Composition for a secondary battery electrode

Abstract

The present invention relates to an electrode-forming composition, the use of said electrode-forming composition in a method for producing an electrode, said electrode and an electrochemical device such as a secondary battery comprising said electrode.

Description

Technical Field

[0001] Cross - reference to related applications This application claims priority to European Patent Application Publication No. 19190460.6 filed in August 2019, and the entire content of this application is incorporated herein by reference for all purposes.

[0002] The present invention relates to an electrode - forming composition, the use of the electrode - forming composition in a method for manufacturing an electrode, an electrochemical device such as the electrode and a secondary battery including the electrode.

Background Art

[0003] Electrochemical devices such as secondary batteries typically include a positive electrode, a negative electrode, a separator, and an electrolyte.

[0004] Electrodes for secondary batteries are usually manufactured by applying an electrode - forming composition onto a metal substrate, also known as a "current collector". The electrode - forming composition is typically formed by mixing a binder with other raw materials such as a powdery electroactive compound and optionally a solvent, a material for enhancing conductivity and / or controlling viscosity. The binder is an important component of the electrode because it must ensure good adhesion to the current collector and the electroactive compound, thus enabling the electroactive material to transfer electrons as required. Current commercially available batteries typically use graphite as the electroactive compound in the anode and a mixed oxide containing nickel and lithium as the electroactive compound in the cathode. The electrode - forming composition is typically applied onto the current collector and dried. The resulting sheet is usually calendered or otherwise mechanically processed and rolled. Individual electrodes are then cut from this sheet.

[0005] It is known in the art that fluoropolymers are suitable as binders for the manufacture of electrodes for use in electrochemical devices such as secondary batteries.

[0006] In related technical fields, vinylidene fluoride polymer (PVDF) is used as an electrode binder for non-aqueous electrolyte secondary batteries. Generally, PVDF homopolymers have insufficient adhesion to metals. To address this problem, several solutions have been proposed. For example, in WO 2008 / 129041 pamphlet, it has been demonstrated that including certain repeating units derived from (meth)acrylic monomers improves the adhesion of PVDF polymers to metals.

[0007] Nevertheless, binders with even better adhesion are still needed.

[0008] Increasing the PVDF molecular weight is known to enhance the performance of binders containing said polymer, particularly from the perspective of adhesion to metals.

[0009] However, increasing the molecular weight of vinylidene fluoride polymers leads to longer times for dissolution in polar solvents and an increase in the viscosity of said solutions, which can limit the coating applicability of the electrode-forming composition containing it.

[0010] The molecular weight of fluorinated copolymers containing pendant functional groups included in the electrode binder can be increased by thermal crosslinking.

[0011] JP-A-07201315 discloses that an electrode binder obtained by thermally crosslinking polyvinylidene fluoride having a hydroxyl group with a polymer having an isocyanate group is used as an electrode binder.

[0012] U.S. Patent Application Publication No. 2018 / 0248193 discloses a method for improving the adhesion of a fluoropolymer to a metal and an active material in an electrode by subjecting an electrode prepared using a fluoropolymer containing at least one side chain containing a carboxyl group to heat treatment to form a crosslinked structure. In a preferred embodiment, the electrode is prepared by using an electrode mixture further containing a second fluoropolymer having a side chain containing a hydroxyl group.

[0013] In the art, there is still a need for both positive and negative electrodes that advantageously enable the production of electrochemical devices exhibiting outstanding capacitance values and good adhesion to a metal substrate.

[0014] The present invention addresses this need by providing a new electrode-forming composition that includes a vinylidene fluoride polymer containing certain side chains containing hydroxyl groups and certain side chains containing carboxyl groups and that can exhibit surprising adhesion performance when used in both positive and negative electrodes. SUMMARY OF THE INVENTION

[0015] The present invention is an electrode-forming composition (C) comprising: (a) at least one vinylidene fluoride (VDF) copolymer [polymer (A)] comprising: (i) repeating units derived from vinylidene fluoride (VDF); (ii) repeating units derived from at least one hydroxyl group-containing vinyl monomer (HA); (iii) repeating units derived from at least one carboxyl group-containing vinyl monomer (CA) wherein: the total amount of repeating units derived from monomer (HA) and repeating units derived from monomer (CA) in the polymer (A) is at most 10.0 mol%, preferably at most 5.0 mol%, more preferably at most 1.5 mol% based on the total moles of repeating units of the polymer (A); At least 40% of the repeating units derived from monomer (HA) and at least 40% of the repeating units derived from monomer (CA) are randomly distributed in the polymer (A), at least one vinylidene fluoride (VDF) copolymer [polymer (A)]; (b) at least one electroactive material (AM); (c) at least one solvent (S) relates to an electrode-forming composition (C) comprising.

[0016] It has been found that incorporating certain monomers capable of undergoing crosslinking into the vinylidene fluoride backbone provides a crosslinkable vinylidene fluoride copolymer that can be suitably used as a binder in the electrode-forming composition. When the electrode-forming composition is cast onto a current collector in an electrode preparation method, the crosslinkable vinylidene fluoride copolymer is thermally crosslinked immediately, thus providing an electrode having improved performance particularly from the viewpoint of adhesion to a metal.

[0017] In a further aspect, the present invention is a method for manufacturing an electrode using the electrode-forming composition (C) as described above, 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) provided in step (ii) onto at least one surface of the metal substrate provided in step (i), thereby providing an assembly comprising a metal substrate coated with the composition (C) on at least one surface; (iv) drying the assembly provided in step (iii) relates to a method comprising.

[0018] The drying in step (iv) is preferably carried out at a temperature included in 50°C to 200°C, preferably 80°C to 180°C, for a time included in 5 minutes to 48 hours, preferably 30 minutes to 24 hours.

