Cured material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

Abstract

To provide a cured product for lithium ion secondary battery improved in charge / discharge cycle characteristics, a negative electrode for lithium ion secondary battery, and a lithium ion secondary battery.SOLUTION: The present invention relates to a cured product configured by curing a curable composition. In the cured product for lithium ion secondary battery, the curable composition contains water soluble polymers including a hydroxy group, a cross-linking agent including a functional group which reacts with the hydroxy group, and water. The cured product has a urethane bond. Water solubility in a case where the cured product is immersed in water is less than 10% and liquid absorptivity in a case where the cured product is immersed in an electrolyte is equal to or more than -10% and less than 5%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a cured material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery. [Background technology]

[0002] In recent years, secondary batteries have been used as power sources for electronic devices such as laptops and mobile phones. Furthermore, hybrid and electric vehicles that use secondary batteries as their power source are being developed to reduce environmental impact. These vehicles require secondary batteries with high energy density, high voltage, and high durability. Lithium-ion secondary batteries have attracted attention as a secondary battery that can achieve high voltage and high energy density.

[0003] However, it is thought that the capacity of the currently used lithium-ion secondary battery, which is mainly composed of lithium cobalt oxide and carbon, is almost at its limit. For this reason, new active materials for the positive and negative electrodes are being developed as an alternative approach to increasing capacity. In particular, for the negative electrode active material, metal materials such as silicon and tin that can be alloyed with lithium are being considered as an alternative to carbon such as graphite. This is because the theoretical charge / discharge capacity of graphite is 372 mAh / g, while that of silicon (Li 4.4 The theoretical capacity of tin (Li) is 4199mAh / g. 4.4 This is because the theoretical capacity of graphite (Sn) is 993 mAh / g, which is approximately 3 to 10 times that of graphite. However, when a metallic material is alloyed with lithium, the volume of the negative electrode may expand several times compared to the volume before alloying due to the alloying reaction. This causes the negative electrode active material layer to expand and contract violently during charge and discharge, resulting in significant stress being applied to the negative electrode. This can lead to problems such as cracks in the negative electrode active material layer formed on the current collector and peeling between the negative electrode active material layer and the current collector, resulting in deterioration of charge and discharge cycle characteristics. Therefore, to address these problems, cured materials for lithium-ion secondary batteries with improved binding properties have been proposed.

[0004] For example, Patent Document 1 proposes a binder composition for lithium secondary batteries containing a crosslinked compound of polyvinyl acrylic acid substituted with an alkali cation and polyvinyl alcohol, and discloses that the crosslinking rate of the binder composition is about 0.1% to about 70%. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-64574 Summary of the Invention [Problem to be solved by the invention]

[0006] However, there was a problem that sufficient charge-discharge cycle characteristics could not be obtained with the lithium ion secondary battery using the binder composition of Patent Document 1. As a result of our extensive investigation, we found that the binder composition is easily soluble in an aqueous solution and therefore does not have sufficient elasticity and binding properties as a binder for lithium ion secondary batteries.

[0007] In view of the above-described problems, one aspect of the present disclosure has an object to provide a cured material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery. [Means for solving the problem]

[0008] In order to solve the above problems, according to one aspect of the present disclosure, there is provided a cured product for a secondary battery, which is obtained by curing a curable composition, the cured product having urethane bonds, a water solubility of less than 10% when the cured product is immersed in water, and a liquid absorption rate of −10% or more and less than 5% when the cured product is immersed in an electrolyte solution.

[0009] From this viewpoint, when a cured material for a secondary battery has urethane bonds, and when the cured material is immersed in water, the water solubility is less than 10%, and when the cured material is immersed in an electrolyte, the water absorption is between -10% and 5%, and the cured material has excellent elasticity, which reduces the volume change of the electrode and suppresses the occurrence of cracks during charge and discharge. Furthermore, by combining sufficient curability and electrolyte resistance, a cured material for a secondary battery with excellent mechanical strength can be realized.

[0010] Also provided is a curable composition for a lithium ion secondary battery, which comprises a water-soluble polymer (A) having a hydroxyl group, a crosslinking agent (B) having a functional group reactive with the hydroxyl group, and water, and the crosslinking agent (B) is contained in an amount of 35 parts by weight or more and less than 400 parts by weight per 100 parts by weight of the water-soluble polymer (A).

[0011] Also provided is a cured material for a lithium ion secondary battery, wherein the water-soluble polymer (A) includes one of polyvinyl alcohol, carboxymethyl cellulose, and methyl cellulose, and the crosslinking agent (B) is an active methylene-blocked diisocyanate.

[0012] Also provided is a cured material for a lithium ion secondary battery, wherein the water-soluble polymer (A) includes one of polyvinyl alcohol, carboxymethyl cellulose, and methyl cellulose, and the crosslinking agent (B) is a polyisocyanate having three or more functional groups.

[0013] Also provided is a cured material for a lithium ion secondary battery, in which the weight average molecular weight of the polyvinyl alcohol is 500 to 200,000.

[0014] From this viewpoint, the number of hydroxyl groups is sufficient to allow the molecular weight to react with active methylene-blocked diisocyanate and polyisocyanate with three or more functional groups, and the reaction can be easily carried out.

[0015] Also provided is a negative electrode for a lithium ion secondary battery, comprising a negative electrode active material, a negative electrode active material layer containing at least the cured material for a lithium ion secondary battery of the present disclosure, and a negative electrode current collector.

[0016] From this viewpoint, it is possible to realize a negative electrode with excellent charge-discharge cycle characteristics.

[0017] Also provided is a lithium ion secondary battery comprising the above-mentioned negative electrode for lithium ion secondary batteries, a positive electrode, an electrolyte, and a separator.

[0018] From this viewpoint, it is possible to realize a lithium ion secondary battery with excellent charge / discharge cycle characteristics. [Effects of the Invention]

[0019] As described above, according to the present disclosure, it is possible to provide a cured material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery that are excellent in charge-discharge cycle characteristics. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a cross-sectional view showing a secondary battery according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0021] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are denoted by the same reference numerals, and redundant explanations will be omitted.

[0022] [Configuration of lithium-ion secondary battery] First, the configuration of a lithium ion secondary battery 100 according to this embodiment will be described with reference to FIG.

[0023] The lithium ion secondary battery 100 includes a positive electrode 20, a negative electrode 30, and a separator 10. The shape of the lithium ion secondary battery 100 is not particularly limited. That is, the lithium ion secondary battery 100 may be cylindrical, rectangular, laminated, button-shaped, or the like.

[0024] The negative electrode 30 has a negative electrode current collector 32 and a negative electrode active material layer 34 provided on one surface thereof.

[0025] The negative electrode current collector 32 may be any conductive plate material, such as a thin metal plate of copper or nickel foil.

[0026] Examples of the negative electrode active material used in the negative electrode active material layer 34 include silicon (Si) and silicon compounds. Two or more of these may be used in combination.

[0027] Examples of silicon compounds include SiO x The compound represented by the formula (I) contains silicon and oxygen as constituent elements. The value of x is preferably in the range of 0.5≦x≦1.5. (Hereinafter, "SiO x ").

[0028] The above SiO x may contain a microcrystalline or amorphous phase of Si, and in this case, the atomic ratio of Si to O is the ratio including the Si in the microcrystalline or amorphous phase of Si. x These include those with a structure in which Si (e.g., microcrystalline Si) is dispersed in an amorphous SiO2 matrix, and the amorphous SiO2 and the Si dispersed therein, combined, should have an atomic ratio x that satisfies 0.5≦x≦1.5. For example, in the case of a compound with a structure in which Si is dispersed in an amorphous SiO2 matrix and the molar ratio of SiO2 to Si is 1:1, x=1, so the structural formula is represented as SiO.

