Electrolyte composition comprising a charge-transfer complex and a lithium salt with improved ionic conduction properties

Abstract

The invention relates to an electrolyte composition comprising a lithium salt LiFTFSI, and 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, the electron acceptor precursor of the charge-transfer complex being benzoquinone or a derivative thereof, and the electron donor precursor of the charge-transfer complex being hydroquinone or a derivative thereof; a method for preparing the electrolyte composition; the use of the electrolyte composition in a rechargeable lithium metal battery or for preparing a solid electrolyte of a rechargeable lithium metal battery; a solid electrolyte for a rechargeable lithium metal battery comprising the electrolyte composition; and a rechargeable lithium metal battery comprising the solid electrolyte.

Description

electrolyte composition comprising a charge-transfer complex and a lithium salt with enhanced ionic conduction properties

[0001] The present invention relates to an electrolyte composition comprising a lithium salt, and 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, said lithium salt being (fluorosulfonyl)(trifluoromethanesulfonyl) lithium imidide LiFTFSI, said precursor of said charge transfer complex, electron acceptor, being benzoquinone or one of its derivatives, and said precursor of said charge transfer complex, electron donor, being hydroquinone or one of its derivatives.It also relates to a process for preparing said electrolyte composition, the use of said electrolyte composition in a rechargeable lithium metal battery or for the preparation of a solid electrolyte for a rechargeable lithium metal battery, a solid electrolyte for a rechargeable lithium metal battery comprising said electrolyte composition, and a rechargeable lithium metal battery comprising said solid electrolyte.

[0002] The invention relates more particularly to an electrolyte composition having improved ionic conduction properties while ensuring good stability.

[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] Other solid electrolytes were proposed in US patent application 2018 / 151914A1, 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] Thus, the aim of the present invention is to overcome the disadvantages of the aforementioned prior art and to provide an electrolyte composition which has improved ionic conduction properties and / or improved stability, while ensuring good mechanical strength, so that it can be used as a solid electrolyte in a rechargeable all-solid lithium metal battery.

[0008] The purpose of the invention is achieved by the electrolyte composition which will be described below.

[0009] The inventors of this application have indeed made a surprising discovery that it is possible to form an electrolyte composition with a specific charge-transfer complex and lithium salt in specific proportions, in order to improve ionic conduction and / or stability with respect to lithium metal.

[0010] The electrolyte composition

[0011] The invention has as its first object an electrolyte composition comprising: - a lithium salt, and - 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, characterized in that: - the lithium salt is the (fluorosulfonyl)(trifluoromethanesulfonyl) lithium imidide LiFTFSI, - the precursor of said charge transfer complex, electron acceptor, corresponds to the following formula (I):

[0012] , 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)R 9 , R 9 being an alkyl, aryl or aryl-alkyl radical, the precursor of said charge-transfer complex, electron donor, corresponds to the following formula (II):

[0013] , 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, and in that the lithium salt represents an amount greater than 30% by mass approximately, relative to the total mass of the electrolyte composition.

[0014] Thanks to the presence of a lithium salt LiFTFSI [(fluorosulfonyl)(trifluoromethanesulfonyl) lithium imidide] associated with a charge transfer complex obtained from the precursors of formulas (I) and (II), said lithium salt being present in a proportion greater than 30% by mass approximately, it is possible to form an electrolyte composition exhibiting improved ionic conduction and / or improved stability with respect to lithium metal.

[0015] 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.

[0016] Lithium salt preferably constitutes at least approximately 40% by mass, particularly preferably at least approximately 50% by mass, and even more preferably at least approximately 60% by mass of the total electrolyte composition. This improves the ionic conductivity of the electrolyte composition.

[0017] The electrolyte composition can be in powder form, as a film, a paste, or a very viscous liquid.

[0018] According to a preferred embodiment of the invention, the electrolyte composition is a solid composition, in particular in powder form or in the form of a film.

[0019] In the invention, the term "solid" is distinguished from a material or composition in the liquid phase. The atomic structure of solids may be crystalline or amorphous. A solid electrolyte composition according to the invention is ionically conductive through the solid and not through a solvent, gel, or liquid phase. Gelled (or wet) polymers and other materials whose ionic conductivity depends on liquids are defined as not being solid electrolyte compositions insofar as their ionic conductivity depends on a liquid phase.

