Rechargeable batteries and battery packs containing them

Abstract

To provide a secondary battery with improved collision characteristics and a battery pack containing the same. To provide a secondary battery with improved adhesion between the separator membrane and the electrode plate and a battery pack containing the same. [Solution] The secondary battery includes a case having an opening; an electrode assembly and electrolyte housed in the case; and a cap-up positioned in the opening. The electrode assembly includes a first electrode plate, a second electrode plate, and a separation membrane located between the first and second electrode plates. The separation membrane includes a substrate and a coating layer located on at least one surface of the substrate. The substrate has a sum of elongation in the mechanical and transverse directions of 200% or less and a sum of tensile strength in the mechanical and transverse directions of 4000 kgf / cm². 2 The following applies: the coating layer includes a binder, the binder includes one or more of aramid resins and acrylic resins, and the electrolyte contains 20% by volume or more of ethyl propionate or ethylene carbonate.

Description

[Technical Field]

[0001] This application claims priority under Republic of Korea Patent Application No. 10-2024-0137997, filed on 10 October 2024, and all content disclosed in the said Republic of Korea Patent Application is incorporated herein by reference.

[0002] This invention relates to a secondary battery and a battery pack containing the same. [Background technology]

[0003] Recently, with the rapid proliferation of electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for rechargeable batteries with high energy density and high capacity has been rapidly increasing. As a result, research and development to improve the performance of lithium-ion rechargeable batteries is actively underway.

[0004] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material that allows for the insertion and deintercalation of lithium ions, and an electrolyte, which produces electrical energy through oxidation and reduction reactions when lithium ions are inserted / deintercalated at the positive and negative electrodes.

[0005] The demand for higher capacity and higher output in lithium-ion secondary batteries necessitates thinner separator membranes. These separator membranes also require high strength to enhance battery safety, such as preventing short circuits during the assembly process and ensuring collision safety.

[0006] The information disclosed above in the technology underlying such inventions is merely for the purpose of improving understanding of the background of the present invention, and therefore may include information that does not constitute prior art. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] One embodiment is aimed at providing a secondary battery with improved collision characteristics and a battery pack including the same.

[0008] Other embodiments are directed towards providing a secondary battery and a battery pack including the same, in which the adhesion between the separator membrane and the electrode plate is improved.

[0009] However, the technical problems that the present invention aims to solve are not limited to those described above, and other problems not mentioned can be clearly understood by those skilled in the art from the description of the invention below. [Means for solving the problem]

[0010] To solve the aforementioned technical problems, a secondary battery according to one embodiment includes a case having an opening; an electrode assembly and electrolyte housed within the case; and a cap-up positioned in the opening, wherein the electrode assembly includes a first electrode plate, a second electrode plate, and a separation membrane located between the first and second electrode plates, the separation membrane includes a substrate and a coating layer located on at least one surface of the substrate, the substrate having a sum of elongation in the mechanical direction (MD) and transverse direction (TD) of 200% or less and a sum of tensile strength in the mechanical direction and transverse direction of 4000 kgf / cm 2 The following applies: the coating layer includes a binder, the binder includes one or more aramid resins and acrylic resins, and the electrolyte contains 20% or more by volume of ethyl propionate or ethylene carbonate. [Effects of the Invention]

[0011] By providing a secondary battery and a battery pack containing the same, in which the collision characteristics and the adhesive strength between the separator membrane and the electrode plate are improved according to one embodiment, the reliability of lithium secondary batteries can be enhanced. [Brief explanation of the drawing]

[0012] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention to be described later. Therefore, the present invention should not be construed as being limited only to the matters described in such drawings.

[0013] [Figure 1] FIG. 1 is a perspective view schematically showing the configuration of a battery pack according to various embodiments of the present invention. [Figure 2] FIG. 2 is a perspective view schematically showing the configuration of a secondary battery according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view schematically showing the configuration of a secondary battery according to an embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining the relationship between the short-circuit area (X-axis) and the heat generation amount (Y-axis) during the evaluation of the collision characteristics of the separator.

MODE FOR CARRYING OUT THE INVENTION

[0014] 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 in the claims should not be interpreted in a manner limited to their general and dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention. Accordingly, the embodiments described herein and the configurations illustrated in the drawings represent only some of the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and it should be understood that there may be a variety of equivalents and modifications that can substitute for them at the time of filing. Furthermore, as used herein, "comprise, include" and / or "comprising, including" specify the presence of the shapes, figures, stages, actions, members, elements and / or groups thereof mentioned, and do not exclude the presence or addition of one or more other shapes, figures, actions, members, elements and / or groups thereof. Furthermore, when describing embodiments of the present invention, "may" and "may include" "one or more embodiments of the present invention."

[0015] Furthermore, to aid in understanding the invention, the accompanying drawings are not depicted to actual scale, and the dimensions of some components may be exaggerated. Also, the same reference numeral may be assigned to the same component in different embodiments.

[0016] The statement that two comparison objects are "identical" means that they are "substantially identical." Therefore, substantially identical objects may include those with deviations considered low in this industry, for example, deviations of 5% or less. Also, the uniformity of parameters within a given region may mean that they are uniform in terms of averages.

[0017] Even if terms like "First," "Second," etc., are used to detail various components, these components are certainly not limited by these terms. These terms are simply used to distinguish one component from another, and unless otherwise specified, the first component may be the second component.

[0018] Throughout the specification, unless otherwise specifically stated, each component may be singular or plural.

[0019] The placement of any component "above (or below)" or "above (or below)" a component does not only mean that the component is placed in contact with the top (or bottom) surface of the component, but may also mean that other components may be interposed between the component and any component placed on (or below) it.

[0020] Furthermore, when it is stated that one component is “connected,” “joined,” or “connected” to another component, it should be understood that the components are directly connected to or can be connected to one another, but that other components are “interposed” between each component, or that each component can be “connected,” “joined,” or “connected” through other components. Also, when it is said that one part is electrically coupled to another part, this includes not only cases where they are directly connected, but also cases where other devices are interposed between them.

[0021] Throughout the specification, when "A and / or B" is written, it means A, B, or A and B unless otherwise specified. That is, "and / or" includes all combinations or any combination of the enumerated items. When "C to D" is written, it means C or greater and D or less unless otherwise specified.

[0022] 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 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.

[0023] The term "use" can be considered synonymous with the term "utilize." As used herein, "substantially," "about," and similar terms are used as approximations, not terms of degree, to account for the inherent variability of measured or calculated values ​​as perceived by a general arter in the art.

[0024] In this specification, terms such as first, second, third, etc., may be used to describe a variety of elements, components, regions, layers, and / or sections, but these elements, components, regions, layers, and / or sections are not limited by these terms. These terms are used to distinguish one element, component, region, drawing layer, or section from other elements, components, regions, drawing layers, or sections. Accordingly, the first elements, components, regions, layers, or sections discussed below may be named second elements, components, regions, layers, or sections without deviating from the teaching of the exemplary embodiments.

