Electrochemical element with a gel-type electrolyte comprising a positive electrode prepared by dry method

Abstract

The present invention relates to a dry process for manufacturing positive electrodes comprising a gel polymer electrolyte for solid-state batteries, the electrochemical elements comprising them, and their manufacture. Figure: None

Description

Title of the invention: Electrochemical element with a gel-type electrolyte comprising a dry-prepared positive electrode

[0001] The present invention relates to the technology of solid electrolyte lithium batteries containing a gel polymer electrolyte and a solvent-free positive electrode.

[0002] An electrochemical element, hereafter referred to as the "element," comprises an electrochemical bundle consisting of alternating positive and negative electrodes framing a separator impregnated with electrolyte. Each positive and each negative electrode consists of a metallic current collector supporting, on at least one of its faces, at least one active material and generally a binder and an electronically conductive material.

[0003] Lithium-ion electrochemical elements are known in the prior art. They are commonly used in many fields such as automotive, telecommunications, electronic devices, and aerospace. Their operating principle is based on the reversible exchange of lithium ions between a positive electrode (cathode), most often a lithium oxide of a transition metal or a lithium phosphate of a transition metal, and a negative electrode (anode), for example, made of graphite. The anode and cathode are separated by a separator. The assembly formed by the anode, cathode, and separator constitutes an electrochemical beam. This beam is impregnated with a liquid organic electrolyte, often consisting of a mixture of alkyl carbonates in which a lithium salt, for example lithium hexafluorophosphate (LiPF6), is dissolved.

[0004] The liquid nature of the electrolyte entails several disadvantages and therefore we seek to avoid the use of a liquid electrolyte.

[0005] All-solid technology refers to solid electrolyte cells, among which we distinguish solid electrolytes proper (SSE) including inorganic solid electrolytes (ISE), solid polymer electrolytes (SPE) and composite polymer electrolytes (CPE), as well as quasi-solid electrolytes (QSSE) also called gel polymer electrolytes (GPE).

[0006] The gel form offers the particular advantage of preventing electrolyte leaks in the event of accidental opening of the element's container. It also prevents lithium dendrites that may form on the surface of the negative electrode from propagating towards the positive electrode and creating micro-short circuits detrimental to the element's lifespan. Compared to a liquid electrolyte, a gel electrolyte therefore improves user safety.

[0007] The gelled electrolyte can typically be obtained by dissolving a polymer in an organic solvent. The gelled electrolyte is then brought into contact with the electrodes, which gradually become saturated with it.

[0008] FR3110776 describes a process for preparing a gelled electrolyte in Li-ion technology based on ionic liquid, poly(vinylidene-co-hexafluoropropylene fluoride) (P(VDF-HFP)) and solvent, it being understood that the gelled electrolyte is then deposited onto the positive and / or negative active material, on either side of the separator. The polymer content relative to the mass of the liquid mixture is generally 10% by mass:

[0009] Application FR2207830, filed on July 29, 2022, describes a process for the in situ gelation of an electrochemical element by impregnating an assembly consisting of a negative electrode, a separator, and a positive electrode comprising an active material of the type lithium manganese iron phosphate (LMFP), with a liquid mixture comprising a solvent, a monomer, a lithium salt, and a radical polymerization initiator, followed by crosslinking of the monomer. According to this process, after impregnation of the liquid into the electrode, the crosslinking agent is activated to induce the formation of a polymer network producing a gel that captures the liquid. The application further describes a monomer content of 5% by mass relative to the amount of liquid electrolyte.

[0010] However, each of these processes involves the prior preparation of the positive electrode by conventional solvent means, i.e. by deposition of an ink in an organic solvent medium.

[0011] It has been observed that for electrolyte impregnation, when the monomer or polymer content is greater than or equal to 10% by mass, the viscosity of the liquid becomes too high and problems of electrode impregnation by the solution appear.

[0012] However, when the polymer content is so low, the safety aspect of the cells is not significantly increased compared to a non-gelled liquid electrolyte.

[0013] It is therefore desirable to increase the polymer content relative to the liquid electrolyte content in order to improve the safety of these cells. Other manufacturing methods for these electrodes should therefore be considered to achieve polymer contents exceeding 10% by mass relative to the liquid electrolyte content.

[0014] Furthermore, a very significant portion of the manufacturing cost of an electrode is related to its manufacturing process. Indeed, the solvent used to prepare the ink (based on active material, optional conductive fillers, and a binder) that will be coated onto the foil to create the electrode must be evaporated. This step therefore requires the use of energy-intensive furnaces.

[0015] It is also desirable to limit the use of harmful solvents in an environmental approach.

[0016] Poly(vinylidene-co-hexafluoropropylene fluoride) (P(VDF-HFP)) has already been used in electrolytes: WO2019 / 053388 describes a solid polymer electrolyte comprising at least one lithium salt and poly(vinylidene-co-hexafluoropropylene fluoride) (P(VDF-HFP)). However, the solid electrolyte layers are in the form of a solid polymer film, applied by co-lamination between the positive and negative electrode films.

