Patent Description:
The present invention relates to a battery case for a secondary battery and a method for manufacturing a gas discharge part, and more specifically, to: a battery case for a secondary battery, in which pressure may be controlled by discharging to the outside a gas present inside a pouch when internal pressure therein increases; and a method for manufacturing a gas discharge part.

In general, as types of secondary batteries, there are nickel-cadmium batteries, nickel-hydrogen batteries, lithium ion batteries, lithium ion polymer batteries, and the like. Such a secondary battery is being applied and used in large products requiring a high output such as electric vehicles or hybrid electric vehicles, and power storage devices and backup-power storage devices for storing surplus generated power and new renewable energy, as well as small products such as digital cameras, P-DVDs, MP3 players, cellular phones, PDAs, portable game devices, power tools, and E-bikes.

The secondary battery is classified into a pouch type, a can type, or the like according to a material of a case that accommodates an electrode assembly. In the pouch type, the electrode assembly is accommodated in a pouch made of a flexible polymer material. Also, in the can type, the electrode assembly is accommodated in a pouch made of a metal or plastic material, or the like.

Here, a gas may be generated in the secondary battery by an internal short circuit due to external impact, overcharging, over-discharging, or the like. In addition, when the secondary battery is kept or stored at a high temperature, an electrochemical reaction between an electrolyte and an electrode active material may be quickly accelerated by the high temperature to thereby generate a gas.

Here, the generated gas increases the internal pressure of the secondary battery and thereby causes problems such as weakening of a bonding force between components, damage of a case of the secondary battery, an early operation of a protection circuit, deformation of an electrode, an internal short circuit, explosion, and the like. To prevent these problem, protection members such as a CID filter and a safety vent are provided in the can-type secondary battery. Thus, when the pressure within the case increases, electrical connection are physically interrupted. However, the protection members are not sufficiently provided in the pouch-type secondary battery according to the related art.

Further prior art is described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

The object of the invention is to provide: a battery case for a secondary battery, in which pressure may be controlled by discharging to the outside a gas present inside a pouch when internal pressure therein increases; and a method for manufacturing a gas discharge part.

The object of the present invention is not limited to the aforesaid, but other objects not described herein will be clearly understood by those skilled in the art from descriptions below.

A battery case for a secondary battery according to an embodiment of the present invention for achieving the object includes: a cup part provided with an accommodation space configured to accommodate an electrode assembly formed by stacking an electrode and a separator; a sealing part extending outward from the cup part; and a gas discharge part which is attached from the inside to a hole formed by perforating at least one of the cup part or the sealing part and through which a gas passes, wherein the gas discharge part includes: a gas discharge layer through which the gas passes; and an outer functional layer which is formed on an outer surface of the gas discharge layer, wherein the outer functional layer has hydrophobicity and includes a plurality of fine protrusions having a diameter of <NUM> to <NUM> pm, preferably <NUM> to <NUM> pm, distributed on an outer surface thereof.

Also, each of the fine protrusions may have a diameter of <NUM> to <NUM>.

Also, the outer functional layer may include oil or a wax component.

Also, the oil may include at least one of fluorocarbon oil, silicone oil, carbon-based oil, or fatty acid amide.

Also, the gas discharge layer may include at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF).

Also, an inner functional layer may be further provided which is formed on an inner surface of the gas discharge layer and has hydrophobicity.

Also, the sealing part may include: an inner area adjacent to the cup part; and an outer area which is positioned outward from the inner area to serve as an edge and sealed to seal the cup part, wherein the hole is formed in the inner area of the sealing part.

Also, the gas discharge part may be provided in plurality.

A method for manufacturing a gas discharge part according to an embodiment of the present invention for achieving the object includes: preparing a gas discharge layer through which a gas passes; preparing an outer functional layer which is formed on an outer surface of the gas discharge layer; manufacturing a mixture by mixing fine particles having a diameter of each particle of <NUM> to <NUM> pm, preferably <NUM> to <NUM> pm, and a polymer solution; spraying the mixture onto at least one surface of the gas discharge layer; and drying the mixture.

Also, the polymer solution may include at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF).

