Composite current collector welding quality detection method

Abstract

The invention relates to a composite current collector welding quality detection method, which belongs to the technical field of batteries, and comprises the following steps: cutting a composite current collector to a certain width and length, stacking a plurality of composite current collectors with a certain size, and welding two ends of the composite current collectors with metal tabs respectively; connecting the positive and negative electrodes of the battery to a battery test system; charging and discharging the battery by using an instantaneous large current, recording voltage and current data, and calculating the direct-current internal resistance of the battery; connecting the composite current collector welded with the double tabs in series in a loop formed by the battery and a battery test system; performing short-time charging and discharging on the battery by adopting the same charging and discharging program, recording voltage and current data, and calculating the direct-current internal resistance in the whole loop; the internal resistance of the composite current collector after the metal tab is welded is obtained through the difference between the two; the temperature sensor is attached to the welding position of the two metal tabs and the composite current collector, the battery is charged and overdischarged for a long time with a certain current, and the highest temperature is recorded in the discharging process.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a method for detecting the welding quality of a composite current collector. Background Art

[0002] In recent years, the rapid development of new energy vehicles has greatly promoted the development of lithium-ion battery technology. The composite current collector with a sandwich structure replaces the existing pure metal foil current collector to significantly improve the mass energy density of lithium batteries, while greatly improving battery safety. In addition, it can reduce the use of metal foil and significantly reduce the production cost of lithium batteries. Due to the insulation of the intermediate layer of the composite current collector, its tab welding requires a special welding process to connect the upper and lower conductive layers, such as ultrasonic roll welding, resistance welding, etc. However, due to the thin metal layer and the insulation in the middle, the welding process of the composite current collector tab is complicated and the yield is low, which seriously limits the large-scale application of the composite current collector. The current research focuses on the development of new composite current collectors and the development of simple tab welding processes. There is little research on the quality detection of composite current collector tab welding. At present, the quality detection of composite current collector tab welding is mainly simple tensile test and needle resistance test, which cannot accurately evaluate the quality of tab welding and reflect the current carrying capacity of the composite current collector tab welding position during actual charging and discharging to meet the needs of different types of composite current collectors in practical applications in batteries. Summary of the invention

[0003] In order to overcome the shortcomings of the prior art, the present invention provides a composite current collector welding quality detection method, which obtains the resistance of the bipolar ear composite current collector by welding the composite current collector to the bipolar ear and directly connects it to the battery charge and discharge circuit, thereby simulating the increase in resistance during the charge and discharge process. The method can be used to evaluate the welding quality of the composite current collector, and can also be used for the quality inspection of newly developed composite current collectors or the evaluation of new ear welding methods.

[0004] The above-mentioned purpose of the present invention is mainly achieved through the following technical solutions:

[0005] A composite current collector welding quality detection method comprises the following steps:

[0006] (1) Selecting a single cell that can be discharged at a constant current;

[0007] (2) Connect the positive and negative electrodes of the battery to the battery test system, perform instantaneous high current charging and discharging on the battery, and record the difference ΔV between the battery voltage before and after the instantaneous high current charging and discharging. 0 , the change in battery voltage at the moment of instantaneous high current charging and discharging ΔV 1 and the instantaneous discharge current I 1 , calculate the battery DC internal resistance DCR 0 , DCR 0=ΔV 0 / I 1 , battery ohmic internal resistance DCR 1 , DCR 1 =ΔV 1 / I 1 ;

[0008] (3) stacking n composite current collectors (1), and welding two ends of the stacked composite current collectors (1) to the first electrode tab (2) and the second electrode tab (3), respectively;

[0009] (4) connecting one of the electrodes of the battery to the corresponding electrode terminal of the battery testing system, connecting the first electrode tab (2) welded to the composite current collector (1) obtained in step (3) to the other electrode of the battery, and connecting the second electrode tab (3) welded to the composite current collector (1) obtained in step (3) to the other electrode terminal of the battery testing system;

[0010] (5) Set up the instantaneous high current charging or discharging program, start the battery test system, and record the voltage difference ΔV before and after the instantaneous high current charging or discharging 2 , the change in battery voltage at the moment of instantaneous high current charging and discharging ΔV 3 and the instantaneous discharge current I 2 ; Calculate the total DC internal resistance DCR of the line 2 , DCR 2 =ΔV 2 / I 2 ; Total ohmic internal resistance of the line DCR 3 , DCR 3 =ΔV 3 / I 2 ;

[0011] (6) Calculate the DC resistance DCR of the composite current collector (1) with a welded tab 4 , DCR 4 =DCR 2 -DCR 0 ; Ohmic internal resistance DCR 5 , DCR 5 =DCR 3 -DCR 1 ;

[0012] (7) Place the temperature collection line close to the welding position between the tab and the composite current collector (1), start the constant current charge and discharge program, test the battery voltage and temperature changes during the charge and discharge process, record the highest temperature during the charge and discharge process, and end the test.

