SOLID ELECTROLYTE FOR ALL-SOLID BATTERIES

Abstract

The present invention relates generally to the field of electrical energy storage in all-solid-state batteries, particularly in secondary Li-ion batteries. More specifically, the invention concerns a solid electrolyte consisting of a polymer matrix and a fibrous reinforcement, which enables the fabrication of a non-porous film exhibiting a very good compromise between ionic conductivity, electrochemical stability, high-temperature stability, and mechanical strength. This film is intended for use as a separator in all-solid-state batteries, particularly for Li-ion batteries. The invention also relates to an all-solid-state battery comprising such a separator and / or such an electrolyte. No figure

Description

Title of the invention: SOLID ELECTROLYTE FOR ALL-SOLID-STATE BATTERY FIELD OF THE INVENTION

[0001] The present invention relates generally to the field of electrical energy storage in all-solid-state batteries, in particular in Li-ion type secondary batteries. More specifically, the invention relates to a solid electrolyte consisting of a polymer matrix and a mechanical reinforcement, which allows the manufacture of a non-porous film having a very good compromise between ionic conductivity, electrochemical stability, thermal stability, mechanical strength and fire resistance. This film is intended for an application as an all-solid-state battery separator or electrolyte, in particular for Li-ion batteries. The invention also relates to an all-solid-state battery comprising such a separator and / or such a non-porous film. TECHNICAL BACKGROUND

[0002] A Li-ion battery comprises at least one negative electrode or anode coupled to a copper current collector, one positive electrode or cathode coupled to an aluminum current collector, a separator and an electrolyte. The electrolyte consists of a lithium salt, generally lithium hexafluorophosphate, mixed with a solvent which is a mixture of organic carbonates, chosen to optimize the transport and dissociation of ions. A high dielectric constant promotes the dissociation of ions, and therefore, the number of ions available in a given volume, while a low viscosity is favorable to ionic diffusion which plays an essential role, among other parameters, in the charging and discharging rates of the electrochemical system.

[0003] Lithium-ion batteries typically use liquid electrolytes composed of solvent(s), lithium salt(s) and additive(s). These electrolytes have good ionic conductivity but are susceptible to leakage or ignition if the battery is damaged.

[0004] The use of solid electrolytes makes it possible to overcome these difficulties. However, solid electrolytes are generally less conductive than liquid electrolytes. The difficulty with solid electrolytes is to reconcile high ionic conductivity, good electrochemical stability and sufficient temperature resistance. The ionic conductivity must be equivalent to that of liquid electrolytes (i.e. of the order of 1 mS / cm at 25°C). The electrochemical stability must allow the use of the electrolyte with cathode materials that can operate at high voltage (> 4.5 V). Similarly, the solid electrolyte must operate at least up to 80°C and not ignite below 130°C.

[0005] Furthermore, sufficient mechanical strength must be obtained at the separator. The latter must, in particular, prevent the formation of dendrites during charge / discharge cycles.

[0006] Generally speaking, the solid electrolyte must demonstrate better safety, but this cannot be done at the expense of other performances.

[0007] Finally, from a processability and implementation point of view, the solid electrolyte must be able to be handled (stretched) and rolled.

[0008] Poly(vinylidene fluoride) (PVDF) and its derivatives are of interest as the main constituent material of the separator for their electrochemical stability, and for their high dielectric constant which promotes the dissociation of ions and therefore conductivity. The P(VDF-HFP) copolymer (copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP)) has been studied as a gelled membrane because it has a lower crystallinity than PVDF. Therefore, the interest of these P(VDF-HFP) copolymers is that they allow greater swellings to be achieved and thus promote conductivity.

[0009] Document US 5296318 describes solid electrolyte compositions comprising a mixture of P(VDF-co-HFP) copolymer, lithium salt, and compatible solvent with a medium boiling point (i.e. between 100°C and 150°C), capable of forming a stretchable and self-supporting film. Example 2 describes the preparation of a film having a thickness of 100 μm from a composition containing a P(VDF-HFP) copolymer, LiPF6 (lithium hexafluorophosphate) and a mixture of ethylene carbonate and propylene carbonate.

[0010] Composite solid electrolytes exhibit improved mechanical properties.

[0011] The publication by Kun Shi et al. in Journal of Membrane Science 638 (2021) 119713 describes PVDF / PP / PVDF composites. The polypropylene (PP) is a microporous Celgard 2400 film. The PVDF is a HSV900 homopolymer from Shenzhen Kejing Star Technology Co. The composite contains 25% by mass of LiC104. A 100 pm PVDF / PP / PVDF tri-layer film displays an ionic conductivity of 0.15 mS / cm at 25°C and increases the Young's modulus from 24 to 102 MPa compared to a PVDF monolayer. However, the tri-layer is prepared in N,N-dimethylformamide (DMF), and a significant amount of free DMF remains trapped in the PVDF after drying, which limits the electrochemical stability.

