Lithium battery detection device based on BB optical pump magnetic imaging

Abstract

A lithium battery detection device based on BB optical pump magnetic imaging comprises a magnetic shielding cylinder and a substrate arranged in the magnetic shielding cylinder, and a laser, an optical lens system, an atomic gas chamber system, an array lens and an array photoelectric detector are sequentially arranged on the working face of the substrate from left to right; the atomic gas chamber system contains alkali metal atoms and buffer gas; a non-magnetic objective table for placing a lithium battery to be tested is arranged above the atomic gas chamber; according to the device, the array lens is adopted to split and focus a single beam of detection laser into small light spots which are respectively irradiated on different photoelectric detectors, and magnetic field information of a plurality of space point locations is detected at one time, so that the consistency and imaging quality of a subsystem are improved, and the system cost is saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical pumping magnetometers, and in particular relates to a lithium battery detection device based on BB optical pumping magnetic imaging. Background Art

[0002] As an important carrier of new energy, lithium batteries have become increasingly important for safety testing technology at the production end. With the expansion of industrial scale, a fast, efficient, and low-cost battery testing method is needed. It can also preliminarily analyze the cause of the fault and locate the fault point, thereby eliminating the risk of use and providing effective feedback to the production end.

[0003] Magnetic field detection is a nondestructive testing method that has been applied to battery defect diagnosis. It can monitor the movement of lithium ions and is sensitive to structural defects such as breakage and cracks. It can also respond to functional defects such as internal short circuits and lithium dendrite growth. Compared with other detection methods, magnetic field detection is low-cost and fast, and can be applied in the industrial field.

[0004] The BB (Bell-Bloom) optically pumped magnetometer is based on the Zeeman splitting of atomic energy levels and the optical pumping effect. It polarizes alkali metal atoms (such as rubidium and cesium) with circularly polarized light. This circularly polarized light is modulated using any of the following frequency, amplitude, and phase methods. If the modulation frequency matches the frequency of the atoms' Zeeman splitting energy levels in a magnetic field, magnetic resonance is stimulated. The intensity change of the transmitted light is detected to accurately measure the magnetic field (formula: B = ω / γ, where ω represents the Zeeman splitting frequency and γ represents the gyromagnetic ratio). Its sensitivity can reach the pT level and is widely used in geomagnetic exploration, space exploration, and fundamental physics research. The advantage of the BB optically pumped magnetometer is that it is an all-optical magnetometer without complex RF excitation coils. However, existing BB optically pumped magnetometer technologies are all single-channel, resulting in bulky systems and limited spatial resolution, making it difficult to detect the weak magnetic field signals generated by the fine structures within the battery.

[0005] Existing array-type magnetic imaging detection solutions are composed of multiple chip magnetic sensors arranged in an array, usually using magnetoresistive effect or Hall effect magnetic sensors. They can be used in the geomagnetic field, are simple and reliable, and their spatial resolution is generally in the millimeter level. However, the chip-type magnetic sensor has low sensitivity and cannot detect the weak magnetic field generated by abnormal discharge inside the battery, so its application occasions are limited.

[0006] Existing SERF (Spin Exchange Relaxation Free) magnetometers, similar to BB magnetometers, can achieve sensitivities in the tens of femtoliters and spatial resolutions on the millimeter scale. However, SERF magnetometers require a well-shielded environment, and their measurement range is typically limited to 10 nT. The coils surrounding the atomic chamber prevent the object being detected from getting close to the chamber. The ambient magnetic field must be below 10 nT, and the system is expensive, limiting the application of this solution. Furthermore, the temperature of the SERF magnetometer chamber is typically above 100°C, requiring the detection battery to maintain a certain distance from the probe to ensure safety.

[0007] Existing SQUID (Superconducting Quantum Interference Device, SQUID) magnetometers have high sensitivity, reaching the femtoliter level, and spatial resolution of the centimeter level. However, their disadvantages are that SQUID magnetometers need to operate in a dewar flask filled with liquid helium, which is large and expensive. They are usually at a certain distance from the object being measured, which affects the detection effect. They are also expensive to use and require liquid helium replenishment, making them unsuitable for industrial promotion. Summary of the Invention

[0008] To address these issues, the present invention proposes a lithium battery detection device based on BB optically pumped magnetic imaging. The device employs an array lens behind an atomic gas chamber to split a single probe laser beam, focusing it into small spots that strike separate photodetectors, allowing simultaneous detection of magnetic field information at multiple spatial locations. This not only improves subsystem consistency and imaging quality, but also reduces system costs.

