Template Synthesis of a Heterostructured MnO₂@SnO₂ Hollow Sphere Composite for High Asymmetric Supercapacitor Performance

We have designed a new type of heterostructured MnO2@SnO2 hollow sphere composite. This particular hollow heterostructured structure material contains two parts: one is the MnO2 hollow spheres and the other is the SnO2 scattered nanoparticles on the surface of MnO2 hollow spheres. The MnO2 hollow spheres are the composite’s “skeletons” and the SnO2 scattered nanoparticles are the “muscle”. MnO2 hollow spheres can enhance the electrochemical effective area of the composites as the supporting role. The SnO2 nanoparticles on the surface of MnO2 hollow spheres have a synergistic effect with the “MnO2 skeletons”. This can affect the efficiencies of the charge transfer and mass transfer in the charge–discharge progress. Thereby, the heterostructured hollow sphere composite, possessing excellent cyclability, can deliver 541.6 F/g at 1 A/g. After 1500 cycles of testing at 2 A/g, the specific capacitance of the MnO2@SnO2 hollow spheres still remains ∼498 F/g. The asymmetric electrochemical capacitor (AEC), which has a high energy density at a high power density, can be assembled by a MnO2@SnO2 hollow sphere composite as the positive electrode and active carbon (AC) as the negative electrode.