Lithium ion battery self-discharge screening method and device, readable storage medium and equipment

Abstract

The invention discloses a lithium ion battery self-discharge screening method and device, a readable storage medium and equipment. A lithium ion battery self-discharge screening method comprises the following steps: setting a standard voltage, and performing formation on activated cells greater than or equal to the standard voltage. And charging the formed battery cell to 95-96% SOC, and discharging the battery cell to a self-discharge test SOC. A first open circuit voltage OCV1 of the electrical core is tested. And aging and standing the battery cell for a first preset duration T1, and testing a second open-circuit voltage OCV2 of the battery cell after aging is finished. And a K1 value is calculated, and the K1 value is equal to (OCV1-OCV2) / T1. K1 value screening and same-tray outlier screening are carried out on the battery cells, and the battery cells larger than a K1 value fixed screening threshold value or a same-tray outlier upper limit value are judged to be unqualified battery cells. The method can improve the screening accuracy and guarantee the delivery quality of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery equipment, and in particular to a lithium ion battery self-discharge screening method, device, readable storage medium and equipment. BACKGROUND

[0002] The power battery is formed by series and parallel connection of single batteries. If a battery has a problem, the whole battery module will be affected, and the difference in battery self-discharge is the focus. The non-uniformity of battery self-discharge will cause overcharge or overdischarge of the battery pack, seriously affecting the service life of other normal batteries, and further affecting the performance and life of the automobile, and more seriously, causing safety hazards.

[0003] Most battery manufacturers use a fixed K value (also known as voltage drop per unit time) screening method (fixed upper and lower limits of K value) or 3∑ screening method. The 3∑ screening method screens 3∑ (average value ± 3*standard deviation) of the battery cells tested on the same day. In mass production, the fixed K value screening method and the 3∑ screening method show poor test accuracy, affecting the quality of the battery at the factory. SUMMARY

[0004] The main purpose of the present application is to provide a lithium ion battery self-discharge screening method, device, readable storage medium and equipment, which aims to solve the technical problem of poor test accuracy of the fixed K value screening method and the 3∑ screening method, affecting the quality of the battery at the factory.

[0005] In order to achieve the above-mentioned application purpose, the first aspect of the present application provides a lithium ion battery self-discharge screening method, comprising the following steps:

[0006] Setting a standard voltage, and performing formation on the completed activation battery cells greater than or equal to the standard voltage;

[0007] Charging the formed battery cells to 95-96% SOC, and discharging to a self-discharge test SOC;

[0008] Testing the first open circuit voltage OCV1 of the battery cell;

[0009] Aging and standing the battery cell for a first preset time T1, and testing the second open circuit voltage OCV2 of the battery cell after aging is completed;

[0010] Calculating the K1 value, wherein K1 value=(OCV1-OCV2) / T1;

[0011] K1 value screening and same tray outlier screening are performed on the battery cell, and the battery cell greater than the fixed screening threshold value of the K1 value or the upper limit value of the same tray outlier is determined as an unqualified battery cell.

[0012] In one of the embodiments, after the step of determining the unqualified battery cells as the battery cells with the K1 value greater than the fixed screening threshold value or the upper limit value of the same tray outlying value, the method further comprises:

[0013] The qualified battery cell is rested for a second preset time length, and a third open circuit voltage OCV3 is tested;

[0014] After the third open circuit voltage OCV3 is tested, the battery cell is rested for a third preset time length T2, and a fourth open circuit voltage OCV4 is tested;

[0015] The K2 value is calculated, wherein the K2 value = (OCV3-OCV4) / T2;

[0016] The battery cell is screened according to the K2 value and the same tray outlying value, and the battery cell with the K2 value greater than the fixed screening threshold value or the upper limit value of the same tray outlying value is determined as the unqualified battery cell.

[0017] In one of the embodiments, the third preset time length is greater than the second preset time length.