[0012] There is still a need to develop new solid electrolytes which present a good compromise between ionic conductivity, electrochemical stability and temperature resistance, and which are suitable for simplified implementation, compatible with an industrial application.

[0013] The invention therefore aims to remedy at least one of the drawbacks of the prior art, namely to propose a solid electrolyte composition having performances at least equivalent to those of a liquid electrolyte.

[0014] The invention also relates to a non-porous polymeric film consisting of said composition having good mechanical strength, ionic conductivity and electrochemical stability properties.

[0015] The invention also aims to provide at least one method of manufacturing this polymeric film.

[0016] Another subject of the invention is a separator, in particular for a Li-ion battery, consisting, in whole or in part, of said film. This separator can also be used in a battery, a capacitor, an electrochemical double-layer capacitor, a membrane-electrode assembly (MEA) for a fuel cell or an electrochromic device.

[0017] Finally, the invention aims to provide all-solid-state batteries, in particular rechargeable Li-ion batteries comprising such a separator. Summary of the invention

[0018] The invention relates firstly to a solid electrolyte composition consisting of a matrix made up of the following components a), b) and c):

[0019] a. at least one copolymer of vinylidene fluoride (VDF) and at least one comonomer compatible with VDF, b. at least one plasticizer, c. at least one lithium salt, and d. at least one mechanical reinforcement (component d).

[0020] By "comonomer compatible with VDF" is meant a comonomer polymerizable with VDF; these monomers are preferably chosen from vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers such as perfluoro(methylvinyl)ether (PMVE), perfluoro(ethylvinyl)ether (PEVE), perfluoro(propylvinyl)ether (PPVE).

[0021] According to one embodiment, the VDF copolymer is a terpolymer.

[0022] According to one embodiment, component a) is at least one copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), or P(VDF-HFP).

[0023] Advantageously, said P(VDF-HFP) copolymer has a mass content of HFP greater than or equal to 5% and less than or equal to 45%.

[0024] According to one embodiment, said lithium salt is chosen from the list: LiFSI, LiTFSI, LiTDI, LiPF6, LiBF4 and LiBOB.

[0025] The reinforcement is made of any material that can improve the me- canics compared to the matrix alone.

[0026] The invention also relates to a non-porous film consisting of said solid electrolyte composition. Advantageously, the film does not contain a low boiling point solvent (i.e. less than 150°C) and has a high ionic conductivity.

[0027] Another object of the invention is a separator, in particular for a Li-ion rechargeable battery, comprising a film as described.

[0028] The invention also relates to an electrochemical device chosen from the group: batteries, capacitor, electrochemical double-layer electric capacitor, and membrane-electrode assembly (MEA) for fuel cell or an electrochromic device, said device comprising a separator as described.

[0029] Another object of the invention is an all-solid-state lithium-based battery, for example a Li-ion battery, or Li-S or Li-air batteries, comprising a negative electrode, a positive electrode and a separator, wherein said separator comprises a film as described.

[0030] The invention also relates to an all-solid-state battery comprising such a non-porous film.

[0031] The present invention overcomes the disadvantages of the prior art. More particularly, it provides a non-porous film capable of functioning as an all-solid battery separator, which combines high ionic conductivity, good electrochemical stability, temperature resistance, and sufficient mechanical strength to allow easy handling.

[0032] The advantage of this invention is to offer a better guarantee of safety compared to a separator or an electrolyte based on liquid electrolyte, for electrochemical performances at least equal to those of liquid electrolytes. There is therefore no possible leakage of electrolyte, and the flammability of the electrolyte is greatly reduced.

[0033] Just like liquid electrolytes, the solid electrolyte according to the invention can be used in a battery with a graphite, silicon or graphite and silicon anode. However, its resistance to dendrite growth on the surface of the anode also allows a lithium metal anode, which allows a gain in energy density compared to conventional Li-ion technologies. BRIEF DESCRIPTION OF THE FIGURES

[0034] [Fig. 1] is a diagram representing the variation of the tensile force as a function of the elongation for two films: comparative film 1, and film 2 according to the invention.

[0035] DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0036] The invention is now described in more detail and in a non-limiting manner in the following description.

