Secondary Battery And Method For Manufacturing The Same

The present invention provides a secondary battery, in which an electrode assembly is embedded in a pouch, and a lead electrically connected to the electrode assembly has one side protruding to the outside of the pouch, the secondary battery comprising: the pouch in which the electrode assembly is embedded, and sealing is performed along an edge thereof; the lead having one end connected to the electrode assembly and the other end protruding to the outside of the pouch; and a lead film disposed between the lead and the pouch and adhering to each of the pouch and the lead when the sealing of the pouch is performed, wherein an expansion part expanded by a predetermined length along a longitudinal direction of the lead is formed on the pouch, and the lead film has an area so that the entire expansion part is accommodated therein.

TECHNICAL FIELD

The present application claims the benefit of the priority of Korean Patent Application No. 10-2020-0154998, filed on Nov. 18, 2020, which is hereby incorporated by reference in its entirety.

The present invention relates to a secondary battery and a method for manufacturing the same, and more particularly, to a secondary battery, in which an expansion part is formed at a portion of a pouch, from which a lead protrudes, to increase in sealing area, thereby improving sealing performance, and a method for manufacturing the same.

BACKGROUND ART

The demand for secondary batteries as energy sources is rapidly increasing in various fields comprising personal portable terminal and electric vehicle fields.

Unlike primary batteries, rechargeable secondary batteries are being developed not only for digital devices but also for vehicles such as electric vehicles.

Secondary batteries are variously classified according to materials and external shapes of a positive electrode and a negative electrode. Among them, since such a lithium secondary battery using a lithium compound material has large capacity and a low self-discharge rate, the lithium secondary battery is being widely used instead of a nickel-cadmium secondary battery according to the related art.

Also, the lithium secondary battery may be manufactured in various shapes. Representatively, the lithium secondary battery may be manufactured in a cylinder type, a prismatic type, or a pouch type.

As shown inFIGS.1aand1b, which illustrate states before and after an electrode assembly is mounted on a pouch having a conventional structure, a pouch-type secondary battery comprises a pouch4and an electrode assembly1embedded in the pouch4to charge and discharge electrical energy.

The electrode assembly1is configured by alternately stacking a negative electrode and a positive electrode together with a separator therebetween, and electrode tabs1aand1bcomprising a negative electrode tab protruding from the negative electrodes and a positive electrode tab protruding from the positive electrodes are welded to leads2aand2bat both sides of the electrode assembly1, respectively. As illustrated in the drawing, the positive electrode tab and the negative electrode tab may be disposed on sides opposite to each other according to a method for manufacturing the positive electrode and the negative electrode.

In addition, ends of the leads2aand2bprotrude out of the pouch4so as to be electrically connected to an external device.

The pouch4is divided into an upper portion5and a lower portion6, which are capable of accommodating the electrode assembly1by covering one side and the other side of the electrode assembly1and is provided in a structure in which the upper portion5and lower portion6are connected to each other at one side.

Recessed grooves5aand6aare formed in the upper portion5and the lower portion6of the pouch4to accommodate the electrode assembly1, respectively, and each of edges5band6bof the grooves5aand6aare formed to be flat along a circumference of the pouch4. Thus, after the electrode assembly1is mounted, when the upper portion5and the lower portion6of the pouch4are closed, the edges5band6bof the upper portion5and the lower portion6are in contact with each other, and in this state, thermal fusion is performed by applying heat and a pressure to form a sealing part.

Here, when the electrode assembly1is mounted, one end of each of the leads2aand2bprotrudes out of the pouch4to prevent the sealing performance of the pouch4from being deteriorated, and simultaneously, lead films3aand3bare mounted in a state of being attached to leads2aand2bso as to secure electrical insulation.

As the secondary battery increases in capacity and is miniaturized, the edges5band6bforming the sealing part of the pouch4tend to be gradually reduced in size. Thus, there is a problem that sealing strength is lowered, and in particular, when the sealing strength is lowered, there is a possibility that electrolyte leakage or the like occurs in the portion from which each of the leads2aand2bprotrudes.

DISCLOSURE OF THE INVENTION

Technical Problem

Therefore, a main object of the present invention is to provide a secondary battery capable of increasing in sealing strength of the pouch at a portion, from which a lead protrudes, and a method for manufacturing the same.

Technical Solution

In order to achieve the above-described object, a method for manufacturing a secondary battery, in which an electrode assembly is embedded in a pouch, and a lead electrically connected to the electrode assembly has one side protruding to the outside of the pouch, provided in the present invention comprises: a pouch providing process of providing the pouch, which has an inner space, in which the electrode assembly is embedded, and in which sealing is performed along an edge, wherein an expansion part protrudes from a position at which a lead having one end connected to the electrode assembly and the other end protruding to the outside is seated; and a sealing process of applying heat along an edge of the pouch to seal the pouch in a state in which the electrode assembly and the lead are mounted in the pouch, and the pouch is closed, wherein, in the sealing process, the sealing is performed so that the expansion part is bonded to the lead.

