Separator for electrochemical device and electrochemical device including same

Abstract

The present invention provides a separator for an electrochemical device, the separator comprising 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 contains a polymeric binder and inorganic particles whose surfaces are modified with one or more compounds selected from coumarin and derivatives thereof, characterized in that radicals or transition metals generated during charging and discharging of the electrochemical device are removed, thereby preventing performance degradation.

Description

Technical Field

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

[0002] The present disclosure relates to a separator for an electrochemical device and an electrochemical device including the same. Background Art

[0003] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions, and lithium secondary batteries have been widely used in recent years due to their high energy density and voltage, long cycle life, and wide use in various applications.

[0004] A lithium secondary battery may include an electrode assembly made of a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and the electrode assembly is housed in a housing together with an electrolyte. The positive electrode is capable of providing lithium ions, and the lithium ions can pass through a separator made of a porous material and move to the negative electrode. The negative electrode may be a carbon-based active material that has an electrochemical reaction potential close to that of lithium metal and is capable of inserting and removing lithium ions.

[0005] The positive electrode active material may contain lithium and various metal or transition metal elements. For example, nickel may improve the capacity of the electrochemical device, cobalt may improve the capacity and cycle stability of the electrochemical device, manganese may improve the stability of the electrochemical device, and aluminum may improve the output characteristics of the electrochemical device. In recent years, positive electrodes having high transition metal contents and electrochemical devices including the positive electrodes have been studied to achieve higher energy density. Summary of the invention

[0006] Technical issues

[0007] The present disclosure provides a separator for an electrochemical device capable of scavenging free radicals generated in an electrochemical device or adsorbing transition metal ions dissolved from a positive electrode, and an electrochemical device including the separator.

[0008] Technical Solution

[0009] According to one aspect, the present disclosure provides a separator for an electrochemical device, which includes a porous polymer substrate and a porous coating formed on at least one surface of the porous polymer substrate, wherein the porous coating contains a polymer binder and inorganic particles whose surfaces are modified with one or more compounds selected from coumarin and its derivatives.

[0010] The compound can be bound to the inorganic particles via the 4-position of coumarin.

[0011] The compound can be used to remove free radicals generated during charging and discharging of an electrochemical device through the 7-position of coumarin.

[0012] The compound can contain functional groups capable of adsorbing transition metal ions generated during charging and discharging of an electrochemical device, and the functional groups can be at least one selected from the following: hydroxyl group, aldehyde group, carboxyl group, nitro group, carbonyl group, ether group, ester group, amine group, phenol group, benzoyl group, pyridyl group, and phosphine group.

[0013] The functional group can be located at the 3-position of coumarin.

[0014] Based on the total weight of the inorganic particles, the separator can contain about 0.01 wt% to 1.5 wt% of the compound.

[0015] The inorganic particles and the polymer binder can be included in a weight ratio of about 95:5 to 70:30.

[0016] The porous coating can be formed on two surfaces of the porous polymer substrate, and the thickness of the separator can be about 6 μm to 20 μm.

[0017] According to another aspect of the present disclosure, there is provided an electrochemical device including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is a separator for an electrochemical device according to the above aspect.

[0018] The electrochemical device can be a lithium secondary battery.

[0019] The positive electrode can contain one or more positive electrode active materials selected from the following: Li 1+x Mn 2-x O4 (0 ≤ x ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2, LiNi 1-x Mn x 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.

[0020] According to another aspect, the present disclosure provides an electrical device including the electrochemical device.

[0021] According to still another aspect, the present disclosure provides a method for manufacturing a separator for an electrochemical device,

[0022] The method includes forming a porous coating layer comprising a polymer binder and inorganic particles on at least one surface of a porous polymer substrate, wherein the inorganic particles are surface-modified with one or more compounds selected from coumarin and its derivatives.

[0023] The step of forming the porous coating layer may include preparing a coating slurry including a polymer binder, inorganic particles, and a dispersion medium, and applying the coating slurry to at least one surface of the porous polymer substrate.

[0024] The step of forming a porous coating layer may further include subjecting the at least one surface of the porous polymer substrate to a corona discharge treatment before applying the coating slurry to the at least one surface of the porous polymer substrate.

[0025] 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 and evaporating the dispersion medium.

[0026] The separator for an electrochemical device according to the present disclosure may remove radicals or transition metal ions generated during the charge and discharge process of the electrochemical device, thereby preventing the performance of the electrochemical device from being deteriorated. DETAILED DESCRIPTION

[0027] Hereinafter, the embodiments of the present disclosure will be described in detail to facilitate the practice of those skilled in the art to which the present disclosure belongs. The present disclosure can be implemented in various different forms and is not limited or constrained by the embodiments described below.

[0028] As used herein, the term "including" is used to list materials, compositions, devices and methods that can be used in the present disclosure and is not limited to the listed examples.

[0029] As used herein, the words "about," "approximately," and "substantially" are used to mean a range or approximation of a value or degree, taking into account inherent manufacturing and material tolerances, and are used to prevent an infringer from taking unfair advantage of the present disclosure where precise or absolute numbers are provided to aid in the understanding of the present disclosure.

