Composition for functional layer of non-aqueous secondary battery, functional layer for non-aqueous secondary battery, separator for non-aqueous secondary battery and non-aqueous secondary battery

Abstract

Provided is a composition for a nonaqueous secondary battery functional layer comprising non-conductive particles, a water-soluble polymer, and water, wherein the BET specific surface area of the non-conductive particles is not more than 25 m2 / g, and the following parameter P is not less than 35. Parameter P = filling factor of the composition for the nonaqueous secondary battery functional layer / Log (BET specific surface area of the non-conductive particles), where the filling factor (%) of the composition for the nonaqueous secondary battery functional layer = \{(solid content (vol%) of the composition for the nonaqueous secondary battery functional layer × volume of the composition for the nonaqueous secondary battery functional layer in a test tube) / volume of deposition layer\}×100%)

Description

[Technical Field]

[0001] The present invention relates to a composition for a functional layer of a non-aqueous secondary battery, a functional layer for a non-aqueous secondary battery, a separator for a non-aqueous secondary battery, and a non-aqueous secondary battery. [Background technology]

[0002] Non-aqueous secondary batteries, such as lithium-ion batteries (hereinafter sometimes referred to as "secondary batteries"), are small, lightweight, have high energy density, and can be repeatedly charged and discharged, making them suitable for a wide range of applications. Non-aqueous secondary batteries generally consist of battery components such as a positive electrode, a negative electrode, and a separator that isolates the positive and negative electrodes to prevent short circuits between them.

[0003] In secondary batteries, battery components are used that are equipped with a functional layer that imparts desired performance (e.g., heat resistance and strength) to the battery components. Specifically, for example, separators formed by forming a functional layer on a separator substrate, and electrodes formed by forming a functional layer on an electrode substrate which has an electrode composite layer on a current collector, are used as battery components. Furthermore, as a functional layer that can improve the heat resistance and strength of the battery components, a functional layer consisting of a porous film layer formed by binding non-conductive particles with a binder is used. This functional layer is formed, for example, by applying a functional layer composition containing non-conductive particles, various polymers that can function as a binder, and a dispersion medium to the surface of a substrate (such as a separator substrate or an electrode substrate), and then drying the applied functional layer composition.

[0004] Therefore, in recent years, in order to further improve the performance of secondary batteries, there has been a great deal of effort to improve non-aqueous secondary battery functional layer compositions (hereinafter sometimes simply referred to as "functional layer compositions") used in the formation of functional layers.

[0005] Specifically, Patent Document 1 proposes a binder composition comprising a water-soluble polymer containing amide group-containing monomer units, acid group-containing monomer units, and hydroxyl group-containing monomer units, wherein the content ratios of the amide group-containing monomer units and acid group-containing monomer units are within a predetermined range, and water. By using this binder composition and a slurry composition for a heat-resistant layer of a non-aqueous secondary battery containing non-conductive inorganic particles, a heat-resistant layer with excellent heat shrinkage resistance can be formed.

[0006] Furthermore, Patent Document 2 proposes a composition for a functional layer of a non-aqueous secondary battery that is excellent in vibration resistance to detachment and heat shrinkage resistance in an electrolyte, by using both a water-soluble polymer having predetermined properties and a non-water-soluble polymer having a particle size within a predetermined range.

[0007] Furthermore, Patent Document 3 proposes a composition for a porous membrane of a secondary battery comprising non-conductive particles and a water-soluble polymer, wherein the water-soluble polymer contains predetermined monomer units in a predetermined proportion, and the storage modulus of the water-soluble polymer under predetermined conditions is greater than or equal to a predetermined value. According to this composition for a porous membrane of a secondary battery, it is possible to manufacture a porous membrane that has a low residual moisture content, can be easily applied, and can improve the performance of the battery, such as high-temperature cycle characteristics. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2021 / 020061 [Patent Document 2] International Publication No. 2017 / 195564 [Patent Document 3] International Publication No. 2015 / 122322 [Overview of the project] [Problems that the invention aims to solve]

[0009] In recent years, there has been a demand to thin the functional layer in order to further increase the density of secondary batteries. However, when the coating film of the conventional functional layer composition applied to the substrate is thinned in order to thin the functional layer, the resulting functional layer sometimes has insufficient heat shrinkage resistance. Furthermore, there was room for further improvement in the conventional functional layer composition in terms of reducing the amount of moisture remaining in the functional layer formed using the functional layer composition, thereby improving the high-temperature cycle characteristics of secondary batteries.

[0010] Therefore, the present invention aims to provide a composition for a functional layer of a non-aqueous secondary battery that ensures excellent heat shrinkage resistance and can form a functional layer for a non-aqueous secondary battery with a low residual moisture content. Furthermore, the present invention aims to provide a functional layer for non-aqueous secondary batteries that ensures excellent heat shrinkage resistance and has a low residual moisture content, thereby enabling non-aqueous secondary batteries to exhibit excellent high-temperature cycle characteristics, and a separator for non-aqueous secondary batteries equipped with the functional layer for non-aqueous secondary batteries. Furthermore, the present invention aims to provide a non-aqueous secondary battery with excellent high-temperature cycling characteristics. [Means for solving the problem]

[0011] The inventors diligently conducted research with the aim of solving the above problems. As a result, the inventors have newly discovered that, for a non-aqueous secondary battery functional layer composition containing non-conductive particles, a water-soluble polymer, and water, by setting the BET specific surface area of ​​the non-conductive particles to a predetermined value or less, and setting the parameter P, which represents the ratio of the filling rate obtained using the non-aqueous secondary battery functional layer composition to the logarithm (Log) of the BET specific surface area of ​​the non-conductive particles to a predetermined value or more, it is possible to form a non-aqueous secondary battery functional layer that has excellent heat shrinkage resistance and low residual moisture content, and thus completed the present invention.

[0012] In other words, the present invention aims to advantageously solve the above problems, and according to the present invention, the following compositions for functional layers of non-aqueous secondary batteries are provided [1] to [8], the following functional layer for non-aqueous secondary batteries is provided [9], the following separator for non-aqueous secondary batteries is provided

[10] , and the following non-aqueous secondary battery is provided

[11] . [1] A composition for a non-aqueous secondary battery functional layer comprising non-conductive particles, a water-soluble polymer, and water, wherein the BET specific surface area of ​​the non-conductive particles is 25 m². 2 The composition for the functional layer of a non-aqueous secondary battery is less than or equal to / g, and the parameter P represented by the following formula (1) is 35 or greater. Parameter P = Packing density of the composition for the functional layer of non-aqueous secondary batteries / Log(BET specific surface area of ​​non-conductive particles) ... (1) In formula (1), the packing ratio of the non-aqueous secondary battery functional layer composition is calculated based on formula (2) below, by determining the mass balance from the height of the sediment obtained by centrifugal sedimentation of the non-aqueous secondary battery functional layer composition packed in a test tube. The packing rate (%) of the composition for the functional layer of a non-aqueous secondary battery = {(Solid content (volume %) in the composition for the functional layer of a non-aqueous secondary battery × Volume of the composition for the functional layer of a non-aqueous secondary battery in the test tube) / Volume of the deposited layer} × 100% ... (2) Thus, by setting the BET specific surface area of ​​the non-conductive particles to a predetermined value or less, and setting the parameter P, which represents the ratio of the packing density obtained using the non-aqueous secondary battery functional layer composition to the logarithm of the BET specific surface area of ​​the non-conductive particles, to a predetermined value or more, it is possible to form a non-aqueous secondary battery functional layer that has excellent heat shrinkage resistance and low residual moisture content. In this invention, "water-soluble polymer" refers to a polymer in which, when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble content is less than 1.0% by mass. Furthermore, in this invention, "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET method.

[0013] [2] The water-soluble polymer contains crosslinkable monomer units, and the content ratio of the crosslinkable monomer units in the water-soluble polymer is 0.1% by mass or more and 10% by mass or less. The composition for a non-aqueous secondary battery functional layer according to [1] above. Thus, if the water-soluble polymer contains crosslinkable monomer units and the content ratio of the crosslinkable monomer units in the water-soluble polymer is within the above range, the molecular weight of the water-soluble polymer can be lowered to improve the coating property of the composition for the functional layer, and at the same time, the water-soluble polymer can be made highly rigid to further improve the heat shrinkage resistance of the functional layer. In the present invention, the polymer "contains monomer units" means that "the repeating units derived from the monomer are contained in the polymer obtained using the monomer". Further, in the present invention, the content ratio of the monomer units in the polymer is 1 measured by using nuclear magnetic resonance (NMR) methods such as 1H-NMR and 13 13C-NMR.

