Article Source: ExtremeTech
Most devices can make do with a solid brick-like battery, but what about wearables and the supposed flexible phones we’ve been promised? A new kind of battery could improve the design and reliability of such devices, but making a flexible design that doesn’t degrade or fail catastrophically is a challenge. Researchers from Columbia University have developed a prototype for a flexible battery based on the shape of the human spine, and it has properties similar to non-flexible batteries.
The internal structure of a battery is vital not only to its capacity, but also to its reliability and safety. As we learned from Samsung’s Galaxy Note 7 battery issues, even small defects in the insulation between layers can cause a battery to fail catastrophically. The Columbia team got around the main safety concerns by building the battery with flexible segments akin to our own spinal discs and ligaments.
The energy storage components of the battery consist of lithium cobaltate cathodes and graphite anodes. An insulator layer runs between them, along with a copper and aluminum current collector. The entire apparatus is attached to a polyethylene supporting film. The energy storing segments are wound around the backbone substrate to give the battery its final flexible shape.
As for capacity, the flexible battery has an energy density of 242Wh/L, which is 86.1 percent of a standard non-flexible battery. The design tested in the video below has a total capacity of 123.53mAh and a mass of 4.86g. A smartwatch like the one tested there would probably need about twice as much juice to be usable for consumers, but the body could be vastly slimmed down if there was a flexible battery in the band. The Huawei Watch in the video has a 300mAh battery, but it’s a whopping 11.3mm thick.
The team found this battery design to be highly durable thanks to the flexible interconnects between cells. There was no structural damage even after 10,000 bends or 1,000 90-degree twists. After 100 charge cycles, the battery retained 94 percent of its capacity, which is close to what you’d expect from a traditional brick-like battery. Rechargeable batteries always lose capacity after repeated charge-discharge cycles.
This prototype is still a long way from a commercial product, but the testing seems surprisingly extensive. The capacity of the initial prototype is a bit low for a smartwatch, but it’s probably already sufficient for low-power fitness trackers, transdermal patches, or smart clothing. Larger versions could be viable in flexible phones or tablets.