Composite electrolyte with self-inserted structure and all-trans F conformation provides fast Li⁺ transport for solid-state Li metal batteries

Abstract

Solid-state Li metal battery has attracted increasing interests for its potentially high energy density and excellent safety assurance, which is a promising candidate for next generation battery system. However, the low ionic conductivity and Li⁺ transport number of solid-state polymer electrolytes limit their practical application. Herein, a composite polymer electrolyte with self-inserted structure is proposed using the layered double hydroxides (LDHs) as dopant to achieve a fast Li⁺ transport channel in poly(vinylidene-co-trifluoroethylene) [P(VDF-TrFE)] based polymer electrolyte. In such a composite electrolyte, P(VDF-TrFE) polymer has an all-trans conformation, in which all fluorine atoms locate on one side of the polymer chain, providing fast Li⁺ transport highways. Meanwhile, the LDH can immobilize the anions of Li salts based on the electrostatic interactions, promoting the dissociation of Li salts, thereby enhancing the ionic conductivity (6.4 × 10^–4 S cm^–1) and Li⁺ transference number (0.76). The anion immobilization effect can realize uniform electric field distribution at the anode surface and suppress the dendritic Li growth. Moreover, the hydrogen bonding interaction between LDH and polymer chains also endows the composite electrolyte with strong mechanical properties. Thus, at room temperature, the Li || Li symmetric cells can be stably cycled over 1000 h at a current density of 0.2 mA cm^–2, and the full cells with LiFePO₄ cathode deliver a high capacity retention (>95%) after 200 cycles. This work offers a promising route to construct solid-state polymer electrolytes with fast Li⁺ transport.

Keywords

LDH / Li metal batteries / Li⁺ transport channel / P(VDF-TrFE) / solid-state polymer electrolytes