阅读说明：本技术 含有炭黑的浆料、电极糊剂、电极的制造方法和二次电池的制造方法 (Slurry containing carbon black, electrode paste, method for producing electrode, and method for producing secondary battery ) 是由 与田晃 永井达也 伊藤哲哉 于 2020-04-17 设计创作，主要内容包括：提供一种含有炭黑的浆料,其可利于减少二次电池的内阻。一种浆料,其为至少含有炭黑和分散介质的浆料,该浆料中的炭黑浓度为5质量％以上且25质量％以下,并且在以激光衍射/散射法测得的炭黑的体积基准的粒度的频率分布中,将粒径0.6μm以上的炭黑的体积浓度设为x(％)、将粒径0.3μm以上且低于0.6μm的炭黑的体积浓度设为y(％)、将粒径低于0.3μm的炭黑的体积浓度设为100-(x+y)(％)时,满足10≤x≤70、30≤y≤90、0≤100-(x+y)≤30。(Provided is a slurry containing carbon black, which can contribute to reduction of internal resistance of a secondary battery. A slurry containing at least carbon black and a dispersion medium, wherein the concentration of carbon black in the slurry is 5-25% by mass, and wherein, in a frequency distribution of the volume-based particle size of carbon black measured by a laser diffraction/scattering method, when the volume concentration of carbon black having a particle size of 0.6 [ mu ] m or more is x (%), the volume concentration of carbon black having a particle size of 0.3-0.6 [ mu ] m or more is y (%), and the volume concentration of carbon black having a particle size of less than 0.3 [ mu ] m is 100- (x + y) (%), 10-x 70, 30-y 90, and 0-100- (x + y) < 30 are satisfied.)

1. A slurry which contains at least carbon black and a dispersion medium,

the carbon black concentration in the slurry is 5 to 25 mass%, and

in the frequency distribution of the volume-based particle size of the carbon black measured by a laser diffraction/scattering method, when the volume concentration of the carbon black having a particle size of 0.6 μm or more is x (%), the volume concentration of the carbon black having a particle size of 0.3 μm or more and less than 0.6 μm is y (%), and the volume concentration of the carbon black having a particle size of less than 0.3 μm is 100- (x + y) (%), 10. ltoreq. x.ltoreq.70, 30. ltoreq. y.ltoreq.90, and 0. ltoreq. 100- (x + y) < 30 are satisfied.

2. The slurry according to claim 1, wherein a cumulative 50% particle size (D50) in a cumulative distribution of volume-based particle sizes of the carbon black measured by a laser diffraction/scattering method is 0.40 to 0.85 μm.

3. The slurry according to claim 1 or 2, wherein the cumulative 90% particle size (D90) in the cumulative distribution of volume-based particle sizes of the carbon black measured by a laser diffraction/scattering method is 1.0 to 30.0 μm.

4. The slurry according to any one of claims 1 to 3, wherein N-methyl-2-pyrrolidone is contained as a dispersion medium.

5. A slurry according to any one of claims 1 to 4, which contains a dispersant.

6. The slurry according to claim 5, wherein a content of the dispersant in the slurry is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the carbon black.

7. The slurry according to claim 5 or 6, wherein a nonionic dispersant is contained as the dispersant.

8. The slurry according to any one of claims 5 to 7, wherein polyvinyl alcohol is contained as a dispersant.

9. The slurry according to claim 8, wherein the polyvinyl alcohol has a saponification degree of 86 to 97 mol%.

10. The slurry of any one of claims 1 to 9, which satisfies 30 ≦ x ≦ 60, 30 ≦ y ≦ 60, 10 ≦ 100- (x + y) ≦ 30.

11. An electrode paste comprising: the slurry, electrode active material and binder according to any one of claims 1 to 10.

12. A method of manufacturing an electrode, comprising the steps of: applying the electrode paste according to claim 11 to a current collector.

13. A method for manufacturing a secondary battery having a positive electrode, a negative electrode, and an electrolyte, the method comprising: by performing the manufacturing method according to claim 12, one or both of a positive electrode and a negative electrode are manufactured.

Technical Field

The present invention relates to a slurry containing carbon black. The present invention also relates to an electrode paste, a method for producing an electrode, and a method for producing a secondary battery.

Background

In recent years, electronic devices have been miniaturized and portable, and accompanying this, there is also a demand for miniaturization and weight reduction of an attached battery. As a specific performance, it is required to increase the energy density per unit volume and unit mass of the battery as much as possible. Among secondary batteries generally used in portable devices, secondary batteries having a high energy density per unit mass and per unit volume are lithium ion secondary batteries, and are widely used as power sources for small consumer devices such as smart phones and tablet personal computers. Further, lithium ion secondary batteries are increasingly used as batteries for electric vehicles and hybrid vehicles, and further, as household secondary batteries, and the demand for medium-and large-sized lithium ion secondary batteries is expected to increase.

Conventionally, a positive electrode of a lithium ion secondary battery is manufactured by applying an electrode paste containing a positive electrode active material, a conductive material, and a binder to a current collector. As the positive electrode active material, lithium-containing composite oxides such as lithium cobaltate and lithium manganate are used. Since the active material itself lacks conductivity, the following operations are performed to impart conductivity: a conductive material such as carbon black having a developed structure (a structure in which a plurality of primary particles are welded together: a primary aggregate) or anisotropic graphite having developed crystals is added (patent document 1).

