Separator for lithium secondary battery, and lithium secondary battery comprising same

Abstract

The present invention relates to a separator for a lithium secondary battery, and a lithium secondary battery comprising same. The separator for a lithium secondary battery comprises a porous substrate and a coating layer positioned on at least one surface of the porous substrate, the coating layer includes a binder and a filler, and the binder includes a monomer mixture copolymer including: a first structural unit including a structural unit derived from an aromatic vinyl-based monomer; a second structural unit derived from a (meth)acrylic monomer containing, in an ester moiety, an alkyl group having four or more carbon atoms in the main chain; and a third structural unit derived from a sulfonic acid group-containing monomer, wherein 5-80 mol% of the first structural unit, 10-40 mol% of the second structural unit and 5-80 mol% of the third structural unit are included on the basis of 100 mol% of the copolymer.

Description

Separator for lithium secondary battery and lithium secondary battery including the same

[0001] The invention relates to a separator for a lithium secondary battery and a lithium secondary battery including the same.

[0002] With the recent rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries is increasing rapidly. Accordingly, research and development to improve the performance of lithium-ion batteries is actively underway.

[0003] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of lithium ion intercalation and deintercalation, and an electrolyte, and produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated and deintercalated from the positive electrode and the negative electrode.

[0004] One embodiment provides a separator for a lithium secondary battery that improves the capacity of the lithium secondary battery by having low membrane resistance.

[0005] Another embodiment provides a separator for a lithium secondary battery that improves the safety and lifespan of the lithium secondary battery by having high adhesion.

[0006] Another embodiment provides a separator for a lithium secondary battery that provides high electrolyte moisture content and improved flexibility to produce a resistance improvement effect.

[0007] Another embodiment provides a separator for a lithium secondary battery that provides a high capacity retention rate and a low rate of change of DC internal resistance at room temperature and high temperature, respectively.

[0008] Another embodiment provides a lithium secondary battery comprising a separator for the lithium secondary battery.

[0009] One embodiment is a separator for a lithium secondary battery.

[0010] 1. A separator for a lithium secondary battery comprises a porous substrate and a coating layer located on at least one surface of the porous substrate, wherein the coating layer comprises a binder and a filler, and the binder comprises a copolymer of a monomer mixture comprising: a first structural unit comprising a structural unit derived from an aromatic vinyl monomer; a second structural unit derived from an alkyl group-containing (meth)acrylic monomer having four or more carbon atoms in the main chain at the ester site; and a third structural unit derived from a sulfonic acid group-containing monomer, wherein, with respect to 100 mol% of the copolymer, the first structural unit is included in an amount of 5 to 80 mol%, the second structural unit in an amount of 10 to 40 mol%, and the third structural unit in an amount of 5 to 80 mol%.

[0011] In 2.1, the copolymer may be a particulate binder.

[0012] In 3.1 and 2, the copolymer may have an average size D50 of 500 to 700 nm.

[0013] In 4.1 to 3, the copolymer may be an adhesive binder.

[0014] In 5.1 to 4, the copolymer may have a glass transition temperature of 60 to 80°C.

[0015] In 6.1 to 5, the copolymer may be included in the coating layer in an amount of 1 to 100 weight percent.

[0016] In 7.1 to 6, with respect to the copolymer, the total sum of the first structural unit, the second structural unit, and the third structural unit may be 95 mol% or more.

[0017] In 8.1 to 7, the structural unit derived from the aromatic vinyl monomer is represented by the following chemical formula 1, and

[0018] [Chemical Formula 1]

[0019]

[0020] (In the above chemical formula 1,

[0021] R 1 and R 2 Each is independently hydrogen or a substituted or unsubstituted C1 to C5 alkyl group,

[0022] Ar is a substituted or unsubstituted, monocyclic or polycyclic C6 to C20 aryl group),

[0023] The above second structural unit is represented by the following chemical formula 4, and

[0024] [Chemical Formula 4]

[0025]

[0026] (In the above chemical formula 4,

[0027] R 7 and R 8 Each independently has a hydrogen or methyl group,

[0028] L 2 is a substituted or unsubstituted, straight-chain or branched-chain C4 to C30 alkyl group),

[0029] The above third structural unit can be represented by any one of the following chemical formulas 5, 6, and 7.

[0030] [Chemical Formula 5]

[0031]

[0032] [Chemical Formula 6]

[0033]

[0034] [Chemical Formula 7]

[0035]

[0036] (In the above chemical formulas 5 to 7,

[0037] R 9 , R 10 , R 11 , R 12 , R 13 and R 14Each is independently hydrogen or a C1 to C3 alkyl group, and

[0038] L 3 , L 5 and L 7 Each is independently -C(=O)-, -C(=O)O-, -OC(=O)-, -O- or -C(=O)NH-, and

[0039] L 4 , L 6 and L 8 Each is independently a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, and

[0040] a, b, c, d, e, and f are each independently integers from 0 to 2, and

[0041] In the above chemical formula 6,

[0042] M is an alkali metal).

[0043] In 9.1 to 8, the first structural unit may further include a unit derived from an alkyl group-containing (meth)acrylic monomer having 1 to 3 carbon atoms in the main chain at the ester site.

[0044] In 10.9, the unit derived from the above (meth)acrylic monomer may be a unit represented by the following chemical formula 3:

[0045] [Chemical Formula 3]

[0046]

[0047] (In the above chemical formula 3,

[0048] R 5 and R 6 Each independently has a hydrogen or methyl group,

[0049] L 1 (substituted or unsubstituted, straight-chain or branched-chain C1 to C3 alkyl groups).

[0050] In 11.9 to 10, the structural unit derived from the aromatic vinyl monomer: the structural unit derived from the (meth)acrylic monomer may be included in a molar ratio of 1:0.5 to 2.

[0051] In 12.9 to 11, with respect to 100 mol% of the copolymer, the copolymer may comprise 5 to 35 mol% of a structural unit derived from the aromatic vinyl monomer, 5 to 35 mol% of a structural unit derived from an alkyl group-containing (meth)acrylic monomer having 1 to 3 carbon atoms in the main chain at the ester site, 20 to 30 mol% of the second structural unit, and 10 to 60 mol% of the third structural unit.

[0052] In 13.9 to 12, the copolymer comprises a structural unit derived from an aromatic vinyl monomer derived from one or more of styrene; alpha-methyl styrene; 4-butyl styrene; 4-butoxy styrene; halo styrene; vinyl toluene; and vinyl naphthalene; A structural unit derived from an alkyl group-containing (meth)acrylate monomer having 1 to 3 carbon atoms in the main chain at the ester site derived from one or more of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and iso-propyl (meth)acrylate; a second structural unit derived from one or more of 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and isodecyl (meth)acrylate; and vinyl The third structural unit may be derived from sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, anethole sulfonic acid, (meth)acrylamidoalkane sulfonic acid, sulfoalkyl (meth)acrylate, or salts thereof.

[0053] In 14.1 to 13, the filler may have a size D50 of 400 nm or less.

[0054] In 15.1 to 14, the copolymer:filler may be included in a mass ratio of 1:10 to 1:50.

[0055] In 16.1 to 15, the coating layer may further include an adhesive binder.

[0056] Another embodiment provides a lithium secondary battery.

[0057] The above lithium secondary battery includes a positive electrode, a negative electrode, and a separator for the lithium secondary battery located between the positive electrode and the negative electrode.

[0058] A separator for a lithium secondary battery according to one embodiment can improve the capacity, safety, and lifespan of the battery by exhibiting low membrane resistance, electrolyte moisture retention and improved flexibility, high adhesion, and high capacity retention rate and low DC internal resistance change rate at room temperature and high temperature, respectively.

[0059] FIGS. 1 to 4 are cross-sectional views schematically showing a lithium secondary battery according to one embodiment.

[0060] FIG. 5 is a cross-sectional view schematically showing a separator for a lithium secondary battery according to one embodiment.

[0061] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0062] Unless otherwise specifically stated in this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between.

[0063] Unless otherwise specified in this specification, a singular form may also include a plural form. Additionally, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0064] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0065] In this specification, 'size D50' refers to the average size of a particle whose cumulative volume is 50% by volume in the particle size distribution. The particle size distribution can be measured by methods widely known to those skilled in the art. For example, the particle size distribution may be measured using a particle size analyzer, or by using a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the D50 value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Or, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasound of about 28 kHz is irradiated at an output of 60 W, and then D50 can be calculated based on 50% of the size distribution in the measuring device.

