①Small batteries arc big problems,

①Small batteries arc big problems, but nobody really pays attention to where they end up. Researchers at the Cellulose & Wood Materials Laboratory are working to address this problem. Their new research paper describes a water-activated paper battery developed from environmentally friendly materials that could eventually present a sustainable alternative to the more harmful batteries common in low-power devices. ②The 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 a cathode, a negatively charged side called an anode, and a conductive material called an electrolyte (电解质)between the two. A traditional battery's components are encased in plastic and metal; in the new battery, the anode and cathode are inks printed onto the front and back of a piece of paper. That paper is filled with salt, which dissolves (溶 解) when the paper is dampened with water The resulting saltwater solution acts as the electrolyte. ③Sustainable materials were a precondition for the researchers, who considered only safe and plentiful ingredients to create their device. "We were fairly confident that we would have something that would work in the end, but developing these materials and ink systems is challenging," says Gustav NystrOm, senior author of the study. ④After trying hundreds of formulations for the battery components, the researchers settled on a graphite ink to make the cathode, a zinc ink for the anode, and salt-filled paper to create the electrolyte. ⑤When the paper is dry, the battery is shelf-stable. Add just a couple of drops of water, however, and the salt dissolves, allowing electrons to flow. Once the paper is dampened, the battery activates within 20 seconds. The new battery's operating performance declines as the paper dries. When the scientists re-wet the paper during testing, the battery regained functionality and lasted an hour before beginning to dry out again. ⑥Although the researchers demonstrated that their battery could power an alarm clock, the paper batteries are unlikely to replace standard ones on store shelves. Nystrdm envisions a future where these paper batteries could make their way into products within the next two to five years. "The performance that you see on this device, I think, is sufficient for a lot of other applications already,” he says. It is mostly a matter of scaling up production and integrating the batteries into systems such as diagnostic tests and environmental sensors.