Lithium ion secondary battery, separation membrane and method for producing the same

Abstract

According to one aspect of the present invention, a lithium-ion secondary battery is provided, which comprises, in sequence, a positive electrode mixture layer, a separator and a negative electrode mixture layer, wherein: the positive electrode mixture layer contains a positive electrode active material, a first lithium salt and a first solvent; the negative electrode mixture layer contains a negative electrode active material, a second lithium salt and a second solvent different from the first solvent; the separator comprises a polymer having lithium ion conductivity, a third lithium salt and a third solvent; and the content of the third solvent is 40% by mass or less based on the total amount of the separator.

Description

Technical Field

[0001] The present invention relates to a lithium ion secondary battery, a separation membrane and a method for producing the same. Background Art

[0002] In recent years, with the popularization of portable electronic devices and electric vehicles, secondary batteries represented by lithium-ion secondary batteries are required to further improve their performance. For example, technologies for improving the performance of lithium-ion secondary batteries by including different types of electrolytes in the positive and negative electrodes are being studied (for example, Patent Document 1).

[0003] [Prior art literature]

[0004] [Patent Document]

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-110447 Summary of the Invention

[0006] [Technical Issues]

[0007] In lithium-ion secondary batteries containing different types of electrolytes in the positive and negative electrodes, it is important that the solvent contained in the electrolyte is sufficiently separated without mixing between the positive and negative electrodes. The present inventors have considered providing a separator membrane between the positive and negative electrodes to separate the solvent from the electrolyte in such lithium-ion secondary batteries. This separator membrane is required to have the property of allowing lithium ions to pass through the separator membrane while substantially preventing the solvent from passing through the separator membrane.

[0008] The present invention aims to provide a separation membrane having excellent separation capability for solvents used in a lithium ion secondary battery containing different types of solvents in the positive electrode mixture layer and the negative electrode mixture layer, a lithium ion secondary battery including the separation membrane, and a method for manufacturing the same.

[0009] [Technical solution]

[0010] According to one aspect of the present disclosure, a lithium-ion secondary battery is provided, which comprises, in sequence, a positive electrode mixture layer, a separator and a negative electrode mixture layer, wherein: the positive electrode mixture layer comprises a positive electrode active material, a first lithium salt and a first solvent; the negative electrode mixture layer comprises a negative electrode active material, a second lithium salt and a second solvent different from the first solvent; the separator comprises a polymer having lithium ion conductivity, a third lithium salt and a third solvent; and the content of the third solvent is 40% by mass or less based on the total amount of the separator.

[0011] According to another aspect of the present disclosure, a separator is provided for being arranged between a positive electrode mixture layer and a negative electrode mixture layer in a lithium ion secondary battery, the lithium ion secondary battery including a positive electrode mixture layer containing a positive electrode active material, a first lithium salt and a first solvent, and a negative electrode mixture layer containing a negative electrode active material, a second lithium salt and a second solvent different from the first solvent, wherein the separator includes a polymer having lithium ion conductivity, a third lithium salt and a third solvent, and the content of the third solvent is 40% by mass or less based on the total amount of the separator.

[0012] According to another aspect of the present disclosure, there is provided a method for manufacturing a lithium-ion secondary battery, the method comprising the following steps: obtaining a positive electrode comprising a positive electrode mixture layer, the positive electrode mixture layer comprising a positive electrode active material, a first lithium salt, and a first solvent; obtaining a negative electrode comprising a negative electrode mixture layer, the negative electrode mixture layer comprising a negative electrode active material, a second lithium salt, and a second solvent different from the first solvent; forming a slurry into the form of a film, the slurry comprising a polymerizable compound capable of forming a polymer having lithium ion conductivity, a third lithium salt, and a third solvent, and then polymerizing the polymerizable compound to obtain a separation membrane; and disposing the separation membrane between the positive electrode and the negative electrode, wherein the content of the third solvent is 40% by mass or less based on the total amount of the slurry.

[0013] According to another aspect of the present disclosure, there is provided a method for manufacturing a separator disposed between a positive electrode mixture layer and a negative electrode mixture layer in a lithium ion secondary battery, the lithium ion secondary battery including a positive electrode mixture layer containing a positive electrode active material, a first lithium salt, and a first solvent, and a negative electrode mixture layer containing a negative electrode active material, a second lithium salt, and a second solvent different from the first solvent, the method comprising: forming a slurry into the form of a film, the slurry including a polymerizable compound capable of forming a polymer having lithium ion conductivity, a third lithium salt, and a third solvent, and then polymerizing the polymerizable compound to obtain a separator, wherein the content of the third solvent is 40% by mass or less based on the total amount of the slurry.

[0014] In each aspect, the content of the third solvent may be 35% by mass or less based on the total amount of the separation membrane or based on the total amount of the slurry.

[0015] In each aspect, the third solvent can be an ionic liquid.

[0016] In each aspect, the separation membrane or slurry may further contain inorganic oxide particles.

[0017] [Beneficial effects]

[0018] According to the present invention, a separator having excellent separation ability for different types of solvents used in a lithium ion secondary battery containing positive and negative electrode mixture layers, a lithium ion secondary battery including the separator, and a method for manufacturing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a perspective view showing a lithium ion secondary battery according to one embodiment; and

[0020] Figure 2 It shows Figure 1 An exploded perspective view of one embodiment of an electrode assembly in a lithium-ion secondary battery is shown. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings as appropriate. However, the present invention is not limited to the following embodiments.

[0022] As used herein, (meth)acrylic acid refers to acrylic acid or its corresponding methacrylic acid. The same applies to other similar expressions such as (meth)acrylate.

[0023] Figure 1 1 is a perspective view showing a lithium ion secondary battery according to one embodiment. Figure 1 As shown, the lithium ion secondary battery 1 of one embodiment is a so-called laminated secondary battery, which includes an electrode group 2 and a pouch-type battery outer package 3 that accommodates the electrode group 2. The electrode group 2 has a positive electrode collector tab 4 and a negative electrode collector tab 5. The positive electrode collector tab 4 and the negative electrode collector tab 5 protrude from the interior of the battery outer package 3 to the outside, so that the positive electrode collector and the negative electrode collector (details will be described later) can be electrically connected to the outside of the lithium ion secondary battery 1. In another embodiment, the lithium ion secondary battery 1 may have a shape other than the laminate shape (coin-shaped, cylindrical, etc.).