[0029] In addition, SiO x When using SiO 2 , it is preferable that the surface of the SiO 2 , SiO 3 , SiO 4 , SiO 5 , SiO 6 , SiO 7 , SiO 8 , SiO 9 , SiO 10 , SiO 11 , SiO 12 , SiO 13 , SiO 14 , SiO 15 , SiO 16 , SiO 17 , SiO 18 , x Since SiO2 has poor conductivity, when used as a negative electrode active material, a negative electrode conductive additive is used to ensure good battery characteristics, and SiO2 in the negative electrode active material layer is x It is necessary to improve the mixing and dispersion of the SiO 2 and the negative electrode conductive additive to form an excellent conductive network. x If the surface of the material is coated with carbon, for example, it becomes possible to simplyx In this case, a conductive network is formed in the negative electrode more satisfactorily than when a mixture of the negative electrode conductive additive and the conductive additive is used.

[0030] The negative electrode active material layer 34 may also contain a negative electrode conductive additive. Examples of the negative electrode conductive additive include carbon powders such as carbon black, carbon nanotubes, carbon materials, metal fine powders such as copper, nickel, stainless steel, and iron, mixtures of carbon materials and metal fine powders, and conductive oxides such as indium tin oxide (ITO). If sufficient conductivity can be ensured using the negative electrode active material alone, the negative electrode active material layer 34 does not need to contain a negative electrode conductive additive.

[0031] The negative electrode active material layer 34 includes a negative electrode cured material. The negative electrode cured material binds the negative electrode active materials together and also binds the negative electrode active materials to the negative electrode current collector 32. The negative electrode cured material is a cured material in which urethane bonds are formed by curing a curable composition.

[0032] Furthermore, the cured product in which urethane bonds are formed has a water solubility of less than 10% when immersed in water, and a liquid absorption rate of -10% or more and less than 5% when immersed in an electrolyte solution.

[0033] The water solubility when immersed in water is determined by measuring the weight of the cured product before immersion in water and the weight of the cured product after immersion in water, and then using the following formula.

[0034] Water solubility (%) = 100 - [weight of cured product after immersion in water / weight of cured product before immersion in water] x 100

[0035] The weight of the cured product before immersion in water was measured, and then the product was immersed in water at 25°C for one week. The cured product was then removed from the water and vacuum dried at 85°C for three hours, and the weight of the cured product after immersion was measured.

[0036] In the cured product in which urethane bonds have been formed, if the water solubility is less than 10%, the crosslinking reaction will have progressed sufficiently, resulting in sufficient urethane bond formation and making it possible to suppress the occurrence of cracks due to repeated charge and discharge. On the other hand, if the temperature is within the typical range of 20 to 95°C where the base reacts and the P water solubility is 10% or more, the above effect will not be achieved.

[0037] The liquid absorption rate when immersed in an electrolytic solution is calculated by measuring the weight of the cured product before and after immersion in the electrolytic solution and using the following formula.

[0038] Liquid absorption rate (%) = [(weight of cured product after immersion in electrolyte - weight of cured product before immersion in electrolyte) / weight of cured product before immersion in electrolyte] x 100

[0039] The electrolyte used to determine the liquid absorption rate is, for example, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7, in which LiPF6 is dissolved as an electrolyte to a concentration of 1 mol / L.

[0040] When determining the liquid absorption rate, the material is immersed in the electrolyte at 25°C for one week. After one week of immersion at 25°C, the cured material reaches a saturated state of liquid absorption. The saturated state of liquid absorption refers to the state in which the weight of the cured material does not increase even if it is further immersed in the electrolyte.

[0041] In a cured product in which urethane bonds have been formed, if the liquid absorption rate is between -10% and 5%, the cured product will not dissolve or swell in the electrolyte, and will therefore function as a cured product. However, if the liquid absorption rate is less than -10%, the cured product will dissolve in the electrolyte, and the above-mentioned effect will not be achieved. On the other hand, if the liquid absorption rate is 5% or more, the cured product will have absorbed the electrolyte, and will therefore lack resistance to the electrolyte, swell, and will not achieve the above-mentioned effect.

[0042] The curable composition according to this embodiment contains a water-soluble polymer (A) having a hydroxyl group, a crosslinking agent (B) having a functional group reactive with the hydroxyl group, and water. The curable composition contains 35 to 400 parts by weight of the crosslinking agent (B) per 100 parts by weight of the water-soluble polymer (A). Each component will be described below with examples.

[0043] <Water-soluble polymer (A)> Examples of the water-soluble polymer (A) having a hydroxyl group (hereinafter sometimes abbreviated as "water-soluble polymer (A)") include polyvinyl alcohol, carboxymethyl cellulose, methyl cellulose, etc. Among these, polyvinyl alcohol is preferred. These water-soluble polymers (A) may be used singly or in combination of two or more. In this specification, a polymer being "water-soluble" means that when a mixture obtained by adding 1 part by weight of polymer (equivalent to solids) to 100 parts by weight of ion-exchanged water and stirring is adjusted to at least one of the following conditions: a temperature of 20 to 95°C and a pH of 3 to 12 (pH adjustment is performed using an aqueous NaOH solution and / or an aqueous HCl solution), and the mixture is passed through a 250-mesh screen, the weight of the solids of the residue that does not pass through the screen and remains on the screen does not exceed 50% by weight of the solids of the polymer added. Even if the mixture of the polymer and water is in an emulsion state that separates into two phases when left to stand, the polymer is considered to be water-soluble if it satisfies the above definition.

[0044] When polyvinyl alcohol is used as the water-soluble polymer (A), there are no particular limitations, but for example, polyvinyl alcohol obtained by saponifying polyvinyl acetate is preferred. Examples of polyvinyl alcohol include vinyl alcohol-vinyl acetate copolymer, vinyl alcohol-vinyl butyral copolymer, and ethylene-vinyl alcohol copolymer, with vinyl alcohol-vinyl acetate copolymer being preferred. The weight-average molecular weight of polyvinyl alcohol is preferably 500 to 200,000. If the weight-average molecular weight is less than 500, the number of hydroxyl groups is small, resulting in a small number of urethane bonds formed by reaction with the crosslinking agent (B) described below. Therefore, when used as a cured product for a lithium-ion secondary battery, excellent charge-discharge cycle characteristics cannot be obtained. On the other hand, if the weight-average molecular weight exceeds 200,000, the viscosity increases, resulting in gelation. Therefore, when the crosslinking agent (B) described below is added, it becomes difficult to achieve a uniform reaction. Furthermore, the viscosity is too high for a cured product for a lithium-ion secondary battery, making it difficult to handle the cured product.

[0045] The copolymerization ratio of polyvinyl alcohol is expressed by the saponification degree. The saponification degree of polyvinyl alcohol according to this embodiment is preferably 60 mol% or more and 99 mol% or less. When the saponification degree of polyvinyl alcohol is 60 mol% or more, a crosslinked structure can be more suitably formed with the crosslinking agent (B) described below. The saponification degree of polyvinyl alcohol can be determined by the amount of alkali consumption required for hydrolysis of copolymerization units such as vinyl acetate or composition analysis by NMR.

[0046] <Crosslinking agent (B)> The crosslinking agent (B) (hereinafter sometimes abbreviated as "crosslinking agent (B)") having a functional group that reacts with the water-soluble polymer (A) having a hydroxyl group may be an active methylene-blocked diisocyanate or a polyisocyanate having three or more functional groups, in which the isocyanate group is protected with a blocking agent. Representative compounds of blocking agents and isocyanates are listed separately here.

