A multi-feature detection device and method for lithium battery thermal runaway based on fiber Bragg grating

Abstract

The present invention discloses a multi-feature detection device and method for lithium battery thermal runaway based on fiber grating. The device includes a micro Bragg grating fiber assembly, a laser spectrometer, a multifunctional optical fiber, a laser emitter and an optical fiber signal processor. The micro Bragg grating fiber assembly is arranged in a spiral between the positive electrode and the diaphragm or between the negative electrode and the diaphragm, and the modulation spectrometer glass layer is at a 45° angle to the fiber core. The multi-feature detection device for lithium battery thermal runaway can be used to detect very early characteristic values ​​of thermal runaway, including hydrogen, temperature, and pressure. Compared with the prior art, the present invention has high measurement accuracy and multiple measurement dimensions. It can obtain the spatial distribution characteristics of the internal characteristic parameters of the battery, accurately obtain the spatial resolution information inside the lithium battery thermal runaway process, and provide a more three-dimensional and reliable basis for the determination of thermal runaway.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a device and method for detecting internal multi-features of thermal runaway of lithium batteries based on fiber gratings. Background Art

[0002] Lithium batteries are now widely used in new energy power, electrochemical energy storage, and digital electronics. As the demand for lithium battery energy density increases, safety issues are becoming increasingly prominent. Taking lithium-ion new energy vehicles as an example, fire and explosion accidents caused by thermal runaway of power batteries have been frequently reported, making the detection and early warning of thermal hazards particularly important. Currently, battery management systems are widely used to monitor real-time temperature, electrical signals, and other data of lithium battery modules. However, the temperature rise and gas production in the early stages of thermal runaway cannot be effectively detected.

[0003] Existing online detection technologies for lithium battery temperature, gas, etc. have certain limitations. For example, the lithium-ion battery and internal temperature measurement method published in Authorization Announcement No. CN102593545, the cylindrical lithium-ion battery temperature monitoring system and method published in Authorization Announcement No. CN 111211377, and the lithium-ion power battery internal temperature testing method and testing system published in Authorization Announcement No. CN111397751 use thermocouples to obtain the internal and external temperatures of lithium batteries. This contact temperature measurement method has many limitations in actual lithium battery embedding. In addition, the lithium battery internal temperature measurement method and device published in Authorization Announcement No. CN105628248 reflects the internal temperature of the lithium battery based on the color change of the packaged temperature test paper. Its temperature accuracy and test reliability need to be improved. The dynamic online measurement method for the internal temperature of lithium-ion batteries published with authorization announcement number CN110221212 provides a method for calculating the temperature changes of new energy power lithium batteries in brakes based on the dynamic impedance phase angle. The application scenarios of this invention are relatively limited, and it is also impossible to know the changes in the internal parameters of the lithium battery during the thermal runaway process.

[0004] With the development of fiber Bragg Bragg grating (FBG) technology, lithium battery internal parameter detection technology based on FBG has gradually been applied. For example, the single-cell temperature, pressure, and gas composite sensing fiber probe, system, and application published under authorization announcement number CN113218427 uses FBG sensors to detect the external temperature, pressure, and gas of single cells within a battery pack. However, it cannot effectively detect the early characteristics of thermal runaway, especially the lack of detection specifically for hydrogen production in the early stages of thermal runaway. The FBG-based integrated online monitoring system and method for the internal multi-parameters of energy storage batteries published under authorization announcement number CN113466701 has FBG sensors arranged between the top shell and the battery cell, failing to achieve real-time online detection of the positive and negative electrode material layers of the battery. Summary of the Invention

[0005] To address the above-mentioned problems, the present invention proposes a multi-feature detection device and method for lithium battery thermal runaway based on fiber Bragg grating (FBG). The device uses the changes in the reflected light signal at the measuring point to calculate the temperature, pressure, and product hydrogen concentration inside the lithium battery, and has the characteristics of non-contact, online, and high reliability.

