Use of an aqueous dispersion of polymer P as a polymer binder in an electrode slurry composition for a negative electrode of a secondary battery

Abstract

The present invention relates to, as a polymer binder in an electrode slurry composition for a negative electrode of a secondary battery, wherein the total amount of monomers (a) to (f) is 100 parts by weight, (a) 40 to 75 parts by weight of at least one vinyl aromatic compound, (b) 22.5 to 55 parts by weight of at least one conjugated aliphatic diene, (c) 0.5 to 10 parts by weight of at least one ethylenically unsaturated monomer containing an acid group, (d1) 1 to 5 parts by weight of acrylamide and / or methacrylamide, (d2) 1 to 10 parts by weight of acrylonitrile and / or methacrylonitrile, (e) 0 to 5 parts by weight of at least one monoethylenically unsaturated monomer having at least one epoxy group, hydroxyl group, N-methylol group, or carbonyl group, (f) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer and a method of using an aqueous dispersion of polymer P obtainable by radical-initiated emulsion polymerization, which comprises a step of polymerizing at a polymerization temperature in the range of 70 to 95°C, the aqueous polymer dispersion itself, and a method of producing the aqueous dispersion by radical-initiated emulsion polymerization, an electrode slurry composition for a negative electrode containing polymer P, a negative electrode of a secondary battery containing polymer P, a method of preparing this negative electrode, and a lithium-ion secondary battery provided with this negative electrode.

Description

Technical Field

[0001] The present invention relates to a method of using an aqueous polymer dispersion containing a vinyl aromatic compound and a conjugated aliphatic diene in a copolymerized form as a binder for producing an electrode slurry composition for a negative electrode. The present invention also relates to an aqueous polymer dispersion and a method for producing an aqueous dispersion by radical-free emulsion polymerization.

Background Art

[0002] Lithium-ion secondary batteries are modern devices for storing energy. Many applications have been considered, from small devices such as mobile phones and laptop computers to automotive batteries and other batteries for e-mobility and energy storage. Various components of the battery, such as the electrolyte, electrode material, and separator, play a decisive role in the performance of the battery. Particular attention has been paid to the electrode material.

[0003] Generally, a secondary battery using a non-aqueous electrolyte includes a negative electrode, a positive electrode, and a non-aqueous electrolyte layer. To form the positive electrode, a positive electrode slurry containing a lithium transition metal oxide as a positive electrode active material, a binder, and a solvent is prepared. The positive electrode slurry is coated on a current collector made of a metal (preferably aluminum) foil, and then drying, pressing, and forming steps are carried out.

[0004] To form the negative electrode, the same method as above is carried out, except that a negative electrode slurry containing a carbon or carbon composite capable of intercalation / deintercalation of lithium ions as a negative electrode active material or silicon or a silicon composite or silicon oxide and an aqueous binder dispersion is used.

[0005] An important requirement for lithium-ion secondary batteries is that they have good charge and discharge characteristics and, therefore, always have good life characteristics with respect to the alternating charge process. Charge and discharge are carried out by the intercalation and de-intercalation of lithium, which causes expansion and contraction of the volume of the negative electrode active material. Therefore, the negative electrode, which is a composite of several materials, is subjected to strong tensile forces that easily cause material damage. Furthermore, since a negative electrode with a high proportion of the negative electrode material, and thus density, is required, the binder content is usually very low. In this regard, a binder with good adhesion is required. Extensive research has been carried out, but there is still room for improvement in the solutions found so far.

[0006] Therefore, European Patent No. 1058327 describes a negative electrode comprising a carrier substrate and a negative electrode active material composition negative electrode containing a polymer binder, a lithium intercalate compound, a conductive agent, and a partially saponified acrylate / vinyl acetate copolymer. The polymer binder is a styrene / butadiene copolymer having acrylic acid and acrylamide as comonomers.

[0007] Pamphlet of International Publication No. 2004 / 091017 describes the production of a slurry of a negative electrode active material using a special dispersant. Carbon is bonded to the styrene / butadiene polymer in the negative electrode.

[0008] European Patent No. 2869372 teaches a negative electrode slurry composition comprising a styrene-butadiene copolymer as a binder resin having a glass transition temperature of -30°C to 60°C, an acrylic polymer latex, a water-soluble polymer, and a negative electrode material which is a combination of a silicon-based active material and a carbon-based material. The styrene-butadiene copolymer latex consists of 62 parts of styrene, 33 parts of 1,3-butadiene, 4 parts of itaconic acid, and 1 part of 2-hydroxyethyl acrylate. Such a polymer shows insufficient strength as a binder in the negative electrode.

[0009] European Patent No. 3007257 discloses an elastic binder composition for secondary batteries, in which butadiene / styrene latex particles having an average particle diameter in the range of 50 nm to 200 nm and acrylic copolymer latex particles having an average particle diameter in the range of 300 nm to 700 nm are used as binders in the electrode mixture. The polymer has a butadiene content of 60% by weight but has a defect in strength.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0011] An object of the present invention is to provide a negative electrode slurry composition that can suppress the expansion of the negative electrode and maintain high adhesion to the negative electrode active material and the current collector during repeated charge and discharge cycles. The binder polymer itself is to exhibit good stress / strain behavior.

Means for Solving the Problems

[0012] This object is achieved by using, as a polymer binder in an electrode slurry composition for the negative electrode of a secondary battery, the amounts of monomers (a) to (f) totaling 100 parts by weight, (a) 40 to 75 parts by weight of at least one vinyl aromatic compound, and (b) 22.5 to 55 parts by weight of at least one conjugated aliphatic diene, (c) 0.5 to 10 parts by weight of at least one ethylenically unsaturated monomer containing an acid group, and (d1) 1 to 5 parts by weight of acrylamide and / or methacrylamide, and (d2) 1 to 10 parts by weight of acrylonitrile and / or methacrylonitrile, and (e) 0 to 5 parts by weight of a monoethylenically unsaturated monomer having at least one epoxy group, hydroxyl group, N-methylol group, or carbonyl group, and (f) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer are polymerized at a polymerization temperature in the range of 70 to 95 °C, and the present invention is achieved by using an aqueous dispersion of polymer P obtainable by radical-initiated emulsion polymerization.

[0013] The present invention also relates to an aqueous polymer dispersion obtainable by radical-initiated aqueous emulsion polymerization, wherein the amounts of monomers (a) to (f) total 100 parts by weight, (a) 40 to 75 parts by weight of at least one vinyl aromatic compound, and (b) 22.5 to 55 parts by weight of at least one conjugated aliphatic diene, and (c) 0.5 to 10 parts by weight of at least one ethylenically unsaturated monomer containing an acid group, and (d1) 1 to 5 parts by weight of acrylamide and / or methacrylamide, and (d2) 1 to 10 parts by weight of acrylonitrile and / or methacrylonitrile, and (e) 0 to 5 parts by weight of a monoethylenically unsaturated monomer having at least one epoxy group, hydroxyl group, N-methylol group, or carbonyl group, and (f) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer are polymerized at a polymerization temperature in the range of 70 to 95 °C, and a method for producing an aqueous dispersion by radical-initiated emulsion polymerization.

[0014] The present invention also relates to an electrode slurry composition for a negative electrode containing polymer P, a negative electrode of a secondary battery containing polymer P, a method for preparing this negative electrode, and a lithium-ion secondary battery provided with the negative electrode.

[0015] Hereinafter, the aqueous dispersion of polymer P is referred to as a polymer dispersion.

[0016] When the amount is reported in parts by weight below, unless otherwise specified, this is based on 100 parts by weight of all monomers.

[0017] The total monomer amount is the total amount of all monomers used in the polymerization and totals 100 parts by weight.

[0018] When the solid content of the aqueous dispersion is referred to in wt%, it is based on the weight of the aqueous dispersion.

[0019] Hereinafter, compounds derived from acrylic acid and methacrylic acid are partially abbreviated by inserting the syllable "(meth)" into the compound derived from acrylic acid.

[0020] An aqueous polymer dispersion can be produced using the following ethylenically unsaturated monomers (a), (b), (c), (d1), (d2), (e), and (f).

[0021] Examples of suitable vinyl aromatic compounds (monomers of group (a)) include styrene, α-methylstyrene, and / or vinyltoluene. It is preferable to select styrene from the monomers of this group.

[0022] The total amount of monomer (a) is 40 to 75 parts by weight, preferably 45 to 70 parts by weight, particularly 47 to 60 parts by weight, based on 100 parts by weight of all monomers (a to f).

[0023] Examples of conjugated aliphatic dienes (monomers of group (b)) that may be mentioned include 1,3-butadiene, isoprene, 1,3-pentadiene, dimethyl-1,3-butadiene, and cyclopentadiene. From the monomers of this group, it is preferable to use 1,3-butadiene and / or isoprene.

