Secondary battery electrode binder

Abstract

The present invention relates to the use of vinylidene fluoride polymers as binders for electrodes in secondary batteries.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European Patent Application No. 22202255.0, filed October 18, 2022, and European Patent Application No. 23157209.0, filed February 17, 2023, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to the use of vinylidene fluoride polymers as binders for electrodes in secondary batteries. [Background technology]

[0003] Fluoropolymers are known in the art to be suitable as binders for the manufacture of electrodes for use in electrochemical devices such as secondary batteries.

[0004] In general, increasing the molecular weight of fluoropolymers is known to improve the performance of articles made from these materials, particularly in terms of mechanical properties and adhesion of the electrode to the current collector.

[0005] However, increasing the molecular weight of the fluoropolymer increases the viscosity of the electrode-forming formulation containing it, also called the electrode slurry, making the handling and coating process in the manufacture of the electrode much more difficult.

[0006] Chinese Patent No. 110183562 discloses the preparation of high molecular weight PVDF by using diisopropyl peroxydicarbonate as an initiator. The resulting PVDF is characterized by a high degree of crystallinity, making electrode slurry compositions containing it useless for electrode production. Therefore, the high-crystallinity PVDF is blended with a VDF-based copolymer to obtain a polymer mixture suitable for use as an electrode binder.

[0007] In the technical field of batteries, and in particular of sodium or lithium batteries, the problem is felt to provide an electrode binder characterized by very good adhesion without at the same time having adverse effects on the electrode manufacturing process, such as by an increase in the viscosity of the slurry for its manufacture. Summary of the Invention

[0008] It has been discovered that certain vinylidene fluoride polymers have very good adhesion to metal substrates and can be used to prepare electrode-forming compositions with improved slurry viscosity at low shear rates.

[0009] An object of the present invention is therefore a VDF-based polymer [polymer (F)] consisting of repeating units derived from VDF and, optionally, repeating units derived from at least one fluorinated comonomer (CF) different from VDF, said polymer (F) having an intrinsic viscosity, measured in dimethylformamide at 25°C, ranging from 0.25 l / g to 0.60 l / g, more preferably from 0.30 l / g to 0.50 l / g, The polymer (F) is represented by the formula (I): -(R a ) x -O-CO-O-CH2-CH3(I) (In the formula, R a is a C1 to C5 linear or branched hydrocarbon group, and x is an integer selected from 1 and zero. and wherein the terminal group of the end groups of formula (I) are present in an amount of at least 0.2 / 10000 VDF units, preferably at least 1.0 / 10000 VDF units and at most 10 / 10000 VDF units, The polymer (F)

[0010] The second object of the present invention is to a) at least one electrode active material (AM); b) at least one binder (B) comprising at least one polymer (F) as defined above; c) at least one solvent (S); The present invention relates to an electrode-forming composition (C) comprising:

[0011] In another aspect, the present invention relates to the use of an electrode-forming composition (C) in a process for producing an electrode [electrode (E)], the process comprising: (I) providing a metal substrate having at least one surface; (II) providing an electrode-forming composition (C) as defined above; (III) applying the composition (C) prepared in step (II) onto at least one surface of the metal substrate prepared in step (I), thereby preparing an assembly including a metal substrate coated with the composition (C) on at least one surface; (IV) drying the assembly prepared in step (III); (V) subjecting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the present invention. Regarding use, including

[0012] In a further object, the present invention relates to an electrode (E) obtainable by the method of the present invention.

[0013] In a still further object, the present invention relates to an electrochemical device comprising at least one electrode (E) of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The term "VDF-based polymer" is intended to mean VDF homopolymers (PVDF) and VDF-based copolymers comprising repeating units derived from VDF and repeating units derived from at least one fluorinated comonomer (CF) different from VDF.

[0015] The VDF-based polymer (F) of the present invention does not contain hydrogenated monomers with polar groups.

[0016] The term "repeating unit derived from vinylidene fluoride" (commonly also designated vinylidene difluoride, 1,1-difluoroethylene, VDF) is intended to mean a repeating unit of formula CF2=CH2.

[0017] Non-limiting examples of suitable fluorinated comonomers (CF) include, among others: (a) tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene, hexafluoroisobutylene, vinyl fluoride; C2 to C8 fluoro and / or perfluoroolefins such as 1,2-difluoroethylene and trifluoroethylene; (b) Formula CH2=CH-R f0 (In the formula, R f0 is a C1-C6 perfluoroalkyl group); (c) chloro-, and / or bromo-, and / or iodo-C2-C6 fluoroolefins such as chlorotrifluoroethylene (CTFE); (d) perfluoro(alkyl) vinyl ethers such as perfluoro(methyl) vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE), and perfluoro(propyl) vinyl ether (PPVE); (e) Perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0018] In a preferred embodiment, the polymer (F) is semi-crystalline and contains 0.1 to 20.0 mol %, preferably 0.3 to 10.0 mol %, more preferably 0.5 to 5.0 mol % of repeat units derived from said fluorinated comonomer (CF).

