Method and system for screening batteries with poor tab welding

Abstract

The invention provides a method for screening batteries with poor tab welding, and belongs to the field of batteries. The method comprises the following steps: S1, carrying out one-time full-full discharge capacity grading on a group of formed and sealed batteries in the same tray; s2, collecting the time in the charging and discharging process and the voltage and capacity of each battery; s3, determining a specific voltage value in a charging and discharging stage; s4, acquiring voltages of all batteries in the tray when the first battery reaches a specific voltage value, determining a voltage median, and calculating a difference value between the voltages of all the batteries and the median, or acquiring corresponding capacities when the batteries reach the same voltage; and S5, screening batteries with poor tab welding according to the difference value of the voltage and the voltage median or the capacity. The battery is charged and discharged once through the capacity grading process, the voltage and capacity of each battery in a specific stage are directly collected by equipment for judgment, cost waste and low efficiency caused by multiple times of charging and discharging can be avoided, the battery with poor tab welding can be accurately and effectively identified, and the method is suitable for a large-scale production line.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a method and system for screening batteries with poor tab welding. Background Art

[0002] Lithium batteries have the advantages of small volume, large capacity, long service life, low self-discharge rate, no memory effect, environmental friendliness, etc., and are currently widely used in commercial vehicles, special vehicles, electric bicycles, energy storage systems, medical devices, etc. With the development of the lithium battery industry, the requirement for battery energy density is getting higher and higher. In order to improve the energy density as much as possible, the most common method is to increase the length of the electrode sheet. As the length of the electrode sheet increases, the number of tabs also increases, and the probability of poor tab welding also increases. Poor tab welding includes loose welding, over-welding, missed welding, etc. As the number of tabs increases, the risk of the tabs being folded or damaged when passing through the rollers during the laser cutting and winding processes increases. Once the tabs are folded or damaged, missed welding will occur during welding. Currently, the industry mainly screens batteries with poor tab welding through ACR and DCR tests after formation and static storage. However, batteries with poor welding do not necessarily show an increase in ohmic internal resistance, and DCR is greatly affected by factors such as temperature and current. Therefore, these two methods currently have limited ability to identify missed tab welding. Once batteries with poor tab welding are not identified in time and flow into the subsequent processes, it will result in poor consistency of the battery pack, thereby affecting product quality and causing losses to the enterprise.

[0003] The patent document with the publication number CN114062930A discloses a method for detecting abnormal contact of battery tabs. It establishes a standard resistance voltage change curve of a standard battery cell based on the difference between the average charging voltage and the average discharging voltage of the standard battery cell during multiple charge and discharge cycles; establishes a target resistance voltage change curve of the battery cell to be detected based on the difference between the average charging voltage and the average discharging voltage of the battery cell to be detected during multiple charge and discharge cycles; if the difference between the target resistance voltage change curve and the standard resistance voltage change curve is greater than a preset threshold within a preset time length, it is determined that the battery tab has a loose connection fault. That is, it needs to judge whether there is a loose connection fault of the tab through multiple charge and discharge cycles, and repeatedly perform charge and discharge for multiple cycles to calculate the average charging voltage and the average discharging voltage. Whether it is from the perspective of charge and discharge cost or efficiency, it is not applicable to large-scale production lines. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to provide a method for screening batteries with poor tab welding that is applicable to large-scale production lines.

[0005] To solve the above technical problem, the present invention provides the following technical solution: A method for screening batteries with poor tab welding, including the following steps:

[0006] S1: Perform a full charge and discharge cycle for a group of formed and sealed batteries in the same tray.

[0007] S2: Determine specific voltage values during the charging and discharging phases.

[0008] S3: Collect the time, voltage, and capacity of each battery during the charge and discharge process.

[0009] S4: Obtain the voltages of all batteries in the tray when the first battery in the tray reaches a specific voltage value and determine the median voltage. Calculate the difference between the voltage of all batteries and the median voltage, or obtain the capacity of the corresponding battery when each battery reaches the same voltage.

[0010] S5: Screen for batteries with poor tab welding based on the difference between the voltage of all batteries and the median voltage or the battery capacity.