[0030] As used herein, the term "electrochemical device" may refer to a primary battery, a secondary battery, or a supercapacitor.

[0031] In an electrochemical device such as a lithium secondary battery that includes a positive electrode with a high transition metal content to provide a high energy density, free radicals may be generated during the charging and discharging process, or transition metal ions may be dissolved from the positive electrode active material. The free radicals may react with the electrolyte or 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 of the electrochemical device. The transition metal ions dissolved from the positive electrode migrate to the negative electrode and precipitate as impurities containing transition metal elements on the surface of the negative electrode and form an uneven film, which may cause the capacity of the electrochemical device to deteriorate.

[0032] Therefore, a separator for use in an electrochemical device that provides a high capacity and is capable of scavenging free radicals generated in the electrochemical device or capturing transition metal ions eluted from a positive electrode, thereby preventing degradation of the electrochemical device is disclosed.

[0033] According to one embodiment of the present disclosure, a separator for an electrochemical device includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate and comprising a polymer binder and inorganic particles whose surfaces are modified with one or more compounds selected from coumarin and its derivatives.

[0034] The porous polymer substrate may be a porous film having a plurality of pores that electrically insulates the positive electrode and the negative electrode to prevent short circuits. For example, when the electrochemical device is a lithium secondary battery, the porous polymer substrate may be an ion-conducting barrier that allows lithium ions to pass while blocking electrical contact between the positive electrode and the negative electrode. At least a portion of the pores may form a three-dimensional network that communicates with the surface and interior of the porous polymer substrate, and a fluid may pass through the porous polymer substrate via the pores.

[0035] The porous polymer substrate can be a material that is physically and chemically stable to an electrolyte that is an organic solvent. Examples of porous polymer substrates include resins, such as polyolefins (e.g., polyethylene, polypropylene, and polybutylene), polyvinyl chloride, polyethylene terephthalate, polycycloolefins, polyethersulfones, polyamides, polyimides, polyimide amides, nylons, polytetrafluoroethylene, and copolymers or mixtures thereof, but are not limited thereto. For example, a polyolefin-based resin can be used. A polyolefin-based resin is suitable for manufacturing an electrochemical device with a higher energy density because it can be processed into a relatively small thickness and is easily coated with a slurry.

[0036] The porous polymer substrate may have a monolayer or multilayer structure. The porous polymer substrate may include two or more polymer resin layers with different melting points (Tm) to provide a shutdown capability during high temperature runaway of the battery. For example, the porous polymer substrate may 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 may be a three-layer structure in which polypropylene, polyethylene, and polypropylene are laminated in this order. When the temperature of the battery rises above a predetermined temperature, the polyethylene layer melts and closes the pores, thereby preventing thermal runaway of the battery.

[0037] The thickness of the porous polymer substrate may be about 1 μm or more and 100 μm or less. For example, the thickness of the porous polymer substrate may 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 may be about 1 μm or more and 30 μm or less. In addition, for example, the thickness of the polymer substrate may be about 5 μm or more and 15 μm or less, or 8 μm or more and 13 μm or less. When the thickness of the porous polymer substrate is adjusted within the above range, the amount of active material contained in the electrochemical device may be increased by minimizing the volume of the electrochemical device while electrically insulating the positive and negative electrodes.

[0038] The porous polymer substrate may include pores having an average diameter of about 0.01 μm or more and 1 μm or less. For example, the size of the pores included 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. When the pore size of the porous polymer substrate is adjusted within the above range, the permeability and ionic conductivity of the entire separator prepared may be controlled.

[0039] The permeability of porous polymer substrate can be about 10 seconds / 100cc or more and 100 seconds / 100cc or less. For example, the permeability of porous polymer substrate can be about 10 seconds / 100cc or more and 90 seconds / 100cc or less, 20 seconds / 100cc or more and 80 seconds / 100cc or less, 30 seconds / 100cc or more and 70 seconds / 100cc or less, or 40 seconds / 100cc or more and 60 seconds / 100cc or less. In addition, for example, the permeability of porous polymer substrate can be about 50 seconds / 100cc or more and 70 seconds / 100cc or less. When the permeability of porous polymer substrate is within the above range, the permeability of the separator prepared can be set in the range suitable for ensuring the output characteristics and cycle characteristics of electrochemical device.

[0040] Permeability (seconds / 100cc) means the time (in seconds) it takes for 100cc of air to pass through a predetermined area of ​​a porous polymer substrate or separator at a constant pressure. Permeability can be measured using a Gurley air permeability tester according to ASTM D726-58, ASTM D726-94, or JIS-P8117. For example, a 4110N instrument from Gurley can be used to measure the permeability of 100cc of air at 0.304 kPa air or 1.215 kN / m 2 The pressure of water passing through 1 square inch (or 6.54 cm 2 For example, the time it takes for 100cc of air to pass through a 1 square inch sample at room temperature under a constant pressure of 4.8 inches of water can be measured using an ASAHI SEIKO EG01-55-1MR instrument.

