JP6720488B2 - Method for producing a composition containing a plurality of positive electrode active materials, a conductive auxiliary agent, a binder and a solvent - Google Patents

Description

The present invention relates to a method for producing a composition containing a plurality of positive electrode active materials, a conductive auxiliary agent, a binder and a solvent.

It is known that various materials are used for the positive electrode active material of the secondary battery, and further, a secondary battery employing a plurality of materials as the positive electrode active material is also known.

For example, Patent Document 1 specifically discloses a lithium-ion secondary battery that employs LiFePO ₄ having an olivine structure and LiNi _0.8 Co _0.15 Al _0.05 O ₂ that is a lithium nickel composite oxide as a positive electrode active material. It is disclosed.

Now, generally, the positive electrode of a lithium ion secondary battery comprises a current collector and a positive electrode active material layer containing a positive electrode active material formed on the current collector. Here, the positive electrode active material layer is produced by applying a composition (slurry) containing a positive electrode active material, a conductive auxiliary agent, a binder and a solvent on a current collector, and removing the solvent from the composition. To be done. Then, the composition containing the positive electrode active material, the conductive additive, the binder, and the solvent is produced by mixing the solid contents of the constituent components of the composition and then adding the solvent, or the composition. It was usually manufactured by mixing all the ingredients of the product at once.

In fact, the composition containing the positive electrode active material and the solvent of Patent Document 1 has a positive electrode active material of LiFePO ₄ and LiNi _0.8 Co _0.15 Al _0.05 O ₂ , a binder of polyvinylidene fluoride, and a conductivity assistant. It is manufactured by a manufacturing method in which carbon as an agent is mixed and N-methyl-2-pyrrolidone as a solvent is added and mixed therein (see paragraph 0084 of the specification of Patent Document 1).

JP 2012-190786 A

The present inventor has found that the physical properties of a composition containing a plurality of positive electrode active materials, a conductive auxiliary agent, a binder, and a solvent change depending on the manufacturing method. Furthermore, it has been found that the resistance of the positive electrode having the positive electrode active material layer formed by removing the solvent from the composition changes depending on the method for producing the composition.

The present invention has been made in view of such circumstances, and is a method for producing a composition containing a plurality of positive electrode active materials, a conductive auxiliary agent, a binder, and a solvent, which can suppress the resistance of the positive electrode to a certain extent. The purpose is to provide.

As a result of diligent study by the present inventors, first, a conductive auxiliary agent, a binder and a solvent were mixed to produce a first dispersion liquid, and then a plurality of positive electrode active materials were added to the first dispersion liquid. It has been found that the composition produced by the production method for producing the second dispersion by using the above method is suitable.

That is, the method for producing the composition of the present invention is a method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
It is characterized by including.

The resistance of the positive electrode manufactured using the composition obtained by the manufacturing method of the present invention is suppressed to a certain extent.

It is a particle size distribution chart of the B-1 dispersion liquid of Example 7 and Example 8.

The best mode for carrying out the present invention will be described below. Unless otherwise specified, the numerical range “x to y” described in the present specification includes the lower limit x and the upper limit y in the range. The upper limit value and the lower limit value, and the numerical values listed in the examples can be arbitrarily combined to form the numerical value range. Further, numerical values arbitrarily selected from the numerical range can be set as upper and lower numerical values.

A method for producing a composition of the present invention is a method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) A step of mixing the conductive additive, the binder, and the solvent to produce the dispersion A (hereinafter, simply referred to as "A step"). ),
B) A step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material, and the second positive electrode active material (hereinafter, simply referred to as “B) step”. ),
It is characterized by including.

The composition produced by the production method of the present invention (hereinafter sometimes referred to as “the composition of the present invention”) comprises a solvent and a solid content other than the solvent. The solid content other than the solvent means a positive electrode active material other than the solvent, a conductive auxiliary agent, a binder, and a dispersant and other additives used as necessary. In the composition of the present invention, the compounding amount of the solid content other than the solvent (hereinafter, may be simply referred to as “solid content”) is preferably in the range of 30 to 90 mass %, and in the range of 50 to 75 mass %. Is more preferable.

The first positive active material may be any material which acts as a positive electrode active material in a secondary battery, for example, the general formula of the layered rock salt _{structure: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b+c+d+e=1, 0≦e<1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, At least one element selected from Cu, Ca, Ir, Hf, Rh, Zr, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, 1 .7≦f≦3), spinel structure materials such as LiMn ₂ O ₄ and non-stoichiometric Li _a Mn _b O ₄ (a+b=2), and layered rock salt structure materials and spinel structure Mention may be made of solid solutions composed of materials.

General _{formula: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Zr, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, In at least one element selected from Bi, S, Si, Na, K, P, and V, 1.7≦f≦3), the values of b, c, and d are not particularly limited as long as the above conditions are satisfied. There is no limitation, but it is preferable that 0<b<1, 0<c<1, 0<d<1, and at least one of b, c, and d is 10/100<b<90/100. 10/100<c<90/100, 5/100<d<70/100 are preferable, and 12/100<b<80/100, 12/100<c<80/100, 10/ The range of 100<d<60/100 is more preferable, and the range of 15/100<b<70/100, 15/100<c<70/100, 12/100<d<50/100 is preferable. Is more preferable.

The values of a, e, and f may be any values within the range defined by the general formula, and preferably 0.5≦a≦1.5, 0≦e<0.2, 1.8≦f≦2.5. , And more preferably 0.8≦a≦1.3, 0≦e<0.1, and 1.9≦f≦2.1.

The shape of the first positive electrode active material is not particularly limited, but the average particle size is preferably 100 μm or less, more preferably 0.1 μm or more and 50 μm or less, and further preferably 0.5 μm or more and 20 μm or less. It is particularly preferably 1 μm or more and 10 μm or less. If the thickness is less than 0.1 μm, the adhesion with the current collector is likely to be impaired when the electrode is manufactured, which may cause problems. If it exceeds 100 μm, problems may occur such as affecting the size of the electrode and damaging the separator that constitutes the secondary battery. In addition, the average particle diameter in this specification means the value of D50 when measured by a general laser diffraction type particle size distribution measuring apparatus, unless otherwise specified.

The second positive electrode active material is a material other than the first positive electrode active material and functions as a positive electrode active material in the secondary battery.

Examples of the second positive electrode active material include spinel structure compounds such as LiMn ₂ O ₄ and Li ₂ Mn ₂ O ₄ , and a general formula: LiM _h PO ₄ (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V). , Ca, Sr, Ba, Ti, Al, Si, B, Te and Mo, at least one element, a compound represented by 0<h<2, LiMVO ₄ or Li ₂ MSiO ₄ (M in the formula Is selected from at least one of Co, Ni, Mn, and Fe), a polyanion compound represented by LiMPO ₄ F (M is a transition metal), a taborolite compound represented by LiMBO ₃ (M is a transition metal). ), a borate-based compound represented by ), Li ₂ MnO _{3, and the} like. As the second positive electrode active material, LiFePO ₄ whose charge/discharge potential in the secondary battery is lower than that of the first positive electrode active material is particularly preferable. If LiFePO ₄ is present in the positive electrode active material layer of the secondary battery, heat generation of the battery can be suppressed to some extent even when the positive electrode and the negative electrode of the battery are short-circuited. As the second positive electrode active material, it is preferable to use a material whose surface is coated with carbon.

The shape of the second positive electrode active material is not particularly limited, but one having an average particle diameter smaller than that of the first positive electrode active material is preferable. The average particle size is preferably 100 μm or less, more preferably 0.01 μm or more and 30 μm or less, still more preferably 0.1 μm or more and 10 μm or less, and particularly preferably 0.5 μm or more and 5 μm or less.

The total compounding amount of the first positive electrode active material and the second positive electrode active material with respect to the solid content of the composition of the present invention is preferably in the range of 60 to 99.5% by mass, more preferably in the range of 70 to 99% by mass. The range of 80 to 98 mass% is more preferable, and the range of 90 to 97 mass% is particularly preferable. Further, the compounding mass ratio of the first positive electrode active material and the second positive electrode active material in the composition of the present invention is preferably within the range of 95:5 to 50:50, and more preferably within the range of 90:10 to 60:40. The range of 85:15 to 70:30 is more preferable, and the range of 82:18 to 77:23 is particularly preferable.

