KR20090105544A - Center pin and secondary battery using the same - Google Patents

Abstract

PURPOSE: A center pin for securing stability of a battery and a secondary battery using the same are provided to reduce production costs and to maintain gas emission and inner circulation of a battery by a center pin. CONSTITUTION: A center pin(200) has a barrel-shaped body in which silver hollow is formed. The diameter of upper and lower parts(210,220) of the body is larger than the diameter of a central part(230). The difference of the upper and lower parts is 0.2~2mm. A secondary battery(100) includes an electrode assembly(30), a can(20), a cap assembly, and a center pin. The can accommodates an electrode assembly. The cap assembly seals the top opening of a can.

Description

Center pin and secondary battery using the same

The present invention relates to a secondary battery including a center pin and the center pin.

As mobile devices are diversified and demand for them increases, many researches have been conducted on secondary batteries used as power sources. Such secondary batteries include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, and lithium secondary batteries. Among them, lithium secondary batteries are rechargeable, compact, and large in capacity, and are attracting attention as power sources for such mobile devices because of their high operating voltage and high energy density per unit weight.

As technology development for mobile devices progresses and demand for them increases, many researches have been conducted on lithium secondary batteries having high energy density and high discharge voltage.

In general, a cylindrical lithium secondary battery includes an electrode assembly, a cylindrical can for accommodating the electrode assembly and an electrolyte, and is assembled to an upper portion of the cylindrical can to seal the cylindrical can and allow a current generated in the electrode assembly to flow to an external device. It is formed including a cap assembly.

The electrode assembly is prewound around the mandrel with a separator interposed between the cathode and the anode to electrically insulate the anode and the cathode, and is made by winding in a jelly-roll method. After removing the mandrel, the electrode assembly is inserted into the can and the electrolyte is injected. After the electrolyte is inserted, the assembly of the battery is completed by coupling the cap assembly to the top of the can. In this case, the electrode assembly is prevented from being deformed in the core direction of the core of the jelly-roll from which the mandrel is removed, and when gas is generated due to an increase in the temperature inside the battery, a role of a passage for gas discharge and circulation maintenance in the safety vent direction is provided. The cylindrical center pin is inserted to make.

Conventionally, a cylindrical center pin corresponding to the shape of the core portion of the jelly-roll having the mandrel removed in the shape of a center pin was used. However, the stress generated during the charging and discharging process is concentrated in the center of the longitudinal direction of the center pin, and the center of the stress concentration is more deformed than the other parts. This deformation causes the electrode assembly to pressurize the electrode assembly. there was.

In addition, fine foreign matters may occur during battery assembly.If foreign matters are concentrated and foreign matter clusters are formed above the thickness of the separator, the insulation of the separator is broken and an internal short circuit occurs, and the battery generates heat by a continuous reaction. As a result, the risk of safety is increased, leading to ignition. These foreign materials tended to concentrate in the gap between the jelly-roll and the center pin.

Since the secondary battery is used in a device that a user carries, such as a mobile device, it is very important to secure stability and prevent performance deterioration of the secondary battery.

Recently, in order to secure the stability of such a battery, a structure has been developed in which a fire extinguishing material is discharged in accordance with the deformation of the center pin by filling a fire extinguishing material in the center pin. However, such a center pin has a disadvantage in that the manufacturing process is complicated, such as filling a separate extinguishing material inside, and the role of gas discharge and circulation inside the battery, which is a purpose of the center pin, is not properly performed.

Therefore, there is an urgent need for the development of a center pin and a secondary battery including the same, which can secure stability of the battery and maintain a function unique to the center pin while having a simple manufacturing process.

The problem to be solved by the present invention is to provide a secondary pin including the center pin and improved safety.

Center pin according to the present invention has a hollow cylindrical body, characterized in that the upper and lower diameters of the body is larger than the diameter of the central portion of the body.

In addition, the difference between the upper and lower diameter of the body and the diameter of the central portion of the body may be 0.2 ~ 2mm.

In addition, the center pin may be tapered so that the width becomes narrower gradually from the upper portion to the center portion, and the width becomes gradually wider from the center portion toward the lower portion of the center pin.

In addition, the upper and lower edges of the center pin may be rounded.

In addition, the center pin may be made of a material selected from metals, alloys, and polymer materials.

The secondary battery according to the present invention has an electrode assembly, a can housing the electrode assembly, a cap assembly for sealing the upper opening of the can, and a cylindrical body inserted into the core part of the electrode assembly and having a hollow body. The upper and lower diameters of the body is characterized in that it comprises a center pin larger than the diameter of the central portion of the body.

In addition, the difference between the diameter of the upper and lower portions of the body of the center pin and the diameter of the center portion of the body may be 0.2 ~ 2mm.

