Temperature and state of charge (SOC) sensor for measuring a thermoluminescent fiber optic battery at the emission peak(s) in a region of variation of the optical absorption spectrum of the electrode insertion material.

Abstract

Temperature and State of Charge (SOC) Sensor for a Metal-Ion Battery, comprising an optical fiber (8) with a free end (82) forming an optical probe (9) with a thermoluminescent material (91) capable of emitting a light peak at at least two wavelengths, at least one of the two peaks being adapted to be in at least a region of variation of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the battery, the ratio of the two peaks being a function of the temperature of the battery and the variation in intensity of at least one of the two peaks being a function of the insertion of the metal ions in the electrode.Figure for the abridged version: Fig. 12.

Description

Title of the invention: Temperature sensor and state of charge (SOC) measurement of a thermoluminescent material(s) optical fiber battery, at the emission peak(s) in a region of variation of the optical absorption spectrum of the electrode insertion material technical field

[0001] The present invention relates to the field of instrumentation, in particular sensors for measuring an operating parameter of 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 for estimating both the temperature and the state of charge of a battery, from a single optical fiber sensor.

[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. 3 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 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 perform in situ (in operando) monitoring of the accumulator.

[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 transmittance 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] However, there are very few that are capable of simultaneously measuring several properties within an accumulator or battery.

[0058] In particular, simultaneous monitoring of the internal temperature and the potential or lithiation state of a battery electrode with a single sensor has never been achieved.

[0059] There is therefore a need to propose such a sensor combining temperature measurement and the lithiation state of a battery electrode,

[0060] The aim of the invention is to meet at least part of this need. Description of the invention

[0061] To this end, the invention relates to a temperature and state of charge (SOC) measurement sensor of a battery, in particular a metal-ion battery, comprising an optical fiber, one free end of which forms an optical probe with thermoluminescent material(s) capable of emitting a peak of light at at least two wavelengths, at least one of the peaks 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.

[0062] Advantageously, the wavelength of one of the two emission peaks is 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.

[0063] According to one embodiment, the optical probe comprises a matrix in which particles of at least one thermoluminescent material are incorporated.

[0064] Preferably, the thermoluminescent material is Gd2O2S or Y2O2S doped Er3+ and Yb3+.

[0065] 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.

[0066] Several sensor implantation variants can be considered: - the sensor can be in direct contact with the electrode whose lithiation state varies; - the sensor can be in direct contact with the face of the battery separator which is opposite to the one in contact with the electrode whose lithiation state varies; - the sensor can be inserted into the separator or sandwiched between two layers of the accumulator separator.

[0067] The invention also relates to the use of a sensor as described above for the simultaneous measurement of temperature and the measurement of the insertion state of ions within a metal-ion battery, in particular the lithiation state of a negative graphite electrode of a Li-ion battery.

[0068] Thus, the invention essentially consists of a fiber optic temperature sensor carrying at its end an optical probe with thermoluminescent material(s) having at least two emission peaks, that is to say, two peaks in at least two different wavelengths, one of which is located in at least one variation region of the optical absorption spectrum of the insertion material of the metal ions of at least one electrode of the accumulator, the ratio of the two peaks being a function of the temperature of the accumulator and the variation in intensity of at least one of the two peaks being a function of the insertion of the metal ions in the electrode.

[0069] Thanks to the invention, a single optical fiber sensor whose probe is thermoluminescence makes it possible to both measure the internal temperature of the accumulator and measure by luminescence absorption the change in the insertion of ions, in particular the lithiation of an electrode, in particular graphite, for a Li-ion accumulator, which is a method for estimating the state of charge of the accumulator (SOC).

[0070] The operating principle of an optical probe sensor according to the invention is as follows.

[0071] The thermoluminescent material probe operates by ratiometry. The probe according to the invention has two transition peaks in the luminescence spectrum, which are used for measurement. The first peak (Pic 1) remains constant as the temperature changes, while the second peak (Pic 2) decreases as the temperature increases ([Fig. 10]). There may be cases where the first peak (Pic 1) also varies, but in all cases, it is the ratio of the two peaks that varies with temperature, as explained in the preamble. Once the probe is positioned to interact optically with the ion insertion material electrode, such as graphite, the light it emits from the luminescent material(s) will be absorbed by this electrode, and this absorption will depend on the wavelength of the peak but also on the insertion state, the lithiation of the graphite in the case of a negative graphite electrode in a Li-ion battery.Therefore, assuming that the temperature does not vary and that the spectrum emitted by the probe is measured as a function of the insertion state, only the unabsorbed light can be measured, and this depends on the insertion state, in particular the lithiation of the graphite.

