Electrolyte composition comprising a charge-transfer complex, a lithium salt and a polymer, and applications thereof

Abstract

The present invention relates to an electrolyte composition comprising a lithium salt, a charge-transfer complex formed from an electron acceptor precursor of the charge-transfer complex and an electron donor precursor of the charge-transfer complex, a film-forming polymer, and a solvent. The invention also relates to a method for preparing this electrolyte composition; the use of the electrolyte composition for preparing a solid electrolyte in the form of a flexible film; a method for preparing a solid electrolyte in the form of a film by applying a coat of the electrolyte composition; the solid electrolyte in the form of a flexible film that can be obtained by implementing this method; a method for producing a rechargeable lithium metal battery comprising such a solid electrolyte; and a rechargeable lithium metal battery comprising the solid electrolyte.

Description

Electrolyte composition comprising a charge transfer complex, a lithium salt and a polymer, and applications

[0001] The present invention relates to an electrolyte composition comprising a lithium salt, a charge-transfer complex formed from an electron-accepting precursor of said charge-transfer complex and an electron-donating precursor of said charge-transfer complex, a film-forming polymer, and a solvent. It also relates to a method for preparing this electrolyte composition, the use of said electrolyte composition for preparing a solid electrolyte in the form of a flexible film, a method for preparing a solid electrolyte in the form of a film by coating said electrolyte composition, the solid electrolyte in the form of a flexible film obtainable by implementing this method, a method for manufacturing a rechargeable lithium-metal battery comprising such a solid electrolyte, and a rechargeable lithium-metal battery comprising said solid electrolyte.

[0002] The invention typically applies to the field of lithium batteries, and in particular to all-solid-state lithium batteries, especially for integration into applications such as electric vehicles and / or storage of intermittent energies such as solar and / or wind power.

[0003] Lithium Metal Polymer (or "LMP") batteries currently on the market ® "") are "all-solid-state" batteries, generally in the form of a thin film wound several times or several stacked thin films. This wound or stacked thin film is approximately one hundred micrometers thick. It typically comprises at least four functional films: a negative electrode (anode) that supplies lithium ions during discharge; a positive electrode (cathode) that acts as a receptacle where the lithium ions are intercalated; a solid polymer electrolyte that conducts lithium ions and is located between the positive and negative electrodes; and a current collector connected to the positive electrode to provide the electrical connection.The negative electrode is usually made of a metallic lithium foil or a lithium alloy; the solid polymer electrolyte is usually composed of a poly(ethylene oxide) (POE) based polymer and at least one lithium salt; the positive electrode comprises an active electrode material, usually based on a metal oxide (such as V2O5, LiV3O8, LiCoO2, LiNiO2, LiMn2O4 or LiNi). 0.5 Mn 0.5 O2) or based on a LiMPO4 type phosphate where M represents a metallic cation selected from the Fe, Mn, Co, Ni and Ti group, and one of their combinations, and possibly carbon; and the current collector is generally made of a metal foil.

[0004] Solid polymer electrolytes offer a significant safety advantage by eliminating the need for potentially hazardous solvents in case of overheating. Such batteries can therefore operate at high temperatures without risk of explosion. However, commonly used polymer electrolytes, such as high molecular weight POE doped with lithium salt, have low ionic conductivity at room temperature, so their operating temperature must be kept relatively high (typically between 70 and 100°C). At these temperatures, however, POE becomes a viscous liquid and loses its dimensional stability. Furthermore, attempts to improve the ionic conductivity of POE by adding plasticizers have led to a deterioration of its mechanical properties.

[0005] It was then proposed to douse POE with a lithium salt or to prepare cationically conductive anionic polymers such as a polystyrene bearing lithium (trifluoromethylsulfonyl)imidide groups. This ionic polystyrene is then used in a mixture with POE to create an electrolyte membrane containing no additional lithium ions. However, the results obtained show a relatively low ionic conductivity for temperatures below 60°C (e.g., on the order of 3.1 x 10⁻³⁴). -6 S / cm).

[0006] US patent application US2018 / 151914A1 proposes solid electrolytes comprising an electron-donating polymer selected from polyphenylene sulfide (PPS), p-phenylene polyoxide (PPO), polyether ether ketone (PEEK), polyphthalamide (PPA), polypyrrole, polyaniline, a liquid crystal polymer (LCP), and polysulfone; a lithium salt; and an electron-accepting dopant selected from 2,3-dicyano-5,6-dichlorodicyanoquinone (DDQ), tetrachloro-1,4-benzoquinone (chloranil), tetracyanoethylene (TCNE), sulfur trioxide (SO3), ozone (O3), oxygen (O2, air), and transition metal oxides (manganese dioxide, MnO2). The electron-donating polymer provides ionic conduction. In particular, PPS and chloranil are mixed in a molar ratio of 4.2:1. The mixture is then heated to a temperature of up to 350°C for 24 hours at atmospheric pressure.A color change is observed, confirming the formation of a charge-transfer complex. The reaction mixture is then ground to obtain particles ranging from 1 to 40 micrometers in diameter, and then LiTFSI powder (12% by weight of the total mixture) is added to the reaction mixture to obtain a solid polymer electrolyte. This electrolyte is described as being usable alone as an electrolyte and separator or in combination with a conventional separator and a liquid electrolyte. In the first case, the solid polymer electrolyte can be thermoformed onto the anode or cathode by being heated and fixed, as in a rolling process, or by being co-extruded and thus formed with the electrode. The reported ionic conductivities at room temperature range from 2.2 x 10⁻¹⁰. -4 S / cm at 1.3 x 10 3S / cm. The examples do not specify the shaping of the solid polymer electrolyte and how it is integrated into a battery as an electrolyte. Furthermore, the aforementioned electron-donating polymers are not easily manipulated to produce electrolytes. They are difficult to soluble and / or require high temperatures (e.g., 250°C) to be processed. Finally, in all-solid-state lithium batteries, the lithium metal anode, although offering the highest energy density, has a low redox potential, which leads to the degradation of most of the materials used.Some solid electrolytes based on an electron-donating polymer (poly(2,6-dimethyl-p-phenylene sulfide, PMPS), an electron-accepting dopant (7,7,8,8-tetracyanoquinodimethane, TCNQ) and a lithium salt (LiTFSI) have also shown a current drop during charge / discharge cycles in a LiFePO4-Li cell probably linked to the appearance of a passivation layer on the lithium, thus preventing the transport of ions.

