Electrode assembly with improved electrolyte impregnation proprety, secondary battery using same, and manufacturing method thereof

Abstract

The present invention relates to an electrode assembly, a secondary battery using the same, and a method for manufacturing the same. One or more pinholes are formed in the positive electrode of the electrode assembly, and an electrolyte is introduced through the pinholes so that the electrolyte can be easily introduced into the space between the positive electrode and the separator, thereby improving the electrolyte impregnation. Accordingly, there is an advantage of improving the stability and lifespan of the battery.

Description

Technology Field

[0001] The present invention relates to an electrode assembly with improved electrolyte impregnation in the space between the anode and the separator, a secondary battery using the same, and a method for manufacturing the same. Background Technology

[0003] Recently, rechargeable secondary batteries are being widely used as an energy source for wireless mobile devices. Furthermore, secondary batteries are attracting attention as an energy source for electric vehicles and hybrid electric vehicles, which are being proposed as solutions to address air pollution caused by conventional gasoline and diesel vehicles that use fossil fuels. Consequently, the types of applications utilizing secondary batteries are becoming highly diversified due to their advantages, and it is expected that secondary batteries will be applied to a wider range of fields and products in the future than they are today.

[0004] These secondary batteries are classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium-polymer batteries depending on the composition of the electrodes and electrolytes; among these, the use of lithium-ion polymer batteries is increasing due to their low risk of electrolyte leakage and ease of manufacturing. Generally, secondary batteries are classified according to the shape of the battery case into cylindrical and prismatic batteries, in which the electrode assembly is housed in a cylindrical or prismatic metal can, and pouch-type batteries, in which the electrode assembly is housed in a pouch-type case made of an aluminum laminate sheet. The electrode assembly housed in the battery case is a power generation element capable of charging and discharging, consisting of a positive electrode, a negative electrode, and a separator structure interposed between the positive and negative electrodes. It is further classified into a jelly-roll type, which is wound with a separator interposed between long sheet-type positive and negative electrodes coated with active material, and a stack type, in which multiple positive and negative electrodes of a predetermined size are sequentially stacked with a separator interposed between them.

[0005] Among these, due to the increase in battery capacity, the large-area processing of cases and thin materials is attracting a lot of attention. Accordingly, pouch-type batteries with a structure in which a stacked or stacked / folding electrode assembly is embedded in a pouch-type battery case made of aluminum laminate sheet are gradually being used for reasons such as low manufacturing costs, small weight, and easy shape deformation. However, in the case of secondary batteries, the electrode assembly is embedded in the battery case together with the electrolyte, and thus exhibits electrical performance by being sufficiently impregnated and wetted by the electrolyte. However, when impregnated with the electrolyte, it is difficult to achieve uniform wetting across the entire surface, including the central part of the electrode assembly, due to the influence of the size and stacked structure of the electrode assembly. Consequently, there is a problem in that it is difficult to achieve a uniform electrode reaction across the entire surface of the electrode when the charge and discharge cycles proceed.

[0006] Meanwhile, when manufacturing an electrode assembly, if the electrode and the separator are in close contact, gas is trapped between the electrode and the separator, causing an uncharged area to form inside the cell, which degrades the performance of the battery. Furthermore, the thickness of the cell becomes uneven, and the electrode detaches, resulting in defects in the cell's appearance and reduced battery safety.

[0007] Furthermore, poor wetting of the electrolyte can accelerate electrode degradation and shorten the battery life, even if other electrode conditions are good.

[0008] As an example, FIG. 1 is a schematic diagram showing a structure (200) in which a conventional electrode assembly is stacked. Each electrode assembly (100) is stacked in the order of a separator (30), an anode (20), a separator (30), and a cathode (40), and the components of the electrode assembly (100) are typically laminated by applying heat and pressure. At this time, when the temperature and pressure are increased for lamination, the gap (A) between the anode (20) and the separator (120) is reduced, making it difficult for the electrolyte to penetrate into the space between the anode (20) and the separator (120). As a result, a problem arises in which the impregnation or wettability of the electrolyte in the space between the anode (20) and the separator (30) is reduced during the process of manufacturing the electrode assembly (100) accompanied by high temperature and high pressure.

[0009] On the other hand, the space between the electrode assemblies (100) is stacked only by pressure, so there is no adhesion, and since the gap (B) between the electrode assemblies (100) is wider than the gap (A) between the anode (20) and the separator (30), the inflow of electrolyte is relatively easy, so electrolyte impregnation is not a major problem.

[0010] That is, in the electrode assembly (100), the electrolyte impregnation in the space between the positive electrode (20) and the separator (30) is significantly reduced, so the electrode assembly is not sufficiently wetted with the electrolyte, which causes a problem of reduced battery efficiency and battery defects due to damage to the separator.

