TMR array in-situ battery weak field detection system and method based on bidirectional magnetic field

Abstract

The application provides a TMR array in-situ battery weak field detection system and method based on a bidirectional magnetic field, belongs to the cross field of electrochemical energy storage and magnetic measurement technology, and comprises a variable magnetic field excitation unit including a pair of bidirectional Helmholtz coils, an in-situ detection array integrated on a flexible polyimide substrate, a precise signal acquisition link adopting a Keithley joint architecture including an electrochemical control end and a magnetic signal monitoring end, and an algorithm analysis module internally embedded with an adaptive signal processing algorithm. Through the bidirectional coil layout design, the application can realize the classified and accurate detection of the material "vertical intrinsic spin magnetic moment" and "in-plane local current anomaly" under the in-situ battery weak field hysteresis loop detection.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of electrochemical energy storage and magnetic measurement technology, and in particular relates to a weak field detection system and method for in-situ TMR array batteries based on a bidirectional magnetic field. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Monitoring the internal state of secondary batteries (such as lithium-ion batteries, sodium-ion batteries, and solid-state batteries) during charging and discharging, especially the real-time characterization of phase transitions in active materials, lithium dendrite growth, and abnormal local current distribution, is a key technical challenge in the field of electrochemical energy storage. Existing technologies mainly suffer from the following shortcomings: 1) Existing work utilizes vibrating sample magnetometers (VSMs) to measure the changes in magnetic moment of battery materials during charge and discharge processes, indirectly characterizing their electrochemical reaction processes and structural evolution behavior. Simultaneously, in electrochemical performance evaluation, methods such as voltmeters, ammeters, and electrochemical impedance spectroscopy (EIS) are typically combined to analyze global electrical signals acquired from the external environment of the battery. However, VSM characterization obtains the overall magnetic response of the sample by scanning an external magnetic field. In complex electrochemical systems, the measurement results are dominated by the volume average magnetic signal, and local weak magnetic changes are easily weakened by the overall response and background signal, thus limiting the ability to resolve subtle magnetic response evolution processes. Furthermore, electrical signal monitoring cannot resolve the spatiotemporal heterogeneity of local current distribution within the battery, making it difficult to capture microscopic anomalies such as lithium dendrite growth.

[0004] 2) Early magnetic sensing technologies mostly used devices such as Hall sensors. These devices have low sensitivity and mainly respond to strong magnetic field signals. Therefore, there are bottlenecks in signal-to-noise ratio and sensitivity. That is, Hall sensors have difficulty identifying weak magnetic field fluctuations at the nanoter level and lack signal decoupling schemes under strong charging and discharging current background. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention provides a weak field detection system and method for in-situ batteries based on a bidirectional magnetic field TMR array, which can accurately detect the classification of material "vertical intrinsic spin magnetic moment" and "in-plane local current anomaly" under the weak field hysteresis loop detection of in-situ batteries.

[0006] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: The first aspect of the present invention provides a weak field detection system for in-situ batteries of TMR array based on bidirectional magnetic field.

[0007] The weak field detection system of in-situ battery based on bidirectional magnetic field TMR array includes: variable magnetic field excitation unit, in-situ detection array, precision signal acquisition link and algorithm analysis module; The variable magnetic field excitation unit includes a pair of Helmholtz coils arranged in a bidirectional manner. In the vertical magnetization path, the pair of Helmholtz coils are horizontally arranged on the upper and lower surfaces of the in-situ cell to generate a uniform scanning magnetic field that passes vertically through the plane of the in-situ cell. In the in-plane magnetization path, the pair of Helmholtz coils are respectively arranged on the left and right sides of the in-situ cell to decouple from the current magnetic field signal through the in-plane magnetic response of the excitation plane. The in-situ detection array is integrated on a flexible polyimide substrate, and metal interconnect lines are constructed on the surface of the flexible polyimide substrate to achieve flexible circuit integration; and the corresponding sensitive surface is actively pressed onto the surface of the in-situ battery by a non-magnetic pressure fixture. The precision signal acquisition link adopts a Keithley joint architecture that includes an electrochemical control terminal and a magnetic signal monitoring terminal; the differential output terminal of the TMR is connected to the Keithley nanovoltmeter used at the magnetic signal monitoring terminal via a double-shielded coaxial cable. The algorithm analysis module has an embedded adaptive signal processing algorithm, which is used to extract the intrinsic magnetic moment signal from the strong background field to realize the detection of the weak field hysteresis loop of the in-situ battery.

