Slurry for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for producing non-aqueous electrolyte secondary battery

Abstract

The present invention provides a slurry for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery having the slurry as an electrode active material layer, and a method for manufacturing the non-aqueous electrolyte secondary battery. A slurry for a nonaqueous electrolyte secondary battery in which solid particles including an electrode active material and a conductive auxiliary agent are dispersed in a nonaqueous electrolyte solution, the nonaqueous electrolyte solution being obtained by dissolving a lithium salt and a polymer (I) in a nonaqueous solvent, the polymer having a weight average molecular weight of 1000-150000, and the polymer having a weight average molecular weight of 1000-150000. The content of the polymer (I) in the nonaqueous electrolyte solution is 0.1-5.0 mass%.

Description

Technical Field

[0001] The present invention relates to a slurry for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a method for manufacturing a non-aqueous electrolyte secondary battery. Background Art

[0002] A non-aqueous electrolyte secondary battery has a structure in which a positive electrode current collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode current collector are laminated in this order. The positive electrode active material layer and the negative electrode active material layer are filled with a non-aqueous electrolyte and separated by a separator. The separator has pores and functions as a positive and negative electrode separation membrane that insulates between the positive and negative electrodes while allowing the non-aqueous electrolyte and ions to pass through in a state of using a normal battery. Charging and discharging can be performed by reciprocating movement of ions between the positive and negative electrodes. Currently, lithium ion secondary batteries are widely popularized, and lithium ions reciprocate between the positive and negative electrodes to repeatedly perform charging and discharging.

[0003] Techniques for increasing the capacity of non-aqueous electrolyte secondary batteries are being studied. For example, Patent Document 1 describes an electrochemical cell containing:

[0004] A positive electrode containing a first active material and an electrolytic solution in a first non-aqueous liquid electrolyte and composed of a non-adhesive body;

[0005] A negative electrode containing a second active material and an electrolytic solution in a second non-aqueous liquid electrolyte and composed of a non-adhesive body; and

[0006] An ion permeable membrane disposed between the positive electrode and the negative electrode, wherein

[0007] Each of the positive electrode and the negative electrode has a thickness of about 200 μm to about 3000 μm.

[0008] According to the technique described in Patent Document 1, as in the above positive electrode and negative electrode, since the electrode active material layers (positive electrode active material layer and negative electrode active material layer) are in a slurry state and non-adhesive state, a thick film can be formed while maintaining the flexibility of the electrode active material layer, an adhesive for bonding solid particles is not required, and the charge capacity and overall energy density can be significantly increased while maintaining the flexibility of the battery.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017 - 147222 Summary of the Invention

[0012] Technical Problem to be Solved by the Invention

[0013] As described in Patent Document 1, the present inventors have repeatedly studied a battery (also referred to as a "quasi-solid secondary battery" in this specification) in which an electrode active material layer is formed as an electrode paste layer in which electrode active material particles are dispersed in a non-aqueous electrolyte, and the capacity has been increased. As a result, it has been found that if the content of the electrode active material particles in the electrode paste layer is increased in order to further achieve a high energy density, the performance of the obtained non-aqueous electrolyte secondary battery (such as the discharge capacity retention rate during high-current discharge) deteriorates.

[0014] An object of the present invention is to provide a non-aqueous electrolyte secondary battery paste suitable for forming an electrode paste layer of a quasi-solid secondary battery, and a paste in which the performance of the obtained non-aqueous electrolyte secondary battery is not easily deteriorated even when the content of the electrode active material is increased. Another object of the present invention is to provide a non-aqueous electrolyte secondary battery having such a paste as an electrode active material layer and a method for manufacturing the same.

[0015] Means for Solving the Technical Problem

[0016] As a result of intensive studies by the present inventors in view of the above problems, it has been found that in a paste in which solid particles containing an electrode active material and a conductive additive are dispersed in a non-aqueous electrolyte, by using a non-aqueous electrolyte prepared by dissolving a specific amount of a polymer having a molecular weight in a specific range together with a lithium salt in a non-aqueous solvent, even when the content of the electrode active material is increased, a quasi-solid secondary battery obtained by forming the paste into an electrode active material layer can achieve a higher discharge capacity during high-current discharge. The present invention has been completed based on this finding through further repeated studies.

[0017] The above problems of the present invention have been solved by the following method.

[0018] 〔1〕

[0019] A non-aqueous electrolyte secondary battery paste, which is a non-aqueous electrolyte secondary battery paste in which solid particles containing an electrode active material and a conductive additive are dispersed in a non-aqueous electrolyte, wherein

[0020] the above non-aqueous electrolyte is prepared by dissolving a lithium salt and a polymer (I) in a non-aqueous solvent, the weight-average molecular weight of the polymer (I) is 1,000 to 150,000, and the content of the polymer (I) in the non-aqueous electrolyte is 0.1 to 5.0% by mass.

[0021] 〔2〕

[0022] The non-aqueous electrolyte secondary battery paste according to 〔1〕, wherein

[0023] the adsorption rate of the above polymer (I) to acetylene black is 15% or more.

[0024] [3]

[0025] The paste for non-aqueous electrolyte secondary battery according to [1] or [2], wherein,

[0026] The above electrode active material is a positive electrode active material, and the adsorption rate of the above polymer (I) to the above positive electrode active material is 10% or more.

[0027] [4]

[0028] The paste for non-aqueous electrolyte secondary battery according to [1] or [2], wherein,

[0029] The above electrode active material is a negative electrode active material, and the adsorption rate of the above polymer (I) to the above negative electrode active material is 10% or more.

[0030] [5]

[0031] The paste for non-aqueous electrolyte secondary battery according to any one of [1] to [4], wherein,

[0032] The above polymer (I) contains at least one of an amino group, a carboxyl group, a phosphoric acid group, a phosphonic acid group, a sulfonic acid group, a hydroxyl group, a carbamoyl group, and an aromatic group.

[0033] [6]

[0034] The paste for non-aqueous electrolyte secondary battery according to any one of [1] to [5], wherein,

[0035] In the above paste for non-aqueous electrolyte secondary battery, the content of the above electrode active material is 40 to 90% by mass, and the content of the above conductive assistant is 0.1 to 10% by mass.

[0036] [7]

[0037] A non-aqueous electrolyte secondary battery having the paste for non-aqueous electrolyte secondary battery according to any one of [1] to [6] as an electrode active material layer.

[0038] [8]

[0039] A method for manufacturing a non-aqueous electrolyte secondary battery, which includes the following steps:

[0040] Adding the paste for non-aqueous electrolyte secondary battery according to any one of [1] to [6] as an electrode active material layer.

[0041] In the present invention and this specification, the numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0042] In the present invention, the "non-aqueous electrolyte" refers to an electrolyte substantially free of water. That is, the "non-aqueous electrolyte" may contain a trace amount of water within the range not impairing the effects of the present invention. In the present invention, the water concentration of the "non-aqueous electrolyte" is 200 ppm (mass basis) or less, preferably 100 ppm or less, and more preferably 20 ppm or less. Additionally, it is actually very difficult for the non-aqueous electrolyte to be completely water-free, and it usually contains more than 1 ppm of water.

[0043] In the present invention, the "non-aqueous solvent" also refers to a solvent substantially free of water. That is, the "non-aqueous solvent" may contain a trace amount of water within the range not impairing the effects of the present invention. In the present invention, the water concentration of the "non-aqueous solvent" is 200 ppm (mass basis) or less, preferably 100 ppm or less, and more preferably 20 ppm or less. Additionally, it is actually very difficult for the non-aqueous solvent to be completely water-free, and it usually contains more than 1 ppm of water.

[0044] In the present invention, the "electrolyte" is a solution. That is, the electrolyte is composed of a solvent and various components dissolved in the solvent. Thus, the "electrolyte" itself does not contain substances that are insoluble in the solvent constituting the electrolyte.

[0045] Advantages of the Invention

[0046] The slurry for non-aqueous electrolyte secondary batteries of the present invention is a slurry suitable for forming an electrode slurry layer of a quasi-solid state secondary battery. Even when the content of the electrode active material is increased, the performance of the obtained non-aqueous electrolyte secondary battery is not easily degraded. During the manufacturing process of the non-aqueous electrolyte secondary battery of the present invention, when the slurry used for forming the electrode slurry layer contains a large amount of electrode active material, a high-performance non-aqueous electrolyte secondary battery can be obtained. According to the manufacturing method of the non-aqueous electrolyte secondary battery of the present invention, even when the slurry used for forming the electrode slurry layer contains a large amount of electrode active material, a high-performance non-aqueous electrolyte secondary battery can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a longitudinal sectional view schematically showing the basic structure of the non-aqueous electrolyte secondary battery of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0048] Preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments except as specified in the present invention.

