Synthesis of Double-Layered NiCo2O4-Nanosheet-Loaded PAN/Lignin-Based Hollow Carbon Nanofibers for High-Performance Supercapacitor

Polyacrylonitrile (PAN) /lignin based hollow carbon nanofibers (HCNF) were fabricated by coaxial electrospinning method followed by carbonization procedure. The results show that the NiCo2O4 oxides were successfully deposited on the surface of HCNF by a facile hydrothermal method without any toxic reagents and NiCo2O4 nanosheets are uniformly deposited on the inner and outer layers of HCNF. The electrochemical results show that NiCo2O4@HCNF composite had excellent electrochemical properties. The electrochemical measurements indicate that the NiCo2O4@HCNF possessed considerable capacitance 1998.18 mF/cm(2) at 2 mA/cm(2) (1665 F/g with the mass loading of 1.2 mg/cm(2)) and an excellent cycling stability, specific capacitance can retain 87% after 5000 cycle numbers under the current density of 10 mA/cm(2). In addition, an asymmetric supercapacitor (NiCo2O4@HCNF//active carbon (AC)) was assembled by NiCo2O4@HCNF (positive electrode) and AC (negative electrode). The device exhibits high capacitance 111 F/g at 1 A/g, excellent energy density (40.3 Wh/kg at 810W/kg), and excellent cycling stability (92% capacitance can retain after 5000 charge-discharge at 5 A/g). The experimental results show that the hollow structure of the hollow carbon nanofiber benefits the double layered growth of NiCo2O4, which can improve the capacitance performance. Therefore, the composite exhibits excellent electrochemical properties.