Method and device for monitoring and optimizing negative pressure formation degree on line

Abstract

The invention relates to the technical field of lithium battery manufacturing, in particular to a method and device for online monitoring and optimizing the negative pressure formation degree. A formation detection step; and judging and supplementing work steps. By introducing an online monitoring and supplementary formation mechanism based on negative pressure detection, the industrial problem that the reaction degree is difficult to quantitatively evaluate and consistently control in the negative pressure formation process of the lithium battery is effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a method and apparatus for online monitoring and optimization of negative pressure formation. Background Technology

[0002] Formation is a key step in the manufacturing process of lithium-ion batteries. Its purpose is to induce the additives in the electrolyte to react during the first charge of the battery, forming a stable solid electrolyte interface film and removing impurities such as moisture from inside the cell. These reactions are usually accompanied by gas generation, and the completeness of the reaction directly affects the battery's performance and consistency. In mass production, a standardized formation process is typically used to treat the cells, along with a negative pressure system to promptly remove the gases generated during the reaction.

[0003] However, existing technologies have several limitations. For example, some solutions employ visual inspection systems. For instance, Chinese patent CN2022226346256 discloses a battery formation venting monitoring device and battery formation equipment. This patent proposes monitoring the storage cavity using an image acquisition device by capturing images of bubbles in the liquid during battery venting, and judging the formation quality based on morphological characteristics. This method requires a light source, camera, and image processing software, resulting in a complex structure, high cost, and difficulty in image recognition due to the rapid bubble movement under negative pressure, leading to limited accuracy. Another Chinese patent CN2021113465806 discloses a cell formation monitoring system, device, and cell formation method. This solution collects venting volume using a gas acquisition module and compares it with preset sample data to determine the formation quality. However, this method is complex and costly under negative pressure systems and relies on a large amount of prior sample data for calibration, making it prone to misjudgment due to insufficient sample representativeness. In addition, a Chinese patent also discloses a lithium battery formation progress detection device, application number: CN2024201651441. This solution directly detects the internal air pressure or gas composition by placing an air pressure sensor or gas composition sensor inside the cell to determine the formation progress. However, this method may interfere with the internal environment of the battery, and the equipment is complex and not suitable for conventional negative pressure formation processes. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for online monitoring and optimization of the degree of negative pressure formation in negative pressure formation systems that is simple in structure, cost-controllable, accurate in judgment, and applicable to negative pressure formation systems.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for online monitoring and optimization of negative pressure formation, comprising the following steps:

[0007] Formation step: charging the battery according to a preset formation process, and applying negative pressure through a negative pressure mechanism to discharge reaction gas;

[0008] Formation detection step: vacuumizing a sealed cavity in communication with the battery to a target negative pressure value P1 and recording; then, stopping vacuumizing and sealing the sealed cavity, and continuing charging the battery with a preset current within a preset pressure maintaining time T; after the pressure maintaining time T ends, recording the negative pressure value P2 in the sealed cavity; based on the total volume V0 of the sealed cavity, the atmospheric pressure P0, the pressure maintaining time T and the negative pressure change amount ΔP (ΔP = |P2-P1|), calculating the average gas production rate Q of the battery within the pressure maintaining time T;

[0009] Judgment and supplement step: comparing the average gas production rate Q with a preset threshold value; if Q is not greater than the preset threshold value, determining that the battery formation is sufficient; if Q is greater than the preset threshold value, performing supplemental formation on the battery, and then optionally returning to the detection step.

[0010] Preferably, the average gas production rate Q is calculated by:

[0011] First, calculating the gas volume V according to the formula V = (ΔP / P0)*V0, and then calculating the average gas production rate Q according to the formula Q = V / T.

[0012] Preferably, the total volume V0 of the sealed cavity is the sum of the volume of the liquid storage tank, the volume of the pipeline between the negative pressure nozzle and the valve, and the volume of the vacuum buffer detection tank.

[0013] Preferably, the duration t of the supplemental formation and the average gas production rate Q satisfy the relationship: t = a + b*Q, where a and b are coefficients determined by fitting experimental data.

[0014] Preferably, the empirical formula is: t = -6.654 + 2.72Q.

