A capacity compensation method for lithium battery mass production line for capacity division

Abstract

The present invention discloses a capacity compensation method for a lithium battery mass production line for capacity division, including step 1, for the same batch of cells, selecting a number of cells as test cells; step 2, testing the test cells in a constant temperature box to obtain the cell capacity data tested at different temperatures; step 3, calculating the capacity coefficient of each cell at different temperatures according to the cell capacity data obtained in step 2; step 4, fitting the functional relationship between temperature and capacity coefficient based on the capacity coefficient; step 5, when the mass production line is divided into capacity, the corresponding compensation capacity value under the current mass production line environment is calculated by the functional relationship, the compensation capacity value is used as the cell divided capacity, and the cell capacity is sorted. The present invention uses the compensation capacity value as the cell divided capacity, which can reduce the influence of the temperature difference of the mass production line divided capacity cabinet on the cell capacity.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery capacity division and determination, and in particular to a capacity compensation method for a lithium battery mass production line used for capacity division. Background Art

[0002] Lithium batteries are greatly affected by temperature. When the temperature is high or low, the capacity test results are different. Therefore, the existing technology can easily lead to the battery cells with different capacities being grouped together for factory or shipment during capacity division, resulting in poor consistency of the battery cells. The power, performance and subsequent life of lithium batteries with poor consistency will be greatly reduced, which are not what battery manufacturers want to see.

[0003] Therefore, the temperature compensation capacity studied by lithium battery manufacturers in the prior art is to study the compensation capacity through temperature, so as to achieve more accurate capacity control. For example, the patent document with patent publication number CN 111842222 A discloses a lithium battery capacity compensation method, which compensates the capacity of the battery by collecting the ambient temperature of the battery capacity and detecting the production capacity of the battery. The ambient temperature used is the temperature of the battery carrier, and the battery carrier includes a tray or a support bar. Its temperature cannot match the temperature change of the battery well, and how to offset or convert the temperature change of the battery into a capacity under a unified standard through conversion is also a matter of consideration.

[0004] The temperature compensation capacity studied by lithium battery manufacturers in the prior art mostly uses ambient temperature for compensation, which is not suitable for mass production lines. For mass production line capacity division cabinets, generally only 4 to 8 ambient temperature sensors are distributed in one storage location, and at least more than 20 battery cells are placed in one storage location, so the ambient temperature of each battery cell cannot be collected. Therefore, it is not suitable for mass production lines; some manufacturers use the temperature of the battery cell body for compensation, and the temperature studied only considers the temperature at the beginning of the battery cell capacity division, and does not consider the temperature of the battery cell during the entire capacity division process.

[0005] Therefore, the existing capacity compensation and capacity division scheme still has defects, and cannot accurately compensate and obtain capacity values, and cannot provide basic parameters for accurate capacity division. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a capacity compensation method for a lithium battery mass production line for capacity division. The temperature of the battery cell in the entire capacity division process is taken into consideration, the battery cell capacity is compensated and converted to obtain a compensation capacity value, and the compensation capacity value is used for sorting. This can reduce the impact of the temperature difference of the mass production line capacity division cabinet on the battery cell capacity, reduce the extreme difference of the battery cell capacity, improve the capacity grouping efficiency and the consistency of the battery cell capacity, and reduce the production cost.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: a capacity compensation method for a lithium battery mass production line for capacity division, comprising the following steps:

[0008] Step 1: For the cells in the same batch, select several cells as test cells;

[0009] Step 2: Test the test cell in a constant temperature box to obtain the cell capacity data tested at different temperatures;

[0010] Step 3: Calculate the capacity coefficient of each battery cell at different temperatures based on the battery cell capacity data obtained in step 2;

[0011] Step 4: Obtain a functional relationship between temperature and capacity coefficient based on capacity coefficient fitting;

[0012] Step 5: When performing capacity separation on the mass production line, the corresponding compensation capacity value under the current mass production line environment is calculated through a functional relationship, the compensation capacity value is used as the cell capacity separation capacity, and the cell capacity is sorted using the compensation capacity value.

[0013] Step 2 includes:

[0014] In a constant temperature box, the selected battery cells are cycled at a specified temperature with a standard capacity, and the last capacity is recorded as C0.

[0015] In the constant temperature box, the selected battery cells are divided at different temperatures according to the mass production line capacity division process to obtain the battery cell capacity C at different temperatures.

[0016] Step three includes: defining the capacity coefficient K of each battery cell as K=C / C0; and calculating the corresponding capacity coefficient K through the capacity data obtained in step two.

