KR101243518B1 - Insulating case for lithium rechargeable battery and Lithium rechargeable battery using the same - Google Patents

Abstract

The present invention relates to an insulating case for a lithium secondary battery and a lithium secondary battery using the same, and more particularly, an ethylene / α-olefin (olefin) prepared by using a high stereoregular homo polypropylene and a single active site catalyst. ) It is manufactured from a resin composition including a copolymer and a nucleating agent, and has an excellent bending strength and heat resistance as compared to the conventional insulating case made of homopolypropylene, and an insulating case that can improve high temperature safety in a lithium secondary battery and using the same. It relates to a lithium secondary battery.

Lithium Secondary Battery, Insulation Case, Flexural Strength, Heat Resistance, High Temperature Safety

Description

Insulating case for lithium rechargeable battery and Lithium rechargeable battery using the same}

1 is an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention.

Description of the Related Art

100-Lithium Secondary Battery 110-Can

120-Electrode Assembly 120-Cap Assembly

170-insulated case

The present invention relates to an insulating case for a lithium secondary battery and a lithium secondary battery using the same, and more particularly, an ethylene / α-olefin (olefin) prepared by using a high stereoregular homo polypropylene and a single active site catalyst. ) It is manufactured from a resin composition including a copolymer and a nucleating agent, and has an excellent bending strength and heat resistance as compared to the conventional insulating case made of homopolypropylene, and an insulating case that can improve high temperature safety in a lithium secondary battery and using the same. It is about a lithium secondary battery.

With the recent rapid development of the electronics, telecommunications, and computer industries, the use of portable electronic products such as camcorders, mobile phones, notebook PCs, etc., as well as the compactness, light weight, and high functionality of the devices are becoming common. The demand for it is increasing. In particular, the rechargeable lithium secondary battery has a high energy density per unit weight of about 3 times higher than conventional lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries, and can be rapidly charged. Development is underway.

Lithium secondary batteries are classified into square, cylindrical, and pouch types according to their shapes. Among these, the rectangular lithium secondary battery is formed to include an electrode assembly, a can housing the electrode assembly, and a cap assembly sealing the upper opening of the can. An insulating case is inserted between the electrode assembly and the cap assembly. The insulating case insulates between the electrode assembly and the cap assembly to prevent an internal short, and supports and fixes the positive and negative tabs so that the positive or negative tab touches the inner wall of the can due to an external shock such as a drop to generate an internal short. It is inserted to prevent it.

In general, the insulating case is formed of a polypropylene material having excellent strength and formability. Insulation case made of homopolypropylene made of homopolymerized polypropylene is excellent in flexural strength, but has a problem in that the impact strength at low temperature is low, thereby exposing weakness in low temperature environment. In addition, the insulation case of the propylene-ethylene block copolymer material is improved to some extent the low-temperature impact strength, there is a problem in that the flexural strength and heat resistance is poor to expose the weakness at room temperature or high temperature environment. Therefore, there is a need to develop an insulation case made of a material capable of improving low-temperature impact strength, flexural strength, and heat resistance.

The present invention has been made to solve the above problems, and particularly includes an ethylene / α-olefin copolymer and a nucleating agent prepared using a high stereoregular homo polypropylene and a single active site catalyst. It is made of a resin composition, which is excellent in flexural strength and heat resistance compared to the conventional insulated case of homopolypropylene material, and to provide an insulated case and a lithium secondary battery using the same to improve the high temperature safety in the lithium secondary battery The purpose is.

Insulation case for a lithium secondary battery of the present invention devised to solve the above problems is homopolypropylene having a stereoregularity (homo polypropylene); Ethylene / α-olefin copolymers prepared using single site catalysts; And a resin composition material comprising a nucleating agent.

In addition, the homopolypropylene has an isotactic pentad fraction of at least 95% by weight, and preferably has a melt index (MI: Melt Index) of 10 to 60 g / 10min at 230 ° C.

In addition, the ethylene / α-olefin copolymer has a density of 0.85 ~ 0.90 g / cm ³ It is preferable that melt index (MI) in 190 degreeC is 1-10 g / 10min. More preferably, the ethylene / α-olefin copolymer may have a melt index (MI) of 1 to 5 g / 10 min at 190 ° C. In addition, the ethylene / α-olefin copolymer may be included in 1 to 20% by weight, the nucleating agent may be included in 0.05 to 0.5% by weight.