[0018] In one of the embodiments, the self-discharge test SOC is determined according to the dV / dQ curve.

[0019] In one of the embodiments, the voltage difference between the third open circuit voltage OCV3 and the fourth open circuit voltage OCV4 is greater than or equal to the tester accuracy*10.

[0020] In one of the embodiments, the resting temperature is 20-35℃.

[0021] In one of the embodiments, the standard voltage is greater than or equal to 80mV.

[0022] The second aspect of the application provides a lithium ion battery self-discharge screening device, comprising:

[0023] A setting module is configured to set a standard voltage, and to perform formation on the completed activation battery cell with the standard voltage greater than the standard voltage.

[0024] A charging and discharging module is configured to charge the formed battery cell to 95-96% SOC, and to discharge the battery cell to a self-discharge test SOC.

[0025] A first testing module is configured to test a first open circuit voltage OCV1 of the battery cell.

[0026] A second testing module is configured to rest the battery cell for a first preset time length T1, and to test a second open circuit voltage OCV2 of the battery cell after the aging is completed.

[0027] A calculation module is configured to calculate a K1 value, wherein the K1 value = (OCV1-OCV2) / T1.

[0028] The screening module is used for K1 value screening and same-tray outlying screening of the battery cell, and the battery cell with a K1 value greater than a fixed screening threshold or a same-tray outlying upper limit value is determined as a unqualified battery cell.

[0029] The third aspect of the present application provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a computer processor to implement the above-mentioned lithium ion battery self-discharge screening method.

[0030] The fourth aspect of the present application provides a computer device, which executes the above-mentioned lithium ion battery self-discharge screening method.

[0031] Beneficial effects:

[0032] The lithium ion battery self-discharge screening method of the present application comprises the following steps: setting a standard voltage, and performing formation on the battery cell with completed activation and greater than or equal to the standard voltage. Charging the battery cell after formation to 95-96% SOC, and discharging to a self-discharge test SOC. Testing a first open circuit voltage OCV1 of the battery cell. Aging and standing the battery cell for a first preset time T1, and testing a second open circuit voltage OCV2 of the battery cell after aging. Calculating a K1 value, wherein the K1 value=(OCV1-OCV2) / T1. Screening the battery cell according to the K1 value and same-tray outlying, and determining the battery cell with a K1 value greater than a fixed screening threshold or a same-tray outlying upper limit value as a unqualified battery cell.

[0033] The K1 value of the present application is calculated based on the difference between the first open circuit voltage OCV1 and the second open circuit voltage OCV2 before and after aging standing and the standing time T1, and directly quantifies the self-discharge rate of the battery cell in the aging stage. Compared with the fixed K value (a unified threshold without distinguishing the process stage) of the prior art, the K1 value of the present application is more consistent with the actual self-discharge characteristics of the battery cell, and reduces the determination deviation caused by batch fluctuation. The same-tray battery cells experience the same activation, formation, aging and test conditions, and have strong consistency in normal self-discharge level. Taking the same-tray outlying upper limit value as the determination standard can avoid the abnormal value interference caused by the mixed statistics of the same batch battery cells across time and temperature in the 3σ screening. The method can improve the screening accuracy and guarantee the quality of the battery out of the factory. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a flowchart of the lithium ion battery self-discharge screening method of an embodiment of the present application.

[0035] Figure 2 is a flowchart of the lithium ion battery self-discharge screening method of another embodiment of the present application.

[0036] Figure 3 is a same batch test data graph of an embodiment of the present application.

[0037] Figure 4 is a rest time data graph of an embodiment of the present application.

[0038] The objectives, features and advantages of the present application will be further illustrated in conjunction with the embodiments with reference to the drawings. DETAILED DESCRIPTION

[0039] It should be understood that the specific embodiments described herein merely exemplify the application and do not impose any limitation on the application.

