Morphology-controlled MnO2 modified silicon diatoms for high-performance asymmetric supercapacitors

Successful conversion of diatomites (SiO2) into silicon diatoms was achieved via the magnesiothermic reduction method followed by deposition of MnO2 nanosheets to fabricate unique 3D silicon-diatom@MnO2 electrodes and demonstrate their application for high-performance supercapacitors. The synergy between the microporous diatom structure and layered MnO2 nanosheets was found to produce excellent electrochemical performance evidenced by high specific capacitance (341.5 F g−1 at a current density of 0.5 A g−1), good rate capability (47.7% retention with current increases around 20 times) and steady cycling performance (84.8% remained after 2000 cycles). The prepared asymmetric supercapacitor based on silicon diatom@MnO2 nanosheets as a positive electrode and active graphene oxide (AGO) as a negative electrode delivered a maximum power density of 2.22 kW kg−1 and an energy density of 23.2 W h kg−1, which is superior to many other silicon-based and MnO2-based materials. These outstanding performances are attributed to the unique 3D microstructures, good conductivity of silicon diatoms and the highly porous surface formed by interconnection of MnO2 nanosheets. Considering the low cost of initial materials and simplicity of the fabrication process, these silicon diatom@MnO2 nanosheet electrodes have significant potential to be used as an electrode material for inexpensive and high-performance supercapacitors.