[0017] One object of the present invention is therefore to propose a new method of manufacturing a gel-type electrochemical element comprising solvent-free positive electrodes, making it possible to avoid the energy-intensive furnaces used for manufacturing electrodes.

[0018] Another object of the invention is also to propose a process for increasing the polymer content within the electrolyte, in particular to more than 10% by mass compared to the liquid electrolyte.

[0019] To this end, the invention relates to an electrochemical element comprising: - A positive electrode comprising • at least one active ingredient; • a mechanical binder; • a solid gel-type electrolyte comprising • an ionically conductive gelling binder, • an electrolyte El comprising a lithium salt and a solvent,

[0020] such that said ionically conductive gelling binder is selected from poly(vinylidene-co-hexafluoropropylene fluoride) (PVDF-HFP) polymers, poly(oxyethylene) (POE) and its derivatives, poly(trimethylene carbonate) (PTMC), polycaprolactone (PCL), polyethylene carbonate (PEC), polypropylene copolymer (PPC), polyacrylonitrile (PAN), acrylates, hydrogenated acrylonitrile butadiene rubber (HNBR), and cellulose and its derivatives; • possibly a carbon-based electronic conductor; and • A porous separator whose pores are impregnated with an E2 type gel electrolyte comprising a matrix which is a polymer obtained by crosslinking a monomer comprising at least two acrylate groups into which is incorporated a mixture comprising at least one solvent, at least one lithium salt and a radical polymerization initiator; • A negative electrode containing an active material.

[0021] According to other advantageous aspects of the invention, said element comprises one or more of the following features, taken individually or in any technically possible combination: The electrochemical element

[0022] The term "electrochemical element" means an elementary electrochemical cell consisting of the positive electrode / separator / negative electrode assembly, which allows the electrical energy supplied by a chemical reaction to be stored and released in the form of a current. The positive electrode

[0023] The term "positive electrode" refers to the electrode where electrons enter, and where discharged cations (Li+) arrive.

[0024] According to one embodiment, the electrode is prepared by a dry process. This term refers to a solvent-free process. It is therefore distinct from electrodes typically consisting of ink deposited on a current collector and the solvent of which is evaporated.

[0025] It is here specified that the term "solvent-free" refers to the solvent used for the process comprising the deposition of an ink, without prejudice to the solvent incorporated in the gelled electrolyte according to the invention.

[0026] According to the invention, the positive electrode is in gel form.

[0027] The mechanical binder

[0028] The term "mechanical binder" refers to compounds capable of giving the electrode cohesion of the different components and its mechanical hold on the current collector, and / or of giving the electrode a certain flexibility for its implementation as an element.

[0029] Typically, said mechanical binder can be selected from fibrillable fluoropolymer binders such as polytetrafluoroethylene (PTFE) and its derivatives such as polyvinylidene-tetrafluoroethylene fluoride (PVDF-TFE), in particular its copolymers such as chlorofluoroethylene, perfluoroalkoxy (PFA), polychlorotrifluoroethylene (PCTFE or PTFCE), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene or poly(ethylene-co-tetrafluoroethylene) (ETFE), tetrafluoroethylene perfluoromethyl vinyl ether (MFA).

[0030] According to one embodiment, said mechanical binder is selected from polytetrafluoroethylene (PTFE) and polyvinylidene-tetrafluoroethylene fluoride (PVDF-TFE) and mixtures thereof.

[0031] According to one embodiment, the mechanical binder represents from 0.1% to 10%, preferably from 0.5% to 5% by mass of the mass of the mixture constituting the positive electrode.

[0032] The electrolyte El

[0033] According to one embodiment, the solvent of the electrolyte El is chosen from saturated cyclic carbonates, unsaturated cyclic carbonates and linear carbonates, linear ethers, cyclic ethers and their derivatives such as trimethylolpropane triglycidyl ether (TTE), and their fluorinated derivatives.

[0034] Preferred saturated cyclic carbonates are propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and mixtures thereof. An example of a fluorinated cyclic carbonate is monofluoroethylene carbonate (FEC). Vinylene carbonate can be used as an unsaturated cyclic carbonate. Preferred linear carbonates are dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), and mixtures thereof. Preferred linear ethers include dimethyl ether (DME), diethyl ether (DEE), and mixtures thereof. Preferred cyclic ethers include lactones, such as gamma-butyrolactone.

[0035] In a preferred embodiment, said at least one solvent is chosen from the group consisting of cyclic carbonates, linear carbonates and a mixture thereof.

[0036] In a preferred embodiment, said at least one solvent comprises fluoroethylene carbonate (FEC).

[0037] In one embodiment, said at least one solvent is a mixture of a linear carbonate and fluoroethylene carbonate (FEC). The linear carbonate may be ethyl methyl carbonate (EMC).

[0038] According to one embodiment, the solvent comprises 20 to 40% by volume of cyclic alkyl carbonate, optionally fluorinated such as monofluoroethylene carbonate (FEC), and 60 to 80% by volume of linear alkyl carbonate.

[0039] According to one embodiment, the solvent comprises ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0040] According to one embodiment, the electrolyte El comprises from 50 to 95% by weight of solvent, preferably between 60% and 85%, the percentage being related to the weight of gelling polymer.

