Mn²⁺/I^- Hybrid Cathode with Superior Conversion Efficiency for Ultrahigh-Areal-Capacity Aqueous Zinc Batteries

Aqueous Zn-Mn²⁺ electrolysis batteries utilizing the two-electron-transfer reaction between Mn²⁺ and MnO₂ attract great attention because of their superior theoretical capacity (616 mAh g^-1). However, the low conductivity of deposited MnO₂ and the poor conversion efficiency of Mn²⁺/MnO₂ inevitably result in limited areal capacity and unsatisfied cycling stability, which have become the main hurdles of aqueous Zn-Mn²⁺ batteries' applications. Herein, we propose a novel Mn²⁺/I^- hybrid cathode that couples the triiodide/iodide redox with the Mn²⁺/MnO₂ redox to optimize the electrolysis kinetics. Because of the synergistically enhanced conversion reaction between Mn²⁺/I^- and the promoter effect of I^- to the dissolution of MnO₂, this hybrid cathode not only exhibits fast reaction kinetics, thus demonstrating ultrahigh rate capability (100 mA cm^-2), but also displays observably enhanced conversion efficiency up to 96.0% with excellent reversibility of 2000 cycles. Especially the superhigh areal capacity of 20 mAh cm^-2 with more than 100 cycles among the reported static Zn-Mn²⁺ electrolysis batteries is demonstrated. The excellent battery performance as well as the facile electrode hybridization approach designed here paves the way for the practical applications of aqueous Zn batteries.