JP2007080652A - Slurry for forming lithium ion battery electrode and lithium ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide slurry for forming lithium ion battery electrode and a lithium ion battery with high discharging capacity at a high speed charging/discharging rate of 10 C or more and sufficient charge/discharge rate property. <P>SOLUTION: The slurry for forming the lithium ion battery electrode contains electrode activator, conductive assistant, a binder and polarized solvent. The conductive assistant is composed of two or more types of particles with different particle diameters or shapes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a slurry for forming an electrode of a lithium ion battery and a lithium ion battery, and in particular, a lithium ion having excellent high-speed charge / discharge characteristics by using a conductive additive composed of two or more kinds of particles having different particle sizes or shapes. The present invention relates to a slurry for battery electrode formation and a lithium ion battery.

In recent years, non-aqueous electrolyte secondary batteries such as lithium ion batteries have been proposed and put into practical use as small, light, and high capacity batteries. This lithium ion battery is composed of a positive electrode and a negative electrode having a property capable of reversibly inserting and removing lithium ions, and a non-aqueous electrolyte.
The negative electrode of a lithium ion battery generally uses a Li-containing metal oxide having a property capable of reversibly removing and inserting lithium ions such as a carbon-based material or lithium titanate (Li ₄ Ti ₅ O ₁₂ ) as a negative electrode active material. It has been.
On the other hand, the positive electrode of a lithium ion battery is composed of a Li-containing metal oxide having a capability of reversibly removing and inserting lithium ions, which is called a positive electrode active material, a conductive additive, and a binder. The positive electrode is formed by applying it to the surface of a metal foil called a current collector.

As the positive electrode active material of this lithium ion battery, lithium cobaltate (LiCoO ₂ ) is usually used, but in addition, lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), lithium iron phosphate Lithium (Li) compounds such as (LiFePO ₄ ) are used.

  Such lithium-ion batteries are lighter, smaller, and have higher energy than secondary batteries such as conventional lead batteries, nickel cadmium batteries, and nickel metal hydride batteries, so mobile phones, notebook personal computers, etc. In recent years, it has been studied as a high-output power source for electric vehicles, hybrid vehicles, electric tools, and the like.

As an electrode active material for batteries used as these high-output power supplies, high-speed charge / discharge characteristics are required, but Li-containing metal oxides having the property of reversibly removing and inserting lithium ions have low electronic conductivity. . Therefore, as a method for improving the electronic conductivity of the electrode active material, a method of adding a conductive additive to the electrode active material is generally employed (see Non-Patent Document 1). As a method of mixing the electrode active material and the conductive auxiliary, a method of mixing the electrode active material and the conductive auxiliary with a stirring blade type mixer such as a ball mill or a planetary mixer is employed. As the conductive assistant, carbon-based conductive assistants such as acetylene black, carbon black, ketjen black, natural graphite, and artificial graphite are generally used.
Yoshiharu Matsuda, Zenichiro Takehara et al., “Battery Handbook 3rd Edition”, Maruzen Co., Ltd., issued February 20, 2001, p. 267

  However, in the conventional method of adding a conductive aid to an electrode active material, a mixer such as a ball mill or a stirring blade type mixer has been used to mix the electrode active material and the conductive aid. In these mixers, There is a problem in that the dispersion of the conductive assistant is not sufficient and the conductivity of the electrode active material is insufficiently improved, resulting in a decrease in capacity during high-speed charge / discharge of the battery.

In order to solve this problem, in the Japanese Patent Application No. 2005-127655, the present inventors have developed an interface (three-phase interface) between an electrode active material, a conductive assistant, and an electrolytic solution that are charged and discharged by the exchange of lithium ions and electrons. = Active point) is effective to increase the number, and for that purpose, it has been found that it is effective to finely disperse the conductive aid, and in order to finely disperse the conductive aid The use of a dispersant is found to be effective, and the number of medium particles is limited when the electrode active material, conductive additive, binder and polar solvent are stirred and dispersed together with the medium particles to form a slurry. It has been found that this is effective, and a slurry for forming an electrode of a lithium ion battery, a manufacturing method thereof, and a lithium ion battery have been proposed.
However, according to Japanese Patent Application No. 2005-127655, when the conductive additive is highly dispersed on the nanometer order, if the charge / discharge rate is 2C or more and less than 10C, the decrease in the discharge capacity can be sufficiently suppressed, but the charge / discharge rate However, when the temperature is 10C or more, the decrease in discharge capacity could not be sufficiently suppressed.

