Methods for assessing the risk of internal short-circuit failure in battery cells

Abstract

This invention provides a method for assessing the risk of internal short-circuit failure in a battery cell. The method includes acquiring the cell's parameter information and calculating the theoretical limiting short-circuit resistance value; preparing a test electrode assembly; performing a needle penetration test on the test electrode assembly; measuring and obtaining the actual short-circuit resistance value of the electrode plates in the test electrode assembly; and comparing the actual short-circuit resistance value with the theoretical limiting short-circuit resistance value to determine the level of short-circuit failure risk of the electrode assembly. This method, by comparing the theoretical limiting short-circuit resistance value with the actual short-circuit resistance value, can quickly assess the level of short-circuit failure risk of the test electrode assembly, shorten the assessment cycle, provide feedback and guidance for product design, and save on cell sample manufacturing and testing costs by using a test electrode assembly instead of a real battery cell.

Description

Technical Field

[0001] This invention relates to the field of battery safety assessment technology, and in particular to a method for assessing the risk of internal short-circuit failure in a battery cell. Background Technology

[0002] With the increasing number of electric vehicles on the market, battery pack safety has received growing attention. Cell safety is fundamental to battery pack safety. At the cell level, a series of safety abuse tests are conducted to simulate battery safety under extreme abuse conditions, the most stringent of which is the nail penetration test. The mechanism of cell nail penetration failure is that the separator is punctured by a needle, causing the positive and negative electrodes to come into contact. A large local current causes the electrode temperature to rise rapidly to its failure temperature, leading to cell fire and explosion.

[0003] Currently, in the design of battery cells, nail penetration testing is frequently used to assess the risk of short-circuit failure. This provides feedback on the safety performance of the battery cells and allows for improvements to the product design. The assessment method involves preparing battery cells with different improvement schemes using positive and negative electrode materials, electrolytes, additives, and mechanical components. Subsequently, nail penetration testing is performed on each of the prepared battery cells to assess the risk of short-circuit failure and evaluate the effectiveness of the improvement schemes.

[0004] The above-mentioned evaluation methods have problems such as long preparation cycle of battery cell samples, high raw material costs, low process maturity of test samples and low yield. In addition, actual testing of the prepared battery cells is required to evaluate the safety of the improved battery cells, which cannot quickly assess the short circuit failure risk of the battery cells and affects the evaluation cycle of the battery cell product improvement plan. Summary of the Invention

[0005] In view of this, the present invention aims to propose a method for assessing the risk of internal short circuit failure in battery cells, so as to shorten the assessment cycle of the risk of internal short circuit failure in battery cells.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for assessing the risk of internal short-circuit failure in a battery cell, comprising:

[0008] Obtain the parameter information of the battery cell and calculate the theoretical limiting short-circuit resistance value;

[0009] Prepare a test electrode assembly, perform a needle penetration test on the test electrode assembly, and measure and obtain the actual short-circuit resistance value of the electrode in the test electrode assembly;

[0010] By comparing the actual short-circuit resistance value with the theoretical limiting short-circuit resistance value, the risk of short-circuit failure of the pole group can be determined.

[0011] Furthermore, the parameter information of the battery cell is obtained, and the theoretical limiting short-circuit resistance value is calculated, including: the theoretical limiting short-circuit resistance value is calculated by the expression U2 / R limit × t=C1m1ΔT+C2m2ΔT+C3m3ΔT+C4m4ΔT; where U is the battery cell voltage, t is the thermal runaway time, C1 is the specific heat capacity of the negative electrode powder material, m1 is the mass of the negative electrode powder material, C2 is the specific heat capacity of the negative electrode current collector, m2 is the mass of the negative electrode current collector, C3 is the specific heat capacity of the positive electrode powder material, m3 is the mass of the positive electrode powder material, C4 is the specific heat capacity of the positive electrode current collector, m4 is the mass of the positive electrode current collector, and ΔT is the temperature difference of the electrode runaway temperature rise.

