N-type organic material-based reference electrode

Abstract

Reference electrode based on N-type organic material. The present invention relates to the use, as a reference electrode in a cell of an electrochemical storage system, of an electrode based on one or more N-type electroactive organic materials, the associated redox reaction of which exhibits a constant electrochemical potential; said N-type organic material(s) being present in a partially reduced, negatively charged form, with charge compensation by at least one cation. It also relates to a cell of an electrochemical storage system, in particular a metal-ion battery, lithium-sulfur battery, or lithium-air battery; or a supercapacitor, in particular a potassium hybrid supercapacitor, comprising three electrodes: a positive electrode, a negative electrode, and such a reference electrode.

Description

Title of the invention: Reference electrode based on N-type organic material Technical field

[0001] The present invention relates to the field of electrochemical storage systems, more precisely the field of electrochemical devices of the metal-ion accumulator or battery type, in particular sodium-ion, lithium-ion, potassium-ion, magnesium-ion batteries; lithium-sulfur or lithium-air batteries; and supercapacitors, for example potassium hybrid supercapacitors.

[0002] It aims more precisely at the implementation of an electrode based on one or more organic active materials of the electron acceptor type, also called N type, present in a partially reduced negatively charged form, with compensation of the negative charges by at least one cation, as a reference electrode in a cell of said electrochemical storage system. Prior art

[0003] Electrochemical devices of the battery type, for example lithium batteries, and supercapacitors, find multiple applications, in particular in the power supply of thin embedded systems, such as credit cards, smart labels, in the power supply of mobile phones, the storage of energy from photovoltaic cells, or even in the power supply of electric vehicles.

[0004] Various electrochemical storage systems or electrochemical generators have been developed, such as metal-ion batteries, in particular sodium-ion, lithium-ion, potassium-ion, magnesium-ion batteries; lithium-sulfur or lithium-air batteries, and more recently supercapacitors.

[0005] These electrochemical generators, for example lithium, conventionally operate on the principle of insertion and deinsertion (or intercalation-deintercalation) of a metal, such as lithium, on at least one electrode. In particular, in a lithium-ion accumulator, the Li+ cations thus go back and forth between the electrodes, respectively positive and negative, at each charge and discharge of the accumulator. The active material of the positive electrode is capable of releasing lithium ions at the time of charging and of incorporating lithium ions at the time of discharging.

[0006] Supercapacitors are energy storage devices that provide power density and energy density that are intermediate between those provided by electrochemical batteries and conventional electrolytic capacitors. In addition, they release energy more quickly than an electrochemical battery. In standard supercapacitors, also known as "symmetrical", the two The electrodes (positive and negative electrodes) are both based on activated carbon, and the electrolyte is typically based on an ammonium salt, typically tetraethylammonium tetrafluoroborate (Et4NBF4) in acetonitrile or propylene carbonate. So-called "hybrid" or "asymmetric" supercapacitors have also been developed, falling somewhere between the symmetrical supercapacitors traditionally used based on activated carbon and batteries. One of the electrodes, typically the positive electrode, is based on activated carbon; the other electrode, typically the negative electrode, is made from a rechargeable battery material. Charge storage in a hybrid supercapacitor occurs at the negative electrode through a redox reaction, while charge storage at the positive electrode occurs through the formation of an electrochemical double layer.

[0007] It is important, for electrochemical storage systems, whether batteries or supercapacitors, to be able to know and monitor the evolution of the potential of each electrode, during the operation of the electrochemical cell. In particular, for cells using electrolytes based on organic solvent(s), it is important that the cell of the electrochemical system does not operate outside the electrochemical stability range of said organic solvent(s), so as not to cause degradation and in particular the production of gas. Similarly, it is important to control, via potential limitation, the lithiation state of certain compounds such as the lamellar oxides LixM02 whose structure is unstable for x<0.5 (case of LiCoO2) or x<0.2 (LixM02 with M=Ni, Co, Mn with low Co content), or to avoid the electrodeposition of lithium in the metallic state at the negative electrode at potentials lower than 0V vs Lr7Li.In order to counter the appearance of any undesirable phenomenon, it is important to be able to know and monitor the evolution of the potential of each electrode, during the operation of the electrochemical cell.

[0008] For this, it is desirable to be able to introduce a so-called reference electrode into the electrochemical system. A reference electrode must have a stable and known potential, making it possible to know at any time the potential of each of the positive and negative electrodes of the system.

[0009] The production of three-electrode systems, in particular for cells in “pouch cell” format, has already been described in the context of metal-ion batteries in document US 9,379,418.

[0010] The reference electrodes proposed so far in electrochemical storage systems, for example in metal-ion batteries, such as lithium-ion batteries, for example in the documents Cengiz et al., J. Electrochem. Soc. 2021 [1], US 2009 / 0104510 or US 9,379,418; are based on lithium-based alloys (for example, LixSn, LixBi, LixAu, LixIn, LixSi, LixAl, etc.), respectively based on sodium, potassium, etc.; LiMO2 intercalation materials with M representing Co, Ni or Mn; or LiM'2O4 with M' representing Ni or Mn; or insertion materials such as LiM”PO4 with M” representing Fe, Co, Mn or Ni; or LL / TisO^ type.

[0011] In the field of supercapacitors, one can also cite document US 2011 / 0043968 which proposes, to evaluate the electrochemical characteristics of standard and hybrid lithium supercapacitor systems, to use a saturated calomel reference electrode (SCE). The use of such a reference electrode is however not compatible with the desired packaging of the cells in a prismatic format, in particular of the “pouch cell” type. Statement of the invention

[0012] The present invention aims precisely to propose electrodes useful as reference electrodes in cells of storage systems or electrochemical generators, such as metal-ion batteries, lithium-sulfur batteries, lithium-air batteries or even supercapacitors.

[0013] The inventors have thus discovered that it is possible to implement an electrode formed from an electrode based on N-type organic electroactive material(s) and whose associated redox reaction has a constant electrochemical potential.

[0014] More particularly, the invention relates, according to a first of its aspects, to the use, as a reference electrode in a cell of an electrochemical storage system, of an electrode based on one or more electroactive organic materials of type N, the associated redox reaction of which has a constant electrochemical potential; said N-type organic material(s) being present in a negatively charged partially reduced form, with charge compensation by at least one cation.

