A rapid capacity grading method for lithium ion battery cells

Abstract

The application discloses a kind of lithium ion cell quick capacity grading methods, comprising the following steps: S1: the capacity of n cell and SOC-OCV curve are obtained, preset charging cut-off voltage V1 in the voltage range where SOC-OCV curve slope is greater;S2: n known capacity cell is charged and discharged, and the discharge curve of n cell is obtained;S3: the cell to be graded is charged and discharged, and the discharge curve of the cell to be graded is obtained;S4: the discharge curve of n cell is compared with the discharge curve of the cell to be graded, and the capacity range of the cell to be graded is obtained according to the position of the discharge curve of the cell to be graded in the discharge curve of n cell;The quick capacity grading method does not need to charge the cell to full when grading, greatly shortens the time and energy consumption of grading, in addition, only the discharge curve of the cell to be graded and the known capacity cell is compared to obtain the interval range of the capacity of the cell to be graded, and is not affected by the grading temperature in the process, improves the accuracy of grading.

Description

Technical Field

[0001] This invention relates to the field of lithium battery manufacturing technology, and in particular to a rapid capacity testing method for lithium-ion cells. Background Technology

[0002] With the further development of electronic digital products and the gradual popularization of new energy vehicles, lithium-ion batteries are being used more and more widely due to their advantages such as being green and environmentally friendly, having high energy density, good cycle performance, and no memory effect. The control of the cost and quality of lithium-ion batteries is also receiving increasing attention.

[0003] Traditional lithium-ion cell capacity testing methods often involve charging the cell to 100% SOC and then discharging it to an empty state, repeating this cycle once or twice or more. This not only results in a long testing time leading to the investment of a large number of testing equipment, but also high energy consumption and production costs. Furthermore, temperature fluctuations during the testing process can cause significant errors in the testing results. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, this invention proposes a rapid capacity division method for lithium-ion cells, which greatly shortens the capacity division time and energy consumption, reduces the cost of capacity division, and improves the accuracy of capacity division.

[0005] The present invention proposes a method for rapid capacity assessment of lithium-ion battery cells, comprising the following steps:

[0006] S1: Obtain the capacity and SOC-OCV curve of n cells, and preset the charging cutoff voltage V1 within the voltage range where the slope of the SOC-OCV curve is large;

[0007] S2: Charge and discharge n cells of known capacity to obtain the discharge curves of the n cells;

[0008] S3: Charge and discharge the cell to be tested to obtain the discharge curve of the cell to be tested.

[0009] S4: Compare the discharge curves of the n cells with the discharge curve of the cell to be rated. Based on the position of the discharge curve of the cell to be rated among the discharge curves of the n cells, the capacity range of the cell to be rated is obtained.

[0010] Further, in step S2: charging and discharging n cells of known capacity to obtain the discharge curves of the n cells, specifically including:

[0011] S21: Charge n battery cells with constant current to the cutoff voltage V1;

[0012] S22: Perform constant current discharge on the n fully charged cells until the lower limit voltage V2 is reached;

[0013] S23: Plot the V-SOC discharge curve of n cells between V1 and V2, which is the relationship between voltage V and capacity SOC.

[0014] Further, in step S21: the n cells are first charged with constant current to the cutoff voltage V1, specifically: the n cells are first charged with constant current to the cutoff voltage V1, and then charged with constant voltage to the set cutoff current.

[0015] Furthermore, the constant current charging current for n cells is 0.2-1C, and the cutoff current for constant voltage charging is 0.05C.

[0016] Furthermore, between steps S21 and S22, before the battery cell discharges, the fully charged battery cell is allowed to rest for a set time.

[0017] Further, in step S3: the cell to be rated is charged and discharged to obtain the discharge curve of the cell to be rated. The charging and discharging of the cell to be rated is consistent with the charging and discharging of n cells with known capacity.

[0018] Furthermore, the cell to be rated is the same model, chemical system, and design as the n cells with known capacities. When the cell to be rated is fixed, its charge and discharge rate is the same as that of the n cells with known capacities.

[0019] Furthermore, the capacity of the n cells is selected according to the cell capacity grading requirements and set as C1, C2, C3...Cn, where 5 < n < 100.

[0020] Furthermore, the relative capacities of the n cells are C1 < C2 < C3 < ... < Cn.

[0021] Furthermore, the capacity of the n cells is the capacity after being recalibrated following a set number of uses.

