JP7548700B2 - Positive electrode resin current collector and lithium ion battery - Google Patents

Description

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

In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to protect the environment. In the automotive industry, there is hope that the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) will help reduce carbon dioxide emissions, and efforts are being made to develop secondary batteries for driving motors, which hold the key to putting these into practical use. As a secondary battery, attention is being focused on lithium-ion batteries, which can achieve high energy density and high power density.

In such lithium-ion batteries, metal foil (metal current collector foil) has traditionally been used as the current collector. In recent years, so-called resin current collectors have been proposed, which are made of resin with added conductive material instead of metal foil. Such resin current collectors are lighter than metal current collector foils, and are expected to improve the output per unit weight of the battery.

For example, 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 a resin collector.

International Publication No. 2015/005116

In recent years, there has been a demand for even higher capacity lithium-ion batteries.
In a lithium-ion battery using a conventional resin collector as a resin collector on the positive electrode side (resin collector for positive electrode) as described in Patent Document 1, when the charging voltage is increased to increase the capacity, it is presumed that a side reaction occurs between the matrix resin of the resin collector and the electrolyte, or between the conductive filler and the electrolyte, and there are problems such as the charging voltage not being able to be increased to a predetermined voltage (the limit is about 4.7 V) and the irreversible capacity increasing. Therefore, in a lithium-ion battery using a conventional resin collector as a resin collector on the positive electrode side, there is room for further improvement in the potential resistance and the magnitude of the irreversible capacity.

The present invention aims to provide a resin current collector for positive electrodes that, even when used as a resin current collector on the positive electrode side of a lithium-ion battery, allows the charging voltage to be increased to increase capacity (charging is possible even with a charging voltage of 5 V) and also reduces the initial irreversible capacity.

As a result of intensive research into solving the above problems, the present inventors have discovered that by using a resin current collector in which the matrix resin contains a polymer having a specific ester compound as an essential constituent monomer and the conductive filler contains aluminum and/or titanium in a specific weight ratio, it is possible to suppress side reactions between the matrix resin and the electrolyte or between the conductive filler and the electrolyte, which are assumed to occur when a conventional resin current collector is used, even when used as a resin current collector on the positive electrode side of a lithium ion battery, making it possible to increase the charging voltage and reduce the initial irreversible capacity, thus completing the present invention.

That is, the present invention provides a resin current collector for a positive electrode in which a conductive filler is dispersed in a matrix resin, the matrix resin containing a polymer having an essential constituent monomer of an ester compound (A) of a monohydric aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid, the conductive filler containing aluminum and/or titanium, and the total weight ratio of aluminum and titanium based on the weight of the conductive filler is 99% by weight or more; and a lithium ion battery including the resin current collector for a positive electrode.

The present invention provides a resin current collector for positive electrodes that, even when used as a resin current collector on the positive electrode side of a lithium-ion battery, allows the charging voltage to be increased in order to increase capacity (charging is possible even with a charging voltage of 5 V) and can reduce the initial irreversible capacity.

[Positive electrode resin current collector]
The present invention relates to a positive electrode resin current collector in which a conductive filler is dispersed in a matrix resin, the matrix resin containing a polymer having, as an essential constituent monomer, an ester compound (A) of a monohydric aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid, the conductive filler containing aluminum and/or titanium, and the total weight ratio of aluminum and titanium based on the weight of the conductive filler is 99% by weight or more.

(Matrix resin)
The matrix resin contains a polymer having, as an essential constituent monomer, an ester compound (A) of a monohydric aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid.

