Imagine a ball of yarn that could power flexible electronics woven into your t-shirt. This is exactly what the engineers at MIT did, creating a rechargeable lithium-ion battery in the form of a very long fiber. According to the authors of the new study, the fiber could even be used to 3D print batteries of any shape.
The proof of concept is 140 meters long, making it the longest flexible fiber battery to date. This length is arbitrary, however, and the researchers claim that the fiber in the battery could still deliver power at much longer lengths. “We could definitely do a kilometer scale length,” Tural Khudiyev, former postdoctoral fellow at MIT and now assistant professor at National University of Singapore, said in a statement.
This is not the first time that scientists have made batteries in the form of fiber. However, all previous attempts have placed lithium and other key materials on the outside of the fiber, while the new system integrates the battery inside the fiber. This protective outer coating is essential for the operation of flexible power supplies, providing both stability and waterproofing.
Manufacturing involves the use of new battery gels with a standard fiberizing system. All of the battery components are placed in a large cylinder which is slowly heated to just below its melting point. The material is then sucked through a narrow opening, causing pressure that compresses the cylinder to a fraction of its original diameter, while maintaining the original arrangement of the parts. The thickness of the fiber device is only a few hundred microns, much thinner than any previous attempt at a fiber battery.
Engineers at MIT were inspired to meet this challenge while researching wearable electronics. Previously, they made fibers that incorporated LEDs, photosensors, communication systems like WiFi, and other digital systems. These components were flexible enough to be worn by users and washable. However, they all relied on an external power source, which made portable products impractical. It was time to turn the battery into fiber too.
“When we integrate the active materials inside the fiber, it means that the sensitive components of the battery already have a good seal,” explains Khudiyev, “and all the active materials are integrated very well, so they don’t change. position during the stretching process. “
To demonstrate the functionality of this proof of concept, the researchers used the fiber battery to power a “Li-Fi” communication system, the kind that uses pulses of light to transmit data rather than radio waves. Li-Fi consists of a microphone, a preamp, a transistor and diodes. They also demonstrated the integration of LED and Li-ion batteries into a single fiber, but more than three or four devices could be combined in the same compact space in the future.
“The beauty of our approach is that we can integrate multiple devices into an individual fiber, unlike other approaches that require the integration of multiple fiber devices,” said Jung Tae Lee, postdoctoral fellow at MIT. “When we integrate these fibers containing multi-devices, the aggregate will advance the realization of a compact fabric computer.”
The 140-meter-long battery fiber has a nominal energy storage capacity of 123 milliampere-hours, just enough to power a smart watch or phone. Battery fibers could be woven to produce two-dimensional fabrics like those used for clothing, but could also be used in 3D printing to create solid objects, such as cases.
In one demonstration, a toy submarine was wrapped in battery fiber and could be powered up. Now imagine incorporating the power source into the structure of the submarine – this would reduce the overall weight and improve the efficiency and range of the device.
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 one-step printing. This is a first, ”said Khudiyev.
The results were described in the journal Materials today.