[0009] The lithium battery detection device based on BB optical pump magnetic imaging includes a magnetic shielding tube 1, the inner cavity of which is provided with a horizontal substrate 9; the working surface of the substrate 9 is provided with a laser 2, an optical lens system 3, an atomic gas chamber system 4, an array lens 5, and an array photodetector 6 from left to right; the atomic gas chamber system 4 contains alkali metal atoms and a buffer gas; a non-magnetic stage 10 is provided above the atomic gas chamber 41 for placing the lithium battery to be tested; the laser 2 is connected to a signal generator 11 outside the magnetic shielding tube 1, and the array photodetector 6 is connected to a photoelectric detection system 12 outside the magnetic shielding tube 1;

[0010] The initial laser emitted by the laser 2 is converted into elliptically circularly polarized light by the optical lens system 3. The light enters the atomic gas chamber system 4 and interacts with the alkali metal atoms at different positions therein to generate optical signals that record magnetic field information. Subsequently, the array lens 5 splits the optical signal and irradiates it onto the array photodetector 6. The optical signals at different positions on the array photodetector 6 record the magnetic field information at the corresponding positions of the atomic system 4. The optical signals on the array photodetector 6 are converted into electrical signals and transmitted to the photoelectric detection system 12. The photoelectric detection system 12 amplifies the electrical signals and filters and analyzes them to obtain the magnetic field values ​​at each point in the space within the atomic gas chamber system 4.

[0011] More specifically, the optical lens system 3 includes a first quarter glass 31. The initial laser passes through the first quarter glass 31 and becomes circularly polarized light. The circularly polarized light passes through a spherical lens group 32 composed of two spherical lenses and becomes a circular light spot. The circular light spot passes through a cylindrical lens group 33 composed of two cylindrical lenses and becomes an elliptically circularly polarized light 34.

[0012] More specifically, the atomic gas chamber system 4 includes a gas chamber 41 , and non-magnetic heating plates 42 are provided on the left and right inner walls of the gas chamber 41 .

[0013] More specifically, the alkali metal atoms in the atomic gas chamber system 4 are one of potassium atoms, rubidium atoms, and cesium atoms; and the buffer gas is one or more of nitrogen, helium, and xenon.

[0014] More specifically, mounting grooves in left and right directions are provided on both sides of the base plate 9; the non-magnetic stage 10 is arranged on the mounting grooves and can slide left and right along the mounting grooves.

[0015] More specifically, the operating temperature of the gas chamber 41 is heated to 60 degrees Celsius by the non-magnetic heating plate 42 .

[0016] More specifically, the magnetic shielding tube 1 has a double-layer structure and is made of silicon steel or Permalloy.

[0017] More specifically, the array lens 5 is composed of two rows of lenses, each row having ten lenses, so that the array photodetector 6 collects a total of twenty magnetic field signals; each lens has a diameter of 5 mm and a focal length of 10 mm.

[0018] More specifically, the distance between the laser 2 and the atomic gas cell system 4 is greater than 30 cm.

[0019] The working steps of the present invention are as follows:

[0020] Step 1: Place the battery to be tested on the non-magnetic stage 10 and fix it. The lithium battery is in any state of charging, discharging, or disconnection. The non-magnetic stage 10 is moved to the initial position.

[0021] Step 2: Turn on each component of the system and set the initial working parameters. These include the laser 2, optical lens system 3, atomic gas chamber system 4, array lens 5, array photodetector 6, signal generator 11, and photoelectric detection system 12, and wait for each device to work stably; define the straight line where the initial laser emitted by the laser 2 is located as the Z axis, and the plane perpendicular to the Z axis is the XY plane; the initial laser emitted by the laser 2 is converted into elliptically circularly polarized light 34 by the optical lens system 3, and the elliptically circularly polarized light 34 enters the rectangular atomic gas chamber 41 and interacts with the alkali metal atoms in the gas chamber 41. The atoms at different positions in the gas chamber 41 feel the magnetic field information generated by the battery and are recorded by the laser. Then the array lens 5 splits the laser beam and irradiates it on the array photodetector 6. The light signals at different positions on the array photodetector 6 record the magnetic field signals corresponding to the corresponding positions of the atomic gas chamber 41.