[0015] A reference electrode as defined above, based on said N-type organic material(s) in a partially reduced state, negatively charged, with cation insertions, is designated more simply in the remainder of the text under the name “reference electrode according to the invention”.

[0016] The N-type materials considered according to the invention may be more particularly chosen from compounds, in particular molecules, oligomers or polymers, carrying redox functions chosen from: - conjugated azo functions (-N=N-) such as azobenzene or one of its derivatives, - disulfide functions (-SS-) such as diphenyl disulfides, tetrathionap- thalene, poly(2,5-dimercapto-1,3,4-thiadiazole), poly(5,8-dihydro-1H,4H-2,3,6,7-tetrathia-anthracene); and - conjugated carbonyl functions, in particular contained within quinonoid structures, such as anthraquinone; anhydride structures such as pyromellitic anhydride, dimide structures such as perylene dimide; or carboxylate structures such as perylene tetracarboxylate.

[0017] As described in the remainder of the text, the reference electrode implemented according to the invention may, for example, be based on perylene tetracarboxylate, also denoted PTCLi4.

[0018] N-type organic electroactive materials [2] have already been proposed for their implementation as active materials of organic electrodes in electrochemical storage systems. For example, publication [3] presents an in-depth study of PTCLi4 and proposes the preparation of composite electrodes with optimized electrochemical performances by combining PTCLi4 with carbon nanotubes and fluorine-free binders.

[0019] On the other hand, to the inventors' knowledge, it has never been proposed to form a reference electrode from these organic electrodes.

[0020] As mentioned above, a reference electrode is defined as being an electrode having a stable and known electrochemical potential, advantageously making it possible to serve as a reference point for independently measuring the potential of the positive and negative electrodes in an electrochemical cell.

[0021] As detailed in the rest of the text, a reference electrode according to the invention can be obtained, prior to its use in said cell of the electrochemical storage system or electrochemical generator, from an electrode based on said N-type organic material(s), by partial reduction of said N-type organic material(s) with compensation of the negative charges created during oxidation by insertion of cations, making it possible to obtain the constant electrochemical potential (in other words, the potential plateau).

[0022] The reference electrode can be implemented for various electrochemical storage systems or electrochemical generators, and in particular for metal-ion batteries, in particular sodium-ion, lithium-ion, potassium-ion, magnesium-ion batteries; lithium-sulfur or lithium-air batteries; and supercapacitors.

[0023] The invention also relates, according to another of its aspects, to a cell of an electrochemical storage system or electrochemical generator, comprising three electrodes: - a positive electrode; - a negative electrode; and - a reference electrode according to the invention.

[0024] Thus, the invention implements a three-electrode system, the positive and negative electrodes of the cell of the electrochemical storage system and, in addition, a reference electrode according to the invention based on N-type organic material(s).

[0025] By way of example, as illustrated in the following examples, the reference electrode may be implemented in a cell of a lithium-ion battery.

[0026] The invention also relates to an electrochemical storage system or electrochemical generator, for example of the metal-ion battery type, lithium-sulfur or lithium-air battery, or supercapacitor, comprising at least one cell as defined previously, integrating a reference electrode based on N-type organic material(s).

[0027] Advantageously, a reference electrode according to the invention is compatible with the packaging of the cells in any desired format, in particular in a prismatic format, advantageously in the form of a flexible sachet type cell, better known as a "pouch cell", as illustrated in the examples which follow.

[0028] The integration of a reference electrode according to the invention within at least one of the cells of an electrochemical storage system or electrochemical generator advantageously makes it possible to access the potentials of each of the positive and negative electrodes. Knowledge and monitoring of the potentials of the positive and negative electrodes makes it possible to detect, where appropriate, potential defects in their operation.

[0029] Thus, the invention relates, according to another of its aspects, to the use of a reference electrode based on N-type organic material(s) as defined above, in a cell of an electrochemical storage system or electrochemical generator, to know the potentials of at least one of the positive and negative electrodes, preferably of each of the positive and negative electrodes, in particular to follow the evolution of the potentials of at least one of the positive and negative electrodes, during the operation of said system.

[0030] Monitoring the potentials of the positive and negative electrodes during operation of the electrochemical storage system, by means of the reference electrode according to the invention, advantageously allows optimized use of said electrochemical system, in particular use at its maximum capacity, without being exposed to risks of malfunction, and thus allows improved safety in the use of said electrochemical system.

[0031] Other characteristics, variants and advantages of a reference electrode according to the invention and of its implementation at the level of a cell of an electrochemical storage system according to the invention will emerge more clearly on reading the description, examples and figures which follow, given for illustrative and non-limiting purposes. the invention. Brief description of the drawings

[0032] [Fig. 1] shows, schematically, in cross-section, an example of assembly 100 of the different elements, including the reference electrode according to the invention, within a cell of an electrochemical storage system according to the invention;

[0033] [Fig.2] shows the galvanostatic cycling profile at C / 10 of a PTCLi4-based electrode in the case of a lithium half-cell;

[0034] [Fig.3] shows, schematically, the lithium-ion cell, in pouch-cell format, as prepared in example 1, comprising a positive electrode, the reference electrode according to the invention and a negative electrode, the electrodes being separated by porous polypropylene membranes, and impregnated with the electrolyte;

[0035] [Fig.4] shows, schematically, the evolution of the electrochemical potential E as a function of the specific mass capacity during the partial lithiation (reduction) of the PTCLi4-based electrode to form the reference electrode in example 1 (evolution of the potential E as a function of the absolute capacity ([Fig.4](a)) and the specific mass capacity ([Fig.4](b));

[0036] [Fig.5] shows the evolution of the lithium-ion battery cell voltage and the potentials of the positive and negative electrodes, obtained using the reference electrode, as described in example 2.

[0037] It should be noted that, for reasons of clarity, the various elements in Figures 1 and 3 are shown in free scale, the actual dimensions of the various parts not being respected.

