Binder for secondary battery

Abstract

The present application provides an adhesive for secondary batteries with excellent adhesion. An adhesive for secondary batteries, comprising a high molecular compound, the high molecular compound comprising repeating units represented by the following formula (1), the following formula (2), and the following formula (3), wherein the total proportion of the repeating units represented by the following formula (3) is 2 mol% or more and 20 mol% or less, provided that the total proportion of the repeating units constituting the high molecular compound is 100 mol%. [In formula (1), R 1 is a hydrogen atom or a methyl group, M is a hydrogen atom or an alkali metal atom, and in formula (3), R 2 is a hydrogen atom or a methyl group].

Description

Technical Field

[0001] This invention relates to adhesives for secondary batteries, adhesives for secondary battery electrodes, electrodes for secondary batteries, and secondary batteries. Background Technology

[0002] In recent years, with increasing attention to solving environmental problems and achieving a sustainable circular society, research on non-aqueous electrolyte secondary batteries, represented by lithium-ion batteries, has been extensive. Lithium-ion batteries have high operating voltage and energy density, and are therefore used as power sources for laptops, mobile phones, electric vehicles, and other applications. These applications require repeated charging and discharging of lithium-ion batteries for reuse, thus demanding long battery life.

[0003] The electrodes of lithium-ion secondary batteries are typically manufactured by mixing active materials (electrode active materials), conductive additives, etc., in a solution or slurry obtained by dissolving the battery electrodes in a solvent or dispersing them in a dispersion medium with a binder. The resulting battery electrodes are then coated onto the current collector with a mixture slurry (hereinafter sometimes simply referred to as slurry). The solvent and dispersion medium are removed by methods such as drying, so that the active materials adhere to the current collector and to each other.

[0004] For example, the positive electrode is obtained by coating and drying a slurry of a positive electrode mixture obtained by dispersing active materials (such as lithium cobalt oxide (LiCoO2)), binders (such as polyvinylidene fluoride (PVDF)), and conductive additives (such as carbon black) on an aluminum foil current collector.

[0005] In addition, the negative electrode is obtained by coating and drying a negative electrode slurry obtained by dispersing active materials (graphite, etc.), binders (carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), PVDF, polyimide, etc.), conductive additives (carbon black), etc. on a copper foil current collector.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 8-264180

[0009] Patent Document 2: Japanese Patent Application Publication No. 4-188559

[0010] Patent Document 3: Japanese Patent Application Publication No. 10-284082

[0011] Patent Document 4: Japanese Patent Application Publication No. 7-240201

[0012] Patent Document 5: Japanese Patent Application Publication No. 10-294112

[0013] Patent Document 6: International Publication No. 2004 / 049475

[0014] Patent Document 7: Japanese Patent Application Publication No. 10-302799

[0015] Non-patent literature

[0016] Non-Patent Document 1: Lithium Secondary Battery, p.132 (Ohmsha Co., Ltd., published March 20, 2011) Summary of the Invention

[0017] The problem that the invention aims to solve

[0018] With the increasing use of lithium-ion secondary batteries, primarily aimed at achieving higher battery capacity, various types of graphite have been studied as negative electrode active materials that directly contribute to the electrode reaction. In particular, it is known that in artificial graphite, the crystallization state changes due to differences in raw materials and carbonization temperature, thereby affecting the energy capacity of the negative electrode active material. Various easily graphitized carbons (soft carbon), difficult-to-graphitize carbons (hard carbon), and carbon fibers have been studied (see Patent Documents 1-3).

[0019] Furthermore, with the aim of further increasing the capacity of lithium-ion secondary batteries, various compounds have been proposed as electrode active materials that directly contribute to the electrode reaction. As negative electrode active materials, silicon (Si), tin (Sn), germanium (Ge), their oxides, and alloys, alloyed with lithium, have been studied. These negative electrode active materials have a higher theoretical capacity density compared to carbon materials. In particular, silicon-containing particles such as silicon particles and silicon oxide particles are inexpensive and have therefore been extensively studied (see Patent Documents 4 and 5 and Non-Patent Document 1).

[0020] However, when silicon-containing particles such as silicon particles and silicon oxide particles are used as negative electrode active materials, it is known that the volume change of the negative electrode active material is significant due to the absorption and release reactions of lithium ions during charging and discharging. Therefore, the negative electrode additive is stripped from the negative electrode current collector, and the negative electrode active material is easily detached.

[0021] Previously, polyvinylidene fluoride (PVDF) used as an adhesive had low adhesive strength and flexibility, thus requiring large quantities. Furthermore, it was only soluble in organic solvents, thus requiring adhesives that could reduce environmental impact (see Patent Documents 6 and 7).

[0022] As an aqueous adhesive intended to reduce environmental impact without compromising adhesion, styrene-butadiene rubber (SBR), a rubber-like polymer, was investigated. However, issues arose regarding adhesion strength when using active materials with large expansion and contraction, such as a negative electrode utilizing silicon-containing particles.

