Fiber bragg sensor and system for monitoring thermal runaway of lithium-ion batteries

Abstract

The application discloses a kind of optical fiber bragg sensor and system for monitoring lithium ion battery thermal runaway, it is related to optical fiber bragg sensor technical field.The optical fiber bragg sensor includes optical fiber core and first pillar element and second pillar element, the first pillar element is coated with Pt-WO3 film outside, the second pillar element is coated with polyether sulfone film outside, the Pt-WO3 film and polyether sulfone film are obtained by solvent evaporation method preparation.The optical fiber bragg sensor can obtain the concentration of lithium ion battery internal hydrogen and carbon dioxide gas simultaneously, according to the concentration of hydrogen and carbon dioxide, judge whether the phenomenon of thermal runaway appears in lithium ion battery inside, so as to take measures as soon as possible, avoid the occurrence of fire;And, since the Pt-WO3 film and polyether sulfone film are obtained by solvent evaporation method preparation, with the characteristics of film layer thickness uniform, target gas response sensitive.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fiber Bragg sensors, in particular to a fiber Bragg sensor and a system for monitoring thermal runaway of a lithium ion battery. BACKGROUND

[0002] Some gases may be produced before or during a fire, which can be used as a basis for judging whether a fire is triggered or has occurred. The existing fire gas detection technology is a technical means for judging whether a fire will occur by monitoring or detecting gases that trigger fire or explosion risks, aiming to discover hidden dangers as soon as possible in order to take appropriate measures to protect life and property. For example, lithium ion batteries may generate heat during charging and discharging, which may easily trigger thermal runaway behavior. During the process of thermal runaway, gases such as hydrogen, carbon monoxide, and carbon dioxide may be produced. By monitoring these gases, the state of the lithium ion battery can be determined, and the occurrence of a fire can be avoided. It is found that, in the simulation of the state of thermal runaway of a lithium ion battery, CO2, CO, H2, C2H4, CH4, C2H6, and C3H6 are the main gas components produced during thermal runaway of the lithium ion battery, and the volume fractions of CO2 and H2 are as high as 35% and 23%, respectively. Therefore, by detecting or monitoring the content of CO2 and H2 gases inside the lithium ion battery, it can be used as a basis for judging whether the lithium ion battery has hidden dangers that may trigger a fire.

[0003] The existing fire gas detection technology includes ionization smoke detectors, photoelectric smoke detectors, carbon monoxide (CO) detectors, flammable gas detectors, flame detectors, thermal imaging cameras, and the like, which are widely used in some fire-prone sites. However, these fire gas detection technologies have the following defects: poor targeting, easy false alarms and false positives; insufficient sensitivity, long reaction time, and still no alarm when the concentration is high, which may delay the opportunity to take emergency measures; large size, high maintenance cost, poor adaptability, and high environmental requirements.

[0004] The fiber Bragg grating sensor is a new type of gas detection method. It utilizes the Bragg reflection principle of the grating and the absorption characteristics of the gas to affect the spectral characteristics of the fiber Bragg grating. Therefore, when the target gas exists, it will absorb light of a specific wavelength, causing the Bragg reflection wavelength of the fiber Bragg grating to change. Therefore, by measuring the reflection spectrum of the grating, the absorption characteristics of the gas in the environment around the grating can be analyzed, and the presence and concentration of the target gas can be determined. Compared with mainstream smoke detectors, flammable gas detectors, and toxic gas detectors, the fiber Bragg grating sensor has the characteristics of high sensitivity, high resolution, real-time monitoring, simultaneous detection of multiple gases, non-invasiveness, remote monitoring, and the like.

[0005] The Chinese patent application with the publication number CN116337787A discloses a kind of optical fiber grating sensor and lithium ion battery internal hydrogen monitoring system, by the optical fiber Bragg grating of setting obtains the change of lithium ion battery internal hydrogen content, and further guarantee the safety of lithium ion battery.But the following defects still exist in the application: (1) only one kind of gas hydrogen can be detected; (2) the optical fiber Bragg grating for detecting hydrogen is with palladium alloy as gas sensitive material, however, palladium membrane is easily damaged by lattice expansion, such as cracking, bubble, delamination, etc., which affects its stability and sensitivity.

