What are the effects of increasing the charge-discharge ratio on the performance of lithium batteries?
COUNTS：113282019-09-17 10:13:08
As we all know, lithium batteries will have less and less capacity as the number of charges and discharges increases. The direct manifestation is that the performance of lithium batteries is getting worse and worse. So what factors affect the performance of lithium batteries?
There are many factors affecting the capacity of lithium-ion batteries, such as service temperature, charge-discharge current, charge-discharge cut-off voltage and so on, which will affect the decline rate of lithium-ion batteries. The mechanism of capacity degradation of lithium batteries can be divided into three categories: increasing internal resistance and polarization, loss of positive and negative active materials, and loss of Li.
Different external factors have different effects on these three factors. For example, LiFePO4 lithium batteries have very good cycle performance, but different operating conditions have an important impact on the cycle life of lithium batteries.
Experiments show that 15C pulse discharge and 15C continuous discharge have different effects on 26650 lithium batteries. The capacity of 26650 lithium battery discharged by 15C pulse decreases very fast. After 40 times of charging and discharging, 15C discharge can not be carried out, but 1C discharge can still be carried out. The capacity decline of 15C continuous discharge battery is slow, and 15C discharge can still be carried out after 60 cycles, but the decay rate of 1C rate is faster than that of 15C pulse discharge.
The mechanism analysis concluded that more LiF appeared in the SEI film of the negative electrode of 15C pulsed discharge battery, and LiF hindered the diffusion of lithium ion even more, which made the Li+ diffusion impedance and charge exchange impedance of battery increase rapidly, so that the polarization voltage of battery during charging and discharging process was too high, which led to the discharge energy of LiFePO4 with high current. The force dropped rapidly.
The research on the influence of lithium battery charging strategy on lithium battery life decline can better guide our design of lithium ion batteries. The effect of different charging control strategies on the lifetime degradation of lithium-ion batteries is studied, and the lifetime degradation model of lithium-ion batteries is proposed.
From the above analysis, we can notice that there is a value both in charge current and cut-off voltage. When the charge current or voltage exceeds this value, it will lead to the acceleration of battery degradation. For the above-mentioned batteries, the value is 1C and 4.2V. When the charge current and cut-off voltage exceed this value, the battery degradation will be accelerated. Drop; When it is less than this value, increasing charging current and cut-off voltage will not significantly increase the decline rate of the battery.
The mechanism of the effect of charging current and cut-off voltage on the decay rate of batteries shows that when charging current is less than 1C, the main effect is the loss of positive and negative active substances, while when cut-off voltage is less than 4.2V, the main effect is Li loss. When charging current and cut-off voltage are higher than this value, the positive and negative activation will be significantly accelerated. Sexual material loss and Li loss.