[0020] The precursor of said charge-transfer complex, electron acceptor, of formula (I)

[0021] The halogen atom can be an atom of iodine, bromine, chlorine or fluorine, and preferably a chlorine atom.

[0022] The electro-withdrawing group is chosen from -CN, -CH(CN)2, -NO2, and -C(=O)R 9 , R 9being an alkyl, aryl or aryl-alkyl radical.

[0023] The alkyl radical as the R group 9 can be linear, branched, cyclic or non-cyclic, and preferably linear.

[0024] 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.

[0025] 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.

[0026] The alkyl-aryl radical as the R group 9It 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.

[0027] The preferred electron-withdrawing groups are halogen atoms.

[0028] 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 hydrogen atoms).

[0029] The precursor of said charge-transfer complex, electron donor, of formula (II)

[0030] The electron-donating group is chosen from an alkyl radical and an alkoxy radical, and preferably an alkyl radical.

[0031] The alkyl radical as an electron-donating group can be linear, branched, cyclic or non-cyclic, and preferably linear.

[0032] 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.

[0033] The alkoxy radical as an electron-donating group can be linear, branched, cyclic or non-cyclic, and preferably linear.

[0034] 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.

[0035] 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 hydrogen atoms).

[0036] 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.

[0037] The electrolyte composition may also include one or more additives chosen from among carbonates (fluorinated carbonates, vinylene carbonate) and dinitriles (malononitrile, glutaronitrile, sebaconitrile). This improves stability on lithium metal.

[0038] The additive(s) preferably represent an amount less than 10% by mass, and particularly preferably less than 5% by mass, relative to the total mass of the electrolyte composition.

[0039] The lithium salt and the transfer complex preferably constitute at least approximately 80% by mass, particularly preferably at least approximately 90% by mass, and particularly preferably at least approximately 95% by mass, of said electrolyte composition. In other words, the electrolyte composition of the invention differs from prior art electrolyte compositions in that it is not a so-called "polymer" or "polymer gel" electrolyte composition. In particular, it does not include any organic polymer(s) (e.g., polyoxyalkylenes such as POE, fluoropolymers such as PVdF, vinyl fluoride copolymers, PTFE, etc.).

[0040] The process of preparing the electrolyte composition

[0041] The invention has as its second object a process for preparing an electrolyte composition in accordance with the first object of the invention, characterized in that it comprises at least the following steps: i) mixing the charge transfer complex or its electron acceptor and electron donor precursors, with the lithium salt, ii) adding an organic solvent to form a suspension, and iii) evaporating the organic solvent at a temperature less than or equal to 50°C, to form a solid.

[0042] Step i)

[0043] Step i) includes mixing the charge transfer complex or its electron acceptor and electron donor precursors with the lithium salt.

[0044] Step i) is preferably carried out by dry method. In particular, the charge transfer complex, in powder form, is mixed with the lithium salt, in powder form.

[0045] Similarly, when the precursors of the charge transfer complex are implemented in step i), these are in particular in powder form and are mixed with the lithium salt in powder form.

[0046] Step i) is preferably carried out at room temperature (e.g. 18-25°C).

[0047] Step ii)

[0048] Step ii) involves adding an organic solvent to the mixture from step i) to form a suspension.

[0049] The organic solvent can be chosen from among aprotic polar organic solvents, such as ketones, ethers, carbonates, dimethyl sulfoxide, or dimethylformamide.

[0050] Acetone is one example of a ketone.

[0051] Examples of ethers include tetrahydrofuran and dioxolane.

[0052] Examples of carbonates include ethylene carbonate and dimethyl carbonate.

[0053] The organic solvent is preferably a ketone, and particularly preferably acetone.

[0054] When the charge transfer complex is implemented in step ii), it can represent approximately 5% to 30% by mass, and preferably approximately 15% to 25% by mass, relative to the total mass of the suspension.

[0055] The charge transfer complex implemented in step i) 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.