[0040] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship shown in the drawings based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0041] In the description of the present application, it should be noted that unless otherwise specifically defined and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, it can be directly connected, or indirectly connected through intermediate medium, it can be the communication between two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0042] In the present application, unless otherwise specifically defined and limited, "on" or "under" of the first feature to the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, "on", "above" and "above" of the first feature to the second feature include that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. "Below", "below" and "below" of the first feature to the second feature include that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0043] The performance of the power battery pack of a new energy vehicle has a significant impact on the performance of the electric vehicle. Because the current market requires the same quality of the vehicle and the battery, electric vehicles have higher requirements for lithium-ion batteries, especially consistency. The power battery is a single battery connected in series and parallel, and a problem with a single battery will affect the entire battery module. The difference in battery self-discharge is the focus. The non-uniformity of battery self-discharge can cause overcharging or over-discharging of the battery pack, seriously affecting the service life of other normal batteries, and thus affecting the performance and life of the vehicle. More seriously, it can cause safety hazards.

[0044] Self-discharge is a phenomenon of natural loss of capacity during storage, generally manifested as a decrease in open-circuit voltage (OCV) after storage for a period of time. Lithium-ion battery self-discharge can be divided into physical self-discharge and chemical self-discharge according to the reaction type. From the impact of self-discharge on the battery, self-discharge can be divided into two categories: self-discharge that can be compensated reversibly for the loss of capacity, and self-discharge that cannot be compensated reversibly for the loss of capacity. Under normal circumstances, the capacity loss caused by physical self-discharge is reversible, while the capacity loss caused by chemical self-discharge is irreversible.

[0045] Self-discharge is divided into physical self-discharge and chemical self-discharge; the reason for physical self-discharge is generally a micro-short circuit inside the battery. When the separator is damaged for some reason, the positive and negative electrodes are in contact, and the transfer path of electrons is the electrolyte, which passes through the separator from the negative electrode to the positive electrode and reacts with the positive electrode material, causing physical self-discharge. The main causes of physical self-discharge are powder particles, current collector puncture, etc.; chemical self-discharge is a phenomenon of capacity reduction caused by spontaneous chemical reactions inside the battery. The main causes of chemical self-discharge are: (1) irreversible reaction of positive electrode with electrolyte, mainly occurring in materials prone to structural defects such as lithium manganate and lithium nickelate, such as the reaction of lithium manganate anode with lithium ions in electrolyte. (2) irreversible reaction of negative electrode with electrolyte (SEI film formed during formation is to protect the negative electrode from corrosion by electrolyte).(3) irreversible reaction caused by impurities in electrolyte (such as CO2 in electrolyte).(4) irreversible reaction of metal impurities with electrolyte, such as metal impurities in the positive electrode dissolving in the positive electrode and precipitating in the negative electrode, puncturing the separator, and causing a large self-discharge phenomenon. From the above two self-discharge methods, battery self-discharge is mainly composed of two parts: internal side reactions of the battery and internal micro-short circuits of the battery.

[0046] Currently, most battery manufacturers use a fixed K value (also known as voltage drop per unit time) screening method (fixed upper and lower limits of K value) or a 3∑ screening method. The 3∑ screening method screens 3∑ (average value ± 3*standard deviation) of the battery tested on the same day. In large-scale production, the fixed K value screening method and the 3∑ screening method show poor test accuracy, affecting the quality of the battery at the factory.

[0047] Fixed K value screening products exist will be unqualified products as qualified products and will be qualified products as unqualified products risk. Because the fluctuation of K value of battery cell between batches. 3∑ screening is high in consistency requirements for time and temperature, time difference and temperature difference in self-discharge test process, product leakage kill (unqualified products as qualified products) and overkill (qualified products as unqualified products) risk is high. The lithium ion battery self-discharge screening method provided by the application solves the above technical problems.

[0048] As shown in Figure 1 In some embodiments, a lithium ion battery self-discharge screening method, comprising the following steps:

[0049] S100, set the standard voltage, and perform formation on the completed activation battery cell greater than or equal to the standard voltage.