The conductive material has a basic function of imparting conductivity to an active material having no conductivity and preventing the electrode active material from repeatedly expanding and contracting during charge and discharge to deteriorate the conductivity. Therefore, in the production of an electrode, it is important to control the size of the structure of carbon black used as a conductive material within a certain range. When the control is insufficient or the dispersion between the active materials is poor, the following problems occur: contact between the active material and carbon black cannot be sufficiently obtained, and a conductive path cannot be secured, and the performance of the lithium-containing composite oxide as the active material cannot be sufficiently exhibited. As a result, a portion having poor conductivity locally appears in the electrode, and the active material is not effectively used, which causes a decrease in discharge capacity and a reduction in battery life.

Therefore, in patent document 2, in order to improve the dispersibility of carbon black in the slurry, the following method is performed: carbon black is dispersed in a solvent in the submicron order by a high-pressure jet mill in the presence of polyvinylpyrrolidone as a dispersant. Patent document 2 describes the following: by using carbon black having a stable dispersion state for the positive electrode, a lithium ion secondary battery having a high capacity and excellent cycle characteristics can be obtained.

Patent document 3 describes that a conductive material exhibiting excellent dispersion stability and conductivity can be obtained by adding a small amount of the conductive material to a positive electrode for a lithium ion secondary battery. Specifically disclosed is a carbon black slurry which is characterized by comprising a dispersion medium composed of N-methyl-2-pyrrolidone, a carbon black having an average particle diameter of 0.1-1 [ mu ] m suspended in the dispersion medium at a ratio of 3-30 mass%, and a vinylpyrrolidone polymer added in an amount of 0.1-10 mass%. In the examples of patent document 3, carbon black having an average particle diameter of 0.3 μm obtained by a laser diffraction/scattering spectroscopy method is described, and it is shown that a lithium ion secondary battery produced using the carbon black as a conductive material of a positive electrode has a high discharge capacity.

Patent document 4 proposes a conductive material dispersion liquid containing: carbon black having an average primary particle diameter of 40nm or less and an average dispersed particle diameter of 400nm or less, or carbon nanotubes having an average outer diameter of 30nm or less and dispersed but not aggregated; and, it contains: a dispersant which is a nonionic dispersant. In patent document 4, conductivity was investigated by applying an electrode paste prepared using the conductive material dispersion to an aluminum foil and measuring resistance.

Patent document 5 describes the following: by using a carbon black dispersion containing carbon black, polyvinyl alcohol as a dispersant and N-methyl-2-pyrrolidone as a solvent, the specific surface area of the carbon black and the amount of polyvinyl alcohol having a saponification degree of 60 to 85 mol% are controlled within predetermined ranges, and the surface resistance of the battery electrode composite material layer and the capacity retention rate after 50 cycles are improved.

Patent document 6 shows: the dispersion state of the positive electrode conductive material paste using granular acetylene black is defined by the particle diameter and the volume frequency, and the direct current resistance value and the power characteristics of the battery can be improved.

Patent document 7 proposes carbon black for lithium ion secondary batteries, in which the average particle diameter of primary particles is 20nm or less and the volatile content is 0.20% or less, in order to provide carbon black which can significantly improve the large-current discharge characteristics for lithium ion secondary batteries by adding a small amount of carbon black.

Patent document 8 proposes a powdery carbon black composition having excellent conductivity-imparting ability and dispersibility. Specifically disclosed is a powdery carbon black composition containing 90-99 mass% of a carbon black powder having a primary particle diameter of 20-30 nm and 10-1 mass% of a polyamine polymer, wherein the BET specific surface area of the powdery carbon black composition is 110-150 m²(ii) a DBP absorption of 190 to 230ml/100 g.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2008-227481

Patent document 2: japanese patent laid-open publication No. 2004-281096

Patent document 3: japanese laid-open patent publication No. 2003-157846

Patent document 4: japanese patent laid-open publication No. 2011-70908

Patent document 5: international publication No. 2014/132809

Patent document 6: japanese patent laid-open publication Nos. 2013-109852

Patent document 7: japanese patent laid-open No. 2014-194901

Patent document 8: japanese patent laid-open publication No. 2018-62545

Disclosure of Invention

Problems to be solved by the invention

As described above, it has been proposed to improve battery characteristics by improving dispersibility of carbon black as a conductive material in an electrode or controlling particle size. However, the relationship between the characteristics of carbon black and the internal resistance of a secondary battery has not been sufficiently studied. Even if the conductivity of the electrode is increased, the internal resistance is not necessarily decreased, and an unexplained portion remains. Since the increase in the amount of current of the internal resistance of the secondary battery becomes a great problem as the battery becomes larger, it would be advantageous if an embodiment of carbon black effective for reducing the internal resistance of the secondary battery could be explained.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a slurry containing carbon black, which is advantageous for reducing the internal resistance of a secondary battery. Another object of one embodiment of the present invention is to provide: an electrode paste containing the slurry. In another embodiment of the present invention, there is provided: a method for producing an electrode using the electrode paste. Another object of the present invention is to provide: a method for manufacturing a secondary battery includes implementing the method for manufacturing the electrode.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that: in order to significantly reduce the internal resistance of the battery, it is not sufficient to finely divide the carbon black into submicron order, and it is effective to prepare an electrode paste using a slurry in which the volume concentration of each of the carbon black having a particle size of 0.6 μm or more, the carbon black having a particle size of 0.3 μm or more and less than 0.6 μm, and the carbon black having a particle size of less than 0.3 μm is appropriately controlled. The present invention has been completed based on the above-described findings, as exemplified below.

