A group of scientists at the University of Maryland, led by Hongbian Li, have devised a way of making batteries from tree leaves.
Where most modern batteries use lithium, the researchers were trying to find a convenient way to use sodium instead. Lithium and sodium are chemically similar, and sodium batteries would be able to hold more charge, but lithium batteries typically resist more charge-discharge cycles. Sodium is also a lot more abundant, making it cheaper to use.
Sodium has larger ions than lithium, so a sodium battery needs a different material for its anode (negative terminal). It turns out, one such material was simply lying on the ground. Leaves have all the right characteristics. Low surface area, porous, and with close packed internal structures large enough for sodium electrolytes to pass through.
To make a trial battery, Li and colleagues carbonised an oak leaf at 1000°C to burn away any underlying structure, leaving a pure carbon framework. They then allowed the leaf to soak up a watery sodium electrolyte solution. The result – carbonised plant leaves make excellent anodes for sodium batteries!
“A leaf is designed by nature to store energy for later use, and using leaves in this way could make large-scale storage environmentally friendly.“
– Liangbing Hu (co-author on the study)
Their study was published here in ACS Applied Materials and Interfaces.