[0019] In a further aspect, the present invention relates to an electrode obtainable from such a method.

[0020] In a further aspect, the present invention relates to an electrochemical device comprising said electrode.

[0021] The electrode-forming composition (C) of the present invention is particularly suitable for the production of a positive electrode for an electrochemical device.

Mode for Carrying Out the Invention

[0022] The term "repeating unit derived from vinylidene fluoride" (generally also referred to as vinylidene fluoride, 1,1-difluoroethylene, VDF) is intended to mean a repeating unit of the formula CF 2 =CH 2

[0023] Suitable hydroxyl group-containing vinyl monomers (HA) are of the formula (I):

Chemical formula

[0024] In a preferred embodiment, the monomer (HA) is of the formula (Ia):

Chemical formula

[0025] Non-limiting examples of the monomer (HA) of formula (Ia) include, inter alia, - hydroxyethyl (meth) acrylate (HEA), - 2-hydroxypropyl acrylate (HPA), - hydroxyethylhexyl (meth) acrylate, and mixtures thereof are included.

[0026] Preferably, at least one monomer (HA) is hydroxyethyl (meth) acrylate (HEA).

[0027] Suitable carboxyl group-containing vinyl monomers (CA) are of formula (II):

Chemical formula

[0028] In a preferred embodiment, the monomer (CA) is of formula (IIa):

Chemical formula

[0029] Non-limiting examples of the monomer (CA) of formula (IIa) include, inter alia - acrylic acid (AA), and - (meth)acrylic acid, and their mixtures are included.

[0030] Preferably, at least one monomer (CA) is acrylic acid (AA).

[0031] The molar ratio between the repeating unit (ii) and the repeating unit (iii) in the polymer (A) is preferably in the range of 20:1 to 1:20, preferably 10:1 to 1:10, more preferably 1:2 to 2:1; even more preferably, the molar ratio is 1:1.

[0032] In the polymer (A), it is essential that at least 40% of the monomer (HA) and at least 40% of the monomer (CA) are randomly distributed in the polymer (A).

[0033] The expression "proportion of randomly distributed monomer (HA)" is the following formula:

Number

[0034] When each of the (HA) repeating units is isolated, i.e., when it is contained between two repeating units of the VDF monomer, the average number of the (HA) sequences is equal to the average total number of the (HA) repeating units. Therefore, the percentage of the randomly distributed units (HA) is 100%, and this value corresponds to a completely random distribution of the (HA) repeating units.

[0035] Thus, as described above, the greater the number of isolated (HA) units with respect to the total number of the (HA) units, the higher the percentage value of the proportion of the randomly distributed units (HA) will be.

[0036] The expression "proportion of randomly distributed monomer (CA)" is intended to mean the percentage ratio between the average number (%) of the (CA) monomer sequences (the said sequences being contained between two repeating units derived from the VDF monomer) and the total average number (%) of the (CA) monomer repeating units, according to the following formula:

Number

[0037]

[0038] The determination of the total average number of the (HA) monomer repeating units and the (CA) monomer repeating units in the polymer (A) can be carried out by any suitable method, and NMR is preferred.

[0039] The proportion of the randomly distributed units (HA) and (CA) is preferably at least 50%, more preferably at least 60%.​

[0040] Polymer (A) preferably contains at least 0.01 mol%, more preferably at least 0.05 mol%, of repeating units derived from the monomer (HA).

[0041] Polymer (A) preferably contains at most 5.0 mol%, more preferably at most 3.0 mol%, even more preferably at most 1.5 mol%, of repeating units derived from the monomer (HA).

[0042] Polymer (A) preferably contains at least 0.1 mol%, more preferably at least 0.2 mol%, of repeating units derived from the monomer (CA).

[0043] Polymer (A) preferably contains at most 7.0 mol%, more preferably at most 5.0 mol%, even more preferably at most 3.0 mol%, of repeating units derived from the monomer (CA).

[0044] Excellent results have been obtained using a polymer (A) containing at least 70 mol% of repeating units derived from VDF.

[0045] Polymer (A) can be an elastomer or a semi-crystalline polymer, preferably a semi-crystalline polymer.

[0046] As used herein, the term "semi-crystalline" means, in DSC analysis, a fluoropolymer having at least one crystal melting point in addition to the glass transition temperature Tg. For the purposes of the present invention, a semi-crystalline fluoropolymer is herein intended to mean a fluoropolymer having a heat of fusion measured according to ASTM D 3418 of at least 0.4 J / g, preferably at least 0.5 J / g, more preferably at least 1 J / g.

[0047] For the purposes of the present invention, the term "elastomer" is intended to denote a true elastomer or a polymeric resin that serves as a basic constituent for obtaining a true elastomer.

[0048] True elastomers are defined by ASTM, Special Technical Bulletin, Standard No. 184 as materials that can be stretched to twice their original length at room temperature and, when released after being held under tension for 5 minutes, return to within 10% of their initial length simultaneously.

[0049] Preferably, the intrinsic viscosity of polymer (A) measured in dimethylformamide at 25 °C is included in the range of 0.05 l / g to 0.60 l / g, more preferably 0.15 l / g to 0.50 l / g, and even more preferably 0.20 l / g to 0.45 l / g.

[0050] The polymer (A) of the present invention usually has a melting temperature (Tm) included in the range of 120 °C to 200 °C.

[0051] The melting temperature can be determined from the DSC curve obtained by differential scanning calorimetry (hereinafter also referred to as DSC). When the DSC curve shows multiple melting peaks (endothermic peaks), the melting temperature (Tm) is determined based on the peak having the largest peak area.

[0052] Polymer (A) may further contain repeating units derived from one or more fluorinated comonomers (CF) different from VDF.

