A battery temperature and strain detection device and battery pack

Abstract

This invention discloses a battery temperature and strain detection device and battery pack, relating to the field of battery monitoring technology. The device includes a light source, a controller, and a detection optical fiber. The detection optical fiber is connected between the light source and the controller to receive and transmit light to the controller. The controller is configured to determine a first wavelength shift caused by temperature influence when light flows through a fiber optic grating in the detection optical fiber, and a second wavelength shift caused by strain influence when light flows through a photonic crystal fiber in the detection optical fiber. Based on the first and second wavelength shifts, and the temperature and strain sensitivity coefficients of the fiber optic grating and the photonic crystal fiber, the temperature change and strain change of the battery are determined. Based on the temperature change, strain change, and preset temperature and strain reference values, the battery temperature and strain values ​​are determined. This solution improves the ability to detect battery temperature and strain.

Description

Technical Field

[0001] This invention relates to the field of battery monitoring technology, and in particular to a battery temperature and strain detection device and battery pack. Background Technology

[0002] With the rapid development of industries such as new energy vehicles and energy storage systems, lithium batteries are prone to generating a coupling effect of temperature gradient and mechanical strain under complex operating conditions such as high-rate charging and discharging and long-term cycling. This can lead to safety hazards such as battery performance degradation and thermal runaway. Therefore, accurate detection of the internal temperature and strain of the battery is crucial.

[0003] Currently, traditional electrical contact sensors collect temperature and strain values ​​by contacting the outer surface of the battery to be tested. However, this detection method is highly invasive to the battery pack, and the electrical signals collected by the electrical contact sensors are easily affected by electrical interference, making it difficult to accurately collect the battery's temperature and mechanical strain. This results in weak detection capabilities for battery temperature and strain, making it difficult to support battery safety management and health assessment. Summary of the Invention

[0004] In view of this, this application provides a battery temperature and strain detection device and a battery pack, the main purpose of which is to solve the technical problem that the detection of battery temperature and strain is easily affected by electrical interference, resulting in weak detection capability.

[0005] According to a first aspect of the present invention, a device for detecting battery temperature and strain is provided, the device comprising a broadband light source, a detection controller, and a detection optical fiber disposed in the battery to be tested;

[0006] The detection optical fiber includes a fiber grating and a photonic crystal fiber connected in series. The detection optical fiber is connected between the broadband light source and the detection controller, and is used to receive the detection light from the broadband light source and send the detection light flowing through it to the detection controller.

[0007] The detection controller is configured to perform the following processes:

[0008] The detection controller determines the first wavelength shift caused by temperature when the detection light flows through the fiber grating, and the second wavelength shift caused by strain when the detection light flows through the photonic crystal fiber.

[0009] Based on the first wavelength drift, the second wavelength drift, and the preset fiber grating temperature sensitivity coefficient, fiber grating strain sensitivity coefficient, photonic crystal fiber temperature sensitivity coefficient, and photonic crystal fiber strain sensitivity coefficient, the temperature change and strain change are determined.

[0010] Based on the temperature change, the strain change, and the preset temperature and strain reference values, the temperature and strain values ​​of the battery under test are determined.

[0011] In an optional embodiment, the detection controller determines the temperature change and strain change based on the first wavelength drift, the second wavelength drift, and preset fiber optic grating temperature sensitivity coefficient, fiber optic grating strain sensitivity coefficient, photonic crystal fiber temperature sensitivity coefficient, and photonic crystal fiber strain sensitivity coefficient. This includes: the detection controller acquiring the preset fiber optic grating temperature sensitivity coefficient, fiber optic grating strain sensitivity coefficient, photonic crystal fiber temperature sensitivity coefficient, and photonic crystal fiber strain sensitivity coefficient; and calculating the temperature change and strain change using the following formulas:

[0012]

[0013] in, The temperature change is... The strain change is the amount of strain. This is the first wavelength shift amount. This is the second wavelength shift amount. The temperature sensitivity coefficient of the fiber grating. The fiber grating strain sensitivity coefficient is... This refers to the temperature sensitivity coefficient of the photonic crystal fiber. The strain sensitivity coefficient of the photonic crystal fiber is given.

[0014] In an optional embodiment, the detection controller determines the first wavelength shift caused by temperature when the detection light flows through the fiber grating, including: the detection controller receiving the spectral signal of the detection light after it flows through the detection fiber, identifying the narrowband Bragg reflection peak from the spectral signal, and locating the center wavelength of the reflection peak of the narrowband Bragg reflection peak; obtaining a preset reference center wavelength of the reflection peak, calculating a first difference between the center wavelength of the reflection peak and the reference center wavelength of the reflection peak, and determining the first difference as the first wavelength shift.

[0015] In an optional embodiment, the detection controller determines the second wavelength drift caused by strain when the detection light flows through the photonic crystal fiber, including: the detection controller receiving the interference spectrum signal of the detection light after it flows through the detection fiber, and identifying the characteristic peak center wavelength of the interference fringe in the interference spectrum signal; obtaining a preset characteristic peak reference center wavelength, calculating a second difference between the characteristic peak center wavelength and the characteristic peak reference center wavelength, and determining the second difference as the second wavelength drift.

[0016] In an optional embodiment, the detection optical fiber further includes a first coreless optical fiber and a second coreless optical fiber; the first end of the fiber grating is connected to the broadband light source, and the fiber grating, the first coreless optical fiber, the photonic crystal fiber, and the second coreless optical fiber are connected in series between the broadband light source and the detection controller; the first coreless optical fiber is used to split the received detection light and deliver the split light to different apertures in the photonic crystal fiber; the second coreless optical fiber is used to recouple the light in different apertures and deliver the recoupled detection light to the detection controller so that the detection controller receives the detection light.

