Lithium ion battery module self-discharge test method and system

Abstract

The invention discloses a self-discharge test method and system for a lithium ion battery module. The method comprises the following steps: adjusting a charge-discharge test of a lithium ion battery module to be tested to a preset charge state; standing for a first preset duration in a preset temperature environment, and measuring a first open-circuit voltage; standing for a second preset time length in the preset temperature environment, and measuring a second open-circuit voltage; then calculating the voltage drop value of each single cell in the module; determining a median in all the voltage drop values, and calculating the offset of the voltage drop value of each single cell relative to the median; according to the analysis of all the offsets, the batteries corresponding to the maximum value and the minimum value of the voltage drop in the module are disassembled and analyzed, and a qualified offset range is determined; the offset range is used as a judgment standard and is used for judging whether self-discharge abnormity exists in later tested modules or not. According to the method, the module with the abnormal self-discharge can be effectively screened out, the test efficiency and accuracy are improved, and the overall performance of the module can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery PACK, and more particularly to a lithium-ion battery module self-discharge test method and system. Background Art

[0002] At present, with the rapid development of the new energy industry, lithium batteries are widely used in the field of new energy vehicles due to their high energy density, light weight, long service life, and environmental protection. Usually, multiple batteries are connected in series or in parallel to form a module. When the lithium battery is in an open circuit state, the phenomenon that its stored electricity is consumed spontaneously is called battery self-discharge, also known as the battery's charge retention capacity, that is, the battery's ability to retain stored electricity under certain environmental conditions.

[0003] Theoretically, the electrodes of the battery are in a thermodynamically unstable state when charged, and physical or chemical reactions will spontaneously occur inside the battery, resulting in the loss of chemical energy of the battery. For a single lithium-ion battery, some batteries with abnormal self-discharge are screened out through aging tests before shipment. However, in the later analysis process, after the batteries are packaged and used in groups, the consistency problems caused by abnormal self-discharge of the cells and the self-discharge differences between the cells themselves greatly affect the electrical performance of the module itself, resulting in undervoltage problems in the module itself.

[0004] Previously, the related art screened out batteries with abnormal self-discharge by detecting the speed of voltage drop (voltage drop AV = (V0-V1) / T), but this method can no longer solve the problem well. Now, a new method is needed to quantitatively test the self-discharge of modules or cells, which can determine whether the fault is caused by battery self-discharge from the perspective of the entire module. That is, determine whether the fault is caused by the self-discharge of the cell itself from the perspective of the entire package / module. Summary of the invention

[0005] In view of this, the present invention provides a lithium-ion battery module self-discharge test method and system, which can better help find the root cause of the overall voltage drop problem of the module, effectively screen out abnormal self-discharge modules, improve the efficiency and accuracy of the test, and help improve the overall performance of the module.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] In a first aspect, an embodiment of the present invention provides a lithium-ion battery module self-discharge test method, comprising the following steps:

[0008] S10, adjusting the charge and discharge test of the lithium-ion battery module to be tested to a preset charge state;

[0009] S20, keeping the lithium-ion battery module stationary for a first preset time in a preset temperature environment, and measuring a first open circuit voltage; the first open circuit voltage includes: the voltage of each single cell in the module;

[0010] S30, keeping the lithium-ion battery module stationary for a second preset time in a preset temperature environment, and measuring a second open circuit voltage; the second open circuit voltage includes: the voltage of each single cell in the module;

[0011] S40, calculating the voltage drop value of each single cell in the module according to the first open circuit voltage and the second open circuit voltage; determining the median of all the voltage drop values, and calculating the offset of the voltage drop value of each single cell relative to the median;

[0012] S50. Based on the analysis of all the offsets, the batteries corresponding to the maximum and minimum voltage drop values ​​in the module are disassembled and analyzed, and a qualified offset range is determined; the offset range will be used as a criterion to determine whether the module to be tested later has self-discharge anomalies.

[0013] Furthermore, the step S10 includes:

[0014] The lithium-ion battery module to be tested is charged at a constant current of 1C, then discharged at a constant current of 1C; and then charged at a constant current of 0.2C to reach a 3% state of charge.