[0014] [3] The viscosity of the composition for a non-aqueous secondary battery functional layer is 10 mPa·s or more and 300 mPa·s or less. The composition for a non-aqueous secondary battery functional layer according to [1] or [2] above. Thus, if the viscosity of the composition for the functional layer is within the above range, the coating property of the composition for the non-aqueous secondary battery functional layer can be further improved. In the present invention, the "viscosity" of the composition for a non-aqueous secondary battery functional layer can be measured using the method described in the examples of this specification.

[0015] [4] The weight average molecular weight of the water-soluble polymer is 50,000 or more and 1,000,000 or less. The composition for a non-aqueous secondary battery functional layer according to any one of [1] to [3] above. Thus, if the weight average molecular weight of the water-soluble polymer is within the above range, the decrease in the viscosity of the composition for the functional layer can be suppressed to further improve the coating property, and at the same time, the water-soluble polymer can be made even more highly rigid to further improve the heat shrinkage resistance of the functional layer. In this invention, the "weight-average molecular weight" of the water-soluble polymer can be measured using the method described in the examples of this specification.

[0016] [5] A non-aqueous secondary battery functional layer composition according to any one of [1] to [4] above, wherein the volume average particle diameter of the non-conductive particles is 0.05 μm or more and 0.45 μm or less. Thus, if the volume-average particle diameter of the non-conductive particles is within the above range, even when the functional layer is thinned and densely packed, excellent heat shrinkage resistance can be sufficiently ensured, and the decrease in ionic conductivity can be suppressed, further improving the high-temperature cycle characteristics of the secondary battery. In this invention, "volume-average particle diameter of non-conductive particles" refers to the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side in the particle diameter distribution (volume-based) measured by laser diffraction accounts for 50%.

[0017] [6] The composition for a non-aqueous secondary battery functional layer according to any one of [1] to [5] above, wherein the water-soluble polymer contains amide group-containing monomer units, and the content ratio of the amide group-containing monomer units in the water-soluble polymer is 70% by mass or more and 98% by mass or less. Thus, if the water-soluble polymer contains amide group-containing monomer units, and the content ratio of amide group-containing monomer units in the water-soluble polymer is within the above range, the dispersion stability of the functional layer composition can be improved, and the water-soluble polymer can be made even more rigid, thereby further improving the heat shrinkage resistance of the functional layer.

[0018] [7] The composition for a non-aqueous secondary battery functional layer according to any one of [1] to [6] above, wherein the water-soluble polymer contains acid group-containing monomer units, and the content ratio of the acid group-containing monomer units in the water-soluble polymer is 1% by mass or more and 20% by mass or less. Thus, if the water-soluble polymer contains acid group-containing monomer units, and the proportion of acid group-containing monomer units in the water-soluble polymer is within the above range, the dispersion stability and coating properties of the functional layer composition can be further improved, and the amount of water adsorbed onto the functional layer due to the interaction between the water-soluble polymer and non-conductive particles can be reduced, thereby further reducing the amount of residual water in the functional layer. In addition, since thixotropy is imparted to the functional layer composition, the coating properties of the functional layer composition can be further improved.

[0019] [8] A non-aqueous secondary battery functional layer composition according to any one of [1] to [7] above, further comprising a surfactant, wherein the content of the surfactant is 0.1 parts by mass or more and 1.0 part by mass or less per 100 parts by mass of the non-conductive particles. Thus, by including surfactants within the above range, the heat shrinkage resistance of the functional layer and the coating properties of the composition for the functional layer can be further improved.

[0020] [9] A functional layer for a non-aqueous secondary battery formed using any of the non-aqueous secondary battery functional layer compositions described in [1] to [8] above. Thus, the functional layer formed using the above-described non-aqueous secondary battery functional layer composition ensures excellent heat shrinkage resistance even when thinned, and because it has a low residual moisture content, it can exhibit excellent high-temperature cycle characteristics in secondary batteries.

[0021]

[10] A separator for a non-aqueous secondary battery, comprising the functional layer for a non-aqueous secondary battery described in [9] above. Thus, a separator for non-aqueous secondary batteries equipped with the above-described functional layer for non-aqueous secondary batteries can enable non-aqueous secondary batteries to exhibit excellent high-temperature cycling characteristics.

[0022]

[11] A non-aqueous secondary battery comprising the separator for non-aqueous secondary batteries described in

[10] above. Thus, secondary batteries equipped with the aforementioned non-aqueous secondary battery separator exhibit excellent high-temperature cycling characteristics. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a composition for a functional layer of a non-aqueous secondary battery that ensures excellent heat shrinkage resistance and can form a functional layer for a non-aqueous secondary battery with a low residual moisture content. Furthermore, according to the present invention, it is possible to provide a functional layer for non-aqueous secondary batteries that ensures excellent heat shrinkage resistance and has a low residual moisture content, thereby enabling non-aqueous secondary batteries to exhibit excellent high-temperature cycle characteristics, and a separator for non-aqueous secondary batteries equipped with the functional layer for non-aqueous secondary batteries. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery with excellent high-temperature cycle characteristics. [Modes for carrying out the invention]

[0024] Embodiments of the present invention will be described in detail below. Here, the non-aqueous secondary battery functional layer composition of the present invention is used as a material when forming the functional layer for a non-aqueous secondary battery. The non-aqueous secondary battery functional layer of the present invention is formed using the non-aqueous secondary battery functional layer composition of the present invention. The non-aqueous secondary battery separator of the present invention comprises at least the non-aqueous secondary battery functional layer of the present invention. The non-aqueous secondary battery of the present invention comprises at least the non-aqueous secondary battery separator of the present invention.

[0025] (Non-aqueous secondary battery functional layer composition) The present invention relates to a slurry composition for a non-aqueous secondary battery functional layer containing non-conductive particles and a water-soluble polymer, and optionally further containing other components other than non-conductive particles and water-soluble polymers, such as particulate polymers and additives, with water as the dispersion medium. Furthermore, the present invention relates to a non-aqueous secondary battery functional layer composition in which the non-conductive particles have a BET specific surface area of ​​25 m². 2 The composition is characterized by having a value of 0.1 / g or less, and a parameter P representing the ratio of the packing density, which can be determined using a non-aqueous secondary battery functional layer composition, to the logarithm (Log) of the BET specific surface area of ​​non-conductive particles, being greater than or equal to a predetermined value.

[0026] Furthermore, the non-aqueous secondary battery functional layer composition of the present invention ensures excellent heat shrinkage resistance and allows for the formation of a non-aqueous secondary battery functional layer with low residual moisture content, as the non-conductive particles have the above-described predetermined properties and the above-described parameter P is above a predetermined value. Furthermore, by using a non-aqueous secondary battery functional layer formed using the non-aqueous secondary battery functional layer composition of the present invention, a non-aqueous secondary battery can exhibit excellent high-temperature cycle characteristics.

[0027] <Non-conductive particles> Here, non-conductive particles are particles that do not dissolve in water, which is the dispersion medium, or in the non-aqueous electrolyte of the secondary battery, and maintain their shape even within these environments. Furthermore, since non-conductive particles are electrochemically stable, they remain stable in the functional layer under the operating conditions of the secondary battery.

[0028] As non-conductive particles, various inorganic and organic fine particles can be used, but inorganic fine particles are usually used. In particular, materials that are stable in the operating environment of non-aqueous secondary batteries and are electrochemically stable are preferred as materials for non-conductive particles. From this viewpoint, preferred examples of non-conductive particles include oxide particles such as aluminum oxide (alumina), aluminum oxide hydrate (boehmite), silicon oxide, magnesium oxide (magnesia), calcium oxide, titanium oxide (titania), BaTiO3, ZrO, and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalent crystalline particles such as silicon and diamond; sparingly soluble ionic crystalline particles such as barium sulfate, calcium fluoride, and barium fluoride; and clay fine particles such as talc and montmorillonite. Furthermore, these particles may be subjected to elemental substitution, surface treatment, solid solution treatment, etc., as needed. Among these, alumina, boehmite, and barium sulfate are preferred as non-conductive particles. The non-conductive particles mentioned above may be used individually or in combination of two or more types.

[0029] Furthermore, examples of non-conductive particle shapes include ellipsoidal, polygonal, tetrapod-shaped, plate-shaped, and flaky shapes. The aspect ratio of the non-conductive particles is not particularly limited, but is preferably between 1.5 and 20.

