KR20110083894A - Secondary battery having structure for preventing internal short-circuit - Google Patents

Abstract

PURPOSE: A secondary battery is provided to improve safety while maintaining the performance of a battery by preventing internal short-circuit caused by contacting an electrode lead and the electrode located on an outmost layer. CONSTITUTION: In a secondary battery, an electrode assembly(300) is installed in the battery case of a laminated sheet, wherein the electrode assembly has a structure where a separator is interposed between positive and negative electrodes. An electrically insulating heat shrinkable member of preventing the short-circuit caused by the contact with an electrode tab surrounds the upper end part of the electrode assembly.

Description

Secondary Battery Having Structure for Preventing Internal Short-circuit}

The present invention relates to a secondary battery having a structure capable of preventing an internal short circuit, and more particularly, a secondary battery in which an electrode assembly having a structure in which a separator is interposed between a positive electrode and a negative electrode is mounted in a battery case of a laminate sheet. The present invention relates to a secondary battery comprising an electrically insulating heat-shrinkable member for preventing a short circuit caused by contact of an electrode tab surrounding an upper end of an electrode assembly.

BACKGROUND ART [0002] In recent years, rechargeable secondary batteries have been widely used as energy sources for wireless mobile devices. In addition, the secondary battery is an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle that has been proposed as a solution for air pollution of existing gasoline and diesel vehicles using fossil fuel. It is attracting attention as a power source such as (Plug-In HEV).

In a small mobile device, one or two or more battery cells are used per device, while a middle- or large-sized battery module such as an automobile is used as a middle- or large-sized battery module in which a plurality of battery cells are electrically connected due to the necessity of a large-

As mobile devices become thinner, battery cells used for them are also required to be lighter and thinner. In addition, since the medium-large battery module is preferably manufactured in as small a size and weight as possible, a battery cell that can be charged with high integration and has a small weight for capacity is required.

In this respect, the usage of square batteries, pouch-type batteries, and the like has recently increased. In particular, a pouch-shaped battery using an aluminum laminate sheet or the like as an exterior member has recently attracted a lot of attention due to its advantages such as small weight, low manufacturing cost, and easy shape deformation.

The pouch-type battery is manufactured in a form in which an electrode assembly having a separator interposed between a positive electrode and a negative electrode is mounted on a battery case of a laminate sheet. The electrode tab is V-formed to increase electrode space efficiency to the electrode lead. Will be connected.

FIG. 1 is a schematic exploded perspective view of a general structure of a conventional pouch type secondary battery.

Referring to FIG. 1, the pouch type secondary battery 100 is welded to an electrode assembly 300, a plurality of electrode tabs 302 and 304 extending from the electrode assembly 300, and electrode tabs 302 and 304. And a case 200 accommodating the electrode leads 400 and 410, and the electrode assembly 300.

The electrode assembly 300 is a structure in which a separator interposed between the anode and the cathode and insulates each other is stacked in the order of anode / separator / cathode. The electrode tabs 302, 304 extend from each pole plate of the electrode assembly 300, and the electrode leads 400, 410 are welded, for example, with a plurality of electrode tabs 302, 304 extending from each pole plate. Each is electrically connected to each other, and a part of the case 200 is exposed to the outside. The case 200 provides a space for accommodating the electrode assembly 300 and has a pouch shape. In the case of the stacked electrode assembly 300 as shown in FIG. 1, a plurality of positive electrode tabs 302 and a plurality of negative electrode tabs 304 may be coupled together to the electrode leads 400 and 410. Is spaced apart from the electrode assembly 300.

FIG. 2 is a partially enlarged view of a top inside a case in which the positive electrode tabs are densely coupled in the secondary battery of FIG. 1 and connected to the positive electrode lead.

Referring to FIG. 2, a plurality of positive electrode tabs 302 extending from the positive electrode collector 310 of the electrode assembly 300 may be formed of, for example, a welded portion 322 integrally coupled by welding. It is connected to the anode lead 400 in the form. The positive lead 400 is sealed by the battery case 200 while the opposite end 402 to which the positive electrode tab fusion unit 322 is connected is exposed. Since the plurality of positive electrode tabs 302 are integrally coupled to form a fusion unit 322, the inner upper end of the battery case 200 is spaced apart from the upper end surface of the electrode assembly 300 by a predetermined distance, and the fusion unit ( The positive electrode tabs 302 of 322 are V-shaped.

