Unlocking High-Rate Sodium Storage in Hard Carbon via Interfacial Conformation Entropy Modulation in Localized...

Ether-based electrolytes are extensively employed in sodium-ion batteries (SIBs) featuring hard carbon (HC) anodes, owing to their favorable interfacial wettability and intrinsically low solvation energy. Nevertheless, conventional NaPF₆-based systems are still hindered by limited initial Coulombic efficiency, suboptimal rate capability, and inadequate low-temperature ion transport. Here, the concept of interfacial conformation entropy (S_ICE) is introduced as a mechanistic descriptor to capture the reconfigurability of solvation sheath and its influence on Na⁺ desolvation and interfacial migration. To validate this concept, a locally high-concentration electrolyte (LHCE) is formulated by incorporating 10 vol% 1,4-dioxane (14DX), a sterically hindered and weakly coordinating cyclic ether, into 1 M NaPF₆ in diethylene glycol dimethyl ether (DEGDME). This tailored solvation microenvironment enhances S_ICE effectively, enabling solvent conformational flexibility that accelerates Na⁺ desolvation and directs the formation of a highly conductive, mechanically robust interphase. Consequently, the HC|Na cell delivers ultrafast-charging durability and maintains a reversible capacity of 154.28 mAh g^-1 after 9000 cycles at 10C with a capacity retention as high as 89.46%. Simultaneously, an Ah-level NVP|HC pouch cell further substantiates the practical viability of this strategy. These findings highlight S_ICE as a powerful paradigm for the rational design of high-rate SIB electrolytes.