6 / 2017-12-14 16:44:05

Yolk-shell structured MnO2 microspheres with oxygen vacancies for high-performance supercapacitors

supercapacitor,yolk-shell structre,oxygen vacancies

The yolk-shell structured MnO2 microspheres with oxygen vacancies (ov-MnO2@MnO2) are successfully constructed by a facile three-step method. Morphology observation shows that the as-obtained ov-MnO2@MnO2 microspheres possess distinctive yolk@void@shell configurations with an average diameter of 1.13 μm. Both the shell and the yolk are assembled by lots of homogeneous MnO2 nanoparticles with an average diameter of 12 nm. The yolk-shell structured ov-MnO2@MnO2 microspheres exhibit large specific surface area (259.83 m2 g-1), and superior conductivity. It is found that the yolk-shell structured ov-MnO2@MnO2 microspheres electrode achieves a high specific capacitance (452.4 F g-1 at 1 A g-1 and 316.1 F g-1 at 50 A g-1), excellent cycling stability (10000 cycles) and superior rate capability (~79.2 % and 69.9 % of initial capacity at 20 A g–1 and 50 A g–1, respectively). Furthermore, the asymmetric supercapacitor (ASC) composed of the yolk-shell structured ov-MnO2@MnO2 microspheres (as positive electrode) and commercial activated carbon (as negative electrode) shows superior energy density of 40.2 Wh kg-1 and a maximum power density of 22275 W kg-1.