Therefore, when the battery falls to its top, i.e., the positive lead 400, or when a physical external force is applied to the top of the battery, the electrode assembly 300 is moved to the top of the inner surface of the case 200 or the top is crushed. As a result, the negative electrode current collector plate of the electrode assembly 300 may contact the positive electrode tab 302 or the positive electrode lead 400 to cause an internal short circuit. This internal short circuit is particularly caused when some positive electrode tabs under the fusion portion 322 are in contact with the negative electrode located at the outermost portion of the electrode assembly 300.

As described above, in order to prevent a short circuit caused by contact between the anode lead and the outermost electrode of the electrode assembly, which occur most frequently, Japanese Laid-Open Patent Application 2003-257496 uses a back coat layer on the electrode of the outermost layer of the electrode assembly. Presenting techniques for shaping. However, the above-described technique is complicated by the process of manufacturing the electrode assembly and forming a back coat layer on the outermost layer electrode or a separate electrode having a back coat layer formed thereon, and thus operating the battery by forming a coating layer. It has disadvantages such as lowering efficiency.

In addition, in Korean Patent Application Publication No. 2007-0108578, the same separator as the separator constituting the electrode assembly is attached to the outer surface of the outermost electrode of the electrode assembly, which is caused by contact between the anode lead and the cathode positioned at the outermost portion during the drop. By preventing the internal short circuit using a separator constituting the electrode assembly without any additional process, it proposes a technology that can ensure the safety while maintaining the performance of the battery. However, the above technique has disadvantages such that the separator may be deformed at a high temperature, and the anode lead does not prevent a short circuit when the anode lead penetrates the separator.

Therefore, there is a high need for a technique capable of fundamentally solving such problems.

The present invention aims to solve the problems of the prior art as described above and the technical problem that has been requested from the past.

That is, an object of the present invention is to prevent the short circuit caused by the incorporation of foreign matter as well as the internal short circuit caused by the contact between the electrode lead, which occurs frequently during the drop, and the electrode located at the outermost part of the electrode assembly, thereby preventing the short circuit of the battery. It is to provide a secondary battery that can further improve safety while maintaining performance.

A secondary battery according to the present invention for achieving the above object is a secondary battery in which an electrode assembly having a structure in which a separator is interposed between a positive electrode and a negative electrode is mounted on a battery case of a laminate sheet, and a short circuit caused by contact of an electrode tab is prevented. The electrically insulating heat-shrinkable member for preventing is comprised surrounding the upper end of the electrode assembly.

When the electrode assembly is mounted in the battery case of the laminate sheet, as described above, the electrode tab is V-formed to be connected to the electrode lead to increase the upper space efficiency. In this process, a short circuit may occur between the electrode and the electrode constituting the outermost part of the electrode assembly due to impact or drop, and the electrode constituting the outermost part of the electrode assembly may be a positive electrode or a negative electrode. Balance between battery and negative electrode design, especially for safety reasons, consist of negative electrode.

In general, in the electrode assembly, the size of the separator is larger than that of the cathode to prevent the risk of short circuit. However, the secondary battery of the present invention has a structure in which the upper end of the electrode assembly is covered with an electrically insulating heat-shrinkable member so as to prevent a short circuit even when the positive electrode leads to the separation membrane. It not only prevents a short circuit due to an external impact such as the back, but also has the advantage of preventing a short circuit due to foreign matter mixing.

Moreover, the structure of wrapping the upper end of the electrode assembly with the electrically insulating heat-shrinkable member also serves to suppress the separation of the electrode plates from the inside position or the gap between the electrode plates in the electrode assembly. That is, when some electrode plates are separated from their original positions during the manufacturing or use of the battery, short circuits may occur and the handling may not be easy during the manufacturing of the battery. By fixing them in place, the effects of short circuit prevention and ease of handling can be obtained. In addition, the battery tends to decrease its operating performance due to an increase in internal resistance as the gap between the electrode plates increases in the course of continuous charging and discharging. Thus, the heat shrinkable member mounted on the upper end of the electrode assembly solves this problem. give.

In the present invention, the laminate sheet constituting the battery case may be, for example, a pouch-type structure including a metal layer and a resin layer, and in one specific example, includes an outer layer made of a polymer resin having weather resistance, a gas and a liquid. It may be a structure including a metal layer having a barrier property against, and an inner layer made of a polymer resin having heat sealability.

