Temperature sensor and measurement of the state of charge (SOC) of a fiber optic accumulator with thermoluminescent material(s), at the emission peak(s) in a zone of variation of the optical absorption spectrum of the insertion material of an electrode

Abstract

Temperature and state of charge (SOC) sensor for an optical fiber accumulator with thermoluminescent material(s), at the emission peak(s) in a variation zone of the optical absorption spectrum of the insertion material of an electrode The invention relates to a temperature and state of charge (SOC) sensor (7) for a metal-ion accumulator, comprising an optical fiber (8) of which a free end (82) forms 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 variation zone of the optical absorption spectrum of the metal ion insertion material 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 metal ions into the electrode.Figure for abstract: Fig. 12.

Description

Title of the invention: Temperature sensor and measurement of the state of charge (SOC) of a fiber optic accumulator with thermoluminescent material(s), at the emission peak(s) in a zone of variation of the optical absorption spectrum of the insertion material of an electrode 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 fiber optic sensors suitable for such a measurement.

[0003] The invention aims to propose 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, an English acronym for "State Of Charge").

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

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

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

[0008] The light radiation emitted by the thermoluminescent material is characterized by an emission spectrum comprising one or more peaks whose intensity and / or The luminescence lifetime varies depending on the temperature to which the material is subjected. Prior art

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0031] According to this principle, a luminescent material has an emission spectrum with several peaks at distinct wavelengths, at least one of which has an intensity which varies with temperature while others will remain constant.

[0032] [Fig. 3] illustrates the luminescence spectrum of a fiber optic sensor based on thermoluminescent particles whose two emission peaks evolve as a function of the temperature to which they are subjected.

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

[0034] [Equation 1]

[0035] in which - FIR is the intensity ratio (or integrals) of the two emission peaks, - T is the temperature, - kB is the Boltzmann constant, - AE is the energy gap between the two energy levels corresponding to the two luminescence peaks and which are thermally coupled, - B a constant.

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

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

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

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

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

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

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

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

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

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

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

[10] .

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

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

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

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

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

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

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

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

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

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

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

[0057] However, there are very few 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 the measurement of temperature and the lithiation state of an accumulator electrode,

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

[0061] To do this, the invention relates to a temperature sensor and a sensor for measuring the state of charge (SOC) of an accumulator, in particular a metal-ion accumulator, comprising an optical fiber, one free end of which forms an optical probe with thermoluminescent material(s) capable of emitting a peak of light at at least two wavelengths, at least one of the peaks being adapted to be in at least one zone of variation of the optical absorption spectrum of the material for inserting the metal ions of at least one electrode of the accumulator.

[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 an alternative 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 with Er3+ and Yb3+.

[0065] The invention also relates to an accumulator (A) or metal-ion battery, in particular li-ion, comprising, inserted within it, at least one sensor as described previously.

[0066] Several sensor installation variants can be envisaged: - 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 accumulator separator which is opposite to that in contact with the electrode whose lithiation state varies; - the sensor can be inserted into the separator or sandwiched between two layers of accumulator separator.

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

[0068] Thus, the invention essentially consists of an optical fiber temperature sensor carrying at the end an optical probe with thermoluminescent material(s) with at least two emission peaks, i.e. two peaks in at least two different wavelengths, one of which is located in at least one variation zone of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the accumulator, 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 into the electrode.

[0069] Thanks to the invention, the same optical fiber sensor whose probe is thermoluminescence makes it possible both to make a measurement of the internal temperature of the accumulator and a measurement by luminescence absorption of the change in the insertion of the ions, in particular of a lithiation of an electrode, in particular made of 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 (Peak 1) remains constant when the temperature changes while the second peak (Peak 2) decreases when the temperature increases ([Fig. 10]). There may be cases where the first peak (Peak 1) also varies but in all cases it is the ratio of the two peaks which varies as a function of the temperature, as explained in the preamble. Once the probe is positioned so as to optically interact with the electrode made of ion insertion material, such as graphite, the light that it will emit by 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, on the lithiation of the graphite in the case of a negative graphite electrode in a Li-ion accumulator.Therefore, considering 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] [Fig. 11] is a schematic view of the evolution of the luminescence spectrum measured as a function of the lithiation state of the graphite of an electrode at constant temperature. Depending on the wavelength of the two peaks (Peak 1, Peak 2), their absorption by the graphite as a function of its lithiation state will not vary in the same proportion. By measuring the variation in intensity of one of the peaks (Peak 1 or Peak 2), or of the two peaks (Peak 1, Peak 2), it is thus possible to follow the lithiation state of the graphite, and therefore the state of charge (SOC) of a Li-ion accumulator.