[0047] Examples of blocking agents include phenols, alcohols, oximes, and lactams.

[0048] Examples of diisocyanate compounds include aromatic diisocyanates having 6 to 20 carbon atoms (excluding carbon atoms in NCO groups, the same applies below), aliphatic diisocyanates having 2 to 18 carbon atoms, alicyclic diisocyanates having 4 to 15 carbon atoms, aromatic aliphatic diisocyanates having 8 to 15 carbon atoms, modified products of these diisocyanates (carbodiimide modified products, urethane modified products, urethodione modified products, etc.), and mixtures of two or more of these.

[0049] Specific examples of the aromatic diisocyanate include 1,3- and / or 1,4-phenylene diisocyanate, 2,4- and / or 2,6-tolylene diisocyanate, m-xylylene diisocyanate, 2,4'- and / or 4,4'-diphenylmethane diisocyanate (hereinafter, diphenylmethane diisocyanate will be abbreviated as MDI), 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane, and 1,5-naphthylene diisocyanate.

[0050] Specific examples of the aliphatic diisocyanate include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethyl caproate, bis(2-isocyanatoethyl)carbonate, and 2-isocyanatoethyl-2,6-diisocyanatohexanoate.

[0051] Specific examples of the alicyclic diisocyanate include isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, cyclohexylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, methylcyclohexylene diisocyanate, bis(2-isocyanatoethyl)-4-cyclohexylene-1,2-dicarboxylate, and 2,5- and / or 2,6-norbornane diisocyanate.

[0052] Specific examples of the araliphatic diisocyanate include m- and / or p-xylylene diisocyanate, α,α,α',α'-tetramethylene xylylene diisocyanate, and the like.

[0053] The polyisocyanate compound having three or more functional groups is not particularly limited as long as it is a compound having 3 to 8 isocyanate groups, and examples thereof include compounds having a chemical structure of triisocyanate, tetraisocyanate, isocyanurate, or biuret.

[0054] Specific examples of triisocyanate compounds include compounds represented by the following chemical formula (1).

[0055] [ka]

[0056] Specific examples of the tetraisocyanate compound include the compound represented by the following chemical formula (2).

[0057] [ka]

[0058] [In the formula, R1 represents an alkylene group.]

[0059] Examples of compounds having an isocyanurate structure include an isocyanurate trimer and an isocyanurate pentamer, and also include isocyanurate heptamer, nonamer, and higher polymers. The isocyanurate trimer is a polyisocyanate consisting of three diisocyanate monomer molecules and having an isocyanurate group, and examples thereof include a compound represented by the following chemical formula (3).

[0060] [C3] TIFF0007794593000003.tif5989

[0061] [In the formula, R represents a residue obtained by removing one isocyanate group from a diisocyanate monomer.]

[0062] An isocyanurate pentamer is a polyisocyanate having an isocyanurate structure and consisting of six diisocyanate monomer molecules, and examples thereof include a compound represented by the following chemical formula (4).

[0063] [ka]

[0064] [In the formula, R represents a residue obtained by removing one isocyanate group from a diisocyanate monomer.]

[0065] The compound having a biuret structure is formed from urea and an isocyanate group, and examples thereof include the compound represented by the following chemical formula (5).

[0066] [ka]

[0067] [In the formula, R represents a residue obtained by removing one isocyanate group from a diisocyanate monomer.]

[0068] Among these, aromatic diisocyanates, alicyclic diisocyanates, and triisocyanates having a biuret structure as their parent structure are preferred, aromatic diisocyanates and triisocyanates having a biuret structure as their parent structure are more preferred, and MDI and HDI biuret forms are particularly preferred.

[0069] The curable composition according to this embodiment preferably contains 35 to less than 400 parts by weight of crosslinking agent (B) per 100 parts by weight of water-soluble polymer (A), more preferably 38 to less than 360 parts by weight. By controlling the crosslinking agent content within this range, a favorable crosslinked structure can be formed, and excellent elasticity and binding properties of the cured product can be ensured. When the crosslinking agent (B) content is less than 35 parts by weight, the number of crosslinking points that react with the hydroxyl groups contained in the water-soluble polymer (A) is small, resulting in reduced elasticity. Therefore, the composition cannot withstand volume changes during charge and discharge, and cracking cannot be suppressed. On the other hand, when the crosslinking agent (B) content is 400 parts by weight or more, the number of crosslinking points that react with the hydroxyl groups contained in the water-soluble polymer (A) is large, resulting in excellent elasticity. However, the number of free hydroxyl groups not involved in crosslinking is very small, resulting in poor binding properties with the negative electrode active material and current collector. Furthermore, the composition may become less dispersible in water or may thicken, potentially resulting in gelation.

[0070] The curing temperature of the cured product obtained by curing the curable composition varies depending on the type of blocking agent used to protect the isocyanate groups, so it cannot be generally specified. However, the curing is typically performed at a temperature of 90 to 180°C for 1 to 3 hours. To reduce the effects of moisture and oxygen in the air, the curing is performed under an inert atmosphere such as nitrogen, resulting in the formation of a crosslinked structure containing urethane bonds. As a result, crosslinking between water-soluble polymers (A) results in a crosslinked structure with excellent elasticity and binding properties, as well as low water solubility and low liquid absorption when immersed in an electrolyte solution. Therefore, by using the curable composition according to this embodiment in a cured product for a lithium-ion secondary battery, it is possible to effectively bind components in the electrode member (e.g., anode active material) and improve the charge / discharge cycle characteristics of the lithium-ion secondary battery. Specifically, the crosslinked structure containing urethane bonds provides excellent elasticity, thereby mitigating volumetric changes in the anode active material layer and suppressing cracking during repeated charge / discharge cycles. Furthermore, the free hydroxyl groups that are not involved in crosslinking interact with the negative electrode active material to improve the binding property, thereby ensuring high adhesion between the negative electrode active material layer and the negative electrode current collector.

[0071] The content of the negative electrode cured material in the negative electrode active material layer 34 is preferably in the range of 0.5 to 20% by weight, more preferably 5 to 20% by weight.

[0072] The negative electrode active material layer 34 is formed, for example, by dispersing a negative electrode active material, a negative electrode conductive additive, and a negative electrode cured material in water as a medium to prepare a coating liquid, applying this coating liquid onto the negative electrode current collector 32, drying, curing at 150°C for 1 to 3 hours in a nitrogen atmosphere, and rolling as necessary.

[0073] The positive electrode 20 has a positive electrode current collector 22 and a positive electrode active material layer 24 provided on one surface of the positive electrode current collector 22. The positive electrode current collector 22 may be made of any conductive material, and may be, for example, a thin metal plate such as aluminum or nickel foil.

[0074] As the positive electrode active material, a material capable of absorbing and releasing lithium ions, such as lithium oxide, lithium sulfide, or a lithium-containing compound such as an intercalation compound containing lithium, is suitable, and a mixture of two or more of these may be used. In particular, to increase the energy density, a material having the general formula Li x Lithium composite oxides represented by MO2 or intercalation compounds containing lithium are preferred. M is preferably one or more transition metals, specifically at least one of cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), aluminum (Al), vanadium (V), and titanium (Ti). x varies depending on the charge / discharge state of the battery, but is typically within the range of 0.05≦x≦1.10. Other materials that can achieve high energy density include manganese spinel (LiMn2O4) with a spinel-type crystal structure and lithium iron phosphate (LiFePO4) with an olivine-type crystal structure, which are also preferred.

