Determining Bulk and Surface Degradation Mechanisms in Potassium Ion Batteries

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Non-technical summary:The development of new types of batteries that do not rely on lithium will enable cheaper and more widespread adoption of renewable energy. Potassium is a particularly attractive option to replace lithium because it has high natural abundance and desirable electrochemical properties. However, simply swapping Li atoms for K leads to severe performance decline in potassium ion battery (KIB) analogues. With this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, Prof. Marbella and her research group gather fundamental information required to develop KIBs. They use nuclear magnetic resonance (NMR) spectroscopy to study each component of the battery at the molecular-level, including the electrode, the electrolyte, and the electrode/electrolyte interface. Specifically, this research program tests the hypothesis that the larger atomic size of K compared to Li leads to unique degradation mechanisms that ultimately contribute to battery failure. The research project aims to identify the relationship between bulk and interfacial degradation modes and electrochemical behavior in KIBs. This provides insight that generate pathways to redesign materials that are optimal for KIB technologies. Broader impacts of this work include research opportunities and workshops created specifically for underrepresented undergraduate women interested in pursuing graduate education. This research project is also closely integrated with educational activities that engage underrepresented and underprivileged students in energy storage research projects at the undergraduate and high school level through partnerships with Barnard College (all women liberal arts college affiliated with Columbia University) and Ellis Preparatory High School for recent immigrants in the Bronx, respectively.Technical summary:Identifying and parsing the complex interplay between bulk and surface degradation modes in beyond-Li ion batteries is critical to realizing cost-effective solutions for the widespread adoption of electrochemical energy storage. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, leverages the high chemical and elemental specificity of nuclear magnetic resonance (NMR) to identify the chemical mechanisms underpinning failure in potentially high capacity tin phosphide anodes for potassium ion batteries (KIBs). The large atomic size of K generates highly disordered and mechanically unstable structures during potassiation of tin phosphides that are susceptible to a loss of electrical connectivity and parasitic side reactions during electrochemical cycling. In the bulk, phase transformations that occur upon K insertion/removal are difficult to measure with traditional materials characterization tools (e.g., diffraction) that require long-range order for structural assignment. In contrast, NMR can directly probe local P and Sn environments in the anodes to identify specific compounds that facilitate reversible K alloying reactions. Further, the volume expansion associated with K insertion exposes fresh surface for electrolyte consumption, presenting the need for strategies that can decipher electrolyte reactivity. NMR is used to describe, at the molecular-level, electrolyte solvation structures that generate unique electrolyte decomposition products. NMR analyses allows the creation of some of the first molecular-level descriptors of bulk phase transformations and interfacial reactivity in KIBs. This research plan is closely integrated with educational activities that engage underrepresented and underprivileged students in energy storage research projects at the undergraduate and high school level through partnerships with Barnard College (all women liberal arts college affiliated with Columbia University) and Ellis Preparatory High School for recent immigrants in the Bronx, respectively.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.