Cable-like double-carbon layers for fast ion and electron transport: An example of CNT@NCT@MnO₂ 3D nanostructure for high-performance supercapacitors

A unique nanostructure consisting of CNTs as carbon matrix, and were sequentially coated with silicon dioxide, N-doped porous carbon tube (NCT) and MnO₂ nanoflowers, the final CNT@NCT@MnO₂ composites with large internal voids between CNT and NCT. CNT@NCT@MnO₂ combines the nanostructural advantages of internal voids and the N-doped porous carbon, presenting fast diffusion paths for ions and electrons, high conductivity and large surface areas. When used as an anode material in supercapacitors, the CNT@NCT@MnO₂ tube-in-tube hierarchical nanostructure exhibite a remarkably excellent electrochemical behavior with a specific capacitance (Csp) of 210 F g⁻¹ at the current density of 0.5 A g⁻¹. Moreover, all-solid-state asymmetrical supercapacitors (ASCs) were fabricated using the CNT@NCT@MnO₂ composites as anode and the CNT@NCT as cathode, Na₂SO₄/PVA gel as the electrolyte and the separator. The all-solid-state ASCs also show the superior performance, such as high energy density of ∼14 Wh kg⁻¹ and a power density of ∼3.6 kW kg⁻¹.