Also, the fine particles may include at least one of silica particles, carbon nanotubes (CNT), or alumina particles.

Also, the silica particles may be contained at <NUM> wt% to <NUM> wt%.

Also, in the spraying of the mixture, the mixture may be sprayed at a distance of <NUM> to <NUM> from the gas discharge layer at pressure of <NUM> Mpa to <NUM> Mpa through a nozzle.

Also, the spraying of the mixture and the drying of the mixture may be repeated two to four times.

A pouch-type secondary battery according to an embodiment of the present invention for achieving the object includes: an electrode assembly formed by stacking an electrode and a separator; and a battery case as described above configured to accommodate therein the electrode assembly.

A method for manufacturing a pouch-type secondary battery as described above according to an embodiment of the present invention for achieving the object includes: forming a cup part by drawing a pouch film; forming a hole by perforating at least one of the cup part or a sealing part that extends outward from the cup part; attaching, from the inside to the hole, a gas discharge part through which a gas passes; accommodating, in an accommodation space provided in the cup part, an electrode assembly formed by stacking an electrode and a separator; and heat-pressing the sealing part.

Also, the gas discharge part may include: a gas discharge layer through which the gas passes; and an outer functional layer which is formed on an outer surface of the gas discharge layer and has hydrophobicity, wherein the pouch film includes a sealant layer which is made of a polymer and positioned as an innermost layer, and in the attaching of the gas discharge part, the outer functional layer is heated and pressed and is sealed to the sealant layer.

Other specific features of the present invention are included in the detailed description and drawings.

According to the embodiments of the present invention, at least the following effects are obtained.

The hole is made in the battery case, and the gas discharge part through which the gas is discharged is attached to the hole. Thus, when the internal pressure of the secondary battery increases, the pressure may be controlled by discharging the gas from the inside to the outside.

Also, the outer functional layer or the inner functional layer are formed in the gas discharge part. Thus, the moisture may be prevented from entering from the outside, and the electrolyte may be prevented from leaking from the inside.

Also, the gas discharge part is attached to the hole from the inside. Thus, the metal of the gas barrier layer exposed to the inner circumferential surface of the hole may be prevented from being corroded by the electrolyte.

The effects according to the present invention are not limited to those exemplified above, and more various effects are included in the present specification.

Advantages and features of the present invention, and implementation methods thereof will be clarified through following embodiments described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in various different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Further, the present invention is defined only by scopes of claims.

Unless otherwise defined, all terms (including technical and scientific terms) used herein may have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a generally used dictionary are not construed ideally or excessively unless defined apparently and specifically.

In this specification, the terms are used only for explaining embodiments while not limiting the present invention. In this specification, the singular forms include the plural forms as well, unless the context clearly indicates otherwise. The meaning of "comprises" and/or "comprising" used in the specification does not exclude the presence or addition of other components besides a mentioned component.

<FIG> is an assembly view of a pouch-type secondary battery <NUM> according to an embodiment of the present invention, and <FIG> is a perspective view of a pouch-type secondary battery <NUM> according to an embodiment of the present invention.

As illustrated in <FIG>, the pouch-type secondary battery <NUM> according to the embodiment of the present invention includes an electrode assembly <NUM> which is formed by stacking a separator and electrodes such as a positive electrode and a negative electrode and a pouch-type battery case <NUM> which accommodates therein the electrode assembly <NUM>.

To manufacture the pouch-type secondary battery <NUM>, slurry, in which an electrode active material, a binder, and a plasticizer are mixed, is applied first to a positive electrode collector and a negative electrode collector to manufacture electrodes such as a positive electrode and a negative electrode. Then, the electrodes are stacked on both sides of a separator to form the electrode assembly <NUM> having a predetermined shape. Subsequently, the electrode assembly <NUM> is inserted into the battery case <NUM>, an electrolyte is injected therein, and then the battery case <NUM> is sealed.

