JP7007944B2 - Positive electrode for lithium-ion batteries and lithium-ion batteries - Google Patents

Description

The present invention relates to a positive electrode for a lithium ion battery and a lithium ion battery.

In recent years, there has been an urgent need to reduce carbon dioxide emissions in order to protect the environment. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and the development of secondary batteries for driving motors, which hold the key to their practical application, is earnest. It is done. As a secondary battery, a lithium ion battery that can achieve high energy density and high output density is attracting attention.

In a lithium ion battery, an electrode is generally formed by applying a positive electrode or a negative electrode active material or the like to a positive electrode or negative electrode current collector using a binder. In the case of a bipolar battery, a positive electrode active material or the like is applied to one surface of the current collector using a binder to form a positive electrode layer, and a binder is used to apply a negative electrode active material to the opposite surface. Etc. are applied to form a bipolar (bipolar) type electrode having a negative electrode layer.

In such a lithium ion battery, a metal foil (metal collector foil) has been conventionally used as a current collector. In recent years, a so-called resin current collector has been proposed, which is composed of a resin to which a conductive material is added instead of a metal foil. Such a resin current collector is lighter than a metal current collector foil, and is expected to improve the output per unit weight of the battery.

Patent Document 1 discloses a dispersant for a resin collector, a material for a resin collector containing a resin and a conductive filler, and a resin collector having the material for the resin collector.

International Publication No. 2015/005116

When a resin current collector as described in Patent Document 1 is used as a positive electrode side resin current collector (positive electrode current collector) in a lithium ion battery, the outer peripheral portion of the positive electrode current collector is used as a negative electrode via a separator. May be in close proximity to active material. When the positive electrode current collector is close to the negative electrode active material without passing through the positive electrode active material, the current may be concentrated in that portion and flow. Such a current is a current that was not initially expected and causes deterioration of the resin current collector.
Therefore, there has been a demand for a means capable of preventing deterioration of the resin current collector when the resin current collector is used.

Based on the above situation, it is an object of the present invention to provide a positive electrode for a lithium ion battery, which is provided with a resin current collector and in which deterioration of the resin current collector is unlikely to occur. Another object of the present invention is to provide a lithium ion battery using the positive electrode for a lithium ion battery.

The present inventors have come up with the present invention as a result of diligent studies to solve the above problems.
That is, the present invention is a positive electrode for a lithium ion battery including a positive electrode active material layer containing a positive electrode active material and a resin current collector in contact with the positive electrode active material layer, wherein the resin current collector is a polyolefin resin and It contains a first conductive resin layer (BX1) and a second conductive resin layer (BX2) made of a resin composition containing a conductive carbon filler, and is included in the first conductive resin layer (BX1). The specific surface area of the first conductive carbon filler (B1) is larger than the specific surface area of the second conductive carbon filler (B2) contained in the second conductive resin layer (BX2), and the specific surface area of the first conductive carbon filler (B2) is larger than that of the first conductive carbon filler (B2). The specific surface area of the conductive carbon filler (B1) is 30 to 800 m ² / g, and the first conductive resin layer (BX1) of the resin collector is arranged on the side in contact with the positive electrode active material layer. A positive electrode for a lithium ion battery; the positive electrode for a lithium ion battery of the present invention is provided.

The positive electrode for a lithium ion battery of the present invention is provided with a resin collector and is a positive electrode for a lithium ion battery in which deterioration of the resin collector is unlikely to occur.

The positive electrode for a lithium ion battery of the present invention is a positive electrode for a lithium ion battery including a positive electrode active material layer containing a positive electrode active material and a resin current collector in contact with the positive electrode active material layer.
The resin collector includes a first conductive resin layer (BX1) and a second conductive resin layer (BX2) made of a resin composition containing a polyolefin resin and a conductive carbon filler.
The specific surface area of the first conductive carbon filler (B1) contained in the first conductive resin layer (BX1) is the specific surface area of the second conductive carbon filler contained in the second conductive resin layer (BX2). It is larger than the specific surface area of (B2), and the specific surface area of the first conductive carbon filler (B1) is 30 to 800 m ² / g.
The first conductive resin layer (BX1) of the resin current collector is arranged on the side in contact with the positive electrode active material layer.

The positive electrode for a lithium ion battery of the present invention contains a resin current collector, and a first conductive resin layer (BX1) containing a first conductive carbon filler (B1) having a large specific surface area is in contact with a positive electrode active material layer. It is placed on the side. Since the first conductive resin layer (BX1) contains the first conductive carbon filler (B1) having a large specific surface area, it has a small resistance and can perform a function similar to that of the resistance reducing layer. Then, even when the resin current collector as the positive electrode current collector is close to the negative electrode active material without passing through the positive electrode active material, the current is not in the thickness direction of the resin current collector but the first conductive resin. It becomes easy to flow in the surface direction of the layer (BX1), and a large current is prevented from flowing in the resin current collector. Therefore, deterioration of the resin current collector is less likely to occur.

The positive electrode for a lithium ion battery of the present invention includes a positive electrode active material layer containing a positive electrode active material and a resin current collector in contact with the positive electrode active material layer.
First, the resin collector contained in the positive electrode for a lithium ion battery of the present invention will be described.

The resin current collector of the present invention includes a plurality of conductive resin layers.
Each conductive resin layer comprises a resin composition containing a polyolefin resin and a conductive carbon filler.
The resin current collector includes a first conductive resin layer (BX1) and a second conductive resin layer (BX2). The resin current collector contains at least two layers of a first conductive resin layer (BX1) and a second conductive resin layer (BX2), but has a configuration of three or more layers including another conductive resin layer. There may be.
In the present specification, a resin current collector including two conductive resin layers, a first conductive resin layer (BX1) and a second conductive resin layer (BX2), will be described below.