[0024] The battery outer package 3 may be a container formed of, for example, a laminated film. The laminated film may be, for example, a laminated film in which a polymer film such as a polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, or stainless steel, and a sealant layer such as polypropylene are laminated in the stated order.

[0025] Figure 2 It shows Figure 1 FIG. 1 is an exploded perspective view of an embodiment of an electrode group 2 in a lithium-ion secondary battery 1. Figure 2As shown, the electrode group 2 of this embodiment includes, in order, a positive electrode 6, a separator 7, and a negative electrode 8. The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 disposed on the positive electrode current collector 9. The positive electrode current collector tab 4 is disposed on the positive electrode current collector 9. The negative electrode 8 includes a negative electrode current collector 11 and a negative electrode mixture layer 12 disposed on the negative electrode current collector 11. The negative electrode current collector tab 5 is disposed on the negative electrode current collector 11.

[0026] The positive electrode current collector 9 is made of, for example, aluminum, titanium, stainless steel, nickel, calcined carbon, a conductive polymer, conductive glass, etc. The thickness of the positive electrode current collector 9 can be, for example, 1 μm or more and 50 μm or less.

[0027] The negative electrode current collector 11 is made of, for example, copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, etc. The thickness of the negative electrode current collector 11 may be, for example, 1 μm or more and 50 μm or less.

[0028] In one embodiment, the positive electrode mixture layer 10 includes a positive electrode active material, a lithium salt (a first lithium salt), and a solvent (a first solvent).

[0029] The positive electrode active material may be, for example, lithium oxide. Examples of lithium oxide include Li x CoO2、Li x NiO2、Li x MnO2、Li x Co y Ni 1-y O2、Li x Co y M 1-y O z 、Li x Ni 1-y M y O z 、Li x Mn2O4 and Li x Mn 2-y M y O4 (in each formula, M represents at least one element selected from Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, V and B (provided that M is an element different from the other elements in each formula), x = 0 to 1.2, y = 0 to 0.9, z = 2.0 to 2.3). Li x Ni 1-y M y O z The lithium oxide represented can be Li x Ni 1-(y1+y2) Co y1 Mn y2 O z(where x and z are the same as above, y1 = 0 to 0.9, y2 = 0 to 0.9, y1 + y2 = 0 to 0.9), and may be, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2. By Li x Ni 1-y M y O z The lithium oxide represented can be Li x Ni 1-(y3+y4) Co y3 Al y4 O z (wherein x and z are the same as above, y3=0 to 0.9, y4=0 to 0.9, y3+y4=0 to 0.9), and may be, for example, LiNi 0.8 Co 0.15 Al 0.05 O2.

[0030] The positive electrode active material may be lithium phosphate. Examples of lithium phosphate include lithium manganese phosphate (LiMnPO4), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), and lithium vanadium phosphate (Li3V2(PO4)3).

[0031] The content of the positive electrode active material based on the total amount of the positive electrode mixture layer may be 70% by mass or more, 80% by mass or more, or 85% by mass or more. The content of the positive electrode active material based on the total amount of the positive electrode mixture layer may be 95% by mass or less, 92% by mass or less, or 90% by mass or less.

[0032] The first lithium salt may be, for example, at least one selected from LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, CF3SO2OLi, LiN(SO2F)2 (LiFSI, lithium difluorosulfonyl imide), LiN(SO2CF3)2 (LiTFSI, lithium bis(trifluoromethane)sulfonyl imide) and LiN(SO2CF2CF3)2.

[0033] The content of the first lithium salt may be 0.5 mol / L or more, 0.7 mol / L or more, or 0.8 mol / L or more, and 1.5 mol / L or less, 1.3 mol / L or less, or 1.2 mol / L or less based on the total amount of the first solvent.

[0034] The first solvent is a solvent for dissolving the first lithium salt. Examples of the first solvent include: cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; cyclic esters such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, and γ-caprolactone; ethers such as tetrahydrofuran, 1,3-dioxane, dimethoxyethane, diethoxyethane, methoxyethoxyethane, glycol dimethyl ether, diglycol dimethyl ether, triglycol dimethyl ether, and tetraglycol dimethyl ether; phosphates such as triesters of phosphate; nitriles such as acetonitrile, benzonitrile, adiponitrile, and glutaronitrile; chain sulfones such as dimethyl sulfone and diethyl sulfone; cyclic sulfones such as cyclopentane; cyclic sulfonates such as propane sultone, etc. The first solvent can be used alone or in combination of two or more types.

[0035] The first solvent preferably includes a solvent having excellent oxidation resistance, such as acetonitrile and ethylene carbonate, thereby improving the oxidation resistance of the positive electrode mixture layer 10 .

[0036] The content of the first solvent contained in the positive electrode mixture layer 10 can be appropriately set within a range in which the first lithium salt can be dissolved, but for example, it can be 10% by mass or more and 80% by mass or less based on the total amount of the positive electrode mixture layer.

[0037] The positive electrode mixture layer 10 may further contain a binder and a conductive material as other components.

[0038] The binder may be a polymer containing at least one monomer unit selected from tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, acrylic acid, maleic acid, ethyl methacrylate, methyl methacrylate, and acrylonitrile, or a rubber such as styrene-butadiene rubber, isoprene rubber, acrylic rubber, etc. The binder is preferably polyvinylidene fluoride or a copolymer containing hexafluoropropylene and vinylidene fluoride as monomer units.

[0039] The content of the binder may be 0.3 mass % or more, 0.5 mass % or more, 1 mass % or more, or 1.5 mass % or more, and 10 mass % or less, 8 mass % or less, 6 mass % or less, or 4 mass % or less, based on the total amount of the positive electrode mixture layer.

[0040] The conductive material may be a carbon material, such as carbon black, acetylene black, graphite, carbon fiber, or carbon nanotube, etc. These conductive materials may be used alone or in combination of two or more types.

[0041] The content of the conductive material may be 0.1% by mass or more, 1% by mass or more, or 3% by mass or more, based on the total amount of the positive electrode mixture layer. From the perspective of suppressing an increase in the volume of the positive electrode 6 and a related decrease in the energy density of the lithium-ion secondary battery 1, the content of the conductive material is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less, based on the total amount of the positive electrode mixture layer.

