Researchers of MIT 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 wearable electronic devices, and might even be used to make 3D-printed batteries in virtually any shape.

The researchers envision new possibilities for self-powered communications, sensing, and computational devices that could be worn like ordinary clothing, as well as devices whose batteries could also double as structural parts.

In a proof of concept, the team behind the new battery technology has produced the world's longest flexible fiber battery, 140 meters long, to demonstrate that the material can be manufactured to arbitrarily long lengths. The work is described in the journal Materials Today.

This submarine drone is powered by a 20-meter-long fiber battery that is wrapped on its surface.

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.

Researchers, including members of this team, have previously demonstrated fibers that contain a wide variety of electronic components, including light emitting diodes (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. Now, this fiber battery, which is also weavable and washable, could enable such devices to be completely self-contained.

The fiber battery continues to power an LED even after partial cutting indicating that the fiber battery system is free from electrolyte loss and from short-circuiting.

The new fiber battery is manufactured using novel battery gels and a standard fiber-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.

While others have attempted to make batteries in fiber form, Tural Khudiyev said, those were structured with key materials on the outside of the fiber, whereas this system embeds the lithium and other materials inside the fiber, with a protective outside coating, thus directly making this version stable and waterproof.

This is the first demonstration of a sub-kilometer long fiber battery which is both sufficiently long and highly durable to have practical applications, he told.

The thermally-drawn fiber battery (right) is fire-resistant due to the gel electrodes and gel electrolyte, whereas the control fiber battery with liquid electrolyte (left) instantly catches fire and expands.

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

“When we embed the active materials inside the fiber, that means sensitive battery components already have a good sealing,” Tural Khudiyev added. “And all the active materials are very well-integrated, so they don’t change their position” during the drawing process.

In addition, the resulting fiber battery is much thinner and more flexible yielding an aspect ratio, that is the length-to-width fraction, up to a million, which is way beyond other designs, which makes it practical to use standard weaving equipment to create fabrics that incorporate the batteries as well as electronic systems.

Researchers of MIT 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 wearable electronic devices, and might even be used to make 3D-printed batteries in virtually any shape.

The researchers envision new possibilities for self-powered communications, sensing, and computational devices that could be worn like ordinary clothing, as well as devices whose batteries could also double as structural parts.

In a proof of concept, the team behind the new battery technology has produced the world's longest flexible fiber battery, 140 meters long, to demonstrate that the material can be manufactured to arbitrarily long lengths. The work is described in the journal Materials Today.

This submarine drone is powered by a 20-meter-long fiber battery that is wrapped on its surface.

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.

Researchers, including members of this team, have previously demonstrated fibers that contain a wide variety of electronic components, including light emitting diodes (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. Now, this fiber battery, which is also weavable and washable, could enable such devices to be completely self-contained.

The fiber battery continues to power an LED even after partial cutting indicating that the fiber battery system is free from electrolyte loss and from short-circuiting.

The new fiber battery is manufactured using novel battery gels and a standard fiber-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.

While others have attempted to make batteries in fiber form, Tural Khudiyev said, those were structured with key materials on the outside of the fiber, whereas this system embeds the lithium and other materials inside the fiber, with a protective outside coating, thus directly making this version stable and waterproof.

This is the first demonstration of a sub-kilometer long fiber battery which is both sufficiently long and highly durable to have practical applications, he told.

The thermally-drawn fiber battery (right) is fire-resistant due to the gel electrodes and gel electrolyte, whereas the control fiber battery with liquid electrolyte (left) instantly catches fire and expands.

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

“When we embed the active materials inside the fiber, that means sensitive battery components already have a good sealing,” Tural Khudiyev added. “And all the active materials are very well-integrated, so they don’t change their position” during the drawing process.

In addition, the resulting fiber battery is much thinner and more flexible yielding an aspect ratio, that is the length-to-width fraction, up to a million, which is way beyond other designs, which makes it practical to use standard weaving equipment to create fabrics that incorporate the batteries as well as electronic systems.