[0066] If the above particle is a spherical particle, the above size may refer to the particle diameter.

[0067] In this specification, '(meth)acrylic' means acrylic and / or methacrylic.

[0068] Unless otherwise defined below, "substitution" means that a hydrogen in a compound is a C1 to C30 alkyl group, C2 to C30 alkenyl group, C2 to C30 alkynyl group, C6 to C30 aryl group, C7 to C30 alkylaryl group, C1 to C30 alkoxy group, C1 to C30 heteroalkyl group, C3 to C30 heteroalkylaryl group, C3 to C30 cycloalkyl group, C3 to C15 cycloalkenyl group, C6 to C30 cycloalkynyl group, C2 to C30 heterocycloalkyl group, halogen (F, Cl, Br, or I), hydroxyl group (-OH), nitro group (-NO2), cyano group (-CN), amino group (-NRR') (wherein R and R' are independently hydrogen or C1 to C6 alkyl groups), or sulfobetaine group (-RR'N + (CH2) n SO3 -, n is a natural number from 1 to 10), carboxybetaine group (-RR'N + (CH2) n COO -, n is a natural number from 1 to 10) (where R and R' are independently C1 to C20 alkyl groups), azido group (-N3), amidino group (-C(=NH)NH2), hydrazino group (-NHNH2), hydrazono group (=N(NH2), carbamoyl group (-C(O)NH2), thiol group (-SH), acyl group (-C(=O)R, where R is hydrogen, a C1 to C6 alkyl group, a C1 to C6 alkoxy group, or a C6 to C12 aryl group), carboxyl group (-COOH) or its salt (-C(=O)OM, where M is an organic or inorganic cation), sulfonic acid group (-SO3H) or its salt (-SO3M, where M is an organic or inorganic cation), phosphate group (-PO3H2) or its salt (-PO3MH or -PO3M2, where M is an organic or inorganic cation) and means being substituted with a substituent selected from a combination thereof.

[0069] In the following, C1 to C3 alkyl groups refer to methyl groups, ethyl groups, or propyl groups. C1 to C10 alkylene groups may be, for example, C1 to C6 alkylene groups, C1 to C5 alkylene groups, or C1 to C3 alkylene groups, and may be, for example, methylene groups, ethylene groups, or propylene groups. C3 to C20 cycloalkylene groups may be, for example, C3 to C10 cycloalkylene groups or C5 to C10 cycloalkylene groups, and may be, for example, cyclohexylene groups. C6 to C20 arylene groups may be, for example, C6 to C10 arylene groups, and may be, for example, phenylene groups. C3 to C20 heterocyclic groups may be, for example, C3 to C10 heterocyclic groups, and may be, for example, pyridine groups.

[0070] In the following, "hetero" means containing one or more heteroatoms selected from N, O, S, Si, and P.

[0071] In addition, in chemical formulas, the * symbol indicates a part connected to the same or different atoms, groups, or structural units.

[0072] Unless otherwise specifically mentioned in the chemical formulas described in this specification, hydrogen may be considered to be bonded in the structure of the chemical formula.

[0073] In the following, "alkali metal" refers to elements belonging to Group 1 of the periodic table, such as lithium, sodium, potassium, rubidium, cesium, or francium, and may exist in a positive or neutral state.

[0074] In this specification, when describing a numerical range, 'X to Y' means 'X or greater and Y or less (X ≤ and ≤ Y).'

[0075] A separator for a lithium secondary battery according to one embodiment comprises a porous substrate and a coating layer located on at least one surface of the porous substrate, wherein the coating layer comprises a binder and a filler, and the binder comprises a copolymer of a monomer mixture comprising: a first structural unit comprising a structural unit derived from an aromatic vinyl monomer; a second structural unit derived from an alkyl group-containing (meth)acrylic monomer having four or more carbon atoms in the main chain at the ester site; and a third structural unit derived from a sulfonic acid group-containing monomer, wherein, with respect to 100 mol% of the copolymer, the first structural unit is included in an amount of 5 to 80 mol%, the second structural unit in an amount of 10 to 40 mol%, and the third structural unit in an amount of 5 to 80 mol%.

[0076] The coating layer can improve the lifespan and safety of a lithium secondary battery by significantly lowering the membrane resistance of the separator. The coating layer can improve the safety of a lithium secondary battery by providing high adhesion. The coating layer can provide a lithium secondary battery that produces a resistance improvement effect by providing a high electrolyte moisture content and improved flexibility. The coating layer can increase the reliability of a lithium secondary battery by providing a high capacity retention rate and a low rate of change of DC internal resistance at room temperature (e.g., 20 to 30°C) and high temperature (e.g., 40 to 50°C), respectively.

[0077] The above separator may have an electrolyte moisture content of 130% by weight or more.

[0078] The above separator may have an adhesion strength to the anode of 0.90 N or more.

[0079] The above separator may have a membrane resistance of 0.65Ω or less when impregnated with an electrolyte.

[0080] The above separator can have a capacity retention rate of 85% or more at room temperature and 70% or more at high temperature.

[0081] The above separator can have a DC internal resistance change rate of 220% or less after 200 cycles at room temperature and a DC internal resistance change rate of 330% or less after 200 cycles at high temperature.

[0082] The above electrolyte moisture content, adhesion to the anode, membrane resistance upon electrolyte impregnation, capacity retention rate at room temperature and high temperature, and retention rate of the rate of change of DC internal resistance at room temperature and high temperature, respectively, can each be measured by the method described below.

[0083] According to one embodiment, the copolymer functions as an adhesive binder to secure adhesion to the electrode of the separator. Membrane resistance and adhesion are in a trade-off relationship. The copolymer can lower the membrane resistance of the separator while also increasing adhesion.

[0084] According to one embodiment, the copolymer is a particulate binder, and the average size D50 may be 500 to 700 nm. Within this range, there may be an effect of increasing adhesion. For example, the D50 may be 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700 nm.

[0085] If the above copolymer has a glass transition temperature, the glass transition temperature may be 60°C to 80°C. In this range, not only is the electrode adhesion excellent, but the ion conductivity may also be good. For example, the glass transition temperature of the above copolymer may be 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80°C.

[0086] The glass transition temperature of the above copolymer can be measured by conventional methods known to those skilled in the art using thermomechanical analysis (TMA) methods. For example, the glass transition temperature can be measured by the following methods:

[0087] 1. Prepare a specimen by cutting the copolymer to be analyzed into a size of 0.5 mm X 8 mm, fasten the specimen to a holder, and then mount it on the specimen probe of the TMA equipment.

[0088] 2. After setting the mechanical load to 0.0150N and the heating rate to 5℃ / min, measure the change in length of the specimen according to temperature.

[0089] 3. The temperature at the point where the slope changes in the graph of data obtained from the TMA equipment is defined as the glass transition temperature.

[0090] The copolymer may be included in an amount of 1 to 100 weight%, more than 1 weight% and less than 100 weight%, specifically 1 to 90 weight%, with respect to the total amount of the coating layer, and specifically 5 to 80 weight%, for example 10 to 80 weight%. Within the above range, adhesion to the electrode is exhibited, and the battery resistance does not increase, so there may be no limitations on capacity realization.

[0091] coating layer

[0092] The above coating layer includes a binder and a filler.

[0093] (bookbinder)

[0094] Among the binders above, the copolymer of the monomer mixture described below may be included in an amount of 95% by weight or more, for example, 95 to 100% by weight, or 100% by weight.

[0095] With respect to the copolymer, the total sum of the first structural unit, the second structural unit, and the third structural unit may be 95 mol% or more, for example, 95 to 100 mol%, for example, 100 mol%. Within this range, the above-described separation membrane effect may be easily realized.

[0096] (1st structural unit)

[0097] The first structural unit above includes a structural unit derived from an aromatic vinyl monomer. The structural unit derived from the aromatic vinyl monomer can provide adhesion so that the coating layer adheres well to the porous substrate and the electrode, and can improve the air permeability of the separator.

