Lithium battery pseudo soldering detection method

Abstract

The lithium battery pseudo soldering detection method comprises the following steps: preparing a plurality of lithium batteries to be detected; processing the plurality of to-be-tested lithium batteries according to a first preset processing method, so that the welding degrees of each roll core and the positive electrode bus bar are different; detecting the internal resistance from a first position point to a second position point in each roll core and positive electrode bus bar to obtain a plurality of first internal resistance values of each group of to-be-detected lithium batteries, and analyzing the plurality of first internal resistance values in each group of to-be-detected lithium batteries according to a six-sigma method to obtain a first standard internal resistance value; processing the plurality of to-be-tested lithium batteries according to a second preset processing method, so that the welding degrees of each roll core and the negative electrode bus bar are different; and detecting the internal resistance from the first position point to the third position point in each roll core and the negative electrode bus bar to obtain a plurality of second internal resistance values of each group of to-be-detected lithium batteries, and analyzing the plurality of second internal resistance values in each group of to-be-detected lithium batteries according to a six-sigma method to obtain a second standard internal resistance value. According to the invention, the defect of pseudo soldering detection by a destructive tension test method can be avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery detection, and in particular to a method for detecting cold solder joints in lithium batteries. Background Art

[0002] Lithium batteries are a type of battery that uses lithium metal or lithium alloy as positive / negative electrode materials and non-aqueous electrolyte solutions. They are widely used in modern electronic devices, including mobile phones, laptops, electric vehicles, etc. Lithium batteries are popular because they have high energy density, long service life, and low self-discharge rate.

[0003] Detecting whether lithium batteries have cold solder joints is a key step in verifying the quality of lithium batteries. In related technologies, destructive tensile testing methods are often used for testing. The principle is that the tensile machine outputs a certain tensile force to pull the battery body and the busbar apart, and the cold solder joint of the lithium battery is judged based on the observed degree of separation. Although this method can verify the degree of cold solder joints in lithium batteries, it is defective because it involves damage to the structural parts of the lithium battery. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a lithium battery cold solder joint detection method, which can determine whether a lithium battery has a cold solder joint without using a destructive tensile test method.

[0005] The first aspect of the present application provides a lithium battery cold soldering detection method, comprising:

[0006] Preparing a plurality of lithium batteries to be tested and grouping the plurality of lithium batteries to be tested, wherein the plurality of lithium batteries to be tested include: a winding core, a positive busbar, and a negative busbar;

[0007] Processing each group of the lithium batteries to be tested according to a first preset processing method, so that the welding degree between the winding core and the positive busbar of each group of the lithium batteries to be tested is different;

[0008] Detecting the internal resistance from the first position point to the second position point in the winding core and the positive busbar of each group of the lithium batteries to be tested, obtaining multiple first internal resistance values ​​of each group of the lithium batteries to be tested, and analyzing the multiple first internal resistance values ​​in each group of the lithium batteries to be tested according to the Six Sigma method to obtain a first standard internal resistance value;

[0009] Processing each group of the lithium batteries to be tested according to a second preset processing method, so that the welding degree between the winding core and the negative electrode busbar of each group of the lithium batteries to be tested is different;

[0010] Detect the internal resistance of the winding core of each group of the lithium batteries to be tested from the first position point to the third position point in the negative electrode busbar to obtain multiple second internal resistance values ​​of each group of the lithium batteries to be tested, and analyze the multiple second internal resistance values ​​in each group of the lithium batteries to be tested according to the Six Sigma method to obtain a second standard internal resistance value.

[0011] Furthermore, in one preferred embodiment, the welding degree between the winding core and the positive busbar of each group of lithium batteries to be tested is different, including:

[0012] The winding core and the positive busbar in the lithium battery to be tested in the current group are pressed flat against each other but not welded; and / or

[0013] The winding core and the positive busbar in the lithium battery to be tested in the current group have two welding tracks, and the welding length is equal to half of the length of the welding track; and / or

[0014] The winding core and the positive busbar in the lithium battery to be tested in the current group have two welding tracks, and the welding length is equal to the welding track length; and / or

[0015] In the lithium battery to be tested in the current group, the winding core and the positive busbar have two welding tracks, but the welding is not firm.

