KR20120124613A - Secondary Battery with Advanced Safety - Google Patents

Abstract

PURPOSE: A secondary battery is provided to maintain performance of a battery in case external impact such as dropping, etc and to effectively prevent internal short of a tap-lead joint by an electrically insulative thermal contraction tube protecting the tap-lead joint. CONSTITUTION: A secondary battery comprises an electrode assembly of a positive electrode/separator/negative electrode in a battery case of a laminate sheet which comprises a resin layer and a metal layer. The electrode taps(301,302) are combined with electrode leads(400,410) and protruded to outside. A heat-shrinkable tube(510) surrounds joints(401,411) of the electrode tap and electrode lead. The electrode assembly is a stack type electrode assembly laminated in a state that a separator is inserted between a plurality of positive electrodes and negative electrodes. The tap-lead joint consists of a structure that a plurality of electrode taps are welded and combined to one electrode lead.

Description

Secondary Battery with Enhanced Safety {Secondary Battery with Advanced Safety}

The present invention relates to a secondary battery having improved safety, and more particularly, an electrode assembly of a cathode / separator / cathode is embedded in a battery case of a laminate sheet including a resin layer and a metal layer, and an electrode tab of the electrode assembly is an electrode lead. The present invention relates to a secondary battery which is coupled to and protrudes out of the battery case and has a structure in which an electrically insulating heat shrinkable tube surrounds the coupling portion ("tab-lead coupling portion") of the electrode tab and the electrode lead.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self- It has been commercialized and widely used.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, a lithium polymer battery, and the like according to the composition of the electrode and the electrolyte, and among them, the amount of leakage of the electrolyte is less likely, and the amount of the lithium ion polymer battery that is easy to manufacture is used. This is increasing. Li-ion polymer battery (LiPB) is a structure in which an electrolyte solution is impregnated into an electrode assembly in which electrodes (anode and cathode) and a separator are heat-sealed. have. Thus, lithium ion polymer batteries are often referred to as pouch cells.

1 and 2 schematically show a general structure of a representative LiPB including a stacked electrode assembly.

Referring to these drawings, the LiPB 100 has an electrode assembly 300 made of a positive electrode, a negative electrode, and a separator disposed therebetween in a pouch-type battery case 200, and the positive and negative electrode tabs thereof 301 and 302 are welded to two electrode leads 400 and 410 and are sealed to be exposed to the outside of the battery case 200.

The battery case 200 is formed of a soft packaging material such as an aluminum laminate sheet, and includes a case body 210 and a body 210 including a recess 230 having a concave shape in which the electrode assembly 300 can be seated. One side is made of a cover 220 is connected. The electrode assembly 300 used in the LiPB 100 may have a jellyroll-type structure in addition to the stacked structure as shown in FIG. 1. In the stacked electrode assembly 300, a plurality of positive electrode tabs 301 and a plurality of negative electrode tabs 302 are welded to the electrode leads 400 and 410, and the electrode leads 400 and 410 are connected to the battery case 200. Insulating film 500 is attached to the upper and lower surfaces to ensure electrical insulation and sealing.

Lithium secondary batteries such as LiPB are exposed to high temperatures, short-circuits caused by overcharge, external short circuit, nail penetration, local crush, drop, etc., and cause a large current to flow within a short time. There is a risk of fire / explosion as the battery heats up. As the temperature of the battery rises, the reaction between the electrolyte and the electrode is accelerated. As a result, heat of reaction is generated to further increase the temperature of the battery, which in turn accelerates the reaction between the electrolyte and the electrode. Thus, the temperature of the battery rises rapidly, which in turn accelerates the reaction between the electrolyte and the electrode. Due to such a vicious cycle, a thermal runaway phenomenon in which the temperature of the battery rises rapidly occurs, and when the temperature rises to a certain level or more, the battery may ignite. In addition, as a result of the reaction between the electrolyte and the electrode, gas is generated to increase the battery internal pressure, and the lithium secondary battery explodes above a certain pressure. The risk of ignition and explosion can be said to be the most fatal disadvantage of lithium secondary batteries.

