A High-Performance Alginate Hydrogel Binder for Aqueous Zn-Ion Batteries

The binder is an indispensable battery component that maintains the integrity of the electrode. Polyvinylidene fluoride (PVDF) is most commonly used as a binder in rechargeable batteries; however, it is associated with the toxic and expensive N-methyl-2-pyrrolidone organic solvent. Here, through the cross-linking of sodium alginate (SA) with metal cations, a high-performance hydrogel binder is developed that maintains the stability of MnO₂ cathodes in an aqueous electrolyte. Owing to the strong adhesion, high hydrophilicity, and good mechanical stability resulting from the strong bonding of Ca²⁺ with SA, a commercial microsized MnO₂ cathode with a Ca-SA binder delivered a capacity above 300 mAh/g at 1 C, which was larger than those of Mn-SA and Zn-SA (∼200 mAh/g) and PVDF (∼150 mAh/g) binders, and a capacity of 250 mAh/g at 3 C for over 200 cycles. These encouraging results could unlock the enormous potential of aqueous binders for practical applications in aqueous batteries.