JP7238253B2 - Positive electrode mixture paste for non-aqueous electrolyte secondary battery and manufacturing method thereof, positive electrode for non-aqueous electrolyte secondary battery and manufacturing method thereof, and non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a positive electrode mixture paste for non-aqueous electrolyte secondary batteries and a method for producing the same, a positive electrode for non-aqueous electrolyte secondary batteries and a method for producing the same, and a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are lightweight and have high energy density, and are currently widely used as compact secondary batteries for mobile phones, laptop computers, and other IT equipment. Demand for small secondary batteries is expanding on a global scale along with the development and spread of IT equipment. Furthermore, in addition to small secondary batteries, the demand for non-aqueous electrolyte secondary batteries is expected to expand in many fields as large industrial secondary batteries for hybrid electric vehicles (HEV), electric vehicles, and power storage. It is

A compound capable of intercalating and deintercalating lithium ions is used as a positive electrode active material for lithium ion secondary batteries. Examples of such compounds include lithium-transition metal composite oxides composed of layered rock salt compounds such as LiCoO ₂ , Li(Co, Ni, Mn)O ₂ and Li(Ni, Co, Al) O ₂ . A lithium-transition metal composite oxide can be produced, for example, by the following method.

First, an aqueous solution of manganese salt, nickel salt, or the like is reacted with an alkaline solution to coprecipitate a transition metal hydroxide. This transition metal hydroxide is dried and recovered after solid-liquid separation. The resulting transition metal hydroxide serves as a precursor material for the positive electrode active material. The particle size and particle shape of the positive electrode active material are factors directly related to the performance of the lithium ion secondary battery after incorporating the positive electrode active material, and the particle shape of the precursor material is determined by the particle size distribution and particle size of the positive electrode active material. It greatly affects the shape. Therefore, the particle size and particle shape of the positive electrode active material can be controlled by controlling the particle size distribution and particle shape of the transition metal hydroxide that is the precursor material. Moreover, in order to obtain a positive electrode active material having properties more suited to the purpose, a transition metal oxide obtained by heat-treating a transition metal hydroxide can also be used as a precursor substance. Next, a lithium compound such as lithium hydroxide or lithium carbonate is added to and mixed with the resulting precursor material, and the mixture is fired to produce a lithium transition metal composite oxide.

A positive electrode active material such as a lithium-transition metal composite oxide is combined with other materials to form the positive electrode of a non-aqueous electrolyte secondary battery. The positive electrode is manufactured, for example, by mixing a positive electrode active material, a conductive aid, a binder, and a solvent to obtain a positive electrode mixture paste, coating the paste on a current collector, and drying it. In the manufacture of the positive electrode, the process of obtaining the positive electrode mixture paste is particularly susceptible to the particle size and shape of the positive electrode active material. , is required to be dispersed. Generally, the positive electrode material mixture paste is produced in one mixing step of simultaneously adding and mixing the above positive electrode materials.

A carbon material such as carbon black, for example, is used as the conductive aid, which is one of the positive electrode materials. However, since the positive electrode active material, which is a highly hydrophilic inorganic substance, and the highly hydrophobic carbon material have significantly different physical properties on the surface of the particles, it is difficult to disperse and mix them uniformly in the positive electrode mixture paste as they are. is. If the positive electrode active material and the conductive additive are not uniformly dispersed and mixed, the performance of the carbon material as the conductive additive cannot be maximized, and significant improvement in battery performance cannot be expected. In addition, when the positive electrode active material and the conductive aid are not sufficiently dispersed, partial aggregates of these powders may be formed. Due to the formation of this aggregate, a resistance distribution occurs on the electrode plate, and when used as a secondary battery, current concentrates, and problems such as partial heat generation and accelerated deterioration may occur. . Therefore, various processes including various mixing methods have been proposed so far in order to mix and disperse the positive electrode mixture paste more uniformly.

For example, Patent Document 1 describes a method for manufacturing a paste-type nickel electrode in which a substrate is filled with a paste obtained by kneading an active material composed of nickel hydroxide and cobalt oxide, a thickener, and a solvent. According to Patent Document 1, in order to obtain a sufficient conductive effect, it is preferable that the nickel hydroxide crystal is coated with cobalt oxide in the process of manufacturing the positive electrode. In order to form such a dispersed state, it is necessary to decompose the secondary agglomeration of the cobalt oxide by applying a shearing force to the mixture in the mixing step for producing the positive electrode mixture.

Further, in Patent Document 2 below, a mixed solution is first prepared by dispersing a conductive agent in a solvent, and then an electrode active material and a binder are added to the mixed solution and mixed and dispersed. It is said to manufacture a positive electrode mixture, or to first manufacture a mixed solution in which a conductive agent is dispersed in a solvent, then add an electrode active material and mix and disperse, and then add a binder and mix and disperse. It is proposed to manufacture the positive electrode paste by sequence. According to Patent Document 2, the electrical resistance of the electrode is lowered by improving the dispersibility of the conductive aid in the positive electrode mixture, and a non-aqueous secondary battery with excellent charge and discharge characteristics, especially high output characteristics is manufactured. It is said that it is possible to manufacture a possible electrode mixture.

By the way, as one method of mixing the positive electrode mixture, the solid components such as the binder, the active material, and the conductive aid are put in first, and after mixing to some extent, the solvent is added little by little while being stirred. , is known as a mixing method called hard kneading, in which the whole is formed into a lump, and the lump is stirred for a certain period of time. In hard kneading, by adding a part of the solvent and mixing in a highly viscous state, shear force during mixing can be made stronger.

For example, in Patent Document 3, a powder-liquid filling state of an active material, a conductive agent, and a thickening agent is kneaded in a funicular state, and a kneading step, and an active material, a conductive agent, and a thickening agent. The active material, the conductive agent and the thickening agent are kneaded by the dilution dispersion step of kneading the powder-liquid filling state in a slurry state, and then the binder is added and kneaded. A method of making the agent is described.

In Patent Document 3, first, the funicular state (the filling phase has three phases, a gas phase, a liquid phase, and a powder phase, and the liquid phase and the powder phase are continuous phases, but the filling phase of the liquid The gas phase becomes a continuous phase or a discontinuous phase depending on the amount, so the viscosity is high), it contains moderate moisture and the viscosity is relatively high. The active material and the conductive agent are kneaded in a uniformly dispersed state without remaining dispersed in a short period of time due to the strong shearing action that acts between the particles. It states that you can Next, it is diluted and dispersed with a thickener added in order to make the amount of the thickener added a predetermined amount, and the slurry state (the liquid phase is a continuous phase, but the powder phase is a discontinuous phase and a gas phase has disappeared and the viscosity is low), a positive electrode mixture that is uniformly dispersed and kneaded can be obtained, and a positive electrode mixture that exhibits good battery performance can be obtained.

Further, in Patent Document 4, a positive electrode mixture constituting a positive electrode material for a lithium ion secondary battery is mixed in two steps of hard kneading and dilution dispersion, and the hardness of the positive electrode mixture mass after hard kneading in the previous stage is However, it is said that uniform dispersion of the positive electrode mixture is effective when the temperature of the mass is in the range of 20 to 60° C. and the rubber hardness is 0 to 35 as measured by a rubber hardness tester (JIS6301 or JISK6253 compliant). By measuring the hardness of the lumps in the kneading process, it is possible to detect the degree of mixing of each material and the state of destruction of agglomerates. It is possible to obtain

Furthermore, in Patent Document 5, for the purpose of providing a non-aqueous electrolyte secondary battery having good high-rate discharge characteristics and using a lithium-transition metal composite oxide as a positive electrode active material, a positive electrode mixture paste preparation process is disclosed. describes that the pore volume per active material weight of the positive electrode mixture layer is controlled to 0.085 to 0.125 ml/g by kneading and diluting the conductive agent in advance and then mixing the active material. there is According to Patent Document 5, by first kneading and diluting components other than the positive electrode active material and then adding the positive electrode active material, the conductive aid and the positive electrode active material can be rapidly dispersed in the solvent. It is said that it is possible to reach the target viscosity quickly.

