The dream of a future with flexible, transparent electronic devices is a tantalizing one, and is a dream constantly being chased by the greatest of engineering minds today. We’re already witnessing the beginnings of what could be the next big step in the way we interact with our digital world; foldable smartphones, complete with foldable screens, and other devices with curved screens are already making waves in the tech industry. Of course, efforts are still underway to achieve a future wherein one can simply store their next see-through tablet in their pocket all folded up. There are a couple of hurdles to overcome, however, before we get anywhere close to that possible future.
One of these hurdles is the balancing act being performed by a flexible transparent device. For one, a flexible device must be just that—flexible. Several combinations of materials, usually consisting of polymers together with functional materials for display technology and the like, come into play and synergize to form the basis of what could be the future of wearable technology and solar power generation. The other hurdle comes in the form of energy storage. After all, a flexible screen won’t be of much use until we attach something that can power it. Researchers are looking into supercapacitors to solve this problem.
Supercapacitors have a high power density but a low energy density, meaning they can charge and discharge far quicker but can’t hold as much charge at one time. Despite these apparent trade-offs, supercapacitors are seen as the future of flexible, transparent technology. To chase this possible new tech, researchers are hard at work creating what are called MXene supercapacitor electrodes. MXenes are a collective term for transitional metal carbides, nitrides, and carbonitrides, and are the functional portion of these supercapacitors. In order to address their energy density problem, researchers opted to create flat sheets of these MXenes and stack them into layers, increasing energy storage capacity. Problem is, these MXenes aren’t usually so flexible; to address this, experts couple them with flexible polymers to add flexibility to the tech, which compromises their storage capacity instead. This is where the authors of a new study, published in Nano Letters, came in; they may have found a way to add flexibility to an MXene supercapacitor without much compromise in storage capacity—and they had to look to an odd musical instrument for their breakthrough.
The team, led by Desheng Kong of Nanjing University, addressed the flexibility issue by creating nanosheets made of titanium carbide, forming the MXene electrode. This electrode was then applied over a sheet of acrylic elastomer. Thing is, this elastomer has been “pre-stretched”—to over 800% of its relaxed size. After application, the stretching force was released, and the elastomer shrinks back to its original size. The applied MXene electrode, then, crumples up as the polymer around them returns to original size, squishing the electrodes into wrinkles; this brings into mind an accordion stretching and squashing itself to create its music.
Kong and the team then applied this flexible MXene electrode to a battery setup, formed by essentially making a “sandwich.” The bread was made of a pair of the flexible MXene electrodes three micrometers thick each, and the filling was a gel made of poly(vinyl alcohol) (PVA) and sulfuric acid. Results from their experiments showed that the supercapacitor was capable of being stretched and relaxed without losing much of its ability to store a charge. Its capacity was apparently comparable to other MXene-based supercapacitors, with the key difference being this one can be stretched to about 800% its original size. The setup also kept 90% of its original capacity even after being stretched for 1,000 times.
Kong and the team believes that their newly-developed supercapacitor can pave the way for “stretchable energy storage devices” and future wearable electronics.
(To find out more, view the video below on this very topic, uploaded by the American Chemical Society.)
References
- American Chemical Society. (2021, September 8). An Accordion-Like Supercapacator That Expands 800%. YouTube. Retrieved September 22, 2021, from https://youtu.be/Y1asjrBcx0M
- American Chemical Society. (2021, September 8). Stretching the capacity of flexible energy storage. ScienceDaily. Retrieved September 22, 2021, from https://www.sciencedaily.com/releases/2021/09/210908084018.htm
- Lavars, N. (2021, September 8). Accordion-inspired supercapacitor blends flexibility and high capacity. New Atlas. Retrieved September 22, 2021, from https://newatlas.com/technology/flexible-high-capacity-supercapacitor-stretch-accordion/
- Feng, S., Wang, X., Wang, M., Bai, C., Cao, S., & Kong, D. (2021). Crumpled mxene electrodes for ultrastretchable and high-area-capacitance supercapacitors. Nano Letters. https://doi.org/10.1021/acs.nanolett.1c02071
