Patent Description:
The present disclosure relates to a battery cell and a battery module including the same, and more particularly, to a battery cell with improved external emission of gas generated inside the battery cell, and a battery module including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. In particular, secondary batteries are of great interest as energy sources not only for mobile devices such as mobile phones, digital cameras, notebooks and wearable devices, but also for power devices such as electric bicycles, electric vehicles and hybrid electric vehicles.

Depending on the shape of a battery case, these secondary batteries are classified into a cylindrical battery and a prismatic battery in which a battery assembly is included in a cylindrical or prismatic metal can, and a pouch-type battery in which the battery assembly is included in a pouch-type case of an aluminum laminate sheet. Here, the battery assembly included in the battery case is a power element including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and capable of charging and discharging, and is classified into a jelly-roll type in which long sheet-type positive and negative electrodes coated with an active material are wound with a separator being interposed therebetween, and a stack type in which a plurality of positive and negative electrodes are sequentially stacked with a separator being interposed therebetween. <CIT>, <CIT> and <CIT> disclose examples of secondary battery.

Among them, in particular, a pouch-type battery in which a stack-type or stack/folding-type battery assembly is included in a pouch-type battery case made of an aluminum laminate sheet is being used more and more due to low manufacturing cost, small weight, and easy modification.

<FIG> is a top view showing a conventional battery cell. <FIG> is a cross-sectional view, taken along the axis a-a' of <FIG>. Referring to <FIG>, a conventional battery cell <NUM> includes a battery case <NUM> having an accommodation portion <NUM> in which a battery assembly <NUM> is mounted, and a sealing portion <NUM> formed by sealing an outer periphery thereof by heat fusion. Here, the battery cell <NUM> includes an electrode lead <NUM> protruding out of the battery case <NUM> via the sealing portion <NUM>, and a lead film <NUM> is located between upper and lower portions of the electrode lead <NUM> and the sealing portion <NUM>.

However, as the energy density of the battery cell increases in recent years, there is a problem that the amount of gas generated inside the battery cell also increases. In the case of the conventional battery cell <NUM>, a component capable of discharging the gas generated inside the battery cell is not included, so a venting may occur in the battery cell due to gas generation. In addition, moisture may penetrate into the battery cell damaged by the venting, which may cause side reactions, and there is a problem that battery performance deteriorates and additional gas is generated. Accordingly, there is an increasing need to develop a battery cell with improved external emission of gas generated inside the battery cell.

The present disclosure is designed to solve the problems of the related art, and therefore the present disclosure is directed to providing a battery cell with improved external emission of gas generated inside the battery cell, and a battery module including the same.

Also, it will be easily understood that the objects and advantages of the present disclosure may be realized by the means shown in the appended claims.

In one aspect of the present disclosure, there is provided a battery cell, comprising: a battery case having an accommodation portion in which an electrode assembly is mounted, and a sealing portion formed by sealing an outer periphery thereof by heat fusion; an electrode lead electrically connected to an electrode tab included in the electrode assembly and protruding out of the battery case via the sealing portion; and a lead film located at a portion corresponding to the sealing portion in at least one of an upper portion and a lower portion of the electrode lead, wherein the lead film has a dented portion recessed toward an inside of the battery case, and the dented portion is opened toward an outside of the battery case, wherein the lead film surrounds a rear surface of the dented portion and an upper surface of the dented portion based on the protruding direction of the electrode lead.

Inner surfaces of the dented portion may be closed based on a protruding direction of the electrode lead.

The battery cell may further comprise an inner layer configured to cover at least one surface of inner surfaces of the dented portion of the lead film.

A material of the inner layer may have a higher melting point compared to a material of the lead film and may not react with an electrolytic solution.

The lead film may contain a polyolefin-based material.

The inner layer may contain at least one of polyolefin-based materials, fluorine-based materials and porous ceramic-based materials.

The dented portion may be located over the electrode lead.

The lead film may have a length greater than a width of the electrode lead.

The dented portion may be located between an end of the electrode lead and an end of the lead film.

The dented portion may include a first dented portion and a second dented portion, the first dented portion may extend along a protruding direction of the electrode lead, and the second dented portion may extend along a longitudinal direction of the sealing portion.

The lead film may have a width greater than a width of the sealing portion and smaller than a length of the electrode lead.

