Patent Description:
Lithium ion secondary batteries are being widely used in portable electronic devices and power sources of hybrid automobiles or electric vehicles because of various advantages, including a high operation voltage, a high energy density per unit weight, and so forth.

The lithium ion secondary battery can be largely classified as a cylinder type secondary battery, a prismatic type secondary battery, a pouch type secondary battery. Specifically, the cylindrical lithium ion secondary battery generally includes a cylindrical electrode assembly, a cylindrical can coupled to the electrode assembly, an electrolyte injected into the can to allow movement of lithium ions, and a cap assembly coupled to one side of the can to prevent leakage of the electrolyte and separation of the electrode assembly.

<CIT> relates to a rechargeable battery.

<CIT> relates to a rechargeable battery which has a heat-resistant insulating layer.

<CIT> relates to a cylindrical sealed battery and a battery pack including such a battery.

Various embodiments of the present invention provide a cylindrical lithium ion secondary battery which, when an internal gas pressure is larger than a predetermined first reference pressure (operating pressure) and is smaller than a predetermined second reference pressure (breaking pressure) during overcharging, can maintain an internal sealing while a current path is blocked by a cap assembly.

Various embodiments of the present invention provide a cylindrical lithium ion secondary battery which can rapidly release the internal gas without any obstructions by allowing the cap assembly to be broken or ruptured (opened) when an internal gas pressure is larger than a predetermined second reference pressure (breaking pressure).

Various embodiments of the present invention provide a cylindrical lithium ion secondary battery which can arbitrarily determine the breaking pressure of the cap assembly according to the location of a welding region formed.

According to various embodiments of the present invention, provided is a cylindrical lithium ion secondary battery comprising: a cylindrical can; an electrode assembly received in the cylindrical can; and a cap assembly for sealing the cylindrical can, wherein the cap assembly comprises a top plate having a flat surface on which a notch is formed, a middle plate coupled to the top plate and including a first through-hole formed through the center thereof, and a bottom plate electrically connected with the electrode assembly, attached to the middle plate with an insulating plate interposed therebetween, and connected to the top plate through the first through-hole of the middle plate.

The top plate may include a flat top surface and a flat bottom surface opposite to the top surface, and the notch is formed on the bottom surface.

The top plate may include a flat upper region positioned on the middle plate, a side region downwardly bent from the upper region and positioned at a side portion of the middle plate, and a lower region bent from the side region and positioned at a bottom portion of the middle plate.

The notch may be formed at an exterior side of a region corresponding to the first through-hole of the middle plate.

The middle plate may further include a plurality of second through-holes formed around the first through-hole.

When the internal gas pressure of the cylindrical can is larger than a predetermined first pressure and smaller than a predetermined second pressure, the top plate may be upwardly convexly deformed by the internal gas pressure, and the top plate may be electrically disconnected from the bottom plate.

When the internal gas pressure of the cylindrical can is larger than the predetermined second pressure, the notch may be broken, and the internal gas of the cylindrical can may then be released to the outside.

To determine the breaking pressure of the top plate, one or more welding regions may further be formed between the top plate and the middle plate.

As the welding regions formed are located far away from the edge of the top plate, the breaking pressure of the top plate may be relatively small.

As described above, in the cylindrical lithium ion secondary battery according to various embodiments, when an internal gas pressure is larger than a predetermined first reference pressure (operating pressure) and is smaller than a predetermined second reference pressure (breaking pressure), an internal sealing can be maintained while a current path is blocked by a cap assembly.

In the cylindrical lithium ion secondary battery according to various embodiments, the internal gas can be released to the outside without any obstructions by allowing the cap assembly to be broken or ruptured (opened) when the internal gas pressure, after a current path is blocked by the cap assembly, is larger than a predetermined second reference pressure (breaking pressure).

In the cylindrical lithium ion secondary battery according to various embodiments, the breaking pressure of the cap assembly can be arbitrarily determined according to the location of a welding region formed.

