KR101082960B1 - Secondary Battery with Excellent Durability - Google Patents

Abstract

The present invention is a secondary battery having a structure in which an electrode assembly having a cathode / separation membrane / cathode structure is mounted on a battery case of a laminate sheet including a metal layer and a resin layer, and then sealed by heat-sealing the outer circumferential surface of the battery case. It is connected to the electrode lead located in the heat-sealing sealing part of the battery case, the insulating film is attached to the upper and lower surfaces of the electrode lead in the heat-sealing sealing portion, the insulating film has its front end and rear end heat It extends from the fusion sealing part, is placed in the corresponding part of the battery case in a state of being previously bonded to the electrode lead, and then thermally fused to the battery case. The non-bonded portion of the insulating film front end portion is not bonded and partially melted during the heat fusion process. Of providing a secondary battery made of a structure which surrounds the end surface.

Description

Secondary Battery with Excellent Durability}

1 is a schematic diagram of a pouch type secondary battery structure including a stacked electrode assembly;

FIG. 2 is a top perspective view of the battery of FIG. 1 assembled; FIG.

3 is a schematic view of the structure of the laminate sheet end;

4 is a schematic view of a process of fusion sealing the battery case and the electrode lead with the insulating film according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a structure in which an insulating film extended from a heat fusion sealing part in FIG. 4 is melted and solidified to surround a cross section of a laminate sheet.

The present invention relates to a secondary battery having excellent durability, and more particularly, an electrode assembly having a cathode / separation membrane / cathode structure is attached to a battery case of a laminate sheet including a metal layer and a resin layer, and then heat-sealed the outer circumferential surface of the battery case. A secondary battery having a structure sealed in such a manner that the electrode of the electrode assembly is connected to an electrode lead positioned in the heat-sealing sealing portion of the battery case, and an insulating film is attached to the upper and lower surfaces of the electrode lead in the heat-sealing sealing portion. The insulating film has a front end portion and a rear end portion extending from the heat fusion sealing portion, and the insulating film is placed on a corresponding portion of the battery case in a state of being pre-bonded to the electrode lead and then heat-sealed to the battery case. The portion of the film that extends longer than the heat-sealing sealing portion is not bonded to the electrode lead, and the above-mentioned portion of the insulating film front end portion It relates to a secondary battery having a structure in which the bonding portion is partially melted during the heat fusion process to surround the end surface of the battery case.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources has been rapidly increasing. Many researches have been conducted on lithium secondary batteries with high energy density and discharge voltage among such secondary batteries. .

Lithium secondary batteries are largely classified into cylindrical batteries, square batteries, pouch-type batteries, and the like according to their appearance, and may be classified into lithium ion batteries, lithium ion polymer batteries, lithium polymer batteries, and the like depending on the type of electrolyte.

Due to the recent trend toward the miniaturization of mobile devices, there is an increasing demand for thinner rectangular batteries and pouch-type batteries. In particular, for pouch-type batteries that are easy to deform, low in manufacturing cost and light in weight. Interest is high.

In general, a pouch type battery refers to a battery in which an electrode assembly and an electrolyte are sealed inside a pouch type case of a laminate sheet including a resin layer and a metal layer. The electrode assembly accommodated in the battery case has a structure of jelly-roll type (wound type), stacked type (stacked type) or stack / folding type.

FIG. 1 schematically illustrates a structure of a pouch type secondary battery including a stacked electrode assembly, and FIG. 2 schematically illustrates a plan view of an assembled state of the battery of FIG. 1.

First, referring to FIG. 1, in the pouch type secondary battery 100, an electrode assembly 30 including a positive electrode, a negative electrode, and a solid electrolyte coating separator disposed therebetween is formed in the pouch type battery case 20. Two electrode leads 40 and 41 electrically connected to the positive and negative electrode tabs 31 and 32 are sealed to be exposed to the outside.

The battery case 20 is composed of a case body 21 including a recess 23 having a concave shape in which the electrode assembly 30 can be seated, and a cover 22 integrally connected to the body 21. have.

In the stack type electrode assembly 30, a plurality of positive electrode tabs 31 and a plurality of negative electrode tabs 32 are fused to each other and coupled to the electrode leads 40 and 41. In addition, when the upper end portion 24 of the case body 21 and the upper end portion of the cover 22 are heat-sealed by the heat sealer, the short circuit between the heat sealer and the electrode leads 40 and 41 is prevented from occurring. In order to ensure the sealing property between the 40 and 41 and the battery case 20, the insulating film 100 is attached to the upper and lower surfaces of the electrode leads 40 and 41.

