Separator and lithium battery including the separator

Abstract

A separator and a lithium battery employing the same are disclosed. The separator comprises a porous substrate having surface irregularities, wherein the area of ​​the protruding grooves in the surface irregularities of the porous substrate is 12% or more and less than 40%. The separator can increase insulation performance through surface morphology control, thereby reducing dV defects and increasing the yield and reliability of the lithium battery.

Description

Technology Field

[0001] This invention relates to a separator and a lithium battery employing the same. Background Technology

[0002] To meet the demands for miniaturization and high performance in various devices, the miniaturization and lightweighting of lithium batteries are becoming increasingly important. Furthermore, discharge capacity, energy density, and cycle characteristics of lithium batteries are becoming critical for applications in fields such as electric vehicles. To meet these requirements, lithium batteries with high discharge capacity per unit volume, high energy density, and excellent lifespan characteristics are required.

[0003] A separator is placed between the positive and negative electrodes in a lithium battery to prevent a short circuit. An electrode assembly comprising a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes is wound to form a jelly roll, and the jelly roll is rolled to improve the adhesion between the positive / negative electrodes and the separator in the electrode assembly.

[0004] As the energy density of batteries continues to rise, separators are increasingly required to be thinned. As separators become thinner, the gap between the positive and negative electrodes becomes physically closer, which leads to an increase in the frequency of micro-shorts inside the battery and an increase in dV defects in the battery.

[0005] Therefore, a separator capable of reducing dV defects is required. The problem to be solved

[0006] One aspect is to provide a separator that can reduce dV failures by increasing insulation through surface morphology control.

[0007] Another aspect is to provide a lithium battery comprising the above-mentioned separator. means of solving the problem

[0008] Depending on one aspect,

[0009] It includes a porous substrate having surface irregularities, and

[0010] A separator is provided in which the area of ​​the protruding grooves in the surface irregularities of the porous substrate is 12% or more and less than 40%.

[0011] According to one embodiment, the separator may have a stationary BDV of 160 V / μm or more per unit thickness.

[0012] According to one embodiment, the difference between the stationary BDV and the moving BDV of the separator may be 500V or less.

[0013] Depending on the other aspect,

[0014] A lithium battery is provided comprising: a positive electrode; a negative electrode; and a separator disposed between the positive electrode and the negative electrode. Effects of the invention

[0015] According to one aspect, the separator can increase insulation through surface morphology control, thereby reducing dV failures and increasing the yield and reliability of the lithium battery. Brief explanation of the drawing

[0016] Figure 1 is a schematic cross-sectional view of a membrane to illustrate the short crystal region in the membrane. Figure 2 is a load curve graph to explain the load area ratio of surface roughness. FIG. 3 is a schematic diagram of a lithium battery including an electrode assembly wound in the form of a flat jelly roll according to an exemplary embodiment. FIG. 4 is a schematic diagram of a lithium battery comprising an electrode assembly wound in the form of a cylinder-shaped jelly roll according to an exemplary embodiment. Specific details for implementing the invention

[0017] The present inventive concept described below is subject to various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present inventive concept to specific embodiments and should be understood to include all modifications, equivalents, or substitutions that fall within the scope of the description of the present inventive concept.

[0018] The terms used below are used merely to describe specific embodiments and are not intended to limit the creative concept. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the following, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, components, materials, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, components, materials, or combinations thereof. The " / " used below may be interpreted as "and" or "or" depending on the context.

[0019] In the drawings, thicknesses have been enlarged or reduced to clearly represent various layers and regions. Throughout the specification, the same reference numerals have been used for similar parts. Throughout the specification, when a part such as a layer, film, region, or plate is described as being "on" or "above" another part, this includes not only cases where it is directly above another part but also cases where there is another part in between. Throughout the specification, terms such as "first," "second," etc., may be used to describe various components, but the components should not be limited by these terms. The terms are used solely for the purpose of distinguishing one component from another.

[0021] A separator and a lithium battery employing the same according to exemplary embodiments are described in more detail below.