Preferably, the laminate sheet may be an aluminum laminate sheet having a metal layer made of aluminum, and a pouch-type battery using the aluminum laminate sheet as an exterior member may have advantages such as low weight, low manufacturing cost, and easy deformation. Have

Since the outer layer should have excellent resistance from the external environment, it is necessary to have a predetermined tensile strength and weather resistance. In such aspect, polyethylene terephthalate (PET) and a stretched nylon film may be preferably used as the polymer resin of the outer layer.

As the polymer resin of the inner layer, a polyolefin-based resin having heat sealability (heat adhesion), low hygroscopicity to suppress invasion of the electrolyte solution, and which does not expand or erode by the electrolyte solution may be preferably used. More preferably, an unstretched polypropylene film (CPP).

In one preferred example, the laminate sheet, the thickness of the outer layer is 5 to 40 ㎛, the thickness of the metal layer may be 20 to 150 ㎛, the thickness of the inner layer may be 10 to 50 ㎛.

In one preferred embodiment, the electrically insulating heat shrinkable member is preferably shrinkage at 70 to 120 ℃. If the shrinkage at too low temperature is not easy to handle in the battery manufacturing process due to over-private heat shrinkage, if the shrinkage at too high temperature the electrode assembly may be damaged by heat in the process for heat shrinkage. . More preferred heat shrink temperature range may be 80 to 100 ℃.

The electrically insulating heat-shrinkable member is not particularly limited as long as it is an insulating material while solving the problems of the prior art as described above. For example, polyethylene, polypropylene, polyvinyl chloride, oriented polystyrene, Polyethylene terephthalate, ethylene propylene rubber, isoprene rubber, chloroprene rubber, styrene butadiene rubber, nitrile butadiene rubber, teflon and the like can be used, and they can be used in one or two or more combinations. Among these, in consideration of the above conditions and the like, it is preferable that one or more selected from the group consisting of polyethylene terephthalate, oriented polystyrene, and polyvinyl chloride is preferable. In the case of polyvinyl chloride, dioxin is released during incineration, which may cause environmental pollution, and in the case of oriented polystyrene, there is a problem that a natural shrinkage occurs after processing. More preferred is polyethylene terephthalate.

In one preferred example, the electrically insulating heat-shrinkable member may have a structure surrounding the upper side of the side of the electrode assembly and the outer peripheral surface of the upper side at the same time.

Specifically, a structure in which the electrically insulating heat-shrinkable member surrounds the upper side of the side of the electrode assembly corresponding to the size of 5 to 30% based on the height of the electrode assembly is preferable. The structure in which the heat-shrinkable member wraps around the upper side of the electrode assembly with an excessively small size is not only difficult to prevent the electrode tab from touching the side portion and to generate a short circuit, but also to handle the electrode in the manufacturing process of the battery or during use of the battery. There is a possibility that the heat shrinkable member is detached from the assembly. On the other hand, the structure in which the heat-shrinkable member wraps around the upper side of the electrode assembly in an excessively large size is not efficient in terms of manufacturing cost and operating efficiency of the battery. For this reason, the structure surrounding the upper side of the electrode assembly corresponding to the size of 10 to 15% is more preferable.

In addition, a structure in which the electrically insulating heat-shrinkable member surrounds the upper outer peripheral surface of the electrode assembly corresponding to the size of 20 to 50% based on the upper width of the electrode assembly is preferable. The structure in which the heat-shrinkable member surrounds the upper outer circumferential surface of the electrode assembly in an extremely small size is not only difficult to exhibit the desired short-circuit prevention function as described above, but also may be detached. On the other hand, a structure in which the heat-shrinkable member surrounds the upper outer circumferential surface of the electrode assembly in an excessively large size may interfere with the impregnation of the electrolyte in the manufacturing process of the battery, resulting in a decrease in productivity of the battery. For this reason, the structure surrounding the upper outer peripheral surface of the electrode assembly corresponding to the size of 20 to 35% based on the upper width is more preferable.

The electrically insulating heat-shrinkable member may be mounted to the upper end of the electrode assembly in various forms, for example, the electrically insulating heat-shrinkable member is composed of an electrically insulating heat-shrinkable film, and a predetermined surplus of such heat-shrinkable film It may be attached to surround the top of the side of the electrode assembly so as to protrude to the top of the additional electrode assembly, and then the excess portion is contracted by heat treatment to surround the top outer peripheral surface of the electrode assembly.