[0072] Figure 11 is a schematic view of the evolution of the measured luminescence spectrum as a function of the lithiation state of the graphite in an electrode at constant temperature. Depending on the wavelength of the two peaks (Pic 1, Pic 2), their absorption by the graphite will not vary proportionally according to its lithiation state. By measuring the variation in intensity of one or both peaks (Pic 1 or Pic 2), the lithiation state of the graphite, and therefore the state of charge (SOC) of a Li-ion battery, can thus be monitored.

[0073] That being said, as explained in the preamble in relation to [Fig.6], the temperature varies within an accumulator during its cycling and according to the current regime applied.

[0074] Therefore, by positioning a thermoluminescent material probe(s) near a battery electrode, in particular graphite, so that its luminescence is absorbed by the insertion material, such as graphite, the probe sensor makes it possible both to monitor the insertion state of the electrode material, in particular the lithiation of the graphite, and to measure the temperature within the battery.

[0075] As shown in [Fig. 12], a peak (Peak 3) in a range of strong optical absorption of the electrode insertion material.

[0076] The measurement of the insertion state (lithiation of the graphite for a Li-ion battery with a negative graphite electrode) is then carried out by monitoring the intensity variation of one of the peaks (Pic 1 or Pic 2 or Pic 3), or of both peaks (Pic 1, Pic 2 or P3), while the temperature variation can be measured from the ratio of the two peaks (Pic 2 - Pic 1).

[0077] In order to optimize the operation of such a sensor for a Li-ion battery with a negative graphite electrode, one or more luminescent materials are advantageously chosen with a luminescence peak (Pic 3) allowing the variation of the lithiation state of the graphite to be followed in a wavelength range above 700 nm, preferably between 700 and 1100 nm), the two peaks (Pic 1, Pic 2) or the reference peak (Pic 1) in a wavelength range weakly affected by the optical absorption of the graphite, preferably between 400 and 600 nm for temperature measurement.

[0078] The chosen Peak 3 is that of a material whose luminescence (that of Peak 3) will not or will vary little as a function of temperature within the usual temperature variation range of an operating accumulator.

[0079] 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

[0080] [Fig.1] [Fig.1] is a schematic exploded perspective view showing the different elements of a lithium-ion battery.

[0081] [Fig.2] [Fig.2] is a front view showing a lithium-ion battery with its flexible packaging according to the state of the art.

[0082] [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.

[0083] [Fig.4] [Fig.4] is the logarithmic response line of the sensor according to [Fig.3].

[0084] [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 Li-ion battery of the A.h, during an electrochemical cycling (charge and discharge) that it undergoes, characterized by the curves at the top of variation of the voltage and current applied.

[0085] [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.

[0086] [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.

[0087] [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.

[0088] [Fig.9] [Fig.9] illustrates the variation of the transmittance spectrum (AT / T) as a function of the state of charge (capacitance) of a battery, measured in situ according to the state of the art by evanescent wave using an optical fiber.

[0089] [Fig. 10] Figure 10 illustrates the variation of the spectrum of a thermo-probe sensor luminescent for temperature measurement by ratiometry of two emission peaks. [Fig.11] [Fig.11] illustrates the variation in peak intensity of a thermoluminescent probe sensor, measured as a function of the lithiation state of graphite at constant temperature.

[0090] [Fig. 12] Figure 12 illustrates the variation of spectra of a thermo-probe sensor luminescent according to the invention capable of simultaneously measuring temperature by luminescence ratiometry (Pic 1 and Pic 2) and the variation of graphite lithiation (Pic 3) by optical absorption.

[0091] [Fig. 13] [Fig. 13] is a longitudinal cross-sectional view of a fiber optic measurement sensor thermoluminescent probe optics according to the invention.

[0092] [Fig.14A], [Fig.14B], [Fig.14C] Figures 14A, 14B, 14C schematically show the optical probe of the sensor according to [Fig. 13], 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.

[0093] [Fig.14D] [Fig.14D] illustrates the variation in intensity of the peaks of the thermoluminescent probe sensor in an environment according to figures 14B or 14C, measured as a function of the lithiation state of the graphite at constant temperature.

[0094] [Fig. 14E] [Fig. 14E] illustrates the variation of spectra of the thermoluminescent probe sensor according to the invention in an environment as shown in Figures 14B or 14Cn capable of simultaneously measuring temperature by luminescence ratiometry (Pic 1 and Pic 2) and the variation of graphite lithiation (Pic 3) by optical absorption.

[0095] [Fig. 15] [Fig. 15] is the luminescence spectrum of Er3+ and Yb3+ doped Gd2O2S under light excitation at 980 nm.

[0096] [Fig. 16] the [Fig. 16] is the variation of the luminescence spectrum of Er3+ and Yb3+ doped Gd2O2S under light excitation at 980 nm, as a function of temperature.

