Lithium-ion battery formation and grading method

Abstract

The present invention relates to a method for forming and grading a lithium-ion battery. When forming the battery cell, the voltage of the battery cell is charged to the same state as the battery shipping voltage; the method for grading the battery cell is as follows: after sealing and cleaning the battery cell, the battery cell is graded according to the stable voltage after cleaning. This method for forming and grading a lithium-ion battery directly grades the battery cell according to the voltage after cleaning, cancels the related steps of aging, polishing the battery cell after cleaning and grading the lithium-ion battery with a grading cabinet in the traditional lithium-ion battery manufacturing process. The grading method is simple, saving power and labor costs; and when forming the battery cell, the voltage of the battery cell is charged to the same state as the battery shipping voltage, which can ensure that the performance of the lithium-ion battery remains unchanged.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion battery manufacturing, and particularly to a method for forming and grading the capacity of a lithium-ion battery. Background Art

[0002] Lithium-ion batteries have the advantages of high voltage, high specific energy, long charge and discharge life, etc., and are thus widely used in products in multiple fields such as electronic products, portable small appliances, energy storage systems, etc.

[0003] In actual use, due to different requirements of products for battery capacity, battery packs composed of several single lithium-ion batteries have been widely used. However, under the same process conditions, the capacities of single lithium-ion batteries produced in batches are different. If these single lithium-ion batteries with different capacities are directly combined into a battery pack in a series-parallel manner, during the charging and discharging process of the battery pack, there will often be a situation where some single lithium-ion batteries are overcharged while some other single lithium-ion batteries are not fully charged, thus affecting the service life of the battery pack. Therefore, it is crucial to perform grading treatment on the processed single lithium-ion batteries.

[0004] The traditional grading method is to age and polish the cleaned battery cells, and then put them into a grading cabinet for grading by using capacity grading or voltage grading. This grading method takes a long time, making the overall time consumed in the manufacturing process of lithium-ion batteries longer, and it is necessary to use a grading cabinet for grading, resulting in a high grading cost. Summary of the Invention

[0005] Based on this, it is necessary to provide a method for forming and grading the capacity of a lithium-ion battery to solve the above problems, which can shorten the manufacturing time of lithium-ion batteries, reduce costs, and ensure the performance of lithium-ion batteries remains unchanged.

[0006] A method for forming and grading the capacity of a lithium-ion battery includes the steps of forming the battery cells and grading the capacity of the battery cells. When forming the battery cells, the voltage of the battery cells is charged to the same state as the battery shipping voltage; the method for grading the capacity of the battery cells is: after sealing and cleaning the battery cells, grading the capacity of the battery cells according to the stable voltage after cleaning.

[0007] In one embodiment, charging the voltage of the battery cells to the same state as the battery shipping voltage is achieved by using an optimized forming method. The optimized forming method is: first perform constant current charging with a current value between 0.03C and 0.07C, and the charging time is between 25 minutes and 35 minutes; then perform constant current charging with a current value between 0.28C and 0.32C, and the charging time is between 115 minutes and 125 minutes; finally, perform constant current charging with a current value between 0.03C and 0.07C again, and the charging time is between 175 minutes and 185 minutes.

[0008] In one embodiment, the optimized formation method is specifically as follows: First, perform constant current charging at 0.05C for 30 minutes; then perform constant current charging at 0.3C for 120 minutes; finally, perform constant current charging at 0.05C for 180 minutes.

[0009] In one embodiment, the specific method for grading the capacity of the battery cell according to the stable voltage after cleaning is as follows: If the voltage value is between 3.85V and 3.90V, the battery cell is determined to be qualified; otherwise, the battery cell is determined to be unqualified.

[0010] In one embodiment, before forming the battery cell, the following steps are further included:

[0011] Bake the battery cell until the moisture in the battery cell is completely evaporated;

[0012] Inject electrolyte into the battery cell for the first time;

[0013] Let the battery cell after injection stand until the electrode plate and the separator are fully wetted.

