A multi-physical quantity measurement system for lithium batteries

Abstract

The application provides a lithium battery multi-physical quantity measurement system in the field of lithium battery physical quantity measurement, and specifically comprises a to-be-measured optical fiber, a pump laser, an optical amplifier, a probe light path, an intensity modulator, a fourth coupler, a wavelength division multiplexer, a measurement interferometer, an auxiliary interferometer, a data acquisition card and an upper computer; the application combines the fiber-optic photothermal spectroscopy system and the OFDR together, and the two systems share the pump laser, and the data upper computer is also shared; the FP cavity for gas concentration measurement and the FUT are connected together, wherein the photothermal spectroscopy system for gas concentration measurement usually uses 1550nm light waves for detection, and the OFDR system adopts a pump light system for detection, and the light wave ranges of the two do not interfere with each other.

Description

Technical Field

[0001] This invention relates to the field of lithium battery physical quantity measurement, and in particular to a lithium battery multi-physical quantity measurement system. Background Technology

[0002] Lithium-ion batteries are receiving increasing attention as key components. Compared to other chemical power sources, lithium-ion batteries offer advantages such as long storage and cycle life, high charge / discharge rates, high energy density, low environmental pollution, and a wide operating range. They are widely used in new energy vehicles, smartphones, and intelligent robots, showing great promise. However, lithium-ion batteries have consistently faced the challenge of thermal runaway during use, caused by mechanical abuse, electrical abuse, and thermal abuse. Especially in applications requiring high-capacity and large-volume batteries, such as new energy vehicles, high-rate charging and discharging of lithium-ion batteries inevitably generates a large amount of heat. In confined spaces, this heat can easily accumulate, leading to thermal runaway. This can result in battery failure, combustion, or even explosion, causing significant property damage and personal injury. Therefore, monitoring the thermal effects of lithium-ion batteries and providing early warnings of thermal runaway is a crucial aspect of ensuring their safe use.

[0003] Currently, commercially available lithium-ion battery modules primarily rely on Battery Management Systems (BMS) for battery monitoring. These systems use various embedded electrical sensors to acquire parameters such as voltage, current, and temperature at specific nodes within the battery module. Combined with specific signal processing algorithms, they determine the battery's State of Charge (SOC) and State of Health (SOH), thereby assessing the overall thermal state of the battery. When the BMS detects a thermal anomaly, it can take timely measures, including shutting down the power and activating the cooling system. However, current lithium-ion battery BMS systems have some limitations. For example, they can only acquire voltage, current, and temperature information from a limited number of points, making it difficult to obtain overall battery status information; the monitored information is only the surface state of the battery, failing to monitor crucial information within the battery's interior where thermal runaway first occurs; and the monitored physical quantities are relatively limited. For instance, existing BMS systems lack the technical means to sense the gas composition and concentration, which are crucial for predicting battery thermal runaway. Therefore, some researchers have proposed that one of the future directions for the development of intelligent lithium battery BMS systems is internal in-situ, multi-dimensional, and multi-point monitoring methods.

[0004] At present, BMS has the following shortcomings when monitoring lithium batteries: (1) Limited measurement data points. In many cases, thermal runaway begins in a local area and then spreads to the entire battery pack. Limited measurement points cannot detect thermal runaway in time; (2) BMS sensors can only be deployed on the battery surface. Most thermal runaway problems first occur inside the battery, and there is a certain lag or no conduction to the surface; (3) BMS acquires multi-dimensional electrical quantity information. In thermal runaway, changes in mechanical quantities can also provide effective information. Existing literature shows that before thermal runaway occurs, the surface strain value of the lithium battery is abnormal. This value is linearly correlated with SOH and can predict the occurrence of thermal runaway earlier than temperature data. Summary of the Invention

[0005] This application aims to at least partially solve one of the technical problems in the related art. Embodiments of the present invention provide a multi-physical quantity measurement system for lithium batteries, improving the efficiency of measuring the physical quantities of lithium batteries. The solution is as follows:

[0006] A multi-physical quantity measurement system for lithium batteries, comprising:

[0007] The optical fiber under test is connected to the lithium battery under test.

