Solvent Co-Intercalation Electrolyte Unlocks Ah-Level Sodium Storage in Hard Carbon at Ultra-Low Temperatures

Sodium ion batteries (SIBs) are attracting extensive interests due to their low cost and the abundant sodium resources. However, SIBs still suffer severe performance degradation at low temperatures due to the conflict between ion desolvation and diffusion. Herein, we design a co-intercalation ether electrolyte (CIE) to achieve solvent co-intercalation in hard carbon (HC) anode, thereby bypassing the slow desolvation process while ensuring rapid ion diffusion in electrolyte and HC. The optimized solvation structure also promotes the formation of a thin, inorganic-rich SEI, facilitating interfacial ion transport. As a result, the CIE enables HC to deliver excellent low temperature performance, with an initial Coulombic efficiency of 80.5% at -50°C and a capacity retention of 93% after 200 cycles. Moreover, an Ah-level full cell retains 163 Wh kg ^− 1 at 25°C and 107 Wh kg ^− 1 at -50°C, demonstrating the practical feasibility of this strategy for all-climate SIBs. This work overcomes the long-standing trade-off between low-temperature ion desolvation and diffusion, offering a new approach for electrolyte design toward all-climate SIBs.