In addition, the center pin may be tapered so that the width becomes narrower gradually from the upper portion to the center portion, and the width becomes gradually wider from the center portion toward the lower portion of the center pin.

In addition, the upper and lower edges of the center pin may be rounded.

In addition, the center pin may be made of a material selected from a metal, an alloy, and a polymer material.

In addition, the interval between the upper portion of the center pin and the core portion of the electrode assembly and the interval between the lower portion of the center pin and the core portion of the electrode assembly may be 50 ~ 200㎛.

According to the present invention, the manufacturing cost is low and the stability of the battery can be ensured while maintaining the role of gas discharge and internal circulation of the battery by the center pin.

The secondary battery 100 according to the present invention includes a cylindrical can 20, a jelly-roll-shaped electrode assembly 30 accommodated inside the can, and a cap assembly 40 coupled to an upper portion of the can 20. have.

The cylindrical can 20 is formed to include a cylindrical side plate having a predetermined diameter and a bottom plate sealing the lower portion of the cylindrical side plate to form a predetermined space in which the cylindrical electrode assembly 30 can be accommodated. An upper portion of the cylindrical side plate is opened to insert the electrode assembly 30. In addition, the cylindrical can 20 is generally formed of nickel (Ni), iron (Fe) or an alloy thereof.

The electrode assembly 30 is accommodated in the cylindrical can 20, and the electrode assembly 30 is wound in a jelly-roll form with a separator 33 interposed between the anode 32 and the cathode 31. The positive electrode 32 has a positive electrode tab 34 attached to the cap assembly 40, and the negative electrode 31 has a negative electrode tab 35 attached to the lower end of the can 20. have. As the negative electrode tab 35 of the electrode assembly 30 is bonded to the center of the lower plate of the cylindrical can 20, the cylindrical can 20 itself serves as a negative electrode.

The positive electrode 31 includes a positive electrode current collector and a positive electrode active material layer coated on both surfaces of the positive electrode current collector. The positive electrode current collector is made of a thin metal plate having excellent conductivity, for example, aluminum (Al) foil, nickel foil, stainless foil, etc. to collect electrons from the positive electrode active material and move them to an external circuit.

In addition, the cathode active material layer may include at least one positive electrode material capable of inhaling and releasing lithium as an electrode reactant, and may include a conductive material such as a carbon material and a binder such as polyvinylidene fluoride as necessary. . Materials that can inhale and release lithium include titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), vanadium oxide (V ₂ O ₅ ), and lithium cobalt composite oxides (Li _x CoO _2). ), lithium-nickel composite oxide (Li _x NiO _2), lithium nickel cobalt composite oxide (Li _x Ni _{1 -} and the like metal sulfides, metal selenides, metal oxides such as _{z Co z O 2, z <} 1).

At both ends of the positive electrode 32, a positive electrode current collector region in which a positive electrode active material layer is not formed, that is, a positive electrode non-coating portion is formed. One end of the positive electrode non-coating portion is generally formed of aluminum (Al), and the positive electrode tab 34 protruding a predetermined length to the upper portion of the electrode assembly 30 is bonded.

In addition, the negative electrode 31 includes a negative electrode current collector made of a conductive metal thin plate, for example, copper (Cu) or nickel (Ni) foil, and a negative electrode active material layer coated on both surfaces thereof. The negative electrode active material layer may include a negative electrode active material, and may further include a conductive material and a binder as necessary.

The negative electrode active material is a metal element or semimetal element capable of forming an alloy with lithium, and specifically, magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), Germanium (Ge), tin (Sn), lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y) , Palladium (Pd), platinum (Pt) and carbonaceous materials such as natural graphite, artificial graphite, non-graphitized carbon, reverse graphitized carbon and the like can be used.

Both ends of the negative electrode 31 are provided with a negative electrode current collector region, that is, a negative electrode non-coating portion, in which a negative electrode active material layer is not formed. One end of the negative electrode non-coating portion is generally formed of nickel (Ni), and the negative electrode tab 35 protruding a predetermined length to the lower portion of the electrode assembly 30 is joined.

In addition, a cap assembly 40 is formed on the electrode assembly. The cap assembly includes an upper cap 41 forming a positive terminal, a positive temperature coefficient element 42, a safety vent 43, an insulating member 44, and a positive electrode tab 34 connected to the positive electrode. The cap plate 45 which is present is structured to be sequentially stacked. The PTC element is a device that blocks the current by increasing the battery resistance significantly when the temperature inside the battery increases, the safety vent is formed to block the current or exhaust the gas when the pressure inside the battery rises, An insulating member is formed to electrically separate the cap plate.

The electrode assembly 30 is a cathode 32, the cathode 31, and the separator 33 are stacked together to be wound in a jelly-roll form, the electrode assembly wound after inserting the cylindrical can 20, The center pin 200 is inserted into the electrode assembly.

