JP2000243359A - Sealing material for lithium secondary battery, sealing material composition and use thereof - Google Patents

Abstract

(57) [Problem] To provide a sealing material for a lithium ion secondary battery suitable for application by a dispenser method. The sealing material for a lithium secondary battery includes a block polymer having a polymer block of a diene monomer and a polymer block of an aromatic vinyl monomer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealing material for a sealed lithium secondary battery, and more particularly, to a sealing material for preventing leakage of an electrolyte of a lithium secondary battery such as a lithium ion secondary battery and a lithium polymer battery. About.

[0002]

2. Description of the Related Art In recent years, notebook personal computers, mobile phones, P
The spread of mobile terminals such as DA is remarkable. For these power supplies, lithium secondary batteries are often used. As the range of use of such mobile terminals has expanded, demands for performance and safety of lithium secondary batteries (hereinafter, may be simply referred to as batteries) serving as these power sources have been increasing. Normally, these batteries are repeatedly used by charge and discharge operations. However, in the case of batteries that repeat charge and discharge, the internal pressure of the battery rises due to electrode volume fluctuation and heat generation due to charge and discharge, and the electrolyte leaks to the outside. In this case, not only deterioration of battery characteristics occurs, but also danger such as ignition or corrosion of equipment is a problem. In addition, lithium secondary batteries have an organic electrolyte that is extremely organic and dislikes water, so it is required to have a high hermeticity that completely prevents water from entering the battery and also completely prevents electrolyte leakage. Is done.

For example, a lithium ion secondary battery has its power generating element housed in a metal container for hermetic sealing. To prevent a short circuit between the positive electrode and the negative electrode, it is necessary to insulate between the positive terminal and the negative terminal. There is. Usually, a gasket made of an insulating material is used in an opening of a metal container containing a power generation element for insulation and sealing between the positive and negative electrodes. It is known that a resin insulating gasket is used as an insulating material (Japanese Patent Publication No. 57-45028, etc.), and a sealing material is applied to a gasket or a metal container in order to further enhance the sealing by such a gasket. In addition, it has been proposed that a sealing material is interposed between the insulating gasket and the container to improve the sealing property between the gasket and the metal container.

As seal materials, pitch-based materials such as coal tar and asphalt, materials obtained by adding a polymer as a modifier to pitch-based materials, resin-based seal materials such as polyolefin adhesives, and rubber-based seal materials are known. Butyl rubber, polybutadiene rubber, butadiene
Diene rubbers such as styrene rubber are known. Among them, diene rubber is known as a sealing material having good sealing properties at high temperatures (JP-A-10-55789).

[0005] As a method of applying a sealing material to a gasket, a dispenser method and a dip coating method (dipping method) in which a process is easy are generally known. In the former, the required amount of sealing material is applied only to the portion of each gasket or container to be sealed using a syringe needle or a fine brush, so that only the necessary amount of sealing material is used. However, it requires extensive coating equipment,
Production efficiency is not always high. The latter is a method in which a gasket is generally immersed in a sealing material composition, the sealing material composition is adhered to the entire surface of the gasket, and the gasket is applied by evaporating a solvent. According to this method, it is also possible to apply a sealing material to a large number of gaskets simultaneously.
Excellent production efficiency. In addition, there is an advantage that simple and low cost is required because no large-scale coating equipment is required. However, in the dip coating method, when mass-producing a gasket coated with a sealing material, a plurality of gaskets are adjacent to each other in the drying process, and the sealing material adheres to the entire surface of the gasket. There is a big problem that the material peels off. This is because if the adhesive strength between the sealing materials of adjacent gaskets is stronger than the adhesive strength between the gasket and the sealing material, the sealing material will be peeled off from the gasket, which is an advantage of the dip coating method. , Which means that the advantage of the dip coating method is reduced. In general, if even a part of the sealing material has poor adhesion, there is a problem that the sealing material is peeled from the part and the peeling is spread. In the dip coating method, since the area of the gasket to which the seal material is applied is large, there is a high possibility that a portion of the gasket where the seal material is poorly adhered is generated, and thus the possibility that the peeling spreads over the whole is also increased.