The conductive aid is added to enhance the conductivity of the electrode. The electrically conductive auxiliary may be a chemically inert electron conductor, and examples thereof include carbonaceous fine particles such as carbon black, graphite, vapor grown carbon fiber (VGCF), and various metal particles. To be done. Examples of carbon black include acetylene black, Ketjen black (registered trademark), furnace black, channel black and the like. These conductive aids may be used alone or in combination of two or more.

The shape of the conductive additive is not particularly limited, but in view of its role, the average particle size is preferably small. Those having an average particle diameter smaller than that of the first positive electrode active material are preferable, and those having an average particle diameter smaller than both of the first positive electrode active material and the second positive electrode active material are more preferable. The average particle diameter of the conductive additive is preferably 10 μm or less, more preferably 0.01 to 5 μm, further preferably 0.02 to 3 μm, and particularly preferably 0.03 to 1 μm. preferable.

The compounding amount of the conductive additive in the composition of the present invention is in the range of 0.5 to 20 mass% with respect to the total compounding amount of the first positive electrode active material and the second positive electrode active material or the solid content of the composition of the present invention. Is preferable, and the range of 1 to 10% by mass is particularly preferable.

The binder holds the positive electrode active material and the conductive auxiliary agent on the surface of the current collector, and plays a role of maintaining the conductive network in the electrode. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, fluorine-containing resins such as fluororubber, thermoplastic resins such as polypropylene and polyethylene, polyimide, imide-based resins such as polyamide-imide, and alkoxysilyl group-containing resins. be able to. Further, a polymer having a hydrophilic group may be adopted as the binder. Examples of the hydrophilic group of the polymer having a hydrophilic group include a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group and a phosphoric acid group. Specific examples of the polymer having a hydrophilic group include polyacrylic acid, carboxymethyl cellulose, polymethacrylic acid, and poly(p-styrene sulfonic acid).

The compounding amount of the binder in the solid content contained in the composition of the present invention is, relative to the total compounding amount of the first positive electrode active material, the second positive electrode active material and the conductive additive or the solid content of the composition of the present invention, A range of 0.5 to 20 mass% is preferable, a range of 1 to 10 mass% is more preferable, and a range of 2 to 5 mass% is particularly preferable. When the compounding amount of the binder is too small, when the composition is used as the positive electrode active material layer, the moldability of the layer may be deteriorated. On the other hand, if the amount of the binder compounded is too large, the amount of the positive electrode active material in the positive electrode active material layer decreases, which may be undesirable.

Specific examples of the solvent include N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as "NMP"), dimethylformamide, dimethylacetamide, methanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, acetic acid. Examples are ethyl and tetrahydrofuran. One type of these solvents may be used alone in the composition of the present invention, or two or more types may be used in combination.

In the composition of the present invention, the compounding amount of the above solvent with respect to the total mass thereof is preferably in the range of 10 to 70% by mass, and particularly preferably in the range of 25 to 50% by mass.

Also, a dispersant is preferably added to the composition of the present invention. Due to the presence of the dispersant, the positive electrode active material and the conductive additive can be preferably maintained in a dispersed state in the composition of the present invention, and as a result, the physical properties of the composition of the present invention can be more preferably maintained. Any dispersant may be used as long as it can disperse the positive electrode active material and the conductive additive in the composition of the present invention.

The amount of the dispersant contained in the composition of the present invention is preferably in the range of 0.01 to 1% by mass, and in the range of 0.05 to 0.7% by mass, based on the solid content of the composition of the present invention. Is more preferable, and the range of 0.1 to 0.5 mass% is particularly preferable.

Specific dispersants include, for example, polymers using at least one monomer selected from acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, styrene, vinylpyrrolidone, vinyl alcohol or alkylene oxide, or a polymer thereof. Derivatives, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and other cellulosic polymers or salts thereof, phosphate esters or salts thereof, polyurethanes, fatty acid amides, alkyl alcohol amines, anionic surfactants, cationic interfaces Examples thereof include an activator, a nonionic surfactant, an amphoteric surfactant, a polymer having a comb structure having an amine value and an acid value, or an acrylic block copolymer having a comb structure having an amine value. When the dispersant is a polymer, its average molecular weight is preferably in the range of 1,000 to 1,000,000, more preferably in the range of 2,000 to 500,000, and particularly preferably in the range of 3,000 to 200,000.

One of these dispersants may be used alone in the composition of the present invention, or two or more thereof may be used in combination.

Preferred dispersants include one or more selected from polyvinylpyrrolidone, a polymer having a comb structure showing an amine value and an acid value, or an acrylic block copolymer having a comb structure showing an amine value. In the polymer having a comb structure showing an amine value and an acid value, the range of the amine value is 5 to 20 mgKOH/g, and the range of the acid value is 10 to 25 mgKOH/g. In the acrylic block copolymer having a comb structure having an amine value, the range of the amine value is, for example, 3 to 70 mgKOH/g.

The comb structure means a polymer structure in which a plurality of side chains are bonded to a linear main chain like comb teeth.

Specific examples of more preferable dispersants include the following.

For example, a viscosity average molecular weight of 5,000 to 200,000 is available under the trade names PVP K-30 (Nippon Shokubai Co., Ltd.), trade name PVP K-85 (Nippon Shokubai Co., Ltd.), and trade name PVP K-15 (ISP Japan Co., Ltd.). Polyvinylpyrrolidone.

For example, a comb-shaped polymer having an amine value and an acid value, which is available under the trade names of Azisper PB821, Azisper PB822, Azisper PB824, and Azisper PB881 (all of which are Ajinomoto Fine-Techno Co., Inc.). The amine value and acid value of each product are as follows.
Azisper PB821: amine value 10 mgKOH/g, acid value 17 mgKOH/g
Azisper PB822: amine value 17 mgKOH/g, acid value 14 mgKOH/g
Azisper PB824: amine value 17 mgKOH/g, acid value 21 mgKOH/g
Azisper PB881: amine value 17 mgKOH/g, acid value 17 mgKOH/g

For example, trade names Efka PX4300, Efka PX4310, Efka PX4320, Efka PX4330, Efka PX4340, Efka PX4350, Efka PX4700, Efka PX4701, Efka PX4731, and Efka PX4731 are all available as Japan's Efka PX4731. Acrylic block copolymer with a comb structure. The amine value of each product is as follows.
Efka PX4300: amine value 56 mg KOH/g
Efka PX4310: amine value 19 mg KOH/g
Efka PX4320: amine value 28 mg KOH/g
Efka PX4330: amine value 28 mg KOH/g
Efka PX4340: amine value 4 mgKOH/g
Efka PX4350: amine value 12 mg KOH/g
Efka PX4700: amine value 60 mg KOH/g
Efka PX4701: amine value 40 mg KOH/g
Efka PX4731: Amine value 25 mg KOH/g
Efka PX4732: amine value 25 mg KOH/g

Next, step A) will be described. The step A) is a step of producing a dispersion A by mixing a conductive auxiliary agent, a binder and a solvent.

As a preferable A) process, the aspect including the following A-1-1) process and A-1-2) process can be mentioned.

A-1-1) A step of mixing the conduction aid and the solvent to produce an A-1 dispersion liquid A-1-2) Mixing the A-1 dispersion liquid and the binder, and A Process of manufacturing dispersion

As another preferable step A), an embodiment including a step of producing a dispersion A by mixing a conductive auxiliary agent, a binder and a solvent at one time can be mentioned.

When the composition of the present invention contains a dispersant, the step A) is a step of producing a dispersion A by mixing a conductive auxiliary agent, a binder, a dispersant and a solvent.

As a preferred step A) in the case where the composition of the present invention contains a dispersant, an embodiment including the following step A-2-1) and step A-2-2) can be mentioned.

A-2-1) A step of mixing the conductive auxiliary agent, the dispersant, and the solvent to produce an A-2 dispersion A-2-2) Mixing the A-2 dispersion and the binder And the process of producing A dispersion

As another preferable step A) in the case where the composition of the present invention contains a dispersant, an embodiment including a step of producing a dispersion A by mixing a conductive auxiliary agent, a binder, a dispersant and a solvent at once. You can

By preparing a mixed solution of a binder, a dispersant, and a solvent in advance, it is possible to suitably impart the dispersion performance of the binder with the dispersion performance of the dispersant and the dispersion performance of the dispersant. Presumed.