[0037] According to a first aspect, the invention relates to a solid electrolyte composition consisting of a matrix made up of the following components a), b) and c):

[0038] a) at least one copolymer of vinylidene fluoride (VDF) and at least one comonomer compatible with VDF,

[0039] b) at least one plasticizer,

[0040] c) at least one lithium salt, and

[0041] d) at least one mechanical reinforcement (component d).

[0042] According to various embodiments, said solid electrolyte film comprises the following characteristics, where appropriate combined. The contents indicated are expressed by weight, unless otherwise indicated. The concentration ranges indicated include the limits, unless otherwise indicated. Component a)

[0043] Component a) consists of at least one copolymer comprising vinylidene difluoride (VDF) units and one or more types of comonomer units compatible with vinylidene difluoride (hereinafter referred to as "VDF copolymer"). The VDF copolymer contains at least 50% by weight of vinylidene difluoride, advantageously at least 70% by weight of VDF and preferably at least 80% by weight of VDF.

[0044] Comonomers compatible with vinylidene difluoride can be halogenated (fluorinated, chlorinated or brominated) or non-halogenated.

[0045] Examples of suitable fluorinated comonomers are: vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, trifluoropropenes and in particular 3,3,3-trifluoropropene, tetrafluoropropenes and in particular 2,3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropenes and in particular 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene, perfluoroalkylvinylethers and in particular those of general formula Rf-O-CF-CF2, Rf being an alkyl group, preferably C1 to C4 (preferred examples being perfluoropropylvinylether and perfluoromethylvinylether). The fluorinated monomer may comprise a chlorine or bromine atom. It may in particular be chosen from bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene and chlorotrifluoropropene.Chlorofluoroethylene may refer to either 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. The 1-chloro-1-fluoroethylene isomer is preferred. Chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.

[0046] According to one embodiment, component a) consists of a VDF copolymer.

[0047] According to one embodiment, component a) consists of a P(VDF-HFP) copolymer. Advantageously, the P(VDF-HFP) copolymer has a mass content of HFP greater than or equal to 5%, preferably greater than or equal to 8%, advantageously greater than or equal to 11%, and less than or equal to 45%, preferably less than or equal to 30%.

[0048] According to one embodiment, said component a) consists of a mixture of two VDF copolymers of different structures.

[0049] According to one embodiment, component a) consists of a VDF copolymer to which a PVDF homopolymer is added in a mass proportion ranging from 0 to 10% based on the weight of said component a).

[0050] According to one embodiment, said component a) consists of a mixture of a PVDF homopolymer (in a proportion of up to 10%) and a P(VDF-HFP) copolymer.

[0051] According to one embodiment, the VDF copolymer and / or the PVDF homopolymer forming part of the composition of component a) comprises monomer units carrying at least one of the following functions: carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups (such as glycidyl), amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, phosphonic. The function is introduced by a chemical reaction which may be grafting, or a copolymerization of the fluorinated monomer with a monomer carrying at least one of said functional groups and a vinyl function capable of copolymerizing with the fluorinated monomer, according to techniques well known to those skilled in the art.

[0052] According to one embodiment, the functional group carries a carboxylic acid function which is a (meth)acrylic acid type group chosen from acrylic acid, methacrylic acid, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate and hydroxyethylhexyl(meth)acrylate.

[0053] According to one embodiment, the units carrying the carboxylic acid function further comprise a heteroatom chosen from oxygen, sulfur, nitrogen and phosphorus.

[0054] The content of functional groups in the VDF copolymer and / or PVDF homopolymer included in the composition of component a) is at least 0.01 mol%, preferably at least 0.1 mol%, and at most 15 mol%, preferably at most 10 mol%.

[0055] According to one embodiment, the VDF copolymer has a high molecular weight. By high molecular weight, as used herein, is meant a copolymer having a melt viscosity greater than 100 Pa.s, preferably greater than 500 Pa.s, more preferably greater than 1000 Pa.s, according to ASTM method D-3835 measured at 232°C and 100 sec A

[0056] The VDF copolymers used in the invention can be obtained by known polymerization methods such as emulsion, solution or suspension polymerization.

[0057] According to one embodiment, they are prepared by an emulsion polymerization process in the absence of fluorinated surfactant.

[0058] According to one embodiment, said VDF copolymer is a random copolymer. This type of copolymer has the advantage of having a homogeneous distribution of the comonomer along the vinylidene fluoride chains.

[0059] According to one embodiment, said VDF copolymer is a so-called “heterogeneous” copolymer, which is characterized by a non-homogeneous distribution of the comonomer along the VDF chains, due to the synthesis process described by the applicant, for example in document US 6187885 or in document US 10570230. A heterogeneous copolymer has two (or more) distinct phases, with a phase rich in PVDF homopolymer and a copolymer phase rich in comonomer.

