Composition for nonaqueous electrolyte battery separator, nonaqueous electrolyte battery separator, and nonaqueous electrolyte battery

Abstract

The present invention relates to: a dispersant composition for a nonaqueous electrolyte battery separator; a separator for a nonaqueous electrolyte battery; and a nonaqueous electrolyte battery.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2020-0144322 filed on November 2, 2020, and Korean Patent Application No. 10-2021-0148317 filed on November 1, 2021, the entire disclosure of which is incorporated herein by reference.

[0003] This disclosure relates to a non-aqueous electrolyte battery separator and a non-aqueous electrolyte battery. Background Technology

[0004] Recently, non-aqueous electrolyte batteries, particularly lithium-ion rechargeable batteries, with high voltage and high energy density have attracted attention as power sources for mobile terminals such as laptops or mobile phones, or for hybrid or electric vehicles. Non-aqueous electrolyte batteries, represented by lithium-ion rechargeable batteries, have high capacity and high energy density, resulting in large current flows during internal or external short circuits. This leads to the following problems: the battery generates heat due to Joule heating caused by the short circuit, which, combined with the gas produced by electrolyte decomposition, causes battery expansion, and battery performance deteriorates.

[0005] To address this problem in existing lithium-ion secondary batteries, a separator with a porous substrate containing, for example, a polypropylene or polyethylene membrane is inserted between the positive and negative electrodes. When the temperature rises due to heat generated by a short circuit, the separator containing the porous substrate melts and blocks the pores. As a result, ion movement is hindered, current flow stops, and battery runaway is suppressed.

[0006] Due to the wider use of lithium-ion rechargeable batteries, there is a current need for batteries with higher heat resistance, especially improved heat resistance during internal short circuits. Specifically, when an internal short circuit occurs, the temperature at the short-circuit region is considered to rise above 600°C due to localized heating. Therefore, in conventional separators comprising porous substrates with micropores, such as polyolefin membranes, the separator shrinks or melts at the short-circuit region due to the heat generated by the short circuit, exposing the battery to the dangers of smoke, fire, and explosion.

[0007] As a technique for preventing short circuits caused by thermal shrinkage or thermal melting of the separator and improving battery reliability, a multilayer separator is proposed that includes a heat-resistant porous layer on one or both surfaces (i.e., the front and back sides) of a porous substrate with micropores, such as a polyethylene film.

[0008] In such separators, the heat-resistant porous layer uses inorganic materials and an ethylene-vinyl acetate polymer as a dispersant to uniformly disperse the inorganic materials. However, while adequate stability of the battery separator can be ensured when the dispersibility of the dispersant is maintained at an appropriate level, when the dispersibility is poor, it is difficult to ensure adequate thermal stability of the separator due to the uneven dispersion of the inorganic material.

[0009] Therefore, it is necessary to study membranes that have excellent adhesion strength and dispersibility while also exhibiting excellent safety at high temperatures. Summary of the Invention

[0010] Technical issues

[0011] One object of this disclosure is to provide a non-aqueous electrolyte battery separator and a non-aqueous electrolyte battery, wherein the separator can firmly adhere inorganic fillers when forming a heat-resistant porous layer of the separator, and further improves the heat resistance of the separator by effectively dispersing the inorganic fillers, while exhibiting excellent safety in high-temperature environments, thus providing high safety in accidents such as smoke, fire or explosion.

[0012] Technical solution

[0013] This document provides a dispersant composition for a non-aqueous electrolyte battery separator, comprising a polymer containing a first repeating unit represented by Chemical Formula 1, a second repeating unit represented by Chemical Formula 2, and a third repeating unit represented by Chemical Formula 3:

[0014] [Chemical Formula 1]

[0015]

[0016] In chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 8 carbon atoms.

[0017] [Chemical Formula 2]

[0018]

[0019] In chemical formula 2, R21 is an acetate (CH3COO-) group.

[0020] [Chemical Formula 3]

[0021]

[0022] In chemical formula 3, R3 is hydrogen or an alkyl group having 1 to 5 carbon atoms, R31 is an alkylene group having 1 to 5 carbon atoms or -(C=O)O-, R32 is a group containing an unsaturated functional group, and at least a portion of R32 can form crosslinks with other repeating units in the copolymer.

[0023] According to one embodiment of this disclosure, R32 may contain one or more unsaturated functional groups selected from the group consisting of vinyl, (meth)acrylate, oxetyl, and glycidyl groups.

[0024] More specifically, R32 may contain one or more of the following chemical formulas:

[0025]

[0026]

[0027] R33 to R37 are each independently a single bond, or a straight-chain or branched alkylene group having 1 to 5 carbon atoms.

[0028] In the polymer containing flame-retardant groups, the ratio of the number of repetitions of the first repeating unit to the total number of repetitions of the first to third repeating units, i.e., the proportion of repeating units derived from olefin monomers, can be from about 0.01 to about 0.5, with a lower limit of about 0.01 or more, or about 0.05 or more, or about 0.1 or more, and an upper limit of about 0.5 or less, or about 0.3 or less, or about 0.2 or less.

[0029] Furthermore, in the polymer containing flame-retardant groups, the ratio of the number of repetitions of the second repeating unit to the total number of repetitions of the first to third repeating units, i.e., the proportion of repeating units derived from vinyl acetate monomers, can be from about 0.4 to about 0.95, with a lower limit of about 0.4 or more, or about 0.5 or more, or about 0.6 or more, and an upper limit of about 0.95 or less, or about 0.85 or less, or about 0.8 or less.