  The present invention has been made in order to solve the above-described problems, and has a high discharge capacity at a high-speed charge / discharge rate of 10 C or higher and a slurry for forming an electrode of a lithium ion battery having sufficient charge / discharge rate performance, and lithium ion An object is to provide a battery.

  As a result of intensive studies to solve the above problems, the present inventors have found that the surface of the electrode using the slurry for forming an electrode of the lithium ion battery of Japanese Patent Application No. 2005-127655, and the back surface of this electrode (the collector side) ) Was observed in detail with an electron microscope. As a result, it was found that the conductive auxiliary agent was present at a high concentration on the surface of the electrode, while the conductive auxiliary agent was hardly present on the back surface of the electrode.

  In addition, when manufacturing an electrode of a lithium ion battery using a conventional method of adding a conductive additive to an electrode active material, it is found that the conductive additive is unevenly distributed due to the following phenomenon. It was. That is, in the conventional method for manufacturing an electrode of a lithium ion battery, as shown in FIG. 4A, the electrode active material 31 and the conductive additive 32 are highly dispersed in the electrolyte solution 33 on the order of nanometers to form an electrode. In order to prepare the slurry 34 and apply the electrode forming slurry 34 to the current collector 35, the electrode forming slurry 34 is dried before the electrode forming slurry 34 is dried (see FIG. 4A). By forming the electrode coating film 36 (see FIG. 4B), the convection (Marangoni convection) due to the difference in concentration and surface tension generated in the electrode coating film 36, and the temperature between the front surface and the back surface of the electrode coating film 36 Due to the convection due to the difference (Benard convection), the conductive auxiliary agent 32 that is finer and lighter than the electrode active material 31 floats on the surface of the electrode coating film 36. As a result, it has also been found that the concentration of the conductive auxiliary agent 32 in the vicinity of the interface between the current collector 35 and the electrode coating film 36 is lowered, and the conductive path of the electrode coating film 36 is interrupted.

Furthermore, in order to solve the problem of uneven distribution of the conductive auxiliary agent due to Marangoni convection or Benard convection, a method of increasing the viscosity of the electrode forming slurry or a method of thinning the electrode coating film can be considered. If the viscosity is increased, coating becomes difficult, and if the electrode coating is made thinner, the battery cannot be increased in capacity.
Therefore, the present inventors, as a method of ensuring a sufficient conductive path in the electrode coating film, flows by convection generated in the electrode coating film until the electrode forming slurry is dried to form the electrode coating film. It has been found that the conductive auxiliary agent is uniformly dispersed by using a conductive auxiliary agent having a size or shape which is difficult to form, and the present invention has been completed.

  That is, the electrode forming slurry of the lithium ion battery of the present invention is a slurry for forming an electrode of a lithium ion battery containing an electrode active material, a conductive assistant, a binder and a polar solvent, and the conductive assistant is It consists of 2 or more types of particle | grains from which a particle size or a shape differs.

  In the slurry for forming an electrode of the lithium ion battery of the present invention, it is preferable that at least one of the particles has a particle size of less than 50 nm, and the other types of particles have a particle size of 50 nm or more.

  In the slurry for forming an electrode of the lithium ion battery of the present invention, it is preferable that at least one of the particles has an aspect ratio of 3 or more.

  In the electrode-forming slurry of the lithium ion battery of the present invention, it is preferable that at least one of the particles is a secondary particle formed by aggregating primary particles.

  The lithium ion battery of the present invention comprises a positive electrode using the slurry for electrode formation of the lithium ion battery of the present invention.

  According to the slurry for forming an electrode of a lithium ion battery of the present invention, it is a slurry for forming an electrode of a lithium ion battery containing an electrode active material, a conductive additive, a binder and a polar solvent, Since it consists of two or more kinds of particles having different particle sizes or shapes, sufficient active sites can be formed on the surface of the electrode active material, and between the electrode active materials and between the electrode active material and the current collector. Therefore, a reduction in discharge capacity at a high-speed charge / discharge rate of 10 C or higher can be improved, and a lithium ion battery having sufficient charge / discharge rate performance can be realized.

