KR101839271B1 - Cylindrical-type secondary battery - Google Patents

Abstract

In the present invention, by using a polymer resin having optimized physical properties according to the position of the gasket in the secondary battery, it is possible to minimize deterioration of the stability of the circular cell due to heat generation that may occur in the battery, The present invention provides a circular secondary battery having an elasticity capable of exhibiting a sufficient buffering effect for a battery to maintain airtightness in the battery.

Description

[0001] CYLINDRICAL-TYPE SECONDARY BATTERY [0002]

The present invention relates to a circular secondary battery, and more particularly, to a circular secondary battery having optimized physical properties according to the position of a gasket, thereby minimizing the deterioration of the stability of the circular secondary battery due to heat generated in the battery, The present invention relates to a circular secondary battery capable of maintaining an airtightness in a battery by having an elastic force capable of exhibiting a sufficient buffering effect against a change in volume within the battery.

2. Description of the Related Art In general, a secondary battery is a battery capable of charging and discharging, unlike a primary battery which can not be charged, and is widely used for power supplies for electronic devices such as mobile phones, notebook computers, camcorders, and electric vehicles. Particularly, the lithium secondary battery has an operating voltage of 3.6 V, which is about three times larger in capacity than a nickel-cadmium battery or a nickel-hydrogen battery widely used as a power source for electronic equipment, and has a high energy density per unit weight. Is rapidly increasing.

These lithium secondary batteries mainly use a lithium-based oxide and a carbonaceous material as a cathode active material and an anode active material, respectively. Also, the lithium secondary battery can be classified into a prismatic battery, a circular battery, and a pouch-type battery.

The lithium ion secondary battery includes an electrode assembly in which an anode / separator / cathode are sequentially arranged, and a casing for sealingly storing the electrode assembly together with the electrolyte solution. In particular, the casing of the rectangular or circular secondary battery has a circular can having an open end and a cap assembly sealingly coupled to the open end of the circular can.

The electrode assembly is classified into a jelly-roll type in which a separator is interposed between an anode and a cathode in the form of sheets coated with an active material, and a stack type in which a separator is interposed between a plurality of positive and negative electrodes of a predetermined size do. The electrode assembly of the jelly-roll type is advantageous in that it is easy to manufacture and has a high energy density per unit weight. In particular, a jelly-roll type electrode assembly is widely used because it can be easily accommodated in a circular can of a circular or prismatic battery. On the other hand, the stacked type electrode assembly is widely used in a pouch type battery.

In the case of the jelly-roll type electrode assembly, the stress is concentrated at the central portion, and the electrode is separated from the separator. Internal shorting tends to occur by penetrating through the metal center pin. Such an internal short circuit is connected to the heat of the battery, decomposing the organic solvent to generate gas, and the pressure inside the battery may be increased to rupture the casing. Of course, an increase in gas pressure inside the battery may also be caused by an internal short circuit due to an external impact.

In order to solve the safety problem of such a battery, the secondary battery basically has a safety element. Particularly, the round cell has safety devices such as a safety vent for discharging high-pressure gas, a current interrupt device (CID) for blocking current when the internal pressure of the battery rises, and a protruding terminal for protecting the devices A cap assembly including a top cap, wherein the cap assembly is sealingly coupled to the circular can by a gasket. In addition to the gasket surrounding the rim of the cap assembly, the circular secondary battery may further include an auxiliary gasket surrounding the outer circumferential surface of the current blocking member.

Generally, the gasket used in the circular battery is composed of polypropylene (PP), but the polypropylene may be damaged or deformed at high temperatures. Particularly, when a circular cell having a larger cross section than the circular can is placed in a high temperature environment, low boiling point solvent vaporizes in the electrolyte to increase the internal pressure of the cell, An increase in internal resistance due to the inflow of air and moisture from the outside, and consequently deterioration of the battery characteristics may be caused.

In order to solve such problems, there is also a demand for efforts to improve the heat resistance of organic electrical materials such as gaskets and sealants having high heat resistance.

Particularly, the auxiliary gasket surrounding the current blocking member blocks the connection between the current blocking member and the safety vent after short-circuiting and short-circuiting of the current blocking member. In a typical circular secondary battery, the position where the current blocking member and the safety vent are present is the inner side of the circular battery and the portion where the positive terminal contacts. In this case, when a high-voltage gas is generated and a high current flows into the battery due to a short circuit from the outside of the battery, high heat may be generated in the current blocking member. Therefore, the auxiliary gasket is exposed to a higher temperature environment than the ordinary gasket, and the auxiliary gasket may be damaged or deformed, so that the safety band and the current blocking member may come into contact with each other even after a short circuit. In this case, A phenomenon may occur. In order to prevent this, research for increasing the heat resistance of the auxiliary gasket is required.

