Hydroxyethyl cellulose optimized cathode–electrolyte interfaces in aqueous zinc ion batteries

Abstract

The impact of three binders, hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), and polyvinylidene fluoride (PVDF), on ion transport at an interface between a manganese oxide (MnO₂) cathode and electrolyte in aqueous zinc ion batteries (AZIBs) was investigated in this work. The results showed that the MnO₂ cathode using hydrophobic PVDF as the binder exhibited inferior electrochemical performance to those using hydrophilic CMC and HEC. Besides the hydrophilicity, it was revealed that the interactions of the functional groups on the binder with zinc ions (Zn²⁺) and protons (H⁺) could also influence their redox reactions with MnO₂, thus affecting the capacity and rate capability of the MnO₂ cathode. The capacities of the MnO₂ cathode using CMC as the binder were lower than those of the cathode with HEC, although the interactions between the carboxyl group in CMC and Zn²⁺/H⁺ were stronger than those between the hydroxyl group in HEC and the cations. The results indicated that the choice of binders for the cathodes in AZIBs should be made judiciously to strike a balance between facilitating interactions with the ions and avoiding excessive hindrance to electrochemical reactions at the cathode–electrolyte interface.