Examples of monohydric aliphatic alcohols having 1 to 12 carbon atoms include monohydric branched or straight-chain aliphatic alcohols having 1 to 12 carbon atoms, such as methanol, ethanol, propanol (n-propanol, iso-propanol), butyl alcohol (n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol), pentyl alcohol (n-pentyl alcohol, 2-pentyl alcohol, neopentyl alcohol, etc.), hexyl alcohol (1-hexanol, 2-hexanol, 3-hexanol, etc.), heptyl alcohol (n-heptyl alcohol, 1-methylhexyl alcohol, 2-methylhexyl alcohol, etc.), octyl alcohol (n-octyl alcohol, 1-methylheptanol, 1-ethylhexanol, etc.), and the like. nonyl alcohol (n-nonyl alcohol, 1-methyloctanol, 1-ethylheptanol, 1-propylhexanol, 2-ethylheptyl alcohol, etc.), decyl alcohol (n-decyl alcohol, 1-methylnonyl alcohol, 2-methylnonyl alcohol, 2-ethyloctyl alcohol, etc.), undecyl alcohol (n-undecyl alcohol, 1-methyldecyl alcohol, 2-methyldecyl alcohol, 2-ethylnonyl alcohol, etc.), lauryl alcohol (n-lauryl alcohol, 1-methylundecyl alcohol, 2-methylundecyl alcohol, 2-ethyldecyl alcohol, 2-butylhexyl alcohol, etc.), etc.

(Meth)acrylic acid means acrylic acid and methacrylic acid.

Examples of the ester compound (A) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-methylhexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate.
Among these, methyl methacrylate is preferred from the viewpoints of availability and cost.
The ester compound (A) may be used alone or in combination of two or more kinds.

The polymer containing the ester compound (A) as an essential constituent monomer may contain a monomer other than the ester compound (A).
Examples of the monomer other than the ester compound (A) include ethylene, propylene, styrene, chloroethylene, trichloroethylene, vinyl fluoride, vinyl chloride, vinyl acetate, vinylidene chloride, (meth)acrylonitrile, and vinylidene fluoride.
Among these, at least one selected from the group consisting of vinyl chloride, vinyl acetate, vinylidene chloride, acrylonitrile and vinylidene fluoride is preferred.
Incidentally, (meth)acrylonitrile means acrylonitrile and methacrylonitrile.

The polymer containing the ester compound (A) as an essential constituent monomer may be a homopolymer consisting of the ester compound (A), but may also be a polymer consisting of two or more kinds of monomers.
When the polymer is a polymer of two or more kinds of monomers, it may be any one of a random copolymer, an alternating copolymer, a block copolymer and a graft copolymer.

The weight average molecular weight of the polymer having the ester compound (A) as an essential constituent monomer is not particularly limited, but from the viewpoint of moldability and resin strength, it is preferably 50,000 to 1,000,000, and more preferably 100,000 to 500,000.

In this specification, the weight average molecular weight means a weight average molecular weight measured by gel permeation chromatography (GPC) under the following measurement conditions.
Apparatus: High-temperature gel permeation chromatograph ["Alliance GPC V2000", Waters Corporation]
Solvent: orthodichlorobenzene Reference material: polystyrene Sample concentration: 3 mg/ml
Column stationary phase: PLgel 10 μm, MIXED-B 2 columns in series [Polymer Laboratories, Inc.]
Column temperature: 135 ° C.

The method for obtaining a polymer having the ester compound (A) as an essential constituent monomer is not particularly limited, and any known method such as radical polymerization can be appropriately selected and used.

The monomer constituting the matrix resin preferably comprises an ester compound (A) and at least one selected from the group consisting of vinyl chloride, vinyl acetate, vinylidene chloride, acrylonitrile and vinylidene fluoride.
In addition, the monomer constituting the matrix resin means a monomer constituting the polymer having the ester compound (A) as an essential monomer when the matrix resin contains only a polymer having the ester compound (A) as an essential monomer, and means a monomer constituting the polymer having the ester compound (A) as an essential monomer when the matrix resin contains a polymer other than the polymer having the ester compound (A) as an essential monomer, and a monomer constituting the polymer other than the polymer having the ester compound (A) as an essential monomer.

The matrix resin may contain a polymer other than the polymer having the ester compound (A) as an essential constituent monomer.