[0016] Further, in one preferred embodiment, the analyzing of the first internal resistance values ​​in each group of the lithium batteries to be tested according to the Six Sigma method to obtain the first standard internal resistance value includes:

[0017] Generate a positive terminal resistance test table and a positive terminal resistance test diagram according to the plurality of first internal resistance values ​​in each group of the lithium batteries to be tested;

[0018] Based on the dispersion and variance of the first internal resistance value, combined with the positive terminal resistance test table and the positive terminal resistance test diagram, the internal resistance standard of the winding core and the positive bus bar is established to obtain a first standard internal resistance value.

[0019] Further, in one preferred embodiment, the detecting of the internal resistance from the first position point to the second position point in the winding core and the positive busbar of each group of the lithium batteries to be tested to obtain multiple groups of first internal resistance values ​​corresponding to different welding degrees includes:

[0020] Calibrate internal resistance tester;

[0021] Using a first probe of the internal resistance tester to contact the first position point;

[0022] Using a second probe of the internal resistance tester to contact the second position point;

[0023] A plurality of groups of first internal resistance values ​​corresponding to different welding degrees are obtained.

[0024] Further, in one preferred embodiment, the first position point is any position point in the foil tab area in the winding core;

[0025] The second position point is any position point of the welding area in the positive electrode bus bar.

[0026] Further, in one preferred embodiment, the welding degree between the winding core and the negative electrode busbar of each group of the lithium batteries to be tested is different, including:

[0027] The winding core and the negative electrode busbar in the lithium battery to be tested in the current group are pressed flat against each other but not welded; and / or

[0028] The winding core and the negative electrode busbar in the lithium battery to be tested in the current group have two welding tracks, and the welding length is equal to half of the length of the welding track; and / or

[0029] The winding core and the negative electrode busbar in the lithium battery to be tested in the current group have two welding tracks, and the welding length is equal to the welding track length; and / or

[0030] In the lithium battery to be tested in the current group, the winding core and the negative electrode busbar have two welding tracks, but the welding is not firm.

[0031] Further, in one preferred embodiment, the analyzing of the plurality of second internal resistance values ​​in each group of the lithium batteries to be tested according to the Six Sigma method to obtain the second standard internal resistance value comprises:

[0032] Generate a negative terminal resistance test table and a negative terminal resistance test diagram according to the plurality of second internal resistance values ​​in each group of the lithium batteries to be tested;

[0033] Based on the dispersion and variance of the second internal resistance value, combined with the negative terminal resistance test table and the negative terminal resistance test diagram, the internal resistance standard of the winding core and the negative bus bar is established to obtain a second standard internal resistance value.

[0034] Further, in one preferred embodiment, the detecting of the internal resistance from the first position point to the third position point in the winding core and the negative electrode busbar of each group of the lithium battery to be tested to obtain multiple groups of second internal resistance values ​​corresponding to different welding degrees includes:

[0035] Calibrate internal resistance tester;

[0036] Using a first probe of the internal resistance tester to contact the first position point;

[0037] Using a second probe of the internal resistance tester to contact the third position point;

[0038] A plurality of groups of second internal resistance values ​​corresponding to different welding degrees are obtained.

[0039] Further, in one preferred embodiment, the first position point is any position point in the foil tab area in the winding core;

[0040] The third position point is any position point of the welding area in the negative electrode bus bar.

[0041] Furthermore, in one preferred embodiment, the number of the lithium batteries to be tested in each group is at least 5.

[0042] The technical solution of the present application includes: preparing a number of lithium batteries to be tested, wherein the number of lithium batteries to be tested include: a winding core, a positive busbar and a negative busbar; processing the number of lithium batteries to be tested according to a first preset processing method so that the degree of welding between each winding core and the positive busbar is different; detecting the internal resistance from a first position point to a second position point in each winding core and the positive busbar to obtain multiple first internal resistance values ​​of each group of lithium batteries to be tested, and analyzing the multiple first internal resistance values ​​in each group of lithium batteries to be tested according to the six sigma method to obtain a first standard internal resistance value; processing the number of lithium batteries to be tested according to a second preset processing method so that the degree of welding between each winding core and the negative busbar is different; detecting the internal resistance from a first position point to a third position point in each winding core and the negative busbar to obtain multiple second internal resistance values ​​of each group of lithium batteries to be tested, and analyzing the multiple second internal resistance values ​​in each group of lithium batteries to be tested according to the six sigma method to obtain a second standard internal resistance value. The present application can obtain multiple groups of first internal resistance values ​​and second internal resistance values ​​by detecting batteries to be tested with different welding degrees. These internal resistance values ​​are analyzed according to the Six Sigma method to obtain the first internal resistance standard value and the second standard internal resistance value. Subsequent testing personnel can then detect whether there is a cold solder joint in the positive and negative electrodes of the lithium battery to be tested based on the first internal resistance standard value and the second standard internal resistance value, thereby effectively avoiding the defect of detecting the cold solder joint by the destructive tensile test method. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0044] Figure 1 It is a flow chart of a lithium battery cold solder joint detection method shown in an embodiment of the present application;

