Functionalized optical fiber, method for its production and its use, in particular for in-situ measurement of lithium concentration in a battery electrolyte

Description

[0001] The present invention relates to a functionalized optical fiber, by grafting onto at least part of its surface a plurality of groups comprising a probe, and its methods of obtaining. The present invention also relates to the uses of said optical fiber, in particular for measuring the lithium concentration, in particular for the in situ, or even in operando, measurement of the lithium concentration in the electrolyte of a battery.

[0002] The advantages of electrochemical propulsion in electric vehicles and the need for efficient large-scale energy storage, particularly in transportation, have led to a growing demand for high-performance batteries—namely, safe, efficient, and reliable batteries—in portable electronics and electric vehicles. The development of larger batteries with higher energy density and stricter safety requirements is therefore crucial.

[0003] In this context, Li-ion batteries have made considerable progress over the past few decades, particularly in issues ranging from thermal safety to cycling stability.

[0004] However, to reach the next level of Li-ion battery innovations, it is necessary to develop sensors that can be used to probe batteries in real-time and operando, to help optimize performance and more accurately determine cell health.

[0005] Conventional battery management systems, which typically rely on parameters such as current, voltage, and temperature, provide limited information about the chemical and physical processes occurring within the battery during operation. Understanding degradation processes and their evolution over time is also limited due to the complex nature of batteries. To improve the lifespan, safety, and reliability of current batteries as well as emerging battery technologies, more detailed information from the cells is required.

[0006] In particular, it is important to be able to know the local lithium ion concentration within the electrolyte of these batteries. This concentration varies during charge and discharge cycles, especially during cell aging. The loss of active lithium through internal cell degradation processes, such as solid-electrolyte interface (SEI) growth, will lead to a loss of performance. Many attempts have been made to observe lithium distributions in the electrodes by techniques such as near-threshold X-ray absorption (XANES), nuclear magnetic resonance (NMR), X-ray diffraction, neutron diffraction, particle-induced γ / x-ray emission (PIGE / PIXE), Raman microspectroscopy and hard X-ray photoelectron spectroscopy (HX-PES).However, these techniques do not allow direct measurement of the lithium concentration in the electrolyte. In addition, these techniques do not allow in situ or even in operando measurement, or even require disassembling the battery to be analyzed. They are also very expensive. These are in fact laboratory techniques that cannot be used for monitoring a battery pack in operation. The documents WAHL MARKUS SOLBERG ET AL: "Towards in-situ State of Health Monitoring of Lithium-Ion Batteries Using Internal Fiber-Optic Sensors", MEETING ABSTRACTS, vol. MA2022-01, no. 52, July 7, 2022, p. 2166 and US 2021 / 122837 A1 disclose fiber optic sensors for in situ measurement of the concentration of lithium ions in batteries obtained by grafting a fluorescent molecule onto the surface of the fiber.

[0007] An objective of the invention is thus to provide a sensor making it possible to measure locally, in situ or even in operando, the lithium concentration at the heart of the battery, in the electrolyte and to provide in particular real-time information that can be used by the battery management system (BMS). To this end, the sensor of the invention is stable in electrolytes, in particular in organic carbonates, and does not disrupt the operation of the battery.

[0008] Another objective of the invention is to provide a sensor which can be easily obtained from common materials (namely optical fibers).

[0009] Yet another objective of the invention is to provide a sensor that can easily be implemented in a simple, rapid and inexpensive method for measuring lithium concentration. This is a simple fluorescence measurement, which therefore meets the aforementioned criteria. Thus, according to a first aspect, the invention relates to an optical fiber carrying on at least part of its surface a plurality of groups of the following formula (I): in which: W and Y are independently selected from O and NH; i and j are independently selected from 0 and 1; X represents a group of the following formula (II): in which: k is selected from 0 and 1; X a and X c are independently selected from: the groups X a1 being linear and branched C 1 -C 12 alkane diyls, in particular the groups of formula -(CH 2 ) n - with n from 1 to 12, or linear and branched C 2 -C 12 alkene diyls, the groups X a1 being in particular linear and branched C 1 -C 12 alkane diyls; the groups of formula -X a1 -NH-X a1 -, where X a1 is at each occurrence independently as defined above, in particular the groups of formula -(CH 2 ) n -NH-(CH 2 ) m - with n and m being independently from 1 to 12; groups of formula -X a1 -NHC(=O)-NH-X a1 - or -X a1 -NHC(=O)-NH-X a1 -NHC(=O)-NH-X a1 -, where X a1 is at each occurrence independently as defined above, in particular groups of formula -(CH 2 ) n -NHC(=O)-NH-(CH 2 ) m - with n and m being independently from 1 to 12;X b is chosen from: linear and branched C 1 -C 12 alkane diyls, in particular groups of formula - (CH 2 ) n - with n from 1 to 12, branched C 1 -C 12 alkane triyls, linear and branched C 2 -C 12 alkene diyls, the groups X b being in particular linear and branched C 1 -C 12 alkane diyls or triyls; optionally carrying, in particular in terminal position(s), at least one group -(O-CH 2 -CH 2 ) p - or -(O-CH 2 -C(CH 3 )H) p -, with p being an integer from 1 to 3; arene diyls and heteroarene diyls; X b being optionally substituted by a group A of the following formula (III): ; X c , Y, j, Z and R being as defined above or below, Z is absent or selected from linear and branched C 1 -C 12 alkane diyls and linear and branched C 2 -C 12 alkene diyls, Z being in particular a linear C 2 alkane or alkene diyl, said group Z being optionally substituted by a -COOH group; R is an aryl or heteroaryl group substituted by at least two vicinal groups selected from -OH and C 1 -C 3 alkoxy groups, in particular -OMe, said vicinal groups being more particularly -OH.

