Method for testing cell extrusion resistance of battery module cushion pad

Abstract

The invention discloses a method for testing the cell extrusion resistance of a battery module buffer pad. The method comprises the following steps: applying a preset target force to a sample at a preset target force application rate; the target force comprises an upper limit target force and a lower limit target force; the upper limit target force and the lower limit target force are respectively an upper limit value and a lower limit value of an extrusion force value applied by the battery cell to the buffer pad in a working stage of the battery cell, and are respectively obtained in charging and discharging processes of the battery cell; the target force application rate comprises an upper limit target force application rate and a lower limit target force application rate, and the upper limit target force and the lower limit target force are linearly loaded according to the upper limit target force application rate and the lower limit target force application rate respectively; the upper limit target force application rate and the lower limit target force application rate are respectively obtained by the speeds of applying the upper limit target force and the lower limit target force to the buffer pad by the battery cell in the charging and discharging processes of the battery cell. According to the test method, the test process is closer to the actual working process of the battery cell, and the test accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery production, and in particular to a method for testing the ability of a battery module buffer pad to withstand cell extrusion. Background Art

[0002] In a battery module, a cell buffer pad is arranged between adjacent cells, or between a cell and the inner wall of a module shell, and plays the role of isolation, buffering, heat insulation, and insulation. The buffer pad is an important factor affecting the overall performance and safety performance of a battery module.

[0003] To ensure the performance of the battery module, the battery cell buffer pad is required to have certain thermal conductivity, insulation and compression rebound properties to adapt to the expansion and contraction of the battery cell during charging and discharging.

[0004] In the prior art, before selecting a battery cell buffer pad, it is often necessary to test the battery cell buffer pad to test the deformation ability and resilience of the battery cell buffer pad to ensure that the battery cell buffer pad can adapt to the breathing effect generated by the battery cell during the charging and discharging process and adapt to the continuous expansion and contraction of the battery cell. The existing test method generally sets a target force and a target force application rate through a pressure testing machine, and according to this target force application rate and target force, the battery cell is repeatedly compressed, squeezed and relaxed for many times, and finally the thickness and resilience of the buffer pad after the test are measured to determine the battery cell extrusion resistance of the test buffer pad. This test method is fast, but during the test process, the characteristics of the battery cell working process are not well taken into account. The target force and target force application rate applied to the test buffer pad are not the same or similar to the extrusion force of the battery cell on the buffer pad during the actual charging and discharging process. Therefore, the test method in the prior art is not accurate, and the qualified buffer pad obtained by the prior art test is not necessarily qualified. Summary of the invention

[0005] In order to overcome at least one of the defects described in the above-mentioned prior art, the present invention provides a method for testing the ability of a battery module buffer pad to withstand battery cell extrusion, by simulating the process in which the battery cell applies extrusion force to the buffer pad during battery charging and discharging to apply a target force to the sample, so that the test process and environment are closer to the actual working process of the battery cell, thereby improving the accuracy of the test.

[0006] The technical solution adopted by the present invention to solve the problem is:

[0007] A method for testing the ability of a battery module buffer pad to withstand cell extrusion, comprising applying a preset target force to a sample at a preset target force application rate, and maintaining the state in which the target force is applied to the sample until a preset steady-state duration ends;

[0008] The target force includes an upper limit target force and a lower limit target force;

[0009] The upper limit target force and the lower limit target force are respectively the upper limit value and the lower limit value of the extrusion force applied to the buffer pad by the battery cell in a working stage of the battery cell, and are respectively obtained during the charging and discharging process of the battery cell;

[0010] The target force application rate includes an upper limit target force application rate and a lower limit target force application rate, and the upper limit target force and the lower limit target force are linearly loaded according to the upper limit target force application rate and the lower limit target force application rate respectively;

[0011] The upper limit target force application rate and the lower limit target force application rate are obtained by the speed at which the battery cell applies the upper limit target force and the lower limit target force to the buffer pad during the charging and discharging process of the battery cell, respectively;

[0012] The steady-state duration includes an upper limit target force steady-state maintaining time and a lower limit target force steady-state maintaining time.

[0013] Further: the target force loading method is:

[0014] First, applying an extrusion force to the sample at the upper limit target force application rate until the extrusion force reaches the upper limit target force, and then maintaining the upper limit target force applied to the sample until the preset upper limit target force steady-state maintenance time ends;

[0015] After the upper limit target force steady-state maintenance time ends, the upper limit target force is removed at the lower limit target force application rate until the lower limit target force is reached, and the lower limit target force is maintained applied to the sample until the preset lower limit target force steady-state maintenance time ends.

[0016] Furthermore: the target force is obtained by at least the squeezing force value of the buffer pad being squeezed by the battery cell in two different working stages of the battery cell.

[0017] Further: before the sample is tested, at least the initial thickness, initial insulation level, initial withstand voltage level and initial thermal conductivity of the sample need to be recorded;

[0018] After the target force is applied, at least the real-time thickness, real-time insulation level, real-time withstand voltage level and real-time thermal conductivity of the sample need to be recorded.

[0019] Further, the following steps are included:

[0020] S11, preparing a sample, wherein the sample is in a sheet shape;

[0021] S12, selecting a fixture and a pressure testing machine, wherein the fixture is installed on the pressure testing machine, and the outer diameter of the fixture is larger than the outer diameter of the sample;

[0022] S13, obtaining test parameters, simulating the charging and discharging working state of the battery cell through software, and sequentially obtaining the extrusion force values ​​applied by the battery cell to the buffer pad in at least three different working stages according to the working process of the battery cell, and the extrusion force application rate of the extrusion force values ​​applied by the battery cell to the buffer pad, and the extrusion force application rate is used as the target force application rate in the test process;

[0023] S14, obtaining the sample parameters before the test, including the initial thickness S10, initial insulation level S10, initial withstand voltage level S10 and initial thermal conductivity S10 of the sample;

[0024] S21, first stage test preloading: placing the sample in the middle of the fixture, setting the target force of the first stage, and starting the pressure testing machine so that the fixture contacts the sample;