[0025] As shown in the drawings, 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. Spatially relative positions should be understood to encompass different directions of the device in use or operation, in addition to the direction depicted in the figure. For example, if the device in the drawing is inverted, an element described as “beneath” or “below” one element may be understood as “above” or “upper” the other element. Thus, the term “beneath” can encompass all directions, including up and down.

[0026] The terms used herein are for the purpose of describing embodiments of the disclosure and are not intended to limit the disclosure.

[0027] Hereinafter, a secondary battery and a battery pack containing the same, according to various embodiments of the present invention, will be described with reference to the attached drawings. In this process, the line thickness and size of components shown in the drawings may be exaggerated for clarity and convenience of explanation. Furthermore, the terms described later are defined in consideration of the function of the present invention, and these may change depending on the intent or convention of the user or operator. Therefore, the definitions of such terms should be based on the content throughout this specification.

[0028] In this specification, “particle size D50” means the average particle size, which is the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. 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 with a particle size analyzer, or with a transmission electron microscope or scanning electron microscope. Alternatively, it may be measured using a measuring device that utilizes dynamic light scattering, and after data analysis to count the number of particles for each particle size range, the D50 value can be calculated from there. Alternatively, it can be measured using the laser diffraction method. More specifically, when measuring by laser diffraction, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac's MT3000), and after irradiating with ultrasound at approximately 28 kHz at an output of 60 W, the D50 on a 100% basis of the particle size distribution in the measuring device can be calculated.

[0029] In this specification, when describing a numerical range, "X~Y" means "X or greater and Y or less (X ≤ value ≤ Y)."

[0030] Figure 1 is a schematic perspective view showing the configuration of a battery pack according to various embodiments of the present invention.

[0031] Referring to Figure 1, various embodiments of the battery pack include a housing 1 and a secondary battery 2.

[0032] Housing 1 forms the general appearance of the battery pack and can provide a space in which a secondary battery 2 can be housed.

[0033] The housing 1 according to this embodiment may include a housing body 11 and a cover 12.

[0034] The housing body 11 can be formed to have a box shape with an open interior and one side open. The cross-sectional shape of the housing body 11 is not limited to the rectangle shown in Figure 1, but can be redesigned to various shapes such as polygons, circles, and ellipses.

[0035] The cover 12 is coupled to the housing body 11 and can close off the internal space of the housing body 11. For example, the cover 12 may be formed to be substantially plate-like and positioned opposite the open side of the housing body 11. The cover 12 can be fixed to the housing body 11 by various types of coupling methods, such as bolting, welding, and fitting.

[0036] The secondary battery 2 can function as a unit structure that stores and supplies power in a battery pack.

[0037] Multiple secondary batteries 2 may be provided. Multiple secondary batteries 2 may be arranged inside the housing 1 to form various patterns such as a grid or a zigzag configuration. Multiple secondary batteries 2 may be arranged side by side. The number of secondary batteries 2 can be varied depending on the size and shape of the housing 1. The detailed configuration of the secondary batteries will be described later.

[0038] Multiple secondary batteries 2 can be electrically connected by a busbar (not shown). Multiple secondary batteries 2 can be connected in series or in parallel by the busbar. For example, the busbar can connect secondary batteries 2 arranged in the same row inside the housing 1 in parallel, and connect secondary batteries 2 arranged in two adjacent rows in series. The busbar can be made of an electrically conductive material such as copper, aluminum, or nickel.

[0039] The following describes the configuration of a secondary battery according to various embodiments of the present invention.

[0040] Figure 2 is a schematic perspective view showing the configuration of a secondary battery according to the first embodiment of the present invention, and Figure 3 is a schematic cross-sectional view showing the configuration of a secondary battery according to the first embodiment of the present invention.

[0041] Referring to Figures 2 and 3, the secondary battery 2 according to this embodiment may include a case 100, an electrode assembly 200, a cap assembly 300, and an electrolyte (not shown).

[0042] In the following explanation, a case where secondary battery 2 is a cylindrical lithium-ion secondary battery will be used as an example. However, the present invention is not limited to this, and secondary battery 2 may be a lithium polymer battery, a prismatic battery, or a pouch-type battery.

[0043] The case 100 can form the general appearance of the secondary battery 2. The case 100 can be electrically conductive. For example, the case 100 may include at least one of the following materials: steel, stainless steel, aluminum, and aluminum alloy. Thereafter, the case 100 can protect the electrode assembly 200 from external shocks and perform a heat dissipation function to release heat associated with the charging and discharging operations of the electrode assembly 200 to the outside.

[0044] The case 100 according to this embodiment may include a cylindrical side wall portion 110 with a central axis C formed in the center. The central axis C of the case 100 described in detail below may mean the central axis of the side wall portion 110. Both ends of the side wall portion 110 perpendicular to the central axis C of the case 100 may be formed to be open.

[0045] The case 100 may further include a bottom portion 120 that closes the lower end of the side wall portion 110. The bottom portion 120 according to this embodiment may be formed to have a substantially disc shape and may be positioned opposite the lower end of the side wall portion 110. The bottom portion 120 may be positioned perpendicular to the central axis C of the case 100. The outer circumferential surface of the bottom portion 120 may be joined to the lower end of the side wall portion 110. The bottom portion 120 may be molded integrally with the side wall portion 110 by a drawing process or the like, or alternatively, it may be manufactured separately from the side wall portion 110 and then joined to the side wall portion 110 by welding or the like.

[0046] The case 100 may further include an opening 130 that opens the upper end of the side wall portion 110. The opening 130 can function as a configuration that provides a path for the electrode assembly 200 (described later) to be inserted into the interior of the case 100 in the upper end region of the case 100, and provides a space in which the cap assembly 300 (described later) can be installed. In this embodiment, the opening 130 may mean an empty space surrounded by the upper end region of the side wall portion 110 located on the opposite side of the bottom portion 120.

[0047] The electrode assembly 200 can function as a unit structure that performs charging and discharging operations in the secondary battery 2. The electrode assembly 200 may include a first electrode plate 210, a second electrode plate 220, and a separation membrane 230 placed between the first electrode plate 210 and the second electrode plate 220.

[0048] The electrode assembly 200 may be placed inside the case 100. The electrode assembly 200 may be inserted into the case 100 through the opening 130 of the case 100.

[0049] The electrode assembly 200 can have a form in which it is wound around a winding shaft. More specifically, the electrode assembly 200 can have a form in which the first electrode plate 210, the separation membrane 230, and the second electrode plate 220 are stacked and wound around the winding shaft in a clockwise or counterclockwise direction. As a result, the electrode assembly 200 can have a substantially roll cake-like form. The cross-sectional shape of the electrode assembly 200 can be designed to be a variety of shapes other than circular, such as elliptical or polygonal. Here, the winding shaft can mean a straight line that penetrates the central part of the electrode assembly 200. The winding shaft of the electrode assembly 200 can be positioned coaxially with the central axis C of the case 100.

