Method for inspecting quality of lithium battery

Abstract

The invention discloses a method for inspecting the quality of a lithium battery, and the method comprises the steps: S1, providing inspection equipment which comprises a charge-discharge motor and a press; s2, pressing a press; s3, charging and discharging the battery cell of the lithium battery; s4, recording voltage data of the battery cell; s5, calculating the number of scattered battery cells according to the battery cell voltage data; s6, executing setting operation according to the calculated number of the scattered battery cells; and S7, performing formation on the battery cell. The method for inspecting the quality of the lithium battery is simple and easy to form, the time consumed for equipment transformation is short, effective inspection of the lithium battery can be achieved, and the risk of missing inspection of defective products is reduced.

Description

Technical Field

[0001] This invention belongs to the field of new energy battery technology. Specifically, this invention relates to a method for testing the quality of lithium batteries. Background Technology

[0002] A lithium / sodium ion battery cell is a rechargeable battery cell that can be repeatedly charged and discharged. It is mainly composed of anode and cathode plates, separator, electrolyte, mechanical parts and other components.

[0003] Currently, lithium / sodium-ion battery cells are becoming increasingly larger, and the required energy density is rising, which also places greater demands on the manufacturing process. First, high-energy-density cells have their internal theoretical space already compressed to the limit, making electrolyte filling very difficult. Second, the main materials are high-density materials with very low porosity, which is detrimental to electrolyte wetting. Third, areal density generally tends towards higher thickness designs, thus lengthening the electrolyte wetting path. These three factors combined significantly increase the difficulty of electrolyte filling and wetting, leading to problems such as poor wetting and lithium plating during the manufacturing process, thereby affecting the cell's cycle performance and safety.

[0004] Currently, in order to maximize production capacity, both baking and soaking times are controlled to the extreme. The method for inspecting the baking effect is random sampling, while the quality of soaking is not inspected. This greatly increases the risk of defective battery cells with substandard baking effect and incomplete soaking being left unprocessed.

[0005] The aim is to provide a simple and easy-to-use method for inspecting the quality of lithium batteries, particularly regarding how to reduce the risk of missing defective products. Summary of the Invention

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a method for inspecting the quality of lithium batteries, with the purpose of achieving the inspection of lithium batteries through a simple and easily adaptable means, thereby reducing the risk of missing defective products.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for inspecting the quality of lithium batteries, comprising the following steps:

[0008] S1. Provide testing equipment, including a charge / discharge machine and a press;

[0009] S2, Pressing press;

[0010] S3. Charge and discharge the lithium battery cells;

[0011] S4. Record cell voltage data;

[0012] S5. Calculate the number of scattered cells based on the cell voltage data;

[0013] S6. Execute the set operation based on the calculated number of scattered cells;

[0014] S7. The battery cell undergoes formation.

[0015] In step S1, every 2 to 10 channels of the charge / discharge machine are connected in series by wiring. Then, the channels of the press are first connected in series and then in parallel to form n series and m parallel channels.

[0016] In step S3, the current for charging the lithium battery cell is controlled between 0.01C and 0.1C.

[0017] In step S3, the charging time for the lithium battery cell is controlled between 2 and 10 seconds.

[0018] Step S3 includes:

[0019] S301, First settling;

[0020] S302, Charging;

[0021] S303, Second settling period.

[0022] In step S301, the first settling time is 0.8 to 1.2 minutes.

[0023] In step S303, the second settling time is 4.0 to 6.0 minutes.

[0024] In step S302, the charging time for the lithium battery cell is controlled to be between 5 and 10 seconds.

[0025] In step S4, the cell voltage data includes the initial cell voltage V1, the voltage after charging V2, and the voltage drop after charging is completed V3.

[0026] In step S6, the setting operation includes:

[0027] If the number of scattered cells is less than or equal to the set value, the abnormal cells are removed directly, and the remaining cells proceed to the next process normally.