[0006] Polybutadiene and a random polymer of butadiene and styrene specifically disclosed in JP-A-10-55789 are disclosed in Japanese Patent Application Laid-Open No. H10-55789 by a dispenser method using a dispenser or a brush. , Fully demonstrate its function. However, as a result of the study of the present inventors, when these diene rubber seal materials are applied to a dip coating method having excellent productivity, the adhesion between the seal materials may be stronger than the adhesion to a gasket. It was found that there was a tendency for the peeling of the sealing material to occur.

[0007]

Based on such prior art, the present inventors have conducted intensive studies to obtain a sealing material which does not peel off from the gasket even by the dip coating method. The present inventors have found that a gasket can be provided with a sealing material layer efficiently by a dip coating method as well as a dip coating method, and have completed the present invention.

[0008]

According to the present invention, there is provided, as a first invention, a lithium secondary battery comprising a block polymer having a polymer block of a diene monomer and a polymer block of an aromatic vinyl monomer. A sealing material for a lithium secondary battery comprising the sealing material and an organic liquid medium having a boiling point of 50 to 400 ° C. is provided as a second invention, and a lithium secondary battery is provided as a third invention. A method for manufacturing a lithium secondary battery is provided, wherein the sealing material according to claim 3 is applied to a battery sealing gasket by a dip coating method. Hereinafter, the present invention will be described in detail.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Sealing Material The sealing material of the present invention contains a block polymer. This sealing material has high adhesiveness to a gasket made of a polyolefin resin such as a commonly used polypropylene gasket or a polyethylene gasket. In particular, even if the gasket is applied to the gasket by the dip coating method using the sealing material of the present invention, no problem such as peeling occurs.

(Block Polymer) Among the sealing materials of the present invention, the most preferred block polymers are a polymer block of a diene monomer (hereinafter sometimes referred to as a diene block) and a polymer block of an aromatic vinyl monomer ( Hereinafter, it may be referred to as an aromatic vinyl block.)
And a diblock or multiblock polymer containing at least The shape may be linear or branched. Such a block polymer used in the present invention does not necessarily need to be a complete block polymer, and even if it includes a partially incomplete block or a randomly polymerized portion, the block may be composed of 60% of the entire polymer. % By weight or more, preferably 70% by weight
Above, more preferably 80% by weight or more. Each block constituting the block polymer used in the present invention may be any block substantially obtained by polymerization of the monomer.

The ratio (weight) of diene block / aromatic vinyl block is from 95/5 to 5/95, preferably 9
5/5 to 30/70, more preferably 95/5 to 65 /
45. If the amount of the diene-based block is too small, the flexibility is reduced, and if the amount of the aromatic vinyl-based block is too large, the adhesion to the gasket is reduced.

As the diene monomer, butadiene,
Examples include isoprene and 1,3-pentadiene, and examples of the aromatic vinyl monomer include styrene, α-methylstyrene, and divinylbenzene. These can be used alone or in combination of two or more.

Specific examples of the block polymer used in the present invention include a styrene-butadiene block polymer,
Diblock block polymers such as styrene-isoprene block polymer, styrene-butadiene-styrene block polymer, styrene-isoprene-styrene block polymer, triblock block polymers such as styrene-butadiene-isoprene block polymer, styrene- Multi-block styrene-containing such as butadiene-styrene-butadiene block polymer, styrene-isoprene-styrene-isoprene block polymer, styrene-butadiene-isoprene-styrene block polymer, styrene-butadiene-styrene-isoprene block polymer, and the like. And block polymers. Of course, these polymers may be used alone, or two or more of them may be mixed and used by appropriately setting the mixing ratio according to the purpose. These (partial) hydrogenated products may be used.