International Publication No. WO 2011-115392 (published on September 22, 2011)

It is an object of the present invention to provide a method for manufacturing a secondary rechargeable battery by minimizing deterioration of the stability of the battery due to heat generated in the rechargeable battery, And to provide a circular secondary battery capable of maintaining airtightness in a battery by having an elastic force capable of exhibiting a sufficient buffering effect against a change.

According to an embodiment of the present invention, there is provided a circular secondary battery including an electrode assembly including a cathode, a cathode, and a separator disposed between the anode and the cathode, Cans; A top cap positioned at an open end of the circular can to seal the circular can and forming a positive terminal; A current blocking member electrically connected to the electrode assembly; The current blocking member is connected to the current blocking member through a connection portion so as to electrically connect the current blocking member and the top cap, and when the gas is generated in the circular can due to an abnormal current, Bent; A first gasket surrounding the outer circumferential surface of the current blocking member and electrically insulated from each other except for a connection portion of the current blocking member and the safety vent; And a second gasket interposed between the circular can and the top cap, wherein the first gasket comprises a high molecular weight resin having a heat deflection temperature (HDT) of 150 ° C to 300 ° C, Wherein the gasket comprises a polymer resin having a flexural modulus of 300 MPa to 2000 MPa and a tensile strength of 15 MPa to 60 MPa.

According to another embodiment of the present invention, there is provided a battery module and a battery pack each including the above-described circular secondary battery as a unit cell.

INDUSTRIAL APPLICABILITY The circular secondary battery according to the present invention has optimized physical properties according to the position of the gasket, thereby minimizing the deterioration of the stability of the battery due to the heat generated in the battery. In particular, by using a heat-resistant polymer resin having a high thermal deformation temperature as the polymer resin of the first gasket which is located at the center of the circular secondary battery and can be exposed to a relatively high temperature, short- The second gasket, which prevents contact with the current blocking member and is more directly in contact with the external impact and the change in the internal volume of the battery, includes an elastic polymer having an excellent elastic force, So that the airtightness in the battery can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a cross-sectional view of a circular secondary battery according to an embodiment of the present invention.
2 is a cross-sectional view of a circular secondary battery according to another embodiment of the present invention.
3 is a cross-sectional view illustrating a gasket used in a circular secondary battery according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

A circular secondary battery according to an embodiment of the present invention is a circular secondary battery including an electrode assembly including a cathode, a cathode, and a separator disposed between the anode and the cathode,

A circular can accommodating the electrode assembly;

A top cap positioned at an open end of the circular can to seal the circular can and forming a positive terminal;

A current blocking member electrically connected to the electrode assembly;

A safety vent which is connected to the current blocking member through a connection portion to electrically connect the current blocking member and the top cap to break the connecting portion when gas is generated in the circular can due to an abnormal current, ;

A first gasket surrounding the outer circumferential surface of the current blocking member and electrically insulated from each other except for a connection portion of the current blocking member and the safety vent; And

And a second gasket interposed between the circular can and the top cap,

The first gasket may include a polymer resin having a thermal deformation temperature of 150 ° C. to 300 ° C. and the second gasket may include a polymer resin having a flexural modulus of 300 MPa to 2000 MPa and a tensile strength of 15 MPa to 60 MPa.

The polymer resin forming the gasket of the secondary battery is required to have electrical insulation and elasticity, mechanical properties such as high heat resistance, impact resistance and durability that can maintain airtightness under severe conditions of high temperature and high humidity inside the battery, Chemical properties are required. Conventional polymer resin gaskets have advantages in mass productivity and the like, but they have low chemical resistance to electrolytic solution, and are liable to be damaged when electrolyte leakage occurs. Also, since the heat resistance is low, airtightness is drastically reduced There was a problem.

On the contrary, in the circular secondary battery according to an embodiment of the present invention, the first gasket and the second gasket have the required optimum physical properties at respective positions, specifically, the heat distortion temperature and the elastic modulus of the above- The generation of heat that can be generated, and the deterioration of the stability of the circular battery due to an external impact or a change in volume in the battery can be minimized.

