A mechanistic calendar aging model of lithium‐ion battery considering solid electrolyte interface growth

Calendar life accounts for most of the lifetime of the power lithium-ion battery applied in electric vehicles, and thus should be investigated in detail. In this paper, a mechanistic calendar aging model of lithium-ion battery is developed by adding the solid electrolyte interface (SEI) growth side reaction to the pseudo-two-dimensional electrochemical model. The model can accurately simulate the capacity degradation and evolution of the charging voltage profiles of a Lix(NiCoMn)1/3O2 - graphite battery during high-temperature (55°C) storage under various states of charge. The model is further validated by comparing the electrode degradations inside the batteries after calendar aging. The model predicted electrode degradations are consistent with the results identified using a dual-tank model and post-mortem analysis, confirming that SEI growth is the dominant degradation mechanism. Based on the validated model, internal changes in electrodes' structure induced by SEI growth during calendaring aging are discussed. The anodes of the calendar-aged batteries suffer from severe pore clogging and film resistance increase, resulting in apparent power performance degradation of lithium-ion battery. Finally, modeling analysis is conducted to find possible solutions to mitigate the battery calendar aging process. Rational designs of SEI by reducing the porosity and solvent diffusivity inside the SEI and the kinetic rate constant turn out to be effective in improving the calendar lifetime of lithium-ion batteries. Novelty Statement Calendar life accounts for most of the lifetime of the lithium-ion battery in electric vehicles. This study establishes a mechanistic calendar aging model of lithium-ion battery considering solid electrolyte interface growth. The model can not only simulate the battery capacity degradation and the evolution of battery charging voltage profiles but also capture the internal degradation of the electrodes during the aging process. Modeling analysis is further conducted to find possible solutions to mitigate the calendar aging process of lithium-ion battery.