[0075] Specifically, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), LiNi x Co y Mn z M aO2 (where x + y + z + a = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ a ≤ 1, and M includes one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), lithium vanadium compound (LiV2O5), olivine-type LiMPO4 (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr, or VO), lithium titanate (Li4Ti5O 12 )、LiNi x Co y Al z O2 (0.9 < x + y + z < 1.1), etc. are included. Also, it is not limited to these materials, and other positive electrode active material materials that can electrochemically insert and desorb lithium ions are not particularly limited.

[0076] As the positive electrode cured product used for the positive electrode 20, solvent-based cured products such as polyvinylidene fluoride (PVDF), polyimide, polyurethane, ethylene vinyl alcohol, polyacrylate, etc., and water-based cured products such as carboxymethyl cellulose (CMC), styrene-butadiene copolymer, etc. can be preferably used.

[0077] For the purpose of improving conductivity, a positive electrode conductive aid may be added. Examples of the positive electrode conductive aid include carbon powders such as carbon blacks, carbon nanotubes, carbon materials, metal fine powders such as copper, nickel, stainless steel, iron, etc., mixtures of carbon materials and metal fine powders, and conductive oxides such as ITO. When sufficient conductivity can be ensured only by the positive electrode active material, the positive electrode active material layer 24 may not contain a positive electrode conductive aid.

[0078] The positive electrode active material layer 24 is formed, for example, by preparing a coating liquid by dispersing a positive electrode active material, a positive electrode conductive aid, and a positive electrode cured product in a suitable organic solvent (such as N-methyl-2-pyrrolidone), coating this coating liquid on the positive electrode current collector 22, drying it, and rolling it as necessary.

[0079] The separator 10 may be formed from an electrically insulating porous structure, and examples thereof include a monolayer or laminate of a film made of polyethylene, polypropylene, or polyolefin, or a stretched film of a mixture of the above resins, or a fibrous nonwoven fabric made of at least one constituent material selected from the group consisting of cellulose, polyester, and polypropylene.

[0080] The separator 10 may also be coated with inorganic particles or a polymer component. Examples of inorganic particles include oxides such as alumina, silica, zirconium oxide, titanium oxide, and magnesium oxide, and dielectric materials such as barium titanate. Examples of polymer components include cured materials for negative electrodes, cured materials for positive electrodes, polymer electrolytes (composites of polymer materials such as polyethylene glycol and polyethylene carbonate with lithium salts), ion exchange resins (polydimethyldiallylammonium salt, polystyrene sulfonate, etc.), and others such as polyvinyl alcohol, CMC, polybutyral, and polyacrylic acid.

[0081] The electrolytic solution contains a lithium salt as an electrolyte and a solvent, such as LiPF, LiBF, LiClO, LiSOCF, LiN(SOF), LiN(SOCF), LiN(SOF)(SOCF), LiN(SOCFCF), LiC(SOCFCF), LiC(SOCF), LiI, LiCl, LiF, LiPF(SOCF), and LiPF(SOCF).

[0082] The concentration of the lithium salt is preferably about 0.8 to 5.0 mol / L.

[0083] Examples of the solvent include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, di-n-propyl carbonate, methyl-n-propyl carbonate, methyl isopropyl carbonate, ethyl-n-propyl carbonate, ethyl isopropyl carbonate, diisopropyl carbonate, 3-fluoropropyl methyl carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, 4-chloro-1,3-dioxolan-2-one, 4-fluoro-1,3-dioxolan-2-one, Carbonate esters such as 4-trifluoromethyl-1,3-dioxolan-2-one, vinylene carbonate, dimethylvinylene carbonate, vinylene carbonate, and fluoroethylene carbonate; carboxylic acid esters such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain sulfonate esters such as dimethyl sulfoxide and dimethyl sulfite; sulfolane, propane sultone cyclic sulfonic acid esters such as acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, succinonitrile, and other nitrile compounds; chain ethers such as 1,2-dimethoxyethane, dimethyl ether, methyl ethyl ether, diethyl ether, butyl methyl ether, dipropyl ether, cyclopentyl methyl ether, dibutyl ether, diisopentyl ether, triglyme, and tetraglyme; oxetane, tetrahydrofuran, tetrahydropyran, 1,3-dioxolatone, and other nitrile compounds; cyclic ethers such as 1,4-dioxane, hydrofluoroethers such as 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, phosphate esters such as triethyl phosphate and trimethyl phosphate, phosphonate esters such as dimethyl methylphosphonate, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,1,2,2,3,4,5,5,Examples of suitable solvents include fluorinated ethers such as 5-decafluoro-3-methoxy-4-(trifluoromethyl)pentane. These may be used alone or in combination. From the viewpoint of solubility of lithium salts, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, triglyme, tetraglyme, and acetonitrile are preferred.

[0084] The solvent may also contain an ionic liquid, which is a compound that is liquid at -30°C to 120°C and contains a cation species and an anion species.

[0085] As the cation species, nitrogen-based cations containing nitrogen, phosphorus-based cations containing phosphorus, and sulfur-based cations containing sulfur can be used. These cation components may be used alone or in combination. Examples of nitrogen-based cations include linear or cyclic ammonium cations such as imidazolium cations, pyrrolidinium cations, piperidinium cations, pyridinium cations, and azoniaspiro cations. Examples of phosphorus-based cations include linear or cyclic phosphonium cations. Examples of sulfur-based cations include linear or cyclic sulfonium cations.

[0086] The anion species is AlCl4 - , NO2 - , NO3 - , I - , BF4 - , PF6 - , AsF6 - , SbF6 - , NbF6 - , TaF6 - , F(HF) 2.3 - , CH3CO2 - , CF3CO2 - , CH3SO3 - , CF3SO3 - , (CF3SO2)3C - , C3F7CO2- , C4F9SO3 - , (CF3SO2)(CF3CO)N - , (CN)2N - , the imide anion ((SO2(CF2) x F)(SO2(CF2) y F)N - (wherein x and y are each independently an integer of 0 to 5.) These anion species may be used alone or in combination of two or more species.

[0087] From the viewpoint of the solubility of the lithium salt, the cation component is preferably a pyrrolidinium cation or a piperidinium cation, and the anion component is preferably an imide anion or a PF6 - , BF4 - The anion (SOF)N is preferred. - , (SO2CF3)2N - , (SO2CF3)(SO2F)N - is more preferred.

[0088] The electrolytic solution may contain various additives (e.g., a solid electrolyte interface (SEI) forming agent, a surfactant, etc.) Examples of such additives include vinylene carbonate, vinylethylene carbonate, phenylethylene carbonate, succinic anhydride, lithium bisoxalate, lithium tetrafluoroborate, dinitrile compounds, propane sultone, butane sultone, propene sultone, 3-sulfolene, fluorinated allyl ether, and fluorinated acrylate.

[0089] The exterior body 50 seals the laminate 40 and the electrolyte solution inside. The exterior body 50 is not particularly limited as long as it can prevent leakage of the electrolyte solution to the outside and intrusion of moisture and the like into the secondary battery 100 from the outside.

[0090] 1, a metal laminate film in which metal foil 52 is coated on both sides with polymer films 54 can be used as the exterior body 50. For example, aluminum foil can be used as the metal foil 52, and a film such as polypropylene can be used as the polymer film 54. For example, a polymer with a high melting point, such as polyethylene terephthalate (PET) or polyamide, is preferred as the material for the outer polymer film 54, and polyethylene (PE), polypropylene (PP), or the like is preferred as the material for the inner polymer film 54.

