Pouch-type secondary battery

Abstract

The pouch-type secondary battery according to the present invention includes an electrode assembly, a pouch-type case including a receiving portion for receiving the electrode assembly and a sealing portion for sealing the receiving portion, an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case through the sealing portion, and a lead film disposed between the electrode lead and the pouch-type case, the lead film having a multi-layer structure and including a filler layer including a polypropylene homopolymer and a ceramic filler, and the ceramic filler is included in an amount of 1 wt % to 14 wt % based on the total weight of the lead film.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0178737, filed December 19, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a pouch-type secondary battery, and more particularly to a pouch-type secondary battery including a lead film. [Background technology]

[0003] Secondary batteries are used in a wide range of fields, from small products such as digital cameras, DVD players, MP3 players, mobile phones, PDAs, portable game devices, power tools, and e-bikes to large products requiring high output such as electric and hybrid vehicles, as well as power storage devices and backup power storage devices for storing surplus generated electricity and new / renewable energy. Types of secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, and lithium-ion polymer batteries.

[0004] A secondary battery can be manufactured by placing an electrode assembly, in which positive electrodes, negative electrodes, and separators interposed therebetween are alternately stacked, in a battery case, injecting an electrolyte, and sealing the battery case. Secondary batteries can be classified into pouch types and can types depending on the material of the case that houses the electrode assembly. Among these, a pouch-type battery can be manufactured by pressing a flexible pouch film laminate to form a cup, placing the electrode assembly in the inner space of the cup, and sealing the sealing portion.

[0005] Meanwhile, pouch-type secondary batteries may generate gas inside the pouch when operated at high temperatures, overcharged, or when a short circuit occurs. When the gas pressure inside the pouch increases, the gas can corrode and vent the pouch's sealing, resulting in explosion or fire. In particular, to ensure the durability of pouch-type secondary batteries, a technology is needed that can improve the corrosion resistance and sealing strength of the sealing portion between the electrode lead and the pouch-type film laminate, which are made of different materials. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention is intended to solve the above-mentioned problems, and provides a pouch-type secondary battery that can prevent the phenomenon in which gas generation inside the pouch causes corrosion of the joint between the electrode lead and the pouch-type film laminate, resulting in peeling of the interface at the joint. [Means for solving the problem]

[0007] According to one embodiment of the present invention, there is provided a pouch-type secondary battery comprising: an electrode assembly; a pouch-type case including a receiving portion for receiving the electrode assembly and a sealing portion for sealing the receiving portion; an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case through the sealing portion; and a lead film disposed between the electrode lead and the pouch-type case, wherein the lead film has a multi-layer structure and includes a filler layer including a polypropylene homopolymer and a ceramic filler, and the ceramic filler is included in an amount of 1 wt % to 14 wt % based on the total weight of the lead film.

[0008] The ceramic filler according to the present invention may contain at least one selected from the group consisting of CaCO3, Ca(OH)2, CaCl2, CaO, KOH, NaOH, and Na2CO3.

[0009] The lead film according to the present invention may include a lead adhesive layer disposed on an electrode lead, a filler layer disposed on the lead adhesive layer, and a case adhesive layer disposed on the filler layer.

[0010] The lead adhesive layer may contain an acid-modified polyolefin and may have a thickness of 45 μm to 80 μm.

[0011] The ceramic filler may be contained in an amount of 3 to 10% by weight based on the total weight of the lead film, and the filler layer may have a thickness of 45 to 80 μm.

[0012] The case adhesive layer may include polypropylene, and the polypropylene may be a copolymer. The case adhesive layer may have a thickness of 55 μm to 85 μm.

[0013] The lead film may have a thickness of 150 μm to 250 μm. In addition, one surface of the electrode lead that directly contacts the lead film may be coated with one or more selected from the group consisting of chromium (Cr), nickel (Ni), aluminum oxide (Al2O3), zirconium (Zr), and titanium (Ti).

[0014] The average particle size D of the ceramic filler 50 The thickness can be 1 μm to 20 μm. [Effects of the Invention]

[0015] The present invention is characterized by absorbing gas generated inside the pouch through a ceramic filler having a specific average particle size and content range in a lead film disposed at the joint between the electrode lead and the pouch-type film laminate, thereby preventing the problem of gas corrosion at the joint between the electrode lead and the pouch-type film laminate and achieving high sealing strength, thereby improving the safety of the pouch secondary battery. [Brief explanation of the drawings]

[0016] The drawings attached to the specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further understand the technical concept of the present invention, and therefore the present invention should not be interpreted as being limited solely to the matters depicted in such drawings.

