Soft package type secondary battery

Abstract

A pouch-type secondary battery according to the present invention comprises: an electrode assembly; a pouch case including an accommodating portion for accommodating the electrode assembly and a sealing portion for sealing the accommodating portion; an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case via the sealing portion; and a lead film provided between the electrode lead and the pouch case. The lead film has a multilayer structure and includes a filler layer including a polypropylene homopolymer and a ceramic filler, and the content of the ceramic filler is 1 wt% to 14 wt% based on the total weight of the lead film.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of priority of Korean Patent Application No. 10 - 2022 - 0178737, filed on December 19, 2022, which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to a pouch - type secondary battery, and more particularly, to a pouch - type secondary battery including a lead film. Background Art

[0005] Secondary batteries are used in various categories, including: small products such as digital cameras, P - DVDs, MP3Ps, mobile phones, PDAs, portable game devices, power tools, electric bicycles, and large products that require high power such as electric vehicles and hybrid vehicles, power storage devices for storing surplus power or renewable energy, and backup power storage devices. Secondary batteries include nickel - cadmium batteries, nickel - metal hydride batteries, lithium - ion batteries, and lithium - ion polymer batteries.

[0006] A secondary battery can be manufactured by accommodating an electrode assembly in which a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are alternately laminated in a battery case, injecting an electrolyte, and then sealing the battery case. Secondary batteries are classified into pouch - type secondary batteries and can - type secondary batteries according to the material of the case that houses the electrode assembly. In particular, a pouch - type battery can be manufactured by performing a pressing process on a flexible pouch film laminate to form a cup portion, and then accommodating the electrode assembly in the accommodation space inside the cup portion and sealing the sealing portion.

[0007] Meanwhile, when operating at high temperatures, over - charging, or short - circuiting, a pouch - type secondary battery may generate gas inside the pouch. When the air pressure inside the pouch rises, the sealing portion of the pouch is corroded and exhausted due to the gas, resulting in an explosion or a fire. In particular, in order to obtain the durability of a pouch - type secondary battery, a technology is needed that can improve the corrosion resistance and sealing strength of the connection portion between the electrode lead of different kinds of materials in the sealing portion and the pouch - type film laminate. Summary of the Invention

[0008] Technical Problem

[0009] One aspect of the present invention provides a pouch - type secondary battery capable of preventing corrosion of the connection portion between the electrode lead and the pouch - type film laminate and preventing separation of the interface of the connection portion due to gas generated inside the pouch.

[0010] Technical Solution

[0011] According to an aspect 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 wire 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 wire and the pouch-type case, wherein the lead film has a multi-layer structure and includes a filler layer, the filler layer includes a polypropylene homopolymer and a ceramic filler, and based on the total weight of the lead film, the content of the ceramic filler is 1 wt% to 14 wt%.

[0012] The ceramic filler according to the present invention may include at least one selected from the group consisting of CaCO3, Ca(OH)2, CaCl2, CaO, KOH, NaOH, and Na2CO3.

[0013] The lead film according to the present invention may include a lead adhesive layer disposed on the electrode lead wire, a filler layer disposed on the lead adhesive layer, and a case adhesive layer disposed on the filler layer.

[0014] The lead adhesive layer may include an acid-modified polyolefin. Additionally, the thickness of the lead adhesive layer may be 45 μm to 80 μm.

[0015] Based on the total weight of the lead film, the content of the ceramic filler may be 3 wt% to 10 wt%. Additionally, the thickness of the base layer may be 45 μm to 80 μm.

[0016] The case adhesive layer may include polypropylene, and the polypropylene may be a copolymer. Additionally, the thickness of the case adhesive layer may be 55 μm to 80 μm.

[0017] The thickness of the lead film may be 150 μm to 250 μm. Additionally, the surface of the electrode lead wire that is in direct contact with the lead film may be coated with at least one selected from the group consisting of chromium (Cr), nickel (Ni), aluminum oxide (Al2O3), zirconium (Zr), and titanium (Ti).

[0018] The average particle diameter D of the ceramic filler 50 may be 1 μm to 20 μm.

[0019] Advantageous Effects

[0020] The present invention relates to absorbing gas generated inside the pouch by having a ceramic filler with a specific average particle diameter and content range in the lead film at the connection portion between the electrode lead wire and the pouch-type film laminate. Therefore, corrosion of the connection portion between the electrode lead wire and the pouch-type film laminate due to gas is prevented, thereby achieving high sealing strength and improving the safety of the pouch-type secondary battery. Brief Description of the Drawings

[0021] The following attached drawings illustrate preferred examples of the present invention by way of example, and are used to enable the technical concept of the present invention to be further understood together with the specific embodiments of the present invention given below. Therefore, the present invention should not be construed only by the content in these drawings.