[0041] The porosity of the porous polymer substrate can be about 10 volume % or more and 60 volume % or less. For example, the porosity of the porous polymer substrate can be about 15 volume % or more and 55 volume % or less, 20 volume % or more and 50 volume % or less, 25 volume % or more and 45 volume % or less, or 30 volume % or more and 40 volume % or less. For example, the porosity of the porous polymer substrate can be about 30 volume % or more and 50 volume % or less. When the porosity of the porous polymer substrate is within the above range, the ionic conductivity of the prepared separator can be set within a range suitable for ensuring the output characteristics and cycle characteristics of the electrochemical device.

[0042] Porosity refers to the ratio of the volume of the pores to the total volume of the porous polymer substrate. Porosity can be measured by methods known in the art. For example, porosity can be measured by Brunauer Emmett Teller (BET) measurement using nitrogen adsorption, capillary flow porometer, or water or mercury permeation method.

[0043] The porous coating is formed on at least one surface of the porous polymer substrate, and may include a polymer binder and inorganic particles whose surfaces are modified by one or more compounds selected from coumarin and / or its derivatives. The porous coating can be formed by coating a surface of the porous polymer substrate with a coating slurry comprising inorganic particles, a polymer binder and a dispersion medium. The inorganic particles may have a surface modified by a compound described later. For example, the separator can be prepared by applying the coating slurry to at least one side of the porous polymer substrate and then drying to remove the dispersion medium. Since the inorganic particles contained in the porous coating are connected by a polymer binder to form an interstitial volume, the porous coating adheres to the porous polymer substrate while allowing lithium ions to pass through the interstitial volume, thereby preventing thermal shrinkage of the porous polymer substrate. For example, a separator for an electrochemical device may have a porous coating formed on both sides of the porous polymer substrate.

[0044] The coating slurry may include a dispersion medium for dissolving or dispersing at least a portion of the polymer binder and dispersing the inorganic particles. By controlling the type and content of the dispersion medium, a coating slurry in which the polymer binder and the inorganic particles are uniformly dispersed may be used. The example of the dispersion medium includes water, ethanol, acetone, isopropyl alcohol (IPA), dimethylacetamide (DMAc), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), acetonitrile, and combinations thereof. For example, the dispersion medium may be water. The above-mentioned type of dispersion medium may be used to form a porous coating in which the inorganic particles are uniformly dispersed.

[0045] The viscosity of the coating slurry may be about 100cps or more and 1,000cps or less. For example, the viscosity of the coating slurry may be about 200cps or more and 900cps or less, 300cps or more and 800cps or less, 400cps or more and 700cps or less, or 500cps or more and 600cps or less. For example, the viscosity of the coating slurry may be 300cps or more and 800cps or less. When the viscosity of the coating slurry exceeds 1,000cps, a slurry (D99 about 100μm) with a very large particle size (D99) is formed, which makes it difficult to manufacture the separator by continuous application on a porous polymer substrate, making it difficult to ensure productivity.

[0046] The coating slurry may also contain additives such as dispersants, surfactants, defoamers, flame retardants and wetting agents to improve dispersibility and flame retardancy and improve the uniformity of the porous coating formed. Examples of dispersants include one or more selected from 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 above-mentioned types of dispersants, the stability of the coating slurry can be improved and the uniformity of the porous coating formed by the coating slurry can be ensured.

[0047] Based on the total weight of the coating slurry, the additive may be included in an amount of about 0 wt % or more and 5 wt % or less. For example, the content of the additive may 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 may be about 3 wt % or more and 5 wt % or less. When the content of the additive is adjusted within the above range, uniform dispersion and stability of the inorganic particles contained in the coating slurry may be achieved.

[0048] After forming the porous coating, the dispersion medium contained in the coating slurry can be removed by drying or heating. For example, the porous coating can contain 5ppm or less dispersion medium. For example, the porous coating can be composed of an acrylic polymer binder, a copolymer binder and inorganic particles. In the process of removing the dispersion medium, a plurality of holes can be formed on the surface and inside of the porous coating. The hole can include the interstitial volume formed between the inorganic particles, and can have a structure in which a three-dimensional network is formed to allow fluid to pass.

[0049] The thickness of the porous coating layer may be about 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. When the thickness of the porous coating layer is adjusted within the above range, the shrinkage of the porous polymer substrate may be minimized and stable adhesion to the porous polymer substrate may be achieved.

[0050] The inorganic particles may have a surface modified by one or more compounds selected from coumarin and its derivatives. Coumarin may be represented by the following formula 1. According to the IUPAC numbering, formula 1 shows the position number shown on the coumarin ring. In the following, "position n" refers to the position number shown in the following formula 1.

[0051] [Formula 1]

[0052]

[0053] Coumarin is a benzopyrone-based compound found in nature as a type of phytoalexin, which is a plant metabolite and is known to have an antioxidant effect. In addition, coumarin or its derivatives can act as a scavenger of free radicals.

