Modulating Transient Solvation for Ultrahigh‐Rate Sodium Metal Batteries

Abstract 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||Na 3 V 2 (PO 4 ) 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.