JP2023147402A - Ptc functional composition, ptc functional composition layer, coated current collector for non-aqueous electrolyte secondary battery, electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

To provide a PTC functional composition with excellent coating properties and slurry stability.SOLUTION: A PTC functional composition includes a conductive material, a water-soluble resin, water-dispersed resin particles, and an aqueous medium, and the water-soluble resin is a nonionic polymer containing a (meth)acrylamide monomer unit or a nonionic polymer containing an N-vinylamide monomer unit.SELECTED DRAWING: None

Description

The present invention relates to a PTC functional composition, a PTC functional composition layer using the PTC functional composition, a coated current collector for a nonaqueous electrolyte secondary battery, an electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte It is related to secondary batteries.

Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are widely used as power sources for smartphones, notebook computers, etc., and have recently been used in large batteries such as those for vehicles. On the other hand, although lithium-ion secondary batteries have the advantage of high energy density, they use non-aqueous electrolytes and require sufficient safety measures. Security has become even more important.

Therefore, lithium-ion secondary batteries are required to have a so-called shutdown function that spontaneously and safely stops charging and discharging in the event of an unexpected accident such as a breakdown, and this function is provided to the separator inside the battery. . However, there are cases where the shutdown by the separator is incomplete and the temperature rises further than the melting point of the separator, or when the external temperature rises, the separator melts and an internal short circuit occurs, so measures are required to further improve safety. It is being

As a countermeasure, a technology has been proposed in which a positive temperature coefficient (PTC) functional composition is formed in the current collector or active material layer that constitutes the electrode of a lithium secondary battery (for example, see Patent Documents 1 and 2). ).

International Publication WO2019/003721 Publication International Publication WO2016/158480 Publication

By the way, in conventionally known PTC functional compositions, aggregates are formed in the slurry due to interactions between functional groups of multiple types of resins used to form the composition, resulting in deterioration of coatability and stability of the slurry. Problems such as sexual deterioration occur. Therefore, when creating a non-aqueous electrolyte secondary battery using a current collector with such a PTC functional composition as a base layer, the thickness of the PTC functional composition becomes large, making it difficult to improve energy density. It becomes an inhibiting factor.

Therefore, the main object of the present invention is to provide a PTC functional composition with excellent coating properties and slurry stability.

That is, aspect 1 of the present invention contains a conductive material, a water-soluble resin, water-dispersed resin fine particles, and an aqueous medium, and the water-soluble resin is a nonionic polymer containing a (meth)acrylamide monomer unit. , or a PTC functional composition which is a nonionic polymer containing an N-vinylamide monomer unit.

A second aspect of the present invention is the PTC functional composition according to the first aspect, wherein the water-dispersed resin particles are a polyolefin material.

Aspect 3 of the present invention is the PTC functional composition of Aspect 2, wherein a part or all of the repeating units of the water-dispersed resin particles are modified with maleic acid.

Aspect 4 of the present invention is the PTC functional composition according to any one of Aspects 1 to 3, wherein the conductive material is made of one or more types of carbon materials.

Aspect 5 of the present invention is the PTC functional composition according to any one of Aspects 1 to 4, wherein the aqueous medium is water or a liquid medium compatible with water.

Aspect 6 of the present invention is that the content of the conductive material is 10 to 70% by mass, and the content of the water-soluble resin is 1 to 50% by mass, with the total solid content of the PTC functional composition being 100% by mass. %, and the content of the water-dispersed resin particles is 5 to 70% by mass.

Another aspect of the present invention is a PTC functional composition layer containing the PTC functional composition of each aspect of the present invention as described above, and the PTC functional composition layer is formed on a current collector. A coated current collector for a non-aqueous electrolyte secondary battery, an electrode for a non-aqueous electrolyte secondary battery equipped with the coated current collector for a non-aqueous electrolyte secondary battery, or a non-aqueous electrolyte secondary battery equipped with the electrode for a non-aqueous electrolyte secondary battery. It includes a water electrolyte secondary battery.

According to the present invention, a PTC functional composition having excellent coating properties and slurry stability can be provided.

There are still some points that are unclear as to why the PTC functional composition according to the embodiments of the present invention provides excellent coating properties and slurry stability. The mechanism considered by the present inventors based on the knowledge obtained up to now will be explained below.

That is, the PTC functional composition of the present embodiment contains a conductive material, a water-soluble resin, water-dispersed resin fine particles, and an aqueous medium, and the water-soluble resin is a nonionic polymer containing a (meth)acrylamide monomer unit. Coalescence or interaction with ions present on the surface of the water dispersion resin particles that contribute to stabilizing the dispersion state of the water dispersion resin particles by being a nonionic polymer containing N-vinylamide monomer units. Since the effect is suppressed, it is possible to suppress the formation of aggregates in the slurry, and it is thought that this makes it possible to exhibit excellent coating properties and slurry stability. Note that the explanation regarding this mechanism is not intended to limit the technical scope of the present invention.

Below, a specific configuration of a secondary battery according to an embodiment of the present invention will be described.

<1. Basic configuration of non-aqueous electrolyte secondary battery>
The lithium ion secondary battery according to this embodiment includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. The shape of the lithium ion secondary battery is not particularly limited, and may be, for example, cylindrical, prismatic, laminated, button-shaped, or the like.

(1-1. Positive electrode)
The positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector.

The positive electrode current collector may be any electrically conductive material, such as a plate or foil, and is preferably made of aluminum, stainless steel, nickel-plated steel, or the like.

