Origami, the centuries-old Japanese paper-folding art, has inspired recent designs for flexible energy-storage technology. But energy-storage device architecture based on origami patterns has so far been able to yield batteries that can change only from simple folded to unfolded positions. They can flex, but not actually stretch. Now an Arizona State University research team has overcome the limitation by using a variation of origami, called kirigami, as a design template for batteries that can be stretched to more than 150 percent of their original size and still maintain full functionality. 
An ASU research team has used a variation of origami, called kirigami, as a design template for batteries that can be stretched to more than 150 percent of their original size and still maintain full functionality. (Photo: Jessica Hochreiter/ASU) A paper published on June 11 in the research journal ("Kirigami-based stretchable lithium-ion batteries") describes how the team developed kirigami-based lithium-ion batteries using a combination of folds and cuts to create patterns that enable a significant increase in stretchability. Hanqing Jiang, an associate professor in the School for Engineering of Matter, Transport and Energy, one of ASU’s Ira A. Fulton Schools of Engineering, leads the team. The kirigami-based prototype battery was sewn into an elastic wristband that was attached to a smart watch. The battery fully powered the watch and its functions – including playing video – as the band was being stretched. “This type of battery could potentially be used to replace the bulky and rigid batteries that are limiting the development of compact wearable electronic devices,” Jiang said. Such stretchable batteries could even be integrated into fabrics – including those used for clothing, he said.
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An ASU research team has used a variation of origami, called kirigami, as a design template for batteries that can be stretched to more than 150 percent of their original size and still maintain full functionality. (Photo: Jessica Hochreiter/ASU) A paper published on June 11 in the research journal ("Kirigami-based stretchable lithium-ion batteries") describes how the team developed kirigami-based lithium-ion batteries using a combination of folds and cuts to create patterns that enable a significant increase in stretchability. Hanqing Jiang, an associate professor in the School for Engineering of Matter, Transport and Energy, one of ASU’s Ira A. Fulton Schools of Engineering, leads the team. The kirigami-based prototype battery was sewn into an elastic wristband that was attached to a smart watch. The battery fully powered the watch and its functions – including playing video – as the band was being stretched. “This type of battery could potentially be used to replace the bulky and rigid batteries that are limiting the development of compact wearable electronic devices,” Jiang said. Such stretchable batteries could even be integrated into fabrics – including those used for clothing, he said.
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Leading members of his ASU research team are: Hongyu Yu, an associate professor in the School of Electrical, Computer and Energy Engineering and the School of Earth and Space Exploration; Zeming Song, a materials science doctoral student; and Xu Wang, a mechanical engineering doctoral student. Jiang credits Song and Wang for ideas for using various kirigami patterns, as well as for conducting experiments and characterizing the properties of the materials used to develop the technology. Other contributors include ASU engineering graduate students Change Lv, Yonghao An, Mengbing Liang, Teng Ma and David He, a Phoenix high school student, along with Ying-Jie Zheng and Shi-Qing Huang from the MOE Key Lab of Disaster Forecast and Control in Engineering at Jinan University, Guangzhou, China. An earlier paper in the research journal ("Origami lithium-ion batteries") by Jiang and some of his research team members and other colleagues provides an in-depth look at progress and obstacles in the development of origami-based lithium-ion batteries. The paper explains technical challenges in flexible-battery development that Jiang says his team’s kirigami-based devices are helping to solve.
