Solid electrolyte for all-solid-state battery

Abstract

The present invention relates to the field of electrical energy storage in all-solid-state batteries, in particular in Li-ion type accumulators. More specifically, the invention relates to a solid electrolyte consisting of a polymer matrix and a fiber reinforcement, which allows the production of a non-porous film that exhibits a very good compromise between ionic conductivity, electrochemical stability, high temperature stability and mechanical strength. This film is intended for separator applications in all-solid-state batteries, in particular Li-ion batteries. The invention also relates to an all-solid-state battery comprising such a separator and / or such an electrolyte.

Description

[Technical field]

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

[0002] A Li-ion battery comprises at least one negative electrode or anode bound to a copper current collector, a positive electrode or cathode bound to an aluminum current collector, a separator, and an electrolyte. The electrolyte consists of a lithium salt, typically lithium hexafluorophosphate, mixed with a solvent, which is a mixture of organic carbonates selected to optimize the transport and dissociation of ions. A high dielectric constant promotes the dissociation of ions and thus increases the number of ions available in a given volume, while a low viscosity promotes ion diffusion, which, among other parameters, plays an essential role in the rate of charge and discharge of electrochemical systems.

[0003] Lithium-ion batteries traditionally use liquid electrolytes, which are composed of solvents, lithium salts and additives. These electrolytes have good ionic conductivity but are prone to leaking and catching fire 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 combine high ionic conductivity with good electrochemical stability and satisfactory temperature stability. The ionic conductivity must be comparable to that of liquid electrolytes (i.e. around 1 mS / cm at 25°C). The electrochemical stability must allow the use of the electrolyte with cathode materials that can operate at high voltages (>4.5V). Likewise, solid electrolytes must operate up to at least 80°C and not ignite below 130°C.

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

[0006] In general, solid electrolytes must demonstrate better safety, but this cannot be achieved to the detriment of other performance qualities.

[0007] Finally, from a processability and implementation standpoint, the solid electrolyte must be capable of being handled (discharged) and wound up.

[0008] Poly(vinylidene fluoride) (PVDF) and its derivatives show advantages as the main constituent material of the separator due to their electrochemical stability and their high dielectric constant, which promotes the dissociation of ions and therefore the conductivity. The copolymer P(VDF-HFP) (a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP)) has been studied as a gelling membrane, since it shows a lower crystallinity than PVDF. For this reason, the advantage of these P(VDF-HFP) copolymers is that it makes it possible to achieve a greater swelling and thus promote the conductivity.

[0009] Document US5296318 describes a solid electrolyte composition comprising a mixture of P(VDF-co-HFP) copolymer, a lithium salt and a compatible solvent with a moderate boiling point (i.e. between 100°C and 150°C), which is 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 comprising a mixture of P(VDF-HFP) copolymer, LiPF6 (lithium hexafluorophosphate) and ethylene carbonate and propylene carbonate.

[0010] The composite solid electrolyte exhibits improved mechanical properties.

[0011] A publication in Journal of Membrane Science, 638 (2021), 119713 by Kun Shi et al. describes a PVDF / PP / PVDF composite. The polypropylene (PP) is a Celgard 2400 microporous film. The PVDF is a homopolymer of HSV900 type from Shenzhen Kejing Star Technology Co. The composite contains 25 wt% LiClO4. A 100 μm PVDF / PP / PVDF trilayer membrane exhibits an ionic conductivity of 0.15 mS / cm at 25 °C and can increase the Young's modulus from 24 to 102 MPa compared to a PVDF monolayer. However, the trilayer is prepared in N,N-dimethylformamide (DMF), and a non-trivial amount of free DMF remains trapped in the PVDF after drying, which limits the electrochemical stability.

[0012] There remains a need to develop new solid electrolytes that exhibit a good compromise between ionic conductivity, electrochemical stability and temperature stability, and are suitable for simplified use compatible with industrial applications. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] U.S. Pat. No. 5,296,318 [Non-patent literature]

[0014] [Non-Patent Document 1] Kun Shi et al., Journal of Membrane Science, 638 (2021), 119713 Summary of the Invention [Problem to be solved by the invention]

[0015] It is therefore an object of the present invention to overcome at least one of the shortcomings of the prior art, namely to provide a solid electrolyte composition that exhibits performance qualities at least equivalent to those of liquid electrolytes.

