Printed paper battery is activated by water

Technology News |
By Nick Flaherty

Researchers in Switzerland have developed a disposable paper battery to reduce the environmental impact of single-use electronics for applications such as point of care diagnosis, smart packaging and environmental sensing.

The battery uses zinc as a biodegradable metal anode and graphite as a nontoxic cathode material and paper as a biodegradable substrate.

The team at the Laboratory for Cellulose and Wood Materials at the Swiss Federal Laboratories for Materials Science and Technology (Empa) developed the electrodes and current collector as inks that can be stencil printed on paper to create water-activated batteries of arbitrary shape and size.

The battery remains inactive until water is provided and absorbed by the paper substrate, taking advantage of its natural wicking behaviour. Once activated, a single cell provides an open circuit potential of 1.2 V and a peak power density of 150 µW/cm2 at 0.5 mA.

As a proof of concept, the team built a two cell battery and used it to power an alarm clock and its liquid crystal display (shown above).

“What’s special about our new battery is that, in contrast many metal air batteries using a metal foil that is gradually consumed as the battery is depleted, our design allows to add only the amount of zinc to the ink that is actually needed for the specific application,” said Gustav Nyström at the lab. Metal foils were more difficult to control and not always fully consumed leading to a waste of materials, so the more zinc the ink contains, the longer the battery is able to operate.

A key factor is the water activation and the battery drying out. After one hour, the one-cell battery’s performance decreased significantly due to the paper drying. However, after the researchers added two extra drops of water, the battery maintained a stable operating voltage of 0.5 volts for more than one additional hour.

“But I am sure this can be engineered differently to get around this problem.” For environmental sensing applications at a certain humidity or in wet environments, however, the drying of the paper would not be an issue he says.

Previously, Nyström’s team had already developed a paper-based degradable super capacitor that could be charged and discharged thousands of times without losing efficiency.

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