Lithium battery AC internal resistance compensation and poor dynamic internal resistance screening method

Abstract

The invention discloses a lithium battery AC internal resistance compensation and dynamic internal resistance defect screening method. The method comprises the following steps: constructing a channel internal resistance compensation database to correct a measurement error; obtaining the compensation internal resistance of a battery cell channel, removing an abnormal value through sigma circulation to obtain an average value / median and a standard deviation, and obtaining the sigma level S1 of a battery cell tray; recalculating the average value / median of the tray according to the S1 range, subtracting the battery core compensation internal resistance from the average value / median to obtain an internal resistance difference value, and integrally analyzing the battery core to obtain a sigma level S2 of the battery core internal resistance difference value for correcting the temperature difference; the average value / median of the welding machine is calculated to construct a welding machine compensation value; a compensation difference value is obtained by subtracting the internal resistance difference value of the battery cell from the average value / median; the average value / median of the compensation difference value of the tray is calculated; the compensation difference value is subtracted from the compensation difference value to obtain a final difference value; analyzing the battery cell according to a welding machine to obtain a sigma level S6 of a final difference value for correcting the difference of the welding machine; and intercepting the battery cell according to the step S6 or the step S2.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries and power batteries, and in particular to a method for compensating alternating current internal resistance and screening poor dynamic internal resistance of a lithium battery. Background Art

[0002] Battery internal resistance is the sum of the resistances within the battery, which are composed of the resistances of the electrolyte, electrode materials, and cell structure. This parameter has a direct impact on the battery's discharge efficiency, energy density, cycle life, and safety. The magnitude of the battery's internal resistance is directly related to the energy loss during operation. The lower the internal resistance, the higher the battery's efficiency, while the lower the internal resistance, the greater the energy loss. Therefore, in battery cell manufacturing, optimizing the battery internal resistance screening scheme is crucial to ensuring consistency across the entire battery pack and is a key step in ensuring battery pack performance and safety.

[0003] Currently, the industry's primary method for screening lithium battery internal resistance is the AC internal resistance test. This method injects an AC signal of a specific frequency into the battery to measure its internal resistance. If the internal resistance meets a preset internal resistance threshold, it meets the standard. This method is highly accurate and suitable for precision sorting, but it also requires high accuracy from the measuring equipment. This method has high environmental requirements and is easily affected by the measurement system during testing (such as temperature and equipment test accuracy). This makes it impossible to effectively screen out batteries using only a fixed internal resistance standard, posing a certain risk of "missing" batteries. Therefore, using this method requires strict environmental control and standardized processes to ensure the accuracy of the measurement data and the consistency of the screening process.

[0004] However, in the actual screening process, the number of cells screened in a batch is huge, and they need to be placed in a static warehouse with a fixed temperature. The static warehouse includes three levels: testing equipment - tray - testing channel; one testing equipment is equipped with multiple trays; each tray is equipped with multiple testing channels, and each channel is used to place a cell. The screening errors include the following aspects: (1) The same testing equipment inputs a pulse current of a certain frequency to the cell of each channel to obtain its AC internal resistance value. Due to the different loss rates between different channels, the deviation in consistency between channels, and the difference in repeatability of different channels, different channels have different deviations when measuring internal resistance; ultimately, in the actual screening, it will be found that the range of internal resistance values ​​measured for different cells in the same batch is too large to make it impossible to unify the standards. (2) Due to the distribution of temperature control facilities and the influence of air flow, there are large differences in temperature inside the static warehouse, such as Figure 1The figure shows that the applicant measured the temperature of different layers (heights) or different columns (horizontal positions) of the static storage at the same time. It can be seen that although the static storage was temperature-controlled, the temperature of different layers and columns of the cells was very different due to the stacking of the cells. Moreover, the temperature difference at different times of the same day would also lead to temperature differences, which would eventually lead to the problem that the range of internal resistance values ​​was too large to make it impossible to unify the standards. (3) During the production welding process, different welding stations would cause deviations in the welding points of the cells.

[0005] According to relevant technical requirements, if it is impossible to unify the standards, the battery cells of this batch need to be manually disassembled and the standards adjusted. This not only poses a serious risk of missing or over-killing, but also seriously affects production efficiency. Summary of the Invention

[0006] 1. Technical problems to be solved: In response to the above technical problems, the present invention provides a method for lithium battery AC internal resistance compensation and dynamic internal resistance defect screening. Based on the Six Sigma quality process management technology, this method introduces a dynamic equipment internal resistance screening scheme for the scenario of battery cell screening equipment. It can effectively reduce the slow fluctuation of the equipment caused by wire loss, eliminate the internal resistance error between different detection channels, eliminate the influence of temperature on internal resistance testing, and eliminate the influence of work station on internal resistance testing.