[0042] The thickness of the positive electrode mixture layer 10 may be 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more, and 100 μm or less, 80 μm or less, 70 μm or less, or 50 μm or less.

[0043] In one embodiment, the negative electrode mixture layer 12 includes a negative electrode active material, a lithium salt (a second lithium salt), and a solvent (a second solvent).

[0044] As the negative electrode active material, those commonly used in the field of energy devices can be used. Specific examples of the negative electrode active material include metallic lithium, lithium titanate (Li4Ti5O 12 ), lithium alloys or other metal compounds, carbon materials, metal complexes, organic polymer compounds, and the like. These negative electrode active materials are used alone or in combination of two or more. Examples of carbon materials may include: graphite such as natural graphite (flake graphite, etc.) and artificial graphite, amorphous carbon, carbon fiber, and carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and the like. From the viewpoint of obtaining a larger theoretical capacity (for example, 500 to 1500 Ah / kg), the negative electrode active material may be a negative electrode active material containing silicon as a constituent element, a negative electrode active material containing tin as a constituent element, and the like. Among them, the negative electrode active material may be a negative electrode active material containing silicon as a constituent element.

[0045] The negative electrode active material containing silicon as a constituent element may be an alloy containing silicon as a constituent element. Examples thereof include alloys containing silicon and at least one element selected from nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. The negative electrode active material containing silicon as a constituent element may be an oxide, nitride, or carbide. Specific examples thereof include silicon oxides such as SiO, SiO2, and LiSiO, silicon nitrides such as Si3N4 and Si2N2O, and silicon carbide such as SiC.

[0046] The content of the negative electrode active material based on the total amount of the negative electrode mixture layer may be 60% by mass or more, 65% by mass or more, or 70% by mass or more. The content of the negative electrode active material based on the total amount of the negative electrode mixture layer may be 99% by mass or less, 95% by mass or less, or 90% by mass or less.

[0047] The type and content of the second lithium salt may be the same as those of the first lithium salt contained in the positive electrode mixture layer 10. The second lithium salt may be the same as or different from the first lithium salt.

[0048] The second solvent is a solvent for dissolving the second lithium salt. The second solvent may be the same solvent as the first solvent, but may also be a different solvent. This allows for the use of suitable solvents for the positive electrode 6 and the negative electrode 8, respectively, thereby improving various properties of the lithium ion secondary battery 1, such as energy density and lifespan.

[0049] The solvent preferably used as the second solvent is a solvent having excellent anti-oxidation properties, such as γ-butyrolactone and tetrahydrofuran. Thus, reductive decomposition of the second solvent contained in the negative electrode mixture layer 12 can be suppressed.

[0050] The content of the second solvent contained in the negative electrode mixture layer 12 can be appropriately set within a range in which the second lithium salt can be dissolved, but may be, for example, 10% by mass or more and 80% by mass or less based on the total amount of the negative electrode mixture layer.

[0051] The negative electrode mixture layer 12 may further contain a binder and a conductive material as other components. If the types and contents of the binder and the conductive material are the same as those in the positive electrode mixture layer 10 described above, their types and contents may be used.

[0052] The thickness of the negative electrode mixture layer 12 may be 10 μm or more, 15 μm or more, or 20 μm or more, and 100 μm or less, 80 μm or less, 70 μm or less, 50 μm or less, 40 μm or less, or 30 μm or less.

[0053] The separator 7 is a membrane provided between the positive electrode mixture layer 10 and the negative electrode mixture layer 12 in the lithium ion secondary battery 1. The separator serves to separate the first solvent and the second solvent contained in the positive electrode mixture layer 10 and the negative electrode mixture layer 12 from each other and prevent them from mixing. The separator 7 allows the exchange of lithium ions.

[0054] The separation membrane 7 contains a polymer having lithium ion conductivity, a lithium salt (third lithium salt), and a solvent (third solvent).

[0055] A polymer with lithium ion conductivity is a polymer that has the property of conducting lithium ions from a lithium salt in the presence of a lithium salt. Whether a polymer can conduct lithium ions can be confirmed by measuring the ionic conductivity of the polymer. If the peak value of the ionic conductivity measured when 1% to 40% by mass of lithium salt is added to the polymer is 1×10 - 6S / cm or higher, the polymer can be said to have lithium ion conductivity.

[0056] The polymer having lithium ion conductivity may be a polymer having at least one group selected from a carbonyl group and an ether group. The ether group includes a chain ether group and a cyclic ether group.

[0057] Examples of such polymers having lithium ion conductivity include polyalkyl (meth)acrylates such as polymethyl (meth)acrylate; poly(polyalkylene glycol di(meth)acrylates) such as poly(polyethylene glycol di(meth)acrylate); poly(meth)acrylic acid; polyacrylamide; polymethacrylamide; poly(N-isopropylacrylamide); polymethyl vinyl ketone; polyvinyl acetate; and polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol.

[0058] The polymer having lithium ion conductivity may be a polymer having a cyclic ether group such as an epoxy group, an oxetane group, a tetrahydrofuran group or a tetrahydropyran group on the side chain of poly(meth)acrylic acid. That is, the polymer having lithium ion conductivity may be a polymer represented by the following formula (1):

[0059] [Chemical Formula 1]

[0060]

[0061] In formula (1), R 11 represents a straight chain or branched alkylene or a single bond, R 12 represents a linear or branched alkylene group, and r represents an integer of 2 or greater.

[0062] In formula (1), R 11 The number of carbon atoms in the alkylene group represented by may be, for example, 2 or more and 5 or less. 12 The number of carbon atoms in the alkylene group represented by may be, for example, 2 or more and 5 or less. r may be, for example, 5 or more and 20 or less.

[0063] Examples of the polymer represented by formula (1) include polyglycidyl (meth)acrylate, poly(3-ethyloxetan-3-yl)methyl (meth)acrylate, and the like.

[0064] From the perspective of membrane formability, the content of the polymer having lithium ion conductivity is preferably 60% by mass or greater, more preferably 70% by mass or greater, and even more preferably 80% by mass or greater, based on the total weight of the separation membrane. From the perspective of further improving the ion conductivity of the separation membrane 7, the content of the polymer having lithium ion conductivity is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less, based on the total weight of the separation membrane.