In particular, LiPB is easily deformed due to drop, external impact, etc., because the battery case is a soft packaging material having a weak strength. As shown in FIG. 1B, a space 230a for connecting the electrode tabs to the electrode leads 400 and 410 by welding is present at an upper end of the electrode assembly 300 of the battery case 200. When the impact is applied from the upper direction of the electrode assembly 300 is moved to the upper space (230a) while the tab-lead coupling portion (mainly, the anode portion) of the electrode lead (400, 410) of the electrode assembly 300 An internal short circuit may be caused by contacting the uppermost electrode (mostly, the negative electrode current collector) or the upper end of the electrode assembly. Since the fall of the battery occurs frequently during the use of the battery, there is a high need for a technology capable of ensuring the safety of the battery in a more efficient manner.

In order to solve the above problem, in order to prevent an internal short circuit due to the movement of the electrode assembly, a method of attaching an adhesive tape to a part of the electrode assembly or inserting a foreign material into the upper space of the electrode assembly is used. However, the above-described method causes a chemical reaction between the adhesive tape and the electrolyte, thereby reducing the performance of the battery.

Therefore, there is a need for a secondary battery having a specific structure that can solve the above problems.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application, after continuing in-depth research and various experiments, not only the contact region of the electrode lead and the battery case, but also the region where the electrode tab and the electrode lead are bonded is wrapped in a heat shrinkable tube, and the bonding region is preferably an electrode. When the electrode tab is configured to extend from the top of the current collector so as to be located away from the assembly, it was confirmed that the thermally shrinkable tube can effectively prevent the internal short without damaging the separator, thus completing the present invention.

A secondary battery according to the present invention for achieving this object, the electrode assembly of the positive electrode / separator / negative electrode is embedded in the battery case of the laminate sheet comprising a resin layer and a metal layer, the electrode tab of the electrode assembly is bonded to the electrode lead And protrudes out of the battery case, and has an electric insulating heat-shrinkable tube enclosing the coupling portion ("tab-lead coupling portion") of the electrode tab and the electrode lead.

Accordingly, since the secondary battery according to the present invention has a structure in which an electrically insulating heat-shrinkable tube surrounds the coupling portion of the electrode tab and the electrode lead ("tab-lead coupling portion"), external shock such as a dropping secondary battery Even when applied to the battery, the electrically insulating heat-shrinkable tube protects the tap-lead joint while maintaining the battery's performance to the maximum, thereby preventing the tap-lead joint from being shorted.

As described above, when the electrode assembly is mounted in the battery case of the laminate sheet in the general pouch type secondary battery, 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. 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 addition, the conventional pouch type secondary battery primarily prevents the risk of short circuit by making the size of the separator larger than that of the negative electrode. However, in order to prevent a short circuit even when the positive electrode leads to the separator, the secondary battery of the present invention has a structure in which a coupling portion between the electrode tab and the electrode lead of the electrode assembly is covered with an electrically insulating heat-shrinkable tube. While maintaining the maximum performance, there is an advantage that can prevent a short circuit due to external impact such as falling.

In one preferred embodiment, the electrode assembly is a stacked electrode assembly in which a plurality of positive electrodes and negative electrodes are stacked with a separator interposed therebetween, and the tab-lead coupling portion includes a plurality of electrode tabs (anode tab or negative electrode tab) as a single electrode assembly. It may have a structure bonded by welding to an electrode lead (anode lead or cathode lead).

In another preferred embodiment, the electrode assembly is a stack / foldable electrode assembly in which unit cells of a bi-cell or full-cell structure are wound by a separation film, and the tab-lead coupling part includes a plurality of electrode tabs (anode tab or The negative electrode tab may be bonded to one electrode lead (anode lead or negative electrode lead).

