Non-Destructive Analysis of Crystal Structure Changes of Component Materials in Cylindrical Lithium-Ion Batteries at Elevated Temperature By Synchrotron Radiation x-Ray Diffraction Measurement

Abstract

Temperature is one of the important factors for lithium-ion battery (LIB) which accelerates degradation of the performance. In many cases, degradation mechanism is studied by post-mortem analysis with destruction of degraded LIBs to obtain their component materials. However, these studies has a risk that any chemical and structural changes may have occurred in the samples during preparation process after destruction. Hence, development of in-situ and non-destructive analytical methods are strongly required. In this study, we report x-ray diffraction (XRD) measurement system using synchrotron radiation facility by which cylindrical LIB itself can be used as the sample without destruction and XRD patterns of cathode and anode layers are obtained separately. In addition, temperature of the sample can be controlled between RT and 250 °C.18650 type cylindrical LIBs were used as the sample of which capacity were ca. 1.2 Ah. The cathode active material was Li(Ni1/3Mn1/3Co1/3)O2 and the anode active material was graphite.XRD measurement was performed at BL46XU in SPring-8 with Huber multi-axis diffractometer. The incident beam was high-energy (72 keV) x-ray. A LaBr3 scintillation counter was used as the detector. The temperature of the sample batteries was controlled by specially designed system. Figure 1 shows XRD patterns of the anode layer of a sample LIB located at 1.65 mm inner from surface of the case. While only stage-1 structure (LiC6) was observed at RT, a new peak of stage-2 (LiC12) appeared and increased after the temperature beyond 90 °C which suggested that self-discharge would be accelerated at 90 °C and above. Figure 1