[0008] Furthermore, the in-situ detection array uses Z-axis sensitive TMR chips to construct a two-dimensional array, meaning that each tunnel magnetoresistive chip is sensitive to the Z-axis magnetic field component.

[0009] Furthermore, the electrochemical control terminal uses a Keithley 2400 source meter to drive the in-situ battery charging and discharging to control the charging and discharging accuracy; the magnetic signal monitoring terminal uses a Keithley 2182A nanovoltmeter to collect nanovolt-level ultra-low noise data; the Keithley 2400 source meter and the Keithley 2182A nanovoltmeter are synchronized by a trigger signal bus.

[0010] Furthermore, the intrinsic magnetic moment signal is extracted from the strong background field based on the adaptive signal processing algorithm, including: constructing a physical model for subtracting the background field; and simultaneously, acquiring the current signal in real time and using a pre-calibrated current-space magnetic field transfer function to remove the excitation magnetic field and current background field components from the original magnetic field signal in real time.

[0011] Furthermore, the physical model is expressed as: ; in, To obtain the original magnetic field signal for testing, It is the current-space magnetic field coupling coefficient obtained through calibration; For the current moment The coil excitation current; The in-situ battery current-magnetic field coupling coefficient obtained through calibration; For the current moment The in-situ battery charge and discharge current, For the current moment to be sought The magnetic field signal caused by the intrinsic vertical spin magnetic moment of the material; For the current moment The background geomagnetic environment.

[0012] Furthermore, the algorithm analysis module is also used to: under the vertical magnetization path, correlate the extracted intrinsic spin magnetic moment signal with the scanning magnetic field strength to reconstruct the in-situ hysteresis loop evolution diagram under different charge states.

[0013] Furthermore, the algorithm analysis module is also used to: under the in-plane magnetization path, invert the magnetic field distribution collected by the tunnel magnetoresistive array into a two-dimensional current density distribution map based on the Biot-Savart law, and locate the local magnetic field strength abrupt change point by comparing it with the expected uniform field model; wherein, the local magnetic field strength abrupt change point corresponds to the local current anomaly caused by lithium dendrite deposition or local short circuit, which is used to achieve micron-level spatial resolution for locating safety hazards.

[0014] The second aspect of the present invention provides a method for weak field detection of in-situ cells in a TMR array based on a bidirectional magnetic field.

[0015] A weak field detection method for in-situ cells of TMR arrays based on bidirectional magnetic fields includes: The packaged in-situ battery is placed horizontally in the central uniform magnetic field region of a pair of Helmholtz coils, and the coils are arranged according to the corresponding magnetization path selected according to the detection target. A two-dimensional array of tunnel magnetoresistive chips integrated on a substrate is actively pressed onto the surface of the in-situ battery using a non-magnetic pressure fixture; The positive and negative terminals of the in-situ battery were connected to a Keithley source meter for constant current charge and discharge testing. At the same time, a variable magnetic field was generated by driving a Helmholtz coil through a programmable current source, and a unified trigger clock was used to synchronize the charge and discharge steps with the magnetic field scanning steps. The collected data is embedded into the analytical module based on the recursive least squares adaptive signal processing algorithm to establish a physical model for subtracting the background field. The extracted intrinsic spin magnetic moment signal is correlated with the scanning magnetic field strength to achieve in-situ weak field hysteresis loop detection of the battery.

[0016] Furthermore, in the vertical magnetization path, the coil is located on the upper and lower surfaces of the in-situ cell; in the in-plane magnetization path, the coil is located on the left and right sides of the in-situ cell.