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

[0074] Consequently, by positioning a probe with thermoluminescent material(s) close to an accumulator 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 accumulator.

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

[0076] The measurement of the insertion state (lithiation of graphite for a Li-ion accumulator with graphite negative electrode) is then done by following the variation in intensity of one of the peaks (Peak 1 or Peak 2 or Peak 3), or of the two peaks (Peak 1, Peak 2 or P3), while the variation in temperature can be measured from the ratio of the two peaks (Peak 2 to Peak 1).

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

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

[0079] Other advantages and characteristics will become more apparent upon reading the detailed description, given for illustrative and non-limiting purposes, with reference to the following figures. Brief description of the drawings

[0080] [Fig.l] [Fig.l] is an exploded perspective schematic view showing the various elements of a lithium-ion accumulator.

[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] [Fig.3] illustrates in the form the luminescence spectrum of a sensor at optical fiber based on thermoluminescent particles whose two emission peaks evolve according to the temperature to which they are subjected.

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

[0084] [Fig.5] [Fig.5] illustrates at the bottom the variation in the intensity of the luminescence signal of a luminescence sensor and the external temperature of a Li-ion accumulator of 1A.h, during an electrochemical cycle (charge and discharge) that it undergoes, characterized by the curves at the top of variation of the voltage and the applied current.

[0085] [Fig.6] [Fig.6] illustrates the variation of the internal temperature compared to the variation of the external temperature of a 1A.h Li-ion accumulator as a function of the electrochemical cycling it undergoes, characterized by the voltage variation curves at the top.

[0086] [Fig.7] [Fig.7] is the reproduction of an image of the surface of an anode in graphite of an accumulator depending on its state of lithiation of the graphite and the state of charge of the anode.

[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 an accumulator.

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

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

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

[0091] [Fig. 13] [Fig. 13] is a longitudinal sectional view of a fiber measuring sensor optical thermoluminescent probe according to the invention.

[0092] [Fig.l4A], [Fig.l4B], [Fig.l4C] Figures 14A, 14B, 14C schematically show the optical probe of the sensor according to [Fig. 13], when the measurement environment constituted by a Li-ion accumulator has respectively no impact on the measurement related to a change in optical absorption, an impact due to lithiation, and to delithiation of the negative graphite electrode of the accumulator.

[0093] [Fig.l4D] [Fig.l4D] 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.l4E] [Fig.l4E] illustrates the variation of spectra of the thermoluminescent probe sensor according to the invention in an environment according to figures 14B or 14Cn capable of simultaneously measuring temperature by luminescence ratiometry (Peak 1 and Peak 2) and the variation of graphite lithiation (Peak 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] [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.l7A], [Fig.l7B], [Fig.l7C] Figures 17A, 17B, 17C illustrate different possible configurations for the installation 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 of 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 accumulator with graphite negative electrode.

[0099] [Fig. 19] [Fig. 19] is an example of measurement for a 4C discharge of a Li-ion accumulator with graphite negative 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 with Er3+ and Yb3+ doped Gd2O2S material whose spectrum is given in [Fig. 16],

[0100] [Fig.20] [Fig.20] is the result of the data processing allowing to extract the contribution due to the optical absorption of the graphite of a negative electrode of a Li-ion accumulator during discharge at 4C to deduce the variation on the variation of the intensity of the H peak. and on the variation of the intensity of the S peak

[0101] [Fig.21] [Fig.21] is the result of the data processing allowing to extract the contribution due to the optical absorption of the graphite of a negative electrode of a Li-ion accumulator during discharge at 4C to deduce the variation on the variation of the intensity of the S peak.

[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 the temperature measured by a thermoluminescence sensor according to the invention after removing 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 later.

[0104] [Fig. 13] shows a fiber optic measuring sensor 7 according to the invention.

[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 consisting 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 organic or hybrid material that is transparent in the wavelength ranges used and that can withstand the environment of the electrolyte of a metal-ion accumulator in which the optical fiber 2 and the optical probe 3 are immersed. Examples of materials of the matrix 30 deposited in particular by sol-gel deposition as described in patent application EP4155700Al. The matrix may also be made of polymethyl methacrylate (PMMA).

