Battery aging is very complex, non-linear and change over time by many parameters, so it is difficult to predict their lifetime. The nature of battery aging happning due to chemical reactions of various components inside the battery. Every time a battery is used, some degree of aging occurs. it's called Cyclic aging Also gradual degradation of batteries over time, even if they are not used e.i self-degradation. That is Calendric aging.  Another is reversible aging like the anode overhang effect describes aging mechanisms that can increase battery lifetime. Each aging mechanism has an impact on the behavior of the battery. The impact can be broken down into two performance parameters: capacity and internal resistance.

There are two main factors influencing the performance of lithium battery pack, namely aging temperature and aging time.

Effect of aging

First effect is due to make the electrolyte soakage better, which is conducive to the stability of lithium battery pack performance;

Second effect is the active substances in the anode and cathode materials can accelerate some side effects, such as gas production, electrolyte decomposition, etc., which can quickly stabilize the electrochemical performance of lithium battery pack;

The third is to select the consistency of lithium battery pack after aging for a period of time. The measured value will deviate from the actual value due to the unstable voltage of the cell after formation, and the voltage and internal resistance of the cell after aging are more stable, which is convenient to select the battery with high consistency.

Temperature has a great influence on the cycle aging rate of lithium batteries. At lower temperature, the cycle life is reduced due to the enhanced lithium plating; High temperature can shorten the battery life due to the aging reaction. 

The main cause of aging in lithium-ion batteries is the growth of the Surface Electrolyte Interphase (SEI). The SEI layer forms on the negative electrode during the first charging cycle. 

Accelerated aging allows for the rapid assessment of battery lifetime characteristics and the development of reliable lifetime prediction models. During service life, ageing is reflected by an alteration of the SoH. Once a predefined threshold for usable capacity and resistance is exceeded, a cell has reached its end of life (EoL).