JP2010067365A - Method for manufacturing composition for positive electrode of nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a composition for a positive electrode of a nonaqueous electrolyte secondary battery capable of decreasing diffusion resistance of active material ions, to provide slurry for the positive electrode, to provide the positive electrode manufactured by employing this, and to provide the nonaqueous electrolyte secondary battery using the positive electrode. <P>SOLUTION: The method for manufacturing the composition for the positive electrode of the nonaqueous electrolyte secondary battery includes: a process 1 obtaining slurry 1 by mixing positive electrode active material particles having specific physical properties and a conductive material 1 having specific physical properties in a solvent 1; and a process 2 obtaining slurry 2 by kneading the positive electrode active material particles, the conductive material 1, a binder and a solvent 2 after the process 1. The kneading in the process 2 is conducted so that the shearing stress to a shear rate in a range of 0.001-0.1 s<SP>-1</SP>of the shear rate is 1,000-40,000 mPa and the gradient ▵ of the shearing stress in the range of the shear rate is -0.30 to 0.30 in rheology characteristics of the slurry 2 measured with a rheology measuring device. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a composition for a positive electrode of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, a slurry for a positive electrode of a non-aqueous electrolyte secondary battery, a positive electrode produced using the slurry, and the positive electrode. The present invention relates to the used nonaqueous electrolyte secondary battery.

  Non-aqueous electrolyte secondary batteries are characterized by a higher operating voltage and higher energy density than conventional nickel cadmium secondary batteries, and are widely used as power sources for mobile electronic devices and batteries for electric vehicles. ing.

  The general structure and working mechanism of a non-aqueous electrolyte secondary battery will be described taking a lithium ion secondary battery as an example. In a lithium ion secondary battery, an electrolytic solution containing a lithium salt in a non-aqueous solvent is used, and a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material are separated via a separator. . In the positive electrode, since the conductivity of the positive electrode active material itself is low, a conductive material such as carbon black is added to improve the conductivity.

In general, the positive electrode as described above is obtained by applying and drying a slurry obtained by mixing a positive electrode active material such as LiMn ₂ O ₄ , a conductive material such as carbon black, a binder, and a solvent onto a metal foil as a current collector. Manufactured. As a result, the fine structure of the positive electrode has a structure in which particles of a positive electrode active material having low conductivity and particles of a conductive material having a smaller particle diameter are dispersed and bonded.

  In the positive electrode of a lithium ion secondary battery, lithium ions are occluded in the positive electrode active material at the time of discharge. At that time, discharge proceeds by the action of lithium ions diffusing to the positive electrode side and electrons conducted from the positive electrode current collector. To do. Further, at the time of charging, electrons and lithium ions are released from the positive electrode active material.

  As a method for preparing a slurry for forming a positive electrode, the following Patent Document 1 discloses a method of dispersing a positive electrode active material, a conductive agent, and a binder in an alcohol solution of vanadium pentoxide. Examples of means include an ultrasonic cleaner, a mixer, and a ball mill.

  Further, in Patent Document 2 below, a conductive agent and active material particles are dispersed in a binder by ultrasonic treatment so that the active material particles are covered with a binder film containing a conductive agent. A method for preparing an agent (slurry) is disclosed.

JP-A-5-29022 JP 2003-331823 A

  In the above Patent Documents 1 and 2, it is described that a dispersion means such as ultrasonic treatment is used when preparing a slurry, but it does not describe to what state the slurry is kneaded. Furthermore, there is no description about the relationship between the rheological properties of the slurry and the diffusion resistance of lithium ions.

  The present invention provides appropriate rheological properties to a slurry containing positive electrode active material particles and a conductive material, and is based on an appropriate three-dimensional network structure formed by the positive electrode active material particles and the conductive material in the slurry. A method for producing a composition for a positive electrode of a nonaqueous electrolyte secondary battery capable of reducing the internal resistance of the battery by drastically reducing the diffusion resistance of active material ions, a slurry for a positive electrode of a nonaqueous electrolyte secondary battery, and the same And a non-aqueous electrolyte secondary battery using the positive electrode.

  The present inventors consider that it is important to optimize the microstructure of the positive electrode active material and reduce the diffusion resistance of the active material ions in the positive electrode in order to improve battery characteristics, particularly high-speed discharge performance. The inventors have found that a stable fine structure can be formed by kneading a slurry having a specific composition until a specific rheological property is obtained, and have completed the present invention.

That is, in the method for producing a positive electrode composition for a non-aqueous electrolyte secondary battery according to the present invention, positive electrode active material particles and conductive material 1 are mixed in solvent 1, and the positive electrode active material particles, conductive material 1 and Step 1 for obtaining a slurry 1 containing the solvent 1, and after the step 1, the positive electrode active material particles, the conductive material 1, a binder and a solvent 2 are kneaded to form the positive electrode active material particles and the conductive material 1. And a step 2 for obtaining a slurry 2 containing the binder and the solvent 2, and a method for producing a composition for a positive electrode of a non-aqueous electrolyte secondary battery,
The positive electrode active material particles have a BET specific surface area of 1 to 6 m ² / g, a total pore volume measured with a mercury porosimeter of 0.1 to 1 cc / g, and a pore distribution measured with a mercury porosimeter. The peak fine diameter 1 that gives the maximum differential pore volume value is in the range of 0.01 to 8 μm, and the peak fine diameter gives a differential pore volume value that is 5% or more of the maximum differential pore volume value. The pore diameter 2 is present in the range of the pore diameter of 0.01 μm or more and less than the peak pore diameter of 1, and the average particle diameter by laser diffraction / scattering particle size distribution measurement is from the peak pore diameter of 1 to 20 μm,
The conductive material 1 has an average particle size of 1 to 50 μm when mixed with the positive electrode active material particles, has self-aggregation, and the content in the slurry 1 is 100 parts by weight of the positive electrode active material particles. 3 to 20 parts by weight with respect to
In the rheological properties of the slurry 2 measured by the rheology measuring device, the shear stress with respect to the shear rate in the range of the shear rate of 0.001 to 0.1 s ⁻¹ is 1000 to 40000 mPa, and the shear stress gradient Δ in the shear rate range is The kneading in the step 2 is performed so as to be −0.30 to 0.30.

The positive electrode slurry of the nonaqueous electrolyte secondary battery of the present invention is a positive electrode slurry of a nonaqueous electrolyte secondary battery containing positive electrode active material particles, conductive material 1, binder and solvent,
The positive electrode active material particles have a BET specific surface area of 1 to 6 m ² / g, a total pore volume measured with a mercury porosimeter of 0.1 to 1 cc / g, and a pore distribution measured with a mercury porosimeter. The peak fine diameter 1 that gives the maximum differential pore volume value is in the range of 0.01 to 8 μm, and the peak fine diameter gives a differential pore volume value that is 5% or more of the maximum differential pore volume value. The pore diameter 2 is present in the range of the pore diameter of 0.01 μm or more and less than the peak pore diameter of 1, and the average particle diameter by laser diffraction / scattering particle size distribution measurement is from the peak pore diameter of 1 to 20 μm,
The conductive material 1 has an average particle size of 1 to 50 μm when mixed with the positive electrode active material particles, has a self-aggregation property, and the content in the positive electrode slurry is 100 weights of the positive electrode active material particles. 3 to 20 parts by weight with respect to parts,
In the rheological properties of the positive electrode slurry measured with a rheology measuring apparatus, the shear stress with respect to the shear rate in the range of the shear rate of 0.001 to 0.1 s ⁻¹ is 1000 to 40000 mPa and the shear stress gradient Δ in the shear rate range. Is −0.30 to 0.30.

