EP4662718A1

EP4662718A1 - Binder composition for a secondary battery

Info

Publication number: EP4662718A1
Application number: EP24703007.5A
Authority: EP
Inventors: Fernand Gauthy; Vincent FINSY; Luca Merlo; Romain DEBORTOLI; Valeriy KAPELYUSHKO; Guillaume DOLPHIJN; Dominique Bascour
Original assignee: Syensqo Specialty Polymers Italy SpA
Current assignee: Syensqo Specialty Polymers Italy SpA
Priority date: 2023-02-07
Filing date: 2024-02-01
Publication date: 2025-12-17
Also published as: CN121058094A; JP2026509112A; KR20250144404A; WO2024165410A1

Abstract

The present invention relates to an electrode-forming composition comprising a tetrafluoroethylene (TFE) (co)polymer having a specific surface area of 4 m^2/g or less, preferably 2 m²/g or less, measured pursuant to the method ISO9277, at least one electroactive material, optionally at least one solid ionic conducting inorganic material and optionally at least one processing aid; to a separator- forming composition comprising said TFE (co)polymer, at least one solid ionic conducting inorganic material, and optionally at least one processing aid; to a process for manufacturing an electrode or a separator by using the compositions, and to an electrode or a separator obtainable by the process. The present invention also relates to a process for manufacturing a gel polymer electrode; to a gel polymer electrode obtainable by the process; to a secondary battery comprising an electrode, a separator or a gel polymer electrode according to the present invention, and to use of the TFE (co)polymer in a binder composition for a secondary battery.

Description

SSPI 2023/004-WO-PCT BINDER COMPOSITION FOR A SECONDARY BATTERY CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims priority to a European patent application No. 23155379.3 filed on February 7, 2023, the whole content of this application being incorporated herein by reference for all purposes. TECHNICAL FIELD [0002] The present invention relates to an electrode-forming composition comprising a tetrafluoroethylene (TFE) (co)polymer having a specific surface area of 4 m²/g or less, preferably 2 m²/g or less, measured pursuant to the method ISO9277, at least one electroactive material, optionally at least one solid ionic conducting inorganic material and optionally at least one processing aid; to a separator-forming composition comprising said TFE (co)polymer, at least one solid ionic conducting inorganic material, and optionally at least one processing aid; to a process for manufacturing an electrode or a separator by using the composition, and to an electrode or a separator obtainable by the process. The present invention also relates to a process for manufacturing a gel polymer electrode; to a gel polymer electrode obtainable by the process; to a secondary battery comprising an electrode, a separator or a gel polymer electrode according to the present invention, and to use of the TFE (co)polymer in a binder composition for a secondary battery. BACKGROUND OF THE INVENTION [0003] Polymerization of TFE proceeds by a free radical mechanism, initiated by a catalyst or by an initiator depending on the reaction temperature, to produce polytetrafluoroethylene (PTFE). [0004] Dry processes for manufacturing an electrode have been developed with a purpose of reducing the drying step which is time-consuming and costly, but indispensable in wet processes. Typically, such dry processes rely on the fibrillation properties of certain fluoropolymers, such as PTFE, which SSPI 2023/004-WO-PCT are particularly inert and stable in the conventional electrolyte solvents for secondary batteries. Accordingly, the stability of an electrode made using PTFE can be higher than those made with other binders. [0005] Two different regimes of polymerization, i.e. suspension polymerization and emulsion polymerization, are well known in this field, in producing two different types of PTFE. [0006] Suspension polymerization is the route to produce granular polymers, where TFE is polymerized in an aqueous solution accompanied by vigorous agitation without any surfactant. To the contrary, emulsion polymerization produces PTFE in a form of colloidal dispersion under mild agitation with an ample amount of a surfactant at elevated temperature and pressure and by coagulating the colloidal dispersion, PTFE fine powders are produced, which is distinguishable from the suspension- polymerized granular PTFE. [0007] It is the emulsion-polymerized PTFE that has been conventionally used in dry processes for manufacturing an electrode, thanks to its excellent fibrillation behavior and ease to fibrillate. However, the emulsion- polymerized PTFE has some disadvantages, such as difficulty in handling, which requires low temperature during the storage and also throughout the transportation to avoid premature fibrillation. Also, relatively large particle size of the emulsion-polymerized PTFE impacts negatively on the homogeneity of the resulting formulation. [0008] Moreover, due to the presence of residual surfactants, its use is better to be avoided. In particular, the surfactant of choice in the synthesis of fluoropolymers is generally a perfluorinated surfactant or a partially fluorinated surfactant. [0009] In this regard, though the processes for preparing fluoropolymers, in particular PTFE, in an aqueous medium using a non-fluorinated hydrocarbon surfactant have been reported, for instance in WO2022/072693 (Chemours FC, LLC) and WO2021/070159 (Gujarat Fluorochemicals Limited), its performance is known to be inferior to the performance of emulsion-polymerized PTFE that is manufactured by using a fluorine-containing surfactant. In addition, there is a remaining issue of SSPI 2023/004-WO-PCT residual hydrocarbon surfactants. Moreover, as above said, handling of such fine powders would require special treatment, i.e. low temperature to be controlled during the storage and also throughout the transportation. [0010] Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), for instance, are two fluorine-containing surfactants widely used in the past. Even though such fluorine-containing surfactants are better at lowering the surface tension of water than comparable hydrocarbon surfactants, fluorine-containing surfactants persist in the environment for a longer duration, continue to be accumulated, and hence detected in humans and wildlife. [0011] Since 2009, PFOS and its derivatives have been included in the international Stockholm Convention to eliminate their use. PFOS has then been restricted under Annex 1 of the EU’s Persistent Organic Pollutants (POPs) Regulation. In addition, the Stockholm Convention regulates the global elimination of PFOA, its salts and PFOA-related compounds. PFOA has been also banned under the POPs Regulation in Europe since July 4, 2020. Additionally, perfluorohexane sulfonic acid (PFHxS), its salts and PFHxS-related compounds are being considered for inclusion in the Stockholm Convention. [0012] In parallel, the manufacture and use of some PFAS is being restricted under Registration, Evaluation, Authorization and Restriction of Chemicals, i.e. REACH. [0013] In the meantime, suspension-polymerized PTFE has relatively small particle size and is easy to handle without particular limitations on storage and transportation, in comparison to emulsion-polymerized PTFE. Especially, suspension polymerization can be implemented under the conditions substantially free from any surfactant, which is either fluorinated or hydrocarbon. [0014] The Applicant surprisingly found that TFE (co)polymer produced via suspension-polymerization can be at least partially fibrillated, while ensuring good performance and hence can be used as a binder for a secondary battery. Accordingly, electrodes and/or separator which are manufactured by using said TFE (co)polymer substantially do not contain SSPI 2023/004-WO-PCT a fluorine-containing surfactant. Even in case a fluorine-containing surfactant is detected, which is feasible due to its omnipresence in the environment, its detection can be controlled in a very low level, for instance 100 parts per billion (ppb), preferably 20 ppb, more preferably 2 ppb, with respect to the total mass of the electrode or the separator. SUMMARY OF THE INVENTION [0015] A first object of the invention is an electrode-forming composition comprising