Particularly, the electrode assembly <NUM> may be a stack structure provided with two types of electrodes such as the positive electrode and the negative electrode and the separator interposed between the electrodes or disposed on the left or right side of one of the electrodes to insulate the electrodes from each other. The stack structure may not be limited to that described above but have various configuration. The positive electrode and the negative electrode having predetermined specifications may be stacked with the separator therebetween, or the stack structure may be wound in a jelly roll shape. The two types of electrodes, that is, the positive electrode and the negative electrode have structures in which active material slurry is applied to the electrode collectors having metal foil or metal mesh shapes including aluminum and copper, respectively. The slurry may be generally formed by mixing granular active materials, subsidiary conductors, binders, plasticizers, and the like in a state where a solvent is added. The solvent is removed during a subsequent process.

The electrode assembly <NUM> include an electrode tab <NUM> as illustrated in <FIG>. The electrode tab <NUM> is connected to each of the positive electrode and the negative electrode of the electrode assembly <NUM>, and protrudes outward from the electrode assembly <NUM> to serve as a path through which electrons may move between the inside and the outside of the electrode assembly <NUM>. The collector of the electrode assembly <NUM> is provided as a portion which is coated with the electrode active material and an end portion, that is, a non-coating portion which is not coated with the electrode active material. Also, the electrode tab <NUM> may be formed by cutting the non-coating portion or formed by connecting a separate conductive member to the non-coating portion through ultrasonic welding or the like. Although the electrode tab <NUM> may protrude from one side of the electrode assembly <NUM> side by side in the same direction as illustrated in <FIG>, the embodiment is not limited thereto. The electrode tab may protrude in different directions.

An electrode lead <NUM> is connected to the electrode tab <NUM> of the electrode assembly <NUM> through spot welding or the like. Also, a portion of the electrode lead <NUM> is surrounded by an insulation part <NUM>. The insulation part <NUM> is positioned to be limited to a sealing part <NUM>, in which an upper case <NUM> and a lower case <NUM> of the battery case <NUM> are heat-fused, and is boded to the battery case <NUM>. Also, electricity generated from the electrode assembly <NUM> is prevented from flowing to the battery case <NUM> through the electrode lead <NUM>, and the sealing of the battery case <NUM> is maintained. Thus, the insulation part <NUM> is made of a non-conductor having non-conductivity in which the electricity does not flow well. Generally, although relatively thin insulation tape easily attached to the electrode lead <NUM> is widely used as the insulation part <NUM>, the embodiment is not limited thereto. Various members capable of insulating the electrode lead <NUM> may be used.

The electrode lead <NUM> includes a positive electrode lead <NUM> which has one end connected to a positive electrode tab <NUM> and extends in a direction in which the positive electrode tab <NUM> protrudes and a negative electrode lead <NUM> which has one end connected to a negative electrode tab <NUM> and extends in a direction in which the negative electrode tab <NUM> protrudes. Here, the other ends of both the positive electrode lead <NUM> and the negative electrode lead <NUM> protrude outward from the battery case <NUM> as illustrated in <FIG>. Accordingly, the electricity generated inside the electrode assembly <NUM> may be supplied to the outside. Also, since the positive electrode tab <NUM> and the negative electrode tab <NUM> may protrude in various directions, the positive electrode lead <NUM> and the negative electrode lead <NUM> may extend in various directions, respectively.

The positive electrode lead <NUM> and the negative electrode lead <NUM> may have materials different from each other. That is, the positive electrode lead <NUM> may have the same aluminum (Al) material as the positive electrode collector, and the negative electrode lead <NUM> may have the same copper (Cu) material or nickel (Ni)-coated copper material as the negative electrode collector. Also, a portion of the electrode lead <NUM> protruding outward from the battery case <NUM> serves as a terminal part and is electrically connected to an external terminal.