[1]

A slurry which contains at least carbon black and a dispersion medium,

the carbon black concentration in the slurry is 5 to 25 mass%, and

in the frequency distribution of the volume-based particle size of the carbon black measured by a laser diffraction/scattering method, when the volume concentration of the carbon black having a particle size of 0.6 μm or more is x (%), the volume concentration of the carbon black having a particle size of 0.3 μm or more and less than 0.6 μm is y (%), and the volume concentration of the carbon black having a particle size of less than 0.3 μm is 100- (x + y) (%), 10. ltoreq. x.ltoreq.70, 30. ltoreq. y.ltoreq.90, and 0. ltoreq. 100- (x + y) < 30 are satisfied.

[2]

The slurry according to [1], wherein a cumulative 50% particle size (D50) in a cumulative distribution of volume-based particle sizes of the carbon black measured by a laser diffraction/scattering method is 0.40 to 0.85 μm.

[3]

The slurry according to [1] or [2], wherein a cumulative 90% particle size (D90) in a cumulative distribution of volume-based particle sizes of the carbon black measured by a laser diffraction/scattering method is 1.0 to 30.0 μm.

[4]

The slurry according to any one of [1] to [3], which contains N-methyl-2-pyrrolidone as a dispersion medium.

[5]

The slurry according to any one of [1] to [4], which contains a dispersant.

[6]

The slurry according to item [5], wherein a content of the dispersant in the slurry is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the carbon black.

[7]

The slurry according to [5] or [6], which contains a nonionic dispersant as a dispersant.

[8]

The slurry according to any one of [5] to [7], which contains a polyvinyl alcohol as a dispersant.

[9]

The slurry according to [8], wherein the saponification degree of the polyvinyl alcohol is 86 to 97 mol%.

[10]

The slurry according to any one of [1] to [9], which satisfies 30. ltoreq. x.ltoreq.60, 30. ltoreq. y.ltoreq.60, 10. ltoreq. 100- (x + y).ltoreq.30.

[11]

An electrode paste comprising: [1] the slurry, the electrode active material and the binder according to any one of [1] to [10 ].

[12]

A method of manufacturing an electrode, comprising the steps of: applying the electrode paste described in [11] to a current collector.

[13]

A method for manufacturing a secondary battery having a positive electrode, a negative electrode, and an electrolyte, the method comprising: by carrying out the production method according to [12], one or both of a positive electrode and a negative electrode are produced.

ADVANTAGEOUS EFFECTS OF INVENTION

By preparing an electrode paste using the carbon black-containing slurry according to one embodiment of the present invention and using an electrode prepared using the electrode paste, a secondary battery having significantly reduced internal resistance and excellent capacity retention rate can be obtained.

Drawings

Fig. 1 is a diagram showing an example of a basic configuration of a lithium-ion secondary battery.

Detailed Description

(1. slurry containing carbon Black)

According to an embodiment of the present invention, there is provided a slurry containing at least carbon black and a dispersion medium. The carbon black plays a role of a buffer material for expansion/contraction of the active material while maintaining the conductivity of the entire electrode. Examples of the carbon black include thermal black, furnace black, lamp black, channel black, and acetylene black. Among them, acetylene black is preferable in terms of high purity.

The carbon black concentration in the slurry is preferably 5% by mass or more and 25% by mass or less. When the lower limit of the carbon black concentration in the slurry is less than 5% by mass, the concentration is low, and the ratio of costs for transportation and dispersion media becomes high, which leads to an expensive price. The lower limit of the carbon black concentration in the slurry is more preferably 6% by mass or more, and still more preferably 7% by mass or more. If the upper limit of the carbon black concentration in the slurry exceeds 25 mass%, the viscosity becomes too high and dispersion becomes difficult, and it becomes difficult to obtain the desired conductivity-imparting effect. The upper limit of the carbon black concentration in the slurry is more preferably 23% by mass or less, still more preferably 20% by mass or less, still more preferably 14% by mass or less, and still more preferably 11% by mass or less.

In the carbon black in the slurry, in a frequency distribution of volume-based particle sizes of the carbon black measured by a laser diffraction/scattering method, when a volume concentration of the carbon black having a particle size of 0.6 μm or more is defined as x (%), a volume concentration of the carbon black having a particle size of 0.3 μm or more and less than 0.6 μm is defined as y (%), and a volume concentration of the carbon black having a particle size of less than 0.3 μm is defined as 100- (x + y) (%), it is preferable that 10. ltoreq. x.ltoreq.70, 30. ltoreq. y.ltoreq.90, and 0. ltoreq. 100- (x + y) < 30 are satisfied. By using carbon black having such a particle size distribution as a conductive material, the internal resistance of a battery can be significantly reduced. More preferably, 10. ltoreq. x.ltoreq.60, 30. ltoreq. y.ltoreq.80, 5. ltoreq.100- (x + y). ltoreq.30, still more preferably, 30. ltoreq. x.ltoreq.60, 30. ltoreq. y.ltoreq.60, 10. ltoreq.100- (x + y). ltoreq.30.

