Patent Description:
A rechargeable battery differs from a primary battery in that it can be repeatedly charged and discharged, while the latter is incapable of being recharged. Low-capacity rechargeable batteries may be used in portable electronic devices, such as mobile phones, laptop computers, and camcorders, and large-capacity batteries are widely used as power sources for driving a motor, such as for hybrid vehicles.

Representative rechargeable batteries include a nickel-cadmium (NiCd) battery, a nickel metal hydride (NiMH) battery, a lithium (Li) battery, and a lithium ion (Li ion) rechargeable battery. In particular, lithium ion rechargeable batteries are about three times higher in operating voltage than the nickel-cadmium batteries or nickel metal hydride batteries, which are widely used as power sources for portable electronic equipment. Further, lithium ion rechargeable batteries is widely used because of its high energy density per unit weight.

In particular, in recent years, as the demand for wearable devices, such as headphones, earphones, smartwatches, and body-attached medical devices using Bluetooth increases, the need for ultra-small rechargeable batteries with high energy density is increasing.

Such a micro rechargeable battery includes an electrode terminal positioned on an outer surface thereof and an electrode assembly disposed inside and connected to the electrode terminal.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and, therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

<CIT>, <CIT>, <CIT> and <CIT> disclose a rechargeable battery in which the cap plate and the electrode terminal is made of different materials or of same materials.

According to an aspect of embodiments of the present invention, a micro rechargeable battery capable of being manufactured with various metals is provided.

According to one or more embodiments of the present invention, a rechargeable battery is provided as defined in claim <NUM>.

The electrode terminal may be electrically connected to, preferably directly electrically connected to a positive electrode of the electrode assembly, and may be made of a same metal as an electrode current collector of the positive electrode.

The electrode terminal may be made of aluminum.

The cap plate may be electrically connected to, preferably directly electrically connected to a negative electrode of the electrode assembly, and may be made of a different metal from that of an electrode current collector of the negative electrode.

The cap plate may be made of stainless steel or nickel.

The cap plate may be welded to, preferably directly welded to the case, and the cap plate and the case may be made of a same metal.

The rechargeable battery may further include a thermal bonding layer positioned between the cap plate and the flange portion and insulatingly bonded between the cap plate and the flange portion.

The thermal bonding layer may melt at a predetermined temperature.

According to embodiments of the present invention, a micro rechargeable battery capable of being manufactured with various metals is provided.

The present invention will be described more fully herein with reference to the accompanying drawings, in which some example embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the scope of the present invention. The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

In addition, unless explicitly described to the contrary, it is to be understood that terms such as "comprises," "includes," or "have" used in the present specification specify the presence of stated features, numerals, steps, operations, components, parts, or a combination thereof, but do not preclude the presence or addition of one or more other features, numerals, steps, operations, components, parts, or a combination thereof.

Also, in this specification, it is to be understood that when one component is referred to as being "connected" or "coupled" to another component, it may be connected or coupled directly to the other component or connected or coupled to another component with one or more other components intervening therebetween.

Singular forms are to include plural forms unless the context clearly indicates otherwise.

It is to be understood that, although the terms "first," "second," etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, a first element could be termed a "second" element, and, similarly, a second element could be termed a "first" element, without departing from the scope of example embodiments of the inventive concept. The terms of a singular form may include plural forms unless the context clearly indicates otherwise.

In addition, terms such as "below," "lower," "above," "upper," and the like are used to describe the relationship of the configurations shown in the drawings. However, the terms are used as a relative concept and are described with reference to the direction indicated in the drawings.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the inventive concept pertains. It is also to be understood that terms defined in commonly used dictionaries should be interpreted as having meanings consistent with the meanings in the context of the related art, and are expressly defined herein unless they are interpreted in an ideal or overly formal sense.

Herein, a rechargeable battery according to an embodiment will be described with reference to the drawings.

The rechargeable battery according to an embodiment of the present invention, which is a micro rechargeable battery, may be a coin cell or button cell battery, but the present invention is not limited thereto, and may be a cylindrical or pin-type battery.

Herein, the coin cell or button cell battery, which is a thin coin or button cell, may indicate a battery in which a ratio of a height to a diameter (height/diameter) is <NUM> or less, <NUM> or less, or <NUM> or less, but the present invention is not limited thereto.

