Binder for secondary battery electrode

Abstract

The present invention relates to a vinylidene fluoride polymer for use as a binder for electrodes in secondary batteries.

Description

Cross-references to previous applications

[0001] This application claims priority to European application number 23210250.9, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0002] This invention relates to vinylidene fluoride polymers used as adhesives for electrodes in secondary batteries. Background Technology

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

[0004] It is generally known that increasing the molecular weight of fluoropolymers can improve the performance of articles made from these materials, particularly in terms of mechanical properties and the adhesion of electrodes to current collectors.

[0005] However, increasing the molecular weight of fluoropolymers will increase the viscosity of electrode forming formulations (also known as electrode slurries) containing them, making the handling and coating processes in electrode manufacturing more difficult.

[0006] In the field of battery technology, especially lithium battery technology, there is a problem of providing electrode adhesives that have excellent adhesion without negatively impacting the electrode manufacturing process (such as the negative impact on electrode production due to increased slurry viscosity).

[0007] This invention provides an improvement over current technology by not increasing the viscosity of the electrode slurry in the manufacturing process and by enabling the electrode to have better adhesion to the current collector. Summary of the Invention

[0008] It has been found that certain vinylidene fluoride copolymers possess excellent adhesion to metal substrates and can be used to prepare electrode forming compositions with improved adhesion without any increase in slurry viscosity at low shear rates.

[0009] Therefore, the object of the present invention is a VDF-based polymer [polymer (F)], which comprises the following:

[0010] - (i) Repeating units derived from vinylidene fluoride (VDF) monomers, and

[0011] - (ii) Optionally, repeating units derived from one or more fluorinated comonomers (CF) different from VDF,

[0012] The polymer (F) is characterized by containing chain end groups having formula (I):

[0013] CH3-O-CO-C(CH3)2-(I)

[0014] Furthermore, the intrinsic viscosity of the polymer (F) measured in dimethylformamide at 25°C ranges from 0.15 l / g to 0.70 l / g.

[0015] Preferably, these chain end bases having formula (I) are present in an amount of at least 0.1 / 10000 VDF units, more preferably at least 0.5 / 10000 VDF units, and even more preferably at least 1.0 / 10000 VDF units.

[0016] A second object of the present invention relates to an electrode forming composition (C) comprising:

[0017] a) At least one electrode active material (AM);

[0018] b) At least one adhesive (B), wherein the adhesive (B) comprises at least one polymer (F) as defined above; and

[0019] c) At least one solvent (S).

[0020] In another object, the present invention relates to the use of an electrode forming composition (C) in a method for manufacturing an electrode [electrode (E)], said method comprising:

[0021] (A) Provide a metal substrate having at least one surface;

[0022] (B) Provide an electrode forming composition as defined above (C);

[0023] (C) Applying the composition (C) provided in step (B) to at least one surface of the metal substrate provided in step (A) to provide an assembly comprising a metal substrate having the composition (C) coated on the at least one surface;

[0024] (D) Dry the components provided in step (C);

[0025] (E) The dried component obtained in step (D) is subjected to a compression step to obtain the electrode (E) of the present invention.

[0026] In another object, the present invention relates to an electrode (E) obtainable by the method of the present invention.

[0027] In another object, the present invention relates to an electrochemical device comprising at least one electrode (E) of the present invention. Detailed Implementation

[0028] The term "VDF-based polymer" is intended to refer to VDF homopolymers (PVDF) and VDF-based copolymers comprising repeating units derived from VDF and repeating units derived from at least one fluorinated comonomer (CF) other than VDF.

[0029] The VDF-based polymer (F) of the present invention does not contain any hydrogenated monomers with polar groups.

[0030] The term "repeating unit derived from vinylidene fluoride" (also commonly referred to as VDF or VDF unit) is intended to represent a repeating unit having the formula -CF2-CH2-.

[0031] In polymer (F), the end group of formula (I) is connected to a repeating unit derived from VDF, and thus to a unit having the formula -CF2-CH2-. The end group of formula (I) can be connected to a repeating unit having the formula -CF2-CH2- (i.e., a normal or reverse repeating VDF unit) via a -CF2 or -CH2 group.

[0032] The polymer (F) can be an elastomer or a semi-crystalline polymer, preferably a semi-crystalline polymer.

[0033] As used herein, the term "semi-crystalline" refers to a fluoropolymer that, according to DSC analysis, possesses at least one crystalline melting point in addition to its glass transition temperature (Tg). For the purposes of this invention, "semi-crystalline fluoropolymer" is intended to refer herein to a fluoropolymer having a heat of fusion of 10 to 90 J / g, preferably 30 to 80 J / g, more preferably 35 to 75 J / g, as measured according to ASTM D3418-08.