[0017] In an optional embodiment, the detection fiber further includes a first single-mode fiber and a second single-mode fiber; the first single-mode fiber is disposed between the fiber grating and the first coreless fiber, and is used for low-loss optical transmission between the fiber grating and the first coreless fiber; the second single-mode fiber is disposed between the second coreless fiber and the detection controller, and is used for low-loss optical transmission between the second coreless fiber and the detection controller.

[0018] In an optional embodiment, the detection optical fiber is embedded between the electrode active layer and the separator inside the battery under test by puncture. The extension direction of the detection optical fiber is parallel to the winding direction of the battery under test and is in direct contact with the active material layer inside the battery under test.

[0019] In an optional embodiment, the outer surface of the detection optical fiber is coated with a silica coating, and the outer surface of the silica coating is coated with a fluorinated polymer coating.

[0020] In an optional embodiment, the fluoropolymer coating comprises at least one of polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, and fluorinated ethylene propylene copolymer.

[0021] According to a second aspect of the invention, a battery pack is provided, the device including the battery temperature and strain detection device as described above.

[0022] This invention provides a battery temperature and strain detection device and battery pack. By embedding a detection optical fiber as a fiber optic sensor component within the battery, interference with the external structure of the battery pack is avoided. This allows for accurate capture of the battery's internal temperature and strain state without occupying additional space within the battery pack. Furthermore, the device achieves temperature and strain detection based on the wavelength shift of the optical signal, fundamentally solving the problem of electromagnetic interference in traditional electrical parameter monitoring. This enables high-precision data acquisition, improves the detection capability of battery temperature and strain, and provides reliable data support for battery safety management and health assessment.

[0023] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0025] Figure 1 This diagram illustrates one of the structural schematics of a battery temperature and strain detection device provided in an embodiment of the present invention;

[0026] Figure 2 A schematic diagram of an experimental optical fiber disposed in a constant temperature chamber according to an embodiment of the present invention is shown;

[0027] Figure 3 A schematic diagram of the spectral response characteristic curves of an experimental optical fiber at different temperatures provided in an embodiment of the present invention is shown.

[0028] Figure 4 A schematic diagram of an experimental optical fiber set at a high-precision stretching stage according to an embodiment of the present invention is shown.

[0029] Figure 5 A schematic diagram of the spectral response characteristic curves of an experimental optical fiber under different strains provided in an embodiment of the present invention is shown.

[0030] Figure 6 The second schematic diagram shows the structure of a battery temperature and strain detection device provided in an embodiment of the present invention;

[0031] Figure 7 This diagram illustrates a structural schematic of a detection optical fiber provided in an embodiment of the present invention.

[0032] Figure 8This diagram illustrates the relationship between the second wavelength drift and the strain experienced by the detection fiber, according to an embodiment of the present invention.

[0033] Figure 9 This diagram illustrates the wavelength response difference between a fiber optic grating and a Mach-Zehnder interferometer under strain, according to an embodiment of the present invention.

[0034] Figure 10 This diagram illustrates the difference in wavelength response between a fiber optic grating and a Mach-Zehnder interferometer under temperature variations, as provided in an embodiment of the present invention.

[0035] in, Figures 1 to 10 The correspondence between the reference numerals and component names in the attached drawings is as follows:

[0036] 100 Broadband Light Source, 200 Detection Controller, 300 Battery Under Test, 400 Detection Fiber, 410 Fiber Bragg Grating, 420 Photonic Crystal Fiber, 110 Spectrometer, 120 Constant Temperature Chamber, 130 Experimental Fiber, 140 High-Precision Stretching Stage, 430 First Coreless Fiber, 440 Second Coreless Fiber, 510 First Fiber Single-Mode Patch Cord, 520 Second Fiber Single-Mode Patch Cord, 450 First Single-Mode Fiber, 460 Second Single-Mode Fiber. Detailed Implementation

[0037] The present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the present application can be combined with each other.

[0038] With the rapid development of industries such as new energy vehicles and energy storage systems, lithium batteries are prone to internal temperature gradients and mechanical strain coupling effects under complex operating conditions such as high-rate charging and discharging and long-term cycling. This can lead to safety hazards such as battery performance degradation and thermal runaway. Therefore, accurate detection of the internal temperature and strain of the battery is crucial. Currently, traditional electrical contact sensors collect temperature and strain values ​​by contacting the outer surface of the battery to be tested. However, this detection method is highly invasive to the battery pack space, and the electrical signals collected by electrical contact sensors are easily affected by electrical interference, making it difficult to accurately collect the battery's temperature and mechanical strain. This results in weak detection capabilities for battery temperature and strain, making it difficult to support battery safety management and health assessment.

[0039] To address the above problems, in one embodiment, such as Figure 1As shown, a battery temperature and strain detection device is provided. Taking the use of this device to detect the temperature and strain of a battery as an example, the battery temperature and strain detection device includes a broadband light source 100, a detection controller 200, and a detection optical fiber 400 disposed in the battery 300 to be tested. The detection controller 200 can be a computer device.