[0015] Furthermore, the step S20 includes:

[0016] After the lithium-ion battery module is left to stand at 25±5°C for 12 to 24 hours, the voltage VA of each single cell in the module is measured. i ; Wherein, i∈(1,n), n represents the number of single cells.

[0017] Furthermore, the step S30 includes:

[0018] After the lithium-ion battery module is left to stand at 25±5°C for 96 to 120 hours, the voltage VB of each single cell in the module is measured. i .

[0019] Furthermore, the step S40 includes:

[0020] Calculate the voltage drop of each cell in the module: Δv i =VA i -VB i ;

[0021] Determine all pressure drop values ​​Δv i The median M in

[0022] Calculate the offset Z of the voltage drop value of each single cell relative to the median i :Z i =Δv i -M.

[0023] Furthermore, the step S50 includes:

[0024] According to all offsets Z i Analysis of the maximum voltage drop Z in the module max and the minimum value Z min The corresponding batteries are disassembled and analyzed;

[0025] According to the disassembly analysis results, the relationship between the physical defects of the battery cell and the voltage offset is determined, so as to determine the offset Z i The concentrated area is taken as the offset range; the battery cells within the offset range have no physical defects or electrical abnormalities;

[0026] The above offset range will be used as the judgment standard. When the Z value of the single cell in the module is i If it is not within this range, it is determined that there is a self-discharge abnormality.

[0027] Furthermore, in the steps S20 and S30, a 34980 tester is used to measure the first open circuit voltage and the second open circuit voltage.

[0028] In a second aspect, an embodiment of the present invention further provides a lithium-ion battery module self-discharge test system, comprising:

[0029] A charge and discharge adjustment module, used to adjust the charge and discharge test of the lithium-ion battery module to be tested to a preset charge state;

[0030] The first OCV measurement module is used to keep the lithium-ion battery module stationary for a first preset time in a preset temperature environment to measure a first open circuit voltage; the first open circuit voltage includes: the voltage of each single cell in the module;

[0031] The second OCV measurement module is used to keep the lithium-ion battery module stationary for a second preset time in a preset temperature environment to measure a second open circuit voltage; the second open circuit voltage includes: the voltage of each single cell in the module;

[0032] A calculation module, used to calculate the voltage drop value of each single cell in the module according to the first open circuit voltage and the second open circuit voltage; determine the median of all the voltage drop values, and calculate the offset of the voltage drop value of each single cell relative to the median;

[0033] The range determination module is used to disassemble and analyze the batteries corresponding to the maximum and minimum voltage drop values ​​in the module based on the analysis of all offsets, and determine a qualified offset range; the offset range will be used as a judgment standard to determine whether the module tested later has self-discharge anomalies.

[0034] It can be seen from the above technical solution that compared with the prior art, the present invention has the following advantages:

[0035] 1. Accurately identify abnormal batteries: Through detailed charge and discharge tests and multiple open circuit voltage measurements, this method can accurately calculate the voltage drop value of each single cell in the module and determine the offset by calculating the median. This method can effectively identify batteries with abnormal self-discharge and help improve the reliability of the entire battery module.

[0036] 2. Improve module consistency: By disassembling and analyzing the batteries corresponding to the maximum and minimum voltage drop values, we can gain a deeper understanding of the physical defects of these batteries and their impact on voltage deviation. This analysis process helps to determine the qualified deviation range, thereby improving the consistency of the cells within the module and avoiding the degradation of module performance due to inconsistent cells.

[0037] 3. Establish standardized testing standards: This method ultimately provides a reliable judgment standard for subsequent testing by disassembling and analyzing the offset range. This standardized testing process can be widely used in lithium-ion battery module production and testing to ensure the consistency and qualification of mass-produced battery modules in terms of self-discharge characteristics.

[0038] 4. Reduce product defect rate: By screening out abnormal self-discharge batteries at an early stage and removing them, this method can significantly reduce the outflow of defective modules and reduce the product failure rate caused by self-discharge problems of batteries. This not only improves the overall quality of the module, but also enhances customer satisfaction.

[0039] 5. Improve test efficiency and accuracy: This method provides a systematic test process with clear steps and basis from initial testing to final judgment criteria establishment. Compared with traditional methods, this process not only has a significant improvement in accuracy, but also has an efficient test process and is suitable for large-scale applications.