[0024] The total amount of monomer (b) is 22.5 to 55 parts by weight, preferably 28 to 50 parts by weight, particularly 32 to 45 parts by weight, based on 100 parts by weight of all monomers.

[0025] Examples of ethylenically unsaturated monomers containing an acid group that may be mentioned (monomer (c)) include ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, and vinylphosphonic acid. The ethylenically unsaturated carboxylic acid used is preferably an α,β-ethylenically unsaturated mono- and dicarboxylic acid having 3 to 6 carbon atoms in the molecule. Examples of these are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, vinylacetic acid, and vinyl lactic acid. Examples of suitable ethylenically unsaturated sulfonic acids include vinylsulfonic acid, styrenesulfonic acid, acrylamidomethylpropanesulfonic acid, sulfopropyl acrylate, and sulfopropyl methacrylate. It is preferable to use acrylic acid, methacrylic acid, and itaconic acid. The cited acids can be used as a single component or in combination thereof.

[0026] The monomer containing an acid group can be used for polymerization in the form of the free acid or in a form partially or completely neutralized with a suitable base. It is preferable to use a sodium hydroxide solution, a potassium hydroxide solution, or ammonia as the neutralizing agent.

[0027] The total amount of monomer (c) is one or more monomers containing an acid group, which is 0.5 to 10 parts by weight, preferably 1 to 8 parts by weight, particularly 2 to 5 parts by weight, based on 100 parts by weight of all monomers.

[0028] The total amount of monomer (d1) is 1 to 5 parts by weight, preferably 1 to 3 parts by weight, particularly 1 to 2 parts by weight of acrylamide and / or methacrylamide, preferably acrylamide, based on 100 parts by weight of all monomers.

[0029] The total amount of monomer (d2) is 1 to 10 parts by weight, preferably 1 to 8 parts by weight, particularly 1 to 7 parts by weight of acrylonitrile and / or methacrylonitrile, preferably acrylonitrile, based on 100 parts by weight of all monomers.

[0030] The monomer (e) that typically increases the internal strength of the polymer matrix in film form usually has at least one epoxy group, hydroxyl group, N-methylol group, or carbonyl group. Particularly preferred is a monoethylenically unsaturated compound having at least one N-methylol group selected from the group including N-methylolacrylamide and N-methylolmethacrylamide.

[0031] The total amount of monomer (e) is 0.1 to 5 parts by weight, preferably 0.2 to 4.5 parts by weight, particularly 0.4 to 4 parts by weight, of one or more monomers containing an acid group, based on 100 parts by weight of all monomers.

[0032] The other monomethylenically unsaturated monomer (f) is a monomer different from the monomers in groups (a), (b), (c), (d), and (e). They are preferably vinyl esters of saturated C 1 ~C 18 carboxylic acids, preferably vinyl acetate, and monovalent C of acrylic acid and methacrylic acid 1 ~C 18Esters of alcohols, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, pentyl acrylate, pentyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, allyl esters of saturated carboxylic acids, vinyl ethers, vinyl ketones, dialkyl esters of ethylenically unsaturated carboxylic acids, N-vinylpyrrolidone, N-vinylpyrrolidine, N-vinylformamide, N,N-dialkylaminoalkylacrylamides, N,N-dialkylaminoalkylmethacrylamides, N,N-dialkylaminoalkyl acrylates, N,N-dialkylaminoalkyl methacrylates, vinyl chloride, and vinylidene chloride ((monomers of group (f)) selected therefrom).

[0033] The monomers (f) of this group are optionally used for the modification of the polymer P. The total amount of the other monomers (f) can be at most 20 parts by weight based on 100 parts by weight of all the monomers. Based on 100 parts by weight of all the monomers, the proportion of one or more monomers of group (f) is from 0 to 20 parts by weight, preferably from 0.1 to 15 parts by weight, particularly from 0.5 to 10 parts by weight.

[0034] Monomers in which the vinyl aromatic compound is styrene and / or methylstyrene, particularly styrene, and the conjugated aliphatic diene is 1,3-butadiene and / or isoprene, particularly 1,3-butadiene, are preferred.

[0035] The amounts of the monomers (a) to (f) total 100 parts by weight, (a) 45 to 68.9 parts by weight of at least one vinyl aromatic compound, and (b) 28 to 50 parts by weight of at least one conjugated aliphatic diene, and (c) 1 to 8 parts by weight of at least one ethylenically unsaturated carboxylic acid, and (d1) 1 to 3, preferably 1 to 2 parts by weight of acrylamide, and (d2) 1 to 8, preferably 1 to 7 parts by weight of acrylonitrile, and (e) 0.1 to 4 parts by weight of a monoethylenically unsaturated monomer having at least one N-methylol group, and (f) 0 to 15 parts by weight of at least one other monoethylenically unsaturated monomer It is advantageous to polymerize.

[0036] The amounts of monomers (a) to (f) total 100 parts by weight, (a) 45 to 68.9 parts by weight of at least one styrene, and (b) 28 to 50 parts by weight of at least one 1,3-butadiene, and (c) 1 to 8 parts by weight of at least one ethylenically unsaturated carboxylic acid selected particularly from the group consisting of acrylic acid, methacrylic acid, and itaconic acid, and (d1) 1 to 3 parts by weight of acrylamide, and (d2) 1 to 8 parts by weight of acrylonitrile, and (e) 0.1 to 4 parts by weight of a monoethylenically unsaturated monomer selected from the group comprising N-methylol acrylamide and N-methylol methacrylamide, and (f) 0.1 to 15 parts by weight of at least one other monoethylenically unsaturated monomer It is particularly preferred to polymerize.

[0037] Emulsion polymerization is carried out in an aqueous medium. This can be, for example, completely deionized water, or a mixture of water and a water-miscible solvent such as methanol, ethanol, ethylene glycol, glycerol, a sugar alcohol such as sorbitol or tetrahydrofuran. The total amount of the aqueous medium is here adjusted so that the resulting aqueous polymer dispersion has a solids content of 20% to 70% by weight, frequently 30% to 65% by weight, and often 40% to 60% by weight.

[0038] The method according to the invention uses a free radical initiator (also called a free radical polymerization initiator), i.e. an initiator which forms free radicals under the reaction conditions. These can be peroxides or azo compounds. Redox initiator systems are of course also suitable.

[0039] The peroxides used can in principle be inorganic peroxides and / or organic peroxides. Examples of suitable inorganic peroxides are hydrogen peroxide and peroxodisulfates, such as the mono- or dialkali metal salts or ammonium salts of peroxodisulfuric acid, such as its mono- and disodium salts, mono- and dipotassium salts, or ammonium salts. Examples of suitable organic peroxides are alkyl hydroperoxides, such as tert-butyl hydroperoxide, aryl hydroperoxides, such as p-menthyl or cumene hydroperoxide, and dialkyl or diaryl peroxides, such as di-tert-butyl, dibenzoyl, or dicumene peroxide.

[0040] The azo compounds used are essentially 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(N,N'-dimethylenebis(isobutyramidine)) dihydrochloride, and 2,2'-azobis(amidinopropyl) dihydrochloride (corresponding to V-50 from Wako Chemicals).

[0041] The redox initiator system is a composite system composed of at least one organic or inorganic reducing agent and at least one peroxide. The oxidizing agent suitable for the redox initiator system is essentially the above-mentioned peroxide. The corresponding reducing agents that can be used are sulfur compounds in a low oxidation state, such as alkali metal sulfites, such as potassium sulfite and / or sodium sulfite, alkali metal bisulfites, such as potassium bisulfite and / or sodium bisulfite, alkali metal metabisulfites, such as potassium metabisulfite and / or sodium metabisulfite, acetone bisulfite, formaldehyde sulfoxylate, such as potassium formaldehyde sulfoxylate and / or sodium formaldehyde sulfoxylate, alkali metal salts, specifically potassium salts and / or sodium salts of aliphatic sulfinic acids and alkali metal hydrogen sulfides, such as potassium hydrogen sulfide and / or sodium hydrogen sulfide, salts of polyvalent metals, such as iron(II) sulfate, ammonium iron(II) sulfate, iron(II) phosphate, enediols, such as dihydroxymaleic acid, benzoin and / or ascorbic acid, and reducing saccharides, such as sorbose, glucose, fructose and / or dihydroxyacetone.

[0042] Preferred free radical initiators are inorganic and organic peroxides, preferably ammonium salts or alkali metal salts of peroxomonosulfuric acid or peroxodisulfuric acid, and tert-butyl, p-menthyl and cumyl hydroperoxides, particularly selected from sodium peroxodisulfate and potassium peroxodisulfate, tert-butyl hydroperoxide and cumyl hydroperoxide. Here, it is particularly preferred to use both at least one inorganic peroxide, preferably peroxodisulfate, particularly sodium peroxodisulfate, and / or one organic peroxide, preferably an alkyl hydroperoxide, particularly t-butyl hydroperoxide.