[0011] Therefore, there is a high need for technology that can fundamentally solve these problems. Prior art literature

[0013] Korean Patent Publication No. 2013-0031076 The problem to be solved

[0014] The present invention was devised to solve the above-mentioned problems and aims to provide an electrode assembly with improved electrolyte impregnation in the space between the anode and the separator, a secondary battery using the same, and a method for manufacturing the same. means of solving the problem

[0016] The present invention provides an electrode assembly having a pin hole in the anode. In one example, the electrode assembly according to the present invention comprises an anode, a cathode, and a separator interposed between the anode and the cathode, wherein at least one of the plurality of anodes forming the electrode assembly has a structure in which n pin holes are formed, and n may be an integer greater than or equal to 1.

[0017] In addition, the pinhole is a structure formed in one or more of the anodes, excluding the anode positioned at the outermost angle among the plurality of anodes.

[0018] In addition, regarding the overlapping area among the regions divided into three equal intervals based on the MD (machine direction) direction on the surface of the anode and the regions divided into three equal intervals based on the TD (traverse direction) direction on the surface of the anode, the pin hole is formed in the area where the intermediate region in the MD direction and the intermediate region in the TD direction intersect.

[0019] Meanwhile, the pinhole may have an area of ​​0.001% to 1% of the total area of ​​one side of the anode.

[0020] In another example, the electrode assembly includes at least one pin hole in the cathode, wherein the pin hole formed in the cathode may be formed at a position corresponding to the pin hole formed in the anode.

[0021] Furthermore, the pinhole formed in the cathode may have the same size as the pinhole formed in the anode.

[0023] Meanwhile, the present invention provides a secondary battery comprising an electrode assembly.

[0024] In one example, a secondary battery according to the present invention may include an electrode assembly described above, a case surrounding the electrode assembly, and an electrolyte injected into the case and impregnated into the electrode assembly.

[0025] Furthermore, it may be a pouch-type secondary battery comprising the electrode assembly described above, a pouch surrounding the electrode assembly, and an electrolyte injected into the case and impregnated into the electrode assembly.

[0027] Meanwhile, the present invention provides a method for manufacturing a secondary battery including an electrode assembly.

[0028] In one example, a method for manufacturing a secondary battery according to the present invention may include the steps of: manufacturing an electrode assembly by stacking a positive electrode with a pinhole formed therein, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; housing the electrode assembly in a case; and injecting an electrolyte into the case.

[0029] In addition, the pin hole formed in the anode can be formed simultaneously when notching the anode to form an electrode tab.

[0030] In addition, after the step of injecting the electrolyte into the above case, a step of waiting for 1 minute to 30 hours may be further included. Effects of the invention

[0032] The present invention has at least one pin hole formed in the anode, and allows the electrolyte to flow in through the pin hole, thereby increasing the electrolyte impregnation of the electrode assembly and preventing the phenomenon of gas being trapped between the anode and the separator through the pin hole, which can improve the safety of the battery and reduce the occurrence of defects. Brief explanation of the drawing

[0034] Figure 1 illustrates a stacked conventional electrode assembly. FIG. 2 illustrates an anode with a pin hole formed therein, which is an embodiment of the present invention. FIG. 3 shows a cross-section of the center of an electrode assembly including an anode with a pin hole formed therein, which is an embodiment of the present invention. FIG. 4 shows a cross-section of the center of an electrode assembly including an anode and a cathode with a pin hole formed therein, which is an embodiment of the present invention. Specific details for implementing the invention

[0035] The present invention will be described in detail below. Prior to this, terms or words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor may appropriately define the concepts of terms to best describe their invention, they must be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0037] The present invention provides an electrode assembly with improved electrolyte impregnation in the space between the anode and the separator.

[0038] In one example, the electrode assembly according to the present invention comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein at least one of the plurality of positive electrodes forming the electrode assembly forms n pin holes, and n may be an integer greater than or equal to 1. n represents the number of positive electrodes forming the electrode assembly or the number of positive electrodes stacked to overlap within the electrode assembly. For example, the electrode assembly is an electrode assembly forming a pouch-type battery, and the number of positive electrodes may be selected from the range of 1 to 100.

[0039] Among the plurality of anodes forming the electrode assembly, there may be at least one anode having a pinhole formed therein. For example, the electrode assembly may be formed by stacking electrode assemblies from bottom to top in the order of a separator, a cathode, a separator, and an anode, and if the anodes of the electrode assembly are stacked in four layers, the anodes stacked in the order of the second and third from the bottom surface may have a pinhole formed therein. In this case, the anodes stacked in the order of the second and third may have one or more pinholes formed therein.

[0040] This allows for the appropriate selection of an anode to form a pinhole by considering the degree of stacking of multiple electrode assemblies and the electrolyte impregnation properties.