'Organic electronics', based on conducting polymers, are hailed as a promising future market. (Cover illustration of Advanced Materials. Artwork: Christoph Hohmann / Nanosystems Initiative Munich) Solar cells out of a printer? This seemed unthinkable only a few years ago. There were hardly any alternatives to classical silicon technology available. In the mean time touch screens, sensors and solar cells can be made of conducting synthetics. Flexible monitors and glowing wall paper made of organic light emitting diodes, so-called OLEDs, are in rapid development. The “organic electronics” are hailed as a promising future market. However, the technology also has its pitfalls: To manufacture the components on an industrial scale, semiconducting or insulating layers – each a thousand times thinner than a human hair – must be printed onto a carrier film in a predefined order. “This is a highly complex process, whose details need to be fully understood to allow custom-tailored applications,” explains Professor Peter Müller-Buschbaum of the Chair of Functional Materials at TU München. A further challenge is the contacting between flexible, conducting layers. Hitherto electronic contacts made of crystalline indium tin oxide were frequently used. However, this construction has numerous drawbacks: The oxide is more brittle than the polymer layers over them, which limits the flexibility of the cells. Furthermore, the manufacturing process also consumes much energy. Finally, indium is a rare element that exists only in very limited quantities. Polymers in X-ray light A few months ago, researchers from the Lawrence Berkeley National Laboratory in California for the first time succeeded in observing the cross-linking of polymer molecules in the active layer of an organic solar cell during the printing process. In collaboration with their colleagues in California, Müller-Buschbaum’s team took advantage of this technology to improve the characteristics of the polymer electronic elements. The researchers used X-ray radiation generated in the Berkley synchrotron for their investigations. The X-rays are directed to the freshly printed synthetic layer and scattered. The arrangement and orientation of the molecules during the curing process of the printed films can be determined from changes in the scattering pattern. “Thanks to the very intensive X-ray radiation we can achieve a very high time resolution,” says Claudia M. Palumbiny. In Berkeley the physicist from the TUM investigated the “blocking layer” that sorts and selectively transports the charge carriers in the organic electronic components. The TUM research team is now, together with its US colleagues, publishing the results in the trade journal ("The Crystallization of PEDOT:PSS Polymeric Electrodes Probed In Situ during Printing"). Custom properties “In our work, we showed for the first time ever that even small changes in the physico-chemical process conditions have a significant influence on the build-up and properties of the layer,” says Claudia M. Palumbiny. “Adding solvents with a high boiling point, for example, improves segregation in synthetics components. This improves the crystallization in conducting molecules. The distance between the molecules shrinks and the conductivity increases. In this manner stability and conductivity can be improved to such an extent that the material can be deployed not only as a blocking layer, but even as a transparent, electrical contact. This can be used to replace the brittle indium tin oxide layers. “At the end of the day, this means that all layers could be produced using the same process,” explains Palumbiny. “That would be a great advantage for manufacturers.” To make all of this possible one day, TUM researchers want to continue investigating and optimizing the electrode material further and make their know-how available to industry. “We have now formed the basis for pushing ahead materials development with future investigations so that these can be taken over by industrial enterprises,” explains Prof. Müller-Buschbaum.
Gallium arsenide nanowire arrays grown on a silicon substrate are studied using photoelectrochemistry. The middle photograph shows a scanning electron micrograph of a vertically aligned nanowire array; the figure on right is the band energy diagram of the rectifying nanowire/liquid junction; the figure on the left illustrates oxidative redox reactions of ferrocene to ferrocenium molecules at nanowire surfaces. The Impact This research demonstrates that it is possible to join Si and GaAs, two semiconductors that optimally absorb a different portion of the solar spectrum, to create two high energy species that can catalyze different chemical reactions. Such an arrangement may enable the development of a device that generates storable solar fuels by splitting water into hydrogen and oxygen using fused semiconductors. Summary The intermittent nature of sunlight makes it desirable to store solar energy in the form of chemical fuels, as nature accomplishes through photosynthesis. The light-driven electrolysis or “splitting” of water can be used to produce hydrogen gas, a transportable fuel that can be utilized without carbon emissions. However, it has been difficult to develop materials that absorb a large portion of the solar spectrum yet still have sufficient energy to drive water electrolysis. To address this challenge, researchers at the Joint Center for Artificial Photosynthesis, an Energy Innovation Hub, and the Center for Energy Nanoscience, an Energy Frontier Research Center, combined efforts to grow GaAs nanowires on Si substrates. The Si-GaAs nanowire design enables two semiconductors to optimally absorb different portions of the solar spectrum, creating two species that could potentially produce oxygen with one semiconductor and hydrogen with the other. The sequential stacking of the highly efficient GaAs and Si semiconductors produced the light absorption, photovoltage, and high current densities needed for the water-splitting reaction in an artificial photosynthesis system. This experimental approach could be used to develop new devices incorporating multiple semiconductors to achieve light-driven water electrolysis.