Manipulating Oxygen Vacancies by K + Doping and Controlling Mn 2+ Deposition to Boost Energy Storage in β-MnO 2 .

Aqueous zinc-ion batteries (ZIBs) have gained wide attention for their low cost, high safety, and environmental friendliness in recent years. β-MnO 2 , a potential cathode material for ZIBs, has been restricted by its small channels for efficient charge storage. Herein, β-MnO 2 nanorods with oxygen vacancies are fabricated by a K + -doping strategy to improve the performance of ZIBs. The assembled batteries exhibit a capacity of 468 mAh g -1 , a power density of 2605 W kg -1 , and an energy density of 179 Wh kg -1 , which outperforms most reported ZIBs. Such a performance is owing to the synergistic combination of the oxygen vacancies in β-MnO 2 and concurrent deposition of ε-MnO 2 from Mn 2+ in the electrolyte. Furthermore, superior cycling stability with negligible capacity decay in these batteries is demonstrated over 1000 cycles at a high current of 2 A g -1 . This study reveals the importance of oxygen vacancies and Mn 2+ deposition effect in understanding the mechanism of charge storage in MnO 2 -based ZIBs.