Examples of the polymer other than the polymer having the ester compound (A) as an essential constituent monomer include polymers having vinyl chloride, vinyl acetate, vinylidene chloride, (meth)acrylonitrile, vinylidene fluoride, ethylene, propylene, styrene chloroethylene, trichloroethylene, vinyl fluoride, etc. as a monomer.
In particular, from the viewpoint of withstand potential and initial irreversible capacity, it is preferable that the monomer of the polymer other than the polymer having the ester compound (A) as an essential constituent monomer is at least one selected from the group consisting of vinyl chloride, vinyl acetate, vinylidene chloride, acrylonitrile, and vinylidene fluoride.

The polymer other than the polymer having the ester compound (A) as an essential constituent monomer may be a homopolymer consisting of the above-mentioned monomers, or may be a polymer consisting of two or more kinds of monomers.
When the polymer is a polymer of two or more kinds of monomers, it may be any one of a random copolymer, an alternating copolymer, a block copolymer and a graft copolymer.

The weight average molecular weight of the polymer other than the polymer having the ester compound (A) as an essential constituent monomer is not particularly limited, but is preferably 50,000 to 1,000,000, and more preferably 100,000 to 500,000.

The method for obtaining a polymer other than the polymer having the ester compound (A) as an essential constituent monomer is not particularly limited, and any known method can be appropriately selected and used.

The weight proportion of the ester compound (A) contained in the monomers constituting the matrix resin is preferably 50 to 100% by weight based on the total weight of the monomers constituting the matrix resin, from the viewpoint of suitably reducing the initial irreversible capacity.
The weight proportion of the ester compound (A) contained in the monomers constituting the matrix resin is more preferably 80 to 100% by weight, and further preferably 90 to 100% by weight, based on the total weight of the monomers constituting the matrix resin.
The total weight of the monomers constituting the matrix resin is the sum of the weight of the monomers constituting the polymer having the ester compound (A) as an essential constituent monomer and the weight of the monomers constituting the polymer other than the polymer having the ester compound (A) as an essential constituent monomer.

From the viewpoint of strength, the content of the matrix resin is preferably 40 to 98% by weight, and more preferably 50 to 95% by weight, based on the weight of the positive electrode resin collector.

(Conductive filler)
The conductive filler includes aluminum and/or titanium.
From the viewpoint of suitably reducing the initial irreversible capacity, the conductive filler preferably contains only aluminum.
The aluminum may be pure aluminum or an aluminum alloy, and the titanium may be pure titanium or an alloy containing titanium as a main material.

The total weight percentage of aluminum and titanium is 99% by weight or more based on the weight of the conductive filler.
If the total weight ratio of aluminum and titanium is less than 99% by weight, the conductive filler other than aluminum or titanium becomes a source of side reactions, and side reactions between the matrix resin and the electrolyte or between the conductive filler and the electrolyte cannot be sufficiently suppressed, so that the charging voltage cannot be increased to increase the capacity, and the initial irreversible capacity cannot be reduced.
Based on the weight of the conductive filler, the total weight percentage of aluminum and titanium is preferably 99.5% by weight or more, more preferably 99.7% by weight or more, and even more preferably 100% by weight.
The above-mentioned total weight percentage means the total weight percentage of aluminum element and titanium element based on the weight of the conductive filler.
In other words, the above phrase "the total weight ratio of aluminum and titanium is 99% by weight or more, based on the weight of the conductive filler" means that, when aluminum and/or titanium is an alloy, the total weight ratio of aluminum element and titanium element is 99% by weight or more, based on the weight of the conductive filler.

Examples of conductive fillers other than aluminum or titanium include metals other than aluminum and titanium [nickel, stainless steel (SUS), silver, copper, etc.], carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.)], and mixtures thereof.
The weight percentage of the conductive filler other than aluminum or titanium is 1% by weight or less, based on the weight of the conductive filler.

The shape (form) of the conductive filler is not particularly limited and may be spherical, flake-like, leaf-like, dendritic, plate-like, needle-like, rod-like, grape-like, etc.