[0098] The structural unit derived from the above aromatic vinyl monomer is represented by the following chemical formula 1, and the copolymer may include one or more units represented by the following chemical formula 1:

[0099] [Chemical Formula 1]

[0100]

[0101] (In the above chemical formula 1,

[0102] R 1 and R 2 Each is independently hydrogen or a substituted or unsubstituted C1 to C5 alkyl group,

[0103] Ar is a substituted or unsubstituted, monocyclic or polycyclic C6 to C20 aryl group).

[0104] In the above chemical formula 1, Ar is a C6 to C20 monocyclic or polycyclic aryl group, and can be, for example, a phenyl group, a naphthalenyl group, anthracenyl group, a pyrenyl group, etc.

[0105] The structural unit derived from the above aromatic vinyl monomer is represented by the following chemical formula 2, and the copolymer may include one or more structural units represented by the following chemical formula 2:

[0106] [Chemical Formula 2]

[0107]

[0108] (In the above chemical formula 2,

[0109] R 3 and R 4 Each is independently a hydrogen or a substituted or unsubstituted C1 to C5 alkyl group,

[0110] R is one selected from the group consisting of a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C1 to C20 alkoxy group and a substituted or unsubstituted C3 to C20 aryl group, and

[0111] m is an integer from 0 to 5).

[0112] In the above formula 2, R may be a substituted or unsubstituted C1 to C20 alkyl group or a substituted or unsubstituted C1 to C20 alkoxy group. In one embodiment, in the above formula 2, m may be 0 or 1.

[0113] The above aromatic vinyl monomer may include one or more of the following: styrene; alpha-methyl styrene; 4-butyl styrene including 4-n-butyl styrene, 4-iso-butyl styrene, 4-t-butyl styrene, etc.; butoxy styrene including 4-n-butoxy styrene, 4-iso-butoxy styrene, 4-t-butoxy styrene, etc.; halo styrene including chloro styrene, bromostyrene, fluorostyrene, etc.; vinyl toluene including 4-vinyl toluene, 3-vinyl toluene, 2-vinyl toluene, etc.; and vinyl naphthalene including 1-vinyl naphthalene, 2-vinyl naphthalene, etc.

[0114] The first structural unit may additionally include a structural unit derived from an alkyl group-containing (meth)acrylic monomer having 1 to 3 carbon atoms in the main chain at the ester site, in addition to the structural unit derived from the aromatic vinyl monomer. The structural unit derived from the (meth)acrylic monomer may further provide an effect of improving adhesion.

[0115] The structural unit derived from the above (meth)acrylic monomer is represented by the following chemical formula 3, and the copolymer may include one or more structural units represented by the following chemical formula 3:

[0116] [Chemical Formula 3]

[0117]

[0118] (In the above chemical formula 3,

[0119] R 5 and R 6 Each independently has a hydrogen or methyl group,

[0120] L 1 (substituted or unsubstituted, straight-chain or branched-chain C1 to C3 alkyl groups).

[0121] The above (meth)acrylic monomer may include one or more of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and iso-propyl (meth)acrylate.

[0122] The above (meth)acrylic monomer may have a glass transition temperature of 50°C or higher, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150°C, or 50 to 150°C. Within the above range, the glass transition temperature of the copolymer described above can be easily reached. For example, such (meth)acrylic monomer may be methyl methacrylate, ethyl methacrylate, etc.

[0123] In this specification, "glass transition temperature of a homopolymer" may refer to the glass transition temperature (Tg) measured using TMA for a homopolymer of a monomer to be measured.

[0124] 1. Prepare a specimen by cutting the copolymer to be analyzed into a size of 0.5 mm X 8 mm, fasten the specimen to a holder, and then mount it on the specimen probe of the TMA equipment.

[0125] 2. After setting the mechanical load to 0.0150N and the heating rate to 5℃ / min, measure the change in length of the specimen according to temperature.

[0126] 3. The temperature at the point where the slope changes in the graph of data obtained from the TMA equipment is defined as the glass transition temperature.

[0127] With respect to 100 mol% of the copolymer, the first structural unit is included in an amount of 5 to 80 mol%. If the first structural unit is included in an amount of 5 mol% or more, the electrolyte moisture content is improved and the capacity retention rate at high temperatures may be high. If the first structural unit is included in an amount of 80 mol% or less, the membrane resistance does not increase, and the capacity retention rate at room temperature and high temperatures, respectively, may be high. For example, with respect to 100 mol% of the copolymer, the first structural unit 5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80 mol%, e.g. 10 to 70 mol%, 30 to 60 It may be included in mol%. When included within the above range, the separator may exhibit low membrane resistance, excellent adhesion to porous substrates and electrodes, air permeability, and oxidation resistance.

[0128] With respect to 100 mol% of the above copolymer, the structural unit derived from the aromatic vinyl monomer is 5 to 80 mol%, for example 5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80 mol%, e.g. 10 to 70 mol%, 10 to It may be included in 60 mol%, 10 to 35 mol%, 15 to 30 mol%, and 5 to 35 mol%. Within the above range, it may be easy to implement the effect of the above-described separation membrane.

[0129] With respect to 100 mol% of the above copolymer, the structural unit derived from the (meth)acrylic monomer is 5 to 80 mol%, for example 5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80 mol%, e.g. 10 to 70 mol%, 10 to It may be included in 60 mol%, 10 to 35 mol%, 15 to 30 mol%, and 5 to 35 mol%. Within the above range, it may be easy to implement the effect of the above-described separation membrane.

[0130] According to one embodiment, with respect to 100 mol% of the copolymer, the structural unit derived from the aromatic vinyl monomer and the structural unit derived from the (meth)acrylic monomer may be included in a molar ratio of 1:0.5 to 2, for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:1 to 1:2, for example, 1:1. Within the above range, it may be easy to implement the effect of the aforementioned separation membrane.

[0131] (Second structural unit)

[0132] The second structural unit is derived from an alkyl group-containing (meth)acrylic monomer having an ester site and a main chain having four or more carbon atoms. The second structural unit can improve the dispersibility of the coating layer slurry and improve the electrolyte moisture content and flexibility of the coating layer.

[0133] The unit derived from the above (meth)acrylic monomer is represented by the following chemical formula 4, and the copolymer may include one or more structural units represented by the following chemical formula 4:

[0134] [Chemical Formula 4]

[0135]

[0136] (In the above chemical formula 4,

[0137] R 7 and R 8 Each independently has a hydrogen or methyl group,

[0138] L 2 is a substituted or unsubstituted, straight-chain or branched-chain C4 to C30 alkyl group).

[0139] Here, the alkyl group may have a main chain of C4 to C20 alkyl, C4 to C10 alkyl, or C4 to C8 alkyl.

[0140] The above (meth)acrylic monomer may include one or more of 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and isodecyl (meth)acrylate.

[0141] With respect to 100 mol% of the copolymer, the second structural unit is included in an amount of 10 to 40 mol%. If the second structural unit is 10 mol% or more, the membrane resistance is lowered during electrolyte impregnation, and the capacity retention rate may be high at room temperature and high temperature, respectively. If the second structural unit is 40 mol% or less, the air permeability is improved, and the capacity retention rate may be high at room temperature and high temperature, respectively.

[0142] With respect to 100 mol% of the copolymer, the second structural unit may be included in 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 mol%, for example, 15 to 35 mol%, 20 to 30 mol%. Within the above range, it may be easy to increase the adhesion and flexibility of the coating layer to the porous substrate and electrode.

[0143] (Third structural unit)

[0144] The above third structural unit is a structural unit derived from a sulfonic acid group-containing monomer. The structural unit derived from the above sulfonic acid group-containing monomer can lower the membrane resistance of the separator by increasing the possibility of lithium ion mobility in the presence of the above first structural unit and the above second structural unit.

[0145] The third structural unit comprises a bulky functional group derived from (meth)acrylamidosulfonic acid or a salt thereof, thereby increasing the glass transition temperature of the copolymer and providing a structural stability effect. Additionally, if the third structural unit is a functional group derived from a salt of (meth)acrylamidosulfonic acid, metals (M) can move through the third structural unit by means of a metal (M) substituted sulfonic acid functional group, which can exhibit the effect of significantly lowering the membrane resistance of the separator.