The first conductive resin layer (BX1) and the second conductive resin layer (BX2) are both resin compositions containing a polyolefin resin and a conductive carbon filler, but the ratio to each conductive resin layer is Contains conductive carbon fillers with different surface areas.
Specifically, the first conductive resin layer (BX1) contains the first conductive carbon filler (B1), and the second conductive resin layer (BX2) contains the second conductive. Contains carbon filler (B2). The specific surface area of the first conductive carbon filler (B1) is larger than that of the second conductive carbon filler (B2).
That is, when there is a resin current collector composed of two conductive resin layers containing a polyolefin resin and a conductive carbon filler, a conductive resin composed of a resin composition containing a conductive carbon filler having a relatively large specific surface area. The layer is defined as a first conductive resin layer (BX1), and the conductive resin layer made of a resin composition containing a conductive carbon filler having a relatively small specific surface area is defined as a second conductive resin layer (BX2). be able to.

The specific surface area of the conductive carbon filler in the present specification is a value measured as a BET specific surface area according to "Method for measuring the specific surface area of powder (solid) by adsorbing JIS Z8830 gas".

When the first conductive resin layer (BX1) or the second conductive resin layer (BX2) contains two or more kinds of conductive carbon fillers, the first conductive resin layer (BX1) contains the most. As a representative value, the specific surface area of the type of conductive carbon filler contained most in the second conductive resin layer (BX2) is used as a representative value, and the specific surface area of the type of conductive carbon filler contained most in the second conductive resin layer (BX2) is used as a representative value. Compare the representative values of the specific surface area of.
As a result of comparison, the conductive resin layer containing the conductive carbon filler having a large specific surface area becomes the first conductive resin layer (BX1).

Both the first conductive resin layer (BX1) and the second conductive resin layer (BX2) contain a polyolefin resin.
The polyolefin resin may be the same resin or different resins in the first conductive resin layer (BX1) and the second conductive resin layer (BX2).

Preferred examples of the polyolefin resin include polyolefins [polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), etc.]. More preferably, it is polyethylene (PE), polypropylene (PP) and polymethylpentene (PMP).
Further, it may be a modified product (hereinafter referred to as modified polyolefin) or a mixture of these polyolefin resins.
As the polyolefin resin, for example, the following are available from the market.
PE: "Novatec LL UE320""Novatec LL UJ960" All made by Nippon Polyethylene Co., Ltd. PP: "SunAllomer PM854X""SunAllomerPC684S""SunAllomerPL500A""SunAllomerPC630S""SunAllomerPC630A""SunAllomerPB522M""SunAllomerCM688" All made by SunAllomer Ltd., "Prime Polymer J-2000GP" made by Prime Polymer Co., Ltd., "Wintech WFX4T" made by Nippon Polypro Co., Ltd. PMP: "TPX" made by Mitsui Chemicals Co., Ltd.

Examples of the modified polyolefin include polyethylene, polypropylene or a copolymer thereof in which a polar functional group is introduced, and examples of the polar functional group include a carboxyl group, a 1,3-dioxo-2-oxapropylene group and a hydroxyl group. Examples thereof include an amino group, an amide group and an imide group.

As an example of modified polyolefin in which a polar functional group is introduced into polyethylene, polypropylene or a copolymer thereof, Admer series manufactured by Mitsui Chemicals, Inc. and the like are commercially available.

The first conductive carbon filler (B1) contained in the first conductive resin layer (BX1) is a conductive carbon filler having a specific surface area of 30 to 800 m ² / g.

Examples of the first conductive carbon filler (B1) include, but are not limited to, carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.) and the like. Of these, acetylene black is preferred.

The first conductive carbon filler (B1) available on the market is the trade name "Denka Black (69m ² / g)""Denka Black Li-400 (39m ² / g)" [manufactured by Denka Co., Ltd. ], Product name "Ensako 250G granular (68m ² / g)" [manufactured by Imerys], product name "EC300J (800m ² / g)" [manufactured by Lion Co., Ltd.] and the like.
The value described in parentheses after the product name is the specific surface area of the filler.

Further, it is preferable that the volume average particle diameter of the first conductive carbon filler (B1) is 3 to 500 nm.
In the present specification, the volume average particle size of the conductive carbon filler means the particle size (Dv50) at an integrated value of 50% in the particle size distribution obtained by the microtrack method (laser diffraction / scattering method). The microtrack method is a method for obtaining a particle size distribution using scattered light obtained by irradiating particles with laser light. A microtrack manufactured by Nikkiso Co., Ltd. can be used for measuring the volume average particle size.

The first conductive carbon filler (B1) may contain two or more types of conductive carbon fillers having different types, specific surface areas, or volume average particle diameters.

Further, it is preferable that the total surface area of the first conductive carbon filler (B1) contained in 1 g of the first conductive resin layer (BX1) is 10 to 100 m ² .
In the present specification, the total surface area of the conductive carbon filler contained in 1 g of the conductive resin layer is calculated by the following formula.
Total surface area (m ² ) of the conductive carbon filler contained in 1 g of the conductive resin layer
= Weight of conductive carbon filler in 1 g of conductive resin layer (g) x Specific surface area of conductive carbon filler (m ² / g)

The weight ratio of the first conductive carbon filler (B1) in the first conductive resin layer (BX1) is preferably 10 to 30% by weight.
The weight ratio of the polyolefin resin in the first conductive resin layer (BX1) is preferably 70 to 90% by weight.

As the conductive carbon filler, the conductive resin layer containing the first conductive carbon filler (B1) (for example, acetylene black) having a large specific surface area and a small volume average particle diameter often has good moldability. Therefore, by using a resin current collector using the first conductive resin layer (BX1) having good moldability, it is possible to obtain a resin current collector whose overall shape is maintained.