The battery case <NUM> is a pouch made of a flexible material. Also, the battery case <NUM> is sealed after accommodating the electrode assembly <NUM> such that a portion of the electrode lead <NUM>, i.e., the terminal part is exposed. The battery case <NUM> includes the upper case <NUM> and the lower case <NUM> as illustrated in <FIG>. The lower case <NUM> includes a cup part <NUM> to provide an accommodation space <NUM> in which the electrode assembly <NUM> may be accommodated, and the upper pouch <NUM> covers the accommodation space <NUM> from above so that the electrode assembly <NUM> is not separated to the outside of the battery case <NUM>. Here, as illustrated in <FIG>, the upper case <NUM> also include the cup part <NUM> in which the accommodation space <NUM> is provided, and thus, the electrode assembly <NUM> may be accommodated from above. However, the embodiment is not limited thereto and may be configured in various shapes. The cup part <NUM> may be formed only in the lower case <NUM>. Also, although the upper case <NUM> and the lower case <NUM> may be manufactured such that one sides thereof are connected to each other as illustrated in <FIG>, the embodiment is not limited thereto. The cases may be diversely manufactured, for example, individually manufactured and separated from each other.

The battery case <NUM> includes a gas discharge part <NUM> through which a gas passes. The gas discharge part <NUM> is attached from the inside to a hole <NUM> formed by perforating at least one of the cup part <NUM> or the sealing part <NUM> and through which a gas passes.

The hole <NUM> is formed in at least one of the upper case <NUM> or the lower case <NUM>. That is, only one hole <NUM> may be formed, but the plurality of holes may be possible. Also, as illustrated in <FIG>, the sealing part <NUM> extending outward from the cup part <NUM> includes an inner area <NUM> adjacent to the cup part <NUM> and an outer area <NUM> which is positioned outward from the inner area <NUM> to serve as an edge and sealed to seal the cup part <NUM>. Here, it is desirable that the hole <NUM> is formed in the inner area <NUM> rather than in the outer area <NUM> in the sealing part <NUM>. Also, when the sealing part <NUM> is sealed subsequently, it is desirable not to seal the inner area <NUM> in which the hole <NUM> is positioned but to seal only the outer area <NUM>. Accordingly, two sealing parts <NUM> of the upper and lower cases <NUM> and <NUM> come into contact with each other to close the hole <NUM> in a normal state. Thus, the moisture may be prevented from entering from the outside, and the electrolyte may be prevented from leaking from the inside. Also, when a large amount of gases is generated inside the secondary battery <NUM>, the volume of the secondary battery <NUM> expands, and the inner areas <NUM> of the two sealing parts <NUM> in contact with each other are spaced apart from each other. As a result, the hole <NUM> is open, and the gas may be discharged to the outside through the gas discharge part <NUM>. However, the embodiment is not limited thereto, and the hole <NUM> may be formed at various positions, for example, formed in one surface of the cup part <NUM> as long as it may easily discharge the gas.

It is desirable that a gas may easily pass through the gas discharge part <NUM>, but a liquid such as water or an electrolyte does not easily pass therethrough. The gas discharge part <NUM> will be described later in detail.

When the electrode lead <NUM> is connected to the electrode tab <NUM> of the electrode assembly <NUM>, and the insulation part <NUM> is provided on the portion of the electrode lead <NUM>, the electrode assembly <NUM> is accommodated in the accommodation space <NUM> provided in the cup part <NUM> of the lower case <NUM>, and the upper case <NUM> covers the space from above. Then, the electrolyte is injected to the inside, and the sealing parts <NUM> provided on the edges of the upper case <NUM> and the lower case <NUM> are sealed. The electrolyte is to move lithium ions generated by an electrochemical reaction of the electrode during charging and discharging of the secondary battery <NUM>. Also, the electrolyte may include a non-aqueous organic electrolyte, which is a mixture of a lithium salt and a high-purity organic solvent, or may include a polymer using a polymer electrolyte. Through the method described above, the pouch-type secondary battery <NUM> may be manufactured as illustrated in <FIG>.

<FIG> is a cross-sectional view of the gas discharge part <NUM> according to an embodiment of the present invention.

The gas discharge part <NUM> is attached from the inside to the hole <NUM> formed by perforating at least one of the cup part <NUM> or the sealing part <NUM>, and the gas passes therethrough. As illustrated in <FIG>, the gas discharge part <NUM> includes a gas discharge layer <NUM> through which the gas passes and an outer functional layer <NUM> which is formed on an outer surface of the gas discharge layer <NUM> and has hydrophobicity. Also, an inner functional layer <NUM> may be further provided which is formed on an inner surface of the gas discharge layer <NUM> and has hydrophobicity.