[0034] For the purposes of this invention, the term "elastomer" is intended to specify a true elastomer or a polymeric resin used as a base component for obtaining a true elastomer.

[0035] A true elastomer is defined by ASTM, Special Technical Bulletin, 184 as a material that can be stretched to twice its intrinsic length at room temperature and, after being held under tension for 5 minutes, recovers to no more than 10% of its initial length within the same time after being released.

[0036] The polymer (F) of the present invention typically has a melt temperature (Tm) in the range of 120°C to 200°C.

[0037] The polymer (F) of the present invention has a quasi-linear structure with a very low branching content, which results in a significant reduction in the insoluble portion due to the long branches.

[0038] The polymer (F) of the present invention preferably has a low fraction of insoluble components in a standard polar aprotic solvent (such as NMP) used for VDF polymers. More preferably, the solution of polymer (F) in the standard polar aprotic solvent remains homogeneous and stable for several weeks, with substantially no insoluble residues.

[0039] Because of the low amount of insoluble components, the GPC and NMR analyses of polymer (F) are unaffected, and there are no issues with reliability and reproducibility.

[0040] The melting temperature can be determined by a DSC curve obtained through differential scanning calorimetry (hereinafter also referred to as DSC). In cases where the DSC curve shows multiple melting peaks (endothermic peaks), the melting temperature (Tm) is determined based on the peak with the largest peak area.

[0041] Non-limiting examples of suitable fluorinated comonomers (CF) include, in particular, the following:

[0042] (a) C2-C8 fluoroolefins and / or perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene;

[0043] (b) C2-C8 hydrogenated monofluoroolefins, such as fluoroethylene; 1,2-difluoroethylene and trifluoroethylene;

[0044] (c) Having the formula CH2=CH-R f0 Perfluoroalkyl ethylene, wherein R f0 It is a C1-C6 perfluoroalkyl group;

[0045] (d) Chlorinated and / or brominated and / or iodinated C2-C6 fluoroolefins, such as trifluorochloroethylene (CTFE).

[0046] (e) Perfluoro(alkyl) vinyl ethers, such as perfluoro(methyl) vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE) and perfluoro(propyl) vinyl ether (PPVE).

[0047] (f) Perfluorinated (1,3-dioxacyclopentene); Perfluorinated (2,2-dimethyl-1,3-dioxacyclopentene) (PDD).

[0048] The fluorinated comonomer (CF) is preferably HFP.

[0049] In a preferred embodiment, the polymer (F) is semi-crystalline and contains 0.1% to 15.0% (more preferably 0.3% to 10.0% (more preferably 0.5% to 5 ...

[0050] It should be understood that segments of different chain ends, defects or other impurities than those defined above may be included in polymer (F) without impairing its properties.

[0051] The polymer (F) more preferably comprises repeating units derived from:

[0052] - Vinylidene fluoride (VDF) of at least 70%, preferably at least 75%, and more preferably at least 85% by molar weight.

[0053] - Optionally, 0.5% to 5.0% of repeating units derived from at least one fluorinated comonomer (CF) on a molar basis.

[0054] The intrinsic viscosity of polymer (F) measured in dimethylformamide at 25°C is between 0.15 l / g and 0.70 l / g, preferably between 0.20 l / g and 0.60 l / g.

[0055] A preferred method for preparing polymer (F) includes polymerizing vinylidene fluoride (VDF) monomer and optionally comonomer (CF) in an aqueous medium in the presence of a free radical initiator that leaves chain-end groups of formula (I) in the polymer, the method being carried out by maintaining the pressure in the reactor vessel above the critical pressure of vinylidene fluoride.

[0056] Suitable free radical initiator systems include free radical initiators such as azo compound initiators like 2,2′-azobis(2-methylpropionic acid) dimethyl ester (AIBME).

[0057] The amount of initiator required for polymerization depends on its activity and the temperature used in the polymerization. The total amount of initiator used is typically between 100 and 30,000 ppm by weight, based on the total weight of monomers used.

[0058] Initiators can be added in pure form, as a solution, as a suspension, or as an emulsion, depending on the initiator chosen.

[0059] In one embodiment, when the initiator is added in solution form, it can dissolve in an optional chain transfer agent used in the polymerization.

[0060] In one embodiment, when the initiator is added in solution form, it can be soluble in branched fatty alcohols such as isopropanol, tert-butanol, pinacol, 2,4-dimethyl-3-pentanol, 2,4,4-trimethyl-1,3-pentanediol, or mixtures thereof.

[0061] In one embodiment, when the initiator is added in solution form, it can dissolve in a mixture of chain transfer agent and branched fatty alcohol used in the polymerization.

