Stable Manganese‐Oxide Composites as Cathodes for Zn‐Ion Batteries: Interface Activation from In Situ Layer Electrochemical Deposition under 2 V

A set of multiphase manganese‐oxide composite materials (Mn 2 O 3 @Mn 3 O 4 and Mn 3 O 4 @Mn 5 O 8 ), and a birnessite‐type K x MnO 2 oxide are prepared and evaluated as cathodes for Zn‐ion batteries. The species formed when the electrodes are subjected to 2 V in aqueous solutions of MnSO 4 and ZnSO 4 are analyzed, suggesting an interphase activation leading to enhancement of electrochemical response. For the first time, it is shown that a Zn 4 (SO 4 )(OH) 6 .xH 2 O phase coats the composite‐type electrodes in the charging stage, contributing to extending the lifetime of the batteries. K x MnO 2 electrode with layered birnessite structure shows long cycling life at low current densities (122 mAh g −1 at 30 mA g −1 after 50 cycles) and good efficiencies (ca. 99%) in the 0.1 Mn 2+ electrolyte. In contrast, in the 0.5 m Mn 2+ electrolyte, high values of specific capacity are delivered by the cell at higher rates, that is, 150 mAh g −1 at 600 mA g −1 . In Mn 5 O 8 @Mn 3 O 4 the good performance is due to the synergistic effect of the two compounds forming the composite. Thus, after more than 100 cycles this composite displays specific capacity values of 175 mAh g −1 at 2150 mA g −1 in the 0.1 m Mn 2+ /1 m Zn 2+ electrolyte.