[0011] The present invention performs a full charge and discharge cycle on the battery through the grading process, and directly collects the voltage and capacity of each battery at specific stages through the grading equipment to determine whether the battery has poor tab welding. There is no need to perform multiple cycle charge and discharge calculations to obtain the average voltage, thus greatly saving time costs. It can also avoid the cost waste and battery damage caused by multiple charge and discharges of the battery. That is, the present invention saves time costs and production costs, improves production efficiency, and is applicable to large-scale production lines.

[0012] The present invention can accurately and effectively identify batteries with poor tab welding during the grading process. It can not only use the battery voltage or battery capacity alone to determine whether the battery is abnormal, but also comprehensively consider both the battery voltage and battery capacity, which can more accurately and effectively identify batteries with poor tab welding, avoid abnormal batteries from flowing into the battery pack, improve the consistency of the battery pack and product quality, and can also reduce rework and lower production costs.

[0013] Preferably, the full charge and discharge cycle in step S1 includes charging the battery to the charging cut-off voltage and then discharging it to the discharging cut-off voltage.

[0014] Preferably, the grading ratio for the full charge and discharge in step S1 is 0.3C - 1C.

[0015] The advantage of selecting a grading ratio of 0.3C - 1C for the full charge and discharge in the present invention is that if there is poor tab welding, it will cause the polarization of the battery to increase during the charge and discharge process. The smaller the charge and discharge current, the smaller the polarization. Therefore, selecting 0.3C - 1C in the present invention not only avoids the conflict between the smaller polarization caused by the smaller charge and discharge current and the larger polarization of the battery caused by poor tab welding, but also avoids the influence of too large charge and discharge current on battery capacity and other characteristics.

[0016] Preferably, the full charge and discharge forming includes the following steps: charging the battery at a constant current and constant voltage at a rate of 0.3C - 1C until the charging cut-off voltage is reached, limiting the current at a rate of 0.05C - 0.1C, standing for 3 - 5 minutes, and then discharging at a constant current at the same rate as the charging stage until the discharge cut-off voltage is reached.

[0017] Preferably, the specific voltage values in step S2 include 3450 mV - 3650 mV in the charging stage or 2950 mV - 3150 mV in the discharging stage.

[0018] Preferably, in step S4, the battery capacity corresponding to each battery when reaching the same voltage is obtained, and the same voltage is 3450 mV - 3550 mV.

[0019] Preferably, the specific process of step S5 is as follows:

[0020] S501: Set the threshold range of the absolute value of the difference between the voltage of all batteries and the median voltage, and the threshold range of the battery capacity.

[0021] S502: If the difference between the battery voltage and the median voltage is greater than the threshold range of the absolute value of the voltage difference or the battery capacity exceeds the threshold range of the battery capacity, it is determined that the tab welding of the battery is defective.

[0022] For batteries with defective tab welding, especially those with folded tabs or damaged tabs resulting in less or no tab welding, the polarization is relatively large during the charge and discharge process. Specifically, when charging at a constant current to a certain voltage, the voltage rise rate is significantly faster than that of normal batteries. The present invention can quickly identify batteries with defective tab welding by comparing the relationship between the difference between the battery voltage and the median voltage and the threshold of the absolute value of the voltage difference; and defective tab welding will also show that the charging capacity corresponding to a certain stage during charging is significantly lower than that of normal batteries. The present invention can also quickly identify batteries with defective tab welding by judging whether the battery capacity exceeds the threshold range of the battery capacity. In particular, the present invention can not only use the battery voltage or the battery capacity alone to judge whether the battery is abnormal, but also comprehensively consider from both aspects of the battery voltage and the battery capacity, and can flexibly select the judgment method according to the actual situation and actual working requirements.

[0023] Preferably, in step S501, the threshold range of the absolute value of the difference between the voltage of all batteries and the median voltage is 0 - 50 mV, and the threshold range of the battery capacity is 315 Ah - 340 Ah.

[0024] The present invention also provides a system for screening batteries with defective tab welding, including the following modules:

[0025] Forming module: used to perform a full charge and discharge forming on a group of batteries that have been formed and sealed in the same tray.