[0038] In the rest of the text, the expressions “between ... and ...”, “ranging from ... to ...” and “varying from ... to ...” are equivalent and are intended to mean that the limits are included, unless otherwise stated. Detailed description REFERENCE ELECTRODE

[0039] As indicated previously, the invention uses a reference electrode prepared from an electrode based on one or more N-type electroactive organic materials whose associated redox reaction has a constant electrochemical potential.

[0040] By material, also called compound, “organic”, we mean a compound, in particular of molecular, oligomeric or polymeric nature, of carbon chemistry, comprising carbon and hydrogen atoms, and one or more heteroatoms chosen from oxygen, nitrogen, sulfur, phosphorus, these atoms and heteroatoms being linked only by covalent bonds, this compound being able to be in the form of a salt, for example a metallic salt.

[0041] By “N-type” or “electron acceptor” electroactive material is meant an organic material which can undergo, due to the nature of its electroactive functions, a reversible reduction from the neutral state to a negatively charged state, with cationic charge compensation.

[0042] N-type materials therefore have the mechanism of inserting cations during their reduction.

[0043] The electrochemical mechanism associated with an N-type material can be schematized as follows:

[0044] [Chem.l]

[0045] The electrochemical oxidation-reduction reaction, also called redox reaction, associated with the reversible passage from the oxidized state of said N-type organic material used according to the invention to a reduced, negatively charged state, has the particularity of having a constant electrochemical potential. In particular, the N-type electroactive organic material of the electrode has a constant potential over a major part of the capacity operating range.

[0046] As described in the examples, the constant electrochemical potential, associated with an N-type active material, can be identified by a cycling test of the electrode based on said N-type organic material assembled in a half-cell or complete cell, for example in the form of a button cell, by carrying out a charge or a discharge in galvanostatic mode. The constant electrochemical potential corresponds to the potential plateau observed at the level of the charge / discharge curves at constant current (for example, curves of variation of the potential E as a function of time or as a function of the absolute or specific mass capacity during cycling in galvanostatic mode). It should be noted that in a complete cell (this is always the case in a half-cell with a lithium counter-electrode), this potential plateau is only observable if the counter-electrode used (which then acts as a reference) also has a potential plateau during its charge / discharge at constant current.

[0047] As illustrated in the remainder of the text, the value of the potential plateau associated with the reference electrode depends on the nature of the said N-type organic material(s) used, and in particular on the type of redox functionality of the N-type organic material used.

[0048] As detailed in the rest of the text, a reference electrode according to the invention can be obtained, prior to its use, from an electrode based on at least one N-type organic material, by partial reduction of said N-type organic material(s) with compensation for the negative charges created during the reduction by insertion of cations.

[0049] Electrode based on N-type organic material(s)

[0050] As indicated previously, an N-type organic material comprises electrochemically active functions (motifs or fragments) or redox functions, which can change from an oxidized, neutral form to a negatively charged reduced form, the negative charge being compensated by at least one cation.

[0051] The N-type organic material according to the invention may be chosen from organic materials, molecules, oligomers or organic polymers, already proposed as active materials for organic electrodes, for example for batteries. Such materials are documented in the literature [2].

[0052] In particular, said N-type organic material(s) according to the invention may be chosen from compounds, in particular molecules, oligomers or polymers, carrying redox functions chosen from: - conjugated azo functions (-N=N-) such as azobenzene or one of its derivatives, - disulfide functions (-SS-) such as diphenyl disulfides, tetrathionap-thalene, poly(2,5-dimercapto-1,3,4-thiadiazole), poly(5,8-dihydro-1H,4H-2,3,6,7-tetrathia-anthracene); and - conjugated carbonyl functions, in particular contained within quinonoid structures, such as anthraquinone; anhydride structures such as pyromellitic anhydride, dimide structures such as perylene dimide; or carboxylate structures such as perylene tetracarboxylate.

[0053] It is understood that the reference electrode may be based on a single N-type organic material or a mixture of at least two N-type organic materials, in particular chosen from the compounds described above.

[0054] The N-type organic compound may in particular be in the form of a molecule, an oligomer or a polymer. According to a particular embodiment, it is in the form of a polymer, in particular having redox units such as listed above, and more particularly of which at least one of the repeating units carries groups having at least one redox unit as mentioned above.

[0055] By “polymer” is meant both homopolymers and copolymers.

[0056] Advantageously, the N-type redox organic material is in the form of a crosslinked polymer. For the purposes of the invention, the term "crosslinked polymer" means polymers resulting from the use, during polymerization, of a crosslinking agent or branching, that is to say presenting several polymerizable functions, preferably bi- or tri-functionalized.

[0057] These redox organic materials can be prepared according to conventional methods known to those skilled in the art.

[0058] Examples of N-type organic compounds are described more specifically below.

[0059] Compounds carrying conjugated azo functions

[0060] According to a particular embodiment, the N-type organic material can be chosen from compounds carrying one or more azo functions (-N=N-).

[0061] The redox mechanism associated with an azo function can be schematized as follows:

[0062] [Chem.2]

[0063] Generally speaking, the redox reaction, associated with the passage of the azo function from its neutral form to its negatively charged reduced form with cationic charge compensation, has a constant potential of between 0.5 and 2 V vs Li+ / Li.

[0064] The compound carrying one or more azo functions may be, for example, azobenzene or one of its derivatives. It may have the following general structure, in its neutral, non-oxidized form:

[0065] [Chem.3]

[0066] with R, identical or different, preferably identical, being chosen, for example, from a hydrogen atom, a functionalized or non-functionalized alkyl chain, carboxylate, sulfonate, phosphonate and alcoholate functions.

[0067] As an example, lithium azobenzene 4,4-dicarboxylate (ADALS) may be mentioned.

[0068] Compounds carrying disulfide functions

[0069] According to a particular embodiment, the N-type organic material can be chosen from compounds carrying one or more disulfide functions (-SS-).

[0070] The redox mechanism associated with a disulfide function can be schematized as follows:

[0071] [Chem.4]

[0072] Generally speaking, the redox reaction, associated with the passage of the disulfide function from its neutral form to its negatively charged reduced form (two -S groups) with cationic charge compensation, has a constant potential between 1.5 and 3 V vs Lr7Li.