[0006] The present invention proposes a multi-feature internal detection device for lithium battery thermal runaway based on fiber Bragg gratings (FBGs), comprising a micro Bragg grating (MBR) fiber assembly, a laser spectrometer connected via optical fibers, and a laser emitter and fiber signal processor. The MBR fiber assembly comprises a core, a fiber Bragg grating (FBG), a cladding, a modulated spectrometer glass layer, a longitudinal measurement protection window, a transverse measurement protection window, and a coating. The MBR fiber assembly is arranged in a spiral pattern between the positive electrode and the diaphragm or between the negative electrode and the diaphragm. The laser emitter and fiber signal processor generates a continuous laser beam, which propagates along the optical fiber to the laser spectrometer. After spectrometry, the laser enters the MBR fiber assembly, propagates along the core, passes through the Bragg grating, is partially reflected, and another portion reaches the modulated spectrometer glass layer. After spectrometry, one portion passes through the longitudinal measurement protection window and another portion passes through the transverse measurement protection window. The optical signal reflected by the Bragg grating is received by the laser emitter and fiber signal processor, and the degree of deviation of the center wavelength of the reflected light received by the laser emitter and fiber signal processor reflects the internal temperature, pressure, and hydrogen concentration of the battery.

[0007] Furthermore, the fiber core and cladding are made of quartz material, the longitudinal measurement protection window and the transverse measurement protection window are made of high-temperature resistant and corrosion-resistant special glass, and the diameter of the longitudinal measurement protection window is less than 90 μm.

[0008] Furthermore, the central wavelength of the fiber core is 1550 nm.

[0009] Furthermore, the modulation splitting glass layer forms an angle of 45° with the fiber core, and the splitting ratio is 1:(N+i-1), where N is the number of longitudinal measurement protection windows, and i is the number of the current longitudinal measurement protection window.

[0010] Furthermore, the coating is a film containing palladium metal or tungsten trioxide material.

[0011] The present invention also proposes a multi-feature detection method for internal thermal runaway of lithium batteries based on fiber Bragg gratings, comprising the following steps: an emission step, in which a laser emission device emits a laser, and the laser propagates along the optical fiber through a laser spectrometer to reach a micro Bragg grating optical fiber assembly; a receiving step, in which an optical fiber signal processor receives two sets of different optical signals and demodulates the optical signals; a judgment step, in which a data acquisition terminal receives the optical signal of a photodetector, and the temperature, pressure and hydrogen concentration at the measuring point cause deformation of the optical fiber, and the offset of the central wavelength of the optical signal can be analyzed to obtain the temperature, pressure and hydrogen concentration.

[0012] Furthermore, in the above-mentioned fiber Bragg grating-based internal multi-feature detection method for lithium battery thermal runaway, the light beam emitted by the detection light source passes through a laser spectrometer and propagates through a multifunctional optical fiber to a measurement area with a micro Bragg grating optical fiber assembly. The hydrogen concentration will affect the shedding / addition of the coating (depending on the coating properties), generating axial strain; the temperature will cause thermal expansion and contraction as well as pressure, thereby affecting the central wavelength of the reflected light signal passing through the grating. The influence of the three on the central wavelength of the grating can be expressed by the following formula:

[0013]

[0014] Where, P e is the effective elastic-optical coefficient of the optical fiber, Δε is the axial strain of the micro Bragg grating optical fiber assembly, α f is the thermal expansion coefficient of the optical fiber material, ξ is the thermo-optical coefficient, α sub is the thermal expansion coefficient of the thermo-optical coefficient coating;

[0015] The axial strain Δε of the micro Bragg grating fiber assembly is related to the hydrogen concentration and pressure in the environment. When the hydrogen concentration increases, the axial stress generated by the coating increases. When the pressure increases, the micro Bragg grating fiber assembly first generates radial strain and then generates axial strain. The relationship is described as follows:

[0016]

[0017] Where K p is the pressure sensitivity of the sensor, which can be obtained through experimental calibration; ΔP is the pressure change at the measuring point; is the change in hydrogen concentration at the measuring point; The expressions of axial stress and hydrogen concentration are obtained through experimental calibration.