[0065] The third lithium salt may be of the same type as the first lithium salt contained in the positive electrode mixture layer 10. The third lithium salt may be the same as or different from the first and / or second lithium salts.

[0066] From the perspective of excellent ion conductivity of the separation membrane, the content of the third lithium salt is preferably 5% by mass or greater, more preferably 13% by mass or greater, and even more preferably 17% by mass or greater, based on the total amount of the third lithium salt and the third solvent. From the perspective of solvent viscosity, the content of the third lithium salt is preferably 35% by mass or less, more preferably 23% by mass or less, and even more preferably 20% by mass or less, based on the total amount of the third lithium salt and the third solvent.

[0067] From the viewpoint of further improving the ion conductivity of the separation membrane 7 , the content of the third lithium salt is preferably 2 mass % or more, more preferably 3 mass % or more, and even more preferably 5 mass % or more, based on the total weight of the separation membrane.

[0068] From the viewpoint of further improving the ion conductivity of the separation membrane 7 , the content of the third lithium salt is preferably 12 mass % or less, more preferably 9 mass % or less, and even more preferably 6 mass % or less, based on the total weight of the separation membrane.

[0069] The third solvent is a solvent for dissolving the third lithium salt. From the viewpoint of suppressing volatilization from the separation membrane, the third solvent is preferably an ionic liquid or glyme represented by the following formula (2), and more preferably an ionic liquid.

[0070] R 21 O-(CH2CH2O) k -R 22 (2)

[0071] [Wherein, in formula (2), R 21 and R 22 each independently represents an alkyl group having 1 to 4 carbon atoms, and k represents an integer of 3 to 6]

[0072] The ionic liquid contains the following anion components and cationic components. Also, the ionic liquid used herein is a liquid material at -20°C or higher.

[0073] The anion component of the ionic liquid is not particularly limited, but includes: halogen anions such as Cl - Br - or I - ; Inorganic anions such as BF4 - or N(SO2F)2 - ([FSI] - ); organic anions such as B(C6H5)4 - 、CH3SO2O- CF3SO2O - 、N(SO2C4F9)2 - 、N(SO2CF3)2 - ([TFSI] - ) or N(SO2C2F5)2 - The anion component of the ionic liquid preferably contains at least one anion component represented by the following formula 3.

[0074] N(SO2C m F 2m+1 )(SO2C n F 2n+1 ) - (3)

[0075] [Wherein, in formula (3), m and n each independently represent an integer of 0 to 5. m and n may be the same as or different from each other, and are preferably the same as each other.]

[0076] The anion component represented by formula (3) is, for example, N(SO2C4F9)2 - 、N(SO2F)2 - ([FSI] - )、N(SO2CF3)2 - ([TFSI] - ) or N(SO2C2F5)2 - From the viewpoint of improving the ion conductivity of the lithium ion secondary battery 1, the anion component of the ionic liquid more preferably contains (SO2C4F9)2 - ,CF3SO2O - ,[FSI] - ,[TFSI] - and N(SO2C2F5)2 - At least one of, more preferably including [FSI] - .

[0077] The cationic component of the ionic liquid is not particularly limited, but is preferably at least one selected from the group consisting of a chain quaternary onium cation, a piperidinium cation, a pyrrolidinium cation, a pyridinium cation, and an imidazolium cation.

[0078] The chain quaternary onium cation is, for example, a compound represented by the following formula (4).

[0079] [Chemical Formula 2]

[0080]

[0081] [Wherein, in formula (4), R 31 to R 34Each independently represents a chain alkyl group having 1 to 20 carbon atoms or RO-(CH2) n - (wherein R represents a methyl group or an ethyl group, and n represents an integer from 1 to 4), and X represents a nitrogen atom or a phosphorus atom. 31 to R 34 The number of carbon atoms in the alkyl group represented is preferably 1 to 20, more preferably 1 to 10, still more preferably 1 to 5].

[0082] The piperidinium cation is a nitrogen-containing six-membered cyclic compound represented by, for example, the following formula (5).

[0083] [Chemical Formula 3]

[0084]

[0085] [Wherein, in formula (5), R 35 and R 36 Each independently represents an alkyl group having 1 to 20 carbon atoms or a radical consisting of RO-(CH2) n -(wherein R represents a methyl group or an ethyl group, and n represents an integer from 1 to 4). 35 and R 36 The number of carbon atoms in the alkyl group represented is preferably 1 to 20, more preferably 1 to 10, still more preferably 1 to 5].

[0086] The pyrrolidinium cation is, for example, a five-membered cyclic compound represented by the following formula (6).

[0087] [Chemical Formula 4]

[0088]

[0089] [Wherein, in formula (6), R 37 and R 38 Each independently represents an alkyl group having 1 to 20 carbon atoms or a radical consisting of RO-(CH2) n -(wherein R represents a methyl group or an ethyl group, and n represents an integer from 1 to 4). 37 and R 38 The number of carbon atoms in the alkyl group represented is preferably 1 to 20, more preferably 1 to 10, still more preferably 1 to 5].

[0090] The pyridinium cation is, for example, a compound represented by the following formula (7).

[0091] [Chemical Formula 5]

[0092]

[0093] [Wherein, in formula (7), R39 to R 43 Each independently is an alkyl group having 1 to 20 carbon atoms or a radical consisting of RO-(CH2) n - (wherein R represents a methyl group or an ethyl group, and n represents an integer from 1 to 4), or a hydrogen atom. 39 to R 43 The number of carbon atoms in the alkyl group represented is preferably 1 to 20, more preferably 1 to 10, still more preferably 1 to 5].

[0094] The imidazolium cation is, for example, a compound represented by the following formula (8).

[0095] [Chemical Formula 6]

[0096]

[0097] [Wherein, in formula (8), R 44 to R 48 Each independently represents an alkyl group having 1 to 20 carbon atoms or a radical consisting of RO-(CH2) n - (wherein R represents a methyl group or an ethyl group, and n represents an integer from 1 to 4), or a hydrogen atom. 44 to R 48 The number of carbon atoms in the alkyl group represented is preferably 1 to 20, more preferably 1 to 10, still more preferably 1 to 5].

