Electrode binder polymer, electrode binder composition, electrode slurry, electrode, nonaqueous secondary battery, method for producing electrode binder polymer, method for producing electrode binder composition, method for producing electrode slurry, and method for producing electrode

Abstract

This invention contains 10 mol% to 50 mol% of the first structural unit (-CH2CR). 1 (CONR) 2 R 3 ) -), 25 mol% to 80 mol% of the second structural unit (-CH2CR) 4 (COOX)-), and 1.0 mol% to 45 mol% of the third structural unit (-CH2CR) 5 (C≡N)-), and the weight-average molecular weight is over 1.5 million.

Description

Technical Field

[0001] This disclosure relates to electrode binder polymers for non-aqueous secondary batteries, electrode binder compositions for non-aqueous secondary batteries, electrode slurries for non-aqueous secondary batteries, electrodes for non-aqueous secondary batteries, non-aqueous secondary batteries, methods for manufacturing electrode binder polymers for non-aqueous secondary batteries, methods for manufacturing electrode binder compositions for non-aqueous secondary batteries, methods for manufacturing electrode slurries for non-aqueous secondary batteries, and methods for manufacturing electrodes for non-aqueous secondary batteries. Background Technology

[0002] Secondary batteries using non-aqueous electrolytes (non-aqueous secondary batteries) offer advantages over those using aqueous electrolytes in terms of higher voltage, miniaturization, and weight reduction. Therefore, non-aqueous secondary batteries are widely used as power sources for laptops, mobile phones, power tools, electronic devices, and communication equipment. Furthermore, from the perspective of environmentally conscious vehicles, non-aqueous batteries are increasingly being used in electric and hybrid vehicles. Against this backdrop, there is a strong demand for non-aqueous secondary batteries to achieve higher output power, higher capacity, and longer lifespan.

[0003] Lithium-ion batteries are a prime example of non-aqueous secondary batteries. A non-aqueous secondary battery has a positive electrode with metal oxides or similar active materials, a negative electrode with carbon materials such as graphite as active materials, and a non-aqueous electrolyte solvent centered on carbonates or flame-retardant ionic liquids. A non-aqueous secondary battery is a type of secondary battery that charges and discharges by moving ions between the positive and negative electrodes. The positive electrode is obtained by coating a slurry containing metal oxides and a binder onto the surface of a positive current collector such as aluminum foil, drying it, and then cutting it to an appropriate size. The negative electrode is obtained by coating a slurry containing carbon materials and a binder onto the surface of a negative current collector such as copper foil, drying it, and then cutting it to an appropriate size. The binder acts to bond the active materials together and to the current collector, thereby preventing the active materials from peeling off from the current collector in both the positive and negative electrodes.

[0004] Polyvinylidene fluoride (PVDF) binders, using N-methylpyrrolidone (NMP) as an organic solvent, are widely known as binders. However, using this binder results in poor adhesion between active materials and between the active material and the current collector. Therefore, large quantities of this binder are required in practical applications, leading to a reduction in the capacity of non-aqueous secondary batteries. Furthermore, the use of NMP, a high-cost organic solvent, makes it difficult to reduce manufacturing costs.

[0005] To address this problem, for example, Patent Document 1 discloses the use of copolymers containing a mixture of monomers having amide bonds, such as N-vinylacrylamide, and (meth)acrylate monomers as copolymers for binders in non-aqueous battery electrodes.

[0006] In addition, Patent Document 2 describes a copolymer of acrylamide and acrylonitrile with acrylic acid or its salt as a polymer component contained in the negative electrode of a secondary battery.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2017 / 150200

[0010] Patent Document 2: International Publication No. 2021 / 060737 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, in non-aqueous secondary batteries, the appearance quality of the electrodes is a crucial factor in fully realizing their performance, requiring the suppression of streaks, agglomerates, and other defects. Furthermore, in non-aqueous secondary batteries, the electrodes are immersed in the electrolyte, necessitating the maintenance of high peel strength of the active material layer even under these conditions. Additionally, non-aqueous secondary batteries require electrodes with excellent appearance and high peel strength of the active material layer, and demand improved discharge capacity retention during charge-discharge cycles.

[0013] Therefore, the object of this disclosure is to provide an electrode binder polymer for non-aqueous secondary batteries, which can form a non-aqueous secondary battery electrode with excellent appearance and excellent peel strength of the electrode active material layer, and can produce a non-aqueous secondary battery with improved discharge capacity retention during charge-discharge cycles. Furthermore, the object of this disclosure is to provide a non-aqueous secondary battery electrode with excellent appearance and excellent peel strength of the electrode active material layer. Additionally, the object of this disclosure is to provide a non-aqueous secondary battery having an electrode with excellent appearance and excellent peel strength of the electrode active material layer, and improved discharge capacity retention during charge-discharge cycles.

[0014] Furthermore, the purpose of this disclosure is to provide an electrode binder composition for non-aqueous secondary batteries and an electrode slurry for non-aqueous secondary batteries comprising the aforementioned electrode binder polymer for non-aqueous secondary batteries.

[0015] In addition, the objective is to provide the aforementioned electrode binder polymer for non-aqueous secondary batteries, the aforementioned electrode binder composition for non-aqueous secondary batteries, the aforementioned electrode slurry for non-aqueous secondary batteries, and the respective manufacturing methods of the aforementioned electrodes for non-aqueous secondary batteries.

[0016] Methods for solving problems

[0017] This disclosure includes the following methods.

[0018] <1> A non-aqueous secondary battery electrode binder polymer, comprising 10 mol% to 50 mol% of a first structural unit represented by the following formula (1), 25 mol% to 80 mol% of a second structural unit represented by the following formula (2), and 1.0 mol% to 45 mol% of a third structural unit represented by the following formula (3), and having a weight-average molecular weight of 1.5 million or more.

[0019] Equation (1): -CH2CR 1 (CONR) 2 R 3 )-

[0020] [In formula (1), R] 1 R 2 and R 3 Each atom can be independently a hydrogen atom or an alkyl group.

[0021] Equation (2): -CH2CR 4 (COOX) -

[0022] [In formula (2), R] 4 It is a hydrogen atom or an alkyl group. COOX is at least one selected from carboxyl groups and their salts.

[0023] Equation (3): -CH2CR 5 (C≡N)-

[0024] [In formula (3), R] 5 It can be a hydrogen atom, an alkyl group, or an alkoxy group.

[0025] <2> The non-aqueous secondary battery electrode binder polymer described in <1> has a solubility of more than 5.0 g / 100 g H2O in water at 25°C.

[0026] <3> The electrode binder polymer for non-aqueous secondary batteries as described in <1> or <2>, wherein the total content of the first structural unit, the second structural unit and the third structural unit is 70 mol% or more.

[0027] <4> According to any one of <1> to <3>, the electrode binder polymer for non-aqueous secondary batteries, wherein R2 and R 3 It is an alkyl group with 3 or fewer hydrogen atoms or carbon atoms.

[0028] <5> The glass transition temperature of the non-aqueous secondary battery electrode binder polymer described in any one of <1> to <4> is 100°C or higher.

[0029] <6> The electrode binder polymer for non-aqueous secondary batteries according to any one of <1> to <5> further comprises a fourth structural unit represented by the following formula (4).

[0030] Equation (4): -CH2CR 6 (NR) 7 COR 8 )-

[0031] [In equation (4), R] 6 It can be a hydrogen atom or an alkyl group. R 7 It can be a hydrogen atom or a hydrocarbon group. R 8 It can be a hydrogen atom or a hydrocarbon group.

[0032] <7> The electrode binder polymer for non-aqueous secondary batteries described in <6> contains 0.30 mol% to 30 mol% of the above-mentioned fourth structural unit.

[0033] <8> An electrode binder composition for a non-aqueous secondary battery, comprising the electrode binder polymer for a non-aqueous secondary battery as described in any one of <1> to <7> and an aqueous medium.

[0034] <9> The electrode binder composition for non-aqueous secondary batteries described in <8> is wherein the electrode binder polymer for non-aqueous secondary batteries is completely dissolved in the above-mentioned aqueous medium at 25°C.

[0035] <10> An electrode slurry for a non-aqueous secondary battery, comprising:

[0036] Electrode binder polymer for non-aqueous secondary batteries as described in any of <1> to <7>,

[0037] Electrode active materials, and

[0038] Aqueous medium.

[0039] <11> An electrode for a non-aqueous secondary battery, comprising:

[0040] Current collector, and

[0041] An electrode active material layer is disposed on at least a portion of the surface of the current collector and includes an electrode active material and an electrode binder polymer for non-aqueous secondary batteries as described in any one of <1> to <7>.

