Electron‐Delocalized Solvation Enhances Charge Transfer Kinetics and Structural Stability for Sustainable Sodium‐Based Dual‐Ion Batteries

Abstract High‐voltage operation and fast charging are essential for next‐generation batteries, however, these demands are often hindered by electrolyte instability and sluggish ion transport, especially in sodium dual‐ion batteries (SDIBs), where anions intercalate at high potentials. Here, an electrolyte design strategy leveraging electron‐delocalized solvation structures (EDSS) that enhance anion rotational dynamics in the solvation shell and high‐voltage stability is introduced. This strategy shifts the focus from single‐molecule properties to the collective solvation shell's electron distribution, yielding a robust solvation environment that resists oxidative decomposition above 5.2 V (vs Na/Na + ) and facilitates rapid rotational motion of the anion. Consequently, SDIB cells with EDSS electrolyte achieve a specific capacity of 100.5 mAh g −1 at an ultrahigh 50 C rate and maintain 76.4% capacity retention over 7000 cycles at 20 C. Surface analyses confirm the formation of a thin, uniform SEI on Na metal, enabling stable plating/stripping even at high current densities of 10 mA cm −2 . The findings provide a new paradigm for electrolyte design, underscoring the importance of solvation‐shell‐level electronic structure in simultaneously improving stability and reaction kinetics across a broad range of battery systems.