JP2017054649A - Method of producing composition containing plural positive electrode active materials, conductive assistant, binder and solvent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a composition containing a plurality of positive electrode active materials, a conductive assistant, a binder and a solvent, capable of preferably suppressing positive electrode resistance.SOLUTION: A method of producing a composition containing a first positive electrode active material, a second positive electrode active material, a conductive assistant, a binder and a solvent is characterized to include the steps of: A) mixing the conductive assistant, the binder and the solvent to produce a fluid dispersion A; and B) mixing the fluid dispersion A, the first positive electrode active material, the second positive electrode active material to produce a fluid dispersion B.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a composition containing a plurality of positive electrode active materials, a conductive additive, 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, secondary batteries adopting a plurality of materials as the positive electrode active material are also known.

For example, Patent Document 1 specifically describes 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 having a lithium nickel composite oxide as a positive electrode active material. It is disclosed.

  In general, a positive electrode of a lithium ion secondary battery includes a current collector and a positive electrode active material layer including a positive electrode active material formed on the current collector. Here, the positive electrode active material layer is manufactured by applying a composition (slurry) containing a positive electrode active material, a conductive additive, a binder and a solvent on a current collector, and removing the solvent from the composition. Is done. And the composition containing a positive electrode active material, a conductive additive, a binder and a solvent is produced by mixing the solid components of the composition and then adding the solvent and mixing, or the composition It was usually produced by mixing all the ingredients of the product at once.

Actually, the composition containing the positive electrode active material and the solvent in Patent Document 1 includes LiFePO ₄ and LiNi _0.8 Co _0.15 Al _0.05 O ₂ as the positive electrode active material, polyvinylidene fluoride as the binder, conductive assistant. It is manufactured by a manufacturing method in which carbon of the agent is mixed, and N-methyl-2-pyrrolidone as a solvent is added thereto and mixed (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, conductive assistants, binders and solvents vary depending on the production method. Furthermore, it has been found that the resistance of the positive electrode including the positive electrode active material layer formed by removing the solvent from the composition varies depending on the method for producing the composition.

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

  As a result of intensive studies by the inventor, first, a conductive auxiliary agent, a binder and a solvent are mixed to produce a first dispersion, and then a plurality of positive electrode active materials are blended in the first dispersion. It was found that the composition produced by the production method for producing the second dispersion was suitable.

That is, the method for producing a composition of the present invention is a method for producing a composition comprising a first positive electrode active material, a second positive electrode active material, a conductive additive, a binder, and a solvent,
A) A step of producing a dispersion A by mixing the conductive assistant, the binder and the solvent,
B) A step of producing a 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 this specification includes the lower limit x and the upper limit y. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

A method for producing a composition of the present invention is a method for producing a composition comprising a first positive electrode active material, a second positive electrode active material, a conductive additive, a binder, and a solvent,
A) The step of producing the dispersion A by mixing the conductive auxiliary agent, the binder and the solvent (hereinafter, simply referred to as “A step”). ),
B) The 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” may be referred to. ),
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. Solid content other than a solvent means positive electrode active materials other than a solvent, a conductive support agent, a binder, a dispersant and other additives used as necessary. In the composition of the present invention, the blending amount of solids other than the solvent (hereinafter sometimes simply referred to as “solids”) is preferably in the range of 30 to 90% by mass, and in the range of 50 to 75% by 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; 0.7 ≦ f ≦ 3), spinel structure material of LiMn ₂ O ₄ and non-stoichiometric composition Li _a Mn _b O ₄ (a + b = 2), and layered rock salt structure material and spinel structure A solid solution composed of materials can be mentioned.

General formula: Li _a Ni _b Co _c Mn _{d De} 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 particularly those satisfying the above conditions Although there is no limitation, it is preferable that 0 <b <1, 0 <c <1, 0 <d <1, and at least one of b, c, d is 10/100 <b <90/100. 10/100 <c <90/100, preferably 5/100 <d <70/100, <B <80/100, 12/100 <c <80/100, 10/100 <d <60/100 are more preferable, and 15/100 <b <70/100, 15/100 <c. More preferably, the ranges are <70/100, 12/100 <d <50/100.

  a, e, f may be any numerical value within the range defined by the general formula, and preferably 0.5 ≦ a ≦ 1.5, 0 ≦ e <0.2, 1.8 ≦ f ≦ 2.5 More preferably, 0.8 ≦ a ≦ 1.3, 0 ≦ e <0.1, 1.9 ≦ f ≦ 2.1 can be exemplified.

  The shape of the first positive electrode active material is not particularly limited, but is preferably 100 μm or less, more preferably 0.1 μm or more and 50 μm or less, and even more preferably 0.5 μm or more and 20 μm or less in terms of the average particle diameter. 1 μm or more and 10 μm or less is particularly preferable. If the thickness is less than 0.1 μm, there may be a problem that, when the electrode is manufactured, the adhesion to the current collector is easily impaired. If it exceeds 100 μm, the size of the electrode may be affected, or the separator constituting the secondary battery may be damaged. 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 device unless otherwise specified.

