Lithium secondary battery comprising Si-based negative electrode active material

Abstract

A lithium secondary battery with reduced high-potential (Hi-pot) defects and improved capacity retention rate is provided. According to one aspect of the present invention, in a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, the negative electrode contains a Si-based negative electrode active material, the separator has a large number of pores and comprises a separator substrate containing a polyolefin resin, the polydispersity index (PDI) of the polyolefin resin is 2.5 to 4.2, the average diameter of the pores is 20 nm to 40 nm, and the maximum diameter of the pores is 50 nm or less. A lithium secondary battery is provided.

Description

Technical Field

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2022-0072073, filed with the Korean Intellectual Property Office on June 14, 2022, and all of its contents are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery comprising an Si-based negative electrode active material as a negative electrode active material.

Background Art

[0003] As a separator for lithium secondary batteries, a film substrate based on a polymer resin such as polyolefin having a large number of pores is used. Usually, an electrode assembly is manufactured through a lamination process of joining a separator and an electrode by heat and pressure. The higher the heat and pressure applied in this process, the higher the adhesion between the electrode and the separator. In recent years, the process speed has been increased for the purpose of improving productivity. However, since the time for heat to be applied to the separator has been shortened, the adhesion is ensured by increasing the pressure, but there is concern about deformation due to high pressure. Also, during the lamination process, the thickness of the polymer film substrate decreases significantly and the damage to the pores increases. As a result, not only the performance of the battery but also the dielectric breakdown voltage of the separator decreases, resulting in problems such as Hi-pot failure and a decrease in the capacity retention rate.

[0004] In particular, when an Si-based negative electrode active material such as Si, SiO, or Si alloy is applied as a negative electrode active material of a lithium secondary battery, the volume expansion of the negative electrode is large. Therefore, during charging / discharging, the compressive deformation of the separator due to the increase in pressure inside the cell becomes more severe. In addition, since the Si negative electrode active material has larger particle size, roughness, and hardness compared to the graphite negative electrode active material, it may cause local damage to the separator during lamination with the separator.

[0005] Accordingly, there is a further need to develop a separator with improved compressibility when applying an Si-based negative electrode active material.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention provides a lithium secondary battery including an Si-based negative electrode active material, aiming to provide a lithium secondary battery with reduced Hi-pot defects and improved capacity retention rate.

[0007] It will be easily understood that the objects and advantages of the present invention can be achieved by the means or methods described in the claims and combinations thereof.

Means for Solving the Problems

[0008] According to a first aspect of the present invention, in a lithium secondary battery including a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, the negative electrode contains an Si-based negative electrode active material, the separator has a large number of pores, includes a separator substrate containing a polyolefin resin, the polydispersity index (PDI) of the polyolefin resin is 2.5 to 4.2, the average diameter of the pores is 20 nm to 40 nm, and the maximum diameter of the pores is 50 nm or less, a lithium secondary battery is provided.

[0009] A second aspect of the present invention is a lithium secondary battery including a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode,

[0010] the negative electrode contains an Si-based negative electrode active material,

[0011] the separator has a large number of pores and includes a separator containing a polyolefin resin,

[0012] the polydispersity index (PDI) of the polyolefin resin is 2.5 to 4.2,

[0013] the average diameter of the pores is 20 nm to 40 nm, and the maximum diameter of the pores is 50 nm or less,

[0014] the separator substrate is,

[0015] When a tensile deformation force is applied at 60 °C and 15 MPa for 60 seconds, the deformation rate is 25% or less,

[0016] When a tensile deformation force is applied at 70 °C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% is 200 seconds or less.

[0017] A lithium secondary battery can be provided.

[0018] A third aspect of the present invention is in the first aspect or the second aspect,

[0019] The polydispersity index (PDI) of the polyolefin resin is 2.5 to 4.0,

[0020] The average diameter of the pores is 20 nm to 39 nm, and the maximum diameter of the pores is 48 nm or less.

[0021] The separation membrane substrate,

[0022] When a tensile deformation force is applied at 60 °C and 15 MPa for 60 seconds, the deformation rate is 23% or less.

[0023] When a tensile deformation force is applied at 70 °C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% is 190 seconds or less.

[0024] A lithium secondary battery can be provided.

[0025] A fourth aspect of the present invention is in the third aspect,

[0026] The polydispersity index (PDI) of the polyolefin resin is 2.6 to 3.9,

[0027] The average diameter of the pores is 21 nm to 38 nm, and the maximum diameter of the pores is 46 nm or less.

[0028] The separation membrane substrate,

[0029] When a tensile deformation force is applied at 60 °C and 15 MPa for 60 seconds, the deformation rate is 21% or less,

[0030] When a tensile deformation force is applied at 70 °C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% is 180 seconds or less.

[0031] A lithium secondary battery can be provided.

[0032] A fifth aspect of the present invention is, in the fourth aspect,

[0033] The average diameter of the pores is 22.2 nm to 36.1 nm,

[0034] The separator substrate is,

[0035] When a tensile deformation force is applied at 60 °C and 15 MPa for 60 seconds, the deformation rate is 20.1% or less,

[0036] When a tensile deformation force is applied at 70 °C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% is 178 seconds or less.

[0037] A lithium secondary battery can be provided.

[0038] A sixth aspect of the present invention is, in any one of the first to fifth aspects,

[0039] The polyolefin resin has a weight average molecular weight of 500,000 g / mol to 1,500,000 g / mol, and a lithium secondary battery can be provided.

[0040] In a seventh aspect of the present invention, in any one of the first to sixth aspects,

[0041] The separator substrate includes a core portion made of a mixture of polyethylene and polypropylene, and a skin portion of polyethylene laminated on both sides of the core portion, and a lithium secondary battery can be provided.

[0042] According to an eighth aspect of the present invention, in any one of the first to seventh aspects,

[0043] a lithium secondary battery can be provided, wherein the separator substrate is manufactured by a wet manufacturing method in which a pore-forming agent is extracted to form pores.