[0042] <12> A non-aqueous secondary battery having electrodes for a non-aqueous secondary battery as described in <11>.

[0043] <13> A method for manufacturing an electrode binder polymer for non-aqueous secondary batteries, used to manufacture the electrode binder polymer for non-aqueous secondary batteries described in any one of <1> to <7>.

[0044] The manufacturing method uses (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-ethyl (meth)acrylamide, or N-propyl (meth)acrylamide as the source compound for the first structural unit, and at least one selected from (meth)acrylic acid and its salts as the source compound for the second structural unit, and (meth)acrylonitrile as the source compound for the third structural unit, to carry out free radical polymerization in an aqueous medium.

[0045] <14> A method for manufacturing an electrode binder composition for a non-aqueous secondary battery, wherein the non-aqueous electrode binder polymer described in any one of <1> to <7> is mixed with an aqueous medium.

[0046] <15> A method for manufacturing an electrode slurry for a non-aqueous secondary battery, wherein the non-aqueous secondary battery electrode binder polymer, the electrode active material, and the aqueous medium described in any one of <1> to <7> are mixed.

[0047] <16> A method for manufacturing an electrode for a non-aqueous secondary battery, wherein the electrode slurry for a non-aqueous secondary battery described in <10> is coated onto at least a portion of the surface of a current collector and then dried.

[0048] Invention Effects

[0049] According to this disclosure, an electrode binder polymer for non-aqueous secondary batteries can be provided, which can form electrodes for non-aqueous secondary batteries with excellent appearance and excellent peel strength of the electrode active material layer, and can produce non-aqueous secondary batteries with improved discharge capacity retention during charge-discharge cycles. Furthermore, an electrode binder composition for non-aqueous secondary batteries, an electrode slurry for non-aqueous secondary batteries, an electrode for non-aqueous secondary batteries, and a non-aqueous secondary battery comprising the electrode binder polymer of this disclosure can be provided.

[0050] Alternatively, the above-mentioned electrode binder polymer for non-aqueous secondary batteries, the above-mentioned electrode binder composition for non-aqueous secondary batteries, the above-mentioned electrode slurry for non-aqueous secondary batteries, and the respective manufacturing methods of the above-mentioned electrodes for non-aqueous secondary batteries can be provided. Detailed Implementation

[0051] The embodiments will now be described in detail. However, this disclosure is not limited to the embodiments described below. In the embodiments described below, the constituent elements (including element steps, etc.) are not essential unless specifically stated otherwise. The same applies to numerical values ​​and their ranges; this disclosure is not limited thereto.

[0052] In this disclosure, the numerical range represented by “~” includes the minimum and maximum values ​​recorded before and after “~”, respectively.

[0053] In the numerical ranges described in segments in this disclosure, the upper or lower limit value described in one numerical range can be replaced with the upper or lower limit value of another numerical range. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that range can be replaced with the values ​​shown in the embodiments.

[0054] In this disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in the composition, etc., the content or percentage of each component, unless otherwise specified, refers to the total content or percentage of the multiple substances present in the composition, etc.

[0055] In this disclosure, the term "layer" includes not only the case where the layer is formed throughout the entire region, but also the case where it is formed only in a part of the region.

[0056] In this disclosure, "(meth)acrylic acid" refers to one or both of methacrylic acid and acrylic acid. "(meth)acrylamide" refers to one or both of methacrylamide and acrylamide. "(meth)acrylonitrile" refers to one or both of methacrylonitrile and acrylonitrile. "(meth)acryloyloxy" refers to one or both of methacryloxy and acryloyloxy.

[0057] In this disclosure, "weight-average molecular weight" is the converted value of amylopectin calculated using gel permeation chromatography (GPC).

[0058] Unless otherwise specified, the term "olefin unsaturated bond" in this disclosure refers to an olefin unsaturated bond that is capable of free radical polymerization.

[0059] Taking structural unit A from compound X having an olefinic unsaturated bond B as an example, in structural unit A contained in the polymer, the chemical structure of compound X other than the portion corresponding to the olefinic unsaturated bond B is the same as the chemical structure of compound X before polymerization, excluding the olefinic unsaturated bond B. For example, in a polymer having a structural unit from acrylonitrile, the aforementioned structural unit has a chemical structure of "-CH2CH(C≡N)-".

[0060] Furthermore, regarding the compound X that serves as the source of structural unit A in the polymer, it refers to a compound having a structure in which the two carbon atoms bonded to other structural units are replaced by olefinic unsaturated bonds. For example, acrylonitrile is a compound that serves as the source of the structural unit "-CH2CH(C≡N)-".

[0061] In this disclosure, when a structural unit having an ionic functional group undergoes ion exchange after polymerization, the structural unit is named based on the structure of the polymer after ion exchange. That is, for example, when a structural unit derived from sodium acrylate undergoes ion exchange after polymerization, the structural unit in the polymer becomes "-CH2CH(COOH)-". In this case, the structural unit is referred to as "the structural unit derived from acrylic acid".

[0062] In this disclosure, the term "functional group salt" refers to a form in which a portion of the dissociated ion of the functional group bonds with a counterion other than hydrogen ions and hydroxide ions. For example, the term "carboxyl group salt" refers to a COO salt. - The form in which ions are bonded to cations other than hydrogen ions. As an example, the so-called sodium salt of a carboxyl group refers to the structure represented by COONa.

[0063] In this disclosure, the term "non-volatile component" refers to the component remaining after weighing 1 g of the composition in an aluminum dish with a diameter of 5 cm and drying it at 110°C for 5 hours under air circulation in a desiccator at 1 atmosphere (1013 hPa). The composition can be in the form of a solution, dispersion, slurry, etc., but is not limited to these. Furthermore, the term "non-volatile component concentration" in this disclosure refers to the mass percentage (mass%) of the non-volatile component after drying under the above conditions, relative to the mass (1 g) of the composition before drying.

[0064] <1. Electrode binder polymers for non-aqueous secondary batteries>

[0065] The electrode binder polymer for non-aqueous secondary batteries disclosed herein (hereinafter sometimes simply referred to as "binder polymer") comprises 10 mol% to 50 mol% of a first structural unit represented by the following formula (1), 25 mol% to 80 mol% of a second structural unit represented by the following formula (2), and 1.0 mol% to 45 mol% of a third structural unit represented by the following formula (3), and has a weight-average molecular weight of 1.5 million or more.

[0066] Equation (1): -CH2CR 1 (CONR) 2 R 3 )-

[0067] [In formula (1), R] 1R 2 and R 3 Each atom can be independently a hydrogen atom or an alkyl group.

[0068] Equation (2): -CH2CR 4 (COOX) -

[0069] [In formula (2), R] 4 X is a hydrogen atom or an alkyl group. COOX is at least one selected from carboxyl groups and their salts. That is, X is at least one selected from H and the structure corresponding to the cation. For example, COOX is COONa when it is a sodium salt, and COONH4 when it is an ammonium salt.

[0070] Equation (3): -CH2CR 5 (C≡N)-

[0071] [In formula (3), R] 5 It can be a hydrogen atom, an alkyl group, or an alkoxy group.

[0072] If the binder polymer described above is used, an electrode for a non-aqueous secondary battery with excellent appearance and excellent peel strength of the electrode active material layer can be manufactured. In addition, if the binder polymer described above is used, a non-aqueous secondary battery with an electrode for a non-aqueous secondary battery having excellent appearance and excellent peel strength of the electrode active material layer, and excellent discharge capacity retention rate can be manufactured.

[0073] [1-1. First Structural Unit]

[0074] The first structural unit is represented by the following formula (1).

[0075] Equation (1): -CH2CR 1 (CONR) 2 R 3 )-

[0076] In the above equation (1), R 1 R 2 and R 3 Each is independently a hydrogen atom or an alkyl group. R 1 R 2 and R 3 Each of the components is preferably an alkyl group having 3 or fewer carbon atoms, and more preferably a hydrogen atom or a methyl group. 1 and CONR 2 R 3 The spatial relationships of the components are not limited. That is, the optical isomers in the first structural unit are not distinguished and can be any optical isomer. R 1 R 2 and R 3The structures can all be the same, or any two can be the same and the remaining one different, or all can be different. In particular, R is preferred. 2 and R 3 It is an alkyl group having 3 or fewer carbon atoms, more preferably a hydrogen atom or a methyl group. The first structural unit further preferably contains R. 1 For hydrogen atoms or methyl groups, R 2 and R 3 The first structural unit is a hydrogen atom, and more preferably, it is a structural unit derived from (meth)acrylamide. The content of the (meth)acrylamide structural unit in the first structural unit is preferably 80 mol% or more, particularly preferably 90 mol% or more, and may also be 100 mol%.