[0049] [Slurry for Non-aqueous Electrolyte Secondary Batteries]

[0050] The paste for non-aqueous electrolyte secondary batteries of the present invention (also referred to as "the paste of the present invention") is a paste in which solid particles containing an electrode active material and a conductive assistant are dispersed in a non-aqueous electrolyte, and is a paste suitable for forming an electrode paste layer of a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte uses a non-aqueous solvent as a medium, and a solute containing a lithium salt and a specific polymer is dissolved therein. In addition to the lithium salt, the non-aqueous electrolyte may contain metal salts other than the lithium salt (for example, potassium salts, sodium salts, calcium salts, magnesium salts, etc.). The metal salt contained in the electrolyte is usually a lithium salt. In this case, the paste of the present invention is used as a paste for so-called lithium ion secondary batteries.

[0051] It is considered that in the paste of the present invention, the polymer (I) also acts as a dispersant for the solid particles in the paste, can inhibit the aggregation of the solid particles in the paste, and effectively improve the dispersibility of the solid particles.

[0052] Each component constituting the paste of the present invention will be described.

[0053] <Non-aqueous electrolyte>

[0054] The non-aqueous electrolyte is formed by dissolving a lithium salt and the polymer (I) in a non-aqueous solvent.

[0055] (Non-aqueous solvent)

[0056] The non-aqueous electrolyte constituting the paste of the present invention uses a non-aqueous solvent as a medium.

[0057] As the non-aqueous solvent, a non-protic organic solvent is preferred, and among them, a non-protic organic solvent having 2 to 10 carbon atoms is more preferred.

[0058] Examples of such non-aqueous solvents include chain or cyclic carbonate compounds, lactone compounds, chain or cyclic ether compounds, ester compounds, nitrile compounds, amide compounds, oxazolidinone compounds, nitro compounds, chain or cyclic sulfone or sulfoxide compounds, and phosphate ester compounds.

[0059] In addition, compounds having an ether bond, a carbonyl bond, an ester bond, or a carbonate bond are preferred. These compounds may have substituents.

[0060] Examples of the nonaqueous solvent include ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, , methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate, ethyl trimethyl acetate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N, N-dimethylformamide, N-methylpyrrolidone, N-methyloxazolidinone, N, N'-dimethylimidazolidinone, nitromethane, nitroethane, cyclopentane, trimethyl phosphate, dimethyl sulfoxide or dimethyl sulfoxide phosphoric acid, etc. They can be used alone or in combination with more than two kinds. Among them, preferably at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and γ-butyrolactone, more preferably a combination of high viscosity (high dielectric constant) solvents such as ethylene carbonate or propylene carbonate (for example, relative dielectric constant ε≥30) and low viscosity solvents such as dimethyl carbonate, methyl ethyl carbonate or diethyl carbonate (for example, viscosity≤1mPa·s). By using such a mixed solvent combination, the dissociation property of the electrolyte salt and the mobility of ions are improved. The non-aqueous solvent is particularly preferably a combination of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

[0061] In addition, the nonaqueous solvent used in the present invention is not limited to these.

[0062] In the above-mentioned electrolyte solution, the content of the nonaqueous solvent may be an amount such that the total of the content of the lithium salt, the content of the polymer (I) and the content of the nonaqueous solvent is 100% by mass.

[0063] In the non-aqueous electrolyte, the content of the non-aqueous solvent is preferably 49.9 to 89.9% by mass, more preferably 60.0 to 89.9% by mass, further preferably 70.0 to 88.0% by mass, and further preferably 70.0 to 85.0% by mass.

[0064] (Lithium Salt)

[0065] The lithium salt is preferably a lithium salt generally used in an electrolyte of a lithium ion secondary battery, and examples thereof include the following lithium salts.

[0066] (L-1) Inorganic lithium salt: LiPF 6 , LiBF 4 、LiAsF 6 、LiSbF 6 Inorganic fluoride salts, LiClO 4 、LiBrO4 , LiIO 4 and other perhalates, LiAlCl 4 and other inorganic chloride salts, etc.

[0067] (L-2) Fluorinated organic lithium salts: LiCF 3 SO 3 and other perfluoroalkyl sulfonates, LiN(CF 3 SO 2 ) 2 , LiN(CF 3 CF 2 SO 2 ) 2 , LiN(FSO 2 ) 2 , LiN(CF 3 SO 2 )(C 4 F 9 SO 2 ) and other perfluoroalkylsulfonylimide salts, LiC(CF 3 SO 2 ) 3 and other perfluoroalkylsulfonylmethylide salts, Li[PF 5 (CF 2 CF 2 CF 3 ), Li[PF 4 (CF 2 CF 2 CF 3 ) 2 , Li[PF 3 (CF 2 CF 2 CF 3 ) 3 , Li[PF 5 (CF 2 CF 2 CF 2 CF 3 ), Li[PF 4 (CF 2 CF 2 CF 2 CF 3 ) 2 , Li[PF 3 (CF 2 CF 2 CF 2 CF 3 ) 3 and other perfluoroalkyl fluorophosphates, etc.

[0068] (L-3) Oxalate borates: lithium bis(oxalate)borate, lithium difluorooxalate borate, etc.

[0069] Among these, LiPF is preferred 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiClO 4 , Li(R f1 SO 3 ), LiN(R f1 SO 2 ), 2 , LiN(FSO 2 ), 2 or LiN(R f1 SO 2 )(R f2 SO 2 ). More preferably, LiPF 6 , LiBF 4 , LiN(R f1 SO 2 ), 2 , LiN(FSO 2 ), 2 or LiN(R f1 SO 2 )(R f2 SO 2 ). Particularly preferably, LiPF 6 . Here, R f1 and R f2 each represent a perfluoroalkyl group, and the number of carbon atoms is preferably 1 to 6.

[0070] In addition, the lithium salt used in the above non-aqueous electrolyte may be used alone or in any combination of two or more.

[0071] In the above non-aqueous electrolyte, the concentration of the lithium salt is usually 10.0 to 50.0% by mass, preferably 15.0 to 30.0% by mass. In the electrolyte of the present invention, the concentration of the lithium salt may be 11.0 to 30.0% by mass or 12.0 to 20.0% by mass. As the concentration, 0.5 to 1.5 M is preferred.

[0072] (Polymer (I))

[0073] The weight average molecular weight of Polymer (I) is 1000 to 150000, and there is no particular limitation as long as it is a polymer soluble in the above non-aqueous solvent.

[0074] The weight-average molecular weight of the polymer (I) is 1,000 to 150,000. If the weight-average molecular weight of the polymer (I) is less than 1,000, the effect of suppressing the performance degradation of the secondary battery cannot be obtained. Moreover, when the molecular weight of the polymer (I) in the non-aqueous electrolyte exceeds 150,000, the effect of suppressing the performance degradation of the secondary battery also deteriorates. The weight-average molecular weight of the polymer (I) is preferably 1,000 to 120,000, more preferably 1,000 to 100,000, still more preferably 1,000 to 70,000, and particularly preferably 1,000 to 50,000.

[0075] (Method for measuring the weight-average molecular weight)

[0076] In the present invention, the weight-average molecular weight of the polymer is measured by gel permeation chromatography (GPC). The weight-average molecular weight is the weight-average molecular weight in terms of polyethylene oxide. As the method for measuring the weight-average molecular weight, in principle, the value obtained by measuring by the following method is adopted. Among them, as long as the appropriate eluent is appropriately selected and used according to the type of the polymer.

[0077] Measuring instrument: HLC-8320GPC (trade name, manufactured by Tosoh Corporation)

[0078] Column: TOSOH TSKgel guardcolumn SuperHZ-L, Super HZM-H, Super HZ4000, Super HZ2000 (trade name, manufactured by Tosoh Corporation)

[0079] Carrier: THF (tetrahydrofuran) solution

[0080] Measurement temperature: 40 °C

[0081] Carrier flow rate: 0.35 mL / minute

[0082] Sample concentration: 0.2 mass%

[0083] Detector: RI (refractive index) detector

[0084] The adsorption rate of polymer (I) to acetylene black is preferably 15% or more. This adsorption rate is preferably 16% or more, more preferably 18% or more, further preferably 20% or more, further preferably 22% or more, and particularly preferably 24% or more. Also, this adsorption rate is usually 90% or less, and is actually set to 80% or less. Thus, the adsorption rate of polymer (I) to acetylene black is preferably 15-90%, more preferably 16-90%, further preferably 18-90%, further preferably 20-90%, further preferably 22-90%, and further preferably 24-80%. The adsorption rate of polymer (I) to acetylene black can be measured by the following method.