[0014] In one embodiment, between forming the battery cell and grading the capacity of the battery cell, the following steps are further included:

[0015] Inject electrolyte into the formed battery cell for the second time;

[0016] Seal the battery cell with steel balls;

[0017] Clean the sealed battery cell.

[0018] In one embodiment, after forming the battery cell, the voltage of the battery cell is 3.9V.

[0019] In one embodiment, 75% - 85% of the electrolyte is injected into the battery cell for the first time, and 15% - 25% of the electrolyte is injected into the formed battery cell for the second time.

[0020] In one embodiment, 80% of the electrolyte is injected into the battery cell for the first time, and 20% of the electrolyte is injected into the formed battery cell for the second time.

[0021] The beneficial effects of the above lithium-ion battery formation and grading method are as follows: The lithium-ion battery formation and grading method directly grades the capacity of the battery cell according to the voltage after cleaning, cancels the related steps of aging, polishing the battery cell after cleaning and grading the lithium-ion battery with a grading cabinet in the traditional lithium-ion battery manufacturing process, the grading method is simple, saving power and labor costs; and when forming the battery cell, the voltage of the battery cell is charged to the same state as the battery shipping voltage, which can ensure that the performance of the lithium-ion battery remains unchanged. Description of the Drawings

[0022] Figure 1 Flow chart of the formation and grading method for a lithium-ion battery according to an embodiment;

[0023] Figure 2 For verification Figure 1 Comparison data graph of the cycle performance of two groups of battery cells A and B for verifying the feasibility of the formation and grading method of the lithium-ion battery in the shown embodiment;

[0024] Figure 3 For verification Figure 1 Relationship graph between the voltage and capacity of each battery cell after cleaning for verifying the feasibility of the formation and grading method of the lithium-ion battery in the shown embodiment. Detailed implementation manner

[0025] As Figure 1 shown, in the lithium-ion battery formation and grading method provided in the embodiment of the present invention, by optimizing the formation method, grading can be performed according to the voltage after cleaning, the grading method is simple, and the performance of the battery cells can be ensured to remain unchanged.

[0026] The formation and grading method of a lithium-ion battery according to an embodiment includes the following steps.

[0027] S101. Bake the battery cell until the moisture in the battery cell is completely evaporated.

[0028] S102. Inject 75% - 85% of the electrolyte into the battery cell for the first time.

[0029] Specifically, the percentage of the electrolyte injected into the battery cell for the first time is 80%.

[0030] S103. Leave the battery cell after injection until the electrode sheet and the separator are fully wetted.

[0031] S104. Perform formation on the battery cell and charge the voltage of the battery cell to the same state as the battery shipping voltage.

[0032] Among them, in this embodiment, charging the voltage of the battery cell to the same state as the battery shipping voltage is achieved by adopting an optimized formation method. The optimized formation method is: first perform constant current charging with a current value between 0.03C and 0.07C, and the charging time is between 25 minutes and 35 minutes; then perform constant current charging with a current value between 0.28C and 0.32C, and the charging time is between 115 minutes and 125 minutes; finally, perform constant current charging with a current value between 0.03C and 0.07C, and the charging time is between 175 minutes and 185 minutes.

[0033] Specifically, the optimized formation method is as follows: First, perform constant current charging at 0.05C for 30 minutes; then perform constant current charging at 0.3C for 120 minutes; finally, perform constant current charging at 0.05C for 180 minutes.

[0034] It should be noted that the charging current and charging time in each of the above stages can also be other values within the corresponding value ranges, as long as the voltage value of the battery cell after formation is the same as the shipping voltage value of the battery.

[0035] Specifically, the voltage of the battery cell after formation is 3.9V.

[0036] S105. Inject 15% - 25% of the electrolyte into the battery cell after formation for the second time.

[0037] Specifically, the percentage of the electrolyte injected into the battery cell after formation for the second time is 20%.

[0038] It should be noted that the percentages of the electrolyte injected for the first and second times can also be other values within their respective percentage ranges, as long as the percentage of the electrolyte injected for the first time is greater than that for the second time, and the sum of the two percentages is 100%.

[0039] S106. Seal the battery cell with steel balls.

