Rechargeable battery and battery pack including the same

Abstract

The invention relates to a secondary battery and a battery pack including the same, wherein the secondary battery comprises an electrode assembly having a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate; and an electrolyte impregnated with the electrode assembly, wherein the separator comprises a substrate and an adhesive layer located on at least one surface of the substrate, wherein the adhesive layer comprises a copolymer of a monomer mixture comprising an unsaturated monomer having a carboxylic acid group or a salt thereof and an unsaturated monomer having an aromatic group, wherein the copolymer has a glass transition temperature of 90 to 150°C, and the electrolyte comprises a non-aqueous organic solvent, wherein the volume ratio of ethylene carbonate : dimethyl carbonate : ethylmethyl carbonate is 20 to 30% : 30 to 40% : 30 to 40% based on 100% of the total volume of the non-aqueous organic solvent.

Description

Technology Field

[0001] This relates to a secondary battery and a battery pack containing the same. Background Technology

[0003] Recently, accompanied by the 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 rapidly increasing. Accordingly, research and development to improve the performance of lithium-ion batteries is actively underway.

[0004] 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.

[0005] The information described above disclosed in the background technology of this invention is intended only to enhance understanding of the background of the present invention and may therefore include information that does not constitute prior art. The problem to be solved

[0007] One embodiment provides a secondary battery in which the adhesive layer of the separator becomes less film-like after a long period of time in the battery.

[0008] Another embodiment provides a secondary battery with a low rate of change in the permeability of the separator after a long period of time within the battery.

[0009] Another embodiment provides a secondary battery comprising a separator that does not have adhesion between separators and detachment of the adhesive layer from the separator when the separator in a wound state is withdrawn.

[0010] However, the technical problems that the present invention aims to solve are not limited to those described above, and other unmentioned problems can be clearly understood by those skilled in the art from the description of the invention below. means of solving the problem

[0012] To solve the above technical problem, a secondary battery according to one embodiment comprises: an electrode assembly having a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate; and an electrolyte impregnated with the electrode assembly, wherein the separator comprises a substrate and an adhesive layer located on at least one surface of the substrate, and the adhesive layer comprises a copolymer of a monomer mixture comprising an unsaturated monomer having a carboxylic acid group or a salt thereof and an unsaturated monomer having an aromatic group, wherein the copolymer has a glass transition temperature of 90 to 150°C, and the electrolyte comprises a non-aqueous organic solvent, wherein the volume ratio of ethylene carbonate : dimethyl carbonate : ethylmethyl carbonate is 20 to 30% : 30 to 40% : 30 to 40% based on 100% of the total volume of the non-aqueous organic solvent. Effects of the invention

[0014] According to one embodiment, a secondary battery with improved lifespan is provided by preventing an increase in resistance of the separator by minimizing the film formation of the adhesive layer of the separator within the battery.

[0015] According to another embodiment, a secondary battery with excellent reliability was provided, in which the rate of change in the air permeability of the separator within the battery is low, thereby extending the lifespan of the separator.

[0016] According to another embodiment, a secondary battery with excellent manufacturing processability was provided, in which there is no adhesion between separators and no detachment of the adhesive layer from the separator. Brief explanation of the drawing

[0018] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the detailed description of the invention provided below; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings. FIG. 1 is a schematic perspective view of a pouch-type secondary battery according to one embodiment. FIG. 2 is a cross-sectional view of a separator according to one embodiment. FIG. 3 is a cross-sectional view schematically showing a cylindrical secondary battery according to one embodiment. FIG. 4 is a cross-sectional view schematically showing a prismatic secondary battery according to one embodiment. FIG. 5 is a schematic perspective view of a pouch-type secondary battery according to one embodiment. Specific details for implementing the invention

[0019] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. 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. Instead, based on the principle that the inventor may appropriately define the concepts of terms to best describe his invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention. Therefore, it should be understood that the embodiments described in this specification and the configurations illustrated in the drawings are merely some of the most preferred embodiments of the present invention and do not represent all of the technical spirit of the present invention; thus, various equivalents and modifications that can replace them may exist at the time of filing this application. Furthermore, as used in this specification, "comprise" or "include" and / or "comprising" or "including" specify the presence of the mentioned features, numbers, steps, actions, parts, elements, and / or groups thereof, and do not exclude the presence or addition of one or more other features, numbers, actions, parts, elements, and / or groups. Additionally, when describing embodiments of the present invention, "may" or "may be" may include "one or more embodiments of the present invention."

[0020] Additionally, to aid in understanding the invention, the attached drawings are not drawn to actual scale, and the dimensions of some components may be exaggerated. Furthermore, the same reference numerals may be assigned to identical components in different embodiments.

[0021] The statement that two subjects of comparison are 'identical' means that they are 'substantially identical.' Therefore, substantial identity may include deviations considered low in the industry, for example, deviations within 5%. Additionally, the statement that a parameter is uniform in a given area may mean that it is uniform from an average perspective.

[0022] Although terms such as "first," "second," etc., are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used merely to distinguish one component from another, and unless specifically stated otherwise, the first component may also be the second component.

[0023] Throughout the specification, unless specifically stated otherwise, each component may be singular or plural.

[0024] The fact that any configuration is placed on the "upper (or lower)" of a component or on the "upper (or lower)" of a component may mean not only that any configuration is placed in contact with the upper (or lower) surface of said component, but also that another configuration may be interposed between said component and any configuration placed on (or below) said component.

[0025] Furthermore, where it is stated that one component is "connected," "coupled," or "connected" to another component, it should be understood that while said components may be directly connected or connected to each other, another component may be "interposed" between each component, or that each component may be "connected," "coupled," or "connected" through another component. Additionally, when it is stated that a part is electrically coupled with another part, this includes not only cases where they are directly connected but also cases where they are connected with other elements in between.