[0050] The first electrode plate 210 can function as the positive electrode of the electrode assembly 200. The first electrode plate 210 may be formed in the form of a foil containing a metallic material such as aluminum or an aluminum alloy. The type, size, and shape of the first electrode plate 210 are not particularly limited, as long as it does not induce a chemical change in the secondary battery and is conductive.

[0051] A first active material layer may be applied to at least a portion of the first electrode plate 210. The first active material layer may be applied to both sides of the first electrode plate 210, or alternatively, it may be applied to only one side of the first electrode plate 210.

[0052] When the first electrode plate 210 functions as a positive electrode, the first active material layer may contain a positive electrode active material.

[0053] The positive electrode active material may be a compound (lithiated insertion compound) that allows for reversible insertion and removal of lithium. More specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, iron, and combinations thereof can be used.

[0054] As an example, the positive electrode active material can include at least one of lithium-iron-phosphate (LiFePO4, LFP), lithium-manganese-iron-phosphate (LiMnFePO4, LMFP), and lithium-nickel-cobalt-manganese oxide (LiNi x Co y Mn z O2, NCM). Here, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 can be satisfied. The positive electrode active material can include any one of lithium-iron-phosphate (LiFePO4, LFP), lithium-manganese-iron-phosphate (LiMnFePO4, LMFP), and lithium-nickel-cobalt-manganese oxide (LiNi x Co y Mn z O2, LNCM), and can include any two of or all of lithium-iron-phosphate (LiFePO4, LFP), lithium-manganese-iron-phosphate (LiMnFePO4, LMFP), and lithium-nickel-cobalt-manganese oxide (LiNi x Co y Mn z O2, LNCM).

[0055] The first active material layer can further include a positive electrode conductive material.

[0056] The positive electrode conductive material is used to impart conductivity to the first active material layer, and any material can be used as long as it does not cause a chemical change and is an electron conductive material. Examples of the positive electrode conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube, metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc., conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0057] The first active material layer can further include a positive electrode binder.

[0058] The positive electrode binder serves to ensure that the particles constituting the positive electrode active material adhere well to each other, and also to ensure that the positive electrode active material adheres well to the first electrode plate 210.

[0059] Examples of positive electrode binders include non-aqueous binders, aqueous binders, dry binders, or combinations thereof.

[0060] Examples of 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.

[0061] The water-based binder may be selected from styrene-butadiene rubber, styrene-butadiene (meth)acrylate rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0062] When an aqueous binder is used as the positive electrode binder, it may further contain a cellulose series compound that can impart viscosity. This cellulose series compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. As the alkali metal, Na, K, or Li can be used.

[0063] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0064] The first electrode plate 210 can be electrically connected to a cap assembly 300, which will be described later. When the first electrode plate 210 functions as the positive electrode of the electrode assembly 200, the cap assembly 300 can function as the positive electrode terminal of the secondary battery 2. As an example, the first electrode plate 210 can be electrically connected to the cap assembly 300 by a first electrode tap E1. The first electrode tap E1 according to this embodiment may include a conductive metallic material such as copper, a copper alloy, nickel, or a nickel alloy. The first electrode tap E1 is positioned above the electrode assembly 200, and both ends can be connected to the first electrode plate 210 and the cap assembly 300, respectively. One end of the first electrode tap E1 can be directly connected to the first electrode plate 210, or it can be indirectly connected to the first electrode plate 210 via a separate current collector plate (not shown) connected to the first electrode plate 210.

[0065] However, the first electrode plate 210 is not limited to these matters, and can also be directly connected to the cap assembly 300 without the first electrode tap E1.

[0066] The second electrode plate 220 can function as the negative electrode of the electrode assembly 200. The second electrode plate 220 may be formed in the form of a foil containing a metallic material such as copper, a copper alloy, nickel, or a nickel alloy. The second electrode plate 220 may be positioned opposite the first electrode plate 210 at a predetermined distance apart.

[0067] The type, size, and shape of the second electrode plate 220 are not particularly limited, as long as it does not induce a chemical change in the secondary battery and is conductive.

[0068] A second active material layer may be applied to at least a portion of the second electrode plate 220. The second active material layer may be applied to both sides of the second electrode plate 220, or conversely, it may be applied to only one side of the second electrode plate 220.

[0069] The second electrode plate 220 functions as a negative electrode, allowing the second active material layer to contain a negative electrode active material.

[0070] The negative electrode active material may include a material capable of reversibly inserting / de-inserting lithium ions, lithium metal, an alloy of lithium metal, a lithium-doped and de-doped material, or a transition metal oxide.

[0071] Materials capable of reversibly inserting / deinserting lithium ions include carbon-based negative electrode active materials, which may include, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, while examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, and calcined coke.

[0072] As lithium metal alloys, alloys of lithium with a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0073] As materials that can be doped and dedoped with lithium, Si-based anode active materials or Sn-based anode active materials can be used. Si-based anode active materials include silicone, silicone-carbon composites, and SiO x (x=1 or 2), Si-Q alloy (where 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 combinations thereof. The Sn-based anode active material may be Sn, SnO2, Sn-based alloy, or combinations thereof.

[0074] The silicone-carbon composite may be a composite of silicone and amorphous carbon. According to one embodiment, the silicone-carbon composite may be in the form of silicone particles and amorphous carbon coated on the surface of the silicone particles. For example, it may include secondary particles (core) assembled from primary silicone particles and an amorphous carbon coating layer (shell) located on the surface of these secondary particles. The amorphous carbon may also be located between the primary silicone particles, for example, the primary silicone particles may be coated with amorphous carbon. The secondary particles may be dispersed in the amorphous carbon matrix.

[0075] The silicone-carbon composite may further contain crystalline carbon. For example, the silicone-carbon composite may include a core containing crystalline carbon and silicone particles and an amorphous carbon coating layer located on the surface of this core.

[0076] Si-based or Sn-based anode active materials can be used in combination with carbon-based anode active materials.

[0077] The second active material layer may further contain a negative electrode conductive material and a negative electrode binder.

[0078] The negative electrode conductive material is used to impart conductivity to the second active material layer, and any material that does not undergo chemical changes and is electrically conductive can be used. Examples of negative electrode conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0079] The negative electrode binder serves to ensure that the particles constituting the negative electrode active material adhere well to each other, and also to ensure that the negative electrode active material adheres well to the second electrode plate 220.

[0080] Examples of negative electrode binders include non-aqueous binders, aqueous binders, dry binders, or combinations thereof. Examples of 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.

[0081] The aqueous binder may be selected from styrene-butadiene rubber, (meth)styrene-butadiene rubber acrylate, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof. When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose series compound that can impart viscosity. As this cellulose series compound, one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof can be used in combination. As the alkali metal, Na, K, or Li can be used.