On the other hand, for the purpose of improving the conductivity of the positive electrode mixture layer, it is known to use conductive aids having different average particle diameters as the positive electrode material. For example, Patent Literature 6 and Patent Literature 7 describe a method of manufacturing an electrode using a first conductive agent and a second conductive agent having different average particle diameters.

JP-A-7-114919 JP-A-11-54113 JP-A-2000-348713 JP 2012-59466 A Japanese Patent Application Laid-Open No. 2001-283831 JP 2006-179367 A JP 2016-111013 A

As in Patent Documents 1 to 7 above, various technical improvements have been proposed in order to stably produce a positive electrode mixture in which electrode materials are uniformly dispersed. The characteristics are becoming more and more improved, and it is expected that the maximum capacity required for the secondary battery will be further increased in order to extend the cruising distance. In addition, it is also necessary to further improve the output characteristics of the secondary battery in order to generate large torque.

In addition, in order to improve the output characteristics, it is desirable to maximize the specific surface area of the positive electrode active material involved in the charge/discharge reaction. In order to improve the specific surface area of the positive electrode active material, another particle of the positive electrode active material is stacked inside the internal pores of the positive electrode active material in a nested structure, and the interfacial area of these particles is also used to move lithium ions. Material design that promotes In order to disperse the conductive aid inside the positive electrode active material having such a complicated internal structure, a more advanced positive electrode mixture dispersion technology is required.

In view of the above circumstances, the present invention provides a positive electrode mixture paste that can improve the mixability of a positive electrode active material and a conductive aid, and can improve the battery capacity and output characteristics when used as the positive electrode of a secondary battery. intended to provide Another object of the present invention is to provide a simple and stable method for producing the positive electrode mixture paste, and a method for producing a positive electrode using the same.

In a first aspect of the present invention, the positive electrode active material and the first conductive aid are mixed to obtain a mixture powder, and the mixture powder, the second conductive aid, the binder, and the solvent are mixed. and wherein the first conductive aid and the second conductive aid are the same or different conductive aids. be.

Further, the positive electrode active material and the first conductive aid may be mixed by pulverizing the positive electrode active material in the presence of the first conductive aid. Further, in the above manufacturing method, the method for manufacturing the positive electrode active material includes mixing a transition metal compound and a lithium compound to obtain a lithium mixture, firing the lithium mixture to obtain a lithium transition metal composite oxide, pulverizing the lithium transition metal composite oxide.

Further, in the above manufacturing method, the method for manufacturing the positive electrode active material includes mixing a transition metal compound and a lithium compound to obtain a lithium mixture, firing the lithium mixture to obtain a lithium transition metal composite oxide, The lithium-transition metal composite oxide after firing and not pulverized may be mixed with the first conductive aid.

Moreover, it is preferable that the transition metal compound is a transition metal hydroxide or transition metal oxide, and the lithium compound is lithium hydroxide or lithium carbonate. Also, the average particle size of the first conductive aid is preferably 1/10 or less of the average particle size of the positive electrode active material. Also, the average particle diameter of the first conductive aid is preferably 1 μm or less. Also, the average particle size of the second conductive aid is preferably larger than the average particle size of the first conductive aid. Moreover, the average particle size of the second conductive aid is preferably 0.5 μm or more larger than the average particle size of the first conductive aid.

Also, the first conductive aid may contain a carbon nanomaterial. Also, the carbon nanomaterial preferably contains one or more of carbon nanotubes, carbon nanofibers, and carbon nanohorns. In addition, the carbon nanomaterial preferably has an average minor axis length of 10 nm or less. In addition, the carbon nanomaterial preferably has an average major axis length of 2 μm or less.

In a second aspect of the present invention, the positive electrode mixture paste for a non-aqueous electrolyte secondary battery obtained by using the above production method is applied to a current collector, and the current collector coated with the positive electrode mixture paste and drying the body.

A third aspect of the present invention comprises a positive electrode active material, a first conductive aid, a second conductive aid, a binder, and a solvent, and the second conductive aid has an average particle diameter of A positive electrode material mixture paste for a non-aqueous electrolyte secondary battery is provided, which has a larger average particle size than the conductive aid.

Moreover, it is preferable that the positive electrode material mixture paste for a non-aqueous electrolyte secondary battery has a higher content of the second conductive aid than that of the first conductive aid. Also, the average particle size of the first conductive aid is preferably 1/10 or less of the average particle size of the positive electrode active material. Moreover, it is preferable that the average particle size of the first conductive aid is 1 μm or less. Moreover, it is preferable that the average particle diameter of the second conductive agent is larger than that of the first conductive agent by 0.5 μm or more.

In a fourth aspect of the present invention, a positive electrode active material, a first conductive aid, a second conductive aid, a binder, and a solvent are included, and the first conductive aid has an aspect ratio (average long axis length/average short axis length) is 100 or more, the second conductive additive has a spherical shape, and the average particle size of the second conductive additive is the carbon nanomaterial Provided is a positive electrode mixture paste for a non-aqueous electrolyte secondary battery having an average major axis length greater than 0.9 times.

Also, the carbon nanomaterial preferably contains one or more of carbon nanotubes, carbon nanofibers, and carbon nanohorns. In addition, the carbon nanomaterial preferably has an average minor axis length of 10 nm or less. In addition, the carbon nanomaterial preferably has an average major axis length of 2 μm or less.

A fifth aspect of the present invention provides a positive electrode for a non-aqueous electrolyte secondary battery using the above positive electrode mixture paste.

A sixth aspect of the present invention provides a secondary battery comprising the positive electrode for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte.

According to the positive electrode mixture paste for non-aqueous electrolyte secondary batteries and the method for producing the same of the present invention, the miscibility between the positive electrode active material and the conductive aid is improved, and when used in a secondary battery, the battery capacity and output characteristics A positive electrode for a non-aqueous electrolyte secondary battery, which has a further improved resistance, can be obtained simply and stably. Further, according to the positive electrode for a non-aqueous electrolyte secondary battery of the present invention and the method for producing the same, it is possible to obtain a secondary battery with improved battery capacity and output characteristics.

It is the figure which showed an example of the manufacturing method of the positive mix paste of this embodiment. FIG. 2 is a schematic diagram showing an example of a method for producing a positive electrode material mixture paste according to the present embodiment; It is the figure which showed an example of the manufacturing method of the positive mix paste of this embodiment. It is the figure which showed an example of the manufacturing method of the positive mix paste of this embodiment. It is the figure which showed an example of the manufacturing method of the positive electrode of this embodiment. FIG. 3 is a schematic diagram showing an example of the state around the positive electrode active material in the positive electrode of the present embodiment. 1 is a schematic cross-sectional view of a 2032-type coin battery used for battery evaluation; FIG. It is a figure which showed an example of a Nyquist plot, and the equivalent circuit used for impedance evaluation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in the drawings, in order to make each configuration easy to understand, some parts are emphasized or some parts are simplified, and the actual structure, shape, scale, etc. may differ.

[Method for producing positive electrode mixture paste for non-aqueous electrolyte secondary battery]
A method for producing a positive electrode mixture paste for a non-aqueous electrolyte secondary battery (hereinafter also referred to as "positive electrode mixture paste") of the present embodiment comprises a positive electrode containing a positive electrode active material, a conductive aid, a binder, and a solvent. A method for producing a mixture paste. A secondary battery including a positive electrode manufactured using this positive electrode mixture paste can improve battery capacity and output characteristics.