[0026] Throughout the specification, "A and / or B" means A, B, or A and B unless specifically stated otherwise. That is, "and / or" includes any combination or any combination of the enumerated items. "C to D" means C or more and D or less, unless specifically stated otherwise.

[0027] When syntax such as "at least one of A, B, and C", "at least one of A, B, or C", "at least one selected from the group of A, B, and C", or "at least one selected from A, B, and C" is used to specify a list of elements A, B, and C, the syntax can refer to any suitable combination.

[0028] The term "use" may be considered synonymous with the term "utilize." As used herein, "substantially," "about," and similar terms are used as terms of approximation rather than degree, and are intended to account for the inherent variation of measured or calculated values ​​that a person skilled in the art would recognize.

[0029] In this specification, terms such as first, second, third, etc. may be used to describe various elements, components, regions, layers, and / or sections, but these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Accordingly, the first element, component, region, layer, or section discussed below may be named the second element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

[0030] Spatial relative terms such as "beneath," "below," "lower," "above," and "upper" may be used herein for ease of explanation to describe the relationship between one element or feature and another element(s) or feature(s) as illustrated in the drawings. Spatially relative positions are to be understood as encompassing different orientations of the device in use or operation, in addition to the orientations depicted in the figures. For example, if the device in the drawing is inverted, an element described as "below" or "below" is understood as "above" or "upper" of another element. Thus, the term "below" may encompass both the up and down directions.

[0031] The terms used in this specification are intended to describe embodiments of the present disclosure and are not intended to limit the present disclosure.

[0032] Hereinafter, a secondary battery and a battery pack including the same according to various embodiments of the present invention will be described with reference to the attached drawings. In this process, the thickness of lines or the size of components shown in the drawings may be exaggerated for clarity and convenience of explanation. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intention or convention of the user or operator. Therefore, the definitions of these terms should be based on the content throughout this specification.

[0033] In this specification, 'particle size D50' refers to the average particle size, meaning the diameter 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 irradiated with ultrasound of about 28 kHz at an output of 60 W, and then D50 can be calculated based on 100% of the particle size distribution in the measuring device.

[0034] In this specification, when describing a numerical range, 'X to Y' means 'X or greater and Y or less (X ≤ and ≤ Y).'

[0035] The present invention improves the lifespan of the separator by preventing an increase in resistance, as the adhesive layer of the separator undergoes minimal film formation after a long period in the battery. The present invention demonstrates excellent reliability by extending the separator's lifespan, as the rate of change in the separator's air permeability after a long period in the battery is low. The present invention improves the manufacturing processability of the battery by including a separator that prevents adhesion between separators and detachment of the adhesive layer from the separator when the separator is ejected from a wound state.

[0036] According to one embodiment, the secondary battery comprises an electrode assembly having a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate; and an electrolyte impregnated with the electrode assembly, wherein the separator comprises a substrate and an adhesive layer located on at least one surface of the substrate, wherein the adhesive layer comprises a copolymer of a monomer mixture comprising an unsaturated monomer having a carboxylic acid group or a salt thereof and an unsaturated monomer having an aromatic group, wherein the copolymer has a glass transition temperature of 90 to 150°C, and the electrolyte comprises a non-aqueous organic solvent having a volume ratio of ethylene carbonate : dimethyl carbonate : ethylmethyl carbonate of 20 to 30% : 30 to 40% : 30 to 40%.

[0037] FIG. 1 is a perspective view of a secondary battery according to one embodiment of the present invention.

[0038] Referring to FIG. 1, a pouch-type secondary battery 100 may include an electrode assembly 110 and a pouch 130 that accommodates the electrode assembly 110.

[0039] The electrode assembly 110 may be formed by winding or stacking a laminate of a first electrode plate 112, a separator 116, and a second electrode plate 114, which are formed in a thin plate or film shape.

[0040] In the case where the electrode assembly 110 is a wound laminate, the winding axis may be parallel to the longitudinal direction of the sealing portion. Additionally, the electrode assembly 110 may be a stack type rather than a wound type, and the shape of the electrode assembly is not limited in the present invention.

[0041] In addition, the electrode assembly 110 may be a Z stack electrode assembly in which a first electrode plate and a second electrode plate are inserted on both sides of a separator folded into a Z stack.

[0042] The electrode assembly 110 may be stored inside a sealing portion by stacking one or more electrode assemblies so that their long sides are adjacent to each other, and the number of electrode assemblies is not limited in the present invention.

[0043] The electrode assembly 110 is impregnated in an electrolyte (not shown) contained within a pouch 130.

[0044] By including the separator described below, the lithium secondary battery can achieve excellent manufacturing processability by preventing adhesion between separators and detachment of the adhesive layer from the separator. By including the separator and electrolyte described below, the lithium secondary battery can achieve excellent reliability. Even after prolonged storage, the adhesive layer of the separator is minimally film-formed, thereby preventing an increase in separator resistance and improving lifespan. Additionally, the low rate of change in air permeability extends the separator's lifespan. The separator may form a film when impregnated with the electrolyte. If the separator forms a film, the pores within the separator become clogged, hindering the proper movement of lithium ions and potentially increasing resistance. Furthermore, the rate of change in air permeability may increase when the separator is impregnated with the electrolyte. This, too, can increase resistance by blocking the normal movement of lithium ions within the separator.

[0045] The separation membrane is described in detail below.

[0046] Separator

[0047] Referring to FIG. 2, the separator comprises a substrate 1; and a heat-resistant layer 2 and an adhesive layer 3 sequentially located on both sides of the substrate 1, wherein the adhesive layer 3 comprises a copolymer 5.

[0048] FIG. 2 illustrates a substrate 1 and a heat-resistant layer 2 and an adhesive layer 3 sequentially located on both sides of substrate 1, but the present invention is not limited thereto. A separator comprising a substrate 1 and a heat-resistant layer 2 and an adhesive layer 3 sequentially located on one side of substrate 1 may also be included in the battery of the present invention.