[0060] According to one embodiment, the heterogeneous copolymer consists of discontinuous, discrete and individual copolymer domains of comonomer-rich phase, which are distributed homogeneously in a continuous phase rich in PVDF. This is then referred to as a non-continuous structure.

[0061] According to another embodiment, the heterogeneous copolymer is a copolymer having two (or more) continuous phases which are intimately linked together and cannot be physically separated. This is then referred to as a co-continuous structure.

[0062] According to one embodiment, said heterogeneous copolymer comprises two or more co-continuous phases which comprise:

[0063] a) from 25 to 50 percent by weight of a first co-continuous phase comprising 90-100 percent by weight of vinylidene fluoride monomer units and 0 to 10 percent by weight of other fluoromonomer units, and

[0064] b) from more than 50 wt% to 75 wt% of a second co-continuous phase comprising from 65 to 95 wt% of vinylidene fluoride monomer units and an effective amount of one or more comonomers, such as hexafluoropropylene and perfluorovinyl ether, to cause phase separation of the second co-continuous phase from the first continuous phase.

[0065] The heterogeneous copolymer may be made by forming an initial polymer that is rich in VDF monomer units, generally greater than 90% by weight VDF, preferably greater than 95% by weight, and in a preferred embodiment, a PVDF homopolymer, and then adding a co-monomer to the reactor well into the polymerization to produce a copolymer. The VDF-rich polymer and copolymer will form separate phases, resulting in an intimate heterogeneous copolymer.

[0066] Copolymerization of VDF with a comonomer, for example with HFP, results in a latex generally having a solids content of 10 to 60% by weight, preferably 10 to 50%, and having a weight average particle size of less than 1 micrometer, preferably less than 800 nm, and more preferably less than 600 nm. The weight average particle size is generally at least 20 nm, preferably at least 50 nm, and advantageously the average size is in the range of 100 to 400 nm. The polymer particles may form agglomerates having a weight average size of 1 to 30 micrometers, and preferably 2 to 10 micrometers. The agglomerates may break into discrete particles during formulation and application to a substrate.

[0067] The VDF copolymers used in the invention may form a gradient between the core and the surface of the particles, in terms of composition (comonomer content, for example) and / or molecular weight.

[0068] According to certain embodiments, the VDF copolymers contain bio-sourced VDF. The term "bio-sourced" means "derived from biomass". This makes it possible to improve the ecological footprint of the membrane. The bio-sourced VDF can be characterized by a renewable carbon content, i.e. carbon of natural origin and originating from a biomaterial or biomass, of at least 1 atomic % as determined by the 14C content according to standard NF EN 16640. The term "renewable carbon" indicates that the carbon is of natural origin and originates from a biomaterial (or biomass), as indicated below.According to certain embodiments, the bio-carbon content of the VDF may be greater than 5%, preferably greater than 10%, preferably greater than 25%, preferably greater than or equal to 33%, preferably greater than 50%, preferably greater than or equal to 66%, preferably greater than 75%, preferably greater than 90%, preferably greater than 95%, preferably greater than 98%, preferably greater than 99%, advantageously equal to 100%. Component b)

[0069] The second component of the solid electrolyte composition of the invention consists of at least one plasticizer.

[0070] According to one embodiment, said plasticizer is an ionic liquid.

[0071] An ionic liquid is a salt that is liquid at room temperature, i.e. it has a melting point below 100°C under atmospheric pressure. It is formed by the association of an organic cation and an anion whose ionic interactions are sufficiently weak not to form a solid.

[0072] As examples of organic cations, mention may be made of the cations: ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and their mixtures. According to one embodiment, this cation may comprise a C1-C30 alkyl group, such as 1-butyl-1-methylpyrrolidinium, 1-ethyl-3-methylimidazolium, N-methyl-N-propylpyrrolydinium or N-methyl-N-butylpiperidinium.

[0073] According to one embodiment, the anions associated with them are chosen from: imides, in particular bis(fluorosulfonyl)imide and bis(trifluoromethanesulfonyl)imide; borates; phosphates; phosphinates and phosphonates, in particular alkylphosphonates; amides, in particular dicyanamide; aluminates, in particular tetrachloroaluminate; halides (such as bromide, chloride, iodide anions); cyanates; acetates (CH3COO), in particular trifluoroacetate; sulfonates, in particular methanesulfonate (CH3SO3), trifluoromethanesulfonate; and sulfates, in particular hydrogen sulfate.