FIG. 1 is a flow chart showing an example of a method for producing a positive electrode mixture paste according to this embodiment. In the method for producing the positive electrode mixture paste of the present embodiment, the positive electrode active material and the first conductive aid are mixed to obtain a mixture powder (step S10; hereinafter also referred to as "first mixing step"). and mixing the mixture powder, the second conductive agent, the binder, and the solvent (step S20; hereinafter also referred to as “second mixing step”). As shown in FIG. 1, in the manufacturing method of the present embodiment, the conductive aid is mixed in at least two steps to improve the miscibility between the positive electrode active material and the conductive aid, and the positive electrode has a good A conductive network is formed.

FIG. 2(A) is a schematic diagram showing an example of the powder mixture 10 obtained in the first mixing step (step S10). Mixture powder 10 includes positive electrode active material 1 and first conductive aid C1. FIG. 2B is a schematic diagram showing an example of the positive electrode mixture paste 20 obtained in the second mixing step (step S20). The positive electrode mixture paste 20 includes a positive electrode active material 1 , a first conductive agent C<b>1 , a second conductive agent C<b>2 , a binder (not shown), and a solvent 2 . The manufacturing process of the positive electrode mixture paste will be described below with reference to FIGS.

First, the positive electrode active material 1 and the first conductive aid C1 are mixed to obtain the mixture powder 10 (step S10). In the first mixing step (step S10), the positive electrode active material 1 and the first conductive aid C1 can be dry mixed. By dry mixing, the first conductivity aid C1 can be uniformly adhered to the surface of the positive electrode active material 1 . For example, even in a positive electrode active material with a large specific surface area manufactured for the purpose of improving output characteristics, by mixing a part of the conductive auxiliary agent (first conductive auxiliary agent C1) with the positive electrode active material in advance, In addition, a specific conductive aid can be dispersed over the entire surface of the positive electrode active material. As a result, the obtained positive electrode mixture paste 20 can obtain a positive electrode in which a uniform and excellent conductive network is formed with a minimum necessary amount of conductive aid, and the positive electrode active material contained per unit area of the positive electrode can be increased to increase the maximum capacity of the secondary battery.

The positive electrode active material 1 is not particularly limited, and conventionally known lithium metal composite oxides can be used. Examples of lithium metal composite oxides include lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. , lithium iron phosphate compounds, lithium manganese phosphate compounds, lithium cobalt phosphate compounds, lithium vanadium phosphate compounds, and the like. These may be used alone or in combination of two or more. Among these, layered rock salt compounds such as LiCoO ₂ , Li(Co, Ni, Mn)O ₂ and Li(Ni, Co, Al) O ₂ are preferably used as lithium metal composite oxides. Moreover, from the viewpoint of further improving the charge/discharge capacity of the secondary battery, a lithium metal composite oxide containing nickel is preferable.

The average particle diameter D50 of the positive electrode active material 1 is not particularly limited, but can be, for example, 2 μm or more and 50 μm or less, preferably 3 μm or more and 30 μm or less, more preferably 8 μm or more and 15 μm or less. When the average particle size D50 of the positive electrode active material 1 is within the above range, the contact area between the positive electrode active material and the electrolytic solution is ensured to maintain the battery capacity and output characteristics, and the positive electrode fillability is sufficient. can do. The average particle diameter D50 can be obtained as a volume-based median diameter (D50: 50% volume average particle diameter) measured by a laser diffraction scattering method.

The first conductive agent C1 is not particularly limited as long as it is an electron conductive material that is chemically stable in the battery. The first conductive aid C1 is, for example, natural graphite (flaky graphite, etc.), graphite such as artificial graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, carbon black such as thermal black. , conductive fibers such as carbon fibers and metal fibers, metal powders such as aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, organic conductive materials such as polyphenylene derivatives Materials such as carbon fluoride can be used. These may be used alone or in combination of two or more. Among these, carbon blacks such as acetylene black and ketjen black are preferably used from the viewpoint of cost, productivity, and the like.

The shape of the first conductive agent C1 may be spherical, or may be other shapes. Other shapes may be scaly, needle-like, tubular, fibrous, or irregular. In addition, in this specification, a spherical shape includes a substantially spherical shape, and a spherical shape (including a substantially spherical shape) is preferable as the shape of the first conductive agent C1.

The average particle size of the first conductive aid C1 is preferably smaller than the average particle size of the positive electrode active material 1, and more preferably 1/10 or less of the average particle size of the positive electrode active material 1. When the average particle size of the first conductive agent C1 is within the above range, the first conductive agent C1 can be more uniformly dispersed on the surface of the positive electrode active material 1 . The lower limit of the average particle size of the first conductive aid C1 is not particularly limited, but from the viewpoint of cost, ease of handling, etc., it is 1/100 or more, preferably 1/50 or more. . In addition, the average particle size of the first conductive aid C1 may be 1/20 or more of the average particle size D50 of the positive electrode active material 1. In this case, the formation of a good conductive network improves battery characteristics and , cost and ease of handling can be well balanced.

For example, when the shape of the first conductive additive C1 is spherical (including substantially granular), the average particle size of the first conductive additive C1 is a volume-based median measured by a laser diffraction scattering method. It can be determined as a diameter (D50: 50% volume average particle diameter). Further, when the first conductive additive C1 is scaly, needle-like, tubular, fibrous, or the like, the average particle size in the long axis direction (average long axis length) may be used as the average particle size. The average particle size (average major axis length) in this case can be observed using, for example, a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and between any two points on the contour line of the particle. The average value of the maximum length of the distances may be used as the major axis length.

Also, the average particle size of the first conductive agent C1 is preferably 2 μm or less, more preferably 1 μm or less. Although the lower limit of the average particle size D50 of the first conductive agent C1 is not particularly limited, it is preferably 0.1 μm or more, preferably 0.2 μm or more, from the viewpoint of cost, ease of handling, and the like.

Moreover, the first conductive agent C1 may contain a carbon nanomaterial, or may be made of a carbon nanomaterial. Here, the carbon nanomaterial refers to a substance containing a graphene sheet having a six-membered ring of carbon, and may contain elements other than carbon such as boron and nitrogen.

Examples of carbon nanomaterials that can be used include carbon nanotubes (CNT), carbon nanofibers (CNF), carbon nanohorns (CNH), graphene, and fullerene. Among these, the first conductive agent C1 preferably contains one or more of carbon nanotubes, carbon nanofibers, and carbon nanohorns, and may be carbon nanotubes. A carbon nanotube has a structure in which a graphene sheet is closed in a cylindrical shape, and may be single-layered or multi-layered.

When a carbon nanomaterial is used as the first conductive agent C1, the aspect ratio (average major axis length/average minor axis length) is preferably 100 or more, more preferably 200 or more. When the aspect ratio is within the above range, the battery characteristics can be further improved. Although the details of the reason for this are unknown, at least part of the carbon nanomaterial penetrates into the inside of the particles of the positive electrode active material 1, and is considered to be an electronic conduction path from the surface of the positive electrode active material particles to the inside. Therefore, compared with the case where the surface of the positive electrode active material is coated with a conventional conductive aid, the electronic conductivity in the positive electrode of the secondary battery is further increased, and the internal resistance of the secondary battery can be reduced. Moreover, the carbon nanomaterial may be arranged, for example, in a form in which one end thereof is arranged inside the positive electrode active material 1 and the other end protrudes from the surface of the positive electrode active material 1 .

The average long axis length of the carbon nanomaterial refers to the average length of the carbon nanomaterial in the long axis direction, and for carbon nanotubes, for example, it refers to the fiber length. Further, the average minor axis length of a carbon nanomaterial refers to the diameter or major axis of a cross section having the maximum area among cross sections perpendicular to the major axis direction, and for example, refers to the fiber diameter (diameter) in the case of carbon nanotubes.

