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

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.