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

Abstract

A method for processing the signal from a temperature sensor of a metal-ion battery, using an optical fiber whose free end forms an optical probe with thermoluminescent material(s), with emission peak(s) in at least one region of variation of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the battery. The invention relates to a method for processing the measurement signal from a temperature sensor of a metal-ion battery, 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 region of variation of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the battery. Figure for the abstract: Fig. 12

Description

Title of the invention: Method for processing the signal of a temperature sensor of a metal-ion battery, with optical fiber whose free end forms an optical probe with thermo-luminescent material(s). technical field

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

[0002] It relates more particularly to optical fiber sensors adapted for such a measurement.

[0003] The invention aims to provide a solution that allows the contribution of optical absorption from the measurement environment, such as an accumulator or battery, to be extracted from 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, Anglo-Saxon acronym for "State Of Charge").

[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 whose anode or cathode material has an optical absorption that changes with its state of charge.

[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 The luminescence lifetime varies depending on the temperature to which the material is subjected. Previous technique

[0009] As schematically illustrated 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 package 6 arranged to contain the electrochemical cell with sealing while being traversed 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 architectural 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 stacked 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 impregnated with organic or ionic liquid electrolyte(s) that allows the movement of lithium ions from the cathode to the anode for charging and vice versa for discharging, thereby generating 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 silicon-based or silicon-based composite.

[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 one on top of the other.

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

[0021] It is essential to be able to measure in real time a number of parameters of a lithium-ion battery 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 a battery or a set of batteries 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 in particular the function of stopping the applications of current as soon as threshold voltage values ​​are reached, i.e. a difference of potentials between the two active insertion materials.

[0023] The BMS therefore stops current applications (charging, discharging) as soon as threshold voltages (potential difference between 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 battery (0 and 100%) due to a lack of exchangeable lithium ions. 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] In order to function optimally, a BMS needs real-time measurements of physical parameters such as voltage, current, temperature.

[0025] However, the trend is towards increasing the number of quantities to be measured in order to improve the performance of BMS. For example, the European roadmap Battery2030+ is adopted in this direction: [1],

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

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

[0028] Fiber optic sensors offer numerous advantages, including their miniaturization, allowing them to be installed in environments with limited space. Furthermore, they are electrically non-conductive and enable the exploitation of light's properties to probe various physical parameters or chemicals at the heart of an element, especially of an accumulator or battery: [3], [4], [5].

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

[0030] Existing fiber optic sensors based on thermoluminescent particles implement a thermoluminescence principle 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 that varies with temperature while others will remain constant.

[0032] 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.

[0033] 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:

[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 difference between the two energy levels corresponding to the two luminescence peaks, which are thermally coupled. - B is 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 a slope of _ AL, which is a constant kB depending solely on the luminescent probe used.

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

[0038] 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.

[0039] During operation, absorption or excitation light radiation 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 (of 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 optical fiber sensor is described in patent application EP4155700A1.

[0041] 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.

[0042] Figure 5 illustrates the variation in the intensity of the sensor's luminescence signal and the external temperature of the 1 Ah Li-ion battery during a cycle (charge and discharge). The curves shown represent, from top to bottom, the variation in voltage, the variation in the applied current of the battery, the temperature measured by thermocouple, and the spectral intensity as a function of time over a wavelength range centered on the second luminescence peak, which decreases as 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 Text as a function of the cycling undergone by the accumulator.

[0044] We observe that these two curves are almost identical, which indicates that the sensor is reliable and accurate.

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

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

[10] .

[0047] The sensor used and its operation can be summarized as follows: - The optical fiber is prepared to create a zone that generates an evanescent wave on its surface. To achieve this, the fiber cladding is removed over a distance of approximately 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 figures in publications [6] and

[10] for an example of optical fiber implantation), - The estimation of the lithiation state is performed by injecting light that can be either broadband, for example generated by a xenon lamp, or one or more narrowband light sources, notably white light, generated by LED sources, and then quantifying the light transmitted through the fiber and the optical absorption at the part of the fiber generating the evanescent wave. Indeed, just as graphite changes color depending on its lithiation state, so too does its optical absorption.

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

[0049] The work further showed that the variation of the optical absorption spectrum of graphite takes place 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 in the color of graphite depending on its lithiation state (levels II, III and IV) and the charge state of the electrode between 40 and 80%; - a variation in 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 single negative electrode (post-mortem), - a variation of the reflectance spectrum (AT / T) as a function of the state of charge (capacitance) of a battery, measured in-situ by evanescent wave using an optical fiber.