[0049] adhesive layer

[0050] Adhesive layer 3 comprises a copolymer 5 of a monomer mixture comprising an unsaturated monomer having a carboxylic acid group or its salt and an unsaturated monomer having an aromatic group, wherein the copolymer 5 has a glass transition temperature of 90 to 150°C.

[0051] The copolymer 5 above has excellent adhesion to the first electrode plate 112 or the second electrode plate 114, prevents adhesion between separators and detachment of the adhesive layer from the separator when the separator in a wound state is unwound, reduces the film formation of the adhesive layer in the separator after a long period of time in the battery, and can provide the effect of lowering the rate of change in air permeability of the separator after a long period of time in the battery.

[0052] When the glass transition temperature of the copolymer is 90°C or higher, it is easy to ensure that the adhesive layer does not detach from the separator when the separator is wound onto a winder and then removed to manufacture a secondary battery, and to ensure that the adhesive layer in the separator becomes less film-like and the rate of change in air permeability of the separator is low after being left in the electrolyte described below for a long period of time. When the glass transition temperature of the copolymer is 150°C or lower, the adhesive strength of the separator is excellent, and when the separator is wound onto a winder and then removed to manufacture a secondary battery, it is easy to ensure that the adhesive layer does not detach from the separator, and to ensure that the adhesive layer in the separator becomes less film-like and the rate of change in air permeability of the separator is low after being left in the electrolyte described below for a long period of time.

[0053] For example, the glass transition temperature of the copolymer may be 90 to 130°C or 90 to 110°C. Within this range, along with the above-described effect, the discharge capacity recovery rate is high even after multiple cycles in the battery, so the performance of the battery may be excellent.

[0054] The glass transition temperature of the copolymer can be measured using a method known to those skilled in the art by using a DSC (differential scanning calorimeter). For example, the glass transition temperature can be determined by obtaining data on the endothermic transition curve when the temperature is raised to 180°C at a heating rate of 20°C / min, slowly cooled to -100°C, and then raised to 100°C at a heating rate of 10°C / min, and the inflection point of the endothermic transition curve is determined as the glass transition temperature.

[0055] A copolymer of a monomer mixture having a glass transition temperature of 90 to 150°C but lacking either an unsaturated monomer having a carboxylic acid group or its salt or an unsaturated monomer having an aromatic group may not be able to provide all the effects described above.

[0056] The copolymer 5 described above can be made to facilitate reducing the film formation of the adhesive layer within the battery when the heat-resistant layer 2 described below is positioned, and to reduce the rate of change in the air permeability of the separator after a long period of time within the battery.

[0057] The copolymer 5 above comprises an unsaturated monomer-derived unit having a carboxylic acid group or its salt and an unsaturated monomer-derived unit having an aromatic group.

[0058] The unsaturated monomer having the above-mentioned carboxylic acid group or its salt may be represented by any one of the following chemical formulas 1 to 3:

[0059] [Chemical Formula 1] [Chemical Formula 2] [Chemical Formula 3]

[0060]

[0061] (In the above Chemical Formulas 1 to 3,

[0062] * is the connection point of the element,

[0063] R 1 to R 6 Each is independently hydrogen or a C1 to C10 alkyl group, and

[0064] M is an alkali metal.

[0065] For example, R in Chemical Formulas 1 to 3 1 to R 6 Each can be a hydrogen or a methyl group.

[0066] In one embodiment, the unsaturated monomer having the carboxylic acid group or its salt may be (meth)acrylic acid, etc.

[0067] The unsaturated monomer having the carboxylic acid group or its salt may be included in the monomer mixture in an amount of 0.5 to 99 mol%, for example, 0.5 to 30 mol%, for example, 1 to 10 mol%. Within this range, the adhesion to the first electrode plate or the second electrode plate may be high.

[0068] The unsaturated monomer having the above aromatic group can be represented by the following chemical formula 4:

[0069] [Chemical Formula 4]

[0070]

[0071] (In the above chemical formula 4,

[0072] * is the connection point of the element,

[0073] R 7 and R 8 Each is independently hydrogen or a substituted or unsubstituted C1 to C5 alkyl group,

[0074] Ar is a substituted or unsubstituted, monocyclic or polycyclic C6 to C20 aryl group).

[0075] In one embodiment, in the above formula 4, Ar is a C6 to C20 monocyclic or polycyclic aryl group, such as a phenyl group, naphthalenyl group, anthracenyl group, pyrenyl group, etc.

[0076] In one embodiment, the unsaturated monomer having the aromatic group can be represented by the following chemical formula 5:

[0077] [Chemical Formula 5]

[0078]

[0079] (In the above chemical formula 5,

[0080] * is the connection point of the element,

[0081] R 7 and R 8 Each is independently hydrogen or a substituted or unsubstituted C1 to C5 alkyl group,

[0082] 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, a substituted or unsubstituted C3 to C20 aryl group, a halogen, and a substituted or unsubstituted C2 to C20 alkenyl group, and

[0083] m is an integer from 0 to 5).

[0084] In one embodiment, R in Formula 5 may be a substituted or unsubstituted C1 to C20 alkyl group, a halogen, or a substituted or unsubstituted C1 to C20 alkoxy group. In one embodiment, m in Formula 5 may be 0 or 1.

[0085] For example, the unsaturated monomer having the aromatic group 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.

[0086] For example, the unsaturated monomer having the above aromatic group may include one or more of styrene and alpha-methyl styrene.

[0087] The unsaturated monomer having the above aromatic group may be included in the monomer mixture in an amount of 1 to 99.5 mol%, for example, 0.5 to 40 mol%, for example, 1 to 30 mol%. Within this range, there may be a binder Tg-increasing effect.

[0088] In one embodiment, the mixture of the unsaturated monomer having a carboxylic acid group and the unsaturated monomer having an aromatic group may be included in the monomer mixture in an amount of 50 mol% or more, for example, 50 to 100 mol%, 95 to 100 mol%, or 100 mol%.