[0018] Furthermore, in order to simultaneously obtain the three quantities of temperature, pressure and hydrogen concentration, three micro Bragg grating fiber assemblies (assemblies 1, 2, and 3) need to be used simultaneously. The micro Bragg grating fiber does not have a coating added. Micro Bragg grating fiber assembly 1 senses positive stress, and micro Bragg grating fiber assembly senses negative stress. In this way, the temperature, pressure and hydrogen concentration are obtained by solving the simultaneous equations.

[0019]

[0020] Where λ B,1 ,λ B,2 ,λ B,3 are the original reflected light wavelengths of micro Bragg grating fiber components 1, 2, and 3, respectively, and Δλ B,1 ,Δλ B,2 ,Δλ B,3 are the center wavelength offsets of the reflected light from the micro Bragg grating fiber assemblies 1, 2, and 3, respectively.

[0021] Beneficial effects

[0022] To address the limitations of online lithium battery testing, this invention innovatively designs fiber Bragg gratings (FBGs) to adapt the spiral arrangement of lithium battery positive and negative electrode materials. This allows for real-time online monitoring of temperature, pressure, and gas flow during thermal runaway between the positive and negative electrodes, and between the positive and negative electrodes, respectively. Compared to existing technologies, this invention offers high measurement accuracy and multiple measurement dimensions. It can determine the spatial distribution of characteristic parameters within the battery, accurately capturing spatially resolved information within the lithium battery thermal runaway process, and providing a more comprehensive and reliable basis for determining thermal runaway. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the arrangement of a micro Bragg grating fiber assembly in an embodiment of the present invention;

[0024] Figure 2 A simplified diagram of the device structure in an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of the overall structure of a micro Bragg grating fiber assembly;

[0026] Figure 4 Schematic diagram of the internal structure of a micro Bragg grating fiber assembly

[0027] Explanation of the marks in the figure: 1 micro Bragg grating fiber assembly; 1-1 fiber core; 1-2 fiber Bragg grating; 1-3 cladding; 1-4 modulation and splitting glass layer; 1-5 longitudinal measurement protection window; 1-6 transverse measurement protection window; 1-7 coating; 2 laser spectrometer; 3 multifunctional optical fiber; 4 laser emission and optical fiber signal processor. DETAILED DESCRIPTION

[0028] The present invention will be described in more detail below with reference to the accompanying drawings and in conjunction with embodiments. It should be noted that the embodiments of the present invention and the features therein may be combined with each other unless they conflict. It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The specific examples are described as follows:

[0030] like Figure 2 , 3 and 4 show a multi-feature internal detection device for lithium battery thermal runaway based on fiber Bragg gratings. The device comprises: a micro Bragg grating fiber assembly 1, a laser spectrometer 2 connected via optical fibers, and a laser emission and fiber signal processor 4. The micro Bragg grating fiber assembly 1 comprises a fiber core 1-1, a fiber Bragg grating 1-2; a cladding 1-3; a modulation spectrometer glass layer 1-4; a longitudinal measurement protection window 1-5; a transverse measurement protection window 1-6; and a coating 1-7. The fiber core 1-1 and cladding 1-3 are primarily made of quartz glass. The longitudinal and transverse measurement protection windows 1-5 and 1-6 must be made of high-temperature and corrosion-resistant special glass, with the longitudinal observation window diameter being less than 90 μm. The coating must be a film containing palladium metal or tungsten trioxide, such as a 520 nm Pd / Ag composite film.

[0031] like Figure 1 As shown, the micro Bragg grating fiber assembly 1 is arranged in a spiral between the positive electrode material A and the diaphragm C or between the negative electrode material B and the diaphragm C, and is in direct contact with the electrolyte between the electrodes, as shown in FIG. Figure 1 The laser emission and fiber optic signal processor 4 generates a continuous laser beam. The laser propagates along the optical fiber and reaches the laser spectrometer 2. After being split, the laser enters the micro Bragg grating fiber assembly 1, propagates along the fiber core 1-1, and a portion of it is reflected by the Bragg grating 1-2. The other portion reaches the modulated spectrometer glass layer 1-4 and is split according to a splitting ratio of 1:(N+i-1). One portion will pass through the longitudinal measurement protection window 1-5, and the other portion will pass through the transverse measurement protection window 1-6. The optical signal reflected by the Bragg grating is received by the laser emission and fiber optic signal processor 4.