  Moreover, the positive electrode of the non-aqueous electrolyte secondary battery of the present invention is a positive electrode of a non-aqueous electrolyte secondary battery comprising the above-described dried slurry for positive electrode of the present invention.

  Moreover, the nonaqueous electrolyte secondary battery of this invention is a nonaqueous electrolyte secondary battery provided with the positive electrode of the said invention.

  In addition, unless otherwise indicated, the various physical-property values in this invention are values measured by the measuring method as described in an Example.

  According to the production method of the present invention, appropriate rheological properties are imparted to the slurry containing the positive electrode active material particles and the conductive material, and the appropriate three-dimensional formed by the positive electrode active material particles and the conductive material in the slurry. It is possible to provide a method for producing a composition for a positive electrode of a non-aqueous electrolyte secondary battery that can reduce the internal resistance of the battery by greatly reducing the diffusion resistance of the active material ions considered to be based on the network structure. Moreover, according to the slurry for positive electrodes, the positive electrode, and the nonaqueous electrolyte secondary battery of the present invention, it is possible to provide a nonaqueous electrolyte secondary battery that can reduce the internal resistance of the battery for the same reason as described above.

  In the method for producing a positive electrode composition of the present invention, positive electrode active material particles and a conductive material 1 are mixed in a solvent 1 to obtain a slurry 1 containing the positive electrode active material particles, the conductive material 1 and the solvent 1. Step 1 and after Step 1, the positive electrode active material particles, the conductive material 1, the binder and the solvent 2 are kneaded to contain the positive electrode active material particles, the conductive material 1, the binder and the solvent 2 And obtaining a slurry 2 to be processed 2. The positive electrode active material particles are porous positive electrode active material particles having specific physical properties to be described later. The conductive substance 1 is a self-aggregating conductive substance having specific physical properties to be described later. In the production method of the present invention, as described later, these are mixed at a predetermined ratio (step 1), and kneaded with a binder in a solvent until a specific rheological property is obtained (step 2). It is considered that a stable fine structure can be obtained by the porous structure of the active material particles and the three-dimensional network structure by an appropriate aggregation form of the self-aggregating conductive material. Therefore, according to the present invention, it is considered that the positive electrode composition can be obtained in which the movement of the active material ions becomes smooth and the diffusion resistance of the active material ions in the positive electrode can be greatly reduced. In either of the steps 1 and 2, the order of mixing the components is not particularly limited.

As a material constituting the positive electrode active material particles, lithium composite oxide is preferably used. The lithium composite oxide is preferably a Li · Mn composite oxide such as lithium manganate (such as LiMn ₂ O ₄ ) that can release lithium ions, and cobalt acid from the viewpoint of securing high output and output characteristics. Li / Co composite oxides such as lithium (LiCoO ₂ etc.), Li / Ni composite oxides such as lithium nickelate (LiNiO ₂ etc.), Li / Fe composite oxides such as lithium ferrate (LiFeO ₂ etc.) Such as things. Of these, lithium cobaltate, lithium nickelate, and lithium manganate are preferable, and lithium manganate is more preferable from the viewpoint of excellent thermal stability, capacity, and output characteristics.

As the lithium manganate, the crystal phase is preferably a spinel type. Specifically, the main peak obtained by X-ray diffraction measurement is JCPDS (Joint Committee on Powder Diffraction Standards): No. It may be the same as or equivalent to LiMn ₂ O ₄ shown in 35-782.

  The method for producing the positive electrode active material particles is not particularly limited as long as the specific physical properties described below can be obtained, but the spray granulation method, the rolling granulation method, the compression granulation method, in which the physical properties are easily controlled, An agitation granulation method is preferred, and a spray granulation method is more preferred from the viewpoint of particle size and shape control.

As the positive electrode active material particles, those having a BET specific surface area of 1 to 6 m ² / g are used from the viewpoint of improving the adhesion by the binder. From the same viewpoint, BET specific surface area of the positive active material particles is preferably ^{1~4m 2 / g, 1~2.5m 2 /} g is more preferable. The BET specific surface area corresponds to the area of the reaction interface of the active material and also corresponds to the effective area involved in the adhesion. If the BET specific surface area is within the above range, it is considered that the adhesion by the binder is improved, the conductive structure is maintained, the reactivity of the electrode is improved, and the internal resistance of the battery can be reduced.

  Adjustment of the BET specific surface area of the positive electrode active material particles includes adjustment of the average primary particle diameter and average aggregate particle diameter of the positive electrode active material raw material particles for producing the positive electrode active material particles, adjustment of the firing temperature, adjustment of the firing time, etc. Can be performed.

  The gap between the positive electrode active material particles is preferably continuous from the viewpoint of promoting the permeability of the electrolytic solution and the diffusion of the active material ions. For this purpose, the average primary particle diameter of the positive electrode active material raw material particles is preferably 0.1 to 5 μm, more preferably 0.5 to 3 μm, and still more preferably 0.5 to 2 μm. From the same viewpoint, the average aggregate particle diameter of the positive electrode active material raw material particles is preferably 1 to 20 μm, more preferably 1 to 15 μm, and still more preferably 1 to 10 μm.

  Moreover, in order to ensure the shape stability of the positive electrode active material particles and not lower the adhesiveness, it is desirable that the inside of the positive electrode active material particles be moderately porous. In order for the positive electrode active material particles to be appropriately porous, the positive electrode active material particles are preferably sintered to become porous particles by firing. For this purpose, the firing temperature is preferably 650 to 950 ° C., and 700 to 900 ° C. Is more preferable, 750-850 degreeC is still more preferable, and the baking time is the said baking temperature, 5 to 40 hours are preferable, 5 to 30 hours are more preferable, and 10 to 30 hours are still more preferable.

  Furthermore, the porous particles are obtained by spray-drying a slurry prepared by mixing positive electrode active material raw material particles and pore forming resin particles in an aqueous solvent under heating, and obtaining the positive electrode active material raw material particles and the empty particles. It is preferable that the powder containing the pore-forming resin particles is obtained by firing at a temperature higher than the decomposition temperature of the pore-forming resin particles. The positive electrode active material raw material particles are preferably particles having the preferred primary particle size and the preferred aggregated particle size described above. The average particle diameter of the pore-forming resin particles is preferably 0.5 to 10 μm, more preferably 1 to 9 μm, and still more preferably 2 to 6 μm.

  The aqueous solvent is preferably water, a mixed solvent of water and an organic solvent, or the like, and more preferably water. Examples of the organic solvent include alkyl alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol, and alkyl ketones such as acetone and methyl ethyl ketone. Of these, alcohols are preferred.

  The decomposition temperature of the resin particles for pore formation is preferably 250 to 450 ° C, more preferably 280 to 430 ° C, and still more preferably 300 to 400 ° C. Regarding the heating condition, the hot air supply temperature is preferably 10 ° C. or more higher than the boiling point of the aqueous solvent, more preferably 20 ° C. or more, and further preferably 25 ° C. or more. The hot air supply temperature is preferably 70 ° C. or more lower than the decomposition temperature of the pore forming resin particles, more preferably 80 ° C. or more, and further preferably 100 ° C. or more. The firing temperature of the powder may be the above-described suitable firing temperature in the case of many pore-forming resin particles.

