JP2001185113A - Sealed non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous electrolyte secondary battery that can be injected and sealed without interposing a charging step for degassing at the time of initial charging, and does not increase internal pressure due to gas accumulation even during normal use. I do. SOLUTION: A first safety valve 1 has a spring 3 and a metal flat plate 4 functioning as a valve in a cylinder whose tip opening is narrowed by a battery lid 7, and the metal flat plate 4 is attached to the spring 3. It is being rushed. The second safety valve 2 has a thin portion 5 formed in a metal thin film. At the time of initial charging, the first safety valve 1 is activated by a gradual increase in internal pressure during normal use or the like, and the second safety valve 2 is also activated when the battery is abnormal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed non-aqueous electrolyte secondary battery, and more particularly, to a safety valve for a sealed non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art Non-aqueous electrolyte batteries deteriorate battery performance when electrodes and electrolyte come into contact with moisture or oxygen in the air. To prevent performance degradation, batteries are caulked by laser welding or the like. It is common to provide a closed structure that closes off the air and cuts off contact with the outside air. However, when gas is generated inside the battery due to overcharging, short-circuit, or the like, the internal pressure of the battery may significantly increase due to the sealed type. In order to avoid such a phenomenon, a sealed nonaqueous electrolyte battery is provided with a safety valve for releasing an internal pressure such as a metal thin film having a sculpture or an etching groove, as disclosed in, for example, Japanese Patent Application Laid-Open No. 10-284034. It is usually attached.

[0003] When a graphite-based carbon material is used as a negative electrode material in a nonaqueous electrolyte secondary battery, gas may be generated by a side reaction between the electrolyte and the negative electrode material at the time of initial charging. In such a case, in the case of a small non-aqueous electrolyte battery or the like in which it is difficult to provide a vent hole separately from the safety valve, once the metal thin film safety valve having the engraved or etched groove is operated once, it can be resealed. Since it is impossible, it is necessary to provide a charging step for initially charging the battery before caulking or welding the battery lid to the battery can, and then perform a plurality of steps such as a sealing step for sealing the battery can.

[0004]

However, this sealing step must be performed under conditions that are sufficiently isolated from moisture and oxygen, such as in a glove box, and the sealing device must be placed in the glove box. If this is not possible, complicated steps such as transportation with a temporary lid or a desiccator must be interposed, resulting in a problem of increased costs.

In a non-aqueous electrolyte secondary battery, gas is also generated by repeating charge and discharge in a normal use state, so that the internal pressure of the battery may gradually (slowly) increase. In small batteries that do not have a gas release mechanism that releases gas to the outside in addition to the safety valve, the generated gas fills the inside and raises the internal pressure of the battery significantly, or the safety valve is activated when the amount of generated gas is large. There is a problem that the function as a battery is lost.

In view of the above proposal, the present invention provides a sealed type that can be injected and sealed without interposing a charging step for degassing after the injection at the time of initial charging, and does not involve an increase in internal pressure due to gas accumulation even during normal use. It is an object to provide a non-aqueous electrolyte secondary battery.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention opens a gas at a predetermined operating pressure in response to a low pressure and a gradual rise in internal pressure, discharges gas to the outside, and reduces the difference between the pressure and the external pressure. A first safety valve that closes and a second safety valve that opens at a predetermined operating pressure against a high pressure and a rapid increase in internal pressure and that discharges gas to the outside are provided. In the present invention, the first safety valve releases low-pressure gas generated in the battery at the time of initial charging, and gas that is accumulated by repeating normal charge and discharge and slowly increases the internal pressure. Since the safety valve 1 is closed, it is possible to inject and seal the nonaqueous electrolyte without injecting a charging step for degassing after injecting the nonaqueous electrolyte, and to prevent a significant increase in the internal pressure of the battery. Further, when the battery internal pressure increases rapidly and at a high pressure in the event of a battery abnormality or the like, the second safety valve also operates to release gas to the outside, so that the safety of the battery can be ensured.

[0008] In this case, if the first safety valve is closed to provide a reproducible safety valve, and if the second safety valve is opened, the safety valve does not close again, the second safety valve is opened and then closed. Is not required to be reproduced, and a simple structure can be used. Therefore, the cost can be lower than that of the first safety valve, so that the cost of the whole battery can be reduced, and the operation of the first and second safety valves can be reduced. Since the operating pressure of the second safety valve can be set higher than that of the first safety valve by providing a pressure difference, the second safety valve that does not close again can be operated only when the battery is abnormal. Further, if the opening area of the second safety valve when the second safety valve is operated is made larger than the opening area of the first safety valve when the first safety valve is operated, the opening area becomes large when the battery is abnormal. Since a gas passage having an opening area can be secured, the safety of the battery can be further enhanced. At this time, the operating pressure of the first safety valve is 3 × 10 ⁵ Pa to ⁵ ×
10 ⁵ Pa, it is preferred operating pressure of the second safety valve is ¹⁰ 6 Pa or more.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a sealed nonaqueous electrolyte secondary battery to which the present invention can be applied will be described with reference to the drawings.