The positive electrode mixture layer includes at least a positive electrode active material, and may further include a conductive agent and a positive electrode binder.

The positive electrode active material is, for example, a transition metal oxide or solid solution oxide containing lithium, and is not particularly limited as long as it is a material that can electrochemically insert and release lithium ions. Examples of transition metal oxides containing lithium include Li _1.0 Ni _0.88 Co _0.1 Al _0.01 Mg _0.01 O ₂ , but also LiCoO ₂ and the like. , Li/Ni/Co/Mn based complex oxides such as _LiNix Co _y Mn _z O ₂ , Li/Ni based complex oxides such as LiNiO ₂ , or LiMn ₂ O ₄ etc. Examples include Li/Mn-based composite oxides. Solid solution oxides include Li _a Mn _x Co _y Ni _z O ₂ (1.150≦a≦1.430, 0.45≦x≦0.6, 0.10≦y≦0.15, 0.20 z≦0.28), LiMn _1.5 Ni _0.5 O ₄ and the like. Note that the content (content ratio) of the positive electrode active material is not particularly limited, and may be any content that can be applied to the positive electrode mixture layer of a nonaqueous electrolyte secondary battery. Further, these compounds may be used alone or in combination.

The conductive agent is not particularly limited as long as it is used to enhance the conductivity of the positive electrode. Specific examples of the conductive agent include those containing one or more selected from carbon black, natural graphite, artificial graphite, and fibrous carbon. Examples of carbon black include furnace black, channel black, thermal black, Ketjen black, acetylene black, and the like. Examples of fibrous carbon include carbon nanotubes, graphene, carbon nanofibers, and the like. The content of the conductive agent is not particularly limited, and may be any content that can be applied to the positive electrode mixture layer of a non-aqueous electrolyte secondary battery.

Examples of the positive electrode binder include fluorine-containing resins such as polyvinylidene fluoride, ethylene-containing resins such as styrene-butadiene rubber, ethylene-propylene diene terpolymer, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, Examples include polyethylene, polyvinyl alcohol, carboxymethylcellulose or carboxymethylcellulose derivatives (salts of carboxymethylcellulose, etc.), nitrocellulose, and the like. The positive electrode binder is not particularly limited as long as it can bind the positive electrode active material and the conductive agent onto the positive electrode current collector.

(1-2. Negative electrode)
The negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector.

The negative electrode current collector may be of any type as long as it is a conductor, such as a plate or foil, and is preferably made of copper, stainless steel, nickel-plated steel, etc. .

The negative electrode mixture layer includes at least a negative electrode active material, and may further include a conductive agent and a negative electrode binder.

The negative electrode active material is not particularly limited as long as it can electrochemically insert and release lithium ions, but examples include graphite active materials (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, (natural graphite coated with artificial graphite, etc.), Si-based active material or Sn-based active material (e.g., mixture of graphite active material with fine particles of silicon (Si) or tin (Sn) or their oxides, Possible materials include fine particles, alloys based on silicon or tin), metallic lithium, titanium oxide compounds such as Li ₄ Ti ₅ O ₁₂ , and lithium nitride. As the negative electrode active material, one type of those listed above may be used, or two or more types may be used in combination. Note that the silicon oxide is represented by SiOx (0≦x≦2).

The conductive agent is not particularly limited as long as it enhances the conductivity of the negative electrode, and for example, the same materials as those described in the section regarding the positive electrode can be used.

The negative electrode binder is not particularly limited as long as it can bind the negative electrode active material and the conductive agent onto the negative electrode current collector. Examples of the negative electrode binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), metal salt of carboxymethyl cellulose (CMC), etc. It's okay. One type of binder may be used alone, or two or more types may be used.

(1-3. Separator)
The separator is not particularly limited, and any separator may be used as long as it can be used as a separator for lithium ion secondary batteries. As the separator, it is preferable to use porous membranes, nonwoven fabrics, etc., which exhibit excellent high rate discharge performance, alone or in combination. Examples of resins constituting the separator include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene copolymer. Copolymer, vinylidene fluoride-perfluorovinylether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexane Fluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, Examples include vinylidene fluoride-ethylene-tetrafluoroethylene copolymer. Note that the porosity of the separator is not particularly limited, and any porosity that a separator of a conventional lithium ion secondary battery has can be applied.

On the surface of the separator, there may be a heat-resistant layer containing inorganic particles to improve heat resistance, or a layer containing an adhesive to bond to the electrodes and fix the battery element. Examples of the above-mentioned inorganic particles include Al ₂ O ₃ , AlOOH, Mg(OH) ₂ , and SiO ₂ . Examples of adhesives include vinylidene fluoride-hexafluoropropylene copolymers, acid-modified vinylidene fluoride polymers, and styrene-(meth)acrylate copolymers.

(1-4. Nonaqueous electrolyte)
As the non-aqueous electrolyte, the same non-aqueous electrolyte as conventionally used in lithium ion secondary batteries can be used. The nonaqueous electrolyte has a composition in which an electrolyte salt is contained in a nonaqueous solvent that is a solvent for the electrolyte.

Examples of the nonaqueous solvent include cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, vinylene carbonate, cyclic esters such as γ-butyrolactone and γ-valerolactone, and dimethyl carbonate. , chain carbonates such as diethyl carbonate and ethyl methyl carbonate, chain esters such as methyl formate, methyl acetate, methyl butyrate, ethyl propionate, and propyl propionate, tetrahydrofuran or its derivatives, 1,3-dioxane, 1, 4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, ethers such as methyl diglyme, ethylene glycol monopropyl ether, propylene glycol monopropyl ether, nitriles such as acetonitrile, benzonitrile, Dioxolane or its derivatives, ethylene sulfide, sulfolane, sultone or its derivatives, etc. can be used alone or in combination of two or more thereof. In addition, when using a mixture of two or more types of the above-mentioned non-aqueous solvents, the mixing ratio of each non-aqueous solvent can be applied to the mixing ratio used in conventional lithium ion secondary batteries.

