Binder for secondary battery functional layer, slurry composition for secondary battery functional layer, functional layer for secondary battery, and secondary battery

Abstract

The purpose of this invention is to provide an adhesive for a secondary battery functional layer capable of forming a functional layer with excellent heat shrinkage resistance and electrolyte affinity. The adhesive for a secondary battery functional layer of this invention is characterized by comprising a particulate polymer, wherein the particulate polymer comprises cyano-containing monomer units, cyclic ether-containing monomer units, and carboxyl-containing monomer units, and the proportion of cyclic ether-containing monomer units in the particulate polymer is 5% by mass or more.

Description

Technical Field

[0001] This invention relates to adhesives for functional layers of secondary batteries, slurry compositions for functional layers of secondary batteries, functional layers for secondary batteries, and secondary batteries. Background Technology

[0002] Lithium-ion batteries and other rechargeable batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, making them suitable for a wide range of applications. Furthermore, rechargeable batteries typically include battery components such as electrodes (positive and negative) and spacers to isolate the positive and negative electrodes and prevent short circuits between them.

[0003] Here, as a battery component for a secondary battery, a component having a functional layer comprising a bonding material and optionally containing particles (hereinafter referred to as "functional particles") that are configured to perform the desired function of the battery component is used.

[0004] Specifically, as a spacer for a secondary battery, a spacer is used that has an adhesive layer containing a bonding material and a porous membrane layer containing the bonding material and non-conductive particles as functional particles on a spacer substrate. Furthermore, as an electrode for the secondary battery, an electrode is used that has the aforementioned adhesive layer and porous membrane layer on an electrode substrate formed by disposing an electrode composite material layer on a current collector.

[0005] Then, in order to further improve the performance of secondary batteries, attempts are being made to improve the bonding materials. For example, Patent Document 1 discloses a binder for the functional layer of a non-aqueous secondary battery, which comprises a particulate polymer containing (meth)acrylate alkyl monomer units, aromatic monovinyl monomer units, epoxy / N-hydroxymethyl crosslinking monomer units, and polyolefin unsaturated crosslinking monomer units in a specified proportion. The swelling degree of the particulate polymer in a non-aqueous electrolyte is within a specified range. Then, according to Patent Document 1, by using this binder, a functional layer with excellent adhesion before and after electrolyte immersion can be formed, thereby improving the life characteristics of the non-aqueous secondary battery having this functional layer.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 6515574. Summary of the Invention

[0009] The problem the invention aims to solve

[0010] In order to achieve high capacity in secondary batteries, it is necessary to thin the battery components. However, when the functional layer formed using the binder described in the prior art is thinned, there is room for improvement in the heat shrinkage resistance of the functional layer.

[0011] Furthermore, to achieve high capacity in secondary batteries, it is also necessary to increase their density. However, when increasing the density of secondary batteries, the electrolyte injection rate during manufacturing, i.e., the electrolyte injection performance of the secondary battery, decreases. Therefore, to achieve high battery density and ensure sufficiently high electrolyte injection performance, it is necessary to improve the affinity of the functional layers of the secondary battery to the electrolyte (hereinafter, sometimes referred to as "electrolyte affinity"). However, there is room for improvement in electrolyte affinity of the functional layers formed using the aforementioned prior art binders.

[0012] Therefore, the object of the present invention is to provide a binder for a secondary battery functional layer capable of forming a functional layer with excellent heat shrinkage resistance and electrolyte affinity.

[0013] Furthermore, the present invention aims to provide a slurry composition for a secondary battery functional layer capable of forming a functional layer with excellent heat shrinkage resistance and electrolyte affinity.

[0014] Furthermore, the present invention aims to provide a functional layer for secondary batteries with excellent heat shrinkage resistance and electrolyte affinity.

[0015] Therefore, the purpose of this invention is to provide a secondary battery having this functional layer.

[0016] Solution for solving the problem

[0017] The inventors conducted in-depth research with the aim of solving the above-mentioned problems. Then, the inventors made a new discovery: by using a binder containing a specified particulate polymer, the heat shrinkage resistance and electrolyte affinity of the functional layer can be improved, thus completing the present invention.

[0018] In other words, the object of the present invention is to advantageously solve the above-mentioned problems. The binder for the functional layer of a secondary battery according to the present invention is characterized in that it comprises a particulate polymer, wherein the particulate polymer comprises cyano-containing monomer units, cyclic ether-containing monomer units, and carboxyl-containing monomer units, and the proportion of the cyclic ether-containing monomer units in the particulate polymer is 5% by mass or more. If a binder comprising a particulate polymer having the above-described composition is used, a functional layer with excellent heat shrinkage resistance and electrolyte affinity can be formed.

[0019] Furthermore, in this invention, "comprising monomer units" means "the polymer obtained using the monomer contains repeating units derived from that monomer." Additionally, in this invention, the "content ratio (mass %)" of each monomer unit (each repeating unit) contained in the polymer can be determined using... 1 H-NMR, 13 The measurements were performed using nuclear magnetic resonance (NMR) methods such as C-NMR.

[0020] Here, the binder for the secondary battery functional layer of the present invention preferably contains 40% by mass or less of the cyclic ether monomer units in the above-mentioned particulate polymer. If the content of the cyclic ether monomer units in the particulate polymer is less than or equal to the above-mentioned specified value, the heat shrinkage resistance and electrolyte affinity of the functional layer can be further improved, and the adhesion of the functional layer can be improved.

[0021] Furthermore, the adhesive for the secondary battery functional layer of the present invention preferably has the aforementioned particulate polymer having one glass transition temperature. If the particulate polymer has one glass transition temperature, the adhesion of the functional layer can be improved.

[0022] Furthermore, the adhesive for the secondary battery functional layer of the present invention preferably has a glass transition temperature of 20°C or less than that of the particulate polymer. If the glass transition temperature of the particulate polymer is below the aforementioned specified value, the adhesion of the functional layer can be improved.

[0023] Furthermore, in this invention, the glass transition temperature of the particulate polymer can be determined using the methods described in the embodiments of this specification.

[0024] Furthermore, the binder for the functional layer of the secondary battery of the present invention preferably contains 2% by mass or more and 30% by mass or less of the cyano-containing monomer units in the particulate polymer. If the content of the cyano-containing monomer units in the particulate polymer is within the above-specified range, the electrolyte affinity of the functional layer can be further improved, and the adhesion of the functional layer can be enhanced. Furthermore, if the content of the cyano-containing monomer units in the particulate polymer is within the above-specified range, the internal resistance of the secondary battery having the functional layer can be reduced.

[0025] Furthermore, the binder for the secondary battery functional layer of the present invention preferably contains carboxyl-containing monomer units in the above-mentioned particulate polymer at a ratio of 0.1% by mass or more and 10% by mass or less. If the ratio of carboxyl-containing monomer units in the particulate polymer is within the above-specified range, the electrolyte affinity of the functional layer can be further improved, and the adhesion of the functional layer can be improved.

[0026] Furthermore, the binder for the secondary battery functional layer of the present invention preferably comprises, in the form of a particulate polymer, an alkyl methacrylate monomer unit, wherein the content of the alkyl methacrylate monomer unit in the particulate polymer is 40% by mass or more and 92% by mass or less. If the content of the alkyl methacrylate monomer unit in the particulate polymer is within the aforementioned range, the heat shrinkage resistance and electrolyte affinity of the functional layer can be further improved, and the adhesion of the functional layer and the cycle characteristics of the secondary battery having the functional layer can be improved.

[0027] Furthermore, the binder for the functional layer of the secondary battery of the present invention preferably has a gel content of 85% by mass or more in the particulate polymer described above. If the gel content of the particulate polymer is 85% by mass or more, the cycle characteristics of the secondary battery having the functional layer can be improved.

[0028] Furthermore, in this invention, the "gel content of the particulate polymer" can be determined using the methods described in the embodiments of this specification.

[0029] Furthermore, the binder for the secondary battery functional layer of the present invention preferably has a volume average particle size of the aforementioned particulate polymer of 0.05 μm or more and 0.25 μm or less. If the volume average particle size of the particulate polymer is within the aforementioned range, the adhesion and electrolyte affinity of the functional layer can be further improved.

[0030] In addition, in this invention, "volume-average particle size" refers to the particle size that accounts for 50% of the cumulative volume from the smallest particle size side in the particle size distribution (volume standard) determined using laser diffraction.

[0031] Furthermore, the object of the present invention is to advantageously solve the above-mentioned problems. The slurry composition for the functional layer of a secondary battery according to the present invention is characterized in that it contains any of the above-mentioned binders. If a slurry composition containing any of the above-mentioned binders is used, a functional layer with excellent heat shrinkage resistance and electrolyte affinity can be formed.

[0032] Here, the slurry composition for the secondary battery functional layer of the present invention can further include functional particles.

[0033] For example, in the slurry composition for a secondary battery functional layer of the present invention, the aforementioned functional particles may include non-conductive particles. The slurry composition for a secondary battery functional layer of the present invention, which includes non-conductive particles as functional particles, is suitable for the formation of porous membranes.

