Ion-Anchored Strategy\nfor MnO<sub>2</sub>/Mn<sup>2+</sup> Chemistry without “Dead\nMn” and Corrosion

The utilization of MnO<sub>2</sub>/Mn<sup>2+</sup> chemistry\nin\nnear-neutral pH acetate aqueous electrolytes provides an opportunity\nto achieve a higher energy density (theoretical capacity 616 mA h/g,\ndischarge platform >1.5 V). However, this Zn-MnO<sub>2</sub> aqueous\nbattery suffers from inevitable “dead Mn” and proton\ncorrosion. In this study, we discover that the diffusion of the cathode\nreaction intermediate Mn<sup>3+</sup> is intrinsic for the generation\nof “dead Mn”, and the accumulation of “dead Mn”\nincreases the H<sup>+</sup> which shuttles to the anode, inducing\nserious corrosion. A pH-neutral hydrogel ion-anchored strategy is\nproposed here not only to restrict the diffusion of Mn<sup>3+</sup> but also to suppress the proton transference. This hydrogel ion\nanchor is designed by deprotonating a series of monomers undergoing\nin situ free radical polymerization at the cathode interface. The\nanionic monomer with a moderate binding energy to manganese ions is\nscreened to anchor Mn<sup>3+</sup>, which enhances the reversibility\nof the MnO<sub>2</sub>/Mn<sup>2+</sup> reaction. Simultaneously, a\nsubstantial amount of anionic groups and hydrophilic functional groups\nin the hydrogel effectively constrains the proton shuttle to corrode\nthe anode. Consequently, the Zn/MnO<sub>2</sub> battery achieves exceptional\ncyclic stability of the MnO<sub>2</sub>/Mn<sup>2+</sup> reaction,\nsustaining 8500 cycles even at a relatively low current density and\ndischarge current density of 1 mA/cm<sup>2</sup>. Our findings highlight\nthe importance of anchoring Mn<sup>3+</sup> at the cathode interface\nand offer valuable insights for advancing practical applications of\nMnO<sub>2</sub>/Mn<sup>2+</sup> reactions.