[0022] Figure 1 is an exploded view of a pouch-type secondary battery according to the present invention.

[0023] Figure 2 is a cross-sectional view of a sealed pouch-type secondary battery; and

[0024] Figure 3 is a cross-sectional view of a lead film according to an embodiment of the present invention. Detailed Description of the Embodiments

[0025] Advantages and features of the present disclosure and methods for realizing the same can be more easily understood with reference to the detailed description of the following embodiments and the accompanying drawings. However, the present disclosure may be implemented in different forms, and these embodiments are provided only to make the present disclosure thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art. Therefore, the present disclosure is defined only by the scope of the appended claims. Throughout the specification, the same reference numerals denote the same elements.

[0026] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are not ideally or overly interpreted unless clearly and specifically defined.

[0027] The terms used herein are not intended to limit the inventive concept, but to describe embodiments. As used herein, unless the context clearly indicates otherwise, the singular forms also include the plural forms. The meaning of "comprising" and / or "including" used herein does not exclude the presence or addition of one or more other components other than the components mentioned.

[0028] In this document, when an element "comprises" a component, unless there is a clear contrary description, this may mean that the element does not exclude another component, but may also include another component.

[0029] In this document, the description "A and / or B" means A or B or A and B.

[0030] In this document, unless otherwise indicated, "%" means wt%.

[0031] The term "D" used herein 50” can be defined as the particle diameter when the cumulative volume in the particle size distribution curve of the particles is 50%. For example, D can be measured by using a laser diffraction method. 50 The laser diffraction method generally allows the measurement of particle diameters in the range from sub-micrometers to several millimeters and can produce highly reproducible and high-resolution results.

[0032] As used herein, the “specific surface area” is measured by the BET method. Specifically, it can be calculated using BELSORP-minoII from BELJAPAN or Micromertics ASAP 2020 from Microtrac based on the amount of nitrogen adsorbed at liquid nitrogen temperature (77K).

[0033] 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 via the sealing portion; and a lead film provided between the electrode lead and the pouch-type case, wherein the lead film has a multi-layer structure and includes a base layer containing a polypropylene homopolymer, and the base layer includes a ceramic filler in an amount of 1 wt% to 14 wt% based on the total weight of the base layer.

[0034] Hereinafter, each component of the pouch-type secondary battery of the present invention will be described in more detail with reference to the drawings.

[0035] Figure 1 is an exploded view of the pouch-type secondary battery 100 according to the present invention, and Figure 2 is a cross-sectional view of the sealed pouch-type secondary battery 100. In Figure 2 , for convenience of understanding, some components of the pouch-type secondary battery 100 are not provided. As Figure 1 and Figure 2 shown, 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.

[0036] (1) Pouch-type case

[0037] The pouch-type case 110 can store 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 sequence.

[0038] The base layer is formed on the outermost layer of the pouch film laminate to protect the secondary battery from external friction and collision. Since the base layer is made of a polymer, it can electrically insulate the electrode assembly from the outside.

[0039] The base layer can be made of at least one material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, poly(p-phenylene terephthalamide benzoxazole), polyarylate, Teflon, and glass fiber. Preferably, the base layer can be made of polyethylene terephthalate (PET), nylon, or a combination thereof having abrasion resistance and heat resistance.

[0040] The base layer can have a single-layer film structure made of any one material. Alternatively, the base layer can have a composite film structure in which two or more materials are formed into layers respectively.

[0041] The thickness of the base layer can be 5 μm to 50 μm, specifically 7 μm to 40 μm, and more specifically 25 μm to 38 μm. When the thickness of the base layer satisfies the above range, the external insulation is excellent, and the entire pouch is not thick, so the energy density and volume ratio of the secondary battery can be excellent.

[0042] 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 outside the secondary battery, and prevent the electrolyte from leaking from the inside of the pouch-type case.

[0043] The gas barrier layer can be formed of a metal, and specifically, can be formed of an aluminum alloy thin film. When an aluminum alloy thin film is used to form the gas barrier layer, the gas barrier layer can have a predetermined level of mechanical strength and is lightweight, and can supplement the electrochemical performance caused by the electrode assembly and the electrolyte and dissipate heat. The aluminum alloy thin film can include metal elements other than aluminum (A1), for example, can include at least one selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0044] The thickness of the gas barrier layer can be 40 μm to 100 μm, specifically 50 μm to 90 μm, and more specifically 55 μm to 85 μm. When the thickness of the gas barrier layer satisfies the above range, the formability and gas barrier performance are excellent when molding the cup part.