[0030] In the polymer containing flame-retardant groups, the ratio of the number of repetitions of the third repeating unit to the total number of repetitions of the first to third repeating units, i.e., the proportion of repeating units with introduced flame-retardant groups, can be from about 0.01 to about 0.3, with a lower limit of about 0.01 or more, or about 0.05 or more, or about 0.1 or more, or about 0.13 or more, and an upper limit of about 0.3 or less, or about 0.2 or less, or about 0.17 or less.

[0031] According to another embodiment of this disclosure, the weight-average molecular weight of the polymer containing flame-retardant groups can be from 100,000 to 500,000 g / mol, with a lower limit of about 100,000 g / mol or more, or about 150,000 g / mol or more, or about 250,000 g / mol or more, and an upper limit of about 500,000 g / mol or less, or about 400,000 g / mol or less, or about 350,000 g / mol or less.

[0032] The dispersant composition for non-aqueous electrolyte battery separators may further include inorganic fillers.

[0033] At this time, the inorganic filler may contain one or more selected from the group consisting of: inorganic oxides, inorganic nitrides, insoluble ionic crystal microparticles, covalently bonded crystals, clay, substances derived from mineral resources, lithium titanium phosphate, and combinations thereof.

[0034] On the other hand, according to another embodiment of the present disclosure, a non-aqueous electrolyte battery separator is provided, the separator comprising: a porous substrate and a heat-resistant porous layer formed on one surface of the porous substrate, wherein the heat-resistant porous layer comprises the above-described dispersant composition for the non-aqueous electrolyte battery separator.

[0035] At this time, the porous substrate may contain one or more resins selected from the group consisting of: polyolefin resins, polyester resins, polyacetal resins, polyamide resins, polycarbonate resins, polyimide resins, polyetheretherketone resins, polyethersulfone resins, and combinations thereof.

[0036] On the other hand, according to yet another embodiment of this disclosure, a non-aqueous electrolyte battery is provided, comprising: a positive electrode, a negative electrode, a non-aqueous electrolyte battery separator, and an electrolyte.

[0037] The terms “first”, “second”, etc., are used to explain various elements, and these terms are only used to distinguish one constituent element from other constituent elements.

[0038] The technical terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the scope of the invention. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” or “described” are intended to include the plural forms. It should be understood that the terms “comprising,” “including,” “having,” etc., are used herein to specify the presence of described features, numbers, steps, components, or combinations thereof, but do not exclude the presence or addition of more than one other feature, number, step, component, or combination thereof.

[0039] Furthermore, as used herein, when referring to a layer or element being formed "on" a layer or element, it means that the layer or element is formed directly on the layer or element, or that other layers or elements may be formed separately between layers, on an object, or on a substrate.

[0040] Although this disclosure may take various forms and can be modified in various ways, specific embodiments will be exemplified and described in detail. However, this is not intended to limit this disclosure to the disclosed forms, and it should be understood that all variations, equivalents, or substitutions within the ideas and technical scope of this disclosure are included in this disclosure.

[0041] Compositions, non-aqueous electrolyte battery separators comprising the present disclosure, and non-aqueous electrolyte batteries according to specific embodiments thereof will now be described in more detail.

[0042] Polymers and Compositions

[0043] According to one embodiment of this disclosure, a dispersant composition for a non-aqueous electrolyte battery separator is provided, comprising a polymer containing a first repeating unit represented by the following chemical formula 1, a second repeating unit represented by the following chemical formula 2, and a third repeating unit represented by the following chemical formula 3:

[0044] [Chemical Formula 1]

[0045]

[0046] In chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 8 carbon atoms.

[0047] [Chemical Formula 2]

[0048]

[0049] In chemical formula 2, R21 is an acetate (CH3COO-) group.

[0050] [Chemical Formula 3]

[0051]

[0052] In chemical formula 3, R3 is hydrogen or an alkyl group having 1 to 5 carbon atoms, R31 is an alkylene group having 1 to 5 carbon atoms or -(C=O)O-, R32 is a group containing an unsaturated functional group, and at least a portion of R32 can form crosslinks with other repeating units in the copolymer.

[0053] As used herein, an unsaturated functional group refers to a group containing, for example, an alkene unsaturated bond with a carbon-carbon double bond, or an alkyne unsaturated bond with a carbon-carbon triple bond, or an unsaturated group containing heteroatoms other than carbon, such as an epoxy group.

[0054] The inventors have experimentally confirmed that, in the polymer used as a heat-resistant porous layer in a non-aqueous electrolyte battery separator, introducing cross-linked unsaturated functional groups into the polymer side chains and controlling the proportions of the repeating units constituting the polymer, i.e., the degree of introduction of ethylene-based, vinyl acetate-based, and unsaturated functional groups, can improve the adhesion and dispersibility of the inorganic filler, thereby improving the heat resistance of the separator and enhancing the high-temperature stability of the separator itself. This completes the present disclosure.

[0055] It is well known that in non-aqueous electrolyte battery separators, polymers containing cyanoethyl groups or polymers containing flame-retardant groups act as adhesives for firmly adhering inorganic fillers. However, specific methods for imparting properties such as crosslinking bonds between repeating units by introducing functional groups into the side chains of such polymers are not yet known.

[0056] The polymer used in the composition according to one aspect of this disclosure acts as a binder to firmly adhere inorganic fillers when forming the heat-resistant porous layer of the diaphragm, and also acts as a dispersant capable of effectively dispersing inorganic fillers, particularly forming cross-links between repeating units or polymer chains, so that a diaphragm with significantly improved binding properties and high-temperature stability compared to the prior art can be achieved.

