KR102379222B1 - Pouch-type case for secondary battery - Google Patents

Abstract

The present invention relates to a pouch-type case for a secondary battery comprising a cross-linked polyolefin as a resin layer of a laminate sheet constituting a pouch-type secondary battery, and a lithium secondary battery including the same.

Description

Pouch-type case for secondary batteries {POUCH-TYPE CASE FOR SECONDARY BATTERY}

The present invention relates to a pouch-type case for a secondary battery, and more particularly, to a pouch-type case for a secondary battery comprising a cross-linked polyolefin as a resin layer of a laminate sheet constituting a pouch-type secondary battery.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and widely used.

In addition, as interest in environmental issues has increased in recent years, electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, have been developed. A lot of research is going on. Although nickel-metal hydride (Ni-MH) secondary batteries are mainly used as power sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs), lithium secondary batteries with high energy density, high discharge voltage and output stability are used. Research is being actively conducted, and some have been commercialized.

Lithium secondary batteries may be largely classified into cylindrical batteries, prismatic batteries, pouch-type batteries, etc. according to their external appearance, and may be classified into lithium ion batteries, lithium ion polymer batteries, lithium polymer batteries, etc. according to the type of electrolyte.

Due to the recent trend toward miniaturization of mobile devices, the demand for thin prismatic batteries and pouch-type batteries is increasing. Interest is high. A pouch-type battery is a battery in which an electrode assembly having a positive electrode/separator/negative electrode structure is embedded in a battery case made of a laminate sheet including a resin layer and a metal layer in a pouch shape.

In general, a laminate sheet used in a pouch-type battery has a metal layer and a resin layer formed on both surfaces of the metal layer. One resin layer formed on both sides of the metal layer forms the outer shell of the pouch-type battery, and one is positioned inside. The resin layer (outer layer) forming the outer shell of the pouch-type battery has a function of protecting the battery from the outside, and the resin layer (inner layer) positioned on the inside has a function of sealing the pouch-type battery by bonding to each other. On the other hand, the metal layer has a function of preventing air, moisture, etc. from entering the inside of the battery, while preventing the penetration of materials.

Polyolefin-based resin such as polypropylene having heat sealing properties is used as the inner layer for sealing, and polyethylene terephthalate (PET) or nylon resin is generally used for the outer layer as the outer layer.

The polyolefin-based resin used as the inner layer is melted by heat and adhered to each other. However, the polyolefin-based resin has a problem in that its thickness is reduced during heat sealing, and insulation performance is reduced due to the reduced thickness.

On the other hand, the PET or nylon resin used as the outer layer is mainly used because they do not change due to high temperature during heat sealing. do.

Accordingly, there is a demand for the development of a pouch-type case for a secondary battery that does not change the thickness of the sealing portion, improves sealing properties and insulation, and does not cause discoloration on the outside of the pouch-type battery and thus does not have an appearance defect.

KR 10-0645607 B1

SUMMARY OF THE INVENTION An object of the present invention is to provide a pouch-type case for secondary batteries having improved sealing properties and insulating properties, and having no appearance defects.

Another object of the present invention to be solved is to provide a lithium secondary battery including the pouch-type case for secondary batteries.

In order to solve the above problems, the present invention is a metal layer; an outer layer positioned on one surface of the metal layer; And a pouch-type secondary battery case comprising a laminate sheet including an inner layer located on the other surface of the metal layer, wherein the outer layer and the inner layer each independently include a crosslinked polyolefin-based resin, a pouch-type case for secondary batteries to provide.

In addition, the present invention provides a lithium secondary battery including the pouch-type case for the secondary battery in order to solve the other problem.

The pouch-type case for secondary batteries according to the present invention contains cross-linked polyolefin as a resin layer of the laminate sheet constituting the pouch-type secondary battery, so that when the pouch-type secondary battery case is sealed, the sealing property of the resin layer of the sealing part is improved, and the pouch Since discoloration of the external resin layer does not occur, it can be usefully used in the manufacture of a pouch-type secondary battery.