[0022] Generally, short circuits are prone to occur in separators where the thickness is thin. Figure 1 is a schematic cross-sectional view of a separator to explain the short-circuit determination site in the separator. As shown in Figure 1, the deepest of the protrusions on the surface irregularities of both surfaces come into contact with each other; that is, the area where the distance between the protrusions on both sides is shorter (e.g., area A) than the area where the distance is longer (e.g., area B) is weaker in insulation, so a short circuit is likely to occur. In the separator illustrated in Figure 1, the area where the distance between the protrusions on both sides is shortest (area A) becomes the short-circuit determination site of the separator.

[0023] A separator according to one embodiment has surface morphology control performed to increase the insulating properties of the separator.

[0024] A separator according to one embodiment comprises a porous substrate having surface irregularities, and the area of ​​the protruding grooves in the surface irregularities of the porous substrate is 12% or more and less than 40%.

[0025] The above separator has surface irregularities on at least one or both sides of a porous substrate, and by controlling the surface morphology so that the area of ​​the protruding grooves in the surface irregularities of the porous substrate is 12% or more and less than 40%, the insulation of the separator can be increased and dV defects can be reduced. Accordingly, the yield and reliability of the lithium battery can be increased.

[0026] If the area of ​​the protruding bone is less than 12%, weak points are concentrated and insulation becomes poor, and if the area of ​​the protruding bone is 40% or more, electrolyte wettability becomes very low and the resistance of the battery may increase.

[0027] In this specification, the protruding bone portion and the area of ​​the protruding bone portion are defined as follows.

[0028] FIG. 2 is a load curve graph for explaining the load area ratio of surface roughness. Referring to FIG. 2, a load curve is created by measuring the surface roughness of the porous substrate of the separator membrane, and the surface roughness can be measured, for example, based on ISO 25178. Parameters for the load area ratio can be calculated using the load curve.

[0029] "Load area ratio" refers to the ratio of the load area (the area of ​​the region where the height is greater than or equal to c) to a certain height c in surface roughness. "Load curve" refers to a curve representing the height at which the load area ratio changes from 0% to 100%. "Equivalent straight line" is defined as a straight line where the slope of the secant line of a load curve with a load area ratio difference of 40% is gentlest at the center of the load curve, and the squared deviation term in the vertical axis direction is minimized with respect to this center. As shown in Fig. 2, the load area ratio corresponding to the load curve corresponding to the value (y-intercept) corresponding to the load area ratio of 0% of the equivalent straight line is called Smr1. The load area ratio corresponding to the load curve corresponding to the value corresponding to the load area ratio of 100% of the equivalent straight line is called Smr2. The Smr1 to Smr2 portion is called the "core portion," 0% to Smr1 is called the "protruding mound portion," and Smr2 to 100% is called the "protruding bone portion."

[0030] In the load curve graph of FIG. 2, Smr1 represents the load area ratio at the intersection of the height of the upper part of the core and the load curve, and Smr2 represents the load area ratio at the intersection of the height of the lower part of the core and the load curve. In the load curve graph of FIG. 2, the area corresponding to 0% to Smr1 is the protruding peak, the area corresponding to Smr1 to Smr1 is the core, and the area corresponding to Smr2 to 100% is the protruding valley.

[0031] In a separator according to one embodiment, the area of ​​such protruding grooves obtained by measuring surface roughness in the surface irregularities of a porous substrate is 12% or more and less than 40%. For example, the area of ​​protruding grooves in the surface irregularities of a porous substrate may be 13% to 35%, and specifically, for example, 15% to 30%. Within the above range, the insulation performance of the separator is improved, and dV defects can be reduced.

[0032] The insulating properties of the above separator can be evaluated by measuring the breakdown voltage (BDV). The stationary BDV and moving BDV of the above separator can be measured, for example, by the methods of Evaluation Examples 3 and 4 described below.

[0033] According to one embodiment, the separator may have a static BDV of 160 V / μm or more per unit thickness. For example, the separator may have a static BDV of 160 V / μm to 200 V / μm per unit thickness. For example, the separator may have a static BDV of 165 V / μm to 180 V / μm per unit thickness. Within the above range, the separator has high insulation properties and can reduce dV defects. Here, as the area of ​​the protruding groove increases, the areas vulnerable to insulation loss become widely dispersed, and the value of the static BDV increases relatively.