[0044] According to a ninth aspect of the present invention, in any one of the first to eighth aspects,

[0045] a lithium secondary battery can be provided, wherein the Si-based negative electrode active material is a negative electrode active material containing at least one selected from the group consisting of Si, SiO, and Si alloys.

[0046] According to a tenth aspect of the present invention, in any one of the first to ninth aspects,

[0047] a lithium secondary battery can be provided, wherein the negative electrode is a negative electrode active material further containing graphite.

[0048] According to an eleventh aspect of the present invention, in any one of the first to tenth aspects,

[0049] the separator further includes an organic / inorganic composite coating layer on at least one surface of the separator substrate, and the organic / inorganic composite coating layer can include a crystalline binder and an amorphous binder.

[0050] According to a twelfth aspect of the present invention, in the eleventh aspect,

[0051] the lithium secondary battery further includes an electrolyte, and the crystalline binder and the amorphous binder can each independently have a concentration gradient in the thickness direction of the organic / inorganic composite coating layer.

[0052] According to a thirteenth aspect of the present invention, in the twelfth aspect,

[0053] The organic / inorganic composite coating layer includes a first portion adjacent to the separation membrane substrate and a second portion facing the first portion, and the concentration of the crystalline binder in the second portion may be higher than the concentration of the crystalline binder in the first portion.

Advantages of the Invention

[0054] The polyolefin separation membrane provided in the lithium secondary battery according to the present invention has the polydispersity index of the polyolefin resin, the average diameter of the pores formed in the separation membrane, and the maximum diameter of the pores controlled within a predetermined range, and the deformation rate and recovery rate of the separation membrane are suppressed to a certain value or less under predetermined conditions, thereby improving the compression resistance of the separation membrane.

[0055] As a result, during the lamination process for manufacturing an electrode assembly with a Si-based negative electrode having a large volume expansion or hardness, etc., the reduction rate of the thickness of the separation membrane and the damage to the separation membrane due to the pressure applied are small, so the high-pot (Hi-pot) defect is reduced and the capacity retention rate is improved. Furthermore, the process speed can be increased and the processability is also improved.

[0056] The accompanying drawings illustrate preferred embodiments of the present invention and explain the principle of the present invention together with the detailed description, and the scope of the invention is not limited thereto. On the other hand, the shape, size, scale or ratio of the elements in the drawings described in this specification may be exaggerated for the purpose of emphasizing a clearer explanation.

Brief Description of the Drawings

[0057]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0058] Hereinafter, the present invention will be described in detail. Prior to this, terms or words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way, they must be construed in a meaning and concept consistent with the technical idea of the present invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention. At the time of filing this application, there may be various equivalents and modifications that can replace these.

[0059] Throughout the specification of this application, when a certain part states that a certain component "includes", unless otherwise stated to the contrary, it does not mean excluding other components, but rather means that other components can be further included.

[0060] In the specification of this application, the separation membrane has a porous property including a large number of pores and serves as a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the negative electrode and the positive electrode in a lithium secondary battery. In the specification of this application, the property of "having pores" means that a fluid in a gas phase and / or a liquid phase can pass from one side to the other side of the object due to a structure in which the object includes a plurality of pores and the pores are connected to each other.

[0061] In the present invention, the polyolefin separation membrane is meant to include all cases where it is applied as the separation membrane itself or as a component of the separation membrane. Therefore, the polyolefin separation membrane described in the present invention can have other layers further arranged on at least one surface of the separation membrane substrate from the aspects of materials and functions as required. In one embodiment of the present invention, the separation membrane may have an organic / inorganic composite coating layer containing inorganic particles and / or a binder resin formed on at least one side or both sides of the porous substrate.

[0062] Also, in the present invention, a lithium secondary battery is one in which lithium ions are used as an ion conductor, and examples thereof include, but are not limited to, a non-aqueous electrolyte secondary battery containing a liquid electrolyte, an all-solid battery containing a solid electrolyte, a lithium polymer battery containing a gel polymer electrolyte, and a lithium metal battery using lithium metal as a negative electrode.

[0063] Hereinafter, the lithium secondary battery according to the present invention will be described in detail.

[0064] According to the present invention, in a lithium secondary battery including a negative electrode, a positive electrode, and a separation membrane interposed between the negative electrode and the positive electrode,

[0065] the negative electrode contains a Si-based negative electrode active material,

[0066] the separation membrane has a large number of pores and includes a separation membrane substrate containing a polyolefin resin,

[0067] the polydispersity index (PDI) of the polyolefin resin is 2.5 to 4.2,

[0068] the average diameter of the pores is 20 nm to 40 nm, and the maximum diameter of the pores is 50 nm or less,

[0069] the separation membrane substrate,

[0070] when a tensile deformation force of 15 MPa is applied at 60 °C for 60 seconds, the deformation rate is 25% or less.

[0071] When removing after applying a tensile deformation force at 70 °C and 2 MPa for 180 seconds, the time required for the recovery rate to reach 70% is 200 seconds or less.

[0072] A lithium secondary battery can be provided.

[0073] In the present invention, the negative electrode contains a Si-based negative electrode active material. The Si-based negative electrode active material can be, but is not limited to, a negative electrode active material containing at least one or more selected from the group consisting of Si, SiO, and Si alloys. In addition to the Si-based negative electrode active material, the negative electrode can further contain other negative electrode active materials such as graphite, for example, in an amount of 10% to 90% by weight based on the total weight of the negative electrode active material.

[0074] Si-based negative electrode active materials such as Si, SiO, and Si alloys are negative electrode active materials that are continuously researched and developed in consideration of factors such as capacity. When applied as the negative electrode active material of a lithium secondary battery, there is a problem that the volume expansion of the negative electrode is large, so during charge / discharge, the compression deformation of the separator due to the increase in pressure inside the cell becomes more intense. In addition, since Si-based negative electrode active materials have larger particle size, roughness, and hardness compared to graphite negative electrode active materials, there is also a possibility of causing local damage to the separator during lamination with the separator.