[0045] When sealing the pouch-type case that houses the electrode assembly inside to completely seal the inside of the pouch-type case, the sealant layers are heat-bonded together at the sealing part. For this purpose, the sealant layer can be formed of a material having excellent heat-sealing strength.

[0046] The sealant layer can be formed of a material having insulation, corrosion resistance, and sealing properties. Specifically, the sealant layer is in direct contact with the electrode assembly and / or electrolyte inside the pouch-type housing, and can thus be formed of a material having insulation and corrosion resistance. Additionally, the sealant layer should completely seal the interior of the pouch-type housing and block the movement of substances between the inside and the outside, and can thus be formed of a material having high sealing performance (e.g., excellent heat seal strength). To ensure obtaining such insulation, corrosion resistance, and sealing properties, the sealant layer can be formed of a polymer material. For example, the sealant layer can include polypropylene, but is not limited thereto.

[0047] The pouch film laminate can be pulled out, molded, or stretched by punching or the like to manufacture the pouch-type housing 110. Thus, the pouch-type housing 110 can include a cup portion 122 and a receiving portion 124. The receiving portion 124 is the location for storing the electrode assembly, and can represent a receiving space formed in a pocket shape inside the cup portion 122 when the cup portion 122 is formed.

[0048] According to an embodiment of the present invention, the pouch-type housing 110 can include a first housing 120 and a second housing 130, as Figure 1 shown. The first housing 120 can include a receiving portion 124 capable of accommodating the electrode assembly 160, and the second housing 130 can cover the receiving portion 124 from above to prevent the electrode assembly 160 from separating to the outside of the pouch-type housing 110. As Figure 1 shown, the first housing 120 and the second housing 130 can be manufactured in such a way that one side of the first housing 120 and one side of the second housing 130 can be connected to each other, but the embodiments of the present invention are not limited thereto, and the first housing 120 and the second housing 130 can be manufactured differently, for example, separately manufactured separately from each other.

[0049] According to another embodiment of the present invention, when forming the cup portion in the pouch film laminate, two symmetric cup portions 122 and 132 can be stretched and molded adjacent to each other in one pouch film laminate. In this case, the cup portions 122 and 132 can be formed in the first housing 120 and the second housing 130, respectively, as Figure 1As shown. After the electrode assembly 160 is received in the receiving portion 124 provided in the cup portion 122 of the first housing 120, the bridging portion 140 formed between the two cup portions 122 and 132 can be folded so that the two cup portions 122 and 132 face each other. In this case, the cup portion 132 of the second housing 130 can receive the electrode assembly 160 from above. Therefore, the two cup portions 122 and 132 accommodate one electrode assembly 160, and thus an electrode assembly 160 that is thicker than when only one cup portion 122 is present can be accommodated. In addition, one edge of the secondary battery 100 is formed by folding the pouch-type housing 110, so that the number of edges to be sealed can be reduced when the sealing process is performed later. Therefore, the process speed of the pouch-type secondary battery 100 can be increased and the number of sealing processes can be reduced.

[0050] The pouch-type housing 110 can be sealed while receiving the electrode assembly 160 so that a part of the electrode lead 180, that is, the terminal portion, which will be described later, is exposed. Specifically, when the electrode lead 180 is connected to the electrode tab 170 of the electrode assembly 160 and the lead film 190 is formed on a part of the electrode lead 180, the electrode assembly 160 can be received in the receiving portion 124 provided in the cup portion 122 of the first housing 120, and the second housing 130 can cover the receiving portion 124 from above. Then, the electrolyte is injected into the receiving portion 124, and the sealing portion 150 formed on the edges of the first housing 120 and the second housing 130 can be sealed.

[0051] The sealing portion 150 can be used to seal the receiving portion 124. Specifically, the sealing portion 150 can be formed along the edge of the receiving portion 124, and thus the receiving portion 124 can be sealed.

[0052] The temperature at which the sealing portion 150 is sealed can be 180°C to 250°C, specifically 200°C to 250°C, and more specifically 210°C to 240°C. When the sealing temperature satisfies the above numerical range, the pouch-type housing 110 can obtain sufficient sealing strength through thermal sealing.

[0053] (2) Electrode assembly

[0054] The electrode assembly 160 can be inserted into the pouch-type housing 110 and sealed by the pouch-type housing 110 after the electrolyte is injected.

[0055] The positive electrode, the separator, and the negative electrode can be laminated in sequence to form the electrode assembly 160. Specifically, the electrode assembly 160 can include two types of electrodes, namely the positive electrode and the negative electrode, and a separator interposed between the electrodes to insulate the electrodes from each other.