[0146] The third structural unit above may be represented by the following chemical formula 5, chemical formula 6, or chemical formula 7. The copolymer may include one or more of the following chemical formulas 5, chemical formula 6, and chemical formula 7.

[0147] [Chemical Formula 5]

[0148]

[0149] [Chemical Formula 6]

[0150]

[0151] [Chemical Formula 7]

[0152]

[0153] (In the above chemical formulas 5 to 7,

[0154] R 9 , R 10 , R 11 , R 12 , R 13 and R 14 Each is independently hydrogen or a C1 to C3 alkyl group, and

[0155] L 3 , L 5 and L 7 Each is independently -C(=O)-, -C(=O)O-, -OC(=O)-, -O- or -C(=O)NH-, and

[0156] L 4 , L 6 and L8 Each is independently a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, and

[0157] a, b, c, d, e, and f are each independently integers from 0 to 2, and

[0158] In the above chemical formula 6,

[0159] M is an alkali metal).

[0160] In the above chemical formulas 5 to 7,

[0161] L 3 , L 5 and L 7 Each is independently -C(=O)NH-, and

[0162] L 4 , L 6 and L 8 Each is independently a C1 to C10 alkylene group, and

[0163] a, b, c, d, e, and f can be integers of 1.

[0164] The above sulfonate group-containing structural unit may include only one of the structural unit represented by Chemical Formula 5, the structural unit represented by Chemical Formula 6, and the structural unit represented by Chemical Formula 7, or it may include two or more types. For example, the above sulfonate group-containing structural unit may include the structural unit represented by Chemical Formula 6, and for another example, the above sulfonate group-containing structural unit may include the structural unit represented by Chemical Formula 6 and the structural unit represented by Chemical Formula 7.

[0165] The above sulfonate group-containing structural unit may be a structural unit derived from, for example, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, anethole sulfonic acid, (meth)acrylamidoalkane sulfonic acid, sulfoalkyl (meth)acrylate, or salts thereof.

[0166] Here, the alkane may be a C1 to C20 alkane, a C1 to C10 alkane, or a C1 to C6 alkane, and the alkyl may be a C1 to C20 alkyl, a C1 to C10 alkyl, or a C1 to C6 alkyl. The salt refers to a salt composed of the aforementioned sulfonic acid and a suitable ion. The ion may be, for example, an alkali metal ion, in which case the salt may be an alkali metal sulfonic acid salt.

[0167] The above (meth)acrylamidoalkane sulfonic acid may be, for example, 2-(meth)acrylamido-2-methylpropanesulfonic acid, and the above sulfoalkyl (meth)acrylate may be, for example, 2-sulfoethyl (meth)acrylate, 3-sulfopropyl (meth)acrylate, etc.

[0168] The above third structural unit is included in an amount of 5 to 80 mol% of 100 mol% of the copolymer. If the above third structural unit is included in an amount of 5 mol% or more, the membrane resistance of the separator is lowered, and the rate of change of DC internal resistance at room temperature and high temperature, respectively, can be lowered. If the above third structural unit is included in an amount of 80 mol% or less, the capacity retention rate of the battery is higher at room temperature and high temperature, respectively, and the rate of change of DC internal resistance at room temperature and high temperature, respectively, can be lowered.

[0169] For example, the third structural unit comprises 5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80 mol% of 100 mol% of the copolymer, For example, it may be included in an amount of 10 to 60 mole%. For example, the third structural unit may be included in an amount of 20 to 60 mole% or 30 to 60 mole% of 100 mole% of the copolymer. When the third structural unit is included in the above range, the membrane resistance of the binder and the separator containing it may be significantly lowered, the capacity retention rate of the battery may be increased at room temperature and high temperature respectively, and the rate of change of DC internal resistance may be lowered at room temperature and high temperature respectively.

[0170] The copolymer of the monomer mixture may include an alkali metal. The alkali metal may exist in a cation form and may be, for example, lithium, sodium, potassium, rubidium, or cesium. For example, the alkali metal may be combined with the copolymer binder of the monomer mixture and exist in the form of a salt. The alkali metal may assist in the synthesis of the copolymer binder of the monomer mixture in an aqueous solvent, improve the adhesion of the coating layer, and improve the air permeability and oxidation resistance of the separator.

[0171] The copolymer of the above monomer mixture may have a glass transition temperature of 60°C to 80°C. In a specific example, the glass transition temperature may be 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80°C, 62 to 78°C, for example, 64 to 75°C. Within the above range, the coating layer may have excellent adhesion, and the separator containing it may exhibit excellent air permeability and oxidation resistance.

[0172] The alkali metal may be included in an amount of 1 to 40 weight% in a binder comprising a copolymer of the alkali metal and the monomer mixture, for example, 1 to 30 weight%, or 1 to 20 weight%, or 10 to 20 weight%. For example, the copolymer binder of the monomer mixture and the alkali metal may be included in a weight ratio of 99:1 to 60:40, a weight ratio of 99:1 to 70:30, for example, a weight ratio of 99:1 to 80:20, or for example, a weight ratio of 90:10 to 80:20.

[0173] The alkali metal may be included in an amount of 0.1 to 1.0 mol% relative to the total content of the copolymer of the alkali metal and the monomer mixture. When the alkali metal is included within this range, the coating layer may have excellent adhesion, and the separator containing it may exhibit excellent air permeability and oxidation resistance.

[0174] The binder containing the copolymer of the above monomer mixture may be in various forms, such as an alternating polymer in which the structural units are alternately distributed, a randomly distributed polymer, or a graft polymer in which some structural units are grafted.

[0175] The weight-average molecular weight of the binder containing the copolymer of the monomer mixture may be 100,000 to 1,000,000 g / mol, 100,000 to 500,000 g / mol, 100,000 to 150,000 g / mol, 130,000 to 200,000 g / mol, or 300,000 to 900,000 g / mol. When the weight-average molecular weight of the copolymer binder of the monomer mixture satisfies the above range, excellent adhesion and low resistance can be exhibited. The weight-average molecular weight may be the polystyrene equivalent average molecular weight measured using gel permeation chromatography.

[0176] A binder containing a copolymer of the above monomer mixture can be prepared by a solution polymerization method.

[0177] According to one embodiment, the copolymer binder of the monomer mixture may be included in the coating layer of the separator in the form of a film.

[0178] (Filler)

[0179] The above filler may have a size D50 of 400 nm or less, for example, 200 to 250 nm. Within this range, the resistance of the separator can be lowered compared to a coating layer containing the binder alone.

[0180] The filler having a size D50 of 400 nm or less may be included in an amount of 95% by weight or more of the total filler in the coating layer, for example, 95 to 100% by weight, 98 to 100% by weight, or 100% by weight. Within the above range, the effect of the separator membrane of the present invention may be easily realized.

[0181] The above filler may not be surface modified.

[0182] The above filler may be, for example, an inorganic filler, an organic filler, an organic-inorganic composite filler, or a combination thereof. The above inorganic filler may be a ceramic material capable of improving heat resistance. The above inorganic filler may include, for example, a metal oxide, a metal metal oxide, a metal fluoride, a metal hydroxide, or a combination thereof. The above inorganic filler may include, for example, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof, but is not limited thereto. The above organic filler may include an acrylic compound, an imide compound, an amide compound, or a combination thereof, but is not limited thereto. The above organic filler may have a core-shell structure, but is not limited thereto. For example, the above filler may preferably be boehmite.

[0183] The above filler may be spherical, plate-shaped, cubic, or amorphous. Preferably, the filler may be cubic, and the cubic shape may facilitate further improvement of the effect of the above-described separation membrane.

[0184] The above filler should be included in an appropriate amount with respect to the binder, for example, the copolymer. According to one embodiment, the copolymer:the filler may be included in a mass ratio of 1:10 to 1:50, for example, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, or 1:20 to 1:30. Within this range, there may be an effect of improving heat resistance properties in the electrolyte.

[0185] The above filler may be included in an amount of 50% to 99% by weight, for example 70% to 99% by weight, for example 75% to 99% by weight, for example 80% to 99% by weight, for example 85% to 99% by weight, for example 90% to 99% by weight, for example 95% to 99% by weight, of the total amount of the coating layer. When the above filler is included within the above range, excellent heat resistance, durability, oxidation resistance, and stability may be exhibited.