[0045] Figure 2 is a schematic diagram of welding processing of the positive terminal of a lithium battery to be tested shown in one embodiment of the present application;

[0046] Figure 3 is a schematic diagram of welding processing of the negative terminal of a lithium battery to be tested shown in one embodiment of the present application;

[0047] Figure 4 This is a positive terminal resistance test diagram shown in an embodiment of the present application;

[0048] Figure 5 This is a negative terminal resistance test diagram shown in an embodiment of the present application. DETAILED DESCRIPTION

[0049] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively with reference to the accompanying drawings. The preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0050] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

[0051] 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 herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0052] In related technologies, destructive tensile testing is often used for detection. The principle is that the tensile machine outputs a certain tensile force to separate the battery body and the busbar, and the degree of separation is observed to determine the degree of cold soldering of the lithium battery. Although this method can verify the degree of cold soldering of lithium batteries, it involves damage to the structural parts of the lithium battery, resulting in defects in this method.

[0053] Therefore, in order to solve the above technical problems, the present application provides a lithium battery cold solder joint detection method, which can determine whether a lithium battery has a cold solder joint without using a destructive tensile test method.

[0054] The technical solution of the present application is described in detail below with reference to the accompanying drawings.

[0055] Figure 1A schematic diagram of the process of a lithium battery cold solder joint detection method in an embodiment of the present invention is shown.

[0056] See also Figure 1 , a lithium battery cold soldering detection method, comprising the following steps:

[0057] Step S110, preparing a plurality of lithium batteries to be tested, and grouping the plurality of lithium batteries to be tested, wherein the plurality of lithium batteries to be tested include: a winding core, a positive busbar, and a negative busbar.

[0058] It should be noted that the lithium battery to be tested is a lithium battery. The lithium battery to be tested in this embodiment includes components such as a winding core, a positive bus bar and a negative bus bar. At this time, the lithium battery to be tested is in a state to be tested, and the winding core and the positive bus bar, and the winding core and the negative bus bar are still in an unwelded state.

[0059] The core is the core structure of lithium-ion batteries, which is composed of alternating layers of positive electrodes, negative electrodes and separators, and is finally wound into a cylindrical or flat shape. The design of the core directly affects the capacity, safety and cycle life of the battery.

[0060] The positive busbar is a metal component that connects the positive electrode active material layer to the external circuit of the battery, usually made of aluminum. Its function is to transfer current from the positive electrode to the external circuit.

[0061] Negative busbar, similar to the positive busbar, is a metal component that connects the negative active material layer to the external circuit of the battery, usually made of copper. Its function is to transfer current from the negative electrode to the external circuit.

[0062] Cold soldering refers to poor welding phenomenon that occurs during the welding process, which may lead to increased contact resistance and affect battery performance. During the battery manufacturing process, the positive busbar and the negative busbar need to be connected to the external circuit of the battery through welding. If a cold soldering occurs during the welding process. Studies have shown that the increase in the positive electrode internal resistance and the negative electrode internal resistance may be caused by cold soldering. When the welding between the positive or negative electrode and the busbar is poor, the contact resistance will increase, thereby increasing the positive electrode internal resistance or the negative electrode internal resistance. Therefore, due to this phenomenon, the positive electrode internal resistance and the negative electrode internal resistance of the lithium battery to be tested can be detected to determine whether the current lithium battery to be tested has a cold soldering phenomenon, which can well avoid the problem of the defect of detecting cold soldering by the destructive tensile test method.

[0063] In this embodiment, the number of lithium batteries to be tested in each group is at least 5, that is, the number of winding cores, positive bus bars, and negative bus bars are all at least 5, wherein a single winding core, positive bus bar, and negative bus bar form a pair, that is, each group in this embodiment has at least 5 pairs.