[0041] Meanwhile, there may be at least one pinhole formed in the anode. The number of pinholes can be appropriately selected by considering the anode area, the degree of adhesion between the anode and the separator, the degree of stacking of the electrode assembly unit cells, and the space between the anode and the separator. If the number of pinholes is insufficient, it becomes difficult to achieve the objective of impregnating the electrolyte between the anode and the separator; if the number is too large, the manufacturing process becomes complicated, and there is a risk of internal short circuits occurring due to direct contact between the anode and the cathode in the event of separator damage; therefore, an appropriate number of pinholes must be formed.

[0042] Pinholes can be circular, elliptical, or polygonal in planar form. The shape of the pinhole is not particularly restricted, as long as it allows for smooth flow of the electrolyte. Additionally, if more than one pinhole is formed, the shapes of each pinhole do not necessarily have to match.

[0043] Meanwhile, the pinhole may have an area of ​​0.00.1% to 1% of the total area of ​​one side of the anode. If the pinhole area is less than 0.00.1%, it becomes difficult for the electrolyte to flow through the pinhole, so the desired effect of improving electrolyte impregnation cannot be achieved, and if it exceeds 1%, the unusable area of ​​the electrode assembly increases, which may cause a problem of reduced capacity relative to the size of the electrode assembly.

[0044] Meanwhile, pinholes may be formed in one or more of the anodes among the plurality of anodes, excluding the anode positioned at the outermost position. Specifically, the anode positioned at the outermost position among the plurality of anodes forming the electrode assembly may have better electrolyte impregnation properties because it has a larger surface area in contact with the electrolyte than the anode located on the inner side. Therefore, when the number of pinholes is limited, pinholes may be formed preferentially in one or more of the anodes among the plurality of anodes forming the electrode assembly, excluding the anode positioned at the outermost position. As a result, the penetration of the electrolyte between the anode located on the inner side and the separator among the plurality of anodes forming the electrode assembly can be facilitated, thereby improving electrolyte impregnation properties. Additionally, gases formed on the inner side during the charging and discharging of the battery can be properly discharged through the pinholes, preventing the occurrence of gas traps.

[0045] Meanwhile, regarding the overlapping area among the regions divided into three equal intervals based on the MD (machine direction) direction on the surface of the anode and the regions divided into three equal intervals based on the TD (traverse direction) direction on the surface of the anode, the pinhole is formed in the area where the intermediate region in the MD direction and the intermediate region in the TD direction intersect. At this time, MD (machine direction) is the direction in which the active material layer is applied during the process of applying the active material layer to the surface of the anode, and TD (traverse direction) is a direction perpendicular to the direction in which the active material layer is applied.

[0046] When a pinhole is placed in the innermost region of the overlapping area, the electrolyte that flows in most efficiently through the pinhole can move evenly through the space between the anode and the separator. This improves the impregnation of the electrolyte in the central region, where it is difficult to flow the electrolyte compared to other parts of the electrode assembly. Consequently, uniform wetting of the electrolyte is possible throughout the entire space between the anode and the separator, thereby improving the electrical performance of the battery and increasing the productivity of the battery by shortening the time required for electrolyte wetting.

[0047] Meanwhile, during the charging and discharging process of a secondary battery, gas is generated inside the electrode assembly of the secondary battery. If this gas is not properly discharged to the outside of the electrode assembly, a swelling phenomenon occurs in which the secondary battery bulges. In this case, a secondary battery manufactured using an electrode assembly including a positive electrode having a pinhole according to the present invention can utilize the pinhole as a passage for the gas generated inside the electrode assembly, thereby preventing the gas from being trapped and facilitating its proper discharge to the outside of the electrode assembly. Therefore, by improving the swelling phenomenon through the pinhole formed in the positive electrode, the structural stability of the secondary battery can be enhanced.

[0048] As another example, in an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, the electrode assembly may include at least one pinhole in the negative electrode, wherein the pinhole formed in the negative electrode may be formed at a position corresponding to the pinhole formed in the positive electrode. Specifically, when a pinhole is formed in the negative electrode, it must be formed at the same position as the pinhole formed in the corresponding positive electrode with the separator in between. This is because lithium ions released from the positive electrode move to the negative electrode during the charging process, and if there is no negative electrode to receive the lithium ions, electrochemical problems may occur. If the pinhole formed in the negative electrode is not formed at the same position as the pinhole formed in the corresponding positive electrode, lithium ions moving toward the negative electrode may cause dendrites to precipitate as lithium metal at the edge of the pinhole formed in the negative electrode, and the continuously growing dendrite metal may cause a short circuit in the battery.