[0186] (Structure of the coating layer)

[0187] The coating layer comprises the binder and filler and may have a single layer or a multilayer structure.

[0188] The above coating layer may include only the first layer comprising the binder and filler.

[0189] The coating layer comprises a first layer including the binder and filler and a second layer located on the first layer, and the second layer may include an adhesive binder. The adhesive binder may be the copolymer described above or may include a conventional adhesive binder known to those skilled in the art. For example, the adhesive binder may include one or more of an acrylic adhesive binder and a polyvinylidene fluoride adhesive binder.

[0190] In another embodiment, the coating layer may comprise only a first layer comprising the binder, the filler, and the adhesive binder. The adhesive binder may comprise a conventional adhesive binder known to those skilled in the art. For example, the adhesive binder may comprise one or more of an acrylic adhesive binder and a polyvinylidene fluoride adhesive binder.

[0191] The coating layer may have a thickness of 0.01㎛ to 20㎛, and within the above range, may have a thickness of 0.01㎛ to 5㎛, or 0.1㎛ to 3㎛, or 0.1㎛ to 1.5㎛.

[0192] The ratio of the thickness of the coating layer to the thickness of the porous substrate may be 0.1 to 0.8, for example, 0.1 to 0.7, or 0.15 to 0.6. Within the above range, the separator may exhibit excellent air permeability, heat resistance, and adhesion. Here, 'thickness of the coating layer' refers to the thickness of one coating layer when the coating layer is formed only on one side of the porous substrate, and refers to the total thickness of two coating layers when the coating layer is formed on both sides of the porous substrate.

[0193] porous substrate

[0194] The porous substrate may be a substrate having a number of pores and typically used in electrochemical devices. The porous substrate may be, but is not limited to, any one polymer selected from the group consisting of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a polymer membrane formed from two or more copolymers or mixtures of these.

[0195] The porous substrate may be a polyolefin-based substrate including, for example, a polyolefin, and the polyolefin-based substrate may contribute to improving the safety of the battery by having an excellent shutdown function. The polyolefin-based substrate may be selected from, for example, a polyethylene single membrane, a polypropylene single membrane, a polyethylene / polypropylene double membrane, a polypropylene / polyethylene / polypropylene triple membrane, and a polyethylene / polypropylene / polyethylene triple membrane. In addition, the polyolefin-based resin may include a non-olefin resin in addition to the olefin resin, or may include a copolymer of an olefin and a non-olefin monomer.

[0196] The porous substrate may have a thickness of 1 μm to 40 μm, and, for example, may have a thickness of 1 μm to 30 μm, 1 μm to 20 μm, or 5 μm to 15 μm.

[0197] A separator for a lithium secondary battery according to one embodiment may exhibit excellent air permeability and may have an air permeability value of, for example, less than 250 sec / 100cc, for example, 230 sec / 100cc or less, or 200 sec / 100cc or less. That is, it may have an air permeability value of less than 40 sec / 100cc·1㎛ per unit thickness, for example, 30 sec / 100cc·1㎛ or less, or 25 sec / 100cc·1㎛ or less. Here, air permeability refers to the time (in seconds) required for 100cc of air to pass through a unit thickness of the separator. The air permeability per unit thickness can be obtained by measuring the air permeability over the entire thickness of the separator and then dividing by the thickness. The air permeability can be measured by using an air permeability measuring device (Asahi Seiko, EG01-55-1MR) to measure the time (in seconds) required for 100cc of air to pass through.

[0198] The above-mentioned separator for a secondary battery can be manufactured by applying a composition for forming a coating layer to one or both sides of a porous substrate and then drying it.

[0199] A method for manufacturing a separator for a lithium secondary battery may include the step of coating a separator coating composition containing the binder on at least one surface of a porous substrate; and the step of drying the porous substrate coated with the separator coating composition to form a coating layer.

[0200] FIG. 5 is a schematic cross-sectional view of a separator for a lithium secondary battery according to one embodiment. Referring to FIG. 5, the separator for a lithium secondary battery comprises a porous substrate 1 and a coating layer 2 formed on one side and the other side of the porous substrate 1, and the coating layer 2 may comprise a binder 3 and a filler 4.

[0201] lithium secondary battery

[0202] Another embodiment provides a lithium secondary battery comprising a separator for a lithium secondary battery according to one embodiment; a positive electrode; and a negative electrode.

[0203] The separator for a lithium secondary battery is described above. The separator for a lithium secondary battery can be positioned between the positive electrode and the negative electrode.

[0204] positive electrode active material

[0205] As a positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0206] The above composite oxide may be a lithium transition metal composite oxide, and specific examples include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0207] As an example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b X b O2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b About 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c About 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c About 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); Li a FePO4(0.90≤a≤1.8).

[0208] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al, or a combination thereof.

[0209] For example, the above-mentioned positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0210] anode

[0211] A positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material and may further include a binder and / or a conductive material.

[0212] For example, the above anode may further include an additive that can serve as a sacrificial anode.

[0213] The content of the positive active material is 90% to 99.5% by weight with respect to 100% by weight of the positive active material layer, and the content of the binder and the conductive material may each be 0.5% to 5% by weight with respect to 100% by weight of the positive active material layer.

[0214] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0215] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0216] Al may be used as the current collector mentioned above, but is not limited thereto.

[0217] cathode active material

[0218] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0219] A material capable of reversibly intercalating / deintercalating the above lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0220] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0221] As a material capable of doping and undoping the above lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (wherein Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0222] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include a secondary particle (core) assembled from silicon primary particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particle. The amorphous carbon may also be located between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0223] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0224] The above Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0225] cathode

[0226] A negative electrode for a lithium secondary battery comprises a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer comprises a negative electrode active material and may further comprise a binder and / or a conductive material.

[0227] For example, the negative electrode active material layer may comprise 90% to 99% by weight of negative electrode active material, 0.5% to 5% by weight of binder, and 0% to 5% by weight of conductive material.

[0228] The above binder serves to effectively bond the negative electrode active material particles to each other and also to effectively bond the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof may be used.

[0229] Examples of the above-mentioned non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or combinations thereof.

[0230] The above-mentioned water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0231] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0232] The above dry binder is a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0233] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0234] As the above-mentioned cathode current collector, a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof may be used.

[0235] electrolyte

[0236] The electrolyte for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0237] The above-mentioned non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0238] The above-mentioned non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0239] The above carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc.

[0240] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0241] As ether-based solvents, dibutyl ether, tetraglame, diglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Additionally, as ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. may be used.

[0242] The above-mentioned non-aqueous organic solvent can be used alone or in a mixture of two or more types.

[0243] In addition, when using a carbonate-based solvent, a mixture of cyclic carbonates and chain carbonates can be used, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0244] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and facilitating the movement of lithium ions between the anode and cathode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 It may include one or more selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0245] In one embodiment, the electrolyte may be an electrolyte containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC = 3:5:2 and containing 1 to 1.5 M of LiPF6.

[0246] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, coin, etc., depending on their shape. FIGS. 1 to 4 are schematic diagrams illustrating a lithium secondary battery according to one embodiment. FIG. 1 may be a cylindrical battery, FIG. 2 a prismatic battery, and FIGS. 3 and 4 a pouch battery. Referring to FIGS. 1 to 4, the lithium secondary battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is housed. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as in FIG. 1. In addition, in FIG. 2, the lithium secondary battery (100) may include a positive lead tab (11) and a positive terminal (12), a negative lead tab (21) and a negative terminal (22). As shown in FIG. 3 and FIG. 4, the lithium secondary battery (100) may include an electrode tab (70), namely a positive tab (71) and a negative tab (72), which serve as an electrical path to guide the current formed in the electrode assembly (40) to the outside.

[0247] A lithium secondary battery according to one embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electric devices, etc., but the present invention is not limited thereto.

[0248]

[0249] Examples and comparative examples of the present invention are described below. However, the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0250] Preparation Example 1

[0251] In a 3L four-neck detachable flask equipped with a stirrer, thermometer, and condenser, 1249.72 g of distilled water, 20% aqueous lithium hydroxide solution (203.69 g), styrene (SM, 36.45 g, 0.35 mol), methyl methacrylate (MMA, 35.04 g, 0.35 mol), 2-ethylhexyl acrylate (EHA, 36.83 g, 0.20 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 20.73 g, 0.10 mol) were used, sodium dodecylbenzenesulfonate (16.02 g, 0.05 mol) was added, and the internal pressure was reduced to 10 mmHg using a diaphragm pump, and the internal pressure was returned to atmospheric pressure using nitrogen, and this operation was repeated three times.