[0082] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0083] The second electrode plate 220 can be electrically connected to the case 100. For example, the second electrode plate 220 can be electrically connected to the case 100 by a second electrode tap E2. By the second electrode plate 220 functioning as the negative electrode of the electrode assembly 200, the case 100 can function as the negative electrode terminal of the secondary battery 2. The second electrode tap E2 according to this embodiment may include a conductive metallic material such as copper, a copper alloy, nickel, or a nickel alloy. The second electrode tap E2 is positioned on the underside of the electrode assembly 200, and both ends may be connected to the second electrode plate 220 and the bottom 120 of the case 100, respectively. One end of the second electrode tap E2 may be directly connected to the second electrode plate 220, or it may be indirectly connected to the second electrode plate 220 via a separate current collector plate (not shown) connected to the second electrode plate 220.

[0084] However, the second electrode plate 220 is not limited by these considerations and can also be directly connected to the case 100 without the second electrode tap E2.

[0085] The separation membrane 230 may be placed between the first electrode plate 210 and the second electrode plate 220. The separation membrane 230 can function to prevent short circuits between the first electrode plate 210 and the second electrode plate 220 while allowing the movement of lithium ions between them.

[0086] The separation membranes 230 may be provided in pairs. The pair of separation membranes 230 may be positioned to face both sides of the first electrode plate 210 or the second electrode plate 220, respectively. The pair of separation membranes 230 may be wound together with the first electrode plate 210 and the second electrode plate 220 around a winding shaft.

[0087] The separation membrane 230 will be explained in more detail below.

[0088] A first insulating plate 201 and a second insulating plate 202 may be placed on either side of the electrode assembly 200. The first insulating plate 201 and the second insulating plate 202 may include insulating materials such as rubber, polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET).

[0089] The first insulating plate 201 according to this embodiment may be formed to have a substantially disc shape. The first insulating plate 201 may be placed between the upper surface of the electrode assembly 200 and the cap assembly 300. Thereafter, the first insulating plate 201 can prevent the upper surface of the electrode assembly 200 from directly contacting the cap assembly 300, thereby insulating the electrode assembly 200 and the cap assembly 300 from each other. The first insulating plate 201 may have a through hole (not shown) through which the first electrode tap E1 can pass.

[0090] The second insulating plate 202 according to this embodiment may be formed to have a substantially disc shape. The second insulating plate 202 may be placed between the lower surface of the electrode assembly 200 and the bottom 120 of the case 100. Thereafter, the second insulating plate 202 can prevent the lower surface of the electrode assembly 200 from directly contacting the bottom 120 of the case 100, thereby insulating the electrode assembly 200 and the bottom 120 of the case 100 from each other. The second insulating plate 202 may have a through hole (not shown) through which the second electrode tap E2 can pass.

[0091] The cap assembly 300 can be coupled to the case 100 and seal the opening 130 of the case 100. For example, the cap assembly 300 may be positioned at the upper end of the side wall 110, i.e., at the opening 130. The side wall 110 may have a beading part 140 formed in a concave shape toward the central axis C of the case 100. The beading part 140 is positioned on the underside of the cap assembly 300 and can restrict the cap assembly 300 from being inserted into the case 100 beyond a set distance. Above the beading part 140, a crimping part 150 may be formed where the upper end of the side wall 110 is bent toward the central axis C of the case 100. The crimping part 150 is positioned on the upper side of the cap assembly 300 and can prevent the cap assembly 300 from detaching from the case 100. A gasket G may be placed between the case 100 and the cap assembly 300. The gasket G, through its own elastic restoring force, fixes the cap assembly 300 in position at the opening 130, electrically insulates the case 100 and the cap assembly 300 from each other, and functions to prevent moisture or electrolyte from flowing in or out between the case 100 and the cap assembly 300. The cap assembly 300 may include a cap up 310, a cap down 320, a vent plate 330, an extension 340, and a contact portion 350. The cap-up 310 forms the upper exterior of the cap assembly 300 and can be positioned in the opening 130. The cap-up 310 can be electrically connected to the first electrode plate 210 by the cap-down 320 and vent plate 330, which will be described later. The cap-down 320 is positioned opposite the cap-up 310 and can be electrically connected to the electrode assembly 200. The cap-down 320 may have a cap-down hole 321 that penetrates it vertically. The vent plate 330 can be positioned between the cap-up 310 and the cap-down 320. The extension 340 extends from the vent plate 330 and can be connected to the cap-up 310. The extension 340 can function as a configuration that supports the vent plate 330 relative to the cap-up 310 and provides an electrical connection between the cap-up 310 and the vent plate 330. The extension 340 according to this embodiment may include a support portion 341 and a hinge portion 342. The support portion 341 forms one outer surface of the extension portion 340 and can be connected to the cap-up portion 310. The hinge portion 342 forms the other outer surface of the extension portion 340 and can be positioned between the support portion 341 and the vent plate 330. The hinge portion 342 interconnects the support portion 341 and the vent plate 330 and can function as a configuration that guides the deformation of the vent plate 330 when the internal pressure of the case 100 increases. The contact portion 350 protrudes from the vent plate 330 toward the cap down 320 and can come into contact with the cap down 320. The secondary battery 2 according to this embodiment may further include a notch 360. The secondary battery 2 according to this embodiment may further include the recess 370. The recess 370 may be formed in a concave shape extending from the vent plate 330 toward the contact portion 350. The recess 370 can function as a configuration that reduces the thickness of the central region of the vent plate 330, which is relatively thickened by the contact portion 350, thereby inducing smooth deformation of the vent plate 330 when the internal pressure of the case 100 increases.

[0092] The gasket G according to this embodiment may include an insulating material such as rubber, polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET). The gasket G may be formed to be substantially ring-shaped and positioned inside the beading portion 140 and / or crimping portion 150. The outer surface of the gasket G may be in close contact with the inner surface of the beading portion 140 and / or crimping portion 150, and the inner surface of the gasket G may be in close contact with the outer surface of the cap assembly 300.

[0093] A gasket G may be placed inside the beading portion 140 and / or the crimping portion 150. The gasket G may be electrically connected to the first electrode plate 210 by the first electrode tap E1. With the first electrode plate 210 functioning as the positive electrode of the electrode assembly 200, the cap assembly 300 can function as the positive electrode terminal of a secondary battery.

[0094] The cap assembly 300 can disconnect the electrical connection between the secondary battery 2 and the external device if the pressure inside the case 100 rises due to an overcurrent or the like. The cap assembly 300 can rupture if the pressure inside the case 100 rises above a set level, potentially connecting the internal space of the case 100 to the external space of the case 100. In this way, the cap assembly 300 can reduce the risk of explosion of the secondary battery 2 in the event of an overcurrent.

[0095] The separation membrane 230 and the electrolyte will be described in detail below.

[0096] The lithium secondary battery 2 can have improved impact characteristics by including a release film 230 and an electrolyte in the electrode assembly. Here, "improved impact characteristics" may mean that the pass-through rate during the impact characteristics evaluation described below is 90% or higher. Improved impact characteristics can increase the reliability of the lithium secondary battery when it is exposed to external physical shocks.

[0097] The impact characteristics of a lithium secondary battery can be improved by preventing any rupture of the separator membrane when the battery is subjected to an external impact. Alternatively, when the lithium secondary battery is subjected to an external impact, the separator membrane may rupture excessively, widening the short-circuit area. This can reduce heat generation and improve impact characteristics by preventing current concentration compared to when the short-circuit area is locally narrow.