[0062] Chain transfer agents (CTAs) can be added to the free radical initiator system used for polymerization. Suitable CTAs for this polymerization are known in the art and are typically short-chain hydrocarbons (like ethane and propane), esters (such as ethyl acetate or diethyl maleate, diethyl carbonate, and others). When an organic peroxide is used as the initiator, it can also act as an effective CTA during the free radical polymerization process. However, additional CTA can be added all at once at the start of the reaction, or it can be added in batches, or it can be added continuously throughout the reaction. The amount of CTA and its mode of addition depend on the desired properties.

[0063] Preferably, CTAs are those that produce polar oxygen-containing end groups, such as diethyl carbonate.

[0064] In the preferred preparation method, the pressure is maintained above the critical pressure of vinylidene fluoride. Typically, the pressure is maintained at a value greater than 50 bar, preferably greater than 75 bar, and even more preferably greater than 100 bar.

[0065] Preferably, the method of the present invention is carried out at a temperature above the critical temperature of the VDF monomer (i.e., at least 31°C).

[0066] In a preferred embodiment of the present invention, the method for preparing the polymer (F) as defined above includes:

[0067] - To polymerize vinylidene fluoride (VDF) monomer and optionally comonomer (CF) in an aqueous medium in the presence of a free radical initiator system; and

[0068] - Maintain the pressure in the reactor vessel above the critical pressure of vinylidene fluoride.

[0069] The initiator system includes azo compound initiators and chain transfer agents.

[0070] In a more preferred embodiment of the present invention, the method for preparing the polymer (F) as defined above includes:

[0071] - To polymerize vinylidene fluoride (VDF) monomer and optionally comonomer (CF) in an aqueous medium in the presence of a free radical initiator system; and

[0072] - Maintain the pressure in the reactor vessel above the critical pressure of vinylidene fluoride.

[0073] The initiator system contains dimethyl 2,2′-azobis(2-methylpropionic acid) (AIBME) and diethyl carbonate.

[0074] The polymer (F) is typically provided in powder form according to the methods described above.

[0075] The polymer (F) in powder form may optionally be further extruded to provide the polymer (F) in granular form.

[0076] The polymer (F) detailed above can be used in the adhesives of electrodes in secondary batteries.

[0077] A second object of the present invention relates to an electrode forming composition (C) comprising:

[0078] a) At least one electrode active material (AM);

[0079] b) At least one adhesive (B), wherein the adhesive (B) comprises at least one polymer (F) as defined above; and

[0080] c) At least one solvent (S).

[0081] For the purposes of this invention, the term "electroactive material (AM)" is intended to refer to a compound capable of binding or inserting alkali metal or alkaline earth metal ions into its structure and substantially releasing alkali metal or alkaline earth metal ions therefrom during the charging and discharging phases of an electrochemical device. The compound (AM) is preferably capable of binding or inserting and releasing lithium or sodium ions.

[0082] The properties of the compound (AM) in composition (C) depend on whether the composition is used to manufacture a positive electrode [electrode (Ep)] or a negative electrode [electrode (En)].

[0083] In the case of forming the positive electrode (Ep) for sodium-ion secondary batteries, the active material is typically selected from Na-based layered transition metal oxides, Prussian blue analogs, and polyanionic materials.

[0084] In some embodiments, the active material is a Na-based layered transition metal oxide, which is classified into O3-, P2-, and P3- types according to the stacking order of the oxygen layers. The P2- type structure generally corresponds to the general formula NaxMO2, where M represents a transition metal ion such as Co or Mn, and x is 2 / 3.

[0085] In some embodiments, the active material is a material having the general formula A x P[R(CN)6] 1-y □ y Prussian blue analogues of mH2O (PBA), where A is an alkali metal ion, P is an N-coordinated transition metal ion, R is a C-coordinated transition metal ion, and □ is a [R(CN)6] vacancy, where 0 ≤ x ≤ 2 and 0 ≤ y < 1, such as 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 Ni 0.12 Mn 0.88 [Fe(CN)6] 0.98 Na2Ni x Co 1-x Fe(CN)6 (where 0 ≤ x ≤ 1, e.g., Na2CoFe(CN)6).