[0091] The leads 60, 62 are formed from a conductive additive material such as aluminum. Then, by a known method, the leads 60, 62 are welded to the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the separator 10 is sandwiched between the positive electrode active material layer 24 of the positive electrode 20 and the negative electrode 30 and the negative electrode active material layer 34. This state is then inserted into the exterior body 50 together with an electrolyte, and the entrance of the exterior body 50 is sealed, thereby producing the secondary battery 100. [Example]

[0092] The present disclosure will be specifically described below with reference to examples. For Examples 1 to 81, curable compositions were prepared, the water solubility and liquid absorption of the cured products were measured, and negative electrodes and lithium ion secondary batteries were fabricated using the compositions, and the charge / discharge cycle characteristics of the lithium ion secondary batteries were evaluated. For comparison, Comparative Examples 1 to 15 were also fabricated and evaluated in the same manner. The results are shown in Tables 1 and 2.

[0093] Example 1 [Preparation of curable composition] 100 g of carboxymethyl cellulose (water-soluble polymer (A)) was added to water, the temperature was raised from room temperature to 95°C, and the mixture was stirred until completely dissolved. The carboxymethyl cellulose aqueous solution was then cooled to room temperature, and 33.0 g of blocked diphenylmethane diisocyanate (crosslinking agent (B)) was added and stirred to obtain a curable composition (the water was adjusted to a solids concentration of 30 wt%). The curable composition was cured at 150°C for 1 hour under a nitrogen atmosphere to obtain a cured product with urethane bonds. The water solubility of the cured product of Example 1 was 9%, and the liquid absorption rate was -8.8%.

[0094] [Fabrication of negative electrode active material layer and negative electrode] SiO2 disproportionated by heat treatment at 1000°C under reduced pressure was used as the negative electrode active material. x A coating solution was prepared by dispersing 25 g of the above-mentioned acrylic resin, 1.4 g of Super-P (registered trademark) as a negative electrode conductive additive, and 4.5 g of the curable composition of the above-mentioned negative electrode cured product (solid content concentration 30%) in water as a medium. The total solid content concentration in the coating solution was 35 wt%. The coating solution was then applied to a copper foil negative electrode current collector using a doctor blade, vacuum dried at 100°C for 2 hours, cured at 150°C for 1 hour in a nitrogen atmosphere, and rolled to form a negative electrode active material layer 34. A 22 × 32 mm electrode size was punched out using a mold to prepare a negative electrode.

[0095] [Preparation of positive electrode] A coating solution was prepared by mixing and dispersing 96 wt% lithium cobalt oxide (LiCoO2) as the positive electrode active material, 2 wt% Ketjen black as a conductive additive, 2 wt% PVDF as a cured material, and N-methyl-2-pyrrolidone as a solvent. The coating solution was then applied to an aluminum foil positive electrode current collector using a doctor blade, vacuum dried at 100°C for 2 hours, and rolled to form a positive electrode active material layer 24. A 20 x 30 mm electrode size was punched out using a mold to produce a positive electrode.

[0096] [Fabrication of lithium-ion secondary batteries] The prepared negative electrode and positive electrode were laminated with a 16 μm-thick polyethylene separator measuring 24 × 35 mm to produce an electrode assembly. Furthermore, a nickel negative electrode lead was attached to the protruding end of the copper foil on which the negative electrode active material layer was not formed, while an aluminum positive electrode lead was attached to the protruding end of the aluminum foil on which the positive electrode active material layer was not formed using an ultrasonic fusion machine. The electrode assembly was then fused to an aluminum laminate film for the exterior case, and the laminate film was folded to insert the electrode assembly into the exterior case. An opening was formed by heat-sealing all but one edge of the exterior case, and an electrolyte solution prepared to a concentration of 1 mol / L of LiPF6 in a mixed solvent of EC:DEC in a ratio of 3:7 was injected through this opening. The opening of the exterior case was then heat-sealed under reduced pressure using a vacuum sealer to produce a lithium-ion secondary battery.

[0097] [Charge / discharge cycle characteristics] The lithium-ion secondary battery was repeatedly charged and discharged under the following conditions to evaluate its charge-discharge cycle characteristics. The charge-discharge cycle test consisted of charging the battery at a constant current of 0.5 C to 4.2 V (CC-CV charging) at 25°C, and measuring the charge capacity. The battery was then discharged at a constant current of 1.0 C (CC discharge) until the battery voltage reached 2.5 V, and measuring the discharge capacity. This constituted one cycle, and the charge-discharge cycle characteristics were evaluated based on the discharge capacity retention rate after 100 cycles.

[0098] 0.5C refers to the current value at which charging and discharging of a battery cell with a nominal capacity is completed in two hours when the cell is charged or discharged at a constant current. 1C refers to the current value at which charging and discharging is completed in one hour.

[0099] The discharge capacity retention rate after 100 cycles is defined by the following formula: Discharge capacity retention rate after 100 cycles (%)=(discharge capacity after 100 cycles / discharge capacity after 1 cycle)×100

[0100] Example 2 The same procedure was carried out as in Example 1, except that in compounding the curable composition, blocked diphenylmethane diisocyanate was replaced with blocked 1,3-bis(isocyanatomethyl)cyclohexane as the crosslinking agent (B). The water solubility of the cured product in Example 2 was 7%, and the liquid absorption rate was -9%.

[0101] Example 3 The curable composition was prepared in the same manner as in Example 1, except that the water-soluble polymer (A) was changed from carboxymethyl cellulose to methyl cellulose, and the crosslinking agent (B) was changed from blocked diphenylmethane diisocyanate to blocked xylylene diisocyanate. The water solubility of the cured product in Example 3 was 8%, and the liquid absorption rate was 4%.

[0102] Example 4 The same procedure as in Example 1 was carried out except that in compounding the curable composition, carboxymethyl cellulose was used as the water-soluble polymer (A). The water solubility of the cured product in Example 4 was 8% and the liquid absorption rate was -9.2%.

[0103] Example 5 The same procedure as in Example 3 was carried out to prepare the curable composition, except that methyl cellulose was replaced with polyvinyl alcohol having a weight-average molecular weight of 500 as the water-soluble polymer (A). The cured product of Example 5 had a water solubility of 7% and a liquid absorption rate of -4.7%.

[0104] Example 6 The same procedure was carried out as in Example 5, except that in the preparation of the curable composition, the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 500 to polyvinyl alcohol having a weight-average molecular weight of 2,000, and the crosslinking agent (B) was changed from blocked xylylene diisocyanate to blocked diphenylmethane diisocyanate. The water solubility of the cured product in Example 6 was 6%, and the liquid absorption rate was -3.9%.

[0105] Example 7 The same procedure as in Example 6 was carried out to prepare a curable composition, except that the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 2,000 to polyvinyl alcohol having a weight-average molecular weight of 30,000. The cured product of Example 7 had a water solubility of 6% and a liquid absorption rate of -5%.

[0106] (Examples 8 to 11) The same procedure as in Example 2 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 44.0 g, 88.0 g, 176.0 g, and 352.0 g. The water solubility of the cured product of Example 8 was 7%, and the liquid absorption rate was -7.7%. The water solubility of the cured product of Example 9 was 6%, and the liquid absorption rate was -6%. The water solubility of the cured product of Example 10 was 6%, and the liquid absorption rate was 4%. The water solubility of the cured product of Example 11 was 5%, and the liquid absorption rate was 4.8%.

[0107] Example 12 The same procedure as in Example 4 was carried out except that the amount of crosslinking agent (B) added was changed from 33.0 g to 380 g in the preparation of the curable composition. The water solubility of the cured product in Example 12 was 1% and the liquid absorption rate was 3%.

[0108] Example 13 The same procedure was carried out as in Example 5, except that in compounding the curable composition, the crosslinking agent (B) was changed from blocked xylylene diisocyanate to blocked diphenylmethane diisocyanate and the amount of crosslinking agent (B) added was changed from 33.0 g to 44.0 g. The water solubility of the cured product in Example 13 was 7% and the liquid absorption rate was 3%.