1 is a view showing a cross-section of a laminate sheet constituting a conventional pouch-type case for secondary batteries, and a cross-section of the laminate sheet in a sealing portion of the pouch-type case for secondary batteries.
2 is a view showing a cross-section of a laminate sheet constituting a pouch-type case for secondary batteries according to an example of the present invention, and a cross-section of the laminate sheet in a sealing portion of the pouch-type case for secondary batteries.
3 is a view illustrating a connection form when a plurality of lithium secondary batteries including a pouch-type case for secondary batteries according to an example of the present invention are connected to form a module.
4 is a photograph taken after exposing the outer peripheral surface of the laminate sheet of Preparation Example 1 to an electrolyte and then storing it at 60° C. for 4 weeks.
5 is a photograph taken after exposing the outer peripheral surface of a conventional pouch-type secondary battery to an electrolyte and then storing it at 60° C. for 4 weeks.

Hereinafter, the present invention will be described in more detail to help the understanding of the present invention.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

A pouch-type case for a secondary battery of the present invention includes a metal layer; an outer layer positioned on one surface of the metal layer; and a laminate sheet including an inner layer positioned on the other surface of the metal layer, wherein the outer layer and the inner layer each independently include a crosslinked polyolefin-based resin.

The pouch-type case for a secondary battery of the present invention may have the shape of a battery case of a conventional pouch-type secondary battery.

The metal layer may exhibit a function of improving the strength of the battery case in addition to the function of preventing the inflow or leakage of foreign substances such as gas and moisture, and may be, for example, a layer of aluminum.

The outer layer forms an outer shell of the pouch-type secondary battery case, and allows the battery case to have excellent resistance to external environments. Accordingly, the outer layer needs to have adequate tensile strength and weather resistance. In the pouch-type secondary battery case of the present invention, the outer layer includes a cross-linked polyolefin-based resin, and since a part of the polyolefin is cross-linked in the cross-linked polyolefin-based resin, it can have appropriate tensile strength and weather resistance, and can be easily heated by heat. may not melt. In addition, since the cross-linked polyolefin-based resin included in the outer layer has electrolyte resistance, color change does not occur even when in contact with the electrolyte.

The crosslinked polyolefin-based resin of the outer layer may have a crosslinking degree of 10% to 70%, and specifically may have a crosslinking degree of 30% to 50%.

Since the crosslinked polyolefin-based resin included in the outer layer has a crosslinking degree of 10% to 70%, the outer layer may have appropriate tensile strength and weather resistance. In addition, since some non-crosslinking regions exist in the polyolefin-based resin, after mounting the electrode assembly in the pouch-type secondary battery case, the laminate sheet is overlapped and sealed to form a sealing part, and then the sealing part is bent to form the pouch. The bent portion may be thermally bonded to the pouch-type secondary battery case, and when a separate module is installed in the pouch-type secondary battery case, the module may be thermally bonded to the outer layer of the pouch-type secondary battery case.

The pouch-type case for a secondary battery may include a sealing part formed along an edge, and in the sealing part, the laminate sheet may be overlapped so that the inner layers face each other and sealed to each other by thermal bonding. For the thermal bonding, the inner layer may have thermal sealing properties.

Since the inner layer includes the cross-linked polyolefin-based resin, it has low hygroscopicity to suppress the penetration of the electrolyte, and may have a property of not being swelled or eroded by the electrolyte.

The crosslinked polyolefin-based resin of the inner layer may have a crosslinking degree of 10% to 70%, and specifically may have a crosslinking degree of 30% to 50%.

Since the crosslinked polyolefin-based resin included in the inner layer has a crosslinking degree of 10% to 70%, it is easily melted to the inside in the direction of the metal layer of the resin constituting the inner layer by heat during thermal bonding to increase the thickness of the inner layer By not reducing, the thickness of the inner layer is maintained when the inner layer forms the sealing part, so that the sealing properties and insulating properties of the sealing part are improved. The thickness of the inner layer after thermal bonding may be specifically 60% to 100% based on the thickness before thermal bonding, and more specifically 80% to 100%.

In the outer layer or inner layer, the polyolefin-based resin may be at least one selected from the group consisting of polypropylene (PP) and polyethylene (PE), and the cross-linked polyolefin-based resin is specifically cross-linked polyethylene , cross-linked polypropylene, or a mixture thereof, and more specifically, cross-linked polypropylene.