[0034] According to one embodiment, the difference between the stationary BDV and the moving BDV of the separator may be 600V or less. For example, the difference between the stationary BDV and the moving BDV of the separator may be 550V or less. For example, the difference between the stationary BDV and the moving BDV of the separator may be 500V or less. For example, the difference between the stationary BDV and the moving BDV of the separator may be 450V or less. Within the above range, the separator can reduce dV defects while maintaining high insulation performance. Here, in a separator with a small area of ​​protruding grooves, the parts vulnerable to insulation are concentrated and become more vulnerable compared to those with widely distributed grooves, and since the moving BDV measures a larger area than the stationary BDV, a larger difference between the two measurements may occur.

[0035] The porous substrate included in the above separator may be a porous membrane containing polyolefin. Polyolefin has an excellent short-circuit prevention effect and can also improve battery stability through a shutdown effect. For example, the porous substrate may be a membrane composed of a resin such as polyolefins including polyethylene, polypropylene, polybutene, and polyvinyl chloride, or mixtures or copolymers thereof, but is not necessarily limited to these; any porous membrane that can be used in the relevant technical field is acceptable. For example, a porous membrane composed of a polyolefin-based resin; a porous membrane woven from polyolefin-based fibers; a nonwoven fabric containing polyolefin; or an aggregate of insulating material particles may be used. For example, a porous membrane containing polyolefin has excellent applicability of a binder solution for manufacturing a coating layer formed on the porous substrate, and can increase the capacity per unit volume by reducing the membrane thickness of the separator and increasing the proportion of active material in the battery.

[0036] The polyolefin used as a material for the porous substrate may be, for example, a homopolymer, copolymer, or mixture thereof, such as polyethylene or polypropylene. The polyethylene may be low-density, medium-density, or high-density polyethylene, and high-density polyethylene may be used for mechanical strength. In addition, two or more types of polyethylene may be mixed for the purpose of imparting flexibility. The polymerization catalyst used in the preparation of polyethylene is not particularly limited, and Ziegler-Natta-based catalysts, Phillips-based catalysts, or metallocene-based catalysts may be used. For the purpose of achieving both mechanical strength and high permeability, the weight-average molecular weight of the polyethylene may be 100,000 to 12 million, for example, 200,000 to 3 million. The polypropylene may be a homopolymer, a random copolymer, or a block copolymer, and may be used alone or in a mixture of two or more. Furthermore, the polymerization catalyst is not particularly limited, and Ziegler-Natta catalysts or metallocene catalysts may be used. In addition, the stereoregularity is not particularly limited, and isotactic, syndiotactic, or atactic types may be used, but inexpensive isotactic polypropylene may be used. Furthermore, to the extent that the effects of the present invention are not compromised, additives such as polyolefins other than polyethylene or polypropylene and antioxidants may be added to the polyolefin.

[0037] The porous substrate included in the separator may include polyolefins such as polyethylene and polypropylene, for example, and a multilayer membrane of two or more layers may be used. Mixed multilayer membranes such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used, but are not limited to these; any material and composition that can be used as a porous substrate in the relevant technical field is acceptable. The porous substrate included in the separator may include, for example, a diene-based polymer prepared by polymerizing a monomer composition containing a diene-based monomer. The diene-based monomer may be a conjugated diene monomer or a non-conjugated diene monomer. For example, the above diene monomer includes one or more selected from the group consisting of 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, chloroprene, vinylpyridine, vinylnorbornene, dicyclopentadiene, and 1,4-hexadiene, but is not necessarily limited to these, and any monomer that can be used as a diene monomer in the relevant technical field is acceptable.

[0038] The thickness of the porous substrate included in the separator may be 1 μm to 100 μm. For example, the thickness of the porous substrate may be 1 μm to 50 μm. For example, the thickness of the porous substrate may be 1 μm to 30 μm. For example, the thickness of the porous substrate may be 5 μm to 20 μm. For example, the thickness of the porous substrate may be 5 μm to 15 μm. For example, the thickness of the porous substrate may be 5 μm to 10 μm. If the thickness of the porous substrate is less than 1 μm, it may be difficult to maintain the mechanical properties of the separator, and if the thickness of the porous substrate exceeds 100 μm, the internal resistance of the lithium battery may increase. The porosity of the porous substrate included in the separator may be 5% to 95%. If the porosity is less than 5%, the internal resistance of the lithium battery may increase, and if the porosity exceeds 95%, it may be difficult to maintain the mechanical properties of the porous substrate. The pore size of the porous substrate in the separator may be 0.01 μm to 50 μm. For example, the pore size of the porous substrate in the separator may be 0.01 μm to 20 μm. For example, the pore size of the porous substrate in the separator may be 0.01 μm to 10 μm. If the pore size of the porous substrate is less than 0.01 μm, the internal resistance of the lithium battery may increase, and if the pore size of the porous substrate exceeds 50 μm, it may be difficult to maintain the mechanical properties of the porous substrate.