[0108] The different 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 luminophores then excited emit light whose emission spectrum with peaks is characteristic of the nature of the luminophore.

[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 returns to the optical fiber without being modified by the environment (figure 14A).

[0112] When the optical probe 9 is positioned within a Li-ion accumulator, 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 a part of it will be absorbed by the graphite (figures 14B and 14C).

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

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

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

[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 accumulator of which the lithiation state of the negative electrode is to be measured.

[0118] Thus, the probe 9 of the sensor can be placed facing the negative graphite electrode, inserted into it or even on the other side of the separator of the accumulator, provided that the latter is optically transparent in the wavelengths of interest for monitoring the lithiation of the graphite. This is for example the case of a porous polymer separator conventionally used in Li-ion accumulators such as Celgard®. Such a separator soaked in electrolyte is transparent and the probe 9 of the sensor can therefore measure the state of lithiation of the graphite electrode below, even with the separator arranged 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 implantation configurations, respectively as follows: - the sensor 7 is in direct contact with the graphite electrode 3, - the sensor 7 is directly in 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 of Figures 17B and 17C assume that the separator 1 is transparent in the wavelength range used to monitor the absorption of graphite.

[0122] The inventors carried out tests on a Li-ion accumulator, with flexible packaging ("pouch"), consisting of a negative graphite electrode, a positive NMC622 electrode and a Celgard® separator without coating.

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

[0124] This optical probe was positioned within the Li-ion accumulator.

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

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

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

[0131] It appears that the ratio varies depending on the charging or discharging phase of the accumulator (current plateaus) for low regimes. We also see that the shape of the intensity of the peak S depends on the charging or discharging regime and the current intensity.

[0132] In other words, when the accumulator undergoes slow cycling and the temperature does not change, the response of the optical sensor evolves well as a function of the cycling. This evolution corresponds to a variation in the optical absorption within the cell and is correlated to the variation in lithiation of the graphite.

[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 the lithiation of graphite during the discharge on the intensity of the H and S peaks is clearly visible (increase then relaxation). The effect of the temperature is visible but to a lesser extent on the ratio.

[0135] By extracting the contribution of the absorption due to the lithiation of graphite on the signal of the H and S peaks, it is possible to extract the contribution of the signal due to the temperature. For this, it is considered that the intensity of the H peak must remain constant. The contribution due to the absorption by the graphite is then deduced by difference. This then makes it possible to correct the variation of the S peak. This processing makes it possible to extract the variation of the ratio between S and H peaks linked to the temperature.

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

[0137] [Fig.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 in the intensity ratio of the H and S peaks after correction of the contribution of the graphite absorption, and the internal temperature Tint calculated from the calibration curve of the thermoluminescence sensor, as illustrated in [Fig.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 produced according to the techniques, in particular by sol-gel according to patent application EP4155700A1. The invention can be applied to any other type of optical thermoluminescence 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 thereof depending on the state of lithiation, more generally on the state of insertion of the insertion material of an electrode in a metal-ion accumulator.

[0141] Thus, if the invention has been described in relation to a negative graphite electrode, the sensor according to the invention can quite easily be implemented in a metal-ion accumulator with another chemistry of the anode or cathode materials insofar as this(these) material(s) has an optical absorption which changes with its state of charge and if this change can be measured in the same way without disturbing the measurement of the temperature by thermoluminescence.

[0142] For the production 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

Claims

1. Sensor (7) for temperature and measurement of the state of charge (SOC) of an accumulator, in particular a metal-ion accumulator, comprising an optical fiber (8) of which a free end (82) forms an optical probe (9) with thermoluminescent material(s) (91) capable of emitting a peak of light at at least two wavelengths, at least one of the two peaks being adapted to be in at least one zone of variation of the optical absorption spectrum of the material for inserting 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 into 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 one of the preceding claims, the thermoluminescent material being Gd2O2S or Y2O2S doped with Er3+ and Yb3+.

5. Accumulator (A) or metal-ion battery, in particular li-ion, comprising, inserted therein, at least one sensor (7) according to 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 separator of the accumulator which is opposite to that in contact with the electrode whose lithiation state varies.

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

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

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