[0097] [Fig.17A], [Fig.17B], [Fig.17C] Figures 17A, 17B, 17C illustrate different possible implantation configurations of a sensor according to the invention within a Li-ion accumulator.

[0098] [Fig. 18] [Fig. 18] is an example of variation of the intensity of the S peak as well as the intensity ratio of the H and S peaks of Er3+ and Yb3+ doped Gd2O2S whose spectrum is given in [Fig. 16], during the cycling of a Li-ion battery with a negative graphite electrode.

[0099] [Fig. 19] [Fig. 19] is an example of a measurement for a 4C discharge of a Li-ion battery with a negative graphite electrode showing the variation of the 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. 16],

[0100] [Fig.20] [Fig.20] 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 intensity of peak H and on the intensity of peak S

[0101] [Fig.21] [Fig.21] 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 peak S.

[0102] [Fig.22] [Fig.22] 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 thermoluminescence sensor according to the invention after the removal of the contribution of graphite in the signal. Detailed description

[0103] Figures 1 to 12 have already been described in the preamble. They will therefore not be detailed further.

[0104] A fiber optic measurement sensor 7 according to the invention is shown in [Fig. 13].

[0105] It comprises an optical fiber 8 consisting of a core 80 adapted to propagate light and a sheath 81 surrounding the core.

[0106] A free end 82 of the fiber carries an optical probe 9 made up of a matrix 90 comprising thermoluminescent particles also called luminophores 91.

[0107] The matrix 30 may be a silica sol-gel, a polymer, or any other transparent organic or hybrid material within the wavelength ranges used and capable of withstanding the electrolyte environment of a metal-ion battery in which the optical fiber 2 and optical probe 3 are immersed. Examples of matrix 30 materials deposited, in particular, by sol-gel deposition as described in patent application EP4155700A1. The matrix may also be made of polymethyl methacrylate (PMMA).

[0108] The various figures 14A to 14C show different configurations in which the sensor 7 according to the invention operates.

[0109] To probe the phosphors 91, an excitation light whose wavelength depends on the type of phosphors used is sent by the core 80 of the fiber.

[0110] The excited phosphors then emit light whose emission spectrum with peaks is characteristic of the nature of the phosphor.

[0111] If the optical probe 9 of the sensor 7 is outside or in an environment without optical impact, then the luminescence spectrum of the probe 9 is emitted in all directions and a part of it returns to the optical fiber without being modified by the environment (Fig. 14A).

[0112] When the optical probe 9 is positioned within a Li-ion battery, so as to interact optically with the graphite of the electrode, the lithiation state of the latter will modify the luminescence spectrum which is recovered by the optical fiber 8 since part of it will be absorbed by the graphite (figures 14B and 14C).

[0113] This absorption difference is then measured by spectral measurement, as illustrated in Figures 14D and 14E. This optical absorption difference can also be measured using photodetectors centered on the peaks of interest, Pic 1, Pic 2, Pic 3.

[0114] The luminophores 91 can be made of a single thermoluminescent material whose luminescence spectrum includes several peaks, some of which are dedicated to temperature measurement and others to measuring the lithiation state of graphite.

[0115] Gd2O2S, or Y2O2S, or NaYF4, or NaGdF4 or Er3+ and Yb3+-doped YVO4 are perfectly suitable materials that can be excited at a wavelength of 980 or 1500 nm. The luminescence spectrum of Gd2O2S-Er3+'Yb3+' excited at 980 nm is shown in [Fig. 15]: the three peaks correspond to the transitions named H, S, and F. The S and H peaks or transitions are thermally coupled, and the temperature can be determined by ratiometry.

[0116] Fig. 16 illustrates the variation of the luminescence spectrum of Gd2O2S-Er3+ Yb3+' under excitation at 980 nm as a function of temperature.

[0117] The sensor 7 according to the invention has the primary advantage of being able to be inserted at a single point in a Li-ion battery whose lithiation state of the negative electrode is to be measured.

[0118] Thus, the sensor probe 9 can be positioned facing the negative graphite electrode, inserted into it, or on the other side of the battery separator, provided that the latter is optically transparent at the wavelengths of interest for monitoring graphite lithiation. This is, for example, the case with a porous polymer separator commonly used in Li-ion batteries such as Celgard®. Such a separator, when impregnated with electrolyte, is transparent, and the sensor probe 9 can therefore measure the lithiation state of the graphite electrode below it, even with the separator positioned between the two.

[0119] When the accumulator separator is transparent in the wavelength range of interest for monitoring graphite lithiation, the sensor 7 can also be placed in the thickness of the separator or between two successive layers of separator.

[0120] Figures 17A, 17B and 17C show different mounting configurations, respectively as follows: - Sensor 7 is in direct contact with graphite electrode 3, - the sensor 7 is in direct contact with the face of the separator 1 which is opposite to that in contact with the graphite electrode 3, - the sensor 7 is inserted into the separator or sandwiched between two layers of separator.