[0073] The compound carrying one or more disulfide functions may be chosen, for example, from diphenyl disulfides, tetrathionapphthalene, poly(2,5-dimercapto-1,3,4-thiadiazole), poly(5,8-dihydro-1H,4H-2,3,6,7-tetrathia-anthracene).

[0074] Compounds carrying conjugated carbonyl functions

[0075] According to a particular embodiment, the N-type organic material may be chosen from compounds carrying one or more conjugated carbonyl functions, in particular contained within quinonoid structures, such as for example anthraquinone; anhydride structures (-C(O)-OC(O)-) such as for example pyromellitic anhydride, dimides (-C(O)-NC(O)-) such as for example perylene dimide; or carboxylates (R-COOX) such as for example perylene tetracarboxylate.

[0076] The redox mechanism associated with a carbonyl function can be schematized as follows:

[0077] [Chem.6]

[0078] Generally speaking, the redox reaction, associated with the passage of the carbonyl function from its neutral form to its negatively charged reduced form with cationic charge compensation, has a constant potential of, in the case of a quinonoid type structure, between 1.5 and 3.5 V vs Lr7Li; in the case of an anhydride type structure, between 1.5 and 3.5 V vs Lr7Li; in the case of a dimide type structure, between 1.5 and 3.5 V vs Li+ / Li; and in the case of a carboxylate structure, between 0.5 and 1.5 V vs Lr7Li.

[0079] In a particular embodiment, the N-type organic material may be chosen from compounds, in particular molecules, oligomers or polymers, quinonoids, in particular chosen from benzoquinone compounds, nap- compounds thoquinones and anthraquinone compounds.

[0080] Examples of benzoquinone compounds that may be mentioned are 1,4-benzoquinone; 1,2-benzoquinone, substituted or unsubstituted; and polymers derived therefrom, for example poly(benzoquinolyl sulfide).

[0081] Examples of naphthoquinone compounds include the compounds 1,4-naphthoquinone; 1,2-naphthoquinone 1,5-naphthoquinone; 1,7-naphthoquinone; 2,3-naphthoquinone; 2,6-naphthoquinone, substituted or unsubstituted; and polymers derived therefrom.

[0082] Examples of anthraquinone compounds include 9,10-anthraquinone; 1,2-anthraquinone, 1,4-anthraquinone; 1,10-anthraquinone; 2,9-anthraquinone; 1,5-anthraquinone; 1,7-anthraquinone; 2,3-anthraquinone; 2,6-anthraquinone, substituted or unsubstituted; and polymers derived therefrom.

[0083] The substituent(s) optionally carried by the substituted benzoquinone, naphthoquinone and anthraquinone structures may be chosen from a hydrogen atom, a functionalized or non-functionalized alkyl chain, carboxylate, sulfonate, phosphonate and alcoholate functions.

[0084] In a particular embodiment, the N-type organic material may be chosen from compounds, in particular molecular, oligomeric or polymeric, comprising one or more carboxylate groups, in particular lithiated carboxylates.

[0085] Examples of carboxylate compounds, in particular lithiated ones, which may be cited are dilithium terephthalate, lithiated naphthalene carboxylate, lithiated perylene carboxylate, or oligomers or polymers functionalized by carboxylate groups, such as polythiophene terephthalate.

[0086] The N-type organic material may also be chosen from compounds, in particular molecular, oligomeric or polymeric compounds, comprising one or more anhydride functions, for example pyromellitic dianhydride.

[0087] It may also be chosen from compounds, in particular molecular, oligomeric or polymeric, comprising carbonyl functions conjugated in diimide-type structures, for example perylene diimide or naphthalene diimide.

[0088] In a particular embodiment, the N-type organic material is a compound comprising one or more lithiated carboxylate functions, in particular lithiated perylene tetracarboxylate (PTCLi4), the structure of which is recalled below:

[0089] [Chem.7] ÜÛOCMy —4 ^-00011 MM A™ /

[0090] It is within the knowledge of a person skilled in the art to adjust the form in which presents the N-type organic material in order to ensure that the reference electrode material, when used at the cell level of the electrochemical storage system, does not degrade, in particular does not dissolve in the electrolyte of the electrochemical cell in which it is implemented.

[0091] Several strategies are known to insolubilize redox organic compounds.

[0092] As seen previously, one of the most commonly used strategies consists of preparing the organic redox compound in the form of polymers or copolymers, crosslinked or not, with pendant or intramolecular redox functions.

[0093] Another strategy for insolubilizing electroactive organic compounds consists of producing composite structures by physisorption, with an inorganic substrate, for example silica, alumina, carbon, within which weak bonds are created (hydrogen, ji-ji interactions, Van der Waals), making it possible to limit, or even prevent, the dissolution of the redox organic compound.

[0094] It is also possible to graft the electroactive organic compound onto an inorganic solid (silica, alumina, carbon, etc.) via ionic or covalent bonds, for example by acid-base reaction with the hydroxyls of the silica surface or by reaction of diazonium salts with the carbon surface, in order to form an insoluble organic / inorganic hybrid compound.

[0095] Another strategy consists of adding ionic functions to the electroactive organic compound, for example of the carboxylate, sulfonate, alcoholate, imide, enolate type, etc., making it possible to limit the dissolution of the compound in an organic medium.

[0096] Thus, an electrode based on one or more organic materials of type N considered according to the invention means an electrode comprising one or more organic compounds of type N, carrying redox units as considered above, said compound(s) being able to be in different forms, as considered above, for example in form associated with other materials within composites, provided that they allow the electrochemical reaction associated with said organic material of type N, in particular its reduction with compensation of cationic charges.

[0097] Preparation of the electrode based on the N-type organic material(s)

[0098] The electrode based on said N-type organic electroactive material(s), from which a reference electrode according to the invention is obtained, can be prepared by any method known to those skilled in the art.

[0099] The electrode may typically be composed of a layer comprising a mixture of said N-type organic electroactive material(s), one or more binders and optionally one or more electronically conductive additives, on the surface of a current collector.

[0100] The preparation of said electrode may comprise, in general, at minus the following steps: - preparation of a dispersion, more commonly called ink, comprising, in one or more aqueous and / or organic solvents, at least said organic material of type N, in particular as described above; one or more electronically conductive additives, and optionally one or more binders; - depositing the ink on the surface of a current collector; and - evaporation of said solvent(s) from the ink to form the electrode film.