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

As the second positive electrode active material, spinel structure compounds such as LiMn ₂ O ₄ and Li ₂ Mn ₂ O ₄ , 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, 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), LiMBO ₃ (M is a transition metal) ) -Based borate compounds, 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. When 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 negative electrode of the battery are short-circuited. As the second positive electrode active material, it is preferable to employ a carbon coated surface.

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

  The total 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, and more preferably in the range of 70 to 99% by mass. Preferably, it is more preferably within the range of 80 to 98% by mass, and particularly preferably within the range of 90 to 97% by mass. Moreover, the blending 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 in the range of 95: 5 to 50:50, more preferably in 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 assistant is added to increase the conductivity of the electrode. The conductive assistant may be a chemically inert electronic conductor, and examples thereof include carbon black, graphite, vapor grown carbon fiber (VGCF), and various metal particles. Is done. Examples of carbon black include acetylene black, ketjen black (registered trademark), furnace black, and channel black. These conductive assistants can be used alone or in combination of two or more.

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

  The blending amount of the conductive additive in the composition of the present invention is in the range of 0.5 to 20% by mass with respect to the total blending 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. The inside is preferable, and the range of 1 to 10% by mass is particularly preferable.

  The binder serves to keep the positive electrode active material and the conductive auxiliary agent on the surface of the current collector and maintain the conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to. Moreover, you may employ | adopt the polymer which has a hydrophilic group as a 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 phosphate group. Specific examples of the polymer having a hydrophilic group include polyacrylic acid, carboxymethylcellulose, polymethacrylic acid, and poly (p-styrenesulfonic acid).

  The blending amount of the binder in the solid content contained in the composition of the present invention is based on the total blending 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. The range of 0.5 to 20% by mass is preferable, the range of 1 to 10% by mass is more preferable, and the range of 2 to 5% by mass is particularly preferable. If the blending amount of the binder is too small, the moldability of the layer may be lowered when the composition is used as a positive electrode active material layer. Further, if the amount of the binder is too large, the amount of the positive electrode active material in the positive electrode active material layer decreases, which may not be preferable.

  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 thereof include ethyl and tetrahydrofuran. One of these solvents may be used alone in the composition of the present invention, or two or more thereof may be used in combination.

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

  Moreover, it is preferable that a dispersing agent is mix | blended with the composition of this invention. Due to the presence of the dispersant, the positive electrode active material and the conductive additive can be suitably maintained in the dispersed state in the composition of the present invention, and as a result, the physical properties of the composition of the present invention are more favorably maintained. Any dispersant can 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 blending 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 with respect to the solid content of the composition of the present invention. The inside is more preferable, and the inside of the range of 0.1 to 0.5% by mass is particularly preferable.

  Specific examples of the dispersant include, for example, a polymer using at least one monomer selected from acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, styrene, vinyl pyrrolidone, vinyl alcohol, and alkylene oxide, or the like. Cellulose polymers such as derivatives, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxypropylcellulose or hydroxypropylmethylcellulose or salts thereof, phosphate esters or salts thereof, polyurethanes, fatty acid amides, alkyl alcohol amines, anionic surfactants, cationic interfaces Activating agent, nonionic surfactant, amphoteric surfactant, comb-shaped polymer showing amine value and acid value, or comb-shaped acrylic block showing amine value Mention may be made of a polymer. When the dispersant is a polymer, the average molecular weight is preferably in the range of 1000 to 1000000, more preferably in the range of 2000 to 500000, and particularly preferably in the range of 3000 to 200000.

  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.

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

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

  Specific examples of more preferable dispersants include the following.

  For example, the viscosity average molecular weight 5000-200000 which can be obtained as a brand name PVP K-30 (Nippon Catalyst Co., Ltd.), a brand name PVP K-85 (Nippon Catalyst Co., Ltd.), and a brand name PVP K-15 (ISP Japan Corporation). Of polyvinylpyrrolidone.

For example, a polymer having a comb structure showing an amine value and an acid value, which are available as trade names Ajisper PB821, Ajisper PB822, Azisper PB824, and Azisper PB881 (all of which are Ajinomoto Fine Techno Co., Ltd.). 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
Ajisper 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, Efka PX4732 Comb-shaped acrylic block copolymer. The amine value of each product is as follows.
Efka PX4300: amine value 56 mgKOH / g
Efka PX4310: amine value 19 mgKOH / g
Efka PX4320: amine value 28 mgKOH / g
Efka PX4330: amine value 28 mgKOH / g
Efka PX4340: amine value 4 mgKOH / g
Efka PX4350: amine value 12 mgKOH / g
Efka PX4700: amine value 60 mgKOH / g
Efka PX4701: amine value 40 mgKOH / g
Efka PX4731: amine value 25 mgKOH / g
Efka PX4732: amine value 25 mgKOH / g

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

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

A-1-1) A step of producing an A-1 dispersion by mixing the conductive assistant and the solvent. A-1-2) A-1 by mixing the A-1 dispersion and the binder. Process for producing dispersion

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

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

  As a preferable A) step when the composition of the present invention contains a dispersant, an embodiment including the following steps A-2-1) and A-2-2) can be mentioned.