Examples of electrolyte salts include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LIPF ₆ -x (C _n F _2n+1 )x [where 1<x<6, n=1or2], LiSCN, LiBr, LiI, Inorganic ionic salts containing one of lithium (Li), sodium (Na) or potassium (K) such as Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN; _{LiCF3SO3 ,} LiN( _{CF3SO2 ) 2 ,} LiN( _{C2F5SO2 ) 2 ,} LiN( _{CF3SO2 )} ( _{C4F9SO2 )} , LiC( _{CF3SO2 ) 3} , _LiC ( _{C2F5SO2 ) 3} , ( _CH3 ) _{4NBF4 , ( CH3} ) _{4NBr ,} ( _C2H5 ) _{4NClO4 ,} ( _C2H5 ) _4NI , _{( C3H7} ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, ( Examples include organic ionic salts such as C ₂ H ₅ ) ₄ N-phtalate, lithium stearyl sulfonate, lithium octylsulfonate, and lithium dodecylbenzenesulfonate, and these ionic compounds may be used alone or in combination of two or more. It is possible to use Note that the concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte used in conventional lithium ion secondary batteries, and is not particularly limited. In this embodiment, it is preferable to use a non-aqueous electrolytic solution containing the above-mentioned lithium compound (electrolyte salt) at a concentration of about 0.8 mol/l or more and 1.5 mol/l or less.

Note that various additives may be added to the non-aqueous electrolyte. Such additives include negative electrode additives, positive electrode additives, ester additives, carbonate ester additives, sulfate ester additives, phosphate ester additives, and boric ester additives. , acid anhydride-based additives, electrolyte-based additives, and the like. Any one of these additives may be added to the non-aqueous electrolyte, or multiple types of additives may be added to the non-aqueous electrolyte.

<2. Method for manufacturing a non-aqueous electrolyte secondary battery according to the present embodiment>
Next, a method for manufacturing a lithium ion secondary battery will be explained.
The positive electrode is produced as follows. First, a positive electrode slurry is formed by dispersing a mixture of a positive electrode active material, a conductive agent, and a positive electrode binder in a desired ratio in a positive electrode slurry solvent. Next, this positive electrode slurry is applied onto a positive electrode current collector and dried to form a positive electrode mixture layer. Note that the coating method is not particularly limited, and examples thereof include a knife coater method, a gravure coater method, a reverse roll coater, a slit die coater, and the like. The following coating steps are also performed in the same manner. Next, the positive electrode mixture layer is pressed using a press so that it has a desired density. In this way, a positive electrode is produced.

The negative electrode is produced in the same way as the positive electrode. First, a negative electrode slurry is prepared by dispersing a mixture of materials constituting the negative electrode mixture layer in a negative electrode slurry solvent. Next, a negative electrode mixture layer is formed by applying the negative electrode slurry onto the negative electrode current collector and drying it. Next, the negative electrode mixture layer is pressed using a press so that it has a desired density. In this way, a negative electrode is produced.

Next, an electrode structure is produced by sandwiching the separator between a positive electrode and a negative electrode. Next, the electrode structure is processed into a desired shape (for example, cylindrical, square, laminated, button-shaped, etc.) and inserted into a container of the desired shape. Next, by injecting the non-aqueous electrolyte into the container, each pore in the separator and the voids in the positive and negative electrodes are impregnated with the electrolyte. In this way, a lithium ion secondary battery is manufactured.

<3. Characteristic configuration of non-aqueous electrolyte secondary battery according to this embodiment>
Below, the characteristic structure of the non-aqueous electrolyte secondary battery according to this embodiment will be explained.

(3-1. PTC functional composition layer)
The above-described positive electrode and negative electrode further include a PTC functional composition layer containing a positive temperature coefficient (PTC) functional composition as an underlayer.

The PTC functional composition layer contains at least a conductive material, a water-soluble resin, water-dispersed resin particles, and an aqueous medium. The PTC functional composition layer may be formed between the positive electrode current collector and the negative electrode current collector, for example, between the positive electrode current collector and the positive electrode mixture layer, and/or between the negative electrode current collector and the negative electrode mixture layer. In this embodiment, the PTC functional composition layer is provided both between the positive electrode current collector and the positive electrode mixture layer and between the negative electrode current collector and the negative electrode mixture layer.

<Conductive material>
The conductive material is a particulate material that has conductivity, and includes carbon materials such as graphite, carbon black, furnace black, graphitized furnace black, conductive carbon fibers (carbon nanotubes, carbon nanofibers, carbon fibers), fullerene, etc. It consists of one or more of the following.

When the content of the conductive material is low, the electrical resistance of the PTC functional composition layer at the battery operating temperature increases, the voltage drop increases, and battery characteristics such as cell capacity, cell voltage, load characteristics, and cycle characteristics deteriorate. There is a fear. On the other hand, if the content of the conductive material is too large, the content of the water-dispersed resin will be relatively reduced, and the PTC function may become insufficient. Therefore, the content of the conductive material is preferably 10% by mass or more and 70% by mass or less, and 17.5% by mass or more and 35% by mass, based on 100% by mass of the entire solid content excluding liquid components such as solvents from the PTC functional composition. It is more preferably at most 22.5% by mass and at most 35% by mass.