[0089] The copolymer may further include a unit derived from an (meth)acrylic monomer containing an alkyl group having 1 to 10 carbon atoms in the main chain at the ester site. The unit may facilitate the control of the adhesive strength and glass transition temperature of the adhesive layer.

[0090] The above (meth)acrylic monomer can be represented by the following chemical formula 6:

[0091] [Chemical Formula 6]

[0092]

[0093] (In the above chemical formula 6,

[0094] * is the connection point of the element,

[0095] R 9 and R 10 Each independently has a hydrogen or methyl group,

[0096] L 1 (substituted or unsubstituted, straight-chain or branched-chain C1 to C10 alkyl groups).

[0097] In one embodiment, the (meth)acrylic monomer may include one or more of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, iso-propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0098] For example, the above (meth)acrylic monomer may include one or more of n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate.

[0099] The above (meth)acrylic monomer may be included in the monomer mixture in an amount of 50 to 99 mol%, for example, 60 to 98 mol%. Within this range, the adhesive properties of the separator may be exhibited.

[0100] In one embodiment, the mixture of the unsaturated monomer having the carboxylic acid group or its salt, the unsaturated monomer having the aromatic group, and the (meth)acrylic monomer may be included in the monomer mixture in an amount of 95 mol% or more, for example, 95 to 100 mol%, 95 to 100 mol%, or 100 mol%.

[0101] The copolymer 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 and exist in the form of a salt. The alkali metal may aid in the synthesis of the copolymer in an aqueous solvent, improve the adhesion of the adhesive layer, and improve the heat resistance, air permeability, and oxidation resistance of the separator.

[0102] The alkali metal may be included in the alkali metal and the copolymer in an amount of 1 to 40 weight%, for example, 1 to 30 weight%, or 1 to 20 weight%, or 10 to 20 weight%. For example, the copolymer 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.

[0103] The alkali metal may be included in an amount of 0.1 to 1.0 mol% relative to the total content of the alkali metal and the copolymer. When the alkali metal is included within this range, the adhesive layer may have excellent adhesion, and the separator containing it may exhibit excellent heat resistance, air permeability, and oxidation resistance.

[0104] The copolymer may be in various forms, such as an alternating polymer in which the structural units are alternately distributed, a random polymer in which they are randomly distributed, or a graft polymer in which some structural units are grafted.

[0105] The weight-average molecular weight of the copolymer may be 100,000 to 1,000,000 g / mol, 100,000 to 500,000 g / mol, 100,000 to 150,000 g / mol, 200,000 to 130,000 g / mol, or 300,000 to 900,000 g / mol. When the weight-average molecular weight of the copolymer 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.

[0106] The above copolymer can be prepared by a solution polymerization method.

[0107] According to one embodiment, the copolymer is a particulate adhesive binder, and the average particle size D50 may be 0.1 to 1.0 μm, for example, 0.3 to 1.0 μm. Within this range, it may be easy to form an adhesive layer.

[0108] The thickness of the adhesive layer 3 can be 0.1 to 5 μm, for example, 0.1 to 3 μm.

[0109] heat-resistant layer

[0110] The heat-resistant layer 2 can reduce the thermal shrinkage rate of the separator by including filler 4.

[0111] Filler 4 may include one or more types of inorganic fillers and organic fillers.

[0112] The above organic filler may include a cross-linked polymer filler. The cross-linked polymer filler can lower the moisture content, thereby further reducing the thermal shrinkage rate of the separator and improving insulation properties. The above cross-linked polymer filler may be included in the combination of the above (meth)acrylic binder and the above inorganic filler to facilitate the reduction of the thermal shrinkage rate of the separator.

[0113] The inorganic filler may be a ceramic material. For example, the inorganic filler may include, for instance, metal oxides, metal metal oxides, metal fluorides, metal hydroxides, or combinations thereof. The inorganic filler may include, for example, alumina (e.g., Al2O3), SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or combinations thereof, but is not limited thereto.

[0114] Filler 4 may have an average particle size D50 of 20 to 300 nm, for example, 50 to 200 nm, or 50 to 150 nm.

[0115] Filler 4 can be plate-shaped, spherical, cubic, or a combination thereof. Preferably, the filler can be spherical.

[0116] Filler 4 may be included in the heat-resistant layer 2 in an amount of 50% or more by weight, for example, 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. When the filler is included within the above range, it may exhibit excellent heat resistance, durability, oxidation resistance, and stability.

[0117] Heat-resistant layer 2 may further include a binder, for example, a (meth)acrylic binder.

[0118] The heat-resistant layer 2 may have a thickness of 1 to 10 μm, for example, 1 to 5 μm.

[0119] write

[0120] Substrate 1 may be porous. Substrate 1 can increase the air permeability of the separator to increase the movement of lithium ions.

[0121] The material 1 may be a polymer film formed from 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 copolymer or mixture of two or more of these.

[0122] In one embodiment, the substrate 1 may be a polyolefin-based substrate including a polyolefin, and may be, for example, a polyethylene substrate.

[0123] The above polyolefin-based substrate has excellent shutdown capabilities and can contribute to improving the safety of the battery. The above 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 above polyolefin-based resin may include a non-olefin resin in addition to an olefin resin, or may include a copolymer of an olefin and a non-olefin monomer.

[0124] In one embodiment, the polyolefin resin may have a weight-average molecular weight of 600,000 g / mol or more, for example, 600,000 to 4,000,000 g / mol, or 600,000 to 3,000,000 g / mol. Here, the weight-average molecular weight can be obtained as a polystyrene equivalent value by gel permeation chromatography.

