Optical fiber temperature sensor whose free end forms an optical probe comprising a matrix in which thermoluminescent particles are incorporated, and a layer covering the matrix, reflective and / or diffusing at the emission wavelengths of the particles.

Abstract

A fiber optic temperature sensor whose free end forms an optical probe comprising a matrix in which thermoluminescent particles are incorporated, and a coating over the matrix, reflective and / or diffusive at the emission wavelengths of the particles. The invention relates to a temperature sensor, comprising an optical fiber whose free end forms an optical probe comprising at least one thermoluminescent material capable of emitting a light peak at at least two wavelengths, and at least one coating over the matrix, the coating being made of at least one material reflective and / or diffusive at at least at the two emission wavelengths of the thermoluminescent material. Figure for the abstract: Fig. 8

Description

Title of the invention: Optical fiber temperature sensor whose free end forms an optical probe comprising a matrix in which thermoluminescent particles are incorporated, and a layer covering the matrix, reflective and / or diffusing at the emission wavelengths of the particles. technical field

[0001] The present invention relates to the field of instrumentation, in particular temperature sensors.

[0002] It relates more particularly to optical fiber temperature sensors.

[0003] The invention aims to provide a solution to overcome or at least reduce the constraints of the environment on the actual measurement of this type of sensor.

[0004] The invention is described with reference to a use for measuring temperatures within electrochemical accumulators or batteries, particularly of the metal-ion type, in order to better understand the phenomena that lead to overheating and / or thermal runaway of the accumulators.

[0005] Although described with reference to a Lithium-ion battery, the invention applies to temperature measurements of any metal-ion electrochemical battery, i.e. also sodium-ion, Magnesium-ion, Aluminium-ion batteries...or more generally to any electrochemical battery.

[0006] In general, a sensor according to the invention can be implemented in any industrial, medical, biological application requiring, at one time or another, the determination of a temperature, in particular in a range of -180°C to 400°C.

[0007] By "thermoluminescence", we mean here and within the framework of the invention, the ability of a material to emit almost instantaneously, at a given temperature and under the effect of light radiation called absorption or excitation radiation, light radiation of the same wavelength or of a different wavelength called emission radiation.

[0008] The light radiation emitted by the thermoluminescent material is characterized by an emission spectrum comprising one or more peaks whose intensity and / or luminescence lifetime varies as a function of the temperature to which the material is subjected. Previous technique

[0009] Optical fiber temperature sensors have been developed to collect precise thermal data on structures or in devices, in particular to detect anomalies that could affect their safety and reliability.

[0010] These optical fiber sensors offer numerous advantages, including the ability to be miniaturized and therefore to be installed in environments with limited space. Furthermore, they are electrically non-conductive and allow the properties of light to be exploited to probe various physical or chemical parameters within a component, particularly a battery or accumulator: [1], [2], [3].

[0011] Fiber optic sensors based on thermoluminescent particles put in works a principle of thermoluminescence by radiometry of emission peaks.

[0012] According to this principle, a luminescent material has an emission spectrum with several peaks at distinct wavelengths, at least one of which has an intensity that varies with temperature while others will remain constant.

[0013] Fig. 1 illustrates the luminescence spectrum of a thermoluminescent particle-based optical fiber sensor whose two emission peaks evolve as a function of the temperature to which they are subjected.

[0014] If we choose from among the peaks having thermal coupling a constant peak and a temperature-dependent peak, we can then recover the temperature measurement by measuring the luminescence using the relationship according to equation 1 as follows:

[0015] [Equation 1] ln(F / «) = —- —— (-) + ln(B) k B W

[0016] in which - FIR is the intensity ratio (or integrals) of the two emission peaks, - T is the temperature, - kB is the Boltzmann constant, - AE is the energy difference between the two energy levels corresponding to the two luminescence peaks, which are thermally coupled. - B is a constant.

[0017] This logarithmic response of the sensor according to [Fig.1] is illustrated in [Fig.2].

[0018] A conventional embodiment of a thermo-particle-based optical fiber sensor luminescent, consists of creating a probe based on said particles deposited at one end of an optical fiber and / or at sites along the length of an optical fiber by a sol-gel process.

[0019] During operation, absorption or excitation light is sent through the optical fiber to reach the probe. The resulting emitted radiation is recovered and sent back through the same fiber to a detector (such as a photodiode, photomultiplier, spectrophotometer, etc.) which allows the measurement of the fluorescence signal and thus the measurement of the temperature by signal processing.

[0020] An example of this type of optical fiber sensor is described in patent application EP4155700A1.

[0021] The inventors carried out temperature measurement tests during a cycle of a liquid electrolyte Li-ion battery impregnated in a conventional separator, using such a sensor by positioning it between the positive NMC (Nickel Manganese Cobalt) electrode and the separator.