[0017] In step 2, the battery cell temperature adopts the top cover temperature of the battery cell, and the top cover temperature of each battery cell and the corresponding battery cell capacity data obtained by the test are collected and counted.

[0018] Step 4 includes: based on the capacity coefficient of each battery cell at each temperature obtained in step 3, a number of data points corresponding to the temperature X and the capacity coefficient can be obtained; mathematically fitting the corresponding data points of the temperature X and the capacity coefficient to obtain a functional correspondence between the two.

[0019] The expression of the corresponding relationship of the fitted function is:

[0020] C / C0=AX 3 -BX 2 +DX+E;

[0021] Among them, A, B, D, and E are constants, and their values ​​are determined by fitting; X is the average temperature of the top cover of the battery cell in the mass production line; and K is the capacity coefficient.

[0022] Step five includes, when the mass production line is divided into capacities, performing a capacity division test according to the mass production line capacity division process to obtain the current capacity value C and the corresponding average temperature X of the top cover of the mass production line battery cell under the capacity division process, and bringing the collected current capacity value C and the corresponding average temperature X of the top cover of the mass production line battery cell under the capacity division process into the fitted function correspondence to calculate the compensation capacity value.

[0023] In step 5, the compensation capacity value calculation includes: compensation capacity value = current capacity value C / (AX 3 -BX 2 +DX+E), where X is the average temperature of the top cover of the battery cells in the mass production line under the capacity division process.

[0024] The fitted function formula is input into the upper computer system of the capacity distribution cabinet. The upper computer system of the capacity distribution cabinet calculates the compensation capacity value through the function formula according to the capacity and temperature obtained from the current capacity distribution process, and then uploads the capacity distribution compensation capacity result to the MES system for recording and sorting.

[0025] The advantages of the present invention are: considering the temperature of the battery cell in the entire capacity division process, compensating and converting the battery cell capacity to obtain a compensation capacity value, and sorting with the compensation capacity value, it can reduce the impact of the temperature difference of the capacity division cabinet of the mass production line on the battery cell capacity, reduce the extreme difference of the battery cell capacity, improve the capacity grouping efficiency and the consistency of the battery cell capacity, and reduce the production cost. It also has the following technical advantages:

[0026] ① Reduced the impact of temperature on battery cell capacity, improved the accuracy of battery cell capacity, and reduced rework of battery cell capacity;

[0027] ② It reduces the extreme difference of cell capacity in mass production lines, improves the efficiency of cell capacity grouping, reduces the number of cells that cannot be grouped, reduces production costs, and improves cell capacity consistency;

[0028] ③ The battery cell temperature involved in the method of the present invention is not only applicable to the battery cell top cover temperature, but also to the battery cell large surface temperature, battery cell pole / ear temperature, etc., and has strong applicability;

[0029] ④The present invention is suitable for mass production lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The following is a brief description of the contents expressed in the drawings of the present invention and the symbols in the drawings:

[0031] Figure 1 This is a flow chart of the capacity temperature compensation method of the present invention;

[0032] Figure 2 This is a schematic diagram of the top cover temperature sampling position of the present invention;

[0033] Figure 3 The temperature setting of the volume distribution in the thermostat of the present invention;

[0034] Figure 4 It is the capacity coefficient & top cover maximum temperature fitting curve of the present invention;

[0035] Figure 5 It is the capacity coefficient & top cover average temperature fitting curve in the present invention;

[0036] Figure 6 Schematic diagram of batch verification of temperature compensation capacity. DETAILED DESCRIPTION

[0037] The specific implementation of the present invention will be further explained in detail below by describing the optimal embodiment with reference to the accompanying drawings.

[0038] This solution provides a capacity compensation method for a lithium battery mass production line for capacity division, which includes two parts:

[0039] 1. Before capacity separation for a batch of battery cells, select several battery cells for testing to obtain the capacity coefficient C / C0 of the battery cells at different temperatures, and then fit the functional relationship between the temperature and capacity coefficient to obtain the functional relationship between the two;

[0040] 2. Then, for this batch of battery cells, start the mass production line capacity division process. In the mass production line capacity division process, obtain the temperature during the capacity division process and the capacity C during the capacity division; then calculate a capacity compensation value based on the functional relationship, use the capacity compensation value as the capacity when the battery cells are divided, and then sort them based on the capacity compensation value, that is, the battery cells with capacity compensation values ​​in the same range are sorted as a group.

[0041] In the above scheme, the first step of testing includes the following steps:

[0042] In a constant temperature box, the selected battery cells are cycled at a specified temperature with a standard capacity, and the last capacity is recorded as C0.

