The aging of lithium-ion batteries during actual use includes two types: calendar aging and cycle aging.
Calendar aging refers to the phenomenon where a battery’s capacity slowly decreases with increasing storage time during storage.
During battery storage, the dominant aging factor is LLI (loss of usable lithium ions) caused by the slow thickening of the SEI film on the negative electrode. This is mainly affected by factors such as the battery’s state of charge (SOC) and ambient temperature. Generally, the higher the SOC and the higher the storage temperature, the faster the calendar aging of the battery. Research from the Technical University of Munich further shows that the calendar aging rate of lithium-ion batteries is not directly proportional to the SOC. When the SOC is between 30% and 60%, the calendar aging rate is basically equal, while after 60% SOC, the calendar aging rate increases rapidly with increasing SOC. This is because the essential factor affecting the side reaction of SEI film thickening is the negative electrode equilibrium potential. The lower the negative electrode equilibrium potential, the faster the SEI film grows. Batteries should be kept away from high SOC range and high ambient temperature as much as possible to delay their calendar aging.
Cyclic aging refers to the irreversible capacity loss that occurs in lithium-ion batteries during charge-discharge cycles, primarily influenced by factors such as discharge current, charge/discharge cutoff voltage, operating state of charge (SOC) range, ambient temperature, and depth of discharge (DOD).
Understanding the aging characteristics of batteries under various cycling conditions is crucial for optimizing battery use and extending their lifespan. Researchers at the Free University of Brussels, Belgium, evaluated the capacity degradation characteristics of lithium iron phosphate batteries under various charging methods. Their results showed that periodically applying small-amplitude discharge pulses during battery charging helps reduce concentration polarization and thus extend battery life. However, this study lacks effective support regarding the aging mechanism of batteries under various charging methods.