The second dented portion may be located between an end of the sealing portion and an end of the lead film.

The lead film may include a first lead film and a second lead film, the first lead film may be located at an upper portion of the electrode lead, and the second lead film may be located at a lower portion of the electrode lead.

The electrode lead may be located between the first lead film and the second lead film, and the first lead film and the second lead film may be connected to each other.

The dented portion may be located in at least one of the first lead film and the second lead film.

An end of the dented portion recessed into the lead film may be located inner than an inner surface of the battery case.

An end of the dented portion opened toward the outside of the battery case may be located outer than an outer surface of the battery case.

Based on a protruding direction of the electrode lead, a width of the lead film surrounding a rear surface of the dented portion may be <NUM> or more.

A thickness of the lead film surrounding an upper surface of the dented portion may be <NUM> to <NUM>.

The lead film may have gas permeability of <NUM> Barrer to <NUM> Barrer at <NUM>.

The lead film may have a moisture penetration amount of <NUM> to <NUM> for <NUM> years at <NUM>, <NUM> %RH.

In another aspect of the present disclosure, there is also provided a battery module, comprising the battery cell described above.

According to the embodiments, the present disclosure provides a battery cell including an electrode lead to which a lead film having a dented portion recessed toward the inside of the battery case and opened toward the outside of the battery case is attached, and a battery module including the same, so it is possible to improve the external emission of gas generated inside the battery cell.

The effect of the present disclosure is not limited to the above effects, and the effects not mentioned here will be clearly understood by those skilled in the art from this specification and the accompanying drawings.

Hereinafter, with reference to the accompanying drawings, various embodiments of the present disclosure will be described in detail so as to be easily implemented by those skilled in the art. The present disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

In order to clearly explain the present disclosure, parts irrelevant to the description are omitted, and identical or similar components are endowed with the same reference signs throughout the specification.

In addition, since the size and thickness of each component shown in the drawings are arbitrarily expressed for convenience of description, the present disclosure is not necessarily limited to the drawings. In order to clearly express various layers and regions in the drawings, the thicknesses are enlarged. Also, in the drawings, for convenience of explanation, the thickness of some layers and regions is exaggerated.

In addition, throughout the specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

In addition, throughout the specification, when referring to "top view", it means that the target part is viewed from above, and when referring to "cross-sectional view", it means that a vertically-cut section of the target part is viewed from a side.

Hereinafter, a pouch battery cell <NUM> according to an embodiment of the present disclosure will be described. However, here, the description will be made based on one side surface of both side surfaces of the pouch battery cell <NUM>, but it is not necessarily limited thereto, and the same or similar contents may be described in the case of the other side surface.

<FIG> is a top view showing a battery cell according to this embodiment.

Referring to <FIG>, the battery cell <NUM> according to this embodiment includes a battery case <NUM>, an electrode lead <NUM>, and a lead film <NUM>.

The battery case <NUM> includes an accommodation portion <NUM> in which an electrode assembly <NUM> is mounted, and a sealing portion <NUM> formed by sealing an outer periphery thereof by heat fusion. The battery case <NUM> may be a laminate sheet including a resin layer and a metal layer. More specifically, the battery case <NUM> may be made of a laminate sheet, and may include an outer resin layer forming the outermost layer, a barrier metal layer preventing penetration of materials, and an inner resin layer for sealing.

Also, the electrode assembly <NUM> may have a structure of a jelly-roll type (winding type), a stack type (lamination type), or a composite type (stack/folding type). More specifically, the electrode assembly <NUM> may include a positive electrode, a negative electrode, and a separator disposed therebetween.

Hereinafter, the electrode lead <NUM> and the lead film <NUM> will be mainly described.

<FIG> is a perspective view showing an electrode lead included in the battery cell of <FIG>.

Referring to <FIG>, the electrode lead <NUM> is electrically connected to an electrode tab (not shown) included in the electrode assembly <NUM>, and protrudes out of the battery case <NUM> via the sealing portion <NUM>. In addition, the lead film <NUM> is located at a portion corresponding to the sealing portion <NUM> in at least one of an upper portion and a lower portion of the electrode lead <NUM>. Accordingly, the lead film <NUM> may improve the sealing properties of the sealing portion <NUM> and the electrode lead <NUM> while preventing a short circuit from occurring in the electrode lead <NUM> during heat fusion.