  According to the lithium ion battery of the present invention, since the electrode using the slurry for the electrode of the lithium ion battery of the present invention is provided, the charge / discharge capacity (particularly, discharge capacity) of the electrode can be improved, and the charge / discharge cycle Can be stabilized and the output can be increased. Therefore, a high output lithium ion battery can be provided.

The best mode of a slurry for forming an electrode of a lithium ion battery and a lithium ion battery of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

The slurry for forming an electrode of the lithium ion battery of the present invention is a slurry for forming an electrode of a lithium ion battery containing an electrode active material, a conductive assistant, a binder and a polar solvent, and the conductive assistant has a particle size or a shape. It consists of two or more kinds of particles having different.
In addition, at least one of the particles constituting the conductive additive has a particle size of less than 50 nm, and the other types of particles have a particle size of 50 nm or more.
Further, at least one of the particles constituting the conductive assistant has an aspect ratio of 3 or more.
Furthermore, at least one of the particles constituting the conductive assistant is a secondary particle formed by aggregating primary particles.

Here, the particle size is an average particle size measured by an image analysis method using a transmission electron microscope, a reflection electron microscope, an optical microscope, or the like, and specifically, one particle. Is the size represented by the average value of the minimum and maximum portions.
The particles having an aspect ratio of 3 or more are particles having a major axis / minor axis ratio of 3 or more.

The electrode active material may be any Li-containing metal oxide having a capability of reversibly removing and inserting lithium ions. As the electrode active material for the positive electrode, for example, lithium iron phosphate (LiFePO ₄ ), lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ) and the like are preferably used. As the electrode active material for the negative electrode, for example, lithium titanate (Li ₄ Ti ₅ O ₁₂ ) or the like is preferably used.
As these electrode active materials, those produced by conventional methods such as a solid phase method, a liquid phase method, and a gas phase method are used.

  Further, the shape and size of the electrode active material are not particularly limited, but in order to use the electrode active material at a high-speed charge / discharge rate of 10 C or more, the average particle size of the electrode active material is preferably 5 μm or less, and more preferably 2 μm or less. When the average particle diameter of the electrode active material exceeds 5 μm, when used at a high-speed charge / discharge rate of 10 C or more, the battery discharge capacity may be significantly reduced.

  Here, the average particle diameter is a number average particle diameter measured by various particle size distribution measuring apparatuses using a transmission method or a scattering method, and specifically, an optical measurement method such as a laser diffraction scattering method. Or the average particle diameter measured by an image analysis method of an electron microscope or the like.

The conductive auxiliary agent is used to increase the output of the lithium ion battery, and a carbon-based conductive auxiliary agent is preferably used.
For example, carbon black, acetylene black, ketjen black, natural graphite, artificial graphite and the like are preferably used as the particles having a particle size of less than 50 nm and the particles having a particle size of 50 nm or more. For these particles having a particle size of less than 50 nm and particles having a particle size of 50 nm or more, two different types of conductive assistants can be used. In addition, by using only particles having a particle size of less than 50 nm, and dispersing and aggregating the particles, particles having a particle size of less than 50 nm and particles having a particle size of 50 nm or more are preferably used.

  Moreover, as a particle | grain with an aspect ratio of 3 or more which comprises a conductive support agent, a carbon nanotube, carbon fiber, etc. are used suitably, for example.

  Particles having a particle size of less than 50 nm constituting the conductive auxiliary agent are adsorbed on the surface of the electrode active material, forming an active point (three-phase interface) between the electrode active material and the electrolytic solution, and lithium ions and electrons. Give and receive. In order to exchange lithium ions and electrons at a high speed charge / discharge rate, it is effective to have a large number of active sites. Therefore, if the conductive auxiliary agent is a particle having a particle size of less than 50 nm, a large number of active points can be formed.

  Particles having a particle diameter of 50 nm or more or particles having an aspect ratio of 3 or more constituting the conductive auxiliary agent form a conductive path between the electrode active materials and between the electrode active material and the current collector.

  The content of particles having a particle size of less than 50 nm with respect to the electrode active material is appropriately adjusted so as to sufficiently form the above active sites, but the particles having a particle size of less than 50 nm with respect to 100 parts by weight of the electrode active material. Is preferably contained in a proportion of 2 parts by weight or more and 30 parts by weight or less, and more preferably 5 parts by weight or more and 15 parts by weight or less. The reason why the content of particles having a particle diameter of less than 50 nm with respect to 100 parts by weight of the electrode active material is 2 parts by weight or more and 30 parts by weight or less is that the content of particles having a particle diameter of less than 50 nm is less than 2 parts by weight. An active point sufficient for charging cannot be formed. On the other hand, when the content of particles having a particle size of less than 50 nm exceeds 30 parts by weight, the ratio of the electrode active material becomes small, so that the battery has a small capacity.