[0017] [Figure 1] 1 is an exploded view of a pouch-type secondary battery according to the present invention; [Figure 2] FIG. 2 is a cross-sectional view of a sealed pouch-type secondary battery. [Figure 3] 1 is a cross-sectional view of a lead film according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The advantages and features of the present invention, as well as methods for achieving them, will become clearer with reference to the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various different forms. However, the present embodiments are provided to fully disclose the present invention and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains, and the present invention is defined only by the scope of the claims. The same reference symbols refer to the same elements throughout the specification.

[0019] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the sense that can be commonly understood by a person having ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless they are clearly and specifically defined.

[0020] The terms used in this specification are for the purpose of describing embodiments and are not intended to limit the present invention. In this specification, the singular includes the plural unless otherwise specified. The words "comprises" and / or "comprising" used in this specification do not exclude the presence or addition of one or more other elements in addition to the elements mentioned.

[0021] In this specification, when a part is said to include a certain component, this does not mean that it may further include other components, unless otherwise specified to the contrary.

[0022] In this specification, the phrase "A and / or B" means A, or B, or A and B.

[0023] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0024] In this specification, D 50 means the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0025] In this specification, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan or a Micromertics ASAP 2020 manufactured by Microtrac.

[0026] The pouch-type secondary battery according to the present invention includes an electrode assembly, a pouch-type case including a receiving portion for receiving the electrode assembly and a sealing portion for sealing the receiving portion, an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case through the sealing portion, and a lead film disposed between the electrode lead and the pouch-type case, wherein the lead film has a multi-layer structure and includes a filler layer including a polypropylene homopolymer, and the filler layer includes 1 wt % to 14 wt % of a ceramic filler based on the total weight of the lead film.

[0027] Hereinafter, each component of the pouch-type secondary battery of the present invention will be described in more detail with reference to the drawings.

[0028] Fig. 1 is an exploded view of a pouch-type secondary battery 100 according to the present invention, and Fig. 2 is a cross-sectional view of the sealed pouch-type secondary battery 100. In Fig. 2, some of the components of the pouch-type secondary battery 100 are omitted for ease of understanding. As shown in Figs. 1 and 2, the pouch-type secondary battery 100 according to the present invention includes a pouch-type case 110, an electrode assembly 160, an electrode lead 180, and a lead film 190.

[0029] (1) Pouch-type case The pouch-type case 110 can house the electrode assembly 160 inside. The pouch-type case 110 can be manufactured by molding a pouch film laminate. In this case, the pouch film laminate can include a base layer, a gas barrier layer, and a sealant layer. In the pouch film laminate, the base layer, the gas barrier layer, and the sealant layer can be laminated in this order.

[0030] The substrate layer is formed on the outermost layer of the pouch film laminate to protect the secondary battery from external friction and impact. The substrate layer is made of a polymer and can electrically insulate the electrode assembly from the outside.

[0031] The substrate layer may be made of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon (registered trademark), and glass fiber. Preferably, the substrate layer is made of polyethylene terephthalate (PET), nylon, or a combination thereof, which are abrasion-resistant and heat-resistant.

[0032] The substrate layer may have a single film structure made of any one material, or alternatively, the substrate layer may have a composite film structure made of two or more materials each formed into a layer.

[0033] The thickness of the substrate layer can be 5 μm to 50 μm, specifically 7 μm to 40 μm, more specifically 25 μm to 38 μm. When the thickness of the substrate layer satisfies this range, the external insulation is excellent and the overall thickness of the pouch is not large, so that the energy density relative to the volume of the secondary battery can be excellent.

[0034] The gas barrier layer is laminated between the base layer and the sealant layer to ensure the mechanical strength of the pouch, block the entry and exit of gas or moisture from outside the secondary battery, and prevent electrolyte leakage from inside the pouch-type case.

[0035] The gas barrier layer may be formed of a metal, specifically, an aluminum alloy thin film. When an aluminum alloy thin film is used to form the gas barrier layer, it can ensure a certain level of mechanical strength, be lightweight, and ensure electrochemical compatibility between the electrode assembly and the electrolyte, as well as heat dissipation. The aluminum alloy thin film may contain at least one metal element other than aluminum (Al), such as iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0036] The thickness of the gas barrier layer can be 40 μm to 100 μm, specifically 50 μm to 90 μm, more specifically 55 μm to 85 μm. When the thickness of the gas barrier layer satisfies this range, excellent moldability and gas barrier performance are achieved when the cup portion is formed.