[0050] S200, charge the formed battery cell to 95-96% SOC, and discharge to the self-discharge test SOC.

[0051] S300, test the first open circuit voltage OCV1 of the battery cell.

[0052] S400, the battery cell is aged and placed for a first preset time T1, and the second open circuit voltage OCV2 of the battery cell is tested after aging.

[0053] S500, calculate K1 value, wherein K1 value = (OCV1-OCV2) / T1.

[0054] S600, K1 value screening and same tray outlier screening are performed on the battery cell, and the battery cell greater than K1 value fixed screening threshold or same tray outlier upper limit value is determined as unqualified battery cell.

[0055] The K1 value of the application is calculated based on the difference between the first open circuit voltage OCV1 and the second open circuit voltage OCV2 before and after aging and the aging time T1, which directly quantifies the self-discharge rate of the battery cell in the aging stage. Compared with the fixed K value of the prior art (a unified threshold that does not distinguish between process stages), the K1 value of the application is more consistent with the actual self-discharge characteristics of the battery cell, and reduces the judgment deviation caused by batch fluctuation. The same tray battery cell experiences the same activation, formation, aging and test conditions, and its normal self-discharge level has strong consistency. With "same tray outlier upper limit" as the judgment standard, the abnormal value interference caused by "mixing statistics of same batch battery cells across time and temperature" in 3∑ screening is avoided. As shown in Figure 3 As shown in 320EA battery cells produced in the same batch, fixed K value screening and 3∑ on the same day have no defects, and 4 battery cells in a single tray have defects (defect rate 1.25%). The method can improve the screening accuracy and ensure the quality of the battery out of the factory.

[0056] In some embodiments, when setting the standard voltage, the standard voltage before formation can be determined according to the type of the battery cell (such as a lithium iron phosphate power lithium ion battery). The voltage of each battery cell after activation (after liquid injection and completion of standing) is tested by a voltage detection device, and the battery cell with a lower cabinet voltage than the standard voltage is directly degraded, and only the battery cell with a voltage greater than the standard voltage is reserved for the formation process. This step can remove the battery cell with abnormal initial voltage and basic performance defects in advance, avoiding the invalid cost investment in the subsequent formation process.

[0057] Specifically, the standard voltage is the lower limit value of the cabinet voltage standard.

[0058] Specifically, the standard voltage can be greater than or equal to 80 mV.

[0059] Specifically, the standing temperature is 20-35°C, which reduces the temperature control cost.

[0060] In some embodiments, when the battery cell after formation is charged to 95-96% SOC, a series formation cabinet is used, and the battery cell is charged according to a preset multi-stage constant current charging process. After reaching the set time of each process, it is automatically switched, and after the charging is completed, it is standing for 5 minutes, and then the battery cell SOC is adjusted to the self-discharge test SOC by discharging at a constant current of 1C for a specific time. The self-discharge test SOC needs to be selected in combination with the dV / dQ curve, and the voltage needs to be as low as possible (to reduce the safety risk of standing). The standard of the SOC width corresponding to the peak value of dV / dQ is > ± 2% (such as selecting 20% SOC to ensure that the dV / dQ of all battery cells under the same voltage is close to the peak value). This step reduces the interference of the capacity difference of the battery cell on the subsequent K1 value determination by accurately controlling the charging and discharging process and the SOC interval. For example, the capacity of a certain batch of battery cells has a difference of 99 Ah-101 Ah, and in the 20% SOC test interval, the dV / dQ of each battery cell under the same voltage is close to the peak value, avoiding the self-discharge determination deviation caused by the capacity difference.