[0041] According to one embodiment, the electrode comprises 15 to 35% by volume of electrolyte EL

[0042] The ionically conductive gelling binder

[0043] The term "ionically conductive gelling binder" refers to agents capable of increasing the viscosity of the electrolyte El to give it the consistency of a gel, while allowing the conduction of lithium ions.

[0044] Said ionically conductive gelling binder can be selected from poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymers, poly(oxyethylene) (POE) and its derivatives such as polyethylene glycol diacrylate (PEGDA), poly(ethylene glycol) methyl ether acrylate (PEGMEA), trimethylolpropane triacrylate (TMPTA), poly(trimethylene carbonate) (PTMC), polycaprolactone (PCL), polyethylene carbonate (PEC), polypropylene copolymer (PPC), polyacrylonitrile (PAN), acrylates, hydrogenated acrylonitrile butadiene rubber (HNBR), and cellulose and its derivatives.

[0045] According to the invention, said gelling binder can be present in high concentrations within the electrolyte El, in particular in mass concentrations greater than 10%.

[0046] According to one embodiment, the mass ratio (ionic conductive gelling binder / electrolyte El) is between 10 and 50%, preferably between 20 and 30%.

[0047] Lithium salts

[0048] The electrolyte El contains lithium salts.

[0049] According to one embodiment, said lithium salts of electrolyte E1 and E2, identical or different, may be selected from lithium perchlorate LiC104, lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsF6, lithium hexafluorantimonate LiSbF6, lithium trifluoromethanesulfonate LiCF3SO3, lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), lithium bis(trifluoromethanesulfonyl)imidide LiN(CF3SO2)2 (LiTFSI), lithium tris(fluoromethanesulfonyl)methylide LiC(CF3SO2)3 (LiTFSM), lithium bis(pentafluoroethylsulfonyl)imidide LiN(C2F(SO2)2) (LiBeTI), the lithium-4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LIDFOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (LiFAP), lithium difluorophosphate LiPO2F2, and mixtures thereof.

[0050] A first preferred mixture of lithium salts consists of LiPF6 and LiDFOB. A second preferred mixture of lithium salts consists of LiPF6, LiFSI and / or LiTFSI and LiDFOB. Preferably, this second mixture consists of LiPF6, LiFSI and LiDFOB.

[0051] According to one embodiment, the concentration of lithium salts in the electrolyte El is between 0.5 and 2 mol.L*.

[0052] Active ingredient

[0053] The active material of the positive electrode is not particularly limited. It can be chosen from the following groups or mixtures thereof:

[0054] - nickel-manganese-cobalt (NMC) type compounds, in particular oxides lamellar with high nickel content, that is typically those for which the molar ratio of nickel, relative to the total of the elements nickel, manganese and cobalt, is greater than or equal to 0.6, in particular greater than or equal to 0.8;

[0055] - nickel-cobalt-aluminium (NCA) type compounds

[0056] - lithium iron phosphate (LFP) type compounds;

[0057] - lithium vanadium fluorophosphate (LVPF) compounds, in particular those of LixVPO4F formula with 0.8 <x<l,2, ou l’un de ses dérivés de formule LixVi _ yMyPO4Fz où0,8<x<l,2 ; 0<y<0,5 ; 0,8<z<l,2 et M est choisi dans le groupe consistant en Ti, Al, Y, Cr, Cu, Mg, Mn, Fe, Co, Ni, et Zr ;

[0058] - lithium iron phosphate (LFMP) type compounds, in particular of formula LixFei yMyPO4(LFMP) where M is chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; and 0.8 <x<l,2 ; 0<y<0,9 .

[0059] The conductive element

[0060] A conductive element can also be added for the preparation of the positive electrode. It can be chosen from among electronically conductive carbon materials, such as graphite, activated carbon, carbon black, acetylene black, soot, graphene, carbon fibers, carbon nanotubes or a mixture thereof.

[0061] The mixture comprising at least one active material, the mechanical binder, the gel-type electrolyte comprising the ionically conductive gelling binder and the electrolyte El comprising a lithium salt and a solvent, and optionally the carbon-based electronic conductor constitutes the electrode formulation.

[0062] According to one embodiment, the electrodes can consist of a conductive support used as a current collector which is coated with the formulation according to the invention, after shaping.

[0063] A current collector is understood to be an element such as a pad, plate, sheet or other, made of conductive material, connected to the positive or negative electrode, and ensuring the conduction of the flow of electrons between the electrode and the terminals of the battery.

[0064] The current collector is preferably a two-dimensional conductive support such as a solid or perforated metal strip.

[0065] In the case of the positive electrode, the current collector is typically an aluminium strip, in particular covered with a carbon coating.

[0066] According to one embodiment, the positive electrode does not contain a radical polymerization initiator. The impregnated separator

[0067] The porous separator

[0068] The separator can be of any type of ionically conductive porous separator. One example is the separators used in Li-ion cells. For instance, the separator may consist of a layer of a material chosen from the group comprising polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), or polyester such as... Polyethylene terephthalate (PET), polyethylene butylene terephthalate (PBT), cellulose, polyimide, glass fibers. The separator can consist of several layers of the aforementioned materials, the layers being of the same or different types.