[0017] Furthermore, the output of the tunnel magnetoresistive array is connected to a Keithley nanovoltmeter via a double-shielded coaxial cable to acquire the original magnetic field signal in real time, and simultaneously acquire the coil excitation current and the in-situ battery current.

[0018] The above one or more technical solutions have the following beneficial effects: This invention employs a bidirectional Helmholtz coil layout in a variable magnetic field excitation unit, generating only a very small, weak scanning magnetic field under a vertical magnetization path. Simultaneously, the in-situ detection array is integrated onto a flexible polyimide substrate and actively pressed against the in-situ battery surface using a non-magnetic clamp, enabling in-situ monitoring without damaging the battery structure. Furthermore, through an algorithm analysis module, this invention correlates the extracted intrinsic spin magnetic moment signal with the scanning magnetic field strength under a vertical magnetization path, reconstructing the in-situ hysteresis loop evolution map under different charge states. Under an in-plane magnetization path, it decouples the spin magnetic moment signal from the current magnetic field signal, inverting the magnetic field distribution acquired by the TMR array into a two-dimensional current density distribution map based on the Biot-Savart law. By comparing this map with a predicted uniform field model, it locates local magnetic field strength abrupt changes, thereby analyzing the spatiotemporal heterogeneity of the local current distribution within the in-situ battery. This allows for precise detection of microscopic anomalies such as lithium dendrite deposition or local short circuits, ultimately achieving micron-level spatial resolution for locating safety hazards.

[0019] This invention employs a Z-axis sensitive TMR chip to construct a two-dimensional array, significantly improving the signal-to-noise ratio by utilizing the near-field gain effect. It can identify weak magnetic field fluctuations at the nanoter level, far superior to Hall sensors that only respond to strong magnetic field signals. Simultaneously, the precision signal acquisition link of this invention adopts a Keithley joint architecture, embedding an adaptive signal processing algorithm within the algorithm parsing module. This algorithm can remove the strong background field generated by the excitation magnetic field and charging / discharging current from the original magnetic field signal in real time, thus successfully extracting the intrinsic magnetic moment signal even under strong charging / discharging current background, achieving high signal-to-noise ratio detection of magnetic signals in weak field environments.

[0020] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0022] Figure 1 This is a schematic diagram showing the layout switching of the bidirectional Helmholtz coil in Embodiment 1 of the present invention; wherein, Figure 1 (a) in the diagram represents the layout of a bidirectional Helmholtz coil under a vertical magnetization path. Figure 1(b) in the diagram represents the layout of a bidirectional Helmholtz coil under a horizontal magnetization path.

[0023] Figure 2 This is a detailed diagram of the cantilever clamping structure between the TMR array and the in-situ battery surface in Embodiment 1 of the present invention; wherein, Figure 2 (a) in the diagram represents a schematic diagram of the side structure of the device. Figure 2 (b) in the figure represents a schematic diagram of the TMR array integrated on a flexible PI substrate.

[0024] Figure 3 This is a schematic diagram illustrating the functional relationship of the precision acquisition link based on Keithley 2400 and 2182A in Embodiment 1 of the present invention.

[0025] Figure 4 This is a schematic diagram of the TMR array in Embodiment 1 of the present invention.

[0026] In the diagram: 1. Vertical coil; 2. Horizontal coil; 3. In-situ battery; 4. Non-magnetic pressure fixture; 5. Flexible PI substrate; 6. TMR array; 7. Metal circuit; 8. DAQ cable interface; 9. Sensing distance; 10. Vcc power supply pin; 11. V- output pin; 12. V+ output pin; 13. GND ground pin; 14. NC empty pin. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0029] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0030] Example 1 This embodiment discloses a weak field detection system for in-situ batteries of a TMR array based on a bidirectional magnetic field.

