KR20080030702A - Cylindrical secondary battery including isolating member preventing movement of jelly-roll and center pin - Google Patents

Abstract

A cylindrical secondary battery including an insulation member is provided to prevent a short caused by movements of a jelly roll and/or a center pin upon the application of strong impacts such as dropping, and to allow effective discharge of a large amount of gas generated inside a battery. A cylindrical secondary battery comprises a jelly roll received in a cylindrical battery casing, and a plate-like insulation member(600) mounted to the top of the jelly roll, the insulation member having a central opening(610) and a plurality of through holes(620) around the central opening for the discharge of gases and connection of electrode terminals. The plate-like insulation member has a trapezoidal protrusion(630) covering 30-50% of the area of an imaginary circle corresponding to the central opening, wherein the top surface of the protrusion locates in the vicinity of the central line of the circle. The plate-like insulation member has a thickness of 0.2-0.6 mm.

Description

Cylindrical Secondary Battery Including Isolating Member Preventing Movement of Jelly-roll and Center Pin}

1 is a schematic cross-sectional view showing a representative upper structure of a conventional cylindrical secondary battery;

2 is a plan view of an insulating member used in the secondary battery of FIG. 1;

3 is a plan view of an insulating member that can be preferably used in the cylindrical secondary battery according to one embodiment of the present invention;

Figure 4 is an actual picture of the insulating member according to Example 1 and Comparative Examples 1 and 2 used in Experimental Examples 1 and 2 of the present invention, and the insulating member used in the prior art;

Figure 5a is a graph comparing the impact strength of the insulating member according to Example 1 and Comparative Examples 1 and 2 with respect to the center pin in Experimental Example 1 of the present invention;

Figure 5b is a graph comparing the impact strength of the insulating member according to Example 2 and Comparative Examples 3 and 4 with respect to the center pin in Experimental Example 1 of the present invention;

6 is a graph comparing the impact strength of the insulating members according to Examples 1, 3 to 6 and the insulating members according to Examples 2, 7 to 9 for the jelly-roll in Experimental Example 2 of the present invention;

7 is photographs showing whether the center pin protrudes according to the thickness of the insulating member when the battery is dropped in Experimental Example 4 of the present invention;

8 is X-ray photographs showing whether the jelly-roll flows according to the thickness of the insulating member when the battery falls in Experimental Example 4 of the present invention;

FIG. 9 is X-ray photographs illustrating the movement of the center pin and the jelly-roll according to the thickness and number of drops of the insulating members when the battery is dropped in Experimental Example 4 of the present invention.

The present invention relates to a cylindrical secondary battery including an insulating member for preventing the flow of the jelly-roll and the center pin, and more particularly, a secondary battery having a structure in which the jelly-roll is mounted in a cylindrical battery case, and discharges gas. And a plate-shaped insulation member mounted at the top of the jelly-roll having an opening drilled in the center and a plurality of through holes periphery thereof for connection of the electrode terminal, and the plate-shaped insulation member mounted at the center opening thereof. The secondary battery is characterized in that the trapezoidal protrusion of the shape of the top surface is located near the centerline of the virtual circle is closed, and the area of 30 to 50% based on the virtual circle of, has a thickness of 0.2 ~ 0.6 mm to provide.

As the development and demand for mobile devices increases, the demand for this secondary battery as an energy source is increasing rapidly. Among the secondary batteries, a lot of research has been conducted on the lithium secondary battery with high energy density and high discharge voltage. It is widely used.

When a secondary battery is used as a power source for a mobile phone or a laptop, a secondary battery that provides a stable output is required, whereas when used as a power source of a power tool such as an electric drill, it provides instantaneous high output while vibrating There is a need for a secondary battery that can be stable against external physical shocks such as falling and the like.