[0032] The degree of deviation of the center wavelength of the reflected light received by the laser emission and the optical fiber signal processor 4 reflects the temperature, pressure, and hydrogen concentration. Changes in the temperature, pressure, and hydrogen concentration inside the battery will cause the grating pitch of the Bragg grating to change, ultimately affecting the center wavelength of the received reflected light. The relationship between the two is shown in the following expression:

[0033]

[0034] Where, P e is the effective elastic-optical coefficient of the optical fiber, Δε is the axial strain of the micro Bragg grating optical fiber assembly, α f is the thermal expansion coefficient of the optical fiber material, ξ is the thermo-optical coefficient, α sub is the thermal expansion coefficient of the thermo-optical coating.

[0035] The axial strain Δε of the micro Bragg grating fiber assembly is related to the hydrogen concentration and pressure in the environment. When the hydrogen concentration increases, the axial stress generated by the coating increases. When the pressure increases, the micro Bragg grating fiber assembly first generates radial strain and then generates axial strain. The relationship is described as follows:

[0036]

[0037] Where K p is the pressure sensitivity of the sensor, which can be obtained through experimental calibration; ΔP is the pressure change at the measuring point; is the change in hydrogen concentration at the measuring point; The expressions of axial stress and hydrogen concentration are obtained through experimental calibration.

[0038] In order to simultaneously obtain the three quantities of temperature, pressure and hydrogen concentration, three micro Bragg grating fiber assemblies (assemblies 1, 2, and 3) need to be used simultaneously. Micro Bragg grating fiber 2 is not coated, micro Bragg grating fiber assembly 1 senses positive stress, and micro Bragg grating fiber assembly 3 senses negative stress. In this way, the temperature, pressure, and hydrogen concentration can be obtained by solving the simultaneous equations.

[0039]

[0040] Where λ B,1 ,λ B,2 ,λ B,3 are the original reflected light wavelengths of micro Bragg grating fiber components 1, 2, and 3, respectively, and Δλ B,1 ,Δλ B,2 ,Δλ B,3 are the center wavelength offsets of the reflected light from the micro Bragg grating fiber assemblies 1, 2, and 3, respectively.

[0041] Ultimately, online real-time monitoring of temperature, pressure and hydrogen concentration data based on the distribution of lithium battery structure can be achieved. Once thermal runaway occurs, the failure area inside the lithium battery can be quickly located, providing data support for subsequent failure analysis.

[0042] The present invention proposes a multi-feature detection method for internal thermal runaway of a lithium battery based on fiber Bragg grating, comprising the following steps: an emission step, in which a laser emission device emits a laser, and the laser propagates along the optical fiber through a laser spectrometer to reach a micro Bragg grating optical fiber assembly; a receiving step, in which an optical fiber signal processor receives two sets of different optical signals and demodulates the optical signals; and a judgment step, in which a data acquisition terminal receives the optical signal of a photodetector, and the temperature, pressure and hydrogen concentration at the measuring point cause the optical fiber to deform. The offset of the central wavelength of the optical signal can be analyzed to obtain the temperature, pressure and hydrogen concentration.

[0043] Furthermore, in the above-mentioned multi-feature detection method for lithium battery thermal runaway based on fiber Bragg grating, the light beam emitted by the detection light source passes through a laser spectrometer and propagates through a multifunctional optical fiber to the measurement area with a micro Bragg grating fiber assembly. The hydrogen concentration will affect the shedding / addition of the coating (depending on the coating properties), generating axial strain; the temperature will cause thermal expansion and contraction as well as pressure, thereby affecting the center wavelength of the reflected light signal passing through the grating. The influence of the three on the center wavelength of the grating can be expressed by the following formula:

[0044]

[0045] Where, P e is the effective elastic-optical coefficient of the optical fiber, Δε is the axial strain of the micro Bragg grating optical fiber assembly, α f is the thermal expansion coefficient of the optical fiber material, ξ is the thermo-optical coefficient, α sub is the thermal expansion coefficient of the thermo-optical coating.

