Oxygen Vacancy-Rich δ-MnO2 Cathode Materials for Highly Stable Zinc-Ion Batteries

As an emerging secondary battery system, aqueous zinc-ion batteries (AZIBs) show a broad application prospect in the fields of large-scale energy storage and wearable devices. Manganese-based cathode materials have been widely investigated by many researchers due to their high natural abundance, low toxicity, and multiple variable valence states. However, limited active sites, insufficient solvation, and reactivity kinetics of Mn2+ lead to the attenuation of their electrochemical performance. Herein, we introduce appropriate oxygen vacancies into the δ-MnO2 structure by modulating the annealing temperature. The obtained δ-MnO2-400 electrode provided 503 mAh/g capacity at 0.2 A/g and 99% capacity retention after 3000 times cycling at 1 A/g.