[0019] The polymer (F) can be an elastomeric or semi-crystalline polymer, preferably a semi-crystalline polymer.

[0020] As used herein, the term "semi-crystalline" means a fluoropolymer that has at least one crystalline melting point in addition to a glass transition temperature Tg by DSC analysis. For the purposes of the present invention, semi-crystalline fluoropolymer is intended herein to mean a fluoropolymer that has a heat of fusion of 10 to 90 J / g, preferably 30 to 80 J / g, more preferably 35 to 75 J / g, measured according to ASTM D3418-08.

[0021] For purposes of the present invention, the term "elastomer" is intended to denote a true elastomer or a polymer resin that serves as a building block to obtain a true elastomer.

[0022] True elastomers are defined by ASTM, Special Technical Bulletin, No. 184 Standard as materials that can be stretched to twice their inherent length at room temperature and that, when released after being held under tension for 5 minutes, simultaneously return to within 10% of their original length.

[0023] The polymer (F) of the present invention usually has a melting temperature (Tm) within the range of 100 to 200°C.

[0024] The polymer (F) of the present invention has a pseudo-linear structure with very few branches, so that the insoluble portion caused by long branched chains is so small that it can be practically ignored.

[0025] The polymer (F) of the present invention in fact preferably has a low proportion of insoluble components in standard polar aprotic solvents for VDF, such as NMP, and more preferably, solutions of the polymer (F) in said standard polar aprotic solvents remain homogeneous and stable for several weeks, substantially free of insoluble residues.

[0026] Due to the small amount of insoluble components, the GPC and NMR analysis of polymer (F) is not affected and there are no problems with reliability and reproducibility.

[0027] The melting temperature can be determined from a DSC curve obtained by differential scanning calorimetry (hereinafter also referred to as DSC). When a DSC curve shows multiple melting peaks (endothermic peaks), the melting temperature (Tm) is determined based on the peak with the largest peak area.

[0028] It is understood that moieties of chain ends, defects or other impurity types different from those defined above can be contained in polymer (F) without these impairing its properties.

[0029] According to a particular embodiment of the invention, polymer (F) is characterized in that it comprises an end group of formula (I) as defined above, in which x is zero.

[0030] According to another embodiment of the present invention, the polymer (F) has the structure: x is 1 and R a is a C2-C3 linear or branched alkyl radical, preferably a C3 linear or branched alkyl radical,

[0031] According to another embodiment of the present invention, polymer (F) comprises end groups of formula (I) as defined above, where x is zero, and end groups of formula (I) where x is 1, and R a is a C2-C3 linear or branched alkyl radical, preferably a C3 linear or branched alkyl radical.

[0032] Polymer (F) is characterized by having a particle size distribution with a D50 value of less than 240 microns as measured using laser diffraction according to ISO 13320.

[0033] D50 indicates the particle size below which half of the population falls and half above.

[0034] The applicant has surprisingly found that polymer (F) having a particle size distribution with a D50 value of less than 240 microns and an intrinsic viscosity in the range of 0.25 l / g to 0.60 l / g, preferably 0.30 l / g to 0.50 l / g, as measured in dimethylformamide at 25°C, is particularly suitable for use in an electrode-forming composition having good adhesion to a current collector and optimal slurry viscosity.

[0035] The polymer (F) is - polymerizing, in an aqueous medium, vinylidene fluoride (VDF) and, optionally, a comonomer (CF) in the presence of a radical initiator system which introduces the end group of formula (I) into the polymer chain; - maintaining a pressure in the reaction vessel above the critical pressure of vinylidene fluoride; It can be obtained by a method comprising:

[0036] Suitable radical initiator systems include radical initiators such as di(ethyl)peroxydicarbonate and hydroethylperoxydicarbonate.

[0037] The amount of radical initiator required for polymerization depends on its activity and the temperature used for polymerization. The total amount of radical initiator used is generally 100 to 30,000 ppm by weight based on the total weight of the monomers used.

[0038] The radical initiator may be added in pure form, in solution, in suspension, or in emulsion, depending on the initiator selected.

[0039] The radical initiator system may include a chain transfer agent (CTA).