a binder composition comprising a tetrafluoroethylene (TFE) (co)polymer having a specific surface area of 4 m²/g or less, preferably 2 m²/g or less, measured pursuant to the method ISO9277, at least one electroactive material, optionally at least one solid ionic conducting inorganic material, and optionally at least one processing aid. [0016] A second object of the invention is a separator-forming composition comprising a binder composition according to the present invention, at least one solid ionic conducting inorganic material, and optionally at least one processing aid. [0017] A third object of the invention is a process for manufacturing an electrode or a separator, by using an electrode-forming composition or a separator- forming composition according to the present invention. [0018] A fourth object of the invention is an electrode or a separator obtainable by a process according to the present invention. [0019] A fifth object of the invention is a process for manufacturing a gel polymer electrode by using a binder composition according to the present invention. [0020] A sixth object of the invention is a gel polymer electrode obtainable by a process according to the present invention. [0021] A seventh object of the invention is a secondary battery comprising an electrode, a separator or a gel polymer electrode according to the present invention. [0022] Another object of the invention is use of a TFE (co)polymer having a specific surface area of 4 m²/g or less, preferably 2 m²/g or less, measured pursuant to the method ISO9277 in a binder composition for a secondary battery. SSPI 2023/004-WO-PCT [0023] It was surprisingly found by the inventors that a TFE (co)polymer produced via suspension-polymerization may deliver a particularly advantageous combination of properties, i.e. fibrillation feature sufficient to enable a dry process for manufacturing an electrode and/or a separator for a secondary battery without compromise on a battery performance as well as its mechanical properties. On top of its benefits, the fact that a fluorine- containing surfactant is not required in manufacturing a TFE (co)polymer adds its value in solving the fluorine-containing surfactant-related issues, i.e. its persistence in the ecosystem and its bioaccumulation in humans and animals. DETAILED DESCRIPTION OF THE INVENTION [0024] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. In the context of the present invention, the term ‘percent by weight’ (wt%) indicates the content of a specific component in a mixture, calculated as the ratio between the weight of the component and the total weight of the mixture. [0025] It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. Accordingly, various changes and modifications described herein will be apparent to those skilled in the art. Moreover, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. [0026] The present invention provides an electrode-forming composition comprising a binder composition comprising a TFE (co)polymer, at least one electroactive material, optionally at least one solid ionic conducting inorganic material and optionally at least one processing aid, wherein the TFE (co)polymer has a specific surface area of 4 m²/g or less, preferably 2 m²/g or less, measured pursuant to the method ISO9277. SSPI 2023/004-WO-PCT [0027] In comparison, the specific surface area of an emulsion-polymerized TFE (co)polymer is generally in the range of 5 m²/g or more, preferably 6.5 m²/g or more, more preferably 8.0 m²/g or more, measured pursuant to the method ISO9277. [0028] In some embodiments, the TFE (co)polymer of the present invention is polymerized by a suspension polymerization process in an aqueous media applying vigorous agitation at high pressure, for instance from 0.3 to 2.8 MPa and at a moderate temperature, for instance from 40℃ to 90℃. Inorganic radical initiators such as ammonium persulfate, potassium persulfate, potassium permanganate, etc. can be applied for the suspension polymerization process. Generally, the TFE (co)polymer discharged from a polymerization reactor is in a form of irregular stringy shaped particles such that post-treatment steps of dewatering, drying, milling, etc. may be implemented to prepare fine cut suspension TFE (co)polymers in powders having a determined particle size, for instance from 10 μm to 100 μm, typically from 15 μm to 40 μm. [0029] For the purpose of the present invention, by the term “a secondary battery” it is intended to denote a rechargeable battery. [0030] In one embodiment, the TFE (co)polymer is a TFE homopolymer, a TFE copolymer or blends thereof. [0031] In a particular embodiment, the TFE copolymer comprises additional recurring units derived from: - C₂-C₈ perfluoroolefins different from TFE, such as hexafluoropropylene (HFP); - hydrogen-containing C2-C8 fluoroolefins, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutylene; - (per)fluoroalkyl ethylenes of formula CH₂=CH-R_f, wherein R_f is a C₁-C₆ (per)fluoroalkyl group; - (per)fluoroalkyl vinylethers (PAVE) of formula CF₂=CFOR_f, wherein R_f is a C1-C6 (per)fluoroalkyl group; - (per)fluorooxyalkyl vinylethers of formula CF2=CFOX, wherein X is a C1- C12 ((per)fluoro)oxyalkyl comprising at least one catenary oxygen atom; - (per)fluorodioxoles having formula SSPI 2023/004-WO-PCT wherein R_f3, R_f4, R_f5, and R_f6, equal or different from each other, are independently selected among fluorine atoms and C1-C6 (per)fluoroalkyl groups, optionally comprising at least one oxygen atom; and - (per)fluoromethoxy vinylethers (MOVE) of formula CFX₂=CX₂OCF₂OR”_f, wherein R”_f is selected among linear or branched C₁-C₆ (per)fluoroalkyls, C5-C6 cyclic (per)fluoroalkyls, and linear or branched C2-C6 (per)fluorooxyalkyls comprising from 1 to 3 catenary oxygen atoms, and X2 is F or H; preferably R”_f is –CF₂CF₃ (MOVE1), -CF₂CF₂OCF₃ (MOVE2), or –CF3 (MOVE3) and X2 is F. [0032] In a more particular embodiment, the TFE copolymer comprises said additional recurring units in an amount of 5% by moles (mol%) or less, preferably 1 mol% or less, with respect to the total moles of the recurring units of the TFE copolymer. [0033] In another particular embodiment, the binder composition further comprises an additional polymer different from the TFE (co)polymer. [0034] In a more particular embodiment, the additional polymer different from the TFE (co)polymer is ionically non-conductive. [0035] Non-limitative examples of the additional polymer different from the TFE (co)polymer comprises (alkyl) acrylate polymer, styrene (alkyl)acrylate copolymer, polyvinylpyrrolidone (PVP) (co)polymer, diene or olefin-based rubber such as isobutylene-isoprene rubber (IIR, aka butyl rubber), butadiene rubber (BR), isoprene rubber (IR), ethylene-propylene-diene monomer rubber (EPDM), styrene-butadiene rubber (SBR), styrene- ethylene-butylene-styrene copolymer (SEBS), nitrile butadiene rubber (NBR), hydrogenated NBR (hNBR), ethylene-propylene rubber, etc., modified polysaccharide-based (co)polymer such as caboxymethylcellulose (CMC), polyamide (PA), polyaryletherketone (PAEK) (co)polymer such as polyether ether ketone (PEEK), SSPI 2023/004-WO-PCT polyamideimide (PAI), perfluoroalkoxy alkane (PFA), poly(acrylonitrile) (PAN), styrene-acrylonitrile rubber (SAN, vinyl alcohol or vinyl acetate- containing (co)polymer, such as polyvinylalcohol (PVOH), polyvinyl acetate (PVA), such as polyvinyl butyrate (PVB), etc. [0036] In the other particular embodiment, the additional polymer different from the TFE (co)polymer is a vinylidene difluoride (VDF)-based (co)polymer. [0037] In a preferred embodiment, the VDF-based (co)polymer comprises at least 50 mol%, preferably at least 60 mol% of recurring units derived from VDF with respect to all recurring units of the VDF-based (co)polymer. [0038] In a more preferred embodiment, the VDF-based (co)polymer further comprises recurring units derived from at least one comonomer different from VDF. [0039] In a particular embodiment, the recurring units derived from at least one comonomer different from VDF is selected from a group consisting of - a hydrophilic (meth)acrylic comonomer according to the formula: wherein each of R1, R2, R3, equal or different from each other, is independently a hydrogen atom or a C1-C3 hydrocarbon group, and ROH is a hydroxyl group or a C1-C5 hydrocarbon moiety