Surfactant incorporation enhancing the two-electron transfer reaction of MnO2 cathode materials in aqueous Zn batteries.

MnO2 cathodes would undergo one-electron or two-electron transfer reactions in aqueous zinc batteries, with the latter providing doubled theoretical capacity. However, with the proton as one of the reactants for the two-electron reduction, its contribution is limited in typical mildly acidic zinc batteries. The long-term stability is further hindered by irreversible material loss. Herein, we incorporate a surfactant of sodium dodecyl benzene sulfonate (SDBS) into MnO2 to regulate its reaction preference. SDBS not only prevents MnO2 nucleus aggregation but also enhances electrostatic attractions for cations in the system. The resulting proton adsorption facilitates the two-electron dissolution reaction during discharge, and this is further promoted by the weaker Mn binding in the lattice after SDBS interaction. Meanwhile, the attraction of Mn2+ together with homogenized flux enables its reversible back-deposition following the three-dimensional instantaneous nucleation model during charge. As a result, the MnO2/SDBS cathode delivers 446 mAh g-1 high capacity at 0.1 A g-1 and realizes 84% capacity retention over 10 000 cycles at 2 A g-1 in the ZnSO4 electrolyte without pre-added Mn2+. It also achieves over 2.5 mAh cm-2 capacity with 10 mg cm-2 high loading. The strategy is further validated with another surfactant containing the featured negatively charged head and alkyl tail.