  As the pore-forming resin particles, those that are solid at room temperature and oxidatively decompose at a temperature at which the lithium composite oxide is sintered can be suitably used. For example, polystyrenes (polystyrene, poly α-methylstyrene, etc.), polyolefins (polyethylene, polypropylene, etc.), fluorine-containing resins (polyvinylidene fluoride, polytetrafluoroethylene, etc.), poly (meth) acrylic acid esters, poly (Meth) acrylonitriles, poly (meth) acrylamides and copolymers thereof, or homopolymers such as vinylidene fluoride, ethylene fluoride, acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, butyl methacrylate, or Examples thereof include copolymers and organic polymers (preferably thermoplastic resins) such as polyvinyl alcohol and polyvinyl butyral. Furthermore, thermosetting resins such as urethane resins, phenol resins, and epoxy resins, polyolefin elastomers, and the like can also be used. Further, organic short fibers (diameter: 0.1 to 100 μm) such as polyamide, acrylic, acetate, and polyester, or organic polymer particles such as polymethyl methacrylate (PMMA) having a diameter of 0.1 to 100 μm can also be used. Among these, from the point that the affinity with water is particularly excellent and the particle size can be adjusted relatively easily in the range of 0.1 to 10 μm, polymerized particles of methyl methacrylate, t-butyl methacrylate, etc. Polymerized particles of butyl methacrylate or commercially available polymethyl methacrylate particles are preferred.

  From the viewpoint of reducing the internal resistance of the battery, the positive electrode active material particles have a total pore volume of 8 μm or less measured by a mercury porosimeter of 0.1 to 1 cc / g. From the same viewpoint, the total pore volume of the positive electrode active material particles is preferably 0.3 to 1 cc / g, and more preferably 0.5 to 0.8 cc / g. If the total pore volume is within the above range, the diffusion path of the active material ions is maintained, the diffusion rate of the active material ions in the positive electrode is improved, and the electrolyte permeability in the positive electrode is improved. It is thought that the internal resistance can be reduced.

  From the viewpoint of reducing the diffusion resistance of active material ions, the positive electrode active material particles have a pore diameter (hereinafter referred to as peak pore diameter 1) that gives the maximum differential pore volume value in the pore distribution measured with a mercury porosimeter. A pore size (hereinafter referred to as peak pore size 2) that exists in a pore size range of 0.01 to 8 μm and gives a differential pore volume value of 5% or more of the maximum differential pore volume value. The extraction method will be described later. )) Having a pore diameter of 0.01 μm or more and less than the peak pore diameter of 1 is used. From the same viewpoint, those having a peak pore diameter 1 in the range of 1 to 6 μm and a peak pore diameter 2 in the range of 0.01 μm or more and less than the peak pore diameter 1 are preferable. More preferably, the pore diameter 1 is in the range of 2 to 6 μm and the peak pore diameter 2 is in the range of 0.1 μm or more and less than the peak pore diameter 1. From the viewpoint of reducing the diffusion resistance of active material ions, the peak pore diameter 2 is a peak that gives a differential pore volume value that is 5 to 70% of the maximum differential pore volume value corresponding to the peak pore diameter 1. The peak giving a differential pore volume value of 10 to 30% is more preferable. Here, the “differential pore volume value” means that the total volume V is differentiated by the common logarithm logR of the pore diameter R, where R is the pore diameter and V is the total volume of pores larger than the pore diameter. Value (value of dV / dlogR). In the normal case, the “peak pore diameter 1” corresponds to the peak of the void diameter between the positive electrode active material particles, and the “peak pore diameter 2” corresponds to the peak of the pore diameter in the positive electrode active material particles. It is done.

  The method for extracting the peak pore diameter 2 will be described with reference to FIGS. 1A to 1C are pore distribution data used when extracting the peak pore diameter 2 in an example of the positive electrode active material particles. First, using the analysis software OriginPro 7.5J SR6 (manufactured by OriginLab Corporation), the pore diameter of the positive electrode active material particles measured with a mercury porosimeter is taken as the X axis, and the differential pore volume value for each pore diameter is taken as the Y axis. A graph (solid line in FIG. 1A) is created. A single peak Lorentz fitting process is performed on this graph, and the obtained data is taken as fitting data (broken line in FIG. 1B). Then, a difference process between the data in FIG. 1A and the fitting data in FIG. 1B is performed by a subtraction process of arithmetic operation to obtain difference data (a chain line in FIG. 1C). At this time, the maximum peak of the difference data confirmed in the pore diameter range lower than the pore diameter giving the maximum peak of the fitting data is set as the peak pore diameter 2.

  The porous structure of the positive electrode active material particles described above is important from the viewpoints of electrolyte permeability, active material ion diffusivity, and positive electrode active material particle shape stability. The adjustment method can be performed by the same method as the adjustment method of the BET specific surface area of the positive electrode active material particles described above.

  From the viewpoint of reducing the internal resistance of the battery, the positive electrode active material particles are those having an average particle diameter measured by laser diffraction / scattering particle size distribution of 1 to 20 μm. From the same viewpoint, the average particle diameter of the positive electrode active material particles is preferably 1 to 15 μm, and more preferably 3 to 10 μm. If the average particle diameter of the positive electrode active material particles is within the above range, the dispersibility of the positive electrode active material particles in the positive electrode is improved, the diffusion path of the active material ions is continuously constructed, and the internal resistance of the battery can be reduced. it is conceivable that. In addition, when the average particle diameter of the positive electrode active material particles is within the above range, sufficient strength can be obtained to maintain the shape of the positive electrode active material particles during pressing when producing the positive electrode.

  The average particle diameter of the positive electrode active material particles is important from the viewpoint of shape stability of the positive electrode active material particles and securing a porous structure and voids. The adjustment method can be performed by the same method as the adjustment method of the BET specific surface area of the positive electrode active material particles described above.

  From the viewpoint of reducing the internal resistance of the battery, the conductive material 1 has an average particle size (measurement method will be described later) of 1 to 50 μm when mixed with the positive electrode active material particles. From the same viewpoint, the average particle diameter is preferably 1 to 10 μm, and more preferably 1 to 8 μm. If the average particle diameter of the conductive material 1 is within the above range, the dispersibility of the conductive material 1 in the positive electrode is improved, the diffusion path of the active material ions is continuously constructed, and the internal resistance of the battery can be reduced. it is conceivable that.

  About the measuring method of the average particle diameter of the electroconductive substance 1 at the time of mixing with a positive electrode active material particle, 1) When mixing a positive electrode active material particle after mixing the electroconductive substance 1 with the solvent 1, 2) The solvent 1 In the following description, the conductive material 1 is mixed after the positive electrode active material particles are mixed with each other, or the positive electrode active material particles and the conductive material 1 are mixed with the solvent 1 at the same time.

1) When mixing positive electrode active material particles after mixing conductive material 1 with solvent 1 Immediately before mixing with positive electrode active material particles, about 1 cc of the slurry in which conductive material 1 is mixed with solvent 1 is sampled and delayed. Without using a laser diffraction / scattering particle size distribution analyzer (LA-920, manufactured by Horiba Ltd.), the dispersion medium is set to ethanol, the relative refractive index is set to 1.5, the circulation speed is set to level 4, and the ultrasonic irradiation intensity level 7 Obtained by measuring the volume median particle size (D50) of the conductive material 1 in the sampling solution after sonication for 1 minute.

2) When mixing the positive electrode active material particles with the solvent 1 and then mixing the conductive material 1 or when simultaneously mixing the positive electrode active material particles and the conductive material 1 with the solvent 1, the conductive material 1 with ethanol (100 g) About 1 cc of the slurry obtained by mixing (0.5 g) is sampled and measured under the same conditions as in 1) above.