[0025] S22, first stage test loading: according to the extrusion pressure values ​​and extrusion pressure application rates respectively obtained by the battery cell in at least three different working stages in S13, set the first upper limit target force, the first upper limit target force application rate, the first upper limit target force steady-state maintenance time, the first lower limit target force, the first lower limit target force application rate and the first lower limit target force steady-state maintenance time, start the pressure testing machine again, apply the first upper limit target force to the specimen at the first upper limit target force application rate, and maintain the first upper limit target force for the first upper limit target force steady-state maintenance time; after the first upper limit target force steady-state maintenance time ends, cancel the first upper limit target force to the first lower limit target force at the first lower limit target force application rate, and maintain the first lower limit target force for the first lower limit target force steady-state maintenance time until the first lower limit target force steady-state maintenance time ends;

[0026] S23, repeat step S22 for several cycles, after which the sample is removed from the pressure testing machine, and the sample after the first stage test is measured to obtain the real-time thickness S20, the real-time insulation level S20, the real-time withstand voltage level S20 and the real-time thermal conductivity S20;

[0027] S31, second stage test preloading: placing the sample after step S23 in the middle of the fixture again, setting the target force of the second stage, and starting the pressure testing machine so that the fixture contacts the sample;

[0028] S32, second stage test loading: according to the extrusion pressure values ​​respectively obtained by the battery cell in at least three different working stages in S13, the extrusion pressure value corresponding to the working stage following the working stage corresponding to the extrusion pressure value adopted in step S22 and the extrusion pressure application rate in the corresponding working stage selected in this step are selected, and the second upper limit target force, the second upper limit target force application rate, the second upper limit target force steady-state maintenance time, the second lower limit target force and the second lower limit target force application rate and the second lower limit target force steady-state maintenance time are set, and the pressure testing machine is started again, and the second upper limit target force is applied to the specimen at the second upper limit target force application rate, and the second upper limit target force is maintained for the second upper limit target force steady-state maintenance time; after the second upper limit target force steady-state maintenance time ends, the second upper limit target force is revoked to the second lower limit target force at the second lower limit target force application rate, and the second lower limit target force is maintained for the second lower limit target force steady-state maintenance time until the second lower limit target force steady-state maintenance time ends;

[0029] S33, repeat step S32 for several cycles, after which the sample is removed from the pressure testing machine, and the sample after the second stage test is measured to obtain the real-time thickness S30, the real-time insulation level S30, the real-time withstand voltage level S30 and the real-time thermal conductivity S30;

[0030] S41, third stage test preloading: placing the sample after step S33 in the middle of the fixture again, setting the target force of the third stage, and starting the pressure testing machine so that the fixture contacts the sample;

[0031] S42, third stage test loading: according to the extrusion pressure values ​​respectively obtained by the battery cell in at least three different working stages in S13, the extrusion pressure value corresponding to the working stage following the working stage corresponding to the extrusion pressure value adopted in step S32 and the extrusion pressure application rate in the corresponding working stage selected in this step are selected, and the third upper limit target force, the third upper limit target force application rate, the third upper limit target force steady-state maintenance time, the third lower limit target force and the third lower limit target force application rate and the third lower limit target force steady-state maintenance time are set, and the pressure testing machine is started again, and the third upper limit target force is applied to the specimen at the third upper limit target force application rate, and the third upper limit target force is maintained for the third upper limit target force steady-state maintenance time; after the third upper limit target force steady-state maintenance time ends, the third upper limit target force is revoked to the third lower limit target force at the third lower limit target force application rate, and the third lower limit target force is maintained for the third lower limit target force steady-state maintenance time until the third lower limit target force steady-state maintenance time ends;

[0032] S43, repeat step S42 for several cycles, after which the sample is removed from the pressure testing machine, and the sample after the third stage test is measured to obtain the real-time thickness S40, the real-time insulation level S40, the real-time withstand voltage level S40 and the real-time thermal conductivity S40;

[0033] S51. Analyze the extrusion resistance of the sample.

[0034] Furthermore, the analysis method of the sample's extrusion resistance is:

[0035] According to the initial thickness S10 and the real-time thickness S20, the real-time thickness S30 and the real-time thickness S40, the thickness attenuation rate of the sample is obtained, and the thickness attenuation rate of the sample is compared with the specified thickness attenuation rate. If the thickness attenuation rate of the sample is less than the specified thickness attenuation rate, the thickness attenuation of the sample is qualified;

[0036] According to the initial insulation level S10 and the real-time insulation level S20, the real-time insulation level S30 and the real-time insulation level S40, the insulation level attenuation rate of the sample is obtained; the insulation level attenuation rate of the sample is compared with the specified insulation level attenuation rate, if the insulation level attenuation rate of the sample is less than the specified insulation level attenuation rate, the insulation level attenuation of the sample is qualified;

[0037] According to the initial withstand voltage level S10 and the real-time withstand voltage level S20, the real-time withstand voltage level S30 and the real-time withstand voltage level S40, the withstand voltage level attenuation rate of the sample is obtained; the withstand voltage level attenuation rate of the sample is compared with the specified withstand voltage level attenuation rate. If the withstand voltage level attenuation rate of the sample is less than the specified withstand voltage level attenuation rate, the withstand voltage level attenuation of the sample is qualified;

[0038] According to the initial thermal conductivity S10 and the real-time thermal conductivity S20, the real-time thermal conductivity S30 and the real-time thermal conductivity S40, the thermal conductivity attenuation rate of the sample is obtained; the thermal conductivity attenuation rate of the sample is compared with the specified thermal conductivity attenuation rate. If the thermal conductivity attenuation rate of the sample is less than the specified thermal conductivity attenuation rate, the thermal conductivity attenuation of the sample is qualified;

[0039] The battery module buffer pad's ability to withstand cell extrusion is qualified only when the sample thickness attenuation, sample insulation level attenuation, sample voltage resistance level attenuation and sample thermal conductivity attenuation are all qualified.

[0040] Furthermore, in step S11, the number of samples participating in the test at one time is one or several samples. When several samples are tested at the same time, the samples are stacked or laid flat at the same height.

[0041] Furthermore, the thickness of the sample is 1 to 3 mm.

[0042] Furthermore, in step S12, the distance between the edge of the fixture and the edge of the sample that is closer is greater than half the size of the sample.