The secondary batteries may be classified according to the shape of the electrode assembly in the battery case. The cylindrical batteries are embedded in the cylindrical metal cans, the rectangular batteries in the rectangular metal cans, and the pouch type cases of the aluminum laminate sheets. There is a pouch type battery. Among them, the cylindrical battery has the advantage of relatively large capacity and structurally stable.

In general, a cylindrical secondary battery is welded to the bottom of the can while the jelly-roll type electrode assembly is mounted in a cylindrical metal can, and the top of the top of the electrode assembly and the electrolyte is sealed to seal the battery in the state. It is manufactured by welding the anode of the electrode assembly to the protruding terminal of the top cap coupled to.

However, lithium secondary batteries which are the mainstream of secondary batteries have a disadvantage of low safety. For example, when the battery is overcharged to about 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, and the like occur. In this process, heat is accompanied, such decomposition reactions and a number of side reactions are rapidly progressed, and the air supply may cause the battery to ignite and explode.

Therefore, in order to solve this problem, a general cylindrical secondary battery is equipped with a CID (Current Interruptive Device) to cut off the current during abnormal operation of the battery and to solve the high withstand voltage in the space between the electrode assembly and the top cap.

In this regard, a structure of a conventional cylindrical secondary battery is shown in FIG. 1, and an insulating member generally used in a cylindrical secondary battery is schematically illustrated in FIG. 2 as a plan view.

Referring to these drawings, the cylindrical secondary battery 100 has a cylindrical can 200, a jelly-roll type electrode assembly 300 accommodated in the can 200, and a cap coupled to an upper portion of the can 200. It is composed of an assembly 400.

The jelly-roll 300 is a structure in which the anode 310, the cathode 320, and the separator 330 are sequentially stacked and wound. The jelly-roll 300 has a cylindrical center pin 350 at its core (center of the jelly-roll). It is inserted. The center pin 350 has a structure in which a plate is rounded, and a through hole 351 is formed at the center thereof, and serves to discharge a large amount of gas generated inside the battery through the through hole 351.

The cap assembly 400 may include a top cap 410 forming a positive electrode terminal, a positive temperature coefficient element 420 blocking a current by greatly increasing battery resistance when the temperature inside the battery increases, and a pressure increase inside the battery. Safety vanes 430 for blocking current and / or exhausting gas, insulating members 440 for electrically separating the safety vanes 430 from the cap plate 450, except for certain parts, and connected to the anode 310. The cap plate 450 to which the positive electrode tab 340 is connected is laminated sequentially.

Therefore, under normal operating conditions, the positive electrode tab 340 of the jelly roll 300 is connected to the upper cap 410 via the cap plate 450, the safety vent 430, and the PTC element 420 to conduct electricity. Achieve.

However, when gas is generated from the jelly-roll 300 side due to a cause such as overcharge and the like, the internal pressure increases, the safety van 430 protrudes upward while its shape is reversed, and the safety van 430 is The current is cut off from the cap plate 450. Therefore, overcharging does not proceed any more to ensure safety. Nevertheless, if the internal pressure continues to increase, the safety vent 430 is ruptured and the pressurized gas is exhausted through the exhaust port of the upper cap 410 via such a rupture portion, thereby preventing the explosion of the battery.

Therefore, when the series of processes are sequentially performed, the safety of the battery can be ensured.

On the other hand, the upper surface of the jelly roll 300 is equipped with an insulating member 500 of the plate-like structure, the gas can be discharged and the positive electrode tab 340 of the jelly roll 300 of the cap assembly 400 An opening 510 is formed at a center thereof in communication with the through hole 351 of the center pin 350 so that it can be connected to the cap plate 450, and a plurality of through holes 520 are formed around the opening 510. Formed. However, when an external impact is applied, the center pin protrudes through the opening 510, which may cause an unnecessary CID short circuit.

In order to prevent the center pin 350 from protruding during an external impact such as a drop of the battery, the diameter of the opening 510 is conventionally formed to be smaller than that of the center pin 350. However, in this case, the opening of the insulating member is made small, which makes it difficult to connect the positive electrode tabs through it.