[0075] In order to solve the problems associated with the use of the above-described Si-based negative electrode active material, the present invention applies a compression-resistant polyolefin-based separator having the above-described characteristics.

[0076] The polyolefin separation membrane according to the present invention is produced using a polyolefin resin as the base resin. Examples of polyolefin resins include polyethylene, polypropylene, polypentene, etc., and one or more of these can be included. A porous separation membrane produced using such a polyolefin resin as the base resin, that is, a separation membrane having a large number of pores, is advantageous from the viewpoint of imparting a shutdown function at an appropriate temperature. In particular, when polyethylene and polypropylene are simultaneously included as the polyolefin resin, physical properties such as shutdown characteristics and mechanical strength can be improved simultaneously.

[0077] Generally, in terms of the aspect that the higher the molecular weight of the resin, the more advantageous the compression resistance, the weight average molecular weight of the polyolefin resin can be higher than before, from 500,000 g / mol to 1,500,000 g / mol. When mixing and using different polyolefin resins, or forming a separation membrane with a multilayer structure composed of different polyolefin resins, the weight average molecular weight of the polyolefin resin is calculated by adding the weight average molecular weights corresponding to the content ratios of the respective polyolefin resins.

[0078] In addition to the above-mentioned polyolefin-based resin, other resin components can be further mixed as necessary. In addition to the resin components, for example, filler particles can be included. The filler particles can be introduced for the purpose of a pressure barrier so that the thickness of the separation membrane substrate, the size of the pores, and the porosity do not decrease excessively with respect to the high pressure applied in the lamination process described later. The filler particles can include organic fillers or inorganic fillers having a predetermined particle size, and are not limited to specific components as long as they have a strength higher than that of the polyolefin resin.

[0079] In the present invention, the polydispersity index (PDI) of the polyolefin resin is 2.5 to 4.2, the average diameter of the pores is 20 nm to 40 nm, and the maximum diameter of the pores is 50 nm or less. That is, in the present invention, the polydispersity index of the polyolefin resin is low, and the average diameter and the maximum diameter of the pores are small. When this range is satisfied simultaneously, the compression resistance is improved. If the polydispersity index is less than 2.5, there is a problem that the processability deteriorates and the uniformity of the film deteriorates. If it exceeds 4.2, there is a problem that the compression resistance deteriorates. Further, if the average diameter of the pores is less than 20 nm, there is a problem that the air permeability deteriorates and a phenomenon occurs in which by-products block small pores during charging and discharging of the battery. If it exceeds 40 nm, the thickness of the separator is not uniform, thickness deformation occurs, and there is a problem that the compression resistance deteriorates due to local thickness deformation. Further, if the maximum diameter of the pores exceeds 50 nm, there is also a problem that the compression resistance deteriorates.

[0080] The size of the pores can be calculated from the pore size distribution measured by the Capillary Flow Porometer method. For example, first, the separator to be measured is wetted with a wetting agent such as a galwick solution, and then the air pressure on one side of the substrate is gradually increased. At this time, when the applied air pressure becomes larger than the capillary attraction of the wetting agent present in the pores, the wetting agent blocking the pores is expelled, and the size and distribution of the pores are measured through the pressure and flow rate at the moment of expulsion, and the average diameter (size) and the maximum diameter of the pores can be confirmed therefrom.

[0081] In such an aspect, the polydispersity index (PDI) of the polyolefin resin can be 2.5 to 4.0, more specifically 2.6 to 3.9. Further, the average diameter of the pores can be 20 nm to 39 nm, more specifically 21 nm to 38 nm, and most specifically 22.2 nm to 36.1 nm. Further, the maximum diameter of the pores can be 48 nm or less, more specifically 46 nm or less.

[0082] On the one hand, in the present invention, when a tensile deformation force is applied to the separation membrane substrate at 60°C and 15 MPa for 60 seconds, the deformation rate is 25% or less. At the same time, when the tensile deformation force is applied at 70°C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% is 200 seconds or less.

[0083] If the deformation rate under the above conditions exceeds 25%, or the time required for the recovery rate to reach 70% exceeds 200 seconds, the compressive resistance after the lamination process with the Si-based negative electrode will decrease.

[0084] In such an aspect, the polyolefin separation membrane substrate

[0085] when a tensile deformation force is applied at 60°C and 15 MPa for 60 seconds, the deformation rate is 23% or less. When the tensile deformation force is applied at 70°C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% can be 190 seconds or less.

[0086] More specifically, when a tensile deformation force is applied at 60°C and 15 MPa for 60 seconds, the deformation rate is 21% or less. When the tensile deformation force is applied at 70°C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% can be 180 seconds or less.

[0087] Most specifically, when a tensile deformation force is applied at 60°C and 15 MPa for 60 seconds, the deformation rate is 20.1% or less. When the tensile deformation force is applied at 70°C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% can be 178 seconds or less.

[0088] The above-described polyolefin separation membrane substrate can be manufactured as follows, but is not limited thereto.

[0089] In one embodiment of the present invention, the separation membrane may be manufactured by a method (wet method) in which a polyolefin resin is kneaded with diluents at a high temperature to form a single phase, the polymer material and the diluent are phase-separated during the cooling process, and then the diluent is extracted to form pores, followed by stretching and heat setting treatments. In particular, the polyolefin separation membrane may include a core portion made of a mixture of polyethylene and polypropylene, and a skin portion of polyethylene laminated on both surfaces of the core portion, but is not limited thereto.

[0090] The average pore diameter and the maximum pore diameter of the separation membrane substrate can be easily manufactured by adjusting the mixing ratio of the diluent, the stretching ratio, the heat setting treatment temperature, etc. so that those skilled in the art can conform to the scope of the present invention.