As the conductive material 1, a material having self-aggregation property is used from the viewpoint of securing rheological characteristics described later. When the conductive material 1 has self-aggregation properties, a three-dimensional network structure is formed by an appropriate aggregation form of the positive electrode active material particles and the conductive material 1, and these become a composite to form a positive electrode slurry (slurry 2). It is considered that the appropriate rheological characteristics of the battery can be secured and the internal resistance of the battery can be reduced. Here, “having self-aggregation” means that an ultrasonic homogenizer (Nippon Seiki Co., Ltd.) was added to a slurry obtained by mixing ethanol (100 g) with conductive material 1 (0.5 g) having an average particle size of x ₀ μm. US-300T, manufactured by Seisakusho Co., Ltd., was irradiated with ultrasonic waves at a frequency of 19 kHz and an output of 300 W, and conductive material 1 after it seconds (i is a natural number) every t (= 60) seconds from the start of ultrasonic irradiation. When the average particle size x _{i of the above} is measured, it _{means that n} satisfying x _n−1 <x _n <x ₀ and n ≧ 2 exists. From the viewpoint of more easily forming a three-dimensional network structure, the ratio of _xn to _xn-1 ( _xn / _xn-1 ) is preferably 1.1 to 4, more preferably 1.1 to 3. More preferably, it is 1.1-2.

As for the above “average particle size x _i after it seconds”, the slurry (about 1 cc) is sampled immediately after the ultrasonic irradiation is stopped after it seconds, and the laser diffraction / scattering particle size distribution measuring apparatus without delay. (Horiba Seisakusho, LA-920) Sampling after ultrasonic dispersion for 1 minute at ultrasonic irradiation intensity level 7 with ethanol as dispersion medium, relative refractive index 1.5, circulation rate set to level 4 It is obtained by measuring the volume median particle size (D50) of the conductive substance 1 in the liquid. The “average particle size x ₀ ” is obtained by sampling the slurry (about 1 cc) before ultrasonic irradiation and measuring under the same conditions as the “average particle size x _i after it seconds”. .

  Since the conductive material 1 having self-aggregating property described above usually has a high structure structure, it is difficult to uniformly disperse even if it is mixed with normal positive electrode active material particles in a solvent. Uniform dispersion is possible with the porous positive electrode active material particles described above. Although the reason is not certain, it is considered that the porous positive electrode active material particles described above have a function of solving the initial aggregation state of the conductive material 1 to an appropriate state.

  The conductive substance 1 is not particularly limited as long as it has the specific physical properties described above, and examples thereof include self-aggregating carbon black and self-aggregating fibrous carbon.

  The above carbon black can be produced by any decomposition method such as thermal black method, acetylene black method, channel black method, gas furnace black method, oil furnace black method, pine smoke method, and lamp black method. Although manufactured ones can also be used, furnace black, acetylene black, and ketjen black (registered trademark) are preferably used from the viewpoint of self-aggregation, and ketjen black is more preferable. These may be used alone or in combination of two or more.

Examples of the fibrous carbon include carbon fibers made from a polymer typified by polyacrylonitrile (PAN), pitch-based carbon fibers made from pitch, carbon nanotubes (one surface of graphite, that is, a graphene sheet wrapped around a tube) Vapor growth type carbon fiber (for example, VGCF: registered trademark) using a hydrocarbon gas as a raw material (fine particle engineering large volume I volume P651, Fuji Techno System Co., Ltd.), So-called carbon nanotubes in a narrow sense (hereinafter simply referred to as carbon nanotubes in a narrow sense) obtained by an arc discharge method, a laser evaporation method, a chemical vapor deposition method, or the like are preferably used. The carbon nanotube is, for example, an arc discharge method in which a graphite electrode is evaporated by arc discharge under an atmospheric gas such as He, Ar, CH ₄ , or H ₂ , and graphite containing a metal catalyst such as Ni, Co, Y, or Fe. An arc discharge method in which electrodes are evaporated by arc discharge, a YAG laser is applied to graphite mixed with a metal catalyst such as Ni-Co, Pd-Rd, and the laser is sent to an electric furnace heated to about 1200 ° C. with an Ar air stream. It can be obtained by an evaporation method, a HiPCO method in which pentacarbonyl iron (Fe (CO) ₅ ) is used as a catalyst, and carbon monoxide is thermally decomposed at high pressure.

DBP oil absorption of the conductive material 1, in order to ensure the self-cohesiveness, preferably 300 cm ^3/100 g or more, more preferably 350 cm ^3/100 g or more, more preferably 400 cm ^3/100 g or more, even more preferably it is 450cm ³ / 100g or more. Further, in order to obtain a slurry 2 having a specific rheological properties described below are, DBP oil absorption amount is preferably from 600 cm ^{3/100 g,} more preferably 575cm 3 / 100g or ^less, more preferably less 550 cm 3/100 g. In view of the overall aspects of the foregoing, DBP oil absorption amount of the conductive material 1 is preferably 300~600cm ³ / 100g, more preferably 350~575cm ³ / 100g, more preferably 400 to 550, is 450 to 550 Even more preferred.

  When preparing the slurry 1 in step 1 of the present invention, the content of the conductive material 1 in the slurry 1 is positive from the viewpoint of reducing the diffusion resistance of active material ions and ensuring good coating properties. It is prepared so as to be 3 to 20 parts by weight with respect to 100 parts by weight of the active material particles. From the same viewpoint, the content of the conductive material 1 with respect to 100 parts by weight of the positive electrode active material particles is preferably 5 to 10 parts by weight, and more preferably 6 to 8 parts by weight.

  In the present invention, after the step 1 and before the step 2, the conductive material 1 in the slurry 1 is aggregated together with the positive electrode active material particles, and aggregated particles containing the positive electrode active material particles and the conductive material 1 are obtained. You may further have the aggregation process to obtain. By aggregating the conductive material 1 and the positive electrode active material particles, it is considered that the positive electrode active material particles can be incorporated into the three-dimensional network structure of the conductive material 1 in an appropriate state. This is because the diffusion path can be easily secured. As a method for obtaining the aggregated particles, the positive electrode active material particles and the conductive material 1 are left dispersed in a solvent, and the aggregated particles are obtained by the self-aggregation property of the conductive material 1. A method of obtaining the agglomerated particles by aggregating the conductive material 1 together with the positive electrode active material particles while removing is exemplified. The latter method is preferred in order to easily obtain aggregated particles.

  When obtaining aggregated particles while removing the solvent 1, it is preferable to use a solvent having a boiling point of 100 ° C. or lower as the solvent 1. This is because the solvent 1 can be easily removed by distilling off the solvent 1. Examples of the solvent having a boiling point of 100 ° C. or lower include methyl ethyl ketone (boiling point 79.5 ° C.), tetrahydrofuran (boiling point 66 ° C.), acetone (boiling point 56.3 ° C.), ethanol (boiling point 78.3 ° C.), ethyl acetate (boiling point 76 .8 ° C.) is preferably used. As a method for removing the solvent 1, a method other than distillation may be used. For example, the solvent 1 may be removed by spray drying the slurry 1.

  In the step 1, it is preferable to irradiate the slurry 1 with ultrasonic waves so that the average particle size of the conductive material 1 in the slurry 1 is 10 μm or less. It is considered that the conductive material 1 and the positive electrode active material particles can be uniformly aggregated by utilizing the self-aggregation property of the conductive material 1 after the ultrasonic irradiation, thereby facilitating the diffusion path of the active material ions. This is because it is considered that it can be secured. From the same viewpoint as described above, it is more preferable to irradiate the ultrasonic wave so that the average particle diameter of the conductive material 1 is 7 μm or less, and it is even more preferable to irradiate the ultrasonic wave so as to be 5 μm or less. The average particle size of the conductive material 1 in the slurry 1 is obtained by sampling about 1 cc of the slurry 1 immediately after the ultrasonic irradiation is stopped, and a laser diffraction / scattering type particle size distribution measuring apparatus (manufactured by Horiba, Ltd.) without delay. LA-920), the dispersion medium is ethanol, the relative refractive index is set to 1.5, the circulation speed is set to level 4, and the ultrasonic conductivity of the sample solution after ultrasonic treatment at ultrasonic irradiation intensity level 7 for 1 minute. It is obtained by measuring the volume median particle size (D50) of substance 1.

