Binder composition for nonaqueous secondary battery positive electrodes, composition for nonaqueous secondary battery positive electrodes, positive electrode for nonaqueous secondary batteries, and nonaqueous secondary battery

Abstract

The purpose of the present invention is to provide: a binder composition for nonaqueous secondary battery positive electrodes, which has excellent durability with respect to an electrolyte solution and excellent dispersion stability of a positive electrode active material, and with which it is possible to form a secondary battery that has excellent battery characteristics such as charge / discharge efficiency and capacity retention rate; a composition for nonaqueous secondary battery positive electrodes, which contains this binder composition for positive electrodes; a positive electrode for nonaqueous secondary batteries, which is formed of this composition for positive electrodes; and a secondary battery which comprises this positive electrode. As a result of investigations, the invention of a binder composition for nonaqueous secondary battery positive electrodes was completed, the binder composition containing a polyamide-imide that has a repeating unit represented by chemical formula (1). (In the chemical formula (1), R1, R2, and R3 are each independently a hydrogen atom or a methyl group, and at least one of the moieties is a methyl group.)

Description

Binder composition for positive electrode of non-aqueous secondary battery, composition for positive electrode of non-aqueous secondary battery, positive electrode for non-aqueous secondary battery and non-aqueous secondary battery

[0001] The present invention relates to a binder composition for the positive electrode of a non-aqueous secondary battery, a composition for the positive electrode of a non-aqueous secondary battery, a positive electrode for a non-aqueous secondary battery, and a non-aqueous secondary battery.

[0002] Non-aqueous secondary batteries (non-aqueous electrolyte secondary batteries), such as lithium-ion secondary batteries, are rapidly being deployed in hybrid vehicles, electric vehicles, and home energy storage systems, leveraging their high energy density and the ability to repeatedly charge and discharge, thus expanding their range of applications. In recent years, with the advancement of high performance and miniaturization of various portable electronic and communication devices, there has been a growing demand for secondary batteries that are small, lightweight, have higher capacity, and exhibit further improvements in various battery characteristics such as cycle characteristics and discharge rate characteristics. To further enhance the performance of non-aqueous secondary batteries, improvements to various battery components such as electrodes are being considered. A positive electrode for a non-aqueous secondary battery typically comprises a current collector and an electrode layer (positive electrode material layer) formed on the current collector. This positive electrode material layer is formed from a slurry-like positive electrode composition, for example, obtained by dispersing a composition containing a positive electrode active material and a binder (binding agent) in a dispersion medium. Lithium-cobalt composite oxide (LCO) and lithium-nickel-manganese-cobalt composite oxide (NMC), which have high operating voltages and excellent capacity characteristics, have been put into practical use as positive electrode active materials for lithium-ion secondary batteries. However, LCO and NMC have problems with poor thermal properties due to the destabilization of their crystal structure caused by delithiation, and the high cost of cobalt makes mass production of lithium-ion secondary batteries difficult.

[0003] In recent years, compared to lithium, it has an operating voltage of ~3.5V and a load of approximately 3.6g / cm³. ３Lithium iron phosphate (LFP) compounds, which have a high volumetric density, a theoretical capacity of approximately 170 mAh / g, and superior high-temperature stability and low cost compared to cobalt, are attracting attention as positive electrode active materials for lithium-ion secondary batteries. Although LFP compounds are structurally stable positive electrode active materials, they have low electrical and ionic conductivity. Therefore, the electrical conductivity is improved by coating the surface of the LFP compound with carbon, and the ionic conductivity is further improved by reducing the particle size of the LFP compound before use.

[0004] On the other hand, in the positive electrode of lithium-ion secondary batteries, binders other than polyvinylidene fluoride (PVDF) or fluorine-based polymers with a similar composition are hardly used in practice. PVDF has excellent and well-balanced properties such as oxidation resistance, heat resistance, adhesion, and electrolyte resistance, making it easy to obtain compositions for positive electrodes. For example, Patent Document 1 proposes a binder composition containing polyvinylidene fluoride and a polymer having structural units derived from a specific fluorine-based compound. However, when the particle size of the LFP-based compound, which is the positive electrode active material, is reduced, the specific surface area increases, and when PVDF is used as a binder composition, there is a problem that the particles of the LFP-based compound aggregate, worsening the dispersion stability.

[0005] Japanese Patent Publication No. 2022-061830

[0006] Therefore, there is a strong demand for a cathode binder that possesses excellent electrolyte resistance similar to PVDF, and that suppresses aggregation of LFP-based compound particles when the particle size of the LFP-based compound used as the cathode active material is reduced, thereby exhibiting high dispersion stability.

[0007] The object of the present invention is to provide a binder composition for a positive electrode of a non-aqueous secondary battery that is excellent in durability to the electrolyte and dispersion stability of the positive electrode active material, and that can form a secondary battery with excellent battery characteristics such as charge-discharge efficiency and capacity retention rate, a binder composition for a non-aqueous secondary battery containing such a binder composition, a positive electrode for a non-aqueous secondary battery formed from such a positive electrode composition, and a secondary battery having such a positive electrode.

[0008] As a result of intensive studies by the present inventors to solve these problems, it has been found that when a composition containing a polyamideimide having a specific structural unit is used as a binder composition for a positive electrode, the resulting positive electrode material layer has excellent durability against an electrolytic solution, excellent dispersion stability of a positive electrode active material, and is effective for improving battery characteristics such as charge-discharge efficiency and capacity retention rate, and thus the present invention has been completed.

[0009] The present invention has the following aspects. [1] A binder composition for a non-aqueous secondary battery positive electrode, comprising a polyamideimide having a repeating unit represented by the following chemical formula (1). (In Chemical Formula (1), R １ , R ２ , R ３ are each independently a hydrogen atom or a methyl group, and at least one is a methyl group.) [2] The binder composition for a non-aqueous secondary battery positive electrode according to [1], comprising a polyamideimide having a repeating unit (1a) in which R １ in the chemical formula (1) is a methyl group, and R ２ and R ３ are hydrogen atoms. [3] A repeating unit (1a) in which R １ in the chemical formula (1) is a methyl group, and R ２ and R ３ are hydrogen atoms, and R １ is a hydrogen atom, and R ２ and R ３A binder composition for a positive electrode of a non-aqueous secondary battery according to [1], comprising a repeating unit (1b) in which one of the repeating units (1a) is a methyl group and the other is a hydrogen atom, and a polyamide imide having . [4] A binder composition for a positive electrode of a non-aqueous secondary battery according to [3], wherein the molar ratio (1a) / (1b) of the content of the repeating unit (1a) to the repeating unit (1b) is 1 / 99 or more and 99 / 1 or less. [5] A binder composition for a positive electrode of a non-aqueous secondary battery according to any one of [1] to [4], wherein the weight-average molecular weight of the polyamide imide is 10,000 or more and 500,000 or less. [6] A binder composition for a positive electrode of a non-aqueous secondary battery comprising a polyamide-imide, wherein the glass transition temperature of the polyamide-imide is 150°C or more and 290°C or less, and the polyamide-imide is dissolved in an organic solvent (S1) which is one or more selected from the group consisting of N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, and dimethylacetamide, and the degree of swelling after immersing a film formed from the polyamide-imide in an organic solvent (S2) which is an ethylene carbonate / ethyl methyl carbonate = 30 / 70 mixed solution (volume ratio) at 60°C for 12 hours is 1% by mass or more and 100% by mass or less. [7] A binder composition for a positive electrode of a non-aqueous secondary battery comprising a positive electrode active material, a conductive material, and the binder composition for a positive electrode of a non-aqueous secondary battery according to any one of [1] to [6]. [8] A positive electrode for a non-aqueous secondary battery comprising a positive electrode material layer formed using the non-aqueous secondary battery positive electrode composition described in [7]. [9] A non-aqueous secondary battery comprising the positive electrode for a non-aqueous secondary battery described in [8], a negative electrode, an electrolyte, and a separator.

