Chalk, bismuth, and nanotubes set new supercapacitor records

Researchers from Nigde Omer Halisdemir University and Kayseri University in Turkiye have developed a new composite material for supercapacitors that enhances energy storage capabilities. The composite consists of bismuth oxide, precipitated calcium carbonate, and multi-walled carbon nanotubes, integrated into a polymer matrix of polyvinylidene fluoride dissolved in dimethylformamide. This ternary combination achieves a specific capacitance of 1359.5 farads per gram at a current density of 1 ampere per gram, outperforming simpler combinations and positioning itself among the top composite electrodes in recent studies.

The study emphasizes the nanoscale division of labor within the composite. Bismuth oxide, in its alpha crystalline phase, serves as the redox-active component, facilitating rapid charge transfer. Multi-walled carbon nanotubes provide a conductive network, ensuring efficient electron flow. Precipitated calcium carbonate acts as a structural stabilizer, maintaining a mesoporous architecture that allows free movement of electrolyte ions.

Extensive characterization confirmed the presence and cooperation of all three components. X-ray diffraction and Fourier transform infrared spectroscopy identified the chemical composition, while scanning electron microscopy revealed the composite's interconnected morphology. Brunauer-Emmett-Teller analysis confirmed a mesoporous structure, crucial for high-rate performance.

Electrochemical testing highlighted the composite's capabilities. It achieved 1359.5 farads per gram at 1 ampere per gram and maintained 899.6 farads per gram at 10 amperes per gram, demonstrating strong rate retention. The composite's energy density reached 196 watt-hours per kilogram, surpassing typical carbon-based supercapacitors and rivaling some lithium-ion batteries. Low charge-transfer resistance, measured at 0.87 ohms, indicates efficient ion and electron movement.

The fabrication method, using electrospinning-assisted coating, is noteworthy. This approach creates a porous, high-surface-area film, enabling the integration of chemically diverse phases without compromising structural integrity. However, long-term durability remains a challenge, as the composite retained only 37 percent of its initial capacitance after 10,000 cycles at 30 amperes per gram.

The inclusion of calcium carbonate is a novel aspect, offering a cost-effective and abundant structural additive that enhances electrode performance. The study suggests that calcium carbonate helps preserve the mesoporous network, preventing collapse and maintaining ion transport. Bismuth oxide, known for its redox properties and environmental benefits, continues to gain interest in energy storage applications.

Future research will focus on optimizing the ternary architecture to improve cycling durability while maintaining high capacitance and low resistance. Potential strategies include adjusting component ratios, engineering protective coatings, and refining electrospinning parameters. This research demonstrates the potential of combining bismuth oxide, calcium carbonate, and carbon nanotubes in advancing high-power energy storage solutions.