The carbon black in the slurry preferably has a cumulative 50% particle size (D50) in a cumulative distribution of volume-based particle sizes of the carbon black measured by a laser diffraction/scattering method of 0.40 to 0.85 [ mu ] m. By controlling D50 according to the frequency distribution of the volume-based particle size of the carbon black, the internal resistance of the battery can be further reduced. D50 is more preferably 0.45 to 0.80 μm, and still more preferably 0.45 to 0.75. mu.m.

The carbon black in the slurry preferably has a cumulative 90% particle size (D90) in a cumulative distribution of volume-based particle sizes of the carbon black measured by a laser diffraction/scattering method of 1.0 to 30.0 [ mu ] m. By controlling D90 according to the frequency distribution of the volume-based particle size of the carbon black, the internal resistance of the battery can be further reduced. D90 is more preferably 1.0 to 27.5 μm, and still more preferably 1.0 to 25.0. mu.m.

In the present specification, the volume-based particle size distribution of carbon black by the laser diffraction/scattering method can be measured by the following method using a particle size distribution measuring apparatus (for example, a "Microtrac MT3300 EXII" manufactured by Microtrac Bel Inc.; "very Small volume circulator USVR").

The measurement conditions were as follows: measurement range/0.02-2000 μm, particle permeability/absorption, particle shape/nonspherical shape, solvent/N-methylpyrrolidone, and cycle power/5

Sample input amount: adding and adjusting the slurry to the optimum concentration range displayed when the sample is put

The particle size distribution of the carbon black measured here is not a particle size distribution of the primary particle diameter of the carbon black but a particle size distribution of a structure in which primary particles of the carbon black are aggregated.

The dispersion medium is not limited, and examples thereof include aliphatic hydrocarbon solvents such as pentane, n-hexane, octane, cyclopentane and cyclohexane, aromatic hydrocarbon solvents such as benzene, toluene, xylene and cymene, aldehyde solvents such as furfural, ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone and cyclohexanone, butyl acetate, ethyl acetate, methyl acetate, butyl propionate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, 3-methoxybutyl acetate and ethylene glycol diacetate, ether solvents such as tetrahydrofuran, dioxane and ethylene glycol dimethyl ether, alcohol solvents such as methanol, ethanol, n-propanol, isopropanol, butanol, polyhydric alcohol solvents such as glycerol, ethylene glycol and diethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethanol, isopropanol, butanol, cyclohexanol, allyl alcohol, benzyl alcohol, cresol and furfuryl alcohol, polyhydric alcohol solvents such as glycerol, ethylene glycol and diethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol, and mixtures thereof, An alcohol ether solvent such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and diethylene glycol monobutyl ether, an aprotic polar solvent such as N-methyl-2-pyrrolidone, dimethyl sulfoxide, and dimethylformamide, and water. The solvent may be used alone in 1 kind, or may be used in combination of 2 or more kinds. Among them, when polyvinylidene fluoride is used as the binder, N-methyl-2-pyrrolidone is preferable in view of solubility.

The slurry preferably contains a dispersant to improve the dispersion stability of the carbon black. As the dispersant, a dispersant which does not affect the battery characteristics and does not decompose when a voltage is applied to the battery is preferable. As the dispersant, for example, a nonionic dispersant having no ionic functional group can be used. The nonionic dispersant may have a small amount of ionic functional groups. Specific examples of the dispersant include polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene, polypropylene, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic acid, polyvinyl butyral, polyacrylamide, polyurethane, polydimethylsiloxane, epoxy resin, acrylic resin, polyester resin, melamine resin, phenol resin, various rubbers, lignin, pectin, gelatin, xanthan gum, welan gum, succinoglycan, polyvinyl alcohol, polyvinyl acetal, cellulose-based resin, polyalkylene oxide, polyvinyl ether, polyvinyl pyrrolidone, chitin, chitosan, starch, polyamine, and the like. The dispersant may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

As the dispersant, polyvinyl alcohol, which also has an effect as a binder, is preferable. The polyvinyl alcohol may be either of a completely saponified type and a partially saponified type, and is preferably a polyvinyl alcohol having a saponification degree of 86 to 97 mol% and is as low in side reactions as possible when a high voltage is applied to the positive electrode, and is more preferably a polyvinyl alcohol having a saponification degree of 86 to 90 mol%. Degree of saponification was measured according to JIS K6726: 1994. That is, the residual acetoxy group (mol%) in the sample was determined by subtracting it from 100 with sodium hydroxide.

The content of the dispersant in the slurry is preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the carbon black. When the lower limit of the content of the dispersant in the slurry is less than 5 parts by mass relative to 100 parts by mass of the carbon black, dispersibility is poor during dispersion, and re-aggregation tends to cause poor dispersion when mixed with an active material. The lower limit of the dispersant content in the slurry is more preferably 6 parts by mass or more, and still more preferably 7 parts by mass or more, per 100 parts by mass of the carbon black. If the upper limit of the dispersant content in the slurry exceeds 20 parts by mass relative to 100 parts by mass of the carbon black, not only is there a concern about degradation of battery characteristics, but also, at the time of dispersion treatment, breakage of the structure of the carbon black is further promoted. The upper limit of the content of the dispersant in the slurry is more preferably 15 parts by mass or less, and still more preferably 10 parts by mass or less, per 100 parts by mass of the carbon black.

