Scientists invent paper battery – just add water

Discarded electronics accumulate quickly, prompting researchers to explore creative ways to reduce the resulting trash, known as e-waste. Now, a team has made a water-activated, disposable battery made of paper and other sustainable materials.

The wires, screens, and batteries that make up our devices—not to mention the plastic, metal, and other materials that encase them—fill landfills with hazardous waste. Some e-waste is relatively large: old flip phones, air conditioners and radios to name a few common items. Other e-waste is more insidious, such as single-use electronic diagnostic kits, environmental sensors and smart tags that contain single-use batteries and other equipment.

“These little batteries are big problems,” said Dele Ogunseitan, a professor of public health at the University of California, Irvine and an environmental technology researcher and adviser to major technology companies who was not involved in the development of the paper battery. “No one really cares where they end up.”

Researchers at the Cellulose and Wood Materials Laboratory at the Swiss Federal Laboratories for Materials Science and Technology (Empa) are working to address this neglected problem. This week they published an article in Scientific reports describing a new water-activated paper battery they developed from environmentally friendly materials. Such a device could eventually provide a sustainable alternative to the more harmful batteries that are common in low-power devices.

The new paper battery has the same key components as standard batteries, but packages them differently. Like a typical chemical battery, it has a positively charged side called the cathode, a negatively charged side called the anode, and a conductive material called an electrolyte between the two. The components of a traditional battery are encased in plastic and metal; in the new battery, the anode and cathode are inks printed on the front and back of a sheet of paper. This paper is impregnated with salt, which dissolves when the paper is wetted with water. The resulting salt water solution acts as an electrolyte.

Sustainable materials were a prerequisite for the researchers, who considered only non-toxic and abundant ingredients to create their device. “We were pretty confident that we would have something that would work in the end, but developing these materials and ink systems is far from trivial,” says Gustav Nyström, head of the Cellulose and Wood Materials Laboratory and senior author of the study. After trying hundreds of formulations for the various components, the scientists settled on graphite ink to make the cathode, zinc ink for the anode, and salt-soaked paper to create the electrolyte. When the paper is dry, the battery is stable in storage. Add just a few drops of water, however, and the embedded salt dissolves, allowing the electrons to flow. Once the paper is wet, it takes about 20 seconds to activate the battery. At this point, it produces a steady 1.2 volts of electricity until the paper dries. (For comparison, an AA battery provides 1.5 volts.) When the researchers rewetted the paper, the battery produced 0.5 volts for more than an hour.

Although the researchers demonstrated that their battery could power an alarm clock, disposable paper batteries are unlikely to replace standard AAs on store shelves. Instead, Nyström envisions a future where these batteries are embedded in diagnostic tests and environmental sensors, ideally with other sustainable components such as screens and packaging. That future may not be so far away.

It is difficult to predict a timeline for producing such items at scale, but Nyström says he is in contact with potential industry partners and believes these batteries could enter products within the next two to five years. “The performance you’re seeing in this device is, in my opinion, already sufficient for many of these applications,” he says. This is mostly a matter of scaling up production and integrating batteries into systems such as diagnostic tests and environmental sensors.

Most importantly, Nyström says his team created the battery without compromising sustainability criteria. “It’s work that really starts with developing sustainable materials,” he explains. From there, he says, “I think we’ve been able to create something that’s pretty useful.”

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