[0007] 2. Technical solution: A method for compensating AC internal resistance and screening for poor dynamic internal resistance of a lithium battery, characterized by comprising: Step 1: Equipment compensation: Obtain historical internal resistance data of the testing equipment, analyze the historical data to obtain channel internal resistance compensation values ​​corresponding to all detection channels included in the testing equipment, and build a channel internal resistance compensation database; the channel internal resistance compensation values ​​are used to compensate for the channel internal resistance of the battery cells to be tested produced on the production line; Step 2: Position and temperature compensation; the internal resistance measurement value of each battery cell in the entire batch of batteries is matched to its channel internal resistance compensation value to obtain the channel-compensated internal resistance value for the following analysis; the battery cells in this batch are analyzed separately in units of individual trays, and the channel-compensated internal resistance values ​​of the batteries in the same tray are analyzed to obtain the mean / median and standard deviation of all batteries in the tray to obtain the channel-compensated sigma level S of each battery cell. 1N ; Preset single pallet Sigma level S 1NThe standard range is N2, and data outside the ±N2 times sigma level are eliminated; the data of the remaining battery cells are calculated again until the internal resistance value after channel compensation meets the sigma standard range of ±N2; the mean / median of the internal resistance value of the tray at this time is obtained, and the difference between the mean / median and the internal resistance value of a single battery cell after channel compensation is calculated, and the difference is defined as the internal resistance difference; the single tray internal resistance difference sigma level S1 of a single battery cell is preset to the standard range of N3 for the entire batch analysis, and all battery cells in the tray with an internal resistance difference within ±N3 are selected; the mean / median and standard deviation of all battery cells in the batch that meet the ±N3 range are calculated, and the sigma level S2 of the internal resistance difference of a single battery cell in the battery cell batch is obtained; Step 3: Correct welder differences at key welder stations; trace the corresponding key welder station information for the entire batch of battery cells and group them according to the welder station; calculate the battery cell internal resistance difference corresponding to each welder station to obtain the station mean and station standard deviation of the battery cell internal resistance difference, and obtain the station sigma level S3; use the welder mean / median to construct the welder compensation value, and subtract the welder compensation value from the internal resistance difference of each battery cell to obtain the compensation difference; combine the compensation difference of the battery cell corresponding to the pallet, and use the compensation difference of each battery cell to subtract the mean / median of the pallet compensation difference to obtain the final difference. Finally, use the preset sigma standard N9 to calculate the mean / median and standard deviation of the final difference to obtain the sigma level of the final difference of the station; Step 4: Abnormal battery cell interception; if the battery cell has welding station information, it is intercepted according to the sigma level S6 of the final difference of the station; otherwise, it is intercepted according to the sigma level S2 of the internal resistance difference; the battery cell after interception is imported into the battery cell disabling system to automatically downgrade the battery cell.

[0008] Furthermore, step one specifically includes: S11: Acquire testing equipment information; the testing equipment information includes the testing equipment number, the testing channel number, the tray number, the welding station number, and the number of the tested battery cell; each testing equipment includes multiple testing trays, each tray is provided with multiple testing channels, and each testing channel is used to test the internal resistance of a battery cell; during testing, the battery cell internal resistance detected by each testing channel is transmitted to the computer system for processing; the welding station is the welding station corresponding to the battery cell on the production line; S12: Obtain historical internal resistance values ​​of a preset data volume of the detection device, and remove abnormal values ​​of the internal resistance value of a single battery cell in the historical internal resistance values ​​that exceed the internal resistance standard range; the exceeding internal resistance standard range includes exceeding a preset internal resistance value range and exceeding the single pallet sigma standard range N1 of the battery cell internal resistance historical data; the single pallet sigma standard is calculated based on the historical data of each pallet, and the internal resistance value of a single battery cell is within the sigma range of N1 times; the internal resistance values ​​exceeding the internal resistance standard range are removed, and the remaining data is saved in the internal resistance compensation database; S13: Analyze the historical data of each detection channel in the internal resistance compensation database to obtain the channel internal resistance compensation value of the corresponding channel; the channel internal resistance compensation value calculation process is: obtain the historical average value / median X1 of the battery cell internal resistance of all battery cells of the detection equipment, obtain the historical average value / median μ of the battery cell internal resistance of the detection channel, and then obtain the channel internal resistance compensation value C=X1-μ of the corresponding detection channel; update the channel internal resistance compensation value to the internal resistance compensation database.