Therefore, a lot of researches have been conducted on techniques for effectively preventing the discharge of the gas through the opening and the connection of the positive electrode tab, and effectively preventing the protrusion of the center pin due to external impact.

As an example of such a technique, Japanese Patent Application Laid-Open No. 2001-210384 proposes a technique in which a protrusion is formed in the central opening of the insulating member, thereby preventing protrusion of the center pin due to impact. However, according to the experimental results carried out by the inventors of the present application, it is confirmed that the insulation member preferably proposed in the above technique does not effectively prevent the movement of the center pin when a strong impact is applied to the secondary battery by a predetermined value or more. . This fact can be more clearly confirmed through the following examples and comparative examples.

That is, the insulating member according to the prior art is not stable to a strong impact because the portion in contact with the insulating member main body in the protrusion of the opening is very narrow, can damage the electrode tab and the insulating tape of the electrode tab, CID short circuit There are many problems such as this can occur. In addition, if the weight of the center pin is reduced in order to minimize the movement of the center pin, the diameter of the center pin is also reduced. Therefore, when the impact is applied while the center pin is biased from the center of the opening to one side opposite to the protrusion, the center The pin can be easily moved because it is completely out of the protrusion or abuts the end of the protrusion.

On the other hand, the cylindrical secondary battery has a problem that a short circuit is caused by moving the center pin as well as the jelly-roll when the impact is applied to break the insulating member. In particular, since the jelly-roll has a greater weight than the center pin, the insulation member is severely damaged, and since the jelly-roll includes a positive electrode and a negative electrode, the risk of short circuit is very high.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

The inventors of the present application, after repeated in-depth studies and various experiments, in the cylindrical secondary battery, the center opening is closed at 30 to 50% by a trapezoidal protrusion, and the insulating member having a thickness of 0.2 to 0.6 mm is jelly- When mounted on top of the roll, it is possible to prevent CID short circuit due to the movement of the center pin and / or the jelly-roll upon application of a strong impact such as dropping of the battery, and the jelly-roll electrode to the cap assembly through the opening. It was confirmed that the configuration can be connected to the tab, it is possible to effectively discharge a large amount of gas generated inside the battery, and came to complete the present invention.

Accordingly, the cylindrical secondary battery according to the present invention is a secondary battery having a structure in which a jelly-roll is mounted in a cylindrical battery case, and has openings in the center for gas discharge and connection of electrode terminals, and a plurality of peripheral batteries thereof. A plate-shaped insulating member having a perforated hole is mounted on the top of the jelly roll, and the plate-shaped insulating member closes the area of 30 to 50% of its virtual circle in the central opening and near the center line of the virtual circle. The trapezoidal protrusion of the shape which the upper surface is located in is formed, and it is comprised by having a thickness of 0.2-0.6 mm.

The cylindrical secondary battery, by the insulating member of the above structure mounted on the top of the jelly-roll, by suppressing the movement of the center pin and the jelly-roll located at the center of the jelly-roll when the external shock such as dropping Prevents CID operation short circuit due to protrusion of the center pin, and facilitates connection of the electrode tab to the cap assembly despite the suppression of movement of the center pin, and effectively discharges a large amount of gas generated inside the battery. It has advantages.

The preferred structure of the insulating member can be more easily confirmed in FIG. 2 which is schematically shown as a plan view. Since the insulating member as shown in FIG. 2 may be preferably applied to a conventional cylindrical secondary battery generally used, the configuration of the cylindrical secondary battery except for the insulating member is substantially the same as that of FIG. 1.

