What factors will affect the life of lithium battery?

The service life of lithium battery is an index that must be paid attention to in the use of lithium ion battery. In general, the service life of lithium ion batteries is mainly affected by two factors:

1) Service time;
2) Number of cycles.

According to the decay rate of lithium ion battery, the decay rate of battery can be divided into early linear decay rate and late nonlinear decay rate. The typical feature of the nonlinear decline process is that the capacity of the battery decreases significantly in a short time, which is commonly referred to as capacity diving, which is very unfavorable to the use of the battery and the use of the steps.

In the experiment, Simon F. Schuster used IHR20250A battery from E-One Moli Energy. The cathode material is NMC material, the anode material is graphite, and the nominal capacity is 1.95Ah. The effects of voltage window, charge rate, discharge rate and temperature on the nonlinear attenuation of the battery were analyzed. The specific experimental arrangement is shown in the following table.

The main results are as follows:

1. The influence of the operating voltage window on the growth of negative SEI films is that because of the wide electrochemical window, the dissolution of positive transition metal elements is enhanced, and the dissolved transition metal elements migrate to the negative electrode surface, which accelerates the growth of negative electrode transition metal films. The results show that the kinetic conditions of the negative electrode accelerate the decay of lithium, so the precipitation of lithium in the negative electrode in advance leads to the earlier nonlinear decay.
2. Influence of charge discharge ratio

Because the nonlinear attenuation of lithium ion battery is mainly caused by the precipitation of lithium metal on the negative electrode surface, the charge discharge current is closely related to the occurrence of the nonlinear attenuation of lithium ion battery. The most influential factor is the battery charging current. The battery charged at the rate of 1C shows a nonlinear attenuation trend almost from the beginning, but if we reduce the charging current to 0.5C, Then the time node of the battery is nonlinear decay, which will be greatly delayed. The influence of discharge current on the nonlinear attenuation of battery can be almost ignored. This is mainly because the polarization of the negative electrode increases significantly with the increase of the charging current, which leads to a significant increase in the risk of lithium release from the negative electrode. The precipitated porous metal metal promotes the decomposition of electrolyte and accelerates. The degradation of the dynamic performance of the negative electrode leads to the early occurrence of nonlinear decay.

3. Effect of temperature

The temperature has a very important influence on the dynamic characteristics of the negative electrode, so the temperature also has an important influence on the occurrence time of the nonlinear attenuation of the batter
The battery at 35 ° C cycle has a non-linear decline at the latest. If we reduce the voltage window of the battery to 3.17-4.11v, the decay rate of the battery at 35 ° C and 50 ° C in the early period is relatively consistent, but at the end of its life, the battery at 35 ° C begins to show a nonlinear decline. This is mainly due to the deterioration of the kinetic conditions of the battery at low temperatures, which makes the cathode easier to be analyzed as lithium, thus accelerating the growth of the sei film, leading to further deterioration of the kinetic conditions of the cathode, leading to the nonlinear decline of early lithium ion batteries.