A-2-1) A step of producing an A-2 dispersion by mixing the conductive additive, the dispersant and the solvent. A-2-2) Mixing the A-2 dispersion and the binder. And the process for producing the A dispersion

  As another preferable step A) in the case where the composition of the present invention contains a dispersing agent, an embodiment including a step of producing a dispersion A by mixing a conductive additive, a binder, a dispersing agent and a solvent at a time. Can do.

  By providing a mixed solution in which a binder, a dispersant, and a solvent are mixed in advance, a dispersion performance that combines the dispersion performance of the binder and the dispersion performance of the dispersant can be suitably imparted to the conductive additive. Presumed.

  A) As A dispersion liquid, A-1 dispersion liquid or A-2 dispersion liquid produced in the step, D50 is in the range of 0.6 to 3 μm, and D90 is 3 to 7 μm. Those within the range are preferred. The positive electrode using the A dispersion, A-1 dispersion or A-2 dispersion in which D50 and D90 are too small or too large may have a high resistance value. In the positive electrode having a high resistance value, it is presumed that the formation of the conductive path by the conductive assistant is not sufficient.

  In addition, the value of the particle size distribution of A dispersion liquid, A-1 dispersion liquid, or A-2 dispersion liquid is a value measured by applying each dispersion liquid to a general laser diffraction particle size distribution measuring apparatus under the following conditions. means. The value of the particle size distribution of the A dispersion, the A-1 dispersion, or the A-2 dispersion is substantially the same as that in the step A), the step A-1-1), or the step A-2-1). The dispersion state of is shown.

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

<Conditions>
The dispersion is diluted with a circulating solvent to the optimum measured 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, examples of the solid content other than the solvent include 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 and defoaming device. Specific mixing devices include trade name Disper Mixer (Primics Co., Ltd.), trade name Claremix (M Technique Co., Ltd.), trade name Filmix (Primics Co., Ltd.), trade name Paint Conditioner (Red Devil Corporation), Product name DYNO-MILL (Shinmaru Enterprises Co., Ltd.), product name Eirich Intensive Mixer (Japan Eirich Co., Ltd.), product name defoaming machine DP-200 (M Technique Co., Ltd.), product name Awatori Netaro (stock) (Sinky Company), trade name Star Mill (Ashizawa Finetech Co., Ltd.), and trade name Homo Disper (Primics Co., Ltd.).

  The mixing speed and mixing time in the step A) may be set as appropriate so that the respective components can be suitably dispersed or dissolved. A specific mixing speed may be appropriately set within a range of, for example, a rotational speed of 500 to 50000 rpm and a peripheral speed of 5 to 70 m / s. For example, as described above as a suitable A dispersion, the A50 process is performed so that the A dispersion exhibits 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. It is preferable to appropriately set the mixing speed and mixing time. Depending on the mixing speed and mixing time, aggregation of the conductive assistant contained in the dispersion A is promoted or canceled, or the shape of the conductive assistant changes, so that the particle size distribution of the dispersion A varies. Therefore, it is preferable to determine the mixing speed and mixing time while appropriately measuring the particle size distribution of the A dispersion.

  In 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. Also in the positive electrode manufactured using the composition obtained by this manufacturing method, since the conductive auxiliary agent is suitably dispersed, it is presumed that the resistance of the positive electrode is preferably suppressed.

  Next, step B) will be described. The step B) is a step for 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 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 the following steps B-1) and B-2). Is preferred.
B-1) A step of producing a B-1 dispersion by mixing the A dispersion and the second cathode active material B-2) A B dispersion by mixing the B-1 dispersion and the first cathode active material Manufacturing process

  In general, the aggregation of particles proceeds more rapidly as the average particle size is smaller and the specific surface area is larger. In the composition including 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 has priority over the aggregation of the first positive electrode active material. Arise. However, in the production method of the present invention including the steps B-1) and B-2), the binder and the solvent are present around the second positive electrode active material particles by performing the step B-1) first. Since the aggregation of the second positive electrode active material particles is suppressed, the increase in viscosity and non-uniformity of the composition accompanying the aggregation can be suppressed. This principle holds also in the relationship between the conductive additive and the positive electrode active material.

  The B-1 dispersion produced in the step B-1) is preferably a B-1 dispersion having a D50 in the range of 0.1 to 3 μm with respect to the particle size distribution. The positive electrode using the B-1 dispersion having an excessively small or large D50 may have a high resistance value. The value of the particle size distribution of the B-1 dispersion means a value obtained by subjecting the B-1 dispersion to a general laser diffraction type particle size distribution measuring apparatus and measuring under the following conditions. The value of the particle size distribution of the B-1 dispersion substantially indicates the dispersion state of the conductive additive and the second positive electrode active material in the step B-1).

<Conditions>
Dilute B-1 dispersion with circulating solvent to 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 blended with known additives that can be blended in the positive electrode active material layer, or may be blended with a positive electrode active material other than the first positive electrode active material and the second positive electrode active material. Also good.