[0098] More specifically, the ionic liquid may be N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(trifluoromethanesulfonyl)imide (DEME-TFSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(fluorosulfonyl)imide (DEME-FSI), 1-ethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide (EMI-FSI), or I), N-methyl-N-propylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py13-TFSI), N-methyl-N-propylpyrrolidinium-bis(fluorosulfonyl)imide (Py13-FSI), N-ethyl-N-methylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py12-TFSI), N-ethyl-N-methylpyrrolidinium-bis(fluorosulfonyl)imide (Py12-FSI) and 1-ethyl-3-methylimidazolium-dicyanamide (EMI-DCA), etc.

[0099] In the glyme represented by the above formula (2), R in the formula (2) 21 and R 22Each independently represents an alkyl group having 4 or fewer carbon atoms or a fluoroalkyl group having 4 or fewer carbon atoms, and k represents an integer from 1 to 6. R 21 and R 22 are each independently preferably methyl or ethyl.

[0100] Glycol dimethyl ether can specifically be monoglycol dimethyl ether (k = 1), diglycol dimethyl ether (k = 2), triglycol dimethyl ether (k = 3), tetraethylene glycol dimethyl ether (k = 4), pentaethylene glycol dimethyl ether (k = 5), or hexaethylene glycol dimethyl ether (k = 6).

[0101] When the separation membrane 7 contains glycol dimethyl ether as a solvent, part or all of the glycol dimethyl ether can form a complex with a lithium salt (the third lithium salt).

[0102] In order to obtain a separation membrane 7 with excellent separation ability for solvents (the first solvent and the second solvent), based on the total amount of the separation membrane, the content of the third solvent is 40% by mass or less. From the same perspective, based on the total amount of the separation membrane, the content of the third solvent can be 38% by mass or less, 35% by mass or less, 33% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 18% by mass or less, 15% by mass or less, 13% by mass or less, or 10% by mass or less. From the perspective of further improving the ion conductivity of the separation membrane 7, based on the total amount of the separation membrane, the content of the third solvent is 5% by mass or more, 8% by mass or more, 18% by mass or more, or 27% by mass or more.

[0103] The separation membrane 7 may further contain inorganic oxide particles. Thereby, the ion conductivity of the separation membrane 7 can be made more excellent.

[0104] The inorganic oxide particles can be, for example, particles of Li2O, Al2O3, TiO2, GeO2, SiO2, or P2O5. The inorganic oxide particles can be those having a main crystal phase of Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1, preferably 0 ≤ x ≤ 0.4, 0 < y ≤ 0.6, more preferably 0.1 ≤ x ≤ 0.3, 0.1 < y ≤ 0.4). The inorganic oxide particles can be used alone or in combination of two or more types.

[0105] The average particle size of the inorganic oxide particles can be 2 μm or more, 10 μm or more, or 50 μm or more, and 250 μm or less, 180 μm or less, or 100 μm or less. The average particle size of the inorganic oxide particles is measured by measuring the particle size distribution with a laser diffraction type particle size distribution measuring device.

[0106] From the perspective of further improving the ion conductivity of the separation membrane 7, the content of the inorganic oxide particles is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the total amount of the separation membrane. From the perspective of further improving the separation capacity of the separation membrane 7, the content of the inorganic oxide particles is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0107] From the perspective of further improving the separation capacity of the separation membrane 7, the thickness of the separation membrane 7 is preferably 100 μm or more, 200 μm or more, or 500 μm or more. From the perspective of improving the energy density of the separation membrane 7, the thickness of the separation membrane 7 is preferably 800 μm or less, 600 μm or less, or 400 μm or less.

[0108] Next, a method for manufacturing the lithium-ion secondary battery 1 will be described. The method for manufacturing the lithium-ion secondary battery 1 according to one embodiment includes the following steps: obtaining a positive electrode 6 comprising a positive electrode mixture layer 10 containing a positive electrode active material, a first lithium salt, and a first solvent; obtaining a negative electrode 8 comprising a negative electrode mixture layer 12 containing a negative electrode active material, a second lithium salt, and a second solvent different from the first solvent; forming a slurry containing a polymerizable compound capable of forming a polymer having lithium ion conductivity, a third lithium salt, and a third solvent into a film form; polymerizing the polymerizable compound to obtain a separator 7; and providing the separator 7 between the positive electrode 6 and the negative electrode 8. The order of each step is arbitrary.

[0109] In this manufacturing method, specific aspects of the positive electrode active material, the first lithium salt, the first solvent, the negative electrode active material, the second lithium salt, the second solvent, the third lithium salt, and the third solvent are as described above.

[0110] In the step of obtaining the positive electrode and the step of obtaining the negative electrode, the positive electrode 6 and the negative electrode 8 can be obtained using a known method. For example, the materials for the positive electrode mixture layer 10 or the negative electrode mixture layer 12 are dispersed in an appropriate amount of a dispersion medium using a kneader, a disperser, etc. to obtain a slurry-like positive electrode mixture or a negative electrode mixture. Then, the positive electrode mixture or the negative electrode mixture is applied to the positive electrode current collector 9 or the negative electrode current collector 11 by a doctor blade method, an immersion method, a spray method, etc., and the dispersion medium is volatilized to obtain the positive electrode 6 and the negative electrode 8. At this time, the dispersion medium may be water, N-methyl-2-pyrrolidone (NMP), etc.

[0111] In the step of obtaining the separation membrane, in one embodiment, a slurry containing a polymerizable compound capable of forming a polymer having lithium ion conductivity, a third lithium salt, and a third solvent is prepared. Specific embodiments of the polymer having lithium ion conductivity are as described above, and the polymerizable compound capable of forming a polymer having lithium ion conductivity (hereinafter also referred to as the "polymerizable compound") is a compound used to form the polymer.

[0112] Examples of polymerizable compounds include: alkyl (meth)acrylates such as methyl (meth)acrylate; polyalkylene glycol di(meth)acrylates such as polyethylene glycol di(meth)acrylate; (meth)acrylic acid; acrylamide; methacrylamide; N-isopropylacrylamide; methyl vinyl ketone; vinyl acetate; alkylene glycols such as ethylene glycol, propylene glycol and tetramethylene ether glycol, etc.

