JPH09120842A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery of lithium ions in which eventual internal shortcircuiting influences on adjoining positive and negative electrode by affixing a metal foil to each surface of a heat resistant insulative film, and using either or both of the positive electrode current collector and negative electrode current collector of the battery. SOLUTION: A lithium ion secondary battery is composed of a negative electrode 3 formed by applying an active material 6 to a negative electrode current collector 7 and a positive electrode 2 made in the same manner, which are laminated one over the other while a separator 8 is interposed. The current collector 7 is prepared by affixing a metal foil to both surfaces of a heat resistant insulative film 7a, which should lessen conduction of the heat generated at internal shortcircuiting so as to prevent its influencing upon adjoining positive and negative electrode one after another. An equivalent effect will be obtained if a positive electrode current collector of similar construction to the negative is used or are used both of them which are constructed in such a structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-capacity lithium ion secondary battery suitable for use in, for example, an electric vehicle, a UPS (Uninterruptible Power Supply), load leveling and the like.

[0002]

2. Description of the Related Art Conventionally, lithium-ion secondary batteries have been researched and developed in many fields related to environmental problems such as electric vehicles, UPS, load leveling, and have large capacity, high output, high voltage, and long-term storability. What is excellent is required.

In this lithium ion secondary battery, during charging, lithium is dissolved out of the positive electrode active material of the positive electrode as lithium ions into the electrolytic solution in the separator and enters the negative electrode active material of the negative electrode, and during discharge, this Lithium ions that have entered the negative electrode active material of the negative electrode are released into the electrolytic solution, and return to the positive electrode active material of the positive electrode to perform the charging / discharging operation.

In order to increase the energy density of a conventional small lithium ion secondary battery, an active material is applied to both the front and back surfaces of a metal foil current collector to form sheet-shaped positive and negative electrodes, and a polyethylene or polypropylene electrode is used. In most cases, this is a prismatic battery in which a large number of electrode pairs of a predetermined size are sequentially laminated with a separator, or a cylindrical battery structure in which long positive and negative electrodes are wound with a polyethylene or polypropylene separator. It was

[0005]

A large-capacity lithium-ion secondary battery is formed by sequentially laminating positive and negative electrodes in which an active material is applied on both sides of a current collector in the same manner as the small-sized lithium-ion secondary battery described above. When configured, due to the large capacity, when an internal short circuit occurs, that portion will generate heat, the separator between the adjacent positive and negative electrodes will melt by heat, and the internal short circuit will expand, resulting in the release of a large amount of heat to the surroundings. However, there is a problem that a large amount of gas may be ejected.

[0006] Generally, as a simulation test of an internal short circuit of a battery, a nail puncture test is carried out in which a nail is pierced from outside the battery to artificially short the positive and negative electrodes. The present inventor has found that, in a process in which a large-capacity lithium ion secondary battery as described above reaches a large amount of gas jetting at the time of nail sticking, heat generation due to resistance of the nail sticking portion becomes a fire, and a separator between adjacent positive and negative electrodes is It was found that heat is melted and heat is generated due to a direct reaction between the positive and negative electrodes, and successive heat generation is generated, that is, heat melting of the separator between the adjacent electrodes next to each other, and finally large heat is generated due to reaction of all electrodes. It was

In order to prevent such inconvenience, by sandwiching a heat-resistant insulating film such as polyimide for each pair of the negative electrode and the positive electrode, heat transfer at the time of internal short circuit is reduced and the internal short circuit is propagated. It is possible to prevent this.

However, in this case, since the heat resistant insulating film is sandwiched between each pair of the negative electrode and the positive electrode, the positive electrode and the negative electrode are not in contact with each other where the heat resistant insulating film is sandwiched. To obtain the same capacity as a lithium-ion secondary battery without sandwiching a heat-resistant insulating film, approximately 2
There was the inconvenience of requiring double the volume.

In view of the above, the present invention prevents the influence of an internal short circuit of a large-capacity lithium ion secondary battery from spreading between adjacent positive and negative electrodes, and damages the battery itself and the surrounding environment. It is intended to minimize the influence of the above and to make this battery relatively small.

[0010]

The lithium ion secondary battery of the present invention comprises a positive electrode current collector coated with a positive electrode active material and a negative electrode current collector coated with a negative electrode active material via a separator. In the lithium ion secondary battery laminated as above, one or both of the positive electrode current collector and the negative electrode current collector in which a metal foil is coated on both sides of a heat resistant insulating film is used.

According to the present invention, since one or both of the positive electrode current collector and the negative electrode current collector are coated with metal foil on both sides of the heat resistant insulating film, even if an internal short circuit occurs. , The heat transfer due to this is reduced by this heat resistant insulating film and this heat resistant insulating film is not melted by this heat, so that internal short circuit is prevented from spreading to the adjacent positive and negative electrodes, and the battery itself is damaged. In addition, the influence on the surroundings can be minimized, and the volume can be increased by the thickness of the heat-resistant insulating film to make the size relatively small.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the lithium ion secondary battery of the present invention will be described below with reference to FIGS. 1, 2 and 3. In FIG. 3, reference numeral 10 denotes a flat rectangular battery case, and the flat rectangular battery case 10 has, for example, a thickness of 300.
A battery case body 10a having a lateral length of approximately 300 mm, a vertical length of approximately 115 mm, and a thickness of approximately 22 mm, and a top cover made of a stainless steel plate having a thickness of 1.5 mm. And 10b.