[0053] The term "fluorinated comonomer (CF)" is herein intended to mean an ethylenically unsaturated comonomer containing at least one fluorine atom.

[0054] Non-limiting examples of suitable fluorinated comonomers (CF) include, inter alia, (a) C 2 ~C 8Fluoro and / or perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene, and hexafluoroisobutylene; (b) C 2 ~C 8 Hydrogen-containing monofluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene, and trifluoroethylene; (c) The formula CH 2 =CH-R f0 (wherein R f0 is a C 1 ~C 6 perfluoroalkyl group) perfluoroalkyl ethylene; (d) Chloro- and / or bromo- and / or iodo-C 2 ~C 6 fluoroolefins, such as chlorotrifluoroethylene (CTFE), etc. are included.

[0055] In one embodiment of the present invention, the polymer (A) contains repeating units derived from the fluorinated comonomer (CF) in an amount of 0.1 mol% to 10.0 mol%, preferably 0.3 mol% to 5.0 mol%, more preferably 0.5 mol% to 3.0 mol%.

[0056] It is understood that chain ends, defects, or other impurity type moieties can be included in the polymer (A) without impairing the properties of the polymer.

[0057] The polymer (A) is more preferably - At least 70 mol%, preferably at least 75 mol%, more preferably at least 85 mol% of vinylidene fluoride (VDF), - 0.01 mol% to 3.0 mol%, preferably 0.05 mol% to 1.5 mol%, more preferably 0.08 mol% to 1.0 mol% of at least one hydroxyl group-containing monomer (HA); - From 0.05 mol% to 3.0 mol%, preferably from 0.1 mol% to 1.5 mol%, more preferably from 0.15 mol% to 1.0 mol% of at least one carboxyl group-containing vinyl monomer (CA) derived repeating units; - Optionally, repeating units derived from 0.5 mol% to 3.0 mol% of at least one fluorinated comonomer (CF) are included.

[0058] The preparation procedure of polymer (A) involves polymerizing vinylidene fluoride (VDF) monomer, monomer (HA) and monomer (CA) and optionally comonomer (CF) in an aqueous medium in the presence of a radical initiator in a reaction vessel, and the method comprises - Continuously supplying an aqueous solution containing monomer (HA) and monomer (CA); - Maintaining the pressure in the reaction vessel above the critical pressure of vinylidene fluoride are included.

[0059] During the overall polymerization, the pressure is maintained above the critical pressure of vinylidene fluoride. Generally, the pressure is maintained at a value above 50 bar, preferably above 75 bar, even more preferably above 100 bar.

[0060] Generally, the polymerization is carried out at a temperature included in the range of 5 °C to 130 °C.

[0061] The polymerization can be carried out, for example, according to the procedures typically described in WO 2008 / 129041 pamphlet, either in a suspension in an organic medium or in an aqueous emulsion as typically described in the art (see, for example, US Patent No. 4,016,345, US Patent No. 4,725,644 and US Patent No. 6,479,591).

[0062] It is essential that the continuous supply of the aqueous solution containing monomer (HA) and monomer (CA) is carried out during the polymerization.

[0063] Thus, it is possible to obtain a substantially statistical distribution of both monomer (HA) and monomer (CA) within the VDF monomer polymer backbone of polymer (A).

[0064] The expressions "continuous supply" or "supplied continuously" mean that, at least up to a conversion of 70 mol% of the VDF monomer, a slow, small, and gradually increasing addition of the aqueous solutions of monomer (HA) and monomer (CA) is carried out for most of the polymerization duration.

[0065] The aqueous solutions of monomer (HA) and monomer (CA) continuously supplied during the polymerization are at least 50% by weight of the total amount of monomer (HA) and monomer (CA) supplied during the reaction (i.e., the initial charge and the continuous supply). Preferably at least 60% by weight, more preferably at least 70% by weight, and most preferably at least 80% by weight of the total amount of monomer (HA) and monomer (CA) are continuously supplied during the polymerization. Even if this requirement is not essential, a gradually increasing addition of the VDF monomer can be achieved during the polymerization.

[0066] Generally, the method of the present invention is carried out at a temperature of at least 35°C, preferably at least 40°C, more preferably at least 45°C.

[0067] When the polymerization is carried out in a suspension, polymer (A) is typically provided in the form of a powder.

[0068] When the polymerization for obtaining polymer (A) is carried out in an emulsion, polymer (A) is typically provided in the form of an aqueous dispersion (D), and the dispersion (D) can be used as directly obtained by emulsion polymerization or after a concentration step. Preferably, the solids content of polymer (A) in the dispersion (D) is in the range of 20% to 50% by weight.

[0069] The polymer (A) obtained by emulsion polymerization can be isolated from the aqueous dispersion (D) by concentration and / or coagulation of the dispersion, and can be obtained in powder form by subsequent drying.

[0070] The polymer (A) in powder form can optionally be further extruded to provide the polymer (A) in pellet form.

[0071] The extrusion is preferably carried out in an extruder. The duration of extrusion is preferably in the range of several seconds to 3 minutes.

[0072] The polymer (A) can be dissolved in any suitable organic solvent to provide a solution (Sol) of the polymer (A). Preferably, the solid content of the polymer (A) in the solution (Sol) is in the range of 2 wt% to 30 wt%.

[0073] Non-limiting examples of suitable organic solvents for dissolving the polymer (A) are N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate and trimethyl phosphate, aliphatic ketones, alicyclic ketones, alicyclic esters. These organic solvents can be used alone or as a mixture of two or more chemical species.

[0074] The electrode-forming composition (C) of the present invention contains one or more electroactive materials (AM). For the purposes of the present invention, the term "electroactive material" is intended to mean a compound that can incorporate or insert alkali or alkaline earth metal ions into its structure and then substantially release them during the charge and discharge stages of an electrochemical device. The electroactive material preferably can incorporate or insert lithium ions and release them.