[0056] Lithium salt can represent from 1 to 50% by mass approximately, preferably from 10 to 45% by mass approximately and particularly preferably from 25 to 35% by mass approximately, relative to the total mass of the suspension.

[0057] When the charge transfer complex precursors are implemented in step ii), each of said precursors may represent approximately 2% to 15% by mass, and preferably approximately 7.5% to 12.5% ​​by mass, relative to the total mass of the suspension.

[0058] Each of the precursors used in step i) can have a particle size ranging from 0.5 to 800 µm, and particularly preferably from 20 to 500 µm.

[0059] Step ii) is preferably carried out under stirring. This allows a homogeneous suspension to be formed.

[0060] Step ii) preferably includes maintaining agitation for at least 3 hours, and preferably for 4 to 8 hours, after the addition of the organic solvent.

[0061] According to one embodiment of the invention, step ii) is carried out in a sealed container. This prevents evaporation of the solvent or sublimation of a molecule of the complex.

[0062] Step ii) is preferably carried out at room temperature (e.g. 18-25°C).

[0063] Step iii)

[0064] Step iii) is an evaporation step of the organic solvent at a temperature less than or equal to 50°C, to form a solid.

[0065] Step iii) can be carried out at a temperature ranging from 20°C to 45°C, and preferably at room temperature (e.g. 18-25°C).

[0066] Step iii) can be carried out in air, under an inert atmosphere (e.g. argon), in particular in an open container, in contact with air (ambient) or the inert atmosphere (inert atmosphere flow), or under vacuum (i.e. pressure less than 10 mbar).

[0067] This step is carried out at low temperatures, which allows control of the molar ratio of the precursors when they are used in step i). This notably prevents their sublimation.

[0068] Step iii) can last at least 24 hours, preferably from 3 to 15 days, and particularly preferably from 4 to 10 days.

[0069] Step iii) is preferably carried out under an inert atmosphere, and in particular with an argon flow. This promotes the evaporation of the solvent.

[0070] The charge transfer complex can be used as is in step i), especially if it is commercially available, or it can be prepared beforehand (before step i)).

[0071] In particular, the charge transfer complex of step i) is pre-prepared according to the following steps: a) mix the precursors of said charge transfer complex, electron donor and electron acceptor, b) add an organic solvent to form a suspension, c) evaporate the organic solvent at a temperature less than or equal to 60°C, to form a solid, and d) grind the solid.

[0072] Step a)

[0073] Step a) is a mixing step of the precursors of said charge transfer complex, electron donor and electron acceptor.

[0074] Step a) is preferably carried out under an inert atmosphere.

[0075] 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.

[0076] Step a) is preferably carried out at room temperature (e.g. 18-25°C).

[0077] Step b)

[0078] Step b) involves adding an organic solvent to the mixture from step a) to form a suspension.

[0079] The organic solvent can be chosen from among aprotic polar organic solvents, such as ketones, ethers, carbonates, dimethyl sulfoxide, or dimethylformamide.

[0080] Acetone is one example of a ketone.

[0081] Examples of ethers include tetrahydrofuran and dioxolane.

[0082] Examples of carbonates include ethylene carbonate and dimethyl carbonate.

[0083] The organic solvent is preferably a ketone, and particularly preferably acetone.

[0084] Each of the said precursors may represent from 1% to 20% by mass approximately, preferably from 2% to 15% by mass approximately, and particularly preferably from 7.5% to 12.5% ​​by mass approximately, relative to the total mass of the suspension.

[0085] Step b) is preferably carried out under stirring. This allows a homogeneous suspension to be formed.

[0086] Step b) preferably includes maintaining agitation for at least 1 hour, and preferably for 1 to 3 hours, after the addition of the organic solvent.

[0087] According to one embodiment of the invention, step b) is carried out in a sealed container. This prevents evaporation of the solvent or sublimation of a molecule of the complex.

[0088] Step b) is preferably carried out at room temperature (e.g. 18-25°C).

[0089] Step c)

[0090] Step c) is an evaporation step of the organic solvent at a temperature less than or equal to 60°C, to form a solid.

[0091] Evaporation can be carried out at a temperature ranging from 25°C to 50°C, and preferably at room temperature (e.g. 18-25°C).