The lead may be mounted together with a lead film, and when the sealing of the expansion part is performed, the expansion part may be thermally fused to the lead film, and the lead film may be thermally fused to a surface of the lead.

The lead film may have an area so that the entire expansion part is accommodated therein. The lead film may have a width greater than that of the lead.

A protruding length of the expansion part from one side of the pouch, in which the expansion part is formed, may be less than 50% of a protruding length of the lead from one side of the pouch, in which the expansion part is formed.

A secondary battery, in which an electrode assembly is embedded in a pouch, and a lead electrically connected to the electrode assembly has one side protruding to the outside of the pouch, and which is manufactured through the manufacturing method, according to the present invention comprises: the pouch in which the electrode assembly is embedded, and sealing is performed along an edge thereof; the lead having one end connected to the electrode assembly and the other end protruding to the outside of the pouch; and a lead film disposed between the lead and the pouch and adhering to each of the pouch and the lead when the sealing of the pouch is performed, wherein an expansion part expanded by a predetermined length along a longitudinal direction of the lead is formed on the pouch, and the lead film has an area so that the entire expansion part is accommodated therein.

The expansion part may be thermally fused to the lead film, and the lead film may be thermally fused to a surface of the lead.

The expansion part may have a width less than or equal to that of the lead, and the lead film may have a width greater than that of the lead.

A protruding length of the expansion part from one side of the pouch, in which the expansion part is formed, may be less than 50% of a protruding length of the lead from one side of the pouch, in which the expansion part is formed.

Advantageous Effects

In the present invention having the configuration as described above, since the expansion part is formed on the pouch, and the sealing area increases by the increasing area by the expansion part, the sealing performance in the portion at which the lead is disposed may be further improved, and thus, the possibility of the leakage of the electrolyte and the possibility of the damage of the lead may be further reduced.

The lead film may be thermally fused to the expansion part and the lead of the pouch. Here, since the lead film has the area and width, which are greater than those of the expansion part, the effect of increasing in width of the sealed point may be expected.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings in such a manner that the technical idea of the present invention may easily be carried out by a person with ordinary skill in the art to which the invention pertains. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein.

In order to clearly describe the present invention, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification.

Also, terms or words used in this specification and claims should not be restrictively interpreted as ordinary meanings or dictionary-based meanings, but should be interpreted as meanings and concepts conforming to the scope of the present invention on the basis of the principle that an inventor can properly define the concept of a term to describe and explain his or her invention in the best ways.

The present invention relates to a secondary battery and a method for manufacturing the same, and more particularly, to a secondary battery, in which expansion parts51a,51b,61a, and61bare formed at portions of a pouch40, from which leads20aand20bprotrude, to increase in sealing area, thereby improving sealing performance, and a method for manufacturing the same. Hereinafter, embodiments according to the present invention will be described in more detail with reference to the accompanying drawings.

First Embodiment

FIG.2is a view illustrating a state before an electrode assembly is mounted in a pouch according to the present invention, andFIG.3is a view illustrating a state in which the electrode assembly is mounted in the pouch, and then, sealing is performed according to the present invention, and is an enlarged view of a region, in which a lead protrudes.

Referring toFIGS.2and3, a secondary battery provided in this embodiment has a structure, in which an electrode assembly10is embedded in a pouch40, and one side of each of leads20aand20belectrically connected to the electrode assembly10protrudes to the outside of the pouch40.

That is, in this embodiment, the secondary battery comprises the electrode assembly10, the pouch40(50and60), the leads20(20aand20b), and lead films30(30aand30b), the pouches40have a structure in which expansion parts51and61(51a,51b,61a, and61b) are formed.

The electrode assembly10is configured by alternately stacking a negative electrode and a positive electrode together with a separator therebetween, and a negative electrode tab protruding from the negative electrodes and a positive electrode tab protruding from the positive electrodes are welded to the leads20aand20bat both sides of the electrode assembly10, respectively.

In addition, ends of the leads20aand20bare mounted in the pouch40so as to protrude to the outside of the pouch40so that the leads20aand20bare electrically connected to an external device. The pouch40is divided into an upper portion50and a lower portion60, which are capable of accommodating the electrode assembly10by covering one side and the other side of the electrode assembly10and is provided in a structure in which the upper portion50and lower portion60are connected to each other at one side. Alternatively, in some cases, the upper portion50and lower portion60may be provided in a completely separated state.

Recessed grooves50aand60aare formed in the upper portion50and the lower portion60of the pouch40to accommodate the electrode assembly10, respectively, and each of edges50band60bof the grooves50aand60aare formed to be flat along a circumference of the pouch40. After the electrode assembly10is mounted, when the upper portion50and the lower portion60of the pouch40are closed, the edges50band60bof the upper portion50and the lower portion60are in contact with each other, and in this state, thermal fusion is performed by applying heat and a pressure to form a sealing part.