[0016] The present invention also relates to a non-porous polymeric film made from said composition exhibiting good properties of mechanical strength, ionic conductivity and electrochemical stability.

[0017] The present invention also aims to provide at least one process for producing this polymer film.

[0018] Another subject of the invention is a separator, in particular for Li-ion batteries, which consists entirely or partly of said film, which can also be used in batteries, capacitors, electrochemical double layer capacitors and membrane-electrode assemblies (MEAs) for fuel cells or electrochromic devices.

[0019] Finally, the present invention aims to provide an all-solid-state battery, in particular a rechargeable Li-ion battery, comprising such a separator. [Means for solving the problem]

[0020] The present invention first relates to a solid electrolyte composition comprising a matrix composed of the following components a), b) and c): 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 at least one mechanical reinforcement (component d).

[0021] The term "comonomers compatible with VDF" is understood to mean comonomers that can be polymerized with VDF. These monomers are preferably selected from vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP) or perfluoro(alkyl vinyl) ethers, such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) or perfluoro(propyl vinyl) ether (PPVE).

[0022] According to one embodiment, the VDF copolymer is a terpolymer.

[0023] According to one embodiment, component a) is a copolymer of at least vinylidene fluoride (VDF) and hexafluoropropylene (HFP), ie P(VDF-HFP).

[0024] Advantageously, said P(VDF-HFP) copolymer has a content of HFP of at least 5% and at most 45% by weight.

[0025] According to one embodiment, the lithium salt is selected from the following list: LiFSI, LiTFSI, LiTDI, LiPF6, LiBF4 and LiBOB.

[0026] The reinforcement consists of any material that makes it possible to improve the mechanical properties compared to the matrix alone.

[0027] The present invention also relates to a non-porous film of said solid electrolyte composition, which advantageously does not contain solvents with low boiling points (i.e. below 150° C.) and exhibits high ionic conductivity.

[0028] Another subject of the invention is a separator comprising said film, in particular a separator for a rechargeable Li-ion battery.

[0029] The present invention also relates to an electrochemical device selected from the following groups: a battery, a capacitor, an electrochemical double layer electric capacitor, and a membrane-electrode assembly (MEA) for a fuel cell or an electrochromic device, comprising said separator.

[0030] Another subject of the invention is a lithium-based all-solid-state battery, such as a Li-ion battery, or a Li-S or Li-air battery, comprising an anode, a cathode and a separator, the separator comprising said film.

[0031] The present invention also relates to an all-solid-state battery comprising such a non-porous film.

[0032] The present invention makes it possible to overcome the drawbacks of the prior art, and more particularly to provide a non-porous film capable of acting as a separator in an all-solid-state battery, combining high ionic conductivity, good electrochemical stability, temperature stability and sufficient mechanical strength to facilitate handling.

[0033] The advantage of the present invention is that it provides better safety assurance compared to separators or electrolytes based on liquid electrolytes, with electrochemical performance qualities at least equal to those of liquid electrolytes, and therefore there is no possibility of electrolyte leakage, thereby greatly reducing the flammability of the electrolyte.

[0034] Just like liquid electrolytes, the solid electrolyte according to the invention can be used in batteries having anodes made of graphite, silicon, or graphite and silicon, but its resistance to dendrite growth at the surface of the anode also allows for lithium metal anodes, which allows for energy density savings compared to conventional Li-ion technology. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 is a diagram illustrating the variation of tensile strength as a function of elongation for two films, namely comparative film 1 and film 2 according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The invention will now be explained in more detail and in a non-limiting manner in the following description.

[0037] According to a first aspect, the present invention relates to a solid electrolyte composition consisting of a matrix composed of the following components a), b) and c): 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 at least one mechanical reinforcement (component d).

[0038] According to various embodiments, the solid electrolyte membrane comprises the following features, in combination where appropriate: Contents given are by weight unless otherwise indicated. Concentration ranges given are inclusive of limits unless otherwise indicated.

