Binder composition for secondary battery separator coating and secondary battery comprising same

Abstract

The present invention relates to: a binder composition comprising a copolymer, which includes an acrylamide-based monomer unit and a vinyl pyrrolidone monomer unit, and a first crosslinking agent; a slurry comprising the binder composition; a separator; and a secondary battery comprising the binder composition. The binder composition according to the present invention can produce a separator having high heat resistance, and the secondary battery comprising same has excellent performance.

Description

Binder composition for coating a secondary battery separator and a secondary battery containing the same

[0001] The present invention relates to a binder composition for coating a secondary battery separator, a slurry containing the same, a separator, and a secondary battery containing the same.

[0002]

[0003] A lithium secondary battery refers to a battery comprising a positive electrode containing a positive electrode active material capable of inserting / extracting lithium ions, a negative electrode containing a negative electrode active material capable of inserting / extracting lithium ions, and an electrode assembly having a microporous separator interposed between the positive electrode and the negative electrode, wherein the electrode assembly contains a non-aqueous electrolyte containing lithium ions.

[0004] Due to their high energy density, lithium-ion batteries are widely used in the electrical, electronic, telecommunications, and computer industries. Following small lithium-ion batteries for portable electronic devices, their applications are expanding to include high-capacity batteries for hybrid and electric vehicles. With this expansion of applications, there is a growing demand for lithium-ion batteries that offer both high capacity and long lifespan.

[0005] However, as the use of secondary batteries increases, various accidents originating from secondary batteries are also on the rise.

[0006] Consequently, the safety of secondary batteries is emerging as a social issue, and interest in secondary batteries with enhanced safety is steadily increasing.

[0007] One of the key functions of a separator is to prevent physical contact between the positive and negative electrodes. If the positive and negative electrodes come into physical contact and an internal short circuit occurs, an overcurrent is induced, and the risk of the lithium secondary battery igniting or exploding increases rapidly.

[0008] However, repeated charging and discharging of a secondary battery generates heat, and if the thermal shrinkage rate of the separator is not excellent, deformation of the separator can cause the positive and negative electrodes to come into contact, which can increase the risk of fire or explosion.

[0009] Ultimately, since the safety of secondary batteries is directly linked to the safety of separators, there is a demand for separators with enhanced safety. Consequently, there is a need for research and development of separators with excellent heat resistance characteristics, including thermal shrinkage rates, as well as methods for manufacturing said separators and secondary batteries containing said separators.

[0010]

[0011] [Prior Art Literature]

[0012] [Patent Literature]

[0013] (Patent Document 1) Korean Published Patent Application No. 10-2008-0021270 (March 7, 2008)

[0014]

[0015] The objective of the present invention to solve the problems of the prior art is to provide a binder composition with improved heat resistance and a secondary battery containing the same.

[0016] Specifically, the aim is to enhance safety by improving the heat resistance of the binder through chemical crosslinking of the copolymer and manufacturing a secondary battery using this.

[0017] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other problems not mentioned but intended to be solved will be clearly understood by those skilled in the art to which the present invention belongs from the content to be described below.

[0018]

[0019] One aspect of the present invention is a copolymer comprising an acrylamide-based monomer unit and a vinylpyrrolidone monomer unit; and

[0020] including a first crosslinking agent,

[0021] A composition is provided.

[0022] Another aspect of the present invention provides a binder comprising the above composition.

[0023] Another aspect of the present invention provides a slurry comprising the binder and inorganic particles.

[0024] Another aspect of the present invention provides a separation membrane comprising a porous substrate coated with the above slurry.

[0025] Another aspect of the present invention comprises the step of coating the slurry onto a porous substrate; and a heat treatment process,

[0026] A method for manufacturing a separation membrane is provided, wherein the temperature of the heat treatment process is 50℃ to 100℃.

[0027] The remaining aspect of the present invention provides a secondary battery comprising the above-mentioned separator.

[0028]

[0029] The composition of the present invention can form chemical crosslinks of a copolymer, and a separator manufactured using the same can have high heat resistance, and therefore a secondary battery including the separator can have excellent performance.

[0030]

[0031] Hereinafter, the operation and effects of the invention will be described in more detail through specific embodiments and drawings. However, these embodiments are merely examples of the invention and do not define the scope of the invention.

[0032] Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0033] Therefore, it should be understood that the configuration of the embodiments described in this specification is merely one of the most preferred embodiments of the present invention and does not represent all of the technical ideas of the present invention, and that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0034] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0035] Where various parameters in this specification are given as an enumeration of ranges, preferred ranges, preferred upper limits, and preferred lower limits, it should be understood that any pair of any upper range limit or preferred value and any lower range limit or preferred value specifically discloses all ranges formed by any pair of any upper range limit or preferred value, regardless of whether the range is disclosed separately.

[0036] Where a range of numerical values ​​is mentioned in this specification, unless otherwise described, the range is intended to include its endpoint and all integers and fractions within the range.

[0037] The scope of the present invention is not intended to be limited to specific values ​​mentioned when defining the scope.

[0038] In the present specification, "a to b" and "a~b" indicating numerical ranges are defined as ≥a and ≤b.

[0039] Embodiments of the present invention have been described in detail below, but the present invention is not limited thereto.

[0040]

[0041] The composition of the present invention may include a copolymer comprising an acrylamide-based monomer unit and a vinylpyrrolidone monomer unit and a first crosslinking agent.