[0043] Further, in step S23, step S22 is repeated for a number of cycles between 1500 and 2500 times; in step S33, step S32 is repeated for a number of cycles between 1500 and 2500 times; in step S43, step S42 is repeated for a number of cycles between 1500 and 2500 times.

[0044] In summary, the test method for the battery module buffer pad's resistance to cell extrusion provided by the present invention has the following technical effects:

[0045] 1. During the test, the preset upper limit target force and lower limit target force are applied to the sample according to the preset upper limit target force application rate and lower limit target force application rate. The upper limit target force and the lower limit target force are respectively the upper limit value and the lower limit value of the extrusion force applied to the buffer pad by the battery cell in one working stage, and are obtained during the charging and discharging process of the battery cell, respectively. The upper limit target force application rate and the lower limit target force application rate are respectively obtained by the speed at which the battery cell applies the upper limit target force and the lower limit target force to the buffer pad during the charging and discharging process of the battery cell, so that the target force and the target force application rate during the test process are as close as possible to the extrusion force and the extrusion speed applied to the buffer pad during the actual working process of the battery cell, so that the test process is close to the working process of the battery cell, and the test precision and accuracy are improved.

[0046] 2. During the test, first apply the upper limit target force to the sample. After the upper limit target force is maintained for a certain period of time (upper limit target force steady-state maintenance time), slowly withdraw part of the loading force and adjust it to the lower limit target force, and then maintain it for a certain period of time (lower limit target force steady-state maintenance time). This process is as close as possible to the squeezing process of the buffer pad during the charging and discharging process of the battery cell, so as to improve the test precision and accuracy.

[0047] 3. During the test, the software is used to simulate the charging and discharging working state of the battery cell. According to the working process of the battery cell, the extrusion pressure values ​​applied by the battery cell to the buffer pad in at least three different working stages and the target force application rate of the extrusion pressure values ​​applied by the battery cell to the buffer pad are obtained in sequence; each different working stage simulates the charging and discharging state of the battery cell at different periods in its service life cycle, so that the test process and environment are as close as possible to the working process of the battery cell, thereby improving the precision and accuracy of the test.

[0048] 4. During the test, it is necessary to record multiple parameters such as the sample thickness, insulation level, voltage resistance level and thermal conductivity, increase the number of test parameters, analyze the test sample performance from multiple dimensions and angles, and obtain a more reliable battery cell buffer. DETAILED DESCRIPTION

[0049] For better understanding and implementation, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention.

[0050] In addition, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0051] The present invention discloses a testing method for the ability of a battery module buffer pad to withstand cell extrusion, which is used to inspect and detect the insulation ability, pressure resistance and thermal conductivity of a material selected as a battery cell buffer pad. At the same time, the effective thickness of the material as the buffer pad can be determined to avoid using the buffer pad too thick, which affects the volume of the battery module, and to avoid using the buffer pad too thin, which results in poor isolation and buffering effects and affects the performance of the battery module.

[0052] A method for testing the ability of a battery module buffer pad to withstand cell extrusion includes applying a preset target force to a sample at a preset target force application rate, and maintaining the target force applied to the sample until a preset steady-state duration ends. The target force includes an upper target force and a lower target force.

[0053] The upper target force and the lower target force are respectively the upper limit and the lower limit of the extrusion force applied to the buffer pad by the battery cell in a working stage, and are obtained during the charging and discharging process of the battery cell respectively.

[0054] The target force application rate includes an upper limit target force application rate and a lower limit target force application rate, and the upper limit target force and the lower limit target force are linearly loaded according to the upper limit target force application rate and the lower limit target force application rate, respectively.

[0055] The upper limit target force application rate and the lower limit target force application rate are obtained by the speed at which the battery cell applies the upper limit target force and the lower limit target force to the buffer pad during the charging and discharging process of the battery cell, respectively.

[0056] The steady-state duration includes the upper limit target force steady-state maintenance time and the lower limit target force steady-state maintenance time.

[0057] Based on the above scheme, the so-called "working stage" refers to the division of the rated service life of the battery cell into several cycles according to the approximate range of the force generated by the battery cell due to its own expansion under the working state. Each cycle or several cycles with similar working states are combined into one "working stage". Generally, within the rated service life of the battery cell, the "working stage" of the battery cell includes at least "early stage", "middle stage" and "late stage".

[0058] After the battery module is put into use, the period of time it begins to be used is called the "early stage", also known as the initial use stage. In this working stage, the battery capacity is relatively high, usually with performance close to or equal to the nominal capacity, a stable voltage platform, a small voltage drop, a small internal resistance, a high charge and discharge efficiency, and the chemical substances inside the battery cell are highly active, participating in the charge and discharge reactions at a fast rate.

[0059] After the "early stage" comes the "middle stage", also known as the stable use stage. In the "middle stage" of this working stage, the battery capacity gradually decays, but the decay rate is relatively slow. The internal resistance of the battery will gradually increase, which will affect the battery's charging and discharging efficiency and thermal management. During the charging and discharging process of the battery cell, the heat of the battery cell increases.

[0060] After the "middle stage" comes the "late stage", also known as the aging stage. In this working stage, the battery capacity decreases significantly, the battery voltage platform decreases, the battery voltage drops rapidly during discharge, and the internal resistance of the battery increases significantly, which may cause severe battery heating, reduced charging and discharging efficiency, and reduced chemical activity inside the battery cell, resulting in a slowdown in the charging and discharging reaction rate and a large deformation or expansion of the battery.

[0061] Based on the above scheme, the upper limit target force and the lower limit target force are respectively the upper limit value and the lower limit value of the extrusion force applied to the buffer pad by the battery cell in a working stage, and are obtained during the charging and discharging process of the battery cell, respectively. The upper limit target force and the lower limit target force are set for the target force because the battery expands greatly during charging, and a gradually increasing extrusion force is applied to the buffer pad. When charging is completed, or when charging is about to be completed, the extrusion force applied by the battery cell to the buffer pad is the largest, and this maximum value is the upper limit target force. During the discharge process of the battery cell, the expansion of the battery cell will gradually shrink, and the extrusion force of the battery cell on the buffer pad will gradually decrease from the maximum extrusion force. However, after the battery cell expands due to charging, even if the discharge expansion shrinks, it is impossible to return to the original state before use. The battery cell still has a certain extrusion force on the buffer pad, and this minimum extrusion force is the lower limit target force.

