A microscopic image of bee pollen, which the researchers studied for use as an anode for lithium-ion batteries
(Credit: Purdue University image/Jialiang Tang, Kay J. Hagen)
As our dependence on mobile devices grows and we continue the shift to electric vehicles, there is a need to not only develop better performing batteries but find more accessible and sustainable materials with which to build them. To this end, researchers have now developed an anode for lithium-ion batteries using something those with allergies certainly wouldn't miss: pollen from bees and cattails.
Though widely used, the graphite that serves as the anode in much of today's lithium-ion batteries has its fair share of weaknesses. Aside from its limited storage capacity, preparing the material for use involves treatment with chemicals such as hydrofluoric and sulfuric acids, which results in hazardous waste, something that is neither cheap or friendly to the environment.
In search of more eco-friendly solutions, researchers have turned to a number of natural or recycled materials in order to build the anode, which is the electrode that stores the lithium ions as the battery is charging. These have included portabella mushrooms, packing peanuts and even old car tires.
Taking a similarly sustainable approach, researchers at Purdue University were able to use pollen from bees and cattails to produce carbon architecture for a battery anode. This involved exposing the pollen to high temperatures in a chamber containing argon gas, a process called pyrolysis, which resulted in pure carbon. These carbon particles were then heated at a lower temperature of around 300° C (572° F) in the presence of oxygen, which brought about pores in the structures, in turn increasing their energy storage capacity.
The team then tested out the anode at temperatures of 25 and 50° C (77 and 122° F) to explore how it might hold up in different climates. They found that it delivered impressive lithium storage capacity of 590 mAh/g at 50° C and 382 mAh/g at 25° C (the theoretical capacity of today's graphite anodes is 372 mAh/g). And while it took 10 hours to charge fully, one hour resulted in more than half of a full charge. The team reports that cattail pollens were better performing than bee pollen.
"Our findings have demonstrated that renewable pollens could produce carbon architectures for anode applications in energy storage devices," says Vilas Pol, an associate professor at Purdue University.
The researchers do emphasize that the work is very much in its early, conceptual stages, concerning only the pollen-derived anodes. They now aim to explore how practical this approach might be by researching how they perform in full-cell batteries with a commercial cathode.