Supercapacitors can store and deliver energy faster than conventional batteries. But to realize advanced applications, supercapacitors need better electrodes, which connect the supercapacitor to the devices that depend on their energy. These electrodes need to be both quicker and cheaper to make on a large scale, and also able to charge and discharge their electrical load faster.
A novel method of manufacturing supercapacitor electrode materials that will meet stringent industrial and usage demands was developed that begins with carbon-rich materials dried into a low-density aerogel. This aerogel, on its own, can act as a crude electrode, but the new method doubled its capacitance, or its ability to store electric charge. The inexpensive starting materials, coupled with a streamlined synthesis process, minimize two common barriers to industrial application: cost and speed.
Effective supercapacitor electrodes are synthesized from carbon-rich materials that also have a high surface area. The latter requirement is critical because of the unique way supercapacitors store electric charge. While a conventional battery stores electric charges via the chemical reactions occurring within it, a supercapacitor instead stores and separates positive and negative charges directly on its surface. As a result, supercapacitors can act much faster than batteries because they are not limited by the speed of the reaction or byproducts that can form. They also can charge and discharge very quickly, making them adept at delivering pulses of power. For example, where a battery is too slow to meet energy demands, a supercapacitor with a high-surface-area electrode could “kick in” quickly and make up for the energy deficit.
The aerogels used are wet, gel-like substances that have gone through a special treatment of drying and heating to replace their liquid components with air or another gas. These methods preserve the gel's 3D structure, giving it a high surface area and extremely low density. One gram of aerogel contains about as much surface area as a football field. The aerogels were made from a gel-like polymer created from formaldehyde and other carbon-based molecules. This ensured that the device, like today's supercapacitor electrodes, would consist of carbon-rich materials.
The aerogels were loaded with thin sheets of either molybdenum disulfide or tungsten disulfide — both used widely in industrial lubricants. Both materials were treated with high-frequency sound waves to break them up into thin sheets; they were then incorporated into the carbon-rich gel matrix. A fully loaded wet gel was synthesized in less than two hours, while other methods would take many days. After obtaining the dried, low-density aerogel, it was combined with adhesives and another carbon-rich material to create an industrial “dough” that could be rolled out to sheets a few thousandths of an inch thick. Half-inch discs were cut from the dough and assembled into simple coin cell battery casings to test the material's effectiveness as a supercapacitor electrode. The electrode exhibited a capacitance at least 127 percent greater than the carbon-rich aerogel alone.
Aerogels loaded with sheets of molybdenum disulfide or tungsten disulfide less than 10 to 100 atoms thick could show even better performance.