(2. production of slurry containing carbon Black)

An example of a method for producing the slurry containing the carbon black will be described. First, a raw material gas such as hydrocarbon is supplied from a nozzle provided at the top of the reactor, and carbon black powder is produced by a pyrolysis reaction and/or a partial combustion reaction, and is collected from a bag filter directly connected to the lower portion of the reactor. The raw material gas to be used is not particularly limited, and gaseous hydrocarbons such as acetylene, methane, ethane, propane, ethylene, propylene, and butadiene, and oily hydrocarbons such as toluene, benzene, xylene, gasoline, kerosene, light oil, and heavy oil may be gasified. The raw material gas may be used alone in 1 kind, or may be used in combination in 2 or more kinds. As the raw material gas, acetylene gas containing a small amount of impurities such as sulfur is preferably used.

The average particle diameter of the primary particles of the carbon black powder is preferably 15 to 30 nm. If the average particle diameter is less than 15nm, the dispersion treatment described later cannot be performed, and if it exceeds 30nm, it is difficult to obtain an appropriate size of the structure, and the desired conductivity-imparting ability cannot be obtained. The average particle diameter of the primary particles is a value obtained by averaging particle diameters measured based on a photograph taken with a transmission electron microscope or the like. The particle diameter is a circle-equivalent diameter calculated from the area of the primary particles. Specific examples of the carbon black powder include commercially available acetylene blacks Li-435 and FX-35 manufactured by Denka Company Limited and processed products thereof.

Next, a slurry containing carbon black can be produced by adding predetermined amounts of carbon black powder and a dispersant to a dispersion medium and performing a dispersion treatment. The dispersion treatment apparatus used for ordinary dispersion or the like can be used as long as the particle size distribution of the carbon black can be controlled. Examples thereof include mixers such as a disperser, a homomixer, a Henschel mixer and a planetary mixer, a dispersion treatment apparatus using a medium such as a bead mill, and a dispersion treatment apparatus without a medium such as an ultrasonic homogenizer and a wet-type micronizing apparatus. The dispersion treatment apparatus is not limited to these. The dispersion treatment apparatus is not limited to one type of apparatus, and various types of apparatuses may be used in combination as appropriate.

In the case of using any dispersion treatment apparatus, it is important to set the dispersion treatment conditions so that the volume concentration (%) of carbon black having a particle diameter of 0.6 μm or more, the volume concentration (%) of carbon black having a particle diameter of 0.3 μm or more and less than 0.6 μm, and the volume concentration (%) of carbon black having a particle diameter of less than 0.3 μm fall within predetermined ranges. The larger the energy and the longer the dispersion treatment, the more the volume concentration (%) of the carbon black having a particle diameter of less than 0.3 μm increases because elimination of secondary aggregation of the carbon black powder and breakage of the structure proceed. Further, the smaller the energy and time required for the dispersion treatment, the larger the volume concentration (%) of carbon black having a particle diameter of 0.6 μm or more, the more the elimination of secondary aggregation of carbon black powder and the breakage of the structure are, the more the dispersion treatment is.

(3. preparation of electrode paste)

An electrode paste can be produced by adding an electrode active material and a binder to a slurry containing the carbon black of the present invention. For example, 95 to 99 parts by mass, preferably 97 to 99 parts by mass of the electrode active material may be added to 1 part by mass of the carbon black in the slurry. The carbon black in the slurry may be added in an amount of 1 to 2 parts by mass, preferably 0.5 to 1 part by mass, based on 1 part by mass of the binder. The electrode active material includes a positive electrode active material and a negative electrode active material. The slurry of the present invention can be used for producing either a positive electrode paste or a negative electrode paste.

The positive electrode active material is not limited, and Li can be used_xMO₂(wherein M is at least one transition metal and x is 0.05-1.0) lithium composite oxide and TiS as main components₂、FeS、MoS₂、NbSe₂And V₂O₅Etc. do not contain lithium metal sulfides and metal oxides. Among them, LiCoO is preferable in that the electromotive force of the battery can be increased₂、LiNi_1/3Mn_{1/ 3}Co_1/3O₂、LiMn₂O₄And the like lithium-containing transition metal oxides containing cobalt and/or manganese. As other positive electrode active materials, there can be used: placing a part of the cobalt inLiNi obtained by conversion to nickel or aluminum_xCo_yAl_zO₂LiNi in which a part of cobalt and manganese is replaced with nickel and the nickel content is increased_xMn_yCo_zO₂(x>y, z), LiNi obtained by substituting a part of manganese with nickel_xMn₂O₄And the like. Further, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene may be used. The positive electrode active material may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

