What is lithium battery safety testing?

What is lithium battery safety testing?

1)Test purpose: To verify the electrical abuse performance of the single cell battery, simulate the potential safety risks that may occur when the battery is over-discharged, thereby evaluating whether the sample meets the design requirements.

2)Test equipment: Single cell battery charge-discharge equipment, constant temperature test chamber, multimeter, etc.

3)Test method and procedures:

① Pre-treat the single cell battery at room temperature and then fully charge it.

② Discharge at a constant current of 1/3I(energy type) or (power type) to the discharge cut-off voltage of the single cell battery, and then forcibly discharge at I current for 90 min.

4)Data processing and evaluation criteria: Observe whether the sample exhibits fire or explosion during the test and within the 1-hour observation period after the test.

1)Test purpose: To verify the electrical abuse performance of the single cell battery, simulate the potential safety risks that may occur when the battery is overcharged, thereby evaluating whether the sample meets the design requirements.

2)Test equipment: Single cell battery charge-discharge equipment, constant temperature test chamber, multimeter, etc.

3)Test method and procedures:

① Pre-treat the single cell battery at room temperature and then fully charge it.

② Continue constant current charging until the voltage of the single cell battery reaches 1.1 times its maximum working voltage, or the charged capacity of the single cell battery reaches 115% SOC.

4)Data processing and evaluation criteria: Observe whether the sample exhibits fire or explosion during the test and within the 1-hour observation period after the test.

1)Test purpose: To verify the electrical abuse performance of the single cell battery, simulate the potential safety risks that may occur when an external short circuit happens to the battery, thereby evaluating whether the sample meets the design requirements.

2)Test equipment: Single cell battery charge-discharge equipment, constant temperature test chamber, multimeter, etc.

3)Test method and procedures:

① Pre-treat the single cell battery at room temperature and then fully charge it.

② Short-circuit the positive and negative terminals of the single cell battery externally for 10 min, with the external circuit resistance less than 5 mΩ.

4)Data processing and evaluation criteria: Observe whether the sample exhibits fire or explosion during the test and within the 1-hour observation period after the test.

1)Test purpose: To verify the mechanical abuse performance of the single cell battery, simulate the potential safety risks that may occur when the battery is crushed, thereby evaluating whether the sample meets the design requirements.

2)Test equipment: Single cell battery charge-discharge equipment, constant temperature test chamber, power battery crush test bench, multimeter, etc.

3)Test method and procedures:

① Pre-treat the single cell battery at room temperature and then fully charge it.

② Crushing direction: Apply pressure perpendicular to the plate direction of the single cell battery, or in the direction most likely to be crushed in the vehicle layout.

a. Crush plate form: A semi-cylinder with a radius of 75 mm, and the length (L) of the semi-cylinder is greater than the size of the crushed single cell battery.

b. Crushing speed: Not greater than 2 mm/s.

c. Crushing degree: Stop crushing when the voltage reaches 0 V or the deformation reaches 15%, or the crushing force reaches 100 kN or 1000 times the weight of the test object.

③ Hold for 10 min.

4)Data processing and evaluation criteria: Observe whether the sample exhibits fire or explosion during the test and within the 1-hour observation period after the test.

1)Test purpose: To verify the thermal runaway performance of the smallest battery unit that can be monitored by the battery management system, conduct safety evaluation on the core hazard source that poses danger to electric vehicle occupants and vehicle systems, thereby evaluating whether the sample meets the design requirements.

2)Test equipment: Single cell battery charge-discharge|discharge equipment, constant temperature test chamber, heating device, temperature acquisition system, multimeter, etc.

3)Test method and procedures:

① Use a flat or rod-shaped heating device, and its surface shall be covered with ceramic, metal or insulating layer. The power selection requirements for the heating device are shown in Table 6-10. Complete the assembly of the test object and the heating device. The heating device shall be in direct contact with the single cell battery, and the size of the heating device shall not be larger than the heated surface of the test object. Install temperature monitors, with the temperature sensor at the monitoring point placed on the side away from heat conduction, i.e., on the opposite side of the heating device. The sampling interval of temperature data shall be less than 1 s, with an accuracy requirement of 2 ℃, and the position of the temperature sensor tip shall be less than 1 mm.

