JP7398925B2 - Resin current collector for lithium ion batteries - Google Patents

Description

The present invention relates to a resin current collector for lithium ion batteries.

Lithium ion batteries have been widely used in a variety of applications in recent years due to their high voltage and high energy density characteristics.
In lithium ion batteries, metal foil (metal current collector foil) has conventionally been used as a current collector. In recent years, a so-called resin current collector made of resin to which metal powder is added instead of metal foil has been proposed (see, for example, Patent Document 1). 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.

However, in conventional resin current collectors, the dispersibility of the conductive filler is insufficient, resulting in problems such as a decrease in performance as a battery such as charge/discharge characteristics. To address this problem, efforts have been made to optimize the matrix resin, conductive filler, and dispersant for the conductive filler that constitute the resin current collector (see, for example, Patent Document 2).

Japanese Patent Application Publication No. 2012-150896 International Publication No. 2015/005116

Resin current collectors are required to have low electrical resistance and be as thin as possible. However, when the resin current collector material described in Patent Document 2 and the like is made into a thin film, defects such as pinholes are likely to occur. Therefore, it can be said that there is still room for improvement in order to obtain a thin resin current collector without pinholes.
An object of the present invention is to provide a resin current collector for lithium ion batteries that has a low electrical resistance value and excellent thin film formability.

The present inventors have made extensive studies to solve these problems, and as a result, have arrived at the present invention. That is, the present invention provides a resin current collector for a lithium ion battery having a conductive resin layer containing a matrix resin, a conductive filler, and a dispersant for the conductive filler, wherein the dispersant for the conductive filler is a block (A1 ) and a block (A2), the block (A1) is a block containing ethylene and propylene as essential constituent monomers, and the block (A2) is an ethylenic copolymer having a carboxyl group. A block having an unsaturated monomer (a) as an essential constituent monomer, the acid value of the dispersant for conductive filler is 15 to 55 mgKOH/g, and the melting point of the dispersant for conductive filler is 120 to 145. This is a resin current collector for lithium ion batteries with a temperature of ℃.

According to the present invention, it is possible to obtain a resin current collector for a lithium ion battery that has a low electrical resistance value and excellent thin film formability.

The present invention will be explained in detail below.
The present invention is a resin current collector for a lithium ion battery having a conductive resin layer containing a matrix resin, a conductive filler, and a dispersant for the conductive filler, wherein the dispersant for the conductive filler forms a block (A1). and a block (A2), the block (A1) is a block containing ethylene and propylene as essential constituent monomers, and the block (A2) is a copolymer having an ethylenic monomer having a carboxyl group. A block having saturated monomer (a) as an essential constituent monomer, the acid value of the dispersant for conductive filler is 15 to 55 mgKOH/g, and the melting point of the dispersant for conductive filler is 120 to 145 ° C. This is a resin current collector for lithium ion batteries.

The resin current collector for a lithium ion battery of the present invention has a conductive resin layer containing a matrix resin, a conductive filler, and a dispersant for the conductive filler. Note that the term "matrix resin" as used in the present invention refers to a resin that serves as a base material for the conductive resin layer.

(matrix resin)
Examples of the matrix resin include polyethylene, polypropylene, polymethylpentene, polycycloolefin, polyethylene terephthalate, polyether nitrile, polytetrafluoroethylene, styrene butadiene rubber, polyacrylonitrile, polymethyl acrylate, polymethyl methacrylate, polyvinylidene fluoride, and epoxy. Examples include resins, silicone resins, and mixtures thereof.
From the viewpoint of electrical stability, polyethylene, polypropylene, polymethylpentene and polycycloolefin are preferred, and polyethylene, polypropylene and polymethylpentene are more preferred.

From the viewpoint of resin strength, the content of the matrix resin is preferably 20 to 98% by weight, more preferably 40 to 95% by weight, particularly preferably 60 to 92% by weight, based on the weight of the conductive resin layer. Weight%.

(conductive filler)
The conductive filler is not particularly limited as long as it is a conductive material, and specific examples include metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.], carbon [graphite and carbon black]. (acetylene black, Ketjen black, furnace black, channel black, thermal lamp black, etc.), mixtures thereof, etc., but are not limited thereto.
These conductive fillers may be used alone or in combination of two or more.
Also, alloys or metal oxides of these may be used.
From the viewpoint of electrical stability, the conductive filler is preferably nickel, aluminum, stainless steel, carbon, silver, copper, titanium, and mixtures thereof, and more preferably nickel, silver, aluminum, stainless steel, and carbon. Among them, nickel and carbon are particularly preferred. Further, these conductive fillers may be formed by coating a particulate ceramic material or a resin material with a conductive material (metal among the conductive fillers described above) by plating or the like.