[0085] (Method for determining the adsorption rate to acetylene black)

[0086] In a mixed solvent obtained by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a mass ratio of EC:DMC:EMC = 3:4:3, LiPF as a lithium salt was mixed 6 until the concentration reached 1 M, and polymer (I) was mixed until the concentration reached 3% by mass, thereby preparing electrolyte (i). At 25 °C, the electrolyte (i) and acetylene black (average primary particle size (median particle size D50 based on volume) 35 nm, specific surface area 68 m 2 / g, powdery) were mixed so that the mass ratio of acetylene black to the electrolyte was 5:95 to obtain 10 g of a mixture. After standing for 1 hour, the electrolyte (referred to as electrolyte (ii)) was taken out. The amount of polymer (I) remaining in electrolyte (ii) was determined by H-NMR measurement. The adsorption rate of polymer (I) to acetylene black was calculated by the following formula. In the calculation of this adsorption rate, before and after the mixing of acetylene black and the electrolyte, the amount of the electrolyte was set to 9.5 g and in the same manner, the amount of polymer (I) in 9.5 g of the electrolyte before and after mixing was calculated and applied to the following formula. Thus, in the following formula, the amounts of electrolyte (i) and electrolyte (ii) are the same.

[0087] Adsorption rate of polymer (I) (%) = 100 - {[Amount of polymer (I) in electrolyte (ii) (g)] / [Amount of polymer (I) in electrolyte (i) (g)]} × 100

[0088] As the above acetylene black, for example, Denka Black (trade name) manufactured by Denka Company Limited can be used.

[0089] Moreover, in the test of the "adsorption rate of acetylene black" mentioned above, the "powder form" of the acetylene black used refers to the shape of powder (powder containing primary particles and / or aggregates (secondary particles) formed by aggregation of primary particles). For example, it does not include powder obtained by pressing the powder, granular powder, etc.

[0090] In the case of using commercially available acetylene black, the average particle size of the acetylene black is the value described in the manufacturer's catalog.

[0091] In the case where information on the average particle size of the manufacturer cannot be obtained or in the case of using synthetic acetylene black, the average particle size value (median particle size D50 based on volume in water) obtained by dispersing the acetylene black in water and measuring it using a laser diffraction / scattering particle size distribution measuring device (e.g., Particle LA-960V2 manufactured by HORIBA, Ltd.) is adopted.

[0092] In a non-aqueous electrolyte secondary battery, carbonaceous materials such as acetylene black (monomeric carbon materials) are often used as the negative electrode active material of the negative electrode active material layer and, moreover, as a conductive assistant for the negative electrode active material layer. And, in the positive electrode active material layer, carbonaceous materials are also usually used as a conductive assistant. For example, carbonaceous materials such as carbon black, graphite, activated carbon, carbon fiber, carbon nanotube, coke, soft carbon, and hard carbon are used as the negative electrode active material and, moreover, as a conductive assistant.

[0093] The fact that the polymer (I) shows a high adsorption rate of 15% or more for acetylene black means that the polymer (I) has a higher affinity for the negative electrode active material or the conductive assistant. Thus, when the electrode paste containing the electrolyte in which the polymer (I) is dissolved is applied to a secondary battery with an increased content of the electrode active material, its performance can be further improved.

[0094] The polymer (I) preferably shows an adsorption rate of 10% or more not only for the above-mentioned specific acetylene black but also for other carbonaceous materials contained in the electrode paste using the polymer (I). The adsorption rate of the polymer (I) for the carbonaceous material can be determined by the same method as the method for determining the adsorption rate for acetylene black, except that the carbonaceous material is used. The preferred range of the adsorption rate of the polymer (I) for the carbonaceous material can be set to be the same as the preferred range of the adsorption rate of the polymer (I) for acetylene black.

[0095] When the polymer (I) is used in the electrode paste for the negative electrode active material layer, the adsorption rate of the polymer (I) to the negative electrode active material used in the electrode paste is preferably 8% or more. The adsorption rate to the negative electrode active material is preferably 10% or more, more preferably 12% or more, further preferably 14% or more, and further preferably 18% or more. And, this adsorption rate is usually 80% or less, and is actually set to 70% or less. Thus, this adsorption rate is preferably 8 to 80%, more preferably 10 to 70%, further preferably 12 to 70%, further preferably 14 to 70%, and further preferably 18 to 70%. The adsorption rate of the polymer (I) to the negative electrode active material can be determined by the same method as the method for determining the adsorption rate to acetylene black, except that the negative electrode active material is used.

[0096] That the polymer (I) shows a high adsorption rate of 8% or more to the above-mentioned negative electrode active material means that the polymer (I) has a higher affinity for the negative electrode active material.

[0097] When the polymer (I) is used in the electrode paste for the positive electrode active material layer, the adsorption rate of the polymer (I) to the positive electrode active material used in the electrode paste is preferably 8% or more. The adsorption rate to the positive electrode active material is preferably 10% or more, more preferably 12% or more, and further preferably 14% or more. And, this adsorption rate is usually 80% or less, and is actually set to 70% or less. Thus, this adsorption rate is preferably 8 to 80%, more preferably 10 to 70%, further preferably 12 to 70%, and further preferably 14 to 70%. The adsorption rate of the polymer (I) to the positive electrode active material can be determined by the same method as the method for determining the adsorption rate to acetylene black, except that the positive electrode active material is used.

[0098] That the polymer (I) shows a high adsorption rate of 8% or more to the above-mentioned positive electrode active material means that the polymer (I) has a higher affinity for the positive electrode active material.

[0099] The above-mentioned polymer (I) preferably satisfies at least one of the following (a) to (d).

[0100] (a) Aromatic ring content: 40% by mass or more

[0101] (b) Acid value: 30 mgKOH / g or more

[0102] (c) Amine value: 30 mgKOH / g or more

[0103] (d) Hydroxyl value: 30 mgKOH / g or more

[0104] Satisfying at least one of the above (a) to (d) means that the polymer (I) contains a large amount of groups having an affinity for solid particles at a predetermined level, and more preferably groups having an affinity for carbonaceous materials.

[0105] The aromatic ring content of the above (a) is preferably 40% by mass or more, more preferably 45% by mass or more, and still more preferably 50% by mass or more. The upper limit is not particularly limited, but is actually 70% by mass or less. Thus, the aromatic ring content of the above (a) is preferably 40 to 70% by mass, more preferably 45 to 70% by mass, and still more preferably 50 to 70% by mass.

[0106] The aromatic ring content is calculated by the following formula.

[0107] Aromatic ring content = [total mass of aromatic rings constituting the polymer (I) / total mass of the polymer (I)] × 100

[0108] The mass of each aromatic ring in the above formula means the mass of the aromatic ring when the substituent is replaced by a hydrogen atom in the case where the aromatic ring has a substituent. That is, the mass of each aromatic ring is the mass of the structure composed of the ring-constituting atoms of the aromatic ring and the hydrogen atoms bonded to the ring-constituting atoms.

[0109] The acid value of the above (b) is more preferably 30 mgKOH / g or more, and still more preferably 45 mgKOH / g or more. The upper limit is not particularly limited, but is actually 60 mgKOH / g or less. Thus, the acid value of the above (b) is preferably 30 to 60 mgKOH / g, and more preferably 45 to 60 mgKOH / g.

[0110] The amine value of the above (c) is more preferably 30 mgKOH / g or more, and still more preferably 45 mgKOH / g or more. The upper limit is not particularly limited, but is actually 60 mgKOH / g or less. Thus, the amine value of the above (c) is preferably 30 to 60 mgKOH / g, and more preferably 45 to 60 mgKOH / g.

[0111] The hydroxyl value of the above (d) is more preferably 30 mgKOH / g or more, and still more preferably 45 mgKOH / g or more. The upper limit is not particularly limited, but is actually 60 mgKOH / g or less. Thus, the hydroxyl value of the above (d) is preferably 30 to 60 mgKOH / g, and more preferably 45 to 60 mgKOH / g.

[0112] The acid value of the above (b) can be determined by the neutralization titration method of JIS K 0070:1992.

[0113] The amine value in (c) above can be determined in accordance with ASTM D2074-07 (total amine value).

[0114] The hydroxyl value in (d) above can be determined by the neutralization titration method of JIS K 0070:1992.

[0115] The polymer (I) above preferably contains a group having an adsorptivity for solid particles in the adsorption slurry. Specifically, the polymer (I) above preferably contains at least one of an amino group, a carboxyl group, a phosphoric acid group, a phosphonic acid group, a sulfonic acid group, a hydroxyl group, a carbamoyl group, and an aromatic group (hereinafter, also referred to as an adsorptive group). Such a group is a group that exhibits an adsorptivity for solid particles in the slurry and contributes to improving the affinity with a positive electrode active material, a negative electrode active material, a conductive assistant, etc. In addition, the values of (a) to (d) above can be adjusted by controlling the content (the amount introduced into the polymer) of each of the above groups.

[0116] The amino group above may be any of an unsubstituted amino group, a mono-substituted amino group, and a di-substituted amino group. When the amino group is a substituted amino group, the substituent possessed by the amino group is preferably an alkyl group (preferably having 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, still more preferably 1 to 4 carbon atoms, and still more preferably a methyl group or an ethyl group).

[0117] The carboxyl group, phosphoric acid group (-OP(=O)(-OH)OH), phosphonic acid group (-P(=O)(-OH)OH), and sulfonic acid group above may be in the structure of a salt. And they may be in the structure of an acid anhydride. That is, in the present invention, when simply referred to as a "carboxyl group", it means a group containing a salt of a carboxyl group and a group formed by dehydration condensation of a carboxyl group in addition to the carboxyl group (-COOH). The same applies to the phosphoric acid group, phosphonic acid group, and sulfonic acid group.