[0007] The object of the present invention is to overcome all or part of the drawbacks of the aforementioned prior art and to provide a solid electrolyte that can be used in a rechargeable all-solid lithium metal battery, said solid electrolyte having good properties in terms of mechanical strength and ionic conduction both at room temperature (25°C) and at a temperature of 60 to 80°C, all while reducing or eliminating dendritic growth within the battery in which it is likely to be incorporated in order to guarantee good electrochemical performance, in particular in terms of cycle life and faradaic efficiency, said battery thus being able to be used safely.

[0008] These goals are achieved by the invention which will be described below.

[0009] The inventors of the present application have indeed discovered, surprisingly, that it is possible to form a solid electrolyte in the form of a flexible film using an electrolyte composition comprising a selected lithium salt, a charge-transfer complex formed from an electron-accepting precursor of said charge-transfer complex and an electron-donating precursor of said charge-transfer complex, a selected film-forming polymer and a selected solvent, said solid electrolyte exhibiting good mechanical properties and improved ionic conduction properties both at room temperature and at temperatures of 60 to 80°C.

[0010] The invention therefore has as its primary object an electrolyte composition comprising at least one lithium salt, a charge transfer complex formed from a precursor of said charge transfer complex, electron acceptor, and a precursor of said charge transfer complex, electron donor, a film-forming polymer and an organic solvent, said electrolyte composition being characterized in that:

[0011] - The lithium salt is selected from lithium bis(trifluoromethanesulfonyl) imidide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl) imidide (LiFTFSI) and mixtures thereof, and is present in a mass quantity Q Li ,

[0012] - the precursor of said charge-transfer complex, electron acceptor, corresponds to the following formula (I):

[0013] ,

[0014] in which:

[0015] - R 1 , R 2 , R 3 , and R 4These symbols, whether identical or different, represent a hydrogen atom, a halogen atom, or an electron-withdrawing group chosen from -CN, -CH(CN)2, -NO2, and -C(=O)R 9 , R 9 being an alkyl, aryl or aryl-alkyl radical,

[0016] - the precursor of said charge-transfer complex, electron donor, corresponds to the following formula (II):

[0017] ,

[0018] in which R 5 , R 6 , R 7 , and R 8 , identical or different, represent a hydrogen atom or an electron-donating group chosen from an alkyl radical and an alkoxy radical,

[0019] - the charge transfer complex is present in a quantity by mass Q CTC ,

[0020] - the film-forming polymer is a copolymer of vinylidene fluoride and hexafluoropropylene (PVdF-HFP) and is present in an amount greater than or equal to 5% by mass relative to the total mass of the electrolyte composition,

[0021] - the solvent is chosen from among aprotic polar organic solvents,

[0022] and in that:

[0023] - the quantity Q Li represents at least 30% of the total mass Q Li + Q CTC .

[0024] Thanks to the presence of a suitably selected lithium salt, combined with a charge-transfer complex obtained from precursors of formulas (I) and (II), with said lithium salt present in a proportion exceeding approximately 30% by mass, and a PVdF-HFP copolymer in an amount exceeding 5% by mass in the electrolyte composition, it is possible to obtain, after solvent evaporation, a solid electrolyte in the form of a flexible film exhibiting good mechanical strength (self-supporting and easy to handle), and improved ionic conductivity both at room temperature and at higher temperatures, particularly in the range of 60 to 80°C. This is quite surprising given that the PVdF-HFP copolymer is not an ionic conductor.

[0025] Charge-transfer complexes are characterized by a partial intermolecular transfer of electrons between electron donors and acceptors. The charge-transfer complex of the invention is capable of transporting lithium ions in the solid state.

[0026] The quantity Q LI of lithium salt preferably represents at least about 40% by mass, particularly preferably at least about 50% by mass, and even more preferably at least about 60% by mass relative to the total mass Q Li + Q CTC This allows for the improvement of the ionic conductivity of said electrolyte composition.

[0027] According to a preferred embodiment of the invention, the lithium salt is LiTFSI.

[0028] The precursor of said charge-transfer complex, electron acceptor, of formula (I)

[0029] The halogen atom can be an atom of iodine, bromine, chlorine or fluorine, and preferably a chlorine atom.

[0030] The electro-withdrawing group is chosen from -CN, -CH(CN)2, -NO2, and -C(=O)R 9 , R 9 being an alkyl, aryl or aryl-alkyl radical.

[0031] The alkyl radical as the R group 9 can be linear, branched, cyclic or non-cyclic, and preferably linear.

[0032] The alkyl radical as the R group 9 may comprise from 1 to 5 carbon atoms, preferably from 1 to 3 carbon atoms, and particularly preferably is a methyl radical.

[0033] The aryl radical as the R group 9 is a monocyclic or polycyclic aromatic hydrocarbon group, which may comprise from 4 to 20 carbon atoms, preferably from 5 to 15 carbon atoms, and particularly preferably is a phenyl radical.

[0034] The alkyl-aryl radical as the R group 9 It comprises at least one alkyl radical and at least one aryl radical that are directly linked by a carbon (of the alkyl radical)-carbon (of the aryl radical) covalent bond. It can be covalently linked to the carbonyl carbon by either the alkyl radical or the aryl radical. The definitions of the alkyl and aryl radicals are as described above. Preferably, the alkyl-aryl radical is a benzyl radical.

[0035] The preferred electron-withdrawing groups are halogen atoms.

[0036] In a particularly preferred embodiment, the precursor of said charge-transfer, electron-accepting complex of formula (I) is benzoquinone (i.e., R 1 , R 2 , R 3 , and R 4 are identical and represent a hydrogen atom).

