Solvent-Free Superionic Polymer Conductors from a Bicontinuous Network Nanostructure

Abstract

In traditional ion conducting polymers, the lithium-ion transport is strongly coupled with segmental motion of a polymer chain. The resulted severe weakness of room-temperature ion conductivity and mechanical strength necessitates the development of superionic conductors, which decouple lithium-ion conduction from polymer segmental relaxation. Here, we demonstrate a simple and efficient superionic lithium conductor system based on polyacrylonitrile (PAN)-grafted ferroelectric poly(vinylidene fluoride) (PVDF), i.e., PVDF-g-PAN. A bicontinuous network nanostructure is constructed through the microphase segregation. The ferroelectric PVDF network not only presents a high dielectric constant, facilitating dissociation of high-concentration lithium salts, but also strongly interacts with fluorinated anions to enhance the lithium transference number (>0.6). The PAN-rich network with abundant polar nitrile groups and high glass transition temperature serves as the Li⁺ hopping channels, enabling high ion conductivity (5.8 × 10^–4 S cm^–1, 30 °C), low activation energy (0.21 eV), as well as excellent mechanical strength (>200 MPa). In particular, a nearly solvent-free condition is realized, enabling long-term stability of ion conducting performance.