One-Step Polyoxometalates-Assisted Synthesis of Manganese Dioxide for Asymmetric Supercapacitors with Enhanced Cycling Lifespan

Transition metal oxides have attracted a lot of interest for the high energy density in asymmetric supercapacitors, but the fast capacity fading, low electrical conductivity and hard clean industrialization still limit the practical applications. In order to overcome the challenge, a novel type of polyoxometalate-assisted hydrothermal strategy for the synthesis of manganese dioxide as an example for asymmetric supercapacitors is reported. The samples are prepared in one step fashion, avoiding complicated equipment and acid corrosion process simultaneously, which are fully researched the morphology, chemical components and the surface area thereby finding its impact on electrochemical performance. Results in electrochemical test demonstrate that the alpha-MnO2 have good capacitance (235 F g(-1)) in neutral electrolytes. The asymmetric capacitors assembled by manganese dioxide and activated carbon (AC) as electrode materials possessed large specific energy (27.6 Wh kg(-1) at 200 W kg(-1) and 19.4 Wh kg(-1) at 5000 W kg(-1), respectively) and long cycling lifespan (about 100% electric capacity retention after 1000 cycle as well as about 94% after 5000 cycle) in the large voltage range of 0-2 V. The encouraging result shows enormous potential in energy storage devices, which can present both large specific energy and excellent cycle stability for practical implementation.