[0074] According to one embodiment, the anions are chosen from tetrafluoroborate (BF4), bis(oxalato)borate (BOB), hexafluorophosphate (PF6), hexafluoroarsenate (AsF6), triflate or trifluoromethylsulfonate (CF3SO3), bis(fluorosulfonyl)imide (FSI), bis-(trifluoromethanesulfonyl)imide (TFSI), nitrate (NO3) and 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI).

[0075] According to one embodiment, said anion of the ionic liquid is chosen from TDI, FSI, TFSI, PF6, BF4, NO3 and BOB.

[0076] According to one embodiment, said anion of the ionic liquid is FSI.

[0077] According to one embodiment, said component b) is a mixture of at least two ionic liquids chosen from those described above.

[0078] According to one embodiment, component b) of the solid electrolyte composition of the invention is a mixture of at least one ionic liquid and at least one solvent with a high boiling point (greater than 160°C). According to one embodiment, said solvent is chosen from:

[0079] - vinylene carbonate (VC) (CAS: 872-36-6),

[0080] - fluoroethylene carbonate or 4-fluoro-1,3-dioxolan-2-one (FEC or F1EC) (CAS: 114435-02-8),

[0081] - trans-4,5-difluoro-l,3-dioxolan-2-one (F2EC) (CAS: 171730-81-7),

[0082] - ethylene carbonate (EC) (CAS: 96-49-1),

[0083] - propylene carbonate (PC) (CAS: 108-32-7),

[0084] - (2-cyanoethyl)triethoxysilane (CAS: 919-31-3),

[0085] - 3-methoxypropionitrile (CAS No. 110-67-8),

[0086] - sulfolane (126-33-0),

[0087] - ethers such as polyethylene glycol dimethyl ethers, in particular diethylene glycol dimethyl ether (EG2DME), triethylene glycol dimethyl ether (EG3DME), and tetraethylene glycol dimethyl ether (EG4DME).

[0088] Plasticizers make it possible to obtain improved conductivity properties, electrochemical stability, thermal stability, electrode compatibility, capacity retention compared to conventional liquid electrolytes.

[0089] Examples of component b) according to the invention are the following mixtures:

[0090] - l-ethyl-3-methylimidazolium-FSI and FEC,

[0091] - l-ethyl-3-methylimidazolium-FSI and tetraethylene glycol dimethyl ether,

[0092] - 1-butyl-l-methylpyrrolidinium-FSI and FEC,

[0093] - l-ethyl-3-methylimidazolium-TFSI and FEC,

[0094] - l-ethyl-3-methylimidazolium-FSI,

[0095] - 1-butyl-l-methylpyrrolidinium-FSI.

[0096] According to one embodiment, in the mixture of at least one ionic liquid and one solvent, the mass ratio between the ionic liquids and the solvents forming compound b) varies from 10:0.1 to 0.1:10. Component c)

[0097] The lithium salt present in the solid electrolyte composition comprises the same anion as those of the ionic liquid present in component b).

[0098] According to one embodiment, said lithium salt is chosen from: LiPF6 LiFSI, LiTFSI, LiTDI, LiBF4, LiNO3 and LiBOB. Component d)

[0099] The mechanical reinforcement is made of any material (porous membrane, woven or non-woven) making it possible to improve the mechanical properties compared to the matrix alone (components a+b+c). This may be, in a non-limiting manner:

[0100] - of a microporous film based on polyolefins, such as polyethylene (PE), poly ethylene terephthalate (PET), polypropylene (PP), Celgard® Li-ion separator,

[0101] - a porous film based on PVDF, polyethersulfone (PES) or polysulfone (PSU),

[0102] - a woven substrate (for example PP, PE, PET, PVDF, PES, PSU, inor fibers organic),

[0103] - of a non-woven substrate of the melt-blown type (for example PP, PET, PVDF, PES, PSU), a spunbond substrate (for example PP, PET, PVDF, PES, PSU),

[0104] - of a cellulose separator,

[0105] - short fiber staples, or

[0106] - of melt-spun fibers.

[0107] According to one embodiment, the mechanical reinforcement is a multilayer material with at least one layer of polyolefin and at least one inorganic layer, for example Celgard® PP coated with a layer of alumina on both sides.

[0108] The mechanical reinforcement can be chosen from polymers (for example polyolefin, PVDF, PTFE, polyamide, polyimide, polyaramide, polybenzoaxoles, polybenzi-midazoles, polybenzthiazoles, polyphosphazenes, PEKK, PEEK, PES, PSU), carbon fibers (e.g. vapor grown carbon fibers (VGCF®)), carbon nanotubes (CNTs), inorganic fibers (e.g. glass fibers), and plant fibers (e.g. paper, lignin, cellulose, cellulose nanowhiskers).