Table 6-10 Heating device selection requirements

Test object energy E/Wh	Maximum power of heating device/W
E<100	30～300
100≤E<400	300～1000
400≤E<800	300～2000
E≥800	>600

② Pre-treat the single cell battery at room temperature and then charge it to 100% SOC. Then continue charging the test object with 1/1 current for 12 min. Immediately start the heating device and continuously heat the test object at its maximum power. When thermal runaway occurs or the temperature at the monitoring point reaches 300 ℃, stop heating and turn off the heating device.

③ Conditions for determining whether thermal runaway occurs

a. The test object experiences a voltage drop, and the drop exceeds 25% of the initial voltage.

b. The temperature at the monitoring point reaches the maximum operating temperature specified by the battery manufacturer.

c. The temperature rise rate at the monitoring point dT/dt ≥ 1 ℃/s and lasts for more than 3 s. Thermal runaway is determined to have occurred when a and c or b and c occur.

4) Data processing and evaluation criteria: Observe whether the sample exhibits fire or explosion during the heating process and within 1 h after the heating is completed.

1)Test purpose: To simulate the impact on the battery pack/system during a vehicle collision, thereby evaluating whether the structural strength of the sample can meet the design requirements.

2)Test equipment: Battery system charge-discharge equipment, constant temperature test chamber, simulated crash test bench, insulation resistance tester, etc.

3)Test method and procedures: Referring to the installation position of the test object in the vehicle and the requirements of GB/T 2423.43-2008, the test object shall be horizontally mounted on a sled with a fixture. According to the usage environment of the test object and in combination with the vehicle's acceleration/deceleration pulse, this pulse shall meet the boundary conditions specified in Table 6-11 and Figure 6-1 (the vehicle traveling direction is the x-axis, and the other horizontal direction perpendicular to the traveling direction is the y-axis, with the vehicle curb weight being m). When the test object has multiple installation directions (x/y/z), the installation direction with the greater acceleration shall be selected for the test. After the test, observe for 2 hours at the test ambient temperature.

Figure 6-1 Schematic of Simulated Crash Test Acceleration Pulse

Table 6-11 Pulse parameters for simulated crash test

Test	Pulse width /ms	m≤3.5 t		3.5 t < m ≤7.5 t		m > 7.5 t
		x-direction acceleration/g	y-direction acceleration/g	x-direction acceleration/g	y-direction acceleration/g	x-direction acceleration/g	y-direction acceleration/g
A	20	20	8	10	5	6.6	5
B	50	20	8	10	5	6.6	5
C	65	20	8	10	5	6.6	5
D	100	0	0	0	0	0	0
E	0	10	4.5	5	2.5	4	2.5
F	50	28	15	17	10	12	10
G	80	28	15	17	10	12	10
H	120	0	0	0	0	0	0

4)Data processing and evaluation criteria:

① Record whether the battery pack/system exhibits leakage, rupture, fire, or explosion during the test and the observation period;

② Record the insulation resistance values before and after the test.

1)Test purpose: To simulate the potential safety risks that may occur when the battery pack/system is crushed, thereby evaluating whether the structural strength of the sample meets the design requirements.

2)Test equipment: Battery system charge-discharge equipment, constant temperature test chamber, battery system crush test bench, insulation resistance tester, etc.

3)Test method and procedures: The crushing directions are the x-direction and y-direction (vehicle traveling direction is the x-axis, and the other horizontal direction perpendicular to the traveling direction is the y-axis). The crushing speed shall not exceed 2 mm/s. Stop crushing and hold for 10 min when the crushing force reaches 100 kN or the deformation reaches 30% of the overall dimension in the crushing direction. After the test, observe for 1 h at the test ambient temperature. The schematic diagram of the crush plate form is shown in Figure 6-2. One of the following two types may be selected:

① A semi-cylinder with a radius of 75 mm, and the length (L) of the semi-cylinder is greater than the height of the test object but not exceeding 1 m, as shown in Figure 6-2a.