[0022] Step 3: Set up signal generator 11 and frequency-modulate the initial laser light emitted by laser 2 through the laser current modulation interface. When the signal frequency of the initial laser light matches the Zeeman splitting frequency corresponding to the magnetic field, the elliptically circularly polarized light 34 converted from the initial laser light interacts most strongly with the alkali metal atoms in atomic gas chamber 41. The changes in the magnetic field caused by the battery under test in various parts of the space are recorded within gas chamber 41.

[0023] Step 4: Photoelectric detection system 12 collects signals from array photodetector 6 and performs filtering and analysis to obtain magnetic field data. Laser light, which records the magnetic field information at each point in space, is split by lens array 5 and irradiated onto array photodetector 6. Photoelectric detection system 12 collects laser light information at different locations, i.e., magnetic field information at each point in the XY plane.

[0024] Step 5: Non-magnetic stage 10 moves along the Z axis through the mounting slots on substrate 9 and repeats the previous step to measure the magnetic field. The non-magnetic stage 10 moves along the Z axis sequentially, dividing the measurement intervals according to the battery size, to detect the Z-direction magnetic field distribution of the entire battery.

[0025] Step 6: Analyze the state of the battery based on the three-dimensional magnetic field distribution information. The differences in magnetic patterns based on different states can be used to analyze the location and cause of battery failure.

[0026] The beneficial effects produced by the present invention include:

[0027] 1. An array lens is used to split the detection laser beam, focusing it into small spots that hit different photodetectors. Since the laser spot is smaller after the lens converges, the lasers in adjacent channels will not crosstalk, the system has better vibration resistance, the generated light splitting consistency is strong, and the imaging quality is high.

[0028] 2. The magnetic imaging system composed of BB-type atomic magnetometers has high spatial resolution, low cost, and low requirements for magnetic shielding. It can detect both structural and functional defects of batteries with high sensitivity.

[0029] 3. The system uses only one laser beam and one gas chamber, without the need for an excitation coil, which saves costs, is easy to operate, and can be used for industrial production.

[0030] 4. The sensitive axis of the magnetic imaging system composed of the BB-type atomic magnetometer is in the vertical direction of the laser. The non-magnetic stage can be set above the atomic gas chamber without interfering with the optical path system. The battery to be tested can be close to the atomic gas chamber to obtain a stronger magnetic field signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a structural diagram of a lithium battery detection device based on BB optical pump magnetic imaging of the present invention.

[0032] Figure 2 It is a structural diagram of the optical lens system of the present invention.

[0033] Figure 3 It is a schematic diagram of the light splitting of the array lens of the present invention.

[0034] Figure 4 It is a signal transmission flow chart of the present invention.

[0035] Figure 5 It is a perspective view of the array light spot of the present invention.

[0036] Figure 6 It is a workflow diagram of the present invention. DETAILED DESCRIPTION

[0037] The specific implementation of the embodiment of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the embodiment of the present invention and is not used to limit the embodiment of the present invention.

[0038] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0040] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0041] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0042] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0043] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with exemplary embodiments.

[0044] A BB optically pumped magnetic imaging device based on rubidium atoms has a spatial resolution of about 5mm and a lateral detection width of about 5cm.

[0045] The system includes a double-layer magnetic shielding tube 1, which is made of low-cost silicon steel material, with a diameter of 50 cm, a length of 80 cm, and a 20 cm center opening at both ends. The magnetic shielding tube 1 can attenuate the geomagnetic field by about 10 times, while still having a residual magnetic field of about 5000 nT. A horizontal substrate is fixed inside the shielding layer, and the optical components are placed on the substrate.

[0046] A DFB laser was used as the light source. Laser 2 was placed to the left of substrate 9, greater than 30 cm from atomic gas chamber system 4 to prevent the interference magnetic field generated by it from affecting the measurement. The initial laser was adjusted to a horizontal position, with its central axis serving as the optical axis. The laser used a wavelength of 795 nm, which resonates with the D1 line of rubidium atoms. The laser output power was above 50 mW, and the spot size was a circular approximately 2 mm. After emission, the initial laser entered optical lens system 3.