Examples of the method for producing the cross-linked polyolefin-based resin include a method of forming a cross-linked structure by irradiating the polyolefin-based resin with radiation such as electron beams or gamma rays; a method of irradiating radiation after adding a functional monomer such as a crosslinking agent to the polyolefin-based resin; and a method of irradiating UV or the like after adding a functional monomer such as a crosslinking agent to the polyolefin-based resin, but is not particularly limited as long as it is a method capable of forming a crosslinked structure on the polyolefin-based resin.

The polyolefin-based resin that can be used in the process of preparing the cross-linked polyolefin-based resin may be at least one selected from the group consisting of a homopolymer of the polyolefin and a copolymer including two or more olefin-derived repeating units. When the cross-linked polyolefin-based resin is, for example, cross-linked polypropylene, the cross-linked polypropylene is a homo polypropylene and/or random ter-polypropylene containing 1 mol% to 10 mol% of ethylene and butene, respectively. polypropylene; RTPP).

The functional monomer such as the crosslinking agent is not particularly limited as long as it is a crosslinking agent capable of accelerating the crosslinking of the polyolefin-based resin. For example, triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), trimethyl and trimethylolpropanetriacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTMA), ethylene glycol dimethacrylate, or polyethylene glycol dimethacrylate.

In the specification of the present invention, that the outer layer and the inner layer each independently include a cross-linked polyolefin-based resin means that the outer layer and the inner layer include a cross-linked polyolefin-based resin, but the type and/or degree of cross-linking are the same or , which means that each may be different.

The degree of crosslinking of the crosslinked polyolefin-based resin may be measured using the ASTM D2765 method. Specifically, a predetermined amount of the sample is pulverized and prepared in powder form, then put into a timble filter, and then, using xylene contained in a reactor connected to a cooler, the sample is heated at 110° C. for 12 hours. After dissolving all of the non-crosslinked components by circulation, it can be obtained by measuring the weight of the crosslinked and undissolved sample compared to the weight of the initially added sample, and then calculating by the following formula.

Crosslinking degree (%) = (weight of sample not dissolved in solvent / weight of sample initially added) × 100

The pouch-type secondary battery case is, for example, prepared by preparing two laminate sheets, placing the laminate sheets one by one on the upper and lower surfaces of the electrode assembly, and then bringing the outer peripheral surfaces of the laminate sheets located on the upper and lower surfaces into contact with each other. , may be formed by combining them with each other, and alternatively, after bending the middle of one laminate sheet so that one laminate sheet is superimposed on each other, and then placing the electrode assembly inside the bent laminate sheet, the laminate sheet After making the outer peripheral surface of the contact with each other, it can be formed by combining them with each other.

An adhesive layer may be additionally included between the outer layer and the metal layer, between the inner layer and the metal layer, or both. The adhesive layer may serve to improve the adhesion of the cross-linked polyolefin-based resin including the outer layer and the inner layer to a metal. The adhesive layer is not particularly limited, but may include, for example, a composition containing a urethane-based material, an acryl-based material, a thermoplastic elastomer, and a combination thereof.

The pouch-type case for a secondary battery may be used as a case for a lithium secondary battery, and thus the present invention provides a lithium secondary battery including the pouch-type case for a secondary battery.

The lithium secondary battery according to an example of the present invention may be a pouch-type secondary battery in which an electrode assembly is embedded in a pouch-type secondary battery case including a laminate sheet including a metal layer, an outer layer, and an inner layer.

The battery case of the laminate sheet may have a pouch shape, and the electrode assembly may be embedded in the pouch.

It may be formed by placing an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode on the inside of the surface of the laminate sheet, that is, an inner layer, and then wrapping the electrode assembly with the laminate sheet.

The sealing part may be formed along the edge of the pouch-type secondary battery case, and the width of the sealing part may be 100 μm to 5 mm, specifically, 1 mm to 3 mm.

The electrode assembly included in the pouch-type secondary battery may be an electrode assembly for a lithium secondary battery, and thus the pouch-type secondary battery of the present invention may be a pouch-type lithium secondary battery.

The lithium secondary battery may include a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the lithium secondary battery may be a stack type or stack and folding type lithium secondary battery there is.