[0040] Suitable CTAs for the polymerization process to prepare the polymer (F) according to the invention are known in the art and are typically selected from the group consisting of short hydrocarbon chains such as ethane and propane, esters such as ethyl acetate and diethyl maleate, and diethyl carbonate. When an organic peroxide is used as an initiator, it could also serve as an effective CTA during the free radical polymerization.

[0041] When used, the CTA may be added all at once at the beginning of the reaction, or in portions, or continuously throughout the course of the reaction. The amount of CTA and its mode of addition depend on the desired properties of the resulting polymer (F).

[0042] A preferred CTA for use in the method of the present invention is diethyl carbonate.

[0043] In the process for preparing polymer (F), the pressure is maintained above the critical pressure of vinylidene fluoride. Generally, the pressure is maintained at a value greater than 50 bar, preferably greater than 75 bar, and even more preferably greater than 100 bar.

[0044] Preferably, the process of the present invention is carried out at a temperature above the critical temperature of the VDF monomer, ie at a temperature of at least 31°C.

[0045] The polymer (F) is typically provided in powder form according to the process described above.

[0046] The polymer (F) in the form of a powder can optionally be further extruded to obtain the polymer (F) in the form of pellets.

[0047] The polymer (F) detailed above can be used as a binder for electrodes of secondary batteries.

[0048] The second object of the present invention is to a) at least one electrode active material (AM); b) at least one binder (B) comprising at least one polymer (F) as defined above; c) at least one solvent (S); The present invention relates to an electrode-forming composition (C) comprising:

[0049] For the purposes of the present invention, the term "electrode active material (AM)" is intended to denote a compound that can incorporate or intercalate into its structure and subsequently release alkali or alkaline earth metal ions therefrom during the charge and discharge phases of an electrochemical device. The compound (AM) is preferably capable of incorporating or intercalating and releasing lithium or sodium ions.

[0050] The nature of the compound (AM) in the composition (C) depends on whether said composition is used to manufacture a positive electrode (electrode (Ep)) or a negative electrode (electrode (En)).

[0051] The electrode active material (AM) of the positive electrode is preferably a compound capable of inserting lithium ions or sodium ions.

[0052] Conventional active materials (AM) in the positive electrodes of sodium-ion batteries are generally selected from Na-based layered transition metal oxides, Prussian blue analogues, and polyanion-type materials.

[0053] In some embodiments, the active materials are Na-based layered transition metal oxides classified as O3-type, P2-type, and P3-type depending on the stacking order of the oxygen layers. The P2-type structures generally respond to the general formula NaxMO2, where M represents a transition metal ion such as Co, Mn, and x is 2 / 3.

[0054] In some embodiments, the active material is Na 0.81 Fe[Fe(CN)6] 0.79 □ 0.21 , NaFe2(CN)6, Na1 .63 Fe 1.89 (CN)6, Na 1.72 MnFe(CN)6, Na 1.76 Ni0.12 Mn 0.88 [Fe(CN)6] 0.98 , Na2Ni x Co 1-x A compound of the general formula A, where 0≦x≦2 and 0≦y<1, such as Fe(CN)6 (0≦x≦1, e.g., Na2CoFe(CN)6), A is an alkali metal ion, P is an N-coordinated transition metal ion, R is a C-coordinated transition metal ion, and □ is an [R(CN)6] vacancy. x P[R(CN)6] 1-y □ y It is a Prussian blue analogue (PBA) of .mH2O.

