Hierarchically Porous NaCoPO₄-Co₃O₄ Hollow Microspheres for Flexible Asymmetric Solid-State Supercapacitors

Abstract

A template-free hydrothermal method is developed to prepare hierarchical hollow precursors. An inside-out Ostwald ripening mechanism is proposed to explain the formation of the hollow structure. After the calcination in the air, hierarchically meso/macroporous NaCoPO4–Co3O4 hollow microspheres can easily be obtained. When being evaluated as electrode materials for a supercapacitor, the hierarchically porous NaCoPO4–Co3O4 hollow microspheres electrode shows a specific capacitance of 268 F g−1 at 0.8 A g−1 and offers a good cycle life. More importantly, the obtained materials are successfully applied to fabricate flexible solid-state asymmetric supercapacitors. The device exhibits a specific capacitance of 28.6 mF cm−2 at 0.1 mA cm−2, a good cycling stability with only 5.5% loss of capacitance after 5000 cycles, and good mechanical flexibility under different bending angles, which confirms that the hierarchically porous NaCoPO4–Co3O4 hollow microspheres are promising active materials for the flexible supercapacitor.