  The content of the particles having a particle size of 50 nm or more with respect to the electrode active material is appropriately adjusted so as to sufficiently form the above-described conductive path, but the particles having a particle size of 50 nm or more with respect to 100 parts by weight of the electrode active material. Is preferably contained in a proportion of 1 part by weight or more and 30 parts by weight or less, more preferably 1 part by weight or more and 15 parts by weight or less. The reason why the content of particles having a particle size of 50 nm or more with respect to 100 parts by weight of the electrode active material is 1 part by weight or more and 30 parts by weight or less is that the content of particles having a particle size of 50 nm or more is less than 1 part by weight. A conductive path sufficient for charging cannot be formed. On the other hand, when the content of particles having a particle size of 50 nm or more exceeds 30 parts by weight, the ratio of the electrode active material becomes small, resulting in a battery having a small capacity.

  The content of the particles having an aspect ratio of 3 or more with respect to the electrode active material is appropriately adjusted so as to sufficiently form the above conductive path. However, the particles having an aspect ratio of 3 or more with respect to 100 parts by weight of the electrode active material. Is preferably contained in a proportion of 1 part by weight or more and 30 parts by weight or less, more preferably 1 part by weight or more and 15 parts by weight or less. The reason why the content of particles having an aspect ratio of 3 or more with respect to 100 parts by weight of the electrode active material is 1 part by weight or more and 30 parts by weight or less is that the content of particles having an aspect ratio of 3 or more is less than 1 part by weight. A conductive path sufficient for charging cannot be formed. On the other hand, when the content of particles having an aspect ratio of 3 or more exceeds 30 parts by weight, the ratio of the electrode active material becomes small, so that a battery with a small capacity is obtained.

  The compounding ratio of particles having a particle size of less than 50 nm to particles having a particle size of 50 nm or more and / or particles having an aspect ratio of 3 or more is a particle having a particle size of less than 50 nm: particles having a particle size of 50 nm or more and / or Particles with an aspect ratio of 3 or more = 5% by weight: 95% by weight or more and 95% by weight: 5% by weight or less, particles having a particle size of less than 50 nm: particles having a particle size of 50 nm or more and / or an aspect ratio of 3 The above particles = 15 wt%: 85 wt% or more and 95 wt%: 5 wt% or less are more preferable. The blending ratio of particles having a particle size of less than 50 nm, particles having a particle size of 50 nm or more and / or particles having an aspect ratio of 3 or more was set to 5 wt%: 95 wt% or more and 95 wt%: 5 wt% or less. The reason is that when the blending ratio of the particles having a particle size of less than 50 nm is less than 5% by weight, there is no conductive auxiliary agent that can form a sufficient active site, so that the decrease in capacity at a charge / discharge rate of 10 C or more is suppressed. Can not do it. On the other hand, when the blending ratio of particles having a particle size of less than 50 nm exceeds 95% by weight, the number of particles is reduced because a conductive path is formed, and the reduction in capacity at a charge / discharge rate of 10 C or more cannot be improved.

  The compounding ratio of the particles having a particle size of 50 nm or more and the particles having an aspect ratio of 3 or more is: particles having a particle size of 50 nm or more: particles having an aspect ratio of 3 or more = 0 wt%: 100 wt% to 100 wt%: In the range of 0% by weight, the above-mentioned conductive path is appropriately adjusted in consideration of the particle size and aspect ratio of the particles.

  Here, the reason why at least one of the particles constituting the conductive additive is a particle having a particle size of less than 50 nm is that the particles having a particle size of more than 50 nm are sufficient for charging and discharging at a charge / discharge rate of 10 C or more. This is because a number of active points cannot be formed on the surface of the electrode active material.

  In addition, among the particles constituting the conductive assistant, the particles other than the particles having a particle size of less than 50 nm are particles having a particle size of 50 nm or more and / or particles having an aspect ratio of 3 or more. The particles having an aspect ratio of less than 3 float on the surface of the electrode coating film due to convection generated in the electrode coating film until the electrode forming slurry is dried to form the electrode coating film. This is because the conductive auxiliary agent is unevenly distributed in the electrode coating film and the conductive path is interrupted.