[0023] Under these circumstances, the main objective of the present invention is to provide an adhesive for secondary batteries with excellent adhesion. Furthermore, an objective of the present invention is to provide an adhesive for secondary battery electrodes, secondary battery electrodes, and a secondary battery utilizing this adhesive.

[0024] Methods for solving problems

[0025] The inventors conducted in-depth research to solve the aforementioned problems. As a result, they discovered that in a secondary battery adhesive containing a polymer compound, when the polymer compound comprises repeating units as shown in formulas (1), (2), and (3) below, and the total proportion of repeating units constituting the polymer compound is set to 100 mol%, the total proportion of repeating units containing lactone structures as shown in formula (3) below is set to a predetermined proportion, thereby exhibiting excellent adhesive strength. This invention was completed based on further repeated and in-depth research based on this insight.

[0026] [Chemical Formula 1]

[0027]

[0028] In equation (1), R 1 R is a hydrogen atom or a methyl group, M is a hydrogen atom or an alkali metal atom, in formula (3), R 2 (For hydrogen atoms or methyl groups).

[0029] That is, the present invention provides an invention having the following structure.

[0030] Item 1. An adhesive for secondary batteries, comprising a polymer compound,

[0031] The aforementioned polymeric compounds contain repeating units as shown in formula (1), formula (2), and formula (3) below.

[0032] When the total percentage of repeating units constituting the above-mentioned polymeric compound is denoted as 100 mol%, the total percentage of repeating units shown in the following formula (3) is 2 mol% or more and 20 mol% or less.

[0033] [Chemical Formula 2]

[0034]

[0035] In equation (1), R 1 R is a hydrogen atom or a methyl group, M is a hydrogen atom or an alkali metal atom, in formula (3), R 2 (For hydrogen atoms or methyl groups).

[0036] Item 2. The adhesive for secondary batteries according to Item 1, wherein, when the total proportion of repeating units constituting the above-mentioned polymer compound is denoted as 100 mol%, the total proportion of repeating units shown in the above formula (3) is 2 mol% or more and 15 mol% or less.

[0037] Item 3. The adhesive for secondary batteries according to Item 1 or 2, wherein, when the total proportion of repeating units constituting the above-mentioned polymer compound is denoted as 100 mol%, the total proportion of repeating units shown in the above formula (1) is 5 mol% or more and 50 mol% or less.

[0038] Item 4. A secondary battery electrode binder comprising any one of items 1 to 3, and an active substance.

[0039] Item 5. The secondary battery electrode compound according to Item 4, wherein the active material comprises a carbon material.

[0040] Item 6. The secondary battery electrode compound according to Item 4 or 5, wherein the active material comprises at least one of silicon and silicon oxide.

[0041] Item 7. An electrode for a secondary battery, comprising any one of items 4 to 6.

[0042] Item 8. A secondary battery comprising the electrodes for a secondary battery as described in Item 7.

[0043] Item 9. A lithium-ion secondary battery comprising the electrode for a secondary battery as described in Item 7.

[0044] Invention Effects

[0045] According to the present invention, an adhesive for secondary batteries with excellent adhesion can be provided. Furthermore, according to the present invention, an object is also to provide an adhesive for secondary battery electrodes, secondary battery electrodes, and secondary batteries (such as lithium-ion secondary batteries) utilizing the adhesive for secondary batteries. Detailed Implementation

[0046] The adhesive for secondary batteries of the present invention comprises a polymer compound, characterized in that the polymer compound comprises repeating units shown in formulas (1), (2), and (3) below, wherein, when the total proportion of the repeating units constituting the polymer compound is 100 mol%, the total proportion of the repeating units shown in formula (3) below is 2 mol% or more and 20 mol% or less. The adhesive for secondary batteries of the present invention (hereinafter sometimes referred to as "adhesive") exhibits excellent adhesive properties by having such characteristics. Hereinafter, the adhesive for secondary batteries of the present invention, and the adhesive for secondary battery electrodes utilizing the same, the electrode for secondary batteries, and the secondary battery (lithium-ion secondary battery, etc.) will be described in detail.

[0047] [Chemical Formula 3]

[0048]

[0049] In equation (1), R 1 R is a hydrogen atom or a methyl group, M is a hydrogen atom or an alkali metal atom, in formula (3), R 2 (For hydrogen atoms or methyl groups).

[0050] It should be noted that in this specification, "comprising" means "consisting essentially of" and "consisting of". Furthermore, in this specification, "(meth)acrylic acid" means "acrylic acid or methacrylic acid", and "(meth)acrylate" means "acrylate or methacrylate".

[0051] Furthermore, in this specification, the values ​​connected by "~" refer to the range of values ​​before and after "~" as the lower and upper limits. When multiple lower and upper limits are listed separately, any lower and upper limits can be selected and connected by "~".

[0052] 1. Adhesive for secondary batteries

[0053] The adhesive for secondary batteries of the present invention is an adhesive for secondary batteries comprising a polymer compound. The polymer compound comprises repeating units shown in formulas (1), (2), and (3) above. Furthermore, when the total proportion of the repeating units constituting the polymer compound is 100 mol%, the total proportion of the repeating units shown in formula (3) above is 2 to 20 mol%.