[0012] Furthermore, the parameter information of the battery cell is obtained, including: the parameter information includes the battery cell voltage, thermal runaway time, temperature difference of the electrode runaway temperature rise, positive electrode parameters, and negative electrode parameters; the positive electrode parameters include the mass of the positive electrode powder material, the specific heat capacity of the positive electrode powder material, the mass of the positive electrode current collector, the specific heat capacity of the positive electrode current collector, and the runaway ignition temperature of the positive electrode; the negative electrode parameters include the mass of the negative electrode powder material, the specific heat capacity of the negative electrode powder material, the mass of the negative electrode current collector, the specific heat capacity of the negative electrode current collector, and the runaway ignition temperature of the negative electrode.

[0013] Furthermore, obtaining parameter information of the battery cell includes: determining the thermal runaway time and the temperature difference of the uncontrolled temperature rise of the electrode based on the runaway ignition temperature of the positive electrode and the runaway ignition temperature of the negative electrode.

[0014] Furthermore, the preparation of the test electrode assembly includes: obtaining a test positive electrode sheet and a test negative electrode sheet, fabricating the test electrode assembly based on the test positive electrode sheet and the test negative electrode sheet; hot-pressing the test electrode assembly, and performing a withstand voltage insulation test on the hot-pressed test electrode assembly.

[0015] Furthermore, a needle penetration test is performed on the test electrode assembly to measure and obtain the true short-circuit resistance value of the electrode in the test electrode assembly, including: immersing the test electrode assembly in a lithium-free battery solvent before the needle penetration test.

[0016] Furthermore, a needle penetration test is performed on the test electrode group to measure and obtain the actual short-circuit resistance value of the electrode in the test electrode group, including: the test parameters of the needle penetration test include needle penetration speed, needle penetration depth and needle diameter.

[0017] Furthermore, a needle penetration test is performed on the test electrode group to measure and obtain the true short-circuit resistance value of the electrode in the test electrode group, including: there are multiple electrode pieces, and the true short-circuit resistance value includes a first true short-circuit resistance value between two tabs of the same electrode piece, and a second true short-circuit resistance value between two adjacent electrode pieces.

[0018] Furthermore, the electrode includes the test positive electrode and the test negative electrode.

[0019] Furthermore, comparing the actual short-circuit resistance value with the theoretical limit short-circuit resistance value to determine the level of short-circuit failure risk of the electrode group includes: selecting the first actual short-circuit resistance value and the second actual short-circuit resistance value that are smaller than the theoretical limit short-circuit resistance value as high-risk short-circuit failure points, and determining the level of short-circuit failure risk of the test electrode group based on the number of high-risk short-circuit failure points.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The method for assessing the risk of short-circuit failure within a battery cell described in this invention can quickly evaluate the risk of short-circuit failure of the test electrode group by comparing the theoretical limit short-circuit resistance value with the actual short-circuit resistance value, thus shortening the assessment cycle, providing feedback and guidance for product design. At the same time, using the test electrode group instead of the actual battery cell for testing can also save on the cost of battery cell sample manufacturing and testing, thereby improving the practicality of the assessment method. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0023] Figure 1 This is a flowchart illustrating the method for assessing the risk of internal short-circuit failure in a battery cell according to an embodiment of the present invention. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0025] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] This embodiment relates to a method for assessing the risk of short-circuit failure inside a battery cell. It can quickly assess the level of short-circuit failure risk of the test electrode group, shorten the assessment cycle, and reduce testing costs, thus having good practicality.

