Optimized K+ pre-intercalation in layered manganese dioxide nanoflake arrays with high intercalation pseudocapacitance

Intercalation pseudocapacitance is emerging as a highly promising mechanism for high rate energy storage applications. However, it is still debatable how the alkali metal ion pre-intercalation in layered metal oxides affects the intercalation pseudocapacitance. Herein，the layered birnessite-MnO2 nanoflakes with K+ pre-intercalation were in- situ fabricated on the graphene foam via a one-step facile hydrothermal method. The amount of pre-intercalated K+ can be controlled by adjusting the reaction parameter. The electrochemical tests indicate that the amount of pre-intercalated ions has the optimal value and intercalated slight or excessive amount of ions may lead to the pseudocapacitance decline. The K0.19MnO2/graphene foam electrode shows a high pseudocapaitance of 344 F g−1 (based on the mass of the whole electrode) at a scan rate of 2 mV s−1, which is the best among the as-prepared samples. Cycling tests demonstrate that the pre-intercalated K+ can greatly improve the cycling stability of layered birnessite-MnO2 nanoflakes. This work provides new insights on understanding the role of pre-intercalation ions and brings new strategies to further improve the performance of layered metal oxide electrodes.