[0042] In one embodiment, the acrylamide-based monomer unit may include a first acrylamide monomer unit and a second acrylamide monomer unit.

[0043] Accordingly, a composition according to one embodiment may include a copolymer comprising a first acrylamide monomer unit, a second acrylamide monomer unit, and a vinylpyrrolidone monomer unit, and a first crosslinking agent.

[0044] In one embodiment, the first acrylamide monomer unit may additionally include a carbonyl group (-C(=O)-), and the carbonyl group may be a ketone group.

[0045] That is, the first acrylamide monomer unit may additionally include a carbon-oxygen double bond (C=O) in addition to the acrylamide group.

[0046] In one embodiment, the first acrylamide monomer unit may be formed by polymerizing diacetone acrylamide.

[0047] In one embodiment, the second acrylamide monomer unit may be formed by polymerizing acrylamide, methacrylamide, N-[3-(dimethylamino)propyl]methacrylamide, N-ethylacrylamide, N-(tert-butyl)acrylamide, N-methylacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, or a combination thereof.

[0048] In one embodiment, the copolymer may be represented by the following chemical formula 1.

[0049]

[0050] [Chemical Formula 1]

[0051]

[0052]

[0053] In the above chemical formula 1,

[0054] R1 can be hydrogen (H) or a methyl group (CH3), and

[0055] a+b+c=1, and

[0056] a, b, and c can each be positive numbers greater than 0 and less than 1.

[0057] For example, a+b can be 0.3 to 0.9, and c can be 0.1 to 0.7.

[0058] a, b, and c may represent the weight fraction of copolymer monomer units based on the total copolymer weight of 1.

[0059] For example, if a+b is 0.9 and c is 0.1, the sum of the weight of monomer units a and monomer units b can be 9 times the weight of monomer units c.

[0060] In one embodiment, the weight ratio of the acrylamide-based monomer unit and the vinyl pyrrolidone monomer unit (weight of acrylamide-based monomer unit: weight of vinyl pyrrolidone monomer unit) may be 0.4 to 9:1.

[0061] For example, the weight ratio of the acrylamide-based monomer unit and the vinyl pyrrolidone monomer unit (weight of acrylamide-based monomer unit: weight of vinyl pyrrolidone monomer unit) may be 0.43:1, 0.5:1, 0.8:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 5.7:1, 6:1, 7:1, or 8:1.

[0062] In one embodiment, the weight ratio of the first acrylamide monomer unit and the second acrylamide monomer unit (weight of the first acrylamide monomer unit: weight of the second acrylamide monomer unit) may be 1:1.5 to 9.

[0063] For example, the weight ratio of the first acrylamide monomer unit and the second acrylamide monomer unit (weight of the first acrylamide monomer unit:weight of the second acrylamide monomer unit) may be 1:1.8, 1:3, 1:4, 1:5, 1:6, 1:6.5, 1:7, or 1:8.

[0064] Accordingly, in one embodiment, the copolymer may have a weight ratio of the first acrylamide monomer unit, the second acrylamide monomer unit, and the vinylpyrrolidone monomer unit of 1:6.5:2.5, 2:6:2, or 3:5.5:1.5.

[0065] In one embodiment, the copolymer may be crosslinked by a second crosslinking agent.

[0066] That is, the copolymer composition may include a copolymer crosslinked by the second crosslinking agent and a first crosslinking agent.

[0067] The copolymer is partially cross-linked by the second cross-linking agent, and the copolymer polymer can be further cross-linked by the first cross-linking agent as it is applied to manufacture a separation membrane and undergoes coating and heat treatment.

[0068] In one embodiment, the second crosslinking agent may include two or more polymerizable unsaturated groups capable of bonding with the acrylamide-based monomer unit, the vinylpyrrolidone monomer unit, or a combination thereof.

[0069] The above second crosslinking agent may include two or more of the above polymerizable unsaturated groups to crosslink the copolymer.

[0070] The above polymerizable unsaturated group may include a vinyl group (-CH=CH2), an allyl group (-CH2-CH=CH2), an isoprenyl group (-CH2-C(CH3)=CH2), an acryloyl group (-CH=CH-CO-), an acrylate group (-(C=O)-O-), or a combination thereof.

[0071] In one embodiment, the second crosslinking agent is methylenebisacrylamide (MBA), ethylenebisacrylamide (EBA), divinylbenzene (DVB), butadiene, hexadiene, isoprene, divinyl ether, diallyl phthalate (DAP), diallyl ether, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate (TMPTMA), ethylene glycol diacrylate, 1,4-butanediol diacrylate, It may include 1,6-hexanediol diacrylate, polyethylene diacrylate, or a combination thereof.

[0072] For example, the above methylenebisacrylamide can be represented by the following chemical formula 2.

[0073]

[0074] [Chemical Formula 2]

[0075]

[0076]

[0077] In one embodiment, the weight of the second crosslinking agent may be 0.05 to 0.5 parts by weight based on 100 parts by weight of the total weight of the monomers of the copolymer.

[0078] For example, the weight of the second crosslinking agent may be 0.1 to 0.4 parts by weight, 0.13 to 0.3 parts by weight, 0.15 to 0.25 parts by weight, or 0.17 to 0.23 parts by weight, based on 100 parts by weight of the total weight of the monomers of the copolymer.

[0079] If the weight of the second crosslinking agent is lower than that of the present invention, the degree of crosslinking formed by the copolymer may be low, and the binder prepared using the copolymer may not have excellent heat resistance and may dissolve in the electrolyte inside the battery containing the binder.

