Sensor for measuring the state of charge (SOC) of a metal-ion accumulator, with optical fiber whose free end forms an optical probe with emission in the optical absorption spectrum of an electrode. Associated measurement system.

Abstract

Sensor for measuring the state of charge (SOC) of a metal-ion accumulator, with an optical fiber whose free end forms an optical probe with at least one luminescent material with one or more emission wavelength peaks in the optical absorption spectrum of the material of an electrode of the accumulator. Associated measurement system. The invention relates to a sensor (7) for measuring the state of charge (SOC) of a metal-ion accumulator, comprising an optical fiber (8) whose free end (82) forms an optical probe (9) with at least one luminescent material with one or more emission wavelength peaks adapted to emit 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. Figure for abstract: Fig. 10

Description

Title of the invention: Sensor for measuring the state of charge (SOC) of a metal-ion accumulator, with optical fiber whose free end forms an optical probe with emission in the optical absorption spectrum of an electrode. Associated measurement system. 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 the state of charge of a battery, using an 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 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 measurements of the state of charge (SOC) 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] By "luminescence" is meant here and within the framework of the invention, the capacity of a material to emit almost instantaneously 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 with an emission spectrum comprising one or more peaks of intensities which may be different. Prior art

[0007] 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 for contain the electrochemical cell with sealing while being crossed by a part of the current collectors 4, 5.

[0008] The architecture of conventional lithium-ion batteries comprises an anode, a cathode and an electrolyte. Several types of conventional architecture geometry are known:

[0009] - a cylindrical geometry as disclosed in the patent application US2006 / 0121348,

[0010] - a prismatic geometry as disclosed in US patents 7348098, US 7338733;

[0011] - a stacking geometry as disclosed in the patent applications US2008 / 060189, US 2008 / 0057392, and US patent 7335448.

[0012] 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.

[0013] 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).

[0014] 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.

[0015] The current collector 4 connected to the positive electrode is generally made of aluminum.

[0016] The current collector 5 connected to the negative electrode is generally made of copper, nickel-plated copper or aluminum.

[0017] A lithium-ion battery or accumulator can obviously comprise a plurality of electrochemical cells which are stacked on top of each other.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] To be able to function optimally, a BMS needs real-time measurements of physical parameters such as voltage, current, temperature.

[0023] 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],

[0024] 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.

[0025] This is why many works, notably the ISNTABAT project: [2], focus on the development of sensors which can be implanted within an accumulator.

[0026] 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 chemical parameters at the heart of an element, in particular an accumulator or battery: [3], [4], [5].

[0027] 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.

[0028] Based on this observation, researchers have developed a fiber optic sensor to monitor the color change of a negative graphite electrode within a accumulator and therefore its state of lithiation from an optical fiber. Several publications on this work have been made: [6], [7], [8], [9],

[10] .

[0029] 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.

[0030] 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.

[0031] The work further showed that the variation of the optical absorption spectrum of graphite occurs over a fairly wide spectral band.

[0032] An illustration of this work is reproduced in Figures 3, 4 and 5.

[0033] 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 relative 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.

[0034] The evanescent wave technique which has just been described has numerous drawbacks, including:

[0035] - the need to use a broadband light source or LEDs of suitable wavelength,

[0036] - 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,

[0037] - the passage constitutes a point of mechanical fragility of the optical fiber.

[0038] There is therefore a need to improve fiber optic sensors for measuring the lithiation state of a negative graphite electrode of Li-ion accumulators, in order to overcome the aforementioned drawbacks.

[0039] More generally, there is a need to propose reliable and precise fiber optic sensors for measuring the state of charge (SOC) of metal-ion accumulators, at least one of the electrodes of which is made of a material whose state of insertion of the metal ions modifies its optical absorption.

[0040] The aim of the invention is to respond at least in part to this(these) need(s). Statement of the invention

[0041] To do this, the invention relates to a sensor for measuring the state of charge (SOC) of an accumulator, in particular a metal-ion accumulator, comprising an optical fiber whose free end forms an optical probe with at least one luminescent material with one or more emission wavelength peaks adapted to emit in at least one zone of variation of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the accumulator.