[0010] According to the present invention, it is possible to provide a binder composition for a positive electrode of a non-aqueous secondary battery that is excellent in durability to the electrolyte and dispersion stability of the positive electrode active material, and that is excellent in battery characteristics such as charge-discharge efficiency and capacity retention rate, a binder composition for a non-aqueous secondary battery containing such a binder composition, a positive electrode for a non-aqueous secondary battery formed from such a positive electrode composition, and a secondary battery having such a positive electrode.

[0011] Embodiments of the present invention will be described in detail below by non-limiting descriptions. In this specification, "mass" is synonymous with "weight." Also, in this specification, numerical ranges indicated using "~" indicate a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. <<Binder composition for positive electrode of non-aqueous secondary battery according to the first embodiment>>

[0012] A binder composition for the positive electrode of a non-aqueous secondary battery according to a first aspect of the present invention (hereinafter also referred to as "binder composition A for positive electrode") is characterized by containing a polyamide imide having repeating units represented by the following chemical formula (1). First, let's describe the binder composition A of the present invention. (Structure)

[0013] In the above chemical formula (1), R １ , R ２ , R ３ Each of these is independently either a hydrogen atom or a methyl group, and at least one is a methyl group. The positive electrode binder composition A containing polyamide-imide having the repeating unit of chemical formula (1) exhibits excellent durability to the electrolyte and dispersion stability of the positive electrode active material. Non-aqueous secondary batteries equipped with a positive electrode formed from such positive electrode binder composition A tend to have improved battery performance. The reason for these effects is presumed to be the high concentration of non-polar aromatic rings in the polyamide-imide, which gives it excellent durability to the electrolyte, a polar solvent. Furthermore, although aromatic, it has a bent structure, and the polymer chain can move freely in organic solvents, so it is presumed to have excellent dispersion stability of the positive electrode active material due to its high adsorption to the active material and dispersibility in organic solvents.

[0014] Polyamide-imide is R in the chemical formula (1) １ is a methyl group, R ２ and R ３ It is preferable that the polyamide-imide has repeating units (1a) in which hydrogen atoms are present. The presence of these repeating units (1a) in the polyamide-imide further enhances the molecular mobility of the polymer main chain, resulting in particularly excellent dispersion stability of the positive electrode active material.

[0015] In addition to the repeating unit (1a), the polyamide-imide further comprises R １ is a hydrogen atom, R ２ and R ３ It is preferable that the polyamide-imide has a repeating unit (1b) in which one of the elements is a methyl group and the other is a hydrogen atom. By having the repeating units (1a) and (1b) of the polyamide-imide, it is possible to achieve an excellent balance between the degree of swelling in the electrolyte and the glass transition temperature, have appropriate swelling while maintaining durability in the electrolyte, and ensure high strength and heat resistance. Furthermore, since the molecular mobility of the polymer main chain is further enhanced, the dispersion stability of the positive electrode active material is particularly excellent.

[0016] The content of the repeating unit (1a) in the polyamide imide is preferably 0.05 mol% to 99.5 mol%, more preferably 5 mol% to 95 mol%, and even more preferably 10 mol% to 50 mol%. The content of the repeating unit (1b) in the polyamide imide is preferably 0.05 mol% to 99.5 mol%, more preferably 5 mol% to 95 mol%, and even more preferably 50 mol% to 90 mol%.

[0017] The molar ratio (1a) / (1b) of the content of the repeating unit (1a) to the repeating unit (1b) is preferably 1 / 99 or more and 99 / 1 or less, and more preferably 20 / 80 or more and 80 / 20 or less. A cathode binder composition A containing polyamide-imide that satisfies the above characteristics is even better in terms of the balance between the degree of swelling in the electrolyte and the glass transition temperature. (Solvent)

[0018] The positive electrode binder composition A of the present invention may contain an organic solvent. The organic solvent is preferably an organic solvent that can dissolve the polyamide-imide, preferably an aprotic solvent, and more preferably an aprotic polar solvent. Examples of such aprotic polar solvents include acetone, tetrahydrofuran, acetonitrile, propionitrile, N-methylpyrrolidone, N-ethylpyrrolidone, dimethylformamide, dimethylacetamide, diethylformamide, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphoric triamide. These organic solvents may be used alone or in combination of two or more. Among these, N-methylpyrrolidone, dimethylformamide, and dimethyl sulfoxide are preferred. When the positive electrode binder composition A of the present invention further contains an organic solvent, the polyamide-imide content relative to the total positive electrode binder composition A of the present invention is preferably in the range of 5 to 90% by mass, more preferably in the range of 10 to 80% by mass, and even more preferably in the range of 20 to 70% by mass. (Other resins)

[0019] The positive electrode binder composition A of the present invention may further contain resins other than polyamide-imide (hereinafter referred to as "other resins") as necessary, to the extent that they do not impair the effects of the present invention. When the binder composition A of the present invention further contains the other resins, the content of the other resins is preferably in the range of 50% by mass or less, more preferably in the range of 40% by mass or less, and even more preferably in the range of 30% by mass or less, based on 100% by mass of the non-volatile content of the binder composition A. (Additives, etc.)

[0020] The positive electrode binder composition A of the present invention may further contain various additives (hereinafter referred to as "various additives") such as surfactants, antioxidants, light stabilizers, plasticizers, viscosity modifiers, and organic or inorganic fillers, as necessary, to the extent that they do not impair the effects of the present invention. When the positive electrode binder composition A of the present invention further contains various additives, the content of the various additives is preferably in the range of 10% by mass or less, more preferably in the range of 5% by mass or less, and even more preferably in the range of 2% by mass or less, based on 100% by mass of the non-volatile content of the binder composition A. (Synthesis method)

[0021] Examples of methods for synthesizing the polyamide-imide contained in the positive electrode binder composition A of the present invention include the isocyanate method and the amine method. Examples of the amine method include the acid chloride method, the low-temperature solution polymerization method and the room-temperature solution polymerization method. Of these, the isocyanate method is preferred.

[0022] When synthesizing the polyamide-imide by the isocyanate method, for example, trimellitic acid or its anhydride, halogen, or other derivatives, along with an aromatic diisocyanate, are added to an organic solvent, and a catalyst is added as needed to obtain a reactive solution. This reactive solution is heated at a temperature of preferably 10 to 200°C for 1 to 24 hours to allow the reaction to proceed, thereby obtaining a polyamide-imide solution. Since the polyamide-imide obtained by the isocyanate method does not generate water as a byproduct during its synthesis, the amount of water in the system can be easily controlled. In a positive electrode material layer formed from a positive electrode composition containing the positive electrode binder composition A of the present invention containing such polyamide-imide, the degradation of the positive electrode active material can be suppressed by controlling and reducing the amount of water. Battery performance such as charge-discharge characteristics and discharge capacity retention rate of a secondary battery equipped with such a positive electrode is easily improved.

