A high-energy hybrid supercapacitor based on a yolk-shell nickel‑bismuth intermetallic compound electrode and coffee grounds derived carbon electrode

The enhancement of energy and power density represents a significant challenge in the advancement of electrode materials derived from glycerides. In this study, we unveil a novel integrated design of both electrodes for high-performance hybrid supercapacitors. For the positive, a low-crystalline bismuth nickel cobalt glycerate (BNCG) was synthesized using an optimized solvothermal method. By utilizing the Kirkendall effect, BNCG@NB/Bi 2 O 3 materials with a yolk-shell structure were successfully synthesized. Notably, NiBi intermetallic compounds (NB-IMCs) are introduced as an electrode material for supercapacitors, formed on the outer microsphere layer alongside Bi 2 O 3 . This judicious architecture, combining the conductive NB phase with Bi 2 O 3 , synergistically contributes to its outstanding charge storage capacity (480.6 mAh g −1 ) at 1 A g −1 . After pretreatment with Fenton's reagent, the carbon derived from coffee grounds (FKCC-21) demonstrates a remarkable capacitance of 258.25 F g −1 when tested at a current density of 1 A g −1 . A button-type supercapacitor, BNCG@NB/Bi 2 O 3 //FKCC-21, this device exhibits a specific capacitance of 303.51 F g −1 at 1 A g −1 . It achieves a remarkable energy density of 107.91 Wh kg −1 at a power density of 1043.77 W kg −1 , and it retains a commendable capacitance retention rate of 85.97%, attributed to the performance optimization of composites using metal glycerol salts as precursors. This work not only demonstrates the application of NB in supercapacitors but also provides a novel pathway for the integrated design of glycerate-derived composites and biomass-derived carbon toward next-generation energy storage systems.