[0028] If the number of scattered cells exceeds the set value, the immersion time for all cells will be increased.

[0029] The method for inspecting the quality of lithium batteries according to the present invention is simple and easy to implement, requires little time for equipment modification, and can effectively inspect lithium batteries, reducing the risk of missing defective products. Attached Figure Description

[0030] This manual includes the following figures, which illustrate the following:

[0031] Figure 1This is a flowchart of the method for testing the quality of lithium batteries according to the present invention;

[0032] Figure 2 This is a diagram showing the initial voltage V1 distribution of the battery cell;

[0033] Figure 3 This is a voltage distribution diagram of V2 after charging;

[0034] Figure 4 This is a distribution diagram of the drop-off voltage V3 after charging is completed;

[0035] Figure 5 These are comparison images of the interfaces in Example 1;

[0036] Figure 6 This is a comparison chart of the interfaces in Example 1;

[0037] Figure 7 This is a comparison chart of the interfaces in Comparison 2. Detailed Implementation

[0038] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, in order to help those skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solutions of the present invention, and to facilitate its implementation.

[0039] It should be noted that in the following embodiments, the terms "first" and "second" do not represent an absolute distinction in structure and / or function, nor do they represent the order of execution, but are merely for the convenience of description.

[0040] like Figure 1 As shown, the present invention provides a method for inspecting the quality of lithium batteries, comprising the following steps:

[0041] S1. Provide testing equipment, including a charge / discharge machine and a press;

[0042] S2, Pressing press;

[0043] S3. Charge and discharge the lithium battery cells;

[0044] S4. Record cell voltage data;

[0045] S5. Calculate the number of scattered cells based on the cell voltage data;

[0046] S6. Execute the set operation based on the calculated number of scattered cells;

[0047] S7. The battery cell undergoes formation.

[0048] Specifically, theoretically, defective battery cells with substandard baking results or incomplete wetting will have relatively large polarization, resulting in significant voltage changes. In this invention, a tiny current is applied to the battery cells for a brief charge before formal formation. By observing the voltage changes, cells with abnormal voltage are screened out, thus achieving quality inspection of the battery cells.

[0049] In step S1 above, the charger / discharger is modified before the low-current charging / discharging. Every 2 to 10 channels of the charger / discharger are connected in series via wiring. Then, the channels of the press are first connected in series and then in parallel, forming n series and m parallel channels. n and m are both positive integers, and their values ​​are determined by the total number of press channels, the total current of the charger / discharger, and the total voltage. Prioritizing increasing the number of channels connected in series reduces the interference of inconsistent current and voltage output from the charger on cell differences.

[0050] In step S3 above, the charging current of the lithium battery cell is controlled between 0.01C and 0.1C (C represents the current corresponding to the battery's nominal capacity), thus charging the cell with a small current. The minimum current is determined by the minimum accuracy setting, and the upper limit of the current is controlled by the number of cells connected in parallel and the minimum current during the cell formation process. A complete overhaul will increase the number of control switches and the number of series and parallel control equipment channels.

[0051] In step S3 above, the charging time for the lithium battery cell is controlled between 2 and 10 seconds. If the charging time is too short, the voltage change will be too small; if the charging time is too long, it will affect the subsequent formation effect.

[0052] Step S3 above includes:

[0053] S301, First settling;

[0054] S302, Charging;

[0055] S303, Second settling period.

[0056] In step S301 above, the first settling time of the battery cell is 0.8 to 1.2 minutes. For example, the first settling time can be 0.9 minutes, 1.0 minutes or 1.1 minutes.

[0057] In step S303 above, the second settling time of the battery cell is 4.0 to 6.0 minutes, and the first settling time can be 4.5 minutes, 5.0 minutes, or 5.5 minutes.

[0058] The two settling periods provide buffer time for the equipment. The initial settling period not only gives the equipment time to react but also helps the operator determine whether the contact between the battery cell and the equipment is normal. The final settling period helps the operator observe the voltage changes during the cell voltage depolarization process.

