Rational Design of a Trifunctional Binder for Hard Carbon Anodes Showing High Initial Coulombic Efficiency and Superior Rate Capability for Sodium‐Ion Batteries

Hard carbon (HC) has emerged as a promising anode material for sodium‐ion batteries (SIBs), whereas it suffers from low initial Coulombic efficiency (ICE) and poor rate capability. Binders endowed with high electron/ion transport and strong mechanical integrity are expected to boost the practical application of HC anodes, which cannot be realized via the functional design of commercially available binders. Herein, a trifunctional sodium alginate (SA)/polyethylene oxide (PEO) binder with massive hydrophilic functional groups and abundant Na+ is synthesized via a feasible esterification reaction. The binder forms a passivation film on glucose‐derived carbon (GC) to suppress the electrolyte decomposition and offer stronger adhesion strength. Furthermore, the sluggish Na+ conduction is improved via sufficient ionic transfer channels provided by PEO. Notably, effects of Na+ compensation and interfacial ionic transport of Na+‐containing binder for HC anodes are revealed. Therefore, the SA/PEO binder for the GC anode delivers a high ICE up to 87% and a high capacity of 270 mA h g−1 at 0.1 A g−1, both 10% and 80 mA h g−1 higher than that of poly(vinylidene fluoride) binder, respectively. Significantly, this SA/PEO binder can also be applied to coal‐based and polymer‐based carbon anodes, exhibiting universal applicability. A trifunctional sodium alginate/polyethylene oxide (SA/PEO) binder is proposed for glucose‐derived carbon anodes, exhibiting excellent sodium storage. The initial Coulombic efficiency and capacity of the carbon anode using the SA/PEO binder are 10% and 80 mAh g−1 higher than that of poly(vinylidene fluoride) binder, respectively, owing to the synergic effects of extra Na+ sources, rich Na+ channels, and stable H‐bonds.