LG Chem, a manufacturer of batteries, has been developing lithium-ion cable batteries which are flexible, knottable, and can be integrated into textiles and headphone cords.

The flexibility of these batteries and the benefits of that are reminiscent of flexible solar panels, which can be integrated into almost anything, and save space.

Battery packs are square or rectangular, and cells (which is what battery packs are made of, just small batteries) are usually cylindrical (I have seen a few prismatic ones, though).
 

 
This is also reminiscent of batteries that Volvo developed that can be shaped into car body panels. These batteries can be integrated into cell phones, jewelry to recharge wearable electronics, or other objects.

This design isn’t currently very powerful, but is expected to improve as LG Chem researchers develop more efficient formulations, and they said that these batteries could be mass-produced in 5 years.

This is not the first flexible battery technology. It’s predecessors were made of sheets, which limited what they could be used to manufacture, according to Je Young Kim, the general manager of battery R&D at LG Chem.

Kim’s R&D team found a way around these limitations with a spring-like, spiral electrode that incorporates the materials used in traditional lithium-ion batteries. He said: “This structure allows the device to compensate for any external mechanical distortion while maintaining its structural integrity, and it enables the battery to be more flexible in three dimensions.”

Source: Technology Review