The stack-type lithium secondary battery may be a lithium secondary battery including an electrode assembly manufactured by vertically stacking a negative electrode, a separator, and a positive electrode, and the stack-and-folding type lithium secondary battery is a positive electrode/separator/ Manufactured by rolling or folding a full cell with a cathode structure or a bicell with a cathode (cathode)/separator/cathode (anode)/separator/anode (cathode) structure using a long continuous separation film. It may be a lithium secondary battery including an electrode assembly.

The positive electrode may be manufactured by a conventional method known in the art. For example, a positive electrode can be manufactured by mixing and stirring the positive electrode active material with a solvent and, if necessary, a binder, a conductive material, and a dispersant, then applying (coating) it to a current collector made of a metal material, compressing it, and drying it. there is.

The current collector of the metallic material is a metal with high conductivity, and is a metal to which the slurry of the positive electrode active material can be easily adhered. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. In addition, by forming fine irregularities on the surface of the current collector, the adhesive force of the positive electrode active material may be increased. The current collector may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body, and may have a thickness of 3 to 500 μm.

In the method of manufacturing a lithium secondary battery of the present invention, the positive active material may include, for example, lithium cobalt oxide (LiCoO ₂ ); lithium nickel oxide (LiNiO ₂ ); Li[Ni _a Co _b Mn _c M ¹ _d ]O ₂ (Wherein, M ¹ is any one selected from the group consisting of Al, Ga, and In, or two or more of them, 0.3≤a<1.0, 0 ≤b≤0.5, 0≤c≤0.5, 0≤d≤0.1, a+b+c+d=1); Li(Li _e M ² _fe-f' M ³ _f' )O _{2 -g A g} (wherein, 0≤e≤0.2, 0.6≤f≤1, 0≤f'≤0.2, 0≤g≤0.2, and , M ² is Mn and Ni, Co, Fe, Cr, V, Cu, Zn and Ti includes at least one selected from the group, M ³ is Al, Mg and 1 selected from the group consisting of B more than one species, and A is at least one selected from the group consisting of P, F, S and N) or a layered compound such as a compound substituted with one or more transition metals; Li _{1 + h} Mn _{2 -h} O _{4 (} 0≤h≤0.33 in the above formula), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ Lithium manganese oxide such as; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site type lithium nickel oxide represented by the formula LiNi _{1 - i} M ⁴ _i O ₂ (wherein, M ⁴ is Co, Mn, Al, Cu, Fe, Mg, B or Ga, and 0.01≤i≤0.3); Formula LiMn _{2 - j} M ⁵ _j O ₂ (wherein M ⁵ is Co, Ni, Fe, Cr, Zn or Ta, 0.01≤j≤0.1) or Li ₂ Mn ₃ M ⁶ O ₈ (wherein, M ⁶ is a lithium manganese composite oxide represented by Fe, Co, Ni, Cu or Zn); LiMn ₂ O ₄ in which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; LiFe ₃ O ₄ , Fe ₂ (MoO ₄ ) ₃ , and the like may be mentioned, but are not limited thereto.

Examples of the solvent for forming the positive electrode include organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, and dimethyl acetamide or water, and these solvents are used alone or in two or more types. can be mixed and used. The amount of the solvent used is sufficient as long as it is capable of dissolving and dispersing the positive electrode active material, the binder, and the conductive material in consideration of the application thickness of the slurry and the production yield.

As the binder, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and a polymer in which hydrogen is substituted with Li, Na or Ca, or the like; or Various types of binder polymers such as various copolymers may be used.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, farness black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. The conductive material may be used in an amount of 1 wt% to 20 wt% based on the total weight of the positive electrode slurry.

The dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The negative electrode may be manufactured by a conventional method known in the art, for example, by mixing and stirring the negative electrode active material and additives such as a binder and a conductive material to prepare a negative electrode active material slurry, which is then applied to the negative electrode current collector and dried It can be prepared by compression afterwards.

The binder may be used to bind the negative active material particles to maintain the molded body, and is not particularly limited as long as it is a conventional binder used in preparing a slurry for the negative electrode active material, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxy non-aqueous binder. Propylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyethylene or polypropylene, etc. can be used, and acrylic as an aqueous binder Any one selected from the group consisting of lonitrile-butadiene rubber, styrene-butadiene rubber, and acrylic rubber, or a mixture of two or more thereof may be used. Aqueous binders are economical and eco-friendly compared to non-aqueous binders, are harmless to workers' health, and have a superior binding effect compared to non-aqueous binders. Preferably, a styrene-butadiene rubber may be used.