The negative electrode active material is not limited, and various carbonaceous materials such as natural graphite, artificial graphite, activated carbon, coke, needle coke, liquid coke, mesophase microbeads, carbon fibers, and pyrolytic carbon can be used. Examples of the negative electrode active material include metallic lithium or an alloy thereof (such as LiSn alloy, LiSi alloy, LiBi alloy, and LiPb alloy), a lithium composite oxide (such as lithium titanate, lithium vanadate, lithium silicate, and iron oxide containing lithium), and a conductive polymer (such as polyacetylene and polyphenylene). The negative electrode active material may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

The binder is not limited, and any of the conventional binders such as polyethylene, nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene-butadiene rubber, polysulfide rubber, nitrocellulose, cetyl methylcellulose, polyvinyl alcohol, tetrafluoroethylene resin, polyvinylidene fluoride, and polychloroprene can be used. The binder may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

The average particle diameter of the electrode active material is preferably in the range of 0.05 to 100 μm, and more preferably in the range of 0.1 to 50 μm. In the present specification, the average particle diameter of the electrode active material is an average value of the particle diameter of the electrode active material measured by an electron microscope. The particle diameter is a circle-equivalent diameter calculated from the area of the primary particles.

(4. production of electrode)

The electrode can be made as follows: the electrode paste is applied to a current collector such as a metal foil, and then the solvent is evaporated and dried, so that a laminate in which an electrode composite material layer is laminated on the current collector can be produced. As the electrode, either a positive electrode or a negative electrode can be manufactured. The material of the current collector used for the electrode is not limited, and metals such as gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, and titanium, and alloys (stainless steel and the like) containing any of these as a main component can be used. Among them, aluminum is preferably used for the positive electrode, and copper is preferably used for the negative electrode. The current collector is usually provided in the form of a foil, but is not limited thereto, and an open-pore foil-like or mesh-like current collector may be used.

The method of applying the electrode paste to the current collector is not limited, and examples thereof include die coating, dip coating, roll coating, doctor blade coating, spray coating, gravure coating, screen printing, and electrostatic coating. As the drying method, a standing dryer, an air blower dryer, a hot air dryer, an infrared heater, a far infrared heater, or the like can be used, but the drying method is not particularly limited thereto.

After coating, rolling treatment using a flat press, a calender roll, or the like may be performed. The current collector and the electrode composite material layer are pressed and adhered to each other by a roll press or the like, whereby a target electrode can be obtained.

(5. production of Battery)

According to an embodiment of the present invention, a secondary battery can be manufactured using one or both of the positive electrode and the negative electrode obtained in the above-described steps. Examples of the secondary battery include a lithium ion secondary battery, a sodium ion secondary battery, a magnesium secondary battery, an alkaline secondary battery, a lead storage battery, a sodium-sulfur secondary battery, and a lithium air secondary battery, and among the secondary batteries, conventionally known electrolytes, separators, and the like can be suitably used.

For example, in the case of a lithium ion secondary battery, an electrolyte containing lithium may be used as the electrolyte and dissolved in a nonaqueous solvent. Specific examples thereof include LiBF₄、LiClO₄、LiPF₆、LiAsF₆、LiSbF₆、LiCF₃SO₃、Li(CF₃SO₂)₂N、LiC₄F₉SO₃、Li(CF₃SO₂)₃C、LiI、LiBr、LiCl、LiAlCl、LiHF₂LiSCN or LiBPh₄And the like. The electrolyte may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

The nonaqueous solvent is not limited, and examples thereof include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ -butyrolactone, γ -valerolactone and γ -octanolide; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 4-methyl-1, 3-dioxolane, 1, 2-methoxyethane, 1, 2-ethoxyethane and 1, 2-dibutoxyethane; esters such as methyl formate, methyl acetate and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. The solvent may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

As the electrolyte, an organic solid electrolyte and/or an inorganic solid electrolyte may be used. Examples of the organic solid electrolyte include, but are not limited to, a polymer electrolyte such as polyethylene oxide (PEO) and an organic electrolyte salt such as lithium bistrifluoromethanesulfonimide (LiTFSI). The inorganic solid electrolyte includes, but is not limited to, sulfide-based inorganic solid electrolytes (e.g., LPS-based and LGPS-based) and oxide-based inorganic solid electrolytes (e.g., LLZ-based).

As the separator interposed between the positive electrode and the negative electrode as needed, any separator may be used as long as it has sufficient strength, such as an electrically insulating porous film, a net, or a nonwoven fabric. In particular, a separator which has low resistance to ion migration of the electrolyte and is excellent in solution retention can be used. The material is not particularly limited, and examples thereof include inorganic fibers such as glass fibers, organic fibers, synthetic resins such as polyethylene, polypropylene, polyester, polytetrafluoroethylene, and polytetrafluoroethylene synthetic resins, and layered composites thereof. From the viewpoint of adhesiveness and safety, polyethylene, polypropylene, or a layered composite film thereof is desired. Examples thereof include a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a polyamide nonwoven fabric, and those subjected to hydrophilic treatment, but are not particularly limited thereto.

The secondary battery may be formed into various shapes according to the purpose of use, such as a paper type, a cylindrical type, a button type, and a laminated type.

The application of the lithium ion secondary battery of the present invention is not particularly limited. For example, it can be used as a power source for small consumer appliances such as smart phones, tablet personal computers, household appliances, and electric power tools. Further, the present invention can be used as various large-sized power sources such as a power source for electric vehicles, hybrid vehicles, and the like, an industrial facility such as an elevator having a system for recovering at least a part of kinetic energy, and a power source for various office and household power storage systems.

