KR20190094828A - A cylindrical type Li-ion secondary battery - Google Patents

Abstract

The present invention relates to a cylindrical lithium secondary battery having a structure in which a cap assembly is mounted on an open upper end of a cylindrical can where an electrode assembly is accommodated together with an electrolyte. The cylindrical lithium secondary battery comprises: a can member in which the electrode assembly is embedded; a cap assembly which includes a safety vent for discharging a gas when an internal pressure of a cylindrical can is increased by a generated gas; and a shape memory alloy member which is deformed when reaching a specific temperature and causes cracks of the can member, wherein the shape memory alloy member is included in a part of the can member. The cylindrical lithium secondary battery of the present invention has, on a part of a cylindrical can member, a fracture portion made of a different material from the can member so as to lengthen a gas ejection passage through which an internal gas of the can member is ejected, thereby preventing gas ejection from being concentrated only on a lid of an upper portion of the can member and reducing gas explosive power. Also, the cylindrical lithium secondary battery includes the shape memory alloy member which causes cracks of the can member by deformation when reaching a specific temperature, in a part of the can member, thereby discharging a gas through a can vent induced by cracks of the can member before a top cap safety vent by an internal pressure is operated, to prevent explosion and prevent ignition which may be generated while being heated by external heat.

Description

Cylindrical lithium secondary battery {A cylindrical type Li-ion secondary battery}

The present invention relates to a cylindrical lithium secondary battery, wherein a portion of the cylindrical can member is formed with a break portion of a different material from the can member to increase the gas ejection passage through which the internal gas of the can member is ejected, whereby It is possible to reduce the gas explosion force by preventing the concentration of only the cap, and by forming a shape memory alloy in a specific section of the inner circumference of the cylindrical can member, cracking by expansion or contraction of the cylindrical can member when the specific temperature is reached. The gas can be discharged and generated, and the shape memory alloy is formed by selecting a shape memory alloy formed in a specific section around the inside of the cylindrical can member by selecting a specific shape pattern, a specific shape point and a straight shape. It can be made in various forms to provide the convenience of the manufacturer, and the flow of gas from the existing secondary battery Can be improved from the use of the cylindrical secondary battery by adding a safety device through the configuration of the shape memory alloy in a specific section of the periphery of the inside of the can member. A secondary battery technology.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches on lithium secondary batteries with high energy density and discharge voltage have been conducted and commercialized. It is widely used.

According to the shape of the battery case, the secondary battery is a cylindrical battery cell in which the electrode assembly is embedded in a cylindrical or rectangular metal can and a pouch type battery cell in which the rectangular battery cell and the electrode assembly are embedded in a pouch type case of an aluminum laminate sheet. Are classified. Among them, the cylindrical battery cell has a relatively large capacity and structurally stable.

The electrode assembly embedded in the battery case is a power generator capable of charging and discharging including a positive electrode (cathode), a separator, and a negative electrode (anode), and a jelly wound between a long sheet-type positive electrode and a negative electrode coated with an active material through a separator. It is classified into a roll type and a stack type in which a plurality of positive and negative electrodes of a predetermined size are sequentially stacked in a state where a separator is interposed therebetween. Among them, the jelly-roll type electrode assembly has advantages of easy manufacturing and high energy density per weight.

In this regard, Figure 1 schematically shows a vertical cross-sectional perspective view of a typical cylindrical battery cell.

Referring to FIG. 1, the cylindrical battery cell 100 receives a jelly-roll type (wound) electrode assembly 120 in a cylindrical can 130 and injects an electrolyte solution into the cylindrical can 130, followed by a case 130. ) Is manufactured by combining the top cap 140 having an electrode terminal (for example, a positive electrode terminal; not shown) formed at an open upper end thereof.

The electrode assembly 120 has a structure in which a cathode 121, a cathode 122, and a separator 123 are interposed therebetween, and are wound in a round shape. A cylindrical center pin is formed at its core (center of jelly-roll). 150 is inserted. The center pin 150 is generally made of a metal material to impart a predetermined strength, and has a hollow cylindrical structure in which a plate is rounded. The center pin 150 acts as a passage for fixing and supporting the electrode assembly and for discharging gas generated by internal reaction during charging and discharging and operation.

On the other hand, lithium battery cells have the disadvantage of low safety. For example, when the battery is overcharged to approximately 4.5 V or more, decomposition reaction of the positive electrode active material occurs, dendrite growth of lithium metal at the negative electrode, decomposition reaction of electrolyte solution, etc. occur between the electrodes. In this process, heat is accompanied, such decomposition reactions and a number of side reactions are rapidly progressed, generating a large amount of gas, which causes a so-called swelling phenomenon in which the battery cells swell.