[0049] In addition, the pinhole formed on the negative electrode may have the same size as the pinhole formed on the positive electrode. As previously mentioned, it is desirable for the stability of the battery that the pinhole on the negative electrode, corresponding to the pinhole on the positive electrode, not only be formed in the same location but also in the same size. This is because if the size of the pinhole on the negative electrode is smaller than the size of the pinhole on the positive electrode, the lithium ions released from the positive electrode during charging will not reach the negative electrode corresponding to the positive electrode from which the lithium ions were released, potentially causing dendrites to form on the aforementioned negative electrode surface. Furthermore, this may be closely related to the capacity ratio (N / P ratio or negative ratio) of the positive and negative electrodes. That is, depending on the area of ​​the pinhole formed on the negative electrode, the negative electrode's negative electrode area becomes smaller, which can lead to a decrease in the battery's N / P ratio. Therefore, it is desirable to make the size of the pinhole on the positive electrode and the size of the pinhole on the negative electrode the same, and it would be even more desirable for the pinhole on the positive electrode and the pinhole on the negative electrode to have the same shape.

[0051] In addition, the present invention provides a method for manufacturing a secondary battery with improved electrolyte impregnation in the space between the anode and the separator.

[0052] Meanwhile, the method for manufacturing a secondary battery may include content that overlaps with the aforementioned electrode assembly, and overlapping descriptions may be omitted.

[0053] In one example, a method for manufacturing a secondary battery according to the present invention may include the steps of: manufacturing an electrode assembly by stacking a positive electrode with a pinhole formed therein, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; housing the electrode assembly in a case; and injecting an electrolyte into the case.

[0054] The step of manufacturing the above electrode assembly may include the process of manufacturing an anode and a cathode. The manufacturing of the anode and cathode involves applying an electrode slurry to one or both sides of a current collector to form a composite layer, wherein the electrode slurry may include an electrode active material, a conductive material, and a binder, and may be composed of various materials as described below.

[0055] In addition, the step of manufacturing the electrode assembly may include a process of forming a pinhole in the anode. The pinhole refers to forming at least one pinhole penetrating the composite layer and the current collector in the retaining portion, which is the part of the anode where the composite layer is formed. The size, shape, number, location, etc., of the pinhole may vary depending on the characteristics and size of the electrode assembly, the degree of stacking of the anodes of the electrode assembly, etc.

[0056] Meanwhile, among the plurality of anodes forming the electrode assembly, one or more of the anodes forming the pinholes may form n pinholes, and n may be an integer greater than or equal to 1. The anodes may be selected by considering the degree of stacking of the anodes of the electrode assembly as described above.

[0057] In the above electrode assembly, the method of bonding the positive or negative electrode of the electrode assembly to the separator may be a conventional bonding method that applies heat and pressure.

[0058] Next, the step of housing the electrode assembly in a case and injecting the electrolyte into the case includes a process of impregnating the electrolyte into the electrode assembly inserted into the case. At this time, the electrolyte may flow into the space between the laminated anode and the separator, into the space between the laminated cathode and the separator, and into the space between the stacked electrode assemblies. As previously mentioned, the space between the stacked electrode assemblies has no adhesive force and is relatively wider than the space between the laminated anode and the separator or between the cathode and the separator, making it easy for the electrolyte to flow in. In contrast, the space between the laminated anode and the separator or between the cathode and the separator has a narrow gap due to adhesion, making it difficult for the electrolyte to flow in. However, the penetration of the electrolyte into the space between the laminated anode and the separator through the pinhole formed in the anode can be facilitated, thereby improving the impregnation of the electrolyte. In addition, as described above, a pinhole can be formed on the cathode at a position corresponding to the pinhole formed on the anode, and in this case, the electrolyte can be easily introduced into the space between the laminated cathode and the separator.

[0059] In addition, the pinhole formed on the anode can be formed simultaneously when notching the anode to form the electrode tab. This allows for reducing process steps and increasing production efficiency by simultaneously performing the notching process and the pinhole formation process during the anode cutting process.

[0060] In addition, after the step of injecting the electrolyte into the above case, a step of waiting for 1 minute to 30 hours may be further included. Through the waiting time, the electrolyte can sufficiently penetrate into the electrode assembly to further improve impregnation.

[0062] In addition, the present invention provides a secondary battery with improved electrolyte impregnation in the space between the anode and the separator.

[0063] In one example, the secondary battery may be a secondary battery comprising a plurality of positive electrodes forming an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrodes forms n pinholes and n is an integer greater than or equal to 1, a case surrounding the electrode assembly, and an electrolyte injected into the case and impregnated into the electrode assembly.

[0064] In another example, the secondary battery may be a pouch-type secondary battery comprising an electrode assembly in which at least one of a plurality of positive electrodes forming an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode forms n pinholes, wherein n is an integer greater than or equal to 1, a pouch surrounding the electrode assembly, and an electrolyte injected into the case and impregnated into the electrode assembly.

