This Stretchable Lithium-Ion Battery Proves a Powerful Solution for Better Wearables

Researchers from the Nanjing University of Posts & Telecommunications have created a battery that could deliver power to future flexible electronics: a fully-stretchable lithium-ion battery, with a rubbery electrolyte capable of expanding in size by 5,000 percent without damage.

"Stretchable lithium-ion batteries (LIBs) are important potential power sources for flexible electronics," the team writes of its research. "Here, we propose an integrated in situ poymerization-transfer strategy to construct intrinsically stretchable LIBs (is-LIBs). The results suggest a new avenue for the development of stretchable energy storage devices."

While flexible and even stretchable electronics are nothing new, powering the devices has always been a problem. Lithium-ion batteries, the most common form of rechargeable batteries for portable electronics, have a high energy capacity but are extremely vulnerable to mechanical damage — with a short between layers enough to cause overheating and a potential fire. Safer, more flexible alternatives exist but fail to deliver a high enough energy capacity.

Rather than adopting a structural approach, as with rival research projects that create sponge-like or origami- and kirigami-inspired battery designs capable of stretching without damage, the Nanjing team opted to approach the problem from a different direction: modifying the battery so that it is intrinsically stretchable.

To do so, the team built their battery from scratch using a layer of conductive paste containing silver nanowires, carbon black, and lithium-based anode materials, then added a film of flexible polydimethysiloxane (PDMS). On top of this went a clever polymer lithium-salt electrolyte, treated with light to form a rubber-like substance, followed by another conductive paste layer to form the cathode.

The electrolyte itself, the team found, was capable of stretching by 5,000 percent without damage; testing of the overall battery revealed a charge capacity some six times higher than liquid-electrolyte batteries while also offering a longer lifespan. "Based on these excellent characteristics," the researchers conclude, "the assembled solid-state is-LIBs exhibited good cell performance. Undoubtedly, this work can further promote the development of stretchable energy devices for wearable/implantable electronics."

The team's work has been published in the journal ACS Energy Letters.