[0023] The resulting polyamide-imide solution can be used as is as the positive electrode binder composition A of the present invention, or it may be diluted with an organic solvent as needed before being used as the positive electrode binder composition A of the present invention.

[0024] Aromatic diisocyanates used in the synthesis of the polyamide-imide include 2,4-toluene diisocyanate and 2,6-toluene diisocyanate. These two aromatic diisocyanates may be used individually or in combination. In addition to these two, other aromatic diisocyanates such as diphenylmethane diisocyanate, naphthalene-1,5-diisocyanate, orthotolidine diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate may also be included. The total content of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate is preferably in the range of 50 mol% or more relative to the total aromatic diisocyanates.

[0025] When synthesizing the polyamide-imide, the monomer used may include, for example, about 10% of a polyfunctional isocyanate having three or more functional groups, as long as it does not hinder the effects of the present invention. However, since the polyamide-imide is preferably linear in structure, the content of the polyfunctional isocyanate having three or more functional groups is preferably 5% or less relative to the total isocyanate component including the aromatic diisocyanate.

[0026] Examples of organic solvents used in synthesizing the polyamide-imide include acetone, tetrahydrofuran, acetonitrile, propionitrile, N-methylpyrrolidone, N-ethylpyrrolidone, dimethylformamide, dimethylacetamide, diethylformamide, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphoric triamide, with N-methylpyrrolidone, dimethylformamide, and dimethyl sulfoxide being preferred. These organic solvents may be used individually or in combination of two or more.

[0027] Examples of catalysts used in synthesizing the polyamide-imide include organic amine compounds such as triethylamine, diethylenetriamine, and diazabicycloundecene; and metal compounds such as potassium fluoride, sodium fluoride, cesium fluoride, and sodium methoxide. These catalysts may be removed from the cathode binder composition A after synthesis, but they may also be used without removal as long as it does not affect the performance of the non-aqueous secondary battery equipped with the cathode formed from the cathode binder composition A. (Molecular weight)

[0028] The weight-average molecular weight (Mw) of the polyamide-imide contained in the positive electrode binder composition A of the present invention is preferably 10,000 to 500,000, and more preferably 30,000 to 500,000. When the Mw of the polyamide-imide is within the above range, it is preferable from the viewpoint that the battery characteristics such as charge-discharge characteristics and capacity retention rate of the non-aqueous secondary battery having a positive electrode formed from the positive electrode binder composition A of the present invention will be improved. Furthermore, it is preferable that the polyamide-imide has a linear structure. When the polyamide-imide has a linear structure, the polyamide-imide dissolves easily in the aforementioned organic solvent and solution polymerization is possible, while the durability to the electrolyte and the degree of swelling in the electrolyte can be easily controlled in the positive electrode material layer formed from the positive electrode composition containing the positive electrode binder composition A of the present invention. (Glass Transition Temperature) The glass transition temperature of the polyamide-imide contained in the positive electrode binder composition A of the present invention is preferably 150°C to 290°C, more preferably 160°C to 285°C, and even more preferably 200°C to 280°C. The effects obtained by containing a polyamide-imide that satisfies the above characteristics are the same as those described in the section on positive electrode binder composition B later. Details of the method for measuring the glass transition temperature will be described later in the Examples section. (Electrolyte Swelling Degree)

[0029] It is preferable that the degree of swelling after immersing a film formed from the polyamide-imide contained in the positive electrode binder composition A of the present invention in an organic solvent (S2) which is a ethylene carbonate / ethyl methyl carbonate = 30 / 70 mixed solution (volume ratio) at 60°C for 12 hours is 1% by mass or more and 100% by mass or less. More preferably, the degree of swelling after immersing a film formed from polyamide-imide in the organic solvent (S2) at 60°C for 12 hours is 5% by mass or more and 90% by mass or less, and even more preferably 5% by mass or more and 50% by mass or less. The effects obtained by containing a polyamide-imide that satisfies the above characteristics are the same as those described in the section on positive electrode binder composition B later. Details of the method for measuring the degree of swelling will be described later in the section on examples. A detailed explanation of the Hansen solubility parameter will be described later in the section on the second embodiment of the non-aqueous secondary battery positive electrode binder composition. <Second embodiment of the non-aqueous secondary battery positive electrode binder composition>

[0030] Furthermore, the binder composition for the positive electrode of a non-aqueous secondary battery according to the second aspect of the present invention (hereinafter also referred to as "positive electrode binder composition B") contains a polyamide-imide, the glass transition temperature of the polyamide-imide is 150°C or more and 290°C or less, and the polyamide-imide is dissolved in an organic solvent (S1) (hereinafter simply referred to as "organic solvent (S1)") which is one or more selected from the group consisting of N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, and dimethylacetamide, and the degree of swelling after immersion of a film formed from the polyamide-imide in an organic solvent (S2) (hereinafter simply referred to as "organic solvent (S2)") which is an ethylene carbonate / ethyl methyl carbonate = 30 / 70 mixed solution (volume ratio) at 60°C for 12 hours is 1% by mass or more and 100% by mass or less. (Glass transition temperature)

[0031] The glass transition temperature of the polyamide-imide contained in the positive electrode binder composition B of the present invention is preferably 150°C to 290°C, more preferably 160°C to 285°C, and even more preferably 200°C to 280°C. The positive electrode binder composition B containing polyamide-imide satisfying the above characteristics exhibits high molecular mobility, resulting in excellent dispersion stability when mixed with positive electrode active material, while also ensuring sufficient strength and heat resistance. A non-aqueous secondary battery equipped with a positive electrode formed from such a positive electrode binder composition B is likely to exhibit improved battery performance. Details of the glass transition temperature measurement method will be described later in the Examples section. (Electrolyte swelling degree)

[0032] In this specification, "polyamide-imide dissolves in organic solvent (S1)" means that the polyamide-imide dissolves in organic solvent (S1) as a uniform solution without leaving any undissolved material or gel-like foreign matter. The degree of swelling after immersing a film formed from polyamide-imide in organic solvent (S2) at 60°C for 12 hours is more preferably 5% by mass or more and 90% by mass or less, and even more preferably 5% by mass or more and 50% by mass or less. Details of the method for measuring the degree of swelling will be described later in the Examples section. A positive electrode binder composition B containing polyamide-imide that satisfies the above characteristics has appropriate swelling while being durable against the electrolyte, and a non-aqueous secondary battery equipped with a positive electrode formed from such a positive electrode binder composition B is likely to have improved battery performance. (Hansen solubility parameter)

[0033] Furthermore, the organic solvent (S2) has a dispersion term (δd) of 15 MPa in the Hansen solubility parameter. ０．５ Above 21 MPa ０．５ Less than 6 MPa, polarity term (δp) ０．５ Above 22 MPa ０．５ Less than 3 MPa, hydrogen bond term (δh) ０．５ Above 10 MPa ０．５It is an organic solvent with a value less than δ[(cal / cm²). Here, the dispersion term (δd), polarity term (δp), and hydrogen bonding term (δh) in the Hansen solubility parameter are parameters that take into account the polarity of a substance, expressed in three-dimensional space by dividing the solubility parameter (SP value: δ) introduced by Hildebrand into three components: dispersion term δd, polarity term δp, and hydrogen bonding term δh, and the following relationship holds: δ[(cal / cm²) ３ ) ０．５ ]] = (δd ２ +δp ２ +δh ２ ) ０．５ The dispersion term δd, polarity term δp, and hydrogen bonding term δh mentioned above have been determined by Hansen and subsequent researchers, and are published, for example, in the Polymer Handbook (4th edition), VII-698 to 711. In addition, Hansen's solubility parameters for many solvents and resins have been investigated, and these solubility parameters are described, for example, in the Industrial Solvents Handbook (by Wesley L. Archer). They can also be determined using the Hansen Solubility Parameters in Practice (HSPiP) software.