[0125] In one embodiment, the polyolefin resin may have a melting temperature (Tm) of 130 to 140°C. Here, Tm can be determined by referring to a product catalog of polyolefin-based materials or by methods known to those skilled in the art. For example, the melting temperature may be measured by the following method:

[0126] Using a Differential Scanning Calorimeter (DSC, device name: DSC Q20, manufacturer: TA instrument), the temperature was increased to heat the polyethylene composition to 200°C at a rate of 10°C / min (Cycle 1), isothermal at 200°C for 1 minute, then cooled to 40°C at a rate of 10°C / min, and isothermal at 40°C for 1 minute, then heated again to 200°C at a rate of 10°C / min (Cycle 2). In the DSC curve obtained through this process, the temperature at the point of maximum endothermic peak was measured as the melting temperature (Tm, °C), and the temperature at the point of maximum exothermic peak was measured as the crystallization temperature (Tc, °C). At this time, the melting temperature (Tm) and crystallization temperature (Tc) are the results measured in the second temperature increase and decrease section (Cycle 2), respectively.

[0127] The above substrate may be manufactured by stretching an unoriented film containing the above resin using a wet method. Specifically, the above substrate may be manufactured by a filler extraction method, but is not limited thereto. The filler extraction method involves mixing a polyolefin-based resin with a filler, forming pores by extracting the filler after rolling, and then manufacturing a porous substrate by a stretching process. In one embodiment, the stretching temperature may be 90 to 130°C, for example, 90 to 110°C. Within this range, the sum of the tensile strengths and the sum of the elongation rates can be easily reached. In one embodiment, the stretching ratio may be 4 to 10 times, for example, 5 to 8 times. In one embodiment, the stretching may be performed by MD and TD uniaxial stretching of the above unoriented film, MD and TD biaxial stretching, etc.

[0128] The substrate 1 may have a thickness of 10㎛ or less, for example, 1㎛ to 10㎛ or 1㎛ to 8㎛.

[0129] Electrolyte

[0130] The electrolyte contains a non-aqueous organic solvent, and the volume ratio of ethylene carbonate (EC) : dimethyl carbonate (EMC) : ethylmethyl carbonate (DMC) is 20 to 30% : 30 to 40% : 30 to 40% based on 100% of the total volume of the non-aqueous organic solvent.

[0131] During battery operation, the adhesive layer of the separator can be in continuous contact with the electrolyte. In this process, the copolymer in the adhesive layer may dissolve in the electrolyte and form a film, which increases the rate of change in the separator's air permeability and can lead to an increase in resistance.

[0132] A non-aqueous organic solvent satisfying the above volume ratio can reduce the film formation of the adhesive layer after a long period of time and lower the rate of change in air permeability when the separator in the secondary battery is impregnated.

[0133] If the content of ethylene carbonate is less than 20 volume%, the copolymer may easily dissolve in the electrolyte, which can increase the resistance of the battery. If the content of ethylene carbonate exceeds 30 volume%, the dissolution of the copolymer becomes severe, which significantly increases the resistance of the battery and causes the adhesion to become excessively high, resulting in a poor discharge capacity recovery rate during battery life evaluation and a problem where the separator becomes film-like.

[0134] If the dimethyl carbonate content is less than 30 volume%, it fails to reduce the offset of adhesive strength by ethylene carbonate, resulting in lower adhesive strength of the adhesive layer within the separator. This increases the likelihood of adhesive detachment during battery operation, which may lower battery reliability and increase the rate of change in separator air permeability. If the dimethyl carbonate content exceeds 40 volume%, there may be a problem of film formation in the separator.

[0135] If the content of ethyl methyl carbonate is less than 30 volume%, the effect of delaying the dissolution of the copolymer by ethylene carbonate is weak, so the resistance of the battery increases, and the film formation of the separator and the rate of change in air permeability may increase. If the content of ethyl methyl carbonate exceeds 40 volume%, there may be a problem in that the rate of change in air permeability of the separator increases.

[0136] In one embodiment, the volume ratio of ethylene carbonate (EC) : dimethyl carbonate (EMC) : ethylmethyl carbonate (DMC) based on 100% of the total volume of the non-aqueous organic solvent may be 20:40:40 or 30:30:40 or 30:40:30, for example, 20:40:40.

[0137] In one embodiment, the total amount of ethylene carbonate and ethylmethyl carbonate in the non-aqueous organic solvent may be 55 to 65 volume% based on 100 volume% of the total volume. Within this range, the film formation of the coating layer and the rate of change in air permeability are significantly low, thereby preventing an increase in the resistance of the battery and providing a long lifespan for the battery.

[0138] In one embodiment, the mixture of ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate may be included in the non-aqueous organic solvent in an amount of 95 volume% or more, for example, 95 to 100 volume%, or 100 volume%. Within this range, there may be no side reactions in the electrolyte.

[0139] The above electrolyte may include a lithium salt.

[0140] The above lithium salt is a material that is dissolved in the above-mentioned non-aqueous organic solvent and acts as a source of lithium ions within the battery to enable the basic operation of a lithium secondary battery and to promote the movement of lithium ions between the anode and the 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).

[0141] The above lithium salt may be included in the above electrolyte at a concentration of 0.1 to 2.0 M, for example 0.5 to 1.5 M, for example 1.0 to 1.7 M.

[0142] The above electrolyte may further include conventional additives in addition to the above-mentioned non-aqueous organic solvent and the above-mentioned lithium salt.

[0143] The above additive may include one or more of FEC (fluoroethylene carbonate), VEC (vinyl ethylene carbonate), and PS (propylene sulfone).

[0144] In one embodiment, with respect to 100 volume% of the non-aqueous organic solvent, the FEC may be included in an amount of 5 to 10 volume%, for example 7 volume%, the VEC in an amount of 0.1 to 5 volume%, for example 1 volume%, and the PS in an amount of 1 to 5 volume%, for example 3 volume%.

[0145] Referring again to FIG. 1, the first electrode plate 112 may include a first electrode tab 112a electrically connected to a first electrode active material portion coated with a first electrode active material and a first uncoated portion, which is an area where the first electrode active material is not coated. The first electrode tab 112a may serve as a passage for current flow between the first electrode plate 112 and a first current collector (not shown). In some examples, the first electrode tab 112a may be formed by cutting it to protrude to one side in advance when manufacturing the first electrode plate, and may protrude further to one side than the separator without separate cutting.