[0055] In some other embodiments, the active material comprises a series of tetrahedral anionic units (XO4) n - and their derivatives (X m O 3m+1 ) n- having the general formula Na x M y (XO4) n (wherein X = S, P, Si, As, Mo, and W, and M is a transition metal) are polyanion-type materials. Among these, phosphates such as NaMPO4, NaFePO4, Na 0.7 FePO4 or NaMnPO4; general formula Na x Sodium superionic conductors with NASICON-type structure of M2(XO4)3 (1≦x≦4, M=V, Fe, Ni, Mn, Ti, Cr, Zr...; X=P, S, Si, Se, Mo...) (single transition metal types such as Na3V2(PO4)3(NVP), Na3Cr2(PO4)3, Na3Fe2(PO4)3; binary transition metal types such as Na2VTi(PO4)3, Na3FeV(PO4)3, Na4MnV(PO4)3, Na3MnZr(PO4)3, Na3MnTi(PO4)3, Na4Fe3(PO4)2(P2O7)(NFPP)); pyrophosphates Na2FeP2O7, Na2MnP2O7, Na2CoP2O7, Na 4-x Fe 2+x / 2 (P2O7)2(2 / 3≦x≦7 / 8), e.g., Na 3.12 Fe 2.44 (P2O7)2 or Na 3.32 Fe2.34 (P2O7)2, Na2(VO)P2O7, Na7V3(P2O7)4; fluorophosphates NaVPO4F, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VO 1-x PO4)2F 1+2x (0≦x≦1), such as Na3(VOPO4)2F or Na3V2(PO4)2F3(NVPF); fluorosulfates, such as NaMSO4F (M=Fe, Co, Ni); phosphate / pyrophosphate mixtures of the general formula Na4M3(PO4)2(PO2O7) (M represents a transition metal), such as Na4Mn3(PO4)2(PO2O7), Na4Co3(PO4)2(PO2O7), Na4Ni3(PO4)2(PO2O7), Na4Fe3(PO4)2(PO2O7)(NFPP), Na7V4(PO2O7)4(PO4); sulfates, such as Na2Fe2(SO4)3, Na 2+2x Fe 2-x (SO4)3, Na 2+2x Co 2-x (SO4)3, Na 2+2x Mn 2-x (SO4)3 (0≦x≦1); silicates of the general formula Na2MSiO4 (M=Mn, Fe, Co, and Ni).

[0056] In some preferred embodiments, the active material is preferably NaVPOF, NaCoPOF, NaFePOF, NaMnPOF, Na(VO 1-x PO4)2F 1+2x (0≦x≦1), for example, a fluorophosphate selected from the list consisting of Na3(VOPO4)2F or Na3V2(PO4)2F3(NVPF).

[0057] Conventional active materials (AM) for the positive electrode of lithium-ion batteries may include complex metal chalcogenides of the formula LiMQ2 (wherein M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr, and V, and Q is a chalcogen such as O or S). Among these, it is preferable to use lithium-based complex metal oxides of the formula LiMO2 (wherein M is the same as defined above). Preferred examples of these include LiCoO2, LiNiO2, LiNix Co 1-x O2 (0 < x < 1) and spinel-structured LiMn2O4 can be mentioned.

[0058] As an alternative form, furthermore, the electrode active material is of the formula M1M2(JO4) f E 1-f (where M1 is lithium that can be partially replaced by another alkali metal that occupies less than 20% of the M1 metal, M2 is a transition metal of +2 oxidation level selected from Fe, Mn, Ni or a mixture thereof that can be partially replaced by one or more further metals that occupy less than 35% (including 0) of the M2 metal at an oxidation level of +1 to +5, JO4 is any oxyanion, where J is any of P, S, V, Si, Nb, Mo or a combination thereof, E is a fluoride, hydroxide or chloride anion, and f is the molar fraction of the JO4 oxyanion, usually included in 0.75 to 1) and may include a lithiated or partially lithiated transition metal oxyanion-based electrode active material.

[0059] M1M2(JO4) defined above f E 1-f The electrode active material is preferably phosphate-based and may have an ordered or modified olivine structure.

[0060] More preferably, the electrode active material is of the formula Li 3-x M’ y M’’ 2-y (JO4)3 (where  0 ≦ x ≦ 3, 0 ≦ y ≦ 2, M’ and M’’ are the same or different metals, at least one of them being a transition metal, JO4 is preferably PO4 that can be partially substituted by another oxyanion, where J is any of S, V, Si, Nb, Mo or a combination thereof). Even more preferably, the electrode active material (AM) is a phosphate-based electrode active material of the following formula Li x A y D z PO4 (In the formula, A is selected from the group consisting of Mn, Fe, Co, Ni, and Cu, D is selected from the group consisting of Mg, Ca, Sr, and Ba, and x, y, and z are numbers satisfying the following relationships: 0 < x < 2, 0 < y < 1.5, 0 ≦ z < 1.5).

[0061] The A component is preferably Fe, Mn, and Ni, and particularly preferably Fe.

[0062] The D component is preferably Mg or Ca.

[0063] Examples of the compound having an olivine structure include lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and lithium manganese phosphate.

[0064] Furthermore, as the positive electrode active material (AM), it is also possible to use a material whose surface is partially or entirely coated with carbon in order to supplement conductivity.

[0065] The amount of the coated carbon is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and still more preferably 5 parts by weight or less based on 100 weights of the positive electrode active material.

[0066] The compound having an olivine structure is present in the composition (C) in an amount of 70% by mass or more based on 100% by mass of the entire positive electrode active material (AM).

[0067] More preferably, this is 90% by mass or more, and most preferably, the positive electrode active material (AM) is composed only of the compound having an olivine structure.