The second conductive carbon filler (B2) contained in the second conductive resin layer (BX2) is preferably a conductive carbon filler having a specific surface area of 10 m ² / g or less.
Further, it is more preferable that the specific surface area of the second conductive carbon filler (B2) is 0.1 m ² / g or more.
In order for the specific surface area of the second conductive carbon filler (B2) to be 10 m ² / g or less, it is preferable that the volume average particle size of the conductive carbon filler is 5.0 μm or more.

Examples of the second conductive carbon filler (B2) include, but are not limited to, natural or artificial graphite (graphite) and hard carbon (non-graphitized carbon) and mixtures thereof. Of these, graphite is preferred. The shape may be spherical, scaly or lumpy, but spherical is preferable.

The products available on the market as the second conductive carbon filler (B2) are the trade names "UP20N (3.33m ² / g)", "CGB20 (4.72m ² / g)" and "CPB (6.95m ² )". / G) ”[manufactured by Nippon Graphite Industry Co., Ltd.]“ SG-BH (4.84 m ^{2 / g) ”“ SG-BL30 (4.28 m 2 / g) ”“ SG-BL40 (3.19 m 2 / g} ) ) "" RP99-150 (5.13m ² / g) "" PC99-300M (3.87m ² / g) "" SRP-150 (5.61m ² / g) "" PC-30 (6.04m ² ) / G) "[Both manufactured by Ito Graphite Industry Co., Ltd.], Product name" SNG-WXA1 (1.8m ² / g) "" SNG-P1A1 (0.6m ² / g) "[Both are JFE chemicals ( Made by Co., Ltd.] and the like.
The value described in parentheses after the product name is the specific surface area of the filler.

Further, it is preferable that the volume average particle diameter of the second conductive carbon filler (B2) is 5.0 to 11.5 μm.

The second conductive carbon filler (B2) may contain two or more types of conductive carbon fillers having different types, specific surface areas, or volume average particle diameters.

Further, it is preferable that the total surface area of the second conductive carbon filler (B2) contained in 1 g of the second conductive resin layer (BX2) is 0.2 to 8 m ² .

The weight ratio of the second conductive carbon filler (B2) in the second conductive resin layer (BX2) is preferably 30 to 50% by weight.
The weight ratio of the polyolefin resin in the second conductive resin layer (BX2) is preferably 50 to 70% by weight.

Here, the first conductive resin layer (BX1) contains the first conductive carbon filler (B1) having a large specific surface area, and the electrolytic solution easily permeates into such a conductive resin layer. If the amount of the electrolytic solution infiltrated is large, a phenomenon called "liquid bleeding" in which the electrolytic solution exudes from the resin current collector may occur, which is not preferable.
Here, the amount of the electrolytic solution permeated into the second conductive resin layer (BX2) containing the second conductive carbon filler (B2) (for example, graphite) having a small specific surface area and a large volume average particle diameter is large. Since the amount is small, the occurrence of liquid bleeding is suppressed by using a resin current collector that also uses the second conductive resin layer (BX2).

The weight ratio of the first conductive carbon filler (B1) and the second conductive carbon filler (B2) contained in the resin collector is [1st conductive carbon filler (B1) / 2nd conductive]. Sex carbon filler (B2)] = 0.12 to 0.80 is preferable.
When the above ratio is 0.12 or more, the ratio of the second conductive carbon filler (B2) having a small specific surface area and relatively low conductivity in the entire resin collector is not too large, so that the resin collection is performed. The amount of filler required to reduce the electric resistance value of the electric body can be reduced, and the thinning of the resin current collector becomes easier.
When the ratio is 0.80 or less, the ratio of the first conductive carbon filler (B1) having a large specific surface area does not become too large in the entire resin current collector, so that liquid bleeding is less likely to occur.

The total weight ratio of the first conductive carbon filler (B1) and the second conductive carbon filler (B2) contained in the resin collector is 20 to 40% by weight with respect to the weight of the resin collector. It is preferable to have.
When the weight ratio is 20% by weight or more, the amount of the conductive carbon filler contained in the entire resin collector is sufficient, so that the electric resistance value can be further lowered. Further, when the weight ratio is 40% by weight or less, the ratio of the polyolefin resin contained in the entire resin current collector does not become too low, so that the influence on the moldability of the resin current collector is small and the resin current collector is not affected. It is more suitable for thinning the body.

The proportion of the polyolefin resin contained in the resin current collector is preferably 60 to 80% by weight. The ratio of the polyolefin resin contained in the resin collector is the ratio of the polyolefin resin to the total weight of the resin collector.
When the proportion of the polyolefin resin is in the above range, the moldability is good and it is suitable for thinning the entire resin current collector.

The conductive resin layer may contain a conductive material different from the conductive carbon filler.
Examples of the material of the conductive material include metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.], alloys thereof, and mixtures thereof. From the viewpoint of electrical stability, nickel is preferable.
Further, as the conductive material, a conductive material (a metal among the above-mentioned conductive materials) may be coated around a particle-based ceramic material or a resin material by plating or the like.

In addition to the polyolefin resin and the conductive carbon filler, the conductive resin layer contains other components [dispersant for conductive material, colorant, ultraviolet absorber, general-purpose plasticizer (containing phthalic acid skeleton), if necessary. Compounds, trimellitic acid skeleton-containing compounds, phosphate group-containing compounds, epoxy skeleton-containing compounds, etc.)] and the like may be appropriately contained. From the viewpoint of electrical stability, the total amount of the other components added is preferably 0.001 to 5 parts by weight, more preferably 0.001 to 3 parts by weight, based on 100 parts by weight of each conductive resin layer. be.

As the dispersant for the conductive material, the Youmex series manufactured by Sanyo Chemical Industries, Ltd., the Hardren series manufactured by Toyobo Co., Ltd., the Toyo Tuck series and the like can be used.