The method for producing the block polymer is not particularly limited, and any known method may be used. A living polymerization method using a lithium-based polymerization initiator will be described as an example of the production method.
In a hydrocarbon solvent, in the presence of a lithium-based polymerization initiator, an aromatic vinyl-based monomer is first polymerized to form an aromatic vinyl-based block, and then a diene-based monomer is added to form a diene-based block. It is formed successively on the aromatic vinyl-based block. Further, an aromatic vinyl monomer,
A linear block polymer is obtained by sequentially polymerizing the diene monomers. of course,
After forming a block of butadiene as a diene-based monomer, a block of the same kind of monomer can be continuously formed, such as forming a block of isoprene, which is a diene-based monomer. In this method for producing a linear block polymer, a branching reaction is carried out by reacting a polyfunctional compound (coupling agent) having 2 to 7 reactive groups which reacts with lithium derived from a polymerization initiator bonded to a terminal. Block polymer can be obtained.

The weight average molecular weight (hereinafter referred to as weight average molecular weight or Mw) of the above block polymer in terms of polystyrene calculated by gel permeation chromatography using n-hexane is 20,000.
00 to 1,000,000, preferably 50,000 to
500,000, more preferably 100,000-40
It is 0000. If the weight average molecular weight is too high, the viscosity will be too high, and it will be difficult to control the thickness of the sealing material layer when applying to the insulating gasket. Conversely, if the weight average molecular weight is too low, the strength as the sealing material will be weak, When the insulating gasket is attached, a crack may be formed in the sealing material layer.

(2) Sealing Material Composition The sealing material composition of the present invention can be prepared by dissolving or dissolving the above-mentioned block polymer in an organic liquid medium having a boiling point of 50 to 400 ° C. at normal pressure (hereinafter sometimes referred to as a medium). They are dispersed. Further, other polymers can be added as needed. (Other Polymers) In the present invention, the sealing material composition may contain a polymer other than the block polymer. Such other polymers include ethylene-propylene rubber, ethylene-propylene-diene rubber, butadiene-styrene rubber (random copolymer),
Acrylonitrile-butadiene rubber, polybutadiene rubber, butyl rubber, fluororubber, and the like are preferable in that the sealing material of the present invention is less likely to impair the sealing property and the effect of adhesion to a gasket. When another polymer is added, the use ratio of the block polymer of the present invention is 1% by weight or more, preferably 5% by weight or more. Even when the amount of other polymers is large and the amount of the block polymer is small, the adhesion to the gasket is remarkably effective.

(Colorant) A colorant can be added to the sealant composition so that the state of application of the sealant can be visually inspected. It is desirable that the coloring agent does not react with the electrolytic solution and does not dissolve in the electrolytic solution, and examples thereof include various organic and inorganic pigments. Among them, carbon black, particularly carbon black having a particle size of 0.1 μm or less, such as furnace black and channel black, is preferred. When such a coloring agent is added, it is necessary to dissolve or disperse it sufficiently uniformly in the composition, and when using a granulated or aggregated one, a ball mill, sand mill, ultrasonic wave, etc. It is good to disperse with.
The amount of such an additive such as a coloring agent may be any amount as necessary, but is usually 0.01% by weight to 20% by weight based on the total amount of the block polymer as a sealing material and other polymers.
% By weight, preferably 0.01% to 5% by weight, more preferably 0.02% to 3% by weight. If the amount of the additive is too large, the insulation resistance of the sealing material becomes small, and the flexibility of the sealing material becomes small, which may cause cracks, which is not preferable.

Further, additives usually used for rubber, such as an antioxidant and an ultraviolet absorber, which do not deteriorate the performance of the insulating gasket and do not react with or dissolve in the electrolytic solution, may be added to the sealing material of the present invention. it can.