[0109] According to one embodiment, the woven or non-woven fabric is made of fibers and has a weight of less than 50 g / m2, preferably less than 30 g / m2, preferably less than 20 g / m2 and advantageously less than 15 g / m2.

[0110] According to one embodiment, the solid electrolyte composition consists of:

[0111] a) 8 to 66.5% of VDF copolymer(s),

[0112] b) 4 to 76% of plasticizer(s), and

[0113] c) 0.8 to 28.5% of lithium salt(s),

[0114] d) 5 to 60% mechanical reinforcement,

[0115] the sum of all constituents being 100%.

[0116] According to one embodiment, the solid electrolyte composition consists of:

[0117] - 18 to 45% of component a),

[0118] - 24 to 63% of component b),

[0119] - 1.8 to 9% of component c), and

[0120] - 10 to 40% of component d).

[0121] According to one embodiment, the solid electrolyte composition consists of a P(VDF-HFP) copolymer, an EMIM-FSI / EG4DME, LiFSI blend, and a PVDF nonwoven in a mass proportion of 32 / 44.8 / 3.2 / 20, the EMIM-FSI / EG4DME mass ratio being 1:1.

[0122] The invention also relates to a non-porous film or membrane consisting of said solid electrolyte composition. Advantageously, the film does not contain a solvent and has a high ionic conductivity. Advantageously, the film is self-supporting, i.e. it can be handled without the aid of a support. Advantageously, the film is capable of being wound, i.e. it can be handled so that it can be wound onto a reel.

[0123] According to one embodiment, said film has a thickness of 5 to 60 μm, preferably of 5 to 30 μm, more preferably of 7 μm to 20 μm.

[0124] According to one embodiment, the film according to the invention has an ionic conductivity ranging from 0.01 to 5 mS / cm, preferably from 0.05 to 5 mS / cm, advantageously from 0.5 to 5 mS / cm, at 25°C. The conductivity is measured by electrochemical impedance spectroscopy. According to one embodiment, the non-porous film is placed between two gold electrodes in a sealed conductivity cell under an inert atmosphere (CESH, Biology) and an electrochemical impedance spectroscopy is carried out between 1 Hz and 1 MHz with an amplitude of 10 mV. The resistance R of the film by linear regression of the curve -Im(Z) = f (Re(Z)). The conductivity a is then given by the following relation:

[0126] where l is the film thickness and S its surface area. For each composition, the conductivity value at a given temperature is obtained by averaging at least two measurements taken on different samples.

[0127] Advantageously, the film according to the invention has good electrochemical stability over the temperature range from -20°C to 80°C.

[0128] Advantageously, the film according to the invention has a content of solvent(s) with a boiling point lower than 150°C, lower than 1% by weight, preferably lower than 0.1%, preferably lower than 10 ppm.

[0129] Advantageously, the film retains its properties up to 80°C and does not ignite below 130°C.

[0130] According to one embodiment, the film according to the invention has a mechanical strength characterized by an elastic modulus, measured at 1 Hz and 23°C by dynamic mechanical analysis, greater than 0.1 MPa, preferably greater than IMPa, even more preferably greater than 10 MPa.

[0131] The invention also aims to provide at least one method of manufacturing this non-porous polymeric film.

[0132] According to one embodiment, said film is manufactured by immersion in a solution containing a, b and c. Said at least one VDF copolymer is solubilized at room temperature in a solvent chosen from: n-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl formamide, methyl ethyl ketone, acetonitrile, and acetone. Said at least one lithium salt is dissolved in a solution of at least one plasticizer, to obtain a lithium salt solution. The two solutions are mixed. A mechanical reinforcement is then immersed in the final solution. The film is then dried, for example at 60°C under vacuum for 1 night. In the case of acetone, it can be dried in a ventilated oven. A perfectly homogeneous and transparent self-supporting film is finally obtained.

[0133] According to one embodiment, said film is manufactured by coating. Said at least one VDF copolymer is solubilized at room temperature in a solvent chosen from: n-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl formamide, methyl ethyl ketone, acetonitrile, and acetone. Said at least one lithium salt is dissolved in the ionic liquid / plasticizer mixture, to obtain a lithium salt solution. The two solutions are mixed.

[0134] A mechanical reinforcement is coated on one or both sides, with the mixture thus obtained, for example using a doctor blade. The film is then dried, for example at 60°C under vacuum for 1 night. In the case of acetone, it can be dried in a ventilated oven. The final result is a perfectly homogeneous and transparent self-supporting film.

[0135] Another object of the invention is a separator for an all-solid-state battery consisting, in whole or in part, of said film.