[0039] The above-described membrane can be manufactured, for example, through wet and / or dry methods commonly known in the art.

[0040] A lithium battery according to another embodiment includes a positive electrode, a negative electrode, and the aforementioned separator disposed between the positive electrode and the negative electrode. According to one embodiment, the lithium battery includes an electrode assembly comprising a positive electrode, a negative electrode, and the aforementioned separator disposed between the positive electrode and the negative electrode, and the electrode assembly may have a form wound in the shape of a jelly roll. By including the aforementioned separator in the lithium battery, black spot defects can be reduced, thereby improving quality, and since the adhesion between the electrodes (positive and negative electrodes) and the separator is increased, volume change during charging and discharging of the lithium battery can be suppressed. Accordingly, degradation of the lithium battery accompanied by volume change can be suppressed, thereby improving the lifespan characteristics of the lithium battery.

[0041] Lithium batteries can be manufactured, for example, in the following ways.

[0042] First, a negative electrode active material composition is prepared by mixing a negative electrode active material, a conductive material, a binder, and a solvent. The negative electrode active material composition is directly coated onto a metal current collector to manufacture a negative electrode plate. Alternatively, the negative electrode active material composition may be cast onto a separate support, and then a film peeled from the support is laminated onto a metal current collector to manufacture a negative electrode plate. The negative electrode is not limited to the forms listed above and may be in a form other than those listed above.

[0043] The cathode active material may be a carbon-based material. The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as natural graphite or artificial graphite in a non-shaped, plate-like, flake-like, spherical, or fibrous form, and the amorphous carbon may be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, etc.

[0044] In addition, a composite of the carbon-based material and the non-carbon-based material may be used as the cathode active material, or a non-carbon-based material may be additionally included in addition to the carbon-based material.

[0045] Non-carbon materials may include, for example, one or more selected from the group consisting of a metal capable of forming an alloy with lithium, an alloy of a metal capable of forming an alloy with lithium, and an oxide of a metal capable of forming an alloy with lithium.

[0046] For example, the metals that can be alloyed with the lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloys (wherein Y is an alkali metal, alkaline earth metal, group 13–16 element, transition metal, rare earth element, or a combination thereof, and is not Si), Sn-Y alloys (wherein Y is an alkali metal, alkaline earth metal, group 13–16 element, transition metal, rare earth element, or a combination thereof, and is not Sn), etc. The element Y may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

[0047] For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc.

[0048] For example, the above non-transfer metal oxides are SnO2, SiO2 x (0 <x<2) 등일 수 있다.

[0049] Specifically, the above negative electrode active material is Si, Sn, Pb, Ge, Al, SiOx(0 <x≤2), SnOy(0<y≤2), Li4Ti5O 12It may be one or more selected from the group consisting of TiO2, LiTiO3, and Li2Ti3O7, but is not necessarily limited to these, and any non-carbon-based negative electrode active material used in the relevant technical field is acceptable.

[0050] As conductive materials, acetylene black, ketjenblack, natural graphite, artificial graphite, carbon black, acetylene black, ketjenblack, carbon fiber, metal powders such as copper, nickel, aluminum, and silver, metal fibers, etc., may be used, and one or more types of conductive materials such as polyphenylene derivatives may be used in combination, but are not limited to these, and any material that can be used as a conductive material in the relevant technical field may be used. In addition, the aforementioned crystalline carbon-based material may be added as a conductive material.

[0051] As a binder, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber-based polymer may be used, but are not limited to these, and any that can be used as a binder in the relevant technical field may be used.

[0052] As a solvent, N-methylpyrrolidone, acetone, or water may be used, but is not limited to these, and any solvent that can be used in the relevant technical field may be used.