[0113] The polymerizable compound may be a compound having a cyclic ether group such as an epoxy group, an oxetane group, a tetrahydrofuran group, or a tetrahydropyran group on the side chain of (meth)acrylic acid, such as glycidyl (meth)acrylate and (3-ethyloxetane-3-yl)methyl (meth)acrylate. This polymerizable compound can be used to form a polymer represented by the above formula (1).

[0114] The content of the polymerizable compound in the slurry may be the same as the content of the polymer having lithium ion conductivity contained in the separation membrane 7 .

[0115] The content of the third solvent in the slurry is 40% by mass or less based on the total amount of the slurry. Therefore, the content of the third solvent contained in the separation membrane 7 can be set within the above range. Based on the total amount of the slurry, the content of the third solvent can be 38% by mass or less, 35% by mass or less, 33% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 18% by mass or less, 15% by mass or less, 13% by mass or less, or 10% by mass or less. From the perspective of further improving the ion conductivity of the separation membrane 7, the content of the third solvent can be 5% by mass or more, 8% by mass or more, 18% by mass or more, or 27% by mass or more based on the total amount of the slurry.

[0116] When the separation membrane 7 includes the inorganic oxide particles, the inorganic oxide particles may be added to the slurry. The content of the inorganic oxide particles in the slurry may be the same as the content of the inorganic oxide particles contained in the separation membrane 7 .

[0117] A polymerization initiator may be added to the slurry. This can advantageously polymerize the polymerizable compound and advantageously prepare a separation membrane from the slurry. The polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator and may be appropriately selected according to the purpose.

[0118] Examples of the thermal polymerization initiator include azobisisobutyronitrile and azobis(2-methylbutyronitrile).

[0119] Examples of the photopolymerization initiator include 2-hydroxy-2-methyl-1-phenylpropanone, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and the like.

[0120] The content of the polymerization initiator may be 0.5% by mass or more, 1% by mass or more, 10% by mass or more, or 20% by mass or more, and 50% by mass or less, 40% by mass or less, 30% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less, based on the total amount of the slurry.

[0121] In the step of obtaining the separation membrane, subsequently, the above-mentioned slurry is formed into the form of a membrane, and then the polymerizable compound is polymerized.

[0122] The slurry can be formed into a film by, for example, providing a frame of any size on one surface of a substrate such as a PET sheet and injecting the slurry therein. Alternatively, the slurry can be formed into a film by applying the slurry to one surface of the substrate by a doctor blade method, a dipping method, a spraying method, or the like.

[0123] The method for polymerizing the polymerizable compound is to heat the slurry under predetermined conditions when the slurry contains a thermal polymerization initiator. The heating temperature can be, for example, 80 to 90° C. The heating time can be appropriately adjusted according to the heating temperature, for example, 1 to 10 minutes.

[0124] The method of polymerizing the polymerizable compound is a method of irradiating light under predetermined conditions when the syrup contains a photopolymerization initiator. In one embodiment, the polymerizable compound can be polymerized by irradiating with light (ultraviolet light) having a wavelength in the range of 200 to 400 nm.

[0125] In the step of placing the separator 7 between the positive electrode 6 and the negative electrode 8, the positive electrode 6, the separator 7, and the negative electrode 8 are laminated, for example. Thus, the electrode group 2 including the positive electrode 6, the negative electrode 8, and the separator 7 placed between the positive electrode 6 and the negative electrode 8 can be obtained. Furthermore, the lithium ion secondary battery 1 can be obtained by housing the electrode group 2 in the battery outer packaging 3.

[0126] Example

[0127] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[0128] [Example 1]

[0129] A polymerizable compound represented by the following formula (9) (wherein n=14, product name: NK Ester A-600, purchased from Shin-Nakamura Chemical Co., Ltd.), a lithium salt (LiTFSI), a solvent (diethylene glycol dimethyl ether (diglyme)) and a thermal polymerization initiator (azobisisobutyronitrile) were mixed to prepare a slurry. The composition of each material is shown in Table 1 below. A silicone rubber frame (4 cm × 4 cm, thickness: 1 mm) was mounted on a PET sheet (8 cm × 8 cm, thickness: 0.035 mm), and the prepared slurry was placed in the frame. Then, the polymerizable compound was polymerized by heating at 80° C. for 3 minutes using a hot plate to obtain a separation membrane. The separation membrane was separated from the frame and used in the test shown below.

[0130] [Chemical Formula 7]

[0131]

[0132] [Examples 2 to 3]

[0133] A separation membrane was manufactured in the same manner as in Example 1, except that the heating conditions of the slurry were changed as shown in Table 1 below.

[0134] [Example 4]

[0135] A separation membrane was manufactured in the same manner as in Example 1, except that the composition of the slurry and the heating conditions were changed as shown in Table 1 below.

[0136] [Example 5]

[0137] A separation membrane was manufactured in the same manner as in Example 1, except that inorganic oxide particles (SiO 2 ) were added to the slurry and the heating conditions of the slurry were changed as shown in Table 1 below.

[0138] [Example 6]

[0139] A polymerizable compound represented by the following formula (9) (wherein n=14, product name: NK Ester A-600, purchased from Shin-Nakamura Chemical Co., Ltd.), a lithium salt (LiTFSI), a solvent (EMI-TFSI) and a thermal polymerization initiator (2-hydroxy-methyl-1-phenylpropanone) were mixed to prepare a slurry. The composition of each material is shown in Table 2 below. A silicone rubber frame (4 cm×4 cm, thickness: 1 mm) was mounted on a PET sheet (8 cm×8 cm, thickness: 0.035 mm), and the prepared slurry was placed in the frame. Then, the polymerizable compound was polymerized by ultraviolet light (wavelength: 365 nm) for 30 minutes to obtain a separation membrane. The separation membrane was separated from the frame and used in the test shown below.

[0140] [Examples 7 to 8]

[0141] A separation membrane was manufactured in the same manner as in Example 6, except that the composition of the slurry was changed as shown in Table 2 below.

[0142] [Comparative Example 1]

[0143] A separation membrane was manufactured in the same manner as in Example 1, except that the composition of the slurry and the heating conditions of the slurry were changed as shown in Table 2 below.

[0144] [Comparative Example 2]

[0145] A separation membrane was manufactured in the same manner as in Example 1, except that inorganic oxide particles (SiO 2 ) were added to the slurry.