[0080] If the weight of the second crosslinking agent exceeds that of the present invention, the viscosity of the copolymer may be excessively high or gelation may occur, and as a result, the process of coating the porous substrate may not be easily performed.

[0081] In one embodiment, the copolymer may be a random or block copolymer depending on the synthesis process.

[0082] In one embodiment, the first crosslinking agent may include two or more functional groups capable of bonding to the acrylamide-based monomer unit.

[0083] In one embodiment, the functional group of the first crosslinking agent may include two or more nitrogen atoms.

[0084] In one embodiment, the first crosslinking agent may include two or more hydrazide groups, amino groups, amine groups, or a combination thereof.

[0085] For example, the first crosslinking agent may include two hydrazide groups, or two amino groups, or one hydrazide group and one amino group.

[0086] In one embodiment, the first crosslinking agent may include adipic acid dihydrazide (ADH), oxalyl dihydrazide, decan dihydrazide, isophthalic dihydrazide, succinic dihydrazide, carbohydrazide, dodecane dihydrazide, ethylenediamine (EDA), 1,3-propanediamine, 1,6-hexanediamine, cyclohexanediamine, phenylenediamine, hexamethylenediamine, or a combination thereof.

[0087] For example, adipic acid dihydrazide can be represented by the following chemical formula 3.

[0088]

[0089] [Chemical Formula 3]

[0090]

[0091]

[0092] In one embodiment, the molar ratio of the first crosslinking agent and the first acrylamide monomer unit (mol of the first crosslinking agent:mol of the first acrylamide monomer unit) may be 0.3 to 3:1.

[0093] For example, the molar ratio of the first crosslinking agent and the first acrylamide monomer unit (moles of the first crosslinking agent:moles of the first acrylamide monomer unit) may be 0.5:1, 1:1, 1.5:1, 2:1, or 2.5:1.

[0094] If the content of the first crosslinking agent exceeds that of the present invention, some of the first crosslinking agent may not participate in the crosslinking, and the first crosslinking agent that does not participate in the crosslinking reaction may act as an impurity in the secondary battery, which may cause side effects such as shortened durability of the secondary battery or deterioration of electrochemical performance.

[0095] If the content of the first crosslinking agent is lower than that of the present invention, the crosslinking of the copolymer may not occur sufficiently, and heat resistance properties including thermal shrinkage rate may be poor.

[0096] A binder according to another aspect of the present invention may include the above composition.

[0097] A slurry according to another aspect of the present invention may include the binder and inorganic particles.

[0098] The above-mentioned inorganic particles can be used without limitation as long as they are insulating particles, and preferably, they can be high dielectric constant insulating particles.

[0099] Specific examples of the above-mentioned inorganic particles include aluminum oxide (Al2O3), aluminum oxide hydroxide (AlOOH), silicon dioxide (SiO2), titanium dioxide (TiO2), zirconium dioxide (ZrO2), zinc oxide (ZnO), nickel oxide (NiO), calcium oxide (CaO), tin dioxide (SnO2), yttrium oxide (Y2O3), magnesium oxide (MgO), barium titanate (BaTiO3), calcium titanate (CaTiO3), strontium titanate (SrTiO3), silicon carbide (SiC), lithium phosphate (Li3PO4), lead zirconium titanate (Pb(Zr,Ti)O3, PZT), raceded lead zirconium titanate ((Pb,La)(Zr,Ti)O3, PLZT), and mixtures thereof.

[0100] The above inorganic particles are not subject to any special size limitations, but for example, the average particle size may be 0.01 μm to 30 μm, and more preferably 0.1 μm to 10 μm. If the average particle size of the inorganic particles is below the above preferred range, dispersibility may be reduced, and if it exceeds the above preferred range, the thickness of the coating layer after coating may increase, and mechanical properties may be degraded.

[0101] In addition, the above-mentioned inorganic particles have no particular restrictions on shape and may be, for example, spherical, plate-shaped, elliptical, or irregular.

[0102] A separation membrane according to another aspect of the present invention may include a porous substrate coated with the slurry.

[0103] In one embodiment, a separator can be manufactured by coating the slurry composition on at least one surface of a porous substrate film, or by manufacturing the slurry composition into a film form and laminating it onto a porous substrate film.

[0104] As an example of manufacturing a separation membrane, the method may include: (a) a step of preparing a polymer solution by dissolving or dispersing the binder in a solvent; (b) a step of adding and mixing inorganic particles to the polymer solution of step a); and (c) a step of coating and drying one or more regions selected from the group consisting of the surface of a polyolefin-based separation membrane substrate and a portion of the pores in the substrate with the mixture of step b).

[0105] First, 1) the above binder is prepared and manufactured in the form of a polymer solution by dissolving or dispersing it in a suitable solvent.

[0106] As for the solvent, it is preferable to have a solubility index similar to that of the copolymer used as a binder and a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or mixtures thereof. More preferably, it can be used in a water-dispersed state.

[0107] 2) Inorganic particles are added and dispersed in the prepared polymer solution to prepare a mixture of inorganic particles and polymer.

[0108] It is desirable to carry out a dispersion process of the polymer solution and inorganic particles. At this time, the dispersion time may be appropriately 1 to 50 hours. As a dispersion method, a ball mill or a conventional method using a mechanical stirrer can be used, and the ball mill method is particularly preferred.