[0040] This method has significant advantages in self-discharge detection and quality control of lithium-ion battery modules, providing a strong guarantee for improving the performance and reliability of battery products. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0042] Figure 1 This is a flow chart of the self-discharge testing method for a lithium-ion battery module provided by the present invention.

[0043] Figure 2 The Z value and the qualified range value Z provided by the present invention a ~Z b Comparison chart of .

[0044] Figure 3 This is the appearance diagram of the abnormal battery of HRYT1245231013064 disassembled provided by the present invention.

[0045] Figure 4 The internal structure diagram of the abnormal battery of HRYT1245231013064 disassembled provided by the present invention. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Embodiment 1:

[0048] The embodiment of the present invention discloses a lithium-ion battery module self-discharge test method, which is applied to module self-discharge screening, collects certain data, and obtains a qualified standard through analysis of the collected data. The whole set of equipment and data standards are subsequently used to determine whether the module has abnormal self-discharge; the self-discharge abnormal module can be effectively eliminated, the consistency of the battery in the module is enhanced, and the service life of the module is increased.

[0049] Specific reference Figure 1 As shown, the following steps are included:

[0050] S10, adjusting the charge and discharge test of the lithium-ion battery module to be tested to a preset charge state;

[0051] S20, keeping the lithium-ion battery module stationary for a first preset time in a preset temperature environment, and measuring a first open circuit voltage; the first open circuit voltage includes: the voltage of each single cell in the module;

[0052] S30, keeping the lithium-ion battery module stationary for a second preset time in a preset temperature environment, and measuring a second open circuit voltage; the second open circuit voltage includes: the voltage of each single cell in the module;

[0053] S40, calculating the voltage drop value of each single cell in the module according to the first open circuit voltage and the second open circuit voltage; determining the median of all the voltage drop values, and calculating the offset of the voltage drop value of each single cell relative to the median;

[0054] S50. Based on the analysis of all the offsets, the batteries corresponding to the maximum and minimum voltage drop values ​​in the module are disassembled and analyzed, and a qualified offset range is determined; the offset range will be used as a criterion to determine whether the module to be tested later has self-discharge anomalies.

[0055] In order to screen out those battery modules that consume power too quickly when not in use, the testing method of the present invention can determine which battery modules have normal self-discharge and which have problems.

[0056] The present invention will be further described below through specific embodiments:

[0057] 1. Preparation

[0058] First, charge or discharge the assembled battery module to a lower power level, about 3% SOC (State of Charge, SOC), which is equivalent to 3% of the battery capacity. In the process of testing and use, SOC is a very important parameter used to indicate the charging state of the battery. For example: 100% SOC means the battery is fully charged. 50% SOC means the battery has half of its power. 0% SOC means the battery is dead.

[0059] Therefore, 3% SOC usually means that the battery is very close to being fully discharged, and there is very little power left. This battery test at a low SOC state can help evaluate the performance of the battery when it is close to the discharge limit, especially to detect battery self-discharge.

[0060] For example, the self-discharge test method of the present invention is described by taking a 12V 45Ah soft pack battery module as an example:

[0061] 1) Leave for 10 seconds;

[0062] 2) 1C constant current charging, upper limit single cell voltage 3.65V;

[0063] 3) Leave for 5 minutes;

[0064] 4) 1C constant current discharge, lower limit single cell voltage 2.7V;

[0065] 5) Leave for 1 minute;

[0066] 6) 0.2C constant current charging, cut-off condition 9min; reach 3% state of charge.

[0067] The module is fully charged at 1C first to ensure a certain amount of expansion. The battery cell is stressed, the internal short-circuit points can be contacted more effectively, and the self-discharge problem is accelerated. The module is charged at 0.2C to 3% SOC to reduce the large current polarization phenomenon, stay away from the voltage plateau, and the voltage changes significantly.

[0068] During the battery charging and discharging process, 1C and 0.2C are units used to express the charging and discharging rate. They are related to the rated capacity of the battery.

[0069] 1C: Indicates that the current intensity of charging or discharging is equal to the rated capacity of the battery. For example, if the rated capacity of the battery is 45Ah (ampere-hour), then the charging or discharging current of 1C is 45A (ampere).