In addition, the resin composition may be a melt index of 6 ~ 30 g / 10min at 230 ℃.

In addition, the lithium secondary battery of the present invention comprises a lithium secondary battery comprising an electrode assembly, a can housing the electrode assembly, a cap assembly for sealing the can and an insulating case located between the electrode assembly and the cap assembly. In the insulating case is made of a resin composition comprising a homopolypropylene having a stereoregularity, ethylene / α-olefin copolymer and nucleating agent prepared using a single active site catalyst It is characterized by being formed.

In addition, the homopolypropylene has an isotactic pentad fraction of at least 95% by weight, and preferably has a melt index (MI: Melt Index) of 10 to 60 g / 10min at 230 ° C.

In addition, the ethylene / α-olefin copolymer has a density of 0.85 ~ 0.90 g / cm ³ It is preferable that melt index (MI) in 190 degreeC is 1-10 g / 10min. More preferably, the ethylene / α-olefin copolymer may have a melt index (MI) of 1 to 5 g / 10 min at 190 ° C. In addition, the ethylene / α-olefin copolymer may be included in 1 to 20% by weight, the nucleating agent may be included in 0.05 to 0.5% by weight.

In addition, the resin composition may be a melt index of 6 ~ 30 g / 10min at 230 ℃.

Hereinafter, the present invention will be described in more detail.

1 is an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention.

In the lithium secondary battery 100 according to the exemplary embodiment of the present invention, referring to FIG. 1, the electrode assembly 120 including the positive electrode plate 123, the negative electrode plate 125, and the separator 124 may be filled with an electrolyte ( The upper end opening 110a of the can 110 is housed in the 110 and sealed by the cap assembly 130. The lithium secondary battery 100 includes a long side and a front surface and a rear surface formed to face each other, a short side, and both sides formed to face each other, and a top surface on which the cap plate 140 is located and a bottom surface facing the top surface. And 110b.

The electrode assembly 120 is formed by winding a separator 124 between the positive electrode plate 123 and the negative electrode plate 125.

The positive electrode plate 123 includes a positive electrode current collector made of a thin metal plate having excellent conductivity, for example, aluminum (Al) foil, and a positive electrode active material layer coated on both surfaces thereof. Lithium oxides, such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, are used as the said positive electrode active material. At both ends of the positive electrode plate 123, 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 126 protruding a predetermined length to the upper portion of the electrode assembly 120 is bonded.

The negative electrode plate 125 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. Both ends of the negative electrode plate 125 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 127 protruding a predetermined length to the lower portion of the electrode assembly 120 is bonded. In addition, a lower portion of the electrode assembly 120 may further include an insulating plate for preventing contact with the can 110.

The separator 124 may be interposed between the positive electrode plate 123 and the negative electrode plate 125 and may extend to surround the outer circumferential surface of the electrode assembly 120. The separator 124 is formed of a porous membrane polymer material to prevent short circuit between the positive electrode plate 123 and the negative electrode plate 125 and to allow lithium ions to pass therethrough.

The can 110 is formed in a substantially box shape including a pair of long side walls 112 and a pair of short side walls 113 and a bottom plate 110b having an approximately rectangular shape, and the upper portion is opened to open the upper portion. It comprises 110a. In addition, when the can 110 is formed in a substantially box shape, the cross section in the horizontal direction may be formed in various shapes such as a rectangular shape or an elliptical shape. The electrode assembly 120 is inserted into the upper opening 110a. In addition, the electrolyte is impregnated between the electrode assembly 120 to enable the movement of lithium ions are injected. The material of the can 110 is mainly light aluminum (Al). The upper portion of the can 110 is sealed by the cap assembly 130, the leakage of the electrolyte is prevented. The long side wall 112 and the short side wall 113 of the can 110 are formed to have a thickness of about 0.2 to 0.4 mm, and the bottom plate 110b has a thickness of about 0.2 to 0.7 mm. However, the thickness of the long side wall 112, the short side wall 113, and the bottom plate 110b is not limited thereto. The can 110 is preferably formed by a deep drawing method, and the long side wall 112, the short side wall 113, and the bottom plate 110b are integrally formed. However, the method of forming the can 110 is not limited thereto.

