A method for testing the fire hazard of lithium-ion batteries

Abstract

The present invention relates to a lithium ion battery fire hazard classification test method, the maximum heat release rate Q max , thermal runaway temperature T0 is set as two parameters in the two-dimensional coordinates, the two-dimensional coordinates are divided into a risk matrix consisting of N*N small rectangular blocks, and the fire hazard is divided into N risk levels; the two-dimensional coordinates are divided into N risk levels by Q max The highest point, T0 the lowest point to Q max lowest 、 N stepped areas are formed in the highest direction of T0, and each stepped area corresponds to a corresponding risk level of fire hazard. The heating program of the lithium-ion battery is: heating at a set rate for a set time t1, and maintaining a constant temperature for t2 to form a temperature rise step as a program unit, and progressing through several program units until the lithium-ion battery suffers thermal runaway.

Description

Technical Field

[0001] The invention relates to a method for testing the fire hazard of a lithium-ion battery, belonging to the technical field of lithium battery fire hazard testing and evaluation. Background Art

[0002] The grading and evaluation of lithium-ion battery fire hazards can provide a scientific basis for fire prevention and control in power battery systems, electric vehicles, and energy storage systems. However, there is currently no experimental method at home or abroad that uses a single experiment to detect the fire hazard of lithium-ion batteries. The existing methods that use multiple experiments to assess battery fire hazards have poor consistency and cannot eliminate the errors caused by differences in battery samples. Summary of the Invention

[0003] The purpose of the present invention is to provide a lithium-ion battery fire hazard classification test method, which comprehensively evaluates the fire hazard of lithium-ion batteries from two aspects: thermal runaway probability (maximum heat release rate) and fire power (thermal runaway temperature).

[0004] The present invention adopts the following technical solutions:

[0005] A test method for the classification of fire hazards of lithium-ion batteries, maximum heat release rate Q max , thermal runaway temperature T0 is set as two parameters in the two-dimensional coordinates, the two-dimensional coordinates are divided into a risk matrix consisting of N*N small rectangular blocks, and the fire hazard is divided into N risk levels; the two-dimensional coordinates are divided into N risk levels by Q max The highest point, T0 the lowest point to Q max lowest 、 N stepped regions are formed in the highest direction of T0, and each stepped region corresponds to a corresponding risk level of fire hazard. The heating program of the lithium-ion battery is as follows: heating at a set rate for a set time t1, and maintaining a constant temperature for t2 to form a temperature rise step as a program unit, and progressing through several program units until the lithium-ion battery experiences thermal runaway. The determination and adjustment of the occurrence of thermal runaway of the lithium-ion battery is as follows: the following conditions A) and B) are simultaneously met:

[0006] A) The battery voltage drops below the set percentage of the initial voltage;

[0007] B) Battery heating surface temperature rise rate - the battery heating rate is greater than or equal to the first set value, and the total heating time exceeds the second set value;

[0008] The method for determining the thermal runaway temperature T0 is as follows: if the battery experiences thermal runaway during the constant temperature process, the thermal runaway temperature is the constant temperature minus a set number of degrees Celsius; if the battery experiences thermal runaway during the heating stage, the heating surface temperature at the time of thermal runaway is the thermal runaway temperature.

[0009] Preferably, the method comprises the following steps:

[0010] S1. Charge and discharge the lithium-ion battery for 2 cycles at a constant current of not less than 0.3C and charge it to 100% state of charge;

[0011] S2. Arrange thermocouples and heating plates on the battery surface, fix them with clamps, and place them on the lifting platform 3;

[0012] S3. Conduct temperature-programmed thermal runaway triggering and cone calorimetry combustion joint measurement experiments;

[0013] S4. Obtaining the fire hazard level of the lithium-ion battery according to the risk matrix.

