The charge-discharge cycle performance of lithium batteries at room temperature has been analyzed

Charge-discharge cycle performance of lithium-ion batteries at room temperature

At room temperature, after a lithium-ion battery has been charged and discharged according to time, how does it perform during and after this process? This is the improvement direction of lithium-ion battery related technologies, which requires the application of some test parameter interpretation, because the popularity of new energy vehicles in China is accelerating, the selection of large-capacity lithium-ion battery test data collection, help to understand the performance and characteristics of power lithium-ion batteries.

Through the test of Lithium Batteries, the following general conclusions can be drawn: according to the constant current and constant voltage charging stages, the ratio of constant current charging capacity to charging capacity decreases with the increase of the number of cycles; the discharge capacity of 3.7V~4.2V discharge platform accounts for more than 90% of the total discharge capacity, and the charging and discharging efficiency is not affected by the number of cycles. Here is a detailed description.

Before describing the data, it is necessary to explain the test environment: BYD 80Ah lithium cobalt oxide battery is selected for the charge and discharge test at room temperature (10℃~250℃).

Charge and discharge system design: The charge is constant current and constant voltage. First, charge to 4.2V at 1C or 80A constant current. 2.10 minutes later, use 80A constant current to 2.75V; 3. After 10 minutes of continuous discharging, perform a new round of charge and discharge cycle, repeat 500 times.

During this process, the relevant data should be collected to form the appropriate graph: constant current/constant voltage charge characteristic curve; 2.2. The relationship between the ratio of constant current charge capacity to total charge capacity and the number of cycles; 3. the discharge curve; 4. the charge and discharge efficiency curve.

As can be seen in the figure above:

1. Starting from the constant current charging stage, the charging platform of lithium-ion batteries is 3.8V~4.1V, and the charging capacity of this stage accounts for more than 80% of the total charging capacity. As the number of cycles increases, the voltage rise speed is accelerated, the charging time is shortened and the charging amount is gradually reduced.

2. As the number of cycles increases, the percentage of constant current charge capacity in the total charge capacity decreases, and the percentage of constant voltage charge capacity in the total charge capacity increases. This shows that as the number of charge and discharge cycles of Li-ion batteries increases, the lower the current, the better the charging effect.

3. According to the discharge curve, the discharge platform (the discharge curve is stable in a certain voltage range, close to a straight line, rather than the distance between the previous rising and falling slope line) with the increase of the number of cycles, and 4.2V~3.7 published discharge platform accounts for 90% of the total electricity.

4. Charge and discharge efficiency: that is, the percentage of released electricity to charge electricity. Indicates the discharge capacity of the battery, from the charge-discharge efficiency curve, the value remains basically unchanged, reaching more than 99%.

We understand that the capacity of LiFePO4 Battery decreases as the number of charge and discharge cycles increases, which can be seen from the above data. The specific performance is that the discharge platform is reduced, the lithium-ion battery charging time is reduced and the constant current charging ratio is reduced. The final performance is that the charge capacity decreases with the number of new cycles, and the rate of decrease becomes faster and faster. After 500 cycles, the capacity must be at least 80% to qualify.