[0118] The amino group possessed by the carbamoyl group (aminocarbonyl) above may be any of an unsubstituted amino group, a mono-substituted amino group, and a di-substituted amino group. When the amino group possessed by the carbamoyl group is a substituted amino group, the substituent possessed by the amino group is preferably an alkyl group (preferably having 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, still more preferably 1 to 4 carbon atoms, and still more preferably a methyl group or an ethyl group).

[0119] The above aromatic group refers to a monovalent group obtained by removing one hydrogen atom from an aromatic ring. The aromatic group may be an aromatic hydrocarbon group or an aromatic heterocyclic group, and is more preferably an aromatic hydrocarbon group. The number of carbon atoms in the aromatic group is preferably 5 to 20. In addition, the above aromatic group may have a substituent. Thus, the above aromatic hydrocarbon group and the above aromatic heterocyclic group may also have a substituent. The aromatic ring constituting the aromatic group may be a monocyclic ring or a fused ring, and is preferably a monocyclic ring. The above aromatic group is particularly preferably a phenyl group.

[0120] As long as the polymer (I) satisfies the provisions of the present invention, it may be a homopolymer or a copolymer, and is usually a copolymer. The polymerization mode of the copolymer may be any one of random and block.

[0121] The polymer (I) may be a polymer based on addition polymerization or a polymer based on condensation polymerization, and is preferably a polymer based on addition polymerization (a polymer whose main chain is composed of carbon-carbon bonds). By introducing the above adsorptive group into these polymers, the target polymer (I) can be obtained. As the monomer for introducing the above adsorptive group, for example, (meth)acrylic acid; maleic anhydride; (meth)acrylamide; styrene; vinyl compounds or acrylic compounds having an amino group, a phosphoric acid group, a phosphonic acid group, a sulfonic acid group, a hydroxyl group or a carbamoyl group, etc. can be cited. And the polymer (I) preferably further has a constituent derived from an alkyl (meth)acrylate, an aryl (meth)acrylate, etc. as a constituent.

[0122] The polymer (I) used in the present invention can be obtained by a usual polymer synthesis method corresponding to the polymerization mode.

[0123] In the non-aqueous electrolyte, the content of the polymer (I) is 0.1 to 5.0% by mass. If the content of the polymer (I) in the non-aqueous electrolyte is less than 0.1% by mass, the effect of suppressing the performance degradation of the obtained secondary battery cannot be sufficiently obtained. And when the content of the polymer (I) in the non-aqueous electrolyte exceeds 5.0% by mass, the effect of suppressing the performance degradation of the obtained secondary battery also decreases. In the non-aqueous electrolyte, the content of the polymer (I) is preferably 0.3 to 5.0% by mass, more preferably 0.4 to 4.0% by mass, and further preferably 0.5 to 3.0% by mass.

[0124] The electrolyte constituting the slurry of the present invention can be obtained as follows: mixing a non-aqueous solvent, a lithium salt and the polymer (I) and dissolving the lithium salt and the polymer (I) in the non-aqueous solvent.

[0125] <Positive electrode active material>

[0126] (Positive electrode active material)

[0127] The positive electrode active material is preferably a material capable of reversibly inserting and releasing lithium ions. As long as the material has the above characteristics, there is no particular limitation, and it can be a transition metal oxide, an organic substance, sulfur, or other elements capable of combining with Li, or a complex of sulfur and a metal.

[0128] Among them, as the positive electrode active material, it is preferable to use a lithium-containing transition metal oxide, and more preferably a lithium-containing transition metal oxide having a transition metal element M a (one or more elements selected from Co, Ni, Fe, Mn, Cu, and V). Moreover, elements M b (elements such as elements of Group 1 (Ia), Group 2 (IIa), Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, or B of the periodic table other than lithium) can also be mixed in the lithium-containing transition metal oxide. As the mixing amount, relative to the amount of the transition metal element M a (100 mol%) is preferably 0 to 30 mol%. It is more preferably a substance synthesized by mixing so that the molar ratio of Li / Ma becomes 0.3 to 2.2.

[0129] Specific examples of the lithium-containing transition metal oxide include (MA) a transition metal oxide having a layered rock salt structure, (MB) a transition metal oxide having a spinel structure, (MC) a lithium-containing transition metal phosphate compound, (MD) a lithium-containing transition metal halophosphate compound, and (ME) a lithium-containing transition metal silicate compound, etc.

[0130] Specific examples of the transition metal oxide having a layered rock salt structure (MA) include LiCoO 2 (lithium cobaltate [LCO]), LiNi 2 O 2 (lithium nickelate), LiNi 0.85 Co 0.10 Al 0.05 O 2 (lithium nickel cobalt aluminate [NCA]), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (lithium nickel manganese cobaltate [NMC]), and LiNi 0.5 Mn 0.5 O 2 (lithium manganese nickelate).

[0131] Specific examples of the transition metal oxide having a spinel structure (MB) include LiMn 2 O 4 (LMO), LiCoMnO 4 , Li 2FeMn 3 O 8 , Li 2 CuMn 3 O 8 , Li 2 CrMn 3 O 8 Li 2 NiMn 3 O 8 .

[0132] Examples of the lithium-containing transition metal phosphate compound (MC) include LiFePO 4 Li 3 Fe 2 (PO 4 ) 3 Olivine type iron phosphate, LiFeP 2 O 7 Iron pyrophosphate, LiCoPO 4 Cobalt phosphates and Li 3 V 2 (PO 4 ) 3 (lithium vanadium phosphate) and other monoclinic NASICON-type vanadium phosphate salts.

[0133] Examples of the lithium-containing transition metal halophosphate compound (MD) include Li 2 FePO 4 F and other fluoroferric phosphates, Li 2 MnPO 4 F and other manganese fluorophosphates and Li 2 CoPO 4 F and other cobalt fluorophosphates.

[0134] Examples of the lithium-containing transition metal silicate compound (ME) include Li 2 FeSiO 4 , Li 2 MnSiO 4 Li 2 CoSiO 4 wait.

[0135] In the present invention, the positive electrode active material is preferably a lithium-containing transition metal phosphate compound (MC), more preferably LiFePO 4 .

[0136] The shape of the positive electrode active material is not particularly limited, and is preferably particulate. The average particle size (average particle size converted to a sphere) of the positive electrode active material is not particularly limited. For example, it can be set to 0.1 to 50 μm. In order to make the positive electrode active material into a predetermined particle size, a usual pulverizer or classifier can be used. The positive electrode active material obtained by the calcination method can be used after being washed with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent.

[0137] In the case of using a commercially available positive electrode active material, the average particle size of the positive electrode active material is the value described in the manufacturer's catalog.

[0138] In the case where information on the average particle size of the manufacturer cannot be obtained or in the case of using a synthesized positive electrode active material, the average particle size value (median particle size D50 based on volume in water) obtained by dispersing the positive electrode active material in water and measuring it using a laser diffraction / scattering particle size distribution measuring device (for example, Particle LA-960V2 manufactured by HORIBA, Ltd.) is adopted.

[0139] The chemical formula of the compound obtained by the above calcination method can be calculated by using inductively coupled plasma (ICP) emission spectrometry as the measurement method. As a simplified method, it can be calculated based on the mass difference of the powder before and after calcination.

[0140] The surface of the positive electrode active material can be surface-coated with other oxides such as metal oxides, carbon-based materials, etc.

[0141] Examples of the surface coating material include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specifically, spinel titanate, tantalum-based oxides, niobium-based oxides, and lithium niobate-based compounds can be mentioned. For example, Li 4 Ti 5 O 12 、Li 2 Ti 2 O 5 、LiTaO 3 、LiNbO 3 、LiAlO 2 、Li 2 ZrO 3 、Li 2 WO 4 、Li 2 TiO 3 、Li 2 B 4 O 7 、Li 3 PO 4 、Li 2 MoO4 , Li 3 BO 3 , LiBO 2 , Li 2 CO 3 , Li 2 SiO 3 , SiO 2 , TiO 2 , ZrO 2 , Al 2 O 3 , B 2 O 3 and Li 3 AlF 6 . Also, carbon-based materials such as C, SiC, and SiOC (carbon-doped silicon oxide) can also be used as surface coating materials.

[0142] From the viewpoint of increasing the electron conductivity to a desired level, the positive electrode active material can be surface-coated with a carbon-based material. The positive electrode active material is preferably surface-coated with carbon (C). In the presence of an additive (organic substance) as a carbon source, a carbon-based surface coating can be formed by calcining the positive electrode active material. As the additive, for example, styrene-maleic anhydride copolymer, polystyrene, polycarbonate, etc. can be used.

[0143] Also, the surface of the positive electrode active material can be surface-treated with sulfur or phosphorus.