[0043] In the constant temperature box, the selected battery cells are divided at different temperatures according to the mass production line capacity division process to obtain the battery cell capacity C at different temperatures.

[0044] The capacity coefficient K of each battery cell is defined as K=C / C0; the corresponding capacity coefficient K is calculated from the capacity data obtained through the test steps. Since the standard capacity C0 of each battery cell is recorded during the experiment; and the capacity C under the mass production line capacity division process at different temperatures; in this way, the temperature data and the corresponding capacity coefficient C / C0 under the temperature data can be obtained; since the two are in a one-to-one correspondence, it can be regarded as the horizontal axis is temperature, the vertical axis is capacity coefficient, and the corresponding mathematical relationship is fitted. Among them, the battery cell temperature adopts the top cover temperature of the battery cell, and the top cover temperature of each battery cell and the corresponding battery cell capacity data obtained by the test are collected and counted.

[0045] The capacity coefficient of each battery cell at each temperature obtained during the test can obtain several data points corresponding to the temperature X and the capacity coefficient; the corresponding data points of the temperature X and the capacity coefficient are mathematically fitted to obtain the functional correspondence between the two. The expression of the fitted functional correspondence is: C / C0=AX 3 -BX 2 +DX+E;

[0046] Among them, A, B, D, and E are constants, and their values ​​are determined by fitting; X is the average temperature of the top cover of the battery cell in the mass production line; and K is the capacity coefficient. The capacity coefficient at different temperatures obtained during the test process can be fitted to the function expression to obtain the values ​​of the constants ABDE to obtain the determined function expression.

[0047] When the mass production line is divided into capacities, the capacity division test is performed according to the mass production line capacity division process to obtain the current capacity value C and the corresponding average temperature X of the top cover of the mass production line battery cell under the capacity division process. The current capacity value C and the corresponding average temperature X of the top cover of the mass production line battery cell under the capacity division process are brought into the fitted function correspondence to calculate the compensation capacity value C0. The compensation capacity value calculation includes: compensation capacity value C0 = current capacity value C / (AX 3 -BX 2 +DX+E), where X is the average temperature of the cell top cover of the mass production line under the capacity division process. The compensation capacity value is used as the capacity value of the capacity division. During the mass production line test, the temperature X and the capacity C under the mass production line test can be obtained. The two are taken as variable values ​​and brought into the function relationship to obtain the capacity division compensation value C0. The compensation value can be uploaded to the MES system for recording and sorting.

[0048] The following is an explanation of the principle in combination with a specific battery cell batch:

[0049] The present invention compensates for the cell capacity by using the average temperature in the entire process of cell capacity division charging and discharging, which makes up for the shortcomings of the prior art, takes into account the entire temperature rise in the cell capacity division process, reduces the influence of the temperature difference of the cell capacity division cabinets in the mass production line on the cell capacity, narrows the cell capacity extreme difference, improves the capacity grouping efficiency and the cell capacity consistency, and reduces the production cost.

[0050] The present invention is applicable to the capacity temperature compensation method of the lithium battery cell mass production line, which reduces the influence of the capacity distribution cabinet temperature on the capacity and improves the accuracy of capacity distribution. The present invention takes a square aluminum shell cell as an example. Figure 1 As shown, a capacity compensation method for a lithium battery mass production line for capacity division includes the following steps:

[0051] S1. In a constant temperature box, perform standard capacity cycles on the selected battery cells at a specified temperature, and take the last capacity as C0;

[0052] S2. In a constant temperature box, the selected battery cells are divided according to the mass production line capacity division process at different temperatures to obtain the battery cell capacity C at different temperatures; this step and step S1 are for the same batch of battery cells;

[0053] S3, calculate the capacity coefficient of each battery cell at different temperatures = C / C0;

[0054] S4. Fit the capacity coefficient and cell temperature;

[0055] The cell temperature used in the embodiment of the present invention refers to the top cover temperature of the cell, and the fitting coefficients of the maximum top cover temperature and the average top cover temperature are compared to obtain the capacity coefficient & top cover average temperature fitting curve R 2 Higher value.

[0056] S5, get the capacity coefficient & battery temperature fitting formula: C / C0=2*10 -6 X 3 -0.0003X 2 +0.0135X+0.8027 (X represents the average temperature of the top cover)

[0057] S6, mass production line temperature compensation capacity = C / (2*10 -6 X 3 -0.0003X 2 +0.0135X+0.8027)(C is the capacity of the battery cell of the mass production line, X is the average temperature of the top cover of the battery cell of the mass production line);

[0058] S7. Input the formula into the upper computer system of the capacity cabinet. The equipment automatically calculates the compensation capacity and uploads the result data to the MES system. Then, each battery cell is sorted according to the compensation capacity value.