[0046] The axial strain Δε of the micro Bragg Grating fiber assembly is related to the hydrogen concentration and pressure in the environment. When the hydrogen concentration increases, the axial stress generated by the coating increases; when the pressure increases, the micro Bragg Grating fiber assembly first generates radial strain and then axial strain. The relationship is described as follows:

[0047]

[0048] Where K p is the pressure sensitivity of the sensor, which can be obtained through experimental calibration; ΔP is the pressure change at the measuring point; is the change in hydrogen concentration at the measuring point; The expressions of axial stress and hydrogen concentration are obtained through experimental calibration.

[0049] In order to simultaneously obtain the three quantities of temperature, pressure and hydrogen concentration, three micro Bragg grating fiber assemblies (assemblies 1, 2, and 3) need to be used simultaneously. Micro Bragg grating fiber 2 is not coated, micro Bragg grating fiber assembly 1 senses positive stress, and micro Bragg grating fiber assembly 3 senses negative stress. In this way, the temperature, pressure, and hydrogen concentration can be obtained by solving the simultaneous equations.

[0050]

[0051] Where λ B,1 ,λ B,2 ,λ B,3 are the original reflected light wavelengths of micro Bragg grating fiber components 1, 2, and 3, respectively, and Δλ B,1 ,Δλ B,2 ,Δλ B,3 are the center wavelength offsets of the reflected light from the micro Bragg grating fiber assemblies 1, 2, and 3, respectively.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-feature internal detection device for lithium battery thermal runaway based on fiber Bragg grating, characterized by: The invention comprises a micro Bragg grating fiber assembly, a laser spectrometer connected by optical fibers, a laser emitter, and an optical fiber signal processor; the micro Bragg grating fiber assembly comprises a fiber core, a fiber Bragg grating, a cladding, a modulation spectrometer glass layer, a longitudinal measurement protection window, a transverse measurement protection window, and a coating; the micro Bragg grating fiber assembly is arranged in a spiral between the positive electrode and the diaphragm or between the negative electrode and the diaphragm; The laser emission and fiber optic signal processor generates a continuous laser beam, which propagates along the optical fiber to reach the laser spectrometer. After the laser is split, it enters the micro Bragg grating fiber assembly, propagates along the fiber core, passes through the Bragg grating, and is partially reflected, and the other part reaches the modulated spectrometer glass layer. After the laser is split, one part passes through the longitudinal measurement protection window, and the other part passes through the transverse measurement protection window. The light signal reflected by the Bragg grating is received by the laser emission and fiber optic signal processor. The degree of deviation of the central wavelength of the reflected light received by the laser emission and fiber optic signal processor reflects the internal temperature, pressure and hydrogen concentration of the battery. Changes in the internal temperature, pressure and hydrogen concentration of the battery will cause the grating pitch of the fiber Bragg grating to change, which ultimately affects the central wavelength of the received reflected light. The influence of the central wavelength of the grating is expressed by the following formula: Where λ B Original reflected light center wavelength, Δλ B are the center wavelength offset of the reflected light, P e is the effective elastic-optical coefficient of the optical fiber, Δε is the axial strain of the micro Bragg grating optical fiber assembly, α f is the thermal expansion coefficient of the optical fiber material, ξ is the thermo-optical coefficient, α sub is the thermal expansion coefficient of the thermo-optical coefficient coating; The axial strain Δε of the micro Bragg grating fiber assembly is related to the hydrogen concentration and pressure in the environment. When the hydrogen concentration increases, the axial stress generated by the coating increases. When the pressure increases, the micro Bragg grating fiber assembly first generates radial strain and then generates axial strain. The relationship is described as follows: Where K p is the pressure sensitivity of the sensor, obtained through experimental calibration; ΔP is the pressure change at the measuring point; is the change in hydrogen concentration at the measuring point; The expressions for axial stress and hydrogen concentration were obtained through experimental calibration. Three uncoated micro Bragg grating fiber assemblies were used. One micro Bragg grating fiber assembly sensed positive stress, while the other sensed negative stress. Simultaneously, three sets of equations were used to solve the internal temperature, pressure, and hydrogen concentration of the battery. Where λ B,1 ,λ B,2 ,λ B,3 are the original reflected light wavelengths of the three micro Bragg grating fiber assemblies, Δλ B,1 ,Δλ B,2 ,Δλ B,3 are the center wavelength offsets of the reflected light from the three micro Bragg grating fiber assemblies.