[0061] In some embodiments, when testing the first open circuit voltage OCV1 of the battery cell, a tester with an accuracy of ≤±0.2 mV is selected. Specifically, the tester can be an Agilent 34461 tester. After the battery cell is formed and adjusted to the self-discharge test SOC, OCV1 test is immediately performed on each battery cell, and the specific voltage data of each battery cell is recorded. High-precision testing ensures the accuracy of OCV1 data, providing a reliable basis for subsequent K1 value calculation.

[0062] In some embodiments, when the battery cell is left to age for a first preset time T1, the battery cell that has completed the OCV1 test is placed in a high-temperature aging environment of 40–50°C. During the aging process, the ambient temperature is monitored in real time to ensure temperature stability. After aging, the OCV2 tester is used to test and record the data. High-temperature aging can accelerate the self-discharge process of the battery cell, shorten the test cycle, and ensure the consistency of aging conditions through a stable temperature environment.

[0063] When calculating the K1 value, the formula K1 value = (OCV1 - OCV2) / T1 is used. The OCV1 and OCV2 test data for each cell, along with the T1 duration, are substituted into the calculation to obtain the K1 value (unit: mV / h) for each cell. This quantitative calculation converts the self-discharge rate into a specific numerical value, facilitating subsequent screening and comparison. For example, for a cell with OCV1 = 3.300V, OCV2 = 3.288V, and T1 = 48H, the calculated K1 value is (3300mV - 3288mV) / 48H = 0.25mV / h. When screening cells based on their K1 value and for outliers within the same tray, a fixed screening threshold for the K1 value is first set. Cells with a K1 value greater than this fixed threshold are considered unqualified. Next, the K1 value of all cells in the same tray is statistically analyzed, and the median value for that tray is calculated. For example, if the median K1 value of 50 cells in a tray is 0.15mV / h, an outlier limit is set: median + 0.07mV / h, which is 0.22mV / h. Cells with K1 values ​​greater than this outlier limit are also judged as unqualified. This dual screening method avoids the batch fluctuation problem of fixed K-value screening and reduces over- and under-selection by leveraging the high consistency of the cell environment within the same tray. For example, if a cell in a tray has a K1 value of 0.23mV / h, although it is within the fixed range of 0-0.3mV / h, it is greater than the outlier limit of 0.22mV / h and is judged as unqualified, effectively eliminating abnormal cells in the same environment. It should be noted that the core of the fixed range is a unified judgment standard based on the preset "self-discharge baseline and quality redundancy of qualified cells," which is specifically determined according to the process verification logic and examples disclosed in the document. The outlier limit is a dynamic standard calculated based on "the median K1 value and the small deviation threshold of cells in the same tray". The core logic is to capture relatively abnormal cells by using "consistency of the same tray environment".

[0064] like Figure 2 As shown, in some embodiments, after the step of screening the battery cells by K1 value and outlier screening within the same tray, and determining the battery cells with a K1 value greater than a fixed screening threshold or an upper limit for outlier values ​​within the same tray as unqualified battery cells, the method further includes:

[0065] S610. After the qualified battery cell has been left to stand for a second preset time, test the third open-circuit voltage OCV3.

[0066] S620, resting for a third preset time T2 after testing the third open circuit voltage OCV3, and testing a fourth open circuit voltage OCV4.

[0067] S630, calculating a K2 value, wherein the K2 value = (OCV3-OCV4) / T2.

[0068] S640, K2 value screening and same-tray outlier screening are performed on the battery cell, and the battery cell with a K2 value greater than a fixed screening threshold or a same-tray outlier upper limit value is determined as an unqualified battery cell.

[0069] It should be noted that S610: when the qualified battery cell is rested for a second preset time and the third open circuit voltage OCV3 is tested, the battery cell that passes the K1 value screening and the same-tray outlier screening is first transferred to a normal temperature resting environment of 20-35°C. The second preset time is set to 12-13H. During the resting process, the battery cell is prevented from being subjected to external interference such as vibration and extrusion, and after the resting is completed, the OCV3 of each battery cell is tested by using an Agilent 34461 tester with a precision of ≤±0.15mV, and the data is recorded. This step eliminates the influence of the previous high-temperature aging on the voltage of the battery cell by normal temperature resting, and at the same time, the high-precision testing provides a more accurate reference voltage for subsequent K2 value calculation. For example, 500 battery cells of a certain batch that pass the K1 value screening are tested for OCV3 after being rested at 25°C for 12H, and the voltage data deviation of each battery cell is controlled within ±0.15mV, thereby avoiding the interference of voltage error on the subsequent self-discharge determination.