As another example, the electrically insulating heat-shrinkable member is made of an electrically insulating heat-shrinkable tube, and a predetermined surplus of such heat-shrinkable tube is inserted while surrounding the top of the side of the electrode assembly so as to protrude to the top of the electrode assembly. The surplus may be shrunk by heat treatment to surround the upper outer circumferential surface of the electrode assembly.

The excess protruding to the top of the electrode assembly is preferably 20 to 50%, more preferably 25 to 45% based on the height of the electrically insulating heat-shrinkable film or tube. When the ratio of the protruding surplus is too small, the ratio of surrounding the side portion or the outer circumferential surface of the electrode assembly may be small, and thus, it may be difficult to achieve a desired effect. , Not preferred.

In one preferred embodiment, the heat shrinkage for fixing the heat shrinkable member to the upper end of the electrode assembly is heat shrinkable for 2 to 20 seconds with hot air of 80 to 120 ° C. for 2 to 20 seconds, more preferably for 3 to 5 seconds for hot wind of 90 to 110 ° C. It can be achieved by addition to the member. Too low a temperature and a short time treatment do not cause smooth heat shrinkage, and a too high temperature and a long time treatment may cause damage to the electrode assembly is undesirable.

The electrode assembly is an electrode assembly having a high risk of short circuit as described above, for example, separating a unit cell, such as a stacked structure, a full cell or a bi-cell, a plurality of electrode plates stacked with a separator therebetween Although it may be a stack / folding structure etc. of the structure wound by the film, it is not limited only to these.

The secondary battery of the present invention is not particularly limited as long as the electrode assembly is mounted on the battery case of the laminate sheet, but may preferably be a lithium secondary battery.

Such a lithium secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and the like, as is known in the art, and will be described below.

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive agent, and a binder onto a positive electrode current collector, followed by drying, and optionally, a filler may be further added to the mixture.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Li _{1 + x} Mn _{2 - x} O ₄ (Where x is 0 to 0.33), lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3; Formula LiMn _2-x M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive agent is typically added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Such a conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding the active material and the conductive agent to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is manufactured by applying and drying a negative electrode material on the negative electrode current collector, and if necessary, the components as described above may be further included.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Li _x WO ₂ (0 ≦ _x ≦ 1), Sn _x Me _{1 - x} Me _y O _z (Me: Mn, Fe, Pb, Ge; Me: Al Metal complex oxides such as B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The lithium salt-containing non-aqueous electrolyte consists of a solvent for a nonaqueous electrolyte and a lithium salt. As the solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl Lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile Nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxoron derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In some cases, an organic solid electrolyte, an inorganic solid electrolyte, or the like may be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) may be further included. carbonate), PRS (propene sultone), FEC (Fluoro-Ethlene carbonate) and the like may be further included.

The secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but also includes a plurality of battery cells as a unit cell in a battery module used as a power source for a medium and large device in which safety is an issue. It can be used preferably.

Preferred examples of the medium-to-large device include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and the like.

As described above, the secondary battery according to the present invention is an internal short circuit due to the internal short circuit and foreign matter mixed by the contact between the positive electrode lead that occurs frequently during the drop and the negative electrode located on the outermost side of the electrode assembly, the upper end of the electrode assembly It is possible to further secure the safety while maintaining the performance of the battery by preventing the wrapping of the electrically insulating heat-shrinkable member.

1 is an exploded perspective view of a general structure of a conventional pouch type secondary battery;
FIG. 2 is a partially enlarged view of a top inside a case in which the positive electrode tabs are densely coupled and connected to the positive electrode lead in the secondary battery of FIG. 1;
3 is a vertical cross-sectional schematic diagram of an electrode assembly according to one embodiment of the present invention;
4 is a schematic perspective view of an electrode assembly according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the drawings according to embodiments of the present invention, but the scope of the present invention is not limited thereto.

3 schematically illustrates a vertical cross-sectional view of an electrode assembly according to one embodiment of the present invention, and FIG. 4 schematically illustrates a perspective view thereof.

Referring to these drawings, first, a plurality of positive electrode tabs 302 protruding from an upper end of the positive electrode 310 are ultrasonically fused to one positive electrode lead 400, and thermally fused to a pouch type battery case (not shown). An insulating film 420 is attached to the anode lead 400 corresponding to the sealing portion. When the insulating film 420 is sealed by heat-sealing the battery case (not shown), the insulating film 420 serves to increase the sealing property while ensuring the insulation to the positive electrode lead 400. The relationship between the negative electrode tabs 304 and the negative electrode lead 410 is the same as above.