[0043] The polymerization is generally carried out using 0.1 to 5 parts by weight, preferably 0.5 to 4 parts by weight, of a free radical initiator based on 100 parts by weight of the total monomers.

[0044] The start of the polymerization reaction is understood to mean the start of the polymerization reaction of the monomers present in the polymerization vessel as a result of the decomposition of the free radical initiator.

[0045] Preferably, the process of the present invention is a monomer supply process. The monomer supply process means that a large amount, typically at least 90%, preferably at least 93%, of the monomers to be polymerized are supplied to the polymerization reaction under polymerization conditions.

[0046] Here, prior to the start of polymerization, it is possible to include a part of the monomers in the initial charge to the polymerization vessel. According to this preferred variant, the polymerization can then be started with an initial charge containing 1 to 10 parts by weight of the total monomers, and then the monomers and the emulsifier are continuously metered. More specifically, it is possible to include up to 5% of each monomer in the initial charge and then start the polymerization.

[0047] The polymerization conditions generally mean the amount of the radical initiator and the temperature and pressure at which the radical-initiated aqueous emulsion polymerization does not stop. The polymerization here mainly depends on the nature and amount of the radical initiator used. The relationship between temperature and decomposition rate is well known to those skilled in the art for common polymerization initiators or can be confirmed by routine experiments.

[0048] According to a preferred embodiment, the monomers and the emulsifier are continuously metered. In other words, the monomer metering and also the emulsifier metering are carried out at a continuous mass flow rate, i.e., without interruption.

[0049] According to the present invention, the polymerization is carried out in a temperature range of 70 to 95 °C, preferably 75 °C or higher and 90 °C or lower.

[0050] The metered supply of the conjugated aliphatic diene is generally carried out at high pressure. The metered supply of the conjugated aliphatic diene is preferably carried out at a pressure in the range of 5 to 15 bar. High pressure has, for example, the effect that 1,3-butadiene, which is a gas at standard pressure and room temperature, is mainly present in the polymerization mixture.

[0051] The monomers are preferably metered in continuously, i.e., without interruption. In this case, the monomers are preferably metered at a metering rate that deviates by no more than 30%, preferably no more than 20%, from the average value of the entire supply. According to a preferred embodiment, the metering rate of the monomers (increase in monomers) approximately corresponds to the polymerization rate of the monomers (decrease in monomers).

[0052] It is possible to use protective colloids and / or emulsifiers typically used to promote the emulsification of the monomers in the aqueous medium. A comprehensive description of suitable protective colloids can be found in Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Volume XIV / 1, Makromolekulare Stoffe [Macromolecular Materials], Georg-Thieme-Verlag, Stuttgart, 1961, pages 411 - 420.

[0053] Useful emulsifiers typically include surfactants having a number average molecular weight of less than 2000 g / mol, or preferably less than 1500 g / mol, while the number average molecular weight of the protective colloid is more than 2000 g / mol, for example 2000 - 100000 g / mol, especially 5000 - 50000 g / mol. Suitable emulsifiers are described in WO 2020 / 114798, page 9, line 40 - page 10, line 22.

[0054] When further using an emulsifier and / or a protective colloid as an auxiliary agent for dispersing the monomers, the amount used is, for example, 0.1 - 5 parts by weight based on 100 parts by weight of the monomers.

[0055] Generally used emulsifiers are, for example, ethoxylated mono-, di- and trialkylphenols (EO level: 3 - 50, alkyl group: C 4 ~C 12 ), ethoxylated fatty alcohols (EO level: 3 - 50; alkyl group: C 8 ~C 36 ), as well as alkali metal salts and ammonium salts of alkyl sulfates (alkyl group: C 8 ~C 12 ), sulfuric acid monoesters of ethoxylated alkanols (EO level: 3 - 30, alkyl group: C 12 ~C 18 ), and sulfuric acid monoesters of ethoxylated alkylphenols (EO level: 3 - 50, alkyl group: C 4 ~C 12 ), alkyl sulfonic acids (alkyl group: C 12 ~C 18 ), and alkylaryl sulfonic acids (alkyl group: C 9 ~C 18 ). Further preferred emulsifiers can be found in Houben - Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Volume XIV / 1, Makromolekulare Stoffe [Macromolecular substances], pages 192 - 208, Georg - Thieme - Verlag, Stuttgart, 1961.

[0056] Even more suitable surface - active substances are compounds of general formula I

Chemical formula

[0057] When a dispersion aid is included in the preparation of the aqueous dispersion of polymer P, the total amount of the dispersion aid used, particularly the emulsifier, is 0.1% to 5% by weight, preferably 1% to 3% by weight, based on the total amount of the monomers in each case. In an advantageous embodiment, the emulsifier is used as the only dispersion aid.

[0058] When a dispersion aid is included in the preparation of the aqueous dispersion of polymer P, it is possible, in some cases, to initially charge part or all of the dispersion aid as a component of the aqueous medium containing polymer A. Alternatively, it is possible to meter in all or any remaining residue of the dispersion aid together with monomer P during the polymerization reaction. The manner in which all or any remaining residue of the dispersion aid is metered into the aqueous polymerization medium here may be discontinuous in one or more portions, or may be continuous at a constant or varying flow rate.

[0059] According to one embodiment of the present invention, the polymerization is carried out in the presence of degraded starch. In emulsion copolymerization, it is preferable to use 15 to 100 parts by weight of degraded starch per 100 parts by weight of the monomer.

[0060] Degraded starch is generally known and is described, for example, on pages 15 to 16, line 2 of WO 2020 / 249406 pamphlet.

[0061] Degraded natural starch, particularly natural starch degraded into maltodextrin, is preferable.

[0062] Degraded starch having an intrinsic viscosity ηi of 0.07 dl / g or less, preferably 0.05 dl / g or less, is preferable. The intrinsic viscosity ηi of the degraded starch is preferably in the range of 0.02 to 0.06 dl / g. The intrinsic viscosity ηi is determined according to DIN EN1628 at a temperature of 23°C.

[0063] According to a more preferred embodiment, no degraded starch is present during the polymerization.

[0064] Similar to the seed-free preparation mode, the polymer particle size can also be adjusted by carrying out emulsion polymerization for the preparation of polymer P by the seed latex process or in the presence of in-situ produced seed latex. Such methods are known to those skilled in the art and can be found in the prior art (see, for example, EP 40 419 A, EP 567 812 A, EP 614 922 A and "Encyclopedia of Polymer Science and Technology", Volume 5, page 847, John Wiley & Sons Inc., New York, 1966).

[0065] According to one preferred variant of the emulsion polymerization process, seed latex is employed.

[0066] By seed latex, a person skilled in the art would generally understand a polymer dispersion in which the seed particles act as the core for particle formation in the polymerization process.

[0067] According to a preferred process variant, an aqueous polymer dispersion with a weight-average particle size Dw50 in the range of 20 to 60 nm and a ratio Dw50 / Dn50 of 2 or less is used as the seed latex.

[0068] In the following, the weight-average particle size is understood to mean the weight-average Dw50 value determined by the method of an analytical ultracentrifuge, and the number-average Dn50 value determined by the same method is understood to mean the average particle size (see S.E. Harding et al., Analytical Ultracentrifugation in Biochemistry 5 and Polymer Science, Royal Society of Chemistry, Cambridge, Great Britain 1992, Chapter 10, Analysis of Polymer Dispersions with an Eight-Cell-AUC-Multiplexer: High Resolution Particle Size Distribution and Density Gradient Techniques, W. Machtle, pages 147 - 175). In the context of this specification, a narrow particle size distribution is understood when the ratio [Dw50 / Dn50] of the weight-average particle size Dw50 and the number-average particle size Dn50 determined by the method of an analytical ultracentrifuge is 2.0 or less, preferably 1.5 or less, particularly preferably 1.2 or less or 1.1 or less.

[0069] The production of seed latex is known to a person skilled in the art and is usually carried out in the presence of a large amount of emulsifier, as a result of which a small particle size and a narrow particle size distribution are obtained. Polymerization carried out in the presence of such an exogenous seed latex is generally observed to be characterized by uniform particle growth, in contrast to in-situ seed latex. Seed latex is usually used in the form of an aqueous dispersion, as the name suggests.

[0070] Seed latex is preferably a styrene polymer and / or a methyl methacrylate polymer having a glass transition temperature of 50 °C or higher, 60 °C or higher, 70 °C or higher, 80 °C or higher, or 90 °C or higher, measured in accordance with DIN EN ISO 11357-2 (2013-09).

[0071] Preferably, 0.01 to 3 parts by weight, particularly 0.02 to 1 part by weight, of seed latex (calculated as a solid) based on all monomers is used.

[0072] Preferably, the polymerization is initiated by an initial charge into a polymerization vessel containing an aqueous dispersion of polystyrene seed latex of up to 3 parts by weight based on 100 parts by weight of all monomers, followed by continuously added monomers and emulsifiers.

[0073] To modify the properties of the polymer, it is possible to carry out emulsion polymerization in the presence of optionally at least one free radical chain transfer agent, and sulfur, nitrogen and / or phosphorus-containing free radical chain transfer agents having a solubility of water 5 g / 100 g or more in deionized water at 20 °C and 1 atm are particularly preferred. These are typically used to reduce or control the molecular weight of the polymer obtainable by free radical aqueous emulsion polymerization.

[0074] The sulfur-containing free radical chain transfer agents used are, for example, alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan and n-stearyl mercaptan, mercapto alkanols such as 2-mercaptoethanol, 2-mercaptopropanol or 3-mercaptopropanol, alkyl esters of thioglycolic acid such as 2-ethylhexyl thioglycolate, alkyl esters of 3-mercaptopropionic acid such as isooctyl mercaptopropionate, alkali metal bisulfites such as sodium bisulfite or potassium bisulfite, and thiosulfuric acid and its alkali metal salts, or 3-mercapto-2-aminopropionic acid (cysteine). The nitrogen-containing free radical chain transfer agents used are, for example, hydroxylamine (ammonium) compounds such as hydroxylammonium sulfate. The phosphorus-containing free radical chain transfer agents used are, for example, phosphorous acid, hypophosphorous acid, metaphosphoric acid, orthophosphoric acid, pyrophosphoric acid or polyphosphoric acid and their alkali metal salts, especially their sodium or potassium salts, preferably sodium hypophosphite or sodium dihydrogen phosphate, and thiuram compounds such as terpinolen.

[0075] Particularly preferably, the free radical chain transfer agent is selected from hypophosphorous acid and its alkali metal salts, especially sodium hypophosphite, alkali metal bisulfites, especially sodium bisulfite, hydroxylammonium sulfate and / or 2-mercaptoethanol, t-dodecyl mercaptan and terpinolen.

[0076] According to a preferred embodiment, the free radical chain transfer agent used in the polymerization is in an amount in the range of 1 part by weight or less, preferably in the range of 0.1 to 1 part by weight, preferably in the range of 0.2 to 0.8 part by weight, based on 100 parts by weight of all the monomers used in the polymerization.

[0077] To complete the polymerization reaction, in most cases, it is sufficient to stir the reaction mixture for an additional 0.2 to 3 hours at the polymerization temperature, for example, after adding all the monomers. At this point, typically, a conversion rate of about 95% has been achieved.

[0078] To further increase the conversion rate, for example, additional free radical initiators from the above-mentioned group of initiators can be added to the reaction mixture, or the addition can be extended, and a polymerization known as "post-polymerization", i.e., a polymerization that achieves a conversion rate of over 95% to a maximum of 99%, is possible.

[0079] Such post-polymerization can be carried out at the same temperature as the main polymerization, a lower temperature, or a higher temperature. For example, 0.1 to 1.5 parts by weight of an inorganic peroxide, preferably sodium peroxydisulfate, based on 100 parts by weight of the monomers used in the polymerization, is metered into this phase as an initiator, and the polymerization temperature is set to a temperature in the range of 70 to 95 °C.

[0080] During the polymerization, the pH can be, for example, between 1 and 5. After the completion of the polymerization at a conversion rate of over 95%, the pH is adjusted to a value between, for example, 6 and 7.

[0081] Furthermore, chemical deodorization can also be carried out. If trace amounts of residual monomers still need to be removed, this can also be done chemically by the action of a redox initiator system, as described in German Patent Application Publication No. 44 35 423, German Patent Application Publication No. 44 19 518, and German Patent Application Publication No. 44 35 422. Suitable oxidizing agents are, in particular, the above-mentioned organic and / or inorganic peroxides. Suitable reducing agents preferably include sodium bisulfite, sodium hydrogen sulfite, sodium dithionite, sodium hydroxymethanesulfinate, formamidine sulfinic acid, acetone bisulfite (= addition product of sodium hydrogen sulfite to acetone), ascorbic acid or reducing sugar compounds, or water-soluble mercaptans, such as mercaptoethanol.

[0082] The treatment with the redox initiator system is carried out in the temperature range of 60 to 100 °C, preferably 70 to 90 °C. The redox partners can each be added independently, wholly, partially, or continuously to the dispersion over a period of 10 minutes to 4 hours. To improve the post-polymerization action of the redox initiator system, soluble salts of metals with various valences, such as iron, copper, or vanadium salts, can be added to the dispersion. Complexing agents that keep the metal salts in solution under the reaction conditions are also frequently added.

[0083] Following the polymerization reaction (main polymerization + post-polymerization) and optional chemical deodorization, it may be necessary to make the aqueous polymer dispersion contain little to no odor carriers, such as residual monomers and other volatile organic components, which is also called physical deodorization. This can be achieved by physical means such as distillation removal (especially by steam distillation) or stripping with an inert gas, by methods known per se.

[0084] According to the present invention, the aqueous dispersion of polymer P is used as a polymer binder in the electrode slurry composition for the negative electrode of a secondary battery.

[0085] At least 8 N / mm 2 preferably in the range of 8 to 20 N / mm 2 and having a breaking stress in the range of at least 150% strain is preferred.

[0086] The present invention also relates to an electrode slurry composition for a negative electrode, comprising polymer P, a negative electrode active material, a conductive material, a binder, and a dispersion medium.

[0087] The proportion of polymer P in the electrode slurry composition for the negative electrode is in the range of 0.5 to 20% by weight, preferably 0.7 to 10% by weight, based on the electrode slurry composition for the negative electrode, both based on the solid content.

[0088] The negative electrode active material can be any material capable of intercalating lithium.

[0089] Preferred negative electrode active materials include silicon, silicon oxide, graphite, silicon-carbon composite materials, tin, lithium, aluminum, lithium titanate, and lithium silicon. Graphite, such as artificial graphite, natural graphite, and fibrous graphite, as well as silicon, silicon oxide, and silicon-carbon composite materials are particularly preferred.

[0090] The amount of the negative electrode active material in the electrode slurry composition for the negative electrode is in the range of 50 to 98% by weight, preferably 75 to 98% by weight, based on the electrode slurry composition for the negative electrode, both based on the solid content.

[0091] The conductive material can be any one selected from the group consisting of carbon black, acetylene black, carbon fiber, multi-walled carbon nanotubes, single-walled carbon nanotubes, ketjen black, and mixtures thereof.

[0092] The amount of the conductive material in the electrode slurry composition for the negative electrode is in the range of 0.01% to 20% by weight, preferably 0.02% to 10% by weight, based on the electrode slurry composition for the negative electrode, both based on the solid content.

[0093] The binder can be any one water-soluble polymer selected from the group consisting of methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, hydroxyalkyl methyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl pyridine, polyacrylonitrile, polyethylene oxide, and mixtures thereof. Preferred binders are selected from the group consisting of methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, and hydroxyalkyl methyl cellulose.

[0094] The amount of the binder ranges from 0.5% to 20% by weight, preferably from 0.7% to 5% by weight (both calculated as solids) of the electrode slurry composition for the negative electrode.

[0095] The dispersion medium can be any one selected from the group consisting of acetone, dimethylformamide, N-methyl-2-pyrrolidone, tetrahydrofuran, isopropanol, ethanol, methanol, and water, and mixtures thereof. Water is preferred as the dispersion medium. The amount of the dispersion medium in the negative electrode active material containing the slurry ranges from 20% to 70% by weight, preferably from 30% to 60% by weight.

[0096] Based on 100% by weight of the solid content of the electrode slurry composition for the negative electrode and the dispersion medium, 0.5 to 20% by weight of polymer P, 50 to 98% by weight of the negative electrode active material, 0.01 to 20% by weight of the conductive material, 0.5 to 20% by weight of the binder The electrode slurry composition for the negative electrode containing is preferred.

[0097] Also, according to another aspect of the present disclosure, a negative electrode is provided that includes a current collector and a negative electrode active material composition layer formed by coating the above-described electrode slurry on one or both sides of the current collector, for example, by slot die, dipping, reverse roll, direct roll, gravure, extrusion, doctor blade, immersion, brushing, or dipping, and then drying.

[0098] Non-limiting examples of the current collector can include foils obtained from copper, gold, nickel, aluminum, copper-containing alloys, or combinations thereof.

[0099] The present invention also relates to a method for preparing a negative electrode of a secondary battery, (a) combining an aqueous dispersion of polymer P, a negative electrode active material, a conductive material, a binder, and a dispersion medium to form an electrode slurry composition; (b) preparing a current collector; (c) coating the current collector with the electrode slurry composition; (d) drying the coated current collector; (e) optionally shaping the dried coated current collector and a method comprising the steps of.