[0008] A pump laser, the output of which is connected to an optical amplifier and a fourth coupler via the third coupler;

[0009] An optical amplifier, the output of which is connected to the intensity modulator;

[0010] A detection optical path is provided, which is used to emit detection light and is connected to the wavelength division multiplexer, the intensity modulator, and the host computer.

[0011] An intensity modulator, the output of which is connected in sequence to an isolator, a first coupler and a wavelength division multiplexer, wherein the intensity modulator modulates the intensity of the received light wave through the modulation signal output from the probe optical path, wherein the isolator is used to transmit the light wave output by the intensity modulator unidirectionally to the wavelength division multiplexer;

[0012] The fourth coupler has its output connected to a measurement interferometer and an auxiliary interferometer, respectively. The measurement interferometer transmits the received light waves to the wavelength division multiplexer via the first coupler. The measurement interferometer also transmits the light waves returned from the wavelength division multiplexer to the third detector. The output of the third detector is connected to the data acquisition card.

[0013] The output of the auxiliary interferometer is connected to the fourth detector, and the output of the fourth detector is connected to the data acquisition card.

[0014] A wavelength division multiplexer combines the probe light wave emitted from the probe optical path, the pump light wave modulated by the intensity modulator, and the light wave emitted by the measurement interferometer. The combined light wave is transmitted to the optical fiber under test for action. The light wave after action in the optical fiber under test is split back to the probe optical path and the measurement interferometer by the wavelength division multiplexer.

[0015] The data acquisition card is connected to the host computer, and the host computer outputs the internal gas concentration information, temperature, and stress change of the lithium battery under test based on the received data.

[0016] Preferably, the optical fiber under test includes: a bare optical fiber, a loose tube, and an FP cavity;

[0017] One end of the bare optical fiber is connected to the wavelength division multiplexer, and the other end of the bare optical fiber is equipped with the FP cavity, which is located inside the lithium battery under test.

[0018] One portion of the bare optical fiber is directly spirally wound onto the outer wall of the lithium battery under test, while the other portion of the bare optical fiber is installed in the loose tube and then spirally wound onto the outer wall of the lithium battery under test.

[0019] Preferably, the detection optical path includes:

[0020] A detection laser, which is used to emit laser light, is connected to a first circulator and a servo controller respectively;

[0021] A first circulator, the first interface of which is connected to the probe laser, the second interface of which is connected to the wavelength division multiplexer, and the third interface of which is connected to the second coupler;

[0022] The second coupler splits the optical signal output from the third interface of the first circulator into two paths. One path of the optical signal output from the third interface of the first circulator is transmitted to the first detector by the second coupler, and the other path of the optical signal output from the third interface of the first circulator is transmitted to the second detector by the second coupler.

[0023] The first detector converts the received light wave signal into an electrical signal and then transmits the electrical signal to the servo controller.

[0024] The second detector converts the received optical signal into an electrical signal and then transmits the electrical signal to the lock-in amplifier.

[0025] A lock-in amplifier is connected to the intensity modulator and the host computer. After the lock-in amplifier demodulates the phase modulation magnitude generated by the photothermal effect of the gas inside the lithium battery under test, the lock-in amplifier transmits the signal to the host computer. The host computer processes the signal to obtain the concentration of the internal gas of the lithium battery under test.

[0026] Preferably, the measuring interferometer includes:

[0027] The sixth coupler splits the light wave received from the fourth coupler into the second circulator and the intrinsic optical path;

[0028] The second circulator has a first interface connected to the sixth coupler, a second interface connected to the first coupler via a sensing optical path, and a third interface connected to the seventh coupler.

[0029] The intrinsic optical path, the output of which is connected to the seventh coupler;

[0030] A seventh coupler, which is connected to the third detector.

[0031] Preferably, the auxiliary interferometer includes:

[0032] The fifth coupler splits the light wave received from the fourth coupler into two Faraday rotator mirrors;

[0033] A time-delay fiber, wherein a time-delay fiber is disposed between one of the Faraday rotator mirrors and the fifth coupler;

[0034] The light waves processed by the two Faraday rotators return to the fifth coupler via their original paths, and the fifth coupler transmits the light waves processed by the Faraday rotators to the fourth detector.

[0035] Preferably, the diameter of the FP cavity is less than 2 mm.

[0036] Preferably, the diameter of the bare optical fiber is less than 250 μm.