[0037] The sealant layer is thermally bonded to the sealing portion when the pouch-shaped case accommodating the electrode assembly therein is sealed, thereby completely sealing the inside of the pouch-shaped case. For this purpose, the sealant layer may be made of a material having excellent thermal adhesive strength.

[0038] The sealant layer may be formed of a material having insulating properties, corrosion resistance, and sealing properties. Specifically, since the sealant layer is in direct contact with the electrode assembly and / or electrolyte inside the pouch-type case, it may be formed of a material having insulating properties and corrosion resistance. Furthermore, since the sealant layer must completely seal the inside of the pouch-type case and prevent the transfer of materials between the inside and outside, it may be formed of a material having high sealing properties (e.g., excellent thermal adhesive strength). To ensure such insulating properties, corrosion resistance, and sealing properties, the sealant layer may be formed of a polymer material. For example, the sealant layer may include, but is not limited to, polypropylene.

[0039] The pouch film laminate may be drawn and stretched using a punch or the like to manufacture the pouch-type case 110. As a result, the pouch-type case 110 may include a cup portion 122 and a receiving portion 124. The receiving portion 124 is a location for receiving the electrode assembly, and may refer to a bag-shaped receiving space formed inside the cup portion 122 as the cup portion 122 is formed.

[0040] According to an embodiment of the present invention, the pouch-type case 110 may include a first case 120 and a second case 130, as shown in Fig. 1. The first case 120 includes a receiving portion 124 that can receive the electrode assembly 160, and the second case 130 can cover the receiving portion 124 from above to prevent the electrode assembly 160 from falling out of the battery case 110. The first case 120 and the second case 130 may be manufactured with one side connected to each other as shown in Fig. 1, but are not limited to this and may be manufactured in various ways, such as being separated from each other and manufactured separately.

[0041] According to another embodiment of the present invention, when forming cup portions in a pouch film laminate, two symmetrical cup portions 122, 132 may be formed adjacent to each other by drawing one pouch film laminate. In this case, as shown in FIG. 1, the first case 120 and the second case 130 may be formed with the cup portions 122, 132, respectively. After the electrode assembly 160 is accommodated in the accommodating portion 124 of the cup portion 122 of the first case 120, the bridge portion 140 formed between the two cup portions 122, 132 may be folded so that the two cup portions 122, 132 face each other. In this case, the cup portion 132 of the second case 130 may accommodate the electrode assembly 160 from above. Therefore, because two cup portions 122, 132 accommodate one electrode assembly 160, an electrode assembly 160 that is thicker than when there is only one cup portion 122 can be accommodated. In addition, folding the pouch-type case 110 forms one corner of the secondary battery 100, which reduces the number of corners to be sealed during a subsequent sealing process, thereby improving the processing speed of the pouch-type secondary battery 100 and reducing the number of sealing processes.

[0042] The pouch-type case 110 may be sealed with the electrode assembly 160 housed therein such that a portion, i.e., a terminal portion, of the electrode lead 180 (described below) is exposed. Specifically, when the electrode lead 180 is connected to the electrode tab 170 of the electrode assembly 160 and a lead film 190 is formed on a portion of the electrode lead 180, the electrode assembly 160 may be housed in a housing portion 124 provided in the cup portion 122 of the first case 120, and the second case 130 may cover the housing portion 124 from above. Next, an electrolyte may be injected into the housing portion 124, and the sealing portions 150 formed on the peripheries of the first case 120 and the second case 130 may be sealed.

[0043] The sealing part 150 may serve to seal the receiving part 124. Specifically, the sealing part 150 may be formed along the periphery of the receiving part 124 to seal the receiving part 124.

[0044] The temperature for sealing the sealing part 150 may be 180°C to 250°C, specifically 200°C to 250°C, and more specifically 210°C to 240°C. When the sealing temperature is within the above range, the pouch-type case 110 can be thermally bonded to ensure sufficient sealing strength.

[0045] (2) Electrode assembly The electrode assembly 160 may be inserted into the pouch-type case 110 and sealed by the pouch-type case 110 after the electrolyte is injected.

[0046] The electrode assembly 160 may be formed by sequentially stacking a positive electrode, a separator, and a negative electrode. Specifically, the electrode assembly 160 may include two electrodes, a positive electrode and a negative electrode, and a separator interposed between the electrodes to insulate the electrodes from each other.

[0047] The positive and negative electrodes may each have a structure in which an active material slurry is applied to an electrode current collector in the form of a metal foil or metal mesh containing aluminum and copper, respectively. The slurry may be formed by stirring a granular active material, a supplemental conductor, a binder, a conductive material, and the like in a solvent. The solvent may be removed in a subsequent process.