[0101] The ink solvent may comprise water and / or one or more organic solvents, for example chosen from N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), acetone, N,N-dimethylformamide (DMF), acetonitrile and ethanol.

[0102] Electronically conductive additives are used to improve the electronic conductivity of the electrode. They can be chosen, for example, from carbon fibers, carbon black, carbon nanotubes and mixtures thereof.

[0103] Said electronically conductive additive(s), when present, may preferably be implemented in a content ranging from 0.5 to 50% by mass, in particular from 1 to 20% by mass, relative to the mass of the electrode. It is understood that the total mass of the electrode does not include the mass of the current collector.

[0104] The binders are used to ensure the mechanical strength of the electrode on the current collector, the cohesion of the different components of the electrode or even its flexibility properties. They can be chosen from polymer binders, in particular chosen from fluorinated polymers, for example from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polymers derived from carboxymethylcellulose, polysaccharides and latexes, in particular of the styrene-butadiene rubber (BR) type.

[0105] For example, the binder is carboxymethylcellulose.

[0106] Said binder(s) may be present in an amount less than or equal to 20% by mass, relative to the total mass of the electrode, in particular less than or equal to 5% by mass, in particular between 1 and 3% by mass, relative to the total mass of the electrode. It is understood that the total mass of the electrode does not include the mass of the current collector.

[0107] The ink may be homogenized before spreading.

[0108] The deposition of the ink on the surface of the current collector can be carried out by any technique known to those skilled in the art, for example by coating, by a printing technique, by extrusion or by co-lamination.

[0109] The current collector may be solid, for example in the form of a strip or in the form of a grid.

[0110] The current collector may be made of a metallic material chosen from copper, aluminum, nickel or stainless steel potentially coated with carbon.

[0111] The evaporation of the solvent(s) from the ink may be carried out by drying, for example in an oven, at a temperature of between 20°C and 150°C, in particular between 50°C and 80°C, in particular for a period of between 1 and 15 hours.

[0112] Said N-type organic material(s) may represent from 50 to 98% by mass, in particular from 70 to 95% by mass, relative to the total mass of the electrode, excluding the mass of the current collector.

[0113] Preferably, the grammage of the electrode (defined as the mass of N-type organic material in grams per unit area in cm2) is between 0.1 mg / cm2 and 50 mg / cm2, in particular between 1 mg / cm2 and 20 mg / cm2. The grammage of the electrode made of N-type organic material, in other words the mass of N-type organic material per unit area, can be adjusted by controlling the rate of N-type organic material and the thickness of deposition, in particular coating, of the ink formulated on the current collector. Obtaining the reference electrode

[0114] As indicated previously, the reference electrode is accessed by carrying out a partial reduction of said N-type organic material(s), so as to reach the constant electrochemical potential associated with the redox reaction.

[0115] The partial reduction of said N-type organic materials more particularly involves compensation of the negative charges created during the reduction by insertion of cations.

[0116] More precisely, obtaining a reference electrode according to the invention involves the following steps: (i) providing an electrochemical cell, comprising said electrode based on said N-type organic material(s) as a working electrode, a counter electrode; and an electrolyte based on at least one ionic salt; and (ii) reduction of the working electrode of said cell under conditions suitable for reaching a potential plateau.

[0117] According to a first variant embodiment, the electrochemical cell for the preparation of the reference electrode may be an electrochemical cell distinct from the cell of the electrochemical storage system in which the reference electrode is intended to be used.

[0118] According to another alternative embodiment, as illustrated in the examples which follow, the reference electrode can be prepared directly at the level of the electrochemical cell of the electrochemical storage system in which it is intended to be used, the positive or negative electrode then serving as a counter-electrode for the preparation of the reference electrode.

[0119] The material of the counter-electrode can be of various natures, provided that it can oxidize; for example, this is an electrode based on lithium, sodium, LiFePO4 or LiMO2, with M representing Co, Ni or Mn.

[0120] Also, any type of counter-cations can be implemented to compensate for the negative charge of said organic material in partially reduced form. These can be monovalent or polyvalent cations, for example divalent.

[0121] It may be for example one or more organic cations, for example chosen from cations of alkylammonium type (RN4+ with R representing an alkyl group), of tetraalkyl phosphonium type (R4P+, with R, identical or different, representing alkyl groups), imidazolium, pyrrolinidium, or even inorganic cations, in particular alkali or alkaline-earth metal cations, in particular chosen from Li+, Na+, K+, Ca2+ or Mg2+.

[0122] The anions associated with the cations, for example lithium, within the salt used can be of any type, for example they can be inorganic anions such as for example PF6, BF4, C1O4, F, Cl, Br, I, NO3 and HSO4.

[0123] Advantageously, but in a non-restrictive manner, said cation(s) are of the same nature as said cation(s) entering into the composition of the electrolyte, and more particularly into the composition of said salt(s) of the electrolyte, of said cell of the electrochemical storage system in which said reference electrode is intended to be implemented.

[0124] By way of example, in the case where the reference electrode according to the invention is intended to be implemented at the level of a lithium battery (respectively, sodium, potassium, calcium, magnesium), for example a lithium-ion battery (respectively, sodium-ion, potassium-ion, calcium-ion, magnesium-ion), the counter-cation, for the compensation of the negative charges of the organic material in its partially reduced form, can be lithium.

[0125] As an example, for the preparation of a reference electrode according to the invention based on perylene tetracarboxylate (PTCLij), the two-electron electrochemical reaction, associated with the reduction of two lithiated carboxylate functions of PTCLi4 with compensation by Li+ cations (lithiation) can be schematized as follows:

[0126] [Chem.8] Mr.

[0127] The reference electrode can be prepared by directly carrying out a partial reduction of the N-type organic material, during which the negative charges created due to the partial reduction of the N-type organic material are compensated by cations, until the potential plateau is reached.

[0128] Alternatively, the reference electrode can be prepared by carrying out a partial reduction of the N-type organic material, during which the positive charges created due to the reduction of the N-type organic material are compensated by cations. It is also possible to carry out a complete reduction, followed by a partial oxidation, in order to reach the potential plateau.