[0054] The present disclosure applies a compound selected from coumarin and its derivatives to a separator of an electrochemical device, and determines that modifying the surface of an inorganic particle contained in a porous coating of the separator with the compound can remove free radicals generated during charging and discharging of the electrochemical device while preventing undesirable performance degradation of the separator. Typically, when the compound is contained in a porous polymer substrate or an electrolyte instead of in an inorganic particle, it may not provide a barrier effect to byproducts generated by charging and discharging of the electrochemical device, so that the surface of the separator may be directly damaged by dendrites formed on the surface of the negative electrode. Damage to the separator as described above can be evaluated by the permeability of the separator and may result in a reduction in the retention rate of battery performance.

[0055] The compound may be a group consisting of coumarin and / or a coumarin derivative having a partial structural change including one or more of positions 1 to 10 of coumarin. The structural change may include substitution of constituent elements or bonding of functional groups. Specifically, the compound is capable of modifying the surface of inorganic particles (which will be described later) and can remove free radicals generated during the charging and discharging process of the electrochemical device through position 7. The compound may be chemically synthesized or commercially available, but is not limited thereto.

[0056] Modifying the surface of the inorganic particle with the compound may include forming a chemical bond between the compound and the inorganic particle. For example, the inorganic particle whose surface is modified by the compound may be an inorganic particle in which the compound forms a chemical bond with the inorganic particle.

[0057] For example, the compound can form a chemical bond with an inorganic particle. In the compound, the position for forming a chemical bond with an inorganic particle can be at least one position other than position 7. For example, the compound can be bound to an inorganic particle through position 4 of coumarin. In addition, for example, the compound can be a coumarin derivative having a halogen at position 4 of coumarin, and the inorganic particle can be silica. After introducing an amino group to the surface of silica using, for example, 3-aminopropylethoxysilane (APTES), the compound can be anchored at the position of the amino group in the presence of a toluene solvent in an alkaline environment.

[0058] At this time, the relative content of the inorganic particles and the compound added to the solvent can be adjusted to adjust the degree of surface modification of the inorganic particles. For example, based on the total mass of the toluene solvent, the compound can be added in an amount of about 0.05% by weight to 0.15% by weight. When a separator is prepared from a coating slurry comprising inorganic particles modified by adding the above-mentioned compound in an amount within the above range, the separator includes the compound at a ratio of about 0.01% by weight to 1.5% by weight based on the total weight of the inorganic particles. For example, based on the total weight of the inorganic particles, the separator may include the compound at a ratio of about 0.1% by weight to 1.0% by weight, 0.1% by weight to 0.5% by weight, or 0.1% by weight to 0.3% by weight. When the weight ratio of the inorganic particles to the compound modified to the inorganic particles meets the above range, the free radicals or transition metal ions generated during the charge and discharge of the electrochemical device can be removed without degrading the performance of the electrochemical device. When the content of the compound is less than about 0.01 wt % based on the total weight of the inorganic particles, a significant effect on preventing battery performance degradation cannot be confirmed. Even when the compound is mixed so that the content exceeds about 1.5 wt %, modification capable of significantly improving the transition metal adsorption capacity of the inorganic particles cannot be achieved.

[0059] The compound can remove free radicals generated during the charging and discharging process of the electrochemical device through the 7th position of coumarin. The free radical can be a free radical generated by a side reaction between an electrode and an electrolyte during the charging and discharging process of the electrochemical device, generated during the decomposition of the electrolyte at high temperature, or generated by impurities inside the electrochemical device, but is not limited thereto. The free radical can be a superoxide, a hydroxyl radical, an alkoxy radical, or a carbonate radical, and can be a hydroxyl radical. The compound can remove free radicals generated in the electrochemical device by providing electrons to the free radical to form a free radical that is more stable than the free radical. The compound is capable of removing one or more free radicals. For example, the free radical generated inside the electrochemical device can be a hydroxyl radical, and the compound can be coumarin. Coumarin can remove the free radical to form 7-hydroxycoumarin.

[0060] The compound may also contain a functional group capable of adsorbing transition metal ions generated during the charge and discharge process of the electrochemical device. The transition metal ions may be those dissolved 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 may be nickel ions, manganese ions, cobalt ions, copper ions or aluminum ions, for example, nickel ions, manganese ions or copper ions. The compound may remove the transition metal ions contained in the electrolyte through the functional group, thereby preventing the transition metal ions from migrating to the electrode and precipitating as impurities.

[0061] The functional group may be one or more selected from the following: hydroxyl, aldehyde, carboxyl, nitro, carbonyl, ether, ester, amine, phenol, benzoyl, pyridyl, and phosphine. The compound having the functional group may adsorb transition metal ions contained in the electrolyte by coordinating with or forming hydrogen bonds. One or more compounds having the functional group may adsorb one or more transition metal ions.

[0062] The position of the functional group may be at least one position other than position 4 and position 7 of coumarin. For example, the functional group may be located at position 3 of coumarin. For example, the compound may be a coumarin derivative having a benzoyl group at position 3 of coumarin, and the benzoyl group may coordinate the transition metal ion with the ketone at position 2 of coumarin. The transition metal ion may be adsorbed and removed from the electrolyte solution in a manner where two or more of the compounds coordinate with one transition metal ion.

