Method for processing the signal from a temperature sensor of a metal-ion accumulator, with optical fiber whose free end forms an optical probe with thermoluminescent material(s).

Abstract

Method for processing the signal of a temperature sensor of a metal-ion accumulator, with an optical fiber whose free end forms an optical probe with thermoluminescent material(s), at the emission peak(s) in at least one zone of variation of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the accumulator. The invention relates to a method for processing the measurement signal of a temperature sensor of a metal-ion accumulator, comprising an optical fiber whose free end forms an optical probe with thermoluminescent material(s) capable of emitting a light peak at at least two wavelengths, at least one of the two peaks (H, S) being adapted to be in at least one zone of variation of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the accumulator. Figure for abstract: Fig. 12

Description

Title of the invention: Method for processing the signal from a temperature sensor of a metal-ion accumulator, with optical fiber, the free end of which forms an optical probe with thermoluminescent material(s). Technical field

[0001] The present invention relates to the field of instrumentation, in particular sensors for measuring the temperature of an accumulator or a battery.

[0002] It relates more particularly to fiber optic sensors suitable for such a measurement.

[0003] The invention aims to propose a solution which makes it possible to extract the contribution of the optical absorption of the measurement environment, such as an accumulator or battery, in the measurement signal of a fiber optic sensor dedicated to temperature measurement.

[0004] The invention is described with reference to a use for measurement within electrochemical accumulators or batteries, in particular of the metal-ion type, in order to estimate as quickly as possible the temperature and simultaneously the operating parameter which is the state of charge (SOC, an English acronym for "State Of Charge").

[0005] Although described with reference to a Lithium-ion accumulator, the invention applies to temperature measurements of any metal-ion electrochemical accumulator, i.e. also sodium-ion, Magnesium-ion, Aluminum-ion accumulators, etc., or more generally to any electrochemical accumulator whose anode or cathode material has an optical absorption which changes with its state of charge.

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

[0007] By "thermoluminescence" is meant here and within the framework of the invention, the capacity 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 The luminescence lifetime varies depending on the temperature to which the material is subjected. Prior art

[0009] As illustrated schematically in Figures 1 and 2, a lithium-ion battery or accumulator usually comprises at least one electrochemical cell consisting of an electrolyte constituent 1 between a positive electrode or cathode 2 and a negative electrode or anode 3, a current collector 4 connected to the cathode 2, a current collector 5 connected to the anode 3 and finally, a packaging 6 arranged to contain the electrochemical cell with sealing while being crossed by a part of the current collectors 4, 5.

[0010] The architecture of conventional lithium-ion batteries comprises an anode, a cathode and an electrolyte. Several types of conventional architecture geometry are known:

[0011] - a cylindrical geometry as disclosed in the patent application US2006 / 0121348,

[0012] - a prismatic geometry as disclosed in US patents 7348098, US 7338733;

[0013] - a stacking geometry as disclosed in the patent applications US2008 / 060189, US 2008 / 0057392, and US patent 7335448.

[0014] The electrolyte component 1 may be in solid, liquid or gel form. In the latter form, the component may comprise a polymer, ceramic or microporous composite separator soaked in organic or ionic liquid electrolyte(s) which allows the movement of the Lithium ion from the cathode to the anode for charging and vice versa for discharging, which generates the current. The electrolyte is generally a mixture of organic solvents, for example carbonates to which a lithium salt, typically LiPF6, is added.

[0015] The positive electrode or cathode 2 is made of Lithium cation insertion materials which are generally composite, such as Lithium-Iron-Phosphate (LiFePO4 or LFP), LiCoO2, nickel-manganese-cobalt (NMC) including LiNi0.33Mn0.33Co0.33O2, or nickel-cobalt-aluminium (NCA).

[0016] The negative electrode or anode 3 is very often made of graphite carbon or Li4TiO5Oi2 (titanate material), possibly also based on silicon or a composite formed from silicon.

[0017] The current collector 4 connected to the positive electrode is generally made of aluminum.

[0018] The current collector 5 connected to the negative electrode is generally made of copper, nickel-plated copper or aluminum.

[0019] A lithium-ion battery or accumulator can obviously comprise a plurality of electrochemical cells which are stacked on top of each other.

[0020] Traditionally, a Li-ion battery or accumulator uses a pair of materials at the anode and the cathode allowing it to operate at a high voltage level, typically equal to 3.6 Volts.

[0021] It is essential to be able to measure a certain number of parameters of a lithium-ion accumulator in real time in order to optimize its operation, performance, safety and aging.

[0022] A BMS (English acronym for “Battery Management System”) is used at the scale of an accumulator or an accumulator assembly in the case of a module or a battery pack, in order to protect the elements from factors increasing their danger, such as excessively high currents, unsuitable potentials (too high or too low), limit temperatures and therefore has the particular function of stopping current applications as soon as threshold voltage values ​​are reached, i.e. a difference in potentials between the two active insertion materials.

[0023] The BMS therefore stops the current applications (charging, discharging) as soon as threshold voltages (difference in the potentials of the two active materials) are reached. However, the potentials of the active materials, which cannot be measured by the BMS, no longer reach the threshold values ​​of the extreme initial charge states of the accumulator (0 and 100%) due to the lack of exchangeable lithium ions. The current applications are not stopped early enough in the extreme charge states, which also induces overvoltages on the active materials, leading to their structural and chemical degradation.

[0024] To be able to function optimally, a BMS needs real-time measurements of physical parameters such as voltage, current, temperature.

[0025] However, the trend is to multiply the quantities to be measured to improve the performance of BMS. We can cite for example the European Battery2030+ roadmap which is enacted in this direction: [1],

[0026] Currently, it is difficult to access a number of internal parameters of an accumulator such as the temperature and the potential of the electrodes by external measurements.

[0027] This is why many works, notably the ISNTABAT project: [2], focus on the development of sensors which can be implanted within an accumulator.