2, a central opening 610 and a plurality of through holes 620 are formed in the insulating member 600, and a trapezoidal protrusion 630 is formed in the central opening 610. The protrusion 630 has a lower surface having a relatively longer length than the upper surface, and is stably connected to the insulating member 600 at a lower surface having a long length, and has an opening 610 at the side surface due to a difference in length between the lower surface and the upper surface. ) Therefore, by the trapezoidal protrusion 630, the insulating member 600 can effectively prevent the movement of the center pin (350 in FIG. 1), and the electrode to the cap assembly by the opening secured to a predetermined area. It can release a large amount of gas generated inside the tab connection and inside the cell.

As described above, the central opening has a trapezoidal protrusion formed to close an area of 30 to 50% of its imaginary circle, and if the closed area of the trapezoidal protrusion is less than 30%, the flow of the center pin is reduced. It is difficult to provide a strength and structure that can be prevented and, on the contrary, if it exceeds 50%, it is not preferable because the discharge of gas through the opening and the connection of the electrode tab are not easy.

The insulating member is not particularly limited as long as it is an insulating material, and may be formed of various materials, for example, polypropylene resin. Among them, the high-strength polypropylene resin is particularly preferable because it exhibits excellent mechanical rigidity at the same thickness, and can prevent not only the flow of the center pin but also the movement of the jelly-roll upon application of a strong external impact.

Preferred examples of the high-strength polypropylene resin include a longitudinal tensile strength of approximately 37.4 MPa and a widthwise tensile strength of 33.9 MPa, a longitudinal elongation of 633% and a longitudinal elongation of 562%, and a longitudinal direction of 1250 MPa. It may be a resin having physical properties of an elastic modulus and an elastic modulus in a width direction of 1123 MPa (the high-strength polypropylene resin used in Example 2 below is a resin having the physical properties). Since the high-strength polypropylene resin has a particularly high modulus of elasticity as compared to general polypropylene resin, it is possible to appropriately absorb external shocks and to exhibit more excellent impact mitigation effect.

As a result of experiments performed by the inventors of the present application, the insulating member preferably has a thickness of 0.4 mm or more when made of a general polypropylene resin, and preferably has a thickness of 0.2 mm or more when made of a high strength polypropylene resin. . Since the thickness range of the insulation member is a preferred thickness range for preventing the movement of the jelly-roll made of a relatively large weight, the thickness of the insulating member may be smaller than the center pin. However, if the thickness of the insulating member is too thick, the battery capacity is reduced by causing the size of jelly-roll in the battery case (can) of the same standard, so that the battery capacity is preferably 0.6 mm or less.

As described above, since the cylindrical secondary battery according to the present invention is approximately similar to a conventional secondary battery generally used, a description thereof is omitted herein.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

Using polypropylene, an insulating member having a thickness of 0.2 mm and having a trapezoidal protrusion formed in a central opening having a diameter of 5 φ as shown in FIG. 4 (A) was manufactured. The closure rate of the central opening due to the trapezoidal protrusion was 30%. Then, a cylindrical secondary battery was manufactured such that the insulating member was positioned on the top of the jelly-roll in which the cathode / separator / cathode was wound by a center pin.

Example 2

Except that high strength polypropylene was used, the insulating member and the secondary battery were manufactured in the same manner as in Example 1.

[Examples 3 to 6]

Except that the thickness is 0.3, 0.4, 0.5, and 0.6 mm, respectively, the insulating member and the secondary battery were manufactured in the same manner as in Example 1.

[Examples 7 to 10]

An insulating member and a secondary battery were manufactured in the same manner as in Example 1, except that high-strength polypropylene was used and the thicknesses were 0.3, 0.4, 0.5, and 0.6 mm, respectively.

Comparative Example 1

4B, the insulating member and the secondary battery were completed in the same manner as in Example 1, except that a semicircular protrusion was formed in the central opening.

Comparative Example 2

As shown in FIG. 4C, the insulating member and the secondary battery were completed in the same manner as in Example 1, except that a rectangular protrusion was formed in the central opening.

Comparative Example 3

A high-strength polypropylene was used, and the insulating member and the secondary battery were completed in the same manner as in Example 1 except that a semicircular protrusion is formed in the central opening as shown in FIG.