The shape (form) of the conductive filler is not limited to the particle form, and may be a form other than the particle form, such as a carbon nanotube, which is a form that has been put into practical use as a so-called filler-based conductive resin composition. Good too.

The average particle diameter of the conductive filler is not particularly limited, but from the viewpoint of the electrical characteristics of the battery, it is preferably about 0.01 to 10 μm. In addition, in this specification, "particle diameter" means the maximum distance L among the distances between any two points on the outline of the conductive filler. The value of "average particle diameter" is the average value of the particle diameter of particles observed in several to several dozen fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted.

From the viewpoint of dispersibility of the conductive filler, the content of the conductive filler is preferably 1 to 79% by weight, more preferably 2 to 30% by weight, particularly preferably 2 to 30% by weight, based on the weight of the conductive resin layer. It is 5 to 25% by weight.

(Dispersant for conductive filler)
The conductive resin layer includes the matrix resin, the conductive filler, and a dispersant for the conductive filler. The conductive filler dispersant is used to disperse the conductive filler in the matrix resin.
The dispersant for a conductive filler is a copolymer having a block (A1) and a block (A2), the block (A1) is a block containing ethylene and propylene as essential constituent monomers, and the above-mentioned Block (A2) is a block in which the ethylenically unsaturated monomer (a) having a carboxyl group is an essential constituent monomer.

The block (A1) is a block containing ethylene and propylene as essential constituent monomers. Specific examples include blocks obtained by copolymerizing ethylene and propylene, blocks obtained by copolymerizing ethylene and propylene, and α-olefins having 4 to 30 carbon atoms and/or other monomers.
Examples of the α-olefin include 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1 -octene, 1-nonene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 1-tetracosene, 1-triacontene and the like.
Examples of the other monomers include unsaturated monomers having 4 to 30 carbon atoms and excluding olefins (vinyl acetate, etc.) that are reactive with olefins.

The block (A1) is, for example, an olefin polymer (A'1) produced by a conventional method for producing an olefin polymer (for example, a bulk method, a solution method, a slurry method, a gas phase method, etc.) (for example, ethylene and It is preferable that a double bond is introduced into a propylene copolymer by a thermal degradation reaction or the like.

In the thermal degradation method, the olefin polymer (A'1) is heated at 300 °C under nitrogen gas flow in the absence of (1) an organic peroxide (dicumyl peroxide, di-t-butyl peroxide, etc.). (2) continuous or discontinuous thermal degradation at 180 to 300°C for 0.5 to 10 hours in the presence of an organic peroxide; This includes methods of discontinuous thermal degradation.
Among these methods (1) and (2), preferred is method (1), which facilitates obtaining a block (A1) with a larger number of double bonds at the molecular end and/or in the polymer chain. be.

The number of double bonds in the molecular terminal and/or polymer chain of the block (A1) is preferably 0.4 to 2.0 from the viewpoint of suitably adjusting the acid value of the dispersant for the conductive filler. , more preferably 0.8 to 2.0, particularly preferably 1.2 to 2.0.
The number of double bonds in the block (A1) can be determined from the spectrum of 1H-NMR (nuclear magnetic resonance) spectroscopy. That is, the peaks in the spectrum obtained in the above measurement are assigned, and the integral value derived from the double bond at 4.5 to 6.0 ppm and the integral value derived from the saturated hydrocarbon group at 0.5 to 2.0 ppm are calculated. Calculated from the ratio with the value. The number of double bonds in the Examples described below was measured according to the method.

The weight average molecular weight of the block (A1) [hereinafter abbreviated as Mw]. The measurement is based on the gel permeation chromatography (GPC) method described below. ] is preferably 13,000 to 58,000, more preferably 15,000 to 50,000.

In this specification, the conditions for measuring Mw by GPC are as follows.
Equipment: High temperature gel permeation chromatograph [“Alliance GPC V2000”, manufactured by Waters Co., Ltd.]
Solvent: Orthodichlorobenzene Reference material: Polystyrene Sample concentration: 3mg/ml
Column stationary phase: PLgel 10 μm, MIXED-B 2 in series [manufactured by Polymer Laboratories Co., Ltd.]
Column temperature: 135℃
In addition, the measurement of Mw in the Examples described later was carried out according to the method.

