Resolving the Solvation Effect in Liquid Electrolyte for Advanced Sodium Ion Batteries

ABSTRACT Due to the abundant availability and low cost of sodium resources, rechargeable sodium batteries are considered a promising alternative for next‐generation energy storage systems. In this work, we report the resolution of the solvation effect in liquid electrolytes using cryogenic electron microscopy (Cryo‐EM). By employing this technique, we establish a correlation among the lattice parameter of nanocrystals induced by solvation, the coordination number of Na + , and the salt concentration in the electrolyte. It is demonstrated that electrolytes with weaker solvation effects promote the formation of an anion‐derived solid electrolyte interphase (SEI) with a uniform, dense, and inorganic‐rich structure. Such an SEI provides high mechanical strength for dendrite suppression and favorable ionic conductivity for homogeneous Na + transport, thereby enhancing cycling stability. Furthermore, combining with density functional theory (DFT) calculations, molecular dynamics (MD) simulations, X‐ray photoelectron spectroscopy (XPS), small/wide angle X‐ray scattering(SAXS/WAXS) and Raman spectroscopy analyses, the critical role of solvation chemistry in stabilizing the electrode–electrolyte interface in sodium metal batteries was clarified. This study advances the understanding of solvation chemistry in sodium‐ion battery electrolytes and establishes Cryo‐EM as a robust analytical technique for directly resolving the microstructure of complex liquid electrolytes, thereby enabling rational electrolyte design.