Di-urethanesil hybrid electrolytes doped with Mg(CF3SO3)2

Abstract

Two siloxane-based di-urethanesil frameworks incorporating poly(oxyethylene) (POE) chains have been synthesized by the sol–gel process and doped with magnesium triflate (Mg(CF3SO3)2) with the goal of developing electrolytes for the fabrication of solid-state rechargeable magnesium batteries. In these matrices, short POE chains are covalently bonded to the siloxane network via urethane linkages. The xerogels have been represented by the notation d-Ut(Y) n Mg(CF3SO3)2, where Y = 300 and 600 represents the average molecular weight of the POE chains and n stands for salt composition (molar ratio of OCH2CH2 units per Mg2+). Xerogels with compositions ranging from 2 ≤ n < ∞ were prepared. A crystalline POE/Mg(CF3SO3)2 complex of unknown stoichiometry is formed in the d-Ut(300) n Mg(CF3SO3)2 materials with n ≤ 6 and in the d-Ut(600) n Mg(CF3SO3)2 materials with n ≤ 5. The organically modified silicate electrolytes with the highest conductivity of the d-Ut(300) n Mg(CF3SO3)2 and d-Ut(600) n Mg(CF3SO3)2 series are the samples with n = 6 (3.9 × 10−8 S cm−1 at 26 °C and 8.7 × 10−5 S cm−1 at 97 °C) and n = 100 (2.63 × 10−7 S cm−1 at 20 °C and 1.4 × 10−5 S cm−1 at 85 °C), respectively. Since the electrolytes for Mg batteries that have been proposed up to now have many intrinsic problems and although the room temperature conductivity values exhibited by the systems developed in the present study are still low in view of practical application, this work opens new directions for the development of solid-state Mg ion electrolytes.