When the electrode assembly 30 in which the electrolyte is impregnated is thermally fused to the contact portion of the case body 21 and the cover 22 in a state in which the electrode assembly 30 is seated on the accommodating portion 23, the upper sealing portion 24 and the upper sealing portion 24 as shown in FIG. The side sealing part 25 is formed. Since the side sealing portion 25 unnecessarily extends in both directions, it is bent vertically to manufacture the battery pack.

In the pouch type secondary battery containing the electrode assembly, a metal layer (aluminum layer) is exposed at an end portion during the pouch case cutting process, and the metal layer is damaged while the pouch case is damaged by high heat during the heating and pressing process for sealing the pouch case. It has a problem of being exposed.

In addition, the exposed metal layer of the laminate sheet, the electrode lead, and the nickel plate as the connecting member may be in an electrical connection state unexpectedly during the manufacturing or use of the battery.

Since the aluminum layer of the laminate sheet has a large difference in electromotive force from the electrode lead and nickel as the connecting member, when the secondary battery is charged and discharged in the electrical connection state as described above, corrosion of aluminum proceeds. Therefore, damage to the aluminum layer is caused, thereby shortening the life of the battery rapidly and the safety of the battery is also greatly threatened.

In particular, a secondary battery used in a medium-large battery pack as a power source of an electric vehicle, a hybrid vehicle, etc. needs a long lifespan, and it is very important to secure safety due to the fact that many battery cells are concentrated. Therefore, even when the metal barrier layer of the battery case is electrically connected to the connection member or the like due to unexpected development of the situation, there is a high demand for a technology capable of securing the life and safety of the battery.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past.

Specifically, an object of the present invention is to form a length of the insulating film with respect to the pouch case to a predetermined range when forming the sealing portion by heating / pressure in the pouch-type secondary battery, and optionally adhered to the electrode lead, By performing heat fusion under specific conditions, it is possible to provide a secondary battery that improves durability of the battery by preventing the pouch case from being damaged or exposing the cutting end of the pouch case during sealing.

A secondary battery according to the present invention for achieving the above object, the electrode assembly of the positive electrode / separator / cathode structure is mounted on a battery case of a laminate sheet comprising a metal layer and a resin layer and then sealed by heat-sealing the outer peripheral surface of the battery case In the secondary battery of the structure, the electrode of the electrode assembly is connected to the electrode lead located in the heat-sealing sealing portion of the battery case, the insulating film is attached to the upper and lower surfaces of the electrode lead in the heat-sealing sealing portion, respectively,

(a) the insulating film has a front end portion and a rear end portion thereof extended from the heat-sealing sealing portion,

(b) the insulating film is placed on the corresponding part of the battery case in a state of being previously bonded to the electrode lead and then thermally fused to the battery case,

(c) The portion of the insulating film that extends longer than the heat-sealing sealing portion is not bonded to the electrode lead,

(D) the non-bonded portion of the front end of the insulating film is partially melted during the heat fusion process to surround the end surface of the battery case.

That is, in the secondary battery according to the present invention, the non-bonded portion of the insulating film, which is extended from the heat-sealed sealing portion and is not bonded to the electrode lead, is directly heated and pressurized in the process of heat-sealing the sealing portion of the battery case. However, heat applied to the sealing portion is partially conducted to the unbonded portion to melt the unbonded portion, such that the melt of the insulating film wraps around the end surface of the battery case and seals the end surface of the battery case. The short circuit by the contact between a metal layer and an electrode lead can be prevented.

In addition, according to the prior art, in the process of cutting a laminate sheet composed of a resin layer and a metal layer into a pouch-type battery case, the metal layer (aluminum layer) at the end of the laminate sheet is exposed to the outside, so that the battery case end face is corroded by salt water or the like. Although the secondary battery of the present invention has a problem that the insulating film extending from the heat-sealing sealing part seals the end surface of the battery case, the end surface of the battery case is prevented from being corroded to improve the life of the battery. You can.

In the secondary battery of the present invention, the laminate sheet may be configured to include an inner resin layer that is heat-sealed, a barrier metal layer, and an outer resin layer having excellent durability.