[0077] Examples of compounds that can serve as the source of the first structural unit include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, and N-hexyl(meth)acrylamide. Preferably, the compound that serves as the source of the first structural unit is (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-ethyl(meth)acrylamide, or N-propyl(meth)acrylamide, and more preferably (meth)acrylamide.

[0078] It should be noted that the adhesive polymer disclosed herein may contain only one first structural unit or may contain multiple first structural units in combination.

[0079] [1-2. Second structural unit]

[0080] The second structural unit is represented by the following formula (2).

[0081] Equation (2): -CH2CR 4 (COOX) -

[0082] In equation (2) above, R 4 It is a hydrogen atom or an alkyl group, especially preferably a hydrogen atom or an alkyl group having 3 or fewer carbon atoms, more preferably a hydrogen atom or a methyl group. R 4 The three-dimensional positional relationship of COOX is not limited. That is, the optical isomers in the second structural unit are not distinguished and can be any optical isomer.

[0083] In formula (2) above, COOX is selected from at least one type of carboxyl group (X = H) and its salt. That is, COOX in the second structural unit is selected from at least one type of carboxyl group and salt of carboxyl group and monovalent cation. Regarding COOX in the second structural unit, examples of salts of carboxyl group and monovalent cation include lithium salt of carboxyl group, sodium salt of carboxyl group, potassium salt of carboxyl group, and ammonium salt of carboxyl group.

[0084] In particular, the adhesive polymer of this disclosure preferably comprises a second structural unit in which COOX is a carboxyl group, a second structural unit in which COOX is a carboxyl group of a lithium salt in formula (2) above, or a second structural unit in which COOX is a carboxyl group of a sodium salt in formula (2) above. Furthermore, the adhesive polymer of this disclosure further preferably comprises a second structural unit in which COOX is a carboxyl group of a sodium salt in formula (2) above.

[0085] It should be noted that the adhesive polymer disclosed herein may contain only one type of second structural unit, or may contain a combination of multiple second structural units. The adhesive polymer disclosed herein may contain only a second structural unit in formula (2) where COOX is a carboxyl group, or it may contain only a second structural unit in formula (2) where COOX is a carboxyl salt, or it may contain both a second structural unit in formula (2) where COOX is a carboxyl group and a second structural unit in formula (2) where COOX is a carboxyl salt. Furthermore, when the adhesive polymer disclosed herein contains a second structural unit in formula (2) where COOX is a carboxyl salt, it may contain two or more second structural units of different types of cations constituting the carboxyl salt.

[0086] In particular, the second structural unit in the binder polymer of this disclosure, in which the second structural unit is a sodium salt of COOX with a carboxyl group (i.e., COONa) in formula (2) above, is preferably 20 mol% or more, more preferably 40 mol% or more, further preferably 60 mol% or more, and particularly preferably 80 mol% or more. By setting the second structural unit of the sodium salt of COOX with a carboxyl group (i.e., COONa) in formula (2) above to this range, the peel strength of the electrode active material layer in the electrode containing the binder polymer is further improved before and after electrolyte impregnation. It should be noted that the second structural unit contained in the binder polymer of this disclosure can be composed of the second structural unit of the sodium salt of COOX with a carboxyl group in formula (2) above (i.e., 100 mol%).

[0087] The compound that serves as the source of the second structural unit can be selected from at least one of (meth)acrylic acid and its salts. Examples of (meth)acrylate salts used as the source compounds for the second structural unit include lithium (meth)acrylate, sodium (meth)acrylate, potassium (meth)acrylate, and ammonium (meth)acrylate. In the adhesive polymers of this disclosure, these salts of (meth)acrylate and monovalent cations are preferably used as monomers, and at least one selected from lithium (meth)acrylate, sodium (meth)acrylate, potassium (meth)acrylate, and ammonium (meth)acrylate is preferred as a monomer. More preferably, at least one selected from lithium (meth)acrylate, sodium (meth)acrylate, and ammonium (meth)acrylate is used as a monomer, and most preferably, sodium acrylate is used as a monomer. (Methacrylate) salts are obtained, for example, by neutralizing (meth)acrylic acid with hydroxides, ammonia, etc.; however, from the perspective of availability, it is preferable to obtain them by neutralizing (meth)acrylic acid with sodium hydroxide.

[0088] [1-3. Third structural unit]

[0089] The third structural unit is represented by the following formula (3).

[0090] Equation (3): -CH2CR 5 (C≡N)-

[0091] In the above equation (3), R 5 It is a hydrogen atom, an alkyl group, or an alkoxy group, preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. Additionally, as R... 5 Examples of alkoxy groups include ethoxy groups. R 5 The stereochemical positional relationship of C≡N (nitrile group) is not limited. That is, the optical isomers in the third structural unit are not distinguished and can be any optical isomer.

[0092] Examples of compounds that serve as the source of the third structural unit include (meth)acrylonitrile and 3-ethoxy(meth)acrylonitrile. In particular, (meth)acrylonitrile is preferred, and acrylonitrile is more preferred. In the adhesive polymer of this disclosure, the third structural unit preferably comprises 80 mol% or more of acrylonitrile-derived structural units, more preferably 90 mol% or more, and may also comprise 100 mol%.

[0093] [1-4. Content of each structural unit in the binder polymer]

[0094] The content of the first structural unit in the binder polymer is 10 mol% or more, preferably 20 mol% or more, and more preferably 25 mol% or more. If the content of the first structural unit is within this range, the retention rate of the peel strength of the electrode active material layer after electrolyte impregnation, relative to before electrolyte impregnation, is further increased in the electrode containing the binder polymer. Furthermore, if the content of the first structural unit is within this range, the generation of streaks and agglomerates on the electrode surface can be suppressed when manufacturing the electrode using the binder polymer.

[0095] The content of the first structural unit in the binder polymer is 50 mol% or less, preferably 45 mol% or less, and more preferably 35 mol% or less. If the content of the first structural unit is within this range, the retention rate of the peel strength of the electrode active material layer after electrolyte impregnation in the electrode containing the binder polymer is further increased relative to before electrolyte impregnation.

[0096] Therefore, the content of the first structural unit in the adhesive polymer of this disclosure is 10 mol% to 50 mol%, or 10 mol% to 45 mol%, or 10 mol% to 35 mol%, or 20 mol% to 50 mol%, or 20 mol% to 45 mol%, or 20 mol% to 35 mol%, or 25 mol% to 50 mol%, or 25 mol% to 45 mol%, or 25 mol% to 35 mol%.

[0097] The content of the second structural unit in the binder polymer is 25 mol% or more, preferably 30 mol% or more, and more preferably 35 mol% or more. If the content of the second structural unit is within this range, the peel strength of the electrode active material layer is improved both before and after electrolyte impregnation in the electrode containing the binder polymer.

[0098] The content of the second structural unit in the binder polymer is 80 mol% or less, preferably 70 mol% or less, more preferably 55 mol% or less, and even more preferably 50 mol% or less. If the content of the second structural unit is within this range, the flexibility of the electrode containing the binder polymer can be improved.

[0099] Therefore, the content of the second structural unit in the adhesive polymer can be 25 mol% to 80 mol%, or 25 mol% to 70 mol%, or 25 mol% to 55 mol%, or 25 mol% to 50 mol%, or 30 mol% to 80 mol%, or 30 mol% to 70 mol%, or 30 mol% to 55 mol%, or 30 mol% to 50 mol%, or 35 mol% to 80 mol%, or 35 mol% to 70 mol%, or 35 mol% to 55 mol%, or 35 mol% to 50 mol%.

[0100] The content of the third structural unit in the binder polymer is 1.0 mol% or more, preferably 3.0 mol% or more, more preferably 10 mol% or more, and even more preferably 17.5 mol% or more. If the content of the third structural unit is within this range, the peel strength of the electrode active material layer is improved both before and after electrolyte impregnation in the electrode containing the binder polymer. Alternatively, the content of the third structural unit in the binder polymer can also be 25 mol% or more. Even if the content of the third structural unit is within this range, the peel strength of the electrode active material layer is improved both before and after electrolyte impregnation in the electrode containing the binder polymer.

[0101] The content of the third structural unit in the binder polymer is 45 mol% or less, preferably 40 mol% or less, and more preferably 35 mol% or less. If the content of the third structural unit is within this range, the peel strength of the electrode active material layer in the electrode containing the binder polymer is further improved both before and after electrolyte immersion. Furthermore, if the content of the third structural unit is within this range, the water solubility of the binder polymer can be improved, and separation of the binder polymer during storage can be suppressed. Alternatively, the content of the third structural unit in the binder polymer can also be 25 mol% or less. Even if the content of the third structural unit is within this range, the peel strength of the electrode active material layer in the electrode containing the binder polymer can be improved both before and after electrolyte immersion. Furthermore, even if the content of the third structural unit is within this range, the water solubility of the binder polymer can be improved, and separation of the binder polymer during storage can be suppressed.