[0064] It should be noted that, in order to better understand the technical solution of the present application, a specific case is used to explain the technical solution starting from this step. After processing a number of lithium batteries to be tested in step S110, four groups of lithium batteries to be tested are obtained, namely, group 1, group 2, group 3 and group 4, and the number of lithium batteries to be tested in each group is 5.

[0065] Step S120: Process each group of lithium batteries to be tested according to a first preset processing method, so that the welding degree between the winding core and the positive busbar of each group of lithium batteries to be tested is different.

[0066] In this embodiment, the first preset processing method is used to process a plurality of groups of lithium batteries to be tested, so that the welding degree between the winding core and the positive busbar of each group of lithium batteries to be tested is different. After the processing of this step, the welding degree of 5 groups of lithium batteries to be tested is obtained as follows:

[0067] Group 1: The core and positive busbar of the lithium battery to be tested (positive busbar is Figure 2 The "busbars, the same below" shown in the figure are pressed flat against each other but not welded.

[0068] It should be noted that in the current group, the winding core and the positive busbar of each lithium battery to be tested in the current group are pressed flat against each other, but not welded. The purpose of setting the current group to this welding degree is to detect the internal resistance value of this welding degree detected by the internal resistance tester when the battery is pressed flat without welding. Since this situation is an abnormal welding situation (i.e., a cold weld) of the lithium battery to be tested, the internal resistance value of the lithium battery to be tested under this abnormal situation can be understood by detecting this abnormal situation.

[0069] In this embodiment, the internal resistance tester is a voltage internal resistance tester.

[0070] Group 2: There are two welding tracks between the core and the positive busbar in the lithium battery to be tested, and the welding length is equal to half of the welding track length.

[0071] It should be noted that in the current group, each lithium battery to be tested in the current group has two welding tracks between the winding core and the positive busbar, and the welding length is equal to 1 / 2 of the welding track length. The purpose of setting the current group to this welding degree is to detect the internal resistance value of this welding degree detected by the internal resistance tester when the welding length is equal to 1 / 2 of the welding track length. Since this situation is that the lithium battery to be tested is in the "intermediate state" between normal welding and abnormal welding (i.e., cold welding), the internal resistance value of the lithium battery to be tested in this "intermediate state" can be understood by detecting this "intermediate state".

[0072] Group 3: There are two welding tracks between the core and the positive busbar in the lithium battery to be tested, and the welding length is equal to the welding track length.

[0073] It should be noted that in the current group, each lithium battery to be tested in the current group has two welding tracks between the winding core and the positive busbar, and the welding length is equal to the welding track length. The purpose of setting the current group to this welding degree is to detect the internal resistance value of this welding degree detected by the internal resistance tester when the welding length is equal to the welding track length. Since this situation is that the lithium battery to be tested is in a normal welding state, the size of the internal resistance value of the lithium battery to be tested under this normal condition can be understood by detecting this normal condition.

[0074] Group 4: There are two welding tracks between the core and the positive busbar in the lithium battery under test, but the welding is not firm.

[0075] It should be noted that in the current group, each lithium battery to be tested in the current group has two welding tracks between the winding core and the positive busbar, but the welding is not firm. The purpose of setting the current group to this welding degree is to detect the internal resistance value of this welding degree detected by the voltage internal resistance when there are two welding tracks and the welding is not firm. Since this situation is that the lithium battery to be tested is in an abnormal welding state, the size of the internal resistance value of the lithium battery to be tested in this abnormal state can be understood by detecting this abnormal state.

[0076] In this embodiment, by performing different treatments on 4 groups of lithium batteries to be tested, the welding degrees of the positive terminals of the lithium batteries to be tested are made different. Subsequently, by detecting the internal resistance values ​​corresponding to the 4 groups with different welding degrees (one group of which has a completely normal welding degree), the internal resistance of the positive terminal of the lithium batteries to be tested can be compared when the welding of the lithium batteries to be tested is normal and there is no cold solder joint. In this way, a qualified standard for the internal resistance is established, and then the screening of the lithium batteries to be tested (cold solder joint state) is completed through the qualified standard.

[0077] Step S130, detecting the internal resistance from the first position point to the second position point in the winding core and the positive busbar of each group of lithium batteries to be tested, obtaining multiple first internal resistance values ​​of each group of lithium batteries to be tested, and analyzing the multiple first internal resistance values ​​in each group of lithium batteries to be tested according to the Six Sigma method to obtain a first standard internal resistance value.

