Evaluation method for the bottom impact resistance performance of power battery system

Abstract

This invention provides a method for evaluating the bottom impact resistance performance of a power battery system, comprising the following steps: obtaining the power battery system to be tested; supplying circulating coolant to the power battery system and conducting a ball impact test under preset operating conditions; acquiring the voltage and temperature states of the power battery system during the test, acquiring the rate of increase of the DC internal resistance of the power battery system before and after the test, and acquiring the insulation internal resistance value of the power battery after the test; sequentially performing charge-discharge tests and airtightness tests on the power battery system and acquiring the test results; if the insulation internal resistance value is less than a preset threshold, the test is considered unqualified; if the insulation internal resistance value is not less than the preset threshold, the test is deemed qualified based on the voltage state, temperature state, rate of increase of DC internal resistance, and the test results of the charge-discharge test and airtightness test. This method for evaluating the bottom impact resistance performance of a power battery system can effectively assess product safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power batteries, in particular to a method for evaluating the impact resistance of the bottom of a power battery system. BACKGROUND

[0002] At present, products powered by batteries are applied in various aspects of production and life, such as portable electronic products, electric tools, two-wheeled electric vehicles, unmanned aerial vehicles and new energy vehicles, etc., and improper design and use of battery products may cause safety accidents such as fire and explosion.

[0003] Among them, lithium ion batteries have important applications in the field of new energy vehicles due to their high energy density and long cycle life. With the popularization and application of new energy vehicles, the safety of power batteries has become one of the important technical problems restricting the development of new energy vehicles. At present, there are corresponding specifications in different fields, which stipulate the test requirements that the power battery needs to meet under normal use, reasonable foreseeable misuse, safety abuse or fault conditions.

[0004] The safety performance of the power battery pack / system is not only related to the material system and structural design, but also related to the abuse in the use process. The mechanical reliability test evaluation method for the power battery system mainly includes mechanical vibration, mechanical impact, simulated collision, sliding table, dropping and extrusion, etc. Among them, the extrusion test mainly refers to GB 38031-2020 for extrusion test of the power battery system in X and Y directions (the automobile driving direction is X direction, and the other direction perpendicular to the driving direction is Y direction), which simulates the application scene of the battery pack / system when the source vehicle encounters a safety accident such as collision. However, the damage degree of the power battery pack / system after the test cannot be effectively determined by this extrusion test method, and it is difficult to accurately verify whether the structural strength and mechanical reliability of the bottom of the power battery pack / system meet the design requirements. SUMMARY

[0005] Therefore, the present application aims to provide a method for evaluating the impact resistance of the bottom of a power battery system, which can simulate the actual use conditions of the power battery system and improve the effectiveness of evaluating the structural strength and mechanical reliability of the bottom of the power battery system.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A method for evaluating the impact resistance of the bottom of a power battery system, comprising the following steps:

[0008] Obtaining a power battery system to be tested;

[0009] Supplying circulating coolant to the power battery system and performing ball impact test under a predetermined working condition.

[0010] acquiring a voltage state and a temperature state of the power battery system during the test, acquiring a growth rate of a direct current resistance of the power battery system before and after the test, and acquiring an insulation resistance value of the power battery after the test;

[0011] sequentially performing a charge-discharge test and a gas tightness test on the power battery system, and acquiring test results;

[0012] if the insulation resistance value is less than a preset threshold, the evaluation is unqualified, and if the insulation resistance value is not less than the preset threshold, whether the evaluation is qualified is determined based on the voltage state, the temperature state, the growth rate of the direct current resistance, the test results of the charge-discharge test and the gas tightness test.

[0013] Further, the power battery system is supplied with circulating coolant, and a ball impact test is performed under a preset working condition, including: continuously extruding the power battery system at a preset extrusion speed; when the voltage state and / or the temperature state change sharply during the extrusion of the power battery system to reach a pressure threshold, the evaluation is unqualified; when the extrusion force reaches the pressure threshold, the voltage state and the temperature state do not change sharply, but change sharply after a certain time of extrusion, the evaluation is unqualified.