  As the mixing apparatus used in the step B), the apparatus 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 other types of mixing devices. The mixing speed and mixing time in step B) may be appropriately set at a speed and time at which each component can be suitably dispersed. A specific mixing speed may be appropriately set within a range of, for example, a rotational speed of 500 to 50000 rpm and a peripheral speed of 5 to 70 m / s. In particular, when undergoing step B-1), the B-1 dispersion described above as a suitable B-1 dispersion is a B-1 dispersion exhibiting a particle size distribution having a D50 in the range of 0.1 to 3 μm. It is preferable to appropriately set the mixing speed and mixing time in the step B-1) while selecting the second positive electrode active material showing an appropriate particle size distribution. 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, the same mixing apparatus may be used in the steps B-1) and B-2), and the mixing speed may be the same.

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

  The positive electrode includes 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 inert electronic conductor that keeps a current flowing through an electrode during discharge or charging of a 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 Examples of such a metal material can be given. The current collector may be covered with a known protective layer.

  The current collector can take the form of a foil, a sheet, a film, a line, a bar, and the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 10 μm to 100 μm.

  As a method of forming the positive electrode active material layer on the surface of the current collector, a current collector is used by using 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. The composition of the present invention may be applied to the surface. Specifically, after the coating step of applying the composition of the present invention to the surface of the current collector, the solvent is removed by drying to form a positive electrode active material layer to obtain a positive electrode. If necessary, the positive electrode after drying may be compressed to increase the electrode density. In addition, since the composition of this invention is comparatively excellent in aging stability, it is not necessarily used for the application | coating process immediately after the preparation.

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

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

  The negative electrode active material layer includes a negative electrode active material and, if necessary, a binder and / or a conductive aid.

  What is necessary is just to employ | adopt what was demonstrated with the positive electrode or the composition of this invention for a collector, a binder, and a conductive support agent. Moreover, you may employ | adopt a styrene-butadiene rubber as a binder for negative electrode active material layers.

  Examples of the negative electrode active material include a carbon-based material capable of inserting and extracting lithium, an element that can be alloyed with lithium, a compound having an element that can be alloyed with lithium, a polymer material, and the like.

  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, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

  Specifically, elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. Ge, Sn, Pb, Sb, Bi can be exemplified, and silicon (Si) or tin (Sn) is particularly preferable.

Specific examples of compounds having elements that can be alloyed 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 2 or LiSnO, and SiO _x (0.3 ≦ x ≦ 1.6) is particularly preferable. Moreover, tin compounds, such as a tin alloy (Cu-Sn alloy, Co-Sn alloy, etc.), can be illustrated as a compound which has an element which can be alloyed with lithium.

  Specific examples of the polymer material include polyacetylene and polypyrrole.

Also, a method of synthesizing a layered silicon compound mainly composed of polysilane obtained by reacting CaSi ₂ and acid to remove Ca as a negative electrode active material, and releasing the hydrogen by heating the layered silicon compound at 300 ° C. or higher. The silicon material manufactured by can be mentioned. The silicon material has a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction. This structure can be confirmed by observation with a scanning electron microscope or the like. In consideration of using 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 reaction of lithium ions. Those within the range are preferable, and those within the range of 20 nm to 50 nm are more preferable. The length of the plate-like silicon body in the major axis direction is preferably in the range of 0.1 μm to 50 μm. The plate-like silicon body preferably has a (length in the major axis direction) / (thickness) range of 2 to 1000.

  The silicon material preferably includes amorphous silicon and / or silicon crystallites. The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, still more preferably in the range of 1 nm to 50 nm, and particularly preferably in the range of 1 nm to 10 nm. The size of the silicon crystallite is calculated from the Scherrer equation using X-ray diffraction measurement (XRD measurement) on the silicon material and using the half-value width of the diffraction peak on the Si (111) surface of the obtained XRD chart. Is done.

  As a preferable particle size distribution of the silicon material when measured with a general laser diffraction particle size distribution measuring apparatus, it can be exemplified that the average particle diameter (D50) is in the range of 1 to 30 μm, and more preferably the average particle It can be exemplified 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 and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes. Examples of the separator include a porous film using one or more synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene, or a ceramic porous film.

  The electrolytic solution includes a solvent and an electrolyte dissolved in the 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 chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. 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 substituted with fluorine may be employed. In the electrolytic solution, these solvents may be used alone or in combination.

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 an electrolytic solution, lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiCF ₃ SO ₃ are added in a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate to 0.5 mol / l to 1.7 mol / l. A solution dissolved at a concentration of about can be exemplified.

  As a manufacturing method of a lithium ion secondary battery, what is necessary is just to have the process of arrange | positioning the positive electrode manufactured using the composition of this invention. Hereinafter, a specific method for producing a lithium ion secondary battery will be exemplified. A separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal that communicate with the outside using a lead for current collection, etc., an electrolyte is added to the electrode body and a lithium ion secondary Use batteries.

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

  The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that 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. In addition, this invention is not limited by these Examples.

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

  Acetylene black (Denka Black granular product manufactured by Denki Kagaku Kogyo Co., Ltd .: primary particle size: 35 nm) as a conductive additive was added to the above mixed solution, and mixed with a mixing apparatus to produce an A dispersion of Example 1. The compounding quantity of solids other than a solvent in A dispersion liquid of Example 1 was 13 mass%. Moreover, in the A dispersion liquid of Example 1, the mass ratio of the binder, the conductive additive, and the dispersant was binder: conductive auxiliary agent: dispersant = 3: 2.9: 0.1. .