The dispersion A, the dispersion A-1 or the dispersion A-2 produced in the step A) has a particle size distribution of D50 within a range of 0.6 to 3 μm and D90 of 3 to 7 μm. Those within the range are preferable. The positive electrode using the dispersion A, the dispersion A-1 or the dispersion A-2 in which D50 and D90 are too small or too large may have a high resistance value. It is presumed that the conductive path is not sufficiently formed by the conductive additive in the positive electrode having a high resistance value.

The value of the particle size distribution of A dispersion, A-1 dispersion or A-2 dispersion is the value measured under the following conditions by subjecting each dispersion to a general laser diffraction particle size distribution measuring device. means. The value of the particle size distribution of the dispersion A, the dispersion A-1 or the dispersion A-2 is substantially the same as that of the conductive additive in the step A), the step A-1-1) or the step A-2-1). It shows the dispersed state of.

The value of the particle size distribution of the dispersion A, the dispersion A-1 or the dispersion A-2 is not a value measured by dispersing only the conductive additive which has not been subjected to any dispersion step in the circulating solvent, and the conductive auxiliary. It should be noted that it is not the value of the distribution of particles (so-called primary particles) in a state where the particles of the agent are completely separated from each other.

<Condition>
Dilute dispersion with circulating solvent to an optimum measurement concentration Circulating solvent: N-methyl-2-pyrrolidone Circulating rate: 52 mL/sec.
Particle refractive index: 1.81
Circulating solvent refractive index: 1.479

In the A dispersion, the A-1 dispersion, or the A-2 dispersion, the compounding amount of solids other than the solvent may be in the range of 5 to 30% by mass, 7 to 20% by mass, and 10 to 15% by mass. ..

Examples of the mixing device used in the step A) include a mixing stirrer, a ball mill, a sand mill, a bead mill, a disperser, an ultrasonic disperser, a homogenizer, a homomixer, a planetary mixer, and a planetary stirring defoaming device. Specific mixing devices include Disper Mixer (Primix Co., Ltd.), Clearmix (M Technik Co., Ltd.), Philmix (Primix Co., Ltd.), Paint Conditioner (Red Devil), Product name DYNO-MILL (Shinmaru Enterprises Co., Ltd.), product name Eirich Intensive Mixer (Japan Eirich Co., Ltd.), product name Defoamer DP-200 (M Technique Co., Ltd.), product name Awatori Kentaro Shinky Co., Ltd.), product name Star Mill (Ashizawa Finetech Co., Ltd.), and product name Homo Disper (Primix Co., Ltd.).

Regarding the mixing speed and mixing time in the step A), the speed and time at which each component can be suitably dispersed or dissolved may be appropriately set. As a specific mixing speed, for example, a rotation speed of 500 to 50,000 rpm or a peripheral speed of 5 to 70 m/s may be appropriately set. For example, the A) step so as to obtain an A dispersion having a particle size distribution in which D50 is in the range of 0.6 to 3 μm and D90 is in the range of 3 to 7 μm, which has been described above as a suitable A dispersion. It is preferable to appropriately set the mixing speed and the mixing time in (1). The particle size distribution of the A dispersion changes because the aggregation of the conductive additive contained in the A dispersion is promoted or canceled or the shape of the conductive additive changes depending on the difference in the mixing speed and the mixing time. Therefore, it is preferable to determine the mixing speed and the mixing time while appropriately measuring the particle size distribution of the dispersion A.

In the step A), by dispersing the conductive additive together with the binder in advance before blending the positive electrode active material, the dispersibility of the conductive additive in the composition of the present invention is optimized, and as a result, the present invention is obtained. It is presumed that the resistance of the positive electrode is preferably suppressed because the conductive additive is also in a suitable dispersed state in the positive electrode manufactured by using the composition obtained by the manufacturing method.

Next, step B) will be described. The step B) is a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material.

When the average particle diameter of the second positive electrode active material is smaller than the average particle diameter of the first positive electrode active material, the step B) is an aspect including the following steps B-1) and B-2). Is preferred.
B-1) Step of mixing A dispersion and second positive electrode active material to produce B-1 dispersion B-2) Mixing B-1 dispersion and first positive electrode active material, B dispersion Manufacturing process

In general, the smaller the average particle size, the larger the specific surface area of particles, and the faster the particle aggregation. In the composition containing the first positive electrode active material and the second positive electrode active material having an average particle diameter smaller than that of the first positive electrode active material, the aggregation of the second positive electrode active material takes precedence over the aggregation of the first positive electrode active material. Occurs. However, in the manufacturing method of the present invention including the step B-1) and the step B-2), the step B-1) is first performed so that the binder and the solvent are present around the second positive electrode active material particles. Since the aggregation of the second positive electrode active material particles is suppressed by doing so, it is possible to suppress the increase in viscosity and non-uniformity of the composition due to the aggregation. Note that this principle also holds true in the relationship between the conductive additive and the positive electrode active material.

As the B-1 dispersion liquid produced in the step B-1), a B-1 dispersion liquid having a D50 within a range of 0.1 to 3 μm is preferable due to its particle size distribution. A positive electrode using the B-1 dispersion liquid having an excessively small or excessive D50 may have a high resistance value. The value of the particle size distribution of the B-1 dispersion means the value measured under the following conditions by subjecting the B-1 dispersion to a general laser diffraction type particle size distribution measuring device. The value of the particle size distribution of the B-1 dispersion is substantially the dispersion state of the conductive additive and the second positive electrode active material in the step B-1).

<Condition>
B-1 dispersion is diluted with a circulating solvent to an optimum measurement concentration Circulating solvent: N-methyl-2-pyrrolidone Circulating rate: 52 mL/sec.
Particle refractive index: 1.81
Circulating solvent refractive index: 1.479

Basically, the B dispersion is the composition of the present invention. The composition of the present invention may be mixed with known additives that can be mixed in the positive electrode active material layer, and may be mixed with a positive electrode active material other than the first positive electrode active material and the second positive electrode active material. Is also good.

As the mixing device used in the step B), the one described in the step A) may be used. The mixing device used in the step A) and the mixing device used in the step B) may be the same mixing device or may be other types of mixing devices. Regarding the mixing speed and mixing time in step B), the speed and time at which each component can be suitably dispersed may be set appropriately. As a specific mixing speed, for example, a rotation speed of 500 to 50,000 rpm or a peripheral speed of 5 to 70 m/s may be appropriately set. In particular, when the step B-1) is performed, a B-1 dispersion liquid having a particle size distribution in which D50 is in the range of 0.1 to 3 μm, which is described above as a suitable B-1 dispersion liquid, is obtained. It is preferable to appropriately set the mixing speed and the mixing time in the step B-1) while selecting the second positive electrode active material exhibiting an appropriate particle size distribution. Also in the step B-2) after the step B-1), the speed and time at which each component can be suitably dispersed may be appropriately set. As an example, in the steps B-1) and B-2), the same mixing device may be used and the mixing speeds may be the same.

A positive electrode active material layer can be produced using the composition of the present invention, and further, a positive electrode having the positive electrode active material layer and a secondary battery having the positive electrode can be produced. Hereinafter, a lithium ion secondary battery will be described as an example of a typical secondary battery.

The positive electrode is composed of a current collector and a positive electrode active material layer bound to the surface of the current collector.

The current collector refers to a chemically inactive electron conductor that keeps current flowing through the electrodes during discharging or charging of the lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel. Metal materials such as The current collector may be covered with a known protective layer.

The current collector can be in the form of foil, sheet, film, wire, rod, or the like. Therefore, a metal foil such as a copper foil, a nickel foil, an aluminum foil, or a stainless steel foil can be preferably used as the current collector. When the current collector is in the form of foil, sheet or film, its thickness is preferably in the range of 10 μm to 100 μm.

