CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/KR2017/002651, filed Mar. 13, 2017, which claims priority to and the benefit of Korean Patent Application No. 10-2016-0032092 filed in the Korean Intellectual Property Office on Mar. 17, 2016, the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a manufacturing device of a battery case having improved manufacturing processability and a manufacturing method using the same.

BACKGROUND

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. In particular, among the secondary batteries, a number of researches and commercialization of a lithium secondary battery having a high energy density and a discharge voltage have been conducted.

Typically, in view of a shape of the battery, there is a high demand for a prismatic secondary battery and a pouch type secondary battery that are applicable to products such as mobile phones, etc., due to a thin thickness, and in view of a material of the battery, there is a high demand for lithium secondary batteries such as a lithium ion battery and a lithium ion polymer battery having high energy density, discharge voltage, and output stability.

The secondary battery may be classified into a cylindrical battery cell, a prismatic battery cell, and a pouch type battery cell, etc., depending on its shape. Of these, the pouch type battery cell that is capable of being stacked with a high degree of integration, has a high energy density per unit weight, is inexpensive, and is easy to be modified are attracting much attention.

The pouch type secondary battery includes a flexible laminate sheet as a battery case, and has a structure in which an electrode assembly and an electrolyte solution are embedded in a storage space molded in an electrode assembly shape on the laminate sheet.

Meanwhile, the secondary battery is also used as the energy source gradually even in fields where large-capacity electric power is required, such as electric vehicles, hybrid vehicles, and electric power storage devices, etc., as well as small-sized mobile devices or household appliances, or the like. Accordingly, the demand for the secondary battery having a large capacity is drastically increased as compared to the conventional secondary battery having a small capacity.

A charge/discharge capacity of the secondary battery is proportional to an area of an electrode plate and the number of electrode plates. As the area and the number of the electrode plates are increased, a thickness of the electrode assembly is increased.

Corresponding to this, a shape of the battery case is also required to have a storage part having a deep depth so that the electrode assembly having a relatively thick thickness is stored.

Generally, a method in which the laminate sheet is stretched to a desired depth by using a punch that presses the sheet downward in a state in which the storage part fix the laminate sheet, is used.

However, due to a limit of flexibility of the laminate sheet and frictional force applied when the sheet is pressed by the punch, there are problems that appearance defects such as pin-holes, cracks, or the like, occur on an outer surface of the stretched laminate sheet at a predetermined depth or more, and accordingly, it is difficult to form the depth of the storage part deeply so that the electrode assembly having a large capacity is capable of being accommodated.

Therefore, there is a high need for a manufacturing device of a battery case that is capable of overcoming the above-described technical problem, i.e., that is capable of forming the depth of the storage part deeply without causing the appearance defects.

Technical Problem

The present invention aims to solve the above-described problems of the conventional art and technical problems required from the past.

In detail, the present invention has been made in an effort to provide a manufacturing device having advantages of minimizing frictional force at the time of forced stretching of a laminate sheet, and specifically, provide a manufacturing device and a manufacturing method having advantages of manufacturing a battery case having a desired shape and quality by inducing stretching of the laminate sheet by an air pressure instead of a pressurizing means such as a punch for inducing forced stretching in a state of being in contact with the laminate sheet.

Technical Solution

An exemplary embodiment of the present invention provides a manufacturing device of a battery case in which a storage part for mounting an electrode assembly for a secondary battery is formed on a laminated sheet, the manufacturing device including:

a first mold including a first space part having a shape corresponding to the storage part formed therein;

a second mold including a second space part having a shape corresponding to the storage part and a through-hole communicating with the second space part formed therein, and coupled to the first mold with the laminate sheet interposed therebetween; and

an air pressure regulator mounted in the through-hole in a state in which the first space part and the second space part are isolated from the outside, and increasing or decreasing an air pressure of the second space part through the through-hole to stretch and modify the laminate sheet into a shape corresponding to the first space part or the second space part.