[0129] The charge and, possibly, partial discharge, to reach the potential plateau can be carried out, for example, at a rate ranging from C / 100 to 5C.

[0130] Optionally, in the case where the reference electrode is prepared in a cell separate from the cell of the electrochemical storage system in which it is implemented, the prepared reference electrode may be cleaned prior to its implementation within the cell of the electrochemical storage system. For example, it may be rinsed with dimethyl carbonate, in order to eliminate residual salts at the porosity of the electrode.

[0131] Said N-type organic material(s), in their partially reduced negatively charged form, with compensation by at least one cation, may represent from 5 to 95% by mass, in particular from 30 to 70% by mass and more particularly from 40 to 60% by mass, relative to the total mass of N-type material(s) present in the electrode.

[0132] As indicated above, the reference electrode according to the invention comprises, in addition to said N-type organic material(s) in partially reduced form, one or more electronically conductive additives, in particular as defined above, notably chosen from carbon fibers, carbon black, carbon nanotubes and mixtures thereof, and optionally one or more binders, in particular as defined above, in particular one or more polymer binders, notably chosen from fluorinated polymers, for example from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polymers derived from carboxymethylcellulose, polysaccharides and latexes, notably of the styrene-butadiene rubber type.

[0133] Said binder(s) may represent less than 20% by mass of the total mass of the electrode, in particular less than 5% by mass, in particular between 1 and 3% by mass, of the total mass of the electrode, excluding the mass of the current collector.

[0134] Said electronically conductive additive(s) may represent from 0.5 to 50% by mass, in particular from 5 to 20% by mass, of the total mass of the electrode, excluding the mass of the current collector.

[0135] Preferably, the weight of the reference electrode based on said N-type organic material(s), defined as the mass of N-type organic material(s) in grams per unit area in cm2, is between 0.1 mg / cm2 and 50 mg / cm2, in particular between 1 mg / cm2 and 20 mg / cm2. ELECTROCHEMICAL STORAGE SYSTEM

[0136] As indicated previously, the electrode based on N-type organic material(s), in partially reduced form, as described previously, can be implemented as a reference electrode within at least one cell of an electrochemical storage system or electrochemical generator.

[0137] The electrochemical storage systems in which a reference electrode according to the invention can be incorporated can be diverse. It can be a metal-ion battery, in particular sodium, lithium, potassium, magnesium batteries; a lithium-sulfur or lithium-air battery.

[0138] It may also be a supercapacitor, in particular a “standard” supercapacitor or a so-called “hybrid” supercapacitor, in particular a potassium hybrid supercapacitor.

[0139] Whatever the nature of the electrochemical storage system, the cell of the electrochemical storage system typically comprises a positive electrode, a negative electrode and an electrolyte, in particular impregnating a porous membrane separating said electrodes.

[0140] The reference electrode according to the invention is thus integrated as a third electrode into the cell of the electrochemical storage system.

[0141] A cell of an electrochemical storage system according to the invention is thus a three-electrode system, comprising more particularly: - a positive electrode; - a negative electrode; and - said reference electrode according to the invention, in particular prepared as described above.

[0142] The nature of the elements constituting the cell of the electrochemical storage system, in particular the positive and negative electrodes and the electrolyte, of course depends on the type of device considered, depending on whether it is a metal-ion battery, a lithium-sulfur battery, a lithium-air battery, a supercapacitor, etc.

[0143] Said active material(s) of the negative electrode may in particular be chosen from activated carbon, carbon materials for intercalation of an alkaline element such as graphite; silicon; conversion materials of the MO2 type with M representing for example Sn (SnO2), Si (SiO2), or of the M3O4 type with M representing for example Co (Co3O4), Mn (Mn3O4) etc., metals (Li, Na, K, Mg, Ca) and alloys based on these metals, titanium oxides of the Li4Ti50i2 type.

[0144] Said active material(s) of the positive electrode may in particular be chosen from activated carbon, LiMO2 or LiM2O4 with M representing Mn, Co, Ni or one of their combinations; LiMPO4 with M representing Fe, Mn or one of their combinations.

[0145] The following example, with reference to the implementation of a reference electrode according to the invention at the level of a cell of a lithium-ion battery, is thus given solely as an illustration of the invention, it being understood that the use of a reference electrode is in no way limited to this particular mode of implementation.

[0146] Thus, as an example of implementation, a reference electrode according to the invention is introduced into a lithium battery, in particular a lithium-ion battery.

[0147] A reference electrode according to the invention can for example be implemented at the level of a cell of a lithium-ion battery further comprising: - a positive electrode comprising a positive active material, in particular chosen from LiFexMnyPO4, with the sum of x and y equal to 1, for example LiFePO4; - a negative electrode comprising a negative active material, for example based on titanium oxide with a spinel structure such as for example lithium-titanium oxide Li4 Ti50i2; and - an electrolyte comprising at least one lithium salt, for example LiPF6, in one or more organic solvents, for example chosen from carbonate solvents, such as ethylene carbonate (EC), diethyl carbonate (DEC) and / or dimethyl carbonate (DMC).

[0148] It is understood that the different elements are assembled within the cell of the electrochemical storage system, for example the battery or the supercapacitor, so as, on the one hand, to allow efficient use of the reference electrode, for example for the purpose of knowing the potentials of the positive and negative electrodes and, on the other hand, so that the presence of this third electrode does not interfere negatively with the operation of the cell of said electrochemical storage system.

[0149] In particular, the reference electrode can be used when the cell of said electrochemical storage system is subjected to cycling for currents ranging from C / 2 to 100C, in particular from C / 2 to 5C, at temperatures ranging from -40°C to 100°C.

[0150] Generally speaking, the different electrodes of the cell of the electrochemical storage system are separated from each other by a porous membrane, also called a “separator”, impregnated with the electrolyte.

[0151] Such porous separators can be, for example, made of polyethylene or polypropylene.

[0152] The cell of the electrochemical storage system according to the invention can advantageously have a configuration of superimposed layers. In other words, the assembly of the cell can be carried out by stacking the different elements under the shape of layers.