In addition, the entire solid content of the PTC functional composition refers to the total mass of solids remaining after all the liquid parts are volatilized by drying, that is, when producing the PTC functional composition. It is equal to the total mass of each component used as powder. The same applies below.

<Water-soluble resin>
The water-soluble resin is water-soluble and binds the conductive material and the water-dispersed resin particles. Water-soluble here means, for example, that when 1 g of water-soluble resin (E) is added to 99 g of water at 25°C, stirred, and left at 25°C for 24 hours, the resin can be dissolved in water without separation or precipitation. mean something Specifically, the water-soluble resin of the present invention is characterized in that it is a nonionic polymer containing a (meth)acrylamide monomer unit or a nonionic polymer containing an N-vinylamide monomer unit. shall be.

Examples of (meth)acrylamide monomer units include acrylamide, methacrylamide, N-isopropylacrylamide, N-methylolacrylamide, N-(2-hydroxyethyl)acrylamide, N,N-dimethyl(meth)acrylamide, N , N-diethyl (meth)acrylamide, N-butylacrylamide, N-tertbutylacrylamide, acroylmorpholine and the like.

Among (meth)acrylamide-based monomer units, acrylamide is preferred from the viewpoints of water solubility, adhesion, and low electrolyte swelling property. Examples of the N-vinylamide monomer unit include N-vinylformamide, N-vinylacetamide, N-vinylisobutyramide, and the like. These (meth)acrylamide monomer units and N-vinylamide monomer units may contain one type alone or two or more types in any ratio.

Further, the water-soluble resin may contain other monomer units other than the (meth)acrylamide monomer unit and the N-vinylamide monomer unit. Other monomer units are not particularly limited as long as they are nonionic monomer units that can be copolymerized with the (meth)acrylamide monomer and the N-vinylamide monomer. Examples of other nonionic monomer units include (meth)acrylic acid ester monomer units, vinyl cyanide monomer units, vinyl alcohol, vinyl pyrrolidone, and the like.

If the content of the water-soluble resin is low, the binding properties of the water-soluble resin will be impaired, and PTC functional composition layer components such as conductive agents will fall off from the current collector during manufacturing, making it impossible to obtain sufficient PTC function. There is a fear. On the other hand, if the content of the water-soluble resin is too large, there is a risk that the battery characteristics will be degraded due to a lack of the conductive agent and the PTC function will be degraded due to the lack of the water-dispersible resin. Therefore, the content of the water-soluble resin is preferably 1% by mass or more and 50% by mass or less, and 10% by mass or more and 40% by mass, based on 100% by mass of the entire solid content excluding liquid components such as solvents from the PTC functional composition. % or less, more preferably 22.5% by mass or more and 32.5% by mass or less.

<Water-dispersed resin particles>
Water-dispersed resin fine particles are generally also called aqueous emulsions, and are resin particles that are not dissolved in water but are dispersed in the form of fine particles.

Specifically, the water-dispersed resin particles include, for example, ethylene, propylene, isobutylene, isobutene, 1-butene, 2-butene, 1-pentene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1- Examples include polyolefin materials containing hexene, 1-octene, norbornene, etc. as olefin components. The polyolefin material constituting the water-dispersed resin particles may be a single polymer of these olefin components, or a copolymer of two or more components.

Further, it is preferable that the polyolefin material constituting the water-dispersed resin particles has some or all of its repeating units modified with a compound having maleic acid or ethyl acrylate, and it is particularly preferred that the polyolefin material be modified with maleic acid. preferable.

If the content of water-dispersed resin fine particles is low, there is a risk that the so-called shutdown function, which spontaneously and safely stops charging and discharging, may be insufficient when the battery temperature rises due to an unexpected accident such as a breakdown. On the other hand, if the content of the water-soluble resin fine particles is too large, a shutdown function may be developed at a temperature rise that does not require the development of a so-called shutdown function that stops charging and discharging, and battery performance may deteriorate. Therefore, the content of the water-dispersed resin particles is preferably 5% by mass or more and 70% by mass or less, and 20% by mass or more and 60% by mass, based on 100% by mass of the entire solid content excluding liquid components such as solvents from the PTC functional composition. It is more preferably at most 35% by mass and at most 50% by mass.

<Aqueous medium>
As the aqueous medium, it is preferable to use water, but if necessary, for example, a liquid medium that is compatible with water may be used in order to improve the coating properties on the current collector.

Liquid media that are compatible with water include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, and phosphoric acid esters. ethers, nitriles, etc., and may be used within a range that is compatible with water.

<Other additives>
The PTC functional composition may further contain other additives such as a surfactant, a film forming aid, an antifoaming agent, a leveling agent, a preservative, a pH adjuster, a viscosity adjuster, etc. as necessary. good. Other additives such as surfactants, film-forming aids, antifoaming agents, leveling agents, preservatives, pH adjusters, and viscosity adjusters are preferably nonionic. Other nonionic additives include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene cetyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene alkyl allyl ether, Oxyethylene derivatives, oxyethylene/oxypropylene block copolymers, sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monostearate, sorbitan trioleate, glycerin fatty acid esters, polyoxyethylene fatty acid esters, sucrose fatty acid esters, polyethylene glycol, polypropylene Examples include glycol and the like. If other additives such as surfactants, film-forming aids, antifoaming agents, leveling agents, preservatives, pH adjusters, and viscosity modifiers are used, problems may occur when the above additives are added. The generation of aggregates in the PTC functional composition can be suppressed.