In the cylindrical lithium ion secondary battery according to various embodiments, a relatively large battery capacity can be achieved by making an upper end height of the cap assembly equal to or smaller than that of a cylindrical can.

The cylindrical lithium ion secondary battery according to various embodiments includes a cap assembly including relatively soft pure aluminum or an aluminum alloy, so that the cap assembly is easily broken (opened) when the internal gas pressure reaches a predetermined reference pressure, thereby improving the safety of battery.

The embodiments of the present invention, however, may be modified in many different forms and should not be construed as being limited to the example (or exemplary) embodiments set forth herein. Rather, these example embodiments are provided so that this invention will be thorough and complete and will convey the aspects and features of the present invention to those skilled in the art.

In addition, in the accompanying drawings, sizes or thicknesses of various components are exaggerated for brevity and clarity. In addition, it will be understood that when an element A is referred to as being "connected to" an element B, the element A can be directly connected to the element B or an intervening element C may be present therebetween such that the element A and the element B are indirectly connected to each other.

As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms that the terms "comprise or include" and/or "comprising or including," when used in this specification, specify the presence of stated features, numbers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof.

It will be understood that, although the terms first, second, etc. may be used herein to describe various members, elements, regions, layers and/or sections, these members, elements, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one member, element, region, layer and/or section from another. Thus, for example, a first member, a first element, a first region, a first layer and/or a first section discussed below could be termed a second member, a second element, a second region, a second layer and/or a second section without departing from the teachings of the present invention.

Spatially relative terms, such as "beneath," "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. For example, if the element or feature in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "on" or "above" the other elements or features.

<FIG> and <FIG> are a perspective view and a cross-sectional view of a cylindrical lithium ion secondary battery <NUM> according to various embodiments of the present invention, and <FIG> is an exploded perspective view illustrating only a cap assembly <NUM>.

As illustrated in <FIG>, <FIG> and <FIG>, the cylindrical lithium ion secondary battery <NUM> according to various embodiments may include a cylindrical can <NUM>, an electrode assembly <NUM> and a cap assembly <NUM>. In some cases, the cylindrical lithium ion secondary battery <NUM> may further include a center pin <NUM>. In addition, in the cylindrical lithium ion secondary battery <NUM> according to various embodiments, the cap assembly <NUM> performs a current blocking operation, and thus may be referred to as a current interrupt device in some cases.

The cylindrical can <NUM> includes a circular bottom portion <NUM> and a side wall <NUM> upwardly extending a predetermined length from the periphery of the bottom portion <NUM>. In the process of manufacturing the secondary battery, a top portion or top end of the cylindrical can <NUM> is left open. Therefore, in the process of assembling the secondary battery <NUM>, the electrode assembly <NUM> and the center pin <NUM> may be inserted into the cylindrical can <NUM> together with an electrolyte. The cylindrical can <NUM> may be made of, for example, steel, a steel alloy, aluminum, an aluminum alloy, or an equivalent thereof, but embodiments of the present invention are not limited thereto.

In addition, the cylindrical can <NUM> may include an inwardly recessed beading part <NUM> formed below the cap assembly <NUM> so as to prevent the electrode assembly <NUM> from being separated from the cap assembly <NUM> and an inwardly bent crimping part <NUM> formed on or above the beading part <NUM>.

The electrode assembly <NUM> is received in the cylindrical can <NUM>. The electrode assembly <NUM> includes a negative electrode plate <NUM> coated with a negative electrode active material (e.g., graphite or carbon), a positive electrode plate <NUM> coated with a positive electrode active material (e.g., a transition metal oxide, such as LiCoO<NUM>, LiNiO<NUM>, or LiMn<NUM>O<NUM>), and a separator <NUM> interposed between the negative electrode plate <NUM> and the positive electrode plate <NUM> to prevent a short circuit between the negative electrode plate <NUM> and the positive electrode plate <NUM> while allowing only movement of lithium ions. The negative electrode plate <NUM>, the positive electrode plate <NUM>, and the separator <NUM> are wound in a substantially cylindrical shape or configuration. Here, the negative electrode plate <NUM> may be formed of a copper (Cu) or nickel (Ni) foil, the positive electrode plate <NUM> may be formed of an aluminum (Al) foil, and the separator <NUM> may be made of polyethylene (PE) or polypropylene (PP), but embodiments of the present invention are not limited thereto.