[0069] Electrolyte E2

[0070] The separator is impregnated with gelled electrolyte E2 which is obtained by crosslinking a monomer.

[0071] The term “crosslinking” refers to the formation of a polymer having a three-dimensional structure.

[0072] The monomer

[0073] Said monomer may advantageously be of the acrylate type. Typically, it comprises at least two acrylate groups.

[0074] The term "acrylate groups" includes methacrylate groups in the following. The monomer typically comprises two, three, or four acrylate groups. In a preferred embodiment, crosslinking occurs only in the presence of the monomer having at least two acrylate groups. The crosslinked polymer comprises at least one acrylate group. According to one embodiment, the reaction mixture does not comprise a comonomer. Examples of monomers having two acrylate groups are poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate (PEGDMA), poly(propylene glycol) diacrylate (PPGDA), and poly(propylene glycol) dimethacrylate (PPGDMA). Examples include di(propylene glycol) diacrylate, 1H,1H,6H,6H-perfluoro-1,6-hexyl diacrylate, 1H,1H,5H,5H-perfluoropentane-1,5-diyl diacrylate, and 2,2,3,3-tetrafluoro-1,4-butyl diacrylate.Poly(ethylene glycol) diacrylate (PEGDA) can have a number molecular weight ranging from 5000 to 10000 g / mol or from 6000 to 8000 g / mol. It can also have a molecular weight between 500 and 1000 g / mol, preferably between 600 and 800 g / mol. It has been observed that low molecular weight monomers promote the impregnation of electrode pores by the gelled electrolyte.

[0075] Examples of monomers having three acrylate groups are trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate, trimethylolpropane ethoxylate triacrylate and trimethylolpropane propoxylate triacrylate (TPPTA).

[0076] An example of a monomer having four acrylate groups is pentaerythritol tetraacrylate (PETEA).

[0077] Among the monomers mentioned above, a preferred monomer of electrolyte E2 is trimethylolpropane triacrylate (TMPTA).

[0078] The initiator

[0079] The initiator refers to a thermal or photochemical type radical polymerization initiator.

[0080] Said initiator may be a compound comprising one or more azo groups. Preferred initiators are those that are activated by temperatures ranging from 50 to 100°C, 60 to 90°C, or 70 to 80°C. Moderate temperatures ranging from 55 to 75°C are preferred. A thermal radical polymerization initiator comprising an azo group is razobisisobutyronitrile (AIBN).

[0081] Lithium salts

[0082] Electrolyte E2 contains lithium salts.

[0083] According to one embodiment, said lithium salts of electrolyte E2 may be identical or different from those of electrolyte El as defined above.

[0084] They can be selected from lithium perchlorate LiC104, lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsF6, lithium hexafluorantimonate LiSbF6, lithium trifluoromethanesulfonate LiCF3SO3, lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), lithium bis(trifluoromethanesulfonyl)imidide LiN(CF3SO2)2 (LiTFSI), lithium tris(fluoromethanesulfonyl)methylide LiC(CF3SO2)3 (LiTFSM), lithium bis(pentafluoroethylsulfonyl)imidide LiN(C2F(SO2)2) (LiBeTI), lithium-4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), bis(oxalato)borate of lithium (LiBOB), lithium difluoro(oxalato)borate (LIDFOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (LiFAP), lithium difluorophosphate LiPO2F2, and mixtures thereof.

[0085] A first preferred mixture of lithium salts consists of LiPF6 and LiDFOB. A second preferred mixture of lithium salts consists of LiPF6, LiFSI and / or LiTFSI and LiDFOB. Preferably, this second mixture consists of LiPF6, LiFSI and LiDFOB.

[0086] The solvent

[0087] According to one embodiment, said solvent of electrolyte E2 is a cyclic carbonate or a linear carbonate or a mixture thereof, in particular fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) and a mixture thereof.

[0088] In a preferred embodiment, said at least one solvent comprises fluoroethylene carbonate (FEC). In another embodiment, said at least one solvent is a mixture of a linear carbonate and fluoroethylene carbonate (FEC). The linear carbonate may be ethyl methyl carbonate (EMC).

[0089] According to one embodiment, the solvent comprises 20 to 40% by volume of cyclic alkyl carbonate, optionally fluorinated such as monofluoroethylene carbonate (FEC), and 60 to 80% by volume of linear alkyl carbonate.

[0090] According to one embodiment, the solvent comprises ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0091] In one embodiment, said at least one solvent is a mixture of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) and the salt mixture consists of LiPF6 and LiDFOB.