[0086] In some other embodiments, the active material is a material having the general formula Na. x M y (XO4) n Polyanionic materials (where X = S, P, Si, As, Mo, and W, and M is a transition metal) that possess a series of tetrahedral anionic units (XO4). n- and its derivatives (X) m O 3m+1 ) n- Among them, phosphates such as NaMPO4, NaFePO4, and Na 0.7 FePO4 or NaMnPO4; having the general formula Na xSodium (natrium / sodium) superionic conductors with NASICON-type structures of M2(XO4)3 (where 1 ≤ x ≤ 4, and M = V, Fe, Ni, Mn, Ti, Cr, Zr…; X = P, S, Si, Se, Mo…) – possessing a single transition metal type such as Na3V2(PO4)3 (NVP), Na3Cr2(PO4)3, Na3Fe2(PO4)3; – possessing a binary transition metal type 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 (where 2 / 3 ≤ x ≤ 7 / 8, for example, Na) 3.12 Fe 2.44 (P₂O₇)₂ or Na 3.32 Fe 2.34 (P2O7)2), Na2(VO)P2O7, Na7V3(P2O7)4; fluorophosphate NaVPO4F, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VO 1-x PO4)2F 1+2x (where 0 ≤ x ≤ 1, e.g., Na3(VOPO4)2F or Na3V2(PO4)2F3 (NVPF)); fluorosulfates, such as NaMSO4F (where M = Fe, Co, Ni); mixed phosphates / pyrophosphates with the general formula Na4M3(PO4)2(P2O7) (where M represents a transition metal), such as Na4Mn3(PO4)2(P2O7), Na4Co3(PO4)2(P2O7), Na4Ni3(PO4)2(P2O7), Na4Fe3(PO4)2(P2O7) (NFPP), Na7V4(P2O7)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 (where 0 ≤ x ≤ 1); silicates having the general formula Na2MSiO4 (where M = Mn, Fe, Co and Ni).

[0087] In some preferred embodiments, the active material is preferably a fluorophosphate selected from the list of the following compositions: NaVPO4F, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VO4)2F, Na2(V2PO ... 1-x PO4)2F 1+2x (where 0 ≤ x ≤ 1, for example Na3(VOPO4)2F or Na3V2(PO4)2F3(NVPF)).

[0088] Conventional active materials (AMs) at the positive electrode of lithium-ion batteries can comprise composite metal chalcogenides having the formula LiMQ2, where M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr, and V, and Q is a chalcogen element such as O or S. Among these, lithium-based composite metal oxides having the formula LiMO2 are preferred, where M is the same as defined above. Preferred examples include LiCoO2, LiNiO2, and LiNiO2. x Co 1-x O2 (0 < x < 1) and LiMn2O4 with spinel structure.

[0089] According to another preferred embodiment, the at least one positive electrode active material (AM) is selected from lithium-containing composite metal oxides having general formula (II).

[0090] LiNi x M 1 y M 2 w M 3 z Q2(II)

[0091] Among them, M 1 M 2 and M 3 They may be the same as or different from each other, and are transition metals selected from Al, Co, Fe, Mn, Cr, and V.

[0092] 0.5 ≤ x ≤ 1,

[0093] Where y + w + z = 1 - x, and

[0094] Q is the same as defined above.

[0095] Alternatively, the electrode active material may contain materials having the formula M1M2(JO4). f E 1-fElectroactive materials based on lithiated or partially lithiated transition metal oxygen anions, wherein M1 is lithium, which may be partially substituted by another alkali metal comprising less than 20% of the metal M1; M2 is a transition metal selected from Fe, Mn, Ni or mixtures thereof at an oxidation level of +2, which may be partially substituted by one or more other metals at an oxidation level between +1 and +5 and comprising less than 35% of the metal M2, including 0; JO4 is any oxygen anion, wherein J is P, S, V, Si, Nb, Mo or combinations thereof; E is a fluoride anion, hydroxide anion or chloride anion; f is the mole fraction of JO4 oxygen anion, typically included between 0.75 and 1.

[0096] As defined above, M1M2(JO4) f E 1-f The electroactive material is preferably phosphate-based and may have an ordered or modified olivine structure.

[0097] More preferably, the electrode active material has 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 which is a transition metal, JO4 is preferably PO4, which may be partially substituted by another oxygen anion, wherein J is S, V, Si, Nb, Mo or a combination thereof. More preferably, the electrode active material (AM) is a phosphate-based electroactive material having the following formula.

[0098] Li x A y D z PO4,

[0099] Where 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; x, y, and z are numbers that satisfy the following relationships: 0 < x < 2, 0 < y < 1.5, 0 z < 1.5.

[0100] Component A is preferably Fe, Mn and Ni, and particularly preferably Fe.

[0101] Component D is preferably Mg or Ca.

[0102] Examples of compounds with an olivine structure include lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and lithium manganese phosphate.

[0103] In addition, as a positive electrode active material (AM), materials with their surface partially or completely covered by carbon can be used to supplement conductivity.

[0104] The amount of carbon coated is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less, based on 100 parts by weight of the positive electrode active material.

[0105] In the case of forming a composite negative electrode (En) for a secondary battery, the compound (AM) may preferably contain carbon-based and / or silicon-based materials.