As a method for forming the positive electrode active material layer on the surface of the current collector, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method can be used. The composition of the present invention may be applied to the surface of. Specifically, after the coating step of coating the surface of the current collector with the composition of the present invention, the solvent is removed by drying to form the positive electrode active material layer, which is used as the positive electrode. If necessary, the dried positive electrode may be compressed to increase the electrode density. Since the composition of the present invention is relatively excellent in stability over time, it is not always necessary to use it in the coating step immediately after its preparation.

The lithium-ion secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolytic solution as battery constituent elements.

The negative electrode has a current collector and a negative electrode active material layer bonded to the surface of the current collector.

The negative electrode active material layer contains a negative electrode active material and, if necessary, a binder and/or a conductive auxiliary agent.

As the current collector, the binder and the conduction aid, those described in the positive electrode or the composition of the present invention may be adopted. Also, styrene-butadiene rubber may be adopted as a binder for the negative electrode active material layer.

Examples of the negative electrode active material include a carbon-based material capable of inserting and extracting lithium, an element capable of alloying with lithium, a compound having an element capable of alloying with lithium, or a polymer material.

Examples of the carbon-based material include non-graphitizable carbon, natural graphite, artificial graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon or carbon blacks. Here, the organic polymer compound fired body is obtained by firing a polymer material such as phenols or furans at an appropriate temperature to carbonize it.

Specific examples of the element capable of alloying with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In and Si. , Ge, Sn, Pb, Sb, and Bi can be exemplified, and silicon (Si) or tin (Sn) is particularly preferable.

Specific examples of the compound having an element capable of alloying with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , _{CaSi 2, CrSi 2, Cu 5} Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦2), SnO _w (0<w≦2), SnSiO ₃ , LiSiO or LiSnO can be exemplified, and SiO _x (0.3≦x≦1.6) is particularly preferable. Examples of the compound having an element capable of alloying with lithium include tin compounds such as tin alloys (Cu-Sn alloys, Co-Sn alloys, etc.).

Specific examples of the polymer material include polyacetylene and polypyrrole.

In addition, as a negative electrode active material, a method in which CaSi ₂ is reacted with an acid to synthesize a layered silicon compound containing Ca as a main component and polysilane is removed, and the layered silicon compound is heated at 300° C. or higher to release hydrogen The silicon material manufactured in 1. can be mentioned. The silicon material has a structure in which a plurality of plate-shaped silicon bodies are stacked in the thickness direction. This structure can be confirmed by observation with a scanning electron microscope or the like. Considering the use of the silicon material as an active material of a lithium ion secondary battery, the plate-like silicon body has a thickness in the range of 10 nm to 100 nm for efficient insertion and desorption reactions of lithium ions. Those in the range of 20 nm to 50 nm are more preferable. The length of the plate-shaped silicon body in the long axis direction is preferably within the range of 0.1 μm to 50 μm. Further, the plate-shaped silicon body preferably has a ratio of (length in the major axis direction)/(thickness) of 2 to 1000.

The silicon material preferably comprises amorphous silicon and/or silicon crystallites. The size of the silicon crystallites is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, further preferably in the range of 1 nm to 50 nm, particularly preferably in the range of 1 nm to 10 nm. The size of the silicon crystallite is calculated from Scherrer's formula using the half-value width of the diffraction peak of the Si(111) plane of the obtained XRD chart by performing X-ray diffraction measurement (XRD measurement) on the silicon material. To be done.

As a preferable particle size distribution of the silicon material when measured by a general laser diffraction particle size distribution measuring device, it can be exemplified that the average particle diameter (D50) is in the range of 1 to 30 μm, more preferably the average particle diameter. It can be illustrated that the diameter (D50) is in the range of 1 to 10 μm.

If necessary, the negative electrode active material may be carbon-coated.

The separator separates the positive electrode from the negative electrode, prevents short-circuiting due to contact between both electrodes, and allows lithium ions to pass through. Examples of the separator include a porous film using one or more synthetic resins such as polytetrafluoroethylene, polypropylene or polyethylene, or a ceramic porous film.

The electrolytic solution contains a solvent and an electrolyte dissolved in this solvent.

As the solvent, cyclic esters, chain esters, ethers and the like can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of the chain ester include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester and the like. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. Further, as the solvent, a solvent in which a part or all of hydrogen constituting the chemical structure of the above specific solvent is replaced with fluorine may be adopted. These solvents may be used alone or in combination in the electrolytic solution.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN(CF ₃ SO ₂ ) ₂ .

As the electrolytic solution, a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiCF ₃ SO _{3 is} added to a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, or dimethyl carbonate in an amount of 0.5 mol/l to 1.7 mol/l. An example is a solution dissolved at a concentration of about the same.

The method for producing a lithium ion secondary battery may include a step of disposing a positive electrode produced using the composition of the present invention. Hereinafter, a specific method for manufacturing a lithium ion secondary battery will be illustrated. A separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be either a laminated type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a positive electrode, a separator and a negative electrode are wound. After connecting between the positive electrode current collector and the negative electrode current collector and the positive electrode terminal and the negative electrode terminal, which communicate with the outside, using a current-collecting lead, etc., add an electrolytic solution to the electrode body to add lithium ion secondary Batteries should be used.

The lithium ion secondary battery can be mounted on the vehicle. Since the lithium ion secondary battery maintains a large charge/discharge capacity and has excellent cycle performance, a vehicle equipped with the lithium ion secondary battery becomes a high performance vehicle.

The vehicle may be any vehicle that uses electric energy from a battery as all or part of a power source, and examples thereof include electric vehicles, hybrid vehicles, plug-in hybrid vehicles, hybrid rail vehicles, electric forklifts, electric wheelchairs, and electric assists. Examples include bicycles and electric motorcycles.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. Without departing from the scope of the present invention, various modifications and improvements can be made by those skilled in the art.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The present invention is not limited to these examples.

(Example 1)
Polyvinylidene fluoride as a binder (using an NMP solution containing 8% by mass of polyvinylidene fluoride (L#7208 manufactured by Kureha Battery Materials Japan Co., Ltd.)), PVP K-30 as a dispersant (stock) Nippon Catalyst Co., Ltd., average molecular weight 80,000 to 120,000) and NMP as a solvent were mixed in a mixing device to obtain a mixed liquid.

Acetylene black (Denka Black granules manufactured by Denki Kagaku Kogyo Co., Ltd., primary particle size: 35 nm) as a conduction aid was added to the above mixture, and mixed in a mixing device to prepare an A dispersion of Example 1. The solid content of the dispersion liquid A in Example 1 other than the solvent was 13% by mass. The mass ratio of the binder, the conductive additive, and the dispersant in the dispersion A of Example 1 was binder:conductive auxiliary:dispersant=3:2.9:0.1. ..

LiFePO ₄ having the surface coated with carbon as a second positive electrode active material was added to the dispersion A of Example 1 and mixed in a mixing device to prepare a dispersion B-1 of Example 1. The D50 of the second positive electrode active material used was 2.6 μm.

Then, LiNi _5/10 Co _2/10 Mn _3/10 O ₂ having a layered rock salt structure was added to the B-1 dispersion liquid of Example 1 as a first positive electrode active material, and the mixture was mixed by a mixing device. A B dispersion of 1 was prepared. The D50 of the first positive electrode active material used was 6 μm. The B dispersion of Example 1 was used as the composition of Example 1.

The solid content of the composition of Example 1 other than the solvent was 65% by mass. The mass ratio of the positive electrode active material, the binder, the conductive additive and the dispersant in the composition of Example 1 was as follows: positive electrode active material:binder:conductive auxiliary:dispersant=94:3:2. .9:0.1, and the mass ratio of the first positive electrode active material and the second positive electrode active material was first positive electrode active material:second positive electrode active material=79:21.

The positive electrode of Example 1 was manufactured as follows.

An aluminum foil having a thickness of 15 μm was prepared as a current collector for the positive electrode. The composition of Example 1 was placed on the surface of the aluminum foil, and the composition was applied in a film form using a doctor blade.

The aluminum foil coated with the composition was dried at 100° C. for 10 minutes to remove NMP by volatilization and form a positive electrode active material layer on the surface of the aluminum foil. The aluminum foil having the positive electrode active material layer formed on the surface was compressed using a roll press machine to firmly and firmly bond the aluminum foil and the positive electrode active material layer. The bonded product was heated in a vacuum dryer at 120° C. for 6 hours to obtain the positive electrode of Example 1.

