Researchers from the University of Wollongong (Australia; www.uow.edu.au), led by professor Gordon Wallace and Caiyun Wang, built a battery with electrodes and a solid electrolyte out of silk.
Previous attempts at making such biodegradable, dissolvable batteries used natural, biocompatible materials for the electrodes and electrolytes. The electrolytes were usually solutions of various salts in water. However, liquid electrolytes can leak out and degrade battery electrodes, and they make batteries relatively bulky.
The solid electrolyte enables thinner, flatter and more flexible and robust batteries. Among other applications, the silk battery is ideal for temporary medical implants because it can be made into thin films, is biocompatible and is designed to harmlessly dissolve in the body in a few weeks, once its work has been done.
Thin films are made by dissolving fibroin (a fibrous silk protein derived from silkworm cocoons) in water. The solution is then spread in a mold. After the water evaporates, ultrathin films of silk can be peeled off. The electrolyte is made by infusing a piece of silk membrane with an ionic liquid (choline nitrate). The anode is made by depositing a biocompatible magnesium alloy onto a piece of the silk…