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Designed to power a range of low-power, single-use disposable electronics – such as smart labels for object tracking, environmental sensors and medical diagnostic devices – the battery was developed by Gustav Nyström and colleagues at the Swiss Federal Laboratories for Materials Science and Technology (Empa).
The device is made of 1cm2 cells consisting of three inks printed onto a rectangular strip of paper. Sodium chloride salt is dispersed throughout the paper, which is dipped in wax at one end. An ink containing graphite flakes acts as the cathode on one side, while an ink containing zinc powder acts as an anode on the reverse side. An ink containing graphite flakes and carbon black is also printed on both sides of the paper, connecting the positive and negative ends to two wires at the wax-dipped end.
When a small amount of water is added, the salts within the paper dissolve and charged ions are released. The ions activate the battery by dispersing through the paper, resulting in the zinc at the negative end releasing electrons. Attaching the wires to an electrical device closes the circuit so that electrons can be transferred from the negative end to the positive end, where they are transferred to oxygen in the surrounding air. These reactions generate an electrical current that can power a device.
The researchers demonstrated their creation by combining two cells into a battery that powered an alarm clock with a liquid crystal display.
Analysis of a one-cell battery showed that after two drops of water were added, the battery activated within 20 seconds. When not connected to an energy-consuming device, it reached a stable voltage of 1.2V, slightly less than a standard AA alkaline battery on 1.5V. After one hour, the one-cell battery’s performance decreased significantly due to the paper drying, but two more drops of water brought back a stable operating voltage of 0.5V for another hour.
The biodegradability of paper and zinc could help minimise the environmental impact of disposable, low-power electronics, the researchers said. They aim to boost the sustainability further by minimising the amount of zinc used within the ink.
The research was published in Scientific Reports.
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