[0022] Fig. 3 shows a current profile applied to a lAh Li-ion battery corresponding to one cycle of the latter.

[0023] Fig. 4 illustrates the variation of the intensity of the two peaks of interest, i.e. the two emission peaks of the thermoluminescent material of the sensor, as a function of time, for a lAh Li-ion battery during the cycling according to Fig. 3 to which it is subjected.

[0024] Since the temperature of the Li-ion battery is stable during this cycling, it is therefore observed that the response of the sensor is disturbed by the very operation of the battery, while the temperature of the battery, under these cycling conditions, does not show any measurable heating with this sensor.

[0025] Other tests were carried out on Li-ion batteries comprising the same electrodes as the previous battery but with a separator coated with a layer of alumina (A12O3), positioning the sensor in the same position, i.e. between the positive electrode and the separator.

[0026] With such an alumina layer separator, the inventors did not observe any variation in the intensity of the emission peaks, with the accumulator temperature remaining stable during the cycling identical to that of the previous one.

[0027] Fig. 5 illustrates from top to bottom the current profile identical to that of Fig. 3, as well as the voltage of the accumulator during the cycle, the temperature stability during this cycle, and the intensity of the two luminescence peaks of the material, named H and S.

[0028] It is clear from this [Fig.5] that there is no longer any visible impact of the variation of the current on the signal of the optical sensor: indeed, there is no variation in the intensity of the luminescence peaks H and S during the cycling.

[0029] The inventors were able to identify the origin of the problem observed in [Fig. 4]: it corresponds to an optical interaction between the sensor and the negative graphite electrode of the battery. Indeed, when the latter undergoes lithiation or a During the cycling process, it changes color and therefore the optical absorption of the environment changes the optical response of the sensor.

[0030] This means that in this type of configuration of the measurement sensor within a battery, in particular as described in patent application EP4155700A1, the sensor is sensitive to a change in optical environment on its response.

[0031] Figure 6 schematically shows an existing optical fiber sensor 1. It comprises an optical fiber 2 consisting of a core 20 adapted to propagate light and a cladding 21 surrounding the core. A free end 22 of the fiber carries an optical probe 3 consisting of an array 30 comprising thermoluminescent particles also called phosphors 31.

[0032] Figures 7A to 7C show the impact or not of the optical environment on the operation of this sensor 1.

[0033] In the case of [Fig.7A], the optical response of sensor 1 is not impacted by the environment, because the luminescence emitted by probe 3 is not modified by the environment and returns intact to the fiber, as symbolized by the single arrow which returns to the core 20 of the latter.

[0034] Figures 7B and 7C correspond to two cases where the negative graphite electrode of the accumulator 4 is respectively lithia or delithia: it can then be seen that this environment of accumulator 4 has an impact on the response of the sensor 1, since part of the luminescence emitted by the probe is absorbed by the nearby environment, as symbolized by the additional emission arrow on the left, before being collected by the fiber 2 for measurement.

[0035] To corroborate their analysis, the inventors carried out additional tests with accumulators comprising the same electrodes but for some with a conventional separator, i.e. without any deposit of layer on its surface, and for others with a separator coated with a layer of alumina on the surface.

[0036] When soaked in electrolyte, a conventional separator, without deposit, is optically transparent, while the separator coated with a layer of alumina on the surface appears opaque.

[0037] Thus, it is the opacity of the alumina separator on the surface that optically isolates the sensor from the negative electrode.

[0038] This therefore limits the use of an existing sensor to temperature measurements within accumulators where it is certain that the separator is transparent, i.e., which is not coated with a surface layer that changes the optical behavior of the separator, no longer seeing the absorption variations of the negative electrode during cycling even if the sensor is placed on the side of the positive electrode, or within the separator.

[0039] More broadly, an existing sensor cannot be reliably used when the measurement environment has optical variations that are in the same emission wavelength ranges as the peaks of interest of the thermoluminescent material of the sensor's optical probe.

[0040] There is therefore a need to make the optical response of optical fiber sensors independent of the nearby measurement environment, in order to obtain reliable measurements.

[0041] The aim of the invention is to meet at least part of this need. Description of the invention

[0042] To this end, the invention relates to a temperature sensor, comprising an optical fiber, one free end of which forms an optical probe comprising at least one thermoluminescent material capable of emitting a peak of light at at least two wavelengths, and at least one layer covering the matrix, the layer being made of at least one reflective and / or diffusing material at least at the two emission wavelengths of the thermoluminescent material.

[0043] By "layer of optical diffusing material", it is specified that here and within the framework of the invention, we mean a layer whose material will deflect light at the two emission wavelengths of the thermo-luminescent material in various directions and predominantly not in the direction of the optical fiber.

[0044] According to an advantageous embodiment, the optical probe comprises a matrix in which thermoluminescent particles are incorporated.