[0042] Advantageously, the wavelength of the emission peaks is between 700 and 1100 nm.

[0043] According to an advantageous embodiment, the optical probe comprises a matrix in which particles of at least one luminescent material are incorporated.

[0044] The luminescent material(s) may be organic, inorganic or hybrid.

[0045] Preferably, the organic luminescent material(s) is (are) chosen from fluorescein, rhodamine, porphyrins, and fluorochromes having emissions in the visible and near infrared.

[0046] Preferably, the organic luminescent material(s) is (are) organo-lanthanides based on europium, terbium, ytterbium, praseodymium.

[0047] Preferably, the inorganic luminescent material(s) is (are) chosen from oxides, oxysulfides, fluorides, where appropriate doped with transition or rare earth metals.

[0048] Preferably, the inorganic luminescent material(s) is (are) chosen from Cr3+ doped alumina, Ce and Pr doped YAG, Eu, Tb, Pr, Yb, Er doped Gd2O2 or Y2O2.

[0049] Preferably, the organic luminescent material(s) is (are) semiconductor nanocrystals, or "quantum dots" (QDs), are fluorescent quantum dot nanoparticles.

[0050] The invention also relates to a measuring system comprising: - at least one sensor as described above, intended to be inserted into a metal-ion accumulator - at least one light excitation source (SI, S2), the excitation source being adapted to emit at least one excitation peak of the luminescent material(s) of the sensor, - at least one optical connector to connect the excitation source to the optical fiber of the sensor, - at least one so-called collection optical fiber connected to the optical connector and adapted to collect at least one peak of the luminescence spectrum emitted by the luminescent material(s) of the sensor probe, - a spectrophotometer (SP) connected to the collection optical fiber and adapted to measure the variation in luminescence emitted by the optical probe of the sensor.

[0051] The invention also relates to a measuring system comprising:

[0052] - at least one sensor as described previously, intended to be inserted within a metal-ion accumulator - at least one light excitation source (SI, S2), the excitation source being adapted to emit at least one excitation peak of the luminescent material(s) of the sensor, - at least one optical connector to connect the excitation source to the optical fiber of the sensor, - at least two separate optical fibers, called collection fibers, each connected to the optical connector and each adapted to collect at least one peak of the luminescence spectrum emitted by the luminescent material(s) of the sensor probe, - at least two separate photodiodes (PI, P2), each connected to one of the two optical collection fibers and each adapted to measure the variation in luminescence emitted by the optical probe of the sensor.

[0053] According to an advantageous embodiment, the measuring system comprises at least one bandpass filter (F1, F2) arranged between the excitation source and the optical connector.

[0054] According to another advantageous embodiment, the measuring system comprises at least one bandpass filter (F3, F4) arranged between the optical sensor and the spectrophotometer or each of the two photodiodes.

[0055] 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.

[0056] Several sensor installation variants can be envisaged:

[0057] - the sensor can be directly in contact with the electrode whose lithiation state varies;

[0058] - the sensor can be directly in contact with the face of the separator of the accumulator which is opposite to that in contact with the electrode whose state of lithiation varies;

[0059] - the sensor can be inserted into the separator or sandwiched between two accumulator separator layers.

[0060] The invention also relates to the use of a sensor as described above, for measuring the state of insertion of ions within a metal-ion accumulator, in particular the state of lithiation of a negative graphite electrode of a Li-ion accumulator.

[0061] Thus, the invention essentially consists of an optical fiber sensor carrying at its end an optical probe with at least one luminescent material with at least two emission peaks of the metal ion insertion material of at least one electrode of the accumulator in operation for which it is sought to estimate the state of charge (SOC).

[0062] For a Li-ion accumulator with a graphite negative electrode, the emitted peak(s) are preferably in a zone of strong variation in the absorption spectrum of the graphite depending on its lithiation state. Thus, preferably the wavelength of the peaks is between 700 and 1100 nm.

[0063] One or more luminescent materials are preferably chosen which are not very sensitive to temperature. In the case of sensitivity to temperature, a temperature calibration of the sensor is carried out before operation in order to be able to extract the contribution in the variation of the signal linked to the lithiation state.