The thickness of the resin current collector is preferably 100 μm or less, more preferably 50 to 80 μm.
When the thickness of the resin current collector is 100 μm or less, it can be said that the resin current collector is thin and thin. Since such a resin current collector has a small volume in the battery, it is suitable for increasing the battery capacity of the battery.
Further, when the thickness of the resin current collector is 50 μm or more, the strength of the resin current collector is sufficient, which is preferable.
The thickness of the resin current collector is obtained as the total value of the thicknesses of the plurality of conductive resin layers.
When the resin collector consists of two layers, a first conductive resin layer (BX1) and a second conductive resin layer (BX2), the thickness of the first conductive resin layer (BX1) and the second conductivity. It is the total thickness of the sex resin layer (BX2).
In the resin current collector, the preferred thickness of the first conductive resin layer (BX1) is 25 to 65 μm, and the preferred thickness of the second conductive resin layer (BX2) is 35 to 75 μm.

The surface resistance value of the first conductive resin layer side of the resin collector is preferably 3500 Ω · cm ² or less, and the electric resistance value (penetration resistance value) in the thickness direction of the resin collector is 60. It is preferably ~ 180Ω · cm ² . The surface resistance value on the first conductive resin layer side of the resin collector and the electric resistance value in the thickness direction can be measured by the following methods.

<Measurement of surface resistance value on the first conductive resin layer side of the resin current collector>
Using a resin current collector cut into a strip of 3 cm x 10 cm as a measurement sample, using a low resistivity meter [MCP-T610, manufactured by Mitsubishi Chemical Analytech Co., Ltd.] by the 4-probe method based on JIS K7194. The measured resistance value on the surface of the resin collector on the first conductive resin layer side is taken as the electrical resistance value on the first conductive resin layer side of the resin collector.

<Measurement of electrical resistance in the thickness direction of the resin current collector>
An electrode of an electric resistance measuring instrument [IMC-0240 type, manufactured by Imoto Seisakusho Co., Ltd.] to which a resistance meter [RM3548, manufactured by HIOKI] is connected to a resin current collector cut into a strip of 3 cm x 10 cm as a measuring test piece. A test piece is sandwiched between them, and the resistance value is measured while applying a load of 2.16 kg to the electrodes. The value obtained by multiplying the value 60 seconds after the weighting by the contact area between the electrode and the test piece (3.14 cm ² ) can be used as the electric resistance value in the thickness direction. The electrical resistance measuring instrument [IMC-0240 type, manufactured by Imoto Seisakusho Co., Ltd.] has resistance by sandwiching a test piece conforming to the device used for measuring volumetric electrical resistance in the thickness direction between positive and negative electrodes in JISK6378-5. It is a device for measuring the value.

Subsequently, the positive electrode active material layer containing the positive electrode active material contained in the positive electrode for the lithium ion battery of the present invention will be described.
As the positive electrode active material used for the positive electrode active material layer of the positive electrode for the lithium ion battery of the present invention, a known material can be used. The positive electrode active material may be a coated positive electrode active material coated with a resin such as an acrylic resin. The positive electrode active material layer contains, if necessary, an additive such as a binder and a conductive auxiliary agent together with the positive electrode active material.

In the positive electrode for a lithium ion battery of the present invention, the first conductive resin layer (BX1) of the resin collector is arranged on the side in contact with the positive electrode active material layer.
Since the first conductive resin layer (BX1) contains the first conductive carbon filler (B1) having a large specific surface area, it has a small resistance and can perform a function similar to that of the resistance reducing layer. Then, even when the resin current collector as the positive electrode current collector is close to the negative electrode active material without passing through the positive electrode active material, the current is not in the thickness direction of the resin current collector but the first conductive resin. It becomes easy to flow in the surface direction of the layer (BX1), and a large current is prevented from flowing in the resin current collector. Therefore, deterioration of the resin current collector is less likely to occur.

The resin collector constituting the positive electrode for a lithium ion battery of the present invention can be preferably manufactured by the following method.
First, a material for a resin current collector is obtained by mixing a polyolefin resin, a conductive carbon filler, and other components if necessary.
As the conductive carbon filler, the first conductive carbon filler (B1) can be used to obtain the first resin current collector material for the first conductive resin layer (BX1), and the second The conductive carbon filler (B2) of the above can be used to obtain a material for a second resin current collector for the second conductive resin layer (BX2).

As a mixing method, a method of obtaining a masterbatch of the conductive carbon filler and then further mixing with the polyolefin resin, a method of using a polyolefin resin, a conductive carbon filler, and a masterbatch of other components as necessary, and a method of using a masterbatch of other components, and , There is a method of mixing all the raw materials at once, and for the mixing, a suitable known mixer such as a kneader, an internal mixer, a Banbury mixer, a roll, etc. is used to mix the pellet-like or powder-like components. Can be done.

The order of addition of each component at the time of mixing is not particularly limited. The obtained mixture may be further pelletized or powdered by a pelletizer or the like.

A resin current collector can be obtained, for example, by molding into a film using the first resin current collector material and the second resin current collector material. As a method for forming into a film, a known method that can be used for producing a multilayer film can be used.
Specific examples thereof include a T-die method, an inflation method, and an extrusion laminating method. Further, the film produced by using the first resin collector material and the film produced by using the second resin collector material may be bonded by a method such as heat sealing (heat pressing). ..

The surface of the first conductive resin layer (BX1) of the resin collector obtained as described above is coated with a slurry containing a positive electrode active material and, if necessary, a binder and an additive, and dried. The positive electrode active material layer can be formed by the above method, and the positive electrode for the lithium ion battery of the present invention can be obtained. The positive electrode active material may be a coated positive electrode active material coated with a resin such as an acrylic resin.
A specific example of the method for manufacturing a positive electrode for a lithium ion battery of the present invention is given below.
The coated positive electrode active material, carbon fiber and electrolytic solution are mixed using a known kneading device (“Awatori Rentaro” manufactured by Shinky Co., Ltd., etc.) until uniform, and the obtained positive electrode active material slurry is collected from the resin. It is applied to the surface of the first conductive resin layer (BX1) of the electric body and pressed at a pressure of 5 MPa for about 10 seconds.
When the positive electrode active material is a coated positive electrode active material, the positive electrode active material layer can be formed without using a binder. In addition, the positive electrode active material layer can be formed without drying after coating.