  When irradiating the slurry 1 with ultrasonic waves, the solvent 1 to be used is preferably a solvent having a low viscosity to such an extent that ultrasonic irradiation has the above effects. Examples of the solvent include ethanol, methyl ethyl ketone, and ethyl acetate. Of these, ethanol is preferable. The ultrasonic irradiation conditions are not particularly limited as long as the above effects are achieved. For example, ultrasonic irradiation may be performed under conditions of a frequency of 15 to 25 kHz and an output of 100 to 500 W.

  The content of the solvent 1 in the slurry 1 is preferably 2000 to 20000 parts by weight and more preferably 1000 to 10,000 parts by weight with respect to 100 parts by weight of the positive electrode active material particles, from the viewpoint of effectively exhibiting the above-described effect of ultrasonic irradiation. preferable.

  In the present invention, as described above, the solvent 1 may be removed from the slurry 1, the positive electrode active material particles and the conductive material 1 may be taken out, and the binder and the solvent 2 may be added and kneaded as step 2. After the slurry 1 is obtained in the step 1, a binder may be added to the slurry 1 as the step 2 and kneaded. In the latter case, the solvent 2 is the same as the solvent 1.

  The binder that can be used in the slurry 2 in the step 2 is not particularly limited as long as the specific rheological characteristics described below are obtained. From the viewpoint of adhesion and solubility in a solvent, for example, polyvinylidene fluoride (PVDF), Polyamideimide, polytetrafluoroethylene, polyethylene, polypropylene, polymethyl methacrylate, polyacrylic acid, polyurethane, polyester, epoxy resin, styrene-butadiene rubber, and modified products thereof are preferable, more preferably PVDF, polyacrylic acid , And modified products thereof. Examples of the modified product include those in which a substituent such as a carboxyl group or an amino group is introduced into the above listed polymers. Moreover, these polymeric materials may be used independently and 2 or more types may be mixed and used.

  The content of the binder in the slurry 2 is easily obtained from the viewpoint of improving the balance between the binding performance of the positive electrode active material particles, the conductive material 1 and the like and the conductivity as the positive electrode, and the specific rheological characteristics described later. In view of the above, 2 to 15 parts by weight is preferable with respect to 100 parts by weight of the positive electrode active material particles, and 3 to 10 parts by weight is more preferable.

  The solvent 2 that can be used in the slurry 2 in the step 2 is not particularly limited as long as the specific rheological characteristics described below are obtained. For example, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide , Methyl ethyl ketone, tetrahydrofuran, acetone, ethanol, ethyl acetate, water, diethyl carbonate (DEC), dimethyl carbonate (DMC) and the like are preferably used.

  The content of the solvent 2 in the slurry 2 is preferably 250 to 700 parts by weight, more preferably 300 to 600 parts by weight with respect to 100 parts by weight of the positive electrode active material particles, from the viewpoint of easily obtaining the specific rheological characteristics described below. preferable.

  In the present invention, as long as the above-described effects of the present invention can be obtained, conventionally known additives used for forming the positive electrode can be added to the slurry 2 as other components.

In step 2 of the present invention, in the rheological properties of slurry 2 measured with a rheology measuring device, the shear stress (measurement method will be described later) with respect to the shear rate in the range of the shear rate of 0.001 to 0.1 s ⁻¹ is 1000 to 40000 mPa. The kneading is performed so that the shear stress gradient Δ (calculation method will be described later) in the shear rate range is −0.30 to 0.30. When the positive electrode is formed by applying the slurry 2 having the rheological characteristics on the current collector, the positive electrode active material particles are uniformly arranged in the three-dimensional network structure of the conductive material 1 having an appropriate aggregation form. Conceivable. As a result, the movement of active material ions is facilitated by the porous structure of the porous positive electrode active material particles and the three-dimensional network structure of the conductive material 1 having a self-aggregating property, which is appropriately aggregated. It is considered that a positive electrode composition capable of greatly reducing the diffusion resistance of substance ions can be obtained.

A method for measuring the shear stress and a method for calculating the gradient Δ will be described. First, using a rheology measurement device (manufactured by Physica, MCR300), the shear stress at the return of the second cycle (when decelerating from high-speed shear) in the range of the shear rate of 0.001 to 1000 s ⁻¹ is measured. At this time, the measurement points at the shear rate of 0.001 to 0.1 s ⁻¹ are set to 7 points (6 intervals) so as to be equidistant from the common logarithm of the shear rate. The average value of the shear stress at the seven measurement points is referred to as “the shear stress with respect to the shear rate in the range of the shear rate of 0.001 to 0.1 s ⁻¹ ”. Then, common logarithm values are calculated for the shear rate and shear stress at each measurement point. Next, the common logarithmic values are arranged in descending order of shear rate. The common logarithm of the n-th shear rate r _n (s ⁻¹ ) from the higher shear rate is log (r _n ), and the common logarithm of the shear stress s _n (mPa) at this time is log (s _{As n} ), the value obtained by the following equation between each measurement is defined as “gradient Δ”. In the present invention, kneading is performed so that the gradient Δ between all the measurements (six intervals) is −0.30 to 0.30.
Gradient Δ = (log (s _n ) -log (s _{n + 1} )) / (log (r _n ) -log (r _{n + 1} ))

  From the viewpoint of reducing the diffusion resistance of active material ions and from the viewpoint of coating properties of the slurry 2, the shear stress is preferably 5000 to 35000 mPa, and more preferably 5000 to 30000 mPa.

  Further, from the viewpoint of reducing the diffusion resistance of the active material ions, the gradient Δ is preferably −0.25 to 0.25, and more preferably −0.20 to 0.20.

  The method for kneading the slurry 2 in step 2 is not particularly limited as long as it can be kneaded so as to have the above rheological characteristics, and examples thereof include a kneading method using a kneading means such as a rotation / revolution mixer or a kneader. For example, when a kneader having a rotation mechanism is used, kneading may be performed by adjusting the rotation conditions and the rotation time so as to have the above rheological characteristics.

  When kneading the slurry 2 in step 2, it is preferable to knead at an atmospheric temperature of 20 to 25 ° C., but in order to cool the kneader or adjust the kneading efficiency of the slurry in order to adjust the amount of heat generated during kneading. The kneader may be heated.

  In step 2 of the present invention, the conductive material 2 having no self-aggregation property may be further mixed with the slurry 2. Since the conductive material 2 having no self-aggregating property can be relatively easily dispersed in the solvent 2, it is interposed between the positive electrode active material particles and the self-aggregating conductive material 1, It is considered that the conductivity can be further improved.

DBP oil absorption of the conductive material 2 is preferably 50~250cm ³ / 100g, more preferably 100~250cm ³ / 100g, further preferably 150~230cm ³ / 100g. This is because the conductive material 2 having the DBP oil absorption amount within the above range can be more easily dispersed in the solvent 2 because the structure is not so developed.

  When the conductive material 2 having no self-aggregation property is mixed in the slurry 2, the weight ratio of the conductive material 1 to the conductive material 2 (conductive material 1 / conductive material 2) is 25/75 to 95. / 5 is preferable, 30/70 to 70/30 is more preferable, and 40/60 to 60/40 is still more preferable. This is because if the weight ratio is within the above range, the diffusion path of the active material ions can be easily secured and the conductivity can be further improved.