[0026] Module for determining specific voltage values: used to determine specific voltage values during the charging and discharging phases;

[0027] Acquisition module: used to acquire the time, voltage, and capacity of each battery during the charging and discharging process;

[0028] Module for obtaining voltage or capacity at a specific stage: used to obtain the voltages of all batteries in the tray when the first battery in the tray reaches a specific voltage value, determine the median of the voltages, calculate the difference between the sum of all battery voltages and the voltage median, or obtain the capacity of the corresponding batteries when each battery reaches the same voltage;

[0029] Module for screening abnormal batteries: used to screen batteries with poor tab welding based on the difference between the sum of all battery voltages and the voltage median or the battery capacity.

[0030] Preferably, the module for screening abnormal batteries includes the following units:

[0031] Threshold setting unit: used to set the threshold range of the absolute value of the difference between the sum of all battery voltages and the voltage median, and the threshold range of the battery capacity;

[0032] Determination unit: used to determine that the tab welding of the battery is poor when the difference between the battery voltage and the voltage median is greater than the threshold range of the absolute value of the voltage difference or the battery capacity exceeds the battery capacity threshold range.

[0033] Compared with the prior art, the advantages of the present invention are as follows: By collecting the charging and discharging data of the full charge and full discharge grading process, and only performing one charge and discharge, it is possible to accurately and effectively identify batteries with poor tab welding through the voltage and capacity at specific stages, without the need to perform multiple cycles of charge and discharge to calculate the average voltage, thereby greatly saving time costs. Moreover, it can avoid the cost waste and damage to the batteries caused by multiple charge and discharges of the batteries, and is applicable to large-scale production lines; it avoids abnormal batteries from flowing into the battery pack, improving the consistency of the battery pack and product quality. Brief Description of the Drawings

[0034] Figure 1 It is a flowchart of Embodiment 1 of the present invention;

[0035] Figure 2 It is a voltage curve diagram during the grading process of Embodiment 1 of the present invention;

[0036] Figure 3 It is a flowchart of using voltage as the determination basis in Embodiment 1 of the present invention;

[0037] Figure 4 It is a flowchart of using capacity as the determination basis in Embodiment 1 of the present invention;

[0038] Figure 5For the first battery in the charging stage of Embodiment 1 of the present invention to reach a specific voltage value and the voltages of all batteries in the tray;

[0039] Figure 6 For the first battery in the discharging stage of Embodiment 1 of the present invention to reach a specific voltage value and the voltages of all batteries in the tray;

[0040] Figure 7 The capacity of the battery corresponding to a voltage of 3500 mV in the charging stage of Embodiment 1 of the present invention. Detailed implementation manners

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0042] Embodiment 1

[0043] As Figure 1 shown, this embodiment provides a method for screening batteries with poor tab welding, including the following steps:

[0044] S1: Perform a full charge and discharge capacity grading on a group of formed and sealed batteries in the same tray at a certain rate. Specifically: fully charge and then discharge a group of formed and sealed batteries in the same tray, that is, charge the battery to the charge cut-off voltage and then discharge it to the discharge cut-off voltage. If the charge and discharge current is too small, the polarization is smaller, and because poor tab welding will cause large polarization during the charge and discharge process, the two are in conflict and are not conducive to screening batteries with poor tab welding. Moreover, too large a charge and discharge current will affect the performance of the battery capacity, etc. The capacity grading rate in this embodiment is selected as 0.3C - 1C.

[0045] For example, in this embodiment, the capacity grading rate is taken as 0.5C, and the battery is a lithium iron phosphate battery with a charge cut-off voltage of 3650 mV and a discharge cut-off voltage of 2000 mV. The specific full charge and discharge capacity grading steps are as follows:

[0046] S101: Charge the lithium iron phosphate battery at a constant current and constant voltage at a rate of 0.5C until the charge cut-off voltage of the battery, 3650 mV, is reached, and limit the current at a rate of 0.05C - 1C. In this implementation, the current limiting rate is 0.05C;

[0047] S102: Stand still for 3 - 5 minutes. In this embodiment, it stands still for 5 minutes;

[0048] S103: Discharge at a constant current at a rate of 0.5C until the discharge cut-off voltage of the battery, 2000 mV, is reached.

[0049] S2: The database collects data such as the time, voltage, and capacity of each battery during the formation process.