[0068] Most preferably, the positive electrode active material (AM) consists only of lithium iron phosphate (LFP).

[0069] In the positive electrode composition of the present invention, the active material (AM) has an average particle size of 3 μm or less.

[0070] The average particle size (D50) of the compound having an olivine structure is more preferably in the range of 0.01 to 1.8 μm.

[0071] The average particle size of the positive electrode active material can be measured by a particle size distribution analyzer for dynamic light scattering.

[0072] As the average particle size decreases, the surface area increases and binder flexibility is required because less binder must be used to bond the particles.

[0073] By using a positive electrode active material containing a compound having an olivine structure and an average particle size of 3 μm or less, the electrical characteristics such as output characteristics can be improved when the positive electrode composition for a secondary battery is used as the positive electrode of the battery.

[0074] When forming a composite negative electrode (En) for a secondary battery, the compound (AM) may preferably include a carbon-based material and / or a silicon-based material.

[0075] In some embodiments, the carbon-based material can be, for example, graphite, such as natural or synthetic graphite, graphene, or carbon black.

[0076] These materials may be used alone or as a mixture of two or more of them.

[0077] The carbon-based material is preferably graphite.

[0078] The silicon-based compound may be one or more selected from the group consisting of chlorosilane, alkoxysilane, aminosilane, fluoroalkylsilane, silicon, silicon chloride, silicon carbide, and silicon oxide. More specifically, the silicon-based compound may be silicon oxide or silicon carbide.

[0079] When present in compound (AM), the at least one silicon-based compound is contained in compound (AM) in an amount ranging from 1 to 30% by weight, preferably from 5 to 20% by weight, relative to the total weight of compound (AM).

[0080] The solvent (S) may preferably be an organic polar solvent, examples of which may include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, and trimethyl phosphate. These solvents may be used alone or in a mixture of two or more species.

[0081] An optional conductive agent may be added to improve the conductivity of the resulting electrode (AM).

[0082] Examples may include carbon black, graphite fine powder, carbon nanotubes, graphene or fibers, or other carbonaceous materials, or fine powders 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®.

[0083] The electrode-forming composition (C) of the present invention may optionally further comprise at least one conductive agent.

[0084] If present, the conductive agent is different from the carbon-based material described above.

[0085] In a preferred embodiment of the present invention, an electrode-forming composition (C) for use in the manufacture of a positive electrode (Ep) is provided, said composition comprising: a) at least one positive electrode active material (AM); b) at least one binder (B) comprising at least one polymer (F) as defined above; c) at least one solvent (S); d) at least one conductive agent, preferably selected from carbon black or graphite fine powder and carbon nanotubes; Includes.

[0086] As mentioned above, the polymer (F) of the present invention has a pseudo-linear structure and a very small insoluble fraction when dissolved in a standard polar aprotic solvent such as NMP.

[0087] Due to the small amount of insoluble components, polymer (F) provides a solution in organic solvents that is not adversely affected by the presence of insoluble residue, commonly referred to as "gel," and is therefore more suitable for use in formulating electrode-forming compositions.

[0088] In another aspect, the present invention provides a use of the electrode-forming composition (C) for the manufacture of an electrode (E), comprising: (I) providing a metal substrate having at least one surface; (II) providing an electrode-forming composition (C) as defined above; (III) applying the composition (C) prepared in step (II) onto at least one surface of the metal substrate prepared in step (I), thereby obtaining an assembly including a metal substrate coated with the composition (C) on at least one surface; (IV) drying the assembly obtained in step (III); (V) subjecting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the present invention. Regarding use, including

[0089] In a further object, the present invention relates to an electrode (E) obtainable by the method of the present invention.

[0090] The applicant has surprisingly found that the electrode (E) of the present invention exhibits outstanding adhesion of the binder to the current collector.

[0091] Therefore, the electrode (E) of the present invention is particularly suitable for use in electrochemical devices, in particular in secondary batteries.

[0092] For the purposes of the present invention, the term "secondary battery" is intended to mean a rechargeable battery.

[0093] The secondary battery of the present invention is preferably an alkali metal secondary battery or an alkaline earth metal secondary battery.

[0094] The secondary battery of the present invention is more preferably a sodium ion or lithium ion secondary battery.

[0095] In a still further object, the present invention relates to an electrochemical device comprising at least one electrode (E) of the present invention.

[0096] The electrochemical device according to the present invention, which is preferably a secondary battery, - Positive and negative electrodes Including, At least one of the positive electrode and the negative electrode is the electrode (E) of the present invention.

[0097] In one preferred embodiment of the present invention, - Positive and negative electrodes Including, The negative electrode is the electrode (E) according to the present invention. An electrochemical device is provided that is a secondary battery.