The average particle size of the conductive filler is not particularly limited, but from the viewpoint of battery characteristics, it is preferably about 0.01 to 10 μm.
In this specification, the term "particle diameter" refers to the maximum distance L between any two points on the contour line of the conductive filler. The value of the "average particle diameter" is calculated as the average value of particle diameters of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

The weight proportion of the conductive filler is preferably 15 to 60% by weight based on the weight of the positive electrode resin collector, from the viewpoint of increasing the charging voltage of the lithium ion battery and suitably reducing the initial irreversible capacity.
The weight ratio of the conductive filler is more preferably 15 to 50% by weight, and further preferably 25 to 50% by weight, based on the weight of the positive electrode resin collector.

(Other ingredients)
The positive electrode resin current collector of the present invention may contain other components as necessary.
Examples of other components include dispersants, colorants, ultraviolet absorbers, and plasticizers (such as compounds containing a phthalic acid skeleton, compounds containing a trimellitic acid skeleton, compounds containing a phosphate group, and compounds containing an epoxy skeleton).

Dispersants that can be used include the UMEX series manufactured by Sanyo Chemical Industries, Ltd., the HARDLEN series manufactured by Toyobo Co., Ltd., and the TOYOTAC series.

Colorants, UV absorbers, plasticizers, etc. can be appropriately selected from known materials.

The total content of the other components is preferably 0.001 to 5% by weight based on the weight of the positive electrode resin collector.

(Method for producing a resin current collector for a positive electrode)
The positive electrode resin current collector of the present invention can be produced, for example, by the following method.
First, a matrix resin, a conductive filler, and, if necessary, other components are mixed together to obtain a resin collector material.
The mixing method includes a method in which a master batch of the conductive filler is obtained and then mixed with the matrix resin, a method in which a master batch of the matrix resin, the conductive carbon filler, and, if necessary, other components are used, and a method in which all the raw materials are mixed together. For the mixing, a suitable known mixer such as a kneader, an internal mixer, a Banbury mixer, or a roll can be used for mixing the pellet-like or powder-like components.

The order in which the components are added during mixing is not particularly limited. The resulting mixture may be further pelletized or powdered using a pelletizer or the like.

The obtained resin collector material is molded into, for example, a film to obtain a resin collector for the positive electrode. Methods for molding into a film include known film molding methods such as the T-die method, the inflation method, and the calendar method. Note that the resin collector for the positive electrode can also be obtained by molding methods other than film molding.

The thickness of the resin collector for the positive electrode is not particularly limited, but it is preferably 5 to 150 μm.

[Lithium-ion battery]
The lithium ion battery of the present invention includes the positive electrode resin current collector of the present invention.

The lithium ion battery of the present invention comprises a positive electrode having the positive electrode resin collector of the present invention, a separator, and a negative electrode.

(Positive electrode)
The positive electrode has a positive electrode active material layer on the surface of the positive electrode resin current collector of the present invention. The positive electrode active material layer contains positive electrode active material particles.

Positive electrode active material particles include composite oxides of lithium and transition metals {composite oxides containing one type of transition metal (LiCoO ₂ , LiNiO ₂ , LiAlMnO ₄ , LiMnO ₂ , LiMn ₂ O ₄ , etc.), composite oxides containing two types of transition metal elements (for example, LiFeMnO ₄ , LiNi _1-x Co _x O ₂ , LiMn _1-y Co _y O ₂ , LiNi _1/3 Co _1/3 Al _1/3 O ₂ , and LiNi _0.8 Co _0.15 Al _0.05 O ₂ ), and composite oxides containing three or more types of metal elements [for example, LiM _a M' _b M'' _c O ₂ (wherein M, M' and M'' are different transition metal elements satisfying a+b+c=1, for example LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), etc.}, lithium-containing transition metal phosphates (for example LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ and LiNiPO ₄ ), transition metal oxides (for example MnO ₂ and V ₂ O ₅ ), transition metal sulfides (for example MoS ₂ and TiS ₂ ), and conductive polymers (for example polyaniline, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene and polyvinylcarbazole), etc.
These positive electrode active material particles may be used alone or in combination of two or more kinds.
The lithium-containing transition metal phosphate may have some of the transition metal sites substituted with other transition metals.

