With the increase of charge and discharge times, the capacity of lithium battery will be less and less. The direct performance is that the performance of lithium battery is getting worse and worse. So what factors affect the performance of lithium battery?

There are many factors that affect the capacity of lithium-ion batteries, such as operating temperature, charging and discharging current, charging and discharging cut-off voltage and so on. The mechanism of capacity degradation of lithium battery can be divided into three categories: the increase of internal resistance and polarization, the loss of positive and negative active substances, and the loss of Li.

Different external factors have different effects on the three. For example, LiFePO4 lithium battery has very good cycle performance, but different conditions of use have an important impact on the cycle life of lithium battery.

The results show that 15C pulse discharge and 15C continuous discharge have different effects on 26650 lithium battery. The capacity of 26650 lithium battery with 15C pulse discharge declines rapidly. After 40 times of charging and discharging, 15C discharge can not be carried out, but 1C discharge can still be carried out. However, the capacity degradation of 15C continuous discharge battery is slow, and 15C discharge can still be carried out after 60 times, but the degradation rate of 1C rate is faster than that of 15C pulse discharge.

The results of mechanism analysis show that there are more LIF in the SEI film of the negative electrode in the 15C pulse discharge battery, and the LIF has more hindrance to the diffusion of lithium ion, which makes the Li + diffusion impedance and charge exchange impedance of the battery increase rapidly, so that the polarization voltage of the battery is too large in the process of charging and discharging, which leads to the rapid decline of the large current discharge capacity of LiFePO4.

The research on the influence of lithium battery charging strategy on lithium battery life degradation can better guide our design of lithium-ion battery. In the following, the effect of different charging control strategies on the life degradation of lithium-ion batteries is studied, and the life degradation model of lithium-ion batteries is proposed.

From the above analysis, we can notice that there is a value for both the charging current and the charging cut-off voltage. When the charging current or voltage exceeds this value, it will cause the battery to decline and accelerate. For the above batteries, this value is 1c and 4.2V. When the charging current and the cut-off voltage exceed this value, it will accelerate the battery decline. When it is less than this value, it will increase the charging current and the cut-off voltage. The cut-off voltage does not significantly increase the decay rate of the battery.

The research on the mechanism of the influence of charging current and cut-off voltage on the decay rate of battery shows that when the charging current is lower than 1C, the main influence is the loss of positive and negative active substances, while when the cut-off voltage is lower than 4.2V, the main influence is the loss of Li. When the charging current and cut-off voltage are higher than this value, the loss of positive and negative active substances and the loss of Li will be significantly accelerated.