[0015] The application also discloses an online monitoring and optimization device for determining the degree of negative pressure formation, comprising:

[0016] A negative pressure formation mechanism, comprising a negative pressure nozzle and a liquid storage tank connected by a pipeline, wherein the negative pressure nozzle is used for sealingly connecting with a liquid injection hole of the battery;

[0017] A negative pressure detection system connected upstream of the negative pressure formation mechanism through a pipeline; the negative pressure detection system comprises:

[0018] A vacuum buffer detection tank connected with the liquid storage tank through a pipeline;

[0019] a vacuum gauge connected to the pipeline of the vacuum buffer detection tank through a pipeline for detecting the vacuum degree of the system;

[0020] a vacuum source connected to the pipeline upstream of the valve through a vacuum pipe;

[0021] a formation detection control system connected to the vacuum gauge and the valve through a connection line for receiving the vacuum degree data and controlling the opening and closing of the valve, and connected to a formation power supply control for performing the charging operation.

[0022] Preferably, a valve is further arranged on the pipeline upstream of the vacuum buffer detection tank for controlling the opening and closing of the pipeline.

[0023] Preferably, the valve is an electromagnetic valve.

[0024] Preferably, the volume of the vacuum buffer detection tank is not less than the sum of the volume of the liquid storage tank and the volume of the pipeline connecting the liquid storage tank to the valve.

[0025] Preferably, the pipeline, the vacuum buffer detection tank and the valve in the negative pressure detection system together constitute the closed cavity of the method.

[0026] The present application has the following advantages: the present application uses the existing negative pressure pipeline system, and only needs to add a vacuum buffer tank, a valve and a detection controller to realize the pressure maintaining test in the closed cavity, and accurately calculates the key indicator of the gas production rate through the pressure difference change, so as to change the judgment of the formation degree from the traditional appearance observation or complex gas collection to the accurate numerical judgment. The method does not need expensive visual or gas component sensors, has a simple structure, low modification cost and high judgment accuracy, and greatly reduces the risk of misjudgment. The method not only can identify abnormal gas production caused by impurities such as water, but also can automatically determine the optimal supplement formation time according to the gas production rate, avoiding the overcharging or undercharging problem caused by the "one-size-fits-all" in the traditional process, ensuring the production efficiency, and realizing the individualized and accurate treatment of each battery cell, thereby providing reliable technical support for the high-quality manufacturing of lithium batteries. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a structural schematic diagram of the device in the present application;

[0028] Figure 2 is a fitting line diagram in the present application;

[0029] Figure 3 is a schematic diagram of No. 1 battery in the present application;

[0030] Figure 4 is a schematic diagram of No. 2 battery in the present application;

[0031] Figure 5 is a schematic diagram of No. 3 battery in the present application. DETAILED DESCRIPTION

[0032] The technical solutions of the present application will be described in detail below in combination with the drawings and examples. It should be pointed out that the following examples are only used to explain the present application and do not constitute a limitation on the protection scope of the present application.

[0033] Referring to Figure 1 is a schematic diagram of a preferred embodiment of the device of the present application. The device for online monitoring and optimizing the degree of negative pressure formation mainly comprises a battery 10, a negative pressure formation mechanism 20, a negative pressure detection system 30, a vacuum pipe 40 and a formation detection control system 50.

[0034] The negative pressure formation mechanism 20 is used to connect with the battery 10 and perform basic formation operation, which comprises a negative pressure suction nozzle 21 and a liquid storage tank 22. The negative pressure suction nozzle 21 is tightly connected with the liquid injection hole of the battery 10 through a sealing structure to ensure the air tightness of the system. The liquid storage tank 22 is connected with the negative pressure suction nozzle 21 through a pipeline for collecting a small amount of electrolyte discharged from the inside of the battery 10 during the formation process.

[0035] The negative pressure detection system 30 is the core innovative part of the present application, which is connected with the upstream of the negative pressure formation mechanism 20 through a pipeline. Specifically, the negative pressure detection system 30 comprises a vacuum buffer detection tank 31, a vacuum gauge 32 and a valve 33. The vacuum buffer detection tank 31 is connected with the liquid storage tank 22 through a pipeline for stabilizing the vacuum degree of the system and providing a temporary storage space for gas. The vacuum gauge 32 is connected through a pipeline near or above the vacuum buffer detection tank 31 for real-time detection and transmission of the vacuum degree value in the system. The valve 33, preferably an electromagnetic valve, is arranged on the pipeline upstream of the vacuum buffer detection tank 31 for accurately controlling the on-off between the entire detection system and the vacuum source.

