Smaller, thinner, lighter – batteries for electronic devices have already been modified in many ways to meet the high demands of design flexibility. For the development of portable electronics in particular, however, the limiting factor is often the shape of the battery, and here good solutions are still needed. So what about a battery that is not limited to any fixed shape? Just imagine the motivation for the development of flexible electronics such as roll-up displays or wearable electronics!
Scientists in the Republic of Korea have now presented a cable-type lithium-ion battery in the journal Advanced Materials. The battery shows a level of mechanical flexibility that has never been achieved before, and it can do everything that cables can do: twist, bend, get rolled up or tied into a knot. This allows maximum freedom in device design, as the battery could be placed anywhere and take up any shape. In fact, it could even been worn by the user, for example as a bracelet or around the neck, instead of being mounted inside a device.
The cable-type battery has a unique architecture shown in the image: several electrode (anode) strands are coiled to form a hollow spiral core with a multi-helix structure, surrounded by a polyethylene separator. The next layers are aluminium wire and a tubular outer electrode (cathode), and finally the cable battery is sealed by a shrunken packaging insulator. The hollow electrode structure favors both the electronic and the mechanical properties of the battery.
Conventional batteries can fail under strong external mechanical distortion; can the new cable-type battery do better? The scientists built a prototype cable battery and subjected it to various performance tests: indeed, the cable battery was exceptionally flexible and could suffer large strain without malfunction.
The photographs show the prototype battery successfully operating a red LED screen and MP3 player – no matter if in a loop, a coil, or tight into a knot. Further testing proved stable discharge characteristics regardless of the degree of bending strain.
This new type of lithium-ion battery overcomes all the limitations of current flexible energy storage devices and shows a mechanical robustness that promises to withstand real operating environments. It can be connected or woven in parallel and in series, giving battery units with a variety of shapes and energy and power densities. Undoubtedly, this cable-type battery prototype may be the first of its kind towards flexible batteries in portable, wearable, and flexible electronics in the future.