[0146] <Solvent Content in Separation Membrane>

[0147] The separation membranes of Examples or Comparative Examples were diluted approximately 10-fold with methanol and extracted by ultrasonic irradiation for 15 minutes to obtain an extract. 1.0 μL of this extract was injected into a gas chromatograph to measure the solvent content of the separation membranes of Examples or Comparative Examples. The specific conditions for gas chromatography-mass spectrometry are as follows. The results are shown in Tables 1 and 2 below.

[0148] Equipment name: GC-4000 (manufactured by GL Science)

[0149] Carrier gas: Helium 5.0mL / min

[0150] Column: TC-WAX polyethylene glycol (0.53 mm ID x 30 m, 1.0 μL)

[0151] Split ratio: 1 / 10

[0152] Injection temperature: 250℃

[0153] Detection temperature: 250℃

[0154] Oven temperature: heating from 60°C to 240°C at 20°C / min (1 minute)

[0155] Detector: Spark Ionization Detector (FID)

[0156] Range: 10 2

[0157] <Evaluation of Solvent Partitioning Ability>

[0158] The separation membrane and the diaphragm (UP3085, purchased from Ube industries Ltd.) of the embodiment or comparative example were overlapped and sandwiched between two silicone rubber sheets (thickness: 0.5 mm) placed between H-type batteries. Dimethyl carbonate (DMC) was placed in the battery on one side of the separation membrane, and the appearance of the separation membrane was observed with the naked eye after a predetermined number of days. If the separation membrane has excellent solvent separation ability, DMC hardly penetrates the separation membrane, which makes it difficult for DMC to penetrate the diaphragm. However, if the separation membrane is poor in solvent separation ability, DMC will penetrate the separation membrane and penetrate into the diaphragm. Therefore, by observing the appearance of the diaphragm and confirming whether DMC penetrates the diaphragm, the separation ability of the solvent (corresponding to the first solvent and the second solvent) of the separation membrane can be evaluated. If DMC does not penetrate the diaphragm even after one day from the start of the test, it is expressed as "≥1 day" in the following Tables 1 and 2. In this case, it can be said that the solvent separation ability of the separation membrane is excellent.

[0159] <Evaluation of ion conductivity>

[0160] Test cells were fabricated using the separation membranes of Examples and Comparative Examples to evaluate the ion conductivity of the separation membranes. First, an upper cover (CR2032 cap, purchased from Hohsen Corp.), a 1.6 mm thick leaf spring, two 1.0 mm thick SUS gaskets, a separator, a gasket, and a lower cover (CR2032 cartridge, purchased from Hohsen Corp.) were stacked in this order. The upper and lower covers were plugged together to create a test cell, and the bulk resistance of the separation membrane was measured. The measurement equipment and conditions were as follows.

[0161] Measurement equipment: VSP electrochemical measurement system (purchased from Biologic)

[0162] Measurement temperature: 25℃

[0163] AC amplitude: 10mV

[0164] Frequency range: 10mHz to 1MHz

[0165] After the measurement, the ion conductivity of the separation membrane was calculated according to the following formula (α).

[0166] The results are shown in Tables 1 and 2 below.

[0167] σ=L / RA(α)

[0168] σ(S / cm): ionic conductivity

[0169] L (cm): separation membrane thickness

[0170] R(ω): Bulk resistance

[0171] A(cm 2): Cross-sectional area of ​​SUS gasket

[0172] [Table 1]

[0173]

[0174] [Table 2]

[0175]

[0176] As shown in Tables 1 and 2, the separation membranes of Examples had excellent solvent partitioning capabilities. On the other hand, since the separation membranes of Comparative Examples could not be formed into a membrane form, the performance of the separation membranes could not be evaluated.

[0177] [Explanation of Reference Numerals]

[0178] 1. Lithium-ion secondary battery 2. Electrode assembly

[0179] 3. Battery outer packaging 4. Positive electrode current collector tab

[0180] 5. Negative electrode current collector tab 6. Positive electrode

[0181] 7. Separation membrane 8. Negative electrode

[0182] 9. Positive electrode current collector 10. Positive electrode mixture layer

[0183] 11. Negative electrode current collector 12. Negative electrode mixture layer

Claims

1. A lithium-ion secondary battery comprising, in order, a positive electrode mixture layer, a separator, and a negative electrode mixture layer, wherein: The positive electrode mixture layer comprises a positive electrode active material, a first lithium salt and a first solvent; The negative electrode mixture layer includes a negative electrode active material, a second lithium salt, and a second solvent different from the first solvent; The separation membrane includes a polymer having lithium ion conductivity, a third lithium salt, and a third solvent, and the separation membrane functions to separate the first solvent and the second solvent contained in the positive electrode mixture layer and the negative electrode mixture layer from each other and prevent them from mixing with each other; The content of the third solvent is 11% by mass or more and 40% by mass or less based on the total amount of the separation membrane; and The first solvent includes acetonitrile or ethylene carbonate, The second solvent includes γ-butyrolactone or tetrahydrofuran, The third solvent includes N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(trifluoromethanesulfonyl)imide (DEME-TFSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(fluorosulfonyl)imide (DEME-FSI), 1-ethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide (EMI-FSI), N-methyl- an ionic liquid of N-propylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py13-TFSI), N-methyl-N-propylpyrrolidinium-bis(fluorosulfonyl)imide (Py13-FSI), N-ethyl-N-methylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py12-TFSI), N-ethyl-N-methylpyrrolidinium-bis(fluorosulfonyl)imide (Py12-FSI), or 1-ethyl-3-methylimidazolium-dicyanamide (EMI-DCA), or glyme, and The polymer having lithium ion conductivity is a polymer represented by the following Chemical Formula 1: [Chemical Formula 1] In Chemical Formula 1, R 11 represents a straight chain or branched alkylene or a single bond, R 12 represents a linear or branched alkylene group, and r represents an integer of 2 or greater.

2. The lithium-ion secondary battery according to claim 1, wherein: The content of the third solvent is 17% by mass or more and 35% by mass or less based on the total amount of the separation membrane.

3. The lithium ion secondary battery according to claim 1 or 2, wherein: The separation membrane further comprises inorganic oxide particles.