[0036] The vacuum pipe 40 is connected upstream of the valve 33 and connected with an external vacuum source (such as a vacuum pump, not shown in the figure) to provide the required negative pressure for the system.

[0037] The formation detection control system 50, which can be a PLC (programmable logic controller), an industrial computer or a dedicated control circuit, is signal connected with the vacuum gauge 32 and the valve 33 through a connection line 52. The control system 50 receives the vacuum degree data from the vacuum gauge 32 and sends switching instructions to the valve 33 accordingly. At the same time, the formation detection control system 50 is also connected with a formation power supply (not shown in the figure) for control, which is used to control the charging current, voltage and time of the battery 10.

[0038] In this embodiment, the "closed cavity" is composed of the liquid tank 22, the pipe connecting the negative pressure suction nozzle 21 to the valve 33, and the vacuum buffer detection tank 31. The total volume V0 of the "closed cavity" is a key parameter for calculating the gas production.

[0039] The specific implementation steps of the method are as follows:

[0040] S1: formation step

[0041] The battery 10 is sealed and connected to the negative pressure suction nozzle 21. The valve 33 is opened under the control of the formation detection control system 50, and the vacuum source is started to establish and maintain the target negative pressure (for example, -85 kPa). At the same time, the battery 10 is charged according to the preset conventional formation process, and the gas generated by the chemical reaction inside the battery is continuously extracted.

[0042] S2: formation degree detection step

[0043] After the end of the formation step (or during the last constant current charging phase), the detection step is started.

[0044] S21: vacuum extraction and recording: the valve 33 is kept open under the control of the control system 50 to extract the vacuum in the above-mentioned "closed cavity" to a target value (for example, -95 kPa) lower than the formation negative pressure and stabilize it. At this time, the control system records the stable target negative pressure value P1.

[0045] S22: sealing and continuous charging: the valve 33 is closed under the control of the control system 50 to completely seal the cavity between the battery 10 and the valve 33. At the same time, the current (for example, 0.2C) in the last stage of the formation process is maintained to continue charging the battery 10. This sealed pressure maintaining state lasts for a preset accurate time T, for example, 5 minutes.

[0046] S23: record P2: after the pressure maintaining time T, the control system 50 stops charging the battery and records the negative pressure value P2 in the closed cavity at this time.

[0047] S24: calculate the gas production rate Q: the control system 50 automatically calculates the average gas production rate Q based on the following formula:

[0048] Gas volume V = (|P2-P1| / P0)*V0

[0049] Where P0 is the local atmospheric pressure, which can be preset as the standard atmospheric pressure (~100 kPa) or obtained in real time through a sensor.

[0050] Average gas production rate Q = V / T

[0051] S3: determination and supplementary formation step

[0052] The control system 50 compares the calculated gas generation rate Q with a preset decision threshold (e.g. 2 mL / min).

[0053] S31: If Q≤threshold, it is determined that the battery formation is sufficient, and all formation procedures are ended, and the next process is entered.

[0054] S32: If Q>threshold, it is determined that the battery formation is insufficient, and supplemental formation needs to be performed. The charging current of the supplemental formation is consistent with the current at the end of the formation process, and the duration t thereof is determined according to the gas generation rate Q through an empirical formula. A preferred formula is: t=-6.654+2.72Q (minutes). As shown in the formula. Figure 2

[0055] S33: After the supplemental formation is performed, step S2 is returned to, and the detection step is performed again. This cycle can be set to a maximum number of times, and if the number of times exceeds the maximum number of times and the standard is still not met, an alarm is prompted to indicate that the battery may be abnormal.

[0056] Application Example

[0057] As shown in the formula, in order to verify the effect of the present application, three 324 Ah lithium ion cells are selected for testing. No. 1 cell is a normal control group (moisture 200 ppm), and No. 2 and No. 3 cells are experimental groups (moisture 1000 ppm, simulating abnormality). Figures 3-5

[0058] First, the same negative pressure formation process is performed on all the cells. Then, the detection step is performed. The results are as follows:

[0059] No. 1 control group: P1=-95 kPa, P2=-94 kPa, and the calculated gas generation rate Q=1 mL / min.

[0060] No. 2 experimental group: P1=-95 kPa, P2=-91 kPa, and the calculated gas generation rate Q=4 mL / min.