[0037] The precursor of said charge-transfer complex, electron donor, of formula (II)

[0038] The electron-donating group is chosen from an alkyl radical and an alkoxy radical, and preferably an alkyl radical.

[0039] The alkyl radical as an electron-donating group can be linear, branched, cyclic or non-cyclic, and preferably linear.

[0040] The alkyl radical as an electron-donating group can comprise from 1 to 5 carbon atoms, preferably from 1 to 3 carbon atoms, and particularly preferred is a methyl radical.

[0041] The alkoxy radical as an electron-donating group can be linear, branched, cyclic or non-cyclic, and preferably linear.

[0042] The alkoxy radical as an electron-donating group can comprise from 1 to 5 carbon atoms, preferably from 1 to 3 carbon atoms, and particularly preferred is a methoxy radical.

[0043] In a preferred embodiment, the precursor of said charge-transferring, electron-donating complex of formula (II) is hydroquinone (i.e., R 5 , R 6 , R 7 , and R 8 are identical and represent a hydrogen atom).

[0044] According to a preferred embodiment of the invention, the precursors of said charge-transfer complex are used in the electrolyte composition in an electron acceptor precursor / electron donor precursor molar ratio of 0.8 to 1.2 and particularly preferred of 0.95 to 1.05. A molar ratio of 1 is particularly preferred.

[0045] The copolymer of vinylidene fluoride and hexafluoropropylene preferably represents about 7.5 to 12.5%, and more preferably about 7.5% by mass, relative to the total mass of the electrolyte composition.

[0046] As a polar aprotic organic solvent, we can in particular mention ketones such as acetone, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), tetrahydrofuran (THF) and dimethylacetamide (Dmac).

[0047] According to a particularly preferred embodiment of the invention, the aprotic polar organic solvent is acetone.

[0048] According to a preferred embodiment, the organic solvent content is about 40 to 70% by mass relative to the total mass of the electrolyte composition.

[0049] The second object of the invention is a method for preparing an electrolyte composition as defined according to the first object of the invention, said method being characterized in that it comprises at least the following steps:

[0050] 1) a step of dissolving a vinylidene fluoride and hexafluoropropylene copolymer in a polar aprotic organic solvent, to obtain a solution S1,

[0051] 2) the addition to the solution obtained in step 1) above, either i) of a charge-transfer complex previously formed from a precursor of said charge-transfer complex, electron acceptor, and a precursor of said charge-transfer complex, electron donor, or ii) of a precursor of said charge-transfer complex, electron acceptor, and a precursor of said charge-transfer complex, electron donor, said charge-transfer complex and said precursors being as defined according to the first object of the invention, to obtain a solution S2, and

[0052] 3) the addition to the solution S2 obtained in the previous step, of a quantity Q Liof a lithium salt selected from lithium bis(trifluoromethanesulfonyl) imidide, lithium (fluorosulfonyl)(trifluoromethanesulfonyl) imidide and mixtures thereof, to obtain a solution S3 to obtain said electrolyte composition.

[0053] Steps 1) to 3) of the process defined above are preferably carried out at room temperature, under stirring.

[0054] The duration of step 1) can vary from approximately 2 to 15 hours.

[0055] The aprotic polar organic solvent of step 1) is preferably acetone.

[0056] The duration of steps 2) and 3) can vary from approximately 5 to 10 minutes each.

[0057] According to one embodiment of this process, and where step 2) uses a previously formed charge transfer complex, said charge transfer complex may further be prepared according to a prior process comprising the following steps:

[0058] a) the mixture of precursors of formulas (I) and (II) as defined according to the first object of the invention,

[0059] b) the addition of said precursors to a polar aprotic organic solvent, under agitation in an airtight container to form a suspension,

[0060] c) evaporation of the aprotic polar organic solvent, at room temperature under stirring, to obtain a charge-transfer complex in the form of a solid material,

[0061] d) drying of said solid material at room temperature,

[0062] e) grinding said solid material to obtain a charge transfer complex in the form of a powder. Step a)

[0063] Step a) is a mixing step of the precursors of said charge transfer complex, electron donor and electron acceptor.

[0064] Step a) is preferably carried out under an inert atmosphere.

[0065] Step a) is preferably carried out by dry method. In particular, the precursors of the charge transfer complex are used in step a) in powder form.

[0066] Step a) is carried out at room temperature, i.e. at a temperature of approximately 18 to 25°C. Step b)

[0067] In step b), the polar aprotic organic solvent is preferably acetone.

[0068] Each of the said precursors can represent from 1 to 10% by mass approximately, and preferably from 4 to 6% by mass approximately, relative to the total mass of the suspension.

[0069] Step b) is preferably carried out under stirring. This allows a homogeneous suspension to be formed.

[0070] Step b) preferably includes maintaining agitation for at least 3 hours after the addition of the organic solvent.

[0071] According to one embodiment of the invention, step b) is carried out in a sealed container. This prevents premature evaporation of the solvent and maintains the equimolar donor / acceptor ratio.

[0072] Step b) is carried out at room temperature, i.e. at a temperature of approximately 18 to 30°C. Step c)

[0073] This step c) is carried out at low temperatures, which allows control of the molar ratio of the precursors. This notably prevents their sublimation.

[0074] The duration of step c) is preferably from 30 minutes to 5 hours.

[0075] Step c) is preferably carried out under an inert atmosphere, for example under an argon flow, and in a glove box. Step d)

[0076] Step d) can be carried out in air or under vacuum and preferably under vacuum (i.e. pressure less than 10 mbar).

[0077] Step d) can last at least 24 hours, and preferably from 18 hours to 7 days. Step e)

[0078] Step e) is a grinding step of the solid from step d).

[0079] The charge transfer complex obtained at the end of step e) can have a particle size ranging from 0.5 to 100 µm, particularly preferably from 0.5 to 20 µm, and even more particularly preferred from 0.5 to 1.5 µm.