[0031] The weak field detection system of in-situ battery based on bidirectional magnetic field TMR array includes: variable magnetic field excitation unit, in-situ detection array, precision signal acquisition link and algorithm analysis module; The variable magnetic field excitation unit includes a pair of Helmholtz coils arranged in a bidirectional manner. In the vertical magnetization path, the pair of Helmholtz coils are horizontally arranged on the upper and lower surfaces of the in-situ cell to generate a uniform scanning magnetic field that passes vertically through the plane of the in-situ cell. In the in-plane magnetization path, the pair of Helmholtz coils are respectively arranged on the left and right sides of the in-situ cell to excite the in-plane magnetic response. The in-situ detection array is integrated on a flexible polyimide substrate, and the corresponding sensitive surface is actively pressed onto the surface of the in-situ battery by a non-magnetic pressure tool. The precision signal acquisition link adopts a Keithley joint architecture that includes an electrochemical control terminal and a magnetic signal monitoring terminal; the differential output terminal of the TMR is connected to the Keithley nanovoltmeter used at the magnetic signal monitoring terminal via a double-shielded coaxial cable. The algorithm analysis module has an embedded adaptive signal processing algorithm, which is used to extract the intrinsic magnetic moment signal from the strong background field to realize the detection of the weak field hysteresis loop of the in-situ battery.

[0032] Based on the above systematic structural design, this invention, through a bidirectional coil layout design, enables precise detection of the classification of material "vertical intrinsic spin magnetic moment" and "in-plane local current anomaly" under in-situ battery weak field hysteresis loop detection. To facilitate understanding of the technical solution of this invention, the specific implementation methods are further explained and described below.

[0033] like Figure 1 As shown, the variable magnetic field excitation unit adopts a bidirectional layout, specifically including: a) Path A (vertical magnetization path). For example... Figure 1 As shown in (a), under the vertical magnetization path, a pair of Helmholtz coils are placed horizontally on the upper and lower surfaces of the in-situ battery as vertical coil 1, so as to generate a high uniform scanning magnetic field that passes through the plane of the in-situ battery vertically, and the intensity range of the generated magnetic field is between 0-5000 Oe.

[0034] b) Path B (in-plane magnetization path). For example... Figure 1 As shown in (b), under the horizontal magnetization path (i.e., in-plane magnetization path), a pair of Helmholtz coils are placed as horizontal coils 2 on the left and right sides of the in-situ battery, so that the in-situ battery is in the central uniform magnetic field region, in order to modulate the in-plane magnetic response and achieve signal decoupling, thereby capturing magnetic field distortions such as those caused by lithium dendrites.

[0035] The specific design of the in-situ detection array is as follows: a) Use a Z-axis sensitive TMR chip to construct a 6×6 or higher density two-dimensional array.

[0036] b) Packaging process: The in-situ sensing array is integrated onto a flexible polyimide (PI) substrate. A non-magnetic (PEEK / PTFE) clamp is used to actively press the sensing surface onto the in-situ battery surface. The sensing distance is <0.5 mm, and the near-field gain effect is utilized to improve the signal-to-noise ratio. For example... Figure 2 As shown, Figure 2 (a) in the figure represents a schematic diagram of the side structure of the device. In this schematic diagram, the in-situ battery 3 with an aluminum-plastic film shell is located below; above the in-situ battery 3 is a non-magnetic pressure fixture 4. The non-magnetic pressure fixture 4 uses a fine-tuning screw to precisely control the distance between the in-situ detection array (i.e., TMR array 6) and the battery under test, so as to change the sensing distance 9. Figure 2 (b) in the figure represents a schematic diagram of the TMR array 6 integrated on the flexible PI substrate 5. The TMR array is specifically composed of a 6×6 array and is connected by metal lines 7. At the same time, the TMR array 6 is connected to the back-end data processing through the DAQ cable interface 8 on the outside.

[0037] like Figure 3 As shown, the precision signal acquisition link adopts a Keithley joint architecture that includes an electrochemical control terminal and a magnetic signal monitoring terminal, specifically designed as follows: a) Electrochemical control terminal: Keithley 2400 source meter is used to drive the in-situ battery charging and discharging, so as to achieve microampere level control accuracy.

[0038] b) Magnetic signal monitoring end: The flexible polyimide TMR array transmits the differential output signal to the Keithley 2182A nanovolt meter through a double-shielded coaxial cable to achieve ultra-low noise acquisition at the nanovolt (nV) level.