[0063] The compound can remove free radicals or transition metal ions generated during the charge and discharge process of the electrochemical device, thereby preventing the degradation of the battery performance retention rate of the electrochemical device and reducing the amount of gas generated by side reactions caused by byproducts formed by free radicals or transition metal ions.

[0064] The inorganic particles may be electrochemically stable. The inorganic particles are not particularly limited as long as they are within the operating voltage range of the electrochemical device (e.g., based on Li / Li + In particular, the use of inorganic particles with a high dielectric constant can help increase the dissociation of electrolyte salts (e.g., lithium salts) in liquid electrolytes, thereby improving the ionic conductivity of the electrolyte. For the above reasons, the inorganic particles may include high dielectric constant inorganic particles having a dielectric constant of 5 or greater (which may be 10 or greater). Non-limiting examples of inorganic particles having a dielectric constant of 5 or greater 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), hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, Al(OH)3, SiC, AlOOH, TiO2, and mixtures thereof.

[0065] In addition, inorganic particles having the ability to transfer lithium ions (i.e., inorganic particles containing elemental lithium but not storing lithium and having the ability to transfer lithium ions) can be used as the inorganic particles. Non-limiting examples of inorganic particles having the ability to transfer lithium ions 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 series glasses (0 < x < 4, 0 < y < 13) such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5, lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5) such as Li 3.25 Ge 0.25 P 0.75 S4, lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2) such as Li3N, SiS2 series glasses (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4) such as Li3PO4 - Li2S - SiS2, and P2S5 series glasses (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) such as LiI - Li2S - P2S5, or a mixture of two or more thereof.

[0066] In addition, inorganic particles having flame retardancy can be used to impart flame retardant properties to the separator or to prevent a rapid increase in temperature inside the electrochemical element. Non-limiting examples of 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.

[0067] The average particle size (D50) of the inorganic particles can be about 50nm or more and 5,000nm or less. For example, the average particle size (D50) of the inorganic particles can be about 100nm or more and 4,500nm or less, 200nm or more and 4,000nm or less, 300nm or more and 3,000nm or less, 400nm or more and 2,000nm or less, or 500nm or more and 1,000nm or less. When the average particle size of the inorganic particles is less than about 50nm, due to the increase in specific surface area, an additional polymer binder for bonding between the inorganic particles is required, which is disadvantageous in terms of resistance. When the average particle size of the inorganic particles exceeds about 5,000nm, the uniformity of the surface of the coating may be reduced, and damage to the porous polymer substrate or electrode may occur during lamination.

[0068] The polymer binder may bind the inorganic particles contained in the porous coating layer and provide adhesion to the porous coating layer.The polymer binder may be an acrylic polymer binder, a fluorine-based polymer binder, or a mixture thereof.

[0069] For example, the acrylic polymer binder may have repeating units comprising one or more monomers selected from the group consisting of (meth)acrylic acid, (meth)acrylic acid ester, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl meth ... acrylate, n-hexyl (meth)acrylate, n-ethylhexyl methacrylate, 2-ethylhexyl (meth)acrylate, hydroxyethyl (methacrylate), (meth)acrylonitrile, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate and pentafluorophenyl acrylate.

[0070] For example, the fluorine-based binder may include one or more selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, and polyvinylidene fluoride-chlorotrifluoroethylene.

[0071] The weight average molecular weight (Mw) of the polymer binder can be about 30,000 or more and 100,000 or less. For example, the weight average molecular weight of the polymer binder can be about 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 about 50,000 or more and 80,000 or less. When the weight average molecular weight of the polymer binder is adjusted within the above range, the inorganic particles can be combined to form and maintain the porous structure of the porous coating layer in a range where the viscosity of the coating slurry is no more than about 1000cps.

[0072] The weight average molecular weight of polymer binder can be measured by gel permeation chromatography (gel permeation chromatography, GPC) (PLGPC220, Agilent Technologies).For example, weight average molecular weight can be determined by following: in PL Olexis (Polymer Laboratories) column (column temperature: 160 ℃), trichlorobenzene (trichlorobenzene, TCB) is used as solvent, and under the condition of the sample concentration of 1.0mg / mL, the flow rate of 1.0mL / min and the injection volume of 200μl, Agilent high temperature RI detector is used (adopting cubic function correction, reference: polystyrene).

[0073] The inorganic particles and the polymer binder may be included in a weight ratio of about 95:5 to 70:30. For example, the weight ratio of the inorganic particles and the polymer binder may be about 90:10, 85:15, 80:20, or 75:25. The separator including the inorganic particles and the polymer binder within the above range may maintain adhesion even in a state impregnated with an electrolyte solution, so that the thermal shrinkage rate may be reduced even at a high temperature at which the electrochemical device operates.

[0074] The permeability of the separator for an electrochemical device may be about 100 seconds / 100cc or more and 150 seconds / 100cc or less. For example, the permeability of the separator may be 110 seconds / 100cc or more and 140 seconds / 100cc or less, or 120 seconds / 100cc or more and 130 seconds / 100cc or less. For example, the permeability of the separator may be about 100 seconds / 100cc or more and 120 seconds / 100cc or less. When the permeability of the separator is within the above range, the output, stability and cycle characteristics of the electrochemical device can be ensured.