[0014] Preferably, two thermocouples T1 and T2 are arranged at the center of the lithium-ion battery heating surface, a thermocouple T3 is arranged at the center of the back, and a thermocouple T4 is arranged at the pressure relief valve. A thermal conductive graphite plate of equal size is arranged between the battery and the heating plate, and an insulating cotton layer is arranged between the back of the battery and the clamping plate. The battery is placed on a lifting platform 3. Before the test begins, the height of the lifting platform 3 is adjusted so that the lithium-ion battery jet fire can be completely covered by the cone calorimeter smoke hood 1. A programmed temperature increase based on the real-time temperature T1 feedback of the lithium-ion battery heating surface is used to trigger thermal runaway. The temperature controller detects the feedback temperature in real time to ensure that the battery heating surface temperature T1 rises according to the set heating program until thermal runaway occurs.

[0015] Preferably, the heating procedure of the lithium-ion battery is: the battery is heated to 120°C at a set rate of 5±1°C at room temperature of 25±5°C, and then heated to 130°C at a set rate of 5±1°C, during which the constant temperature is maintained for 10 minutes, and this cycle is repeated until the battery suffers thermal runaway, with a temperature rise step of 10°C.

[0016] Preferably, in the method for determining the thermal runaway temperature T0, the set several degrees Celsius is 5 degrees Celsius.

[0017] Preferably, among the conditions for determining whether a lithium-ion battery has thermal runaway, A) the battery voltage drops by a set proportion exceeding the initial voltage of 25%; B) the battery heating surface temperature rise rate - the battery heating rate is greater than or equal to a first set value of 1°C / min, and the total heating time exceeds a second set value of 3s.

[0018] Preferably, a cone calorimeter based on the oxygen consumption principle is used to measure the heat release rate of a lithium-ion battery fire to obtain the maximum heat release rate Qmax.

[0019] Preferably, according to the thermal runaway temperature T0 and the maximum heat release rate Qmax of the battery, based on the risk matrix, the fire hazard level of the lithium-ion battery is obtained, and the battery fire hazard level is divided into extremely dangerous I, seriously dangerous II, moderately dangerous III and slightly dangerous IV.

[0020] The present invention has the beneficial effect of testing the thermal runaway temperature of lithium-ion batteries in an open environment under the fume hood of a cone calorimeter, unifying the test conditions for the two evaluation parameters and achieving integrated measurement of the battery's thermal runaway temperature and heat release rate under the same test environment. Conventional methods, however, require testing the battery's thermal runaway temperature in a closed hot box and the battery's thermal runaway rate in an open environment, respectively. These two evaluation parameter test conditions cannot be unified, making it impossible to achieve a comprehensive evaluation of the lithium-ion battery's fire hazard through a single test. The present invention can achieve a comprehensive evaluation of the lithium-ion battery's fire hazard through a single, continuous test, eliminating errors caused by differences in battery samples and offering advantages such as convenience and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the risk matrix for fire hazard classification in the present invention.

[0022] Figure 2 It is a schematic diagram of the temperature curve when battery heating triggers programmed temperature rise.

[0023] Figure 3 This is a schematic diagram of the equipment used in the fire hazard classification test of lithium-ion batteries of the present invention. It should be noted that, except for the location and number of thermocouples tested, the rest of the equipment itself belongs to the existing technology.

[0024] Figure 4 This is a schematic diagram of the step-by-step temperature rise that occurs when thermal runaway of a lithium battery is triggered.

[0025] In the picture, 1. Gas collection hood, 2. Camera, 3. Lifting platform, 4. Ruler. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] See also Figure 3 , Figure 3 A device for measuring the fire hazard classification test of lithium batteries is presented. It should be noted that the device itself belongs to the existing technology, and the contribution of the present invention to the existing technology does not lie in the device itself.

[0028] See also Figure 1-4 The present lithium-ion battery fire hazard classification test method comprises the following steps:

[0029] S1. Charge and discharge the lithium-ion battery for two cycles at a constant current of not less than 0.3C according to the method provided by the manufacturer and charge it to 100% state of charge;

[0030] S2. Arrange thermocouples and heating plates on the battery surface, fix them with clamps, and place them on a lifting platform;

[0031] S3. Conduct temperature-programmed thermal runaway triggering and cone calorimetry combustion joint measurement experiments;

[0032] S4. Obtain the fire hazard level of the lithium-ion battery according to the risk matrix.