[0153] Each of the electrodes of a cell of the electrochemical storage system according to the invention may be in the form of a layer of the electrode material, deposited on at least one of the faces or on both faces of a current collector in the form of a thin film, for example in the form of a metal strip.

[0154] According to an alternative embodiment, in the case of an architecture of the cell of the electrochemical storage system in the form of a stack of the different elements, the reference electrode can be positioned between the positive and negative electrodes.

[0155] [Fig.l] schematically represents, in cross-section, an example of assembly 100 of the different elements, integrating a reference electrode according to the invention, within a cell of an electrochemical storage system, for example like the cell of a metal-ion battery.

[0156] As shown in this figure, in an alternative embodiment, a cell of an electrochemical storage system according to the invention, for example a metal-ion battery, may comprise the assembly 100 of the following different elements, in this stacking order: - a positive electrode 22, in particular formed from a layer of active material 220 on a current collector 221, for example made of aluminum; - a porous separator 24, for example made of polypropylene, intended to be impregnated with the electrolyte; - said reference electrode 21, in particular prepared as described above, formed of a layer 211 of the electrode material based on said N-type organic material(s) in a partially reduced form, at the level of a current collector 212, for example made of aluminum;

[0157] - a porous separator 24, for example made of polypropylene, intended to be impregnated by the electrolyte; and - a negative electrode 23, in particular formed from a layer of active material 231 on a current collector 232, for example made of aluminum.

[0158] Within the cell of the electrochemical system, the assembly is soaked with an electrolyte comprising at least one alkali or alkaline-earth metal salt, for example a lithium salt in the case of a lithium battery, in one or more aqueous or organic solvents.

[0159] Porous separators provide electronic insulation between the electrodes, while allowing easy passage of electrolyte ions.

[0160] The reference electrode 21, inserted within the assembly between the positive 22 and negative 23 electrodes, advantageously has a surface in a gold plane orthogonal to the stacking direction of the different elements (electrodes and separators), reduced compared to the surfaces of the positive and negative electrodes in this same plane. Preferably, the projected area of ​​the reference electrode in a plane orthogonal to the stacking direction does not exceed 10%, in particular 5%, of the projected area in this same plane of the positive and negative electrodes.

[0161] The invention is not limited to the arrangement shown in [Fig.l]. Other assemblies may be considered, provided that they allow both the operation of the cell of the electrochemical storage system and the use of the reference electrode. Examples of configuration of cells with three electrodes are for example described in document US 9,379,418.

[0162] A cell of an electrochemical storage system according to the invention may be packaged in a prismatic or cylindrical format. In the prismatic format, the assembly is preferably packaged in a package capable of preventing contamination by air or water of the cell.

[0163] In a particular embodiment, a cell of an electrochemical storage system according to the invention may be packaged in a prismatic format, and in particular in the form of a “pouch cell” as illustrated in the examples. Such a “pouch cell” notably has flexible aluminum-plastic packaging.

[0164] An electrochemical storage system, for example of the battery or supercapacitor type according to the invention, may comprise at least one cell according to the invention integrating a reference electrode.

[0165] Advantageously, the potential difference between the positive electrode (respectively, the negative electrode) and the reference electrode makes it possible to measure and monitor the potential of the positive electrode (respectively, the negative electrode) relative to a known potential value, during operation of the supercapacitor.

[0166] The connections and electrical circuits external to the assembly are not shown in the figures.

[0167] The external circuit between the positive electrode (respectively, the negative electrode) and the reference electrode may be electrically connected to a voltage monitor to enable the potential of the positive electrode (respectively, the negative electrode) to be indicated or recorded.

[0168] The potentials of the positive and negative electrodes can be monitored simultaneously or not, continuously, periodically, randomly or at predetermined times, during the operation of the electrochemical storage system.

[0169] It is understood that all of the characteristics described for the reference electrode and for the different elements of a cell of the electro storage system chemical applies to the cell of the electrochemical storage system, to the electrochemical storage system and to the uses claimed according to the invention.

[0170] The invention will now be described by means of the following figures and examples, given of course for illustrative and non-limiting purposes of the invention. EXAMPLE 1

[0171] Preparation of a reference electrode according to the invention

[0172] A reference electrode according to the invention, based on perylene tetracarboxylate (PTCLi4), was prepared directly at the level of the battery cell in which it is intended to be implemented.

[0173] PTCLi4 is an N-type material, the electrochemical reaction of which associated with the reversible passage from the oxidized state of said material to the reduced, negatively charged state, presents a constant electrochemical potential.

[0174] The electrochemical redox reaction, associated with the reduction of the lithiated carboxylate functions, of PTCLi4, with compensation by Li+ cations, can be schematized as follows:

[0175] [Chem.9]

[0176] [Fig.2] (publication [3]) represents the galvanostatic cycling profile during a charge / discharge cycle at a C / 10 regime of a PTCLi4-based electrode (electrode with PVDF as binder and Super P™ type carbon as conductive additive) in the case of a lithium half-cell. The charge / discharge profile confirms the existence of a potential plateau at approximately 1.1V versus Li / Li+.

[0177] The PTCLi4 (N-type organic material) based electrode is composed of a mixture of 95% PTCLLi; 0.5% carbon nanotubes and 4.5% carboxymethylcellulose (CMC) binder, deposited on an aluminum current collector.

[0178] The PTCLi4-based electrode is introduced into a lithium-ion battery cell

[0179] The assembly is carried out in “pouch cell” format, using the following electrodes: - the PTCLi4-based electrode, intended to subsequently form a reference electrode; - a positive electrode, composed of a mixture of 90.5% LiFePO4; 4.5% Super P carbon and 5% polyvinylidene fluoride (PVDF) binder, deposited on an aluminum current collector; - a negative electrode, composed of a mixture of 90% Li4Ti50i2; 5% Super P carbon and 1% CMC polymer and 4% Styrofan® LD 417 latex, deposited on an aluminum current collector.

[0180] The electrodes are separated by two Celgard ® separators, and the assembly is impregnated with an electrolyte based on ethylene carbonate (EC) / dimethyl carbonate (DMC) and the salt LiPF6.

[0181] [Fig.3] schematically represents the cell in pouch-cell format thus obtained.