[0045] Advantageously, the reflective material of the layer is chosen from gold, aluminum, platinum, aluminum, copper, molybdenum, indium, tantalum or a mixture thereof.

[0046] The reflective material of the layer can also be chosen from silica, alumina, zirconia or a mixture thereof. The layer is then preferably a porous layer deposited by a sol-gel process.

[0047] Preferably, the thickness of the reflective material layer is between 90 and 500 nm, more preferably between 90 and 150 nm.

[0048] According to one embodiment, the reflective and / or diffusing material layer covers the matrix directly or indirectly via at least one interlayer with a refractive index, in particular a layer of poly(methyl methacrylate) (PMMA).

[0049] The invention also relates to the use of a temperature sensor as described above, for measuring temperature within an electrochemical accumulator, in particular a metal-ion accumulator.

[0050] Thus, the invention essentially consists of an optical fiber temperature sensor carrying at the end an optical probe of thermoluminescent material with at least two emission peaks which is coated with at least one reflective and / or diffusing layer forming an optical barrier, at the peaks considered, to the nearby environment whose temperature is to be measured.

[0051] The deposition of the reflective and / or diffusing layer is therefore adapted to the measurement wavelength peaks of the sensor.

[0052] The material of the reflective and / or diffusing layer must be compatible with the measurement environment. In the case of temperature measurement of Li-ion batteries, the material is chemically and electrochemically compatible with the battery during its cycling.

[0053] This eliminates the impact of the environment, whose optical characteristics, particularly light absorption, can change during their operation.

[0054] In the end, a sensor of the invention allows a temperature measurement by radiometry on two peaks by thermoluminescence which is reliable and precise, because its optical probe is optically isolated from the environment and therefore from its potential optical influence.

[0055] Other advantages and features will become clearer upon reading the detailed description, given by way of illustration and not limitation, with reference to the following figures. Brief description of the drawings

[0056] [Fig-1] [Fig.1] illustrates in form the luminescence spectrum of a sensor at optical fiber based on thermoluminescent particles whose two emission peaks evolve according to the temperature to which they are subjected.

[0057] [Fig.2] [Fig.2] is the logarithmic response line of the sensor according to [Fig.1].

[0058] [Fig.3] [Fig.3] is the curve of an example of cycling to which a Li-ion battery whose light we seek to measure with a fiber optic sensor and thermoluminescent material.

[0059] [Fig.4] [Fig.4] illustrates the variation of the intensity of the two emission peaks of the thermo-luminescent material of the sensor, as a function of time, for a lAh Li-ion battery during the cycling according to [Fig.3] to which it is subjected.

[0060] [Fig.5] [Fig.5] illustrates respectively the current profile identical to that of [Fig.3] as well as the voltage of the accumulator during cycling, the temperature stability during this cycling as well as the intensity of the two luminescence peaks of the material, named H and S.

[0061] [Fig.6] [Fig.6] is a longitudinal cross-sectional view of a state-of-the-art optical fiber measurement sensor.

[0062] [Fig.7A], [Fig.7B], [Fig.7C] Figures 7A, 7B, 7C schematically show the optical probe of the sensor according to [Fig.6], when the measurement environment consisting of a Li-ion battery has respectively no impact on the measurement, an impact due to lithiation, and to the delithiation of the negative graphite electrode of the battery.

[0063] [Fig.8] [Fig.8] is a longitudinal sectional view of a fiber optic measurement sensor according to the invention.

[0064] [Fig.9] [Fig.9] is a reprographic reproduction of a Li-ion accumulator in which is arranged a measurement sensor according to the state of the art, such as that of [Fig.6], and a measurement sensor according to the invention, such as that of [Fig.8].

[0065] [Fig. 10] [Fig. 10] illustrates from top to bottom the voltage and current curves of the accumulator according to [Fig. 9], during the cycling it undergoes, the external temperature curve of the accumulator measured with a thermocouple, and the variation of the maximum luminescence intensity of the peak S of the sensor according to the invention over time. Detailed description

[0066] Figures 1 to 7C have already been described in the preamble. They will therefore not be detailed further.

[0067] A fiber optic measurement sensor 1 according to the invention is shown in [Fig.8].

[0068] It comprises an optical fiber 2 consisting of a core 20 adapted to propagate light and a sheath 21 surrounding the heart.

[0069] A free end 22 of the fiber carries an optical probe 3 made up of a matrix 30 comprising thermoluminescent particles also called luminophores 31.

[0070] The materials of the matrix 30 and the luminophore particles 31 as well as the manufacturing techniques, in particular by sol-gel deposition, may advantageously be those described in patent application EP4155700A1.

[0071] A layer of opaque material 32 is deposited on the surface of the matrix 30. This layer 32 is reflective in the emission wavelengths of the luminescent material of the particles 31.

[0072] Thus, this layer 32 optically isolates the probe 3 from its measurement environment.

