High Dielectric Poly(vinylidene fluoride)-Based Polymer Enables Uniform Lithium-Ion Transport in Solid-State Ionogel Electrolytes

Abstract

Ionic liquids (ILs)-incorporated solid-state polymer electrolytes (iono-SPEs) have high ionic conductivities but show non-uniform Li⁺ transport in different phases. This work greatly promotes Li⁺ transport in polymer phases by employing a poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE), PTC] as the framework of ILs to prepare iono-SPEs. Unlike PVDF, PTC with suitable polarity shows weaker adsorption energy on IL cations, reducing their possibility of occupying Li⁺ -hopping sites. The significantly higher dielectric constant of PTC than PVDF facilitates the dissociation of Li-anions clusters. These two factors motivate Li⁺ transport along PTC chains, narrowing the difference in Li⁺ transport among varied phases. The LiFePO₄ /PTC iono-SPE/Li cells cycle steadily with capacity retention of 91.5 % after 1000 cycles at 1 C and 25 °C. This work paves a new way to induce uniform Li⁺ flux in iono-SPEs through polarity and dielectric design of polymer matrix.

Keywords: Ionic Liquids; Lithium Dendrites; Lithium-Ion Transport; PVDF; Solid-State Polymer Electrolytes.