[0100] Drying may include one or more drying steps performed in a temperature range of 20 to 300 ° C, preferably 50 to 150 ° C. By the drying step, the dispersion medium is removed. This is usually dried until weight constancy is achieved.

[0101] Preferably, the dried coated current collector is shaped. Shaping is performed according to conventional methods known in the art. Non-limiting examples of shaping devices are calenders or pressing devices.

[0102] As used herein, "shaped current collector" means a shaped, dried coated current collector having pores inside. The shaped current collector preferably has a porosity of 10 to 60%. Since the expansion and contraction of the negative electrode active material during charge and discharge can be absorbed and reduced, the negative electrode can thereby reliably maintain its shape. More preferably, the porosity is 30 to 50%. The porosity can be controlled by changing the manufacturing conditions of the shaped current collector. For example, when manufacturing a shaped current collector by applying pressure to a dried coated current collector, the compression force can be adjusted to control the porosity. The porosity is the volume V determined from the size of the obtained shaped article 1 and the absolute volume V of the shaped article 0 and can be calculated using, { (V 1 -V 0 ) / V 1} x 100 (%).

[0103] The coating weight of the dry electrode slurry composition for the negative electrode is 10 g / m 2 foil for current collector ~ 300 g / m 2The foil for a current collector, preferably 25 g / m 2 The foil for a current collector ~ 200 g / m 2 is within the range of the foil for a current collector.

[0104] The present invention also relates to a negative electrode of a secondary battery, which is formed by applying an electrode slurry composition for a negative electrode onto a current collector and drying the negative electrode slurry composition. The present invention also relates to a lithium-ion secondary battery including the negative electrode of the secondary battery.

[0105] The positive electrode applied to the secondary battery is not particularly limited and can be manufactured by binding a positive electrode active material to a current collector according to a conventional method known in the art.

[0106] As the positive electrode active material, those generally used for the positive electrode of a secondary battery can be used. Non-limiting examples of the positive electrode active material may include lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, and combinations thereof. Also, non-limiting examples of the current collector for the positive electrode may include foils obtained from iron, aluminum, copper, nickel, or combinations thereof. Such positive electrode active materials are described, for example, in Pamphlet of International Publication No. 2021 / 078626.

[0107] As the separator that can be used in the secondary battery, any one conventionally used in the art can be mentioned, for example, a porous membrane or non-woven fabric made of a polyolefin-based polymer, which is described, for example, on page 10 of the Pamphlet of International Publication No. 2021 / 078626. The separator preferably has a thickness of 5 to 50 μm, but is not limited thereto. Also, the separator has a pore diameter of 30 to 750 nm and a porosity of 10 to 95%, but is not particularly limited thereto.

[0108] In order to improve the mechanical strength of the separator and the safety of the secondary battery, a porous coating layer containing inorganic particles and a polymer binder may be further formed on at least one surface of the separator. The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, in the operating voltage range of the applied secondary battery (for example, 0 to 5 V based on Li / Li + ), no redox reaction occurs.

[0109] Furthermore, a secondary battery is provided that includes a positive electrode, a negative electrode according to the present invention, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. In particular, among the numerous secondary batteries, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferred.

[0110] Assembly can be performed by laminating, stacking or folding the separator and the electrodes, and a winding process. The obtained assembly is rounded or bent according to the shape of the battery, placed in a battery container, an electrolyte is injected into the battery container, and the battery container is sealed. Also, the secondary battery is not limited to its shape. For example, the shape of the battery may be coin, button or pouch, cylindrical, square prism or flat. Also, the secondary battery is not limited to its shape.

[0111] The electrolyte used in the present disclosure contains a lithium salt as an electrolyte salt. The lithium salt can be any one of those conventionally used in electrolytes for lithium secondary batteries. Examples of suitable lithium salts are LiPF 6 、LiBF 4 、LiClO 4 、LiAsF 6 、LiCF 3 SO 3 、LiC(C n F 2n+1 SO 2 ) 3 、lithium imide, for example LiN(C n F 2n+1 SO 2 ) 2(wherein n is an integer in the range of 1 to 20), LiN(SO 2 F) 2 , Li 2 SiF 6 , LiSbF 6 , LiAlCl 4 , and salts of the general formula (C n F 2n+1 SO 2 ) t YLi (wherein m is defined as follows: when Y is selected from oxygen and sulfur, t = 1, when Y is selected from nitrogen and phosphorus, t = 2 when Y is selected from carbon and silicon, t = 3).

[0112] Preferred electrolyte salts are LiC(CF 3 SO 2 ) 3 , LiN(CF 3 SO 2 ) 2 , LiPF 6 , LiBF 4 , LiClO 4 , and are selected from LiPF 6 and LiN(CF 3 SO 2 ) 2 are particularly preferred.

[0113] The electrolytic solution used in the present disclosure contains an organic solvent conventionally used in the electrolytic solution for lithium secondary batteries. For example, the solvent for the electrolyte can be liquid or solid at room temperature, and is preferably selected from cyclic or acyclic ethers, cyclic and acyclic acetals, and cyclic or acyclic organic carbonates.

[0114] Furthermore, the electrolytic solution may contain a thickening agent, such as a polyalkylene glycol, preferably a poly-C 1 ~C 4 -alkylene glycol, particularly polyethylene glycol. Polyethylene glycol, herein, has up to 20 mol% of one or more C 1 ~C 4- It can contain alkylene glycol. The polyalkylene glycol is preferably a polyalkylene glycol having two methyl or ethyl end caps.

[0115] The molecular weight M of a suitable polyalkylene glycol, particularly a suitable polyethylene glycol w can be at least 400 g / mol. The molecular weight M of a suitable polyalkylene glycol, particularly a suitable polyethylene glycol w can be at most 5000000 g / mol, preferably at most 2000000 g / mol.

[0116] Examples of suitable acyclic ethers are, for example, diisopropyl ether, di-n-butyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, with 1,2-dimethoxyethane being preferred.

[0117] Examples of suitable cyclic ethers are tetrahydrofuran and 1,4-dioxane.

[0118] Examples of suitable acyclic acetals are, for example, dimethoxymethane, diethoxymethane, 1,1-dimethoxyethane, and 1,1-diethoxyethane.

[0119] Examples of suitable cyclic acetals are 1,3-dioxane, particularly 1,3-dioxolane.

[0120] Examples of suitable acyclic organic carbonates are dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0121] Examples of suitable cyclic organic carbonates are the compounds according to general formulas (II) and (III)

Chemical formula

[0122] In a particularly preferred embodiment, R 1 is methyl, R 2 and R 3 are each hydrogen, or R 1 , R 2 and R 3 are each hydrogen.

[0123] Another preferred cyclic organic carbonate is vinylene carbonate of formula (IV).

Chemical formula

[0124] The solvent is preferably used in a water-free state, that is, with a water content in the range of 1 ppm to 0.1% by weight, which can be determined, for example, by Karl Fischer titration.

[0125] The polymer P according to the present invention has high adhesiveness to the surface of the negative electrode active material, the solid electrolyte interface (SEI) formed on the negative electrode active material during the first charge, and similarly to the copper foil as the current collector. Furthermore, the polymer P as a binder maintains the adhesion between the negative electrode active material and the current collector during the charge and discharge cycles of the cell. Charge and discharge are performed by the intercalation and deintercalation of lithium, which cause expansion and contraction of the volume of the negative electrode active material. As a result, the adhesiveness of the polymer binder during repeated charge and discharge cycles may weaken, thereby possibly damaging the conductive structure of the electrochemical device. Consequently, the charge and discharge characteristics and the life characteristics, such as the cell capacity, deteriorate.

[0126] The battery according to the present invention exhibits good discharge behavior, very good discharge and cycle behavior, for example, at low temperatures (0 °C or lower, for example, -10 °C or lower).

[0127] The battery according to the present invention can comprise two or more electrochemical cells combined with each other, which may be connected in series or in parallel, for example. Series connection is preferred. In the battery according to the present invention, at least one of the electrochemical cells contains at least one negative electrode according to the present invention. Preferably, in the electrochemical cell according to the present invention, most of the electrochemical cell contains the negative electrode according to the present invention. Even more preferably, in the battery according to the present invention, all the electrochemical cells contain the negative electrode according to the present invention.

[0128] The present invention further relates to the use of the battery according to the present invention in devices, particularly mobile devices. Examples of mobile devices are vehicles, such as automobiles, bicycles, aircraft, or water vehicles, such as boats or ships. Other examples of mobile devices are those that move manually, such as computers, particularly laptops, telephones, or power tools, such as those in the construction sector, particularly drills, battery-powered screwdrivers, or battery-powered staplers.

