Lithium ion secondary battery, separation membrane and method for producing these

Abstract

To provide a separation membrane which is used in a lithium ion secondary battery containing different solvents in a positive electrode mixture layer and a negative electrode mixture layer, and has high ion conductivity, a lithium ion secondary battery having the separation membrane, and a method for producing them.SOLUTION: A lithium ion secondary battery includes a positive electrode mixture layer, a separation membrane, and a negative mixture layer in this order. The positive electrode mixture layer contains a positive electrode active substance, a first lithium salt, and a first solvent. The negative electrode mixture layer contains a negative electrode active substance, a second lithium salt, and a second solvent different from the first solvent. The separation membrane contains a polymer having lithium ion conductivity, a third lithium salt and a third solvent. The polymer is a polymer of a polymerizable component containing a monomer and a thiol compound.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lithium ion secondary battery, a separator, and methods for producing the same. [Background technology]

[0002] In recent years, with the spread of portable electronic devices, electric vehicles, etc., further improvements in the performance of secondary batteries, such as lithium-ion secondary batteries, are being demanded. For example, studies have been conducted to improve the performance of lithium-ion secondary batteries by incorporating different types of electrolytes into the positive electrode and the negative electrode (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-110447 Summary of the Invention [Problem to be solved by the invention]

[0004] In a lithium-ion secondary battery in which different types of electrolytes are contained in the positive and negative electrodes, it is important that the solvents contained in the electrolytes are sufficiently separated without mixing between the positive and negative electrodes. The inventors have considered disposing a separator between the positive and negative electrodes to separate the solvents in the electrolyte in such a lithium-ion secondary battery. It is desirable that the separator used for such purposes has high ionic conductivity.

[0005] One aspect of the present invention aims to provide a separator having high ionic conductivity, which is used in a lithium ion secondary battery containing different solvents in a positive electrode mixture layer and a negative electrode mixture layer, a lithium ion secondary battery including the separator, and methods for manufacturing the separator and the lithium ion secondary battery. [Means for solving the problem]

[0006] One aspect of the present invention provides a lithium ion secondary battery comprising a positive electrode mixture layer, a separator, and a negative electrode mixture layer in this order, 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 contains a polymer having lithium ion conductivity, a third lithium salt, and the third solvent, and the polymer is a polymer of a polymerizable component including a monomer and a thiol compound.

[0007] Another aspect of the present invention provides a separator membrane to be disposed between the positive electrode mixture layer and the negative electrode mixture layer in a 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 separator membrane containing a polymer having lithium ion conductivity, a third lithium salt, and a third solvent, the polymer being a polymer of a polymerizable component including a monomer and a thiol compound.

[0008] Another aspect of the present invention provides a method for manufacturing a lithium-ion secondary battery, the method comprising: obtaining a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a first lithium salt, and a first solvent; obtaining a negative electrode having a negative electrode mixture layer 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 component including a monomer and a thiol compound, a third lithium salt, and the third solvent into a membrane and then reacting the polymerizable component to obtain a separation membrane; and providing the separation membrane between the positive electrode and the negative electrode.

[0009] Another aspect of the present invention provides a method for producing a separator to be disposed between a positive electrode mixture layer and a negative electrode mixture layer in a 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 includes a step of forming a slurry containing a polymerizable component including a monomer and a thiol compound, a third lithium salt, and the third solvent into a membrane, and then reacting the polymerizable component to obtain the separation membrane.

[0010] In each aspect, the thiol compound may have two or more thiol groups.

[0011] In each aspect, the monomers may include a first monomer having two (meth)acryloyl groups and a second monomer having three or more (meth)acryloyl groups. [Effects of the Invention]

[0012] According to one aspect of the present invention, it is possible to provide a separator membrane having high ionic conductivity, which is used in a lithium ion secondary battery containing different solvents in the positive electrode mixture layer and the negative electrode mixture layer, a lithium ion secondary battery including the separator membrane, and methods for manufacturing the same. According to one aspect of the present invention, it is possible to form a separator membrane in a shorter time. According to one aspect of the present invention, a method for manufacturing a separator membrane with improved productivity is provided. Because the separation membrane according to one aspect of the present invention has excellent membrane formability, it is less subject to limitations on the equipment used during membrane formation, and allows for more stable production of separation membranes with larger areas. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view showing a lithium ion secondary battery according to one embodiment; [Figure 2] 2 is an exploded perspective view showing one embodiment of an electrode group in the lithium ion secondary battery shown in FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiments. In the following embodiments, it goes without saying that the components (including element steps, etc.) are not necessarily essential unless otherwise specified or considered to be clearly essential in principle. The same applies to numerical values ​​and ranges, and they should not be construed as unduly limiting the present invention.

[0015] In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. When referring to the amount of each component in a composition in this specification, if there are multiple substances corresponding to each component in the composition, the total amount of those multiple substances present in the composition is meant unless otherwise specified.

[0016] In this specification, (meth)acrylic acid means acrylic acid or its corresponding methacrylic acid. The same applies to other similar expressions such as (meth)acrylate.