The block (A2) is a block whose essential constituent monomer is the ethylenically unsaturated monomer (a) having a carboxyl group.
The ethylenically unsaturated monomer (a) includes unsaturated monocarboxylic acids [having 3 to 15 carbon atoms, such as (meth)acrylic acid, crotonic acid, and cinnamic acid], unsaturated dicarboxylic acids [aliphatic compounds (carbon from 4 to 24, such as maleic acid, fumaric acid, itaconic acid, citraconic acid and mesaconic acid), aromatic compounds (from 10 to 24 carbon atoms, such as dicarboxystyrene) and alicyclic compounds (from 8 to 24 carbon atoms, such as dicarboxystyrene); dicarboxycyclohexene and dicarboxycycloheptene) and their acid anhydrides], trivalent to tetravalent or higher polycarboxylic acids [aliphatic compounds (having 6 to 24 carbon atoms, e.g. aconitic acid) and fatty acids] cyclic (7 to 24 carbon atoms, such as tricarboxycyclopentene, tricarboxycyclohexene, and tricarboxycyclooctene), partial alkyl (1 to 18 carbon atoms) esters of polyhydric carboxylic acids (monomethyl maleate, monomethyl fumarate, etc.) ethyl ester, itaconic acid mono-t-butyl ester, mesaconic acid monodecyl ester, dicarboxycycloheptenedidodecyl ester, etc.) and salts thereof (alkali metal salts and ammonium salts).
Among these, from the viewpoint of reactivity, unsaturated dicarboxylic acids (or their acid anhydrides) are preferred, more preferred are unsaturated dicarboxylic acid anhydrides, and maleic anhydride is particularly preferred.

From the viewpoint of dispersibility of the conductive filler, the proportion of the ethylenically unsaturated monomer (a) constituting the block (A2) is 50 to 100% by weight based on the weight of the block (A2). It is preferably 60 to 100% by weight, particularly preferably 70 to 100% by weight.

The total molar concentration of carboxyl groups in the block (A2) is preferably 0.0001 to 0.03 mol/g, more preferably 0.001 to 0.028 mol/g, from the viewpoint of dispersibility of the conductive filler. /g, particularly preferably 0.01 to 0.025 mol/g.
The total molar concentration of the carboxyl groups in the block (A2) can be calculated by the following formula from the amount of the ethylenically unsaturated monomer (a) charged when producing the conductive filler dispersant. .
Total molar concentration = Σ {(amount of ethylenically unsaturated monomer (a) charged)/(molecular weight of ethylenically unsaturated monomer (a))}/{total amount of charged ethylenically unsaturated monomer (a)}
In addition, when calculating the total molar concentration of the carboxyl groups, if an ethylenically unsaturated monomer (a) having two or more carboxyl groups is used, the amount of the charged ethylenically unsaturated monomer (a) should be The value multiplied by the number of is calculated as the "charged amount of ethylenically unsaturated monomer (a)".

The total molar concentration of carboxyl groups in the conductive filler dispersant is preferably 0.00005 to 0.015 mol/g, more preferably 0.0005 to 0.014 from the viewpoint of dispersibility of the conductive filler. Mol/g.
The total molar concentration of carboxyl groups in the dispersant for conductive filler is determined by measuring ¹³ C-NMR and IR (infrared spectroscopy) of the dispersant for conductive filler, and using a sample whose molar concentration is known. It can be calculated by applying it to the obtained calibration curve.
Further, the total molar concentration of carboxyl groups in the dispersant for conductive filler can also be calculated from the amount charged in producing the dispersant for conductive filler using the following formula.
Total molar concentration = Σ {(amount of ethylenically unsaturated monomer (a) charged)/(molecular weight of ethylenically unsaturated monomer (a))}/(total amount of monomers constituting the dispersant for conductive filler)
In addition, when calculating the total molar concentration of carboxyl groups, when using an ethylenically unsaturated monomer (a) having two or more carboxyl groups, the carboxyl group is added to the charged amount of the ethylenically unsaturated monomer (a). The value multiplied by the number of is calculated as the "charged amount of ethylenically unsaturated monomer (a)".

The dispersant for the conductive filler is a copolymer having the block (A1) and the block (A2), but from the viewpoint of dispersibility of the conductive filler, the weight ratio {block (A1)/block (A2)} is preferably 50/50 to 99/1, more preferably 60/40 to 98/2, particularly preferably 70/30 to 95/5.