[0028] Fiber optic sensors have many advantages, including the ability to be miniaturized and therefore to be installed in an environment with limited space available. They are also non-conductive and allow the properties of light to be used to probe various physical or chemicals at the heart of an element, in particular an accumulator or battery: [3], [4], [5].

[0029] Among these parameters, the temperature of an accumulator, and the lithiation state of an electrode have already been probed with optical fiber sensors.

[0030] Existing thermoluminescent particle-based fiber optic sensors implement a principle of thermoluminescence by ratiometry of emission peaks.

[0031] 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 which varies with temperature while others will remain constant.

[0032] [Fig.l] illustrates the luminescence spectrum of a fiber optic sensor based on thermoluminescent particles whose two emission peaks evolve as a function of the temperature to which they are subjected.

[0033] If we choose among the peaks having a thermal coupling a constant peak and a peak dependent on the temperature we can then go back to the temperature measurement by the luminescence measurement using the relation according to equation 1 as follows:

[0034] [Equation 1]

[0035] 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 gap between the two energy levels corresponding to the two luminescence peaks and which are thermally coupled, - B a constant.

[0036] By plotting the ratio of the intensities of the two peaks as a function of the inverse of the temperature, we obtain a straight line with the direction coefficient _ AL , which is a constant kB depending only on the luminescent probe used.

[0037] This logarithmic response of the sensor according to [Fig.3] is illustrated in [Fig.4].

[0038] A classic embodiment of a thermo-particle-based fiber optic sensor luminescent, consists of producing a probe based on said particles deposited at one end of an optical fiber and / or on sites along the length of an optical fiber by a sol-gel process.

[0039] In operation, absorption or excitation light radiation is sent through the optical fiber to reach the probe. The resulting emission radiation is recovered and returned by the same fiber to a detector (of the type photodiode, photomultiplier, spectrophotometer, etc.) which allows the measurement of the fluorescence signal and therefore the measurement of the temperature by signal processing.

[0040] An example of this type of fiber optic sensor is described in patent application EP4155700A1.

[0041] The inventors carried out temperature measurement tests during cycling of a Li-ion accumulator with liquid electrolyte impregnated in a conventional separator, by means of such a sensor by positioning it between the positive NMC (Nickel Manganese Cobalt) electrode and the separator.

[0042] [Fig.5] illustrates the variation of the intensity of the luminescence signal of the sensor and the external temperature of the 1A.h li-ion accumulator during cycling (charging and discharging). The curves indicated are respectively from top to bottom, the variation of the voltage, the variation of the applied current of the accumulator, the temperature Text measured by thermocouple, the spectral intensity as a function of time over a wavelength range centered on the second luminescence peak which decreases when the temperature increases.

[0043] [Fig.6] illustrates on the two lower curves the variation of the internal temperature Tint measured with a sensor according to patent application EP4155700A1, compared to the variation of the external temperature Texten as a function of the cycling undergone by the accumulator.

[0044] It can be seen that these two curves are almost identical, which indicates that the sensor is reliable and precise.

[0045] One of the remarkable properties of graphite is that its color, in other words its optical absorption, depends on its state of lithiation. This property is already used in particular to measure the state of lithiation of graphite in the context of post-mortem or ex-situ analysis of a battery.

[0046] Based on this observation, researchers have developed a fiber optic sensor to monitor the color change of a negative graphite electrode within an accumulator and therefore its lithiation state using an optical fiber. Several publications on this work have been made: [6], [7], [8], [9],

[10] .

[0047] The sensor implemented and its operation can be summarized as follows: - the optical fiber is prepared to create an area that can generate an evanescent wave on the surface. To do this, the fiber sheath is removed over a distance of about 1 cm. This evanescent wave is used to probe the surface of the negative graphite electrode, - the optical fiber is placed in the accumulator so as to be in contact with the surface of the negative electrode or inserted into its thickness, (see the figures in publications [6] and

[10] for an example of the installation of the optical fiber), - the estimation of the state of lithiation is carried out by injecting light which can be either broad spectral band, for example generated by a xenon lamp, or one or more narrow band light sources, in particular white light, generated by LED sources, then by quantifying the light transmitted through the fiber and the optical absorption at the level of the part of the fiber generating the evanescent wave. Indeed, as graphite changes color depending on its state of lithiation, so does its optical absorption.

[0048] Such a sensor therefore makes it possible to measure the state of lithiation of a negative graphite electrode and to carry out in situ (in operando) monitoring of the accumulator.

[0049] The work further showed that the variation of the optical absorption spectrum of graphite occurs over a fairly wide spectral band.

[0050] An illustration of this work is reproduced in Figures 7, 8 and 9.

[0051] These figures show respectively: - the variation of the color of graphite depending on its state of lithiation (levels II, III and IV) and the state of charge of the electrode between 40 and 80%; - a variation of the reflectance spectrum of graphite as a function of the state of charge in a wavelength range between 500 and 900 nm, measured by reflectance on a negative electrode alone (post mortem), - a variation of the reflectance spectrum (AT / T) as a function of the state of charge (capacity) of an accumulator, measured in situ by evanescent wave using an optical fiber.

[0052] The evanescent wave technique which has just been described has numerous drawbacks, including:

[0053] - the need to use a broadband light source or LEDs of suitable wavelength,

[0054] - a constraint on the installation of the optical fiber which requires crossing the accumulator on both sides. However, the passage between the inside and the outside of an accumulator is always critical, because it is necessary to guarantee long-term sealing, over the entire specified lifetime of the accumulator,

[0055] - the passage constitutes a point of mechanical fragility of the optical fiber.

[0056] Thus, there are several typical fiber optic sensors exploiting different optical phenomena.