[0075] The nature of the electroactive material in the electrode-forming composition of the present invention depends on whether the composition is used for the manufacture of a positive electrode or a negative electrode.

[0076] When forming a positive electrode for a lithium-ion secondary battery, the electroactive compound may include a lithium-containing compound.

[0077] In one preferred embodiment, the lithium-containing compound has the formula LiMQ 2 (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) and may be a metal chalcogenide. Among these, it is preferable to use a lithium-based metal oxide of the formula LiMO 2 (wherein M is the same as defined above). Preferred examples thereof include LiCoO 2 , LiNiO 2 , LiNi x Co 1-x O 2 (0 < x < 1) and spinel-structured LiMn 2 O 4 may be mentioned.

[0078] In another embodiment, further, when forming a positive electrode for a lithium-ion secondary battery, the electroactive compound has the formula M 1 M 2 (JO 4 ) f E 1-f (wherein M 1 is lithium, which may be partially replaced by another alkali metal representing less than 20% of the M 1 metal, M 2 is a transition metal at a +2 oxidation level selected from Fe, Mn, Ni, or mixtures thereof, which may be partially replaced by one or more additional metals representing less than 35% of the M 2 metal at oxidation levels of +1 to +5, JO 4 is any oxyanion where J is any of P, S, V, Si, Nb, Mo, or combinations thereof, E is a fluoride, hydroxide, or chloride anion, and f generally ranges from 0.75 to 1, JO 4It may include a lithiated or partially lithiated transition metal oxyanion-based electroactive material (which is the molar fraction of the oxyanion).

[0079] M as defined above 1 M 2 (JO 4 ) f E 1-f The electroactive material is preferably phosphate-based and may have a regular or modified olivine structure.

[0080] More preferably, when forming the positive electrode, the electroactive compound has the formula Li 3-x M’ y M’’ 2-y (JO 4 ) 3 (where 0 ≦ x ≦ 3, 0 ≦ y ≦ 2, M’ and M’’ are the same or different metals, and at least one of them is a transition metal, and JO 4 is preferably PO which may be partially substituted by another oxyanion 4 and J is any of S, V, Si, Nb, Mo or a combination thereof). Even more preferably, the electroactive compound has the formula Li(Fe x Mn 1-x )PO 4 (where 0 ≦ x ≦ 1, and here x is preferably 1 (i.e., lithium iron phosphate of the formula LiFePO 4 )) which is a phosphate-based electroactive material.

[0081] In the most preferred embodiment, the electroactive material for the positive electrode has the general formula (III) LiNi x M1 y M2 z Y 2 (III) (where M1 and M2 are the same as or different from each other and are transition metals selected from Co, Fe, Mn, Cr and V, 0.5 ≦ x ≦ 1, where y + z = 1 - x, and Y preferably means a chalcogen selected from O and S) is selected from the lithium-containing composite metal oxides.

[0082] The electroactive material in this embodiment is preferably a compound of formula (III) where Y is O. In a further preferred embodiment, M1 is Mn and M2 is Co, or M1 is Co and M2 is Al.

[0083] Examples of such active materials include LiNi x Mn y Co z O 2 (hereinafter referred to as NMC) and LiNi x Co y Al z O 2 (hereinafter referred to as NCA).

[0084] Specifically, with respect to LiNi x Mn y Co z O 2 by changing the content ratios of manganese, nickel and cobalt, the power and energy performance of the battery can be adjusted.

[0085] In a particularly preferred embodiment of the present invention, the compound AM is a compound of formula (III) as defined above (where 0.5 ≤ x ≤ 1, 0.1 ≤ y ≤ 0.5 and 0 ≤ z ≤ 0.5).

[0086] Non-limiting examples of suitable electroactive materials for the positive electrode of formula (III) include, inter alia, LiNi 0.5 Mn 0.3 Co 0.2 O 2 , LiNi 0.6 Mn 0.2 Co 0.2 O 2 , LiNi 0.8 Mn 0.1 Co 0.1 O 2 , LiNi 0.8 Co0.15 Al 0.05 O 2 、 LiNi 0.8 Co 0.2 O 2 、 LiNi 0.8 Co 0.15 Al 0.05 O 2 、 LiNi 0.6 Mn 0.2 Co 0.2 O 2 、 LiNi 0.8 Mn 0.1 Co 0.1 O 2 、 LiNi 0.9 Mn 0.05 Co 0.05 O 2 include the following.

[0087] Compound: LiNi 0.8 Co 0.15 Al 0.05 O 2 、 LiNi 0.6 Mn 0.2 Co 0.2 O 2 、 LiNi 0.8 Mn 0.1 Co 0.1 O 2 、 LiNi 0.9 Mn 0.05 Co 0.05 O 2 are particularly preferred.

[0088] When forming the negative electrode for a lithium-ion secondary battery, the electroactive compound may preferably include one or more carbon-based materials and / or one or more silicon-based materials.

[0089] In some embodiments, the carbon-based material can be selected from graphite such as natural or artificial graphite, graphene, or carbon black. These materials can be used alone or as a mixture of two or more of them. The carbon-based material is preferably graphite.

[0090] The silicon-based compound can be one or more selected from the group consisting of chlorosilane, alkoxysilane, aminosilane, fluoroalkylsilane, silicon, silicon chloride, silicon carbide, and silicon oxide. More particularly, the silicon-based compound can be silicon oxide or silicon carbide.

[0091] When present in the electroactive compound, the silicon-based compound is included in an amount in the range of 1 wt% to 60 wt%, preferably 5 wt% to 20 wt% based on the total weight of the electroactive compound.

[0092] The electrode-forming composition of the present invention includes at least one solvent (S).