[0098] In this regard, the behavior of the separation membrane described above will be explained with reference to Figure 4.

[0099] Figure 4 illustrates the relationship between the short-circuit area (X-axis) and the amount of heat generated (Y-axis) when evaluating the collision characteristics of a separation membrane.

[0100] Referring to Figure 4, when a lithium secondary battery or a separator membrane for a lithium secondary battery is subjected to an external impact, the separator membrane may not rupture at all, or it may rupture and cause a short circuit.

[0101] In Figure 4, region A represents a case where the collision characteristics are good because no rupture of the separation membrane occurs.

[0102] In Figure 4, region B represents a case where the separation membrane is significantly ruptured or frequently ruptured, causing the electrode plate to come into contact with the electrolyte over a wide area. This results in a large short-circuit area, preventing current concentration, thus reducing heat generation and improving collision characteristics.

[0103] On the other hand, in region C of Figure 4, the separation membrane is ruptured, but the short-circuit area is insufficient, causing the current to concentrate relatively more than in region B of Figure 4. This results in significantly higher heat generation and poor collision characteristics.

[0104] In one embodiment, the separation membrane improves collision characteristics through its behavior in region B in Figure 4 described above. That is, in one embodiment, the separation membrane for lithium secondary batteries can improve collision characteristics by making the separation membrane rupture larger or more prone to rupture.

[0105] The lithium secondary battery can provide improved collision characteristics by including a separator membrane 230 and an electrolyte.

[0106] The separation membrane 230 includes a substrate and a coating layer located on at least one surface of the substrate. The substrate has a sum of elongation in the mechanical direction (MD) and transverse direction (TD) of 200% or less and a sum of tensile strength in the mechanical direction and transverse direction of 4000 kgf / cm². 2The coating layer includes a binder, and the binder includes one or more of aramid resins and acrylic resins.

[0107] The electrolyte contains 20% or more by volume of ethyl propionate or ethylene carbonate.

[0108] <Substrate for separation membrane> The substrate of the separation membrane 230 can improve its impact characteristics by satisfying the above range when the sum of the elongation rates in the mechanical direction and the transverse direction and the sum of the tensile strengths are within the above range.

[0109] The sum of the tensile strengths of the base materials is 4000 kgf / cm². 2 When the following conditions are met, the separation membrane ruptures more easily during deformation of the lithium secondary battery, thereby increasing the short-circuit area, and thus reducing the risk of explosion and ignition, and easily providing improved impact characteristics.

[0110] When the sum of the stretch ratios of the substrates is 200% or less, the separation membrane ruptures more easily during deformation of the lithium secondary battery, thereby increasing the short-circuit area. This reduces the risk of explosion and ignition and easily provides improved impact characteristics.

[0111] The sum of the tensile strengths of the base materials is 4000 kgf / cm². 2 The following conditions apply, and when the sum of the elongation ratios is 200% or less, the sum of the tensile strengths is 4000 kgf / cm². 2 The improvement in collision characteristics may be significantly more pronounced compared to the case where the sum of the following and the elongation ratio is 200% or less alone.

[0112] In particular, the sum of the tensile strengths of the base materials is 4000 kgf / cm². 2 The following conditions, where the sum of the elongation rates is 200% or less, can easily improve the collision characteristics of a secondary battery including the coating layer and electrolyte described below.

[0113] In one embodiment, the sum of the tensile strengths of the base materials is 2000 to 4000 kgf / cm². 2For example, 2,000, 2,100, 2,200, 2,300, 2,400, 2,500, 2,600, 2,700, 2,800, 2,900, 3,000, 3,100, 3,200, 3,300, 3,400, 3,500, 3,600, 3,700, 3,800, 3,900, 4,000 kgf / cm² 2 2500~4000 kgf / cm² 2 3300~4000 kgf / cm² 2 This could be the case.

[0114] In one embodiment, the MD tensile strength of the substrate may be higher than the TD tensile strength. In such cases, the sum of the tensile strengths and the sum of the elongation ratios described above can be easily reached.

[0115] For example, the MD tensile strength is 1500-3000 kgf / cm². 2 For example, 1,500, 1,600, 1,700, 1,800, 1,900, 2,000, 2,100, 2,200, 2,300, 2,400, 2,500, 2,600, 2,700, 2,800, 2,900, 3,000 kgf / cm² 2 , 2000~3000 kgf / cm 2 For example, 1800-2500 kgf / cm² 2 , 1900~2500 kgf / cm² 2 , 2000~2500 kgf / cm² 2 This can be achieved. The TD tensile strength is 500-2000 kgf / cm². 2 For example, 500, 600, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,500, 1,600, 1,700, 1,800, 1,900, 2,000 kgf / cm² 2 , 1000~2000 kgf / cm 2 This could be the case.

[0116] In one embodiment, the sum of the stretch ratios of the substrates can be 50-200%, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200%, 80-180%, or 80-160%.

[0117] In one embodiment, the TD elongation rate of the substrate may be higher than the MD elongation rate. In such cases, the sum of the tensile strengths and the sum of the elongation rates described above can be easily reached.

[0118] For example, the MD stretch ratio may be 5-100%, for example, 5, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100%, 10-80%, or 10-70%. The TD elongation rate may be 20-180%, for example, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180%, 20-150%, 20-100%, 50-120%, or 50-100%.

[0119] Here, tensile strength and elongation can be measured by the methods described below.

[0120] Here, "MD" can represent the mechanical direction of the substrate. When the substrate is a resin film, the mechanical direction of the substrate can represent the direction in which the unstretched film is produced when the resin is manufactured by melt extrusion or solution casting. The TD direction is the direction perpendicular to the MD direction when the film is viewed from a plane.

[0121] The resin may be porous. This can increase the permeability of the separation membrane and enhance the movement of lithium ions.

[0122] The resin may be a polymer film formed from any one polymer selected from the group consisting of polyethylene, polypropylene and other polyolefins, 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 from a copolymer or mixture of two or more of these polymers.

[0123] In one embodiment, the resin may be a polyolefin-based substrate containing polyolefin, for example, a polyethylene substrate.

[0124] Polyolefin-based substrates can contribute to improved battery safety due to their excellent shutdown function. Polyolefin-based substrates can be selected from, for example, a single polyethylene film, a single polypropylene film, a polyethylene / polypropylene bilayer, a polypropylene / polyethylene / polypropylene triple layer, and a polyethylene / polypropylene / polyethylene triple layer. Furthermore, the polyolefin resin may contain non-olefin resins in addition to olefin resins, or a copolymer of olefin and non-olefin monomers.

[0125] A substrate that satisfies the sum of elongation ratios and the sum of tensile strengths can be achieved by adjusting the weight-average molecular weight, melting temperature (TM), and / or stretching temperature and / or stretching ratio of the polyolefin resin used in the manufacturing of the substrate.