The bicell is a unit cell in which the electrodes on the outermost sides have the same electrode, and has a basic structure of anode / separator / cathode / separator / anode or cathode / separator / anode / separator / cathode. The full cell is a unit cell in which the outermost electrodes have opposite electrodes, and has a basic structure of an anode, a separator, and a cathode.

In the present invention, the heat-shrinkable tube is preferably mounted independently of the tab-lead coupling portion of the positive electrode and the tab-lead coupling portion of the negative electrode, but may be simultaneously mounted as necessary.

In the heat treatment process for heat shrinkage of heat shrinkable tubes, heat shrinkage at too low a temperature can lead to deterioration of physical properties at that temperature during operation of the cell, whereas heat shrinkage at too high a temperature can damage the electrode assembly during heat shrinkage. Not desirable Thus, in a preferred embodiment, the heat shrinkable tube can be configured to cause shrinkage at 70 ~ 120 ℃.

The degree of heat shrink may vary according to the setting conditions, for example, it may be to shrink to 70% or less of the original size by the application of heat. More preferably, it can be made to shrink 30% to 70% of the original size.

Such a heat-shrinkable tube is not particularly limited in its kind, for example, polyethylene, polypropylene, polybutylene, polyethylene butyrate, polyimide, 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, considering the above conditions and the like, it may be more preferably made of one or more selected from the group consisting of polyimide, polyethylene terephthalate, oriented polystyrene, and polyvinyl chloride.

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. Polyimide and polyethylene terephthalate are more preferred.

It is preferred that the thickness of the heat shrinkable tube in the heat shrinkable tube before the heat shrinkage is 5 μm to 500 μm, and the width of the heat shrinkable tube before the heat shrinkage is slightly larger than the width of the tap-lead joint, for example, the tap-lead joint. It is preferably 30-100% larger based on the width.

On the other hand, when the heat-shrinkable tube has a structure uniaxially stretched in an arc shape in the manufacturing process, the heat shrinkable tube is more easily contracted in one direction.

In one preferred example, the heat-shrinkable tube may be preferably heat-treated for 3 to 8 seconds with a hot air of 70 to 120 ℃ to enclose the tap-lead joint.

Therefore, if the shrinkage at an excessively low temperature is not easy to handle in the battery manufacturing process due to excessively sensitive heat shrinkage, and if the shrinkage at an excessively high temperature the electrode assembly may be damaged by heat in the process for heat shrinkage to be. More preferred heat shrink temperature range may be 80 to 100 ℃.

In general, an insulating film is attached to a contact portion of an electrode lead and a battery case in a pouch-type battery. In this case, the heat shrinkable tube of the present invention may be attached to the bottom of the insulating film in a continuous or somewhat spaced state.

On the other hand, the electrode tab in the present invention may have a structure extending from the top of the current collector to a length that can prevent the separation membrane is damaged by the heat shrinkable tube. In one preferred example, the extending length can be 2 to 8 mm.

The electrode assembly of the present invention is an electrode assembly having a high risk of short circuit as described above, for example, a unit cell such as a stacked structure, a full cell or a bicell, in which a plurality of electrode plates are stacked with a separator therebetween. It may be a stack / folding structure of the structure wound around them with a separation film, but is not limited thereto.

In addition, the secondary battery according to 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. If necessary, 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; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; 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 have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

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 black 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, aluminum, 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 of the active material and the conductive agent to the binder and in binding to the current collector, and is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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 collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

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' Metal complex oxides such as Al, 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.

As the inorganic solid electrolyte, for example, 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, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate), and the like.

The present invention also provides a battery pack including the secondary battery, an electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle that uses the battery pack as a power source and has a limited mounting space and is exposed to frequent vibrations and strong impacts. Provide a car.

It goes without saying that battery packs used as power sources for automobiles can be manufactured in combination according to a desired output and capacity.

Electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles using the battery pack as a power source is known in the art, so a detailed description thereof will be omitted.

As described above, the secondary battery according to the present invention is a tab of the electrode assembly by the internal short circuit caused by 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 of the electrode assembly. -By binding the lead portion (tab-lead connection portion) with an electrically insulating heat-shrinkable tube, it is possible to further secure safety while maintaining battery performance.

1 and 2 are a perspective view showing the assembly process of the battery case and the electrode assembly in a conventional lithium-ion polymer battery using a pouch-type battery case and a plan view in the assembled state;
3 is a plan view showing the upper end of the electrode assembly in the secondary battery according to an embodiment of the present invention.
4 is a vertical cross-sectional schematic diagram of an electrode assembly according to another embodiment of the present invention;
FIG. 5 is a vertical sectional schematic view of the heat shrinkable tube of FIG. 4. FIG.

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

3 schematically illustrates an upper end of an electrode assembly in a secondary battery according to an exemplary embodiment of the present invention.

Referring to FIG. 3, an electrode assembly 300 having a structure in which a separator 330 is interposed between a positive electrode current collector 310 and a negative electrode current collector 320 on which electrode active materials are coated on both surfaces thereof may be formed of each current collector ( The positive electrode tab 301 and the negative electrode tab 302 protrude from the upper ends of 310 and 320.

Since the electrode assembly 300 is composed of a plurality of negative electrodes and positive electrodes, the plurality of positive electrode tabs 301 and the negative electrode tabs 302 are welded to the positive lead 400 and the negative electrode lead 410, respectively. Accordingly, tab-lead coupling parts 401 and 411 are formed at the lower ends of the electrode leads 400 and 410 and the upper ends of the electrode tabs 301 and 302.

The tab-lead coupling parts 410 and 411 may be, for example, when the battery is dropped and the electrode assembly 300 moves, the upper or outermost electrode of the electrode assembly 300 (here, mainly the negative electrode current collector: 320). ) Will cause an internal short circuit.

Accordingly, a heat shrinkable tube 510 is attached to surround the tab-lead coupling portions 401 and 411.

The heat shrinkable tube 510 is continuously attached to the lower end of the insulating film 500 attached to the electrode leads 400 and 410. Like the insulating film 500, the heat shrinkable tube 510 is independently of the positive lead 400 and the negative electrode. It is attached to the lead 410 at the same time.

In general, it is difficult to stably attach a member such as an insulating film to the tab-lead coupling parts 401 and 411, but the heat shrinkable tube 510 is inserted to cover the outer surface of the corresponding area and then heats the tab. The lead coupling portions 401 and 411 may be stably wrapped.

The electrode leads 400 and 410 may be welded to the electrode tabs 301 and 302 with the insulating film 500 already attached to the corresponding portions thereof, or after welding to the electrode tabs 301 and 302. The insulating film 500 may be attached to the.

The electrode tabs 301, 302 extend somewhat longer from the electrode current collectors 310, 320 so that the tab-lead coupling portions 401, 411 are spaced apart from the top of the electrode current collectors 310, 320 by such extension lengths. Will be. Accordingly, the heat shrinkable tube 510 surrounding such tab-lead coupling portions 401 and 411 provides high safety without fear of damaging the separator 330 of the electrode assembly 300.

4 is a vertical cross-sectional schematic diagram of an electrode assembly according to another embodiment of the present invention, Figure 5 is a vertical cross-sectional schematic diagram of the heat shrinkable tube of FIG.

Referring to these drawings, first, a plurality of positive electrode tabs 301 protruding from the 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). The insulating film 500 is attached to the anode lead 400 corresponding to the sealing portion. When the insulating film 500 seals the battery case (not shown) by mutual heat sealing, the insulating film 500 serves to increase the sealing property while ensuring the insulating property for the positive electrode lead 400. The relationship between the negative electrode tabs 302 and the negative electrode lead 410 is the same as above.