The average minor axis length of the carbon nanomaterial can be appropriately selected depending on the shape of the positive electrode active material 1 to be used, etc., and is not particularly limited, but is preferably 10 nm or less, more preferably 5 nm or less, and 2 nm. More preferably: When the average minor axis length is within the above range, the electronic conductivity within the positive electrode of the secondary battery can be further improved. Also, the lower limit of the average minor axis length of the carbon nanomaterial is not particularly limited, but is, for example, 0.5 nm or more.

The average major axis length (average particle size) of the carbon nanomaterial can be appropriately selected depending on the shape of the positive electrode active material 1 to be used, etc., and is not particularly limited. It is more preferable to have Also, the lower limit of the average major axis length of the carbon nanomaterial is not particularly limited, but is, for example, 0.5 μm or more.

The content of the first conductive agent C1 is, for example, 0.1 parts by mass or more and 5 parts by mass or less when the total mass of the solid content of the positive electrode mixture in the obtained positive electrode mixture paste is 100 parts by mass. preferably 0.1 parts by mass or more and 3 parts by mass or less, more preferably 0.5 parts by mass or more and 2 parts by mass or less. When the content of the first conductive aid C1 is within the above range, it can be uniformly adhered to the surface of the positive electrode active material 1, voids inside the particles, and the like. Moreover, by using the production method of the present embodiment, it is possible to stably and efficiently form a good conductive path even with a small amount of the conductive aid, so it is excellent in terms of cost. In addition, the solid content of the positive electrode mixture refers to, for example, a component obtained by removing the solvent from the positive electrode mixture paste.

Also, the first conductive aid C1 may contain a small amount of carbon nanomaterial and other conductive aids. Spherical (substantially spherical) carbon blacks, for example, may be used as other conductive aids. The first conductive additive C1 may contain, for example, 0.1% by mass or more and 50% by mass or less of the carbon nanomaterial with respect to the entire first conductive additive C1.

Mixing of the positive electrode active material 1 and the first conductive aid C1 is not particularly limited as long as it is a method in which the positive electrode active material 1 and the first conductive aid C1 are uniformly mixed. can be mixed using a kneading mixer, a blade type mixer, or the like. The mixture should be uniformly mixed to the extent that the skeleton of the positive electrode active material 1 is not destroyed.

Note that when the first conductive aid C1 contains a carbon nanomaterial and other conductive aids, the positive electrode active material 1 and the first conductive aid C1 may all be mixed at the same time, and the positive electrode active material 1 and After mixing with the carbon nanomaterial, the resulting mixture may be mixed with other conductive aids.

Further, the positive electrode active material 1 and the first conductive aid C1 are mixed (step S10) by pulverizing the positive electrode active material 1 in the presence of the first conductive aid C1, as described later. , may be performed (step S11, see FIG. 4). As used herein, pulverization refers to the particle size after pulverization (e.g., average Refers to an operation to reduce the particle size D50). Moreover, the pulverization in the first mixing step is performed so as to adjust the particle size of the positive electrode active material 1 to a desired range.

In the first mixing step, the positive electrode active material 1 is mixed with the first positive electrode active material 1 while suppressing deformation and surface modification of the positive electrode active material 1 by performing such a pulverizing step alone or in combination with mixing other than pulverization. It can be uniformly mixed with the one conductive aid C1, and the battery capacity and output characteristics of the obtained secondary battery are further improved. Mixing other than pulverization refers to an operation of mixing the positive electrode active material 1 and the first conductive aid C1 before and after mixing to such an extent that the particle size of the positive electrode active material 1 does not change.

3 and 4 are flow charts showing another example of the method for manufacturing the positive electrode mixture paste. The method for producing the positive electrode active material 1 (step S1) includes, for example, mixing a transition metal compound and a lithium compound to obtain a lithium mixture (step S2), and baking the lithium mixture (step S3) to obtain a positive electrode. Active material 1 can be manufactured.

The transition metal compound is not particularly limited, but conventionally known compounds can be used. For example, a compound composed of at least one of transition metal hydroxides, oxyhydroxides, oxides, and carbonates can be used. can be done. Transition metal compounds are preferably transition metal hydroxides, transition metal oxides, or mixtures thereof. The transition metal compound is preferably a transition metal compound containing at least one of nickel, cobalt and manganese. The transition metal oxide can be obtained by heat-treating a transition metal hydroxide.

The lithium compound is not particularly limited, and a known one can be used, but from the viewpoint of easy availability, a compound composed of at least one of lithium hydroxide, lithium nitrate, and lithium carbonate is preferable. Moreover, lithium hydroxide, lithium carbonate, or a mixture thereof is preferably used as the lithium compound from the viewpoint of ease of handling and stability of quality.

The mixing of the transition metal compound and the lithium compound (step S2) can be performed using a conventionally known mixer, as long as the transition metal compound is uniformly mixed to the extent that the skeleton of the transition metal compound is not destroyed. Examples of mixers that can be used include shaker mixers, Loedige mixers, Julia mixers, and V-blenders.

Next, the lithium mixture is baked to obtain a positive electrode active material composed of a lithium-transition metal composite oxide (step S3). When the lithium mixture is calcined, lithium diffuses into the transition metal compound to form a lithium-transition metal composite oxide composed of particles with a polycrystalline structure. Although the firing temperature is not particularly limited, it can be performed at, for example, 700° C. or higher and 1000° C. or lower. The firing time is 1 hour or more, preferably 3 hours or more and 24 hours or less. Although the firing atmosphere is not particularly limited, for example, the firing can be performed in an air atmosphere or an oxygen stream.

As shown in FIG. 3, the lithium-transition metal composite oxide (positive electrode active material 1) obtained by firing may be pulverized (step S4). The fired lithium-transition metal composite oxide contains secondary particles in which a plurality of primary particles are aggregated. These secondary particles may undergo further agglomeration or mild sintering to form agglomerates. In the pulverization step (step S4), the secondary particles formed into aggregates by agglomeration and sintering are crushed into small pieces by applying force such as a shearing force, thereby adjusting the particle size distribution of the positive electrode active material 1. be able to. After firing (step S3), the positive electrode active material 1 obtained by crushing (step S4) is mixed with the first conductive aid C1 (step S10).

The pulverization (step S4) can be performed so that the particle size of the positive electrode active material 1 obtained after pulverization is approximately the same as the particle size of its precursor (transition metal hydroxide or transition metal oxide). For example, the average particle size D50 of the positive electrode active material 1 after pulverization can be carried out within a range of 90% or more and 110% or less of the average particle size D50 of the precursor. In this specification, pulverization means applying mechanical energy to agglomerates generated by sintering or necking between secondary particles that constitute the positive electrode active material during firing, so that the secondary particles themselves are almost completely destroyed. It includes an operation (disaggregation) to separate secondary particles without breaking them and loosen aggregates.

As a pulverization method, a known means can be used, for example, a pin mill, a hammer mill, or the like can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so that the aggregates formed by the secondary particles of the positive electrode active material are crushed but the secondary particles are not destroyed.

As shown in FIG. 4, after firing (step S3), the unpulverized lithium-transition metal composite oxide (positive electrode active material 1) may be mixed with the first conductive aid C1 to obtain a mixture powder. (Step S10). Alternatively, this first mixing may be performed by pulverizing the positive electrode active material 1 in the presence of the first conductive agent C1 (step S11). For example, after lightly mixing the positive electrode active material 1 and the first conductive agent C1, pulverization (mixing) can be performed using a pulverizer (pin mill, hammer mill, or the like).

Generally, as shown in FIG. 3, the lithium-transition metal composite oxide (positive electrode active material 1) is used before mixing with other positive electrode materials in order to loosen aggregates formed in the firing step (step S3). Then, pulverization (crushing) is performed. On the other hand, as shown in FIG. 4, when the positive electrode active material 1 that has not been pulverized after firing and the first conductive aid C1 are mixed by pulverization (step S11), mixing and pulverization are performed at the same time. Therefore, the positive electrode active material 1 and the first conductive agent C1 can be mixed more uniformly, and the battery capacity and output characteristics of the secondary battery can be further improved. In addition, the pulverization step (step S4 in FIG. 3) of the lithium-transition metal composite oxide (positive electrode active material 1) after firing can be omitted, and the mixing processing time in the manufacturing step of the positive electrode mixture can be shortened. It can also contribute to the improvement of production efficiency.