The lithium ion battery of the present invention is characterized by comprising the positive electrode for the lithium ion battery of the present invention.
The lithium ion battery of the present invention includes an electrolytic solution, a separator, and a negative electrode for a lithium ion battery in addition to the positive electrode for the lithium ion battery of the present invention.
In the lithium ion battery of the present invention, known materials can be used as materials for the electrolytic solution, separator and the like. Further, a known material can be used as the negative electrode active material used for the negative electrode for a lithium ion battery, and the negative electrode active material may be a coated negative electrode active material coated with a resin such as an acrylic resin.
The negative electrode current collector used for the negative electrode for a lithium ion battery may be a metal collector foil or a resin current collector.

Next, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the Examples as long as it does not deviate from the gist of the present invention. Unless otherwise specified, parts mean parts by weight and% means parts by weight.

The materials used in the following examples are as follows.
Conductive carbon filler B1-1: Acetylene black [Specific surface area 39 m ² / g, trade name "Denka Black Li-400", manufactured by Denka Co., Ltd.]
B1-2: Acetylene Black [Specific surface area 68 m ² / g, trade name "Ensako 250G (granular)", Imerys B1-3: Acetylene black [Specific surface area 800 m ² / g, Product name "EC300J", Lion Corporation Made]
B1-4: Acetylene Black [Specific surface area 69m ² / g, trade name "Denka Black", manufactured by Denka Co., Ltd.]
B2-1: Graphite particles [specific surface area 3.87 m ² / g, trade name "PC99-300M", manufactured by Ito Graphite Industry Co., Ltd.]
B2-2: Graphite particles [specific surface area 3.19 m ² / g, trade name "SG-BL40", manufactured by Ito Graphite Industry Co., Ltd.]
B2-3: Graphite particles [specific surface area 17.5 m ² / g, trade name "G-6S", manufactured by Chuetsu Graphite Industry Co., Ltd.]
B2-4: Graphite particles [specific surface area 6.04 m ² / g, trade name "PC-30", manufactured by Ito Graphite Industry Co., Ltd.]
B2-5: Graphite particles [specific surface area 0.6 m ² / g, trade name "SNG-P1A1", manufactured by JFE Chemical Co., Ltd.]
Resin (polyolefin resin)
Polypropylene resin [Product name "SunAllomer PC684S", manufactured by SunAllomer Ltd.]
Dispersant [Product name "Youmex 1001 (acid-modified polypropylene)", manufactured by Sanyo Chemical Industries, Ltd.]

<Example 1>
65 parts of polypropylene resin, 30 parts of conductive carbon filler (B1-1), and 5 parts of dispersant are melt-kneaded under the conditions of 180 ° C., 100 rpm, and a residence time of 5 minutes to obtain a first resin current collector material. rice field.
Separately, 55 parts of polypropylene resin, 50 parts of conductive carbon filler (B2-1), and 5 parts of dispersant are melt-kneaded under the conditions of 180 ° C., 100 rpm, and a residence time of 5 minutes to prepare a second resin current collector material. Got
The material for the first resin collector and the material for the second resin collector are co-extruded from the T-die to provide a first conductive resin layer (BX1) and a second conductive resin layer (BX2). A resin current collector was obtained.
Table 1 shows the types and specific surface areas of the conductive carbon fillers used in the first conductive resin layer (BX1) and the second conductive resin layer (BX2). Further, the total surface area of the conductive carbon filler contained in 1 g of the first conductive resin layer (BX1) or 1 g of the second conductive resin layer (BX2) is shown.
Table 1 shows the film thicknesses of the first conductive resin layer (BX1) and the second conductive resin layer (BX2).

<Examples 2 to 13>
The types of the conductive carbon filler used for preparing the material for the first resin collector and the material for the second resin collector are changed as shown in Table 1, respectively, and the first conductive resin layer ( A resin current collector including BX1) and a second conductive resin layer (BX2) was obtained.
The weight ratio (% by weight) of the first conductive carbon filler (B1) used for preparing the material for the first resin current collector was changed as shown in Table 1, and the first conductive carbon filler (B1) was changed. ) And 5% by weight of the dispersant, the weight ratio of the polyolefin resin was changed so that the total was 100% by weight.
The weight ratio (% by weight) of the second conductive carbon filler (B2) used for preparing the material for the second resin current collector was also changed as shown in Table 1, and the total with the dispersant was 5% by weight. The weight ratio of the polyolefin resin was changed so as to be 100% by weight.
Table 1 shows the film thicknesses of the first conductive resin layer (BX1) and the second conductive resin layer (BX2) in each example.

<Comparative Examples 1 to 4>
As shown in Table 1, a resin current collector having one conductive resin layer was obtained by using only one of the first resin current collector material and the second resin current collector material. ..
In Comparative Examples 1 and 2, the weight ratio (% by weight) of the first conductive carbon filler (B1) used for preparing the material for the first resin current collector was changed as shown in Table 1, and the first The weight ratio of the polyolefin resin was changed so that the total of the conductive carbon filler (B1) and 5% by weight of the dispersant was 100% by weight.
In Comparative Examples 3 and 4, the weight ratio (% by weight) of the second conductive carbon filler (B2) used for preparing the material for the second resin collector was changed as shown in Table 1, and the second The weight ratio of the polyolefin resin was changed so that the total of the conductive carbon filler (B2) and 5% by weight of the dispersant was 100% by weight.
The thickness of the resin current collector was set to be the same as in Example 1.