The binder may be included in an amount of 10% by weight or less in the total weight of the slurry for the negative electrode active material, and specifically, it may be included in an amount of 0.1 to 10% by weight. If the content of the binder is less than 0.1% by weight, the effect of using the binder is insignificant and is not preferable. not.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. Examples of the conductive material include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives. The conductive material may be used in an amount of 1 wt% to 9 wt% based on the total weight of the slurry for the negative electrode active material.

The negative electrode current collector used for the negative electrode according to an embodiment of the present invention may have a thickness of 3 μm to 500 μm. The negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, copper, gold, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface Carbon, nickel, titanium, one surface-treated with silver, an aluminum-cadmium alloy, etc. may be used. In addition, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwovens.

In addition, as the separator, a conventional porous polymer film conventionally used as a separator, such as an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer, and an ethylene-methacrylate copolymer such as a polyolefin-based polymer The porous polymer film prepared by ? can be used alone or by laminating them, or a conventional porous nonwoven fabric, such as a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc., can be used, but is not limited thereto.

In the lithium secondary battery, lithium salts commonly used in electrolytes for lithium secondary batteries may be used without limitation, for example, as an anion of the lithium salt, F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may be any one selected from the group consisting of.

Examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries. not.

Hereinafter, the pouch-type secondary battery of the present invention and a method for manufacturing the same will be described in more detail with reference to the drawings, but the drawings are only for illustrating the present invention and the scope of the present invention is not limited thereto. In the drawings of the present invention, the size of each component may be exaggerated for explanation, and may be different from the size actually applied.

1 shows a cross-section of a laminate sheet constituting a conventional pouch-type case for secondary batteries, and a cross-section of the laminate sheet in a sealing portion of the pouch-type case for secondary batteries.

Referring to Figure 1, in the conventional laminate sheet constituting the pouch-type case for secondary batteries, outer layers 11 and 11' are located on one surface of the metal layers 10, 10', and inner layers 12 and 12' are located on the other surface. do. The pouch-type case for secondary batteries is sealed by mounting an electrode assembly (not shown) and bringing the outer peripheral surface of the laminate sheet into contact with each other to form a sealing part, wherein the sealing part is thermally bonded to the inner layers 12 and 12' in contact with each other. formed by becoming The figure shown to the right of the arrow in FIG. 1 shows the cross section of the sealing part of the conventional pouch-type case for secondary batteries. They are heat-sealed to each other and their thickness is reduced.

2 shows a cross-section of a laminate sheet constituting a pouch-type case for secondary batteries according to an example of the present invention, and a cross-section of the laminate sheet in a sealing portion of the pouch-type case for secondary batteries.

2, the laminate sheet constituting the pouch-type case for secondary batteries according to an example of the present invention has outer layers 110 and 110' on one surface of the metal layers 100 and 100', and the metal layers 100 and 100'. The inner layers 120 and 120' are positioned on the other surface. Like FIG. 1, a cross-section of the sealing part of the pouch-type case for secondary batteries according to an example of the present invention is shown on the right side of the arrow in FIG. 2, and with reference to this, the inner layers 120 and 120 in the pouch-type case for secondary batteries according to an example of the present invention. ') is insignificant even if it is heat-sealed to each other by thermal bonding, which is an effect that can be achieved by including the cross-linked polyolefin-based resin in the inner layer.

Meanwhile, FIG. 3 exemplarily shows a connection form when a plurality of lithium secondary batteries according to an example of the present invention including the pouch-type case for secondary batteries are connected to form a module. In the description of FIG. 3 , that the lithium secondary battery cells are connected and that the coupling part is formed means that they can be physically connected or coupled to each other, and does not indicate that they are electrically connected.