[0059] In this embodiment:

[0060] ①, Step S1:

[0061] The present invention selects N (N≥3) battery cells with good battery cell consistency, and performs 10 cycles of standard capacity in a laboratory constant temperature box (the number of cycles may be different depending on the battery cell system) to stabilize the battery cell capacity. The capacity of the last cycle is taken as the standard capacity of the battery cell at 25°C, recorded as C0.

[0062] The temperature of the thermostat is set according to the production line requirements (usually 25°C), and the temperature collection points are as follows: Figure 2 shown.

[0063] The standard capacity process adopted in this embodiment is as follows:

[0064] iLet stand for 2h;

[0065] ii 0.5C constant current discharge to 2.5V, sleep for 30 minutes;

[0066] iii 0.5C constant current and constant voltage charging to 3.65V, cut-off current 0.05C, sleep for 30 minutes;

[0067] iv 0.5C constant current discharge to 2.5V, sleep for 30min;

[0068] v Repeat steps 3-4 10 times

[0069] ②, Step S2:

[0070] In step S1, keep the cells in the incubator and press Figure 3 The capacity is divided in the order and temperature shown, and the capacity division process adopts the mass production line capacity division process; the test results show the capacity of each battery cell at different temperatures T, which is recorded as C;

[0071] The capacity division process adopted is as follows:

[0072] i Adjust the temperature to the specified temperature T and keep it warm for 6 hours;

[0073] ii. Sleep for 1 minute;

[0074] iii 1 / 3C constant current charging to 3.6V, sleep for 5 minutes;

[0075] iv 0.15C constant current and constant voltage charging to 3.65V, cut-off current 0.05C, sleep for 5 minutes;

[0076] v 0.5C constant current discharge to 2.5V, sleep for 5 minutes;

[0077] vi Press Figure 3 Repeat steps i to v at the temperatures and in the order shown.

[0078] ③, Step S3:

[0079] Calculate the capacity coefficient of each battery cell at different temperatures T, capacity coefficient = C / C0.

[0080] ④, Step S4:

[0081] For the cell top cover temperature taken, the maximum temperature of the cell top cover or the average temperature of the top cover in the capacity division process can be used for capacity compensation; the capacity coefficient & maximum temperature of the top cover, the capacity coefficient & average temperature of the top cover are fitted respectively, and the fitting curve is as follows: Figure 4 and Figure 5 .

[0082] ⑤. Step S5:

[0083] Compare the two fitting curves, where the capacity coefficient & top cover average temperature fitting curve R 2 The value is higher, so the present invention adopts the capacity coefficient & top cover average temperature fitting formula: C / C0=2*10 -6 X 3 -0.0003X 2 +0.0135X+0.8027.

[0084] ⑥, Step S6:

[0085] For the capacity of the mass production line, the capacity is greatly affected by temperature during the capacity division process, resulting in a large deviation in the capacity measured by the cell capacity division production line. Therefore, the capacity coefficient relationship curve obtained in the laboratory is introduced into the mass production line. The equipment can calculate the compensation capacity by collecting the average temperature of the top cover of the cell during the capacity division process and the mass production line capacity measured by the capacity division cabinet.

[0086] Temperature compensation capacity of mass production line = C / (2*10 -6 X 3 -0.0003X 2 +0.0135X+0.8027); where C is the capacity of the mass production line battery cells, and X is the average temperature of the top cover of the mass production line battery cells.

[0087] ⑦, step S7:

[0088] Input the compensation capacity formula into the upper computer software of the capacity division equipment, and the equipment can automatically calculate the compensation capacity and upload it to the MES system. The compensation capacity data is used for battery cell grouping and shipment.

[0089] Substitute the compensation capacity formula into the mass production line for batch verification, such as Figure 6 As shown, the use of compensation capacity reduces the extreme difference of capacity distribution, improves the accuracy of capacity and the efficiency of capacity grouping, and reduces production costs.

[0090] Compared with the existing technology, this solution has the following technical advantages:

[0091] ① The present invention selects battery cells with good consistency, and first performs standard capacity cycles on the battery cells to stabilize the capacity of the battery cells, thereby greatly reducing the impact of battery cell cycles on the capacity in subsequent experimental processes.

