Cross-Linked Polyacrylonitrile-Based Elastomer Used as Gel Polymer Electrolyte in Li-Ion Battery

Gel polymer electrolytes (GPEs) based on polyacrylonitrile elastomer (HNBR) are investigated for lithium-ion batteries application. This study examines the acrylonitrile content, as well as the solvent used to make the GPE, to understand their impact on lithium solvation. To do so, we propose a three-component system comprising HNBR:solvent:LiTFSI to pinpoint the correct ratio to provide the GPE with competitive conductivity. Infrared spectroscopy is used to shed light on the interactions between nitriles and lithium ions. Spin–lattice relaxation times (T1) and diffusion coefficients of 7Li and 19F for various HNBR-based GPEs are obtained through PFG-NMR, enabling determination of the transport number of lithium cations (t+) and activation energy (Ea). Among the GPEs tested, those composed of propylene carbonate with 2 M LiTFSI and HNBR with an acrylonitrile content of 50% are the most promising, with an ionic conductivity of 2.1 × 10–3 S/cm, D7Li of 12.0 × 10–8 cm/s, and a t+ of 0.42 at room temperature. When this GPE was tested in Li5Ti4O12/LiFePO4 coin cells, a capacity of 135 mAh/g was obtained at a discharge rate of D/5, showing promising results for its use in Li-ion batteries. This study highlights the benefits of high acrylonitrile content in the polymer and a solvent with a moderate donor number to promote interactions between nitriles and Li+.