[0057] According to one aspect of this disclosure, a dispersant composition for a non-aqueous electrolyte battery separator is provided, comprising a polymer containing a first repeating unit represented by the following chemical formula 1, a second repeating unit represented by the following chemical formula 2, and a third repeating unit represented by the following chemical formula 3:

[0058] [Chemical Formula 1]

[0059]

[0060] In chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 8 carbon atoms.

[0061] [Chemical Formula 2]

[0062]

[0063] In chemical formula 2, R21 is an acetate (CH3COO-) group.

[0064] [Chemical Formula 3]

[0065]

[0066] In chemical formula 3, R3 is hydrogen or an alkyl group having 1 to 5 carbon atoms, R31 is an alkylene group having 1 to 5 carbon atoms or -(C=O)O-, R32 is a group containing an unsaturated functional group, and at least a portion of R32 can form crosslinks with other repeating units in the copolymer.

[0067] In such polymers containing flame-retardant groups, the repeating unit represented by chemical formula 1 can be considered to be an α-olefin derived from, for example, ethylene, propylene, butene, i.e., a repeating unit of olefin monomers, which can be specifically represented by the following chemical formula 1-1.

[0068] [Chemical Formula 1-1]

[0069] R1-CH=CH2

[0070] In chemical formula 1-1, R1 is as defined in chemical formula 1 above.

[0071] Furthermore, the repeating unit represented by chemical formula 2 can be considered as ii) repeating units derived from vinyl acetate monomers, which can be specifically represented by the following chemical formula 2-1.

[0072] [Chemical Formula 2-1]

[0073] CH2=CH-R21

[0074] In chemical formula 2-1, R21 is as defined in chemical formula 2 above.

[0075] Copolymers in which vinyl acetate-based or vinyl alcohol-based repeating units are introduced into ethylene repeating units, or copolymers in which cyanoethyl groups are further introduced, are commonly used to bind and disperse inorganic fillers and substrate components in non-aqueous electrolyte battery separators. In particular, the carbonyl group of vinyl acetate can improve the dispersibility of inorganic fillers by interacting with them.

[0076] Furthermore, it can be considered that the repeating unit represented by chemical formula 3 is derived from i) vinyl monomers in which unsaturated functional groups are introduced, or ii) (meth)acrylic monomers in which unsaturated functional groups are introduced, such monomers can be specifically represented by the following chemical formula 3-1.

[0077] [Chemical Formula 3-1]

[0078]

[0079] In chemical formula 3-1, R3, R31 and R32 are as defined in chemical formula 3 above.

[0080] According to one embodiment of this disclosure, R32 may contain one or more unsaturated functional groups selected from the group consisting of vinyl, (meth)acrylate, oxetyl, and glycidyl groups.

[0081] According to one embodiment of this disclosure, R32 may comprise one or more of the following chemical formulas:

[0082]

[0083] R33 to R37 are each independently a single bond, or a straight-chain or branched alkylene group having 1 to 5 carbon atoms.

[0084] In this case, it is more preferable that R1 and R2 are each independently hydrogen, ammonium ion, alkyl group having 1 to 5 carbon atoms, or phenyl group.

[0085] At least a portion of these unsaturated functional groups can form crosslinks with other repeating units, specifically, for example, repeating units of chemical formulas 1 to 3, during the polymerization reaction used to form the polymer.

[0086] These crosslinks make the polymer's molecular structure more robust, and enable membranes using such polymers to have higher stability than conventional membranes, even at high temperatures.

[0087] In the polymer containing flame-retardant groups, the ratio of the number of repetitions of the first repeating unit to the total number of repetitions of the first to third repeating units, i.e., the proportion of repeating units derived from olefin monomers, can be from about 0.01 to about 0.5, with a lower limit of about 0.01 or more, or about 0.05 or more, or about 0.1 or more, and an upper limit of about 0.5 or less, or about 0.3 or less, or about 0.2 or less.

[0088] When the proportion of the first repeating unit, i.e., the proportion of repeating units derived from olefin monomers, is too low, there may be a problem that the polymer has high fluidity and therefore does not easily form pores in the membrane. When this proportion is too high, the solubility in the solvent used for membrane manufacturing decreases, which may cause problems in the manufacturing process.

[0089] Furthermore, in the polymer containing flame-retardant groups, the ratio of the number of repetitions of the second repeating unit to the total number of repetitions of the first to third repeating units, i.e., the proportion of repeating units derived from vinyl acetate monomers, can be from about 0.4 to about 0.95, with a lower limit of about 0.4 or more, or about 0.5 or more, or about 0.6 or more, and an upper limit of about 0.95 or less, or about 0.85 or less, or about 0.8 or less.

[0090] When the proportion of the second repeating unit, i.e., the proportion of repeating units derived from vinyl acetate monomers, is too low, there may be a problem of low adhesion strength in the membrane, making it easy to separate from the membrane or electrode. When the proportion is too high, there may be a problem of the polymer having high fluidity, making it difficult to form pores in the membrane.

[0091] Furthermore, in the polymer containing flame-retardant groups, the ratio of the number of repetitions of the third repeating unit to the total number of repetitions of the first to third repeating units, i.e., the proportion of repeating units incorporating flame-retardant groups, can be from about 0.01 to about 0.3, with a lower limit of about 0.01 or more, or about 0.05 or more, or about 0.1 or more, or about 0.13 or more, and an upper limit of about 0.3 or less, or about 0.2 or less, or about 0.17 or less.