[0102] Therefore, the content of the third structural unit in the adhesive polymer can be 1.0 mol% to 45 mol%, or 1.0 mol% to 45 mol%, or 1.0 mol% to 35 mol%, or 3.0 mol% to 45 mol%, or 3.0 mol% to 45 mol%, or 3.0 mol% to 35 mol%, or 10 mol% to 45 mol%, or 10 mol% to 35 mol%, or 17.5 mol% to 45 mol%, or 17.5 mol% to 45 mol%, or 17.5 mol% to 35 mol%, or 25 mol% to 35 mol%.

[0103] The total content of the first structural unit, the second structural unit, and the third structural unit in the adhesive polymer is preferably 70 mol% or more, preferably 80 mol% or more, more preferably 85 mol% or more, and may also be 95 mol% or more, or may be 100 mol%.

[0104] [1-5. Other structural units]

[0105] The adhesive polymer may also have other structures that do not conform to the first, second, and third structural units. In the adhesive polymer disclosed herein, examples of other structural units that do not conform to the first, second, and third structural units include structural units derived from (meth)acrylates that are partially hydrocarbons other than (meth)acryloyloxy groups and structural units derived from hydrocarbons having olefinic unsaturated bonds. The total content of these structural units derived from (meth)acrylates that are partially hydrocarbons other than (meth)acryloyloxy groups and structural units derived from hydrocarbons having olefinic unsaturated bonds is preferably 20 mol% or less, more preferably 10 mol% or less, and even more preferably 5.0 mol% or less.

[0106] If the total content of structural units derived from hydrocarbons other than (meth)acryloyloxy groups and structural units derived from hydrocarbons with olefinic unsaturated bonds falls within this range, the solubility of the binder polymer in aqueous media, the retention rate of peel strength of the electrode active material layer after electrolyte impregnation, and the retention rate of discharge capacity during charge-discharge cycles when the battery is manufactured can be further improved. It should be noted that the binder polymer disclosed herein may also be composed of structural units that do not contain either (meth)acryloyloxy groups derived from hydrocarbons other than (meth)acryloyloxy groups or structural units derived from hydrocarbons with olefinic unsaturated bonds.

[0107] Furthermore, the binder polymer disclosed herein is not particularly limited to other structural units, but it preferably includes a fourth structural unit represented by the following formula (4). In an electrode containing the binder polymer, the discharge capacity retention rate during charge-discharge cycles when the battery is manufactured can be further improved.

[0108] The fourth structural unit is represented by the following formula (4).

[0109] Equation (4): -CH2CR 6 (NR) 7 COR 8 )-

[0110] In the above equation (4), R 6 It is a hydrogen atom or an alkyl group, preferably a hydrogen atom or an alkyl group having 3 or fewer carbon atoms, more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom. R 7 It is a hydrogen atom or a hydrocarbon group, preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom or an alkyl group having 5 or fewer carbon atoms, even more preferably a hydrogen atom or an alkyl group having 3 or fewer carbon atoms, and even more preferably a hydrogen atom. R 8 It is a hydrogen atom or a hydrocarbon group, more preferably a hydrogen atom or an alkyl group having 5 or fewer carbon atoms, even more preferably a hydrogen atom or an alkyl group having 3 or fewer carbon atoms, and even more preferably a methyl group. R 6 and NR 7 COR 8 The three-dimensional positional relationships are not limited. That is, the optical isomers in the fourth structural unit are not distinguished and can be any optical isomer.

[0111] When the binder polymer of this disclosure has a fourth structural unit, the content of the fourth structural unit in the binder polymer is preferably 0.30 mol% or more, more preferably 0.80 mol% or more, even more preferably 1.0 mol% or more, even more preferably 1.5 mol% or more, and even more preferably 2.0 mol% or more. If the content of the fourth structural unit is within this range, the discharge capacity retention rate during charge-discharge cycles when manufacturing the battery can be further improved. The content of the fourth structural unit in the binder polymer may also be 8 mol% or more, or 10 mol% or more, or 15 mol% or more. Even if the content of the fourth structural unit is within this range, the discharge capacity retention rate during charge-discharge cycles when manufacturing the battery can be further improved.

[0112] The content of the fourth structural unit in the binder polymer is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 18 mol% or less, and even more preferably 15 mol% or less. If the content of the fourth structural unit is within this range, the discharge capacity retention rate during charge-discharge cycles when the battery is manufactured can be further improved. The content of the fourth structural unit in the binder polymer can also be 10 mol% or less, or 5.0 mol% or more. Even if the content of the fourth structural unit is within this range, the discharge capacity retention rate during charge-discharge cycles when the battery is manufactured can be further improved.

[0113] That is, the content of the fourth structural unit in the adhesive polymer can be 0.30 mol% to 30 mol%, 0.80 mol% to 20 mol%, 1.0 mol% to 10 mol%, 1.5 mol% to 5.0 mol%, or 8.0 mol% to 20 mol%.

[0114] Examples of compounds that can be sources of the fourth structural unit include N-vinylformamide and N-vinylacetamide. In particular, N-vinylacetamide is preferred as a source of the fourth structural unit. When the adhesive polymer of this disclosure has a fourth structural unit, the content of structural units derived from N-vinylformamide and structural units derived from N-vinylacetamide in the fourth structural unit of the adhesive polymer of this disclosure is preferably 80 mol% or more, more preferably 90 mol% or more, and may also be 100 mol%. Furthermore, when the adhesive polymer of this disclosure has a fourth structural unit, the content of structural units derived from N-vinylacetamide in the fourth structural unit of the adhesive polymer of this disclosure is preferably 80 mol% or more, more preferably 90 mol% or more, and may also be 100 mol%.

[0115] [1-6. Molecular weight of adhesive polymers]

[0116] The binder polymer disclosed herein has a weight-average molecular weight of 1.5 million or more, more preferably 2 million or more, even more preferably 2.3 million or more, and may also be 3 million or more. If the weight-average molecular weight of the binder polymer disclosed herein is within this range, the peel strength of the electrode active material layer before and after electrolyte impregnation is further improved in the electrode containing the binder polymer. In addition, if the weight-average molecular weight of the binder polymer disclosed herein is within this range, the discharge capacity retention rate during charge-discharge cycles of non-aqueous secondary batteries using electrodes containing the binder polymer is further improved. These effects are particularly significant in binder polymers containing 10 mol% to 50 mol% of the first structural unit represented by formula (1) above, 25 mol% to 80 mol% of the second structural unit represented by formula (2) above, and 1.0 mol% to 45 mol% of the third structural unit represented by formula (3) above.

[0117] Furthermore, the weight-average molecular weight of the binder polymer is preferably 10 million or less, more preferably 6 million or less, even more preferably 4 million or less, and may also be 3 million or less. By setting the weight-average molecular weight of the binder polymer within this range, the viscosity increase of liquid compositions containing the binder polymer, such as electrode binder compositions and electrode slurries described later, can be suppressed, and the components such as electrode active substances contained in the liquid compositions can be sufficiently dispersed.

[0118] That is, the weight-average molecular weight of the adhesive polymer can be 1.5 million to 10 million, or 1.5 million to 6 million, or 1.5 million to 4 million, or 1.5 million to 3 million, or 2 million to 10 million, or 2 million to 6 million, or 2 million to 4 million, or 2 million to 3 million, or 2.3 million to 10 million, or 2.3 million to 6 million, or 2.3 million to 4 million, or 2.3 million to 3 million, or 3 million to 10 million, or 3 million to 6 million, or 3 million to 4 million. Additionally, the weight-average molecular weight of the adhesive polymer can also be 4 million to 6 million.

[0119] [1-7. Glass transition temperature of adhesive polymers]

[0120] The glass transition temperature Tg of the adhesive polymer disclosed herein is a value calculated using the FOX formula based on the glass transition temperature of each structural unit contained in the adhesive polymer as a homopolymer. The specific method for calculating the glass transition temperature Tg of the adhesive polymer is as follows: it is calculated using the glass transition temperature Tgi of the homopolymer of each structural unit Mi (i = 1, 2, 3, etc., i.e., structural unit 1 to structural unit 3, etc.) and the mass fraction Xi of structural unit Mi in the adhesive polymer (ΣXi(all structural units) = 1), through the following equation (1). In equation (1), both Tg and Tgi are calculated as absolute temperatures (K).