[0039] c) Synchronization logic: The Keithley 2400 source meter and the Keithley 2182A nanovolt meter share the same reference ground (GND) to eliminate common-mode error, and achieve millisecond-level clock synchronization between the source meter and the nanovolt meter through the trigger signal bus.

[0040] d) Magnetic field excitation unit: An external magnetic field is provided by a programmable current source and a Helmholtz coil. The programmable current source provides a stable operating current to the coil. The Helmholtz coil provides a parallel and stable excitation magnetic field to the in-situ battery.

[0041] e) Data Acquisition System: Used to acquire data and decouple signals. A high-sampling-rate data acquisition card (DAQ) synchronously records the magnetic field fluctuations of each TMR channel. The intrinsic magnetic moment signal is extracted and stripped using a decoupling algorithm on the computer.

[0042] It should be noted that the magnetic field excitation unit, electrochemical control terminal and magnetic signal monitoring terminal are independent of each other. The Helmholtz coil is coupled to the in-situ battery through a magnetic field. The TMR array is used to perform non-contact measurement of the local magnetic field generated by the in-situ battery. There is no current series path between the units.

[0043] like Figure 4 The schematic diagram of the TMR array shown shows that the Vcc power supply pin 10, the NC empty pin 14, and the V+ output pin 12 are arranged sequentially on the same side centered on the magnetic sensitivity direction. Correspondingly, the V- output pin 11 and the GND ground pin 13 are arranged sequentially on the other side centered on the magnetic sensitivity direction. Among them, the Vcc power supply pin 10 is provided with a DC stable voltage by an external circuit, and the NC empty pin 14 is left floating.

[0044] The algorithm parsing module embeds an adaptive signal processing algorithm based on recursive least squares (RLS) to extract intrinsic magnetic moment signals from a strong background field. The extraction process of the intrinsic magnetic moment signal includes: a) Construct a physical model for subtracting the background field: ; in, To obtain the original magnetic field signal for testing, It is the current-space magnetic field coupling coefficient obtained through calibration; For the current moment The coil excitation current; The in-situ battery current-magnetic field coupling coefficient obtained through calibration; For the current moment The in-situ battery charge and discharge current, For the current moment to be sought The magnetic field signal caused by the intrinsic vertical spin magnetic moment of the material; For the current moment The background geomagnetic environment.

[0045] b) Dynamic decoupling: The algorithm synchronously acquires the current signal in real time and uses the pre-calibrated "current-space magnetic field transfer function" (i.e. the physical model used to subtract the background field) to remove the excitation magnetic field and current background field components from the original magnetic field signal in real time.

[0046] Based on the systematic design of the variable magnetic field excitation unit, in-situ detection array, precision signal acquisition link, and algorithm analysis module, this invention achieves several technological breakthroughs: 1) Physical separation of detection dimensions: The vertical path focuses on capturing the vertical spin magnetic moment signal accompanying the valence state evolution of active materials, rather than just detecting the external field; the horizontal path maximizes the identification of local magnetic distortion caused by dendrite growth; 2) Extremely high sensitivity: This method can utilize the high gain of TMR in the weak field region below 5000 Oe to achieve nT-level magnetic response detection; 3) Non-invasive in-situ imaging: Two-dimensional current distribution map and in-situ MH hysteresis loop evolution map can be obtained without dissecting the battery; 4) Industrial applicability: It can be compatible with commercial pouch and solid-state batteries, providing multi-dimensional data support for thermal runaway early warning and fast charging safety.

[0047] Furthermore, to facilitate understanding of the technical solution of this invention, this embodiment provides a detailed description of the specific implementation method for pre-conducting the characterization of the vertical intrinsic spin magnetic moment, specifically including: 1) In-situ battery assembly and environmental construction.

[0048] The electrode loaded with Fe3O4 transition metal oxide active material was cut into a rectangle of 2 cm × 3 cm, and assembled with a separator and lithium metal counter electrode using an aluminum-plastic film encapsulation process to form an in-situ pouch cell.