[0092] When the proportion of the number of repetitions of the third repeating unit, i.e., the proportion of repeating units in which flame-retardant groups are introduced, is too low, there may be a problem that the pores formed in the diaphragm cannot maintain their shape at high temperatures and may flow down and become blocked. When the proportion is too high, there may be a problem that the pores are not properly formed because of the low adhesion strength in the diaphragm, which makes them easy to separate from the diaphragm or electrode, and cross-linking occurs before pore formation.

[0093] Such polymers containing flame-retardant groups can be prepared by copolymerization of the following monomers: i) α-olefins, such as ethylene, propylene, butene, i.e., olefinic monomers; ii) vinyl acetate monomers; and iii) vinyl monomers or (meth)acrylate monomers having the aforementioned individual unsaturated functional groups.

[0094] Solution polymerization can be used during polymerization, in which monomers are added to a solvent to prepare a monomer mixture for polymerization, and the polymerization reaction is carried out in the presence of an initiator.

[0095] At this time, solvents that do not affect the polymerization reaction of monomers can be used without particular restriction, such as alcohol solvents such as water, methanol, ethanol, isopropanol, butanol, isobutanol, ketone solvents such as dimethyl ketone, diethyl ketone, methyl ethyl ketone, and methyl isobutyl ketone, aromatic solvents such as toluene and xylene, etc.

[0096] For the polymerization reaction to proceed smoothly, the solvent is preferably used in an amount of about 50 to about 500 parts by weight relative to 100 parts by weight of total monomers.

[0097] Furthermore, the polymerization initiator used during polymerization is a free radical photopolymerization or thermal polymerization initiator commonly used for the polymerization reactions of the aforementioned monomers, and there are no particular restrictions on its type. However, thermal polymerization initiators are preferred to facilitate the polymerization reaction.

[0098] Specifically, the thermal polymerization initiator may include, for example, azo-based or peroxide-based initiators, such as 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-(2,4-dimethylpentanonitrile), 2,2'-azobis-(4-methoxy-2,4-dimethylpentanonitrile), benzoyl peroxide, lauroyl peroxide, tert-butyl peroxyneoplastate, and 1,1'-bis-(bis-tert-butylperoxy)cyclohexane.

[0099] The initiator may be used in an amount of about 0.05 to 5 parts by weight, or about 0.1 to about 3 parts by weight, relative to 100 parts by weight of total monomers.

[0100] These initiators can be prepared as part of the monomer mixture from the outset, or they can be added separately after the pre-prepared monomer mixture has been heated to a suitable polymerization temperature. They can be added separately to form additional crosslinks, either after the polymerization reaction is complete and a polymer has been formed, or in subsequent membrane manufacturing steps.

[0101] The polymerization reaction can be carried out at a temperature of about 100°C from room temperature, and preferably at a temperature above about 40°C or about 50°C and below about 90°C or about 80°C.

[0102] According to another embodiment of this disclosure, the weight-average molecular weight of the polymer containing flame-retardant groups can be from 100,000 to 1,000,000 g / mol, with a lower limit of about 100,000 g / mol or more, or about 150,000 g / mol or more, or about 250,000 g / mol or more, and an upper limit of about 1,000,000 g / mol or less, or about 700,000 g / mol or less, or about 500,000 g / mol or less, or about 400,000 g / mol or less, or about 350,000 g / mol or less.

[0103] Due to complex factors, such as the ratio of repeating units and the molecular weight of the polymer, the adhesion of inorganic fillers can be improved and the inorganic fillers can be effectively dispersed.

[0104] In this regard, the weight-average molecular weight can be measured using polystyrene standards via gel permeation chromatography (GPC).

[0105] Furthermore, the aforementioned polymer is used in dispersant compositions for non-aqueous electrolyte battery separators.

[0106] The dispersant composition for non-aqueous electrolyte battery separators may further include inorganic fillers.

[0107] There are no particular limitations on the inorganic filler, as long as it has a melting point of about 200°C or above, high electrical insulation, electrochemical stability, and is stable in the electrolyte or solvent used for the slurry to form a heat-resistant porous layer.

[0108] The inorganic filler may contain one or more selected from the group consisting of: inorganic oxides, inorganic nitrides, insoluble ionic crystal microparticles, covalently bonded crystals, clay, substances derived from mineral resources, lithium titanium phosphate, and combinations thereof.

[0109] More specifically, the inorganic filler may include, for example, inorganic oxides such as iron oxides, SiO2 (silica), Al2O3 (aluminum oxide), TiO2, BaTiO3, ZrO, PB(Mg3Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, etc. in particulate form; inorganic nitrides such as aluminum nitride, silicon nitride, etc. in particulate form; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, barium sulfate, etc. in particulate form; covalent crystals such as silicon, diamond, etc. in particulate form; clays such as talc, montmorillonite, etc. in particulate form; substances derived from minerals such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, etc.; or lithium titanium phosphate (Li x [[ID=&]]Ti y (PO4)3, where x and y are numbers satisfying 0 < x < 2 and 0 < y < 3, respectively); and any combination thereof.

[0110] There is no particular limitation on the particle size of the inorganic filler, but in order to form a heat-resistant porous layer of uniform thickness and at the same time obtain an appropriate porosity, an inorganic filler having an average particle size of about 5 nm to about 5 μm can be used. Preferably, an inorganic filler having an average particle size of about 0.01 to about 1 μm can be used.

[0111] On the other hand, the average particle size herein can be measured by a device based on the laser diffraction scattering method.

[0112] When the particle size of the inorganic filler is too small, there is a problem that the dispersibility is reduced and thus it may be difficult to adjust the physical properties of the separator.

