A room-temperature sodium–sulfur battery with high capacity and stable cycling performance

TLDR

High‑temperature sodium–sulfur batteries are commercially used for large‑scale energy storage, yet their safety issues limit widespread adoption. The study introduces a room‑temperature sodium–sulfur battery that achieves high electrochemical performance and enhanced safety by using a cocktail‑optimized electrolyte containing propylene carbonate, fluoroethylene carbonate, a highly concentrated sodium salt, and indium triiodide. First‑principle calculations and experiments show that the fluoroethylene carbonate and high salt concentration suppress sodium polysulfide solubility and build a robust solid‑electrolyte interface on the sodium anode, while indium triiodide acts as a redox mediator to accelerate cathode reactions and forms a passivating indium layer on the anode to prevent corrosion. The resulting battery delivers high capacity and long‑term cycling stability.

Abstract

Abstract High-temperature sodium–sulfur batteries operating at 300–350 °C have been commercially applied for large-scale energy storage and conversion. However, the safety concerns greatly inhibit their widespread adoption. Herein, we report a room-temperature sodium–sulfur battery with high electrochemical performances and enhanced safety by employing a “cocktail optimized” electrolyte system, containing propylene carbonate and fluoroethylene carbonate as co-solvents, highly concentrated sodium salt, and indium triiodide as an additive. As verified by first-principle calculation and experimental characterization, the fluoroethylene carbonate solvent and high salt concentration not only dramatically reduce the solubility of sodium polysulfides, but also construct a robust solid-electrolyte interface on the sodium anode upon cycling. Indium triiodide as redox mediator simultaneously increases the kinetic transformation of sodium sulfide on the cathode and forms a passivating indium layer on the anode to prevent it from polysulfide corrosion. The as-developed sodium–sulfur batteries deliver high capacity and long cycling stability.