Examples

Hereinafter, examples of the present invention and comparative examples are shown at the same time, but the examples are provided for better understanding of the present invention and advantages thereof, and are not intended to limit the present invention.

< example 1>

(1. preparation of slurry)

To 89.0 parts by mass of N-methyl-2-pyrrolidone, 1.0 part by mass of polyvinyl alcohol (Poval B05 manufactured by Denka Company Limited, saponification degree: 87%) and 10.0 parts by mass of carbon black powder (acetylene black Li-435 manufactured by Denka Company Limited) were added, and the mixture was stirred with a planetary mixer (Hivis disper Mix model 3D-5 manufactured by Primix Corporation) for 120 minutes to prepare a slurry containing carbon black. The resulting slurry was charged into a bead mill (Mugenflow MGF2-ZA, manufactured by Ashizawa Finetech Ltd.) carrying zirconia beads (diameter: 0.5mm) and subjected to dispersion treatment. After the dispersion treatment, the zirconia beads were taken out by filtration to prepare a slurry.

The frequency distribution and cumulative distribution of volume-based particle sizes of the carbon black in the slurry thus obtained were measured by the aforementioned method using a laser diffraction/scattering type particle size distribution measuring apparatus (model Microtrac MT3300EXII, manufactured by Microtrac bel inc.). When the volume concentration of carbon black having a particle size of 0.6 μm or more in the present example is x (%), the volume concentration of carbon black having a particle size of 0.3 μm or more and less than 0.6 μm is y (%), and the volume concentration of carbon black having a particle size of less than 0.3 μm is 100- (x + y) (%), x is 40.5%, y is 44.1%, and 100- (x + y) (%).

(2. preparation of Positive electrode paste)

To 1.0 part by mass of carbon black in the slurry obtained in the above, 2.0 parts by mass, in terms of solute amount, of an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride as a binder and a lithium nickel cobalt manganese composite oxide LiNi as a positive electrode active material were added_0.5Mn_0.3Co_0.2O₂(manufactured by Jiangxi Jiangste Lithium Battery Inc. "S532") 97 parts by mass and mixed. Further, in order to improve coatability, the shear rate in the viscosity curve measured by a rheometer (MCR 300 manufactured by Anton Paar) was 1 second^-1When the viscosity is less than 10000 mPa.sec, N-methyl-2-pyrrolidone as a dispersion medium is added and mixed to prepare a positive electrode paste.

(3. preparation of Positive electrode)

The positive electrode paste was applied to an aluminum foil having a thickness of 20 μm by a Baker's applicator, dried, and then pressed and cut to prepare a positive electrode.

(4. preparation of cathode)

A negative electrode paste (graphite (manufactured by Shenzhen BTR, "AGP-2A") 96.0 mass%, carbon black (manufactured by Denka Company Limited, "Li-400"), sodium carboxymethylcellulose 1.0 mass%, styrene-butadiene copolymer 2.0 mass%) was applied to a copper foil having a thickness of 10 μm by a Baker type applicator, dried, and then pressed and cut to prepare a negative electrode.

(5. production of Secondary Battery)

As shown in fig. 1, an aluminum tab 5 is connected to the positive electrode 1, a nickel tab 6 is connected to the negative electrode 2, and the positive electrode 1, the polyolefin microporous membrane (separator) 3, and the negative electrode 2 are stacked and laminated together. Then, the laminate type secondary battery is produced by packaging with a case (aluminum laminate film) 4, pre-sealing, injecting an electrolyte solution, formatting the battery, and vacuum-sealing.

(6. measurement of internal resistance)

With the secondary battery thus manufactured, the voltage after 10 seconds when a current of 0.2, 0.4, 0.6, 0.8 and 1.0mA was applied was measured at 25 ℃. At this time, the SOC (depth of charge) was set to 50%. The battery internal resistance R is calculated according to the R ═ V/I, and the average value of the R is obtained. The internal resistance of the battery of example 1 was 1.45 Ω.

(7. Power characteristics (capacity maintenance ratio at 3C discharge))

The fabricated secondary battery was charged at 25 ℃ with a constant current and a constant voltage limited to 4.2V and 0.2C, and then discharged at a constant current of 0.2C to 2.75V. Next, the discharge current was changed to 0.2C and 3C, and the discharge capacity with respect to each discharge current was measured. Then, the capacity retention rate at the time of 3C discharge with respect to the time of 0.2C discharge was calculated. The capacity retention rate at the time of 3C discharge in example 1 was 82.4%.

< example 2>

Slurry, electrode paste, positive electrode, and secondary battery were prepared in the same manner as in example 1 except that the dispersion treatment time and peripheral speed of the bead mill of example 1 were changed, and each evaluation was performed. The results are shown in Table 1.

< example 3>

A slurry, an electrode paste, a positive electrode, and a secondary battery were prepared in the same manner as in example 1 except that a slurry containing carbon black was used in example 1 in which the amount of N-methyl-2-pyrrolidone was changed to 85.5 parts by mass and the amount of carbon black powder was changed to 13.5 parts by mass, respectively, and evaluations were performed. The results are shown in Table 1.