[0053] The content of the negative electrode active material, conductive material, binder, and solvent is at a level typically used in lithium batteries. Depending on the application and composition of the lithium battery, one or more of the conductive material, binder, and solvent may be omitted.

[0054] Meanwhile, the binder used in the above cathode manufacturing may be the same as the coating composition included in the coating layer of the above separator.

[0055] Next, a positive active material composition is prepared by mixing a positive active material, a conductive material, a binder, and a solvent. The positive active material composition is directly coated and dried onto a metal current collector to manufacture a positive plate. Alternatively, the positive active material composition may be cast onto a separate support, and then a film peeled from the support is laminated onto a metal current collector to manufacture a positive plate.

[0056] As a positive electrode active material, it may include one or more selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide, but is not necessarily limited to these, and any positive electrode active material available in the relevant technical field may be used.

[0057] For example, Li a A 1-b B b D2(wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li a E 1-b B b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B b O 4-c D c (In the above equation, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c D α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Co b B c O 2-α F α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Lia Ni 1-b-c Co b B c O 2-α F2(wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c D α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b B c O 2-α F α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c O 2-α F2(wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2(wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d GeO2(wherein the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2(in the above equation, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG bO2(in the above equation, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a MnG b O2(in the above equation, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4(wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); compounds represented by any one of the chemical formulas of LiFePO4 may be used:

[0058] In these chemical formulas, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0059] Of course, a coating layer on the surface of this compound may be used, or a mixture of the compound and a compound having a coating layer may be used. This coating layer may include a coating element compound of an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of a coating element. The compounds forming this coating layer may be amorphous or crystalline. As coating elements included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. For the coating layer formation process, any coating method may be used as long as the compound can be coated using these elements in a way that does not adversely affect the physical properties of the cathode active material (e.g., spray coating, immersion method, etc.). Since this is a matter that is well understood by those skilled in the art, a detailed explanation will be omitted.

[0060] For example, LiNiO2, LiCoO2, LiMn x O 2x (x=1, 2), LiNi 1-x Mn x O2(0 <x<1), LiNi 1-x-y Co x Mn y O2 (0≤x≤0.5, 0≤y≤0.5), LiFeO2, V2O5, TiS, MoS, etc. can be used.

[0061] In the positive electrode active material composition, the conductive material, binder, and solvent may be the same as those used in the negative electrode active material composition. Meanwhile, it is also possible to form pores inside the electrode plate by further adding a plasticizer to the positive electrode active material composition and / or the negative electrode active material composition.

[0062] The content of the cathode active material, conductive material, general binder, and solvent is at a level typically used in lithium batteries. Depending on the application and composition of the lithium battery, one or more of the above conductive material, general binder, and solvent may be omitted.

[0063] Meanwhile, the binder used in the manufacture of the anode may be the same as the coating composition included in the coating layer of the separator.

[0064] Next, the aforementioned composite separator is placed between the anode and the cathode.

[0065] In an electrode assembly comprising an anode, a separator, and a cathode, the separator disposed between the anode and the cathode comprises a fully porous substrate as described above; and a coating layer disposed on both sides of the porous substrate, wherein the coating layer comprises the coating composition for the separator described above.

[0066] The separator may be prepared separately and placed between the positive and negative electrodes. Alternatively, the separator may be prepared by undergoing a formation step in which an electrode assembly comprising a positive electrode, a separator, and a negative electrode is wound into a jelly roll, the jelly roll is placed in a battery case or pouch, the jelly roll is pre-charged by thermally softening it under pressure while it is placed in the battery case or pouch, the charged jelly roll is hot-rolled, the charged jelly roll is cold-rolled, and the charged jelly roll is charged and discharged under pressure.

[0067] Next, the electrolyte is prepared.

[0068] Electrolytes can be in a liquid or gel state.

[0069] For example, the electrolyte may be an organic electrolyte. Additionally, the electrolyte may be a solid. For example, it may be boron oxide, lithium oxynitride, etc., but is not limited to these; any material that can be used as a solid electrolyte in the relevant technical field may be used. The solid electrolyte may be formed on the cathode by a method such as sputtering.

[0070] For example, an organic electrolyte can be prepared. The organic electrolyte can be prepared by dissolving a lithium salt in an organic solvent.