[0034] Based on the Hansen solubility parameters δd, δp, and δh calculated using HSPiP software (6th Edition, 6.0.03), an example of an organic solvent that satisfies the above requirements is ethylene carbonate (δd = 18.0 MPa). ０．５ , δp=21.7MPa ０．５ δh = 5.1 MPa ０．５ ), dimethyl carbonate (δd = 15.5 MPa ０．５ δp = 8.6 MPa ０．５ δh = 9.7 MPa ０．５ ), diethyl carbonate (δd = 15.1 MPa ０．５ δp = 6.3 MPa ０．５ δh = 3.5 MPa ０．５ ), ethyl methyl carbonate (δd = 15.4 MPa ０．５ δp = 8.7 MPa ０．５δh = 6.6 MPa ０．５ ), propylene carbonate (δd = 20.0 MPa ０．５ , δp=18.0MPa ０．５ δh = 4.1 MPa ０．５ ) are some examples.

[0035] Furthermore, as an organic solvent, the Hansen solubility parameter δd is 15 MPa. ０．５ Above 17 MPa ０．５ Less than δp is 10 MPa ０．５ Above 14 MPa ０．５ Less than δh is 3 MPa ０．５ Above 8 MPa ０．５ It is more preferable, from the viewpoint of being able to more practically evaluate the swelling and durability of the positive electrode material layer formed from the positive electrode composition containing the positive electrode binder composition B of the present invention, if the organic solvent is less than δd, δp, and δh. The organic solvent that satisfies the ranges of δd, δp, and δh may be a single type of organic solvent (S2), or a mixed solvent of two or more solvents. For example, a carbonate-based solvent used as an electrolyte for non-aqueous secondary batteries, an ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 30 / 30 / 40 mixed solution (volume ratio), has Hansen solubility parameters of δd = 16.2, δp = 12.6, and δh = 7.1, satisfying the more preferable δd, δp, and δh of the organic solvent described above. (Structure)

[0036] The polyamideimide having the above-described properties with respect to organic solvent (S1) and organic solvent (S2) is preferably a polyamideimide having repeating units represented by the following chemical formula (1).

[0037] In the above chemical formula (1), R １ , R ２ , R ３ Each of these is independently either a hydrogen atom or a methyl group, and at least one is a methyl group. The effect obtained by having the repeating unit of chemical formula (1) in the polyamide-imide is the same as that described in the section for the positive electrode binder composition A.

[0038] ​Polyamide-imide is R in the chemical formula (1) １ is a methyl group, R ２ and R ３ It is preferable that the polyamide-imide has repeating units (1a) in which hydrogen atoms are present. The effects obtained by having the polyamide-imide repeating units (1a) are the same as those described in the section for the positive electrode binder composition A.

[0039] In addition to the repeating unit (1a), the polyamide-imide further comprises R １ is a hydrogen atom, R ２ and R ３ It is preferable that the polyamide-imide has a repeating unit (1b) in which one of the members is a methyl group and the other is a hydrogen atom. The effects obtained by having the repeating units (1a) and (1b) in the polyamide-imide are the same as those described in the section on the positive electrode binder composition A.

[0040] The preferred range for the content of the repeating units (1a) and (1b) in the polyamide-imide is the same as that described in the section for the positive electrode binder composition A. Furthermore, the preferred range for the molar ratio (1a) / (1b) of the content of the repeating units (1a) to (1b) is the same as that described in the section for the positive electrode binder composition A. (Solvent)

[0041] The positive electrode binder composition B of the present invention may contain an organic solvent. The organic solvent is preferably one that can dissolve the polyamide-imide, preferably an aprotic solvent, and more preferably an aprotic polar solvent. Preferred aprotic polar solvents include acetone, tetrahydrofuran, acetonitrile, propionitrile, N-methylpyrrolidone, N-ethylpyrrolidone, dimethylformamide, dimethylacetamide, diethylformamide, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphoric triamide, and the like. These organic solvents may be used individually or in combination of two or more. Among these, N-methylpyrrolidone, dimethylformamide, and dimethyl sulfoxide are preferred. If the positive electrode binder composition B of the present invention further contains an organic solvent, the preferred range of polyamide-imide content relative to the total positive electrode binder composition B of the present invention is the same as that described in the section for positive electrode binder composition A. (Other resins)

[0042] The positive electrode binder composition B of the present invention may further contain resins other than polyamide-imide (hereinafter referred to as "other resins") as needed, within a range that does not impair the effects of the present invention. When the binder composition B of the present invention further contains the other resins, the preferred range of the content of the other resins relative to 100% by mass of the non-volatile content of the binder composition B is the same as that described in the section for the positive electrode binder composition A. (Additives, etc.)

[0043] The positive electrode binder composition B of the present invention may further contain various additives (hereinafter referred to as "various additives") such as surfactants, antioxidants, light stabilizers, plasticizers, viscosity modifiers, and organic or inorganic fillers, as necessary, within a range that does not impair the effects of the present invention. When the positive electrode binder composition B of the present invention further contains various additives, the preferred range of the content of various additives relative to 100% by mass of the non-volatile content of binder composition B is the same as that described in the section for positive electrode binder composition A. (Synthesis method)

[0044] The method for synthesizing the polyamide-imide contained in the positive electrode binder composition B of the present invention is the same as the synthesis method described in the section for positive electrode binder composition A. (Molecular weight)

[0045] The weight-average molecular weight (Mw) of the polyamide-imide contained in the positive electrode binder composition B of the present invention is preferably 10,000 to 500,000, and more preferably 50,000 to 500,000. The Mw of the polyamide-imide is within the above range. The effects obtained by having the Mw of the polyamide-imide within the above range are the same as those described in the section for positive electrode binder composition A. Furthermore, the polyamide-imide is preferably of a linear structure. The effects obtained by having a linear structure of the polyamide-imide are the same as those described in the section for positive electrode binder composition A. <Composition for positive electrode of non-aqueous secondary battery>

[0046] The present invention also relates to a composition for a positive electrode of a non-aqueous secondary battery (hereinafter also simply referred to as "the positive electrode composition of the present invention"), which contains a positive electrode active material, a conductive material, and the above-described binder composition for a positive electrode of a non-aqueous secondary battery (i.e., binder composition A or binder composition B of the present invention). (Positive electrode active material)

[0047] The positive electrode active material is not particularly limited, and in the case of non-aqueous electrolyte secondary batteries, for example, when manufacturing lithium-ion secondary batteries, examples include metal compounds, metal oxides, metal sulfides, and conductive polymers that can dope or intercalate lithium ions. Specifically, for example, lithium iron phosphate (LiFePO4) ４ ), Lithium manganese phosphate (LiMnPO ４ ), LiCoPO2 ４ ), lithium nickel phosphate (LiNiPO ４ ), Lithium iron manganese phosphate (LiFexMnyPO ４ Phosphate compounds having an olivine-type crystal structure such as x + y = 1; lithium cobalt oxide (LiCoO ２ Lithium-cobalt composite oxides (LCOs), lithium nickelate (LiNiO), etc. ２), lithium manganate (LiMnO ２ ), and these composite oxides (LiCoxNiyMnzO ２ , x + y + z = 1; lithium nickel manganese cobalt composite oxide (NMC)); lithium manganese spinel (LiMn ２ O ４ ), lithium vanadium compounds, V ２ O ５ , V ６ O １３ , VO ２ , MnO ２ , TiO ２ , MoV ２ O ８ , TiS ２ , V ２ S ５ , VS ２ , MoS ２ , MoS ３ , Cr ３ O ８ , Cr ２ O ５ ; Conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, and porous carbon can be mentioned. These may be used alone or in combination of two or more. Among these, from the viewpoints of operating voltage, volumetric density, theoretical capacity, high-temperature stability, and economy, it is preferable to use lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP).

