The wires, screens and batteries that make up our devices—not to mention the plastic, metal and other materials that package them—are filling up landfills. Some e-waste is relatively large: old phones and air conditioners, for instance. Other e-waste is more hidden, such as electronic single-use medical diagnostic kits, environmental sensors, and smart labels that contain one-off batteries and other equipment.
"It's these small batteries that are big problems," says public health scientist Dele Ogunseitan, who was not involved in developing the battery. "Nobody really pays attention to where they end up."
Researchers at the Cellulose & Wood Materials Laboratory at the Swiss Federal Laboratories for Materials Science and Technology (Empa) are working to address this problem. Their new paper in Scientific Reports describes a paper battery developed from environmentally friendly materials that could eventually present a sustainable alternative to the more harmful batteries common in low-power devices.
The 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 (正极), a negatively charged side called an anode (负极), and a conductive material called an electrolyte (电解质)between the two. A traditional battery's components are packaged 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.
When 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 becomes active within 20 seconds. The new battery's operating performance declines as the paper dries. When the scientists rewet the paper during testing, the battery regained functionality and lasted an hour before beginning to dry out again.