[0033] See also Figure 1 Two thermocouples T1 and T2 are arranged at the center of the lithium-ion battery heating surface, a thermocouple T3 is arranged at the center of the back, and a thermocouple T4 is arranged at the pressure relief valve. Thermal conductive graphite plates of equal size are arranged between the battery and the heating plate. An insulating cotton layer is arranged between the back of the battery and the clamping plate. The battery is fixed with a torque of 2 N·m or the torque specified by the manufacturer and placed on the lifting platform 3.

[0034] See also Figure 1 Before the test begins, the height of the lifting platform is adjusted so that the lithium-ion battery jet fire can be completely covered by the cone calorimeter smoke collection hood 1;

[0035] Thermal runaway is triggered by a programmed temperature increase based on the real-time temperature (T1) feedback of the lithium-ion battery heating surface. The temperature controller detects the feedback temperature in real time to ensure that the temperature of the battery heating surface rises according to the set program until thermal runaway occurs. The temperature control error of the temperature controller is no more than 2°C.

[0036] The heating procedure for lithium-ion batteries is as follows: the battery is heated to 120°C at a rate of 5±1°C at room temperature of 25±5°C, and then heated to 130°C at a rate of 5±1°C, and the temperature is maintained at a constant temperature for 10 minutes. This cycle is repeated until the battery experiences thermal runaway, with a temperature rise step of 10°C. The rear end of the gas hood 1 is connected to a cone calorimeter based on the oxygen consumption principle, which can directly measure the heat release rate of a lithium-ion battery fire, thereby obtaining the maximum heat release rate Qmax. Here, the heating rate of the battery is actually existing technology. A brief explanation is given: a cone calorimeter based on the oxygen consumption principle is used to measure the heat release rate of a lithium-ion battery fire and obtain the maximum heat release rate Qmax. In other words, the equipment collects combustion gases through the gas hood 1 and determines the combustion rate by measuring the oxygen and other gas components in the gas. Since this part belongs to existing technology, it will not be explained in detail here.

[0037] The thermal runaway temperature T0 of lithium-ion batteries is determined as follows: if thermal runaway occurs during constant temperature, the thermal runaway temperature is the constant temperature minus 5°C; if thermal runaway occurs during the heating stage, the heating surface temperature at the time of thermal runaway is the thermal runaway temperature.

[0038] The conditions for determining thermal runaway of lithium-ion batteries are:

[0039] A. The battery voltage drops by more than 25% of the initial voltage.

[0040] B. The rate of rise of the battery heating surface temperature T2 - the battery heating rate ≥ 1°C / min and exceeds 3s; thermal runaway is determined to have occurred when both A and B are met.

[0041] Finally, according to the thermal runaway temperature T0 and the maximum heat release rate Qmax of the battery, the fire hazard level of the lithium-ion battery is obtained based on the risk matrix. The battery fire hazard level is divided into extremely dangerous (I), seriously dangerous (II), moderately dangerous (III) and slightly dangerous (IV), as shown in Figure 2. Figure 1 shown.

[0042] The present invention tests the thermal runaway temperature of lithium-ion batteries in an open environment under the smoke hood of a cone calorimeter, unifying the test conditions for the two evaluation parameters and achieving integrated measurement of the battery's thermal runaway temperature and heat release rate under the same test environment. In contrast, existing technical methods require testing the battery's thermal runaway temperature in a closed hot box and the battery's thermal runaway rate in an open environment, respectively. The test conditions for the two evaluation parameters cannot be unified, and therefore, a comprehensive evaluation of the fire hazard of lithium-ion batteries cannot be achieved through a single test.

[0043] Through the above embodiment, a comprehensive evaluation of the fire hazard of lithium-ion batteries can be achieved through one continuous test, which can eliminate the errors caused by differences in battery samples and has the advantages of convenience and high efficiency.