In addition, a negative electrode tab <NUM> may be welded to the negative electrode plate <NUM> to downwardly protrude and extend a predetermined length therefrom, and a positive electrode tab <NUM> may be welded to the positive electrode plate <NUM> to upwardly protrude and extend a predetermined length therefrom, or vice versa. In addition, the negative electrode tab <NUM> may be made of copper or nickel, and the positive electrode tab <NUM> may be made of aluminum, but embodiments of the present invention are not limited thereto.

In addition, the negative electrode tab <NUM> of the electrode assembly <NUM> may be welded to the bottom portion <NUM> of the cylindrical can <NUM>. Therefore, the cylindrical can <NUM> may function as a negative electrode. In other embodiments, the positive electrode tab <NUM> may be welded to the bottom portion <NUM> of the cylindrical can <NUM>. In these embodiments, the cylindrical can <NUM> may function as a positive electrode.

Additionally, a first insulating plate <NUM>, which is coupled to the cylindrical can <NUM> and has a first hole 126a formed at its center and a second hole 126b formed around the first hole 126a, may be interposed between the electrode assembly <NUM> and the bottom portion <NUM> of the cylindrical can <NUM>. The first insulating plate <NUM> may prevent the electrode assembly <NUM> from electrically contacting the bottom portion <NUM> of the cylindrical can <NUM>. Specifically, the first insulating plate <NUM> prevents the positive electrode plate <NUM> of the electrode assembly <NUM> from electrically contacting the bottom portion <NUM>. Here, when a relatively large amount of gas is generated due to an abnormality in the secondary battery, the first hole 126a allows the gas to rapidly move upwardly through the center pin <NUM>, and the second hole 126b allows the negative electrode tab <NUM> to pass therethrough to be welded to the bottom portion <NUM>.

In addition, a second insulating plate <NUM>, which is coupled to the cylindrical can <NUM> and has a first hole 127a formed at its center and a plurality of second holes 127b formed around the first hole 127a, may be interposed between the electrode assembly <NUM> and the bottom portion <NUM> of the cylindrical can <NUM>. The second insulating plate <NUM> may prevent the electrode assembly <NUM> from electrically contacting the bottom portion <NUM> of the cylindrical can <NUM>. Specifically, the second insulating plate <NUM> prevents the negative electrode plate <NUM> of the electrode assembly <NUM> from electrically contacting the cap assembly <NUM>. Here, when a relatively large amount of gas is generated due to an abnormality in the secondary battery, the first hole 127a allows the gas to rapidly move to the cap assembly <NUM>, and the second hole 127b allows the positive electrode tab <NUM> to pass therethrough to be welded to the cap assembly <NUM>. In addition, during injection of an electrolyte, the other second hole 127b allows the electrolyte to rapidly flow into the electrode assembly <NUM>.

In addition, since diameters of the first holes 126a and 127a of the first and second insulating plates <NUM> and <NUM> are smaller than a diameter of the center pin <NUM>, it is possible to prevent the center pin <NUM> from electrically contacting the bottom portion <NUM> of the cylindrical can <NUM> or the cap assembly <NUM> due to an external shock.

The center pin <NUM> is shaped of a hollow cylindrical pipe and is coupled to a substantially central portion of the electrode assembly <NUM>. The center pin <NUM> may be made of steel, stainless steel, aluminum, an aluminum alloy, or polybutylene terephthalate, but embodiments of the present invention are not limited to the above materials. The center pin <NUM> prevents the electrode assembly <NUM> from being deformed during charging or discharging of the secondary battery, and may serve as a gas movement path. Of course, in some embodiments, the center pin <NUM> may not be provided.