[0121] 1 / Tg=Σ(Xi / Tgi)…(1)

[0122] It should be noted that when the binder polymer has other structural units besides the first, second and third structural units (e.g., the fourth structural unit), the glass transition temperature Tg of the homopolymer and the mass fraction Xi in the binder polymer can also be substituted into the above equation (1) for the other structural units to calculate the glass transition temperature Tg of the binder polymer.

[0123] The glass transition temperature (Tg) of the adhesive polymer is preferably 100°C (373K) or higher, more preferably 130°C (403K) or higher, even more preferably 150°C (423K) or higher, and may also be 200°C (573K) or higher. The glass transition temperature (Tg) of the adhesive polymer may be 300°C (673K) or lower, or may be 250°C or lower.

[0124] The glass transition temperature (Tg) of the adhesive polymer can be 100℃~300℃, 130℃~300℃, 150℃~300℃, 200℃~300℃, 100℃~250℃, 130℃~250℃, 150℃~250℃, or 200~250℃.

[0125] [1-8. Solubility of binder polymers]

[0126] The adhesive polymer disclosed herein is soluble in an aqueous medium. Here, water and solvents containing water can be included as the aqueous medium. The water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and may also be 95% by mass or more, or even 100% by mass. The aqueous medium may contain hydrophilic solvents other than water. There are no particular limitations on the hydrophilic solvent; examples include methanol, ethanol, and N-methylpyrrolidone.

[0127] The binder polymer of this disclosure preferably has a solubility in water at 25°C of 5.0 g / 100 g H₂O or higher, more preferably 8.0 g / 100 g H₂O or higher, even more preferably 11 g / 100 g H₂O or higher, even more preferably 20 g / 100 g H₂O or higher, and even more preferably 25 g / 100 g H₂O or higher. By setting the solubility of the binder polymer of this disclosure in water at 25°C to this range, electrodes for non-aqueous secondary batteries can be easily fabricated from a slurry in which the binder polymer is dissolved in an aqueous medium.

[0128] <2. Manufacturing method of adhesive polymer>

[0129] The synthesis of the adhesive polymer disclosed herein is not particularly limited, but it is preferably carried out by free radical polymerization in an aqueous medium. More specifically, methods such as polymerization in which all monomers used in polymerization are added at once, or polymerization is carried out while monomers used in polymerization are continuously supplied, can be applied. For example, according to the method of the embodiments described later, all monomers used in the synthesis of the adhesive polymer are converted into structural units of the adhesive polymer. The temperature for carrying out free radical polymerization is not particularly limited, but is preferably 30°C to 90°C.

[0130] In the case of free radical polymerization, ammonium persulfate, sodium persulfate, hydrogen peroxide, tert-butyl hydroperoxide, azo compounds, etc., can be used as polymerization initiators, but are not limited to these. Examples of azo compounds include 2,2'-azobis(2-methylpropanediamine) dihydrochloride. When polymerization is carried out in an aqueous medium, water-soluble polymerization initiators are preferred. Alternatively, redox polymerization can be carried out by combining a free radical polymerization initiator and a reducing agent, as needed. Examples of reducing agents include sodium bisulfite, sodium hydroxide, and ascorbic acid.

[0131] The aqueous medium preferably contains water. The water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and may also be 95% by mass or more, or 100% by mass. The aqueous medium may contain a hydrophilic solvent other than water. There are no particular limitations on the hydrophilic solvent; examples include methanol, ethanol, and N-methylpyrrolidone.

[0132] <3. Electrode binder composition for non-aqueous secondary batteries>

[0133] The electrode binder composition for non-aqueous secondary batteries disclosed herein (hereinafter sometimes referred to as the "electrode binder composition") comprises the aforementioned binder polymer, an aqueous medium, etc. Additionally, the electrode binder composition may, as needed, comprise other components such as pH adjusters and surfactants. The electrode binder composition may comprise only one of the binder polymers disclosed herein, or it may comprise two or more of the binder polymers disclosed herein. The electrode binder composition is obtained by mixing the aforementioned binder polymer with an aqueous medium. Preferably, all the binder polymers in the electrode binder composition are dissolved in the aqueous medium at 25°C. When the electrode binder composition comprises two or more binder polymers, preferably all of these two or more binder polymers are dissolved in the aqueous medium at 25°C.

[0134] Here, "all binder polymers are soluble in the aqueous medium at 25°C" means that the binder polymers are soluble in the aqueous medium within a range below their solubility at 25°C. When the electrode binder composition contains two or more binder polymers, it means that each binder polymer is soluble in the aqueous medium within a range below its respective solubility. Therefore, even in cases where a saturated solution of the binder polymer is initially present, but a portion of the binder polymer precipitates due to a decrease in temperature, or where several of the two or more binder polymers precipitate due to a decrease in temperature, it is still considered that all the binder polymers are soluble in the aqueous medium.

[0135] The aqueous medium in the electrode binder composition preferably contains water. The water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and may also be 95% by mass or more, or even 100% by mass. The aqueous medium may contain a hydrophilic solvent other than water. There are no particular limitations on the hydrophilic solvent; examples include methanol, ethanol, and N-methylpyrrolidone.

[0136] The aqueous medium contained in the electrode binder composition may be the same as or different from the aqueous medium used in the synthesis of the binder polymer.

[0137] The content of the binder polymer in the electrode binder composition is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. If the content of the binder polymer in the electrode binder composition is within this range, the increase in viscosity of the electrode binder composition can be suppressed, and when mixed with electrode active materials such as those described later to prepare an electrode slurry, the electrode active materials such as those described later can be dispersed efficiently.

[0138] The content of the binder polymer in the electrode binder composition is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, and even more preferably 8.0% by mass or more. If the content of the binder polymer in the electrode binder composition is within this range, the amount of volatile components will be suppressed, thereby enabling the preparation of electrode slurry and electrode with less electrode binder composition.

[0139] The pH of the electrode binder composition is preferably 4.0 or higher, more preferably 5.0 or higher, and even more preferably 6.0 or higher. If the pH of the electrode binder composition is within this range, the electrode active materials, etc., can be efficiently dispersed when mixed with them to prepare an electrode slurry. The pH of the electrode binder composition is preferably 10 or lower, more preferably 9.0 or lower, and even more preferably 8.0 or lower. If the pH of the electrode binder composition is within this range, the electrode active materials, etc., can be efficiently dispersed when mixed with them to prepare an electrode slurry. Here, the pH is a value measured using a pH meter at a liquid temperature of 23°C.

[0140] That is, the pH of the electrode binder composition can be 4.0–10.0, 5.0–9.0, or 6.0–8.0.

[0141] <4. Electrode slurry for non-aqueous secondary batteries>

[0142] The electrode slurry for non-aqueous secondary batteries disclosed herein (hereinafter sometimes referred to as "electrode slurry") comprises the aforementioned binder polymer, electrode active material, and aqueous medium. The electrode slurry is obtained by mixing the aforementioned binder polymer, electrode active material, and aqueous medium. Preferably, all the binder polymer in the electrode slurry is dissolved in the aqueous medium.

[0143] Here, the so-called binder polymers are all soluble in aqueous media, which is synonymous with the description in section <3. Electrode binder compositions for non-aqueous secondary batteries>.

[0144] Electrode pastes may contain conductive additives, thickeners, etc., depending on the requirements; however, to simplify the electrode paste manufacturing process, it is preferable not to include thickeners. There are no particular limitations on the method for manufacturing electrode pastes; methods such as using stirring, rotating, or oscillating mixing devices to mix the necessary components can be cited.

[0145] There are no particular limitations on electrode active materials. In the case of non-aqueous secondary batteries, specifically lithium-ion secondary batteries, examples of negative electrode active materials include conductive polymers, carbon materials, lithium titanate, silicon, and silicon compounds. Examples of conductive polymers include polyacetylene and polypyrrole. Examples of carbon materials include petroleum coke, pitch coke, coal coke, and other cokes; carbon black such as organic carbides, carbon fibers, and acetylene black; and graphite such as artificial graphite and natural graphite. Examples of silicon compounds include SiO₂. x (0.1≤x≤2.0), etc. Specific examples of artificial graphite include SCMG-XRs (manufactured by RESONAC Corporation). It should be noted that two or more of the materials mentioned here can be combined as the negative electrode active material. Furthermore, composite materials containing Si and graphite (Si / graphite), etc., can also be used as the negative electrode active material.