[0092] Said separator impregnated with gel electrolyte E2 can be prepared, in particular, by applying and / or adapting the methods described in application number FR2207830. By way of illustration, appropriate quantities of the monomer, said at least one solvent, said at least one lithium salt, and the thermal initiator are mixed to obtain a liquid mixture. Generally, the mass percentage of the monomer ranges from 1 to 20%, or from 5 to 10%, or from 2 to 7%, for a total mass of said at least one solvent, said at least one lithium salt, and the radical polymerization thermal initiator of 100%. A low percentage of monomer results in a lower viscosity of the liquid mixture, which improves the impregnation of the electrodes. The total quantity of the radical polymerization thermal initiator(s) can represent from 0.1 to 3% by mass, ideally from 1 to 1.5% by mass relative to the mass of monomer.The separator can be immersed in the liquid mixture at room temperature. A resting period of 12 to 24 hours is preferably observed to improve the penetration of the liquid mixture into the pores of the separator. The temperature can then be increased to a value sufficient to activate the initiator and induce monomer crosslinking. The temperature is generally set in the range of 50 to 100°C, preferably 60 to 70°C. It can be set in the range of 60 to 70°C when the radical initiator is azobisisobutyronitrile (AIBN). The heat is maintained for 2 to 24 hours, generally 5 to 15 hours depending on the quantities of monomer and radical initiator used.

[0093] The degree of progress of crosslinking can be estimated by measuring the percentage of residual monomers in the reaction medium at different times during the reaction. Residual acrylate monomers are characterized by the presence of a C=C double bond in the vinyl group. This double bond can be detected by Fourier transform infrared (FT-IR) spectroscopy. This technique can be used by those skilled in the art to measure the amount of residual monomers. The use of the FT-IR technique makes it possible to verify whether the reaction mixture still contains compounds with a C=C double bond. Those skilled in the art can then determine when to stop applying heat. The crosslinking conditions are chosen to minimize the amount of residual monomers. The presence of even a small amount of residual monomers can have a detrimental effect on the function of the component. The negative electrode

[0094] The term "negative electrode" refers to the electrode functioning as the anode when the battery is discharging, and as the cathode when the battery is charging. The anode is defined as the electrode where an electrochemical oxidation reaction (electron emission) takes place, while the cathode is the site of reduction. The term "negative electrode" also refers to the electrode from which electrons are released and from which cations (Li+) are released during discharge.

[0095] The negative electrode typically comprises at least one active material, optionally a binder, optionally one or more co-binders, and optionally E2 and / or EL type gel electrolyte

[0096] The active material(s) of the negative electrode may be selected from the group consisting of lithium, a lithium-based alloy, graphite, silicon, mixtures of graphite and silicon, and titanium oxides. In particular, the active material of the anode is lithium or a lithium-based alloy. Process

[0097] According to another object, the present invention also relates to a method of preparing an element according to the invention.

[0098] The process can be carried out according to two alternatives detailed below.

[0099] According to a first alternative, said process comprises: - Preparation of the positive electrode, including: • The fibrillation of a mixture of the active substance, the mechanical binder, the ionically conductive gelling binder, and possibly the electronically conductive material, in powder form; • The shaping of the fibrillated mixture into a film and the deposition of said film onto a positive electrode current collector; - The assembly of said positive electrode thus formed with said separator impregnated with gel electrolyte E2, and said negative electrode; - The impregnation of said positive electrode by said electrolyte El in liquid form comprising said lithium salt and said solvent; and - The gelation of said positive electrode by thermal activation.

[0100] According to this first alternative, the element is prepared by gelation of the positive electrode in situ, i.e. pre-assembled within an element.

[0101] According to this alternative, the active material, the mechanical binder, the ionically conductive gelling binder, and optionally the conductive material ingredients of the positive electrode formulation are each in powder form and mixed.

[0102] The mixing can in particular be carried out with a planetary mixer.

[0103] Following fibrillation (see below), the resulting mixture typically takes the form of granules or agglomerated powder.

[0104] After shaping the positive electrode, it is assembled with the other constituents of the element (separator and negative electrode).

[0105] The positive electrode is then impregnated using liquid electrolyte El. This can be carried out by the usual impregnation methods commonly used for Li-ion electrochemical systems. This impregnation can, for example, be performed by filling, for example by soaking or immersing the positive electrode.

[0106] A schematic representation of this first alternative is illustrated by [Fig.1].

[0107] As shown in [Fig.1], the process can be broken down into 3 steps.

[0108] In a first step A, the mixture in powder form is introduced into a extruder 3, a planetary mixer 4 or an internal mixer 5 in which it is fibrillated. Typically, the fibrillated product obtained can be in the form of flakes or granules (1) or agglomerated powder (2).

[0109] In a second step B, the fibrillated mixture is introduced into a calender 7 for shaping. Figure 1 shows only the calendering of agglomerated powder, but shaping can also be carried out on the fibrillated mixture in the form of flakes or granules. In the case of flakes or granules, it may be appropriate to deagglomerate the mixture to facilitate film production.

[0110] Following this shaping, a film 8 is obtained which is deposited on a current collector.

[0111] In a third step, the film 8 comprising pores 13 is assembled with the separator impregnated with gelled electrolyte E2 11 and a negative electrode 12, thus constituting a precursor of a positive electrode 10. The pores 13 are then impregnated with liquid electrolyte El, and then gelled, so as to form the positive electrode 10'.

[0112] It is understood that the electrodes also include current collectors, not shown here.