[0093] The solvent for the negative electrode-forming composition can include water and can preferably be water. This enables a reduction in the overall use of organic solvents, along with a reduction in the resulting cost, a reduction in combustibles, and a reduction in environmental impact.

[0094] The solvent in the positive electrode-forming composition includes one or more organic solvents, preferably polar solvents, examples of which can include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, and trimethyl phosphate. These organic solvents can be used alone or as a mixture of two or more chemical species.

[0095] The electrode-forming composition (C) of the present invention typically includes 0.5 wt% to 10 wt%, preferably 0.7 wt% to 5 wt% of the polymer (A). The composition also includes 80 wt% to 99 wt% of the electroactive material, and all percentages are weight percentages divided by the total solids of the composition (C).

[0096] The term "total solid content" is intended to mean "all of the raw materials of the electrode forming composition of the present invention excluding the solvent".

[0097] Generally, in the electrode forming composition of the present invention, the solvent is present in an amount of 10% by weight to 90% by weight of the total amount of the composition (C). Particularly for the negative electrode forming composition, the solvent is preferably present in an amount of 25% by weight to 75% by weight, more preferably 30% by weight to 60% by weight of the total amount of the composition.

[0098] For the positive electrode forming composition, the solvent is preferably present in an amount of 5% by weight to 60% by weight, more preferably 15% by weight to 40% by weight of the total amount of the composition.

[0099] The electrode forming composition of the present invention may further contain one or more optional conductive agents in order to improve the conductivity of the electrode resulting from being produced from the composition of the present invention. Conductive agents for batteries are known in the art.

[0100] Examples thereof may include carbonaceous materials such as carbon black, graphite fine powder, carbon nanotubes, graphene or fibers, 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 (registered trademark) or Ketjenblack (registered trademark).

[0101] When present, the conductive agent is different from the above carbon-based materials.

[0102] The amount of the optional conductive agent is preferably 0% by weight to 30% by weight based on the total solid content in the electrode forming composition. Particularly for the positive electrode forming composition, the optional conductive agent is typically 0% by weight to 10% by weight, more preferably 0% by weight to 5% by weight of the total amount of the solid content in the composition (C).

[0103] For a negative electrode forming composition containing no silicon-based electroactive compound, the optional conductive agent is typically 0 wt% to 5 wt%, more preferably 0 wt% to 2 wt% of the total amount of solids in the composition. On the other hand, for a negative electrode forming composition containing a silicon-based electroactive compound, it has been found beneficial to introduce a greater amount of the optional conductive agent, typically 5 wt% to 20 wt% of the total amount of solids in composition (C).

[0104] The electrode forming composition of the present invention may further contain at least one acid donor that preferably serves as an acidic crosslinking catalyst in the thermal crosslinking of the crosslinkable vinylidene fluoride copolymer immediately when the electrode forming composition is applied onto a current collector in an electrode preparation method.

[0105] The at least one acid donor includes, for example, Lewis acids, strong mineral acids such as sulfuric acid, phosphoric acid, polyphosphoric acid, perchloric acid, etc.; saturated aliphatic hydrocarbon sulfonic acids and aromatic hydrocarbon sulfonic acids such as ethanesulfonic acid, propanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, naphthalenesulfonic acid, lower alkyl-substituted benzenesulfonic acid, etc.

[0106] Suitable Lewis acids here are inorganic or organometallic compounds in which the cation is preferably selected from the group consisting of boron, aluminum, tin, antimony, and iron.

[0107] Among the Lewis acids mentioned, in particular, metal halide Lewis acids such as boron trifluoride, aluminum chloride, zinc chloride, stannous chloride, antimony trichloride, ferric chloride, boron trifluoride dimethyl ether complex, boron trifluoride - diethyl ether complex, boron trifluoride - dipropyl ether complex, etc. are particularly preferred, and stannous chloride is particularly preferred.

[0108] Lewis acids include not only the Lewis acid itself but also metals or metal compounds that impart the function of the Lewis acid, such as oxides and sulfides. Antimony trioxide (Sb 2 O 3 )), zinc oxide (ZnO), and zinc sulfide (ZnS) are preferred.

[0109] The acidic crosslinking agent is preferably contained in the composition (C) in an amount of 0.001% by weight to 2.0% by weight, more preferably 0.005% by weight to 0.5% by weight, based on the total solid content of the composition (C).

[0110] The electrode-forming composition of the present invention may further contain at least one water scavenger.

[0111] Without being bound by theory, the inventors believe that the presence of at least one water scavenger can capture the water generated during crosslinking and promote the condensation reaction, thereby promoting the crosslinking reaction between the side chains of the polymer (A) containing hydroxyl groups and those containing carboxyl groups.

[0112] A suitable water scavenger for use in the electrode-forming composition of the present invention is an anhydrous aluminosilicate, particularly zeolite.

[0113] Zeolites suitable for the purposes of the present invention include all those natural or synthetic, preferably synthetic, crystalline inorganic materials having a three-dimensional network structure of tetrahedra linked by common oxygen atoms, SiO 4 and AlO 4 including.

[0114] Preferred zeolites have the general formula: M x D y / 2· Al m Si n O 2(m+n) (wherein M and D are metals that can be partially or completely exchanged with H+ ions or NH 4 ions, usually monovalent and divalent ions of alkali metals or alkaline earth metals) It has a chemical composition in the anhydrous state corresponding thereto. In the formula, m can take any value less than n. When n equal to 1 is substituted, m can vary from 1 to 0.0001. In this regard, synthetic aluminosilicate materials having a structure similar to or the same as that of natural products; aluminosilicate materials known only as synthetic products and having a zeolite structure; synthetic materials based on silica, SiO2, in which the molar Si / Al ratio is high or Al is contained in trace amounts, or the aluminum is replaced by an element whose oxide has amphoteric properties, such as Be, B, Ti, Cr, Mn, Zr, V, Sb or Fe, are preferred, and these materials have a zeolite-type highly porous crystalline structure. Descriptions of the structure, properties and systematic classification of zeolites are given in the literature by D.W. Breck in "Zeolite Molecular Sieves" published by J.Wiley & Sons, N.Y., 1973.