[0113] When the particle size of the inorganic filler is too large, there are problems that the strength of the heat-resistant porous layer is reduced and the smoothness of the surface tends to deteriorate. In addition, the heat-resistant porous layer becomes thicker, and thus it should be understood that the mechanical properties are reduced.

[0114] In addition, the composition for forming the heat-resistant porous layer in the non-aqueous electrolyte battery separator may contain the above polymer containing a flame retardant group, and if necessary, may also contain resins such as a polymer containing cyanoethyl, ethylene-vinyl acetate copolymer (EVA, containing 20 to 35 mol% of repeating units derived from vinyl acetate), acrylate copolymer, styrene-butadiene rubber (SBR), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), polyurethane, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, etc.

[0115] When these resins are used further, the resins can be mixed in an amount of about 10 to about 1,000 parts by weight relative to 100 parts by weight of the polymer containing flame-retardant groups.

[0116] On the other hand, according to another aspect of this disclosure, a non-aqueous electrolyte battery separator is provided, the separator comprising: a porous substrate and a heat-resistant porous layer formed on a surface of the porous substrate, wherein the heat-resistant porous layer comprises the above-described dispersant composition for the non-aqueous electrolyte battery separator.

[0117] The heat-resistant porous layer may further contain inorganic fillers.

[0118] Specifically, the non-aqueous electrolyte battery separator of this disclosure can be a separator comprising a heat-resistant porous layer and a porous substrate, wherein the heat-resistant porous layer contains a dispersant composition and inorganic fillers, wherein the heat-resistant porous layer can be formed on one or both surfaces of the porous substrate, and the interior of the heat-resistant porous layer can have a number of pores generated by the voids between the inorganic fillers.

[0119] When the heat-resistant porous layer is formed on one surface of a porous substrate, the heat-resistant porous layer can be formed on either the positive electrode side or the negative electrode side surface.

[0120] On the other hand, there are no particular limitations on the method for forming the heat-resistant porous layer. For example, the heat-resistant porous layer can be formed by dispersing an inorganic filler in a dispersant composition to prepare a slurry, coating the slurry onto a porous substrate, and then drying and removing the solvent.

[0121] Here, there are no particular limitations on the solvent used in the dispersant composition, as long as the polymer containing the flame-retardant group is dissolved therein. Examples of solvents may include acetone, tetrahydrofuran, cyclohexanone, ethylene glycol monomethyl ether, methyl ethyl ketone, acetonitrile, furfuryl alcohol, tetrahydrofurfuryl alcohol, methyl acetoacetate, nitromethane, N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone, γ-butyrolactone, propylene carbonate, etc.

[0122] The solvent may be used in an amount of about 300 parts by weight to about 5,000 parts by weight relative to 100 parts by weight of the polymer and resin containing flame-retardant groups.

[0123] The method for dispersing inorganic fillers in the above-mentioned dispersant composition can be any known method using a mixer, disperser, pulverizer, etc. In particular, ball milling can be used.

[0124] There are no particular restrictions on the relative content ratio between the dispersant composition and the inorganic filler in the slurry, but it can be adjusted according to the thickness, average pore size and porosity of the heat-resistant porous layer to be prepared.

[0125] Specifically, the content of inorganic filler in the heat-resistant porous layer can be more than about 50% by weight or less than about 95% by weight.

[0126] When the content of the inorganic filler is too low, the pore ratio in the heat-resistant porous layer becomes smaller, which may degrade battery performance or prevent the battery from achieving sufficient heat resistance. When the content of the inorganic filler is too high, the heat-resistant porous layer may become brittle, making it difficult to process.

[0127] On the other hand, because the pores ensure the pathway for ion conduction, the heat-resistant porous layer can have low electrical resistance. There is no particular limitation on the average pore size, as long as it is large enough to allow lithium ions contained in the electrolyte (described later) to pass through. From the viewpoint of the mechanical strength of the heat-resistant porous layer, the average pore size can be from about 5 nm to about 5 μm, preferably from about 0.1 μm to about 3 μm. The porosity can be in the range of about 5% to about 95%, preferably from about 20% to about 70%.

[0128] Here, the average pore size can be measured using a mercury porosimeter. Porosity can be calculated based on the following formula after obtaining the true density (d) of the inorganic filler, the volume (v) of the heat-resistant porous layer, and the weight (m) of the heat-resistant porous layer.

[0129] Porosity (%) = {1 - m / (vd)} × 100

[0130] As mentioned above, heat-resistant porous layers with average pore size and porosity within the aforementioned range can be obtained by controlling the particle size or content of inorganic fillers.

[0131] On the other hand, the porous substrate may contain a thermoplastic resin component.

[0132] If the temperature becomes higher than a certain limit, the thermoplastic resin component can melt and close the pores in the porous substrate, thereby hindering ion movement, stopping the current, and suppressing heating or ignition.

[0133] The thermoplastic resin used as the porous substrate may include polyolefin resins, such as low-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, etc.; polyester resins, such as polyethylene terephthalate, polybutylene terephthalate, etc.; polyacetal resins; polyamide resins; polycarbonate resins; polyimide resins; polyetheretherketone resins; polyethersulfone resins; and any combination thereof.

[0134] On the other hand, the porous substrate is preferably a film. While there is no particular limitation on its thickness, it is preferably from about 2 μm to about 50 μm. When the thickness is too thin, it is difficult to maintain mechanical properties. When the thickness is too thick, it may act as a resistive layer.

[0135] Although there are no particular limitations on the average pore size and porosity of the porous substrate, the average pore size is preferably from about 0.1 μm to about 30 μm, and the porosity is preferably from about 10% to about 90%.

