The critical part of each wearable device is always the battery. It impacts on dimensions, weight and performance of the device. The battery life of some wearable devices is less than 24 hours. The wearable market is pushing a lot on battery research. The explosion of the mobile market didn’t revolutionize anything on batteries, since anyway those super thin batteries are not suitable for high current draining applications such as smartphones. It inspires more innovative design of battery in terms of flexibility and stretch-ability.
Origami, the centuries-old Japanese paper-folding art, has inspired recent designs for flexible energy-storage technology. But energy-storage device architecture based on origami patterns has so far been able to yield batteries that can change only from simple folded to unfolded positions. They can flex, but not actually stretch.
Kirigami stretchable battery. Source: Screen shot from Flex Battery Video from ASU Engineering on Vimeo.
Now an Arizona State Univ. research team has overcome the limitation by using a variation of origami, called kirigami, as a design template for batteries that can be stretched to more than 150% of their original size and still maintain full functionality.
A new design strategy has emerged for making batteries flexible. Companies no longer purely focus on changing the chemistry or thinning the device. Instead, the special arrangement of cells make the existing batteries flexible or even foldable. This will be a quick win for wearable devices in the short-term period as the technology can result in flexible batteries based on traditional battery manufacturing. IDTechEx thinks lithium-ion batteries with special form factors combined with wireless charging (or other energy harvesting methods) will come to the market earlier compared with batteries with intrinsic flexibility. By 2025, the market size for flexible, printed and thin-film battery will reach over $400 million, as stated in IDTechEx’s report Flexible, Printed and Thin Film Batteries 2015-2025.
Stretchable batteries and lithium-ion batteries with special form factors are good candidates for wearable and flexible devices and they may win the future. Those batteries are not truly flexible. The innovation is the design of cells arrangement. There is no new chemistry involved, therefore most of them can be mass produced easily based on traditional battery manufacturing techniques, e.g. slurry coating (LiCoO2 as the cathode and graphite as the anode) using printing or painting followed by packaging procedure. In another word, they are closer to current technology. And at the same time, they are able to provide special form factors and even flexibility.
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