3A shows a form in which lithium secondary batteries are arranged side by side. Referring to (a) of Figure 3, the lithium secondary battery cells 200, the outer peripheral surface 210 of the pouch-type case for a secondary battery of the lithium secondary battery cell is overlapped with each other and thermally bonded to form a coupling portion 220 with each other. . In addition, the form in which the lithium secondary batteries are superimposed on each other is shown in (b) of FIG. Referring to (b) of FIG. 3 , the lithium secondary battery cells 200 are superimposed on each other and connected, and the outer surfaces of the pouch-type case body for the secondary battery of the lithium secondary battery cell are overlapped and thermally bonded to form a coupling portion 230 . can do.

As described above, in the lithium secondary battery including the pouch-type case for secondary batteries of the present invention, since the outer layer of the laminate sheet constituting the pouch-type case of the lithium secondary battery is made of a cross-linked polyolefin-based resin, it has heat-sealability and has a plurality of When a module including a secondary battery cell is configured, it can be physically connected and coupled to each other without a separate adhesive member or a connecting member.

Example

Hereinafter, examples and experimental examples will be described in more detail to describe the present invention in detail, but the present invention is not limited by these examples and experimental examples. Embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Preparation Example 1

After adding 2.96 parts by weight of trimethylolpropane triacrylate (TMPTA) and 0.5 parts by weight of antioxidant to 100 parts by weight of homopolypropylene powder, stirring for 30 minutes, and storing for 24 hours, using an electron beam accelerator, 60 kGy of A 50% crosslinked polypropylene (as measured by ASTM D2765) was prepared by irradiation with an electron beam.

Preparation 2

A 10% crosslinked polypropylene (measured by ASTM D2765) was prepared in the same manner as in Preparation Example 1, except that an electron beam of 2 kGy was irradiated using an electron beam accelerator.

Preparation 3

A 30% cross-linked polypropylene (measured by ASTM D2765) was prepared in the same manner as in Preparation Example 1, except that an electron beam of 3 kGy was irradiated using an electron beam accelerator.

Preparation 4

A 70% crosslinked polypropylene (measured by ASTM D2765) was prepared in the same manner as in Preparation Example 1, except that an electron beam of 5 kGy was irradiated using an electron beam accelerator.

Preparation 5

A homopolypropylene powder (manufactured by OKAMOTO) having a degree of crosslinking of 0% was used as Production Example 5.

Example Preparation Example 1

An aluminum foil having a thickness of 40 μm (manufactured by Dongil Aluminum) was acid degreased by immersion in 5% sulfuric acid solution, and then immersed in 5% sodium hydroxide solution to activate the surface. Then, after applying a polyurethane adhesive resin (manufactured by Hichem Corporation) having a thickness of 4 μm, 50% crosslinked polypropylene prepared in Preparation Example 1 (ASTM D2765 measurement) on both sides of the aluminum foil coated with the polyurethane adhesive resin ) was applied to a thickness of 25 μm and 80 μm, respectively, and then the 50% cross-linked polypropylene was dry-laminated and laminated to prepare a laminate sheet having a total thickness of 153 μm.

In the laminate sheet on which the crosslinked polypropylene layer is formed on both sides, the side on which the crosslinked polypropylene layer of 80 μm thick is formed as the inner layer, and the other side on which the crosslinked polypropylene layer with the thickness of 25 μm is formed as the outer layer. .

Example Preparation 2

In the same manner as in Preparation Example 1, except that the 10% cross-linked polypropylene prepared in Preparation Example 2 (as measured by ASTM D2765) was used, cross-linking having a thickness of 25 μm and 80 μm, respectively, on both sides of the aluminum foil A laminate sheet having a polypropylene layer formed thereon was prepared.

In the laminate sheet on which the crosslinked polypropylene layer is formed on both sides, the side on which the crosslinked polypropylene layer of 80 μm thick is formed as the inner layer, and the other side on which the crosslinked polypropylene layer with the thickness of 25 μm is formed as the outer layer. .

Example Preparation 3

In the same manner as in Preparation Example 1, except that the 30% cross-linked polypropylene prepared in Preparation Example 3 (as measured by ASTM D2765) was used, cross-linking of 25 μm and 80 μm thick on both sides of the aluminum foil, respectively A laminate sheet having a polypropylene layer formed thereon was prepared.

In the laminate sheet on which the crosslinked polypropylene layer is formed on both sides, the side on which the crosslinked polypropylene layer of 80 μm thick is formed as the inner layer, and the other side on which the crosslinked polypropylene layer with the thickness of 25 μm is formed as the outer layer. .