[0040] Specifically, the detection fiber 400 includes a fiber grating 410 and a photonic crystal fiber 420 connected in series. The detection fiber 400 is connected between the broadband light source 100 and the detection controller 200, and is used to receive the detection light from the broadband light source 100 and send the flowing detection light to the detection controller 200. The broadband light source 100 provides detection light with a continuous spectrum, allowing the reflection or interference signals from the fiber grating (FBG) and the photonic crystal fiber (PCF) to appear simultaneously within a single wavelength window. Here, the fiber grating 410 is an optical fiber device that forms periodic refractive index modulation in the core of a single-mode fiber using techniques such as ultraviolet writing. Its core characteristic is that it reflects only light of a specific Bragg wavelength, which drifts with temperature and strain. It exhibits high temperature sensitivity and low strain sensitivity and is commonly used as a temperature sensing unit. Furthermore, the photonic crystal fiber 420 is a special optical fiber with a periodic air-hole structure in its core or cladding. Its mode interference effect is sensitive to both temperature and strain, with a more significant strain response, making it a core component for achieving high-sensitivity strain sensing. When external stress causes deformation of the air-hole structure in the photonic crystal fiber 420, it alters the birefringence and mode coupling conditions, thereby causing interference in the output light to measure strain. Furthermore, the detection controller 200 monitors the detection light within a wavelength range of 1580nm-1680nm.

[0041] Furthermore, the detection optical fiber 400 can be embedded between the electrode active layer and the separator inside the battery under test 300 by puncture. The extension direction of the detection optical fiber is parallel to the winding direction of the battery under test and it is in direct contact with the active material layer inside the battery. Furthermore, the detection optical fiber 400 can be placed inside the battery under test 300 in the following ways:

[0042] First, the battery 300 to be tested undergoes pretreatment and sealing. Specifically, since the soft-pack lithium battery 300 contains liquid electrolyte and a small amount of gas generated by electrochemical reactions, to prevent electrolyte decomposition or electrode corrosion caused by ambient humidity and external oxygen, the external protection circuit and port structure of the battery 300 must be removed first. Then, an opening is made on the edge of the aluminum-plastic film at the top and bottom of the battery 300. The opening position must avoid the battery's electrode tabs and active area, providing a channel for the introduction of the detection optical fiber 400 and maintaining the sealing and uniformity of the electrolyte system of the battery 300 to minimize electrochemical disturbances caused by optical fiber puncture.

[0043] Here, to improve the stability of the optical fiber in the complex chemical environment inside the battery, the outer surface of the detection optical fiber 400 is coated with a silica coating, and the outer surface of this silica coating is coated with a fluorinated polymer coating; wherein, the fluorinated polymer coating includes at least one of polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, and fluorinated ethylene propylene copolymer. Specifically, a dense silica (SiO2) inorganic protective layer can first be deposited on the outer wall of the optical fiber. Its high hardness, strong heat resistance, and electrical insulation properties can isolate the active lithium ions and electrolyte from eroding the optical fiber cladding. Further, a highly chemically inert fluorinated polymer is coated on the silica coating to suppress the adhesion of solid electrolyte interphase (SEI) byproducts and electrolyte swelling. Through this optical fiber structure, the additional loss caused by the sudden change in interface refractive index can be avoided, and the flexibility of the fluorinated polymer can absorb mechanical deformation, ensuring the linearity and repeatability of temperature and strain measurements.

[0044] Then, the detection optical fiber 400 is introduced into the jelly layer structure of the battery 300 to be tested. Specifically, since the jelly layer inside the soft-pack lithium battery is composed of stacked or wound cathode and anode active materials and electrolyte separator layers, its mechanical integrity directly affects the battery performance. Therefore, a micro-puncture method can be used to construct internal channels. A surface-polished needle is slowly penetrated along the direction of the battery electrode of the battery 300 to the upper sealing area, forming a continuous and controllable microchannel. During this process, the puncture speed and angle need to be controlled to prevent short circuits of the electrode or tearing of the separator. Furthermore, immediately after the needle is inserted, the detection optical fiber 400 is slowly embedded along the puncture channel to ensure that the optical fiber is evenly distributed between the electrode layers of the battery 300 to ensure direct contact between the detection optical fiber 400 and the active material layer of the battery 300, and that the extension direction is parallel to the battery winding direction.

[0045] Finally, the detection optical fiber 400 is encapsulated and sealed for reinforcement. Specifically, a secondary seal can be performed on the opening area of ​​the battery to be tested 300 after the optical fiber is embedded. Here, an aluminum film can be cut first to cover the upper and lower openings formed by puncturing the battery to be tested 300, forming the first shielding layer. Further, a UV-curable adhesive is applied to the contact gap between the detection optical fiber 400 and the battery. The capillary action of the UV-curable adhesive completely fills the gap formed by puncture. Then, the UV-curable adhesive is irradiated with a UV lamp for 3-5 minutes to fully cure it, effectively preventing electrolyte evaporation and air infiltration, reducing the risk of electrochemical side reactions in the battery, and not affecting the subsequent charge and discharge performance of the battery.

[0046] Furthermore, the detection controller 200 is configured to perform the following processes:

[0047] First, the detection controller 200 determines the first wavelength shift caused by temperature when the detection light flows through the fiber grating 410, and the second wavelength shift caused by strain when the detection light flows through the photonic crystal fiber 420.

[0048] The fiber grating 410 strongly reflects incident light only at specific wavelengths, forming a narrow-band Bragg reflection peak. The center wavelength of this reflection peak exhibits a stable drift with temperature changes and is minimally affected by strain. Furthermore, the photonic crystal fiber 420 has a periodic porous structure in its core and cladding. Incident light propagates simultaneously along the core and cladding channels within the fiber, forming multiple propagating light paths. The optical path difference between these paths generates interference, ultimately outputting a spectral signal containing periodic interference fringes. This fringe characteristic is highly sensitive to changes in strain within the cell, providing a physical basis for strain detection.