[0098] Electrochemical devices according to the present invention can be prepared by standard methods known to those skilled in the art.

[0099] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference contradicts the statements of this application to the extent that the term may be unclear, the statements of this application shall control.

[0100] The present invention will now be described with reference to the following examples, the purposes of which are merely illustrative and are not intended to limit the scope of the invention. [Example]

[0101] Determination of the intrinsic viscosity of the polymer (F) The intrinsic viscosity (η) [dl / g] was calculated based on the drop time at 25°C of a solution obtained by dissolving the polymer (F) in N,N-dimethylformamide at a concentration of about 0.2 g / dl using an Ubbelhode viscometer, according to the following formula:

number

[0102] DSC analysis DSC analysis was performed according to the ASTM D3418 standard, and the melting point (T f2 ) was determined at a heating rate of 10 °C / min.

[0103] Determination of polar end groups The amount of polar end groups of polymer (F) resulting from the ethyl chloroformate initiator precursor used in the polymerization process is determined by measuring the intensity of the H atom of the CH2 group (in bold in the following formula) relative to the total intensity of the CH2 sites of the VDF monomer units that are the backbone of polymer (F): 1 Determined by H-NMR. CH3-CH2-OCOO-CH2-CF2-

[0104] The content of the terminal group is determined by the following formula: [EG]=(I EG / I VDF ) x 10000 (In the formula, - [EG] is the overall end group content expressed as moles per 10,000 VDF units, -I EG is the intensity of the integral of the end group [EG], normalized to one hydrogen; -I VDFis the intensity, normalized to one hydrogen, of the integrals of the normal and reversed VDF repeat units) was calculated by applying

[0105] Approximately 20 mg of polymer was dissolved in 0.7 ml of hexadeuteroacetone. The H-NMR spectrum recorded at 60 °C showed the aforementioned CH at 4.47 ppm, while the CH signals from the normal and reverse repeat units of VDF resonated as broad peaks centered at 2.93 and 2.36 ppm, respectively.

[0106] Similar NMR methods were applied to determine the end groups derived from the use of diethyl carbonate chain transfer agent (CH-CH-OCOO-CH-CH-, CH-CH-OCOO-CH(CH)-) as well as to determine -CFH and -CFCH end groups, as known to those skilled in the art.

[0107] Example 1: Preparation of Polymer F-1 Into a 4 L reactor equipped with an impeller rotating at a speed of 650 rpm: 2376 g of demineralized water and a solution of 0.4 g of PEO (Alkox®-E45 from Alkorox) per kg of total monomers, 0.5 g of hydroxypropyl methylcellulose (Methocel®-K100 from Dow) per kg of total monomers, and 12.4 g of trisodium phosphate were successively introduced. The oxygen present in the reactor was removed by a sequence of vacuum and nitrogen purges at a fixed temperature of 14° C. This sequence was repeated three times.

[0108] Then 10.16 g of hydrogen peroxide solution (from Brenntag), 3.53 g of ethyl chloroformate (from Framochem), and 1.76 g of diethyl carbonate were introduced into the reactor.

[0109] After 15 minutes at an agitation speed of 880 rpm, 1176 g of VDF was introduced into the reactor, which was then gradually heated until a set point temperature of 35°C was reached.

[0110] The pressure was kept constant and equal to 120 bar during the entire polymerization run by feeding water. A total of 657 g of water was introduced into the reactor. After 162 minutes, the polymerization was stopped by degassing the suspension until atmospheric pressure was reached.

[0111] The polymer was then collected by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried overnight in an oven at 65° C. 882 g of dry powder was recovered.

[0112] A polymer was obtained with an intrinsic viscosity of 0.316 l / g in DMF at 25°C and a T2f of 172.1°C.

[0113] This polymer contained 1.7 / 10000 VDF units of the end group CH3CH2-OCOO-: 0.7 / 10000 VDF units of units derived from the ethyl chloroformate initiator precursor and 1.0 / 10000 VDF units of units derived from diethyl carbonate.

[0114] In addition, the presence of -CF2H end groups at 2.3 / 10000 VDF units and -CF2CH3 end groups at 1.4 / 10000 VDF units was determined.

[0115] Example 2: Preparation of Polymer F-2 Into an 80 L reactor equipped with an impeller rotating at a speed of 250 rpm, the following were successively introduced: 52.4 kg of demineralized water and 0.4 g of hydroxypropylmethylcellulose (Methocel®-K100 from Dow) per kg of VDF. The oxygen present in the reactor was removed by a sequence of vacuum and nitrogen purges at a fixed temperature of 20° C. This sequence was repeated three times.