[0126] 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. Within this range, the sum of tensile strengths and the sum of elongation can be easily obtained. Here, the weight-average molecular weight can be determined as a polystyrene equivalent value by gel permeation chromatography.

[0127] In one embodiment, the polyolefin resin may have a melting temperature (Tm) of 130-140°C. Within this range, the sum of tensile strengths and the sum of elongation can be easily obtained. Here, Tm can be determined by referring to a product catalog of the polyolefin substrate or by a method known to those skilled in the art. For example, the melting temperature can be measured by the following method:

[0128] Using a Differential Scanning Calorimeter (DSC, instrument name: DSC Q20, manufacturer: TA instrument), the polyethylene composition was heated to 200°C at a rate of 10°C / min (Cycle 1), then isothermed at 200°C for 1 minute, cooled to 40°C at a rate of 10°C / min, isothermed at 40°C for 1 minute, and then further heated to 200°C at a rate of 10°C / min (Cycle 2). The temperature at the point of the maximum endothermic peak in the resulting DSC curve was measured as the melting temperature (Tm, °C), and the temperature at the point of the maximum exothermic peak was measured as the crystallization temperature (Tc, °C). In this case, the melting temperature (Tm) and crystallization temperature (Tc) shown are the results measured in the intervals where the second temperature increases and decreases, respectively (Cycle 2).

[0129] The substrate can be manufactured by wet stretching an unstretched film containing a resin. Specifically, the substrate can be manufactured by a filler extraction method, but is not limited thereto. The filler extraction method involves mixing a polyolefin resin with a filler, extracting the filler after rolling to form pores, and then stretching to produce a porous substrate.

[0130] In one embodiment, the stretching temperature can 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 ratios can be easily reached.

[0131] In one embodiment, the elongation ratio can be 4 to 10 times, for example, 5 to 8 times. Within this range, the sum of the tensile strengths and the sum of the elongation ratios can be easily reached.

[0132] In one embodiment, stretching can be performed by MD, TD uniaxial stretching, MD and TD biaxial stretching, etc., of an unstretched film.

[0133] The substrate can have a thickness of 10 μm or less, for example, 1 μm to 10 μm or 1 μm to 8 μm.

[0134] <Coating layer of separation membrane> The coating layer contains a binder, and the binder contains one or more of the following: aramid resins and acrylic resins.

[0135] One or more of aramid resins and acrylic resins can easily improve the collision characteristics of a lithium secondary battery containing a separation membrane with the above-mentioned substrate.

[0136] In one embodiment, one or more aramid resins and acrylic resins may be included in the binder in an amount of 95% by weight or more, for example, 95 to 100% by weight.

[0137] In one embodiment, an aramid resin or acrylic resin may be included in the binder in an amount of 95% by weight or more, for example, 95 to 100% by weight.

[0138] In one embodiment, the coating layer may contain a binder in an amount of 95% by weight or more, for example, 95-100% by weight.

[0139] Aramid resins can easily achieve the adhesive strength of the separation film to the first or second electrode plate described below, thereby reducing the occurrence of short circuits and improving impact characteristics.

[0140] In one embodiment, the aramid resin may contain one or more units from the following chemical formulas 1 and 2:

[0141] [ka]

[0142] (In the above chemical formula 1, R 1 , R 2 (where a and b are each independently substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C6-C10 aryl groups, substituted or unsubstituted C3-C10 cycloalkyl groups, substituted or unsubstituted C7-C10 arylalkyl groups, hydroxyl groups, halogens, cyano groups, or amino groups, and a and b are each independently integers from 0 to 4).

[0143] [ka]

[0144] (In the above chemical formula 2, R 3 , R 4 (Each of these is independently a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C6-C10 aryl group, a substituted or unsubstituted C3-C10 cycloalkyl group, a substituted or unsubstituted C7-C10 arylalkyl group, a hydroxyl group, a halogen, a cyano group, or an amino group, and c and d are independently integers from 0 to 4).

[0145] In one embodiment, the aramid resin may include meta-type or para-type aramid resins.

[0146] Acrylic resins may include copolymers of monomer mixtures containing one or more acrylic monomers, such as carboxylic acid group-containing acrylic monomers, cyano group-containing acrylic monomers, sulfonic acid group-containing acrylic monomers, and alkyl group-containing acrylic monomers.

[0147] The specific types of carboxylic acid group-containing acrylic monomers, cyano group-containing acrylic monomers, sulfonic acid group-containing acrylic monomers, and alkyl group-containing acrylic monomers can be selected by reference to the common types known to those skilled in the art.

[0148] In one embodiment, the acrylic resin may have a glass transition temperature of 70 to 100°C, for example, 70 to 90°C. Within this range, the adhesion strength of the separation film to the first or second electrode plate, as described below, can be easily achieved, thereby reducing the occurrence of short circuits and improving impact characteristics.

[0149] The separation membrane undergoes a pretreatment process that simulates the film deposition process for the first or second electrode plate, and the adhesive strength measured by disassembling the cell at room temperature can be 0.5 gf / mm or more. Within this range, even if the battery's external shape is deformed by an external impact, improved impact characteristics can be easily provided by assisting in the rupture of the electrode plate and the separation membrane, thereby increasing the short-circuit area. If the adhesive strength is less than 0.5 gf / mm, the separation membrane and the electrode plate may easily separate when there is an external impact, and the separation membrane may not easily rupture, making it impossible to secure a sufficient short-circuit area.

[0150] Here, the method for measuring adhesive strength is described in detail in the evaluation methods for the examples and comparative examples below.

[0151] In one embodiment, the adhesive strength can be 0.5 gf / mm to 1.0 gf / mm.

[0152] The coating layer may further contain one or more of the following in addition to the binder: fillers and polyethylene-based waxes.

[0153] In one embodiment, the coating layer may be an adhesive layer containing one or more aramid resins and acrylic resins.

[0154] In other embodiments, the coating layer may include a heat-resistant layer containing a filler and a binder; and an adhesive layer located on the heat-resistant layer and containing one or more aramid resins and acrylic resins.

[0155] The binder included in the heat-resistant layer may include an acrylic binder. A common type of acrylic binder known to those skilled in the art may be used.

[0156] The filler may contain one or more organic fillers and inorganic fillers.

[0157] In one embodiment, the organic filler may include a crosslinked polymer filler. The crosslinked polymer filler can further reduce the thermal shrinkage rate of the separation membrane by lowering the water content and also improve the insulation properties. The crosslinked polymer filler can be included in a combination of a (meth)acrylic binder and an inorganic filler to easily reduce the thermal shrinkage rate of the separation membrane.

[0158] The inorganic filler may be a ceramic material. For example, the inorganic filler may include, for example, metal oxides, quasi-metallic oxides, metal fluorides, metal hydroxides, or combinations thereof. The inorganic filler may include, but is not limited to, alumina (e.g., Al2O3), SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or combinations thereof.

[0159] The filler can have an average particle size D50 of 20-200 nm, for example, 20-150 nm or 50-100 nm.

[0160] The filler may be plate-shaped, spherical, cubic, or a combination thereof. Preferably, the filler may be spherical.

