Patent Description:
Secondary batteries, which can be charged and discharged and which can be repeatedly used, have been used as energy sources for a portable electronic device, a power tool, an electric vehicle, a power storage system, etc., and the demand for high-output and high-capacity secondary batteries has increased.

Based on the shape of a battery case, the secondary batteries are classified into a cylindrical secondary battery having an electrode assembly mounted in a cylindrical metal can, a prismatic secondary battery having an electrode assembly mounted in a prismatic metal can, and a pouch-shaped secondary battery having an electrode assembly mounted in a pouch-shaped case made of an aluminum laminate sheet.

The electrode assembly, which is mounted in the battery case, is a power generating element that is configured to have a structure in which a positive electrode, a separator, and a negative electrode are stacked and that can be charged and discharged. The electrode assembly is classified as a jelly-roll type electrode assembly, which is configured to have a structure in which a sheet type positive electrode and a sheet type negative electrode, to which active materials are applied, are wound in the state in which a separator is disposed between the positive electrode and the negative electrode, or a stacked type electrode assembly, which is configured to have a structure in which a plurality of positive electrodes having a predetermined size and a plurality of negative electrodes having a predetermined size are sequentially stacked in the state in which separators are disposed respectively between the positive electrodes and the negative electrodes. The jelly-roll type electrode assembly has advantages in that it is easy to manufacture the jelly-roll type electrode assembly and in that the jelly-roll type electrode assembly has high energy density per unit weight. For these reasons, the jelly-roll type electrode assembly has been widely manufactured. The jelly-roll type electrode assembly is usually applied to a cylindrical battery.

Generally, in a cylindrical secondary battery, a positive electrode tab of a jelly-roll type electrode assembly is coupled to a cap assembly such that a top cap functions as a positive electrode terminal. The positive electrode tab and the cap assembly are coupled to each other by welding, for example, laser welding.

In the welding process, however, residual foreign matter may be generated, whereby the external appearance of the electrode assembly may be damaged, or the top cap may be distorted.

Therefore, there is a necessity for technology that is capable of solving problems occurring while the positive electrode terminal of the cylindrical secondary battery is formed and of preventing the overcharge of the secondary battery.

In connection therewith, Patent Document <NUM> discloses a structure in which a plurality of first electrode tabs is disposed under a sub plate and a middle plate so as to be joined both to the sub plate and to the middle plate, wherein internal resistance decreases as the tightness of contact of the junction structure is increased, whereby the possibility of poor welding is reduced.

That is, Patent Document <NUM> discloses a structure that is capable of reducing the internal resistance of a secondary battery but does not suggest any coupling method other than a welding method, which may generate foreign matter.

Patent Document <NUM> discloses a structure in which a terminal plate is attached to the upper surface of a conductive adhesive, a negative electrode terminal is electrically connected through a hollow portion formed in the terminal plate, and a negative electrode tab is attached to the lower surface of the conductive adhesive. However, a secondary battery disclosed in Patent Document <NUM> is configured to have a structure in which the conductive adhesive melts or is deformed, and therefore the connected portions of the negative electrode tab and the negative electrode terminal are separated from each other such that the negative electrode tab and the negative electrode terminal are spaced apart from each other, whereby the electrical connection therebetween is released.

Patent Document <NUM> discloses a cap assembly configured to have a structure in which the outer circumferential surface of a stack including a top cap and a safety vent, which are sequentially stacked, is wrapped with a main gasket and in which a current interrupt device, at which the outer circumferential surface of the stack is wrapped with an auxiliary gasket, is joined to the lower side of the safety vent, wherein the drooping of the main gasket is prevented by the auxiliary gasket.

Patent Document <NUM> discloses a structure in which, at the innermost side of an electrode formed by winding a positive electrode, a negative electrode, and a porous separator, a wire is wound at least <NUM> turns around a base plate of one of the positive electrode and the negative electrode to form an electrode core, an electrode tab is attached to a region between the winding start part and the <NUM>-turn part of the base plate, and the end of the electrode tab is connected to a cap assembly.

However, Patent Document <NUM> and Patent Document <NUM> do not suggest a plan that is capable of solving the problems that occur in the process of connecting the electrode terminal and the electrode tab to each other.

Patent document <NUM> discloses a pouch cell having a tab adhesion unit comprising acrylic polyol resin A as adhesive agent and lithium carbonate as a foaming agent, in an amount of <NUM>-<NUM> weight parts of the resin.

Therefore, there is a high necessity for technology that is capable of easily forming a connection structure between a positive electrode tab of a jelly-roll type electrode assembly and a cap assembly in a cylindrical secondary battery, of releasing electrical connection within a short time, and of preventing the occurrence of problems caused by foreign matter, which may occur during welding, etc..

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a cylindrical secondary battery configured such that it is possible to prevent foreign matter from being generated in the process of electrically connecting an electrode tab and a cap assembly to each other or to prevent the cap assembly from shaking in the above process.

In accordance with the present invention, the above and other objects can be accomplished by the provision of a cylindrical secondary battery including
a jelly-roll type electrode assembly configured to have a structure in which a sheet type positive electrode and a sheet type negative electrode are wound in the state in which a separator is disposed between the positive electrode and the negative electrode, a cylindrical battery case configured to receive the jelly-roll type electrode assembly, and a cap assembly mounted to the open upper end of the cylindrical battery case, wherein the lower end surface of the cap assembly is connected to a positive electrode tab of the jelly-roll type electrode assembly via an adhesion unit, and the adhesion unit includes an adhesive material, a conductive material, and a gas-generating material.

The adhesive material may be made of at least one selected from the group consisting of a polyester resin, an epoxy resin, a phenol resin, polyvinyl acetate, polyvinyl butyral, and polyester acrylate.

The conductive material may be made of at least one selected from the group consisting of graphite, carbon black, conductive fiber, gold, silver, copper, aluminum, and an alloy of gold, silver, copper, and aluminum.

The gas-generating material may be lithium carbonate (Li<NUM>CO<NUM>), CaCO<NUM>, K<NUM>CO<NUM>, Na<NUM>CO<NUM>, or BaCO<NUM>.

The content of the gas-generating material is greater than <NUM> wt% to <NUM> wt% of the content of the conductive material.

The reaction of the gas-generating material may commence when the voltage of the cylindrical secondary battery increases, whereby the adhesion unit may swell, particles of the conductive material may become spaced apart from each other, and the flow of current may be interrupted.

The temperature at which the reaction of the gas-generating material commences may be lower than the melting temperature of the adhesive material.

When the voltage of the cylindrical secondary battery increases, the coupling force of the adhesion unit may be reduced due to melting of the adhesive material, whereby the positive electrode tab may be separated from the cap assembly.

The cap assembly is configured to have a structure which comprises a venting member and from which a a PTC element is omitted, the venting member is located at the lower end of the cap assembly, and the jelly-roll type electrode assembly extends so as to have an additional length corresponding to the thicknesses of the PTC element, which is omitted.

In the case in which coupling of the adhesion unit is weakened due to the reaction of the gas-generating material, the shape of a venting member of the cap assembly may be inverted, whereby the venting member may be separated from the positive electrode tab.

According to an alternative embodiment, the cap assembly is configured to have a structure which includes a venting member and from which a PTC element and a current interrupt device are omitted, the venting member is located at the lower end of the cap assembly, and the jelly-roll type electrode assembly extends so as to have an additional length corresponding to the thicknesses of the PTC element and the current interrupt device, which are omitted.

A cylindrical secondary battery according to the present invention may include a jelly-roll type electrode assembly configured to have a structure in which a sheet type positive electrode and a sheet type negative electrode are wound in the state in which a separator is disposed between the positive electrode and the negative electrode, a cylindrical battery case configured to receive the jelly-roll type electrode assembly, and a cap assembly mounted to the open upper end of the cylindrical battery case, wherein the lower end surface of the cap assembly may be connected to a positive electrode tab of the jelly-roll type electrode assembly via an adhesion unit, and the adhesion unit may include an adhesive material, a conductive material, and a gas-generating material.

That is, in the present invention, the adhesion unit is used in order to couple the lower end surface of the cap assembly and the positive electrode tab of the jelly-roll type electrode assembly to each other, and the adhesion unit includes an adhesive material, a conductive material, and a gas-generating material.

Specifically, the adhesion unit of the present invention may include an adhesive material configured to increase the force of coupling between the positive electrode tab and the cap assembly while maintaining the shape of the adhesion unit in a normal state, a conductive material configured to serve as an electrical connection path between the positive electrode tab and the cap assembly, and a gas-generating material configured to commence a reaction when the temperature of the secondary battery increases in order to discharge gas.

As described above, in the cylindrical secondary battery according to the present invention, the adhesion unit, which includes the adhesive material, is added to the lower surface of the cap assembly, to which the positive electrode tab is coupled, without using a conventionally used welding method, such as laser welding, in order to achieve electrical connection between the positive electrode tab and the cap assembly, which functions as a positive electrode terminal.

Consequently, it is possible to prevent the occurrence of a problem in which foreign matter is separated from the electrode assembly as the result of using laser welding for the cylindrical secondary battery, as in the conventional art, whereby the separator is damaged or reacts with an electrolytic solution.

The adhesive material is not particularly restricted, as long as the adhesive material is made of a material that is capable of increasing the force of coupling between the positive electrode tab and the cap assembly. For example, the adhesive material may be made of at least one selected from the group consisting of a polyester resin, an epoxy resin, a phenol resin, polyvinyl acetate, polyvinyl butyral, and polyester acrylate.

The conductive material serves as an electrical connection path between the positive electrode tab and the cap assembly. The conductive material is not particularly restricted, as long as the conductive material is made of a material that exhibits high electrical conductivity. For example, the conductive material may be made of at least one selected from the group consisting of graphite, carbon black, conductive fiber, such as carbon fiber or metal fiber, gold, silver, copper, aluminum, and an alloy of gold, silver, copper, and aluminum.

The gas-generating material is not particularly restricted, as long as the gas-generating material is a material that initiates a reaction to discharge gas when the voltage of the battery increases. For example, the gas-generating material may be lithium carbonate (Li<NUM>CO<NUM>), CaCO<NUM>, K<NUM>CO<NUM>, Na<NUM>CO<NUM>, or BaCO<NUM>.

In the case in which the content of the gas-generating material is less than <NUM> wt% of the content of the conductive material, a small amount of gas is generated, whereby it is difficult to obtain a desired voltage increase effect, which is undesirable. In addition, in the case in which the content of the gas-generating material is greater than the content of the conductive material, the electrical conductivity of the positive electrode terminal becomes an issue, which is also undesirable.

In a concrete example, the cylindrical secondary battery according to the present invention is configured to have a structure in which the adhesion unit, including the gas-generating material, is added. The reaction of the gas-generating material commences when the voltage of the cylindrical secondary battery increases, whereby gas is generated in the adhesion unit. As the gas is generated, as described above, the adhesion unit swells, and gaps between particles of the conductive material, which are arranged in tight contact in a normal state, are filled with gas bubbles, whereby the particles of the conductive material are spaced apart from each other.

As a result, resistance increases, and voltage increases in proportion to the increase in the resistance. Subsequently, the voltage reaches a charge end voltage, and the flow of current is interrupted. That is, unlike the conventional art, in which venting is performed due to an increase in the internal pressure of the battery in the state in which the positive electrode tab is connected to the cap assembly by welding, whereby the positive electrode tab and the cap assembly are physically separated from each other, the adhesion unit, including the gas-generating material, may swell, whereby the particles of the conductive material may become spaced apart from each other and thus the flow of current may be interrupted according to the present invention.

For example, in the case in which lithium carbonate is used as the gas-generating material, the lithium carbonate is decomposed into carbon monoxide and carbon dioxide when the voltage of the battery reaches <NUM>. 8V, whereby gas is formed. As a result, gaps are formed between the particles of the conductive material of the adhesion unit, which are arranged in tight contact, whereby the particles of the conductive material may become spaced apart from each other.

The temperature at which the reaction of the gas-generating material commences may be lower than the melting temperature of the adhesive material. In a specific temperature range, therefore, the adhesive material may not melt, but the reaction of the gas-generating material may commence, thus generating gas. In this state, the physical coupling between the positive electrode tab and the cap assembly is maintained, but the distance between the particles of the conductive material is increased due to the generation of gas, whereby resistance increases. However, when the temperature further increases, whereby the amount of gas that is generated in the gas-generating material increases, and, in addition, the adhesive material melts, whereby the adhesiveness of the adhesive material is reduced, the physical coupling between the positive electrode tab and the cap assembly may be released.

That is, when the voltage of the cylindrical secondary battery increases, resistance may increase due to the generation of gas in the adhesion unit, whereby the voltage may increase to a charge end voltage and thus the flow of current may be interrupted. In consideration of the fact that the general temperature of the battery is about <NUM> or lower when the voltage of the battery reaches the charge end voltage, the adhesive material of the adhesion unit may not melt.

However, in the case in which the temperature of the battery instantaneously increases due to external impact, etc. before the voltage of the battery reaches the charge end voltage, the coupling force of the adhesion unit may be reduced due to melting of the adhesive material, whereby the positive electrode tab may be separated from the cap assembly.

Compared to the conventional case, in which the positive electrode tab is coupled to the cap assembly by welding, therefore, the coupling force of the adhesion unit is relatively low. Consequently, the force necessary to separate the positive electrode tab and the cap assembly from each other is relatively reduced, whereby rapid separation therebetween may be achieved.

In a concrete example, the cap assembly may be configured to have a structure which includes a venting member and from which a PTC element is omitted, the venting member or a current interrupt member may be located at the lower end of the cap assembly, and the jelly-roll type electrode assembly may extend so as to have an additional length corresponding to the thickness of the PTC element, which is omitted.

In the cylindrical secondary battery having the above structure, the jelly-roll type electrode assembly may become relatively long, compared to a conventional cylindrical secondary battery having the same standards, whereby it is possible to provide a high-capacity cylindrical secondary battery.

In addition, the cylindrical secondary battery according to the present invention includes an adhesion unit including a gas-generating material, which generates gas when the voltage of the battery increases. An increase in resistance may be induced due to the gas-generating material, whereby the flow of current may be interrupted. Consequently, it is possible to obtain the same effect even in the case in which the PTC element, which is included in the conventional cylindrical secondary battery, is omitted.

Meanwhile, the venting member may be configured to have a downwardly concave structure. In the case in which coupling of the adhesion unit is weakened due to the reaction of the gas-generating material, the shape of the venting member is inverted, whereby the venting member is separated from the positive electrode tab. Consequently, the positive electrode tab and the cap assembly may be physically separated from each other.

In another concrete example, in consideration of the fact that the cylindrical secondary battery according to the present invention is configured to have a structure in which the adhesion unit swells due to the gas-generating material, whereby resistance increases and thus the flow of current is interrupted, the cap assembly may be configured to have a structure which includes a venting member and from which a PTC element and a current interrupt device are omitted, the venting member may be located at the lower end of the cap assembly, and the jelly-roll type electrode assembly may extend so as to have an additional length corresponding to the thicknesses of the PTC element and the current interrupt device, which are omitted.

That is, in the case in which the structure from which the PTC element and the current interrupt device are omitted is included, as described above, the thickness of the cap assembly is relatively reduced, whereby it is possible to increase the height of the jelly-roll type electrode assembly by a length corresponding to the reduced thickness of the cap assembly and thus it is possible to obtain an effect in which the capacity of the battery is increased.

In addition, in the cylindrical secondary battery having the above structure, the current interrupt device is further omitted, compared to a cylindrical secondary battery configured to have a structure which includes the venting member and from which the PTC element is omitted, whereby the thickness of the cap assembly may be reduced by the thickness of the omitted current interrupt device.

Compared to a cylindrical secondary battery having the same standards, the jelly-roll type electrode assembly may become relatively long, whereby it is possible to provide a high-capacity cylindrical secondary battery.

In the cylindrical secondary battery configured to have a structure from which the PTC element and the current interrupt device are omitted, as described above, the venting member is located under the top cap, and the adhesion unit is added to the lower surface of the venting member, whereby electrical connection with the positive electrode tab may be achieved.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings such that the preferred embodiments of the present invention can be easily implemented by those skilled in the art to which the present invention pertains.

In the case in which one part is said to be connected to another part in the specification, not only may the one part be directly connected to the another part, but also, the one part may be indirectly connected to the another part via a further part.

Embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<FIG> is a vertical sectional view showing a conventional general cylindrical secondary battery.

Referring to <FIG>, the cylindrical secondary battery <NUM> includes a battery case <NUM>, in which a jelly-roll type electrode assembly <NUM> is received, and a cap assembly <NUM> located at the upper part of the battery case <NUM>. A top cap <NUM> is located at the upper end of the cap assembly <NUM>, and a PTC element <NUM>, configured to interrupt the flow of current at high temperature, a venting member <NUM>, configured to discharge high-pressure gas, and a current interrupt device <NUM>, configured to interrupt the flow of current when the inner pressure of the battery increases, are sequentially stacked under the top cap <NUM>.

At the region of contact between the cap assembly <NUM> and the battery case <NUM> is disposed a gasket <NUM> configured to secure the sealing force of the secondary battery, and a positive electrode tab <NUM> of the jelly-roll type electrode assembly is coupled to the lower surface of the current interrupt device <NUM> by welding.

Above the jelly-roll type electrode assembly <NUM> may be located an insulation member <NUM> configured to prevent contact between the positive electrode tab <NUM> and the battery case <NUM>.

<FIG> is a vertical sectional view showing a cylindrical secondary battery according to an embodiment of the present invention, and <FIG> is a vertical sectional view showing the state in which a venting member of <FIG> ruptures.

Referring to <FIG>, the cylindrical secondary battery <NUM> includes a battery case <NUM>, in which a jelly-roll type electrode assembly <NUM> is received, and a cap assembly <NUM> located at the upper part of the battery case <NUM>. A top cap <NUM> is located at the upper end of the cap assembly <NUM>, and a venting member <NUM> is located under the top cap <NUM>.

That is, the cap assembly <NUM> of the cylindrical secondary battery <NUM> is configured to have a structure in which the PTC element <NUM> and the current interrupt device <NUM> are omitted from the structure of the cylindrical secondary battery <NUM>, the top cap <NUM> and the venting member <NUM> are included, and a gasket <NUM> configured to secure sealing force is disposed at the region of contact between the cap assembly <NUM> and the battery case <NUM>.

A positive electrode tab <NUM> of the jelly-roll type electrode assembly <NUM> is coupled to the lower surface of the venting member <NUM> via an adhesion unit <NUM>.

Meanwhile, unlike what is shown in <FIG>, the cylindrical secondary battery <NUM> may be configured to have a structure in which a current interrupt member is further added to the lower surface of the venting member <NUM>, and the positive electrode tab of the electrode assembly may be coupled to the current interrupt member so as to be electrically connected to the top cap via the venting member.

<FIG> is a vertical sectional view showing the state in which the flow of current is interrupted in the cylindrical secondary battery of <FIG>.

Referring to <FIG>, there is shown the state in which, when the pressure in the battery case increases due to repeated charge and discharge of the cylindrical secondary battery, the venting member <NUM>, which does not withstand the pressure, is inverted to an upwardly concave structure, whereby a notch portion of the venting member, which is relatively thin, ruptures.

The adhesion unit <NUM> includes a gas-generating material. In the case in which the pressure in the battery increases, therefore, gas is generated, whereby the adhesion unit swells and thus the coupling force of the adhesion unit is reduced. Consequently, the adhesion unit <NUM>, which is added to the lower surface of the venting member <NUM> in order to maintain coupling between the venting member and the positive electrode tab <NUM>, is divided into two parts. As a result, a portion of the adhesion unit is attached to the lower surface of the venting member <NUM>, and the remaining portion of the adhesion unit is attached to the positive electrode tab <NUM>.

<FIG> is a vertical sectional view showing a cylindrical secondary battery according to another embodiment of the present invention.

Referring to <FIG>, the cylindrical secondary battery <NUM> includes a battery case <NUM>, in which a jelly-roll type electrode assembly <NUM> is received, a cap assembly <NUM>, and a gasket <NUM> disposed between the cap assembly <NUM> and the battery case <NUM>, the gasket <NUM> being configured to secure force for sealing the battery case.

A top cap <NUM> is located at the upper part of the cap assembly <NUM>, and a venting member <NUM> is located under the top cap <NUM>. That is, the cap assembly <NUM> of the cylindrical secondary battery <NUM> is configured to have a structure in which the PTC element <NUM> and the current interrupt device <NUM> are omitted from the structure of the cylindrical secondary battery <NUM>.

A positive electrode tab <NUM> of the jelly-roll type electrode assembly <NUM> is coupled to the lower surface of the venting member <NUM> via an adhesion unit <NUM>, and the venting member <NUM> is connected to the top cap <NUM>, whereby the top cap may function as a positive electrode terminal.

In the present invention, voltage increases due to the gas generated in the adhesion unit, whereby the flow of current is interrupted. That is, the flow of current is interrupted before the venting member ruptures due to an increase in the internal pressure of the battery. Consequently, a venting member <NUM> having a downwardly concave structure, such as the venting member <NUM> of <FIG>, may not be used.

As needed, however, a venting member <NUM> formed in a downwardly concave shape, such as the venting member <NUM> of <FIG>, may be used.

<FIG> is a vertical sectional view showing a comparison of the heights of the electrode assemblies included in the cylindrical secondary batteries of <FIG> and <FIG>.

Referring to <FIG>, the cylindrical secondary battery <NUM> is configured to have a structure in which the PTC element <NUM> and the current interrupt device <NUM> are omitted from the cylindrical secondary battery <NUM>.

Consequently, the thickness h2 of the cap assembly of the cylindrical secondary battery <NUM> is less than the thickness h1 of the cap assembly of the cylindrical secondary battery <NUM>.

In the case in which the thickness of the cap assembly is reduced, as described above, the height h4 of the electrode assembly of the cylindrical secondary battery <NUM> becomes greater than the height h3 of the electrode assembly of the cylindrical secondary battery <NUM>, on the assumption that the overall heights of the cylindrical secondary batteries are equal to each other. Consequently, the cylindrical secondary battery <NUM> may be a higher-capacity secondary battery than the cylindrical secondary battery <NUM>.

<FIG> is an enlarged view showing the states before and after the adhesion unit shown in <FIG> is deformed.

Referring to <FIG>, the upper surface of an adhesion unit is coupled to the venting member <NUM>, and the lower surface of the adhesion unit is coupled to the positive electrode tab <NUM>.

The adhesion unit <NUM> includes an adhesive material <NUM>, a conductive material <NUM>, and a gas-generating material <NUM>.

In a normal state, coupling between the venting member <NUM> and the positive electrode tab <NUM> via the adhesion unit <NUM> is achieved, whereby electrical connection through the conductive material <NUM>, particles of which are arranged in tight contact, is achieved. When the gas-generating material <NUM> commences a reaction due to an increase in the voltage of the battery, however, the volume of the adhesion unit <NUM> expands, whereby the distance between the particles of the conductive material <NUM> increases. As a result, a resistance increase effect is generated, and the increase of voltage is accelerated. Subsequently, when the voltage of the secondary battery increases to a charge end voltage, the flow of current is interrupted. In this case, the flow of current may be interrupted even though no rupture occurs.

Alternatively, the amount of gas may increase (<NUM>') (the gas-generating material being shown in an expanded state) as the result of reaction of the gas-generating material <NUM>, and the coupling force of the adhesion unit <NUM> may be reduced due to the molten adhesive material <NUM>', whereby the physical coupling between the positive electrode tab and the cap assembly may be released.

Hereinafter, the present invention will be described with reference to the following examples. These examples are provided only for easier understanding of the present invention and should not be construed as limiting the scope of the present invention.

Based on the total weight of an adhesion unit, <NUM> wt% of an epoxy resin, as an adhesive material, <NUM> wt% of silver, as a conductive material, and <NUM> wt% of lithium carbonate (Li<NUM>CO<NUM>), as a gas-generating material, were mixed with NMP, and the same was dried to manufacture a paste-phase adhesion unit.

The adhesion unit thus manufactured was added to a positive electrode tab of a cylindrical secondary battery, configured to have the structure shown in <FIG>, and to the lower end of a cap assembly of the cylindrical secondary battery to achieve electrical connection between the positive electrode tab and a current interrupt device. For experimental accuracy, five secondary batteries were manufactured under the same conditions.

A paste-phase adhesion unit was manufactured in the same manner as in Example <NUM>, except that <NUM> wt% of silver, as a conductive material, and <NUM> wt% of lithium carbonate were used, unlike Example <NUM>, and then five cylindrical secondary batteries each having the adhesion unit added thereto were manufactured.

A cylindrical secondary battery configured to have the structure shown in <FIG> was prepared, and five cylindrical secondary batteries, each configured to have a structure in which a positive electrode tab and a cap assembly were coupled to each other by welding, were manufactured.

A paste-phase adhesion unit was manufactured in the same manner as in Example <NUM>, except that <NUM> wt% of silver, as a conductive material, was used and no gas-generating material was used, unlike Example <NUM>, and then five cylindrical secondary batteries, each having the adhesion unit added thereto, were manufactured.

Variation in the resistance of a secondary battery depending on temperature was measured using the cylindrical secondary batteries manufactured according to Examples <NUM> to <NUM> and Comparative Examples <NUM> and <NUM>, and the results are shown in <FIG>.

Resistance measurement was performed by measuring resistance using a <NUM> AC resistor, and <FIG> shows the average of voltages depending on SOC (%) of five samples used under each condition.

Referring to <FIG>, it can be seen that, in the case of Comparative Example <NUM>, in which welding was used in order to couple the positive electrode tab, Comparative Example <NUM>, in which no gas-generating material was added, and Comparative Example <NUM>, in which <NUM> wt% of the gas-generating material was added, voltage increased as charging advanced (SOC increased), and the increase of voltage was relatively prominent in some periods; however, the voltage did not reach a charge end voltage (<NUM>.

Consequently, it is not possible to obtain an effect in which the voltage reaches the charge end voltage and thus the flow of current is interrupted.

However, in the case of Example <NUM>, in which <NUM> wt% of the gas-generating material was added, and Example <NUM>, in which <NUM> wt% of the gas-generating material was added, voltage abruptly increases starting at an SOC of about <NUM>%, and, as a result, the voltage increases to <NUM>. 4V or higher.

Consequently, the flow of current is interrupted, whereby it is possible to prevent the explosion of the battery due to overheating thereof.

Those skilled in the art to which the present invention pertains will appreciate that various applications and modifications are possible based on the above description, within the scope of the appended claims.

As is apparent from the above description, in a cylindrical secondary battery according to the present invention, electrical connection between an electrode assembly and a cap assembly is achieved using an adhesion unit including an adhesive material, whereby it is possible to prevent foreign matter from being generated in the process of connecting the electrode assembly and an electrode terminal to each other.

In addition, the adhesion unit includes a gas-generating material. When the voltage of the battery increases due to an increase in the temperature of the battery, therefore, the reaction of the gas-generating material progresses, whereby the coupling force of the adhesion unit is reduced. Consequently, it is possible to achieve rapid separation between an electrode tab and the cap assembly.

Claim 1:
A cylindrical secondary battery comprising:
a jelly-roll type electrode assembly (<NUM>) configured to have a structure in which a sheet type positive electrode and a sheet type negative electrode are wound in a state in which a separator is disposed between the positive electrode and the negative electrode;
a cylindrical battery case (<NUM>) configured to receive the jelly-roll type electrode assembly (<NUM>); and
a cap assembly (<NUM>) mounted to an open upper end of the cylindrical battery case (<NUM>), wherein
a lower end surface of the cap assembly (<NUM>) is connected to a positive electrode tab (<NUM>) of the jelly-roll type electrode assembly via an adhesion unit (<NUM>), and
the adhesion unit (<NUM>) comprises an adhesive material (<NUM>), a conductive material (<NUM>), and a gas-generating material (<NUM>),
wherein a content of the gas-generating material (<NUM>) is greater than <NUM> wt% to <NUM> wt% of a content of the conductive material (<NUM>), and
wherein the cap assembly (<NUM>) is configured to have a structure which comprises a venting member (<NUM>) and from which a PTC element and a current interrupt device are omitted, the venting member (<NUM>) is located at a lower end of the cap assembly (<NUM>), and the jelly-roll type electrode assembly (<NUM>) extends so as to have an additional length corresponding to a thickness of the PTC element and the current interrupt device, which are omitted.