[0006] In view of the problem that palladium membrane is easily damaged by expansion, the prior art discloses a kind of optical fiber hydrogen sensor based on Pt-WO3 film, which has the advantages of high sensitivity, fast response and good repeatability, but the existing optical fiber hydrogen sensor is made by coating Pt-WO3 powder on the surface of optical fiber, and the traditional coating method is usually lift-off method and static heating method, which is difficult to avoid the influence of gravity, resulting in inconsistent coating thickness, poor repeatability and stability, and the performance of optical fiber Bragg grating is affected.

[0007] It can be seen that the prior art still needs to be improved and improved. SUMMARY

[0008] In view of the above shortcomings of the prior art, the purpose of the present application is to provide a kind of optical fiber Bragg sensor and system for monitoring lithium ion battery thermal runaway, to solve the defects of poor sensitivity and stability of the existing optical fiber Bragg sensor for monitoring lithium ion battery thermal runaway.

[0009] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0010] The first aspect of the present application discloses a kind of optical fiber Bragg sensor, wherein, including optical fiber core and first pillar element and second pillar element, the first pillar element is coated with Pt-WO3 film outside, the second pillar element is coated with polyether sulfone film outside, and the Pt-WO3 film and polyether sulfone film are prepared by solvent evaporation method.

[0011] The solvent evaporation method for preparing Pt-WO3 film in the optical fiber Bragg sensor includes the following steps:

[0012] Step S01. Prepare a coaxial clamp and a hollow tube by 3D printer, and the material used for 3D printing is PVA water-soluble material;

[0013] Step S02. Limit and fix the first pillar element with coaxial clamp and hollow tube;

[0014] Step S03. Injecting Pt-WO3 solution into the gap between the first pillar element and the hollow tube, the solvent of the solution is isopropyl alcohol;

[0015] Step S04. Removing the solvent in the Pt-WO3 solution by evaporation to form Pt-WO3 film on the surface of the fiber Bragg sensor;

[0016] Step S05. Placing the coaxial clamp, the hollow tube and the first pillar element in clean water, after the coaxial clamp and the hollow tube are dissolved, the first pillar element coated with Pt-WO3 film is obtained.

[0017] In the fiber Bragg sensor, the mass ratio of Pt to WO3 in the Pt-WO3 solution is 1:12.

[0018] In the fiber Bragg sensor, the thickness of the Pt-WO3 film is 10 μm.

[0019] In the fiber Bragg sensor, the mass fraction of Pt-WO3 in the Pt-WO3 solution is 20%.

[0020] In the fiber Bragg sensor, the preparation method of the Pt-WO3 includes the steps of:

[0021] Sodium tungstate dihydrate and tartaric acid are dissolved in deionized water and stirred until uniform; hydrochloric acid is added to make the pH value of the solution 1, and stirring is continued until the tungstic acid precipitate is completely precipitated; oxalic acid dihydrate is added to the mixed solution and stirred to obtain a tungstic acid mother liquor; the tungstic acid mother liquor is placed in a reaction kettle and subjected to hydrothermal reaction; after the reaction is completed, the solid particles are separated by centrifugation and washed, and then dried to obtain WO3 powder; acetylacetone platinum and WO3 powder are taken according to the proportion, ground and mixed uniformly, and then sintered to obtain Pt-WO3 nano powder.

[0022] In the fiber Bragg sensor, the mass ratio of sodium tungstate dihydrate to tartaric acid is 1.5:1.

[0023] In the fiber Bragg sensor, the mass ratio of oxalic acid dihydrate to sodium tungstate dihydrate is 4:3-3.5.

[0024] In the fiber Bragg sensor, the temperature of the hydrothermal reaction is 130-160℃, and the time is 12-24h; the sintering temperature is 300-350℃, and the sintering time is 2-3h.

[0025] The second aspect of the present application discloses a system for monitoring thermal runaway of a lithium ion battery, which comprises a computer, a demodulator and a fiber Bragg sensor as described above, and the fiber Bragg sensor is placed above the inside of the lithium ion battery to obtain the concentration of hydrogen and carbon dioxide in the inside of the lithium ion battery.

