Exploration of Li-Ion Batteries during a Long-Term Heat Endurance Test Using 3D Temporal Microcomputed Tomography Investigation

High-resolution computed tomography (micro-CT) was used in this paper to visualize the inner structure of lithium nickel cobalt aluminum oxide 18 650 form-factor batteries non-destructively after and during a heat endurance test. Open circuit relaxation and electrochemical impedance spectroscopy were also conducted. We tested the different heat-aged cells with micro-CT and charge-discharge and electrochemical impedance spectroscopy measurements to find the observable physical changes in the cell and connect them to the loss of performance. We found that the drastic changes in the structure of the cell at higher temperatures are well traceable. At 150 degrees C layer delamination and performance loss were observed, battery failure occurred with the further increase of the temperature, while at the same time, precipitation appeared and the positive temperature coefficient device fractured. Without opening the cell only tomographic methods can provide insight into the inner structure of the cell. We were able to measure the changes in the distances of the layers of the battery and decent shrinkage was observed, which can be linked to the loss of capacity and increased resistance.