[0048] A slurry containing a mixture of an electrode active material, a binder, and / or a conductive material is applied to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, which are then stacked on both sides of a separator to manufacture a predetermined shape of the electrode assembly 160. The electrode assembly 160 may be of a stack type, a jelly roll type, a stack and folding type, or the like, but is not limited thereto.

[0049] The electrode assembly 160 may include an electrode tab 170 .

[0050] The electrode tabs 170 are connected to the positive and negative electrodes of the electrode assembly 160, respectively, and protrude from the electrode assembly 160 to serve as paths for electrons to move between the inside and outside of the electrode assembly 160. The electrode current collector included in the electrode assembly 160 may be composed of a portion coated with an electrode active material and an end portion, i.e., a plain portion, where the electrode active material is not coated. The electrode tabs 170 may be formed by cutting the plain portion or by connecting a separate conductive member to the plain portion by ultrasonic welding, for example. As shown in FIG. 1, the electrode tabs 170 may protrude in different directions from the electrode assembly 160, but are not limited thereto. They may protrude in various directions, such as protruding side by side in the same direction from one side.

[0051] (3) Electrode lead The electrode lead 180 may supply electricity to the outside of the secondary battery 100. The electrode lead 180 may be connected to the electrode tab 170 of the electrode assembly 160 by spot welding or the like.

[0052] The electrode lead 180 is connected to the electrode assembly 160 and may protrude to the outside of the pouch-type case 110 through the sealing portion 150. Specifically, one end of the electrode lead 180 is connected to the electrode assembly 160, particularly to the electrode tab 170, and the other end of the electrode lead 180 may protrude to the outside of the pouch-type case 110.

[0053] The electrode lead 180 may include a positive electrode lead 182 having one end connected to the positive electrode tab 172 and extending in the direction in which the positive electrode tab 172 protrudes, and a negative electrode lead 184 having one end connected to the negative electrode tab 174 and extending in the direction in which the negative electrode tab 174 protrudes. The other ends of both the positive electrode lead 182 and the negative electrode lead 184 may protrude to the outside of the battery case 110. This allows electricity generated inside the electrode assembly 160 to be supplied to the outside. In addition, since the positive electrode tab 172 and the negative electrode tab 174 protrude in different directions, the positive electrode lead 182 and the negative electrode lead 184 may also extend in different directions. The positive electrode lead 182 and the negative electrode lead 184 may be made of different materials. That is, the positive electrode lead 182 may be made of the same aluminum (Al) material as the positive electrode current collector, and the negative electrode lead 184 may be made of the same copper (Cu) material as the negative electrode current collector or a copper material coated with nickel (Ni). A portion of the electrode lead 180 protruding outside the battery case 110 serves as a terminal portion and may be electrically connected to an external terminal.

[0054] The surface of the electrode lead 180 that is in direct contact with the lead film 190 may be coated with one or more selected from the group consisting of chromium (Cr), nickel (Ni), aluminum oxide (Al2O3), zirconium (Zr), and titanium (Ti). In this case, corrosion resistance to the electrolyte and adhesion to the lead film 190 can be ensured.

[0055] (4) Lead film The lead film 190 is intended to prevent electricity generated from the electrode assembly 160 from flowing to the battery case 110 via the electrode lead 180 .

[0056] The lead film 190 may be disposed to wrap the outer periphery of the electrode lead 180. Specifically, at least a portion of the electrode lead 180 may be surrounded by the lead film 190. The lead film 190 may be located only in the sealing portion 150 where the first case 120 and the second case 130 of the pouch-type case 110 are thermally sealed.

[0057] The lead film 190 may be disposed between the electrode lead 180 and the pouch-type case 110. For example, as shown in Fig. 2, the lower case 110, the lead film 190, the electrode lead 180, the lead film 190, and the upper case 110 may be disposed in a stacked state in the sealing portion 150 area. Here, the lead film 190 may be in direct contact with the sealant layer of the battery case 110.

[0058] The lead film 190 may be formed of a non-conductive material that is difficult for electricity to pass through. Typically, the lead film 190 is made of a relatively thin insulating tape that is easily attached to the electrode lead 180 and / or the pouch film laminate, but is not limited thereto and any material that can insulate the electrode lead 180 may be used. Preferably, the lead film 190 is an extruded polypropylene film rather than a cross-linked composite film. The extruded polypropylene film has the advantage that it is easier to control the fluidity with temperature compared to a cross-linked composite film and can fill fine gaps during heat sealing.