comprising at least one hydroxyl group; - C₂-C₈ perfluoroolefins, such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP); - chloro- and/or bromo- and/or iodo-C₂-C₆ fluoroolefin, such as chlorotrifluoroethylene (CTFE); - (per)fluoroalkylvinylethers (PAVE) of formula CF2=CFORf, wherein Rf is a C1-C6 (per)fluoroalkyl group; and - a fluorinated olefin comonomer containing at least one –SO2X functional group, X being selected from X’ and OM, X’ being selected from the consisting of F, Cl, Br, and I; and M being selected from the group consisting of H, an alkaline metal and NH4. SSPI 2023/004-WO-PCT [0040] The hydrophilic (meth)acrylic comonomer preferably complies with formula: wherein each of R1, R2, ROH have the meanings as above defined, and R3 is hydrogen; and more preferably, each of R1, R2, R3 are hydrogen, while R_OH has the same meaning as above detailed. [0041] Non-limitative examples of hydrophilic (meth)acrylic comonomers are notably acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, and hydroxyethylhexyl(meth)acrylates. [0042] The hydrophilic (meth)acrylic comonomer is more preferably selected from the group consisting of: - hydroxyethylacrylate (HEA) of formula: - 2-hydroxypropyl acrylate (HPA) of either of formulae: - acrylic acid (AA) of formula: , and - mixtures thereof. [0043] Even more preferably, the hydrophilic (meth)acrylic comonomer is AA and/or HEA, most preferably AA. SSPI 2023/004-WO-PCT [0044] The fluorinated olefin comonomer containing at least one –SO₂X functional group is preferably selected from the group consisting of: - sulfonyl halide fluoroolefins of formula: CF₂=CF(CF₂)_pSO₂X’, wherein p is an integer between 0 to 10, preferably between 1 to 6, more preferably p is equal to 2 or 3, and preferably X’=F; - sulfonyl halide fluorovinylethers of formula: CF2=CF-O-(CF2)mSO2X’, wherein m is an integer between 1 and 10, preferably between 1 and 6, more preferably between 2 and 4, even more preferably m equals to 2, and preferably X’=F; - sulfonyl halide fluoroalkoxyvinylethers of formula: CF₂=CF-(OCF₂CF(R_F1))_w- O-CF₂(CF(R_F2))_ySO₂X’, wherein w is an integer between 0 and 2, R_F1 and R_F2, equal or different from each other, are independently F, Cl or a C₁-C₁₀ fluoroalkyl group, optionally substituted with one of more ether oxygen atom, y is an integer between 0 and 6, preferably w is 1, R_F1 is –CF₃, y is 1 and R_F2 is F, and preferably X’=F; and - sulfonyl halide aromatic fluoroolefins of formula CF2=CF-Ar-SO2X’ or CF2=CF-O-Ar-SO2X’, wherein Ar is a C5-C15 aromatic or heteroaromatic substituent, and preferably X’=F. [0045] In a more preferred embodiment, the fluorinated olefin comonomer containing at least one –SO₂X functional group is selected from the group consisting of sulfonyl fluorides, i.e. wherein X’=F. Most preferably, b) the fluorinated olefin monomer containing at least one –SO₂X functional group is selected from the group of sulfonyl fluorovinylethers of formula: CF₂=CF-O-(CF₂)_mSO₂F, wherein m is an integer between 1 and 6, preferably between 2 and 4. [0046] In a even more preferred embodiment, the fluorinated olefin comonomer containing at least one –SO2X functional group is perfluoro-5- sulfonylfluoride-3-oxa-1-pentene (CF2=CF-O-CF2CF2-SO2F). [0047] In one embodiment, the TFE (co)polymer is characterized by its high molecular weight having standard specific gravity lower than 2.200, preferably lower than 2.190, more preferably lower than 2.180, measured pursuant to ASTM D792. SSPI 2023/004-WO-PCT [0048] In the present invention, the term “electroactive material” is intended to denote a material that is able to incorporate or insert into its structure and substantially release therefrom metal ions during the charging and discharging phases in a battery. [0049] In one embodiment, the electroactive material is for a positive electrode. [0050] In the other embodiment, the electroactive material is for a negative electrode. [0051] In a particular embodiment, the metal ion is a lithium ion. [0052] In the present invention, the solid ionic conducting inorganic material is not particularly limited as long as it is able to conduct metal ions in its structures. [0053] In a particular embodiment, the solid ionic conducting inorganic material is a sulfide-based solid ionic conducting inorganic particle. [0054] In the present invention, the term “sulfide-based solid ionic conducting inorganic particle” is not particularly limited as long as it is a solid electrolyte material containing sulfur atom(s) in the molecular structure or in the composition. [0055] The sulfide-based solid ionic conducting inorganic particle preferably contains Li, S, and an element of from 13 to 15 groups of Periodic table of the elements, for instance, P, Si, Sn, Ge, Al, As, Sb, or B, to increase lithium-ion conductivity. [0056] The sulfide-based solid ionic conducting inorganic particle according to the present invention is preferably selected from the group consisting of: - lithium tin phosphorus sulfide (“LSPS”) materials, such as Li₁₀SnP₂S₁₂; - lithium phosphorus sulfide (“LPS”) materials, such as glass, crystalline or glass-ceramic of those of formula (Li2S)x-(P2S5)y, wherein x+y=1 and 0≤x≤1, Li7P3S11, Li7PS6, Li4P2S6, Li9.6P3S12 and Li3PS4; - doped LPS, such as Li2CuPS4, Li1+2xZn1−xPS4, wherein 0≤x≤1, Li3.33Mg0.33P2S6, and Li4-3xScxP2S6, wherein 0≤x≤1; - lithium phosphorus sulfide oxygen (“LPSO”) materials of formula LixPySzO, wherein 0.33≤x≤0.67, 0.07≤y≤0.2, 0.4≤z≤0.55; SSPI 2023/004-WO-PCT - lithium phosphorus sulfide materials including X (“LXPS”), wherein X is Si, Ge, Sn, As, or Al, such as Li₁₀SnP₂S_12, Li₁₀GeP₂S_12, Li₁₀SiP₂S₁₂, and Li₂S- P₂S₅-SnS; - lithium phosphorus sulfide oxygen including X (“LXPSO”), wherein X is Si, Ge, Sn, As, or Al; - lithium silicon sulfide (“LSS”) materials, such as Li2SiS3, Li2S-P2S5-SiS2 , Li2S-P2S5-SiS2-LiCl, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S- SiS2, Li9.54Si1.74P1.44S11.7Cl0.3, and Li2S-SiS2-Al2S3; - lithium boron sulfide materials, such as Li3BS3 and Li2S-B2S3-LiI; - lithium tin sulfide materials and lithium arsenide materials, such as Li_0.8Sn_0.8S_2, Li₄SnS₄, Li_3.833Sn_0.833As_0.166S₄, Li₃AsS₄-Li₄SnS₄, and Ge- substituted Li₃AsS₄; - lithium phosphorus sulfide materials of general formula Li_aPS_bX_c, wherein X represents at least one halogen element selected from the group consisting of Cl, Br and I or a combination thereof; and a represents a number from 2.0 to 7.0, b represents a number from 3.5 to 6.0, and c represents a number from 0 to 3.0, such as Li4PS4Cl, Li7P2S8Cl, and Li7P2S8I; and - combinations thereof. [0057] In a more preferred embodiment, the sulfide-based solid ionic conducting inorganic particle is a lithium phosphorus sulfide material of the above general formula Li_aPS_bX_c, more particularly Argyrodite-type sulfide material of formula Li₆PS₅X, wherein X is Cl, Br or I. [0058] In another preferred embodiment, the Argyrodite-type sulfide material of formula Li₆PS₅Y is deficient in sulfur and/or lithium, for instance Li_6-xPS_5- xCl1+x with 0 ≤ x ≤ 0.5, or doped with a heteroatom. [0059] Particularly preferred sulfide-based solid ionic conducting inorganic particles are lithium tin phosphorus sulfide (“LSPS”) materials (e.g. Li10SnP2S12) and Argyrodite-type sulfide materials (e.g. Li6PS5Cl). [0060] In another particular embodiment, the solid ionic conducting inorganic material is an oxide-based solid ionic conducting inorganic particle. [0061] In the present invention, the term “oxide-based solid ionic conducting inorganic particle” is not particularly limited as long as it is a solid SSPI 2023/004-WO-PCT electrolyte material containing oxygen atom(s) in the molecular structure or in the composition. [0062] In one embodiment, the oxide-based solid ionic conducting inorganic particle is a garnet-type inorganic particle. [0063] The term “garnet” as used herein refers to the atomic structure of crystalline or partially crystalline oxide ceramic solid. [0064] In a particular embodiment, the garnet-type inorganic particle has a general formula of M¹aM²bM³cOd, wherein - M¹ is a first cationic element selected from the group consisting of H, Li, Na, Mg, Al and Ga, preferably Li; - M² is a second cationic element selected from the group consisting of La, Ba, Sr, Ca, In, Mg, Y, Sc, Cr, Al, K, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; - M³ is a third cationic element selected from the group consisting of Zr, Ta, Nb, Sb, Sn, Hf, Bi, W, Si, Se, Ga and Ge; and - a, b, c, and d are positive numbers including various combinations of integers and decimals. [0065] In a preferred embodiment, the garnet-type inorganic particle has a general formula of LixLayZrzAwO12, wherein: - A represents one or several dopants selected from the group consisting of Al, Ga, Nb, Fe, Nd, Pt, Ta, W, Mo, Hf, Si, Ca, Sr, Ba, Ge, and mixtures thereof; preferably from the group consisting of Al, Ga, Nb, Fe, Nd, Pt, Ta, W, and mixtures thereof; more preferably from the group consisting of Al, Ga, W, and mixtures thereof; - w, x, y, and z are positive numbers, including various combinations of integers and fractions or decimals; - 0 < y ≤ 3 ; preferably 2 ≤ y ≤ 3 ; preferably 2.5 ≤ y ≤ 3; - 0 < z ≤ 2 ; preferably 1 ≤ z ≤ 2 ; preferably 1.5 ≤ z ≤ 2; - 0 ≤ w ≤ 0.5 ; preferably 0 ≤ w ≤ 0.35 ; more preferably 0 ≤ w ≤ 0.25; and - x is derived from electroneutrality of the garnet structure. [0066] In a more preferred embodiment, the solid inorganic particle is LLZO. The term “LLZO” as used herein refers to the general formula of LixL3yZrzAWO12, with x, y, x, w, and A as described above. According to a particular SSPI 2023/004-WO-PCT embodiment, the solid inorganic particle is LLZO doped with Al, W, Ga or combinations thereof. [0067] The general formulae given in the present application correspond to the stoichiometry of the crystalline structure given by x-ray diffraction (XRD). [0068] In another embodiment, the oxide-based solid ionic conducting inorganic particle is an oxide inorganic particle which is not a garnet-type. [0069] In the other embodiment, the oxide-based solid ionic conducting inorganic particle is a phosphate inorganic particle, such as lithium aluminium germanium phosphate (LAGP), lithium titanium phosphate (LTP), lithium aluminum titanium phosphate (LATP), lithium phosphorous oxynitride (aka LiPON), lithium nitride (Li₃N), lithium halide, lithium hydrate, etc. [0070] An electrode in an electrochemical cell is referred to as either an anode or cathode. The anode is defined as the electrode where electrons leave the cell and oxidation occurs, and the cathode as the electrode where electrons enter the cell and reduction occurs. Each electrode may become either an anode or a cathode depending on the direction of electric current through a cell. A bipolar electrode is an electrode that functions as the anode of one cell and the cathode of another cell. When a cell is being charged, the anode becomes the positive electrode and the cathode becomes the negative electrode, while when a cell is being discharged, the anode becomes the negative electrode and the cathode becomes the positive electrode. [0071] In the present invention, the term “positive electrode” is intended to denote, in particular, the electrode of an electrochemical cell, where reduction occurs during discharging, while the term “negative electrode” is intended to denote, in particular, the electrode of an electrochemical cell, where oxidation occurs during discharging. [0072] In the present invention, the term “processing aid” is intended to denote a substance which may be used in manufacturing an electrode or a separator to ease the formation of a mixture of the ingredients and/or the formation of an electrode or a separator into a thin film, such as a non-aqueous solvent and a lubricant. SSPI 2023/004-WO-PCT [0073] In the present invention, a processing aid may be additionally present in an electrode-forming composition. [0074] There is no specific restriction imposed on the non-aqueous solvent as long as the non-aqueous solvent is compatible with the electroactive material and/or the solid ionic conducting inorganic material of the resulting electrode-forming composition. [0075] In one embodiment, the non-aqueous solvent is selected from the group consisting of nitrile-containing solvents, ethers, esters, thiols, thioethers, ketones, and tertiary amines. [0076] In a preferred embodiment, the non-aqueous solvent is a nitrile-containing solvent with general formula of R-CN, where R represents an alkyl group. Non-limiting examples of nitrile-containing solvents are acetonitrile, butyronitrile, valeronitrile, isobutylnitrile and the like. [0077] In another preferred embodiment, the non-aqueous solvent is an ether with general formula of R₁-O-R₂, where R₁ and R₂ represent independently an alkyl group. Included in the ether solvents are cyclic ethers based on 3, 5 or 6-membered rings. The cyclic ethers can be substituted with alkyl groups, can have unsaturation and can have additional functional elements such as nitrogen or oxygen atoms inside the ring. Non-limiting examples of (cyclic) ether solvents are diethylether, 1,2-dimethoxyether, cyclopentyl methyl ether, diethyl ether, dibutyl ether, 1,3-dioxolane, anisole, tetrahydrofuran, methyl tetrahydrofuran, tetrahydropyran and the like. [0078] In another preferred embodiment, the non-aqueous solvent is an ester with general formula of R₃-C(O)O-R₄, where R₃ and R₄ represent independently an alkyl group. Non-limiting examples of ester solvents are butyl butyrate, heptyl butyrate, isobutyl isobutyrate, ethyl benzoate and the like. [0079] In another preferred embodiment, the non-aqueous solvent is a thiol with general formula of R5=S-H or thioether with general formula of R6-S-R7, where R5, R6 and R7 are independently an alkyl group. Included in the thioether solvents are cyclic thioethers based on 3, 5 or 6-membered rings. The cyclic thioethers can be substituted with alkyl groups, can have SSPI 2023/004-WO-PCT unsaturation and can have additional functional elements such as nitrogen or oxygen atoms inside the ring. Non-limiting examples of thiol solvents are ethanethiol, tert-dodecyl mercaptan, thiophenol, tert-butyl mercaptan, octanethiol, dimethylsulfide, ethylmethylsulfide, methyl benzylsulfide and the like. [0080] In another preferred embodiment, the non-aqueous solvent is a ketone with general formula of R8R9C=O, where R8 and R9 represent independently an alkyl group. Non-limiting examples of ketone solvents are methyl ethyl ketone, methyl isobutyl ketone, di-isobutyl ketone, acetophenone, benzophenone and the like, preferably methyl isobutyl ketone. [0081] In another preferred embodiment, the non-aqueous solvent is a tertiary amine with general formula of R₁₀R₁₁R₁₂N, where R₁₀, R₁₁ and R₁₂ represent independently an alkyl group. The N atom of the tertiary amine can be buried inside a 3, 5 or 6-membered ring. Non-limiting examples of tertiary amine solvents are triethylamine, dimethylbutylamine, tributylamine, cyclohexyldimethylamine, N-ethylpiperidine and the like. [0082] In the present invention, the alkyl groups of R1 to R12 respectively refer to “alkyl groups” including saturated hydrocarbons having one or more carbon atoms, including straight-chain alkyl groups, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl; cyclic alkyl groups (or "cycloalkyl" or "alicyclic" or "carbocyclic" groups), such as cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl; branched-chain alkyl groups, such as isopropyl, tert-butyl, sec-butyl, and isobutyl; alkyl- substituted alkyl groups, such as alkyl-substituted cycloalkyl groups; and cycloalkyl-substituted alkyl groups as defined above. Additionally, the alkyl groups may include functional groups such as 1 or more unsaturation, ether, carbonyl, carboxyl, hydroxyl, thio, thiol, thioxy, sulfo, nitrile, nitro, nitroso, azo, amide, imide, amino, imino or halogen. [0083] In a preferred embodiment, the non-aqueous solvent comprises nitrile- containing solvents, such as acetonitrile; ethers, such as tetrahydrofuran, 2-methyl-tetrahydrofuran, 2,5-dimethyl-tetrahydrofuran, 1,3-dioxolane, SSPI 2023/004-WO-PCT diethyl ether and 1,2-dimethoxyether; esters, such as butyl butyrate; and ketones such as methyl isobutyl ketone. [0084] In a more preferred embodiment, the non-aqueous solvent is an ester, such as butyl butyrate. [0085] In another more preferred embodiment, the non-aqueous solvent is a ketone, such as methyl isobutyl ketone. [0086] Non-limitative examples of the lubricant include aliphatic hydrocarbons, particularly isoparaffinic hydrocarbon compounds and petroleum fractions, and more particularly squalene. Preferred