[0039] <Component a)> Component a) consists of at least one copolymer comprising units of vinylidene difluoride (VDF) and one or more units of a comonomer compatible with vinylidene difluoride (hereinafter "VDF copolymer"), which contains at least 50% by weight of vinylidene difluoride, advantageously at least 70% by weight of VDF, preferably at least 80% by weight of VDF.

[0040] Comonomers compatible with vinylidene difluoride can be halogenated (fluorinated, chlorinated or brominated) or non-halogenated.

[0041] Examples of suitable fluorinated comonomers are vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, trifluoropropene, in particular 3,3,3-trifluoropropene, tetrafluoropropene, in particular 2,3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, in particular 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene, perfluoroalkyl vinyl ethers, in particular those of the general formula Rf-O-CF=CF2, where Rf is an alkyl group, preferably a C1-C4 alkyl group (preferred examples are perfluoropropyl vinyl ether and perfluoromethyl vinyl ether). The fluorinated monomer may contain a chlorine or bromine atom. It may be selected in particular from bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene and chlorotrifluoropropene. Chlorofluoroethylene can represent either 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. The 1-chloro-1-fluoroethylene isomer is preferred. The chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.

[0042] According to one embodiment, component a) consists of a VDF copolymer.

[0043] According to one embodiment, component a) consists of a P(VDF-HFP) copolymer, advantageously having a content of HFP of at least 5% by weight, preferably at least 8% by weight, advantageously at least 11% by weight, and at most 45% by weight, preferably at most 30% by weight.

[0044] According to one embodiment, said component a) consists of a mixture of two VDF copolymers with different structures.

[0045] According to one embodiment, component a) consists of a VDF copolymer to which a PVDF homopolymer has been added in a weight percentage ranging from 0% to 10% by weight relative to the weight of said component a).

[0046] According to one embodiment, said component a) consists of a mixture of PVDF homopolymer (in a proportion of up to 10%) and of P(VDF-HFP) copolymer.

[0047] According to one embodiment, the VDF copolymers and / or PVDF homopolymers participating in the composition of component a) comprise monomer units carrying at least one of the following functional groups: carboxylic acid, carboxylic anhydride, carboxylic ester, epoxy (such as glycidyl), amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenol, ester, ether, siloxane, sulfonic acid, sulfuric acid, phosphoric acid or phosphonic acid. The functional groups are introduced by chemical reaction, which may be grafting or copolymerization, according to techniques well known to those skilled in the art, of a fluorinated monomer with a monomer carrying at least one of said functional groups and a vinyl function capable of copolymerizing with the fluorinated monomer.

[0048] According to one embodiment, the functional groups have carboxylic acid functional groups which are (meth)acrylic acid type groups selected from acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate and hydroxyethylhexyl (meth)acrylate.

[0049] According to one embodiment, the unit having a carboxylic acid functionality further comprises a heteroatom selected from oxygen, sulfur, nitrogen and phosphorus.

[0050] The content of functional groups of the VDF copolymers and / or PVDF homopolymers participating 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 %.

[0051] According to one embodiment, the VDF copolymer has a high molecular weight. As used herein, the term "high molecular weight" refers to a VDF copolymer that is polymerized at 232°C and 100s according to the ASTM D-3835 method. -1 is understood to mean a copolymer having a melt viscosity, measured at 100 Pa.s, preferably at 500 Pa.s and more preferably at 1000 Pa.s.

[0052] The VDF copolymers used in the present invention can be obtained by known polymerization methods such as emulsion, solution or suspension polymerization.

[0053] According to one embodiment, it is prepared by an emulsion polymerization process in the absence of a fluorinated surfactant.

[0054] According to one embodiment, said VDF copolymer is a random copolymer: this type of copolymer presents the advantage of exhibiting a uniform distribution of the comonomer along the vinylidene fluoride chain.

[0055] According to one embodiment, said VDF copolymer is a "heterogeneous" copolymer characterized by a heterogeneous distribution of comonomers along the VDF chain, due to the process of synthesis described by the applicants in, for example, documents US6187885 or US10570230. Heterogeneous copolymers have two (or more) distinct phases, with a PVDF homopolymer-rich phase and a comonomer-rich copolymer phase.

