New biodegradable mini-capacitor for waste-free energy storage

The number of data-transmitting microdevices, for instance, in packaging and transport logistics, will increase sharply in the coming years. All these devices need energy, but the amount of batteries would have a major impact on the environment.

To solve this problem, the researchers from the Swiss research institute Empa have created a biodegradable mini-capacitor – an alternative to conventional batteries – made from cellulose and other non-toxic components.

The 3D-printed prototype device consists of a flexible substrate, on top of which is deposited a conductive layer, an electrode, and finally the electrolyte. The whole thing is then folded up like a sandwich, with the electrolyte in the center.

New biodegradable mini-capacitor for waste-free energy storage
After two months buried in the soil, the capacitor has disintegrated, leaving only a few visible carbon particles. Credit: Empa.

The substrate is made of a mixture of cellulose nanofibers and nanocrystals mixed with glycerol. The conductive layer consists of graphite, carbon black, and natural resin – shellac. The composition of the electrode includes the same materials as the substrate, as well as activated carbon and graphite. And the electrolyte is made of cellulose nanocrystals, glycerin, and a pinch of table salt for ionic conductivity.

The mini-capacitor from the lab can store electricity for hours and can already power a small digital clock. It can withstand thousands of charge and discharge cycles and years of storage, even in freezing temperatures, and is resistant to pressure and shock.

But above all, when you no longer need it, you could toss it in the compost or simply leave it in nature. After two months, the capacitor will have disintegrated, leaving only a few visible carbon particles.

The biodegradable mini-capacitor could soon become a key component for the Internet of Things, researchers expect. “In the future, such capacitors could be briefly charged using an electromagnetic field, for example, then they could provide power for a sensor or a microtransmitter for hours.” This could be used, for instance, to check the contents of individual packages during shipping. Powering sensors in environmental monitoring or agriculture is also conceivable – there’s no need to collect these batteries again, as they could be left in nature to degrade.

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