[0010] Said at least part of the surface is for example located at the end of the fiber, or along the fiber ( figure 3 ).

[0011] According to a particular embodiment, R is chosen from the following groups:

[0012] According to a particular embodiment, (Y) j ZR is chosen from the following groups: and in particular among the following groups:

[0013] According to a particular embodiment, X b is chosen from the following groups:

[0014] A and p being as defined previously.

[0015] According to a particular embodiment, the groups of formula (I) are chosen from the groups of the following formula:

[0016] According to a particular embodiment, the optical fiber according to the present invention is chosen from mineral optical fibers, in particular silica optical fibers, or optical fibers carrying an oxide layer chosen from TiO 2 , ZrO 2 , SnO 2 or HfO 2 , preferably modified by a compound comprising a phosphonic acid group as well as a primary amine, in particular a compound of formula (HO) 2 P(=O)-(CH 2 ) x NH 2 with x = 2, 3 or 4; organic optical fibers, in particular fibers made of or comprising polymethyl methacrylate (PMMA), optionally partially chlorinated polymethyl methacrylate, said polymethyl methacrylate optionally carrying carboxylic acid groups; and optical fibers carrying chains of functional oligomers, in particular chains of PVA, optionally partially acetylated.

[0017] According to a particular embodiment, the optical fiber according to the present invention is chosen from mineral optical fibers, in particular silica optical fibers, with i = 1 and W representing O, or optical fibers carrying an oxide layer chosen from TiO 2 , ZrO 2 , SnO 2 or HfO 2 , preferably modified by a compound comprising a phosphonic acid group as well as a primary amine, in particular a compound of formula (HO) 2 P(=O)-(CH 2 ) x NH 2 with x = 2, 3 or 4, with i = 1 and W representing N; organic optical fibers, in particular fibers made of or comprising polymethyl methacrylate (PMMA), optionally partially chlorinated polymethyl methacrylate, said polymethyl methacrylate optionally carrying carboxylic acid groups, with i = 0; and optical fibers carrying chains of functional oligomers, in particular chains of PVA, optionally partially acetylated, with i = 1 and W representing O.

[0018] According to a particular embodiment, the optical fiber according to the present invention is solid or hollow, at least on said part of its surface.

[0019] The compounds of the present invention may be prepared by a number of methods well known to those skilled in the art, including, but not limited to, those described below, or by modifications of these methods by applying standard techniques known to those skilled in the art of organic synthesis. Suitable modifications and substitutions will be readily apparent and well known or may be readily obtained from the scientific literature by those skilled in the art. In particular, such methods may be found in RC Larock, Comprehensive Organic Transformations, Wiley-VCH Publishers, 1999.

[0020] All methods disclosed in association with the present invention may be carried out at any scale, including milligram, gram, multigram, kilogram, multikilogram, or commercial industrial scale.

[0021] It will be understood that the compounds of the present invention may contain one or more asymmetrically substituted carbon atoms, and may be isolated in optically active or racemic forms. Thus, all chiral, diastereomeric, racemic, isomeric forms of a structure are intended, unless the specific stereochemistry or isomeric form is specifically indicated. How to prepare and isolate such optically active forms is well known to those skilled in the art. For example, mixtures of stereoisomers may be separated by standard techniques including, but not limited to, resolution of racemic forms, conventional, reversed-phase, and chiral chromatography, preferential salt formation, recrystallization, and the like, or by chiral synthesis, either from chiral starting materials or by targeted synthesis of the corresponding chiral centers.

[0022] The compounds of the present invention can be prepared by a variety of synthetic routes. The reagents and starting materials are commercially available, or readily synthesized by techniques well known to those skilled in the art. All substituents, unless otherwise indicated, are as defined above.

[0023] More particularly, the optical fibers of the invention, carrying a plurality of groups of formula (I), comprise the groups -NH-C(=O)-NH- (urea), -NH-C(=O)-O- or -OC(=O)-NH- (urethane), and / or -NH-C(=O)- or -C(=O)-NH- (amide).

[0024] The -NH-C(=O)-NH- group can be formed by any method well known to those skilled in the art, in particular by contacting a compound bearing an -NH 2 group (primary amine) with a compound bearing an -N=C=O group (isocyanate). This reaction can in particular be carried out in an anhydrous solvent, in particular an anhydrous aprotic solvent, for example dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), 1,4-dioxane, acetone. This reaction can be carried out at a temperature of 15 to 80°C, in particular 20 to 60°C, and / or for a period of 30 minutes to 24 hours, in particular 1 to 10 hours.

[0025] The -NH-C(=O)-O- or -OC(=O)-NH group may be formed by any method well known to those skilled in the art, in particular by bringing a compound bearing an -OH group (primary alcohol) into contact with a compound bearing an -N=C=O group (isocyanate), in particular in the presence of a catalyst, in particular chosen from triethylamine, 1,4-diazabicyclo[2,2,2]octane (DABCO), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), dibutyltin dilaurate (DBTDL), 1,8-diazabicylo[5,4,0]undec-7-ene (DBU), 3,4-dihydro-2H-pyrimido[2,1-b]benzothiazole (DHPB), di-isopropylethylamine (DIPEA), 4-dimethylaminopyridine (DMAP), 1,8-bis(dimethylamino)naphthalene (DMAN), for example triethylamine. This reaction can in particular be carried out in an anhydrous solvent, in particular an anhydrous aprotic solvent, for example dimethyl sulfoxide (DMSO).This reaction can be carried out at a temperature of 15 to 80°C, in particular 20 to 60°C, and / or for a time of 30 minutes to 24 hours, in particular 1 to 10 hours. When the -OH group is a silanol, in particular of an optical fiber of an optical fiber, this reaction can in particular be carried out at a temperature of 15 to 30°C, in particular 20 to 25°C, and / or for a time of 30 minutes to 2 hours, in particular 1 hour.