[0109] The composition of the mixture consisting of inorganic particles and polymers is not significantly restricted, but accordingly, the thickness, pore size, and porosity of the organic / inorganic composite porous separation membrane of the present invention finally manufactured can be controlled.

[0110] In other words, as the ratio of inorganic particles (I) to polymers (P) (ratio = I / P) increases, the porosity of the membrane increases, which results in an increase in the thickness of the membrane at the same solid content (weight of inorganic particles + weight of polymers). Additionally, the possibility of pore formation between inorganic particles increases, leading to an increase in pore size. At this time, as the size (particle diameter) of the inorganic particles increases, the interstitial distance between the inorganic particles increases, thus increasing the pore size.

[0111] 3) A mixture of manufactured inorganic particles and polymers can be coated onto a prepared polyolefin-based separator substrate and subsequently dried to obtain the separator of the present invention.

[0112] At this time, the method of coating the mixture of inorganic particles and polymers onto a polyolefin-based separator substrate may use conventional coating methods known in the art, and various methods such as dip coating, die coating, roll coating, comma coating, or a combination thereof may be used. In addition, when coating the mixture of inorganic particles and polymers onto a polyolefin-based separator substrate, the coating may be applied to both sides of the separator substrate or selectively applied to only one side.

[0113] A method for manufacturing a separation membrane according to another aspect of the present invention may include the step of coating the slurry onto a porous substrate and a heat treatment process, and the temperature of the heat treatment process may be 50°C to 100°C.

[0114] For example, the temperature of the heat treatment process may be 60°C to 95°C, 70°C to 90°C, 72°C to 88°C, or 74°C to 86°C.

[0115] If the temperature of the above heat treatment process exceeds that of the present invention, the separator may be damaged due to thermal shrinkage of 2% or more.

[0116] If the temperature of the above heat treatment process is lower than that of the present invention, the crosslinking of the copolymer may not occur sufficiently.

[0117] In one embodiment, the heat treatment process may be performed for 0.5 hours to 24 hours.

[0118] For example, the heat treatment process may be performed for 1 to 23 hours, 2 to 22 hours, 3 to 21 hours, 4 to 20 hours, 5 to 19 hours, 6 to 18 hours, 7 to 17 hours, 8 to 16 hours, 9 to 15 hours, or 10 to 14 hours.

[0119] If the above heat treatment process time exceeds the present invention, the separator may be damaged due to thermal shrinkage of 2% or more.

[0120] If the above heat treatment process time is shorter than that of the present invention, the crosslinking of the copolymer may not occur sufficiently.

[0121] For example, a schematic diagram of the crosslinked state of the copolymer by the first crosslinking agent can be represented by the following chemical formula 4.

[0122]

[0123] [Chemical Formula 4]

[0124]

[0125]

[0126] R2 and R3 of the above chemical formula 4 may each be hydrogen (H) or a methyl group (CH3), and

[0127] d+e+f=1, and

[0128] g+h+i=1 and,

[0129] d, e, f, g, h, and i can each be positive numbers greater than 0 and less than 1.

[0130] For example, d+e can be 0.3 to 0.9, and f can be 0.1 to 0.7.

[0131] Also, g+h can be 0.3 to 0.9, and i can be 0.1 to 0.7.

[0132] d, e, f, g, h, and i may represent the weight fraction of copolymer monomer units based on the total weight of each copolymer 1.

[0133] For example, if d+e is 0.9 and f is 0.1, the sum of the weight of the d monomer unit and the weight of the e monomer unit can be 9 times the weight of the f monomer unit.

[0134] When the above crosslinking is formed, the thermal shrinkage rate of the separator is lowered, and the heat resistance of the separator can be improved.

[0135] In one embodiment, the thermal shrinkage rate after the heat treatment process of the separator can be measured for MD (machine direction) or TD (transverse direction), and the thermal shrinkage rate after the heat treatment process in the MD direction or TD direction may be less than 2% each.

[0136] For example, the thermal shrinkage rate after the heat treatment process of the above-mentioned membrane may be greater than 0.5% and less than 2%.

[0137] If the thermal shrinkage rate after the heat treatment process of the above-mentioned separator exceeds that of the present invention, the separator may be damaged.

[0138] In one embodiment, the final thermal shrinkage rate of the dry state of the separator can be measured in the MD direction or the TD direction, and the final thermal shrinkage rate of the dry state in the MD direction or the TD direction may be less than 5% each.

[0139] For example, the final heat shrinkage rate of the above-mentioned dry state may be 1% or more and 4% or less.

[0140] In one embodiment, the final thermal shrinkage rate during electrolyte impregnation of the separator can be measured in the MD direction or the TD direction, and the final thermal shrinkage rate during electrolyte impregnation in the MD direction or the TD direction may be 35% or less, respectively.

[0141] For example, the final thermal shrinkage rate during electrolyte impregnation in the MD direction or TD direction may be 10% or more and 34% or less, 12% or more and 33% or less, 14% or more and 32% or less, or 16% or more and 31% or less.

[0142] A secondary battery according to another aspect of the present invention may include the above-mentioned separator.

[0143] That is, the above separator can be used as a separator for a secondary battery, for example

[0144] It can be used as a separator for lithium secondary batteries.

[0145] The above secondary battery may include a positive electrode, a negative electrode, a separator, or a combination thereof containing a binder of the present invention.

[0146] The above secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0147] The above secondary battery can be manufactured according to conventional methods known in the art, and as an example thereof, it can be manufactured by assembling the electrode and the separator and then injecting an electrolyte into the assembly.