[0030] Furthermore, the BET specific surface area of ​​non-conductive particles is 25 m². 2 / g or less, 23m 2 It is preferable that the amount be less than or equal to 20m 2 It is more preferable that the BET specific surface area of ​​the non-conductive particles is 25 m² or less. 2 If the amount is less than / g, the amount of residual moisture in the functional layer can be reduced. Furthermore, the BET specific surface area of ​​non-conductive particles can be adjusted, for example, by changing the particle size, particle shape, etc.

[0031] Furthermore, the volume-average particle diameter of the non-conductive particles is preferably 0.05 μm or more, more preferably 0.1 μm or more, even more preferably 0.15 μm or more, preferably 0.45 μm or less, more preferably 0.4 μm or less, and even more preferably 0.35 μm or less. If the volume-average particle diameter of the non-conductive particles is above the lower limit, the decrease in ionic conductivity can be suppressed, and the cycle characteristics of the secondary battery can be further improved. Also, if the volume-average particle diameter of the non-conductive particles is below the upper limit, excellent heat shrinkage resistance can be sufficiently ensured even when the functional layer is made into a thin film and increased in density.

[0032] <Water-soluble polymer> The water-soluble polymer is included as a binder in the functional layer composition of the present invention. Here, it is preferable that the water-soluble polymer contains at least one monomer unit selected from the group consisting of crosslinkable monomer units, amide group-containing monomer units, and acid group-containing monomer units. The water-soluble polymer may also optionally further contain monomer units other than crosslinkable monomer units, amide group-containing monomer units, and acid group-containing monomer units (hereinafter referred to as "other monomer units").

[0033] [Cross-linkable monomer units] As crosslinkable monomers that can form crosslinkable monomer units, monomers that can form a crosslinked structure when polymerized can be used. Specifically, examples include monofunctional monomers having a thermally crosslinkable group and one ethylenically unsaturated bond per molecule, and polyfunctional monomers having two or more ethylenically unsaturated bonds per molecule. Examples of thermally crosslinkable groups contained in monofunctional monomers include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof. Furthermore, the crosslinkable monomer may be hydrophobic or hydrophilic. In this invention, a crosslinkable monomer is considered "hydrophobic" if it does not contain hydrophilic groups, and a crosslinkable monomer is considered "hydrophilic" if it contains hydrophilic groups. Here, "hydrophilic groups" in a crosslinkable monomer refer to carboxylic acid groups, hydroxyl groups, sulfonic acid groups, phosphoric acid groups, epoxy groups, thiol groups, aldehyde groups, amide groups, oxetanyl groups, and oxazoline groups. Examples of hydrophobic, crosslinkable monomers include polyfunctional (meth)acrylates such as allyl (meth)acrylate, ethylene di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and trimethylolpropane-tri(meth)acrylate; polyfunctional allyl / vinyl ethers such as dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, and tetraallyloxyethane; and divinylbenzene. Examples of hydrophilic crosslinkable monomers include vinyl glycidyl ether, allyl glycidyl ether, glycidyl methacrylate, N-methylolacrylamide, and allyl methacrylamide. Among these, glycidyl methacrylate and N-methylolacrylamide are preferred as crosslinkable monomers. Using glycidyl methacrylate or N-methylolacrylamide can further improve the heat shrinkage resistance of the functional layer. Furthermore, the crosslinkable monomer may be used individually or in combination of two or more types in any ratio.

[0034] Furthermore, the content of crosslinkable monomer units in the water-soluble polymer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, preferably 10% by mass or less, more preferably 9% by mass or less, and even more preferably 8% by mass or less. If the content of crosslinkable monomer units is above the lower limit, the water-soluble polymer can be made more rigid, further improving the heat shrinkage resistance of the functional layer. Also, if the content of crosslinkable monomer units is below the upper limit, the molecular weight of the water-soluble polymer can be lowered, improving the coating properties of the functional layer composition.

[0035] [Amide group-containing monomer unit] Examples of amide group-containing monomers that can form amide group-containing monomer units include acrylamide, methacrylamide, dimethylacrylamide, and diethylacrylamide. Herein, in the present invention, an amide group-containing monomer refers to a monomer in which a hydrogen atom or an alkyl group is bonded to the N atom of the amide group. Among these, acrylamide is preferred as the amide group-containing monomer. By using acrylamide, thermal decomposition resistance can be imparted to the main skeleton of the water-soluble polymer, further improving the heat shrinkage resistance of the functional layer. Furthermore, the amide group-containing monomer may be used individually or in combination of two or more types in any ratio.

[0036] Furthermore, the content of amide group-containing monomer units in the water-soluble polymer is preferably 70% by mass or more, more preferably 73% by mass or more, even more preferably 80% by mass or more, preferably 98% by mass or less, more preferably 96% by mass or less, and even more preferably 90% by mass or less. If the content of amide group-containing monomer units is above the lower limit, the water-soluble polymer can be made even more rigid, and the heat shrinkage resistance of the functional layer can be further improved. Also, if the content of amide group-containing monomer units is below the upper limit, the dispersion stability of the composition for the functional layer can be improved.

[0037] [Acid group-containing monomer unit] Examples of acid group-containing monomers that can form acid group-containing monomer units include monomers having a carboxylic acid group, monomers having a sulfonic acid group, monomers having a phosphate group, and monomers having a hydroxyl group.

[0038] Examples of monomers having a carboxylic acid group include monocarboxylic acids and dicarboxylic acids. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of monomers having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, ethyl (meth)acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-alyloxy-2-hydroxypropanesulfonic acid. In this specification, "(meth)allyl" means allyl and / or methallyl, and "(meth)acrylic" means acrylic and / or methacrylic. Furthermore, examples of monomers having a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate. In this specification, "(meth)acryloyl" means acryloyl and / or methacryloyl. Examples of monomers having a hydroxyl group include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate. Among these, acrylic acid is preferred as the acid group-containing monomer. By using acrylic acid, anionic properties can be imparted to the water-soluble polymer, and the interaction between the water-soluble polymer and the non-conductive particle surface can suppress the adsorption of moisture to the functional layer. Furthermore, the acid group-containing monomer may be used individually, or two or more may be used in any ratio.

[0039] Furthermore, the content of acid group-containing monomer units in the water-soluble polymer is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less. If the content of acid group-containing monomer units is above the lower limit, the interaction between the water-soluble polymer and the non-conductive particles is further improved, which further reduces the amount of water adsorbed on the functional layer and further reduces the amount of residual water in the functional layer. In addition, thixotropy is imparted to the functional layer composition, which further improves the coating properties of the functional layer composition. Moreover, if the content of acid group-containing monomer units is below the upper limit, the dispersion stability and coating properties of the functional layer composition are further improved.

[0040] [Other monomeric units] Other monomers that can form other monomer units that the water-soluble polymer may contain are not particularly limited as long as they can copolymerize with any of the crosslinkable monomers, amide group-containing monomers, and acid group-containing monomers mentioned above. Furthermore, the content of other monomer units in the water-soluble polymer is preferably less than 10% by mass, more preferably less than 5% by mass, even more preferably less than 1% by mass, and particularly preferably 0% by mass.

[0041] [Molecular weight of water-soluble polymers] Here, the water-soluble polymer preferably has a weight-average molecular weight (Mw) of 50,000 or more, more preferably 100,000 or more, even more preferably 200,000 or more, preferably 1,000,000 or less, more preferably 900,000 or less, and even more preferably 700,000 or less. If the weight-average molecular weight (Mw) of the water-soluble polymer is above the lower limit, the water-soluble polymer can be made even more rigid, further improving the heat shrinkage resistance of the functional layer. Also, if the weight-average molecular weight (Mw) of the water-soluble polymer is below the upper limit, the coating properties of the functional layer composition will be further improved. Furthermore, the weight-average molecular weight of a water-soluble polymer is not particularly limited and can be controlled, for example, by adjusting the polymerization time during the preparation of the water-soluble polymer, or by adjusting the amount of various additives used in the preparation, particularly polymerization aids such as chain transfer agents and polymerization initiators.

[0042] [Amount of water-soluble polymer] Furthermore, in the functional layer composition of the present invention, the content of the water-soluble polymer is preferably 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of non-conductive particles. If the content of the water-soluble polymer is within the above range, the heat shrinkage resistance of the functional layer can be further improved.

[0043] [Method for preparing water-soluble polymers] Water-soluble polymers can be produced by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent such as water. In this case, the content ratio of each monomer in the monomer composition can be determined in accordance with the content ratio of each repeating unit (monomer unit) in the water-soluble polymer. Furthermore, there are no particular restrictions on the polymerization method; any of the following methods can be used, such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization. In addition, any of the following polymerization reactions can be used, such as ionic polymerization, radical polymerization, or living radical polymerization. Furthermore, commonly used additives such as emulsifiers, dispersants, polymerization initiators, and polymerization aids can be used in polymerization. The amounts of these additives used can also be the amounts commonly used. Polymerization conditions can be adjusted as appropriate depending on the polymerization method and the type of polymerization initiator.

