Interfacial Engineering of Sulfurized Cobalt/Nickel Glycerates Synthesized from Tetrafluoroborate-Based Precursors for High-Performance Hybrid Energy Storage

Metal glycerates have recently attracted increasing attention as promising electrode precursors for energy storage devices, owing to their inherently porous structures, large specific surface areas, and abundant redox-active sites. However, systematic investigations comparing different metal systems synthesized under identical conditions remain scarce. Here, cobalt and nickel glycerates were synthesized using novel fluorine-rich metal precursors, Co(BF4)2 and Ni(BF4)2, to elucidate the influence of metal species and BF4– anions on their redox behavior and charge-storage performance. The presence of BF4– anions facilitates in situ fluorine incorporation, which promotes the formation of metal fluoride intermediates and/or expanded interlayer spacings, thereby enhancing structural stability and electrochemical activity. Subsequent sulfurization further transforms the materials into conductive metal sulfides, significantly improving charge-transfer efficiency and reaction kinetics. The optimized sulfurized Ni glycerate (S–Ni-Gly) electrode delivers a remarkably high specific capacitance of 1318.4 F/g at 10 mV/s and retains 97.4% of its capacitance with 92.0% Coulombic efficiency after 10,000 cycles. When assembled into a battery–supercapacitor hybrid, the S–Ni-Gly device achieves a maximum energy density of 15.5 Wh/kg at 650 W/kg. This work provides insights into the roles of BF4–-based precursors and comparative metal–anion chemistry in designing glycerate-derived hybrid electrodes for high-performance energy storage applications.