[0064] Optionally, in particular for a graphite electrode accumulator, one or more luminescent materials with one or more emission peaks may be provided in a zone of low variation in the optical absorption of the material as a function of its lithiation state.

[0065] Luminescent materials can be organic, inorganic or hybrid.

[0066] Among the organic materials, one can consider fluorescent molecules such as fluorescein, rhodamine, porphyrins, and all fluorochromes having emissions in the visible and near infrared.

[0067] Organo-lanthanides based on europium, terbium, ytterbium, praseodymium, or others can also be used.

[0068] For inorganic materials, all oxides, oxysulfides, fluorides, or others, where appropriate doped with transition or rare earth metals. Cr3+ doped alumina, Ce and Pr doped YAG, Gd2O2 or Y2O2 doped with Eu, Tb, Pr, Yb, Er, are particularly advantageous materials.

[0069] We can also consider semiconductor nanocrystals, or “quantum dots” (QDs), which are fluorescent nanoparticles.

[0070] For the production of the optical probe at the end of an optical fiber, the luminescent material(s) may be in the form of (nano)particles or luminophores incorporated in a matrix.

[0071] This matrix may be made of silica or another transparent material or polymer, such as that described in patent application EP4155700A1.

[0072] A sol-gel technique can be implemented to create the optical probe at the end of the optical fiber.

[0073] The operation of a sensor according to the invention is as follows.

[0074] The sensor is positioned in the accumulator for which the variation in the insertion state of the ions and therefore the charge state is to be estimated so that the luminescence of the optical probe can be at least partly absorbed by the insertion material which changes color and therefore optical absorption depending on the insertion state. For a Li-ion accumulator with graphite electrode, the aim is to estimate its change in lithiation state.

[0075] Once the sensor is properly positioned, an excitation light can be sent into the optical fiber so as to excite the luminescent material(s) or luminophore(s) of the probe. The light emitted by this probe is at least partly absorbed by the insertion material, such as graphite in a Li-ion battery with a graphite negative electrode.

[0076] The intensity and spectrum of the luminescence of the probe which are recovered in return by the optical fiber depend on the state of insertion of the metal ions (lithiation state of the graphite).

[0077] The variation in the insertion state can therefore be quantified / detected, which makes it possible to trace the charge state of the accumulator.

[0078] The invention also relates to a system for detecting the variation in luminescence emitted by the optical probe of the sensor, which comprises either a spectrophotometer or a set of photodiodes preferably associated with optical filters isolating the wavelength zones of interest.

[0079] The advantages of the invention are numerous, among which we can cite: - an easy selection to make for light sources whose excitation wavelength is best suited to the variation in optical absorption that is sought for the insertion material of the accumulator ions, notably graphite. Indeed, using one or more luminescent material(s) and probing them by fluorescence makes it possible to consider using one or even two excitation wavelengths and to fix the luminescence of the material(s); - a less invasive solution in an accumulator. Indeed, compared to a fiber optic sensor operating on the principle of emitting an evanescent wave, as described in the works [6], [7], [8], [9],

[10] previously cited, a sensor according to the invention only needs to be inserted in one place of the accumulator, that is to say that the passage between the interior of the latter and the exterior is made at a single point; - better measurement sensitivity compared to a solution that would simply use the optical absorption of a light source directly by the insertion material, such as graphite. In particular, the implementation of fluorescence in a sensor according to the invention allows, by using several emission wavelengths adapted and spread over the areas of variation of optical absorption of graphite, to have a relative measurement of this as a function of lithiation. By making intensity ratios of the different emission peaks, it is possible to carry out precise monitoring of the variation of the lithiation state of graphite. If we were to do the same thing with optical absorption as recommended by the authors of the works [6], [7], [8], [9],

[10] , it would be necessary to use several LEDs and a spectral measurement.

[0080] 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

[0081] [Fig.l] [Fig.l] is an exploded perspective schematic view showing the various elements of a lithium-ion accumulator.

[0082] [Fig.2] [Fig.2] is a front view showing a lithium-ion battery with its flexible packaging according to the state of the art.