[0044] <Particulate polymer> The particulate polymer that may be optionally included in the functional layer composition of the present invention is a water-insoluble polymer. The particulate polymer is dispersed in the functional layer composition while maintaining its particle shape and functions as a binder together with the water-soluble polymer described above. By using the water-soluble polymer and the particulate polymer in combination as binders, the redispersibility of non-conductive particles can be further improved, and the flexibility of the functional layer formed using the functional layer composition can be enhanced. In this invention, a polymer is considered "water-insoluble" if, at 25°C, 0.5 g of the polymer is dissolved in 100 g of water, resulting in an insoluble content of 90% by mass or more.

[0045] [Composition of particulate polymer] Furthermore, the particulate polymer is not particularly limited, and any known particulate polymer that can be used as a binder when forming a functional layer can be used. Specifically, the particulate polymer is not particularly limited, and can include conjugated diene polymers, fluorine polymers, acrylic polymers, etc., with acrylic polymers being preferred. These particulate polymers may be used individually or in combination of two or more types.

[0046] Here, a conjugated diene polymer that can be preferably used as a particulate polymer is a polymer containing conjugated diene monomer units. Specific examples of conjugated diene polymers include, but are not limited to, copolymers containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units, such as styrene-butadiene copolymer (SBR), butadiene rubber (BR), acrylic rubber (NBR) (a copolymer containing acrylonitrile units and butadiene units), and their hydrides.

[0047] Furthermore, fluorine-based polymers that can be preferably used as particulate polymers are polymers containing fluorine-containing monomer units. Specifically, examples of fluorine-based polymers include homopolymers or copolymers of one or more fluorine-containing monomers, and copolymers of one or more fluorine-containing monomers and monomers that do not contain fluorine (hereinafter referred to as "fluorine-free monomers"). Furthermore, the proportion of fluorine-containing monomer units in a fluorine-based polymer is usually 70% by mass or more, preferably 80% by mass or more, when the total monomer units in the fluorine-based polymer are considered to be 100% by mass. In addition, the proportion of fluorine-free monomer units in a fluorine-based polymer is usually 30% by mass or less, preferably 20% by mass or less, when the total monomer units in the fluorine-based polymer are considered to be 100% by mass.

[0048] Examples of fluorine-containing monomers that can form fluorine-containing monomer units include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl trifluoride, vinyl fluoride, and perfluoroalkyl vinyl ether. Among these, vinylidene fluoride is preferred as the fluorine-containing monomer.

[0049] Furthermore, fluorine-free monomers that can form fluorine-free monomer units include fluorine-free monomers copolymerizable with fluorine-containing monomers, such as 1-olefins like ethylene, propylene, and 1-butene; aromatic vinyl compounds like styrene, α-methylstyrene, pt-butylstyrene, vinyltoluene, and chlorostyrene; unsaturated nitrile compounds like (meth)acrylonitrile; (meth)acrylic acid ester compounds like methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; (meth)acrylamide compounds like (meth)acrylamide, N-methylol(meth)acrylamide, and N-butoxymethyl(meth)acrylamide; and (meth)acrylamide. Examples include vinyl compounds containing carboxyl groups such as acrylic acid, itaconic acid, fumaric acid, crotonic acid, and maleic acid; epoxy group-containing unsaturated compounds such as allyl glycidyl ether and glycidyl (meth)acrylate; amino group-containing unsaturated compounds such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; sulfonic acid group-containing unsaturated compounds such as styrene sulfonic acid, vinyl sulfonic acid, and (meth)allyl sulfonic acid; sulfate group-containing unsaturated compounds such as 3-alyloxy-2-hydroxypropane sulfate; and phosphate group-containing unsaturated compounds such as propyl 3-chloro-2-phosphate (meth)acrylate and 3-alyloxy-2-hydroxypropane phosphate.

[0050] Furthermore, acrylic polymers that can be preferably used as particulate polymers are polymers containing (meth)acrylic acid ester monomer units. Here, alkyl (meth)acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, and 2-ethylhexyl acrylate can be used as (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units. Furthermore, the acrylic polymer preferably contains, in addition to (meth)acrylic acid ester monomer units, at least one monomer unit selected from the group consisting of (meth)acrylonitrile monomer units, acid group-containing monomer units, and crosslinkable monomer units, and more preferably contains (meth)acrylotril monomer units, acid group-containing monomer units, and crosslinkable monomer units. The same monomers as those used in the water-soluble polymer described above can be used as the acid group-containing monomers capable of forming acid group-containing monomer units and the crosslinkable monomers capable of forming crosslinkable monomer units. In this invention, "(meth)acrylonitrile" means acrylonitrile and / or methacrylonitrile.

[0051] [Properties of particulate polymers] Here, the particulate polymer preferably has a volume-average particle diameter of 0.05 μm or more and 1.0 μm or less. By keeping the volume-average particle diameter of the particulate polymer within the above range, the strength and flexibility of the functional layer can be sufficiently enhanced. In this invention, "volume-average particle diameter of particulate polymer" refers to the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side in the particle diameter distribution (volume-based) measured by laser diffraction accounts for 50%.

[0052] Furthermore, the glass transition temperature (Tg) of the particulate polymer is preferably less than 20°C. If the glass transition temperature of the particulate polymer is less than 20°C, both the flexibility and binding properties of the functional layer can be sufficiently enhanced. In this invention, the "glass transition temperature of the particulate polymer" can be measured by differential scanning calorimetry in accordance with JIS K6240.

[0053] [Amount of particulate polymer] Furthermore, the amount of particulate polymer that may be included in the functional layer composition of the present invention is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1.0 part by mass or more, preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of nonconductive particles. By setting the content of particulate polymer to be above the lower limit above, the redispersibility of nonconductive particles can be sufficiently improved, and the flexibility of the functional layer can be sufficiently increased. Furthermore, by setting the content of particulate polymer to be above the lower limit above, sufficient binding force can be ensured, and the shedding (dropping of powder) of nonconductive particles from the functional layer can be suppressed. In addition, by setting the content of particulate polymer to be below the upper limit above, sufficient porosity of the functional layer can be ensured, and a decrease in the output characteristics of the secondary battery can be suppressed.

[0054] [Method for preparing particulate polymers] Particulate polymers can be produced by polymerizing a monomer composition containing monomers used for polymerization of the particulate polymer in an aqueous solvent such as water. In this case, the content ratio of each monomer in the monomer composition can be determined in accordance with the content ratio of each repeating unit (monomer unit) in the particulate polymer. Furthermore, there are no particular restrictions on the polymerization method; any of the following methods can be used, such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization. In addition, any of the following polymerization reactions can be used, such as ionic polymerization, radical polymerization, or living radical polymerization. Furthermore, commonly used additives such as emulsifiers, dispersants, polymerization initiators, and polymerization aids can be used in polymerization. The amounts of these additives used can also be the amounts commonly used. Polymerization conditions can be adjusted as appropriate depending on the polymerization method and the type of polymerization initiator.

[0055] <Additives> The additives that may be optionally included in the functional layer composition of the present invention are not particularly limited as long as they do not affect the battery reaction, and known additives can be used. One type of additive may be used alone, or two or more types may be used in combination. Examples of additives include well-known additives such as surfactants and dispersants.

[0056] <<Surfactants>> The surfactant is not particularly limited, and can be ethylene oxide / propylene oxide-based surfactants (hereinafter also referred to as "EO / PO-based surfactants"), fluorine-based surfactants, silicone-based surfactants, etc. Among these, the use of EO / PO-based surfactants and fluorine-based surfactants is preferred, and the use of EO / PO-based surfactants is more preferred. Here, specific examples of EO·PO-based surfactants include polyoxyalkylene glycol-based surfactants. Specific examples of fluorine-based surfactants include fluorine alkyl esters. Specific examples of silicone-based surfactants include dimethylpolysiloxane. Among these, EO·PO-based surfactants are preferred as surfactants.

[0057] Furthermore, the surfactant content in the functional layer composition is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, preferably 1.0 part by mass or less, more preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less, per 100 parts by mass of non-conductive particles. If the surfactant content is above the lower limit, the coatability of the functional layer composition can be further improved. Also, if the surfactant content is below the upper limit, the heat shrinkage resistance of the functional layer can be further improved.

