State of charge (SOC) sensor for a metal-ion battery, with an optical fiber whose free end forms an optical probe emitting within the optical absorption spectrum of an electrode. Associated measurement system.

Abstract

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

Description

Title of the invention: A state of charge (SOC) sensor for measuring the state of charge of a metal-ion battery, with an optical fiber whose free end forms an optical probe emitting 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 optical fiber sensors adapted for such a measurement.

[0003] The invention aims to provide a solution for estimating the state of charge of a battery, using a fiber optic 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, Anglo-Saxon acronym for "State Of Charge").

[0005] Although described with reference to a Lithium-ion battery, the invention applies to state of charge (SOC) 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] By "luminescence", we mean here and within the framework of the invention, the ability 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 different wavelength called emission radiation with an emission spectrum comprising one or more peaks of intensities which may be different. Previous technique

[0007] 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 component 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 casing 6 arranged to contain the electrochemical cell with sealing while being traversed by 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 architectural 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 stacked 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 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.

[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 silicon-based or silicon-based composite.

[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 one on top of the other.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

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

[0023] 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],

[0024] 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.

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

[0026] Fiber optic sensors offer numerous advantages, including the ability to be miniaturized and therefore to be installed in environments with limited space. Furthermore, they are electrically non-conductive and allow the properties of light to be exploited to probe various physical or chemical parameters within a component, particularly a battery or accumulator: [3], [4], [5].

[0027] 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.

[0028] Based on this observation, researchers developed a fiber optic sensor to track the color change of a negative graphite electrode within a accumulator and therefore its lithiation state 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 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.

[0030] Such a sensor therefore makes it possible to measure the lithiation state of a negative graphite electrode and to monitor the accumulator in situ (in operando).

[0031] The work further showed that the variation of the optical absorption spectrum of graphite takes place 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 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 relative 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.

[0034] The evanescent wave technique just described has many drawbacks, including:

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

[0036] - 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.

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

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

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

[0040] The object of the invention is to meet at least part of this need(s). Description of the invention

[0041] To this end, the invention relates to a state of charge (SOC) measurement sensor of a battery, in particular a metal-ion battery, comprising an optical fiber whose free end forms an optical probe with at least one luminescent material with one or more peaks of emission wavelengths adapted to emit 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.

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

[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 among oxides, oxysulfides, fluorides, where appropriate doped with transition metals or rare earth.

[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 within a metal-ion battery - 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 link the excitation source to the sensor's optical fiber, - at least one optical fiber, 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 optical collection 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 above, intended to be inserted within a metal-ion battery - 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 link the excitation source to the sensor's optical fiber, - 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 measurement system includes at least one bandpass filter (Fl, 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 a metal-ion accumulator (A) or battery, in particular li-ion, comprising, inserted within it, at least one sensor as described above.

[0056] Several sensor implantation variants can be considered:

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

[0058] - the sensor can be in direct contact with the face of the separator the accumulator which is opposite to that in contact with the electrode whose lithiation state 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 insertion state of ions within a metal-ion battery, in particular the lithiation state of a negative graphite electrode of a Li-ion battery.

[0061] Thus, the invention essentially consists of an optical fiber sensor carrying at the end an optical probe with at least one luminescent material with at least two emission peaks of the insertion material of the metal ions of at least one electrode of the operating accumulator for which we seek to estimate the state of charge (SOC).

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

[0063] Preferably, one or more luminescent materials that are relatively insensitive to temperature are chosen. If the material is sensitive to temperature, the sensor is calibrated before operation to determine its contribution to the variation of the signal related to the lithiation state.

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

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

[0066] Among organic materials, fluorescent molecules such as fluorescein, rhodamine, porphyrins, and all fluorochromes with emissions in the visible and near-infrared can be considered.

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

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

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

[0070] For the realization of the optical probe at the end of an optical fiber, the luminescent material(s) can 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 within the battery whose insertion state variation of the ions, and therefore its state of charge, is to be estimated so that the luminescence of the optical probe can be at least partially absorbed by the insertion material, which changes color and thus optical absorption depending on the insertion state. For a Li-ion battery with a graphite electrode, the aim is to estimate its change in lithiation state.

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

[0076] The intensity and spectrum of the probe luminescence which are recovered back by the optical fiber depend on the insertion state 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 back to the state of charge 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 includes either a spectrophotometer or an array of photodiodes preferably associated with optical filters isolating the areas of wavelengths of interest.

[0079] The advantages of the invention are numerous, among which we can mention: - an easy selection process for light sources whose excitation wavelength is best suited to the desired variation in optical absorption for the ion insertion material of the accumulator, particularly 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 fixing 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 at one location in the accumulator, that is to say that the passage between the inside of the latter and the outside takes place at a single point; - improved measurement sensitivity compared to a solution that simply uses 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 adapted emission wavelengths spread across the regions of variation in the graphite's optical absorption, a relative measurement of this absorption as a function of lithiation. By calculating the intensity ratios of the different emission peaks, precise monitoring of the variation in the graphite's lithiation state can be achieved. If the same were to be done with optical absorption, as recommended by the authors of works [6], [7], [8], [9],

[10] , several LEDs and spectral measurement would be required.