[0026] Advantages:

[0027] The application provides a fiber Bragg sensor and a system for monitoring thermal runaway of a lithium ion battery, the fiber Bragg sensor is characterized by being provided with a first pillar element coated with a Pt-WO3 film on the surface and a second pillar element coated with a polyether sulfone film on the surface, the Pt-WO3 film and the polyether sulfone film are both prepared by a solvent evaporation method, and have the characteristics of uniform film layer thickness and sensitive response to target gas. Compared with the prior art, the fiber Bragg sensor can monitor two kinds of gas, is realized through different pillar elements, has better selectivity and sensitivity, and is particularly suitable for monitoring the gas concentration in a lithium ion battery. The system for monitoring thermal runaway of a lithium ion battery using the fiber Bragg sensor can simultaneously obtain the concentrations of hydrogen and carbon dioxide in the lithium ion battery, and judges whether thermal runaway occurs in the lithium ion battery according to the concentrations of hydrogen and carbon dioxide, so that measures can be taken as early as possible to avoid fire. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The application provides structural diagrams of a fiber core, a pillar element, a coaxial clamp and a hollow tube.

[0029] Figure 2 The application provides structural diagrams of a fiber core, a pillar element, a coaxial clamp and a hollow tube.

[0030] In the drawings, 1 is a fiber core, 2 is a pillar element, 3 is a coaxial clamp, and 4 is a hollow tube. DETAILED DESCRIPTION

[0031] The application provides a fiber Bragg sensor and a system for monitoring thermal runaway of a lithium ion battery, in order to make the purpose, technical scheme and effect of the application more clear and explicit, the following examples are used to further describe the application. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0032] The application provides a fiber Bragg sensor (FBG), the FBG includes a fiber core, a first pillar element and a second pillar element, the first pillar element is coated with a Pt-WO3 film, the second pillar element is coated with a polyether sulfone film, and the Pt-WO3 film and the polyether sulfone film are both prepared by a solvent evaporation method.

[0033] The Pt-WO3 film has excellent hydrogen adsorption and dissociation capacity, so when the first pillar element is placed in a hydrogen environment, once hydrogen molecules contact the surface of the Pt-WO3 material, the hydrogen molecules are adsorbed and dissociated under the catalysis of Pt to generate free hydrogen atoms; when the free hydrogen atoms diffuse into the WO3 lattice and react with the WO3 to generate tungsten bronze, the tungsten bronze is very unstable in air and is easy to react with oxygen in the environment to regenerate WO3 and H2O. In the foregoing redox process, the temperature and stress of the fiber core body change, thereby changing the grating pitch of the FBG and the effective refractive index of the fiber core, and finally causing the center wavelength of the strong interference peak of the FBG to drift, and the center wavelength drift is linearly changed with the concentration of hydrogen, so the concentration of hydrogen can be obtained according to the center wavelength drift.

[0034] The polyether sulfone film is a high-molecular material that has good gas sensitivity to carbon dioxide gas, which will expand in a carbon dioxide atmosphere and drive the fiber grating area to elongate, thereby causing the center wavelength to drift, and the center wavelength drift has a good linear relationship with the concentration of carbon dioxide gas, so the concentration of carbon dioxide gas can be obtained according to the center wavelength drift.

[0035] Therefore, in the embodiment, by arranging the first pillar element coated with the Pt-WO3 film and the second pillar element coated with the polyether sulfone film, the fiber Bragg sensor can simultaneously obtain the concentrations of hydrogen and carbon dioxide gas in the lithium ion battery, and whether the thermal runaway phenomenon occurs in the lithium ion battery can be judged according to the concentrations of hydrogen and carbon dioxide, so that measures can be taken as early as possible to avoid the occurrence of fire. Compared with the prior art, the fiber Bragg sensor can monitor two kinds of gases, is realized by different pillar elements, has better selectivity and sensitivity, and is particularly suitable for monitoring the gas concentration in the lithium ion battery, and has better practicability.

[0036] In the prior art, the gas-sensitive film is usually coated on the pillar element by a pulling method or a static heating method, and due to the influence of gravity, the thickness of the gas-sensitive film is difficult to be uniform, which finally affects the stability of the fiber Bragg sensor. In this embodiment, the Pt-WO3 film and the polyether sulfone film are both prepared by a solvent evaporation method. The solvent evaporation method sets a mold with a specific size, forms a gap between the mold and the pillar element, fills the gap with a solution containing a gas-sensitive material, and then the gas-sensitive material is attached to the surface of the pillar element by solvent evaporation to form a gas-sensitive film on the surface of the pillar element. After film formation, the mold is removed by dissolution, so that the obtained gas-sensitive film has good thickness uniformity and can avoid damage to the film surface during demolding.