<Measurement of penetration resistance value>
Cut the resin collector into strips of about 3 cm x 10 cm, and use an electric resistance measuring instrument [IMC-0240 type, manufactured by Imoto Seisakusho Co., Ltd.] and a resistance meter [RM3548, manufactured by HIOKI] to obtain each resin collector. The penetration resistance value was measured.
The resistance value of the resin collector with a load of 2.16 kg applied to the electric resistance measuring instrument is measured, and the value 60 seconds after the load of 2.16 kg is applied is the resistance value of the resin collector. And said. As shown in the following formula, the value obtained by multiplying the area of the contact surface of the jig at the time of resistance measurement (3.14 cm ² ) was taken as the penetration resistance value (Ω · cm ² ).
Penetration resistance value (Ω ・ cm ² ) = resistance value (Ω) × 3.14 (cm ² )
In the column of resistance judgment in the table, when the penetration resistance value is 180Ω · cm ² or less, it is judged to be good and displayed as ○, and when the penetration resistance value exceeds 180Ω · cm ² and is 1000Ω · cm ² or less. Judging that it can be used, it is displayed as Δ, and when the penetration resistance value exceeds 1000 Ω · cm ² , it is displayed as ×.

<Measurement of surface resistance value on the first conductive resin layer side of the resin current collector>
Using a resin current collector cut into a strip of 3 cm x 10 cm as a measurement sample, using a low resistivity meter [MCP-T610, manufactured by Mitsubishi Chemical Analytech Co., Ltd.] by the 4-probe method based on JIS K7194. The measured resistance value on the surface of the resin collector on the first conductive resin layer side was taken as the surface resistance value of the resin collector on the first conductive resin layer side.
In Table 1, when the surface resistance value on the first conductive resin layer side of the resin collector is 2000 Ω · cm ² or less, it is judged to be good and marked with ○ in the resistance value determination column, and the resin collector The case where the surface resistance value on the first conductive resin layer side exceeds 2000 Ω · cm ² is indicated as ×.
In Comparative Examples 1 to 4, only one of the first resin current collector material and the second resin current collector material is used, and there is no distinction between the front and back sides. Therefore, any resin current collector can be used. The surface resistance value was measured for the surface. The value of this surface resistance value is shown in Table 1 as "the surface resistance value on the first conductive resin layer side".

<Comparative Example 5>
55 parts of polypropylene resin, 40 parts of conductive carbon filler (B1-1), and 5 parts of dispersant are melt-kneaded under the conditions of 180 ° C., 100 rpm, and a residence time of 5 minutes to obtain a first resin current collector material. rice field.
Separately, 65 parts of polypropylene resin, 30 parts of conductive carbon filler (B2-1), and 5 parts of dispersant are melt-kneaded under the conditions of 180 ° C., 100 rpm, and a residence time of 5 minutes to prepare a second resin current collector material. Got
The material for the first resin collector and the material for the second resin collector are co-extruded from the T-die to provide a first conductive resin layer (BX1) and a second conductive resin layer (BX2). A resin current collector was obtained.

<Manufacturing of lithium-ion batteries for evaluation>
The positive electrode active material slurry coated on the first conductive resin layer (BX1) side of the resin current collectors obtained in Examples 1 to 13 and Comparative Examples 1 to 4 was used as a positive electrode, and similarly, a copper foil (copper foil). Furukawa Electric Co., Ltd.) coated with a negative electrode active material slurry was used as the negative electrode. The positive electrode and the negative electrode obtained here were bonded to each other via a separator with a frame material to prepare lithium ion batteries 1 to 13 for evaluation and lithium ion batteries 1 to 4 for comparison.
The process is detailed below.

<Manufacturing of positive electrode>
[Preparation of polymer compound for coating and its solution]
70.0 parts of DMF was placed in a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel and a nitrogen gas introduction tube, and the temperature was raised to 75 ° C. Next, a monomer compounding solution containing 20.0 parts of butyl methacrylate, 55.0 parts of acrylic acid, 22.0 parts of methyl methacrylate, 3 parts of sodium allylsulfonate and 20 parts of DMF, and 2,2'-azobis (2). , 4-Dimethylvaleronitrile) 0.4 part and 2,2'-azobis (2-methylbutyronitrile) 0.8 part dissolved in 10.0 parts of DMF Initiator solution and nitrogen in a four-necked flask. Radical polymerization was carried out by continuously dropping the solution with a dropping funnel over 2 hours while stirring. After completion of the dropping, the temperature was raised to 80 ° C. and the reaction was continued for 5 hours to obtain a copolymer solution having a resin concentration of 50%. The obtained copolymer solution was transferred to a Teflon (registered trademark) vat and dried under reduced pressure at 120 ° C. and 0.01 MPa for 3 hours to distill off DMF to obtain a polymer compound for coating.

[Creation of coated positive electrode active material]
Place 100 parts of the positive electrode active material powder (LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, volume average particle diameter 4 μm) in the universal mixer High Speed Mixer FS25 [manufactured by Artecnica Co., Ltd.] at room temperature. While stirring at 720 rpm, 11.2 parts of the coating polymer compound solution obtained by dissolving the coating polymer compound in isopropanol at a concentration of 1.0% by weight was added dropwise over 2 minutes, and further 5 The mixture was stirred for a minute.
Then, in a stirred state, 6.2 parts of acetylene black [Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.] was added as a conductive agent in 2 minutes while being divided, and stirring was continued for 30 minutes. Then, the pressure was reduced to 0.01 MPa while maintaining the stirring, then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of decompression, and the stirring, the degree of decompression and the temperature were maintained for 8 hours to distill off the volatile components. .. The obtained powder was classified with a sieve having an opening of 212 μm to obtain a coated positive electrode active material.