To the A dispersion liquid of Example 1, LiFePO ₄ whose surface was coated with carbon was added as a second positive electrode active material, and mixed with a mixing apparatus to produce the B-1 dispersion liquid of Example 1. The D50 of the second positive electrode active material used was 2.6 μm.

Next, the layered rock salt structure LiNi _5/10 Co _2/10 Mn _3/10 O ₂ was added to the B-1 dispersion of Example 1 as the first positive electrode active material, and mixed in a mixing apparatus. 1 B dispersion 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 compounding quantity of solid content other than a solvent in the composition of Example 1 was 65 mass%. Further, in the composition of Example 1, the mass ratio of the positive electrode active material, the binder, the conductive additive, and the dispersant is as follows: positive electrode active material: binder: conductive auxiliary agent: dispersant = 94: 3: 2. .9: 0.1, and the mass ratio of the first positive electrode active material to 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 positive electrode current collector. The composition of Example 1 was placed on the surface of the aluminum foil, and the composition was applied in a film using a doctor blade.

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

  The production of the positive electrode of Example 1 required a plurality of days, but the operation could be completed without changing the production 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 A dispersion and mixed with a mixing apparatus to produce the B dispersion. The positive electrode of Example 2 was manufactured. However, in the application | coating operation | work of the composition at the time of manufacturing the positive electrode of Example 2, correction of manufacturing conditions was needed with progress of manufacturing time.

(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 production method of the composition was as follows. However, in the application | coating operation | work of the composition at the time of manufacturing the positive electrode of the comparative example 1, correction of manufacturing conditions was needed with progress of manufacturing time.

  The dispersant and the solvent were mixed with a mixing device to obtain a mixed solution. A conductive additive was added to the mixed solution and mixed with a mixing apparatus to produce an A ′ dispersion of Comparative Example 1. The blending amount of solids other than the solvent in the A ′ dispersion of Comparative Example 1 was 15% by mass. Moreover, the mass ratio of the conductive additive to the dispersant in the A ′ dispersion 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 of Comparative Example 1 and mixed with a mixing apparatus to produce the B-1 ′ dispersion of Comparative Example 1.

  Next, the first positive electrode active material was added to the B-1 ′ dispersion of Comparative Example 1 and mixed with a mixing apparatus to produce the B ′ dispersion of Comparative Example 1. The B ′ dispersion of Comparative Example 1 was used as the composition of Comparative Example 1. The blending amount of solids 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 to a size of Φ16 mm. A positive electrode having a size of Φ16 mm was placed in an electric resistance measuring instrument (model IMC-0240: Imoto Seisakusho Co., Ltd.), and the resistance value after 30 seconds was measured with a 5 kg load applied. From the resistance value and the volume of the positive electrode, the volume resistivity (Ω · cm) of the positive electrode was calculated. The results are shown in Table 1. In Table 1 and subsequent tables, the positive electrode having a volume resistivity of less than 200 Ω · cm is indicated by ◎, the positive electrode having a volume resistivity of 200 to 400 Ω · cm is indicated by ○, and the positive electrode having a volume resistivity of more than 400 to 600 Ω · cm is indicated. (Triangle | delta) and the positive electrode whose volume resistivity exceeds 600 ohm * cm are shown by x.

  It has confirmed that the volume resistivity of the positive electrode of Example 1 and Example 2 was suppressed suitably. In particular, the volume resistivity of the positive electrode of Example 1 was significantly suppressed. It can be said that the difference in the manufacturing method of the composition influenced the resistance of the positive electrode.

(Evaluation example 2)
About the composition of Example 1, Example 2, and the comparative example 1, the viscosity immediately after manufacture was measured. Furthermore, the viscosity was measured for each composition after 3 days from manufacture 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 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 × (viscosity after 3 days−viscosity immediately after production) / viscosity immediately after production

  In addition, for coating properties of each composition, ◎ for a composition that could complete the coating operation without changing the manufacturing conditions, and ○ for a composition that required correction of manufacturing conditions over time The composition which cannot complete the coating operation is indicated by x.

  Table 2 shows the results of increase in viscosity and coatability of each composition.

  It can be seen that the viscosity increase rate of the composition of Example 1 is remarkably low and the applicability 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 rate of increase in viscosity and the coating property of the composition.

(Evaluation example 3)
For the positive electrodes of Example 1, Example 2, and Comparative Example 1, a peel strength test based on JIS Z 0237 was performed. The test method will be described in detail. First, the positive electrode active material layer of the positive electrode was fixed to the base of a tensile tester. Next, the current collector was pulled upward at an angle of 90 ° with respect to the pedestal, 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 peel strength of the positive electrode of Example 1 is high. It can be said that the difference in the manufacturing method of the composition influenced the peel strength of the positive electrode.

(Example 3)
PVP K-30 (Nippon Shokubai Co., Ltd., average molecular weight 80000-120000) as a dispersant and NMP as a solvent were mixed with a mixing device to obtain a mixed solution. Acetylene black (Denka black granular product manufactured by Denki Kagaku Kogyo Co., Ltd .: primary particle size: 35 nm) as a conductive auxiliary was added to the mixed solution, and mixed with a mixing apparatus to produce an A-2 dispersion of Example 3.