[0144] In addition, regarding the particle surface of the positive electrode active material, surface treatment can be performed by activating light or active gas (such as plasma) before and after the above surface coating.

[0145] The above positive electrode active material can be used alone or in combination of two or more.

[0146] When forming the positive electrode active material layer, the mass (mg) of the positive electrode active material per unit area (cm 2 ) (weight per unit area) of the positive electrode active material layer is not particularly limited. It can be appropriately determined according to the designed battery capacity.

[0147] (Negative electrode active material)

[0148] The negative electrode active material is preferably a material that can reversibly adsorb (occlude) and release lithium ions. As long as the material has the above characteristics, there is no particular limitation, and examples include carbonaceous materials, silicon-based materials, metal oxides, metal composite oxides, lithium monomers, lithium alloys, or negative electrode active materials that can form alloys with lithium. Among them, from the viewpoint of reliability, carbonaceous materials or silicon-based materials can be preferably used.

[0149] The carbonaceous material used as the negative electrode active material refers to a material substantially composed of carbon. For example, carbonaceous materials obtained by calcining various synthetic resins such as carbon black, graphite (natural graphite, artificial graphite such as vapor-grown graphite, etc.), and PAN (polyacrylonitrile)-based resins or furfuryl alcohol resins can be cited. In addition, various carbon fiber materials such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA (polyvinyl alcohol)-based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers, mesophase microspheres, graphite whiskers, and plate-like graphite can also be cited.

[0150] As the metal oxides and metal composite oxides used as the negative electrode active material, as long as they are oxides capable of adsorbing and releasing lithium, there are no particular limitations. Amorphous oxides are preferred, and chalcogenides, which are reaction products between metal elements and Group 16 elements of the periodic table, can also be preferably cited. The amorphousness mentioned here means a material having a broad scattering band with a peak in the region of 20° to 40° in terms of 2θ value in X-ray diffraction using CuKα radiation, and may also have crystalline diffraction lines.

[0151] Among the compound groups composed of the above amorphous oxides and chalcogenides, amorphous oxides of semi-metal elements and the above chalcogenides are more preferred, and oxides or chalcogenides composed of a single element selected from Group 13 (IIIB) to Group 15 (VB) elements of the periodic table, Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi, or a combination of two or more of these are particularly preferred. As specific examples of the preferred amorphous oxides and chalcogenides, for example, Ga 2 O 3 、GeO、PbO、PbO 2 、Pb 2 O 3 、Pb 2 O 4 、Pb 3 O 4 、Sb 2 O 3 、Sb 2 O 4 、Sb 2 O 8 Bi 2 O 3 、Sb 2 O 8 Si 2 O 3 、Sb 2 O 5 、Bi 2 O 3 、Bi 2 O4 , GeS, PbS, PbS 2 , Sb 2 S 3 and Sb 2 S 5 .

[0152] In terms of the charge-discharge characteristics at high current density, the metal (composite) oxide and the above chalcogenide are preferably composed of at least one of titanium and lithium. As the metal composite oxide containing lithium (lithium composite metal oxide), for example, a composite oxide of lithium oxide and the above metal (composite) oxide or the above chalcogenide can be cited. More specifically, Li 2 SnO 2 .

[0153] The negative electrode active material also preferably contains titanium atoms. More specifically, since TiNb 2 O 7 (titanium niobium oxide [NTO]), Li 4 Ti 5 O 12 (lithium titanate [LTO]) has a small volume change when adsorbing and releasing lithium ions, it is preferred in terms of excellent rapid charge-discharge characteristics, suppressing electrode deterioration and improving the life of the lithium-ion secondary battery.

[0154] Regarding the lithium alloy as the negative electrode active material, as long as it is an alloy commonly used as the negative electrode active material of a secondary battery, it is not particularly limited. For example, a lithium-aluminum alloy can be cited.

[0155] The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is a negative electrode active material commonly used as the negative electrode active material of a secondary battery. As such an active material, a negative electrode active material having a silicon atom or a tin atom, various metals such as Al and In can be cited. A negative electrode active material having a silicon atom (active material containing a silicon atom) capable of achieving a higher battery capacity is preferred, and an active material containing a silicon atom in which the content of silicon atoms is 40 mol% or more of all constituent atoms is more preferred.

[0156] Generally speaking, compared with a carbon negative electrode (such as graphite and acetylene black), a negative electrode containing these negative electrode active materials (for example, a Si negative electrode containing an active material containing a silicon atom, a Sn negative electrode containing an active material having a tin atom) can adsorb more Li ions. That is, the adsorption amount of Li ions per unit mass increases. Therefore, the battery capacity (energy density) can be increased. As a result, it has the advantage of being able to extend the battery driving time.

[0157] As the active material containing silicon atoms, for example, silicon materials such as Si, SiOx (0 < x ≤ 1) can be cited, and further alloys containing titanium, vanadium, chromium, manganese, nickel, copper or lanthanum (for example, LaSi 2 , VSi 2 ) or organized active materials (for example, LaSi 2 / Si) can be cited. In addition, SnSiO 3 , SnSiS 3 and other active materials containing silicon atoms and tin atoms can be cited. In addition, SiOx itself can be used as a negative electrode active material (semi-metal oxide), and Si is generated by the operation of the battery, so it can be used as an active material (its precursor material) capable of alloying with lithium.

[0158] As the negative electrode active material having tin atoms, for example, Sn, SnO, SnO 2 , SnS, SnS 2 can be cited, and further the above-mentioned active materials containing silicon atoms and tin atoms can be cited. And it also contains a composite oxide with lithium oxide, for example, Li 2 SnO 2 .

[0159] In the present invention, the negative electrode active material is preferably a carbonaceous material, and more preferably artificial graphite.

[0160] The shape of the negative electrode active material is not particularly limited, and it is preferably particulate. The average particle size (average particle size in terms of sphere conversion) of the negative electrode active material is preferably 0.1 to 60 μm. In order to obtain a predetermined particle size, a usual pulverizer or classifier can be used. For example, a mortar, a ball mill, a sand mill, a vibration ball mill, a satellite ball mill, a planetary ball mill, a rotary air current type jet mill or a sieve can be preferably used. During pulverization, wet pulverization can also be carried out in the presence of an organic solvent such as water or methanol. In order to obtain the desired particle size, classification is preferably carried out. As the classification method, there is no particular limitation, and a sieve, an air classifier, etc. can be used as needed. Classification can be carried out using both dry and wet methods simultaneously.

[0161] In the case of using a commercially available negative electrode active material, the average particle size of the negative electrode active material is the value described in the manufacturer's catalog.

[0162] In the case where the information on the average particle size of the manufacturer cannot be obtained or in the case of using a synthesized negative electrode active material, the average particle size value (median particle size D50 based on volume in water) obtained by dispersing the negative electrode active material in water and measuring it using a laser diffraction / scattering type particle size distribution measuring device (for example, Particle LA-960V2 manufactured by HORIBA, Ltd.) is adopted.

[0163] The above-mentioned negative electrode active material can be used alone or in combination of two or more kinds. Among them, a combination of an active material containing a silicon atom and a carbonaceous material is preferred, and a combination of SiOx (0 < x ≤ 1) and graphite is particularly preferred. When SiOx (0 < x ≤ 1) and graphite are combined, the mass ratio (SiOx / graphite) is preferably 2 or less, more preferably 1 or less, and further preferably 0.5 or less.

[0164] When forming the negative electrode active material layer, the mass (mg) of the negative electrode active material per unit area (cm 2 ) (weight per unit area) of the negative electrode active material layer is not particularly limited. It can be appropriately determined according to the designed battery capacity.

[0165] The chemical formula of the compound obtained by the above-mentioned calcination method can be calculated by using inductively coupled plasma (ICP) emission spectrometry as the measurement method. As a simplified method, it can be calculated based on the mass difference of the powder before and after calcination.

[0166] <Conductive additive>

[0167] There is no particular limitation on the conductive additive, and known general conductive additives can be used. For example, it can be graphite-based materials such as natural graphite and artificial graphite, which are electron conductive materials, carbon black-based materials such as acetylene black, Ketjen black, and furnace black, amorphous carbon such as needle coke, carbon fiber-based materials such as vapor-grown carbon fiber or carbon nanotube, carbonaceous materials such as graphene or fullerene, or metal powders and metal fibers such as copper and nickel. Conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives can also be used.

[0168] In the present invention, the conductive additive is preferably a carbonaceous material, and more preferably acetylene black.

[0169] When the positive electrode active material and the conductive additive are used simultaneously, among the above-mentioned conductive additives, a conductive additive that does not intercalate and release Li and does not function as an active material during charge and discharge of the battery is used as the conductive additive. Thus, among the conductive additives, a conductive additive that can function as an active material in the active material layer during charge and discharge of the battery is classified as an active material rather than a conductive additive. Whether it functions as an active material during charge and discharge of the battery is not determined by a single factor and can be determined according to the combination with the active material.

[0170] One kind of conductive additive can be used, or two or more kinds can be used.