[0056] According to one embodiment, the heterogeneous copolymer consists of non-continuous, discrete and individual copolymer domains of a comonomer-rich phase homogeneously distributed in a PVDF-rich continuous phase, hence the term "non-continuous structure."

[0057] According to another embodiment, a heterogeneous copolymer is a copolymer having two (or more) continuous phases that are intimately bound to each other and cannot be physically separated, hence the term "co-continuous structure".

[0058] According to one embodiment, the heterogeneous copolymer comprises: a) 25% to 50% by weight of a first bicontinuous phase comprising 90 to 100% by weight of vinylidene fluoride monomer units and 0 to 10% by weight of other fluoromonomer units; b) from 65% to 95% by weight of vinylidene fluoride monomer units and an effective amount of one or more comonomers, such as hexafluoropropylene and perfluorovinyl ether, where the one or more comonomers are for effecting phase separation of the second cocontinuous phase from the first cocontinuous phase; and The mixture comprises two or more co-continuous phases, including

[0059] Heterogeneous copolymers can be produced by forming an initial polymer, in a preferred embodiment a PVDF homopolymer, rich in VDF monomer units, generally containing more than 90% by weight, preferably more than 95% by weight VDF, and then adding comonomer to the reactor at a well advanced point in the polymerization to produce the copolymer. The VDF rich polymer and the copolymer form separate phases giving an intimate heterogeneous copolymer.

[0060] The copolymerization of VDF with a comonomer, such as HFP, generally results in a latex having a solids content of 10% to 60% by weight, preferably 10% to 50% by weight, and a weight average particle size of less than 1 micrometer, preferably less than 800 nm, more preferably less than 600 nm. The weight average size of the particles is generally at least 20 nm, preferably at least 50 nm, advantageously with an average size in the range of 100 to 400 nm. The polymer particles can form aggregates, the weight average size of which is between 1 and 30 micrometers, preferably between 2 and 10 micrometers. The aggregates can break down into separate particles during formulation and application to a substrate.

[0061] The VDF copolymers used in the present invention may form a gradient between the core and the surface of the particle in terms of composition (eg comonomer content) and / or molecular weight.

[0062] According to some embodiments, the VDF copolymer contains bio-based VDF. The term "bio-based" means "obtained from biomass". This allows improving the ecological footprint of the membrane. Bio-based VDF is according to the standard NF EN 16640 14 It can be characterized by a content of at least 1 atomic % of renewable carbon, i.e. carbon of natural origin derived from biological materials or biomass, as determined by the content of C. The term "renewable carbon" indicates that the carbon is of natural origin and derived from biological materials (or biomass), as shown below. According to some embodiments, the biocarbon content of the VDF can be greater than 5%, preferably greater than 10%, preferably greater than 25%, preferably greater than 33%, preferably greater than 50%, preferably greater than 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%.

[0063] <Component b)> The second component of the solid electrolyte composition of the present invention comprises at least one plasticizer.

[0064] According to one embodiment, the plasticizer is an ionic liquid.

[0065] Ionic liquids are liquid salts at ambient temperature, i.e., they have a melting point below 100° C. at atmospheric pressure. They are formed by the combination of organic cations and anions, whose ionic interactions are weak enough so as not to form a solid.

[0066] Examples of organic cations include the following cations: ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and combinations thereof. According to one embodiment, the cation is a C1-C cation such as 1-butyl-1-methylpyrrolidinium, 1-ethyl-3-methylimidazolium, N-methyl-N-propylpyrrolidinium, or N-methyl-N-butylpiperidinium. 30 It may contain an alkyl group.

[0067] According to one embodiment, the anions combined therewith are imides, in particular bis(fluorosulfonyl)imides and bis(trifluoromethanesulfonyl)imides, borates, phosphates, phosphinates and phosphonates, in particular alkylphosphonates, amides, in particular dicyanamides, aluminates, in particular tetrachloroaluminates, halides (such as bromide, chloride or iodide anions), cyanates, acetates (CHCOO - ), especially trifluoroacetates, sulfonates, especially methanesulfonates (CH3SO3 - ) or trifluoromethanesulfonate, and the sulfates, in particular the hydrogen sulfates.

