Empa researchers have developed a water-activated disposable paper battery. It could power a wide range of low-power disposable electronic devices such as smart tags or environmental sensors.
The battery, designed by Gustav Nyström and his team, consists of at least one cell, measuring one centimeter square, made up of three inks printed on a rectangular strip of paper. The Swiss Federal Laboratories for Materials Testing and Research (Empa) announced on Thursday that table salt had been scattered in the strip of paper, which is dipped in wax at one end.
Graphite flake ink, representing the positive end of the battery (cathode), is printed on one of the flat sides of the paper, while zinc powder ink, representing the negative end of the battery (anode), is printed on the reverse side of the paper.
Another ink containing graphite flakes and carbon black is printed on both sides of the paper on top of the other two inks. This ink forms the current collectors that connect the positive and negative poles of the battery to two wires located at the end of the wax-covered paper.
When a small amount of water is added, the salts in the paper dissolve and charged ions are released, making the electrolyte conductive. These ions activate the battery by dispersing throughout the paper, oxidizing the zinc in the ink at the anode and releasing electrons.
By closing the circuit, these electrons can then be transferred from the zinciferous anode – through the graphite and carbon black ink, wires and device – to the graphite cathode. These different reactions create an electrical current that can be used to power an external device.
To demonstrate the capabilities of this invention, Gustav Nystrom’s team combined two cells into a single battery to increase operating voltage and used it to power an alarm clock with an LCD display.
Analysis of the performance of a single-cell battery showed that after adding two drops of water, the battery activated in 20 seconds and, when not connected to a water-consuming device, energy reached a stable voltage of 1.2 volts. The voltage of a standard AA alkaline battery is 1.5 volts.
After an hour, the performance of the single-cell battery dropped significantly due to the paper drying out. However, after the researchers added two more drops of water, the battery maintained a stable operating voltage of 0.5 volts for over an additional hour.
According to the researchers, the biodegradability of paper and zinc could allow their battery to minimize the environmental impact of single-use and low-power electronic devices.
“What’s unique about our new battery is that unlike many metal-air batteries that use a sheet of metal that gradually burns away as the battery wears down, our design allows the ink to only add the amount of zinc that is actually needed.” application is required for the respective product,” explains Gustav Nyström, quoted in the press release.
The more zinc the ink contains, the longer the battery will last. A more critical issue is water activation, adds Gustav Nyström, and the time it takes for the battery to dry out.
“But I’m sure it’s possible to modify the battery design to circumvent this problem,” he says. However, for environmental sensing applications at a certain humidity or in humid environments, drying the paper would not be a problem.
Previously, Gustav Nyström’s team had already developed a degradable paper-based supercapacitor that could be charged and discharged thousands of times without losing its efficiency. Empa concludes that the two systems complement each other. This work is published in the journal Scientific Reports.
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