Specifically, the safety vent and the current blocking member located inside the circular battery generate high-pressure gas at the center of the battery. Particularly, in the current blocking member portion connected to the positive electrode lead, high current due to short- This is where the highest heat is generated. Therefore, in the case of the first gasket surrounding the current blocking member, a higher thermal stability than the second gasket is required. Specifically, the shape of the safety vent bent up to the inside by the high-pressure gas generated inside the battery is reversed upward and short-circuited with the current blocking member, and the current of the circular secondary battery is cut off by this short- When the first gasket surrounding the current blocking member is deformed or damaged due to high temperature, there is a possibility that the safety band is partially in contact with the current blocking member even if its shape is reversed due to high pressure. In this case, since the short circuit of the circular secondary battery is not performed, abnormal charging and discharging due to energization may occur, and as a result, there is a possibility of ignition or explosion of the circular battery.

Accordingly, in the case of the first gasket requiring high heat resistance in the inside of the circular secondary battery, the thermal stability can be improved efficiently in a high temperature environment of the circular secondary battery. On the other hand, in the case of the second gasket in which the sealing property with the outside is emphasized, the gasket has an excellent elastic modulus and a tensile strength, thereby exhibiting a buffering effect against the volume change of the electrode assembly in the circular secondary battery, Further, by showing sufficient mechanical strength required as a gasket, battery safety against physical impact can be further improved.

Specifically, in the circular secondary battery according to an embodiment of the present invention, the polymer resin of the first gasket has a thermal deformation temperature of 150 to 300 캜, more specifically 150 to 260 캜, May have a flexural modulus of 300 MPa to 2000 MPa, a tensile strength of 15 MPa to 60 MPa, more specifically a flexural modulus of 600 MPa to 2000 MPa, and a tensile strength of 25 MPa to 50 MPa.

In the circular secondary battery according to an embodiment of the present invention, the polymer resin of the first gasket and the polymer resin of the second gasket may be in a range satisfying the conditions of the above-mentioned heat distortion temperature, flexural modulus and tensile strength The polymer resin of the first gasket may have a higher thermal deformation temperature than the polymer resin of the second gasket and the polymer resin of the second gasket may have a higher flexural modulus than the polymer resin of the first gasket. When the above-mentioned difference in physical properties is satisfied, it is possible to prevent gasket damage more remarkably and to maintain the airtightness of the battery according to the combination of the first gasket and the second gasket.

In the present invention, the heat distortion temperature can be measured according to ASTM D648, and the flexural modulus can be measured according to ASTM D790 and the tensile strength according to ASTM-D638.

More specifically, in the circular secondary battery according to an embodiment of the present invention, the polymer resin of the first gasket and the second gasket may be a thermoplastic resin satisfying the above-mentioned physical property requirements, The polymer resin of the gasket can be selected from the group consisting of tetrafluoride-perfluoroalkyl vinyl ether copolymer (PFA), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS) and nylon 6 , And 6, and the polymer resin of the second gasket has a flexural modulus of 300 MPa to 2000 MPa, a tensile strength of 15 MPa to 60 MPa, a heat distortion temperature of 120 DEG C to 120 MPa, (PP), tetrafluoride-perfluoroalkyl vinyl ether copolymer (PFA) and polybutylene terephthalate (PBT) at 260 占 폚 It may be one containing any one or a mixture of two or more that are chosen.

Further, in the circular secondary battery according to an embodiment of the present invention, the polymer resin of the first gasket may have an elongation of 40% or more, and the polymer resin of the second gasket may have an elongation of 100% or more. When the elongation percentage satisfies the above-described range of the conditions together with the above-mentioned heat distortion temperature and modulus of elasticity, and further with the above tensile strength, it is possible to further improve battery safety against physical shocks by showing sufficient mechanical strength required as gaskets. In the present invention, the elongation can be measured according to ASTM D638.

Also, in the circular secondary battery according to an embodiment of the present invention, the polymer resin of the first and second gaskets may be made of the same material as that of the first gasket under the condition that the heat distortion temperature, the modulus of elasticity, The polymer resin may have a melting point of 220 캜 to 350 캜 and the polymer resin of the second gasket may have a melting point of 150 캜 to 320 캜. When the above-mentioned physical property condition is satisfied and the above-mentioned melting point range is satisfied, the fluidity of the polymer resin is not exhibited below the melting point even when the electrical short-circuit inside the secondary battery or abnormal overheat due to the external environment is present, Deformation of the structure is suppressed at the portion where the gasket is sealed, and as a result, the airtightness of the gasket can be improved. In the present invention, the melting point can be measured according to ASTM D3418.

Further, in the circular secondary battery according to an embodiment of the present invention, the polymer resin of the first and second gaskets may be made of the same material as the first gasket, And the polymer resin of the second gasket may each independently have a hardness of 150D or less, or 40D to 100D, or 60D to 90D on a Shore Hardness (D-scale) basis. Also, the hardness of 90R to 120R can be expressed based on the R-scale. When the hardness of the polymer resin of the first and second gaskets satisfies the above-described physical conditions and the hardness of the polymer resin of the first and second gaskets satisfies the above-described range, a gap is not opened when the gasket comes into contact with the cap assembly, The risk of breakage can be reduced. In the present invention, the Shore hardness of the D-scale among the hardnesses can be measured according to the method of ASTM D2240, and the hardness of the R-scale can be measured according to ASTM D785.

More specifically, in the circular secondary battery according to an embodiment of the present invention, considering the remarkable improvement effect of the use of the first and second gaskets having optimized physical properties according to respective positions, A high molecular weight resin having a thermal deformation temperature of 150 ° C to 260 ° C, an elongation of 40% or more, and a melting point of 220 ° C to 350 ° C; The second gasket may include a polymer resin having a flexural modulus of 600 MPa to 2000 MPa, a tensile strength of 25 MPa to 50 MPa, an elongation of 100% or more, and a melting point of 150 to 320 ° C.

1 is a cross-sectional view schematically showing a configuration of a circular secondary battery according to an embodiment of the present invention. Referring to FIG. 1, a circular secondary battery 100 according to an embodiment of the present invention includes a circular can 20 for housing an electrode assembly 10 together with an electrolytic solution, an open end of the circular can 20 And a cap assembly 30 that can be sealed.

In the circular secondary battery, the circular can 20 is made of a lightweight conductive metal material such as aluminum or an aluminum alloy, and has a cylindrical structure having an opening portion with an open top and a closed bottom portion opposed to the open portion. The electrode assembly 10 and the electrolytic solution (not shown) are accommodated in the inner space of the circular can 20.

The electrolyte filled in the circular can 20 is for transferring lithium ions generated by the electrochemical reaction of the electrode plate 11 during charging and discharging of the secondary battery 100, A non-aqueous organic electrolytic solution which is a mixture of organic solvents; Or a polymer using a polymer electrolyte.

The electrode assembly 10 housed in the circular can 20 includes two electrode plates 11 having a wide plate shape and different in polarity from each other and having a plurality of electrode plates 11 mutually insulated from each other And a separator 12 interposed between the counter electrode plates 11 or disposed on the left or right of one of the electrode plates 11. The laminated structure may also be wound in the form of a 'jelly roll'. Of course, the positive electrode plate and the negative electrode plate of a predetermined size may be stacked with the separator interposed therebetween. The two electrode plates 11 are a structure in which an active material slurry is applied to a metal foil or metal mesh type current collector including aluminum and copper, respectively. The slurry is usually formed by stirring granular active materials, auxiliary conductors, binders, plasticizers, etc. in a solvent-added state. The solvent is removed in the subsequent process. There may be an uncoated portion where the slurry is not applied to the starting end and the end of the current collector in the direction in which the electrode plate 11 is wound. A pair of leads corresponding to the respective electrode plates 11 are attached to the non-coated portion. The first lead 13 attached to the upper end of the electrode assembly 10 is electrically connected to the cap assembly 30 and the second lead (not shown) attached to the lower end of the electrode assembly 10 is connected to the circular can 20 ). Of course, both the first lead 13 and the second lead may be drawn in the direction of the cap assembly 30. The electrode assembly 10 is disposed on a first insulating plate (not shown) provided on the bottom of the circular can 20 and a second insulating plate (not shown) is disposed on the top of the electrode assembly 10. The first insulating plate insulates between the electrode assembly 10 and the bottom of the circular can 20 and the second insulating plate insulates between the electrode assembly 10 and the cap assembly 30.

A center pin (not shown) is provided at the center of the circular can 20 to prevent the electrode assembly 10 wound in the form of a jelly roll from unwinding and to serve as a gas passage for the interior of the secondary battery 100. May be inserted. A bead portion 24 which is press-bent from the outside to the inside is provided at the upper portion of the circular can 20, that is, at the upper end of the electrode assembly 10, so that the upward and downward movement of the electrode assembly 10 can be prevented .

Also, in the circular secondary battery, the cap assembly 30 is assembled to the opening of the circular can 20 in a state of being hermetically sealed with a gasket interposed therebetween. The circular can is sealed at the open end of the circular can, A top cap 32 forming a positive electrode terminal; A current blocking member (38) electrically connected to the electrode assembly; The current blocking member is connected to the current blocking member through a connection portion to electrically connect the current blocking member and the top cap. When the gas is generated in the circular can due to an abnormal current, And includes a safety vent 36.

In the cap assembly 30, the top cap 32 has electrode terminals (not shown) formed to be electrically connected to the outside.

In addition, in the cap assembly 30, the safety vent 36 is bent so as to surround the outer circumferential surface of the top cap 32. The safety vent 36 protrudes to the center, (CID) < / RTI >

The safety vent 36 functions to cut off current or discharge gas when pressure inside the battery rises, and may be made of a metal material. The thickness of the safety vault 36 may vary depending on material, structure, etc., and is not particularly limited as long as it can discharge gas while being ruptured when a predetermined high pressure is generated in the battery. For example, it may be 0.2 to 0.6 mm. The thickness of the portion of the top cap 32 that is in contact with the safety vault 36 is not particularly limited as long as it can protect various components of the cap assembly from external pressure. For example, 0.3 to 0.5 mm. If the thickness of the portion of the top cap 32 is too thin, it is difficult to exhibit a predetermined mechanical rigidity. On the other hand, if the thickness is too large, the capacity of the battery may be reduced by the increase in size and weight.

In addition, in the cap assembly 30, the current blocking member 38 may be deformed together with the safety vent 36 by the internal pressure of the secondary battery 100, and may be a current interrupt device , CID) gaskets and CID filters.

In the circular secondary battery, the cap assembly 30 may include a positive temperature coefficient (PTC) element 34 between the safety vault 36 and the top cap 32. More specifically, the cap assembly 30 includes a top cap 32 sealing the open end of the circular can 20 and contacting the protrusion of the gasket, A safety vent 36 electrically connected to the electrode assembly 10 is disposed so that one surface thereof is in contact with the PTC device 34 and a part of the other surface is in contact with the concave and convex portions of the gasket, .

The thickness of the PTC device 34 may vary depending on the material and the structure. For example, the thickness of the PTC device 34 may be 0.2 mm To 0.4 mm. If the thickness of the PTC element 34 is larger than 0.4 mm, the internal resistance is increased and the size of the battery can be increased to reduce the capacity of the battery compared to the same standard. On the contrary, if the thickness of the PTC element is thinner than 0.2 mm, it is difficult to exhibit a desired current blocking effect at a high temperature and can be broken even by a weak external impact. Therefore, the thickness of the PTC element 34 can be appropriately determined within the above-mentioned thickness range taking these points into consideration in combination. The thickness of the portion of the top cap 32 that is in contact with the PTC element 34 is not particularly limited as long as it can protect various components of the cap assembly 30 from external applied pressure, 0.3 to 0.5 mm. If the thickness of the portion of the top cap 32 is too thin, it is difficult to exhibit mechanical rigidity. On the other hand, if the thickness is too large, the capacity of the battery may be reduced compared to the same standard due to increase in size and weight.

The circular secondary battery 100 including the cap assembly 30 having the top cap 32, the PTC element 34 and the safety vents 36 can be used as a power source for a mobile phone, a notebook computer, . However, a lithium secondary battery having a structure including a top cap, a PTC device, and a safety vent may be difficult to instantaneously provide a high output, and when an external shock such as vibration occurs, the resistance of the contact surface changes to provide a uniform output There may be difficulties. Specifically, a PTC device generally exhibits an electric resistance of about 7 to 32 mΩ at room temperature, and further causes a steep resistance increase due to a rise in temperature, and as a result, it can act as a large inhibitor to provide a high output instantaneously It is because. This is because the contact surface of the top cap, the PTC device, and the safety vault may not provide a uniform output because the change of resistance becomes very large during an external impact such as vibration.

The circular secondary battery includes a first gasket 42 surrounding the outer circumferential surface of the current blocking member 38 and electrically insulated from each other except for a connection portion between the current blocking member 38 and the safety vent 36 ); And a second gasket 40 interposed between the circular can 20 and the cap assembly 30, more specifically between the circular can 20 and the top cap 32. The types and characteristics of the polymer resin constituting the first gasket 42 and the second gasket 40 are the same as those described above.

Specifically, the first gasket 42 is configured to surround the outer circumferential surface of the current blocking member 38 as a gasket for a current blocking member. Particularly, the first gasket 42 contacts the upper and side portions at the outer peripheral surface of the current blocking member 38 to support the upper and side portions of the current blocking member 38. The first gasket 42 is formed so that the current blocking member 38 and the safety vent 36 are electrically insulated from each other except for a portion where the projecting portion of the safety vault 36 and the current blocking member 38 are in contact with each other. .

One end of the second gasket 40 facing the inner surface of the circular can 20 is open toward the center of the circular can 20, that is, at the clamping portion. A structure bent at right angles is preferable. The other end of the second gasket 40 is initially straightened to be oriented in the axial direction of the circular second gasket 40 and bent at right angles toward the central portion during the pressing process with the circular can 20, And are brought into contact with the top surface of the cap assembly 30 and the inner surface of the round can 20, respectively.

More specifically, the second gasket 40 has a recessed portion 50 formed on the surface of the second gasket 40 contacting the lower surface of the safety vane 36, 2 gasket (40).

Since the interface between the cap assembly 30 and the second gasket 40 and particularly the interface between the second gasket 40 and the safety can 36 is highly likely to leak electrolyte or gas, (50) are formed, it is possible to prevent the leakage of the electrolyte or gas from the interface between the safety vents until the safety vents are short-circuited, thereby greatly improving the safety of the battery.

When the cap assembly 30 is assembled with the circular can of the battery through the second gasket 40 by a mechanical pressing process (a cramping process), the concavoconvex portion 50 is formed in the gap between the cap assembly and the second gasket Thereby improving the bonding force. This is because the contact area between the metallic top cap 32 and the safety vault 36 is increased by providing concave and convex portions on the upper and lower surfaces of the second gasket 40 to increase the contact area between the cap assembly 30 and the second gasket 40 As shown in Fig.

The concavo-convex part 50 may be further formed on the surface of the cap assembly 30 which contacts the gasket. When the concave and convex portions are formed on the surfaces of both the second gasket 40 and the cap assembly 30, which are in contact with each other, the coupling property between the two gaskets is further increased, and leakage of the can-part can be prevented.

The concavo-convex part 50 may be constructed so as to be able to secure the bonding force between the second gasket 40 and the cap assembly 30, and should not have any particular limitation on its position, size, shape, and the like. However, the concave-convex portion may have a triangular, square, trapezoidal or semicircular cross-sectional structure.

The protrusions 60 may be triangular, square, trapezoidal, or semicircular in cross-section, and when assembled with the circular can of the battery, may contact the top surface of the second gasket and cap assembly, Since the contact area of the second gasket is increased and the protrusions are compressed much more than the other portions, the bonding force, adhesion (fixability) and shape bridge between the contacting interfaces can be improved. Further, the protruding portion may be formed with a barbed portion in the form of a conventional fishing needle at the end portion of the protrusion to further improve the bonding force and / or adhesion between the interfaces.

When the second gasket has the protrusions 50 and protrusions 60, the safety vents electrically connected to the electrode assembly are in contact with both the side surface, the top surface, and the bottom surface of the top cap, And may be bent and arranged to be in contact with the projection. When the cap assembly in the circular secondary battery includes a safety vault having the above-described structure, when the cap assembly is used as a power source for a power tool such as an electric drill or the like, it can provide an instantaneous high output, It can also be stable against external physical impacts.

Also, in the cap assembly 30 in which the safety vent 36 is bent so as to surround the top cap 32, the contact surface between the safety vent and the top cap can form one or more connection portions, do. The term "welding" used in the present invention is used not only in terms of welding such as laser welding, ultrasonic welding and resistance welding, but also as a concept including a fastening method such as soldering. Welding may be performed during assembly of the cap assembly itself, or may be performed with the cap assembly installed in the can. Since the upper surface of the safety vent having such a welded portion does not have a smooth surface and can have a somewhat irregular surface irregularities, the protrusions provided on the top and bottom surfaces of the gasket are firmly bonded to the uneven surface to effectively prevent electrolyte leakage can do.

2 is a cross-sectional view schematically showing the configuration of a secondary battery according to another embodiment of the present invention. The same components as those shown in Fig. 1 are the same members having the same function.

2, the second gasket 40 of the cap assembly 30 has a lower end portion extending to the lower portion of the current blocking member 38 and a lower end portion of the second gasket 40 extending downward from the lower portion of the current blocking member 38. [ Respectively. Thus, the second gasket 40 supports and simultaneously protects the current blocking member 38 together with the first gasket 42. According to the structure of the second gasket 40, when the impact is applied to the side surface of the circular can 20 and the circular can 20 is deformed inward, the lower end of the second gasket 40 is pressed against the current- The second gasket 40 more tightly covers the lower portion of the current blocking member 38 because the gasket 40 is further moved inward from the lower portion of the current blocking member 38.

FIG. 3 is a cross-sectional view of a second gasket of a secondary battery according to an embodiment of the present invention before and after the pressing process.

Referring to FIG. 3, the other end of the second gasket 40 extends straight first and is directed in the axial direction of the circular second gasket 40. The second gasket 40 is bent at right angles toward the center portion during the pressing process with the circular can 20 A concavo-convex portion 50 having two or more concavo-convex structures on a lower surface that is bent and facing each other, and a protrusion 60 on the upper surface. The concave-convex part 50 and the protruding part 60 may not be actually observed because they are tightly bonded to the top cap or the safety vant during the assembling process of the battery and are pressed.

In the circular secondary battery, the positive electrode lead welded to the positive electrode foil of the jelly-roll type electrode assembly is electrically connected to the cap assembly and connected to the protruding terminal at the top end of the top cap, And the circular can itself is welded to the closed end to constitute the cathode terminal. When the electrode assembly is housed in the circular can, the electrolyte is injected, and the cap assembly is attached to the open end of the circular can to seal the secondary battery.

The circular secondary battery according to an embodiment of the present invention may be a lithium ion secondary battery having high energy density, discharge voltage, and high output stability. Such a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte containing a lithium salt, and the like. The positive electrode is prepared, for example, by applying a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, followed by drying and, if necessary, further filling a filler. The negative electrode is manufactured by coating and drying the negative electrode active material on the negative electrode collector, and may further include the above-described components as necessary. The separator is interposed between the cathode and the anode, and an insulating thin film having high ion permeability and mechanical strength is used. The lithium salt-containing nonaqueous electrolyte solution is composed of a nonaqueous electrolytic solution and a lithium salt, and the nonaqueous electrolytic solution is a liquid nonaqueous electrolytic solution, a solid electrolyte, an inorganic solid electrolyte, or the like. Here, a current collector, an electrode active material, a conductive material, a binder, a filler, a separator, an electrolytic solution, a lithium salt, and the like are well known in the art, and a detailed description thereof will be omitted.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples. However, the following Examples and Experimental Examples are provided for illustrating the present invention, and the scope of the present invention is not limited by these Examples and Experimental Examples.

Examples 1-1 to 2-4

* A top cap and a circular case were fabricated using SPCE (cold rolled steel plate) plated with Ni, a circular case electrode assembly was mounted, a beading process was performed on a circular case corresponding to the upper end of the electrode assembly, And formed on the inner surface of the crimping portion with a polymer resin as shown in Table 1 below and provided with concavities and convexities having three irregularities of a triangular cross section and projections having a triangular cross section on the upper surface on the lower surface of the bent inner circumferential surface A second gasket was inserted.

Thereafter, a current blocking member was mounted and a first gasket made of the polymer resin described in Table 1 was mounted on the rim of the current blocking member. Thereafter, the current blocking member was joined to the safety vant via laser welding. At this time, welding was performed at a power of about 5% higher than the rated welding power. Then, the PTC element and the top cap were mounted, the upper end of the can was bent inward, and then subjected to a clamping and pressing process to produce a circular preform of 18650 size (18 mm in diameter, 65 mm in length).

Comparative Examples 1-1 to 3-7

A circular secondary battery was fabricated in the same manner as in Example 1, except that the first and second gaskets of the polymer resin having the physical properties as shown in Table 1 were used.

Experimental Example: Evaluation of Heat Resistance and Electrolyte Leakage

The circular secondary batteries prepared in the above Examples and Comparative Examples were stored in a high-temperature storage chamber at 200 ° C for 1 hour to evaluate heat resistance. In addition, it was confirmed whether the electrolytic solution was leaked or not. The results are shown in Table 1 below.

The first gasket polymer resin Second Gasket Polymer Resin Is short circuit (current interruption)? Electrolyte leakage Example 1-1 PFA PP paragraph No leakage Examples 1-2 PBT paragraph No leakage Example 1-3 PPS paragraph No leakage Examples 1-4 Nylon 6,6 paragraph No leakage Comparative Example 1-1 PP Short paragraph No leakage Comparative Example 1-2 TPEE Short paragraph No leakage Comparative Example 1-3 PET Short paragraph No leakage Example 2-1 PFA PBT paragraph No leakage Example 2-2 PBT paragraph No leakage Example 2-3 PPS paragraph No leakage Examples 2-4 Nylon 6,6 paragraph No leakage Comparative Example 2-1 PP Short paragraph No leakage Comparative Example 2-2 TPEE Short paragraph No leakage Comparative Example 2-3 PET Short paragraph No leakage Comparative Example 3-1 PFA PET Short paragraph Leakage Comparative Example 3-2 PBT Short paragraph Leakage Comparative Example 3-3 PPS Short paragraph Leakage Comparative Example 3-4 Nylon 6,6 Short paragraph Leakage Comparative Example 3-5 PP Short paragraph Leakage Comparative Example 3-6 TPEE Short paragraph Leakage Comparative Example 3-7 PET Short paragraph Leakage

The physical properties of the polymer resin used in the gasket fabrication of the above Examples and Comparative Examples are shown in Table 2 below.

PP PFA PBT TPEE PET PPS Nylon 6,6 Heat distortion temperature
(° C) 124 260 154 117 70 170 225 Melting point (캜) 165 306 225 208 253 280 260 Flexural modulus (MPa) 1340 600 2000 358 6500 2200 2200 Tensile Strength (MPa) 28 32 48 18 80 70 65 Elongation (%) > 400 410 100 > 400 59 50 40 Hardness
(R-scale, D-scale) 92R 60D 118R 65D 110R 118R 113R

In Table 2, the heat distortion temperature was measured according to ASTM D648.

The melting point was measured according to ASTM D3418.

The flexural modulus was measured according to ASTM D790.

The tensile strength and elongation were measured according to ASTM-D638.

The shore hardness of the D-scale in terms of hardness was measured by the method of ASTM D2240, and the hardness of the R-scale was measured by ASTM D785.

As a result of the experiment, all of the circular secondary batteries of Examples 1-1 to 1-3, and Examples 2-1 to 2-4 including the first and second gaskets satisfying the physical property requirements of the present invention, The shape was maintained, and short-circuit and electrolyte leakage due to contact between the case and the top cap did not occur. However, in the case of the circular secondary batteries of Comparative Examples 1-1 to 1-3 and Comparative Examples 2-1 to 2-3, which did not satisfy the above physical property requirements, the gasket melted and the case and the top cap contacted with each other and a short circuit occurred . In Comparative Examples 3-1 to 3-7 in which PET, which does not satisfy the conditions of flexural modulus and tensile strength, was used as the second gasket resin, electrolyte leakage was observed irrespective of the type of resin of the first gasket.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

10 Electrode Assembly 11 Electrode Plates
12 Membrane 13 First lead
14 2nd insulation plate 20 round can
24 beading portion 30 cap assembly
32 Top Cap 34 PTC Device
36 Safety Vents 38 Current blocking members
40 second gasket 42 first gasket
50 protrusions 60 protrusions
100 circular secondary battery

Claims (10)

1. A circular secondary battery comprising an electrode assembly comprising an anode, a cathode, and a separation membrane positioned between the anode and the cathode,
A circular can accommodating the electrode assembly ;
A top cap positioned at an open end of the circular can to seal the circular can and forming a positive terminal ;
A current blocking member electrically connected to the electrode assembly ;
A safety vent which is connected to the current blocking member through a connection portion to electrically connect the current blocking member and the top cap to break the connection portion when gas is generated in the circular can due to an abnormal current, ;
A first gasket surrounding the outer circumferential surface of the current blocking member and electrically insulated from each other except for a connection portion of the current blocking member and the safety vent; And
And a second gasket interposed between the circular can and the top cap,
Wherein the first gasket comprises a tetrafluoride-perfluoroalkyl vinyl ether copolymer (PFA), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS) and nylon 6 , ≪ / RTI > 6,
Wherein the second gasket comprises at least one selected from the group consisting of tetrafluoride-perfluoroalkyl vinyl ether copolymer (PFA) and polybutylene terephthalate (PBT). The method according to claim 1,
Wherein the polymer resin of the first gasket has an elongation of 40% or more and the polymer resin of the second gasket has an elongation of 100% or more. The method according to claim 1,
And the second gasket surrounds the lower surface of the first gasket and the current blocking member. The method according to claim 1,
Wherein the second gasket is bent and interposed between an upper end of the circular can and an upper and a lower lateral face opposing between the cap assembly,
Wherein a convex portion is formed in an inner peripheral portion of a lower lateral surface of the gasket, a protruding portion is formed on an inner peripheral portion of the upper lateral surface, and a rim of the safety vent is inserted between the protruding portion and the protruding portion / RTI > 5. The method of claim 4,
Wherein the protrusions and the protrusions independently have a triangular, rectangular, trapezoidal, or semicircular cross-sectional structure. 5. The method of claim 4,
Wherein the protrusions or protrusions further comprise barbs. The method according to claim 1,
And a PTC device disposed to contact the top cap. A battery module comprising the circular secondary battery according to any one of claims 1 to 7 as a unit cell. A battery pack comprising the battery module according to claim 8. 10. The method of claim 9,
Wherein the battery pack is used as a power source for a middle- or large-sized device selected from the group consisting of a power tool, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

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