[0013] The battery type is a lithium-ion battery, a sodium-ion battery or a lead-acid battery, preferably a lithium-ion battery; the battery structure type is a hard-shell battery, a soft-pack battery or a cylindrical battery; the battery state is from more than half-charged to fully charged; the number of batteries is ≥2.

[0014] The battery testing system can meet the charging and discharging requirements of the battery at 3C and above rates, and the voltage sampling accuracy is above 100ms.

[0015] The composite current collector (1) is a composite aluminum foil or a composite copper foil. If the composite current collector (1) is a composite aluminum foil, the tab material is aluminum; if the composite current collector (1) is a composite copper foil, the tab material is copper or copper-plated nickel.

[0016] The pole tabs are of the same model as the pole tabs of the target application cell of the composite current collector, the pole tabs welded at both ends of the composite current collector (1) have the same specifications, and the same welding method and welding parameters are used.

[0017] I 1 =I 2 , the discharge time in step (5) = the discharge time in step (2).

[0018] In step (2), the current I 1 ≧Battery current 2C; discharge time ≧3s.

[0019] In the step (3), the number n of the composite current collectors (1) is the number of laminated layers or winding layers of the target battery cell for the composite current collectors, and the width of the composite current collectors (1) is equal to the width of the empty foil at the battery cell tab position.

[0020] In the step (4), the electrode tab welding method is ultrasonic welding, resistance welding or laser welding; the welding process is direct welding of the composite current collector (1) to the electrode tab or welding the composite current collector (1) to an external metal foil and then to the electrode tab.

[0021] In the step (7), if the electrode tab and the composite current collector (1) are directly welded, the welding mark position of the electrode tab and the composite current collector (1) is collected; if the composite current collector (1) is welded to an external metal foil and then to the electrode tab, both welding positions need to be sampled.

[0022] In the step (7), there are one or more temperature collection points, preferably two, which are respectively close to the positive and negative poles of the battery.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] (1) The present invention aims at the problem that in the current application process of composite current collectors in the lithium battery industry, the iteration speed of new composite current collectors is fast, the electrode ear welding processes are various, and the welding quality detection method is simple, which cannot meet the actual application of composite current collectors in batteries. By welding the composite current collector to the bipolar ear and directly connecting it to the battery charge and discharge circuit, the resistance of the bipolar ear composite current collector is obtained, thereby simulating the increase in resistance during the charge and discharge process. The resistance can be used to evaluate the welding quality of the composite current collector, and can also be used for the quality inspection of newly developed composite current collectors or the evaluation of new electrode ear welding methods.

[0025] (2) The problem of weak current carrying capacity of the composite current collector of the present invention is a pain point in its actual application process. The present invention can effectively test its actual overcurrent capacity by clarifying the width, number of layers and tab specifications of the composite current collector during the detection process, simulating the application scenario of the composite current collector in the target battery cell, and monitoring the tab welding position and temperature changes of the main part of the composite current collector when a large current passes through it, so as to provide guidance for the design, development and application of composite current collector batteries and ensure the safety of the batteries;

[0026] (3) The present invention can promote the standardization and regularization of the composite current collector tab welding inspection method. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of welding the composite current collector of the tab of the present invention;

[0028] Figure 2 The DC internal resistance DCR of the battery in Example 1 of the present invention 0 Test curve;

[0029] Figure 3 is the DC internal resistance DCR in Example 1 of the present invention 2 Test curve;

[0030] Figure 4 The DC internal resistance DCR of the battery in Example 2 of the present invention 0 Test curve;

[0031] Figure 5 is the DC internal resistance DCR in Example 2 of the present invention 2 Test curve. DETAILED DESCRIPTION

[0032] like Figure 1 As shown, a composite current collector welding quality detection method comprises the following steps:

[0033] (1) Selecting a single cell that can be discharged at a constant current;

