One of the major problems plaguing wearable technology today is the lack of batteries that can safely and reliably flex with the movement of clothing without breaking and leaking harmful electrolyte, or even bursting into flames altogether. That’s not to mention how uncomfortable rigid batteries are when affixed to the clothing. Lack of a reliable flexible battery also prevents innovation in flexible electronics such as foldable smartphones, roll-up screens, etc, but that may change soon thanks to a new discovery by a team of researchers at ETH Zurich.
Lead by Markus Niederberger, Professor for Multifunctional Materials at ETH, the team think they may have cracked the code and taken the first steps to a truly flexible, stretchable, bendable battery. Thanks to a new electrolyte that was discovered by doctorial student, Xi Chen, this new lithium-ion battery prototype can be stretched, bent in half, and even twisted into a helix and still remain completely functional without danger of rupture or fire as would be expected with traditional lithium-ion batteries.
Traditional lithium-ion batteries are created by stacking semi-rigid layers of anode, cathode, electrolyte on top of each other, and then encasing the sandwich in a rigid container. This new design is made entirely out of flexible materials, a first, according to the reachers. "To date, no one has employed exclusively flexible components as systematically as we have in creating a lithium-ion battery," Niederberger said.
So why does this new design work where others have failed? That breaks down to the construction of the new design. Both the anode and the cathode are constructed out of a bendable polymer composite that is impregnated with electrically conductive carbon. This composite forms the outer shell of each of the current collectors. On the opposite side of the polymer composite is a layer of silver flakes. These microscopic flakes overlap each other and slide across one another’s surface when the composite is stretched, thus maintaining the electrical connection. Even when stretched to the limit, the composite conductors maintain their conductivity thanks to the electrically conductive carbon that is impregnated into the flexible polymer. While this will lower the output of the battery, the battery will still continue to function even if the silver flake layer is compromised.
Image Credit: ETH Zurich
Researchers then mask off a predefined area of the silver layer and spray a chemical coating onto its surface. The anode receives a vanadium oxide coating, while the cathode is sprayed with lithium manganese oxide. Finally, the anode and cathode are stacked on top of each other with the special electrolyte mentioned earlier. What makes this electrolyte so special is its non-flammable and non-toxic properties. Unlike the electrolyte in current lithium-ion batteries which can spontaneously combust when exposed to air, this new design won’t really do anything if exposed to air thanks to its lithium salt and water-based composition. This makes it safer for wearables, especially when highly-flammable clothing is involved. Additionally, the electrolyte is non-toxic, which is a major step towards cleaning up the dirty process of lithium-ion battery production. "Liquid electrolyte in today's batteries are flammable and toxic,” Niederberger emphasized.
While promising, the team will have to develop a better method for sealing all of the batteries components together and protecting them from harm. For their experiments, the researchers simply used an adhesive to hold everything together, but admit that a better solution for housing the battery’s components had to be found before the flexible battery becomes commercially viable. "If we want to market the battery commercially, we'll have to find another process that will keep it sealed tight for a longer period of time," Niederberger says. That work is being continued by a new doctorial student, as the inventor of the initial prototype, Xi Chen, has returned to his homeland of China.
I’ve covered a lot of Design Challenges here at Element14 over the years, and I have seen so many of the participants sew bulky, rigid batteries into costumes, jackets, and other wearables. I always cringed when they were permanently attached inside those pieces as I have seen first hand the fireball a ruptured 2,000mAh lithium-ion battery makes. The non-flammable property of this new electrolyte has massive ramifications for the lithium-based battery industry and could make things like electric vehicles, alternative energy storage banks, and every day electronic devices safer, and more environmentally friendly. How do you see this new technology impacting the wearable electronics market? Do you think the industry would adopt a new electrolyte if it means their batteries become safer and more eco-friendly to make? I want to hear your thoughts on both of these topics, so leave a comment!