petroleum fractions are gasoline (C₄-C₁₀), naphtha (C₄-C₁₁) and kerosene/paraffin (C₁₀-C₁₆), and mixtures thereof. [0087] In a preferred embodiment, the lubricant is selected from the group consisting of isoparaffinic hydrocarbon compounds and petroleum fractions. [0088] In a particular embodiment, the lubricant is squalene. [0089] In one embodiment, an amount of the lubricant is from 1.0 to 35.0 parts by weight (pbw), preferably from 3.0 to 30.0 pbw and more preferably from 5.0 to 25.0 pbw, with respect to the total weight of the electrode-forming composition comprising a binder composition of the present invention, at least one electroactive material, at least one solid ionic conducting inorganic material and at least one processing aid. including the lubricant. [0090] One or more conductive agents may be added into an electrode-forming composition in order to improve the conductivity of a resulting electrode made according to the process of the present invention. Conductive agents for secondary batteries are known in the art. Non-limitative examples thereof include carbonaceous materials, such as carbon black, graphite fine powder, carbon nanotubes (single wall or multiwall), vapor grown carbon fibers (VGCF), graphene, or fiber, or fine powder or fibers of metals such as nickel or aluminum. The optional conductive agent is preferably carbon black. Carbon black is available, for example, under the brand names, Super P^® or Ketjenblack^®. [0091] The amount of optional conductive agent is preferably from 0 to 20 wt% of the total solids in the electrode-forming composition. For instance, for a SSPI 2023/004-WO-PCT positive electrode-forming composition the optional conductive agent is typically from 0 wt% to 10 wt%, more preferably from 0 wt% to 5 wt% of the total amount of the solids within the composition. In a particular embodiment, the amount of conductive agent is from 0.1 wt% to 10 wt%, preferably from 0.5 wt% to 8 wt%, more preferably from 1 wt% to 5 wt% of the total amount of the solids within the electrode-forming composition. [0092] A second object of the invention is a separator-forming composition comprising a binder composition according to the present invention, at least one solid ionic conducting inorganic material, and optionally at least one processing aid. [0093] In the present invention, the term "separator" is hereby intended to denote a monolayer or multilayer film, which electrically and physically separates the electrodes of opposite polarities in an electrochemical device and is permeable to ions flowing between them. [0094] A third object of the invention is a process for manufacturing an electrode or a separator, comprising the steps of: - processing an electrode-forming composition or a separator-forming composition according to the present invention to fibrillate the TFE (co)polymer; - subsequently calendaring or extruding the composition into a film; and - optionally, laminating said film onto a current collector or on a substrate to produce an electrode or a separator. [0095] In one embodiment, the film is laminated directly on a surface of an electrode to produce a separator. [0096] In a particular embodiment, an additional milling step is implemented prior to the calendaring or extruding step to form a film. [0097] Processing with high shear forces induces at least partial fibrillization of TFE (co)polymer to produce fibrils that eventually form a matrix or lattice for supporting the resulting composition of matter. The resulting agglomerated or dough-like material may be calendared several times to produce a film of desired thickness and density. [0098] In a particular embodiment, TFE (co)polymer according to the present invention possesses two transition temperatures at about 19°C and about SSPI 2023/004-WO-PCT 30°C. Below about 19°C, TFE (co)polymer particles easily slide past each other, while maintaining its identity. The structure of TFE (co)polymer particles, however, becomes looser and more sensitive to mechanical shear above its transition temperature of about 19°C. Accordingly, shearing may unwind the crystalline structure of TFE (co)polymer, initiating so-called fibrillation phenomenon, i.e. creating a three-dimensional (3D) structure consisting of nodes, fibrils interconnecting the nodes, and the free spaces between the fibrils and the nodes. Fibrillation occurs when particles rub against a surface and the fibrils are pulled out of the surface of TFE (co)polymeric particles. At a temperature higher than about 30°C, a higher degree of fibrillation continues. [0099] In a more particular embodiment, the step of fibrillating a TFE (co)polymer is performed at a temperature between 20°C and the melting temperature of the TFE (co)polymer. [00100] In another more particular embodiment, the processing step for fibrillation comprises two sub-steps, i.e. i) homogenizing the composition into powders at a temperature of 19°C or lower and ii) blending the powders into an agglomerated powder or a paste at a temperature of 30°C or higher. [00101] In a preferred embodiment, i) homogenizing sub-step is implemented at a temperature of between about 10°C and about 19°C. [00102] In another preferred embodiment, ii) blending sub-step is implemented at a temperature of between about 20°C and the melting temperature of the TFE (co)polymer. [00103] In a more preferred embodiment, the step of fibrillating a TFE (co)polymer is performed at a temperature between 20°C and 320°C, preferably between 30°C and 300°C, more preferably between 40°C and 250°C. [00104] In the present invention, the device that may be used for the fibrillation is not particularly limited as long as enough shear force and temperature can be applied. Non-limitative examples of such devices are high shear mixers such as kneaders, internal mixers, high shear impact mixers, milling devices such as ball milling devices or jet air milling devices, extruders such as double-screw extruders, 2 or 4-roll roller mills, etc. SSPI 2023/004-WO-PCT [00105] In another particular embodiment, the step of calendaring or extruding is performed at a temperature 320°C or less, preferably 300°C or less, more preferably 250°C or less. [00106] In another more particular embodiment, the step of calendaring or extruding is performed at a temperature between 30°C and 150°C, preferably between 35°C and 120°C, more preferably between 40°C and 100°C. [00107] The step of calendaring may be suitably carried out in a calendar with rolls having a slight speed difference in order to cause shearing forces in the calendaring gap. Such shearing forces may be also provided by subjecting the electrode-forming composition or the separator-forming composition to an extruder. [00108] The electrode-forming composition and the separator-forming composition may be subjected several times to the mechanical compaction, reducing the gap stepwise to apply progressive shearing forces onto the film. Rotational speed and gap of the rolls may be changed in the different passages through the calendaring, in order to produce a film of desired thickness and density. [00109] Said mechanical compaction step may be associated to a thermal consolidation step. The combination of an applied pressure and a heat treatment makes thermal consolidation possible at lower temperatures than if it were done alone. [00110] In one embodiment, a film obtained from the calendaring or extruding step is laminated onto a current collector or on a substrate to produce an electrode or a separator. [00111] In the present invention, the nature of the “current collector” depends on whether the electrode thereby provided is either a positive electrode or a negative electrode. Should the electrode of the invention be a positive electrode, the current collector typically comprises, preferably consists of at least one metal selected from the group consisting of Aluminium (Al), Nickel (Ni), Titanium (Ti), and alloys thereof, preferably Al. Should the electrode of the invention be a negative electrode, the current collector typically comprises, preferably consists of at least one metal selected from SSPI 2023/004-WO-PCT the group consisting of Lithium (Li), Sodium (Na), Zinc (Zn), Magnesium (Mg), Copper (Cu) and alloys thereof, preferably Cu. [00112] A fourth object of the present invention is an electrode or a separator