly (oxyethylene) (POE). The data collected from X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicate that the polymer electrolytes consist of stable macromolecular solutions of these calcium salts. The polymer electrolytes yield conductivities exceeding 0.1 mS cm−1; POE-Ca(CF3SO3)2 reaching, at the moderate concentration O/Ca = 30, a conductivity of 0.47 mS cm−1. This preliminary and fundamental study, which demonstrates the stability of Ca-conducting polymer electrolytes, paves the way to the development of improved polymer electrolytes based on oxyethylene repeat units and new calcium salts.