The inner resin layer is thermally fused to each other by heat and pressure applied in the state in which the electrode assembly is inherent, thereby providing a sealing property, and thus has heat fusion (heat adhesion), and has low hygroscopicity to suppress invasion of the electrolyte. In addition, polyolefin-based resins that are not expanded or eroded by the electrolyte may be preferably used, and more preferably, may be made of an unstretched polypropylene film (CPP).

In addition, the barrier metal layer prevents air, moisture, and the like from entering the inside of the battery, and a material mainly containing aluminum having low ductility and low ductility to enable processing in a thin film form and the like for gas, etc., is used. It is desirable to be.

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

Thus, in one preferred example, the laminate sheet is composed of an inner resin layer mainly comprising cPP, a barrier metal layer mainly comprising aluminum, and an outer resin layer mainly comprising stretched nylon or PET. It is. Herein, mainly containing a specific component means that the component is included in 50% or more of the components of the layer.

In the secondary battery of the present invention, in order to ensure the sealing of the battery case, the front end and the rear end of the insulating film attached to the upper surface and the lower surface of the electrode lead is extended from the heat-sealing sealing portion to a predetermined length, The length is not particularly limited as long as the extended insulating film melts and wraps the end face of the laminate sheet. However, it is preferable to extend the length of about 0.5 to 5 mm, for example.

In addition, the insulating film preferably has a thickness of 5 ~ 200 ㎛, if the thickness is too thin it is difficult to expect the insulation of the laminate sheet and the electrode lead by the adhesion of the insulating film, on the contrary, if the thickness is too thick It is not preferable because sealing can be inhibited.

The material of the insulating film is not particularly limited as long as it is a highly branched resin that includes electrical insulation and is resistant to an electrolyte and causes plastic deformation. For example, polypropylene, polyethylene, polyamide, polyethylene terephthalate, and polybutyl Lene, polyisoprene, and the like, which may be used alone or in combination of two or more.

According to the present invention, since the insulating film is previously attached to the electrode lead, the assembly process of the battery can be very simplified. Such an insulating film may be attached to the positive lead and the negative lead, respectively, and one insulating film may be attached to the positive lead and the negative lead. In particular, the latter form is preferable because of easy handling of the electrode leads and excellent sealing properties between the positive electrode lead and the negative electrode lead at the sealing portion.

As described above, in the insulating film, a portion extending longer than the heat fusion sealing portion is not bonded to the electrode lead, and the unbonded portion is partially melted during the heat fusion process to surround the end surface of the battery case. Thus, the unbonded portion of the insulating film is approximately equal to the length of the front end portion and the rear end portion extending from the heat-sealed sealing portion to a predetermined length, but may be slightly smaller or larger.

As a result of experiments confirmed by the present inventors, even if the front end portion of the insulating film is longer than the heat seal sealing portion, it is difficult to wrap the end surface of the battery case even if partially melted during the heat welding process, if it is bonded to the electrode lead. . Therefore, in order to effectively wrap the end face of the battery case, it is essential that the end portion extending longer than the heat sealing seal portion is not bonded to the electrode lead.

In the present specification, the 'heat fusion sealing portion' is a portion where actual heat fusion is performed by the heat fusion machine, and is determined by the size of the battery fusion contacting the heat fusion machine.

The lithium secondary battery according to the present invention may be preferably used in the manufacture of a medium-large battery module or a battery pack of high output large capacity due to the excellent life and safety of the battery case, the range of the large capacity is not particularly limited.

Accordingly, the present invention provides a medium-large battery module including a plurality of secondary batteries as a unit cell, and a high-output large-capacity battery pack including one or more such medium-large battery modules.

The battery module is a power source of a vehicle such as an electric bicycle (E-bike), an electric motorcycle, an electric vehicle, a hybrid electric vehicle, an industrial device such as an uninterruptible power supply (UPS), an idle reduction, an energy storage device, or the like. Or it can be used as a power source of various fields and products, such as home appliances, in particular, it can be preferably used for charging and discharging power supply of an electric vehicle or a hybrid electric vehicle composed of many secondary batteries.

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

3 schematically shows the structure of the laminate sheet end.

Referring to FIG. 3, the laminate sheet 20 includes an inner resin layer 20c, a barrier metal layer 20b, and an outer resin layer 20a having excellent durability.