obtainable by the process of the present invention, wherein the TFE (co)polymer has a 3D structure consisting of nodes, fibrils interconnecting the nodes, and the free spaces between the fibrils and the nodes. [00113] In one embodiment, a fluorine-containing surfactant is detected in an amount of 100 parts per billion (ppb) or less, preferably 20 ppb or less, more preferably 2 ppb or less, with respect to the total mass of the electrode or the separator. [00114] In another embodiment, a fluorine-containing surfactant is detected in an amount of 5 parts per million (ppm) or less, preferably 1 ppm or less, more preferably 100 ppm or less, with respect to the total mass of the binder composition comprising a TFE (co)polymer. [00115] In the present invention, the term “fluorine-containing surfactant” is intended to denote a surfactant containing fluorocarbon chains, which is effective in reducing the surface tension of water, for instance perfluorosulfonic acid, such as perfluorooctane sulfonate (PFOS) and perfluorocarboxylic acid such as perfluorooctanoic acid (PFOA). [00116] In a particular embodiment, the fluorine-containing surfactant is a perfluorinated C3-C10 alkanoic acid, preferably a perfluorinated C4-C8 alkanoic acid, more preferably a perfluorinated C₄-C₆ alkanoic acid. [00117] In a preferred embodiment, the electrode or the separator obtainable by the process of the present invention is substantially free from a fluorine- containing surfactant. [00118] The term “substantially free” in combination with the amount of the fluorine- containing surfactant is to be meant to exclude the presence of any significant amount of said fluorine-containing surfactant. [00119] A fifth object of the present invention is a process for manufacturing a gel polymer electrode, comprising the steps of: - mixing an electrode-forming composition as defined in the present invention, at least one liquid electrolyte, optionally at least one metal salt, and optionally at least one conductive agent to form a paste; SSPI 2023/004-WO-PCT - processing the paste to fibrillate the TFE (co)polymer; - extruding the paste into a film; and - calendaring and/or laminating the film onto a current collector to obtain a gel polymer electrode. [00120] In one embodiment, the step of extruding the paste is implemented at a temperature less than 120℃, preferably less than 110℃, more preferably less than 100℃. [00121] For the purpose of the present invention, the term “liquid electrolyte” is intended to denote a liquid medium comprising one or more substances in the liquid state at 20℃ under atmospheric pressure. [00122] The choice of the liquid electrolyte is not particularly limited provided that it is suitable for solubilizing a metal salt to provide an electrolyte solution. [00123] In one embodiment, the liquid electrolyte comprises at least one organic carbonate. [00124] In a particular embodiment, the liquid electrolyte is an organic carbonate, which may be partially or fully fluorinated. In the present invention, the organic carbonate may be either cyclic or acyclic. Non-limiting examples of the organic carbonate include, notably, ethylene carbonate (1,3-dioxolan-2- one), propylene carbonate, 4-methylene-1,3-dioxolan-2-one, 4,5- dimethylene-1,3-dioxolan-2-one, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, propyl butyl carbonate, dibutyl carbonate, di-tert-butyl carbonate, butylene carbonate, mono- and difluorinated ethylene carbonate, mono- and difluorinated propylene carbonate, mono- and difluorinated butylene carbonate, 3,3,3- trifluoropropylene carbonate, fluorinated dimethyl carbonate, fluorinated diethyl carbonate, fluorinated ethyl methyl carbonate, fluorinated dipropyl carbonate, fluorinated dibutyl carbonate, fluorinated methyl propyl carbonate, and fluorinated ethyl propyl carbonate. [00125] In the other embodiment, the liquid electrolyte comprises at least one ionic liquid and, optionally, at least one organic carbonate. [00126] For the purpose of the present invention, the term ”ionic liquid” is intended to denote a compound formed by the combination of a positively charged SSPI 2023/004-WO-PCT cation and a negatively charged anion in the liquid state at temperatures below 100°C under atmospheric pressure. [00127] The ionic liquid typically contains: - a positively charged cation selected from the group consisting of imidazolium, pyridinium, pyrrolidinium and piperidinium ions optionally containing one or more C1-C30 alkyl groups, and - a negatively charged anion selected from the group consisting of halides, perfluorinated anions and borates. [00128] Non-limiting examples of C1-C30 alkyl groups include, notably, methyl, ethyl, propyl, iso-propyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, isopentyl, 2,2-dimethyl-propyl, hexyl, 2,3-dimethyl-2-butyl, heptyl, 2,2- dimethyl-3-pentyl, 2-methyl-2-hexyl, octyl, 4-methyl-3-heptyl, nonyl, decyl, undecyl, and dodecyl groups. [00129] The positively charged cation of the ionic liquid is preferably selected from the group consisting of: - a pyrrolidinium cation of formula: wherein R11 and R22, equal to or different from each other, independently represent a C₁-C₈ alkyl group and R₃₃, R₄₄, R₅₅ and R₆₆, equal to or different from each other, independently represent a hydrogen atom or a C₁-C₃₀ alkyl group, preferably a C₁-C₁₈ alkyl group, more preferably a C₁- C₈ alkyl group, and - a piperidinium cation of formula: wherein R11 and R22, equal to or different from each other, independently represent a C₁-C₈ alkyl group and R₃₃, R₄₄, R₅₅, R₆₆ and R₇₇, equal to or different from each other, independently represent a hydrogen atom or a SSPI 2023/004-WO-PCT C₁-C₃₀ alkyl group, preferably a C₁-C₁₈ alkyl group, more preferably a C₁- C₈ alkyl group. [00130] The positively charged cation of the ionic liquid is more preferably selected from the group consisting of: - a pyrrolidinium cation of formula: - a piperidinium cation of formula: [00131] The negatively charged anion of the ionic liquid is preferably selected from the group consisting of: - bis(trifluoromethylsulfonyl)imide of formula (SO2CF3)2N-, - hexafluorophosphate of formula PF₆-, - tetrafluoroborate of formula BF₄-, and - oxaloborate of formula: . [00132] The ionic liquid even more preferably contains a pyrrolidinium cation as defined above and a perfluorinated anion selected from the group consisting of (SO2CF3)2N-, PF6-, and BF4-. [00133] The metal salt is typically selected from the group consisting of: (a) MeI, Me(PF6)n, Me(BF4)n, Me(ClO4)n, Me(bis(oxalato)borate)n (“ Me(BOB)n”), MeCF3SO3, Me[N(CF3SO2)2]n, Me[N(C2F5SO2)2]n, Me[N(CF₃SO₂)(R_FSO₂)]_n, wherein R_F is C₂F₅, C₄F₉ or CF₃OCF₂CF₂, Me(AsF₆)_n, Me[C(CF₃SO₂)₃]_n, Me₂S_n, wherein Me is a metal, preferably a transition metal, an alkaline metal or an alkaline-earth metal, more preferably Me being Li, Na, K or Cs, even more preferably Me being Li, and n is the valence of said metal, typically n being 1 or 2; SSPI 2023/004-WO-PCT wherein R’F is selected from the group consisting of F, CF3, CHF2, CH2F, C2HF4, C2H2F3, C2H3F2, C2F5, C3F7, C3H2F5, C3H4F3, C4F9, C4H2F7, C4H4F5, C5F11, C3F5OCF3, C2F4OCF3, C2H2F2OCF3 and CF2OCF3; and (c) combinations thereof. [00134] In a preferred embodiment, Me is Li. [00135] Non-limitative examples of the lithium salt according to the present invention include, notably, a lithium ion complex such as lithium hexafluorophosphate (LiPF₆), lithium perchlorate (LiClO₄), lithium hexafluoroarsenate (LiAsF₆), lithium hexafluoroantimonate (LiSbF₆), lithium hexafluorotantalate (LiTaF₆), lithium tetrachloroaluminate (LiAlCl₄), lithium tetrafluoroborate (LiBF₄), lithium chloroborate (Li₂B₁₀Cl₁₀), lithium fluoroborate (Li2B10F10), Li2B12FxH12-x wherein x=0-12, LiPFx(RF)6-x and LiBFy(RF)4-y wherein RF represents perfluorinated C1-C20 alkyl groups or perfluorinated aromatic groups, x=0-5 and y=0-3, lithium bis(oxalato)borate [LiB(C2O4)2], lithium bis(malonato)borate [LiB(O2CCH2CO2)2], lithium bis(difluoromalonato) borate [LiB(O2CCF2CO2)2], lithium difluorooxalato borate, and lithium fluoromalonato (difluoro)borate, LiPF₂[O₂C(CX₂)_nCO₂]₂, LiPF₄[O₂C(CX₂)_nCO₂] wherein X is selected from the group consisting of H, F, Cl, C₁-C₄ alkyl groups and fluorinated alkyl groups, and n=0-4, lithium trifluoromethane sulfonate (LiCF₃SO₃), lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), LiN(SO2CmF2m+1)(SO2CnF2n+1) and