Operando laboratory XAS on battery materials using the DANOISE cell in a von Hámos spectrometer

This work presents laboratory-based operando X-ray absorption spectroscopy (XAS) measurements on electrodes for rechargeable batteries. Using the “Developed in Aarhus: New Operando In-house Scattering Electrochemical” (DANOISE) cell, operando XAS measurements were performed with two von Hámos spectrometers, optimized for X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Selected battery electrodes, including commercial LiFePO₄ (LFP) for Li-ion batteries and layered transition metal oxides, Na_xTMO₂ (TM = Fe, Mn), electrodes for Na-ion batteries, were measured to present a proof of principal for the applicability of these spectrometers in battery research. The von Hámos spectrometers used in this study offer a high efficiency and the ability to measure a large spectral bandwidth (up to 1500 eV beyond the edge). Fe K-edge XANES measurements of LFP with an acquisition time of 15 minutes per spectrum successfully captured the transition of Fe species to FePO₄ during cycling. Additionally, Mn K-edge XANES measurements on Na-ion battery materials highlight the challenges associated with Na-ion batteries, particularly due to their higher absorption compared to Li-ion counterparts. Nevertheless, the Mn K-edge was successfully measured, allowing for oxidation state determination in the material. Fe K-edge EXAFS measurements on Na-ion battery materials revealed the transition of Fe species during charging, within an acquisition time of 15 to 25 minutes.