In an embodiment, the coin cell or the button cell battery is cylindrical, such that a horizontal cross-section thereof is circular, but the present invention is not limited thereto, and the horizontal cross-section may have an oval or polygonal shape. In this case, a diameter may indicate a maximum distance based on a horizontal direction of the battery, and a height may indicate a maximum distance (distance from a flat bottom surface to a flat top surface) based on a vertical direction of the battery.

<FIG> illustrates a perspective view of a rechargeable battery according to an embodiment of the present invention; and <FIG> illustrates a cross-sectional view taken along the line II-II of <FIG>.

Referring to <FIG> and <FIG>, a rechargeable battery <NUM> according to an embodiment of the present invention includes an electrode assembly <NUM>, a case <NUM> having an inner space accommodating the electrode assembly <NUM>, a cap plate <NUM> coupled to the case <NUM> to seal the inner space, and an electrode terminal <NUM> electrically connected to the electrode assembly <NUM> through the cap plate <NUM>.

A lower surface of the electrode assembly <NUM> faces an inner bottom surface of the case <NUM>, and an upper surface of the electrode assembly <NUM> faces a lower surface of the cap plate <NUM> covering an opening <NUM> of the case <NUM>.

The electrode assembly <NUM> includes a first electrode <NUM>, a second electrode <NUM>, and a separator <NUM>, and the first electrode <NUM> and the second electrode <NUM> are respectively disposed at opposite sides of the separator <NUM> which is made of an electrically insulating material. However, the present invention is not limited thereto.

In an embodiment, the first electrode <NUM> includes an electrode active region, which is an area where an active material is applied on a thin plate formed by using a long strip-shaped metal foil, and an electrode uncoated region, which is an area where the active material is not applied, and a first electrode tab <NUM> may be connected to, preferably directly connected the electrode uncoated region.

In an embodiment, the electrode uncoated region may be formed at opposite ends of the electrode active region, that is, at opposite ends of the first electrode <NUM> in a longitudinal direction, but the present invention is not limited thereto, and the electrode uncoated region may be formed at one end thereof. In an embodiment, the first electrode <NUM> may be a negative electrode, and the electrode active region may be coated with an active material, such as graphite or carbon, on a metal foil, such as a copper or nickel foil.

In an embodiment, the first electrode tab <NUM> is electrically connected to, preferably directly electrically connected to the electrode uncoated region of the first electrode <NUM> of the electrode assembly <NUM>, and protrudes from the electrode assembly <NUM> and is welded to, preferably directly welded to a bottom surface of the case <NUM> to electrically connect, preferably directly electrically connect to the first electrode <NUM> and the case <NUM>. Accordingly, the case <NUM> connected to, preferably directly connected to the first electrode tab <NUM> has a same polarity as that of the first electrode <NUM>.

In an embodiment, the second electrode <NUM> includes an electrode active region, which is an area where an active material is applied on a thin plate formed by using a long strip-shaped metal foil, and an electrode uncoated region, which is an area where the active material is not applied, and a second electrode tab <NUM> may be connected to, preferably directly connected to the electrode uncoated region.

In an embodiment, the electrode uncoated region may be formed at opposite ends of the electrode active region, that is, at opposite ends of the second electrode <NUM> in a longitudinal direction, but the present invention is not limited thereto, and the electrode uncoated region may be formed at one end thereof.

The second electrode tab <NUM> may be connected to, preferably directly connected to the electrode uncoated region of the second electrode <NUM>, and the second electrode tab <NUM> may protrude from the second electrode <NUM> to be electrically connected to, preferably directly electrically connected to the electrode terminal <NUM>. The second electrode tab <NUM> is made of an electrically conductive material, such as nickel or copper, and may be connected to, preferably directly connected to the electrode uncoated region by welding. In an embodiment, the welding may be laser welding.

In an embodiment, the second electrode <NUM> may be an anode, and an active material, such as a transition metal oxide, may be applied to a metal foil, such as aluminum.

In an embodiment, the second electrode tab <NUM> is electrically connected to, preferably directly electrically connected to the electrode uncoated region of the second electrode <NUM> of the electrode assembly <NUM>, and protrudes from the electrode assembly <NUM> and is welded to, preferably directly welded to a lower surface of the electrode terminal <NUM> to electrically connect, preferably to directly electrically connect the second electrode <NUM> and the electrode terminal <NUM>. The electrode terminal <NUM> has a same polarity as that of the second electrode <NUM> by the second electrode tab <NUM>.

The separator <NUM> is positioned between the first electrode <NUM> and the second electrode <NUM>, and prevents or substantially prevents a short circuit therebetween and enables the movement of lithium ions. The separator <NUM> may be made of, e.g., a composite film of polyethylene, polypropylene, or polyethylene and polypropylene.

