Impact of Graphite Crystallinity and Surface Chemistry on Potassium-ion Intercalation Dynamics

About This Grant

Non-technical summary: The development of new types of batteries that do not rely on lithium will enable cheaper and more readily available energy storage. Potassium is an especially promising alternative to lithium because it is two orders of magnitude more abundant, with processing facilities in place worldwide and significant reserves in the southwest United States (220 million metric tons). However, simply swapping lithium for potassium in batteries that use the same graphitic carbon anodes and analogous electrolytes does not lead to comparable electrochemical behavior. In contrast to lithium, potassium-ion batteries show severe performance degradation during cycling including poor capacity retention and high internal resistance. This project, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research and the Electrochemical Systems Program in the Division of Chemical, Bioengineering, Environmental and Transport Systems, both at NSF, uses advanced characterization tools such as magnetic resonance spectroscopies, diffraction, and imaging to understand how the crystal structure and the surface chemistry of different graphite anode materials influence electrochemical properties. The research creates a fundamental understanding of how graphite crystal structure, particle shape and size, and surface passivation alter the insertion and removal of potassium-ions during battery cycling. Insights from this research provide structure-function relationships that may inform graphite preparation and electrolyte design. Broader impacts of this project include science communication efforts where graduate students collaborate with New York City-based comedians to make easy-to-understand videos about their research for social media. Undergraduate students from Barnard College and Columbia University conduct hands-on battery research during a semester or in the summer, and local high school students visit Columbia University to learn about the history of carbon materials and see scientific instrument demonstrations. Technical summary: Elucidating the precise mechanisms that enable reversible potassium-ion intercalation into graphite anode materials is critical to expanding the number of materials that can potentially be used for various energy storage applications. This project, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research and the Electrochemical Systems Program in the Division of Chemical, Bioengineering, Environmental and Transport Systems, both at NSF, investigates the role of graphite crystallinity and surface chemistry on potassium-ion intercalation dynamics in graphite anodes for potassium-ion batteries (KIBs). In contrast to lithium systems, potassium-ion insertion is highly dependent on graphite microstructure, where structural disorder leads to increased defect concentrations and poor reversibility during cycling. The quantity and type of defects in a range of graphite materials and resulting K-graphite intercalation compounds are evaluated with state-of-the-art X-ray diffraction (XRD), Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. These techniques are used in conjunction with traditional electroanalytical methods to further assess the impact of graphite structure on ion transport and capacity retention. The relationship between graphite surface termination, electrolyte formulation, and the composition of the solid electrolyte interphase (SEI) is evaluated using a combination of solid-state NMR and advanced imaging metrologies. In particular, NMR spectroscopy has the ability to identify structural changes in metal fluoride components in the SEI that may enable ion conduction to further advance these formulations. In situ NMR spectroscopy is leveraged to determine how electrolyte oxidation at the cathode in full cells impacts the stability of electrolyte and electrode components in KIBs, including acid formation, transition metal etching, and crosstalk between the positive and negative electrode during cycling. Overall, the project generates molecular-level descriptors that connect structural disorder in bulk graphite anodes and at interfaces to the electrochemical properties observed in KIBs. This work is tightly integrated with educational initiatives including undergraduate training, high school outreach, and public-facing social media content constructed in a three-minute thesis format in collaboration with local comedians that communicate graduate-level research for general audiences. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.