[0056] The positive electrode and the negative electrode may have a structure in which an active material paste is respectively coated on an electrode current collector in the form of a metal foil or a metal mesh containing aluminum and copper. Generally, granular active material, auxiliary conductor, binder, and conductive material are stirred with an added solvent to form a paste. The solvent can be removed in subsequent processes.

[0057] A paste mixed with an electrode active material, a binder, and / or a conductive material is coated on the positive electrode current collector and the negative electrode current collector to manufacture the positive electrode and the negative electrode, and the positive electrode and the negative electrode are laminated on both sides of a separator. Therefore, the electrode assembly 160 can be manufactured into a predetermined shape. The type of the electrode assembly 160 may include a laminated type, a wound type, and a laminated and folded type, but is not limited thereto.

[0058] The electrode assembly 160 may include an electrode tab 170.

[0059] The electrode tab 170 is connected to each of the positive electrode and the negative electrode of the electrode assembly 160 and protrudes outward from the electrode assembly 160. Therefore, it can be used as a path for electrons to move between the inside and the outside of the electrode tab. The current collector included in the electrode assembly 160 may be provided with a portion coated with the electrode active material and an end portion (i.e., a non-coated portion) not coated with the electrode active material. The electrode tab 170 may be formed by cutting the non-coated portion or by connecting a separate conductive member to the non-coated portion by ultrasonic welding or the like. As Figure 1 shown, the electrode tab 170 may protrude from the electrode assembly 160 in different directions, but is not limited thereto, and may be formed to protrude in various directions. For example, it may protrude from one side in the same direction.

[0060] (3) Electrode lead

[0061] The electrode lead 180 may supply power 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.

[0062] The electrode lead 180 may be connected to the electrode assembly 160 and may protrude to the outside of the pouch-type case 110 via the sealing portion 150. Specifically, one end of the electrode lead 180 may be connected to the electrode assembly 160, particularly the electrode tab 170, and the other end of the electrode lead 180 may protrude to the outside of the pouch-type case 110.

[0063] The electrode lead 180 may include: a positive electrode lead 182, one end of the positive electrode lead 182 being 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, one end of the negative electrode lead 184 being 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 pouch-type case 110. Accordingly, the electric power generated inside the electrode assembly 160 may be supplied to the outside. In addition, the positive electrode tab 172 and the negative electrode tab 174 are each formed to protrude in different directions, and thus 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 from each other. 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) or nickel (Ni)-coated copper material as the negative electrode current collector. A part of the electrode lead 180 that protrudes to the outside of the pouch-type case 110 may serve as a terminal portion and be electrically connected to an external terminal.

[0064] One surface of the electrode lead 180 that is in direct contact with the lead film 190 may be coated with at least one material 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 solution and adhesiveness to the lead film 190 can be obtained.

[0065] (4) Lead film

[0066] The lead film 190 is for preventing the electric power generated from the electrode assembly 160 from flowing through the electrode lead 180 to the pouch-type case 110.

[0067] The lead film 190 may be disposed to surround the outer peripheral surface of the electrode lead 180. Specifically, at least a part of the electrode lead 180 may be surrounded by the lead film 190. The lead film 190 may be placed to be restricted within the sealing portion 150 where the first case 120 and the second case 130 of the pouch-type case 110 are heat-sealed.

[0068] The lead film 190 may be disposed between the electrode lead 180 and the pouch-type case 110. For example, as Figure 2 shown, the lower pouch-type case 110, the lead film 190, the electrode lead 180, the lead film 190, and the upper pouch-type case 110 may be laminated and disposed in the sealing portion 150 in this order. In this case, the lead film 190 may be in direct contact with the sealant layer of the pouch-type case 110.

[0069] The lead film 190 can be formed of a non-conductive non-conductor through which current does not flow well. Generally, as the lead film 190, a relatively thin insulating tape that is easily attached to the electrode lead 180 and / or the soft package laminate is widely used, but embodiments of the present invention are not limited thereto, and thus any member capable of insulating the electrode lead 180 can be used. Preferably, the lead film 190 can be a polypropylene extrusion film rather than a composite cross-linked film, and the polypropylene extrusion film is more easily controlled in fluidity by temperature and fills small gaps during hot melting, so it is preferred.

[0070] The thickness of the lead film 190 can 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 the above numerical range, the tensile properties of the lead film can be improved to obtain the durability of the soft package and the reduction of the energy density of the battery cell can also be prevented.