[0049] Nickel-plated copper wires are used to lead the positive and negative terminals out from inside the aluminum-plastic film, and heat sealing is performed to ensure that the battery interior is strictly isolated from air. The packaged battery is placed horizontally in the central uniform region of a pair of Helmholtz coils wound with high-purity oxygen-free copper to ensure that the magnetic field deviation is less than 1% during subsequent variable field scanning.

[0050] 2) High-precision Z-axis detection array bonding.

[0051] A high-density TMR sensor array was constructed on a flexible polyimide (PI) substrate using micro-nano fabrication technology. A TMR chip sensitive to the Z-axis magnetic field component and exhibiting high linearity was selected, and the array size was set from 4×4 to 20×20; in this embodiment, a 6×6 array was chosen.

[0052] Using a specially designed non-magnetic FR4 epoxy resin clamp, the sensor's sensitive surface is actively pressed onto the surface of the battery's aluminum-plastic film via a "cantilever beam" clamping process. The sensing distance is compressed to the sub-millimeter level (<0.5 mm) by a fine-tuning knob, and the intensity of the captured weak spin magnetic signal is increased by 1-2 orders of magnitude by utilizing the near-field gain effect of the magnetic dipole field (intensity proportional to 1 / r³).

[0053] 3) Synchronous excitation and variable field testing.

[0054] The battery's positive and negative terminals were connected to a Keithley 2400 source meter, and a constant current charge-discharge test was performed with a current density of 60 mA / g. Simultaneously, a Helmholtz coil was driven by a programmable current source to generate a triangular wave variable magnetic field with a frequency of 1 Hz and a scanning range of pm300 Oe. A unified trigger clock was used to ensure that the synchronization accuracy between the electrochemical charge-discharge steps and the magnetic field scanning steps was within milliseconds.

[0055] 4) Signal decoupling and MH curve reconstruction.

[0056] The output of the TMR array is connected to a Keithley 2182A nanovoltmeter via a dual-core shielded differential signal cable. The system acquires the raw total magnetic field signal in real time. It also incorporates the Recursive Least Squares (RLS) adaptive decoupling algorithm.

[0057] The algorithm is based on the real-time synchronously acquired coil excitation current and battery charging and discharging current The background interference field generated by the current is calculated and subtracted online. Finally, the pure atomic valence state (Fe) of the material is extracted. 3+ / Fe 2+ The intrinsic spin magnetic response signal in the vertical direction induced by the evolution (i.e., the magnetic field signal caused by the intrinsic vertical spin magnetic moment of the material). and compared it with the scanning field Correlation, with real-time external scanning magnetic field The x-axis represents the extracted intrinsic magnetic flux density. Or converted magnetic moment Using the ordinate (Y-axis), the in-situ hysteresis loop evolution diagrams under different states of charge (SOC) were reconstructed. Specifically, an in-situ pouch cell (with lithium metal as the counter electrode) assembled from electrodes (2 cm × 3 cm) loaded with Fe3O4 transition metal oxide active material was placed in the central uniform region of a Helmholtz coil wound with high-purity oxygen-free copper. The detection array used a 6 × 6 high-density Z-axis TMR chip, clamped by a non-magnetic FR4 epoxy resin clamp, with the sensing distance controlled within 0.5 mm. A Keithley 2400 source meter was used to drive charging and discharging at a current density of 60 mA / g; a Keithley 2182A nanovoltmeter synchronously acquired the TMR differential output. The system was subjected to a weak scanning magnetic field ranging from 0-5000 Oe, with a scanning frequency of 1 Hz.

[0058] Furthermore, to facilitate understanding of the technical solution of this invention, this embodiment provides a detailed description of the implementation process for pre-performing local current heterogeneity imaging and anomaly monitoring, specifically including: 1) Lateral excitation field layout switching: The Helmholtz coil is switched from a vertical position to a left-right lateral position on the battery, so that the coil axis is parallel to the battery plane. In this layout, the uniform scanning magnetic field generated by the coil mainly propagates along the direction of the battery plane, aiming to enhance the ability to capture small physical structural anomalies in the plane by exciting the in-plane magnetic response.