[0065] Depending on the method of stacking the above electrode assemblies, they can be classified into a wound jelly-roll type and a stack type that stacks sequentially. Additionally, depending on the shape of the battery case, secondary batteries can be classified into cylindrical batteries and prismatic batteries in which the electrode assembly is embedded in a cylindrical or prismatic metal can, and pouch-type batteries in which the electrode assembly is embedded in a pouch-type case made of an aluminum laminate sheet. The secondary battery of the present invention may be a cylindrical, prismatic, or pouch-type secondary battery, and preferably may be a pouch-type secondary battery.

[0066] Meanwhile, the above case may be composed of a laminate sheet comprising a metal layer and a resin layer. Specifically, the laminate sheet may be an aluminum laminate sheet. The battery case of the laminate sheet may be composed of a lower case consisting of a recessed storage portion and an outer portion extending from the storage portion, and an upper case joined to the lower case by heat fusion.

[0067] The components of the secondary battery of the present invention will be described below.

[0068] The positive electrode, which is one of the components of a secondary battery, has a structure in which a layer of positive active material is laminated on one or both sides of a positive current collector. In one example, the layer of positive active material includes a positive active material, a conductive material, and a binder polymer, and, if necessary, may further include a positive additive commonly used in the industry.

[0069] The above-mentioned positive electrode active material may be a lithium-containing oxide, and may be the same or different. As the lithium-containing oxide, a lithium-containing transition metal oxide may be used.

[0070] For example, lithium-containing transition metal oxides are Li x CoO2(0.5 <x<1.3), Li x NiO2(0.5 <x<1.3), Li x MnO2(0.5 <x<1.3), Li x Mn2O4(0.5 <x<1.3), Li x (Ni a Co b Mn c )O2(0.5 <x<1.3, 0<a<1, 0<b<1, 0<c<1, a+b+c=1), Li x Ni 1-y Co y O2(0.5 <x<1.3, 0<y<1), Li x Co 1-y Mn y O2(0.5 <x<1.3, 0혏<1), Li x Ni 1-y Mny O2(0.5 <x<1.3, O혏<1), Li x (Ni a Co b Mn c )O4(0.5 <x<1.3, 0<a<2, 0<b<2, 0<c<2, a+b+c=2), Li x Mn 2-z Ni z O4(0.5 <x<1.3, 0<z<2), Li x Mn 2-z Co z O4(0.5 <x<1.3, 0<z<2), Li x CoPO4(0.5 <x<1.3) 및 Li x FePO4(0.5 <x<1.3)로 이루어진 군으로부터 선택되는 어느 하나 또는 이들 중 2종 이상의 혼합물일 수 있다. 또한, 상기 리튬 함유 전이금속 산화물은 알루미늄(Al) 등의 금속이나 금속 산화물로 코팅될 수도 있다. 또한, 상기 리튬 함유 전이금속 산화물 외에 황화물(sulfide), 셀렌화물(selenide) 및 할로겐화물(halide) 중 1종 이상이 사용될 수 있다.

[0071] The above positive active material may be included in the positive active material layer in a range of 94.0 to 98.5 weight percent. When the content of the positive active material satisfies the above range, it is advantageous in terms of manufacturing a high-capacity battery and providing sufficient conductivity of the positive or adhesion between electrode materials.

[0072] The current collector used in the above-mentioned anode can be any metal that is highly conductive, allows the anode active material slurry to adhere easily, and is non-reactive within the voltage range of the electrochemical device. Specifically, non-limiting examples of current collectors for the anode include foils made of aluminum, nickel, or combinations thereof. The anode active material layer further comprises a conductive material.

[0073] Carbon-based conductive materials are commonly used as the conductive materials mentioned above, including sphere-type or needle-type carbon-based conductive materials. The sphere-type carbon-based conductive material, when mixed with a binder, fills the pores—the empty spaces between active material particles—thereby improving physical contact between active materials, thereby reducing interfacial resistance and enhancing adhesion between the lower positive active material and the current collector.

[0074] Examples of the above-mentioned point-type carbon-based conductive materials include carbon black such as Denka Black, such as FX35 (Denka), SB50L (Denka), and Super-P, but are not limited thereto. Here, 'point-type (sphere type)' means having a spherical particle shape and having an average diameter (D50) of 10 to 500 nm, specifically in the range of 15 to 100 nm or 15 to 40 nm.

[0075] In contrast to the point-type carbon-based conductive material mentioned above, there is a linear (needle-type) carbon-based conductive material. The linear carbon-based conductive material may be a carbon nanotube (CNT), a vapor-grown carbon fiber (VGCF), a carbon nanofiber (CNF), or a mixture of two or more of these. Here, 'linear (needle-type)' means a particle shape such as a needle, for example, having an aspect ratio (length / diameter value) in the range of 50 to 650, specifically 60 to 300 or 100 to 300.

[0076] Point-type carbon-based conductive materials have the advantage of being more dispersed than linear conductive materials, and have the effect of improving the insulation properties of the layer because their electrical conductivity is lower than that of linear carbon-based conductive materials.