[0057] As already indicated, a measuring sensor with thermoluminescent material(s) as described in patent application EP4155700A1, returns a luminescence spectrum with several peaks. The ratio of the two transitions of interest makes it possible to go back to the temperature. In this type of sensor, one of the luminescence peaks has a constant intensity as a function of the temperature (or can be considered as constant) while the other peak varies with temperature. It is the intensity ratio of these two thermally coupled peaks which allows us to go back to the temperature from [Equation 1].

[0058] [Fig. 10] illustrates the variation in the intensity of the two peaks of interest, i.e. the two emission peaks of the thermoluminescent material of such a sensor, as a function of time, for a 1Ah Li-ion accumulator during a cycle to which it was subjected.

[0059] The temperature of the Li-ion accumulator being stable during this cycling, we therefore note that the response of the sensor is disturbed by the operation of the accumulator itself.

[0060] The inventors were able to identify the origin of the problem observed in [Fig. 10]: it corresponds to an optical interaction between the sensor and the negative graphite electrode of the accumulator. Indeed, when the latter undergoes lithiation or delithiation during cycling, it changes color and therefore the optical absorption of the environment changes the optical response of the sensor.

[0061] This means that in a 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.

[0062] [Fig. 11] schematically shows an existing fiber optic sensor 7. It comprises an optical fiber 8 consisting of a core 80 adapted to propagate light and a sheath 81 surrounding the core. A free end 82 of the fiber carries an optical probe 9 consisting of a matrix 90 comprising thermoluminescent particles also called luminophores 91.

[0063] Figures 12A to 12C show the impact or not of the optical environment on the operation of this sensor 1.

[0064] In the case of [Fig. 12A], the optical response of the sensor 7 is not impacted by the environment, because the luminescence emitted by the probe 9 is not modified by the environment and leaves intact in the fiber, as symbolized by the single arrow which leaves in the core 80 of the latter.

[0065] Figures 12B and 12C correspond to two cases where the negative graphite electrode of the accumulator A is respectively lithiated or delithiated: it can then be seen that this environment of the accumulator A has an impact on the response of the sensor 7, 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 8 for the measurement.

[0066] The inventors carried out other tests on a Li-ion accumulator, with flexible packaging ("pouch"), consisting of a negative graphite electrode, a positive NMC622 electrode and a Celgard® separator without coating.

[0067] The sensor 7 implemented has a matrix 90 as described in patent application EP4155700A1, in which particles of Er3+ and Yb3+ doped Gd2O2S marketed under the reference PTIR545UF by the company Phosphor Technology have been incorporated as luminophores 91, the luminescence spectrum of which under excitation at 980 nm is given in [Fig. 13].

[0068] This optical probe was positioned within the Li-ion accumulator.

[0069] The inventors subjected the accumulator to a slow electrochemical charge and discharge cycle.

[0070] Under this regime, the temperature of the accumulator does not increase.

[0071] Then, the accumulator underwent a discharge at 4C which induced an increase in the temperature of the accumulator of approximately 10°C.

[0072] The results of these measurements are illustrated in Figures 14 and 15.

[0073] [Fig. 14] shows the variation curves of the intensity of the S peak as well as the intensity ratio between the H and S peaks during slow-speed cycling.

[0074] It appears that the ratio varies depending on the charging or discharging phase of the accumulator (current plateaus) for low regimes. We also see that the shape of the intensity of the peak S depends on the charging or discharging regime and the current intensity.

[0075] In other words, when the accumulator undergoes slow cycling and the temperature does not change, the response of the optical sensor evolves well as a function of the cycling. This evolution corresponds to a variation in the optical absorption within the accumulator and is correlated with the variation in lithiation of the graphite.

[0076] [Fig. 15] illustrates, for a discharge at 4C, the variation in temperature, the variation in the intensity of H and that of S as well as the ratio between the S and H peaks.

[0077] It appears that the two effects are coupled, the effect of the lithiation of graphite during the discharge on the intensity of the H and S peaks is clearly visible (increase then relaxation). The effect of the temperature is visible but to a lesser extent on the ratio.

[0078] In other words, it is observed that the luminescence signal of a temperature sensor is disturbed by the optical environment, as can be the case with lithium-ion accumulators due to the change in optical absorption by the graphite electrode, the luminescence signal then no longer depending solely on the temperature.

[0079] However, this may limit the use of an existing sensor.

[0080] More broadly, an existing sensor cannot be used reliably for temperature measurement purposes when the measurement environment has optical variations that are in the same emission wavelength ranges of the peaks of interest of the thermoluminescent material of the optical probe of the sensor.

[0081] There is therefore a need to obtain a temperature measurement signal from the fiber optic sensors which is independent of the nearby measurement environment, in order to obtain reliable measurements.

[0082] The aim of the invention is to meet at least part of this need. Statement of the invention

[0083] To do this, the subject of the invention is a method for processing the measurement signal of a temperature sensor of a metal-ion accumulator, comprising an optical fiber, one free end of which forms an optical probe with thermoluminescent material(s) capable of emitting a light peak at at least two wavelengths, at least one of the two peaks (H, S) being adapted to be in at least one variation zone of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the accumulator, comprising the following steps:

[0084] i / first acquisition of the thermoluminescence signal from the sensor, during a first cycling of the metal-ion accumulator, at a rate such that the accumulator does not have time to heat up;

[0085] ii / second acquisition of the thermoluminescence signal from the sensor, during a second cycling of the metal-ion accumulator, at a rate such that the accumulator heats up;

[0086] iii / processing of the data by taking into consideration the time series of the intensities (or integrals) of the two peaks used for the acquisitions of the thermoluminescence signal according to ii / and iii / , so as to extract the contribution linked to the change in optical absorption of the insertion material, the temperature obtained as a function of time then being determined either according to:

[0087] [Equation 2] U 2 ____w____ S(t)W0 - S0H(t) + S0H0

[0088] in which

[0089] Æ is the difference in energy levels between the two peaks considered (H and S), calculated by taking the barycenter of each peak;