In an embodiment, a width of the separator <NUM> may be equal to or greater than that of the first electrode <NUM> and the second electrode <NUM>, and the width of the first electrode <NUM> may be greater than that of the second electrode <NUM>. In this case, the width is a length in a direction in which the electrode assembly is inserted into the case.

In an embodiment, the electrode assembly <NUM> may have a jelly-roll shape by winding the first electrode <NUM>, the separator <NUM>, and the second electrode <NUM> around a rotation axis in an overlapping state, but the present invention is not limited thereto, and may have a structure (not illustrated) in which a first electrode, a separator, and a second electrode which are of a sheet type are repeatedly stacked.

In an embodiment, the electrode assembly <NUM> may be covered with an insulating tape (not illustrated) along an external circumferential surface thereof in a radial direction. The insulating tape electrically insulates between the external circumferential surface of the electrode assembly <NUM> and an inner surface of the case <NUM>, while protecting the outside of the electrode assembly <NUM>.

In an embodiment, the electrode assembly <NUM> may be accommodated in the case <NUM> together with an electrolyte in a direction that is parallel to a rotation axis of the electrode assembly <NUM>. In an embodiment, the electrolyte solution may be composed of an organic solvent, such as any of EC, PC, DEC, EMC, and DMC, and a Li salt such as LiPF<NUM> and LiBF<NUM>. The electrolyte solution may be in a liquid, solid, or gel state.

In an embodiment, a center pin <NUM> penetrating a center of the electrode assembly <NUM> in a vertical direction may be positioned at the center of the electrode assembly <NUM>, and may support the first electrode tab <NUM> and the second electrode tab <NUM>.

The case <NUM> may have a space for accommodating the electrode assembly <NUM> and an electrolyte, and may have an opening <NUM> at one side. The electrode assembly <NUM> may be inserted through the opening <NUM> and accommodated in the inner space of the case <NUM>. In an embodiment, the case <NUM> may have a cylindrical shape having a low height, but the present invention is not limited thereto, and may have any of various shapes. The case <NUM> may accommodate any of various known electrolyte solutions together with the electrode assembly <NUM>, and, in an embodiment, the case <NUM> may be made of stainless steel.

An inner bottom surface of the case <NUM> is connected to the first electrode <NUM> of the electrode assembly <NUM> by the first electrode tab <NUM>, such that the case <NUM> has the same polarity as that of the first electrode <NUM>.

An outer surface of the case <NUM> may be a first electrode terminal of the rechargeable battery <NUM>, and an outer surface of the electrode terminal <NUM> may be a second electrode terminal of the rechargeable battery <NUM>.

The cap plate <NUM> sealing the inner space of the case <NUM> and the electrode terminal <NUM> may be coupled to the opening <NUM> of the case <NUM>, and, in an embodiment, the cap plate <NUM> may be coupled to, preferably directly coupled to the opening <NUM> by welding.

The cap plate <NUM> may be formed to have a shape corresponding to the opening <NUM>, and, in an embodiment, a step portion <NUM> may be formed in the opening <NUM> such that the cap plate <NUM> may be easily seated.

In an embodiment, a terminal hole <NUM> is formed in a center of the cap plate <NUM>, and corresponds to the center of the electrode assembly <NUM> and exposes an upper portion of the electrode assembly <NUM>. The cap plate <NUM> may have a ring shape due to the terminal hole <NUM> formed in the center thereof.

The cap plate <NUM> may be coupled to, preferably directly coupled to the case <NUM> to have the same polarity as that of the first electrode <NUM>, and an outer surface of the cap plate <NUM> may serve as a first electrode terminal of the rechargeable battery <NUM>. In an embodiment, the cap plate <NUM> includes stainless steel, but the present invention is not limited thereto, and the cap plate <NUM> may include metals, such as any of aluminum, nickel, and copper.

The electrode terminal <NUM> may be bonded to the cap plate <NUM> of a different polarity in an insulated state, and may be electrically connected to, preferably directly electrically connected to the second electrode <NUM> of the electrode assembly through the terminal hole <NUM> of the cap plate <NUM>. Accordingly, the electrode terminal <NUM> may be a second electrode terminal of the rechargeable battery <NUM>.

In an embodiment, the electrode terminal <NUM> may include stainless steel, but the present invention is not limited thereto, and may include metals, such as any of aluminum, nickel, and copper.

