The advent of flexible batteries on Smartphones and smartwatches is one step closer now as researchers have developed a flexible, foldable and stretchable lithium-ion battery.

At a time when wearable technology is the core focus of tech companies around the world and bendable displays are almost making it to electronic devices, this discovery will chip away at the disadvantage of being hooked up to a rigid battery.

The project was led by Northwestern University's Yonggang Huang and the University of Illinois' John A. Rogers, who created a rechargeable battery that can stretch, twist and bend and return to normal shape.

According to the scientists, the battery can be stretched up to 300 percent of its original size without losing functionality. The engineers claim the battery can last up to eight or nine hours and can be recharged wirelessly.

The current prototype can continuously power an LED bulb for up to eight hours per charge and it can last up to 20 recharging cycles with little loss in capacity.

The researchers published the paper titled "Stretchable batteries with self-similar serpentine interconnects and integrated wireless recharging systems" in the journal, Nature Communications.

Gizmag's Ben Coxworth explains the science behind the groundbreaking discovery:   

"The battery consists of 100 small, rigid electrode disks arranged in a square array, embedded within a sheet of stretchy silicone elastomer. Those electrodes are interconnected in parallel using metal wires that are each laid out like a flat spring, in the shape of a single squashed letter S. Within each of those single S's, however, the wires in turn take the form of multiple smaller S's joined end-to-end. Just picture a telephone cord arranged in an S shape, and you start to get the idea - the shape acts as a spring, but so does the cord from which it's made.

When the silicone sheet is stretched and the distance between the electrodes increases, the connecting wires uncurl to bridge the gaps. The single larger S of each wire first straightens out, followed by the smaller S's within it. All told, the battery can be stretched by up to 300 percent of its original size, while remaining functional. It also stands up well to repeated folding and twisting."

Check out the video uploaded in the Northwestern University Web Site explaining the invention: