A battery internal short circuit nondestructive detection method based on magnetic field gradient distribution

Abstract

A kind of battery internal short-circuit nondestructive testing method based on magnetic field gradient distribution, it is related to battery technical field, steps include: in the state of battery constant current charging, constant current discharging or in the process of shelving, the external magnetic field distribution of measured battery is detected at any time interval using magnetic sensor;Obtain the relative change distribution of external magnetic field of battery in different time points under corresponding working condition state;The gradient distribution of magnetic field component in y and x direction of the relative change distribution of external magnetic field is calculated, and if the gradient distribution of magnetic field component is all in the same area Gradient sudden change appears, and all along the axis direction Gradient direction reversal appears, then it can be judged that internal short-circuit occurs in this area of the battery, the present application can accurately determine internal short-circuit fault, and can determine internal short-circuit site and internal short-circuit severity.

Description

Technical Field

[0001] This invention belongs to the field of battery testing technology, specifically relating to a non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution. Background Technology

[0002] With the increasing severity of energy shortages and environmental pollution, the automotive industry is actively seeking safer, more efficient, low-carbon, and environmentally friendly new energy solutions. Among the many new energy sources, lithium-ion batteries are widely used in the field of new energy vehicles due to their advantages of high energy density, long lifespan, no memory effect, and environmental friendliness. However, the safety issues of lithium-ion batteries, especially internal short circuits, have become a major bottleneck hindering their large-scale industrial application. Internal short circuits in lithium-ion batteries can severely affect battery performance and even lead to thermal runaway, and are considered a significant safety challenge for lithium-ion batteries.

[0003] Current lithium-ion battery testing methods primarily rely on the electrical characteristics following an internal short circuit. These methods include detecting abnormal drops in battery terminal voltage or state of charge (SOC), and differences in voltage or current between the internally short-circuited battery and the battery pack. However, these methods rely on external short circuits to simulate internal short circuits, obtaining abnormal electrical data to verify accuracy. This differs from actual internal short circuits and cannot accurately identify internal short circuit faults in practical applications. Furthermore, these methods cannot pinpoint the location of the internal short circuit, thus failing to provide insights for subsequent battery design improvements. Both commercially available wound and stacked batteries suffer from these problems. Summary of the Invention

[0004] To address the problems existing in the background technology, the present invention provides a non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution. This method obtains the abnormal magnetic field gradient distribution of the battery caused by internal short circuit current by conducting planar magnetic field distribution tests on the battery during charging, discharging, or storage processes, and detects the location and extent of internal short circuits.

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

[0006] A non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution, the method comprising:

[0007] Step 1: During constant current charging, constant current discharging, or storage of the battery, use a magnetic sensor to measure the distribution of the external magnetic field B of the battery under test. n (i, j) are tested at arbitrary time intervals;

[0008] In this context, the plane formed by the battery's width and length directions is called the xy-plane. The axis containing the width direction is defined as the x-axis, the axis containing the length direction as the y-axis, and the axis containing the battery's thickness direction perpendicular to this plane as the z-axis. i and j represent the coordinates of any point within the battery's xy-plane, where i represents the battery's x-axis coordinate and j represents its y-axis coordinate. x (i, j), B y (i, j) and B z (i, j) are the three magnetic field components of the orthogonal decomposition of B(i, j);

[0009] Step 2: Based on the test results at different detection time points during the battery's constant current charging, constant current discharging, or resting states, obtain the relative change distribution ΔB(i,j) of the external magnetic field under the corresponding operating conditions of the battery, in order to eliminate magnetic field interference generated other than current density. The specific method is as follows:

[0010] ΔB(i,j)=B n (i,j)-B n-1 (i, j), where B n (i, j) and B n-1 (i, j) represent the external magnetic field distributions of the tested battery obtained from the nth and (n-1)th detections, respectively;

[0011] Step 3: Calculate the gradient distribution of the magnetic field components of the external magnetic field ΔB(i,j) in the y and x directions, respectively, under the corresponding operating conditions of the battery at different time points. and

[0012] The gradient distribution of the magnetic field components of ΔB(i,j) is divided into: the magnetic field component ΔB(i,j) in the x-direction. x Gradient of (i, j) along the y-direction The magnetic field component ΔB in the y-direction of ΔB(i,j) y Gradient of (i, j) along the x-direction

[0013] Step 4: Calculate the magnetic field components ΔB(i,j) based on the relative change of the external magnetic field under the battery's corresponding operating conditions at different time points. x (i, j) and ΔB y Gradient distributions of (i, j) in the y and x directions, respectively. and If the gradient distribution of the magnetic field components of the battery under test and If all cells exhibit abrupt gradient changes within the same region and a reversal of gradient direction along the axial direction, it can be determined that an internal short circuit has occurred in that region. The severity of the internal short circuit can be judged based on the size and intensity of the gradient edge at the short circuit site. Specifically, the larger the contour of the gradient edge at the short circuit site, the larger the short circuit area is considered; the higher the intensity of the gradient at the short circuit site, the larger the short circuit current and the more severe the short circuit.