Although it took several days to manufacture the positive electrode of Example 1, the work could be completed without particularly changing the manufacturing conditions.

(Example 2)
The composition of Example 2 was prepared in the same manner as in Example 1 except that the first positive electrode active material and the second positive electrode active material were simultaneously added to the dispersion A and mixed with a mixing device to produce the dispersion B. A positive electrode of Example 2 was manufactured. However, in the coating operation of the composition when manufacturing the positive electrode of Example 2, it was necessary to correct the manufacturing conditions as the manufacturing time passed.

(Comparative Example 1)
A composition of Comparative Example 1 and a positive electrode of Comparative Example 1 were produced in the same manner as in Example 1 except that the method for producing the composition was as follows. However, in the coating operation of the composition when manufacturing the positive electrode of Comparative Example 1, it was necessary to correct the manufacturing conditions as the manufacturing time passed.

The dispersant and the solvent were mixed by a mixing device to obtain a mixed liquid. A conductive additive was added to the mixed liquid and mixed in a mixing device to prepare an A′ dispersion liquid of Comparative Example 1. In the A′ dispersion liquid of Comparative Example 1, the solid content of the components other than the solvent was 15% by mass. The mass ratio of the conductive additive to the dispersant in the A′ dispersion liquid of Comparative Example 1 was conductive additive:dispersant=2.9:0.1.

The NMP solution containing the binder and the second positive electrode active material were added to the A'dispersion liquid of Comparative Example 1 and mixed in a mixing device to prepare a B-1' dispersion liquid of Comparative Example 1.

Next, the first positive electrode active material was added to the B-1' dispersion liquid of Comparative Example 1 and mixed by a mixing device to produce a B'dispersion liquid of Comparative Example 1. The B′ dispersion of Comparative Example 1 was used as the composition of Comparative Example 1. Of the solid content other than the solvent in the composition of Comparative Example 1, the mass ratio of the positive electrode active material, the binder, the conductive additive and the dispersant, and the first positive electrode active material and the second positive electrode active material. The mass ratio is the same as in Example 1.

(Evaluation example 1)
The positive electrodes of Example 1, Example 2, and Comparative Example 1 were each cut into a size of Φ16 mm. A positive electrode having a size of Φ16 mm was placed in an electric resistance measuring device (model IMC-0240: Imoto Manufacturing Co., Ltd.), and the resistance value after 30 seconds was measured with a load of 5 kg applied. The volume resistivity (Ω·cm) of the positive electrode was calculated from the resistance value and the volume of the positive electrode. The results are shown in Table 1. In Tables 1 and later, the positive electrode having a volume resistivity of less than 200 Ω·cm is ⊚, the positive electrode having a volume resistivity of 200 to 400 Ω·cm is ◯, and the positive electrode having a volume resistivity of more than 400 to 600 Ω·cm is shown. Δ, a positive electrode having a volume resistivity of more than 600 Ω·cm is indicated by x.

It was confirmed that the volume resistivities of the positive electrodes of Examples 1 and 2 were appropriately suppressed. In particular, the volume resistivity of the positive electrode of Example 1 was remarkably suitably suppressed. It can be said that the difference in the production method of the composition affected the resistance of the positive electrode.

(Evaluation example 2)
The viscosities of the compositions of Example 1, Example 2 and Comparative Example 1 were measured immediately after production. Further, the viscosity of each composition after 3 days from the production was measured in a sealed state at room temperature. The viscosity was measured with a Brookfield B type viscometer DV-II + Pro using a spindle 64 under the conditions of a spindle rotation speed of 20 rpm and 25°C. The viscosity increase rate was calculated by the following formula.
Viscosity increase rate (%) = 100 x (viscosity after 3 days-viscosity immediately after production)/viscosity immediately after production

Further, with respect to the coating properties of each composition, ◎ for compositions that could be completed the coating operation without particularly changing the manufacturing conditions, ○ for compositions that required modification of the manufacturing conditions over time. The composition for which the coating operation cannot be completed is indicated by x.

Table 2 shows the results of the viscosity increase rate and coating property of each composition.

It can be seen that the viscosity increasing rate of the composition of Example 1 is suppressed to be extremely low and the coating property of the composition of Example 1 is remarkably excellent. It can be said that the difference in the production method of the composition affected the viscosity increase rate of the composition and the coating property.

(Evaluation example 3)
With respect to the positive electrodes of Example 1, Example 2 and Comparative Example 1, a peel strength test based on JIS Z 0237 was conducted. The test method will be described in detail. First, the positive electrode active material layer of the positive electrode was fixed to the pedestal of the tensile tester. Next, the current collector was pulled upward with respect to the pedestal at an angle of 90°, and the load at which the positive electrode active material layer peeled from the current collector was measured. The peel strength (N/cm) was calculated from the measured load and the width of the positive electrode used in the test. The results are shown in Table 3.

It can be seen that the positive electrode of Example 1 has high peel strength. It can be said that the difference in the manufacturing method of the composition affected the peel strength of the positive electrode.

(Example 3)
PVP K-30 (Nippon Shokubai Co., Ltd., average molecular weight 80,000 to 120,000) as a dispersant and NMP as a solvent were mixed in a mixing device to obtain a mixed liquid. Acetylene black (Denka Black granular product manufactured by Denki Kagaku Kogyo Co., Ltd.: primary particle size: 35 nm) as a conduction aid was added to the mixed solution and mixed by a mixing device to prepare an A-2 dispersion of Example 3.

The solid content of the dispersion liquid A-2 in Example 3 other than the solvent was 15% by mass. The mass ratio of the conductive additive to the dispersant in the A-2 dispersion liquid of Example 3 was conductive additive:dispersant=2.9:0.1.

The A-2 dispersion liquid of Example 3 was diluted with NMP to an optimum measurement concentration, and the diluted solution was applied to a laser diffraction particle size distribution analyzer (Microtrac MT3300EXII, Nikkiso Co., Ltd.), and the particle size distribution was measured under the following conditions. ..
Circulation rate: 52 mL/sec.
Particle refractive index: 1.81
Circulating solvent refractive index: 1.479

The particle size distribution of the A-2 dispersion liquid of Example 3 was D50: 0.8 μm and D90: 3.5 μm.

A-2 dispersion liquid of Example 3 and polyvinylidene fluoride as a binder (NMP solution containing 8% by mass of polyvinylidene fluoride (L#7208 manufactured by Kureha Battery Materials Japan Co., Ltd.) was used). Mix to prepare the A dispersion of Example 3. The solid content of the dispersion A in Example 3 other than the solvent was 13% by mass. The mass ratio of the binder, the conductive additive, and the dispersant in the dispersion A of Example 3 was binder:conductive auxiliary:dispersant=3:2.9:0.1. ..

When the particle size distribution of the dispersion A of Example 3 was measured under the above-described conditions, it was D50:0.8 μm and D90:3.5 μm.

Thereafter, the composition of Example 3 and the positive electrode of Example 3 were manufactured in the same manner as in Example 1 except that the dispersion A of Example 3 was used as the dispersion A.

(Example 4)
Composition of A dispersion of Example 4 and Example 4 was prepared in the same manner as in Example 3 except that a binder, a conductive auxiliary agent, a dispersant and a solvent were mixed at once to produce A dispersion. The positive electrode of Example 4 was manufactured. When the particle size distribution of the dispersion A in Example 4 was measured, it was D50: 0.8 μm and D90: 3.5 μm.

(Example 5)
A-2 dispersion of Example 5 and A dispersion of Example 5 were prepared in the same manner as in Example 3, except that the mixing speed and mixing time for producing the A-2 dispersion and the A dispersion were reduced. A liquid, the composition of Example 5, and the positive electrode of Example 5 were produced.

The particle size distribution of the A-2 dispersion liquid of Example 5 was D50:1.5 μm and D90:4.5 μm. The particle size distribution of the dispersion A of Example 5 was D50:1.5 μm and D90:4.5 μm.