[0017] FIG. 1 is a perspective view showing a lithium-ion secondary battery according to one embodiment. As shown in FIG. 1, the lithium-ion secondary battery 1 according to one embodiment is a so-called laminate-type secondary battery including an electrode group 2 and a bag-shaped battery exterior 3 that houses the electrode group 2. The electrode group 2 is provided with a positive electrode current collector tab 4 and a negative electrode current collector tab 5. The positive electrode current collector tab 4 and the negative electrode current collector tab 5 protrude from the inside to the outside of the battery exterior 3 so that the positive electrode current collector and the negative electrode current collector (described in detail below) can be electrically connected to the outside of the lithium-ion secondary battery 1, respectively. In another embodiment, the lithium-ion secondary battery 1 may have a shape other than a laminate shape (such as a coin shape or a cylindrical shape).

[0018] The battery outer casing 3 may be a container formed of, for example, a laminated film. The laminated film may be 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 this order.

[0019] FIG. 2 is an exploded perspective view showing one embodiment of the electrode group 2 in the lithium-ion secondary battery 1 shown in FIG. 1. As shown in FIG. 2, the electrode group 2 according to this embodiment includes a positive electrode 6, a separator 7, and a negative electrode 8, in this order. The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 provided on the positive electrode current collector 9. A positive electrode current collector tab 4 is provided 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 provided on the negative electrode current collector 11. A negative electrode current collector tab 5 is provided on the negative electrode current collector 11.

[0020] The positive electrode current collector 9 is formed of, for example, aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, conductive glass, etc. The thickness of the positive electrode current collector 9 may be, for example, 1 μm or more and 50 μm or less.

[0021] The negative electrode current collector 11 is formed of, for example, copper, stainless steel, nickel, aluminum, titanium, baked 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.

[0022] In one embodiment, the positive electrode mixture layer 10 contains a positive electrode active material, a lithium salt (first lithium salt), and a solvent (first solvent).

[0023] 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 yNi 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 the group consisting of 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), and x = 0 to 1.2, y = 0 to 0.9, and z = 2.0 to 2.3). x Ni 1-y M y O z Lithium oxide represented by Li x Ni 1-(y1+y2) Co y1 Mn y2 O z (where x and z are the same as those described above, y1=0 to 0.9, y2=0 to 0.9, and y1+y2=0 to 0.9), 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 O 2、 LiNi 0.8 Co 0.1 Mn 0.1 It may be O2. x Ni 1-y M y O z Lithium oxide represented by Li x Ni 1-(y3+y4) Co y3 Al y4 O z (where x and z are the same as those described above, y3 = 0 to 0.9, y4 = 0 to 0.9, and y3 + y4 = 0 to 0.9), for example, LiNi0.8 Co 0.15 Al 0.05 It may also be O2.

[0024] The positive electrode active material may be a lithium phosphate, such as lithium manganese phosphate (LiMnPO), lithium iron phosphate (LiFePO), lithium cobalt phosphate (LiCoPO), and lithium vanadium phosphate (LiV(PO)).

[0025] The content of the positive electrode active material may be 70 mass % or more, 80 mass % or more, or 85 mass % or more based on the total amount of the positive electrode mixture layer, and 95 mass % or less, 92 mass % or less, or 90 mass % or less based on the total amount of the positive electrode mixture layer.

[0026] The first lithium salt may be, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, CF3SO2OLi, LiN(SO2F)2 (LiFSI, lithium bisfluorosulfonylimide), LiN(SO2CF3)2 (LiTFSI, lithium bistrifluoromethanesulfonylimide), and LiN(SO2CF2CF3)2.

[0027] 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 may be 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.

[0028] 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, vinylethylene 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-hexanolactone; ethers such as tetrahydrofuran, 1,3-dioxane, dimethoxyethane, diethoxyethane, methoxyethoxyethane, glyme, diglyme, triglyme, and tetraglyme; phosphate esters such as phosphate triesters; nitriles such as acetonitrile, benzonitrile, adiponitrile, and glutaronitrile; chain sulfones such as dimethyl sulfone and diethyl sulfone; cyclic sulfones such as sulfolane; and cyclic sulfonate esters such as propane sultone. The first solvent may be used alone or in combination of two or more.

[0029] A solvent preferably used as the first solvent is a solvent with excellent oxidation resistance, such as acetonitrile, ethylene carbonate, etc. This can enhance the oxidation resistance of the positive electrode mixture layer 10.

[0030] The content of the first solvent contained in the positive electrode mixture layer 10 can be set appropriately within a range in which the first lithium salt can be dissolved, and may be, for example, 10 mass % or more and 80 mass % or less based on the total amount of the positive electrode mixture layer.

[0031] The positive electrode mixture layer 10 may further contain a binder and a conductive material as other components.

[0032] The binder may be a polymer containing at least one selected from the group consisting of tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, acrylic acid, maleic acid, ethyl methacrylate, methyl methacrylate, and acrylonitrile as a monomer unit, or a rubber such as styrene-butadiene rubber, isoprene rubber, or acrylic rubber. The binder is preferably polyvinylidene fluoride or a copolymer containing hexafluoropropylene and vinylidene fluoride as monomer units.

[0033] The content of the binder may be 0.3% by mass or more, 0.5% by mass or more, 1% by mass or more, or 1.5% by mass or more, based on the total amount of the positive electrode mixture layer, and may be 10% by mass or less, 8% by mass or less, 6% by mass or less, or 4% by mass or less.