[0047] The optical lens system 3 includes a first quarter glass slide 31, a spherical lens group 32, and a cylindrical lens group 33. The initial laser passes through the first quarter glass slide 31 and is converted into elliptical circularly polarized light 34 to better polarize the atoms. The initial laser is converted into a circular light spot with a diameter of 20 mm by the spherical lens group 32 with a focal length ratio of 1:10, meeting the size requirements in the X direction; the Y direction is then stretched by the cylindrical lens group 33, and the focal length ratio of the cylindrical lens group 33 is 1:3, so that the light spot of the elliptical circularly polarized light 34 with a major axis of 60 mm and a minor axis of about 20 mm is obtained. The air chamber 41 of the atomic air chamber system 4 has a size of 10*10*50 mm, and the long side is parallel to the major axis of the light spot of the elliptical circularly polarized light 34. The light spot can cover the entire air chamber, and the center of the light spot coincides with the center of the air chamber.

[0048] Gas chamber 41 is filled with rubidium atoms and nitrogen at a pressure of 300 Torr as a buffer gas. At this pressure, the mean free path of the atoms is less than 1 mm, and the atoms are almost motionless. The magnetic field they experience is the magnetic field at that location in space. High-frequency current is injected into non-magnetic heating plates 42 on both sides of the atomic gas chamber to heat the gas chamber, stabilizing the temperature at around 60°C. This is used to increase the number density of alkali metal atoms and, in turn, improve signal strength. The atomic gas chamber system 4 is placed at the center of the spot of elliptically circularly polarized light 34. The expanded laser enters gas chamber 41 and interacts with the atoms to generate a signal.

[0049] After adjusting the wavelength and polarization, the laser can interact with atoms. The battery to be tested is placed on a non-magnetic stage 10 directly above the gas chamber 41. The magnetic anomalies generated by its internal defects are distributed differently at different points in space, with the magnetic field generally decreasing with distance from the anomaly. The Zeeman splitting frequencies of atoms vary under different magnetic fields. Signal generator 11 is then used to frequency-modulate the laser. If the modulation frequency matches the Zeeman splitting frequency corresponding to an atom at a certain position in the gas chamber, the laser's interaction signal with the atom at that location is the strongest, and the laser can then record the magnetic field information at that location.

[0050] After the laser interacts with the atoms in the gas chamber, it passes through a two-dimensional array lens 5. The array lens consists of two rows of lenses, each row with 10 lenses. The diameter of the lens is 5mm and the focal length is 10mm. The array lens coincides with the center of the elliptically circularly polarized light spot. The lens focuses the light beam on the array photodetector, which detects the laser signal after each lens converges. The array photodetector collects a total of 20 magnetic field signals and sends them to the photoelectric signal detection system, which is located as shown in the figure. Figure 4 、 Figure 5 shown.

[0051] Specific work such as Figure 6 As shown:

[0052] Step 1: Place the battery under test on a non-magnetic stage 10 and secure it. The battery is in any of the following states: charging, discharging, or disconnecting. The non-magnetic stage is moved to its initial position. Assuming the battery under test is 100mm*50mm*5mm (length x width x height), the measurement interval is 10mm. The center of the battery is placed directly above the center of the atomic gas chamber, and then slid 50mm to one side to establish the initial position.

[0053] Step 2: Turn on all system components and set initial operating parameters. Laser 2's operating wavelength is set to the rubidium atomic D1 line (795nm). The gas chamber is heated to 60°C. Optical lens system 3 adjusts the laser light into an elliptically circularly polarized beam with a long axis of 60mm and a short axis of 20mm, covering the entire gas chamber and interacting with the atoms. The center of array lens 5 is aligned with the optical axis, and the decomposed light spots are directed onto array photodetector 6.

[0054] Step 3: Set up signal generator 11 and frequency-modulate the initial laser light using the laser current modulation interface. As previously mentioned, if the modulation frequency matches the Zeeman splitting frequency corresponding to an atom at a certain position in the gas chamber, the laser-atom interaction signal is strongest, and the magnetic field information is recorded. The gyromagnetic ratio of rubidium atoms is 7 Hz / nT. If the magnetic field range is approximately 5000 ± 1000 nT, the sweep frequency of signal generator 11 can be set within a range of 35 ± 7 kHz.

[0055] Step 4: The photoelectric detection system 12 collects the signals from the array photoelectric detector 6 and performs filtering and analysis to obtain magnetic field data. After the magnetic field information is recorded, it is filtered to obtain a signal with good signal-to-noise ratio, which can be processed to obtain the magnetic field value at each position in space.

[0056] Step 5: Non-magnetic stage 10 moves along the Z axis through the mounting slots on base plate 9 and repeats the previous step to measure the magnetic field. Based on the battery size, the measurement interval is 10 mm. Non-magnetic stage 10 moves nine times to obtain the complete magnetic field information for a 100 mm battery.