[0062] By analogy, the upper limit target force application rate and the lower limit target force application rate are obtained by the speed at which the battery cell applies the upper limit target force and the lower limit target force to the buffer pad during the charging and discharging process of the battery cell, respectively.

[0063] It is worth noting that the above-mentioned upper and lower target forces are generally the average force of the battery cell in this working stage, or the force maintained for the longest period of time, and not the force applied at a certain time in this work.

[0064] In the above scheme, the target force sets an upper limit target force and a lower limit target force, so that the test process is very close to the working state of the battery cell in the working stage, ensuring the accuracy of the test or detection. The upper limit target force application rate and the lower limit target force application rate are obtained by the speed at which the battery cell applies the upper limit target force and the lower limit target force to the buffer pad during the charging and discharging process of the battery cell, respectively, so that the target force and the target force application rate during the test process are as close as possible to the extrusion force and extrusion speed applied to the buffer pad during the actual working process of the battery cell, so that the test process is close to the working process of the battery cell, improving the precision and accuracy of the test.

[0065] In addition, in the above scheme, the upper limit target force and the lower limit target force as well as the upper limit target force application rate and the lower limit target force application rate can be obtained by simulating the working process of the battery cell through relevant software, or can be obtained in the working process of the sample battery cell in the test environment, or can be obtained in related equipment or devices that can simulate the working of the battery cell, or can be obtained by monitoring the working process of the battery cell in the prior art. There is no restriction on the obtaining conditions here.

[0066] In addition, the "linear loading" mentioned in the above scheme generally refers to applying force to the target at a certain speed at a uniform speed, so that the force acting on the target increases at a uniform speed. In this scheme, "the target force application rate includes an upper limit target force application rate and a lower limit target force application rate, and the upper limit target force and the lower limit target force are linearly loaded according to the upper limit target force application rate and the lower limit target force application rate, respectively", that is, applying force to the sample at a uniform speed at the upper limit target force application rate or the lower limit target force application rate until the force acting on the sample reaches the upper limit target force or the lower limit target force, then stop increasing the force, and keep the final force acting on the sample to squeeze the sample.

[0067] In this technical solution, the target force loading method is:

[0068] First, an extrusion force is applied to the sample at an upper limit target force application rate until the extrusion force reaches the upper limit target force, and then the upper limit target force is maintained on the sample until a preset upper limit target force steady-state maintenance time ends.

[0069] After the upper limit target force steady-state maintenance time ends, the upper limit target force is removed at the lower limit target force application rate until the lower limit target force is reached, and the lower limit target force is maintained applied to the specimen until the preset lower limit target force steady-state maintenance time ends.

[0070] During the discharge process of the battery cell, the squeezing pressure of the battery cell on the buffer pad gradually decreases due to the expansion and contraction of the battery cell. The rate at which this squeezing pressure decreases is the so-called "lower limit target force application rate."

[0071] In the above scheme, "upper limit target force steady-state maintenance time" and "lower limit target force steady-state maintenance time" refer to the holding time of the upper limit target force and the lower limit target force applied to the sample, respectively. The "upper limit target force steady-state maintenance time" and "lower limit target force steady-state maintenance time" are set here mainly to simulate that after the battery cell is charged or discharged, the battery cell does not immediately enter the next working state, and the battery cell may not discharge or charge immediately. Setting the "upper limit target force steady-state maintenance time" and "lower limit target force steady-state maintenance time" can simulate the working process of the battery cell and the working state during the working process as much as possible. For example, in actual use, the battery module used in new energy vehicles may not use the car immediately after the battery module is charged, or the battery module will not discharge immediately, and it will generally be used after a period of time.

[0072] Therefore, during the test, the upper limit target force is first applied to the sample. After the upper limit target force is maintained for a certain period of time, part of the loading force is slowly withdrawn to the lower limit target force, and then maintained for a certain period of time. This process is as close as possible to the squeezing process of the buffer pad during the charging and discharging process of the battery cell, which improves the test precision and accuracy.

[0073] In the technical solution, the target force is obtained by at least the squeezing force value of the buffer pad when the battery cell is squeezed in two different working stages.

[0074] During the service life cycle of a battery cell, it is impossible for the battery cell to always maintain one or a similar working state. For example, the battery operation can be divided into at least "early stage", "middle stage" and "late stage", i.e. the initial use stage, stable use stage and aging stage of the battery. Therefore, when testing here, at least target forces in two different use periods are applied to the sample, so that the test conditions and environment are as close as possible to the actual working process of the battery cell, thereby improving the test accuracy.

[0075] In this technical solution, before the sample is tested, at least the initial thickness, initial insulation level, initial withstand voltage level and initial thermal conductivity of the sample need to be recorded. After the target force is applied, at least the real-time thickness, real-time insulation level, real-time withstand voltage level and real-time thermal conductivity of the sample need to be recorded. The performance of the tested sample is analyzed from multiple dimensions and angles to obtain a more reliable battery cell buffer.

[0076] In the technical solution, the test method of the battery module buffer pad's ability to withstand cell extrusion includes the following steps:

[0077] S11. Prepare a sample in the form of a thin sheet.

[0078] S12. Select a fixture and a pressure testing machine. The fixture is installed on the pressure testing machine, and the outer diameter of the fixture is larger than the outer diameter of the specimen.

[0079] S13. Acquire test parameters, simulate the charging and discharging working state of the battery cell through software, and sequentially acquire the extrusion pressure values ​​applied by the battery cell to the buffer pad in at least three different working stages and the extrusion pressure application rate of the extrusion pressure values ​​applied by the battery cell to the buffer pad according to the working process of the battery cell. The extrusion pressure application rate is used as the target force application rate during the test.

[0080] S14. Obtain the sample parameters before the test, including the initial thickness S10, initial insulation level S10, initial withstand voltage level S10 and initial thermal conductivity S10 of the sample.