[0116] Then, 41.38 g of a solution (75%) of the initiator t-amyl perpivalate (from United Initiators) in isododecane and 250.02 g of diethyl carbonate were introduced into the reactor. Immediately after, the stirring speed was increased to 300 rpm, and 22.99 kg of VDF were added to the reactor. The reactor was then gradually heated until a set-point temperature of 52 °C was reached. The pressure was kept constant at 120 bar by VDF throughout the entire polymerization run. A total of 11.49 kg of VDF was added, and no further VDF was added. The temperature was then increased to 65 °C, and the reaction was then stopped after a total of 169 minutes by degassing the suspension until atmospheric pressure was reached.

[0117] The polymer was then collected by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried overnight in an oven at 65°C. 29.94 kg of dry powder was recovered.

[0118] Polymer A: VDF homopolymer with an intrinsic viscosity of 0.271 l / g in DMF at 25°C and a T2f of 170.2°C.

[0119] The polymer contained 2.2 / 10000 VDF units of end groups CH3CH2-OCOO derived from diethyl carbonate, 0.6 / 10000 VDF units of -C(CH3)3 from the initiator, 4.5 / 10000 VDF units of -CF2H, and 2.4 / 10000 VDF units of -CF2CH3 end groups.

[0120] General preparation of electrodes using NMC811 active material A positive electrode with a final composition of 98 wt % NMC811 (COSMO Advanced Materials & Technology, d50=10.28 μm), 1.1 wt % polymer, and 0.9 wt % conductive additive was prepared as follows.

[0121] The slurry ingredients were added to a mixing cup in the following order: 33.6 g of multi-walled carbon nanotube dispersion with a solids content of 4.1 wt %, 21.1 g of 8 wt % polymer solution in NMP, 150 g of NMC, and 7.9 g of NMP were mixed.

[0122] The mixture was then mixed using a high speed disc impeller at 500 rpm for 5 minutes followed by 1900 rpm for 75 minutes.

[0123] The resulting dispersion was cast onto an aluminum foil having a thickness of 15 μm using a doctor blade, and the coated layer was dried in a vacuum oven at a temperature of 90° C. for about 50 minutes to obtain a positive electrode. The thickness of the dried coating layer was about 150 μm.

[0124] Example 3: Adhesion and Slurry Viscosity Using the polymers of Examples 1 and 2 as binders, electrode compositions were prepared according to the procedures set forth above.

[0125] The slurry viscosity of the above-defined compositions was measured on an AntonPaar Rheolab QC using a concentric cylinder apparatus (measuring cup: C-CC27 / QC-LTD Bob: CC27 / P6) equipped with Peltier temperature control at 25° C. The steady-state viscosity was measured from shear rates of 0.1 to 1000 1 / s.

[0126] The adhesive peel force between the aluminum foil and the electrode was measured as follows: To evaluate the adhesion of the dried coating layer defined above to aluminum foil, a 180° peel test was carried out according to the configuration described in standard ASTM D903 at 20° C. and a speed of 300 mm / min.

[0127] The slurry viscosity and adhesive strength values ​​are shown in Table 1.

[0128] [Table 1]

[0129] General preparation of electrodes using LFP active material A positive electrode with a final composition of 95.75 wt. % LFP (Phostech Lithium, d50=0.5 μm), 3.5 wt. % polymer, and 0.75 wt. % conductive additive was prepared as follows.

[0130] An initial dispersion was prepared by premixing 34.3 g of an 8 wt % solution of polymer in NMP, 75.07 g of LFP, 14.7 g of graphite powder carbon nanotubes pre-dispersed in NMP at 4 wt %, and 15.93 g of NMP in a centrifugal mixer for 10 min.

[0131] The mixture was then mixed for 50 minutes at 1500 rpm using a high-speed butterfly impeller. An additional 5.2 g of NMP was then added to the dispersion, which was then further mixed for 5 minutes using a centrifugal mixer. The resulting composition was cast onto a 15 μm-thick Al foil using a doctor blade, and the coated layer was dried in a vacuum oven at 90°C for approximately 50 minutes to obtain a cathode. The dried coating layer had a thickness of approximately 100 μm.

[0132] Example 4: Adhesion and Slurry Viscosity Electrode compositions were prepared according to the procedures set forth above using the polymers of Examples 1 and 2 as binders, and the viscosity and adhesive strength values ​​of the slurries, measured as defined above, are shown in Table 2.

