Mechanical Behavior of Lithium-Ion Battery Component Materials and Error Sources Analysis for Test Results

As mechanical damage induced thermal runaway of lithium-ion batteries has become one of the research hotspots, it is quite crucial to understand the mechanical behavior of component materials of lithium battery. This study focuses on the mechanical performance of separators and electrodes under different loading conditions and the error sources analysis for test results. Uniaxial tensile tests were conducted under both quasi-static and dynamic loading conditions. The strain was acquired through the combination of high speed camera and digital image correlation (DIC) method while the force was obtained with a customized load cell. Noticeable anisotropy and strain rate effect were observed for separators. The fracture mode of separators is highly correlated to the microscopic fiber orientation. To demonstrate the correlation microscopic images of separator material were obtained through SEM to match the facture edges of tensile tests at different loading directions. Coated electrode materials show higher fracture strength and higher elongation compared to decoated materials in uniaxial tensile tests. Electrode materials show relatively slight strain rate effect, and no apparent anisotropy was found in their test results. An error analysis program was developed through MATLAB to estimate the standard uncertainty of the results. Input quantities such as initial dimensions of specimen and measured load, fast Fourier transform (FFT) of acquired data and deviation of repeated measurements were taken into consideration as main error sources. Contribution of these sources was evaluated and the results turn out that the low-order magnitude of external force and dimension lead to high level FFT smoothing uncertainty and measurement uncertainty, respectively.