[0034] The conductive material may be a carbon material such as carbon black, acetylene black, graphite, carbon fiber, carbon nanotube, etc. These conductive materials may be used alone or in combination of two or more.

[0035] 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 viewpoint of suppressing an increase in the volume of the positive electrode 6 and an accompanying 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.

[0036] 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 may be 100 μm or less, 80 μm or less, 70 μm or less, or 50 μm or less.

[0037] In one embodiment, the negative electrode mixture layer 12 contains a negative electrode active material, a lithium salt (second lithium salt), and a solvent (second solvent).

[0038] The negative electrode active material can be a material commonly used in the field of energy devices. Specific examples of the negative electrode active material include metallic lithium and lithium titanate (Li4Ti5O 12 ), lithium alloys or other metal compounds, carbon materials, metal complexes, organic polymer compounds, etc. These negative electrode active materials may be used singly or in combination of two or more. Examples of carbon materials include graphite such as natural graphite (e.g., flake graphite) and artificial graphite, amorphous carbon, carbon fiber, and carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. From the viewpoint of obtaining a larger theoretical capacity (e.g., 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, etc. Among these, the negative electrode active material may be a negative electrode active material containing silicon as a constituent element.

[0039] The negative electrode active material containing silicon as a constituent element may be an alloy containing silicon as a constituent element, for example, an alloy containing silicon and at least one element selected from the group consisting of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as constituent elements. The negative electrode active material containing silicon as a constituent element may be an oxide, nitride, or carbide, specifically, for example, silicon oxides such as SiO, SiO, and LiSiO, silicon nitrides such as SiN and SiN0, and silicon carbides such as SiC.

[0040] The content of the negative electrode active material may be 60% by mass or more, 65% by mass or more, or 70% by mass or more, based on the total amount of the negative electrode mixture layer, and 99% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total amount of the negative electrode mixture layer.

[0041] The type and content of the second lithium salt may be the same as those of the first lithium salt contained in the above-described positive electrode mixture layer 10. The second lithium salt may be the same type as or different from the first lithium salt.

[0042] The second solvent is a solvent for dissolving the second lithium salt. The second solvent may be the same as the first solvent described above, but may be different from the first solvent. This allows suitable solvents to be used for the positive electrode 6 and the negative electrode 8, respectively, thereby improving various performances of the lithium-ion secondary battery 1, such as energy density and lifespan.

[0043] The second solvent is preferably a solvent with excellent reduction resistance, such as γ-butyrolactone, tetrahydrofuran, etc. This can prevent the second solvent contained in the negative electrode mixture layer 12 from being reductively decomposed.

[0044] The content of the second solvent contained in the negative electrode mixture layer 12 can be set appropriately within a range in which the second lithium salt can be dissolved, and may be, for example, 10 mass % or more and 80 mass % or less based on the total amount of the negative electrode mixture layer.

[0045] The negative electrode mixture layer 12 may further contain a binder and a conductive material as other components. The types and contents of the binder and conductive material may be the same as those of the binder and conductive material in the positive electrode mixture layer 10 described above.

[0046] 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 may be 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.

[0047] The separation membrane 7 is a separation membrane to be disposed between the positive electrode mixture layer 10 and the negative electrode mixture layer 12 in the lithium-ion secondary battery 1. This separation membrane 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 with each other. Lithium ions can be exchanged through the separation membrane 7.

[0048] Separation membrane 7 contains a lithium ion conductive polymer, a lithium salt (third lithium salt), and a solvent (third solvent). The lithium ion conductive polymer is a polymer of polymerizable components including a monomer and a thiol compound.

[0049] A polymer having lithium ion conductivity means a polymer that has the property of being able to conduct lithium ions derived from a lithium salt in the presence of the lithium salt. Whether a polymer can conduct lithium ions or not can be confirmed by measuring the ionic conductivity of the polymer. When 1 to 40 mass % of a lithium salt is added to the polymer, the peak of the ionic conductivity measured is 1×10 -6 If the value is S / cm or more, the polymer can be said to have lithium ion conductivity.

[0050] The lithium ion conductive polymer may be a polymer having at least one group selected from the group consisting of a carbonyl group and an ether group, which includes a chain ether group and a cyclic ether group.

[0051] 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.

[0052] The monomers in the polymerizable component may include a first monomer having two (meth)acryloyl groups and a second monomer having three or more (meth)acryloyl groups, which allows for the formation of a thinner separation membrane with lower resistance.

[0053] The first monomer is a compound having two (meth)acryloyl groups and a linking group connecting the two (meth)acryloyl groups. The linking group may contain a hydrocarbon group and / or a heteroatom-containing group. The linking group may contain an oxygen atom-containing group as the heteroatom-containing group, for example, an ether group (-O-). The linking group may be a divalent group consisting of a hydrocarbon group (e.g., an alkylene group) and a heteroatom-containing group (e.g., an ether group), for example, a polyoxyalkylene group or an oxyalkylene group.

[0054] The first monomer may be a monomer represented by the following formula (1-1). [ka]

[0055] In formula (1-1), R 11 and R 12 each independently represents a hydrogen atom or a methyl group (-CH3).

[0056] n represents an integer of 1 or greater. n may be, for example, 5 or greater, 10 or greater, 15 or greater, or 20 or greater, or may be 40 or less, 35 or less, 30 or less, or 25 or less.