[0252] The reaction was carried out for 12 hours while controlling the heating so that the temperature of the reaction solution stabilized between 65°C and 70°C.

[0253] After cooling to room temperature, about 10 mL of the reaction solution was taken and the non-volatile component (NV) was measured, resulting in a particulate copolymer with 9.8 wt% (theoretical value 10 wt%). In the obtained particulate copolymer, the molar ratio of the first structural unit derived from styrene and methyl methacrylate, the second structural unit derived from 2-ethylhexyl acrylate, and the third structural unit derived from 2-acrylamido-2-methylpropanesulfonic acid in the poly(styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid) lithium salt is 70:20:10, the particle size D50 is 500 nm, and the glass transition temperature (Tg) of the copolymer is 65.1°C.

[0254] Preparation Example 2

[0255] A copolymer was prepared using the same method as in Preparation Example 1 above, except that styrene (SM, 30.20 g, 0.29 mol), methyl methacrylate (MMA, 29.04 g, 0.29 mol), 2-ethylhexyl acrylate (EHA, 40.52 g, 0.22 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 41.45 g, 0.20 mol) were used and the glass transition temperature of the copolymer was 65.0°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 29:29:22:20. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0256] Preparation Example 3

[0257] An acrylic copolymer was prepared using the same method as in Preparation Example 1, except that styrene (SM, 23.95 g, 0.23 mol), methyl methacrylate (MMA, 23.03 g, 0.23 mol), 2-ethylhexyl acrylate (EHA, 44.20 g, 0.24 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 62.18 g, 0.30 mol) were used and the glass transition temperature of the copolymer was 64.0°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 23:23:24:30. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0258] Preparation Example 4

[0259] An acrylic copolymer was prepared using the same method as in Preparation Example 1 above, except that styrene (17.71 g, 0.17 mol), methyl methacrylate (MMA, 35.04 g, 0.17 mol), 2-ethylhexyl acrylate (EHA, 47.88 g, 0.26 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 82.9 g, 0.40 mol) were used and the glass transition temperature of the copolymer was 64.8°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 17:17:26:40. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0260] Preparation Example 5

[0261] An acrylic copolymer was prepared using the same method as in Preparation Example 1, except that styrene (SM, 11.46 g, 0.11 mol), methyl methacrylate (MMA, 11.01 g, 0.11 mol), 2-ethylhexyl acrylate (EHA, 51.56 g, 0.28 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 103.63 g, 0.50 mol) were used and the glass transition temperature of the copolymer was 64.7°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 11:11:28:50. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0262] Preparation Example 6

[0263] An acrylic copolymer was prepared using the same method as in Preparation Example 1, except that styrene (SM, 5.21 g, 0.05 mol), methyl methacrylate (MMA, 5.01 g, 0.05 mol), 2-ethylhexyl acrylate (EHA, 55.25 g, 0.30 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 124.35 g, 0.60 mol) were used and the glass transition temperature of the copolymer was 64.6°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 5:5:30:60. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0264] Preparation Example 7

[0265] An acrylic copolymer was prepared using the same method as in Preparation Example 1 above, except that styrene (SM, 20.83 g, 0.20 mol), 2-ethylhexyl acrylate (EHA, 55.28 g, 0.30 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 103.63 g, 0.50 mol) were used, the glass transition temperature of the copolymer was 60.0°C, and methyl methacrylate was not used. The molar ratio of styrene-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 20:30:50. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0266] Comparative Manufacturing Example 1

[0267] An acrylic copolymer was prepared using the same method as in Preparation Example 1, except that styrene (SM, 2.08 g, 0.02 mol), methyl methacrylate (MMA, 2 g, 0.02 mol), 2-ethylhexyl acrylate (EHA, 55.28 g, 0.30 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 136.785 g, 0.66 mol) were used and the glass transition temperature of the copolymer was 67.1°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 2:2:30:66. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0268] Comparative Manufacturing Example 2

[0269] An acrylic copolymer was prepared using the same method as in Preparation Example 1 above, except that styrene (SM, 44.26 g, 0.425 mol), methyl methacrylate (MMA, 42.55 g, 0.425 mol), 2-ethylhexyl acrylate (EHA, 18.43 g, 0.10 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 10.36 g, 0.05 mol) were used and the glass transition temperature of the copolymer was 85.5°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 42.5:42.5:10:5. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0270] Comparative Manufacturing Example 3

[0271] An acrylic copolymer was prepared using the same method as in Preparation Example 1, except that styrene (SM, 41.66 g, 0.40 mol), methyl methacrylate (MMA, 40.05 g, 0.40 mol), 2-ethylhexyl acrylate (EHA, 9.21 g, 0.05 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 31.09 g, 0.15 mol) were used and the glass transition temperature of the copolymer was 102.97°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 40:40:5:15. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0272] Comparative Manufacturing Example 4

[0273] An acrylic copolymer was prepared using the same method as in Preparation Example 1 above, except that styrene (SM, 20.83 g, 0.20 mol), methyl methacrylate (MMA, 20.02 g, 0.20 mol), 2-ethylhexyl acrylate (EHA, 82.93 g, 0.45 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 31.09 g, 0.15 mol) were used and the glass transition temperature of the copolymer was 20.7°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 20:20:45:15. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0274] Comparative Manufacturing Example 5

[0275] An acrylic copolymer was prepared using the same method as in Preparation Example 1, except that styrene (SM, 41.66 g, 0.40 mol), methyl methacrylate (MMA, 40.05 g, 0.40 mol), 2-ethylhexyl acrylate (EHA, 32.25 g, 0.175 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 5.18 g, 0.025 mol) were used and the glass transition temperature of the copolymer was 67.3°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 40:40:17.5:2.5. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0276] Comparative Manufacturing Example 6

[0277] An acrylic copolymer was prepared using the same method as in Preparation Example 1, except that styrene (SM, 2.6 g, 0.025 mol), methyl methacrylate (MMA, 2.5 g, 0.025 mol), 2-ethylhexyl acrylate (EHA, 18.43 g, 0.10 mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 176.16 g, 0.85 mol) were used and the glass transition temperature of the copolymer was 127.3°C. The molar ratio of styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt was 2.5:2.5:10:85. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0278]

[0279] Table 1 below shows the molar ratio of each monomer among the binders prepared in Preparation Examples 1 to 7 and Comparative Preparation Examples 1 to 6.

[0280] Monomer Molar Ratio Tg (°C) SM M M A H A M S Preparation Example 1 35 35 20 10 6 5.1 Preparation Example 2 29 29 22 20 6 5.0 Preparation Example 3 23 23 24 30 6 4.0 Preparation Example 4 17 17 26 40 6 4.8 Preparation Example 5 11 11 28 50 6 4.7 Preparation Example 6 55 30 6 0 6 4.6 Preparation Example 7 20 30 50 6 0.0 Comparative Preparation Example 1 22 30 6 6 6 7.1 Comparative Preparation Example 2 4 2.5 4 2.5 10 58 5.5 Comparative Preparation Example 3 40 40 51 5 10 2.9 Comparative Preparation Example 4 20 20 45 15 20.7 Comparative Preparation Example 5 40 40 17.5 2.5 6 7.3 Comparative Preparation Example 62.52.51085127.3

[0281]

[0282] Example 1

[0283] Boehmite (size D50: 200 nm, cubic type) was mixed as the binder and filler of Preparation Example 1 in a mass ratio of binder:filler = 1:20 based on solid content, added to a water solvent, and then milled and dispersed using a bead mill at 25°C for 30 minutes to prepare a dispersion.

[0284] As a porous substrate, the adhesive layer composition prepared above was double-sidedly coated at a speed of 80 m / min on both sides of a polyethylene-based film (thickness: 5.5 μm, CZMZ, air permeability: 110 sec / 100 cc, puncture strength: 360 kgf) by a die-coating method, and then 14 g / m at 60°C 3 A separator for a lithium secondary battery was manufactured by drying in the presence of an absolute amount of water vapor (average value) to form an adhesive layer with a total thickness of 1.4 μm.