[0037] Specifically, as shown in FIG. 1, the fiber Bragg sensor comprises a fiber Bragg grating, a first pillar element and a second pillar element. Figure 1As shown, the mold includes a coaxial clamp 3 and a hollow tube 4. The hollow tube 4 is a hollow tubular structure with an inner diameter larger than the outer diameter of the support element 2 and a length greater than the length of the support element 2. When the support element 2 is inserted into the hollow tube 4, an annular gap is formed between the support element 2 and the inner wall of the hollow tube 4. The distance of this gap can be set according to the thickness of the film to be coated. The coaxial clamp 3 has a central through hole for the optical fiber core 1 to pass through and an annular groove for engaging the hollow tube. It is used to close one end of the hollow tube 4 and to fix the optical fiber core 1 and the support element 2. In use, the support element 2 is inserted into the hollow tube 4, with the optical fiber core 1 at one end of the support element 2 passing through the central through hole. Then, the end of the hollow tube 4 is engaged with the annular groove, thus closing one end of the hollow tube 4. Figure 2 As shown, the other end of the hollow tube is used to inject a solution containing a gas-sensitive material.

[0038] Based on the above mold, the solvent evaporation method for preparing Pt-WO3 films includes the following steps:

[0039] Step S01. Prepare the coaxial fixture and hollow tube using a 3D printer. The material used for 3D printing is PVA water-soluble material.

[0040] Step S02. Fix the first support element to the coaxial clamp and the hollow tube, so that the end of the hollow tube opposite to the coaxial clamp faces upward;

[0041] Step S03. Inject Pt-WO3 solution into the gap between the first support element and the hollow tube. The solvent of the solution is isopropanol.

[0042] Step S04. The solvent in the Pt-WO3 solution is removed by evaporation, and a Pt-WO3 film is formed on the surface of the first support element;

[0043] Step S05. Place the coaxial fixture, hollow tube and first support element in clean water. After the coaxial fixture and hollow tube dissolve, the first support element coated with Pt-WO3 film is obtained.

[0044] The solvent evaporation method described above for preparing Pt-WO3 films allows for the acquisition of Pt-WO3 films of specific thicknesses on the surface of support elements. In this method, a Pt-WO3 solution is filled into the gap between the hollow tube and the support element, and a film of specific thickness is obtained by evaporating the solvent. Using water-soluble PVA as the material for both the hollow tube and the coaxial fixture enables 3D printing. Furthermore, the fact that PVA is soluble in water but insoluble in organic solvents facilitates the removal of the hollow tube and coaxial fixture from the support element during demolding, achieving demolding without damaging the Pt-WO3 film.

[0045] In the solvent evaporation method for preparing Pt-WO3 films described above, the selection of materials for the coaxial fixture and hollow tube, as well as the choice of solvent for dissolving Pt-WO3, is crucial. The materials of the coaxial fixture and hollow tube must facilitate molding, i.e., meet the needs of 3D printing, forming a mold of a specific shape after cooling, while simultaneously being incompatible with the solvent used to dissolve the gas-sensitive material. Similarly, the Pt-WO3 solvent must ensure sufficient dissolution and uniform dispersion of Pt-WO3, while also avoiding reaction with PVA to ensure the coaxial fixture and hollow tube do not dissolve before solvent evaporation. Furthermore, the solvent should have a low boiling point for rapid removal during evaporation, preventing the evaporation temperature from reaching the glass transition temperature of PVA. In this embodiment, PVA, a water-soluble material, is selected as the material for the coaxial fixture and hollow tube, and isopropanol is chosen as the solvent for Pt-WO3, achieving both Pt-WO3 film formation and easy demolding.

[0046] In the solvent evaporation method described above for preparing Pt-WO3 films, the mass ratio of Pt to WO3 in the Pt-WO3 solution affects the gas-sensing characteristics of the FBG, particularly its sensitivity to hydrogen. In a preferred embodiment, with the same Pt-WO3 film thickness, a molar ratio of Pt to WO3 of 1:15 to 1:8 exhibits better sensitivity. The resulting fiber Bragg sensor, at a 4% hydrogen concentration, shows a center wavelength shift greater than 330 pm, significantly exceeding the sensor's detection resolution of 1 pm, with a response and recovery time of approximately 60 s. Preferably, when the molar ratio of Pt to WO3 is 1:12, the resulting fiber Bragg sensor, at a 4% hydrogen concentration, shows a center wavelength shift greater than 356 pm, with both a response and recovery time of 57 s.