[0054] The repeating unit shown in the above formula (1) is an acrylic repeating unit.

[0055] In the above formula (1), R1 In polymeric compounds, R is a hydrogen atom or a methyl group. 1 The repeating unit of the hydrogen atom, and R 1 It is sufficient that at least one of the repeating units of methyl is present. That is, the repeating unit of formula (1) contained in the polymer compound can be only R in formula (1). 1 It can be a repeating unit of hydrogen atoms, or it can be simply R in equation (1) above. 1 It can be a repeating unit of methyl, or it can contain both.

[0056] Furthermore, in the above formula (1), M is a hydrogen atom or an alkali metal atom. The polymer compound may contain at least one of the repeating units where M is a hydrogen atom or a repeating unit where M is an alkali metal atom. That is, the repeating unit of the above formula (1) contained in the polymer compound may be only the repeating unit where M is a hydrogen atom in the above formula (1), or only the repeating unit where M is an alkali metal atom in the above formula (1), or both. As an alkali metal atom, Li, Na, K, etc. are preferred examples. When M is an alkali metal atom, M in the above formula (1) of the polymer compound may contain only one type of alkali metal atom or may contain multiple types of alkali metal atoms.

[0057] In the polymer compound, there is no particular limitation on the total proportion of repeating units shown in formula (1) above, as long as the total proportion of repeating units shown in formula (3) above reaches 2 to 20 mol%. From the viewpoint of further improving the adhesive strength of the adhesive for secondary batteries of the present invention, when the total proportion of repeating units constituting the polymer compound is denoted as 100 mol%, the preferred lower limit of the total proportion of repeating units shown in formula (1) above is 5 mol%, the more preferred lower limit is 10 mol%, the preferred upper limit is 95 mol%, the more preferred upper limit is 80 mol%, and the even more preferred upper limit is 50 mol%. The preferred range is 5 to 95 mol%, 5 to 80 mol%, 5 to 50 mol%, 10 to 95 mol%, 10 to 80 mol%, and 10 to 50 mol%.

[0058] The repeating unit shown in equation (2) above is the vinyl alcohol repeating unit.

[0059] In the polymer compound, there is no particular limitation on the total proportion of repeating units shown in formula (2) above, as long as the total proportion of repeating units shown in formula (3) above reaches 2 to 20 mol%. From the viewpoint of further improving the adhesive strength of the adhesive for secondary batteries of the present invention, when the total proportion of repeating units constituting the polymer compound is denoted as 100 mol%, the preferred lower limit of the total proportion of repeating units shown in formula (2) above is 5 mol%, the more preferred lower limit is 20 mol%, the even more preferred lower limit is 50 mol%, the preferred upper limit is 95 mol%, and the more preferred upper limit is 90 mol%. The preferred range is 5 to 95 mol%, 5 to 90 mol%, 20 to 95 mol%, 20 to 90 mol%, 50 to 95 mol%, and 50 to 90 mol%.

[0060] The repeating unit shown in the above formula (3) is a repeating unit with a lactone structure.

[0061] In equation (3) above, R 2 In polymeric compounds, R is a hydrogen atom or a methyl group. 2 The repeating unit of the hydrogen atom, and R 2 It is sufficient that at least one of the repeating units of methyl is present. That is, the repeating unit of formula (3) contained in the polymer compound can be only R in formula (3). 2 It can be a repeating unit of hydrogen atoms, or it can be simply R in equation (3) above. 2 It can be a repeating unit of methyl, or it can contain both.

[0062] In the polymer compound, the total proportion of repeating units shown in the above formula (3) is 2 to 20 mol%, when the total proportion of repeating units constituting the polymer compound is denoted as 100 mol%. The lower limit of the total proportion of repeating units shown in the above formula (3) is 2 mol% or more, preferably 3 mol% or more, more preferably 4 mol% or more, and the upper limit is 20 mol% or less, preferably 15 mol% or less, more preferably 10 mol% or less, and particularly preferably 8 mol% or less.

[0063] In polymer compounds, the arrangement of repeating units shown in formulas (1), (2) and (3) above can be random or block, but from the viewpoint of further improving adhesive strength, random arrangement is preferred.

[0064] When the total proportion of repeating units constituting the polymer compound is denoted as 100 mol%, the total proportion of repeating units shown in formula (1), formula (2), and formula (3) in the polymer compound is preferably 80 mol% or more, more preferably 90 mol% or more, further preferably 95 mol% or more, particularly preferably 95 mol% or more, and may also be 100 mol% (i.e., the repeating units constituting the polymer compound are only the repeating units shown in formulas (1), (2), and (3) above).

[0065] As repeating units constituting polymer compounds, other repeating units different from those shown in formulas (1), (2), and (3) above may also be included. Such other repeating units may be repeating units formed by monomers capable of copolymerizing with monomers that form repeating units shown in formulas (1), (2), and (3) above. Monomers capable of copolymerization may include monomers having olefinic unsaturated bonds. Specifically, monomers having the aforementioned olefinic unsaturated bonds may include acrylates, vinyl acetate, styrene, vinyl chloride, ethylene, butadiene, acrylamide, vinyl sulfonic acid, maleic acid, etc.

[0066] There are no particular limitations on the number average molecular weight of the polymer compound, for example, it is around 10,000 to 8,000,000, preferably around 30,000 to 1,000,000. The number average molecular weight of the polymer compound is a value calculated by GPC (gel permeation chromatography) using standard polyethylene glycol / polyethylene oxide as a reference.

[0067] There are no particular limitations on the manufacturing method of polymeric compounds containing repeating units as shown in formulas (1), (2), and (3) above, and they can be manufactured using known copolymer manufacturing methods. As a known copolymer manufacturing method, an example is the manufacturing method of the copolymer of vinyl alcohol and alkali metal neutralized olefinic unsaturated carboxylic acids described in WO2017 / 168947. After manufacturing this copolymer, a ring-closing reaction is promoted at adjacent positions of the repeating units shown in formula (1) and (2) above to form a lactone structure, and the total proportion of the repeating units shown in formula (3) is adjusted to a range of 2 to 20 mol%. Furthermore, polymeric compounds containing repeating units as shown in formulas (1) and (2) above can also be copolymerized by heating the monomers forming their respective repeating units under acidic conditions. In addition, as a method for forming the lactone structure of the repeating units shown in formula (3) above in polymeric compounds, methods such as adjusting the drying temperature and drying time of the copolymer, and placing the copolymer in a highly acidic environment can be cited.

[0068] In the adhesive of the present invention, the proportion of the above-mentioned polymeric compound is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and may also be 100% by mass (i.e., the adhesive of the present invention is composed only of the above-mentioned polymeric compound) as long as it exhibits excellent adhesive strength.

[0069] The adhesive of the present invention may also contain other adhesive materials different from the polymer compounds described above. Examples of other adhesive materials include water-based adhesives that are soluble or dispersible in water. Specific examples of other adhesive materials include carboxymethyl cellulose (CMC), acrylic resin, sodium polyacrylate, sodium alginate, polyimide (PI), polyamide, polyamide-imide, polyacrylic acid, styrene-butadiene rubber (SBR), styrene-ethylene-butene-styrene copolymer (SEBS), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), etc. The adhesive of the present invention may contain one or more other adhesive materials. When the adhesive of the present invention contains other adhesive materials, their content may be appropriately adjusted within the range of 0 to 100 parts by weight relative to 100 parts by weight of the polymer compound described above.

[0070] The adhesive of the present invention is suitable for use as an adhesive for secondary batteries (for electrodes or separators), and particularly suitable for use as an adhesive contained in an adhesive for secondary battery electrodes. It should be noted that the secondary battery electrode can also be applied to either the positive or negative electrode.

[0071] 2. Compound for secondary battery electrodes

[0072] The secondary battery electrode compound of the present invention (hereinafter sometimes referred to as "electrode compound") is characterized in that it comprises the above-described adhesive for secondary batteries and an active material. As described above, the adhesive of the present invention has excellent adhesive strength, and therefore can be used together with the active material as a secondary battery electrode compound.

[0073] In the electrode binder of the present invention, the content of the binder is preferably 0.5 to 40% by mass, more preferably 1 to 25% by mass, and even more preferably 1.5 to 10% by mass. The content of the binder of the present invention is 0.5% by mass or more, thereby suppressing the deterioration of cycle life characteristics due to insufficient adhesive strength and agglomeration due to insufficient viscosity of the slurry. On the other hand, by setting this content to 40% by mass or less, there is a tendency to obtain high capacity during battery charging and discharging.

[0074] The electrode compound of the present invention can be manufactured using the adhesive of the present invention and a known method. For example, it can be manufactured by mixing the active material, the adhesive of the present invention, water, and further, as needed, conductive additives, dispersants, etc., to form a paste. There is no particular limitation on the timing of adding water. The adhesive of the present invention can be dissolved in water beforehand, and then the active material and the others can be mixed to form a paste. Alternatively, the active material, the adhesive of the present invention, and further, as needed, conductive additives, dispersants, etc., can be mixed in a solid state, and then water can be added to form a paste.

[0075] In the electrode mixture of the present invention, the proportion of water relative to 100 parts by mass of the solid components of the electrode mixture is preferably 40 to 2000 parts by mass, more preferably 50 to 1000 parts by mass. By setting the proportion of water within the above range, there is a tendency to further improve the processability of the electrode mixture (slurry) of the present invention.

[0076] [Active Substances]

[0077] The active material is the electrode active material, which can be either a negative electrode active material or a positive electrode active material. For example, if the active material is a negative electrode active material, it may contain materials such as carbon, and may also contain at least one of silicon and silicon oxide. Specific examples of materials for negative and positive electrode active materials are given below.

[0078] (Negative electrode active material)

[0079] There are no particular limitations on the negative electrode active material; any negative electrode active material used in this technical field can be used, such as crystalline carbon, amorphous carbon, or other carbon materials. Examples of crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft carbon (easily graphitizable carbon) or hard carbon (difficult-to-graphitizable carbon), mesophase pitch carbides, and calcined coke. Furthermore, materials that can absorb and release large amounts of lithium ions, such as silicon (Si), tin (Sn), and titanium (Ti), can be used as negative electrode active materials. As long as such materials are used, even if they are elemental, alloy, compound, solid solution, or composite active materials containing silicon, tin, or titanium, the effects of this invention can be achieved. As silicon-containing materials, alloys, compounds, or solid solutions can be obtained by replacing a portion of Si with at least one element selected from B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn. These can be called silicon or silicon oxides. As tin-containing materials, Ni₂Sn₄, Mg₂Sn, SnO₄ (0 < x < 2), SnO₂, SnSiO₃, LiSnO, etc., can be used. As titanium-containing materials, Li₂TiO₃, Li₄Ti₅O₄, etc., can be used. 12 Examples include lithium titanate and titanium-niobium composite compounds. These materials can be used individually or in combination of two or more. Among these, elemental Si, silicon oxide, or other silicon or silicon oxides are preferred.

[0080] More preferably, silicon or silicon oxide is used as the first negative electrode active material, and carbon material is used as the second negative electrode active material. A composite obtained by mixing the first and second negative electrode active materials is used as the negative electrode active material. In this case, the mixing ratio of the first and second negative electrode active materials is preferably 5 / 95 to 95 / 5 by mass. As for the carbon material, any carbon material commonly used in non-aqueous electrolyte secondary batteries can be used. Examples include crystalline carbon, amorphous carbon, or both. Examples of crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbides, and calcined coke.

[0081] There are no particular restrictions on the manufacturing method of the negative electrode active material. When manufacturing an active material composite obtained by mixing a first negative electrode active material and a second negative electrode active material, there are no particular limitations as long as the two are uniformly dispersed. Examples of manufacturing methods for the negative electrode active material include, for example, mixing the first and second negative electrode active materials using a ball mill. Alternatively, an example is loading a second negative electrode active material precursor onto the surface of particles of the first negative electrode active material and then carbonizing it by heat treatment. As for the second negative electrode active material precursor, any carbon precursor capable of forming a carbon material by heat treatment is acceptable; examples include glucose, citric acid, asphalt, tar, and adhesive materials (e.g., polyvinylidene fluoride, carboxymethyl cellulose, acrylic resin, sodium polyacrylate, sodium alginate, polyimide, polytetrafluoroethylene, polyamide, polyamide-imide, polyacrylic acid, styrene-butadiene rubber, polyvinyl alcohol, ethylene vinyl acetate copolymer, etc.).

[0082] Heat treatment refers to the process of carbonizing carbon precursors in a non-oxidizing atmosphere (reducing atmosphere, inactive atmosphere, reduced pressure atmosphere, or other atmospheres that are difficult to oxidize) at 600–4000°C to obtain electrical conductivity.

[0083] (Positive electrode active material)

[0084] There are no particular limitations on the positive electrode active material; any positive electrode active material used in this technical field can be used. The positive electrode active material can be a lithium-containing composite oxide. Examples of lithium-containing composite oxides include LiMnO2, LiFeO2, LiCoO2, LiMn2O4, Li2FeSiO4, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi x Co y M z O2 (where 0.01 < x < 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, x + y + z = 1, and M is at least one element selected from Mn, V, Mg, Mo, Nb, Fe, Cu, and Al), LiFePO4, etc.

[0085] [Conductive additives]

[0086] There are no particular limitations on the conductive additives used in this technical field; any conductive additive that is conductive can be used. As for the conductive additive, there are no particular limitations as long as it is conductive; carbon powder is preferred. Examples of commonly used carbon powders include acetylene black (AB), Ketjen black (KB), graphite, carbon fiber, carbon nanotubes, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofibers, carbon nanotubes, and other carbon materials. One of these can be used alone, or two or more can be used in combination.

[0087] There is no particular limitation on the proportion of conductive additives. For example, in a total mass percentage of 100% of the active material, binder, and conductive additives, it is preferably 0.1 to 30% by mass, more preferably 0.5 to 10% by mass, and even more preferably 2 to 5% by mass. If the proportion of conductive additives is less than 0.1% by mass, the conductivity of the electrode may not be sufficiently improved. If the proportion of conductive additives is greater than 30% by mass, the proportion of active material is relatively reduced, making it difficult to obtain high capacity during battery charging and discharging. Furthermore, the active material is difficult to disperse evenly due to carbon repelling water, leading to aggregation. Additionally, the surface area is larger than that of the active material, resulting in an increase in the amount of binder used, which is undesirable.

[0088] [Dispersing agent]

[0089] The electrode compound of the present invention may further include a dispersing agent. There are no particular limitations on the dispersing agent, but organic acids or humic acids containing at least one substituent selected from hydroxyl, amino, and imino groups, and a carboxyl group are preferred. Examples of organic acids having hydroxyl and carboxyl groups include lactic acid, tartaric acid, citric acid, malic acid, glycolic acid, malonic acid, glucuronic acid, and humic acid. Examples of organic acids having amino and carboxyl groups include glycine, alanine, phenylalanine, 4-aminobutyric acid, leucine, isoleucine, lysine, glutamic acid, aspartic acid, glutamine, asparagine, histidine, tryptophan, cysteine, and polymers thereof. Examples of organic acids having imino and carboxyl groups include proline, 3-hydroxyproline, 4-hydroxyproline, and piperidinecarboxylic acid. Among these, glucuronic acid, humic acid, glycine, polyglycine, aspartic acid, and glutamic acid are preferred from the viewpoint of ease of acquisition.

[0090] Regarding the proportion of dispersing aids, if the total mass of the active material, binder, and conductive aid is 100 parts by mass, and the amount is 0.01 parts by mass or more, then the active material prepared in the dispersion can be efficiently and effectively micro-dispersed. It should be noted that to maintain micro-dispersion and dispersion stability, an addition amount of 5.0 parts by mass or less is sufficient.

[0091] The electrode compound of the present invention may contain other conventional additives, etc.

[0092] In the electrode adhesive of the present invention, the adhesive is used for the purpose of bonding the active materials to each other, the active materials and the conductive additives, and them to the current collector. That is, it is used to form a good active material layer when the slurry is applied to the current collector of the two electrodes and dried.

[0093] 3. Electrodes for secondary batteries

[0094] The electrode for a secondary battery of the present invention (hereinafter sometimes referred to as "electrode") comprises the electrode binder for a secondary battery described above. The electrode of the present invention is manufactured using the electrode binder for a secondary battery of the present invention (i.e., using the adhesive of the present invention) by means used in the art. That is, the electrode of the present invention is manufactured, for example, by coating and drying the electrode binder for a current collector.

[0095] When the electrode of the present invention is a negative electrode, the raw materials constituting the current collector can be conductive materials such as C, Cu, Ni, Fe, V, Nb, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Al, or alloys containing two or more of these conductive materials (e.g., stainless steel). Furthermore, the current collector can be a material formed by plating Cu onto Fe. From the viewpoint of high electrical conductivity and excellent stability and oxidation resistance in the electrolyte, Cu, Ni, and stainless steel are preferred as raw materials for the current collector as the negative electrode; further, from the viewpoint of material cost, Cu and Ni are preferred.

[0096] When the electrode of the present invention is a positive electrode, conductive materials such as C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Al, or alloys containing two or more of these conductive materials (e.g., stainless steel) can be used as raw materials constituting the current collector. From the viewpoint of high electrical conductivity and excellent stability and oxidation resistance in the electrolyte, C, Al, and stainless steel are preferred as raw materials for the current collector of the positive electrode, and from the viewpoint of material cost, Al is preferred.

[0097] There are no particular restrictions on the shape of the current collector; for example, foil-shaped substrates or three-dimensional substrates can be used. Among these, if a three-dimensional substrate (foamed metal, mesh, woven fabric, non-woven fabric, expanded metal, etc.) is used, even with adhesives that have poor adhesion to the current collector, a high capacity density electrode can be obtained. Furthermore, high-rate charge-discharge characteristics are also excellent.

[0098] 4. Secondary battery

[0099] The secondary battery of the present invention comprises the electrode for a secondary battery described above. The secondary battery of the present invention can have the electrode for a secondary battery described above as either or both of the positive and negative electrodes. As a method for manufacturing the secondary battery of the present invention, it is manufactured using the electrode for a secondary battery described above (i.e., using the adhesive of the present invention) and by means used in the art.

[0100] The secondary battery of the present invention is preferably a non-aqueous electrolyte secondary battery, and particularly preferably a lithium-ion secondary battery. Since a lithium-ion secondary battery needs to contain lithium ions, a lithium salt is preferred as the electrolyte. Examples of such lithium salts include lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium trifluoromethanesulfonylimide. A single electrolyte may be used, or two or more may be used in combination.

[0101] As the electrolyte, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, etc., can be used. A single electrolyte can be used, or two or more can be used in combination. Particularly preferred are elemental propylene carbonate, a mixture of ethylene carbonate and diethyl carbonate, or elemental γ-butyrolactone. It should be noted that the mixing ratio of the aforementioned mixture of ethylene carbonate and diethyl carbonate can be adjusted arbitrarily within the range of 10 to 90% by volume for one of them.

[0102] For the construction of other secondary batteries, the known construction of secondary batteries can be adopted.

[0103] Example

[0104] The present invention will be described in detail below with examples and comparative examples. However, the present invention is not limited to the examples.

[0105] Synthesis of adhesives for secondary batteries

[0106] (Manufacturing Example 1)

[0107] In a reaction vessel equipped with a stirrer, thermometer, N2 gas inlet pipe, reflux cooler, and dropping funnel, 768 parts by mass of water and 12 parts by mass of anhydrous sodium sulfate were added, and N2 gas was purged to deoxygenate the system. Next, 1 part by mass of partially saponified polyvinyl alcohol (88% saponification) and 1 part by mass of lauryl peroxide were added. After the internal temperature was raised to 60°C, a liquid obtained by pre-mixing 51.8 parts by mass of methyl acrylate and 208 parts by mass of vinyl acetate was added dropwise through the dropping funnel over 4 hours. The internal temperature was then maintained at 65°C for 2 hours. The solid components were then filtered off. In the same reaction vessel as above, the above solid components, 450 parts by mass of methanol, 420 parts by mass of water, 132 parts by mass of sodium hydroxide, and 0.52 parts by mass of hydrazine were added, and the mixture was stirred at 30°C for 3 hours. After stirring, the reaction solution was neutralized, the solid was filtered off, washed with methanol, and dried under reduced pressure at 70°C for 8 hours to obtain a vinyl alcohol / alkali metal neutralized copolymer (a binder for secondary batteries). The obtained copolymer was subjected to the following conditions... 1 H-NMR (BRUKER) determination results show that the total proportion of repeating units constituting the copolymer is 100 mol%, and the total proportion of repeating units containing lactone structures as shown in formula (3) above is 2 mol%. The total proportions of each repeating unit as shown in formulas (1), (2) and (3) above constituting the copolymer are shown in Table 1.

[0108] (use 1 Identification of repeating units by H-NMR)

[0109] Measure 2g of the obtained copolymer, add 33g of heavy water, and heat at 90°C for 3 hours to dissolve. Perform NMR analysis on the resulting heavy aqueous solution under the following conditions.

[0110] Device: Bruker AVANCE III HD400 (AVANCE III 400)

[0111] Determination method: 1 H NMR

[0112] Nuclear frequency determination: bf1 (400.1300000)

[0113] Spectrum width: Sw(20.5524)

[0114] Observation point: td(65536)

[0115] Data point: Si(65536)

[0116] Measurement temperature: 27℃

[0117] (Manufacturing Example 2)

[0118] In a 2L reaction vessel equipped with a stirrer, thermometer, N2 gas inlet pipe, and reflux cooler, 21 parts by mass of the copolymer obtained in Manufacturing Example 1 and 189 parts by mass of water were added, and the mixture was stirred at 90°C for 3 hours. Next, 2 parts by mass of 90% acetic acid were added dropwise, and the mixture was stirred under acidic conditions. Then, 1500 parts by mass of acetone were added dropwise, and the mixture was stirred at 5°C for 1 hour. The solid component was then filtered off. The filtered solid component was dried under reduced pressure at 60°C for 8 hours. The resulting copolymer was then processed in the same manner as in Manufacturing Example 1. 1 H-NMR (BRUKER) determination results show that the total proportion of repeating units constituting the copolymer is 100 mol%, and the total proportion of repeating units containing lactone structures as shown in formula (3) above is 5 mol%. The total proportions of each repeating unit as shown in formulas (1), (2) and (3) above constituting the copolymer are shown in Table 1.

[0119] (Manufacturing Example 3)

[0120] The final drying process in Manufacturing Example 1 was carried out under reduced pressure and at 90°C. Otherwise, the vinyl alcohol / alkali metal neutralized copolymer (adhesive for secondary batteries) was obtained in the same manner as in Manufacturing Example 1. The resulting copolymer was subjected to the same process as in Manufacturing Example 1. 1 H-NMR (BRUKER) determination showed that the total proportion of repeating units constituting the copolymer was 100 mol%, and the total proportion of repeating units containing lactone structures as shown in formula (3) above was 11 mol%. The total proportions of each repeating unit as shown in formulas (1), (2) and (3) above constituting the copolymer are shown in Table 1.

[0121] (Manufacturing Example 4)

[0122] The final drying process in Manufacturing Example 1 was performed under reduced pressure at 60°C. Otherwise, the vinyl alcohol / alkali metal neutralized copolymer was obtained in the same manner as in Manufacturing Example 1. The obtained copolymer was then subjected to the same process as described above. 1 The results of H-NMR (BRUKER) determination show that the total proportion of repeating units constituting the copolymer is 100 mol%, and the total proportion of repeating units containing lactone structures as shown in the above formula (3) is 1 mol%. The total proportions of each repeating unit shown in the above formulas (1), (2) and (3) constituting the copolymer are shown in Table 1.