[0034] Furthermore, the slurry composition for the secondary battery functional layer of the present invention preferably has a volume average particle size of 1.5 μm or less for the non-conductive particles. If the volume average particle size of the non-conductive particles is 1.5 μm or less, the adhesion of the formed porous film layer as the functional layer can be improved.

[0035] Furthermore, the object of the present invention is to advantageously solve the above-mentioned problems. The functional layer for secondary batteries of the present invention is characterized in that it is formed using the aforementioned slurry composition for secondary battery functional layers. The functional layer formed from the aforementioned slurry composition exhibits excellent heat shrinkage resistance and electrolyte affinity.

[0036] Furthermore, the object of the present invention is to advantageously solve the above-mentioned problems. The secondary battery of the present invention is characterized by having the aforementioned functional layer for secondary batteries. The secondary battery having the aforementioned functional layer exhibits excellent electrolyte injection properties.

[0037] Furthermore, in this specification, the functional layer containing binder materials and non-conductive particles such as inorganic particles is referred to as a "porous film layer" or "heat-resistant layer," and the functional layer containing binder materials but not containing non-conductive particles such as inorganic particles is referred to as an "adhesive layer." Additionally, the "binder material" mentioned above preferably includes, for example, the adhesive for the secondary battery functional layer of the present invention. Moreover, generally, the porous film layer (heat-resistant layer) functions to improve heat resistance and strength, while the adhesive layer functions to improve adhesion. In addition to improving heat resistance and strength, the porous film layer (heat-resistant layer) may also have the function of improving adhesion; such a porous film layer (heat-resistant layer) is sometimes referred to as a "heat-resistant adhesive layer."

[0038] Invention Effects

[0039] According to the present invention, an adhesive for a secondary battery functional layer that can form a functional layer with excellent heat shrinkage resistance and electrolyte affinity can be provided.

[0040] Furthermore, according to the present invention, a slurry composition for a secondary battery functional layer capable of forming a functional layer with excellent heat shrinkage resistance and electrolyte affinity can be provided.

[0041] Therefore, according to the present invention, it is possible to provide a functional layer for secondary batteries with excellent heat shrinkage resistance and electrolyte affinity.

[0042] Therefore, according to the present invention, it is possible to provide a secondary battery having the functional layer. Detailed Implementation

[0043] The embodiments of the present invention will now be described in detail.

[0044] Here, the binder for the functional layer of a secondary battery according to the present invention (hereinafter, sometimes simply referred to as "binder") is used in the manufacture of any functional layer (e.g., a porous membrane layer and an adhesive layer) within a secondary battery to perform functions such as reinforcement or bonding. For example, the binder for the functional layer of a secondary battery according to the present invention can be used in the preparation of the slurry composition for the functional layer of a secondary battery according to the present invention (hereinafter, sometimes simply referred to as "slurry composition"). Then, the slurry composition for the functional layer of a secondary battery according to the present invention can be used in the formation of the aforementioned functional layer. Furthermore, the functional layer for a secondary battery according to the present invention is formed by the slurry composition for the functional layer of a secondary battery according to the present invention. Then, the secondary battery of the present invention has the functional layer for a secondary battery according to the present invention. For example, the secondary battery of the present invention has a positive electrode, a negative electrode, and a spacer as battery components, and at least one of the aforementioned battery components has the functional layer for a secondary battery according to the present invention. That is, the secondary battery of the present invention includes a battery component having the functional layer of the present invention.

[0045] (Adhesive for the functional layer of secondary batteries)

[0046] The binder of the present invention comprises a defined particulate polymer. Furthermore, the binder of the present invention is typically a composition formed by dispersing the aforementioned particulate polymer in a solvent. In addition, the binder of the present invention may further contain components other than the particulate polymer and the solvent (hereinafter referred to as "other components").

[0047] <Particulate Polymers>

[0048] Particulate polymers are components that function as adhesives, imparting adhesiveness to functional layers formed using slurry compositions containing binders, and preventing components contained in the functional layers (such as functional particles like non-conductive particles) from detaching from the functional layers.

[0049] Here, the aforementioned particulate polymer comprises cyano-containing monomer units, cyclic ether-containing monomer units, and carboxyl-containing monomer units. Furthermore, the proportion of cyclic ether-containing monomer units in the aforementioned particulate polymer is at least a predetermined value. Additionally, the aforementioned particulate polymer may optionally further comprise monomer units other than cyano-containing monomer units, cyclic ether-containing monomer units, and carboxyl-containing monomer units (hereinafter referred to as "other monomer units").

[0050] Furthermore, the adhesive of the present invention comprises a particulate polymer having the above-described composition, thus the functional layer formed using the adhesive of the present invention exhibits excellent heat shrinkage resistance and electrolyte affinity. In addition, the functional layer formed using the adhesive of the present invention also exhibits excellent adhesion.

[0051] The reason why the adhesive of the present invention can improve the heat shrinkage resistance, electrolyte affinity and adhesion of the functional layer is not clear, but it is speculated to be as follows.

[0052] It is initially speculated that because the particulate polymer in the binder of the present invention contains carboxyl-containing monomer units, the particles have excellent stability and high hydrophilicity on the particle surface, thus improving the electrolyte affinity and adhesion of the functional layer.

[0053] Furthermore, it is believed that because the particulate polymer in the binder of the present invention contains cyano-containing monomer units, the interior of the particles is hydrophobic, and the carboxyl groups of the aforementioned carboxyl-containing monomer units are relatively biased to exist on the particle surface, increasing the surface acidity. Therefore, the electrolyte affinity and adhesion of the functional layer are improved.

[0054] Furthermore, because the particulate polymer in the adhesive of the present invention contains cyclic ether monomer units in a specified proportion or higher, it has a cyclic ether structure on the particle surface. It is then presumed that the cyclic ether structure of the particulate polymer interacts with other components such as the surface of the spacer substrate (e.g., a surface hydrophilized through surface treatment) and the water-soluble polymer contained in the functional layer. It is believed that through this interaction, the layer structure of the functional layer is stabilized, thereby improving the heat shrinkage resistance and electrolyte affinity of the functional layer. Furthermore, it is presumed that through this interaction, the adhesiveness of the functional layer is also improved.

[0055] <Cyano-containing monomer unit>

[0056] As cyano-containing monomers capable of forming cyano-containing monomer units, the following can be used: (meth)acrylonitrile, such as acrylonitrile and methacrylonitrile; α-haloacrylonitrile, such as α-chloroacrylonitrile and α-bromoacrylonitrile; 2-cyanoethyl (meth)acrylate, such as 2-cyanoethyl methacrylate; 2-cyanoethyl acrylamide, etc. From the viewpoint of further improving the adhesion of the functional layer, (meth)acrylonitrile is preferred, and acrylonitrile is more preferred. Furthermore, these can be used alone or in combination of two or more in any ratio.

[0057] In addition, in this invention, "(meth)acrylonitrile" means acrylonitrile and / or methacrylonitrile, and "(meth)acrylate" means acrylate and / or methacrylate.

[0058] Then, taking all repeating units (all monomer units) contained in the particulate polymer as 100% by mass, the content of cyano-containing monomer units is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. If the content of cyano-containing monomer units in the particulate polymer is at or above the aforementioned lower limit, the electrolyte affinity and adhesion of the functional layer can be further improved. On the other hand, if the content of cyano-containing monomer units in the particulate polymer is at or below the aforementioned upper limit, the electrolyte affinity and adhesion of the functional layer can be further improved, and the internal resistance of the secondary battery having the functional layer can be reduced.

[0059] <Contains cyclic ether monomer units>

[0060] The cyclic ether monomers capable of forming cyclic ether monomer units are not particularly limited as long as they contain a cyclic ether structure. Examples include monomers containing an epoxy group (epoxy ring) (epoxy-containing monomer units) and monomers containing an oxetyl group (oxetane ring) (oxetyl monomer units). Among these, from the viewpoint of further improving the heat shrinkage resistance, electrolyte affinity, and adhesion of the functional layer, epoxy-containing monomers are preferred.

[0061] Examples of epoxy-containing monomers include allyl glycidyl ether, glycidyl methacrylate, methyl methacrylate-3,4-epoxycyclohexyl methacrylate, and 4-hydroxybutyl acrylate glycidyl ether.

[0062] Then, taking all repeating units (all monomer units) contained in the particulate polymer as 100% by mass, the content of cyclic ether monomer units needs to be 5% by mass or more, preferably 10% by mass or more, preferably 40% by mass or less, and more preferably 30% by mass or less. If the content of cyclic ether monomer units in the particulate polymer is at or above the aforementioned lower limit, the functional layer formed using the binder can exhibit excellent heat shrinkage resistance, electrolyte affinity, and adhesion. Furthermore, if the content of cyclic ether monomer units in the particulate polymer is at or above the aforementioned lower limit, the gel content of the particulate polymer increases, thereby improving the cycle characteristics of the secondary battery with the functional layer. On the other hand, if the content of cyclic ether monomer units in the particulate polymer is at or below the aforementioned upper limit, the heat shrinkage resistance, electrolyte affinity, and adhesion of the functional layer can be further improved.