[0014] In step 1, the test of the external magnetic field distribution of the battery is performed on the battery surface or a plane at a fixed height near the battery surface.

[0015] Furthermore, when testing the external magnetic field of the battery under test, a single magnetic sensor is used for scanning testing, or an array of multiple identical magnetic sensors is used for coverage testing.

[0016] Furthermore, the magnetic sensor is a high-precision magnetic sensor such as a Hall sensor, fluxgate sensor, anisotropic magnetoresistive sensor, or giant magnetoresistive sensor.

[0017] Furthermore, in step 1, during the magnetic field detection process, a magnetic shielding device is used to provide magnetic shielding protection for the battery under test. Various shapes of magnetic shielding devices made of high magnetic permeability metals are used to shield against external magnetic field interference, thereby further improving the detection accuracy for early internal short circuits. In environments without magnetic shielding protection, the complexity of the device is reduced.

[0018] Furthermore, the battery is a stacked battery or a wound battery. Preferably, the battery is a lithium-ion battery or a sodium-ion battery.

[0019] Furthermore, the lithium-ion battery can be any type of commercially available battery, and the positive electrode of the lithium-ion battery includes lithium nickel cobalt manganese oxide, aluminum nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, or lithium iron phosphate, while the negative electrode includes graphite or SiO2. x .

[0020] It should be further explained that the calculation of the relative change of the external magnetic field in steps 2 and 3 must be based on the corresponding battery state, that is, the calculation of ΔB(i,j) of the external magnetic field distribution of the battery under test at any two time points under constant current charging state; or the calculation of ΔB(i,j) of the external magnetic field distribution of the battery under test at any two time points under constant current discharging state; or the calculation of ΔB(i,j) of the external magnetic field distribution of the battery under test at any two time points under the resting state.

[0021] The non-destructive testing method for internal short circuits in batteries described in this invention is applicable to any internal short circuit triggering cause in actual situations, including various internal short circuit triggering causes such as factory burrs, extrusion collisions, high-temperature diaphragm melting, and dendrite punctures.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. This invention detects internal short circuits by mapping abnormal changes in the external magnetic field distribution before and after an internal short circuit to abnormal changes in the internal current density distribution. Compared with electrical characteristic detection methods, this invention can detect the spatial distribution of internal short circuit fault sites, providing strong data support for subsequent fault tracing and fault-tolerant control based on the determination of whether an internal short circuit fault has occurred.

[0024] 2. Based on the mechanism of internal short circuit occurrence, this invention detects internal short circuit faults by targeting the local anomalies in the external magnetic field caused by the concentration of positive and negative current densities during internal short circuits in the battery, which are characterized by the occurrence of positive and negative values ​​in pairs. This method effectively reduces false judgments during internal short circuit detection. Attached Figure Description

[0025] Figure 1 This is a flowchart of the method of the present invention;

[0026] Figure 2 This is a diagram showing the placement of the battery under test.

[0027] Figure 3 This is a gradient distribution diagram showing the relative change in the external magnetic field before and after the battery triggers an internal short circuit. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Example 1:

[0030] This invention provides a non-destructive testing method for internal short circuits in lithium-ion batteries based on magnetic field gradient distribution, such as... Figure 1 As shown, the method includes the following specific steps:

[0031] Step 1: During the resting process, a magnetic sensor is used to detect the distribution of the planar magnetic field on the surface of the battery under test at arbitrary time intervals.

[0032] In this embodiment, the battery under test is a commercial lithium-ion pouch battery with a nominal capacity of 4Ah. Figure 2 The diagram shows the placement of the battery under test. The magnetic field distribution testing equipment uses a multi-axis moving platform with a three-axis fluxgate sensor to scan and test the battery. The external magnetic field shielding uses a 5-layer magnetic shielding barrel for magnetic shielding protection.

