A Highly Reversible Room-Temperature Sodium Metal Anode

TLDR

Sodium metal, prized for its low cost and abundance, is a promising anode for post‑lithium batteries but suffers from poor room‑temperature reversibility due to nonuniform solid electrolyte interphase formation and dendritic growth. This study shows that a simple liquid electrolyte of sodium hexafluorophosphate in glymes can provide highly reversible, nondendritic plating‑stripping of sodium metal anodes at room temperature. The long‑term reversibility arises from a uniform, inorganic solid electrolyte interphase composed of sodium oxide and sodium fluoride that is impermeable to solvent and suppresses dendrite formation. The electrolyte achieved 99.9 % average Coulombic efficiency over 300 cycles at 0.5 mA cm⁻² and enabled a room‑temperature sodium‑sulfur battery, illustrating its practical potential.

Abstract

Owing to its low cost and high natural abundance, sodium metal is among the most promising anode materials for energy storage technologies beyond lithium ion batteries. However, room-temperature sodium metal anodes suffer from poor reversibility during long-term plating and stripping, mainly due to formation of nonuniform solid electrolyte interphase as well as dendritic growth of sodium metal. Herein we report for the first time that a simple liquid electrolyte, sodium hexafluorophosphate in glymes (mono-, di-, and tetraglyme), can enable highly reversible and nondendritic plating-stripping of sodium metal anodes at room temperature. High average Coulombic efficiencies of 99.9% were achieved over 300 plating-stripping cycles at 0.5 mA cm(-2). The long-term reversibility was found to arise from the formation of a uniform, inorganic solid electrolyte interphase made of sodium oxide and sodium fluoride, which is highly impermeable to electrolyte solvent and conducive to nondendritic growth. As a proof of concept, we also demonstrate a room-temperature sodium-sulfur battery using this class of electrolytes, paving the way for the development of next-generation, sodium-based energy storage technologies.