Phase regulation enabling dense polymer-based composite electrolytes for solid-state lithium metal batteries

TLDR

Solid polymer electrolytes, especially poly(vinylidene fluoride)-based ones with residual solvent, are attractive for room‑temperature solid‑state lithium metal batteries but suffer from porous structure and low ionic conductivity that limit practical use. The study proposes a phase‑regulation approach that incorporates MoSe₂ sheets to disrupt PVDF chain symmetry and produce a dense composite electrolyte. The high‑dielectric composite electrolyte enhances solvation, yielding high ionic conductivity and low activation energy, while in‑situ reactions between MoSe₂ and Li metal form Li₂Se fast conductors in the solid electrolyte interphase, boosting Coulombic efficiency and interfacial kinetics. The resulting solid‑state Li||Li cells cycled robustly at 1 mA cm⁻², and Li||LiNi₀.₈Co₀.₁Mn₀.₁O₂ full cells delivered practical high‑rate (3 C), high‑loading (2.6 mAh cm⁻²) performance in pouch‑cell format.

Abstract

Solid polymer electrolytes with large-scale processability and interfacial compatibility are promising candidates for solid-state lithium metal batteries. Among various systems, poly(vinylidene fluoride)-based polymer electrolytes with residual solvent are appealing for room-temperature battery operations. However, their porous structure and limited ionic conductivity hinder practical application. Herein, we propose a phase regulation strategy to disrupt the symmetry of poly(vinylidene fluoride) chains and obtain the dense composite electrolyte through the incorporation of MoSe2 sheets. The electrolyte with high dielectric constant can optimize the solvation structures to achieve high ionic conductivity and low activation energy. The in-situ reactions between MoSe2 and Li metal generate Li2Se fast conductor in solid electrolyte interphase, which improves the Coulombic efficiency and interfacial kinetics. The solid-state Li||Li cells achieve robust cycling at 1 mA cm-2, and the Li||LiNi0.8Co0.1Mn0.1O2 full cells show practical performance at high rate (3C), high loading (2.6 mAh cm-2) and in pouch cell.