[0106] In some embodiments, the carbon-based material may be, for example, graphite (such as natural or artificial graphite), graphene, or carbon black.

[0107] These materials can be used alone or as a mixture of two or more of them.

[0108] The preferred carbon-based material is graphite.

[0109] Silicon-based compounds may be one or more selected from the group consisting of chlorosilanes, alkoxysilanes, aminosilanes, fluoroalkylsilanes, silicon, silicon chloride, silicon carbide, and silicon oxide. More specifically, silicon-based compounds may be silicon oxide or silicon carbide.

[0110] When present in compound (AM), the at least one silicon-based compound is included 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).

[0111] The solvent (S) is preferably an organic polar solvent, examples of which may include: N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, and trimethyl phosphate. These solvents may be used alone or in mixtures of two or more substances.

[0112] An optional conductive agent can be added to the electrode forming composition (C) to improve the conductivity of the resulting electrode.

[0113] When present, the conductive agent differs from the carbon-based materials described above.

[0114] Examples can include: carbonaceous materials such as carbon black, finely powdered graphite, carbon nanotubes, graphene, or fibers, or finely powdered or fibrous metals (such as nickel or aluminum). Carbon black is available, for example, under the trademarks Super P® or Ketjenblack®.

[0115] The electrode forming composition (C) of the present invention may optionally further comprise at least one conductive agent.

[0116] When present, the conductive agent differs from the carbon-based materials described above.

[0117] In a preferred embodiment of the invention, an electrode forming composition (C) for use in the preparation of a positive electrode (Ep) is provided, the composition comprising:

[0118] a) At least one positive electrode active material (AM);

[0119] b) At least one adhesive (B), wherein the adhesive (B) comprises at least one polymer (F) as defined above;

[0120] c) at least one solvent (S); and

[0121] d) At least one conductive agent, preferably selected from carbon black or finely powdered carbon nanotubes.

[0122] As described above, the polymer (F) of the present invention has a quasi-linear structure and the amount of insoluble portion is very low when dissolved in a standard polar aprotic solvent (such as NMP).

[0123] Due to the low amount of insoluble components, the polymer (F) provides a solution in organic solvents that is not adversely affected by the presence of insoluble residues (often referred to as "gels"), and is therefore more suitable for formulating electrode forming compositions.

[0124] In another object, the present invention relates to the use of an electrode forming composition (C) for manufacturing an electrode (E), the method comprising:

[0125] (A) Provide a metal substrate having at least one surface;

[0126] (B) Provide an electrode forming composition as defined above (C);

[0127] (C) Applying the composition (C) provided in step (B) to at least one surface of the metal substrate provided in step (A) to provide an assembly comprising a metal substrate having the composition (C) coated on the at least one surface;

[0128] (D) Dry the components provided in step (C);

[0129] (E) The dried component obtained in step (iv) is subjected to a compression step to obtain the electrode (E) of the present invention.

[0130] In another object, the present invention relates to an electrode (E) obtainable by the method of the present invention.

[0131] The applicant has unexpectedly discovered that the electrode (E) of the present invention exhibits excellent adhesion of the adhesive to the current collector.

[0132] The electrode (E) of the present invention is therefore particularly suitable for use in electrochemical devices, especially in secondary batteries.

[0133] For the purposes of this invention, the term "secondary battery" is intended to refer to a rechargeable battery.

[0134] The secondary battery of the present invention is preferably an alkali metal or alkaline earth metal secondary battery.

[0135] More preferably, the secondary battery of the present invention is a sodium-ion or lithium-ion secondary battery.

[0136] In another object, the present invention relates to an electrochemical device comprising at least one electrode (E) of the present invention.

[0137] The electrochemical device (preferably a secondary battery) according to the present invention comprises:

[0138] - Positive electrode and negative electrode,

[0139] At least one of the positive electrode and the negative electrode is an electrode (E) of the present invention.

[0140] In a preferred embodiment of the present invention, an electrochemical device as a secondary battery is provided, comprising:

[0141] - Positive electrode and negative electrode,

[0142] The positive electrode is the electrode (E) according to the present invention.

[0143] The electrochemical device according to the present invention can be prepared by standard methods known to those skilled in the art.

[0144] If any disclosure of any patent, patent application, or publication incorporated herein by reference conflicts with this specification to the extent that it may obscure the terminology, this specification shall prevail.

[0145] The invention will now be described with reference to the following examples, which are merely illustrative and not intended to limit the scope of the invention.

[0146] Experimental Section

[0147] raw material

[0148] 2,2'-Azobis(2-methylpropionic acid) dimethyl ester is commercially available from Fujifilm.