[0092] This step c) is carried out at low temperatures, which allows control of the molar ratio of the precursors. This notably prevents their sublimation.

[0093] Step c) preferably lasts at least 24 hours, preferably from 3 to 24 days, and particularly preferably from 7 to 18 days.

[0094] Step c) can be carried out in air, under an inert atmosphere (e.g. argon), in particular in an open container, in contact with air (ambient) or the inert atmosphere (inert atmosphere flow), or under vacuum (i.e. pressure less than 10 mbar).

[0095] Step c) is preferably carried out under an inert atmosphere, and in particular with an argon flow. This promotes the evaporation of the solvent.

[0096] Step d)

[0097] Step d) is a grinding step of the solid from step c).

[0098] At the end of step d), we preferably obtain a charge transfer complex having a particle size ranging from 0.5 to 100 µm, particularly preferably ranging from 0.5 to 20 µm, and even more particularly preferred ranging from 0.5 to 1.5 µm.

[0099] The process in general is carried out at low temperatures which makes it possible to control the molar ratio of the precursors and to avoid their sublimation.

[0100] The use of the electrolyte composition

[0101] The invention has as its third object the use of an electrolyte composition conforming to the first object or obtained according to a process conforming to the second object of the invention, in a rechargeable lithium metal battery or for the preparation of a solid electrolyte of a rechargeable lithium metal battery.

[0102] The use of an electrolyte composition according to the present invention in a rechargeable lithium-metal battery, or for the preparation of a polymer electrolyte for a rechargeable lithium-metal battery, leads to an energy storage device exhibiting excellent performance, in particular an ionic conductivity greater than or equal to 10 - 5 S.cm - 1 , preferably greater than or equal to 10 - 4 S.cm - 1 , in a particularly preferred manner greater than or equal to 5x10 - 4 S.cm - 1, and more specifically preferably greater than or equal to 10 - 3 S.cm - 1 , at a temperature of 80°C.

[0103] The use of this electrolyte composition 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 electrolyte composition according to the present invention exhibits high thermal stability (ensuring the safety of the energy storage devices incorporating it) and improved potential stability (e.g., stability up to 4.5 V vs. Li). + / Li).

[0104] The solid electrolyte

[0105] The invention has as its fourth object a solid electrolyte for a rechargeable lithium metal battery characterized in that it comprises a support filled or impregnated with an electrolyte composition conforming to the first object or obtained according to a process conforming to the second object of the invention.

[0106] The support can be a porous separator and the solid electrolyte is a porous separator impregnated with the electrolyte composition; or a spacer and the solid electrolyte is a spacer filled with the electrolyte composition.

[0107] The porous separator can be made of a non-electronically conductive porous material, preferably a porous polymer material based on at least one polyolefin or olefin copolymer (e.g. polyethylene, polypropylene, or polyethylene terephthalate PET), or a polyimide; or based on fibers (e.g. glass fibers or wood fibers).

[0108] The solid electrolyte preferably has a thickness of approximately 30 to 80 µm, and more particularly preferred of approximately 20 to 60 µm.

[0109] When the solid electrolyte comprises (or is made of) a porous separator impregnated with an electrolyte composition conforming to the first object, the porous separator is preferentially coated with the electrolyte composition on a first face and on a second face opposite the first face.

[0110] In this embodiment, the electrolyte composition is preferably applied to the separator in solid form.

[0111] When the solid electrolyte includes (or is made of) a spacer filled with an electrolyte composition conforming to the first object, the spacer is made of an electrically insulating material. It is generally in the form of a ring.

[0112] According to one embodiment of the invention, the solid electrolyte consists of a porous separator impregnated with an electrolyte composition conforming to the first object or obtained according to a process conforming to the second object of the invention or of a spacer filled with an electrolyte composition conforming to the first object or obtained according to a process conforming to the second object of the invention.

[0113] Solid electrolyte is preferably suitable for a rechargeable lithium metal battery.

[0114] Rechargeable lithium metal battery

[0115] The invention has as its fifth object a 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 conforms to the fourth object of the invention.

[0116] The positive electrode

[0117] The positive electrode may include a positive electrode active material, optionally a polymer binder, and optionally an agent generating electronic conductivity.