[0068] According to one embodiment, the anion is tetrafluoroborate (BF4 - ), bis(oxalato)borate (BOB - ), hexafluorophosphate (PF6 -), hexafluoroarsenate (AsF6 - ), triflate, i.e. trifluoromethylsulfonate (CF3SO3 - ), bis(fluorosulfonyl)imide (FSI - ), bis(trifluoromethanesulfonyl)imide (TFSI - ), nitrates (NO3 - ) and 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI - ) is selected.

[0069] According to one embodiment, the anion of the ionic liquid is TDI - , F.S.I. - , TFSI - , PF6 - , BF4 - , NO3 - and B.O.B. - is selected from.

[0070] According to one embodiment, the anion of the ionic liquid is FSI - It is.

[0071] According to one embodiment, said component b) is a mixture of at least two ionic liquids selected from those mentioned above.

[0072] 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 (above 160° C.). According to one embodiment, said solvent is - Vinylene carbonate (VC) (CAS: 872-36-6), - Fluoroethylene carbonate or 4-fluoro-1,3-dioxolan-2-one (FEC or F1EC) (CAS: 114435-02-8), - trans-4,5-difluoro-1,3-dioxolan-2-one (F2EC) (CAS: 171730-81-7), - Ethylene carbonate (EC) (CAS: 96-49-1), - Propylene Carbonate (PC) (CAS: 108-32-7), - (2-cyanoethyl)triethoxysilane (CAS: 919-31-3), - 3-Methoxypropionitrile (CAS number 110-67-8), - Sulfolane (126-33-0), 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); is selected from.

[0073] The plasticizer makes it possible to obtain improved properties in terms of conductivity, electrochemical stability, thermal stability, compatibility with the electrodes, and capacity retention, compared to conventional liquid electrolytes.

[0074] Examples of component b) according to the invention are the following mixtures: - 1-ethyl-3-methylimidazolium FSI and FEC, - 1-ethyl-3-methylimidazolium FSI and tetraethylene glycol dimethyl ether, - 1-Butyl-1-methylpyrrolidinium FSI and FEC, - 1-ethyl-3-methylimidazolium TFSI and FEC, - 1-ethyl-3-methylimidazolium FSI, - 1-Butyl-1-methylpyrrolidinium FSI.

[0075] According to one embodiment, in the mixture of at least one ionic liquid and a solvent, forming component b), the weight ratio of ionic liquid to solvent varies from 10:0.1 to 0.1:10.

[0076] <Ingredient c)> The lithium salt present in the solid electrolyte composition contains the same anion as that of the ionic liquid present in component b).

[0077] According to one embodiment, the lithium salts are LiPF6, LiFSI, LiTFSI, LiTDI, LiBF4, LiNO3 and LiBOB.

[0078] <Component d)> The mechanical reinforcement consists of any material (porous membrane, woven or non-woven fabric) that makes it possible to improve the mechanical properties compared to the matrix alone (components a+b+c). It can be, but is not limited to: - microporous films based on polyolefins such as polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP) and the Li-ion separator Celgard®; - porous films based on PVDF, polyethersulfone (PES) or polysulfone (PSU), - Textile substrates (e.g. PP, PE, PET, PVDF, PES, PSU, inorganic fibers), - the following types of nonwoven substrates: meltblown (e.g. PP, PET, PVDF, PES, PSU), spunbond substrates (e.g. PP, PET, PVDF, PES, PSU), - cellulose separator, - short staple fibres, or - Melt spun fibers.

[0079] According to one embodiment, the mechanical reinforcement is a multi-layer material having at least one polyolefin layer and at least one inorganic layer, for example Celgard® PP coated on both sides with an alumina layer.

[0080] The mechanical reinforcement may be selected from polymers (e.g. polyolefins, PVDF, PTFE, polyamides, polyimides, polyaramids, polybenzoaxoles, polybenzimidazoles, polybenzothiazoles, 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).