[0071] Any organic solvent that can be used as an organic solvent in the relevant technical field may be used. For example, carbonates such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, and dibutyl carbonate; propionates such as ethyl propionate, methyl propionate, and propyl propionate; benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

[0072] Any lithium salt that can be used as a lithium salt in the relevant technical field may be used. For example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (FSO2)2NLi, lithium chloroborate, compounds represented by the following chemical formulas, mixtures thereof, or combinations thereof may be used.

[0073]

[0074] The content of the lithium salt can be, for example, 0.1 to 5 M.

[0075] As shown in FIG. 3, the lithium battery (1) includes a positive electrode (3), a negative electrode (2), and a composite separator (4). The above-described positive electrode (3), negative electrode (2), and separator (4) are wound into an electrode assembly in the form of a flat jelly roll and then housed in a pouch (7). Subsequently, an organic electrolyte is injected into the pouch (7) and sealed to complete the lithium battery (1).

[0076] As shown in FIG. 4, the lithium battery (1) comprises a positive electrode (3), a negative electrode (2), and a separator (4). The aforementioned positive electrode (3), negative electrode (2), and separator (4) are wound into an electrode assembly in the form of a cylinder jelly roll and then housed in a battery case (5). Subsequently, an organic electrolyte is injected into the battery case (5) and sealed with a cap assembly (6) to complete the lithium battery (1). The battery case may be cylindrical, prismatic, thin-film, etc. The lithium battery may be a lithium-ion battery. The lithium battery may be a lithium-polymer battery.

[0077] Lithium batteries are suitable for electric vehicles (EVs) due to their excellent high-rate and lifespan characteristics. For example, they are suitable for hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs).

[0078] The creative concept is explained in more detail through the following examples and comparative examples. However, the examples are intended to illustrate the creative concept and do not limit the scope of the creative concept to these examples alone.

[0080] Example 1

[0081] (Preparation of separator)

[0082] A separator with a thickness of 20 μm and a protruding lobe area of ​​15% was prepared. The protruding lobe area was measured by the method of Evaluation Example 1 described below.

[0083] (Manufacturing of the cathode)

[0084] A cathode active material slurry was prepared by mixing 97 wt% of graphite particles with an average particle size of 25 μm, 1.5 wt% of styrene-butadiene rubber (SBR) binder, and 1.5 wt% of carboxymethylcellulose (CMC), adding the mixture to distilled water, and stirring for 60 minutes using a mechanical stirrer. The slurry was applied onto a copper current collector with a thickness of 10 μm using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, dried again under vacuum conditions at 120°C for 4 hours, and then rolled to produce a cathode plate.

[0085] (Manufacturing of the anode)

[0086] A cathode active material slurry was prepared by mixing 97 wt% LiCoO2, 1.5 wt% carbon black powder as a conductive material, and 1.5 wt% polyvinylidene fluoride (PVdF), adding the mixture to an N-methyl-2-pyrrolidone solvent, and stirring for 30 minutes using a mechanical stirrer. The slurry was applied onto a 20 μm thick aluminum current collector using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, dried again under vacuum conditions at 120°C for 4 hours, and then rolled to produce a cathode plate.

[0087] (Manufacturing of lithium batteries - Manufacturing of electrode assemblies and jelly rolls)

[0088] An electrode assembly jelly roll was prepared by placing a separator between the anode and cathode plates manufactured above and winding them. The jelly roll was inserted into a pouch, an electrolyte was injected, and the pouch was vacuum-sealed.

[0089] The electrolyte used was 1.3 M LiPF6 dissolved in a 3 / 5 / 2 (volume ratio) mixed solvent of ethylene carbonate (EC) / ethylmethyl carbonate (EMC) / diethyl carbonate (DEC).

[0090] 250 kgf / cm² in the jelly roll inserted in the pouch 2While applying pressure, it was thermally softened at a temperature of 70°C for 1 hour and pre-charged to 50% of the SOC.

[0091] 200 kgf / cm² for the above jelly roll 2 Hot pressing was performed at a temperature of 85°C for 180 seconds while applying pressure. During the hot pressing process, the binder transitions from a gel state to a sol state, generating adhesion between the anode / cathode and the separator.