[0146] Among these negative electrode active materials, carbon materials, lithium titanate, silicon, and silicon compounds are preferred from the perspective of high energy density per unit volume. Additionally, coke, carbides of organic compounds, graphite, and other carbon materials are preferred as negative electrode active materials. x Silicon-containing materials such as (0.1≤x≤2.0), Si, and Si / graphite. When using these silicon-containing materials, the adhesive properties of the adhesive polymer disclosed herein are significantly improved.

[0147] On the other hand, examples of positive electrode active materials for lithium-ion secondary batteries include lithium cobalt oxide (LiCoO2); lithium composite oxides containing nickel; spinel-type lithium manganese oxide (LiMn2O4); olivine-type lithium iron phosphate; and chalcogenides such as TiS2, MnO2, MoO3, and V2O5. The positive electrode active material may contain any one of these compounds alone, or it may contain multiple compounds. Additionally, oxides of other alkali metals may also be used. Examples of lithium composite oxides containing nickel include Ni-Co-Mn lithium composite oxides, Ni-Mn-Al lithium composite oxides, and Ni-Co-Al lithium composite oxides. A specific example of a positive electrode active material is LiNi. 1 / 3 Mn 1 / 3 Co 1 / 3 O2, LiNi 3 / 5 Mn 1 / 5 Co 1 / 5 O2, etc.

[0148] The aqueous medium in the electrode paste preferably contains water. The water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and may also be 95% by mass or more, or 100% by mass. The aqueous medium may contain a hydrophilic solvent other than water. There are no particular limitations on the hydrophilic solvent; examples include methanol, ethanol, and N-methylpyrrolidone.

[0149] The aqueous medium contained in the electrode slurry can be the same as the aqueous medium contained in the electrode binder composition, or it can be the same as the aqueous medium used in the synthesis of the binder polymer. Alternatively, the aqueous medium contained in the electrode slurry can be different from the aqueous medium contained in the electrode binder composition and the aqueous medium used in the synthesis of the binder polymer.

[0150] Examples of conductive additives contained in electrode pastes include carbon black and fumed carbon fiber. A specific example of fumed carbon fiber is VGCF-H (RESONAC Co., Ltd.).

[0151] The concentration of non-volatile components in the electrode slurry is preferably 30% by mass or more, more preferably 40% by mass or more. By setting the concentration of non-volatile components in the electrode slurry within this range, a larger layer of active electrode material can be formed with a smaller amount of electrode slurry. Furthermore, the concentration of non-volatile components in the electrode slurry is preferably 70% by mass or less, more preferably 60% by mass or less. That is, the concentration of non-volatile components in the electrode slurry can be 30% by mass to 70% by mass, or 40% by mass to 60% by mass. It should be noted that the concentration of non-volatile components in the electrode slurry can be adjusted by the amount of aqueous medium used.

[0152] The content of the binder polymer in the electrode paste is preferably 0.50% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more, and as an example, it can be set to 3.0% by mass. By setting the content of the binder polymer in the electrode paste within this range, the binder polymer can be used to improve the adhesion between electrode active materials and between the electrode active material and the current collector.

[0153] The content of the binder polymer in the electrode slurry is preferably 7.0% by mass or less, more preferably 5.0% by mass or less, and even more preferably 4.0% by mass or less, relative to the total mass of the electrode active material, conductive additive, and binder polymer. By setting the content of the binder polymer in the electrode slurry within this range, the charge-discharge capacity of the electrode active material layer formed by the electrode slurry can be increased, and the internal resistance during battery fabrication can be reduced.

[0154] Therefore, the content of binder polymer in the electrode slurry relative to the total mass of electrode active material, conductive additive and binder polymer can be 0.50% to 7.0% by mass, 1.0% to 5.0% by mass, or 2.0% to 4.0% by mass.

[0155] <5. Electrodes for non-aqueous secondary batteries>

[0156] The electrode for a non-aqueous secondary battery disclosed herein (hereinafter sometimes referred to as an "electrode") comprises a current collector and an electrode active material layer disposed on at least a portion of the surface of the current collector. The electrode active material layer comprises an electrode active material and the aforementioned binder polymer. Examples of electrode shapes include laminates and coils, and there is no particular limitation. The current collector is not particularly limited, but is preferably a sheet-like metal with a thickness of 0.001 mm to 0.5 mm. Examples of metals include iron, copper, aluminum, nickel, and stainless steel. In the case of a lithium-ion secondary battery, aluminum is preferred as the material for the current collector as the positive electrode, and copper is preferred as the material for the current collector as the negative electrode.

[0157] The electrode disclosed herein can be manufactured by coating the electrode paste onto at least a portion, preferably the entire surface, of the current collector and drying it, but is not limited to this method.

[0158] Methods for coating electrode paste onto current collectors include reverse roller coating, direct roller coating, scraper coating, doctor blade coating, extrusion coating, curtain coating, gravure coating, rod coating, dip coating, and extrusion coating. Among these coating methods, scraper coating, doctor blade coating, or extrusion coating is preferred, with scraper coating being more preferred. This is because these methods are suitable for various physical properties of the electrode paste, such as viscosity, and drying properties, resulting in a coating film with a good surface finish.

[0159] The electrode paste can be applied to only one side of the current collector or to both sides. When applying the electrode paste to both sides of the current collector, it can be applied side-by-side sequentially or simultaneously. Furthermore, the electrode paste can be applied to the current collector continuously or intermittently. The coating amount of the electrode paste can be appropriately determined based on the battery's design capacity and the composition of the electrode paste. The preferred coating amount of the dried electrode active material layer (the coating amount on each side in the case of double-sided coating) is 4 mg / cm³. 2 ~20mg / cm 2 More preferably 6 mg / cm 2 ~16mg / cm 2 .

[0160] The electrode paste coated on the current collector is dried, thereby forming an electrode active material layer on the current collector. The drying method for the electrode paste is not particularly limited; hot air, reduced pressure or vacuum environment, (far)infrared radiation, electron beam, microwave, or low-temperature air can be used alone or in combination. The drying temperature is preferably 40℃ to 180℃, and the drying time is preferably 1 minute to 30 minutes.

[0161] Electrode sheets can be used directly as electrodes, or they can be cut to fit the size and shape of an electrode. There are no particular limitations on the cutting method for electrode sheets; slitting machines, lasers, wire cutting machines, cutting machines, Thomson scissors, etc., can be used.

[0162] Before or after cutting the electrode sheet, it can be pressed as needed. Pressing the electrode sheet makes the active material of the electrode adhere more firmly to the electrode, and further thinning of the electrode enables miniaturization of non-aqueous batteries. Conventional methods can be used for pressing, but molding or rolling is particularly preferred. The pressing pressure is not particularly limited, but is preferably set to 0.5 t / cm. 2 ~5t / cm 2 This is the range within which the insertion and extraction of lithium-ion isotropic electrode active materials will not be affected by suppression.

[0163] <6. Non-aqueous secondary batteries>

[0164] The non-aqueous secondary battery disclosed herein includes electrodes for a non-aqueous secondary battery. The non-aqueous secondary battery of this disclosure is a secondary battery in which ion movement occurs between the positive and negative electrodes during charging and discharging. The non-aqueous secondary battery of this disclosure has a positive electrode active material at the positive electrode and a negative electrode active material at the negative electrode. These positive and negative electrode active materials are materials capable of intercarrying and deintercarrying ions. A lithium-ion secondary battery can be cited as an example of the non-aqueous secondary battery of this disclosure.

[0165] As one embodiment of the non-aqueous secondary battery disclosed herein, a lithium-ion secondary battery will be described; however, the configuration of a non-aqueous secondary battery is not limited to the configuration described below. The lithium-ion secondary battery described in this embodiment is configured to house components such as a positive electrode, a negative electrode, an electrolyte, and spacers used as needed, within an outer casing. In the lithium-ion secondary battery of this embodiment, at least one of the positive and negative electrodes comprises the aforementioned binder polymer.

[0166] As the electrolyte, a non-aqueous liquid with ion conductivity is used. Examples of electrolytes include solutions in which the electrolyte is dissolved in an organic solvent and ionic liquids. However, in order to obtain a battery with low manufacturing cost and low internal resistance, a solution in which the electrolyte is dissolved in an organic solvent is preferred.

[0167] Alkali metal salts can be used as electrolytes, and the appropriate type can be selected based on factors such as the type of electrode active material. Examples of suitable electrolytes include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB2. 10 Cl 10 Examples of electrolytes include LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, and aliphatic lithium carboxylate. Other alkali metal salts can also be used as electrolytes.

[0168] Organic solvents used to dissolve electrolytes are not particularly limited, and examples include carbonate compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); nitrile compounds such as acetonitrile; and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. One of these organic solvents can be used alone, or two or more can be used in combination.

