Multi-shelled Ni6MnO8hollow microspheres for high-performance supercapacitors

Abstract

Binary transition metal oxides have attracted tremendous interest for their excellent redox activity and large natural abundance. They could achieve distinct electrochemical properties by engineering special hollow structures. In this work, we have synthesized triple-shelled Ni6MnO8 hollow microspheres constructed with nanosheets through step by step adsorption of the corresponding metal ions on carbon spheres followed by calcination in air. The as-prepared Ni6MnO8 hollow microspheres with nanosheet shells have an average diameter of ∼900 nm, with a large surface area of 145.011 m2 g-1. They exhibit outstanding capacitive performance as electrode materials, including high specific capacitance (1380 F g-1 at 1 A g-1), distinguished rate capability (68% capacity retention at ultrahigh 100 A g-1) and stable cycling property (98% retention rate at 10 A g-1 after 5000 cycles), which are superior to those of the Ni6MnO8 hollow microspheres with nanoparticle shells. Furthermore, the assembled Ni6MnO8-NS//AC asymmetric supercapacitor demonstrates a high energy density (31.8 W h kg-1 at 750 W kg-1) with a high capacity retention of 93% even after 10,000 cycles. The distinguished performances can be attributed to the synergy of binary metals and the unique hollow structure with nanosheet shells.