[0075] The thickness of the separator for an electrochemical device may be about 6 μm or more and 20 μm or less. For example, the thickness of the porous coating may 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 separator may be about 10 μm or more and 16 μm or less. When the thickness of the separator is adjusted within the above range, electrical insulation between the electrodes can be achieved while maximizing the amount of active material loaded on the electrodes, thereby enabling the electrochemical device to have a higher capacity.

[0076] According to another embodiment of the present disclosure, the electrochemical device includes a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode, wherein the separator is the separator of the above embodiment. The electrochemical device can be manufactured by inserting an electrode assembly including a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode into a housing or a bag, and sealing the housing or the bag. Before the housing or the bag is sealed, the electrode assembly can be impregnated with an electrolyte solution by injecting an electrolyte solution. The shape of the housing or the bag is not limited. For example, the electrochemical device can be a cylindrical, prismatic, coin-shaped or pouch-shaped lithium secondary battery.

[0077] The positive electrode and the negative electrode can be coated by applying an electrode active material on at least one surface of each current collector and drying. The current collector can be a material that has conductivity without causing chemical changes in the electrochemical device. Examples of current collectors for the positive electrode include aluminum, nickel, titanium, fired carbon, and stainless steel; and aluminum or stainless steel subjected to surface treatment with carbon, nickel, titanium or silver, but are not limited thereto. Examples of current collectors for the negative electrode include copper, nickel, titanium, fired carbon, and stainless steel; and copper or stainless steel subjected to surface treatment with carbon, nickel, titanium or silver, but are not limited thereto. The current collector can be in various forms, such as a thin metal plate, a film, a foil, a mesh, a porous material, or a foam.

[0078] The positive electrode includes a positive electrode current collector and a positive electrode active material layer including 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 at least one selected from the following: Li 1+ x Mn 2-x O4(0≤x≤0.33), LiMnO3, LiMn2O3, LiMnO2, LiNi 1-x Mn x O2(0.01≤x≤0.3), LiMn 2-x M xO2 (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.

[0079] 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. The negative electrode active material in the negative electrode includes carbon, such as lithium metal oxide, hard carbon, and graphite carbon; silicon-based materials, such as Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Si, SiO x (0 < x < 2), SiC, and Si alloys; metal composite oxides, such as Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Group 1, Group 2, and Group 3 of the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); 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; and titanium oxides, which can be used alone or in a mixture of two or more of them.

[0080] The conductive material can be any one of the conductive materials selected from the following or a mixture of two or more conductive materials: graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, carbon nanotube, activated carbon, and polyphenylene derivative. The carbon nanotube has a diameter with a nanoscale size and sp 2The cylindrical graphite sheet of the bonding structure, and exhibits conductor or semiconductor properties according to the angle and structure of the graphite sheet rolling. Carbon nanotubes can be divided into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT) and multi-walled carbon nanotubes (MWCNT) based on the number of bonds constituting their walls, and the carbon nanotubes can be appropriately selected based on the application of the dispersion. More specifically, the conductive material can be one selected from the following: natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel carbon black, furnace carbon black, lamp black, summer black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate and titanium oxide, or a mixture of two or more thereof.

[0081] The binder resin that can be used herein can be any binder resin commonly used for the electrode of electrochemical device. The non-limiting examples of binder resin include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, poly(methyl methacrylate), poly(ethylhexyl acrylate), poly(butyl acrylate), polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan and carboxymethyl cellulose.

[0082] The electrolyte can be prepared by making a + B - A salt of the structure of is obtained by dissolving or dissociating in an organic solvent, wherein A + Including alkali metal cations such as Li + 、Na + or K + , or a combination thereof, and B - Including anions such as PF6 - 、BF4 - , Cl - Br - ,I - 、ClO4 - 、AsF6 - 、CH3CO2 - CF3SO3 - 、N(CF3SO2)2 - or C(CF2SO2)3 -, or a combination thereof, the organic solvent being, for example, 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), γ-butyrolactone, or a mixture thereof.

[0083] The electrochemical device including the electrode assembly may be a lithium secondary battery. The battery may be used as a unit cell, and may be used as a battery module including a unit cell and a battery pack including a battery module. The battery pack may be used as a power source for various electrical devices. Examples of electrical devices include small devices such as computers, mobile phones, and power tools; electric vehicles powered by electric motors, including electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV); electric two-wheeled vehicles, including electric bicycles (E-bike) and electric scooters (E-scooters); electric golf carts; and medium to large devices, such as power storage systems, but not limited thereto.

[0084] Another embodiment of the present disclosure provides a method for preparing a separator for an electrochemical device, the method comprising forming a porous coating layer comprising a polymer binder and inorganic particles on at least one surface of a porous polymer substrate. The contents overlapping with those described in the separator for an electrochemical device are replaced with the description of the aforementioned embodiment.

[0085] The step of forming a porous coating layer may include preparing a coating slurry comprising a polymer binder, inorganic particles and a dispersion medium, and applying the coating slurry to at least one surface of the porous polymer substrate, followed by drying. The inorganic particles may have a surface modified by one or more compounds selected from coumarin and its derivatives.

