What are the effects of increasing the charge and discharge rate on the performance of lithium battery?

As we all know, as the increase of cycle life, the capacity of lithium battery will be less and less. The immediate effect is that lithium batteries are getting worse. So what are the factors that affect the performance of lithium-ion batteries?

As we all know, with the increase of cycle count, the capacity of lithium battery will be less and less, The immediate effect is that lithium batteries are getting worse. So what are the factors that affect the performance of lithium-ion batteries?

Many factors influence the effects of lithium battery capacity, the use of factors such as temperature, charge and discharge current, charge and discharge cut-off voltage will affect the failure of drop speed of Lithium ion batteries. Cause the mechanism of lithium battery capacity decline down can be divided into three categories: internal resistance and polarization increases, is the cathode active material loss, Li losses.

Different external factors on the influence of the three are different. Such as material of LiFePO4 lithium-ion battery has the very good performance, but the use of different conditions on the lithium battery cycle life has an important influence. Tests showed that the 26650 lithium batteries continuous discharge pulse discharge 15 c and 15 c, two kinds of discharge system for 26650 lithium batteries have completely different effects. 15 c pulse discharge of 26650 lithium battery capacity decline down very quickly, charge and discharge after 40 times can't again to 15 c discharge, but still be able to 1 c discharge. And 15 c continuous discharge battery capacity decline down slowly, 60 times 15 c discharge will still be able to do much, but 1 c rate of failure rate faster than 15 c pulse discharge.

Mechanism analysis concluded that 15 c pulse discharge of battery in cathode of SEI appear more LiF, and LiF of lithium ion diffusion barrier is bigger, makes the battery of Li + diffusion impedance and charge exchange impedance increase rapidly, so as to make the battery polarization in the process of charging and discharging voltage is too large, resulting in LiFePO4 large current discharge capacity drops rapidly.

Lithium battery charging strategy for lithium battery life failure drop impact study, will be better able to guide us to the design of lithium ion batteries. Under different charging control strategy on the influence of lithium ion battery life failure drop, studied the mechanism of the life of the lithium ion battery failure model reduction is put forward. Studies show that when the charging current and the voltage exceeds a certain value, the lithium ion battery failure drops have been greatly accelerated, in order to decrease failure drop rate of lithium ion battery, need according to different system, need to choose the right to charge and discharge current and the voltage.

From the data as you can see, as the charge ratio increased, the lithium ion battery failure rate is rapidly increasing, and from the point of the slope of the curve, the battery failure drop speed into three different stages, the early failure down faster phase (phase 1), the stability of the intermediate failure down slower phase (phase 2), and failure in the late fall rate accelerated phase (phase 3).For the researches on the mechanism of the three stages of the battery failure drop that phase 1 May be because the battery of SEI growth need to consume part of Li +, so failure is faster. In phase 2 as the stability of the SEI film structure, internal is relatively stable, so failure is slower, in phase 3 as the battery aging, began to produce active material loss, reducing electrode active interface, lead to the battery is very sensitive to the current. Figure C is for different cut-off voltage of the battery failure rate experiment, can see from the result of the experiment, when will lead to increase the charge cut-off voltage to 4.3 V battery cycle of a sharp deterioration in performance, reduce the charge cut-off voltage can effectively improve the cycle performance of battery.

For dynamic resistance of the battery as shown in the figure below, from the figure a test result, when the charging current is less than 1 c, battery dynamic impedance as the change of cell cycle trend is almost the same, but when the charging current more than 1 c, battery dynamic resistance increase rate will be increased with the increase of charging rate increase rapidly. From the point of the test results of figure b, when the charge cut-off voltage of 4.3 V battery dynamic resistance increase very quickly show dynamics condition worsens as high voltage battery, cut-off voltage of 4.1 V and 4.2 V battery dynamic resistance increases more slowly.

From the above analysis we can notice that both charging current and charging voltage has a value, as when the charging current or voltage more than this value will cause the battery failure drop speed, for the battery, this value is 1 c and 4.2 V, when the charging current and by voltage exceeds this value will accelerate cells after failure, when less than this value, increase the charging current and cut-off voltage does not significantly increase the battery failure drop speed. For charging current and the voltage of battery failure drop speed affect the mechanism of the research shows that when the charging current is lower than 1 c is the main influence is the cathode active material loss, and the influence of cut-off voltage below 4.2 V is mainly Li loss, when the charging current and cut-off voltage higher than this value, will be significantly accelerated and Li is the cathode active material loses.

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