[Preparation of positive electrode for evaluation lithium-ion battery]
42 parts of electrolytic solution for lithium ion battery and carbon fiber [Osaka Gas] prepared by dissolving LiPF ₆ in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of 1 mol / L. Donna Carbo Mild S-243 manufactured by Chemical Co., Ltd .: Average fiber length 500 μm, average fiber diameter 13 μm: electric conductivity 200 mS / cm] 4.2 parts and planetary stirring type mixing and kneading device {Awatori Rentaro [Co., Ltd.] Made by Shinky]} was mixed at 2000 rpm for 7 minutes, then 30 parts of the electrolytic solution and 206 parts of the coated positive electrode active material were added, and then further mixed by Rentaro Awatori at 2000 rpm for 1.5 minutes. After adding 20 parts of the electrolytic solution, stirring with Awatori Kentarou was performed at 2000 rpm for 1 minute, and after adding 2.3 parts of the above electrolytic solution, stirring with Awatori Kentarou was mixed at 2000 rpm for 1.5 minutes. , A positive electrode active material slurry was prepared. The obtained positive electrode active material slurry was applied to the first conductive resin layer (BX1) side of Examples 1 to 13 and Comparative Examples 1 to 4, respectively, and pressed at a pressure of 5 MPa for about 10 seconds to obtain Examples 1 to 1. A positive electrode (58 mm × 42 mm) for a lithium ion battery according to No. 13 and Comparative Examples 1 to 4 was produced.

<Manufacturing of negative electrode>
[Preparation of polymer compound for coating and its solution]
The polymer compound for coating used in the above <Preparation of positive electrode> and its solution were prepared.

[Creation of coated negative electrode active material]
100 parts of non-graphitizable carbon powder (volume average particle diameter 20 μm), which is a carbon-based material, was placed in a universal mixer high-speed mixer FS25 [manufactured by Arstecnica Co., Ltd.] and stirred at room temperature at 720 rpm. 9.2 parts of the polymer compound solution for coating obtained by dissolving the polymer compound for coating in isopropanol at a concentration of 19.8% by weight was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes.
Then, in a stirred state, 11.3 parts of acetylene black [Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.], which is a conductive agent, was added in 2 minutes while being divided, and stirring was continued for 30 minutes. Then, the pressure was reduced to 0.01 MPa while maintaining the stirring, then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of decompression, and the stirring, the degree of decompression and the temperature were maintained for 8 hours to distill off the volatile components. .. The obtained powder was classified with a sieve having an opening of 212 μm to obtain a coated negative electrode active material.

[Manufacturing of negative electrode of lithium-ion battery for evaluation]
20 parts of an electrolytic solution for a lithium ion battery and carbon fiber [Osaka Gas] prepared by dissolving LiPF ₆ in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of 1 mol / L. Donna Carbo Mild S-243 manufactured by Chemical Co., Ltd .: Average fiber length 500 μm, average fiber diameter 13 μm: electric conductivity 200 mS / cm] 2 parts and planetary stirring type mixing and kneading device ]} Is mixed at 2000 rpm for 7 minutes, then 50 parts of the electrolytic solution and 98 parts of the coated negative electrode active material are added, and then mixed with Awatori Rentaro at 2000 rpm for 1.5 minutes. After adding 25 parts, stirring with Awatori Kentarou was performed at 2000 rpm for 1 minute, and after further adding 50 parts of the above electrolytic solution, stirring with Awatori Kentarou was mixed at 2000 rpm for 1.5 minutes to activate the negative electrode. A material slurry was prepared.
The obtained negative electrode active material slurry was applied to one side of a copper foil [manufactured by Furukawa Denko Co., Ltd.] and pressed at a pressure of 5 MPa for about 10 seconds to prepare a negative electrode for a lithium ion battery (62 mm × 46 mm).

[Manufacturing of separator body]
A flat plate-shaped cell guard 2500 (made of PP, 25 μm in thickness) was cut into a square of 30 mm × 30 mm to form a separator main body.

[Manufacturing of frame-shaped members]
A laminated film made of low melting point polyethylene (PE) to be a sealing layer was stretched to prepare a stretched film having a thickness of 25 μm (low melting point PE stretched film). After that, a film having a thickness of 250 μm made of polyethylene naphthalate (manufactured by Teijin Co., Ltd., PEN) as a heat-resistant annular support member and an adhesive polyolefin resin film (manufactured by Mitsui Chemicals Co., Ltd., Admer VE300, thickness 50 μm) are heated and rolled. Alternatively, the laminate was prepared by adhering with a laminating machine. After that, the laminate is cut into a rectangle of 66 mm × 50 mm, and further, by punching out a region of φ23 mm in the center, a heat-resistant annular support member (PEN layer) made of PEN and a seal layer (low) made of a low melting point PE stretched film are formed. The melting point PE layer) was laminated to obtain an annular laminate (frame-shaped member) on four sides of the rectangle.

[Joining the separator body and frame-shaped member]
Frame-shaped members on both sides of the separator body so that the center of gravity based on the external dimensions of the frame-shaped member and the center of gravity based on the external dimensions of the separator body overlap, and the PEN layer of each frame-shaped member comes into contact with the separator body. Was bonded together and bonded using an impulse sealer to obtain a separator for a lithium ion battery in which frame-shaped members were arranged in an annular shape along the outer periphery of the separator body.
The seal layer on the side in contact with the positive electrode current collector (low melting point PE layer) is referred to as the first seal layer, and the seal layer on the side in contact with the negative electrode current collector (low melting point PE layer) is referred to as the second seal layer.
The PEN layers are in contact with each other at a portion having a width of 0.5 mm from the outer circumference, but are opposed to each other at a portion having a width of 1.5 mm inside the PEN layer via a separator main body.