The cap assembly 130 includes a cap plate 140, an insulation plate 150, a terminal plate 160, and an electrode terminal 135. The cap assembly 130 is coupled to a separate insulating case 170 to be coupled to the top opening 110a of the can 110 to seal the can 110.

The cap plate 140 is welded to the upper opening of the can 110 to seal the can 110. The cap plate 140 has an electrolyte injection hole 142 formed at one side thereof, and the electrolyte injection hole 142 is press-fitted and welded with a ball or the like. The terminal hole 1 141 is formed in the center of the cap plate 140, and the electrode terminal 135 insulated by the gas cat tube 146 is inserted into the terminal hole 1 141.

The insulating plate 150 is formed of an insulating material such as a gasket and is coupled to the lower surface of the cap plate 140. The insulating plate 150 has a terminal through hole 2 151 into which the electrode terminal 135 is inserted at a position corresponding to the terminal through hole 1 141 of the cap plate 140. A mounting groove 152 corresponding to the size of the terminal plate 160 is formed on the bottom surface of the insulating plate 150 to allow the terminal plate 160 to be seated.

The terminal plate 160 is generally formed of Ni alloy and is mounted on the lower surface of the insulating plate 150. The terminal plate 160 has a terminal through hole 3 161 into which the electrode terminal 135 is inserted at a position corresponding to the terminal through hole 1 141 of the cap plate 140, and the electrode terminal 135. Is insulated by the gasket tube 146 and coupled through the terminal through hole 1 141 of the cap plate 140, so that the terminal plate 160 is electrically insulated from the cap plate 140 while the electrode terminal 135 is insulated from the gasket tube 146. Is electrically connected).

The negative electrode tab 127 coupled to the negative electrode plate 125 is welded to one side of the terminal plate 160, and the positive electrode tab 126 coupled to the positive electrode plate 123 is welded to the other side of the cap plate 140. . Resistance welding, laser welding, or the like is used as a welding method for coupling the negative electrode tab 127 and the positive electrode tab 126, and resistance welding is generally used.

The electrode terminal 135 is connected to the negative electrode tab 127 of the negative electrode plate 125 or the positive electrode tab 126 of the positive electrode plate 123 to act as a negative electrode terminal or a positive electrode terminal.

The insulating case 170 is positioned between the electrode assembly 120 and the cap assembly 130 to prevent a short circuit therebetween, and to fix and support the positive electrode tab 126 and the negative electrode tab 127. do. The insulating case 170 is made of a resin composition comprising a homopolypropylene having a stereoregularity, an ethylene / α-olefin copolymer prepared using a single active site catalyst, and a nucleating agent. Is formed.

The homopolypropylene is a high stereoregular homopolypropylene and has an isotactic pentad fraction, which is a stereoregularity index on Nuclear Magnetic Resonance, of 95% by weight or more, and gel permeation chromatography (Gel Permeation Chromatography). It is preferable that molecular weight distribution by the: GPC) method is 7-12. At this time, the molecular weight distribution is calculated as weight average molecular weight (Mw) / number average molecular weight (Mn). When the isotactic pentad fraction of the homopolypropylene is less than 95% by weight, the heat resistance and rigidity are lowered, and thus, when the temperature inside the battery becomes high due to overcharging or the like, it is warped or warped. As a result, the insulating case 170 does not properly support the positive electrode tab 126 and the negative electrode tab 127, and there is a problem that an internal short may occur in the battery. In addition, when the molecular weight distribution of the homopolypropylene is less than 7, the melt flow is worse than that of other resin compositions having the same melt index, so that the insulation case is not easily formed. When the molecular weight distribution exceeds 12, the metering time is increased during injection molding. There is a problem that productivity is lowered.

