2019 Young Chemist Award Winner
Congratulations to our $10,000 winner: Jeffrey Lopez, Massachusetts Institute of Technology
Metrohm USA is pleased to announce the winner of the 2019 Young Chemist Award, Jeffrey Lopez.
In order to enable the greater utilization of electric vehicles, allow for grid scale energy storage, and meet the demands of new electronic applications, new materials for high energy density batteries must be developed using high capacity electrode materials like lithium metal. Jeffrey’s work has helped to identify methods to stabilize these electrodes with polymer coatings and understand the coating properties that influence lithium deposition.
Lithium ion batteries have become the dominant form of energy storage used in consumer electronics and, recently, electric vehicles. However, high costs have prevented widespread deployment of lithium ion batteries for applications other than portable electronics, and the safety issues associated with traditional materials remain to be addressed. In order to enable the greater utilization of electric vehicles, allow for grid scale energy storage, and meet the demands of new electronic applications, new materials for high energy density batteries must be developed. High capacity electrode materials like lithium metal have the potential to facilitate these technologies, but significant hurdles must first be overcome. Lithium metal suffers from significant side reactions, poor quality deposition, and the potential to form hazardous dendrites. Therefore, strategies to enhance the mechanical and chemical stability of these electrode materials are key to their successful application in commercial batteries.
In this work, new polymeric materials are used to address issues of stability in lithium ion batteries. A supramolecular, self-healing polymer was carefully developed to be used as a coating that enabled the dendrite free deposition of lithium metal anodes. With this new concept, improved lithium deposition was obtained at current densities as high as 5 mA cm-2, and we observed a cycling Coulombic efficiency of over 97% for more than 180 cycles. Further investigation was carried out to understand how polymer coatings generally affected lithium metal deposition. We studied the effects of several rationally chosen polymers with varied chemical and mechanical properties as coatings on the lithium metal anode. By examining the early stages of lithium metal deposition we determine that while global morphology depends on the coating quality and mechanics, the local morphology of the lithium particles is strongly influenced by the chemistry of the polymer coating. We have identified polymer dielectric constant and surface energy as two key descriptors of the lithium deposit size. High dielectric constant polymers increase the exchange current through improved Li+ ion solvation and promote larger lithium deposits, and low surface energy polymers have less interaction with the lithium surface and thus increase the interfacial energy, promoting larger deposits with smaller surface areas. We also note that the thickness of the polymer coating and the polymer reactivity are important parameters to be considered.
Supervised by Prof. Zhenan Bao, Jeffrey’s work has contributed new materials to be used in electric vehicles, grid scale storage, and new electronic devices, and used these materials to develop fundamental understanding about how materials properties affect the stability of lithium ion batteries in each application. This understanding provides direction for the design and synthesis of new polymer materials to better stabilize high capacity anode materials.