[0080] 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

[0081] [Fig.1] [Fig.1] is a schematic exploded perspective view showing the different elements of a lithium-ion battery.

[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 a battery as a function of its lithiation state 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 a battery.

[0085] [Fig. 5] [Fig. 5] illustrates the variation of the transmittance spectrum (AT / T) as a function of the state of charge (capacity) of a battery, measured in-situ according to the state of the art by evanescent wave using an optical fiber.

[0086] [Fig. 6] [Fig. 6] is a longitudinal cross-sectional view of a fiber optic measurement 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 consisting of a Li-ion battery, the light emitted by the particles is collected without modification of spectrum by the optical fiber with no impact on the measurement, and when the optical probe is in the vicinity of the graphite of the negative electrode of the battery, the change of lithiation state (lithia, delithia) modifies the intensity and 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 an 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 battery.

[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 battery, 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 battery, 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 further.

[0095] A fiber optic measurement sensor 7 according to the invention is shown in [Fig.8].

[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 made up of a matrix 90 comprising luminescent particles also called phosphors 91. The phosphors 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 organolanthanide).

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

[0099] The fabrication 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 can be organic, inorganic or hybrid.

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

[0102] The inorganic materials may be selected from oxides, oxysulfides, fluorides, etc., doped with transition metals or rare earth elements. These may include 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 phosphors can be made of a single material. A variant consists of using two distinct materials that are excited in the same wavelength range and whose fluorescence emission is located in two regions of the spectrum of interest for measuring the lithiation state of graphite. For example, one can use a thermoluminescent material that emits in the 300 to 700 nm range and another for monitoring the lithiation of graphite between 700 and 1000 or even 1500 nm.

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

[0106] With regard to the excitation of the phosphors, a single-spectrum excitation source can be used. Alternatively, two different excitations can be used: one allowing the probe(s) of the phosphor material(s) whose luminescence is located in a region where the absorbance variation of the graphite is low, and the other in a region where the variation is high.

[0107] Figure 8 is an example of the excitation and emission spectrum of phosphors 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 Figure 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 battery whose lithiation state of the negative electrode is to be measured.

[0109] 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.

[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: - 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.

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

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

[0114] The system 10 first includes two separate excitation light sources SI, S2 which each emit a distinct excitation wavelength from the other, respectively Xexcl and Xexc2. These sources SI, S2 can be LEDs or lasers.

[0115] The system 10 includes optical fibers 11,12 which allow the light emitted by each of the two sources SI, S2 to be guided.

[0116] At the output of each source SI, S2, a low-pass or band-pass filter Fl, 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 thus retain the other parasitic spectral contributions from the sources SI, S2.

[0117] An optical fiber 13 mixes the two excitation peaks 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 that the probe 9 is within the accumulator, in optical contact with the graphite electrode.

[0118] The phosphor(s) 91 of the probe 9 are then excited and emit a multi-peak luminescence spectrum.

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

[0120] On [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 according to 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 phosphors 91, instead of the SP spectrophotometer of [Fig. 10], an array of photodiodes, for example two PI, P2 as illustrated in [Fig. 12], can be used. Each of these photodiodes is connected by its own optical collection fiber 16, 17 to the optical connector 14.

[0124] Preferably, upstream of each of the photodiodes PI, P2 in the optical path from connector 14, a bandpass filter F3, F4 is arranged to isolate the peaks of interest. This solution reduces 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 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 luminescence optical probe made otherwise.

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

[0128] In the mode of [Fig. 10], instead of a spectrophotometer, an array 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.

[0134] [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.

[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

Demands

1. A state of charge (SOC) measurement sensor (7) of a battery, in particular a metal-ion battery, comprising an optical fiber (8) whose free end (82) forms an optical probe (9) to at least one luminescent material with one or more emission wavelength peaks adapted to emit 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.

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 any 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 selected 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 selected from oxides, oxysulfides, fluorides, where appropriate doped with transition metals or rare earth.

8. Sensor according to claim 7, the inorganic luminescent material(s) being selected from Cr3+ doped alumina, Ce and Pr doped YAG, Eu, Tb, Pr, Yb, Er doped Gd2O2 or 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. A measuring system (10) comprising: - at least one sensor (7) according to any one of the preceding claims, 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 (14) to connect the excitation source to the optical fiber of the sensor, - at least one optical fibre (15), called a collection fibre, 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 optical collection fiber and adapted to measure the variation in luminescence emitted by the optical probe of the sensor.

11. Measurement system (10) comprising: - at least one sensor (7) according to any one of claims 1 to 9, intended to be inserted within a metal-ion battery - 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) to connect the excitation source to the optical fiber of the sensor, - at least two separate optical fibers (16, 17), 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.

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

13. A measuring system according to any 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 within it, at least one sensor (7) according to any 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 accumulator separator which is opposite to that in contact with the electrode whose lithiation state varies.

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

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