Battery micro short circuit detection method and system

Abstract

The invention discloses a battery micro short circuit detection method and system. The detection method comprises the following steps: detecting the open-circuit voltage of a battery to be detected to obtain a first open-circuit voltage value; applying variable stress to the to-be-tested battery for a period of time; after the stress is removed, detecting the open-circuit voltage of the battery to be detected again to obtain a second open-circuit voltage value; calculating to obtain a unit time voltage drop value of the to-be-tested battery; and comparing the unit time voltage drop value of the to-be-detected battery with a unit time voltage drop threshold value determined by a predetermined similar battery according to the same step: if the unit time voltage drop value of the to-be-detected battery is greater than or equal to the unit time voltage drop threshold value, determining that the to-be-detected battery is a micro short circuit defective product, otherwise, determining that the to-be-detected battery is a good product.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a battery micro-short circuit detection method and system. Background Art

[0002] During the manufacturing process of batteries, due to process control and other factors, tiny metal particles in the production environment will fall into the battery core. During the subsequent manufacturing process of the battery and the charging and discharging process of the battery, the battery pole piece will expand and contract, which will exert pressure on these tiny particles, causing these tiny metal particles to pierce the diaphragm, thereby causing a short circuit between the positive and negative poles of the battery and forming a leakage current inside the battery; the appearance of leakage current will accelerate the battery's power consumption, and in extreme cases, this short circuit may cause the battery to catch fire and explode. Therefore, the detection of micro short circuits inside the battery is particularly important to ensure the safety performance of the battery.

[0003] The traditional method of identifying micro short circuits inside batteries is usually the static voltage detection method, which is to analyze the battery leakage current by letting the battery stand. The detection process of this method is: let the battery stand at room temperature for several days to dozens of days, measure the open circuit voltage difference of the battery before and after standing, and judge the size of the micro short circuit leakage current inside the battery by the voltage difference. The disadvantage of this method is that the test cycle is long, usually taking a week or even dozens of days. The main reason for the long test cycle is that the metal particles are usually small in size, and often do not completely pierce the diaphragm in the battery or pierce the diaphragm but the short circuit point area is very small, so the leakage current of the battery is also very small. If the standing time is short, the battery will leak very little electricity, and the corresponding battery voltage drop value will also be very small, which may be less than the error value of the voltage detection device, resulting in inaccurate micro short circuit detection results. In order to improve the accuracy of micro short circuit detection, it is necessary to extend the standing time to cause a significant drop in the battery voltage, and then use the voltage detection device to detect the battery voltage drop. Summary of the invention

[0004] The object of the present invention is to provide a battery micro-short circuit detection method and system to shorten the micro-short circuit detection time.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] In one aspect, the present invention provides a method for detecting a battery micro-short circuit, wherein the detection method comprises the following steps:

[0007] Detecting an open circuit voltage (OCV) of the battery to be tested to obtain a first open circuit voltage value OCV1;

[0008] Applying a variable stress to the battery to be tested for a period of time t;

[0009] After the stress is removed, the open circuit voltage of the battery to be tested is detected again to obtain a second open circuit voltage value OCV2;

[0010] The voltage drop per unit time of the battery to be tested is calculated, that is, K = (OCV1-OCV2) / t;

[0011] The voltage drop per unit time of the battery to be tested is compared with the voltage drop per unit time threshold (for example, K) determined by the same steps for the same battery. NG ) for comparison: If the unit time voltage drop value of the battery to be tested is greater than or equal to the unit time voltage drop threshold value (K NG ), it is a defective product with a slight short circuit, otherwise it is a good product.

[0012] According to the battery micro-short circuit detection method of the present invention, preferably, the voltage drop threshold per unit time is determined by the following method:

[0013] Several defective batteries with micro short circuits were screened out through the static voltage detection method;

[0014] Detecting the open circuit voltage of the defective battery to obtain a series of first open circuit voltage values ​​OCV1;

[0015] Applying a varying stress to the defective battery for a period of time t;

[0016] After the stress is removed, the open circuit voltage of the defective battery is detected again to obtain a series of second open circuit voltage values ​​OCV2;

[0017] The voltage drop per unit time of each defective battery is calculated, and the minimum voltage drop per unit time is selected as the voltage drop threshold per unit time (K NG ).