In an embodiment, the case <NUM> and the cap plate <NUM> may be connected to the first electrode <NUM>, which is a negative electrode, such that the first electrode terminal is a negative terminal, and the electrode terminal <NUM> may be electrically connected to the second electrode <NUM>, which is a positive electrode, such that the second electrode terminal may be a positive terminal.

In an embodiment, the case <NUM> and the cap plate <NUM> may be made of a same material, and the electrode terminal <NUM> may have a lower ionization tendency as compared with the case <NUM> and the cap plate <NUM>. In an embodiment, the case <NUM> and the cap plate <NUM> may have a higher ionization tendency as compared with copper, which is an electrode current collector of the first electrode.

For example, the electrode terminal <NUM> may be made of aluminum, and the case <NUM> and the cap plate <NUM> may be made of stainless steel, nickel, or nickel-plated copper.

Since the electrode terminal <NUM> may be formed into any of various shapes depending on a shape of the battery, the electrode terminal <NUM> may be made of aluminum, which is easier to form than stainless steel.

In addition, when contacting the electrode terminal of stainless steel having relatively high resistance, the case <NUM> and the cap plate <NUM> may be selected from various materials other than stainless steel, and may further include a plating layer in order to reduce surface resistance.

In the above embodiment, the first electrode <NUM> is a negative electrode and the second electrode <NUM> is a positive electrode, or vice versa. That is, the first electrode <NUM> as a positive electrode may be electrically connected to, preferably directly electrically connected to the case <NUM> and the cap plate <NUM> through the first electrode tab <NUM>, and the second electrode <NUM> as a negative electrode may be electrically connected to, preferably directly electrically connected to the electrode terminal <NUM> through the second electrode tab <NUM>. In this case, the case <NUM> and the cap plate <NUM> as the first electrode may be made of aluminum, and the electrode terminal <NUM> as the second electrode may be made of stainless steel, nickel, or the like.

In an embodiment, the electrode terminal <NUM> includes a flange portion <NUM> and a protrusion <NUM>, the flange portion <NUM> may have a wider area (or diameter) than the protrusion <NUM>, and the flange portion <NUM> has a thinner thickness than the protrusion <NUM>. The protrusion <NUM> and the flange portion <NUM> may be integrally formed.

The protrusion <NUM> of the electrode terminal <NUM> is inserted into the terminal hole <NUM> to cover the terminal hole <NUM> of the cap plate <NUM> together with the flange portion <NUM> so as to seal an interior of the case <NUM>. The protrusion <NUM> of the electrode terminal <NUM> is electrically connected to, preferably directly electrically connected to the second electrode tab <NUM> of the electrode assembly <NUM>, such that the electrode terminal <NUM> has the same polarity as that of the second electrode <NUM>. An outer surface of the flange portion <NUM> may serve as a second electrode terminal of the rechargeable battery <NUM>.

<FIG> illustrates an enlarged view of a region "A" of <FIG>.

Referring to <FIG>, in an embodiment, an outer surface of the protrusion <NUM> includes a curved surface CS and an inclined surface IS. The protrusion <NUM> includes the curved surface CS extending from a lower surface of the flange portion <NUM> and the inclined surface IS extending from the curved surface CS and passing through the terminal hole <NUM>.

The curved surface CS may have a radius of curvature (e.g. a predetermined radius of curvature), and the inclined surface IS may have a slope (e.g., a predetermined slope). Accordingly, a surface of the protrusion <NUM> may be relatively far away from an end portion of the cap plate <NUM> exposed through the terminal hole <NUM> from the curved surface CS to an end portion of the inclined surface IS. As such, when the inclined surface IS is formed, a distance of the protrusion <NUM> positioned in a horizontal direction between the cap plate <NUM> and the electrode terminal <NUM> is increased, such that even when an alignment error occurs, a short circuit between the cap plate <NUM> and the protrusion <NUM> of different polarities may be suppressed.

Referring to <FIG> and <FIG> again, the lower surface of the flange portion <NUM> of the electrode terminal <NUM> may be bonded to, preferably directly bonded to a first surface of the cap plate <NUM> through a thermal bonding layer <NUM>. In an embodiment, the opening <NUM> of the case <NUM>, in which the electrode assembly <NUM> is accommodated, is completely sealed by the cap plate <NUM>, the electrode terminal <NUM>, and the thermal bonding layer <NUM> by bonding the thermal bonding layer <NUM> between the cap plate <NUM> and the electrode terminal <NUM>.