4. Use of a separator in a lithium-ion secondary battery, wherein the lithium-ion secondary battery comprises a positive electrode mixture layer containing a positive electrode active material, a first lithium salt, and a first solvent, and a negative electrode mixture layer containing a negative electrode active material, a second lithium salt, and a second solvent different from the first solvent, wherein the separator is disposed between the positive electrode mixture layer and the negative electrode mixture layer. in, The separation membrane includes a polymer having lithium ion conductivity, a third lithium salt, and a third solvent, and the separation membrane functions to separate the first solvent and the second solvent contained in the positive electrode mixture layer and the negative electrode mixture layer from each other and prevent them from mixing with each other; The content of the third solvent is 11% by mass or more and 40% by mass or less based on the total amount of the separation membrane. The first solvent includes acetonitrile or ethylene carbonate, The second solvent includes γ-butyrolactone or tetrahydrofuran, The third solvent includes N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(trifluoromethanesulfonyl)imide (DEME-TFSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(fluorosulfonyl)imide (DEME-FSI), 1-ethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide (EMI-FSI), N-methyl- an ionic liquid of N-propylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py13-TFSI), N-methyl-N-propylpyrrolidinium-bis(fluorosulfonyl)imide (Py13-FSI), N-ethyl-N-methylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py12-TFSI), N-ethyl-N-methylpyrrolidinium-bis(fluorosulfonyl)imide (Py12-FSI), or 1-ethyl-3-methylimidazolium-dicyanamide (EMI-DCA), or glyme, and The polymer having lithium ion conductivity is a polymer represented by the following Chemical Formula 1: [Chemical Formula 1] In Chemical Formula 1, R 11 represents a straight chain or branched alkylene or a single bond, R 12 represents a linear or branched alkylene group, and r represents an integer of 2 or greater.

5. The use according to claim 4, wherein: The content of the third solvent is 17% by mass or more and 35% by mass or less based on the total amount of the separation membrane.

6. The use according to claim 4 or 5, further comprising inorganic oxide particles.

7. A method for manufacturing a lithium ion secondary battery, the method comprising the following steps: obtaining a positive electrode comprising a positive electrode mixture layer, the positive electrode mixture layer comprising a positive electrode active material, a first lithium salt, and a first solvent; obtaining a negative electrode including a negative electrode mixture layer, the negative electrode mixture layer including a negative electrode active material, a second lithium salt, and a second solvent different from the first solvent; forming a slurry containing a polymerizable compound capable of forming a polymer having lithium ion conductivity, a third lithium salt, and a third solvent into a membrane form, and then polymerizing the polymerizable compound to obtain a separation membrane; as well as The separation membrane is provided between the positive electrode and the negative electrode, and the separation membrane functions to separate the first solvent and the second solvent contained in the positive electrode mixture layer and the negative electrode mixture layer from each other and prevent them from mixing with each other; wherein the content of the third solvent is greater than or equal to 11% by mass and less than or equal to 40% by mass based on the total amount of the slurry; and The first solvent includes acetonitrile or ethylene carbonate, The second solvent includes γ-butyrolactone or tetrahydrofuran, The third solvent includes N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(trifluoromethanesulfonyl)imide (DEME-TFSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(fluorosulfonyl)imide (DEME-FSI), 1-ethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide (EMI-FSI), N-methyl- an ionic liquid of N-propylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py13-TFSI), N-methyl-N-propylpyrrolidinium-bis(fluorosulfonyl)imide (Py13-FSI), N-ethyl-N-methylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py12-TFSI), N-ethyl-N-methylpyrrolidinium-bis(fluorosulfonyl)imide (Py12-FSI), or 1-ethyl-3-methylimidazolium-dicyanamide (EMI-DCA), or glyme, and The polymer having lithium ion conductivity is a polymer represented by the following Chemical Formula 1: [Chemical Formula 1] In Chemical Formula 1, R 11 represents a straight chain or branched alkylene or a single bond, R 12 represents a linear or branched alkylene group, and r represents an integer of 2 or greater.

8. The manufacturing method according to claim 7, wherein: The content of the third solvent is 17% by mass or more and 35% by mass or less based on the total amount of the slurry.

9. The manufacturing method according to claim 7 or 8, wherein: The slurry also includes inorganic oxide particles.

10. A method for producing a separator provided between a positive electrode mixture layer and a negative electrode mixture layer in a lithium ion secondary battery, the lithium ion secondary battery comprising a positive electrode mixture layer containing a positive electrode active material, a first lithium salt, and a first solvent, and a negative electrode mixture layer containing a negative electrode active material, a second lithium salt, and a second solvent different from the first solvent, the method comprising: forming a slurry into a film form, the slurry containing a polymerizable compound capable of forming a polymer having lithium ion conductivity, a third lithium salt, and a third solvent, and then polymerizing the polymerizable compound to obtain a separator membrane, the separator membrane having a function of separating the first solvent and the second solvent contained in the positive electrode mixture layer and the negative electrode mixture layer from each other and preventing them from mixing with each other, wherein the content of the third solvent is greater than or equal to 11% by mass and less than or equal to 40% by mass based on the total amount of the slurry; and The first solvent includes acetonitrile or ethylene carbonate, The second solvent includes γ-butyrolactone or tetrahydrofuran, The third solvent includes N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(trifluoromethanesulfonyl)imide (DEME-TFSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(fluorosulfonyl)imide (DEME-FSI), 1-ethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide (EMI-FSI), N-methyl- an ionic liquid of N-propylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py13-TFSI), N-methyl-N-propylpyrrolidinium-bis(fluorosulfonyl)imide (Py13-FSI), N-ethyl-N-methylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (Py12-TFSI), N-ethyl-N-methylpyrrolidinium-bis(fluorosulfonyl)imide (Py12-FSI), or 1-ethyl-3-methylimidazolium-dicyanamide (EMI-DCA), or glyme, and The polymer having lithium ion conductivity is a polymer represented by the following Chemical Formula 1: [Chemical Formula 1] In Chemical Formula 1, R 11 represents a straight chain or branched alkylene or a single bond, R 12 represents a linear or branched alkylene group, and r represents an integer of 2 or greater.

11. The manufacturing method according to claim 10, wherein: The content of the third solvent is 17% by mass or more and 35% by mass or less based on the total amount of the slurry.

12. The manufacturing method according to claim 10 or 11, wherein: The slurry also includes inorganic oxide particles.

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