Separation Membrane for Electrochemical Element and Electrochemical Element Containing the Same

Abstract

The present invention provides a separation membrane for an electrochemical device, which includes a porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer includes inorganic particles whose surface is modified with one or more compounds selected from the group consisting of coumarin and its derivatives, and a polymer binder, and is characterized by removing radicals or transition metals generated during the charge and discharge process of the electrochemical device to prevent performance degradation.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0074059, filed with the Korean Intellectual Property Office on June 9, 2023, the content of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a separation membrane for an electrochemical device and an electrochemical device including the same.

Background Art

[0003] An electrochemical device converts chemical energy into electrical energy by using an electrochemical reaction. In recent years, lithium secondary batteries with high energy density, high voltage, long cycle life, and usable in various fields have been widely used.

[0004] A lithium secondary battery may include an electrode assembly manufactured with a separator disposed between a positive electrode, a negative electrode, and the positive electrode and the negative electrode, and the electrode assembly can be manufactured by housing it together with an electrolyte in a case. The positive electrode can provide lithium ions, and the lithium ions can pass through a separator made of a porous material and move to the negative electrode. For the negative electrode, a carbon-based active material or the like with an electrochemical reaction potential close to that of lithium metal and capable of inserting and desorbing lithium ions can be used.

[0005] The positive electrode active material may include lithium and various metal or transition metal elements. For example, nickel can improve the capacity of the electrochemical device, cobalt can improve the capacity and cycle stability of the electrochemical device, manganese can improve the stability of the electrochemical device, and aluminum can improve the output characteristics of the electrochemical device. In recent years, research has been conducted on positive electrodes with a high content of transition metals and electrochemical devices including the same to ensure a higher energy density.

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a separation membrane for an electrochemical element capable of scavenging radicals generated in the electrochemical element and adsorbing transition metal ions eluted from a positive electrode, and an electrochemical element including the separation membrane.

Means for Solving the Problems

[0007] One aspect of the present invention includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, and the porous coating layer is an inorganic substance whose surface is modified with one or more compounds selected from the group consisting of coumarin and its derivatives. Provided is a separation membrane for an electrochemical element, which includes particles and a polymer binder.

[0008] The compound may be bonded to the inorganic particles via the 4-position of the coumarin.

[0009] The compound may remove radicals generated in the charge and discharge process of the electrochemical element via the 7-position of the coumarin.

[0010] The compound includes a functional group capable of adsorbing transition metal ions generated in the charge and discharge process of the electrochemical element, and the functional group is one or more selected from the group consisting of a hydroxy group, an aldehyde group, a carboxy group, a nitro group, a carbonyl group, an ether group, an ester group, an amine group, a phenol group, a benzoyl group, a pyridine group, and a phosphine group. It may be.

[0011] The functional group may be disposed at the 3-position of the coumarin.

[0012] The separation membrane for an electrochemical element may contain the compound in an amount of about 0.01 to 1.5% by weight based on the total weight of the inorganic particles.

[0013] The inorganic particles and the polymer binder may be contained in a weight ratio of about 95:5 to 70:30.

[0014] The porous coating layer is formed on both sides of the porous polymer substrate, and the thickness of the separation membrane for the electrochemical element may be about 6 μm to 20 μm.

[0015] Another aspect of the present invention provides an electrochemical element including a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, wherein the separation membrane is another separation membrane for an electrochemical element on the one side.

[0016] The electrochemical element may be a lithium secondary battery.

[0017] The positive electrode contains Li 1+x Mn 2-x O4 (0 ≤ x ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2, LiNi 1-x Mn × O2 (0.01 ≤ x ≤ 0.3), LiMn 2-x M x O2 (M = Co, Ni, Fe, Cr, Zn or Ta, and 0.01 ≤ x ≤ 0.1), Li2Mn3MO8 (M = Fe, Co, Ni, Cu or Zn), LiNi x Mn 2-x O4 (0 < x < 0.5) and may contain one or more positive electrode active materials selected from the group consisting of LiMn2O4.

[0018] Another aspect of the present invention may be an electric device including the electrochemical element.

[0019] Another aspect of the present invention provides a method for manufacturing a separation membrane for an electrochemical element, including a step of forming a porous coating layer containing a polymer binder and inorganic particles on at least one surface of a porous polymer substrate, wherein the surface of the inorganic particles is modified with one or more compounds selected from the group consisting of coumarin and its derivatives.

[0020] The step of forming the porous coating layer may include manufacturing a coating slurry including the polymer binder, the inorganic particles, and a dispersion medium, and applying the coating slurry to at least one surface of the porous polymer substrate.

[0021] The step of forming the porous coating layer may further include subjecting at least one surface of the porous polymer substrate to corona discharge treatment before applying the coating slurry to at least one surface of the porous polymer substrate.

[0022] The step of forming the porous coating layer may include drying the coating slurry applied to at least one surface of the porous polymer substrate to evaporate the dispersion medium.

[0023] The separation membrane for an electrochemical device according to the present invention can remove radicals or transition metal ions generated during the charge and discharge process of the electrochemical device, thereby preventing a decrease in the performance of the electrochemical device.

Embodiments for Carrying Out the Invention

[0024] Hereinafter, each configuration of the present invention will be described in more detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, this is merely an example, and the scope of the rights of the present invention is not limited by the following content.

[0025] The term "including" used in this specification is used when listing materials, compositions, devices, and methods useful for the present invention, and is not limited to the listed examples.

[0026] The terms "about", "approximately", and "substantially" used in this specification are used in the sense of a range of that numerical value or degree or close thereto, taking into account inherent manufacturing and material tolerances, and are used to prevent an infringer from improperly using the disclosed content in which an exact numerical value or absolute numerical value is mentioned to assist in the understanding of the present invention.

