Portable electronic devices such as mobile phones, netbooks, and cameras are becoming increasingly more important to our society. How rarely we leave the house without our trusty iPhone or Blackberry! These devices will continue to get cheaper and lighter, and will increasingly incorporate flexible components or displays. To complement this technology, there is a rapidly emerging need for cheap, lightweight, and flexible components to supply the energy and power that these portable devices require. A flexible e-reader type display loses its allure if powered by a heavy, rigid D cell battery!
Professor Grüner at the University of California, Los Angeles, thinks that a device called a supercapacitor, fabricated with carbon nanotube electrodes, may provide part of the solution. In a recent study [Kaempgen, M., et al., Nano Lett. (2009) doi: 10.1021/nl8038579], a supercapacitor was fabricated using materials that are fully compatible with conventional roll-to-roll printing techniques. Carbon nanotube networks comprise both the electrodes and the charge collectors, and are spray coated onto a plastic substrate from solution. A gel electrolyte is used (and compared with a traditional liquid electrolyte), as it enables all components of the supercapacitor to be realized using printable materials. The energy and power densities of this device were measured at 6 W*h/kg and 23 kW/kg, respectively, which are comparable to values found by other research groups (and commercially available devices), despite the lack of a metallic current collector and the use of printable materials. Although the energy density is lower than that obtained by conventional battery technology, the power density is orders of magnitude higher. So what's the next step for research into printed power? The group led by Professor Grüner is currently working on increasing the energy density of their supercapacitors, and he claims to have a route in mind to increase it by ‘an order of magnitude’, which would have immediate applications as power sources for hybrid electric vehicles, or as flexible and light weight charge storage for portable devices (palm, lap top, mobile phone, etc.). Professor Grüner is confident that eventually this concept of printed power will gain traction in the market: “At this stage, it depends entirely on what company is willing to take this technology to the market. There are no technical roadblocks.”