In an embodiment, the thermal bonding layer <NUM> may be thermally bonded between the cap plate <NUM> and the flange portion <NUM> of the electrode terminal <NUM> by using heat or a laser beam.

The thermal bonding layer <NUM> is made of an insulating material to insulate between the electrode terminal <NUM> and the cap plate <NUM>. The thermal bonding layer <NUM> may include any of various known materials for insulatingly bonding between the cap plate <NUM> and the electrode terminal <NUM>.

In an embodiment, the thermal bonding layer <NUM> is in a state that is cured by heat, but may melt at a predetermined temperature. In an embodiment, the predetermined temperature at which the thermal bonding layer <NUM> melts may exceed a temperature of heat for curing the thermal bonding layer <NUM>, but the present invention is not limited thereto.

For example, the thermal bonding layer <NUM> may include any of a thermosetting resin and a thermoplastic resin. In an embodiment, the thermosetting resin and the thermoplastic resin of the thermal bonding layer <NUM> may be stacked to include a plurality of layers, but the prevent invention is not limited thereto. In an embodiment, the thermosetting resin of the thermal bonding layer <NUM> is in a state that is cured by heat, and may include any of various known thermosetting resins, such as any of a phenol resin, a urea resin, a melamine resin, an epoxy resin, and a polyester resin. In an embodiment, the thermoplastic resin of the thermal bonding layer <NUM> includes, but is not limited to, a polypropylene resin that melts at a predetermined temperature, and may include any of various known thermoplastic resins, such as any of polystyrene, polyethylene, and a polyvinyl chloride resin.

In an embodiment, the thermal bonding layer <NUM> melts at a temperature, e.g. a predetermined temperature, and a portion from which the thermal bonding layer <NUM> is removed serves as a ventilation passage through which gas may be discharged. However, the present invention is not limited thereto.

In an embodiment, when an unintended event such as, e.g., a short circuit between both electrodes occurs in the internal space of the rechargeable battery <NUM>, the temperature is increased, the thermal bonding layer <NUM> melts due to the increased temperature, reducing the volume, and a ventilation passage through which gas GA generated inside the rechargeable battery is discharged to the outside is formed. An internal gas is guided from the internal space of the rechargeable battery <NUM> along the curved surface CS of the electrode terminal <NUM> to a space between the flange portion <NUM> and the cap plate <NUM>, which is a vent passage, to be rapidly discharged to the outside, so as to suppress an explosion risk of the rechargeable battery <NUM>.

<FIG> illustrates a cross-sectional view of a rechargeable battery according to an embodiment of the present invention; and <FIG> illustrates a view of a region "B" of <FIG>.

A rechargeable battery <NUM> according to an embodiment of the present invention illustrated in <FIG> and <FIG> is substantially the same as the rechargeable battery of <FIG>, and different parts will be mainly described in further detail.

Referring to <FIG>, according to an embodiment of the present invention, the rechargeable battery <NUM> includes an electrode assembly <NUM>, a case <NUM>, a cap plate <NUM>, an electrode terminal <NUM>, and a thermal bonding layer <NUM>.

The electrode terminal <NUM> is electrically connected to, preferably directly electrically connected to the second electrode <NUM>, and is insulatedly bonded to the cap plate <NUM> through the thermal bonding layer <NUM>. The electrode terminal <NUM> covers the terminal hole <NUM> of the cap plate <NUM>. The electrode terminal <NUM> is positioned between the cap plate <NUM> and the electrode assembly <NUM>.

The electrode terminal <NUM> covers a central area of the opening <NUM> of the case <NUM> exposed by the terminal hole <NUM> of the cap plate <NUM>. In an embodiment, the electrode terminal <NUM> covers, preferably fully covers the central area of the opening <NUM> and the cap plate <NUM> covers, preferably fully covers an outer area of the opening <NUM>, such that the opening <NUM> of the case <NUM> is completely sealed by the electrode terminal <NUM> and the cap plate <NUM>. The electrode terminal <NUM> is connected to, preferably directly connected to the second electrode tab <NUM> of the electrode assembly <NUM> to be electrically connected to, preferably directly electrically connected to the second electrode <NUM> of the electrode assembly <NUM>.

The electrode terminal <NUM> includes a flange portion <NUM> and a protrusion <NUM>. The flange portion <NUM> is positioned between the cap plate <NUM> and the electrode assembly <NUM> in the case <NUM>, and overlaps the cap plate <NUM> to cover the terminal hole <NUM>.