[0048] The average particle size of the positive electrode active material is not particularly limited, but for example, when lithium-cobalt composite oxide (LCO) or lithium-nickel-manganese-cobalt composite oxide (NMC) is used as the positive electrode active material, the average particle size is usually preferably 1 μm to 100 μm, and more preferably 5 μm to 50 μm. Also, when lithium iron phosphate compound (LFP) is used as the positive electrode active material, the average particle size is usually preferably 0.01 μm to 5 μm, and more preferably 0.1 μm to 1 μm. When the average particle size of the positive electrode active material is within the above range, the positive electrode expansion rate during charging and discharging is small when used as a secondary battery, and it is easier to prevent a decrease in the reversible charge-discharge capacity per unit volume. Furthermore, it is easier to suppress peeling of the electrode film (positive electrode material layer) from the current collector during electrode film fabrication. The average particle size of the positive electrode active material is the particle size (D50) at which the cumulative volume reaches 50% when the volume cumulative distribution curve is drawn from the smallest diameter side, based on the particle size distribution measured by dynamic light scattering using a laser diffraction particle size analyzer or the like.

[0049] The positive electrode active material may have at least a portion of its surface covered with a coating material. The coating material is preferably a substance that exhibits electronic conductivity, lithium-ion conductivity, and an effect of suppressing electrolyte decomposition, and examples of electronically conductive substances include carbon, titanium, and nickel. Among these, carbon is preferred, and low-crystallinity carbon is more preferred, from the viewpoint of improving the chemical and thermal stability of the positive electrode active material and suppressing a decrease in the charge-discharge performance of the resulting secondary battery. When at least a portion of the surface of the positive electrode active material is covered with a coating material, the average thickness of the coating layer is preferably 10 nm to 300 nm, and more preferably 20 nm to 200 nm. Furthermore, the content of the coating material is preferably 1 to 30% by mass relative to the total amount of the components of the positive electrode active material and the coating material. (Conductive material)

[0050] Examples of conductive materials include conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, as well as porous carbon. As mentioned above, these can also be used as positive electrode active materials, either individually or in combination of two or more types. (Composition for positive electrode of non-aqueous secondary battery)

[0051] The positive electrode composition of the present invention is obtained by mixing and dispersing the positive electrode active material described above, a conductive material, and the non-aqueous secondary battery positive electrode binder composition of the present invention. There are no particular restrictions on the order of addition during mixing. Furthermore, an organic solvent may be added as appropriate from the viewpoint of adjusting the viscosity of the resulting positive electrode composition of the present invention and improving dispersion stability. Dispersion can be carried out using dispersion equipment such as a stirrer, a rotary-orbit mixer, a ball mill, a super sand mill, or a pressurized kneader. <Secondary Battery>

[0052] The present invention also relates to a positive electrode for a non-aqueous secondary battery, comprising a positive electrode material layer formed using the positive electrode composition of the present invention described above. The present invention also relates to a non-aqueous secondary battery, comprising such a positive electrode, a negative electrode, an electrolyte, and a separator. The binder composition for the positive electrode of the non-aqueous secondary battery of the present invention exhibits excellent durability to the electrolyte and excellent dispersion stability of the positive electrode active material. Therefore, the positive electrode material layer formed from a positive electrode composition containing the binder composition for the positive electrode of the present invention exhibits excellent charge-discharge capacity and capacity retention rate. That is, the non-aqueous secondary battery of the present invention having a positive electrode comprising such a positive electrode material layer exhibits good charge-discharge characteristics and excellent capacity retention rate. As the non-aqueous secondary battery of the present invention, non-aqueous electrolyte secondary batteries and solid-state electrolyte secondary batteries are preferred, and in particular, non-aqueous electrolyte secondary batteries comprising a positive electrode material layer formed using the positive electrode composition for the non-aqueous secondary battery of the present invention tend to exhibit excellent performance. For example, if the secondary battery of the present invention is a wet electrolyte secondary battery, it can be constructed by arranging a positive electrode containing the negative electrode active material and a negative electrode opposite each other via a separator, and then injecting an electrolyte. (Positive electrode)

[0053] The positive electrode of the present invention can be obtained, for example, by applying the above-described non-aqueous secondary battery positive electrode composition of the present invention to a current collector to form a positive electrode material layer as a thin film. Alternatively, the positive electrode can be obtained by molding the positive electrode composition of the present invention into a sheet, pellet, or other shape and integrating it with a current collector.

[0054] Examples of the material of the current collector include copper, nickel, titanium, stainless steel, etc. The shape of the current collector is preferably a strip shape such as a foil shape, a perforated foil shape, or a mesh shape. Further, porous materials such as porous metal (foamed metal) and carbon paper can also be used as the current collector. As a method of applying the positive electrode composition to the current collector, for example, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method, etc. can be mentioned. After coating, it is preferable to perform a rolling treatment using a flat press, a calendar roll, etc. as necessary. Further, after molding the paste-like positive electrode composition into a sheet or a pellet, a positive electrode material layer may be obtained by integrating it with a current collector using a roll, a press, or a combination thereof.

[0055] The positive electrode material layer formed on the current collector or the positive electrode material layer integrated with the current collector is preferably heat-treated. By such heat treatment, the solvent derived from the non-aqueous secondary battery positive electrode binder composition of the present invention can be removed, and the adhesion between the positive electrode active materials and between the positive electrode active material and the current collector can be improved. The heat treatment temperature is preferably in the range of 50 to 220°C, and more preferably in the range of 100 to 200°C. There is no particular limitation on the heat treatment time, and it is usually in the range of 1 minute to 20 hours. Note that the heat treatment is preferably performed in a non-oxidizing gas atmosphere such as helium, argon, nitrogen, or in a vacuum atmosphere from the viewpoint of preventing oxidation of the current collector during the heat treatment. Further, after the heat treatment, the positive electrode composed of the positive electrode material layer formed on the current collector or the positive electrode material layer integrated with the current collector is preferably subjected to a pressing treatment from the viewpoint of adjusting the electrode density. The electrode density of the positive electrode is usually preferably 1 to 1.8 g / cm ３ and more preferably 1.1 to 1.7 g / cm ３ and even more preferably 1.2 to 1.6 g / cm ３ The higher the electrode density, the more likely the adhesion and the volume capacity density of the electrode are to improve. On the other hand, if it is too high, the voids in the electrode decrease, making it difficult to suppress the positive electrode expansion rate and the capacity retention rate may decrease. Therefore, an optimal range of the electrode density is selected. (Negative electrode)

[0056] The negative electrode is obtained in the same way as the positive electrode by forming a negative electrode material layer on the surface of the current collector. For example, a negative electrode material slurry is prepared by kneading a negative electrode active material and an organic binder with a solvent using a dispersion device such as a stirrer, ball mill, super sand mill, or pressurized kneader. This negative electrode material slurry can then be applied to a current collector (e.g., copper foil) to form a negative electrode material layer. Examples of the organic binders include styrene-butadiene rubber copolymers (hereinafter also referred to as "SBR"); ethylenically unsaturated carboxylic acid copolymers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, and unsaturated carboxylic acid copolymers such as (meth)acrylic copolymers made from ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; and polymer compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, polyamideimide, and carboxymethylcellulose (hereinafter also referred to as "CMC"). Depending on their physical properties, these organic binders may be dispersed or dissolved in water, or dissolved in an organic solvent such as N-methyl-2-pyrrolidone.