[0078] In this embodiment, the method for detecting the internal resistance of the positive terminals of the first to fourth groups of lithium batteries to be tested can be as follows: calibrate the internal resistance tester; use the first probe of the internal resistance tester to contact the first position point (i.e. Figure 2 Use the second probe of the internal resistance tester to touch the second position point (i.e. Figure 2 Position 2, the same below); obtain multiple first internal resistance values ​​of each group of lithium batteries to be tested.

[0079] First, the internal resistance tester is calibrated. The purpose of calibration is to detect the internal resistance of the positive terminal of the lithium battery to be tested more accurately, and to avoid inaccurate data as much as possible to cause errors in establishing the internal resistance standard of the positive terminal of the lithium battery to be tested. Therefore, calibration must be performed in advance. Subsequently, the first probe of the internal resistance tester is used to contact the first position point. In this embodiment, the first position point is any position point in the foil ear area of ​​the winding core. Next, the second probe of the internal resistance tester is used to contact the second position point. In this embodiment, the second position point is any position point in the welding area of ​​the positive busbar. At this time, the internal resistance tester can be used to complete the detection of the positive terminal of the lithium battery to be tested. Regarding the selection of the position point, since the positive busbar is the "bridge" connecting the lithium battery to be tested with the external device (equipment), the connection between the busbar and the winding core is generally confirmed first. Based on this, the first position point selects the foil ear area of ​​the winding core, and the second position point selects the welding area of ​​the busbar. By detecting the internal resistance of the first position point and the second position point, it can be well judged whether there is a cold welding at the positive terminal of the lithium battery to be tested.

[0080] In this embodiment, based on the Six Sigma method, multiple first internal resistance values ​​in each group of lithium batteries to be tested are analyzed to obtain a first standard internal resistance value. The specific operation is as follows: a positive terminal resistance test table and a positive terminal resistance test diagram are generated according to multiple first internal resistance values ​​in each group of lithium batteries to be tested; based on the dispersion and variance of the first internal resistance value, combined with the positive terminal resistance test table and the positive terminal resistance test diagram, the internal resistance standard of the winding core and the positive busbar is established to obtain the first standard internal resistance value.

[0081] Based on the above case, the internal resistance values ​​of the following 4 groups of lithium batteries to be tested are obtained using an internal resistance tester, as shown in Table 1.

[0082]

[0083]

[0084] Table 1

[0085] Table 1 is a positive terminal structure test table generated based on multiple first internal resistance values ​​in each group of lithium batteries to be tested. Table 1 can show the internal resistance value range of the positive terminal of the lithium battery to be tested under different welding degrees. Combined with the data in Table 1, the corresponding positive terminal test diagram is generated, such as Figure 4 shown.

[0086] Based on the dispersion and variance of the first internal resistance value, combined with the positive terminal resistance test table (i.e. Table 1) and the positive terminal resistance test diagram (i.e. Figure 4), establish the internal resistance standard of the winding core and the positive busbar, and obtain the first standard internal resistance value. In this embodiment, according to the discreteness and variance of the first internal resistance value, the first internal resistance value of Group 1 has a high discreteness, which verifies that the welding of the lithium batteries to be tested in Group 1 is in an abnormal state. Among the remaining three groups, Group 3 is a situation where the welding of the lithium batteries to be tested is completely normal. Although Groups 2 and 4 have welding, the welding length of Group 2 does not reach 100%. Although the welding length of Group 4 reaches 100%, the welding is not firm. Both groups may have local cold welding, but compared with Group 1, the degree of cold welding is not that high. Therefore, through Groups 2 to 4, Six Sigma can be used to analyze the qualified standard of the internal resistance of the positive terminal of the battery pack to be tested when there is no cold welding. Combined with Table 1 and Figure 4 , it can be determined that in this embodiment, the first standard internal resistance value of the positive terminal of the lithium battery to be tested should be ≤0.2mΩ, that is, it is determined that there is no cold solder joint at the positive terminal. This is because the curves corresponding to the second, third and fourth groups are all below 0.2mΩ, which "echoes" the welding degree of the second to fourth groups.

[0087] Step S140: Process each group of lithium batteries to be tested according to a second preset processing method, so that the welding degree between the winding core and the negative electrode busbar of each group of lithium batteries to be tested is different.