[0092] Subsequently, 200 kgf / cm² to the above jelly roll 2 Cold pressing was performed at a temperature of 22-23°C for 90 seconds while applying pressure. During the hot rolling process, the binder transitioned from a sol state to a gel state.

[0093] Next, degass the above pouch, and 200 kgf / cm² to the jelly roll 2 While applying pressure, constant current charging was performed at a temperature of 45°C for 1 hour at a current rate of 0.2C until the voltage reached 4.3V, and constant voltage charging was performed while maintaining 4.3V until the current reached 0.05C. Subsequently, a formation step was performed by repeating a cycle of discharging at a constant current of 0.2C until the voltage reached 3.0V during discharge 5 times.

[0094] Example 2

[0095] A lithium battery was manufactured by carrying out the same process as in Example 1, except that a separator with a thickness of 14 μm and a protruding groove area of ​​17% was used.

[0096] Example 3

[0097] A lithium battery was manufactured by carrying out the same process as in Example 1, except that a separator with a thickness of 6 μm and a protruding groove area of ​​20% was used.

[0098] Example 4

[0099] A lithium battery was manufactured by carrying out the same process as in Example 1, except that a separator with a thickness of 20 μm and a protruding groove area of ​​30% was used.

[0100] Comparative Example 1

[0101] A lithium battery was manufactured by carrying out the same process as in Example 1, except that a separator with a thickness of 20 μm and an area of ​​11% of the protruding groove was used.

[0102] Comparative Example 2

[0103] A lithium battery was manufactured by carrying out the same process as in Example 1, except that a separator with a thickness of 14 μm and a protruding groove area of ​​10.5% was used.

[0104] Comparative Example 3

[0105] A lithium battery was manufactured by carrying out the same process as in Example 1, except that a separator with a thickness of 6 μm and an area of ​​11% of the protruding groove was used.

[0106] Comparative Example 4

[0107] A lithium battery was manufactured by carrying out the same process as in Example 1, except that a separator with a thickness of 20 μm and a protruding groove area of ​​40% was used.

[0109] Evaluation Example 1: Measurement of the protruding bone area of ​​the separator

[0110] Each separation membrane used in Examples 1 to 4 and Comparative Examples 1 to 4 was laid flat on a slide glass and fixed on all four sides to prepare the sample. The sample was placed on a 3D microscope (KEYENCE VK-X model) and the surface of the sample was observed using an x50 lens.

[0111] The surface roughness of the porous substrate was measured according to ISO 25178, and after plotting the load curve according to thickness, the area of ​​the protruding groove corresponding to (100 - SMR2)% was calculated.

[0112] The calculated area of ​​the protruding bone is shown in Table 1 below.

[0113] Evaluation Example 2: Stationary BDV Measurement

[0114] A SUS plate was connected to the (-) electrode of the voltage tester KIKUSUI (TOS-5300), and the (+) electrode was connected to the broom-shaped probe. The current was set to DC mode, the voltage boost was set to 4500V for 8 seconds, and the detection voltage was set to 0.3mA.

[0115] Each separator used in Examples 1 to 4 and Comparative Examples 1 to 4 was spread flat on a SUS plate, and a probe was placed on the separator. Then, the voltage at the point where the voltage rise stopped (breakdown, short) under the above conditions was measured, and that voltage was set as the breakdown voltage (BDV) value.

[0116] The measured static BDV values ​​and static BDV values ​​per unit thickness are shown in Table 1 below.

[0117] Evaluation Example 3: Moving BDV Measurement

[0118] The initial voltage was set using the [Stop BDV-500]V value measured in Evaluation Example 2 above, and when the set voltage was reached, the probe was moved in the MD direction for 8 seconds without removing it from the separator. When the probe was moved and a breakdown occurred in the separator and current flow occurred, the voltage was set to +100V and the above method was repeated. When a breakdown did not occur three consecutive times and current flow did not occur, this voltage was set as the moving BDV value.

[0119] The measured moving BDV values ​​and the difference between stationary BDV and moving BDV are shown in Table 1 below.

[0120] Evaluation Example 4: dV defect measurement

[0121] For the lithium batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 4, the capacity was charged to 30% and aging was performed at room temperature for 24 hours. The OCV was measured, and the OCV was measured again 80 hours later. The difference between the measured OCV values ​​was averaged, and cells with a value 0.4 mV or lower than the average were defined as dV defective. The dV defect rate was measured using the above method, and the results are shown in Table 1 below.