It is desirable that the gas discharge layer <NUM> is made of a semipermeable membrane so that a gas may easily pass therethrough while a liquid such as water or an electrolyte does not easily pass therethrough. The gas discharge layer <NUM> may include at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF). Also, a biaxially stretching method may be used to manufacture the gas discharge layer <NUM>. That is, a raw material including the materials described above is used and extruded into a film shape, and then the extruded material may be stretched in both a mechanical direction and a transverse direction to manufacture the gas discharge layer <NUM>. However, the embodiment is not limited thereto, and a phase separation method may be used. That is, the raw material including the materials described above is deposited, as a form of film, onto a plate, and then a solvent is evaporated by changing a temperature. Subsequently, the plate may be immersed in a tank filled with the separate solution to manufacture the gas discharge layer <NUM>.

According to an embodiment of the present invention, there is no separate cover for opening and closing the hole <NUM> formed in the battery case <NUM>. If a cover is present, it is not easy for the cover to open the hole <NUM> and then close the hole <NUM> again. Also, to solve the limitation described above, when a separate hinge is installed so that the cover opens and closes the hole <NUM>, a structure thereof may become complicated, and the durability may be deteriorated. However, if the cover is not present, even though it is not easy for the liquid to pass through the gas discharge layer <NUM>, a small amount of moisture may enter from the outside through the gas discharge layer <NUM>.

Thus, as illustrated in <FIG>, the outer functional layer <NUM> having the hydrophobicity is formed on the outer surface of the gas discharge layer <NUM>. Here, the outer surface of the gas discharge layer <NUM> may represent a surface in the outside of the secondary battery <NUM> when the secondary battery <NUM> is manufactured, that is, a surface which is formed in a direction opposite to the electrode assembly <NUM>.

According to the present invention, the outer functional layer <NUM> includes a plurality of fine protrusions distributed on an outer surface thereof. Thus, the plurality of fine protrusions prevents the moisture from being condensed on the outer surface of the outer functional layer <NUM> and thus exhibit the hydrophobicity. Here, the outer surface of the outer functional layer <NUM> represents a surface on the opposite side from the surface bonded to the gas discharge layer <NUM>. A diameter of each of the fine protrusion is <NUM> to <NUM>, and preferably, <NUM> to <NUM>. If the diameter of the fine protrusion is excessively small, the hydrophobicity may be lowered. On the other hand, if the diameter is excessively large, a fusion force between the gas discharge part <NUM> and a pouch film <NUM> may be lowered over time.

The outer functional layer <NUM> include fine particles so that the fine protrusions are distributed, and the fine particles may include at least one of silica particles, carbon nanotubes (CNT), or alumina particles. In particular, is most desirable to include carbon nanotubes (CNT). However, the outer functional layer <NUM> has to exhibit the hydrophobicity, but the silica particles have hydrophilicity. Thus, when the fine particles include the silica particles, it is desirable to include an extremely small amount such as about <NUM> wt% to about <NUM> wt%.

Here, according to another embodiment of the present invention, the outer functional layer <NUM> may include oil or a wax component. Since the oil or the wax component has oleophilicity not to be mixed with moisture, it may exhibit the hydrophobicity. Here, the oil may include at least one of fluorocarbon oil, silicone oil, carbon-based oil, or fatty acid amide. The wax may include at least one of paraffin wax or carbon-based wax.

If the cover is not present in the hole <NUM>, not only a small amount of moisture enters, but also a small amount of electrolyte may leak from the inside through the gas discharge layer <NUM>. Thus, as illustrated in <FIG>, the inner functional layer <NUM> having the hydrophobicity may be formed on the inner surface of the gas discharge layer <NUM>. Here, the inner surface of the gas discharge layer <NUM> may represent a surface in the inside of the secondary battery <NUM> when the secondary battery <NUM> is manufactured, that is, a surface which is formed in a direction toward the electrode assembly <NUM>.