[0113] According to a second alternative, said process comprises: - The preparation of a positive electrode composition comprising the mixture of said active material, mechanical binder, ionically conductive gelling binder, and possibly electronically conductive material with said electrolyte El in liquid form comprising said lithium salt and said solvent; - The fibrillation and gelation of said mixture; - The shaping of the gelled fibrillated mixture into a film and the deposition of said film onto a current collector; - The assembly of said collector thus coated with said separator impregnated with gel electrolyte E2, and said negative electrode.

[0114] According to this second alternative, the element is prepared by assembling its previously prepared constituents. More specifically, according to this alternative, the positive electrode is previously gelled and shaped.

[0115] The method according to the invention according to this second alternative is illustrated in [Fig.2].

[0116] As shown in [Fig.2], the process can be broken down into 3 steps.

[0117] In a first step A, the mixture consisting of the active material, binder mechanical, ionically conductive gelling binder, and optionally electronically conductive material with said electrolyte El is introduced into an extruder 3, a planetary mixer 4 or an internal mixer 5 and heated in which it is fibrillated and gelled.

[0118] Typically, the fibrillated and gelled product obtained can be in the form of gelled powder or gelled flakes, or gelled granules (6').

[0119] In a second step B, the gelled fibrillated mixture 6' is introduced into a calender 7 for shaping.

[0120] Following this shaping, a gelled film 8' is obtained and deposited on a current collector.

[0121] In a third step, the gelled film 8' is assembled with the gelled electrolyte impregnated separator E2 11 and a negative electrode 12, thus constituting a positive electrode 10'.

[0122] It is understood that the electrodes also include current collectors, not shown here.

[0123] Fibrillation

[0124] According to either alternative, fibrillation refers to mixing under mechanical stress, aimed at fibrillating the fluoropolymer type mechanical binder.

[0125] Fibrillation can typically be achieved by extrusion and / or by mixing within a mixer, such as an internal mixer or a planetary mixer.

[0126] "Extrusion" means a thermomechanical process in which the formulation is forced through a sleeve under the action of pressure and / or screw rotation and heat.

[0127] The extrusion step can be adapted according to several parameters, such as the mixing temperature, the type of screw profile of the extruder, the type of die of the extruder, the rotation speed and / or the length of the screws.

[0128] According to one embodiment, fibrillation can be carried out with a single- or twin-screw type extruder, preferably a co-rotating twin-screw extruder.

[0129] According to one embodiment, the screw profile used in the extruder is of the shearing type to fibrillate the fluoropolymer within the extruder. The screw profile may contain one or more mixing zones. The number of mixing zones typically depends on the number of feed zones. The position of the mixing zones in the extruder generally depends on the number of material feed zones. A mixing zone may be added after each material feed zone.

[0130] Typically, the type of screw element used to shear the material can be adapted to the type of active ingredient contained in the premix. If the active ingredient is shear-sensitive, it is preferable to use low- or medium-shear elements. If the active ingredient is not very shear-sensitive, it is possible to use low-, medium-, or high-shear elements.

[0131] The screw rotation speed is generally the same along its entire length. It is generally recommended to run it between 100 rpm and 1000 rpm, specifically between 100 and 750 rpm. The screw rotation speed is generally adjusted according to the desired material flow rate at the extruder outlet. The lower the screw rotation speed, the lower the output flow rates. Note that low rotation speeds result in longer residence times in the extruder. In such cases, if the material inlet flow rate is high, there is a risk of clogging the extruder. With a high screw rotation speed, the output flow rates may fluctuate if the material inlet flow rates are too low.

[0132] The fibrillation step can typically be carried out at a temperature between 40°C and the degradation temperature of the fluoropolymer.

[0133] By way of illustration, for PTFE, the degradation temperature is approximately 350°C (under shear) and the melting temperature is approximately 330°C (this value may vary depending on the grade of PTFE), it being understood that due to the stresses exerted, the extrusion temperature is lower, preferably less than or equal to 260°C.

[0134] When fibrillation and gelation are carried out simultaneously, the temperature of the fibrillation step can advantageously be adjusted to avoid the degradation of one or more ingredients of the formulation. Thus, the appropriate fibrillation temperature may be, in particular, below 200°C, or even below 100°C.

[0135] In the case where fibrillation is carried out by an internal mixer, the same conditions as for the extruder can be implemented.

[0136] Gelation

[0137] This gelation step of the electrolyte El can be initiated by thermal activation by increasing the temperature and / or by photochemical activation, for example by UV irradiation, in particular by irradiation using a UV lamp with wavelength between 200 and 500 nm, preferably between 300 and 400 nm.

[0138] Thermal activation can be carried out at temperatures between 40 and 200°C, preferably between 40 and 130°C, and in particular between 40 and 100°C

[0139] According to an embodiment of the second alternative, fibrillation and gelation can be carried out in the same equipment, at the gelation temperature discussed above. They can be conducted simultaneously or successively.

[0140] Formatting

[0141] According to one or the other of the alternatives, the shaping of the formulation aims to put the formulation into the form of a film, and / or to deposit the formulation and / or the film thus obtained on a current collector.