[0018] According to the battery micro-short circuit detection method of the present invention, the changing stress can be a periodically changing stress or a randomly changing stress; preferably a periodically changing stress. The periodically changing stress can be a sinusoidal wave changing stress, a rectangular wave changing stress, etc., or an ultrasonic excitation signal, etc.

[0019] In the battery micro-short circuit detection method of the present invention, the magnitude of the changing stress is based on the ability to cause force changes without damaging the battery structure; preferably, the magnitude of the changing stress is 0.1-10 MPa.

[0020] According to the battery micro-short circuit detection method of the present invention, preferably, the variable stress is applied to the battery through a stress plate.

[0021] According to the battery micro-short circuit detection method of the present invention, preferably, the variable stress is applied to the two opposite large surfaces of the battery through two stress plates. The "large surface" in the present invention refers to a larger surface of the battery, and the battery can be a soft-pack battery or a square aluminum shell battery.

[0022] According to the battery micro-short circuit detection method of the present invention, preferably, the duration after applying the variable stress is 1 hour to 3 days.

[0023] According to the battery micro-short circuit detection method of the present invention, preferably, the voltage detector is a high-precision voltage detector.

[0024] According to the battery micro-short circuit detection method of the present invention, preferably, at least 20 defective batteries with micro-short circuits are screened out by a static voltage detection method, and more preferably 20 to 500.

[0025] According to the battery micro-short circuit detection method of the present invention, preferably, the process of screening the defective batteries by the static voltage detection method specifically includes:

[0026] Under a constant temperature environment, test the open circuit voltage of the battery sample;

[0027] After standing for 3 to 15 days, test the open circuit voltage again;

[0028] Calculate the open circuit voltage difference before and after standing still, and calculate the voltage drop value K per unit time. Determine whether the battery is a defective battery with a micro-short circuit based on the voltage difference and / or the voltage drop value K per unit time.

[0029] For example, if the open circuit voltage difference of a battery is greater than the average open circuit voltage difference + 4.5σ (σ is the standard deviation of the open circuit voltage difference), the battery can be judged as a defective battery with a micro short circuit. Alternatively, the K value of a good battery is generally less than 2mV / d or 0.08mV / h. The K value judgment standard varies slightly depending on the specific battery type, but the difference is not significant.

[0030] Those skilled in the art will understand that in the battery micro-short circuit detection method of the present invention, the battery sample used in the process of determining the voltage drop threshold per unit time needs to be of the same type as the battery to be tested, and the stress applied in the process of determining the voltage drop threshold per unit time needs to be kept consistent with the stress to which the battery to be tested is subjected during the measurement process (therefore, the voltage drop threshold per unit time needs to be determined by the same steps for the same type of battery). After the type of the battery to be tested changes, the voltage drop threshold per unit time needs to be re-determined accordingly.

[0031] According to the battery micro-short circuit detection method of the present invention, preferably, the battery micro-short circuit detection method is carried out under constant temperature conditions, including the detection process of all open circuit voltages therein. Because the battery voltage will change with the ambient temperature, the influence of ambient temperature fluctuations on the test results needs to be eliminated in the method of the present invention.

[0032] Another aspect of the present invention provides a battery micro-short circuit detection system for implementing the above detection method; wherein the detection system comprises:

[0033] A stress generating unit, used to generate and apply varying stress to the battery surface;

[0034] A voltage detector is used to connect the positive and negative electrodes of the battery to measure the open circuit voltage.

[0035] In the battery micro-short circuit detection system of the present invention, a stress generating unit is used to generate and apply variable stress to the battery, thereby causing repeated action between metal particles inside the battery and the diaphragm and electrodes to increase the generation of micro-short circuits, thereby achieving the purpose of shortening the detection time of battery micro-short circuits.

[0036] According to the battery micro-short circuit detection system of the present invention, preferably, the stress generating unit comprises:

[0037] Stress plates, used to apply varying stresses to the battery surface;

[0038] The stress control module is connected to the stress plate and is used to control the stress plate to generate the changed stress.