The ethylene / α-olefin copolymer has a density of 0.85 to 0.90 g / cm ³ And a melt index at 190 ° C. is from 1 to 10 g / 10 minutes, preferably prepared using a single site catalyst. The density of the ethylene / α-olefin copolymer is 0.85 g / cm ³ If it is less than the low crystalline material in the produced injections will increase, if it exceeds 0.90g / cm ³ transparency is worse. In addition, when the melt index at 190 ° C. of the ethylene / α-olefin copolymer is less than 1 g / 10 min, dispersibility with the homopolypropylene resin is lowered, resulting in poor transparency, and similarly when the melt index is greater than 10 g / 10 min. Dispersion with the homopolypropylene resin is lowered, resulting in poor transparency. In addition, when the ethylene / α-olefin copolymer is not made of a single active site catalyst, but is made of, for example, a Ziegler-Natta catalyst, there is a problem that the low crystalline material in the injection molding increases, resulting in poor physical properties.

The nucleating agent is added to improve the transparency of the resin composition, there is an inorganic nucleating agent or sorbitol-based nucleating agent. Inorganic nucleating agent has a disadvantage in that transparency improvement effect and dispersibility is inferior to sorbitol nucleating agent. Therefore, it is preferable to use a sorbitol-based nucleating agent for improving the transparency of the injection molding, and more preferably 3,4-dimethylbenzylidene sorbitol may be used to impart excellent transparency and minimize the odor problem.

The ethylene / α-olefin copolymer is preferably included 1 to 20% by weight, more preferably 5 to 15% by weight may be included. If the content of the ethylene / α-olefin copolymer is less than 1% by weight, there is no effect of improving the impact characteristics. If the content of the ethylene / α-olefin copolymer is greater than 20%, phase separation of the homopolypropylene and the ethylene / α-olefin copolymer occurs. There is a problem that the phenomenon occurs.

The nucleating agent is preferably contained 0.05 to 0.5% by weight. If the content of the nucleating agent is less than 0.05% by weight does not appear transparency, if the content of more than 0.5% by weight can not be expected to further improve the transparency.

In addition to the above-mentioned materials, various additives such as an antioxidant, a heat stabilizer, a weather stabilizer, an antistatic agent, a lubricant, a slip agent, and a flame retardant may be added to the resin composition, which is a material of the insulating case 170.

There is no particular limitation on the method of preparing the resin composition, and a method of preparing a generally known polyolefin resin composition may be used. The resin composition may be prepared by kneading through a kneader such as a kneader, roll, banbury mixer, or the like and then extruded through a single screw or twin screw extruder. In addition, the insulation case 170 may be manufactured by injection molding the resin composition. However, the manufacturing method of the insulating case 170 is not limited thereto.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples.

Example  And Comparative example

[Production of Resin Composition]

For Examples 1 to 2 and Comparative Examples 1 to 5, homopolypropylene, ethylene / α-olefin copolymer, 3,4-dimethylbenzylidene sorbitol are blended according to the composition ratio of Table 1, and other additives include antioxidants and neutralizing agents. After adding the appropriate amount was mixed by a mixer to prepare a resin composition.

[Manufacture of Insulation Case]

Next, the mixed resin composition was extruded at 200 ° C. to prepare an insulation case. The resin compositions corresponding to the above Examples and Comparative Examples were injection molded through an injection machine, but were molded with a mold temperature of 60 ° C. and an injection pressure of 50 to 120 atm.

[Measurement of Physical Properties]

The insulating case made of a resin composition corresponding to each of the above-described examples and comparative examples was left in a room temperature of 23 ° C. for 72 hours and then measured for physical properties. The results of the measurement are shown in Table 1.

(1) isotactic pentad fraction

Stereoregularity was evaluated by measuring the isotactic fraction (% by weight) as pentad unit in the polypropylene molecular chain using a nuclear magnetic resonance apparatus (C ₁₃ -NMR).

(2) Melt Index (MI)

According to the method of ASTM D1238, the amount of resin (g / 10 min) flowing down for 10 minutes by a load of 2.16 kg at a temperature of 190 ° C or 230 ° C was measured.

(3) Flexural modulus

It measured according to the method of ASTM D790.

(4) heat deflection temperature

It was measured according to the method of ASTM D648.

(5) low temperature impact strength

After injection molding the resin composition into a sheet having a thickness of 2 mm, the weight was dropped to a sheet at a certain height under a temperature of -20 ° C to measure the average breaking height.