Next, the mixture powder 10, the second conductive agent C2, the binder, and the solvent 2 are mixed (step S2). Hereinafter, this step is also referred to as a "second mixing step". The second mixing step can be wet mixing. FIG. 2B is a schematic diagram showing an example of the positive electrode mixture paste obtained in the second mixing step (step S2). The positive electrode mixture paste 20 includes a positive electrode active material 1 , a first conductive agent C<b>1 , a second conductive agent C<b>2 , a binder (not shown), and a solvent 2 .

The second conductive aid C2 is, for example, natural graphite (flaky graphite, etc.), graphite such as artificial graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, carbon black such as thermal black. , conductive fibers such as carbon fibers and metal fibers, metal powders such as aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, organic conductive materials such as polyphenylene derivatives Materials such as carbon fluoride can be used. These may be used alone or in combination of two or more. Among these, carbon blacks such as acetylene black and ketjen black are preferably used from the viewpoint of cost, productivity, and the like.

The second conductive agent C2 may be of the same kind as the first conductive agent C1, or may be of a different kind. The average particle size of the second conductive agent C2 may be the same as or different from the average particle size of the first conductive agent C1. Moreover, the average particle size of the second conductive agent C2 is preferably larger than the average particle size of the first conductive agent C1. When the average particle size of the second conductive agent C2 is larger than the average particle size of the first conductive agent C1, the second conductive agent C2 efficiently connects the positive electrode active materials 1 in the obtained positive electrode. A uniform and excellent conductive network can be formed together with the first conductive additive C1 existing on or near the surface of the positive electrode active material 1 (see FIG. 6).

Moreover, it is preferable that the second conductive agent C2 is larger than the first conductive agent C1 by 0.5 μm or more. When the average particle diameter of the second conductive aid C2 is within the above range, the positive electrode active material 1 in the obtained positive electrode can be more efficiently connected by the second conductive aid C2 having an appropriate size. can be done. The upper limit of the average particle size of the second conductive agent C2 is not particularly limited, and is, for example, approximately 5 μm or less, preferably 3 μm or less.

The content of the second conductive agent C2 is preferably 1 part by mass or more and 10 parts by mass or less when the total mass of the solid content of the positive electrode mixture in the positive electrode mixture paste 20 is 100 parts by mass. Preferably, it is 2 parts by mass or more and 5 parts by mass or less.

In the positive electrode mixture paste 20, the total amount of the first conductive agent C1 and the second conductive agent C2 is preferably 2 parts by mass when the total mass of the solid content of the positive electrode mixture is 100 parts by mass. parts or more and 10 parts by mass or less, more preferably 3 parts by mass or more and 5 parts by mass or less. In addition, the content of the second conductive agent C2 in the positive electrode mixture paste 20 can be larger than that of the first conductive agent C1. It is preferably 2 times or more and 10 times or less. When the content of the second conductive agent C2 is within the above range, good conductive paths can be formed more efficiently, and the content of the first conductive agent C1 can be reduced. Therefore, it can be more cost effective.

The binding agent (binder) plays a role of binding the active material particles, and is not particularly limited, and conventionally known polymer materials can be used. Examples of binders that can be used include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and polyacrylic acid.

The content of the binder in the positive electrode mixture paste 20 is not particularly limited as long as it is an amount capable of binding the positive electrode active material 1 and the like. , preferably 0.5 to 20 parts by mass, more preferably 1 to 10 parts by mass.

Solvent 2 is not particularly limited, and conventionally known solvents capable of dissolving and dispersing the binder can be used. Solvent 2 includes, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide and the like. These solvents 2 may be used alone or in combination of two or more. When polyvinylidene fluoride (PVDF) or the like is used as the binder, it is preferable to use N-methyl-2-pyrrolidone (NMP), which is a good solvent. The content of the solvent 2 is not particularly limited as long as the liquid in which the binder is dissolved has an appropriate viscosity. % or less is preferable.

Note that the positive electrode mixture paste 20 may contain components other than those described above as long as the effects of the present invention are not impaired. As another component, for example, activated carbon or the like can be added.

In the second mixing step (step S20), the order and number of times of mixing each component are not particularly limited. Also, the second conductive aid C2 can be mixed with the mixture powder 10 in a wet or dry manner. For example, the powder mixture 10 obtained in the first mixing step, the second conductive agent C2, the binder, and the solvent 2 may be added and mixed at the same time. In this case, pulverization of the positive electrode active material 1 and production of the positive electrode mixture paste 20 can be performed by only two steps, so productivity is excellent. Moreover, after mixing the mixture powder 10 and the second conductive agent C2, the binder may be mixed, and then the solvent 2 may be mixed. Alternatively, the second conductive agent C2, the binder, and the solvent 2 may be mixed in advance to prepare a slurry solution, and then the mixture powder 10 obtained in the first mixing step may be added to the slurry solution. . In the method for producing the positive electrode mixture paste of the present embodiment, for example, a sufficiently good conductive path is formed in the positive electrode without mixing using a mechanochemical reaction as described in Patent Document 6. can be formed.

[Positive electrode mixture paste]
The positive electrode mixture paste 20 of this embodiment includes, for example, a positive electrode active material 1, a first conductive aid C1, and a second conductive aid C2, as shown in FIG. 2(B). The second conductive additive C2 has an average particle size larger than that of the first conductive additive C1.

The positive electrode mixture paste 20 of the present embodiment can be manufactured simply and stably by using the method for manufacturing the positive electrode mixture paste of the present embodiment described above. Note that materials used in the positive electrode mixture paste 20 of the present embodiment are the same as those described in the method for manufacturing the positive electrode mixture paste, and thus description thereof is omitted.

In the positive electrode mixture paste 20, the first conductive aid C1 is present in contact with the surface of the positive electrode active material 1 or in the vicinity of the surface. In the resulting positive electrode, the first conductive additive C1 is arranged so as to be in uniform contact with the surface of the positive electrode active material 1 and forms a conductive path around the positive electrode active material 1 . The first conductive agent C1 is a positive electrode active material having a complicated internal structure or a high porosity, which is manufactured for the purpose of improving output characteristics, for example, by using the above-described method for manufacturing a positive electrode mixture paste. The positive electrode active material can also be arranged in uniform contact with its surface.

On the other hand, the second conductive agent C2 is arranged in the positive electrode mixture paste 20 at a position farther from the surface of the positive electrode active material 10 than the first conductive agent C1. In the positive electrode after the solvent 2 has been removed, the second conductive aid C2 is uniformly dispersed so as to fill the gaps between the positive electrode active materials 1, and is dispersed between the positive electrode active materials 10 and between the positive electrode active materials 1. A relatively long conductive path is formed between the current collectors (see FIG. 6).

For example, in order for the positive electrode active material 1 to sufficiently contribute to charging and discharging, it is necessary to obtain the maximum conductive effect with the conductive additives C1 and C2 in as small a ratio as possible. By manufacturing using the manufacturing method including the first mixing step and the second mixing step, the maximum conductive effect can be obtained in the positive electrode even with relatively small amounts of the conductive aids C1 and C2. Since the ratio of the positive electrode active material per unit area of the positive electrode (positive electrode mixture layer) can be maximized, the maximum capacity of the secondary battery can be increased. Furthermore, by making the content of the conductive aid C1 with a small average particle size, which tends to increase the cost, less than the content of the conductive aid C2 with a large average particle size, it becomes excellent in terms of cost. .