[0090] k B is the Boltzmann constant;

[0091] Ho is the average value of the intensity of one of the peaks (H), calculated over a time interval (between t1 and t2) corresponding to a period during which the accumulator is not subjected to any current and has a constant reference voltage;

[0092] H(t) is the intensity of the peak (H) measured over time; In(B) ™ ln

[0093] S o is the average value of the intensity of the other peak (S) over the same time interval (between t1 and t2) as that chosen to calculate H 0 ;

[0094] S (t) is the intensity of the other peak (S) measured over time;

[0095] B is the slope coefficient, extracted from the calibration line of thermoluminescence of the sensor;

[0096] either according to

[0097] [Equation 3] AE f ____________n e x , ¾ x SCt) ~ IW) ~ Hol * (¾

[0098] in which

[0099] the values ​​AE, k B, H 0, S 0, H(t) and S(t) are those of the previous equation;

[0100] H'g 0 represents the average value of the intensity of one of the peaks (H), over a time interval (between t3 and t4), after the discharge undergone by the accumulator during the cycling according to ii / , when the temperature of the accumulator is stabilized.

[0101] According to an advantageous variant, the method comprises, before step i / , a preliminary step i0 / of temperature calibration of the sensor once inserted into the accumulator, according to which the variation of the luminescence signal is measured as a function of the temperature. This is in order to establish the parameters of [Equation 1]. During this step io / , the accumulator is at a constant state of charge, for example at 30%. An alternative may consist of carrying out this calibration at different SOC states of the accumulator.

[0102] Advantageously, for cycling with a slow discharge rate (C / 5 or lower) undergone by the accumulator, the time period between t2 and t3 being between 1000 and 2000 s.

[0103] Advantageously again, for cycling with a discharge at 4C undergone by the accumulator, the time period between t3 and t4 being between 500 and 700 s.

[0104] The invention also relates to a measuring sensor, intended to implement the method as described previously, the wavelength of one of the two emission peaks being above 700 nm, preferably between 700 and 1100 nm, while that of the other of the two emission peaks is below 700 nm, preferably between 400 and 600 nm.

[0105] According to an advantageous embodiment, the optical probe comprises a matrix in which particles of at least one thermoluminescent material are incorporated.

[0106] Preferably, the thermoluminescent material is Gd2O2S or Y2O2S doped with Er3+ and Yb3+.

[0107] The invention also relates to an accumulator (A) or metal-ion battery, in particular li-ion, comprising, inserted within it, at least one sensor as described previously.

[0108] Preferably, the sensor is directly in contact with the electrode whose lithiation state varies.

[0109] The invention finally relates to the use of a method as described above, for measuring temperature within a metal-ion accumulator, in particular the lithiation state of a negative graphite electrode of a Li-ion accumulator.

[0110] Other advantages and characteristics will become more apparent upon reading the detailed description, given for illustrative and non-limiting purposes, with reference to the following figures. Brief description of the drawings

[0111] [Fig-1] [Fig. 1] is an exploded perspective schematic view showing the various elements of a lithium-ion accumulator.

[0112] [Fig.2] [Fig.2] is a front view showing a lithium-ion battery with its flexible packaging according to the state of the art.

[0113] [Fig.3] [Fig.3] illustrates in the form of 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.

[0114] [Fig.4] [Fig.4] is the logarithmic response line of the sensor according to [Fig.3].

[0115] [Fig.5] [Fig.5] illustrates at the bottom the variation in the intensity of the luminescence signal of a luminescence sensor and the external temperature of a 1A.h Li-ion accumulator, during an electrochemical cycling (charge and discharge) that it undergoes, characterized by the curves at the top of variation of the voltage and the applied current.

[0116] [Fig.6] [Fig.6] illustrates the variation of the internal temperature compared to the variation of the external temperature of a 1A.h Li-ion accumulator as a function of the electrochemical cycling it undergoes, characterized by the voltage variation curve at the top.

[0117] [Fig.7] [Fig.7] is the reproduction of an image of the surface of an anode in graphite of an accumulator depending on its state of lithiation of the graphite and the state of charge of the anode.

[0118] [Fig.8] [Fig.8] illustrates the variation of the reflectance spectrum of graphite in function of the state of charge in a range of wavelengths measured by reflectance on a single electrode (post mortem), outside of implantation in an accumulator.

[0119] [Fig.9] [Fig.9] illustrates the variation of the transmittance spectrum (AT / T) as a function of the state of charge (capacity) of an accumulator, measured in situ according to the state of the art by evanescent wave using an optical fiber.

[0120] [Fig. 10] [Fig. 10] illustrates the variation in the intensity of the two emission peaks of the thermoluminescent material of the sensor, as a function of time, for a 1Ah Li-ion accumulator during a cycle to which it is subjected.

[0121] [Fig. 11] [Fig. 11] is a longitudinal sectional view of a fiber measuring sensor optical thermoluminescent probe according to the invention.

[0122] [Fig.l2A], [Fig.l2B], [Fig.l2C] Figures 12A, 12B, 12C schematically show the optical probe of the sensor according to [Fig. 11], when the measurement environment constituted by a Li-ion accumulator has respectively no impact on the measurement related to a change in optical absorption, an impact due to lithiation, and to delithiation of the negative graphite electrode of the accumulator.

[0123] [Fig. 13] [Fig. 13] is the luminescence spectrum of Er3+ and Yb3+ doped Gd2O2S under light excitation at 980 nm.

[0124] [Fig. 14] [Fig. 14] is an example of variation of the intensity of the S peak as well as of the intensity ratio of the H and S peaks of Er3+ and Yb3+ doped Gd2O2S whose spectrum is given in [Fig. 13], during the cycling of a Li-ion battery with graphite negative electrode.