[0118] The active material of the positive electrode

[0119] 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.

[0120] The active material of the positive electrode can be: - 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,- a phosphosilicate or phosphate of metal, 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- a metal sulfate, for example iron sulfate Fe2(SO4)3.

[0121] 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.

[0122] 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.

[0126] The polymer binder

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] The carbon coating the active material preferably represents approximately 0.1 to 5% by mass, relative to the mass of active material.

[0132] The carbon layer is preferably in the form of a layer with a thickness varying from approximately 1 to 4 nm.

[0133] Lithium salt

[0134] The positive electrode may also include a lithium salt.

[0135] 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.

[0136] 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.

[0137] The plasticizer

[0138] The positive electrode may also include a plasticizer.

[0139] The plasticizer (or non-aqueous solvent) can be chosen from: - linear and cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl isopropyl carbonate (MiPC); - fluorinated carbonates such as fluoroethylene carbonate; - nitriles such as succinonitrile; - lactones such as γ-butyrolactone; - liquid linear or cyclic polyethers such as dimethyl ether, polyethylene glycol dimethyl ethers (or PEGDME) such as tetraethylene glycol dimethyl ether (TEGDME), or dioxolane; - fluorinated polyethers; - sulfur-containing solvents such as sulfolane or dimethyl sulfoxide; - phosphates such as triethyl phosphate or fluorophosphates; - esters such as ethyl acetate or ethyl butyrate (EB); and one of their mixtures.

[0140] Among such solvents or plasticizers, linear and cyclic carbonates are particularly preferred.

[0141] 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.

[0142] The positive electrode is preferably in the form of a film whose thickness is generally on the order of 20 to one hundred micrometers.

[0143] The current collector

[0144] The rechargeable battery may also include a current collector, connected to the positive electrode.

[0145] The current collector is usually made of a sheet of metal.

[0146] The current collector is preferably a stainless steel or aluminum current collector, possibly coated with a carbon-based layer (anti-corrosion layer).

[0147] The negative electrode

[0148] The negative electrode is preferably in the form of a film whose thickness is generally on the order of 1 to one hundred micrometers.

[0149] 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.

[0150] The negative electrode is preferably made of metallic lithium or one of the lithium alloys.

[0151] The accompanying drawings illustrate the invention. Lamontre shows the evolution of ionic conductivity in S / cm -1 based on the inverse of the temperature in Kelvin -1and the temperature in degrees Celsius (°C) for a solid electrolyte of the invention. The show shows the opposite of the imaginary part of the impedance -Z'' in ohms, as a function of the real part of the impedance Z in ohms for a cell comprising a solid electrolyte of the invention.

[0152] Examples

[0153] The raw materials used in the examples are listed below: - LIFTFSI, Tokyo chemical industry, 192998-62-2, purity > 95%, - benzoquinone, Sigma Aldrich, 106-51-4, purity 98%, - hydroquinone, Sigma Aldrich, 123-31-9, purity >= 99%, - extra dry acetone, Thermo scientific, 67-64-1, purity 99.7%, - polyolefin separator, Viledon, FS2207-25, Freudenberg, - lithium metal foil, Albermale, 125 µm, purity 99.9%, - charge transfer complex obtained from benzoquinone and hydroquinone, Thermo scientific, 106-34-3, purity 98%.

[0154] Unless otherwise stated, all materials were used as received from the manufacturers.

[0155] Example 1: Preparation of electrolyte compositions according to the invention and of electrolyte compositions not according to the invention

[0156] An electrolyte composition CE1 according to the invention was prepared in the manner described below.

[0157] 0.1981 g of benzoquinone and 0.2019 g of hydroquinone (molar ratio of 1:1) were mixed under an inert atmosphere (glove box, argon) (step a)), and then 4 mL of acetone were added (step b)). The resulting mixture was placed under mechanical stirring for 2 hours in a closed container (step b)). The acetone solvent was then evaporated at room temperature (by opening the container) while maintaining stirring under an inert atmosphere for 7 days to obtain a solid (step c)). The resulting dry solid was ground in a mortar to form a charge-transfer complex powder, denoted CTC1 (step d)), which was stored under an inert atmosphere (glove box).