[0071] Meanwhile, the lead film 190 according to the present invention has a multilayer structure and includes a filler layer 220, and in this case, the filler layer 220 includes a polypropylene homopolymer and a ceramic filler. In this case, based on the total weight of the lead film, the content of the ceramic filler can be 1 wt% to 14 wt%, specifically 2 wt% to 12 wt%, and more specifically 3 wt% to 10 wt%. When the amount of the ceramic filler is less than 1 wt% based on the total weight of the lead film 190, the ceramic filler included in the lead film is not sufficient to absorb the gas inside the soft package. When the amount of the ceramic filler is greater than 14 wt% based on the total weight of the lead film 190, separation may occur between the layers due to insufficient mixing between the respective layers included in the lead film 190 during hot melting.

[0072] In addition, preferably, the average particle size D of the ceramic filler 50 can be 1 μm to 20 μm, specifically 1 μm to 10 μm, and more specifically 1 μm to 6 μm. When the ceramic filler having an average particle size within the above range is included in the filler layer 220 of the lead film 190, the advantages are that the extrusion processability of the resin for manufacturing the lead film 190 can be improved, the interlayer separation of the multilayer structure inside the lead film 190 can be effectively prevented, and excellent sealing strength can be maintained.

[0073] The ceramic filler can include at least one selected from the group consisting of CaCO3, Ca(OH)2, CaCl2, CaO, KOH, NaOH, and Na2CO. Preferably, the ceramic filler can include at least one of CaCO3 and Ca(OH)2, which can withstand and easily absorb gases such as hydrofluoric acid (HF).

[0074] In addition, the lead film may further include additives other than the above-mentioned ceramic fillers. The inclusion of additives in the lead film 190 can change the physical properties of the lead film 190. For example, as an additive for controlling the tensile strength of the lead film 190, at least any one of carbon fiber, glass fiber, and aramid fiber may be added.

[0075] Meanwhile, Figure 3 is a cross-sectional view of the lead film 190 according to an embodiment of the present invention. As Figure 3 shown, the lead film 190 may include a lead adhesive layer 210, a filler layer 220, and a case adhesive layer 230 that are sequentially laminated. Specifically, when assembling the soft package, 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. In this case, the filler layer 220 may include the above-mentioned ceramic filler 240. When the ceramic filler 240 of the present invention is included in the filler layer 220, it is easy to absorb the gas generated inside the soft package, and the lead film 190 can also be easily welded and / or sealed with the electrode lead and / or the soft package film laminate.

[0076] The lead adhesive layer 210 is in direct contact with the electrode lead 180 and can be used to bond the lead film 190 to the electrode lead 180.

[0077] The lead adhesive layer 210 may include any material that is 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 acid-modified polypropylene (PPa), acid-modified polyethylene (PEa), or plasma-treated polypropylene (PP), but is not limited thereto.

[0078] 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 the above numerical range, the lead adhesive layer 210 melts during the specific production time (operation time), so that the lead film 190 and the electrode lead 180 can be easily welded.

[0079] The filler layer 220 may be a layer disposed in the middle of the lead film 190. Generally, in the lead film, the intermediate layer located between the case adhesive layer 230 and the lead adhesive layer 210 includes at least one selected from the group consisting of block polypropylene (block PP), random polypropylene (random PP), and linear low-density polyethylene (LLDPE).

[0080] However, according to an embodiment of the present invention, the filler layer 220 provided in the intermediate layer of the lead film 190 includes polypropylene as a homopolymer. In this case, excessive deformation of the lead film 190 during heat sealing is prevented. In particular, as in the filler layer 220 according to an embodiment of the present invention, when a ceramic filler is included in the layer, when a polypropylene homopolymer is not used, the melting point (Tm) is relatively low, thus reducing the sealing strength, and even when the sealing temperature or pressure slightly rises during sealing, the thickness of the filler layer 220 becomes thinner, resulting in delamination of the lead film 190 at the interlayer interface due to the presence of the ceramic filler.

[0081] Therefore, in order to prevent interface delamination and maintain excellent sealing strength, the filler layer 220 does not include a heat-resistant polymer or block copolymer containing crosslinked molecules.

[0082] The thickness of the filler layer 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 the above numerical range, excessive deformation of the lead film 190 due to the heat applied during welding (adhesion of the lead film to the electrode lead) or sealing (adhesion of the lead film to the soft package laminate) can be prevented, and the shape of the lead film 190 can be maintained.

[0083] The case adhesive layer 230 may be a layer that directly contacts the soft package type case 110 (specifically, the sealant layer of the soft package laminate).