[0125] [Fig. 15] [Fig. 15] is an example of measurement for a 4C discharge of a Li-ion accumulator with graphite negative electrode showing the variation of temperature, the variation of the intensity of the H peak and that of the S peak as well as their ratio obtained with a probe with Er3+ and Yb3+ doped Gd2O2S material whose spectrum is given in [Fig. 13].

[0126] [Fig. 16] [Fig. 16] is the result of data processing to extract the contribution due to the optical absorption of the graphite of a negative electrode of a Li-ion accumulator during discharge at 4C to deduce the variation on the variation of the intensity of the H peak and on the variation of the intensity of the S peak.

[0127] [Fig. 17] [Fig. 17] illustrates in the form of curves from top to bottom, the variation of the intensity of the H peak during a cycling pause and discharge at 4C, the variation of the intensity of the H peak as a function only of the temperature which remains constant, to the nearest measurement noise and of the contribution of the variation in color of the graphite calculated by subtracting from the top curve, the average value of H during the cycling pause, i.e. between 0 and 1500 s.

[0128] [Fig. 18] [Fig. 18] illustrates in the form of curves from top to bottom, the variation of the intensity of the S peak during a cycling pause and discharge at 4C, the variation of the intensity of the S peak as a function only of the temperature which remains constant, apart from measurement noise and the contribution of the color variation of the graphite calculated by subtracting from the top curve the average value of S during the cycling pause, i.e. between 0 and 1500 s and indicates the time intervals trt2, and t3-t4 during which it is considered that there is no contribution of graphite to the luminescence intensity for the calculation of the values ​​S 0 and S' 0 according to the method of the invention.

[0129] [Fig. 19] [Fig. 19] repeats [Fig. 17] and indicates the time intervals trt2, and t3-t4 during which it is considered that there is no contribution of graphite to the luminescence intensity for the calculation of the Hg 0 and 7 / ' g 0 values ​​according to the method of the invention.

[0130] [Fig.20] [Fig.20] illustrates the curve S g(t) at the bottom with respect to the variation of the intensity of S(t) at the top, as well as the corrected curve S c (t) = S(t) - S g( / J in the middle, according to the method of the invention.

[0131] [Fig.21] [Fig.21] is a representation of the calibration of the sensor of thermoluminescence from the temperature relaxation after discharge at 4C undergone by the Li-ion accumulator in which the sensor is implanted. [Fig.22] [Fig.22] is the calibration curve of the thermoluminescence sensor giving the linear logarithmic variation of the F1R c(t) value as a function of the inverse of the temperature 1 / T.

[0132] [Fig.23] [Fig.23] is the correlation between the external temperature measured by a thermocouple, the variation of the ratio of the H and S peaks and the temperature measured by a thermoluminescence sensor according to the invention after removing the contribution of graphite in the signal.

[0133] [Fig.24] [Fig.24] illustrates the evolution of the internal temperature of the cell measured using the thermoluminescent sensor, according to a method of the invention and the external temperature measured with a thermocouple, during discharge at 4C of the accumulator. Detailed description

[0134] Figures 1 to 12 have already been described in the preamble. They will therefore not be detailed later.

[0135] We consider a fiber optic measuring sensor 7 as described with reference to [Fig. 11], with a thermoluminescent material 91 like that whose luminescence spectrum has three peaks of transitions S, H and F according to [Fig. 13].

[0136] To extract from the luminescence signal of such a sensor, the optical contribution of the measurement environment and more particularly of the change in absorption of the graphite as a function of its lithiation state, the method according to the invention comprises the following successive steps.

[0137] Step i / : a first acquisition of the thermoluminescence signal is carried out, during a first cycling (charge and discharge) of a Li-ion accumulator whose temperature is to be measured.

[0138] This acquisition can be done at different speeds, knowing that at low speeds, for example at C / 5 or less (C / 10, C / 20) the charge and discharge speeds are so slow that the electrochemical processes do not have time to heat the accumulator. This limit obviously depends on the architecture of the latter and its constituent materials.

[0139] In other words, this first acquisition is carried out by considering that the temperature that we are seeking to determine does not vary sufficiently to have a detectable impact on the luminescence signal.

[0140] Step ii / : a second acquisition of the thermoluminescence signal is carried out, during which it is known that the accumulator is heating up. To do this, the accumulator is cycled according to a second cycle, at a high charge and / or discharge rate. The limit of this rate obviously depends on the performance of the accumulator. Typically, this second acquisition can be that already indicated for the example in Figures 14 to 15, of a 1A.h accumulator which has undergone a discharge at 4C, and for which an increase in temperature of the order of ten degrees Celsius is observed, measured by a thermocouple.

[0141] Step iii / : a processing is then applied to the data by taking into consideration the time series of the intensities (or integrals) of the H and S peaks used for the acquisitions of the thermoluminescence signal according to ii / and iii / , in order to extract the contribution linked to the change in optical absorption of the graphite as a function of its lithiation state.

[0142] Two distinct data processing methods can be considered to extract the contribution of the change in optical absorption of graphite linked to its lithiation state.

[0143] The first method does not make any assumptions about the influence of the change in color of the graphite on the intensity of the luminescence peaks of the sensor. It is described below in relation to sub-steps A.

[0144] Sub-step iii A À / : We first consider the temporal variation of the intensity (or of the integral) of the H peak. If we plot this variation as a function of time, if it varies in a correlated manner with the variations in current and voltage of the accumulator, it is because there is an impact of the lithiation state on the luminescence signal. As an example, this is what we observe in [Fig. 16], the blue curve represents the variation of the maximum intensity of the H peak during a discharge at 4C.

[0145] The quantity H(t) is defined as the variation of the intensity of the H transition over time.

[0146] Sub-step iii A 2 / : We then determine the constant value of the intensity of the peak H which is not disturbed by the optical influence of the graphite. This constant value corresponds to the constant part of the curve of [Fig. 16] which can correspond either to a pause state of the accumulator, without current or voltage applied, in a given state of charge which can serve as a reference. In the example of [Fig. 16], this corresponds to the first 1500 seconds of measurement.