[0169] Metal or aluminum laminate materials can be used as the outer packaging. The battery can be any shape, such as coin-shaped, button-shaped, sheet-shaped, cylindrical, square, or flat.

[0170] Example

[0171] The following is a detailed description of an embodiment of the present disclosure through examples; however, the embodiments are not limited to these examples. The examples and comparative examples shown below are examples of negative electrode binders, negative electrode slurries, negative electrodes, and lithium-ion secondary batteries for manufacturing lithium-ion secondary batteries.

[0172] <1. Preparation of the negative electrode binder composition (electrode binder composition)>

[0173] In Examples 1 to 9 and Comparative Examples 1 to 7, a total of 100 parts by mass of monomer, 0.2 parts by mass of 2,2'-azobis(2-methylpropanediamine) dihydrochloride as a free radical polymerization initiator, 0.05 parts by mass of ammonium persulfate, and 567 parts by mass of water were added to a separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel at 30°C, in the proportions shown in Table 1 (when the monomer is used in solution form, the amount of monomer used in the table indicates the amount of the monomer itself excluding the solvent). The mixture was heated to 80°C and polymerized for 4 hours to generate a copolymer or polymer, resulting in a reaction solution containing the copolymer or polymer. It should be noted that, regarding Comparative Example 6, the monomers were used in the same composition ratio as in Example 2, and the amount of 2,2'-azobis(2-methylpropanediamine) dihydrochloride, which served as a free radical polymerization initiator, was set to 0.6 parts by mass and the amount of ammonium persulfate was set to 0.15 parts by mass. Otherwise, the reaction solution containing the copolymer or polymer was obtained in the same manner as in Example 2.

[0174] It should be noted that "monomer (A)" in Table 1 refers to the compound that serves as the source of the first structural unit. "Monomer (B)" in Table 1 refers to the compound that serves as the source of the second structural unit. "Monomer (C)" in Table 1 refers to the compound that serves as the source of the third structural unit. "Monomer (D)" in Table 1 refers to the compound that serves as the source of the fourth structural unit.

[0175] Water was added to the reaction solution containing the polymerized copolymer or polymer to obtain the negative electrode binder compositions of Examples 1 to 9 and Comparative Examples 1 to 7, with a non-volatile component concentration of 10.0% by mass.

[0176]

[0177] The abbreviations for the monomers listed in Table 1 are as follows.

[0178] AAm: Acrylamide

[0179] AaNa: Sodium acrylate

[0180] AaLi: Lithium acrylate

[0181] AN: Acrylonitrile

[0182] MN: Methacrylonitrile

[0183] NVA: N-vinylacetamide

[0184] <2. Various determinations of negative electrode binder compositions>

[0185] The binder polymer and the negative electrode binder composition were subjected to the following determinations. The results are shown in Table 1.

[0186] [2-1. Weight-average molecular weight of binder polymer]

[0187] The weight-average molecular weight of the binder polymer was determined using gel permeation chromatography (GPC) under the following conditions.

[0188] GPC device: GPC-101 (manufactured by RESONAC Co., Ltd.)

[0189] Solvent: 0.1M NaNO3 aqueous solution

[0190] Sample column: Shodex Column Ohpak SB-806 HQ (8.0mm I.D. × 300mm) × 2

[0191] Reference column: Shodex Column Ohpak SB-800RL (8.0mmI.D.×300mm)×2

[0192] Column temperature: 40℃

[0193] Sample concentration: 0.1% by mass

[0194] Detector: RI-71S (manufactured by Shimadzu Corporation)

[0195] Pump: DU-H2000 (manufactured by Shimadzu Corporation)

[0196] Pressure: 1.3 MPa

[0197] Flow rate: 1 ml / min

[0198] Molecular weight standards: Amylopectin (P-5, P-10, P-20, P-50, P-100, P-200, P-400, P-800, P-1300, P-2500 (manufactured by RESONAC Co., Ltd.))

[0199] [2-2. pH of the negative electrode binder composition]

[0200] The pH of the negative electrode binder composition was measured using a pH meter (manufactured by Toa DKK) at a liquid temperature of 23°C.

[0201] [2-3. Solubility of binder polymers in water]

[0202] The solubility of the negative electrode binder composition in water was evaluated as follows. Specifically, the negative electrode binder composition was dried at 110°C for 5 hours to remove moisture. Then, deionized water was added to the dried material to prepare a concentration of 25 g / 100 g H₂O or 11 g / 100 g H₂O. The mixture was stirred at 25°C for 24 hours, and the presence of turbidity or precipitation was visually confirmed at 25°C.

[0203] <3. Preparation of negative electrode paste (electrode paste)>

[0204] 76.8 parts by weight of SCMG-XRs (manufactured by RESONAC Corporation) as graphite, 19.2 parts by weight of silicon monoxide (SiO) (manufactured by Sigma-Aldrich), 1 part by weight of VGCF-H (manufactured by RESONAC Corporation), 30 parts by weight of a negative electrode binder composition (containing 3 parts by weight of the copolymer and 27 parts by weight of water), and 20 parts by weight of water were mixed. Mixing was performed using a stirring mixer (rotational-revolutionary mixer) at 2000 rpm for 4 minutes. 53 parts by weight of water were further added to the resulting mixture, and the mixture was further stirred using the same mixing apparatus at 2000 rpm for 4 minutes to prepare a negative electrode slurry.

[0205] <4. Battery Manufacturing>

[0206] [4-1. Making the negative electrode]

[0207] The prepared negative electrode slurry was coated onto one side of a 10 μm thick copper foil (current collector) using a scraper, resulting in a dry weight per unit area of ​​8 mg / cm³. 2 A copper foil coated with negative electrode slurry is dried at 60°C for 10 minutes, and then further dried at 110°C for 5 minutes to produce a negative electrode sheet with a negative electrode active material layer. This negative electrode sheet is then pressed using a roller press at a pressure of 10t. The pressed negative electrode sheet is cut into 52mm × 42mm pieces, and conductive electrode tabs are installed to produce the negative electrode.

[0208] [4-2. Production of the positive electrode]

[0209] 90 parts by mass of LiNi were used as the positive electrode active material. 3 / 5 Mn 1 / 5 Co 1 / 5 O2, 5 parts by weight of acetylene black, and 5 parts by weight of polyvinylidene fluoride are mixed, and then 100 parts by weight of N-methylpyrrolidone are mixed to prepare the positive electrode slurry (LiNi in the solid component). 3 / 5 Mn 1 / 5 Co 1 / 5 The mass standard ratio for O2 is 0.90.

[0210] The prepared positive electrode slurry was coated onto one side of a 15 μm thick aluminum foil (current collector) using a scraper method, resulting in a dry weight per unit area of ​​27 mg / cm³. 2Aluminum foil coated with positive electrode slurry was dried at 120°C for 5 minutes, and then pressed using a roller press to produce a positive electrode sheet with a positive electrode active material layer of 100 μm thickness. The obtained positive electrode sheet was cut into 50 mm × 40 mm (5.0 cm × 4.0 cm) pieces, and conductive electrode tabs were installed to produce the positive electrode.

[0211] A mixed solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DMC) in a volume ratio of 30:50:20. LiPF6 was dissolved in this mixed solvent to a concentration of 1.0 mol / L, and ethylene carbonate (VC) and fluoroethylene carbonate (FEC) were dissolved to concentrations of 1.0 wt% and 2.0 wt%, respectively, to prepare an electrolyte. Unless otherwise specified, "electrolyte" refers to the electrolyte prepared herein.

[0212] The positive and negative electrodes are arranged with their respective active material layers facing each other, separated by a spacer made of a porous polyolefin membrane, and housed in an aluminum laminated outer package (battery pack). Electrolyte is injected into the outer package, and the battery is sealed using a vacuum heat sealer to obtain a laminated battery.

[0213] <5. Evaluation of the negative electrode and battery>

[0214] The negative electrode and battery of each embodiment and comparative example were evaluated. The evaluation method is shown below, and the evaluation results are shown in Table 2.

[0215] [5-1. Appearance of the negative electrode]

[0216] The fabricated negative electrode was visually observed to determine the number of coating streaks and agglomerates caused by poor leveling during slurry application. It should be noted that the agglomerates are presumably caused by poor dispersion of the negative electrode active material and conductive additives in the slurry.

[0217] [5-2. Peel strength of the negative electrode active material layer]

[0218] The peel strength of the negative electrode active material layer relative to the current collector was measured as follows. The negative electrode sheet before pressing in the above-described negative electrode fabrication process was cut into 25mm × 100mm pieces to prepare test pieces. Two test pieces were prepared for each example and each comparative example. The peel strength of the negative electrode active material layer was directly measured on one of the two test pieces as a sample before electrolyte immersion. The peel strength of the negative electrode active material layer was measured on the other test piece after electrolyte immersion.