Thus, one end of each of the leads20aand20bis connected to the electrode assembly10, and the other end protrudes to the outside of the pouch40. Here, the lead films30(30aand30b) are attached to sides of the leads20, which protrude to the outside of the pouch40, respectively. Thus, as illustrated inFIG.3, when the sealing is performed, each of the lead films30is disposed between each of the leads20and the pouch40(between the edges of the pouch), and when thermal fusion is performed, one surface of each of the lead films30adheres to the pouch40, and the other side of each of the lead films30adheres to each of the leads20.

Furthermore, the expansion parts51and61, each of which extends by a predetermined length along a longitudinal direction of the lead20, are formed on the pouch40. Here, the lead film30is formed in a size so that the entire expansion parts51and61are accommodated therein.

In the secondary battery provided in this embodiment, a width of the expansion part51is less than or equal to that of the lead20, and a width of the lead film30is greater than that of the lead20. The width as used herein means a length in a direction perpendicular to the longitudinal direction of the lead.

In addition, it is preferable that a protruding length d1of each of the expansion parts51and61from one side of the pouch40, in which the expansion parts51and61are formed, is less than 50% of a protruding length d2of the lead20from one side of the pouch40, in which the expansion parts51and61are formed.

In more detail, it is preferable that the protruding length d1of each of the expansion parts51and61is formed within a range of 20% to 40% of the protruding length d2of the lead20.

When the protruding length d1of each of the expansion parts51and61is formed to be less than 20% of the protruding length d2of the lead20, there is a problem in that an effect of increasing in sealing force due to the formation of the expansion parts51and61is reduced. When the protruding length d1exceeds 40% of the protruding length d2, an exposed area of the lead20is covered too much, and thus, there is a possibility of occurrence of an interference when the lead20is electrically connected to the external device. Therefore, it is preferable to be formed within the above range in order to compromise this state.

Therefore, when the heat and pressure are applied to the pouch40, the heat and pressure are transferred in order of the expansion parts51and61, the lead film30, and the lead20. As a result, the expansion parts51and61are thermally fused to the lead film30, and the lead film30is thermally fused to a surface of the lead20.

Second Embodiment

Furthermore, the present invention provides a method for manufacturing a secondary battery having the above structure as a second embodiment.

The manufacturing method according to this embodiment comprises a pouch providing process and a sealing process.

In the pouch providing process, a pouch40, which has an inner space, in which an electrode assembly10is embedded, and in which sealing is performed along edges50band60b, is provided. Here, each of expansion parts51and61protrudes from a position at which a lead20having one end connected to the electrode assembly10and the other end protruding to the outside is seated.

The pouch40is manufactured by molding and cutting a raw material of the pouch40. Here, portions of upper and lower portions50and60of the pouch40, in which grooves50aand60aare formed, are processed by being pressed by a punch to deform the raw material, and portions of the edges50band60bare processed by cutting the raw material to be fitted with a predetermined size. Here, when the cutting is performed to form the edges50band60bof the upper portion50and the lower portion60, the expansion parts51and61, each of which protrudes to a predetermined size from each of the portions of the edge50band60bon which the lead20is placed, are processed to be provided.

Also, the sealing process comprises an accommodation process of accommodating the electrode assembly10in the pouch40. In the accommodation process, when the electrode assembly10is embedded in the pouch40, a portion of a lead tape30and an end of the lead20are accommodated so as to protrude to the expansion parts51and61.

In addition, in the sealing process, in a state in which the edges50band60bof the upper portion50and the lower portion60of the pouch40are in contact with each other, heat is applied to the edges50band60b, which are in contact with each other, to perform the sealing.

While the edges50band60bare sealed, the extension parts51and61are also sealed to be bonded to the lead20.

Since the lead20is mounted in a state of being coupled to the lead film30, when sealing of the expansion parts51and61is performed, the expansion parts51and61are thermally fused to the lead film30and, the lead film30is thermally fused to a surface of the lead20.

The lead film30has an area so that the entire expansion parts51and61are accommodated therein. The lead film30has a width greater than that of the lead20.

As illustrated inFIG.4, in which a sealing region S is displayed in the secondary battery according to the present invention, in the present invention having the above-described configuration, the expansion parts51and61may be formed in the pouch40, and the sealing area may increase by the areas increasing by the expansion parts51and61to more improve the sealing performance at the portion at which the lead20is disposed. Therefore, possibility of leakage of an electrolyte and possibility of damage of the lead may be further reduced.

The lead film30may be thermally fused to the extension parts51and61and the lead20of the pouch40. Here, since the lead film30has the area and width, which are greater than those of each of the expansion parts51and61, the effect of increasing in width of the sealed point may be expected.

DESCRIPTION OF THE SYMBOLS

10: Electrode assembly40: Pouch50: Upper portion of pouch60: Lower portion of pouch30(30a,30b): Lead film51a,51b,61a,61b: Expansion part