[0039] According to the battery micro-short circuit detection system of the present invention, preferably, the detection system includes two opposing stress plates for applying varying stresses to the opposing large surfaces of the battery. The specific process of applying varying stresses to the battery and detecting the open circuit voltage (OCV) using the system includes:

[0040] Place the battery between two stress plates in a direction in which the large surface is parallel to the stress plates, and move the stress plates until they are in contact with the large surface of the battery;

[0041] Applying a variable stress on the stress plate through a stress control unit for a period of time;

[0042] Remove the stress, separate the battery from the stress plate, and use a voltage detector to detect the open circuit voltage of the battery.

[0043] According to the battery micro-short circuit detection system of the present invention, preferably, the area of ​​the working surface of the stress plate is greater than or equal to the area of ​​the large surface of the battery to avoid possible damage to the battery structure. The working surface of the stress plate refers to the surface where the stress plate contacts the large surface of the battery.

[0044] In the battery micro-short circuit detection system of the present invention, the stress control module can control the stress plate to generate periodic or non-periodic stress; preferably, the stress control module controls the stress plate to generate periodic stress, and the periodic stress can be a sinusoidal stress or a rectangular stress, or an ultrasonic excitation signal. The stress control template can specifically be a pressure controller, an ultrasonic device, etc.

[0045] The present invention uses externally applied pressure to stimulate the metal particles inside the battery to repeatedly interact with the diaphragm under varying stresses, thereby achieving the effect of piercing the diaphragm, increasing the micro-short circuit, increasing the leakage current, and shortening the micro-short circuit detection time (the micro-short circuit detection time can be shortened from 3 to 15 days to 1 hour to 3 days). Figure 2 As shown, metal particles usually have relatively sharp edges and corners. Under the action of changing stress, the metal particles repeatedly interact with the diaphragm and the positive and negative electrodes, eventually causing the sharp corners of the metal particles to pierce the diaphragm, connecting the positive and negative electrodes, and causing a short circuit between the positive and negative electrodes. After the short circuit, the positive and negative electrodes of the battery can be discharged through the short-circuit points generated by the metal particles, causing the battery power to drop. When a voltage detector is connected to the positive and negative electrodes of the battery to detect the open circuit voltage of the battery, a drop in the battery voltage can be observed over time. This method can accelerate the detection of battery micro-short circuits and shorten the detection time. In addition, fixed stress will also exert a compressive effect on the metal particles, and to a certain extent, it can also accelerate the metal particles to pierce the diaphragm to accelerate the micro-short circuit measurement; however, the effect is not as good as the changing stress used in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the process of the battery micro-short circuit detection method of the present invention.

[0047] Figure 2 This is a schematic diagram of the battery micro-short circuit detection method of the present invention.

[0048] Figure 3 Schematic diagram of a battery micro-short circuit detection system in a preferred embodiment.

[0049] Figure 4 Schematic diagram of stress with sinusoidal wave variation.

[0050] Figure 5 Schematic diagram of stress with rectangular wave variation.

[0051] Figure 6 Schematic diagram of randomly changing stress.

[0052] Figure 7 Schematic diagram of the changing stress used in Application Example 1.

[0053] Figure 8This is a point value diagram of the voltage drop per unit time of the defective battery in Application Example 1.

[0054] Description of reference numerals:

[0055] 1. Stress board, 2. Stress control module, 3. Voltage detector, 4. Battery. DETAILED DESCRIPTION

[0056] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0057] The present invention applies a variable stress to the battery surface to stimulate the micro short circuit of the battery, thereby achieving the purpose of shortening the detection time of the battery micro short circuit. First, a battery micro short circuit detection method is provided, such as Figure 1 As shown, the following steps are included:

[0058] S1, detecting the open circuit voltage (OCV) of the battery to be tested, and obtaining a first open circuit voltage value OCV1;

[0059] S2, applying a variable stress to the battery to be tested for a period of time t;

[0060] S3, after the stress is removed, the open circuit voltage of the battery to be tested is detected again to obtain a second open circuit voltage value OCV2;

[0061] S4, calculating and obtaining the voltage drop value per unit time of the battery to be tested, that is, K=(OCV1-OCV2) / t;

[0062] S5, comparing the unit time voltage drop value of the battery to be tested with a pre-determined unit time voltage drop threshold value (e.g., K NG ) for comparison: If the unit time voltage drop value of the battery to be tested is greater than or equal to the unit time voltage drop threshold value (K NG ), it is a defective product with a slight short circuit, otherwise it is a good product.