[0171] The shape of the conductive additive is not particularly limited, and is preferably particulate. The median particle size D50 (volume basis) of the conductive additive is not particularly limited, and is, for example, preferably 0.01 to 50 μm, more preferably 0.02 to 10.0 μm.

[0172] <Other components>

[0173] If necessary, the electrode paste can contain an ionic liquid, a thickener, an antifoaming agent, a leveling agent, a dehydrating agent, an antioxidant, etc.

[0174] <Content of each component>

[0175] The content of the electrode active material in the positive electrode paste and in the negative electrode paste is respectively preferably 40 to 90% by mass, more preferably 50 to 90% by mass, further preferably 60 to 90% by mass, and particularly preferably 65 to 85% by mass.

[0176] The content of the positive electrode active material in the positive electrode paste is not particularly limited, and is preferably 60 to 90% by mass, more preferably 65 to 85% by mass, and further preferably 70 to 80% by mass.

[0177] The content of the negative electrode active material in the negative electrode paste is not particularly limited, and is preferably 50 to 90% by mass, more preferably 55 to 80% by mass, and further preferably 60 to 80% by mass.

[0178] The content of the conductive additive in the positive electrode paste and in the negative electrode paste is respectively preferably 0.1 to 10% by mass, more preferably 0.5 to 5.0% by mass.

[0179] The content of the conductive additive in the positive electrode paste can also be set to 0.5 to 10% by mass, preferably 0.6 to 8.0% by mass, more preferably 0.8 to 5.0% by mass, and further preferably 1.0 to 3.0% by mass.

[0180] The content of the conductive additive in the negative electrode paste can also be set to 0.1 to 3.0% by mass, preferably 0.2 to 2.5% by mass, more preferably 0.5 to 2.0% by mass, and further preferably 0.8 to 1.5% by mass.

[0181] In the paste of the present invention, preferably, the content of the electrode active material is 40 to 90% by mass, and the content of the conductive additive is 0.1 to 10% by mass.

[0182] The content of other components is not particularly limited, and is preferably 1% by mass or less.

[0183] The total content of the solid particles (electrode active material and conductive additive) in the paste of the present invention is preferably 40 to 95% by mass, more preferably 50 to 90% by mass, and further preferably 60 to 85% by mass.

[0184] The content of the non-aqueous electrolyte in the paste of the present invention is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and still more preferably 15 to 40% by mass.

[0185] [Non-aqueous electrolyte secondary battery and method for manufacturing non-aqueous electrolyte secondary battery]

[0186] The non-aqueous electrolyte secondary battery of the present invention (hereinafter, also referred to as "the secondary battery of the present invention") is a non-aqueous electrolyte secondary battery having the paste of the present invention as an electrode active material layer. And, the method for manufacturing the non-aqueous electrolyte secondary battery of the present invention includes the step of adding the paste of the present invention as an electrode active material layer.

[0187] Before describing the secondary battery of the present invention, the structure of a general non-aqueous electrolyte secondary battery will be described.

[0188] Figure 1 It is a cross-sectional view schematically showing the laminated structure of a general non-aqueous electrolyte secondary battery 10 including the working electrode during battery operation. The non-aqueous electrolyte secondary battery 10 has a laminated structure (hereinafter, also referred to as an electrode laminate) having, in order from the negative electrode side, a negative electrode current collector 1, a negative electrode active material layer 2, a separator 3, a positive electrode active material layer 4, and a positive electrode current collector 5. The space between the negative electrode active material layer 2 and the positive electrode active material layer 4 is filled with a non-aqueous electrolyte (not shown) and separated by a separator 3. The separator 3 has pores and functions as a separator between the positive and negative electrodes that insulates the positive and negative electrodes while allowing the electrolyte and ions to pass through the pores. With this structure, for example, in the case of a lithium ion secondary battery, during charging, electrons (e - ) are supplied to the negative electrode side through an external circuit, and at the same time, lithium ions (Li + ) move from the positive electrode to the negative electrode through the electrolyte and accumulate in the negative electrode. On the other hand, during discharging, the lithium ions (Li + ) accumulated in the negative electrode return to the positive electrode side through the electrolyte and supply electrons to the working part 6. In the illustrated example, a light bulb is used in the working part 6 and is lit by discharging.

[0189] In the present invention and this specification, the negative electrode current collector 1 and the negative electrode active material layer 2 are collectively referred to as the negative electrode or the negative electrode layer, the positive electrode active material layer 4 and the positive electrode current collector 5 are collectively referred to as the positive electrode or the positive electrode layer, and the negative electrode and the positive electrode are collectively referred to as the electrode or the electrode layer. And, the negative electrode active material layer 2 and the positive electrode active material layer 4 are collectively referred to as the electrode active material layer.

[0190] Next, the basic structural features of the secondary battery of the present invention will be described. As described above, in the secondary battery of the present invention, the electrode active material layer is an electrode paste layer in which the electrode active material is dispersed in a non-aqueous electrolyte. Thus, in terms of the electrode active material layer being a paste (suspension, dispersion) dispersed in a non-aqueous electrolyte, its structure is different from that of a general non-aqueous electrolyte secondary battery.

[0191] That is, in a general non-aqueous electrolyte secondary battery, a coating liquid is prepared by dispersing an electrode active material in a medium that does not contain an electrolyte, the coating liquid is coated on a current collector to form a coating film, and the coating film is dried to form a thin-film electrode active material layer. A binder material (adhesive) is usually contained in the coating liquid, and the electrode active material particles are firmly bonded together to form a hard electrode active material layer. Since the non-aqueous electrolyte will exist in such a manner on the electrode active material layer thus formed (between the negative electrode active material layer and the positive electrode active material layer), even if there is a part in the electrode active material layer where the non-aqueous electrolyte can penetrate into a part of it, the overall state is that of a hard solid particle layer, rather than a paste layer.

[0192] In contrast, in the secondary battery of the present invention, the electrode active material layer is an electrode paste layer in which solid particles containing an electrode active material and a conductive assistant are dispersed in a non-aqueous electrolyte, and the non-aqueous electrolyte is obtained by dissolving a lithium salt (electrolyte) and a polymer (I) in a non-aqueous solvent. When this electrode paste layer functions as an electrode active material layer, a strong adhesiveness between the electrode active material particles is not required, so the electrode paste layer usually does not contain a binder material. The electrode active material layer is the electrode paste layer and the electrode paste layer contacts the separator. In addition, the basic layer structure of the secondary battery of the present invention is the same as Figure 1 the layer structure shown.

[0193] Hereinafter, a preferred embodiment of the secondary battery of the present invention will be described.

[0194] A preferred embodiment of the secondary battery of the present invention is a secondary battery having a positive electrode active material layer, a separator, and a negative electrode active material layer in sequence, and at least one of the positive electrode active material layer and the negative electrode active material layer is a layer of the paste of the present invention. Both the positive electrode active material layer and the negative electrode active material layer can be the paste layers of the present invention.

[0195] In the case of using an electrode paste other than the paste of the present invention to form any one of the positive electrode active material layer and the negative electrode active material layer, as the electrode active material layer other than the paste of the present invention, an electrode active material layer such as an electrode paste layer usually obtained by using a medium containing an electrolyte can be used.

[0196] Hereinafter, the electrode paste layer serving as the positive electrode active material layer is sometimes referred to as the positive electrode paste layer, and the electrode paste layer serving as the negative electrode active material layer is referred to as the negative electrode paste layer.

[0197] The positive electrode paste layer preferably forms a positive electrode by forming a laminate with the positive electrode current collector.

[0198] The negative electrode paste layer preferably forms a negative electrode by forming a laminate with the negative electrode current collector.

[0199] In the above non-aqueous electrolyte secondary battery, the positive electrode paste layer is preferably sandwiched between the positive electrode current collector and the separator. Also, the negative electrode paste layer is preferably sandwiched between the negative electrode current collector and the separator. That is, it is preferred that the positive electrode layer is composed of a laminate of the positive electrode current collector and the positive electrode paste layer, and the negative electrode layer is composed of a laminate of the negative electrode current collector and the negative electrode paste layer.

[0200] The thickness of the positive electrode paste layer is preferably 100 μm or more, more preferably 150 μm or more, also preferably 200 μm or more, also preferably 250 μm or more, also preferably 300 μm or more. And the thickness of this positive electrode paste layer is usually 1000 μm or less, preferably 800 μm or less, more preferably 700 μm or less, and may also be 650 μm or less. If the thickness of the positive electrode paste layer is expressed as a preferred range, it is preferably 100 to 1000 μm, more preferably 150 to 800 μm, further preferably 200 to 700 μm, further preferably 250 to 700 μm, and particularly preferably 300 to 650 μm.