[0158] 0.4 g of CTC1 were mixed with 0.4 g of lithium salt LiFTFSI (step i)), and then 4 ml of acetone were added (step ii)). The resulting mixture was placed under mechanical stirring for 5 hours in a closed container (step ii)). The acetone solvent was then evaporated at room temperature under argon flow (with the container opened) while maintaining stirring for 1 week to form a solid electrolyte composition CE1 according to the invention (step iii)).

[0159] The electrolyte composition CE1 comprises 50% by mass of lithium salt LiFTFSI relative to the total mass of the electrolyte composition.

[0160] Another electrolyte composition according to invention CE2 was prepared in the same way as above by modifying the respective proportions of lithium salt and CTC1, to form a composition with 70% by mass of lithium salt LiFTFSI, relative to the total mass of the electrolyte composition.

[0161] For comparison, electrolyte compositions not conforming to the invention were prepared according to the same process as described above by replacing the lithium salt (fluorosulfonyl)(trifluoromethanesulfonyl) lithium imidide LiFTFSI with bis(trifluoromethanesulfonyl) lithium imidide LiTFSI, 4,5-dicyano-2-(trifluoromethyl)imidazolide lithium LiTDI, 4,5-dicyano-triazolide lithium LiTDAC or bis(oxalato)borate lithium LiBOB to form respectively the compositions CE3* (50% by mass of LiTFSI), CE4* (70% by mass of LiTFSI), CE5* (50% by mass of LiTDI), CE6* (70% by mass of LiTDI), CE7* (50% by mass of LiTDAC), CE8* (70% by mass of LiTDAC), CE9* (50% by mass of LiBOB), and CE10*(70% by mass of LiBOB).

[0162] For each electrolyte composition, an electrochemical characterization cell (lithium / solid electrolyte / lithium) is then constructed by stacking a lithium foil, a solid electrolyte containing a separator impregnated with the electrolyte composition as prepared above, and another lithium foil in a button cell. The electrolyte composition is applied in excess to the separator using a spatula to ensure complete impregnation.

[0163] The ionic conductivity of the different electrolyte compositions was measured at 80°C by impedance spectroscopy using a device sold under the trade name "VMP3" by the company BioLogic.

[0164] The measurements are carried out with the cells as prepared above, in potentiostatic mode between 100 mHz and 7 MHz for an amplitude of 10 mV at 80°C.

[0165] Table 1 below lists the different ionic conductivities obtained.

[0166]

[0167] Table 1 shows that ionic conductivity increases with the amount of lithium salt present in the electrolyte composition and that the lithium salt LiFTFSI provides particularly interesting ionic conductivity properties compared to the other lithium salts tested.

[0168] Another lithium salt, LiFSI, was also tested under the same preparation and measurement conditions. However, this salt corroded the measuring electrodes of the electrochemical characterization cell. Therefore, it was not possible to determine the ionic conductivity.

[0169] Example 2: Preparation of electrolyte compositions according to the invention and of electrolyte compositions not according to the invention

[0170] An electrolyte composition CE11 according to the invention was prepared in the manner described below.

[0171] 1.11 g of a commercial charge-transfer complex obtained from benzoquinone and hydroquinone (molar ratio of 1:1), denoted CTC2, were mixed with 2.59 g of lithium salt LiFTFSI (step i)), and then 2 g of acetone were added (step ii)). The resulting mixture was placed under mechanical stirring for 6 hours in a closed container (step ii)). The acetone solvent was then evaporated at room temperature under argon flow (with the container opened) while maintaining stirring for 1 week, to form a solid electrolyte composition CE11 according to the invention (step iii)).

[0172] The electrolyte composition CE11 comprises 70% by mass of lithium salt LiFTFSI relative to the total mass of the electrolyte composition.

[0173] An electrochemical characterization cell as described in Example 1 was prepared with electrolyte composition CE11.

[0174] Ionic conductivity was measured by impedance spectroscopy with an apparatus as described in Example 1, and with the cell as prepared above, at a frequency ranging from 100 mHz to 7 MHz for an amplitude of 10 mV, varying the temperature from 10°C to 80°C.

