JP3213635B2 - Cylindrical lithium ion secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery having a built-in safety valve mechanism.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as mobile phones and video cameras have become smaller, lighter, and more sophisticated, the capacity of secondary batteries, which are the power sources of these electronic devices, has been increased and the energy density has been increased. Demands are growing. Recently, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been developed in addition to conventionally used lead secondary batteries and nickel cadmium secondary batteries.

[0003] However, in these secondary batteries, the internal pressure of the battery rises due to, for example, a short circuit, and the battery itself may be damaged relatively quickly, losing the function of the battery, or damaging peripheral devices.

For example, in the lithium ion secondary battery,
When the battery is overcharged or short-circuited due to malfunction or misuse of the device, the inside of the battery is heated, the electrolytic solution is decomposed, gas is generated, the internal pressure of the battery is increased, and the battery sometimes explodes. For this reason, the secondary battery is provided with a safety valve mechanism for explosion protection.

Meanwhile, as a lithium ion secondary battery provided with the safety valve mechanism, one having a structure shown in FIGS. 5 and 6 has been proposed. That is, a straight portion and both ends thereof are V
A pressure releasing groove 22 having a letter shape is formed. The bottom of the groove 22 functions as a valve membrane 23. The groove 22 is formed on the outer surface of the bottom of the outer can 21 by pressing with a punch having the same shape as the groove 22 or by etching. In the secondary battery having such a configuration, when the internal pressure increases due to an overcurrent or the like, the valve membrane 23 is broken to form a hole.
The gas filled in the outer can 21 is released from this hole, and the explosion of the secondary battery is prevented. The operating pressure of the safety valve mechanism is 15 ± 5k to prevent the explosion due to the rise of the internal pressure.
gf / cm ² It is desirable that

However, in order to form the groove 22 by either the press working or the etching work and to form the valve membrane 23 at the bottom thereof, which reliably breaks under the operating pressure, 0.2 to 0 It is necessary to perform the pressing or the etching on the bottom of the outer can 21 having a thickness of 0.4 mm with a large processing amount corresponding to about 9/10 of the thickness. As a result, a molding error easily occurs, and it becomes difficult to accurately form a valve membrane having an intended thickness, and thus the operating pressure tends to vary.

Therefore, in order to reduce the molding error,
It was necessary to increase the thickness of the valve membrane formed on the bottom of the outer can to reduce the amount of processing. However, when the thickness of the valve membrane is increased, the operating pressure is, for example, 40 kg.
f / cm ² When the valve membrane breaks, the contents of the secondary battery jump out of the outer can, resulting in poor safety.

[0008]

[SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems, a cylindrical lithium having a safety valve mechanism including a valve membrane is reliably broken at the desired operating pressure <br / > Provide Mion secondary batteries.

[0009]

DISCLOSURE OF THE INVENTION A cylindrical litch according to the present invention.
Um-ion rechargeable battery has an outer can containing power generation elements ,
A sealing body provided by welding on the outer can and having an arc-shaped pressure release hole , and an insulating material interposed between the sealing body and the sealing body.
A terminal to be attached, the pressure release hole, and an outer surface of the sealing body.
A thin film attached to the thin film;
A circular groove opposed to the pressure hole, formed in the thin film,
A radial groove intersecting with a circular groove, and
And a safety valve mechanism having a shape groove and a bottom portion of the linear groove as a valve membrane.

[0010]

[0011]

According to the present invention, a sealing body attached to an outer can and having a hole for reducing the pressure in the outer can is provided, and a sealing body provided on an outer surface of the sealing body and corresponding to at least the hole. By providing a safety valve mechanism consisting of a thin film with a valve film formed at the bottom of the groove, a thin film is used as the thin film as compared with the outer can bottom which needs to have a sufficient thickness for maintaining strength. be able to. As a result, it is possible to greatly reduce the amount of processing when forming the valve film that is broken at an intended operating pressure in the thin film, so that a molding error (a valve film thickness error) can be significantly reduced. Therefore, it is possible to obtain a safety valve mechanism provided with a valve membrane that is always broken at an intended operating pressure. It is possible to prevent an explosion caused by an excessive increase in the internal pressure due to the breakage with good reproducibility.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a cylindrical lithium ion secondary battery will be described with reference to FIGS.

The outer can 1 houses a power generating element and also serves as, for example, a negative electrode terminal. The sealing body 2 having a hole in the center is hermetically attached to the outer can 1 by laser welding. The positive electrode pin terminal 3 is attached by a hermetic seal via a glass insulating material 4 to a center hole of the sealing body 2 so that both ends thereof protrude from the upper and lower surfaces of the sealing body 2,
The outer can 1 serving as a negative electrode terminal is insulated from the sealing body 2. The outer can 1, the sealing body 2, and the positive electrode pin terminal 3 are made of, for example, stainless steel.