[0086] The step of forming a porous coating layer may further include subjecting at least one surface of the porous polymer substrate to a corona discharge treatment before applying the coating slurry to at least one surface of the porous polymer substrate. The step of subjecting at least one surface of the porous polymer substrate to a corona discharge treatment can prevent the bonding force between the porous polymer substrate surface and the coating surface from being reduced at high temperatures, and prevent the bonding force between the polymer substrate surface and the coating surface from being reduced due to the electrolyte.

[0087] The step of forming a porous coating may include coating the coating slurry on at least one surface of the porous polymer substrate. For example, the coating may be formed by, but not limited to, a rod coater, a wire rod coater, a roller 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, and a direct metering coater. For example, the step of forming a porous coating may include using a rod coater or a slot die coater to simultaneously coat two surfaces of the porous polymer substrate with the coating slurry.

[0088] The step of forming a porous coating may include applying a coating slurry to a porous polymer substrate, followed by drying or heating the coating to evaporate the dispersion medium contained in the coating. The removal of the dispersion medium may be performed at a temperature that allows only the dispersion medium contained in the coating to evaporate without modifying the polymer binder contained in the coating. For example, the removal of the dispersion medium may be achieved by heating the coating to a predetermined temperature, but ensuring that the temperature of the coating surface does not exceed 60°C. When the coating is heated under the above conditions, the thermal energy may be first used to heat the dispersion medium and change the phase, and may not be used to modify the polymer binder.

[0089] Hereinafter, the present disclosure will be described in more detail with reference to Examples and Experimental Examples.The following Examples and Experimental Examples merely illustrate the present disclosure, and the present disclosure is not limited to the following Examples and Experimental Examples.

[0090] Example 1

[0091] Surface modification of inorganic particles

[0092] At room temperature (25°C), Al2O3 (particle size (D50): 500 nm) was added as inorganic particles to a mixture of APTES:CTAB:EtOH:H2SO4 with a molar ratio of 1:0.1:9:0.004, and after reacting at 60°C for 90 minutes, the inorganic particles were separated and dried in air for 24 hours.

[0093] To 1,200 mL of toluene (pH 8.6) was added 10 g of coumarin having an amine group introduced at the 3-position to prepare a coumarin solution having a coumarin content of 0.05 wt / wt % relative to the toluene solvent, and 30 g of inorganic particles (the coumarin content was 0.01 wt % based on the total weight of the inorganic particles) were added and stirred at room temperature for 12 hours to obtain inorganic particles having surfaces modified with coumarin.

[0094] Preparation of coating slurry

[0095] At room temperature, in 100 mL of distilled water, an acrylic polymer binder (Toyoink, CSB130, solid content 40%, average particle size (D50) about 177 nm), carboxymethyl cellulose (GLChem, SG-L02) and a wetting agent were added in a weight ratio of 8:5:1, and 20 g of surface-modified inorganic particles (weight ratio of inorganic particles: polymer binder 90:10) were added. The mixture was stirred with a vibrator for 60 minutes to prepare a coating slurry.

[0096] Preparation of porous polymer substrates

[0097] As the porous polymer substrate, a polyethylene film (MI: 0.2 g / 10 min, Tm: 135° C., porosity: 45%, average pore size: 45 nm) having a size of 20 cm×30 cm and a thickness of 9 μm was used.

[0098] Preparation of separators

[0099] The coating slurry was coated on both surfaces of the polyethylene film using a bar coater to form a coating layer having a thickness of 3 μm.

[0100] The process of applying a low-temperature air flow to the polyethylene film having the coating layer formed thereon and removing the dispersion medium was repeated 5 times to prepare a separator having a total thickness of 15 μm.

[0101] Example 2

[0102] A separator was prepared in the same manner as in Example 1, except that when the surface of the inorganic particles was modified, a coumarin solution having a coumarin content of 0.15 wt / wt % relative to toluene solvent was prepared and 1.5 g of inorganic particles were added thereto (the coumarin content was 0.1 wt % based on the total weight of the inorganic particles).

[0103] Comparative Example 1

[0104] A separator was prepared in the same manner as in Example 1, except that inorganic particles whose surfaces were not modified were used.

[0105] Comparative Example 2

[0106] A polyethylene film was dip-coated in a solution in which the coumarin used in Example 1 was dissolved in a toluene solvent at a concentration of 1 wt %, immersed in distilled water to undergo a phase change, and then dried in a vacuum oven for 12 hours to prepare a separator having a total thickness of 12 μm without a porous coating layer.

[0107] Comparative Example 3

[0108] A separator was prepared in the same manner as in Example 1, except that when the surface of the inorganic particles was modified, a coumarin solution having a coumarin content of 0.3 wt / wt % relative to toluene solvent was prepared and about 1 g of inorganic particles was added thereto (the coumarin content was 30 wt % based on the total weight of the inorganic particles).

[0109] Experimental Example 1. Determination of transition metal adsorption capacity of inorganic particles

[0110] The transition metal adsorption capacities of the inorganic particles or surface-modified inorganic particles prepared in Examples and Comparative Examples were determined and shown in Table 1 below.