Since the manufacturing device induces stretching of the laminate sheet in accordance with increase or decrease in air pressure, the frictional force applied to the laminate sheet during the stretching process may be remarkably low as compared to a structure in which the laminate sheet is pressed in a direct contact state, for example, a deep drawing method using a punch, thereby preventing defects such as cracks and pinholes and stretching the laminate sheet in the form of a storage part having a deeper depth.

Further, in the structure, since complicated pressurizing means such as a punch and a hydraulic cylinder for lifting the punch may be omitted, the manufacturing device may be constituted in a relatively compact structure, and based on this, it is possible to provide economic advantages in view of facility design and maintenance.

In the manufacturing device according to the present invention, a coating layer for reducing frictional force with the laminate sheet may be added to an inner surface of the first and second space parts. For example, the coating layer may be a Teflon resin having a friction coefficient of 0.03 to 0.04.

Generally, the laminate sheet has a characteristic of a soft packaging material to be excellent in stretchability against an external force, but has a low mechanical rigidity. For this reason, the frictional force is formed on the stretched laminate sheet in a state in which the laminate sheet is in close contact with each of the space parts which are inner surfaces of the first and second molds.

Since the frictional force acts as a load on the stretched laminate sheet, a lower flexibility than an inherent flexibility of the laminate sheet is formed at a portion where the laminate sheet and the inner surface of the space parts are in close contact with each other.

Accordingly, when a pressing force stronger than the flexibility formed by the frictional force is applied, the sheet may be forcibly stretched but the crack may occur on the outer surface.

For this reason, it is difficult to set the air pressure for inducing the stretching of the laminate sheet to be large, and substantially, in consideration of the fact that the depth of the storage part is determined by the pressing force by the air pressure, a range of the air pressure should be set within a range where no crack occurs.

Accordingly, in the manufacturing device according to the present invention, at the time of pressing, the coating layer having a relatively low friction coefficient is formed on the inner surfaces of the first space part and the second space part that are in close contact with the laminate sheet, and thus it is possible to minimize deterioration in flexibility inherent to the sheet at a portion where the laminate sheet and the punch are in close contact with each other, thereby forming the depth of the storage part relatively deeply while suppressing the occurrence of crack.

Hereinafter, a structure in which the first mold, the second mold, and the storage part are formed is described in further detail with reference to the following non-limiting examples.

In one specific example, the first mold may include first fixing parts that are in close contact with a lower surface of the laminate sheet along an outer periphery adjacent to a portion for forming the storage part in the laminate sheet;

the second mold may include second fixing parts that are in close contact with an upper surface of the laminate sheet along an outer periphery adjacent to a portion for forming the storage part in the laminate sheet; and

the first space part and the second space part may be isolated from the outside in a state in which the laminate sheet is fixed between the first fixing parts and the second fixing parts.

In addition, as described above, the first space part and the second space part may be isolated from each other by the laminate sheet in a state in which the laminate sheet is fixed between the first fixing parts and the second fixing part.

Therefore, the laminate sheet positioned in the first space part and the second space part may be isolated from the outside, and in particular, may be modified correspondingly when the air pressure in the second space part is changed.

In one specific example, the air pressure regulator may decrease an air pressure of the second space part through the through-hole, and the laminate sheet may be modified into a shape corresponding to the second space part while being stretched in a direction of the second space part in response to the decrease in pressure of the second space part.

In this structure, the air pressure of the second space part becomes lower than the air pressure of the first space part, and the laminate sheet moves in the direction of the second space part based on the first space part. At this time, the laminate sheet is slowly stretched and is molded in a shape in which the laminate sheet is in close contact with the inner surface of the second space part.