[0047] In the solvent evaporation method described above for preparing Pt-WO3 films, the thickness of the Pt-WO3 film affects the sensitivity. A thicker Pt-WO3 film is more sensitive to hydrogen, but a thicker film is more susceptible to humidity and prone to cracking and peeling during repeated response and recovery processes, thus reducing the lifespan of the fiber Bragg sensor. Therefore, in a preferred embodiment, the Pt-WO3 film thickness is 8–13 μm, which provides good sensitivity and prevents cracking and peeling during prolonged use. Preferably, a Pt-WO3 film thickness of 10 μm further enhances both sensitivity and lifespan.

[0048] In the solvent evaporation method described above for preparing Pt-WO3 films, when the gap between the hollow tube and the first support element is fixed, the concentration of Pt-WO3 affects the thickness and uniformity of the Pt-WO3 film. Since Pt-WO3 has low solubility in isopropanol, ultrasonic treatment is usually required to uniformly disperse and dissolve nano-sized Pt-WO3 particles in isopropanol. When the mass percentage of Pt-WO3 is high, sedimentation is still likely to occur, resulting in uneven thickness of the prepared Pt-WO3 film. Conversely, when the mass percentage of Pt-WO3 is low, the obtained Pt-WO3 film thickness is small, and the evaporation time of isopropanol is longer, which can easily cause glass transition in PVA, affecting subsequent demolding. Therefore, in a preferred embodiment, by controlling the mass fraction of Pt-WO3 to be less than or equal to 25%, a uniform Pt-WO3 film can be obtained, enabling the prepared fiber Bragg sensor to have more stable hydrogen sensitivity. More preferably, when the mass fraction of Pt-WO3 is 20%, a Pt-WO3 film with a thickness of 10 μm can be obtained, and the film thickness is uniform, with good sensitivity and short response and recovery times.

[0049] Furthermore, the preparation method of Pt-WO3 affects its particle size and specific surface area, ultimately impacting its gas sensitivity. Therefore, in a preferred embodiment, the preparation method of Pt-WO3 includes the following steps:

[0050] Sodium tungstate dihydrate and tartaric acid were dissolved in deionized water and stirred until homogeneous. Hydrochloric acid was added to adjust the pH of the solution to 1, and stirring was continued until tungstic acid precipitation was complete. The concentration of the hydrochloric acid was 3–6 mol / L. Oxalic acid dihydrate was added to the mixture and stirred until the mixture became clear, yielding a tungstic acid mother liquor. The tungstic acid mother liquor was placed in a reaction vessel and subjected to a hydrothermal reaction at a temperature of 130–160 °C for 12–24 h. After the reaction was completed, the mixture was cooled, centrifuged, and the solid particles were washed with deionized water and dried to obtain WO3 powder. Platinum acetylacetonate and WO3 powder were mixed according to the specified ratio, ground, and sintered at 300–350 °C for 2–3 h to obtain Pt-WO3 nanoparticles.

[0051] In the above-described method for preparing Pt-WO3, the mass ratio of sodium tungstate dihydrate to tartaric acid affects the morphology of WO3. When a larger amount of tartaric acid is added, the obtained WO3 typically has a plate-like structure, while when a smaller amount of tartaric acid is added, a cubic block structure is obtained. The plate-like structure of WO3 is more conducive to Pt deposition, resulting in a fiber Bragg sensor with better sensitivity to hydrogen. Therefore, in a preferred embodiment, a mass ratio of sodium tungstate dihydrate to tartaric acid of 1.5:1 yields a plate-like WO3 structure, which is more conducive to the binding of WO3 and Pt.

[0052] In the above-mentioned preparation method of Pt-WO3, the amount of oxalic acid dihydrate added affects the particle size and specific surface area of ​​WO3. Experiments have shown that a higher ratio of oxalic acid dihydrate to sodium tungstate dihydrate results in larger WO3 particles with a smaller specific surface area, and vice versa. Conversely, a higher ratio results in smaller particles with a larger specific surface area, potentially even forming porous materials. Therefore, in a preferred embodiment, by adjusting the mass ratio of oxalic acid dihydrate to sodium tungstate dihydrate to 4:(2-2.5), WO3 nanosheet particles with smaller particle size and a suitable specific surface area can be obtained.

[0053] It should be noted that controlling the heating rate to 10℃ / min during the sintering of platinum acetylacetonate and WO3 powders results in better sintering performance, and the prepared Pt-WO3 is more sensitive to hydrogen.