[0115] Zeolites are generally used in acidic or neutral alkaline forms.

[0116] In zeolites, other elements such as B, Ga, Fe, Cr, V, As, Sb, Bi or Be or mixtures thereof can be incorporated into the framework in place of aluminum, or silicon can be replaced by another tetravalent element such as Ge, Ti, Zr or Hf.

[0117] The water scavenger is preferably contained in the composition (C) in an amount of 0.01% to 5% by weight, preferably 0.1% to 1% by weight, based on the total solids of the composition (C).

[0118] The electrode-forming composition of the present invention can be used in a method for manufacturing an electrode, and the method comprises (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) provided in step (ii) onto at least one surface of the metal substrate provided in step (i), thereby providing an assembly comprising a metal substrate coated with the composition (C) on at least one surface; (iv) Drying the assembly provided in step (iii) comprising.

[0119] The metal substrate is generally a foil, mesh or net made of a metal such as copper, aluminum, iron, stainless steel, nickel, titanium or silver.

[0120] Under step (iii) of the method of the present invention, the electrode-forming composition is typically applied onto at least one surface of the metal substrate by any suitable procedure such as casting, printing and roll coating.

[0121] Optionally, step (iii) can typically be repeated one or more times by applying the electrode-forming composition provided in step (ii) onto the assembly provided in step (iv).

[0122] Step (iv) is preferably carried out at a temperature included in the range of 50 °C to 200 °C, preferably 80 °C to 180 °C, for a time ranging from 5 minutes to 48 hours, preferably 30 minutes to 24 hours.

[0123] Under step (iv), thermal crosslinking occurs involving the reaction of at least a part of the hydroxyl groups of the repeating units derived from the monomer (HA) in the polymer (A) and at least a part of the carboxyl groups of the repeating units derived from the monomer (CA).

[0124] Due to the cross-linking reaction between the side chain of the polymer (A) containing a hydroxyl group and the one containing a carboxyl group, the adhesion between the polymer (A) contained in the electrode and the electrode active material is improved together with the adhesion between the polymer (A) and the current collector. Therefore, the adhesiveness can be easily improved as compared with the method of using a special adhesive, the method involving complicated processes, etc.

[0125] The assembly obtained in step (iv) may further undergo a compression process such as a calendering process in order to achieve the target porosity and density of the electrode.

[0126] Preferably, the assembly obtained in step (iv) is hot-pressed, and the temperature during the compression process is included in 25°C to 130°C, preferably about 90°C.

[0127] The preferable target porosity for the obtained electrode is included in 15% to 40%, preferably 25% to 30%. The porosity of the electrode is calculated as the one's complement of the ratio between the measured density and the theoretical density of the electrode, where - The measured density is given by the mass divided by the volume of the circular part of the electrode having a diameter equal to 24 mm and the measured thickness; - The theoretical density of the electrode is calculated as the sum of the products of the densities of the components of the electrode multiplied by their volume ratios in the electrode mixture.

[0128] In a further case, the present invention relates to an electrode obtainable by the method of the present invention.

[0129] Therefore, the present invention is - a metal substrate, and - at least one layer directly adhered on at least one surface of the metal substrate, wherein (a) is at least one vinylidene fluoride (VDF) copolymer [polymer (A)], where (i) a repeating unit derived from vinylidene fluoride (VDF); (ii) a repeating unit derived from at least one hydroxyl group-containing vinyl monomer (HA); (iii) At least one repeating unit derived from a carboxyl group-containing vinyl monomer (CA) comprising; In the polymer (A), the total amount of the repeating unit derived from the monomer (HA) and the repeating unit derived from the monomer (CA) is at most 10.0 mol%, preferably at most 5.0 mol%, more preferably at most 1.5 mol% based on the total moles of the repeating units of the polymer (A); At least one vinylidene fluoride (VDF) copolymer [polymer (A)] in which at least 40% of the repeating units derived from the monomer (HA) and at least 40% of the repeating units derived from the monomer (CA) are randomly distributed in the polymer (A); and (b) at least one electroactive material (AM) relates to at least one layer comprising a composition and an electrode comprising the same.

[0130] The layer of the electrode of the present invention typically has a thickness included in the range of 10 μm to 500 μm, preferably 50 μm to 250 μm, more preferably 70 μm to 150 μm.

[0131] The electrode-forming composition (C) of the present invention is particularly suitable for the production of a positive electrode for an electrochemical device.

[0132] The electrode of the present invention is particularly suitable for use in an electrochemical device comprising the electrode, particularly a secondary battery.

[0133] For the purposes of the present invention, the term "secondary battery" is intended to mean a rechargeable battery. The secondary battery of the present invention is preferably an alkaline secondary battery or an alkaline earth secondary battery. The secondary battery of the present invention is more preferably a lithium ion secondary battery. The electrochemical device according to the present invention can be prepared by standard methods known to those skilled in the art.

[0134] If the disclosure of any patent, patent application, and publication incorporated herein by reference conflicts with the description of this application to the extent that it may obscure the terms, the description shall prevail.