(Example 6)
A dispersion of Example 6, a composition of Example 6, a composition of Example 6, and a positive electrode of Example 6 were produced in the same manner as in Example 4, except that the mixing speed and the mixing time when producing the dispersion A were reduced. did.

The particle size distribution of the dispersion A of Example 6 was D50:1.5 μm and D90:4.5 μm.

(Comparative example 2)
The A-2 dispersion and the A-2 dispersion of Comparative Example 2 were compared in the same manner as in Example 3 except that the mixing apparatus for producing the A-2 dispersion and the A dispersion was changed to make the mixing conditions violent. The dispersion A of Example 2, the composition of Comparative Example 2, and the positive electrode of Comparative Example 2 were produced.

The particle size distribution of the A-2 dispersion liquid of Comparative Example 2 was D50:0.4 μm and D90:2.0 μm. The particle size distribution of the dispersion A of Comparative Example 2 was D50:0.4 μm and D90:2.0 μm.

(Comparative example 3)
The A dispersion of Comparative Example 3, the composition of Comparative Example 3, and the Comparative Example were prepared in the same manner as in Example 4 except that the mixing apparatus used to produce the A dispersion was changed to violent mixing conditions. 3 positive electrodes were produced.

The particle size distribution of the dispersion A of Comparative Example 3 was D50:0.4 μm and D90:2.0 μm.

(Evaluation example 4)
With respect to the positive electrodes of Examples 3 to 6 and Comparative Examples 2 to 3, the volume resistivity (Ω·cm) of the positive electrodes was calculated by the same method as in Evaluation Example 1. The results are shown in Table 4 together with the particle size distribution of the dispersion liquid.

The volume resistivities of the positive electrodes of Examples 3 to 6 were appropriately suppressed. It can be seen that the particle size distribution of the A-2 dispersion and the particle size distribution of the A dispersion affected the volume resistivity of the positive electrode. It can be said that when the D50 and D90 of the A-2 dispersion are too small, the volume resistivity of the positive electrode becomes high.

(Example 7)
Polyvinylidene fluoride as a binder (using an NMP solution containing 8% by mass of polyvinylidene fluoride (L#7208 manufactured by Kureha Battery Materials Japan Co., Ltd.)), PVP K-30 as a dispersant (stock) Nippon Catalyst Co., Ltd., average molecular weight 80,000 to 120,000) and NMP as a solvent were mixed in a mixing device to obtain a mixed liquid.

Acetylene black (Denka Black granules manufactured by Denki Kagaku Kogyo Co., Ltd.: primary particle size 35 nm) as a conduction aid was added to the above mixed solution and mixed in a mixing apparatus to prepare an A dispersion of Example 7. The solid content of the dispersion liquid A of Example 7 other than the solvent was 13% by mass. The mass ratio of the binder, the conductive additive, and the dispersant in the dispersion A of Example 7 was binder:conductive auxiliary:dispersant=3:2.9:0.1. ..

LiFePO ₄ having the surface coated with carbon as a second positive electrode active material was added to the dispersion A of Example 7 and mixed by a mixing device to prepare a dispersion B-1 of Example 7. The D50 of the second positive electrode active material used was 0.8 μm. The blending amount of solids other than the solvent in the B-1 dispersion of Example 7 was 35.5% by mass.

The B-1 dispersion liquid of Example 7 was diluted with NMP to an optimum measurement concentration, and the diluted solution was applied to a laser diffraction particle size distribution analyzer (Microtrac MT3300EXII, Nikkiso Co., Ltd.) to measure the particle size distribution under the following conditions. .. A particle size distribution chart is shown in FIG.
Circulation rate: 52 mL/sec.
Particle refractive index: 1.81
Circulating solvent refractive index: 1.479

In the particle size distribution of the B-1 dispersion liquid of Example 7, D50 was 0.6 μm.

LiNi _5/10 Co _2/10 Mn _3/10 O ₂ having a layered rock salt structure was added to the B-1 dispersion liquid of Example 7 as the first positive electrode active material, and the mixture was mixed in a mixing device to obtain the mixture of Example 7. B dispersion was prepared. The D50 of the first positive electrode active material used was 6 μm. The B dispersion of Example 7 was used as the composition of Example 7.

The solid content of the composition of Example 7 other than the solvent was 65% by mass. The mass ratio of the positive electrode active material, the binder, the conductive additive and the dispersant in the composition of Example 7 was as follows: positive electrode active material: binder: conductive additive: dispersant=94:3:2. .9:0.1, and the mass ratio of the first positive electrode active material and the second positive electrode active material was first positive electrode active material:second positive electrode active material=79:21.

Thereafter, the positive electrode of Example 7 was manufactured in the same manner as in Example 1, except that the composition of Example 7 was used as the composition. The density of the positive electrode active material layer of the positive electrode of Example 7 was 2.30 g/cm ³ .

(Example 8)
The B-1 dispersion of Example 8, the composition of Example 8, the composition of Example 8 and the positive electrode of Example 8 were prepared in the same manner as in Example 7, except that the second positive electrode active material having D50 of 2.6 μm was used. Was manufactured. Regarding the particle size distribution of the B-1 dispersion liquid of Example 8, D50 was 2.4 μm. A particle size distribution chart is shown in FIG. The density of the positive electrode active material layer of the positive electrode of Example 8 was 2.25 g/cm ³ .

(Comparative Example 4)
A B-1 dispersion liquid of Comparative Example 4, a composition of Comparative Example 4, and a positive electrode of Comparative Example 4 were produced in the same manner as in Example 7, except that the second positive electrode active material having a D50 of 10 μm was used. did. Regarding the particle size distribution of the B-1 dispersion liquid of Comparative Example 4, D50 was 3.5 μm. The density of the positive electrode active material layer of the positive electrode of Comparative Example 4 was 2.00 g/cm ³ .

(Evaluation example 5)
With respect to the positive electrodes of Examples 7, 8 and Comparative Example 4, the volume resistivity (Ω·cm) of the positive electrode was calculated by the same method as in Evaluation Example 1. The results are shown in Table 5 together with the particle size distribution of the B-1 dispersion and the density of the positive electrode active material layer.

The volume resistivity of the positive electrodes of Examples 7 and 8 was appropriately suppressed. It can be seen that the particle size distribution of the B-1 dispersion liquid affected the density of the positive electrode active material layer and the volume resistivity of the positive electrode. It is estimated that when the D50 of the B-1 dispersion liquid is in an appropriate range, the density of the positive electrode active material layer becomes high, whereby a conductive path is suitably formed, and as a result, the volume resistivity of the positive electrode becomes low. Here, since increasing the density of the positive electrode active material layer causes a substantial increase in the amount of the positive electrode active material layer formed per unit area of the current collector (so-called basis weight), higher capacity of the secondary battery is expected. it can. Further, the relationship between the average particle diameters of the first positive electrode active material and the second positive electrode active material is preferably (average particle diameter of first positive electrode active material)>(average particle diameter of second positive electrode active material). It can be said that there is.

(Example 9)
Polyvinylidene fluoride as a binder (NMP solution containing 8 mass% polyvinylidene fluoride (L#7208 manufactured by Kureha Battery Materials Japan Co., Ltd.) was used, and amine value and acid value as a dispersant were set. The comb-shaped polymer shown (Azisper PB821, Ajinomoto Fine-Techno Co., Inc.) and NMP as a solvent were mixed in a mixing device to prepare a mixed solution.

Acetylene black (Denka Black granules manufactured by Denki Kagaku Kogyo Co., Ltd., primary particle size: 35 nm) as a conduction aid was added to the above mixed solution and mixed in a mixing apparatus to prepare an A dispersion of Example 9. In the dispersion A of Example 9, the amount of solid components other than the solvent was 13% by mass. The mass ratio of the conductive additive, the binder, and the dispersant in the dispersion A of Example 9 was as follows: conductive additive: binder: dispersant = 3:2.85:0.15. ..

LiFePO ₄ having the surface coated with carbon as a second positive electrode active material was added to the dispersion A of Example 9 and mixed by a mixing device to prepare a dispersion B-1 of Example 9. The D50 of the second positive electrode active material used was 2.6 μm.