[0148] Meanwhile, the electrolyte of the above secondary battery is a non-aqueous electrolyte containing a lithium salt, composed of a lithium salt and a solvent, and the solvent used is a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte.

[0149] The above lithium salt is a substance that is easily soluble in the above-mentioned non-aqueous electrolyte, for example, lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), and lithium decachlorodecarborate (LiB 10 Cl 10 ), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonate (LiSbF6), lithium aluminum tetrachloride (LiAlCl4), lithium thiocyanate (LiSCN), lithium octaborate (LiC4BO8), lithium trifluoroacetate (LiCF3CO2), lithium methylsulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)amide (LiN(SO2CF3)2), lithium bis(fluorosulfonyl)amide (LiN(SO2F)2), lithium bis(pentafluoroethylsulfonyl)amide (LiN(SO2C2F5)2), lithium nonafluorobutylsulfonate (LiC4F9SO3), Tris(trifluoromethanesulfonyl)lithium methane (LiC(CF3SO2)3), trifluoromethanesulfonylimide ((CF3SO2)2NLi), lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate imide, etc. may be used.

[0150] Non-aqueous organic solvents are, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfranc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0151] The above organic solid electrolyte may be, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer containing a secondary dissociating group, etc.

[0152] As the above-mentioned inorganic solid electrolyte, for example, lithium nitrides, halides, sulfates, etc., such as lithium triphosphate (Li3N), lithium iodide (LiI), lithium diiodide (Li5NI2), lithium triphosphate-lithium iodide-lithium hydroxide (Li3N-LiI-LiOH), lithium silicate (LiSiO4), lithium silicate-lithium iodide-lithium hydroxide (LiSiO4-LiI-LiOH), lithium silicon disulfide (Li2SiS3), lithium silicon tetroxide (Li4SiO4), and lithium silicon tetroxide-lithium iodide-lithium hydroxide (Li4SiO4-LiI-LiOH) may be used.

[0153] In addition, non-aqueous electrolytes may further include other additives for the purpose of improving charge / discharge characteristics, flame retardancy, etc. Examples of the above additives include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate trialamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propene sulfone (PRS), vinylene carbonate (VC), etc.

[0154] The lithium secondary battery according to the present invention enables lamination stacking and folding processes of the separator and electrode in addition to the general winding process. Furthermore, the battery case may be cylindrical, prismatic, pouch-type, or coin-type.

[0155]

[0156] Hereinafter, the operation and effects of the invention will be explained in more detail through specific embodiments of the invention. However, these embodiments are merely presented as examples of the invention and do not define the scope of the invention.

[0157]

[0158] Example 1

[0159] A monomer mixture was prepared by mixing 10% by weight of diacetone acrylamide, 65% by weight of acrylamide, and 25% by weight of vinylpyrrolidone, based on 100% by weight of the total weight of the monomer mixture.

[0160] 620 parts by weight of distilled water were added to the reaction vessel based on a total weight of 100 parts by weight of the monomer mixture, and the temperature of the reaction vessel was raised to 70°C while injecting high-purity nitrogen gas.

[0161] Afterwards, based on 100 parts by weight of the monomer mixture prepared in the reaction vessel and the monomer mixture, 0.3 parts by weight of ammonium persulfate and 0.2 parts by weight of methylene-bis-acrylamide (MBA) were added to carry out the polymerization reaction, and then a composition was prepared by adding adipic acid dihydrazide (ADH) in a molar amount corresponding to 0.5 times the molar amount of diacetone acrylamide.

[0162] Afterwards, the prepared composition and alumina with an average particle size of 0.5 μm were mixed in a weight ratio of 96:4, distilled water was added to achieve a solid content of 35%, and the mixture was dispersed by a ball mill to prepare a slurry.

[0163] A slurry prepared was applied to a 9㎛ thick porous PE / PP film to a thickness of 2㎛, and a heat treatment process was performed at a temperature of 80℃ for 12 hours to produce a separator.

[0164]

[0165] Example 2

[0166] A separation membrane was prepared in the same manner as in Example 1, except that 20 wt% diacetone acrylamide, 60 wt% acrylamide, and 20 wt% vinylpyrrolidone were mixed based on 100 wt% of the total weight of the monomer mixture.

[0167]

[0168] Example 3

[0169] A separation membrane was prepared in the same manner as in Example 1, except that 30 wt% diacetone acrylamide, 55 wt% acrylamide, and 15 wt% vinylpyrrolidone were mixed based on 100 wt% of the total weight of the monomer mixture.

[0170]

[0171] Example 4

[0172] A separation membrane was prepared in the same manner as in Example 1, except that adipic acid dihydrazide (ADH) was added in a molar amount equivalent to one times the molar amount of diacetone acrylamide.

[0173]

[0174] Example 5

[0175] A separation membrane was prepared in the same manner as in Example 2, except that adipic acid dihydrazide (ADH) was added in a molar amount equivalent to one times the molar amount of diacetone acrylamide.

[0176]

[0177] Example 6

[0178] A separation membrane was prepared in the same manner as in Example 3, except that adipic acid dihydrazide (ADH) was added in a molar amount equivalent to one times the molar amount of diacetone acrylamide.

[0179]

[0180] Example 7

[0181] A separation membrane was prepared in the same manner as in Example 1, except that adipic acid dihydrazide (ADH) was added in a molar amount equivalent to twice the molar amount of diacetone acrylamide.