[0088] Similarly, in this embodiment, the second preset processing method is used to process each group of lithium batteries to be tested, so that the welding degree between the winding core and the negative busbar of each group of lithium batteries to be tested is different (note that the negative end of the lithium batteries to be tested is processed at this time). After the five groups of lithium batteries to be tested are processed in this step, the following welding degrees are obtained:

[0089] Group 1: The winding core and negative busbar of the lithium battery to be tested (the negative busbar is Figure 3 The "busbars, the same below" shown in the figure are pressed flat against each other, but not welded. The purpose of this group of welding can be referred to the first group of positive terminal treatment of the lithium battery to be tested, and will not be repeated here.

[0090] Group 2: There are two welding tracks between the core and the negative busbar in the lithium battery to be tested, and the welding length is equal to 1 / 2 of the welding track length. The purpose of this group of welding can be referred to the second group of positive terminal treatment of the lithium battery to be tested, and will not be repeated here.

[0091] Group 3: There are 2 welding tracks between the winding core and the negative busbar in the lithium battery to be tested, and the welding length is equal to the welding track length. The purpose of this group of welding degree can refer to the third group of positive terminal treatment of the lithium battery to be tested, and will not be repeated here.

[0092] Group 4: There are two welding tracks between the core and the negative busbar in the lithium battery under test, but the welding is not strong. The purpose of the welding degree of this group can be referred to the fourth group of positive terminal treatment of the lithium battery under test, and will not be repeated here.

[0093] In this embodiment, by performing different treatments on 4 groups of lithium batteries to be tested, the welding degrees of the negative terminals of the lithium batteries to be tested are made different. Subsequently, by detecting the internal resistance values ​​corresponding to the 4 groups with different welding degrees (one group of which has a completely normal welding degree), the internal resistance of the negative terminals of the lithium batteries to be tested can be compared when the welding of the lithium batteries to be tested is normal and there is no cold solder joint. In this way, a qualified standard for internal resistance is established, and then the screening of the lithium batteries to be tested (cold solder joint state) is completed through the qualified standard.

[0094] Step S150, detecting the internal resistance from the first position point to the third position point in the winding core and the negative electrode busbar of each group of lithium batteries to be tested, obtaining multiple second internal resistance values ​​of each group of lithium batteries to be tested, and analyzing the multiple second internal resistance values ​​in each group of lithium batteries to be tested according to the Six Sigma method to obtain a second standard internal resistance value.

[0095] In this embodiment, the method for detecting the internal resistance of the negative terminals of the first to fourth groups of lithium batteries to be tested can be as follows: calibrate the internal resistance tester; use the first probe of the internal resistance tester to contact the first position point; use the second probe of the internal resistance tester to contact the third position point (i.e. Figure 3 Position 3); obtain multiple groups of second internal resistance values ​​corresponding to different welding degrees.

[0096] In this embodiment, the internal resistance tester is a voltage internal resistance tester.

[0097] Similarly, first perform a calibration operation on the internal resistance tester to avoid inaccurate data causing errors in establishing the internal resistance standard of the negative terminal of the lithium battery to be tested. Subsequently, the first probe of the internal resistance tester is used to contact the first position point. In this embodiment, the first position point is any position point in the foil ear area of ​​the winding core. Next, the second probe of the internal resistance tester is used to contact the third position point. In this embodiment, the third position point is any position point in the welding area of ​​the negative busbar. At this point, the internal resistance tester can be used to complete the detection of the negative terminal of the lithium battery to be tested. Regarding the selection of the position point, since the negative busbar is the "bridge" connecting the lithium battery to be tested and the external device (equipment), the connection between the busbar and the winding core is generally confirmed first. Based on this, the first position point selects the foil ear area of ​​the winding core, and the second position point selects the welding area of ​​the busbar. By detecting the internal resistance of the first position point and the third position point, it can be well judged whether there is a cold welding at the negative terminal of the lithium battery to be tested.

[0098] In this embodiment, based on the Six Sigma method, multiple second internal resistance values ​​in each group of lithium batteries to be tested are analyzed to obtain the first standard internal resistance value. The specific operation is as follows: multiple groups of second internal resistance values ​​are input and analyzed to obtain the second standard internal resistance value, including: generating a negative terminal resistance value test table and a negative terminal resistance value test chart according to multiple second internal resistance values ​​in each group of lithium batteries to be tested; based on the dispersion and variance of the second internal resistance value, combined with the negative terminal resistance value test table and the negative terminal resistance value test chart, the internal resistance standard of the winding core and the negative busbar is established to obtain the second standard internal resistance value.