Examples of the conductive material 2, DBP oil absorption amount and carbon black 50~250cm ³ / 100g can be exemplified. Among these, acetylene black is preferable from the viewpoint of improving conductivity.

  The average particle diameter of the conductive material 2 is preferably 0.01 to 1 μm, more preferably 0.03 to 1 μm, and still more preferably 0.05 to 1 μm from the viewpoint of improving conductivity and dispersibility.

  About the average particle diameter of the conductive material 2, about 1 cc of the slurry obtained by mixing the conductive material 2 (0.5 g) with ethanol (100 g) is sampled, and the laser diffraction / scattering type particle size distribution measuring device (with no delay) Sampling solution after ultrasonic treatment for 1 minute at ultrasonic irradiation intensity level 7 with a dispersion medium of ethanol, LA-920) manufactured by HORIBA, Ltd. It is obtained by measuring the volume median particle size (D50) of the conductive material 2 therein.

  The slurry 2 is used to form a positive electrode composition for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. According to the slurry 2, it is possible to produce a positive electrode by applying and drying this to a metal foil as a current collector, and further laminating this together with a negative electrode and a separator, and injecting an electrolyte solution, A nonaqueous electrolyte secondary battery can be produced. That is, the slurry for positive electrode of the nonaqueous electrolyte secondary battery of the present invention is the slurry 2 described above. Moreover, the positive electrode of the nonaqueous electrolyte secondary battery of the present invention is a positive electrode comprising the dried product of the slurry 2, and the nonaqueous electrolyte secondary battery of the present invention is a nonaqueous solution comprising the positive electrode of the present invention. It is an electrolyte secondary battery. In addition, the nonaqueous electrolyte secondary battery which is the subject of the present invention may be a battery including a positive electrode produced using the above-described positive electrode slurry of the present invention, and other constituent requirements are not limited at all. It shouldn't be.

  The use of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but for example, it can be used for electronic devices such as notebook computers, electronic book players, DVD players, portable audio players, video movies, portable TVs, mobile phones, It can be used in consumer equipment such as cordless vacuum cleaners, cordless electric tools, batteries for electric vehicles, hybrid cars, etc., and auxiliary power sources for fuel cell vehicles. Among these, it is suitably used as a battery for automobiles that require particularly high output.

  Examples and the like specifically showing the present invention will be described below. In addition, it shows below about the measuring method of an evaluation item, etc.

(Average agglomerated particle diameter of positive electrode active material raw material particles)
Using a laser diffraction / scattering particle size distribution measuring apparatus (LA-920, manufactured by Horiba, Ltd.), water is used as a dispersion medium, and a slurry of 15 g of positive electrode active material raw material particles / 85 g of water is ultrasonically applied at an ultrasonic irradiation intensity level of 1. The value of the volume median particle size (D50) when the particle size distribution after 1 minute irradiation was measured at a relative refractive index of 1.7 was taken as the average aggregated particle size.

(Average primary particle size of positive electrode active material raw material particles)
Using the field emission scanning electron microscope S-4000 (manufactured by Hitachi, Ltd.), among the aggregated particles obtained by aggregating the primary particles, select the aggregated particles having an average aggregated particle size ± (average aggregated particle size × 0.2), and Aggregated particles were observed with the above microscope, and SEM images were taken at a magnification such that 50 to 100 two-dimensional SEM images of primary particles (hereinafter referred to as primary particle images) were included in the microscope field of view. Then, 50 primary particle images were extracted from the photographed primary particle images, their ferret diameters were measured, and the average value of the ferret diameters for the 50 particles was taken as the average primary particle diameter. Note that the ferret diameter of one of the 50 extracted primary particle images is a straight line group parallel to an arbitrary straight line L that passes through (including touches) the one primary particle image. The distance between two parallel lines that are the farthest away. However, the distance between the two parallel lines refers to the length of a line segment that is cut by the two parallel lines from a straight line perpendicular to the two parallel lines.

(BET specific surface area)
The BET specific surface area was measured using a specific surface area measuring apparatus (Shimadzu Corporation, Flowsorb III2305).

(Pore distribution)
Using a mercury porosimeter (manufactured by Shimadzu Corporation, Pore Sizer 9320), the pore distribution in the range of pore diameters of 0.008 μm to 200 μm was measured. Moreover, about the total pore volume, the pore volume of the range of 0.008 micrometers-8 micrometers of pore diameters was measured using the said mercury porosimeter, and the integrated value was made into the total pore volume of the sample.

(Average particle diameter of positive electrode active material particles)
Using a laser diffraction / scattering particle size distribution analyzer (LA-920, manufactured by Horiba, Ltd.), with a dispersion medium of ethanol and 15 g of positive electrode active material particles / 85 g of ethanol, circulation rate setting 4, ultrasonic irradiation intensity level 7, the value of the volume median particle size (D50) when the particle size distribution after irradiation with ultrasonic waves for 5 minutes was measured at a relative refractive index of 1.7 was taken as the average particle size.

(DBP oil absorption)
DBP oil absorption was measured based on JISK6217-4.

(Preparation of positive electrode)
On the aluminum foil (thickness 20 μm) used as a current collector, the coating slurry obtained in each of Examples and Comparative Examples described later was uniformly applied by a coater, and this was applied at 140 ° C. for 10 minutes. Dried over. After drying, it was formed into a uniform film thickness with a press machine, and then cut into a predetermined size (20 mm × 15 mm) to obtain a test positive electrode. The electrode weight of the test positive electrode was 0.0435 g, and the thickness of the electrode layer including the current collector was 57 μm.

(Preparation of negative electrode)
10 parts by weight of polyvinylidene fluoride (manufactured by Kureha Chemical Industry Co., Ltd., # 9210) is added as a binder to 90 parts by weight of hard carbon (manufactured by Kureha Chemical Industry Co., Ltd., Carbotron P powder), and N-methyl-2-pyrrolidone is added thereto. Was added to one side of a rolled copper foil having a thickness of 10 μm and dried at 140 ° C. over 10 minutes. After drying, it was formed into a uniform film thickness with a press machine, and then cut into a predetermined size (20 mm × 15 mm) to obtain a test negative electrode.

(Production of test cell)
A test cell was prepared using the positive electrode and the negative electrode described above, a separator (Celguard # 2400, manufactured by Celgard) and an electrolytic solution. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC: DEC = 1: 1 vol%) was used. After the test cell was assembled, it was left at 25 ° C. for 24 hours, and the following internal resistance evaluation was performed.

(Internal resistance evaluation)
About each said test cell, after charging to 4.2V in CVCC (Constant Voltage Constant Current power supply, constant potential constant current) mode with the constant current of 0.2C, constant potential charge is performed at 4.2V for 1 hour, 0 .2C was discharged to 2V and each test cell was adjusted to a charge state of about 60% of full charge. Thereafter, the battery was charged again to 4.0 V at a constant current of 0.2 C in the CVCC mode, and then discharged for 30 seconds at a constant current of 5 C. During the discharge, the potential drop value 0.2 seconds after the start of discharge and the potential drop value 30 seconds after were measured. Then, the potential drop value after 0.2 seconds is divided by the discharge current value to obtain the initial resistance value of the internal resistance of the test cell, and the potential drop value after 30 seconds is further divided by the discharge current value to obtain the test cell. The total resistance value of the internal resistance. A value obtained by subtracting the initial resistance value from the total resistance value was defined as the differential resistance value. In addition, it is thought that the diffusion resistance of the lithium ion in a positive electrode is so low that the total resistance value of internal resistance and a differential resistance value are low.