[0059] 2) Multi-channel in-plane magnetic imaging acquisition: A two-dimensional TMR array integrated on the FPCB covers the core reaction area of ​​the battery. In this layout, the sensor array synchronously records the magnetic field fluctuations of each channel through a high sampling rate data acquisition card (DAQ). During battery cycling, the system not only monitors the change in magnetic moment in the vertical direction, but also focuses on capturing the edge leakage magnetic field component caused by in-plane current unevenness.

[0060] 3) Current Density Inversion and Safety Location: In the later stages of charge-discharge cycles, when localized uneven reactions or lithium deposition tendencies occur inside the battery, the system initiates a real-time reconstruction procedure. Based on the Biot-Savart law, the magnetic imaging data captured by the array is inverted into a two-dimensional current density distribution map. By comparing the "expected uniform field model" with the "real-time measured field," the system accurately identifies local magnetic field strength "abrupt" points caused by lithium dendrite deposition or local short circuits. These expected magnetic field strength peaks (i.e., simulated abnormal jump points) can be used to achieve micron-level spatial resolution location of internal battery safety hazards, providing crucial physical criteria for thermal runaway early warning.

[0061] Example 2 This embodiment discloses a weak field detection method for in-situ cells of a TMR array based on a bidirectional magnetic field.

[0062] A weak field detection method for in-situ cells of TMR arrays based on bidirectional magnetic fields includes: The packaged battery is placed horizontally in the central uniform magnetic field region of a pair of Helmholtz coils, and the coils are arranged according to the corresponding magnetization path selected according to the detection target. A two-dimensional array of tunnel magnetoresistive chips integrated on a substrate is actively pressed onto the battery surface using a non-magnetic pressure fixture; The positive and negative terminals of the battery are connected to a Keithley source meter for constant current charge and discharge test. At the same time, a Helmholtz coil is driven by a programmable current source to generate a variable magnetic field. A unified trigger clock is used to synchronize the charge and discharge steps with the magnetic field scanning steps. The collected data is embedded into the analytical module based on the recursive least squares adaptive signal processing algorithm to establish a physical model for subtracting the background field. The extracted intrinsic spin magnetic moment signal is correlated with the scanning magnetic field strength to achieve in-situ weak field hysteresis loop detection of the battery.

[0063] Furthermore, in a vertical magnetization path, the coil is located on the top and bottom surfaces of the battery; in an in-plane magnetization path, the coil is located on the left and right sides of the battery.

[0064] Furthermore, the output of the tunnel magnetoresistive array is connected to a Keithley nanovoltmeter via a double-shielded coaxial cable to acquire the original magnetic field signal in real time, and simultaneously acquire the coil excitation current and battery current.

[0065] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A weak field detection system for in-situ cells using a bidirectional magnetic field TMR array, characterized in that, include: Variable magnetic field excitation unit, in-situ detection array, precision signal acquisition link and algorithm analysis module; The variable magnetic field excitation unit includes a pair of Helmholtz coils arranged in a bidirectional manner. In the vertical magnetization path, the pair of Helmholtz coils are horizontally arranged on the upper and lower surfaces of the in-situ cell to generate a uniform scanning magnetic field that passes vertically through the plane of the in-situ cell. In the in-plane magnetization path, the pair of Helmholtz coils are respectively arranged on the left and right sides of the in-situ cell to decouple from the current magnetic field signal by modulating the in-plane response of the magnetic moment. The in-situ detection array is integrated on a flexible polyimide substrate, and the corresponding sensitive surface is actively pressed onto the surface of the in-situ battery by a non-magnetic pressure tool. The precision signal acquisition link adopts a Keithley joint architecture that includes an electrochemical control terminal and a magnetic signal monitoring terminal; The differential output of the TMR is connected to the Keithley nanovoltmeter used at the magnetic signal monitoring end via a double-shielded coaxial cable. The algorithm analysis module embeds an adaptive signal processing algorithm to extract the intrinsic magnetic moment signal from the strong background field, thereby enabling in-situ battery weak-field hysteresis loop detection. Specifically, it constructs a physical model for subtracting the background field. Simultaneously, it acquires current signals in real time and uses a pre-calibrated current-space magnetic field transfer function to remove the excitation magnetic field and current background field components from the original magnetic field signal in real time. The physical model is expressed as follows: ； In the formula, To obtain the original magnetic field signal for testing, It is the current-space magnetic field coupling coefficient obtained through calibration; For the current moment The coil excitation current; The in-situ battery current-magnetic field coupling coefficient obtained through calibration; For the current moment The in-situ battery charge and discharge current, For the current moment to be sought The magnetic field signal caused by the intrinsic vertical spin magnetic moment of the material; For the current moment The background geomagnetic environment.