[0182] Activation of the reference electrode

[0183] In order to carry out a partial lithiation (reduction with compensation of the anionic charges by Li+ cations) of the PTCLi4, the electrode is connected as a working electrode and the LiFePO4 electrode as a counter-electrode.

[0184] A partial reduction of the N-type material is carried out at a C / 100 regime. The lithiation rate is 25%.

[0185] [Fig.4] represents the evolution of the electrochemical potential E as a function of the specific mass capacity. EXAMPLE 2

[0186] Use of the reference electrode to monitor the potentials of the positive and negative electrodes

[0187] The cell prepared in Example 1, incorporating the PTCLi4-based reference electrode, is then connected in a “three-electrode” configuration, with the positive electrode as the working electrode, the negative electrode as the counter electrode, and the PTCLi4 electrode as the reference electrode.

[0188] The cell is charged at a C / 10 rate and it is possible to monitor the potential of the positive and negative electrodes independently, relative to the potential of the reference electrode.

[0189] [Fig.5] represents the cell voltage and the potentials of the negative and positive electrodes during charging. References

[0190] [1] Cengiz et al., J. Electrochem. Soc. 2021;

[0191] [2] Poizot et al., Chem. Rev. https: / / dx.doi.org / 10.1021 / acs.chemrev.9b00482

[0192] [3] lodarche et al., Adv. Sustainable Syst. 2017, 1600032.

Claims

Claims

1. Use, as a reference electrode in a cell of an electrochemical storage system, of an electrode based on one or more electroactive organic materials of type N, the associated redox reaction of which has a constant electrochemical potential; said organic material(s) of type N being present in a partially reduced negatively charged form, with charge compensation by at least one cation.

2. Use according to the preceding claim, in which the said N-type organic material(s) are chosen from compounds, in particular molecules, oligomers or polymers, carrying redox functions chosen from: - conjugated azo functions (-N=N-) such as azobenzene or one of its derivatives; - disulfide functions (-SS-) such as diphenyldisulfides, tetrathionapthalene, poly(2,5-dimercapto-1,3,4-thiadiazole), poly(5,8-dihydro-1H,4H-2,3,6,7-tetrathia-anthracene); and - conjugated carbonyl functions, in particular contained within quinonoid structures, such as for example anthraquinone; of anhydride structures such as pyromellitic anhydride, of dimide structures such as perylene dimide; or of carboxylate structures such as perylene tetracarboxylate.

3. Use according to any one of the preceding claims, in which the said N-type organic material(s) are chosen from compounds, in particular molecular, oligomeric or polymeric compounds, comprising one or more carboxylate groups, in particular lithiated carboxylates, such as dilithium terephthalate, lithiated naphthalene carboxylate, lithiated perylene carboxylate; or else oligomers or polymers functionalized by carboxylate groups, such as polythiophene terephthalate.

4. Use according to any one of the preceding claims, in which the N-type organic material is lithiated perylene tetracarboxylate, denoted PTCLi4.

5. Use according to any one of the preceding claims, wherein said reference electrode comprises, in addition to said N-type organic material(s) in partially reduced form, a or more electronically conductive additives, in particular chosen from carbon fibers, carbon black, carbon nanotubes and mixtures thereof, and optionally one or more binders, in particular one or more polymer binders, in particular chosen from fluorinated polymers, for example from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polymers derived from carboxymethylcellulose, polysaccharides and latexes, in particular of the styrene-butadiene rubber type.

6. Use according to any one of the preceding claims, in which said reference electrode is prepared, prior to its use in said cell, from an electrode based on said N-type organic material(s), by partial reduction of said N-type organic material(s) with compensation of the negative charges created during oxidation by insertion of cations, making it possible to obtain the constant electrochemical potential.

7. Use according to the preceding claim, wherein said reference electrode is obtained via the following steps: (i) providing an electrochemical cell, comprising said electrode based on said N-type organic material(s) as working electrode, a counter electrode; and an electrolyte based on at least one ionic salt; and (ii) reducing the working electrode of said cell under conditions suitable for reaching a potential plateau.

8. Use according to any one of the preceding claims, in which the negative charge of said N-type organic material(s) in partially reduced form is compensated by one or more monovalent or polyvalent cations, in particular chosen from organic cations, such as cations of alkylammonium, tetraalkyl phosphonium, imidazolium, pyrrolinidium type, and inorganic cations, such as alkali or alkaline-earth metal cations, in particular chosen from Li+, Na+, K+, Ca2+ or Mg2+; preferably said cation(s) being of the same nature as said cation(s) entering into the composition of said salt(s) of the electrolyte of said cell of the electrochemical storage system.

9. Use according to any one of the preceding claims, wherein said N-type organic material(s) in their negatively charged partially reduced form represent from 5 to 95% by mass, in particular from 30 to 70% by mass and more particularly from 40 to 60% by mass, relative to the total mass of N-type material(s) present in the electrode.

10. Use according to any one of the preceding claims, in a cell of a metal-ion battery, in particular a sodium-ion, lithium-ion, potassium-ion, magnesium-ion battery; a lithium-sulfur or lithium-air battery; or of a supercapacitor, in particular a potassium hybrid supercapacitor.

11. Use according to any one of the preceding claims, for knowing the potentials of at least one of the positive and negative electrodes, preferably of each of the positive and negative electrodes of said cell of the electrochemical storage system, in particular for monitoring the evolution of the potentials of at least one of the positive and negative electrodes, during the operation of said system.

12. Cell of an electrochemical storage system comprising three electrodes: - a positive electrode; - a negative electrode; and - a reference electrode based on one or more electroactive organic materials of type N, the associated redox reaction of which has a constant electrochemical potential; said organic material(s) of type N being present in a negatively charged partially reduced form, with charge compensation by at least one cation, said reference electrode being in particular as defined in any one of claims 2 to 9.

13. Electrochemical storage system, comprising at least one cell as defined in claim 12, said system being chosen in particular from metal-ion batteries, in particular sodium-ion, lithium-ion, potassium-ion, magnesium-ion batteries; lithium-sulfur or lithium-air batteries; supercapacitors, in particular potassium hybrid supercapacitors.

Images