[0054] After coating the first support element with a Pt-WO3 film, a polyethersulfone (PES) film is coated onto the second support element using the same method. The specific preparation steps are basically the same as those for coating Pt-WO3, except that in step S03, the solution injected into the gap between the second support element and the hollow tube is a PES solution. This solution uses PES as the solute and N,N-dimethylformamide as the solvent, and the mass fraction of PES is 20%. This method forms a PES film on the surface of the second support element. The second support element coated with the PES film exhibits good gas-sensing characteristics for carbon dioxide gas. When the thickness of the PES film is 12 μm, at a CO2 concentration of 45%, the center wavelength shift is approximately 40 pm, and the response time is approximately 3 minutes, making it suitable for carbon dioxide gas detection.

[0055] The aforementioned fiber Bragg sensor, by incorporating a first pillar element sensitive to hydrogen and a second pillar element sensitive to carbon dioxide on the fiber core, utilizes the linear relationship between the center wavelength shift and gas concentration to detect the concentrations of hydrogen and carbon dioxide. By using a hollow tube and coaxial clamps, a Pt-WO3 film can be uniformly coated on the first pillar element, and a polyethersulfone film can be coated on the second pillar element, thus ensuring that the fabricated fiber Bragg sensor possesses stable photosensitivity.

[0056] The second aspect of this invention also discloses a system for monitoring thermal runaway of lithium-ion batteries. The system includes a computer, a demodulator, and a fiber Bragg sensor. The fiber Bragg sensor, as described above, is positioned above the inside of the lithium-ion battery to monitor the concentrations of hydrogen and carbon dioxide inside the battery. By monitoring the concentrations of hydrogen or carbon dioxide, different optical signals are generated. The demodulator receives the optical signals from the fiber Bragg sensor and processes the data. The processed data is then transmitted to the computer. The computer analyzes and compares the data, and based on the comparison results, determines whether the lithium-ion battery is in a state of thermal runaway. Based on the determination, an early warning is issued to allow for timely intervention and prevent losses.

[0057] It should be noted that since computers and demodulators are existing technologies, they will not be described in detail here.

[0058] To further illustrate the fiber optic Bragg sensor provided by the present invention, the following embodiments are provided.

[0059] Example 1

[0060] A fiber Bragg sensor includes an optical fiber core and a first support element and a second support element disposed on the optical fiber core. The surface of the first support element is coated with a Pt-WO3 film with a thickness of 10 μm, and the surface of the second support element is coated with a polyethersulfone film with a thickness of 12 μm. In the Pt-WO3 film, the molar ratio of Pt to WO3 is 1:12. The Pt-WO3 film is prepared using the aforementioned Pt-WO3 film preparation method. The polyethersulfone film is prepared using the same method as the aforementioned polyethersulfone film preparation method.

[0061] The preparation method of Pt-WO3 is as follows: Sodium tungstate dihydrate and tartaric acid are dissolved in deionized water, with a mass ratio of sodium tungstate dihydrate to tartaric acid of 1.5:1, and stirred until homogeneous; 5 mol / L hydrochloric acid is added to adjust the pH of the solution to 1, and stirring is continued until tungstic acid precipitation is complete; oxalic acid dihydrate is taken at a mass ratio of 4:2.2 to sodium tungstate dihydrate and added to the mixture, and stirred until the mixture becomes clear to obtain tungstic acid mother liquor; the tungstic acid mother liquor is placed in a reaction vessel and subjected to hydrothermal reaction at a temperature of 150℃ for 20 h; after the reaction is completed, the mixture is cooled, centrifuged, and the solid particles are washed with deionized water and dried to obtain WO3 powder; platinum acetylacetonate and WO3 powder are taken at a molar ratio of 1:12, ground and mixed, and sintered at 320℃ for 2 h to obtain Pt-WO3 nanoparticles.

[0062] The fiber Bragg sensor described in Example 1 was used for the detection of hydrogen and carbon dioxide gases. The specific detection results are as follows: At a hydrogen concentration of 4%, the center wavelength of the Bragg grating drifted by 356 pm, and the response time and recovery time were both 57 s, showing good repeatability. At a CO2 concentration of 45%, the center wavelength shifted by about 40 pm, and the response time was about 3 min. In addition, a durability test was also conducted. Through repeated response and recovery tests, it was found that after 1000 repeated response and recovery cycles, the gas-sensitive membrane of the FBG did not crack or fall off, showing good stability.