[0175] Lamontre, the evolution of ionic conductivity in S.cm -1 depending on the temperature (measurement of the ratio 1000 / temperature, in Kelvin) -1 (bottom abscissa, and measurement of the ratio 1000 / temperature, in degrees Celsius (°C), top abscissa) for a solid electrolyte obtained from the electrolyte composition CE11 of the invention. The values ​​obtained go up to 10 -3 S / cm. The resulting solid electrolyte exhibits ionic conduction properties between 10 -5 S.cm -1at 10°C up to 10 -3 at 80°C. The residual electronic conductivity value was measured by chronoamperometry. A drop in the measured current value reached a plateau at approximately 3.5 x 10 -5 mA is observed. This allows us to calculate the electronic conductivity value of the solid electrolyte to be approximately 3.5 x 10 -10 S.cm -1 confirming that the solid electrolyte is solely an ionic conductor.

[0176] Larepresents Nyquist diagrams as a function of the measurement temperature. Impedance measurements are performed continuously over time; in parallel, a temperature program allows the temperatures to evolve between 20°C and 80°C throughout the measurements (20°C: curves with pentagons, 30°C: curves with stars, 40°C: curves with triangles, 50°C: curves with squares, 60°C: curves with lines, and 80°C: curves with crosses).

[0177] Lamontre in particular the opposite of the imaginary part of the impedance Z (-Im(Z)) in ohms, as a function of the real part of the impedance Z in ohms for the cell comprising a solid electrolyte of the invention as prepared in example 2 obtained from the electrolyte composition CE11.

[0178] Lamontre notes that the Nyquist diagrams overlap in temperature steps, indicating a stability of the measured ionic conductivity value for each temperature. The solid electrolyte according to the invention, obtained from electrolyte composition CE11, is therefore stable on lithium metal over a temperature range of 20 to 80°C.

Claims

Electrolyte composition comprising: - a lithium salt, and - 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, characterized in that: - the lithium salt is the (fluorosulfonyl)(trifluoromethanesulfonyl) lithium imidide LiFTFSI, - 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)R 9 , R 9 being an alkyl, aryl or aryl-alkyl radical, the precursor of said charge-transfer complex, electron donor, corresponds to the following formula (II): [Chem 4] , 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, and in that the lithium salt represents an amount greater than 30% by mass, relative to the total mass of the electrolyte composition. Composition according to claim 1, characterized in that the lithium salt represents at least 40% by mass, relative to the total mass of the electrolyte composition. Composition according to claim 1 or 2, characterized in that the precursor of said charge-transfer, electron-accepting complex of formula (I) is benzoquinone. Composition according to any one of the preceding claims, characterized in that the precursor of said charge-transferring, electron-donating complex of formula (II) is hydroquinone. Composition according to any one of the preceding claims, characterized in that the precursors are used in the electrolyte composition in an electron acceptor precursor / electron donor precursor molar ratio of 0.8 to 1.

2. A method for preparing an electrolyte composition as defined in any one of the preceding claims, characterized in that it comprises at least the following steps: i) mixing the charge transfer complex or its electron acceptor and electron donor precursors with the lithium salt, ii) adding an organic solvent to form a suspension, and iii) evaporating the organic solvent at a temperature less than or equal to 50°C to form a solid. A process according to claim 6, characterized in that the charge transfer complex of step i) is pre-prepared according to the following steps: a) mixing the precursors of said charge transfer complex, electron donor and electron acceptor, b) adding an organic solvent to form a suspension, c) evaporating the organic solvent at a temperature less than or equal to 60°C, to form a solid, and d) grinding the solid. A process according to claim 6 or 7, characterized in that the organic solvent is acetone. Use of an electrolyte composition as defined in any one of claims 1 to 5, in a rechargeable lithium metal battery or for the preparation of a solid electrolyte for a rechargeable lithium metal battery. Solid electrolyte for a rechargeable lithium metal battery, characterized in that it comprises a support filled or impregnated with an electrolyte composition as defined in any one of claims 1 to 5. 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 and negative electrodes, characterized in that the solid electrolyte is as defined in claim 10.

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