[0285]

[0286] Examples 2 to 7

[0287] A separator for a lithium secondary battery was prepared in the same manner as in Example 1, except that the type of binder was changed in Example 1.

[0288]

[0289] Example 8

[0290] A separator for a lithium secondary battery was prepared in the same manner as in Example 1, except that the filler was changed to boehmite (particle size D50: 250 nm, cubic type) in Example 1.

[0291]

[0292] Comparative Examples 1 to 6

[0293] A separator for a lithium secondary battery was prepared in the same manner as in Example 1, except that the type of binder was changed in Example 1.

[0294]

[0295] Battery manufacturing

[0296] (Manufacturing of the cathode)

[0297] As a cathode active material, 97 wt% of graphite particles with an average particle size D50 of 25 μm, 1.5 wt% of styrene-butadiene rubber (SBR) binder, and 1.5 wt% of carboxymethylcellulose (CMC) were mixed, added to distilled water, and stirred for 60 minutes using a mechanical stirrer to prepare a cathode active material slurry. The slurry was applied onto a copper current collector with a thickness of 10 μm using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, dried once more under vacuum conditions at 120°C for 4 hours, and then rolled to produce a cathode.

[0298] (Manufacturing of the anode)

[0299] 97 wt% of LiCoO2 as the positive active material, 1.5 wt% of carbon black powder as the conductive material, and 1.5 wt% of polyvinylidene fluoride (PVdF) were mixed and added to an N-methyl-2-pyrrolidone solvent, and then stirred for 30 minutes using a mechanical stirrer to prepare a positive active material slurry. The slurry was applied onto an aluminum current collector with a thickness of 20 μm using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, dried once more under vacuum conditions at 120°C for 4 hours, and then rolled to produce a positive electrode.

[0300] (Electrode assembly jelly roll)

[0301] An electrode assembly jellyroll was prepared by interposing a separator obtained according to the examples and comparative examples between the anode and cathode prepared above, and then winding it. The jellyroll was inserted into a pouch, an electrolyte was injected, and the pouch was vacuum-sealed. The electrolyte used was 1.3 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:5:2. 11.7 kgf / cm² of the jellyroll inserted into the pouch 2 A lithium secondary battery was manufactured by applying pressure and pressing at a temperature of 80°C for 3 minutes.

[0302] Air permeability (unit: sec / 100cc)

[0303] The air permeability of the manufactured membrane was measured using a measuring device (EG01-55-1MR, Asahi Seiko) by measuring the time (unit: seconds) required for 100cc of air to pass through the membrane.

[0304] [Permeability Measurement Device Setting Conditions]

[0305] Measured pressure: 0.5 kg / ㎠, Cylinder pressure: 2.5 kg / ㎠, Set time: 10 seconds

[0306] Electrolyte moisture content (Unit: weight%)

[0307] The manufactured binder was dried in a 120°C oven for 12 hours to obtain a film (thickness: 20 µm, weight W1 measured before immersion). The film was placed in the manufactured pouch and immersed in the electrolyte, and the pouch was vacuum-sealed. After leaving the sealed pouch in a 60°C oven for 72 hours, the film was immediately removed and its weight W2 was measured. The electrolyte moisture content was measured as W2 / W1 x 100.

[0308] Anode Adhesion (Unit: N)

[0309] After attaching a separator to the positive electrode (manufactured in the same manner as the above-mentioned battery), insert it into the pouch, inject an electrolyte (a 1.3M LiPF6 mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a 3 / 5 / 2 (volume ratio) ratio), and leave it for 12 hours, then apply a pressure of 10 to 20 kgf / cm² 2 ...is pressed and then disassembled under conditions of a temperature of 70°C to 90°C and a time of 5 to 20 seconds. After removing the separator and anode from the pouch, the anode and separator were spread 180°, and the force required to detach the anode from the separator was measured using a tension meter (Tinius Olsen, HT400).

[0310] Film resistance (unit: Ω)

[0311] The membrane resistance was evaluated using electrochemical impedance spectroscopy (EIS) resistance. The separator prepared in the example and comparative example was impregnated with an electrolyte solution of ethylene carbonate dissolved in 1.5M LiPF6, a mixed solvent of ethylmethyl carbonate and dimethyl carbonate (volume ratio (3 / 5 / 2)), fitted onto an aluminum foil electrode with a lead tab, and sealed in an aluminum pack to prepare a test cell. The resistance (Ω) of the test cell was measured at 20°C using the AC impedance method (measurement frequency 100 kHz).

[0312] 200-Cycle Capacity Retention Rate (Unit: %)

[0313] For the batteries manufactured using the separators of the examples and comparative examples, constant current charging was performed at a rate of 0.5 C at 25°C and 45°C, respectively, until the voltage reached 4.2 V, and then cut off at a rate of 0.025 C in constant voltage mode. Subsequently, a cycle of discharging at a rate of 0.5 C until the voltage reached 2.5 V was repeated 200 times, and the capacity retention rate, i.e., the life characteristics according to the number of cycles, was evaluated and the results were obtained.

[0314] DC-IR: Direct current internal resistance (unit: mΩ)

[0315] Using the separators of the examples and comparative examples, the cells manufactured with a cell capacity of 75 mAh were charged at 25°C and 45°C, respectively, with constant current / constant voltage under cut-off conditions of 0.2C, 4.25V, and 0.05C, and then rested for 10 minutes. Afterward, the cells were discharged under cut-off conditions of constant current of 0.33C and 2.80V, and then rested for 10 minutes. A single charge-discharge cycle was performed, and the voltage drop (V) occurring while flowing a current of 1C for 10 seconds at SOC50 (a state where the total charge capacity of the battery is set to 100%, which means a state where the battery is discharged by 50%) was measured to determine the DC internal resistance (DC-IR).

[0316] The rate of change in DC internal resistance is the ratio of the DC internal resistance after 200 cycles to the initial DC internal resistance expressed as a percentage.

[0317] Example 1 2 3 4 Binder Preparation Example 1 Preparation Example 2 Preparation Example 3 Preparation Example 4 Filler particle size (nm) 200 200 200 200 Total thickness of coating layer 1.4 1.4 1.4 1.4 Air permeability 13 3 13 4 13 2 13 3 Electrolyte moisture content 28 3 24 8 21 0 18 5 Anode adhesion 1.1 4 1.1 2 1.1 3 1.1 5 Membrane resistance upon electrolyte impregnation 0.6 10.5 0.4 6 0.4 2 2 5°C Capacity retention rate (%) 8 5 8 8 9 19 2 2 5°C Initial DC internal resistance (mΩ) 3.5 12.8 8 2.6 5 2.4 2 2 5°C DC internal resistance (mΩ) after 200 cycles 7.7 2 6.0 4 5.5 8 5.00 2 5°C Change rate of DC internal resistance after 200 cycles (%) 220 210 211 20745℃ Capacity Retention Rate (%) 71 73 76 7745℃ Initial DC Internal Resistance (mΩ) 3.19 2.6 12.4 0 2.2045℃ DC Internal Resistance (mΩ) after 200 Cycles 10.5 28.2 37.6 16.8 245℃ Rate of Change in DC Internal Resistance after 200 Cycles (%) 33 03 153 173 11

[0318]

[0319] Example 5 6 7 8 Binder Preparation Example 5 Preparation Example 6 Preparation Example 7 Preparation Example 1 Filler particle size (nm) 200 200 200 250 Total thickness of coating layer 1.4 1.4 1.4 1.4 Air permeability 13 3 13 5 13 6 13 3 Electrolyte moisture content 15 2 13 9 17 12 8 3 Anode adhesion 0.9 8 0.9 0 0.8 2 1.1 4 Membrane resistance upon electrolyte impregnation 0.4 0.3 7 0.4 4 0.6 1 25°C Capacity retention rate (%) 90 8 9 7 6 8 5 25°C Initial DC internal resistance (mΩ) 2.3 0 2.1 3 2.5 3 3.5 1 25°C DC internal resistance (mΩ) after 200 cycles 4.6 0 4.1 5 5.2 6 7.7 2 25°C Change rate of DC internal resistance after 200 cycles (%) 200 19 5 20 8 220 45℃ Capacity Retention Rate (%) 7 5 7 4 6 3 7 145℃ Initial DC Internal Resistance (mΩ) 2.0 9 1.9 3 2.3 0 3.1 945℃ DC Internal Resistance (mΩ) after 200 Cycles 6.2 7 5.6 6 7.1 8 10.5 245℃ Rate of Change in DC Internal Resistance after 200 Cycles (%) 300 29 3 3 12 3 30