[0201] The thickness of the negative electrode paste layer is preferably 100 μm or more, more preferably 150 μm or more, also preferably 200 μm or more, also preferably 250 μm or more, also preferably 300 μm or more. And the thickness of this negative electrode paste layer is usually 1000 μm or less, preferably 800 μm or less, more preferably 700 μm or less, and may also be 650 μm or less. If the thickness of the negative electrode paste layer is expressed as a preferred range, it is preferably 100 to 1000 μm, more preferably 150 to 800 μm, further preferably 200 to 700 μm, further preferably 250 to 700 μm, and particularly preferably 300 to 650 μm.

[0202] The method for forming the laminate (positive electrode layer member) of the positive electrode current collector and the positive electrode paste layer is not particularly limited. For example, by coating a positive electrode paste containing the constituent components (solvent, positive electrode active material, electrolyte, additives as required, conductive aids, etc.) of the positive electrode paste layer on the positive electrode current collector to form a coating film with a desired thickness, a positive electrode layer member can be obtained.

[0203] The coating method of the slurry is not particularly limited. For example, roll coating or drop coating can be used, or stamping (roll stamping or flat stamping) can be performed after uniformly coating the slurry on the current collector, or the slurry can be set and extended within a frame of a specified thickness for coating.

[0204] The method for forming the laminate of the negative electrode current collector and the negative electrode slurry layer (negative electrode layer member) is not particularly limited and can be appropriately formed according to the method for forming the laminate of the positive electrode current collector and the positive electrode slurry layer (positive electrode layer member).

[0205] For each material, component, etc. used in the non-aqueous electrolyte secondary battery of the present invention, in addition to the polymer (I) used in the non-aqueous electrolyte, the materials used in a general non-aqueous electrolyte secondary battery can also be appropriately applied. And regarding the manufacturing method of the non-aqueous electrolyte secondary battery of the present invention, in addition to forming the electrode active material layer into a specific slurry layer, general methods can also be appropriately adopted. For example, Japanese Patent Application Laid-Open No. 2016-201308, Japanese Patent Application Laid-Open No. 2005-108835, Japanese Patent Application Laid-Open No. 2012-185938, Japanese Patent Application Laid-Open No. 2017-147222, etc. can be appropriately referred to.

[0206] <Uses of the non-aqueous electrolyte secondary battery>

[0207] For example, when mounted on an electronic device, the non-aqueous electrolyte secondary battery can be mounted on electronic devices such as laptop computers, pen input computers, mobile computers, e-book readers, mobile phones, wireless phone handsets, pagers, handheld terminals, portable fax machines, portable copiers, portable printers, stereo headphones, video cameras, liquid crystal TVs, handheld vacuum cleaners, portable CDs, floppy disks, electric shavers, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, etc. And as consumer goods, it can be mounted on automobiles, electric vehicles, motors, lighting fixtures, toys, game consoles, load regulators, clocks, flashlights, cameras, and medical devices (pacemakers, hearing aids, shoulder massagers, etc.). In addition, it can be used as various military supplies and aerospace supplies. And it can also be combined with solar cells.

[0208] Among them, it is preferably applicable to applications that require high capacity and high-rate discharge characteristics. For example, in energy storage devices and the like where large capacity is expected in the future, high safety is essential, and at the same time, the performance of the battery must also be compatible. And it is expected that electric vehicles and the like will be equipped with high-capacity secondary batteries for daily charging at home. According to the present invention, it can appropriately cope with such usage modes and exhibit its excellent effects.

[0209] Examples

[0210] The present invention will be further described in detail according to embodiments, but the present invention is not limited to these embodiments.

[0211] [Preparation of Polymer]

[0212] [Preparation of Polymer 1]

[0213] Polymer 1a composed of the constituent components shown in Table 1 described later was prepared as follows.

[0214] At room temperature, 10 g of styrene, 6 g of maleic anhydride, 4 g of methyl methacrylate, 1.5 g of azobisisobutyronitrile, and 40 g of methyl ethyl ketone were mixed to prepare Solution A.

[0215] While purging nitrogen into a three-necked flask equipped with a stirring device, a thermometer, a reflux condenser, a thermostat, and a dropping pump, 100 g of methyl ethyl ketone was added, and while stirring, the temperature was raised to 85°C. Using the dropping pump, Solution A prepared above was dropped into the three-necked flask at a constant rate over 1 hour. After the dropping was completed, stirring was carried out at the same temperature, and the reaction was terminated after 5 hours. After the reaction was completed, Polymer 1a was obtained by concentrating the solution. The weight-average molecular weight of the obtained Polymer 1a was 10,000.

[0216] In the preparation of the above Polymer 1a, except for changing the addition amount of azobisisobutyronitrile so that the obtained polymer has the weight-average molecular weight shown in Table 2, Polymers 1b to 1f were prepared in the same manner as the preparation of Polymer 1a.

[0217] [Preparation of Polymers 2 and 3]

[0218] In the preparation of the above Polymer 1a, except for setting the types and blending amounts (parts by mass) of the monomers as described in Table 1 described later, Polymers 2 and 3 were prepared in the same manner as the preparation of Polymer 1a.

[0219] [Table 1]

[0220] Table 1: Polymer Composition

[0221]

[0222] The abbreviations in Table 1 above are as follows.

[0223] St: Styrene

[0224] MA: Maleic Anhydride

[0225] DM: Dimethylaminoethyl Methacrylate

[0226] HEMA: 2-Hydroxyethyl Methacrylate

[0227] MMA: Methyl methacrylate

[0228] The blank column indicates the absence of the component. The unit of the blending amount of each component is parts by mass.

[0229] The weight-average molecular weight (Mw) of each of the above polymers was measured as described above. The results are shown in Table 2.

[0230] In addition, the adsorption rate of each polymer to the following 3 kinds of solid particles (powders) was determined according to the method for determining the adsorption rate of acetylene black described above. In the case where the solid particle is a solid particle other than acetylene black, the adsorption rate was calculated in the same manner as the adsorption rate to acetylene black, except that the solid particle was used instead of acetylene black. The results are shown in the "Adsorption rate of polymer" column of Table 2 according to the type of solid particle used.

[0231] - Solid particles used -

[0232] LFP: LiFePO 4 , manufactured by Gelon Co., Ltd.

[0233] AB: Acetylene black, Denka Black (trade name), manufactured by Denka Company Limited, powdery, average primary particle size (median particle size D50 based on volume) 35 nm, specific surface area 68 m 2 / g

[0234] Artificial graphite: UF-G30 (trade name), manufactured by SHOWA DENKO K.K.

[0235] Polymers 1a to 1f, 2, and 3 all have an aromatic ring content of 40% by mass or more. Furthermore, the acid value of polymers 1a to 1f is 30 mgKOH / g or more. The amine value of polymer 2 is 30 mgKOH / g or more. The hydroxyl value of polymer 3 is 30 mgKOH / g or more. The determination of the aromatic ring content, acid value, amine value, and hydroxyl value was carried out by the methods described above.

[0236] An electrode paste containing each of the above polymers was prepared as follows, and a secondary battery was prepared using the obtained electrode paste.

[0237] [Preparation of electrode paste]

[0238] <Preparation of electrolyte solution>

[0239] As a solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:DMC:EMC = 3:4:3, and LiPF was mixed as a lithium salt 6The concentration was made to reach 1 M, and the mixed polymer 1a was added to make its concentration in the electrolyte reach 0.1% by mass, thereby preparing the electrolyte used in Example 1.

[0240] In the preparation of the electrolytes used in Example 1 above, the types of polymers, Mw, and polymer content were changed as shown in Table 2 to prepare the electrolytes used in Examples 2 to 10 and the electrolytes used in Comparative Examples 2 and 3. In the preparation of the electrolyte used in Example 1, the electrolyte used in Comparative Example 1 was prepared without adding a polymer.

[0241] In the electrolytes containing these polymers, each polymer was dissolved.

[0242] <Preparation of Positive Electrode Slurry>

[0243] With LiFePO as the active material 4 (manufactured by Gelon Co., Ltd.) at 74% by mass, acetylene black (manufactured by Denka Company Limited, Denka Black (trade name)) as a conductive aid for the carbonaceous material at 1.5% by mass, and each of the electrolytes obtained above at 24.5% by mass were mixed, and a centrifugal planetary mixer (manufactured by THINKY CORPORATION: Awatori Rentaro) was used to stir at 1000 rpm for 120 seconds, thereby obtaining the positive electrode slurries of Examples 1A to 10A and Comparative Examples 1A to 3A.

[0244] <Preparation of Negative Electrode Slurry>

[0245] Artificial graphite (manufactured by SHOWA DENKO K.K., UF-G30 (trade name)) as the active material of the carbonaceous material at 64% by mass, acetylene black (manufactured by Denka Company Limited, Denka Black (trade name)) as a conductive aid for the carbonaceous material at 1% by mass, and each of the electrolytes obtained above at 35% by mass were mixed, and a centrifugal planetary mixer (manufactured by THINKY CORPORATION: Awatori Rentaro) was used to stir at 1000 rpm for 120 seconds, thereby obtaining the negative electrode slurries of Examples 1B to 10B and Comparative Examples 1B to 3B.

