Preparation of ion conductive inorganic–organic composite systems by in situ sol–gel reaction of polymerizable ionic liquids

Inorganic–organic composites that conduct lithium ions were prepared by in situ sol–gel processing, with polymerizable ionic liquids and functional silicate or borosilicate network. In the presence of lithium salts, radical polymerization of 1‐ethyl‐3‐vinylimidazolium bis(trifluoromethane sulfonyl) imide ([evim][Tf2N]) was performed in parallel with the hydrolysis/polycondensation reaction of tetramethoxysilane (TMOS) with various trialkoxyboranes such as trimethoxyboran (TMOB), triisopropoxyborane (TiPOB) or mesityldimethoxyborane (Mes‐DMOB). Many of the resulting composites were obtained as transparent or translucent glass‐like solids. The composites had high decomposition temperatures above 300°C, due to the high thermal stability of both the inorganic network and the polymerized ionic liquids. The ionic conductivity was increased by increasing the fraction of organic compounds. The ionic conductivity of the compound was also altered by the addition of LiTf2N, up to at least 10−5 S cm−1 at room temperature. The ionic conductivity of the LiSO3CF3 doped system was about one order of magnitude less than that. The ionic conductivity was found to be influenced by the boron content of the inorganic matrix. Interaction between the triflate anion and the empty p‐orbital of boron may enhance the salt dissociation. This interaction appears to increase the lithium ion transference number. In situ sol–gel processing is a valuable way to provide mechanical strength, as well as specific functions, of polymerized ionic liquids.