Battery life includes cycle life and calendar life. Generally speaking, battery life is a performance indicator based on cycle life.
The battery cycle life test is performed by a battery cycle life tester, and the cycle life is evaluated by simulating the actual working conditions of the battery to obtain various performance indicators after a certain number of cycles.
The performance indicators of battery cycle life mainly include internal resistance, capacity and peak power, etc., to quantify the relationship between battery performance and cycle times. There are many factors that affect the battery cycle life, such as operating temperature, current rate of charge and discharge, and SOC range, etc.
1) Battery Internal Resistance Test
The internal resistance test of the battery is mainly based on the HPPC method. The DC internal resistance of the battery is measured by loading a pulse current with a specific duration on the battery and obtaining a voltage excitation.
2) Battery Capacity Test
The battery capacity test is to charge the battery to 100% SOC at 0.33C, and then discharge it to the discharge termination voltage at 0.33C, and calculate the amount of power released by the battery during the discharge process.
3) Battery Peak Power Test
The battery peak power test is mainly based on the USABC method, that is, the battery is loaded with a pulse current of a specific duration.
Battery Internal Resistance Calculation Formula
R=(Vt1-Vt0)/(It1-It0)
Vt0 and It0 are the voltage and resistance values at time t0; Vt1 and It1 are the voltage and resistance values at time t1.
Battery Power Calculation Formula
P1=-(2*VIRFree2)/9R
P2=-Vmin*(VIRFree-Vmin)/R
P3=Imax*(VIRFree+Imax*R)
VIRFree=V-IR
Typically, standard cycle life tests are employed to verify the deep cycle life of a battery. The table below is for reference.
|
NO. |
Test steps |
Remarks |
|
01 |
Step 1: Discharge the battery cells at a rate of XC to the cut-off voltage specified by the battery cell manufacturer. |
X can be adjusted according to battery performance, such as 1C or 0.5C, etc. The specific ambient temperature can be achieved by the battery high and low temperature test chamber. |
|
02 |
Step 2: Let stand for 30min. |
Specific ambient temperature. |
|
03 |
Step 3: Charge the cells with a constant current of XC to the cut-off voltage, and then charge it with a constant voltage until the current drops to a rate of 0.05C. |
X can be adjusted according to battery performance, such as 1C or 0.5C, etc. Specific ambient temperature. |
|
04 |
Step 4: Let stand for 2 hours. |
25℃ |
|
05 |
Step 5: At a specific temperature, the battery cells are discharged at a rate of 1C to the cut-off voltage specified by the battery cell manufacturer, and the discharge capacity is recorded. |
25℃ |
|
06 |
Step 6: Repeat steps 2 to 5 several times, the discharge capacity and discharge energy were recorded. |
- |
|
07 |
Step 7: Change the ambient temperature and repeat the above battery deep cycle life test. |
- |
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