[0161] The filler may be included in the coating layer in amounts 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. When the filler is included within the above ranges, it can exhibit excellent heat resistance, durability, oxidation resistance, and safety.

[0162] In one embodiment, the binder:filler in the heat-resistant layer may be included in a mass ratio of 1:10 to 1:50, for example, 1:20 to 1:30. Within this range, the effects of the separation membrane described above can be easily achieved, and improvements in heat resistance and durability can be obtained.

[0163] Polyethylene-based waxes can improve battery safety by lowering the shutdown temperature of the separation membrane.

[0164] Each coating layer may have a thickness of 10 μm or less, and may be 0.1 μm to 10 μm, 0.1 μm to 5 μm, or 0.5 μm to 2 μm.

[0165] The separation membrane can be manufactured by applying a coating layer composition to at least one surface of a substrate and drying it. In this case, it is preferable to further increase the adhesive strength by applying pressure at a predetermined pressure after drying.

[0166] The electrolyte contains 20% or more by volume of ethyl propionate (EP) or ethylene carbonate (EC).

[0167] The electrolyte can easily ensure the adhesion of the separation membrane to the first or second electrode plate.

[0168] In one embodiment, the electrolyte may contain 20% by volume or more of ethyl propionate (EP). For example, the electrolyte may contain 20 to 80% by volume of ethyl propionate.

[0169] The electrolyte may further contain one or more of ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP). For example, the electrolyte may contain 10-30% by volume of ethylene carbonate (EC), 10-30% by volume of propylene carbonate (PC), 20-40% by volume of ethyl propionate (EP), and 30-60% by volume of propyl propionate (PP).

[0170] In one embodiment, the electrolyte may contain 20% or more by volume of ethylene carbonate (EC). For example, the electrolyte may contain 20 to 80% by volume of ethylene carbonate.

[0171] The electrolyte may further contain one or more of ethyl propionate (EP), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). For example, the electrolyte may contain 20-30% by volume of ethylene carbonate (EC), 10-40% by volume of ethyl methyl carbonate (EMC), and 30-70% by volume of dimethyl carbonate (DMC).

[0172] The electrolyte may further contain lithium salts.

[0173] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in batteries, enabling the operation of basic lithium secondary batteries and promoting the movement of lithium ions between the positive and negative electrodes. Typical 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, and LiN(C x F 2x+1 SO2)(C y F 2y+1(SO2)(where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOP), lithium bis(oxalato)borate (LiBOB), and may include one or more selected therefrom.

[0174] Examples and comparative examples of the present invention will be described below. However, the following examples are only one example of the present invention, and the present invention is not limited by the examples described below.

[0175] Measurement of MD and TD tensile strength and elongation of the substrate:

[0176] <MD Tensile Strength> The substrate was cut into test pieces with a size of 10 cm × 1 cm in MD × TD, and using a tensile strength measurement equipment (3343, instron), it was pulled at a speed of 100 mm / min in the MD direction to measure the tensile strength, and the average value for 5 substrates was set as the tensile strength.

[0177] The substrate was cut into test pieces with a size of 1 cm × 5 cm in MD × TD, and using a tensile strength measurement equipment (3343, instron), it was pulled at a speed of 100 mm / min in the TD direction to measure the tensile strength, and the average value for 5 substrates was set as the tensile strength.

[0178] <MD Elongation> The substrate was cut into test pieces with a size of 10 cm × 1 cm in MD × TD, and through an Instron (3343, instron) equipment, it was pulled at a speed of 100 mm / min in the MD direction at room temperature until it broke, and the length by which the test piece was stretched was measured. The ratio of increase compared to the initial length of the test piece was calculated, and the average value for 5 substrates was set as the elongation.

[0179] Test specimens were manufactured by cutting the substrate into 1cm x 5cm pieces using MD x TD. The specimens were then stretched at 100mm / min using TD at room temperature through an Instron (3343) device, and the length of the specimens stretched until fracture was measured. The percentage increase compared to the initial specimen length was calculated, and the average value for five substrates was set as the elongation rate.

[0180] <Example 1> Manufacturing of separation membranes A dispersion was prepared by dispersing alumina (spherical, average particle size D50: 50 nm) and an acrylic binder in a polar solvent (such as NMP / DMAc), and then milling the mixture using a bead mill at 25°C for 30 minutes. Water was added to produce a heat-resistant layer composition with a total solid content of 20% by weight. The weight ratio of acrylic binder to alumina in the heat-resistant layer composition was 1:20.

[0181] A dispersion was prepared by dispersing an aramid resin in a polar solvent (such as NMP / DMAc) and then milling it using a bead mill at 25°C for 30 minutes. Water was added to the dispersion to produce an adhesive layer composition with a total solid content of 20% by weight. The aramid resin was produced by polymerizing paraphenylenediamine and terephthalic acid chloride.

[0182] A heat-resistant layer composition was coated onto one surface of a polyethylene film using a die-coating method, and then dried at 70°C for 10 minutes to form a heat-resistant layer (thickness: 2 μm).

[0183] A separation membrane was manufactured by coating a heat-resistant layer with an adhesive layer composition using a die-coating method, and then drying it at 70°C for 10 minutes to form an adhesive layer (thickness: 2 μm).

[0184] A porous substrate was used, consisting of polyethylene film (the weight-average molecular weight of the polyethylene resin was 3 million g / mol, the temperature (Tm) was 132-136°C, the thickness was 8 μm, and it was manufactured by stretching).

[0185] (Manufacturing of negative electrodes) A slurry of 90.4% by weight of graphite particles with an average particle size of 13 μm, 7.1% by weight of silicone carbon composite, 1.5% by weight of styrene-butadiene rubber (SBR) binder, and 1.0% by weight of carboxymethylcellulose (CMC) was mixed, then added to distilled water and stirred for 60 minutes using a mechanical stirrer to produce a negative electrode active material slurry. The slurry was applied to a copper current collector with a thickness of 10 μm and dried in a hot air dryer at 100°C for 0.5 hours. After that, it was dried again under vacuum and at 120°C for 4 hours, and then rolled (roll pressed) to produce a negative electrode.

[0186] (Manufacturing of positive electrodes) A slurry of lithium cobalt nickel aluminum oxide (91 mol% nickel), 1.0 wt% carbon black powder, and 1.3 wt% polyvinylidene fluoride (PVDF) was mixed and placed in an N-methyl-2-pyrrolidone solvent. The mixture was then stirred for 30 minutes using a mechanical stirrer to produce a cathode active material slurry. The slurry was applied to a 15 μm thick aluminum current collector and dried in a 100°C hot air dryer for 0.5 hours. After drying again under vacuum and at 120°C for 4 hours, the slurry was rolled (roll pressed) to produce a cathode.

[0187] (Battery manufacturing) A separation membrane was placed between the positive and negative electrodes, and the positive electrode-sample-negative electrode-sample laminate was rolled into a jelly roll and placed in a cylindrical case. 6 g of electrolyte (ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:10:70 based on a total volume of 100 liters, with 1.5 M LiPF6 dissolved in it) was injected to completely hydrate the laminate with the electrolyte. After sealing, the battery was manufactured by charging and discharging and leaving it at 25°C for 12 hours and at 60°C for 24 hours.