[0182]

[0183] Example 8

[0184] A separation membrane was prepared in the same manner as in Example 2, except that adipic acid dihydrazide (ADH) was added in a molar amount equivalent to twice the molar amount of diacetone acrylamide.

[0185]

[0186] Example 9

[0187] A separation membrane was prepared in the same manner as in Example 3, except that adipic acid dihydrazide (ADH) was added in a molar amount equivalent to twice the molar amount of diacetone acrylamide.

[0188]

[0189] Comparative Example 1

[0190] A separation membrane was prepared in the same manner as in Example 1, except that adipic acid dihydrazide (ADH) was not added.

[0191]

[0192] Comparative Example 2

[0193] A separation membrane was prepared in the same manner as in Example 2, except that adipic acid dihydrazide (ADH) was not added.

[0194]

[0195] Comparative Example 3

[0196] A separation membrane was prepared in the same manner as in Example 3, except that adipic acid dihydrazide (ADH) was not added.

[0197]

[0198] Comparative Example 4

[0199] A separation membrane was prepared in the same manner as in Example 1, except that the heat treatment process was not performed.

[0200]

[0201] Comparative Example 5

[0202] A separation membrane was prepared in the same manner as in Example 2, except that the heat treatment process was not performed.

[0203]

[0204] Comparative Example 6

[0205] A separation membrane was prepared in the same manner as in Example 3, except that the heat treatment process was not performed.

[0206]

[0207] Comparative Example 7

[0208] A separation membrane was prepared in the same manner as in Example 4, except that the heat treatment process was not performed.

[0209]

[0210] Comparative Example 8

[0211] A separation membrane was prepared in the same manner as in Example 5, except that the heat treatment process was not performed.

[0212]

[0213] Comparative Example 9

[0214] A separation membrane was prepared in the same manner as in Example 6, except that the heat treatment process was not performed.

[0215]

[0216] Comparative Example 10

[0217] A separation membrane was prepared in the same manner as in Example 7, except that the heat treatment process was not performed.

[0218]

[0219] Comparative Example 11

[0220] A separation membrane was prepared in the same manner as in Example 8, except that the heat treatment process was not performed.

[0221]

[0222] Comparative Example 12

[0223] A separation membrane was prepared in the same manner as in Example 9, except that the heat treatment process was not performed.

[0224]

[0225] The content of diacetone acrylamide, acrylamide, and vinylpyrrolidone, and the ratio of the number of moles of adipic acid dihydrazide to the number of moles of diacetone acrylamide in Examples 1 to 9 and Comparative Examples 1 to 12 are shown in Table 1 below.

[0226]

[0227] DAAM Content (Weight %) AM Content (Weight %) VP Content (Weight %) ADH Non-heat Treatment Process Presence / Absence Example 1 1065250.5O Example 2 2060200.5O Example 3 3055150.5O Example 4 1065251O Example 5 2060201O Example 6 3055151O Example 7 1065252O Example 8 2060202O Example 9 3055152O Comparative Example 1 1065250O Comparative Example 2 2060200O Comparative Example 3 3055150O Comparative Example 4 1065250.5X Comparative Example 5 2060200.5X Comparative Example 6 3055150.5X Comparative Example 71065251XComparative Example 82060201XComparative Example 93055151XComparative Example 101065252XComparative Example 112060202XComparative Example 123055152X

[0228]

[0229] In Table 1 above, DAAM content, AM content, and VP content represent the weight percent of diacetone acrylamide, acrylamide, and vinylpyrrolidone, respectively, based on 100 weight percent of the total weight of the monomer mixture.

[0230] In Table 1 above, the ADH ratio refers to the value obtained by dividing the number of moles of adipic acid dihydrazide by the number of moles of diacetone acrylamide (number of moles of adipic acid dihydrazide / number of moles of diacetone acrylamide).

[0231] "O" indicates that the heat treatment process has been undergone, and "X" indicates that the heat treatment process has not been undergone.

[0232]

[0233] Evaluation Example 1 - Evaluation of thermal shrinkage rate after heat treatment process

[0234] The thermal shrinkage rate of the membranes of Examples 1 to 9 and Comparative Examples 1 to 3 after the heat treatment process was checked in the MD direction (mechanical direction) and the TD direction (transverse direction).

[0235] Samples measuring 5 cm x 5 cm in width and 4 cm in height were prepared using the membranes of Examples 1 to 9 and Comparative Examples 1 to 3, and four reference points were marked in a square shape (4 cm x 4 cm in width) so that the MD direction and the TD direction were perpendicular.

[0236] The thermal shrinkage rate was calculated by measuring the distance between reference points in the MD and TD directions before the heat treatment process and the distance between reference points in the MD and TD directions after the heat treatment process, respectively.

[0237] The thermal shrinkage rate after the above heat treatment process was calculated by the following Equation 1 and is shown in Table 2.

[0238]

[0239] [Equation 1]

[0240] Thermal shrinkage rate after heat treatment (%) = [(4 cm - distance between reference points after heat treatment) / 4 cm] x 100 (%)

[0241]

[0242] Thermal shrinkage rate after heat treatment process (%, (MD / TD)) Example 10 / 0 Example 20 / 1 Example 30 / 1 Example 4 1 / 1 Example 5 1 / 1 Example 60 / 1 Example 7 1 / 1 Example 80 / 1 Example 9 1 / 1 Comparative Example 10 / 1 Comparative Example 20 / 0 Comparative Example 30 / 1

[0243]

[0244] It was confirmed that the separators of Examples 1 to 9 and Comparative Examples 1 to 3 were heat-shrinked by less than 2% in both the MD direction and the TD direction.