[0027] As used herein, "electrochemical device" may mean a primary battery, a secondary battery, a supercapacitor, etc.

[0028] In order to provide a high energy density, in an electrochemical device such as a lithium secondary battery including a positive electrode with a high content of transition metal, radicals may be generated or transition metal ions may be eluted from the positive electrode active material during the charge and discharge process. Radicals may react with the electrolyte and the electrode active material used in the electrochemical device to form undesirable by-products, which may shorten the life of the electrochemical device or reduce the output. The transition metal ions eluted from the positive electrode may move to the negative electrode and precipitate as impurities containing the transition metal on the surface of the negative electrode, forming a non-uniform film and causing capacity degradation of the electrochemical device.

[0029] Therefore, there is a need for a separator for use in an electrochemical device that provides a high capacity, which can remove radicals generated in the electrochemical device or capture transition metal ions eluted from the positive electrode to prevent deterioration of the electrochemical device.

[0030] One specific example of the present invention provides a separator for an electrochemical device, including a porous polymer substrate, inorganic particles whose surface is modified with one or more compounds selected from the group consisting of coumarin and its derivatives, and a polymer binder, and including a porous coating layer formed on at least one surface of the porous polymer substrate.

[0031] The porous polymer substrate is a porous membrane in which a plurality of pores are formed, and may electrically insulate the positive electrode and the negative electrode to prevent short circuit. For example, when the electrochemical device is a lithium secondary battery, the porous polymer substrate may be an ion conductive barrier that can allow lithium ions to pass through while blocking electrical contact between the positive electrode and the negative electrode. At least a part of the pores can form a three-dimensional network communicating the surface and the inside of the porous polymer substrate, and fluid can pass through the porous polymer substrate through the pores.

[0032] For the porous polymer substrate, a material that is physically and chemically stable against the electrolytic solution which is an organic solvent can be used. For example, the porous polymer substrate can include, but is not limited to, resins such as polyolefins such as polyethylene, polypropylene, and polybutylene, polyvinyl chloride, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimide amide, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof. For example, polyolefin resins can be used. Polyolefin resins can be processed into a relatively thin thickness and are easy to apply as a coating slurry, so they are suitable for manufacturing electrochemical elements having a higher energy density.

[0033] The porous polymer substrate can have a single-layer or multi-layer structure. The porous polymer substrate can include two or more polymer resin layers having different melting points (Tm) to provide a shutdown function during thermal runaway of the battery. For example, the porous polymer substrate can include a polypropylene layer with a relatively high melting point and a polyethylene layer with a relatively low melting point. For example, the porous polymer substrate can have a three-layer structure laminated in the order of polypropylene, polyethylene, and polypropylene. As the temperature of the battery rises above a predetermined temperature, the polyethylene layer can melt while shutting down the pores to prevent thermal runaway of the battery.

[0034] The thickness of the porous polymer substrate can be approximately 1 μm or more and 100 μm or less. For example, the thickness of the porous polymer substrate can be about 10 μm or more and 90 μm or less, 20 μm or more and 80 μm or less, 30 μm or more and 70 μm or less, or 40 μm or more and 60 μm or less. For example, the thickness of the polymer substrate can be about 1 μm or more and 30 μm or less. Also, for example, the thickness of the polymer substrate can be about 5 μm or more and 15 μm or less, or 8 μm or more and 13 μm or less. By adjusting the thickness of the porous polymer substrate within the above-described range, the volume of the electrochemical element can be minimized while electrically insulating the positive electrode and the negative electrode, and the amount of the active material contained in the electrochemical element can be increased.

[0035] The porous polymer substrate may include pores having an average diameter of approximately 0.01 μm or more and 1 μm or less. For example, the size of the pores contained in the porous polymer substrate may be about 0.01 μm or more and 0.09 μm or less, 0.02 μm or more and 0.08 μm or less, 0.03 μm or more and 0.07 μm or less, or 0.04 μm or more and 0.06 μm or less. For example, the size of the pores may be about 0.02 μm or more and 0.06 μm or less. By adjusting the size of the pores of the porous polymer substrate within the above-described range, the air permeability and ion conductivity of the entire produced separation membrane can be adjusted.

[0036] The porous polymer substrate can have an air permeability of approximately 10 s / 100 cc or more and 100 s / 100 cc or less. For example, the air permeability of the porous polymer substrate may be about 10 s / 100 cc or more and 90 s / 100 cc or less, 20 s / 100 cc or more and 80 s / 100 cc or less, 30 s / 100 cc or more and 70 s / 100 cc or less, or 40 s / 100 cc or more and 60 s / 100 cc or less. For example, the air permeability of the porous polymer substrate may be about 50 s / 100 cc or more and 70 s / 100 cc or less. When the air permeability of the porous polymer substrate is within the above-described range, the air permeability of the produced separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical element.

[0037] The air permeability (s / 100 cc) means the time (seconds) required for 100 cc of air to pass through a porous polymer substrate or separation membrane having a predetermined area under a constant pressure. The air permeability can be measured using a permeability tester (Gurley densometer) in accordance with ASTM D 726-58, ASTM D726-94, or JIS-P8117. For example, using a 4110N device from Gurley, under a pressure of air at 0.304 kPa or water at 1.215 kN / m 2 of the pressure of 100 cc of air passes through 1 square inch (or 6.54 cm 2The time for passing through the sample of ) can be measured. For example, using the EG01-55-1MR device of Asahi Seiko, the time for 100 cc of air to pass through a 1 square inch sample can be measured under a constant pressure of water at 4.8 inches at room temperature.