[0059] In step S4 above, the cell voltage data includes the initial cell voltage V1, the voltage after charging V2, and the drop-off voltage V3 after charging is completed.

[0060] In step S6 above, the setting operation includes:

[0061] If the number of scattered cells is less than or equal to the set value, the abnormal cells are removed directly, and the remaining cells proceed to the next process, i.e., the normal cells are formed.

[0062] If the number of scattered cells exceeds the set value, the immersion time for all cells will be increased. The specific time depends on the size of the cell, and the increased immersion time will be at least 2 hours.

[0063] In step S7 above, the series and parallel connections between channels are disconnected, and the cell is normalized. Small current disturbances can also promote further electrolyte wetting, which is helpful for cell performance and can also guide the setting of the cell wetting process time.

[0064] The above-mentioned method for testing the quality of lithium batteries has the following advantages:

[0065] 1. This method is simple and easy to implement;

[0066] 2. The principle is simple and the modification time is short;

[0067] 3. Reduce the risk of missing defective products;

[0068] 4. It improved the cell interface to some extent;

[0069] 5. Provide guidance on mass production process timing settings;

[0070] 5. Costs are controllable and the operation is highly feasible.

[0071] Example 1

[0072] In this embodiment, the battery cell is a 305Ah lithium iron phosphate aluminum-cased battery cell (new process).

[0073] The method for inspecting the quality of lithium batteries provided in this embodiment includes the following steps:

[0074] Circuit modification of the formation and charging cable machine: The five presses in one cabinet of the experimental line were manually modified into 6-series, 4-parallel channels. One formation cabinet has five presses, and each press has 24 channels. Since this is for experimental verification, the wiring was done manually, data was manually retrieved during the experiment, and the wiring was manually disconnected afterward. For mass production, intelligent modifications can be performed on a batch basis.

[0075] Experimental Verification Process: 1. Prepare 120ea cells to be formed, place them in a tray, and send them to the modified press. The soaking time of the cells is controlled to be less than 2 hours below the lower limit of the specification to ensure that cells with poor soaking will appear in the experiment. 2. Press the press and issue the inspection procedure: ①. Let stand for 1 minute; ②. Charge the cells with a constant current of 6.1A for 5 seconds, with the upper limit voltage set to 4.95V (the upper limit voltage is set to 5V); ③. Let stand for 5 minutes; record and organize the initial voltage V1, the voltage V2 after charging, and the voltage drop V3 after charging for each cell. 3. According to the voltage distribution, one cell with an abnormal voltage was found, marked, and proceeded directly to the next process. 4. Disconnect the circuit and restore the charge / discharge machine to its original state. 5. Perform normal formation, electrolyte replenishment, and capacity testing on the cells. 6. Fully charge and disassemble the scattered cells and randomly selected normal cells, and compare the interfaces. The voltage distribution and interface are shown in the attached figure. In Example 1, the voltage distribution is relatively concentrated, and the scattered points clearly show high charging and low discharging. The disassembly interface reveals a shadow in the middle area of ​​the scattered points, while the interface of the normal points is very clear.

[0076] Comparative Example 1: 305Ah lithium iron phosphate aluminum-cased cell (traditional process + simple low-current charging)

[0077] Experimental Verification Process: 1. Prepare 120ea cells from the same batch to be formed, place them in a tray, and send them to the press. The press does not need modification. The immersion time of the cells is controlled to be less than the lower limit of the specification by 2 hours to ensure that cells with poor immersion will appear in the experiment. 2. Press the press and issue the inspection procedure: ①. Let stand for 1 minute; ②. Charge with a constant current of 6.1A for 5 seconds, with the upper limit voltage set to the upper limit of the single cell voltage of 3.65V; ③. Let stand for 5 minutes; record and organize the initial cell voltage V1, the voltage after charging V2, and the drop voltage V3 after charging for each cell. 3. According to the voltage distribution, it was found that the voltage distribution of the cells was relatively scattered, without any particular scattered points, so proceed directly to the next process.