[0133] [Table 2]

[0134] Those skilled in the art know that the adhesion value of a binder to a current collector is greatly affected by the particle size of the active material used to fabricate the electrode, so that for the same percentage amount of active material in the electrode, using active materials with different particle sizes will have a significant effect on the adhesion value.

[0135] Apart from the above, the results in Tables 1 and 2 show that the polymers of the present invention perform well and provide excellent adhesion to the current collector.

Claims

1. A VDF-based polymer [polymer (F)] consisting of repeating units derived from VDF and optionally comprising repeating units derived from at least one fluorinated comonomer (CF) different from VDF, said polymer (F) having an intrinsic viscosity measured in dimethylformamide at 25° C. in the range of 0.25 l / g to 0.60 l / g, preferably 0.30 l / g to 0.50 l / g, determined according to the method reported in the specification, The polymer (F) has the formula (I): -(R ａ ) ｘ -O-CO-O-CH ２ -CH ３ (I) (In the formula, R ａ is C １ ~C ５ and x is an integer selected from 1 and 0. and wherein the terminal group of said end groups of formula (I) are present in an amount of at least 0.2 / 10000 VDF units, preferably at least 1.0 / 10000 VDF units and at most 10 / 10000 VDF units, determined according to the method reported in the specification, the polymer (F) has a particle size distribution with a D50 value of less than 240 microns as measured using laser diffraction according to ISO 13320; Polymer (F).

2. 2. The polymer (F) according to claim 1, which is a VDF homopolymer.

3. 2. Polymer (F) according to claim 1, which is a VDF-based copolymer comprising repeating units derived from VDF and repeating units derived from at least one fluorinated comonomer (CF) different from VDF.

4. The fluorinated comonomer (CF) (a) C fluoroethylenes such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene, hexafluoroisobutylene, vinyl fluoride; 1,2-difluoroethylene and trifluoroethylene ２ ~C ８ Fluoro- and / or perfluoroolefins; (b) Formula CH ２ =CH-R ｆ０ (In the formula, R ｆ０ is C １ ~C ６ perfluoroalkyl ethylenes, each of which is a perfluoroalkyl group; (c) chloro-, and / or bromo-, and / or iodo-C, such as chlorotrifluoroethylene (CTFE) ２ ~C ６ Fluoroolefins; (d) perfluoro(alkyl) vinyl ethers such as perfluoro(methyl) vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE), and perfluoro(propyl) vinyl ether (PPVE); (e) Perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD) The polymer (F) according to any one of claims 1 to 3, selected from the group consisting of:

5. 5. The polymer (F) according to claim 4, wherein the polymer (F) comprises 0.1 mol% to 20.0 mol%, preferably 0.3 mol% to 10.0 mol%, more preferably 0.5 mol% to 5.0 mol% of repeat units derived from the fluorinated comonomer (CF).

6. containing an end group of formula (I) where x is zero and / or an end group of formula (I) where x is 1, R ａ is C ２ ~C ３ The polymer (F) according to any one of claims 1 to 5, wherein the alkyl radical is a linear or branched alkyl radical of the formula:

7. A process for preparing the polymer (F) according to any one of claims 1 to 6, comprising the steps of: - polymerizing, in aqueous medium, vinylidene fluoride (VDF) monomer and, optionally, comonomer (CF), in the presence of a radical initiator system that introduces the end group of formula (I) into the polymer chain; maintaining the pressure in the reaction vessel above the critical pressure of vinylidene fluoride; A method comprising:

8. 8. The method of claim 7, wherein the radical initiator system comprises radical initiators such as di(ethyl) peroxydicarbonate and hydroethyl peroxydicarbonate.

9. 9. The method of claim 8, wherein the radical initiator system comprises a chain transfer agent (CTA).

10. a) at least one electrode active material (AM); b) at least one binder (B) comprising at least one polymer (F) according to any one of claims 1 to 6; c) at least one solvent (S); An electrode-forming composition (C) comprising:

11. The electrode-forming composition (C) of claim 10, wherein the at least one electrode active material (AM) is an LFP.

12. A method for producing an electrode [electrode (E)], comprising the steps of: (I) providing a metal substrate having at least one surface; (II) preparing the electrode-forming composition (C) according to claim 10 or 11; (III) applying the composition (C) prepared in step (II) onto at least one surface of the metal substrate prepared in step (I), thereby preparing an assembly including a metal substrate coated with the composition (C) on at least one surface; (IV) drying the assembly prepared in step (III); (V) subjecting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the present invention. A method comprising:

13. Electrode (E) obtainable by the method according to claim 12.

14. Electrochemical device comprising at least one electrode (E) according to claim 13.

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