Further, the positive electrode mixture paste 20 of the present embodiment includes the positive electrode active material 1, the first conductive aid C1, the second conductive aid C1, the binder, and the solvent 2, and the first conductive aid C1 may contain a carbon nanomaterial having an aspect ratio (average major axis length/average minor axis length) of 100 or more. Note that the carbon nanomaterial used for the positive electrode mixture paste 20 of the present embodiment is the same as the material described in the manufacturing method of the positive electrode mixture paste described above, so description thereof is omitted.

Further, when the first conductive aid C1 is a carbon nanomaterial, the second conductive aid C2 has a spherical (including substantially spherical) shape, and the average particle size of the second conductive aid C2 is preferably greater than 0.9 times the average major axis length of the carbon nanomaterial. When the second conductive agent C2 has a shape within the above range, it can be combined with the carbon nanomaterial to form a better conductive path in the positive electrode of the secondary battery.

The presence of the first conductive agent C1 and the second conductive agent C2 in the positive electrode mixture paste 20 can be confirmed by, for example, observation using an electron microscope.

[Method for producing positive electrode for non-aqueous electrolyte secondary battery]
FIG. 5 is a flow chart showing an example of a method for manufacturing a positive electrode. A method for manufacturing a positive electrode includes coating the positive electrode mixture paste on the surface of a current collector (step S30), drying the current collector coated with the positive electrode mixture paste (step S40), including.

First, the positive electrode material mixture paste 20 is applied to the surface of a current collector such as an aluminum foil (step S30). The coating method is not particularly limited, and a conventionally known method can be used. For example, a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, a curtain coating method, and the like can be used. . Note that the current collector is not limited to aluminum foil, and may be any chemically inactive electron current that allows current to continue to flow through the electrode during charging and discharging of the secondary battery.

Next, the current collector coated with the positive electrode mixture paste 20 is dried (step S40). By drying, the solvent 2 in the positive electrode mixture paste 20 is scattered, and a positive electrode in which a positive electrode mixture layer is formed on a current collector is obtained. Moreover, the dried positive electrode material mixture layer may be pressurized by a roll press or the like so as to increase the electrode density. The shape of the positive electrode is not particularly limited, and it can be cut into a desired size depending on the intended secondary battery. The shape of the positive electrode can be, for example, a sheet shape. Note that the method for manufacturing the positive electrode is not limited to the above examples, and other methods may be used.

FIG. 6 is a schematic diagram showing an example of the state around the positive electrode active material in the positive electrode. The positive electrode 30 manufactured using the positive electrode mixture paste 20 described above is uniformly dispersed so that the conductive additives C1 and C2 are sufficiently in contact with the surface of the positive electrode active material 1 and fill the gaps between the positive electrode active materials 1. to form a good conductive path. A secondary battery using this positive electrode 30 has improved battery capacity and output characteristics. Further, when the first conductive agent C1 and the second conductive agent C2 having different average particle diameters are used, the first conductive agent C1 having a small average particle diameter is sufficiently in contact with the surface of the positive electrode active material 1. , the second conductive agent C2 having a large average particle size is uniformly dispersed between the positive electrode active materials 1 so as to fill the gaps between the positive electrode active materials 1, thereby further improving battery capacity and output characteristics. Further, as described above, the positive electrode 30 can form a good conductive path even when the content of the first conductive agent C1 is less than the content of the second conductive agent C2. .

[Non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery (hereinafter also referred to as a “secondary battery”) of the present embodiment includes the positive electrode active material or positive electrode described above. A secondary battery includes, for example, a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. In addition, the secondary battery of the present embodiment may be composed of components similar to those of known lithium-ion secondary batteries, and may include a positive electrode, a negative electrode, and a solid electrolyte.

Hereinafter, as an example of the secondary battery of the present embodiment, a secondary battery containing a non-aqueous electrolytic solution will be described for each component. It should be noted that the embodiments described below are merely examples, and the secondary battery can be implemented in various modified and improved forms based on the knowledge of those skilled in the art, including the following embodiments. Moreover, the secondary battery is not particularly limited in its application.

(negative electrode)
Metallic lithium, a lithium alloy, or the like can be used for the negative electrode. In addition, the negative electrode is prepared by mixing a negative electrode active material capable of intercalating or deintercalating lithium ions with a binder, adding an appropriate solvent to form a paste, and applying the negative electrode mixture on the surface of a metal foil current collector such as copper. It may be applied to the surface, dried, and compressed to increase the electrode density as necessary.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used. Similar to the positive electrode, a fluorine-containing resin such as PVDF can be used as the negative electrode binder. Organic solvents such as N-methyl-2-pyrrolidone can be used as solvents for dispersing these active materials and binders.

(separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and known separators can be used. The separator is a thin film made of, for example, synthetic resins such as polyethylene, polypropylene, polytetrafluoroethylene, polyimide, polyamide, and polyester, polysaccharides such as cellulose and amylose, natural polymers, and electrical insulating materials such as ceramics. , a membrane having a large number of micropores can be used.

(Non-aqueous electrolyte)
The non-aqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, and the like, or a mixture of two or more. can be done.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , composite salts thereof, and the like can be used. Furthermore, the non-aqueous electrolytic solution may contain radical scavengers, surfactants, flame retardants, and the like.

(Shape and configuration of secondary battery)
The non-aqueous electrolyte secondary battery of the present invention, which is composed of the positive electrode, negative electrode, separator and non-aqueous electrolytic solution described above, can have various shapes such as a cylindrical shape and a laminated shape. Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolytic solution, and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collecting lead or the like, and sealed in a battery case to complete the secondary battery.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, the evaluation of battery characteristics in Examples and Comparative Examples was performed based on the results of measurement using the following apparatus and method.

[Composition analysis]
After dissolving the obtained sample in nitric acid, it was measured with an ICP emission spectrometer (ICPS-8100 manufactured by Shimadzu Corporation).
[Measurement of average particle diameter D50]
A laser diffraction scattering type particle size distribution analyzer (Microtrac HRA manufactured by Nikkiso Co., Ltd.) was used.

[Production of secondary battery for evaluation]
For evaluation of battery characteristics, a 2032-type coin battery BA (hereinafter also referred to as "coin battery BA") shown in FIG. 7 was used. The coin-type battery BA is composed of a case and electrodes accommodated in the case.

The case has a hollow cathode can PC with one end open, and an anode can NC arranged in the opening of the cathode can PC. When the anode can NC is arranged in the opening of the cathode can PC, A space for accommodating the electrodes is formed between the negative electrode can NC and the positive electrode can PC.

The electrodes are composed of a positive electrode PE, a separator SE and a negative electrode NE, which are stacked in this order so that the positive electrode PE contacts the inner surface of the positive electrode can PC and the negative electrode NE contacts the inner surface of the negative electrode can NC. is housed in a case.

The case is provided with a gasket GA, and this gasket GA fixes relative movement between the positive electrode can PC and the negative electrode can NC so as to maintain a non-contact state. The gasket GA also has the function of sealing the gap between the positive electrode can PC and the negative electrode can NC to airtightly and liquidtightly isolate the inside of the case from the outside.

A method for manufacturing the coin-type battery BA will be described below.
A positive electrode sheet obtained by applying and drying the positive electrode mixture paste was punched out into circular electrodes of 14 mm in diameter using a circular punch to obtain a positive electrode PE. As the negative electrode NE, a lithium metal punched into a circular electrode of 14 mmφ was used. A coin battery BA was produced in an Ar atmosphere glove box with a controlled dew point of -80°C.

[Measurement of charge/discharge capacity]
The coin battery BA was left for about 24 hours, and after the open circuit voltage OCV (open circuit voltage) was stabilized, the current density to the positive electrode was set to 0.5 mA / cm ² and charged to the cutoff voltage of 4.3 V to obtain the charge capacity. The capacity when the battery was discharged to a cut-off voltage of 3.0 V after resting for a period of time was measured as the discharge capacity.