[0091] In the present invention, the polyolefin separation membrane substrate prepared by the method described above may have a thickness of 5 μm to 30 μm.

[0092] On the other hand, in one embodiment of the present invention, the separation membrane may further include an organic / inorganic composite coating layer formed on at least one surface of the polyolefin separation membrane substrate.

[0093] The organic / inorganic composite coating layer includes a binder resin and inorganic particles and has porous characteristics. In one embodiment of the present invention, among the organic / inorganic composite coating layers, the binder resin and the inorganic particles may be included in a weight ratio of 1:99 to 30:70. The ratio can be appropriately adjusted within the above range. For example, the binder resin may be 1 wt% or more, 5 wt% or more, or 10 wt% or more, and the inorganic particles may be 80 wt% or more, 85 wt% or more, 90 wt% or more, or 95 wt% or more out of a total of 100 wt% of the binder resin and the inorganic particles.

[0094] The organic / inorganic composite coating layer can be formed by binding inorganic particles with a binder resin and accumulating them inside the side surface. The pores inside the organic / inorganic composite coating layer may be caused by the interstitial volume, which is the empty space between the inorganic particles.

[0095] In one embodiment of the present invention, the porosity (porosity of the heat-resistant layer) of the organic / inorganic composite coating layer can be 30 vol% to 70 vol%. When the porosity is 70 vol% or less, mechanical properties that can withstand the pressing process of adhering to the electrode can be ensured, and the surface aperture ratio does not become too high, making it suitable for ensuring adhesion. On the other hand, when the porosity is 30 vol% or more, it is advantageous from the perspective of ion permeability.

[0096] The thickness of the organic / inorganic composite coating layer can be formed to be 1 μm to 20 μm with respect to either one of the separation membrane substrates, but it is not particularly limited thereto. The thickness can be adjusted by those skilled in the art within an appropriate range from the perspective of heat resistance or electrical resistance.

[0097] In the present invention, non-limiting examples of the binder resin that can be used in the organic / inorganic composite coating layer include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose. Any one of the polymer resins selected from the group consisting of these or a mixture of two or more of them can be mentioned. However, it is not particularly limited thereto.

[0098] In a specific embodiment of the present invention, the inorganic particles that can be used in the organic / inorganic composite coating layer are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as oxidation and / or reduction reactions do not occur within the operating voltage range of the applied electrochemical element (for example, 0 V to 5 V based on Li / Li + ).

[0099] Non-limiting examples of the inorganic particles include BaTiO3, Pb(Zr,Ti)O3 (PZT), b 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, Al(OH)3, TiO2, aluminum peroxide, zinc tin hydroxide (ZnSn(OH)6), tin-zinc oxides (Zn2SnO4, ZnSnO3), antimony trioxide (Sb2O3), antimony tetroxide (Sb2O4), antimony pentoxide (Sb2O5), etc., and one or more of these can be included.

[0100] Also, the average diameter (D 50 ) of the inorganic particles is not particularly limited, but is preferably in the range of 0.3 μm to 1 μm for forming a coating layer with a uniform thickness and an appropriate porosity. If it is less than 0.3 μm, the dispersibility of the inorganic particles in the slurry prepared for the production of the heat-resistant layer may decrease, and if it exceeds 1 μm, the thickness of the formed coating layer may increase.

[0101] In one embodiment of the present invention, the method for forming the organic / inorganic composite coating layer is as follows, for example. First, a binder resin is dissolved in a suitable organic solvent to produce a polymer solution. As the solvent, it is preferable that the solubility index is similar to the binder polymer to be used and the boiling point is low. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or mixtures thereof.

[0102] Next, inorganic particles are added and dispersed in the produced polymer solution. In the present invention, the content ratio of the inorganic particles to the binder is as described above, and is appropriately adjusted in consideration of the thickness, pore size, and porosity of the heat-resistant layer of the present invention finally produced.

[0103] Next, the inorganic particle slurry produced above is applied to at least one surface of the prepared separation membrane substrate and dried. The method of applying the slurry to the surface of the separation membrane substrate is not particularly limited to any one method, and ordinary methods known in the art can be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a mixed method thereof can be used.

[0104] In the drying step, the temperature and time conditions are appropriately set in order to minimize the generation of surface defects in the organic / inorganic composite coating layer. For the drying, drying auxiliary devices such as a drying oven or hot air can be used within an appropriate range.

[0105] When the separation membrane includes an organic / inorganic composite porous layer, damage caused by pressing inorganic particles can be reduced on the surface of the separation membrane substrate facing the organic / inorganic composite porous layer during the lamination process.

[0106] In this specification, the crystallinity can be expressed as a percentage of the measured melting enthalpy value by DSC (differential scanning calorimetry) measurement with respect to the melting enthalpy value of a theoretically perfect crystal (crystallinity 100%). The amorphous binder according to the present invention means that the crystallinity is 30% or less, and the crystalline binder may mean that the crystallinity is more than 30%.

[0107] According to another embodiment of the present invention, the separation membrane further includes an organic / inorganic composite coating layer on at least one surface of the separation membrane substrate, and the organic / inorganic composite coating layer can include a crystalline binder and an amorphous binder. According to another embodiment of the present invention, when the organic / inorganic composite coating layer includes a crystalline binder and an amorphous binder, the adhesive force (wet adhesive force) with the electrode can be ensured by the crystalline binder when the electrolyte is present. For example, in the absence of the electrolyte, the crystalline binder and the amorphous binder can be randomly distributed on the surface of the separation membrane substrate. When adhering the electrode to the separation membrane, the amorphous binder having a relatively low glass transition temperature (Tg) and a larger surface area is deformed by temperature and pressure during adhesion and can be present in a larger amount on the surface, forming a dry adhesive force with the electrode. When the electrolyte is injected, the amorphous binder having high solubility and fluidity in the electrolyte may swell and may move inside the organic / inorganic composite coating layer or inside the electrode. For example, when an organic solvent is used, the polymer binder rich in amorphous regions can swell compared to the highly crystalline binder. The swelling of the polymer binder may generate fluidity and move inside the organic / inorganic composite coating layer or inside the electrode. Therefore, since the crystalline binder mainly exists on the surface of the organic / inorganic composite coating layer, when the electrolyte is present, the wet adhesive force with the electrode can be formed by the crystalline binder.