[0057] The content of organic binder in the negative electrode material layer of the lithium-ion secondary battery negative electrode is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, and even more preferably 3 to 15% by mass. When the content of organic binder is 1% by mass or more, adhesion is improved, and the destruction of the negative electrode structure due to expansion or contraction during charging and discharging is more easily suppressed. On the other hand, when it is 30% by mass or less, the increase in electrode resistance is more easily suppressed.

[0058] The negative electrode slurry may further contain conductive additives as needed. Examples of conductive additives include carbon black, graphite, acetylene black, conductive oxides, and nitrides. If the negative electrode slurry further contains conductive additives, the amount is preferably in the range of 1 to 15% by mass relative to the negative electrode active material.

[0059] Examples of materials for the current collector include copper, nickel, titanium, and stainless steel. The shape of the current collector is preferably a strip shape such as foil, perforated foil, or mesh. In addition, porous materials such as porous metal (foamed metal) and carbon paper can also be used as current collectors. Examples of methods for applying the negative electrode material slurry to the current collector include metal mask printing, electrostatic painting, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, and screen printing. After application, it is preferable to perform rolling treatment using a flat plate press or calender roll as needed.

[0060] Alternatively, the negative electrode material layer may be obtained by forming a paste-like negative electrode material slurry into a sheet or pellet, and then integrating it with a current collector using a roll, press, or a combination thereof. Furthermore, the negative electrode material layer can also be prepared by adding carbon materials such as natural graphite, artificial graphite, hard carbon, or amorphous carbon such as soft carbon to the negative electrode material slurry.

[0061] The negative electrode material layer formed on the current collector or the negative electrode material layer integrated with the current collector is preferably heat-treated according to the type of organic binder used. For example, when using a water-based styrene-butadiene rubber copolymer (SBR), heat treatment is preferably performed at 100 to 130°C, and when using an organic binder with polyimide or polyamide-imide as the main backbone, heat treatment is preferably performed at 150 to 450°C. Such heat treatment removes solvents derived from the organic binder, promotes increased strength due to the hardening of the organic binder, and improves adhesion between particles and between particles and the current collector. It is preferable to perform the heat treatment in a non-oxidizing gas atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, from the viewpoint of preventing oxidation of the current collector during heat treatment.

[0062] Furthermore, after heat treatment, the negative electrode, which consists of a negative electrode material layer formed on the current collector or a negative electrode material layer integrated with the current collector, is preferably subjected to pressurization from the viewpoint of adjusting the electrode density. The electrode density of the negative electrode is usually 1 to 1.8 g / cm³. ３ Preferably, it is 1.1 to 1.7 g / cm³. ３ It is more preferable that the concentration be 1.2 to 1.6 g / cm³. ３It is even more preferable that the electrode density is as follows: While higher electrode density tends to improve adhesion and electrode volumetric density, if it is too high, the void space within the electrode decreases, making it difficult to suppress the negative electrode expansion rate and potentially reducing the capacity retention rate. Therefore, an optimal range for electrode density is selected. (Separator)

[0063] As a separator, nonwoven fabrics, cloths, microporous films, or combinations thereof, primarily composed of polyolefins such as polyethylene and polypropylene can be used. However, if the positive and negative electrodes of the non-aqueous electrolyte secondary battery being manufactured do not come into direct contact, a separator is not necessary. (Electrolyte)

[0064] Examples of electrolytes include LiClO ４ LiPF ６ LiAsF ６ LiBF ４ LiSO ３ CF ３ A so-called organic electrolyte can be used, in which lithium salts such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, etc. are dissolved in one or more non-aqueous solvents. (Battery structure)

[0065] The structure of a secondary battery using the non-aqueous secondary battery positive electrode binder composition of the present invention is not particularly limited, but it is common to have a structure in which the positive electrode, negative electrode, and a separator, if necessary, are wound in a flat spiral shape to form a wound electrode plate group, or these are stacked as flat plates to form a stacked electrode plate group, and these electrode plate groups are sealed in an outer casing. Secondary batteries using the non-aqueous secondary battery positive electrode binder composition of the present invention can be used as, for example, paper type batteries, button type batteries, coin type batteries, stacked type batteries, cylindrical type batteries, prismatic type batteries, etc. The non-aqueous secondary battery positive electrode binder composition of the present invention can also be applied to electrochemical devices in general that use the insertion and removal of lithium ions as a charge and discharge mechanism, such as hybrid capacitors and solid lithium secondary batteries. Furthermore, since the non-aqueous secondary battery positive electrode binder composition of the present invention does not mainly contain fluorine-based compounds such as PVDF, it can be used without problems even if fluorine compounds become subject to international regulations due to legal regulations on perfluoro and polyfluoroalkyl compounds (so-called PFAS regulations), etc.

[0066] The binder composition for the positive electrode of a non-aqueous secondary battery, the composition for the positive electrode, the positive electrode, and the secondary battery having the positive electrode of the present invention have been described above. However, the present invention is not limited to the configurations of the embodiments described above. For example, the binder composition for the positive electrode of a non-aqueous secondary battery, the composition for the positive electrode, the positive electrode, and the secondary battery having the positive electrode of the present invention may each have additional configurations in addition to the configurations of the embodiments described above, or may be replaced with any configuration that performs similar functions.

[0067] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples described below. The raw materials used in each example and comparative example are listed below.

[0068] TMA: Trimellitus anhydride <Isocyanate components> 2,4-TDI: 2,4-toluene diisocyanate 2,6-TDI: 2,6-toluene diisocyanate MDI: diphenylmethane diisocyanate NDI: naphthalene-1,5-diisocyanate TDI: orthotolidine diisocyanate HMDI: dicyclohexylmethane diisocyanate IPDI: isophorone diisocyanate