[0034] (2) Connect the positive and negative electrodes of the battery to the battery test system, perform instantaneous high current charging and discharging on the battery, and record the difference ΔV between the battery voltage before and after the instantaneous high current charging and discharging. 0 , the change in battery voltage at the moment of instantaneous high current charging and discharging ΔV 1 and the instantaneous discharge current I 1 , calculate the battery DC internal resistance DCR 0 , DCR 0 =ΔV 0 / I 1 , battery ohmic internal resistance DCR 1 , DCR 1 =ΔV 1 / I 1 ;

[0035] (3) stacking n composite current collectors (1), and welding two ends of the stacked composite current collectors (1) to the first electrode tab (2) and the second electrode tab (3), respectively;

[0036] (4) connecting one of the electrodes of the battery to the corresponding electrode terminal of the battery testing system, connecting the first electrode tab (2) welded to the composite current collector (1) obtained in step (3) to the other electrode of the battery, and connecting the second electrode tab (3) welded to the composite current collector (1) obtained in step (3) to the other electrode terminal of the battery testing system;

[0037] (5) Set up the instantaneous high current charging or discharging program, start the battery test system, and record the voltage difference ΔV before and after the instantaneous high current charging or discharging 2 , the change in battery voltage at the moment of instantaneous high current charging and discharging ΔV 3 and the instantaneous discharge current I 2 ; Calculate the total DC internal resistance DCR of the line 2 , DCR 2 =ΔV 2 / I 2 ; Total ohmic internal resistance of the line DCR 3 , DCR 3 =ΔV 3 / I 2 ;

[0038] (6) Calculate the DC resistance DCR of the composite current collector (1) with a welded tab 4 , DCR 4 =DCR 2 -DCR 0 ; Ohmic internal resistance DCR 5 , DCR 5 =DCR 3 -DCR 1 ;

[0039] (7) Place the temperature collection line close to the welding position between the tab and the composite current collector (1), start the constant current charge and discharge program, test the battery voltage and temperature changes during the charge and discharge process, record the highest temperature during the charge and discharge process, and end the test.

[0040] The battery type is a lithium-ion battery, a sodium-ion battery or a lead-acid battery, preferably a lithium-ion battery; the battery structure type is a hard-shell battery, a soft-pack battery or a cylindrical battery; the battery state is from more than half-charged to fully charged; the number of batteries is ≥2.

[0041] The battery testing system can meet the charging and discharging requirements of the battery at 3C and above rates, and the voltage sampling accuracy is above 100ms.

[0042] The composite current collector 1 is a composite aluminum foil or a composite copper foil. If the composite current collector 1 is a composite aluminum foil, the tab material is aluminum. If the composite current collector 1 is a composite copper foil, the tab material is copper or copper plated with nickel.

[0043] The pole tabs are of the same model as the pole tabs of the target application cell of the composite current collector, the pole tabs welded at both ends of the composite current collector 1 have the same specifications, and the same welding method and welding parameters are used.

[0044] I 1 =I 2 , the discharge time in step (5) = the discharge time in step (2).

[0045] In step (2), the current I 1 ≧Battery current 2C, preferably 3C, 5C; discharge time ≧3s, preferably 5s, 10s.

[0046] In the step (3), the number n of composite current collectors 1 is the number of laminated layers or winding layers of the target battery cell for which the composite current collectors are applied, and the width of the composite current collector 1 is equal to the width of the empty foil at the battery cell tab position.

[0047] In the step (4), the electrode tab welding method is ultrasonic welding, resistance welding or laser welding; the welding process is direct welding of the composite current collector 1 to the electrode tab or welding the composite current collector 1 to an external metal foil and then to the electrode tab.

[0048] In the step (7), if the electrode tab and the composite current collector 1 are directly welded, the welding mark position of the electrode tab and the composite current collector 1 is collected; if the composite current collector 1 is welded to the external metal foil and then to the electrode tab, both welding positions need to be sampled.

[0049] In the step (7), there are one or more temperature collection points, preferably two, which are respectively close to the positive and negative poles of the battery.

[0050] All charging and discharging processes are preferably carried out at 25±3°C.

[0051] After the line connection process is completed, it is necessary to carefully check whether each connection position is correct and whether the connection is tight; check whether the voltage data collected by the battery test system is normal.

[0052] Since the composite current collector of the welded tab is similar to a wire, its DC internal resistance only includes the ohmic internal resistance, so theoretically the DCR here is 4 , DCR 5 The numerical values ​​should be highly consistent, so comparing the two can verify the reliability of the experiment and reduce the number of experiments.