[0136] When the pore size is too small or the porosity is too low, the ion conductivity may be degraded. When the average pore size is too large or the porosity is too high, the mechanical strength may be degraded. Therefore, the substrate may not function as a substrate.

[0137] The average pore size can be measured in the same manner as for heat-resistant porous layers. On the other hand, the porosity can be calculated based on the following formula after obtaining the true density (d), volume (v), and weight (m) of the porous substrate.

[0138] Porosity (%) = {1 - m / (vd)} × 100

[0139] On the other hand, methods for coating the slurry onto a porous substrate can include coating methods commonly used in the art, and are not particularly limited, as long as they can achieve the desired film thickness or coating area. Examples of such methods can include gravure coating, reverse roller coating, transfer roller coating, kiss coating, dip coating, knife coater method, air knife coating, blade coater method, bar coating, extrusion coating, cast coating, mold coating, screen printing, spray coating, etc.

[0140] There is no particular limitation on the total thickness of the non-aqueous electrolyte battery separator thus obtained, and it can be adjusted considering the battery's application and performance. From the viewpoint of ensuring isolation between the positive and negative electrodes, the total thickness can preferably be in the range of about 2 to about 55 μm.

[0141] Non-aqueous electrolyte batteries

[0142] On the other hand, a non-aqueous electrolyte battery according to one aspect of this disclosure may include a positive electrode, a negative electrode, the aforementioned non-aqueous electrolyte battery separator, and an electrolyte.

[0143] Specifically, the non-aqueous electrolyte battery separator is disposed between the positive and negative electrodes and is immersed in the electrolyte to manufacture a non-aqueous electrolyte battery.

[0144] When using a non-aqueous electrolyte battery separator in which a heat-resistant porous layer is formed on one surface of a porous substrate, the separator can be positioned such that the surface of the heat-resistant porous layer faces either the positive or negative electrode.

[0145] The non-aqueous electrolyte battery of the present disclosure may include, for example, a lithium secondary battery, such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, a lithium ion polymer secondary battery, etc.

[0146] On the other hand, the positive electrode and the negative electrode can generally be manufactured by coating an electrode current collector with an electrode mixture prepared by dispersing a positive electrode or negative electrode active material and a conductive assistant in an adhesive solution.

[0147] The positive electrode active material may include a lithium-containing transition metal oxide having a layered structure, represented by the chemical formula Li 1+ x MO2 (-0.1 < x < 0.1, M: Co, Ni, Mn, Al, Mg, Zr, Ti, Sn, etc.); a lithium manganese oxide having a spinel structure, such as LiMn2O4 or a composition obtained by substituting a part thereof with one or more other elements; and an olivine-type compound represented by LiMPO4 (M: Co, Ni, Mn, Fe, etc.).

[0148] The lithium-containing transition metal oxide having a layered structure may include, for example, LiCoO2 or LiNi 1-x Co x-y Al y O2 (0.1 ≤ x ≤ 0.3, 0.01 ≤ y ≤ 0.2), and an oxide containing at least Co, Ni, and Mn (LiMn 1 / 3 Ni 1 / 3 Co 1 / 3 O2, LiMn 5 / 12 Ni 5 / 12 Co 1 / 6 O2, LiNi 3 / 5 Mn 1 / 5 Co 1 / 5 O2, etc.).

[0149] On the other hand, the negative electrode active material may include, for example, lithium metal, a lithium alloy such as a lithium aluminum alloy, etc., a carbonaceous material capable of storing and releasing lithium, graphite, coke such as phenolic resin, furan resin, etc., carbon fiber, vitreous carbon, pyrolytic carbon, activated carbon, etc.

[0150] On the other hand, the positive electrode current collector may include, for example, a thin metal foil made of aluminum, nickel, or a combination thereof. The negative electrode current collector may include, for example, a thin metal foil made of copper, gold, nickel, a copper alloy, or a combination thereof.

[0151] On the other hand, the conductive additive may include, for example, carbon black, such as acetylene black, Ketjen black, etc.; metal fibers, such as aluminum, nickel, etc.; natural graphite, thermally expanded graphite, carbon fiber, ruthenium oxide, titanium oxide, etc. Among these, acetylene black or Ketjen black may be preferred because they can provide the desired conductivity with a small amount added.

[0152] On the other hand, the adhesive may include a variety of known adhesives. Examples include polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, crosslinked polymers of fluoroolefin copolymers, styrene-butadiene copolymers, polyacrylonitrile, polyvinyl alcohol, etc.

[0153] The adhesive may include an adhesive dissolved in a solvent. Examples of the solvent may include N-methyl-2-pyrrolidone (NMP).

[0154] On the other hand, regarding the electrolyte, a solution in which the lithium salt is dissolved in an organic solvent can be used. There are no particular restrictions on the lithium salt, as long as it dissociates in the solvent to form Li. + The ions should be readily soluble and not prone to side reactions such as decomposition within the voltage range of the battery in use.

[0155] Examples of suitable lithium salts include inorganic lithium salts such as LiClO4, LiPF6, LiBF4, LiAsF6, and LiSbF6, as well as organic lithium salts such as LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiN(CF3SO2)2, LiC(CF3SO2)3, and LiCnF4. 2n+1 SO3 (n≥2), LiN(RfOSO2)2, etc. (where Rf represents a fluoroalkyl group). Preferred examples of lithium salts may include LiPF6, LiClO4, LiAsF6, LiBF4, LiCF3SO3, and Li(CF3SO2)2N.