[0109] (Examples 14 to 15) The same procedure as in Example 6 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 44.0 g and 88.0 g. The cured product of Example 14 had a water solubility of 5% and a liquid absorption of 2.5%. The cured product of Example 15 had a water solubility of 4% and a liquid absorption of 2%.

[0110] (Examples 16 to 20) The same procedure as in Example 7 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 44.0 g, 88.0 g, 176.0 g, 352.0 g, and 400.0 g. The cured product of Example 16 had a water solubility of 3% and a liquid absorption rate of -8.5%. The cured product of Example 17 had a water solubility of 6% and a liquid absorption rate of -3.8%. The cured product of Example 18 had a water solubility of 4% and a liquid absorption rate of 3.6%. The cured product of Example 19 had a water solubility of 1% and a liquid absorption rate of -0.7%. The cured product of Example 20 had a water solubility of 3% and a liquid absorption rate of 0.5%.

[0111] Example 21 The same procedure was carried out as in Example 13, except that in compounding the curable composition, blocked diphenylmethane diisocyanate was replaced with blocked 1,3-bis(isocyanatomethyl)cyclohexane as the crosslinking agent (B). The water solubility and liquid absorption rate of the cured product of Example 21 were 1% and 1%, respectively.

[0112] Example 22 The same procedure as in Example 14 was carried out to prepare a curable composition, except that the crosslinking agent (B) was changed from blocked diphenylmethane diisocyanate to blocked 1,3-bis(isocyanatomethyl)cyclohexane. The water solubility of the cured product in Example 22 was 5% and the liquid absorption rate was 2.2%.

[0113] Example 23 The same procedure was carried out as in Example 15, except that in compounding the curable composition, blocked diphenylmethane diisocyanate was replaced with blocked 1,3-bis(isocyanatomethyl)cyclohexane as the crosslinking agent (B). The water solubility of the cured product in Example 23 was 4%, and the liquid absorption rate was 1.2%.

[0114] Example 24 The same procedure as in Example 16 was carried out to prepare a curable composition, except that the crosslinking agent (B) was changed from blocked diphenylmethane diisocyanate to blocked 1,3-bis(isocyanatomethyl)cyclohexane. The water solubility of the cured product in Example 24 was 3%, and the liquid absorption rate was -8%.

[0115] (Examples 25 to 27) The same procedure as in Example 24 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 44.0 g to 88.0 g, 176.0 g, and 352.0 g. The cured product of Example 25 had a water solubility of 4% and a liquid absorption rate of -4%. The cured product of Example 26 had a water solubility of 3% and a liquid absorption rate of 3.2%. The cured product of Example 27 had a water solubility of 1% and a liquid absorption rate of 0.3%.

[0116] Example 28 The curable composition was prepared in the same manner as in Example 5, except that the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 500 to polyvinyl alcohol having a weight-average molecular weight of 70,000, and the amount of crosslinking agent (B) added was changed from 33.0 g to 352.0 g. The cured product of Example 28 had a water solubility of 2% and a liquid absorption rate of -1.3%.

[0117] Example 29 The same procedure was carried out as in Example 21, except that in the preparation of the curable composition, the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 500 to polyvinyl alcohol having a weight-average molecular weight of 160,000, and the amount of crosslinking agent (B) added was changed from 44.0 g to 400.0 g. The water solubility of the cured product of Example 29 was 3%, and the liquid absorption rate was 0.8%.

[0118] Example 30 The same procedure as in Example 20 was carried out to prepare a curable composition, except that the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 30,000 to polyvinyl alcohol having a weight-average molecular weight of 200,000. The cured product of Example 30 had a water solubility of 3% and a liquid absorption rate of 1.2%.

[0119] Example 31 The same procedure was carried out as in Example 7, except that in compounding the curable composition, the crosslinking agent (B) was changed from blocked diphenylmethane diisocyanate to blocked xylylene diisocyanate and the amount of crosslinking agent (B) added was changed from 33.0 g to 38.0 g. The water solubility of the cured product in Example 31 was 9%, and the liquid absorption rate was -0.2%.

[0120] Example 32 The same procedure was carried out as in Example 5, except that the amount of crosslinking agent added in compounding the curable composition was changed from 33.0 g to 35.0 g. The water solubility of the cured product in Example 32 was 2%, and the liquid absorption rate was 3.5%.

[0121] Example 33 The same procedure was carried out as in Example 15, except that in compounding the curable composition, blocked diphenylmethane diisocyanate was used as the crosslinking agent (B) instead of blocked xylylene diisocyanate. The water solubility of the cured product of Example 33 was 1%, and the liquid absorption rate was 3%.

[0122] Example 34 The same procedure was carried out as in Example 31, except that the amount of crosslinking agent (B) added was changed from 38.0 g to 152.0 g in preparing the curable composition. The water solubility of the cured product in Example 34 was 2%, and the liquid absorption rate was -4.0%.

[0123] Example 35 The same procedure as in Example 34 was carried out, except that the amount of crosslinking agent (B) added in compounding the curable composition was changed from 152.0 g to 305.0 g. The water solubility of the cured product in Example 35 was 7% and the liquid absorption rate was 0.4%.

[0124] Example 36 The same procedure was carried out as in Example 1, except that in compounding the curable composition, blocked diphenylmethane diisocyanate was replaced with blocked 1,3,5-tris(6-isocyanatohexyl) biuret as the crosslinking agent (B). The water solubility of the cured product in Example 36 was 8%, and the liquid absorption rate was -7.9%.

[0125] Example 37 The same procedure was carried out as in Example 36, except that in compounding the curable composition, a blocked 1,3,5-tris(6-isocyanatohexyl) biuret compound was used as the crosslinking agent (B) instead of a blocked 1,2,4-triisocyanatobenzene compound. The water solubility of the cured product in Example 37 was 9%, and the liquid absorption rate was -9%.

[0126] Example 38 The same procedure was carried out as in Example 36, except that in the preparation of the curable composition, carboxymethyl cellulose was changed to methyl cellulose as the water-soluble polymer (A) and block 1,3,5-tris(6-isocyanatohexyl) biuret was changed to block 1,3,5-tris(isocyanatomethyl)benzene as the crosslinking agent (B). The water solubility of the cured product in Example 38 was 9%, and the liquid absorption rate was -8.7%.

[0127] Example 39 The same procedure as in Example 36 was carried out, except that in preparing the curable composition, carboxymethyl cellulose was replaced with methyl cellulose as the water-soluble polymer (A). The water solubility of the cured product of Example 39 was 7% and the liquid absorption rate was -8%.

[0128] Example 40 The same procedure as in Example 38 was carried out to prepare a curable composition, except that methyl cellulose was replaced with polyvinyl alcohol having a weight-average molecular weight of 500 as the water-soluble polymer (A). The cured product of Example 40 had a water solubility of 5% and a liquid absorption rate of -6.4%.

[0129] (Examples 41 to 42) The same procedure as in Example 36 was repeated to prepare the curable cured product, except that the carboxymethyl cellulose was replaced with polyvinyl alcohol having a weight-average molecular weight of 2,000 and polyvinyl alcohol having a weight-average molecular weight of 30,000 as the water-soluble polymer (A). The cured product of Example 41 had a water solubility of 5% and a liquid absorption rate of 3%. The cured product of Example 42 had a water solubility of 5% and a liquid absorption rate of 2.8%.

