Ions and Interfaces: Probing Fundamental Dynamics of Lithium-Ion Batteries

Abstract

Lithium-ion batteries have revolutionized the technological world as we know it today, however upgrades to next-generation materials will be required to meet the needs of a clean energy future. Group IV semiconductors such as silicon (Si) offer a high-capacity alternative to the current anode material (graphite). However, due to a difference in lithiation mechanism and surface chemistry, Si electrodes exhibit unstable cycling performance which impedes their commercialization. This thesis focuses on fundamental studies of interfacial processes at the anode/electrolyte interface using in situ vibrational spectroelectrochemistry. First, we study the kinetically-resolved correlations between interfacial ion speciation and lithium-ion storage in a model system by applying global analysis to our spectroelectrochemical data. We observe that it may be more kinetically viable for lithium to be extracted from contact ion pairs to contribute to faster charging rather than fully-solvated lithium. Next, we use a dipole surface modification to dynamically respond to weak spots of Si electrodes during cycling. This strategy allows for interfacial energetic tuning to mitigate unwanted parasitic reactions within the electrode and enhance cycling stability. In situ spectroelectrochemistry and electrochemical methods were used to probe the origin of enhanced stability. The fundamental studies presented in this thesis are meant to contribute to a deeper understanding of how interfacial processes behave in LIBs and inform future design of next-generation electrochemical energy storage systems.