[0084] The case adhesive layer 230 may include at least one selected from the group consisting of polypropylene, random polypropylene (random PP), and linear low density polyethylene (LLDPE), but is not limited thereto. Preferably, when polypropylene as a copolymer is included, the case adhesive layer 230 melts sufficiently at the sealing temperature, so that the lead film 190 and the soft package type case 110 can be easily sealed.

[0085] 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 the above numerical range, the case adhesive layer 230 melts during a specific production time (operation time), so that the lead film 190 and the soft package type case 110 can be easily sealed.

[0086] (5) Electrolyte

[0087] 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 move lithium ions generated by an electrochemical reaction through the electrodes during charging and 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. Additionally, the electrolyte may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a polymer-based solid electrolyte, and such a solid electrolyte may be flexible and thus easily deformed under an external force.

[0088] Hereinafter, the present invention will be described in more detail through specific examples. However, the examples shown below are only for understanding the present invention, and the scope of the present invention concept is not limited thereto. It will be apparent to those skilled in the art that various modifications and changes can be made within the scope and technical scope of the present invention, and such modifications and changes fall within the scope of the claims included herein.

[0089] Examples and Comparative Examples

[0090] Example 1

[0091] (1) Manufacturing a lead assembly

[0092] CaCO3 (average particle size D 50 : 2.8 μm) was mixed with a polypropylene homopolymer and extruded to a thickness of 62.4 μm to prepare a polypropylene homopolymer film, and an acid-modified polypropylene film (lead adhesive layer) with a thickness of 62.4 μm, a polypropylene homopolymer film (filler layer), and a polypropylene copolymer film (case adhesive layer) with a thickness of 72.4 μm were sequentially laminated to prepare a lead film.

[0093] In this case, the amount of CaCO3 was measured using a thermogravimetric analyzer (TGA, METTLER TOLEDO) in the temperature range of 50 °C to 800 °C by purging with N2 at a heating rate of 10 °C / min, and based on the total weight of the lead film, this amount was determined to be 10 wt%.

[0094] Then, the lead film was set to surround the outer peripheral surface of an electrode lead having a thickness of 40 μm to manufacture a lead assembly.

[0095] (2) Manufacturing a pouch-type case

[0096] 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, and a polyethylene terephthalate (PET) film with a width of 266 mm, a length of 50 m, and a thickness of 12 μm are laminated on one side of an aluminum alloy film with a width of 266 mm, a length of 50 m, and a thickness of 60 μm, and a polypropylene film with a width of 266 mm, a length of 50 m, and a thickness of 80 μm is laminated on the other side to prepare a soft package laminate with a polyethylene terephthalate / nylon / aluminum alloy film / polypropylene film structure.

[0097] In this case, the first adhesive film, the nylon film, the second adhesive film, and the polyethylene terephthalate film are base layers, the aluminum alloy film is a gas barrier layer, and the polypropylene film is a sealant layer.

[0098] The soft package laminate is molded to manufacture a soft package type housing including a receiving portion and a sealing portion.

[0099] (3) Manufacturing a soft package type secondary battery

[0100] The positive electrode, the negative electrode, and the porous polyethylene separator are assembled using a lamination method and then laminated to manufacture an electrode assembly. After that, the lead assembly is combined with the electrode assembly.

[0101] LiPF6 is dissolved in a solvent (volume ratio of EC:EMC:DMC = 3:3:4) to 1.0 M to prepare an electrolyte. The electrode assembly is housed in the soft package type housing, the front end portion of the lead assembly protrudes to the outside, and the electrolyte is injected.

[0102] After that, the sealing portion of the soft package type housing is sealed for 2 seconds under the conditions of a sealing strip area of 200 mm × 5 mm, 220 °C, and 0.1 MPa to prepare a soft package type secondary battery. In this case, in the sealing portion, the portion forming the lead assembly has a structure of successively laminating a lower housing / lead film / electrode lead / lead film / upper housing.

[0103] Example 2

[0104] A lead assembly is manufactured in the same manner as in Example 1 except that it contains 7 wt% of CaCO3 based on the total weight of the lead film.

[0105] A soft package type housing and a secondary battery are manufactured in the same manner as in Example 1 except that the above lead assembly is used.

[0106] Example 3

[0107] A lead assembly is manufactured in the same manner as in Example 1 except that it contains 3 wt% of CaCO3 based on the total weight of the lead film.

[0108] Except for using the above-mentioned lead wire assembly, the pouch-type casing and the secondary battery are manufactured in the same manner as in Example 1.

[0109] Example 4

[0110] Except for including CaCO3 in an amount of 5 wt% based on the total weight of the lead wire film, the lead wire assembly is manufactured in the same manner as in Example 1.