[0070] S620: when the OCV3 is tested and the OCV4 is tested after resting for a third preset time T2, the battery cell is kept in the normal temperature environment of 20-35°C, and the resting time T2 is set to 48-96H. The ambient temperature is recorded in real time during the resting period, and after the resting is completed, the OCV4 is tested by using the tester with a precision of ≤±0.15mV, and the data is recorded. This step ensures that the voltage drop caused by the self-discharge of the battery cell is obvious enough by reasonably setting the resting time, and at the same time, the relaxed temperature requirement is suitable for large-scale production. For example, the average voltage difference between OCV3 and OCV4 of a certain tray battery cell is 2.0mV after being rested at 28°C for 72H, which meets the requirement of ≥1.5mV, and the self-discharge rate can be accurately calculated.

[0071] S630: When calculating the K2 value, according to the formula K2 value = (OCV3-OCV4) / T2, the OCV3, OCV4 test data and actual standing time T2 of each battery are substituted into the calculation to obtain the K2 value (unit: mV / h) of each battery. This step quantifies the self-discharge rate during normal temperature standing, and is complementary to the above-mentioned K1 value (self-discharge rate during high temperature aging), to comprehensively evaluate the self-discharge performance of the battery under different environments, for example, OCV3 = 3.285V, OCV4 = 3.283V, T2 = 72H, and the calculated K2 value = (3285mV-3283mV) / 72H≈0.0278mV / h.

[0072] S640: When screening the K2 value of the battery and screening the same tray outliers, first set a fixed screening threshold for the K2 value, and determine that the battery with a K2 value greater than the fixed screening threshold is unqualified, then calculate the median of the K2 value of all batteries in the same tray (for example, the median of the K2 value of 60 batteries in a tray is 0.018mV / h), set an outlier upper limit value (median + 0.005mV / h, i.e. 0.023mV / h), and determine that the battery with a K2 value greater than the outlier upper limit is also unqualified. This double screening further eliminates batteries with abnormal self-discharge at normal temperature, and the same tray screening is not affected by the environmental differences between other trays in the batch, for example, there are 2 batteries in a tray with K2 values of 0.026mV / h (greater than the fixed range) and 0.024mV / h (greater than the outlier upper limit), both of which are determined to be unqualified, effectively avoiding the flow of batteries with abnormal self-discharge at normal temperature to the downstream, and forming a double guarantee with the K1 value screening to improve the overall screening accuracy.

[0073] Specifically, the third preset time period is greater than the second preset time period.

[0074] Specifically, the voltage difference between the third open circuit voltage OCV3 and the fourth open circuit voltage OCV4 is greater than or equal to the accuracy of the tester*10. Specific embodiments:

[0076] Step 1: Perform formation on the lithium iron phosphate power lithium ion battery that has completed activation (resting after liquid injection), and downgrade the battery with a formation cabinet voltage below 80mV.

[0077] Step 2: Perform formation on the battery with a qualified formation cabinet voltage, use series formation for the formation cabinet, charge the battery at 0.1C (0.2H), 0.2C (1H), 0.5C (1.15H), 0.4C (0.3H), 0.2C (0.1H), and 0.1C (0.2H) constant current to 95%-96% SOC, and cut off the time of each step, then rest for 5 minutes, and then discharge the battery at 1C constant current for 0.75H to adjust the SOC state of the battery to 20%.

