Follow U.S. Investment Immigration and stay updated on U.S. technological developments: U.S. scientists recently discovered that by folding paper-based lithium-ion batteries using the Miura-ori pattern, their energy density and capacity per unit area can be increased by as much as 14 times.
In a recent issue of Nano Letters, scientists from Arizona State University, including Qian Cheng and other researchers, co-authored a paper introducing this latest research achievement in the field of foldable paper-based lithium-ion batteries.
"Foldable batteries could be very helpful for devices with limited space for power boards," said Candace Chan, an assistant professor at the School for Engineering of Matter, Transport and Energy at Arizona State University and a co-author of the paper. Furthermore, recent research by other groups on foldable paper-based electronic devices suggests that a foldable battery pack is essential for integrating power sources and other components into a single, fully foldable mobile device.
In the current study, scientists used lithium-ion batteries made with carbon nanotube (CNT) ink as current collectors, traditional lithium powder as electrodes, and thin, porous Kimwipes™ as the paper substrate. The researchers also added a polyvinylidene fluoride (PVDF) coating to improve the adhesion of the CNT ink to the paper substrate. The resulting battery exhibits good electrical conductivity and relatively stable energy.
The researchers experimented with simple half-folding and the more complex Miura-ori folding method. They found that when using the simple half-folding method, folding once, twice, and three times increased the energy density and capacity per unit area by 1.9, 4.7, and 10.6 times, respectively, compared to a flat battery. The Miura-ori folding method was more effective: folding a 6 cm × 7 cm battery into 25 layers increased the energy density and capacity per unit area by 14 times, while reducing its total footprint to 1.68 square centimeters.
"We express the increase in energy density in terms of energy density per unit area," Chan explained. "This is different from energy density per unit mass, because the mass remains constant when the battery is folded and unfolded."
Overall, in simple folding modes, the electrochemical performance of the folded battery is similar to that of a flat battery. The coulombic efficiency of the folded batteries is higher than that of the unfolded ones, which may be due to increased contact between the electrode material and the carbon nanotubes after the battery is folded.
Compared to flat batteries, some performance metrics of batteries folded using the Miura-ori method were slightly reduced, including a decrease in discharge capacity and capacitance. Researchers believe these losses may be due to delamination at the intersections of the vertical folds, as these batteries contain 16 vertices. To protect the battery, researchers used a flexible insulating film between the layers: Parylene-C.
This research achievement provides the first glimpse into the potential of using folding methods to increase the energy density and capacity per unit area of lithium-ion batteries. In the future, with advancements in geometric folding algorithms, computational tools, and robotic manipulation techniques, more complex folding patterns may emerge, making the development of large-scale batteries for commercial use possible.
Due to their low cost, simple manufacturing methods, and flexibility, paper-based batteries are already quite attractive. If the performance of paper-based batteries can be further enhanced through folding, it could lead to the creation of high-performance batteries for a variety of applications.
"Using folding methods and origami concepts can create new geometries, geometric designs, and new functions for paper-based energy storage devices; this field has unlimited potential," said Chan.