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.