[0080] Following this preliminary process, the CTC powder thus obtained can be used immediately for step 2) or stored under an inert atmosphere, for example in a glove box, for later use.

[0081] As demonstrated in the examples illustrating this application, this embodiment (variant i) of step 2)) is particularly preferred insofar as the electrolyte composition obtained using a CTC previously formed in step 2) leads to a solid electrolyte exhibiting a higher ionic conductivity than that obtained when the CTC is formed from its precursors in step 2) according to variant ii).

[0082] According to another embodiment of this process and when step 2) implements the precursors of the charge transfer complex (variant ii)), each of the precursors implemented in step 2) can have a particle size ranging from 0.5 to 800 µm, and particularly preferably ranging from 20 to 500 µm.

[0083] A third object of the invention is the use of an electrolyte composition as defined according to the first object for the preparation of a solid electrolyte, in particular a solid electrolyte in the form of a flexible film.

[0084] A fourth object of the invention is a method for preparing a solid electrolyte in the form of a flexible film. This method is characterized in that it comprises at least the following steps:

[0085] - the coating of an electrolyte composition as defined according to the first object of the invention onto a support, and

[0086] - evaporation of the aprotic polar organic solvent under vacuum to form a solid electrolyte.

[0087] At the end of the evaporation step, the resulting solid electrolyte is in the form of a flexible film that can be easily separated from the support used to coat the electrolyte composition.

[0088] The coating step can, for example, be carried out using a coating bar (or, in English, a "Bar coater"), on a flat, non-porous surface, such as a stainless steel plate.

[0089] Preferably, the coating of the electrolyte composition has a thickness of approximately 150 to 300 µm, more preferably approximately 180 to 220 µm.

[0090] The solvent evaporation step leads to the drying of the coated electrolyte composition and its solidification into a flexible film. This evaporation is preferably carried out at a temperature of 18 to 30°C (ambient temperature).

[0091] The duration of the evaporation stage is preferably 10 to 24 hours, more preferably 10 to 12 hours. The solid electrolyte

[0092] The invention also relates, as a fifth object, to the solid electrolyte obtainable by implementing the process as defined above according to the fourth object of the invention. Such a solid electrolyte is characterized in that it is in the form of a self-supporting flexible film comprising a polymer matrix based on a vinylidene fluoride and hexafluoropropylene copolymer, said polymer matrix representing more than 10% by mass relative to the total mass of said solid electrolyte, said matrix containing:

[0093] - at least one lithium salt selected from lithium bis(trifluoromethanesulfonyl) imidide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl) imidide LiFTFSI and mixtures thereof, and

[0094] - at least one charge transfer complex formed from a precursor of said charge transfer complex, electron acceptor, and a precursor of said charge transfer complex, electron donor as defined according to the first object of the invention.

[0095] Such a solid electrolyte typically has a thickness of about 60 to 200 µm, more preferably about 80 to 100 µm.

[0096] According to a preferred embodiment of the invention, the polymer matrix represents 15 to 25% by mass and even more preferably 15 to 20% by mass relative to the total mass of said solid electrolyte.

[0097] The lithium salt content is preferably from 7.5 to 52.5% by mass and even more preferably from 22.5 to 37.5% relative to the total mass of said solid electrolyte.

[0098] The charge transfer complex content is preferably from 22.5 to 67.5% by mass and even more preferably from 22.5 to 37.5% relative to the total mass of said solid electrolyte. The use of solid electrolyte

[0099] The sixth object of the invention is the use of a solid electrolyte conforming to the fifth object or obtained according to a process conforming to the fourth object of the invention, in a rechargeable lithium metal battery.

[0100] The use of such a solid electrolyte in a rechargeable lithium metal battery leads to an energy storage device with excellent performance, in particular an ionic conductivity greater than or equal to 10 - 7 S.cm - 1 , preferably greater than or equal to 10 - 6 S.cm - 1 , in a particularly preferred manner greater than or equal to 1x10 - 6 S.cm- 1 , at room temperature or at a temperature of 80°C and more particularly preferably greater than or equal to 1.10 - 5 S.cm - 1 , at a temperature of 80°C.

[0101] The use of this solid electrolyte also limits the dendritic growth of lithium, thus enabling fast and safe charging. Indeed, the problem with lithium-metal battery technology is the formation of heterogeneous lithium electrodeposits (including dendrites) during charging, which reduces cycle life and can lead to short circuits. The solid electrolyte according to the present invention also exhibits good mechanical strength, high thermal stability (ensuring the safety of the energy storage devices incorporating it), and potential stability up to 3.7 V vs. Li + / Li.

[0102] The lithium battery manufacturing process

[0103] The invention also has as its seventh object a method for manufacturing a rechargeable lithium metal battery comprising a solid electrolyte as defined according to the fifth object of the invention or as obtained according to the method according to the fourth object of the invention, said manufacturing method being characterized in that it comprises at least:

[0104] - a step of positioning said solid electrolyte between a negative electrode comprising lithium metal or a lithium metal alloy and a positive electrode, optionally supported by a current collector, to form an assembly, and

[0105] - a thermal activation step at a temperature of at least 80°C.

[0106] The thermal activation step is essential to allow the solid electrolyte to transition from an insulating state to an ionic conductor state.

[0107] The duration of the thermal activation stage is preferably greater than or equal to approximately 24 hours, and even more preferably in the order of approximately 9 to 12 hours.

[0108] The temperature of the thermal activation stage is preferably around 80°C.

[0109] According to a particular and preferred embodiment of the invention, this thermal activation step is further carried out by subjecting said assembly to a pressure of at least 200 bars, and even more particularly of about 500 to 600 bars.