[0081] According to one embodiment, the woven or nonwoven fabric is made of fibers and has a density of 50 g / m 2 Less than 30 g / m 2 Less than 20 g / m 2 less than 15 g / m 2 This indicates the weight per unit area less than 100 mm.

[0082] According to one embodiment, the solid electrolyte composition comprises: a) 8% to 66.5% VDF copolymer(s), b) 4% to 76% plasticizer(s); c) 0.8% to 28.5% lithium salt(s); and d) 5% to 60% mechanical reinforcement (However, the total of all components is 100%) It consists of:

[0083] According to one embodiment, the solid electrolyte composition comprises: - 18% to 45% of components a), - 24% to 63% of components b), - 1.8% to 9% of component c) and - 10% to 40% of the components d) It consists of:

[0084] According to one embodiment, the solid electrolyte composition is composed of P(VDF-HFP) copolymer in a weight ratio of 32 / 44.8 / 3.2 / 20, an EMIM-FSI / EG4DME mixture, LiFSI, and a PVDF non-woven fabric, with the weight ratio of EMIM-FSI / EG4DME being 1:1.

[0085] The present invention also relates to a non-porous film or membrane made of said solid electrolyte composition. Advantageously, the film is solvent-free and exhibits high ionic conductivity. Advantageously, the film is self-supporting, i.e., can be handled without the aid of a support. Advantageously, the film can be wound, i.e., can be handled so that it can be wound on a reel.

[0086] According to one embodiment, said film exhibits a thickness ranging from 5 μm to 60 μm, preferably from 5 μm to 30 μm and more preferentially from 7 μm to 20 μm.

[0087] According to one embodiment, the film according to the invention exhibits an ionic conductivity in the range of 0.01-5 mS / cm, preferably 0.05-5 mS / cm, advantageously 0.5-5 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 under an inert atmosphere (CESH, Biologic) in a leak-proof conductivity cell and electrochemical impedance spectroscopy is carried out between 1 Hz and 1 MHz at an amplitude of 10 mV. The resistance R of the film is then determined by linear regression of the curve -Im(Z)=f(Re(Z)). The conductivity σ is given by:

[0088]

number

[0089] Advantageously, the films according to the present invention exhibit good electrochemical stability over a temperature range extending from -20°C to 80°C.

[0090] Advantageously, the film according to the invention has a content of less than 1% by weight of solvents with a boiling point below 150° C., preferably less than 0.1%, preferably less than 10 ppm.

[0091] Advantageously, the film retains its properties up to 80°C and does not ignite below 130°C.

[0092] According to one embodiment, the film according to the invention exhibits a mechanical strength characterized by a modulus of elasticity greater than 0.1 MPa, preferentially greater than 1 MPa and more preferentially greater than 10 MPa, measured by dynamic mechanical analysis at 1 Hz and 23° C.

[0093] The present invention also aims to provide at least one process for producing the non-porous polymeric film.

[0094] According to one embodiment, the film is produced by immersion in a solution containing a, b and c. The at least one VDF copolymer is dissolved at ambient temperature in a solvent selected from N-methyl-2-pyrrolidone, dimethylsulfoxide, dimethylformamide, methyl ethyl ketone, acetonitrile and acetone. The at least one lithium salt is dissolved in a solution of at least one plasticizer to obtain a lithium salt solution. These two solutions are mixed. A mechanical reinforcement is then immersed in the final solution. The film is then dried, for example overnight under vacuum at 60° C. In the case of acetone, it is possible to dry in a ventilated oven. A completely homogeneous, transparent and self-supporting film is finally obtained.

[0095] According to one embodiment, the film is produced by coating. The at least one VDF copolymer is dissolved at ambient temperature in a solvent selected from N-methyl-2-pyrrolidone, dimethylsulfoxide, dimethylformamide, methylethylketone, acetonitrile and acetone. The at least one lithium salt is dissolved in an ionic liquid / plasticizer mixture to obtain a lithium salt solution. The two solutions are mixed.

[0096] One or both sides of the mechanical reinforcement are coated with the mixture thus obtained, for example using a doctor blade. The film is then dried, for example overnight under vacuum at 60° C. In the case of acetone, it is possible to dry in a ventilated oven. A completely homogeneous, transparent, self-supporting film is finally obtained.