[0050] S3: Determine the specific voltage values in the charging and discharging stages. Specifically, the specific voltage values include the specific voltage values during the charging process and the specific voltage values during the discharging process. As Figure 2 shown, it is the voltage curve graph during the formation process collected. During the charging process, the specific voltage can be selected from 3400 mV to 3650 mV. In this embodiment, 3600 mV is selected. During the discharging process, the specific voltage can be selected from 2950 mV to 3150 mV. In this embodiment, 3000 mV is selected.

[0051] S4: Obtain the voltages of all the batteries in the tray when the first battery in the tray reaches the specific voltage value, and determine the median of the voltages. Calculate the difference between the sum of all the battery voltages and the voltage median, or obtain the corresponding battery capacities when each battery reaches the same voltage.

[0052] S5: Screen the batteries with poor tab welding according to the difference between the sum of all the battery voltages and the voltage median or the battery capacities. Specifically:

[0053] Due to poor tab welding, especially folded tabs or damaged tabs resulting in less welding or missed welding of tabs, the polarization of the battery during charging and discharging is relatively large. Specifically, during constant current charging to the plateau voltage. In this embodiment, the battery selected is a lithium iron phosphate battery, and its plateau voltage is 3200 mV. When charging at a constant current to above the plateau voltage, the voltage rise rate is significantly faster than that of normal batteries. When discharging to below the plateau voltage, the voltage drop rate is significantly faster than that of other batteries.

[0054] As Figure 3 shown, if the determination is made according to the difference between the battery voltage and the voltage median, the specific process is as follows:

[0055] A5011: First, determine the specific voltage values in the charging and discharging stages. In this embodiment, the specific voltage value in the charging stage is 3600 mV, and the specific voltage value in the discharging stage is 3000 mV.

[0056] A5012: When the first battery in the tray reaches the specific voltage, obtain the voltages of all the batteries in the same tray and determine the median of the voltages.

[0057] As Figure 5 shown, in this embodiment, the voltage of battery 10 reaches 3600 mV first during the charging stage. At this time, the voltages of other batteries in the same tray are relatively low, and the voltage median is 3441.9 mV.

[0058] As Figure 6As shown, in the discharging stage of this embodiment, the voltage of battery 10 reaches 3000 mV first. At this time, the voltages of other batteries on the same tray are relatively high, and the median voltage is 3160.1 mV.

[0059] A5013: Calculate the difference between the voltage of each battery in the same tray and the median voltage. In this embodiment, the difference between the voltage of battery 10 and the median voltage of each battery in the charging stage is 158.1 mV, which is much larger than the difference between the voltages of other batteries and the median voltage. In the discharging stage, the difference between the voltage of battery 10 and the median voltage of each battery in the discharging stage is -159.8 mV, and the absolute value of this difference is much larger than the absolute value of the difference between the voltages of other batteries and the median voltage.

[0060] A5014: If the absolute value of the difference between the battery voltage and the voltage exceeds the specified threshold range, the battery is determined to have a loose tab welding. The threshold can be determined according to the actual situation, and can be taken as 0 - 50 mV. In this embodiment, the upper limit of the specified threshold is 50 mV. It can be seen that the absolute value of the voltage difference of battery 10 in both the charging stage and the discharging stage exceeds 50 mV. Therefore, battery 10 is determined to be a battery with poor tab welding, that is, an abnormal battery.

[0061] After performing the above determination on all batteries in each tray, after the determination is completed, the grading software marks the tray where the abnormal battery is located and the position of the abnormal battery in the tray, and sends an instruction to the manipulator. The manipulator recognizes the tray code and grabs the abnormal battery according to the position sent by the software. In this embodiment, it is battery 10 and places it in the NG channel.

[0062] Taking the capacity at the same voltage as the determination criterion, during the charging process, when the voltage reaches a specific stage, if the corresponding charging capacity is significantly lower than that of other batteries, it can be determined as a battery with poor tab welding.

[0063] As Figure 4 shown, if the determination is made according to the battery capacity, the specific process is as follows:

[0064] B5011: First, determine the voltage value. The voltage in the charging stage is generally above the plateau voltage, and the selectable range is 3450 mV - 3550 mV. In this embodiment, it is set to 3500 mV.

[0065] B5012: Here, the batteries for which the determination is made according to the battery capacity are in different trays from the batteries for which the determination is made according to the difference between the battery voltage and the median voltage. Obtain the capacity corresponding to each battery at 3500 mV voltage as Figure 7 shown. It can be seen that the capacity of battery 8 is 304.64 Ah, and the capacity of battery 22 is 283.77 Ah, which is significantly lower than that of other batteries.

