Feature-packed wearable devices have a bit of a bulk problem – non-"smart" clothing is thin and oftentimes a bit stretchy. The latter may not be a property that comes to mind when you think of electronics, batteries in particular. However, an Arizona State University research team has created a "stretchable" battery, which may disruptively impact wearable designs.
Associate Professor in the School for Engineering Matter, Transport and Energy Hanqing Jiang and his team drew inspiration from kirigami, a variation of origami that involves cutting as well as folding, adding an extra step for flexibility that other origami-inspired batteries haven't. The kirigami-inspired lithium ion battery involves three special patterns that are especially suited for stretchability and bending (See the patterns in the team's Scientific Reports article: opsy.st/KirigamiPaper). The batteries can stretch to more than 150 percent without losing functionality, and a "plastic rolling" technique is used in the design's creases to reduce fracturing in the battery due to cutting and folding.
In a demonstration, a prototype was sewn into an elastic wristband attached to a Samsung Gear 2 smartwatch, which retained all functionality when stretched (See a video of the demo: opsy.st/KirigamiVideo).
The Samsung Gear 2's original battery has a 300 mAh energy capacity, whereas the team's 51.3 mm long x 27 mm wide x 2.6 mm thick (size when compacted) kirigami battery is 80 mAh. If scaled up to cover the full band size (250 mm long x 30 mm wide x 3 mm thick), its capacity increases to about 700 mAh, exceeding the Samsung Gear 2's original lithium-ion battery, and has an energy density at 160 Wh/Kg, which is comparable to smartphone batteries.
Another advantage besides flexibility and thickness appears to be temperature; where the original Samsung Gear 2 battery's temperature increases during a discharge test, the kirigami battery's temperature stayed consistent with the ambient air temperature.