  The compounding quantity of solids other than a solvent in the A-2 dispersion liquid of Example 3 was 15 mass%. Moreover, in the A-2 dispersion liquid of Example 3, the mass ratio of the conductive auxiliary agent to the dispersing agent was conductive auxiliary agent: dispersant = 2.9: 0.1.

The A-2 dispersion liquid of Example 3 was diluted with NMP to an optimal measurement concentration, and subjected to a laser diffraction particle size distribution measuring device (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.

  The A-2 dispersion of Example 3 and polyvinylidene fluoride as a binder (using NMP solution containing 8% by mass of polyvinylidene fluoride (L # 7208 manufactured by Kureha Battery Materials Japan Co., Ltd.)) The A dispersion liquid of Example 3 was produced by mixing. The compounding quantity of solids other than a solvent in A dispersion liquid of Example 3 was 13 mass%. In the A dispersion liquid of Example 3, the mass ratio of the binder, the conductive additive, and the dispersant was binder: conductive auxiliary agent: dispersant = 3: 2.9: 0.1. .

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

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

Example 4
The composition of the A dispersion of Example 4 and the composition of Example 4 were the same as in Example 3, except that the binder, conductive additive, dispersant and solvent were mixed at a time to produce the A dispersion. The positive electrode of Example 4 was manufactured. The particle size distribution of the A dispersion liquid of Example 4 was measured and found to be D50: 0.8 μm and D90: 3.5 μm.

(Example 5)
The A-2 dispersion of Example 5 and the A dispersion of Example 5 were the same as in Example 3, except that the mixing speed and mixing time in producing the A-2 dispersion and A dispersion were reduced. The 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, the composition of Example 6, and the positive electrode of Example 6 were produced in the same manner as in Example 4 except that the mixing speed and mixing time in producing the A dispersion 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)
A-2 dispersion liquid and A-2 dispersion liquid of Comparative Example 2 were compared in the same manner as in Example 3 except that the mixing apparatus for producing the A dispersion liquid and the A dispersion liquid was changed and the mixing conditions were changed to violent conditions. The A dispersion 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)
A dispersion liquid of Comparative Example 3, the composition of Comparative Example 3 and Comparative Example were the same as in Example 4 except that the mixing apparatus for producing the A dispersion was changed and the mixing conditions were changed to intense 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 electrode was calculated in the same manner as in Evaluation Example 1. The results are shown in Table 4 together with the particle size distribution of the dispersion.

  In the positive electrodes of Examples 3 to 6, the volume resistivity was suitably 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. If D50 and D90 of the A-2 dispersion are too small, it can be said that the volume resistivity of the positive electrode is increased.

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

  Acetylene black (Denka Black granular product manufactured by Denki Kagaku Kogyo Co., Ltd .: primary particle size: 35 nm) as a conductive additive was added to the above mixed solution, and mixed with a mixing apparatus to produce an A dispersion of Example 7. The compounding quantity of solids other than a solvent in A dispersion liquid of Example 7 was 13 mass%. Moreover, in the A dispersion liquid of Example 7, the mass ratio of the binder, the conductive additive, and the dispersant was binder: conductive auxiliary agent: dispersant = 3: 2.9: 0.1. .

To the A dispersion liquid of Example 7, LiFePO ₄ whose surface was coated with carbon was added as the second positive electrode active material, and mixed with a mixing apparatus to produce the B-1 dispersion liquid of Example 7. The D50 of the second positive electrode active material used was 0.8 μm. Moreover, the compounding quantity of solid content other than the solvent in the B-1 dispersion liquid of Example 7 was 35.5 mass%.

The B-1 dispersion of Example 7 was diluted with NMP to an optimal measurement concentration, and subjected to a laser diffraction particle size distribution measuring device (Microtrac MT3300EXII, Nikkiso Co., Ltd.), and the particle size distribution was measured under the following conditions. . FIG. 1 shows a particle size distribution chart.
Circulation rate: 52 mL / sec.
Particle refractive index: 1.81
Circulating solvent refractive index: 1.479

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

To the B-1 dispersion of Example 7, LiNi _5/10 Co _2/10 Mn _3/10 O ₂ having a layered rock salt structure as a first positive electrode active material was added and mixed using a mixing apparatus. A 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 compounding quantity of solid content other than the solvent in the composition of Example 7 was 65 mass%. In the composition of Example 7, the mass ratio of the positive electrode active material, the binder, the conductive auxiliary agent, and the dispersant is as follows: positive electrode active material: binder: conductive auxiliary agent: dispersant = 94: 3: 2. .9: 0.1, and the mass ratio of the first positive electrode active material to 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 produced in the same manner as in Example 1 except that the composition of Example 7 was used as the composition. In addition, 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 and the positive electrode of Example 8 were the same as in Example 7, except that a second positive electrode active material having a D50 of 2.6 μm was used. Manufactured. As for the particle size distribution of the B-1 dispersion of Example 8, D50 was 2.4 μm. FIG. 1 shows a particle size distribution chart. In addition, 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 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 a second positive electrode active material having a D50 of 10 μm was used. did. As for the particle size distribution of the B-1 dispersion liquid of Comparative Example 4, D50 was 3.5 μm. In addition, 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)
For the positive electrodes of Example 7, Example 8, and Comparative Example 4, the volume resistivity (Ω · cm) of the positive electrode was calculated in the same manner 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.