Mode for Carrying Out the Invention

[0129] Examples Unless the context indicates otherwise, percentages always indicate weight percentages. The reported contents relate to the contents in aqueous solutions or dispersions. The indication pphm (parts per 100 parts of monomer) indicates the weight ratio based on 100 parts by weight of the monomer.

[0130] When water is used in the context of the examples, deionized water was used. Measurement methods Particle size: Analytical ultracentrifuge (AUC)

[0131] The diameter and also the particle size distribution of the particles in the polymer dispersion were determined using an analytical ultracentrifuge (AUC) with a turbidity-based optical system and Mie correction of the transmission intensity per size. In turbidity detection, all components with diameters from 30 nm to 5 μm are measured.

[0132] This method uses uniform starting sedimentation. This method is carried out according to the guidelines of ISO 13318-1, and the specific settings are described in W. Machtle, L. Borger, "Analytical Ultracentrifugation of Polymers and Nanoparticles", Chapter 3, Springer Science and Business Media, Berlin 2006. The evaluation starts from the spherical solid particle form with a skeletal density determined by the comonomer composition. The results are reported on a volume measurement basis with the equivalent spherical diameter.

[0133] For the measurement, the dispersion is diluted to a concentration of 4 g (solids) / liter with an aqueous surfactant solution of 0.05 wt% and subjected to measurement under the same conditions. The weight fraction of the particle population is directly obtained from the integration of the measured values.

[0134] Hydrodynamic chromatography (HDC) Also, the diameter and particle size distribution of the particles in the polymer dispersion were determined using hydrodynamic chromatography (HDC). HDC is a liquid chromatography technique that separates analytes based on their size in solution. Measurements were carried out using a PL-PSDA particle size distribution measuring device (Polymer Laboratories, Inc.). A small sample of the polymer latex was injected into an aqueous eluent containing an emulsifier to obtain a concentration of about 0.5 g / l. The mixture was pumped through a glass capillary tube with a diameter of about 15 mm filled with polystyrene spheres. Smaller particles can sterically access regions of slower flow within the capillary so that, on average, smaller particles receive a slower elution flow as determined by the hydrodynamic diameter. Finally, the fractions were monitored using a UV detector that measures absorbance at a fixed wavelength of 254 nm.

[0135] Solids content: The solids content of the polymer dispersion was determined by dispensing 0.5 - 1.5 g of the polymer dispersion onto a metal lid with a diameter of 4 cm, and then drying it in a forced-air drying cabinet at 140 °C for 30 minutes. The solids content of the polymer dispersion was obtained by the ratio of the mass of the sample after drying under the above conditions to the mass at the time of sampling.

[0136] Glass transition temperature T g The glass transition temperature was determined in accordance with DIN 53765 using a DSC820 instrument of the TA8000 series manufactured by Mettler-Toledo Int. Inc.

[0137] The starting materials used in the examples were as follows: Emulsifier A: Sodium lauryl sulfate (Disponil® SDS manufactured by BASF) as a 15 wt% solution Emulsifier B: Sodium dodecyl diphenyloxide disulfonate 45 wt% Complexing agent: EDTA (Trilon® BX manufactured by BASF) as a 2 wt% solution Seed latex: Polystyrene seed in the form of a 29.7 wt% dispersion with a particle size of 30 nm (determined by an analytical ultracentrifuge) Initiator A: 7 wt% solution of sodium peroxodisulfate (NaPS) Initiator B: 10 wt% solution of tert-butyl hydroperoxide Reducing agent: 13 wt% solution of acetone bisulfite

[0138] Unless otherwise specified, water was deionized water. In all examples, the feeds were metered at a uniform volumetric flow rate.

[0139] Preparation of emulsion polymer The following amounts in pphm (parts per 100 parts of monomer) are based on 100 parts by weight of the total monomers.

[0140] Example 1 - Binder 1 Initial charge: 339.56 g of water 14.48 g (0.20 pphm) of a 29.7 wt% dispersion of polystyrene latex with an average particle size of 30 nm 3.01 g (0.14 pphm) of acrylic acid 184.29 g (0.6 pphm) of a 7 wt% aqueous solution of itaconic acid 32.25 g (0.03 pphm) of a 2 wt% solution of EDTA (complexing agent) 2.15 g (0.05 pphm) of a 50 wt% solution of acrylamide 1.43 g (0.01 pphm) of a 15 wt% solution of sodium lauryl sulfate (emulsifier A) 4.30 g (0.09 pphm) of 45 wt% sodium dodecyl diphenyloxide disulfonate (emulsifier B) 43.00 g (2.0 pphm) of styrene 21.50 g (1.0 pphm) of butadiene Addition 1: 61.43 g (0.20 pphm) of a 7 wt% solution of sodium peroxodisulfate (initiator A) Feed 1: 55.04 g (1.28 pphm) of a 50 wt% solution of acrylamide 34.40 g (0.24 pphm) of a 15 wt% solution of sodium lauryl sulfate 24.84 g (0.52 pphm) of 45 wt% sodium dodecyl diphenyloxide disulfonate (emulsifier B) 35.83 g (0.25 pphm) of a 15 wt% sodium hydroxide solution 715.72 ml of water Feed 2: 71.81 g (3.34 pphm) of acrylic acid 1070.27 g (49.78 pphm) of styrene 107.5 g (5.0 pphm) of acrylonitrile 8.60 g (0.4 pphm) of tert-dodecyl mercaptan Feed 3: Butadiene 791.42 g (36.81 pphm) Feed 4: 7 wt% solution of sodium peroxydisulfate 251.86 g (0.82 pphm) Feed 5: 10 wt% solution of tert-butyl hydroperoxide (Initiator B) 75.25 g (0.35 pphm) Feed 6: 13.1 wt% solution of acetone bisulfite 80.82 g (0.53 pphm) Feed 7: 15 wt% sodium hydroxide solution 104.63 g (0.73 pphm)

[0141] The initial charge components were charged into a 6 l pressure reactor and mixed. The initial charge was heated to 85 °C. When 85 °C was reached, Initiator A (Addition 1) was added over 5 minutes to initiate polymerization. The mixture was stirred for an additional 5 minutes.

[0142] Immediately thereafter, Feeds 1, 2, 3 and 4 were started (time: 0 minutes), and the temperature was continuously decreased to 80 °C over 20 minutes. Feeds 1, 2 and 4 were carried out over 6 hours. Feed 3 was carried out over 5 hours 30 minutes.

[0143] After the metered addition of Feeds 1, 2 and 4 was completed, the polymerization mixture was stirred for an additional 30 minutes. Thereafter, 308.1 ml (14.33 pphm) of water was added.

[0144] Thereafter, Feeds 5 and 6 were started and carried out over 90 minutes. Feed 7 was started 15 minutes before the end of Feeds 5 and 6 and carried out over 15 minutes. After the end of Feeds 5, 6 and 7, the polymerization mixture was cooled to room temperature.

[0145] The solids content of the dispersion was 50.5 wt%. The glass transition temperature T g of the dispersion polymer was 7.2 °C.

[0146] The polymer dispersion was analyzed using HDC: Particle size distribution: peak maximum at 268 nm with tailing.

[0147] Examples 2 - 10, Binders 2 - 10 Similar to Example 1, additional dispersions were prepared with the monomer compositions shown in Table 1.

[0148] Example 2 - Binder 2 (not according to the present invention) Emulsion polymerization was carried out in the same manner as in Example 1 of the present invention, except that Feed 2 did not contain acrylonitrile and instead the styrene content of Feed 2 was increased.

[0149] The solids content of the dispersion was 50.5 wt%. The glass transition temperature T of the dispersion polymer g was 2 °C.

[0150] The polymer dispersion was analyzed using HDC: Bimodal particle size distribution: The population of "smaller" particles had a peak maximum at 271 nm. The fraction as a percentage of the total polymer was 96 wt%.

[0151] The population of "larger" particles had a peak maximum at 468 nm. The fraction as a percentage of the total polymer was 4 wt%.

[0152] Example 4 - Binder 4 (according to the present invention) Emulsion polymerization was carried out in the same manner as in Example 1 of the present invention, except that Feed 1 contained 143.33 g (1.0 pphm) of a 15 wt% solution of N - methylolmethacrylamide and instead the styrene content of Feed 2 was decreased. Further, the amount of water in Feed 1 was decreased to 593.89 ml.

[0153] The solids content of the dispersion was 50.5 wt%. The glass transition temperature T of the dispersion polymer g was 6.6 °C.

[0154] The polymer dispersion was analyzed using HDC: Bimodal particle size distribution: The particle population of "smaller" particles had a peak maximum at 265 nm. The fraction as a percentage of the total polymer was 80 wt%.

[0155] The particle population of "larger" particles had a peak maximum at 484 nm. The fraction as a percentage of the total polymer was 20 wt%.

