Scientists turn leaves into batteries

fallen leaves
CC BY 2.0 A_Peach

We've seen scientists looking for alternative materials for making batteries for a long time now. As we increasingly rely on batteries to power the things we use from our gadgets to our cars and more, the importance of batteries being made from the most sustainable, easily accessible materials possible has grown.

A team of researchers at University of Maryland has tackled this issue by discovering one of the simplest possible ways to make a battery: find a leaf, bake it and add sodium. Well, at least the anode of a battery.

"Leaves are so abundant. All we had to do was pick one up off the ground here on campus," said Hongbian Li, a visiting professor in the department of materials science and engineering in UMD’s A. James Clark School of Engineering.

The researchers are working on making batteries that use sodium where most rechargeable batteries use lithium because sodium can hold a greater charge although it cannot withstand as many charge and discharge cycles as lithium.

The problem so far with sodium batteries has been finding an anode that works with sodium since it is slightly larger than lithium. Graphene has been explored, but the processes were too complicated, but using the leaf couldn't have bene easier. The researchers heated it at 1,000 degrees Celsius for an hour which burned off everything but the basic carbon structure.

The underside of the leaf is porous, typically used to absorb water, but in this case the pores absorb the sodium electrolyte. The top side is tough nanostructured carbon that absorbs the sodium and holds the charge.

"The natural shape of a leaf already matches a battery’s needs: a low surface area, which decreases defects; a lot of small structures packed closely together, which maximizes space; and internal structures of the right size and shape to be used with sodium electrolyte," said Fei Shen, a visiting student in the department of materials science and engineering and the other lead author of the paper.

This same team has also explored using wood fibers in their quest to make a sodium-ion battery. These natural materials are ideal because they are built for the swelling and contracting of water absorption and evaporation, which mimics the swelling and contracting that is necessary for a battery anode as it absorbs and discharges sodium ions. Other materials are too brittle or break down after only a few charge and discharge cycles.

The team will now move on to testing different type of leaves to find the best thickness, structure and flexibility for use in the battery. This research was funded by the Department of Energy’s Energy Frontier Research Center program, as part of Nanostructures for Electrical Energy Storage.

Tags: Batteries | Technology

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