[0063] The voltage drop threshold per unit time can be determined by the following method:

[0064] Several defective batteries with micro short circuits were screened out through the static voltage detection method;

[0065] Detecting the open circuit voltage of the defective battery to obtain a series of first open circuit voltage values ​​OCV1;

[0066] Applying a varying stress to the defective battery for a period of time t;

[0067] After the stress is removed, the open circuit voltage of the defective battery is detected again to obtain a series of second open circuit voltage values ​​OCV2;

[0068] The voltage drop per unit time of each defective battery is calculated, and the minimum voltage drop per unit time is selected as the voltage drop threshold per unit time (K NG ).

[0069] At least 20 defective batteries are required to provide sufficient samples, preferably 20 to 500. In addition, all open circuit voltage measurement processes in the battery micro-short circuit detection method of the present invention are carried out under constant temperature conditions, including the unit time voltage drop threshold (K NG ) to eliminate the impact of ambient temperature fluctuations on test results.

[0070] The process of screening the defective batteries by the static voltage detection method preferably includes:

[0071] Under a constant temperature environment, test the open circuit voltage of the battery sample;

[0072] After standing for 3 to 15 days, test the open circuit voltage again;

[0073] Calculate the open circuit voltage difference before and after standing still, and calculate the voltage drop value K per unit time. Determine whether the battery is a defective battery with a micro-short circuit based on the voltage difference and / or the voltage drop value K per unit time.

[0074] For example, if the open circuit voltage difference of a battery is greater than the average open circuit voltage difference + 4.5σ (σ is the standard deviation of the open circuit voltage difference), the battery can be judged as a defective battery with a micro short circuit. Alternatively, the K value of a good battery is generally less than 2mV / d or 0.08mV / h. The K value judgment standard varies slightly depending on the specific battery type, but the difference is not significant.

[0075] The present invention uses externally applied pressure to stimulate the metal particles inside the battery to repeatedly interact with the diaphragm under varying stresses, thereby achieving the effect of piercing the diaphragm, increasing the micro-short circuit, increasing the leakage current, and shortening the micro-short circuit detection time. Figure 2As shown, metal particles usually have sharper edges and corners. Under the action of changing stress, the metal particles repeatedly interact with the diaphragm and the positive and negative electrodes, eventually causing the sharp corners of the metal particles to pierce the diaphragm, connecting the positive and negative electrodes, and causing a short circuit between the positive and negative electrodes. After the short circuit, the positive and negative electrodes of the battery can be discharged through the short-circuit points generated by the metal particles, thereby causing the battery power to drop. When a voltage detector is connected to the positive and negative electrodes of the battery to detect the open circuit voltage of the battery, a drop in the battery voltage can be observed over time. This method can accelerate the detection of battery micro-short circuits and shorten the detection time. It is easy for those skilled in the art to understand that fixed stress will also exert pressure on the metal particles, and to a certain extent, it can also accelerate the metal particles to pierce the diaphragm to accelerate the micro-short circuit measurement; however, the effect is not as good as the changing stress used in the present invention, and the present invention is not described in more detail here.

[0076] A battery micro-short circuit detection system for implementing the above detection method provided by the present invention comprises:

[0077] A stress generating unit, used to generate and apply varying stress to the battery surface;

[0078] A voltage detector is used to connect the positive and negative electrodes of the battery to measure the open circuit voltage.

[0079] By generating and applying varying stress to the battery through a stress generating unit, the metal particles inside the battery are prompted to interact repeatedly with the diaphragm and the electrodes to increase the generation of micro-short circuits, thereby achieving the purpose of shortening the detection time of battery micro-short circuits.