[0110] Applying such pressure during the thermal activation step improves the ionic conductivity of the solid electrolyte. Rechargeable lithium metal battery

[0111] The invention relates as an eighth object to a rechargeable lithium-metal battery, characterized in that it comprises:

[0112] - a negative electrode comprising lithium metal or a lithium metal alloy,

[0113] - a positive electrode, possibly supported by a current collector, and

[0114] - a solid electrolyte positioned between the positive and negative electrodes,

[0115] characterized in that the solid electrolyte conforms to the fifth object or is obtained according to a process conforming to the fourth object of the invention. The positive electrode

[0116] The positive electrode may include a positive electrode active material, optionally a polymer binder, and optionally an agent generating electronic conductivity. The active material of the positive electrode

[0117] The active material of the positive electrode is a reversible lithium ion active material. In other words, it can reversibly insert or remove lithium ions.

[0118] The active material of the positive electrode can be:

[0119] - a metal oxide such as vanadium oxide VO₂ x (2 ≤ x ≤ 2.5), LiV3O8, Li y Ni1 - x Co x O2(0 ≤ x ≤ 1 ; 0 ≤ y ≤ 1), a manganese spinel Li y Mn1 - x M x O2(M = Cr, Al, V, Ni, 0 ≤ x ≤ 0.5; 0 ≤ y ≤ 2), V2O5, a lithium oxide such as LiCoO2, LiNiO2, LiMn2O4, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 (NMC), LiNi 0,8 Co 0,15 Al 0,05 O2(NCA), or LiNi 0,5 Mn 0,5 O2,

[0120] - a phosphosilicate or metal phosphate, for example Li3V2(PO4)3 or LiMPO4, where M represents a metal cation selected from the Fe, Mn, Co, Ni and Ti group, and one of their combinations, or

[0121] - a metal sulfate, for example iron sulfate Fe2(SO4)3.

[0122] The active material of the positive electrode can represent approximately 50 to 90% by mass, and preferably approximately 55 to 80% by mass, relative to the total mass of the positive electrode. The agent generating electronic conductivity

[0123] The agent generating electronic conductivity can be chosen from carbon blacks, acetylene blacks, carbon fibers and nanofibers, carbon nanotubes, graphene, graphite, metallic particles and fibers of at least one conductive metal such as aluminum, platinum, iron, cobalt or nickel, and one of their mixtures.

[0124] The agent generating electronic conductivity is preferably carbon black.

[0125] The agent generating electronic conductivity can represent approximately 0.1 to 10% by mass, and preferably approximately 0.5 to 5% by mass, relative to the total mass of the positive electrode. The polymer binder

[0126] The polymer binder can represent approximately 10 to 50% by mass, and preferably approximately 20 to 40% by mass, relative to the total mass of the positive electrode.

[0127] The polymer binder can be chosen from ethylene homopolymers and copolymers; propylene homopolymers and copolymers; ethylene oxide homopolymers and copolymers (e.g.POE (POE copolymer), methylene oxide, propylene oxide, epichlorohydrin, allylglycidyl ether, and mixtures thereof; halogenated polymers such as homopolymers and copolymers of vinyl chloride, vinylidene fluoride (PVdF), vinylidene chloride, ethylene tetrafluoride, chlorotrifluoroethylene, or mixtures thereof; anionic non-conductive polymers such as poly(styrene sulfonate), poly(acrylic acid), poly(glutamate), alginate, pectin, gelatin, or mixtures thereof; Cationic polymers such as polyethyleneimine (PEI), polyaniline in the form of emeraldine salt (ES), quaternized poly(N vinylimidazole), poly(acrylamide-dialyldimethyl ammonium co-chloride) (AMAC) or mixtures thereof; polyacrylates; elastomers such as homopolymers or copolymers of ethylene, propylene, styrene, butadiene or chloroprene; and mixtures thereof.

[0128] The polymer binder can represent approximately 5 to 35% by mass, and preferably approximately 10 to 25% by mass, relative to the total mass of the positive electrode.

[0129] According to a preferred embodiment of the invention, the active material of the positive electrode is coated with a carbon layer. The presence of the carbon layer improves the interface between the active material and the polymer binder.

[0130] The carbon coating the active material preferably represents approximately 0.1 to 5% by mass, relative to the mass of active material.

[0131] The carbon layer is preferably in the form of a layer with a thickness varying from approximately 1 to 4 nm. Lithium salt

[0132] The positive electrode may also include a lithium salt.

[0133] The lithium salt can be chosen from lithium fluorate (LiFO3), lithium bis(trifluoromethanesulfonyl) imidide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium fluoroborate (LiBF4), lithium metaborate (LiBO2), lithium perchlorate (LiClO4), lithium nitrate (LiNO3), lithium bis(fluorosulfonyl) imidide (LiFSI), lithium bis(pentafluoroethylsulfonyl) imidide (LiBETI), LiAsF6, LiCF3SO3, LiSbF6, LiSbCl6, Li2TiCl6, Li2SeCl6, Li2B 10 Cl 10 , Li2B 12 Cl 12 , lithium bis(oxalato)borate (LiBOB), lithium (fluorosulfonyl)(trifluoromethanesulfonyl) imidide (LiFTFSI) and one of their mixtures.

[0134] Lithium salt preferably represents 5 to 30% by mass, and even more preferably 10 to 25% by mass, relative to the total mass of the positive electrode. The plasticizer

[0135] The positive electrode may also include a plasticizer.

[0136] The plasticizer (or non-aqueous solvent) can be chosen from:

[0137] - linear and cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl-isopropyl carbonate (MiPC);

[0138] - fluorinated carbonates such as fluoroethylene carbonate;

[0139] - nitriles such as succinonitrile;

[0140] - lactones such as gamma-butyrolactone;

[0141] - linear or cyclic liquid polyethers such as dimethyl ether, polyethylene glycol dimethyl ethers (or PEGDME) such as tetraethylene glycol dimethyl ether (TEGDME), or dioxolane;

[0142] - fluorinated polyethers;

[0143] - sulfur-containing solvents such as sulfolane or dimethyl sulfoxide;

[0144] - phosphates such as triethylphosphate or fluorophosphates;

[0145] - esters such as ethyl acetate or ethyl butyrate (EB); and

[0146] - one of their mixtures.