[0245] Comparative Examples 4 to 12 did not perform a heat treatment process, so the thermal shrinkage rate after the heat treatment process could not be measured.

[0246]

[0247] Evaluation Example 2 - Evaluation of final heat shrinkage rate in dry state

[0248] The final thermal shrinkage rate of the separator membranes in the dry state of Examples 1 to 9 and Comparative Examples 1 to 12 was confirmed in the MD direction and the TD direction.

[0249] Samples measuring 5 cm in width and 5 cm in length were prepared using the membranes of Examples 1 to 9 and Comparative Examples 1 to 12, and dried in an 80°C oven for 12 hours.

[0250] After drying each sample, four reference points were marked in a square shape (4 cm wide x 4 cm high) so that the MD direction and the TD direction were perpendicular.

[0251] Each sample marked with a reference point was additionally heat-treated in a 150℃ oven for 1 hour to check the final heat shrinkage rate in the dry state.

[0252] The final thermal shrinkage rate in the dry state was calculated by measuring the distance between reference points in the MD and TD directions before additional heat treatment and the distance between reference points in the MD and TD directions after additional heat treatment, respectively.

[0253] The final heat shrinkage rate of the above dry state was calculated by the following Equation 2 and is shown in Table 3.

[0254]

[0255] [Equation 2]

[0256] Final heat shrinkage rate in dry state (%) = [(Length between reference point 4 cm - after additional heat treatment at 150℃) / 4 cm] x 100 (%)

[0257]

[0258] Evaluation of final heat shrinkage rate in dry state (%, (MD / TD)) Example 1 4 / 5 Example 2 3 / 4 Example 3 4 / 4 Example 4 3 / 3 Example 5 2 / 2 Example 6 2 / 3 Example 7 3 / 3 Example 8 3 / 4 Example 9 4 / 4 Comparative Example 1 7 / 6 Comparative Example 2 7 / 8 Comparative Example 3 7 / 7 Comparative Example 4 6 / 6 Comparative Example 5 5 / 7 Comparative Example 6 6 / 6 Comparative Example 7 4 / 5 Comparative Example 8 4 / 4 Comparative Example 9 5 / 5 Comparative Example 10 6 / 5 Comparative Example 11 5 / 5 Comparative Example 12 6 / 6

[0259]

[0260] As a result of the measurement, it was confirmed that the final heat shrinkage rate in the dry state of Examples 1 to 9 was lower than the final heat shrinkage rate in the dry state of Comparative Examples 1 to 12.

[0261] Specifically, Examples 1 to 9 showed a final thermal shrinkage rate of less than 5% in the dry state, whereas the comparative example showed a final thermal shrinkage rate of at least 4% and at most 8% in the MD direction or TD direction in the dry state.

[0262] In other words, it was confirmed that the example shrinks less when heat is applied compared to the comparative example.

[0263] This is interpreted as follows: whereas Examples 1 to 9 had sufficient time to form cross-links during the heat treatment process at 80°C, Comparative Examples 4 to 12 were exposed to a high temperature of 150°C without a heat treatment process and shrank rapidly in a state where there was insufficient time to form cross-links.

[0264] In addition, Comparative Examples 1 to 3 had a heat treatment process at 80°C, but since the crosslinking agent adipic acid dihydrazide was not added, additional chemical crosslinking could not be formed, so it can be interpreted that the thermal shrinkage rate was large.

[0265]

[0266] Evaluation Example 3 - Evaluation of Final Thermal Shrinkage Rate During Electrolyte Impregnation

[0267] The final thermal shrinkage rate of the separator membranes of Examples 1 to 9 and Comparative Examples 1 to 12 during electrolyte impregnation was confirmed in the MD direction and the TD direction.

[0268] Samples measuring 5 cm in width and 5 cm in length were prepared using the membranes of Examples 1 to 9 and Comparative Examples 1 to 12, and dried in an 80°C oven for 12 hours.

[0269] After drying each sample, four reference points were marked in a square shape (4 cm wide x 4 cm high) so that the MD direction and the TD direction were perpendicular.

[0270] The electrolyte and a sample marked with a reference point were placed inside a pouch, sealed, and impregnated for 12 hours. After creating a gas outlet in the pouch, it was additionally heat-treated in a 150°C oven for 1 hour to check the final thermal shrinkage rate during electrolyte impregnation.

[0271] The final thermal shrinkage rate during electrolyte impregnation was calculated by measuring the distance between reference points in the MD and TD directions before electrolyte impregnation and the distance between reference points in the MD and TD directions after electrolyte impregnation and additional heat treatment, respectively.

[0272] The final heat shrinkage rate during the above impregnation was calculated by the following Equation 3 and is shown in Table 4.