[0027] In terms of overall design philosophy, as a preferred implementation method, such as Figure 1 As shown, the method for assessing the risk of internal short-circuit failure of the battery cell in this embodiment mainly includes the following steps:

[0028] S1: Obtain the parameter information of the battery cell and calculate the theoretical limit short-circuit resistance value;

[0029] S2, Prepare the test electrode group, perform a needle penetration test on the test electrode group, and measure and obtain the true short-circuit resistance value of the electrode in the test electrode group;

[0030] S3. Compare the actual short-circuit resistance value with the theoretical limit short-circuit resistance value to determine the level of risk of short-circuit failure of the pole group.

[0031] In this embodiment S1, the preferred implementation involves obtaining the parameter information of the battery cell and calculating the theoretical limiting short-circuit resistance value, including by using the expression U2 / R limit × t = C1m1ΔT + C2m2ΔT + C3m3ΔT + C4m4ΔT to calculate the theoretical limiting short-circuit resistance value.

[0032] Where U is the cell voltage, t is the thermal runaway time, C1 is the specific heat capacity of the negative electrode powder material, m1 is the mass of the negative electrode powder material, C2 is the specific heat capacity of the negative electrode current collector, m2 is the mass of the negative electrode current collector, C3 is the specific heat capacity of the positive electrode powder material, m3 is the mass of the positive electrode powder material, C4 is the specific heat capacity of the positive electrode current collector, m4 is the mass of the positive electrode current collector, and ΔT is the temperature difference due to the uncontrolled temperature rise of the electrode.

[0033] Specifically, in this embodiment S1, the parameter information includes cell voltage, thermal runaway time, temperature difference during uncontrolled heating of the electrode, positive electrode parameters, and negative electrode parameters. The positive electrode parameters include the mass of the positive electrode powder material, the specific heat capacity of the positive electrode powder material, the mass of the positive electrode current collector, the specific heat capacity of the positive electrode current collector, and the uncontrolled ignition temperature of the positive electrode. The negative electrode parameters include the mass of the negative electrode powder material, the specific heat capacity of the negative electrode powder material, the mass of the negative electrode current collector, the specific heat capacity of the negative electrode current collector, and the uncontrolled ignition temperature of the negative electrode.

[0034] Meanwhile, in this embodiment S1, the preferred implementation obtains the parameter information of the battery cell, including determining the thermal runaway time and the temperature difference of the electrode runaway temperature based on the runaway ignition temperature of the positive electrode and the runaway ignition temperature of the negative electrode. Specifically, the electrode with the lower temperature value between the runaway ignition temperature of the positive electrode and the runaway ignition temperature of the negative electrode is designated as the weak electrode in thermal runaway of the battery cell. For example, if the runaway ignition temperature of the negative electrode is lower, then the negative electrode is the weak electrode in thermal runaway of the battery cell. At the same time, the thermal runaway time refers to the time it takes for the negative electrode to rise from its initial temperature to its runaway ignition temperature.

[0035] The present invention S1 will be specifically described in conjunction with the following specific embodiments.

[0036] First, obtain a normally discharged battery cell (taking a 2VDANi50 system battery cell as an example), and determine the battery cell's parameter information based on the battery cell, such as the battery cell voltage, thermal runaway time, positive electrode powder material mass, positive electrode powder material specific heat capacity, positive electrode current collector mass and specific heat capacity, as well as negative electrode powder material mass, negative electrode powder material specific heat capacity, negative electrode current collector mass and specific heat capacity.

[0037] Then, the battery cells were disassembled in a drying room, and the negative and positive electrodes were removed. Ten sets of hot plate experiments were then conducted on the positive and negative electrodes separately in a glove box under nitrogen atmosphere to obtain the runaway ignition temperature of the electrodes (taking the 2VDANi50 system battery cell as an example). The runaway ignition temperature of the negative electrode was 240℃ and that of the positive electrode was 285℃. Based on the lower runaway ignition temperature of the negative electrode, it can be determined that the negative electrode is the weak electrode in thermal runaway of the battery cell (the weak point in the battery cell runaway).