[0009] Furthermore, step 2 specifically includes: S21: Testing a single batch of battery cells coming off the production line using a corresponding type of testing equipment; obtaining internal resistance test values ​​for all battery cells in the batch; removing all internal resistance test values ​​that exceed a preset internal resistance measurement value range; and obtaining a channel internal resistance compensation value C corresponding to the battery cell based on the channel in which the battery cell is located. S22: During the test, the internal resistance test value of each battery cell is represented by ACR, and its corresponding channel internal resistance compensation value is C. Then, the internal resistance value of the battery cell after channel compensation is ACR1=ACR-C; S23: Analyze a single pallet as a unit and calculate the mean / median X2 and internal resistance standard deviation σ1 of the channel-compensated internal resistance ACR1 of all channels involved in the test for each pallet. Calculate the single pallet internal resistance sigma level S for each battery cell after channel compensation. 1N , then S 1N = (ACR1- X2) / (σ1); S24: Single tray sigma level S for a single cell after preset channel compensation 1N The standard range is ± N2 times. After removing the battery cell data outside the ± N2 times sigma level, recalculate the channel compensation of the remaining battery cells and calculate the single tray internal resistance sigma level S. 1N , repeat the comparison and elimination until the sigma level of the remaining cells is S 1N If both are within the preset standard range N2, the process goes to step S25; S25: Calculate the difference between the internal resistance of the remaining cells in the tray after channel compensation and the average / median internal resistance of the remaining cells in the tray after channel compensation. Define this difference as the internal resistance difference of a single cell. Then, the internal resistance difference of each cell, Z1 = (ACR1-X2). S26: Preset the sigma level S1 of the internal resistance difference of a single battery cell on a single tray for the standard range N3 for the overall analysis; select battery cells within the range of ±N3; analyze the entire batch and calculate the overall sigma level S2 of the internal resistance difference of a single battery cell based on the mean / median X3 and standard deviation σ2 of the internal resistance difference of the selected battery cells, where S2 = (Z1-X3) / σ2.

[0010] Furthermore, step three specifically includes: S31: Obtain the process data of the key welding machine stations of each battery cell in the batch, and group the battery cells according to the welding stations; analyze the battery cell data of each group of welding stations, and preset the average / median sigma standard range of the resistance difference of the single battery cell at the station to be N4 and the standard deviation sigma level of the resistance difference to be N5; select the internal resistance difference of the single battery cell with the sigma level S2 within the range of ±N4 to calculate the average / median internal resistance difference of the station X4, select the internal resistance data of the single battery cell with the sigma level S2 within ±N5 to calculate the standard deviation σ3 of the internal resistance difference of the station; then calculate the sigma level S3 of the internal resistance difference of the selected single battery cell at the single station, where S3=(Z1-X4) / σ3; update S3 to the database; S32: Preset the mean / median standard range of the sigma level S3 of the internal resistance difference of a single cell for intra-group analysis to N6, select cell data that meet the range of ±N6 times, and use the internal resistance difference Z1 of the selected cell to calculate the mean X5 of the internal resistance difference of the cell and the mean X6 of the internal resistance difference of all cells in the batch; Preset the mean / median standard range of the sigma level S3 of the internal resistance difference of a single cell for intra-group analysis to N7, select cells that meet the range of ±N7, calculate their standard deviation σ4, and obtain the sigma level S4 of each cell for intra-group analysis, that is, S4=(Z1-X5) / σ4; S33: Using the average value X5 of the internal resistance difference of the workstation and the average value X6 of the internal resistance difference of the entire batch, the compensation difference C2 of the workstation is obtained, that is, C2 = X5 - X6; based on the compensation difference C2, the compensation difference Z2 of each battery cell is obtained, where Z2 = Z1 - C2; S34: Analyze the cell compensation difference Z2 in each pallet and calculate the average value of the cell compensation difference Z2 to obtain the average value of the single pallet compensation difference X7, and obtain the final difference Z3 of each cell, that is, Z3 = Z2 - X7; S35: Preset the standard sigma range of the standard deviation of the final difference Z3 of a single battery cell to N8, select the battery cells whose sigma level S4 of a single battery cell is within the range of ±N8 times the sigma level, and obtain the standard deviation σ5 of the final difference of a single station at each station; Preset the standard sigma range of the mean of the final difference Z3 of a single station to N9, select the battery cells whose sigma level S4 of a single battery cell is within the range of ±N9 times, and obtain the mean X8 of the final difference of a single station at each station; S36: Analyze a single piece of equipment as a unit. According to the standard table of preset welding machine station standard deviations, obtain the mean value X9 of the preset standard deviation of a single station and the standard deviation σ6 of the preset standard deviation, thereby obtaining the current sigma level S5 of the single station, where S5 = (σ5-X9) / σ6; S37: Preset the comparison table of the current sigma level S5 range and N8 value of a single workstation; match the corresponding standard N8 in the comparison table according to the current sigma level S5 of a single workstation. If there is a difference, update N8 and return to step S35. Otherwise, the sigma level S6 of the final difference of a single battery cell at a single workstation is obtained, that is, S6=(Z3-X8) / σ5.