LiC(SO2CkF2k+1)(SO2CmF2m+1) (SO2CnF2n+1) wherein k=1-10, m=1-10 and n=1-10, LiN(SO2CpF2pSO2) and LiC(SO2CpF2pSO2)(SO2CqF2q+1) wherein p=1-10 and q=1-10, or combinations thereof. [00136] In a preferred embodiment, the lithium salt is lithium bis(trifluoromethanesulfonyl) imide (LiN(CF3SO2)2) (LiTFSI). [00137] In another preferred embodiment, the lithium salt is LiFSI. [00138] In the other preferred embodiment, the lithium salt is LiPF₆. SSPI 2023/004-WO-PCT [00139] The sixth object of the present invention is a gel polymer electrode obtainable by a process according to the present invention. [00140] In one embodiment, a fluorine-containing surfactant is detected in an amount of 100 ppb or less, preferably 20 ppb or less, more preferably 2 ppb or less, with respect to the total mass of the gel polymer electrode or the gel polymer separator. [00141] In another embodiment, a fluorine-containing surfactant is detected in an amount of 5 ppm or less, preferably 1 ppm or less, more preferably 100 ppb or less, with respect to the total mass of the binder composition. [00142] In a preferred embodiment, the gel polymer electrode obtainable by the process of the present invention are substantially free from a fluorine- containing surfactant. [00143] The seventh object of the present invention is a secondary battery comprising an electrode and/or a separator according to the present invention. [00144] The present invention also relates to a secondary battery comprising a gel polymer electrode according to the present invention. [00145] Another object of the present invention is use of a TFE (co)polymer having a specific surface area of 4 m²/g or less, preferably 2 m²/g or less, measured pursuant to the method ISO9277 in a binder composition for a secondary battery. [00146] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence. [00147] The invention will be now explained in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention. [00148] EXAMPLES [00149] Raw Materials - Algoflon®F5: suspension-polymerized PTFE having specific surface area of 2.5 m²/g, commercially available from Solvay Specialty Polymers Italy SSPI 2023/004-WO-PCT - Algoflon®DF120: emulsion-polymerized PTFE having specific surface area of 6.8 m²/g, commercially available from Solvay Specialty Polymers Italy - LPSCl (Li₆PS₅Cl), crystalline sulfide-based solid ionic conducting inorganic particles, commercially available from NEI corporation; - NMC622 (Cellcore®NMC KHX12): cathode electroactive material, commercially available from Umicore; and - C-NERGY^TM Super C65: carbon black as a conductive agent, commercially available from Imerys. [00150] Preparation of Positive Electrodes (E1 & CE1) [00151] Positive electrodes (E1 & CE1) were prepared by a two-step process. [00152] In the first step, NMC622 and C65 were mixed in a high-shear mixer at low speed for 30 seconds and at moderate speed for 3 minutes. Then, Algoflon®F5 or Algoflon®DF120 were respectively added to the mixture and blended in the same mixer at high speed for 2 minutes and subsequently for 30 seconds at higher speed. The mass ratio in the electrode-forming compositions was 95:2:3 (NMC622:C65: Algoflon®F5 or Algoflon®DF120). In the very last phase, the temperature increased from about 26°C to about 33°C in the mixer. [00153] The second step was a hot-rolling step in a two-roll calendar which was preheated to 120°C. The calendar rolls were set to have a slight speed difference in order to cause shearing forces in the calendaring gap, with a ratio of 1.2:1.0. The main roll was driven at a rotational speed of 2.0 rpm and the second roll at a speed of 2.4 rpm. The powder from the first step was then introduced into the reduced calendaring gap in order to produce a cohesive film slightly sticking to the roll. The film was then detached from the roll and subsequently subjected to the calendar five times, reducing the gap in a stepwise manner from 2000 μm to 250 μm by applying progressive shearing forces onto the membrane, thus avoiding excessive increment in terms of compaction forces. At each occurrence, the gap became about 75% of the previous gap. Once the calendar gap reached about 250 μm, the membrane was folded in four and rotated 90° before being inserted and processed again into the calendar pursuant to the SSPI 2023/004-WO-PCT same methodology, starting from 1000 μm and going down to 250 μm via about six to seven times of passages through the gap. [00154] As a result, a self-standing membrane having thickness of about 250 μm was obtained. The thickness of the positive electrode as produced was further reduced by using another calendaring device having two rolls rotating at the same speed, but allowing a gap between the rolls as low as 50 μm. Accordingly, a positive electrode having thickness of about 90 μm was obtained. The whole process was implemented without using any solvent. [00155] The positive electrode was then co-laminated onto an Al sheet having thickness of 20 μm at a temperature 180°C and under a pressure of 25 bar. [00156] Preparation of Positive Electrodes with sulfide-based solid ionic conducting inorganic particles (E2) [00157] Positive electrodes were prepared in a similar manner to E1, except that the sulfide-based solid ionic conducting inorganic particles (LPSCl) were added subsequently to the mixture of NCM622 and C65. The resulting mixture was then mixed at moderate speed for 3 minutes. Finally, Algoflon®F5 was added and the mixture was blended for 30 seconds at low speed and then for 3 minutes at very high speed, i.e.15 m/s of tip speed. [00158] The mass ratio in the electrode-forming composition was 75:20:2:3 (NMC622:LPSCl:C65:Algoflon®F5). [00159] Eventually, the positive electrode-forming composition as prepared from the previous mixing step was calendared into a GK 300L calendaring machine with friction ratio of 1.5:1, while heating up to 120°C. The powders were calendared at a kinetic force of around 300 N/mm with an initial gap of 70 μm, which was repeated twice to produce a film. The film was then released from the rolls and a free-standing film was obtained. The film could be calendared directly on to a carbon-coated Al current collector to produce a positive electrode. [00160] Measurement of Mechanical Properties SSPI 2023/004-WO-PCT [00161] In order to demonstrate that the mechanical property of the positive electrode prepared by using Algoflon®F5 (E1) is comparable to that of the positive electrode prepared by using Algoflon®DF120 (CE1), the machine direction (MD) tensile strength (TS) was measured according to the method ASTM D88-00. MD TS value of E1 was recorded as 0.87 MPa, and MD TS value of CE1 was recorded as 0.79 MPa. [00162] The MD TS value of E2 was also measured and recorded as 0.34 MPa. [00163] The inventors demonstrated that positive electrodes can be prepared by using either Algoflon®F5 or Algoflon®DF120, exhibiting comparable mechanical properties to each other. In particular, by using Algoflon®F5, a positive electrode that substantially does not contain a fluorine-containing surfactant could be obtained without compromising other properties. It was clearly evidenced by the fact that said positive electrodes were processed into self-standing membranes. Good mechanical properties were also observed in a positive electrode with sulfide-based solid ionic conducting inorganic particles (E2). [00164] Preparation of a separator with sulfide-based solid ionic conducting inorganic particles (E3) [00165] A separator was produced in the form of a film, by directly applying a separator-forming composition composed of LPSCl and Algoflon®F5, with the mass ratio of 97:3 (LPSCl:Algoflon®F5) on a surface of the positive electrode with a thickness of about 84 μm. [00166] The procedure was similar to E2, except that the mixing was implemented with very high speed for 5 minutes instead of 3 minutes. The separator- forming composition was processed into a calendaring machine twice with the same protocol as E2, except that the friction ratio was 2:1 instead of 1.5:1. Eventually, the separator was colaminated onto the positive electrode (corresponding to E2 as above described, directly applied on the current collector) to form a layered structure, i.e. a separator, a positive electrode and a current collector in an order.