[0063] <Carboxyl-containing monomer unit>

[0064] Examples of carboxyl-containing monomers capable of forming carboxyl-containing monomer units include monocarboxylic acids and their derivatives, dicarboxylic acids and their anhydrides and their derivatives.

[0065] Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.

[0066] Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid.

[0067] Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.

[0068] Examples of dicarboxylic acid derivatives include: methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid; nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, fluoroalkyl maleate, and other maleic acid monoesters.

[0069] Examples of anhydrides that are dicarboxylic acids include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.

[0070] In addition, as a carboxyl-containing monomer, acid anhydrides that generate carboxyl groups through hydrolysis can also be used.

[0071] These can be used alone or in combination of two or more. Moreover, from the viewpoint of further improving the electrolyte affinity and adhesion of the functional layer, acrylic acid, methacrylic acid, and itaconic acid are preferred, and acrylic acid and methacrylic acid are more preferred.

[0072] Then, when all repeating units (all monomer units) contained in the particulate polymer are taken as 100% by mass, the content of carboxyl-containing monomer units is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, preferably 10% by mass or less, and more preferably 5% by mass or less. If the content of carboxyl-containing monomer units in the particulate polymer is at or above the above lower limit, the electrolyte affinity and adhesion of the functional layer can be further improved. On the other hand, if the content of carboxyl-containing monomer units in the particulate polymer is at or below the above upper limit, the adhesion of the functional layer can be further improved.

[0073] <Other Monomer Units>

[0074] The particulate polymer may contain monomer units other than those described above, including cyano-containing monomer units, cyclic ether-containing monomer units, and carboxyl-containing monomer units. There are no particular limitations on the monomer units, but alkyl (meth)acrylate monomer units and crosslinking monomer units are preferred. If the particulate polymer further contains alkyl (meth)acrylate monomer units, the adhesion of the functional layer can be further improved. Furthermore, if the particulate polymer further contains crosslinking monomer units, the heat shrinkage resistance of the functional layer can be further improved.

[0075] Furthermore, as described above, the (meth)acrylate alkyl monomer unit and the crosslinking monomer unit are monomer units other than those containing cyano monomer units, cyclic ether monomer units, and carboxyl monomer units. Therefore, the (meth)acrylate alkyl monomers capable of forming (meth)acrylate alkyl monomer units and the crosslinking monomers capable of forming crosslinking monomer units do not include the aforementioned cyano monomers, cyclic ether monomers, and carboxyl monomers.

[0076] Additionally, in this invention, (meth)acrylic acid means acrylic acid and / or methacrylic acid.

[0077] <<(Meth)acrylate alkyl ester monomer unit>>

[0078] Examples of alkyl methacrylate monomers capable of forming alkyl methacrylate monomer units include: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isoamyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, etc.; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isoamyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, glycidyl methacrylate, etc. These can be used alone or in combination of two or more. Moreover, among them, from the viewpoint of further improving the adhesion of the functional layer and further improving the heat shrinkage resistance, 2-ethylhexyl acrylate and butyl acrylate are preferred, and butyl acrylate is more preferred.

[0079] When all repeating units (all monomer units) contained in the particulate polymer are taken as 100% by mass, the content of (meth)acrylate alkyl monomer units is preferably 40% by mass or more, more preferably 50% by mass or more, preferably 92% by mass or less, and more preferably 80% by mass or less. If the content of (meth)acrylate alkyl monomer units in the particulate polymer is at or above the above-mentioned lower limit, the adhesion of the functional layer can be further improved. On the other hand, if the content of (meth)acrylate alkyl monomer units in the particulate polymer is at or below the above-mentioned upper limit, the heat shrinkage resistance of the functional layer can be further improved, and the cycle characteristics of the secondary battery with the functional layer can be improved.

[0080] <<Cross-linked monomer unit>>

[0081] Crosslinking monomers that can form crosslinking monomer units are monomers that can form crosslinking structures during or after polymerization by heating or irradiation with energy lines.

[0082] Examples of crosslinking monomers include polyfunctional monomers having two or more polymerization-reactive groups. Examples of such polyfunctional monomers include: divinylbenzene, 1,3-butadiene, isoprene, allyl methacrylate, and other divinyl monomers; alkyl di(meth)acrylate monomers such as ethylene dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate (EDMA), diethylene glycol diacrylate, and 1,3-butanediol diacrylate; alkyl tri(meth)acrylate monomers such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; N-hydroxymethyl (meth)acrylamide and other N-hydroxymethyl monomers; and γ-methacryloyloxypropyltrimethoxysilane. These can be used alone or in combination of two or more. Then, among them, from the viewpoint of further improving the heat shrinkage resistance of the functional layer, divinylbenzene, allyl methacrylate, ethylene glycol dimethacrylate, and N-hydroxymethylacrylamide are preferred, and allyl methacrylate and N-hydroxymethylacrylamide are more preferred.

[0083] When all repeating units (all monomer units) contained in the particulate polymer are taken as 100% by mass, the content of crosslinking monomer units is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.4% by mass or more, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. If the content of crosslinking monomer units in the particulate polymer is at or above the above lower limit, the heat shrinkage resistance of the functional layer can be further improved. On the other hand, if the content of crosslinking monomer units in the particulate polymer is at or below the above upper limit, the adhesion of the functional layer can be further improved.

[0084] <Properties of Particulate Polymers>

[0085] The structure of the particulate polymer contained in the adhesive of the present invention is not particularly limited, and can be any of the block copolymers, graft copolymers and random copolymers, preferably random copolymers.

[0086] In addition, the particulate polymer may have a core-shell structure having a core and a shell covering at least a portion of the outer surface of the core, but preferably does not have a core-shell structure.

[0087] Therefore, particulate polymers are particularly preferred to be random copolymers that do not have a core-shell structure.

[0088] <<Structure and Glass Transition Temperature of Particulate Polymers>>

[0089] By using a random copolymer without a core-shell structure, the particulate polymer can be homogenized, improving its durability (electrolyte resistance) relative to the electrolyte and enhancing its dispersibility in the slurry composition. Furthermore, the viscosity of the slurry composition can be suppressed, making it easier to remove moisture from the functional layer during drying. As a result, the adhesion of the functional layer can be further improved.

[0090] Then, in this invention, the glass transition temperature is measured to determine whether the particulate polymer is a random copolymer without a core-shell structure.

[0091] Specifically, when the particulate polymer as a copolymer has one glass transition temperature, the particulate polymer satisfies both (1) it does not have a core-shell structure and (2) it is a random copolymer (i.e., it belongs to a random copolymer without a core-shell structure). On the other hand, when the particulate polymer has two or more glass transition temperatures, the particulate polymer does not satisfy at least one of (1) and (2) above (i.e., it does not belong to "a random copolymer without a core-shell structure").

[0092] Furthermore, the glass transition temperature of the particulate polymer is preferably below 20°C, more preferably below 10°C, and even more preferably below 0°C. If the glass transition temperature of the particulate polymer is below the above-mentioned upper limit, the adhesion of the functional layer can be further improved. In addition, the lower limit of the glass transition temperature of the particulate polymer is not particularly limited, and is generally above -100°C.

[0093] <<Electrolyte Swelling Degree>>

[0094] In this invention, the "electrolyte swelling degree" of the particulate polymer can be calculated as the weight after immersion (multiple) of a membrane (adhesive membrane) formed from the particulate polymer and immersed in a specific non-aqueous electrolyte under specified conditions, divided by the weight before immersion. Specifically, the adhesive membrane can be formed using the method described in the embodiments of this specification, and the measurement can be performed using the measurement method described in the same embodiment.

[0095] The swelling degree of the electrolyte of the particulate polymer is preferably 2 times or more, more preferably 3 times or more, more preferably 8 times or less, and more preferably 6 times or less. If the swelling degree of the electrolyte of the particulate polymer is within the above-mentioned range, the internal resistance of the secondary battery can be reduced.

[0096] The swelling degree of the electrolyte in particulate polymers can be adjusted by changing the type and amount of monomers used, as well as the conditions of the polymerization reaction (such as polymerization temperature, polymerization reaction time, etc.).

[0097] <<Volume Average Particle Size>>

[0098] The volume average particle size of the particulate polymer is preferably 0.05 μm or more, more preferably 0.10 μm or more, even more preferably 0.14 μm or more, preferably 0.25 μm or less, and more preferably 0.20 μm or less. If the volume average particle size of the particulate polymer is at or above the lower limit mentioned above, the air permeability of the functional layer is improved, thus further enhancing the electrolyte affinity of the functional layer. On the other hand, if the volume average particle size of the particulate polymer is at or below the upper limit mentioned above, the adhesion and electrolyte affinity of the functional layer can be further improved.

[0099] <<Gel Content>>

[0100] The gel content of the particulate polymer is preferably 85% by mass or more, more preferably 90% by mass or more. If the gel content of the particulate polymer is at or above the lower limit mentioned above, the amount of components leached into the electrolyte can be reduced, thereby improving the cycle characteristics of the secondary battery with the functional layer. Furthermore, the upper limit of the gel content of the particulate polymer is not particularly limited, and is typically 99% by mass or less.

