JPH09199099A - Lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and high-reliability lithium ion battery storing a power generating element in a bag-like storage body made of a functional member by providing a pressure releasing means on the bag-like storage body. SOLUTION: An electrode group is stored in a bag-like storage body 5 made of a film laminated with polyethylene on both faces of an aluminum foil and opened at one end, a prescribed quantity of an electrolyte is injected, then the opening section of the bag-like storage body 5 is sealed by thermal deposition to obtain a battery. A pressure release valve 6 fitted to the bag-like storage body 5 is operated to rupture the storage body 5 only when the internal pressure of the storage body 5 becomes the prescribed value or above, and the operating pressure is set to 1.2-20kg/cm<2> .

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium ion battery.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has realized a reduction in size and weight of electronic devices one after another. Along with this, there is an increasing demand for batteries that are power sources to be further reduced in size, weight, and energy density.

Comparing the approximate energy densities of various small secondary batteries used as power sources for portable equipment,
20-40 Wh / kg, 50-100 Wh /
1, 30-60 Wh / k for nickel cadmium battery
g, 100 to 160 Wh / l, 4 for nickel metal hydride batteries
5 to 65 Wh / kg and 160 to 200 Wh / l, while the lithium ion battery has 60 to 125 Wh / kg,
It is said to be 190 to 310 Wh / l. in this way,
Since lithium-ion batteries have higher energy density than other batteries, they are expected to be put to practical use.

A lithium ion battery which has been generally developed in the past includes a wound electrode plate group housed in a cylindrical or rectangular case, or a laminated plate electrode plate and a separator. Some are stored in a rectangular case.

However, since the case used for these lithium ion batteries is formed of a metal container which also serves as a negative electrode terminal, it is unavoidable that the material cost and the manufacturing cost become high. Therefore, as a means of providing a cheaper lithium-ion battery, a positive and negative electrode plate and a separator, one by one, are laminated in a polyethylene sheet or an aluminum sheet into a bag-shaped body made of a film member having non-gas permeability. It has been proposed to store and then bond and seal it by heat welding or the like. Such a schematic structure is not intended for a lithium ion battery, but is disclosed in, for example, Japanese Utility Model Laid-Open No. 60-16236.
As disclosed in No. 2, a heat-sensitive adhesive layer from the inside,
Seal the plate electrode with a laminate film consisting of aluminum foil and polymer film, form a metal vapor deposition film to be the lead body on the heat sensitive layer of the laminate film, and contact one end of the metal vapor deposition film with the electrode rod. Those sealed with a laminate film (see FIG. 1) and JP-A-61-2061
As disclosed in Japanese Patent No. 57, there is one in which a flat electrode plate is inserted into a tubular laminated film member, and then both ends are heat-welded and sealed (see FIG. 2).

[0006]

However, the lithium ion battery having the above-mentioned structure in which the electrode group is housed in the bag-shaped body made of the film member can be manufactured at a low cost and can be applied to small equipment. Since the battery was pursued to be thin, the electrode plate group is inevitably thin and the capacity is 0.
It was only 2 Ah or less. However, with the recent diversification of various electronic devices, the advent of lithium ion batteries with higher capacity and lower cost is desired.

In order to meet such a demand, the inventors of the present invention have proposed an invention of a sealed type secondary battery characterized in that a winding type electrode plate group is housed in a bag-shaped housing made of a functional film member, An electrode plate group using a lithium titanate or a carbon material having a (002) plane spacing of 3.7 angstroms or more by a wide-angle X-ray diffraction method as a negative electrode material is formed into a bag-shaped container made of a functional film member. The invention of the lithium-ion battery, which is characterized in that it is housed, is made and a patent is applied.

In the process of developing various high-capacity lithium ion batteries by applying such a technique, a relatively high-capacity lithium ion in which the power generation element is housed in a bag-shaped container made of a functional film member. In the case of batteries, we obtained the knowledge that in order to further improve battery performance and reliability in use, consideration must be given to the rise in internal pressure of the storage,
The present invention has been accomplished.

That is, the present invention effectively copes with an increase in internal pressure of the lithium ion battery in which the power generation element is housed in a bag-shaped housing made of a functional film member.
It is therefore an object of the present invention to provide a lithium ion battery that is inexpensive and highly reliable in terms of performance and use.