[0070] 0.2C: Indicates that the current intensity of charging or discharging is 0.2 times the rated capacity of the battery. For example, for a 45Ah battery, a 0.2C charging or discharging current is 9A (45Ah×0.2=9A).

[0071] 2. First measurement

[0072] Next, place the battery module in an environment with a temperature of approximately 25°C (+ / - 5°C) for 12 to 24 hours. After that, use the 34980 tester to measure the open circuit voltage (OCV1) of the module and record the voltage VA of each single cell. i ; Where i∈(1,n), n represents the number of single cells, which are denoted as VA1, VA2, VA3, ... VA n etc. and upload the data to the database.

[0073] Among them, OCV refers to the open circuit voltage (OCV) of the battery module measured at different time points. The open circuit voltage refers to the voltage across the battery when there is no load connected (i.e. no current flowing). Because the battery is not used during the static process, this voltage reflects the intrinsic potential of the battery in its current state. OCV is an important indicator for evaluating the health status of the battery, self-discharge characteristics, etc.

[0074] 3. Second measurement

[0075] Then, let the battery module stand at the same temperature for 96 to 120 hours, measure the open circuit voltage (OCV2) of the module again, and record the voltage VB of each single cell. i, respectively denoted as VB1, VB2, VB3...VB n etc. and upload the data to the database.

[0076] 4. Calculate self-discharge

[0077] OCV1 is the voltage measured after a short rest time and is used as an initial reference value.

[0078] OCV2 is the voltage measured after a longer period of rest and is used to evaluate the voltage drop of the battery during this period, that is, the self-discharge condition.

[0079] By comparing the differences between OCV1 and OCV2, especially the voltage changes of each single cell, the degree of self-discharge of the battery can be calculated and those batteries or battery modules with abnormal self-discharge can be screened out.

[0080] Next, the self-discharge is evaluated by calculating the voltage drop (voltage drop) of each battery during this period. Specifically, the voltage drops Δv1 = VA1-VB1, Δv2 = VA2-VB2, Δv3 = VA3-VB3, ... Δv n =VA n -VB n .

[0081] 5. Analyze the results

[0082] Next, we find the voltage drop values ​​Δv1, Δv2, Δv3, ..., Δv n The median M of the voltage drop is calculated, and the offset of the voltage drop of each cell relative to the median is called Z i Value: Z1=Δv1-M, Z2=Δv2-M, Z3=Δv3-M...Z n =Δv n -M. By analyzing Z i By using the value, we can find the battery with the largest and smallest voltage drop in the module, which are denoted as Z max =MAX(Z1, Z2, Z3...Z n ) and Z min =MIN(Z1, Z2, Z3...Z n ).

[0083] The median is an important concept in statistics. It has strong anti-interference ability and is not affected by extreme values ​​(outliers). It can represent the value in the middle of a set of data and can reflect the central trend of the data. In this embodiment, the calculated median M is the middle value of all battery voltage drop data, which is used as a benchmark to facilitate subsequent analysis and comparison.

[0084] 6. Determine the scope of eligibility

[0085] Finally, for Z max and Z min The corresponding battery cells are disassembled and analyzed to determine a qualified offset range Z a to Z b .like Figure 2 As shown, the Z value and the qualified range Z a ~Z b This range will be used as a criterion to determine whether the module tested later has self-discharge anomalies. a ~Z b The value range is , and the batteries with unqualified self-discharge are eliminated.

[0086] For example, the median offset is 0.0011V (Z min )、0.0044V(Z max ), dismantle the module battery corresponding to the cell module code HRYT1245231013008, HRYT1245231013064, dismantle and find that the internal diaphragm has tiny holes when observed through light, causing internal short circuit, such as Figure 3 , Figure 4 shown.

[0087] The disassembly and analysis process includes separating the cells from the module and conducting internal structure inspection and physical analysis. The key points of the analysis include:

[0088] Diaphragm status: Check whether the diaphragm inside the battery cell is penetrated, damaged, or has other defects that may cause internal short circuit.

[0089] Electrode condition: Check the integrity of the positive and negative electrodes, possible signs of corrosion, and the connection status of the electrodes.

[0090] Uniformity and leakage of electrolyte: Check whether the electrolyte inside the battery cell is evenly distributed and whether there is any leakage or drying up.