[0101] In addition, the gel content can be adjusted by changing the polymerization temperature, the type and amount of additives such as molecular weight regulators, and the conversion rate (monomer consumption) at the end of the reaction. For example, reducing the amount of molecular weight regulator used during polymerization can increase the gel content, while increasing the amount of molecular weight regulator used during polymerization can decrease the gel content.

[0102] <Preparation of Particulate Polymers>

[0103] Particulate polymers are prepared by polymerizing monomer compositions containing the monomers described above.

[0104] Here, the proportion of each monomer in the monomer composition is usually the same as the proportion of monomer units in the desired particulate polymer.

[0105] There are no particular limitations on the polymerization method of the particulate polymer; any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. As the polymerization reaction, addition polymerization such as ionic polymerization, free radical polymerization, or living radical polymerization can be used. Furthermore, the emulsifiers, dispersants, polymerization initiators, polymerization auxiliaries, etc., used in the polymerization can be those commonly used, and their amounts are also set to the commonly used amounts.

[0106] In the case of preparing particulate polymers formed from random copolymers without a core-shell structure, it is sufficient to suppress the formation of block copolymers and graft copolymers by initiating polymerization in the state of monomers rather than in the state of oligomers that polymerize monomers in a monomer composition to some extent.

[0107] <Solvent>

[0108] As a solvent that can be included in the binder of the present invention, a known solvent capable of dispersing the above-mentioned particulate polymer can be used. Water is preferably used as the solvent. Furthermore, at least a portion of the solvent that can be included in the binder is not particularly limited, and can be a polymerization solvent used for the preparation of the particulate polymer.

[0109] <Preparation of binders for functional layers of non-aqueous secondary batteries>

[0110] The preparation method of the binder of the present invention is not particularly limited. For example, when the particulate polymer is prepared in a solvent such as water and the particulate polymer is obtained as a dispersion, the dispersion of the particulate polymer can be used directly as a binder, or other components can be arbitrarily added to the dispersion of the particulate polymer as a binder. Here, other components described later in the section "Slurry Composition for Functional Layer of Secondary Battery" can be cited as examples of other components.

[0111] (Slurry composition for functional layer of secondary battery)

[0112] The slurry composition of the present invention is a composition for forming a functional layer, comprising the binder described above, and optionally further containing functional particles and other components. That is, the slurry composition of the present invention typically contains a particulate polymer and a solvent, and optionally further contains functional particles and other components. Furthermore, because the slurry composition of the present invention contains the binder described above, by drying the slurry composition of the present invention on, for example, a substrate, a functional layer with excellent heat shrinkage resistance and electrolyte affinity can be obtained. In addition, the adhesion of this functional layer is also excellent.

[0113] Furthermore, as mentioned above, this functional layer exhibits excellent electrolyte affinity, thus providing excellent electrolyte filling performance for secondary batteries with this functional layer. In particular, even when secondary batteries with this functional layer are manufactured in high-density quantities for purposes such as increasing the capacity of secondary batteries, sufficiently high electrolyte filling performance can still be ensured.

[0114] <Adhesive>

[0115] As a binder, the binder of the present invention described above, which contains at least a particulate polymer, is used.

[0116] Furthermore, the amount of binder in the slurry composition is not particularly limited. For example, when the slurry composition contains functional particles such as non-conductive particles (described later), the amount of binder in the slurry composition, converted from solid content, is preferably 0.5 parts by weight or more, more preferably 1.0 parts by weight or more, more preferably 6.0 parts by weight or less, and more preferably 3.0 parts by weight or less, relative to 100 parts by weight of functional particles. If the amount of binder in the slurry composition is at or above the aforementioned lower limit, the adhesion of the functional layer can be further improved. On the other hand, if the amount of binder in the slurry composition is at or below the aforementioned upper limit, the air permeability of the functional layer is increased, thereby further improving the electrolyte affinity of the functional layer.

[0117] <Functional Particles>

[0118] Here, as functional particles used to enable the functional layer to perform the desired function, non-conductive particles can be used, for example, when the functional layer is a porous film layer.

[0119] In particular, because the functional layer formed using the slurry composition of the present invention exhibits excellent heat shrinkage resistance, the slurry composition of the present invention, which contains non-conductive particles as functional particles, is suitable for use in the formation of porous film layers that improve the heat resistance and strength of battery components.

[0120] <<Non-conductive particles>>

[0121] Specifically, the non-conductive particles used in the porous membrane layer of a secondary battery are not particularly limited; both inorganic and organic particles can be used, with inorganic particles typically preferred. Among these, materials that are stable and electrochemically stable under the operating conditions of a secondary battery are preferred. Preferred examples of non-conductive particle materials from this perspective include: oxide particles such as alumina (bauxite), hydrated alumina (boehmite), silicon dioxide, magnesium oxide (magnesia), calcium oxide, titanium dioxide (Titania), BaTiO3, ZrO, and bauxite-silica composite oxides; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles such as silicon and diamond; sparingly soluble ionic crystal particles such as barium sulfate, calcium fluoride, and barium fluoride; and clay particles such as talc and montmorillonite. Furthermore, these particles can be subjected to elemental substitution, surface treatment, or solid solution treatment as needed.

[0122] Then, from the viewpoint of suppressing agglomeration and improving the dispersibility of the slurry composition for the functional layer, bauxite, boehmite, and barium sulfate are preferred as materials for non-conductive particles.

[0123] In addition, the aforementioned non-conductive particles can be used alone or in combination of two or more.

[0124] The volume average particle size of the non-conductive particles is preferably 0.1 μm or more, more preferably 0.3 μm or more, even more preferably 0.6 μm or more, preferably 1.5 μm or less, and more preferably 1.0 μm or less. If the volume average particle size of the non-conductive particles is at or above the lower limit mentioned above, the air permeability of the functional layer is improved, thus further enhancing the electrolyte affinity of the functional layer. On the other hand, if the volume average particle size of the non-conductive particles is at or below the upper limit mentioned above, the adhesion of the functional layer can be further improved.

[0125] <Other Ingredients>

[0126] In addition to the components mentioned above, the slurry composition may further contain other components. There are no particular limitations on the other components as long as they do not have an overly adverse effect on the battery reaction in the secondary battery with the functional layer. Furthermore, there may be one or more other components.

[0127] Other components include surfactants, wetting agents, leveling agents, dispersants, electrolyte decomposition inhibitors, and water-soluble polymers.

[0128] Then, from the viewpoint of further improving the heat shrinkage resistance of the functional layer, water-soluble polymers are preferred as other components.

[0129] Furthermore, in this invention, "water-soluble" polymer means that when 0.5g of the polymer is dissolved in 100g of water at 25°C, the insoluble component is less than 1% by mass.

[0130] As water-soluble polymers, there are no particular limitations, but from the viewpoint of further improving the heat shrinkage resistance of the functional layer, carboxymethyl cellulose and polyacrylamide are preferred, and carboxymethyl cellulose is more preferred.

[0131] The amount of water-soluble polymer in the slurry composition is not particularly limited. For example, when the slurry composition contains functional particles such as non-conductive particles (described later), the amount of water-soluble polymer in the slurry composition, converted to solid content, is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, more preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1.5 parts by mass or less, relative to 100 parts by mass of functional particles. If the amount of water-soluble polymer in the slurry composition is at or above the aforementioned lower limit, the heat shrinkage resistance of the functional layer can be further improved. On the other hand, if the amount of water-soluble polymer in the slurry composition is at or below the aforementioned upper limit, sufficiently high coating stability can be ensured when the slurry composition is coated on a substrate to form a functional layer.

[0132] Furthermore, from the viewpoint of improving the stability of the slurry composition, it is preferable to use a dispersant as another component. There are no particular limitations on the dispersant; for example, sodium polyacrylate can be used. Additionally, the dispersant is a component different from the water-soluble polymers mentioned above.

[0133] The amount of dispersant in the slurry composition is not particularly limited. For example, when the slurry composition contains functional particles such as non-conductive particles (described later), the amount of dispersant in the slurry composition, converted from solid content, is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, further preferably 0.5 parts by mass or more, preferably 2 parts by mass or less, and more preferably 1 part by mass or less, relative to 100 parts by mass of functional particles. If the amount of dispersant in the slurry composition is at or above the aforementioned lower limit, the stability of the slurry composition can be further improved. On the other hand, if the amount of dispersant in the slurry composition is at or below the aforementioned upper limit, the moisture content of the functional layer formed by coating the slurry composition onto the substrate can be kept low.

[0134] Furthermore, from the viewpoint of improving the coatability of the slurry composition, it is preferable to use a surfactant as another component. There are no particular limitations on the surfactant; for example, a polyethylene glycol-type surfactant can be used. Additionally, the surfactant is a component different from the water-soluble polymers and dispersants mentioned above.