Here, a degree of the decrease in pressure of the second space part through the air pressure regulator may be set in consideration of a thickness of the laminate sheet and a desired depth of the storage part. However, when the degree of the decrease in pressure is set to be excessively high in order to simply increase a volume and a depth of the storage part, defects such as cracks and pinholes on the sheet surface may be caused due to excessive stretching and frictional force on the laminate sheet, the through-hole may be sealed by a portion of the laminate sheet before being molded in a desired storage part form.

In addition, the laminate sheet includes a resin layer and a metal layer, due to a characteristic of a material, when sheet is excessively thin, a small amount of moisture particles may be transmitted through the resin layer. In particular, the transmission phenomenon may be promoted at a portion where the thickness is relatively thinned due to the stretching.

Accordingly, it is preferable that the laminate sheet has a thickness capable of securing reliability with respect to moisture even in the state that the laminate sheet is stretched.

Accordingly, the present inventors found that at the time of decreasing the pressure by sucking air at a pressure of 10×105dyn/cm2to 99×105dyn/cm2by the air pressure regulator, the previously described two conditions may be satisfied, that is, the reliability of moisture permeation through the storage part may be secured without causing defects and through-hole blocking caused by excessive stretching of the laminate sheet.

In some cases, the decreasing in pressure of the second space part may be progressively performed from a relatively high pressure to a low pressure satisfying the above-described pressure range.

Meanwhile, a vertical cross-sectional area of the through-hole through which the air flows may have a size of 0.01% to 5% compared to a total area of the laminated sheet positioned in the second space part before the decrease in pressure.

When the vertical cross-sectional area is less than the above range, an excessive suction pressure may be formed in the through-hole, and the laminate sheet adjacent to the through-hole may be torn. When the vertical cross-sectional area is more than the above range, a portion to be further stretched through the through-hole in the laminate sheet may be formed relatively wide, and a shape of the through-hole may be formed in the laminate sheet, and thus the storage part may not be molded in a desired form.

As described above, a plurality of through-holes satisfying the size range may be formed in the second mold so as to prevent the laminate sheet in an undesired form due to the through-hole from being molded, and to prevent the sheet from being damaged.

In another specific example, the air pressure regulator may increase the air pressure of the second space part, and the sheet may be modified into a shape corresponding to the first space part while being stretched in a direction of the first space part in response to the air pressure formed in the second space part.

In this structure, the air pressure of the second space part becomes higher than the air pressure of the first space part, and the laminate sheet moves in the direction of the first space part based on the second space part. At this time, the laminate sheet is slowly stretched and is molded in a shape in which the laminate sheet is in close contact with the inner surface of the first space part.

Here, similar to the above-described decrease in pressure, the air pressure regulator may increase a pressure in a pressure range in which reliability with respect to moisture permeation through the storage part may be secured without causing excessive stretching of the laminate sheet and through-hole blocking, and specifically, may increase the pressure by introducing air at a pressure of 10×105dyn/cm2to 99×105dyn/cm2.

In some cases, the decrease in pressure of the second space part may be progressively performed from a relatively low pressure to a high pressure satisfying the above-described pressure range.

The laminate sheet in the present invention means a sheet composed of an upper layer of a polymer resin, an intermediate layer of a barrier metal, and a lower layer of a polymer resin.

The upper layer of the polymer resin is a resin layer forming the outer surface of the battery case, and is required to have tensile strength and weather resistance having a predetermined level or more so as to have excellent resistance to external environment. In this respect, polyethylene terephthalate (PET) and stretched nylon film may be used as the polymer resin of the outer layer of the resin.

The lower layer of the polymer resin may be preferably formed of a polyolefin-based resin that has heat fusion property (heat adhesive property) and low hygroscopicity to suppress penetration of an electrolyte solution, and that is not swollen or eroded by the electrolyte solution.

Aluminum may be used as the intermediate layer of the barrier metal so as to improve strength of a cell case in addition to prevent the inflow or outflow of foreign substances such as gas, moisture, and the like.

In general, the barrier metal plays a dominant role in the stretching of the laminate sheet.