[0058] <<Dispersant>> The dispersant is not particularly limited, and examples include acrylic acid-sulfonic acid monomer copolymers, special sodium polyacrylate salts, and special ammonium polyacrylate salts.

[0059] Furthermore, the dispersant content in the functional layer composition is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less, per 100 parts by mass of non-conductive particles. If the dispersant content is 5 parts by mass or less, the amount of residual moisture in the functional layer can be further reduced, and the heat shrinkage resistance of the functional layer can be further improved.

[0060] <Dispersion medium> The non-aqueous secondary battery functional layer composition of the present invention contains water as a dispersion medium. The non-aqueous secondary battery functional layer composition may also contain a small amount of a medium other than water, such as an organic solvent, as a dispersion medium.

[0061] <Preparation of compositions for functional layers of non-aqueous secondary batteries> The non-aqueous secondary battery functional layer composition of the present invention is not particularly limited and can be obtained by mixing the above-mentioned non-conductive particles, a water-soluble polymer, and any particulate polymer, surfactant, dispersant, etc., as needed, in the presence of water as a dispersion medium.

[0062] Here, the method and order of mixing the above-mentioned components are not particularly limited, but it is preferable to use a disperser as the mixing device in order to efficiently disperse each component. The disperser is preferably a device that can uniformly disperse and mix the above components. Examples of dispersers include ball mills, sand mills, bead mills, pigment dispersers, lye crushers, ultrasonic dispersers, homogenizers, and planetary mixers.

[0063] <Properties of compositions for the functional layer of non-aqueous secondary batteries> Furthermore, the functional layer composition of the present invention preferably has a viscosity of 10 mPa·s or more, more preferably 30 mPa·s or more, more preferably 300 mPa·s or less, and more preferably 200 mPa·s or less. If the viscosity of the functional layer composition is within the above range, the coating properties of the functional layer composition are further improved.

[0064] <Parameter P> Furthermore, the functional layer composition of the present invention has a parameter P, expressed by the following formula (1), which represents the ratio of the packing density obtained using the functional layer composition to the logarithm (Log) of the BET specific surface area of ​​the non-conductive particles contained in the functional layer composition, that is 35 or more, preferably 35.5 or more, and preferably 36 or more. If the parameter P is 35 or more, even when the functional layer is made into a thin film and increased in density, excellent heat shrinkage resistance can be ensured, and the amount of residual moisture in the functional layer can be reduced. Parameter P = Packing density of the composition for the functional layer of non-aqueous secondary batteries / Log(BET specific surface area of ​​non-conductive particles) ... (1) Here, in formula (1) above, the packing rate of the non-aqueous secondary battery functional layer composition is calculated from the mass balance of the sediment obtained by centrifugal sedimentation of the non-aqueous secondary battery functional layer composition packed in a test tube, and determined based on formula (2) below. The packing rate (%) of the composition for the functional layer of a non-aqueous secondary battery = {(Solid content (volume %) in the composition for the functional layer of a non-aqueous secondary battery × Volume of the composition for the functional layer of a non-aqueous secondary battery in the test tube) / Volume of the deposited layer} × 100% ... (2)

[0065] (Functional layer for non-aqueous secondary batteries) The functional layer for non-aqueous secondary batteries of the present invention is formed from the above-described non-aqueous secondary battery functional layer composition, and can be formed, for example, by applying the above-described functional layer composition to the surface of a suitable substrate to form a coating film, and then drying the formed coating film. The functional layer for non-aqueous secondary batteries of the present invention consists of the dried product of the above-described functional layer composition and usually contains the above-described predetermined non-conductive particles and a water-soluble polymer. Furthermore, since the functional layer for non-aqueous secondary batteries of the present invention is formed using the above-described functional layer composition, it exhibits excellent heat shrinkage resistance and low residual moisture content in the functional layer. Therefore, by using the functional layer for non-aqueous secondary batteries of the present invention, excellent high-temperature cycle characteristics can be achieved in non-aqueous secondary batteries.

[0066] <Base material> Here, there are no restrictions on the substrate to which the functional layer composition is applied; for example, separator substrates or electrode substrates can be used as substrates.

[0067] [Separator substrate] The separator substrate is not particularly limited, but known separator substrates such as organic separator substrates can be used. Organic separator substrates are porous members made of organic materials. Examples of organic separator substrates include microporous membranes or nonwoven fabrics containing polyethylene, polyolefin resins such as polypropylene, and aromatic polyamide resins. Among these, polyethylene microporous membranes and nonwoven fabrics are preferred due to their excellent strength. The thickness of the separator substrate can be any thickness, preferably 5 μm to 30 μm, more preferably 5 μm to 20 μm, and even more preferably 5 μm to 18 μm. Sufficient stability can be obtained if the thickness of the separator substrate is 5 μm or more. Furthermore, if the thickness of the separator substrate is 30 μm or less, the thermal shrinkage force of the separator substrate can be suppressed, thereby improving its heat shrinkage resistance.

[0068] [Electrode base material] The electrode substrates (positive electrode substrate and negative electrode substrate) are not particularly limited, but examples include electrode substrates in which an electrode composite material layer is formed on a current collector. Here, known materials can be used for the current collector, the electrode active material in the electrode composite layer (positive electrode active material, negative electrode active material), the binder for the electrode composite layer (binder for the positive electrode composite layer, binder for the negative electrode composite layer), and the method for forming the electrode composite layer on the current collector. For example, those described in Japanese Patent Application Publication No. 2013-145763 and International Publication No. 2015 / 129408 can be used.

[0069] <Method for forming a functional layer for non-aqueous secondary batteries> The following methods can be used to form a functional layer on a substrate such as the separator substrate or electrode substrate mentioned above. 1) A method of applying the non-aqueous secondary battery functional layer composition of the present invention to the surface of a separator substrate or electrode substrate (in the case of an electrode substrate, the surface on the electrode composite layer side, the same applies hereinafter), and then drying it; 2) A method of immersing a separator substrate or electrode substrate in the non-aqueous secondary battery functional layer composition of the present invention, and then drying it; 3) A method of applying the non-aqueous secondary battery functional layer composition of the present invention onto a release substrate, drying it to produce a functional layer, and transferring the obtained functional layer to the surface of a separator substrate or electrode substrate; Among these, method 1) is particularly preferred because it allows for easy control of the thickness of the functional layer. Method 1) more specifically includes a step of applying a functional layer composition onto a substrate (coating step) and a step of drying the functional layer composition applied onto the substrate to form a functional layer (functional layer formation step).

[0070] [Coating process] Furthermore, there are no particular limitations on the method of applying the functional layer composition onto the substrate during the coating process. Examples include the doctor blade method, reverse roll method, direct roll method, gravure method, extrusion method, and brush coating method.

[0071] [Functional layer formation process] Furthermore, in the functional layer formation process, the method for drying the functional layer composition on the substrate is not particularly limited and known methods can be used, such as drying with hot air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams. The drying conditions are not particularly limited, but the drying temperature is preferably 50 to 150°C and the drying time is preferably 3 to 30 minutes.

[0072] Furthermore, from the viewpoint of ensuring sufficient heat shrinkage resistance of the functional layer, the thickness of the functional layer formed as described above is preferably 0.1 μm or more, preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less.

[0073] (Separator for non-aqueous secondary batteries) The separator for non-aqueous secondary batteries of the present invention (hereinafter also referred to as "separator for secondary batteries") comprises a functional layer for non-aqueous secondary batteries formed using the functional layer composition of the present invention described above. Specifically, the separator for non-aqueous secondary batteries of the present invention comprises the functional layer for non-aqueous secondary batteries described above on at least one surface of the separator substrate. Here, the separator substrate used for the secondary battery separator is not particularly limited, and any of the separator substrates listed above as substrates to which the functional layer composition is applied can be used. Furthermore, the method for manufacturing the separator for secondary batteries is not particularly limited, and it can be manufactured according to the method described in the section on the method for forming a functional layer for non-aqueous secondary batteries above.

[0074] (Non-aqueous secondary battery) The secondary battery of the present invention is equipped with the non-aqueous secondary battery separator of the present invention described above. More specifically, the non-aqueous secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is the non-aqueous secondary battery separator of the present invention described above. Furthermore, because the secondary battery of the present invention is equipped with the non-aqueous secondary battery separator, it exhibits excellent high-temperature cycle characteristics.

[0075] <Positive electrode, negative electrode, and separator> The separator used in the secondary battery of the present invention is the separator of the present invention described above. Furthermore, the positive electrode and negative electrode are not particularly limited, and known positive and negative electrodes can be used.