2. The in-situ weak field detection system for TMR array batteries based on a bidirectional magnetic field as described in claim 1, characterized in that, The in-situ detection array uses Z-axis sensitive TMR chips to construct a two-dimensional array, meaning that each tunnel magnetoresistive chip is sensitive to the Z-axis magnetic field component.

3. The in-situ weak field detection system for TMR array batteries based on a bidirectional magnetic field as described in claim 1, characterized in that, The electrochemical control terminal uses a Keithley 2400 source meter to drive the in-situ battery charging and discharging to control the charging and discharging accuracy; the magnetic signal monitoring terminal uses a Keithley 2182A nanovolt meter to collect nanovolt-level ultra-low noise data; the Keithley 2400 source meter and the Keithley 2182A nanovolt meter are synchronized by a trigger signal bus.

4. The in-situ weak field detection system for TMR array batteries based on a bidirectional magnetic field as described in claim 1, characterized in that, The algorithm analysis module is also used to: under the vertical magnetization path, correlate the extracted intrinsic spin magnetic moment signal with the scanning magnetic field strength to reconstruct the in-situ hysteresis loop evolution diagram under different charge states.

5. The in-situ weak field detection system for TMR array batteries based on a bidirectional magnetic field as described in claim 1, characterized in that, The algorithm analysis module is also used to: under the in-plane magnetization path, invert the magnetic field distribution collected by the tunnel magnetoresistive array into a two-dimensional current density distribution map based on the Biot-Savart law, and locate the local magnetic field strength abrupt change point by comparing it with the expected uniform field model; wherein, the local magnetic field strength abrupt change point corresponds to the local current anomaly caused by lithium dendrite deposition or local short circuit, which is used to achieve micron-level spatial resolution for locating safety hazards.

6. A method for weak field detection of in-situ TMR array cells based on a bidirectional magnetic field, used in the weak field detection system for in-situ TMR array cells as described in any one of claims 1-5, characterized in that, include: The packaged in-situ battery is placed horizontally in the central uniform magnetic field region of a pair of Helmholtz coils, and the coils are arranged according to the corresponding magnetization path selected according to the detection target. A two-dimensional array of tunnel magnetoresistive chips integrated on a substrate is actively pressed onto the surface of the in-situ battery using a non-magnetic pressure fixture; The positive and negative terminals of the in-situ battery were connected to a Keithley source meter for constant current charge and discharge testing. At the same time, a variable magnetic field was generated by driving a Helmholtz coil through a programmable current source, and a unified trigger clock was used to synchronize the charge and discharge steps with the magnetic field scanning steps. The collected data is embedded into the analytical module based on the recursive least squares adaptive signal processing algorithm to establish a physical model for subtracting the background field. The extracted intrinsic spin magnetic moment signal is correlated with the scanning magnetic field strength to achieve in-situ weak field hysteresis loop detection of the battery.

7. The method for weak field detection of in-situ TMR array cells based on bidirectional magnetic field as described in claim 6, characterized in that, In a vertical magnetization path, the coil is located on the top and bottom surfaces of the in-situ cell; in an in-plane magnetization path, the coil is located on the left and right sides of the in-situ cell.

8. The method for weak field detection of in-situ TMR array cells based on bidirectional magnetic field as described in claim 6, characterized in that, The output of the tunnel magnetoresistive array is connected to a Keithley nanovoltmeter via a double-shielded coaxial cable to acquire the original magnetic field signal in real time, and simultaneously acquire the coil excitation current and the in-situ battery current.

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