We all know that as the number of charge and discharge cycles increases, the capacity of lithium-ion batteries will decrease, which is directly reflected in the deteriorating performance of lithium-ion batteries. So what factors affect the performance of lithium-ion batteries?
There are many factors that affect the capacity of lithium-ion batteries, such as operating temperature, charging and discharging current, and charging and discharging cut-off voltage, which can all affect the degradation rate of lithium-ion batteries. The mechanisms that cause capacity degradation in lithium-ion batteries can be divided into three categories: internal resistance and polarization increase, loss of positive and negative active materials, and Li loss.
The impact of different external factors on these three is also different. For example, lithium-ion batteries made of LiFePO4 material have excellent cycling performance, but different usage conditions have a significant impact on the cycling life of lithium-ion batteries. Experimental results have shown that the two discharge regimes of 15C pulse discharge and 15C continuous discharge have completely different effects on the 26650 lithium-ion battery. The capacity degradation of 26650 lithium-ion battery with 15C pulse discharge is very fast. After 40 cycles of charging and discharging, 15C discharge cannot be carried out again, but 1C discharge can still be carried out. The capacity degradation of 15C continuous discharge batteries is slower, and after 60 cycles, 15C discharge can still be carried out. However, the degradation rate of 1C rate is faster than that of 15C pulse discharge.
Charging temperature: 0~45 ℃
-Discharge temperature: -40~+55 ℃
-Maximum discharge rate at 40 ℃: 1C
-40 ℃ 0.5 discharge capacity retention rate ≥ 70%
The conclusion drawn from the mechanism analysis is that the 15C pulse discharge battery exhibits more LiF in the SEI film of the negative electrode, and LiF has a greater hindrance to the diffusion of lithium ions, resulting in a rapid increase in the Li+diffusion impedance and charge exchange impedance of the battery. This leads to an excessive polarization voltage during the charging and discharging process, resulting in a rapid decrease in the high current discharge ability of LiFePO4.
The research on the charging strategy of lithium-ion batteries and the impact of their lifespan degradation can better guide our design of lithium-ion batteries. The following discusses the impact of different charging control strategies on the lifespan degradation of lithium-ion batteries, investigates their usage mechanisms, and proposes a lifespan degradation model for lithium-ion batteries. Research experiments have shown that when the charging current and cut-off voltage exceed certain values, the degradation of lithium-ion batteries will be greatly accelerated. In order to reduce the degradation rate of lithium-ion batteries, appropriate charging and discharging currents and cut-off voltages should be selected for different systems.
