Dr. Jodie L. Lutkenhaus, associate professor, holder of the William and Ruth Neely Faculty Fellowship and recently named Presidential Impact Fellow in the Artie McFerrin Department of Chemical Engineering at Texas A&M University, just published a paper in Nature Materials. The findings presented in this paper represent a significant step toward Lutkenhaus’s ultimate goal: the creation of a battery made entirely of polymers.
A major hurdle to creating a metal-free, 100-percent polymer battery is finding a polymer that is electrochemically active -- meaning it has to be able to store and exchange electrons. Lutkenhaus, along with a team of researchers including doctoral candidate Shaoyang Wang, think that the organic radical polymers will do the trick. Owing to their chemical structure, organic radical polymers are very stable and reactive. As shown in the image below, organic radical polymers have a single electron on the radical group. This unpaired electron allows rapid charge transfer in these polymers during redox reactions.
According to Lutkenhaus, the main appeal of this class of polymer lies in the speed of the reaction. “These polymers are very promising for batteries because they can charge and discharge way faster than any common battery in a phone or similar device. This rapid charging could dramatically change the way electric vehicles are used today.”
The redox-active properties of organic radical polymers have been known for some time. However, prior to this research the exact mechanism by which electrons and ions are transported through the polymer had not been described. In part, the scale and speed at which these reactions take place make it difficult to capture reliable data. However, Lutkenhaus and her team were able to capture incredibly detailed measurements using a specialized device, an electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D).
The use of an EQCM-D is actually quite simple, but it operates on tremendously small scales. Lutkenhaus explained the experimental setup: “As we charge and discharge the polymer we are actually weighing it, so we know exactly how much it weighs even down to nanogram accuracy. The device is so sensitive that we can measure ions going in and out of the organic radical polymer.”
The results of the EQCM-D analysis led to somewhat unexpected results. Before this research the consensus was that only anions were transported in this process. However, the results show that lithium ions are transported as well. Further, the behavior and transport of the ions seems to be more dependent on the electrolyte than the polymer itself.
With this deeper understanding of the underlying processes, Lutkenhaus plans to take a closer look at the electrolyte polymer interactions.
This work was supported by the grant DE-SC0014006, funded by the U.S. Department of Energy, Office of Science.