[0049] Specifically, the detection controller 200 determines the first wavelength shift caused by temperature when the detection light flows through the fiber grating 410 in the following way: the detection controller 200 receives the spectral signal of the detection light after it flows through the detection fiber 400, identifies the narrowband Bragg reflection peak from the spectral signal, and determines the center wavelength of the reflection peak of the narrowband Bragg reflection peak; here, the detection controller 200 can first receive the spectral signal fed back after the detection light flows through the detection fiber 400, and use a spectral recognition algorithm to filter out the narrowband Bragg reflection peak corresponding to the spectral signal, and locate the center wavelength of its real-time reflection peak.

[0050] Furthermore, the detection controller 200 can acquire a preset reference center wavelength of the reflection peak, calculate a first difference between the center wavelength of the reflection peak and the reference center wavelength of the reflection peak, and determine the first difference as the first wavelength drift. The preset reference center wavelength of the reflection peak is the initial center wavelength of the narrowband Bragg reflection peak recorded after the sensor analyzes the spectral signal of the detection light from the transmission detection fiber 400 under a calibrated environment with no strain and a reference temperature, used to eliminate initial state differences of the device. Here, by calculating the first difference between the real-time center wavelength of the reflection peak and the reference center wavelength of the reflection peak, the first wavelength drift caused solely by temperature changes can be directly obtained.

[0051] Furthermore, the detection controller 200 determines the second wavelength drift caused by strain when the detection light flows through the photonic crystal fiber 420 by means of: the detection controller 200 receives the interference spectrum signal output after flowing through the detection fiber 400 and identifies the center wavelength of the characteristic peak of the interference fringes in the interference spectrum signal; specifically, the detection controller 200 can identify the interference fringe signal corresponding to the photonic crystal fiber 420 from the complex spectrum through a spectral analysis algorithm, select the characteristic peak of the interference fringe signal, and locate its real-time center wavelength. Further, a preset reference center wavelength of the characteristic peak is obtained, and a second difference between the center wavelength of the characteristic peak and the reference center wavelength of the characteristic peak is calculated, and the second difference is determined as the second wavelength drift. The preset reference center wavelength of the characteristic peak is the initial characteristic wavelength of the interference fringes of the photonic crystal fiber 420 recorded after analyzing the spectral signal of the detection light from the transmission detection fiber 400 under strain-free and reference temperature conditions during the sensor calibration stage, used to eliminate interference from the initial state of the device. Here, the detection controller 200 can obtain the strain-dominated second wavelength drift by calculating the second difference between the real-time characteristic wave peak center wavelength and the characteristic wave peak reference center wavelength.

[0052] Then, based on the first wavelength drift, the second wavelength drift, and the preset fiber grating temperature sensitivity coefficient, fiber grating strain sensitivity coefficient, photonic crystal fiber temperature sensitivity coefficient, and photonic crystal fiber strain sensitivity coefficient, the temperature change and strain change are determined.

[0053] Specifically, the detection controller 200 can acquire preset fiber optic grating temperature sensitivity coefficient, fiber optic grating strain sensitivity coefficient, photonic crystal fiber temperature sensitivity coefficient, and photonic crystal fiber strain sensitivity coefficient, and calculate the temperature change and strain change using Formula 1:

[0054] (1)

[0055] in, The temperature change is... The strain change is the amount of strain. This is the first wavelength shift amount. This is the second wavelength shift amount. The temperature sensitivity coefficient of the fiber grating. The fiber grating strain sensitivity coefficient is... This refers to the temperature sensitivity coefficient of the photonic crystal fiber. The strain sensitivity coefficient of the photonic crystal fiber is given.

[0056] To achieve dual-parameter measurement of temperature and strain (or stress) of the fiber optic 400, it is necessary to obtain its independent response characteristics under different physical quantities through rigorous calibration experiments, and determine the fiber optic grating temperature sensitivity coefficient, fiber optic grating strain sensitivity coefficient, photonic crystal fiber temperature sensitivity coefficient, and photonic crystal fiber strain sensitivity coefficient.

[0057] Here, the temperature sensitivity coefficient of the fiber grating can be calculated using formula 2:

[0058] (2)

[0059] in, The temperature sensitivity coefficient of the fiber grating. The coefficient of thermal expansion of fiber Bragg grating 410 is given. The thermo-optic coefficient of fiber Bragg grating 410. Let T be the initial wavelength of the detection light emitted by the broadband light source 100, and T be the temperature. Based on this, the fiber grating temperature sensitivity coefficient of the fiber grating 410 under the detection light can be determined.

[0060] Furthermore, the temperature sensitivity coefficient of the photonic crystal fiber can be determined based on Equation 3:

[0061] (3)

[0062] in, This refers to the temperature sensitivity coefficient of the photonic crystal fiber. Let L be the interference phase change of the transmitted light in the photonic crystal fiber 420, and L be the effective sensing length of the photonic crystal fiber 420, i.e., the length of the fiber segment participating in mode interference. π represents the change in ambient temperature, n represents the mathematical constant pi, and n is the effective refractive index of photonic crystal fiber 420. α is the center wavelength of the detection light emitted by the broadband light source 100, and α is the thermal expansion coefficient of the photonic crystal fiber 420. Let be the temperature coefficient of the refractive index of the photonic crystal fiber 420. Here, the parameters required for Formula 4 can be determined experimentally. The amount of interference phase change of the transmitted light in the photonic crystal fiber 420 can be determined by emitting a detection beam into the photonic crystal fiber 420. The difference between the experimental temperature and the room temperature is the change in ambient temperature.