Specifically, as the thickness of the barrier metal is increased, a range in which the laminate sheet is capable of being stretched may be relatively wide. However, when the thickness thereof is excessively increased, flexibility may be deteriorated due to rigidity of the thicker barrier metal.

On the contrary, as the thickness of the barrier metal is thinner, the range in which the laminate sheet is capable of being stretched may be relatively narrow, but the mechanical rigidity of the thin barrier metal may be low, and thus the flexibility may be increased.

In particular, in the deep drawing method using a punch, molding of the laminate sheet is performed by instantaneous pressing of the punch, and thus it is advantageous for the thickness of the barrier metal to be thick for mechanical rigidity, wherein the thickness may be from about 50 micrometers to about 150 micrometers. However, since the manufacturing cost is greatly increased as the thickness of the barrier metal is increased, the deep drawing method has an economical disadvantage.

On the other hand, in the present invention, the stretching of the laminate sheet is slowly induced by using the air pressure, and thus the thickness of the barrier metal is preferably relatively thin. For this reason, the present invention has an economical advantage compared to the deep drawing method. Accordingly, in the present invention, the thickness of the barrier metal may be 15 micrometers to 50 micrometers, and more specifically 25 micrometers to 50 micrometers.

When the thickness of the barrier metal is less than 15 micrometers, the stretching range may be narrow, and thus the metal may break during the stretching process. When the thickness thereof is more than the above range, it is not preferable since the stretching to air pressure is not available.

Another embodiment of the present invention provides a manufacturing method for forming a storage part for mounting an electrode assembly for a secondary battery on a laminate sheet.

The manufacturing method specifically includes,

disposing the laminate sheet between a first mold and a second mold, and coupling the first mold and the second mold in a form in which a first space part formed in the first mold and a second space part formed in the second mold are isolated from each other;

changing a pressure of the second space part by a through-hole communicating with the second space part of the second mold and an air pressure regulator coupled to the through-hole; and

stretching the sheet in a shape corresponding to the first space part or the second space part in response to a pressure change of the second space part.

That is, the method according to the present invention induces the stretching of the laminate sheet by changing the air pressure in an isolated space. Thus, the frictional force applied to the laminate sheet during the stretching process may be remarkably low as compared to the general deep drawing method, and accordingly, the laminate sheet may be stretched to a deep depth, thereby providing excellent advantages in view of manufacturing processability.

In this method, the pressure change may be performed by selecting a process of decreasing a pressure by sucking air in the second space part by the air pressure regulator, or a process of increasing the pressure by introducing air into second space part by the air pressure regulator.

The decreasing of the pressure may be gradationally performed by a primary decrease in pressure with a pressure of 10×105dyn/cm2to 60×105dyn/cm2at an atmospheric pressure, and a secondary decrease in pressure with a pressure of 110% to 400% compared to the pressure of the primary decrease in pressure.

Similar to this, the increasing of the pressure may be gradationally performed by a primary increase in pressure with a pressure of 10×105dyn/cm2to 60×105dyn/cm2at an atmospheric pressure, and a secondary increase in pressure with a pressure of 110% to 400% compared to the pressure of the primary increase in pressure.

This is intended to gradually induce the stretching of the laminate sheet to increase dimensional accuracy of the storage part, and simultaneously, to prevent defects such as cracks and pinholes that may occur when the laminate sheet is stretched in a short time.

Further, the increase in pressure and the decrease in pressure by stages may induce relatively uniform stretching of each portion of the laminate sheet, for example, a portion that is positioned in the first space and the second space and is directly pressurized by the air pressure, and a portion engaged between the first mold and the second mold, and thus the thickness of the storage part may be uniformly formed.

Yet another embodiment of the present invention provides a battery case including the storage part formed by the manufacturing method as described above.

The storage part of the battery case may include an electrode assembly and an electrolyte solution embedded therein, and in this state, an outer circumferential portion of the battery case may be heat fused and sealed to form a secondary battery.