According to the embodiment of the present invention, the inner functional layer <NUM> may also include a plurality of fine protrusions distributed on an outer surface thereof. To this end, the inner functional layer <NUM> also include the fine particles, and the fine particles may include at least one of silica particles, carbon nanotubes (CNT), or alumina particles. Here, the outer surface of the inner functional layer <NUM> represents a surface on the opposite side from the surface bonded to the gas discharge layer <NUM>.

Here, according to another embodiment of the present invention, the inner functional layer <NUM> may include oil or a wax component. Here, the oil may include at least one of fluorocarbon oil, silicone oil, carbon-based oil, or fatty acid amide.

As described above, as the outer functional layer <NUM> and the inner functional layer <NUM> are provided, the moisture may be further effectively prevented from entering from the outside, and the electrolyte may be further effectively prevented from leaking from the inside.

<FIG> is a flowchart showing a method for manufacturing a gas discharge part <NUM> according to an embodiment of the present invention.

The method for manufacturing the gas discharge part <NUM> according to an embodiment of the present invention includes: preparing the gas discharge layer <NUM> through which a gas passes; manufacturing a mixture by mixing fine particles and a polymer solution; spraying the mixture onto at least one surface of the gas discharge layer <NUM>; and drying the mixture.

In particular, the gas discharge layer <NUM> through which the gas passes is prepared first (S401). As described above, it is desirable that the gas discharge layer <NUM> is made of the semipermeable membrane so that a gas may easily pass therethrough while a liquid such as water or an electrolyte does not easily pass therethrough. The gas discharge layer <NUM> may include at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF).

Then, the fine particles and the polymer solution are mixed to manufacture the mixture (S402). Here, the fine particles may include at least one of silica particles, carbon nanotubes (CNT), or alumina particles. However, the outer functional layer <NUM> has to exhibit the hydrophobicity, but the silica particles have hydrophilicity. Thus, when including the silica particles, it is desirable to include an extremely small amount such as about <NUM> wt% to about <NUM> wt%.

According to the invention, a diameter of each of the fine particles is <NUM> to <NUM>, and preferably, <NUM> to <NUM>. If the diameter of the fine particle is excessively small, the hydrophobicity may be lowered. On the other hand, if the diameter is excessively large, a fusion force between the gas discharge part <NUM> and the pouch film <NUM> may be lowered over time.

The polymer solution may include at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF). That is, since the polymer solution may have the same or similar material as the gas discharge layer <NUM>, the outer functional layer <NUM> or the inner functional layer <NUM> may be easily stacked on the gas discharge layer <NUM>.

Then, the mixture is sprayed onto the at least one surface of the gas discharge layer <NUM> (S403). When sprayed onto the outer surface of the gas discharge layer <NUM>, the outer functional layer <NUM> is formed, and when sprayed onto the inner surface of the gas discharge layer <NUM>, the inner functional layer <NUM> is formed.

When the mixture is sprayed, a spray coating method may be used. For example, the mixture is sprayed at a distance of about <NUM> to about <NUM>, and particularly, <NUM> from the gas discharge layer <NUM> at pressure of <NUM> Mpa to <NUM> Mpa, and particularly, <NUM> Mpa through a nozzle. However, the embodiment is not limited thereto, and various coating methods may be used.

Subsequently, heat is applied to dry the mixture (S404). Here, when the temperature of heat to be applied is excessively low, an excessively long period of time may be consumed to dry the mixture, and when the temperature is excessively high, a shape of the gas discharge layer <NUM> may be deformed. Thus, it is desirable to apply heat at a temperature of <NUM> to <NUM>, and particularly, <NUM> to <NUM>.

Accordingly, the outer functional layer <NUM> or the inner functional layer <NUM> may be formed. Also, the step (S403) and the step (S404) may be repeated two to four times.

<FIG> is a cross-sectional view of a pouch film <NUM> according to an embodiment of the present invention.