[0038] Furthermore, the thermal runaway time is obtained based on the time it takes to reach the runaway ignition temperature of the negative electrode. Based on the runaway ignition temperature of the negative electrode being 240℃, combined with the room temperature (assumed to be 25℃), the temperature difference of the runaway temperature of the electrode is obtained as 215℃ (240℃-25℃).

[0039] Finally, using the expression U2 / R_limit × t = C1m1ΔT + C2m2ΔT + C3m3ΔT + C4m4ΔT, the theoretical limiting short-circuit resistance value R_limit = 2.85mΩ is calculated. Taking the 2VDA Ni50 system cell as an example, the parameter information is shown in the table below:

[0040]

[0041]

[0042] Furthermore, in this embodiment, as a preferred implementation, the preparation of the test electrode assembly in S2 includes obtaining a test positive electrode sheet and a test negative electrode sheet, and fabricating the test electrode assembly based on the test positive electrode sheet and the test negative electrode sheet. Subsequently, the test electrode assembly is hot-pressed, and a withstand voltage insulation test is performed on the hot-pressed test electrode assembly.

[0043] Simultaneously, in a preferred implementation, a nail penetration test is performed on the test electrode assembly to measure and obtain the actual short-circuit resistance value of the electrode sheets in the test electrode assembly. This includes immersing the test electrode assembly in a lithium-salt-free battery solvent before the nail penetration test to ensure the wettability of the test electrode assembly and better simulate the real environment inside the battery cell. Here, the immersion time of the test electrode assembly can be set and adjusted according to the actual needs of simulating the real environment inside the battery cell, for example, the immersion time can be 8 to 24 hours, specifically 8 hours, 16 hours, or 24 hours.

[0044] In this embodiment, a needle penetration test is performed on the test electrode group to measure and obtain the actual short-circuit resistance value of the electrode in the test electrode group. The test parameters of the needle penetration test include the needle penetration speed, the needle penetration depth, and the needle diameter. The specific parameters of the needle penetration speed, the needle penetration depth, and the needle diameter can be set and adjusted according to the actual test requirements. For example, the needle penetration speed is 25 mm / s, the needle penetration depth is to pierce the electrode group, and the needle diameter is 8 mm.

[0045] In addition, in this embodiment, a needle penetration test is performed on the test electrode group to measure and obtain the true short-circuit resistance value of the electrode in the test electrode group. The test electrode group also includes multiple electrode groups, and the true short-circuit resistance value includes the first true short-circuit resistance value between two tabs of the same electrode group and the second true short-circuit resistance value between two adjacent electrode groups.

[0046] Specifically, the aforementioned electrode includes a test positive electrode and a test negative electrode. The first true short-circuit resistance value is measured and obtained between two tabs of the same test positive electrode or the same test negative electrode. The second true short-circuit resistance value is measured and obtained between adjacent test positive electrodes and test negative electrodes. Preferably, a pair of opposite tabs of the test positive electrode and the test negative electrode are selected for testing during the measurement.

[0047] In this embodiment, the actual short-circuit resistance value is compared with the theoretical limiting short-circuit resistance value to determine the level of short-circuit failure risk of the electrode group. This includes selecting a first actual short-circuit resistance value and a second actual short-circuit resistance value that are smaller than the theoretical limiting short-circuit resistance value as high-risk short-circuit failure points. The number of high-risk short-circuit failure points determines the level of short-circuit failure risk of the tested electrode group. Specifically, the more high-risk short-circuit failure points, the higher the short-circuit failure risk of the tested electrode group.

[0048] The present invention S2 and S3 will be specifically described in conjunction with the following specific embodiments.

[0049] First, the test electrode assembly is prepared, and the specific steps are as follows:

[0050] a) Prepare DOE (Design of Experiment) sample electrodes. Here, 6 test negative electrodes and 5 test positive electrodes are selected. Then, the test positive electrode / separator / test negative electrode layers are stacked according to the stacking process to obtain the test electrode assembly.