[0111] Except for using the above-mentioned lead wire assembly, the pouch-type casing and the secondary battery are manufactured in the same manner as in Example 1.

[0112] Comparative Example 1

[0113] Except for the lead wire film not including CaCO3, the lead wire assembly is manufactured in the same manner as in Example 1.

[0114] Except for using the above-mentioned lead wire assembly, the pouch-type casing and the secondary battery are manufactured in the same manner as in Example 1.

[0115] Comparative Example 2

[0116] Except for including CaCO3 in an amount of 20 wt% based on the total weight of the lead wire film, the lead wire assembly is manufactured in the same manner as in Example 1.

[0117] Except for using the above-mentioned lead wire assembly, the pouch-type casing and the secondary battery are manufactured in the same manner as in Example 1.

[0118] Comparative Example 3

[0119] Except for including CaCO3 in an amount of 15 wt% based on the total weight of the lead wire film and having an average particle diameter D 50 of 0.1 μm, the lead wire assembly is manufactured in the same manner as in Example 1.

[0120] Except for using the above-mentioned lead wire assembly, the pouch-type casing and the secondary battery are manufactured in the same manner as in Example 1.

[0121] Comparative Example 4

[0122] Except for including CaCO3 in an amount of 15 wt% based on the total weight of the lead wire film and having an average particle diameter D 50 of 22 μm, the lead wire assembly is manufactured in the same manner as in Example 1.

[0123] Except for using the above-mentioned lead wire assembly, the pouch-type casing and the secondary battery are manufactured in the same manner as in Example 1.

[0124] Comparative Example 5

[0125] The lead assembly was manufactured in the same manner as in Example 1, except that block polypropylene (block PP) was applied instead of the polypropylene homopolymer film as the filler layer and CaCO3 was included in an amount of 15 wt% based on the total weight of the lead film.

[0126] The pouch-type case and the secondary battery were manufactured in the same manner as in Example 1, except that the above lead assembly was used.

[0127] Comparative Example 6

[0128] The lead assembly was manufactured in the same manner as in Example 1, except that block polypropylene (block PP) was applied instead of the polypropylene homopolymer film as the filler layer and CaCO3 was included in an amount of 7 wt% based on the total weight of the lead film.

[0129] The pouch-type case and the secondary battery were manufactured in the same manner as in Example 1, except that the above lead assembly was used.

[0130] Experimental Example 1: Evaluation of the extrusion processability of the polypropylene homopolymer film

[0131] The extrusion processability of the polypropylene homopolymer films prepared in Examples 1 to 4 and Comparative Examples 1 to 6 was evaluated. Specifically, when extruding the polypropylene homopolymer resin containing CaCO3, the appearance of the extruded film was visually observed, and its extrusion processability is shown in Table 1 below.

[0132] Experimental Example 2: Evaluation of the adhesion strength between the electrode lead and the lead film

[0133] The adhesion strength of the lead assemblies manufactured in Examples 1 to 4 and Comparative Examples 1 to 6 to the electrolyte solution was measured. Specifically, the lead assemblies were immersed in an electrolyte solution (volume ratio of EC:EMC:DMC = 3:3:4, 1.0 M LiPF6) and stored in a chamber at 60 °C and 90% humidity for 2 weeks. The lead assemblies were taken out of the electrolyte solution, the remaining electrolyte solution was washed off and placed in air. Before and after immersing the above lead assemblies in the electrolyte solution, the electrode lead was bent and broken at a portion 10 mm away from one edge of the lead assembly, then the two ends of the lead assembly were respectively connected to the lower and upper jigs of the UTM, and then stretched in the direction of 180 °C at a speed of 50 mm / min for 30 mm to calculate the average value (N / 10 mm) of the flat section of the measured adhesion strength curve. The sealing strength between the electrode lead and the lead film after immersion in the electrolyte solution and the decrease rate (%) of the sealing strength after immersion in the electrolyte solution compared to before immersion in the electrolyte solution were measured by the above method and are shown in Table 1 below.

[0134] Experimental Example 3: Evaluation of the sealing strength and interlayer separation of the pouch-type secondary battery

[0135] The sealing strength of the pouch-type secondary batteries fabricated in Measurement Examples 1 to 4 and Comparative Examples 1 to 6 was measured, and delamination in the sealed portion of the pouch-type secondary batteries was observed.

[0136] Specifically, in the pouch-type secondary battery, the sealed portion where the lead assembly and the pouch film laminate were sealed was cut at 15-mm intervals, and then the electrode lead was connected to the lower jig of the UTM and the pouch film laminate was connected to the upper jig, and then the resulting product was pulled 30 mm in the direction of 180° at a rate of 5 mm / min at room temperature of 25°C to calculate the sealing strength from the average value of the flat section of the measured adhesion strength curve. Further, when the sealed portion was opened, the cross section of the sealed portion was observed to determine the presence of delamination in the lead film. The results are shown in Table 1 below.