[0219] The electrolyte impregnation process was carried out as follows: the test piece was immersed in the electrolyte in a sealed container, stored at 45°C for 72 hours, then removed and immersed in ethyl methyl carbonate (EMC) for 1 minute, and further dried at 23°C and 50% RH for 2 hours.

[0220] The peel strength of the negative electrode active material layer was measured as shown below. First, the negative electrode active material layer on the test piece was attached to a 50mm wide and 200mm long stainless steel (SUS) plate using double-sided tape (NITTOTAPE No. 5, manufactured by Nitto Denko Corporation), ensuring that the center of the test piece was aligned with the center of the SUS plate. It should be noted that the double-sided tape was applied to cover the entire area of ​​the test piece.

[0221] Then, after placing the test piece against the SUS board for 10 minutes, the negative electrode active material layer was peeled off 20 mm from one end of the test piece along its length, and the copper foil side of the test piece was folded back 180°. The folded portion (the copper foil side of the test piece where the negative electrode active material layer was peeled off) was clamped with the upper clamp of the testing machine. Meanwhile, one end of the SUS board with the negative electrode active material layer peeled off was clamped with the lower clamp of the same testing machine. In this state, the copper foil was peeled off from the test piece at a speed of 100 ± 10 mm / min, obtaining a curve of peel length (mm) - peel force (mN). The average peel force (mN) from the peel length of 10 mm to 45 mm was calculated from the obtained curve. The average peel force was divided by the width of the test piece, 25 mm, and the resulting value was taken as the peel strength of the negative electrode active material layer (mN / mm). It should be noted that in any of the embodiments and comparative examples, no peeling occurred between the double-sided tape and the SUS plate, or between the double-sided tape and the negative electrode active material layer during the test.

[0222] [5-3. Battery Characteristics]

[0223] Using the laminated batteries fabricated in each embodiment and comparative example, the discharge capacity retention rate during charge-discharge cycles was calculated, thereby evaluating the battery characteristics.

[0224] First, under conditions of 25°C, a series of operations from steps (i) to (iv) shown below, performed once, are considered as one cycle for charging and discharging. The time integral value of the current in steps (i) and (ii) is defined as the charging capacity, and the time integral value of the current in step (iv) is defined as the discharging capacity. Subsequently, the discharging capacity of the first cycle and the discharging capacity of the 100th cycle are measured, and the discharge capacity retention rate after 100 cycles is calculated using the following formula.

[0225] Formula: Discharge capacity retention rate (%) after 100 cycles = 100 × (Discharge capacity of the 100th cycle / Discharge capacity of the 1st cycle)

[0226] (i) Charge at a current of 0.5C to a voltage of 4.2V (constant current (CC) charging).

[0227] (ii) Charge at a voltage of 4.2V until the current is 0.05C (constant voltage (CV) charging).

[0228] (iii) Let stand for 30 minutes.

[0229] (iv) Discharge at a current of 0.5C to a voltage of 2.75V (constant current (CC) discharge).

[0230] [5-4. Experimental Results]

[0231] The results regarding the peel strength of the negative electrode active material layer, battery characteristics, and negative electrode appearance evaluated above are presented in Table 2.

[0232]

[0233] <Evaluation Results>

[0234] As shown in Table 2, in Examples 1 to 9, compared with Comparative Examples 1 to 7, electrodes with excellent negative electrode appearance and excellent peel strength of the negative electrode active material layer can be produced. Furthermore, in Examples 1 to 9, batteries with excellent discharge capacity retention can be produced, exhibiting electrodes with excellent negative electrode appearance and excellent peel strength of the negative electrode active material layer. Specifically, by using a binder polymer containing 10 mol% to 50 mol% of a first structural unit represented by Formula (1), 25 mol% to 80 mol% of a second structural unit represented by Formula (2), 1.0 mol% to 45 mol% of a third structural unit represented by Formula (3), and a weight-average molecular weight of 1.5 million or more, electrodes with excellent appearance and high peel strength of the electrode active material layer even after immersion in an electrolyte can be produced. Furthermore, non-aqueous secondary batteries with excellent appearance, excellent peel strength of the electrode active material layer, and excellent discharge capacity retention can be produced.

[0235] The entire contents of the disclosure of Japanese Patent Application No. 2023-223505 are incorporated herein by reference. All documents, patent applications and technical standards described in this specification are incorporated herein by reference to the same extent that each document, patent application and technical standard is specifically and separately described and incorporated herein by reference.

Claims

1. A non-aqueous secondary battery electrode binder polymer, comprising 10 mol% to 50 mol% of a first structural unit represented by the following formula (1), 25 mol% to 80 mol% of a second structural unit represented by the following formula (2), and 1.0 mol% to 45 mol% of a third structural unit represented by the following formula (3), and having a weight-average molecular weight of 1.5 million or more; Equation (1): -CH2CR 1 (CONR) 2 R 3 )- In equation (1), R 1 R 2 and R 3 Each is independently a hydrogen atom or an alkyl group; Formula (2): -CH2CR 4 (COOX)- In equation (2), R 4 It is a hydrogen atom or an alkyl group; COOX is at least one selected from carboxyl groups and their salts; Equation (3): -CH2CR 5 (C≡N)- In equation (3), R 5 It can be a hydrogen atom, alkyl group, or alkoxy group.

2. The electrode binder polymer for non-aqueous secondary batteries according to claim 1 has a solubility of 5.0 g / 100 g H2O or higher in water at 25°C.

3. The electrode binder polymer for non-aqueous secondary batteries according to claim 1, wherein, The combined content of the first structural unit, the second structural unit, and the third structural unit is 70 mol% or more.

4. The electrode binder polymer for non-aqueous secondary batteries according to claim 1, wherein, R 2 and R 3 It is an alkyl group with 3 or fewer hydrogen atoms or carbon atoms.

5. The electrode binder polymer for non-aqueous secondary batteries according to claim 1, wherein the glass transition temperature is above 100°C.

6. The electrode binder polymer for non-aqueous secondary batteries according to claim 1, further comprising a fourth structural unit represented by the following formula (4): Equation (4): -CH2CR 6 (NR) 7 COR 8 )- In equation (4), R 6 R is a hydrogen atom or an alkyl group; 7 It is a hydrogen atom or a hydrocarbon group; R 8 It consists of hydrogen atoms or hydrocarbon groups.

7. The electrode binder polymer for non-aqueous secondary batteries according to claim 6, comprising 0.30 mol% to 30 mol% of the fourth structural unit.

8. An electrode binder composition for a non-aqueous secondary battery, comprising the electrode binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 7 and an aqueous medium.

9. The electrode binder composition for non-aqueous secondary batteries according to claim 8, wherein, The electrode binder polymer for non-aqueous secondary batteries is completely soluble in the aqueous medium at 25°C.

10. An electrode slurry for non-aqueous secondary batteries, comprising: Electrode binder polymer for non-aqueous secondary batteries according to any one of claims 1 to 7 Electrode active materials, and Aqueous medium.

11. An electrode for a non-aqueous secondary battery, comprising: Current collector, and An electrode active material layer is disposed on at least a portion of the surface of the current collector and comprises an electrode active material and an electrode binder polymer for non-aqueous secondary batteries according to any one of claims 1 to 7.

12. A non-aqueous secondary battery comprising the electrode for a non-aqueous secondary battery as described in claim 11.

13. A method for manufacturing an electrode binder polymer for non-aqueous secondary batteries. It manufactures the electrode binder polymer for non-aqueous secondary batteries according to any one of claims 1 to 7. The manufacturing method uses (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-ethyl (meth)acrylamide, or N-propyl (meth)acrylamide as the source compound for the first structural unit, at least one selected from (meth)acrylic acid and its salts as the source compound for the second structural unit, and (meth)acrylonitrile as the source compound for the third structural unit, in an aqueous medium for free radical polymerization.

14. A method for manufacturing an electrode binder composition for a non-aqueous secondary battery, wherein, The non-aqueous secondary battery electrode binder polymer according to any one of claims 1 to 7 is mixed with an aqueous medium.

15. A method for manufacturing an electrode slurry for a non-aqueous secondary battery, wherein, The non-aqueous secondary battery electrode binder polymer, electrode active material, and aqueous medium according to any one of claims 1 to 7 are mixed.

16. A method for manufacturing an electrode for a non-aqueous secondary battery, wherein, The electrode slurry for the non-aqueous secondary battery as described in claim 10 is applied to at least a portion of the surface of the current collector and then dried.

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