[Measurement of reaction resistance]
The coin battery BA was charged at a charging potential of 4.1 V and measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (1255B, manufactured by Solartron) to obtain the Nyquist plot shown in the upper part of FIG. Since this Nyquist plot is expressed as the sum of characteristic curves showing solution resistance, negative electrode resistance and its capacity, and reaction resistance and its capacity, the equivalent circuit shown in the lower part of FIG. 8 is used based on this Nyquist plot. A fitting calculation was performed to calculate the value of the reaction resistance (positive electrode resistance).

[Example 1]
A cathode active material for a lithium ion secondary battery was produced as follows. Crystals of nickel sulfate, manganese sulfate, and cobalt sulfate were weighed so that the molar ratio of nickel:manganese:cobalt was 1:1:1 to prepare a 2 mol/liter raw sulfate solution. Next, 60 liters of pure water was put into a reaction tank with an effective volume of 60 liters, and while maintaining the temperature inside the tank at 40° C., the raw sulfate salt solution, 40% aqueous sodium hydroxide solution, and 25% aqueous ammonia were added. dripped continuously. The dropping rate of each solution was 80 ml/min for the raw sulfate solution and 20 ml/min for the aqueous ammonia solution. The particle size distribution of the transition metal hydroxide generated in the tank is monitored, and the dropping speed of the aqueous sodium hydroxide solution is adjusted so that the average particle size D50 of the transition metal hydroxide in the tank reaches the target particle size. continued to react. The transition metal composite hydroxide produced is continuously recovered from the overflow port of the reaction vessel, washed with a 40% sodium hydroxide aqueous solution and pure water, and solid-liquid separated using a Denver. , and vacuum-dried to recover the transition metal composite hydroxide. The resulting transition metal composite hydroxide was represented by a chemical composition formula of Ni _0.33 Mn _0.33 Co _0.34 (OH) ₂ and had an average particle size D50 of 10.3 μm.

Next, this composite hydroxide was mixed with lithium carbonate in a molar ratio of Li/(Ni+Mn+Co)=1.10. The resulting mixture was charged into an alumina sagger and fired in an air atmosphere at 955° C. for 3 hours using a batch-type firing furnace to synthesize a lithium-transition metal composite oxide. The lithium-transition metal composite oxide after synthesis has a part where the particles are sintered together, and sintered particles with a diameter of 50 μm or more where aggregation has progressed in some parts are mixed. A short grinding treatment was added by The chemical composition _{formula of} the lithium-transition metal composite oxide after pulverization was _{Li1.11Ni0.34Mn0.33Co0.33O2} , and the average particle size _D50 was 9.9 _µm .

33.00 g of the obtained lithium-transition metal composite oxide and 0.35 g of acetylene black having an average particle size D50 of 0.7 μm as a first conductive agent were weighed, and 45 g of zirconia beads (3 mmφ) were placed in polypropylene It was placed in a dedicated mixing container and mixed twice for 15 seconds at 1500 rpm using a rotation/revolution mixer: Awatori Rentaro ARE-310 (manufactured by Thinky Co., Ltd.). After removing the zirconia beads by sieving, 1.10 g of acetylene black having an average particle size D50 of 0.7 μm, which is the same as the first conductive additive, was added to the obtained mixture powder as a second conductive additive, and bound. 15.11 g of Kureha's PVDF solution KF#1120 (PVDF 12 wt%/NMP 88 wt%) and 11.0 g of viscosity adjusting solvent NMP were added as agents, and kneaded again for 5 minutes at 1500 rpm using the Awatori Rentaro. , to obtain a positive electrode mixture paste.

Ethanol was sprayed on a 380 mm long, 230 mm wide glass coating plate, and an aluminum current collector having a length of 180 mm, a width of 120 mm, and a thickness of 20 μm was placed thereon, and was pressed and fixed with a rubber squeegee. An appropriate amount of the positive electrode mixture paste was placed on the starting point of coating at the end of the aluminum current collector, and a baker-type applicator (width 150 mm, clearance setting 250 μm) was slid to spread the paste clumps onto the current collector. , to form a substantially rectangular coating film. The coating film thus obtained was placed in a vacuum dryer: VOS-451SD (manufactured by Tokyo Rikakiki Co., Ltd.) together with the coating plate and the current collector, and preliminarily dried in an air atmosphere at 60° C. for 10 minutes. After that, the inside of the dryer was evacuated to 1 Pa, and in order to completely remove the residual solvent, drying treatment was performed in a reduced pressure atmosphere at 120°C over 8 hours to obtain a positive electrode sheet. Using this positive electrode sheet, battery characteristics were evaluated. Table 1 shows the results.

[Example 2]
A positive electrode mixture paste was obtained under the same conditions as in Example 1, except that 1.10 g of acetylene black having an average particle size D50 of 1.5 μm was added as the second conductive aid. Using the obtained positive electrode material mixture paste, a positive electrode sheet was produced under the same conditions as in Example 1, and battery characteristics were evaluated. Table 1 shows the results.

[Example 3]
Acetylene black having an average particle size D50 of 0.7 μm was added to 100 g of the lithium-transition metal composite oxide obtained under the same conditions as in Example 1 after firing, except that the pulverization treatment was not performed. 1.06 g was added and lightly mixed in a polyethylene bag, followed by a short comminution treatment with a hammer mill. 33.35 g of the mixed powder of the positive electrode active material after pulverization and the first conductive aid was weighed, and 1.10 g of acetylene black having an average particle size D50 of 1.5 μm as the second conductive aid, and a binder were added. 15.11 g of Kureha's PVDF solution KF # 1120 (PVDF 12 wt% / NMP 88 wt%) and 11.0 g of viscosity adjusting solvent NMP are added as a rotation / revolution mixer: Awatori Rentaro ARE-310 (manufactured by Thinky Co., Ltd.) was kneaded for 5 minutes at a rotation speed of 1500 rpm to obtain a positive electrode mixture paste. Using the obtained positive electrode material mixture paste, a positive electrode sheet was produced in the same manner as in Example 1, and battery characteristics were evaluated. Table 1 shows the results.

[Example 4]
0.35 g of acetylene black having an average particle size D50 of 1.2 μm as the first conductive aid, and 1.10 g of acetylene black having an average particle size D50 of 2.0 μm as the second conductive aid were added. A positive electrode mixture paste was obtained under the same conditions as in Example 1. Using the obtained positive electrode material mixture paste, a positive electrode sheet was produced under the same conditions as in Example 1, and battery characteristics were evaluated. Table 1 shows the results.

[Example 5]
The same conditions as in Example 1 except that acetylene black with an average particle size D50 of 0.7 μm was used as the first conductive agent, and acetylene black with an average particle size D50 of 1.0 μm was used as the second conductive agent. to prepare a positive electrode sheet, and evaluate the battery characteristics. Table 1 shows the results.

[Example 6]
A positive electrode sheet was prepared under the same conditions as in Example 1 except that Aldrich single-walled carbon nanotubes (average short axis diameter: 1.3 nm, average long axis length: 1 μm) were used as the first conductive aid. It was produced and the battery characteristics were evaluated. Table 1 shows the results.

[Comparative Example 1]
33.00 g of a lithium transition metal composite oxide obtained under the same conditions as in Example 1, 1.45 g of acetylene black having an average particle size D50 of 0.7 μm as a conductive aid, and Kureha's PVDF solution KF as a binder. 15.11 g of #1120 (PVDF 12 wt% / NMP 88 wt%) and 11.0 g of NMP, a solvent for viscosity adjustment, are weighed and placed in a dedicated polypropylene mixing container together with 45 g of zirconia beads (3 mmφ). Mixing was performed twice for 15 seconds at 1500 rpm using Taro ARE-310 (manufactured by Thinky Co., Ltd.). After the zirconia beads were removed by sieving, the resulting mixture was kneaded again for 5 minutes at 1500 rpm using the Awatori Rentaro to obtain a positive electrode mixture paste. Using the obtained positive electrode material mixture paste, a positive electrode sheet was produced in the same manner as in Example 1, and battery characteristics were evaluated. Table 1 shows the results.

