The rechargeable battery is woven and washable and can power fiber-based electronic devices.

Researchers have created a rechargeable lithium battery using an ultra-long fiber. This ultra-long fiber can be used to weave into fabrics. This battery can be used to create a variety of wearable electronic devices and could even be used for 3D printing batteries in any shape.

Researchers see new possibilities in self-powered sensing and computing devices. These devices could be worn as ordinary clothing.

The team behind the new technology for battery manufacturing has created the world’s most extended flexible fiber battery (140 meters) as a proof-of-concept. This is to show that the material can be made to any length. Materials Today published the work on December 20, 2021. The paper’s lead authors are Tural Khudiyev, MIT postdoc (now an assistant professor at the National University of Singapore), and Benjamin Grena SM ’13, Ph.D. ’17 (currently at Apple). Yoel Fink and Ju Li from MIT, as well as seven other researchers at MIT, are co-authors.

This team includes researchers who have demonstrated fibers that include a variety of electronic components. These include photosensors, light-emitting diodes (LEDs), communications, and digital systems. These fibers are washable and can be washed, which makes them suitable for wearable products. However, all of them have relied on external power sources. This fiber battery is also washable and wearable. It could allow such devices to be fully self-contained.

The new fiber battery uses novel gels and a standard fiber drawing system. This starts with a larger cylindrical containing all components and heats it until it reaches its melting point. It is drawn through narrow openings to compress the material to a fraction of its original dimensions. This allows for the preservation of the original arrangement of the parts.

Khudiyev explains that other attempts to make batteries in fiber form have failed. Those were made with critical materials on one side of the fiber. This system embeds lithium and other materials within the thread with an outer coating. This makes this version waterproof and stable. He says this is the first demonstration of a fiber battery that is sufficiently long and durable to be practical.

They were able to make a 140-meter-long fiber battery. This shows that there is no upper limit. He says that they could undoubtedly make a length of a kilometer. The demonstration device that used the new fiber battery included a Li-Fi communications system. This uses pulses of light to transmit data. It also had a microphone, transistor, pre-amp, transistor, and diodes to establish optical data links between two woven fabric devices.

Khudiyev explains, “when we embed the active material inside the fiber, it means sensitive battery components have a good sealing.” “All the active materials are well-integrated, so they don’t change their positions during the drawing process. The resulting fiber battery is thinner and more flexible, yielding an aspect ratio of up to a million. This makes it possible to use standard weaving equipment for fabrics that include electronic systems and batteries.

Battery example. The thermally-drawn fiber battery (right) is resistant to fire due to the gel electrodes, gel electrolyte, and the control fiber battery with the liquid electrolyte. However, the control fiber battery immediately catches fire and expands. Credit: MIT

He claims that the 140-meter-long fiber has an energy storage capability of 123 milliamp hours, sufficient to charge smartphones and smartwatches. This fiber device is thinner than any other attempt to make fiber-form batteries. It measures only a few hundred millimeters thick.

Lee said their approach’s beauty is that it can embed multiple devices within a single fiber. He believes more than three to four devices can be combined in small spaces. The aggregate of these multi-device fibers will help us realize a compact fabric computer by integrating them.

The material can make one-dimensional fibers or be woven into two-dimensional fabrics. It can also be used for 3D printing and custom-shape to create solid objects such as casings. These could provide both the device’s structure and power source. A toy submarine was wrapped in the battery fiber to give it power. The power source could be integrated into the device’s design to reduce its overall weight and increase its range and efficiency.

Khudiyev claims this is the first 3D printer to print a fiber-based battery device. He says that 3D printing with a battery device is the best way to create complex objects. You don’t need to add anything after printing because everything is already in the fiber, including all metals and all active materials. It is a simple one-step printing. It’s just a one-step printing.

He says that computation units can now be placed inside everyday objects like Li-Fi.

The team filed the patent application. They are still working on further improvements to power capacity and other variations of the materials that improve efficiency. Khudiyev believes that such fiber batteries may be commercially available in a few years.

Martin Winter, a German professor of Physical Chemistry at the University of Muenster, said that the shape flexibility of the new cell allowed for designs and applications that were not possible before. He was not involved with this research. He called this work “very innovative.” He added, “most academic works on batteries focus now on grid storage and electric cars, so this is a remarkable deviation from the mainstream.”