[0078] 4. Perform normal formation, electrolyte replenishment, and capacity testing on the battery cells. 5. Select three cells with the highest / medium / lowest voltage distribution for disassembly and interface comparison. See the attached diagram for voltage distribution and interface. The voltage distribution is relatively large with no significant scattered points, presumably due to interference. Except for the cell with the lowest voltage variation, which shows a relatively good interface, all other interfaces have dark shadows.

[0079] Comparative Example 2: 305Ah Lithium Iron Phosphate Aluminum-Cast Cell (Conventional Process)

[0080] Experimental Verification Process: 1. Prepare 120ea cells from the same batch to be formed, place them in a tray, and send them to the press. The press does not need modification. The immersion time of the cells is controlled to be less than the lower limit of the specification by 2 hours to ensure that cells with poor immersion appear in the experiment. 2. Press the press, issue the normal formation process, and take the initial voltage V1 before formation. 4. Perform normal electrolyte replenishment and capacity testing on the cells. 5. Select three cells with the highest / middle / lowest voltage based on the initial voltage distribution for disassembly and interface comparison. The voltage distribution and interface are shown in the attached figure. The initial voltage distribution is relatively scattered. The interface with a large voltage difference has not only shadows but also black spots, which is more serious than Example 1 and Comparative Example 1. Even the minimum voltage difference has a faint shadow. Therefore, adding a small current perturbation will promote immersion.

[0081] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution; or the direct application of the inventive concept and technical solution to other situations without modification, are all within the protection scope of the present invention.

Claims

1. A method for inspecting the quality of lithium batteries, characterized in that, Including the following steps: S1. Provide testing equipment, including a charge / discharge machine and a press; S2, Pressing press; S3. Charge and discharge the lithium battery cells; S4. Record cell voltage data; S5. Calculate the number of scattered cells based on the cell voltage data; S6. Execute the set operation based on the calculated number of scattered cells; S7. The battery cell undergoes formation.

2. The method for inspecting the quality of lithium batteries according to claim 1, characterized in that, In step S1, every 2 to 10 channels of the charge / discharge machine are connected in series by wiring. Then, the channels of the press are first connected in series and then in parallel to form n series and m parallel channels.

3. The method for inspecting the quality of lithium batteries according to claim 1, characterized in that, In step S3, the current for charging the lithium battery cell is controlled between 0.01C and 0.1C.

4. The method for inspecting the quality of lithium batteries according to any one of claims 1 to 3, characterized in that, In step S3, the charging time for the lithium battery cell is controlled between 2 and 10 seconds.

5. The method for inspecting the quality of lithium batteries according to any one of claims 1 to 3, characterized in that, Step S3 includes: S301, First settling; S302, Charging; S303, Second settling period.

6. The method for inspecting the quality of lithium batteries according to claim 5, characterized in that, In step S301, the first settling time is 0.8 to 1.2 minutes.

7. The method for inspecting the quality of lithium batteries according to claim 5, characterized in that, In step S303, the second settling time is 4.0 to 6.0 minutes.

8. The method for inspecting the quality of lithium batteries according to claim 5, characterized in that, In step S302, the charging time for the lithium battery cell is controlled to be between 5 and 10 seconds.

9. The method for testing the quality of lithium batteries according to any one of claims 1 to 8, characterized in that, In step S4, the cell voltage data includes the initial cell voltage V1, the voltage after charging V2, and the voltage drop after charging is completed V3.

10. The method for testing the quality of lithium batteries according to any one of claims 1 to 8, characterized in that, In step S6, the setting operation includes: If the number of scattered cells is less than or equal to the set value, the abnormal cells are removed directly, and the remaining cells proceed to the next process normally. If the number of scattered cells exceeds the set value, the immersion time for all cells will be increased.

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