Examples of the method for producing the conductive filler dispersant include a method in which the block (A2) is added to the block (A1) into which a double bond has been introduced by the above-mentioned thermal degradation reaction or the like.

The conductive filler dispersant can be obtained, for example, by reacting the block (A1) and the block (A2) in the presence of a radical generating source [radical initiator (b), heat, light, etc.] . The reaction here refers to an addition reaction of the block (A2) to the double bond of the block (A1). The presence or absence of a reaction is determined by the decrease in the number of double bonds in the mixture before and after the reaction {the mixture of block (A1) and block (A2)}.
The number of double bonds can be determined from the spectrum of 1H-NMR (nuclear magnetic resonance) spectroscopy. That is, the peak in the spectrum obtained in the measurement is assigned, and the number of double bonds in the mixture is determined from the integral value derived from the double bond at 4.5 to 6.0 ppm of the mixture and the integral value derived from the mixture. The relative value of the number of carbon atoms in the mixture is calculated, and the number of double bonds in the molecular terminal and/or polymer chain per 1,000 carbon atoms in the mixture is calculated. The presence or absence of a reaction during the production of a dispersant in the Examples described below was also confirmed according to the same method.

Examples of the radical initiator (b) include azo compounds [azobisisobutyronitrile, azobisisovaleronitrile, etc.], peroxides [monofunctional (one having one peroxide group in the molecule)] (benzoyl peroxide, , di-t-butyl peroxide, lauroyl peroxide, dicumyl peroxide, etc.) and polyfunctional (those having two or more peroxide groups in the molecule) [2,2-bis(4,4-di-t- butylperoxycyclohexyl)propane, di-t-butylperoxyhexahydroterephthalate, diallylperoxydicarbonate, etc.].
Among these, preferred as the radical initiator (b) from the viewpoint of reactivity between the block (A1) and the block (A2) are peroxides, more preferred are monofunctional peroxides, and particularly preferred are monofunctional peroxides. These are di-t-butyl peroxide, lauroyl peroxide, and dicumyl peroxide.

The amount of the radical initiator (b) used is preferably 0.05 to 10% by weight based on the total weight of the block (A1) and the block (A2), from the viewpoint of reactivity and suppression of side reactions, and The amount is preferably 0.2 to 5% by weight, particularly preferably 0.5 to 3% by weight.

The acid value of the dispersant for the conductive filler is 15 to 55 mgKOH/g. If the acid value of the dispersant for the conductive filler is less than 15 mgKOH/g, the dispersibility of the conductive filler in the matrix resin will deteriorate and the electrical resistance of the resin current collector will increase, and the dispersant for the conductive filler If the acid value of the dispersant exceeds 55 mgKOH/g, the thin film formability of the resin current collector tends to deteriorate.
The acid value of the dispersant is preferably 35 to 55 mgKOH/g.

The acid value of the conductive filler dispersant is a value obtained by measuring according to the following procedures (i) to (iii) in accordance with JIS K 0070.
(i) 1 g of the conductive filler dispersant is dissolved in 100 g of xylene whose temperature is adjusted to 100°C.
(ii) Using phenolphthalein as an indicator, neutralize with 0.1 mol/L potassium hydroxide ethanol solution [trade name "0.1 mol/L ethanolic potassium hydroxide solution", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] Perform titration.
(iii) Calculate the acid value (unit: mgKOH/g) by converting the amount of potassium hydroxide required for neutralization titration into mg.
In addition, in the above measurement, a result is obtained in which one acid anhydride group is equivalent to one carboxyl group. The acid values in the Examples described below were determined according to the method.

As a method for setting the acid value of the dispersant for conductive filler in the above range, the acid value is adjusted by controlling the weight ratio of the ethylenically unsaturated monomer (a) in the dispersant for conductive filler. be able to.

The melting point of the conductive filler dispersant is 120 to 145°C. If the melting point of the conductive filler dispersant is less than 120° C. or higher than 145° C., the difference in viscosity from the matrix resin becomes too large, resulting in poor dispersibility of the conductive filler.
From the viewpoint of dispersibility of the conductive filler, the melting point of the dispersant for the conductive filler is preferably 135 to 145°C, more preferably 140 to 145°C.
In the present invention, the melting point refers to the melting peak temperature measured using DSC (differential scanning calorimetry) according to JIS K 7122 (transition heat measurement method). Examples of the device used for DSC include DSC2910 [trade name, manufactured by TA Instruments Co., Ltd.]. The melting points in the Examples described below were measured using the method and equipment described above.