[0136] The invention also relates to an electrochemical device chosen from the group: batteries, capacitor, electrochemical double-layer electric capacitor, and membrane-electrode assembly (MEA) for fuel cell or an electrochromic device, said device comprising a separator as described.

[0137] Another object of the invention is an all-solid-state battery, for example a Li-ion battery, or Li-S or Li-air batteries, comprising a negative electrode, a positive electrode and a separator, wherein said separator comprises a film as described above.

[0138] According to one embodiment, said battery comprises a lithium metal anode.

[0139] The invention also relates to an all-solid-state battery comprising an anode, a cathode and a separator, in which the anode and / or the cathode comprise such a non-porous film. EXAMPLES

[0140] The following examples illustrate in a non-limiting manner the scope of the invention.

[0141] 1. Preparation of solid electrolyte for Li-ion battery separator by immersion

[0142] 0.4 g of P(VDF-HFP) (poly(vinylidene fluoride)-co-hexafluoropropylene) (containing 11% HFP by weight) are dissolved in 1.93g of acetone at room temperature. 0.056g of LiFSI (lithium bis(fluorosulfonyl)amide) are further dissolved in 0.276g of EMIM-FSI (1-ethyl-3-methylimidazolium bis(fluorosulfonyl imide) and 0.281g of tetraethylene glycol dimethyl ether (EG4DME). The latter solution is added to the P(VDF-HFP) solution and then mixed. A polypropylene nonwoven (thickness 40 μm, porosity approximately 50%, weight 18 g / m2) is then immersed for 5 min in the final solution. It is then dried at 60°C under vacuum for 1 night. A transparent self-supporting film of approximately 60 μm is finally obtained.

[0143] The residual solvent is measured by GC-MS. The amount of acetone is below the detection limit of this technique, i.e. 10 ppm.

[0144] 2. Preparation of a solid electrolyte for a Li-ion battery separator by coating

[0145] A solid electrolyte of the same composition as Example 1 is prepared with a different imbibition method. 0.4 g of P(VDF-HFP) (containing 11% HFP by weight) is dissolved in 1.93 g of acetone at room temperature. 0.056 g of LiFSI (lithium bis(fluorosulfonyl)amide) is further dissolved in 0.276 g of EMIM-FSI (1-ethyl-3-methylimidazolium bis(fluorosulfonyl imide) and 0.281 g of tetraethylene glycol dimethyl ether (EG4DME). This latter solution is added to the P(VDF-HFP) solution and then mixed. The final solution is then coated onto a polypropylene non-woven fabric (thickness 40 µm, porosity approximately 50%, weight 18 g / m2) using a doctor blade. The doctor blade height is greater than the thickness of the non-woven fabric. It is then dried at 60°C under vacuum for 1 night. The final result is a transparent self-supporting film of approximately 60 µm.

[0146] The residual solvent is measured by GC-MS. The amount of acetone is below the detection limit of this technique, i.e. 10 ppm.

[0147] 3. Measurement of the conductivity of an all-solid separator

[0148] The conductivity is evaluated by electrochemical impedance spectroscopy by placing the solid electrolyte (prepared under an inert atmosphere) between the two gold electrodes of a sealed conductivity cell under an inert atmosphere (CESH, Bilogic). 0.26 mS / cm at 25°C is measured on the immersed solid electrolyte and 0.21 mS / cm at 25°C on the coated solid electrolyte.

[0149] [Fig. 1] shows the result of a tensile test carried out on two solid electrolyte films, in the form of a graph showing the tensile force applied to each specimen as a function of the elongation. Film (1) is composed solely of a polymer matrix without mechanical reinforcement, while film (2) is composed of a matrix (the same matrix as film 1) with mechanical reinforcement in the form of polypropylene non-woven fabric.

[0150] These results show that, to lengthen the film by 10%, it is necessary to apply a force approximately 10 times higher in the case of the film containing mechanical reinforcement.

Claims

Claims

1. Solid electrolyte composition consisting of a matrix made up of the following components a), b) and c): a) at least one vinylidene fluoride (VDF) copolymer and at least one VDF-compatible comonomer, b) at least one plasticizer, c) at least one lithium salt, and at least one mechanical reinforcement (component d).

2. The composition of claim 1, wherein said comonomer is selected from vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoro(methylvinyl)ether, perfluoro(ethylvinyl)ether, and perfluoro(propylvinyl)ether.

3. Composition according to one of claims 1 or 2, in which said VDF copolymer is a copolymer of vinylidene fluoride and hexafluoropropylene (HFP) having a mass content of HFP greater than or equal to 5%, preferably greater than or equal to 8%, advantageously greater than or equal to 11%, and less than or equal to 45%, preferably less than or equal to 30%.