< example 4>

A slurry, an electrode paste, a positive electrode, and a secondary battery were prepared in the same manner as in example 1 except that a carbon black-containing slurry was used in example 1 in which the amount of N-methyl-2-pyrrolidone was changed to 83.5 parts by mass, the amount of polyvinyl alcohol was changed to 1.5 parts by mass, and the amount of carbon black powder was changed to 15.0 parts by mass, respectively, and evaluations were performed. The results are shown in Table 1.

< example 5>

A slurry, an electrode paste, a positive electrode, and a secondary battery were prepared in the same manner as in example 1 except that a carbon black-containing slurry was used in example 1 in which the amount of N-methyl-2-pyrrolidone was changed to 80.2 parts by mass, the amount of polyvinyl alcohol was changed to 1.8 parts by mass, and the amount of carbon black powder was changed to 18.0 parts by mass, respectively, and evaluations were performed. The results are shown in Table 1.

< example 6>

A slurry, an electrode paste, a positive electrode, and a secondary battery were prepared in the same manner as in example 1 except that a slurry containing carbon black was used in example 1 in which the amount of N-methyl-2-pyrrolidone was changed to 78.0 parts by mass, the amount of polyvinyl alcohol was changed to 2.0 parts by mass, and the amount of carbon black powder was changed to 20.0 parts by mass, respectively, and evaluations were performed. The results are shown in Table 1.

< example 7>

Slurry, electrode paste, positive electrode, and secondary battery were prepared in the same manner as in example 2 except that the dispersion treatment time and peripheral speed of the bead mill were changed, and each evaluation was performed. The results are shown in Table 1.

< example 8>

A slurry, an electrode paste, a positive electrode, and a secondary battery were prepared in the same manner as in example 1 except that a carbon black-containing slurry was used in example 1 in which the amount of N-methyl-2-pyrrolidone was changed to 72.5 parts by mass, the amount of polyvinyl alcohol was changed to 2.5 parts by mass, and the amount of carbon black powder was changed to 25.0 parts by mass, respectively, to perform the respective evaluations. The results are shown in Table 1.

< example 9>

An electrode paste, a positive electrode, and a secondary battery were prepared in the same manner AS in example 1 except that 95.0 parts by mass of N-methyl-2-pyrrolidone and 5.0 parts by mass of carbon black powder (acetylene black Li-435, manufactured by Denka Company Limited) were put in a 50ml vial, and stirred in an ultrasonic cleaner (ASU-6, manufactured by AS ONE corporation) for 60 minutes to prepare a slurry containing carbon black, and then each evaluation was performed. The results are shown in Table 1.

< comparative example 1>

Slurry, electrode paste, positive electrode, and secondary battery were prepared in the same manner as in example 3 except that the dispersion treatment time and peripheral speed of the bead mill were changed, and each evaluation was performed. The results are shown in Table 1.

< comparative example 2>

Slurry, electrode paste, positive electrode, and secondary battery were prepared in the same manner as in example 4 except that the dispersion treatment time and peripheral speed of the bead mill were changed, and each evaluation was performed. The results are shown in Table 1.

< comparative example 3>

Slurry, electrode paste, positive electrode, and secondary battery were prepared in the same manner as in comparative example 1 except that the dispersion treatment time and peripheral speed of the bead mill were changed, and each evaluation was performed. The results are shown in Table 1.

< comparative example 4>

A slurry, an electrode paste, a positive electrode, and a secondary battery were produced in the same manner as in example 1 except that the slurry containing carbon black was used in example 1 in which the amount of N-methyl-2-pyrrolidone was changed to 94.5 parts by mass, the amount of polyvinyl alcohol was changed to 0.5 part by mass, and the amount of dispersion treatment time and the peripheral speed of the bead mill were changed to 5.0 parts by mass, respectively, and evaluations were performed. The results are shown in Table 1.

< comparative example 5>

A slurry, an electrode paste, a positive electrode, and a secondary battery were prepared in the same manner as in example 8 except that the dispersion treatment time and the peripheral speed of the bead mill were changed, and each evaluation was performed. The results are shown in Table 1.

< comparative example 6>

A slurry, an electrode paste, a positive electrode, and a secondary battery were prepared in the same manner as in example 1 except that a slurry containing carbon black was used in example 1 in which the amount of N-methyl-2-pyrrolidone was changed to 69.2 parts by mass, the amount of polyvinyl alcohol was changed to 2.8 parts by mass, and the amount of carbon black powder was changed to 28.0 parts by mass, respectively, and evaluations were performed. The results are shown in Table 1.

< comparative example 7>

A slurry, an electrode paste, a positive electrode, and a secondary battery were prepared in the same manner as in comparative example 1 except that a carbon black-containing slurry was used in comparative example 1 in which the amount of N-methyl-2-pyrrolidone was changed to 95.6 parts by mass, the amount of polyvinyl alcohol was changed to 0.4 part by mass, and the amount of carbon black powder was changed to 4.0 parts by mass, respectively, and evaluations were performed. The results are shown in Table 1.

[ Table 1]

Description of the reference numerals

1 nonaqueous Secondary Battery Positive electrode

2 negative electrode for nonaqueous secondary battery

3 insulating layer (polyolefin microporous film)

4 outer cover

5 aluminium system utmost point ear

6 nickel tab