[0130] (Examples 43 to 46) The same procedure as in Example 37 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 39.0 g, 79.0 g, 158.0 g, and 316.0 g. The cured product of Example 43 had a water solubility of 8% and a liquid absorption of 3%. The cured product of Example 44 had a water solubility of 6% and a liquid absorption of 4%. The cured product of Example 45 had a water solubility of 3% and a liquid absorption of -2%. The cured product of Example 46 had a water solubility of 5% and a liquid absorption of 4%.

[0131] Example 47 The same procedure as in Example 39 was carried out, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 380.0 g in the preparation of the curable composition. The water solubility of the cured product in Example 47 was 4% and the liquid absorption rate was 3%.

[0132] Example 48 The same procedure was carried out as in Example 40 to prepare a curable composition, except that the crosslinking agent (B) was changed from blocked 1,3,5-tris(isocyanatomethyl)benzene to blocked 1,3,5-tris(6-isocyanatohexyl) biuret and the amount of crosslinking agent (B) added was changed from 33.0 g to 39.0 g. The water solubility of the cured product of Example 48 was 6%, and the liquid absorption rate was 2.8%.

[0133] (Examples 49 to 50) The same procedure as in Example 41 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 39.0 g and 79.0 g. The cured products of Example 49 and Example 50 had water solubility of 5% and liquid absorption of 3%.

[0134] (Examples 51 to 55) The same procedure as in Example 42 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 39.0 g, 79.0 g, 158.0 g, 316.0 g, and 400.0 g. The cured product of Example 51 had a water solubility of 6% and a liquid absorption of 1.6%. The cured product of Example 52 had a water solubility of 6% and a liquid absorption of 2%. The cured product of Example 53 had a water solubility of 9% and a liquid absorption of 1%. The cured product of Example 54 had a water solubility of 7% and a liquid absorption of 1%. The cured product of Example 55 had a water solubility of 5% and a liquid absorption of 1.5%.

[0135] Example 56 The same procedure as in Example 48 was carried out to prepare a curable composition, except that the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 500 to polyvinyl alcohol having a weight-average molecular weight of 70,000. The cured product of Example 56 had a water solubility of 5% and a liquid absorption rate of 0.6%.

[0136] (Examples 57 to 58) The same procedure as in Example 56 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 39.0 g to 79.0 g and 158.0 g, respectively. The cured product of Example 57 had a water solubility of 8% and a liquid absorption of 1%. The cured product of Example 58 had a water solubility of 6% and a liquid absorption of 1%.

[0137] Example 59 The same procedure as in Example 48 was carried out to prepare a curable composition, except that as the water-soluble polymer (A), polyvinyl alcohol having a weight-average molecular weight of 500 was used instead of polyvinyl alcohol having a weight-average molecular weight of 160,000. The cured product of Example 59 had a water solubility of 2% and a liquid absorption rate of 2.5%.

[0138] (Examples 60 to 62) The same procedure as in Example 59 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 39.0 g to 79.0 g, 158.0 g, and 316.0 g. The cured product of Example 60 had a water solubility of 4% and a liquid absorption of 2%. The cured product of Example 61 had a water solubility of 7% and a liquid absorption of 1.6%. The cured product of Example 62 had a water solubility of 5% and a liquid absorption of 1%.

[0139] Example 63 The same procedure as in Example 54 was carried out to prepare a curable composition, except that as the water-soluble polymer (A), polyvinyl alcohol having a weight-average molecular weight of 30,000 was used instead of polyvinyl alcohol having a weight-average molecular weight of 200,000. The water-solubility of the cured product in Example 63 was 2%, and the liquid absorption rate was 2.8%.

[0140] Example 64 The same procedure was carried out as in Example 48, except that in compounding the curable composition, a blocked 1,3,5-tris(6-isocyanatohexyl) biuret compound was used as the crosslinking agent (B) instead of a blocked 1,2,4-triisocyanatobenzene compound. The water solubility of the cured product of Example 64 was 4%, and the liquid absorption rate was 6%.

[0141] Example 65 The same procedure as in Example 64 was carried out to prepare a curable composition, except that as the water-soluble polymer (A), polyvinyl alcohol having a weight-average molecular weight of 500 was used instead of polyvinyl alcohol having a weight-average molecular weight of 2,000. The water-solubility of the cured product in Example 65 was 4%, and the liquid absorption rate was -3%.

[0142] Example 66 The same procedure was carried out as in Example 65, except that the amount of crosslinking agent (B) added was changed from 39.0 g to 79.0 g in the preparation of the curable composition. The water solubility of the cured product of Example 66 was 5% and the liquid absorption rate was 2%.

[0143] Example 67 The same procedure as in Example 64 was carried out to prepare a curable composition, except that as the water-soluble polymer (A), polyvinyl alcohol having a weight-average molecular weight of 500 was used instead of polyvinyl alcohol having a weight-average molecular weight of 30,000. The water-solubility of the cured product in Example 67 was 2%, and the liquid absorption rate was 3%.

[0144] (Examples 68 to 70) The same procedure as in Example 67 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 39.0 g to 79.0 g, 158.0 g, and 316.0 g. The cured product of Example 68 had a water solubility of 2% and a liquid absorption of 3.5%. The cured product of Example 69 had a water solubility of 3% and a liquid absorption of -1%. The cured product of Example 70 had a water solubility of 4% and a liquid absorption of 2.5%.

[0145] Example 71 The same procedure as in Example 70 was carried out to prepare a curable composition, except that as the water-soluble polymer (A), polyvinyl alcohol having a weight-average molecular weight of 70,000 was used instead of polyvinyl alcohol having a weight-average molecular weight of 30,000. The cured product of Example 71 had a water solubility of 4% and a liquid absorption rate of 2%.

[0146] Example 72 The same procedure was carried out as in Example 64, except that in the preparation of the curable composition, polyvinyl alcohol having a weight-average molecular weight of 500 as the water-soluble polymer (A) was changed to polyvinyl alcohol having a weight-average molecular weight of 160,000, and the amount of crosslinking agent (B) added was changed from 39.0 g to 400.0 g. The water solubility of the cured product in Example 72 was 3%, and the liquid absorption rate was 2.5%.

[0147] Example 73 The same procedure as in Example 72 was carried out to prepare a curable composition, except that the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 160,000 to polyvinyl alcohol having a weight-average molecular weight of 200,000. The cured product of Example 73 had a water solubility of 2% and a liquid absorption rate of -3%.

[0148] Example 74 The same procedure was carried out as in Example 51, except that in compounding the curable composition, a blocked 1,3,5-tris(6-isocyanatohexyl) biuret compound was used as the crosslinking agent (B) instead of a blocked 1,3,5-tris(isocyanatomethyl)benzene. The water solubility of the cured product of Example 74 was 7%, and the liquid absorption rate was 1%.

[0149] Example 75 The same procedure was carried out as in Example 40, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 35.0 g in preparing the curable composition. The water solubility of the cured product of Example 75 was 9%, and the liquid absorption rate was -0.5%.

[0150] Example 76 The same procedure was carried out as in Example 50, except that in compounding the curable composition, a blocked 1,3,5-tris(6-isocyanatohexyl) biuret compound was used as the crosslinking agent (B) instead of a blocked 1,3,5-tris(isocyanatomethyl)benzene. The water solubility and liquid absorption rate of the cured product of Example 76 were 3% and 3%, respectively.

[0151] Example 77 The same procedure was carried out as in Example 53, except that in compounding the curable composition, a blocked 1,3,5-tris(6-isocyanatohexyl) biuret compound was used as the crosslinking agent (B) instead of a blocked 1,3,5-tris(isocyanatomethyl)benzene. The water solubility of the cured product of Example 77 was 4%, and the liquid absorption rate was -1.5%.