[0135] Here, the present invention will be described in connection with the following examples, which are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example

[0136] Raw materials Comparative Polymer 1: A VDF-AA (0.9 mol%) polymer having an intrinsic viscosity of 0.30 l / g in DMF at 25°C and a T of 162°C, obtained as described in WO 2008 / 129041 pamphlet. 2f with

[0137] Polymer A-1: A VDF-AA (0.5 mol%)-HFP (0.1 mol%) polymer having an intrinsic viscosity of 0.32 l / g in DMF at 25°C and a T of 165.4°C. 2f with

[0138] Initiator (TAPPI): t-Amyl-perpivalate in isododecane (75 wt% solution of t-amyl perpivalate in isododecane), commercially available from Arkema.

[0139] Bermocoll® E230FQ, manufactured by AkzoNobel.

[0140] Active material NMC: LiNi 0.6 Co 0.2 Mn 0.2 O 2 、commercially available from Umicore SA.

[0141] Active material LCO: Lithium cobalt oxide (LiCoO 2 ), commercially available from Umicore SA.

[0142] Conductive additive: C-NERGY (trademark) SUPER C65 (SC-65), commercially available from Imerys Graphite & Carbon.

[0143] Measurement of the intrinsic viscosity of the polymer The intrinsic viscosity (η) [dl / g] was obtained based on the drop time at 25 °C of a solution obtained by dissolving the polymer in N,N-dimethylformamide at a concentration of about 0.2 g / dl using an Ubbelhode viscometer, according to the following formula:

Equation

[0144] DSC analysis DSC analysis was carried out according to the ASTM D 3418 standard; the melting point (T f2 ) was determined at a heating rate of 10 °C / min.

[0145] Preparation of polymer A-1: VDF-AA-HEA To a 4-liter reactor equipped with an impeller operating at a speed of 650 rpm, deionized water (2237 g) and 0.6 g of Bermocoll® E230FQ per kg of Mni (the initial monomer added to the reactor before the set point temperature) were introduced in sequence. The reactor was purged with a series of vacuums (30 mmHg) and nitrogen purges at 20 °C. Then, 2.65 g of TAPPI was introduced. Acrylic acid (0.28 g) and hydroxyethyl acrylate (0.07 g) were introduced at a speed of 880 rpm. Finally, 1166 g of vinylidene fluoride (VDF) was introduced into the reactor. The reactor was gradually heated to the set point temperature of 50 °C and fixed at 120 bar. By supplying an aqueous solution containing acrylic acid and hydroxyethyl acrylate during the polymerization, the pressure was always kept equal to 120 bar. After 6.37 g of acrylic acid and 1.59 g of hydroxyethyl acrylate were supplied, no more aqueous solution was introduced and the pressure began to drop. The polymerization was stopped after 9 hours by degassing the reactor until atmospheric pressure was reached. A monomer conversion rate of 82% was achieved. The polymer thus obtained was then recovered, washed with deionized water, and dried at 65 °C overnight.

[0146] General preparation of an electrode using NMC active material To compare the adhesion behavior of Comparative Polymer 1 and Polymer A-1, a composition was prepared by premixing 14.9 g of an 8 wt% solution of the polymers (A-1 and Comparative 1) in NMP, 115.4 g of NMC, 2.4 g of SC-65, and 21.9 g of NMP in a centrifuge mixer for 10 minutes.

[0147] The mixture was then mixed using a high-speed disk impeller at 2000 rpm for 1 hour. The binder composition thus obtained was cast onto an Al foil with a thickness of 20 μm using a doctor blade, and a positive electrode was obtained by drying the coating layer thus obtained in an oven at a temperature of 130 °C for about 70 minutes. The thickness of the dried coating layer was about 110 μm.

[0148] A positive electrode having the following composition was obtained: Electrode E1: 97 wt% NMC, 1 wt% Comparative Polymer 1, 2 wt% conductive additive. Electrode E2: 97 wt% NMC, 1 wt% Polymer A -1, 2 wt% conductive additive.

[0149] General preparation of electrodes using NMC / LCO blend active material To compare the adhesion behavior of Comparative Polymer 1 and Polymer A-1, a composition was prepared by premixing 14.9 g of an 8 wt% solution of the polymer (A-1 and Comparative 1) in NMP, 11.55 g of NMC, 103.9 g of LCO, 2.4 g of SC-65, and 21.9 g of NMP in a centrifuge mixer for 10 minutes.

[0150] The mixture was then mixed using a high-speed disk impeller at 2000 rpm for 1 hour. The composition thus obtained was cast onto an Al foil with a thickness of 20 μm using a doctor blade, and the resulting coating layer was dried in a vacuum oven at a temperature of 130 °C for about 70 minutes to obtain a positive electrode. The thickness of the dried coating layer was about 110 μm.

[0151] A positive electrode having the following composition was obtained: Electrode E3: 9.7 wt% NMC, 83.7 wt% LCO, 1 wt% Comparative Polymer 1, 2 wt% conductive additive. Electrode E4: 9.7 wt% NMC, 83.7 wt% LCO, 1 wt% Polymer A -1, 2 wt% conductive additive.

[0152] Adhesion peel force method To evaluate the adhesion of the dried coating layer to the Al foil, a peel test was performed on the electrodes prepared as described above using the setup described in standard ASTM D903 at a speed of 300 mm / min at 20 °C. The results for E1 and E2 are shown in Table 1. The results for E3 and E4 are shown in Table 2.

[0153]

Table 1

[0154]

Table 2

[0155] The results, unexpectedly, show that the electrodes prepared by using Polymer A-1 (where Polymer A-1 has repeating units derived from both monomer AA and monomer HEA uniformly distributed in the polymer main chain) as a binder have much higher adhesiveness to the metal foil than those obtained by using Comparative Polymer 1, which has only repeating units derived from monomer AA uniformly distributed in the polymer main chain.

