For me, one of the most interesting areas of the industry is flexible electronics. Traditional devices are designed onto a circuit board and enclosed in a box. The advent of the Internet of Things has meant that electronic designs have to be integrated into all sorts of places, some of which have no room for any size of rigid equipment. In some cases, these designs are even integrated into the clothes that we wear. There have been many advances in flexible electronics, so we can use all types of components in flexible designs, except batteries, well until now that is.
Engineers at MIT have designed a battery that can be woven into materials and washed. To demonstrate how flexible the discovery is, the team have produced a version that is 140 metres long. The main use for the battery will be to power fibre-based electronic devices and sensors, a potentially large market in the near future. The rechargeable lithium-ion battery takes the form of an ultra-long fibre. The 140 meters long proof-of-concept battery shows that the material can be manufactured to long lengths with no obvious upper limit. The battery has an energy storage capacity of 123 milliamp-hours and is only a few hundred microns thick.
Researchers, including members of this team, have previously produced fibres that contain a wide variety of electronic components, including LEDs, photosensors, communications, and digital systems. Many of these are weavable and washable, making them practical for use in wearable products, but all have so far relied on an external power source. The new fibre battery could allow these devices to be completely self-contained, using standard weaving equipment.
The fibre battery is produced with battery gels and a standard fibre-drawing system that starts with a larger cylinder containing all the components and then heats it to just below its melting point. The material is drawn through a narrow opening to compress all the parts to a fraction of their original diameter, while maintaining all the original arrangement of parts. Others have attempted to make batteries in fibre form, but those were structured with key materials on the outside of the fibre, whereas this system embeds the lithium and other materials inside the fibre, with a protective outside coating, making it stable and waterproof.
In addition to one-dimensional fibres, the material can also be used in 3D printing or custom-shape systems to create solid objects, such as casings that could provide both the structure of a device and its power source. To demonstrate this capability, a toy submarine was wrapped with the battery fibre to provide it with power. Incorporating the power source into the structure of devices could lower the overall weight and improve efficiency and range.
The team has applied for a patent on the process and continues to try to gain improvements in power capacity and efficiency. The work has been published in the journal Materials Today. MIT postdoc Tural Khudiyev (now an assistant professor at National University of Singapore), former MIT postdoc Jung Tae Lee (now a professor at Kyung Hee University), and Benjamin Grena SM ’13, PhD ’17 (currently at Apple) are the lead authors on the paper. Other co-authors are MIT professors Yoel Fink, Ju Li, and John Joannopoulos, and seven others at MIT and elsewhere.
The research was supported by the MIT MRSEC program of the National Science Foundation, the U.S. Army Research Laboratory through the Institute for Soldier Nanotechnologies, the National Science Foundation’s graduate research fellowship program, and the National Research Foundation of Korea.