[0083] [Fig.3] [Fig.3] is the reproduction of an image of the surface of a graphite anode of an accumulator as a function of its state of lithiation of the graphite and the state of charge of the anode.

[0084] [Fig.4] [Fig.4] 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.

[0085] [Fig.5] [Fig.5] 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.

[0086] [Fig.6] [Fig.6] is a longitudinal sectional view of a fiber measuring sensor optics according to the invention.

[0087] [Fig.7A], [Fig.7B], [Fig.7C] Figures 7A, 7B, 7C schematically show the optical probe of the sensor according to [Fig.6], respectively, when there is no interaction with the measurement environment constituted by a Li-ion accumulator, the light emitted by the particles being collected without modification of the spectrum by the optical fiber no impact on the measurement, and when the optical probe is in the vicinity of the graphite of the negative electrode of the accumulator, the change of lithiation state (lithiated, delithiated) modifies the intensity and the spectrum of the light collected by the optical fiber since part of the luminescence of the particles is absorbed.

[0088] [Fig.8] [Fig.8] illustrates an example of excitation and emission spectrum of a luminescent material of a sensor according to the invention in the case of one or two excitation wavelength peaks and with one or more emission wavelength peaks.

[0089] [Fig.9A], [Fig.9B], [Fig.9C] Figures 9A, 9B, 9C illustrate different possible implantation configurations of a sensor according to the invention within a Li-ion accumulator.

[0090] [Fig. 10] [Fig. 10] is a schematic view of a first embodiment of a system for measuring the lithiation state of a graphite electrode of a Li-ion accumulator, in which an optical fiber sensor according to the invention is inserted.

[0091] [Fig. 11] [Fig. 11] illustrates an example of excitation and emission spectrum detected by the system according to [Fig. 10].

[0092] [Fig. 12] [Fig. 12] is a schematic view of a second embodiment of a system for measuring the lithiation state of a graphite electrode of a Li-ion accumulator, in which an optical fiber sensor according to the invention is inserted.

[0093] [Fig. 13] [Fig. 13] illustrates an example of excitation and emission spectrum detected by the system according to [Fig. 12]. Detailed description

[0094] Figures 1 to 5 have already been described in the preamble. They will therefore not be detailed later.

[0095] [Fig.8] shows a fiber optic measuring sensor 7 according to the invention.

[0096] It comprises an optical fiber 8 consisting of a core 80 adapted to propagate light and a sheath 81 surrounding the core.

[0097] A free end 82 of the fiber carries an optical probe 9 consisting of a matrix 90 comprising luminescent particles also called luminophores 91. The luminophores can also be in the form of molecules or even a glass or a polymer with a suitable composition. It can also be a luminescent MOF (organometallic, or organo-lanthanide).

[0098] The matrix 90 may be made of silica or polymer, advantageously such as those described in patent application EP4155700A1.

[0099] The production of the probe 9 at the end of the optical fiber 8 can be done by a sol-gel deposition technique.

[0100] The luminophore particles 91 may be organic, inorganic or hybrid.

[0101] The fluorescent organic materials can be chosen from fluorescein, rhodamine, porphyrins, and all fluorochromes having emissions in the visible and near infrared. They can also be organolanthanides based on europium, terbium, ytterbium, praseodymium, etc.

[0102] The inorganic materials can be chosen from oxides, oxysulfides, fluorides, etc. doped with transition or rare earth metals. They can be Cr3+ doped alumina, Ce and Pr doped YAG, Eu, Tb, Pr, Yb, Er, Tm doped Gd2O2 or Y2O2 or Eu, Tb, Pr, Yb, Tm doped YVO4, etc.

[0103] Luminophores can also be implemented in the form of semiconductor nanocrystals, or “quantum dots” (QDs).

[0104] The luminophores can be made of a single material. A variant consists of using two distinct materials, but which excite in the same wavelength range and whose fluorescence emission is located in two areas of the spectrum of interest for measuring the state of lithiation of graphite. For example, one can use a thermoluminescent material which emits in the region of 300 to 700 nm and another for monitoring the lithiation of graphite between 700 and 1000 or even 1500 nm.