[0246] [Battery Fabrication]

[0247] Each of the positive electrode slurries obtained as described above was coated on an aluminum current collector (aluminum foil) to a thickness of 300 μm, thereby fabricating a positive electrode having a current collector and a positive electrode active material layer. Further, each of the negative electrode slurries obtained as described above was coated on a copper current collector (copper foil) to a thickness of 300 μm, thereby fabricating a negative electrode having a current collector and a negative electrode active material layer. Then, a polypropylene separator (thickness 25 μm) was laminated on the negative electrode, and then the positive electrode was laminated, thereby obtaining an electrode laminate composed of a copper current collector - negative electrode active material layer - separator - positive electrode active material layer - aluminum current collector.

[0248] By ultrasonic welding, an aluminum sheet and a nickel sheet were respectively welded to the ends of the aluminum current collector and the copper current collector of each of the obtained electrode laminates to form electrode groups. These electrode groups were sandwiched between two aluminum laminated films, three sides were heat-sealed, and the remaining one side was vacuum-sealed, thereby fabricating a laminated battery (non-aqueous electrolyte secondary battery).

[0249] In addition, when preparing the electrode laminate, a positive electrode slurry and a negative electrode slurry containing the same polymer were used in combination. For example, the positive electrode slurry of Example 1A and the negative electrode slurry of Example 1B were used in combination to form an electrode laminate. For convenience, the battery made using the positive electrode slurry of Example 1A and the negative electrode slurry of Example 1B was referred to as the secondary battery of Example 1. The same applies to Examples 2 to 10 and Comparative Examples 1 to 3.

[0250] Under the following conditions, each laminated battery was charged to 3.6 V at 0.1C and then discharged to 2.0 V, thereby completing the initialization of the battery. The discharge capacity during this initialization was obtained as the initial discharge capacity. The initial discharge capacity of the laminated battery of Example 1 was 100 mAh / g.

[0251] - Initialization conditions (charge-discharge conditions at 0.1C) -

[0252] Charge: Constant current (CC) constant voltage (CV) charging, CC current 10 mA, cut-off voltage 3.6 V, CV cut-off current 0.5 mA

[0253] Discharge: Constant current (CC) discharge, CC current 10 mA, cut-off voltage 2.0 V

[0254] [Battery performance]

[0255] The battery performance of each initialized laminated battery was evaluated as follows.

[0256] Specifically, under the following conditions, the above-mentioned initialized laminated battery was charged and discharged at 1C, and the discharge capacity during discharge was obtained as the discharge capacity at 1C.

[0257] Based on the initial discharge capacity (discharge capacity at 0.1C) and the discharge capacity at 1C obtained as described above, the discharge capacity retention rate was calculated using the following formula, and the evaluation was carried out according to the following evaluation criteria.

[0258] - Charge and discharge conditions at 1C -

[0259] Constant current (CC) constant voltage (CV) charging: CC current 10 mA, cut-off voltage 3.6 V, CV cut-off current 0.5 mA

[0260] Constant current (CC) discharge: CC current 100 mA, cut-off voltage 2.0 V

[0261] [Discharge capacity retention rate (%)] = [(Discharge capacity at 1C) / (Initial discharge capacity at 0.1C)] × 100

[0262] - Evaluation criteria for discharge capacity retention rate -

[0263] A: 90% or more

[0264] B: 88% or more and less than 90%

[0265] C: 85% or more and less than 88%

[0266] D: Less than 85%

[0267] [Wettability evaluation]

[0268] Through the wettability test of granular solid particles, the wettability of the electrolytes containing each polymer obtained above for the solid particles constituting the positive electrode and the negative electrode was evaluated.

[0269] <Positive electrode pressed powder>

[0270] 1 g of the powder obtained by mixing LiFePO 4 (LFP) and acetylene black in a mass ratio of 75:1.5 was pressed under a pressure of 10 MPa to form cylindrical particles with a diameter of 1 cm, thereby obtaining the pressed powder.

[0271] The time until the electrolyte droplet penetrated into the particles was measured when 100 μl of the electrolyte obtained above was dropped on the surface of the particles, and the evaluation was carried out according to the following evaluation criteria. The state of droplet penetration was observed using a contact angle measuring instrument, and the time until the droplet disappeared from the surface after dropping the droplet was measured.

[0272] - Evaluation criteria for wettability of positive electrode pressed powder -

[0273] A: Less than 1 second

[0274] B: 1 second or more and less than 5 seconds

[0275] C: More than 5 seconds and less than 10 seconds

[0276] D: More than 10 seconds

[0277] <Negative electrode compacted powder>

[0278] 1 g of a powder obtained by mixing artificial graphite and acetylene black at a mass ratio of 64:1 was applied with a pressure of 10 MPa to form cylindrical particles with a diameter of 1 cm, thereby obtaining a compacted powder.

[0279] The time until the electrolyte droplet penetrated into the particles when 100 μl of the electrolyte obtained above was dropped on the surface of the particles was measured, and the following evaluation criteria were applied for evaluation. The state of penetration of the droplet was observed using a contact angle measuring instrument, and the time until the droplet disappeared from the surface after the droplet was dropped was measured.

[0280] - Evaluation criteria for wettability of negative electrode compacted powder -

[0281] A: Less than 1 second

[0282] B: 1 second or more and less than 5 seconds

[0283] C: 5 seconds or more and less than 10 seconds

[0284] D: 10 seconds or more

[0285] [Table 2]

[0286]

[0287] When the electrode slurries of Comparative Example 1 obtained using an electrolyte without a polymer, the electrode slurries of Comparative Example 2 obtained using an electrolyte with an excessive polymer content, and the electrode slurries of Comparative Example 3 obtained using an electrolyte with an excessively large weight-average molecular weight of the polymer were all used in a secondary battery, the discharge capacity retention rate was less than 85%. It is considered that this is because the affinity between the solid particles and the electrolyte is low in these electrode slurries. In fact, in the wettability test of the electrolyte used in the preparation of the electrode slurries of Comparative Examples 1 to 3 on the particles of the solid particles constituting the positive and negative electrodes, it took more than 10 seconds to disappear from the particle surface.

[0288] In contrast, the electrode slurries of Examples 1 to 10 using electrolytes containing 0.1 to 5.0% by mass of polymers 1a to 1e, 2, and 3 with a weight-average molecular weight of 1000 to 150000 all had excellent discharge capacity retention rates when fabricated into secondary batteries.

[0289] The present invention has been described together with its embodiments. However, unless otherwise specified, it is considered that the present invention should not be limited to any details in the description, and should be interpreted broadly without departing from the spirit and scope of the invention shown in the appended claims.

[0290] This application claims priority based on Japanese Patent Application No. 2022-175037, which was filed in Japan on October 31, 2022, and its content is incorporated herein by reference as part of the description of this specification.

[0291] Symbol Explanation

[0292] 10 - Non-aqueous electrolyte secondary battery, 1 - Negative electrode current collector, 2 - Negative electrode active material layer, 3 - Separator, 4 - Positive electrode active material layer, 5 - Positive electrode current collector, 6 - Working part (light bulb).

Claims

1. A slurry for a non-aqueous electrolyte secondary battery, which is a slurry for a non-aqueous electrolyte secondary battery obtained by dispersing solid particles containing an electrode active material and a conductive additive in a non-aqueous electrolyte. Among them, the non-aqueous electrolyte is obtained by dissolving a lithium salt and a polymer (I) in a non-aqueous solvent. The weight-average molecular weight of the polymer (I) is 1,000 to 150,000, and the content of the polymer (I) in the non-aqueous electrolyte is 0.1 to 5.0% by mass.

2. The slurry for a non-aqueous electrolyte secondary battery according to claim 1, Among them, the adsorption rate of the polymer (I) to acetylene black is 15% or more.

3. The slurry for a non-aqueous electrolyte secondary battery according to claim 1, Among them, the electrode active material is a positive electrode active material, and the adsorption rate of the polymer (I) to the positive electrode active material is 10% or more.

4. The slurry for a non-aqueous electrolyte secondary battery according to claim 1, Among them, the electrode active material is a negative electrode active material, and the adsorption rate of the polymer (I) to the negative electrode active material is 10% or more.

5. The slurry for a non-aqueous electrolyte secondary battery according to claim 1, Among them, the polymer (I) contains at least one of an amino group, a carboxyl group, a phosphoric acid group, a phosphonic acid group, a sulfonic acid group, a hydroxyl group, a carbamoyl group, and an aromatic group.

6. The slurry for a non-aqueous electrolyte secondary battery according to claim 1, Among them, in the slurry for a non-aqueous electrolyte secondary battery, the content of the electrode active material is 40 to 90% by mass, and the content of the conductive additive is 0.1 to 10% by mass.

7. A non-aqueous electrolyte secondary battery having the slurry for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6 as an electrode active material layer.

8. A method for manufacturing a non-aqueous electrolyte secondary battery, which includes the following steps: Adding the slurry for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6 as an electrode active material layer.

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