As a method for bringing the melting point of the conductive filler dispersant into the range, the heating temperature and heating time may be adjusted in the thermal degradation method (1). The higher the heating temperature and the longer the heating time, the lower the melting point of the dispersant tends to be.

The weight average molecular weight of the conductive filler dispersant [hereinafter abbreviated as Mw]. The measurement is based on the gel permeation chromatography (GPC) method described below. ] is preferably 20,000 to 60,000. When the Mw of the conductive filler dispersant is within the above range, the mechanical strength of the resin current collector is improved.
The Mw of the conductive filler dispersant is more preferably 20,000 to 50,000, particularly preferably 25,000 to 40,000.

The conditions for measuring Mw by GPC in the present invention are as follows.
Equipment: High temperature gel permeation chromatograph [“Alliance GPC V2000”, manufactured by Waters Co., Ltd.]
Solvent: Orthodichlorobenzene Reference material: Polystyrene Sample concentration: 3mg/ml
Column stationary phase: PLgel 10 μm, MIXED-B 2 in series [manufactured by Polymer Laboratories Co., Ltd.]
Column temperature: 135℃

In order to bring the Mw of the conductive filler dispersant into the above range, the heating temperature and heating time may be adjusted in the thermal degradation method (1). The higher the heating temperature and the longer the heating time, the smaller the dispersant Mw tends to be.

The content of the conductive filler dispersant is preferably 0.1 to 10% by weight, more preferably 1 to 7% by weight, particularly preferably 3 to 5% by weight, based on the weight of the conductive resin layer. Weight%. When the content of the conductive filler dispersant is 0.1 to 10% by weight based on the weight of the conductive resin layer, the mechanical strength of the resin current collector is improved.

(Resin current collector for lithium ion batteries)
The resin current collector for lithium ion batteries of the present invention can be manufactured, for example, by the following method.
First, a resin current collector material is obtained by mixing a matrix resin, a conductive filler, a dispersant for conductive filler, and other components as necessary.
The mixing method is to obtain a master batch of the conductive filler and then mix it with the matrix resin, or to prepare a master batch of the matrix resin, conductive carbon filler, dispersant for the conductive filler, and other components as necessary. There are a batch method and a method of mixing all the raw materials at once.For mixing, pellet or powder components are mixed using an appropriate known mixer, such as a kneader, internal mixer, or Banbury mixer. and rolls can be used.

There is no particular limitation on the order of addition of each component during mixing. The obtained mixture may be further pelletized or powdered using a pelletizer or the like.

By molding the obtained resin current collector material into a film shape, for example, a conductive resin layer included in the resin current collector for a lithium ion battery of the present invention can be obtained. Examples of methods for forming into a film include known film forming methods such as a T-die method, an inflation method, and a calendar method. Note that the conductive resin layer can also be obtained by a molding method other than film molding.

As the resin current collector for lithium ion batteries of the present invention, the conductive resin layer can be used as it is as a current collector, or it can be used by laminating it with other conductive resin layers or metal layers. .
Examples of the material constituting the metal layer include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof. Furthermore, a conductive film can be formed on the surface of the conductive resin layer by metal plating, vapor deposition, sputtering, etc., and can be used as a current collector.

EXAMPLES Next, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the examples unless it departs from the gist of the present invention. In addition, unless otherwise specified, parts mean parts by weight, and % means weight %.

<Manufacture example 1: Manufacture of block (A1-1)>
A reaction vessel was charged with 100 parts of a polyolefin (A0-1) using a metallocene catalyst containing propylene and ethylene as constituent units (trade name: "Wintech WFX6", manufactured by Nippon Polypro Co., Ltd.), and industrial grade was added to the gas phase. While blowing nitrogen (purity 99.999% by volume), the mixture was heated and melted using a mantle heater, and heat degradation was performed at 360° C. for 18 minutes while stirring to obtain a block (A1-1). The number of double bonds at the end of the molecule per 1000 carbon atoms in block (A1-1) was 0.4, and the Mw was 50,000.