[0014] Further, the temperature of the coolant is 25°C, the flow rate of the coolant is 10 L / min; and if the water cooling system of the power battery system leaks, the evaluation is unqualified.

[0015] Further, if the insulation resistance value is not less than the preset threshold, whether the evaluation is qualified is determined based on the voltage state, the temperature state, the growth rate of the direct current resistance, the test results of the charge-discharge test and the gas tightness test, including: when the voltage state and the temperature state change sharply, the evaluation is unqualified; when the voltage state and / or the temperature state do not change sharply, at least one of the direct current resistance growth rate, the charge-discharge test and the gas tightness test is unqualified, and the evaluation is unqualified.

[0016] Further, the charge-discharge test and the gas tightness test are sequentially performed on the power battery system, and the test results are acquired, including: the charge-discharge test is at least one complete fast charging and discharging process; if at least one of each electrical device and each connection point of the power battery system is damaged, the charge-discharge test is unqualified.

[0017] Further, the charge-discharge test and the gas tightness test are sequentially performed on the power battery system, and the test results are acquired, including: if the gas tightness value of the gas tightness test is greater than a leakage threshold, the gas tightness test is unqualified.

[0018] Further, the power battery system to be tested is obtained, including: determining an initial value of the direct current resistance according to the power battery system, and adjusting the power battery system to a full charge state.

[0019] Further, the power battery system is supplied with circulating cooling liquid, and a ball impact test is performed under a preset working condition, including: determining a final value of the direct current resistance according to the power battery system after the ball impact test, and determining a growth rate of the direct current resistance according to the initial value and the final value.

[0020] Further, the power battery system to be tested is obtained, including: determining an initial value of the direct current resistance according to the power battery system, and adjusting the power battery system to a full charge state.

[0021] Further, the ball impact test is performed under a preset working condition, including: the ball impact positions of the ball impact test include position points of corresponding cooling liquid plate joints at the bottom of the power battery system, position points of corresponding battery modules, position points of corresponding conductive rows, position points of corresponding fuses, position points of corresponding BDUs, and position points of corresponding BMSs.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] The power battery system bottom impact resistance performance evaluation method provided by the present application can effectively evaluate the structural strength and mechanical reliability of the power battery system bottom, feedback the product design link, and be beneficial to the improvement of product performance and quality. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The present application is not limited by the accompanying drawings.

[0025] Figure 1 The flowchart of the power battery system bottom impact resistance performance evaluation method according to the present application is shown.

[0026] Figure 2 The structural diagram of the ball impact equipment according to the present application is shown. DETAILED DESCRIPTION

[0027] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0028] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0029] The present embodiment relates to a method for evaluating the impact resistance of the bottom of a power battery system. The method simulates the actual use conditions of the power battery system, performs a ball impact test on the power battery system, and comprehensively analyzes relevant factors such as the test results of the insulation resistance value, voltage state, temperature state, growth rate of direct current resistance, charge and discharge test, and air tightness test, to evaluate the structural strength and mechanical reliability of the bottom of the power battery system, thereby improving the evaluation effectiveness.

[0030] Based on the above design idea, one preferred embodiment of the method for evaluating the impact resistance of the bottom of the power battery system according to the present embodiment, as shown in Figure 1 , mainly includes the following steps:

[0031] S1, obtaining a power battery system to be tested.

[0032] S2, supplying circulating coolant to the power battery system and performing a ball impact test under a preset condition.

[0033] S3, obtaining the voltage state and temperature state of the power battery system during the test, obtaining the growth rate of the direct current resistance of the power battery system before and after the test, and obtaining the insulation resistance value of the power battery after the test.

[0034] S4, sequentially performing charge and discharge test and air tightness test on the power battery system, and obtaining the test results.

[0035] S5, if the insulation resistance value is less than a preset threshold, the evaluation is unqualified, and if the insulation resistance value is not less than the preset threshold, the voltage state, temperature state, growth rate of direct current resistance, test results of charge and discharge test and air tightness test are used to determine whether the evaluation is qualified.