[0108] Specifically, the lithium secondary battery further includes an electrolytic solution, and the crystalline binder and the amorphous binder can each independently have a concentration gradient in the thickness direction of the organic / inorganic composite coating layer. For example, after applying a slurry to at least one surface of the separator substrate, it can be moved to a heating zone to dry the slurry to form an organic / inorganic composite coating layer. The separator substrate coated with the slurry can be dried while moving at a predetermined speed through a heating zone heated to a predetermined temperature to form a separator with an organic / inorganic composite coating layer formed thereon. According to one example, the heating temperature of the heating zone can be 45°C to 65°C. The porous separator substrate can move through the heating zone at a speed of 25 m / min to 150 m / min, specifically 40 m / min to 60 m / min. The drying conditions of the organic / inorganic composite coating layer can be determined by the morphological differences between the binder and the inorganic particles, and the drying conditions can determine the concentration gradient of each binder and inorganic particle distributed in the thickness direction of the coating layer.

[0109] According to another embodiment of the present invention, the organic / inorganic composite coating layer can include a first portion adjacent to the separator substrate and a second portion facing the first portion. Specifically, the concentration of the crystalline binder in the second portion may be higher than the concentration of the crystalline binder in the first portion. Here, the first portion adjacent to the separator substrate can be a portion relatively close to the separator substrate with reference to the mid surface of the organic / inorganic composite coating layer cut in the plane direction, and specifically can be in contact with the separator substrate. For example, the second portion can be a portion relatively closer to the electrode than the first portion with reference to the mid surface of the organic / inorganic composite coating layer cut in the plane direction, and specifically can be in contact with the electrode. According to one example, the average thickness of the first portion can be 0.1 μm to 10 μm, 0.1 μm to 5 μm, 0.1 μm to 1.5 μm, 0.1 μm to 1.0 μm, 0.1 μm to 0.5 μm, or 0.1 μm to 0.3 μm, and the average thickness of the second portion can be the same as the average thickness of the first portion.

[0110] According to another embodiment of the present invention, the crystalline binder and the amorphous binder can each independently include an aqueous emulsion type binder.

[0111] For example, the crystalline binder may be a polyvinylidene fluoride type, and the amorphous binder may be an acrylate type.

[0112] Specifically, the crystalline binder may be one or more selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyvinylidene fluoride - hexafluoropropylene (PVDF - HFP), polyvinylidene fluoride - trichloroethylene (PVDF - TCE), and polyvinylidene fluoride - chlorotrifluoroethylene (PVDF - CTFE), and in detail, it may be a copolymer containing polyvinylidene fluoride.

[0113] According to another embodiment of the present invention, the crystalline binder has an average particle diameter (D 50 ) of 200 nm or more, preferably 200 nm to 350 nm.

[0114] According to another embodiment of the present invention, the weight average molecular weight (Mw) of the crystalline binder can be 10,000 g / mol to 10,000,000 g / mol. The density of the crystalline binder can be 1.1 g / cm 3 ~1.5 g / cm 3

[0115] ​According to another embodiment of the present invention, the crystalline binder may have a glass transition temperature of 80°C to 200°C, preferably 80°C to 150°C, more preferably 110°C to 145°C, and may exhibit high oxidation resistance to the electrolyte.

[0116] According to another embodiment of the present invention, the non-crystalline binder may contain an acrylate-based polymer, specifically, it may be a copolymer containing acrylate as a monomer.

[0117] Optionally, the non-crystalline binder may further contain one or more selected from the group consisting of styrene-butadiene rubber, nitril-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber.

[0118] The non-crystalline binder has an average particle size (D 50 ) of 350 nm or more, preferably 350 nm to 500 nm, more preferably 350 nm to 450 nm. When the average particle size of the non-crystalline binder exceeds 500 nm, the mobility to the interface between the electrode and the coating layer decreases when there is no electrolyte, and the adhesive force between the electrode and the separator becomes weak, so that the electrode assembly cannot be manufactured, and it becomes difficult to achieve a uniform coating quality during the formation of the coating layer. Based on the same binder content, the number of binder particles decreases, thereby reducing the contact points between adjacent inorganic substances, increasing the possibility of desorption of the inorganic substances, reducing the interstitial volume, and reducing the electrical resistance characteristics.

[0119] The non-crystalline binder has an average particle size (D 50) is provided with a larger one, and has a larger contact area with the electrode compared to the crystalline binder, and can provide better dry adhesion.

[0120] The weight average molecular weight of the amorphous binder can be 10,000 g / mol to 10,000,000 g / mol. The density of the amorphous binder is 0.5 g / cm 3 ~1.1 g / cm 3 and can be.

[0121] The amorphous binder has a glass transition temperature of 40 °C or higher, preferably can be 45 °C to 60 °C, and more preferably can be 48 °C to 60 °C. Conventionally, acrylic binder particles with a relatively small particle size of 100 nm to 150 nm were used. Generally, the acrylic binder particles contain diene-based butadiene rubber, have a low glass transition temperature, and have a problem that side reactions with the electrolytic solution occur due to the presence of double bonds, resulting in gas generation. Therefore, as the amorphous binder, instead of directly using an acrylic binder with a glass transition temperature as low as less than 0 °C, a copolymer obtained by copolymerizing acrylic and styrene, etc., with a high glass transition temperature is used to prevent side reactions with the electrolytic solution. Also, within the above-mentioned range of the glass transition temperature, the amorphous binder can be maintained without its shape collapsing even during the drying of the first coating layer, and can exhibit dry adhesion to the electrode.