In the flat rectangular battery case 10, as shown in FIG. 2, the sheet-shaped positive electrode 2 is housed in the bag-shaped separator 8 and the sheet-shaped negative electrode 3 is housed in the bag-shaped separator 8. The electrode laminated body 14 in which the negative electrode units are alternately laminated is housed.

In this example, the positive electrode 2 is manufactured as follows. Li / lithium carbonate and cobalt carbonate
Mix so that Co (molar ratio) = 1 and in air 90
The positive electrode active material (LiCoO ₂ ) was synthesized by firing at 0 ° C. for 5 hours. This positive electrode active material is crushed using an automatic mortar,
LiCoO ₂ powder having an average particle size of 15 μm was obtained.

91 parts by weight of a mixture obtained by mixing 95 parts by weight of the LiCoO ₂ powder thus obtained and 5 parts by weight of lithium carbonate, 6 parts by weight of graphite as a conductive material, and fluorinated as a binder. 3 parts by weight of vinylidene resin are mixed to form a positive electrode mixture, which is dispersed in N-methyl-2-pyrrolidone to form a slurry, and the slurry-like positive electrode mixture is used as the positive electrode current collector 5. A strip of aluminum foil having a thickness of 20 μm, which is coated on both sides with the lead portions left, dried, and compression-molded by a roller press machine, and the positive electrode active material (positive electrode mixture) 4 is coated on both sides of the positive electrode current collector 5. The positive electrode raw material is prepared.

The size of the coated portion of the positive electrode active material 4 in which the strip-shaped raw material of the positive electrode electrode is continuous with the lead portion is, for example, 107 mm.
The die-cut sheet-shaped positive electrode 2 was applied with the positive electrode active material 4 to a thickness of 25 mm.
Bag-shaped separator 8 in which two microporous polypropylene films each having a size of 112 μm and a size of 112 mm × 273 mm are bonded together
To be a positive electrode unit. In this case, the positive electrode 2
The lead portion 5a of the above is exposed from the separator 8.

Further, in this example, the negative electrode 3 is manufactured as follows. Petroleum pitch was used as a starting material, and 10 to 20% of oxygen was introduced into this as a functional group (so-called oxygen cross-linking). obtain.

90 parts by weight of this carbon material as a negative electrode active material and 10 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, and this was mixed with N-methyl-2-pyrrolidone. To form a slurry, and the slurry-like negative electrode mixture is applied on both surfaces of the strip-shaped negative electrode current collector 7 leaving the lead portions, dried, and then compression-molded by a roller press machine to form a negative electrode current collector. A strip-shaped negative electrode raw material in which the negative electrode active material (negative electrode mixture) 6 is applied to both surfaces of 7 is prepared.

In this example, as this negative electrode current collector 7, as shown in FIG. 1, a copper foil 7b having a thickness of 8 μm is adhered to both sides of a polyimide film 7a having a thickness of 25 μm as a heat-resistant insulating film. Use what you did. As the heat resistant insulating film 7a, a polyphenylene sulfide film, a polyamide film or the like can be used in addition to the polyimide film.

In order to prepare such a negative electrode current collector 7 as shown in FIG. 1, the above heat-resistant insulating resin is melted at a high temperature, and the melted heat-resistant insulating resin is applied between two copper foils 7b. And a method of bonding the copper foil 7b to both surfaces of the heat resistant insulating film 7a by using an adhesive such as urethane resin, and a method of making the heat resistant insulating film 7a. There is a method of depositing copper on both surfaces.

In addition, the strip-shaped negative electrode electrode raw material has a size, for example, of a portion where the negative electrode active material 6 applied to the lead portion has a size of 1
The die was punched out so as to have a size of 09 mm × 270 mm, and the die-pressed portion of the negative electrode 3 coated with the negative electrode active material 6 was 25 μm thick.
m, and the size of 112 mm × 273 mm of polypropylene microporous film is accommodated in the bag-shaped separator 8 which is pasted together to form a negative electrode unit. In this case, the lead portion 7a of the negative electrode 3 is exposed from the separator 8.

In this example, as shown in FIG. 2, 20 sheets of the negative electrode 3 housed in the bag-shaped separator 8 and 19 sheets of the positive electrode 2 housed in the bag-shaped separator 8 were alternately laminated. Then, an adhesive tape is wrapped around the outer periphery and fixed to form the electrode laminate 14. In this case, the lead portion 5 of the positive electrode 2
a is on one side and the lead portion 7 of the negative electrode 3
Let a be the other side.