[0038] The porous polymer substrate can have a porosity of approximately 10 vol% or more and 60 vol% or less. For example, the porosity of the porous polymer substrate can be about 15 vol% or more and 55 vol% or less, 20 vol% or more and 50 vol% or less, 25 vol% or more and 45 vol% or less, or 30 vol% or more and 40 vol% or less. For example, the porosity of the porous polymer substrate can be about 30 vol% or more and 50 vol% or less. When the porosity of the porous polymer substrate is within the above-described range, the ionic conductivity of the produced separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical device.

[0039] The porosity means the volume ratio of pores to the total volume of the porous polymer substrate. The porosity can be measured by methods known in the art. For example, it can be measured by the Brunauer - Emmett - Teller (BET) measurement method using nitrogen gas adsorption, the capillary flow porometer, or the water or mercury penetration method.

[0040] The porous coating layer is formed on at least one surface of the porous polymer substrate, and may include inorganic particles whose surfaces are modified with one or more compounds selected from the group consisting of coumarin and its derivatives and a polymer binder. The porous coating layer can be formed by coating one surface of the porous polymer substrate with a coating slurry containing the inorganic particles, the polymer binder, and a dispersion medium. The inorganic particles may be those whose surfaces are modified with a compound described later. For example, the separation membrane can be manufactured by applying the coating slurry to at least one surface of the porous polymer substrate and then drying to remove the dispersion medium. The porous coating layer includes an interstitial volume formed by connecting the inorganic particles with the polymer binder, allows lithium ions to pass through, and can be adhered to the porous polymer substrate to prevent thermal shrinkage of the porous polymer substrate. For example, the separation membrane for an electrochemical element may be one in which the porous coating layers are formed on both surfaces of the porous polymer substrate.

[0041] The coating slurry contains a dispersion medium, and can dissolve or disperse at least a part of the polymer binder and disperse the inorganic particles. The coating slurry can be one in which the polymer binder and the inorganic particles are uniformly dispersed by adjusting the type and content of the dispersion medium. For example, the dispersion medium may be one selected from the group consisting of water, ethanol, acetone, isopropyl alcohol (IPA), dimethylacetamide (DMAc), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), acetonitrile, and combinations thereof. For example, it may be water. Using the dispersion media of the types described above, a porous coating layer in which the inorganic particles are uniformly dispersed can be formed.

[0042] The coating slurry can have a viscosity of approximately 100 cps or more and 1,000 cps or less. For example, the viscosity of the coating slurry can be about 200 cps or more and 900 cps or less, 300 cps or more and 800 cps or less, 400 cps or more and 700 cps or less, or 500 cps or more and 600 cps or less. For example, the viscosity of the coating slurry can be about 300 cps or more and 800 cps or less. When the viscosity of the coating slurry exceeds 1,000 cps, a slurry with a very large particle size (D99) (D99~100 μm) is formed, making it difficult to manufacture a separation membrane by continuous coating on a porous polymer substrate and unable to ensure productivity.

[0043] The coating slurry further includes additives such as a dispersant, a surfactant, an antifoaming agent, a flame retardant, and a wetting agent, which can improve dispersibility and flame retardancy and enhance the uniformity of the formed porous coating layer. For example, the dispersant can include one or more selected from the group consisting of oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, sorbitan fatty acid esters, tannic acid, pyrogallic acid, and polyacrylic acid. By using the dispersant of the above-mentioned type, the stability of the coating slurry can be improved, and the uniformity of the porous coating layer formed from the coating slurry can be ensured.

[0044] Based on the total weight of the coating slurry, the additive can be included in an amount of approximately 0 wt% or more and 5 wt% or less. The content of the additive can be about 0.01 wt% or more and 4 wt% or less, 0.1 wt% or more and 3 wt% or less, or 1 wt% or more and 2 wt% or less. For example, the content of the additive can be about 3 wt% or more and 5 wt% or less. By adjusting the content of the additive within the above-mentioned range, uniform dispersion and stability of the inorganic particles contained in the coating slurry can be achieved.

[0045] The dispersion medium contained in the coating slurry may be removed by drying or heating after the formation of the porous coating layer. For example, the porous coating layer may contain the dispersion medium at 5 ppm or less. For example, the porous coating layer may be composed of an acrylic polymer binder, a copolymer binder, and inorganic particles. In the process of removing the dispersion medium, a plurality of pores may be formed on the surface and inside of the porous coating layer. The pores may include the interstitial volume formed between the inorganic particles and may have a structure that forms a three-dimensional network through which fluids can pass.

[0046] The thickness of the porous coating layer may be approximately 1 μm or more and 15 μm or less. For example, the thickness of the porous coating layer may be about 2 μm or more and 14 μm or less, 3 μm or more and 13 μm or less, 4 μm or more and 12 μm or less, 5 μm or more and 11 μm or less, 6 μm or more and 10 μm or less, or 7 μm or more and 9 μm or less. For example, the thickness of the porous coating layer may be about 1 μm or more and 5 μm or less. By adjusting the thickness of the porous coating layer within the above-described range, shrinkage of the porous polymer substrate can be minimized, and stable adhesion to the porous polymer substrate can be achieved.

[0047] As the inorganic particles, those whose surfaces are modified with one or more compounds selected from the group consisting of coumarin and its derivatives can be used. The coumarin can be represented by the following Chemical Formula 1. Chemical Formula 1 shows the position numbers in accordance with the IUPAC definition on the coumarin ring (IUPAC numeration), and in the following, "n-position" refers to the position number shown in the following Chemical Formula 1.

