Tracking Structural Changes of Carbon Nanotube Electrodes for Lithium–Air Batteries by Time-Resolved <i>Operando</i> Wide- and Small-Angle X‑ray Scattering

In this study, we prepared single-walled carbon nanotube electrodes for lithium–air batteries (LABs) to investigate the structural changes of the electrodes during the discharge–charge cycle coupled with the precipitation and decomposition of Li oxide. Wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) were used for the structural analysis. A new test cell was designed and fabricated to perform these measurements under operando conditions. From the results of the WAXS measurements during discharge tests, diffraction peaks indicating crystalline oxides and a broad peak indicating amorphous components were observed. The intensities of these peaks increased rapidly in the later stages of the discharge. Moreover, the WAXS measurements showed that the peak of the amorphous component preferentially disappears during the charging process. Furthermore, the nanoscale structural changes associated with the precipitation and decomposition of Li oxide were analyzed using SAXS. The results suggest that the electrode expansion caused electrolyte depletion in the electrode. The post-test electrode thickness was also analyzed, and the results support interpreting the data obtained from WAXS and SAXS. We think that the structural analysis approach and the pore formation discovered in this study will enable LABs to be used more effectively in the future