[0066] B5013: Set the specified capacity threshold range. The threshold range can be determined according to the actual situation. In this embodiment, it is set to 315 Ah - 340 Ah.

[0067] B5014: For a battery whose capacity exceeds the specified threshold range, it is determined that the welding of the tab is defective. It can be seen that the capacities of battery 8 and battery 22 both exceed the threshold range. Therefore, it is determined that battery 8 and battery 22 are batteries with defective tab welding, that is, abnormal batteries.

[0068] After making the above determination for all the batteries in each tray, after the determination is completed, the grading software marks the tray where the abnormal battery is located and the position of the abnormal battery in the tray, and sends an instruction to the manipulator. The manipulator recognizes the tray code and grabs the abnormal batteries, here are battery 8 and 22, according to the position sent by the software and places them in the NG channel.

[0069] Based on the difference between the voltage of all batteries and the median voltage or the battery capacity, the batteries with defective tab welding are determined and screened. The voltage or the capacity can be used alone as the determination condition, or the two can be combined for comprehensive determination and screening of abnormal batteries.

[0070] In this embodiment, by using the grading process to perform a single charge and discharge on the battery, and directly collecting the voltage and capacity of each battery at a specific stage through the grading equipment to determine whether it is a battery with defective tab welding, it can avoid the cost waste caused by multiple charge and discharge operations on the battery and the damage to the battery, save time cost and manufacturing cost, improve manufacturing efficiency, be applicable to large-scale production lines, accurately and effectively identify the batteries with defective tab welding, prevent abnormal batteries from flowing into the battery pack, improve the consistency of the battery pack and product quality, and at the same time reduce the production cost.

[0071] Embodiment 2

[0072] Corresponding to Embodiment 1 of the present invention, this embodiment provides a system for screening batteries with defective tab welding, including the following modules:

[0073] Grading module: used to perform a full charge and discharge grading on a group of formed and sealed batteries in the same tray. Specifically, the battery is fully charged and then discharged, that is, the battery is charged to the charge cut-off voltage and then discharged to the discharge cut-off voltage.

[0074] Acquisition module: used to acquire the time, voltage and capacity of each battery during the charge and discharge process.

[0075] Determine specific voltage value module: used to determine specific voltage values in the charge and discharge stages.

[0076] Obtain voltage or capacity in specific stage module: used to obtain the voltages of all batteries in the tray when the first battery in the tray reaches a specific voltage value and determine the median of the voltages, calculate the difference between the voltages of all batteries and the median voltage, or obtain the capacities of the batteries corresponding to the same voltage of each battery.

[0077] Screening abnormal battery modules: used to screen batteries with poor tab welding according to the difference between all battery voltages and the median voltage or the battery capacity, specifically including the following units:

[0078] Threshold setting unit: used to set the threshold of the absolute value of the difference between all battery voltages and the median voltage, as well as the battery capacity threshold;

[0079] Determination unit: used to determine that the tab welding of the battery is poor when the difference between the battery voltage and the median voltage is greater than the threshold of the absolute value of the voltage difference or the battery capacity exceeds the battery capacity threshold range:

[0080] If the determination is made according to the difference between the battery voltage and the median voltage, the specific process is as follows:

[0081] First, determine the specific voltage values in the charging and discharging stages; when the voltage of the first battery in the tray reaches the specific voltage, obtain the voltages of all the batteries in the same tray and determine the median voltage; calculate the difference between the voltages of all the batteries in the same tray and the median voltage; if the absolute value of the difference between the battery voltage and the voltage exceeds the specified threshold range, it is determined as a battery with poor tab welding, and the threshold can be determined according to the actual situation; perform the above determination on all the batteries in each tray. After the determination is completed, the grading software marks the tray where the abnormal battery is located and the position of the abnormal battery in the tray, and sends an instruction to the manipulator. The manipulator identifies the tray code and grabs the abnormal battery according to the position sent by the software and places it in the NG channel.