[0010]

Therefore, in a lithium ion battery in which a power generating element is housed in a bag-shaped housing made of a functional film member, the working pressure is 1.2 to 20 Kg / cm.
^The above problem is solved by the invention of a lithium-ion battery characterized in that the pressure releasing means as ² is attached to the bag-shaped container.

In the present invention, the functional film member means that when it is brought into contact with an electrode group consisting of a positive electrode, a negative electrode, a separator, etc., an electrolytic solution, etc., a chemical change occurs, the electrolytic solution leaks, and oxygen It is a generic term for sheet-shaped members provided with various functionalities so that hydrogen, gas such as organic vapor, water vapor and the like are not easily permeated or broken. For example, a gas barrier layer formed of a metal foil film such as aluminum or a foil film formed of an inorganic material such as glass, a reinforcing layer made of a synthetic resin, and an adhesive layer can be laminated, but it is not always necessary. It is not necessary that a plurality of types of sheet members are laminated, and a single layer may be used as long as they have equivalent functional performance.

In the present invention, the bag-shaped container made of a functional film member is mainly composed of the functional film member, and the electrode plate group and the electrolytic solution can be freely contained in the container itself. It is a generic term for battery containers configured to be hermetically sealed by the heat-welding property of the functional film member itself or another bonding member without having a pressing force capable of suppressing swelling.

Further, in the present invention, the power generating element is a general term for positive and negative electrodes, electrolytic solution, separator and the like, but it is well known and commonly used by those skilled in the art that auxiliary members such as output leads are arranged inside the battery. It is a technical means.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not limited to the following Examples, and various modifications may be made without departing from the scope of the invention. It is possible.

[Preparation of Positive Electrode Active Material] LiNi _0.75 Co
A composite oxide having a composition of _0.2 Al _0.05 O ₂ was prepared. As an adjusting method, β-Ni _1-x Co _x (O
H) ₂ and Al (OH) ₃ were mixed at a predetermined ratio, and then fired and synthesized in oxygen at 720 ° C. for 40 hours.
After firing, these were pulverized to an average of 3.5 μm to obtain a positive electrode active material for a lithium secondary battery. The firing temperature is 6
You may set suitably in the range of 00-950 degreeC. [Adjustment of Positive Electrode] 93 parts by weight of LiNi _0.75 Co _0.2 A
2.5 parts by weight of acetylene black was mixed with 1 _0.05 O ₂ , and polyvinylidene fluoride as a binder was added thereto so that the total amount was 4.5 parts by weight, and N-methylpyrrolidone was further added as a solvent. An active material paste was obtained by kneading. Next, this active material paste is applied to an electrode base made of aluminum foil and having a width of 50 mm,
It was dried to prepare a positive electrode for a lithium secondary battery.

Examples of binders other than those mentioned above include polytetrafluoroethylene, rubber-based polymers, mixtures of these with cellulose-based polymers, and copolymers mainly containing polyvinylidene fluoride.

[Adjustment of Negative Electrode] The average particle size is 15 μm,
Graphite particles having a (002) plane spacing of 3.35 Å as a lithium ion intercalation member and styrene-butadiene rubber as a binder were applied to a copper foil base having a width of 5 mm and dried to prepare a negative electrode. did.

[Preparation of Separator] A polyethylene microporous film having a thickness of 25 μm was used as a separator. The separator is not particularly limited, and various types of conventionally used separators can be used.

[Adjustment of electrode plate group] The wound electrode plate in which the positive and negative electrodes and the separator are wound in a flat spiral shape, and the positive and negative electrodes and the separator are laminated in a flat plate shape. A laminated electrode group having the same capacity as the group was prepared. This is shown in FIG. In this figure, 1 is a positive electrode plate, 2 is a separator, 3 is a negative electrode plate, 4 is an output lead, and 7 is a flat spiral wound electrode plate group. In this embodiment, the flat spiral wound type electrode plate group is used. However, as shown in FIG. 4, a laminated type electrode plate group in which a plate-shaped electrode plate and a separator are laminated may be used.

[Preparation of Non-Aqueous Electrolyte] LiPF ₆ was dissolved at 1 mol / l in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 4: 6 to prepare a non-aqueous electrolyte. The non-aqueous electrolytic solution is not limited to the above, and LiBF ₆ , LiClO _4, etc. in a mixed solvent with a solvent such as propylene carbonate, 1,2-butylene carbonate, dimethyl carbonate, diethyl carbonate, sulfolane, and gamma butyrolactone. Various solutions such as a solution obtained by dissolving the solute can be used.