[0156] On the other hand, there are no particular restrictions on the organic solvents used in the electrolyte, as long as they can dissolve the lithium salt and are not likely to cause side reactions such as decomposition within the voltage range of the battery in use. Examples include cyclic carbonates such as propylene carbonate, ethylene carbonate, etc., chain carbonates such as ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, etc., or mixtures thereof, but not limited to these.

[0157] When using a mixture of cyclic carbonates or chain carbonates, from the viewpoint of optimizing dielectric constant and viscosity, the volume ratio of cyclic carbonate to chain carbonate is preferably from about 4:1 to about 1:4.

[0158] On the other hand, the non-aqueous electrolyte battery of this disclosure may include a prismatic or cylindrical shape, wherein a steel or aluminum can is used as the shell (i.e., the can casing). Furthermore, it may be a packaged battery, wherein a metal-deposited laminate is used as the shell, but is not particularly limited thereto.

[0159] Beneficial effects

[0160] The non-aqueous electrolyte battery separator composition disclosed herein can firmly adhere inorganic fillers when forming a heat-resistant porous layer of the separator, and can further improve the heat resistance of the separator by effectively dispersing the inorganic fillers, and can also have excellent safety even at high temperature environments. Detailed Implementation

[0161] The effects and functions of the present invention will now be described in more detail with reference to specific exemplary embodiments thereof. However, these exemplary embodiments are for illustrative purposes only, and the scope of the present invention is not intended to be limited thereto.

[0162] <Example>

[0163] Polymer preparation

[0164] <Synthesis example 1>

[0165] Add 1500g of vinyl acetate to a 3L reactor, followed by 200g of methanol. While stirring, add 200g of ethylene, and then wait until the ethylene dissolves in the solution and the reactor pressure stabilizes.

[0166] The reactor temperature was raised to approximately 60°C, and an initiator solution, obtained by dissolving 0.5 g of initiator AIBN in 50 g of methanol, was added to the reactor. At this point, the internal pressure of the reactor was 30 bar.

[0167] The polymerization temperature was kept constant, and the polymerization reaction was carried out for approximately 5 hours. After the reaction was completed, a reaction terminator solution, obtained by dissolving 0.5 g of sorbic acid in 50 g of methanol, was added to the reactor.

[0168] The reactor is cooled to room temperature and the gas is slowly vented to remove unreacted ethylene, and the polymerization product is obtained from the bottom of the reactor.

[0169] The obtained polymer product was dried in a vacuum oven set at 75°C for approximately 24 hours to remove unreacted monomers and methanol. This yielded an ethylene-vinyl acetate copolymer.

[0170] (Mw: 300,000, Ethylene fraction: 20 mol%)

[0171] <Synthesis example 2>

[0172] Add 1350g of vinyl acetate and 150g of glycidyl acrylate to a 3L reactor, and then add 200g of methanol. While stirring, add 200g of ethylene and wait until the ethylene dissolves in the solution and the reactor pressure stabilizes.

[0173] The reactor temperature was raised to approximately 60°C, and an initiator solution, obtained by dissolving 0.5 g of initiator AIBN in 50 g of methanol, was added to the reactor. At this point, the internal pressure of the reactor was 30 bar.

[0174] The polymerization temperature was kept constant, and the polymerization reaction was carried out for approximately 5 hours. After the reaction was completed, a reaction terminator solution, obtained by dissolving 0.5 g of sorbic acid in 50 g of methanol, was added to the reactor.

[0175] The reactor is cooled to room temperature, and the gas is slowly vented to remove unreacted ethylene, yielding the polymerization product from the bottom of the reactor.

[0176] The obtained polymer product was dried in a vacuum oven set at 75°C for approximately 24 hours to remove unreacted monomers and methanol. This yielded an ethylene-vinyl acetate-glycidyl acrylate copolymer.

[0177] (Mw: 320,000, Ethylene fraction: 20 mol%, Vinyl acetate fraction: 73 mol%, Glycidyl acrylate fraction: 7 mol%)

[0178] Manufacturing of dispersant compositions (slurries) and diaphragms

[0179] <Comparative Example 1>

[0180] With an average particle size of 0.7 μm and a BET of 4 m 2 / g of alumina was dispersed in acetone. The copolymer prepared in Synthesis Example 1 and the alumina dispersion were mixed at a polymer:alumina weight ratio of 20:80, and the mixture was pulverized and mixed in a ball mill for 20 minutes using two types of zirconia beads (0.5mm:1mm = 1:1) to prepare a slurry.

[0181] The slurry prepared above is applied to a surface of a porous polyethylene substrate using a scraper and dried to create a membrane with a coating formed thereon.

[0182] <Comparative Example 2>

[0183] With an average particle size of 0.7 μm and a BET of 4 m 2 / g of alumina was dispersed in acetone. Polyvinylidene fluoride (Mw: 400,000) and the alumina dispersion were mixed at a polymer:alumina weight ratio of 20:80, and pulverized and mixed in a ball mill for 20 minutes using two types of zirconia beads (0.5mm:1mm = 1:1) to prepare a slurry.

[0184] The slurry prepared above is applied to a surface of a porous polyethylene substrate using a scraper and dried to create a membrane with a coating formed thereon.

[0185] <Example 1>

[0186] With an average particle size of 0.7 μm and a BET of 4 m 2 / g of alumina was dispersed in acetone. The copolymer prepared in Synthesis Example 2 and the alumina dispersion were mixed at a polymer:alumina weight ratio of 20:80. The mixture was then pulverized and mixed in a ball mill using two types of zirconia beads (0.5mm:1mm = 1:1) for 20 minutes to prepare a slurry.