[0076] <Electrolyte> Typically, an organic electrolyte is used as the electrolyte, which is obtained by dissolving a supporting electrolyte in an organic solvent. For example, in lithium-ion secondary batteries, lithium salts are used as the supporting electrolyte. 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 because they are easily soluble in the solvent and exhibit a high degree of dissociation. Note that one type of electrolyte may be used alone, or two or more types may be used in any ratio. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0077] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. However, in lithium-ion secondary batteries, for example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl 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 are preferably used. Mixtures of these solvents may also be used. Among these, carbonates are preferred because they have a high dielectric constant and a wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolyte solution can be adjusted as appropriate. Furthermore, known additives may be added to the electrolyte solution.

[0078] (Manufacturing method for non-aqueous secondary batteries) The non-aqueous secondary battery of the present invention can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator in between, winding or folding them as needed according to the battery shape, placing them in a battery container, injecting an electrolyte into the battery container, and sealing it. The separator used is the non-aqueous secondary battery separator of the present invention. In addition, to prevent pressure rise inside the secondary battery, overcharge and overdischarge, etc., an overcurrent prevention element such as a fuse or PTC element, expanded metal, lead plates, etc. may be provided as needed. The shape of the secondary battery may be any of the following: coin type, button type, sheet type, cylindrical type, rectangular type, flat type, etc. [Examples]

[0079] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" used to express quantities refer to mass unless otherwise specified. Furthermore, in polymers produced by polymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer is, unless otherwise specified, usually equal to the ratio (starting ratio) of that particular monomer to the total monomers used in the polymerization of the polymer. In the examples and comparative examples, the weight-average molecular weight of the water-soluble polymer, the volume-average particle diameter of the non-conductive particles, the BET specific surface area of ​​the non-conductive particles, the packing density of the functional layer composition, the viscosity of the functional layer composition, parameter P, the dispersion stability of the functional layer composition, the coatability of the functional layer composition, the heat shrinkage resistance of the functional layer, the moisture content of the functional layer, and the high-temperature cycle characteristics of the secondary battery were measured and evaluated by the following methods.

[0080] <Weight-average molecular weight of water-soluble polymers> Aqueous solutions containing the water-soluble polymers prepared in the examples and comparative examples were diluted to a concentration of 0.05%. The solutions were then filtered through a 0.45 μm PTFE membrane filter to obtain the samples. These samples were analyzed by gel permeation chromatography under the following conditions to determine the weight-average molecular weight of the water-soluble polymers. Equipment: Gel permeation chromatograph (GPC) (Agilent, product name "1260 Infinity II HPLC") Detector: Differential refractive index detector (RI) (Agilent Corporation, product name "1260 Infinity II RI Detector") Column: TSKgel GMPWXL, 2 pieces (φ7.8mm x 30cm, manufactured by Tosoh) Solvent: 0.1 M Tris buffer (pH 9, with 0.1 M potassium chloride added) Flow rate: 0.7mL / min Column temperature: 40℃ Injection volume: 0.2mL Standard sample: Monodisperse polyethylene oxide (PEO) manufactured by Tosoh and Sigma-Aldrich.

[0081] <Volume-average particle diameter of non-conductive particles> In accordance with JIS Z8825, the particle diameter at which the cumulative volume calculated from the smallest diameter side reaches 50% (D50) in the particle size distribution (volume basis) of non-conductive particles measured by laser diffraction was defined as the volume-average particle diameter of non-conductive particles.

[0082] <BET specific surface area of ​​non-conductive particles> The BET specific surface area of ​​non-conductive particles was determined using a wet specific surface area measuring device (Shimadzu Corporation, "Flowsorb III 2305").

[0083] <Filling density of functional layer composition> 45 mL of the functional layer composition prepared in the examples and comparative examples was packed into a 50 mL polypropylene test tube. The functional layer composition packed in the test tube was subjected to centrifugal sedimentation by centrifugation at 4000 rpm for 3 hours to obtain a deposited layer. The mass balance was calculated from the height of this deposited layer, and the packing rate of the functional layer composition was determined according to the following formula. The packing rate (%) of the functional layer composition = {(Solid content (volume %) in the functional layer composition × Volume of the functional layer composition in the test tube) / Volume of the deposited layer} × 100% The solid content (volume %) in the functional layer composition was calculated from the solid content (mass %) using the specific gravity of each solid content contained in the functional layer composition. The specific gravity of each solid content component is shown below (unit: kg / m 3 ). Boehmite (AlOOH): 3.0 Aluminum oxide (Al2O3): 4.0 Barium sulfate (BaSO4): 4.5 Ammonium polyacrylate: 1.2 Water-soluble polymer: 1.1 Polyoxyalkylene glycol-based surfactant (EO·PO): 1.1

[0084] <Viscosity of the functional layer composition> Measured with a single cylindrical rotational viscometer (25°C, rotation speed = 60 rpm, spindle shape: 2) in accordance with JIS Z8803:1991, and the value 60 seconds after the start of measurement was taken as the viscosity of the functional layer composition.

[0085] <Parameter P> Using the BET specific surface area of the non-conductive particles obtained as described above and the filling rate of the functional layer composition, parameter P was determined according to the following formula. Parameter P = Filling rate of the functional layer composition / Log (BET specific surface area of non-conductive particles)

[0086] <Dispersion stability of the functional layer composition> 1 kg of the functional layer composition prepared in the examples and comparative examples was placed in a 1 L plastic bottle and allowed to stand for 10 days. The standing plastic bottle was stirred together with the bottle for 30 minutes using a mix rotor. After stirring, the functional layer composition in the plastic bottle was sampled from within 1 cm from the top, and then the sampling sample was placed in an aluminum dish and weighed (mass: W0 [g]). Then, the aluminum dish containing the sampling sample was placed on a hot plate heated to 130°C and dried for 30 minutes, and then weighed (mass: W1 [g]). And the solid content of the sampled supernatant was measured according to the following formula (I). In the following formula (I), a represents the mass [g] of the aluminum dish. Solid content of the supernatant (%) = {(W1 - a) / (W0 - a)} × 100% ··· (I) Furthermore, after stirring, the poly bottle containing the functional layer composition was weighed (mass: W2 [g]), then the functional layer composition was removed from the poly bottle, and the poly bottle was weighed (mass: W3 [g]). The amount of solidified material at the bottom was then measured according to the following formula (II). In the following formula (II), b represents the mass [g] of an empty 1L poly bottle. Amount of adhering material (%) = {(W3-b) / (W2-b)} × 100% ... (II) Then, based on the solid content (%) of the supernatant obtained from formula (I) and the amount of adsorbed material (%) obtained from formula (II), the following criteria were used for evaluation. A higher percentage of solid content and a lower amount of adsorbed material in the supernatant after stirring indicates higher dispersion stability of the functional layer composition. A: The solid content of the supernatant after stirring is 39.5% or more, and the amount of adhering material is 0% or more but less than 0.5%. B: The solid content of the supernatant after stirring is 39.5% or more, but the amount of adhering material is 0.5% or more.

[0087] <Coating properties of functional layer compositions> The functional layers of the secondary battery separators (separators with a functional layer on one side) prepared in the examples and comparative examples were visually inspected and evaluated according to the following criteria. The wider the area where aggregates, streaks, and / or repulsion are not observed, the better the coating properties of the functional layer composition. A: An area of ​​30cm x 30cm or larger that does not show aggregates, streaks, and / or repellency. B: Areas where aggregates, streaks, and / or repellency are not observed are between 10cm x 10cm and less than 30cm x 30cm.

