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

Abstract

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.