[0048]

Chemical Formula

[0049] Coumarin is a benzopyrone compound and was discovered as a type of phytoalexin, which is a plant metabolite in its natural state, and is known to have an antioxidant effect. Further, the coumarin or its derivative can act as a scavenger for radicals.

[0050] The inventors of the present invention apply a compound selected from the group consisting of the coumarin and its derivatives to a separation membrane of an electrochemical device. However, when the surface of the inorganic particles contained in the porous coating layer of the separation membrane is modified with the compound, it was confirmed that the radicals generated during charge and discharge of the electrochemical device can be removed while preventing an unfavorable performance degradation of the separation membrane, and thus the present invention was completed. Specifically, when the compound is contained not in inorganic particles but in a porous polymer substrate or an electrolytic solution, it cannot provide a barrier effect against by-products generated by charge and discharge of the electrochemical device, and there is a possibility that direct damage to the surface of the separation membrane may occur due to dendrites formed on the surface of the negative electrode. Damage to the separation membrane as described above can be evaluated by the air permeability of the separation membrane and may cause a decrease in the cell performance maintenance rate.

[0051] The compound may be a group consisting of derivatives in which a partial structure containing one or more of the 1st to 10th positions of the coumarin or the coumarin has changed. The change in the structure may include substitution of constituent elements and bonding of functional groups. Specifically, the compound can modify the surface of the inorganic particles described later and can remove radicals generated during the charge and discharge process of the electrochemical device via the 7th position. As the compound, those chemically synthesized or commercially available can be used, but it is not limited thereto.

[0052] The expression that the surface of the inorganic particles is modified with the compound may mean including that the compound and the inorganic particles form a chemical bond. For example, the inorganic particles whose surface is modified with the compound may be those in which the compound and the inorganic particles form a chemical bond.

[0053] For example, the compound can form a chemical bond with the inorganic particles. The position where the compound forms a chemical bond with the inorganic particles in the compound can be one or more positions other than the 7th position. For example, the compound can be bonded to the inorganic particles via the 4th position of the coumarin. For example, the compound can be a coumarin derivative having a halogen at the 4th position of the coumarin, and the inorganic particles can be silica. After introducing an amino group onto the surface of the silica using 3-aminopropylethoxysilane (APTES) or the like, the compound can be anchored at the position of the amino group in the presence of a toluene solvent in a basic environment.

[0054] At this time, the relative content of the inorganic particles and the compound introduced into the solvent can be adjusted to control the degree of surface modification of the inorganic particles. For example, the compound can be introduced at a content of approximately 0.05 to 0.15% by weight relative to the total mass of the toluene solvent. When a separation membrane is manufactured using a coating slurry containing the inorganic particles modified by introducing the compound at the content within the above-described range, the separation membrane will contain the compound at a ratio of approximately 0.01 to 1.5% by weight based on the total weight of the inorganic particles. For example, the separation membrane can contain the compound at a ratio of approximately 0.1 to 1.0% by weight, 0.1 to 0.5% by weight, or 0.1 to 0.3% by weight based on the total weight of the inorganic particles. When the weight ratio of the inorganic particles to the compound for modifying them satisfies the above-described range, radicals or transition metal ions generated during charge and discharge of the electrochemical device can be removed without degrading the performance of the electrochemical device. When the content of the compound relative to the total weight of the inorganic particles is less than approximately 0.01% by weight, a meaningful effect for preventing degradation of cell performance cannot be confirmed. Even if the compound is mixed such that its content exceeds approximately 1.5% by weight, a modification that can significantly increase the transition metal adsorption ability of the inorganic particles is not achieved.

[0055] The compound can remove radicals generated during the charge and discharge process of the electrochemical device through the 7-position of the coumarin. The radicals can be free radicals generated by side reactions between the electrode and the electrolyte during the charge and discharge process of the electrochemical device, or generated during the decomposition process of the electrolyte at high temperature, or generated by impurities inside the electrochemical device, but are not limited thereto. The radicals can be superoxide, hydroxyl radical, alkoxyl radical, carbonate radical, and can be hydroxyl radical. The compound can scavenge radicals generated in the electrochemical device in a manner of providing electrons to the radicals to form more stable radicals than the radicals. The compound can scavenge one or more radicals. For example, the radicals generated inside the electrochemical device can be hydroxyl radicals, and the compound can be coumarin. The coumarin can scavenge the radicals to form 7-hydroxycoumarin.

[0056] The compound may further include a functional group capable of adsorbing transition metal ions generated during the charge and discharge process of the electrochemical device. The transition metal ions can be those eluted from the positive electrode active material into the electrolyte during the charge and discharge process of the electrochemical device. For example, the transition metal ions can be nickel ions, manganese ions, cobalt ions, copper ions, aluminum ions, and can be, for example, nickel ions, manganese ions or copper ions. The compound can remove the transition metal ions contained in the electrolyte through the functional group to prevent the transition metal ions from moving to the electrode and precipitating as impurities.

[0057] The functional group(s) can be one or more selected from the group consisting of a hydroxy group, an aldehyde group, a carboxy group, a nitro group, a carbonyl group, an ether group, an ester group, an amine group, a phenol group, a benzoyl group, a pyridine group, and a phosphine group. The compound having the functional group(s) can coordinate with transition metal ions contained in the electrolytic solution or adsorb the transition metal ions in a manner of forming hydrogen bonds. One or more of the compounds having the functional group(s) can adsorb one or more transition metal ions.

[0058] The position of the functional group(s) can be one or more positions other than the 4-position and 7-position of the coumarin. For example, the functional group can be located at the 3-position of the coumarin. For example, the compound can be a coumarin derivative having a benzoyl group at the 3-position of the coumarin, and the benzoyl group can coordinate with transition metal ions together with the ketone at the 2-position of the coumarin. Two or more of the compounds can adsorb the transition metal ions in a manner of coordinating with one transition metal ion and remove them from the electrolytic solution.

