A disposable paper battery that can be activated by water

A disposable paper battery that can be activated by water


The paper battery is composed of two electrochemical cells at both ends of the paper strip, separated by a water barrier (between the letters “m” and “p”) and connected in series. Empa sda-ats

This content was published on July 28, 2022 – 17:00

(Keystone-ATS)

Empa researchers have developed a water-activated disposable paper battery. It could power a wide range of low-power, single-use 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 square centimeter and composed of three inks printed on a rectangular strip of paper. Table salt is scattered in the strip of paper, one end of which has been dipped in wax, the Federal Laboratory for Materials Testing and Research (Empa) said in a statement on Thursday.

An ink containing graphite flakes, which is the positive end of the battery (cathode), is printed on one of the flat sides of the paper, while an ink containing zinc powder, which is the negative of the battery (anode), is printed on the back 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 constitutes the current collectors which connect the positive and negative poles of the battery to two wires located at the end of the paper covered with wax.

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 in the paper, which has the effect of oxidizing the zinc in the ink at the anode and releasing electrons.

By closing the circuit, these electrons can then be transferred from the zinc-containing anode – via the ink containing graphite and carbon black, the wires and the device – to the graphite cathode. These various reactions generate an electrical current that can be used to power an external device.

Proof of concept

To demonstrate the capabilities of this invention, Gustav Nyström’s team combined two cells into a single battery to increase the operating voltage and used it to power an alarm clock with an LCD display.

Analysis of the performance of a single-cell battery revealed that after adding two drops of water, the battery activated in 20 seconds and, when not connected to a water-consuming device, energy, it reached a stable voltage of 1.2 volts. The voltage of a standard AA alkaline battery is 1.5 volts.

After one hour, the performance of the single-cell battery decreased significantly due to drying of the paper. 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.

Biodegradable

According to the researchers, the biodegradability of paper and zinc could allow their battery to minimize the environmental impact of disposable and low-power electronic devices.

“What’s special about our new battery is that, unlike many metal-air batteries that use a metal foil which gradually burns away as the battery wears out, our design only adds to the ink than the amount of zinc actually needed for the specific application”, explains Gustav Nyström, quoted in the press release.

The more zinc the ink contains, the longer the battery is able to operate. A more critical point 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 get around this problem,” he says. For environmental sensing applications at a certain humidity or in humid environments, however, drying of 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. The two systems are complementary, Empa concludes. This work is published in the journal Scientific Reports.

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