[0152] Example 78 The same procedure as in Example 77 was carried out except that the amount of crosslinking agent (B) added was changed from 158.0 g to 305.0 g in the preparation of the curable composition. The water solubility of the cured product in Example 78 was 2% and the liquid absorption rate was 1%.

[0153] Example 79 The same procedure was carried out as in Example 54, except that in compounding the curable composition, a blocked 1,3,5-tris(6-isocyanatohexyl) biuret was used as the crosslinking agent (B) instead of a blocked polymethylene polyphenyl polyisocyanate. The water solubility and liquid absorption rate of the cured product of Example 79 were 3% and 3%, respectively.

[0154] (Example 80) The same procedure was carried out as in Example 56, except that in compounding the curable composition, a blocked 1,3,5-tris(6-isocyanatohexyl) biuret was used as the crosslinking agent (B) instead of a blocked polymethylene polyphenyl polyisocyanate. The water solubility of the cured product of Example 80 was 2%, and the liquid absorption rate was 2.5%.

[0155] Example 81 The same procedure was carried out as in Example 80, except that in preparing the curable composition, polyvinyl alcohol having a weight-average molecular weight of 160,000 was used as the water-soluble polymer (A) instead of polyvinyl alcohol having a weight-average molecular weight of 70,000. The cured product of Example 81 had a water solubility of 4% and a liquid absorption rate of -1%.

[0156] (Comparative Example 1) The same procedure as in Example 7 was carried out except that the crosslinking agent (B) was not added in preparing the curable composition. The water solubility of the cured product in Comparative Example 1 was 100%, and the liquid absorption rate was 7.4%.

[0157] (Comparative Example 2) The same procedure as in Example 7 was carried out except that the amount of crosslinking agent (B) added was changed from 33.0 g to 25.0 g in the preparation of the curable composition. The water solubility of the cured product in Comparative Example 2 was 70% and the liquid absorption rate was 7%.

[0158] (Comparative Example 3) The same procedure as in Example 7 was carried out except that the amount of crosslinking agent (B) added was changed from 33.0 g to 605.0 g in the preparation of the curable composition. However, the amount of crosslinking agent (B) added was too large, causing an increase in viscosity and making it impossible to evaluate.

[0159] (Comparative Examples 4 to 6) The same procedure as in Example 7 was repeated to prepare the curable compositions, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 10.0 g, 15.0 g, and 18.0 g. The cured product of Comparative Example 4 had a water solubility of 50% and a liquid absorption rate of 50%. The cured product of Comparative Example 5 had a water solubility of 52% and a liquid absorption rate of -15%. The cured product of Comparative Example 6 had a water solubility of 40% and a liquid absorption rate of 10%.

[0160] (Comparative Example 7) The curable composition was prepared in the same manner as in Example 13, except that the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 500 to polyvinyl alcohol having a weight-average molecular weight of 300, and the amount of crosslinking agent (B) added was changed from 44.0 g to 35.0 g. The cured product of Comparative Example 7 had a water solubility of 93% and a liquid absorption rate of 7.2%.

[0161] (Comparative Example 8) In preparing the curable composition, 100 g of polyvinyl alcohol with a weight-average molecular weight of 250,000 was added as the water-soluble polymer (A) to water, and the mixture was heated from room temperature to 95°C and stirred until completely dissolved. At this stage, the viscosity was too high and the mixture gelled, making it impossible to add the crosslinker (B).

[0162] (Comparative Example 9) The curable composition was prepared in the same manner as in Example 5, except that the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 500 to polyvinyl alcohol having a weight-average molecular weight of 45,000, the crosslinking agent (B) was changed from blocked xylylene diisocyanate to polyacrylic acid, and the amount of crosslinking agent (B) added was changed from 33.0 g to 380.0 g. The cured product of Comparative Example 9 had a water solubility of 72% and a liquid absorption rate of -30%.

[0163] (Comparative Example 10) The same procedure was carried out as in Example 42, except that the amount of crosslinking agent (B) added was changed from 33.0 g to 25.0 g in the preparation of the curable composition. The water solubility of the cured product in Comparative Example 10 was 75%, and the liquid absorption rate was 7.1%.

[0164] (Comparative Example 11) The same procedure as in Example 74 was carried out to prepare a curable composition, except that the amount of crosslinking agent (B) added was changed from 39.0 g to 605.0 g. However, the amount of crosslinking agent (B) added was too large, causing an increase in viscosity and making it impossible to evaluate.

[0165] (Comparative Example 12) The same procedure was carried out as in Example 74, except that the amount of crosslinking agent (B) added was changed from 39.0 g to 10.0 g in preparing the curable composition. The water solubility and liquid absorption of the cured product of Comparative Example 12 were 50% and 50%, respectively.

[0166] (Comparative Examples 13 to 14) The same procedure as in Example 51 was repeated to prepare the curable composition, except that the amount of crosslinking agent (B) added was changed from 39.0 g to 15.0 g and 18.0 g, respectively. The cured product of Comparative Example 13 had a water solubility of 47% and a liquid absorption rate of -15%. The cured product of Comparative Example 14 had a water solubility of 42% and a liquid absorption rate of 10%.

[0167] (Comparative Example 15) The same procedure was carried out as in Example 48, except that in preparing the curable composition, the water-soluble polymer (A) was changed from polyvinyl alcohol having a weight-average molecular weight of 500 to polyvinyl alcohol having a weight-average molecular weight of 300, and the amount of crosslinking agent (B) added was changed from 39.0 g to 35.0 g. The cured product of Comparative Example 15 had a water solubility of 95% and a liquid absorption rate of 7%.

[0168] [Table 1]

[0169] [Table 2]

[0170] These results show that a lithium ion secondary battery using the cured material according to the embodiment of the present disclosure as a cured material for a lithium ion secondary battery can obtain good charge / discharge cycle characteristics. [Explanation of symbols]

[0171] 10... separator, 20... positive electrode, 22... positive electrode current collector, 24... positive electrode active material layer, 30... negative electrode, 32... negative electrode current collector, 34... negative electrode active material layer, 40... laminate, 50... exterior body, 52... metal foil, 54... polymer film, 60, 62... leads, 100... lithium ion secondary battery

Claims

1. A cured product obtained by curing a curable composition, The curable composition includes a water-soluble polymer (A) having a hydroxyl group, a crosslinking agent (B) having a functional group reactive with the hydroxyl group, and water; The water-soluble polymer (A) includes one or more of polyvinyl alcohol, carboxymethyl cellulose, and methyl cellulose, The weight average molecular weight of the polyvinyl alcohol is 2,000 to 200,000, The cured product has a urethane bond, the cured product has a water solubility of less than 10% when immersed in water, and a liquid absorption rate of -10% or more and less than 5% when immersed in an electrolyte; Hardened material for lithium-ion secondary batteries.

2. The curable composition comprises Per 100 parts by weight of the water-soluble polymer (A), The crosslinking agent (B) is contained in an amount of 35 parts by weight or more and less than 400 parts by weight. The cured product for a lithium ion secondary battery according to claim 1 .

3. The crosslinking agent (B) is an active methylene diisocyanate. be, The cured product for a lithium ion secondary battery according to claim 1 or 2.

4. The crosslinking agent (B) is a polyisocyanate having three or more functional groups. The cured product for a lithium ion secondary battery according to claim 1 or 2.

5. a negative electrode active material; A negative electrode active material layer containing at least the cured material for a lithium ion secondary battery according to any one of claims 1 to 4, and a negative electrode current collector; 1. A negative electrode for a lithium-ion secondary battery comprising:

6. The negative electrode for a lithium ion secondary battery according to claim 5 , A positive electrode and An electrolyte; A lithium ion secondary battery comprising:

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