JP2950863B2 - Flat lithium-thionyl chloride battery - Google Patents

Description

The present invention relates to a flat lithium-thionyl chloride battery.

[Conventional technology]

In recent years, with the development of electronic devices, lithium batteries having a small self-discharge and a long life have been used in many cases.
Therefore, a lithium-thionyl chloride battery with a cylindrical shape and a metal-glass (or ceramic) -metal so-called hermetic seal has been developed as a power supply for COMS RAM memory backup, and this battery has a high hermeticity and has been used for more than 10 years. Because of its long-term use, demand is growing rapidly.

In addition, due to demands for reduction of current consumption of ICs of electronic devices and downsizing and weight reduction of electronic devices, small and thin memory backup batteries are also demanded, and the present inventors respond to such demands. Therefore, various flat lithium-thionyl chloride batteries have been developed (for example, Japanese Patent Application No. 63-214575,
Japanese Patent Application No. 63-214576).

This lithium-thionyl chloride battery has a hermetically sealed structure, as described above, because the positive electrode active material, thionyl chloride, lithium constituting the negative electrode, and the like are very easy to react with water. Although it has the advantage of being high and having excellent storage properties, on the other hand, because of its high sealing properties and the use of lithium with a low melting point as the metal for the negative electrode, the battery is accidentally thrown into fire, etc. When the battery is exposed to abnormally high temperatures, the lithium in the negative electrode melts, and the liquefied lithium passes through the separator made of glass fiber nonwoven fabric and moves to the positive electrode side, causing a rapid reaction on the positive electrode. Then, there is a danger that sudden heat generation occurs, the internal pressure of the battery rapidly rises, and the battery ruptures under high pressure.

Thus, as described in EP 188,144, formula (I) CnH ₂ n-CmX ₂ m (I) wherein X is F or C1, n> 1 and m <6 By using a polymer microporous film having a repeating unit represented by the following formula for the separator, it is conceivable to suppress the movement of the molten lithium to the positive electrode side.

However, in a flat lithium-lithium chloride battery, a sufficient effect cannot be obtained only by using a microporous film of the above polymer as a separator. That is, in the flat lithium-thionyl chloride battery, as shown in FIG. 3, the outer diameter of the positive electrode (2) is set to be less than that of the battery (5) in order to prevent the positive electrode (2) from contacting the battery container (5) also serving as the negative electrode terminal. Designed to be smaller than the inner diameter of the container (5),
On the other hand, since the outer peripheral surface of the negative electrode (1) is designed to be in close contact with the inner peripheral surface of the battery container (5), the outer diameter of the positive electrode (2) is smaller than the outer diameter of the negative electrode (1). The generated lithium pushes up the peripheral portion (3E) of the separator (3), moves to the positive electrode (2) side, and reacts abruptly on the positive electrode (2), which may cause the battery to burst. In addition, during the battery assembling process, when the separator (3) is inserted on the negative electrode (1), a displacement occurs, and as shown in FIG. 4, the separator (3) covers the surface of the negative electrode (1). Some parts do not appear. In such a case, the molten lithium moves from the portion where the separator (3) does not exist to the positive electrode (2) side and reacts abruptly on the positive electrode (2) to cause the battery to burst. .

When a polymer microporous film having a repeating unit represented by the above formula (I) is used alone as a separator, the polymer microporous film does not have sufficient electrolytic solution holding power, so that discharge is not caused. When the reaction proceeds and the reaction product accumulates on the surface of the positive electrode (2), the amount of electrolyte at the interface where the discharge reaction occurs becomes insufficient, so that the discharge cannot proceed sufficiently and the discharge utilization rate decreases and There is a problem that a high discharge capacity cannot be obtained, and in a flat battery having a small volume, a decrease in the discharge capacity due to the small electrolyte holding power of the separator has a great effect.