[0059] The compound can remove radicals or transition metal ions generated during the charge and discharge process of the electrochemical device, prevent a decrease in the cell performance maintenance rate of the electrochemical device, and reduce the amount of gas generated by side reactions caused by by-products formed by the radicals and transition metal ions.

[0060] Inorganic particles that are electrochemically stable can be used. The inorganic particles are within the operating voltage range of the electrochemical device (e.g., Li / Li +It is not particularly limited as long as no oxidation and / or reduction reaction occurs at a reference of 0 to 5 V. In particular, when using inorganic particles with a high dielectric constant as the inorganic particles, it is possible to contribute to an increase in the dissociation degree of an electrolyte salt in the liquid electrolyte, for example, a lithium salt, and improve the ionic conductivity of the electrolyte solution. For the reasons described above, the inorganic particles include inorganic particles with a high dielectric constant having a dielectric constant of 5 or more, for example, 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 (PMN - PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, Al(OH)3, SiC, AlOOH, TiO2, or mixtures thereof, etc.

[0061] In addition, as the inorganic particles, inorganic particles having lithium ion transfer ability, that is, inorganic particles containing a lithium element, but not storing lithium and having a function of moving lithium ions can be used. Non-limiting examples of inorganic particles having lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge0.25 P 0.75 Lithium germanium thiophosphate such as S4 (Li x Ge y P z S w 、 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N (Li x N y 、 0 < x < 4, 0 < y < 2), SiS2-based glass such as Li3PO4-Li2S-SiS2 (Li x Si y S z 、 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass such as LiI-Li2S-P2S5 (Li x P y S z 、 0 < x < 3, 0 < y < 3, 0 < z < 7), or a mixture thereof, etc.

[0062] In addition, as the inorganic particles, inorganic particles having flame retardancy can be used, which can impart flame retardant properties to the separation membrane or prevent the temperature inside the electrochemical device from rising rapidly. Non-limiting examples of the inorganic particles having flame retardancy include Sb2O3, Sb2O4, Sb2O5, SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, Zn2SnO4, ZnSnO3, ZnSn(OH)6, ZrO2, Y2O3, SiO2, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, H3BO3, HBO2, and mixtures thereof, etc.

[0063] The average particle size (D50) of the inorganic particles can be approximately 50 nm or more and 5,000 nm or less. For example, the average particle size (D50) of the inorganic particles can be about 100 nm or more and 4,500 nm or less, 200 nm or more and 4,000 nm or less, 300 nm or more and 3,000 nm or less, 400 nm or more and 2,000 nm or less, or 500 nm or more and 1,000 nm or less. When the average particle size of the inorganic particles is less than approximately 50 nm, as the specific surface area increases, a polymer binder for bonding between the inorganic particles is further required, which is disadvantageous in terms of electrical resistance. When the average particle size of the inorganic particles exceeds approximately 5,000 nm, the uniformity of the coating layer surface decreases, and there is a possibility of causing damage to the porous polymer substrate or the electrode during lamination.

[0064] The polymer binder can bind the inorganic particles contained in the porous coating layer and impart adhesive force to the porous coating layer. The polymer binder can be an acrylic polymer binder, a fluorine-based polymer binder, or a mixture thereof.

[0065] For example, the acrylic polymer binder may contain, as repeating units, one or more monomers selected from the group consisting of (meth)acrylic acid, (meth)acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, (meth)acrylonitrile butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate.

[0066] For example, the fluorine-based binder may contain one or more selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyvinylidene fluoride - hexafluoropropylene, polyvinylidene fluoride - trichloroethylene, and polyvinylidene fluoride - chlorotrifluoroethylene.

[0067] The weight average molecular weight (Mw) of the polymer binder can be approximately 30,000 or more and 100,000 or less. For example, the weight average molecular weight of the polymer binder can be approximately 40,000 or more and 90,000 or less, 50,000 or more and 80,000 or less, or 60,000 or more and 70,000 or less. For example, the weight average molecular weight of the polymer binder can be approximately 50,000 or more and 80,000 or less. By adjusting the weight average molecular weight of the polymer binder within the above-described range so that the viscosity of the coating slurry does not exceed approximately 1000 cps, the inorganic particles can be bound to form and maintain the porous structure of the porous coating layer.

[0068] The weight average molecular weight of the polymer binder can be measured by gel permeation chromatography (GPC: gel permeation chromatography, PL GPC220, Agilent Technologies). For example, for the weight average molecular weight, using trichlorobenzene (TCB) as the solvent for a PL Olexis (Polymer Laboratories) column (column temperature is 160 °C), with a sample concentration of 1.0 mg / mL, a flow rate of 1.0 mL / min, and an injection volume of 200 μl, it can be measured using an Agilent High Temperature differential refractive index detector (RI detector) (corrected with a cubic function, reference: polystyrene).

[0069] The inorganic particles and the polymer binder can be included in a weight ratio of approximately 95:5 to 70:30. For example, the weight ratio of the inorganic particles to the polymer binder can be about 90:10, 85:15, 80:20, or 75:25. A separation membrane containing inorganic particles and a polymer binder within the above-described range can maintain adhesion even when impregnated with an electrolytic solution, and can reduce the thermal shrinkage rate even at high temperatures at which the electrochemical device operates.