The center pin according to the present invention has a hollow cylindrical body. The center pin according to the present invention preferably has a horizontal cross section of an elliptical or circular shape similar to the shape of the core portion so as to maintain the shape of the jelly-roll, and as shown in FIG. 2, the diameter (x) of the upper and lower parts of the body is It is larger than the diameter y of the center portion. It is preferable that the difference of the diameter between the diameter (x) of the upper and lower part of a center pin, and the diameter (y) of a center part is 0.2-2 mm. In the case of the conventional cylindrical center pin, the stress is concentrated in the center, but if the center pin is formed such that the diameter of the upper and lower parts is larger than the center part, the stress is efficiently distributed to prevent the electrode short circuit due to the expansion of the center pin part. Can be.

In FIG. 2, the diameter decreases gradually from the upper portion 210 to the central portion 230, and the diameter decreases gradually from the lower portion 220 to the central portion 230, and the center pin has a tapered shape toward the upper and lower portions. Although shown in the figure, the center portion is intended to prevent disconnection of the electrode due to deformation of the central portion where stress is concentrated, so that the center portion may have a narrower diameter than the upper and lower portions.

In order to prevent the disconnection of the electrode due to the deformation of the center pin due to the concentration of stress, the center pin having a conventional cylindrical shape may be smaller than the diameter of the core portion of the jelly-roll even if it is swollen by charging and discharging. Reducing the diameter compared with the prior art reduces the risk of disconnection of the electrode when the center pin is deformed. However, when the diameter of the center pin itself is reduced as a whole, referring to FIG. 1, the void volume is increased because the interval z increases between the center pin and the core of the jelly-roll. Generally, when gas is generated due to disconnection of the electrode or overcharging during the charge / discharge process of the secondary battery, the gas generated inside the battery may escape through the safety vent formed in the cap assembly before ignition or explosion. To ensure the safety of the secondary battery. However, when the void volume increases, even if the pressure inside the battery increases due to heat generation inside the battery, the operation time of the safety vent is delayed because more pressure is required as the void volume.

In addition, as the distance z between the center pin and the core of the jelly-roll increases, foreign matters generated during assembly of the battery may be concentrated in this gap portion. That is, since foreign matters generated during assembly of the battery are concentrated between these intervals (z), when foreign matter clusters are formed beyond the thickness of the separator, the insulation of the separator is broken and an internal short circuit occurs, and the battery generates heat by a continuous reaction. As a result, it is more likely to cause ignition and pose a danger to the safety of the battery.

Therefore, in the present invention, the diameter (x) of the upper and lower parts of the center pin is almost equal to the diameter of the core of the jelly-roll to prevent concentration of foreign matter, and only the diameter (y) of the center part of the center pin where stress is concentrated is on the upper and lower ends. Compared to the above, the increase in the void volume in the battery is not large. Therefore, it is possible to secure the stability of the battery without delaying the operation of the safety vent.

It is preferable to match the diameter of the upper and lower parts of the center pin with the diameter of the core part of the jelly-roll to prevent the concentration of foreign matter. However, since the center pin is inserted after the winding of the electrode assembly, It is preferable that the space | interval z between the core parts of a jelly roll is 50-200 micrometers.

Accordingly, in the present invention, it is possible to prevent the disconnection of the electrode caused by the deformation due to the stress concentration of the center pin, and to prevent the internal short circuit due to the concentration of foreign substances, thereby improving the stability of the battery.

In addition, the center pin according to the present invention can be rounded corners as shown in the right side of Figure 3, according to the smooth insertion of the center pin, the core portion of the core of the jelly-roll due to the edge that may occur during the flow The bursting phenomenon can be prevented.

Since the center pin according to the present invention is used inside the battery, it should be excellent in chemical resistance and acid resistance, and it is preferable to use a material having excellent porosity and productivity. As such a material, a metal such as nickel, copper, aluminum, titanium, chromium, carbon, iron, cobalt, molybdenum, gold, silver, vanadium, stainless steel, alloys thereof, or polymer materials may be used. Non-limiting examples of polymeric materials that can be used include ethylene vinyl acetate (EVA), polystyrene, polyphenylene ether (PPE), polychlorotrifluoroethylene, polyvinyl chlorite (PVC), polyethylene terephthalate (PET), Polyamide, polycaprolactam, polycarbonate (PC), poly- (p-xylene), polyimide (PI), polyoxybenzoate (POB), polyetheretherketone (PEEK), polyphenylene sulfide (PPS) ), Polyether sulfone (PES), polysulfone (PSU), silicone resin, acrylic resin, urethane resin, epoxy resin, rubber, polyethylene, polypropylene, polybutene, polyacetaldehyde, polyformaldehyde, polypropylene oxide, poly Methyl methacrylate, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride and the like, and these may be used alone or in combination of two or more thereof.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.