[0011] Furthermore, the abnormal cell interception in step 4 includes: S41: If the battery cell has welding station information, it is intercepted according to the preset standard m1 based on the sigma level S6 of the final difference Z3 of the station; otherwise, it is intercepted according to the preset standard m2 based on the sigma level S2 of the internal resistance difference Z1; the battery cell after interception is imported into the battery cell disabling system to automatically downgrade the battery cell.

[0012] Furthermore, step one also includes: S15: Data update; when the detection equipment enters the maintenance and channel calibration process, the original database is cleared and the channel internal resistance compensation library is rebuilt from the breakpoint; when the amount of historical data exceeds the preset value, the data with the longest time from the present is deleted and the real-time compensation value of the internal resistance is recalculated.

[0013] Furthermore, the grouping according to welding machine workstations includes a wire body, a workstation and a fixture according to workstation information; the wire body is information about the welding machine, and the wire body is provided with multiple workstations; each workstation is provided with multiple fixtures.

[0014] Furthermore, when it is applied, manual EXCEL macro implementation and / or automated programming software implementation are adopted; the automated programming software includes one of Python and JAVA.

[0015] 3.Beneficial effects: (1) This method provides a method for lithium battery AC internal resistance compensation and dynamic internal resistance defect screening. In order to solve the internal resistance value distribution problem caused by equipment reasons, each detection channel is first analyzed from the equipment aspect to obtain the channel internal resistance compensation value of each detection channel. In the subsequent analysis, the channel compensation of the battery cell internal resistance is first performed to effectively eliminate the problems caused by the internal resistance error between different detection channels.

[0016] (2) This method provides a method for AC internal resistance compensation and dynamic internal resistance defect screening of lithium batteries. The internal resistance data after channel compensation are analyzed. The sigma quality management method is used to obtain the internal resistance data of the cells tested in the batch in a single tray after channel compensation. The sigma level after channel compensation in the tray is analyzed, and the cells that do not meet the sigma level requirements are eliminated. The sigma level of the internal resistance difference of the remaining cells is then screened. Finally, the internal resistance difference of the cells is screened in the entire batch. The sigma level of a single cell in the entire batch is obtained. This process can effectively eliminate the temperature changes caused by the difference in the static warehouse position.

[0017] (3) In the method for AC internal resistance compensation and dynamic internal resistance screening of lithium batteries provided by this method, based on the above data analysis, the cell data of the batch of welding stations are analyzed; by removing the abnormal values ​​of the internal resistance difference from the whole batch coarse screening to the abnormal values ​​of the internal resistance difference of the single station fine screening, and finally to the abnormal values ​​of the final difference of the single station fine screening, the screening accuracy is improved layer by layer, and the most standard sigma level of the station compensation difference is obtained; through this process, the problem of large internal resistance fluctuation caused by the consistency difference of the welding stations can be effectively eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The impact of the level and column level of the static storage on the temperature; Figure 2 The temperature waveform diagram of the static storage at different times for 7 days; Figure 3 This is a flow chart of step one of the method; Figure 4 This is a flow chart of step 2 in this method; Figure 5 This is a flowchart of step three in this method; Figure 6 This is a flow chart of step four in this method; Figure 7 It is a specific data diagram in a specific embodiment; Figure 8 The standard table of welding machine position standard deviation and the comparison table of S5 and N8 values ​​in the specific embodiment; Figure 9 The overall flow chart of this method is shown in Figure 2. DETAILED DESCRIPTION

[0019] The present invention will be described in detail below with reference to the accompanying drawings.

[0020] Currently, the most common internal resistance test calibration method in the industry is to use an internal resistance standard block for probe pressure calibration. This calibration method is affected by the test fluctuations of the equipment itself (internal resistance test MSA) and the contact area and pressure between the probe and the standard block. The internal resistance between different channels always fluctuates within a certain range, and the range of the channel internal resistance mean difference is usually 0.003-0.008mΩ. Internal resistance test equipment is usually composed of a high-precision internal resistance tester, circuits, acquisition boards, conversion boards, cylinders, etc. At the same time, due to equipment design issues, the service life of different channels varies. As use increases, the internal resistance of each channel changes inconsistently. Some channels test internal resistance and some channels test internal resistance and some channels test internal resistance and some channels test internal resistance and some channels test internal resistance and no significant change. Therefore, if you want to rely on internal resistance to screen assembly and welding problems, you must first solve the problems caused by the test channel equipment.