[0057] Z 11 represents an alkylene group. 11 may be, for example, an alkylene group having 1 to 6 or 1 to 3 carbon atoms. 11 may be, for example, -CH2-CH2-, -CH(CH3)-CH2-.

[0058] The ionic conductivity of the first monomer at 25°C may be, for example, 0.01 mS / cm or more, 0.05 mS / cm or more, or 0.10 mS / cm or more, and may be 1.0 mS / cm or less, 0.50 mS / cm or less, or 0.30 mS / cm or less.

[0059] The ionic conductivity of the first monomer at 25° C. can be measured by the following method. <Preparation of separation membrane for measuring ionic conductivity> A first monomer, a lithium salt, a solvent, and a photopolymerization initiator are mixed to prepare a slurry. A silicone rubber frame (4 x 4 cm, 1 mm thick) is placed on a PET sheet (8 x 8 cm, 0.035 mm thick), and the prepared slurry is placed in the frame. The first monomer is then polymerized by irradiating it with ultraviolet light (365 nm wavelength) to obtain a separation membrane. The separation membrane is removed from the frame and subjected to the following tests. The lithium salt may be LiN(SOCF) (LiTFSI, lithium bistrifluoromethanesulfonylimide). The solvent may be 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI). The photopolymerization initiator may be 2-hydroxy-2-methyl-1-phenylpropanone. The irradiation time with ultraviolet light (365 nm wavelength) may be 15 minutes. <Measurement of ionic conductivity> The ionic conductivity of the separation membrane is evaluated by preparing a test cell using the separation membrane. The top cover (CR2032 cap, manufactured by Hosen Co., Ltd.), a 1.6 mm thick leaf spring, two 1.0 mm thick SUS spacers, the separation membrane, a gasket, and a bottom cover (CR2032 case, manufactured by Hosen Co., Ltd.) are stacked in this order, and the top and bottom covers are crimped together to prepare a test cell. The measurement equipment and conditions are as follows: Measurement device: VSP electrochemical measurement system (manufactured by BioLogic) Measurement temperature: 25℃ AC amplitude: 10mV Frequency range: 10mHz to 1MHz After the measurement, the ionic conductivity of the separation membrane was calculated according to the following formula (α). σ=L / RA (α) σ (S / cm): ionic conductivity L (cm): thickness of the separation membrane R(Ω): bulk resistance A(cm 2 ): Cross-sectional area of ​​SUS spacer

[0060] Examples of the first monomer include polyethylene glycol #1000 diacrylate (for example, trade name: NK Ester A-1000, manufactured by Shin-Nakamura Chemical Co., Ltd.) and polyethylene glycol #800 diacrylate (for example, trade name: NK Ester A-800, manufactured by Shin-Nakamura Chemical Co., Ltd.).

[0061] The first monomer may be used alone or in combination of two or more.

[0062] The content of the first polymer contained as a monomer unit in the polymer may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, based on the total mass of the separation membrane, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less.

[0063] The second monomer is a monomer having three or more (meth)acryloyl groups. The number of (meth)acryloyl groups in the second monomer may be, for example, 3 to 6, 3 to 4, or 4.

[0064] The second monomer may be a compound having three or more (meth)acryloyl groups and a linking group connecting these (meth)acryloyl groups. The linking group may contain a hydrocarbon group and / or a heteroatom-containing group. The linking group may contain an oxygen atom-containing group as the heteroatom-containing group, for example, an ether group (-O-). The linking group may be a divalent group consisting of a hydrocarbon group (e.g., an alkylene group) and a heteroatom-containing group (e.g., an ether group), for example, a polyoxyalkylene group or an oxyalkylene group.

[0065] The second monomer having three (meth)acryloyl groups may be a monomer represented by the following formula (1-2). [ka]

[0066] In formula (1-2), R 13 , R 14 and R 15 each independently represents a hydrogen atom or a methyl group.

[0067] Z 2 , Z 3 and Z 4 each independently represents an alkylene group. 2 , Z 3 and Z 4 The alkylene group represented by the formula (I) may be an alkylene group having 1 to 6 or 1 to 3 carbon atoms, or may be a methylene group (-CH2-).

[0068] Z 5 represents an alkyl group. Z 5 may be, for example, an alkyl group having 1 to 10, 1 to 6, or 1 to 3 carbon atoms, or may be an ethyl group (-CH2-CH3). The monovalent hydrocarbon group represented by X may be, for example, an alkyl group.

[0069] An example of the second monomer having three (meth)acryloyl groups is trimethylolpropane triacrylate (for example, trade name: NK Ester A-TMPT, manufactured by Shin-Nakamura Chemical Co., Ltd.).

[0070] The second monomer having four (meth)acryloyl groups may be a monomer represented by the following formula (1-3). [ka]

[0071] In formula (1-3), R 16 , R 17 , R 18 and R 19each independently represents a hydrogen atom or a methyl group.

[0072] Z 6 , Z 7 , Z 8 and Z 9 each independently represents an alkylene group. 2 , Z 3 and Z 4 The alkylene group represented by the formula (I) may be an alkylene group having 1 to 6 or 1 to 3 carbon atoms, or may be an ethylene group (-CH2-CH2-).