Further, as shown in FIG. 3, this electrode laminated body 1
One side of 4, ie, the lead portion 5a exposed from the separator 8 of the positive electrode 2 is ultrasonically welded and connected to the positive electrode terminal 11 made of aluminum. The lead portion 7a exposed from the other side of the electrode laminated body 14, that is, the separator 8 of the negative electrode 3 is welded and connected to the negative electrode terminal 12 made of copper by ultrasonic welding.

As shown in FIG. 3, the outer periphery of the electrode laminate 14 to which the positive electrode terminal 11 and the negative electrode terminal 12 are welded and connected is covered with insulating sheets 15a and 15b.
At the positive electrode terminal 11 and the negative electrode terminal 12, the bolts 1 are inserted through O-rings 16a and 17a and insulating rings 16b and 17b.
It is fastened and fixed by 6c and 17c, then inserted into the battery case body 10a, and then the upper lid 10b is welded to the battery case body 10a by laser welding and hermetically fixed.

In this case, an organic electrolyte solution in which LiPF ₆ is dissolved in a mixed solvent of propylene carbonate and diethyl carbonate at a ratio of 1 mol / l is injected into the flat rectangular battery case 10.

The upper lid 10b is provided with a safety valve 13 for venting the gas inside when the internal pressure of the closed flat rectangular battery case 10 becomes higher than a predetermined value.

According to the lithium ion secondary battery of this example, a large capacity lithium ion secondary battery having a capacity of 20 Ah can be obtained.

According to this example, since the negative electrode current collector 7 has the heat-resistant insulating film 7a and the copper foils 7b adhered on both sides thereof, even if an internal short circuit occurs, the heat transfer due to this occurs. The heat-resistant insulating film 7a becomes smaller, and the heat-resistant insulating film 7a is not melted by this heat, so that it is possible to prevent an internal short circuit from spreading between adjacent positive and negative electrodes, and damage the battery itself. Also, the influence on the surroundings can be minimized.

Incidentally, when the lithium-ion secondary battery according to this example was subjected to the next puncture test, only smoke was emitted from the holes pierced by the nails, and no enlargement of the internal short circuit was observed.

However, as a comparative example (conventional example), the negative electrode current collector 7 of the negative electrode 3 of the above-mentioned embodiment was composed of only a copper foil having a thickness of 10 μm, and the others were the same as those of the above-mentioned embodiment. When a nail penetration test was performed on the secondary battery, gas was ejected.

Further, according to the present example, the lithium ion secondary battery has a relatively small volume as compared with the conventional one, because the volume of the negative electrode current collector 7 increases as the thickness of the negative electrode current collector 7 increases. There is a profit that can be made.

In the above embodiment, the negative electrode current collector 7 is a heat-resistant insulating film 7a coated with copper foils 7b on both sides, but the positive electrode current collector 5 is used instead.
As the heat-resistant insulating film may be coated with aluminum foil on both sides, or both may be used, and in this case also, it is easy to obtain the same effect as the above. You can understand.

Further, in the above-mentioned embodiments, the example in which the present invention is applied to the flat type lithium ion secondary battery has been described, but it goes without saying that the present invention can also be applied to the cylindrical lithium ion secondary battery. .

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.

[0035]

According to the present invention, one or both of the positive electrode current collector and the negative electrode current collector having the heat-resistant insulating film coated with the metal foil are used. Therefore, even if an internal short circuit occurs. Since the heat transfer due to this is reduced by the heat resistant insulating film and the heat resistant insulating film is not melted by this heat, it is possible to prevent the internal short circuit from spreading to the adjacent positive and negative electrodes. The damage to the battery itself and the influence on the surroundings can be minimized, and the volume of the lithium ion secondary battery is increased by the thickness of the heat resistant insulating film, so that the lithium ion secondary battery can be made relatively small.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view showing a main part of an embodiment of a lithium ion secondary battery of the present invention.

FIG. 2 is an enlarged sectional view showing an example of a main part of the present invention.

FIG. 3 is an exploded perspective view showing an example of a lithium ion secondary battery.

[Explanation of symbols]

 2 Positive electrode 3 Negative electrode 4 Positive electrode active material 5 Positive electrode current collector 6 Negative electrode active material 7 Negative electrode current collector 7a Heat resistant insulating film 7b Copper foil 8 Bag separator 10 Flat rectangular battery case 11 Positive electrode terminal 12 Negative electrode terminal 13 Safety valve 14 electrode stack

Claims (3)

[Claims] 1. A lithium ion secondary battery in which a positive electrode having a positive electrode current collector coated with a positive electrode active material and a negative electrode having a negative electrode current collector coated with a negative electrode active material are laminated via a separator. A lithium ion secondary battery, wherein one or both of the positive electrode current collector and the negative electrode current collector is a heat-resistant insulating film coated with a metal foil. 2. The lithium-ion secondary battery according to claim 1, wherein the heat-resistant insulating film is made of polyimide. 3. The lithium-ion secondary battery according to claim 1, wherein one or both of the positive electrode current collector and the negative electrode current collector melt a heat-resistant insulating resin at a high temperature, and use it to form two metal foils. A lithium ion secondary battery, which is produced by pressing while pouring it in between.