Since the outer resin layer 20a must have excellent resistance from the external environment, it is a polymer resin having a predetermined tensile strength and weather resistance, and is made of polyethylene terephthalate (PET), a stretched nylon film, and the like, and the barrier metal layer 20b is A material containing aluminum having a barrier property against a gas and the like and a ductility that enables processing in a thin film form is used. The inner resin layer 20c has heat sealability (heat adhesion), has low hygroscopicity to suppress the invasion of the electrolyte, and is an unstretched polypropylene film (CPP) -based resin that is not expanded or eroded by the electrolyte. This is used. When the sealing part is heat-sealed, the inner resin layers 20c of the case body and the cover are melted and bonded to each other to seal the pouch-type secondary battery.

FIG. 4 is a schematic diagram illustrating a process of thermally sealing and sealing an electrode lead having a battery case and an insulating film according to an embodiment of the present invention, and FIG. 5 is extended from the heat fusion sealing part of FIG. 4. A schematic diagram is shown of a structure in which an insulating film is melted and solidified to surround a cross section of a laminate sheet.

Referring to these drawings, an insulating film 100 is attached to an upper surface and a lower surface of the electrode lead 200 in the heat sealing sealing portion A, and the electrode lead 200 to which the insulating film 100 is attached. When only the sealing portion A of the laminate sheet 20 is heated and pressurized in the direction of the arrow, the inner resin layer 20c and the insulating film on the inner surface of the laminate sheet 20, as shown in FIG. Sealed while fused.

The portion 120 that extends longer than the heat fusion sealing portion A from the upper end of the insulating film 100 is not bonded to the electrode lead 200 and is not directly heated in the heat fusion process by heat and pressure. Partially melted while thermal conduction occurs, and the melt shrinks while wrapping the ends of the laminate sheet 20 to form a sealing portion 122 covering the barrier metal layer 20b of the laminate sheet 20.

The extended portion 120 is also formed at the rear end (not shown) of the insulating film 100, and acts as a surplus in the heat fusion process by heat and pressure to prevent damage to the battery case.

Although described above with reference to the drawings according to an embodiment of the present invention, those skilled in the art will be able to perform a variety of applications and modifications within the scope of the present invention based on the above contents.

As described above. In the secondary battery according to the present invention, the insulating film, which is not bonded to the electrode lead and extends from the heat fusion sealing part, is partially melted and solidified in the heat fusion process to surround the end surface of the battery case. Prevents short circuit caused by contact of the metal layer on the end face of the case with the electrode lead, prevents the end face from being corroded by salt water, etc. It is effective to let.

Claims (9)

A secondary battery having a structure in which an electrode assembly having a cathode / separation membrane / cathode structure is mounted in a battery case of a laminate sheet including a metal layer and a resin layer, and then sealed by heat fusion sealing the outer circumferential surface of the battery case. It is connected to the electrode lead located in the heat-sealing sealing part, the insulating film is attached to the upper and lower surfaces of the electrode lead in the heat-sealing sealing part, respectively. (a) the insulating film has a front end portion and a rear end portion thereof extended from the heat-sealing sealing portion, (b) the insulating film is placed on a corresponding portion of the battery case in a state of being previously bonded to the electrode lead and then heat-sealed to the battery case, (c) The portion of the insulating film that extends longer than the heat-sealing sealing portion is not bonded to the electrode lead, (D) the secondary battery, characterized in that the portion extending longer than the heat-sealing sealing portion of the insulating film front end portion is partially melted during the heat-sealing process to surround the end surface of the battery case. The secondary battery of claim 1, wherein the laminate sheet comprises an inner resin layer that is heat-sealed, a barrier metal layer, and an outer resin layer having excellent durability. The method of claim 2, wherein the inner resin layer comprises at least 50% of the components of the inner resin layer cPP, the barrier metal layer comprises at least 50% of the components of the barrier metal layer, the outer water The layer is a secondary battery, characterized in that it contains at least 50% of the components of the stretched nylon or PET of the outer resin layer. The secondary battery of claim 1, wherein the front end portion and the rear end portion of the insulating film extend from a heat seal seal portion in a length of 0.5 to 5 mm. The secondary battery of claim 1, wherein the insulating film has a thickness of about 5 μm to about 200 μm. The secondary battery of claim 1, wherein the insulating film is made of one or two or more combinations selected from the group consisting of polypropylene, polyethylene, polyamide, polyethylene terephthalate, polybutylene, and polyisoprene. The secondary battery according to claim 1, wherein the battery is a lithium secondary battery of a pouch type battery case. A high output large-capacity battery module comprising the secondary battery according to any one of claims 1 to 7 as a unit cell. The battery module according to claim 8, wherein the battery module is used as a power source for an electric vehicle or a hybrid electric vehicle.

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