  As the binder, organic binders such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) are suitable. Used for.

  The content of the binder with respect to the electrode active material is appropriately adjusted according to the strength of the desired electrode coating film, but the ratio of the binder is 1 part by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the electrode active material. Preferably, it is contained in a proportion of 3 parts by weight or more and 15 parts by weight or less. The reason why the binder content relative to 100 parts by weight of the electrode active material is 1 part by weight or more and 20 parts by weight or less is that when the binder content is less than 1 part by weight, it is difficult to adhere the electrode coating to the current collector. Become. On the other hand, if the content of the binder exceeds 20 parts by weight, the ratio of the electrode active material is decreased, so that not only the electrode has a small capacity but also the binder is insulative, so that the resistance of the electrode is increased and the battery is May not work.

  Examples of the polar solvent include organic solvents that can dissolve and disperse the electrode active material, the conductive additive, and the binder, such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, trimethyl phosphate, methyl ethyl ketone, and tetrahydrofuran.

  The content of the polar solvent with respect to the total amount of the electrode active material, conductive additive and binder is appropriately adjusted according to the viscosity of the electrode forming slurry of the desired lithium ion battery, but the electrode active material, conductive aid and binder It is preferable that the polar solvent is blended in a proportion of 20 parts by weight or more and 80 parts by weight or less, more preferably 30 parts by weight or more and 70 parts by weight or less, with respect to 100 parts by weight of the total amount. preferable. The reason for setting the content of the polar solvent to 20 parts by weight or more and 80 parts by weight or less with respect to 100 parts by weight of the total amount of the electrode active material, the conductive additive and the binder is that if the content of the polar solvent is less than 20 parts by weight, If the ratio is too high, the viscosity of the electrode forming slurry becomes high, and it becomes difficult to apply the electrode forming slurry to the current collector. On the other hand, when the content of the polar solvent exceeds 80 parts by weight, the ratio of the solid content is too low, and it becomes difficult to form an electrode coating film having a sufficient thickness.

  When preparing the slurry for electrode formation of the lithium ion battery of the present invention, a normal dispersion and mixing method can be used, but an electrode active material, a conductive additive, a binder, and a polar solvent are placed in a container of a medium stirring type dispersion device. , The amount of electrode active material, conductive additive, binder, polar solvent, and medium particles are adjusted so that the number of medium particles in 1 ml of slurry is 3500 or more. It is desirable to use a method of stirring and dispersing.

  Usually, in order to prepare the slurry for electrode formation, an electrode active material, a conductive support agent, a binder, and a polar solvent are mixed using a ball mill, a stirring mixer, or the like. However, in this method, since a large shear stress is not applied to the electrode active material and the conductive auxiliary agent, the conductive auxiliary agent is not sufficiently dispersed, and particles having a particle diameter of less than 50 nm constituting the conductive auxiliary agent are sufficiently dispersed. It is difficult. Therefore, in the present invention, it is desirable to use a medium stirring type dispersing device that is often used as a pigment dispersing device for dispersing the conductive additive.

  This medium agitating type dispersing apparatus is composed of an electrode active material, a conductive additive, a binder and a polar solvent (these are collectively referred to as a material to be dispersed) and a large number of medium particles in a container. By stirring at a high speed, the medium particles flow at a high speed, and when the medium particles collide with each other, the electrode active material and the conductive auxiliary agent are trapped between the medium particles, and are dispersed by receiving impact and shearing action due to the collision. Is. Examples of the medium stirring type dispersing device include a sand mill, a paint shaker, an attritor, a planetary ball mill, and a vibration ball mill. Among these, a sand mill capable of stirring medium particles at high speed is preferable.

In this medium stirring type dispersing apparatus, the ultimate dispersed particle diameter and the dispersion time depend on the number N of medium particles per slurry volume made of the material to be dispersed.
Here, the number N of medium particles can be calculated by the following equation (1).

However, in Formula (1), Vm represents the apparent volume (cm ³ ) of the medium particles, Dm represents the diameter (cm) of the medium particles, and Vs represents the volume (ml) of the slurry to be dispersed.