[0149] Determination of the intrinsic viscosity of polymer (F)

[0150] The intrinsic viscosity (η) [dl / g] is measured using an Ubbelhode viscometer based on the fall time of a solution obtained by dissolving the polymer (F) in N,N-dimethylformamide at a concentration of approximately 0.2 g / dl at 25°C:

[0151]

[0152] Where c is the polymer concentration [g / dl], η r It is the relative viscosity, which is the ratio between the fall time of the sample solution and the fall time of the solvent, η. sp It is the specific viscosity, i.e., η. r -1, and Γ is the experimental factor, which corresponds to 3 for polymer (F) and polymer (A).

[0153] DSC analysis

[0154] DSC analysis was performed according to ASTM D 3418 standard; melting point (T f2 The value was determined at a heating rate of 10°C / min.

[0155] End groups in the polymer were determined by NMR.

[0156] The amount of polar end groups in polymer (F) produced by the initiator 2,2'-azobis(2-methylpropionic acid) dimethyl ester used in the polymerization process is determined by... 1 H-NMR determined the intensity of the H atoms of the CH3 group (shown in bold in the following formula) relative to the total intensity of the CH2 portion of the VDF monomer unit in the polymer (F) main chain:

[0157] CH3-O-CO-C(CH3)2-.

[0158] Approximately 20 mg of the polymer was dissolved in 0.7 ml of hexadeuterated acetone. Results were recorded at 60°C. 1 H-NMR spectra show that the CH3 signal is at 3.66 ppm, while the CH2 signals from the normal and reverse repeating units of the VDF are broad peak resonances centered at 2.93 ppm and 2.36 ppm, respectively.

[0159] The amount of polar end groups of the polymer produced by diethyl carbonate, a chain transfer agent used in the polymerization process, is determined by... 1H-NMR determined the intensity of the H atoms of the CH2 group (for the straight-chain end) and the CH group (for the branched-chain end) (shown in bold in the following formula) relative to the total intensity of the CH2 portion of the VDF monomer unit in the polymer (F) main chain:

[0160] CH3-CH2-O-CO-O-CH2-CH2- and CH3-CH2-O-CO-O-CH-(CH3)-.

[0161] Approximately 20 mg of the polymer was dissolved in 0.7 ml of hexadeuterated acetone. Results were recorded at 60°C. 1 H-NMR spectra show that CH2 is at 4.05 ppm and CH is at 5.1 ppm, while the CH2 signals from the normal and reverse repeating units of the VDF are broad peak resonances centered at 2.93 ppm and 2.36 ppm, respectively.

[0162] The content of chain end groups is calculated by applying the following formula:

[0163] [EG] = (IEG / IVDF) × 10000

[0164] in:

[0165] - [EG] is the content of universal chain end groups, expressed as moles / 10000 VDF units.

[0166] - IEG is the integral strength of the chain end group [EG], normalized to a single hydrogen atom.

[0167] - IVDF is the integral intensity of the repeating units of normal and reverse VDF, normalized to a single hydrogen atom.

[0168] Example 1: Preparation of Polymer F-1

[0169] In a 4 L reactor equipped with a stirrer running at 650 rpm, 1750 g of demineralized water and 0.54 g of hydroxypropyl methylcellulose (Methocel®-K100 from Dow Chemical Company and DuPont Nutrition Biosciences SAS) were introduced sequentially per kg of total monomer. Oxygen present in the reactor was removed by sequential vacuum and nitrogen purging at a fixed temperature of 14°C. This sequence was repeated three times.

[0170] Then, a solution obtained by dissolving 3.37 g of the initiator 2,2'-azobis(2-methylpropionic acid) dimethyl ester in 5.39 g of diethyl carbonate is introduced into the reactor.

[0171] The stirring speed was then increased to 880 rpm, and 1346 g of VDF was added to the reactor. The reactor was then gradually heated until the set point temperature of 65°C was reached. Throughout the polymerization run, the pressure was maintained at a constant 120 bar by feeding a total of 1367 g of demineralized water into the reactor. After 459 minutes, the polymerization was stopped by degassing the suspension until atmospheric pressure was reached.

[0172] 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. 1241 g of dried powder was collected.

[0173] A polymer with an intrinsic viscosity of 0.306 l / g in DMF at 25°C and a T2f of 169.2°C was obtained.

[0174] In addition, the presence of -CF2H end groups in the 4.2 / 10000 VDF unit and -CF2CH3 end groups in the 2.7 / 10000 VDF unit was confirmed.

[0175] Furthermore, the presence of end groups derived from 2,2'-azobis(2-methylpropionic acid) dimethyl ester in the 2.2 / 10000 VDF unit was confirmed.

[0176] In addition, the presence of diethyl carbonate end groups in the 0.9 / 10000 VDF units was confirmed.