<Production example 2: Production of block (A1-2)>
A reaction vessel was charged with 100 parts of a polyolefin (A0-2) using a Ziegler-Natta catalyst containing propylene and ethylene as constituent units (trade name: "Sun Allomer PM854X", manufactured by Sun Allomer Co., Ltd.), and the gas phase was filled with industrial nitrogen ( (purity 99.999%) was heated and melted using a mantle heater while venting, and heat degradation was performed at 360° C. for 37 minutes while stirring to obtain a block (A1-2). The number of double bonds at the end of the molecule per 1000 carbon atoms in block (A1-2) was 2.0, and the Mw was 15,000.

<Manufacture example 3: Manufacture of block (A1-3)>
A reaction vessel was charged with 100 parts of a polyolefin (A0-3) using a Ziegler-Natta catalyst containing propylene and ethylene as constituent units (trade name: "Sun Allomer PZA-20A", manufactured by Sun Allomer Co., Ltd.), and industrial grade polyolefin was added to the gas phase. While blowing nitrogen (purity 99.999%), the mixture was heated and melted using a mantle heater, and heat degradation was performed at 360° C. for 30 minutes while stirring to obtain a block (A1-3). The number of double bonds at the end of the molecule per 1000 carbon atoms in block (A1-3) was 1.2, and the Mw was 15,000.

<Production example 4: Production of block (A1-4)>
A reaction vessel was charged with 100 parts of polyolefin (A0-4) using a metallocene catalyst containing propylene and ethylene as constituent units (trade name "Versify 3000", manufactured by Dow Chemical Co., Ltd.), and industrial nitrogen was added to the gas phase. (purity 99.999%) was heated and melted in a mantle heater while aerated, and thermally degraded at 360° C. for 37 minutes while stirring to obtain a block (A1-4). The number of double bonds at the end of the molecule per 1000 carbon atoms in block (A1-4) was 2.0, and the Mw was 16,000.

<Manufacture example 5: Manufacture of block (A1-5)>
A reaction vessel was charged with 100 parts of the polyolefin (A0-2), and while industrial nitrogen (purity 99.999%) was introduced into the gas phase, it was heated and melted using a mantle heater, and then heated at 360°C for 26 hours while stirring. Thermal degradation was performed for a minute to obtain a block (A1-5). The number of double bonds at the end of the molecule per 1000 carbon atoms in block (A1-5) was 0.8, and the Mw was 40,000.

<Production Example 6: Production of block (A1-6)>
100 parts of the polyolefin (A0-1) was charged into a reaction vessel, heated and melted with a mantle heater while blowing industrial nitrogen (purity 99.999%) into the gas phase, and heated at 360°C for 15 minutes while stirring. Thermal degradation was performed for a minute to obtain a block (A1-6). The number of double bonds at the end of the molecule per 1000 carbon atoms in block (A1-6) was 0.2, and the Mw was 64,000.

<Production Example 7: Production of block (A1-7)>
100 parts of the polyolefin (A0-3) was charged into a reaction vessel, and heated and melted with a mantle heater while blowing industrial nitrogen (purity 99.999%) into the gas phase. Thermal degradation was performed for a minute to obtain a block (A1-7). The number of double bonds at the end of the molecule per 1000 carbon atoms in block (A1-7) was 2.2, and the Mw was 8,000.

<Production Example 8: Production of block (A1-8)>
100 parts of the polyolefin (A0-2) was charged into a reaction vessel, and heated and melted with a mantle heater while blowing industrial nitrogen (99.999% purity) into the gas phase, and heated at 360°C for 15 minutes while stirring. Thermal degradation was performed for a minute to obtain a block (A1-8). The number of double bonds at the end of the molecule per 1000 carbon atoms in block (A1-8) was 0.2, and the Mw was 60,000.

<Production Example 9: Production of dispersant (1) for conductive filler>
A reaction vessel was charged with 100 parts of block (A1-1) and 3 parts of maleic anhydride as block (A2), heated to 200°C under ventilation with industrial nitrogen (purity 99.999%), and stirred for 10 hours. continued. Thereafter, unreacted maleic anhydride was distilled off under reduced pressure (1.5 kPa, the same applies hereinafter) to obtain a dispersant for conductive filler (1). The dispersant for conductive filler (1) had an acid value of 15 mgKOH/g, a melting point of 120° C., and an Mw of 52,000.

<Production Example 10: Production of dispersant (2) for conductive filler>
The same operation as in Production Example 9 was carried out except that the block (A1-1) in Production Example 9 was changed to block (A1-2) and the amount of maleic anhydride was changed from 3 parts to 11 parts. Agent (2) was obtained. The dispersant for conductive filler (2) had an acid value of 55 mgKOH/g, a melting point of 145° C., and an Mw of 28,000.