[0105] The luminophores can be made of a single material with several emission lines or several materials having emission lines in a region of the spectrum in which the absorption of the graphite varies little or not at all with the lithiation as well as in a region where the variation of the absorption spectrum of the graphite varies greatly. The ratio or the relative variation of intensity of each of the peaks makes it possible to go back to the lithiation state of the graphite.

[0106] As regards the excitation of the phosphors, a single-spectrum excitation source can be used. Two different excitations can also be used: one for probing the material(s) of the phosphors whose luminescence is located in a zone where the variation in absorbance of the graphite is low and the other in a zone where the variation is high.

[0107] [Fig.8] is an example of the excitation and emission spectrum of the luminophores 91 in the case of one or two excitation wavelengths and with one or two emission wavelengths, obtained with a sensor 7 according to the invention. It can be seen that the intensity of the luminescence signal recovered in the core 80 of the optical fiber 8 will depend on the lithiation state of the graphite, as symbolized by the arrows in this [Fig.8].

[0108] 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.

[0109] 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.

[0110] 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.

[0111] Figures 9A, 9B and 9C 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.

[0112] As already mentioned, the configurations of Figures 9B and 9C assume that the separator 1 is transparent in the wavelength range used to monitor the absorption of graphite.

[0113] [Fig. 10] shows a first mode of complete measuring system 10 comprising a sensor 7 according to the invention, implanted within a Li-ion accumulator. This system 10 therefore makes it possible to measure the variation in luminescence emitted by the optical probe 9 of the sensor 7.

[0114] The system 10 firstly comprises two distinct excitation light sources SI, S2 which each emit an excitation wavelength distinct from the other, respectively Xexcl and Xexc2. These sources SI, S2 may be LEDs or lasers.

[0115] The system 10 comprises optical fibers 11, 12 which make it possible to guide the light emitted by each of the two sources S1, S2.

[0116] At the output of each source SI, S2, a low-pass or band-pass filter F1, F2 can be arranged to transport downstream in the optical fibers 11, 12 only the light with the desired excitation peak for the phosphors 91 and therefore retain the other parasitic spectral contributions coming from the sources SI, S2.

[0117] An optical fiber 13 mixes the two excitation peaks coming from the filters F, F2 and sends them to a connector 14 which connects the optical fiber 13 to the optical fiber 8 of the sensor 7 so the probe 9 is within the accumulator, in optical contact with the graphite electrode.

[0118] The luminophore(s) 91 of the probe 9 are then excited and emit a luminescence spectrum with several peaks.

[0119] This spectrum is collected in return by the fiber 8 of the sensor and sent through an optical collection fiber 15, towards the spectrophotometer SP for the actual measurement.

[0120] In [Fig. 10], the arrows indicate the direction of propagation of the light signal in the different components of the system.

[0121] [Fig. 11] shows the positions of the different light spectra within the system of [Fig. 10], namely the filtered spectra Fl, F2 for excitation and the emission spectrum F3 by the phosphors are represented using the same color code as in the figure.

[0122] [Fig. 12] is an alternative embodiment to that of [Fig. 11]. The excitation part of the system is identical, so it is not described again.

[0123] Here, for the detection of the emission spectrum of the luminophores 91, instead of the spectrophotometer SP of [Fig. 10], it is possible to put a set of photodiodes, for example two PI, P2 as illustrated in [Fig. 12]. Each of these photodiodes is connected by a collection optical fiber 16, 17 which is specific to it, to the optical connector 14.

[0124] Preferably, upstream of each of the photodiodes P1, P2 in the optical path from the connector 14, a bandpass filter F3, F4 is arranged so as to isolate the peaks of interest. This solution makes it possible to reduce the cost of the system 10.

[0125] Other variants and improvements may be envisaged without departing from the scope of the invention.

[0126] The sensor 1 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 luminescence probe produced differently.

[0127] The intended application is the monitoring of the lithiation state of lithium-ion batteries with graphite electrode. This principle could also work for other technology if the anode or cathode material has a similar behavior, i.e. its optical absorption changes with its state of charge.