[0320] Comparative Example 1 2 3 4 5 6 Binder Comparison Preparation Example 1 Comparative Preparation Example 2 Comparative Preparation Example 3 Comparative Preparation Example 4 Comparative Preparation Example 5 Comparative Preparation Example 6 Filler Particle Size (nm) 200 200 200 200 200 200 Total Coating Layer Thickness 1.4 1.4 1.4 1.4 1.4 1.4 Air Permeability 13 11 28 126 320 134 125 Electrolyte Moisture Impregnation 126 32 130 54 10 334 105 Anode Adhesion 0.7 8 0.6 10.5 5 3.0 11.1 10.35 Membrane Resistance upon Electrolyte Impregnation 0.3 4 0.8 11.5 2.8 0.8 8 3.2 25℃ Capacity Retention Rate (%) 80 70 45 50 89 40 25℃ Initial DC Internal Resistance (mΩ) 1.96 4.66 8.63 16.10 5.06 18.40 25℃ After 200 cycles DC Internal Resistance (mΩ) 3.95 14.11 34.50 80.50 15.18 82.80 25℃ After 200 cycles DC Internal Resistance Change Rate (%) 20 230 3400 500 300 450 45℃ Capacitance Retention Rate (%) 67 58 38 427 433 45℃ Initial DC Internal Resistance (mΩ) 1.78 4.23 7.84 14.64 4.60 16.73 45℃ After 200 cycles DC Internal Resistance (mΩ) 5.39 19.24 47.05 109.77 20.70 112.91 45℃ After 200 cycles DC Internal Resistance Change Rate (%)303455600750450675

[0321]

[0322] As shown in Tables 2 and 3 above, the separator of the example exhibits low membrane resistance, which can improve the capacity, safety, and lifespan of the battery. In addition, the separator for a lithium secondary battery of the example has high adhesion to an electrode, for example, a positive electrode, which can increase reliability.

[0323] As shown in Table 4 above, the separator of the comparative example could not achieve the effect of the separator of the example.

[0324]

[0325] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

1. A porous substrate and a coating layer located on at least one surface of the porous substrate, and The above coating layer comprises a binder and a filler, and The above binder comprises a copolymer of a monomer mixture comprising: a first structural unit comprising a structural unit derived from an aromatic vinyl monomer; a second structural unit derived from an alkyl group-containing (meth)acrylic monomer having four or more carbon atoms in the main chain at the ester site; and a third structural unit derived from a sulfonic acid group-containing monomer. A separator for a lithium secondary battery, comprising, with respect to 100 mol% of the copolymer, 5 to 80 mol% of the first structural unit, 10 to 40 mol% of the second structural unit, and 5 to 80 mol% of the third structural unit.

2. In claim 1, the copolymer is a particulate binder, a separator for a lithium secondary battery.

3. The copolymer according to claim 1 or 2, wherein the copolymer has an average size D50 of 500 to 700 nm, a separator for a lithium secondary battery.

4. A separator for a lithium secondary battery, wherein, in any one of claims 1 to 3, the copolymer is an adhesive binder.

5. A separator for a lithium secondary battery, wherein, in any one of claims 1 to 4, the copolymer has a glass transition temperature of 60 to 80°C.

6. A separator for a lithium secondary battery, wherein, in any one of claims 1 to 5, the copolymer is included in the coating layer at a weight of 1 to 100%.

7. A separator for a lithium secondary battery according to any one of claims 1 to 6, wherein the total sum of the first structural unit, the second structural unit, and the third structural unit is 95 mol% or more with respect to the copolymer.

8. In any one of claims 1 to 7, the structural unit derived from the aromatic vinyl monomer is represented by the following chemical formula 1, and [Chemical Formula 1] (In the above chemical formula 1, R 1 and R 2 Each is independently hydrogen or a substituted or unsubstituted C1 to C5 alkyl group, Ar is a substituted or unsubstituted, monocyclic or polycyclic C6 to C20 aryl group), The above second structural unit is represented by the following chemical formula 4, and [Chemical Formula 4] (In the above chemical formula 4, R 7 and R 8 Each independently has a hydrogen or methyl group, L 2 is a substituted or unsubstituted, straight-chain or branched-chain C4 to C30 alkyl group), A separator for a lithium secondary battery, wherein the above-mentioned third structural unit is represented by any one of the following chemical formula 5, the following chemical formula 6, and the following chemical formula 7: [Chemical Formula 5] [Chemical Formula 6] [Chemical Formula 7] (In the above chemical formulas 5 to 7, R 9 , R 10 , R 11 , R 12 , R 13 and R 14 Each is independently hydrogen or a C1 to C3 alkyl group, and L 3 , L 5 and L 7 Each is independently -C(=O)-, -C(=O)O-, -OC(=O)-, -O- or -C(=O)NH-, and L 4 , L 6 and L 8 Each is independently a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, and a, b, c, d, e, and f are each independently integers from 0 to 2, and In the above chemical formula 6, M is an alkali metal).

9. A separator for a lithium secondary battery according to any one of claims 1 to 8, wherein the first structural unit further comprises a unit derived from an alkyl group-containing (meth)acrylic monomer having 1 to 3 carbon atoms in the main chain at the ester site.

10. A separator for a lithium secondary battery according to claim 9, wherein the unit derived from the (meth)acrylic monomer is a unit represented by the following chemical formula 3: [Chemical Formula 3] (In the above chemical formula 3, R 5 and R 6 Each independently has a hydrogen or methyl group, L 1 (substituted or unsubstituted, straight-chain or branched-chain C1 to C3 alkyl groups).

11. A separator for a lithium secondary battery according to claims 9 and 10, wherein the structural unit derived from the aromatic vinyl monomer and the structural unit derived from the (meth)acrylic monomer are included in a molar ratio of 1:0.5 to 2.

12. In any one of claims 9 to 11, with respect to 100 mol% of the copolymer, 5 to 35 mol% of structural units derived from the above aromatic vinyl monomer, 5 to 35 mol% of structural units derived from (meth)acrylic monomers containing alkyl groups having 1 to 3 carbon atoms in the main chain at the above ester site, The above second structural unit 20 to 30 mol%, and A separator for a lithium secondary battery comprising 10 to 60 mol% of the above-mentioned third structural unit.

13. In any one of claims 9 to 12, the copolymer Structural unit derived from the above aromatic vinyl monomer derived from one or more of styrene; alpha-methyl styrene; 4-butyl styrene; 4-butoxy styrene; halo styrene; vinyl toluene; and vinyl naphthalene; A structural unit derived from an alkyl group-containing (meth)acrylic monomer having 1 to 3 carbon atoms in the main chain at the ester site derived from one or more of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and iso-propyl (meth)acrylate, The second structural unit derived from one or more of 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and isodecyl (meth)acrylate, and A separator for a lithium secondary battery having the third structural unit derived from vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, anethole sulfonic acid, (meth)acrylamidoalkane sulfonic acid, sulfoalkyl (meth)acrylate, or salts thereof.

14. In any one of claims 1 to 13, the filler is a separator for a lithium secondary battery having a size D50 of 400 nm or less.

15. A separator for a lithium secondary battery, wherein, in any one of claims 1 to 14, the copolymer : the filler is included in a mass ratio of 1:10 to 1:

50.

16. A separator for a lithium secondary battery, wherein, in any one of claims 1 to 15, the coating layer further comprises an adhesive binder.

17. A separator for a lithium secondary battery according to any one of claims 1 to 16, wherein the coating layer comprises a first layer comprising the binder and the filler, and a second layer located on the first layer comprising an adhesive binder.

18. A separator for a lithium secondary battery, wherein, in any one of claims 1 to 17, the thickness of the coating layer is 0.1 μm to 3 μm.

19. A lithium secondary battery comprising: a positive electrode; a negative electrode; and a separator for a lithium secondary battery according to any one of claims 1 to 18 located between the positive electrode and the negative electrode.

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