[0177] Example 2 (Comparison): Preparation of Polymer A

[0178] In an 80 L reactor equipped with an agitator running at 250 rpm, the following were introduced sequentially: 52.4 kg of demineralized water per kg VDF and 0.4 g of hydroxypropyl methylcellulose (Methocel®-K100 from Dow Chemical Company). Oxygen present in the reactor was removed by sequential vacuum and nitrogen purging at a fixed temperature of 20°C. This sequence was repeated three times.

[0179] Then, a solution (75%) of 41.38 g of tert-amyl perpentanoate (from United Initiators) in isododecane and 250.02 g of diethyl carbonate were introduced into the reactor. The stirring speed was then immediately increased to 300 rpm, and 22.99 kg of VDF was added to the reactor. The reactor was then gradually heated until the setpoint temperature of 52°C was reached.

[0180] Throughout the polymerization run, the pressure was maintained at a constant 120 bar using VDF. A total of 11.49 kg of VDF was charged, and no more VDF was added. The temperature was then raised to 65°C, and the reaction was stopped after a total of 169 minutes by degassing the suspension until atmospheric pressure was reached.

[0181] 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 dried powder was collected.

[0182] Polymer A: A VDF homopolymer with an intrinsic viscosity of 0.271 l / g in DMF at 25°C and a T2f of 170.2°C.

[0183] The polymer contains 2.2 / 10000 VDF units with diethyl carbonate-derived end groups, 0.6 / 10000 VDF units with (CH3)3-C- end groups derived from the initiator, 4.5 / 10000 VDF units with -CF2H, and 2.4 / 10000 VDF units with -CF2CH3 end groups.

[0184] Example 3: Preparation of polymer F-2

[0185] In a 4 L reactor equipped with a stirrer running at 650 rpm, the following were introduced sequentially: 1.73 kg of demineralized water per kg of total monomer, followed by 0.40 g of hydroxypropyl methylcellulose (Methocel®-K100, sourced from). Oxygen present in the reactor was removed by sequential vacuum and nitrogen purging at a fixed temperature of 14°C. This sequence was repeated three times.

[0186] The solution obtained by dissolving 3.33 g of the initiator 2,2'-azobis(2-methylpropionic acid) dimethyl ester in 5.33 g of tert-butanol (from ThermoFisher Scientific) was then introduced into the reactor.

[0187] The stirring speed was then increased to 880 rpm, and 1.33 kg of VDF was added to the reactor. The reactor was then gradually heated until the set point temperature of 65°C was reached. Throughout the polymerization run, the pressure was maintained at a constant 120 bar by feeding a total of 1.36 kg of demineralized water into the reactor. After 547 minutes, the polymerization was stopped by degassing the suspension until atmospheric pressure was reached.

[0188] 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. 1.25 kg of dried powder was collected.

[0189] A polymer with an intrinsic viscosity of 0.475 l / g in DMF at 25°C and a T2f of 168.7°C was obtained.

[0190] The overall results for intrinsic viscosity (which are related to the CTA, initiator, and polymerization temperature used to prepare F-1, F-2, and A polymers) are shown in Table 1.

[0191] Table 1

[0192]

[0193] Example F-2 shows that tert-butanol is a good solvent for the initiator because it has almost no effect as a CTA.

[0194] Preparation of electrodes with NMC active materials

[0195] The positive electrode is prepared as follows, having a final composition of 96.5% NMC by weight, 1.5% polymer (F-1) or polymer (A) by weight, and 2% conductive additive by weight.

[0196] The first dispersion was prepared by premixing 34.7 g of a solution of 6% by weight of polymer in NMP, 133.8 g of NMC, 2.8 g of SC-65 and 8.8 g of NMP in a centrifuge mixer for 10 minutes.

[0197] The mixture was then mixed for 50 minutes at 2000 rpm using a high-speed disc stirrer. Subsequently, an additional 7.2 g of NMP was added to the dispersion, and it was further mixed for 20 minutes at 1000 rpm using a butterfly stirrer to obtain the positive electrode slurry.

[0198] The positive electrode was obtained by casting the obtained composition onto a 15 μm thick Al foil using a doctor blade and drying the coated layer in a vacuum oven at 90°C for approximately 50 minutes. The thickness of the dried coating was approximately 110 µm.

[0199] Slurry viscosity measurement

[0200] The viscosity of the positive electrode slurry obtained as described above was measured by Anton Paar Rheolab QC using a concentric cylinder apparatus (measuring cup: C-CC27 / QC-LTD Bob: CC27 / P6), with the Peltier temperature controlled at 25°C. Steady-state viscosity was measured at shear rates from 0.1 to 200 1 / s.

[0201] The results are shown in Table 2.