[0022] The advantages of the rapid capacity rating method for lithium-ion battery cells provided by this invention are as follows: The rapid capacity rating method for lithium-ion battery cells provided by this invention eliminates the need to fully charge the battery cell during the rating process, greatly shortening the rating time and reducing energy consumption. Furthermore, the decrease in the battery cell's state of charge (SOC) significantly reduces safety risks during charging and discharging, making it suitable for large-scale production. Additionally, the range of the battery cell's capacity can be determined simply by comparing the discharge curves of the cell to be rated with those of a known capacity cell, without being affected by the rating temperature during the process, thus reducing the cost of battery cell rating and improving the accuracy of rating. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process of the present invention;

[0024] Figure 2It is the SOC-OCV curve of a known cell capacity;

[0025] Figure 3 This is the complete discharge curve of the capacity-controlled battery cell;

[0026] Figure 4 yes Figure 3 A magnified view of the complete discharge curve of a medium-capacity battery cell. Detailed Implementation

[0027] The technical solution of the present invention will now be described in detail through specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] like Figures 1 to 4 As shown, the present invention proposes a method for rapid capacity testing of lithium-ion cells, comprising the following steps:

[0029] S1: Obtain the capacity and SOC-OCV curve of n cells, and preset the charging cutoff voltage V1 within the voltage range where the slope of the SOC-OCV curve is large;

[0030] The capacities of n battery cells are selected according to the cell capacity grading requirements, and are designated as C1, C2, C3...Cn, with the relative capacity relationship being C1 < C2 < C3 <...Cn. ＜ n ＜ The larger n is, the more accurate the capacity. It is not limited to cases less than 100; for cases greater than 100, the process can be followed sequentially as in this embodiment. The n cells with known capacities can be used 20 to 200 times, depending on the cell cycle performance. The capacity obtained after using them a set number of times and then re-capacitating is taken as the capacity of the n cells obtained in this embodiment. It is possible that the capacities of C1, C2, C3, ..., Cn decrease sequentially.

[0031] By setting the capacity to decrease or increase sequentially, a continuous capacity range can be formed, increasing the capacity range within which the capacitor to be calibrated is determined.

[0032] The region with a steep slope on the SOC-OCV curve indicates that the OCV in this region is more sensitive to changes in the cell's SOC. Using this region as the cutoff voltage V1 can make the voltage differentiation between cells of different capacities more obvious, which is beneficial to improving the accuracy of capacity grading.

[0033] S2: Charge and discharge n cells of known capacity to obtain the discharge curves of the n cells;

[0034] Specifically, it includes:

[0035] S21: First, charge n cells with constant current to the cutoff voltage V1, then charge with constant voltage to the set cutoff current, and then let the fully charged cells rest for a set time t1.

[0036] The cutoff voltage V1 is often less than or equal to the upper voltage limit of the battery cell, meaning that the battery cell does not need to be charged to 100% SOC during capacity grading. The constant current charging current of n battery cells can be set to 0.2-1C, and the cutoff current of constant voltage charging can be set to 0.05C. Generally, 60min > t1 > 0min.

[0037] S22: Perform constant current discharge on the n fully charged cells until the lower limit voltage V2 is reached;

[0038] The lower limit voltage V2 is equal to the lower limit of the cell voltage. That is, the cell needs to be discharged to a depleted state during capacity discharge, and the discharge current is 0.2C to 1C.

[0039] S23: Plot the V-SOC discharge curve of n cells between V1 and V2, which is the relationship between voltage V and capacity SOC.

[0040] S3: Charge and discharge the cell to be tested to obtain the discharge curve of the cell to be tested.

[0041] The charging and discharging of the cell to be rated is consistent with the charging and discharging of n cells with known capacities; the cell to be rated is the same model, chemical system, and design as the n cells with known capacities, and the charging and discharging rate of the cell to be rated is consistent with that of the n cells with known capacities when the cell is rated.

[0042] S4: Compare the discharge curves of the n cells with the discharge curve of the cell to be rated. Based on the position of the discharge curve of the cell to be rated among the discharge curves of the n cells, the capacity range of the cell to be rated is obtained.

[0043] When the discharge curve of the cell to be rated is located between two cells with known capacities, the capacity of the cell to be rated is located within the capacity range of the two cells with known capacities. The discharge curve is a time-voltage curve or a capacity-voltage curve.

[0044] Through steps S1 to S4, it is not necessary to fully charge the battery cell during capacity testing, which greatly shortens the testing time and reduces energy consumption. Furthermore, the decrease in the cell's state of charge (SOC) significantly reduces the safety risks during charging and discharging, making it suitable for large-scale production. In addition, the range of the cell's capacity can be determined simply by comparing the discharge curves of the cell to be tested with those of a cell with a known capacity, without being affected by the testing temperature during the process. This reduces the cost of cell testing and improves the accuracy of testing.

[0045] As an example: Let n equal 5, and obtain the capacities of the 5 cells as C1 = 100Ah, C2 = 100.5Ah, C3 = 101Ah, C4 = 101.5Ah, and C5 = 102Ah.