In the electrode assembly 300, a separator 330 is interposed between the positive electrode current collector 310 and the negative electrode current collector 320, and the outermost electrode is configured as the negative electrode 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, the outermost negative electrode 320 and the positive electrode tab 301 is impacted by wrapping the electrode tab and the electrode lead of the electrode assembly 300 by using an electrically insulating heat shrink tube 510. It is possible to solve the problem causing the short circuit and to provide a secondary battery with improved safety.

Specifically, since the heat-shrinkable tube 510 according to the present invention has a uniaxially stretched structure in an arc shape, it is easily inserted into the positive lead 400 and the negative lead 410 of the electrode assembly. As the heat shrinkable tube is also shown in Figure 5, since the thickness of the cross-section is different in the A and B directions, respectively, a stronger shrinkage may occur when the heat is applied, it is possible to be easily inserted into the tab-lead coupling portion.

Therefore, as described above, by more effectively wrapping the connection portion of the tab-lead, it is possible to prevent the internal short circuit due to external impact or the like.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (15)

The electrode assembly of the anode / separator / cathode is embedded in the battery case of the laminate sheet including the resin layer and the metal layer, and the electrode tab of the electrode assembly is coupled to the electrode lead and protrudes out of the battery case. A secondary battery, characterized in that the tube is mounted in a structure surrounding the coupling portion ("tab-lead coupling portion") of the electrode tab and the electrode lead. The electrode assembly of claim 1, wherein the electrode assembly is a stacked electrode assembly in which a plurality of anodes and cathodes are stacked with a separator interposed therebetween, and the tab-lead coupling part comprises a plurality of electrode tabs (anode tabs or cathode tabs). A secondary battery comprising a structure in which an electrode lead (anode lead or cathode lead) is welded and bonded. The electrode assembly of claim 1, wherein the electrode assembly is a stack / foldable electrode assembly in which unit cells having a bi-cell or full cell structure are wound by a separation film, and the tab-lead coupling part includes a plurality of electrode tabs (anode tab or A secondary battery comprising a structure in which a negative electrode tab is welded to and bonded to one electrode lead (anode lead or negative electrode lead). The secondary battery of claim 1, wherein the heat-shrinkable tube is mounted to the tab-lead coupling portion of the positive electrode and the tab-lead coupling portion of the negative electrode, respectively. The secondary battery of claim 1, wherein the heat shrinkable tube shrinks to 70% or less of the original size by application of heat. {Preferably shrink to size 30-70%} The secondary battery of claim 1, wherein the heat shrinkable tube is made of a material that shrinks at 70 to 120 ° C. 3. The secondary battery of claim 1, wherein the heat shrinkable tube comprises at least one selected from the group consisting of polyethylene, polypropylene, polybutylene, polyethylene terephthalate, polyethylene butyrate, and polyimide. The secondary battery of claim 1, wherein the heat shrinkable tube has a thickness of about 5 μm to about 500 μm. The secondary battery of claim 1, wherein the heat-shrinkable tube has a characteristic of being uniaxially stretched in an arc shape during the manufacturing of the tube. The secondary battery of claim 1, wherein the heat-shrinkable tube is heat-treated with a hot air of 70 to 120 ° C. for 3 to 8 seconds to surround the tab-lead coupling part. The secondary battery of claim 1, wherein an insulating film is attached to a contact portion of the electrode lead and the battery case. The secondary battery of claim 1, wherein the electrode tab extends from the top of the current collector in a length that can prevent the separator from being damaged by the heat shrinkable tube. The secondary battery of claim 12, wherein the protrusion length is 2 to 8 mm. A battery pack comprising the secondary battery according to claim 1. The battery pack according to claim 14, wherein the battery pack is used as a power source for an electric vehicle, a hybrid electric vehicle, an electric bicycle, and an electric motorcycle.

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