(Constitution) As a positive electrode active material, lithium (L
i) Lithium manganate (LiMn ₂ O ₄ ) capable of reversibly releasing / storing i) is used, and scaly graphite is added as a conductive material thereto. Polyvinylidene fluoride (PVdF) is used as a binder. Then, the positive electrode plate was obtained by coating on the aluminum foil on which the current collecting tab was formed. In addition, graphite capable of semi-reversibly inserting and releasing lithium as a negative electrode active material was used, and a negative electrode plate was obtained by coating a copper foil with polyvinylidene fluoride as a binder. These have a thickness of 4
It was wound through a polyethylene separator through which 0 μm lithium ions could pass to produce an electrode group.

As shown in FIG. 1, this group of electrodes is accommodated in a cylindrical conductive bottomed battery can 6 and a positive electrode current collecting tab is joined to a positive electrode external output terminal 8 with a positive electrode lead inside the battery. Similarly, after joining the negative electrode lead led out from the negative electrode plate to the bottom of the battery can 6, the battery can 6 contains lithium hexafluorophosphate (LiPF ₆ ) in a solvent containing ethylene carbonate or the like.
Is injected in an argon atmosphere having a dew point of −60 ° C. or less, and the battery lid 7 provided with the first and second safety valves 1 and 2 is attached to the battery can 6 by caulking and sealed, The sealed nonaqueous electrolyte secondary battery 10 was completed.

As shown in FIG. 2, the first safety valve 1 has a spring 3 having a desired urging force in a cylinder whose tip opening area is narrowed by a battery lid 7, and a first tip opening of the cylinder which functions as a valve. And a disc-shaped metal flat plate 4 having an area larger than the partial area. The spring 3 biases the metal flat plate 4. On the other hand, the second safety valve 2 has a structure in which a thin portion 5 is formed in a substantially C-shape by etching or engraving a metal thin film (see also FIG. 1).
The opening area when the thin portion 5 is torn is set to be larger than the opening area of the cylindrical tip of the first safety valve 1.

(Operation) The first safety valve 1 according to the present embodiment is designed to allow the internal pressure of the battery can 6 to be increased when the internal pressure increases at a slow speed due to gas generation at the time of initial charging or repeated charging and discharging. Gas pressure against metal plate 4 against urging force of spring 3
Is pushed upward and the spring 3 is compressed and opened,
Releases gas. If the pressure difference between the gas pressure inside the battery can 6 and the outside air becomes smaller than the urging pressure of the spring 3 for urging the metal flat plate 4 by discharging the gas, the spring 3
Extend again to close the metal plate 4. Thereby, the sealed type non-aqueous electrolyte secondary battery 10 reproduces the sealed state. The operating pressure of the first safety valve 1, that is, the urging pressure for urging the metal flat plate 4 of the spring 3, prevents the battery performance from deteriorating, and reduces the pressure inside the battery can 11 when the internal pressure rises slowly and slowly. However, 3 × 10 ⁵
The range is from Pa to ⁵ × 10 ⁵ Pa (about ^{3 to 5} kgf / cm ² ).

On the other hand, the second safety valve 2 rapidly and rapidly turns on the battery can 11 when the battery is placed in an abnormal state such as overcharge or internal short circuit.
When the inside is in a high-pressure state, the thin-walled portion 5 is torn, and a passage for a gas having a relatively large diameter is secured. The operating pressure of the second safety valve 2, that is, the tearing pressure of the thin portion 5 is 10 ⁶
It is set to Pa or more, and the second safety valve 2 does not close again like the first safety valve 1 once activated.

(Example) According to the present embodiment, the first safety
Operating pressure of valve 1 is 3 × 10⁵Pa, operating pressure of second safety valve 2
Is 1.4 × 10⁶Sealed non-aqueous electrolyte secondary battery with Pa
20 (hereinafter referred to as the battery of the example).
The second safety valve 2 (operating pressure: 1.4 × 10 ⁶Pa) only
The first safety valve 1 is not provided, and the others are the same as those of the battery of the embodiment.
Various comparative batteries were produced. In addition, the safety valve of both batteries
Pressure is applied to the bottom of the battery can 6 opposite to the side of the attached battery lid 7
The sensor was attached.

Next, in order to examine the behavior of the example and the comparative example at the time of the first charge, the battery was charged at 0.125 C to 40% of the rated capacity, and the pressure change at that time was measured.