[0147] Among such solvents or plasticizers, linear and cyclic carbonates are particularly preferred.

[0148] The plasticizer can represent approximately 5 to 35% by mass, and preferably approximately 10 to 25% by mass, relative to the total mass of the positive electrode.

[0149] The positive electrode is preferably in the form of a film whose thickness is generally on the order of 20 to one hundred micrometers. The current collector

[0150] The rechargeable battery may also include a current collector, connected to the positive electrode.

[0151] The current collector is usually made of a sheet of metal.

[0152] The current collector is preferably a stainless steel or aluminum current collector, possibly coated with a carbon-based layer (anti-corrosion layer). The negative electrode

[0153] The negative electrode is preferably in the form of a film whose thickness is generally on the order of 1 to one hundred micrometers.

[0154] The negative electrode can be made of metallic lithium or one of the lithium alloys such as an alloy of lithium with sodium, silicon, tin, aluminum, magnesium, silver, zinc, or even germanium.

[0155] The negative electrode is preferably made of metallic lithium or one of the lithium alloys.

[0156] The present invention is illustrated by the following embodiments, to which it is not, however, limited.

[0157] The attached drawings illustrate the invention:

[0158] gives scanning electron microscopy (SEM) images of the solid electrolytes ES1 and ES2 of the invention prepared in examples 1 and 2 at different magnifications (Fig. 1a: ES2 at x50 magnification; Fig. 1b: ES2 at x100 magnification; Fig. 1c: ES1 at x50 magnification; Fig. 1d: ES1 at x100 magnification),

[0159] is a graph showing the ionic conductivity (S / cm) of solid electrolytes according to the invention (ES1, ES3 and ES4) compared to a comparative solid electrolyte not part of the invention (ES5), at 25°C (black bars) and at 80°C (grey bars),

[0160] is a graph giving the ionic conductivity (S / cm) of a solid electrolyte according to the invention (ES1) as a function of the applied pressure (MPa) during a thermal activation step in a characterization cell. EXAMPLES

[0161] The raw materials used in the examples are listed below:

[0162] - benzoquinone (Sigma Aldrich, purity 98%),

[0163] - hydroquinone (Sigma Aldrich, purity greater than or equal to 99%),

[0164] - extra dry acetone (Sigma Aldrich, 99.7% purity),

[0165] - PVdF-HFP copolymer sold under reference 427160 by Sigma Aldrich (CAS No. 9011-17-0),

[0166] - charge transfer complex obtained from benzoquinone and hydroquinone.

[0167] Unless otherwise stated, all materials were used as received from the manufacturers.

[0168] EXAMPLE 1: Preparation of a solid electrolyte according to the invention

[0169] A solid electrolyte ES1 according to the invention was prepared in the manner described below.

[0170] 1.1 Preparation of a charge-transfer complex CTC1

[0171] 0.1981 g of benzoquinone and 0.2019 g of hydroquinone (molar ratio of 1:1) were mixed under an inert atmosphere (glove box), and then 4 mL of acetone were added. The resulting mixture was placed under mechanical stirring for 2 hours in a closed container. The acetone solvent was then evaporated at room temperature (after opening the container) while maintaining stirring. The resulting solid material was dried under vacuum at room temperature for 7 days. The dried solid was then ground in a mortar to form a charge-transfer complex powder, designated CTC1, which was stored under an inert atmosphere (glove box). 1.2. Preparation of the solid electrolyte ES1

[0172] 0.2 g of PVdF-HFP were dissolved in 3 mL of acetone for 12 hours in a glove box.

[0173] 0.42 g of charge transfer complex CTC1 as obtained above in the previous step were added under stirring and at room temperature to the PVdF-HFP in acetone solution formed above, then 0.18 g of LiTFSI were then added, still under stirring until complete dissolution of the powders (approximately 5 to 10 minutes).

[0174] A viscous solution was obtained and coated onto a stainless steel plate using a coating bar. The coated viscous solution was then dried under vacuum at room temperature for 12 hours.

[0175] A solid electrolyte ES1 was obtained in the form of a film with a thickness of 100 µm and whose final composition (% by mass) was as follows:

[0176] - PVdF-HFP copolymer: 25%,

[0177] - Charge transfer complex CTC1: 52.5%

[0178] - lithium salt LiTFSI: 22.5%.

[0179] EXAMPLE 2: Preparation of a solid electrolyte according to the invention

[0180] A solid electrolyte ES2 according to the invention was prepared in the manner described below.

[0181] 0.2 g of PVdF-HFP copolymer were dissolved in 3 mL of acetone for 12 hours in a bag.

[0182] 0.2081 g of benzoquinone and 0.2119 g of hydroquinone (molar ratio of 1 / 1) were added at room temperature and under stirring to the PVdF-HFP solution in acetone prepared above, as well as 0.18 g of lithium salt LiTFSI, still under stirring until complete dissolution of the powders (approximately 5 to 10 minutes).

[0183] An electrolyte composition was obtained in the form of a viscous solution which was coated onto a stainless steel plate using a coating bar. The coated viscous solution was then dried under vacuum at room temperature for 12 hours.

[0184] A solid electrolyte ES2 was obtained in the form of a film with a thickness of 100 µm and whose final composition (% by mass) was as follows:

[0185] - PVdF-HFP copolymer: 25%,

[0186] - Charge transfer complex CTC1: 52.5%

[0187] - lithium salt LiTFSI: 22.5%.

[0188] EXAMPLE 3: Electrochemical characterizations of solid electrolytes ES1 and ES2 according to the invention compared to a pelletized solid electrolyte ESP not forming part of the invention

[0189] After drying, 10mm diameter discs are cut from the electrolyte films ES1 and ES2 as prepared above in examples 1 and 2 above in order to be introduced into an electrochemical characterization cell called an "all-solid cell": stainless steel / solid electrolyte / stainless steel (ref. KP-Solid Cell sold by Hohsen Corp. Japan).