[0026] The NH-C(=O)- or -C(=O)-NH- group may be formed by any method well known to those skilled in the art, in particular by bringing a compound bearing a -COOH group (carboxylic acid) into contact with a compound bearing a -N=C=O group (isocyanate), in particular in the presence of a catalyst, in particular chosen from triethylamine, 1,4-diazabicyclo[2,2,2]octane (DABCO), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), dibutyltin dilaurate (DBTDL), 1,8-diazabicylo[5,4,0]undec-7-ene (DBU), 3,4-dihydro-2H-pyrimido[2,1-b]benzothiazole (DHPB), di-isopropylethylamine (DIPEA), 4-dimethylaminopyridine (DMAP), 1,8-bis(dimethylamino)naphthalene (DMAN), for example triethylamine. This reaction can in particular be carried out in an anhydrous solvent, in particular an anhydrous aprotic solvent, for example dimethyl sulfoxide (DMSO).This reaction can be carried out at a temperature of from 15 to 80°C, in particular from 20 to 60°C, and / or for a period of from 30 minutes to 24 hours, in particular from 1 to 10 hours.

[0027] According to another aspect, the present invention also relates to a method for preparing an optical fiber as defined above, comprising the following step: (i) Contacting at least a portion of the surface of an optical fiber bearing -OH, -NH 2 or -COOH groups with a compound (A) of the following formula: in which X, Y, j, Z and R are as defined above.

[0028] By "optical fiber carrying -OH, -NH 2 or -COOH groups" is meant in particular that the optical fiber directly carries -OH, -NH 2 or -COOH groups on its surface, or that the fiber is functionalized by groups themselves carrying one or more -OH, -NH 2 or -COOH groups.

[0029] When the optical fiber carries -OH groups, i = 1 and W represents -O-.

[0030] When the optical fiber carries -NH2 groups, i = 1 and W represents -NH-.

[0031] When the optical fiber carries -COOH groups, i = 0.

[0032] According to a particular embodiment, the optical fiber according to the present invention is chosen from mineral optical fibers, in particular silica optical fibers, with i = 1 and W representing O, or optical fibers carrying an oxide layer chosen from TiO 2 , ZrO 2 , SnO 2 or HfO 2 , preferably modified by a compound comprising a phosphonic acid group as well as a primary amine, in particular a compound of formula (HO) 2 P(=O)-(CH 2 ) x NH 2 with x = 2, 3 or 4, with i = 1 and W representing N; organic optical fibers, in particular fibers made of or comprising polymethyl methacrylate (PMMA), optionally partially chlorinated polymethyl methacrylate, said polymethyl methacrylate optionally carrying carboxylic acid groups, with i = 0; and optical fibers carrying chains of functional oligomers, in particular chains of PVA, optionally partially acetylated, with i = 1 and W representing O.

[0033] According to another aspect, the present invention also relates to a method for preparing an optical fiber as defined above, comprising the following step: (i') bringing at least part of the surface of an optical fiber carrying -OH, -NH 2 or -COOH groups into contact with a compound (B) of the following formula: [Chem 10] O=C=NXN=C=O (B), in which X is as defined previously, to obtain an optical fiber carrying on at least part of its surface a plurality of groups of the following formula (C): in which W, i and X are as defined previously, (ii') bringing the fiber obtained in the previous step (i') into contact with a compound of the following formula (D): in which Z and R are as defined above, and in which Y' is: a -NH 2 group when j = 1 and Y is -NH-; a -OH group when j = 1 and Y is -O-; a -COOH group when j = 0.

[0034] By "optical fiber carrying -OH, -NH 2 or -COOH groups" is meant in particular that the optical fiber directly carries -OH, -NH 2 or -COOH groups on its surface, or that the fiber is functionalized by groups themselves carrying one or more -OH, -NH 2 or -COOH groups.

[0035] When the optical fiber carries -OH groups, i = 1 and W represents -O-.

[0036] When the optical fiber carries -NH2 groups, i = 1 and W represents -NH-.

[0037] When the optical fiber carries -COOH groups, i = 0.

[0038] The steps defined above are optionally carried out in the presence of a catalyst, in particular chosen from triethylamine, 1,4-diazabicyclo[2,2,2]octane (DABCO), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), dibutyltin dilaurate (DBTDL), 1,8-diazabicylo[5,4,0]undec-7-ene (DBU), 3,4-dihydro-2H-pyrimido[2,1-b]benzothiazole (DHPB), di-isopropylethylamine (DIPEA), 4-dimethylaminopyridine (DMAP), 1,8-bis(dimethylamino)naphthalene (DMAN), for example triethylamine, preferably when a urethane or amide group is formed.

[0039] The steps defined above are in particular carried out in an anhydrous solvent, in particular an anhydrous aprotic solvent, for example dimethyl sulfoxide (DMSO).

[0040] The steps defined above are in particular carried out at a temperature of 15 to 80°C, in particular 20 to 60°C, and / or for a duration of 30 minutes to 24 hours, in particular 1 to 10 hours.

[0041] According to another aspect, the present invention also relates to the use of an optical fiber as defined above, for measuring the concentration of a monovalent ion, in particular of an alkali metal ion, more particularly of lithium ion.