[0063] Example 2

[0064] A fiber Bragg sensor, whose structure and preparation method are basically the same as those in Example 1, differs in that: (1) the thickness of the Pt-WO3 film is 8 μm, and the molar ratio of Pt to WO3 is 1:8; (2) the thickness of the polyethersulfone film is 13 μm. It should be noted that the molar ratio of platinum acetylacetonate to WO3 powder and the concentration of Pt-WO3 solution are appropriately adjusted.

[0065] The fiber Bragg sensor described in Example 2 was used for the detection of hydrogen and carbon dioxide gases. The specific detection results are as follows: at a hydrogen concentration of 4%, the center wavelength of the Bragg grating drifted by 330 pm, the response time was 60 s, and the recovery time was 62 seconds; at a CO2 concentration of 45%, the center wavelength shifted by about 40 pm, and the response time was about 3 minutes; at the same time, after 1000 durability tests, no cracking or detachment of the gas-sensitive membrane was observed, indicating good stability.

[0066] Example 3

[0067] A fiber Bragg sensor has a structure that is basically the same as that in Example 1, except that: (1) the thickness of the Pt-WO3 film is 13 μm and the mass ratio of Pt to WO3 is 1:15; (2) the thickness of the polyethersulfone film is 8 μm. It should be noted that the molar ratio of platinum acetylacetonate to WO3 powder and the concentration of Pt-WO3 solution are appropriately adjusted.

[0068] The fiber Bragg sensor described in Example 3 was used for the detection of hydrogen and carbon dioxide gases. The specific detection results are as follows: at a hydrogen concentration of 4%, the center wavelength of the Bragg grating drifted by 337 pm, the response time was 59 s, and the recovery time was 61 pm; at a CO2 concentration of 45%, the center wavelength shifted by about 40 pm, and the response time was about 3 min; at the same time, after 1000 durability tests, no cracking or detachment of the gas-sensitive membrane was observed, indicating good stability.

[0069] Comparative Example 1

[0070] A fiber Bragg sensor has a structure that is basically the same as that of Example 1, and the Pt-WO3 nanopowder is the same as that of Example 1. The difference is that the Pt-WO3 film and the polyethersulfone film are coated onto the first support element and the second support element respectively by the dip-coating method. During the coating process, the concentration of the Pt-WO3 solution and the concentration of the polyethersulfone solution are the same as those of Example 1.

[0071] The detection results of the fiber Bragg sensor described in Comparative Example 1 for hydrogen and carbon dioxide gases are as follows: At a hydrogen concentration of 4%, the center wavelength of the Bragg grating drifted by 171 pm, the response time was 71 s, and the recovery time was 65 seconds; at a CO2 concentration of 45%, the center wavelength shifted by approximately 23 pm, and the response time was approximately 4.2 min; after 460 durability tests, cracking occurred.

[0072] Comparative Example 2

[0073] A fiber Bragg sensor has a structure and preparation method that are basically the same as those in Example 1, except that the thickness of the Pt-WO3 film is 20 μm and the thickness of the polyethersulfone film is 20 μm.

[0074] The detection results of the fiber Bragg sensor described in Comparative Example 2 for hydrogen and carbon dioxide gases are as follows: At a hydrogen concentration of 4%, the center wavelength of the Bragg grating drifted by 352 pm. After more than 120 repeated tests, the Pt-WO3 film showed cracking and peeling. At a CO2 concentration of 45%, the center wavelength shifted by about 44 pm, the response time was about 3.4 min, and after 300 durability tests, the polyethersulfone film showed cracking and peeling.

[0075] Comparative Example 3

[0076] A fiber Bragg sensor has a structure and preparation method that are basically the same as those in Example 1, except that the thickness of the Pt-WO3 film is 5 μm and the thickness of the polyethersulfone film is 5 μm.

[0077] The detection results of the fiber Bragg sensor described in Comparative Example 3 for hydrogen and carbon dioxide gases are as follows: At a hydrogen concentration of 4%, the center wavelength of the Bragg grating drifted by 204 pm, with a response time of 86 s and a recovery time of 54 s; at a CO2 concentration of 45%, the center wavelength shifted by approximately 12 pm, with a response time of approximately 5.3 min and a recovery time of 3.1 min. No cracking or detachment was observed during the durability test.