[0123] [Supplements for secondary battery electrodes and preparation of electrodes]

[0124] (Example 1)

[0125] Four parts by mass of the copolymer obtained in Manufacturing Example 1 were dissolved in 96 parts by mass of water to obtain an aqueous solution of the binder (binder composition). Next, 90.2 parts by mass of artificial graphite (manufactured by Hitachi Chemicals Co., Ltd., MAG-D), 6.8 parts by mass of silicon monoxide (OSAKA Titanium Technologies), and 75 parts by mass of the binder aqueous solution, which are used as electrode active materials, were added and kneaded. Further, 96 parts by mass of water for viscosity preparation were added and kneaded to prepare a slurry-like negative electrode mixture. The obtained negative electrode mixture was coated onto a rolled copper foil with a thickness of 18 μm. After drying, the rolled copper foil and coating were tightly bonded using a rolling mill (manufactured by Ohno Roller Co., Ltd.), followed by heat treatment (reduced pressure, 120°C, 12 hours or more) to produce a negative electrode. The thickness of the active material layer in the obtained negative electrode was 42 μm, and the capacity density of this negative electrode was 3.24 mAh / cm³. 2 .

[0126] (Example 2)

[0127] The copolymer obtained in Manufacturing Example 2 was used as the binder, and the negative electrode was made in the same manner as in Example 1.

[0128] (Example 3)

[0129] The copolymer obtained in Manufacturing Example 3 was used as the binder, and the negative electrode was otherwise made in the same manner as in Example 1.

[0130] (Comparative Example 1)

[0131] The copolymer obtained in Manufacturing Example 4 was used as the binder, and the negative electrode was otherwise made in the same manner as in Example 1.

[0132] (Comparative Example 2)

[0133] As an existing adhesive for secondary batteries, styrene-butadiene rubber (SBR) / carboxymethyl cellulose (CMC) = (mass ratio 50 / 50) is used, and the negative electrode is made in the same manner as in Example 1.

[0134] [Adhesive strength]

[0135] For the negative electrodes obtained in Examples 1-3 and Comparative Examples 1-2, the peel strength (N / 15mm) when the active material layer was peeled off from the copper foil serving as the current collector was measured and recorded as the adhesive force. Specifically, the negative electrode was cut to a width of 80mm × 15mm. Adhesive tape was attached to the surface (the side of the active material layer of the negative electrode), and then double-sided tape was used to attach it to a stainless steel plate to fix the negative electrode (the side of the current collector), which was used as an evaluation sample. Using this evaluation sample, a 90-degree peel test (a 90-degree peel test of the adhesive tape to the negative electrode fixed on the stainless steel plate) was performed using a tensile testing machine (Shimadzu Corporation EZ-SX small desktop testing machine) to measure the peel strength between the active material layer and the current collector in the negative electrode. Table 1 shows the evaluation results of the peel test (peel strength).

[0136] [Table 1]

[0137]

[0138] The electrodes (negative electrodes) of Examples 1-3 are electrodes for secondary batteries that utilize an electrode mixture containing the adhesive (a copolymer (polymer compound) manufactured in Examples 1-3, wherein the copolymer contains repeating units shown in Formula (1), Formula (2), and Formula (3) above, and the total proportion of repeating units shown in Formula (3) is 2 mol% or more and 20 mol% or less when the total proportion of repeating units constituting the copolymer is 100 mol%. It can be seen that the adhesive in the electrodes of Examples 1-3 has high adhesive strength.

Claims

1. A binder for a secondary battery, comprising a high molecular compound, the high molecular compound comprises a repeating unit represented by the following formula (1), the following formula (2), and the following formula (3), in the case where a total proportion of the repeating units constituting the high molecular compound is taken as 100 mol%, a total proportion of the repeating unit represented by the following formula (3) is 2 mol% or more and 20 mol% or less, in the case where a total proportion of the repeating units constituting the high molecular compound is taken as 100 mol%, a total proportion of the repeating unit represented by the above formula (1) is 5 mol% or more and 50 mol% or less, ； In formula (1), R 1 is a hydrogen atom or a methyl group, and M is a hydrogen atom or an alkali metal atom. In formula (3), R 2 is a hydrogen atom or a methyl group.

2. The binder for secondary batteries according to claim 1, wherein, in the case where a total proportion of the repeating units constituting the high molecular compound is taken as 100 mol%, a total proportion of the repeating unit represented by the above formula (3) is 2 mol% or more and 15 mol% or less.

3. The binder for secondary batteries according to claim 1 or 2, wherein, in the case where a total proportion of the repeating units constituting the high molecular compound is taken as 100 mol%, a total proportion of the repeating unit represented by the above formula (1) is 10 mol% or more and 50 mol% or less.

4. A mixture for a secondary battery electrode, comprising the binder for a secondary battery according to any one of claims 1 to 3 and an active material.

5. The mixture for a secondary battery electrode according to claim 4, wherein the active material comprises a carbon material.

6. The mixture for a secondary battery electrode according to claim 4 or 5, wherein the active material comprises at least one of silicon and silicon oxide.

7. An electrode for a secondary battery, comprising the mixture for a secondary battery electrode according to any one of claims 4 to 6.

8. A secondary battery, comprising the electrode for a secondary battery according to claim 7.

9. A lithium ion secondary battery, comprising the electrode for a secondary battery according to claim 7.

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