Chemical Lithiation-Induced Oxygen Vacancies in MnO₂ at Room Temperature for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have attracted extensive attention due to their high safety, low cost, and environment-friendliness. However, the use of AZIBs is limited by the unsatisfactory conductivity, poor cycle life, and low specific capacity of MnO 2 cathode materials. Herein, the layered oxygen-deficient δ-MnO 2 (birnessite, V O -MnO 2 ) with an inter-layer distance of around 7.0 Å is synthesized at room temperature through chemical prelithiation of MnO 2 in lithium naphthalene solution. The results confirm that the existence of oxygen vacancies improves the conductivity, provides accessible channels for Zn 2+ and/or H +, facilitates reversible adsorption/desorption of Zn 2+ and/or H +, and enables the fast transport of electron and ion. The as-designed V O -MnO 2 @CNF cathode achieves a high capacity of 303 mA h g –1 at 300 mA g –1, excellent rate capability (148 mA h g –1 at 1000 mA g –1 ), and long-term cycling performance (a reversible capacity of 135 mA h g –1 at 1000 mA g –1 after 740 cycles). The results provide a potential of the V O -MnO 2 @CNF cathode for AZIB, which is expected to be used in practical applications. This work paves the way to guide the future electrode materials for high performance AZIBs via defect engineering at room temperature.