Printed solar panels are now a reality due to special dyes. But who ever thought of printed batteries? Research in the field of supercapacitors has brought this innovation into question, and, with the help of the almighty carbon nanotubes, printable supercapacitors have now been realized. They perform just as well as other supercapacitors, but excel in lightness and flexibility.
Thus, researchers from UCLA and Stanford, have devised a fabrication method that is both simple and cheap. They use “dirt-cheap technologies,” says George Gri¼ner from UCLA. He was helped by Yi Cui, assistant professor of materials science and engineering at Stanford.
The method for making these ultralight and ultrathin supercapacitors is pretty simple: they spray carbon nanotubes on two pieces of plastic, and put a thin layer of gel electrolyte between them. So, one nanotube layer acts as the anode, and the other as the cathode. After that, everything goes the same old way: when you apply a voltage on the capacitor, the charge is stored in the two conducting nanotube layers. “The performance of the device is comparable to other devices,” says Cui. “The key is that everything is printable.”
The printing process goes like this: carbon nanotubes are suspended in water and sprayed onto the plastic with an air gun resembling that of an ink-jet printer. The water evaporated, and leaves two 0.6 micrometer thick layers. The gel is made of powedered polyvinyl alcohol and an acid, mixed in a mold. The gel electrolyte doesn’t spill, and that makes the newly created supercapacitors flexible.
The energy density of the flexible nanotube supercapacitors compares well with existing supercapacitors, made using other technologies – even higher. The energy density is of about 70kW/kg, higher than that of commercial devices. The prototype, though, doesn’t have enough capacity to do anything useful, but the researchers are now studying methods to increase the energy density, so that one day supercapacitors could replace old lithium-based batteries for good, and spare important environmental resources now ruined by mining for lithium.