[0036] The evaluation of whether it is qualified or not qualified refers to whether the structural strength and mechanical reliability of the bottom of the power battery system meet the design requirements. Moreover, the method for evaluating the impact resistance of the bottom of the power battery system according to the present embodiment can simulate the application scenarios of the bottom of the power battery pack / system being damaged by the impact of obstacles thrown from the bottom direction during normal use, and realize the test and evaluation of the structural strength and mechanical reliability of the bottom of the power battery pack / system.

[0037] In a preferred embodiment, the power battery system is supplied with circulating coolant, and a ball impact test is performed under a preset working condition, including continuously pressing the power battery system at a preset pressing speed. When the voltage state and / or the temperature state of the power battery system change sharply during the pressing process until the pressing force reaches a pressure threshold, the power battery system is evaluated as unqualified. When the voltage state and the temperature state do not change sharply when the pressing force reaches the pressure threshold, but change sharply after the power battery system is pressed for a certain period of time, the power battery system is evaluated as unqualified.

[0038] In a preferred embodiment, the temperature of the coolant is 25°C, and the flow rate of the coolant is 10 L / min, so as to better simulate the actual use condition of the power battery. If the water cooling system of the power battery system leaks, the power battery system is evaluated as unqualified, otherwise, the power battery system is evaluated as qualified.

[0039] Of course, the flow rate of the coolant is 10 L / min, which is used to simulate the flow rate of the coolant in the actual working condition. The specific value of the flow rate can be changed according to the change of the actual working condition, and is not limited to 10 L / min. For example, the flow rate can be set to 8 L / min or 12 L / min.

[0040] In a preferred embodiment, if the insulation resistance value is not less than a preset threshold, the voltage state, the temperature state, the growth rate of the direct current resistance, the test results of the charge and discharge test and the air tightness test are used to determine whether the power battery system is qualified, including that when the voltage state and the temperature state change sharply, the power battery system is evaluated as unqualified. When the voltage state and the temperature state do not change sharply, at least one of the growth rate of the direct current resistance, the charge and discharge test and the air tightness test is unqualified, and the power battery system is evaluated as unqualified.

[0041] In addition, in order to evaluate the charge and discharge performance of the power battery system after the bottom of the power battery system is impacted, the power battery system is sequentially subjected to a charge and discharge test and an air tightness test, and test results are obtained, including that the charge and discharge test is at least one complete fast charging and discharging process. If at least one of the electrical devices and the connection points of the power battery system is damaged, the charge and discharge test is unqualified.

[0042] In addition, in order to evaluate the charge and discharge performance of the power battery system after the bottom of the power battery system is impacted, the power battery system is sequentially subjected to a charge and discharge test and an air tightness test, and test results are obtained, including that the charge and discharge test is at least one complete fast charging and discharging process. If at least one of the electrical devices and the connection points of the power battery system is damaged, the charge and discharge test is unqualified.

[0043] In order to effectively determine the insulation performance of the power battery system, in the embodiment, a power battery system to be tested is obtained, including determining an initial value of the direct current resistance according to the power battery system, and adjusting the power battery system to a full charge state.

[0044] In the embodiment, the power battery system is supplied with circulating coolant, and the ball impact test is performed under preset working conditions. The final value of the direct current internal resistance is determined according to the power battery system after the ball impact test, and the growth rate of the direct current internal resistance is determined according to the initial value and the final value.

[0045] In addition, in the embodiment, as a preferred implementation, the power battery system to be tested is obtained, and the initial value of the insulation internal resistance is determined according to the power battery system. If the initial value of the insulation internal resistance is less than a preset threshold, the power battery system is evaluated as unqualified.

[0046] In the embodiment, in order to ensure the objectivity and accuracy of the ball impact test, the ball impact test is performed under preset working conditions, and the ball impact positions of the ball impact test include position points of corresponding coolant plate joints at the bottom of the power battery system, position points of corresponding battery modules, position points of corresponding conductive rows, position points of corresponding fuses, position points of corresponding BDUs, and position points of corresponding BMSs. In addition, the preset working conditions in the embodiment also include ball impact speed and ball impact diameter.