[0059] The thickness of the lead film 190 may be 150 μm to 250 μm, specifically 170 μm to 230 μm, and more specifically 190 μm to 210 μm. When the thickness of the lead film 190 satisfies this numerical range, the tensile properties of the lead film can be improved, ensuring the durability of the pouch and preventing a decrease in the cell energy density.

[0060] Meanwhile, the lead film 190 according to the present invention has a multilayer structure and includes a filler layer 220, which includes a polypropylene homopolymer and a ceramic filler. In this case, the ceramic filler is included in an amount of 1 to 14 wt %, specifically 2 to 12 wt %, and more specifically 3 to 10 wt %, based on the total weight of the lead film 190. If the ceramic filler content is less than 1 wt % based on the total weight of the lead film 190, the ceramic filler contained in the lead film may not be able to adequately adsorb gas inside the pouch. If the ceramic filler content is more than 14 wt % based on the total weight of the lead film 190, the layers contained in the lead film 190 may not be sufficiently mixed during heat sealing, which may result in delamination.

[0061] In addition, the average particle size of the ceramic filler D 50 is preferably 1 μm to 20 μm, specifically 1 μm to 10 μm, and more specifically 1 μm to 6 μm. When a ceramic filler having an average particle size in this range is contained in the filler layer 220 in the lead film 190, the extrusion processability of the resin used to manufacture the lead film 190 can be improved, the problem of delamination between layers in the multilayer structure in the lead film 190 can be effectively prevented, and excellent sealing strength can be maintained.

[0062] The ceramic filler may include at least one selected from the group consisting of CaCO3, Ca(OH)2, CaCl2, CaO, KOH, NaOH, and Na2CO. Preferably, the ceramic filler may include at least one of CaCO3 and Ca(OH)2, which are inexpensive and easily adsorb gases such as hydrofluoric acid (HF).

[0063] Furthermore, the lead film 190 may further include additives other than the above-mentioned ceramic filler. By including additives in the lead film 190, it is possible to change the physical properties of the lead film 190. For example, at least one of carbon fiber, glass fiber, and aramid fiber may be further added as an additive to adjust the tensile strength of the lead film 190.

[0064] 3 is a cross-sectional view of a lead film 190 according to one embodiment of the present invention. As shown in FIG. 3, the lead film 190 may include a lead adhesive layer 210, a filler layer 220, and a case adhesive layer 230, which are laminated in this order. Specifically, when assembling a pouch, the lead adhesive layer 210 may be disposed on the electrode lead 180, the filler layer 220 may be disposed on the lead adhesive layer 210, and the case adhesive layer 230 may be disposed on the filler layer 220. Here, the filler layer 220 may include the above-described ceramic filler 240. When the ceramic filler 240 of the present invention is included in the filler layer 220, gas generated inside the pouch can be easily adsorbed, and the lead film 190 can be easily fused and / or sealed to the electrode lead and / or the pouch film laminate.

[0065] The lead adhesive layer 210 can be in direct contact with the electrode lead 180 and can be used to adhere the lead film 190 to the electrode lead 180 .

[0066] The lead adhesive layer 210 may include any material that can be easily bonded to the electrode lead 180. Specifically, the lead adhesive layer 210 may include acid-modified polyolefin. For example, the lead adhesive layer 210 may include at least one of PPa (acid modified polypropylene), PEa (acid modified polyethylene), and plasma-treated PP (plasma-treated polypropylene), but is not limited thereto.

[0067] The thickness of the lead adhesive layer 210 may be 45 μm to 80 μm, specifically 50 μm to 70 μm, and more specifically 55 μm to 65 μm. When the thickness of the lead adhesive layer 210 satisfies this numerical range, the lead adhesive layer 210 melts within a predetermined production time (tact time), and the lead film 190 and the electrode lead 180 can be easily fused together.

[0068] The filler layer 220 may be a layer located at the center of the lead film 190. Generally, in the lead film, the middle layer located between the case adhesive layer 230 and the lead adhesive layer 210 includes one or more selected from the group consisting of block polypropylene (Block PP), random polypropylene (Random PP), and linear low-density polyethylene (LLDPE).

[0069] However, according to one embodiment of the present invention, the filler layer 220 disposed in the middle of the lead film 190 is characterized by including polypropylene, a homopolymer. This prevents excessive deformation of the lead film 190 during thermal sealing. In particular, when a ceramic filler is included in the filler layer 220 according to one embodiment of the present invention, if a polypropylene homopolymer is not used, the melting point (Tm) is relatively low, resulting in reduced sealing strength. Furthermore, even if the sealing temperature or pressure is slightly increased during sealing, the thickness of the filler layer 220 becomes thin, which can cause interlayer delamination of the lead film 190 due to the presence of the ceramic filler.