[0088] <Heat shrinkage resistance of the functional layer> The secondary battery separators prepared in the examples and comparative examples were cut into squares measuring 12 cm wide x 12 cm long, and a square with sides of 10 cm was drawn inside these squares to create test specimens. The test specimens were then placed in a 150°C constant temperature bath for 1 hour, and the change in the area of ​​the square drawn inside (= {(Area of ​​the square before - Area of ​​the square after) / Area of ​​the square before} × 100%) was calculated as the thermal shrinkage rate and evaluated according to the following criteria. A smaller thermal shrinkage rate indicates that the functional layer has superior heat shrinkage resistance. A: Thermal shrinkage rate is less than 10% B: Heat shrinkage rate of 10% or more but less than 20% C: Heat shrinkage rate of 20% or more

[0089] <Moisture content of the functional layer> The secondary battery separators prepared in the examples and comparative examples were cut to a size of 10 cm wide x 10 cm long to serve as test specimens. These test specimens were left at a temperature of 25°C and a dew point of -60°C for 24 hours. Subsequently, the moisture content of the test specimens was measured using a coulometric titration moisture meter and the Karl Fischer method (JIS K-0068 (2001) moisture vaporization method, vaporization temperature 150°C). The obtained moisture content was defined as the moisture content of the functional layer and evaluated according to the following criteria. A lower moisture content indicates a lower amount of residual moisture in the functional layer. A: Moisture content is less than 800 ppm B: Moisture content between 800 ppm and less than 1000 ppm C: Moisture content of 1000 ppm or more

[0090] <High-temperature cycle characteristics of secondary batteries> The lithium-ion secondary batteries prepared in the examples and comparative examples were charged to 4.2V (cutoff condition: 0.02C) at 45°C using a constant voltage-constant current (CC-CV) method with a charge rate of 0.3C, and then discharged to 3.0V using a constant current (CC) method with a discharge rate of 1C. The initial capacity C0 was measured. Furthermore, the same charge-discharge operation was repeated under a 45°C environment, and the capacity C1 was measured after 300 cycles. The capacity retention rate ΔC = (C1 / C0) × 100 (%) was then calculated and evaluated according to the following criteria. A higher value for this capacity retention rate indicates less decrease in discharge capacity and better high-temperature cycle characteristics for the secondary battery. A: Capacity retention rate ΔC is 75% or more B: Capacity retention rate ΔC is 60% or more but less than 75% C: Capacity retention rate ΔC is less than 60%

[0091] (Example 1) <Preparation of aqueous solution containing water-soluble polymer> In a 2L flask with a septum, 1267g of deionized water and 34g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added and heated to 40°C, and the flask was purged with nitrogen gas at a flow rate of 100mL / min. Next, 224g (86.0%) of acrylamide as an amide group-containing monomer, 23g (9.0%) of acrylic acid as an acid group-containing monomer, and 13g (5.0%) of glycidyl methacrylate as a crosslinking monomer were mixed and injected into the flask using a syringe. Subsequently, 36g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator was added to the flask using a syringe, and the reaction temperature was set to 60°C. After 2 hours, in order to further increase the reaction conversion rate, 18g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 17g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After another 2 hours, 18 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 17 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After another 2 hours, 6.8 g of a 5% aqueous solution of sodium nitrite as a reaction terminating agent was added to the flask and stirred. The flask was then cooled to 40°C to create an air atmosphere, and an aqueous solution containing water-soluble polymer A was prepared by adjusting the pH of the system to 8.0 using an 8% aqueous lithium hydroxide solution. The weight-average molecular weight of the obtained water-soluble polymer A was then measured. The results are shown in Table 1.

[0092] <Preparation of compositions for the functional layer of secondary batteries> As non-conductive particles, boehmite A particles (manufactured by Nabaltec, product name "ACTILOX 200SM", volume average particle size: 0.3 μm, BET specific surface area: 17 m²) are used. 2 The sample was divided into grams and ammonium polyacrylate (manufactured by Toagosei Co., Ltd., product name "Aron A30SL") was used as a dispersant. 100 parts non-conductive particles, 1.0 part dispersant, and deionized water were mixed and treated for 1 hour in a bead mill (manufactured by Ashizawa Finetech Co., Ltd., product name "LMZ015") to obtain a dispersion. Furthermore, 2.5 parts of the aqueous solution containing the water-soluble polymer obtained as described above was mixed with 0.2 parts of a polyoxyalkylene glycol-based surfactant (manufactured by Sunopco, product name "Noptex ED-052") to prepare a functional layer composition with a solid content of 40%. The packing density of the functional layer composition obtained in this manner was determined. Then, the parameter P (= packing density of the functional layer composition / Log(BET specific surface area)), the viscosity of the functional layer composition, the dispersion stability of the functional layer composition, and the coating properties of the functional layer composition were evaluated from the obtained packing density of the functional layer composition and the BET specific surface area of ​​the non-conductive particles. The results are shown in Table 1.

[0093] <Fabrication of separators for secondary batteries> A polyethylene separator substrate (manufactured by Asahi Kasei Corporation, product name "ND412", thickness: 12 μm) was prepared as the separator substrate. The functional layer composition prepared above was applied to one side of this separator substrate at a speed of 10 m / min using a gravure coater, and then dried in a drying oven at 50°C to obtain a separator with a functional layer on one side of the separator substrate (functional layer thickness: 2 μm). The functional layer-equipped separator obtained in this manner was used as a separator for secondary batteries, and the heat shrinkage resistance and moisture content of the functional layer were evaluated. The results are shown in Table 1.

[0094] <Fabrication of the negative electrode> In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as a carboxylic acid group-containing monomer, 63.5 parts of styrene as an aromatic vinyl monomer, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of deionized water, and 0.5 parts of potassium persulfate as a polymerization initiator were added and thoroughly stirred. Polymerization was then started by heating to 50°C. When the polymerization conversion rate reached 96%, the mixture was cooled to stop the polymerization reaction, and a mixture containing particulate binder (styrene-butadiene copolymer) was obtained. A 5% aqueous sodium hydroxide solution was added to the above 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 a binder for the negative electrode. 48.75 parts of artificial graphite (theoretical capacity: 360 mAh / g) and 48.75 parts of natural graphite (theoretical capacity: 360 mAh / g) as negative electrode active materials, and 1 part of carboxymethylcellulose (equivalent to solid content) as a thickener were added to a planetary mixer. Furthermore, the mixture was diluted with deionized water to a solid content concentration of 60%, and then kneaded at a rotation speed of 45 rpm for 60 minutes. Subsequently, 1.5 parts (equivalent to solid content) of the aqueous dispersion containing the negative electrode binder obtained as described above was added, and kneaded at a rotation speed of 40 rpm for 40 minutes. Finally, deionized water was added to achieve a viscosity of 3000 ± 500 mPa·s (measured with a B-type viscometer at 25°C and 60 rpm) to prepare a slurry composition for the negative electrode composite layer. The above slurry composition for the negative electrode composite layer is applied to the surface of a 15 μm thick copper foil current collector using a comma coater, at a rate of 11 ± 0.5 mg / cm². 2 The mixture was applied in this manner. Subsequently, the copper foil coated with the slurry composition for the negative electrode composite layer was transported at a speed of 400 mm / min in an oven at 80°C for 2 minutes, and then in an oven at 110°C for another 2 minutes, thereby drying the slurry composition on the copper foil and obtaining a negative electrode base with the negative electrode composite layer formed on the current collector. Subsequently, the negative electrode composite layer side of the fabricated negative electrode base material was roll-pressed at a temperature of 25±3℃ and a linear pressure of 11t (tons), resulting in a negative electrode composite layer density of 1.60 g / cm³. 3 The negative electrode was obtained.

[0095] <Fabrication of the positive electrode> In the planetary mixer, the Co-Ni-Mn lithium composite oxide active material NMC532 (LiNi 0.5 Mn 0.3 Co 0.2 A slurry composition for the cathode composite layer was prepared by adding 96 parts of O2, 2 parts of acetylene black as a conductive material (manufactured by Denka Co., Ltd., product name "HS-100"), and 2 parts of polyvinylidene fluoride as a binder (manufactured by Kureha Chemical Co., Ltd., product name "KF-1100"), and then adding N-methyl-2-pyrrolidone (NMP) as a dispersion medium to a total solid content concentration of 67% and mixing. Next, the obtained slurry composition for the positive electrode composite layer is applied to a 20 μm thick aluminum foil current collector using a comma coater at a rate of 20 ± 0.5 mg / cm². 2 It was applied in this manner. Furthermore, the slurry composition on the aluminum foil was dried by transporting it at a speed of 200 mm / min through an oven at 90°C for 2 minutes, and then through an oven at 120°C for another 2 minutes, thereby obtaining a positive electrode base with a positive electrode composite layer formed on the current collector. Subsequently, the cathode composite layer side of the fabricated cathode base material was roll-pressed at a temperature of 25±3℃ and a linear pressure of 14t (tons), resulting in a cathode composite layer density of 3.20 g / cm³. 3 The positive electrode was obtained.

[0096] <Manufacturing of lithium-ion secondary batteries> The pressed positive and negative electrodes, as well as the secondary battery separator, obtained as described above, were cut out. The cut secondary battery separator was then placed on the positive electrode composite layer of the pressed positive electrode with the functional layer side facing outwards. Furthermore, the negative electrode composite layer of the pressed negative electrode was placed on the uncoated side of the placed secondary battery separator that was not in contact with the positive electrode, with the negative electrode composite layer side facing outwards, thereby obtaining a battery component laminate (positive electrode / functional layer / separator substrate / negative electrode). Next, the resulting laminate was wrapped in an aluminum packaging material to serve as the battery's outer casing, and the electrolyte (solvent: ethylene carbonate (EC) / diethyl carbonate (DEC) = 30 / 70 (weight ratio), electrolyte: 1 mol / L LiPF6, additive: vinylene carbonate 2 vol% (solvent ratio)) was injected, ensuring no air remained. Then, the opening of the aluminum packaging material was heat-sealed at 150°C, sealing the aluminum packaging material tightly to produce a 40 mAh laminated lithium-ion secondary battery. The high-temperature cycling characteristics of this lithium-ion secondary battery were evaluated. The results are shown in Table 1.