[0037] Preferably, the splitting coefficient of the third coupler is 50%:50%.

[0038] Preferably, the splitting coefficient of the fourth coupler is 1% to 99%, wherein 1% of the light waves enter the auxiliary interferometer.

[0039] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0040] 1) Integrate the fiber optic thermal spectroscopy system with OFDR, with both systems sharing a swept-frequency light source (also known as a "pump laser"), and simultaneously using a data processing system (i.e.... Figure 1 The computers in the building are also shared;

[0041] 2) The FP cavity used for gas concentration measurement is connected in series with the FUT. The photothermal spectroscopy system for gas concentration measurement usually uses 1550nm light wave for detection, while the OFDR system uses a pump light system as the detection light source. The light wave ranges of the two do not interfere with each other. Therefore, multiple physical quantities can be measured simultaneously.

[0042] 3) To achieve the measurement of multiple physical quantities in lithium batteries, this invention designs a specific optical fiber arrangement, dividing the optical fiber under test into three segments. This simultaneously enables the measurement of external strain, internal and external temperatures, and internal gas concentration within the battery. Because bare optical fibers possess advantages such as small diameter (~250 μm), corrosion resistance, and electromagnetic interference immunity, and the FP cavity diameter made from them can also be very small (<2 mm), they are highly suitable for monitoring the internal physical quantities of lithium batteries. Furthermore, the OFDR system allows for distributed temperature and strain measurements, providing multidimensional data for monitoring the thermal effects of lithium batteries. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the structure of the device provided by the present invention;

[0045] Figure 2 Figure (a) in the figure is a schematic diagram of the arrangement of the optical fiber under test outside the lithium battery under test;

[0046] Figure 2 Figure (b) shows a schematic diagram of the arrangement of the optical fiber under test inside the lithium battery under test. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0048] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an,” “a,” or “the,” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising,” “including,” or “including,” and similar terms mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. The terms “connected,” “linked,” or “connected,” and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0049] It should be noted that the terms "up", "down", "left", "right", "front", and "back" used in this invention are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0050] Fiber optic sensors are considered a potentially effective means of monitoring thermal runaway in lithium-ion batteries. Compared to traditional electronic sensors, they offer advantages such as high sensitivity, small size, resistance to electromagnetic interference, and good electrical insulation, making them ideal for in-situ monitoring of lithium-ion batteries. Furthermore, fiber optic sensors can easily achieve multiplexing and distributed measurements using a single fiber, providing multi-point information about the lithium-ion battery and module, helping the BMS system to make more accurate judgments about thermal effects. The multiplexing and distributed capabilities also help reduce the cost of individual measurement points. Currently, several research groups both domestically and internationally have attempted to apply fiber optic sensors to the monitoring of thermal effects in lithium-ion batteries. For example, in practical applications, a femtosecond etched FBG (fiber optic cable) embedded in the lithium-ion battery has been used to obtain temperature data with a higher signal-to-noise ratio, achieving in-situ and continuous monitoring.

[0051] For the reasons mentioned above, this invention aims to provide a multi-physical quantity measurement system for lithium batteries, such as... Figure 1 As shown, the components include: the fiber under test, pump laser, optical amplifier, probe optical path, intensity modulator, fourth coupler, wavelength division multiplexer, measurement interferometer, auxiliary interferometer, data acquisition card, and host computer.

[0052] The optical fiber under test is connected to the lithium battery under test; the output of the pump laser is connected to the optical amplifier and the fourth coupler via the third coupler; the output of the optical amplifier is connected to the intensity modulator; the probe optical path is used to emit probe light, and the probe optical path is connected to the wavelength division multiplexer, the intensity modulator, and the host computer; the output of the intensity modulator is connected to the isolator, the first coupler, and the wavelength division multiplexer in sequence, and the intensity modulator modulates the intensity of the received light wave through the modulation signal output by the probe optical path, wherein the isolator is used to unidirectionally transmit the light wave output by the intensity modulator to the wavelength division multiplexer; the output of the fourth coupler is connected to the measurement interferometer and the auxiliary interferometer; the measurement interferometer transmits the received light wave to the wavelength division multiplexer via the first coupler, and the measurement interferometer... The measurement interferometer transmits the light wave returned from the wavelength division multiplexer to the third detector, and the output of the third detector is connected to the data acquisition card; the output of the auxiliary interferometer is connected to the fourth detector, and the output of the fourth detector is connected to the data acquisition card; the wavelength division multiplexer combines the probe light wave emitted from the probe optical path, the pump light wave modulated by the intensity modulator, and the light wave emitted from the measurement interferometer, and the combined light wave is transmitted to the fiber under test for action, and the light wave after action in the fiber under test is split back to the probe optical path and the measurement interferometer by the wavelength division multiplexer; the data acquisition card is connected to the host computer, and the host computer outputs the internal gas concentration information, temperature, and stress change of the lithium battery under test based on the received data.