[0053] After the DC internal resistance test is completed, the voltage collection line at the electrode end of the battery testing system connected to the composite current collector pole ear position is transferred to the battery electrode position for collecting the battery voltage. It is necessary to ensure that the current line and voltage line of the selected battery testing system cable are separated. The purpose of this step is to ensure that the voltage collected by the battery testing system is always the battery voltage when subsequently measuring the long-term high-current overcurrent capability, thereby ensuring safety during the test process.

[0054] The setting of constant current charging or discharging program includes charging and discharging time and current, which are calculated according to the actual target battery cell overcurrent capacity requirements. The temperature detection results can be used as welding guidance parameters or battery cell design guidance parameters. If the temperature is too high, the welding process can be optimized, or the battery cell design can be improved by increasing the lug area, reducing the current size, etc.

[0055] Example 1

[0056] (1) Take two square-shell batteries with a rated capacity of 12Ah and use a voltmeter to measure their voltages to ensure that the battery charge states are roughly the same. The voltages are 4.218V and 4.216V respectively.

[0057] (2) Connect the positive and negative electrodes of a battery to the battery testing system respectively, use a large current of 60A to discharge the battery for 5s, set the sampling time to 0.1s, and record the voltage change during the discharge process. The results are shown in Table 1.

[0058] Table 1 Battery voltage changes during discharge

[0059]

[0060] Calculate the battery DC internal resistance DCR 0 , DCR 0 =ΔV 0 / I=2.427mΩ;

[0061] Calculate the battery ohmic internal resistance DCR 1 , DCR 1 =ΔV 1 / I=1.442mΩ

[0062] (3) Select a PET composite aluminum foil current collector with a thickness of 10 μm as the research object, and cut the composite aluminum foil into several 30 mm × 100 mm strips;

[0063] (4) Select 15 long strips of composite aluminum foil of the same size and without burrs on the edges, align them up and down and stack them together, and directly weld the two ends of the stacked composite foil pile to the metal tabs, and the metal tabs are 0.2mm*28um aluminum tabs;

[0064] (5) Select the second battery and connect the positive electrode of the second battery to the positive electrode line of the battery testing system;

[0065] (6) Connecting the electrode tab at one end of the composite current collector with the welded electrode tab to the negative electrode post of the battery;

[0066] (7) Connect the other end of the composite current collector with the welded tab to the negative terminal 2 of the battery test system. After the connection is completed, carefully check whether the connection is reliable to ensure that all connections are not loose and reduce the impact of resistance and heat generation caused by poor connection on the test results.

[0067] (8) Set the same discharge program as step (2), start the battery test system, and record the sampling voltage changes during the charge and discharge process, as shown in Table 2:

[0068] Table 2 Sampling voltage changes during discharge

[0069]

[0070] Calculate the total DC resistance DCR of the line 2 , DCR 2 =ΔV 2 / I=7.009mΩ;

[0071] Calculate the total ohmic internal resistance of the circuit as DCR 3 , DCR 3 =ΔV 3 / I=5.910mΩ;

[0072] (9) Calculate the resistance DCR of the composite current collector with welded tabs 4 , DCR 4 =DCR 2 -DCR 0 =4.582mΩ;

[0073] Calculating DCR 5 =DCR 3 -DCR 1 =4.468mΩ.

[0074] DCR 4 DCR is the increase in the total DC internal resistance of the circuit after the composite current collector is connected in series in the circuit. 5 It is the increase in the total ohmic resistance of the circuit after the composite current collector is connected in series in the loop. Theoretically, the composite current collector is similar to a conductor, and its DC internal resistance is equal to the ohmic internal resistance. Therefore, the calculation results show that the error between the two tests is very small and the data is reliable.

[0075] (10) After the DC internal resistance test is completed, the voltage collection line of the negative terminal of the battery test system connected to the composite current collector tab 2 is transferred to the negative electrode of the battery, so that the voltage collected by the battery test system is the voltage of the battery;

[0076] (11) Place the temperature acquisition sensor close to the welding position between the tab and the composite current collector, discharge the battery at a current of 180 A for 2 min, and collect the temperature changes at the tab welding position during the charge and discharge process. The highest temperature recorded during the discharge process is 69.8 °C, which is within a reasonable range, indicating that the welding quality is good.