[0046] Then, the SOC-OCV curves of the five cells were tested at a temperature of 25℃ and a current of 1 / 3C. The SOC-OCV curves are shown in the attached figure. Figure 2 As shown, the region with a larger slope is determined to be 50% to 85% SOC. The cell charging cutoff voltage is set to the voltage corresponding to 55% SOC, i.e., V1 = 3.77V.

[0047] Five cells with known capacities were charged at a constant current to 3.77V, then charged at a constant voltage to a cutoff voltage of 0.05C. After resting for 5 minutes, they were discharged at a constant current to a cutoff voltage V2. The discharge current was 1 / 3C, and the discharge cutoff voltage V2 = 2.8V. The discharge curves of the five cells with known capacities were obtained, as shown below. Figure 3 and 4 As shown.

[0048] The cells to be rated are charged with a constant current to 3.77V, then switched to a constant voltage to the cutoff voltage of 0.05C. After resting for 5 minutes, they are discharged with a constant current to the cutoff voltage V2. The discharge current is 1 / 3C, and the discharge cutoff voltage V2 = 2.8V. The cells to be rated can be selected according to actual needs. In this embodiment, 5 cells are selected. The discharge curve is shown below. Figure 3 and 4 As shown.

[0049] Compare the discharge curves of 5 cells with known capacity and 5 cells to be rated for capacity, as follows: Figure 2 and Figure 3 As shown, the capacity ranges of the cells to be tested are 100–100.5 Ah, 100.5–101 Ah, 101–101.5 Ah, 101–101.5 Ah, and 101.5–102 Ah. The testing process takes 125 minutes.

[0050] This embodiment allows for the direct determination of the capacity range of the battery cell to be categorized. When there are a sufficient number of battery cells with known capacities, the resulting capacitance range will be smaller, and the obtained capacity range of the battery cell to be categorized will be more accurate.

[0051] Furthermore, in the actual battery cell production process, it is only necessary to know the accurate range of the battery cell capacity to classify them, without needing to know the absolute value of the battery cell capacity. Therefore, through this embodiment, the capacity classification of battery cells to be classified can be realized in the actual production process.

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for rapid sizing of lithium ion cells, characterized in that, Comprising the following steps: S1: obtaining the capacity and SOC-OCV curve of n battery cells, and presetting a charging cutoff voltage V1 in a voltage range where the SOC-OCV curve has a large slope; S2: charging and discharging n battery cells with known capacity to obtain the discharge curves of the n battery cells; S3: charging and discharging a battery cell to be sized to obtain the discharge curve of the battery cell to be sized, wherein the battery cell to be sized and the n battery cells with known capacity are battery cells of the same model, the same chemical system and the same design, the charging and discharging rate of the battery cell to be sized is consistent with that of the n battery cells with known capacity, and the charging and discharging of the battery cell to be sized is consistent with that of the n battery cells with known capacity; S4: comparing the discharge curves of the n battery cells with the discharge curve of the battery cell to be sized, and obtaining the capacity range of the battery cell to be sized according to the position of the discharge curve of the battery cell to be sized in the discharge curves of the n battery cells.

2. The method of claim 1, wherein the method further comprises: In step S2: charging and discharging n battery cells with known capacity to obtain the discharge curves of the n battery cells, specifically comprising: S21: charging the n battery cells to the cutoff voltage V1 at a constant current; S22: discharging the n battery cells charged to the cutoff voltage V1 at a constant current to the lower limit voltage V2; S23: drawing a V-SOC discharge curve graph between the voltage V and the capacity SOC of the n battery cells between V1 and V2.

3. The method of claim 2, wherein the method further comprises: In step S21: charging the n battery cells to the cutoff voltage V1 at a constant current, specifically comprising: charging the n battery cells to the cutoff voltage V1 at a constant current, and then charging to the set cutoff current at a constant voltage.

4. The method of claim 3, wherein the method further comprises: The current for charging the n battery cells at a constant current is 0.2-1C, and the cutoff current for charging at a constant voltage is 0.05C.

5. The method of claim 2, wherein the method further comprises: Between step S21 and step S22, the charged battery cells are allowed to stand for a set time before discharging.

6. The method of claim 1-5, wherein the method further comprises: The capacities of the n battery cells are selected according to the battery cell capacity grading requirement, and are set as C1, C2, C3,..., Cn, 5 7. The method of claim 6, wherein the method further comprises: The relative relationship of the capacities of the n battery cells is C1 8. The method of claim 6, wherein the method further comprises: The capacities of the n battery cells are the capacities after re-sizing after being used for a set number of times.

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