Therefore, in order to solve this problem, a typical cylindrical battery cell has a current interrupting member (CID) and a safety vent for blocking current and releasing internal pressure during abnormal operation of the battery. It is mounted in the space between the caps.

Nevertheless, such a conventional cylindrical secondary battery has a high internal pressure gas in a test such as a direct thermal shock that does not give enough time for the safety device such as the current interrupt device (CID), vent (Vent), etc. When the gas is ejected to the outside instantaneously because the ejection opening is a single top cap, the discharge pressure is increased, the internal electrode assembly is discharged to the outside with the exhaust gas has a problem that a strong explosion occurs.

Korea Patent Publication 10-2007-0006248 (Published: 2007.01.11.)

Accordingly, the present invention is conceived to solve the above problems, by forming a break portion of the can member and the other material in a portion of the cylindrical can member to increase the gas ejection passage through which the internal gas of the can member is ejected, the gas ejection can member It is an object of the present invention to provide a cylindrical lithium secondary battery capable of reducing concentration of gas explosion by preventing concentration on only the upper top cap vent.

It is still another object of the present invention to provide a cylindrical lithium secondary battery having improved safety for preventing ignition by adding a safety device in response to an increase in temperature inside and outside the battery.

Another object of the present invention is to configure the shape memory alloy formed in a specific section of the inner circumference of the cylindrical can member by selecting from a specific pattern, a specific shape of the point and a straight shape, the configuration of the shape memory alloy in various forms It can be to provide a cylindrical lithium secondary battery that can provide the convenience of the manufacturer.

The present invention provides a cylindrical lithium secondary battery having a cap assembly mounted on an open upper end of a cylindrical can in which an electrode assembly is accommodated together with an electrolyte, including: a can member in which the electrode assembly is embedded; When the internal pressure of the cylindrical can is increased by the generated gas, the cap assembly including a safety vent for discharging the gas; And a shape memory alloy member in which shape deformation occurs when a specific temperature is reached to cause cracking of the can member, which is included in a part of the can member.

In one embodiment of the present invention, the shape memory alloy member may be one or two or more shape memory alloys selected from the group consisting of nickel-titanium alloy, copper-zinc alloy, gold-cadmium alloy and indium thallium alloy.

In one embodiment of the present invention, the shape memory alloy member may shrink at a temperature of 130 ° C. or higher to cause cracking of the can member. At this time, the volume shrinkage of the shape memory alloy member at a temperature of 130 ℃ or more may be 90% or less.

In one embodiment of the present invention, the shape memory alloy member may be expanded at a temperature of 130 ° C. or more to cause cracking of the can member. In this case, the volume expansion ratio of the shape memory alloy member at a temperature of 130 ° C. or more may be 110 to 200% of the volume expansion ratio of the can member.

In one embodiment of the present invention, the shape memory alloy member may be formed in the horizontal direction of the can member along the circumference of the can member.

In one embodiment of the present invention, the shape memory alloy member does not completely cross the can member, and is formed only on a part of the can member to prevent the can member from being divided into two parts when a crack occurs.

In one embodiment of the present invention, the shape memory alloy member may be formed to traverse in the vertical direction of the can member along the circumference of the can member.

In one embodiment of the present invention, the shape memory alloy member may have one or two or more patterns selected from comb-patterns, straight patterns, check patterns, and cross patterns.

In one embodiment of the present invention, the shape memory alloy member may have one or two or more forms selected from a circle, a rectangle, a triangle, an oval, a rhombus.

Cylindrical lithium secondary battery according to the present invention has the following effects.

First, the present invention forms a break portion of the can member and a different material on a part of the cylindrical can member to increase the gas ejection passage through which the internal gas of the can member is ejected, thereby preventing the gas ejection from being concentrated only on the lid of the upper portion of the can member. It can reduce the gas explosion force.

Secondly, the present invention provides a part of the can member by including a shape-alloy member that forms a crack in the can member when the inside or outside of the battery is exposed to a high temperature environment of 130 ° C. or higher, causing deformation of the can member. Even before the top cap safety vent is operated due to internal air pressure, it prevents explosion by discharging gas through the can vent due to cracking of the can member, and prevents ignition that may occur when heated by internal or external heat. have.

Third, the present invention reacts more sensitively to temperature compared to a case in which a material having a different thermal expansion coefficient is included in a part of the can member, thereby reacting more sensitively to temperature. It can be prevented more efficiently, so that the safety is enhanced.