From the viewpoint of the electrical characteristics of the battery, the volume average particle diameter of the positive electrode active material particles is preferably 0.01 to 100 μm, more preferably 0.1 to 35 μm, and even more preferably 2 to 30 μm.

The positive electrode active material particles may be coated positive electrode active material particles, at least a part of the surface of which is coated with a coating material containing a polymer compound.
When the positive electrode active material particles are covered with a coating material, the volume change of the positive electrode is alleviated, and the expansion of the positive electrode can be suppressed.

As the polymer compound constituting the coating material, those described as active material coating resins in JP 2017-054703 A and WO 2015-005117 A, etc., can be suitably used.

The coating material may include a conductive material.
Examples of conductive materials include, but are not limited to, 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.)], and mixtures thereof.
These conductive fillers may be used alone or in combination of two or more.

The positive electrode active material layer may contain an adhesive resin.
As the adhesive resin, for example, a resin for coating a non-aqueous secondary battery active material described in JP 2017-054703 A in which a small amount of an organic solvent is mixed to adjust the glass transition temperature to room temperature or lower, and a resin described as an adhesive in JP 10-255805 A can be suitably used.
The adhesive resin means a resin having adhesiveness (the property of adhering by applying slight pressure without using water, solvent, heat, etc.). On the other hand, the above-mentioned solvent drying type binder for lithium ion batteries means a binder that is solidified without having adhesiveness by volatilizing and distilling off the solvent.
Therefore, the above-mentioned binder and adhesive resin are different materials.

The positive electrode active material layer may contain a conductive assistant.
As the conductive assistant, any of the conductive materials used in the coating material described above can be appropriately selected and used.

The weight ratio of the conductive assistant in the positive electrode active material layer is preferably 3 to 10% by weight.

The positive electrode active material layer may contain an electrolyte.
As the electrolyte, a known electrolyte can be used.
As the electrolyte, electrolytes used in known electrolytic solutions can be used, for example, lithium salts of inorganic anions such as _LiPF6 , _LiBF4 , _LiSbF6 , _LiAsF6 , _LiClO4 , and LiN( _FSO2 ) ₂ , and lithium salts of organic anions such as LiN( _CF3SO2 ) ₂ , LiN( _{C2F5SO2 ) 2} , and LiC( _CF3SO2 ) ₃ . Of these, LiN( _FSO2 ) ₂ is preferred from the viewpoint of battery output and _{charge /} discharge cycle characteristics _.

The solvent may be a non-aqueous solvent used in known electrolyte solutions, such as lactone compounds, cyclic or chain carbonates, chain carboxylates, cyclic or chain ethers, phosphates, nitrile compounds, amide compounds, sulfones, sulfolane, and mixtures thereof.

The positive electrode active material layer can be produced, for example, by a method of applying a mixture containing positive electrode active material particles and an electrolyte solution to the surface of a positive electrode resin current collector or a substrate and removing excess electrolyte solution, or by a method of molding the mixture containing positive electrode active material particles and an electrolyte solution by applying pressure to the substrate.
When the positive electrode active material layer is formed on the surface of the substrate, the positive electrode active material layer may be combined with a positive electrode resin current collector by a method such as transfer.
The mixture may contain a conductive assistant and an adhesive resin, if necessary. The positive electrode active material particles may be coated positive electrode active material particles.

The thickness of the positive electrode active material layer is not particularly limited, but from the viewpoint of battery performance, it is preferably 150 to 600 μm, and more preferably 200 to 450 μm.