[0202] Adhesion measurement

[0203] The adhesion peel force between the aluminum foil and the electrode obtained as described above was measured as follows:

[0204] A 180° peel test was performed at 20°C and 300 mm / min according to the settings described in standard ASTM D903 to evaluate the adhesion of the dried coating to the Al foil.

[0205] The results are shown in Table 2.

[0206] Table 2

[0207]

[0208] The results show that, compared with polymers in the prior art, the polymers of the present invention can be used to prepare electrode slurry compositions, so that the electrodes are endowed with improved adhesion to the current collector without compromising the viscosity of the slurry.

Claims

1. A VDF-based polymer [polymer (F)], comprising the following: - (i) Repeating units derived from vinylidene fluoride (VDF) monomers, and - (ii) Optionally, repeating units derived from one or more fluorinated comonomers (CF) different from VDF, The polymer (F) is characterized by containing chain end groups having formula (I): CH3-O-CO-C(CH3)2-(I) Furthermore, the intrinsic viscosity of the polymer (F) measured in dimethylformamide at 25°C ranges from 0.15 l / g to 0.70 l / g.

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

3. The 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 polymer (F) according to any one of claims 1 to 3, wherein, The fluoride The comonomers (CF) are selected from the following groups: (a) C2-C8 fluoroolefins and / or perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene; (b) C2-C8 hydrogenated monofluoroolefins, such as fluoroethylene; 1,2-difluoroethylene and trifluoroethylene; (c) Having the formula CH2=CH-R f0 Perfluoroalkyl ethylene, wherein R f0 It is a C1-C6 perfluoroalkyl group; (d) Chlorinated and / or brominated and / or iodinated C2-C6 fluoroolefins, such as trifluorochloroethylene (CTFE). (e) Perfluoro(alkyl) vinyl ethers, such as perfluoro(methyl) vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE) and perfluoro(propyl) vinyl ether (PPVE). (f) Perfluorinated (1,3-dioxacyclopentene); Perfluorinated (2,2-dimethyl-1,3-dioxacyclopentene) (PDD).

5. The polymer (F) according to any one of the preceding claims, wherein, These end bases having formula (I) are present in an amount of at least 0.1 / 10000 VDF units, more preferably at least 0.5 / 10000 VDF units, and even more preferably at least 1.0 / 10000 VDF units.

6. The polymer (F) according to any one of the preceding claims, wherein, The intrinsic viscosity of polymer (F) measured in dimethylformamide at 25°C is between 0.15 l / g and 0.70 l / g, preferably between 0.20 l / g and 0.60 l / g.

7. The polymer (F) according to claim 4, wherein, The polymer (F) comprises 0.1% to 15.0% (more preferably 0.3% to 10.0% (more preferably 0.5% to 5.0% (more preferably 0.5% to 5.0% (more preferably 0.5% to 5.0% (more preferably 0.1% to 1 ...

8. A method for preparing the polymer (F) according to any one of claims 1 to 7, the method comprising: - Polymerize vinylidene fluoride (VDF) monomer and optionally comonomer (CF) in an aqueous medium in the presence of a free radical initiator system; as well as - Maintain the pressure in the reactor vessel above the critical pressure of the vinylidene fluoride. The initiator system includes an azo compound initiator and a chain transfer agent.

9. The method according to claim 8, wherein, The free radical initiator system contains dimethyl 2,2′-azobis(2-methylpropionic acid) (AIBME) and diethyl carbonate.

10. An electrode forming composition (C) comprising: a) At least one electrode active material (AM); b) At least one adhesive (B), wherein the adhesive (B) comprises at least one polymer (F) according to any one of claims 1 to 7; and c) At least one solvent (S).

11. The electrode forming composition (C) according to claim 10, used for preparing a positive electrode (Ep), said composition comprising: a) At least one positive electrode active material (AM); b) At least one adhesive (B), wherein the adhesive (B) comprises at least one polymer (F) as defined above; c) at least one solvent (S); and d) At least one conductive agent, preferably selected from carbon black or finely powdered carbon nanotubes.

12. A method for manufacturing an electrode [electrode (E)], the method comprising: (I) Provide a metal substrate having at least one surface; (II) Providing an electrode forming composition (C) according to any one of claims 10 or 11; (III) Applying the composition (C) provided in step (II) to at least one surface of the metal substrate provided in step (I) to provide an assembly comprising a metal substrate having the composition (C) coated on the at least one surface; (IV) Dry the component provided in step (III); (V) The dried component obtained in step (IV) is subjected to a compression step to obtain the electrode of the present invention (E).

13. An electrode (E) that is obtainable by the method according to claim 12.

14. An electrochemical device, preferably a secondary battery such as a lithium-ion or sodium-ion secondary battery, the electrochemical device comprising at least one electrode (E) according to claim 13.

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