Electronic devices are getting closer and closer to becoming disposable. Planned obsolescence, which is the practice of designing products to have a limited lifespan, is rampant. When you go and buy a fancy new smartphone, you know that you'll end up selling it or throwing it into a box within a couple of years, never to be used again. The problem, aside from consumerism, is that many of our discarded electronic devices end up in landfills. They contain materials that are bad for the environment, especially in their batteries. In order to create devices that are more responsibly disposable, a team of researchers from the Swiss Federal Laboratories for Materials Science and Technology (Empa) developed a biodegradable capacitor.
A capacitor, like a battery, is a component that stores electricity. Compared to batteries, capacitors charge and discharge faster, but usually have a lower energy density. Engineers use capacitors to store electricity for a short amount of time and to filter power or electrical signals. Almost all modern electronic devices contain several capacitors. But capacitors today, which are commodity components, contain materials that do not break down easily. Some, like ceramic, are harmless, but many of the materials in capacitors won't biodegrade at all. These new biodegradable capacitors will break down in a standard compost pile within a couple of months.
The team was able to fabricate these capacitors using a special 3D printer that extrudes gelatinous "ink." The ink, which is the real breakthrough here, is a mixture of cellulose nanofibers, cellulose nanocrystallites, carbon black, graphite, and activated carbon. They mixed those with glycerin, water, alcohol, and salt to create this gel ink. The printer lays down four layers: a flexible substrate, conductive material, electrode material, and then the electrolyte in the form of the gel described above. By folding the resulting layer cake over like a sandwich, the team created a functional capacitor. It can store power for hours, can handle thousands of charge/discharge cycles, and can withstand reasonable operating conditions.
3D printing these capacitors is too inefficient to be practical at scale, but these same materials would work with mass production techniques. There are still other components in most electronic devices that contain hazardous materials, but these capacitors bring us one step close to safe, disposable devices.