In 1799, Alessandro Volta modeled the first battery—a stack of zinc and copper discs called the “voltaic pile”—after the body of the electric eel. The discovery was pivotal and enabled a series of other important innovations. Nearly two centuries later, the sea creature has inspired yet another energy technology—a bio-compatible soft battery.
Electric eels produce electricity in an organ that contains thousands of electrocytes. These electrocytes pump out positively charged potassium and sodium ions, creating voltages that cancel one another out while the animal is relaxed.
When the eel is ready to strike, however, the electrocytes flip and pump positive ions in the opposite direction. This switch makes each electrocyte’s front end positive and back end negative, creating a small voltage chain across the cell. It creates a voltage of about 150 millivolts that adds up like a lineup of AAA batteries to generate hundreds of volts.
Inspired by this marvel of marine biology, a team of researchers led by Michael Mayer at the University of Fribourg developed an energy storage technology that mimics the eel’s electricity-producing cells. The battery is made up of four color-coded hydrogels, water-based polymer mixes that are arranged in rows similar to the eel’s electrocytes.
The four gels are blue, green, yellow, and red. The green gel allows positive ions to flow through, while the yellow one only lets negative ions pass, explains Ed Yong in The Atlantic. Therefore, positive ions flow into the blue gels from only one side, while negative ions flow in from the other, creating a voltage across the blue gel.
Each four-gel cell generates 130 to 185 millivolts. The researchers were able to link 612 of them in tandem to produce 110 volts.
The energy-generation process takes place when the gels press together. Therefore, the fact that the gels are spread out on a large sheet presented an early design challenge. Max Shtein, an engineer at the University of Michigan, suggested origami as a solution. And by folding the sheet of gels so that the corresponding gels match up and come into contact in the correct order, the team was able to produce power in a very small space with moldable technology.
Since they can be made from soft, water-based materials that are bio-compatible, researchers feel that these batteries could influence the next generation of medical technology. What are your thoughts?