(Georgia Institute of Technology, 2023-05-02)
Krishnan, Abiram
Tracking changes in the electronic structure of target elements is crucial to investigate the nature of redox reactions occurring in battery electrodes. Core-hole characterization techniques such as X-ray Emission Spectroscopy (XES) and X-ray Absorption Fine Structure (XAFS) perform this role well through the generation/quenching of core holes in the sample. Laboratory-based core hole x-ray spectroscopy techniques have recently gained popularity as they are more accessible and provide energy resolution close to that of a synchrotron source.
In this study, the use of a lab-scale XAFS/XES to investigate the change in the electronic structure around transition elements present in electrode materials for lithium-ion storage is explored under operando conditions. This enables real-time monitoring of chemical shifts resulting from changing electrode potential. The relationship between energy shifts and oxidation/spin state is obtained using K-edge XANES and Kβ1,3 XES measurements of transition metals present using reference compounds. This relationship is utilized to predict the change in chemical environment during the cycling of cathode/anode materials for energy storage. Additionally, the spin sensitivity of Kα and Kβ fluorescence is utilized to explore the magnetic behavior of LCO cathodes in the first 10% of lithium removal along with K-edge XAFS for oxygen and cobalt to investigate local and electronic structure changes.