Nanocomposites of hierarchical ultrathin MnO2 nanosheets/hollow carbon nanofibers for high-performance asymmetric supercapacitors

A novel hierarchical hollow nanostructure composed of δ-MnO₂ nanosheets deposited by in-situ growth on hollow carbon nanofibers (MnO₂/HCNFs) was facilely synthesized using the hydrothermal method. Benefitting from its distinctive hollow structure, nanocomposite of MnO₂/HCNFs exhibited an enhanced electrochemical property with higher specific capacitance (293.6 F g⁻¹ at 0.5 A g⁻¹ in 1 M Na₂SO₄ electrolyte) compared to non-hollow structure. Further, an asymmetric supercapacitor (ASC) coin cell was assembled with the MnO₂/HCNFs nanocomposites (positive electrode) and KOH-activated porous carbon nanofibers (PCNFs) (negative electrode). The asymmetric supercapacitor coin cell exhibited a maximum specific capacitance of 63.9 F g⁻¹ at a high operating voltage window up to 2 V. Moreover, the ASC coin cell possessed a high energy density of 35.1 Wh kg⁻¹ and showed a remarkable cycling stability and only 8.9% capacitance loss was found after 10,000 cycles, which implied the practicability for energy storage.