[0070] The separation membrane for the electrochemical element can have an air permeability of approximately 100 s / 100 cc or more and 150 s / 100 cc or less. For example, the air permeability of the separation membrane can be about 110 s / 100 cc or more and 140 s / 100 cc or less, or 120 s / 100 cc or more and 130 s / 100 cc or less. For example, the air permeability of the separation membrane can be about 100 s / 100 cc or more and 120 s / 100 cc or less. When the air permeability of the separation membrane is within the above-described range, the output, stability, and cycle characteristics of the electrochemical element can be ensured.

[0071] The thickness of the separation membrane for the electrochemical element can be approximately 6 μm or more and 20 μm or less. For example, the thickness of the porous coating layer can be about 7 μm or more and 19 μm or less, 8 μm or more and 18 μm or less, 9 μm or more and 17 μm or less, 10 μm or more and 16 μm or less, 11 μm or more and 15 μm or less, or 12 μm or more and 14 μm or less. For example, the thickness of the separation membrane can be about 10 μm or more and 16 μm or less. By adjusting the thickness of the separation membrane within the above-described range, electrical insulation between the electrodes can be achieved, and at the same time, the loading amount of the active material of the electrode can be maximized to manufacture an electrochemical element having a higher capacity.

[0072] Another specific example of the present invention is an electrochemical element including a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the separation membrane is the separation membrane for the electrochemical element of the above-described specific example. The above-described electrochemical element can be manufactured by inserting and sealing an electrode assembly including a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode into a case or a pouch. Before sealing the case or the pouch, an electrolytic solution can be injected to impregnate the electrode assembly with the electrolytic solution. The shape of the case or the pouch is not limited. For example, the electrochemical element can be a cylindrical, rectangular, coin-shaped, or pouch-type lithium secondary battery.

[0073] The positive electrode and the negative electrode may be those in which an electrode active material is applied and dried on at least one surface of each current collector to form a coating. As the current collector, a material having conductivity without causing a chemical change in the electrochemical element can be used. For example, the current collector for the positive electrode may be aluminum, nickel, titanium, fired carbon, stainless steel; or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc., but is not limited thereto. For example, the current collector for the negative electrode may be copper, nickel, titanium, fired carbon, stainless steel; or a material obtained by surface-treating the surface of copper or stainless steel with carbon, nickel, titanium, silver, etc., but is not limited thereto. The current collector can be in various forms such as a thin metal plate, film, foil, net, porous body, foam, etc.

[0074] The positive electrode includes a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The positive electrode active material may include one or more selected from the group consisting of Li 1+x Mn 2-x O4 (0 ≤ x ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2, LiNi 1-x Mn × O2 (0.01 ≤ x ≤ 0.3), LiMn 2-x M x O2 (M = Co, Ni, Fe, Cr, Zn or Ta, and 0.01 ≤ x ≤ 0.1), Li2Mn3MO8 (M = Fe, Co, Ni, Cu or Zn), LiNi x Mn 2-x O4 (0 < x < 0.5) and LiMn2O4.

[0075] The negative electrode includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. As the negative electrode active material, carbon such as lithium metal oxide, graphitized carbon, graphite-based carbon; silicon-based materials such as LixFe2O3 (0 ≤ x ≤ 1), LixWO2 (0 ≤ x ≤ 1), Si, SiO x (0 < x < 2), SiC, Si alloy; Sn x Me1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), etc. metal composite oxides; lithium metal; lithium alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; one or more mixtures selected from titanium oxides may be included.

[0076] The conductive material may be any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, carbon nanotube, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. The carbon nanotube has a cylinder shape with a nanosize diameter of the graphite sheet and sp 2It has a bonding structure and exhibits the characteristics of a conductor or semiconductor according to the angle and structure around which the graphite plane is wound. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) according to the number of walls they have, and these carbon nanotubes can be appropriately selected according to the use of the dispersion liquid. More specifically, it may be one kind selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0077] As the binder resin, a binder resin usually used for the electrodes of an electrochemical device can be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyetylexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

[0078] The electrolyte is A + B - a salt having a structure such as, A + is Li + , Na + , K +An ion containing an alkali metal cation such as, or a combination thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - Anion such as, or a combination thereof, and a salt containing the ion can be dissolved or dissociated in an organic solvent composed of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone, or a mixture thereof.

[0079] The electrochemical element including the electrode assembly can be a lithium secondary battery. The battery can be used as a unit cell, and can be used as a battery module including the unit cell and a battery pack including the battery module. The battery pack can be used as a power source for various electric devices. Examples of the electrical equipment include small devices such as computers, mobile phones, and power tools, and electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc. that are powered by electric motors; electric bicycles (E-bikes), electric scooters (E-scooters); electric golf carts; and medium to large-sized devices such as power storage systems, but are not limited thereto.

[0080] Another specific example of the present invention provides a method for manufacturing a separation membrane for an electrochemical element, including the step of forming a porous coating layer containing a polymer binder and inorganic particles on at least one surface of a porous polymer substrate. Contents overlapping with those described in the separation membrane for the electrochemical element shall be replaced with the description of the previous specific example.

[0081] The step of forming the porous coating layer may include manufacturing a coating slurry containing a polymer binder, inorganic particles, and a dispersion medium, and applying and drying the coating slurry on at least one surface of the porous polymer substrate. The inorganic particles may be those whose surfaces are modified with one or more compounds selected from the group consisting of coumarin and its derivatives.

[0082] The step of forming the porous coating layer may further include the step of subjecting at least one surface of the porous polymer substrate to corona discharge treatment before applying the coating slurry on at least one surface of the porous polymer substrate. The step of subjecting at least one surface of the porous polymer substrate to corona discharge treatment can prevent a decrease in the adhesion between the surface of the porous polymer substrate and the surface of the coating layer at high temperatures and prevent a decrease in the adhesion between the surface of the polymer substrate and the surface of the coating layer due to the electrolyte.

