ISU scientists have developed a working battery that dissolves and disperses in water. Image: Ashley Christopherson.
ISU scientists have developed a working battery that dissolves and disperses in water. Image: Ashley Christopherson.

Self-destructing electronic devices could keep military secrets out of enemy hands. Or they could save patients the pain of removing a medical device. Or they could allow environmental sensors to wash away in the rain.

Making such devices possible is the goal of a relatively new field called ‘transient electronics’. Such transient devices could perform a variety of functions – until exposure to light, heat or liquid triggers their destruction.

Reza Montazami, assistant professor of mechanical engineering at Iowa State University (ISU) and an associate of the US Department of Energy's Ames Laboratory, has been working on transient technology for years. The latest development from his lab is a self-destructing, lithium-ion battery capable of delivering 2.5 volts, and then dissolving or dissipating in 30 minutes when dropped in water. The battery can power a desktop calculator for about 15 minutes.

Montazami said this is the first transient battery to demonstrate the power, stability and shelf life for practical use. He and his team at ISU recently reported their discovery in a paper in the Journal of Polymer Science, Part B: Polymer Physics. The team comprises: Nastaran Hashemi, assistant professor of mechanical engineering; Simge Çinar, a postdoctoral research associate; Yuanfen Chen and Reihaneh Jamshidi, graduate students; Kathryn White, an Ames Laboratory intern; and Emma Gallegos, an undergraduate student.

"Unlike conventional electronics that are designed to last for extensive periods of time, a key and unique attribute of transient electronics is to operate over a typically short and well-defined period, and undergo fast and, ideally, complete self-deconstruction and vanish when transiency is triggered," the scientists wrote in their paper.

But this requires equally transient batteries. "Any device without a transient power source isn't really transient," Montazami said. "This is a battery with all the working components. It's much more complex than our previous work with transient electronics."

Montazami's previous, proof-of-concept project involved electronics printed on a single layer of a degradable polymer composite. The new transient battery is made up of eight layers, including an anode, a cathode and the electrolyte separator, all wrapped up in two layers of a polyvinyl alcohol-based polymer.

The battery itself is tiny – about 1mm thick, 5mm long and 6mm wide. Montazami said the battery components, structure and electrochemical reactions are all very similar to current commercial battery technology.

But when you drop the battery in water, the polymer casing swells, breaks apart the electrodes and dissolves away. Montazami is quick to say that the battery doesn't completely disappear: it contains nanoparticles that don't degrade, but they do disperse as the battery's casing breaks the electrodes apart. He calls that "physical-chemical hybrid transiency".

And what about applications that require a longer-lasting charge? Larger batteries with higher capacities could provide more power, but they would also take longer to self-destruct, according to the scientists' paper, which suggests that applications requiring higher power levels could be connected to several smaller batteries.

Even though batteries are a tried-and-tested technology, Montazami said the transient battery project presented three major challenges for his research group. First, the battery had to produce a similar voltage to commercial batteries because many devices won't operate if the voltage is low or unsteady. Second, the batteries require multiple layers and a complex structure. And third, fabricating the batteries was difficult and took repeated attempts.

"This is a challenging materials problem, and there are not many groups working on similar projects," Montazami said.

This story is adapted from material from Iowa State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.