[0135] The amount of surfactant in the slurry composition is not particularly limited. For example, when the slurry composition contains functional particles such as non-conductive particles (described later), the amount of surfactant in the slurry composition, converted from solid content, is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or less, and more preferably 0.3 parts by mass or less, relative to 100 parts by mass of functional particles. If the amount of surfactant in the slurry composition is at or above the aforementioned lower limit, the coatability of the slurry composition to the substrate can be sufficiently ensured. On the other hand, if the amount of surfactant in the slurry composition is at or below the aforementioned upper limit, the adhesion of the functional layer can be sufficiently high. Furthermore, the lower limit of the amount of surfactant in the slurry composition is not particularly limited, and is generally 0.1 parts by mass or more.

[0136] <Preparation of Slurry Composition>

[0137] There are no particular limitations on the preparation method of the slurry composition.

[0138] For example, when the slurry composition is a slurry composition for porous membrane layers, the slurry composition can be prepared by mixing a binder, non-conductive particles, and other components as needed in the presence of a solvent.

[0139] Furthermore, when the slurry composition is a slurry composition for an adhesive layer, for example, the binder, which is a dispersion of a particulate polymer, can be used directly or diluted with a solvent as the slurry composition. Alternatively, the binder and other components to be used as needed can be mixed in the presence of a solvent to prepare the slurry composition.

[0140] Furthermore, the solvent used in preparing the slurry composition can be the solvent described in the section on "Binder for Functional Layers of Secondary Batteries" (e.g., water). In addition, the solvent used in preparing the slurry composition also contains the components included in the binder composition. Then, there are no particular limitations on the mixing method; mixing can be performed using a commonly used mixer or disperser.

[0141] (Functional layer for secondary batteries)

[0142] The functional layer of the present invention is a layer that performs functions such as reinforcement or adhesion within a secondary battery. Examples of functional layers include porous membrane layers that improve heat resistance and / or strength, and adhesive layers that improve adhesion. Furthermore, the functional layer of the present invention is formed from the aforementioned slurry composition of the present invention, and can be formed by, for example, applying the aforementioned slurry composition to a suitable substrate surface to form a coating film, followed by drying. That is, the functional layer of the present invention is formed from the dried product of the aforementioned slurry composition, and typically contains at least particulate polymers, optionally further containing functional particles and other components. In addition, each component included in the functional layer is also included in the aforementioned slurry composition; therefore, the preferred proportions of these components are the same as the preferred proportions of the components in the slurry composition.

[0143] Then, the functional layer of the present invention is formed from the slurry composition of the present invention containing the binder of the present invention, and therefore has excellent heat shrinkage resistance and electrolyte affinity. Furthermore, the adhesiveness of the functional layer of the present invention is also excellent.

[0144] Furthermore, as described above, the functional layer of the present invention has excellent electrolyte affinity, thus providing excellent electrolyte injection performance for secondary batteries having this functional layer. In particular, even when secondary batteries having this functional layer are manufactured in high-density quantities for purposes such as increasing the capacity of secondary batteries, sufficiently high electrolyte injection performance can still be ensured.

[0145] <Substrate>

[0146] Here, the substrate for applying the slurry composition is not limited. For example, a coating of the slurry composition can be formed on the surface of a release substrate, the coating can be dried to form a functional layer, and the release substrate can be peeled off from the functional layer. The functional layer peeled off from the release substrate in this way can also be used as a self-supporting film to form a battery component for a secondary battery.

[0147] However, from the viewpoint of improving the manufacturing efficiency of battery components by eliminating the step of peeling off the functional layer, spacer substrates or electrode substrates are preferred as the substrate. Specifically, when preparing porous films and adhesive layers, it is preferable to apply a slurry composition onto the spacer substrate or electrode substrate.

[0148] Furthermore, from the viewpoint of improving the adhesion between the formed functional layer and substrates such as spacer substrates and electrode substrates, the surface of the aforementioned substrates can be hydrophilized by performing surface treatments such as corona treatment or plasma treatment.

[0149] <<Current collector>>

[0150] <<Spacer Substrate>>

[0151] There are no particular limitations on the spacer substrate, and known spacer substrates such as organic spacer substrates can be cited. Organic spacer substrates are porous components formed from organic materials. When citing examples of organic spacer substrates, microporous membranes or nonwoven fabrics containing polyolefin resins such as polyethylene and polypropylene, aromatic polyamide resins, etc. are cited. Because of their excellent strength, microporous membranes made of polyethylene and nonwoven fabrics made of polyethylene are preferred.

[0152] <<Electrode Substrate>>

[0153] There are no particular limitations on the electrode substrate (positive electrode substrate and negative electrode substrate), but an example of an electrode substrate in which an electrode composite material layer containing electrode active material particles and a binder material is formed on the current collector can be given.

[0154] The current collector is made of a material that is both electrically conductive and electrochemically durable. Specifically, current collectors made of materials such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum can be used. Among these, copper foil is particularly preferred as a current collector for the negative electrode. Furthermore, aluminum foil is particularly preferred as a current collector for the positive electrode. In addition, one of the above-mentioned materials can be used alone, or two or more can be used in any ratio.

[0155] The electrode active material particles included in the electrode composite layer of the electrode substrate are not particularly limited, and known electrode active material particles can be used. Furthermore, the binder material included in the electrode composite layer of the electrode substrate can be any binder material suitable for the electrode composite layer.

[0156] <Methods for forming functional layers>

[0157] The following methods can be cited as methods for forming a functional layer on the aforementioned spacer substrate, electrode substrate, and other substrates.

[0158] 1) A method of applying the slurry composition of the present invention to the surface of a substrate (the surface of the electrode composite layer in the case of an electrode substrate, the same below) and then drying it;

[0159] 2) A method of impregnating a substrate in the slurry composition of the present invention and then drying it; and

[0160] 3) A method of applying the slurry composition of the present invention onto a release substrate, drying it to produce a functional layer, and transferring the resulting functional layer onto the surface of the substrate.

[0161] Of these, method 1) above is particularly preferred because it allows for easy control of the film thickness of the functional layer. In detail, method 1) above includes a step of applying a slurry composition to a substrate (coating step) and a step of drying the slurry composition applied to the substrate to form a functional layer (drying step).

[0162] <<Coating Process>>

[0163] Then, in the coating process, there are no particular limitations on the method of applying the paste composition to the substrate, and examples include, for example, doctor blade coating, reverse roller coating, direct roller coating, gravure printing, extrusion, brush coating, etc.

[0164] <<Drying Process>>

[0165] Furthermore, in the drying process, there are no particular limitations on the method for drying the slurry composition on the substrate, and known methods can be used. Examples of drying methods include: drying using warm air, hot air, or low-humidity air; vacuum drying; and drying using infrared radiation, electron beams, etc. The drying conditions are not particularly limited, but the drying temperature is preferably 40°C to 150°C, and the drying time is preferably 2 minutes to 30 minutes.

[0166] Furthermore, the thickness of the formed functional layer is preferably 0.5 μm or more, more preferably 1 μm or more, more preferably 4 μm or less, and even more preferably 3 μm or less. If the thickness of the functional layer is at or above the aforementioned lower limit, it is possible to ensure that the heat shrinkage resistance of the functional layer is sufficiently high. On the other hand, if the thickness of the functional layer is at or below the aforementioned upper limit, it is possible to easily achieve high capacity in the secondary battery by thinning the functional layer.

[0167] (Battery component with functional layer)

[0168] Battery components (spacers and electrodes) having the functional layer of the present invention may also have constituent elements other than the functional layer and substrate of the present invention described above, as long as they do not significantly affect the effect of the present invention. Such constituent elements are not particularly limited, and examples include porous film layers and adhesive layers that are not part of the functional layer of the present invention.

[0169] Furthermore, the battery components can have various functional layers of the present invention. For example, the spacer can have a porous membrane layer formed by the porous membrane layer slurry composition of the present invention on the spacer substrate, and an adhesive layer formed by the adhesive layer slurry composition of the present invention on the porous membrane layer.

[0170] The battery component having the functional layer of the present invention has excellent heat shrinkage resistance and electrolyte affinity, and can adhere well to adjacent battery components.

[0171] (Secondary battery)

[0172] The secondary battery of the present invention is a secondary battery having the functional layer of the present invention described above. More specifically, the secondary battery of the present invention has a positive electrode, a negative electrode, a spacer, and an electrolyte, and the functional layer for the secondary battery described above is included in at least one of the positive electrode, the negative electrode, and the spacer, which are battery components.

[0173] Furthermore, the secondary battery of the present invention has a functional layer with high electrolyte affinity, thus exhibiting excellent electrolyte injection performance. In particular, even when the secondary battery of the present invention is made high-density for purposes such as increasing capacity, sufficiently high electrolyte injection performance can still be ensured.

[0174] Furthermore, because the secondary battery of the present invention has the functional layer of the present invention with high adhesion, the battery components are well bonded to each other, resulting in excellent battery characteristics such as cycle characteristics.

[0175] <Positive electrode, negative electrode, and spacer>

[0176] At least one of the positive electrode, negative electrode, and spacer in the secondary battery used in this invention is a battery component having the functional layer of this invention as described above. Furthermore, there are no particular limitations on the positive electrode, negative electrode, and spacer that do not have the functional layer of this invention, and known positive electrodes, negative electrodes, and spacers can be used.