Claims

SSPI 2023/004-WO-PCT Claims Claim 1. An electrode-forming composition comprising: - a binder composition comprising a tetrafluoroethylene (TFE) (co)polymer; - at least one electroactive material; - optionally at least one solid ionic conducting inorganic material; and - optionally at least one processing aid, wherein the TFE (co)polymer has a specific surface area of 4 m²/g or less, preferably 2 m²/g or less, measured pursuant to the method ISO9277. Claim 2. The composition according to claim 1, wherein the TFE (co)polymer is a TFE homopolymer, a TFE copolymer or blends thereof. Claim 3. The composition according to claim 2, wherein the TFE copolymer comprises additional recurring units derived from at least one comonomer different from TFE in an amount of 5% by moles (mol%) or less, preferably 1 mol% of less, with respect to the total moles of the recurring units of the TFE copolymer. Claim 4. The composition according to any one of claims 1 to 3, wherein the binder composition further comprises a vinylidene difluoride (VDF)-based (co)polymer comprising at least 50 mol%, preferably at least 60 mol% of recurring units derived from VDF with respect to all recurring units of the VDF- based (co)polymer and optionally recurring units derived form at least one comonomer different from VDF, preferably a hydrophilic (meth)acrylic comonomer according to the formula: wherein each of R1, R2, R3, equal or different from each other, is independently a hydrogen atom or a C1-C3 hydrocarbon group, and ROH is a hydroxyl group or a C1-C5 hydrocarbon moiety comprising at least one hydroxyl group. SSPI 2023/004-WO-PCT Claim 5. The composition according to any one of claims 1 to 4, wherein the solid ionic conducting inorganic material is a sulfide-based solid ionic conducting inorganic particle selected from the group consisting of: - lithium tin phosphorus sulfide (“LSPS”) materials, such as Li₁₀SnP₂S₁₂; - lithium phosphorus sulfide (“LPS”) materials, such as glasses, crystalline or glass-ceramic of those of formula (Li2S)x-(P2S5)y, wherein x+y=1 and 0≤x≤1, Li7P3S11, Li7PS6, Li4P2S6, Li9.6P3S12 and Li3PS4; - doped LPS, such as Li₂CuPS₄, Li Li_1+2xZn_1−xPS₄, wherein 0≤x≤1, Li3.33Mg0.33P2S6, and Li4-3xScxP2S6, wherein 0≤x≤1; - lithium phosphorus sulfide oxygen (“LPSO”) materials of formula LixPySzO, where 0.33≤x≤0.67, 0.07≤y≤0.2, 0.4≤z≤0.55, 0≤w≤0.15; - lithium phosphorus sulfide materials including X (“LXPS”), wherein X is Si, Ge, Sn, As, Al, such as Li10GeP2S12 and Li10SiP2S12; - lithium phosphorus sulfide oxygen including X (“LXPSO”), wherein X is Si, Ge, Sn, As, Al; - lithium silicon sulfide (“LSS”) materials; - lithium boron sulfide materials, such as Li₃BS₃ and Li₂S- B₂S₃-LiI; - lithium tin sulfide materials and lithium arsenide materials, such as Li0.8Sn0.8S2, Li4SnS4, Li3.833Sn0.833As0.166S4, Li3AsS4-Li4SnS4, Ge- substituted Li3AsS4; and - lithium phosphorus sulfide materials of general formula Li_aPS_bX_c, wherein X represents at least one halogen element selected in the group of Cl, Br and I or a combination thereof; and a represents a number from 2.0 to 7.0, b represents a number from 3.5 to 6.0, and c represents a number from 0 to 3.0, preferably Argyrodite-type sulfide material of formula Li6PS5Y, wherein Y is Cl, Br or I, the compounds being possibly deficient in sulfur, lithium or halogen, for instance Li6-xPS5-xCl1+x with 0 ≤ x ≤ 0.5, or doped with a heteroatom. Claim 6. The composition according to any one of claims 1 to 5, wherein the processing aid is a non-aqueous solvent selected from the group consisting of nitrile-containing solvents, ethers, esters, thiols, thioethers, ketones and SSPI 2023/004-WO-PCT tertiary amines or a lubricant selected from the group consisting of isoparaffinic hydrocarbon compounds and petroleum fractions. Claim 7. A separator-forming composition comprising: - a binder composition comprising a tetrafluoroethylene (TFE) (co)polymer; - at least one solid ionic conducting inorganic material; and - optionally at least one processing aid, wherein the TFE (co)polymer has a specific surface area of 4 m²/g or less, preferably 2 m²/g or less, measured pursuant to the method ISO9277. Claim 8. The composition according to claim 7, wherein the TFE copolymer comprises additional recurring units derived from at least one comonomer different from TFE in an amount of 5% by moles (mol%) or less, preferably 1 mol% of less, with respect to the total moles of the recurring units of the TFE copolymer. Claim 9. A process for manufacturing an electrode or a separator, comprising the steps of: - processing an electrode-forming composition according to any one of claims 1 to 6 or a separator-forming composition according to claim 7 or 8 to fibrillate the TFE (co)polymer; - subsequently calendaring or extruding the composition into a film; and - optionally, laminating said film onto a current collector or on a substrate to produce an electrode or a separator. Claim 10. An electrode or a separator obtainable by the process according to claim 9, wherein the TFE (co)polymer has a three-dimensional (3D) structure consisting of nodes, fibrils interconnecting the nodes, and the free spaces between the fibrils and the nodes. Claim 11. The electrode or the separator according to claim 10, wherein a fluorine-containing surfactant is detected in an amount of 100 parts per billion SSPI 2023/004-WO-PCT (ppb) or less, preferably 20 ppb or less, more preferably 2 ppb or less, with respect to the total mass of the electrode or the separator. Claim 12. A process for manufacturing a gel polymer electrode, comprising the steps of: - mixing a binder composition as defined in any one of claims 1 to 4, at least one liquid electrolyte, optionally at least one metal salt, and optionally at least one conductive agent to form a paste; - processing the paste to fibrillate the TFE (co)polymer; - extruding the paste into a film; and - calendaring and/or laminating the film onto a current collector to obtain a gel polymer electrode. Claim 13. A gel polymer electrode obtainable by the process according to claim 12, wherein the TFE (co)polymer has a three-dimensional (3D) structure consisting of nodes, fibrils interconnecting the nodes, and the free spaces between the fibrils and the nodes. Claim 14. The gel polymer electrode according to claim 13, wherein a fluorine-containing surfactant is detected in an amount of 100 parts per billion (ppb) or less, preferably 20 ppb or less, more preferably 2 ppb or less, with respect to the total mass of the gel polymer electrode. Claim 15. A secondary battery comprising an electrode and/or a separator according to claim 10 or 11 or a gel polymer electrode according to claim 13 or 14. Claim 16. Use of a tetrafluoroethylene (TFE) (co)polymer having a specific surface area of 4 m²/g or less, preferably 2 m²/g or less, measured pursuant to the method ISO9277 in a binder composition for a secondary battery.