[Problems to be solved by the invention]

The present invention is a conventional flat lithium-thionyl chloride battery, as described above, such as when the battery is accidentally thrown into fire, when the battery is exposed to abnormally high temperatures, the lithium of the negative electrode melts, This solves the problem that the molten lithium reaches the positive electrode side through the separator and reacts abruptly on the positive electrode, possibly causing the battery to rupture. Another object of the present invention is to provide a flat lithium-thionyl chloride battery which prevents battery rupture and prevents a reduction in discharge capacity due to the rupture prevention measures.

[Means for solving the problem]

In the present invention, the separator is made of a glass fiber nonwoven fabric and the following formula (I) CnH ₂ n-CmX ₂ m (I) wherein X is F or C1, n> 1 and m <6. The above object has been achieved by comprising a microporous film of a polymer having a repeating unit represented by the formula (1) and bending the peripheral portion of the separator along the outer peripheral surface of the positive electrode.

Examples of the polymer having a repeating unit represented by the above formula (I) include ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, ethylene-1,1-dichloro-2,2-difluoroethylene copolymer, ethylene- 1,2-dichloro-1,2
-Difluoroethylene copolymer, ethylene-trichlorofluoroethylene copolymer, ethylene-tetrachloroethylene copolymer and the like.

The pores of these polymer microporous films are almost uniform micropores, and their paths are complicatedly bent. It is harder to pass than Therefore, it is possible to prevent the molten lithium from passing through the separator and reacting abruptly on the positive electrode to cause the battery to burst.

Further, since the separator is configured by using a glass fiber nonwoven fabric having a large electrolyte holding force and a microporous film of the polymer in combination, the adverse effects of using the polymer microporous film alone are prevented, A battery having a large discharge capacity can be obtained.

Since the peripheral portion of the separator is bent along the outer peripheral surface of the positive electrode, molten lithium is prevented from pushing up the peripheral portion of the separator and moving to the positive electrode side.

Bending of the peripheral portion of the separator may be bent prior to assembling the battery and formed into a container having a shallow bottom and then used for battery assembly.Also, the diameter of the separator is set to be larger than the inner diameter of the battery container, When the separator is inserted on the negative electrode housed in the battery container, the peripheral portion may be bent toward the positive electrode. Regardless of the bending, by bending the peripheral portion, the displacement of the separator is also prevented, and the negative electrode surface is not covered with the separator.

In the present invention, the glass fiber nonwoven fabric as a constituent member of the separator preferably has a porosity of 50 to 95% by volume, particularly 75 to 95% by weight, and a thickness of 100 to 1000 μm.

On the other hand, a polymer microporous film having a repeating unit represented by the formula (I) has a porosity of 40 to 80% by volume.
It is suitable that the thickness is 20 to 200 μm.

〔Example〕

 Next, an embodiment of the present invention will be described with reference to the drawings.

Example 1 FIG. 1 is a sectional view showing a battery according to Example 1 of the present invention, and FIG. 2 is an enlarged sectional view of a main part of the battery shown in FIG.

First, the overall configuration of the battery will be schematically described.
(1) is a negative electrode made of lithium, (2) is a positive electrode made of a carbon porous molded body, (3) is a separator, and the separator (3) is represented by the glass fiber nonwoven fabric (3a) and the above formula (I). In this example, the polymer microporous film (3b) having a repeating unit represented by the formula (I) is an ethylene-tetrafluoroethylene copolymer Is used.
(4) is an electrolytic solution, (5) is a stainless steel battery container, and (6) is a battery lid. The battery cover (6) has an annular stainless steel body (7), an annular insulating layer (8) made of glass, and a positive electrode terminal (9) made of stainless steel.
The outer periphery (7a) of the body (7) is welded to the open end (5a) of the battery container (5). Reference numeral (10) denotes a current collector on the positive electrode side, which is made of a stainless steel net, and spot-welded to a lower portion of the positive electrode terminal (9). (1
1) Insulation material made of nonwoven glass fiber, positive electrode (2)
Also, the current collector (10) on the positive electrode side and the body (7) of the battery lid (6) are insulated. (12) is an electrolyte inlet, and (13) is a sealing stopper. The sealing stopper (13) is made of stainless steel, and an electrolyte is injected into the battery from the electrolyte inlet (12). Thereafter, the shaft is inserted into the electrolyte inlet (12), and its head is welded to the bottom of the battery container (5) around the electrolyte inlet (12). This battery is a disk-shaped flat battery having an outer diameter of 33 mm and a total battery height of 6.5 mm.