[0177] Electrolyte

[0178] As an electrolyte, an organic electrolyte in which the supporting electrolyte is dissolved in an organic solvent is typically used. As a supporting electrolyte, lithium salts can be used, for example, in lithium-ion secondary batteries. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, LiPF6, LiClO4, and CF3SO3Li are preferred due to their high solubility in solvents and high degree of dissociation. Furthermore, a single electrolyte can be used, or two or more can be used in combination. Generally, there is a tendency for higher degree of dissociation in the supporting electrolyte to result in higher lithium-ion conductivity; therefore, the lithium-ion conductivity can be adjusted according to the type of supporting electrolyte.

[0179] The organic solvent used as the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, in lithium-ion secondary batteries, preferred solvents include: dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butyl carbonate (BC), methyl ethyl carbonate (EMC), and vinylene carbonate (VC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. Mixtures of these solvents can also be used. Among these, carbonates are preferred due to their high dielectric constant and wide stable potential range. Generally, there is a tendency for lower solvent viscosity to result in higher lithium-ion conductivity; therefore, the lithium-ion conductivity can be adjusted according to the type of solvent.

[0180] Furthermore, the concentration of the electrolyte in the electrolyte solution can be appropriately adjusted. Additionally, known additives can be added to the electrolyte solution.

[0181] <Manufacturing Method of Secondary Batteries>

[0182] The secondary battery of the present invention described above is manufactured, for example, by overlapping the positive and negative electrodes with a spacer in between, and then, as needed, winding, folding, or placing them into a battery container, injecting electrolyte into the battery container, and sealing it. Furthermore, at least one of the positive electrode, negative electrode, and spacer is used as a battery component having the functional layer of the present invention. In addition, porous metal mesh, fuses, PTC elements, or other overcurrent protection components, conductive plates, etc., can be placed in the battery container as needed to prevent pressure rise and overcharging / discharging inside the battery. The battery shape can be, for example, coin-shaped, button-shaped, sheet-shaped, cylindrical, square, or flat.

[0183] Example

[0184] The present invention will now be specifically described based on embodiments, but the present invention is not limited to these embodiments. Furthermore, in the following description, unless otherwise specified, "%" and "parts" refer to quantities based on mass.

[0185] Furthermore, unless otherwise specified, in polymers made by copolymerizing multiple monomers, the proportion of repeating units (monomer units) formed by polymerizing a particular monomer in the polymer is generally consistent with the proportion (addition ratio) of that particular monomer in all monomers used in the polymerization of the polymer.

[0186] In the examples and comparative examples, the volume average particle size of the particulate polymer, glass transition temperature, gel content and electrolyte swelling degree, adhesion of the functional layer, electrolyte affinity and heat shrinkage resistance, and cycle characteristics of the secondary battery were measured and evaluated using the following methods.

[0187] <Volume average particle size of particulate polymers>

[0188] The volume-average particle size of the particulate polymer was determined using laser diffraction. Specifically, an aqueous dispersion containing the particulate polymer (with the solid content adjusted to 0.1% by mass) was used as the sample. Then, in the particle size distribution (volume basis) measured using a laser diffraction particle size distribution measuring device (Beckman Coulter, product name "LS-13320"), the particle size D50, which represents 50% of the cumulative volume calculated from the smallest particle size side, was taken as the volume-average particle size.

[0189] <Glass transition temperature of particulate polymers>

[0190] The prepared aqueous dispersion containing particulate polymer was pre-dried for 3 days at a relative humidity of 50% and a temperature of 23–26°C, resulting in a pre-film with a thickness of 2 ± 0.5 mm. The pre-film was then dried in a vacuum dryer at 120°C for 10 hours. Subsequently, the dried film was used as a sample, and the glass transition temperature (°C) was determined using a differential scanning calorimeter (SII Corporation, DSC7200) at a measurement temperature of -100°C to 180°C and a heating rate of 5°C / min, according to JIS K7121.

[0191] <Gel content of particulate polymers>

[0192] The prepared aqueous dispersion containing particulate polymer was dried at 50% humidity and 23–25°C to form a film with a thickness of 1 ± 0.3 mm. The film was then dried in a vacuum dryer at 60°C for 10 hours. Afterward, the dried film was cut into 3–5 mm squares, and approximately 1 g was weighed. The mass of the cut film was designated as w0. This film was then immersed in 50 g of tetrahydrofuran (THF) for 24 hours. Subsequently, the film removed from the THF was vacuum dried at 105°C for 3 hours, and the mass of the insoluble component, w1, was measured. The gel content was then calculated using the following formula.

[0193] Gel content (mass%) = (w1 / w0) × 100

[0194] <Electrolyte swelling degree of particulate polymers>

[0195] The prepared aqueous dispersion containing particulate polymer was dried at a relative humidity of 50% and a temperature of 23–25°C to form a film with a thickness of approximately 0.1 mm. A 2 cm square section of the film was cut and its weight (weight before immersion) was measured. Subsequently, the film was immersed in an electrolyte at 60°C for 72 hours. The immersed film was lifted, the electrolyte was wiped off, and its weight (weight after immersion) was measured immediately. The ratio of (weight after immersion) to (weight before immersion) was taken as the electrolyte swelling degree. The electrolyte used was a solution of LiPF6 dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate and methyl ethyl carbonate at a mass ratio of 3:7. Furthermore, a smaller electrolyte swelling degree for the particulate polymer indicates higher electrolyte resistance.

[0196] <Adhesion of Functional Layers>

[0197] The spacers with functional layers produced in the examples and comparative examples were cut into test pieces with a width of 10 mm and a length of 50 mm.

[0198] Next, a stainless steel plate with double-sided tape (manufactured by Nitto Denko Corporation, No. 5608) was prepared, and the functional layer of the aforementioned test piece was adhered to the double-sided tape. Then, one end of the spacer substrate was stretched at a speed of 50 mm / min with the peel surface at 180°, and it was peeled off. The peel strength was measured, and the adhesion of the functional layer was evaluated according to the following criteria.

[0199] A: Peel strength is above 10 N / m

[0200] B: Peel strength is above 5N / m and below 10N / m

[0201] C: Peel strength less than 5 N / m

[0202] <Electrolyte affinity of functional layers>

[0203] The prepared aqueous dispersion containing particulate polymer was coated onto a 20 μm thick aluminum foil using a doctor blade coater and dried at 50°C for 15 minutes to form a functional layer with a thickness of 20 ± 2 μm. The aluminum foil with the functional layer was then dried in a vacuum dryer at 60°C for 10 hours. Subsequently, the aluminum foil with the functional layer was cut into 100 mm squares, and the electrolyte contact angle at 10 points was measured using a portable contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., PCA-11). The average value was calculated, and the electrolyte affinity of the functional layer was evaluated according to the following criteria. Furthermore, the lower the electrolyte contact angle value, the higher the wettability of the functional layer to the electrolyte and the higher the electrolyte affinity.

[0204] A: The average contact angle of the electrolyte is less than 40°.

[0205] B: The average contact angle of the electrolyte is greater than 40° and less than 50°.

[0206] C: The average contact angle of the electrolyte is above 50°.

[0207] <Resistant to heat shrinkage of functional layers>

[0208] The spacers with functional layers fabricated in the examples and comparative examples were cut into squares 12cm wide and 12cm long. Squares with 10cm sides were drawn inside each square to serve as test pieces. The test pieces were then heated in a 150°C constant-temperature bath for 1 hour. The change in area of ​​the drawn squares (={(area of ​​the square before heating - area of ​​the drawn square after heating) / area of ​​the square before heating}×100%) was calculated as the heat shrinkage rate. The heat shrinkage resistance of the functional layer was evaluated according to the following criteria: the smaller the heat shrinkage rate, the better the heat shrinkage resistance of the functional layer.

[0209] A: Heat shrinkage rate is less than 10%.

[0210] B: The heat shrinkage rate is 10% or more but less than 20%.

[0211] C: The heat shrinkage rate is 20% or more but less than 30%.

[0212] D: The heat shrinkage rate is over 30%.

[0213] <Cycle Characteristics of Secondary Batteries>

[0214] The prepared lithium-ion secondary battery was left to stand at 25°C for 24 hours. Subsequently, the following charge and discharge operations were performed at 25°C: it was charged at a charge rate of 1C using constant voltage and constant current (CC-CV) mode to 4.2V (current interruption condition: 0.02C), and discharged at a discharge rate of 1C using constant current (CC) mode to 3.0V. The initial capacity C0 was measured.

[0215] Then, the same charge-discharge operation was repeated at 25°C, and the capacity C1 after 300 cycles was measured. The capacity retention rate ΔC = (C1 / C0) × 100 (%) was then calculated and evaluated using the following criteria. A higher capacity retention rate indicates less capacity loss and better cycle characteristics.

[0216] A: Capacity retention rate ΔC is above 85%.

[0217] B: Capacity retention ΔC is 75% or higher and less than 85%.

