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

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. [ABSTRACT FROM AUTHOR]