[0073] a, b, c, and d each independently represent an integer of 0 or greater or 1. a+b+c+d may be 4 or greater, 10 or greater, 20 or greater, or 30 or greater, and may be 50 or less, or 40 or less.

[0074] An example of the second monomer having three (meth)acryloyl groups is ethoxylated pentaerythritol tetraacrylate (for example, trade name: NK Ester A-TM35E, manufactured by Shin-Nakamura Chemical Co., Ltd.).

[0075] The ionic conductivity of the second monomer at 25°C may be, for example, 0.001 mS / cm or more, or 0.01 mS / cm or more, and 0.5 mS / cm or less, or 0.05 mS / cm or less. The ionic conductivity of the second monomer at 25°C can be measured using the second monomer by the same method as the above-mentioned method for measuring the ionic conductivity of the first monomer at 25°C. In measuring the ionic conductivity of the second monomer at 25°C, the irradiation time of ultraviolet light (wavelength 365 nm) may be 2 minutes.

[0076] The second monomer may be used alone or in combination of two or more.

[0077] The content of the second polymer contained as a monomer unit in the polymer may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, based on the total mass of the separation membrane, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less.

[0078] The ratio (C2 / C1) of the mass (C2) of the second monomer to the mass (C1) of the first monomer contained as monomer units in the polymer may be 5 or less, 4 or less, 3 or less, 2 or less, 1 or less, or 1 / 2 or less, from the viewpoint of further reducing the resistance value of the separation membrane. The ratio (C2 / C1) of the mass (C2) of the second monomer to the mass (C1) of the first monomer contained as monomer units in the polymer may be 1 / 5 or more, 1 / 4 or more, 1 / 3 or more, 1 / 2 or more, 1 or more, or 2 or more, from the viewpoint of further improving the separation ability of the separation membrane.

[0079] The total content of monomers contained as monomer units may be 60% by mass or more, 70% by mass or more, or 80% by mass or more, and may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0080] A thiol compound is a compound that has at least one thiol group (-SH). A separation membrane containing a polymer formed by a polymerization reaction in the presence of a thiol compound has high ionic conductivity. In addition, when the polymerizable component contains a thiol compound, it becomes possible to form a membrane in a shorter time. There is no particular limitation as to why it becomes possible to form a membrane in a shorter time, but the following is thought to be the reason. A thiol compound steals a radical from a long-chain polymer whose reactivity has decreased during the polymerization reaction, and generates a thiyl radical (-S · Since the thiyl radicals can react with other medium-sized polymers and / or unreacted monomers, it is believed that the generation of thiyl radicals promotes the polymerization reaction, resulting in shorter film formation times.

[0081] The number of thiol groups per molecule of the thiol compound is 1 or more, and may be, for example, 2 or more, 3 or more, or 4 or more, or may be 4 or less, or 3 or less.

[0082] The thiol compound may have a primary thiol group or a secondary thiol group. The thiol group in the thiol compound may be a secondary thiol group, from the viewpoint of enabling film formation in an even shorter time. The thiol compound may be a compound having 3 to 4 secondary thiol groups, from the viewpoint of having higher ionic conductivity and enabling film formation in an even shorter time. The secondary thiol group is a thiol group bonded to a carbon atom bonded to two carbon atoms and one hydrogen atom.

[0083] The thiol compound may be a compound represented by the following formula (1-4): [ka] In formula (1-4), X 1 , X 2 and X 3 each independently represents a monovalent group having a thiol group, and Y 1 is an alkyl group or -OX 4 It is represented by X 4 represents a monovalent group having a thiol group. 1 may be an alkyl group having 1 to 8, 1 to 6, or 1 to 3 carbon atoms, or may be a methyl group.

[0084] The monovalent group having a thiol group may be a group having a secondary thiol group represented by the following formula (1-5). [ka]

[0085] In formula (1-5), Y 2 represents an alkylene group. 2 may be an alkylene group having 1 to 8, 1 to 6, or 1 to 3 carbon atoms, or may be a methylene group (-CH2-). In formula (1-5), * represents a bond (a bonding site to an oxygen atom).

[0086] Examples of thiol compounds include pentaerythritol tetrakis(3-mercaptobutyrate) (e.g., Karenz MT (registered trademark) PE-1 manufactured by Showa Denko K.K.), and trimethylolpropane tris(3-mercaptobutyrate) (e.g., Karenz MT (registered trademark) TPMB manufactured by Showa Denko K.K.).

[0087] The thiol compounds exemplified above can be used alone or in combination of two or more.

[0088] The amount of the thiol compound may be 1 mass% or more, 2 mass% or more, 3 mass% or more, or 4 mass% or more, and may be 20 mass% or less, or 15 mass% or less, based on the total amount of the separation membrane, from the viewpoint of further improving the separation ability of the separation membrane and further increasing the ionic conductivity of the separation membrane.

[0089] The polymer content may be 60 mass % or more, 70 mass % or more, or 80 mass % or more, and may be 90 mass % or less, 80 mass % or less, or 70 mass % or less, based on the total mass of the separation membrane.

[0090] The type of the third lithium salt may be the same as the first lithium salt contained in the above-described positive electrode mixture layer 10. The third lithium salt may be the same type as the first lithium salt and / or the second lithium salt, or may be different from the first lithium salt and / or the second lithium salt.

