Mn 2+ /I - Hybrid Cathode with Superior Conversion Efficiency for Ultrahigh-Areal-Capacity Aqueous Zinc Batteries.

Aqueous Zn-Mn 2+ electrolysis batteries utilizing the two-electron-transfer reaction between Mn 2+ and MnO 2 attract great attention because of their superior theoretical capacity (616 mAh g -1 ). However, the low conductivity of deposited MnO 2 and the poor conversion efficiency of Mn 2+ /MnO 2 inevitably result in limited areal capacity and unsatisfied cycling stability, which have become the main hurdles of aqueous Zn-Mn 2+ batteries' applications. Herein, we propose a novel Mn 2+ /I - hybrid cathode that couples the triiodide/iodide redox with the Mn 2+ /MnO 2 redox to optimize the electrolysis kinetics. Because of the synergistically enhanced conversion reaction between Mn 2+ /I - and the promoter effect of I - to the dissolution of MnO 2 , 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-Mn 2+ 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.