(Organic Liquid Medium) The organic liquid medium constituting the sealing material composition of the present invention has a boiling point at normal pressure of 50 to 40.
0 ° C, preferably 70-300 ° C, more preferably 80 ° C.
~ 200 ° C. If the boiling point of the medium is too low, the volatility may be too high and the operability may be reduced. Conversely, if the boiling point is too high, drying after coating is time-consuming and productivity is poor. Further, those in which the above-mentioned sealing material of the present invention dissolves are preferable in terms of applicability and the like. Specific examples of the organic liquid medium are described below. The number in parentheses after the compound name is the boiling point at normal pressure (unit: ° C.), and the values after the decimal point are rounded or truncated. When the boiling point has a range, the lower limit was confirmed to be 80 ° C. or higher, and the upper limit was described.

Substitutable hydrocarbons: heptane (98), n
-Octane (125), isooctane (117), n-
Nonan (150), Decane (174), Decalin (19)
4), α-pinene (156), β-pinene (163),
δ-pinene (161), 1-chlorooctane (18
2), 1,2-dichloroethane (83), chlorodecane (223), tetrachloroethylene (121), cyclohexane (81), cycloheptane (118), methylcyclopentane (101), 2-methylcyclohexane (racemic 165) , 3-methylcyclohexanone (racemate: 170), 4-methylcyclohexanone (171), 4-ethylcyclohexane (194), chlorocyclohexane (144), cyclohexene (8
3), cycloheptene (115), benzene (80),
Toluene (111), o-xylene (144), m-xylene (139), p-xylene (138), styrene (145), chlorobenzene (132), o-chlorotoluene (159), m-chlorotoluene (162) ), P
-Chlorotoluene (162), ethylbenzene (13
6), propylbenzene (159), diisopropenylbenzene (231), butylbenzene (183), isobutylbenzene (173), n-amylbenzene (20)
2), cumene (152) and the like.

Alcohols: 1-propanol (9
7), 2-propanol (82), 1-butanol (1
17), t-butanol (83), 1-pentanol (138), 2-pentanol (119), 3-pentanol (116), 1-hexanol (157), 2-
Hexanol (139), 3-hexanol (13
5), 1-octanol (195), 2-octanol (179), benzyl alcohol (205), 4-t-
Butyl catechol (285), cyclopentanol (1
41), glycerin (290) and the like. Ketones: ethyl methyl ketone (80), 2-pentanone (102), 2
-Hexanone (127), 3-hexanone (125),
Cyclopentanone (131), cyclohexanone (15
6), cycloheptanone (180), 2,6-dimethyl-4-heptanone (168), 4-methyl-2-pentanone (117), isophorone (215) and the like.

Ethers: propyl ether (91),
Butyl ether (142), isobutyl ether (12
3), n-amyl ether (188), isoamyl ether (173), methyl n-amyl ether (10
0), ethyl butyl ether (92), ethyl isobutyl ether (81), ethyl n-amyl ether (12
0), ethyl isoamyl ether (112), phenenol (170), 1,3-dioxane (106), 1,
4-dioxane (101) and the like. Esters: propyl formate (82), butyl formate (10
7), pentyl formate (132), isopropyl acetate (8
9), n-propyl acetate (101), n-butyl acetate (126), s-butyl acetate (112), t-butyl acetate (98), methyl lactate (144), ethyl lactate (15
4), butyl lactate (187), methyl benzoate (20
0), ethyl benzoate (213) and the like.

Amines: o-toluidine (200), m
-Toluidine (203), p-toluidine (200),
Dimethylaniline (194), piperidine (105) and the like. Amides: N, N-dimethylformamide (153),
N-methylpyrrolidone (202), N, N-dimethylacetamide (194) and the like. Sulfur-containing compounds: dimethyl sulfoxide (189) and the like. Nitrile group-containing compounds: lactonitrile (18
4), ethylene cyanohydrin (220), azibonitrile (295) and the like.

