Scientists have discovered that lignin, a plentiful byproduct of the pulp and paper industry, can be used to store an electrical charge. They've used the material to create a prototype lignin-based rechargeable battery, and suggest that it could one day be used as a less expensive, safer alternative to the precious metals currently utilized in battery cathodes.
Lignin is found in plants, and is the second-most common polymer naturally produced by a living organism – after cellulose. When wood fiber is processed, its lignin content is removed to leave the cellulose required for paper production. Organic compounds known as quinones occur naturally within that lignin, and are central to the experimental battery.
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Grzegorz Milczarek, from Poland’s Poznan University of Technology, along with Olle Inganäs from Sweden’s Linköping University, blended a lignin derivative with a conductive polymer known as polypyrrole. When the resulting composite was subjected to an electrical charge, the quinones in the lignin shed a proton, and stored the charge in its place. The polypyrrole held onto that proton, allowing it to return to the lignin once the stored charge was released.
Although the battery does lose its charge when sitting idle, Milczarek and Inganäs found that different types of lignin derivatives offered different levels of performance, and believe that they could find one that allows for better charge storage.