Example Preparation 4

Except for using the 70% cross-linked polypropylene prepared in Preparation Example 4 (as measured by ASTM D2765), in the same manner as in Preparation Example 1, cross-linking of 25 μm and 80 μm thick on both sides of the aluminum foil, respectively A laminate sheet having a polypropylene layer formed thereon was prepared.

In the laminate sheet on which the crosslinked polypropylene layer is formed on both sides, the side on which the crosslinked polypropylene layer of 80 μm thick is formed as the inner layer, and the other side on which the crosslinked polypropylene layer with the thickness of 25 μm is formed as the outer layer. .

Example Preparation 5

An aluminum foil having a thickness of 40 μm (manufactured by Dongil Aluminum) was acid degreased by immersion in 5% sulfuric acid solution, and then immersed in 5% sodium hydroxide solution to activate the surface. Thereafter, after applying a polyurethane adhesive resin (manufactured by Hichem) having a thickness of 4 μm, 30% crosslinked polypropylene prepared in Preparation Example 3 (ASTM D2765 measurement) on both sides of the aluminum foil coated with the polyurethane adhesive resin ) and 50% cross-linked polypropylene prepared in Preparation Example 1 (as measured by ASTM D2765) were applied to a thickness of 25 μm and 80 μm, respectively, and then the 50% cross-linked polypropylene was laminated by dry laminating to a total thickness of 153 A laminate sheet of μm was prepared.

In the laminate sheet on which the polypropylene layer is formed on both sides, the side on which the polypropylene layer having a thickness of 80 μm is formed is set as the inner layer, and the other side on which the polypropylene layer having the thickness of 25 μm is formed is set as the outer layer.

Comparative Preparation Example 1

An aluminum foil having a thickness of 40 μm (manufactured by Dongil Aluminum) was acid degreased by immersion in 5% sulfuric acid solution, and then immersed in 5% sodium hydroxide solution to activate the surface. Then, after applying a polyurethane adhesive resin (manufactured by Hichem) having a thickness of 4 μm, the homo polypropylene of Preparation Example 5 was applied to both sides of the aluminum foil coated with the polyurethane adhesive resin to a thickness of 25 μm and 80 μm, respectively. After application, the homopolypropylene was laminated by dry laminating to prepare a laminate sheet having a total thickness of 153 μm.

Experimental Example 1: Measurement of PP Residual Rate and Sealing Strength

After preparing the laminate sheets prepared in Examples 1 to 4 and Comparative Preparation Example 1 to a size of 160 mm × 100 mm, the inner resin layers were folded in contact with each other, and the outer peripheral surface was heat-sealed at 200° C. using a heat sealing device. By doing so, a pouch-type case was manufactured.

After cutting the sealed film to have a sample width of 15 mm, the thickness of the sealing part was measured, and the sealing strength was measured using UTM equipment (test speed: 50 mm/min, jig spacing: 30 mm, strength: 5 N). did . 5 each of the laminate films prepared in Preparation Examples 1 to 4 and Comparative Preparation Example 1 were prepared and tested 5 times each, and the results are shown in Table 1.

Thickness after sealing (㎛) PP residual rate after sealing Sealing strength (N/15mm) practice
production example
One #One 284 86% 96.32 #2 281 84% 74.74 #3 281 84% 82.16 #4 281 84% 92.92 #5 286 88% 88.60 Average 282.6 85% 86.95 practice
production example
2 #One 250 65% 80.70 #2 253 67% 86.80 #3 252 66% 85.28 #4 252 66% 81.92 #5 252 66% 78.92 Average 251.8 66% 82.72 practice
production example
3 #One 266 75% 119.28 #2 272 79% 113.92 #3 268 76% 128.62 #4 267 76% 122.86 #5 265 74% 121.80 Average 267.6 76% 121.30 practice
production example
4 #One 291 91% 76.72 #2 291 91% 76.96 #3 296 94% 71.02 #4 292 91% 75.52 #5 292 91% 70.28 Average 292.4 92% 74.10 comparison
production example
One #One 233 54% 55.48 #2 233 54% 50.9 #3 228 51% 55.10 #4 229 52% 45.44 #5 231 53% 57.78 Average 230.8 53% 52.94

In Table 1, the PP residual ratio after sealing is a value obtained by dividing the thickness after heat sealing of the inner layer (sealing part) by the thickness before heat sealing.