4. A composition according to any one of claims 1 to 3, wherein said plasticizer is an ionic liquid which comprises an anion selected from tetrafluoroborate (BF4), bis(oxalato)borate BOB, hexafluorophosphate (PF6), hexafluoroarsenate (AsF6), triflate or trifluoromethylsulfonate (CF3SO3), bis(fluorosulfonyl)imide (FSI), bis-(trifluoromethanesulfonyl)imide (TFSI), nitrate (NO3) and 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI), and a cation selected from the list: ammonium, sulfonium, pyridinium, pyrrolidinium, imi-dazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and their mixtures.

5. Composition according to any one of claims 1 to 3, in which said plasticizer is a mixture of at least one ionic liquid and at least one solvent with a boiling point above 160°C chosen from: vinylene carbonate, fluoroethylene carbonate, trans-4,5-difluoro-1,3-dioxolan-2-one, ethylene carbonate, propylene carbonate, (2-cyanoethyl)triethoxysilane, 3-methoxypropionitrile, sulfolane, and polyethylene glycol dimethyl ethers.

6. A composition according to any one of claims 1 to 5, wherein said lithium salt is selected from: LiPF6 LiFSI, LiTFSI, LiTDI, LiBF4, LiNO3 and LiBOB.

7. A composition according to any one of claims 1 to 6, wherein said reinforcement is selected from the list: microporous film, woven substrate, meltblown or spunbonded nonwoven substrate, cellulose separator, short fiber staples, or meltspun fibers.

8. Composition according to any one of claims 1 to 6, in which said reinforcement is chosen from: polymers, carbon fibers, carbon nanotubes, inorganic fibers and plant fibers.

9. A composition according to any one of claims 1 to 6, wherein said reinforcement is selected from: polymers, for example polyolefin, PVDF, PTFE, polyamide, polyimide, polyaramide, polybenzoaxoles, polybenzimidazoles, polybenzthiazoles, polyphosphazenes, PEKK, PEEK, PES or PSU; carbon fibers; carbon nanotubes; inorganic fibers, for example glass fibers; and plant fibers, for example paper, lignin, cellulose, or cellulose nanowhiskers.

10. Composition according to any one of claims 1 to 9 consisting of: a) 8 to 66.5% of VDF copolymer(s), b) 4 to 76% of plasticizer(s), and c) 0.8 to 28.5% of lithium salt(s), d) 5 to 60% of mechanical reinforcement(s), the sum of all the constituents being 100%.

11. Non-porous film consisting of the composition according to one of claims 1 to 10.

12. Film according to claim 11, having a content of solvent(s) with a boiling point below 150°C, less than 1% by weight, preferably less than 0.1%, preferably less than 10 ppm.

13. Film according to one of claims 11 or 12, having an ionic conductivity of 0.01 to 5 mS / cm, preferably of 0.05 to 5 mS / cm, advantageously of 0.5 to 5 mS / cm at 25°C, measured by electrochemical impedance spectroscopy.

14. Process for preparing the film according to one of claims 11 to 13 by immersion, said process comprising the following steps: - solubilizing said at least one VDF copolymer at temperature ambient in a solvent chosen from: n-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl formamide, methyl ethyl ketone, acetonitrile, and acetone; - dissolving said at least one lithium salt in a plasticizer, to obtain a lithium salt solution; - mixing the VDF copolymer and lithium salt solutions, - immersing a fibrous reinforcement in the mixture obtained, - drying the film thus obtained.

15. A method of preparing the film according to one of claims 11 to 13 by coating, said method comprising the following steps: - solubilizing said at least one VDF copolymer at room temperature in a solvent chosen from: n-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl formamide, methyl ethyl ketone, acetonitrile, and acetone; - dissolving said at least one lithium salt in a plasticizer, to obtain a lithium salt solution; - mixing the VDF copolymer and lithium salt solutions, - coating a fibrous reinforcement with the mixture thus obtained, - drying the film thus obtained.

16. A separator for a Li-ion rechargeable battery, comprising the film according to one of claims 11 to 13.

17. Electrochemical device selected from the group: batteries, capacitor, electrochemical double layer electric capacitor, and membrane-electrode assembly (MEA) for fuel cell or an electrochromic device, said device comprising a film according to one of claims 11 to 13.

18. An all-solid-state battery comprising an anode, a cathode and a separator, wherein said separator comprises the film according to one of claims 11 to 13.

19. An all-solid-state battery comprising an anode, a cathode and a separator, wherein the anode and / or the cathode comprise a non-porous film according to one of claims 11 to 13.

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