Since the first lithium-ion battery was developed in 1991, scientists have been looking for ways to enhance its efficiency, especially when it comes to its graphite anode. According to a previous research, portabella mushrooms, known for their high degree of porosity, could be used in place of graphite as anodes inside Li-ion batteries. This time around, a team from Purdue University has turned once again to nature, particularly pollen as potential substitutes for graphite anodes.

Infamous as allergens, pollen, the researchers believe, could be used as a cheap, renewable alternative to graphite in lithium-ion batteries. The team’s research has revealed that these nature-derived microstructures are actually capable of enhancing battery performance. Batteries contain two electrodes, namely cathode (or positive terminal) and anode (or negative terminal). When connected with the help of a wire, the two electrodes form a circuit through which electrons can flow, thereby producing electricity. Vilas Pol, a professor of chemical and materials engineering at Purdue, said:

Our findings have demonstrated that renewable pollen could produce carbon architectures for anode applications in energy storage devices.

In today’s lithium-ion batteries, which are widely used to power electronic devices such as smartphones, tablets and laptops, the anodes are commonly made from graphite, a material that has its own set of limitations when it comes to physical stress and storage. For the research, the scientists tested pollen-derived carbon structures as anodes. Speaking about the study, recently published in Nature’s Scientific Reports journal, Jialiang Tang, a doctoral student at Purdue, said:

I started looking into pollen when my mom told me she had developed pollen allergy symptoms about two years ago. I was fascinated by the beauty and diversity of pollen microstructures. But the idea of using them as battery anodes did not really kick in until I started working on battery research and learned more about carbonization of biomass.

The team worked with two types of pollen, bee and cattail, subjecting each to a process of carbonization. Unlike bee pollen, which is usually a mixture of different kinds of pollen collected by honeybees, cattail pollen are uniform in shape and size, a property that renders them more suitable for use as anodes. Pol added:

Both are abundantly available. The bottom line here is we want to learn something from nature that could be useful in creating better batteries with renewable feedstock.

According to the scientists, the pollen were processed via pyrolysis, in a special chamber containing argon gas at high temperatures. This in turn produced pure carbon microstructures resembling the original pollen particles in shape. Further heating to around 300 degrees Celsius, in the presence of oxygen, resulted in the formation of tiny pores along the spheres’ outer surface, thus increasing their energy-storage capacity.

As the researchers point out, each of these pollen anodes can be charged at varying rates, with full charging taking nearly 10 hours to complete. More than half of a full charge can be achieved via only a hour of charging. When tested at various temperatures, the cattail pollen-derived carbon anodes performed much better than the bee pollen counterparts, delivering an incredibly high capacity of up to 590 mAh/g at 50 degrees Celsius and around 382 milliamp hour per gram at 25 degrees Celsius. Pol added:

The theoretical capacity of graphite is 372 milliamp hours per gram, and we achieved 200 milliamp hours after 1 hour of charging… We are just introducing the fascinating concept here. Further work is needed to determine how practical it might be.

Source: Purdue University