Next, the main constituent members will be described in detail.
The negative electrode (1) is formed by pressing a ring-shaped punched lithium sheet onto the inner surface of the bottom of the battery container (5), and is composed of only lithium as a negative electrode active material.
Has an outer diameter of 32 mm, and its outer peripheral surface is in close contact with the inner peripheral surface of the battery container (5). The positive electrode (2) is made of a porous carbon molded body mainly composed of carbon obtained by adding polytetrafluoroethylene as a binder to acetylene black, and has a diameter of 30 mm and a thickness of 3.6. mm. The electrolyte solution (4) is composed of a solution of thionyl chloride in which 1.0 mol / l of lithium aluminum tetrachloride is dissolved in thionyl chloride. As described above, thionyl chloride is both a solvent for the electrolyte solution and a positive electrode active material. As is clear from the fact that thionyl chloride is used as the positive electrode active material, the positive electrode (2) does not react by itself, but is ionized and eluted from the positive electrode active material thionyl chloride and the negative electrode. It provides a place for reaction with the lithium ions.

Glass fiber nonwoven fabric (3a) constituting separator (3)
A glass fiber nonwoven fabric having a porosity of 95% by volume and a thickness of 50 μm is used. As a polymer microporous film (3b) having a repeating unit represented by the formula (I), a porosity of 80% by volume and a thickness of A microporous film of 100 μm ethylene-tetrafluoroethylene copolymer is used, a glass fiber nonwoven fabric (3a) is disposed on the negative electrode (1) side, and a microporous film of a polymer having a repeating unit represented by the formula (I) (3b) is arranged on the positive electrode (2) side.

The separator (3) has a diameter of 34 mm, which is larger than the outer diameter of the positive electrode (2). The peripheral portion (3E) of the separator (3) is bent along the outer peripheral surface of the positive electrode (2), ) Covers a part of the outer peripheral surface.

The battery case (5) is made of a stainless steel plate having a thickness of 0.5 mm and is formed in a container shape having an outer diameter of 33 mm and a height of 6 mm.
Comprises a stainless steel body (7), an annular insulating layer (8) made of glass, and a positive electrode terminal (9) made of stainless steel as described above. The insulating layer (8) made of glass is The outer peripheral surface is welded to the inner peripheral surface of the stainless steel body (7), and the inner peripheral surface is welded to the outer peripheral surface of the stainless steel positive electrode terminal (9).
It has a glass-metal hermetic seal and, as described above, the outer periphery (7a) of the body (7) of the battery lid (6).
Is welded to the open end (5a) of the battery container (5),
This battery is configured to have a so-called completely sealed structure.

Comparative Example 1 A flat lithium-thionyl chloride battery was produced in the same manner as in Example 1 except that a glass fiber nonwoven fabric cut into a disk shape having a porosity of 95% by volume, a thickness of 500 μm, and a diameter of 32 mm was used alone as a separator. Was prepared.

The battery of Comparative Example 1 had the structure shown in FIG. 3, in which the separator (3) was composed only of a glass fiber nonwoven fabric, the separator (3) had a diameter of 32 mm, and had the same dimensions as the outer diameter of the negative electrode (1). Although the peripheral portion of the separator (3) is not bent along the outer peripheral surface of the positive electrode (2), the other configuration is the same as that of the battery of Example 1 shown in FIG. 1 and corresponds to a conventional battery. Things.

Comparative Example 2 A microporous film of an ethylene-tetrafluoroethylene copolymer cut into a disk having a porosity of 80% by volume, a thickness of 100 μm, and a diameter of 32 mm was used in the same manner as in Example 1 except that it was used alone as a separator. Thus, a flat lithium-thionyl chloride battery was manufactured.

The battery of Comparative Example 2 has the same structure as that shown in FIG. 3, except that the separator (3) is made of a microporous film of an ethylene-tetrafluoroethylene copolymer. Is different.

In the battery of Example 1, the separator (3) was composed of only a microporous film of an ethylene-tetrafluoroethylene copolymer, the separator (3) had a diameter of 32 mm, and the outer diameter of the negative electrode (1). Example 1 is different from that of Example 1 in that the peripheral portion of the separator (3) is not bent along the outer peripheral surface of the positive electrode (2).
It is configured in the same manner as the above battery.

Twenty batteries of each of Example 1 and Comparative Examples 1 and 2 were thrown into a fire, and whether or not rupture occurred was examined. Table 1 shows the results.

The denominator of the numerical values in Table 1 indicates the number of batteries subjected to the fire throw-in test, and the numerator indicates the number of batteries that had burst.
As shown in the table, the battery of Example 1 of the present invention did not cause any rupture, but the batteries of Comparative Examples 1 and 2 did rupture according to the respective configurations.

Next, the batteries of Example 1 and Comparative Examples 1 and 2 were
The discharge duration when the battery was continuously discharged at 1 ° C. and 1 kΩ (final voltage: 3.0 V) was examined. Table 2 shows the results.

As shown in Table 2, the battery of Example 1 had the same discharge duration as the battery of Comparative Example 1 using the glass fiber non-woven fabric for the separator (3), and the discharge capacity of the battery in preventing the battery from bursting was reduced. Little decrease was observed. On the other hand, in the battery of Comparative Example 2, the discharge characteristic time was shorter than that of the battery of Comparative Example 1, and the discharge capacity was reduced due to the adoption of the battery burst prevention measures.

〔The invention's effect〕

As described above, in the present invention, the separator (3)
Is composed of a glass fiber nonwoven fabric (3a) and a microporous film (3b) of a polymer having a repeating unit represented by the formula (I), and the peripheral portion (3E) of the separator (3) is By bending along the outer peripheral surface, the battery is prevented from bursting when exposed to high-temperature heating, such as when the battery is accidentally thrown into a fire. A flat lithium-thionyl chloride battery without a decrease in capacity could be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of the flat lithium-thionyl chloride battery of the present invention, and FIG. 2 is an enlarged sectional view of a main part of the battery shown in FIG. FIG. 3 is a sectional view showing a conventional flat lithium-thionyl chloride battery, and FIG.
FIG. 2 is an enlarged cross-sectional view of a main part of the battery in a state where the separator is misaligned in the battery shown in FIG. (1) ... negative electrode, (2) ... positive electrode, (3) ... separator,
(3a): glass fiber non-woven fabric, (3b): polymer microporous film, (3E): peripheral part, (4) ... electrolyte, (5) ...
Battery container, (5a) ... open end, (6) ... battery lid, (7)
... body, (7a) ... outer peripheral part, (8) ... insulating layer, (9) ...
Terminal

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-145234 (JP, A) JP-A-56-7353 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 6/14 H01M 2/16-2/18 JOIS

Claims (1)

(57) [Claims] 1. A negative electrode (1) made of lithium, a positive electrode (2) made of a porous carbon molded body, a separator (3), a separator (3), and an electrolyte (4) using thionyl chloride as a solvent for a positive electrode active material and an electrolytic solution. )
, A battery container (5), and a battery lid (6). The negative electrode (1), the positive electrode (2), the separator (3), and the electrolyte (4) are contained in the battery container (5). The battery lid (6) is made of a metal annular body (7),
An annular insulating layer (8) made of glass or ceramic and located on the inner peripheral side of the annular body (7); and a terminal (9) of one electrode located at the center of the annular insulating layer (8) Wherein the outer periphery (7a) of the body (7) of the battery lid (6) is welded to an open end (5a) of the battery container (5). The separator (3) includes a glass fiber nonwoven fabric (3a),
(I) CnH ₂ n-CmX ₂ m (I) wherein X is F or C1, n> 1, and m <6. The separator (3) is disposed between the negative electrode (1) and the positive electrode (2), and the peripheral portion (3E) of the separator (3) is formed on the outer peripheral surface of the positive electrode (2). A flat lithium-thionyl chloride battery characterized by being bent along.