Oxygen-containing heterocyclic compound: furfural (16
2) etc. Nitrogen-containing heterocyclic compounds: pyridine (116), pyrrole (130), pyrrolidine (88) and the like. Cellosolve acetates: ethyl cellosolve acetate (192) and the like. Glycols: ethylene glycol (198), diethylene glycol (186), propylene glycol (1
88). Ethylene glycol alkyl ethers: diethylene glycol monoethyl ether (195), diethylene glycol dimethyl ether (159), diethylene glycol monobutyl ether (230), triethylene glycol dimethyl ether (222) and the like. Lactones: γ-butyrolactone (206), γ-valerolactone (207), γ-caprolactone (216)
Such. Lactams: β-butyrolactam (245), δ-valerolactam (256) and the like.

[0025] The total polymer component in the sealing material composition of the present invention is from 0.1% by weight to 50% by weight, preferably from 0.5% by weight to 40% by weight, more preferably 1% by weight, based on the medium. ３０30% by weight. If the concentration of the polymer is too high, the viscosity of the composition tends to be high, and the coatability tends to decrease. Conversely, if the concentration is too low, the amount of the medium in the composition is too large, and the seal moldability tends to be poor.

(3) Method for Manufacturing Lithium Secondary Battery When manufacturing a lithium secondary battery using the above-described sealing material (composition), a dip coating method which is excellent in production efficiency can be employed. This will be described below by taking the manufacture of a lithium ion secondary battery as an example. In the case of a lithium ion secondary battery, a battery in which a layer made of the above-described sealing material of the present invention is provided between a metal container which is a battery outer container and an insulating gasket is manufactured. The material of the metal container, the power generation element, and the insulating gasket may be those commonly used. In this lithium ion secondary battery, the power generating element is housed in a metal container and sealed. The power generating elements of the lithium ion secondary battery include an electrolyte solution composed of a supporting electrolyte and an organic electrolyte solution solvent, active materials for a positive electrode and a negative electrode, and separators. The active material for the negative electrode of a lithium ion secondary battery is usually a carbonaceous material. Specifically, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites (natural graphite, artificial Graphite, fibrous graphite, spherical graphite, etc.) and glassy carbons.

As a positive electrode active material of a lithium ion secondary battery, a metal oxide is generally used.
i _x MO ₂ (where M represents one or more transition metals, preferably at least one of CoMn or Ni, and
0>x> 0.05) or Li _x M ₂ O
₄ (where M represents one or more transition metals, preferably Mn, and 1.10>x> 0.05). More specifically, in addition to LiCoO ₂ , Li
NiO ₂ , LiNi _y Co _(1-y) O ₂ (however,
1.10>x> 0.05, 1>y> 0), LiMn ₂ O
_{And the} like.

The electrolyte for the lithium ion secondary battery may be any commonly used non-aqueous electrolyte.
Ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, phosphate compounds, sulfolane compounds, etc. In general, carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate are preferred. The supporting electrolyte constituting the electrolytic solution is, for example, LiClO ₄ , LiBF ₄ , C
F ₃ SO ₃ Li, LiI, LiAlCl, LiPF ₆ ,
LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ S
And electrolytes commonly used in lithium ion secondary batteries such as O ₃ and Li (CF ₃ SO ₂ ) ₂ N.

As the insulating gasket, a polyolefin resin such as polyethylene, polypropylene, and ethylene copolymerized polypropylene, which is generally said to have high resistance to electrolytic solution, is used. Particularly, the heat deformation temperature measured according to JIS K7207 is 90 to 200 ° C. Preferably 90 to 150
C, more preferably 95-130C. If the temperature is higher than 200 ° C., the flexural modulus at room temperature is too high, and deformation may occur at the time of mounting the insulating gasket, which may cause a crack or a crack. And the hermeticity decreases. Among such polyolefin resins, it is preferable to use ethylene copolymerized polypropylene as the insulating gasket because of its good balance between strength and elastic modulus.

In order to form the sealing material layer on the gasket surface by the dip coating method, for example, it may be formed by the following procedure. That is, the insulating gasket is immersed in the sealing material composition by, for example, putting the insulating gasket into the sealing material composition of the present invention contained in a container such as a bucket, a bat, and a tank, and the sealing material composition adheres to the gasket surface. After that, the gasket is taken out of the container containing the sealing material composition, and if necessary, through a process of shaking off the excessively adhered sealing material composition, this is naturally dried or heated and dried.
The organic liquid medium is removed to form a sealing material layer. The thickness of the sealing material layer may be arbitrarily selected depending on the size of the metal container and the insulating gasket, and is usually 0.1 to 1000 μm. Preferably it is 0.5-100 μm, more preferably 1-50 μm. If the thickness of the layer is insufficient, problems such as leakage of electrolyte solution and intrusion of moisture may occur, and the layer may be cut. Conversely, if the layer is too thick, layer formation may be difficult. Although the sealing material of the present invention is suitable for the dip coating method, it can also be used as a sealing material in a dispenser method.

The insulating gasket to which the sealing material of the present invention has been applied can be sealed even if a plurality of the insulating gaskets are stacked in a car, a box, a stock tank, or the like, and then removed one by one for mounting in a battery can. Since the material layer does not peel off, it is suitable for handling an insulating gasket coated with a large number of sealing materials.

[0032]

The sealing material of the present invention has an extremely high sealing property and a high adhesiveness to a polyolefin gasket, so that a stable sealing material layer can be formed even in a simple sealing material coating method such as a dip coating method. Thus, a lithium secondary battery can be obtained with high productivity.

[0033]

The present invention will be described more specifically below with reference to examples. Parts and% in each example are based on weight unless otherwise specified. Also, weight average molecular weight (Mw)
Is a value measured by gel permeation chromatography using n-hexane as a solvent and polystyrene as a standard.

(Example 1) (Production of sealing material composition) A styrene-isoprene diblock type polymer (styrene content 15%, Mw 320,000) produced using n-butyllithium as a catalyst was dissolved in ethylcyclohexane. Then, ethylene-propylene rubber (trade name “Mitsui EPT004 manufactured by Mitsui Chemicals, Inc.)
5)) was dissolved so that the ratio of block polymer / ethylene propylene rubber was 10:90 (weight ratio) to prepare a sealing material composition having a total polymer concentration of 5% by weight.

(Application of Sealing Material) An insulating gasket made of polypropylene is put into the sealing material, pulled up after the generation of air bubbles has been eliminated, shaken off the excessively adhered sealing material composition, and then air-dried at 40 ° C. Drying was carried out for 6 hours with a machine to form a sealing material layer. The thickness of the sealing material layer after drying was about 8 μm. Fifty insulating gaskets on which the sealing material layer was formed were put into a 500 ml beaker, shaken several times, taken out, and the sealing material layer was observed, but no peeling of the sealing material from the insulating gasket was observed.

(Production and Evaluation of Battery) A negative electrode was prepared by kneading natural graphite together with a binder using water as a solvent, applying a paste to a copper foil, followed by drying and pressing. The positive electrode was prepared by adding kneaded paste of LiCoO ₂ to acetylene black, N-methylpyrrolidone together with a binder, applying the kneaded paste to an aluminum foil, followed by drying and pressing. These were wound together with a polyethylene porous separator to form an electrode group. Then, the electrode group was set to 16 mm in inner diameter and 50 m in height.
m (17500 type) was inserted into a nickel-plated iron can, and a bead was formed near the opening for fixing the sealing portion. After that, the mixture was put into a vacuum dryer to completely dry the water adsorbed on the electrode group, and Li was added to a 1: 2 (vol) mixed solvent of ethylene carbonate and methyl ethyl carbonate.
After injecting 1 mol of PF ₆ as an electrolytic solution,
As described above, the insulating gasket coated with the sealing material by the dip coating method was attached, and the battery was sealed. After the batteries were allowed to stand for 2 days after the electrolyte injection and sealing, the battery was charged at a constant current of 1 C until the battery voltage reached 4.2 V, and then at a constant voltage of 4.2 V after reaching 4.2 V. Initial charging was performed by charging for 5 hours. The five batteries charged to 4.2 V were heated in a constant temperature bath at 100 ° C. for 72 hours, and the weight change before and after heating was determined (constant temperature test). Further, five batteries also charged to 4.2 V were exposed to 80 ° C. for 30 minutes, and subjected to a heat shock test 100 times at −20 ° C. for 30 minutes.