[0083] The step of forming the porous coating layer may include coating the coating slurry on at least one surface of the porous polymer substrate. For example, the coating can be formed by methods such as a bar coater, a wire bar coater, a roll coater, a spray coater, a spin coater, an inkjet coater, a screen coater, a reverse coater, a gravure coater, a knife coater, a slot die coater, a hot melt coater, a comma coater, a direct metering coater, etc., but is not limited thereto. For example, the step of forming the porous coating layer may be to simultaneously coat both surfaces of the porous polymer substrate with the coating slurry using a bar coater or a slot die coater.

[0084] The step of forming the porous coating layer may be to apply the coating slurry to the porous polymer substrate and then dry or heat the coating layer to evaporate the dispersion medium contained in the coating layer. The removal of the dispersion medium can be carried out at a temperature that can evaporate only the dispersion medium contained in the coating layer without deforming the polymer binder contained in the coating layer. For example, the removal of the dispersion medium is to heat the coating layer at a predetermined temperature, provided that the surface temperature of the coating layer does not exceed 60°C. When heating the coating layer under the above conditions, the thermal energy may first be used to heat the dispersion medium to cause a phase change and may not be used to deform the polymer binder.

[0085] Hereinafter, the present invention will be described in more detail through examples and experimental examples. The following examples and experimental examples are for illustrative purposes of the present invention, and the present invention is not limited by the following examples and experimental examples.

[0086] Example 1 Surface modification of inorganic particles At room temperature (25 °C), Al2O3 (particle size (D50): 500 nm) as inorganic particles was added to a mixture in which APTES: CTAB: EtOH: H2SO4 were mixed at a molar ratio of approximately 1:0.1:9:0.004, reacted at 60 °C for 90 minutes, and then the inorganic particles were separated and dried in air for 24 hours.

[0087] 10 g of coumarin with an amine group introduced at the 3-position was added to 1200 mL of toluene (pH 8.6) to prepare a coumarin solution with a coumarin content of 0.05 w / w% with respect to the toluene solvent. After adding 30 g of the inorganic particles (coumarin content 0.01 wt% compared to the total weight of the inorganic particles), the mixture was stirred at room temperature for 12 hours to obtain inorganic particles with a surface modified with the coumarin.

[0088] Preparation of coating slurry At room temperature, an acrylic polymer binder (Toyo ink, CSB130, solid content 40%, average particle size (D50) 177 nm): carboxymethyl cellulose (GL Chem, SG-L02): wetting agent were introduced into 100 mL of distilled water at a weight ratio of 8:5:1, and 20 g of surface-modified inorganic particles were introduced (weight ratio of inorganic particles: polymer binder 90:10). The mixture was stirred with a shaker for 60 minutes to produce a coating slurry.

[0089] Preparation of porous polymer substrate As the porous polymer substrate, (MI: 0.2 g / 10 min, Tm: 135 °C, porosity: 45%, average pore size: 45 nm), a polyethylene film with a size of 20 cm × 30 cm and a thickness of 9 μm was used.

[0090] Manufacture of separation membrane The coating slurry was coated on both sides of the polyethylene film using a bar coater to form a coating layer with a thickness of 3 μm for each coating.

[0091] A low-temperature air volume was applied to a polyethylene film with a coating layer formed thereon, and the process of removing the dispersion medium was repeated 5 times to produce a separation membrane with an overall thickness of 15 μm.

[0092] Example 2 When modifying the surface of the inorganic particles, a coumarin solution with a coumarin content of 0.15 w / w% in toluene solvent was prepared, and 1.5 g of inorganic particles (coumarin content of 0.1 wt% compared to the total weight of the inorganic particles) were added. A separation membrane was produced in the same manner as in Example 1 except for this.

[0093] Comparative Example 1 A separation membrane was produced in the same manner as in Example 1 except that inorganic particles with an unmodified surface were used.

[0094] Comparative Example 2 A polyethylene film was dip-coated in a solution in which coumarin used in Example 1 was dissolved at a concentration of 1 wt% in toluene solvent, the film was immersed in distilled water for phase transition, and then dried in a vacuum oven for 12 hours to produce a separation membrane with an overall thickness of 12 μm in which a porous coating layer was not formed.

[0095] Comparative Example 3 When modifying the surface of the inorganic particles, a coumarin solution with a coumarin content of approximately 0.3 w / w% in toluene solvent was prepared, and 1 g of inorganic particles (coumarin content of 30% compared to the total weight of the inorganic particles) were added. A separation membrane was produced in the same manner as in Example 1 except for this.

[0096] Experimental Example 1. Confirmation of the transition metal adsorption ability of inorganic particles The transition metal adsorption ability of the inorganic particles produced in the examples and comparative examples, or the surface-modified inorganic particles, was confirmed and is shown in Table 1 below.

[0097] An adsorption evaluation solution was prepared by dissolving nickel and manganese as transition metals in dimethyl carbonate (DMC) at room temperature in saturated amounts (2000 ppm) respectively. After adding 1 g of each inorganic particle to 15 g of the adsorption evaluation solution, it was stirred with a shaker for 12 hours, and the inorganic particles were recovered using a centrifuge. Then, the adsorption evaluation solution was subjected to inductively coupled plasma mass spectrometry (ICP-MS) using ICP-OES (Thermo Fisher) to confirm the concentration of transition metal ions remaining in the solution, and the amount of transition metal ions adsorbed on the inorganic particles was derived.