② Overall dimensions of 600 mm × 600 mm or smaller, with three semi-cylinders each having a radius of 75 mm and spaced 30 mm apart, as shown in Figure 6-2b.

Figure 6-2 Schematic Diagram of Extruded Plate Forms

1)Test purpose: To test the potential safety risks of the battery pack/system under water ingress conditions and evaluate whether it meets the design requirements.

2)Test equipment: Battery system charge-discharge equipment, constant temperature test chamber, seawater immersion test chamber, insulation resistance tester, etc.

3)Test method and procedures: The test object shall be connected with wiring harnesses, connectors and other components according to the vehicle connection method. Select one of the following two methods for testing:

① Place the test object in a 3.5% (mass fraction) sodium chloride solution for 2 h in the actual vehicle assembly orientation, with water depth sufficient to completely submerge the test object;

② Conduct the test according to the method and procedure described in 14.2.7 of GB/T 4208-2017. The test object shall be fully immersed in water in the installation state specified by the manufacturer. For test objects with height less than 850 mm, the lowest point shall be 1000 mm below the water surface; for test objects with height equal to or greater than 850 mm, the highest point shall be 150 mm below the water surface. The test duration is 30 min. The temperature difference between water and the test object shall not exceed 5 ℃. After removing the battery pack from water, keep it stationary and observe for 2 h at the test ambient temperature.

4)Data processing and evaluation criteria: For tests conducted according to method ①, record whether the battery pack/system exhibits fire, explosion or other phenomena during the test and the subsequent observation period. For tests conducted according to method ②, record the insulation resistance value of the battery pack/system after the test, whether it meets the IPX7 requirement, and whether there is leakage, shell rupture, fire or explosion.

1)Test purpose: To test the potential safety risks of the battery pack/system when exposed to external fire and evaluate whether it meets the design requirements.

2)Test equipment: Battery system charge-discharge equipment, constant temperature test chamber, external fire exposure test bench, insulation resistance tester, anemometer, etc.

3)Test method and procedures: The ambient temperature shall be above 0 ℃ and wind speed shall not exceed 2.5 km/h. During the test, the size of the gasoline tray shall exceed the horizontal projection dimension of the test object by 20 cm but not more than 50 cm, and the tray height shall not exceed 8 cm above the gasoline surface. The test object shall be placed centrally. The distance between the gasoline liquid level and the bottom of the test object shall be set to 50 cm or the ground clearance of the test object bottom surface when the vehicle is unloaded. Water shall be injected into the bottom layer of the tray. The schematic diagram of external fire exposure is shown in Figure 6-3.

Figure 6-3 External Fire Test Schematic

External fire exposure test is divided into the following 4 stages:

① Preheating: Ignite the gasoline at a location at least 3 m away from the test object. After 60 s of preheating, place the gasoline tray beneath the test object. If the gasoline tray is too large to be moved, the test object and its support may be moved instead.

② Direct flame exposure: The test object is directly exposed to the flame for 70 s.

③ Indirect flame exposure: Cover the gasoline tray with a fire-resistant shield. The test object is tested in this state for 60 s. Alternatively, upon agreement between both parties, continue direct exposure to the flame for another 60 s. The fire-resistant shield is assembled from standard refractory bricks, and its dimensions and technical data are shown in Figure 6-4.

$Figure 6-4 Dimensions and Technical Data of Refractory Partition Plate$

④ Removal from fire source: Move the gasoline tray or the test object away, and observe for 2 h at the test ambient temperature or until the external surface temperature of the test object drops below 45 ℃.

4) Data processing and evaluation criteria:

① Record whether the battery pack/system exhibits fire, explosion or other phenomena during the test and the observation period.

② If there is a flame, record whether it extinguishes within 2 min after the fire source is removed.

1)Test purpose: To test the safety risks of the battery pack/system when a single battery cell undergoes thermal runaway and evaluate whether it meets the design requirements.