[0047] It is worth mentioning that the ball impact device 3 in the embodiment can adopt a conventional ball impact device product, for example Figure 2 As shown in the figure, the ball impact device 3 has a test platform, and a ball head and a moving device 2 located below the test platform. In use, the test sample 1 (i.e., the power battery system or the power battery pack) is fixed on the test platform, and after the ball impact device 3 is turned on, the ball head is pressed against the test sample under the drive of the moving device.

[0048] In the embodiment, the ball impact test process of the application is specifically described in combination with the following specific embodiments. The specific test steps are as follows:

[0049] ①Preset environmental requirements: temperature 22±5℃, relative humidity: 10%-90%, atmospheric pressure 86kpa~106kPa. The environmental requirements can be adjusted according to the actual simulated working condition requirements.

[0050] ②Pre-test detection: check the initial appearance state of the power battery system, and detect the insulation resistance to obtain the initial value of the insulation internal resistance.

[0051] ③Direct current internal resistance test: record the initial value R1 of the direct current internal resistance. After the internal resistance test is completed, the power battery system is adjusted to a full charge state.

[0052] (4) Ball impact test platform setup: The voltage and temperature states of the battery cells in the power battery system need to be monitored during the entire test process. The ball impact position needs to be marked in advance at the bottom (the position needs to be selected according to the structural characteristics of the power battery system, such as the position corresponding to the cold liquid plate joint, the position corresponding to the battery module, the position corresponding to the conductive row, the position corresponding to the fuse, the position corresponding to the BDU, and the position corresponding to the BMS, etc.

[0053] (5) Perform ball impact test: Fix the power battery system on the test platform of the ball impact equipment (such as Figure 2 ), close the relay, connect the water cooling machine with the inlet and outlet of the power battery system water cooling pipe, and continuously circulate cooling liquid with a flow rate of 10 L / min at 25°C.

[0054] Turn on the ball impact equipment. The ball head of the ball impact equipment is an extruded ball head with a diameter of 150 mm. The extruded ball head is driven by the movement device to extrude the selected weak position at a speed of 1 mm / s. During the bottom ball impact test, if the extrusion force does not reach 25 KN (pressure threshold) and the voltage state or temperature state of the battery cell changes sharply, it is determined that the power battery system cannot withstand 25 KN extrusion force, and the test fails. If the voltage state and temperature state of the battery cell do not change sharply, stop extruding and keep the displacement for 10 min. Monitor the voltage and temperature information during the keeping process.

[0055] (6) After the ball impact test is completed: Continue to circulate cooling liquid with a flow rate of 10 L / min at 25°C for 1 h. After the observation is completed, complete the final value test of the direct current resistance according to step ②, and record the final value R2 of the direct current resistance.

[0056] (7) Charge and discharge test: At room temperature, charge the power battery system from 10% SOC to 95% SOC, then stand for not more than 1 h, and finally discharge at a preset current to 10% SOC. Observe whether the power battery system can complete the test.

[0057] (8) Air tightness detection: inflation pressure 5 kPa, inflation time 60 s, leakage amount ≤100 Pa / min.

[0058] In addition, the post-test inspection items and test pass determination criteria are as follows:

[0059] (1) The power battery system should not explode, catch fire, or leak liquid.

[0060] (2) The cooling liquid in the power battery system has no leakage, meeting the requirements of relevant standards.

[0061] ③The voltage state and the temperature state do not change sharply during the test, the growth rate of the direct current resistance before and after the test is not greater than 10%, a complete charging and discharging process can be performed, and there is no burning mark on all electrical components and connections in the power battery system.

[0062] ④The insulation resistance value (including the initial value of the insulation resistance) is greater than or equal to 2.5 MΩ.

[0063] ⑤The air tightness value of the water cooling plate is less than the maximum leakage required by the manufacturer.