[0070] Therefore, the filler layer 220 is characterized by not containing a heat-resistant polymer or block copolymer containing cross-linking molecules, in particular, to suppress interfacial peeling problems and maintain excellent sealing strength.

[0071] The thickness of the filler layer 220 may be 45 μm to 80 μm, specifically 50 μm to 70 μm, and more specifically 55 μm to 65 μm. When the thickness of the filler layer 220 satisfies this numerical range, excessive deformation of the lead film 190 due to heat applied during fusion (adhesion of the lead film and the electrode lead) or sealing (adhesion of the lead film and the pouch film laminate) can be prevented, and the shape of the lead film 190 can be maintained.

[0072] The case adhesive layer 230 can be the layer that directly contacts the battery case 110, specifically the sealant layer of the pouch film laminate.

[0073] The case adhesive layer 230 may include, but is not limited to, one or more selected from the group consisting of polypropylene, random polypropylene (Random PP), and linear low-density polyethylene (LLDPE). Preferably, when the case adhesive layer 230 includes polypropylene, which is a copolymer, it melts sufficiently within the sealing temperature, allowing the lead film 190 and the battery case 110 to be easily sealed.

[0074] The thickness of the case adhesive layer 230 may be 55 μm to 85 μm, specifically 60 μm to 80 μm, and more specifically 65 μm to 75 μm. When the thickness of the case adhesive layer 230 satisfies this range, the case adhesive layer 230 melts within a predetermined production time (tact time), allowing the lead film 190 and the battery case 110 to be easily sealed.

[0075] (5) Electrolyte The pouch-type secondary battery 100 according to the present invention may further include an electrolyte (not shown) injected into the pouch-type case 110. The electrolyte is used to transport lithium ions generated by an electrochemical reaction of the electrodes during charging / discharging of the secondary battery 100, and may include a non-aqueous organic electrolyte solution that is a mixture of a lithium salt and an organic solvent, or a polymer using a polymer electrolyte. Furthermore, the electrolyte may include a sulfide-based, oxide-based, or polymer-based solid electrolyte, and such a solid electrolyte may have flexibility that makes it easily deformable under external force.

[0076] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for the purpose of facilitating understanding of the present invention and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present description and technical concept, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0077] Examples and Comparative Examples Example 1 (1) Manufacturing of lead assemblies CaCO3 (average particle size D 50 A polypropylene homopolymer film was prepared by mixing a polypropylene homopolymer (2.8 μm thick) and extruding it to a thickness of 62.4 μm. A lead film was then prepared by laminating, in order, a 62.4 μm thick acid-modified polypropylene film (lead adhesive layer), the polypropylene homopolymer film (filler layer), and a 72.4 μm thick polypropylene copolymer film (case adhesive layer).

[0078] Here, the CaCO3 content was measured using a thermogravimetric analyzer (TGA, manufactured by Mettler-Toledo) in the temperature range of 50°C to 800°C at a heating rate of 10°C / min with N2 purging, and was confirmed to be 10 wt% of the total weight of the lead film.

[0079] Next, the lead film was disposed so as to wrap around the outer periphery of an electrode lead having a thickness of 40 μm, thereby producing a lead assembly.

[0080] (2) Manufacturing pouch-type cases A pouch film laminate with a polyethylene terephthalate / nylon / aluminum alloy thin film / polypropylene film structure was produced by laminating a first adhesive film with a width of 266 mm, a length of 50 m, and a thickness of 3 μm, a nylon film with a width of 266 mm, a length of 50 m, and a thickness of 25 μm, a second adhesive film with a width of 266 mm, a length of 50 m, and a thickness of 3 μm, and a polyethylene terephthalate (PET) film with a width of 266 mm, a length of 50 m, and a thickness of 12 μm on one side of an aluminum alloy thin film with a width of 266 mm, a length of 50 m, and a thickness of 60 μm on the other side.

[0081] Here, the first adhesive film, nylon film, second adhesive film, and polyethylene terephthalate film are base layers, the aluminum alloy thin film is a gas barrier layer, and the polypropylene film is a sealant layer.

[0082] The pouch film laminate was molded to prepare a pouch-type case including a receiving portion and a sealing portion.

[0083] (3) Manufacturing of pouch-type secondary batteries The negative and positive electrodes and a porous polyethylene separator were stacked and then laminated to prepare an electrode assembly, which was then connected to a lead assembly.

[0084] An electrolyte was prepared by dissolving LiPF6 in a solvent (volume ratio of EC:EMC:DMC = 3:3:4) to a concentration of 1.0 M. With the tip of the lead assembly extended to the outside, the electrode assembly was housed in the pouch-type case, and the electrolyte was poured into it.