[0091] The content of the third lithium salt is preferably 5% by mass or more, more preferably 13% by mass or more, and even more preferably 15% by mass or more, based on the total amount of the third lithium salt and the third solvent, from the viewpoint of excellent ionic conductivity of the separation membrane. 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, from the viewpoint of viscosity of the solvent.

[0092] The content of the third lithium salt is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on the total amount of the separation membrane, from the viewpoint of further increasing the ionic conductivity of the separation membrane 7. The content of the third lithium salt is preferably 12% by mass or less, more preferably 9% by mass or less, and even more preferably 6% by mass or less, based on the total amount of the separation membrane, from the viewpoint of further increasing the ionic conductivity of the separation membrane 7.

[0093] 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 a glyme represented by the following formula (2), and more preferably an ionic liquid. R 21 O-(CH2CH2O) k -R 22 (2) [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.

[0094] The ionic liquid contains the following anion component and cation component: In this specification, the ionic liquid is a substance that is liquid at temperatures of −20° C. or higher.

[0095] The anion component of the ionic liquid is not particularly limited, but may be Cl - , Br - , I - Anions of halogens such as BF4 - , N(SO2F)2 - ([FSI] - ), inorganic anions such as B(C6H5)4 - , CH3SO2O - , CF3SO2O - , N(SO2C4F9)2 - , N(SO2CF3)2 - ([TFSI] - ), N(SO2C2F5)2 - The anion component of the ionic liquid preferably contains at least one anion component represented by the following formula (3): N(SO2C m F 2m+1 )(SO2C n F 2n+1 ) - (3) [In formula (3), m and n each independently represent an integer of 0 to 5. m and n may be the same or different, and are preferably the same.]

[0096] The anion component represented by formula (3) is, for example, N(SO2C4F9)2 - , N(SO2F)2 - ([FSI] - ), N(SO2CF3)2 - ([TFSI] - ) and N(SO2C2F5)2 - From the viewpoint of improving the ionic conductivity in the lithium ion secondary battery 1, the anion component of the ionic liquid is more preferably N(SO2C4F9)2 - , CF3SO2O - , [FSI] - , [TFSI] - , and N(SO2C2F5)2 - and more preferably contains at least one selected from the group consisting of [FSI] - Contains:

[0097] 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.

[0098] The chain quaternary onium cation is, for example, a compound represented by the following formula (4). [ka] [In formula (4), R 31 ~R 34 are each independently 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 of 1 to 4), and X represents a nitrogen atom or a phosphorus atom. 31 ~R 34 The number of carbon atoms in the alkyl group represented by the formula (I) is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5.]

[0099] The piperidinium cation is, for example, a nitrogen-containing six-membered ring compound represented by the following formula (5). [ka] [In formula (5), R 35 and R 36 are each independently an 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 of 1 to 4). 35 and R 36 The number of carbon atoms in the alkyl group represented by the formula (I) is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5.]

[0100] The pyrrolidinium cation is, for example, a five-membered ring compound represented by the following formula (6). [ka] [In formula (6), R 37 and R 38 are each independently an 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 of 1 to 4). 37 and R 38 The number of carbon atoms in the alkyl group represented by the formula (I) is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5.]

[0101] The pyridinium cation is, for example, a compound represented by the following formula (7). [ka] [In formula (7), R 39 ~R 43 are each independently an alkyl group having 1 to 20 carbon atoms, RO-(CH2) n - (wherein R represents a methyl group or an ethyl group, and n represents an integer of 1 to 4), or a hydrogen atom. 39 ~R 43 The number of carbon atoms in the alkyl group represented by the formula (I) is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5.]

[0102] The imidazolium cation is, for example, a compound represented by the following formula (8). [ka] [In formula (8), R 44 ~R 48 are each independently an alkyl group having 1 to 20 carbon atoms, RO-(CH2) n - (wherein R represents a methyl group or an ethyl group, and n represents an integer of 1 to 4), or a hydrogen atom. 44 ~R 48 The number of carbon atoms in the alkyl group represented by the formula (I) is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5.]

[0103] More specifically, the ionic liquids include 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), and 1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide (EMI-FSI). , 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), 1-ethyl-3-methylimidazolium dicyanamide (EMI-DCA), and the like.

[0104] In the glyme represented by the above formula (2), in formula (2), R 21 and R 22 each independently represents an alkyl group having 4 or less carbon atoms or a fluoroalkyl group having 4 or less carbon atoms, and k represents an integer of 1 to 6. 21 and R 22 are each independently preferably a methyl group or an ethyl group.

[0105] Specifically, the glyme may be monoglyme (k=1), diglyme (k=2), triglyme (k=3), tetraglyme (k=4), pentaglyme (k=5), or hexaglyme (k=6).

[0106] When separation membrane 7 contains glyme as a solvent, part or all of the glyme may form a complex with a lithium salt (third lithium salt).

[0107] The content of the third solvent may be 40% by mass or less, 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, based on the total amount of the separation membrane, from the viewpoint of obtaining a separation membrane 7 having excellent solvent (first solvent and second solvent) separation ability. The content of the third solvent may 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 separation membrane, from the viewpoint of further increasing the ionic conductivity of the separation membrane 7.

