Morphology, Structure, and Thermal Stability Analysis of Aged Lithium-Ion Battery Materials

The morphology, structure and thermal stability of anode, cathode and separator of lithium-ion batters at different states of health (SOHs: 100%, 91.02%, 83.90% and 71.90%) under 100% state of charge were studied. The morphology analysis showed that the anode material was getting powdery with aging, and the inhomogeneity of lithium in anode increased. The change of cathode was not obvious, while the number and diameter of separator pores decreased, resulting in the increase of impedance. The analysis of structural and thermal stability showed that the grain size of cathode material decreased with aging, while the thermal decomposition temperature did not change significantly. The anode had the greatest impact on the battery safety based on the DSC test. The initial decomposition temperature of solid electrolyte interphase (SEI) decreased from 65.5 °C (100% SOH) to 61.5 °C (71.90% SOH), and the corresponding heat release increased by 59.7%, indicating that the initial self-heating reaction was more serious. The heat released by graphite collapse significantly reduced with aging, which was beneficial to reduce the high temperature hazard after thermal runaway. The research results can provide guidance for the reuse of retired batteries.