Example 1
(Preparation of positive electrode active material particles)
As positive electrode active material raw material particles, 100 g of lithium manganate having an average primary particle diameter of 1.2 μm and an average aggregate particle diameter of 3 μm was used, and t-butyl methacrylate particles having an average particle diameter of 6 μm (trade name: MR-7G, manufactured by Soken Chemical Co., Ltd.) 8 g was mixed with 666 g of ion-exchanged water to obtain a lithium manganate slurry (solid concentration: 13% by weight). Using this slurry, spray drying was performed with a spray dryer (manufactured by EYELA, SPRAY DRYER SD-1000) under conditions of a hot air supply temperature of about 125 ° C. and a dryer outlet temperature of about 75 ° C. Next, the obtained powder was heated to 800 ° C. at a temperature rising rate of 400 ° C./hr and baked at 800 ° C. for 30 hours to obtain positive electrode active material particles. Table 1 shows the characteristics of the obtained positive electrode active material particles. The method for measuring the average particle size of the t-butyl methacrylate particles used as the pore-forming resin particles is as follows.

(Measurement method of average particle size of t-butyl methacrylate particles)
Using a laser diffraction / scattering particle size distribution measuring device (LA-920, manufactured by HORIBA, Ltd.), with a dispersion medium of ethanol and a slurry of 15 g of t-butyl methacrylate particles / 85 g of ethanol, circulation rate setting 4, ultrasonic irradiation intensity The value of volume median particle size (D50) when the particle size distribution after irradiation with ultrasonic waves at level 7 was measured at a relative refractive index of 1.7 was taken as the average particle size.

(Preparation of slurry for coating)
Ethanol 500 parts by weight, Ketjen black DBP oil absorption 495cm ³ / 100g is a conductive material 1 7 parts by weight was added, an ultrasonic homogenizer (Nippon Seiki Seisakusho Co., Ltd., US-300T) with frequency 19kHz Then, ultrasonic irradiation was performed at an output of 300 W for 6 minutes to obtain a dispersion of ketjen black having an average particle size of 5 μm. To this dispersion, 100 parts by weight of the positive electrode active material particles described above were added to prepare slurry 1, and this slurry 1 was irradiated with ultrasonic waves for 2 minutes at a frequency of 19 kHz and an output of 300 W using the above ultrasonic homogenizer. Thereafter, ethanol was distilled off to obtain aggregated particles containing positive electrode active material particles and ketjen black. This and aggregated particles 107 parts by weight, DBP oil absorption of a conductive material 2 180cm ^3/100 g carbon black (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, HS-100) and 5.5 parts by weight, 5 wt% N polyvinylidene fluoride -Slurry (100 g) in which 250 parts by weight of a methyl-2-pyrrolidone solution (Kureha Chemical Industries, # 7305) and 137.5 parts by weight of N-methyl-2-pyrrolidone were mixed with rotation / revolution propeller. Kneading was performed using a system mixer (manufactured by THINKY, Awatori Nertaro ARE-250) to obtain slurry 2 (coating slurry). In the kneading process, the slurry was placed in a dedicated container (capacity 300 ml) of the mixer, and the conditions were an ambient temperature of 23 ° C., a rotation speed of 800 rpm, a revolution speed of 2000 rpm, and a kneading time of 0.5 hours.

(Example 2)
The same kind of positive electrode active material particles (100 parts by weight) as Example 1 and the same kind of conductive material 1 (7 parts by weight) as Example 1 were added to 137.5 parts by weight of N-methyl-2-pyrrolidone. A slurry was prepared. Next, a conductive material 2 of the same type as in Example 1 (5.5 parts by weight) and a 5% by weight N-methyl-2-pyrrolidone solution of polyvinylidene fluoride (# 7305, manufactured by Kureha Chemical Industry Co., Ltd.) 250 in the slurry. Weight parts were mixed, and the resulting slurry (100 g) was kneaded under the same conditions as in Example 1 to obtain a coating slurry.

(Example 3)
Adding conductive material 1 to N-methyl-2-pyrrolidone, irradiating the conductive material 1 with ultrasonic waves so that the average particle size of the conductive material 1 is 24 μm, and then mixing with the positive electrode active material particles; kneading time; A slurry for coating was obtained in the same manner as in Example 2 except that was set to 1.0 hour.

Example 4
A slurry for coating was obtained in the same manner as in Example 1 except that the positive electrode active material particles were prepared by the method shown below.

(Preparation of positive electrode active material particles used in Example 4)
As positive electrode active material raw material particles, 100 g of lithium manganate having an average primary particle size of 1.2 μm and an average aggregated particle size of 3 μm was used, mixed with 666 g of ion-exchanged water, and a lithium manganate slurry (solid content concentration 13 weight) %). Using this slurry, spray drying was performed with a spray dryer (manufactured by EYELA, SPRAY DRYER SD-1000) under conditions of a hot air supply temperature of about 125 ° C. and a dryer outlet temperature of about 75 ° C. Next, the obtained powder was heated to 800 ° C. at a temperature rising rate of 200 ° C./hr and baked at 800 ° C. for 30 hours to obtain positive electrode active material particles.

(Example 5)
A slurry for coating was obtained in the same manner as in Example 1 except that the positive electrode active material particles were prepared by the method shown below.

(Preparation of positive electrode active material particles used in Example 5)
As positive electrode active material raw material particles, 100 g of lithium manganate having an average primary particle diameter of 1.2 μm and an average aggregated particle diameter of 3 μm was used, together with 16 g of crosslinked acrylic particles having an average particle diameter of 1 μm (trade name: MR-7G, manufactured by Soken Chemical). Mixing with 666 g of ion-exchanged water, a lithium manganate slurry (solid content concentration of 12.7% by weight) was obtained. Using this slurry, spray drying was performed with a spray dryer (manufactured by EYELA, SPRAY DRYER SD-1000) under conditions of a hot air supply temperature of about 125 ° C. and a dryer outlet temperature of about 75 ° C. Next, the obtained powder was heated to 800 ° C. at a temperature rising rate of 200 ° C./hr and baked at 800 ° C. for 5 hours to obtain positive electrode active material particles.

(Example 6)
A slurry for coating was obtained in the same manner as in Example 1 except that the ultrasonic irradiation time for obtaining the ketjen black dispersion was 4 minutes.

(Example 7)
A slurry for coating was obtained in the same manner as in Example 1 except that the ultrasonic irradiation time for obtaining the ketjen black dispersion was 8 minutes.

(Example 8)
When obtaining ketjen black dispersion, 5 parts by weight of ketjen black was added, and when obtaining slurry for coating, 7.5 parts by weight of carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., HS-100) was mixed. Except for this, a slurry for coating was obtained in the same manner as in Example 1.

Example 9
10 parts by weight of ketjen black was added when obtaining a ketjen black dispersion, and 2.5 parts by weight of carbon black (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) was mixed when obtaining a slurry for coating. Except for this, a slurry for coating was obtained in the same manner as in Example 1.

(Example 10)
A coating slurry was obtained in the same manner as in Example 1 except that 470.8 parts by weight of N-methyl-2-pyrrolidone was mixed when obtaining the coating slurry.

(Example 11)
As the conductive material 1, DBP oil absorption of 420 cm ^3/100 g carbon black (Degussa Corp., XE-2B) of except for using, to obtain a coating slurry in the same manner as in Example 1.

Example 12
As the conductive material 2, DBP oil absorption of 69cm ^3/100 g of carbon black (manufactured by Mitsubishi Chemical Corporation, # 25) of except for using, to obtain a coating slurry in the same manner as in Example 1.