[0122] In one specific example, the crystalline binder can have characteristics similar to those of the binder used for the positive electrode, and the amorphous binder can have characteristics similar to those of the binder used for the negative electrode.

[0123] Specifically, since the positive electrode can use a polyvinylidene fluoride-based homopolymer with a crystallinity of 95% or more and high crystallinity, for example, homo PVDF that can be used as a crystalline binder can be included in the positive electrode mixture. The negative electrode can include an aqueous emulsion type amorphous acrylic binder in the negative electrode mixture.

[0124] Thus, by using a binder having characteristics similar to those of the binders used for the positive electrode and the negative electrode in the separator coating layer, the adhesive force between the positive electrode and the separator, and between the negative electrode and the separator can be improved. For example, the same binder can be used for the coating layer and the corresponding positive electrode and negative electrode. Alternatively, the crystalline binder can have the same polymer backbone as the binder used for the positive electrode, and the amorphous binder can have the same polymer backbone as the binder used for the negative electrode. As an example, the binder that can be used for the positive electrode or the negative electrode can be a homopolymer of PVdF, and the binder used for the separator can be a PVdF-HFP binder with an HFP substitution rate of 10%.

[0125] According to another embodiment of the present invention, the weight ratio of the crystalline binder to the amorphous binder can be 1:9 to 9:1, and more specifically, it can be 3:7 to 7:3. Based on the total weight of the crystalline binder and the amorphous binder, when the weight ratio of the crystalline binder and the amorphous binder satisfies the above numerical range, it is possible to embody an excellent effect simultaneously on the dry adhesive force, which is the adhesive force when no electrolyte is present, and the wet adhesive force, which is the adhesive force when an electrolyte is present.

[0126] According to another embodiment of the present invention, the wet adhesion of the separation membrane to the electrode can be 10 to 15 gf / 20 mm. For example, the wet adhesion of the separation membrane to the electrode can be measured through the steps of cutting the electrode and the separation membrane into predetermined sizes, placing them in a pouch, injecting an electrolytic solution; pressurizing the pouch filled with the electrolytic solution to prepare a test piece for measuring the wet adhesion; and performing a 90° peel test using a UTM device of Instron at a condition of 200 mm / min to measure the adhesion of the separation membrane to the electrode.

[0127] The separation membrane manufactured by the method described above is interposed between a negative electrode containing a Si-based negative electrode active material and a positive electrode, and is manufactured as an electrode assembly by a lamination process of applying heat and / or pressure to bond them. In one embodiment of the present invention, the lamination process can be performed by a roll press device including a pair of pressure rollers. That is, the negative electrode, the separation membrane, and the positive electrode are sequentially laminated, and this is put between the pressure rollers to achieve interlayer bonding. At this time, the lamination process can be performed by a hot pressing method.

[0128] In the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer containing a Si-based negative electrode active material, a binder resin, and optionally a conductive material on at least one surface of the current collector. As the negative electrode active material, a Si-based negative electrode active material can be used alone, or selectively combined with a carbon-based negative electrode active material such as graphite.

[0129] The positive electrode includes a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The positive electrode active material is a layered compound such as lithium manganese composite oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; the chemical formula Li 1+x Mn 2-xO4 (where x is from 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3), Ni-site type lithium nickel oxide represented by the formula; chemical formula LiMn 1-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or lithium manganese composite oxide represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; It can contain one or a mixture of two or more of Fe2(MoO4)3.

[0130] In a specific embodiment of the present invention, the conductive material can be, for example, any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon and polyphenylene derivative, or a mixture of two or more of these conductive materials. More specifically, it can be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate and titanium oxide, or a mixture of two or more of these conductive materials.

[0131] As the binder resin, a polymer commonly used for electrodes in the art can be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, etc., and are not limited thereto.

[0132] The electrode assembly prepared as described above can be placed in a suitable case and an electrolytic solution can be injected to manufacture a battery.

[0133] In the present invention, the electrolytic solution is A+ B - A salt having a structure such as + wherein A + is Li + , Na + , K - or an ion consisting of an alkali metal cation such as these, or a combination thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - or an anion consisting of a combination thereof, and there is a salt dissolved or dissociated in an organic solvent consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-butyrolactone), or a mixture thereof, but is not limited thereto.

[0134] The present invention also provides a battery module including the electrode assembly as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include a power tool powered by a battery-operated motor; an electric vehicle such as an Electric Vehicle (EV), a Hybrid Electric Vehicle (HEV), a Plug-in Hybrid Electric Vehicle (PHEV); an electric two-wheeler including an E-bike and an E-scooter; an electric golf cart; a power storage system, etc., but are not limited thereto.

[0135] Hereinafter, examples will be given for a specific description of the present invention. However, the examples according to the present invention can be deformed into various different forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more fully explain the present invention to those with average knowledge in the industry.

[0136] [Example 1]

[0137] Manufacture of the separation membrane

[0138] Manufacturing steps of the separation membrane substrate:

[0139] A resin obtained by mixing polyethylene (weight average molecular weight: 9 million g / mol) and polypropylene (weight average molecular weight: 3.5 million g / mol) at a weight ratio of 93:7 is used as the core part, and polyethylene (weight average molecular weight: 9 million g / mol) resin is positioned on both side surfaces of the core part and co-extruded with the skin part. The stretching temperature is adjusted to 105 °C and the heat setting temperature is adjusted to 130 °C, and a polyolefin separation membrane substrate (total thickness: about 9 μm, core part thickness: 7 μm, total thickness of both skin parts: 2 μm) is manufactured by the wet method.

