Configuration-Entropy-Driven Electrolyte with Anion-Enhanced Solvation Structures for Fast-Charging Sodium Metal Batteries

Traditional strong-solvating electrolytes exhibit high ionic conductivity but are limited by solvent-dominated solvation structures. The unstable solvent-derived electrode-electrolyte interfaces (EEIs) are detrimental to the fast-charging performance of sodium metal batteries (SMBs). Herein, a configuration-entropy-driven electrolyte with diverse solvation structures induced by a strongly solvating anion and cosolvent is proposed to realize a trade-off between high ionic conductivity and anion-enhanced solvation structures. The electrolyte possesses 75 types of Na⁺ solvation structure, contributing to its higher solvation configurational entropy (ΔS_conf, 33.09 J mol⁻¹ K⁻¹) compared to the conventional strong-solvating ester electrolyte (24.28 J mol⁻¹ K⁻¹). The high ΔS_conf facilitates ion transport and endows the electrolyte with diverse anion-coordination solvation structures, which promote the formation of inorganic-rich and stable EEIs. Therefore, the configuration-entropy-driven electrolyte with anion-enhanced solvation structures can reinforce the stability of Na metal anode and enable superior rate performances and cycling stability of Na||Na₃V₂(PO₄)₃ (NVP) cells. The modified Na||NVP cells deliver a high capacity retention of 98.2% at an ultrahigh rate of 60 C after 10 000 cycles. Even paired with high-loading NVP (≈12 mg cm⁻²), the Na||NVP cells steadily operate for over 600 cycles. This work provides a unique insight into electrolyte design from the perspective of solvation configurational entropy. © 2025 Wiley-VCH GmbH.