[0042] The presence of one or more urea functions, in particular aliphatic or linked to aromatic or heteroaromatic cycles, urethane linked to aromatic or heteroaromatic cycles and / or amide linked to aromatic or heteroaromatic cycles, by virtue of their own fluorescence, makes it possible to generate a reference peak during fluorescence, insensitive to the presence or absence of lithium.

[0043] According to a particular embodiment, the present invention relates to the use as defined previously, for measuring the lithium ion concentration in a Li-ion battery, in particular within the electrolyte of said battery.

[0044] According to another aspect, the present invention also relates to a method for measuring the concentration of a monovalent ion, in particular an alkali metal ion, more particularly lithium ion, comprising the following steps: (i) A step of bringing the groups of formula (I) carried by at least part of the surface of the optical fiber as defined previously into contact with the medium in which the monovalent ion concentration is to be measured; (ii) A step of excitation by transmission of light in said optical fiber; (iii) A step of measuring the fluorescence emitted and transmitted by said optical fiber.

[0045] According to a particular embodiment, the light of step (ii) is UV light or violet visible light, and in particular has a wavelength of 350 to 450 nm. When said at least one part of the surface is for example located at the end of the fiber, the fluorescence measurement can be done by reflectance ( figure 3 , case 1).

[0046] When said at least part of the surface is for example located along the fiber, evanescent wave measurement points can be created. In this case, the measurement can be made by transmittance through the fiber, the excitation being sent to one end and the measurement being made at the other end. It is also possible to make a measurement by reflectance, but in this case, it is preferable to add a reflective deposit at the end of the fiber in order to maximize the reflectance ( figure 3 , case 2). Definitions

[0047] As used herein, the value ranges of "xy" or "from x to y" or "between x and y" include the bounds x and y as well as the integers between these bounds. For example, "1-5", or "from 1 to 5" or "between 1 and 5" denote the integers 1, 2, 3, 4 and 5. Preferred embodiments include each individual integer in the value range, as well as any subcombination of these integers. For example, preferred values ​​for "1-5" may include the integers 1, 2, 3, 4, 5, 1-2, 1-3, 1-4, 1-5, 2-3, 2-4, 2-5, etc.

[0048] As used herein, the term "alkyl" means a straight or branched chain, especially straight, alkyl group having the number of carbon atoms indicated before said term, especially 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, etc. Thus, a term such as "C1-C3 alkyl" means an alkyl radical containing from 1 to 3 carbon atoms.

[0049] The same is true for the term "alkane".

[0050] By "diyl" is meant in particular a residue linked to two groups by a single bond between the residue and each of these two groups.

[0051] As used herein, the term "arene" means a mono- or bicyclic, substituted or unsubstituted, hydrocarbon aromatic ring system having 6 to 10 carbon atoms in the ring. Examples include benzene and naphthalene. Preferred arenes include unsubstituted or substituted benzene and naphthalene. Included within the definition of "arene" are fused ring systems, including, for example, ring systems in which an aromatic ring is fused to a cycloalkyl ring. Examples of such fused ring systems include, for example, indane, indene, and tetrahydronaphthalene.

[0052] As used herein, the term "heteroarene" means a cyclic aromatic system containing 5 to 10 carbon atoms in which one or more ring carbon atoms are replaced by at least one heteroatom such as -O-, -N- or -S-, particularly -N- and / or -O-. Examples of heteroarenes include pyrrole, furan, thiophene, pyrazole, imidazole, thiazole, isothiazole, isoxazole, oxazole, oxathiol, oxadiazole, triazole, oxatriazole, furazane, tetrazole, pyridine, pyrazine, pyrimidine, pyridazine, triazine, indole, isoindole, indazole, benzofuran, isobenzofuran, purine, quinazoline, quinoline, isoquinoline, benzoimidazole, benzothiazole, benzothiophene, thianaphthene, benzoxazole, benzisoxazole, cinnoline, phthalazine, naphthyridine and quinoxaline. Included in the definition of "heteroarene" are fused ring systems, including, for example, ring systems in which an aromatic ring is fused to a heterocycloalkyl ring.Examples of such fused ring systems include, for example, phthalamide, phthalic anhydride, indoline, isoindoline, tetrahydroisoquinoline, chromane, isochromane, chromene, and isochromene. FIGURES

[0053] There figure 1 corresponds to the emission spectra for excitation at 350 nm of compound (4) (example 4) in an electrolyte solution composed of ethylene carbonate (EC) and diethylene carbonate (DEC) in a 1:1 proportion with different lithium ion concentrations (LiPF6), as follows: (1) in the absence of lithium (reference); (2) reference + 75 mg Li; (3) reference + 252 mg Li; (4) reference + 379 mg Li; (5) reference + 529 mg Li. figure 2 corresponds to the emission spectra for excitation at 320 nm and excitation for emission at 360 nm of the compound (2') (example 2) in an electrolyte solution composed of Ethylene Carbonate (EC) and Diethylene Carbonate (DEC) in proportion 1:1 with different concentrations of lithium ion (LiPF6), as follows: (1) in the absence of lithium (reference); (2) reference + 70 mg Li; (3) reference + 210 mg Li. figure 3 corresponds to the fluorescence measurements using an optical fiber according to the invention as described in example 5. EXAMPLES Example 1: Preparation of a functionalized silica optical fiber according to the invention

[0054] The density of silanol groups on the surface of a glass can be estimated at 5 groups per square nm. It can also be estimated that generally, about 10% of these sites are likely to be grafted.