The cap assembly <NUM> may include a top plate <NUM>, a middle plate <NUM>, an insulating plate <NUM> and a bottom plate <NUM>.

The top plate <NUM> includes a substantially flat top surface 141a and a substantially flat bottom surface 141b opposite to the top surface <NUM> a. Particularly, the top plate <NUM> may further at least one notch 141c formed on the bottom surface 141b. Here, the notch 141c may have a substantially inverted V ("Λ") shaped cross section. In addition, when viewed from below, the notch 141c may have, for example, a substantially circular, elliptical or "C" shape, but embodiments of the present invention are not limited to the above shapes. The notch 141c is broken or ruptured when the internal gas pressure of the secondary battery is larger than a predetermined reference pressure, thereby rapidly releasing the internal gas of the battery to the outside and ultimately securing the safety of battery.

In addition, the top plate <NUM> may include an upper region 141d, a side region 141e, and a lower region 141f. The upper region 141d may be positioned on the middle plate <NUM> and may be substantially flat. The upper region 141d may serve as a terminal of the secondary battery, and thus may be electrically connected to an external device (e.g., a load or a charger). The side region 141e may be downwardly bent from the upper region 141d to substantially encompass a side portion of the middle plate <NUM>. The lower region 141f is horizontally inwardly bent from the side region 141e to then be positioned at a bottom portion of the middle plate <NUM>. In such a manner, the top plate <NUM> may be combined with the middle plate <NUM> by the upper region 141d, the side region 141e, and the lower region 141f.

Additionally, a height of the upper region 141d of the top plate <NUM> may be made to be equal to or smaller than that of the crimping part <NUM> of the cylindrical can <NUM>, which increases the internal volume of the cylindrical can <NUM>, thereby increasing the capacity of the secondary battery. Here, the height means a height ranging from the bottom portion <NUM> of the cylindrical can <NUM>.

The top plate <NUM> may be made of, for example, aluminum, aluminum, an aluminum alloy or equivalents thereof, but embodiments of the present invention are not limited to the above materials. Accordingly, a bus bar, an external lead or an external device, made of aluminum, may be easily connected (or welded) to the top plate <NUM>.

Here, the top plate <NUM> may be made of one selected from the group consisting of 1XXX series alloys, that is, pure aluminum of <NUM>% or greater purity, 2XXX series alloys, that is, Al-Cu alloys, 3XXX series alloys, that is, Al-Mn alloys, 4XXX series alloys, that is, Al-Si alloys, 5XXX series alloys, that is, Al-Mg alloys, 6XXX series alloys, that is, Al-Mg-Si alloys, and 7XXX series alloys, that is, Al-Zn-(Mg, Cu) alloys.

Specifically, the top plate <NUM> is preferably made of soft aluminum among the above-mentioned series alloys. For example, the top plate <NUM> may be made of, but not limited to, a 5XXX series (e.g., <NUM>, <NUM>, <NUM>, or <NUM>) Al-Mg alloy having a high strength, excellent corrosion resistance and good weldability. Additionally, a 1XXX, 3XXX or 4XXX series alloy, which is a non-heat treatable alloy, may be used as a material of the top plate <NUM>.

In some cases, the top plate <NUM> may further include a bent region <NUM> formed on the upper region 141d. When viewed from below, the bent region <NUM> may be shaped of a substantially circular ring. As an example, the upper region 141d located inside the bent region <NUM> may be positioned higher than the upper region 141d located outside the bent region <NUM>. In addition, the notch 141c may be formed on the upper region 141d located inside the bent region <NUM>.

The middle plate <NUM> may be positioned under the top plate <NUM> and may be substantially flat. In addition, the middle plate <NUM> may include a first through-hole 142a formed at a roughly central portion. Moreover, the middle plate <NUM> may include a plurality of second through-holes 142b formed around the first through-hole 142a.