Referring to Table 1, when a pouch-type case was manufactured using the laminate resin of Preparation Examples 1 to 4 containing a crosslinked polypropylene resin, the laminate resin of Comparative Preparation Example 1 containing a general non-crosslinked polypropylene resin It was confirmed that the sealing strength was increased after sealing compared to when the pouch-type case was manufactured using

In addition, when a pouch-type case was manufactured using the laminate resin of Preparation Examples 1 to 4 containing a cross-linked polypropylene resin, the pouch-type case was prepared using the laminate resin of Comparative Preparation Example 1 containing a non-cross-linked polypropylene resin. It was confirmed that the reduction in the thickness of the sealing part after sealing was reduced compared to the time of manufacturing , and thus the insulation was improved as well as the improved sealing properties.

As can be seen from the above experimental results, as the degree of crosslinking increases, the change in the thickness of the sealing part after sealing decreases, and as the degree of crosslinking decreases, the sealing strength increases. The degree of crosslinking may be appropriately selected and controlled.

Experimental Example 2: Confirmation of discoloration due to electrolyte

After preparing the laminate sheet of Preparation Example 1 in a size of 160 mm x 100 mm, the inner layers were folded in contact with each other, and the outer peripheral surface was heat-sealed at 200 ° C. using a heat sealing device to prepare a pouch-type case. In addition, ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 30:70 in a pouch-type case for lithium secondary batteries manufactured using a laminate sheet laminated in the form of polypropylene/aluminum/nylon/PET. A dummy cell in which an electrolyte solution in which 1M LiPF ₆ is dissolved in one solvent is injected was prepared. PET, and the outermost layer is PET.

After dropping an electrolyte solution in which 1M LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 30:70 on the outer peripheral surface of the outer layer of each pouch-type case, 4 After weekly storage, it was checked whether the location of the electrolyte exposed was discolored, and the results are shown in FIGS. 4 and 5 .

Referring to FIG. 4 , it can be confirmed that the laminate sheet of Preparation Example 1 did not cause discoloration at the electrolyte contact area even after being stored at 60° C. for 4 weeks after being in contact with the electrolyte. However, as can be seen in FIG. 5 , in the conventional pouch-type lithium secondary battery in which the outer layer is made of a PET resin layer as the outermost layer, it was confirmed that the electrolyte contact area was discolored to yellow.

10, 10', 100, 100': metal layer
11, 11', 110, 110': outer layer
12, 12', 120, 120': inner layer
210: the outer peripheral surface of the pouch-type case for secondary batteries
220, 230: 101: bonding portion of the metal layer
112: coupling portion of the first resin layer

Claims (8)

metal layer; an outer layer positioned on one surface of the metal layer; And as a pouch-type secondary battery case comprising a laminate sheet comprising an inner layer located on the other surface of the metal layer,
The outer layer and the inner layer each independently include a crosslinked polyolefin-based resin,
The crosslinked polyolefin-based resin has a crosslinking degree of 30% to 50%, a pouch-type case for a secondary battery.
delete The method of claim 1,
The polyolefin-based resin is at least one selected from the group consisting of polypropylene (PP) and polyethylene (PE), a pouch-type case for secondary batteries.
The method of claim 1,
A pouch-type case for secondary batteries, further comprising an adhesive layer positioned between the outer layer and the metal layer, between the inner layer and the metal layer, or both.
5. The method of claim 4,
The adhesive layer comprises a composition containing a urethane-based material, an acrylic material, a thermoplastic elastomer, and a combination thereof, a pouch-type case for a secondary battery.
The method of claim 1,
The pouch-type case for secondary batteries includes a sealing part formed along the edge,
In the sealing part, the laminate sheet overlaps so that the inner layers face each other and is sealed by thermal bonding, a pouch-type case for a secondary battery.
7. The method of claim 6,
The inner layer has a thickness after thermal bonding of 80% to 100% based on the thickness before thermal bonding, a pouch-type case for secondary batteries.
A lithium secondary battery comprising the pouch-type case for a secondary battery according to claim 1.

Images