[0021] As attached Figure 3 As shown, in this method, a channel internal resistance compensation database is set up to eliminate the problem of the test channel by means of channel internal resistance compensation. At the same time, in order to reduce the influence of usage time, the data of the internal resistance compensation library needs to be updated in a timely manner. The size of the channel internal resistance compensation value in this solution is calculated based on the historical average / median of the channel and the historical average / median of all standard-compliant battery cells in the data set. Since the data is updated in real time (it can be updated according to the amount of data in the database or according to the data time), its compensation value can relatively reduce the instability problem caused by the equipment itself. The preset standards in this step include the preset range of internal resistance values, and also include the preset single-tray sigma level standard (N1 in the figure) of a single battery cell in its corresponding tray; data with internal resistance values ​​outside the range and the single-tray sigma level standard are eliminated.

[0022] Due to design defects of the production line and the influence of the climate in the production base area, there is a serious temperature difference phenomenon in the process of this type of battery cell in the normal temperature storage warehouse in this area: Figure 1 In the temperature trend chart of a static warehouse for seven days, it can be clearly seen that the higher the number of layers of the sub-warehouse, the higher the temperature inside the sub-warehouse; the larger the number of columns, the lower the temperature; as shown in the attached figure Figure 2 As shown in the figure, the relationship diagram between the static storage layer / column and the internal resistance mean and the relationship diagram between the static storage and the internal resistance mean are summarized. It can be clearly seen that the trend of the internal resistance mean is inversely related to the seven-day storage temperature.

[0023] In order to eliminate the influence of location or temperature, Figure 4As shown in the flowchart for step 2, this step analyzes pallets within the same batch (controlling for essentially identical testing times to eliminate temperature variations at different times of the day), at the same testing location (i.e., the same pallet), and with approximately the same temperature. Test data from different test channels within the same pallet is obtained and channel-compensated before processing in the following steps. The compensated internal resistance values ​​of each cell, along with the average / median internal resistance values ​​and standard deviation for the entire pallet, are used to determine the sigma level for each channel within the pallet (i.e., individual cells). Substandard cells are then eliminated. The difference between the compensated channel resistance values ​​of the retained cells and the average / median resistance values ​​for the corresponding pallet is then taken to define the internal resistance difference. This internal resistance difference compensates for channel (equipment) variations while also accounting for variations in pallet. Within the pallet, the internal resistance difference values ​​of each cell are calculated and the corresponding sigma level S1 for the individual pallet internal resistance difference is calculated. A sigma standard N3 for the individual pallet internal resistance difference is preset for batch-wide analysis, and substandard cell data is eliminated. Finally, the sigma level of the internal resistance difference of the remaining cells in the entire batch is calculated.

[0024] In order to eliminate the influence of different welding positions on the distribution of internal resistance data during the production process, the battery cells are analyzed according to the different welding positions. Figure 5As shown, first analyze the internal resistance value of each workstation, group the workstations, and each workstation corresponds to a group. This step is based on the internal resistance difference data of each battery cell obtained above to analyze the sigma level of each battery cell in the group, and analyze the mean and standard deviation of the internal resistance difference. In the workstation, the mean sigma standard and the standard deviation sigma standard are preset respectively, and the battery cells with the mean within the preset mean sigma standard are selected and the mean / median X4 of the workstation is obtained; the battery cells with the standard deviation within the preset standard deviation sigma standard are selected and their standard deviation at the workstation is obtained; and then the single-station sigma level S3 of a single battery cell is obtained; the single-station sigma level S3 of a single battery cell in a single workstation is preset with the mean sigma level N6 and the standard deviation sigma level N7, the battery cell internal resistance difference that meets N6 is selected to calculate the single-station mean / median, and the internal resistance difference that meets N7 is selected to calculate the single-station standard deviation; the difference between the single-station mean / median of each workstation and the internal resistance mean of the entire batch is obtained, which is the workstation compensation value of the workstation, and the value obtained by taking the difference between the internal resistance difference of each battery cell and the workstation compensation value is the compensation difference Z2 of the battery cell. Then, the average / median value X7 of the compensation differences of the battery cells contained in each pallet is obtained. The difference between the average / median value and the final difference Z3 of each battery cell in the pallet is calculated. The sigma level standard for the standard deviation of the final difference of each battery cell at a single station is preset to N8, and the sigma level standard for the mean is N9. Based on the standard table of welding machine station standard deviations and the comparison table of S5 and N8 values, standard N8 is matched to obtain the final standard deviation used to calculate the final difference of the single station. The final difference that meets N9 is selected to calculate the average / median value X8 of the single station, and then the sigma level S6 of the final difference of the single battery cell at a single station is obtained.

[0025] This method provides two ways to intercept the battery cell, as shown in the attached Figure 6 As shown, if welding station data is available, interception is performed based on the final difference. If the sigma level of the final difference of a single cell at a single station is outside the preset range, interception is performed and the system is disabled. If there is no welding station information, interception is performed based on the sigma level of the entire batch of single cells within the preset sigma standard.