[0063] Furthermore, the fiber grating strain sensitivity coefficient can be calculated based on Equation 4:

[0064] (4)

[0065] in, The fiber grating strain sensitivity coefficient is... The initial wavelength of the detection light emitted by the broadband light source 100 is [wavelength]. The Poisson's ratio for fiber Bragg grating 410. In response, This represents the wavelength shift caused by temperature changes. The wavelength shift caused by temperature changes can be determined experimentally by detecting the effect of the fiber grating 410 on the wavelength of the detection light at different temperatures.

[0066] Furthermore, the strain sensitivity coefficient of the photonic crystal fiber can be calculated according to Formula 5:

[0067] (5)

[0068] in, This represents the strain sensitivity coefficient of a photonic crystal fiber. The Poisson's ratio for photonic crystal fiber 420. In response, The center wavelength of the detection light emitted by the broadband light source 100.

[0069] In addition, the slope of the wavelength versus optical power curves of fiber optic grating 410 and photonic crystal fiber 420 at different temperatures can be experimentally detected to determine the temperature sensitivity coefficients of fiber optic grating 410 and photonic crystal fiber 420.

[0070] Specifically, such as Figure 2As shown, a fiber optic grating and a photonic crystal fiber can be fused together in series to form an experimental fiber 130, which is then placed inside a constant temperature chamber 120. Furthermore, a broadband light source 100 can emit detection light into the experimental fiber 130, which is then transmitted to a spectrometer 110. Here, the spectrometer 110 is used to detect the spectral response characteristic curve of the detection light flowing through the experimental fiber 130. Here, without mechanical loading and without strain on the experimental fiber 130, the constant temperature chamber 120 can be gradually heated and cooled while maintaining a stable temperature, recording the narrow-band Bragg reflection peak and characteristic peaks of the interference fringes of the spectral response characteristic curves at different temperatures.

[0071] Specifically, such as Figure 3 As shown, the spectral response curve of the detected light can include narrow-band Bragg reflection peaks from the spectral response curves at different temperatures. Since the slopes of all narrow-band Bragg reflection peaks are the same, the slope of these peaks can be determined as the temperature sensitivity coefficient of the fiber grating. Similarly, the spectral response curve of the detected light can include characteristic peaks of interference fringes from the spectral response curves at different temperatures. Since the slopes of these characteristic peaks are the same, the slope of these characteristic peaks can be determined as the temperature sensitivity coefficient of the photonic crystal fiber.

[0072] Furthermore, the slope of the wavelength versus optical power curves of fiber gratings and photonic crystal fibers under different strains can be experimentally measured to determine the strain sensitivity coefficients of the fiber gratings and photonic crystal fibers.

[0073] Here, as Figure 4 As shown, a fiber optic grating and a photonic crystal fiber can be fused together to form an experimental fiber 130, which is then placed on a high-precision stretching stage 140. A broadband light source 100 can emit detection light into the experimental fiber 130, which is then transmitted to a spectrometer 110 via the experimental fiber 130. In the actual experiment, the prepared experimental fiber 130 can be fixed to the high-precision stretching stage 140, with both ends of the high-precision stretching stage 140 fixedly connected to the experimental fiber 130. By controlling the displacement of the high-precision stretching stage 140 along the length of the experimental fiber 130, the experimental fiber 130 is subjected to different strains. Simultaneously, the experimental temperature is kept constant to eliminate the influence of temperature disturbances, and the narrow-band Bragg reflection peak and characteristic peaks of the interference fringes of the spectral response characteristic curves of the detection light under different strains are recorded.

[0074] Specifically, such as Figure 5As shown, the spectral response characteristic curve of the detected light can include narrow-band Bragg reflection peaks of the spectral response characteristic curves under different strains. Here, the slope of each narrow-band Bragg reflection peak is the same, and the slope of the narrow-band Bragg reflection peak can be determined as the strain sensitivity coefficient of the fiber grating. At the same time, the spectral response characteristic curve of the detected light can include characteristic peaks of interference fringes of the spectral response characteristic curves under different strains. Here, the slope of each characteristic peak of interference fringes is the same, and the slope of the characteristic peak of interference fringes can be determined as the strain sensitivity coefficient of the photonic crystal fiber. Compared to traditional methods of measuring temperature and strain sensitivity coefficients, the sensitivity coefficient method proposed in this application, which involves sequential calibration using pure strain and pure temperature, has significant advantages. It eliminates parametric coupling and, through separate loading of temperature and strain, achieves a highly controllable calibration environment, accurately distinguishing the contributions of the two types of physical quantities to spectral drift and improving the accuracy and uniqueness of the sensitivity coefficient. Secondly, the experimental environment is simple, relying only on conventional instruments such as a stretching table and a constant temperature chamber, without the need for complex external field construction or empirical fitting models. Thirdly, it has a wide range of applications; only the output characteristic quantity needs to be replaced to adapt to various fiber optic structures, exhibiting strong versatility and portability.

[0075] Finally, based on the temperature change, the strain change, and the preset temperature and strain reference values, the temperature and strain values ​​of the battery under test 300 are determined.

[0076] The temperature reference value can be the initial temperature of the battery recorded under strain-free conditions during the sensor calibration phase, which is typically room temperature or ambient temperature. Furthermore, the strain reference value is the initial strain of the battery under no mechanical loading during this calibration phase, with a default value of 0. Further, by adding the temperature reference value to the temperature change, the real-time temperature value of the battery under test (300°C) can be obtained; by adding the strain reference value to the strain change, the real-time strain value of the battery under test (300°C) can be obtained, achieving precise quantification and acquisition of the battery's core physical quantities.