[0057] Step 6: Analyze the battery's internal state based on the three-dimensional magnetic field distribution information. The battery under test moves along the Z axis, generating 10 sets of data, corresponding to magnetic field information at 10*10*2 points in space. Using the magnetic field dipole model, this spatial magnetic field information is inverted to determine the internal magnetic field distribution of the battery. This magnetic field distribution information can be used to determine the battery's state and the location of the fault.

[0058] The above description of the present invention is only part of the preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A lithium battery detection device based on BB optical pump magnetic imaging, characterized by: The invention comprises a magnetic shielding tube (1), wherein a horizontal substrate (9) is provided in the inner cavity of the magnetic shielding tube; a working surface of the substrate (9) is provided with (2), an optical lens system (3), an atomic gas chamber system (4), an array lens (5), and an array photoelectric detector (6) in sequence from left to right; the atomic gas chamber system (4) contains alkali metal atoms and a buffer gas; a non-magnetic stage (10) for placing a lithium battery to be tested is provided above the atomic gas chamber (41); a laser (2) is connected to a signal generator (11) outside the magnetic shielding tube (1), and an array photoelectric (6) is connected to a photoelectric detection system (12) outside the magnetic shielding tube (1); The initial laser light emitted by the laser (2) is converted into elliptically circularly polarized light (34) by the optical lens system (3). The elliptically circularly polarized light (34) enters the atomic gas chamber system (4) and interacts with alkali metal atoms at different positions in the atomic gas chamber system (4) to generate optical signals that record magnetic field information. Subsequently, the array lens (5) splits the optical signal and irradiates it onto the array photodetector (6). The optical signals at different positions on the array photodetector (6) record the magnetic field signals at corresponding positions of the atomic gas chamber system (4). The optical signals on the photodetector array (6) are converted into electrical signals and transmitted to the photoelectric detection system (12). The photoelectric detection system (12) amplifies the electrical signals and performs filtering processing and analysis to obtain the magnetic field values ​​of various points in the space of the atomic gas chamber system (4).

2. A lithium battery detection device based on BB optical pumping magnetic imaging according to claim 1, characterized in that: The optical lens system (3) includes a first quarter glass (31). The initial laser light is converted into circularly polarized light after passing through the first quarter glass (31). The circularly polarized light is converted into a circular light spot after passing through a spherical lens group (32) composed of two spherical lenses. The circular light spot is converted into elliptical circularly polarized light (34) after passing through a cylindrical lens group (33) composed of two cylindrical lenses.

3. The lithium battery detection device based on BB optical pumping magnetic imaging according to claim 1, characterized in that: The atomic gas chamber system (4) comprises a gas chamber (41), and the left and right outer walls of the gas chamber (41) are provided with non-magnetic heating plates (42).

4. The lithium battery detection device based on BB optical pumping magnetic imaging according to claim 1, characterized in that: The alkali metal atoms in the atomic gas chamber system (4) are one of potassium atoms, rubidium atoms and cesium atoms; the buffer gas is one or more of inert gases such as nitrogen, helium and xenon.

5. The lithium battery detection device based on BB optical pumping magnetic imaging according to claim 1, characterized in that: The base plate (9) is provided with mounting grooves in left and right directions on both the front and rear sides; the non-magnetic loading platform (10) is arranged on the mounting grooves and can slide left and right along the mounting grooves.

6. The lithium battery detection device based on BB optical pumping magnetic imaging according to claim 1, characterized in that: The working temperature of the gas chamber (41) is heated to 60 degrees Celsius by the non-magnetic heating plate (42).

7. The lithium battery detection device based on BB optical pumping magnetic imaging according to claim 1, characterized in that: The magnetic shielding tube (1) has a double-layer structure and is made of silicon steel or Permalloy.

8. The lithium battery detection device based on BB optical pumping magnetic imaging according to claim 1, characterized in that: The array lens (5) is composed of two upper and lower rows of lenses, with ten lenses in each row, so that the array photoelectric detector (6) collects a total of twenty magnetic field signals; the diameter of each lens is 5 mm and the focal length is 10 mm.

9. The lithium battery detection device based on BB optical pumping magnetic imaging according to claim 1, characterized in that: The distance between the laser (2) and the atomic gas chamber system (4) is greater than 30 cm.

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