[0055] Thus, the concentration of the reagents to be used can be determined by knowing the section of the optical core of the glass fiber to be functionalized.

[0056] Generally, syntheses are carried out in anhydrous DMSO. Generally, anything not covalently bonded is removed by rinsing in DMSO, then rinsing in an ethylene carbonate / diethylene carbonate mixture. These rinses remove all impurities adsorbed on the surface of the optical fiber.

[0057] The hydroxylated surfaces were first dehydrated. This can be done, for example, at 150°C in anhydrous DMSO under argon sparging. 2 hours are generally sufficient to remove the water.

[0058] Diisocyanate, for example hexane diisocyanate, was then added to the anhydrous DMSO at room temperature, along with triethylamine (1 mol% relative to the diisocyanate used) as a catalyst. This addition can be done, for example, with 15 ml of a 0.1 M solution of diisocyanate in anhydrous DMSO. After typically 1 hour at room temperature, the urethane function is formed between the surface silanols and one of the isocyanate groups.

[0059] Finally, 3,4-dihydroxy-L-phenylalanine, particularly in stoichiometric amount relative to the diisocyanate as mentioned above, was added to a solution of the chain-grafted intermediate bearing an isocyanate group in anhydrous DMSO at a temperature of 50°C, for 3 hours.

[0060] The following optical fiber (1) was thus obtained:

[0061] Other products of the invention were obtained by replacing 3,4-dihydroxy-L-phenylalanine with dopamine or caffeic acid, according to a procedure notably described in the following example.

[0062] Optionally, before contacting with the compound of the 3,4-dihydroxy-L-phenylalanine, dopamine or caffeic acid type, the chain-grafted intermediate carrying an isocyanate group can be hydrolyzed by adding at room temperature a stoichiometric quantity of water corresponding to half the molar of the diisocyanate involved. Washing with anhydrous DMSO is then carried out to remove traces of catalyst and unattached by-products. Then anhydrous DMSO was added, then the resulting mixture was brought to 150°C under argon flushing, to remove any adsorbed water. Diisocyanate, with at most 1 molar of the second isocyanate relative to the first grafted, for example hexane diisocyanate, is then added to the anhydrous DMSO at room temperature. This optional sequence therefore makes it possible to lengthen the chain linking the surface of the optical fiber to the catechol-type group.This optional sequence can optionally be repeated to obtain longer chains.

[0063] Alternatively, the surface of the silica optical fiber can be directly brought into contact, at room temperature, with a medium comprising an intermediate prepared for example according to one of the following operating methods: in 50ml of anhydrous DMSO, 0.1 molar of 3,4-dihydroxy-L-Phenylalanine is added, then 0.1 molar of hexane diisocyanate. The reaction medium is left stirring for 3 hours at 50°C; in 50ml of anhydrous DMSO, 0.1 molar of dopamine hydrochloride is added. The mixture is then transferred onto an inversion frit containing 1.5g of NaOH pearl (Alfa Aesar) previously dried for 5 hours under primary vacuum at 50°C and conditioned under argon. The solution is left in contact with the sodium hydroxide for 5 minutes and then filtered. The filtrate obtained contains, in the anhydrous DMSO, dopamine. The filtrate is stored away from light, then 0.08 molar of hexane diisocyanate is added. The reaction medium is then left stirring for 3 hours at 50°C; in 50ml of anhydrous DMSO, 0.1 molar of caffeic acid is added, then 0.1 molar of hexane diisocyanate and 0.01 molar of triethylamine. The reaction medium is then left stirring for 5 hours at 50°C. Example 2: Preparation of another functionalized silica optical fiber according to the invention

[0064] An optical fiber carrying longer chains than those described in the previous example was also obtained.

[0065] In a manner analogous to that described in Example 1, the hydroxylated surfaces were first dehydrated. Then, again in a manner analogous to that described in Example 1, diisocyanate, for example hexane diisocyanate, was added. First operating mode:

[0066] To a solution of the chain-grafted intermediate bearing an isocyanate group in DMSO, a stoichiometric amount of water corresponding to half the molar amount of the diisocyanate involved is added at room temperature. This results in a silanol surface covered with a pendant hexyl group covalently bearing a primary amine function of formula -OC(=O)NH(CH 2 ) 6 NH 2 .

[0067] Anhydrous DMSO washing was then carried out to remove traces of catalyst and unattached by-products. Then anhydrous DMSO was added, and the resulting mixture was heated to 150°C under argon sparging to remove any adsorbed water. Second method of operation:

[0068] Alternatively, to a solution of the chain-grafted intermediate bearing an isocyanate group in DMSO, a stoichiometric amount of ethylenediamine is added at room temperature, this amount corresponding to half the molar amount of the diisocyanate involved. A silanol surface covered with hexyl groups covalently bearing a primary amine function of the following formula: -OC(=O)NH(CH 2 ) 6 NH(CH 2 ) 2 NH 2 , was thus obtained.

[0069] Anhydrous DMSO washing was then carried out to remove traces of catalyst and unattached by-products. Then anhydrous DMSO was added, and the resulting mixture was heated to 150°C under argon sparging to remove any adsorbed water.

[0070] The chain formed can optionally be extended by repeating the treatment with the diisocyanate then the first or second procedure below, with at most 1 molar of the second isocyanate relative to the first grafted.

