Fiber medicine

The rechargeable battery can be woven and washed, and could power fiber-based electronic devices and sensors. –ScienceDaily

Researchers have developed a rechargeable lithium-ion battery in the form of an ultra-long fiber that could be woven into fabrics. The battery could enable a wide variety of portable electronic devices, and could even be used to make 3D-printed batteries in virtually any shape.

The researchers envision new possibilities for autonomous communication, sensing, and computing devices that could be worn like ordinary clothes, as well as devices whose batteries could also serve as structural parts.

In a proof of concept, the team behind the new battery technology produced the world’s longest flexible fiber battery, 140 meters long, to demonstrate that the material can be made to arbitrarily long lengths. The work is described today in the journal materials today. MIT postdoctoral fellow Tural Khudiyev (now an assistant professor at the National University of Singapore), former MIT postdoctoral fellow Jung Tae Lee (now a professor at Kyung Hee University) and Benjamin Grena SM ’13, PhD ’17 (currently at Apple) are the leading authors on the paper. Other co-authors are MIT professors Yoel Fink, Ju Li, and John Joannopoulos, and seven others at MIT and elsewhere.

Researchers, including members of this team, have previously demonstrated fibers containing a wide variety of electronic components, including light-emitting diodes (LEDs), photosensors, communications, and digital systems. Many of them are woven and washable, making them convenient for use in wearable products, but all have until now relied on an external power source. However, this fiber battery, also braidable and washable, could allow such devices to be completely autonomous.

The new fiber battery is made using new battery gels and a standard fiber drawing system that starts with a larger cylinder containing all the components, then heats it to just below its melting point . Material is drawn through a narrow opening to compress all parts to a fraction of their original diameter, while retaining all of the parts’ original layout.

While others have attempted to make batteries in fiber form, Khudiyev says, these were structured with key materials outside the fiber, whereas this system integrates lithium and other materials into the fiber. fiber interior, with a protective outer coating, which directly makes this version stable and waterproof. This is the first demonstration of a sub-mile long fiber battery that is both long enough and very durable to have practical applications, he says.

The fact that they were able to make a 140-meter fiber battery shows that “there is no obvious upper limit to length. We could definitely do a mile-scale length,” he says. . A demonstration device using the new fiber optic battery incorporated a “Li-Fi” communications system – a system in which pulses of light are used to transmit data, and included a microphone, preamp, transistor and diodes to establish an optical data link between two woven fabric devices.

“When we embed the active materials inside the fiber, it means that the sensitive battery components already have a good seal,” says Khudiyev, “and all the active materials are very well integrated, so they do not change position” while drawing. to treat. Additionally, the resulting fiber battery is much thinner and more flexible, resulting in an aspect ratio, i.e., length-to-width fraction, of up to one million, which is well above beyond other designs, making it practical to use standard weaving equipment to create fabrics that incorporate batteries as well as electronic systems.

The 140-meter fiber produced so far has an energy storage capacity of 123 milliamp-hours, which can charge smart watches or phones, he says. The fiber device is only a few hundred microns thick, thinner than any previous attempt to produce batteries in fiber form.

“The beauty of our approach is that we can integrate multiple devices into an individual fiber,” Lee says, “unlike other approaches that require multiple fiber devices to be integrated.” They demonstrated the integration of LED and of Li-ion battery in a single fiber, and he believes that more than three or four devices can be combined in such a small space in the future.” When we integrate these fibers containing multiple devices, the aggregate will advance the realization of a compact fabric computer.”

In addition to individual one-dimensional fibers, which can be woven together to produce two-dimensional fabrics, the material can also be used in 3D printing or in custom-shape systems to create strong objects, such as enclosures that could provide both the structure of a device and its power source. To demonstrate this ability, a toy submarine was wrapped with the battery fiber to supply it with power. Incorporating the power source into the structure of such devices could reduce the overall weight and thus improve the efficiency and range they can achieve.

“This is the first 3D print of a fiber drum device,” Khudiyev says. “If you want to make complex objects” through 3D printing that incorporates a battery-powered device, he says, this is the first system that can achieve that. “After printing, you don’t need to add anything else, because everything is already inside the fiber, all the metals, all the active materials. It’s just a print in one step. It’s a first.”

This means that now, he says, “computing units can be placed inside everyday objects, including Li-Fi.”

The team has already filed a patent application on the process and continues to develop further improvements in power capacity and variations on the materials used to improve efficiency. Khudiyev says these fiber batteries could be ready for use in commercial products within a few years.

The research was supported by the National Science Foundation’s MIT MRSEC program, the U.S. Army Research Laboratory through the Institute for Soldier Nanotechnologies, the National Science Foundation Graduate Research Fellowship program, and the National Research Foundation of Korea.