Fabrication of high-performance Bi-doped NiCo₂O₄ // polymer-derived porous carbon (C800) supercapacitor

For NiCo₂O₄ supercapacitor electrode materials, simultaneously improving energy density and long-term cycling performance remains a challenge. This is because the lower conductivity and the lattice distortion induced during cycling restrict the utilization of active sites and cycling stability. In this work, a binder-free Bi-doped NiCo₂O₄ urchin-like electrode was grown in situ on nickel foam by a hydrothermal method followed by heat treatment, and the regulatory effect of Bi incorporation on the structure and electrochemical behavior of the NiCo₂O₄ urchin-like electrode was investigated. Appropriate Bi doping can reconstruct the local coordination environment, thereby inducing the formation of oxygen vacancies and increasing the specific surface area and electrochemical performance, thus accelerating ion/electron transport and improving the reversibility of the Faradaic reaction. Results show that the 5% Bi-NiCo₂O₄ electrode exhibits optimal electrochemical performance, with a specific capacitance of 2866.6 F g^-1 at 0.5 A g^-1, and the ionic conductivity increases by 34.8% compared to the undoped sample. Furthermore, an asymmetric supercapacitor device (Bi-NCO//C800) was assembled using Bi-NiCo₂O₄ as the positive electrode and polymer-derived porous carbon (C800) as the negative electrode. The device demonstrates an outstanding specific capacitance of 154.7 F g^-1 at 0.5 A g^-1, achieves a maximum energy density of 48.4 Wh kg^-1 and a maximum power density of 7500 W kg^-1, and maintains 115% capacitance retention over 11,000 cycles, exhibiting excellent cycling stability.