[0071] Whether the procedure used is the first or the second, moreover, an intermediate is prepared for example according to one of the following procedures: in 50ml of anhydrous DMSO, 0.1 molar of 3,4-dihydroxy-L-Phenylalanine is added, then 0.1 molar of hexane diisocyanate. The reaction medium is left stirring for 3 hours at 50°C; in 50ml of anhydrous DMSO, 0.1 molar of dopamine hydrochloride is added. The mixture is then transferred onto an inversion frit containing 1.5g of NaOH pearl (Alfa Aesar) previously dried for 5 hours under primary vacuum at 50°C and conditioned under argon. The solution is left in contact with the sodium hydroxide for 5 minutes and then filtered. The filtrate obtained contains, in the anhydrous DMSO, dopamine. The filtrate is stored away from light, then 0.08 molar of hexane diisocyanate is added. The reaction medium is then left stirring for 3 hours at 50°C; In 50 ml of anhydrous DMSO, 0.1 molar of caffeic acid is added, then 0.1 molar of hexane diisocyanate and 0.01 molar of triethylamine. The reaction medium is then left stirring for 5 hours at 50°C.

[0072] These different reaction media were added to the supported grafts bearing pendant amine functions, as obtained at the end of the first or second procedure described above. To do this, a quantity of 1 molar of the catechol grafts versus the theoretical number of pendant amine grafts was added. The reaction mixture is stirred for at least 1 hour at room temperature. The product obtained is washed thoroughly with anhydrous DMSO to remove impurities, followed by washing in EC / DC medium. The preservation of the covalent grafted products can in particular be done in EC / DC medium.

[0073] A silica optical fiber (2) carrying chains of the following formula was thus obtained:

[0074] A silica optical fiber (2') carrying chains of the following formula was obtained in a similar manner: Example 3: Functionalization of other optical fibers according to the invention

[0075] In a first embodiment, the optical fiber is functionalized by hydrolysis of a silane coupling agent.

[0076] In the case of silane coupling agents of the type (OR) 3 Si(CH 2 ) 3 NH 2 with R = Me, Et or (OR) 2 SiX(CH 2 ) 3 NH 2 with R = Et, Me and X = Me, there is no need to add an acid or basic catalyst to initiate the hydrolysis. The anhydrous solvent can be acetone, ethanol, THF. Water is added to the formulation at 0.1 mol% relative to the silane coupling agent titer which is between 0.1M and 0.5M. The reaction is rapid (typically 0.5 to 1h at room temperature) for the former, longer for the latter. At the end of the reaction, the fiber is covered with a pendant NH 2 graft.

[0077] In the case of silane coupling agents of the type (OR) 3 Si(CH 2 ) 3 NCO with R=Et,Me and (OR) 2 SiX(CH 2 ) 3 NCO with R=Et,Me and X=Me, the hydrolysis is carried out in an aprotic solvent without acid or base catalysis and typically takes 4 or 5 hours at room temperature. The concentration of silane coupling agent is notably between 0.2M and 0.5M. The fiber thus treated is stored in a controlled atmosphere for the rest of the grafting.

[0078] In a second embodiment, a functional oligomer was grafted onto the optical fiber. It may in particular be an oligomer comprising a monomer carrying at least one -OH group. PVA (fully hydrolyzed (PVOH) or partially hydrolyzed (PVOH-PVOAc type)) was thus used.

[0079] The PVA was contacted with diisocyanate, for example hexane diisocyanate, in a manner analogous to that described in Example 1. The amount of diisocyanate used can be calculated from the molecular weight of the PVA used. For example, with a molecular weight of 10000, PVA has 227 graftable OH sites, knowing that a maximum of 50% of these sites are actually grafted (above this, insoluble particles are likely to be formed).

[0080] Then, the functionalized PVA was grafted onto an optical fiber. For example, 1.36g of PVA (PM=18000) was added to 75g of anhydrous 1,4-dioxane. The medium was heated to 150°C for 5 hours on a Sohxlet containing a cartridge of anhydrous MgSO 4. After 5 hours, a clear solution of anhydrous PVA in dioxane was obtained.

[0081] Previously, 0.4g of diisocyanate and 0.36g of caffeic acid were reacted in 60g of anhydrous dioxane. 100mg of trimethylamine was added as a catalyst. The mixture was heated for 4 hours at 50°C.

[0082] The two products are mixed and left for 5 hours at 70°C with a second addition of 100mg of trimethylamine.

[0083] Finally, the catechol residue was introduced as described in Example 1, for example using caffeic acid.

[0084] Alternatively, the PVA functionalized by the chains carrying a diisocyanate group can be reacted with the compound carrying the catechol, for example caffeic acid, under conditions analogous to those described above, before grafting the PVA thus obtained onto the optical fiber.

[0085] In a third embodiment, the optical fiber was a mineral optical fiber with a TiO 2 , ZrO 2 , SnO 2 or HfO 2 surface. The surface of this fiber was first modified with a compound comprising a functional phosphonic acid as well as a chain carrying a pendant free primary amine, in particular of the following formula: (HO) 2 P(=O)-(CH 2 ) x -NH 2 with x = 2, 3 or 4.

[0086] An optical fiber was thus obtained carrying pendant free primary amine type groups, on which an isocyanate group can react, as indicated above, in particular in example 1.

[0087] An aluminum or alkaline earth salt or a titanium or zirconium alkoxide can also be hydrolyzed on a silica optical fiber. The optical fiber is then coated with the following functions: Al-OH, Mg-OH, Ti-OH or Zr-OH, on which a phosphonic acid carrying a primary amine function can be reacted, as for example mentioned above.