[0064] The power battery system bottom impact resistance performance evaluation method of the embodiment can simulate the actual use condition of the power battery system by supplying circulating cooling liquid to the power battery system and implementing ball impact test under the preset working condition, and can determine whether it is qualified after comprehensively analyzing the test results of the insulation resistance value, the voltage state, the temperature state, the growth rate of the direct current resistance, the charging and discharging test and the air tightness test and other related factors, so as to effectively evaluate the structural strength and mechanical reliability of the bottom of the power battery system, feedback the product design link, and be beneficial to the improvement of the product performance and quality.

[0065] The above is only a preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for evaluating the impact resistance of a power battery system bottom, characterized in that, The method comprises the following steps: acquiring a power battery system to be tested; supplying the power battery system with circulating coolant and performing a ball impact test under a preset working condition; acquiring a voltage state and a temperature state of the power battery system during the test, acquiring a growth rate of a direct current internal resistance of the power battery system before and after the test, and acquiring an insulation internal resistance value of the power battery after the test; sequentially performing a charge-discharge test and a gas tightness test on the power battery system, and acquiring test results; if the insulation internal resistance value is less than a preset threshold, evaluating as unqualified, and if the insulation internal resistance value is not less than the preset threshold, judging whether the evaluation is qualified or not based on the voltage state, the temperature state, the growth rate of the direct current internal resistance, the charge-discharge test and the gas tightness test; if the insulation internal resistance value is not less than the preset threshold, judging whether the evaluation is qualified or not based on the voltage state, the temperature state, the growth rate of the direct current internal resistance, the charge-discharge test and the gas tightness test, comprising: when the voltage state and the temperature state change sharply, evaluating as unqualified; when the voltage state and / or the temperature state does not change sharply, at least one of the growth rate of the direct current internal resistance, the charge-discharge test and the gas tightness test is unqualified, and then evaluating as unqualified.

2. The method of claim 1, wherein, supplying the power battery system with circulating coolant and performing a ball impact test under a preset working condition, comprising: continuously extruding the power battery system at a preset extrusion speed; when the voltage state and / or the temperature state changes sharply during the extrusion of the power battery system until the extrusion force reaches a pressure threshold, evaluating as unqualified; when the extrusion force reaches the pressure threshold, the voltage state and the temperature state do not change sharply, but change sharply after a certain time of maintaining the extrusion state, and then evaluating as unqualified.

3. The method according to claim 2, wherein: the temperature of the coolant is 25°C, and the flow rate of the coolant is 10 L / min; and if the water cooling system of the power battery system leaks, evaluating as unqualified.

4. The method of claim 1, wherein, sequentially performing a charge-discharge test and a gas tightness test on the power battery system, and acquiring test results, comprising: the charge-discharge test is at least one complete fast charging and discharging process; if at least one of each electrical device and each connection point of the power battery system is damaged, the charge-discharge test is unqualified.

5. The method of claim 1, wherein, sequentially performing a charge-discharge test and a gas tightness test on the power battery system, and acquiring test results, comprising: if the gas tightness value of the gas tightness test is greater than a leakage threshold, the gas tightness test is unqualified.

6. The method of claim 1, wherein, acquiring a power battery system to be tested, comprising: determining an initial value of a direct current internal resistance according to the power battery system, and adjusting the power battery system to a full charge state.

7. The method of claim 6, wherein, supplying the power battery system with circulating coolant and performing a ball impact test under a preset working condition, comprising: determining a final value of the direct current internal resistance according to the power battery system after the ball impact test, and determining a growth rate of the direct current internal resistance according to the initial value and the final value.

8. The method of claim 1, wherein, Acquiring a power battery system to be tested, comprising: Determining an initial value of insulation resistance according to the power battery system; If the initial value of insulation resistance is less than a preset threshold, the power battery system is evaluated as unqualified.

9. The method of claim 1 to 8, wherein, Implementing a ball impact test under a preset working condition, comprising: The ball impact position of the ball impact test comprises a position point of a corresponding cold liquid plate joint at the bottom of the power battery system, a position point of a corresponding battery module, a position point of a corresponding conductive row, a position point of a corresponding fuse, a position point of a corresponding BDU, and a position point of a corresponding BMS.

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