[0026] This solution has been put into the screening of specific production processes. Compared with the original screening solution, this solution introduces a dynamic equipment internal resistance calibration solution, which has the following technical effects: it eliminates the slow fluctuation of the equipment caused by wire loss; eliminates the internal resistance error between different measurement channels; introduces the concept of internal resistance difference, eliminates the influence of temperature difference during internal resistance testing; introduces the concept of welding machine station compensation, and screens based on a single welding machine station, eliminating the influence of the welding machine station on the internal resistance difference of the battery cell; it truly realizes the dynamic internal resistance standard of the 6SIGMA management method, which not only eliminates the problem of poor internal resistance outflow, but also effectively reduces the over-kill rate of internal resistance screening. According to existing data, it can be reduced by at least about 50%. Specific embodiment 1: As attached Figure 7 As shown, part of the data of a batch of battery cells screened using this solution is shown in the figure; the figure includes the battery cell coding information, the measured internal resistance information, the tray and channel information corresponding to the battery cell, and the work station information; each row represents the data of a battery cell; the F column is the internal resistance of the battery cell after channel compensation; the data in the G column is the sigma level S1 after channel compensation; the K column is the internal resistance difference of the battery cell; the N column is the sigma level S2 of the internal resistance difference of a single battery cell in the batch of battery cells; the S column is the sigma level S3 of the internal resistance difference Z1 of the corresponding battery cell work station; the T column is the sigma level S4 of the internal resistance difference Z1 of the corresponding battery cell work station; the U column is the compensated difference Z2 of the battery cell; the V column is the final difference Z3 of the battery cell; and the W column is the sigma level S6 of the final difference Z3 of the battery cell work station. Specific embodiment 2: As attached Figure 8 The figure shows an embodiment of a standard table of preset welding machine station standard deviations and a comparison table of S5 and N8 values ​​in steps S36 and S37 of step three. In the table, there is a progressive relationship between the line body, station and fixture: the welding machine includes multiple stations, and a station includes multiple fixtures, which are the numbers of the welding stations in this solution. The left figure provides the average standard deviation X9 and the standard deviation σ6 corresponding to each station number. According to the station number, they can be obtained, and then the current sigma level S5 of the single station of the station can be calculated; the right figure is a comparison table of S5 and N8 values. The specific value of N8 is obtained according to the range of the calculated S5. The "production line investigation" in the figure indicates that the data may correspond to a production line failure or collection error, so it needs to be investigated.

[0029] Although the present invention has been disclosed above in terms of preferred embodiments, they are not intended to limit the present invention. Anyone skilled in the art can make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims of this application.

Claims

1. A method for compensating AC internal resistance and screening for poor dynamic internal resistance in lithium batteries, characterized by: include: Step 1: Equipment compensation; Obtain historical internal resistance data of the testing equipment, analyze the historical data to obtain channel internal resistance compensation values ​​corresponding to all detection channels included in the testing equipment, and build a channel internal resistance compensation database; the channel internal resistance compensation values ​​are used to compensate for the channel internal resistance of the battery cells to be tested produced on the production line; Step 2: Position and temperature compensation; the internal resistance measurement value of each battery cell in the entire batch of batteries is matched to its channel internal resistance compensation value to obtain the channel-compensated internal resistance value for the following analysis; the battery cells in this batch are analyzed separately in units of individual trays, and the channel-compensated internal resistance values ​​of the batteries in the same tray are analyzed to obtain the mean / median and standard deviation of all batteries in the tray to obtain the channel-compensated sigma level S of each battery cell. 1N ; Preset single pallet Sigma level S 1N The standard range is N2, and data outside the ±N2 times sigma level are eliminated; the data of the remaining battery cells are calculated again until the internal resistance value after channel compensation meets the sigma standard range of ±N2; the mean / median of the internal resistance value of the tray at this time is obtained, and the difference between the mean / median and the internal resistance value of a single battery cell after channel compensation is calculated, and the difference is defined as the internal resistance difference; the single tray internal resistance difference sigma level S1 of a single battery cell is preset to the standard range of N3 for the entire batch analysis, and all battery cells in the tray with an internal resistance difference within ±N3 are selected; the mean / median and standard deviation of all battery cells in the batch that meet the ±N3 range are calculated, and the sigma level S2 of the internal resistance difference of a single battery cell in the battery cell batch is obtained; Step 3: Correct welder differences at key welder stations; trace the corresponding key welder station information for the entire batch of battery cells and group them according to the welder station; calculate the battery cell internal resistance difference corresponding to each welder station to obtain the station mean and station standard deviation of the battery cell internal resistance difference, and obtain the station sigma level S3; use the welder mean / median to construct the welder compensation value, and subtract the welder compensation value from the internal resistance difference of each battery cell to obtain the compensation difference; combine the compensation difference of the battery cell corresponding to the pallet, and use the compensation difference of each battery cell to subtract the mean / median of the pallet compensation difference to obtain the final difference. Finally, use the preset sigma standard N9 to calculate the mean / median and standard deviation of the final difference to obtain the sigma level of the final difference of the station; Step 4: Abnormal battery cell interception; If the battery cell has welding station information, it is intercepted according to the sigma level S6 of the final difference of the station; otherwise, it is intercepted according to the sigma level S2 of the internal resistance difference; the battery cell after interception is imported into the battery cell disabling system to automatically downgrade the battery cell.