[0081] S21. Preloading of the first stage test: Place the specimen in the middle of the fixture, set the target force for the first stage, and start the pressure testing machine so that the fixture contacts the specimen.

[0082] S22, first stage test loading: according to the extrusion pressure values ​​and extrusion pressure application rates respectively obtained by the battery cell in at least three different working stages in S13, set the first upper limit target force, the first upper limit target force application rate, the first upper limit target force steady-state maintenance time, the first lower limit target force and the first lower limit target force application rate and the first lower limit target force steady-state maintenance time, start the pressure testing machine again, apply the first upper limit target force to the specimen at the first upper limit target force application rate, and maintain the first upper limit target force for the first upper limit target force steady-state maintenance time; after the first upper limit target force steady-state maintenance time ends, cancel the first upper limit target force to the first lower limit target force at the first lower limit target force application rate, and maintain the first lower limit target force for the first lower limit target force steady-state maintenance time until the first lower limit target force steady-state maintenance time ends.

[0083] S23. Repeat step S22 for several cycles. After the end, remove the sample from the pressure testing machine and measure the sample after the first stage test to obtain the real-time thickness S20, real-time insulation level S20, real-time withstand voltage level S20 and real-time thermal conductivity S20.

[0084] S31, second stage test preloading: place the sample that has passed step S23 in the middle of the fixture again, set the target force for the second stage, start the pressure testing machine, and make the fixture contact with the sample.

[0085] S32, second stage test loading: according to the extrusion pressure values ​​respectively obtained by the battery cell in at least three different working stages in S13, select the extrusion pressure value corresponding to the working stage after the working stage corresponding to the extrusion pressure value adopted in step S22, and the extrusion pressure application rate in the corresponding working stage selected in this step, set the second upper limit target force, the second upper limit target force application rate, the second upper limit target force steady-state maintenance time, the second lower limit target force and the second lower limit target force application rate and the second lower limit target force steady-state maintenance time, start the pressure testing machine again, apply the second upper limit target force to the specimen at the second upper limit target force application rate, and maintain the second upper limit target force for the second upper limit target force steady-state maintenance time; after the second upper limit target force steady-state maintenance time ends, cancel the second upper limit target force to the second lower limit target force at the second lower limit target force application rate, and maintain the second lower limit target force for the second lower limit target force steady-state maintenance time until the second lower limit target force steady-state maintenance time ends.

[0086] S33. Repeat step S32 for several cycles. After completion, remove the sample from the pressure testing machine and measure the sample after the second stage test to obtain the real-time thickness S30, real-time insulation level S30, real-time withstand voltage level S30 and real-time thermal conductivity S30.

[0087] S41, third stage test preloading: place the sample that has passed step S33 in the middle of the fixture again, set the target force for the third stage, start the pressure testing machine, and make the fixture contact with the sample.

[0088] S42, third stage test loading: according to the extrusion pressure values ​​respectively obtained by the battery cell in at least three different working stages in S13, the extrusion pressure value corresponding to the working stage following the working stage corresponding to the extrusion pressure value adopted in step S32 and the extrusion pressure application rate in the corresponding working stage selected in this step are selected, and the third upper limit target force, the third upper limit target force application rate, the third upper limit target force steady-state maintenance time, the third lower limit target force and the third lower limit target force application rate and the third lower limit target force steady-state maintenance time are set, and the pressure testing machine is started again, and the third upper limit target force is applied to the specimen at the third upper limit target force application rate, and the third upper limit target force is maintained for the third upper limit target force steady-state maintenance time; after the third upper limit target force steady-state maintenance time ends, the third upper limit target force is revoked to the third lower limit target force at the third lower limit target force application rate, and the third lower limit target force is maintained for the third lower limit target force steady-state maintenance time until the third lower limit target force steady-state maintenance time ends.

[0089] S43. Repeat step S42 for several cycles. After the end, remove the sample from the pressure testing machine and measure the sample after the third stage test to obtain the real-time thickness S40, real-time insulation level S40, real-time withstand voltage level S40 and real-time thermal conductivity S40.

[0090] S51. Analyze the extrusion resistance of the sample.

[0091] In the above test steps, the software is used to simulate the charging and discharging working state of the battery cell. According to the working process of the battery cell, the extrusion pressure values ​​applied by the battery cell to the buffer pad in at least three different working stages and the target force application rate of the extrusion pressure values ​​applied by the battery cell to the buffer pad are obtained in sequence; each different working stage simulates the charging and discharging state of the battery cell at different periods in its service life cycle, so that the test process and environment are as close as possible to the working process of the battery cell, thereby improving the precision and accuracy of the test.

[0092] In the above test steps, by using a thin sheet-shaped sample, the sample shape and structure are made as close as possible to the actual buffer pad in use, thereby improving the test accuracy.

[0093] The above-mentioned testing process is more in line with the actual working conditions of the battery cell and can more accurately determine whether the cyclic extrusion fatigue resistance of the battery module buffer pad meets the performance requirements of the battery module.

[0094] In the above test steps, step S22 is repeated for several cycles, step S32 is repeated for several cycles, and step S42 is repeated for several cycles, which can simulate the repeated charge and discharge process of the battery cell in a certain period of use.

[0095] In the above test steps, the performance of the tested samples is analyzed from multiple dimensions and angles to obtain a more reliable battery cell buffer.