[0092] ② The temperature gradient studied in this invention covers the maximum and minimum temperatures that the cells in the capacity distribution cabinet can reach, and the resulting capacity compensation formula can cover the temperature changes of the mass production line. It should be noted that the temperature range studied needs to be adaptively changed for different cell models and capacity distribution cabinet designs.

[0093] ③ The top cover temperature selected by the present invention is that the capacity distribution cabinet of the mass production line measures 100% of the battery cells, so the capacity of each battery cell can be compensated, which is suitable for use in the mass production line.

[0094] ④ The present invention compares the selected top cover temperature with the maximum temperature of the top cover or the average temperature of the top cover, selects the average temperature of the top cover with a better fitting effect, and improves the accuracy of the compensation capacity.

[0095] Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, they are all within the protection scope of the present invention.

Claims

1. A capacity compensation method for a lithium battery mass production line for capacity division, characterized in that : Includes the following steps: Step 1: For the cells in the same batch, select several cells as test cells; Step 2: Test the test cell in a constant temperature box to obtain the cell capacity data tested at different temperatures; Step 3: Calculate the capacity coefficient of each battery cell at different temperatures based on the battery cell capacity data obtained in step 2; Step 4: Obtain a functional relationship between temperature and capacity coefficient based on capacity coefficient fitting; Step 5. When performing capacity separation on the mass production line, the corresponding compensation capacity value under the current mass production line environment is calculated through a functional relationship, the compensation capacity value is used as the cell capacity separation capacity, and the compensation capacity value is used to perform cell capacity separation.

2. A capacity compensation method for a lithium battery mass production line for capacity division as claimed in claim 1, characterized in that Step 2 includes: In a constant temperature box, the selected battery cells are cycled at a specified temperature with a standard capacity, and the last capacity is recorded as C0.

3. A capacity compensation method for a lithium battery mass production line for capacity division as claimed in claim 1, characterized in that : In a constant temperature box, the selected battery cells are divided at different temperatures according to the mass production line capacity division process to obtain the battery cell capacity C at different temperatures.

4. A capacity compensation method for a lithium battery mass production line for capacity division as claimed in claim 3, characterized in that Step three includes: defining the capacity coefficient K of each battery cell as K=C / C0; and calculating the corresponding capacity coefficient K using the capacity data obtained in step two.

5. A capacity compensation method for a lithium battery mass production line for capacity division as described in any one of claims 1 to 4, characterized in that : In step 2, the battery cell temperature adopts the top cover temperature of the battery cell, and the top cover temperature of each battery cell and the corresponding battery cell capacity data obtained by the test are collected and counted.

6. A capacity compensation method for a lithium battery mass production line for capacity division as described in any one of claims 1 to 4, characterized in that : Step 4 includes: based on the capacity coefficient of each battery cell at each temperature obtained in step 3, a number of data points corresponding to the temperature X and the capacity coefficient can be obtained; mathematically fitting the corresponding data points of the temperature X and the capacity coefficient to obtain a functional correspondence between the two.

7. A capacity compensation method for a lithium battery mass production line for capacity division as claimed in claim 6, characterized in that : The expression of the corresponding relationship of the fitted function is: C / C0=AX 3 -BX 2 +DX+E; Among them, A, B, D, and E are constants, and their values ​​are determined by fitting; X is the average temperature of the top cover of the battery cell in the mass production line; and K is the capacity coefficient.

8. A capacity compensation method for a lithium battery mass production line for capacity division as described in any one of claims 1 to 4, characterized in that : Step five includes, when the mass production line is divided into capacities, performing a capacity division test according to the mass production line capacity division process to obtain the current capacity value C and the corresponding average temperature X of the top cover of the mass production line battery cell under the capacity division process, and bringing the collected current capacity value C and the corresponding average temperature X of the top cover of the mass production line battery cell under the capacity division process into the fitted function correspondence to calculate the compensation capacity value.

9. A capacity compensation method for a lithium battery mass production line for capacity division as claimed in claim 8, characterized in that : In step 5, the compensation capacity value calculation includes: compensation capacity value = current capacity value C / (AX 3 -BX 2 +DX+E), where X is the average temperature of the top cover of the battery cells in the mass production line under the capacity division process.

10. A capacity compensation method for a lithium battery mass production line for capacity division as claimed in any one of claims 1 to 4, characterized in that : Input the fitted function formula into the upper computer system of the capacity distribution cabinet. The upper computer system of the capacity distribution cabinet calculates the compensation capacity value through the function formula according to the capacity and temperature obtained from the current capacity distribution process, and then uploads the capacity distribution compensation capacity result to the MES system for recording and sorting.

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