LiNi _5/10 Co _2/10 Mn _3/10 O ₂ having a layered rock salt structure was added to the B-1 dispersion liquid of Example 9 as the first positive electrode active material, and the mixture was mixed by a mixing device to obtain the mixture of Example 9. B dispersion was prepared. The D50 of the first positive electrode active material used was 6 μm. The B dispersion of Example 9 was used as the composition of Example 9.

The solid content of the composition of Example 9 other than the solvent was 65% by mass. The mass ratio of the first positive electrode active material, the second positive electrode active material, the conductive additive, the binder, and the dispersant in the composition of Example 9 was as follows: first positive electrode active material:second positive electrode active material: Conductivity assistant: Binder: Dispersant=69:25:3:2.85:0.15.

The positive electrode of Example 9 and the lithium ion secondary battery of Example 9 were manufactured as follows.

An aluminum foil having a thickness of 15 μm was prepared as a current collector for the positive electrode. The composition of Example 9 was placed on the surface of the aluminum foil, and the composition was applied to form a film using a doctor blade.

The aluminum foil coated with the composition was dried at 100° C. for 10 minutes to remove NMP by volatilization and form a positive electrode active material layer on the surface of the aluminum foil. The aluminum foil having the positive electrode active material layer formed on the surface was compressed using a roll press machine to firmly and firmly bond the aluminum foil and the positive electrode active material layer. The bonded product was heated at 120° C. for 6 hours with a vacuum dryer and cut into a rectangular shape to obtain a positive electrode of Example 9.

The negative electrode was manufactured as follows.

As the negative electrode active material, SiO having an average particle diameter D ₅₀ of 4 μm and natural graphite having an average particle diameter D ₅₀ of 20 μm were prepared. A polyamide-imide resin was prepared as a binder. Acetylene black was prepared as a conductive additive.

The negative electrode active material, the conductive additive and the binder were mixed in a weight ratio of SiO:graphite:conductive additive:binder=32:50:8:10. An appropriate amount of NMP as a solvent was added to the above mixture and mixed to obtain a negative electrode slurry.

This slurry was applied to one surface of a copper foil having a thickness of 20 μm, which is a negative electrode current collector, in a film form using a doctor blade. The current collector coated with the slurry was dried at 100° C. for 10 minutes and then pressed to obtain a bonded product. The bonded product was heated at 120° C. for 6 hours with a vacuum dryer and cut into a rectangular shape to obtain a negative electrode.

A laminated lithium-ion secondary battery was manufactured using the above positive electrode and negative electrode. Specifically, a 25 μm-thick rectangular sheet made of a resin film having a three-layer structure of polypropylene/polyethylene/polypropylene as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. This electrode plate group was covered with a set of two laminated films, three sides were sealed, and then an electrolyte solution was injected into the bag-shaped laminated film. As the electrolytic solution, 1 part of LiPF ₆ was added to a solvent in which ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed at EC:EMC:DMC=3:3:4 (volume ratio). A solution was used which was dissolved so as to be mol/l. Then, by sealing the remaining one side, the four sides were hermetically sealed to obtain the lithium ion secondary battery of Example 9 in which the electrode plate group and the electrolytic solution were sealed. The positive electrode and the negative electrode each include a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery.

(Example 10)
Conducted in the same manner as in Example 9, except that the mass ratio of the conductive aid, the binder, and the dispersant was set to the conductive aid: binder: dispersant = 3:2.95:0.05. The dispersion A of Example 10, the dispersion B-1 of Example 10, the composition of Example 10, the positive electrode of Example 10, and the lithium ion secondary battery of Example 10 were produced.

(Example 11)
Conducted in the same manner as in Example 9, except that the mass ratio of the conductive aid, the binder, and the dispersant was set to the conductive aid: the binder: the dispersant = 3:2.7:0.3. The dispersion A of Example 11, the dispersion B-1 of Example 11, the composition of Example 11, the positive electrode of Example 11, and the lithium ion secondary battery of Example 11 were produced.

(Example 12)
The mass ratio of the conductive auxiliary agent, the binder and the dispersant is set to the conductive auxiliary agent: the binder: the dispersant = 5:2.75:0.25, and the first positive electrode active material, the second positive electrode active material and the conductive material. The mass ratio of the auxiliary agent, the binder, and the dispersant is the first positive electrode active material: the second positive electrode active material: the conductive auxiliary agent: the binder: the dispersant=67.5:24.5:5:2.75. : A dispersion of Example 12, B-1 dispersion of Example 12, composition of Example 12, positive electrode of Example 12, and the same procedure as in Example 9 except that the amount was 0.25. The lithium ion secondary battery of Example 12 was manufactured.

(Example 13)
A dispersion of Example 13, Example 13 was prepared in the same manner as in Example 9, except that a comb-type acrylic block copolymer having an amine value (Efka PX4732, BASF Japan Ltd.) was used as the dispersant. The B-1 dispersion liquid of Example 13, the composition of Example 13, the positive electrode of Example 13, and the lithium ion secondary battery of Example 13 were produced.

(Example 14)
A dispersion of Example 14, Example A was prepared in the same manner as in Example 10, except that a comb-type acrylic block copolymer having an amine value (Efka PX4732, BASF Japan Ltd.) was used as the dispersant. 14 B-1 dispersion liquid, the composition of Example 14, the positive electrode of Example 14, and the lithium ion secondary battery of Example 14 were manufactured.

(Example 15)
A dispersion of Example 15, Example 15 was prepared in the same manner as in Example 11 except that a comb-type acrylic block copolymer having an amine value (Efka PX4732, BASF Japan Ltd.) was used as the dispersant. The B-1 dispersion liquid of Example 15, the composition of Example 15, the positive electrode of Example 15, and the lithium ion secondary battery of Example 15 were manufactured.

(Example 16)
A dispersion of Example 16, Example 16 was prepared in the same manner as in Example 12, except that a comb-type acrylic block copolymer having an amine value (Efka PX4732, BASF Japan Ltd.) was used as the dispersant. 16 B-1 dispersion, the composition of Example 16, the positive electrode of Example 16, and the lithium ion secondary battery of Example 16 were produced.

(Example 17)
As a dispersant, polyvinylpyrrolidone (PVP K-30, Nippon Shokubai Co., Ltd., average molecular weight 80,000-120,000) was used in the same manner as in Example 9, and the dispersion liquid A in Example 17 and Example 17 were used. The B-1 dispersion, the composition of Example 17, the positive electrode of Example 17, and the lithium ion secondary battery of Example 17 were produced.

(Comparative example 5)
Without using a dispersant, the mass ratio of the conductive auxiliary agent to the binder was set to conductive auxiliary agent:binder=3:3, and the first positive electrode active material, the second positive electrode active material, the conductive auxiliary agent and the binder were used. Of Comparative Example 5 in the same manner as in Example 9 except that the mass ratio of the first positive electrode active material: the second positive electrode active material: conductive additive: binder = 69:25:3:3. A composition was produced. An attempt was made to manufacture a positive electrode by using the composition of Comparative Example 5 in the same manner as in Example 9, but the composition of Comparative Example 5 had too high a viscosity, so that the positive electrode could not be manufactured.

(Evaluation example 6)
The lithium ion secondary batteries of Examples 9 to 17 were charged to a potential difference of 3.6 V, and the resistance of the batteries when discharged for 10 seconds from this state was measured. The results are shown in Table 6. The meanings of the abbreviations used in Table 6 and thereafter are as follows.
PB821: Addisper PB821
PX4732: Efka PX4732
PVP: PVP K-30

Among the lithium-ion secondary batteries of Examples 9 to 17, the lithium-ion secondary batteries of Examples 9, 10, 12, 13, 14, and 16 have relatively low resistance, and in particular, the lithium-ion secondary batteries of Examples 12 and 16 are the same. It can be seen that the resistance of the lithium ion secondary battery is extremely low.