[0091] Then the offset range Z a to Z b Determination of:

[0092] Through Z max and Z min Disassemble and analyze the corresponding battery cells to determine the relationship between the physical defects of these battery cells and the voltage offset. Combine the disassembly analysis results, empirical data, and the consistency requirements of the actual battery cells to formulate a reasonable voltage drop median offset range Z a to Z b This range should ensure:

[0093] 1) Batteries within this range will not have obvious physical defects or electrical abnormalities.

[0094] 2) This range can effectively distinguish normal cells from potential abnormal cells to avoid misjudgment.

[0095] Additionally, it is possible to verify and optimize:

[0096] The above test and disassembly analysis were performed on multiple batches of cells to verify the initially determined offset range Z a to Z b Whether abnormal cells can be accurately screened out. If the deviation range is found to be too wide or too narrow in multiple verifications, further optimization of Z a to Z b to improve the screening accuracy.

[0097] By means of the module self-discharge test method of the present invention, cells with abnormal self-discharge in the module can be effectively screened out, the outflow ratio of defective modules can be reduced, and customer satisfaction can be enhanced.

[0098] The core of the present invention is to find and screen out batteries with abnormal self-discharge through a series of tests and calculations, thereby ensuring the overall performance and reliability of the battery module. In the future, through this standard and test equipment, it can be more accurately determined whether the battery module meets the requirements.

[0099] In addition, in order to further verify whether the determined offset range is appropriate, 50 lithium-ion battery modules, each including 4 single cells, were tested, and the obtained data are shown in Table 1:

[0100] Table 1 Voltage drop loss of each battery in some modules

[0101]

[0102]

[0103] The data in the table shows the calculation results of battery voltage drop and median offset for different modules.

[0104] for example:

[0105] The median M of module 1 is -0.00205V, Z max It is 5E-05V, Z min It is -0.00015V.

[0106] The median M of module 2 is -0.0021V, Z max It is 1E-04V, Z min It is -0.0001V.

[0107] According to the calculation, the qualified offset range Z a to Z b It is -0.001V to 0.001V.

[0108] Verification results: After disassembling several battery modules, it was found that the median deviation of the battery cells was greater than the qualified range. There were tiny holes inside these batteries, causing short circuits. Therefore, these batteries were considered to have abnormal self-discharge.

[0109] Analyzing the above data and disassembling the battery cells, we can get Z a ~Z b =-0.001~0.001V, and the accuracy of the module screened by the method of the present invention will be verified. This test method identifies batteries with abnormal self-discharge by measuring the change in the open circuit voltage of the battery module. After testing and analysis, problematic cells can be effectively screened out, thereby reducing the proportion of defective modules and improving product quality and customer satisfaction.

[0110] Embodiment 2:

[0111] Based on the same inventive concept, an embodiment of the present invention further provides a lithium-ion battery module self-discharge test system, comprising:

[0112] A charge and discharge adjustment module, used to adjust the charge and discharge test of the lithium-ion battery module to be tested to a preset charge state;

[0113] The first OCV measurement module is used to keep the lithium-ion battery module stationary for a first preset time in a preset temperature environment to measure a first open circuit voltage; the first open circuit voltage includes: the voltage of each single cell in the module;

[0114] The second OCV measurement module is used to keep the lithium-ion battery module stationary for a second preset time in a preset temperature environment to measure a second open circuit voltage; the second open circuit voltage includes: the voltage of each single cell in the module;

[0115] A calculation module, used to calculate the voltage drop value of each single cell in the module according to the first open circuit voltage and the second open circuit voltage; determine the median of all the voltage drop values, and calculate the offset of the voltage drop value of each single cell relative to the median;

[0116] The range determination module is used to disassemble and analyze the batteries corresponding to the maximum and minimum voltage drop values ​​in the module based on the analysis of all offsets, and determine a qualified offset range; the offset range will be used as a judgment standard to determine whether the module tested later has self-discharge anomalies.

[0117] The various modules in the system work together to achieve a fully automated test process from charge and discharge adjustment to final offset range determination. It not only reduces manual operation errors, but also greatly improves test efficiency, making it suitable for batch testing of large-scale battery modules. By integrating various functional modules, the system can achieve efficient, accurate, and automated self-discharge testing and screening processes, greatly improving the detection efficiency and product quality of lithium-ion battery modules.