[0140] Manufacturing steps of the composition for forming an organic / inorganic composite coating layer:

[0141] As the inorganic particles, alumina (Sumitomo, AES11) with an average particle size (D 50 ) of 500 nm, a density of 4 g / cm 3 , an aspect ratio of 1.3, and a BET specific surface area of 8 m 2 / g was used. As the crystalline polymer, a fluorine-based aqueous dispersion emulsion (Arkema, Aquatec 9530, solid content 30 wt%) with an average particle size (D 50 ) of 200 nm was used. As the amorphous polymer, an acrylic-based aqueous dispersion emulsion (LGC, SA22, solid content 30 wt%) with an average particle size (D 50 ) of 350 nm and a density of 1 g / cm 3 was used. As the dispersant, carboxymethyl cellulose (LG Chem, SG-L02) was used. A mixture of these in a weight ratio of 79:18:2:1 (inorganic particles:crystalline polymer:amorphous polymer:dispersant) was added to a solvent (water) to produce a composition for forming an organic / inorganic composite coating layer (viscosity at 20°C = 50 cP) with a total solid content of 30 wt%.

[0142] Step of forming an organic / inorganic composite coating layer on both sides of the separation membrane substrate:

[0143] The composition for forming an organic / inorganic composite coating layer was applied onto both sides of the polyolefin separation membrane substrate using a bar coater. While moving the polyolefin separation membrane substrate coated with the composition for forming an organic / inorganic composite coating layer at a speed of 40 m / min, it was introduced into seven heating zones under the conditions of 65°C, 65°C, 60°C, 55°C, 50°C, 45°C, 45°C, and then dried for a total of 2 - 3 minutes to form an organic / inorganic composite coating layer (each thickness: 3 μm) respectively, and finally a separation membrane was manufactured.

[0144] Manufacture of the positive electrode

[0145] Positive electrode active material (LiNi0.8 Mn 0.1 Co 0.1 O2), a conductive material (carbon black), a dispersant, and a binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water at a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for a positive electrode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry was applied to the surface of an aluminum thin film (thickness 10 μm) and dried to produce a positive electrode having a positive electrode active material layer (thickness 120 μm).

[0146] Manufacture of negative electrode

[0147] An Si-based negative electrode material (20% SiO2, 80% graphite), a conductive material (carbon black), a dispersant, and a binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water at a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for a negative electrode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry was applied to the surface of a copper thin film (thickness 10 μm) and dried to produce a negative electrode having a negative electrode active material layer (thickness 120 μm).

[0148] Lamination process

[0149] The manufactured negative electrode and positive electrode were laminated with a separator of the example and comparative example interposed therebetween, and a lamination process was performed to obtain an electrode assembly. The lamination process was performed for 10 seconds under the conditions of 70 °C and 5.2 MPa using hot pressing.

[0150] Electrolyte injection process

[0151] An electrolyte having a composition of LiPF6 1.0 M, EC / EMC = 3 / 7, and VC = 2.0 was injected into the electrode assembly to manufacture a cell.

[0152] [Example 2]

[0153] A cell was manufactured in the same manner as in Example 1 except that the stretching temperature was adjusted to 120 °C and the heat setting temperature was adjusted to 115 °C when manufacturing the separator substrate.

[0154] [Example 3]

[0155] A cell was produced in the same manner as in Example 1, except that the heat setting temperature was adjusted to 115°C when producing the separation membrane substrate.

[0156] [Comparative Example 1]

[0157] A cell was produced in the same manner as in Example 1, except that a resin obtained by mixing polyethylene (weight average molecular weight: 9 million g / mol) and polypropylene (weight average molecular weight: 350,000 g / mol) at a weight ratio of 97:3 was used as the skin part when producing the separation membrane substrate, and the stretching temperature was adjusted to 120°C.

[0158] [Comparative Example 2]

[0159] A cell was produced in the same manner as in Example 1, except that a resin obtained by mixing polyethylene (weight average molecular weight: 9 million g / mol) and polypropylene (weight average molecular weight: 350,000 g / mol) at a weight ratio of 97:3 was used as the skin part when producing the separation membrane substrate, and the heat setting temperature was adjusted to 115°C.

[0160] [Comparative Example 3]

[0161] A cell was produced in the same manner as in Example 1, except that a resin obtained by mixing polyethylene (weight average molecular weight: 9 million g / mol) and polypropylene (weight average molecular weight: 350,000 g / mol) at a weight ratio of 97:3 was used as the skin part when producing the separation membrane substrate.

[0162] [Comparative Example 4]

[0163] A cell was produced in the same manner as in Example 1, except that a resin obtained by mixing polyethylene (weight average molecular weight: 9 million g / mol) and polypropylene (weight average molecular weight: 350,000 g / mol) at a weight ratio of 97:3 was used as the skin part when producing the separation membrane substrate, the stretching temperature was adjusted to 120°C, and the heat setting temperature was adjusted to 115°C.

[0164] [Experimental Example 1: Physical Property Evaluation of Separation Membrane Substrate]

[0165] The PDI, average pore diameter, maximum pore diameter of the manufactured polyolefin separation membrane substrate, the deformation rate (referred to as the recovery deformation rate) when a tensile deformation force is applied at 60°C and 15 MPa for 60 seconds, and the time required for the recovery rate to reach 70% (referred to as the recovery time) when the tensile deformation force is applied at 70°C and 2 MPa for 180 seconds and then removed are shown in Table 1 below.

[0166] [Equation 1: PDI measurement]

[0167] PDI = (weight average molecular weight) / (number average molecular weight)

[0168] At this time, the values of the weight average molecular weight and the number average molecular weight were obtained by cutting the separation membrane substrate into a predetermined size and using the values derived by GPC (Gel Permeation Chromatography) analysis.

[0169] [Measurement of average and maximum pore diameters]

[0170] Measurement was carried out according to the pore size distribution using the Capillary Flow Porometer (CFP) method.