[0085] Next, the sealing portion of the pouch-type case was sealed with a seal bar (area: 200mm x 5mm) at 220°C and 0.1MPa for 2 seconds to manufacture a pouch-type secondary battery. Here, the portion of the sealing portion where the lead assembly was formed had a structure in which the lower case / lead film / electrode lead / lead film / upper case were stacked in this order.

[0086] Example 2 A lead assembly was manufactured in the same manner as in Example 1, except that the CaCO3 content was 7 wt % based on the total weight of the lead film.

[0087] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0088] Example 3 A lead assembly was manufactured in the same manner as in Example 1, except that the CaCO3 content was 3 wt % based on the total weight of the lead film.

[0089] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0090] Example 4 A lead assembly was manufactured in the same manner as in Example 1, except that the CaCO3 content was 5 wt % based on the total weight of the lead film.

[0091] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0092] Comparative Example 1 A lead assembly was produced in the same manner as in Example 1, except that the lead film did not contain CaCO3.

[0093] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0094] Comparative Example 2 A lead assembly was manufactured in the same manner as in Example 1, except that the CaCO3 content was 20 wt % based on the total weight of the lead film.

[0095] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0096] Comparative Example 3 Average particle size D 50 A lead assembly was manufactured in the same manner as in Example 1, except that CaCO3 having a particle size of 0.1 μm was contained in an amount of 15 wt % based on the total weight of the lead film.

[0097] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0098] Comparative Example 4 Average particle size D 50 A lead assembly was manufactured in the same manner as in Example 1, except that CaCO3 having a particle size of 22 μm was contained in an amount of 15 wt % based on the total weight of the lead film.

[0099] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0100] Comparative Example 5 A lead assembly was manufactured in the same manner as in Example 1, except that block-polypropylene (block-PP) was used as the filler layer instead of polypropylene homopolymer film, and the CaCO3 content was 15 wt % based on the total weight of the lead film.

[0101] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0102] Comparative Example 6 A lead assembly was manufactured in the same manner as in Example 1, except that block-polypropylene (block-PP) was used as the filler layer instead of polypropylene homopolymer film, and the CaCO3 content was 7 wt % based on the total weight of the lead film.

[0103] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0104] Experimental Example 1: Extrusion processability evaluation of polypropylene homopolymer film The extrusion processability was evaluated for the polypropylene homopolymer films produced in Examples 1 to 4 and Comparative Examples 1 to 6. Specifically, when a polypropylene homopolymer resin containing CaCO3 was extruded, the appearance of the extruded film was visually inspected, and the extrusion processability was shown in Table 1 below.

[0105] Experimental example 2: Evaluation of adhesive strength between electrode lead and lead film The electrolyte-resistant adhesive strength of the lead assemblies fabricated in Examples 1 to 4 and Comparative Examples 1 to 6 was measured. Specifically, the lead assemblies were immersed in an electrolyte (EC:EMC:DMC = 3:3:4 volume ratio, LiPF61.0M) and then stored in a chamber at 60°C and 90% humidity for two weeks. The lead assemblies were removed from the electrolyte, the remaining electrolyte was washed away, and the assembly was then left in the air. Before and after immersion in the electrolyte, the lead assemblies were bent 10 mm from one corner to break the electrode leads. Then, both ends of the lead assemblies were attached to the lower and upper jigs of the UTM, respectively, and the assembly was pulled 30 mm in a 180° direction at a speed of 50 mm / min. The average value (N / 10 mm) of the flat section of the adhesive strength graph was calculated. The sealing strength between the electrode lead and the lead film after impregnation with the electrolyte measured by the above method, and the reduction (%) in sealing strength after impregnation with the electrolyte compared to before impregnation with the electrolyte are shown in Table 1 below.

[0106] Experimental Example 3: Evaluation of sealing strength and delamination of pouch-type secondary batteries The sealing strength of each of the pouch-type secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 6 was measured, and the presence or absence of delamination at the sealing portion of the pouch-type secondary batteries was confirmed.

[0107] Specifically, the sealing portion of the pouch-type secondary battery, where the lead assembly and pouch film laminate were sealed, was cut at 15 mm intervals. The electrode lead was then attached to the lower fixture of the UTM, and the pouch film laminate was attached to the upper fixture. The UTM was then pulled in a 180° direction at a rate of 5 mm / min at room temperature (25°C). The sealing strength was calculated from the average value of the flat section of the adhesive strength graph. When the sealing portion was opened, the cross section of the sealing portion was observed to check for delamination in the lead film. The results are shown in Table 1 below.