[0069] (Example 1) (1) Preparation of the positive electrode binder composition In a reaction vessel equipped with a stirrer, thermometer, cooling tube and nitrogen gas inlet, 680 parts by mass of N-methylpyrrolidone (NMP) as a solvent, 192.13 parts by mass (1.0 mol) of TMA, 87.08 parts by mass (0.5 mol) of 2,4-TDI, 87.08 parts by mass (0.5 mol) of 2,6-TDI, and 0.581 parts by mass of potassium fluoride were charged. The mixture was heated to 140°C while stirring and reacted at 140°C for 10 hours. After that, the mixture was cooled to room temperature, and NMP was added to obtain positive electrode binder composition 1 so that the solid content concentration was 20% by mass. The weight-average molecular weight (standard polystyrene equivalent) of the polyamide-imide constituting positive electrode binder composition 1 was measured using the following apparatus and measurement conditions and was found to be 80,000. Apparatus: Tosoh Corporation "HLC-8320 GPC (product name)" Guard column: Tosoh Corporation "HXL-L (product name)" Columns: "TSK-GEL G2000HXL", "TSK-GEL G3000HXL", "TSK-GEL G4000HXL", "TSK-GEL G5000HXL", and "TSK-GEL G6000HXL" connected in series in this order (all manufactured by Tosoh Corporation, product names) Column temperature: 40°C Developing solvent: N,N-dimethylformamide (containing 0.1% by mass lithium bromide) Developing solvent flow rate: 1.0 ml / min Detector: RI (differential refractometer) Data processing: Tosoh Corporation "GPC workstation" EcoSEC-WorkStation created a calibration curve using monodisperse polystyrenes with known molecular weights manufactured by Tosoh Corporation, namely "A-500," "A-1000," "A-2500," "A-5000," "F-1," "F-2," "F-4," "F-10," "F-20," "F-40," "F-80," and "F-128" (all product names), as standard polystyrenes.

[0070] (2) Preparation of compositions for the positive electrode of non-aqueous secondary batteries As the positive electrode active material, olivine-type lithium iron phosphate (LiFePO) ４ 94.0 parts by mass of (1) and 3.0 parts by mass of acetylene black as a conductive material were weighed out and stirred for 30 seconds in a rotating-orbit mixer (Thinky "ARE-310 (product name)") at a rotation speed of 1000 rpm and an orbital speed of 2000 rpm. Thereafter, stirring using the rotating-orbit mixer was performed using the same apparatus and conditions unless otherwise specified. Next, 27.0 parts by mass (2.16 parts by mass in terms of solid content) of the positive electrode binder composition 1 obtained in (1) above and 19.0 parts by mass of NMP were added and mixed until the whole was paste-like, and then stirred in a rotating-orbit mixer for 2 minutes. Since heat was generated by stirring, it was cooled to room temperature with ice water, stirred again in a rotating-orbit mixer for 2 minutes, and then cooled to room temperature with ice water. Next, 10.5 parts by mass (2.1 parts by mass in terms of solid content) of the positive electrode binder composition 1 obtained in (1) above, and 5 parts by mass of NMP were added to this mixture and mixed until the mixture was homogenized. The viscosity of the resulting slurry was measured with a B-type viscometer at 25°C and 30 rpm, and NMP was added until it was in the range of 2000 to 4000 mPa·s. Finally, the mixture was stirred for 30 seconds in a rotary-orbit mixer to prepare a slurry-like positive electrode composition 1.

[0071] (3) After the preparation and drying of the positive electrode, the gap of the bar coater was adjusted so that the coating amount (surface density) of the positive electrode composition 1 was 25.0 mg / cm². Using this bar coater, the positive electrode composition 1 obtained above was coated onto the carbon-coated aluminum foil, which is the current collector, and dried for 10 minutes in a forced-air dryer set to 80°C. The dried electrode was cut to a width of 40 mm and a roll press machine (Small Desktop Roll Press SA-602, manufactured by Tester Industries Co., Ltd.) was used to create a layer with a density of 2.5 g / cm². ３ After pressing in this manner, the electrode was vacuum-dried at 110°C for 10 hours to obtain positive electrode 1.

[0072] (4) Preparation of the negative electrode composition 48.75 parts by mass of artificial graphite and 48.75 parts by mass of natural graphite were weighed out as negative electrode active materials and stirred in a rotary-orbit mixer for 30 seconds. Next, 48.0 parts by mass (0.96 parts by mass in terms of solid content) of an aqueous solution (hereinafter referred to as "CMC solution") prepared by dissolving carboxymethylcellulose sodium salt ("Sunrose MAC350HC" manufactured by Nippon Paper Industries Co., Ltd.) in distilled water and adjusting the non-volatile content to 2.0% was added and mixed until the mixture became a paste, and then stirred in a rotary-orbit mixer for 2 minutes. Since heat was generated by stirring, it was cooled to room temperature with ice water, stirred again in a rotary-orbit mixer for 2 minutes, and then cooled to room temperature with ice water. Subsequently, 27.0 parts by mass (0.54 parts by mass in terms of solid content) of the above CMC solution was added to this mixture and mixed until the mixture was uniform, then stirred in a rotary-orbit mixer for 2 minutes, and then cooled to room temperature with ice water. Ten parts by weight of distilled water and 2.95 parts by mass (1.5 parts by mass in terms of solid content) of styrene-butadiene copolymer (DIC Corporation's "DS407H (trade name)," solid content concentration 50.8% by mass) were added, and the mixture was stirred again in a rotary-orbit mixer for 2 minutes, then cooled to room temperature with ice water. The viscosity of the resulting slurry was measured with a B-type viscometer at 25°C and 30 rpm, and distilled water was added until the viscosity was in the range of 2000 to 4000 mPa·s. Finally, the mixture was stirred in a rotary-orbit mixer for 30 seconds to prepare a slurry-like negative electrode composition.

[0073] (5) Preparation of the negative electrode The gap of the bar coater was adjusted so that the amount of negative electrode composition coating (surface density) after drying was 8.8 mg / cm2. The negative electrode composition was coated onto the copper foil, which was the current collector, using this bar coater, and dried for 8 minutes in a forced-air dryer set to 80°C. The dried electrode was cut to a width of 40 mm, pressed using a roll press machine (Small Tabletop Roll Press SA-602 manufactured by Tester Industries Co., Ltd.) to a layer density of 1.55 g / cm3, and then vacuum dried at 110°C for 10 hours to obtain the negative electrode.

[0074] (6) Fabrication of a secondary battery The negative electrode fabricated above was cut into a 24 mm x 24 mm square with a tab, and the positive electrode 1 fabricated above was cut into a 22 mm x 22 mm square with a tab, using a die-cutting blade. Nickel tab leads were welded to the tab portion of the cut electrodes, and aluminum tab leads were welded to the tab portion of the negative electrode and positive electrode 1, respectively. Meanwhile, a 25 μm thick polyethylene microporous membrane was cut into a 28 mm x 3.8 cm rectangle using a die-cutting blade as a separator. The positive electrode 1 and the negative electrode were placed opposite each other via this separator, wrapped in laminate film, and the tab portion was fixed by heat sealing. Then, LiPF ６ A laminate-type secondary battery 1 was fabricated by dissolving the compound in a 30 / 30 / 40 mixed solution of ethylene carbonate / dimethyl carbonate / methyl ethyl carbonate at a concentration of 1 mol / L, adding 1 vol% vinyl carbonate and 5 vol% fluoroethylene carbonate to obtain a non-aqueous electrolyte solution, adding 300 μL of the solution, and completely sealing it by vacuum lamination.

[0075] (Examples 2-14, Comparative Examples 1-5) Cathode binder compositions 2-19 were obtained in the same manner as in Example 1(1), except that the type and amount of isocyanate component were changed as shown in Table 1. Subsequently, the same procedure as in Examples 1(2)-(6) was performed, except that in Example 1(2), cathode binder compositions 2-19 were used instead of cathode binder composition 1, to obtain cathode compositions 2-19, cathodes 2-19, and laminate-type secondary batteries 2-19 using each cathode binder composition. The weight-average molecular weight of the polyamide-imide constituting each cathode binder composition was measured in the same manner as in Example 1. The results are summarized in Table 1.

