Facile synthesis of homogeneous core-shell Co₃O₄ mesoporous nanospheres as high performance electrode materials for supercapacitor

Homogeneous core-shell Co₃O₄ mesoporous nanospheres are successfully fabricated by virtue of a solvothermal method and subsequent rapid calcination treatment. Note that the solid precursor nanospheres turn into homogeneous core-shell Co₃O₄ nanostructure only after 10 min of calcination. The stacking density of sub-nanoparticles and the thickness of the Co₃O₄ shell can be well adjusted by altering the annealing time. A formation mechanism based on a thermally driven contraction process caused by non-equilibrium heat treatment is proposed. The tunable mesoporous and core-shell structure can effectively facilitate the ions and electrons transportation and meanwhile accommodate the strain of oxide electrode upon cycling. Consequently, the optimal core-shell Co₃O₄ electrode exhibits a high specific capacitance of 837.7 F g⁻¹ at 1 A g⁻¹ and good capacitance retention of 87.0% after 2000 cycles at a high current density of 5 A g⁻¹. More importantly, it possesses an excellent rate capability with high capacitance retention of 93.6% when the current density raises from 1 to 10 A g⁻¹. Besides, an asymmetric supercapacitor (ASC) is constructed using the core-shell Co₃O₄ nanospheres as positive electrode and graphene aerogel as negative electrode. The ASC delivers a high specific capacitance of 101.4 F g⁻¹ at 1 A g⁻¹ and an energy density of 35.8 Wh kg⁻¹ at a power density of 797.4 W kg⁻¹. Moreover, the assembled ASC displays a good cycling stability with 88.2% capacitance retention after 2000 cycles at 1 A g⁻¹. All of these results make the homogeneous core-shell Co₃O₄ mesoporous nanostructure a promising electrode for high-performance supercapacitors.