Research on aging mechanism and capacity attenuation of automotive lithium-ion batteries

In order to investigate the internal mechanism and the variation law of capacity attenuation of LIBs, a simplified electrochemical model of the LIBs was established using the nickel-cobalt-aluminum LIBs as the research object, and the aging model of solid electrolyte interface SEI growth and lithium evolution was added to simulate the electrochemical behavior of the batteries. The results showed that the porosity of the anode/diaphragm reduced continually at the start of the cycle, while the SEI film grew continuously. The loss of active materials accelerated as the number of cycles increased, while the side reaction of lithium development continued. Finally, the aging mechanism was confirmed by using microscopic morphology. The results show that the negative particles are obviously crushed and contain white deposited substances. The formation of these compounds increases the oxygen content, reduces the carbon content, reduces the porosity of the electrode, increases the overpotential of the electrolyte transport, and becomes the main reason for the attenuation of the battery life. Finally, the positive particles expand and break, which leads to the sudden reduction of the battery capacity. This study determined the evolution process of aging mechanism in the whole life cycle, and provided a theoretical basis for the establishment of mechanism aging model.