  Examples of the medium particles include glass beads, alumina beads, zirconia beads, zircon beads, and titania beads. The diameter of the medium particles is not particularly limited as long as the number of media per unit volume of the electrode forming slurry can be obtained. If the diameter of the medium particles is small, the number of medium particles can be increased with a smaller amount of medium particles used. Therefore, the smaller the particle diameter of the medium, the better.

  However, if the medium particle diameter is too small, the size of the surface area of the medium particles cannot be ignored, and the fluidity decreases. Therefore, in order to obtain the desired fluidity, it is necessary to increase the amount of the polar solvent, but since the amount of the material to be dispersed, which is relatively solid, decreases, there arises a problem that the production efficiency deteriorates. . Moreover, since the mass of one medium particle becomes light, the impact and shear force become small and the problem that a dispersion force falls arises. Accordingly, the diameter of the medium particles is preferably 10 μm or more and 1 mm or less.

  As a method for producing a slurry for forming an electrode of a lithium ion battery using this medium stirring type dispersing device, usually, an electrode active material, a conductive additive, a binder, and a polar solvent are mixed in advance and then dispersed using a medium stirring and dispersing device. However, the electrode active material and the conductive additive may be separately dispersed until a predetermined particle size is obtained, and then mixed.

  Further, by a dispersion method using the above-mentioned medium agitation type dispersion device, particles having a particle size of less than 50 nm and particles having a particle size of 50 nm or more and / or particles having an aspect ratio of 3 or more constituting the conductive auxiliary agent. However, only particles having a particle size of less than 50 nm may be dispersed by the dispersion method using the above-mentioned medium stirring type dispersing device, and particles having a particle size of 50 nm or more and / or particles having an aspect ratio of 3 or more. May be dispersed by a conventional dispersion method.

In addition, the slurry for electrode formation of the lithium ion battery of the present invention is applied to a current collector by a usual coating method such as a roll coater, a die coater, a bar coater, an applicator, and then dried to form an electrode coating film. Thus, an electrode of a lithium ion battery can be obtained. In general, a negative electrode is obtained if a copper current collector is used, and a positive electrode is obtained if an aluminum current collector is used.
Here, FIG. 1 shows a slurry for forming an electrode of a lithium ion battery comprising an electrode active material 1, a conductive assistant 2 having a particle size of less than 50 nm, and a conductive assistant 3 having a particle size of 50 nm or more. It is a conceptual diagram which shows the electrode coating film formed by drying after apply | coating to 4. FIG.
FIG. 2 also shows a slurry for forming an electrode for a lithium ion battery comprising an electrode active material 1, a conductive assistant 2 having a particle size of less than 50 nm, and a conductive assistant 5 having an aspect ratio of 3 or more. It is a conceptual diagram which shows the electrode coating film formed by drying after apply | coating to.

By using both the negative electrode and the positive electrode, or either the negative electrode or the positive electrode, the lithium ion battery of the present invention can be obtained.
The lithium battery is not particularly limited in terms of electrolyte, separator, and battery shape.
In this lithium battery, both the negative electrode and the positive electrode, or either the negative electrode or the positive electrode has high filling property and high purity, and has a sufficient active point on the surface of the electrode active material. Since it is formed by the electrode material obtained by the present invention having a sufficient conductive path between the electrode active materials and between the electrode active material and the current collector, it does not depend on the temperature environment and is highly charged. It has a discharge capacity and stable charge / discharge cycle performance, and achieves high output.

EXAMPLES Hereinafter, although this invention is demonstrated concretely by Examples 1-3 and Comparative Examples 1 and 2, this invention is not limited by these Examples.
For example, in this example, only LiFePO ₄ was used as the electrode active material, but the present invention is not limited to this, and other positive electrode active materials and negative electrode active materials may be used as the electrode active material. Good.
In this example, in order to reflect the behavior of the electrode material itself in the data, metal Li was used for the negative electrode. However, a negative electrode material such as a carbon material, a Li alloy, or Li ₄ Ti ₅ O ₁₂ may be used. . A solid electrolyte may be used instead of the electrolytic solution and the separator.