[0077] Furthermore, the detection controller 200 may include a spectrometer and a demodulation unit. The spectrometer monitors changes in the reflected signal of the detection light, typically with a resolution less than 0.01 nm, and can detect minute temperature or strain disturbances. The demodulation unit identifies the drift of characteristic peaks of the narrow-band Bragg reflection peak and interference fringes to extract temperature and strain signals. Specifically, the detection light transmitted through the detection fiber 400 is first received by the spectrometer, which then performs spectral processing to generate a complete spectral curve. Simultaneously, it identifies and extracts spectral features such as the Bragg reflection peak corresponding to the fiber grating and the interference fringes corresponding to the photonic crystal fiber, and performs subsequent parameter calculations. Furthermore, the demodulation unit is used to acquire spectral features such as spectral curves, Bragg reflection peaks corresponding to fiber optic gratings, and interference fringes corresponding to photonic crystal fibers. It also retrieves reference spectral data from the calibration stage, calculates the first difference between the center wavelength of the reflection peak and the reference center wavelength of the reflection peak as the first wavelength shift, and calculates the second difference between the center wavelength of the characteristic wave peak and the reference center wavelength of the characteristic wave peak as the second wavelength shift. Furthermore, it combines a preset sensitivity coefficient matrix to complete the decoupling operation of temperature and strain, and finally outputs the real-time temperature and strain values ​​of the battery 300 under test, realizing the "optical-electrical" mapping between spectral signals and physical parameters.

[0078] In an optional embodiment, such as Figure 6 As shown, the detection optical fiber also includes a first coreless optical fiber 430 and a second coreless optical fiber 440.

[0079] Specifically, the first end of the fiber optic grating 410 can be connected to the broadband light source 100. The fiber optic grating 410, the first coreless fiber 430, the photonic crystal fiber 420, and the second coreless fiber 440 are connected in series between the broadband light source 100 and the detection controller 200. Furthermore, the fiber optic grating 410 can be connected to the broadband light source 100 via the first single-mode fiber optic jumper 510, and the second coreless fiber 440 can be connected to the detection controller 200 via the second single-mode fiber optic jumper 520.

[0080] Here, the first coreless fiber 430 is used to split the received detection light beam and deliver the split light beam to different apertures in the photonic crystal fiber 420, thereby improving the sensitivity of the photonic crystal fiber 420 to micro-strain sensing. Furthermore, the second coreless fiber 440 is used to recouple the light beams from the different apertures of the photonic crystal fiber 420 to reduce optical signal distortion caused by modal dispersion, and delivers the recoupled detection light beam to the detection controller 200 so that the detection controller 200 receives the detection light beam.

[0081] The embodiments provided in this application optimize the transmission and coupling effect of the detection light by connecting the first and second coreless optical fibers in series. The first coreless optical fiber can split the detection light and send it into different apertures of the photonic crystal fiber, enhancing its response to micro-strain and significantly improving strain sensing sensitivity. The second coreless optical fiber can recouple the light of different apertures, effectively reducing optical signal distortion caused by mode dispersion and ensuring signal integrity.

[0082] In an optional embodiment, such as Figure 7 As shown, the detection optical fiber also includes a first single-mode optical fiber 450 and a second single-mode optical fiber 460.

[0083] Specifically, the first single-mode fiber 450 is disposed between the fiber grating 410 and the first coreless fiber 430, and is used for low-loss optical transmission between the fiber grating 410 and the first coreless fiber 430 to ensure the strength of the optical signal before splitting. Here, the single-mode fiber has the characteristics of low transmission loss and strong mode stability, which can effectively solve the optical coupling loss problem caused by core diameter mismatch and refractive index difference between the fiber grating 410, the first coreless fiber 430 and the photonic crystal fiber 420.

[0084] Furthermore, the second single-mode fiber 460 is disposed between the second coreless fiber 440 and the detection controller (not shown in the figure) for low-loss optical transmission between the second coreless fiber 440 and the detection controller. This ensures that the optical signal coupled from the second coreless fiber 440 is stably delivered to the detection controller, avoiding spectral signal distortion caused by mode distortion during transmission, thereby improving the detection accuracy and stability of the overall detection system. Here, the second single-mode fiber 460 can be connected in series with the second coreless fiber 440 and the second single-mode fiber jumper (not shown in the figure), through which the detection light is transmitted to the detection controller.

[0085] Here, the fiber grating 410, photonic crystal fiber 420, first coreless fiber 430, second coreless fiber 440, first single-mode fiber 450, and second single-mode fiber 460 can be seamlessly connected through fiber tapering and high-precision fusion splicing. The aforementioned fiber segments can be fused together using the fusion taper method to form a low-loss mode transition region. The fiber fusion taper method optimizes the interface optical field matching, thereby reducing coupling loss. High-precision fusion splicing prevents the collapse of the photonic crystal fiber's aperture structure, thus ensuring the mechanical stability of the connection. The embodiment provided in this application, by setting the first and second single-mode fibers, optimizes the optical transmission performance of the detection fiber link, effectively solving the coupling loss problem caused by core diameter mismatch and refractive index differences between different types of fibers, ensuring the intensity and stability of the detection light signal, avoiding spectral distortion caused by mode distortion, and significantly improving the detection accuracy of the detection system.