[Property Measurement Results]

[Table 1]

According to Table 1, Example 2 has a reduced flexural modulus and a low temperature impact strength as the content of the ethylene / α-olefin copolymer is reduced compared to Example 1.

In Comparative Example 1, 20 wt% or more of the ethylene / α-olefin copolymer and no nucleating agent were included, and the flexural modulus was inferior to that of Example 1.

In Comparative Example 2, the isotactic pentad fraction of homopolypropylene was lower than that of Example 1, and 20 wt% or more of the ethylene / α-olefin copolymer was included, and the flexural modulus was inferior.

Comparative Example 3 does not contain an ethylene / α-olefin copolymer, and compared with Example 1, the low temperature impact strength is too low to use in a low temperature environment.

In Comparative Example 4, the ethylene / α-olefin copolymer and the nucleating agent were not included, and thermal deformation temperature, low temperature impact strength, and the like were inferior to those of Example 1.

As described above, the present invention is not limited to the above-described specific preferred embodiments, and any person skilled in the art may apply the present invention without departing from the gist of the present invention. It is to be understood that various changes and modifications may be practiced within the scope of the appended claims.

According to the insulating case and the lithium secondary battery according to the present invention, the flexural strength and heat resistance are superior to the conventional insulating case of the homopolypropylene material, and there is an effect of improving the high temperature safety in the lithium secondary battery.

Claims (12)

Homopolypropylene with stereoregularity; Ethylene / α-olefin copolymers prepared using single site catalysts; And It is formed of a resin composition material containing a nucleating agent, The homopolypropylene has an isotactic pentad fraction of at least 95% by weight, a melt index (MI: Melt Index) of 10 to 60 g / 10 min at 230 ° C., and gel permeation chromatography (Gel). Insulation case for a lithium secondary battery, characterized in that the molecular weight distribution by Permeation Chromatography (GPC) is 7 to 12. delete The method of claim 1, The ethylene / α-olefin copolymer has a density of 0.85 to 0.90 g / cm ³ And a melt index (MI) at 190 ° C. of 1 to 10 g / 10 min. The method of claim 3, The ethylene / α-olefin copolymer is an insulation case for a lithium secondary battery, characterized in that the melt index (MI) at 190 ℃ 1 ~ 5 g / 10min. The method of claim 1, The ethylene / α-olefin copolymer is contained in 1 to 20% by weight, the nucleating agent is an insulating case for a lithium secondary battery, characterized in that it is contained in 0.05 to 0.5% by weight. The method of claim 1, The resin composition is an insulation case for a lithium secondary battery, characterized in that the melt index at 230 ℃ 6 ~ 30 g / 10min. In a lithium secondary battery comprising an electrode assembly, a can containing the electrode assembly, a cap assembly for sealing the can and an insulating case located between the electrode assembly and the cap assembly, The insulating case is homo polypropylene (stereo polypropylene) having a stereoregularity, Ethylene / α-olefin copolymers prepared using a single site catalyst and It is formed of a resin composition material containing a nucleating agent, The homopolypropylene has an isotactic pentad fraction of at least 95% by weight, a melt index (MI: Melt Index) of 10 to 60 g / 10 min at 230 ° C., and gel permeation chromatography (Gel). Permeation Chromatography: Lithium secondary battery, characterized in that the molecular weight distribution by 7 to 12 by GPC. delete 8. The method of claim 7, The ethylene / α-olefin copolymer has a density of 0.85 to 0.90 g / cm ³ And a melt index (MI) at 190 ° C. is 1 to 10 g / 10 min. 10. The method of claim 9, The ethylene / α-olefin copolymer is a lithium secondary battery, characterized in that the melt index (MI) at 190 ℃ 1 ~ 5 g / 10min. 8. The method of claim 7, The ethylene / α-olefin copolymer is contained in 1 to 20% by weight, the nucleating agent is a lithium secondary battery, characterized in that it is contained in 0.05 to 0.5% by weight. 8. The method of claim 7, The resin composition is a lithium secondary battery, characterized in that the melt index at 230 ℃ 6 ~ 30 g / 10min.

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