In Situ Formation of a Stable Interface in Solid-State Batteries

TLDR

Solid polymer electrolytes are promising for solid‑state batteries, but conventional casting leaves residual solvent that causes serious side reactions during charging. The authors present a novel, self‑removing method that eliminates residual solvent through spontaneous reactions. By selecting appropriate salt, solvent, and additives—specifically NaFSI, H₂O, and Al₂O₃/SiO₂ nanoparticles—the method consumes the solvent and forms stable hydrates such as AlF₃·6H₂O, enabling the preparation of PEO‑based SPEs. Resulting solid‑state sodium batteries with PEO/NaFSI‑Al₂O₃‑AQ electrolytes exhibit excellent reversibility with Na₃V₂(PO₄)₃, high rate capability, 92.8 % capacity retention after 2000 cycles, and high Coulombic efficiency, while the aqueous process is environmentally friendly and low‑cost.

Abstract

Solid polymer electrolytes (SPEs) are considered as promising candidates for solid-state batteries. SPEs with a conventional solution casting technique have serious side reactions during charging because of the residual solvent. Here we report a creative method that can self-remove it via spontaneous reactions. The core idea is to consume the residual solvent and form stable products by choosing proper salt, solvent, and additives. Inspired by the hydrolysis of sodium bis(fluorosulfonyl)imide (NaFSI), during which the proton carrier changes from H2O to HF and HF further reacts with metal oxide to form a stable hydrate, like AlF3·6H2O, NaFSI, H2O, and Al2O3/SiO2 nanoparticles are thus employed to prepare poly(ethylene oxide) (PEO)-based SPEs. Solid-state sodium batteries with PEO/NaFSI-Al2O3-AQ electrolytes exhibit good reversibility with Na3V2(PO4)3 as the active materials, high rate performance, long-term cycling stability (92.8% after 2000 cycle), and high Coulombic efficiency. Furthermore, environmentally friendly and low-cost preparation of PEO-based SPEs is realized with this aqueous technique.