Structure and Dynamics in Self-Healing Polymer Electrolytes Based on PVDF-HFP for Battery Applications

Abstract

Lithium dendrite formation is a key limitation in rechargeable Li metal batteries. Here we report on a novel polymer electrolyte with self-healing capabilities, consisting of PVdF-HFP membranes imbibed with an ionic liquid electrolyte EMIM-TFSI + LiTFSI and mechanically reinforced by alumina nanowires. Similar membranes were reported to have self-healing capability via resistance to dendrite formation at the electrode-electrolyte interface.1 We have investigated the structure and dynamics in these membranes by nuclear magnetic resonance (NMR). Double resonance and 2D NMR methods show that the EMIM cation interacts with CF3 group present in HFP, forming an ion-dipole association which may be related to the desired self-healing properties. Moreover, addition of alumina nanowires has been reported2 to increase the ionic conductivity in the membrane in addition to imparting mechanical strength. We have used pulsed field gradient (PFG) NMR to investigate how alumina nanowire doping into the PVDF-HFP-IL matrix improves the Li+ diffusivity. Additional characterizations such as electron dispersion X-ray (EDX) spectroscopy to study nanowire distribution in the polymer and ionic conductivity measurements, will also be discussed. Keywords: Ionic Liquids, Self-healing, Dendrite formation, PVDF-HFP membranes, NMR spectroscopy, EDX References Chen, T. et al. Ionic liquid-immobilized polymer gel electrolyte with self-healing capability, high ionic conductivity and heat resistance for dendrite-free lithium metal batteries. Nano Energy 54, 17–25 (2018).Kwon, S. J. et al. Influence of Al2O3 Nanowires on Ion Transport in Nanocomposite Solid Polymer Electrolytes. Macromolecules 51, 10194–10201 (2018).