[0096] The analysis method of the sample's extrusion resistance is:

[0097] According to the initial thickness S10 and the real-time thickness S20, the real-time thickness S30 and the real-time thickness S40, the thickness attenuation rate of the sample is obtained, and the thickness attenuation rate of the sample is compared with the specified thickness attenuation rate. If the thickness attenuation rate of the sample is less than the specified thickness attenuation rate, the thickness attenuation of the sample is qualified;

[0098] According to the initial insulation level S10 and the real-time insulation level S20, the real-time insulation level S30 and the real-time insulation level S40, the insulation level attenuation rate of the sample is obtained; the insulation level attenuation rate of the sample is compared with the specified insulation level attenuation rate, if the insulation level attenuation rate of the sample is less than the specified insulation level attenuation rate, the insulation level attenuation of the sample is qualified;

[0099] According to the initial withstand voltage level S10 and the real-time withstand voltage level S20, the real-time withstand voltage level S30 and the real-time withstand voltage level S40, the withstand voltage level attenuation rate of the sample is obtained; the withstand voltage level attenuation rate of the sample is compared with the specified withstand voltage level attenuation rate. If the withstand voltage level attenuation rate of the sample is less than the specified withstand voltage level attenuation rate, the withstand voltage level attenuation of the sample is qualified;

[0100] According to the initial thermal conductivity S10 and the real-time thermal conductivity S20, the real-time thermal conductivity S30 and the real-time thermal conductivity S40, the thermal conductivity attenuation rate of the sample is obtained; the thermal conductivity attenuation rate of the sample is compared with the specified thermal conductivity attenuation rate. If the thermal conductivity attenuation rate of the sample is less than the specified thermal conductivity attenuation rate, the thermal conductivity attenuation of the sample is qualified;

[0101] The battery module buffer pad's ability to withstand cell extrusion is qualified only when the sample thickness attenuation, sample insulation level attenuation, sample voltage resistance level attenuation and sample thermal conductivity attenuation are all qualified.

[0102] In the aforementioned step S11, the number of samples participating in the test at one time is one or more samples. When more than one sample is tested at the same time, the samples are stacked or laid flat at the same height. Using multiple samples for testing at one time improves the test efficiency, increases the test comparison ratio, and improves the test accuracy.

[0103] During the test, the thickness of the sample was 1 to 3 mm, which is close to the thickness of the battery cells in the battery module, improving the test accuracy.

[0104] In the aforementioned step S12, the distance between the edge of the fixture and the edge of the sample that is closer is greater than half the size of the sample, so as to ensure that the tested sample is subjected to uniform extrusion force.

[0105] In the aforementioned step S23, the number of repetitions of step S22 is between 1500 and 2500. In step S33, the number of repetitions of step S32 is between 1500 and 2500. In step S43, the number of repetitions of step S42 is between 1500 and 2500. The number of cycles is close to or similar to the number of charge and discharge times in the working cycle of the battery cell, thereby improving the test accuracy.

[0106] In order to facilitate further understanding of the present solution by those skilled in the art, a specific embodiment of the testing process is proposed below.

[0107] Step 1: Preparation before testing

[0108] Step A1, prepare a sample. The sample is in the form of a thin sheet with a size of 100*200*2mm. The number of samples tested this time is one sheet.

[0109] Step A2, select a fixture and a pressure testing machine, the fixture is a circular pressure plate with a diameter of 300 mm.

[0110] Step A3, obtain the test parameters, simulate the charging and discharging working state of the battery cell through software, and obtain the extrusion pressure values ​​applied to the buffer pad in the three different working stages of "early", "middle" and "late" in the working life cycle of the battery cell in sequence according to the working process of the battery cell, as well as the extrusion pressure application rate of the extrusion pressure values ​​applied by the battery cell to the buffer pad. The extrusion pressures applied in the three different working stages are the first upper limit target force, the second upper limit target force and the third upper limit target force, respectively, and the extrusion pressure application rates are the first upper limit target force application rate, the second upper limit target force application rate and the third upper limit target force application rate. And the working stage corresponding to the second upper limit target force is the working stage behind the working stage corresponding to the first upper limit target force, and the working stage corresponding to the third upper limit target force is the working stage behind the working stage corresponding to the second upper limit target force. Similarly, the working stages corresponding to the first upper limit target force application rate, the second upper limit target force application rate and the third upper limit target force application rate are also in accordance with the front and back order in the working stage of the battery cell.

[0111] Step A4: Obtain the sample parameters before the test, including the initial thickness S10 (D 0 =2mm), initial insulation grade S10, initial withstand voltage grade S10 and initial thermal conductivity S10.

[0112] Step 2: Testing

[0113] Step B1, first stage test preloading: place the sample in the middle of the fixture, set the first stage target force to 1000N, start the pressure testing machine, and make the fixture contact with the sample.

[0114] Step B2, first stage test loading: according to the extrusion pressure value and target force application rate obtained in step A3, set the first upper limit target force of 5000N, the first upper limit target force application rate of 70N / s, the first upper limit target force steady-state maintenance time of 10s, the first lower limit target force of 1000N, the first lower limit target force application rate of 70N / s and the first lower limit target force steady-state maintenance time of 10s. Start the pressure testing machine again, apply the first upper limit target force of 5000N to the specimen at the first upper limit target force application rate of 70N / s, and maintain the first upper limit target force of 5000N for the first upper limit target force steady-state maintenance time of 10s. After the first upper limit target force steady-state maintenance time of 10s ends, cancel the first upper limit target force of 5000N to the first lower limit target force of 1000N at the first lower limit target force application rate of 70N / s, and maintain the first lower limit target force of 1000N for the first lower limit target force steady-state maintenance time of 10s until the first lower limit target force steady-state maintenance time of 10s ends.

[0115] Step B3 and step B2 are repeated for 2000 cycles. After the cycle is completed, the sample is removed from the pressure testing machine, and the sample after the first stage test is measured to obtain the real-time thickness S20, real-time insulation level S20, real-time withstand voltage level S20 and real-time thermal conductivity S20.

[0116] Step B4, second stage test preloading: place the sample after step B3 in the middle of the fixture again, set the target force of the second stage to 5000N, start the pressure testing machine, and make the fixture contact with the sample.

[0117] Step B5, second stage test loading: according to the extrusion pressure value and target force application rate obtained in step A3, select the extrusion pressure value corresponding to the subsequent working stage of the extrusion pressure value corresponding to the working stage adopted in step B2, and the extrusion pressure application rate in the corresponding working stage selected in this step, set the second upper limit target force of 10000N, the second upper limit target force application rate of 85N / s, the second upper limit target force steady-state maintenance time of 10s, the second lower limit target force of 5000N, the second lower limit target force application rate of 85N / s, and the second lower limit target force steady-state maintenance time of 10s. Start the pressure testing machine again, apply the second upper limit target force of 10000N to the sample at the second upper limit target force application rate of 85N / s, and maintain the second upper limit target force of 10000N and the second upper limit target force steady-state maintenance time of 10s. After the second upper limit target force steady-state maintaining time of 10s ends, the second upper limit target force of 10000N is reduced to the second lower limit target force of 5000N at the second lower limit target force application rate of 85N / s, and the second lower limit target force of 5000N is maintained for 10s until the second lower limit target force steady-state maintaining time of 10s ends.

