The profusion of microelectronic devices in our daily lives has created demand for micro-batteries with longer lifetimes, greater power, faster charge times and smaller and more flexible form factors. In a paper published in a recent issue of the journal Science, titled ‘Monolithic carbide-derived carbon films for micro-supercapacitors,’ John Chmiola and his team from Berkeley Lab’s environmental energy technologies division and other institutes describe a new technique for integrating high-performance microsized supercapacitors into multiple portable electronic devices through common microfabrication techniques. Electrochemical capacitors or supercapacitors are proposed as a solution for the longevity problem of conventional batteries.
The team etched monolithic carbon film-based electrodes into a conducting substrate of titanium carbide, thereby increasing energy storage density to twice that of the best supercapacitors currently available and equally rapid cycle times. Used in conjunction with microbatteries, a significant performance boost can be expected. Titanium carbide was selected as the substrate due to its amenability to selective etching with halogens such that a monolithic carbon film is left behind. In addition, titanium carbide is relatively inexpensive and can be used at the same temperatures as other microfabrication processes. An existing rich data source on titanium carbide would also significantly ease the work of the researchers.
Titanium carbide ceramic plates were cut and polished to 300 micrometres thickness. Then, using chlorine, the titanium was selectively etched from one face of the plate at high temperatures, like in dry-etching techniques for micro-electromechanical systems (MEMS) fabrication. The chlorination of titanium retains a monolithic carbon film. The use of microfabrication techniques ensured good contact with electro-active particles in the electrode, minimised the void spaces between particles and also ensured good contact between the electro-active materials and the external circuitry. Two electrolytes were used by the team to measure electrical charge storage densities of the micro-supercapacitors and indicated extremely promising values.
According to the researchers, the next step is to scale down the size of the electrodes and increase compatibility with microfabrication techniques by improving the dry etching procedure for removing metal atoms from metal carbides. Novel electrolytes that could increase the energy storage densities are a major area of study, in addition to attempts at understanding the factors that control usable voltage windows of various electrolytes at carbon electrodes.
Such devices promise virtually unlimited cycle lives, and seem ideally poised for energy storage solutions from renewable energy technologies currently undergoing rapid development.
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)18 464 2402, patrick.cairns@frost.com, www.frost.com
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