(3-2. Method for producing PTC functional composition layer)
The above-described PTC functional composition is suspended in a solvent such as water or NMP to form a slurry, and the thickness after drying is preferably 0.1 μm or more and 5 μm or less, more preferably on a positive electrode current collector or negative electrode current collector. can be formed by applying the coating to a thickness of 0.3 μm or more and 2 μm or less and drying it. In this specification, a current collector having a PTC functional composition layer formed on its surface is referred to as a coated current collector. It is preferable that the thickness of the PTC functional composition layer of the coated current collector is 0.1 μm or more, since the PTC function can be sufficiently exhibited during abnormal heat generation. Further, it is preferable that the thickness of the PTC functional composition layer of the coated current collector is 5 μm or less, since it is possible to secure the content ratio of the active material in the electrode and suppress a decrease in battery capacity. By forming a mixture layer on the PTC functional composition layer included in this coated current collector, an electrode for a secondary battery that becomes a positive electrode or a negative electrode can be produced.

More specifically, the positive electrode is formed by forming a positive electrode mixture layer on the PTC functional composition layer of a coated current collector for a positive electrode that includes a PTC functional composition layer and a positive electrode current collector. can do. Similarly, the negative electrode can be formed by forming a negative electrode mixture layer on the PTC functional composition layer of a coated current collector for a negative electrode that includes a PTC functional composition layer and a negative electrode current collector. can.

Hereinafter, the present invention will be explained in more detail based on specific examples. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

<Synthesis of water-soluble resin>
(Synthesis of water-soluble resin (B-1))
60.0 g of acrylamide and 1125.0 g of ion-exchanged water were charged into a 2000 mL separable flask equipped with a mechanical stirrer, stirring rod, and thermometer, and the mixture was stirred at 400 rpm.The inside of the system was replaced with nitrogen, and the jacket temperature was lowered. The temperature was raised to a setting of 85°C. When the temperature inside the system reached 60°C, an aqueous initiator solution containing 1217 mg of 2,2'-azobis(2-methyl-N-2-hydroxyethylpropionamide) dissolved in 15.0 g of ion-exchanged water was added. With the jacket temperature set at 85° C., stirring was continued for 12 hours from the addition of the initiator described above to obtain a colorless and transparent polymer aqueous solution. The nonvolatile content of the aqueous solution after the reaction was measured and found to be 5.1% by mass. This was collected to obtain an aqueous solution containing 5.1% by mass of water-soluble resin (B-1) and having a pH of 7.2.

(Synthesis of water-soluble resin (B-2))
45.0 g of acrylamide, 45.0 g of methacrylamide, and 790.0 g of ion-exchanged water were charged into a 2000 mL separable flask equipped with a mechanical stirrer, a stirring rod, and a thermometer. After stirring at 400 rpm, the system was filled with nitrogen. After the replacement, the jacket temperature was set at 85°C and the temperature was raised. When the system temperature reached 60° C., an aqueous initiator solution containing 1,675 mg of 2,2'-azobis(2-methyl-N-2-hydroxyethylpropionamide) dissolved in 20.0 g of ion-exchanged water was added. With the jacket temperature set at 85° C., stirring was continued for 12 hours from the addition of the initiator described above to obtain a colorless and transparent polymer aqueous solution. The nonvolatile content of the aqueous solution after the reaction was measured and found to be 10.0% by mass. This was recovered to obtain an aqueous solution containing 10.0% by mass of water-soluble resin (B-2) and having a pH of 7.8.

(Synthesis of water-soluble resin (B-3))
In a 2000 mL separable flask equipped with a mechanical stirrer, a stirring rod, and a thermometer, 100.0 g of N-vinylformamide and 880.0 g of ion-exchanged water were charged and stirred at 400 rpm, and then the system was replaced with nitrogen. The jacket temperature was set at 85° C. and the temperature was raised. When the temperature inside the system reached 60° C., an aqueous initiator solution containing 2,028 mg of 2,2′-azobis(2-methyl-N-2-hydroxyethylpropionamide) dissolved in 20.0 g of ion-exchanged water was added. With the jacket temperature set at 85°C, stirring was continued for 6 hours from the addition of the above-mentioned initiator, and then 2028 mg of 2,2'-azobis(2-methyl-N-2-hydroxyethylpropionamide) was added to 20.0 g of ion-exchanged water. An aqueous initiator solution dissolved in the solution was added and stirring was continued for an additional 6 hours to obtain a colorless and transparent aqueous polymer solution. The nonvolatile content of the aqueous solution after the reaction was measured and found to be 10.0% by mass. This was collected to obtain an aqueous solution containing 10.0% by mass of water-soluble resin (B-3) and having a pH of 7.5.

<Selection of water-soluble resin>
A 1.36% by mass aqueous solution of sodium salt of carboxymethylcellulose was used as the water-soluble resin (B-4). Further, a 25.0% by mass solution of sodium salt of polyacrylic acid was used as the water-soluble resin (B-5).

<Preparation of PTC functional composition>
(Example 1)
Add 70.0 g of conductive material (A-1) as a conductive carbon material, 588 g of a 5.1% aqueous solution (30 g as solid content) of water-soluble resin (B-1) as a binder, and 100.0 g of water. Mixing was performed for 20 minutes at 3000 rpm using a disper. The above mixture was subjected to high-pressure dispersion treatment using NanoVator manufactured by Yoshida Kogyo Kikai Co., Ltd. at a pressure of 80 MPa. The high-pressure dispersion treatment was repeated three times to obtain a dispersion of conductive material (A-1). Next, 120 g (30 g as solid content) of the water-dispersed resin particles (C-1) was mixed with the dispersion using a mixer at 500 rpm for 10 minutes to obtain a PTC functional composition.