[0040] S107. Clean the battery cell after sealing.

[0041] S108. Perform grading on the battery cell according to the stable voltage after cleaning, and screen out qualified and unqualified battery cells.

[0042] Among them, the specific method of grading is as follows: If the voltage value is between 3.85V and 3.90V, it is determined that the battery cell is qualified, and the qualified battery cells are stored in the warehouse; otherwise, it is determined that the battery cell is unqualified, and the unqualified battery cells are downgraded.

[0043] It should be noted that in the traditional formation method, after the battery cell is formed, the voltage of the battery cell is less than the shipping voltage of the battery. However, in the present invention, by adopting the optimized formation method, the voltage of the battery cell after formation is the same as the shipping voltage of the battery, so that in step 108, grading can be performed according to the stable voltage after cleaning.

[0044] The traditional grading method is as follows: After the cleaned battery cells are aged and polished, a grading cabinet is used to grade the lithium-ion batteries. Therefore, compared with the traditional grading method, in the grading method for lithium-ion batteries provided by the present invention, the steps of aging, polishing, and grading using a grading cabinet are omitted, and grading is directly performed according to the voltage after cleaning. The grading method is simple and saves power and labor costs.

[0045] In addition, although the optimized formation method in the present invention takes slightly longer than the traditional formation method, in view of the entire process of the lithium-ion battery formation and grading method of the present invention, the steps of aging, polishing, and grading using a grading cabinet in the traditional formation and grading process are omitted, and the total time consumed by these steps is much longer than the time increased by the optimized formation method compared to the traditional formation method. Therefore, overall, the present invention shortens the time of the entire formation and grading process of the lithium-ion battery, thereby improving the manufacturing efficiency of the lithium-ion battery.

[0046] To verify the feasibility of the optimized formation method for the battery cells in this embodiment, two groups of battery cells, namely Group A and Group B, are selected for experimental verification, and the nominal capacity of the battery cells in both Group A and Group B is 1300 mAh.

[0047] The specific experimental method is as follows: First, both Group A and Group B battery cells are sequentially executed steps S101, S102, and S103. Then, step S104 is executed on Group A battery cells, that is, the optimized formation method provided by the present invention is used for formation of Group A battery cells, while the traditional method is used for formation of Group B battery cells. The traditional formation method is as follows: First, a constant current charge of 0.05C is carried out for 40 minutes, and then a constant current charge of 0.3C is carried out for 50 minutes. After the formation of both Group A and Group B battery cells is completed, the voltage of Group A battery cells is 3.9V, while the voltage of Group B battery cells is lower than 3.9V. Finally, both groups of battery cells are sequentially executed steps S105, S106, and S107.

[0048] After cleaning both Group A and Group B battery cells, various experimental verifications are carried out on both Group A and Group B battery cells to obtain experimental data. Specifically: First, both Group A and Group B battery cells are aged, and then 0.5C grading is carried out on both Group A and Group B battery cells respectively, and their respective capacities are recorded. After grading, comparative tests on the rate performance, high-temperature storage, and cycle performance are carried out on both Group A and Group B battery cells respectively. The experimental data are shown in Table 1 and Figure 2 as follows.

[0049] Table 1 Comparison of experimental data of two groups of battery cells

[0050]

[0051] Among them, columns 5 and 6 in Table 1 are the experimental data on the rate performance, and columns 7 to 10 are the experimental data on high-temperature storage.

[0052] As can be seen from Table 1, the capacity of Group A is slightly lower than that of Group B, but the difference is within the acceptable range of the nominal capacity, that is, 1300 mAh. The sizes and internal resistances of both Group A and Group B are relatively close. In terms of the rate performance, Group A is stronger than Group B. In terms of high-temperature storage, the thermal size growth rate and cold size growth rate of Group A are stronger than those of Group B, and the capacity retention and capacity recovery data of both groups are close.

[0053] Figure 2 It is a comparison data graph of the cycling performance of two groups of cells, namely Group A and Group B. It can be seen from the cycling data in Figure 2 that the capacity attenuation trends of Group A and Group B are basically the same, and the capacities are basically above 85% after 200 cycles.