2. The multi-feature internal detection device for lithium battery thermal runaway based on fiber Bragg grating according to claim 1, characterized in that: The fiber core and cladding are made of quartz material, the longitudinal measurement protection window and the transverse measurement protection window are made of high-temperature resistant and corrosion-resistant special glass, and the diameter of the longitudinal measurement protection window is less than 90 μm.

3. The multi-feature internal detection device for lithium battery thermal runaway based on fiber Bragg grating according to claim 1, characterized in that: The central wavelength of the fiber core is 1550 nm.

4. The multi-feature internal detection device for lithium battery thermal runaway based on fiber Bragg grating according to claim 1, characterized in that: The modulation splitting glass layer forms an angle of 45° with the fiber core, and the splitting ratio is 1:(N+i-1), where N is the number of longitudinal measurement protection windows and i is the number of the current longitudinal measurement protection window.

5. The multi-feature internal detection device for lithium battery thermal runaway based on fiber Bragg grating according to claim 1, characterized in that: The coating is a film containing palladium metal or tungsten trioxide material.

6. The method for detecting internal multi-features of thermal runaway of lithium batteries based on fiber Bragg grating according to claim 1, characterized in that: The following steps are involved: 1) an emission step, wherein the laser emitting device emits a laser, and the laser propagates along the optical fiber through the laser splitting device to reach the micro Bragg grating optical fiber assembly; 2) Receiving step: the optical fiber signal processor receives two different sets of optical signals and demodulates the optical signals; 3) Judgment step: The data acquisition terminal receives the optical signal from the photodetector. The temperature, pressure and hydrogen concentration at the measuring point cause the optical fiber to deform. The offset of the central wavelength of the optical signal is analyzed to obtain the temperature, pressure and hydrogen concentration.

7. The method for detecting internal multi-features of thermal runaway of lithium batteries based on fiber Bragg grating according to claim 6, characterized in that: The light beam emitted by the detection light source passes through the laser spectrometer and propagates through the optical fiber to the measurement area with the micro Bragg grating fiber assembly. The hydrogen concentration affects the shedding / addition of the coating, generating axial strain. The temperature causes thermal expansion and contraction as well as pressure, which in turn affects the center wavelength of the reflected light signal passing through the grating. The influence of the center wavelength of the grating is expressed by the following formula: Where, P e is the effective elastic-optical coefficient of the optical fiber, Δε is the axial strain of the micro Bragg grating optical fiber assembly, α f is the thermal expansion coefficient of the optical fiber material, ξ is the thermo-optical coefficient, α sub is the thermal expansion coefficient of the thermo-optical coefficient coating; The axial strain Δε of the micro Bragg grating fiber assembly is related to the hydrogen concentration and pressure in the environment. When the hydrogen concentration increases, the axial stress generated by the coating increases. When the pressure increases, the micro Bragg grating fiber assembly first generates radial strain and then generates axial strain. The relationship is described as follows: Where K p is the pressure sensitivity of the sensor, obtained through experimental calibration; ΔP is the pressure change at the measuring point; is the change in hydrogen concentration at the measuring point; The expressions of axial stress and hydrogen concentration are obtained through experimental calibration.

8. The method for detecting internal multi-features of thermal runaway of lithium batteries based on fiber Bragg grating according to claim 7, characterized in that: Three micro Bragg grating fiber assemblies are used simultaneously. The micro Bragg grating fiber does not have a coating. The micro Bragg grating fiber assembly senses positive stress and the micro Bragg grating fiber assembly senses negative stress. The temperature, pressure, and hydrogen concentration are obtained by solving the simultaneous equations: Where λ B,1 ,λ B,2 ,λ B,3 are the original reflected light wavelengths of the three micro Bragg grating fiber assemblies, Δλ B,1 ,Δλ B,2 ,Δλ B,3 are the center wavelength offsets of the reflected light from the three micro Bragg grating fiber assemblies.

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