(Examples 2 to 20)
According to the composition ratio shown in Table 4, a PTC functional composition, a secondary battery cell, and a positive electrode symmetrical cell were prepared using the same procedure except that the types and amounts of the conductive material, water-soluble resin, and water-dispersed resin particles were changed. Ta.

(Comparative Examples 1 to 11)
According to the composition ratio shown in Table 4, a PTC functional composition, a secondary battery cell, and a positive electrode symmetrical cell were prepared using the same procedure except that the types and amounts of the conductive material, water-soluble resin, and water-dispersed resin particles were changed. Ta.

<Production of lithium ion secondary battery>
(Coated current collector)
A PTC functional composition was coated onto an aluminum current collector foil having a thickness of 10 μm using a gravure coater to a thickness of 1.5 μm or 3 μm and dried to prepare a coated current collector.

(Cathode production)
By dispersing and mixing LiCoO ₂ , acetylene black, and polyvinylidene fluoride in an N-methyl-2-pyrrolidone solvent at a solid content mass ratio of 97.7:1.0:1.3, a positive electrode mixture slurry was prepared. Created. Next, the slurry was applied to one side of the coated current collector on which the PTC functional composition had been applied and dried so that the amount of mixture applied (area density) after drying was 18.9 mg/cm ² on one side. After that, the mixture was pressed using a roll press machine so that the mixture layer density was 4.15 g/cc to prepare a positive electrode.

(Negative electrode production)
After dispersing and mixing 100.0 g of artificial graphite active material, 75.42 g of a 1.36 mass% aqueous solution of sodium salt of carboxymethylcellulose (CMC), and 25.86 g of ion-exchanged water, the modified styrene-butadiene copolymer was dissolved in the water solvent. A negative electrode mixture slurry was prepared by adding 3.85 g of a 40% by mass aqueous dispersion of particulate dispersion a dispersed in . Next, the slurry was coated on one side of the copper foil so that the coating amount (area density) of the mixture after drying was 11.15 mg/cm ² on one side. After drying, the mixture layer density was 11.15 mg/cm 2 with a roll press machine. A negative electrode was produced by pressing to a density of .42 g/cc.

(Secondary battery cell production)
After welding nickel and aluminum lead wires to the above-mentioned single-sided negative electrode and single-sided positive electrode, respectively, they are laminated with one single-sided negative electrode sandwiched between one single-sided positive electrode with a porous polyethylene separator interposed between them to form an electrode laminate. was created. Next, the above-mentioned electrode laminate was housed in an aluminum laminate film with the lead wire drawn out to the outside, and an electrolytic solution was injected and the film was sealed under reduced pressure to produce a secondary battery cell before initial charging. The electrolyte contains 1.3M LiPF6 and 6.0% by mass of fluorocarbon in a solvent mixed with ethylene carbonate/dimethyl carbonate/ethylpropionate/propylpropionate in a ratio of 15/15/30/40 (volume ratio). A solution containing ethylene carbonate and 0.5% by mass of vinylene carbonate was used.

(Creation of positive electrode symmetrical cell)
A positive and counter electrode cell was manufactured in the same manner as described above except that the single-sided negative electrode was changed to a single-sided positive electrode.

<Evaluation of PTC functional composition, coated current collector, electrode, and non-aqueous secondary battery>
(Presence or absence of aggregates)
In Examples 1 to 20 and Comparative Examples 1 to 11, the diameter of fine particles dispersed in the PTC functional composition was measured according to JIS-K5600-2-5 using a BYK grind meter (0-50 μm). did. The point at which noticeable spots began to appear was read, and if it was less than 15 μm, it was determined that there was no aggregation, and if it was 15 μm or more, it was determined that there was agglutination.

(increased resistance)
A method for evaluating the PTC function of the PTC functional composition in this example will be described. A positive electrode symmetrical cell was installed in an electric furnace and connected to a battery tester. Next, a K thermocouple was attached to the surface of the positive electrode symmetrical cell using heat-resistant tape. Next, the temperature inside the electric furnace was raised from room temperature to 100° C., and the 1 kHz impedance and cell surface temperature were measured using the battery tester and the K thermocouple. Taking the resistance value of Comparative Example 1 at the time of temperature rise as 100%, the relative ratio of the resistance value of each sample at the time of temperature rise was calculated as "resistance increase (%)" and is listed in Table 4.

(High temperature cycle life)
The secondary battery cells produced in Examples 1 to 20 and Comparative Examples 1 to 11 were subjected to a constant current of 0.1 CA in a constant temperature bath at 25° C. under the conditions of an end-of-charge voltage of 4.45 V and an end-of-discharge voltage of 3.0 V. Charge, perform one cycle of constant voltage charging at 0.05 CA, constant current discharging at 0.1 CA, then constant current charging at 0.2 CA under the conditions of charge end voltage 4.45 V and discharge end voltage 3.0 V, 0.05 CA. Two cycles of constant voltage charging and constant current discharging were performed at 0.2 CA. This secondary battery was transferred to a constant temperature chamber at 45°C, and charged at a constant current of 0.2CA, charged at a constant voltage of 0.05CA, and charged at a constant voltage of 0.2CA under the conditions of an end-of-charge voltage of 4.45V and an end-of-discharge voltage of 3.0V. 1 cycle of constant current discharge, 49 cycles of constant current charging at 0.2CA, constant voltage charging at 0.05CA, constant current discharging at 0.2CA under the conditions of charge end voltage 4.45V and discharge end voltage 3.0V. Ta. After the 51st cycle, the above charge/discharge pattern was repeated up to 200 cycles. The capacity retention rate (%) at the 200th cycle was calculated as (discharge capacity at 200th cycle)÷(initial discharge capacity)×100.