"Example 1"
As a positive electrode active material, 85 parts by weight of LiFePO ₄ (ultrafine particle LiFePO ₄ , NP-1, manufactured by Sumitomo Osaka Cement), 5 parts by weight of carbon black (manufactured by Degussa) with an average primary particle size of 11 nm, polyvinylidene fluoride (PVdF, Kureha) 5 parts by weight of Chemical Co., Ltd. and 71.25 parts by weight of 1-methyl-2-pyrrolidone (NMP) were mixed to obtain a mixture.
The mixture was dispersed for 1 hour using a zirconia bead having a diameter of 0.25 mm as a medium particle and using a sand mill at a disc rotating peripheral speed of 10 m / sec.
Next, 5 parts by weight of acetylene black (DENKA BLACK, manufactured by Denki Kagaku Kogyo Co., Ltd.) having an average primary particle size of 35 nm is mixed with this mixture and mixed for 30 minutes at a disk rotational peripheral speed of 6 m / sec. A material slurry was obtained.
Thereafter, when the obtained positive electrode active material slurry was observed with a scanning electron microscope (SEM), most of the carbon black having an average primary particle size of 11 nm was dispersed as particles having an average particle size of about 20 nm. Most of acetylene black having an average primary particle size of 35 nm was dispersed as particles having an average particle size of about 120 nm.

"Example 2"
The same as Example 1 except that 5 parts by weight of single wall carbon nanotubes (manufactured by Carbon Nanotechnologies Inc.) having a minor axis of 5 nm, a major axis of 1500 nm, and an aspect ratio of 300 were used instead of 5 parts by weight of acetylene black having an average primary particle size of 35 nm. Thus, a positive electrode active material slurry was obtained.
Thereafter, when the obtained positive electrode active material slurry was observed with a scanning electron microscope (SEM), most of the carbon black having an average primary particle size of 11 nm was dispersed as particles having an average particle size of about 20 nm.

"Example 3"
Example 1 except that 5 parts by weight of carbon fiber (VG-CF, Showa Denko KK) having a minor axis of 15 nm, a major axis of 150 nm, and an aspect ratio of 10 was used instead of 5 parts by weight of acetylene black having an average primary particle size of 35 nm. Similarly, a positive electrode active material slurry was obtained.
Thereafter, when the obtained positive electrode active material slurry was observed with a scanning electron microscope (SEM), most of the carbon black having an average primary particle size of 11 nm was dispersed as particles having an average particle size of about 20 nm.

Example 4
Instead of 5 parts by weight of acetylene black having an average primary particle size of 35 nm, 2.5 parts by weight of acetylene black having an average primary particle size of 35 nm, single wall carbon nanotubes having a short diameter of 5 nm, a long diameter of 1500 nm and an aspect ratio (manufactured by Carbon Nanotechnologies Inc.). ) A positive electrode active material slurry was obtained in the same manner as in Example 1 except that 2.5 parts by weight were used.
Thereafter, when the obtained positive electrode active material slurry was observed with a scanning electron microscope (SEM), most of the carbon black having an average primary particle size of 11 nm was dispersed as particles having an average particle size of about 20 nm. Most of acetylene black having an average primary particle size of 35 nm was dispersed as particles having an average particle size of about 120 nm.

“Comparative Example 1”
As a positive electrode active material, 85 parts by weight of LiFePO ₄ (ultrafine particle LiFePO ₄ , NP-1, manufactured by Sumitomo Osaka Cement), 10 parts by weight of carbon black (manufactured by Degussa) with an average primary particle size of 11 nm, polyvinylidene fluoride (PVdF, Kureha) 5 parts by weight of Chemical Co., Ltd. and 71.25 parts by weight of 1-methyl-2-pyrrolidone (NMP) were mixed to obtain a mixture.
For this mixture, zirconia beads having a diameter of 0.25 mm were used as medium particles, and dispersion was performed for 1 hour at a disk rotating peripheral speed of 10 m / sec using a sand mill, to obtain a positive electrode active material slurry. .
Thereafter, when the obtained positive electrode active material slurry was observed with a scanning electron microscope (SEM), most of the carbon black having an average primary particle size of 11 nm was dispersed as particles having an average particle size of about 20 nm.

"Comparative Example 2"
A positive electrode active material slurry was obtained in the same manner as in Comparative Example 1 except that 10 parts by weight of acetylene black (Denka Black, Denki Kagaku Kogyo Co., Ltd.) having an average primary particle size of 35 nm was used instead of 10 parts by weight of carbon black. .
Thereafter, when the obtained positive electrode active material slurry was observed with a scanning electron microscope (SEM), most of the acetylene black having an average primary particle size of 35 nm was dispersed as particles having an average particle size of about 120 nm.