[0146] The second electrode plate 114 may include a second electrode tab 114a electrically connected to a second electrode active material portion coated with a second electrode active material and a second uncoated portion, which is an area not coated with the second electrode active material. The second electrode tab 114a may serve as a passage for current flow between the second electrode plate 114 and a second current collector (not shown). In some examples, the second electrode tab 114a may be formed by cutting it to protrude to the other side when manufacturing the second electrode plate, and may protrude further to the other side than the separator without separate cutting.

[0147] The first electrode tab 112a and the second electrode tab 114a may be located on one side in the same direction with respect to the electrode assembly 110. However, the present invention is not limited thereto. The first electrode tab 112a may be located on the left end side of the electrode assembly 110, and the second electrode tab 114a may be located on the right end side of the electrode assembly 110. Here, the left and right sides are for convenience of explanation based on the secondary battery shown in FIG. 1, and their positions may change when the secondary battery rotates left and right or up and down.

[0148] The first electrode tab 112a and the second electrode tab 114a are each welded to the negative lead 152 and the positive lead 154 of the external terminal, respectively, and are electrically connected to the outside. A tab film 156 for insulation from the pouch 130 is attached to the negative lead 152 and the positive lead 154. The negative lead 152, the positive lead 154, and the tab film 156 can form an integrated tab film 150.

[0149] The sealing portion 132 of the pouch 130 is made of a heat-sealable material and has a structure in which a seal is achieved by bonding the heat-sealable layers together. Since heat-sealable materials generally have weak adhesion to metal, a thin film-type tab film 156 is attached to the tab and fused with the pouch 130.

[0150] The first electrode plate 112 of the electrode assembly 110 can act as a negative electrode, and the second electrode plate 114 can act as a positive electrode. Of course, the opposite is also possible.

[0151] The anode and cathode are explained below.

[0152] anode

[0153] The anode may include a current collector and an anode active material layer formed on the current collector. The anode active material layer may include an anode active material and may further include a binder and / or a conductive material. As an example, the anode may further include an additive capable of acting as a sacrificial anode.

[0154] 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.

[0155] 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.

[0156] As an example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 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 O 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 O 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).

[0157] 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.

[0158] 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.

[0159] The content of the above positive active material is 90% to 99.5% by weight of 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.

[0160] 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.

[0161] 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.

[0162] Al may be used as the current collector mentioned above, but is not limited thereto.

[0163] cathode

[0164] The cathode includes a current collector and a cathode active material layer located on the current collector. The cathode active material layer includes a cathode active material and may further include a binder and / or a conductive material.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] The above Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] In the foregoing, it has been explained that the secondary battery is a lithium-ion secondary battery and is a pouch-type battery. However, the present invention is not limited thereto, and the secondary battery may be a cylindrical battery, a prismatic battery, or a pouch-type battery.

[0181] Figure 3 is a perspective view of a cylindrical battery.

[0182] Referring to FIG. 3, a cylindrical battery 200 may include an electrode assembly 110 having a separator 116 interposed between a first electrode plate 112 and a second electrode plate 114, and a case 50 in which the electrode assembly 110 is housed. The first electrode plate 112, the second electrode plate 114, and the separator 116 may be impregnated with an electrolyte (not shown). The lithium secondary battery 200 may include a sealing member 60 that seals the case 50 as shown in FIG. 3.

[0183] Figure 4 is a perspective view of a rectangular battery.

[0184] Referring to FIG. 4, a prismatic battery 300 may include an electrode assembly 110 having a separator 116 interposed between a first electrode plate 112 and a second electrode plate 114, and a case 50 in which the electrode assembly 110 is housed. The first electrode plate 112, the second electrode plate 114, and the separator 116 may be impregnated with an electrolyte (not shown). A lithium secondary battery 300 may include a case 50 as shown in FIG. 4. In FIG. 4, the lithium secondary battery 300 may include a positive lead tab 11 and a positive terminal 12, a negative lead tab 21 and a negative terminal 22.

[0185] FIG. 5 is a perspective view of a pouch-type battery of another embodiment.

[0186] Referring to FIG. 5, a pouch-type battery 400 may include an electrode assembly 110 having a separator 116 interposed between a first electrode plate 112 and a second electrode plate 114, and a case 50 in which the electrode assembly 110 is housed. The first electrode plate 112, the second electrode plate 114, and the separator 116 may be impregnated with an electrolyte (not shown). In FIG. 5, the lithium secondary battery 400 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for inducing current formed in the electrode assembly 110 to the outside.

[0188] 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.

[0190] Example 1

[0191] Separator manufacturing

[0192] A composition for forming a heat-resistant layer was prepared by dispersing boehmite (particle size D100: 2㎛, particle size D50: 0.3㎛, plate-like) in water and mixing it with an acrylic binder.

[0193] A copolymer of a monomer mixture containing styrene and acrylic acid (glass transition temperature: 90°C) was dispersed in a polar solvent (NMP (N-methyl-2-pyrrolidone) / DMA (dimethylacetamide), etc.), and then milled using a bead mill at 25°C for 30 minutes to prepare a dispersion. Water was added to make the total solid content 20% by weight to prepare a composition for an adhesive layer.

[0194] A polyethylene film (weight-average molecular weight of the polyethylene resin is 3 million g / mol, Tm is 132 to 136°C, thickness: 8 μm, manufactured by stretching) was used as the porous substrate.

[0195] A separator was prepared by coating both sides of the porous substrate with the composition for forming the heat-resistant layer and drying at 70°C for 10 minutes, then coating with the composition for forming the adhesive layer and drying at 70°C for 10 minutes, thereby sequentially forming a heat-resistant layer (thickness: 5 μm) and an adhesive layer (thickness: 2 μm) on each side of the porous substrate.

