Molecular‐Level Design of High Flash Point Solvents Enables High‐Safety and Dual‐Function Chemical Presodiation of Hard Carbon and Alloy Anodes for High‐Performance Sodium‐Ion Batteries

Abstract Hard carbon (HC) is subjected to low initial Coulombic efficiency (ICE) and unsteady solid electrolyte interphase (SEI), which limits the energy density and cycling performance. Meanwhile, studies related to emerging chemical presodiation have specifically focused on proper redox potential and overlooked its safety hazard. To address these drawbacks of HC and chemical presodiation, a series of high‐safety chemical presodiation solutions based on tetraethylene glycol dimethyl ether (TEGDME) are proposed for uniform and fast presodiation of HC and Bi anodes. Among them, Na‐4‐methylbiphenyl in TEGDME solution exhibits the lowest redox potential (0.146 V vs Na + /Na), which achieves the inhibition of initial irreversible sodium uptake. Meantime, the potential‐driven decomposition of fluoroethylene carbonate endows presodiated HC (pNa‐HC) a fast‐ion conducting and robust F‐rich SEI. Accordingly, pNa‐HC delivers an ideal ICE of 99.1% compared to HC (65.28%). Meanwhile, pNa‐HC exhibits significantly enhanced rate performance and cycling life (193.39 mAh g −1 after 2300 cycles at 1000 mA g −1 ) benefiting from reduced kinetic energy barriers. When pNa‐HC pairs with Na 3 V 2 (PO 4 ) 3 cathode, the full cell demonstrates a desirable ICE of 91.25%. This work provides a novel and universal solvent design strategy to realize high‐safety chemical pre‐metallation.