[0077] Figure 2 The DC internal resistance DCR of the battery in this embodiment is shown as 0 Test curve; Figure 3 The DC internal resistance DCR in this embodiment is shown as 2 Test curve.

[0078] The battery cell is a square-shell lithium-ion battery with a rated capacity of 12Ah and a maximum continuous discharge current of 240A; the maximum current range of the battery testing equipment is 300A and the sampling accuracy is 100ms.

[0079] Example 2

[0080] (1) Take two square-shell batteries with a rated capacity of 12Ah and use a voltmeter to measure their voltages to ensure that the battery states of charge are roughly the same. The voltages are 3.772V and 3.772V respectively.

[0081] (2) Connect the positive and negative electrodes of a battery to the battery testing system respectively, discharge the battery for 5 seconds with a high current of 60A, set the sampling time to 0.1s, and record the voltage change during the discharge process. The results are shown in Table 3.

[0082] Table 3 Battery voltage changes during discharge

[0083]

[0084] Calculate the battery DC internal resistance DCR 0 , DCR 0 =ΔV 0 / I=2.090mΩ;

[0085] Calculate the battery ohmic internal resistance DCR 1 , DCR 1 =ΔV 1 / I=1.095mΩ.

[0086] (3) Select a PET composite aluminum foil current collector with a thickness of 10 μm as the research object, and cut the composite aluminum foil into several 40 mm × 100 mm strips;

[0087] (4) Select 25 long strips of composite aluminum foil of the same size and without burrs on the edges, align them up and down and stack them together, and directly weld the two ends of the stacked composite foil pile to the metal tabs, and the metal tabs are 0.2mm*36um aluminum tabs;

[0088] (5) Select the second battery and connect the positive electrode of the second battery to the positive electrode line of the battery testing system;

[0089] (6) Connecting the electrode tab at one end of the composite current collector with the welded electrode tab to the negative electrode post of the battery;

[0090] (7) Connect the other end of the composite current collector with the welded tab to the negative terminal 2 of the battery test system. After the connection is completed, carefully check whether the connection is reliable to ensure that all connections are not loose and reduce the impact of resistance and heat generation caused by poor connection on the test results.

[0091] (8) Set the same discharge program as step (2), start the battery test system, and record the changes in the sampled voltage during the charge and discharge process, as shown in Table 4:

[0092] Table 4 Battery voltage changes during discharge

[0093]

[0094] Calculate the total DC resistance DCR of the line 2 , DCR 2 =ΔV 2 / I=5.477mΩ;

[0095] Calculate the total ohmic internal resistance of the circuit as DCR 3 , DCR 3 =ΔV 3 / I=4.386mΩ;

[0096] (9) Calculate the resistance DCR of the composite current collector with welded tabs 4 , DCR 4 =DCR 2 -DCR 0 =3.387mΩ;

[0097] Calculating DCR5 =DCR 3 -DCR 1 =3.291mΩ.

[0098] DCR 4 DCR is the increase in the total DC internal resistance of the circuit after the composite current collector is connected in series in the circuit. 5 It is the increase in the total ohmic resistance of the circuit after the composite current collector is connected in series in the loop. Theoretically, the composite current collector is similar to a conductor, and its DC internal resistance is equal to the ohmic internal resistance. Therefore, the calculation results show that the error between the two tests is very small and the data is reliable.

[0099] (10) After the DC internal resistance test is completed, the voltage collection line of the negative terminal of the battery test system connected to the composite current collector tab is transferred to the negative electrode of the battery, so that the voltage collected by the battery test system is the voltage of the battery;

[0100] (11) The temperature acquisition sensor was placed close to the welding position between the tab and the composite current collector, and the battery was discharged at a current of 240 A for 1 min. The temperature changes at the tab welding position during the charge and discharge process were collected, and the highest temperature recorded during the discharge process was 89.6 °C.

[0101] The battery cell is a square-shell lithium-ion battery with a rated capacity of 12Ah and a maximum continuous discharge current of 240A; the battery test equipment selected in step S2 has a maximum current range of 300A and a sampling accuracy of 100ms.

[0102] Figure 4 The DC internal resistance DCR of the battery in this embodiment is shown as 0 Test curve; Figure 5 The DC internal resistance DCR in this embodiment is shown as 2 Test curve.