[0077] The above conductive material may be included in the positive electrode active material layer in a range of 0.5 to 5 weight percent. When the content of the conductive material satisfies the above range, it provides sufficient conductivity to the positive electrode and has the effect of lowering the interfacial resistance between the electrode current collector and the active material.

[0078] The binder polymer may be any binder commonly used in the industry without limitation. For example, the binder may be a water-insoluble polymer that is soluble in organic solvents and insoluble in water, or a water-soluble polymer that is insoluble in organic solvents and soluble in water. The water-insoluble polymer may be one or more selected from the group comprising polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), polyethylene oxide-propylene oxide copolymer (PEO-PPO), polytetrafluoroethylene (PTFE), polyimide (PI), polyetherimide (PEI), styrene butadiene rubber (SBR), polyacrylate, and derivatives thereof.

[0079] The water-soluble polymer may be one or more selected from the group including various cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), and hydroxypropylmethylcellulose phthalate (HPMCP).

[0080] The above binder polymer content is proportional to the conductive material content included in the upper and lower positive active material layers. This is because it is intended to impart adhesion to the conductive material, which has a relatively very small particle size compared to the active material; conversely, increasing the conductive material content requires more binder polymer, while decreasing the conductive material content allows for the use of less binder polymer.

[0081] The above-mentioned cathode has a structure in which a cathode active material layer is laminated on one or both sides of a cathode current collector. In one example, the cathode active material layer includes a cathode active material, a conductive material, and a binder polymer, and, if necessary, may further include a cathode additive commonly used in the industry.

[0082] The above-mentioned negative electrode active material may include carbon materials, lithium metal, silicon, or tin. When carbon materials are used as the negative electrode active material, both low-crystallinity carbon and high-crystallinity carbon may be used. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum and coal-based coke.

[0083] Non-limiting examples of current collectors used in the above-mentioned cathode include foils made of copper, gold, nickel, copper alloys, or combinations thereof. Additionally, the current collector may be used by laminating substrates made of the above materials.

[0084] In addition, the above cathode may include a conductive material and a binder commonly used in the field.

[0085] The above separator can be any porous substrate used in lithium secondary batteries, and for example, a polyolefin-based porous membrane or nonwoven fabric can be used, but is not specifically limited thereto.

[0086] Examples of the above-mentioned polyolefin-based porous membranes include membranes formed from polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polybutylene, and polypentene, either individually or as a mixture thereof.

[0087] In addition to polyolefin-based nonwoven fabrics, the above nonwoven fabric may be formed from polymers such as polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, either individually or in a mixture thereof. The structure of the nonwoven fabric may be a spunbond nonwoven fabric or a melt-blown nonwoven fabric composed of long fibers.

[0088] The thickness of the porous substrate is not particularly limited, but may be 5 to 50 μm, and the pore size and porosity present in the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.

[0089] Meanwhile, to improve the mechanical strength of the separator composed of the above porous substrate and to suppress short circuits between the anode and the cathode, a porous coating layer comprising inorganic particles and a binder polymer may be further included on at least one surface of the above porous substrate.

[0090] The above electrolyte may include an organic solvent and an electrolyte salt, and the electrolyte salt is a lithium salt. The lithium salt may be any that are commonly used in non-aqueous electrolytes for lithium secondary batteries without limitation. For example, Li as a cation + It includes, and as anion, F - , Cl - , Br - , I - , NO 3- , N(CN) 2- , BF 4- , ClO 4- , AlO 4- , AlCl 4- , PF 6- , SbF 6- , AsF 6- , BF2C2O 4- , BC4O 8- , (CF3)2PF 4- , (CF3)3PF 3- , (CF3)4PF 2- , (CF3)5PF - , (CF3)6P - , CF3SO 3- , C4F9SO 3- , CF3CF2SO 3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO 3- , CF3CO 2- , CH3CO 2- , SCN - and (CF3CF2SO2)2N - It may include at least one selected from the group consisting of

[0091] The organic solvents included in the aforementioned electrolyte may be those commonly used in electrolytes for secondary batteries without limitation, and for example, ethers, esters, amides, linear carbonates, cyclic carbonates, etc., may be used individually or in a mixture of two or more types. Among these, representative examples may include carbonate compounds that are cyclic carbonates, linear carbonates, or mixtures thereof.

[0092] Specific examples of the above-mentioned cyclic carbonate compounds include any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more of these. Examples of their halides include, but are not limited to, fluoroethylene carbonate (FEC).

[0093] In addition, specific examples of the above linear carbonate compounds may include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, or a mixture of two or more of these, but are not limited thereto.

[0094] In particular, among the carbonate-based organic solvents mentioned above, cyclic carbonates such as ethylene carbonate and propylene carbonate are high-viscosity organic solvents with high dielectric constants, which can dissociate lithium salts in the electrolyte more effectively. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with higher electrical conductivity can be produced.