[0053] The optical fiber under test includes: a bare optical fiber, a loose tube, and an FP cavity. One end of the bare optical fiber is connected to the wavelength division multiplexer, and the other end of the bare optical fiber is installed with the FP cavity, which is located inside the lithium battery under test. A portion of the bare optical fiber is directly spirally wound on the outer wall of the lithium battery under test, and another portion of the bare optical fiber is installed in the loose tube and then spirally wound on the outer wall of the lithium battery under test.

[0054] The detection optical path includes: a detection laser, a first circulator, a second coupler, a first detector, a second detector, and a lock-in amplifier. The detection laser emits laser light and is connected to both the first circulator and a servo controller. The first interface of the first circulator is connected to the detection laser, the second interface is connected to the wavelength division multiplexer, and the third interface is connected to the second coupler. The second coupler splits the optical signal output from the third interface of the first circulator into two paths. One path, the optical signal output from the third interface of the first circulator, is transmitted by the second coupler to the first detector. The optical signal output from the third interface of the first circulator is transmitted to the second detector by the second coupler; the first detector converts the received optical signal into an electrical signal and transmits the electrical signal to the servo controller; the second detector converts the received optical signal into an electrical signal and transmits the electrical signal to the lock-in amplifier; the lock-in amplifier is connected to the intensity modulator and the host computer respectively. After the lock-in amplifier demodulates the phase modulation magnitude generated by the photothermal effect of the gas in the lithium battery under test, the lock-in amplifier transmits the signal to the host computer, and the host computer processes the signal to obtain the concentration of the internal gas of the lithium battery under test.

[0055] like Figure 1This system mainly consists of two parts: a photothermal spectroscopy system and an optical frequency domain reflection (OFDR) system. The photothermal spectroscopy system is mainly used for measuring the gas concentration inside the lithium battery. It can be further divided into the following parts: pump light part, probe light part, and gas chamber part. The composition and function of each part are described as follows: (1) Pump light part: Select a pump laser with a suitable wavelength for the type of gas inside the lithium battery that needs to be detected. The wavelength of this pump laser can be scanned near the gas absorption line, and the scanning range is about 1nm to 2nm. To achieve a certain detection accuracy, an optical amplifier can be used to amplify the output light wave signal of the pump laser. After the amplified light wave passes through an intensity modulator and an isolator, it is combined with the probe light in the OFDR system through coupler 1. Then, it is combined with the probe light wave through a wavelength division multiplexer (WDM) and enters a small gas cell composed of a fiber Fabry-Pérot (FP) cavity. Here, the amplified light wave is intensity modulated. The modulation signal comes from a lock-in amplifier. The purpose of adding modulation is to improve gas detection. (2) Probe light section: The probe light generally uses a commercial near-infrared narrow linewidth laser, such as a fiber laser with a wavelength of around 1550nm. After the probe light passes through the first port of the first circulator, it is output from the second port. Together with the pump light, it is combined with the WDM and enters the gas cell. After returning from the gas cell, it passes through the third port of the first circulator and is split into two paths by the second coupler after the third port of the first circulator. The two paths are received by two detectors (first detector and second detector) and converted into electrical signals. The signal output from the first detector is sent to a servo controller, which then adjusts the wavelength of the detector laser by outputting voltage to make it work at the orthogonal working point of the returning interference signal; the signal output from the second detector enters a lock-in amplifier, which demodulates the phase modulation magnitude generated by the gas photothermal effect, and then sends the modulation signal to the host computer for processing to obtain the concentration of gas in the battery; (3) Gas chamber section: the gas chamber section is as follows Figure 2 As shown in Figure (b), the gas cell is constructed using an intrinsic fiber optic FP interferometer (i.e., an FP cavity). This interferometer can have a diameter less than 1 mm, allowing it to be placed inside a lithium battery to detect the internal gas concentration. Simultaneously, a diaphragm can be used outside the interferometer to allow gas from the electrolyte inside the lithium battery to enter the FP cavity. This allows the pump light and the gas under test to interact within the FP cavity, generating a photothermal signal that modulates the phase of the optical path. Note that the gas cell is connected after the bare fiber portion of the fiber under test (FUT).