(high temperature storage)
The secondary battery cells produced in Examples 1 to 20 and Comparative Examples 1 to 11 were subjected to a constant current of 0.1 CA in a constant temperature bath at 25° C. under the conditions of an end-of-charge voltage of 4.45 V and an end-of-discharge voltage of 3.0 V. Charging, constant voltage charging at 0.05 CA, constant current discharging at 0.1 CA for one cycle, then constant current charging at 0.2 CA under conditions of charge end voltage 4.45 V and discharge end voltage 3.0 V, and constant current charging at 0.05 CA. Two cycles of constant voltage charging and constant current discharging at 0.2 CA were performed, and constant current charging at 0.2 CA and constant voltage charging at 0.05 CA were performed at a charge end voltage of 4.45 V to bring the secondary battery into a fully charged state. I made it. The cell voltage and 1 kHz impedance of the fully charged secondary battery were measured using a battery tester, and the battery was stored in a constant temperature bath at 60°C. The stored fully charged secondary batteries were returned to room temperature on the 1st, 3rd, and 7th days, and the OCV and 1 kHz impedance were measured using a battery tester, and then stored in a constant temperature bath at 60°C. After returning the stored fully charged secondary battery to room temperature on the 14th day and measuring the OCV and 1kHz impedance with a battery tester, it was heated at 0.2CA at a discharge end voltage of 3.0V in a 25℃ thermostatic chamber. Constant current discharge, then 2 cycles of constant current charging at 0.2 CA, constant voltage charging at 0.05 CA, and constant current discharging at 0.2 CA under the conditions of a charge end voltage of 4.45 V and a discharge end voltage of 3.0 V, Residual capacity and recovered capacity were measured.

(Evaluation of resistance increase during high temperature storage)
The increase in resistance (%) during high temperature storage was calculated as (1 kHz impedance of the secondary battery measured on the 14th day of high temperature storage) ÷ (1 kHz impedance of the secondary battery measured immediately before high temperature storage) x 100%.

(Evaluation of voltage drop during high temperature storage)
The voltage drop (V) during high-temperature storage was calculated as (OCV of the secondary battery measured immediately before high-temperature storage) - (OCV of the secondary battery measured on the 14th day of high-temperature storage).

(Residual capacity during high temperature storage)
After measuring the 1 kHz impedance and OCV on the 14th day of high-temperature storage, constant current discharge was performed at 0.2 CA at a discharge end voltage of 3.0 V in a constant temperature bath at 25°C. The discharge capacity obtained in this measurement was divided by the full charge capacity before high temperature storage and multiplied by 100% to calculate the remaining capacity during high temperature storage.

(Recovery capacity during high temperature storage)
After measuring the remaining capacity during high-temperature storage, constant current charging at 0.2CA and constant voltage charging at 0.05CA at 0.2CA and constant voltage charging at 0.2CA under the conditions of charge end voltage 4.45V and discharge end voltage 3.0V in a 25℃ constant temperature oven. Two cycles of constant current discharge were performed. The discharge capacity at the second cycle was divided by the full charge capacity before high-temperature storage, and the product was multiplied by 100% to calculate the recovery capacity during high-temperature storage.

(Evaluation results)
Table 1 shows the physical properties of the conductive materials (A-1) to (A-5) used in the Examples and Comparative Examples described above. The structural formulas of the water-soluble resins (B-1) to (B-3) are shown in Table 2, and the physical properties and solid content concentrations of the water-dispersed resin particles (C-1) to (C-5) are shown in Table 3. Furthermore, the evaluation results of Examples 1 to 20 and Comparative Examples 1 to 11 are summarized in Table 4.

First, in Comparative Example 1 without an undercoat, the increase in resistance due to temperature rise was insufficient. Furthermore, in Comparative Examples 2 to 11 in which PTC functional compositions were prepared using anionic water-soluble resins, agglomeration occurred and coated current collectors that could be used for practical use could not be obtained. It is thought that the polyolefin water dispersion used as the water-dispersed resin particles in the embodiment of the present invention maintains an emulsion state by introducing modified functional groups, adjusting the pH, adding a surfactant, etc. The water-soluble resins (B-4) and (B-5) used in Examples 2 to 11 are ionic resins, and their addition makes the dispersion state of the polyolefin water dispersion unstable and causes aggregation. It is thought that it will form.

On the other hand, in Examples 1 to 20, it was confirmed that no aggregation occurred during the preparation of the PTC functional compositions, and that the compositions had excellent coating properties and slurry stability. This is because the water-soluble resins (B-1), (B-2), and (B-3) used in Examples 1 to 20 are nonionic, and the introduction of modified functional groups, pH adjustment, and surfactant This is thought to be due to the fact that the dispersion state of the polyolefin particles maintained by the addition was not destabilized. Furthermore, in Examples 1 to 20, it was confirmed that the electrical resistance increased sufficiently when the temperature rose, and that PTC (positive temperature coefficient) functionality was expressed.