[0122] Evaluation Example 5: Cell Resistance Measurement

[0123] An ion blocking cell for resistance measurement was manufactured by carrying out the following method using each of the separators used in Examples 1 to 4 and Comparative Examples 1 to 4 and the electrolyte obtained according to the method below.

[0124] As the electrolyte, a solution containing 1.1M LiPF6 dissolved in a solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3 was used. For the fabrication of the ion blocking cell, the separator was cut into a circular shape with a diameter of 19mm, the separator was placed on the top of the case, a gasket was placed on top of it, and 1 to 2 drops of the electrolyte were applied. A spacer with a thickness of 1mm was placed on top, followed by a spacer with a thickness of 0.5mm. Subsequently, a spring was placed on top of the resulting product to prevent upper and lower gaps from forming inside the CR2032, and a cap was placed over it to seal it using a dedicated clamper. For the manufacture of the CR2032, the CR2032 material from Hohsen was used.

[0125] The resistance of the ion blocking cell 6 hours after the injection of the electrolyte was measured using electrochemical impedance spectroscopy (EIS), and the results are shown in Table 1 below.

[0126] Thickness (㎛) Area of ​​protruding bone (%) Stop BDV(V) At-station BDV per unit thickness (V / ㎛) Move BDV(V) Stop BDV-Move BDV(V) dV defect rate / thickness (ppm / ㎛) Cell resistance (mΩ) 6 hours after electrolyte injection Example 1 20 15 3456 172.8 3000 456 50 0.020 Example 2 14 17 2347 167.6 2000 347 51 0.015 Example 3 6 20 1079 179.8 600 479 49 0.012 Example 4 20 30 3444 172.2 3100 344 48 0.025 Comparative Example 1 20 11 2631 131.6 1900 731 100 0.020 Comparative Example 2 14 10.5 2153 153.8 1500 653 103 0.015 Comparative Example 3 6 11 850 141.7 200 650 98 0.012 Comparative Example 4 20 40 3420 171.0 3200 220 43 0.300

[0127] As shown in Table 1, it can be seen that the separators of Examples 1 to 4 have increased insulation properties compared to the separators of Comparative Examples 1 to 4, resulting in a decrease in dV defects. It can be seen that when the area of ​​the protruding groove is 40% or more (Comparative Example 4), the electrolyte wettability is very low, and the resistance of the battery increases.

[0129] Although one embodiment has been described above with reference to the drawings and examples, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the scope of protection of the present invention should be determined by the appended claims. Explanation of the symbols

[0130] 1: Lithium battery 2: Negative electrode 3: Positive electrode 4: Separator 5: Battery case 6: Cap assembly 7: Pouch

Claims

Claim 1 A separator comprising a porous substrate having surface irregularities, wherein the area of ​​the protruding grooves in the surface irregularities of the porous substrate is 15% to 30% based on the total surface area, and the area of ​​the protruding grooves is calculated as a 100% difference from the Smr2 value on the load curve obtained by measuring the surface roughness of the porous substrate, and the Smr2 value represents the load area ratio at the intersection of the height of the lower part of the core and the load curve. Claim 2 delete Claim 3 In claim 1, the separator is a separator having a stationary BDV of 160 V / μm or more per unit thickness. Claim 4 In claim 1, the separator is a separator having a stationary BDV per unit thickness of 160 V / μm to 200 V / μm. Claim 5 In claim 1, the separator is a separator in which the difference between the stationary BDV and the moving BDV is 600V or less. Claim 6 A separation membrane according to claim 1, wherein the thickness of the porous substrate is in the range of 1 to 100 μm. Claim 7 In claim 1, the porous substrate is a separator that is a porous membrane comprising a polyolefin. Claim 8 A lithium battery comprising: a positive electrode; a negative electrode; and a separator according to any one of claims 1, 3 to 7. Claim 9 In claim 8, the lithium battery is a lithium battery in which an electrode assembly comprising the positive electrode, the negative electrode, and the separator is wound in a jelly roll shape. Claim 10 A separator according to claim 1, wherein the dV defect rate / thickness (ppm / μm) relative to the thickness of the separator is 48 ppmμm to 51 ppm / μm.

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