[0076] (Comparative Example 6) In Example 1 (1), the same procedure as in Example 1 was performed except that an NMP solution of PVDF (Kureha KF Polymer W #7200, manufactured by Kureha Corporation) with a solid content concentration of 20% by mass was used instead of the positive electrode binder composition 1 obtained in Synthesis Example 1. A positive electrode composition, a positive electrode, and a laminate-type secondary battery were prepared.

[0077] (Evaluation of the degree of swelling of polyamide-imide in electrolyte) The positive electrode binder compositions prepared in each example and comparative example were coated onto a release PET film and dried at 140°C for 2 hours, then at 110°C for 10 hours to produce a film with a thickness of 40 μm. A 1 cm × 1 cm test piece was cut out and its mass was measured (M1). This test piece was then subjected to LiPF ６ The polyamide-imide was dissolved in a non-aqueous electrolyte solution at a concentration of 1.2 mol / L in a mixed solution of ethylene carbonate / ethyl methyl carbonate = 30 / 70 (volume ratio). After immersion at 60°C for 12 hours, the sample was removed, the non-aqueous electrolyte solution was wiped off the surface of the sample, and the mass was measured again (M2). The degree of swelling of the polyamide-imide in relation to the electrolyte was calculated using the following formula: Swelling degree (%) = 100 × (M2 - M1) / M1

[0078] (Evaluation of glass transition temperature of polyamide-imide) The above films prepared from the cathode binder compositions prepared in each example and comparative example were heated from room temperature to 300°C at a rate of 20°C / min using a PerkinElmer DSC system (Pyris Diamond), and held at 300°C for 5 minutes. Then, the samples were cooled to room temperature at a rate of 150°C / min, and then heated again at a rate of 20°C / min to measure the glass transition temperature (Tg) (°C) of the polyamide-imide.

[0079] (Evaluation of dispersion stability of positive electrode active material) The viscosity of the positive electrode compositions prepared in each example and comparative example immediately after preparation (initial viscosity) was measured using a B-type viscometer at 25°C and 30 rpm. The positive electrode compositions were placed in glass screw tubes, sealed tightly, and stored in a 30°C incubator for two weeks. After storage, the viscosity was measured using a B-type viscometer at 25°C and 30 rpm (viscosity after storage). The viscosity change rate of the positive electrode composition was calculated using the following formula, and the dispersion stability of the positive electrode active material was evaluated according to the following criteria. Viscosity change rate = 100 × (viscosity after storage - initial viscosity) / initial viscosity <Evaluation criteria> ◎: Viscosity change rate is less than 5% ○: Viscosity change rate is 5% or more and less than 10% △: Viscosity change rate is 10% or more and less than 20% ×: Viscosity change rate is 20% or more

[0080] (Evaluation of Peel Strength of Positive Electrode) Test pieces measuring 25 mm in width and 100 mm in length were cut from the positive electrodes prepared in each example and comparative example. The positive electrode active material side of the test piece was used as the adhesion surface and attached to a stainless steel plate using double-sided tape (Nitto Denko Corporation's "No. 5015"). On the other hand, approximately 10 mm of the edge of the carbon-coated aluminum foil was peeled off, and polyimide tape was attached to it to serve as the attachment point for the peel test equipment (Shimadzu Corporation's "Autograph AG-XPlus"). A 180° peel test was performed using the peel test machine, and the peel strength was measured.

[0081] (Evaluation of initial charge / discharge efficiency and capacity retention rate) The secondary batteries prepared in each example and comparative example were mounted on a charge / discharge device and left at 25°C for 3 hours. After that, one charge / discharge cycle was performed at 0.1C, and the initial charge / discharge efficiency was measured. Next, the charge / discharge cycle was repeated 50 times at 60°C and 0.2C. The discharge capacity retention rate after 50 cycles at 60°C (after 50 cycles) relative to the first discharge capacity at 0.2C (initial discharge capacity) was measured using the following formula: Capacity retention rate (%) = 100 × 50th discharge capacity (mAh / g) / Initial discharge capacity (mAh / g)

[0082] The results above are summarized in Table 1.

[0083]

[0084] The results in Table 1 show that the positive electrode binder composition of the present invention exhibits excellent dispersion stability of the positive electrode active material. Furthermore, the positive electrode formed from the positive electrode binder composition of the present invention exhibits excellent durability against the electrolyte, and secondary batteries equipped with such positive electrodes have a high initial charge-discharge efficiency of 94% or more, and moreover, a capacity retention rate of 90% or more, indicating an excellent balance of battery characteristics.

[0085] The positive electrode binder composition of the present invention exhibits excellent durability to the electrolyte and dispersion stability of the positive electrode active material, enabling the formation of a positive electrode and secondary battery with excellent battery characteristics such as charge-discharge efficiency and capacity retention rate. A secondary battery equipped with such a positive electrode has excellent battery characteristics such as charge-discharge characteristics and can be effectively used in portable electronic devices, for example, as a paper battery, button battery, coin battery, stacked battery, cylindrical battery, or prismatic battery.

Claims

1. A binder composition for the positive electrode of a non-aqueous secondary battery, comprising a polyamide-imide having repeating units represented by the following chemical formula (1). (In chemical formula (1), R １ , R ２ , R ３ Each of these is independently either a hydrogen atom or a methyl group, and at least one of them is a methyl group.

2. R in the above chemical formula (1) １ is a methyl group, R ２ and R ３ A binder composition for a positive electrode of a non-aqueous secondary battery according to claim 1, comprising a polyamide-imide having repeating units (1a) in which hydrogen atoms.

3. R in the chemical formula (1) １ is a methyl group, R ２ and R ３ are hydrogen atoms, and the repeating unit (1a), and R １ is a hydrogen atom, either R ２ and R ３ is a methyl group and the other is a hydrogen atom, and the repeating unit (1b), and a polyamideimide having the same is included. The non-aqueous secondary battery positive electrode binder composition according to claim 1.

4. The binder composition for a positive electrode of a non-aqueous secondary battery according to claim 3, wherein the molar ratio (1a) / (1b) of the content of the repeating unit (1a) to the repeating unit (1b) is 1 / 99 or more and 99 / 1 or less.

5. The binder composition for a positive electrode of a non-aqueous secondary battery according to claim 1, wherein the weight-average molecular weight of the polyamide-imide is 10,000 or more and 500,000 or less.

6. A binder composition for a positive electrode of a non-aqueous secondary battery comprising polyamide-imide, wherein the glass transition temperature of the polyamide-imide is 150°C or higher and 290°C or lower, the polyamide-imide is dissolved in an organic solvent (S1) which is one or more selected from the group consisting of N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, and dimethylacetamide, and the degree of swelling after immersing a film formed from the polyamide-imide in an organic solvent (S2) which is an ethylene carbonate / ethyl methyl carbonate = 30 / 70 mixed solution (volume ratio) at 60°C for 12 hours is 1% by mass or higher and 100% by mass or lower.

7. A composition for a positive electrode of a non-aqueous secondary battery, comprising a positive electrode active material, a conductive material, and a binder composition for a positive electrode of a non-aqueous secondary battery according to any one of claims 1 to 6.

8. A positive electrode for a non-aqueous secondary battery comprising a positive electrode material layer formed using the non-aqueous secondary battery positive electrode composition described in claim 7.

9. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, as described in claim 8.

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