According to an embodiment of the present invention, the hole <NUM> is made in the battery case <NUM>, and the gas discharge part <NUM> through which a gas passes is attached to the hole <NUM>. Thus, when the internal pressure of the secondary battery <NUM> increases, the pressure may be controlled by discharging the gas from the inside to the outside. Also, the outer functional layer <NUM> or the inner functional layer <NUM> are formed in the gas discharge part <NUM>. Thus, the moisture may be prevented from entering from the outside, and the electrolyte may be prevented from leaking from the inside. Also, the gas discharge part <NUM> is attached to the hole <NUM> from the inside. Thus, a metal of a gas barrier layer <NUM> exposed to an inner circumferential surface <NUM> of the hole <NUM> may be prevented from being corroded by the electrolyte.

To this end, according to an embodiment of the present invention, the battery case <NUM> for the secondary battery <NUM> includes: the cup part <NUM> provided with the accommodation space <NUM> for accommodating the electrode assembly <NUM> formed by stacking an electrode and a separator; the sealing part <NUM> extending outward from the cup part <NUM>; and the gas discharge part <NUM> which is attached from the inside to the hole <NUM> formed by perforating at least one of the cup part <NUM> or the sealing part <NUM> and through which a gas passes. The gas discharge part <NUM> includes: the gas discharge layer <NUM> through which the gas passes; and the outer functional layer <NUM> which is formed on an outer surface of the gas discharge layer <NUM> and has hydrophobicity. Also, the inner functional layer <NUM> may be further provided which is formed on an inner surface of the gas discharge layer <NUM> and has hydrophobicity.

To manufacture the battery case <NUM>, the cup part <NUM> is formed by drawing and stretching the pouch film <NUM> first. As illustrated in <FIG>, the pouch film <NUM> include a gas barrier layer <NUM>, a surface protection layer <NUM>, and a sealant layer <NUM>.

The gas barrier layer <NUM> ensures the mechanical strength of the battery case <NUM>, blocks a gas or moisture entering from the outside of the secondary battery <NUM>, and prevent a electrolyte from leaking. Generally, the gas barrier layer <NUM> includes a metal, and it is desirable that an aluminum foil is mainly used. The aluminum may be lightweight while ensuring a predetermined level of more of the mechanical strength, and also may supplement electrochemical properties by the electrode assembly <NUM> and the electrolyte and ensure heat radiation or the like. However, the embodiment is not limited thereto, and the gas barrier layer <NUM> may include various materials. For example, the materials may be one or more materials selected from the group consisting of iron (Fe), carbon (C), chrome (Cr), manganese (Mn), nickel (Ni) and aluminum (Al). Here, when the gas barrier layer <NUM> is made of a material containing iron, the mechanical strength is improved, and when made of a material containing aluminum, the flexibility is enhanced. Thus, the material may be used, by taking into consideration each characteristics thereof.

The surface protection layer <NUM> is made of a polymer, is positioned as an outermost layer, and electrically insulates the electrode assembly <NUM> from the outside while protecting the secondary battery <NUM> from friction and collision with the outside. Here, the outermost layer represents a layer which is positioned farthest away from the gas barrier layer <NUM> in the direction toward the side opposite to the electrode assembly <NUM>. The polymer used to manufacture the surface protection layer <NUM> may be one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acryl-based polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon, and glass fiber. In particular, it is desirable to mainly use polymers having the wear resistance and thermal resistance such as nylon resin or polyethylene terephthalate (PET). Also, the surface protection layer <NUM> may have a single layer structure which is made of one material or a composite layer structure in which two or more materials respectively constitute layers.