<FIG> is a cross-sectional view, taken along the axis c-c' of <FIG>. <FIG> is a cross-sectional view, taken along the axis d-d' of <FIG>.

Referring to <FIG> and <FIG>, the lead film <NUM> has a dented portion <NUM> recessed toward the inside of the battery case <NUM>, and the dented portion <NUM> is opened toward the outside of the battery case <NUM>. Also, the inner surface of the dented portion <NUM> may be closed based on the protruding direction of the electrode lead <NUM>.

Accordingly, in the lead film <NUM>, the gas generated inside the battery case <NUM> may be discharged to the dented portion <NUM> due to the pressure difference between the inside and the outside of the dented portion <NUM>, and the gas introduced into the dented portion <NUM> may be discharged toward the outside. In addition, since the dented portion <NUM> of the lead film <NUM> is opened toward the outside, the dented portion <NUM> may not be exposed to the electrolytic solution inside the battery case <NUM>, and the airtightness and durability of the pouch may be secured. In addition, the lead film <NUM> may maximize the area for gas penetration by the dented portion <NUM> and thus discharge a large amount of gas.

In addition, referring to <FIG> and <FIG>, the lead film <NUM> may further include an inner layer <NUM> covering at least one of the inner surfaces of the dented portion <NUM>.

For example, referring to <FIG> and <FIG>, the inner layer <NUM> in the dented portion <NUM> may cover the entire surface of the lead film <NUM>. That is, the inner layer <NUM> may be formed on the entire inner surface of the dented portion <NUM> exposed for the opened surface.

Accordingly, even if the lead film <NUM> is heat-fused together with the sealing portion <NUM> in a state of being located in at least one of the upper and lower portions of the electrode lead <NUM>, the dented portion <NUM> may be preserved in a non-heat-fused state by the inner layer <NUM>.

As another example, referring to <FIG> and <FIG>, the inner layer <NUM> may cover an upper surface or a lower surface among the inner surfaces of the dented portion <NUM>. That is, the dented portion <NUM> may have an inner layer <NUM> formed on at least one of the upper and lower surfaces facing each other.

Accordingly, while the lead film <NUM> minimizes the inner layer <NUM> formed in the dented portion <NUM>, the dented portion <NUM> may be preserved in a non-heat-fused state by the inner layer <NUM>. In addition, the manufacturing process may be simplified and the cost may be reduced.

More specifically, the inner layer <NUM> may be made of a material having a higher melting point compared to the material constituting the lead film <NUM>. In addition, the inner layer <NUM> may be made of a material that does not react with the electrolytic solution contained in the battery case <NUM>. Accordingly, since the inner layer <NUM> is made of the above-described material, the inner layer <NUM> does not separately react with the electrolytic solution and does not cause heat fusion, thermal deformation, or the like in the high-temperature heat fusion process, so that the dented portion <NUM> may be kept blank. In addition, the gas generated in the battery case <NUM> may be easily discharged to the outside.

In one embodiment of the present disclosure, the thickness of the inner layer <NUM> may be <NUM> or less.

In one embodiment of the present disclosure, the gas permeability of the inner layer <NUM> may be <NUM> Barrer or more. For example, the carbon dioxide permeability of the inner layer <NUM> may satisfy the above range.

For example, the lead film <NUM> may contain a polyolefin-based material, and the inner layer <NUM> may include at least one of polyolefin-based materials, fluorine-based materials, and porous ceramic-based materials. For example, the inner layer <NUM> may include at least one of polyolefin-based materials, fluorine-based materials, and porous ceramic-based materials that satisfies the above gas permeability value. The polyolefin-based material may include at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinyl difluoride (PVDF). The fluorine-based material may include at least one material selected from the group consisting of polytetrafluoroethylene and polyvinylidene fluoride. In addition, the inner layer <NUM> may include a getter material, so that gas permeability may be increased while water permeability may be minimized. As an example, the getter material may be calcium oxide (CaO), barium oxide (BaO), lithium chloride (LiCl), silica (SiO<NUM>), or the like, and any material reacting with water (H<NUM>O) can be used without being limited thereto.

