Defect Engineering of Oxygen‐Deficient Manganese Oxide to Achieve High‐Performing Aqueous Zinc Ion Battery

A major limitation of MnO 2 in aqueous Zn/MnO 2 ion battery applications is the poor utilization of its electrochemical active surface area. Herein, it is shown that by generating oxygen vacancies ( V O ) in the MnO 2 lattice, Gibbs free energy of Zn 2+ adsorption in the vicinity of V O can be reduced to thermoneutral value (≈0.05 eV). This suggests that Zn 2+ adsorption/desorption process on oxygen‐deficient MnO 2 is more reversible as compared to pristine MnO 2 . In addition, because of the fact that fewer electrons are needed for ZnO bonding in oxygen‐deficient MnO 2 , more valence electrons can be contributed into the delocalized electron cloud of the material, which aids in enhancing the attainable capacity. As a result, the stable Zn/oxygen‐deficient MnO 2 battery is able to deliver one of the highest capacities of 345 mAh g −1 reported for a birnessite MnO 2 system. This excellent electrochemical performance suggests that generating oxygen vacancies in MnO 2 may aid in the future development of advanced cathodes for aqueous Zn ion batteries.