Macromolecule‐Enriched Solvation Enabling High‐Voltage Sodium‐Ion Batteries

Abstract Sodium‐ion batteries (SIBs) are emerging as a viable alternative for sustainable and cost‐effective energy storage, yet their energy density is curtailed by relatively low voltage outputs (< 4 V) due to the lack of high‐voltage electrolytes. Here, for the first time, we describe a high‐voltage Na + electrolyte featuring a macromolecule‐enriched solvation architecture. The vulnerable small molecules in the Na + solvation shell are replaced by macro polyamide (PA) molecules with high thermodynamic resilience, ensuring a wide electrochemical stability window for the electrolytes with suppressed oxidative/reductive decomposition. Concomitantly, the anions engage in H‐bonding with the amido groups of PA, which not only stabilizes the anions against hydrolysis, but also delivers a high Na + transference number of 0.93. Importantly, the nitrogen‐rich composition of the macromolecule‐enriched electrolyte (MEE) fosters the formation of robust nitride interphases that impart enduring stability to both the cathode and anode. As a result, the hard carbon (HC) || NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) full cells demonstrate significant rechargeability even with an ultrahigh cutoff voltage of 4.4 V. Our approach distinctively avoids the use of fluorinated molecules typically found in (localized‐) high‐concentration electrolytes, presenting a novel principle that could revolutionize high‐voltage electrolyte design.