Generating Oxygen Vacancies in MnO Hexagonal Sheets for Ultralong Life Lithium Storage with High Capacity.

The polar surface of (001) wurtzite-structured MnO possesses substantial electrostatic instabilities that facilitate a wurtzite to graphene-like sheet transformation during the lithiation/delithiation process when used in battery technologies. This transformation results in cycle instability and loss of cell efficiency. In this work, we synthesized MnO hexagonal sheets (HSs) possessing abundant oxygen vacancy defects (MnO-Vo HSs) by pyrolyzing and reducing MnCO3 HSs under an atmosphere of Ar/H2. The oxygen vacancies (Vos) were generated in the reduction process and have been characterized using a range of techniques: X-ray absorption fine structure, electron-spin resonance, X-ray absorption near edge structure, Artemis modeling, and R space Feff modeling. The data arising from these analyses inform us that the introduction of one Vo defect within each O atom layer can reduce the charge density by 3.2 × 10-19 C, balancing the internal nonzero dipole moment and rendering the wurtzite structure more stable, so inhibiting the change to a graphene-like structure. Density function theory calculations demonstrate that the incorporation of Vos sites significantly improves the charge accumulation around Li atoms and increases Li+ adsorption energies (-2.720 eV). When used as an anode material for lithium ion batteries, the MnO-Vo HSs exhibit high specific capacity (1228.3 mAh g-1 at 0.1 A g-1) and excellent cell cycling stabilities (∼88.1% capacity retention after 1000 continuous charge/discharge cycles at 1.0 A g-1).