[0108] The content of the third solvent can be measured by the following method. First, the separation membrane is diluted approximately 10 times with methanol, and then subjected to ultrasonic extraction for 15 minutes to obtain an extract. 1.0 μL of this extract is injected into a gas chromatograph, and gas chromatography mass spectrometry is performed. The specific conditions for gas chromatography mass spectrometry are as follows: Device name: GC-4000 (GL Sciences) Carrier gas: Helium 5.0 mL / min Column: TC-WAX polyethylene glycol (0.53 mm ID x 30 m, 1.0 μL) Split ratio: 1 / 10 Injection temperature: 250℃ Detection temperature: 250℃ Oven temperature: 60°C (1 minute) then increase at 20°C / minute to 240°C Detector: Flame ionization detector (FID) Range: 10 2

[0109] Separation membrane 7 may further contain, for example, inorganic oxide particles as other components, but may not contain them from the viewpoint of further improving the ionic conductivity of the separation membrane.

[0110] From the viewpoint of further enhancing the separation ability of separation membrane 7, the thickness of separation membrane 7 may be 80 μm or more or 85 μm or less, or may be 400 μm or less, 300 μm or less, 200 μm or less, or 100 μm or less.

[0111] The ionic conductivity of the separation membrane may be, for example, more than 0.05 mS / cm, or 0.06 mS / cm or more, and may be, for example, 0.15 mS / cm or less. The ionic conductivity of the separation membrane is measured by the method described in the examples below.

[0112] 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 steps of obtaining a positive electrode 6 including 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 including 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 component including a monomer and a thiol compound, a third lithium salt, and the third solvent into a membrane and then polymerizing the polymerizable component to obtain a separation membrane 7, and providing the separation membrane 7 between the positive electrode 6 and the negative electrode 8. The order of the steps is arbitrary.

[0113] In the above-described production 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.

[0114] In the steps of obtaining a positive electrode and a negative electrode, the positive electrode 6 and the negative electrode 8 can be obtained using known methods. For example, the material used for the positive electrode mixture layer 10 or the negative electrode mixture layer 12 is dispersed in an appropriate amount of a dispersion medium using a kneader, disperser, or the like to obtain a slurry of the positive electrode mixture or the negative electrode mixture. Thereafter, this 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, a dipping method, a spray method, or the like, and the dispersion medium is volatilized to obtain the positive electrode 6 and the negative electrode 8. In this case, the dispersion medium may be water, N-methyl-2-pyrrolidone (NMP), or the like.

[0115] In one embodiment, the step of obtaining the separation membrane includes preparing a slurry containing a polymerizable component including a monomer and a thiol compound, a third lithium salt, and a third solvent. Specific aspects of the polymerizable component including a monomer and a thiol compound are as described above.

[0116] The total content of the monomers in the slurry may be 60% by mass or more, or 70% by mass or more, and may be 90% by mass or less, or 80% by mass or less, based on the total amount of the slurry.

[0117] The content of the thiol compound in the slurry may be 1 part by mass or more, 2 parts by mass or more, 3 parts by mass or more, or 4 parts by mass or more, and may be 20 parts by mass or less, or 15 parts by mass or less, relative to 100 parts by mass of the total amount of monomers.

[0118] The content of the third solvent in the slurry may be 40% by mass or less, 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, based on the total amount of the slurry. From the viewpoint of further increasing the ionic conductivity of separation membrane 7, the content of the third solvent may 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. This allows the content of the third solvent in separation membrane 7 to be within the above-mentioned range.

[0119] A polymerization initiator may be added to the slurry. This allows the polymerizable compound to be polymerized appropriately, and a separation membrane can be suitably produced from the slurry. The polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator, and can be appropriately selected depending on the purpose.

[0120] Examples of the thermal polymerization initiator include azobisisobutyronitrile and azobis(2-methylbutyronitrile).

[0121] Examples of the photopolymerization initiator include 2-hydroxy-2-methyl-1-phenylpropanone and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

[0122] 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 may be 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.

[0123] The slurry may further contain an inorganic filler as another component, or may not contain an inorganic filler.

[0124] In the process of obtaining a separation membrane, the above-mentioned slurry is subsequently formed into a membrane, and then the polymerizable component is polymerized.

[0125] The method for forming the slurry into a film is, for example, to place a frame of a desired size on one surface of a substrate such as a PET sheet and pour the slurry into the frame, or to form the slurry into a film by applying the slurry onto one surface of the substrate by a doctor blade method, a dipping method, a spraying method, or the like.

[0126] When the slurry contains a thermal polymerization initiator, the polymerizable component is polymerized by applying heat under predetermined conditions. The heating temperature may be, for example, 80 to 90° C. The heating time may be adjusted appropriately depending on the heating temperature, but is, for example, 1 to 10 minutes.

[0127] When the slurry contains a photopolymerization initiator, the polymerizable component is polymerized by irradiating the slurry with light under predetermined conditions. In one embodiment, the polymerizable component may be polymerized by irradiating the slurry with light having a wavelength in the range of 200 to 400 nm (ultraviolet light).