[Comparative Example 4]

High-strength polypropylene was used, and the insulating member and the secondary battery were completed in the same manner as in Example 1, except that a protrusion having a rectangular shape was formed in the central opening as shown in FIG.

[Comparative Example 5]

As in FIG. 2, the insulating member and the battery were manufactured in the same manner as in Example 1, except that the protrusion was not formed in the central opening.

Experimental Example 1

One. Impact test on the center pin

Impact tests on the center pins were performed on the insulating members manufactured in Examples 1 and 2 and Comparative Examples 1 to 4, respectively, and the results were classified according to the materials used for the insulating members. Respectively. In the impact test on the center pin, each of the insulating members was performed in turn, and after mounting the insulating members in the push pull device, the center pin having a diameter of 3.45 φ and a weight of 1 g was directed toward the central opening of the insulating member. The impact force was applied, and the maximum impact force applied to the insulating member was measured until the center pin moved 0.5 mm from the contact with the surface of the insulating member.

2. Overcharge Experiment

The overcharge experiments were performed on the secondary batteries prepared in Example 1 and Comparative Examples 1 and 2, respectively, and the results are shown in Table 1 below. In the overcharging experiment, the overcharge condition was performed up to 250% of the rated capacity at 1 C under full discharge, and the CID short time was measured.

TABLE 1

As shown in Figure 5a and 5b and Table 1, the insulating member of Example 1 of the present invention exhibited a great resistance when the center pin is moved, the battery composed of such insulating member effectively discharges the gas during overcharging to appropriately CID It could short circuit in time. That is, it can be seen that the trapezoidal protrusion formed in the opening of the insulating member effectively prevents the movement of the center pin and can effectively discharge the gas inside the battery. In addition, when the high-strength propylene was used, the overall resistance of the center pin was greatly improved.

While the insulating member of Comparative Example 1 exhibited high resistance when the center pin moved, the CID short circuit was delayed because the internal gas was not effectively discharged. As a result, the battery may not fire and current may ignite. This is because the semicircular projection formed in the opening of the insulating member is connected to the insulating member in a wide width and stable to the impact of the center pin.

In addition, the insulating member of Comparative Example 2 effectively discharged gas inside the battery during overcharging, but had very low resistance when the center pin moved. This is because a rectangular protrusion similar to the structure in which the insulating member of Comparative Example 2 is conventionally used is formed in the opening, so that the opening can be opened to a large extent and is easy to discharge the gas, but is connected to the insulating member in a narrow width so that the center can be easily opened. This is because the pin is not stable to impact.

Experimental Example 2

Impact experiments on the jelly rolls were performed on the insulation members manufactured in Examples 1 to 9, respectively, and the results are classified according to materials and shown in FIG. 6 as graphs. In the impact test on the jelly-roll, it was carried out on each of the insulating members in turn using a rod similar to the jelly-roll, and after mounting the insulating members in the push-pull apparatus, they faced the central opening of the insulating member. An impact was applied to a rod having a diameter of 7 φ and a weight of 50 g so as to measure the maximum impact force applied to the insulating member until the rod moved 0.5 mm from the contact with the surface of the insulating member.

The maximum impact force exerted on the insulating member by the jelly-roll during free fall of the battery is approximately 0.5 kgf by applying the weight of the jelly-roll and the falling speed. That is, as shown in Figure 6, the insulating members of Examples 1 and 3, in which the rod moves by 0.5 mm at a value smaller than 0.5 kgf, do not suppress the movement of the jelly-roll. Therefore, the thickness of the insulating member which can prevent the movement of the jelly-roll when the battery falls is 0.4 mm or more for polypropylene and 0.2 mm or more for high-strength polypropylene. Although the impact force was less than 5 kgf in this experiment, the safety of the center pin was confirmed in Experimental Example 1, Examples 1 and 3 using an insulation member made of polypropylene and having a thickness of 0.2 mm and 0.3 mm, respectively Expressed as However, in the present invention, Examples 1 and 3 are not included as preferred embodiments.