[0171] [Measurement of the deformation rate when a tensile deformation force is applied at 60°C and 15 MPa for 60 seconds]

[0172] The deformation rate was measured by applying stress at 60°C and 15 MPa for 60 seconds through the creep evaluation of Dynamic Mechanical Analysis.

[0173] [Measurement of the time required for the recovery rate to reach 70% when the tensile deformation force is applied at 70°C and 2 MPa for 180 seconds and then removed]

[0174] Using dynamic mechanical analysis, after applying stress at 70 °C and 2 MPa for 180 seconds, the time taken for the recovery rate to reach 70% was measured.

[0175]

Table 1

[0176] [Experimental Example 2: Evaluation of Cell Characteristics]

[0177] [Capacity Retention Rate]

[0178] For the manufactured battery, charge and discharge were performed at 25 °C under the conditions of 2C / 2C for 200 cycles, and then charge and discharge were repeated 3 times at 0.33C to measure the cell capacity, and the capacity change rate before and after evaluation was calculated.

[0179] [Pass Rate of Hi-pot Evaluation]

[0180] For 10 manufactured batteries, the test was carried out under the conditions of 50V and <0.5 mA (lamp up: 0 s, time: 0.1 s), and the defective ones were identified.

[0181] The above-mentioned measurement results are shown in Table 2 below.

[0182]

Table 2

[0183] [Example 4: Production of a Separation Membrane Containing an Organic / Inorganic Composite Coating Layer Composed Only of Amorphous Polymer]

[0184] The separation membrane was produced in the same manner as in Example 1, but the weight ratio of 79:18:2:1 (inorganic particles: crystalline polymer: amorphous polymer: dispersant) was changed to a weight ratio of 79:20:1 (inorganic particles: amorphous polymer: dispersant).

[0185] [Experimental Example 3: Measurement of Wet Adhesion Force of Separator-Electrode Assembly Specimens According to Example 1 and Example 4]

[0186] The positive electrode of Example 1 and each separator manufactured by the method according to Example 1 and Example 4 were cut to a width of 20 mm and placed in a pouch, and then a carbonate-based electrolyte was injected. The pouch filled with the electrolyte was pressurized under the conditions of 5 kgf, 70 °C, and 4 minutes to prepare two separator-electrode assembly samples for measuring the wet adhesion force. To measure the adhesion force of the separator to the positive electrode, a 90° peel test was performed using an Instron UTM device at a condition of 200 mm / min.

[0187] [Table 3]

[0188] Referring to Table 3 above, in the case of the separator-electrode assembly according to Example 1, compared with Example 4, since both the crystalline and amorphous binders are included in the organic / inorganic composite coating layer, it can be confirmed that the adhesion force of the separator to the electrode in the wet state with the electrolyte injected is increased to the appropriate level in the range of 10 to 15 gf / 20 mm.

Claims

1. A lithium secondary battery comprising: a negative electrode; a positive electrode; and a separator interposed between the negative electrode and the positive electrode, the negative electrode contains a Si-based negative electrode active material, The separation membrane has a separation membrane substrate having a large number of pores and containing a polyolefin resin, The polyolefin resin has a polydispersity index of 2.5 to 4.2; The average diameter of the pores is 20 nm to 40 nm, and the maximum diameter of the pores is 50 nm or less. Lithium secondary battery.

2. The polyolefin resin has a polydispersity index of 2.5 to 4.0; the average diameter of the pores is 20 nm to 39 nm, and the maximum diameter of the pores is 48 nm or less; The separation membrane substrate is The deformation rate is 23% or less when a tensile deformation force of 15 MPa is applied at 60°C for 60 seconds, When a tensile force is applied at 70°C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% is 190 seconds or less. The lithium secondary battery according to claim 1 .

3. The polyolefin resin has a polydispersity index of 2.6 to 3.9; the average pore diameter is 21 nm to 38 nm, and the maximum pore diameter is 46 nm or less; The separation membrane substrate is The deformation rate is 21% or less when a tensile deformation force of 15 MPa is applied at 60°C for 60 seconds, When a tensile force is applied at 70°C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% is 180 seconds or less. The lithium secondary battery according to claim 1 .

4. the average diameter of the pores is 22.2 nm to 36.1 nm; The separation membrane substrate is The deformation rate when a tensile force of 15 MPa is applied at 60°C for 60 seconds is 20.1% or less; When a tensile force is applied at 70°C and 2 MPa for 180 seconds and then removed, the time required for the recovery rate to reach 70% is 178 seconds or less. The lithium secondary battery according to claim 3 .

5. 2. The lithium secondary battery according to claim 1, wherein the polyolefin resin has a weight average molecular weight of 500,000 g / mol to 1,500,000 g / mol.

6. 2. The lithium secondary battery according to claim 1, wherein the separator substrate comprises a core made of a mixture of polyethylene and polypropylene, and skins made of polyethylene laminated on both sides of the core.

7. The separation membrane is The separator further comprises an organic / inorganic composite coating layer on at least one surface of the separator substrate; The organic / inorganic composite coating layer is including crystalline binders and amorphous binders, The lithium secondary battery according to any one of claims 1 to 6.

8. The lithium secondary battery further comprises an electrolyte; The crystalline binder and the non-crystalline binder each independently comprise: The organic / inorganic composite coating layer has a concentration gradient in the thickness direction thereof. The lithium secondary battery according to claim 7.

9. the organic / inorganic composite coating layer includes a first portion adjacent to the separator substrate and a second portion facing the first portion, the concentration of the crystalline binder in the second portion is higher than the concentration of the crystalline binder in the first portion; The lithium secondary battery according to claim 7.

10. 2. The lithium secondary battery according to claim 1, wherein the Si-based negative electrode active material is a negative electrode active material containing at least one selected from the group consisting of Si, SiO, and a Si alloy.

11. 10. The lithium secondary battery according to claim 1, wherein the negative electrode further comprises graphite.

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