The sealant layer <NUM> is made of a polymer, is positioned as an innermost layer, and is in direct contact with the electrode assembly <NUM>. Here, the innermost layer represents a layer which is positioned farthest away from the gas barrier layer <NUM> in the direction toward the electrode assembly <NUM>. Thus, the gas barrier layer <NUM> is disposed between the surface protection layer <NUM> and the sealant layer <NUM> as illustrated in <FIG>. The sealant layer <NUM> has to have insulating characteristics because it is in direct contact with the electrode assembly <NUM>, and also has to have corrosion resistance because it comes into contact with the electrolyte. Also, the sealant layer <NUM> has to have high sealing characteristics because it has to completely seal the inside to block the movement of materials between the inside and the outside. The sealing parts <NUM> in which the sealant layers <NUM> are bonded to each other have to have excellent thermal bonding strength. Generally, the polymer used to manufacture the sealant layer <NUM> may be one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acryl-based polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon, and glass fiber. In particular, it is desirable to mainly use polyolefin-based resin such as polypropylene (PP) or polyethylene (PE). Since the polypropylene (PP) has excellent mechanical properties such as tensile strength, rigidity, surface hardness, wear resistance, and thermal resistance, and excellent chemical properties such as corrosion resistance, it is mainly used to manufacture the sealant layer <NUM>. Furthermore, it may be constituted by casted polypropylene or polypropylene-butylene-ethylene terpolymer. Also, the sealant layer <NUM> may have a single layer structure which is made of one material or a composite layer structure in which two or more materials respectively constitute layers.

Here, adhesive layers <NUM> may be further provided between the gas barrier layer <NUM>, the surface protection layer <NUM>, and sealant layer <NUM> to bond these layers.

When the pouch film <NUM> having the stack structure described above is drawn using a punch or the like, a portion thereof is stretched to form the cup part <NUM> that includes the accommodation space <NUM> having a bag shape. Also, the hole <NUM> is made by perforating at least one of the cup part <NUM> or the sealing part <NUM>.

When the hole <NUM> is made, the gas discharge part <NUM> manufactured to allow the gas to pass therethrough is attached from the inside to the hole <NUM> as illustrated in <FIG>. Only one hole <NUM> may be formed, but the plurality of holes may be also possible. Accordingly, one gas discharge part <NUM> may be formed, but the plurality of gas discharge parts may be also possible.

Here, if the gas discharge part <NUM> is attached from the outside the metal of the gas barrier layer <NUM> exposed to the inner circumferential surface <NUM> of the hole <NUM> may be corroded by the electrolyte. Also, the gas discharge part <NUM> is attached to the hole <NUM> from the inside. Accordingly, the metal of the gas barrier layer <NUM> exposed to the inner circumferential surface <NUM> of the hole <NUM> may be prevented from being corroded by the electrolyte.

When the gas discharge part <NUM> is attached to the hole <NUM>, the outer functional layer <NUM> of the gas discharge part <NUM> is bonded to one surface of the sealant layer <NUM>. Particularly, it is desirable that the sealing is made by applying the heat and pressure to prevent the boding from easily tearing off due to the electrolyte. Thus, it is desirable that the sealant layer <NUM> and the outer functional layer <NUM> have the same or similar material so that the outer functional layer <NUM> is easily sealed to the sealant layer <NUM>.

When the electrode assembly <NUM> is accommodated in the inside of the accommodation space <NUM> provided in the cup part <NUM>, the electrolyte is injected. Subsequently, the upper case <NUM> and the lower case <NUM> are brought into contact with each other, and the sealing part <NUM> is heat-pressed. Accordingly, the sealant layers <NUM> are bonded to each other to seal the battery case <NUM>. Consequently, the secondary battery <NUM> according to the embodiment of the present invention may be manufactured.

Claim 1:
A battery case (<NUM>) for a secondary battery (<NUM>), the battery case (<NUM>) comprising:
a cup part (<NUM>) provided with an accommodation space (<NUM>) configured to accommodate an electrode assembly (<NUM>) formed by stacking an electrode and a separator;
a sealing part (<NUM>) extending outward from the cup part (<NUM>); and
a gas discharge part (<NUM>) which is attached from the inside to a hole (<NUM>) formed by perforating at least one of the cup part (<NUM>) or the sealing part (<NUM>) and through which a gas passes,
wherein the gas discharge part (<NUM>) comprises:
a gas discharge layer (<NUM>) through which the gas passes; and
an outer functional layer (<NUM>) which is formed on an outer surface of the gas discharge layer (<NUM>),
characterized in that the outer functional layer (<NUM>) has hydrophobicity and comprises a plurality of fine protrusions having a diameter of <NUM> to <NUM> pm, preferably <NUM> to <NUM> pm, and distributed on an outer surface thereof.