[0095] In addition, among the above organic solvents, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methylpropyl ether, and ethyl propyl ether, or a mixture of two or more of these may be used, but is not limited thereto.

[0096] And among the above organic solvents, any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone, and β-caprolactone, or a mixture of two or more of these may be used, but is not limited thereto.

[0097] The electrode assembly may be a lamination / stack type structure in which unit cells are stacked with a separator interposed therein, or a stack / folding type structure in which unit cells are wound by a separator sheet.

[0098] An electrode assembly is manufactured by forming a composite layer by applying an electrode active material to positive and negative current collectors, then producing positive and negative electrodes with pinholes formed in the electrode tabs and electrode plates through a notching device, and bonding the positive and negative electrodes to a separator that does not contain pinholes. The type of separator is not limited, but may be an organic / inorganic composite porous SRS (Safety-Reinforcing Separators) separator.

[0099] Specifically, the above-described SRS separator is manufactured using inorganic particles and a binder polymer as active layer components on a polyolefin-based separator substrate. It has a uniform pore structure formed by the interstitial volume between the inorganic particles, which are the active layer components, in addition to the pore structure contained within the separator substrate itself. When using such an organic / inorganic composite porous separator, there is an advantage in that the increase in battery thickness due to swelling during the formation process can be suppressed compared to when a conventional separator is used. Furthermore, if a polymer capable of gelling when impregnated with a liquid electrolyte is used as the binder polymer component, it can also be used simultaneously as an electrolyte. In addition, the above-described organic / inorganic composite porous separator can exhibit excellent adhesion characteristics by controlling the content of the inorganic particles and the binder polymer, which are the active layer components within the separator, thus enabling the battery assembly process to be easily performed.

[0101] The present invention will be described in more detail below with reference to the drawings. Since the present invention is susceptible to various modifications and may take various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0103] (First embodiment)

[0104] FIG. 2 illustrates an anode with a pin hole formed therein, which is an embodiment of the present invention. FIG. 3 illustrates a cross-sectional view taken from the center of an electrode assembly including an anode with a pin hole formed therein, which is an embodiment of the present invention.

[0105] Referring to FIGS. 2 and 3, the electrode assembly comprises an anode (20), a cathode (40), and a separator (30) interposed between the anode (20) and the cathode (40), and the electrode assembly (100) is formed by stacking the separator (30), anode (20), separator (30), and cathode (40) in that order.

[0106] As can be seen in FIG. 2, the anode (20) is divided into a retaining portion (not shown) in which a composite layer is formed and a non-retaining portion (not shown) in which a composite layer is not formed, and an anode tab (50) is formed by notching the non-retaining portion of the anode. In the retaining portion area of ​​the anode (20), a single pin hole (10) penetrating the composite layer and the anode current collector is formed in the innermost area of ​​the overlapping region between the area divided into three equal intervals based on the MD (machine direction) direction on the surface of the anode (20) and the area divided into three equal intervals based on the TD (traverse direction) direction on the surface of the anode (20). The shape of the pin hole (10) is not limited, but as an example, it is circular, and the pin hole (10) has an area of ​​0.00.1% to 1% of the total area of ​​one surface of the anode.

[0107] FIG. 3 illustrates a cross-section of the electrode assembly (100) cut at the center using an anode (20) having a single pin hole (10) formed in FIG. 2, wherein the anode (20) is positioned between a separator (30), and the anode (20) and the separator (30) are bonded and stacked by heat and pressure. At this time, the gap (A) between the anode (20) and the separator (30) is very narrow, so the electrolyte does not easily penetrate into the space. However, by forming a pin hole (10) in the innermost area of ​​the overlapping region between the area divided into three equal intervals based on the MD (machine direction) direction on the surface of the anode (20) and the area divided into three equal intervals based on the TD (traverse direction) direction on the surface of the anode (20), the electrolyte can penetrate into the space between the anode (20) and the separator (30) through the pin hole (10), thereby improving the electrolyte wettability of the electrode assembly. In addition, by discharging the gas generated between the positive electrode (20) and the separator (30) due to the charging and discharging of the battery through the pin hole (10), the gas is prevented from being trapped inside the electrode assembly, thereby improving the occurrence of swelling.

[0108] Accordingly, the electrode assembly according to the first embodiment of the present invention and the secondary battery including the same can improve impregnation by forming a pin hole (10) in the positive electrode (20) to introduce an electrolyte into the space between the positive electrode (20) and the separator (30), and thereby minimize the unusable area of ​​the electrode assembly, thereby improving the problem of reduced battery capacity.

[0110] (Second embodiment)

[0111] FIG. 4 shows a cross-section of the center of an electrode assembly (100) including an anode (20) and a cathode (40) having a pin hole formed therein, which is an embodiment of the present invention.