[0051] b) Perform hot-pressing treatment on the test electrode assembly according to the production process requirements (hot-pressing parameters are based on the cell manufacturing process parameters);

[0052] c) Perform a withstand voltage insulation test on the hot-pressed test electrode group to determine the insulation performance of the test electrode group (only test electrode groups that pass the withstand voltage insulation test can be tested subsequently, and to ensure the overall insulation performance of the test electrode group, multiple withstand voltage insulation tests should be avoided).

[0053] Secondly, the prepared test electrode assembly is processed in a dust-free and dry environment, specifically including:

[0054] a) Number the electrodes in the test electrode group. The negative electrode of test group 1 is named negative 1, the positive electrode of test group 1 is named positive 1, the negative electrode of test group 2 is named negative 2, and so on...;

[0055] b) Pour an appropriate amount of battery solvent (a mixture of chain carbonate and cyclic carbonate) into the container. The volume of the solvent should be enough to immerse the test electrode assembly. The solvent should be free of lithium salts to avoid ionic conductivity between the electrodes, which would affect the accuracy of the measurement of the true short-circuit resistance value.

[0056] c) Immerse the test electrode assembly in the above solvent for 8–24 hours to ensure the wettability of the test electrode assembly and better simulate the real internal environment of the battery cell.

[0057] Subsequently, the immersed test electrode group was subjected to a needle puncture test, the specific steps of which were as follows:

[0058] a) The test electrode group is clamped by a fixture. The preload of the fixture is simulated as the initial preload of the test electrode group in the cell, for example, 3000N.

[0059] b) Select a steel needle of a specific material and diameter, and pierce the test electrode group (or pierce to a specific depth) at a specific piercing speed. For example, select a high-temperature resistant steel needle with a diameter of 8mm and pierce the center of the large surface of the test electrode group at a speed of 25mm / s. Stop the test when the test electrode group is pierced.

[0060] c) After the test is completed, immediately remove the test electrode group while maintaining the clamped state (be careful not to touch the steel needle to avoid affecting the short-circuit resistance). In the drying room, use an AC impedance meter to test the short-circuit resistance according to the following test sequence. The test method is as follows:

[0061] 1) Perform impedance measurement on the same electrode (test positive electrode or test negative electrode): Use an impedance meter to connect the two tabs of the electrode to measure and obtain the first true short-circuit resistance value;

[0062] 2) Perform impedance measurement between adjacent electrodes (adjacent test positive electrode and test negative electrode): Use an impedance meter to connect to the tab 1 of the two electrodes or the tab 2 of the two electrodes to measure and obtain the second true short-circuit resistance value.

[0063] Based on the fact that this test electrode group has a total of 6 negative electrodes and 5 positive electrodes, the test data is as follows:

[0064]

[0065] As shown in the table above, the actual short-circuit resistance values ​​of items 5, 10, and 17 are all less than the theoretical limit short-circuit resistance value, meaning that there are three high-risk short-circuit failure points in this test electrode group. This test result reflects the safety performance of the test electrode group and can be used to design new battery cell products.

[0066] The method for assessing the risk of short-circuit failure within the battery cell in this embodiment can quickly evaluate the level of short-circuit failure risk of the test electrode group by comparing the theoretical limit short-circuit resistance value with the actual short-circuit resistance value, shortening the evaluation cycle, providing feedback and guidance for product design. At the same time, using the test electrode group instead of the actual battery cell for testing can also save on the cost of battery cell sample manufacturing and testing, thereby improving the practicality of the evaluation method.