[0078] As can be seen from the above embodiments 1-3, the fiber Bragg sensor of the present invention has good gas sensitivity to hydrogen and carbon dioxide, especially to hydrogen. It has high sensitivity, short response and recovery time, and can timely obtain the hydrogen content inside the lithium-ion battery, thus having a good predictive effect on the internal thermal runaway of the lithium-ion battery.

[0079] In contrast, the fiber Bragg sensor described in Comparative Example 1, due to the use of the dip-coating method to prepare the Pt-WO3 and polyethersulfone films, suffers from uneven film thickness due to gravity. This leads to decreased sensitivity to hydrogen and carbon dioxide, and a prolonged response time. Therefore, the uniformity of the gas-sensitive film thickness directly affects the sensor's sensitivity to the target gas. Furthermore, the uneven film thickness makes it prone to cracking at thicker sections, resulting in insufficient durability.

[0080] In Comparative Example 2, both the Pt-WO3 film and the polyethersulfone film are relatively thick. Although they have good gas sensitivity, their durability will decrease. They are prone to cracking or falling off during repeated use, which will shorten the service life of the sensor.

[0081] In Comparative Example 3, the thickness of both the Pt-WO3 film and the polyethersulfone film was thinner than that in Example 1, which reduced their sensitivity and prolonged their response time, thus limiting the application of the sensor.

[0082] In the description of the embodiments of the present invention, it should be noted that the terms "inner," "outer," "upper," "lower," "left," and "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0083] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; or they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances.

[0084] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A fiber Bragg sensor, characterized by, The optical fiber includes a fiber core and a first pillar element and a second pillar element, the first pillar element is coated with a Pt-WO3 film, and the second pillar element is coated with a polyether sulfone film, and the Pt-WO3 film and the polyether sulfone film are both prepared by a solvent evaporation method; The solvent evaporation method for preparing the Pt-WO3 film includes the following steps: S01. A coaxial clamp and a hollow tube are prepared by a 3D printer, and a PVA water-soluble material is used as the material for 3D printing; S02. The first pillar element is fixed in position with the coaxial clamp and the hollow tube; S03. A Pt-WO3 solution is injected into the gap between the first pillar element and the hollow tube, and the solvent of the solution is isopropyl alcohol; S04. The solvent in the Pt-WO3 solution is removed by evaporation to form a Pt-WO3 film on the surface of the fiber Bragg sensor; S05. The coaxial clamp, the hollow tube and the first pillar element are placed in clean water, and after the coaxial clamp and the hollow tube are dissolved, the first pillar element coated with the Pt-WO3 film is obtained; In the Pt-WO3 solution, the mass ratio of Pt to WO3 is 1:12; The preparation method of the Pt-WO3 includes the following steps: Sodium tungstate dihydrate and tartaric acid are dissolved in deionized water and stirred until uniform; hydrochloric acid is added to make the pH value of the solution 1, and stirring is continued until the tungstic acid precipitate is completely precipitated; oxalic acid dihydrate is taken and added to the mixed solution, and stirring is performed to obtain a tungstic acid mother liquor; the tungstic acid mother liquor is placed in a reaction kettle and subjected to a hydrothermal reaction; after the reaction is completed, the solid particles are cooled, centrifuged and washed, and dried to obtain WO3 powder; acetylacetone platinum and WO3 powder are taken in a predetermined ratio, ground and mixed uniformly, and then sintered to obtain Pt-WO3 nano-powder; The mass ratio of the sodium tungstate dihydrate to the tartaric acid is 1.5:

1. The temperature of the hydrothermal reaction is 130-160°C, and the time is 12-24h; the sintering temperature is 300-350°C, and the sintering time is 2-3h.

2. A fibre Bragg sensor according to claim 1, characterised in that, The thickness of the Pt-WO3 film is 10μm.

3. The fiber Bragg sensor according to claim 1, characterized in that, In the Pt-WO3 solution, the mass fraction of Pt-WO3 is 20%.

4. The fiber Bragg sensor of claim 1, wherein, The mass ratio of the oxalic acid dihydrate to the sodium tungstate dihydrate is 4:(2-2.5).

5. A system for monitoring thermal runaway of a lithium-ion battery, the system comprising: The system includes a computer, a demodulator and the fiber Bragg sensor according to any one of claims 1-4, the fiber Bragg sensor is arranged above the inside of the lithium ion battery, and is used to obtain the concentration of hydrogen and carbon dioxide in the inside of the lithium ion battery.

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