[0187] The slurry prepared above is applied to a surface of a porous polyethylene substrate using a scraper and dried to create a membrane with a coating formed thereon.

[0188] Dispersion stability

[0189] The slurries prepared in the examples and comparative examples were rotated at 300 rpm using a dispersion stability analyzer (LUMiSizer, LS651) and the settling velocity of the slurry particles in the slurry was measured at 25°C.

[0190] Adhesion strength

[0191] The prepared diaphragm was cut into two pieces with a size of 15mm × 100mm.

[0192] Two prepared separators were overlapped and sandwiched between 100 μm PET films, then passed through a roller laminator at 100°C for adhesion. Simultaneously, the film was heated for 30 seconds at a roller laminator speed of 0.3 m / min, with a pressure of 2 kgf / cm². 2 .

[0193] The ends of the two adhered diaphragms were mounted on a UTM instrument (LLOYD Instruments, LF Plus) to measure the strength required to separate the adhered diaphragms by applying force in both directions at a measurement speed of 100 mm / min.

[0194] Breathability

[0195] Air permeability was measured using a Gurley air permeability meter according to JIS P-8117 standard. At this point, 100 mL of air was measured passing through a diameter of 28.6 mm and an area of ​​645 mm². 2 The time required.

[0196] Air permeability after high temperature test

[0197] The diaphragms manufactured in the examples and comparative examples were placed in an oven and placed in a vacuum oven at 70°C for about 1 hour.

[0198] Then, the diaphragm was removed from the oven and its permeability was measured using a Gley-type air permeability meter according to JIS P-8117 standard. At this point, the permeability of 100 mL of air passing through a membrane with a diameter of 28.6 mm and an area of ​​645 mm² was measured. 2 The time required.

[0199] The evaluation results are summarized in the table below.

[0200] Table 1

[0201]

[0202] Referring to Table 1, it can be confirmed that, in the case of Example 1, the values ​​of dispersion stability and air permeability (before the high temperature test) are not significantly different from those of Comparative Example 1 or Comparative Example 2.

[0203] However, it can be confirmed that the adhesion strength of Comparative Example 1 and Example 1, which use ethylene-vinyl acetate adhesives, is greater than that of Comparative Example 2, which uses PVDF. It can be clearly confirmed that Example 1, which uses a copolymer containing functional groups capable of crosslinking between molecules or between repeating units, maintains excellent air permeability even after exposure to high temperatures, compared to Comparative Example 1.

Claims

1. A non-aqueous electrolyte battery separator, the separator comprising: a porous substrate, and a heat-resistant porous layer formed on one surface of the porous substrate. The heat-resistant porous layer comprises a dispersant composition for a non-aqueous electrolyte battery separator, the dispersant composition comprising a polymer containing a first repeating unit represented by Chemical Formula 1, a second repeating unit represented by Chemical Formula 2, a third repeating unit represented by Chemical Formula 3, and an inorganic filler: [Chemical Formula 1] In chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 8 carbon atoms. [Chemical Formula 2] In chemical formula 2, R21 is an acetate (CH3COO-) group. [Chemical Formula 3] In chemical formula 3, R3 is hydrogen or an alkyl group having 1 to 5 carbon atoms, R31 is an alkylene group having 1 to 5 carbon atoms or -(C=O)O-, and R32 is a group containing an unsaturated functional group. At least a portion of R32 can form crosslinks with other repeating units in the copolymer. The ratio of the number of repetitions of the first repeating unit to the total number of repetitions from the first repeating unit to the third repeating unit in the polymer is between 0.01 and 0.

3. The ratio of the number of repetitions of the second repeating unit to the total number of repetitions of the first to the third repeating units in the polymer is between 0.4 and 0.

95. The ratio of the number of repetitions of the third repeating unit in the polymer to the total number of repetitions from the first repeating unit to the third repeating unit is 0.01 to 0.

3.

2. The non-aqueous electrolyte battery separator according to claim 1, wherein R32 comprises one or more unsaturated functional groups selected from the group consisting of vinyl and (meth)acrylate groups.

3. The non-aqueous electrolyte battery separator according to claim 1, wherein R32 is a group containing an unsaturated functional group, which is replaced by one or more groups selected from the group consisting of oxobutyl and glycidyl groups.

4. The non-aqueous electrolyte battery separator according to claim 2 or 3, wherein R32 comprises one or more of the following chemical formulas: , , , and , in, R33 to R37 are each independently a single bond, or a straight-chain or branched alkylene group having 1 to 5 carbon atoms.

5. The non-aqueous electrolyte battery separator according to claim 1, wherein the polymer has a weight-average molecular weight of 100,000 to 1,000,000.

6. The non-aqueous electrolyte battery separator according to claim 1, wherein the inorganic filler comprises one or more selected from the group consisting of: inorganic oxides, inorganic nitrides, insoluble ionic crystal microparticles, covalently bonded crystals, clay, and lithium titanium phosphate.

7. The non-aqueous electrolyte battery separator according to claim 1, wherein the inorganic filler comprises a substance derived from mineral resources.

8. The non-aqueous electrolyte battery separator according to claim 1, wherein the porous substrate comprises one or more resins selected from the group consisting of: polyolefin resin, polyester resin, polyacetal resin, polyamide resin, polyimide resin, polyetheretherketone resin, and polyethersulfone resin.

9. The non-aqueous electrolyte battery separator according to claim 1, wherein the porous substrate comprises polycarbonate resin.

10. A non-aqueous electrolyte battery, comprising: a positive electrode, a negative electrode, a non-aqueous electrolyte battery separator according to claim 1, and an electrolyte.

Images