[0112] Referring to FIG. 4, the electrode assembly comprises an anode (20), a cathode (40), and a separator (30) interposed between the anode (20) and the cathode (40), and the electrode assembly (100) is configured by stacking the separator (30), anode (20), separator (30), and cathode (40) in that order. In the area of ​​the retaining portion of the anode (20), the area of ​​the surface of the anode (20) is divided into three equal intervals based on the MD (machine direction) direction, and the area of ​​the surface of the anode (20) is divided into three equal intervals based on the TD (traverse direction) direction. In the overlapping area, a single pin hole (10) penetrating the composite layer and the anode current collector can be formed in the innermost area.

[0113] Additionally, a pin hole (10) penetrating the composite layer and the positive current collector can be formed in the same location as the pin hole (10) formed in the positive electrode (20) within the retaining portion of the negative electrode (40). The pin hole (10) formed in the negative electrode (40) corresponding to the pin hole (10) formed in the positive electrode (20) is formed in the same location. Furthermore, the pin hole (10) formed in the positive electrode (20) and the pin hole (10) formed in the negative electrode (40) are formed in the same shape, that is, circular, and in the same size. As previously described, in order to prevent the formation of lithium dendrites and to prevent the N / P ratio value from decreasing, thereby building an electrochemically stable battery, it is preferable that the pin hole (10) formed in the positive electrode (20) and the pin hole (10) formed in the negative electrode (40) be formed under the same conditions. In addition, the area of ​​the pin hole (10) formed in the positive electrode (20) and the pin hole (10) formed in the negative electrode (40) has an area of ​​0.00.1% to 1% of the total area of ​​one side of the positive electrode or one side of the negative electrode.

[0114] In addition to forming a pin hole (10) in the innermost area of ​​the overlapping area among the areas divided into three equal intervals based on the MD (machine direction) direction on the surface of the anode (20) and the areas divided into three equal intervals based on the TD (traverse direction) direction on the surface of the anode (20), if a pin hole (10) is additionally formed in the cathode (40) at a position corresponding to the pin hole formed in the anode (20), the penetration of the electrolyte into the space between the anode (20) and the separator (30) through the pin hole (10) formed in the anode (20) can be facilitated, and the penetration of the electrolyte into the space between the cathode (40) and the separator (30) can be facilitated through the pin hole (10) formed in the same position as the pin hole (10) formed in the anode of the cathode (40). Therefore, the electrolyte can be uniformly impregnated inside the electrode assembly, and the gas generated inside the electrode assembly can be discharged through the pinhole (10) formed in the positive electrode (20) and the negative electrode (40) to improve swelling and thus improve the structural stability of the battery.

[0115] Although preferred embodiments of the present invention have been described above with reference to the drawings, those skilled in the art or those with ordinary knowledge in the relevant technical field will understand that various modifications and changes can be made to the present invention without departing from the spirit and technical scope of the invention as described in the claims.

[0116] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims. Explanation of the symbols

[0118] 10: Pinhole 20 : Anode 30: Separator 40: Cathode 50: Positive tab 100 : Electrode assembly 200: Electrode assembly laminated structure

Claims

Claim 1 An electrode assembly comprising an anode, a cathode, and a separator interposed between the anode and the cathode, wherein at least one of the plurality of anodes forming the electrode assembly has a structure in which n pin holes are formed, and the anode disposed at the outermost edge of the electrode assembly has a structure in which no pin holes are formed, wherein n is an integer greater than or equal to 1, and the cathode has a structure in which no pin holes are formed. Claim 2 delete Claim 3 delete Claim 4 In claim 1, the pinhole is an electrode assembly having an area of ​​0.001% to 1% of the total area of ​​one side of the anode. Claim 5 delete Claim 6 delete Claim 7 A secondary battery comprising: an electrode assembly according to claim 1; a case surrounding the electrode assembly; and an electrolyte injected into the case and impregnated into the electrode assembly. Claim 8 A pouch-type secondary battery comprising: an electrode assembly according to claim 1; a pouch surrounding the electrode assembly; and an electrolyte injected into the pouch and impregnated into the electrode assembly. Claim 9 A method for manufacturing a secondary battery comprising: a step of manufacturing an electrode assembly according to claim 1 by stacking a positive electrode having a pinhole formed therein, a negative electrode without a pinhole formed therein, and a separator interposed between the positive and negative electrodes, wherein the positive electrode without a pinhole formed therein is stacked at the outermost edge; and a step of housing the electrode assembly in a case and injecting an electrolyte into the case. Claim 10 In claim 9, a method for manufacturing a secondary battery in which a pin hole formed in the positive electrode is formed simultaneously when notching the positive electrode to form an electrode tab. Claim 11 A method for manufacturing a secondary battery according to claim 9, further comprising the step of waiting for 1 minute to 30 hours after the step of injecting an electrolyte into a case.

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