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

A major limitation of MnO2 in aqueous Zn/MnO2 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 MnO2 lattice, Gibbs free energy of Zn2+ adsorption in the vicinity of V-O can be reduced to thermoneutral value (approximate to 0.05 eV). This suggests that Zn2+ adsorption/desorption process on oxygen-deficient MnO2 is more reversible as compared to pristine MnO2. In addition, because of the fact that fewer electrons are needed for ZnO bonding in oxygen-deficient MnO2, 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 MnO2 battery is able to deliver one of the highest capacities of 345 mAh g(-1) reported for a birnessite MnO2 system. This excellent electrochemical performance suggests that generating oxygen vacancies in MnO2 may aid in the future development of advanced cathodes for aqueous Zn ion batteries.