[0056] In a preferred embodiment, the measurement interferometer includes: a sixth coupler, a second circulator, an intrinsic optical path, and a seventh coupler; the sixth coupler splits the light wave received from the fourth coupler into the second circulator and the intrinsic optical path; the first interface of the second circulator is connected to the sixth coupler, the second interface of the second circulator is connected to the first coupler through a sensing optical path, and the third interface of the second circulator is connected to the seventh coupler; the output end of the intrinsic optical path is connected to the seventh coupler; and the seventh coupler is connected to the third detector.

[0057] In a preferred embodiment, the auxiliary interferometer includes: a fifth coupler, a time-delay fiber, and two Faraday rotators. The fifth coupler splits the light wave received from the fourth coupler into the two Faraday rotators. A time-delay fiber is disposed between one of the Faraday rotators and the fifth coupler. The light waves processed by the two Faraday rotators return to the fifth coupler along the original path, and the fifth coupler transmits the light waves processed by the Faraday rotators to the fourth detector.

[0058] One specific implementation method. The pump light in the above-mentioned photothermal spectroscopy gas concentration detection system is linearly scanned. This light source can be further used to measure the temperature and stress of lithium batteries. The scheme adopted is optical frequency domain reflectometer technology. The composition and function of each part of the OFDR system in this invention are described as follows. (1) The frequency sweeping light source part, which is the pump laser of the above-mentioned photothermal spectroscopy system. Since both need to use wavelength scanning light sources, this part can be shared. The third coupler can be used to split the light wave output by the scanning light source into the photothermal spectroscopy system and the OFDR system (the splitting coefficient is recommended to be 50%:50%). (2) The auxiliary interferometer part, the frequency sweeping light wave output by the third coupler is then passed through the fourth coupler (the splitting coefficient is recommended to be 1%:99%) and enters a Mach-Zehnder (MZ) interferometer (1% of the light wave of one path). The MZ interferometer consists of a fifth coupler, two Faraday Rotation Mirrors (FRMs, used to eliminate polarization fading problems) at the end, and a delay fiber. The auxiliary interferometer can be used to obtain the instantaneous optical frequency of the swept light source output, and is used for nonlinear correction of the swept light source in the OFDR system. The optical signal output by the auxiliary interferometer is converted into an electrical signal by PD4 and then sent to the acquisition card for processing by the computer; (3) In the measurement interferometer section, the swept light source output by the third coupler passes through the fourth coupler and then enters the measurement interferometer. The measurement interferometer is composed of the sixth coupler, the seventh coupler, the second circulator, etc. Among them, the optical path to be measured is the optical path that reaches the seventh coupler after passing through the sixth coupler and the second circulator. In the optical path to be measured, the light wave is output from the first port of the second circulator and then combined with the probe light and pump light in the photothermal spectroscopy system through the first coupler and the wavelength division multiplexer, and finally output to the FUT together. The optical signal output by the measurement interferometer is converted into an electrical signal by the third detector and then sent to the acquisition card for processing by the host computer. The host computer can be a computer.