Claims

1. An electrode-forming composition (C), comprising: (a) at least one vinylidene fluoride (VDF) copolymer [polymer (A)], comprising: (i) repeating units derived from vinylidene fluoride (VDF); (ii) repeating units derived from at least one hydroxyl group-containing vinyl monomer (HA); (iii) repeating units derived from at least one carboxyl group-containing vinyl monomer (CA); wherein the total amount of the repeating units derived from monomer (HA) and the repeating units derived from monomer (CA) in the polymer (A) is at most 10.0 mol% based on the total moles of the repeating units of the polymer (A); at least 40% of the repeating units derived from monomer (HA) and at least 40% of the repeating units derived from monomer (CA) are randomly distributed in the polymer (A); at least one vinylidene fluoride (VDF) copolymer [polymer (A)]; (b) at least one electroactive material (AM); (c) at least one solvent (S). An electrode-forming composition (C) comprising the above components.

2. The electrode-forming composition (C) according to Claim 1, wherein the hydroxyl group-containing vinyl monomer (HA) is a compound of formula (I): 【Chemical 1】 (wherein R, which may be the same or different from each other １ , R ２ and R ３ are each independently selected from a hydrogen atom, a halogen atom and a C １ -C ３ hydrocarbon group, and R ＯＨ contains at least one hydroxyl group and, in the chain, optionally contains one or more oxygen atoms, carbonyl groups or carboxy groups, and is a C ２ -C １０ hydrocarbon chain moiety)

3. The electrode-forming composition (C) according to Claim 2, wherein the monomer (HA) is a compound of formula (Ia): 【Chemical 2】 (wherein R, which may be the same or different from each other １ , R ２ and R ３ are each independently selected from a hydrogen atom and a C １ - C ３ hydrocarbon group, and R' ＯＨ is a C １ - C ５ hydrocarbon moiety containing at least one hydroxyl group)

4. The monomer (HA) of formula (Ia) is selected from the group consisting of: - hydroxyethyl (meth)acrylate (HEA), - 2-hydroxypropyl acrylate (HPA), - hydroxyethylhexyl (meth)acrylate, and mixtures thereof. The electrode-forming composition (C) according to Claim 3.

5. The electrode-forming composition (C) according to Claim 1, wherein the carboxyl group-containing vinyl monomer (CA) is a compound of formula (II): [Chemical Formula 3] (wherein R, which may be the same or different from each other １ , R ２ and R ３ are independently selected from a hydrogen atom and a C １ - C ３ hydrocarbon group, and R Ｈ is a C １ - C １０ hydrocarbon chain moiety containing at least one carboxyl group)

6. The electrode-forming composition (C) according to Claim 5, wherein the monomer (CA) is a compound of formula (IIa): [Chemical Formula 4] (wherein R, which may be the same as or different from each other １ , R ２ and R ３ are independently selected from a hydrogen atom and a C １ - C ３ hydrocarbon group, and R' Ｈ is hydrogen or a C １ - C ５ hydrocarbon moiety containing at least one carboxyl group).

7. The monomer (CA) of formula (IIa) is selected from the group consisting of acrylic acid (AA), (meth)acrylic acid, and mixtures thereof. The electrode-forming composition (C) according to Claim 6.

8. The electrode-forming composition (C) according to any one of Claims 1 to 7, wherein the molar ratio between the monomer (HA) and the monomer (CA) in the polymer (A) is in the range of 20:1 to 1:

20.

9. The electrode-forming composition (C) according to any one of claims 1 to 8, further comprising repeating units derived from one or more fluorinated comonomers (CF) different from VDF.

10. - 0.5 wt% to 10 wt% of polymer (A); - 80 wt% to 99 wt% of at least one electroactive material (AM) The electrode-forming composition (C) according to any one of claims 1 to 9, wherein all percentages are weight percentages based on the total solids of the composition (C).

11. The electrode-forming composition (C) according to any one of claims 1 to 10, further comprising at least one acid donor.

12. A positive electrode-forming composition, wherein the at least one electroactive material (AM) has the general formula (III) LiNi ｘ M1 ｙ M2 ｚ Y ２ (III) (wherein M1 and M2 are the same as or different from each other and are transition metals selected from Co, Fe, Mn, Cr and V, 0.5 ≦ x ≦ 1, where y + z = 1 - x, and Y means a chalcogen selected from O and S) The electrode-forming composition (C) according to any one of claims 1 to 11, selected from lithium-containing composite metal oxides of.

13. A method for manufacturing an electrode, comprising: (i) providing a metal substrate having at least one surface; (ii) providing the electrode-forming composition (C) according to any one of claims 1 to 12; (iii) applying the composition (C) provided in step (ii) onto the at least one surface of the metal substrate provided in step (i), thereby providing an assembly comprising a metal substrate coated with the composition (C) on the at least one surface; (iv) drying the assembly provided in step (iii) A method comprising.

14. - A metal substrate, and - at least one layer directly adhered onto at least one surface of the metal substrate, (a) at least one vinylidene fluoride (VDF) copolymer [polymer (A)], (i) repeating units derived from vinylidene fluoride (VDF); (ii) repeating units derived from at least one hydroxyl group-containing vinyl monomer (HA); (iii) repeating units derived from at least one carboxyl group-containing vinyl monomer (CA) Containing; The total amount of the repeating unit derived from the monomer (HA) and the repeating unit derived from the monomer (CA) in the polymer (A) is at most 10.0 mol% based on the total moles of the repeating units of the polymer (A); at least 40% of the repeating unit derived from the monomer (HA) and at least 40% of the repeating unit derived from the monomer (CA) are randomly distributed in the polymer (A), at least one vinylidene fluoride (VDF) copolymer [polymer (A)]; and (b) at least one electroactive material (AM) comprising at least one layer consisting of a composition containing an electrode.

15. An electrochemical device comprising at least one electrode according to claim 14.

16. A secondary battery comprising a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode according to claim 14, the electrochemical device according to claim 15.

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