The inner layer <NUM> may have an adhesive material between the lead film <NUM> and the inner layer <NUM> or may be extruded together with the lead film <NUM> and adhered to the lead film <NUM>. The adhesive material may include an acryl-based material. In particular, when the inner layer <NUM> is extruded together with the lead film <NUM>, the gas permeability of the inner layer <NUM> may be <NUM> Barrer or more.

Referring to <FIG>, the lead film <NUM> may include a first lead film and a second lead film, the first lead film may be located at an upper portion of the electrode lead <NUM>, and the second lead film may be located at a lower portion of the electrode lead <NUM>. At this time, the electrode lead <NUM> may be heat-fused together with the sealing portion <NUM> in a state of being located between the first lead film and the second lead film, so that the first lead film and the second lead film may be connected to each other.

Accordingly, the lead film <NUM> may prevent the side surface of the electrode lead <NUM> from being exposed to the outside, while improving the sealing properties of the sealing portion <NUM> and the electrode lead <NUM>.

For example, in the lead film <NUM>, the dented portion <NUM> may be located in at least one of the first lead film and the second lead film. More specifically, in the lead film <NUM>, the dented portion <NUM> may be formed in the first lead film or the second lead film based on the electrode lead <NUM>, or the dented portion <NUM> may be formed on both the first lead film and the second lead film based on the electrode lead <NUM>. However, the number of the dented portion <NUM> is not limited to the above, and the lead film <NUM> may be formed in an appropriate number.

Accordingly, by adjusting the number of the dented portions <NUM> formed in the lead film <NUM>, the durability and airtightness of the lead film <NUM> may be controlled. In addition, by minimizing the number of the dented portion <NUM> as necessary, it is possible to simplify the manufacturing process and reduce the cost.

<FIG> is an enlarged view showing the electrode lead in the battery cell of <FIG>. <FIG> is an enlarged view showing the electrode lead according to a location of the sealing portion in (a) of <FIG>.

Referring to <FIG>, in the lead film <NUM>, the dented portion <NUM> may be formed at various positions with respect to the electrode lead <NUM>.

For example, as shown in <FIG>, in the lead film <NUM>, the dented portion <NUM> may be located over the electrode lead <NUM>. More specifically, the dented portion <NUM> may be formed at a position corresponding to the center of the electrode lead <NUM>.

As another example, as shown in <FIG>, the length of the lead film <NUM> may be greater than the width of the electrode lead <NUM>, and the dented portion <NUM> may be located between the end of the electrode lead <NUM> and the end of the lead film <NUM>. Here, the length of the lead film <NUM> means a maximum value of the distance between one end and the other end of the lead film <NUM> in a direction orthogonal to the protruding direction of the electrode lead <NUM>, and the width of the electrode lead <NUM> means a maximum value of the distance between one end and the other end of the electrode lead <NUM> in a direction orthogonal to the protruding direction of the electrode lead <NUM>. In other words, in the lead film <NUM>, the dented portion <NUM> may be formed at a position avoiding the electrode lead <NUM>. However, the position of the dented portion <NUM> is not limited to the above, and the dented portion <NUM> may be formed at an appropriate position within the lead film <NUM>.

Accordingly, by adjusting the position of the dented portion <NUM> formed in the lead film <NUM>, the durability and airtightness of the lead film <NUM> may be controlled. In addition, if necessary, by adjusting the size of the dented portion <NUM> according to the position of the dented portion <NUM>, it is possible to simplify the manufacturing process and reduce the cost. Referring to <FIG>, in the lead film <NUM>, the dented portion <NUM> may be formed in various shapes.

For example, the dented portion <NUM> may include a first dented portion <NUM> and a second dented portion <NUM>, where the first dented portion <NUM> may extend along the protruding direction of the electrode lead <NUM> and the second dented portion <NUM> may extend along the longitudinal direction of the sealing portion <NUM>. Here, the longitudinal direction of the sealing portion <NUM> refers to a direction perpendicular to the protruding direction of the electrode lead <NUM>.

