Solvent Chain‐Length Engineering Enables All‐Climate Sodium‐Ion Batteries

Abstract Achieving high‐rate capability, long‐term cycling stability, high‐voltage tolerance, and wide‐temperature adaptability in sodium‐ion batteries (SIBs) remains a challenge due to intrinsic solvent trade‐offs. Here, we propose a molecular‐scale electrolyte design strategy addressing this multi‐objective optimization through solvent chain‐length engineering. By coupling short‐chain ethers (low‐temperature kinetics) and long‐chain glycol ethers (high‐voltage/thermal stability) with 1,3‐dioxolane (DOL) and fluoroethylene carbonate (FEC), we construct a hybrid‐solvent electrolyte that redefines Na⁺ solvation chemistry. Systematic solvent–solvent interaction modulation weakens Na⁺‐solvent binding to accelerate ion transport, while FEC‐induced anion‐rich coordination shells enhance interfacial stability. The hybrid electrolyte enables Na 3 V 2 (PO 4 ) 3 ||Na cells to deliver an 82.75 mAh g −1 discharge capacity after 9500 cycles at 10 C, sustain 600‐day operation at 1 C, and function across −40 to 60 °C. Symmetric Na||Na cells demonstrate stable cycling for over one year. Moreover, the electrolyte exhibits good compatibility with various commercial cathode materials within a wide voltage window of 2.0–4.5 V and demonstrates excellent wide‐temperature adaptability in full‐cell systems. This work demonstrates solvent chain‐length‐driven solvation engineering as a viable strategy to concurrently address kinetic, thermodynamic, and interfacial challenges, offering a practical pathway toward all‐climate SIBs with balanced multi‐performance metrics.