[0033] To test the change in external magnetic field distribution before and after an internal short circuit in a lithium-ion battery, this embodiment uses paraffin wax instead of a partial separator, and heats the membrane to trigger an internal short circuit to simulate the state of a real internal short-circuit battery.

[0034] According to the test method in step 1, firstly, an external magnetic field test is performed on the lithium-ion battery that has not triggered an internal short circuit in the resting state to obtain B0(i, h). Then, the internal short circuit of the battery is triggered by melting paraffin through heating, and the external magnetic field distribution B of the lithium-ion battery in the resting state with internal short circuit is obtained through the test steps in step 1. isc (i, j).

[0035] Step 2: Based on the test results before and after the internal short circuit in the battery's resting state, obtain the relative change distribution ΔB(i,j) of the external magnetic field of the battery before and after the internal short circuit, where ΔB(i,j) = B. isc (i,j)-B0(i,j) is used to eliminate magnetic field interference generated other than current density.

[0036] In this embodiment, the relative change of the external magnetic field ΔB(i,j) before and after triggering the internal short circuit is used to simulate the relative change of the external magnetic field ΔB(i,j) between test results at different time points during actual use.

[0037] Step 3: Based on the relative change distribution of the external magnetic field before and after the internal short circuit in the lithium-ion battery under the storage state in Step 2, calculate the magnetic field component ΔB of the relative change distribution of the external magnetic field ΔB(i,j). x (i, j) and ΔB y Gradient distributions of (i, j) in the y and x directions, respectively. and

[0038] In this embodiment, based on the gradient distribution diagram of the relative change of the external magnetic field after the lithium-ion battery triggers an internal short circuit and before the internal short circuit in step 2, as shown in the figure... Figure 3 As shown in (a) and (b). Figure 3 (a) represents the relative change ΔB of the magnetic field component when the battery is in a resting state. x Gradient distribution of (i, j) Figure 3 (b) Relative change of magnetic field component ΔB when the battery is in storage y Gradient distribution of (i, j)

[0039] Step 4: Based on the gradient distribution of the magnetic field components of the tested battery in Step 3. and If a sudden change in gradient occurs in the same region and the gradient direction reverses along the axis, it can be determined that the battery has an internal short circuit in this region.

[0040] In this embodiment, based on the gradient distribution of the relative changes in the external magnetic field components obtained before and after the internal short circuit of the lithium-ion battery, by Figure 3 (a) and (b) show that there is a significant change in the direction and reversal of the local magnetic field gradient near the center of the battery. This gradient increase caused by the convergence / divergence of the internal current density of the battery leads to the determination that the battery has an internal short circuit. In addition, the influence range of the internal short circuit region of the battery can be determined based on the shape of the gradient change.

[0041] Example 2:

[0042] This invention provides a non-destructive testing method for internal short circuits in lithium-ion batteries based on magnetic field gradient distribution, such as... Figure 1 As shown, the method includes the following specific steps:

[0043] Step 1: Under 0.1C constant current charging, use a magnetic sensor to detect the planar magnetic field distribution on the surface of the battery under test at arbitrary time intervals.

[0044] In this embodiment, the battery under test is a commercial lithium-ion pouch battery with a nominal capacity of 4Ah. Figure 2 The diagram shows the placement of the battery under test. The magnetic field distribution testing equipment uses a multi-axis moving platform with a three-axis fluxgate sensor to scan and test the battery. The external magnetic field shielding uses a 5-layer magnetic shielding barrel for magnetic shielding protection.

[0045] To test the change in external magnetic field distribution before and after an internal short circuit in a lithium-ion battery, this embodiment uses paraffin wax instead of a partial separator, and heats the membrane to trigger an internal short circuit to simulate the state of a real internal short-circuit battery.

[0046] According to the test method in step 1, firstly, an external magnetic field test is performed on the lithium-ion battery that has not triggered an internal short circuit under 0.1C constant current charging state to obtain B0(i,j). Then, the internal short circuit of the battery is triggered by melting paraffin through heating. The external magnetic field distribution B of the lithium-ion battery under 0.1C constant current charging state with internal short circuit is obtained through the test steps in step 1. isc (i, j).

[0047] Step 2: Based on the test results before and after the internal short circuit under 0.1C constant current charging state, obtain the relative change distribution ΔB(i,j) of the external magnetic field of the battery before and after the internal short circuit, where ΔB(i,j) = B isc (i,j)-B0(i,j) is used to eliminate magnetic field interference generated other than current density.