[Preparation of Battery] Next, a film obtained by laminating polyethylene on both sides of an aluminum foil,
The above electrode plate group was housed in the bag-shaped container 5 having one end opened, a predetermined amount of electrolytic solution was injected, and the opening of the bag-shaped container 5 was sealed by a heat welding method to obtain a lithium ion having a nominal capacity of 4 Ah. I got a battery. FIG. 5 is a schematic view showing a side wall of the lithium ion battery. In this embodiment, the bag-shaped container 5 has an internal pressure of 3
It is designed to withstand over 0 Kg / cm ² .

Numeral 6 is a pressure release valve attached to the bag-shaped container 5, and the operating pressure is 1.0, 1.2, 6.0, 20.
0 and 30.0 Kg / cm ² were prepared. In this embodiment, as a pressure release valve, a rupture film configured to be broken only when the internal pressure of the container becomes a predetermined value or more (made of the same member as the bag-shaped container, and has a kerf for breaking). However, the present invention is not limited to this, and the heat welding strength may be set so that a part of the heat welding sealing portion of the bag-shaped container 5 opens at a predetermined pressure, or another pressure valve. May be used.

In the above examples, a sheet obtained by laminating polyethylene on both sides of an aluminum foil was used. However, instead of polyethylene, a thermoplastic resin such as polyethylene terephthalate, polypropylene or nylon may be used, or polyvinylidene chloride or ethylene vinyl acetate copolymer may be used. Saponified,
It is also possible to use a functional film laminated with a barrier layer such as polyacrylonitrile.

Further, in the above embodiment, the bag-shaped container having one end opened is used, but a method of sandwiching the electrode plate group between two functional film members and joining the peripheries, or a cylinder having both ends opened. It is also possible to employ a method of joining the openings at both ends using a strip.

[Test] The above-mentioned various batteries having different operating pressures of the pressure valves were first subjected to a drop test. As a result, it was found that when the operating pressure was 1.0 kg / cm ² , the valve was opened only by dropping it from a height of 1 m above the ground, and there was a problem in practical use. None of the others had any problems in practical use in the drop test.

Next, these batteries were subjected to 400 mA constant current /
After charging under the condition of 4.1V constant voltage x 12h (25 degrees C),
It was subjected to the "nail stick test". The "nail piercing test" is, for example, a test of piercing and penetrating a flat portion of the spiral electrode plate group with a 5 inch nail in FIG. 5, which causes an internal short circuit.
The pressure inside the container rises due to rapid heat generation and gas generation.

As a result, the operating pressure is 1.2, 6.0, 2
In the case of 0.0 kg / cm ² , no event was observed in which the pressure valve actuated to release the internal pressure and damage the peripheral equipment. On the other hand, the operating pressure is 30.0 kg /
It was found that in the case of cm ^2, the internal power generating element spouts together with the gas at the same time as the pressure valve is activated, and damages the peripheral equipment, which is a problem in practical use.

In the above example, the battery having the nominal capacity of 4 Ah was described, but the same test result showed that the same result was obtained for the batteries having the nominal capacity of 0.2 Ah or more.

As described above, in the lithium ion battery in which the power generating element is housed in the bag-shaped container made of the functional film member, the pressure release means having an operating pressure of 1.2 to 20 kg / cm ² is housed in the bag. Attaching to the body is suitable for practical use.

[0030]

As described above, in the lithium ion battery according to the present invention, the power generation element is housed in the bag-shaped container made of the functional film member, and the working pressure is 1.2 to 20 kg /.
It is characterized in that a pressure releasing means of cm ² is attached to the bag-shaped container.

This makes it possible to provide a lithium ion battery which is inexpensive and has high performance, and which has no problem in practical use even when the battery pressure rises.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional example.

FIG. 2 is a diagram showing a conventional example.

FIG. 3 is a diagram showing a flat spiral wound electrode group.

FIG. 4 is a diagram showing a laminated electrode group.

FIG. 5 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Separator 3 Negative electrode 4 Output lead 5 Bag-shaped storage body 6 Pressure release valve 7 Flat spiral wound electrode plate group 8 Flat laminated electrode plate group

Claims (1)

[Claims] 1. A lithium ion battery in which a power generation element is housed in a bag-shaped container made of a functional film member, and a pressure release means having an operating pressure of 1.2 to 20 kg / cm ² is provided in the bag-shaped container. A lithium-ion battery characterized by being attached.