[0196] (Manufacturing of the cathode)

[0197] As a cathode active material, 90.4 wt% of graphite particles with an average particle size D50 of 13 μm, 7.1 wt% of a silicon-carbon composite, 1.5 wt% of a styrene-butadiene rubber (SBR) binder, and 1 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 foil with a thickness of 10 μm, dried in a hot air dryer at 100°C for 0.5 hours, dried again under vacuum at 120°C for 4 hours, and then rolled to produce a cathode.

[0198] (Manufacturing of the anode)

[0199] A cathode active material slurry was prepared by mixing 97.7 wt% of lithium cobalt-nickel-aluminum oxide (nickel 91 mol%) as the cathode active material, 1 wt% of carbon black powder as the conductive material, and 1.3 wt% of polyvinylidene fluoride (PVDF) as the binder, adding the mixture to the solvent N-methyl-2-pyrrolidone, and stirring for 30 minutes using a mechanical stirrer. The slurry was applied onto an aluminum foil 15 μm thick and dried in a hot air dryer at 100°C for 0.5 hours, then dried again under vacuum at 120°C for 4 hours, and then rolled to produce a cathode.

[0200] (Battery manufacturing)

[0201] The manufactured separator was positioned between the anode and the cathode, and the anode-separator-cathode-separator laminate was wound into a Jelly Roll shape and placed in a pouch-type case.

[0202] 6g of electrolyte (a non-aqueous organic solvent containing 1.5M LiPF6 dissolved in ethylene carbonate (EC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) in a volume ratio of 20:40:40 based on a total volume of 100)) was injected to completely immerse the laminate in the electrolyte, seal it, and then perform charging and discharging and leave it at 25°C for 12 hours and at 60°C for 24 hours to manufacture a pouch-type battery.

[0203] Example 2

[0204] A pouch-type battery was manufactured in the same manner as in Example 1, except that a copolymer of styrene and acrylic acid (glass transition temperature: 90°C) was used in Example 1 and the non-aqueous organic solvent in the electrolyte was changed as shown in Table 1 below.

[0205] Examples 3 to 5

[0206] A battery was manufactured in the same manner as in Example 1, except that a copolymer of styrene and acrylic acid with a glass transition temperature changed as shown in Table 1 below was used instead of the copolymer of styrene and acrylic acid (glass transition temperature: 90°C) in Example 1. The glass transition temperature was achieved by changing the molar percentage range of styrene and acrylic acid in the monomers.

[0207] Comparative Examples 1 to 4

[0208] A battery was manufactured in the same manner as in Example 1, except that a copolymer of styrene and acrylic acid with a glass transition temperature changed as shown in Table 1 below was used instead of the copolymer of styrene and acrylic acid (glass transition temperature: 90°C) in Example 1. The glass transition temperature was achieved by changing the molar percentage range of styrene and acrylic acid in the monomers.

[0209] Comparative Examples 5 to 10

[0210] A battery was manufactured in the same manner as in Example 1, except that non-aqueous organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) dissolved in 1.5M LiPF6 were included as electrolytes, and the volumes of EC, DMC, and EMC were each changed as shown in Table 1 below based on a total volume of 100.

[0211] The following physical properties were evaluated for the batteries of the examples and comparative examples.

[0212] Battery discharge capacity recovery rate (Unit: %)

[0213] For the batteries prepared in the examples and comparative examples, 0.8C CC / CV charging (4.3V, 0.05C CUT-OFF) and 0.8C CC discharging (4.3V CUT-OFF) were repeated three times at 25°C, and the discharge capacity was measured on the third cycle. The discharge capacity was measured after 150 cycles.

[0214] The discharge capacity recovery rate was calculated as (discharge capacity after 150 cycles) / (3rd discharge capacity) x 100.

[0215] Separator adhesion (Unit: %)

[0216] The adhesion strength of the separation membrane was measured using a single column (Instron-3344).

[0217] The batteries prepared in the examples and comparative examples were compressed at high temperature and high pressure, left at room temperature (25°C) for one day, and then the positive electrode, separator, and negative electrode were removed. For the removed positive electrode, separator, and negative electrode samples, a jig equipped with a load cell with a maximum load of 1 kN was connected to the separator and the positive electrode, respectively, and the adhesion between the positive electrode and the separator was measured while peeling at 180° at a speed of 100 mm / min.

[0218] It is expressed as the ratio (percentage) of the adhesive strength measured in the examples and comparative examples to the adhesive strength measured for Example 1. For the reliability of the battery, a ratio of 80% or more of adhesive strength may be desirable.

[0219] Rate of change in membrane air permeability (Unit: %)

[0220] The air permeability T1 of the separator was measured for the batteries manufactured in the examples and comparative examples.

[0221] After leaving the above battery at room temperature for 7 days, the separator was removed, and the air permeability T2 was measured using the same method as above. Air permeability was measured using a measuring device (EG01-55-1MR, Asahi Seiko) by measuring the time (in seconds) required for 100cc of air to pass through the separator.

[0222] [Permeability Measurement Device Setting Conditions]

[0223] Measured pressure: 0.5 kg / ㎠, Cylinder pressure: 2.5 kg / ㎠, Set time: 10 seconds

[0224] The rate of change in air permeability was calculated as (T2 - T1) / T1 x 100. For the reliability of the battery, a rate of change in air permeability of 10% or less may be desirable.

[0225] Film formation of the separator

[0226] The batteries prepared in the examples and comparative examples were left at room temperature for 7 days. The separator was removed from the batteries and its surface image was observed using SEM. It was evaluated as ◎ if the separator was not filmed, ○ if 1 / 4 or less of the separator was filmed, △ if more than 1 / 4 and less than 1 / 2 of the separator was filmed, and X if more than 1 / 2 of the separator was severely filmed.

