Energy storage devices that bend, flex and can be worked into fabrics could have a big part to play in the future of wearable electronics, and MIT engineers have just produced one with some unique properties. The rechargeable lithium-ion battery is only a few hundred microns thick but 140 meters (460 ft) long, and could be integrated into ordinary clothing, and be produced at lengths far greater than that.

Batteries fashioned into weavable fibers is something we've seen before, with one example back in 2014 formed through composite yarns that could theoretically be integrated into any textile to act as a power source. We've also seen other types of flexible batteries that actually resemble fabrics themselves, and could even power wearables by drawing on bacterial cells in the user's sweat.

The MIT scientists approached the problem through the use of a standard fiber-drawing system for generating fibers, in which all the necessary components are placed in a large cylinder and heated to just below melting point. The materials are then pushed through a narrow opening which compresses them to a fraction of their original diameter, while maintaining the desired arrangement.

What separates this design from previous efforts in this space, according to the team, is that the key materials such as lithium are structured on the inside of the fiber, with a protective coating placed on the outside. It also incorporates novel gel electrodes and a gel electrolyte, which makes the battery fire-resistant.