[0111] The adsorption evaluation solution was prepared by dissolving nickel or manganese as a transition metal in dimethyl carbonate (DMC) at a saturated amount (2000 ppm) at room temperature. 1 g of inorganic particles was added to 15 g of the adsorption evaluation solution, stirred with a vibrator for 12 hours, and the inorganic particles were recovered using a centrifuge. The adsorption evaluation solution was then subjected to inductively coupled plasma mass spectrometry (ICP-MS) using ICP-OES (Thermo Fisher) to determine the concentration of transition metal ions retained in the solution, thereby obtaining the amount of transition metal ions adsorbed by the inorganic particles.

[0112] [Table 1]

[0113]

[0114] The inorganic particles of Comparative Example 1 did not show significant adsorption capacity for transition metal ions due to the lack of surface modification. In Examples 1 and 2, it was determined that the adsorption capacity for transition metal ions increased with the increase in the degree of surface modification of the inorganic particles, but when the content of the coumarin-based compound was 0.1 wt % based on the total weight of the inorganic particles, the transition metal ions could be adsorbed and treated in a saturated electrolyte.

[0115] Experimental Example 2. Determination of the characteristics of the separator

[0116] The properties of the separators prepared in Examples and Comparative Examples were determined and shown in Table 2 below.

[0117] Permeability measurement

[0118] The permeability was measured using a Gurley densometer (Gurley, 4110N) to determine the flow rate of 100 cc of air through a 28.6 mm diameter and 645 mm area. 2 The time taken for the separators to be

[0119] Measurement of battery performance retention

[0120] The amount of lithium manganese composite oxide (LiMnO2): conductive material (Denka Black): binder (PVdF) was weighed into a weight ratio of 95:2.5:2.5, added to N-methylpyrrolidone (NMP) and mixed to prepare a positive electrode active material slurry, which was then coated on a 20 μm thick aluminum foil to a thickness of 200 μm, followed by rolling and drying to prepare a positive electrode.

[0121] A Li metal plate having a thickness of 200 μm was used as a negative electrode, and the positive electrode and the negative electrode were stacked with the separator of the example or the comparative example in between, and then inserted into an aluminum bag.

[0122] Into an aluminum bag was injected 1 g of an electrolyte 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 in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a weight ratio of 3 / 7, and the bag was sealed to prepare a battery.

[0123] The prepared battery was subjected to single charge and discharge at 0.1C in a voltage range of 3.0V to 4.4V in a 25°C room, followed by 400 cycles of 0.33C charge and 0.33C discharge to determine the performance retention rate. The performance retention rate was calculated as the ratio of the discharge capacity after 400 cycles to the initial discharge capacity.

[0124] In addition, the resistance was measured before and after 400 cycles to determine the resistance increase rate.

[0125] Measurement of the amount of gas generated

[0126] After piercing the battery that had undergone 400 cycles to collect the gas inside the battery, the amounts of carbon monoxide, carbon dioxide, methane, and ethane contained in the gas were quantified using a flame ionization detector (FID) and a thermal conduction detector (TCD).

[0127] [Table 2]

[0128]

[0129] From the foregoing, it will be understood that, for illustrative purposes, various embodiments of the present disclosure are described herein, and various modifications may be made without departing from the scope and spirit of the present disclosure. Therefore, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the appended claims.

Claims

1. A separator for an electrochemical device, comprising: a porous polymer substrate; and forming a porous coating layer on at least one surface of the porous polymer substrate, The porous coating layer comprises a polymer binder and inorganic particles whose surfaces are modified by one or more compounds selected from coumarin and its derivatives. 2 . The separator according to claim 1 , wherein the compound is bonded to the inorganic particles through the 4-position of the coumarin. 3 . The separator according to claim 1 , wherein the compound removes free radicals generated during charge and discharge of the electrochemical device through position 7 of the coumarin.

4. The separator according to claim 1, wherein the compound contains a functional group capable of adsorbing transition metal ions generated during charge and discharge of the electrochemical device, and The functional group is at least one selected from the group consisting of a hydroxyl group, an aldehyde group, a carboxyl group, a nitro group, a carbonyl group, an ether group, an ester group, an amine group, a phenol group, a benzoyl group, a pyridyl group, and a phosphine group. The separator according to claim 4 , wherein the functional group is located at position 3 of the coumarin. The separator according to claim 1 , wherein the separator comprises 0.01 wt % to 1.5 wt % of the compound based on the total weight of the inorganic particles. 7 . The separator 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 separator according to claim 1, wherein the porous coating layer is formed on both surfaces of the porous polymer substrate, and The separator has a thickness of 6 μm to 20 μm.

9. An electrochemical device comprising: positive electrode; negative electrode; and A separator disposed between the positive electrode and the negative electrode, The separator is the separator for an electrochemical device according to claim 1.

10. The electrochemical device according to claim 9, wherein the positive electrode comprises one or more positive electrode active materials selected from the following: Li 1+x Mn 2-x O4 (0 ≤ x ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2, LiNi 1-x Mn x 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.

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