<Production Example 11: Production of dispersant (3) for conductive filler>
Conductive filler A dispersant (3) for use was obtained. The dispersant for conductive filler (3) had an acid value of 35 mgKOH/g, a melting point of 135° C., and an Mw of 32,000.

<Comparative Production Example 1: Production of dispersant (4) for conductive filler>
The same operation as in Production Example 9 was carried out except that the block (A1-1) in Production Example 9 was changed to block (A1-4) and the amount of maleic anhydride was changed from 3 parts to 11 parts. Agent (4) was obtained. The dispersant for conductive filler (4) had an acid value of 55 mgKOH/g, a melting point of 115° C., and an Mw of 30,000.

<Comparative Production Example 2: Production of dispersant (5) for conductive filler>
Conductive filler A dispersant (5) for use was obtained. The dispersant for conductive filler (5) had an acid value of 26 mgKOH/g, a melting point of 150° C., and an Mw of 45,000.

<Comparative Production Example 3: Production of dispersant (6) for conductive filler>
Conductive filler A dispersant (6) for use was obtained. The dispersant for conductive filler (6) had an acid value of 11 mgKOH/g, a melting point of 124° C., and an Mw of 70,000.

<Comparative Production Example 4: Production of dispersant (7) for conductive filler>
Conductive filler A dispersant (7) was obtained. The dispersant for conductive filler (7) had an acid value of 60 mgKOH/g, a melting point of 135° C., and an Mw of 28,000.

<Comparative Production Example 5: Production of dispersant (8) for conductive filler>
Conductive filler A dispersant (8) was obtained. The dispersant for conductive filler (8) had an acid value of 11 mgKOH/g, a melting point of 150° C., and an Mw of 65,000.

<Example 1>
In a twin-screw extruder, 70 parts of polypropylene [trade name "Sunallomer PC684S", manufactured by Sunallomer Co., Ltd.] as a matrix resin, and 25 parts of furnace black [trade name "#3030B", manufactured by Mitsubishi Chemical Corporation] as a conductive filler. A resin current collector material for a positive electrode was obtained by melting and kneading 5 parts of the conductive filler dispersant (1) at 180° C., 100 rpm, and residence time of 5 minutes. The obtained positive electrode resin current collector material was rolled using a hot press machine to form a conductive resin layer, which was used as a positive electrode resin current collector (W-1).

<Examples 2 and 3 and Comparative Examples 1 to 5>
A resin current collector material for a positive electrode was obtained in the same manner as in Example 1 except that the composition was changed to the one shown in Table 2, and conductive resin layers were formed by rolling with a hot press machine. Resin current collectors (W-2), (W-3), and (RW-1) to (RW-5) were used.

<Example 4>
In a twin-screw extruder, 32 parts of polypropylene [trade name "Sun Allomer PC684S", manufactured by Sun Allomer Co., Ltd.] as a matrix resin, 65 parts of nickel particles [Type 255, manufactured by Vale Japan Ltd.] as a conductive filler, and conductive A resin current collector material for a negative electrode was obtained by melting and kneading 3 parts of the filler dispersant (1) at 180° C., 100 rpm, and a residence time of 5 minutes. The obtained negative electrode resin current collector material was rolled using a hot press machine to form conductive resin layers, and this was used as a negative electrode resin current collector (Z-1).

<Examples 5 and 6 and Comparative Examples 6 and 7>
A resin current collector material for a negative electrode was obtained in the same manner as in Example 4 except that the composition was changed to the one shown in Table 3, and conductive resin layers were formed by rolling with a hot press machine. Resin current collectors (Z-2), (Z-3), (RZ-1), and (RZ-2) were used.

[Thin film formability evaluation]
Using the resin current collector materials obtained in Examples 1 to 6 and Comparative Examples 1 to 7, the film thickness was adjusted by changing the rolling conditions in the hot press in Examples 1 to 6 and Comparative Examples 1 to 7. Ta. As a result of the following pinhole test, the film thickness of the thinnest resin current collector without pinholes was used as an index of thin film formability. The results are listed in Tables 2 and 3.

<Film thickness measurement>
The film thickness of the resin current collectors obtained in Examples 1 to 6 and Comparative Examples 1 to 7 was measured at 5 locations for each sample using a micrometer [manufactured by Mitutoyo], and the average value was calculated as the film thickness of the sample. Made thick. The results are listed in Tables 2 and 3.