[0059] Figure 2 This demonstrates a special deployment design for the fiber optic unit (FUT) inside and outside the lithium battery, designed to simultaneously monitor internal gas concentration, internal and external temperature, and external stress. The FUT consists of three parts; the first part is bare optical fiber with loose tubing, such as... Figure 2 As shown by the gray line segment in Figure (a), this part is only sensitive to temperature due to the isolation effect of the loose tube, and can be fixed to the outside of the lithium battery; the second part is the bare optical fiber, which is sensitive to both temperature and strain, as shown in Figure (a). Figure 2 As shown by the black line segment in Figure (a). Fixing the optical fibers of Part 1 and Part 2 side-by-side outside the battery can decouple temperature and strain. Part 3 is the internal measurement section of the battery, consisting of a bare optical fiber and an optical fiber FP cavity at its tail, as shown... Figure 2As shown in Figure (b), a section of bare optical fiber can be used to measure the internal temperature of the battery, while the fiber optic FP cavity is used to measure the internal gas concentration. In summary, the bare optical fiber, or the bare optical fiber with a sheath, utilizes the Rayleigh scattering effect in the fiber to acquire temperature and strain information at various points inside and outside the battery through an OFDR system. The fiber optic FP cavity forms a gas cell, connected in series at the tail of the FUT, and acquires specific gas concentration information inside the battery through a photothermal spectroscopy system. In some cases, to increase the signal-to-noise ratio of the received light wave in the OFDR and improve the measurement accuracy of temperature and strain, fiber grating strings can be continuously etched onto the FUT. It is important to note that the reflection center wavelength of these fiber gratings should be within the wavelength range of the swept-frequency light source.

[0060] The method for using computers to calculate the gas concentration inside the battery, the internal and external temperatures of the battery, and strain parameters from the collected data is existing technology and will not be elaborated here.

[0061] This invention ingeniously utilizes the linear scanning characteristic of the pump light in a fiber optic thermal spectroscopy gas detection system, transforming the pump light, originally used only for gas absorption, into temperature and strain sensing. This enables simultaneous measurement of gas concentration, temperature, and strain, which is the key feature of this invention. To achieve this, in embodiments of this invention, the fiber optic thermal spectroscopy system is combined with an OFDR (Optical Frequency Reduction) system. Both systems share a frequency-scanning light source (also known as a "pump laser"), while a data processing system (i.e.,...) is also used. Figure 1 The computer in the system is also shared; the FP cavity used for gas concentration measurement is connected in series with the FUT. The photothermal spectroscopy system for gas concentration measurement typically uses 1550nm light waves for detection, while the OFDR system uses a pump light system for detection. The light wave ranges of the two do not interfere with each other, thus enabling simultaneous measurement of multiple physical quantities. To achieve the measurement of multiple physical quantities in lithium batteries, this invention designs a specific fiber optic arrangement, dividing the fiber under test into three segments, simultaneously realizing the measurement of external strain, internal and external temperatures, and internal gas concentration. Because bare optical fibers have advantages such as small diameter (~250μm), corrosion resistance, and electromagnetic interference resistance, and the diameter of the FP cavity made from them can also be very small (<2mm), they are very suitable for monitoring the internal physical quantities of lithium batteries. Simultaneously, the OFDR system can be used to form distributed temperature and strain measurements, providing multidimensional data for monitoring the thermal effects of lithium batteries.

[0062] The combination of the above three points can provide a multi-physical-quantity, multi-point monitoring solution for lithium battery monitoring; at the same time, this solution is also expected to reduce the cost of fine monitoring of multiple physical quantities of lithium batteries.

[0063] The following points need to be explained:

[0064] (1) The accompanying drawings of the embodiments of the present invention only involve the structures involved in the embodiments of the present invention. Other structures can refer to the general design.

[0065] (2) For clarity, the thickness of layers or regions is enlarged or reduced in the drawings used to describe embodiments of the present invention; that is, these drawings are not drawn to actual scale. It is understood that when an element such as a layer, film, region, or substrate is referred to as being “above” or “below” another element, the element may be “directly” located “above” or “below” the other element, or there may be intermediate elements.

[0066] (3) Where there is no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to obtain new embodiments.