[0067] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for assessing the risk of internal short-circuit failure in a battery cell, characterized in that: Obtain the parameter information of the battery cell and calculate the theoretical limiting short-circuit resistance value; Prepare a test electrode assembly, perform a needle penetration test on the test electrode assembly, and measure and obtain the actual short-circuit resistance value of the electrode in the test electrode assembly; By comparing the actual short-circuit resistance value with the theoretical limiting short-circuit resistance value, the risk of short-circuit failure of the pole group can be determined. Obtain the parameter information of the battery cell and calculate the theoretical limiting short-circuit resistance value, including: Through expression The theoretical limiting short-circuit resistance value is calculated using this method. Where U is the cell voltage, t is the thermal runaway time, C1 is the specific heat capacity of the negative electrode powder material, m1 is the mass of the negative electrode powder material, C2 is the specific heat capacity of the negative electrode current collector, m2 is the mass of the negative electrode current collector, C3 is the specific heat capacity of the positive electrode powder material, m3 is the mass of the positive electrode powder material, C4 is the specific heat capacity of the positive electrode current collector, and m4 is the mass of the positive electrode current collector. The temperature difference caused by the uncontrolled heating of the electrode. A needle penetration test is performed on the test electrode group to measure and obtain the actual short-circuit resistance value of the electrode in the test electrode group, including: The electrode is a plurality of electrodes, and the actual short-circuit resistance value includes a first actual short-circuit resistance value between two tabs of the same electrode, and a second actual short-circuit resistance value between two adjacent electrodes. Comparing the actual short-circuit resistance value with the theoretical limiting short-circuit resistance value to determine the level of short-circuit failure risk of the pole group includes: The first actual short-circuit resistance value and the second actual short-circuit resistance value, which are less than the theoretical limit short-circuit resistance value, are selected as high-risk short-circuit failure points. The level of short-circuit failure risk of the test electrode group is judged based on the number of high-risk short-circuit failure points.

2. The method for assessing the risk of internal short-circuit failure of a battery cell according to claim 1, characterized in that, Obtain the parameter information of the battery cell, including: The parameter information includes cell voltage, thermal runaway time, temperature difference during electrode runaway temperature rise, positive electrode parameters, and negative electrode parameters. The positive electrode parameters include the mass of the positive electrode powder material, the specific heat capacity of the positive electrode powder material, the mass of the positive electrode current collector, the specific heat capacity of the positive electrode current collector, and the runaway ignition temperature of the positive electrode. The negative electrode parameters include the mass of the negative electrode powder material, the specific heat capacity of the negative electrode powder material, the mass of the negative electrode current collector, the specific heat capacity of the negative electrode current collector, and the runaway ignition temperature of the negative electrode.

3. The method for assessing the risk of internal short-circuit failure of a battery cell according to claim 2, characterized in that, Obtain the parameter information of the battery cell, including: The thermal runaway time and the temperature difference of the uncontrolled temperature rise of the electrode are determined based on the runaway ignition temperature of the positive electrode and the runaway ignition temperature of the negative electrode.

4. The method for assessing the risk of internal short-circuit failure of a battery cell according to claim 1, characterized in that, Preparation of the test electrode assembly includes: Obtain a test positive electrode and a test negative electrode, and fabricate the test electrode assembly based on the test positive electrode and the test negative electrode; The test electrode assembly is hot-pressed, and a withstand voltage insulation test is performed on the hot-pressed test electrode assembly.

5. The method for assessing the risk of internal short-circuit failure of a battery cell according to claim 1, characterized in that, A needle penetration test is performed on the test electrode group to measure and obtain the actual short-circuit resistance value of the electrode in the test electrode group, including: Prior to the needle penetration test, the test electrode assembly was immersed in a lithium-free battery solvent.

6. The method for assessing the risk of internal short-circuit failure of a battery cell according to claim 1, characterized in that, A needle penetration test is performed on the test electrode group to measure and obtain the actual short-circuit resistance value of the electrode in the test electrode group, including: The test parameters for the acupuncture test include acupuncture speed, acupuncture depth, and needle diameter.

7. The method for assessing the risk of internal short-circuit failure of a battery cell according to claim 4, characterized in that: The electrode includes the test positive electrode and the test negative electrode.

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