  In the positive electrodes of Examples 7 and 8, the volume resistivity was suitably suppressed. It can be seen that the particle size distribution of the B-1 dispersion affected the density of the positive electrode active material layer and the volume resistivity of the positive electrode. When D50 of the B-1 dispersion is in an appropriate range, the density of the positive electrode active material layer is increased, whereby a conductive path is suitably formed. As a result, it is estimated that the volume resistivity of the positive electrode is decreased. Here, the increase in the density of the positive electrode active material layer results in a substantial increase in the amount of the positive electrode active material layer formed (so-called basis weight) with respect to the unit area of the current collector. it can. 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 the first positive electrode active material)> (average particle diameter of the second positive electrode active material). It can be said that there is.

Example 9
Polyvinylidene fluoride as a binder (using NMP solution containing 8% by mass of polyvinylidene fluoride (L # 7208 manufactured by Kureha Battery Materials Japan Co., Ltd.)), amine value and acid value as a dispersant A comb-shaped polymer (Ajisper PB821, Ajinomoto Fine Techno Co., Ltd.) and NMP as a solvent were mixed with a mixing device to obtain a mixed solution.

  Acetylene black (Denka Black granular product manufactured by Denki Kagaku Kogyo Co., Ltd .: primary particle size: 35 nm) as a conductive auxiliary agent was added to the above mixed solution, and mixed with a mixing apparatus to produce an A dispersion of Example 9. The compounding quantity of solid content other than a solvent in A dispersion liquid of Example 9 was 13 mass%. Moreover, the mass ratio of the conductive additive, the binder, and the dispersant in the dispersion A of Example 9 was conductive additive: binder: dispersant = 3: 2.85: 0.15. .

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

To the B-1 dispersion of Example 9, LiNi _5/10 Co _2/10 Mn _3/10 O ₂ having a layered rock salt structure as the first positive electrode active material was added and mixed with a mixing apparatus. A 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 compounding quantity of solid content other than a solvent in the composition of Example 9 was 65 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 is as follows: first positive electrode active material: second positive electrode active material: Conductive aid: 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 positive electrode current collector. 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, whereby NMP was removed by volatilization, and a positive electrode active material layer was formed on the aluminum foil surface. The aluminum foil having the positive electrode active material layer formed on the surface was compressed using a roll press machine, and the aluminum foil and the positive electrode active material layer were firmly bonded. The joined product was heated in a vacuum dryer at 120 ° C. for 6 hours, cut into a rectangular shape, and the positive electrode of Example 9 was obtained.

  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 aid.

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

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

A laminate type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode. Specifically, a rectangular sheet having a thickness of 25 μm made of a resin film having a three-layer structure of polypropylene / polyethylene / polypropylene was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. As an electrolytic solution, LiPF ₆ was added to a solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at EC: EMC: DMC = 3: 3: 4 (volume ratio). A solution dissolved so as to be mol / l was used. Thereafter, the remaining one side was sealed, whereby the four sides were hermetically sealed, and the lithium ion secondary battery of Example 9 in which the electrode plate group and the electrolyte solution were sealed was obtained. Note that the positive electrode and the negative electrode have 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)
Implemented in the same manner as in Example 9 except that the mass ratio of the conductive additive, the binder, and the dispersant was changed to conductive additive: binder: dispersant = 3: 2.95: 0.05. The A dispersion liquid of Example 10, the B-1 dispersion liquid 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)
Implemented in the same manner as in Example 9 except that the mass ratio of the conductive additive, the binder, and the dispersant was changed to conductive additive: binder: dispersant = 3: 2.7: 0.3. The A dispersion liquid of Example 11, the B-1 dispersion liquid 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 conductive auxiliary agent: binder agent: dispersant = 5: 2.75: 0.25, and the first positive electrode active material, the second positive electrode active material, and the conductive material are electrically conductive. The mass ratio of the auxiliary agent, the binder, and the dispersing agent is the first positive electrode active material: the second positive electrode active material: the conductive auxiliary agent: the binder: the dispersing agent = 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, except for 0.25 The lithium ion secondary battery of Example 12 was manufactured.

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

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

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

(Example 16)
The dispersion A of Example 16 and Example were the same as Example 12 except that an acrylic block copolymer (Efka PX4732, BASF Japan Ltd.) having a comb structure showing an amine value 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)
Except for using polyvinylpyrrolidone (PVP K-30, Nippon Shokubai Co., Ltd., average molecular weight 80000-120000) as a dispersant, the same procedure as in Example 9 was followed. 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 manufactured.

(Comparative Example 5)
Without using a dispersant, the mass ratio of the conductive auxiliary agent to the binder is 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. And the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive auxiliary agent: the binder = 69: 25: 3: 3. A composition was prepared. In addition, although it tried to manufacture a positive electrode by the method similar to Example 9 using the composition of the comparative example 5, since the viscosity of the composition of the comparative example 5 was too high, manufacture of the positive electrode was not able to be performed.