[0086] Furthermore, when determining the lengths of the fiber grating, photonic crystal fiber, first coreless fiber, second coreless fiber, first single-mode fiber, and second single-mode fiber, the center wavelength of the fiber grating and its initial length can be selected by considering the type of battery under test and the wavelength range of the light source; here, the initial length of the fiber grating can be 25 mm, and the center wavelength can be 1580 nm. Further, initial structural parameters are set as follows: 2 mm for the first single-mode fiber and 1 mm for the second single-mode fiber; 1 mm for the first coreless fiber and 1 mm for the second coreless fiber; and 20 mm for the photonic crystal fiber. Further, after completing the taper splicing of the fiber grating, photonic crystal fiber, first coreless fiber, second coreless fiber, first single-mode fiber, and second single-mode fiber, and connecting them to a single-mode fiber jumper to form a test fiber, the assembled test fiber is placed in a tensile testing table, and spectral testing is conducted under a variable strain environment. Test light is emitted into the test fiber, and the peak and valley characteristics of the transmitted light's spectral curve are observed. The clarity of the peaks and valleys is then manually determined. Similarly, the same detection fiber can be transferred to a constant temperature chamber for spectral testing under a variable temperature environment. Detection light is also emitted to it, and the peak and valley characteristics of the transmitted light's spectral curve are observed. The clarity of the peak and valley characteristics is then manually determined to preliminarily verify the basic sensing performance of the fiber structure.

[0087] Furthermore, if the spectral peaks and valleys of the initial structure are not obvious, the fiber length adjustment stage begins. Maintaining variable control logic, the lengths of each fiber segment are iteratively adjusted in a gradient manner: increasing the length of single-mode fiber by 1 mm, coreless fiber by 1 mm, and photonic crystal fiber by 10 mm. After each set of fiber length adjustments is completed, a test fiber segment is placed on a stretching table and in a constant temperature chamber for spectral testing to determine if the peak and valley characteristics of the transmitted light spectral curve are obvious, until a clear peak and valley curve is observed. The core of this process is to utilize the characteristic that different fiber segment lengths affect mode coupling efficiency and interference fringe spacing. By adjusting the length ratio of each fiber segment, the sensitivity of the transmission spectrum of the test fiber to temperature and strain changes is enhanced, thereby improving the detection accuracy of the detection device for temperature and strain.

[0088] Furthermore, once the spectral peaks and valleys of the transmitted light from a detection fiber of a certain length combination reach a clear standard, its actual compatibility needs to be further verified. Specifically, the detection fiber of this structure is embedded into the battery using a micro-puncture method, and a traditional thermocouple sensor is simultaneously implanted into the battery. Multi-field coupling tests are conducted, and the spectral data of the detection fiber and the temperature reference data of the thermocouple are collected. If the characterization states of the two types of sensors are consistent, that is, the temperature value determined based on the spectral data of the detection fiber is the same as the temperature value collected by the thermocouple, then this length combination can be determined as the optimal structure. This structure can provide highly recognizable spectral features for subsequent dual-parameter decoupling. Conversely, if the characterization states of the two types of sensors are inconsistent, the lengths of each fiber segment are adjusted iteratively in a gradient manner: "increase the length of single-mode fiber by 1 mm, the length of coreless fiber by 0.5 mm, and the length of photonic crystal fiber by 5 mm" to obtain a new detection fiber. The new detection fiber is then implanted into the battery through the same micro-puncture path and depth. The above coupling condition test is then carried out again, and the spectral response data of the new detection fiber and the temperature reference data of the thermocouple are collected simultaneously. The temperature values ​​characterized by the two are compared again, and the above process is repeated until the temperature values ​​collected by the two types of sensors are consistent. Finally, the optimal combination of fiber segment lengths suitable for the battery environment is determined.

[0089] Furthermore, Figure 8 The relationship between the second wavelength drift measured by this device and the strain on the detection fiber is given, as follows: Figure 8 As shown, the coordinate system uses strain (unit: microstrain με) as the horizontal axis and the second wavelength drift (unit: nanometers nm) as the vertical axis. The data points and the fitted line show the linear relationship between the two. The slope of this linear relationship is 0.769 picometers per microstrain (pm / με), that is, for every 1 με change in strain, the second wavelength drift changes by 0.769 pm. At the same time, the Pearson correlation coefficient and other indicators show that the correlation and fit of this linear fit are high, thus reflecting the wavelength response characteristics and linear sensitivity of the detection fiber under strain.

[0090] Furthermore, Figure 9 The differences in wavelength response under strain between two sensing structures, fiber optic gratings (FBG) and Mach-Zehnder interferometers (MZ), are presented; for example... Figure 9 As shown, the coordinate system has strain (unit: microstrain με) as the horizontal axis and wavelength (unit: nanometer nm) as the vertical axis. The wavelength corresponding to the Mach-Zehnder interferometer shows a significant decreasing trend with increasing strain, while the wavelength corresponding to the fiber grating shows a slow increasing trend with increasing strain. This reflects the difference in the response characteristics of the two structures to change and enables differentiated perception of strain parameters.

[0091] Furthermore, Figure 10The differences in wavelength response between fiber gratings (FBG) and Mach-Zehnder interferometers (MZ) under temperature variations are presented; for example... Figure 10 As shown, this coordinate system uses temperature (in degrees Celsius, °C) as the horizontal axis and wavelength (in nanometers, nm) as the vertical axis. The wavelength corresponding to the Mach-Zehnder interferometer shows a significant decreasing trend with increasing temperature, while the wavelength corresponding to the fiber grating shows a slow increasing trend with increasing temperature. This reflects the difference in the temperature response characteristics of the two structures, enabling differentiated perception of temperature parameters and providing a basis for subsequent decoupling of temperature and strain.