[0048] In this embodiment, the relative change of the external magnetic field ΔB(i,j) before and after triggering the internal short circuit is used to simulate the relative change of the external magnetic field ΔB(i,j) between test results at different time points during actual use.

[0049] Step 3: Based on the relative change distribution of the external magnetic field before and after the internal short circuit in the 0.1C constant current charging state of the lithium-ion battery in Step 2, calculate and solve the magnetic field component ΔB of the relative change distribution of the external magnetic field ΔB(i,j). x (i, j) and ΔB y Gradient distributions of (i, j) in the y and x directions, respectively. and

[0050] In this embodiment, based on the gradient distribution diagram of the relative change of the external magnetic field after the lithium-ion battery triggers an internal short circuit and before the internal short circuit in step 2, as shown in the figure... Figure 3 As shown in (c) and (d). Figure 3 (c) The relative change ΔB of the magnetic field component during the 0.1C constant current charging state of the battery. x Gradient distribution of (i, j) Figure 3 (d) Relative change ΔB of magnetic field component during 0.1C constant current charging of the battery y Gradient distribution of (i, j)

[0051] Step 4: Based on the gradient distribution of the magnetic field components of the tested battery in Step 3. and If a sudden change in gradient occurs in the same region and the gradient direction reverses along the axis, it can be determined that the battery has an internal short circuit in this region.

[0052] In this embodiment, based on the gradient distribution of the relative changes in the external magnetic field components obtained before and after the internal short circuit of the lithium-ion battery, by Figure 3 (c) and (d) show that there is a significant change in the direction and reversal of the local magnetic field gradient near the center of the battery. This rapid increase in the gradient of the relative change of the external magnetic field caused by the convergence / divergence of the current density inside the battery indicates that the battery has an internal short circuit. In addition, the influence range of the internal short circuit region of the battery can be determined based on the shape of the gradient change.

[0053] Example 3:

[0054] This invention provides a non-destructive testing method for internal short circuits in lithium-ion batteries based on magnetic field gradient distribution, such as... Figure 1 As shown, the method includes the following specific steps:

[0055] Step 1: During the 0.1C constant current discharge process, a magnetic sensor is used to detect the planar magnetic field distribution on the surface of the battery under test at arbitrary time intervals.

[0056] In this embodiment, the battery under test is a commercial lithium-ion pouch battery with a nominal capacity of 4Ah. Figure 2The diagram shows the placement of the battery under test. The magnetic field distribution testing equipment uses a multi-axis moving platform with a three-axis fluxgate sensor to scan and test the battery. The external magnetic field shielding uses a 5-layer magnetic shielding barrel for magnetic shielding protection.

[0057] To test the change in external magnetic field distribution before and after an internal short circuit in a lithium-ion battery, this embodiment uses paraffin wax instead of a partial separator, and heats the membrane to trigger an internal short circuit to simulate the state of a real internal short-circuit battery.

[0058] According to the test method in step 1, firstly, an external magnetic field test is performed on the lithium-ion battery that has not triggered an internal short circuit under 0.1C constant current discharge state to obtain B0(i, h). Then, the internal short circuit of the battery is triggered by melting paraffin through heating, and the external magnetic field distribution B of the lithium-ion battery under 0.1C constant current discharge state with internal short circuit is obtained through the test steps in step 1. isc (i, j).

[0059] Step 2: Based on the test results before and after the internal short circuit under the 0.1C constant current discharge state of the battery, obtain the relative change distribution of the external magnetic field of the battery before and after the internal short circuit, ΔB(i,j), where ΔB(i,j) = B. isc (i,j)-B0(i,j) is used to eliminate magnetic field interference generated other than current density.

[0060] In this embodiment, the relative change of the external magnetic field ΔB(i,h) before and after triggering the internal short circuit is used to simulate the relative change of the external magnetic field ΔB(i,h) between test results at different time points during actual use.