[0052] The evanescent wave technique just described has many drawbacks, including:

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

[0054] - a constraint on the installation of the optical fiber which requires crossing the battery on both sides. However, the transition between the inside and outside of a battery is always critical, as it is necessary to guarantee long-term sealing, throughout the entire specified lifespan of the battery.

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

[0056] Thus, there are several types of optical fiber sensors exploiting different optical phenomena.

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

[0058] Fig. 10 illustrates the variation of 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 lAh Li-ion battery during a cycle to which it has been subjected.

[0059] Since the temperature of the Li-ion accumulator is stable during this cycling, it is therefore observed that the response of the sensor is disturbed by the very operation of the accumulator.

[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 battery. Indeed, when the latter undergoes lithiation or delithiasis 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 measuring 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] Figure 11 schematically shows an existing optical fiber sensor 7. It comprises an optical fiber 8 consisting of a core 80 adapted to propagate light and a cladding 81 surrounding the core. A free end 82 of the fiber carries an optical probe 9 consisting of an array 90 comprising thermoluminescent particles also called phosphors 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 returns intact to the fiber, as symbolized by the single arrow which returns to 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 lithia or delithia: it can then be seen that this environment of 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 measurement.

[0066] The inventors carried out further tests on a Li-ion battery, in a flexible pouch, consisting of a negative graphite electrode, a positive NMC622 electrode and an uncoated Celgard® separator.

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

[0068] This optical probe has been positioned within the Li-ion battery.

[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 battery underwent a discharge at 4C which induced an increase in the battery temperature of approximately 10°C.

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

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

[0074] It appears that the ratio varies according to the charging or discharging phase of the battery (current plateaus) for low operating conditions. It is also seen that the shape of the peak intensity S depends on the charging or discharging regime and the current intensity.

[0075] In other words, when the battery undergoes slow cycling and the temperature remains constant, the response of the optical sensor does indeed change with the cycling. This change corresponds to a variation in optical absorption within the battery and is correlated with the variation in graphite lithiation.

[0076] Fig. 15 illustrates, for a 4C discharge, 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 graphite lithiation during discharge on the intensity of the H and S peaks is clearly visible (increase followed by relaxation). The effect of 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 batteries 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 reliably used for temperature measurement purposes 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.

[0081] There is therefore a need to obtain a temperature measurement signal from optical fiber sensors that 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. Description of the invention

[0083] To this end, the invention relates to a method for processing the measurement signal of a temperature sensor of a metal-ion battery, comprising an optical fiber having a free end forming 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 region of variation of the optical absorption spectrum of the insertion material of the metal ions of at least one electrode of the battery, comprising the following steps:

[0084] i / first acquisition of the thermoluminescence signal from the sensor, during a first cycle 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 cycle of the metal-ion accumulator, at a regime such that the accumulator heats up;

[0086] iii / data processing 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 related 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 center of gravity of each peak;

[0090] k B is the Boltzmann constant;

[0091] Hoest 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, 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 embodiment, the method includes, prior to step i / , a preliminary temperature calibration step i0 / of the sensor once it is inserted into the battery, in which the variation of the luminescence signal as a function of temperature is measured. This is done to establish the parameters of [Equation 1]. During this step i0 / , the battery is at a constant state of charge, for example, 30%. An alternative may be to perform this calibration at different state-of-charge (SOC) states of the battery.

[0102] Advantageously, for a cycle 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 still, for a cycle 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 measurement sensor, intended to implement the process as described above, 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 Er3+ and Yb3+.

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

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

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

[0110] 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

[0111] [Fig-1] [Fig. 1] is a schematic exploded perspective view showing the different elements of a lithium-ion battery.

[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] Figure 3 illustrates the luminescence spectrum of a sensor 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 line of response of the sensor according to [Fig.3].

[0115] [Fig.5] Figure 5 illustrates at the bottom the variation in the intensity of the luminescence signal of a luminescence sensor and the external temperature of a 1Ah Li-ion battery, 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 in internal temperature compared to the variation of the external temperature of a lA.h Li-ion battery as a function of the electrochemical cycling it undergoes, characterized by the voltage variation curve at the top.

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

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

[0120] [Fig. 10] Figure 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 lAh Li-ion battery during a cycle to which it is subjected.

[0121] [Fig. 11] [Fig. 11] is a longitudinal cross-sectional view of a fiber optic measurement sensor thermoluminescent probe optics according to the invention.

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

[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 in the intensity of peak S as well as 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 a negative graphite electrode.

[0125] [Fig. 15] [Fig. 15] is an example of a measurement for a 4C discharge of a negative electrode Li-ion battery in graphite 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 of Gd2O2S material doped Er3+ and Yb3+ whose spectrum is given in [Fig. 13].