[0118] Step B6, repeat step B5 2000 times. After completion, remove the sample from the pressure testing machine and measure the sample after the second stage test to obtain the real-time thickness S30, real-time insulation level S30, real-time withstand voltage level S30 and real-time thermal conductivity S30.

[0119] Step B7, third stage test preloading: place the sample after step B6 in the middle of the fixture again, set the target force of the third stage to 10000N, start the pressure testing machine, and make the fixture contact with the sample;

[0120] Step B8, third stage test loading: according to the extrusion pressure value and target force application rate obtained in step A3, select the extrusion pressure value corresponding to the subsequent working stage of the extrusion pressure value corresponding to the working stage adopted in step B5, and the extrusion pressure application rate in the corresponding working stage selected in this step, set the third upper limit target force to 20000N, the third upper limit target force application rate to 170N / s, the third upper limit target force steady-state maintenance time to 10s, the third lower limit target force to 10000N, the third lower limit target force application rate to 170N / s, and the third lower limit target force steady-state maintenance time to 10s, and start the pressure testing machine again. Apply the third upper limit target force of 20000N to the specimen at the third upper limit target force application rate of 170N / s, and maintain the third upper limit target force of 20000N and the third upper limit target force steady-state maintenance time to 10s. After the third upper limit target force steady-state maintaining time of 10s ends, the third upper limit target force of 20000N is reduced to the third lower limit target force of 10000N at the third lower limit target force application rate of 170N / s, and the third lower limit target force of 10000N is maintained for 10s until the third upper limit target force steady-state maintaining time ends.

[0121] Step B9 repeats step B8 for several cycles. After completion, the sample is removed from the pressure testing machine and the sample is measured after the third stage test to obtain the real-time thickness S40, real-time insulation level S40, real-time withstand voltage level S40 and real-time thermal conductivity S40.

[0122] The third step is to analyze the extrusion resistance of the sample.

[0123] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical schemes composed of any combination of the above-mentioned technical features. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims

1. A method for testing the ability of a battery module buffer pad to withstand cell extrusion, characterized in that: The method comprises applying a preset target force to the sample at a preset target force application rate, and maintaining the state where the target force is applied to the sample until a preset steady-state duration ends; The target force includes an upper limit target force and a lower limit target force; The upper limit target force and the lower limit target force are respectively the upper limit value and the lower limit value of the extrusion force applied to the buffer pad by the battery cell in a working stage, and are respectively obtained during the charging and discharging process of the battery cell; The target force application rate includes an upper limit target force application rate and a lower limit target force application rate, and the upper limit target force and the lower limit target force are linearly loaded according to the upper limit target force application rate and the lower limit target force application rate respectively; The upper limit target force application rate and the lower limit target force application rate are obtained by the speed at which the battery cell applies the upper limit target force and the lower limit target force to the buffer pad during the charging and discharging process of the battery cell, respectively; The steady-state duration includes an upper limit target force steady-state maintaining time and a lower limit target force steady-state maintaining time.

2. The method for testing the battery module buffer pad's ability to withstand cell extrusion according to claim 1, characterized in that: The target force loading method is: First, applying an extrusion force to the sample at the upper limit target force application rate until the extrusion force reaches the upper limit target force, and then maintaining the upper limit target force applied to the sample until the preset upper limit target force steady-state maintenance time ends; After the upper limit target force steady-state maintenance time ends, the upper limit target force is removed at the lower limit target force application rate until the lower limit target force is reached, and the lower limit target force is maintained applied to the sample until the preset lower limit target force steady-state maintenance time ends.

3. The method for testing the battery module buffer pad's ability to withstand cell extrusion according to claim 1, characterized in that: The target force is obtained by at least the squeezing force value of the buffer pad being squeezed by the battery cell in two different working stages of the battery cell.

4. The method for testing the battery module buffer pad's ability to withstand cell extrusion according to claim 1, characterized in that: Before the sample is tested, at least the initial thickness, initial insulation level, initial withstand voltage level and initial thermal conductivity of the sample need to be recorded; After the target force is applied, at least the real-time thickness, real-time insulation level, real-time withstand voltage level and real-time thermal conductivity of the sample need to be recorded.