[0078] Step 3: After the end of the formation of the battery cell, use Agilent 34461 tester to test the battery cell OCV1.

[0079] Step 4: After the battery cell is aged at 40-50℃ for 48H (T1), use Agilent 34461 tester to test the battery cell OCV2.

[0080] Step 5: Calculate the battery cell K1 value = (OCV1-OCV2) / aging time T1, fixed value screening (0-0.3mV / h) and same tray outlier screening (median of same tray +0.07mV / h), the battery cell greater than the fixed screening threshold value or the upper limit value of the same tray outlier is degraded, and the qualified battery cell is transferred to the next process.

[0081] Step 6: The battery cell is placed in an environment of 20-35℃ for 12-13H, and then tested for OCV3 using Agilent 34461 tester.

[0082] Step 7: The battery cell is placed in an environment of 20-35℃ for 72H (T2), and then tested for OCV4 using Agilent 34461 tester.

[0083] Step 8: Calculate the battery cell K2 value = (OCV3-OCV4) / aging time T2, fixed screening threshold (0-0.025mV / h) and same tray outlier screening (median of same tray +0.005mV / h), the battery cell greater than the fixed screening threshold value or the upper limit value of the same tray outlier is degraded, and the qualified battery cell is transferred to the next process.

[0084] Step 9: The qualified battery cell is transferred to the next process.

[0085] The above embodiment can reduce the self-discharge failure rate by 90%. The self-discharge test resting time is reduced from more than 7 days to less than 4 days. As shown in Figure 4 600EA battery cells produced in the same batch, the time difference within the same tray is within 0.1H, and the time difference between different trays is up to 9H; a large number of battery cells produced in one day can reach 20000EA, and the resting time difference can be greater than 9H. The turnover time of the activated fourth open circuit voltage OCV4 is reduced from more than 14 days to less than 9 days. The resting time of the third open circuit voltage OCV3 to the fourth open circuit voltage OCV4 is only 60-102H, which requires less storage space and shorter product turnover time. The two same tray battery cell screenings have high product consistency, time consistency and temperature consistency, are not affected by individual abnormal battery cells, and have high screening accuracy.

[0086] In another embodiment, a lithium ion battery self-discharge screening device comprises:

[0087] A setting module is configured to set a standard voltage, and to form the activated battery cell greater than the standard voltage.

[0088] Charging and discharging module, for charging the formed battery cell to 95-96% SOC, and discharging to self-discharge test SOC.

[0089] The first test module is used for testing the first open circuit voltage OCV1 of the battery cell.

[0090] The second test module is used for aging and standing the battery cell for a first preset time T1, and testing the second open circuit voltage OCV2 of the battery cell after the aging is completed.

[0091] The calculation module is used for calculating the K1 value, wherein the K1 value=(OCV1-OCV2) / T1.

[0092] The screening module is used for K1 value screening and same-tray outlier screening of the battery cell, and the battery cell greater than the K1 fixed screening threshold or the same-tray outlier upper limit value is determined as an unqualified battery cell.

[0093] In another embodiment, a computer readable storage medium has a computer program stored thereon, and the computer program is executed by a computer processor to implement the above-mentioned lithium ion battery self-discharge screening method.

[0094] The computer readable storage medium in the embodiments can be a computer readable signal medium or a computer readable storage medium or any combination of the two. The computer readable storage medium may, for example, be an electronic, magnetic, optical, electromagnetic, infrared or semiconductor system, device or apparatus, or any combination of the above. More specific examples of the computer readable storage medium can include, but are not limited to, an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In the embodiments, the computer readable storage medium can be any tangible medium that contains or stores a program used by or in connection with an instruction execution system, apparatus or device. In the embodiments, the computer readable signal medium can include a data signal carried in a baseband or as part of a carrier wave, in which the computer readable program code is carried. The propagated data signal can take a variety of forms, including but not limited to, an electromagnetic signal, an optical signal or any suitable combination of the above. The computer readable signal medium can also be any computer readable medium that is not a storage medium and that can communicate, propagate or transport program for use by or in connection with an instruction execution system, apparatus or device. The program code contained on the computer readable storage medium can be transmitted by any suitable medium, including but not limited to, wireless, wire line, optical fiber cable, RF, etc., or any suitable combination of the above.

