This stretchable, wearable battery can power a smart watch

A lithium-ion battery made of gels and composites can be stretched to one-and-a-half times its original length and still work, even after more than 1,000 tugs, researchers report in a new study (ACS Nano 2022, DOI: 10.1021/acsnano.1c08405). Because all the materials start as pastes, the battery can also be printed directly on fabric, says study coauthor Jeong Gon Son of the Korea Institute of Science and Technology.

To make stretchy batteries for wearable electronics such as smart watches and health sensors, researchers have typically deposited rigid materials on elastic or wavy substrates. The new battery is the first in which every part—electrodes, separator, current collectors, and outer cover—is made of intrinsically elastic materials, Son says. The heart of the battery consists of stacked films of an organogel made of poly(vinylidene fluoride) fibers soaked in acetone. To make the cathode and anode, Son and his colleagues add lithium iron phosphate and lithium tin oxide particles, respectively, to the gel. A gel film soaked in electrolyte separates the electrodes from each other.

Polyisobutylene films loaded with metal microparticles and carbon nanotubes act as current collectors at each electrode. All these layers are encapsulated in polyisobutylene with electrolyte injected into the pouch to give a stretchable battery with a power density of 2.5 mWh/cm², enough to power a smart watch.

The team also printed pastes of the materials through stencils directly on a sleeve made of stretchy fabric. In this case, the fabric served as the separator, with electrodes and current collectors printed on either side. The battery continuously powered a smart watch even as a tester put on the sleeve and stretched it or bent their elbow.