Claims

1. A lithium-ion battery fire hazard classification test method, characterized by: Maximum heat release rate Q max , the thermal runaway temperature T0 is set as two parameters in a two-dimensional coordinate, the two-dimensional coordinate is divided into a risk matrix consisting of N*N small rectangular blocks, and the fire hazard is divided into N risk levels; The two-dimensional coordinates are from Q max The highest point, T0 the lowest point to Q max The lowest and highest directions of T0 form N-layer stepped areas, and each stepped area corresponds to the corresponding risk level of fire hazard; The heating program of the lithium-ion battery is as follows: heating at a set rate for a set time t1, and maintaining a constant temperature for t2 to form a temperature rise step as a program unit, and progressing a number of program units until the lithium-ion battery suffers from thermal runaway; The determination condition for thermal runaway of the lithium-ion battery is: the following conditions A) and B) are met simultaneously: A) The battery voltage drops below the set percentage of the initial voltage; B) Battery heating surface temperature rise rate - the battery heating rate is greater than or equal to the first set value, and the total heating time exceeds the second set value; The thermal runaway temperature T0 is determined as follows: if the battery thermal runaway occurs during the constant temperature process, the thermal runaway temperature is the constant temperature minus a set number of degrees Celsius. If the battery thermal runaway occurs during the temperature rise stage, the heating surface temperature at the time of thermal runaway is the thermal runaway temperature. The following steps are involved: S1. Charge and discharge the lithium-ion battery for 2 cycles at a constant current of not less than 0.3C and charge it to 100% state of charge; S2. Arrange thermocouples and heating plates on the battery surface, fix them with clamps, and place them on a lifting platform (3); S3. Conduct temperature-programmed thermal runaway triggering and cone calorimetry combustion joint measurement experiments; S4. Obtaining the fire hazard level of the lithium-ion battery according to the risk matrix.

2. The lithium-ion battery fire hazard classification test method according to claim 1, wherein: Two thermocouples T1 and T2 are arranged at the center of the lithium-ion battery heating surface, a thermocouple T3 is arranged at the center of the back surface, a thermocouple T4 is arranged at the pressure relief valve, a heat-conducting graphite plate of equal size is arranged between the battery and the heating plate, a heat-insulating cotton layer is arranged between the back surface of the battery and the clamping plate, and the battery is placed on a lifting platform (3); before the test begins, the height of the lifting platform (3) is adjusted so that the lithium-ion battery jet fire can be completely covered by the cone calorimeter smoke hood (1); Thermal runaway is triggered by a programmed temperature rise based on the real-time temperature T1 feedback of the lithium-ion battery heating surface. The temperature controller detects the feedback temperature in real time to ensure that the battery heating surface temperature T1 rises according to the set heating program until thermal runaway occurs.

3. The lithium-ion battery fire hazard classification test method according to claim 1, wherein: The heating procedure for the lithium-ion battery is as follows: the battery is heated to 120°C at a set rate of 5±1°C at room temperature of 25±5°C, and then heated to 130°C at a set rate of 5±1°C, during which the constant temperature is maintained for 10 minutes, and this cycle is repeated until the battery experiences thermal runaway, with a temperature rise step of 10°C.

4. The lithium-ion battery fire hazard classification test method according to claim 1, wherein: In the method for determining the thermal runaway temperature T0, the set several degrees Celsius is 5 degrees Celsius.

5. The lithium-ion battery fire hazard classification test method according to claim 1, wherein: Among the criteria for determining thermal runaway of lithium-ion batteries, A) The battery voltage drops by 25% over the initial voltage. B) Battery heating surface temperature rise rate - the battery heating rate is greater than or equal to the first set value of 1°C / min, and the total heating time exceeds the second set value of 3s.

6. The lithium-ion battery fire hazard classification test method according to claim 1, wherein: The heat release rate of lithium-ion battery fire was measured using a cone calorimeter based on the oxygen consumption principle to obtain the maximum heat release rate Qmax.

7. The lithium-ion battery fire hazard classification test method according to claim 1, wherein: According to the thermal runaway temperature T0 and the maximum heat release rate Qmax of the battery, the fire hazard level of the lithium-ion battery is obtained based on the risk matrix. The battery fire hazard level is divided into extremely dangerous (I), seriously dangerous (II), moderately dangerous (III) and slightly dangerous (IV).

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