The safety valve mechanism 5 has a hole 6 opened in the sealing body 2 and a bottom portion formed by a groove 7 provided at a location corresponding to the hole 6 in a gas-tight manner by laser welding on the outer surface of the sealing body 2. And a thin film 9 on which a valve film 8 is formed. The hole 6 includes, for example, three arc-shaped holes formed concentrically with the center of the sealing body 2. The groove 7 includes, for example, a circular groove 10 provided at a position corresponding to the hole 6 and a linear groove 11 intersecting with the circular groove 10 and extending radially from the center of the sealing body 2. It is formed. The thin film 9 has, for example, a ring shape. Further, since the thin film 9 is attached to the sealing body 2 by laser welding, it is preferable that the thin film 9 is formed of the same material as the sealing body 2, for example, stainless steel.

According to such a configuration, three arc-shaped holes 6 opened in the sealing body 2 attached to the outer can 1 and formed concentrically with the center of the sealing body 2; Body 2
And a thin film 9 having a valve film 8 formed at the bottom thereof by a groove 7 provided at a position corresponding to the hole 6 and hermetically attached by laser welding to the valve valve 8. It can be provided on the thin film 9 which is thinner than the bottom of the outer can 1 whose thickness is restricted in order to maintain strength. As a result, the processing amount for providing the valve membrane 8 that breaks at an intended operating pressure is greatly reduced as compared with the related art, so that the molding error is reduced and the variation in the operating pressure of the safety valve mechanism 5 is reduced. be able to.

In a lithium ion secondary battery incorporating such a safety valve mechanism 5, an abnormal current flows due to a short circuit due to overcharge or misuse, and the temperature inside the battery rises.
When the electrolyte of the power generation element housed in the outer can 1 is decomposed, gas is generated, and the inner pressure of the outer can 1 increases,
The gas applies pressure to the valve membrane 8 of the thin film 9 through the arc-shaped hole 6 of the safety valve mechanism 5 formed in the sealing body 2. The valve membrane 8 of the safety valve mechanism 5 includes the thin film 9
Is formed with a small thickness error and a small thickness, the gas (operating pressure) is reliably broken by the pressure, the gas can escape to the outside, and an explosion caused by an excessive increase in battery internal pressure can be prevented. it can.

FIG. 4 shows the relationship between the thickness of the valve membrane 8 formed at the bottom of the groove 7 and the tearing pressure (operating pressure) of the safety valve mechanism 5. From FIG. 4, the preferable operating pressure for preventing the explosion of the secondary battery is 15 ± 5 kgf / c.
m ² It is. Therefore, from the viewpoint of forming the valve membrane 8 that is broken by the operating pressure on the thin film 9 and reducing the molding error, the thickness of the thin film 9 is set in the range of 50 to 60 μm,
Further, it is desirable that the thickness of the valve membrane 8 be in the range of 20 to 33 μm. In the above embodiment, the number of the holes 6 is three, but the number of the holes 6 can be, for example, two or four.

In the above embodiment, the circular groove 10 provided at a position corresponding to the hole 6 and the linear groove 11 intersecting with the circular groove and extending radially from the center of the sealing body 2 are formed in the thin film 9. However, for example, an arc-shaped groove or the like provided at a location corresponding to the hole 6 can also be used. In the above-described embodiment, the description has been made by applying the present invention to a cylindrical lithium ion secondary battery. However, the present invention can be similarly applied to a prismatic lithium ion secondary battery.

[0019]

As described above in detail, according to the present invention, an explosion caused by an increase in the internal pressure of the battery can be effectively prevented, and a highly safe cylindrical lithium ion secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view of a safety valve mechanism of a cylindrical lithium ion secondary battery according to an embodiment.

FIG. 2 is an exploded view of a safety valve mechanism of the cylindrical lithium ion secondary battery of FIG.

FIG. 3 is an enlarged sectional view of FIG. 1;

FIG. 4 is a characteristic diagram showing a change in a cutting pressure with respect to a change in a valve membrane thickness in a safety valve mechanism.

FIG. 5 is a perspective view of a safety valve mechanism of a conventional cylindrical lithium ion secondary battery of the present invention.

FIG. 6 is a sectional view of a safety valve mechanism of the cylindrical lithium ion secondary battery of FIG. 5;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Battery outer can, 2 ... Sealing body, 5 ... Safety valve mechanism, 6 ...
Hole, 7 ... groove, 8 ... valve membrane, 9 ... thin film.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masamichi Kawabe 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Horikawacho Plant (72) Inventor Isao Kuribayashi 1-1-2 Yurakucho, Chiyoda-ku, Tokyo Asahi Kasei Inside Industrial Co., Ltd. (72) Inventor Shigeo Kasahara 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Co., Ltd. (56) References JP-A-61-121261 (JP, A) JP-A-4-349347 (JP, A) JP-A-64-23873 (JP, U) (58) Fields investigated (Int .Cl. ⁷ , DB name) H01M 2/12 101 H01M 2/08 H01M 10/40

Claims (1)

(57) [Claims] And outer can 1. A housing a power generating element, wherein provided by welding outer can, and the sealing body release pressure holes <br/> arc shape is open, via an insulating material in the sealing body A terminal to be attached, the pressure release hole, and a thin film attached to the outer surface of the sealing body
And a circle provided on the thin film and facing the pressure release hole.
Grooves, radially formed in the thin film and intersecting the circular grooves
And a linear groove of the circular groove and the linear groove.
A cylindrical lithium ion secondary battery comprising: a safety valve mechanism having a bottom portion as a valve membrane.