(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 from this state for 10 seconds was measured. The results are shown in Table 6. The meanings of the abbreviations used in Table 6 and after 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 resistances of the lithium ion secondary batteries of Examples 9, 10, 12, 13, 14, and 16 are relatively low. It can be seen that the resistance of the lithium ion secondary battery is extremely low.

(Evaluation example 7)
About the composition of Examples 9-17 and the comparative example 5, the viscosity immediately after manufacture was measured. Furthermore, the viscosity was measured for each composition after one week had passed since 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 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 an extremely high initial viscosity. Of the compositions of Examples 9 to 17, the initial viscosities of the compositions of Examples 9, 11 to 13, and 15 to 17 were low. With respect to the composition after one week, the compositions of Example 17 and Comparative Example 5 were gelled, so the viscosity could not be measured. The viscosity increase rate of the compositions of Examples 9, 11 to 13 and 15 was low, and in particular, the viscosity increase rate of the compositions of Examples 11 and 15 was remarkably low.

  From the viewpoint of stability of the composition over time, it may be advantageous to select a comb-shaped polymer exhibiting an amine value and an acid value or an acrylic block copolymer having a comb-shaped structure exhibiting an amine value as a dispersant.

Claims (21)

A method for producing a composition comprising a first positive electrode active material, a second positive electrode active material, a conductive additive, a binder and a solvent,
A) A step of producing a dispersion A by mixing the conductive assistant, the binder and the solvent,
B) A step of producing a 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: A) The process is
A-1-1) mixing the conductive auxiliary agent and the solvent to produce an A-1 dispersion,
A-1-2) mixing the A-1 dispersion and the binder to produce an A dispersion;
The manufacturing method of the composition of Claim 1 containing this. A) is a step in which the conductive auxiliary agent, the binder and the solvent are mixed at a time to produce an A dispersion,
The manufacturing method of the composition of Claim 1 containing this. The composition includes a dispersant;
The method for producing a composition according to claim 1, wherein the step A) is a step of producing the dispersion A by mixing the conductive additive, the binder, the dispersant and the solvent.   5. The composition according to claim 4, wherein the dispersant is at least one of polyvinyl pyrrolidone, a comb-shaped polymer exhibiting an amine value and an acid value, or an acrylic block copolymer having a comb-shaped structure exhibiting an amine value. Production method. A) The process is
A-2-1) A step of producing an A-2 dispersion by mixing the conductive additive, the dispersant and the solvent,
A-2-2) A step of producing the A dispersion by mixing the A-2 dispersion and the binder.
The manufacturing method of the composition of Claim 4 or 5 containing this. A) is a step in which the conductive auxiliary agent, the binder, the dispersant, and the solvent are mixed at a time to produce an A dispersion.
The manufacturing method of the composition of Claim 4 or 5 containing this.   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. The manufacturing method of the composition of any one of 1-7. An average particle size of the second positive electrode active material is smaller than an average particle size of the first positive electrode active material;
Step B)
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 mixing the B-1 dispersion and the first positive electrode active material to produce a B dispersion,
The manufacturing method of the composition in any one of Claims 1-8 containing these.   The particle size distribution of the said B-1 dispersion is a manufacturing method of the composition of Claim 9 whose D50 exists in the range of 0.1-3 micrometers. The first positive electrode active material has a general formula: Li _a Ni _b Co _c Mn _{d De} 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, 11. At least one element selected from Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and V, 1.7 ≦ f ≦ 3). A method for producing the composition according to 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 The manufacturing method of the composition of any one of Claims 1-11 represented by the at least 1 element chosen from Mo, 0 <h <2).   The manufacturing method of a positive electrode including the application | coating process which apply | coats the composition manufactured with the manufacturing method of any one of Claims 1-12 to a collector.   A method for producing a secondary battery, comprising: arranging a positive electrode produced by the production method according to claim 13.   A dispersion comprising a conductive auxiliary agent and a solvent, wherein D50 is in the range of 0.6 to 3 μm and D90 is in the range of 3 to 7 μm.   Furthermore, the dispersion liquid of Claim 15 containing a dispersing agent and / or a binder. Conductive aid, binder, 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 A dispersion comprising at least one element selected from Mo, a positive electrode active material represented by 0 <h <2), and a solvent, wherein D50 is in the range of 0.1 to 3 μm.   Furthermore, the dispersion liquid of Claim 17 containing a dispersing agent. A composition comprising a first positive electrode active material, a second positive electrode active material, a conductive additive, a binder, a dispersant, and a solvent,
The said dispersing agent is at least 1 sort (s) of the polymer of the comb structure which shows an amine value and an acid value, or the acrylic block copolymer of the comb structure which shows an amine value. A positive electrode active material layer including a first positive electrode active material, a second positive electrode active material, a conductive additive, a binder, and a dispersant;
The positive electrode active material layer, wherein the dispersant is at least one of a comb-shaped polymer exhibiting an amine value and an acid value, or an acrylic block copolymer having a comb-shaped structure exhibiting an amine value.   A lithium ion secondary battery comprising the positive electrode active material layer according to claim 20.