[0188] <Example 2> In Example 1, the polyethylene film was replaced with a polyethylene film having the tensile strength and elongation ratio shown in Table 1 below. The polyethylene film was manufactured at a higher stretching temperature compared to the polyethylene film in Example 1.

[0189] A dispersion was prepared by dispersing alumina (spherical, average particle size D50:50nm) and an acrylic binder in a polar solvent (such as NMP / DMAc), and then milling the mixture using a bead mill at 25°C for 30 minutes. Water was added to produce a heat-resistant layer composition with a total solid content of 20% by weight. The weight ratio of acrylic binder to alumina in the heat-resistant layer composition was 1:20.

[0190] An acrylic binder (glass transition temperature: 80°C) was dispersed in a polar solvent (such as NMP / DMAc), and then dispersed using a bead mill at 25°C for 30 minutes to produce a dispersion. Water was added to produce a heat-resistant layer composition with a total solid content of 20% by weight.

[0191] The above heat-resistant layer composition was coated onto one surface of a polyethylene film using a die-coating method, and then dried at 70°C for 10 minutes to form a heat-resistant layer (thickness: 2 μm).

[0192] A separation membrane was manufactured by coating a heat-resistant layer with an adhesive layer composition using a die-coating method, and then drying it at 70°C for 10 minutes to form an adhesive layer (thickness: 2 μm).

[0193] <Example 3> In Example 1, the separation membrane was manufactured using the same method as in Example 1, except that the polyethylene film was changed to a polyethylene film having the tensile strength and elongation ratio shown in Table 1 below, and the composition of the electrolyte was changed. The polyethylene film was manufactured at a higher stretching temperature compared to the polyethylene film in Example 1.

[0194] <Comparative Example 1 to Comparative Example 6> In Examples 1 to 3, the stretching temperature and stretching ratio were changed, and the polyethylene film shown in Table 1 below was used instead of the polyethylene film, and / or the adhesive layer was omitted as shown in Table 1 below, but the separation membrane was manufactured in the same manner as in Example 1.

[0195] Positive electrode adhesion strength (unit: gf / mm, wet adhesion strength) After attaching the separation membrane to the positive electrode (manufactured in the same manner as the battery), it was inserted into a pouch, the electrolyte (same as the battery) was injected, and after vacuum sealing, a pressure of 300 kgf and a temperature of 75°C were applied for 1 hour. Subsequently, the pouch was dismantled at room temperature, and a laminated test specimen (2.5 cm x 8 cm) of the positive electrode and separation membrane was prepared. The force required to remove the positive electrode from the separation membrane by spreading the positive electrode and separation membrane to 180° was measured using a tension measuring instrument (Tinius Olsen, HT400).

[0196] Collision Rating (Unit: %): The samples were evaluated using the UN collision assessment method (dropping a 9.1 kg object from a certain height and checking for explosion and ignition). The percentage of samples that passed the collision assessment out of the total number of samples evaluated was calculated.

[0197] [Table 1]

[0198] *In Table 1 above, adhesive strength was evaluated as ○ if it was 0.5 gf / mm or higher, and X if it was less than 0.5 gf / mm.

[0199] *In Table 1 above, PC: Propylene carbonate, EP: Ethyl propionate, PP: Propyl propionate.

[0200] As shown in Table 1 above, the lithium secondary battery of the embodiment showed improved collision characteristics.

[0201] On the other hand, the lithium secondary battery used in the comparative example did not have good collision characteristics.

[0202] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings, and these also naturally fall within the scope of the present invention.

Claims

1. A case with an open section; Electrode assemblies and electrolytes housed in the aforementioned case; and Includes a cap-up that is positioned in the opening, The electrode assembly includes a first electrode plate, a second electrode plate, and a separation membrane located between the first electrode plate and the second electrode plate. The separation membrane includes a substrate and a coating layer located on at least one surface of the substrate. The aforementioned substrate has a sum of elongation in the mechanical direction (MD) and transverse direction (TD) of 200% or less, and a sum of tensile strength in the mechanical direction and transverse direction of 4000 kgf / cm². 2 The following: The coating layer comprises a binder, and the binder comprises one or more of aramid resins and acrylic resins. A secondary battery wherein the electrolyte contains 20% by volume or more of ethyl propionate or ethylene carbonate.

2. The secondary battery according to claim 1, wherein the MD tensile strength of the substrate is higher than the TD tensile strength.

3. The aforementioned MD tensile strength is 1500 to 3000 kgf / cm². 2 The aforementioned TD tensile strength is 500 to 2000 kgf / cm². 2 The secondary battery according to claim 1.

4. The secondary battery according to claim 1, wherein the TD stretching rate of the substrate is higher than the MD stretching rate.

5. The secondary battery according to claim 1, wherein the MD stretching rate is 5 to 100%, and the TD stretching rate is 20 to 180%.

6. The secondary battery according to claim 1, wherein the substrate is a porous polyolefin-based substrate.

7. The secondary battery according to claim 6, wherein the polyolefin-based substrate comprises a polyolefin-based resin having a weight-average molecular weight of 600,000 g / mol or more.

8. The secondary battery according to claim 6, wherein the polyolefin-based substrate comprises a polyolefin-based resin having a melting temperature (Tm) of 130 to 140°C.

9. The secondary battery according to claim 1, wherein the aramid resin includes a meta-type or para-type aramid resin.

10. The secondary battery according to claim 1, wherein the acrylic resin has a glass transition temperature of 70 to 100°C.

11. The secondary battery according to claim 1, wherein the separation membrane has an adhesive force of 0.5 gf / mm or more to the first electrode plate or the second electrode plate.

12. The secondary battery according to claim 1, wherein the electrolyte comprises 10 to 30 volume percent of ethylene carbonate (EC), 10 to 30 volume percent of propylene carbonate (PC), 20 to 40 volume percent of ethyl propionate (EP), and 30 to 60 volume percent of propyl propionate (PP).

13. The secondary battery according to claim 1, wherein the electrolyte comprises 20 to 30 volume percent of ethylene carbonate (EC), 10 to 40 volume percent of ethyl methyl carbonate (EMC), and 30 to 70 volume percent of dimethyl carbonate (DMC).

14. The secondary battery according to claim 1, wherein the coating layer further comprises one or more of a filler and a polyethylene-based wax.

15. The secondary battery according to claim 14, wherein the filler has an average particle size D50 of 20 to 200 nm.

16. The secondary battery according to claim 14, wherein the filler comprises spherical alumina.

17. The secondary battery according to claim 1, wherein the coating layer is an adhesive layer containing one or more of the aramid resin and acrylic resin.

18. The secondary battery according to claim 1, wherein the coating layer comprises a heat-resistant layer containing a filler and a binder; and an adhesive layer located on the heat-resistant layer and containing one or more of the aramid resin and acrylic resin.

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