[0147] Thus the average value of the intensity of H, when the contribution of graphite is negligible (or considered as a reference point), is defined by the quantity H 0 according to equation 4:

[0148] [Equation 4] 0 ~ r* ât J****® ly

[0149] in which

[0150] A / is the measurement time interval;

[0151] 6 and 12 are the initial and final times respectively of the interval considered as constant.

[0152] Sub-step iii A 3 / : We can then calculate the contribution of the variation in graphite lithiation on the intensity of H over time. It can be designated as equal to the difference between H(t) and H 0 according to equation 3:

[0153] [Equation 5] H g (t) = H(t) - H o

[0154] Sub-step iii A 4 / : Once the variation of lithiation of graphite on the intensity of H over time has been calculated, we can then calculate this contribution for the variation of the intensity (or the integral) of S over time, which we call S g.

[0155] For this we consider that the ratio between the intensity of S and H remains constant if there is no change in temperature. This amounts to formulating equation 4:

[0156] [Equation 6]

[0157] with S 0 the average value of the intensity (or the integral) of the peak at room temperature when no voltage or current is applied to the accumulator and over the same time interval (ti to t2) as that chosen for the calculation of H 0, i.e.

[0158] [Equation 7]

[0159] Sub-step iii A 5 / : Once the contributions H g (t) and S g (t) have been calculated, these can be removed from the luminescence signal to calculate the corrected intensities Sc and Hc (or the integrals if we work with the integral of the peaks for the calculation of the temperature), i.e.:

[0160] [Equation 8]

[0161] [Equation 9]

[0162] Like:

[0163] [Equation 10]

[0164] So

[0165] [Equation 11] H c (t) = H(t) - HW +

[0166] Let

[0167] [Equation 12]

[0168] The FIRC ratio of the intensities, after removing the contribution of graphite, is then written

[0169] [Equation 13]

[0170] Or in other words

[0171] [Equation 14]

[0172] By replacing S g (t) by its expression which depends on H g (t), then H g(t) by its expression we obtain the following equation 13:

[0173] [Equation 15]

[0174] So,

[0175] [Equation 16] F / / U0 =-------------r S(t) - (H(t) - Ho) x ÿ

[0176] Let

[0177] [Equation 17] F / RXO =--------7777^---- c / «(.O he xo “Mtv - '

[0178] [Equation 18] / / / FIRc^ ""

[0179] [Equation 19] cW S(t)H0 - S0(H(t) - H B )

[0180] [Equation 20] w2 HRc(t) " S(t)H0 - SoH^ + S e Ho

[0181]

[0182] Taking equation 1: [Equation 1]

[0183] considering the FIRc ratio of the intensities, this gives

[0184] [Equation 21]

[0185] Let

[0186] [Equation 22]

[0187] Which gives, in the case of a measurement of the temperature as a function of time during accumulator cycling, the following formula:

[0188] [Equation 2]

[0189] in which

[0190] Æ is the difference in energy levels between the two transition peaks considered H and S which is calculated by taking the barycenter of the luminescence peak, associated with each transition peak;

[0191] k B is the Boltzmann constant;

[0192] H o is the average value of the intensity of the luminescence peak of the H transition calculated over a time interval (between t1 and t2) corresponding to the pause in the cycling during which the accumulator is not subjected to any current and which has a constant reference voltage. In the example given, this corresponds to a state of charge of 100% or to complete lithiation of the graphite electrode before the discharge at 4C;

[0193] S0 is the average value of the intensity of the transition luminescence peak S over the same time interval (t1 to t2) as that chosen to calculate Ho;

[0194] B is the direction coefficient, extracted from the thermoluminescence calibration line of the sensor as shown in [Fig.2].

[0195] This coefficient can be extracted during the calibration of the sensor before its insertion into the accumulator or during its insertion that a temperature calibration is done outside of cycling, that is to say without applying current or voltage variation to the accumulator. A third way to obtain this coefficient is to use the cooling of the accumulator after a high current discharge, for example the discharge at 4C. Indeed, when the discharge is finished and the current returns to 0, the accumulator which has previously heated up will cool down until it reaches thermal equilibrium with the ambient temperature. The measurement of this cooling using an external thermocouple which thus makes it possible to have the temperature variation.This variation can then be used to plot the calibration curve of the sensor since in this case, it is only affected by the temperature and not by the variation in optical absorption linked to a change in the lithiation state of the graphite electrode. The second method is applied when the impact of the change in graphite color on the luminescence cannot be determined precisely. It is described below in relation to sub-steps B.

[0196] Sub-step iii B i / : As for sub-step iii Al / , the quantity H(t) is used as the variation of the intensity of the intensity (or of the integral) of the peak of the H transition over time. When the temperature does not vary and the cell is not subjected to any current stress, the potential of the graphite electrode remains constant, therefore the intensity of the peak H is constant. In the example given below, this corresponds to the first 1700 seconds. When the lithiation of the graphite changes when a current is applied to the cell, this intensity will vary due to the change in color of the graphite but also the temperature.

[0197] Sub-step iii B 2 / : The quantity Ho is calculated in the same way as for sub-step iii A2.

[0198] Sub-step iii B 2 h We can then calculate the contribution of the variation in graphite lithiation on the intensity of H over time. This, which we call H g, is equal to the difference between H(t) and H 0, as follows:

[0199] [Equation 10] Hg(t) = H(t) - H a

[0200] The three curves in [Fig. 17] illustrate the obtaining of the variation in the intensity of the H peak during the pause and the discharge at 4C (top curve), of the contribution of the variation in the color of the graphite (bottom curve) calculated by subtracting from the top curve the average value of H during the pause phase of the cycling, i.e. between 0 and 1500 s, and finally the variation of H depending only on the temperature which is constant (middle curve), apart from the measurement noise.