As a result, in both the thermostatic test and the heat shock test, no odor peculiar to the electrolytic solution was felt, no significant weight change was observed, and the battery contents were sufficiently sealed. It was confirmed that.

Example 2 Butadiene rubber obtained by solution polymerization using a cobalt catalyst instead of ethylene propylene rubber (1,3-butadiene content 100%, Mw 4
80,000) was used in the same manner as in Example 1 except that the ratio of block polymer / butadiene rubber was 85:15 (weight ratio) to prepare a sealing material composition having a concentration of 12% by weight. . (Application of Sealing Material) A sealing material layer was formed on the surface of the cylindrical insulating gasket in the same manner as in Example 1. The thickness of this layer was 4 μm. Peeling was observed in the same manner as in Example 1, but no peeling of the sealing material was observed. (Production and Evaluation of Battery) Using the insulating gasket coated with the sealing material, a test similar to that of Example 1 was performed. As a result, no odor was detected in any of the five batteries, and the weight change was substantially unchanged. It was confirmed that the battery using the sealing material of the present invention sufficiently sealed the battery contents.

Comparative Example 1 Natural rubber was dissolved in toluene to prepare a sealing material composition having a concentration of 5% by weight. A sealing material layer was formed on the surface of the cylindrical insulating gasket in the same manner as in Example 1. The thickness of this layer was 8 μm.
When the insulating gaskets were brought into contact with each other in a beaker in the same manner as in Example 1, peeling of the sealing material was observed in 17 of the 50 gaskets.

(Comparative Example 2) A random copolymer rubber of butadiene / styrene (butadiene / styrene = 60/40, Mw 21,000) obtained by solution polymerization using a blocker catalyst instead of the block polymer was used. Except for this, an insulating gasket coated with a sealing material was manufactured in the same manner as in Example 1. When this gasket was brought into contact in a beaker in the same manner as in Example 1, peeling of the sealing material layer was observed in 5 out of 50 gaskets.

Example 3 The block polymer of Example 1 alone was used at a concentration of 5% by weight without using ethylene propylene rubber.
A battery was manufactured in the same manner as in Example 1, except that the sealing material composition was prepared. As a result, the insulating gasket 50
In the peel test in each beaker, no peeling of the sealing material was observed in any of the gaskets. Using this insulating gasket to which the sealing material was applied, batteries were manufactured and tested in the same manner as in Example 1. As a result, in both the constant temperature test and the heat shock test, odor was detected for all batteries. No change in weight was substantially observed, and it was confirmed that the battery using the sealing material of the present invention sufficiently sealed the battery contents.

From the above results, it was found that when a sealing material containing a specific block polymer was used, high sealing properties could be ensured even in the dip coating method.

Claims (4)

[Claims] 1. A sealing material for a lithium secondary battery comprising a block polymer having a polymer block of a diene monomer and a polymer block of an aromatic vinyl monomer. 2. The sealing material according to claim 1 and a boiling point of 50 to 4.
A sealing material composition for a lithium secondary battery containing an organic liquid medium at 00 ° C. 3. The method of claim 2, further comprising a non-block polymer.
The sealing material composition for a lithium secondary battery according to the above. 4. A method for producing a lithium secondary battery, comprising applying the sealing material composition according to claim 2 to a gasket for sealing a lithium secondary battery by a dip coating method.