<Pinhole test>
A SUS container filled with methanol with a thickness of about 1 to 2 mm was prepared, and the resin current collectors obtained in Examples 1 to 6 and Comparative Examples 1 to 7 cut into 10 cm x 20 cm were floated there. The top surface of the resin current collector was tapped lightly while being careful not to sink the resin current collector, and it was visually confirmed whether methanol oozed out onto the surface of the resin current collector. If methanol seeped out even in one place, it was assumed that there was a pinhole.

In the above pinhole test, if there were no pinholes and the film thickness of the thinnest resin current collector produced was 50 μm or less, it would be ◎ (excellent), and if it was more than 50 μm and 80 μm or less, it would be rated ○ ( Good), cases exceeding 80 μm and 90 μm or less were evaluated as Δ (fair), and cases exceeding 90 μm were evaluated as × (poor). The results are listed in Tables 2 and 3.

[Electrical resistance evaluation]
For each of the thinnest resin current collectors obtained in the thin film moldability evaluation, the penetration resistance value was measured as an index of electrical resistance. The penetration resistance value is an index of the bulk (thickness direction) electrical resistance of the battery material. The results are listed in Tables 2 and 3.

<Penetration resistance value measurement>
The penetration resistance value was measured as follows.
The thinnest resin current collector obtained in the above thin film formability evaluation was cut into strips of approximately 3 cm x 10 cm, and an electrical resistance measuring device [IMC-0240 model, Imoto Seisakusho Co., Ltd.] and a resistor [RM3548] were cut into strips of about 3 cm x 10 cm. , manufactured by HIOKI] was used to measure the resistance value of each resin current collector.
Measure the resistance value of the resin current collector with a load of 2.16 kg applied to an electrical resistance measuring device, and the value 60 seconds after applying the 2.16 kg load is the resistance value of the resin current collector. And so. As shown in the following formula, the value multiplied by the area (3.14 cm ² ) of the contact surface of the jig at the time of resistance measurement was defined as the penetration resistance value. The results are listed in Tables 2 and 3.
Penetration resistance value (Ω・cm ² ) = resistance value (Ω) × 3.14 (cm ² )

<Penetration resistance value evaluation>
◎ (excellent) if the penetration resistance value obtained in the measurement of ^the penetration resistance value is 3.0Ω/ ^cm2 or ^less ; 〇 (good) if it exceeds 8.0 Ω/ ^cm2 and 16.0 Ω/ ^cm2 or less, △ (acceptable) if it exceeds 16.0 Ω/cm2, × (bad) if it exceeds 16.0 Ω/ ^cm2 And so. The results are listed in Tables 2 and 3.

It was confirmed that the resin current collectors for lithium ion batteries obtained in Examples 1 to 6 had low electrical resistance values and excellent thin film formability.
On the other hand, from the results of the resin current collectors for lithium ion batteries obtained in Comparative Examples 1, 2, 5, and 7, it was found that when the melting point of the dispersant for conductive filler was lower than 120°C or higher than 145°C, the electrical resistance evaluation was poor. It was confirmed that the situation worsened.
Furthermore, from the results of the resin current collectors for lithium ion batteries obtained in Comparative Examples 3 to 5, 6, and 7, it was found that when the acid value of the dispersant for the conductive filler was less than 15 mgKOH/g, the electrical resistance evaluation deteriorated. However, it was confirmed that when it exceeds 55 mgKOH/g, the evaluation of thin film formability deteriorates.

The resin current collector for lithium ion batteries of the present invention is particularly useful as a current collector for lithium ion batteries used for mobile phones, personal computers, hybrid vehicles, and electric vehicles.

Claims (2)

A resin current collector for a lithium ion battery having a conductive resin layer containing a matrix resin, a conductive filler, and a dispersant for the conductive filler,
The conductive filler dispersant is a copolymer having a block (A1) and a block (A2),
The block (A1) is a block containing ethylene and propylene as essential constituent monomers,
The block (A2) is a block whose essential constituent monomer is an ethylenically unsaturated monomer (a) having a carboxyl group,
The acid value of the dispersant for the conductive filler is 15 to 55 mgKOH/g,
A resin current collector for a lithium ion battery, wherein the conductive filler dispersant has a melting point of 120 to 145°C. The resin current collector for a lithium ion battery according to claim 1, wherein the weight average molecular weight of the conductive filler dispersant is 20,000 to 60,000.