[0099] Since several lithium batteries to be tested have been grouped before, and a first standard internal resistance value has been established for the positive terminal of the lithium battery to be tested, a second standard internal resistance value should be established for the negative terminal of the lithium battery to be tested, and the second standard internal resistance value can be used to determine whether there is a cold solder joint at the negative terminal of the lithium battery to be tested.

[0100] Based on the above case, the internal resistance values ​​of the following four groups of lithium batteries to be tested are obtained using an internal resistance tester, as shown in Table 2.

[0101]

[0102]

[0103] Table 2

[0104] Table 2 is a negative terminal structure test table generated based on the second internal resistance values ​​of each group of the lithium batteries to be tested. Table 2 can show the internal resistance value range of the negative terminal of the lithium battery to be tested under different welding degrees. Combined with the data in Table 2, a corresponding negative terminal test diagram is generated, such as Figure 5 shown.

[0105] Based on the dispersion and variance of the second internal resistance value, combined with the negative terminal resistance test table (i.e. Table 2) and the negative terminal resistance test diagram (i.e. Figure 5 ), establish the internal resistance standard of the winding core and the negative busbar, and obtain the second standard internal resistance value. In this embodiment, according to the dispersion and variance of the second internal resistance value, the second internal resistance value of the fourth group has a high dispersion, which verifies that the welding of the lithium battery to be tested in the fourth group is in an abnormal state. Among the remaining three groups, the third group is a completely normal welding situation for the lithium battery to be tested, and the first and second groups are both in the welding abnormality situation. Therefore, through the third group, the six sigma analysis can be used to determine what the qualified standard of the internal resistance is when there is no cold solder joint at the negative end of the battery to be tested. Combined with Table 2 and Figure 5 , it can be determined that in this embodiment, the second standard internal resistance value of the negative terminal of the lithium battery to be tested should be ≤0.1mΩ, that is, it is determined that there is no cold solder joint at the negative terminal. This is because the curves corresponding to the third group are all below 0.1mΩ, which "echoes" the welding degree of the third group.

[0106] The technical solution of this embodiment can obtain multiple groups of first internal resistance values ​​and second internal resistance values ​​by detecting batteries to be tested with different welding degrees. These internal resistance values ​​are analyzed according to the Six Sigma method to obtain the first internal resistance standard value and the second standard internal resistance value. Subsequent testing personnel can then detect whether there is a cold solder joint at the positive terminal and the negative terminal of the lithium battery to be tested based on the first internal resistance standard value and the second standard internal resistance value, thereby effectively avoiding the defect of detecting the cold solder joint by the destructive tensile test method.

[0107] Subsequently, for lithium batteries that need to undergo cold solder joint verification testing, after the core is welded to the positive and negative bus bars, the welding effect of each battery cell can be tested and confirmed using automated testing equipment with an internal resistance tester. This can effectively solve the waste of raw materials caused by destructive testing such as hand tearing or tensile testing. The technical solution of this application can monitor the production of each battery cell, improve efficiency, enhance product consistency, and reduce costs.

[0108] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A lithium battery cold solder joint detection method, characterized in that: include: Preparing a plurality of lithium batteries to be tested, and grouping the plurality of lithium batteries to be tested, wherein the plurality of lithium batteries to be tested include: a winding core, a positive busbar, and a negative busbar; Processing each group of the lithium batteries to be tested according to a first preset processing method, so that the welding degree between the winding core and the positive busbar of each group of the lithium batteries to be tested is different; Detecting the internal resistance from the first position point to the second position point in the winding core and the positive busbar of each group of the lithium batteries to be tested, obtaining multiple first internal resistance values ​​of each group of the lithium batteries to be tested, and analyzing the multiple first internal resistance values ​​in each group of the lithium batteries to be tested according to the Six Sigma method to obtain a first standard internal resistance value; Processing each group of the lithium batteries to be tested according to a second preset processing method, so that the welding degree between the winding core and the negative electrode busbar of each group of the lithium batteries to be tested is different; Detect the internal resistance of the winding core of each group of the lithium batteries to be tested from the first position point to the third position point in the negative electrode busbar to obtain multiple second internal resistance values ​​of each group of the lithium batteries to be tested, and analyze the multiple second internal resistance values ​​in each group of the lithium batteries to be tested according to the Six Sigma method to obtain a second standard internal resistance value.