[0054] Therefore, comprehensively considering the experimental data in terms of capacity, size, internal resistance, rate, high-temperature storage, and cycling performance, the performances of the two groups of cells, Group A and Group B, are close, indicating that when the cells are formed using the optimized forming method provided by the present invention, their performances are close to those of the cells formed using the traditional forming method, thus verifying the feasibility of the optimized forming method provided by the present invention.

[0055] In addition, in order to verify the feasibility of performing grading according to the stable voltage after cell cleaning in the forming and grading method provided by the present invention, the following experiment is conducted for verification.

[0056] The experimental method is as follows: Stick glue on the positive electrode tab of the core of the cell. Since the width of the glue is inversely proportional to the capacity of the cell, a series of cells with gradually decreasing capacities can be designed by sticking glue with gradually increasing widths on the positive electrode tabs of the cores of different cells. Then, all the cells are executed according to steps S101 to S107 provided by the present invention, and the voltages of the cells after cleaning are recorded. Then, 0.5C grading is performed on each cell after cleaning to obtain the capacity of each cell. Figure 3 It shows a relationship graph of the voltage and capacity of each cell after cleaning.

[0057] It can be seen from Figure 3 that the capacity of the cell decreases as the cleaning voltage increases, and the voltages of the cells corresponding to the nominal capacity of 1300 mAh and the A2-grade capacity of 1325 mAh are both around 3.9 V after cleaning. Therefore, the experimental results verify the feasibility of grading the cells according to the voltage after cleaning.

[0058] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0059] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A method for forming and grading a lithium-ion battery cell, comprising the steps of forming the battery cell and grading the battery cell, characterized in that: when forming the battery cell, the voltage of the battery cell is charged to the same state as the battery shipping voltage; charging the voltage of the battery cell to the same state as the battery shipping voltage is achieved by adopting an optimized forming method, and the optimized forming method is: first perform constant current charging with a current value between 0.03C and 0.07C, and the charging time is between 25 minutes and 35 minutes; then perform constant current charging with a current value between 0.28C and 0.32C, and the charging time is between 115 minutes and 125 minutes; finally, perform constant current charging with a current value between 0.03C and 0.07C again, and the charging time is between 175 minutes and 185 minutes; the method for grading the battery cell is: after sealing and cleaning the battery cell, grade the battery cell according to the stable voltage after cleaning; the specific method for grading the battery cell according to the stable voltage after cleaning is: if the voltage value is between 3.85V and 3.90V, it is determined that the battery cell is qualified; otherwise, it is determined that the battery cell is unqualified.

2. The method for forming and grading a lithium-ion battery cell according to claim 1, characterized in that, the optimized forming method is specifically: first perform constant current charging at 0.05C for 30 minutes; then perform constant current charging at 0.3C for 120 minutes; finally perform constant current charging at 0.05C for 180 minutes.

3. The method for forming and grading a lithium-ion battery cell according to claim 2, characterized in that, the voltage of the battery cell after forming is 3.9V.

4. The method for forming and grading a lithium-ion battery cell according to claim 2, characterized in that, before forming the battery cell, the following steps are further included: bake the battery cell until the moisture in the battery cell is completely evaporated; inject electrolyte into the battery cell for the first time; set aside the battery cell after injection until the electrode sheet and the separator are fully wetted.

5. The method for forming and grading a lithium-ion battery cell according to claim 4, characterized in that, the following steps are further included between forming the battery cell and grading the battery cell: inject electrolyte into the formed battery cell for the second time; seal the battery cell with steel beads; clean the sealed battery cell.

6. The method for forming and grading a lithium-ion battery cell according to any one of claims 1 to 5, characterized in that, inject 75% - 85% of the electrolyte into the battery cell for the first time, and inject 15% - 25% of the electrolyte into the formed battery cell for the second time.

7. The method for forming and grading a lithium-ion battery cell according to any one of claims 1 to 6, characterized in that, inject 80% of the electrolyte into the battery cell for the first time, and inject 20% of the electrolyte into the formed battery cell for the second time.

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