[0082] If the determination is made according to the battery capacity, the specific process is as follows:

[0083] First, determine the voltage value. The voltage in the charging stage is generally above the platform voltage; obtain the capacities corresponding to each battery at the same voltage; set the specified capacity threshold range, and if the capacity exceeds the specified threshold range, it is determined as a battery with poor tab welding; perform the above determination on all the batteries in each tray. After the determination is completed, the grading software marks the tray where the abnormal battery is located and the position of the abnormal battery in the tray, and sends an instruction to the manipulator. The manipulator identifies the tray code and grabs the abnormal battery according to the position sent by the software and places it in the NG channel.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for screening batteries with poor tab welding, characterized in that: The following steps are involved: S1: Perform a full charge and discharge capacity separation on a group of batteries that have been formed and sealed in the same tray; S2: Collect the time of charge and discharge and the voltage and capacity of each battery; S3: Determine specific voltage values ​​during the charging and discharging phases; S4: obtaining the voltages of all batteries in the tray when the first battery in the tray reaches a specific voltage value and determining the median of the voltages, calculating the difference between the voltages of all batteries and the median of the voltages, or obtaining the capacity of the corresponding batteries when all batteries reach the same voltage; S5: Filter batteries with poor tab welding based on the difference between all battery voltages and the median voltage or the battery capacity.

2. A method for screening batteries with poor tab welding according to claim 1, characterized in that: The full charge and discharge capacity division in step S1 includes charging the battery to a charge cut-off voltage and then discharging it to a discharge cut-off voltage.

3. A method for screening batteries with poor tab welding according to claim 2, characterized in that: The volume division ratio of full filling and discharging in step S1 is 0.3C-1C.

4. A method for screening batteries with poor tab welding according to claim 3, characterized in that: The full charge and discharge capacity division includes the following steps: charging the battery at a constant current and constant voltage rate of 0.3C-1C until the charging cut-off voltage is reached, limiting the current at a rate of 0.05C-0.1C, and discharging at a constant current rate at the same rate in the charging stage after standing for 3-5 minutes until the discharge reaches the discharge cut-off voltage.

5. The method for screening batteries with poor tab welding according to claim 1, characterized in that: The specific voltage value in step S2 includes 3450mV-3650mV in the charging stage or 2950mV-3150mV in the discharging stage.

6. The method for screening batteries with poor tab welding according to claim 1, characterized in that: In step S4, the battery capacities corresponding to the batteries reaching the same voltage are obtained, and the same voltage is 3450mV-3550mV.

7. The method for screening batteries with poor tab welding according to claim 1, characterized in that: The specific process of step S5 is as follows: S501: Setting a threshold of the absolute value of the difference between all battery voltages and the voltage median and a battery capacity threshold range; S502: If the difference between the battery voltage and the voltage median is greater than the voltage difference absolute value threshold or the battery capacity exceeds the battery capacity threshold range, it is determined that the battery tab welding is poor.

8. A method for screening batteries with poor tab welding according to claim 7, characterized in that: In step S501, the range of the absolute value threshold of the difference between all battery voltages and the voltage median is 0-50mV, and the range of the battery capacity threshold is 315Ah-340Ah.

9. A system for screening batteries with poor tab welding, characterized in that: Includes the following modules: Capacity division module: used to conduct full-charge and discharge capacity division on a group of batteries that have been formed and sealed in the same tray; Acquisition module: used to collect the time during the charging and discharging process and the voltage and capacity of each battery; Determine specific voltage value module: used to determine specific voltage values ​​during charging and discharging stages; Obtaining voltage or capacity at a specific stage module: used to obtain the voltage of all batteries in the tray when the first battery in the tray reaches a specific voltage value and determine the median of the voltage, calculate the difference between the voltage of all batteries and the median voltage, or obtain the capacity of the corresponding battery when each battery reaches the same voltage; Screening abnormal battery modules: used to screen batteries with poor tab welding based on the difference between all battery voltages and the median voltage or the battery capacity.

10. A system for screening batteries with bad tab welding according to claim 9, characterized in that: The abnormal battery screening module includes the following units: Threshold setting unit: used to set the threshold range of the absolute value of the difference between all battery voltages and the voltage median and the battery capacity threshold range; Determination unit: used to determine that the battery tab welding is bad when the difference between the battery voltage and the voltage median is greater than the voltage difference absolute value threshold range or the battery capacity exceeds the battery capacity threshold range.

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