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

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 Na₃V₂(PO₄)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.