[0097] (Examples 2, 3) In preparing the aqueous solution containing the water-soluble polymer of Example 1, the amounts of acrylamide, acrylic acid, and glycidyl methacrylate used were changed so that the content ratios of various monomer units in the resulting water-soluble polymer were as shown in Table 1. Otherwise, aqueous solutions containing water-soluble polymer B (Example 2) and aqueous solutions containing water-soluble polymer C (Example 3) were prepared in the same manner as in Example 1. Then, the functional layer composition, secondary battery separator, negative electrode, positive electrode, and lithium-ion secondary battery were prepared and manufactured in the same manner as in Example 1, except that the aqueous solution containing water-soluble polymer B (Example 2) and aqueous solution containing aqueous polymer C (Example 3) were used instead of the aqueous solution containing water-soluble polymer A. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0098] (Example 4) In preparing the aqueous solution containing the water-soluble polymer of Example 1, 13 g (5.0%) of N-methylolacrylamide was used as the crosslinkable monomer instead of glycidyl methacrylate to prepare an aqueous solution containing water-soluble polymer D. Then, the functional layer composition, secondary battery separator, negative electrode, positive electrode, and secondary battery were prepared and manufactured in the same manner as in Example 1, except that the aqueous solution containing water-soluble polymer D was used instead of the aqueous solution containing water-soluble polymer A. Various measurements and evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0099] (Examples 5-7) In the preparation of the functional layer composition in Example 1, alumina A particles were used instead of boehmite A particles as the non-conductive particles in Example 5 (Example 5: Sumitomo Chemical Co., Ltd., product name "AKP-20", volume average particle diameter: 0.42 μm, BET specific surface area: 4.6 m²). 2 ( / g), in Example 6, alumina B particles (Sumitomo Chemical Co., Ltd., product name "AKP-53", volume average particle size: 0.17 μm, BET specific surface area: 13.7 m²) 2 In Example 7, barium sulfate particles (manufactured by Takehara Chemical Co., Ltd., product name "TS-2", volume average particle size: 0.36 μm, BET specific surface area: 7.5 m²) were used. 2 / g) was used. Otherwise, the functional layer composition, secondary battery separator, negative electrode, positive electrode, and secondary battery were prepared and manufactured in the same manner as in Example 1. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0100] (Comparative Example 1) In preparing the aqueous solution containing the water-soluble polymer of Example 1, the amounts of acrylamide and acrylic acid used were changed, and glycidyl methacrylate was not used, so that the content ratios of various monomer units in the resulting water-soluble polymer were as shown in Table 1, thereby preparing an aqueous solution containing water-soluble polymer E. Then, a functional layer composition, a separator for a secondary battery, a negative electrode, a positive electrode, and a secondary battery were prepared and manufactured in the same manner as in Example 1, except that an aqueous solution containing aqueous polymer E was used instead of an aqueous solution containing water-soluble polymer A. Various measurements and evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0101] (Comparative Examples 2-3) In the preparation of the functional layer composition in Example 1, boehmite A particles were replaced as non-conductive particles in Comparative Example 2 with boehmite B particles (Nabaltec, product name "APYRAL AOH 60", volume average particle diameter: 0.9 μm, BET specific surface area: 6 m²). 2 In Comparative Example 3, boehmite C particles (manufactured by Nabaltec, product name "APYRAL AOH EXK 012-20", volume average particle size: 0.12 μm, BET specific surface area: 45 m²) were used. 2 / g) was used. Otherwise, the functional layer composition, secondary battery separator, negative electrode, positive electrode, and secondary battery were prepared and manufactured in the same manner as in Example 1. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0102] [Table 1]

[0103] Note that in Table 1, "AAm" represents the acrylamide unit. "AA" indicates the unit of acrylic acid. "GMA" indicates the glycidyl methacrylate unit. "NMA" indicates the N-methylolacrylamide unit. "PAA" stands for ammonium polyacrylate. "EO·PO" indicates a polyoxyalkylene glycol-based surfactant.

[0104] Table 1 shows that using the functional layer compositions of Examples 1 to 7 yields a functional layer with excellent heat shrinkage resistance and low residual moisture content. Furthermore, it can be seen that a secondary battery equipped with a separator formed using the functional layer compositions of Examples 1 to 7 exhibits excellent high-temperature cycle characteristics. On the other hand, Table 1 shows that using the functional layer compositions of Comparative Examples 1 to 3 does not result in a functional layer with excellent heat shrinkage resistance and low residual moisture content. Furthermore, it can be seen that secondary batteries equipped with separators formed using the functional layer compositions of Comparative Examples 1 to 3 exhibit reduced high-temperature cycle characteristics. [Industrial applicability]

[0105] According to the present invention, it is possible to provide a composition for a secondary battery functional layer that has excellent heat shrinkage resistance and low moisture content, and that forms a functional layer for non-aqueous secondary batteries. Furthermore, according to the present invention, it is possible to provide a functional layer for secondary batteries and a separator for secondary batteries that can enable secondary batteries to exhibit excellent high-temperature cycle characteristics. Furthermore, according to the present invention, it is possible to provide a secondary battery with excellent high-temperature cycle characteristics.

Claims

1. A composition for a non-aqueous secondary battery functional layer, comprising non-conductive particles, a water-soluble polymer, and water, The BET specific surface area of ​​the non-conductive particles is 25 m². ２ / g or less, The non-aqueous secondary battery functional layer composition is a non-aqueous secondary battery functional layer composition in which the parameter P represented by the following formula (1) is 36 or more. Parameter P = Filling density of the composition for the functional layer of non-aqueous secondary batteries / Log (BET specific surface area of ​​non-conductive particles) ... (1) In formula (1), the packing rate of the non-aqueous secondary battery functional layer composition is calculated from the height of the sediment obtained by treating the non-aqueous secondary battery functional layer composition packed in a test tube at 4000 rpm for 3 hours and performing centrifugal sedimentation, and is determined based on the following formula (2). The packing rate (%) of the composition for the functional layer of a non-aqueous secondary battery = {(Solid content (volume %) in the composition for the functional layer of a non-aqueous secondary battery × Volume of the composition for the functional layer of a non-aqueous secondary battery in the test tube) / Volume of the deposited layer} × 100% ... (2)

2. The composition for a non-aqueous secondary battery functional layer according to claim 1, wherein the water-soluble polymer contains crosslinkable monomer units, and the content ratio of the crosslinkable monomer units in the water-soluble polymer is 0.1% by mass or more and 10% by mass or less.

3. The non-aqueous secondary battery functional layer composition according to claim 1, wherein the viscosity of the non-aqueous secondary battery functional layer composition is 10 mPa·s or more and 300 mPa·s or less.

4. The composition for a non-aqueous secondary battery functional layer according to claim 1, wherein the weight-average molecular weight of the water-soluble polymer is 50,000 or more and 1,000,000 or less.

5. The composition for a non-aqueous secondary battery functional layer according to claim 1, wherein the volume-average particle diameter of the non-conductive particles is 0.05 μm or more and 0.45 μm or less.

6. The composition for a non-aqueous secondary battery functional layer according to claim 1, wherein the water-soluble polymer contains amide group-containing monomer units, and the content ratio of the amide group-containing monomer units in the water-soluble polymer is 70% by mass or more and 98% by mass or less.

7. The composition for a non-aqueous secondary battery functional layer according to claim 1, wherein the water-soluble polymer contains acid group-containing monomer units, and the content ratio of the acid group-containing monomer units in the water-soluble polymer is 1% by mass or more and 20% by mass or less.

8. The composition for a non-aqueous secondary battery functional layer according to claim 1, further comprising a surfactant, wherein the amount of the surfactant is 0.1 parts by mass or more and 1.0 part by mass or less per 100 parts by mass of the non-conductive particles.

9. A functional layer for a non-aqueous secondary battery, formed using the composition for a non-aqueous secondary battery functional layer described in claim 1.

10. A separator for a non-aqueous secondary battery, comprising the functional layer for a non-aqueous secondary battery described in claim 9.

11. A non-aqueous secondary battery comprising the separator for non-aqueous secondary batteries described in claim 10.

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