In the electrode assembly 300, a separator 330 is interposed between the anode 310 and the cathode 320, and the outermost electrode is formed of the cathode 320.

In the electrode assembly 300, the separator 330 is larger than the negative electrode 320 in terms of safety, and the negative electrode 320 is larger than the positive electrode 310 in terms of battery design balance. Therefore, the risk of a short circuit may be primarily prevented by the separator 330 larger than the cathode 320. However, only the structure of the electrode assembly 300 may not prevent a short circuit when the separator 330 causes thermal deformation at a high temperature or when the anode lead penetrates the separator 330.

On the other hand, in the present invention, by wrapping the upper end of the electrode assembly 300 using an electrically insulating heat-shrinkable member, the outermost negative electrode 320 and the positive electrode tab 302 solve the problem of short-circuiting due to the impact and safety It is possible to provide an improved secondary battery.

Specifically, while wrapping the upper side of the side of the electrode assembly 300 corresponding to the size of 5 to 30% based on the height of the electrode assembly 300, 20 to 50 based on the width of the top surface of the electrode assembly 300 By surrounding the upper outer circumferential surface of the electrode assembly 300 corresponding to the size of%, even if the positive electrode tab 302 or the positive electrode lead 400 is bent due to various reasons, the negative electrode 320 by the electrically insulating heat shrinkable member 500 ) Can be avoided.

In addition, it does not prevent the electrolyte solution from being impregnated by not covering the entire upper surface of the electrode assembly 300, and by fixing the electrode assembly 300, it is possible to minimize the use of an adhesive during assembly, thereby preventing a decrease in electrical performance.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (16)

A secondary battery in which an electrode assembly having a structure in which a separator is interposed between a positive electrode and a negative electrode is mounted in a battery case of a laminate sheet. Secondary battery, characterized in that consisting of a structure surrounding the. The secondary battery of claim 1, wherein the laminate sheet has a pouch-type structure including a metal layer and a resin layer. The secondary battery of claim 2, wherein the laminate sheet comprises an outer layer made of a polymer resin having weather resistance, a metal layer having a barrier to gas and a liquid, and an inner layer made of a polymer resin having heat sealing property. . The secondary battery of claim 1, wherein the heat shrinkable member is made of a material that shrinks at 70 to 120 ° C. 3. The secondary battery of claim 1, wherein the heat shrinkable member is formed of at least one selected from the group consisting of polyethylene terephthalate, oriented polystyrene, and polyvinyl chloride. The secondary battery according to claim 5, wherein the heat shrinkable member is polyethylene terephthalate. The secondary battery of claim 1, wherein the heat-shrinkable member has a structure that simultaneously surrounds an upper end of the side of the electrode assembly and an outer circumferential surface of the upper end of the electrode assembly. The secondary battery of claim 7, wherein the heat shrinkable member surrounds an upper end of a side surface of the electrode assembly corresponding to a size of 5 to 30% based on the height of the electrode assembly. The secondary battery of claim 7, wherein the heat shrinkable member surrounds an upper outer circumferential surface of the electrode assembly corresponding to a size of 20 to 50% based on the upper width of the electrode assembly. The electrode assembly of claim 1, wherein the heat-shrinkable member is attached while enclosing the heat-shrinkable film around the top of the side surface of the electrode assembly such that a predetermined surplus protrudes toward the upper end of the electrode assembly, and then shrink the excess part by heat treatment. Secondary battery, characterized in that to wrap the outer peripheral surface of the top. The electrode assembly of claim 1, wherein the heat shrinkable member is inserted while the heat shrinkable tube surrounds the upper end of the side surface of the electrode assembly such that a predetermined surplus protrudes toward the upper end of the electrode assembly, and then the excess part is contracted by heat treatment. Secondary battery, characterized in that to wrap the outer peripheral surface of the top. The secondary battery according to claim 10 or 11, wherein the excess portion protruding from the upper end of the electrode assembly is 20 to 50% based on the height of the heat shrinkable film or the heat shrinkable tube. The secondary battery of claim 1, wherein the heat-shrinkable member is heat-treated with a hot air of 80 to 120 ° C. for 3 to 8 seconds to surround the electrode assembly. The secondary battery of claim 1, wherein the secondary battery is a lithium secondary battery. The secondary battery of claim 1, wherein the secondary battery is used as a unit battery of a battery module used as a power source of a medium-large device. The secondary battery of claim 15, wherein the medium-to-large device is an electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

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