[0273]

[0274] [Equation 3]

[0275] Final thermal shrinkage rate (%) during electrolyte impregnation = [(4 cm - length between reference points after additional heat treatment at 150°C following electrolyte impregnation) / 4 cm] x 100 (%)

[0276]

[0277] Final thermal shrinkage rate in electrolyte (%, (MD / TD)) Example 1 26 / 30 Example 2 27 / 27 Example 3 31 / 31 Example 4 21 / 23 Example 5 19 / 22 Example 6 21 / 24 Example 7 24 / 29 Example 8 26 / 27 Example 9 27 / 29 Comparative Example 1 37 / 36 Comparative Example 2 38 / 36 Comparative Example 3 37 / 38 Comparative Example 4 33 / 31 Comparative Example 5 31 / 27 Comparative Example 6 30 / 33 Comparative Example 7 27 / 30 Comparative Example 8 26 / 26 Comparative Example 9 27 / 30 Comparative Example 10 29 / 32 Comparative Example 11 30 / 31 Comparative Example 12 33 / 31

[0278]

[0279] The final thermal shrinkage rate in the electrolyte also showed a similar trend to Evaluation Example 2.

[0280] It was confirmed that Examples 1 to 9 had a lower thermal shrinkage rate compared to Comparative Examples, and it was confirmed that Comparative Examples 1 to 3 showed a higher thermal shrinkage rate compared to Comparative Examples 4 to 12 because they did not include an additional crosslinking agent, even though they included a heat treatment process.

[0281] Specifically, it was confirmed that the final thermal shrinkage rate during electrolyte impregnation in the MD direction or TD direction of Examples 1 to 9 was at least 19% and at most 31%, whereas the final thermal shrinkage rate during electrolyte impregnation in the MD direction or TD direction of Comparative Examples 1 to 12 was measured to be at least 26% and at most 38%.

[0282]

[0283] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0284] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

[0285]

[0286] The composition of the present invention can form chemical crosslinks of a copolymer, and a separator manufactured using the same can have high heat resistance, and therefore a secondary battery including the separator can have excellent performance.

Claims

1. A copolymer comprising an acrylamide-based monomer unit and a vinylpyrrolidone monomer unit; and including a first crosslinking agent, Composition.

2. In Paragraph 1, The above acrylamide-based monomer unit comprises a first acrylamide monomer unit and a second acrylamide monomer unit, Composition.

3. In Paragraph 2, The above first acrylamide monomer unit further comprises a carbonyl group (-CO-), Composition.

4. In Paragraph 2, The above-mentioned first acrylamide monomer unit is formed by the polymerization of diacetone acrylamide, Composition.

5. In Paragraph 2, The above second acrylamide monomer unit is formed by polymerizing acrylamide, methacrylamide, N-[3-(dimethylamino)propyl]methacrylamide, N-ethylacrylamide, N-(tert-butyl)acrylamide, N-methylacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, or a combination thereof. Composition.

6. In Paragraph 1, A weight ratio of the acrylamide-based monomer unit and the vinyl pyrrolidone monomer unit (weight of acrylamide-based monomer unit:weight of vinyl pyrrolidone monomer unit) of 0.4 to 9:1, Composition.

7. In Paragraph 2, The weight ratio of the first acrylamide monomer unit and the second acrylamide monomer unit (weight of the first acrylamide monomer unit: weight of the second acrylamide monomer unit) is 1:1.5 to 9. Composition.

8. In Paragraph 1, The above copolymer is cross-linked by a second cross-linking agent, Composition.

9. In Paragraph 8, The second crosslinking agent comprises two or more polymerizable unsaturated groups capable of bonding to the acrylamide-based monomer unit, the vinylpyrrolidone monomer unit, or a combination thereof. Composition.

10. In Paragraph 9, The above-mentioned polymerizable unsaturated group comprises a vinyl group (-CH=CH2), an allyl group (-CH2-CH=CH2), an isoprenyl group (-CH2-C(CH3)=CH2), an acryloyl group (-CH=CH-CO-), an acrylate group (-(C=O)-O-), or a combination thereof. Composition.

11. In Paragraph 8, The above second crosslinking agent is methylenebisacrylamide (MBA), ethylenebisacrylamide (EBA), divinylbenzene (DVB), butadiene, hexadiene, isoprene, divinyl ether, diallyl phthalate (DAP), diallyl ether, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate (TMPTMA), ethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, polyethylene diacrylate, or a combination thereof, comprising Composition.

12. In Paragraph 1, The first crosslinking agent comprises two or more functional groups capable of binding to the acrylamide-based monomer unit. Composition.

13. In Paragraph 12, The functional group of the first crosslinking agent comprises two or more nitrogen atoms. Composition.

14. In Paragraph 1, The first crosslinking agent comprises two or more hydrazide groups, amino groups, amine groups, or a combination thereof. Composition.

15. In Paragraph 1, The first crosslinking agent comprises adipic acid dihydrazide (ADH), oxalyl dihydrazide, decane dihydrazide, isophthalic dihydrazide, succinic dihydrazide, carbohydrazide, dodecane dihydrazide, ethylenediamine (EDA), 1,3-propanediamine, 1,6-hexanediamine, cyclohexanediamine, phenylenediamine, hexamethylenediamine, or a combination thereof. Composition.

16. In Paragraph 2, A molar ratio (moles of the first crosslinking agent:moles of the first acrylamide monomer unit) of the first crosslinking agent and the first acrylamide monomer unit is 0.3 to 3:

1. Composition.

17. A composition comprising any one of claims 1 to 16, bookbinder.

18. Comprising the binder and inorganic particles of paragraph 17, Slurry.

19. A porous substrate coated with the slurry of claim 18, comprising Separator.

20. A step of coating the slurry of claim 18 onto a porous substrate; and Includes a heat treatment process, The temperature of the above heat treatment process is 50℃ to 100℃, Method for manufacturing a separator.

21. Including the separator of paragraph 19, Secondary battery.

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