[0126] [Fig. 16] [Fig. 16] is the result of data processing allowing extraction the contribution due to the optical absorption of graphite from a negative electrode of a Li-ion battery 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 top-to-bottom curves, 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, within measurement noise and the contribution of the variation of the 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 S peak intensity as a function solely of temperature (which remains constant, within measurement noise) and the contribution of graphite color variation calculated by subtracting from the top curve the average value of S during the pause in cycling, 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 on the intensity of luminescence for the calculation of the values ​​S 0 and S' 0 according to the method of the invention.

[0129] [Fig. 19] [Fig. 19] reproduces [Fig. 17] and indicates the time intervals trt2, and t3-t4 during which it is considered that there is no contribution of graphite on the intensity of luminescence for the calculation of the values ​​Hg 0 and 7 / ' g 0 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 Thermoluminescence from the temperature relaxation after discharge to 4C of the Li-ion battery in which the sensor is embedded. [Fig. 22] [Fig. 22] is the calibration curve of the thermoluminescence sensor showing the linear logarithmic variation of the value F1R c(t) 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 of the temperature measured by a thermo-luminescence sensor according to the invention after the removal of the contribution of graphite in the signal.

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

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

[0135] We consider a fiber optic measurement sensor 7 as described with reference to [Fig. 11], with a thermoluminescent material 91 such as that whose luminescence spectrum has three peaks of S, H and F transitions 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 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 cycle (charge and discharge) of a Li-ion battery whose temperature we seek to measure.

[0138] This acquisition can take place at different operating regimes, bearing in mind that at low regimes, for example at C / 5 or less (C / 10, C / 20), the charging and discharging regimes are so slow that the electrochemical processes do not have time to heat the battery. This limit obviously depends on the battery's architecture and its constituent materials.

[0139] In other words, this first acquisition is carried out assuming that the temperature that we are trying 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 performed, during which it is known that the battery is heating up. To do this, the battery is cycled a second time, at a high charge and / or discharge rate. The limit of this rate obviously depends on the battery's performance. Typically, this second acquisition can be the one already described for the example in Figures 14 to 15, of a 1 Ah battery that has undergone a discharge at 4°C, and for which a temperature increase of approximately ten degrees Celsius is observed, as measured by a thermocouple.

[0141] Step iii / : we then apply processing to the data 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 related to the change in optical absorption of 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 related to its lithiation state.

[0143] The first method makes no assumptions about the influence of the color change of the graphite on the intensity of the luminescence peaks of the sensor. It is described below in relation to substeps A.

[0144] Substep iii A TO / : We first consider the temporal variation of the intensity (or integral) of the H peak. If we plot this variation as a function of time, and if it varies in a manner correlated with the variations in current and voltage of the battery, then 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 4C discharge.

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

[0146] Substep iii A 2 / : The constant value of the intensity of peak H, which is not affected by the optical influence of the graphite, is then determined. This constant value corresponds to the constant portion of the curve in [Fig. 16], which can correspond either to a rest state of the battery, with no current or voltage applied, in a given state of charge that 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] Substep iii A 3 / : The contribution of the variation in graphite lithiation on the intensity of H over time can then be calculated. It can be denoted by 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] Substep iii A 4 / : Once calculated the variation of lithiation of graphite on the intensity of H over time, 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 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] Substep 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 working with the integral of the peaks for the temperature calculation), i.e.:

[0160] [Equation 8]

[0161] [Equation 9]

[0162] As:

[0163] [Equation 10]

[0164] So

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

[0166] Either

[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) with its expression which depends on H g (t), then H g(t) with its expression, we obtain the following equation 13:

[0173] [Equation 15]

[0174] Therefore,

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

[0176] Or

[0177] [Equation 17] F / RXO =--------7777^---- c / «(.O il 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] Returning to equation 1: [Equation 1]

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

[0184] [Equation 21]

[0185] Either

[0186] [Equation 22]

[0187] This gives, in the case of a temperature measurement as a function of time during an accumulator cycle, 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] Ho is the average value of the peak luminescence intensity of the H transition calculated over a time interval (between t1 and t2) corresponding to the pause in the cycling during which the battery 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 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 for calculating Ho;

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

[0195] This coefficient can be extracted during sensor calibration before insertion into the battery, or during insertion when a temperature calibration is performed outside of cycling, i.e., without applying any current or voltage variation to the battery. A third way to obtain this coefficient is to use the battery's cooling after a high-current discharge, for example, a 4C discharge. Indeed, when the discharge is complete and the current returns to 0, the battery, which has previously heated up, will cool down until it reaches thermal equilibrium with the ambient temperature. This cooling is measured using an external thermocouple, which thus provides the temperature change.This variation can then be used to plot the sensor calibration curve since, in this case, the sensor is only influenced by 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 graphite color change on luminescence cannot be precisely determined. It is described below in relation to substeps B.