(Separator)
Examples of the separator include known separators for lithium ion batteries, such as porous films made of polyethylene or polypropylene, laminated films of porous polyethylene films and porous polypropylene, nonwoven fabrics made of synthetic fibers (polyester fibers, aramid fibers, etc.) or glass fibers, and those having ceramic fine particles such as silica, alumina, or titania attached to their surfaces.

(Negative electrode)
The negative electrode includes a negative electrode current collector and a negative electrode active material layer.

As the negative electrode current collector, a known metal current collector and a resin current collector composed of a conductive resin composition containing a conductive material and a resin (such as the resin current collectors described in JP 2012-150905 A and WO 2015-005116 A) can be used.
From the viewpoint of battery characteristics and the like, the negative electrode current collector is preferably a resin current collector.
The thickness of the negative electrode current collector is not particularly limited, but is preferably 5 to 150 μm.

The negative electrode active material layer contains negative electrode active material particles.
Examples of the negative electrode active material particles include carbon-based materials [graphite, non-graphitizable carbon, amorphous carbon, resin baked bodies (e.g., phenolic resin, furan resin, etc. baked and carbonized), cokes (e.g., pitch coke, needle coke, petroleum coke, etc.), and carbon fibers, etc.], silicon-based materials [silicon, silicon oxide (SiOx), silicon-carbon composites (carbon particles whose surfaces are coated with silicon and/or silicon carbide, silicon particles or silicon oxide particles whose surfaces are coated with carbon and/or silicon carbide, silicon carbide, etc.), and silicon alloys (silicon-aluminum Examples of the conductive material include: conductive polymers (e.g., polyacetylene and polypyrrole), metals (e.g., tin, aluminum, zirconium and titanium), metal oxides (e.g., titanium oxide and lithium-titanium oxide), metal alloys (e.g., lithium-tin alloy, lithium-aluminum alloy and lithium-aluminum-manganese alloy), and mixtures of these with carbon-based materials.
These negative electrode active material particles may be used alone or in combination of two or more kinds.

From the viewpoint of the electrical characteristics of the battery, the volume average particle diameter of the negative electrode active material particles is preferably 0.01 to 100 μm, more preferably 0.1 to 20 μm, and even more preferably 2 to 10 μm.

The negative electrode active material particles may be coated negative electrode active material particles, at least a part of the surface of which is coated with a coating material containing a polymer compound.
When the negative electrode active material particles are covered with a coating material, the volume change of the negative electrode is alleviated, and the expansion of the negative electrode can be suppressed.

As the coating material, the same coating material as described above for the positive electrode active material particles can be suitably used.

The negative electrode active material layer may contain an adhesive resin.
As the adhesive resin, the same adhesive resin as the optional component of the positive electrode active material layer can be suitably used.

The negative electrode active material layer may contain a conductive assistant.
As the conductive assistant, a conductive material similar to the conductive filler contained in the positive electrode active material layer can be suitably used.
The weight ratio of the conductive assistant in the negative electrode active material layer is preferably 2 to 10% by weight.

The negative electrode active material layer may contain an electrolyte.
As the electrolyte, any of those described in the positive electrode active material layer can be appropriately selected and used.

The negative electrode active material layer can be prepared, for example, by a method in which a mixture containing negative electrode active material particles and an electrolyte is applied to the surface of a negative electrode current collector or a substrate, and excess electrolyte is removed.
When the negative electrode active material layer is formed on the surface of the substrate, the negative electrode active material layer may be combined with the negative electrode current collector by a method such as transfer.
If necessary, the mixture may contain a conductive assistant, an adhesive resin, etc. The negative electrode active material particles may be coated negative electrode active material particles.

The thickness of the negative electrode active material layer is not particularly limited, but from the viewpoint of battery performance, it is preferably 150 to 600 μm, and more preferably 200 to 450 μm.

(Method of manufacturing lithium-ion batteries)
The lithium ion battery of the present invention can be produced, for example, by stacking a positive electrode, a separator, and a negative electrode in this order, and then injecting an electrolyte solution as necessary.