[0118] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0119] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A lithium-ion battery module self-discharge test method, characterized in that: The following steps are involved: S10, adjusting the charge and discharge test of the lithium-ion battery module to be tested to a preset charge state; S20, keeping the lithium-ion battery module stationary for a first preset time in a preset temperature environment, and measuring a first open circuit voltage; the first open circuit voltage includes: the voltage of each single cell in the module; S30, keeping the lithium-ion battery module stationary for a second preset time in a preset temperature environment, and measuring a second open circuit voltage; the second open circuit voltage includes: the voltage of each single cell in the module; S40, calculating the voltage drop value of each single cell in the module according to the first open circuit voltage and the second open circuit voltage; determining the median of all the voltage drop values, and calculating the offset of the voltage drop value of each single cell relative to the median; S50. Based on the analysis of all the offsets, the batteries corresponding to the maximum and minimum voltage drop values ​​in the module are disassembled and analyzed, and a qualified offset range is determined; the offset range will be used as a criterion to determine whether the module to be tested later has self-discharge anomalies.

2. A lithium-ion battery module self-discharge test method according to claim 1, characterized in that: The step S10 comprises: The lithium-ion battery module to be tested is charged at a constant current of 1C, then discharged at a constant current of 1C; and then charged at a constant current of 0.2C to reach a 3% state of charge.

3. A lithium-ion battery module self-discharge test method according to claim 1, characterized in that: The step S20 comprises: After the lithium-ion battery module is left to stand at 25±5°C for 12 to 24 hours, the voltage VA of each single cell in the module is measured. i ; Wherein, i∈(1,n), n represents the number of single cells.

4. A lithium-ion battery module self-discharge test method according to claim 3, characterized in that: The step S30 includes: After the lithium-ion battery module is left to stand at 25±5°C for 96 to 120 hours, the voltage VB of each single cell in the module is measured. i .

5. A lithium-ion battery module self-discharge test method according to claim 4, characterized in that: The step S40 includes: Calculate the voltage drop of each cell in the module: Δv i =VA i -VB i ; Determine all pressure drop values ​​Δv i The median M in Calculate the voltage drop value of each single cell relative to the median offset Z i :Z i =Δv i -M.

6. A lithium-ion battery module self-discharge test method according to claim 5, characterized in that: The step S50 comprises: According to all offsets Z i Analysis of the maximum voltage drop Z in the module max and the minimum value Z min The corresponding batteries are disassembled and analyzed; According to the disassembly analysis results, the relationship between the physical defects of the battery cell and the voltage offset is determined, so as to determine the offset Z i The concentrated area is taken as the offset range; the battery cells within the offset range have no physical defects or electrical abnormalities; The above offset range will be used as the judgment standard. When the Z value of the single cell in the module is i If it is not within this range, it is determined that there is a self-discharge abnormality.

7. A lithium-ion battery module self-discharge test method according to claim 4, characterized in that: In the steps S20 and S30, a 34980 tester is used to measure the first open circuit voltage and the second open circuit voltage.

8. A lithium-ion battery module self-discharge test system, characterized in that: include: A charge and discharge adjustment module, used to adjust the charge and discharge test of the lithium-ion battery module to be tested to a preset charge state; The first OCV measurement module is used to keep the lithium-ion battery module stationary for a first preset time in a preset temperature environment to measure a first open circuit voltage; the first open circuit voltage includes: the voltage of each single cell in the module; The second OCV measurement module is used to keep the lithium-ion battery module stationary for a second preset time in a preset temperature environment to measure a second open circuit voltage; the second open circuit voltage includes: the voltage of each single cell in the module; A calculation module, used to calculate the voltage drop value of each single cell in the module according to the first open circuit voltage and the second open circuit voltage; determine the median of all the voltage drop values, and calculate the offset of the voltage drop value of each single cell relative to the median; The range determination module is used to disassemble and analyze the batteries corresponding to the maximum and minimum voltage drop values ​​in the module based on the analysis of all offsets, and determine a qualified offset range; the offset range will be used as a judgment standard to determine whether the module tested later has self-discharge anomalies.

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