[0092] The battery temperature and strain detection device provided in this embodiment achieves spatial decoupling of temperature and strain by constructing a composite heterogeneous fiber structure of "fiber grating + single-mode fiber + coreless fiber + photonic crystal fiber + coreless fiber + single-mode jumper" through cascaded detection optical fibers embedded inside the lithium battery. This overcomes the technical bottleneck of traditional homogeneous fiber sensing structures, which struggle to distinguish multi-parameter responses. Furthermore, this solution utilizes the microstructure air holes of photonic crystal fibers and the energy leakage characteristics of coreless fibers to make mode interference in the sensing area more sensitive and controllable, significantly improving detection resolution and response sensitivity. Simultaneously, based on designable fiber structure parameters, the detection device achieves tunability and customization, providing a scalable new solution for high-precision monitoring in multi-field coupling environments. Moreover, based on the above technical solution, a neural network can be used to estimate the battery's SOC. Addressing the strong coupling and nonlinear relationship between temperature and strain signals in this multi-parameter fiber sensing system, decoupling is achieved by constructing a multi-parameter matrix, enabling accurate detection of battery temperature and stress. This provides an emergency solution for electrical parameter monitoring failure scenarios and solves the problem of traditional electrical parameter monitoring being susceptible to electromagnetic interference. Ultimately, this detection device can counteract the coupling interference of temperature and strain as well as the influence of environmental noise, outputting high-precision and high-reliability thermal safety early warning results, enabling early prediction and timely intervention of lithium battery thermal risks.

[0093] On the other hand, embodiments of this application also provide a battery pack, wherein each individual cell in the battery pack corresponds to a battery temperature and strain detection device as described above, so as to realize the detection of temperature and strain of each individual cell in the battery pack.

[0094] The serial numbers in this application are for descriptive purposes only and do not represent the superiority or inferiority of any particular implementation scenario. The above disclosures are merely a few specific implementation scenarios of this application; however, this application is not limited thereto, and any variations conceived by those skilled in the art should fall within the protection scope of this application.

Claims

1. A device for detecting battery temperature and strain, characterized in that, The device includes a broadband light source, a detection controller, and a detection optical fiber disposed in the battery to be tested. The detection optical fiber is embedded between the electrode active layer and the separator inside the battery to be tested by puncture. The extension direction of the detection optical fiber is parallel to the winding direction of the battery to be tested and is in direct contact with the active material layer inside the battery to be tested. The detection fiber includes a first coreless fiber, a second coreless fiber, a fiber grating, a first single-mode fiber, a second single-mode fiber, and a photonic crystal fiber connected in series. The detection fiber is connected between the broadband light source and the detection controller, and is used to receive the detection light from the broadband light source and send the flowing detection light to the detection controller. The fiber grating is connected to the broadband light source at its first end. The fiber grating, the first single-mode fiber, the first coreless fiber, the photonic crystal fiber, the second coreless fiber, and the second single-mode fiber are connected in series between the broadband light source and the detection controller. The photonic crystal fiber utilizes the mode interference effect to provide a high-sensitivity response to strain, thereby improving the detection accuracy of strain. The first coreless optical fiber is used to split the received detection light and transmit the split light to different apertures in the photonic crystal fiber; The second coreless optical fiber is used to recouple light rays from different apertures and transmit the recoupled detection light rays to the detection controller so that the detection controller receives the detection light rays; The first single-mode fiber is used for low-loss optical transmission between the fiber grating and the first coreless fiber. The second single-mode fiber is used for low-loss optical transmission between the second coreless fiber and the detection controller; The detection controller is configured to perform the following processes: The detection controller receives the spectral signal of the detection light flowing through the detection optical fiber, identifies the narrowband Bragg reflection peak from the spectral signal, and locates the center wavelength of the narrowband Bragg reflection peak; obtains a preset reference center wavelength of the reflection peak, calculates a first difference between the center wavelength of the reflection peak and the reference center wavelength of the reflection peak, and determines the first difference as a first wavelength shift. The detection controller receives the interference spectrum signal of the detection light after it flows through the detection optical fiber, and identifies the center wavelength of the characteristic peak of the interference fringe in the interference spectrum signal; obtains the preset reference center wavelength of the characteristic peak, calculates the second difference between the center wavelength of the characteristic peak and the reference center wavelength of the characteristic peak, and determines the second difference as the second wavelength drift. The detection controller acquires preset fiber optic grating temperature sensitivity coefficient, fiber optic grating strain sensitivity coefficient, photonic crystal fiber temperature sensitivity coefficient, and photonic crystal fiber strain sensitivity coefficient. The temperature change and strain change can be calculated using the following formulas: in, The temperature change is... The strain change is the amount of strain. This is the first wavelength shift amount. This is the second wavelength shift amount. The temperature sensitivity coefficient of the fiber grating. The fiber grating strain sensitivity coefficient is... This refers to the temperature sensitivity coefficient of the photonic crystal fiber. The strain sensitivity coefficient of the photonic crystal fiber; Based on the temperature change, the strain change, and the preset temperature and strain reference values, the temperature and strain values ​​of the battery under test are determined.

2. The battery temperature and strain detection device according to claim 1, characterized in that, The outer surface of the detection optical fiber is coated with a silicon dioxide coating, and the outer surface of the silicon dioxide coating is coated with a fluorinated polymer coating.

3. The battery temperature and strain detection device according to claim 2, characterized in that, The fluorinated polymer coating includes at least one of polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, and fluorinated ethylene propylene copolymer.

4. A battery pack, characterized in that, The battery pack includes a battery temperature and strain detection device as described in any one of claims 1 to 3.

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