A Spatially-Resolved <i>operando</i> High-Energy Confocal X-ray Diffraction Method for Observing Non-Uniform Degradation Phenomena in a Practical Cylindrical Lithium-ion Battery

Abstract

We report the results of spatially-resolved non-destructive operando electrode reaction analysis for practical cylindrical 18650 battery cells by using a high-energy confocal X-ray diffraction (XRD). A combination of highenergy X-rays (72 keV) and a confocal XRD method, which extracts structural information in a limited area that satisfies a confocal condition, allows us to observe electrode reactions in a cylindrical battery cell in a nondestructive way, resolving the double-side-coating electrode structure. We observed that electrode reactions were faster in the outer-part electrode than in the inner-part at the initial state reflecting intrinsic cell structure (position of current tab). For a battery cell deteriorated after 500 charge/ discharge cycles, in contrast, electrode reactions were faster in the inner-part electrode than in the outer-part, suggesting that the outer-part is more deteriorated than the inner part. The results of characterization of disassembled electrodes show that the observed slow response of the outer-electrode of a 500-cycled cell is attributed to various factors increasing resistance such as cracks in cathode particles, formation of insulating surface oxide-phase, and anomalous growth of solid electrolyte interphases (SEIs). As shown here, the high-energy confocal XRD is effective for non-destructive analysis of electrode reactions.

Nondestructive quantitative imaging for spatially nonuniform degradation in a commercial lithium-ion battery using a pulsed neutron beam

“…The developed nondestructive imaging becomes one of the useful techniques for the sequential observations of resistance change during degradation; actual measurements of the cell-position-dependent resistive value require destructive analysis. 13) A nondestructive quantitative neutron Bragg-edge imaging of commercial fresh and fatigue prismatic LIB cells was performed on the negative electrode material (graphite). Bragg-edge fitting was performed using the graphite nonrandom crystalline-orientation evaluated in this work, and the column density images of C or Li atoms/ions for five crystalline phases were successfully obtained.…”

“…The LIB health status can be analyzed nondestructively by observing the changes in the crystal structure of the electrode materials via high-energy X-ray or neutron diffraction measurements. Baba et al 13) performed confocal high-energy X-ray diffraction measurements and revealed that the outer part of the positive electrode deteriorated more than the inner part in a deteriorated cell. Mühlbauer et al 14) performed neutron diffraction measurements and reported that the lithium distribution in the negative electrode in the charged state was nonuniform in the radial direction in a fatigued cell.…”