Experimental Example 3

Dropping experiments were performed on the batteries prepared in Examples 1, 2, 4, and 5 and Comparative Examples 2 and 5, respectively, and the results are shown in Tables 2 and 7, 8, and 9, respectively. The drop test was carried out by dropping the motorola method (top / back / side one time each) up to 15 times, and then freely falling in the top direction from 15 times to 30 times, and the short circuit was estimated by measuring the internal voltage of the battery. . In addition, as a result, it is shown in Table 2 by measuring the number of short-circuited batteries at each drop, the disassembly of the battery was confirmed whether the protruding center pin and a photograph thereof is shown in Figure 7, every drop The movement of the center pin and jelly-roll was taken with X-ray photographs and is shown in FIGS. 8 and 9.

TABLE 2

As shown in Table 2, in the battery according to Example 1 using polypropylene having a thickness of 0.2 mm, one short circuit occurred at each of 9, 25, and 30 drops. This is because, as described in Experimental Example 2, the flow of the center pin is suppressed by changing the shape of the insulating member, but the flow of the jelly-roll cannot be suppressed. However, in the cell according to Example 2 using high-strength polypropylene and Example 4 using a general PP having a thickness of 0.4 mm, no short circuit occurred in the drop test. That is, by forming a protrusion in the center opening and mounting an insulating member having a desired thickness on the top of the jelly roll, not only the center pin movement but also the movement of the jelly roll could be prevented.

On the other hand, the batteries of Comparative Examples 2 and 5 was confirmed that the short circuit occurs in a plurality of batteries. It can be seen that the cause of such a short circuit is due to the protrusion of the center pin as shown in FIGS. 7 and 9 or the movement of the jelly-roll as shown in FIGS. 8 and 9.

First, referring to Figure 7, in the battery of the embodiments according to the present invention was not found protruding traces of the center pin during disassembly, but in Comparative Example 5 as shown by the red circle in the battery to find the protruding traces of the center pin Could. 8 and 9, it can be seen that not only the center pin but also the jelly-roll is moved by the empty space inside when the battery falls. In the battery of the embodiments according to the present invention, the insulating member reliably suppresses the movement of the center pin and the jelly-roll in the area where it is located, whereas in the battery of Comparative Example 5, the insulating member moves the center pin and the jelly-roll. It was confirmed that do not suppress. That is, polypropylene has a thickness of 0.4 mm or more, high strength polypropylene has a thickness of 0.2 mm or more, and an insulating member having a trapezoidal protrusion formed in the central opening has a center pin and jelly when the battery is dropped. It can be seen that it has a structure and strength that can suppress the movement of the roll.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

As described above, the secondary battery including the insulating member according to the present invention can prevent the CID short circuit due to the movement of the center pin and / or jelly-roll during the application of a strong impact such as a drop, it is generated inside There is an effect that can effectively discharge a large amount of gas.

Claims (4)

A secondary battery having a structure in which a jelly roll is mounted in a cylindrical battery case, and a plate-shaped insulating member having a perforated hole in the center and a plurality of through holes perforated therein for jelly gas discharge and electrode terminal connection. Mounted on the top of the roll, the plate-shaped insulating member has a trapezoidal protrusion having a shape in which the top surface is located near the center line of the imaginary circle and closes the area of 30 to 50% of its imaginary circle in the central opening. It is formed, the secondary battery characterized in that it has a thickness of 0.2 ~ 0.6 mm. The secondary battery of claim 1, wherein the insulation member is made of polypropylene. The secondary battery of claim 1, wherein the insulation member is made of high-strength polypropylene. The secondary battery according to claim 2 or 3, wherein the polypropylene has a thickness of 0.4 mm or more and the high strength polypropylene has a thickness of 0.2 mm or more.

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