Ordinarily, electronic devices are made to last a long(ish) time. That isn't the case, however, when it comes to "transient electronics." These are designed to degrade in the presence of environmental triggers such as heat, light or moisture, once they've served their purpose. Now, scientists at Iowa State University have created a battery for such devices, that falls apart along with them when exposed to water.
First of all, why would anyone want electronics that are designed not to last?
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Well, they could find use in environmental sensors that don't need to be retrieved after use, temporary medical implants that don't have to be removed, or consumer goods that biodegrade after being discarded. If these items contain batteries that don't break down, however, then it kind of defeats the purpose.
That's why a team led by Prof. Reza Montazami created a 2.5-volt lithium-ion battery that can power a desktop calculator for approximately 15 minutes, but that also dissolves within about half an hour once immersed in water. According to Montazami, "It's the first transient battery to demonstrate the power, stability and shelf life for practical use."
The tiny battery is composed of eight layers including an anode, cathode and electrolyte separator, all of which are contained within two layers of a polyvinyl alcohol-based polymer. That polymer swells and breaks apart when it gets wet, taking the electrodes (the anode and cathode) out with it as it does so. Nanoparticles contained within the battery are subsequently released, which do not degrade but are instead dispersed into the environment.
While it would be possible to make larger batteries capable of delivering more power, they would accordingly take longer to degrade. Instead, Montazami and his team suggest that multiple smaller batteries would work better for such applications.
A paper on the research was recently published in the Journal of Polymer Science, Part B: Polymer Physics.
Source: Iowa State University