Non-Destructive Characterization of Electrode Films for Lithium-Ion Battery Cells with an Optoelectronic Terahertz FMCW Radar

We present a novel system concept for non-destructive thickness measurement of electrode coatings for production of lithium-ion (Li-ion) batteries. The optoelectronic frequency-modulated continuous-wave (FMCW) radar generates an extreme broadband chirp signal by photomixing the optical signals of two lasers. The available bandwidth of the system allows inspection of very thin samples down to a theoretical optical thickness of 90 µm. In case of electrode films, high conductivity of the coatings make them highly reflective in terahertz regime with a very short skin depth. To validate its performance, we conducted experiments using electrode films made of various materials and through different production processes. The results demonstrate that the proposed method can measure the thicknesses of the electrode films with high accuracy and precision and can distinguish between different types of electrode materials. The non-destructive method can be utilized in situ for use in industrial applications.