Comparing Examples 1 to 12 and Examples 13 to 16, it was confirmed that Examples 1 to 12 had better high temperature cycle life and high temperature storage characteristics. The water-dispersed resin particles (C-1), (C-4), and (C-5) used in Examples 1 to 12 were modified with a compound having maleic acid, and the water-dispersed resin particles used in Examples 13 to 16 were Particles (C-2) and (C-3) are modified with a compound containing ethyl acrylate. From the viewpoint of improving high-temperature cycle characteristics and high-temperature storage characteristics, it is considered preferable that the water-dispersed resin particles be modified using a compound containing maleic acid.

Comparing Examples 1 to 10, it is confirmed that the greater the content of water-dispersed resin particles in the PTC functional composition, the greater the resistance increase. From the viewpoint of improving the PTC function, it is considered that the larger the content of water-dispersed resin particles in the PTC functional composition is, the more preferable it is. On the other hand, when comparing the high-temperature cycle characteristics and the increase in resistance during high-temperature storage in Examples 1 to 10, it was found that the smaller the content of water-dispersed resin particles in the PTC functional composition, the better the high-temperature cycle characteristics and cell characteristics during high-temperature storage. A positive trend is confirmed. For example, from the viewpoint of improving cell characteristics at high temperatures such as 45° C. and 60° C., it is considered that the smaller the content of water-dispersed resin particles in the PTC functional composition, the better. When the content of water-dispersed resin particles in the PTC functional composition is changed in this way, there is a trade-off relationship between the PTC function and the cell properties. If the total solid content excluding liquid components is 100% by mass, and the content of water-dispersed resin particles is 5% by mass or more and 70% by mass or less, PTC function and cell properties can be achieved simultaneously, and 20% by mass or more and 60% by mass. If it is below, the PTC function and the cell characteristics can be more highly compatible, and if it is 35% by mass or more and 50% by mass or less, the PTC function and the cell characteristics can be compatible even more highly.

Comparing Examples 1 to 10, it is confirmed that the smaller the content of carbon material in the PTC functional composition, the greater the resistance increase. From the viewpoint of improving the PTC function, it is considered that the smaller the content of the carbon material in the PTC functional composition, the more preferable it is. On the other hand, when comparing the high-temperature cycle characteristics and resistance increase during high-temperature storage of Examples 1 to 10, it is found that the higher the content of carbon material in the PTC functional composition, the better the high-temperature cycle characteristics and cell characteristics during high-temperature storage. is confirmed. For example, from the viewpoint of improving cell characteristics at high temperatures such as 45° C. and 60° C., it is considered that the higher the content of the carbon material in the PTC functional composition, the more preferable it is. When the content of carbon material in the PTC functional composition is changed in this way, there is a trade-off relationship between the PTC function and the cell properties. The PTC function and cell properties can be achieved both if the carbon material content is 10% by mass or more and 70% by mass or less, and if the total solid content excluding 100% by mass is 17.5% by mass or more and 35% by mass or less. If it is 22.5% by mass or more and 35% by mass or less, the PTC function and cell characteristics can be compatible to a higher degree.

Comparing the increase in resistance in Example 1 and the increase in resistance in Example 17, it is confirmed that the increase in resistance in Example 17 is large. In Example 1 and Example 17, the composition of the PTC functional composition is the same, but the thickness of the PTC functional composition is different. It is thought that when the thickness of the PTC functional composition is large, the electrical resistance of the PTC functional composition layer after the PTC function is expressed becomes large, so that the PTC function becomes large. On the other hand, the PTC functional composition layer provided in the secondary battery cell as described in the embodiment of the present invention does not contain a general active material for non-aqueous electrolyte secondary battery electrodes. From the viewpoint of improving the energy density of the secondary battery cell, it is considered that the smaller the thickness of the PTC functional composition layer, the more preferable it is. When the thickness of the PTC functional composition layer is changed in this way, there is a trade-off relationship between the PTC function and the cell characteristics. If the thickness of the functional composition is 0.1 μm or more and 5 μm or less, PTC function and cell characteristics can be compatible, and if the thickness is 0.3 μm or more and 2 μm or less, they can be compatible to a higher degree.

Claims (10)

Contains a conductive material, a water-soluble resin, water-dispersed resin particles, and an aqueous medium,
A PTC functional composition, wherein the water-soluble resin is a nonionic polymer containing a (meth)acrylamide monomer unit or a nonionic polymer containing an N-vinylamide monomer unit. The PTC functional composition according to claim 1, wherein the water-dispersed resin particles are a polyolefin material. The PTC functional composition according to claim 2, wherein a part or all of the repeating units of the water-dispersed resin particles are modified with a compound having maleic acid. The PTC functional composition according to any one of claims 1 to 3, wherein the conductive material is made of one or more types of carbon materials. The PTC functional composition according to any one of claims 1 to 4, wherein the aqueous medium is water or a liquid medium compatible with water. The total solid content of the PTC functional composition is 100% by mass,
The content of the conductive material is 10 to 70% by mass,
The content of the water-soluble resin is 1 to 50% by mass,
The PTC functional composition according to any one of claims 1 to 5, wherein the content of the water-dispersed resin particles is 5 to 70% by mass. A PTC functional composition layer containing the PTC functional composition according to any one of claims 1 to 6. A coated current collector for a non-aqueous electrolyte secondary battery, comprising the PTC functional composition layer according to claim 7. An electrode for a non-aqueous electrolyte secondary battery, comprising the coated current collector for a non-aqueous electrolyte secondary battery according to claim 8. A non-aqueous electrolyte secondary battery comprising the electrode for a non-aqueous electrolyte secondary battery according to claim 9.