[0061] The control system determines that No. 1 cell is qualified, and No. 2 cell is unqualified. The supplemental formation is performed on No. 2 cell according to the formula t=-6.654+2.72*4≈4.2 minutes. After the supplemental formation, the detection is performed again, and the gas generation rate is reduced to 1 mL / min, which is determined to be qualified.

[0062] Subsequent disassembly of the cells finds that the interfaces of No. 1 and No. 2 cells are good, and the interface of No. 3 cell which is not treated by the present application has black spots caused by insufficient gas generation and discharge. This example fully proves that the present application can effectively identify abnormal cells and optimize the formation degree of the cells through supplemental formation, thereby improving the consistency of the battery pack.

[0063] ​​The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and shall be covered within the protection scope of the present application.

Claims

1. A method for online monitoring and optimization of negative pressure formation, characterized in that, Includes the following steps: Formation step: The battery (10) is charged according to the preset formation process, and negative pressure is applied through the negative pressure mechanism to discharge the reaction gas. Formation detection steps: Evacuate a sealed cavity connected to the battery (10) to the target negative pressure value P1 and record it; then stop evacuating and seal the sealed cavity, and continue to charge the battery (10) with a preset current within a preset holding time T; after the holding time T ends, record the negative pressure value P2 in the sealed cavity; based on the total volume V0 of the sealed cavity, atmospheric pressure P0, holding time T and negative pressure change ΔP (ΔP=|P2-P1|), calculate the average gas production rate Q of the battery within the holding time T; Judgment and supplementary steps: Compare the average gas production rate Q with a preset threshold; If Q is not greater than the preset threshold, then the battery is determined to be fully formed; If Q is greater than the preset threshold, then supplementary formation is performed on the battery, and then optionally the detection step is returned.

2. The method according to claim 1, characterized in that, The average gas production rate Q is calculated in the following way: First, calculate the gas production volume V using the formula V=(△P / P0)*V0, and then calculate the average gas production rate Q using the formula Q=V / T.

3. The method according to claim 1, characterized in that, The total volume V0 of the sealed cavity is the sum of the volume of the liquid storage tank (22), the volume of the pipeline between the negative pressure suction nozzle (21) and the valve (33), and the volume of the vacuum buffer detection tank (31).

4. The method according to claim 1, characterized in that, The duration t of the supplementary formation and the average gas production rate Q satisfy the following relationship: t = a + b * Q, where a and b are coefficients determined by fitting experimental data.

5. The method according to claim 4, characterized in that, The empirical formula is: t = -6.654 + 2.72Q.

6. An apparatus for online monitoring and optimization of negative pressure formation degree in implementing the method of any one of claims 1-5, characterized in that, include: The negative pressure formation mechanism (20) includes a negative pressure suction nozzle (21) and a liquid storage tank (22) connected by a pipeline. The negative pressure suction nozzle (21) is used to seal the connection with the liquid injection hole of the battery (10). A negative pressure detection system (30) is connected upstream of the negative pressure formation mechanism (20) via a pipeline; the negative pressure detection system (30) includes: A vacuum buffer detection tank (31) is connected to the liquid storage tank (22) via a pipeline; A vacuum gauge (32), which is connected to the vacuum buffer detection tank (31) via a pipeline, is used to detect the system vacuum level; A vacuum source, which is connected to the pipeline upstream of the valve (33) via a vacuum tube (40); The formation detection and control system (50) is connected to the vacuum gauge (32) and valve (33) via a connecting line (52) to receive vacuum data and control the opening and closing of the valve (33). The formation detection and control system (50) is also connected to a formation power supply control to perform charging operations.

7. The apparatus according to claim 6, characterized in that, It also includes a valve (33), which is located on the pipeline upstream of the vacuum buffer detection tank (31) for controlling the opening and closing of the pipeline.

8. The apparatus according to claim 7, characterized in that, The valve (33) is a solenoid valve.

9. The apparatus according to claim 6, characterized in that, The volume of the vacuum buffer detection tank (31) is not less than the sum of the volume of the liquid storage tank (22) and the pipeline connecting it to the valve (33).

10. The apparatus according to claim 6, characterized in that, The pipelines, vacuum buffer detection tank (31), and valves (33) in the negative pressure detection system (30) together constitute the sealed cavity of the method.

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