[0196] Substep iii B i / : As in substep iii Al / , the quantity H(t) is used as the variation in intensity (or the integral) of the peak intensity of the H transition over time. When the temperature does not vary and the cell is not subjected to any current, the potential of the graphite electrode remains constant, therefore the intensity of the H peak 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 graphite color as well as the temperature.

[0197] Substep iii B 2 / : The quantity Ho is calculated in the same way as for substep iii A2.

[0198] Substep iii B 2 h The contribution of the variation in graphite lithiation on the intensity of H over time can then be calculated. This, called 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 variation in the intensity of the H peak during the pause and discharge at 4C (top curve), and the contribution of the graphite color variation (bottom curve) calculated by subtracting the average value of H during the pause phase of cycling from the top curve, i.e., between 0 and 1500 s, and finally the variation of H depending only on the temperature which is constant (medium curve), within measurement noise.

[0201] Substep iii B 4 / : It is now necessary to recalculate the shape that the variation of the intensity of the S transition peak should have over time if it did not undergo the impact of the change in absorption of graphite.

[0202] It is recalled that: - S(t) denotes the intensity of the S transition measured over time; - Hg(t) is the contribution of the variation of graphite lithiasis on the intensity of the peak H over 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 the 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, Hg0 represents the average value of Hg(t) over the time interval from t1 to t2, which corresponds to the pause before the discharge of the accumulator. During this period, the graphite is in a state of charge and does not change 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 Hg(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 temperature were the only factor influencing the variation of the luminescence signal, the values ​​of HgO and H'g0 should be equal. However, 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 ratio of proportionality 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] However, H g0 is considered to be 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 on the signal S g(t) as well as the corrected curve S c (t) = S(t) - S g (t). Figure [Fig. 20] represents respectively the curves of S(t) at the top, Sg(t) at the bottom and Sc(t) in the middle. Substep 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 of 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] By 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 j and 12 before discharge and between times 13 and 14.

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

[0236]

[0237] the same before and after discharge. The expression for 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 has been corrected for the contribution of graphite, the temperature is calculated in the same way as before from the formula below.

[0241] [Equation 32]

[0242] Either

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

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

[0245] First, for the temperature calibration of the sensor, we take the temperature relaxation of the accumulator after 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 withdrawal of the contribution of graphite is taken into consideration in this case even if it is constant.

[0249] Figure 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 of the intensity ratio of the peaks H and S after correction of the contribution of the absorption of the graphite, and the internal temperature Tint calculated from the calibration curve of the thermo-luminescence sensor, as illustrated in [Fig.23].

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

[0254] The sensor 7 according to the illustrated example is made 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 with at least two emission peaks.

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

[0256] In general, the processing method according to the invention can be implemented for any optical fiber sensor whose thermo-luminescent material(s) allows a temperature measurement and whose measurement environment in which the sensor is implanted is likely to present in a variation of optical absorption, the method allowing the contribution of this variation in the measurement signal to be extracted in order to retain only that related 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. Demands A method for processing the measurement signal of a temperature sensor of a battery, in particular a metal-ion battery, comprising an optical fiber having a free end forming 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 region of variation of the optical absorption spectrum of the insertion material of the metal ions of at least one electrode of the battery, comprising the following steps: i / first acquisition of the thermoluminescence signal from the sensor, during a first cycle of the metal-ion battery, at a rate such that the battery does not have time to heat up; ii / second acquisition of the thermoluminescence signal from the sensor, during a second cycle of the metal-ion battery, at a regime such that the battery heats up; iü / data processing 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 related 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 centroid 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 intensity of the peak (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 t1 and t2) as that chosen to calculate H0; S(t) is the intensity of the other peak (S) measured over time; B is the slope, extracted from the thermoluminescence calibration line of the sensor; either according to [Equation 3] toE 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 the cycling according to ii / , when the temperature of the accumulator is stabilized. Method according to claim 1, for a cycle 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. Method according to claim 1 or 2, for a cycle with a discharge at 4C undergone by the accumulator, the time period between t3 and t4 being between 500 and 700 s. Measurement sensor, intended to implement the method according to any 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 thermo-luminescent material being Gd2O2S or Y2O2S doped Er3+ and Yb3+. Accumulator (A) or metal-ion battery, in particular li-ion, comprising, inserted within it, at least one sensor (7) according to any 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 any one of claims 1 to 3, for measuring temperature within a metal-ion battery, in particular the lithiation state of a negative graphite electrode of a Li-ion battery.

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