BatTera: Non-Destructive Lithium-ion Battery Coating Measurement with Terahertz

Electrode coating measurement is a crucial task in practical lithium-ion battery systems, where the thickness and refractive index of the electrode coating directly reflect the battery's quality, energy density, capacity, and lifespan. In this paper, we propose the design, implementation, and evaluation of BatTera, the practical system for an accurate, high-resolution, non-destructive, and safe electrode coating measurement, with the ability to simultaneously measure coating thickness and refractive index. BatTera's contributions are twofold. Firstly, we build a comprehensive mathematical model that characterizes the arrival time of echo signals from both sides of the electrode coating by thoroughly analyzing the electrode structure based on “coating-foil-coating”. This model serves as a theoretical foundation guiding the measurement of coating thickness and refractive index. Secondly, we propose a series of effective signal-processing algorithms to address the practical challenges of double-side coating misalignment and deformation interference, thus adaptive improving the signal-to-noise ratio of Terahertz signals and pushing BatTera one big step closer to real adoptions. We implement BatTera based on the commercial Terahertz device QT-TO1000 and conduct extensive experiments using five types of cathode electrode samples in three different sizes, collected from one of the world's largest new energy battery manufacturers. The results show that BatTera achieves high measurement accuracy with a mean average error of 6.106$\upmu$m for thickness and 0.230 for refractive index.