[0201] Sub-step iii B 4 / : It is now necessary to recalculate the form that the variation in the intensity of the peak of the S transition should have over time if it were not subject to the impact of the change in absorption of the graphite.

[0202] We remind you that: - S(t) denotes the intensity of the transition S measured over time; - H g (t) is the contribution of the variation of graphite lithiation on the intensity of the H peak over the time defined previously.

[0203] To do this, we calculate on the raw signal of S the average value of the luminescence signal before the discharge at 4C (between ti and t2) which corresponds to the quantity S 0 defined previously, i.e.:

[0204] [Equation 7] . _If £s st) LL

[0205] We also calculate the quantity S ' 0 corresponding to the average value of the signal after cooling of the accumulator between t3 and t4, i.e.:

[0206] [Equation 23]

[0207] [Fig. 18] illustrates the time intervals tb t2, t3 and t4 during which graphite is considered to have no contribution to the luminescence intensity for the calculation of So and S ' 0.

[0208] We then calculate similar quantities on the variation of H g (t), as follows

[0209] [Equation 24] ^(¢)

[0210] Thus, H g0 represents the average value of H g (t) over the time interval from ti to t2, which corresponds to the pause before the discharge undergone by the accumulator. During this period the graphite is in a state of charge and does not vary since the accumulator is not subjected to any stress.

[0211] [Equation 25]

[0212]

[0213]

[0214]

[0215]

[0216]

[0217]

[0218]

[0219]

[0220]

[0221]

[0222]

[0223] H ' g0 thus represents the average value of H g (t) over the time interval between t3 and t4, which corresponds to a period of time after the discharge undergone by the accumulator, when the temperature is stabilized. If only the temperature contribution were present on the variation of the luminescence signal, the values ​​of H gO and H ' g0 should be equal. However, we see that this is not the case. We therefore calculate the part S g (t) of the signal of S due to graphite by considering that the proportionality ratio between H g (t) and S g (t) is equal to the ratio of the difference between the two levels S" 0 and S 0 and the difference of the two levels H ' g0 and H g0. Which gives the formula: [Equation 26] Now, we consider that H g0 is equal to 0 by construction, as illustrated in [Fig. 19], which allows us to simplify the formula: [Equation 27] s a co = hjh x5,1 7 s ° From this formula we calculate the contribution of graphite to the signal S g(t) as well as the corrected curve S c (t) = S(t) - S g (t). [Fig.20] represents respectively the curves of S(t) at the top, S g(t) at the bottom and S c (t) in the middle. Sub-step iii B 5 / : Once the contributions H c (t) and S c (t) have been calculated, the FIRc ratio of the intensities, after removing the contribution from graphite, is then written: [Equation 13] with [Equation 9] ^(0 =

[0224] As:

[0225] [Equation 10] H g (t) =

[0226] and

[0227] [Equation 911]

[0228]

[0229] SO [Equation 12]

[0230] And

[0231] [Equation 8] S c (t) = S(t) “ Sg(t)

[0232] [Equation 28] S e (t) = S(t) - Hg {t)

[0233] Replacing H g(t) with its expression, we obtain: [Equation 29] s c ® = s(t) - IMO x - j \ /

[0234] With this method, it is guaranteed that the corrected signal S c has the same level between times 1 and 12 before the discharge and between times 13 and 14.

[0235] Similarly for the corrected signal of the transition H, H c, the level before the discharge is

[0236]

[0237] the same before discharge and after discharge. The expression of the ratio is therefore: [Equation 30]

[0238]

[0239] Either [Equation 31] PIRc(t) Ho x Hg o x S(t) - IXCO - «ol x (Si - S o )

[0240] Once the expression of the FIR is corrected for the contribution of graphite, the temperature is calculated in the same way as previously using the formula below.

[0241] [Equation 32]

[0242] Let

[0243] [Equation 3] AË' Ho X B', XS(t) - (H(t) - H,,]

[0244] An example of temperature measurement results from this method during accumulator cycling with a 4C discharge is now presented.

[0245] First of all, we take for the temperature calibration of the sensor, the temperature relaxation of the accumulator after the discharge at 4C ([Fig.21]).

[0246] During this period of time, as explained previously, the accumulator is discharged and the lithiation of the graphite no longer changes, only the temperature changes.

[0247] We can therefore apply linear regression directly by taking the ratio of the maximum intensities H c (t) / S c (t).

[0248] The removal of the contribution of graphite is taken into consideration in this case even if it is constant.

[0249] [Fig.22] shows the calibration curve giving the variation of ln(FIR c(t)) as a function of 1 / T. In this example, ln(B) is equal to 3.04.

[0250] We can thus go back to the internal temperature of the accumulator during discharge at 4C from equation 3.

[0251] The results of this calculation of the internal temperature are shown in [Fig.23].

[0252] After data processing according to the invention, a correlation can therefore be established between the external temperature Text of the accumulator measured by thermocouple, the variation in the intensity ratio of the H and S peaks after correction of the contribution of the graphite absorption, and the internal temperature Tint calculated from the calibration curve of the thermoluminescence sensor, as illustrated in [Fig.23].

[0253] The comparison between the internal temperature of the accumulator measured using the thermoluminescent sensor and the external temperature measured with a thermocouple during discharge at 4C is shown in [Fig.24]. Other variants and improvements can be envisaged without departing from the scope of the invention.

[0254] The sensor 7 according to the illustrated example 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 luminophores and another type of material for the matrix with at least two emission peaks.

[0255] Thus, if the invention has been described in relation to a negative graphite electrode, the sensor according to the invention can quite easily be implemented in a metal-ion accumulator with another chemistry of the anode or cathode materials insofar as this(these) material(s) has an optical absorption which changes with its state of charge.