[0156] Example 6 - Binder 6 (According to the present invention) Emulsion polymerization was carried out in the same manner as in Example 1 of the present invention, except that Feed 1 contained 430.00 g (3.0 pphm) of a 15 wt% solution of N-methylolmethacrylamide, and instead, the styrene content of Feed 2 was reduced by about 1.5 pphm and the butadiene content was reduced by about 1.5 pphm. Further, the amount of water in Feed 1 was reduced to 350.22 ml.

[0157] The solids content of the dispersion was 50.5 wt%. The glass transition temperature T g of the dispersion polymer was 10 °C.

[0158] The polymer dispersion was analyzed using an analytical ultracentrifuge: Bimodal particle size distribution: The particle population of "smaller" particles had a peak maximum at 260 nm. The fraction as a percentage of the total polymer was 50 wt%.

[0159] The particle population of "larger" particles had a peak maximum at 490 nm. The fraction as a percentage of the total polymer was 50 wt%.

[0160] Example 7 - Binder 7 (According to the present invention) This was polymerized in the same manner as in Example 1, except that the polymerization was carried out at 90 °C. The solids content of the dispersion was 50.5 wt%. The glass transition temperature T g of the dispersion polymer was 13.5 °C.

[0161] The polymer dispersion was analyzed using HDC: Particle size distribution: peak maximum at 215 nm with tailing.

[0162] Example 8 - Binder 8 (according to the present invention) This was polymerized in the same manner as in Example 1, except that the polymerization was carried out at 95 °C.

[0163] The solids content of the dispersion was 50.5% by weight. The glass transition temperature T of the dispersion polymer g was 15.7 °C.

[0164] The polymer dispersion was analyzed using HDC: Particle size distribution: peak maximum at 188 nm with tailing.

[0165] Example 9 - Binder 9 (according to the present invention) Emulsion polymerization was carried out in the same manner as in Example 1 of the present invention, except that Feed 1 contained 71.67 g (0.5 pphm) of a 15% by weight solution of N-methylolmethacrylamide and instead the styrene content of Feed 2 was decreased. Further, the amount of water in Feed 1 was decreased to 660.60 ml.

[0166] The solids content of the dispersion was 50.5% by weight. The glass transition temperature T of the dispersion polymer g was 8.4 °C.

[0167] The polymer dispersion was analyzed using HDC: Particle size distribution: peak maximum at 240 nm with tailing.

[0168] Example 10 - Binder 10 (according to the present invention) Emulsion polymerization was carried out in the same manner as in Example 1 of the present invention, except that Feed 1 contained 215 g (1.5 pphm) of a 15% by weight solution of N-methylolmethacrylamide and instead the styrene content of Feed 2 was decreased. Further, the amount of water in Feed 1 was decreased to 538.77 ml.

[0169] The solid content of the dispersion was 50.5% by weight. The glass transition temperature T of the dispersion polymer g was 7.4 °C.

[0170] The polymer dispersion was analyzed using HDC: Bimodal particle size distribution: The particle population of "smaller" particles had a peak maximum at 281 nm. The fraction as a percentage of the total polymer was 88% by weight.

[0171] The particle population of "larger" particles had a peak maximum at 435 nm. The fraction as a percentage of the total polymer was 12% by weight.

[0172] Example 12 - Binder 12 (not according to the present invention) Emulsion polymerization was carried out in the same manner as in Example 1 of the present invention, except that the polymer composition and the amount of free radical chain transfer agent were the same as those in Example 1 of European Patent No. 2869372: styrene 61.91 pphm, butadiene 33.33 pphm, itaconic acid 3.81 pphm, 2-hydroxyethyl acrylate 0.95 pphm, and tert-dodecyl mercaptan 0.3 pphm.

[0173] Initial charge: Water 310.38 g 29.7% by weight dispersion of polystyrene latex with an average particle size of 30 nm 13.47 g (0.20 pphm) 2% by weight solution of EDTA (complexing agent) 30.00 g (0.03 pphm) 15% by weight solution of sodium lauryl sulfate (emulsifier A) 1.33 g (0.01 pphm) 45% by weight sodium dodecyl diphenyloxide disulfonate (emulsifier B) 4.00 g (0.09 pphm) Styrene 40.00 g (2.0 pphm) Butadiene 20.50 g (1.0 pphm) Addition 1: 57.14 g (0.20 pphm) of a 7 wt% solution of sodium peroxydisulfate (Initiator A) Feed 1: 32.00 g (0.24 pphm) of a 15 wt% solution of sodium lauryl sulfate 23.11 g (0.52 pphm) of 45 wt% sodium dodecyl diphenyloxide disulfonate (Emulsifier B) 33.33 g (0.25 pphm) of a 15 wt% sodium hydroxide solution 1088.57 g (3.81 pphm) of a 7 wt% aqueous solution of itaconic acid Feed 2: 71.81 g (0.95 pphm) of 2-hydroxyethyl acrylate 1198.16 g (59.91 pphm) of styrene 6.00 g (0.3 pphm) of tert-dodecyl mercaptan Feed 3: 646.6 g (32.33 pphm) of butadiene Feed 4: 234.29 g (0.82 pphm) of a 7 wt% solution of sodium peroxydisulfate Feed 5: 70.00 g (0.35 pphm) of a 10 wt% solution of tert-butyl hydroperoxide (Initiator B) Feed 6: 75.18 g (0.53 pphm) of a 13.1 wt% solution of acetone bisulfite Feed 7: 97.33 g (0.73 pphm) of a 15 wt% sodium hydroxide solution

[0174] The initial charge components were charged into a 6 l pressure reactor and mixed. The initial charge was heated to 85 °C. Once 85 °C was reached, Initiator A (Addition 1) was added over 5 minutes to initiate polymerization. The mixture was stirred for an additional 5 minutes.

[0175] Immediately thereafter, feeds 1, 2, 3, and 4 were started (time: 0 minutes), and the temperature was continuously decreased to 80 °C over 20 minutes. Feeds 1, 2, and 4 were carried out for 6 hours. Feed 3 was carried out for 5 hours and 30 minutes.

[0176] After the metered addition of feeds 1, 2, and 4 was completed, the polymerization mixture was stirred for an additional 30 minutes. Thereafter, 287 ml (14.33 pphm) of water was added.

[0177] Thereafter, feeds 5 and 6 were started and carried out for 90 minutes. Feed 7 was started 15 minutes before the end of feeds 5 and 6 and carried out for 15 minutes. After the completion of feeds 5, 6, and 7, the polymerization mixture was cooled to room temperature.

[0178] The solids content of the dispersion was 48.5 wt%. The glass transition temperature T of the dispersion polymer g was 9 °C.

[0179] The polymer dispersion was analyzed using HDC: Particle size distribution: Peak maximum of 217 nm showing a shoulder in the lower nm range.

[0180] Example 13 - Binder 13 (not according to the present invention) Emulsion polymerization was carried out in the same manner as in Comparative Example 1, except that Feed 2 contained 100 g (5 pphm) of acrylonitrile and instead the styrene content of Feed 2 was decreased.

[0181] The solids content of the dispersion was 48.5 wt%. The glass transition temperature T of the dispersion polymer g was 15 °C.

[0182] The polymer dispersion was analyzed using HDC: Particle size distribution: Peak maximum of 199 nm showing a shoulder in the lower nm range.

[0183]

Table 1

[0184] Manufacture of Polymer Film By pouring the dispersion into a silicone mold, a film with a theoretical thickness of 0.5 mm was manufactured. The film was dried and peeled off at room temperature for 18 hours. The taken-out film was dried in a drying oven at 60 °C for 2 hours. Then, the film was stored at 40 °C for 2 hours and at 70 °C for 2 hours.

[0185] For electrolyte immersion, by pouring the dispersion into a silicone mold, a film with a theoretical thickness of 0.5 mm was manufactured. The film was dried and peeled off at room temperature for 18 hours. The taken-out film was dried in a drying oven at 60 °C for 2 hours. Then, the film was stored at 40 °C for 2 hours, at 70 °C for 2 hours, and finally in LP57 electrolyte (1 M LiPF6 ethylene carbonate: ethyl methyl carbonate, 3:7) at 70 °C for 3 days.

[0186] Evaluation of Mechanical Properties of Polymer Film Breaking Stress and Elongation at Break (Stress / Strain Measurement) The polymer film was characterized by a quasi-static tensile test until polymer failure.

[0187] Sample Preparation: Test pieces were prepared from the obtained polymer film by a punching process. For punching, a shoulder rod shape with a length of 75 mm was used for the test piece geometry according to DIN 53504. A dumbbell shape with a size of 75 mm × 4 mm was used (according to DIN 54504S2). The thickness of the test piece was obtained from the average value of three measurements. Then, the test pieces were tested in a climatic chamber at 23 °C and 50% relative air humidity and stored for 15 hours.