[0080] In a preferred embodiment, the specific stress generating unit includes: a stress plate for applying a variable stress to the battery surface; and a stress control module connected to the stress plate for controlling the stress plate to generate the variable stress.

[0081] In a preferred embodiment, if Figure 3 As shown, the battery micro-short circuit detection system includes:

[0082] Two opposing stress plates 1 are used to apply variable stress to the opposing large surfaces of the battery 4;

[0083] A stress control module 2, connected to the stress plate 1, for controlling the stress plate 1 to generate a variable stress;

[0084] The voltage detector 3 is used to connect the positive and negative electrodes of the battery 4 to measure the open circuit voltage.

[0085] The “large surface” refers to a larger surface of the battery, and the battery 4 may be a soft-pack battery or a square aluminum shell battery, etc. The area of ​​the stress plate 1 is preferably greater than or equal to the area of ​​the large surface of the battery 4 .

[0086] use Figure 3 In the battery micro-short circuit detection method performed by the preferred system, the specific process of applying a variable stress to the battery and detecting the open circuit voltage (OCV) includes:

[0087] Place the battery 4 between the two stress plates 1 in a direction in which the large surface is parallel to the stress plate 1, and move the stress plate 1 until it contacts the large surface of the battery 4;

[0088] Applying a variable stress to the stress plate 1 through the stress control module 2 for a period of time t;

[0089] The stress is removed to separate the battery 4 from the stress plate 1 , and the open circuit voltage of the battery 4 is detected using the voltage detector 3 .

[0090] The stress control module 2 can control the stress plate 1 to produce periodic or non-periodic stress. The periodic stress can be as follows: Figure 4 Sinusoidal stress as shown, or Figure 5 The stress of the rectangular wave change shown in the figure can also be an ultrasonic auspicious signal. Non-periodic changes such as Figure 6 The stress control module 2 can be a pressure controller, an ultrasonic device, etc. Figure 6 When the randomly changing stress is shown, the process of determining the voltage drop threshold per unit time and the stress with the same waveform change used in the battery detection process are shown.

[0091] The magnitude range of the stress applied to the battery 4 is based on the range that can cause the force change without damaging the battery structure, and is preferably 0.1 to 10 MPa.

[0092] Preferably, the voltage detector 3 is a high-precision voltage detector.

[0093] The present invention is described in more detail below by providing a specific application example.

[0094] Application Example 1

[0095] use Figure 3 The preferred system performs micro short circuit detection on a soft pack battery to be tested, comprising the following steps:

[0096] S101, screen out 20 defective batteries with micro short circuits of the same type as the battery to be tested by a static voltage detection method; specifically, the following process is included:

[0097] Under a constant temperature environment, test the open circuit voltage of the battery sample;

[0098] After standing for 7 days, test the open circuit voltage again;

[0099] Calculate the difference in open circuit voltage before and after standing still, and calculate the voltage drop value K per unit time. If K ≥ 0.08 mV / h, the defective batteries with micro short circuits are screened out. A total of 20 batteries are screened out.

[0100] S102. In a constant temperature environment, the open circuit voltage (OCV) of the selected defective batteries is tested with a high-precision voltage detector to obtain a series of OCV1, as shown in Table 1 below:

[0101] Table 1

[0102] Battery ID 1 2 3 4 5 6 7 8 9 10 OCV1(V) 3.6015 3.6053 3.592 3.5852 3.616 3.6039 3.5928 3.614 3.6166 3.5701 Battery ID 11 12 13 14 15 16 17 18 19 20 OCV1(V) 3.5804 3.5743 3.6057 3.5902 3.6103 3.5795 3.5843 3.5984 3.5762 3.5998

[0103] S103, using the system of the present invention to apply periodic stress (specifically Figure 7 The specific test process includes:

[0104] Place the battery 4 between the two stress plates 1 in a direction in which the large surface is parallel to the stress plate 1, and move the stress plate 1 until it contacts the large surface of the battery 4;

[0105] Applying a variable stress to the stress plate 1 through the stress control module 2 for 24 hours;