[0103] The above description is only the best specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

[0104] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A composite current collector welding quality detection method, characterized in that: The following steps are involved: (1) Selecting a single cell that can be discharged at a constant current; (2) Connect the positive and negative electrodes of the battery to the battery testing system, perform instantaneous high-current charge and discharge on the battery, record the difference ΔV0 of the battery voltage before and after the instantaneous high-current charge and discharge, the change ΔV1 of the battery voltage at the instant of the instantaneous high-current charge and discharge, and the instantaneous discharge current I1, calculate the battery DC internal resistance DCR0, DCR0 = ΔV0 / I1, and the battery ohmic internal resistance DCR1, DCR1 = ΔV1 / I1; (3) stacking n composite current collectors (1), and welding two ends of the stacked composite current collectors (1) to the first electrode tab (2) and the second electrode tab (3), respectively; (4) connecting one of the electrodes of the battery to the corresponding electrode terminal of the battery testing system, connecting the first electrode tab (2) welded to the composite current collector (1) obtained in step (3) to the other electrode of the battery, and connecting the second electrode tab (3) welded to the composite current collector (1) obtained in step (3) to the other electrode terminal of the battery testing system; (5) Set up the instantaneous high current charging or discharging program, start the battery test system, record the voltage difference ΔV2 before and after the instantaneous high current charging and discharging, the change in the battery voltage ΔV3 at the instant of the instantaneous high current charging and discharging, and the instantaneous discharge current I2; calculate the total DC internal resistance DCR2 of the line, DCR2 = ΔV2 / I2; the total ohmic internal resistance DCR3 of the line, DCR3 = ΔV3 / I2; (6) Calculate the DC resistance DCR4 of the composite current collector with the electrode tab welded thereto, DCR4=DCR2-DCR0; the ohmic internal resistance DCR5, DCR5=DCR3-DCR1; (7) Place the temperature collection line close to the welding position between the tab and the composite current collector (1), start the constant current charge and discharge program, test the battery voltage and temperature changes during the charge and discharge process, record the highest temperature during the charge and discharge process, and end the test.

2. A composite current collector welding quality detection method according to claim 1, characterized in that: The battery type is a lithium-ion battery, a sodium-ion battery or a lead-acid battery, preferably a lithium-ion battery; the battery structure type is a hard-shell battery, a soft-pack battery or a cylindrical battery; the battery state is from more than half-charged to fully charged; the number of batteries is ≥2.

3. A composite current collector welding quality detection method according to claim 1, characterized in that: The battery testing system can meet the charging and discharging requirements of the battery at 3C and above rates, and the voltage sampling accuracy is above 100ms.

4. A composite current collector welding quality detection method according to claim 1, characterized in that: The composite current collector (1) is a composite aluminum foil or a composite copper foil. If the composite current collector (1) is a composite aluminum foil, the tab material is aluminum; if the composite current collector (1) is a composite copper foil, the tab material is copper or copper-plated nickel.

5. A composite current collector welding quality detection method according to claim 1, characterized in that: The pole tabs are of the same model as the pole tabs of the target application cell of the composite current collector, the pole tabs welded at both ends of the composite current collector (1) have the same specifications, and the same welding method and welding parameters are used.

6. A composite current collector welding quality detection method according to claim 1, characterized in that: I1=I2, the discharge time in step (5)=the discharge time in step (2).

7. A composite current collector welding quality detection method according to claim 1, characterized in that: In the step (2), the current I1≧battery 2C current; Discharge time ≧3s.

8. A composite current collector welding quality detection method according to claim 1, characterized in that: In the step (3), the number n of the composite current collectors (1) is the number of laminated layers or winding layers of the target battery cell for the composite current collectors, and the width of the composite current collectors (1) is equal to the width of the empty foil at the battery cell tab position.

9. A composite current collector welding quality detection method according to claim 1, characterized in that: In the step (4), the electrode tab welding method is ultrasonic welding, resistance welding or laser welding; the welding process is direct welding of the composite current collector (1) to the electrode tab or welding the composite current collector (1) to an external metal foil and then to the electrode tab.

10. A composite current collector welding quality detection method according to claim 9, characterized in that: In the step (7), if the electrode tab and the composite current collector (1) are directly welded, the welding mark position of the electrode tab and the composite current collector (1) is collected; if the composite current collector (1) is welded to an external metal foil and then to the electrode tab, both welding positions need to be sampled.

11. A composite current collector welding quality detection method according to claim 1, characterized in that: In the step (7), there are one or more temperature collection points, preferably two, which are respectively close to the positive and negative poles of the battery.

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