As shown in FIG. 3, in the battery of the embodiment, when the internal pressure reaches the operating pressure of the safety valve, the first safety valve 1 on the low pressure side formed by the spring 3 and the metal plate 4 is operated, and any further increase in pressure is observed. On the other hand, in the battery of the comparative example, although the thin portion 5 of the second safety valve 2 was not torn, the internal pressure reached 7 × 10 ⁵ Pa and a slight swelling was observed in the second safety valve 2. Was. Thus, the first safety valve 1
(And the second safety valve 2) can discharge gas to the outside of the battery in response to an increase in internal pressure due to gas generation during initial charging. Since this generated gas can be released outside the battery, it can be sealed before the first charge, so that the process can be simplified and the cost can be reduced.

Further, in order to examine the behavior of the batteries of the example and the comparative example when the internal pressure suddenly rises in an abnormal state, an overcharge test was performed. In this overcharge test, both batteries were
The battery was overcharged to 250% SOC (State Of Charge) with C.

As shown in FIG. 4, in the battery of the embodiment, when the internal pressure reaches the operating pressure of the first safety valve 1 on the low pressure side formed by the spring 3 and the metal plate 4, the first safety valve 1 is operated and the gas is gradually increased. In the battery of the comparative example, the second safety valve 2 was torn at around 210% SOC, and violent white smoke was emitted, whereas overcharging up to SOC 250% did not cause white smoke emission. Happened. Thus, the first
It is apparent that the battery of the example having the safety valve 1 and the second safety valve 2 has a higher safety margin than the battery of the comparative example which is a conventional product.

[0020]

As described above, according to the present invention,
The first safety valve releases low-pressure gas generated in the battery at the time of initial charging, and gas that accumulates due to repetition of normal charge / discharge and slowly increases the internal pressure. When the difference from the external pressure decreases, the first safety valve is activated. As it is closed, it is possible to inject the non-aqueous electrolyte without injecting the charging process
The battery can be sealed, and the internal pressure of the battery can be prevented from remarkably increasing. If the internal pressure of the battery increases rapidly and rapidly in the event of a battery abnormality, the second safety valve operates to release gas to the outside. Therefore, the effect that the safety of the battery can be ensured can be obtained.

[Brief description of the drawings]

FIG. 1 is a partial perspective view near a battery cover of a sealed nonaqueous electrolyte secondary battery according to an embodiment to which the present invention can be applied.

FIG. 2 is a cross-sectional view of a first safety valve and a second safety valve of the sealed nonaqueous electrolyte secondary battery of the embodiment.

FIG. 3 is a graph showing changes in internal pressure of a sealed nonaqueous electrolyte secondary battery at the time of initial charging, with the vertical axis representing the internal pressure of the battery and the horizontal axis representing the state of charge.

FIG. 4 is a graph showing a change in internal pressure of a sealed nonaqueous electrolyte secondary battery at the time of overcharge, with the vertical axis representing the internal pressure of the battery and the horizontal axis representing the state of charge.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st safety valve (1st safety valve) 2 2nd safety valve (2nd safety valve) 3 Spring (a part of 1st safety valve) 4 Metal plate (part of a 1st safety valve) 5 Thin part (2nd) Part of safety valve) 6 Battery can 7 Battery cover 10 Sealed non-aqueous electrolyte secondary battery

Continuation of the front page (72) Inventor Mitsuru Koseki 2-8-7 Nihonbashi Honcho, Chuo-ku, Tokyo Inside Shin-Kobe Electric Machinery Co., Ltd. (72) Inventor Tatsuo Horiba 2-87 Nihonbashi Honcho, Chuo-ku, Tokyo Shin-Kobe Electric Co., Ltd. In-house F-term (reference) 5H012 AA01 BB02 CC01 DD01 DD05 DD11 DD17 EE04 EE09 FF01 GG01 GG07 GG10 JJ10 5H029 AJ12 AJ14 AK03 AL07 AM03 AM07 BJ02 BJ14 BJ27 DJ02 EJ01 HJ07 HJ15

Claims (5)

[Claims] 1. A first safety valve that opens at a predetermined operating pressure to release gas to the outside in response to a low pressure and a gradual rise in internal pressure, and closes when the difference between the pressure and the external pressure becomes small, And a second safety valve that opens at a predetermined operating pressure to release gas to the outside. 2. The safety valve according to claim 1, wherein the first safety valve is a safety valve that can be closed to reproduce a closed state, and the second safety valve is a safety valve that does not close again when opened. Sealed non-aqueous electrolyte secondary battery. 3. An opening area of the second safety valve when the second safety valve is operated is larger than an opening area of the first safety valve when the first safety valve is operated. The sealed nonaqueous electrolyte secondary battery according to claim 1. 4. The operating pressure of the first safety valve is 3 × 10 ⁵
2. The pressure is from Pa to ⁵ × 10 ⁵ Pa.
The sealed non-aqueous electrolyte secondary battery according to claim 3. 5. The operating pressure of the second safety valve is 10 ⁶ Pa.
The sealed non-aqueous electrolyte secondary battery according to claim 1, wherein: