JPH11329405A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a current interruption without the leakage of electrolyte to the outside, and prevent the opening of a current path due to a falling electric shock by forming a diaphragm and an internal terminal plate by use of aluminum, and specifying the thickness of the internal terminal plate situated in the connecting part. SOLUTION: The thickness of an internal terminal plate situated in the connecting part between a diaphragm and the internal terminal plate in a nonaqueous electrolyte secondary battery is set to 90% or less of the thickness of the diaphragm situated in the connecting part. The lower end periphery of metal case 13 is bent inward, and a circular diaphragm 18 consisting of aluminum is supported and fixed to the bent part 17 with electric conduction and airtightness. The internal terminal plate 21 consisting of aluminum is formed of a disk part 23 situated on the lower surface of an insulating plate 20 and having a raise part 22 on the periphery and a strip lead through part 24 integrated thereto and having the other end extended to the lower face near the left side of a plate gasket 10. A circular thin part 25 is formed near the center of the disk part 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having a current path interrupting mechanism.

[0002]

2. Description of the Related Art In recent years, with the miniaturization, weight reduction, and cordlessness of electronic devices such as personal computers, there is a demand for a small, lightweight, high energy density, repetitive charge / discharge battery as a driving power source.

A secondary battery of this type uses lithium, a lithium alloy, or the like as a negative electrode active material, and oxides such as vanadium, titanium, molybdenum, and niobium as positive electrode active materials.
Those using sulfides and selenides are known. Recently, lithium ion secondary batteries using carbon as the negative electrode active material and lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide as the positive electrode active material have been developed and commercialized.

[0004] Specifically, a conductive agent is mixed with a binder in the active material of the positive and negative electrodes, and these pastes are respectively pressed and formed into a current collector to form a positive electrode and a negative electrode.
Subsequently, a porous film made of polyethylene or the like is interposed between the positive and negative electrodes and wound to produce a power generating element.
Thereafter, the power generating element is housed in an outer can, a non-aqueous electrolyte is housed therein, and a lid is hermetically attached to the opening of the outer can to provide a non-aqueous solution such as a sealed lithium ion secondary battery. The electrolyte produces a secondary battery.

[0005] In addition to the coin shape and the cylindrical shape, there is a growing demand for a battery having excellent volumetric efficiency when stored, such as a rectangular shape or an oval shape, due to a demand for thinner and space-saving equipment.

When the above-described non-aqueous electrolyte secondary battery is overcharged or overdischarged during charging and discharging, gas is generated in the battery due to decomposition of the active material of the power generation element and the electrolyte, and the internal pressure rises. Occur. If this internal pressure rise is left, the battery will burst or the electrolyte will be scattered, and the electronic equipment on which the battery is mounted will be damaged.

For this reason, the conventional non-aqueous electrolyte secondary battery incorporates a current path breaking mechanism having an internal terminal plate and a deformable diaphragm connected thereto in a current path between the power generating element and the external terminal. Have been. In this current path cutoff mechanism, the internal terminal plate and the diaphragm are normally connected, and when the internal pressure rises, the diaphragm is deformed and separated from the internal terminal plate to cut off the current path.

[0008]

However, in the conventional current path breaking mechanism, the diaphragm is broken when the internal pressure rises due to the connection structure between the diaphragm and the internal terminal plate, and the electrolyte leaks from the broken part, There has been a problem that a hole is opened in the diaphragm to release the internal pressure and the current cutoff function does not work, or the diaphragm and the internal terminal plate are detached due to a drop or the like and the internal path is opened.

According to the present invention, when the internal pressure rises due to the generation of gas during overcharge / overdischarge, the current can be reliably shut off without the electrolyte leaking to the outside, and the drop impact can be prevented. An object of the present invention is to provide a non-aqueous electrolyte secondary battery that can prevent an open current path.

An object of the present invention is to provide a non-aqueous electrolyte secondary battery further provided with a safety valve mechanism for releasing a gas to the outside to prevent an explosion when an internal pressure rises due to gas generation during an internal short circuit. It is assumed that.

[0011]

According to the present invention, there is provided a non-aqueous electrolyte secondary battery according to the present invention, wherein the diaphragm and the internal terminal plate are made of aluminum, and the thickness of the internal terminal plate located at the junction is: The thickness is not more than 90% of the thickness of the diaphragm located at the joint.

[0012] In the nonaqueous electrolyte secondary battery according to the present invention, it is possible to further provide a safety valve mechanism for releasing internal pressure to a member having a different polarity with respect to the current path cutoff mechanism.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery according to the present invention will be described below in detail with reference to the drawings, taking a rectangular non-aqueous electrolyte secondary battery as an example. Here, the square shape means that the shape when the outer can is cut at the surface including the power generation element is a rectangle, but allows the corner to be rounded.

FIG. 1 is a perspective view showing a non-aqueous electrolyte secondary battery according to the present invention, for example, a prismatic lithium ion secondary battery.
FIG. 2 is an enlarged sectional view of a main part of FIG.

An outer can 1 in the form of a bottomed rectangular tube made of metal
Has, for example, a negative electrode terminal, and an insulating film (not shown) is arranged on the inner surface of the bottom. Electrode body 2 as power generation element
Are stored in the outer can 1. The electrode body 2
Is manufactured by spirally winding a negative electrode, a separator, and a positive electrode such that the negative electrode is positioned at the outermost periphery, and then press-molding the flat electrode into a flat shape. A protective member 4 made of a synthetic resin and having a bottomed rectangular cylindrical shape having a lead extraction hole 3 near the center is disposed on the electrode body 2 in the outer can 1.

The metal lid 5 is hermetically joined to the upper end opening of the outer can 1 by, for example, laser welding. An electrolyte injection hole 6 is opened near the center of the lid 5, and a circular hole 7 for taking out a positive electrode terminal is opened at a location of the lid 5 away from the injection hole 6 to the right. ing. The plug 8 is inserted into the injection hole 6 after the electrolyte is injected into the outer can 1. Safety valve 9 consisting of an annular thin film
Is formed in a portion of the lid 5 located on the left side of the liquid injection hole 6.

The plate-shaped insulating gasket 10 made of synthetic resin is
A circular hole 11 is fixed to the entire back surface of the right side from the vicinity of the liquid injection hole 6 of the lid 5 and coincides with the circular hole 7 for taking out the positive electrode terminal. A cap-shaped aluminum or aluminum alloy case 13 having a circular hole 12 at the top is arranged on the back surface of the plate-shaped insulating gasket 10 such that the circular hole 12 faces the circular hole 11 of the gasket 10. A cylindrical external terminal 15 having a flange 14 at an upper end is provided with a synthetic resin cylindrical hole in the circular hole 7 for taking out the positive electrode terminal of the lid 5, the circular hole 11 of the plate gasket 10, and the circular hole 12 of the case 13. For example, the external terminal 1 is inserted through an insulating gasket 16.
By bending the lower end of 5 to the inner surface of the metal case 13 to fix the case 13 to the lid 5, the case 13 is electrically connected to the external terminal 15.

The case 13 has a lower peripheral edge bent inward, and a circular diaphragm 18 made of aluminum is supported and fixed to the bent portion 17 with electrical conduction and airtightness. A circular insulating plate 20 having a circular hole 19 opened in the vicinity of the center is disposed from the bottom surface of the case 13 to the upper surface of the bent portion 17.

The internal terminal plate 21 made of aluminum is
It is located on the lower surface of the insulating plate 20 and has a rising portion 2 at the periphery.
2 and a strip-shaped lead-out portion 24 integrated with the disc portion 23 and having the other end extending to the lower surface near the left end of the plate-like gasket 10. The disk part 2
3 is supported and fixed to the case 13 by bending the rising portion 22 inward at the bent portion 17 of the metal case 13 via the insulating plate 20. Near the center of the disk portion 23, a circular thin portion 25 having a thickness of 90% or less of the thickness of the diaphragm 18 is formed, and the upper surface of the circular thin portion 25 passes through the circular hole 19 of the insulating plate 20. The lower surface of the diaphragm 18 is joined by, for example, ultrasonic welding, resistance welding, or laser welding. The disk portion 23 has a plurality of gas flow holes 26 concentrically opened around the circular thin portion 25.

The positive electrode lead 27 has one end connected to the positive electrode (not shown) of the electrode body 2 and the other end connected to the internal terminal plate 21 through the lead extraction hole 3 of the holding member 4.
Is connected to the strip-shaped lead-out section 24.

In such a structure, the positive electrode (not shown) of the electrode body 2 is connected to the positive electrode lead 27 and the internal terminal plate 2.
1, the band-shaped lead-out portion 24, the circular portion 22, and the diaphragm 1
8. Connected to the external terminal 15 through the case 13.

The positive electrode of the electrode body 2 and the external terminal 15
The current path cut-off mechanism is constituted by the internal terminal plate 21, the insulating plate 20, and the diaphragm 18 arranged in the current path.

The plate-shaped gasket 10 and the strip-shaped lead-out portion 24 facing the liquid injection hole 6 have holes 2 respectively.
8, 29 are open.

The outer can is made of, for example, stainless steel or iron.

The negative electrode has a structure in which, for example, a paste containing a carbonaceous substance through which lithium ions are taken in and out is held on a current collector such as a thin copper plate.

The positive electrode has a structure in which a paste containing an active material such as lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide is held on a current collector such as an aluminum thin plate.

As the separator, for example, a porous film made of a synthetic resin such as polyethylene is used.

As the electrolyte, for example, a solution obtained by dissolving an electrolyte such as lithium perchlorate, lithium borofluoride, lithium hexafluoride, and lithium hexafluoride in an organic solvent such as ethylene carbonate or propylene carbonate is used. Can be

The diaphragm 18 and the internal terminal plate 2
Examples of aluminum used for A1 include A105
0, A1070, A1100, A1200, A1N30
And the like.

The reason why the thickness of the circular thin portion 25 of the internal terminal plate 21 joined to the diaphragm 18 is specified to be 90% or less of the thickness of the diaphragm 18 is as follows. . If the thickness of the thin portion 25 exceeds 90% of the thickness of the diaphragm 18, it becomes difficult to make the breaking strength at the joint of the thin portion 25 smaller than the breaking strength of the diaphragm 18. It becomes difficult to cut off the route. More preferably, the thickness of the circular thin portion 25 is the same as that of the diaphragm 18.
40 to 80% of the thickness.

The operating pressure of the safety valve 9 is set higher than the operating pressure of the current interrupt mechanism.

According to such a configuration, the gas is generated by the decomposition of the active material in the positive and negative electrodes constituting the electrode body 2 in the outer can 1 and the decomposition of the non-aqueous electrolyte at the time of overcharge or overdischarge during charge and discharge. When the internal pressure rises due to the generation of the gas, the gas flows into the protective member 4.
Flows into a plurality of gas flow holes 26 opened in the circular portion 23 of the internal terminal board 21 through the lead extraction holes 3 of the internal terminal board 21, and further presses the diaphragm 18 through the circular holes 19 of the insulating plate 20. Are bent upward away from the disk portion 23 of the internal terminal plate 21.

At this time, since the internal terminal plate 21 is joined to the diaphragm 18 at a portion of the circular thin portion 25 having a thickness of 90% or less of the thickness of the diaphragm 18, the circular thin portion at the joint portion is formed. The breaking strength of the portion 25 is smaller than the breaking strength of the diaphragm 18. As a result, as shown in FIG. 3 and FIG. 4, only the thin portion 25 is broken, and the broken pieces 30 are transferred to the lower surface of the diaphragm 18, so that the diaphragm 18 itself can be prevented from being broken. Therefore, the internal terminal plate 21 and the diaphragm 1
8 is cut off, and the current path of the cylindrical external terminal 14 fixed to the positive electrode of the electrode body 2 in the outer can 1 and the lid 5 via the cylindrical insulating gasket 16 is cut off. The charge state or the overdischarge state is stopped to prevent an excessive increase in the internal pressure.

Also, since the diaphragm 18 itself can be prevented from being broken when the conduction between the internal terminal plate 21 and the diaphragm 18 is interrupted, the electrolyte in the outer can 1 leaks out of the broken portion and damages the electronic equipment on which the battery is mounted. Can be prevented.

Further, in the current path interrupting mechanism, the thin portion 25 of the circular portion 23 of the internal terminal plate 21 and the diaphragm 18 are made of aluminum, and these members are joined in good electrical and mechanical connection. Has been
It is possible to prevent the joints from coming off due to an impact such as dropping and becoming electrically open.

Further, by forming the safety valve 9 composed of an annular thin film portion on the cover 5, an internal pressure rise during the overcharge / overdischarge is sharp, or an internal short circuit which cannot be dealt with by the current path interruption mechanism occurs. When the internal pressure rises,
As shown in the figure, the lid 5 is opened by the safety valve 9.
As a result, it is possible to prevent an accident such as an abrupt increase in the internal pressure or an internal short circuit that cannot be dealt with by the current path cutoff mechanism, causing the outer can 1 to burst or the like.

[0037]

FIG. 1 and FIG. 2 show an embodiment of the present invention.
This will be described in detail with reference to the prismatic lithium ion secondary battery shown in FIG.

(Example 1) First, insulating paper (not shown) is placed on the bottom surface of a rectangular outer can 1 made of iron, and the electrode body 2 is housed in the outer can 1 and then placed in the center. A rectangular tubular protective member 4 with a bottom and a lead extraction hole 3 opened at the portion was disposed on the electrode body 2.

The electrode body 2 was manufactured by the following method. First, a paste was prepared by mixing a lithium-cobalt composite oxide, a conductive agent, and a binder in the presence of a solvent, and the paste was applied to an aluminum substrate, dried, and compressed to obtain a positive electrode. Also, a paste is prepared by mixing graphite and a binder in the presence of a solvent,
This paste was applied to a copper substrate, dried and compressed to obtain a negative electrode. Subsequently, an electrode body was manufactured by spirally winding the separator 5 made of a porous film made of polyethylene between the positive and negative electrodes and forming the spirally flat shape.

Next, an iron lid 5 was hermetically joined to the opening of the outer can 1 by laser welding. The lid 5 has an injection hole 6 opened at the center and an operating pressure of 18.
A safety valve 9 comprising an annular thin film portion of 0 to 30.0 kgf;
It includes a current path cutoff mechanism having a case 13 made of aluminum, a diaphragm 18 and an internal terminal plate 21, and an external terminal 15 connected to the cutoff mechanism. Also,
Prior to laser welding of the lid 5, the positive electrode lead 27 of the electrode body 2 was connected to the internal terminal plate 21.

As the diaphragm 18 constituting the current path interrupting mechanism, an aluminum plate of A1100 having a thickness of 130 μm was used. As the internal terminal plate 21 constituting the blocking mechanism, an A1050 aluminum plate having a thickness of 250 μm was used, and a circular thin portion 25 having a thickness of 70 μm was formed by crushing the joint with the diaphragm 18.
Thin portion 2 of diaphragm 18 and internal terminal plate 21
5 was joined by ultrasonic welding. The current path interruption mechanism having such a structure has a current interruption pressure of 7.0 to 12.0 kg.
f.

Next, a non-aqueous solvent-based electrolyte obtained by dissolving an electrolyte of lithium hexafluoride in ethylene carbonate and methyl ethyl carbonate was injected into the outer can 1 through the injection hole 6 of the lid 5. The injection hole 6 was welded to a stopper 8 made of stainless steel (SUS304) and sealed, thereby producing the rectangular lithium ion secondary battery having the structure shown in FIGS. 1 and 2 described above.

(Comparative Example 1) A prismatic lithium ion secondary battery having a current path cutoff mechanism similar to that of Example 1 except that an A1050 without a circular thin portion and an aluminum plate having a thickness of 250 µm were used as internal terminal plates. Was manufactured. In addition,
The current path cutoff mechanism has a current cutoff pressure of 7.0 to 12.
The range was 0 kgf.

(Comparative Example 2) A square lithium ion secondary battery having the same current path interrupting mechanism as in Example 1 except that an A5052 without a circular thin portion and an aluminum alloy plate having a thickness of 250 µm were used as internal terminal plates. A battery was manufactured. The current path cutoff mechanism has a current cutoff pressure of 7.0-1.
The range was 2.0 kgf.

Example 1 and Comparative Examples 1 and 2
An overcharge test was performed on five secondary batteries. The results are shown in Table 1 below.

Further, 15 of Example 1 and Comparative Examples 1 and 2
A test of dropping the secondary batteries from a height of 150 cm onto the oak wood surface was performed. The results are shown in Table 1 below.

[0047]

[Table 1]

As is clear from Table 1, in Example 1, the current path cutoff mechanisms of all the secondary batteries were activated, and the operation was terminated in a very safe state without leakage of the electrolyte. The exothermic temperatures were all 70 ° C. or less. Furthermore, no significant change in the internal resistance due to the connectivity between the diaphragm and the internal terminal plate was observed in any of the batteries even after 100 drop tests.

On the other hand, in Comparative Example 1, the battery exploded in 5 out of 15 rechargeable batteries, and leaked out of the remaining 10 rechargeable batteries from the vicinity of the external terminal connected to the current path cutoff mechanism. Occurred. The secondary battery in which the electrolyte leaked from the vicinity of the external terminal was disassembled and examined. as a result,
It was confirmed that current was interrupted by the diaphragm being deformed and damaged, and that the electrolyte leaked from the damaged part.

Further, in the secondary battery of Comparative Example 2, the current path cutoff mechanisms of all the secondary batteries were activated, and the electrolyte did not leak.
After each drop, the two cells cause an increase in internal resistance, resulting in a 50
After 13 drops, the remaining 13 cells had increased internal resistance. The battery with increased internal resistance was disassembled and examined. As a result, it was confirmed that the joint between the diaphragm and the internal terminal plate was detached and opened.

In the first embodiment, the outer can and the lid are made of iron, and a positive electrode external terminal connected to the positive electrode of the electrode body through a current system cutoff mechanism is attached to the lid via an insulating gasket. Although the secondary battery has been described, the present invention is not limited to this. For example, the outer can and the lid are made of aluminum or an aluminum alloy, a positive electrode external terminal connected to the positive electrode of the electrode body through a current path breaking mechanism is directly attached to the lid, and a negative electrode external terminal is attached to the lid with an insulating gasket. And the external terminal may be connected to the negative electrode of the electrode body through a lead.

Although the first embodiment has been described by taking a rectangular lithium ion secondary battery as an example, the present invention can be similarly applied to a cylindrical lithium ion secondary battery and the like.

[0053]

As described above in detail, according to the present invention, when the internal pressure rises due to the generation of gas during overcharge / overdischarge, the current is reliably shut off without the electrolyte leaking out. It is possible to provide a highly reliable non-aqueous electrolyte secondary battery which can be performed and can prevent the current path from being opened by a drop impact.

Further, according to the present invention, when the internal pressure rises due to gas generation at the time of internal short circuit, a more reliable non-aqueous electrolysis is further provided with a safety valve mechanism for releasing gas to the outside to prevent explosion. A liquid secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway sectional view showing a prismatic lithium ion secondary battery according to the present invention.

FIG. 2 is an enlarged sectional view of a main part of the secondary battery of FIG.

FIG. 3 is a partially cutaway sectional view showing an operation state of a current path cutoff mechanism and a safety valve of the rectangular lithium ion secondary battery of FIG. 1;

FIG. 4 is an enlarged sectional view of a main part of the secondary battery of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Outer can, 2 ... Electrode body, 5 ... Lid body, 6 ... Liquid injection hole, 9 ... Safety valve, 13 ... Metal case, 18 ... Diaphragm, 21 ... Internal terminal board, 25 ... Circular thin part, 26 ... Gas circulation Hole 27, positive electrode lead.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshiaki Azami 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Inside AT Battery Co., Ltd.

Claims (3)

[Claims] 1. A mechanism for disconnecting a current path by separating the diaphragm from an internal terminal plate electrically and mechanically joined to a desired portion by a deformation of the diaphragm due to a rise in internal pressure, the mechanism comprising: The internal terminal plate is made of aluminum, and the thickness of the internal terminal plate located at the joint is 90% or less of the thickness of the diaphragm located at the joint. Electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the internal terminal plate has a smaller thickness at a joint with the diaphragm than at a peripheral portion thereof. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the safety valve mechanism for releasing the internal pressure is formed in a member having a different polarity with respect to the current path cutoff mechanism.