The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples as long as they do not deviate from the spirit of the present invention. Note that, unless otherwise specified, parts are parts by weight and % is % by weight.

Example 1
A positive electrode resin current collector material was obtained by melt-kneading 50 parts of polymethyl methacrylate [PMMA, product name "Methyl methacrylate (polymer)", manufactured by Nacalai Tesque, Inc.] as a matrix resin and 50 parts of aluminum [product name "Aluminum (powder)", manufactured by Nacalai Tesque, Inc.] as a conductive filler in a twin-screw extruder at 180°C, 100 rpm, and a residence time of 5 minutes. The obtained positive electrode resin current collector material was rolled by a hot press machine to produce a positive electrode resin current collector.
The weight ratio of the ester compound (A) contained in the monomers constituting the matrix resin was 100% by weight based on the total weight of the monomers constituting the matrix resin.

Example 2
A resin current collector for a positive electrode was prepared in the same manner as in Example 1, except that 50 parts of titanium (trade name "Titanium/Powder", manufactured by Nilaco Corporation) was used as the conductive filler.
The weight ratio of the ester compound (A) contained in the monomers constituting the matrix resin was 100% by weight based on the total weight of the monomers constituting the matrix resin.

Example 3
A positive electrode resin collector was prepared in the same manner as in Example 1, except that 25 parts of polymethyl methacrylate [PMMA, product name "methyl methacrylate (polymer)", manufactured by Nacalai Tesque, Inc.] and 25 parts of polyvinyl chloride [PVC, product name "polyvinyl chloride", manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.] were used as the matrix resin.
The weight ratio of the ester compound (A) contained in the monomers constituting the matrix resin was 50% by weight based on the total weight of the monomers constituting the matrix resin.

Example 4
A positive electrode resin collector was prepared in the same manner as in Example 1, except that 10 parts of polymethyl methacrylate [PMMA, product name "methyl methacrylate (polymer)", manufactured by Nacalai Tesque, Inc.] and 40 parts of polyvinyl chloride [PVC, product name "polyvinyl chloride", manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.] were used as the matrix resin.
The weight ratio of the ester compound (A) contained in the monomers constituting the matrix resin was 20% by weight based on the total weight of the monomers constituting the matrix resin.

Example 5
A positive electrode resin current collector was prepared in the same manner as in Example 1, except that 25 parts of aluminum [product name "Aluminum (powder)" manufactured by Nacalai Tesque, Inc.] and 25 parts of titanium [product name "Titanium/powder" manufactured by Nilaco Corporation] were used as the conductive filler.
The weight ratio of the ester compound (A) contained in the monomers constituting the matrix resin was 100% by weight based on the total weight of the monomers constituting the matrix resin.

Example 6
A positive electrode resin current collector was prepared in the same manner as in Example 1, except that 49.5 parts of aluminum [trade name "Aluminum (powder)" manufactured by Nacalai Tesque, Inc.] and 0.5 parts of carbon black [ENSACO, trade name "E-250G" manufactured by Imerys GC Japan, Inc.] were used as the conductive filler.
The weight ratio of the ester compound (A) contained in the monomers constituting the matrix resin was 100% by weight based on the total weight of the monomers constituting the matrix resin.

<Comparative Example 1>
A positive electrode resin collector was prepared in the same manner as in Example 1, except that 50 parts of polypropylene [PP, product name "SunAllomer PC684S", manufactured by SunAllomer Co., Ltd.] was used as the matrix resin.
The weight proportion of the ester compound (A) contained in the monomers constituting the matrix resin was 0% by weight based on the total weight of the monomers constituting the matrix resin.

<Comparative Example 2>
A positive electrode resin collector was prepared in the same manner as in Example 1, except that 50 parts of polypropylene [PP, product name "SunAllomer PC684S", manufactured by SunAllomer Co., Ltd.] was used as the matrix resin, and 50 parts of carbon black [ENSACO, product name "E-250G", manufactured by Imerys GC Japan Co., Ltd.] was used as the conductive filler.
The weight proportion of the ester compound (A) contained in the monomers constituting the matrix resin was 0% by weight based on the total weight of the monomers constituting the matrix resin.

