Modulating Transient Solvation for Ultrahigh-Rate Sodium Metal Batteries

Cation solvation in sodium battery electrolytes has been extensively studied in the bulk solution phase; however, its dynamic behavior under strong interfacial electric-field remains poorly understood. This behavior governs ion transport and interphase formation at electrode surfaces. Herein, we elucidate the electric-field-induced solvation dynamics and propose a transient solvation electrolyte design, utilizing pseudo-diluent to stabilize the interface and facilitate Na⁺ transport. The transient solvation is activated under the interfacial electric-field through dipole-cation interactions, forming intermediate complexes that effectively reduce the desolvation energy barrier and accelerate charge-transfer kinetics. This interaction weakens solvent binding and alleviates the constraints around Na⁺, inducing anion decomposition to form an inorganic-rich interphase. Among various candidates, cyclopentyl methyl ether (CPME) is identified as the optimal pseudo-diluent owing to its non-solvating nature in the bulk phase and strong field-induced polarizability. The CPME-based electrolyte enables excellent cycling stability for 4.3 V Na||Na₃V₂(PO₄)₃ (NVP) cells, achieving a capacity retention of 90.2% after 7000 cycles even at 20C. Furthermore, the Na||NVP cells with a limited sodium excess (N/P ratio = 1.7) retain 92.6% capacity retention after 5500 cycles at 5C, compared to 700 cycles with CPME-absent electrolyte. This work provides critical insights into instructive electrolyte design principles for fast-charging battery technologies.