Here, a bottom plate <NUM>, which will later be described, may pass through the first through-hole 142a to then be electrically connected to the top plate <NUM>, and may allow the internal gas pressure to be directly applied to the top plate <NUM>. In addition, the second through-holes 142b may also allow the internal gas pressure to be directly applied to the top plate <NUM>.

The notch 141c formed on the bottom surface 141b of the top plate <NUM> may be located to correspond to, for example, a region between the first through-hole 142a and each of the second through-holes 142b of the middle plate <NUM>.

Additionally, the middle plate <NUM> may also include a bent region 142c formed on a region corresponding to the bent region <NUM> of the top plate <NUM>. In addition, the second through-holes 142b may be formed in the bent region 142c. Therefore, the middle plate <NUM> may be generally configured such that it makes a close contact with the bottom surface 141b of the top plate <NUM>.

The middle plate <NUM> may be made of, for example, aluminum, aluminum, an aluminum alloy or equivalents thereof, but embodiments of the present invention are not limited thereto.

The insulating plate <NUM> may be positioned under (attached to a bottom portion of) the middle plate <NUM> and may include a through-hole 143a located to correspond to the first through-hole 142a. When viewed from below, the insulating plate <NUM> may be shaped of a substantially circular ring having a predetermined width. As an example, the insulating plate <NUM> may be located to correspond to a region between the first through-hole 142a and each of the second through-holes 142b of the middle plate <NUM>. In addition, the insulating plate <NUM> serves to insulate the middle plate <NUM> and the bottom plate <NUM> from each other. For example, the insulating plate <NUM> may be positioned between the middle plate <NUM> and the bottom plate <NUM> and may be subjected to ultrasonic welding, but embodiments of the present invention are not limited thereto.

The insulating plate <NUM> may be made of, for example, polyethylene (PE), polypropylene (PP), ethylene propylene diene monomer (M-class) rubber (EPDM rubber), or equivalents thereof, but embodiments of the present invention are not limited to the above materials. These insulating materials do not react with an electrolyte, and thus the insulating plate <NUM> may not be deformed even after the long-period use of the secondary battery <NUM>.

The bottom plate <NUM> is electrically connected to the top plate <NUM> through the through-hole 143a of the insulating plate <NUM> and the first through-hole 142a of the middle plate <NUM> to then be attached to the insulating plate <NUM>. That is to say, the bottom plate <NUM> may include a first area 144a connected (welded) to the upper region 141d of the top plate <NUM>, a second area 144b bent from the first area 144a and passing through the through-hole 142a of the middle plate <NUM> and the through-hole 143a of the insulating plate <NUM>, and a third area 144c substantially outwardly bent from the second area 144b and attached to the insulating plate <NUM>. In <FIG>, undefined reference numeral 144e refers to a welding region in which the first area 144a of the bottom plate <NUM> is welded to the bottom surface 141b of the upper region 141d of the top plate <NUM>.

Here, the positive electrode tab <NUM> may be electrically connected to the third area 144c of the bottom plate <NUM>. In addition, the third area 144c is spaced apart from the middle plate <NUM> and is also spaced apart from the third region 141f of the top plate <NUM>. In addition, the first area 144a of the bottom plate <NUM> may further include one or more concavely recessed grooves 144d. When the internal gas pressure of the battery is larger than a predetermined pressure, the top plate <NUM> is upwardly convexly deformed. In this case, the grooves 144d may serve to make the first area 144a of the bottom plate <NUM> easily separated from the second area 144b. Consequently, a current path between the top plate <NUM> and the bottom plate <NUM> may be blocked.

The bottom plate <NUM> may be made of, for example, aluminum, aluminum, an aluminum alloy or equivalents thereof, and thus the positive electrode tab <NUM> made of aluminum may be easily welded thereto.

The cap assembly <NUM> may further include an insulating gasket <NUM> insulating the top plate <NUM> and the sidewall <NUM> of the cylindrical can <NUM> from each other. Here, the insulating gasket <NUM> is configured to be substantially compressed between the beading part <NUM> and the crimping part <NUM> formed on the sidewall <NUM> of the cylindrical can <NUM>. In addition, the insulating gasket <NUM> may substantially encompass the side region 141e of the top plate <NUM>, and the top region 141d and the lower region <NUM> located therearound, thereby sealing the interior of the battery.

Additionally, an electrolyte (not shown) is injected into the cylindrical can <NUM>, and lithium ions generated by an electrochemical reaction in the negative electrode plate <NUM> and the positive electrode plate <NUM> in the secondary battery during charging and discharging are allowed to move. The electrolyte may be a non-aqueous, organic electrolyte including a mixture of a lithium salt and a high-purity organic solvent. In addition, the electrolyte may be a polymer using a polymer electrolyte or a solid electrolyte. However, embodiments of the present invention are not limited to the above electrolytes.

With such features of the cap assembly <NUM>, the cylindrical lithium ion secondary battery <NUM> according to the embodiment may have a relatively large capacity by making the upper end height of the cap assembly <NUM> equal to or smaller than that of the cylindrical can <NUM>. In addition, the cylindrical lithium ion secondary battery <NUM> includes the cap assembly <NUM> including relatively soft pure aluminum or an aluminum alloy, so that the cap assembly <NUM> is easily broken or ruptured (opened) when the internal gas pressure reaches a predetermined reference pressure, thereby improving the safety of battery.

<FIG> and <FIG> are cross-sectional views illustrating states in which the cap assembly <NUM> operates and ruptures in the cylindrical lithium ion secondary battery <NUM> according to an embodiment of the present invention.

As illustrated in <FIG>, in the cylindrical lithium ion secondary battery <NUM> according to various embodiments, when the internal gas pressure of the cylindrical can <NUM> is larger than a predetermined first reference pressure (operating pressure) and is smaller than a predetermined second reference pressure (breaking pressure), the top plate <NUM> is upwardly convexly deformed (inverted), and the top plate <NUM> may be electrically disconnected from the bottom plate <NUM>. That is to say, the first area 144a of the bottom plate <NUM> is broken to then be separated from the second area 144b. In other words, the grooves 144d of the first area 144a are ruptured, and some regions of the first area 144a upwardly move in a state in which they are still connected to the top plate <NUM>. Consequently, a current path between the top plate <NUM> and the bottom plate <NUM> may be blocked.

However, when the internal gas pressure of the secondary battery is smaller than the predetermined second reference pressure (breaking pressure), a sealing of the secondary battery may be maintained, thereby preventing the internal gas from being released to the outside.

When the battery is overcharged, when an internal short-circuit occurs to the cylindrical secondary battery due to penetration and/or collapse, or when an external short-circuit occurs to the battery, internal gas may be generated due to decomposition of an electrolyte and/or decomposition of an active material, resulting in an increase in the internal gas pressure of the secondary battery. Here, the secondary battery is designed such that the second reference pressure (breaking pressure) is larger than the first reference pressure (operating pressure). Such an increase in the internal gas pressure of the secondary battery may suggest that the secondary battery is at an abnormal state, and thus the current path is first blocked by the above-mentioned mechanical mechanism (charge current, discharge current, short-circuit current, or overcurrent), thereby improving the safety of the secondary battery.

As illustrated in <FIG>, in the cylindrical lithium ion secondary battery <NUM> according to various embodiments, when the internal gas pressure of the cylindrical can <NUM> is larger than the predetermined second pressure (breaking pressure), the top plate <NUM> is ruptured to thus rapidly release the internal gas without any obstructions. That is to say, as the notch 141c formed on the bottom surface 141b of the top plate <NUM> is ruptured, the gas existing within the secondary battery <NUM> is rapidly released to the outside, thereby preventing explosion of the secondary battery <NUM> and ultimately increasing the safety of the secondary battery <NUM>. From the viewpoint of safety, releasing the internal gas to the outside in advance is more advantageous than letting the secondary battery <NUM> explode under a high pressure as described above.

In addition, the breaking pressure (or the second pressure) of the top plate <NUM> may be adjusted by the depth of the notch 141c formed. For example, the breaking pressure may be increased by forming the notch 141c so as to have a relatively small depth, and the breaking pressure may be reduced by forming the notch 141c so as to have a relatively large depth.

As described above, when the internal gas pressure is larger than the predetermined first reference pressure (operating pressure) and is smaller than the predetermined second reference pressure (breaking pressure), the cylindrical lithium ion secondary battery <NUM> according to the embodiments may primarily block the current path by the cap assembly <NUM>. Here, the internal sealing of the battery is still maintained. In addition, when the internal gas pressure, after the current path is blocked by the cap assembly <NUM>, is larger than the predetermined second reference pressure (breaking pressure), the cap assembly <NUM> is broken or ruptured (opened), and thus the cylindrical lithium ion secondary battery <NUM> according to the embodiments may secondly release the internal gas to the outside without any obstructions.

That is to say, the cylindrical lithium ion secondary battery <NUM> according to the embodiments may perform a safety-related operation in two steps by primarily blocking the current path when the internal gas pressure is larger than the predetermined first reference pressure, and secondly releasing the internal gas to the outside when the internal gas pressure is larger than the predetermined second reference pressure.

Meanwhile, the breaking pressure of the top plate <NUM> may be determined by a hinge point formed during operation (inversion) of the top plate <NUM> as well as by the depth of the notch 141c. That is to say, when the top plate <NUM> is inverted, there may be a hinge point at which the inversion is initiated. For example, the hinge point may be a boundary region between the insulating gasket <NUM> and the top plate <NUM>. That is to say, the hinge point may be a region of the upper region 141d of the top plate <NUM>, which corresponds to an end of the insulating gasket <NUM>. Therefore, the breaking pressure of the top plate <NUM> may vary according to the location of the hinge point, which will be described below.

<FIG> and <FIG> are cross-sectional views illustrating cap assemblies 140A and 140B of the cylindrical lithium ion secondary battery <NUM> according to various embodiments of the present invention.

As illustrated in <FIG> and <FIG>, in the cylindrical lithium ion secondary battery <NUM> according to various embodiments, in order to determine (adjust) the breaking pressure of the top plate <NUM>, the cap assemblies 140A and 140B may further include one or more welding regions 146A and 146B formed between the top plate <NUM> and the middle plate <NUM>, respectively. The welding regions 146A and 146B may be formed by, for example, laser welding, resistance welding or ultrasonic welding, but embodiments of the present invention are not limited thereto. When viewed from above, for example, the welding regions 146A and 146B may be shaped such that substantially continuously circular rings or points are arranged, but embodiments of the present invention are not limited thereto. In addition, the welding regions 146A and 146B may be formed at regions near the edges of the top plate <NUM> and the middle plate <NUM>, for example, but embodiments of the present invention are not limited thereto. That is to say, the welding regions 146A and 146B may be formed at regions of the top plate <NUM> and the middle plate <NUM>, which correspond to a location between each of the second through-holes 142b of the middle plate <NUM> and the periphery of the middle plate <NUM>, but embodiments of the present invention are not limited thereto.

Here, the breaking pressure of the top plate <NUM> may be gradually decreased as the welding regions 146A and 146B formed are getting far from the edge of the top plate <NUM>. In other words, the breaking pressure of the top plate <NUM> may be gradually increased as the welding regions 146A and 146B formed are getting close to the edge of the top plate <NUM>. Here, the breaking pressure means a pressure at which the notch 141c formed in the top plate <NUM> is broken or ruptured.

As an example, as illustrated in <FIG>, when the welding region 146A is located relatively far from the edge of the top plate <NUM> (that is, when the welding region 146A is located relatively close to the center of the top plate <NUM>), the breaking pressure of the top plate <NUM> may be relatively small. That is to say, the notch 141c of the top plate <NUM> may be broken or ruptured by a relatively small internal pressure of the battery.