[0227] Resistance (Unit: Ω)

[0228] Coin cells were fabricated using the anode-separator-cathode-separator stacks prepared in the examples and comparative examples, and then evaluated using the electrochemical impedance spectroscopy (EIS) measurement method.

[0229] Tg electrolyte Discharge capacity recovery rate adhesive power Rate of change in air permeability Separator film formation resistance EC DMC EMC Example 1 90 20 40 40 98.7 100 7 ◎ 0.80 Example 2 90 30 40 30 96.0 140 10 ○ 1.06 Example 3 110 20 40 40 98.1 80 5 ◎ 0.73 Example 4 130 20 40 40 96.9 80 5 ◎ 0.74 Example 5 150 20 40 40 95.3 80 5 ◎ 0.70 Comparative Example 1 30 20 40 40 93.2 500 50 X 1.60 Comparative Example 2 60 20 40 40 96.1 200 27 X 1.20 Comparative Example 3 -10 20 40 40 87.1 600 73 X 1.70 Comparative Example 4 160 20 40 40 95.0 430 5 ○ 0.70 Comparative Example 5 90 10 80 10 94.9 170 15 △ 1.20 Comparative Example 6 90 40 20 40 94.0 200 30 X 1.34 Comparative Example 7 90 20 20 60 98.0 80 10 ○ 0.75 Comparative Example 8 90 20 50 30 96.4 110 11 △ 1.02 Comparative Example 9 90 20 60 20 95.9 140 15 △ 1.27 Comparative Example 10 90 20 30 50 98.2 80 10 ○ 0.77

[0231] As shown in Table 1 above, the lithium secondary battery of the example exhibited minimal film formation of the adhesive layer in the separator after a long period of time within the battery, and a low rate of change in the separator's air permeability. This indicates that the discharge capacity recovery rate of the battery was high and the resistance was low. Furthermore, it can be seen that the lithium secondary battery of the example maintained an appropriate range of adhesion even after the separator was impregnated with the electrolyte.

[0232] However, as shown in Table 1 above, it can be seen that the effect of the example cannot be obtained in the same electrolyte when the glass transition temperature of the copolymer in the adhesive layer is less than 90°C or greater than 150°C. In addition, as shown in Table 1 above, it can be seen that the effect of the example cannot be obtained when the composition of the electrolyte deviates from the composition of the present invention.

[0234] 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

Claim 1 A secondary battery comprising: an electrode assembly having a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate; and an electrolyte impregnated with the electrode assembly, wherein the separator comprises a substrate and an adhesive layer located on at least one surface of the substrate, wherein the adhesive layer comprises a copolymer of a monomer mixture comprising an unsaturated monomer having a carboxylic acid group or a salt thereof and an unsaturated monomer having an aromatic group, wherein the copolymer has a glass transition temperature of 90 to 150°C, and the electrolyte comprises a non-aqueous organic solvent, wherein the volume ratio of ethylene carbonate : dimethyl carbonate : ethylmethyl carbonate is 20 to 30% : 30 to 40% : 30 to 40% based on 100% of the total volume of the non-aqueous organic solvent. Claim 2 In claim 1, the unsaturated monomer having the carboxylic acid group or its salt is represented by any one of the following chemical formulas 1 to 3, a secondary battery: [Chemical Formula 1] [Chemical Formula 2] [Chemical Formula 3] (In the above chemical formulas 1 to 3, * represents the connecting part of the element, R 1 to R 6 Each is independently hydrogen or a C1 to C10 alkyl group, and M is an alkali metal. Claim 3 In claim 1, the unsaturated monomer having the aromatic group is represented by the following chemical formula 5, a secondary battery: [Chemical Formula 5] (In the above chemical formula 5, * is the connecting site of the element, R 7 and R 8 is each independently hydrogen or a substituted or unsubstituted C1 to C5 alkyl group, 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, a substituted or unsubstituted C3 to C20 aryl group, a halogen, and a substituted or unsubstituted C2 to C20 alkenyl group, and m is an integer from 0 to 5). Claim 4 A secondary battery according to claim 1, wherein the mixture of the unsaturated monomer having a carboxylic acid group and the unsaturated monomer having an aromatic group comprises 50 mol% or more of the monomer mixture. Claim 5 A secondary battery according to claim 1, wherein the monomer mixture further comprises a (meth)acrylic monomer. Claim 6 In claim 5, the above (meth)acrylic monomer is a secondary battery represented by the following chemical formula 6: [Chemical Formula 6] (In the above chemical formula 6, * is the connecting site of the element, R 9 and R 10 Each independently contains a hydrogen or methyl group, L 1 (substituted or unsubstituted, straight-chain or branched-chain C1 to C10 alkyl groups). Claim 7 A secondary battery according to claim 5, wherein the mixture of the unsaturated monomer having a carboxylic acid group, the unsaturated monomer having an aromatic group, and the (meth)acrylic monomer comprises 95 mol% or more of the monomer mixture. Claim 8 A secondary battery according to claim 1, wherein the copolymer is a copolymer of (meth)acrylic acid and styrene. Claim 9 A secondary battery according to claim 1, wherein the copolymer is a copolymer of (meth)acrylic acid, styrene, and n-butyl (meth)acrylate. Claim 10 A secondary battery according to claim 1, wherein the copolymer is a particulate binder having an average particle size D50 of 0.1 to 1.0 μm. Claim 11 A secondary battery according to claim 1, wherein a heat-resistant layer is further laminated between the substrate and the adhesive layer, and the heat-resistant layer comprises a filler. Claim 12 In claim 11, the secondary battery wherein the filler comprises 50 weight percent or more of the heat-resistant layer. Claim 13 In claim 11, the filler is a secondary battery having an average particle size D50 of 20 to 300 nm. Claim 14 A secondary battery according to claim 1, wherein the electrolyte comprises a lithium salt of 0.1 to 2.0 M. Claim 15 In claim 1, the secondary battery is a pouch-type battery.

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