[0098]

Table 1

[0099] The inorganic particles of Comparative Example 1 were not surface-modified and could not show a significant adsorption capacity for transition metal ions. In Examples 1 and 2, as the degree of surface modification of the inorganic particles increased, the adsorption capacity for transition metal ions increased. However, it was confirmed that when the content of the coumarin-based compound with respect to the total weight of the inorganic particles reached 0.1% by weight, the adsorption treatment of transition metal ions was possible with a saturated electrolyte solution.

[0100] Experimental Example 2. Confirmation of Physical Properties of Separation Membrane The physical properties of the separation membranes produced in the examples and comparative examples were confirmed and are shown in Table 2 below.

[0101] Measurement of air permeability The air permeability was measured using an air permeability tester (Gurley densometer) (Gurley, model 4110N) to measure the time required for about 100 cc of air to permeate through a separation membrane with a diameter of 28.6 mm and an area of 645 mm 2 of the separation membrane.

[0102] Measurement of cell performance retention rate Lithium manganese composite oxide (LiMnO2): conductive material (Denka black): binder (PVdF) were weighed so that the weight ratio was 95:2.5:2.5, then put into N-methylpyrrolidone (NMP) and mixed to produce a positive electrode active material slurry. After coating the positive electrode active material slurry on an aluminum foil with a thickness of 20 μm to a thickness of 200 μm, it was rolled and dried to produce a positive electrode.

[0103] As the negative electrode, a Li metal plate with a thickness of 200 μm was used. After laminating the positive electrode and the negative electrode with the separator of the example or comparative example in between, it was inserted into an aluminum pouch.

[0104] 1 g of an electrolytic solution containing 3 mol of vinylene carbonate (VC), 1.5 mol of propane sultone (PS), 1 mol of ethylene sulfate (ESa), and 1 mol of lithium salt LiPF6 as additives was injected into a solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) was mixed at a weight ratio of 3 / 7 into the aluminum pouch, and the pouch was sealed to manufacture a cell.

[0105] The manufactured cell was charged and discharged once at 0.1C in a voltage range of 3.0V to 4.4V in a 25°C chamber, and the performance retention rate was confirmed while repeating 0.33C charge and 0.33C discharge 400 times. The performance retention rate was calculated as the ratio of the discharge capacity after 400 cycles of repetition compared to the initial discharge capacity.

[0106] Also, the resistance before and after the 400 cycles was measured to confirm the resistance increase rate.

[0107] Measurement of gas generation amount After piercing the cell that had undergone 400 cycles of repetition to collect the gas inside the cell, the amounts of carbon monoxide, carbon dioxide, methane, and ethane contained in the gas were quantified using a hydrogen flame ionization detector (FID) and a thermal conductivity detector (TCD).

[0108]

Table 2

[0109] In the above, various embodiments of the present invention have been described with reference thereto. However, it will be understood by those skilled in the art or those having ordinary knowledge in the art that the present invention can be variously modified and changed without departing from the spirit and technical scope of the present invention described in the claims to be described later. Therefore, the technical scope of the present invention should be determined by the claims, rather than being limited to the content described in the detailed description of the specification.

Claims

1. A porous polymer substrate; and A porous coating layer formed on at least one surface of the porous polymer substrate; comprising The porous coating layer includes inorganic particles whose surface is modified with one or more compounds selected from the group consisting of coumarin and its derivatives, and a polymer binder, and is a separation membrane for an electrochemical device.

2. The separation membrane for an electrochemical device according to claim 1, wherein the compound is bonded to the inorganic particles via the 4-position of the coumarin.

3. The separation membrane for an electrochemical device according to claim 1, wherein the compound removes radicals generated during the charge and discharge process of the electrochemical device via the 7-position of the coumarin.

4. The compound includes a functional group capable of adsorbing transition metal ions generated during the charge and discharge process of the electrochemical device, The functional group is one or more selected from the group consisting of a hydroxy group, an aldehyde group, a carboxy group, a nitro group, a carbonyl group, an ether group, an ester group, an amine group, a phenol group, a benzoyl group, a pyridine group, and a phosphine group. The separation membrane for an electrochemical device according to claim 1.

5. The separation membrane for an electrochemical device according to claim 4, wherein the functional group is disposed at the 3-position of the coumarin.

6. The separation membrane for an electrochemical device includes the compound in an amount of 0.01 to 1.5% by weight based on the total weight of the inorganic particles. The separation membrane for an electrochemical device according to claim 1.

7. The separation membrane for an electrochemical device according to claim 1, wherein the inorganic particles and the polymer binder are included in a weight ratio of 95:5 to 70:

30.

8. The porous coating layer is formed on both surfaces of the porous polymer substrate, The thickness of the separation membrane for an electrochemical device is 6 μm to 20 μm. The separation membrane for an electrochemical device according to claim 1.

9. An electrochemical device including a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, wherein the separation membrane is the separation membrane for an electrochemical device according to any one of claims 1 to 8. The electrochemical device.

10. The positive electrode is Li １＋ｘ Mn ２－ｘ O ４ (0 ≤ x ≤ 0.33), LiMnO ３ 、LiMn ２ O ３ 、LiMnO ２ 、LiNi １－ｘ Mn × O ２ (0.01 ≤ x ≤ 0.3), LiMn ２－ｘ M ｘ O ２ (M = Co, Ni, Fe, Cr, Zn or Ta, and 0.01 ≤ x ≤ 0.1), Li ２ Mn ３ MO ８ (M = Fe, Co, Ni, Cu or Zn), LiNi ｘ Mn ２－ｘ O ４ (0 < x < 0.5) and LiMn ２ O ４ The electrochemical device according to claim 9, comprising one or more cathode active materials selected from the group consisting of

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