Nanocomposite Polymer Gel Electrolyte Based on TiO₂ Nanoparticles for Lithium Batteries

In this article, the specific features of competitive ionic and molecular transport in nanocomposite systems based on network membranes synthesized by radical polymerization of polyethylene glycol diacrylate in the presence of LiBF4, 1-ethyl-3-methylimidazolium tetrafluoroborate, ethylene carbonate (EC), and TiO2 nanopowder (d~21 nm) were studied for 1H, 7Li, 11B, 13C, and 19F nuclei using NMR. The membranes obtained were studied through electrochemical impedance, IR-Fourier spectroscopy, DSC, and TGA. The ionic conductivity of the membranes was up to 4.8 m Scm−1 at room temperature. The operating temperature range was from −40 to 100 °C. Two types of molecular and ionic transport (fast and slow) have been detected by pulsed field gradient NMR. From quantum chemical modeling, it follows that the difficulty of lithium transport is due to the strong chemisorption of BF4– anions with counterions on the surface of TiO2 nanoparticles. The theoretical conclusion about the need to increase the proportion of EC in order to reduce the influence of this effect was confirmed by an experimental study of a system with 4 moles of EC. It has been shown that this approach leads to an increase in lithium conductivity in an ionic liquid medium, which is important for the development of thermostable nanocomposite electrolytes for Li//LiFePO4 batteries with a base of lithium salts and aprotonic imidasolium ionic liquid.