Next Step In Eco-Friendly Technology: High-Capacity Soft Batteries Made From Trees

by Monica Joshi

Ah trees, what would we do without them? They give us oxygen, cool us down in the summer, change colours in the fall to make pretty landscapes and even affect our mood. Now, scientists have developed a way to make them even more useful by turning them into high-capacity, soft batteries that can store significantly more power in lesser space than is possible with conventional batteries.

Using nanocellulose, a light solid substance obtained from plant matter, a team from KTH Royal Institute of Technology and Stanford University have developed the elastic, foam-like battery material that can withstand both shock and stress.

Lead researcher Max Hamedi from KTH and Harvard University says that:

"It is possible to make incredible materials from trees and cellulose."

Unlike today's batteries, these new batteries could be used to create 3-D structures and even line flexible or oddly-shaped materials such as clothes or the bodies of vehicles. Their results, published in the journal Nature Communications, come only days after another group of researchers made huge strides in creating a biodegradable computer chip.

The batteries and supercapacitors, which are devices that store and release power much faster than batteries, were made out of a wood-based aerogel. The aerogel was created by breaking down the cellulose, the fiber found in trees, and then making the cellulose one million times thinner. They then dissolved this nanocellulose and freeze-dried it. The freeze-drying process allows the moisture to evaporate without the material ever going through a liquid state. The molecules in the material are then stabilised, so that it does not collapse.

On the final result of the process, Hamedi added that:

"The result is a material that is both strong, light and soft. The material resembles foam in a mattress, though it is a little harder, lighter and more porous. You can touch it without it breaking."

Finally, this aerogel is coated with a special ink that conducts electricity within the aerogel, thereby giving it the electronic properties that a battery requires. The resulting foam-like battery material, when unraveled from its battery form, can stretch to be the length of a lung. In 3-D states, such as clothes or cars, the limits to how thin a battery can be are virtually non-existent.

Using this material as a base, the team carefully engineered a 3-D supercapacitor with carbon nanotube electrodes. They also engineered a hybrid battery. While both of them were fully functional even at 75 percent compression, the supercapacitor worked stably for 400 charge cycles.

Hamedi further notes that the research builds on previously marketed objects:

"While flexible and stretchable electronics already exist, the insensitivity to shock and impact are somewhat new."

There are roughly 3 billion batteries purchased in the US each year, of which about 70 percent are disposed of incorrectly and only 16 percent of those bought are rechargeable. The benefits of this new research are numerous. These new batteries could potentially be used to line the bodies of electric cars, thereby reducing the environmental impact. While the use of these batteries is a long ways away, there are a few concerns from environmentalists. The next step but possibly biggest objection to this line of research: commercial farming for trees, in a world where deforestation is already a grand-scale issue.