[0190] For comparison, a non-conforming solid electrolyte pelletized according to the present invention ESPa was also prepared by mixing the constituents in powder form, namely 0.2081 g of benzoquinone and 0.2119 g of hydroquinone (molar ratio of 1:1) with 0.18 g of lithium salt LiTFSI. The resulting powder mixture was then pelletized in the chemical characterization cell at a pressure of approximately 55 MPa using a torque wrench, in the form of a compact pellet with a diameter of 10 mm and a thickness of 300 µm.

[0191] For each of the electrolytes ES1 and ES2, pressure was also applied to the film when closing the cell using a torque wrench of approximately 55 MPa.

[0192] The solid electrolytes ES1, ES2, and ESP require thermal activation to change from insulators to ionic conductors. This activation was carried out under pressure (in the electrochemical characterization cell) at 80°C for a minimum of 9 hours.

[0193] The ionic conductivity of electrolytes ES1, ES2 and ESPa was then measured at 25°C and 80°C by impedance spectroscopy using a device sold under the commercial name VMP300 by the company Biologic, in potentiostatic mode between 100 mHz and 1 MHz for an amplitude of 100 mV.

[0194] Table 1 below gives the values ​​of ionic conductivities obtained:

[0195] Solid electrolyte Ionic conductivity at 25°C (S / cm) Ionic conductivity at 80°C (S / cm) ES12.10 -6 2.10 -4 ES23,6.10 -6 1,2.10 -5 ESP*1.10 -6 7.9.10 -6

[0196] (*) Comparative electrolyte not forming part of the invention

[0197] According to the results presented in Table 1 above, the electrolytes ES1 and ES2 in film form according to the invention exhibit higher ionic conductivity values ​​than the electrolyte in powder form. Furthermore, the ionic conductivities are higher for electrolyte ES1, with values ​​around 2 x 10⁻¹³. -4 S.cm -1 at 80°C and values ​​between 10 -5 and 10 -4 S.cm -1At room temperature (25°C), a gain of an order of magnitude is observed for both temperatures between electrolyte ES1, based on the already formed CTC, and electrolyte ES2. Furthermore, the difference in conductivity between the values ​​at 80°C and room temperature is smaller (less than an order of magnitude) for electrolyte ES2 in film form according to the invention, compared to electrolyte ESP, which is not part of the invention. Without wishing to be bound by any particular theory, the inventors of this application believe that this better ionic conductivity of solid electrolyte ES1 compared to solid electrolyte ES2 can be explained by differences in morphology. Indeed, as can be seen from the attached images which provide scanning electron microscopy (SEM) images of the solid electrolytes ES1 and ES2 at different magnifications (Fig. 1a: ES2 at x50 magnification; Fig. 1b: ES2 at x100 magnification; Fig. 1c: ES1 at x50 magnification; Fig.1d: ES1 at magnification x100), the CTC grains are smaller for the CTC of the electrolyte ES1 already formed because it is not soluble in acetone compared to the electrolyte ES2 whose CTC is formed during the preparation of the coating solution.

[0198] EXAMPLE 4: Preparation and study of the ionic properties of solid electrolytes with different PVdF-HFP copolymer ratios

[0199] Solid electrolytes were prepared following the preparation protocol of Example 1, but varying the amounts of PVdF-HFP copolymer used so as to obtain electrolyte films with different PVdF-HFP copolymer contents.

[0200] The composition of the different solid electrolytes thus prepared (% by mass) is given in Table 2 below:

[0201] Solid electrolytePVdF-HFPCTC1LiTFSIES12552,522,5ES3205624ES41559,525,5ES5 (*)106327

[0202] (*) Comparative electrolyte not forming part of the invention

[0203] The ionic conductivity of each of these solid electrolytes was tested in an electrochemical characterization cell in accordance with the protocol set out in Example 3 above, at 25°C and 80°C.

[0204] The corresponding results are given by the appendix on which the ionic conductivity (S / cm) is given for each of the solid electrolytes ES1, ES3, ES4 and ES5, at 25°C (black bars) and at 80°C (grey bars).

[0205] Although it exhibited acceptable ionic conductivity, particularly at a temperature of 80°C, the solid electrolyte ES5 with 10% by mass of PVdF-HFP copolymer (therefore not part of the invention), did not, however, exhibit sufficient mechanical strength to be handled.

[0206] The 15% (ES4), 20% (ES3), and 25% (ES1) solid electrolytes of PVdF-HFP copolymer according to the invention all possessed sufficient film adhesion and good mechanical strength. Furthermore, the 15% and 20% PVdF-HFP copolymer electrolytes demonstrated the highest ionic conductivity properties, ranging from 10 -4 and 10 -3 S / cm, both at 80°C and at room temperature (25°C).

[0207] Similar tests were carried out according to the same protocol, replacing the PVdF-HFP copolymer in electrolyte ES1 with 25% by mass of other polymer binders, namely poly(butyl methacrylate) (PBMA) and poly(methyl methacrylate) (PMMA). Neither of the two solid electrolytes obtained using the other polymer binders exhibited sufficient mechanical strength for handling.

[0208] EXAMPLE 5: Demonstration of the effect of the pressurization step of the solid electrolyte on its ionic conductivity

[0209] A study of the pressure value applied to solid electrolytes was carried out in order to investigate the impact of pressure on their ionic conductivity values ​​measured at 80°C.

[0210] To this end, the solid electrolyte ES1, as prepared above in Example 1, was incorporated into an electrochemical characterization cell according to the protocol detailed above in Example 3, by applying varying pressures when closing the cell. The ionic conductivity was then measured at a temperature of 80°C, in potentiostatic mode between 100 mHz and 7 Hz for an amplitude of 10 mV.

[0211] The results are reported in the attached table, where the ionic conductivity (S / cm) is expressed as a function of the applied pressure (MPa) at the time the characterization cell was closed. These results show that the highest ionic conductivity values ​​with the lowest standard deviation were obtained at a pressure of 55 MPa.

