Competitive Solvation Structures via Hetero‐Salt Additive Strategy Enables Temperature‐Adaptive Sodium‐Ion Batteries

Abstract Sodium metal batteries (SMBs) are the ultimate choice for high‐energy density sodium‐based batteries. However, their practicality is still constrained by the uncontrolled side reactions and unstable solid electrolyte interface (SEI) between the electrolyte and Na‐metal anode. Herein, a hetero‐salt additive (Lithium difluorophosphate, LiDFP) strategy is proposed to optimize the solvation structure of pseudo gel‐polymer electrolyte (pGPE) and construct robust SEI on Na metal anode, thereby enhancing Na⁺ deposition/stripping kinetics. Detailed characterization reveals that Li⁺ with lower binding energy to solvent molecules can steal solvent molecules from Na⁺ coordination environment, and then push anions to further coordinate with Na⁺. The formed anion‐enriched solvation structure can assist to restrain side reactions and form a robust inorganics‐dominated SEI on Na metal anode. Consequently, such optimization effectively realizes outstanding electrochemical performance of the cells under wide operation temperature (−20 to 70 °C) and prolongs cycling life (1900 h) of Na plating/stripping. Furthermore, paired with commercial NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) cathode and hard carbon (HC) anode, the pouch cell using pGPE+0.5%LiDFP delivers a high‐capacity retention of 87.5% at 45 °C after 250 cycles. It is believed that this work affords emerging chances for the rational electrolyte design of stable wide‐temperate SIBs.