|Fig. 1: CSIRO's Flexible Integrated Energy Device would enable the wearer to use electronic devices by simply plugging them into their clothing. (Courtesy of CSIRO Australia.)|
Since the 1870s when electric motors first were invented, electrical energy has become the most important secondary energy source and the primary form of consumed energy. In recent years, the trend of electric wearable technologies and zero-emission electric vehicle, as well as the increase in the global population has created a dependence on higher power and energy density. This desire for high-performance energy storage has increased the demand for the advancement in new energy creating and storing materials. Electrochemical energy storage devices, including batteries and supercapacitors, play an especially vital part. However, there has been a focus on hybrid energy storage devices that utilize triboelectric capabilities to produce energy through motion, moving away from rigid battery cells.  This technology is especially attractive in the world of wearables.
Wearable electronics are undergoing are under pressure to shift from big and rigid to sleek and ultra-thin. Traditional rigid electronics are not naturally compatible with human skin.  Although flexible, stretchable batteries do exist, they are often relatively flimsy and have very short battery lifetimes. Therefore, in the past decade researchers and companies have been developing a suite of stretchable wearables to compliment the human skin.
Researcher have successfully created a wearable fabric that generates electricity through triboelectric materials. Triboelectricity is a charge of electricity generated by friction. The underlying phenomenon is the triboelectric effect is electricity generation through electrostatic induction. When two different materials repeatedly touch each other, electrons shift causing opposite charges to build up on the two surfaces producing an electric charge.  In other words, the textile generates electricity from motion while the user is moving. By harvesting solar and mechanical energy, electric charge will allow the consumer to charger all your electronic needs just by walking in daytime as well as at night.  One example can be seen in Fig 1. As the person wearing the garment moves, the vibrations they create can be harvested and channelled into recharging the battery or powering plug-in electronic device or devices. The device will be used to store and provide energy over a continuous period of time and can be charged by plugging into an electrical power point or through vibration energy harvesting.
The textile typically has two components which are woven together to create the energy generating effect. The fiber that creates the triboeletric effect is using a strip of metal coated fiber. These materials range from fibers coated in silver or coated in silver, zinc oxide nanorods to thin flat strips of copper coated with a Teflon-like polymer.  The other power-generating component is the fiber solar cells. Researchers produce the solar cell fibers by growing light-sensitive zinc oxide nanowires on manganese and copper-coated plastic wires.  The two materials are woven together using an industrial sewing machine.  The interlaced triboelectric strips and fiber solar cells with copper-coated plastic threads that serve as electrodes produce a electricity from friction when the subject moves. When the fabric bends, the copper threads brush against the Teflon strips and generate electricity.
The lightweight, breathable fabric is 0.32-mm in thickness made from low-cost materials.  Zhong Lin Wang at Georgia Tech, Xing Fan at Chongqing University in Chongqing, China, and their colleagues write in a research published todayin the journal Nature Energy, A flexible, wearable 4 cmx 5 cm power patch made by mixing wool fibers with the triboelectric and photovoltaic component charged a 2-millifarad commercial capacitor up to 2 Volt in one minute.  Wangcites they can scale textiles to sizes much larger as long as they can producer a larger industrial weaving machine. Wang and his colleague report that a patch of the power textile wrapped on a persons hand chargeda cell phone and a watch when the person stood in daylight in ambient wind conditions and moved their hand.
Researchers have yet to test the textiles durability but according to Wang, the output does not drop even after it is has been bent five hundred times.  Possible uses for this technology could be in apparel, tents, curtains, giving everyday items a purpose. No longer will the curtain be a lifeless entity but rather a power-generator due to its position to the sun. The hybrid power is most sought out in the world of self-powered wearable technologies.
The future of fabric is here as a push to create more flexible fabrics that create energy as well as store it efficiently. anticipate that a better enhancement of the output power density will be achieved in the next few years. There has already been extensive research into how geometric patterns affect the energy generation. The triboelectrification is possible not only for self-powered portable electronics but also as a new energy technology with potential to contribute to the large-scale energy harvesting through engineering design in the future.
© Paige Voigt. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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