[0088] In a fourth embodiment, the optical fiber was an organic optical fiber, in particular based on PMMA, optionally halogenated. The optical fiber was treated to form free carboxylic acid functions on its surface, which will form an amide bond by reaction with an isocyanate group, as indicated above, in particular in example 1. To form free COOH functions on PMMA, the PMMA fiber is, for example, immersed in a 1M aqueous HCl solution containing 0.1% by mass of butanol for 10 minutes. After 10 minutes, the fiber is rinsed and the fiber is dehydrated by immersing it in an anhydrous dioxane solution. A 0.1 molar solution of diisocyanate in anhydrous DMSO containing 1% by mass of trimethylamine is added. The pendant carboxylic acid functions react with an isocyanate function forming an amide function with release of CO 2 . Typically, the reaction takes place at 50°C and lasts 4 hours. Example 4: Preparation of functionalized optical fibers carrying chains comprising a multivalent platform

[0089] In a manner similar to that described in Example 1, the hydroxylated surfaces were first dehydrated. Then, again in a manner similar to that described in Example 1, diisocyanate, for example hexane diisocyanate, was added to anhydrous DMSO at room temperature, as well as triethylamine (1 mol% relative to the diisocyanate used), as a catalyst. This addition can, for example, be made with 15 ml of a 0.1 M solution of diisocyanate in anhydrous DMSO. After typically 1 hour at room temperature, the urethane function is formed between the surface silanols and one of the isocyanate groups. The pendant isocyanate-modified fiber is thoroughly rinsed with anhydrous DMSO and finally stored in anhydrous DMSO.

[0090] Then 1 molar equivalent of 1,5-Diaminonaphthalene or Melamine (1,3,5-triazine-2,4,6-triamine) is added, relative to the diisocyanate introduced in the first step. This step takes place at 30°C in anhydrous DMSO without catalyst and lasts 1 hour. The modified fibers are washed with anhydrous DMSO and the fibers are stored in anhydrous DMSO. 0.4g of hexyl diisocyanate and 0.36g of caffeic acid were reacted in 60g of anhydrous DMSO. 100mg of trimethylamine are added as a catalyst. The mixture is heated for 4 hours at 50°C.

[0091] Then, respectively, 1 molar equivalent of caffeic acid-grafted hexyl isocyanate is added relative to the 1,5-Diaminonaphthalene grafted onto the fiber or 2 molar equivalents of caffeic acid-grafted hexyl isocyanate relative to the melamine grafted onto the fiber. This step takes place at 30°C in anhydrous DMSO and is carried out without a catalyst. The optical fibers thus modified are washed thoroughly with anhydrous DMSO and are stored in a mixture of organic carbonates. Example 5: Fluorescence measurements

[0092] Fluorescence measurements, emission spectrum and excitation spectrum, were recorded with a Horiba Jobin Yvon model Fluorolog-3 model FL3-22 spectrometer having the R928 Hamamatsu detector and a 450W Xenon lamp as excitation source.

[0093] The emission spectrum is obtained by exciting the sample with an absorbed wavelength, usually the absorption (or excitation) peak of maximum intensity. The emission monochromator scans the luminescence over a wavelength interval. The generally most important parameters are i) the excitation wavelength and ii) the slit width, and can be easily determined by the skilled person. The emission spectra were corrected for the spectral response of the monochromators and detector, using typical correction spectra provided by the manufacturer.

[0094] The excitation spectrum is measured by fixing the emission monochromator at a given emission wavelength (e.g., the one corresponding to the maximum of the emission spectrum). The excitation monochromator is then scanned in a given wavelength interval and the luminescence intensity corresponding to the monitored emission wavelength is measured. The most important parameters are usually i) the monitoring wavelength and ii) the slit width, and can easily be determined by the person skilled in the art. The excitation spectra were corrected from 240 to 600 nm for the spectral distribution of the lamp intensity using a silicon photodiode reference detector ( figures 1 And 2 ).

[0095] To assess the sensor's sensitivity to lithium concentration, the emission and excitation spectra of the probe molecule in solution (EC+DEC) were measured. This is a reference measurement. Then, different concentrations of lithium in solution (EC+DEC+LiPF6) were added to the reference / initial solution and the emission and excitation spectra were recorded for each concentration.

[0096] For the dopamine-based probe, the emission spectrum was measured by exciting at a wavelength of 320 nm and with 1.5 mm slits for the emission spectrometer and 0.3 mm slits for the excitation spectrometer. The excitation spectrum was measured by monitoring at a wavelength of 360 nm and with 0.4 mm slits for the emission spectrometer and 0.8 mm slits for the excitation spectrometer.

[0097] For the melamine-based probe the emission spectrum was measured by exciting at a wavelength of 350 nm and with 1.5 mm slits for the emission spectrometer and 0.3 mm slits for the excitation spectrometer.

[0098] This example was obtained with optical fibers with grafting of probe molecules at the end of the fiber, for a measurement by reflectance, as presented in particular in figure 3 , case 1.

[0099] It is also possible to graft molecules along the fiber on areas where the cladding has been removed in order to create evanescent wave measurement points, as notably presented in

[0100] there figure 3, case 2. In this case, the measurement is made by transmittance through the fiber. The excitation is sent to one end and the measurement is made at the other end. It is also possible in case 2 to make a measurement by reflectance, but in this case it is preferable to add a reflective deposit at the end of the fiber in order to maximize the reflectance.