2)Test equipment: Battery system charge-discharge equipment, constant temperature test chamber, battery system penetration test bench, heating device, temperature acquisition system, insulation resistance tester, anemometer, etc.

3)Test conditions: The test shall be conducted in an environment with ambient temperature above 0 ℃, relative humidity of 10 %–90 %, and atmospheric pressure of 86–106 kPa. Before the test starts, adjust the SOC of the test object. For battery packs/systems designed for external charging, the SOC shall be adjusted to not less than 95 % of the normal SOC operating range specified by the enterprise. For battery packs/systems designed to be charged only by the vehicle's own energy device, the SOC shall be adjusted to not less than 90 % of the normal SOC operating range specified by the enterprise. Before the test starts, all test devices shall operate normally. The test sample shall be modified as little as possible, and the enterprise shall submit a list of any modifications made. The test shall be conducted indoors or in an environment with wind speed not greater than 2.5 km/h.

4)Test method and procedures: The thermal runaway trigger object is a single battery cell within the test object. Select a single cell located at the very center of the battery pack/system or surrounded by other single cells.

① Nail penetration method to trigger thermal runaway: The penetration needle shall be made of steel with a diameter of 3–8 mm; the needle tip shall be conical with an angle of 20°–60°; the penetration speed shall be 0.1–10 mm/s; the penetration position and direction shall be chosen to trigger thermal runaway in the single battery cell (for example, perpendicular to the electrode plate direction).

② Heating method to trigger thermal runaway: Use a flat or rod-shaped heating device with its surface covered by ceramic, metal or insulating layer. For a block-shaped heating device with the same dimensions as the single cell battery, this heating device may replace one of the single cells and be in direct contact with the surface of the trigger object; for a thin-film heating device, it shall remain attached to the surface of the trigger object at all times; the heated area of the heating device shall not be larger than the surface area of the single cell battery; the heating surface of the heating device shall be in direct contact with the surface of the single cell battery, and the position of the heating device shall correspond to the position of the specified temperature sensor; after installation is completed, the heating device shall be activated within 24 h and heat the trigger object at its maximum power; the power selection of the heating device is shown in Table 6-12; stop triggering when thermal runaway occurs or the corresponding temperature sensor reaches 300 ℃.

Table 6-12 Heating device power selection

Test object energy E/Wh	Maximum power of heating device/W
E<100	30～300
100≤E<400	300～1000
400≤E<800	300～2000
E≥800	>600

③ Recommended monitoring point arrangement scheme: Voltage or temperature shall be monitored using the original circuit or an additional test circuit. The sampling interval of temperature data shall be less than 1 s, with an accuracy requirement of ±2 ℃. During nail penetration triggering, the temperature sensor shall be positioned as close as possible to the short-circuit point; the temperature of the nail may also be used (schematic diagram of temperature sensor arrangement positions during nail penetration triggering is shown in Figure 6-5). During heating triggering, the temperature sensor shall be placed on the side away from heat conduction, i.e., on the opposite side of the heating device (see Figure 6-6).

Figure 6-5 Schematic of Temperature Sensor Placement During Acupuncture Triggering

5)Recommended criteria for determining thermal runaway occurrence:

① The test object experiences a voltage drop exceeding 25 % of the initial voltage.

② The temperature at the monitoring point reaches the maximum operating temperature specified by the battery manufacturer.

③ The temperature rise rate at the monitoring point dT/dt ≥ 1 ℃/s and lasts for more than 3 s. Thermal runaway is determined to have occurred when ① and ③ or ② and ③ occur.

1)If the recommended method is used as the thermal runaway triggering method and no thermal runaway occurs, to ensure that thermal propagation will not endanger vehicle occupants, it must be proven that thermal runaway will not occur using both of the following recommended methods.

2)If thermal runaway occurs, record the time from when the thermal runaway alarm signal is issued until fire or explosion occurs outside the test object (whichever occurs first); this time shall be not less than 5 min.

Figure 6-6 Schematic Diagram of Heating Trigger Temperature Sensor Placement