[0218] C: Capacity retention rate ΔC is less than 75%.

[0219] (Example 1)

[0220] <Preparation of Aqueous Dispersions Containing Particulate Polymers>

[0221] In a reactor equipped with a stirrer, 90 parts of ion-exchanged water, 0.05 parts of sodium dodecylbenzenesulfonate (manufactured by Kao Chemical Co., Ltd., "neopelex G-15") as an emulsifier, and 0.23 parts of ammonium persulfate were supplied respectively. The gas phase was replaced with nitrogen and the temperature was raised to 70°C.

[0222] On the other hand, in another container, 50 parts of deionized water, 0.1 parts of sodium dodecylbenzenesulfonate (manufactured by Kao Chemical Co., Ltd., "neopelex G-15") as an emulsifier, 76.6 parts of butyl acrylate (BA) as an alkyl methacrylate monomer, 10 parts of acrylonitrile (AN) as a cyano-containing monomer, 10 parts of allyl glycidyl ether (AGE) as a cyclic ether monomer, 3 parts of acrylic acid (AA) as a carboxyl-containing monomer, and 0.4 parts of allyl methacrylate (AMA) as a crosslinking monomer were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor described above over 4 hours for polymerization. During the addition process, the reaction was carried out at 70°C. After the addition was completed, the temperature was raised to 80°C and stirred for 3 hours to terminate the reaction, producing an aqueous dispersion (binder) containing particulate polymer. The volume-average particle size, glass transition temperature, gel content, electrolyte swelling degree, and electrolyte affinity of the functional layer were measured and evaluated using the obtained aqueous dispersion (binder) containing particulate polymer. The results are shown in Table 1.

[0223] Furthermore, since the obtained particulate polymer has only one glass transition temperature, it is confirmed that the particulate polymer is a random copolymer without a core-shell structure.

[0224] <Preparation of Slurry Compositions for Functional Layers>

[0225] Alumina particles (AKP-3000, manufactured by Sumitomo Chemical Co., Ltd., volume average particle size D50 = 0.7 μm) were prepared as non-conductive particles; sodium polyacrylate (ARON T-50, manufactured by Toa Synthetic Co., Ltd.) was prepared as a dispersant; and carboxymethyl cellulose (Daicel Finchem Co., Ltd., product name 1220), with a degree of etherification of 0.8 to 1.0, was prepared as a water-soluble polymer. Furthermore, the viscosity of a 1% aqueous solution of carboxymethyl cellulose was 10 to 20 mPa·s.

[0226] Then, 100 parts of non-conductive particles, 0.5 parts of dispersant, and ion-exchanged water were mixed and treated with a bead mill (manufactured by Ashizawa Finetech Co., Ltd., LMZ015) for 1 hour to obtain a dispersion. Next, 3 parts (equivalent to solids) of an aqueous dispersion containing particulate polymer as a binder, 1.5 parts (equivalent to solids) of a 1% aqueous solution of carboxymethyl cellulose (CMC) as a water-soluble polymer, and 0.3 parts of a polyethylene glycol-type surfactant (manufactured by SAN NOPCO Co., Ltd., NOPTECHS ED-052) were mixed to prepare a functional layer slurry composition with a solids concentration of 40% by mass.

[0227] <Fabrication of a spacer with a functional layer on one side (spacer with a functional layer)>

[0228] A polyethylene spacer substrate (manufactured by Asahi Kasei Corporation, trade name "ND412", thickness: 12 μm) was prepared. The functional layer slurry composition prepared above was coated onto the surface of the prepared spacer substrate and dried at 50°C for 3 minutes to obtain a spacer with a functional layer (porous membrane) on one side (spacer with functional layer; functional layer thickness: 3 μm). The adhesion of the functional layer was evaluated using the obtained spacer with functional layer. The results are shown in Table 1.

[0229] <Making the Negative Electrode>

[0230] In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene (an aliphatic conjugated diene monomer), 3.5 parts of itaconic acid (a carboxylic acid-containing monomer), 63.5 parts of styrene (an aromatic vinyl monomer), 0.4 parts of sodium dodecylbenzenesulfonate (an emulsifier), 150 parts of deionized water, and 0.5 parts of potassium persulfate (a polymerization initiator) were added. After thorough stirring, the mixture was heated to 50°C to initiate polymerization. The polymerization reaction was terminated by cooling when the polymerization conversion reached 96%, yielding a mixture containing a particulate binder (styrene-butadiene copolymer) used as a binder for the negative electrode. A 5% sodium hydroxide aqueous solution was added to the mixture to adjust the pH to 8, and unreacted monomers were removed by heated vacuum distillation. The mixture was then cooled to below 30°C to obtain an aqueous dispersion containing the binder for the negative electrode.

[0231] 48.75 parts of artificial graphite (theoretical capacity: 360 mAh / g) and 48.75 parts of natural graphite (theoretical capacity: 360 mAh / g) as the negative electrode active material, and 1 part of carboxymethyl cellulose as a thickener (based on the solids content) were added to a planetary mixer. The mixture was then diluted with deionized water to a solids concentration of 60%, and then kneaded at 45 rpm for 60 minutes. Next, 1.5 parts of the above-mentioned aqueous dispersion containing the negative electrode binder (based on the solids content) were added, and kneaded at 40 rpm for 40 minutes. Then, deionized water was added to achieve a viscosity of 3000 ± 500 mPa·s (measured at 25°C and 60 rpm using a Type B viscometer), thereby preparing a slurry composition for the negative electrode composite layer.

[0232] The above-mentioned negative electrode composite material layer slurry composition was applied using a corner-cutting wheel coating machine at a coating amount of 11 ± 0.5 mg / cm². 2 The paste composition was applied to the surface of a 15 μm thick copper foil, which serves as the current collector. Subsequently, the copper foil coated with the negative electrode composite layer paste composition was transported at a speed of 400 mm / min in an oven at 80°C for 2 minutes, and then further transported in an oven at 110°C for 2 minutes, thereby drying the paste composition on the copper foil and obtaining a negative electrode raw material with a negative electrode composite layer formed on the current collector.

[0233] Subsequently, the negative electrode composite material layer of the prepared negative electrode raw material was rolled at a temperature of 25±3℃ under a linear pressing condition of 11t (tons) to obtain a negative electrode composite material layer with a density of 1.60 g / cm³. 3 The negative electrode was then placed in an environment with a temperature of 25±3℃ and a relative humidity of 50±5% for one week.

[0234] <The Making of Positive Electrode>

[0235] Add 96 parts of Co-Ni-Mn lithium composite oxide active material (NMC111, LiNi) as positive electrode active material to a planetary mixer. 1 / 3 Co 1 / 3 Mn 1 / 3 O2), 2 parts of acetylene black (manufactured by Denka Co., Ltd., trade name "HS-100") as a conductive material, 2 parts of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name "KF-1100") as a binder, and then N-methyl-2-pyrrolidone (NMP) as a dispersion medium are added and mixed to prepare a slurry composition for a positive electrode composite layer.

[0236] Next, the obtained slurry composition for the positive electrode composite layer was coated with a corner-cutting wheel coating machine at a coating amount of 20 ± 0.5 mg / cm². 2 It is applied to a 20μm thick aluminum foil that serves as a current collector.

[0237] Then, the material is transported at a speed of 200 mm / min in an oven at 90°C for 2 minutes, and then further transported in an oven at 120°C for 2 minutes, thereby drying the paste composition on the aluminum foil and obtaining the positive electrode raw material on which a positive electrode composite layer is formed on the current collector.

[0238] Subsequently, the cathode composite material layer of the prepared cathode raw material was rolled at a temperature of 25±3℃ under a linear pressing condition of 14t (tons) to obtain a cathode composite material layer with a density of 3.40 g / cm³. 3 The positive electrode was then placed in an environment with a temperature of 25±3℃ and a relative humidity of 50±5% for one week.

[0239] <Making a Secondary Battery>

[0240] The pressed positive electrode obtained above was cut into 4cm × 4cm squares, and the pressed negative electrode was cut into 4.2cm × 4.2cm squares. Furthermore, the spacer with the functional layer obtained above was cut into 5cm × 5cm squares. Next, on the positive electrode composite material layer of the pressed positive electrode, the functional layer side of the spacer with the functional layer was placed facing the positive electrode composite material layer. Then, on the side of the spacer with the functional layer that does not contact the positive electrode, the negative electrode composite material side of the pressed negative electrode was placed facing that side, resulting in a battery component laminate (positive electrode / functional layer / spacer substrate / negative electrode). Next, the laminate was packaged in an aluminum outer packaging material as the battery outer packaging, and an electrolyte (solvent: ethylene carbonate (EC) / diethyl carbonate (DEC) / ethylene carbonate (VC) (volume ratio = 68.5 / 30 / 1.5), electrolyte: 1mol / L LiPF6) was injected in a manner that leaves no air residue. Then, the opening of the aluminum packaging was heat-sealed at 150°C to seal the outer packaging, thus manufacturing a 40mAh stacked lithium-ion secondary battery. The cycle characteristics were evaluated using this lithium-ion secondary battery. The results are shown in Table 1.

