MIT Engineers Produce the World’s Longest Lithium-Ion Flexible Fiber Battery

The rechargeable battery that can be woven into garments and which is also washable can be used to power fiber-based electronic gadgets and sensors.

A rechargeable lithium-ion battery in the shape of an ultra-long fiber that can be woven into garments has been developed by researchers. The battery may power a wide range of wearable electrical gadgets, and it could even be used to create 3D-printed batteries of any shape.

The researchers anticipate new possibilities for self-powered communications, sensing, and computational devices that might be worn like regular clothing, as well as devices with batteries that could also serve as structural components.

To demonstrate that the material can be made to arbitrarily long lengths, the team behind the new battery technology created the world’s largest flexible fiber battery, measuring 140 meters in length.

The research was published in the journal Materials on December 20, 2021. The paper’s principal authors are MIT Postdoc Tural Khudiyev (now an assistant professor at the National University of Singapore), former MIT PostDoc Jung Tae Lee (now a professor at Kyung Hee University), and Apple’s Benjamin Grena SM ’13, Ph.D. ’17. Yoel Fink, Ju Li, and John Joannopoulos, all of MIT, are co-authors, as are seven others from MIT and elsewhere.

Fibers containing a wide variety of electronic components, including light-emitting diodes (LEDs), photosensors, communications, and digital systems, have already been shown by researchers, including members of this team. Many of these are wearable and washable, making them suitable for use in wearable products, however, they all require external power. This fiber battery, which is both wearable and washable, may now be able to make such gadgets self-contained.

The new fiber battery is made with innovative battery gels and a standard fiber-drawing technology that begins with a bigger cylinder holding all of the components and warms it to just below the melting point. The material is drawn through a small aperture, compressing all of the components to a fraction of their original diameter while keeping the original part arrangement.

Others have tried to make batteries in fiber form, but they were structured with key materials on the outside of the fiber, according to Khudiyev, whereas this system embeds the lithium and other materials inside the fiber, with a protective outside coating, making this version directly stable and waterproof. According to him, this is the first demonstration of a sub-kilometer-long fiber battery that is both long and durable enough to have practical applications.

The fact that they were able to create a 140-meter fiber battery demonstrates that “the length has no evident upper limit.” He argues, “We could probably do a kilometer-scale length.” A demonstration device using the novel fiber battery includes a microphone, pre-amp, transistor, and diodes to form an optical data link between two woven fabric devices, as well as a “Li-Fi” communications system — one in which light pulses are used to transport data.

When we embed the active materials inside the fiber, that means sensitive battery components are already well-sealed,” Khudiyev explains, “and all the active materials are very well-integrated, so they don’t change their position” during the drawing process. Furthermore, the resulting fiber battery is much thinner and more flexible, with an aspect ratio of up to a million, which is far greater than existing designs, allowing regular weaving machinery to be used to create fabrics that contain the batteries as well electronic components.

According to him, the 140-meter fiber created so far has a 123 milliamp-hour energy storage capacity, which may charge smartwatches or phones. The fiber device is only a few hundred microns thick, much thinner than any previous fiber-based battery attempts.

Unlike other systems that require the integration of several fiber devices,” Lee explains, “the beauty of our approach is that we can embed multiple devices in a single fiber.” They exhibited LED and Li-ion battery integration in a single fiber, and he believes that in the future, more than three or four devices can be coupled in such a compact space. “The aggregation will promote the realization of a small fabric computer when we integrate these fibers holding multi-devices.”

Individual one-dimensional strands can be woven into two-dimensional fabrics, but the material can also be utilized in 3D printing or custom-shape methods to build solid items, such as casings that could offer both the structure and power supply for a gadget. To illustrate this potential, the battery fiber was wrapped around a toy submarine to give power. By incorporating the power source into the framework of such devices, the overall weight of the devices might be reduced, improving their efficiency and range.

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

The team has already filed a patent application for the technique and is working on further improvements in power capacity and material changes to boost efficiency. Fiber batteries, according to Khudiyev, might be ready for commercial usage in a few years.

“The shape flexibility of the new battery cell allows designs and applications that have not been possible before,” says Martin Winter, a professor of physical chemistry at the University of Muenster in Germany, who was not involved in this work. Calling this work “very creative,” he adds: “As most academic works on batteries look now at grid storage and electric vehicles, this is a wonderful deviation from the mainstream.”