Development And Application Of Multifactorial Aging Model For Lithium-ion Battery

In the new era of rapid development of electric vehicle industry, the aging of lithium-ion battery is a thorny problem. As a result of aging, frequent scheduled maintenance and replace for batteries make the cost of electric vehicle keeping high. Research on the aging behavior of battery can help to guide the application of battery, and to prolong its life. Furtherly, developing an aging model, which can predict the aging state of battery, can lower maintenance costs. In addition, the aging model is also significant in planning stagger utilization of batteries and avoiding energy waste. Therefore, this subject aims at studying the aging evolution process of lithium-ion battery during normal use and developing a multifactorial aging model with the indicator of capacity.In order to study the aging evolution process, a relationship between inner degradation process and outside characteristics is established through operating stoichiometry window. Based on existing research, five different main aging mechanisms, which may decide capacity loss, are discussed in details, and their influence on outside characteristics are analyzed in operating stoichiometry window. The five main aging mechanisms are loss of lithium inventory, loss of lithiated active material in positive electrode, loss of delithiated active material in positive electrode, loss of lithiated active material in negative electrode and loss of delithiated active material in negative electrode.Based on the aforementioned work, all possible combinations of main aging mechanisms are obtained, so are the changes of outside characteristics under each combination. Finally, a diagnostic method of main aging mechanisms for Li Fe PO4 battery is formed in theory. Considering the application of this method in practical, some suggestions on how to obtain experimental data for diagnosis are proposed. Then the aging evolution process of lithium-ion battery is carried out with data obtained from designed experiments.Supported by the aging evolution process, two mathematical models respectively for two related main aging mechanisms are developed, and then a multifactorial aging model is formed for the whole life of battery. The holistic model are parameterized with aging data under constant stress experiment, and the reliability of this model is validated with aging data of dynamic stress test. It turns out that this model can be used to estimate the amount of capacity loss under dynamic operating condition. With the advantages of acceptable accuracy and simplicity during practical application, this model has the potential to estimate the amount of capacity loss on board.