Core-shell MnO₂@Fe₂O₃ nanospindles as a positive electrode for aqueous supercapacitors

Supercapacitors display high power density and long cycling life that are particularly amenable for use in the field of energy storage. However, the cost is a big issue for practical application. Here, cheap Fe₂O₃ spindles from a rich natural resource are used as the positive electrode. Through the twining of MnO₂ nanoflakes via a simple and cost-effective hydrothermal method, a unique structure of a core-shell MnO₂@Fe₂O₃ nanospindle has been prepared. The electrochemical performance of the nanospindles including capacitance and cycling life is markedly improved compared with the pristine Fe₂O₃ spindles. Its specific capacitance is up to 159 F g^-1 at a current density of 0.1 A g^-1 and especially, the capacitance retention is 97.4% after 5000 cycles in a 0.5 mol L^-1 K₂SO₄ neutral aqueous electrolyte. Combined with activated carbon as the negative electrode, the energy density can be up to 43.8 W h kg^-1 on the basis of the weights of the two electrodes. These results reveal that the core-shell MnO₂@Fe₂O₃ nanospindles are a promising positive electrode for practical supercapacitors.