[0108] ○: The interface between the lead adhesive layer or the case adhesive layer is peeled off ×: The interface between the lead adhesive layer or the case adhesive layer is not peeled off.

[0109] [Table 1]

[0110] Table 1 shows that in Examples 1 to 4, in which the ceramic filler content was 1 to 14 wt % based on the total weight of the lead film and a polypropylene homopolymer was used in the filler layer containing the ceramic filler, the extrusion processability of the polypropylene homopolymer film was good, and the lead assembly after electrolyte impregnation exhibited excellent properties such as adhesive strength, adhesive strength reduction, and sealing strength. However, in Comparative Example 1, which did not contain a ceramic filler, the adhesive strength of the lead assembly after electrolyte impregnation was low and the adhesive strength reduction was very large, indicating poor durability. In Comparative Example 2, the ceramic filler content was high, resulting in low sealing strength. In Comparative Examples 3 and 4, the ceramic filler content was high, resulting in low sealing strength and interlayer delamination.

[0111] Furthermore, in Comparative Examples 5 and 6, the use of block polypropylene as the filler layer resulted in very low sealing strength and even delamination. Comparing these two Comparative Examples with Example 1 and Comparative Example 2, it was found that the use of block polypropylene resulted in poor effectiveness regardless of whether the ceramic filler content was within the 1 wt% to 14 wt% range. However, the use of polypropylene homopolymer resulted in significant differences in the adhesive strength and sealing strength of the lead assembly after electrolyte impregnation, depending on whether the range was met. This suggests that the ceramic filler content and the type of filler layer containing the ceramic filler mutually exert a synergistic effect. [Explanation of symbols]

[0112] 100 Pouch-type secondary battery 110 Pouch-type case 120 Case 1 122 Cup section 124 Storage unit 130 Case 2 132 Cup section 140 Bridge section 150 sealing part 160 Electrode assembly 170 Electrode Tab 172 Positive electrode tab 174 Negative electrode tab 180 Electrode Lead 182 Positive lead 184 Negative lead 190 Lead Film 210 Lead adhesive layer 220 Filler layer 230 Case adhesive layer 240 Ceramic Filler

Claims

1. an electrode assembly; a pouch-type case including a receiving portion for receiving the electrode assembly and a sealing portion for sealing the receiving portion; an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case through the sealing portion; a lead film disposed between the electrode lead and the pouch-shaped case, The lead film has a multilayer structure and includes a filler layer containing a polypropylene homopolymer and a ceramic filler, and the ceramic filler is contained in an amount of 1 wt % to 14 wt % relative to the total weight of the lead film.

2. The ceramic filler is CaCO ３ , Ca(OH) ２ , CaCl ２ , CaO, KOH, NaOH and Na ２ CO ３ The pouch-type secondary battery according to claim 1 , comprising at least one selected from the group consisting of:

3. 2. The pouch-type secondary battery according to claim 1, wherein the lead film includes a lead adhesive layer disposed on the electrode lead, a filler layer disposed on the lead adhesive layer, and a case adhesive layer disposed on the filler layer.

4. The pouch-type secondary battery according to claim 3 , wherein the lead adhesive layer contains an acid-modified polyolefin.

5. 4. The pouch-type secondary battery according to claim 3, wherein the lead adhesive layer has a thickness of 45 μm to 80 μm.

6. 2. The pouch-type secondary battery according to claim 1, wherein the ceramic filler is contained in an amount of 3% by weight to 10% by weight based on the total weight of the lead film.

7. 2. The pouch-type secondary battery according to claim 1, wherein the filler layer has a thickness of 45 μm to 80 μm.

8. the case adhesive layer comprises polypropylene; The pouch-type secondary battery according to claim 3 , wherein the polypropylene is a copolymer.

9. 4. The pouch-type secondary battery according to claim 3, wherein the case adhesive layer has a thickness of 55 μm to 85 μm.

10. 2. The pouch-type secondary battery according to claim 1, wherein the lead film has a thickness of 150 μm to 250 μm.

11. The surface of the electrode lead that is in direct contact with the lead film is made of chromium (Cr), nickel (Ni), aluminum oxide (Al ２ O ３ 2. The pouch-type secondary battery according to claim 1, wherein the pouch-type secondary battery is coated with one or more selected from the group consisting of zinc (Zn), zirconium (Zr), and titanium (Ti).

12. The average particle diameter D of the ceramic filler ５０ The pouch-type secondary battery according to claim 1, wherein the thickness is 1 μm to 20 μm.

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