Structure and Conductivity of Crosslinked Ca‐POE Polymer Electrolytes for Secondary Batteries

Abstract Poly(oxyethylene) (POE) is frequently used as suitable component to prepare solid polymer electrolytes (SPEs), due to its: (i) ability to coordinate and dissociate doping salts; (ii) good mechanical properties; and (iii) high chemical and electrochemical stability. With the aim to obtain calcium secondary batteries, here we describe the preparation and studies of crosslinked Ca‐polycondensate (NPCY) electrolytes with formula NPCY/(CaTf 2 ) x based on fragments of POE chains and CaTf 2 . The molecular weight of POE precursors is Y=400 and 1000 g ⋅ mol −1 . The effect of POE molecular weight on the thermal, structural, and electrical properties of NPCY/(CaTf 2 ) x is investigated revealing that in mesoscale this materials show: (i) two different nanodomains with polyether chains both “free” (not coordinating the cation) and involved in 4–4 coordination cages of Ca 2+ metal ions; (ii) f α‐fast , f α‐cross and f α‐slow relaxation modes of polyether chains, detected by broadband electrical spectroscopy, which are coupled with the long‐range charge migration pathways of SPEs; (iii) that triflate (Tf − ) anions, which act as plasticizers, modulate the inter‐chain migration processes of Ca 2+ between polyether coordination sites. Finally, the conductivity values of NPCY/(CaTf 2 ) x , which is up to 10 −4 S ⋅ cm −1 at 80 °C, classify NPCY/(CaTf 2 ) x as promising SPEs for the development of calcium secondary batteries.