[0067] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-physical quantity measurement system for lithium batteries, characterized in that, include: The optical fiber under test is connected to the lithium battery under test. A pump laser, the output of which is connected to an optical amplifier and a fourth coupler via a third coupler; An optical amplifier, the output of which is connected to an intensity modulator; A detection optical path is provided, which is used to emit detection light and is connected to the wavelength division multiplexer, the intensity modulator and the host computer respectively. An intensity modulator, the output of which is connected in sequence to an isolator, a first coupler and a wavelength division multiplexer, wherein the intensity modulator modulates the intensity of the received light wave through the modulation signal output from the probe optical path, wherein the isolator is used to transmit the light wave output by the intensity modulator unidirectionally to the wavelength division multiplexer; The fourth coupler, the output of which is connected to the measuring interferometer and the auxiliary interferometer respectively; The measurement interferometer transmits the received light wave to the wavelength division multiplexer via the first coupler. The measurement interferometer transmits the light wave returned from the wavelength division multiplexer to the third detector. The output of the third detector is connected to the data acquisition card. The output of the auxiliary interferometer is connected to the fourth detector, and the output of the fourth detector is connected to the data acquisition card. A wavelength division multiplexer combines the probe light wave emitted from the probe optical path, the pump light wave modulated by the intensity modulator, and the light wave emitted by the measurement interferometer. The combined light wave is transmitted to the optical fiber under test for action. The light wave after action in the optical fiber under test is split back to the probe optical path and the measurement interferometer by the wavelength division multiplexer. The data acquisition card is connected to the host computer, and the host computer outputs the internal gas concentration information, temperature, and stress change of the lithium battery under test based on the received data.

2. The lithium battery multi-physical quantity measurement system according to claim 1, characterized in that, The optical fiber under test includes: bare optical fiber, loose tube, and FP cavity; One end of the bare optical fiber is connected to the wavelength division multiplexer, and the other end of the bare optical fiber is equipped with the FP cavity, which is located inside the lithium battery under test. One portion of the bare optical fiber is directly spirally wound onto the outer wall of the lithium battery under test, while the other portion of the bare optical fiber is installed in the loose tube and then spirally wound onto the outer wall of the lithium battery under test.

3. The lithium battery multi-physical quantity measurement system according to claim 1, characterized in that, The detection optical path includes: A detection laser, which is used to emit laser light, is connected to a first circulator and a servo controller respectively; A first circulator, the first interface of which is connected to the probe laser, the second interface of which is connected to the wavelength division multiplexer, and the third interface of which is connected to the second coupler; The second coupler splits the optical signal output from the third interface of the first circulator into two paths. One path of the optical signal output from the third interface of the first circulator is transmitted to the first detector by the second coupler, and the other path of the optical signal output from the third interface of the first circulator is transmitted to the second detector by the second coupler. The first detector converts the received light wave signal into an electrical signal and then transmits the electrical signal to the servo controller. The second detector converts the received optical signal into an electrical signal and then transmits the electrical signal to the lock-in amplifier. A lock-in amplifier is connected to the intensity modulator and the host computer. After the lock-in amplifier demodulates the phase modulation magnitude generated by the photothermal effect of the gas inside the lithium battery under test, the lock-in amplifier transmits the modulation signal to the host computer. The host computer processes the modulation signal to obtain the concentration of the internal gas of the lithium battery under test.

4. The lithium battery multi-physical quantity measurement system according to claim 1, characterized in that, The measuring interferometer includes: The sixth coupler splits the light wave received from the fourth coupler into the second circulator and the intrinsic optical path; The second circulator has a first interface connected to the sixth coupler, a second interface connected to the first coupler via a sensing optical path, and a third interface connected to the seventh coupler. The intrinsic optical path, the output of which is connected to the seventh coupler; A seventh coupler, which is connected to the third detector.

5. The lithium battery multi-physical quantity measurement system according to claim 1, characterized in that, The auxiliary interferometer includes: The fifth coupler splits the light wave received from the fourth coupler into two Faraday rotator mirrors; A time-delay fiber, wherein a time-delay fiber is disposed between one of the Faraday rotator mirrors and the fifth coupler; The light waves processed by the two Faraday rotators return to the fifth coupler via their original paths, and the fifth coupler transmits the light waves processed by the Faraday rotators to the fourth detector.

6. The lithium battery multi-physical quantity measurement system according to claim 2, characterized in that, The diameter of the FP cavity is less than 2 mm.

7. The lithium battery multi-physical quantity measurement system according to claim 2, characterized in that, The diameter of the bare optical fiber is less than 250 μm.

8. The lithium battery multi-physical quantity measurement system according to claim 1, characterized in that, The splitting coefficient of the third coupler is 50%:50%.

9. The lithium battery multi-physical quantity measurement system according to claim 2, characterized in that, The splitting coefficient of the fourth coupler is 1% to 99%, wherein 1% of the light waves enter the auxiliary interferometer.

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