An upper surface of the flange portion <NUM> is in contact with, preferably in direct contact with the thermal bonding layer <NUM>, and the flange portion <NUM> is insulatedly bonded to, preferably directly insulatedly bonded to the cap plate <NUM> by the thermal bonding layer <NUM>. In an embodiment, a lower surface of the flange portion <NUM> is electrically connected to, preferably directly electrically connected to the second electrode tab <NUM>. Since the flange portion <NUM> is connected to, preferably directly connected to the second electrode tab <NUM>, the protrusion <NUM> and the flange portion <NUM> of the electrode terminal <NUM> have a same polarity as that of the second electrode <NUM>.

The protrusion <NUM> passes through the terminal hole <NUM> to be exposed outside the case <NUM>. An outer surface of the protrusion <NUM> may serve as a second electrode terminal of the rechargeable battery <NUM>.

The outer surface of the protrusion <NUM> may be positioned on a same plane as the outer surface of the cap plate <NUM> or on a different plane. For example, a height of the outer surface of the protrusion <NUM> may be the same as that of the outer surface of the cap plate <NUM>, but the present invention is not limited thereto, and the height of the outer surface of the protrusion <NUM> may be higher or lower than the height of the outer surface of the cap plate <NUM>.

In an embodiment, an outer surface of the protrusion <NUM> includes a curved surface CS and an inclined surface IS.

The protrusion <NUM> includes the curved surface CS extending from a lower surface of the flange portion <NUM> and the inclined surface IS extending from the curved surface CS and passing through the terminal hole <NUM>.

The curved surface CS may have a radius of curvature, e.g. a predetermined radius of curvature, and the inclined surface IS may have a slope, e.g. a predetermined slope. Accordingly, a surface of the protrusion <NUM> may be relatively far away from the cap plate <NUM>, which is an edge of the terminal hole <NUM>, from the curved surface CS to an end portion of the inclined surface IS. As such, when the inclined surface IS is formed, a distance of the protrusion <NUM> positioned in a horizontal direction between the cap plate <NUM> and the electrode terminal <NUM> is increased, such that even when an alignment error occurs, a short circuit between the cap plate <NUM> and the protrusion <NUM> of different polarities may be suppressed.

Claim 1:
A rechargeable battery (<NUM>) comprising:
an electrode assembly (<NUM>) comprising a first electrode (<NUM>), a second electrode (<NUM>), and a separator (<NUM>) between the first electrode (<NUM>) and the second electrode (<NUM>);
a case (<NUM>) comprising an inner space to accommodate the electrode assembly (<NUM>) and having an opening (<NUM>) at a side thereof;
a cap plate (<NUM>) coupled to the opening (<NUM>) of the case (<NUM>) and comprising a terminal hole (<NUM>) to expose the inner space; and
an electrode terminal (<NUM>) electrically connected to the electrode assembly (<NUM>) through the terminal hole (<NUM>) and overlapping the cap plate (<NUM>),
wherein the cap plate (<NUM>) and the electrode terminal (<NUM>) are made of different metals, wherein
the cap plate (<NUM>) is electrically connected to the electrode assembly (<NUM>), and
the cap plate (<NUM>) and the electrode terminal (<NUM>) are respectively electrically connected to different electrodes (<NUM>, <NUM>) of the electrode assembly (<NUM>),
wherein the cap plate (<NUM>) is made of a metal having a higher ionization tendency than that of an electrode (<NUM>, <NUM>) of the electrode assembly (<NUM>) electrically connected to the cap plate (<NUM>), wherein the cap plate (<NUM>) is made of a metal having a lower ionization tendency than that of the electrode terminal (<NUM>),
wherein the electrode terminal (<NUM>) comprises:
a flange portion (<NUM>) configured to cover the terminal hole (<NUM>) and overlapping the cap plate (<NUM>); and
a protrusion (<NUM>) integrally formed with the flange portion (<NUM>) to protrude from the flange portion (<NUM>) toward the terminal hole (<NUM>),
wherein
an outer surface of the protrusion (<NUM>) comprises a curved surface (CS) and an inclined surface (IS), a distance from the curved surface (CS) to an end portion of the cap plate (<NUM>) exposed to the terminal hole (<NUM>) is shorter than a distance from the inclined surface (IS) to an end portion of the cap plate (<NUM>) exposed to the terminal hole (<NUM>), and
the distance from the inclined surface (IS) to the end portion of the cap plate (<NUM>) exposed to the terminal hole (<NUM>) becomes longer toward an end portion of the inclined surface (IS).