“Production of lithium-ion batteries”
The positive electrode active material slurry obtained in Example 1 was applied onto an aluminum (Al) foil having a thickness of 30 μm, then vacuum-dried using a vacuum dryer, and then pressure-bonded to form a positive electrode (positive electrode ).
Subsequently, the lithium ion battery of Example 1 was produced using the 2016 coin type cell made from stainless steel (SUS) in dry Ar atmosphere.
Metal Li was used for the negative electrode, a porous polypropylene film was used for the separator, and a 1 mol / L LiPF ₆ solution was used for the electrolyte solution. As a solvent for this LiPF ₆ solution, a solvent having a ratio of ethylene carbonate to diethyl carbonate of 1: 1 was used.

  Further, each of the positive electrode active material slurries of Examples 2 to 4 and Comparative Examples 1 and 2 was used, and the lithium ion batteries of Examples 2 to 4 and Comparative Examples 1 and 2 were exactly the same as the lithium ion battery of Example 1. Was made.

"Battery charge / discharge test"
The charge / discharge test of each lithium ion battery in Examples 1 to 4 and Comparative Examples 1 and 2 was performed.
Here, the cut-off voltage was changed from 2 to 4.5 V, the charge / discharge rate was changed in the range of 0.1 C to 50 C, and the environmental temperature of the test was 25 ° C. (room temperature).
The charge / discharge test results of the lithium ion batteries of Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1 and FIG.
Here, the ratio of the discharge capacity at 30 C to the discharge capacity at 1 C was defined as output performance.

  According to the above results, in the lithium ion batteries of Examples 1 to 4, compared with the lithium ion batteries of Comparative Examples 1 and 2, over the range of the low speed charge / discharge rate of 0.1C to the high speed charge / discharge rate of 50C, It was found that both the discharge capacity and the output performance are excellent, and it is possible to achieve a high output while maintaining a high energy density. In particular, it has been found that there is little reduction in discharge capacity even at a high-speed charge / discharge rate of 10 C or higher.

  Since the slurry for electrode formation of the lithium ion battery of the present invention contains an electrode active material, a conductive assistant, a binder and a polar solvent, and the conductive assistant is composed of two or more kinds of particles having different particle sizes or shapes, the slurry is 10C or more. It is possible to produce a lithium-ion battery with little reduction in discharge capacity even at a high-speed charge / discharge rate, and it is possible to achieve high output while maintaining the high energy density that is characteristic of lithium-ion batteries. In addition, it can also be applied to fields such as power sources for mobile bodies such as electric vehicles and hybrid vehicles that require high output, power sources such as electric tools, and load leveling applications for power generation facilities. The effect is very large.

It is a conceptual diagram which shows an example of the electrode coating film formed using the slurry for electrode formation of the lithium ion battery of this invention. It is a conceptual diagram which shows the other example of the electrode coating film formed using the slurry for electrode formation of the lithium ion battery of this invention. It is a graph which shows the charging / discharging test result of a lithium ion battery. It is a conceptual diagram which shows an example of the electrode coating film formed using the slurry for electrode formation of the conventional lithium ion battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode active material 2 Conductive auxiliary agent with a particle size of less than 50 nm 3 Conductive auxiliary agent with a particle size of 50 nm or more 4 Current collector 5 Conductive auxiliary agent with an aspect ratio of 3 or more

Claims (5)

A slurry for forming an electrode of a lithium ion battery comprising an electrode active material, a conductive additive, a binder and a polar solvent,
2. The electrode forming slurry for a lithium ion battery, wherein the conductive auxiliary agent comprises two or more kinds of particles having different particle sizes or shapes.   2. The slurry for forming an electrode of a lithium ion battery according to claim 1, wherein at least one of the particles has a particle size of less than 50 nm, and the other particles have a particle size of 50 nm or more.   The slurry for forming an electrode of a lithium ion battery according to claim 1, wherein at least one of the particles has an aspect ratio of 3 or more.   The slurry for forming an electrode of a lithium ion battery according to any one of claims 1 to 3, wherein at least one of the particles is a secondary particle formed by aggregating primary particles. A lithium ion battery comprising an electrode using the slurry for forming an electrode for a lithium ion battery according to claim 1.

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