[0106] S104, remove the stress, separate the battery 4 from the stress plate 1, and use a high-precision voltage detector to detect the open circuit voltage (OCV) of the battery again to obtain a series of OCV2; as shown in Table 2 below:

[0107] Table 2

[0108] Battery ID 1 2 3 4 5 6 7 8 9 10 OCV2(V) 3.5908 3.5947 3.5812 3.5741 3.6063 3.5936 3.5827 3.6041 3.6070 3.5583 Battery ID 11 12 13 14 15 16 17 18 19 20 OCV2(V) 3.5689 3.5630 3.5957 3.5800 3.6006 3.5678 3.5735 3.5882 3.5646 3.5895

[0109] S105. Calculate the voltage drop per unit time of each defective battery: K = (OCV1 - OCV2) / t, as shown in Table 3 and Figure 8 As shown, the smallest K value is defined as K NG ; K NG =0.401mV / h.

[0110] Table 3

[0111]

[0112]

[0113] S106. According to the above steps S2-S5, the OCV1 of the battery to be tested is detected to be 3.5913, OCV2 is detected to be 3.5804, and K is calculated to be 0.454 mV / h, ≥ K NG , which is a micro short circuit defective product.

[0114] In this application example, the K of this type of soft pack battery NG After confirmation, the battery to be tested can be tested in just 24 hours, greatly shortening the testing time (from 7 days to 1 day).

[0115] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A battery micro-short circuit detection method, wherein: The detection method comprises the following steps: Detecting an open circuit voltage of a battery to be tested to obtain a first open circuit voltage value; Applying a varying stress to the battery to be tested for a period of time; After the stress is removed, the open circuit voltage of the battery to be tested is detected again to obtain a second open circuit voltage value; Calculating and obtaining the voltage drop value per unit time of the battery to be tested; The voltage drop value per unit time of the battery to be tested is compared with a voltage drop threshold per unit time determined by a predetermined similar battery according to the same steps: if the voltage drop value per unit time of the battery to be tested is greater than or equal to the voltage drop threshold per unit time, it is a micro-short circuit defective product, otherwise it is a good product.

2. The battery micro-short circuit detection method according to claim 1, wherein: The voltage drop threshold per unit time is determined by the following method: Several defective batteries with micro short circuits were screened out through the static voltage detection method; Detecting the open circuit voltage of the defective battery to obtain a series of first open circuit voltage values; Applying varying stresses to the defective battery for a period of time; After the stress is removed, the open circuit voltage of the defective battery is detected again to obtain a series of second open circuit voltage values; The voltage drop per unit time of each defective battery is calculated, and the minimum voltage drop per unit time value is selected as the voltage drop per unit time threshold.

3. The battery micro-short circuit detection method according to claim 1 or 2, wherein: The changing stress is a periodically changing stress.

4. The battery micro-short circuit detection method according to claim 1 or 2, wherein: The magnitude of the changing stress is 0.1-10 MPa.

5. The battery micro-short circuit detection method according to claim 1 or 2, wherein: The varying stress is applied to the battery through the stress plate.

6. The battery micro-short circuit detection method according to claim 1 or 2, wherein: The variable stress is applied to the two opposite large surfaces of the battery through two stress plates.

7. The battery micro-short circuit detection method according to claim 1, wherein: The battery micro-short circuit detection method is carried out under constant temperature conditions.

8. A battery micro-short circuit detection system for implementing the detection method according to any one of claims 1 to 7, wherein: The detection system comprises: A stress generating unit, used to generate and apply varying stress to the battery surface; A voltage detector is used to connect the positive and negative electrodes of the battery to measure the open circuit voltage.

9. The battery micro-short circuit detection system according to claim 8, wherein: The stress generating unit comprises: Stress plates, used to apply varying stresses to the battery surface; The stress control module is connected to the stress plate and is used to control the stress plate to generate the changed stress.

10. The battery micro-short circuit detection system according to claim 9, wherein: The detection system includes two opposite stress plates for applying variable stress to two opposite large surfaces of the battery.

11. The battery micro-short circuit detection system according to claim 9 or 10, wherein: The area of ​​the working surface of the stress plate is greater than or equal to the area of ​​the large surface of the battery.

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