Claims

1. An optical fiber carrying on at least part of its surface a plurality of groups of the following formula (I) wherein: W and Y are independently selected from O and NH; i and j are independently selected from 0 and 1; X represents a group of the following formula (II) wherein: k is chosen from 0 and 1, Xa and Xc are independently selected from: - the groups Xa1 being linear and branched C1-C12 alkanediyls, in particular groups of the formula -(CH2)n- with n from 1 to 12, or linear and branched C2-C12 alkenediyls, the groups Xa1 being in particular linear and branched C1-C12 alkanediyls, - the groups of formula -Xa1-NH-Xa1-, wherein Xa1 is at each occurrence independently as defined above, in particular groups of formula -(CH2)n-NH-(CH2)m- with n and m independently being from 1 to 12, - the groups of formula -Xa1-NHC(=O)-NH-Xa1- or -Xa1-NHC(=O)-NH-Xa1-NHC(=O)-NH-Xa1-, wherein Xa1 is in each occurrence independently as defined above, in particular groups of formula -(CH2)n -NHC(=O)-NH-(CH2)m- with n and m independently being from 1 to 12, Xb is selected from: - C1-C12-branched and linear alkanediyls, in particular groups of the formula -(CH2)n-where n is from 1 to 12, C1-C12-branched alkanetriyls, C2-C12-branched and linear alkenediyls, the groups Xb being in particular C1-C12-branched and linear alkanediyls or triyls ; optionally bearing, notably in terminal position(s), at least one -(O-CH2CH2)p- or -(O-CH2-C(CH3)H)p- group, with p being an integer from 1 to 3, - the arene diyls and heteroarene diyls, Xb being optionally substituted by a group A of the following formula (III) Xc, Y, j, Z and R being as defined above or below, Z is absent or selected from C1-C12 linear and branched alkanediyls and C2-C12 linear and branched alkenediyls, Z being in particular a C2 linear alkane or alkenediyl, said Z group being optionally substituted by a -COOH group, R is an aryl or heteroaryl group substituted with at least two vicinal groups selected from OH and C1-C3 alkoxy groups, in particular -OMe, said vicinal groups being more particularly -OH.

2. The optical fiber of claim 1, wherein R is selected from the following groups:

3. The optical fiber according to any of the preceding claims, wherein (Y)jZR is selected from the following groups: and in particular from the following groups:

4. The optical fiber according to any one of the preceding claims, wherein Xb is selected from the following groups: A and p being as defined in claim 1.

5. The optical fiber according to any one of the preceding claims, wherein the groups of formula (I) are selected from groups of the following formula:

6. The optical fiber according to any one of the preceding claims, which is selected from inorganic optical fibers, in particular silica optical fibers, or the optical fibers bearing an oxide layer selected from TiO2, ZrO2, SnO2 or HfO2, preferably modified with a compound comprising a phosphonic acid group as well as a primary amine, in particular a compound of formula (HO)2 P(=O) (CH2)xNH2 with x = 2, 3 or 4; organic optical fibers, in particular fibers made of or comprising polymethyl methacrylate (PMMA), optionally partially chlorinated polymethyl methacrylate, said polymethyl methacrylate optionally carrying carboxylic acid groups; and optical fibers carrying functional oligomer chains, in particular PVA chains, optionally partially acetylated, said optical fiber being in particular selected from inorganic optical fibers, more particularly silica optical fibers, with i = 1 and W representing O, or optical fibers bearing an oxide layer selected from TiO2, ZrO2, SnO2 or HfO2, preferably modified with a compound comprising a phosphonic acid group and a primary amine, in particular a compound of formula (HO)2P(=O)-(CH2)xNH2 with x = 2, 3 or 4, where i = 1 and W represents N; organic optical fibers, in particular fibers consisting of or comprising polymethyl methacrylate (PMMA), optionally partially chlorinated polymethyl methacrylate, said polymethyl methacrylate optionally carrying carboxylic acid groups, with i = 0; and optical fibers carrying functional oligomer chains, in particular PVA chains, optionally partially acetylated, with i = 1 and W representing 0.

7. The optical fiber according to any one of the preceding claims, which is solid or hollow, at least over said part of its surface.

8. A method for preparing an optical fiber according to any one of the preceding claims, comprising the following step of (i) Contacting at least part of the surface of an optical fiber carrying -OH, -NH2 or - COOH groups with a compound (A) of the following formula: wherein X, Y, j, Z and R are as defined in claim 1 or the following steps of: (i') contacting at least a portion of the surface of an optical fiber carrying -OH, -NH2 or - COOH groups, with a compound (B) of the following formula:         O=C=N-X-N=C=O     (B), wherein X is as defined in claim 1, to obtain an optical fiber carrying on at least part of its surface a plurality of groups of the following formula (C): wherein W, i and X are as defined in claim 1, (ii') contacting the fiber obtained in the previous step (i') with a compound of the following formula (D): wherein Z and R are as defined in claim 1, and wherein Y' is: - an -NH2 group when j = 1 and Y is -NH-; - an -OH group when j = 1 and Y is -O-; - a -COOH group when j = 0.

9. An use of an optical fiber according to any one of claims 1 to 7, for measuring the concentration of a monovalent ion, in particular an alkali metal ion, more particularly a lithium ion.

10. The use according to claim 9 for measuring the lithium ion concentration in a Li-ion battery, in particular within the electrolyte of said battery.

11. A method for measuring the concentration of a monovalent ion, in particular an alkali metal ion, more particularly a lithium ion, comprising the following steps: (i) A step of contacting the groups of formula (I) carried by at least part of the surface of the optical fiber according to any one of claims 1 to 7 with the medium in which the monovalent ion concentration is to be measured; (ii) An excitation step by transmitting light into said optical fiber, (iii) A step for measuring the fluorescence emitted and transmitted by said optical fiber.

12. The method according to claim 11, wherein the light of step (ii) is UV light or visible violet light, and in particular has a wavelength of 350 to 450 nm.