[0073] The inventors notably carried out the deposition of this gold layer 32 by a vacuum evaporation technique, on the end of fiber 2, directly on the matrix 30 of probe 3. The thickness of the deposit is on the order of one hundred nm.

[0074] This gold-coated 32-layer sensor 1 was then inserted into a Li-ion battery identical to the one tested, under the same conditions as in [Fig.3], and in the same location, i.e. between the positive electrode (NMC) and the separator without external coating.

[0075] For comparison, a state-of-the-art optical fiber sensor 1, such as that in [Fig. 6], comprising the same optical fiber 2 and a probe, was also tested. optics 3 with the same matrix 30 and phosphors 31 as those of sensor 1 according to the invention.

[0076] Fig. 6 shows the arrangement of the two sensors 1 respectively according to the invention and according to the prior art, as inserted in a Li-ion battery with a negative graphite electrode, a separator without an external coating and a positive NMC electrode.

[0077] This accumulator was cycled according to a protocol at different charge and discharge rates and the luminescence signal of the sensor was monitored over time as well as the surface temperature of the accumulator using a thermocouple.

[0078] The conditions of this cycle and the results obtained with a sensor 1 according to the invention whose probe matrix 30 is covered with a layer of gold 32 are presented in [Fig. 10].

[0079] It is observed that at a slow rate of the cycle, the temperature of the accumulator changes very little. The variations that can be seen are less than one degree Celsius and correspond on the curve probably to an external event, such as an opening of the test chamber.

[0080] There is no correlation between these variations and the cycling of the accumulator.

[0081] It can be seen that the luminescence signal of the sensor 1 according to the invention, which The peak S emission value, which translates to the maximum S value, is almost constant (bottom curve of [Fig. 10]). The very small variation observed is barely greater than the noise and stems from the variation in the source intensity.

[0082] More broadly, it is observed that there is no variation in the intensity of the S and H peaks as a function of the charging and discharging conditions of the cycling, as was seen with a sensor according to the state of the art.

[0083] This therefore proves that the sensor 1 according to the invention with an outer layer 32 of gold on its optical probe 3 is insensitive to the optical conditions of the measurement environment.

[0084] Other variants and improvements may be envisaged without departing from the scope of the invention.

[0085] The sensor 1 according to the illustrated example is made with the constituent materials and is produced according to the techniques, in particular by sol-gel according to patent application EP4155700A1. The invention can be applied to any other type of thermoluminescence optical probe using another type of particles or molecules as phosphors and another type of material for the matrix.

[0086] More generally, the invention can also be applied to other types of optical fiber temperature sensors with a probe manufactured at the end of the fiber and which operate by either reflectance or luminescence and whose signal must be isolated from optical interactions with the external environment. List of cited references:

[0087] [1]: Wang, R., Zhang, H., Lin, Q. Lin, F., Han, X., Lin, X., Li, K., Xiao, G., Albert, J., Lu, X. & Guo, T. « Operando monitoring ofion activities in aqueous batteries with plasmonic fiber -optic sensors. » Nature Communications 13, 547 (2022).

[0088] [2] : Lu, X., Tarascon, J.-M. & Huang, J. « Perspective on commercializing smart sensing for batteries ». eTransportation 14, 100207 (2022).

[0089] [3] : Hedman, J., Mogensen, R., Younesi, R. & Bjôrefors, F. « Fiber Optic Sensors for Détection of Sodium Plating in Sodium-Ion Batteries ». ACS Applied Energy Materials (2022) doi:10.1021 / acsaem.2c00595

Claims

Demands

1. Temperature sensor (1), comprising an optical fiber (2) having a free end (22) forming an optical probe (3) comprising at least one thermoluminescent material (31) with a matrix (30) in which thermoluminescent particles are incorporated, the material being capable of emitting a peak of light at at least two wavelengths, and at least one layer (32) covering the matrix, the layer being made of at least one reflective and / or diffusing material at least at the two emission wavelengths of the thermoluminescent material, the reflective material of the layer being selected from gold, aluminum, platinum, copper, molybdenum, indium, tantalum, silica, alumina, zirconia or a mixture thereof.

2. Temperature sensor according to claim 1, the layer of silica, alumina or zirconia or a mixture thereof being a porous layer deposited by a sol-gel process.

3. Temperature sensor according to any one of the preceding claims, the thickness of the reflective material layer being between 90 and 500 nm, preferably between 90 and 150 nm.

4. Temperature sensor according to any one of the preceding claims, the reflective and / or diffusing material layer covering the matrix directly or indirectly via at least one interlayer of refractive index, in particular a layer of poly(methyl methacrylate) (PMMA).

5. Use of a temperature sensor according to any one of the preceding claims, for measuring temperature within an electrochemical accumulator, in particular a metal-ion accumulator.

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