[0128] In the step of providing 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 stacked, for example, by lamination. This makes it possible to obtain an electrode group 2 including the positive electrode 6, the negative electrode 8, and the separator 7 provided between the positive electrode 6 and the negative electrode 8. Furthermore, by housing this electrode group 2 in a battery outer casing 3, a lithium ion secondary battery 1 can be obtained. [Example]

[0129] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0130] [Example 1] A monomer represented by the following formula (A) (where n = 23, product name: NK Ester A-1000, manufactured by Shin-Nakamura Chemical Co., Ltd.), a monomer represented by the following formula (B) (where a + b + c + d = 35, product name: NK Ester ATM-35E, manufactured by Shin-Nakamura Chemical Co., Ltd.), a lithium salt (LiTFSI), a solvent (EMI-TFSI), a photopolymerization initiator (methylbenzoylformate), and a thiol compound represented by the following formula (C) (pentaerythritol tetrakis(3-mercaptobutyrate), product name: KarenzMT (registered trademark) PE1, manufactured by Showa Denko K.K.) were mixed to prepare a slurry. The composition of each material is shown in Table 1. A silicone rubber frame (4 × 4 cm, 1 mm thick) was placed on a PET sheet (8 × 8 cm, 0.035 mm thick), and the prepared slurry was placed in the frame. The slurry was then irradiated with ultraviolet light (wavelength 365 nm) to polymerize the monomer, yielding a separation membrane. The separation membrane was removed from the frame and subjected to the following tests. The separation membrane formation time (minimum exposure time) was 50 seconds. [ka] [ka] [ka]

[0131] [Example 2] The composition of the slurry was changed as shown in Table 1, and a separation membrane was produced in the same manner as in Example 1. The separation membrane formation time (minimum exposure time) was 30 seconds.

[0132] [Example 3] The composition of the slurry was changed as shown in Table 1, and a separation membrane was produced in the same manner as in Example 1. The film formation time (minimum exposure time) for the separation membrane was 20 seconds.

[0133] [Example 4] The composition of the slurry was changed as shown in Table 1, and a separation membrane was produced in the same manner as in Example 1. The film formation time (minimum exposure time) for the separation membrane was 20 seconds.

[0134] [Comparative Example 1] The composition of the slurry was changed as shown in Table 1, and a separation membrane was produced in the same manner as in Example 1. The film formation time (minimum exposure time) for the separation membrane was 60 seconds.

[0135] <Evaluation of ionic conductivity> The ionic conductivity of the separation membranes of the examples and comparative examples was evaluated by preparing test cells using the separation membranes. First, an upper cover (a cap for CR2032, manufactured by Hosensha), a 1.6 mm thick leaf spring, two 1.0 mm thick SUS spacers, a separation membrane, a gasket, and a lower cover (a case for CR2032, manufactured by Hosensha) were stacked in this order, and the upper and lower covers were crimped to prepare a test cell, and the bulk resistance of the separation membrane was measured. The measurement device and measurement conditions were as follows: Measurement device: VSP electrochemical measurement system (manufactured by BioLogic) Measurement temperature: 25℃ AC amplitude: 10mV Frequency range: 10mHz to 1MHz

[0136] After the measurement, the ionic conductivity of the separation membrane was calculated according to the following formula (α). The results are shown in Table 1. σ=L / RA (α) σ (S / cm): ionic conductivity L (cm): thickness of the separation membrane R(Ω): bulk resistance A(cm 2 ): Cross-sectional area of ​​SUS spacer

[0137] [Table 1]

[0138] As shown in Table 1, the separation membranes according to the examples had higher ionic conductivities than the separation membranes according to the comparative examples.

[0139] The separation membrane according to the example could be formed in a shorter time than the separation membrane according to the comparative example.

[0140] <Evaluation of solvent separation ability> A separation membrane according to an example or comparative example and a separator (UP3085, manufactured by Ube Industries, Ltd.) were stacked, sandwiched between two silicone rubber sheets (0.5 mm thick), and placed between H-shaped cells. Dimethyl carbonate (DMC) was placed in the cell on the separation membrane side, and the appearance of the separator was visually observed after a predetermined number of days. If the separation membrane has excellent solvent separation ability, DMC does not easily permeate the separation membrane, and therefore does not easily permeate the separator. However, if the separation membrane has poor solvent separation ability, DMC permeates the separation membrane and penetrates into the separator. Therefore, the separation ability of the separation membrane for solvents (solvents corresponding to the first solvent and the second solvent) can be evaluated by observing the appearance of the separator and confirming whether or not DMC has permeated the separator.

[0141] The separation membranes according to the examples did not experience penetration of DMC into the separator even after 3 days had passed since the start of the test, demonstrating that the separation membranes according to the examples have excellent solvent separation capabilities. [Explanation of symbols]

[0142] 1... lithium ion secondary battery, 2... electrode group, 3... battery exterior, 4... positive electrode current collecting tab, 5... negative electrode current collecting tab, 6... positive electrode, 7... separator, 8... negative electrode, 9... positive electrode current collector, 10... positive electrode mixture layer, 11... negative electrode current collector, 12... negative electrode mixture layer.

Claims

[Claim 1] A lithium ion secondary battery including a positive electrode mixture layer, a separator, and a negative electrode mixture layer in this order, 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 contains a polymer having lithium ion conductivity, a third lithium salt, and a third solvent; The lithium ion secondary battery, wherein the polymer is a polymer of a polymerizable component including a monomer and a thiol compound.

Images