[0142] The shaping can typically be carried out by calendering using a heated roller calender, typically having a different or similar roller speed, or an external roller mixer.

[0143] The film thus obtained can then be deposited on a current collector to form an electrode.

[0144] According to another object, the present invention also relates to an electrochemical module comprising the stacking of at least two elements according to the invention, each element being electrically connected with one or more other element(s).

[0145] The term “module” therefore refers here to the assembly of several electrochemical elements, said assemblies being able to be in series and / or parallel.

[0146] Another object of the invention is yet another battery comprising one or more modules according to the invention.

[0147] The term “battery” or accumulator means the assembly of several modules according to the invention.

[0148] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings. Figures

[0149] [Fig. 1] [Fig. 1] illustrates the method according to the invention according to the first alternative.

[0150] [Fig. 2] [Fig. 2] illustrates the method according to the invention according to the second alternative.

[0151] [Fig.3] Fig.3 schematically represents the structure of a positive electrode prepared in dry mode before introduction of the liquid electrolyte part.

[0152] [Fig.4] Figure 4 illustrates the structure of a positive electrode prepared by dry method after introduction of the liquid electrolyte portion and gelation of EL

[0153] [Fig.5] The [Fig.5] illustrates the study of the gelation range of a PVDF-HFP binder with a liquid electrolyte.

[0154] [Fig.6] Fig.6 (A and B) illustrates the cycling results at 25°C for a battery button prepared in the examples. Examples Example 1: Preparation of the positive electrode

[0155] The formulation used for the production of dry-process positive electrodes for a polymer electrolyte-based element comprises: NMC622 or 811 type active material, an electronic conductor (carbon black), a mechanical binder (PTFE) and PVDF-HFP as an ionically conductive gelling binder.

[0156] In a first step, the NMC, the CB and the two binders are mixed in order to be distributed homogeneously.

[0157] This step is carried out in a planetary mixer.

[0158] Next, the mechanical binder is fibrillated. This step can be carried out either in a planetary mixer or in a twin-screw extruder or an internal mixer.

[0159] During this step, the mechanical binder is transformed, changing from a spherical particle to a fiber. This gives the electrode its mechanical strength.

[0160] The second step consists of shaping the electrode and placing it on a current collector. A calender is then used.

[0161] Fig. 3 represents the structure after shaping, comprising the active material 1 and the conductor 3, and the gelling binder 4 distributed in the fibre network made up of the fibrillated mechanical binder 2. This formulation is deposited on a current collector 5.

[0162] Once the electrode is made ([Fig.3]), it is assembled and then impregnated with a liquid electrolyte.

[0163] Upon contact with the gelling ionic conductive binder, heated to 60°C, the liquid and the latter will form a gel represented in [Fig.4]: a matrix 6 consisting of the gelling binder, lithium salts and solvent incorporates the fibril network of the mechanical binder 3 and within which the active material 1 and the conductor 3 are distributed. The gel thus formed is deposited on a current collector 5.

[0164] Since the content of gelling binder and the proportion of porosity of the electrode (therefore of liquid electrolyte which will be introduced) are controlled, it is therefore possible to modulate the ratio of gelling polymer / liquid electrolyte and thus define the desired polymer content.

[0165] As shown in [Fig.4], after shaping the electrode, it has a good mechanical structure due to the fibrous PTFE binder which helps to hold the different particles together.

[0166] The porosity content of the electrode is fixed during the implementation of the electrode, this depending on the desired ratio of gelling polymer electrolyte / liquid electrolyte. Furthermore, since PTFE has no particular affinity for the electrolyte, it can therefore properly play its role as a mechanical binder.

[0167] Once the liquid electrolyte is introduced, the system is heated to 60°C in order to gel the ionically conductive binder (PVDF-HFP). A gel polymer (GPE, Gel Polymer Electrolyte) is then formed within the positive electrode. Example 2: Properties

[0168] To ensure proper gelation of the PVDF-HFP polymer, various ex-situ tests were first carried out: several types of PVDF-HFP were selected, as well as different types of liquid electrolytes. For each case, different PVDF-HFP / liquid electrolyte ratios were tested to determine the range within which the polymer is capable of gelling. In addition, the impact of temperature on the gelling capacity of these systems was studied.

[0169] For a given liquid electrolyte, regardless of the type of PVDF-HFP, it has been shown that gelation occurs advantageously from a PVDF-HFP content of around 10% by mass up to 30% by mass.

[0170] Indeed, below 10%, the mixture may be liquid, while above 30%, the quantity of liquid electrolyte may not be sufficient to saturate the entire polymer.

[0171] The gel structure also changes with the PVDF-HFP content. Figure 5 illustrates, for a given PVDF-HFP, how the gel structure changes as a function of the polymer / liquid electrolyte ratio. Example 3: Electrochemical characterizations

[0172] In order to electrochemically test the prepared positive electrodes, these electrodes were gelled (introduction of liquid electrolyte at 25°C for 2h then the electrode is heated to 60°C to activate gelling) and then assembled with a separator soaked in electrolyte E2 and a Li metal counter electrode.