Example  One

After inserting the center pin according to the present invention into the jelly-roll core of the cylindrical lithium secondary battery, charge and discharge were performed 100 times in succession.

Example  2

Proceeded in the same manner as in Example 1, but charged and discharged 200 times.

Example  3

The same procedure as in Example 1 was carried out, but charging and discharging was performed 300 times.

Comparative example  One

Proceed in the same manner as in Example 1, the center pin was used as the center pin of the existing center pin, not the center pin according to the present invention.

Example  4

The jelly-roll with the center pin prepared in the same manner as in Example 1 was inserted into the can and assembled. Before assembly, it was prepared by inserting 1 ~ 10㎛ circular powder of foreign substance composed of ceramic component on the upper and lower ends of jelly-roll. After fabrication, the charge and discharge was repeated 10 times. The foreign body flow in it was observed.

Comparative example  2

Proceeded in the same manner as in Example 4, instead of using a center pin according to the present invention, a cylindrical center pin was used.

Determination of the strain of jelly-roll

The total volume expansion of the jelly-rolls of Examples 1 to 3 was observed, and the diameters of the upper, middle, and lower portions of the jelly-rolls after completion of charging and discharging were measured.

The total volume increased more in Examples 2 and 3 than in Example 1 and expanded more in Example 3 than in Example 2.

In addition, the diameter of the center portion of the jelly-roll was not significantly different from the diameter of the upper and lower portions of the jelly-roll.

However, in the case of Comparative Example 1, the expansion of the entire volume is similar to that of Example 1, but the diameter of the center portion of the jelly-roll expands more than the diameter of the upper and lower portions, so that disconnection occurs, thereby generating heat generation.

Therefore, in the case of using the existing center pin, the stress is concentrated in the center part, and the deformation of the center part of the jelly roll occurs most. However, when using the center pin according to the present invention, the deformation of the center part of the jelly roll is similar to other parts. I could see.

Accordingly, when using the center pin according to the present invention it can be seen that the disconnection caused by the deformation of the jelly-roll is prevented.

Observation of Foreign Body Flow

Comparative Example 2 and Example 4 was compared to examine the movement of the foreign material.

In Comparative Example 2, the foreign material was concentrated on the upper and lower portions of the core of the jelly-roll, and heat generation started due to an internal short circuit, but in Example 4, no foreign material was concentrated on the upper and lower portions of the core and no heating was observed.

Accordingly, when using the center pin according to the present invention was found that the risk of internal short circuit due to foreign matter concentration can be reduced.

1 is a schematic cross-sectional view of a secondary battery including a center pin according to the present invention.

Figure 2 shows one embodiment of a center pin according to the present invention.

Figure 3 shows the edge of the center pin according to the present invention compared before and after the rounding process.

<Brief description of the symbols in the drawings>

100: secondary battery

20: cans

30: electrode assembly

31: negative electrode, 32: positive electrode, 33: separator, 34: positive electrode tab, 35: negative electrode tab

40: cap assembly

41: upper cap, 42: PTC element, 43: safety vent, 44: insulating member, 45: cap plate

200: center pin

Claims (11)

Has a cylindrical body with a hollow, The center pin of the upper and lower parts of the body, characterized in that larger than the diameter of the central portion of the body. The method according to claim 1, Center pins, characterized in that the difference between the diameter of the upper and lower parts of the body and the diameter of the center portion of the body is 0.2 ~ 2mm. The method according to claim 1, The center pin is tapered so that the width becomes narrower gradually from the upper portion to the center portion, and the tapered shape is tapered so as to become wider from the center portion toward the lower portion of the center pin. The method according to claim 1, Upper and lower edges of the center pin is a center pin, characterized in that the rounded process. The method according to claim 1, The center pin is a center pin, characterized in that made of a material selected from metals, alloys, polymer materials. Electrode assembly; and Cans for receiving the electrode assembly; And A cap assembly for sealing the top opening of the can; And Inserted into the core portion of the electrode assembly, the secondary battery including a center pin, characterized in that having a hollow cylindrical body, the upper and lower diameters of the body is larger than the diameter of the central portion of the body. The method according to claim 6, The difference between the upper and lower portions of the center pin and the diameter of the center portion is a secondary battery, characterized in that 0.2 ~ 2mm. The method according to claim 6, The center pin is tapered so that the width becomes narrower gradually from the upper portion to the center portion, and the tapered shape is gradually tapered from the center portion toward the lower portion of the center pin. The method according to claim 6, The upper and lower edges of the center pin is a secondary battery characterized in that the rounded process. The method according to claim 6, The center pin is a secondary battery, characterized in that made of a material selected from metals, alloys, polymer materials. The method according to claim 6, The interval between the upper portion of the center pin and the core portion of the electrode assembly and the interval between the lower portion of the center pin and the core portion of the electrode assembly are 50 ~ 200㎛ each.

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