[Manufacturing of lithium-ion batteries for evaluation]
A separator with a frame material, in which the separator is previously moistened with an electrolytic solution, is placed on the negative electrode (the surface on the negative electrode at this time is the surface opposite to the surface on which the separator is attached to the frame material), and the negative electrode and the separator with the frame material are placed. The positive electrode for the lithium ion battery according to Examples 1 to 13 and Comparative Examples 1 to 4 was superposed on the one integrated with the above. After superimposing, the three sides were sealed with a heating sealer in the order of long side, short side, and long side. For the last one side, the inside of the cell was evacuated using Tospack (manufactured by TOSEI), and the short side was sealed. The cell obtained at this time was put into an aluminum lamicelle (positive electrode: carbon coated aluminum, negative electrode: copper foil) and a charging test was performed.

[Manufacturing of a comparative lithium ion battery according to Comparative Example 5]
In the production of the positive electrode of the lithium ion battery, the resin collector of Comparative Example 5 is used as the resin collector, and the positive electrode active material slurry is applied to the second conductive resin layer (BX2) side to collect the resin. The comparative lithium-ion battery 5 according to Comparative Example 5 was produced in the same manner as in the production of the above-mentioned evaluation lithium-ion battery except that the front and back surfaces of the conductive resin layer (BX1) and (BX2) of the body were exchanged.

<Charge / discharge test of lithium-ion battery>
At 45 ° C., the evaluation lithium ion batteries 1 to 13 and the comparative lithium ion batteries 1 to 5 were evaluated by the following method using the charge / discharge measuring device "HJ-SD8" [manufactured by Hokuto Denko Co., Ltd.]. .. The results are shown in Table 2.
After charging to 4.2 V by the constant current constant voltage method (0.1 C) and resting for 10 minutes, the battery was discharged to 2.6 V by the constant current method (0.1 C). The constant current constant voltage charging method (also called CCCV mode) measures the voltage and current after 0 seconds of discharge at 0.1C and the voltage and current after 10 seconds of discharge at 0.1C, and calculates the internal resistance by the following formula. did. The smaller the internal resistance, the better the battery characteristics.
The voltage 0 seconds after discharge is a voltage measured at the same time as discharge (also referred to as discharge voltage).
[Internal resistance (Ω)] = [(voltage after 0 seconds of discharge at 0.1C)-(voltage after 10 seconds of discharge at 0.1C)] ÷ [(current after 0 seconds of discharge at 0.1C)- (Current after 10 seconds of discharge at 0.1 C)]

[Judgment of liquid bleeding]
With respect to the evaluation lithium ion batteries 1 to 13 and the comparative lithium ion batteries 1 to 5, visually check whether there is liquid bleeding such as droplets permeating from the inside of the cell on the outside of the resin collector of the cell after the charge / discharge test. Confirmed in. If there were no droplets derived from the electrolytic solution, the liquid bleeding judgment was judged as ◯, and if the droplets were oozing out, the liquid bleeding judgment was judged as x.

Examples 1 to 13 relating to the resin current collector provided with the first conductive resin layer (BX1) and the second conductive resin layer (BX2) specified in the present invention are on the side of the first conductive resin layer. Since the surface resistance value is low, by forming the positive electrode active material layer on the surface on the side of the first conductive resin layer, the first conductive resin layer can perform a function similar to that of the resistance reducing layer.
Further, by using the second conductive resin layer (BX2) together, it is possible to prevent liquid bleeding from the resin current collector.
On the other hand, in Comparative Examples 1 and 2 having only the first conductive resin layer (BX1), liquid bleeding from the resin collector has occurred, and Comparative Example 3 having only the second conductive resin layer (BX2). In 1 and 4, the surface resistance value of the resin collector was high, and the penetration resistance value and the internal resistance were high.
Further, in Comparative Example 5, since the second conductive resin layer (BX2) is arranged on the side in contact with the positive electrode active material layer, the internal resistance is high.

The positive electrode for a lithium ion battery of the present invention is particularly useful as a positive electrode for a lithium ion battery used for a mobile phone, a personal computer, a hybrid vehicle, and an electric vehicle.

Claims (7)

A positive electrode for a lithium ion battery including a positive electrode active material layer containing a positive electrode active material and a resin current collector in contact with the positive electrode active material layer.
The resin collector includes a first conductive resin layer (BX1) and a second conductive resin layer (BX2) made of a resin composition containing a polyolefin resin and a conductive carbon filler.
The specific surface area of the first conductive carbon filler (B1) contained in the first conductive resin layer (BX1) is the specific surface area of the second conductive carbon filler contained in the second conductive resin layer (BX2). It is larger than the specific surface area of (B2), and the specific surface area of the first conductive carbon filler (B1) is 30 to 800 m ² / g.
A positive electrode for a lithium ion battery, wherein the first conductive resin layer (BX1) of the resin collector is arranged on a side in contact with the positive electrode active material layer. The positive electrode for a lithium ion battery according to claim 1, wherein the specific surface area of the second conductive carbon filler (B2) is 10 m ² / g or less. The positive electrode for a lithium ion battery according to claim 1 or 2, wherein the total surface area of the first conductive carbon filler (B1) contained in 1 g of the first conductive resin layer (BX1) is 10 to 100 m ² . The lithium according to any one of claims 1 to 3, wherein the total surface area of the second conductive carbon filler (B2) contained in 1 g of the second conductive resin layer (BX2) is 0.2 to 8 m ² . Positive electrode for ion batteries. The weight ratio of the first conductive carbon filler (B1) contained in the resin collector to the second conductive carbon filler (B2) is [1st conductive carbon filler (B1) / first. 2. The positive electrode for a lithium ion battery according to any one of claims 1 to 4, wherein the conductive carbon filler (B2)] = 0.12 to 0.80. The total weight ratio of the first conductive carbon filler (B1) and the second conductive carbon filler (B2) contained in the resin collector is 20 to 40 weight with respect to the weight of the resin collector. The positive electrode for a lithium ion battery according to any one of claims 1 to 5. A lithium ion battery comprising the positive electrode for a lithium ion battery according to any one of claims 1 to 6.