[0241] (Examples 2-10, 13-16, 20, Comparative Examples 1-5)

[0242] In the preparation of the aqueous dispersion containing particulate polymer in Example 1, the types and amounts of monomers used were varied so that the content ratios of various monomer units in the resulting particulate polymer were as shown in Tables 1 and 2. Otherwise, the process was the same as in Example 1, producing aqueous dispersions containing particulate polymers, slurry compositions for functional layers, spacers with functional layers, negative electrodes, positive electrodes, and secondary batteries, and performing various measurements and evaluations. The results are shown in Tables 1 and 2.

[0243] (Example 11)

[0244] In the preparation of the aqueous dispersion containing particulate polymer in Example 1, the amount of butyl acrylate (BA), used as an alkyl methacrylate monomer, was changed from 76.6 parts to 77.6 parts; 2 parts of methacrylic acid (MAA) was used instead of 3 parts of acrylic acid (AA) as the carboxyl-containing monomer; and the amount of emulsifier (sodium dodecylbenzenesulfonate) used in the reactor was changed from 0.05 parts to 0.02 parts. Otherwise, the process was the same as in Example 1, producing an aqueous dispersion containing particulate polymer, a slurry composition for a functional layer, a spacer with a functional layer, a negative electrode, a positive electrode, and a secondary battery, and performing various measurements and evaluations. The results are shown in Table 1.

[0245] (Example 12)

[0246] In the preparation of the aqueous dispersion containing particulate polymer in Example 1, the amount of butyl acrylate (BA), used as an alkyl methacrylate monomer, was changed from 76.6 parts to 77.6 parts; 2 parts of methacrylic acid (MAA) was used instead of 3 parts of acrylic acid (AA) as the carboxyl-containing monomer; and the amount of emulsifier (sodium dodecylbenzenesulfonate) used in the reactor was changed from 0.05 parts to 0.1 parts. Otherwise, the process was the same as in Example 1, producing an aqueous dispersion containing particulate polymer, a slurry composition for a functional layer, a spacer with a functional layer, a negative electrode, a positive electrode, and a secondary battery, and performing various measurements and evaluations. The results are shown in Table 1.

[0247] (Example 17)

[0248] In the preparation of the functional layer slurry composition of Example 1, boehmite particles (Nabaltec, APYRAL AOH60, particle size 0.9 μm) were used instead of bauxite particles (Sumitomo Chemical Co., Ltd. AKP-3000, volume average particle size D50 = 0.7 μm) as inorganic particles. Otherwise, the process was the same as in Example 1, producing an aqueous dispersion containing the particulate polymer, a functional layer slurry composition, a spacer with a functional layer, a negative electrode, a positive electrode, and a secondary battery, and performing various measurements and evaluations. The results are shown in Table 2.

[0249] (Example 18)

[0250] In the preparation of the functional layer slurry composition of Example 1, barium sulfate particles (manufactured by Takehara Chemical Industry Co., Ltd., TS-3, particle size 0.6 μm) were used instead of bauxite particles (manufactured by Sumitomo Chemical Co., Ltd., AKP-3000, volume average particle size D50 = 0.7 μm) as inorganic particles. Otherwise, the same procedure as in Example 1 was followed to prepare an aqueous dispersion containing particulate polymer, a functional layer slurry composition, a spacer with a functional layer, a negative electrode, a positive electrode, and a secondary battery, and various measurements and evaluations were performed. The results are shown in Table 2.

[0251] (Example 19)

[0252] In the preparation of the functional layer slurry composition in Example 1, anionic polyacrylamide (manufactured by Arakawa Chemical Industry Co., Ltd., Polystron 117) was used instead of carboxymethyl cellulose (CMC) as the water-soluble polymer. Otherwise, the process was the same as in Example 1, producing an aqueous dispersion containing particulate polymer, a functional layer slurry composition, a spacer with a functional layer, a negative electrode, a positive electrode, and a secondary battery, and performing various measurements and evaluations. The results are shown in Table 2.

[0253] In addition, in Tables 1 and 2 shown below,

[0254] “BA” represents butyl acrylate unit.

[0255] “2EHA” represents the 2-ethylhexyl acrylate unit.

[0256] “EA” represents the ethyl acrylate unit.

[0257] “AN” represents an acrylonitrile unit.

[0258] “MAN” represents the methacrylonitrile unit.

[0259] “AGE” represents allyl glycidyl ether unit.

[0260] “GMA” represents glycidyl methacrylate unit.

[0261] “AA” represents acrylic unit.

[0262] "MAA" represents methacrylic acid unit.

[0263] "AMA" represents allyl methacrylate unit.

[0264] “NMA” represents N-hydroxymethylacrylamide unit.

[0265] "CMC" stands for carboxymethyl cellulose.

[0266] "PEG type" indicates that the surfactant is polyethylene glycol type.

[0267] [Table 1]

[0268]

[0269] [Table 2]

[0270]

[0271] As shown in Tables 1-2, if the binder of Examples 1-20, which contains a particulate polymer containing cyano monomer units, cyclic ether monomer units, and carboxyl monomer units, and the proportion of cyclic ether monomer units is more than a specified value, is used, a functional layer with excellent heat shrinkage resistance and electrolyte affinity can be formed.

[0272] On the other hand, it can be seen that when using the binder of Comparative Example 1, which contains a particulate polymer with a proportion that does not meet the specified value, the heat shrinkage resistance and electrolyte affinity of the formed functional layer are both poor.

[0273] Furthermore, it is known that when using binders that do not contain cyclic ether monomer units, the heat shrinkage resistance and electrolyte affinity of the formed functional layer are also poor.

[0274] It can be further seen that when using the binder of Comparative Example 4, which contains a particulate polymer without cyano monomer units, the formed functional layer has good heat shrinkage resistance but poor electrolyte affinity.

[0275] Furthermore, it is known that when using the binder of Comparative Example 5, which contains a particulate polymer without carboxyl monomer units, the formed functional layer has good heat shrinkage resistance but poor electrolyte affinity.

[0276] Industrial availability

[0277] According to the present invention, an adhesive for a secondary battery functional layer that can form a functional layer with excellent heat shrinkage resistance and electrolyte affinity can be provided.

[0278] Furthermore, according to the present invention, a slurry composition for a secondary battery functional layer capable of forming a functional layer with excellent heat shrinkage resistance and electrolyte affinity can be provided.

[0279] Therefore, according to the present invention, it is possible to provide a functional layer for secondary batteries with excellent heat shrinkage resistance and electrolyte affinity.

[0280] Therefore, according to the present invention, it is possible to provide a secondary battery having the functional layer.

Claims

1. A binder for a functional layer of a secondary battery, comprising a particulate polymer and a solvent. The particulate polymer comprises cyano-containing monomer units, cyclic ether-containing monomer units, carboxyl-containing monomer units, and crosslinking monomer units. The cyano-containing monomer units in the particulate polymer are present in a proportion of 2% by mass or more and 30% by mass or less. The cyclic ether monomer unit contained in the particulate polymer is present in a proportion of 5% by mass or more and 40% by mass or less. The carboxyl-containing monomer units in the particulate polymer are present in a proportion of 0.1% by mass or more and 10% by mass or less. The crosslinkable monomer units in the particulate polymer are present in a proportion of 0.4% by mass or more and 2% by mass or less. The crosslinking monomer unit is a repeating unit derived from a polyfunctional monomer having two or more polymerization reactive groups. The crosslinking monomer unit does not include the cyano-containing monomer unit or the cyclic ether-containing monomer unit. The solvent is water.

2. The binder for the functional layer of a secondary battery according to claim 1, wherein The particulate polymer has one glass transition temperature.

3. The binder for the functional layer of the secondary battery according to claim 1, wherein, The glass transition temperature of the particulate polymer is below 20°C.

4. The binder for the functional layer of a secondary battery according to claim 1, wherein The particulate polymer further comprises (meth)acrylate monomer units. The alkyl methacrylate monomer unit in the particulate polymer is present in a proportion of 40% by mass or more and 92% by mass or less.

5. The binder for the functional layer of a secondary battery according to claim 1, wherein The gel content of the particulate polymer is 85% by mass or more.

6. The binder for the functional layer of a secondary battery according to claim 1, wherein The volume average particle size of the particulate polymer is greater than 0.05 μm and less than 0.25 μm.

7. A slurry composition for a secondary battery functional layer, comprising the binder for a secondary battery functional layer according to any one of claims 1 to 6.

8. The slurry composition for a secondary battery functional layer according to claim 7, further comprising functional particles.

9. The slurry composition for a secondary battery functional layer according to claim 8, wherein, The functional particles comprise non-conductive particles.

10. The slurry composition for a secondary battery functional layer according to claim 9, wherein The volume average particle size of the non-conductive particles is less than 1.5 μm.

11. A functional layer for a secondary battery, formed using the slurry composition for a secondary battery functional layer according to any one of claims 7 to 10.

12. A secondary battery having the functional layer for a secondary battery as described in claim 11.

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