[0097] Another subject of the invention is a separator for an all-solid-state battery, consisting entirely or partly of said film.

[0098] The present invention also relates to an electrochemical device selected from the group of a battery, a capacitor, an electrochemical double layer electric capacitor, and a membrane-electrode assembly (MEA) for a fuel cell or an electrochromic device, comprising said separator.

[0099] Another subject of the invention is an all-solid-state battery, for example a Li-ion battery, or a Li-S or Li-air battery, comprising an anode, a cathode and a separator, the separator comprising the film described above.

[0100] According to one embodiment, the battery includes a lithium metal anode.

[0101] The present invention also relates to an all-solid-state battery comprising an anode, a cathode and a separator, wherein the anode and / or the cathode comprises such a non-porous film. EXAMPLES

[0102] The following examples illustrate, but do not limit, the scope of the invention.

[0103] 1. Preparation of solid electrolyte for separator of Li-ion battery by immersion 0.4 g of P(VDF-HFP) (poly(vinylidene fluoride)-co-hexafluoropropylene) (containing 11% by weight of HFP) is dissolved in 1.93 g of acetone at ambient temperature. Additionally, 0.056 g of LiFSI (lithium bis(fluorosulfonyl)imide) is 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). The latter solution is added to the P(VDF-HFP) solution and then mixed. A polypropylene nonwoven fabric (thickness 40 μm, porosity about 50%, weight per unit area 18 g / m) is then prepared. 2 ) is immersed in the final solution for 5 minutes. It is then dried overnight at 60° C. under vacuum. Finally, a transparent, self-supporting film of about 60 μm is obtained.

[0104] Residual solvents are measured by GC-MS: the amount of acetone is below the detection limit of the technique, i.e. 10 ppm.

[0105] 2. Preparation of solid electrolyte for Li-ion battery separator by coating A solid electrolyte with the same composition as in Example 1 is prepared by a different impregnation process. 0.4 g of P(VDF-HFP) (containing 11% by weight of HFP) is dissolved in 1.93 g of acetone at ambient temperature. Additionally, 0.056 g of LiFSI (lithium bis(fluorosulfonyl)imide) is 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). The latter solution is added to the P(VDF-HFP) solution and then mixed. The final solution is then applied to a polypropylene nonwoven fabric (thickness 40 μm, porosity about 50%, weight per unit area 18 g / m) using a doctor blade. 2) The height of the doctor blade is greater than the thickness of the nonwoven fabric. This is followed by drying overnight at 60° C. under vacuum. Finally, a transparent, self-supporting film of about 60 μm is obtained.

[0106] Residual solvents are measured by GC-MS: the amount of acetone is below the detection limit of the technique, i.e. 10 ppm.

[0107] <3. Measurement of conductivity of all-solid separator> The conductivity is evaluated by electrochemical impedance spectroscopy by placing the solid electrolyte (prepared under inert atmosphere) between two gold electrodes in a leak-proof conductive cell under inert atmosphere (CESH, Biologic). 0.26 mS / cm is measured at 25°C on the immersed solid electrolyte and 0.21 mS / cm is measured at 25°C on the coated solid electrolyte.

[0108] The results of the tensile tests carried out on the two solid electrolyte films are shown in the form of a graph showing the tensile force applied to each specimen as a function of elongation in Figure 1. Film (1) consists only of a polymer matrix without mechanical reinforcement, while film (2) consists of a matrix (the same matrix as film (1)) with mechanical reinforcement in the form of a polypropylene nonwoven fabric.

[0109] These results indicate that to stretch a film by 10%, approximately 10 times the force must be applied to the film containing the mechanical reinforcement.

Claims

1. A solid electrolyte composition comprising a matrix composed of the following components a), b) and c): 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 at least one mechanical reinforcement (component d).

2. 2. The composition of claim 1, wherein the comonomer is selected from vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, and perfluoro(propyl vinyl) ether.

3. 2. The composition according to claim 1, wherein the VDF copolymer is a copolymer of vinylidene fluoride and hexafluoropropylene (HFP) having a content of HFP of at least 5% by weight, preferably at least 8% by weight, advantageously at least 11% by weight, and at most 45% by weight, preferably at most 30% by weight.