[0128] In the mode of [Fig. 10], instead of a spectrophotometer, a set of LEDs can be provided.

[0129] The measurement systems are implemented with a data acquisition and processing system. List of cited references#:

[0130] [1] : https: / / battery2030.eu / research / roadmap /

[0131] [2] : https: / / www.instabat.eu /

[0132] [3]: Wang, R., Zhang, H., Liu, Q„ Liu, F., Han, X., Liu, X., Li, K., Xiao, G., Albert, J., Lu,

[0133] [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.

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[0135] [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).

[0136] [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.

[0137] [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).

[0138] [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)

[0139]

[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

Claims

1. Sensor (7) for measuring the state of charge (SOC) of an accumulator, in particular a metal-ion accumulator, comprising an optical fiber (8) whose free end (82) forms an optical probe (9) with at least one luminescent material with one or more emission wavelength peaks adapted to emit in at least one zone of variation of the optical absorption spectrum of the metal ion insertion material of at least one electrode of the accumulator.

2. Sensor according to claim 1, the wavelength of the emission peaks being between 700 and 1100 nm.

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

4. Sensor according to one of the preceding claims, the luminescent material(s) being organic, inorganic or hybrid.

5. Sensor according to claim 4, the organic luminescent material(s) being chosen from fluorescein, rhodamine, porphyrins, and fluorochromes having emissions in the visible and near infrared.

6. Sensor according to claim 4, the organic luminescent material(s) being organolanthanides based on europium, terbium, ytterbium, praseodymium.

7. Sensor according to claim 4, the inorganic luminescent material(s) being chosen from oxides, oxysulfides, fluorides, where appropriate doped with transition or rare earth metals.

8. Sensor according to claim 7, the inorganic luminescent material(s) being chosen from Cr3+ doped alumina, Ce and Pr doped YAG, Gd2O2 or Eu, Tb, Pr, Yb, Er doped Y2O2.

9. Sensor according to claim 4, the organic luminescent material(s) being semiconductor nanocrystals, or “quantum dots” (QDs), are fluorescent quantum dot nanoparticles.

10. Measuring system (10) comprising: - at least one sensor (7) according to one of the preceding claims, intended to be inserted into a metal-ion accumulator - at least one light excitation source (SI, S2), the excitation source being adapted to emit at least one excitation peak of the luminescent material(s) of the sensor, - at least one optical connector (14) for connecting the excitation source to the optical fiber of the sensor, - at least one optical fiber (15) called a collection fiber connected to the optical connector and adapted to collect at least one peak of the luminescence spectrum emitted by the luminescent material(s) of the sensor probe, - a spectrophotometer (SP) connected to the collection optical fiber and adapted to measure the variation in luminescence emitted by the optical probe of the sensor.

11. A measuring system (10) comprising: - at least one sensor (7) according to one of claims 1 to 9, intended to be inserted into a metal-ion accumulator - at least one light excitation source (SI, S2), the excitation source being adapted to emit at least one excitation peak of the luminescent material(s) of the sensor, - at least one optical connector (14) for connecting the excitation source to the optical fiber of the sensor, - at least two optical fibers (16, 17) called collection fibers, distinct, each connected to the optical connector and each adapted to collect at least one peak of the luminescence spectrum emitted by the luminescent material(s) of the sensor probe, - at least two separate photodiodes (PI, P2), each connected to one of the two optical collection fibers and each adapted to measure the variation in luminescence emitted by the optical probe of the sensor.

12. Measuring system according to claim 10 or 11, comprising at least one bandpass filter (F1, F2) arranged between the excitation source and the optical connector.

13. Measuring system according to one of claims 10 to 12, comprising at least one bandpass filter (F3, F4) arranged between the optical sensor and the spectrophotometer or each of the two photodiodes.

14. 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 9.

15. Accumulator according to claim 14, the sensor being in direct contact with the electrode whose lithiation state varies.

16. Accumulator according to claim 14, 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.

17. Accumulator according to claim 14, the sensor being inserted into the separator or sandwiched between two layers of separator of the accumulator.

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

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