Tessellated-Pattern Dense-Pattern Multi-Pass Cavity Enhanced Raman Spectroscopy for In Situ Analysis of Gases Inside...

Multigases generated inside the lithium-ion batteries during operation are strongly correlated with the electrochemical state. However, basic research on gas generation features is insufficient due to the lack of nondestructive in situ analysis approaches. We propose an enhanced Raman sensing method using a tessellated dense multipass cavity with an elaborately designed battery module for in situ analysis of gases inside the battery. More than 360 dense-reflected intracavity beams passing through the same point are realized using two 2 in. diameter spherical mirrors with identical optical parameters. The detection limits reach the sub-ppm level for gases at 0.1 MPa total pressure. For the battery module, the battery cell and electrolyte are placed at the bottom, allowing the generated gases to diffuse into the upper gas cell for Raman scattering excitation. Battery gas analysis demonstrates that the concentrations of C₂H₄, CO₂, CO, and H₂ increase during charging or discharging, which is generally consistent with the current knowledge at the qualitative level. This validates our method's applicability for in situ analysis of gases within the battery, laying the foundation for future elucidation of the mechanism of battery failures based on gas analysis.