4. The plasticizer is tetrafluoroborate (BF ４ － ), bis(oxalato)borate (BOB － ), hexafluorophosphate (PF ６ － ), hexafluoroarsenate (AsF ６ － ), triflate, i.e., trifluoromethylsulfonate (CF ３ SO ３ － ), bis(fluorosulfonyl)imide (FSI － ), bis(trifluoromethanesulfonyl)imide (TFSI － ), nitrate (NO ３ － ) and 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI － 10. The composition of claim 1, wherein the ionic liquid comprises an anion selected from the group consisting of ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and combinations thereof.

5. 2. The composition of claim 1, wherein the plasticizer is a mixture of at least one ionic liquid and at least one solvent having a boiling point greater than 160° C. selected 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 ether.

6. The lithium salt is LiPF ６ 、LiFSI、LiTFSI、LiTDI、LiBF ４ , LiNO ３ and LiBOB.

7. 10. The composition of claim 1, wherein the reinforcing material is selected from a microporous film, a woven substrate, a nonwoven substrate of the meltblown or spunbond type, a cellulosic separator, short staple fibers, or melt-spun fibers.

8. The composition of claim 1 , wherein the reinforcing material is selected from polymers, carbon fibers, carbon nanotubes, inorganic fibers, and plant fibers.

9. 2. The composition of claim 1, wherein the reinforcing material is selected from polymers such as polyolefins, PVDF, PTFE, polyamides, polyimides, polyaramids, polybenzoaxoles, polybenzimidazoles, polybenzothiazoles, polyphosphazenes, PEKK, PEEK, PES or PSU, carbon fibers, carbon nanotubes, inorganic fibers such as glass fibers, and plant fibers such as paper, lignin, cellulose or cellulose nanowhiskers.

10. a) 8% to 66.5% VDF copolymer; b) 4% to 76% plasticizer; c) 0.8% to 28.5% of a lithium salt, and d) 5% to 60% mechanical reinforcement (However, the total of all components is 100%) The composition of claim 1 consisting of:

11. A non-porous film comprising the composition according to any one of claims 1 to 10.

12. 12. A film according to claim 11, having a content of solvents with a boiling point below 150°C of less than 1% by weight, preferably less than 0.1%, preferably less than 10 ppm.

13. 12. A film according to claim 11, exhibiting an ionic conductivity at 25°C of 0.01 to 5 mS / cm, preferably 0.05 to 5 mS / cm, advantageously 0.5 to 5 mS / cm, measured by electrochemical impedance spectroscopy.

14. 12. A process for producing the film of claim 11 by dipping, comprising the steps of: - dissolving said at least one VDF copolymer in a solvent chosen from N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylformamide, methyl ethyl ketone, acetonitrile and acetone at ambient temperature, - dissolving said at least one lithium salt in a plasticizer to obtain a lithium salt solution; - mixing a VDF copolymer solution and a lithium salt solution, - immersing a fiber reinforcement in the mixture obtained; drying the film thus obtained.

15. 12. A process for producing the film of claim 11 by coating, comprising the steps of: - dissolving said at least one VDF copolymer in a solvent chosen from N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylformamide, methyl ethyl ketone, acetonitrile and acetone at ambient temperature, - dissolving said at least one lithium salt in a plasticizer to obtain a lithium salt solution; - mixing a VDF copolymer solution and a lithium salt solution, - coating the fiber reinforcement with the mixture thus obtained, drying the film thus obtained.

16. A separator for a rechargeable Li-ion battery comprising the film of claim 11.

17. 12. An electrochemical device selected from the group of batteries, capacitors, electrochemical double layer electric capacitors, and membrane-electrode assemblies (MEAs) for fuel cells or electrochromic devices, comprising the film of claim 11.

18. 12. An all-solid-state battery comprising an anode, a cathode, and a separator, the separator comprising the film of claim 11.

19. An all-solid-state battery comprising an anode, a cathode, and a separator, wherein the anode and / or the cathode comprises the non-porous film according to claim 11.

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