1 is a schematic diagram of a cylindrical lithium secondary battery according to the prior art.
Figure 2 is a schematic diagram showing a cylindrical lithium secondary battery according to an embodiment of the present invention.
FIG. 3 is a developed view illustrating the can member in FIG. 2.
4 is a schematic view showing a cylindrical lithium secondary battery according to another embodiment of the present invention.
FIG. 5 is a developed view illustrating the can member in FIG. 4.
6A to 6C illustrate a shape memory alloy having a specific shape of a pattern, a specific shape of a point, and a straight line in a specific section of a circumference of a cylindrical can member in each cylindrical lithium secondary battery according to another embodiment of the present invention. It is a figure which shows the form.
7 to 9 are schematic views of the cap assembly according to an embodiment of the present invention.
10A is a photograph of a shape after performing a thermal shock test on the cylindrical secondary battery of the embodiment of the present invention.
10B is a photograph of a shape after the thermal shock test is performed on the cylindrical secondary battery of the comparative example.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. However, the present invention is not limited or limited by the following examples.

2 is a perspective view illustrating a rechargeable battery according to an exemplary embodiment of the present invention, and FIG. 3 is a developed view illustrating the can member in FIG. 2.

2 to 3, the secondary battery 200 according to an embodiment of the present invention includes an electrode assembly (not shown) in which a cathode, a separator, and an anode are stacked, and a can member in which the electrode assembly is embedded. When the internal pressure of the cylindrical can is increased by the generated gas, a cap assembly 220 including a safety vent (not shown) for discharging the gas and a shape deformation occurs when a specific temperature is reached may cause cracking of the can member. The shape memory alloy member 230 is a structure included in a part of the can member.

In the conventional cylindrical secondary battery, when the internal pressure increases, the place where the internal gas is discharged was one top cap safety vent, but in the secondary battery of the present invention, a vent capable of discharging gas to a part of the can member in addition to the top cap safety vent. By forming a gas outlet, the gas outlet can be dispersed to reduce the risk of explosion.

Then, by using the shape memory alloy member in which the shape deformation occurs when a specific temperature is reached, when the internal or external temperature is exposed to a specific temperature of 130 ° C. or more, the shape memory alloy member responding to the specific temperature can be expanded or contracted. By causing a crack in the member, the gas inside can be discharged through the crack, thereby preventing the ignition. That is, in addition to the increase in internal air pressure, there is a feature in that a safety device according to the increase in temperature is added.

The shape memory alloy may be restored to a circular shape after expansion or contraction according to temperature. According to an embodiment of the present invention, the shape memory alloy member may be a nickel-titanium alloy, a copper-zinc alloy, or a gold-cadmium alloy. And it may be one or two or more selected from the group consisting of indium thallium alloy.

In the present invention, the can member refers to a side surface of the cylindrical secondary battery 200, which is not the top / bottom of the battery, and the material of the can member is used as a material of the can member of a general secondary battery. (steel) and the like.

In the present invention, the shape memory alloy member is included in a part of the can member. Since the shape memory alloy is sensitive to a specific temperature, the shape memory alloy member can be effectively reduced even at a minimum ratio as compared with the case where a material having a different thermal expansion coefficient is applied. May cause cracks.

In one embodiment of the present invention, the shape memory alloy member occupies the area of the can member may be 5% to 20% of the total area of the can member, more preferably 10% to 20%. If the area occupied by the shape memory alloy member is less than 5%, it may be insufficient to achieve the object of the present invention, if it exceeds 20%, it is not preferable in terms of economics and morphological stability.

When heat is applied to the can member by a test procedure such as direct thermal shock, the process in which the can member is cracked by the shape-alloy member will be described in more detail.

The shape memory alloy member may shrink or expand in response to a specific temperature, and the shape memory alloy that shrinks at a specific temperature will be described. The shape memory alloy member shrinking at a specific temperature is reduced in volume by heat, while the can member is about to expand, so that a crack occurs between the shape memory alloy member and the can member, and the internal gas can be discharged through the crack. .

In one embodiment of the present invention, the shape memory alloy member may shrink at a temperature of 130 ℃ or more may cause cracking of the can member. At this time, the volumetric shrinkage of the shape memory alloy member at a temperature of 130 ℃ or more may be 90% or less, more preferably 75% or less.

Contrary to the above, when the shape memory alloy member is expanded at a specific temperature, the cracking process of the can member is as follows. When the shape memory alloy member is expanded by heat, a difference in expansion volume occurs between the shape memory alloy member and the can member. That is, the shape memory alloy member is significantly increased in volume due to heat, and the volume increase rate of the can member does not follow the volume increase rate of the shape memory alloy member, causing cracks between the can member and the shape memory alloy member.