Claims

An electrolyte composition comprising at least one lithium salt, a charge-transfer complex formed from an electron-accepting precursor of said charge-transfer complex and an electron-donating precursor of said charge-transfer complex, a film-forming polymer, and an organic solvent, said electrolyte composition being characterized in that: - the lithium salt is selected from lithium bis(trifluoromethanesulfonyl) imidide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl) imidide (LiFTFSI), and mixtures thereof, and is present in a mass quantity Q Li - the precursor of said charge-transfer complex, electron acceptor, corresponds to the following formula (I): , in which R 1 , R 2 , R 3 , and R 4 These symbols, whether identical or different, represent a hydrogen atom, a halogen atom, or an electron-withdrawing group chosen from -CN, -CH(CN)2, -NO2 and -C(O)R9 in which R 9 represents an alkyl, aryl or aryl-alkyl radical, - the precursor of said charge-transferring complex, electron donor, corresponds to the following formula (II): , in which R 5 , R 6 , R 7 , and R 8 These elements, whether identical or different, represent a hydrogen atom or an electron-donating group chosen from an alkyl radical and an alkoxy radical. The charge-transferring complex is present in a mass quantity Q. CTC - The film-forming polymer is a copolymer of vinylidene fluoride and hexafluoropropylene (PVdF-HFP) and is present in an amount greater than or equal to 5% by mass relative to the total mass of the electrolyte composition. - The solvent is chosen from among aprotic polar organic solvents, and in that: - the quantity Q Li represents at least 30% of the total mass Q Li + Q CTC . Electrolyte composition according to claim 1, characterized in that the quantity Q LI lithium salt represents at least 40% by mass relative to the total mass Q Li + Q CTC . Electrolyte composition according to claim 1 or 2, characterized in that the precursor of said charge-transfer complex, electron acceptor, is benzoquinone. Electrolyte composition according to any one of the preceding claims, characterized in that the precursor of said charge transfer complex, electron donors, is hydroquinone. Electrolyte composition according to any one of the preceding claims, characterized in that the precursors of said charge transfer complex are used in the electrolyte composition in an electron acceptor precursor / electron donor precursor molar ratio of 0.8 to 1.

2. Electrolyte composition according to any one of the preceding claims, characterized in that the vinylidene fluoride and hexafluoropropylene copolymer represents from 7.5 to 12.5% ​​by mass relative to the total mass of the electrolyte composition. Electrolyte composition according to any one of the preceding claims, characterized in that the aprotic polar organic solvent is acetone. A method for preparing an electrolyte composition as defined in any one of claims 1 to 7, characterized in that it comprises at least the following steps: 1) a step of dissolving a vinylidene fluoride-hexafluoropropylene copolymer in a polar aprotic organic solvent, to obtain a solution S1; 2) the addition to the solution S1 obtained in the preceding step of either i) a charge-transfer complex previously formed from an electron-accepting precursor of said charge-transfer complex and an electron-donating precursor of said charge-transfer complex, or ii) an electron-accepting precursor of said charge-transfer complex and an electron-donating precursor of said charge-transfer complex, said charge-transfer complex and said precursors being as defined in any one of claims 1, 3 and 4, to obtain a solution S2.and 3) the addition to the solution S2 obtained in the previous step, of a quantity Q, Li of a lithium salt selected from lithium bis(trifluoromethanesulfonyl) imidide, lithium (fluorosulfonyl)(trifluoromethanesulfonyl) imidide and mixtures thereof, to obtain a solution S3 to obtain said electrolyte composition. A process according to claim 8, characterized in that step 2) employs a previously formed charge transfer complex, and in that said charge transfer complex is prepared according to a prior process comprising the following steps: a) mixing the precursors of formulas (I) and (II) as defined in claim 1, b) adding said precursors to an aprotic polar organic solvent, under stirring in a sealed container to form a suspension, c) evaporating the aprotic polar organic solvent, at room temperature under stirring, to obtain a charge transfer complex in the form of a solid material, d) drying said solid material at room temperature, e) grinding said solid material to obtain a charge transfer complex in the form of a powder. A process according to claim 8 or 9, characterized in that the aprotic polar organic solvent is acetone. Use of an electrolyte composition as defined in any one of claims 1 to 7, for the preparation of a solid electrolyte. A process for preparing a solid electrolyte in the form of a flexible film, said process is characterized in that it comprises at least the following steps: - coating an electrolyte composition as defined in any one of claims 1 to 7 onto a support, and - evaporating the aprotic polar organic solvent under vacuum to form a solid electrolyte. Solid electrolyte obtainable by implementing the process as defined in claim 12, characterized in that it is in the form of a self-supporting flexible film comprising a polymer matrix based on a vinylidene fluoride and hexafluoropropylene copolymer, said polymer matrix representing more than 10% by mass relative to the total mass of said solid electrolyte, said matrix containing: - at least one lithium salt selected from lithium bis(trifluoromethanesulfonyl) imidide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl) imidide LiFTFSI and mixtures thereof, and - at least one charge-transfer complex formed from an electron-accepting precursor of said charge-transfer complex and an electron-donating precursor of said charge-transfer complex, said complex being as defined in any one of claims 1, 3 or 4. Use of a solid electrolyte as defined according to claim 13, in a rechargeable lithium metal battery. A method for manufacturing a rechargeable lithium metal battery comprising a solid electrolyte as defined according to claim 13, said manufacturing method being characterized in that it comprises at least: - a step of positioning said solid electrolyte between a negative electrode comprising lithium metal or a lithium metal alloy and a positive electrode, optionally supported by a current collector, to form an assembly, and - a step of thermal activation at a temperature of at least 80°C. Method according to claim 15, characterized in that the thermal activation step is further carried out by subjecting said assembly to a pressure of at least 200 bars. Rechargeable lithium metal battery, characterized in that it comprises: - a negative electrode comprising lithium metal or a lithium metal alloy, - a positive electrode, optionally supported by a current collector, and - a solid electrolyte positioned between the positive electrode and the negative electrode, characterized in that the solid electrolyte is as defined in claim 13.

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