[Comparative Example 2]
The same procedure as in Example 2 except that the lithium transition metal composite oxide, the first conductive aid, the second conductive aid, the binder, and the solvent for viscosity adjustment were added at the same time to obtain a positive electrode mixture paste. A positive electrode sheet was produced under the conditions, and battery characteristics were evaluated. Table 1 shows the results.

(Evaluation results)
Table 1 shows the test conditions of the above examples and comparative examples and the evaluation results of the battery characteristics. As shown in Table 1, in the secondary batteries of Examples 1 to 6 in which the conductive aid was added in two portions, one or two conductive aids were added at the same time as other battery materials, It is clear that the charge/discharge capacity is higher and the reaction resistance is lower than the mixed secondary battery of Comparative Example 1 or Comparative Example 2, and the battery capacity and output characteristics are improved.

Further, in the secondary batteries of Examples 2 and 3, in which the average particle size D50 of the second conductive aid is larger than the average particle size D50 of the first conductive aid, the charge/discharge capacity is higher. , the reaction resistance is low. In particular, Example 3, in which the lithium transition metal oxide (positive electrode active material) was not pulverized after firing and was pulverized after being mixed with the first conductive aid, had a higher charge-discharge capacity and a lower reaction resistance. It's becoming

In addition, in Examples 1 to 3 in which the first conductive aid is 1 μm or less, the charge-discharge capacity is higher and the reaction resistance is lower than in Example 4 in which the first conductive aid exceeds 1 μm. .

In the present embodiment, a positive electrode mixture paste capable of obtaining a positive electrode for a non-aqueous electrolyte secondary battery with improved battery capacity and output characteristics can be easily obtained by an industrial production method.

The positive electrode active material of the present embodiment is a small secondary battery for mobile phones, laptop computers, and other IT devices, and a large industrial secondary battery for hybrid vehicles (HEV), electric vehicles, power storage, etc. can be suitably used as the positive electrode of In addition, the secondary battery for electric vehicles includes not only the power source for electric vehicles driven purely by electric energy, but also the so-called secondary battery for hybrid vehicles used in combination with a combustion engine such as a gasoline engine or a diesel engine.

Reference Signs List 1 Positive electrode active material 2 Solvent C1 First conductive aid C2 Second conductive aid 10 Mixture powder 20 Positive electrode mixture paste 30 Positive electrode BA Coin battery PE Positive electrode (evaluation electrode)
NE... Negative electrode SE... Separator GA... Gasket PC... Positive electrode can NC... Negative electrode can

Claims (23)

mixing a transition metal compound and a lithium compound to obtain a lithium mixture;
calcining the lithium mixture to obtain a lithium transition metal composite oxide;
mixing the unpulverized lithium-transition metal composite oxide after firing with a first conductive aid to obtain a mixture powder;
mixing the mixture powder, a second conductive agent, a binder, and a solvent;
The first conductive aid and the second conductive aid are the same or different conductive aids,
A method for producing a positive electrode mixture paste for a non-aqueous electrolyte secondary battery. The calcined non-pulverized lithium transition metal composite oxide and the first conductive aid are mixed in the presence of the calcined non-pulverized lithium transition metal The method for producing a positive electrode material mixture paste for a non-aqueous electrolyte secondary battery according to claim 1, which is carried out by pulverizing the composite oxide . The transition metal compound is a transition metal hydroxide or transition metal oxide,
wherein the lithium compound is lithium hydroxide or lithium carbonate;
The method for producing the positive electrode material mixture paste for a non-aqueous electrolyte secondary battery according to claim 1 or 2 . The average particle size of the first conductive aid is 1/10 or less of the average particle size of the non-pulverized lithium-transition metal composite oxide after firing. A method for producing the positive electrode material mixture paste for a non-aqueous electrolyte secondary battery according to the above item. The average particle size of the first conductive aid is 1 μm or less.
A method for producing a positive electrode mixture paste for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4 . The average particle size of the second conductive aid is larger than the average particle size of the first conductive aid.
A method for producing a positive electrode material mixture paste for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5 . The average particle size of the second conductive aid is 0.5 μm or more larger than the average particle size of the first conductive aid,
A method for producing a positive electrode mixture paste for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6 . The first conductive aid contains a carbon nanomaterial,
A method for producing a positive electrode mixture paste for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7 . The carbon nanomaterial includes any one or more of carbon nanotubes, carbon nanofibers, and carbon nanohorns.
The method for producing the positive electrode material mixture paste for non-aqueous electrolyte secondary batteries according to claim 8 . The carbon nanomaterial has an average short axis length of 10 nm or less,
The method for producing the positive electrode material mixture paste for a non-aqueous electrolyte secondary battery according to claim 8 or 9 . The carbon nanomaterial has an average major axis length of 2 μm or less,
The method for producing a positive electrode material mixture paste for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 10 . Coating a positive electrode mixture paste for a non-aqueous electrolyte secondary battery obtained using the production method according to any one of claims 1 to 11 on a current collector;
drying the current collector coated with the positive electrode mixture paste;
A method for producing a positive electrode for a non-aqueous electrolyte secondary battery. A positive electrode mixture paste for a non-aqueous electrolyte secondary battery produced by the production method according to any one of claims 1 to 11 ,
Lithium-transition metal composite oxide, a first conductive aid, a second conductive aid, a binder, and a solvent, wherein the average particle size of the second conductive aid is the same as that of the first conductive aid larger than the average particle size,
Positive electrode mixture paste for non-aqueous electrolyte secondary batteries. The content of the second conductive aid is greater than the content of the first conductive aid,
The positive electrode material mixture paste for a non-aqueous electrolyte secondary battery according to claim 13 . 15. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 13 or 14 , wherein the average particle size of said first conductive aid is 1/10 or less of the average particle size of said lithium-transition metal composite oxide. mixture paste. The positive electrode mixture paste for a non-aqueous electrolyte secondary battery according to any one of claims 13 to 15 , wherein the first conductive aid has an average particle size of 1 µm or less. The non-aqueous electrolyte according to any one of claims 13 to 16 , wherein the average particle size of the second conductive aid is larger than the average particle size of the first conductive aid by 0.5 μm or more. Positive electrode mixture paste for secondary batteries. A positive electrode mixture paste for a non-aqueous electrolyte secondary battery produced by the production method according to any one of claims 1 to 11 ,
containing a lithium transition metal composite oxide, a first conductive aid, a second conductive aid, a binder, and a solvent;
The first conductive aid contains a carbon nanomaterial having an aspect ratio (average major axis length/average minor axis length) of 100 or more,
The second conductive aid has a spherical shape,
A positive electrode mixture paste for a non-aqueous electrolyte secondary battery, wherein the average particle size of the second conductive aid is larger than 0.9 times the average major axis length of the carbon nanomaterial. The carbon nanomaterial includes any one or more of carbon nanotubes, carbon nanofibers, and carbon nanohorns.
The positive electrode material mixture paste for a non-aqueous electrolyte secondary battery according to claim 18 . The carbon nanomaterial has an average short axis length of 10 nm or less,
The positive electrode material mixture paste for a non-aqueous electrolyte secondary battery according to claim 18 or 19 . The carbon nanomaterial has an average major axis length of 2 μm or less,
The positive electrode material mixture paste for non-aqueous electrolyte secondary batteries according to any one of claims 18 to 20 . A positive electrode for a non-aqueous electrolyte secondary battery, comprising the positive electrode mixture paste according to any one of claims 13 to 21 . A secondary battery comprising the positive electrode for a non-aqueous electrolyte secondary battery according to claim 22 , a negative electrode, and a non-aqueous electrolyte.

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