2. The lithium battery cold solder joint detection method according to claim 1, characterized in that: The welding degree between the winding core and the positive busbar of each group of lithium batteries to be tested is different, including: The winding core and the positive busbar in the lithium battery to be tested in the current group are pressed flat against each other but not welded; and / or The winding core and the positive busbar in the lithium battery to be tested in the current group have two welding tracks, and the welding length is equal to half of the length of the welding track; and / or The winding core and the positive busbar in the lithium battery to be tested in the current group have two welding tracks, and the welding length is equal to the welding track length; and / or In the lithium battery to be tested in the current group, the winding core and the positive busbar have two welding tracks, but the welding is not firm.

3. The lithium battery cold solder joint detection method according to claim 2, characterized in that: The step of analyzing the first internal resistance values ​​of each group of the lithium batteries to be tested according to the Six Sigma method to obtain the first standard internal resistance value includes: Generate a positive terminal resistance test table and a positive terminal resistance test diagram according to the plurality of first internal resistance values ​​in each group of the lithium batteries to be tested; Based on the dispersion and variance of the first internal resistance value, combined with the positive terminal resistance test table and the positive terminal resistance test diagram, the internal resistance standard of the winding core and the positive bus bar is established to obtain a first standard internal resistance value.

4. The lithium battery cold solder joint detection method according to claim 1, characterized in that: The detecting the internal resistance from the first position point to the second position point in the winding core and the positive electrode busbar of each group of the lithium batteries to be tested, and obtaining multiple groups of first internal resistance values ​​corresponding to different welding degrees, comprises: Calibrate internal resistance tester; Using a first probe of the internal resistance tester to contact the first position point; Using a second probe of the internal resistance tester to contact the second position point; A plurality of groups of first internal resistance values ​​corresponding to different welding degrees are obtained.

5. The lithium battery cold solder joint detection method according to claim 4, characterized in that: The first position point is any position point in the foil tab area of ​​the winding core; The second position point is any position point of the welding area in the positive electrode bus bar.

6. The lithium battery cold solder joint detection method according to claim 1, characterized in that: The welding degree between the winding core and the negative electrode busbar of each group of the lithium batteries to be tested is different, including: The winding core and the negative electrode busbar in the lithium battery to be tested in the current group are pressed flat against each other but not welded; and / or The winding core and the negative electrode busbar in the lithium battery to be tested in the current group have two welding tracks, and the welding length is equal to half of the length of the welding track; and / or The winding core and the negative electrode busbar in the lithium battery to be tested in the current group have two welding tracks, and the welding length is equal to the welding track length; and / or In the lithium battery to be tested in the current group, the winding core and the negative electrode busbar have two welding tracks, but the welding is not firm.

7. The lithium battery cold solder joint detection method according to claim 6, characterized in that: The step of analyzing the plurality of second internal resistance values ​​in each group of the lithium batteries to be tested according to the Six Sigma method to obtain a second standard internal resistance value includes: Generate a negative terminal resistance test table and a negative terminal resistance test diagram according to the plurality of second internal resistance values ​​in each group of the lithium batteries to be tested; Based on the dispersion and variance of the second internal resistance value, combined with the negative terminal resistance test table and the negative terminal resistance test diagram, the internal resistance standard of the winding core and the negative bus bar is established to obtain a second standard internal resistance value.

8. The lithium battery cold solder joint detection method according to claim 1, characterized in that: The detecting the internal resistance from the first position point to the third position point in the winding core and the negative electrode busbar of each group of the lithium batteries to be tested, and obtaining multiple groups of second internal resistance values ​​corresponding to different welding degrees, comprises: Calibrate internal resistance tester; Using a first probe of the internal resistance tester to contact the first position point; Using a second probe of the internal resistance tester to contact the third position point; A plurality of groups of second internal resistance values ​​corresponding to different welding degrees are obtained.

9. The lithium battery cold solder joint detection method according to claim 8, characterized in that: The first position point is any position point in the foil tab area of ​​the winding core; The third position point is any position point of the welding area in the negative electrode bus bar.

10. The lithium battery cold solder joint detection method according to any one of claims 1 to 9, characterized in that: The number of the lithium batteries to be tested in each group is at least 5.

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