(Example 13)
A coating slurry was obtained in the same manner as in Example 8 except that carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., HS-100) was not mixed when obtaining the coating slurry.

(Comparative Example 1)
A coating slurry was obtained in the same manner as in Example 1 except that lithium manganate having an average primary particle size of 1.2 μm and an average aggregated particle size of 3 μm was used as the positive electrode active material particles.

(Comparative Example 2)
As the conductive material 1, DBP oil absorption 180cm ^3/100 g of carbon black (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, HS-100) of except for using, to obtain a coating slurry in the same manner as in Example 1.

(Comparative Example 3)
Except that 25 parts by weight of ketjen black was added as the conductive substance 1, and 19.5 parts by weight of carbon black (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) was mixed as the conductive substance 2. A slurry for coating was obtained in the same manner as in Example 1.

(Comparative Example 4)
Except that 2 parts by weight of ketjen black was added as the conductive material 1 and 10.5 parts by weight of carbon black (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) was mixed as the conductive material 2. A slurry for coating was obtained in the same manner as in Example 1.

(Comparative Example 5)
A coating slurry was obtained in the same manner as in Example 1 except that the kneading time was 10 hours.

(Comparative Example 6)
A coating slurry was obtained in the same manner as in Example 3 except that the kneading time was 10 hours.

  For each of the above examples and comparative examples, details of the constituent materials are shown in Table 1, and slurry preparation conditions and evaluation results are shown in Table 2. Incidentally, the peak pore diameter 2 of Comparative Example 1 was not present in the pore distribution of Comparative Example 1. Further, the rheological properties and internal resistance evaluation of the coating slurry of Comparative Example 3 could not be measured because a fluid coating slurry was not obtained.

  As shown in Table 2, in Examples 1 to 13, good results were obtained for internal resistance evaluation as compared with Comparative Examples 1 to 6. In Comparative Examples 5 and 6, since the kneading time was too long, the gradient Δ was outside the range of ± 0.30, and it is considered that the total resistance value and the differential resistance value were increased.

A to C are pore distribution data used when extracting the peak pore diameter 2 in an example of the positive electrode active material particles that can be used in the present invention.

Claims (16)

Step 1 of mixing the positive electrode active material particles and the conductive material 1 in the solvent 1 to obtain the slurry 1 containing the positive electrode active material particles, the conductive material 1 and the solvent 1, and after this step 1, the positive electrode A non-aqueous step of kneading active material particles, the conductive material 1, a binder, and a solvent 2 to obtain a slurry 2 containing the positive electrode active material particles, the conductive material 1, the binder, and the solvent 2. A method for producing a positive electrode composition for an electrolyte secondary battery, comprising:
The positive electrode active material particles have a BET specific surface area of 1 to 6 m ² / g, a total pore volume measured with a mercury porosimeter of 0.1 to 1 cc / g, and a pore distribution measured with a mercury porosimeter. The peak fine diameter 1 that gives the maximum differential pore volume value is in the range of 0.01 to 8 μm, and the peak fine diameter gives a differential pore volume value that is 5% or more of the maximum differential pore volume value. The pore diameter 2 is present in the range of the pore diameter of 0.01 μm or more and less than the peak pore diameter of 1, and the average particle diameter by laser diffraction / scattering particle size distribution measurement is from the peak pore diameter of 1 to 20 μm,
The conductive material 1 has an average particle size of 1 to 50 μm when mixed with the positive electrode active material particles, has self-aggregation, and the content in the slurry 1 is 100 parts by weight of the positive electrode active material particles. 3 to 20 parts by weight with respect to
In the rheological properties of the slurry 2 measured by the rheology measuring device, the shear stress with respect to the shear rate in the range of the shear rate of 0.001 to 0.1 s ⁻¹ is 1000 to 40000 mPa, and the shear stress gradient Δ in the shear rate range is -The manufacturing method of the composition for positive electrodes of the nonaqueous electrolyte secondary battery which kneads the said process 2 so that it may become -0.30-0.30.   After the step 1 and before the step 2, the conductive material 1 in the slurry 1 is aggregated together with the positive electrode active material particles to contain the positive electrode active material particles and the conductive material 1 The method for producing a positive electrode composition according to claim 1, further comprising an aggregation step for obtaining aggregated particles.   The manufacturing method of the composition for positive electrodes of Claim 2 which aggregates the said electroconductive substance 1 with the said positive electrode active material particle while removing the said solvent 1 in the said aggregation process.   The method for producing a positive electrode composition according to claim 3, wherein a solvent having a boiling point of 100 ° C. or lower is used as the solvent 1.   5. The ultrasonic wave is applied to the slurry 1 so that the average particle diameter of the conductive material 1 in the slurry 1 is 10 μm or less in the step 1. The manufacturing method of the composition for positive electrodes of this. Manufacturing method of the DBP oil absorption of the conductive material 1, a positive electrode composition according to claim 1 which is 300~600cm ³ / 100g.   In the said process 2, the manufacturing method of the composition for positive electrodes of any one of Claims 1-6 which further mixes the electroconductive substance 2 which does not have self-aggregation property with the said slurry. Manufacturing method of the DBP oil absorption of the conductive material 2 is, positive electrode composition according to claim 7 is 50~250cm ³ / 100g.   9. The composition for a positive electrode according to claim 7, wherein a weight ratio of the conductive material 1 to the conductive material 2 (conductive material 1 / conductive material 2) is 25/75 to 95/5. Production method. A slurry for a positive electrode of a nonaqueous electrolyte secondary battery containing positive electrode active material particles, conductive material 1, a binder and a solvent,
The positive electrode active material particles have a BET specific surface area of 1 to 6 m ² / g, a total pore volume measured with a mercury porosimeter of 0.1 to 1 cc / g, and a pore distribution measured with a mercury porosimeter. The peak fine diameter 1 that gives the maximum differential pore volume value is in the range of 0.01 to 8 μm, and the peak fine diameter gives a differential pore volume value that is 5% or more of the maximum differential pore volume value. The pore diameter 2 is present in the range of the pore diameter of 0.01 μm or more and less than the peak pore diameter of 1, and the average particle diameter by laser diffraction / scattering particle size distribution measurement is from the peak pore diameter of 1 to 20 μm,
The conductive material 1 has an average particle size of 1 to 50 μm when mixed with the positive electrode active material particles, has a self-aggregation property, and the content in the positive electrode slurry is 100 weights of the positive electrode active material particles. 3 to 20 parts by weight with respect to parts,
In the rheological properties of the positive electrode slurry measured with a rheology measuring apparatus, the shear stress with respect to the shear rate in the range of the shear rate of 0.001 to 0.1 s ⁻¹ is 1000 to 40000 mPa and the shear stress gradient Δ in the shear rate range. Is a slurry for positive electrode of a non-aqueous electrolyte secondary battery, which is −0.30 to 0.30. The DBP oil absorption of the conductive material 1, a positive electrode slurry according to claim 10 which is 300~600cm ³ / 100g.   The slurry for positive electrodes of Claim 10 or 11 which further contains the electroconductive substance 2 which does not have self-aggregation property. The DBP oil absorption of the conductive material 2 is, positive electrode slurry according to claim 12 which is 50~250cm ³ / 100g.   The slurry for positive electrodes according to claim 12 or 13, wherein a weight ratio (conductive material 1 / conductive material 2) between the conductive material 1 and the conductive material 2 is 25/75 to 95/5.   The positive electrode of the nonaqueous electrolyte secondary battery formed by containing the dry body of the slurry for positive electrodes of any one of Claims 10-14.   A nonaqueous electrolyte secondary battery comprising the positive electrode according to claim 15.

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