[0173] The SEL that has been prepared comprises a standard Celgard separator soaked in a solution containing liquid electrolyte (approximately 90%) and a monomer, TMPTA (approximately 10%).

[0174] The latter was polymerized and crosslinked using thermal activation (12h at 70°C).

[0175] Given the weights used (21-24 mg / cm²) and the Li metal counter electrode, the formation regimes (C / 20 and D / 20) and the cycling regimes (C / 10 and D / 10) were intentionally chosen to be slow. The theoretical capacity of the system is 7.5 mAh and the actual capacity recovered during the formation carried out at 25°C is 7.4 mAh.

[0176] The cycling results at 25°C are described in [Fig.6].

Claims

Demands

1. Electrochemical element comprising: - A positive electrode comprising • at least one active material; • a mechanical binder; • a solid gel-type electrolyte comprising • an ionically conductive gelling binder, • an electrolyte El comprising a lithium salt and a solvent, such that said ionically conductive gelling binder is selected from poly(vinylidene-co-hexafluoropropylene fluoride) (PVDF-HFP), poly(oxyethylene) (POE) and its derivatives, poly(trimethylene carbonate) (PTMC), polycaprolactone (PCL), polyethylene carbonate (PEC), polypropylene copolymer (PPC), polyacrylonitrile (PAN), acrylates, hydrogenated acrylonitrile butadiene rubber (HNBR), and cellulose and its derivatives; • optionally a carbon-based electronic conductor;and - A porous separator whose pores are impregnated with a gel-type electrolyte E2 comprising a matrix which is a polymer obtained by crosslinking a monomer comprising at least two acrylate groups into which is incorporated a mixture comprising at least one solvent, at least one lithium salt and a radical polymerization initiator; - A negative electrode comprising an active material.

2. Element according to claim 1 such that the mass ratio (ionic conductive gelling binder / electrolyte El) is between 10 and 50%, preferably between 20 and 30%.

3. Element according to claim 1 or 2 wherein said mechanical binder is selected from polytetrafluoroethylene (PTFE) and polyvinylidene tetrafluoroethylene fluoride (PVDF-TFE) and mixtures thereof.

4. An element according to any one of the preceding claims, wherein said lithium salts of electrolytes E1 and E2, whether identical or different, are selected from lithium perchlorate LiC104, lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsF6, lithium hexafluorantimonate LiSbF6, lithium trifluoromethanesulfonate LiCF3SO3, lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), lithium bis(trifluoromethanesulfonyl)imidide LiN(CF3SO2)2 (LiTFSI), lithium tris(fluoromethanesulfonyl)methylide LiC(CF3SO2)3 (LiTFSM), lithium bis(pentafluoroethylsulfonyl)imidide LiN(C2F(SO2)2) (LiBeTI), the lithium-4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LIDFOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (LiFAP), lithium difluorophosphate LiPO2F2,and their mixtures.

5. An element according to any one of the preceding claims such that the positive electrode does not contain a radical polymerization initiator.

6. An element according to any one of the preceding claims, such that the solvent of the electrolyte El is selected from saturated cyclic carbonates, unsaturated cyclic carbonates and linear carbonates, ethers and their derivatives.

7. Electrochemical element according to any one of the preceding claims, wherein said solvent of electrolyte E2 is a cyclic carbonate or a linear carbonate or a mixture thereof, in particular fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) and a mixture thereof.

8. Electrochemical element according to any one of the preceding claims, wherein the radical polymerization initiator present in the separator is azobisisobutyronitrile (AIBN).

9. Electrochemical element according to any one of the preceding claims, wherein said monomer of electrolyte E2 is trimethylolpropane triacrylate (TMPTA).

10. A method for preparing an element according to any one of the preceding claims comprising: - The preparation of the positive electrode, comprising: • The fibrillation of a mixture of the active material, the mechanical binder, the ionically conductive gelling binder, and optionally the electronically conductive material in powder form; • The shaping of the fibrillated mixture into a film and the deposition of said film onto a positive electrode current collector; - The assembly of said positive electrode thus formed with said separator impregnated with gel electrolyte E2, and said negative electrode; - The impregnation of said positive electrode with said electrolyte El in liquid form comprising said lithium salt and said solvent; and - The gelation of said positive electrode by thermal activation.

11. A method for preparing an element according to any one of claims 1 to 9 comprising: - The preparation of a positive electrode composition comprising the mixture of said active material, mechanical binder, ionically conductive gelling binder, and optionally electronically conductive material with said electrolyte El in liquid form comprising said lithium salt and said solvent; - The fibrillation and gelling of said mixture; - The shaping of the gelled fibrillated mixture into a film and the deposition of said film on a current collector; - The assembly of said collector thus coated with said separator impregnated with the gel electrolyte E2, and said negative electrode.

12. A method according to claim 10 or 11 wherein fibrillation is carried out by extrusion and / or by mixing within an internal mixer or a planetary mixer.

13. A method according to claim 10, 11 or 12 wherein gelation includes thermal activation by increasing the temperature between 40 and 200°C, preferably between 40 and 130°C.

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