Low-Temperature-Resistant Sodium-Metal Batteries Enabled by Amphiphilic Diluent-Enhanced Electrolyte Design

Sodium metal batteries (SMBs) are a promising solution for grid-scale energy storage due to their high theoretical capacity, cost-effectiveness, and abundant sodium resources. However, their practical deployment is significantly constrained by unstable electrode-electrolyte interphases (EEIs) and sluggish interfacial kinetics, especially at low temperatures, leading to poor temperature tolerance and rapid capacity degradation. Herein, we present a rational electrolyte design strategy incorporating an amphiphilic diluent to modulate the solvation environment for low-temperature SMBs. This diluent enhances Na⁺ transport within the electrolyte compared to traditional non-coordinating diluents and promotes anion incorporation into the Na⁺ solvation sheath, thereby enabling the construction of robust, anion-derived, inorganic-rich EEIs. As a result, Na||Al/C half cells achieve impressive Coulombic efficiencies of 97.84% at 25°C and 93.85% at -20°C. Additionally, Na||sulfurized polyacrylonitrile full cells demonstrate outstanding cycling stability, retaining 93.4% of their capacity over 500 cycles at 1000 mA g^-1 and 25°C. Notably, the optimized electrolyte maintains stable low-temperature performance for 200 cycles at -20°C. This work introduces a versatile electrolyte-engineering strategy that stabilizes sodium metal interfaces, paving the way for durable, low-temperature-resistant sodium-sulfur batteries and beyond.