[0095] In another embodiment, a computer device performs the above-described lithium ion battery self-discharge screening method.

[0096] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation, or direct or indirect application in other related technical fields, which is made by using the content of the specification and drawings of the present application, is also included in the patent protection scope of the present application.

Claims

1. A method of self-discharge screening of lithium-ion batteries, characterized in that, The method comprises the following steps: setting a standard voltage, and performing formation on the completed activated battery cells greater than or equal to the standard voltage; charging the formed battery cells to 95-96% SOC, and discharging to a self-discharge test SOC; testing a first open circuit voltage OCV1 of the battery cells; aging and standing the battery cells for a first preset time T1, and testing a second open circuit voltage OCV2 of the battery cells after aging is completed; calculating a K1 value, wherein the K1 value=(OCV1-OCV2) / T1; performing K1 value screening and same-tray outlier screening on the battery cells, and determining the battery cells greater than a fixed screening threshold value of the K1 value or a same-tray outlier upper limit value as unqualified battery cells.

2. The lithium-ion battery self-discharge screening method of claim 1, wherein, The method further comprises the following steps after the step of performing K1 value screening and same-tray outlier screening on the battery cells, and determining the battery cells greater than a fixed screening threshold value of the K1 value or a same-tray outlier upper limit value as unqualified battery cells: standing the qualified battery cells for a second preset time, and testing a third open circuit voltage OCV3; standing for a third preset time T2 after testing the third open circuit voltage OCV3, and testing a fourth open circuit voltage OCV4; calculating a K2 value, wherein the K2 value=(OCV3-OCV4) / T2; performing K2 value screening and same-tray outlier screening on the battery cells, and determining the battery cells greater than a fixed screening threshold value of the K2 value or a same-tray outlier upper limit value as unqualified battery cells.

3. The lithium-ion battery self-discharge screening method of claim 2, wherein, The third preset time is greater than the second preset time.

4. The lithium-ion battery self-discharge screening method of claim 1, wherein, The self-discharge test SOC is determined according to a dV / dQ curve.

5. The lithium-ion battery self-discharge screening method of claim 1, wherein, The voltage difference between the third open circuit voltage OCV3 and the fourth open circuit voltage OCV4 is greater than or equal to a tester accuracy*10.

6. The lithium-ion battery self-discharge screening method of claim 1, wherein, The standing temperature is 20-35°C.

7. The lithium-ion battery self-discharge screening method of claim 1, wherein, The standard voltage is greater than or equal to 80 mV.

8. A lithium-ion battery self-discharge screening device, characterized in that, The method comprises: a setting module for setting a standard voltage, and performing formation on the completed activated battery cells greater than or equal to the standard voltage; a charging and discharging module for charging the formed battery cells to 95-96% SOC, and discharging to a self-discharge test SOC; a first testing module for testing a first open circuit voltage OCV1 of the battery cells; a second testing module for aging and standing the battery cells for a first preset time T1, and testing a second open circuit voltage OCV2 of the battery cells after aging is completed; a calculation module for calculating a K1 value, wherein the K1 value=(OCV1-OCV2) / T1; a screening module for performing K1 value screening and same-tray outlier screening on the battery cells, and determining the battery cells greater than a fixed screening threshold value of the K1 value or a same-tray outlier upper limit value as unqualified battery cells.

9. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by a computer processor to implement the lithium ion battery self-discharge screening method in any one of claims 1-7.

10. A computer device, comprising: The computer program is executed by a computer processor to implement the lithium ion battery self-discharge screening method in any one of claims 1-7.

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