[0121] As already mentioned, the configurations in Figures 17B and 17C assume that the separator 1 is transparent in the range of wavelengths used to track the absorption of graphite.

[0122] The inventors carried out 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.

[0123] The sensor 7 implemented is matrix 90 as described in patent application EP4155700A1, in which have been incorporated, as luminophores 91, Er3+ and Yb3+ doped Gd2O2S particles marketed under the reference PTIR545UF by Phosphor Technology, whose luminescence spectrum under excitation at 980 nm is given in [Fig. 15].

[0124] This optical probe has been positioned within the Li-ion battery.

[0125] The temperature measurement was made by determining the ratio of the two emission peaks H and S. As already mentioned, the H peak remains constant regardless of the temperature, while the S peak decreases as the temperature increases ([Fig. 16]).

[0126] The inventors subjected the accumulator to a slow electrochemical charge and discharge cycle.

[0127] Under this regime, the temperature of the accumulator does not increase.

[0128] Then, the battery underwent a discharge at 4C which induced an increase in the battery temperature of approximately 10°C.

[0129] The results of these measurements are illustrated in figures 18 and 19.

[0130] Fig. 18 shows the curves of variation of the intensity of the S peak as well as the ratio of intensity between the H and S peaks during slow regime cycling.

[0131] 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.

[0132] 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 cell and is correlated with the variation in graphite lithiation.

[0133] Fig. 19 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.

[0134] 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.

[0135] By extracting the contribution of absorption due to graphite lithiation to the H and S peak signals, it is possible to extract the signal contribution due to temperature. For this, the intensity of the H peak is assumed to remain constant. The contribution due to absorption by graphite is then deduced by subtraction. This allows the variation of the S peak to be corrected. This process makes it possible to extract the temperature-related variation of the ratio between the S and H peaks.

[0136] Fig. 20 illustrates the variation in the intensity of the H peak during the discharge at 4C.

[0137] Figure 21 illustrates the variation in the intensity of peak S during this same dump.

[0138] After this data processing, a correlation can be established between the external temperature Text of the accumulator measured by thermocouple, the variation ratio of intensity of the H and S peaks 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.22].

[0139] Other variants and improvements may be envisaged without departing from the scope of the invention.

[0140] 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 luminophores and another type of material for the matrix with at least two emission peaks, one of which is constant at the temperature and the other in an optical absorption zone, preferably in a zone of strong variation of the latter depending on the lithiation state, more generally on the insertion state of the insertion material of an electrode in a metal-ion battery.

[0141] Thus, if 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 other anode or cathode material chemistry insofar as this / these material(s) exhibits an optical absorption that changes with its state of charge and if this change can be measured in the same way without disturbing the temperature measurement by thermoluminescence.

[0142] For the realization of the sensor, other materials called "up-converter" materials which have thermoluminescence properties can be considered. List of cited references#:

[0143] [1] :https: / / battery2030.eu / research / roadmap /

[0144] [2]: https: / / www.instabat.eu /

[0145] [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 ofion activities in aqueous batteries with plasmonic fiber -optic sensors » Nature Communications 13, 547 (2022).

[0146] [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.

[0147] [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.

[0148] [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).

[0149] [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.

[0150] [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).

[0151] [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)

[0152]

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

Claims

Demands

1. A temperature and state of charge (SOC) sensor (7) for measuring the state of charge of a battery, in particular a metal-ion battery, comprising an optical fiber (8) having a free end (82) forming an optical probe (9) with thermoluminescent material(s) (91) capable of emitting a light peak at at least two wavelengths, at least one of the two peaks 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, the ratio of the two peaks being a function of the temperature of the battery and the variation in intensity of at least one of the two peaks being a function of the insertion of the metal ions in the electrode.

2. Sensor according to claim 1, 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.

3. Sensor according to claim 1 or 2, the optical probe comprising a matrix (90) in which particles (91) of at least one thermoluminescent material are incorporated.

4. Sensor according to any one of the preceding claims, the thermoluminescent material being Gd2O2S or Y2O2S doped Er3+ and Yb3+.

5. 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 1 to 4.

6. Accumulator according to claim 5, the sensor being in direct contact with the electrode whose lithiation state varies.

7. Accumulator according to claim 5, the sensor being directly in contact with the face of the accumulator separator which is opposite to that in contact with the electrode whose lithiation state varies.

8. Accumulator according to claim 5, the sensor being inserted in the separator or sandwiched between two layers of the accumulator separator.

9. Use of a sensor according to any one of claims 1 to 4, for measuring temperature simultaneously with measuring the insertion state of ions within a metal-ion battery, in particular the state of lithiation of a graphite negative electrode of a Li-ion battery.

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