Counter-ion insertion of chloride in Mn3O4 as cathode for dual-ion batteries: A new mechanism of electrosynthesis for reversible anion storage

Abstract

Irreversible reductive insertion of Zn2+ transforms Mn3O4 such that the resulting Zn0.2Mn3O4 exhibits highly reversible storage properties of chloride ions, thus rendering Zn0.2Mn3O4 an excellent cathode of aqueous dual-ion batteries. With Zn2+ trapped, Zn0.2Mn3O4 delivers the chloride-storage capacity over 200 mAh/g at an average potential of 1.6 V vs Zn2+/Zn by reversibly forming a new ionic compound equivalent to Zn0.2Mn3O4Cl1.7. Electrochemical quartz crystal microbalance results suggest chloride as the primary charge carrier in the reversible oxidative anion insertion. The Mn3O4 anion-hosting cathode couples with Zn metal anode in a full-cell dual-ion battery, demonstrating stable cycling in practical pouch cells with an energy density of 150 Wh/kg based on the mass of both electrodes.