[0061] Step 3: Based on the relative change distribution of the external magnetic field before and after the internal short circuit in the 0.1C constant current discharge state of the lithium-ion battery in Step 2, calculate and solve the magnetic field component ΔB of the relative change distribution of the external magnetic field ΔB(i,j). x (i, j) and ΔB y Gradient distributions of (i, j) in the y and x directions, respectively. and

[0062] In this embodiment, based on the gradient distribution diagram of the relative change of the external magnetic field after the lithium-ion battery triggers an internal short circuit and before the internal short circuit in step 2, as shown in the figure... Figure 3 As shown in (e) and (f). Figure 3 (e) represents the relative change ΔB of the magnetic field component in the 0.1C constant current discharge state of the battery. x Gradient distribution of (i, j) Figure 3 (f) Relative change ΔB of magnetic field component in 0.1C constant current discharge state of the battery y Gradient distribution of (i, j)

[0063] Step 4: Based on the gradient distribution of the magnetic field components of the tested battery in Step 3. and If a sudden change in gradient occurs in the same region and the gradient direction reverses along the axis, it can be determined that the battery has an internal short circuit in this region.

[0064] In this embodiment, based on the gradient distribution of the relative changes in the external magnetic field components obtained before and after the internal short circuit of the lithium-ion battery, by Figure 3 (e) and (f) show that there is a significant change in the direction and reversal of the local magnetic field gradient near the center of the battery. This rapid increase in the gradient of the relative change of the external magnetic field caused by the convergence / divergence of the current density inside the battery indicates that the battery has an internal short circuit. In addition, the influence range of the internal short circuit region can be determined based on the shape of the gradient change.

[0065] This invention detects the location and extent of internal short circuits in a battery by detecting abnormal distributions of the external magnetic field under different conditions. Compared to detection methods based on abnormal electrical characteristics, this invention can accurately determine the type of internal short circuit fault by observing changes in the abnormal distribution of external magnetic field characteristics caused by the internal short circuit, preventing misdiagnosis. Furthermore, it can accurately pinpoint the location of the internal short circuit, providing effective data support for subsequent fault tracing and battery design improvements.

[0066] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution, characterized in that, Includes the following steps: Step 1: Under constant current charging, constant current discharging, or idle conditions, use a magnetic sensor to measure the distribution of the external magnetic field B of the battery under test. n (i, j) are tested at arbitrary time intervals; Step 2: Based on the detection results at different time points during the constant current charging state, constant current discharging state, or standby state of the battery, obtain the relative change distribution ΔB(i,j) of the external magnetic field under the corresponding operating conditions of the battery. Step 3: Calculate the gradient distribution of the magnetic field components of the external magnetic field ΔB(i,j) in the y and x directions, respectively, under the corresponding operating conditions of the battery at different time points. and ; Step 4: If the gradient distribution of the magnetic field components of the battery under test is... and If the gradient changes abruptly in the same region and the gradient direction reverses along the axis, it can be determined that the battery has an internal short circuit in this region. Here, the plane formed by the width and length directions of the battery is called the xy plane, i and j represent the coordinates of any point in the xy plane of the battery, and ΔB x (i, j), ΔB y (i, j) are the magnetic field components of ΔB(i, j) orthogonally decomposed in the x and y directions, respectively; The severity of an internal short circuit is determined by the size and intensity of the gradient edge at the short circuit point. The larger the contour of the gradient edge at the short circuit point, the larger the short circuit area is considered to be. The higher the intensity of the gradient at the short circuit point, the larger the short circuit current is considered to be, and the more severe the short circuit is.

2. The non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution according to claim 1, characterized in that: In step two, the method for calculating the relative change distribution ΔB(i,j) of the external magnetic field under the corresponding battery operating conditions is ΔB(i,j)=B n (i,j)-B n-1 (i, j), where B n (i, j) and B n-1 (i, j) represent the external magnetic field distributions of the tested battery obtained from the nth and (n-1)th tests, respectively.

3. The non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution according to claim 1, characterized in that: The magnetic sensor includes a Hall sensor, a fluxgate sensor, a giant magnetoresistive sensor, or anisotropic magnetoresistive sensor.

4. The non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution according to claim 1, characterized in that: In step one, during the magnetic field detection process, a magnetic shielding device is used to provide magnetic shielding protection for the battery under test.

5. The non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution according to claim 1, characterized in that: The battery is a stacked battery or a wound battery.

6. The non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution according to claim 1, characterized in that: In step one, when testing the external magnetic field of the battery under test, the test is performed on the battery surface or on a plane at a fixed height from the battery surface.

7. The non-destructive testing method for internal short circuits in batteries based on magnetic field gradient distribution according to claim 1, characterized in that: In step one, when testing the external magnetic field of the battery under test, a single magnetic sensor is used for scanning testing or an array of multiple identical magnetic sensors is used for coverage testing.

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