Here, the width of the lead film <NUM> may be greater than the width of the sealing portion <NUM> and may be smaller than the length of the electrode lead <NUM>. Here, the width of the lead film <NUM> means a maximum value of the distance between one end and the other end of the lead film in the protruding direction of the electrode lead <NUM>. The width of the sealing portion <NUM> means a maximum value of the distance between one end and the other end of the sealing portion <NUM> in the protruding direction of the electrode lead <NUM>. The length of the electrode lead <NUM> means a maximum value of the distance between one end and the other end of the electrode lead <NUM> in the protruding direction of the electrode lead <NUM>. At this time, the second dented portion <NUM> may be located between the end of the sealing portion <NUM> and the end of the lead film <NUM>. However, the shape of the dented portion <NUM> is not limited to the above, and the dented portion <NUM> may be formed in an appropriate shape within the lead film <NUM>.

Accordingly, by adjusting the shape of the dented portion <NUM> formed in the lead film <NUM>, the durability and airtightness of the lead film <NUM> may be controlled. In addition, by changing the shape of the dented portion <NUM> as necessary, it is possible to simplify the manufacturing process and reduce cost.

Referring to <FIG>, in the lead film <NUM>, the end of the dented portion <NUM> is opened toward the outside may be formed adjacent to the end of the lead film <NUM>, the end of the dented portion <NUM> recessed toward the inside may be located between the end of the sealing portion <NUM> and the end of the lead film <NUM>. In addition, the end of the dented portion <NUM> recessed toward the inside may be spaced apart from the end of the sealing portion <NUM> by a predetermined distance, or may be located adjacent thereto.

As an example, comparing <FIG>, even if the position of the sealing portion <NUM> in contact with the lead film <NUM> is changed, it may be found that there is no influence applied to the end of the dented portion <NUM> recessed toward the inside.

Accordingly, in this embodiment, within the error range according to the positions of the lead film <NUM> and the sealing portion <NUM> generated during the heat fusion process, the area in which the end of the dented portion <NUM> recessed toward the inside is located at an inside with respect to the battery case <NUM> may be uniformly maintained, and the area in which the gas in the battery case <NUM> may be introduced into the dented portion <NUM> and discharged to the outside may also be maintained uniformly. Accordingly, there is an advantage that the gas exhaust effect by the dented portion <NUM> may also be maintained.

<FIG> is a cross-sectional view, taken along the axis b-b' of <FIG>.

Referring to <FIG>, the end of the dented portion <NUM> recessed into the lead film <NUM> may be located inner than the inner surface of the battery case <NUM>. Here, the inner surface of the battery case <NUM> means an end of the sealing portion <NUM> of the battery case <NUM> at the inner side of the battery. In addition, the end of the dented portion <NUM> opened toward the outside of the battery case <NUM> may be located outer than the outer surface of the battery case <NUM>. Here, the outer surface of the battery case <NUM> means an end of the sealing portion <NUM> of the battery case <NUM> at the outer side of the battery.

Accordingly, the lead film <NUM> may maximize the area of the dented portion <NUM> and discharge a large amount of gas.

Referring to <FIG>, the thickness H of the lead film <NUM> surrounding the upper surface of the dented portion <NUM> may be <NUM> to <NUM>, or <NUM> to <NUM>. If the thickness H of the lead film <NUM> surrounding the upper surface of the dented portion <NUM> satisfies the above range, the gas inside the battery case <NUM> may be more easily discharged to the outside.

Referring to <FIG>, based on the protruding direction of the electrode lead <NUM>, the width W of the lead film <NUM> surrounding the rear surface of the dented portion <NUM> may be <NUM> or more, or <NUM> to <NUM>. Here, the width of the lead film <NUM> surrounding the rear surface of the dented portion <NUM> means a maximum value of the distance between the recessed end of the dented portion <NUM> and the inner end of the battery case <NUM> of the lead film <NUM>. If the width W of the lead film <NUM> surrounding the rear surface of the dented portion <NUM> satisfies the above range, the phenomenon that the lead film <NUM> is torn while the gas generated inside the battery case <NUM> is discharged to the outside may be easily prevented.

<FIG> is a diagram showing the flow of gas generated inside the battery cell and discharged to the outside in <FIG>.

Referring to <FIG>, the gas generated inside the battery cell <NUM> may be discharged toward the dented portion <NUM> of the lead film <NUM>. Here, the internal pressure of the battery cell <NUM> is higher than the internal pressure of the dented portion <NUM>, and the resulting pressure difference may act as a driving force of the gas. Here, since the dented portion <NUM> is opened toward the outside, the pressure inside the dented portion <NUM> may be the same as the pressure of the outside.