In this case, the volume expansion ratio of the shape memory alloy member at a temperature of 130 ° C. or more may be 110 to 200% of the volume expansion ratio of the can member, and more preferably 130 to 200%.

In general, since the can member used in the secondary battery has a property of expanding in volume at a high temperature, when a part of the can member uses a shape memory alloy that shrinks in response to a high temperature, the can member may expand in volume. On the other hand, since the shape memory alloy shrinks, cracking may be better.

However, even when the shape memory alloy whose volume expands in response to a high temperature is used, the volume expansion rate of the shape memory alloy member is larger than the volume expansion rate of the can member, so that sufficient cracking may occur to discharge gas into the can member.

Since the shape memory alloy has a characteristic of rapidly expanding or contracting volume in response to a specific temperature, when the shape memory alloy is included in a part of the can member as in the present invention, a material having a different thermal expansion coefficient from the can member in a part of the can member When compared with the case that includes, the breakage of the can member can occur more quickly.

Thus, by forming the shape memory alloy material on a part of the can member, it is possible to respond quickly to the change of the temperature of the can member, thereby increasing the safety of the secondary battery, and the gas vent is formed in the safety vent and the can member of the cap assembly. When the high-pressure gas is blown, the air pressure is lowered to reduce the explosive force, thereby ensuring the safety of the secondary battery.

A top cap assembly according to an embodiment of the present invention will be described with reference to FIGS. 7 to 9.

Referring to these drawings, the top cap 10 has a positive electrode terminal formed in a protruding shape, and an exhaust port is perforated, and a PTC element for blocking current due to a large increase in battery resistance when the temperature inside the battery increases. Positive temperature coefficient element: 20), in the normal state has a downwardly protruding shape, the safety vent 30 to explode and exhaust gas when the pressure inside the battery rises, and the upper one side is coupled to the safety vent 30 The connection plate 50, which is connected to the anode of the electrode assembly 40, is positioned sequentially.

Therefore, under normal operating conditions, the anode of the electrode assembly 40 is connected to the top cap 10 through the lead 42, the connection plate 50, the safety vent 30, and the PTC element 20 to conduct electricity. .

However, when gas is generated from the electrode assembly 40 due to a cause such as overcharge and the internal pressure increases, as shown in FIG. 3, the safety vent 30 protrudes upward while its shape is reversed. Vent 30 is separated from the connection plate 50, the current is cut off, or as the safety vent 30 is protruded when the pressure rises as shown in Figure 9 bursts to release the gas to the outside to ensure safety.

In the conventional secondary battery, the gas outlet was one safety vent included in the top cap assembly, but in the present invention, by additionally forming a can vent in the top cap safety vent, the gas outlet is dispersed in two places to reduce the risk of explosion. It is effective in preventing ignition by explosion.

In particular, when a fire occurs due to one defective battery during the manufacturing process of the secondary battery, there may be a case where the temperature of the adjacent battery is increased due to radiant heat, but the secondary battery having the top cap vent and the can vent as in the present invention. In this case, cracks in the can member are prevented by the shape memory alloy member reacting at a temperature of 130 ° C. or higher to prevent explosion, thereby preventing chain explosion and fire.

4 is a perspective view illustrating a rechargeable battery according to another exemplary embodiment of the present invention, and FIG. 5 is a developed view illustrating the can member in FIG. 4.

8 to 9, in the secondary battery according to another embodiment of the present invention, the shape memory alloy member 230 may be formed in the horizontal direction of the can member 210 along the circumference of the can member 210. Can be.

In this case, the shape memory alloy member 230 may be formed only on a part of the circumference of the can member 210 without completely crossing the can member 210 to prevent the can member 210 from being bisected when a crack occurs.

6A to 6C illustrate the shape memory alloy member 230 having a specific shape of a pattern and a specific shape in a specific section of the circumference of the cylindrical can member 210 in each cylindrical lithium secondary battery according to an embodiment of the present invention. It is a figure which shows the form comprised with a point and a straight line form.

The shape memory alloy member 230 is configured in a specific section of the circumference of the can member 210, and is configured by selecting from a pattern of a specific shape, a point of a specific shape, and a straight line.

As shown in FIGS. 6A to 6C, a single shape or a plurality of patterns are selected from the shape of the shape memory alloy member 230, and the shape memory alloy member 230 may be selected. As shown in FIGS. 6A to 6C, a single point or a plurality of points may be selected from a circle, a rectangle, a triangle, an ellipse, and a rhombus.

On the other hand, the following describes the effect of the secondary battery according to the present invention through examples, comparative examples and experimental examples. However, the components of the secondary battery used in Examples and Comparative Examples, for example, a positive electrode active material, a negative electrode active material, an electrolyte solution, a separator, etc. are illustrative ones for easily explaining the invention, the secondary battery configuration of the present invention is carried out Not only can be implemented by the configurations used in the examples and comparative examples, but the scope of the present invention is not limited to these alone.

<Production of Electrode Assembly>

A negative electrode slurry was prepared using carbon as a negative electrode active material, carbon black as a conductive material, and SBR and CMC as a binder, and a negative electrode was prepared by coating, drying, and rolling a slurry on a 10 μm Cu foil. A cathode slurry was prepared using Ni rich NMC composite oxide as a cathode active material, carbon black as a conductive material, and PVdF as a binder, and a slurry was coated, dried, and rolled on a 15 µm Al foil to prepare a cathode. After the separation film was interposed between these anodes and cathodes, it was wound up to prepare a jelly-roll electrode assembly.

<Example>

A cylindrical secondary battery was manufactured by accommodating the prepared electrode assembly together with an electrolyte in a cylindrical can including a cap assembly structure illustrated in FIG. 7 and a can member illustrated in FIGS. 2 and 3. At this time, the shape memory alloy member included in a part of the can member made of steel is a nickel-titanium alloy, and expands at a temperature of 130 ° C. or higher, and is 130% of the volume expansion rate of the can member.

Comparative Example

A cylindrical secondary battery was manufactured in the same manner as in the example, except that the entire can member was made of a general steel material.

Experimental Example

After leaving the secondary batteries of Examples and Comparative Examples at a temperature of 135 ° C. for 10 minutes, it was visually checked for ignition and the results are shown in FIGS. 10A and 10B.

As shown in Figure 10a, while the secondary battery of the embodiment cracks due to the expansion of the can member, the safety device works with the top cap vent to reduce the explosive force, did not occur ignition. However, in the secondary battery of the comparative example, as shown in FIG. 10B, the ignition occurred due to the increase in temperature and the increase in the internal pressure, and the electrode assembly was discharged to the outside of the can.

As described above, in the secondary battery of the present invention, cracks are generated in the can member due to external temperature, and thus, a plurality of gas outlets are formed, so that the explosive force is reduced and the safety is improved.

200: secondary battery
210: can member
220: cap assembly
230: shape memory alloy member

Claims (11)

A cylindrical lithium secondary battery having a cap assembly mounted on an open top of a cylindrical can in which an electrode assembly is accommodated together with an electrolyte,
A can member having the electrode assembly embedded therein;
When the internal pressure of the cylindrical can is increased by the generated gas, the cap assembly including a safety vent for discharging the gas; And
The cylindrical lithium secondary battery, characterized in that the shape memory alloy member which causes deformation of the can member when a certain temperature is reached, is included in a part of the can member.
The method of claim 1,
The shape memory alloy member is a cylindrical lithium secondary battery, characterized in that one or two or more shape memory alloys selected from the group consisting of nickel-titanium alloy, copper-zinc alloy, gold-cadmium alloy and indium thallium alloy.
The method of claim 1,
The shape memory alloy member is contracted at a temperature of 130 ° C. or more to cause a cylindrical lithium secondary battery.
The method of claim 1,
The shape memory alloy member is expanded at a temperature of 130 ℃ or more to cause the cylindrical lithium secondary battery, characterized in that the crack of the can member.
The method of claim 3, wherein
A cylindrical lithium secondary battery, characterized in that the volumetric shrinkage of the shape memory alloy member at a temperature of 130 ℃ or more.
The method of claim 4, wherein
A cylindrical lithium secondary battery, characterized in that the volume expansion rate of the shape memory alloy member at a temperature of 130 ℃ or more is 110 to 200% of the volume expansion rate of the can member.
The method of claim 1,
The shape memory alloy member is a cylindrical lithium secondary battery, characterized in that formed in the horizontal direction of the can member along the circumference of the can member.
The method of claim 7, wherein
The shape memory alloy member is formed in only a part of the can member without crossing the can member completely, and a cylindrical lithium secondary battery, characterized in that the can member is prevented from being divided into two when a crack occurs.
The method of claim 1,
The shape memory alloy member is formed to traverse in the vertical direction of the can member along the circumference of the can member.
The method of claim 1,
The shape memory alloy member has a cylindrical lithium secondary battery, characterized in that it has one or two or more patterns selected from the comb pattern, straight pattern, check pattern and cross pattern.
The method of claim 1,
The shape memory alloy member is a cylindrical lithium secondary battery, characterized in that it has a form of one or two or more selected from circular, square, triangular, oval, rhombus.

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