[0256] Generally speaking, the processing method according to the invention can be implemented for any optical fiber sensor whose thermoluminescent material(s) allows a temperature measurement and whose measurement environment in which the sensor is implanted is likely to present a variation in optical absorption, the method making it possible to extract the contribution of this variation in the measurement signal in order to retain only that linked to the temperature. List of cited references#:

[0257] [1]: https: / / battery2030.eu / research / roadmap /

[0258] [2]: https: / / www.instabat.eu /

[0259] [3]: Wang, R., Zhang, H., Liu, Q„ Liu, F., Han, X., Liu, X., Li, K., Xiao, G., Albert, J., Lu, X. & Guo, T. « Operando monitoring of ion activities in aqueous batteries with plasmonic fiber-optic sensors » Nature Communications 13, 547 (2022).

[0260] [4]: Lu, X., Tarascon, J.-M. & Huang, J. « Perspective on commercializing smart sensing for batteries ». eTransportation 14, 100207 (2022).Wang, R., Zhang, H., Liu, Q., Liu, F., Han.

[0261] [5]: 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.

[0262] [6]: Ghannoum, A., Noms, R. C., lyer, K., Zdravkova, L., Yu, A. & Nieva, P. « Optical Characterization of Commercial Lithiated Graphite Battery Electrodes and in Situ Fiber Optic Evanescent Wave Spectroscopy. » ACS Applied Materials and Interfaces 8, 18763-18769 (2016).

[0263] [7]: Ghannoum, A., lyer, K., Nieva, P. & Khajepour, A. « Fiber optic monitoring of lithium-ion batteries: A novel tool to understand the lithiation of batteries ». in Proceedings of IEEE Sensors (2017). doi: 10.1109 / ICSENS.2016.7808695.

[0264] [8]: Ghannoum, A., Nieva, P., Yu, A. & Khajepour, A. « Development of Embedded Fiber-Optic Evanescent Wave Sensors for Optical Characterization of Graphite Anodes in Lithium-Ion Batteries. » ACS Appl. Mater. Interfaces 9, 41284-41290 (2017).

[0265] [9]: Ghannoum, A. & Nieva, P. « Graphite lithiation and capacity fade monitoring of lithium ion batteries using optical fibers. » Journal of Energy Storage 28, 101233 (2020)

[0266]

[10] : Modrzynski, C., Roscher, V., Rittweger, F., Ghannoum, A., Nieva, P. & Riemschneider, K. « Integrated Optical Fibers for Simultaneous Monitoring of the Anode and the Cathode in Lithium Ion Batteries. » in 2019 IEEE SENSORS 1-4 (2019). doi: 10.1109 / SENSORS43011.2019.8956755.

Claims

1. Claims Method for processing the measurement signal of a temperature sensor of an accumulator, in particular a metal-ion accumulator, comprising an optical fiber, one free end of which forms an optical probe with thermoluminescent material(s) capable of emitting a light peak at at least two wavelengths, at least one of the two peaks (H, S) being adapted to be in at least one variation zone of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the accumulator, comprising the following steps: i / first acquisition of the thermoluminescence signal from the sensor, during a first cycling of the metal-ion accumulator, at a rate such that the accumulator does not have time to heat up; ii / second acquisition of the thermoluminescence signal from the sensor, during a second cycling of the metal-ion accumulator, at a rate such that the accumulator heats up; iü / data processing by taking into consideration the time series of the intensities (or integrals) of the two peaks used for the acquisitions of the thermoluminescence signal according to ii / and iii / , so as to extract the contribution linked to the change in optical absorption of the insertion material, the temperature obtained as a function of time then being determined either according to: [Equation 2] in which Æ is the difference in energy levels between the two peaks considered (H and S), calculated by taking the barycenter of each peak; k B is the Boltzmann constant; H o is the average value of the intensity of one of the peaks (H), calculated over a time interval (between t1 and t2) corresponding to a period during which the accumulator is not subjected to any current and has a constant reference voltage; H (t) is the peak intensity (H) measured over time;

2.

3.

4.

5.

6.

7. SO is the average value of the intensity of the other peak (S) over the same time interval (between tl and t2) as that chosen to calculate H 0; S(t) is the intensity of the other peak (S) measured over time; B is the direction coefficient, extracted from the thermoluminescence calibration line of the sensor; or according to [Equation 3] àE xx S(t) - [MO - x (¾ Yû in which the values AE, k B, H 0, SO, B, H(t) and S(t) are those of the previous equation; H ' g0 represents the average value of the intensity of one of the peaks (H), over a time interval (between t3 and t4), after the discharge undergone by the accumulator during cycling according to ii / , when the temperature of the accumulator is stabilized. Method according to claim 1, for cycling with a slow discharge (C / 5 or lower) undergone by the accumulator, the time period between t2 and t3 being between 1000 and 2000 s. Method according to claim 1 or 2, for cycling with a discharge at 4C undergone by the accumulator, the time period between t3 and t4 being between 500 and 700 s. Measuring sensor, intended to implement the method according to one of claims 1 to 3, the wavelength of one of the two emission peaks being above 700 nm, preferably between 700 and 1100 nm, while that of the other of the two emission peaks is below 700 nm, preferably between 400 and 600 nm. Sensor according to claim 4, the optical probe comprising a matrix (90) in which particles (91) of at least one thermoluminescent material are incorporated. Sensor according to claim 4 or 5, the thermoluminescent material being Gd2O2S or Y2O2S doped with Er3+ and Yb3+. Accumulator (A) or metal-ion battery, in particular li-ion, comprising, inserted therein, at least one sensor (7) according to one of claims 4 to 6. 28

8. Accumulator according to claim 7, the sensor being in direct contact with the electrode whose lithiation state varies.

9. Use of a method according to one of claims 1 to 3, for measuring temperature within a metal-ion accumulator, in particular the lithiation state of a negative graphite electrode of a Li-ion accumulator.

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