Accordingly, the gas generated inside the battery cell <NUM> may be discharged toward the dented portion <NUM>, and the gas introduced into the dented portion <NUM> may be easily discharged toward the outside. In addition, the amount of gas generated inside the battery cell <NUM> and discharged to the outside may also be increased.

In one embodiment of the present disclosure, the gas permeability of the lead film <NUM> may be <NUM> Barrer to <NUM> Barrer, or <NUM> Barrer to <NUM> Barrer at <NUM>. For example, the carbon dioxide permeability of the lead film <NUM> may satisfy the above range. In addition, the gas permeability may satisfy the above range at <NUM> based on the thickness of the lead film <NUM> of <NUM>. If the gas permeability of the lead film <NUM> satisfies the above range, the gas generated inside the secondary battery may be more effectively discharged.

In this specification, the gas permeability is measured by ASTM F2476-<NUM>.

In one embodiment of the present disclosure, the moisture penetration amount of the lead film <NUM> may be <NUM> to <NUM>, or <NUM> to <NUM>, or <NUM>, or <NUM> for <NUM> years at <NUM>, <NUM> %RH. If the moisture penetration amount of the lead film <NUM> satisfies the above range, the penetration of moisture from the lead film <NUM> may be more effectively prevented.

In one embodiment of the present disclosure, the lead film <NUM> may have a gas permeability of <NUM> Barrer to <NUM> Barrer at <NUM> and a moisture penetration amount of <NUM> to <NUM> at <NUM>, <NUM> %RH for <NUM> years. If the gas permeability and the moisture penetration amount of the lead film <NUM> satisfy the above ranges, the penetration of moisture from the outside may be more effectively prevented while discharging the gas generated inside the secondary battery.

The moisture penetration amount of the lead film <NUM> is measured by adopting the ASTM F <NUM> method. At this time, the moisture penetration amount may be measured using equipment officially certified by MCOON.

In one embodiment of the present disclosure, the lead film <NUM> may include a polyolefin-based resin. For example, the lead film <NUM> may include a polyolefin-based resin satisfying the gas permeability and/or moisture penetration amount values described above. The polyolefin-based resin may include at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinyl difluoride (PVDF). While the lead film <NUM> contains polypropylene, the gas permeability of the lead film <NUM> may be <NUM> Barrer to <NUM> Barrer at <NUM>. Also, the moisture penetration amount may be <NUM> to <NUM>. In this case, the gas generated inside the secondary battery may be more effectively discharged, and the penetration of moisture from the outside may be easily prevented.

In addition, since the lead film <NUM> is made of the above-described material, the lead film <NUM> may maintain the airtightness of the battery cell <NUM> and prevent leakage of the internal electrolytic solution.

As an example, the dented portion <NUM> may be partially expanded toward the upper and lower sides as compared with <FIG> by the gas inside the battery cell <NUM>. However, in this embodiment, since the dented portion <NUM> is opened to the outside, the degree of expansion may be relatively small, and the deformation of the components may also be small accordingly.

A battery module according to another embodiment of the present disclosure includes the battery cell described above. Meanwhile, one or more battery modules according to this embodiment may be packaged in a pack case to form a battery pack.

Claim 1:
A battery cell (<NUM>), comprising:
a battery case (<NUM>) having an accommodation portion (<NUM>) in which an electrode assembly (<NUM>) is mounted, and a sealing portion (<NUM>) formed by sealing an outer periphery thereof by heat fusion;
an electrode lead (<NUM>) electrically connected to an electrode tab included in the electrode assembly (<NUM>) and protruding out of the battery case (<NUM>) via the sealing portion; and
a lead film (<NUM>) located at a portion corresponding to the sealing portion (<NUM>) in at least one of an upper portion and a lower portion of the electrode lead (<NUM>),
wherein the lead film (<NUM>) has a dented portion (<NUM>) recessed toward an inside of the battery case (<NUM>), and
the dented portion (<NUM>) is opened toward an outside of the battery case,
wherein the lead film (<NUM>) surrounds a rear surface of the dented portion (<NUM>) and an upper surface of the dented portion (<NUM>) based on the protruding direction of the electrode lead (<NUM>).