2. The method for compensating AC internal resistance and screening for poor dynamic internal resistance of a lithium battery according to claim 1, characterized in that: Step 1 specifically includes: S11: Acquire testing equipment information; the testing equipment information includes the testing equipment number, the testing channel number, the tray number, the welding station number, and the number of the tested battery cell; each testing equipment includes multiple testing trays, each tray is provided with multiple testing channels, and each testing channel is used to test the internal resistance of a battery cell; during testing, the battery cell internal resistance detected by each testing channel is transmitted to the computer system for processing; the welding station is the welding station corresponding to the battery cell on the production line; S12: Obtain historical internal resistance values ​​of a preset data volume of the detection device, and remove abnormal values ​​of the internal resistance value of a single battery cell in the historical internal resistance values ​​that exceed the internal resistance standard range; the exceeding internal resistance standard range includes exceeding a preset internal resistance value range and exceeding the single pallet sigma standard range N1 of the battery cell internal resistance historical data; the single pallet sigma standard is calculated based on the historical data of each pallet, and the internal resistance value of a single battery cell is within the sigma range of N1 times; the internal resistance values ​​exceeding the internal resistance standard range are removed, and the remaining data is saved in the internal resistance compensation database; S13: Analyze the historical data of each detection channel in the internal resistance compensation database to obtain the channel internal resistance compensation value of the corresponding channel; the channel internal resistance compensation value calculation process is: obtain the historical average value / median X1 of the battery cell internal resistance of all battery cells of the detection equipment, obtain the historical average value / median μ of the battery cell internal resistance of the detection channel, and then obtain the channel internal resistance compensation value C=X1-μ of the corresponding detection channel; update the channel internal resistance compensation value to the internal resistance compensation database.

3. The method for compensating AC internal resistance and screening for poor dynamic internal resistance of a lithium battery according to claim 2, characterized in that: Step 2 specifically includes: S21: Testing a single batch of battery cells coming off the production line using a corresponding type of testing equipment; obtaining internal resistance test values ​​for all battery cells in the batch; removing all internal resistance test values ​​that exceed a preset internal resistance measurement value range; and obtaining a channel internal resistance compensation value C corresponding to the battery cell based on the channel in which the battery cell is located. S22: During the test, the internal resistance test value of each battery cell is represented by ACR, and its corresponding channel internal resistance compensation value is C. Then, the internal resistance value of the battery cell after channel compensation is ACR1=ACR-C; S23: Analyze a single pallet as a unit and calculate the mean / median X2 and internal resistance standard deviation σ1 of the channel-compensated internal resistance ACR1 of all channels involved in the test for each pallet. Calculate the single pallet internal resistance sigma level S for each battery cell after channel compensation. 1N , then S 1N = (ACR1- X2) / (σ1); S24: Single tray sigma level S for a single cell after preset channel compensation 1N The standard range is ± N2 times. After removing the cell data outside the ± N2 times sigma level, recalculate the channel compensation of the remaining cells and calculate the single tray internal resistance sigma level S. 1N , repeat the comparison and elimination until the sigma level of the remaining cells is S 1N If both are within the preset standard range N2, the process goes to step S25; S25: Calculate the difference between the internal resistance of the remaining cells in the tray after channel compensation and the average / median internal resistance of the remaining cells in the tray after channel compensation. Define this difference as the internal resistance difference of a single cell. Then, the internal resistance difference of each cell, Z1 = (ACR1-X2). S26: Preset the sigma level S1 of the internal resistance difference of a single battery cell on a single tray for the standard range N3 for the overall analysis; select battery cells within the range of ±N3; analyze the entire batch and calculate the overall sigma level S2 of the internal resistance difference of a single battery cell based on the mean / median X3 and standard deviation σ2 of the internal resistance difference of the selected battery cells, where S2 = (Z1-X3) / σ2.