<Comparative Example 3>
A positive electrode resin collector was prepared in the same manner as in Example 1, except that 50 parts of carbon black [ENSACO, product name "E-250G", manufactured by Imerys GC Japan Co., Ltd.] was used as the conductive filler.
The weight ratio of the ester compound (A) contained in the monomers constituting the matrix resin was 100% by weight based on the total weight of the monomers constituting the matrix resin.

<Comparative Example 4>
A positive electrode resin current collector was prepared in the same manner as in Example 1, except that 48 parts of aluminum [trade name "Aluminum (powder)" manufactured by Nacalai Tesque, Inc.] and 2 parts of carbon black [ENSACO, trade name "E-250G" manufactured by Imerys GC Japan, Inc.] were used as the conductive filler.
The weight ratio of the ester compound (A) contained in the monomers constituting the matrix resin was 100% by weight based on the total weight of the monomers constituting the matrix resin.

<Preparation of Evaluation Battery>
Half cells were produced using the positive electrode resin current collectors produced in Examples 1 to 6 and Comparative Examples 1 to 4 by the following method.
From the positive electrode side, carbon-coated aluminum foil [product name "Carbon-Coated Aluminum Foil", manufactured by Toyo Aluminium K.K.], a positive electrode resin current collector (thickness 0.5 mm, 6.25 ^cm2 ), a separator [product name "#3501", manufactured by Celgard], lithium metal foil (6.25 ^cm2 ) [product name "Lithium Foil (thickness 0.5 mm)", manufactured by Honjo Metals Co., Ltd.], and copper foil (6.25 ^cm2 ) [product name "Electrolytic Copper Foil (thickness 0.2 mm)", manufactured by Furukawa Electric Co., Ltd.] were stacked in this order and an electrolyte was injected to prepare a half cell.
The electrolytic solution used contained 1M LiN(FSO ₂ ) ₂ as an electrolyte and ethylene carbonate and propylene carbonate in a weight ratio of 1:1 as a solvent.

<Measurement of initial irreversible capacity when charging at 5 V>
The produced half cell was used to carry out constant current charging and discharging at 10 μA with an upper limit voltage of 5.0 V.
Each half-cell was checked to see if it could be charged to 5.0 V. If it could be charged to 5.0 V, the initial irreversible capacity (mAh/g) was measured from the difference between the initial charge capacity and the initial discharge capacity. The results are shown in Table 1.

The examples confirmed that by using a positive electrode resin collector in which the matrix resin contains a polymer having a specific ester compound as an essential constituent monomer and the conductive filler contains aluminum and/or titanium in a specific weight ratio, it is possible to increase the charging voltage and reduce the initial irreversible capacity.

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

Claims (5)

A positive electrode resin current collector in which a conductive filler is dispersed in a matrix resin,
the matrix resin contains a polymer having, as an essential constituent monomer, an ester compound (A) of a monohydric aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid;
The conductive filler contains aluminum and/or titanium, and the total weight percentage of aluminum and titanium is 99% by weight or more based on the weight of the conductive filler. The positive electrode resin collector according to claim 1, wherein the weight ratio of the ester compound (A) contained in the monomers constituting the matrix resin is 50 to 100% by weight based on the total weight of the monomers constituting the matrix resin. The positive electrode resin collector according to claim 1 or 2, wherein the monomer constituting the matrix resin is composed of the ester compound (A) and at least one selected from the group consisting of vinyl chloride, vinyl acetate, vinylidene chloride, acrylonitrile, and vinylidene fluoride. The positive electrode resin collector according to any one of claims 1 to 3, wherein the weight ratio of the conductive filler contained in the positive electrode resin collector is 15 to 60% by weight based on the weight of the positive electrode resin collector. A lithium ion battery comprising a positive electrode resin collector according to any one of claims 1 to 4.