[0188] Execution of Test: The tensile test was carried out on a Zwick Type 110846 testing machine. The test piece was fixed to the machine so that the test track was 40 mm. The pulling speed was 200 mm / min. The values of stress and strain were output by the testing machine.

[0189]

Table 2

[0190] Good stress values after electrolyte impregnation show retention of at least 60% of the initial value.

[0191] According to the present invention, the binder polymer shows good stress / strain behavior. These maintain high stress values even after electrolyte impregnation.

[0192] Manufacture of the negative electrode slurry Components used: Texturecell (trademark) 2000 PA 07, a granular carboxymethyl-cellulose (CMC) from IFF (average molecular weight 450 - 500 kmol / g, viscosity of 2% aqueous solution 2000 mPas and degree of substitution 0.7) Timcal Super C65 carbon black from Imerys (BET = 62 m 2 / g) Synthetic graphite SMG A5 from Showa Denko (particle size D10 = 7.6 μm, D50 = 18.5 μm, D90 = 33.5 μm, BET = 3.0 m 2 / g, Silicon monoxide KSC 1265 from Shin-Etsu (Japan) (non-lithium-doped SiOx type particle size D10 = 4.1 μm, D50 = 6.5 μm, D90 = 9.3 μm

[0193] An aqueous solution of 2 wt% carboxymethyl cellulose was prepared and stored for 24 hours.

[0194] To prepare the anode slurry, this 2 wt% carboxymethyl cellulose solution was prepared, degassed several times while applying a light vacuum (300 mbar), and stirred at 2000 rpm for 30 minutes using a dissolution stirrer. Then, soot was added, a slight vacuum was applied again (300 mbar), and it was dispersed at a speed of 3500 rpm. Then, graphite for four batches was added first, and then SiOx for four batches was added. After adding the solids, a light vacuum (300 mbar) was applied for dispersion (speed 3500 rpm). Next, the polymer dispersion of each example was stirred at 500 rpm for 10 minutes, and then stirred at 150 rpm for 10 minutes during the degassing process (300 mbar vacuum). Finally, the solid content was set to a value in the range of 48 - 50%.

[0195]

Table 3

[0196] Preparation of the silicon-containing anode according to the present invention Each anode slurry was applied to a single-piece (250 mm × 150 mm) copper sheet (manufacturer, thickness: 10 μm) using a doctor blade with a gap dimension of 250 μm. Then, the coated anode was dried at 60°C for 2 minutes and at 120°C for 1 minute. Then, the coated copper sheet was calendared to a density of 1.45 g / cm 3 (target density).

[0197] Finally, the coated copper sheet was stored in a climate chamber at 23°C and 50% humidity for 24 hours, and then mechanically characterized.

[0198] Mechanical property evaluation of the silicon-containing anode by 90° peel test Preparation of test pieces: The coated copper sheet was cut into strips with a width of 25 mm and a length of 150 mm. HDPE test pieces (20 × 3 cm 2( ) was used as the carrier material. A double-sided adhesive tape was attached to the carrier material. The coated negative electrode strip was placed on the adhesive strip of the coated surface and pressed bubble-free using a rubber roller (ineffective). Then, the layers were joined to each other in a defined manner by rotating a 2 kg hand roller twice without force on the composite material. The test piece thus produced was stored in a climate chamber at 23 °C and 50% humidity for 24 hours.

[0199] The test is carried out with a Zwick tearing machine.

[0200] Test parameters: Device: Zwick tearing machine Trigger angle: 90° Measurement speed: 50 mm / min Preload: 0.1 N Clamp length: 20 mm Measurement distance: 60 mm Evaluation: 10 - 50 mm Evaluation N / m

[0201]

Table 4

[0202] The coating with the binder according to the present invention has a peel strength of 15 N / m or more.

Claims

1. Use of an aqueous dispersion of a polymer P obtainable by radical-initiated emulsion polymerization, which comprises a step of polymerizing, at a polymerization temperature in the range of 70 to 95°C, monomers (a) to (f) in a total amount of 100 parts by weight, as a polymer binder in an electrode slurry composition for a negative electrode of a secondary battery, wherein: (a) 40 to 75 parts by weight of at least one vinyl aromatic compound; and (b) 22.5 to 55 parts by weight of at least one conjugated aliphatic diene; and and and and and Use of an aqueous dispersion of a polymer P obtainable by radical-initiated emulsion polymerization, which comprises a step of polymerizing, at a polymerization temperature in the range of 70 to 95°C, monomers (a) to (f) in a total amount of 100 parts by weight, as a polymer binder in an electrode slurry composition for a negative electrode of a secondary battery, wherein:

2. The use according to claim 1, wherein the monomer (e) is selected from the group consisting of N-methylolacrylamide and N-methylolmethacrylamide.

3. The polymer P is obtainable by radical-initiated emulsion polymerization, which comprises a step of polymerizing monomers (a) to (f) in a total amount of 100 parts by weight, wherein: and and and and andand and and The use according to claim 1 or 2, wherein the polymer P is obtainable by radical-initiated emulsion polymerization, which comprises a step of polymerizing monomers (a) to (f) in a total amount of 100 parts by weight, wherein:

4. The use according to any one of claims 1 to 3, wherein the polymer P is obtainable by radical-initiated emulsion polymerization, which comprises a step of polymerizing at a polymerization temperature in the range of 75 to 90°C.

5. The use according to any one of claims 1 to 4, wherein the polymer P is obtainable by radical-initiated emulsion polymerization, which comprises a step of polymerizing in the presence of a seed latex.

6. ​ The use according to any one of claims 1 to 5, which can be obtained by radical-initiated emulsion polymerization, wherein the polymer P is polymerized in the presence of a free radical chain transfer agent of 1 part by weight or less based on 100 parts by weight of all monomers.

7. As described in this specification, the polymer P has a breaking stress of at least 8 N / mm ２ and a strain of at least 150%, and is used according to any one of claims 1 to 6.

8. An electrode slurry composition for a negative electrode, comprising the polymer P according to any one of claims 1 to 7, a negative electrode active material, a conductive material, a binder, and a dispersion medium.

9. Based on 100% by weight of the solid content of the electrode slurry composition for a negative electrode, the dispersion medium, 0.5 to 20% by weight of the polymer P, 50 to 98% by weight of the negative electrode active material, 0.01 to 20% by weight of the conductive material, 0.5 to 20% by weight of the binder The electrode slurry composition for a negative electrode according to claim 8.

10. A method for preparing a negative electrode of a secondary battery, comprising: (a) combining an aqueous dispersion of the polymer P according to any one of claims 1 to 7, the negative electrode active material, the conductive material, the binder, and the dispersion medium to form an electrode slurry composition; (b) preparing a current collector; (c) coating the current collector with the electrode slurry composition; (d) drying the coated current collector; (e) optionally shaping the coated current collector A method comprising.

11. A negative electrode of a secondary battery, formed by applying the electrode slurry composition for a negative electrode according to claim 8 or 9 onto a current collector and drying the negative electrode slurry composition.

12. A lithium ion secondary battery comprising the negative electrode of the secondary battery according to claim 9.

13. The total amount of monomers (a) to (f) is 100 parts by weight. (a) 40 to 75 parts by weight of at least one vinyl aromatic compound; (b) 22.5 to 55 parts by weight of at least one conjugated aliphatic diene; (c) 0.5 to 10 parts by weight of at least one ethylenically unsaturated monomer containing an acid group; (d1) 1 to 5 parts by weight of acrylamide and / or methacrylamide; (d2) 1 to 10 parts by weight of acrylonitrile and / or methacrylonitrile; (e) 0 to 5 parts by weight of at least one monoethylenically unsaturated monomer having at least one epoxy group, hydroxyl group, N-methylol group, or carbonyl group; (f) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer An aqueous dispersion of polymer P according to any one of claims 1 to 7, which can be obtained by radical-initiated aqueous emulsion polymerization and includes a step of polymerizing at a polymerization temperature in the range of 70 to 95 °C.

14. In an aqueous medium, the total amount of monomers (a) to (f) is 100 parts by weight. (a) 40 to 75 parts by weight of at least one vinyl aromatic compound, (b) 22.5 to 55 parts by weight of at least one conjugated aliphatic diene, (c) 0.5 to 10 parts by weight of at least one ethylenically unsaturated monomer containing an acid group, (d1) 1 to 5 parts by weight of acrylamide and / or methacrylamide, (d2) 1 to 10 parts by weight of acrylonitrile and / or methacrylonitrile, (e) 0 to 5 parts by weight of a monoethylenically unsaturated monomer having at least one epoxy group, hydroxyl group, N-methylol group, or carbonyl group, (f) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer A method for producing an aqueous dispersion of polymer P according to any one of claims 1 to 7 by radical-initiated aqueous emulsion polymerization, which includes a step of radical polymerizing at a polymerization temperature in the range of 70 to 95 °C.

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