4. The method for compensating AC internal resistance and screening for poor dynamic internal resistance of a lithium battery according to claim 3, characterized in that: Step three specifically includes: S31: Obtain the process data of the key welding machine stations of each battery cell in the batch, and group the battery cells according to the welding stations; analyze the battery cell data of each group of welding stations, and preset the average / median sigma standard range of the resistance difference of the single battery cell at the station to be N4 and the standard deviation sigma level of the resistance difference to be N5; select the internal resistance difference of the single battery cell with the sigma level S2 within the range of ±N4 to calculate the average / median internal resistance difference of the station X4, select the internal resistance data of the single battery cell with the sigma level S2 within ±N5 to calculate the standard deviation σ3 of the internal resistance difference of the station; then calculate the sigma level S3 of the internal resistance difference of the selected single battery cell at the single station, where S3=(Z1-X4) / σ3; update S3 to the database; S32: Preset the mean / median standard range of the sigma level S3 of the internal resistance difference of a single cell for intra-group analysis to N6, select cell data that meet the range of ±N6 times, and use the internal resistance difference Z1 of the selected cell to calculate the mean X5 of the internal resistance difference of the cell and the mean X6 of the internal resistance difference of all cells in the batch; Preset the mean / median standard range of the sigma level S3 of the internal resistance difference of a single cell for intra-group analysis to N7, select cells that meet the range of ±N7, calculate their standard deviation σ4, and obtain the sigma level S4 of each cell for intra-group analysis, that is, S4=(Z1-X5) / σ4; S33: Using the average value X5 of the internal resistance difference of the workstation and the average value X6 of the internal resistance difference of the entire batch, the compensation difference C2 of the workstation is obtained, that is, C2 = X5 - X6; based on the compensation difference C2, the compensation difference Z2 of each battery cell is obtained, where Z2 = Z1 - C2; S34: Analyze the cell compensation difference Z2 in each pallet and calculate the average value of the cell compensation difference Z2 to obtain the average value of the single pallet compensation difference X7, and obtain the final difference Z3 of each cell, that is, Z3 = Z2 - X7; S35: Preset the standard sigma range of the standard deviation of the final difference Z3 of a single battery cell to N8, select the battery cells whose sigma level S4 of a single battery cell is within the range of ±N8 times the sigma level, and obtain the standard deviation σ5 of the final difference of a single station at each station; Preset the standard sigma range of the mean of the final difference Z3 of a single station to N9, select the battery cells whose sigma level S4 of a single battery cell is within the range of ±N9 times, and obtain the mean X8 of the final difference of a single station at each station; S36: Analyze a single piece of equipment as a unit. According to the standard table of preset welding machine station standard deviations, obtain the mean value X9 of the preset standard deviation of a single station and the standard deviation σ6 of the preset standard deviation, thereby obtaining the current sigma level S5 of the single station, where S5 = (σ5-X9) / σ6; S37: Preset the comparison table of the current sigma level S5 range and N8 value of a single workstation; match the corresponding standard N8 in the comparison table according to the current sigma level S5 of a single workstation. If there is a difference, update N8 and return to step S35. Otherwise, the sigma level S6 of the final difference of a single battery cell at a single workstation is obtained, that is, S6=(Z3-X8) / σ5.

5. The method for compensating AC internal resistance and screening for poor dynamic internal resistance of a lithium battery according to claim 4, characterized in that: The abnormal cell interception in step 4 includes: S41: If the battery cell has welding station information, it is intercepted according to the preset standard m1 based on the sigma level S6 of the final difference Z3 of the station; otherwise, it is intercepted according to the preset standard m2 based on the sigma level S2 of the internal resistance difference Z1; the battery cell after interception is imported into the battery cell disabling system to automatically downgrade the battery cell.

6. The method for compensating AC internal resistance and screening for poor dynamic internal resistance of a lithium battery according to claim 1, characterized in that: Step 1 also includes: S15: Data update; when the detection equipment enters the maintenance and channel calibration process, the original database is cleared and the channel internal resistance compensation library is rebuilt from the breakpoint; when the amount of historical data exceeds the preset value, the data with the longest time from the present is deleted and the real-time compensation value of the internal resistance is recalculated.

7. The method for compensating AC internal resistance and screening for poor dynamic internal resistance of a lithium battery according to claim 1, characterized in that: The grouping according to the welding machine workstation includes a wire body, a workstation and a fixture according to the workstation information; the wire body is the information of the welding machine, and the wire body is provided with multiple workstations; each workstation is provided with multiple fixtures.

8. The method for compensating AC internal resistance and screening for poor dynamic internal resistance of a lithium battery according to claim 1, characterized in that: When the system is used, manual EXCEL macro implementation or / and automated programming software implementation are adopted; the automated programming software includes one of Python and JAVA.

Images