As another example, as illustrated in <FIG>, when the welding region 146B is located relatively close to the edge of the top plate <NUM> (that is, when the welding region 146B is located relatively far from the center of the top plate <NUM>), the breaking pressure of the top plate <NUM> may be relatively large. That is to say, the notch 141c of the top plate <NUM> may be broken or ruptured by a relatively large internal pressure of the battery.

Such a change in the breaking pressure is attributable to a volumetric change for breaking.

In other words, the welding regions 146A and 146B may be considered to be hinge points, and the upper region 141d of the top plate <NUM> may be considered to be an inverted region.

As the welding regions 146A and 146B are getting close to the periphery of the top plate <NUM> (that is, getting far from the center), the volume for inverting the top plate <NUM> may be increased, and thus a relatively large internal pressure may be required for operating or breaking the top plate <NUM>. Accordingly, the breaking pressure/operating pressure may be increased.

However, as the welding regions 146A and 146B are getting far from the periphery of the top plate <NUM> (that is, getting close to the center), the volume for inverting the top plate <NUM> may be decreased, and thus a relatively small internal pressure may be required for operating or breaking the top plate <NUM>. Accordingly, the breaking pressure/operating pressure may be reduced.

That is, according to the present invention, the welding regions 146A and 146B, instead of contact boundary regions of the insulating gasket <NUM> and the top plate <NUM>, are arbitrarily determined as the hinge points of the top plate <NUM>, thereby allowing the secondary battery <NUM> to arbitrarily adjust the operating pressure and/or the breaking pressure of the top plate <NUM>.

In addition, the operating pressure and/or the breaking pressure of the top plate <NUM> in any type of secondary battery may be uniformly controlled by adjusting the operating pressure and/or the breaking pressure of the top plate <NUM> using the welding regions 146A and 146B.

Practically, the breaking pressure and the operating pressure may be increased or decreased together.

<FIG> and <FIG> are a cross-sectional view and a graph illustrating the relationship between rupture pressures/operating pressures and welding regions of the cap assembly <NUM> in the cylindrical lithium ion secondary battery <NUM> according to various embodiments of the present invention. In <FIG>, the X-axis indicates the distance of a welding region from the center, and the Y-axis indicates the rupture pressure/operating pressure.

As illustrated in <FIG> and <FIG>, the breaking pressure of a top plate is gradually increased away from the center of welding regions of the top plate toward the periphery of the top plate. In other words, as a welding region is formed to be closer to the periphery of the top plate, the pressure required for operating or breaking the top plate is increased. In still other words, as a welding region is formed to be closer to the center of the top plate, the pressure required for operating or breaking the top plate is decreased.

In addition, as illustrated in <FIG> and <FIG>, the breaking pressure of the top plate is gradually decreased away from the center of welding regions of the top plate toward the center of the top plate. In other words, as the welding region is formed to be closer to the center of the top plate, the pressure required for operating or breaking the top plate is decreased. In still other words, as the welding region is formed to be closer to the periphery of the top plate, the pressure required for operating or breaking the top plate is increased.

Claim 1:
A cylindrical lithium ion secondary battery (<NUM>) comprising:
a cylindrical can (<NUM>); an electrode assembly (<NUM>) received in the cylindrical can (<NUM>); and
a cap assembly (<NUM>) for sealing the cylindrical can (<NUM>),
wherein the cap assembly (<NUM>) comprises a top plate (<NUM>) having a flat surface on which a notch (141c) is formed, a middle plate (<NUM>) coupled to the top plate (<NUM>) and including a first through-hole (142a) formed through the center thereof, and a bottom plate (<NUM>) electrically connected with the electrode assembly (<NUM>), attached to the middle plate (<NUM>) with an insulating plate (<NUM>) interposed therebetween, and connected to the top plate (<NUM>) through the first through-hole (142a) of the middle plate (<NUM>).