5. The method for testing the battery module buffer pad's ability to withstand cell extrusion according to any one of claims 1 to 4, characterized in that: The following steps are involved: S11, preparing a sample, wherein the sample is in a sheet shape; S12, selecting a fixture and a pressure testing machine, wherein the fixture is installed on the pressure testing machine, and the outer diameter of the fixture is larger than the outer diameter of the sample; S13, obtaining test parameters, simulating the charging and discharging working state of the battery cell through software, and sequentially obtaining the extrusion force values ​​applied by the battery cell to the buffer pad in at least three different working stages according to the working process of the battery cell, and the extrusion force application rate of the extrusion force values ​​applied by the battery cell to the buffer pad, and the extrusion force application rate is used as the target force application rate in the test process; S14, obtaining the sample parameters before the test, including the initial thickness S10, initial insulation level S10, initial withstand voltage level S10 and initial thermal conductivity S10 of the sample; S21, first stage test preloading: placing the sample in the middle of the fixture, setting the target force of the first stage, and starting the pressure testing machine so that the fixture contacts the sample; S22, first stage test loading: according to the extrusion pressure values ​​and extrusion pressure application rates respectively obtained by the battery cell in at least three different working stages in S13, set the first upper limit target force, the first upper limit target force application rate, the first upper limit target force steady-state maintenance time, the first lower limit target force, the first lower limit target force application rate and the first lower limit target force steady-state maintenance time, start the pressure testing machine again, apply the first upper limit target force to the sample at the first upper limit target force application rate, and maintain the first upper limit target force for the first upper limit target force steady-state maintenance time; After the first upper limit target force steady-state maintenance time ends, the first upper limit target force is withdrawn to the first lower limit target force at the first lower limit target force application rate, and the first lower limit target force is maintained to maintain the first lower limit target force steady-state maintenance time until the first lower limit target force steady-state maintenance time ends; S23, repeat step S22 for several cycles, after which the sample is removed from the pressure testing machine, and the sample after the first stage test is measured to obtain the real-time thickness S20, the real-time insulation level S20, the real-time withstand voltage level S20 and the real-time thermal conductivity S20; S31, second stage test preloading: placing the sample after step S23 in the middle of the fixture again, setting the target force of the second stage, and starting the pressure testing machine so that the fixture contacts the sample; S32, second stage test loading: according to the extrusion pressure values ​​respectively obtained by the battery cell in at least three different working stages in S13, the extrusion pressure value corresponding to the working stage following the working stage corresponding to the extrusion pressure value adopted in step S22 and the extrusion pressure application rate in the corresponding working stage selected in this step are selected, and the second upper limit target force, the second upper limit target force application rate, the second upper limit target force steady-state maintenance time, the second lower limit target force and the second lower limit target force application rate and the second lower limit target force steady-state maintenance time are set, and the pressure testing machine is started again, and the second upper limit target force is applied to the sample at the second upper limit target force application rate, and the second upper limit target force is maintained for the second upper limit target force steady-state maintenance time; After the second upper limit target force steady-state maintenance time ends, the second upper limit target force is withdrawn to the second lower limit target force at the second lower limit target force application rate, and the second lower limit target force is maintained to maintain the second lower limit target force steady-state maintenance time until the second lower limit target force steady-state maintenance time ends; S33, repeat step S32 for several cycles, after which the sample is removed from the pressure testing machine, and the sample after the second stage test is measured to obtain the real-time thickness S30, the real-time insulation level S30, the real-time withstand voltage level S30 and the real-time thermal conductivity S30; S41, third stage test preloading: placing the sample after step S33 in the middle of the fixture again, setting the target force of the third stage, and starting the pressure testing machine so that the fixture contacts the sample; S42, third stage test loading: according to the extrusion pressure values ​​respectively obtained by the battery cell in at least three different working stages in S13, the extrusion pressure value corresponding to the working stage following the working stage corresponding to the extrusion pressure value adopted in step S32 and the extrusion pressure application rate in the corresponding working stage selected in this step are selected, and the third upper limit target force, the third upper limit target force application rate, the third upper limit target force steady-state maintenance time, the third lower limit target force and the third lower limit target force application rate and the third lower limit target force steady-state maintenance time are set, and the pressure testing machine is started again, and the third upper limit target force is applied to the sample at the third upper limit target force application rate, and the third upper limit target force is maintained for the third upper limit target force steady-state maintenance time; After the third upper limit target force steady-state maintenance time ends, the third upper limit target force is withdrawn to the third lower limit target force at the third lower limit target force application rate, and the third lower limit target force is maintained to maintain the third lower limit target force steady-state maintenance time until the third lower limit target force steady-state maintenance time ends; S43, repeat step S42 for several cycles, after which the sample is removed from the pressure testing machine, and the sample after the third stage test is measured to obtain the real-time thickness S40, the real-time insulation level S40, the real-time withstand voltage level S40 and the real-time thermal conductivity S40; S51. Analyze the extrusion resistance of the sample.

6. The method for testing the battery module buffer pad's ability to withstand cell extrusion according to claim 5, characterized in that: The analysis method of the sample's extrusion resistance is as follows: According to the initial thickness S10 and the real-time thickness S20, the real-time thickness S30 and the real-time thickness S40, the thickness attenuation rate of the sample is obtained, and the thickness attenuation rate of the sample is compared with the specified thickness attenuation rate. If the thickness attenuation rate of the sample is less than the specified thickness attenuation rate, the thickness attenuation of the sample is qualified; According to the initial insulation level S10 and the real-time insulation level S20, the real-time insulation level S30 and the real-time insulation level S40, the insulation level attenuation rate of the sample is obtained; the insulation level attenuation rate of the sample is compared with the specified insulation level attenuation rate, if the insulation level attenuation rate of the sample is less than the specified insulation level attenuation rate, the insulation level attenuation of the sample is qualified; According to the initial withstand voltage level S10 and the real-time withstand voltage level S20, the real-time withstand voltage level S30 and the real-time withstand voltage level S40, the withstand voltage level attenuation rate of the sample is obtained; the withstand voltage level attenuation rate of the sample is compared with the specified withstand voltage level attenuation rate. If the withstand voltage level attenuation rate of the sample is less than the specified withstand voltage level attenuation rate, the withstand voltage level attenuation of the sample is qualified; According to the initial thermal conductivity S10 and the real-time thermal conductivity S20, the real-time thermal conductivity S30 and the real-time thermal conductivity S40, the thermal conductivity attenuation rate of the sample is obtained; Compare the thermal conductivity attenuation rate of the sample with the specified thermal conductivity attenuation rate. If the thermal conductivity attenuation rate of the sample is less than the specified thermal conductivity attenuation rate, the thermal conductivity attenuation of the sample is qualified. The battery module buffer pad's ability to withstand cell extrusion is qualified only when the sample thickness attenuation, sample insulation level attenuation, sample voltage resistance level attenuation and sample thermal conductivity attenuation are all qualified.

7. The method for testing the battery module buffer pad's ability to withstand cell extrusion according to claim 5, characterized in that: In step S11, the number of samples participating in the test at one time is one or more samples. When more than one sample is tested at the same time, the samples are stacked or laid flat at the same height.

8. The method for testing the battery module buffer pad's ability to withstand cell extrusion according to claim 5, characterized in that: The thickness of the test specimen is 1 to 3 mm.

9. The method for testing the battery module buffer pad's ability to withstand cell extrusion according to claim 5, characterized in that: In step S12, the distance between the edge of the fixture and the edge of the sample that is closer is greater than half the size of the sample.

10. The method for testing the battery module buffer pad's ability to withstand cell extrusion according to claim 5, characterized in that: In step S23, step S22 is repeated for a number of cycles between 1500 and 2500 times; in step S33, step S32 is repeated for a number of cycles between 1500 and 2500 times; in step S43, step S42 is repeated for a number of cycles between 1500 and 2500 times.