[0137] O: There is a separation interface between the lead adhesive layer and the case adhesive layer

[0138] X: There is no separation interface between the lead adhesive layer and the case adhesive layer

[0139] [Table 1]

[0140]

[0141] According to Table 1, for Examples 1 to 4, in which the amount of the ceramic filler was 1 wt% to 14 wt% based on the total weight of the lead film and the filler layer containing the ceramic filler was also applied as a polypropylene homopolymer, it can be seen that the extrusion processability of the polypropylene homopolymer film was satisfactory and that, after electrolyte precipitation, the performance of the lead film (such as adhesion strength, the rate of decrease in adhesion strength, and sealing strength) was excellent. However, for Comparative Example 1, the ceramic filler was not included, and thus it can be seen that the adhesion strength of the lead assembly was low after electrolyte precipitation and that the adhesion strength decreased significantly, resulting in poor durability; for Comparative Example 2, it can be seen that the sealing strength was low due to the high amount of the ceramic filler; and for Comparative Examples 3 and 4, it can be seen that the sealing strength was relatively low due to the high amount of the ceramic filler and that delamination occurred.

[0142] Further, for Comparative Examples 5 and 6, in which block polypropylene was applied as the filler layer, it can be seen that the sealing strength was very low and that delamination even occurred, and when these two comparative examples were compared with Example 1 and Comparative Example 2, it can be seen that when block polypropylene was applied, the effect was poor regardless of whether the amount of the ceramic filler was within the range of 1 wt% to 14 wt%, but when polypropylene homopolymer was applied, it can be seen that, after electrolyte precipitation, there was a significant difference in the adhesion strength and sealing strength of the lead assembly depending on whether the above range was satisfied. Therefore, it can be inferred that the amount of the ceramic filler and the type of the filler layer containing the ceramic filler produced a mutual synergistic effect.

[0143] Description of Reference Numerals

[0144] 100: Soft-pack secondary battery

[0145] 110: Soft-pack housing

[0146] 120: First housing

[0147] 122: Cup portion

[0148] 124: Accommodating portion

[0149] 130: Second housing

[0150] 132: Cup portion

[0151] 140: Bridging portion

[0152] 150: Sealing portion

[0153] 160: Electrode assembly

[0154] 170: Electrode tab

[0155] 172: Positive electrode tab

[0156] 174: Negative electrode tab

[0157] 180: Electrode lead

[0158] 182: Positive electrode lead

[0159] 184: Negative electrode lead

[0160] 190: Lead film

[0161] 210: Lead adhesive layer

[0162] 220: Base layer

[0163] 230: Housing adhesive layer

[0164] 240: Ceramic filler

Claims

1. A pouch-type secondary battery, comprising: An electrode assembly; A pouch-type housing, the pouch-type housing including a receiving portion for receiving the electrode assembly and a sealing portion for sealing the receiving portion; An electrode lead, the electrode lead being connected to the electrode assembly and protruding to the outside of the pouch-type housing via the sealing portion; And A lead film, the lead film being disposed between the electrode lead and the pouch-type housing, Wherein the lead film has a multi-layer structure and includes a filler layer, the filler layer including a polypropylene homopolymer and a ceramic filler, and based on the total weight of the lead film, the content of the ceramic filler is 1 wt% to 14 wt%.

2. The pouch-type secondary battery according to claim 1, wherein, The ceramic filler includes at least one selected from the group consisting of CaCO3, Ca(OH)2, CaCl2, CaO, KOH, NaOH, and Na2CO3.

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

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

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

6. The pouch-type secondary battery according to claim 1, wherein, Based on the total weight of the lead film, the content of the ceramic filler is 3 wt% to 10 wt%.

7. The pouch-type secondary battery according to claim 1, wherein, The thickness of the base layer is 45 μm to 80 μm.

8. The pouch-type secondary battery according to claim 3, wherein, The housing adhesive layer contains polypropylene, and The polypropylene is a copolymer.

9. The pouch-type secondary battery according to claim 3, wherein, The thickness of the housing adhesive layer is 55 μm to 80 μm.

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

11. The pouch-type secondary battery according to claim 1, wherein, The surface of the electrode lead in direct contact with the lead film is coated with at least one selected from the group consisting of chromium (Cr), nickel (Ni), alumina (A12O3), zirconium (Zr), and titanium (Ti).

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

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