(Evaluation example 7)
The viscosity of the compositions of Examples 9 to 17 and Comparative Example 5 was measured immediately after production. Further, the viscosity of each composition was measured after one week from the production in a sealed state at room temperature. The viscosity was measured with a Brookfield B type viscometer DV-II + Pro using a spindle 64 under the conditions of a spindle rotation speed of 20 rpm and 25°C. The viscosity increase rate was calculated by the following formula. The results are shown in Table 7.
Viscosity increase rate (%)=100×(viscosity after 1 week-viscosity immediately after production)/viscosity immediately after production

The composition of Comparative Example 5 had a remarkably high initial viscosity. Among the compositions of Examples 9 to 17, the initial viscosity of the compositions of Examples 9, 11 to 13 and 15 to 17 was low. With regard to the compositions after one week, the compositions of Example 17 and Comparative Example 5 were gelled and the viscosity could not be measured. The compositions of Examples 9, 11 to 13 and 15 had a low viscosity increase rate, and particularly the compositions of Examples 11 and 15 had a significantly low viscosity increase rate.

From the viewpoint of stability over time of the composition, it can be said that it is advantageous to select, as the dispersant, a polymer having a comb structure showing an amine value and an acid value or an acrylic block copolymer having a comb structure showing an amine value.

Claims (23)

A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
The average particle size of the second positive electrode active material is smaller than the average particle size of the first positive electrode active material,
The step B) includes
B-1) a step of mixing the A dispersion and the second positive electrode active material to produce a B-1 dispersion,
B-2) a step of producing the B dispersion by mixing the B-1 dispersion and the first positive electrode active material,
B50, the particle size distribution of the B-1 dispersion has a D50 in the range of 0.1 to 3 μm . A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
Step A)
A-1-1) A step of mixing the conductive additive and the solvent to produce an A-1 dispersion,
A-1-2) A step of producing the A dispersion by mixing the A-1 dispersion and the binder.
Including
The particle size distribution of the A dispersion or the A-1 dispersion has a D50 in the range of 0.6 to 3 μm and a D90 in the range of 3 to 7 μm . A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
Step A)
A-1-1) A step of mixing the conductive additive and the solvent to produce an A-1 dispersion,
A-1-2) A step of producing the A dispersion by mixing the A-1 dispersion and the binder.
Including
The average particle size of the second positive electrode active material is smaller than the average particle size of the first positive electrode active material,
The step B) includes
B-1) a step of mixing the A dispersion and the second positive electrode active material to produce a B-1 dispersion,
B-2) a step of producing the B dispersion by mixing the B-1 dispersion and the first positive electrode active material,
A method for producing the composition, comprising: A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
The step A) includes a step of preparing the dispersion A by mixing the conductive additive, the binder, and the solvent all at once.
The particle size distribution of the A dispersion is a method for producing a composition, wherein D50 is in the range of 0.6 to 3 μm and D90 is in the range of 3 to 7 μm . A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
The step A) includes a step of preparing the dispersion A by mixing the conductive additive, the binder, and the solvent all at once.
The average particle size of the second positive electrode active material is smaller than the average particle size of the first positive electrode active material,
The step B) includes
B-1) a step of mixing the A dispersion and the second positive electrode active material to produce a B-1 dispersion,
B-2) a step of producing the B dispersion by mixing the B-1 dispersion and the first positive electrode active material,
A method for producing the composition, comprising: A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
The composition comprises a dispersant,
The step A) is a step of producing the dispersion A by mixing the conductive auxiliary agent, the binder, the dispersant, and the solvent.
The particle size distribution of the A dispersion is a method for producing a composition, wherein D50 is in the range of 0.6 to 3 μm and D90 is in the range of 3 to 7 μm . A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
The composition comprises a dispersant,
The step A) is a step of producing the dispersion A by mixing the conductive auxiliary agent, the binder, the dispersant, and the solvent.
The average particle size of the second positive electrode active material is smaller than the average particle size of the first positive electrode active material,
The step B) includes
B-1) a step of mixing the A dispersion and the second positive electrode active material to produce a B-1 dispersion,
B-2) a step of producing the B dispersion by mixing the B-1 dispersion and the first positive electrode active material,
A method for producing the composition, comprising: A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
The composition comprises a dispersant,
The step A) is a step of producing the dispersion A by mixing the conductive auxiliary agent, the binder, the dispersant, and the solvent.
The method for producing a composition, wherein the dispersant is at least one of a comb structure polymer having an amine value and an acid value, or a comb structure acrylic block copolymer having an amine value . A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
The composition comprises a dispersant,
The step A) is a step of manufacturing the dispersion A by mixing the conductive auxiliary agent, the binder, the dispersant, and the solvent all at once.
The method for producing a composition, wherein the dispersant is at least one of polyvinylpyrrolidone, a polymer having a comb structure having an amine value and an acid value, or an acrylic block copolymer having a comb structure having an amine value . A method for producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive auxiliary agent, a binder and a solvent,
A) a step of mixing the conductive additive, the binder, and the solvent to produce an A dispersion,
B) a step of producing the B dispersion by mixing the A dispersion, the first positive electrode active material and the second positive electrode active material,
A method for producing a composition comprising :
The particle size distribution of the A dispersion is such that D50 is in the range of 0.6 to 3 μm and D90 is in the range of 3 to 7 μm.
The average particle size of the second positive electrode active material is smaller than the average particle size of the first positive electrode active material,
The step B) includes
B-1) a step of mixing the A dispersion and the second positive electrode active material to produce a B-1 dispersion,
B-2) a step of producing the B dispersion by mixing the B-1 dispersion and the first positive electrode active material,
A method for producing the composition, comprising: Step A)
A-1-1) A step of mixing the conductive additive and the solvent to produce an A-1 dispersion,
A-1-2) A step of producing the A dispersion by mixing the A-1 dispersion and the binder.
Method of making a composition according to claim 1 or 10 comprising a. The step A) is a step of producing the dispersion A by mixing the conductive additive, the binder, and the solvent at one time;
Method of making a composition according to claim 1 or 10 comprising a. The composition comprises a dispersant,
The method of producing a composition according to claim 1 or 10 , wherein the step A) is a step of producing the dispersion A by mixing the conductive additive, the binder, the dispersant, and the solvent. Any said dispersing agent is polyvinylpyrrolidone, the comb structure shown an amine number and an acid number polymer, or, according to claim 6, 7, 13 is at least one acrylic block copolymer of the comb structure shown an amine value A method for producing the composition according to item 1 . Step A)
A-2-1) A step of mixing the conduction aid, the dispersant, and the solvent to produce an A-2 dispersion,
A-2-2) A step of producing the A dispersion by mixing the A-2 dispersion and the binder.
The method for producing the composition according to any one of claims 6, 7, 8, 9, 13, and 14 , comprising: The step A) is a step of producing the dispersion A by mixing the conductive auxiliary agent, the binder, the dispersant, and the solvent all at once.
The method for producing the composition according to any one of claims 6, 7, 8, 9, 13, and 14 , comprising: The particle size distribution of the A dispersion, the A-1 dispersion, or the A-2 dispersion is such that D50 is in the range of 0.6 to 3 μm and D90 is in the range of 3 to 7 μm. A method for producing the composition according to any one of 1 , 3 , 5 , 7 , 8, 9 , and 15 .
The average particle size of the second positive electrode active material is smaller than the average particle size of the first positive electrode active material,
The step B) includes
B-1) a step of mixing the A dispersion and the second positive electrode active material to produce a B-1 dispersion,
B-2) a step of producing the B dispersion by mixing the B-1 dispersion and the first positive electrode active material,
The method for producing the composition according to any one of claims 2, 4, 6, 8, and 9 , comprising: The method for producing a composition according to any one of claims 3, 5, 7, 10, and 18, wherein the particle size distribution of the B-1 dispersion has a D50 within a range of 0.1 to 3 µm . The first positive electrode active material has the general _{formula: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Zr, Fe, Ge, Zn, Ru, sc, Sn, in, Y, Bi, S, Si, Na, K, P, at least one element selected from V, 1.7 either ≦ f ≦ 3) according to claim 1 to 19, represented by 1 A method for producing the composition according to the item. The second positive electrode active material has a general formula: LiM _h PO ₄ (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te and at least one element, 0 <method of manufacturing a composition as claimed in any one of claims 1 to 20, represented by h <2) selected from Mo. Coating step, the positive electrode manufacturing method, including the claims 1 composition produced by the production method according to any one of 21, is applied to the current collector. A method for manufacturing a secondary battery, comprising: disposing the positive electrode manufactured by the manufacturing method according to claim 22 .