Closed secondary battery and its manufacturing method

A closed secondary battery having a sealing structure for preventing electrolyte leak for a long period is presented. An annular packing is chemically bonded in a ring form to the surface of a disk-shaped flange formed inside of a battery of a terminal pole projecting from inside to outside of the battery, by penetrating through a cover member of closed secondary battery. Fitting an annular spring while pulling the terminal to outside of the battery, the terminal pole is fixed in the cover member. At this time, the annular packing is compressed against the cover member, and the passage of electrolyte leak is shut by this compression.

TECHNICAL FIELD 
The present invention relates to a secondary battery and more particularly 
to a closed secondary battery. 
BACKGROUND OF THE INVENTION 
The structure near the terminal pole of a conventional closed secondary 
battery is shown in a sectional view in FIG. 2. In FIG. 2, a terminal pole 
21 is disposed by penetrating a cover 22 of a closed secondary battery 20 
from inside to outside of the battery. An annular packing 25 is fitted 
into an annular groove 24 formed in a disk-shaped flange 23 positioned 
inside of the battery of the terminal pole 21. By fitting in an annular 
spring 27 while pulling up a pole of this terminal hole 21 to the outside 
of the battery, the terminal pole 21 is fixed at a specified position as 
shown in FIG. 2. By the pulling action when fixing the terminal pole 21, 
the annular packing 25 placed in the annular groove 25 of the flange 23 is 
compressed between the flange 23 and the inner surface of the cover 22. A 
sealing agent such as asphalt pitch is applied around the packing 25, 
which enhances the effect of preventing electrolyte leak by the addition 
of this sealing agent. In such constitution, the passage of the leaking 
electrolyte from the gap between the cover 22 and terminal pole to the 
outside of the battery is shut off, so that electrolyte leak from inside 
of the battery can be prevented. 
However, when the closed secondary battery 20 is used for a long time, the 
sealing agent deteriorates, and the effect of preventing the electrolyte 
leak of the battery declines, and the electrolyte contained in the closed 
secondary battery may escape outside. 
The invention solves the problems of the prior art, and presents a closed 
secondary battery enhanced in the effect of preventing electrolyte leak. 
SUMMARY OF THE INVENTION 
A closed secondary battery of the invention comprises a battery container, 
electrolyte contained in the battery container, a cover member installed 
at an end of the container, having a penetration hole, a terminal pole 
installed by penetrating through the penetration hole, and a sealing 
member installed between the upper surface of the flange and the inner 
surface of the cover member, at a position enclosing the pole. The 
terminal pole has a flange and a pole projecting from the flange. An upper 
surface of the flange confronts an inner surface of the cover member in 
the container, and the pole penetrates in a direction from inside to 
outside of the container through the penetration hole, having a gap formed 
between the penetration hole and the pole. The sealing member can be 
deformed by an external force, and a lower side of the sealing member is 
chemically bonded to the flange. An upper side of the sealing member is 
compressed by a pressing force between the upper surface of the flange and 
an inner surface of the cover member, to contact with the inner surface of 
the cover member. 
A manufacturing method of a closed secondary battery of the invention which 
comprises a battery container, electrolyte contained in the battery 
container, a cover member installed at an end of the container, a terminal 
pole installed by penetrating through a penetration hole, and a seating 
member installed between an upper surface of a flange and an inner surface 
of the cover member is a manufacturing method comprising (a) a step of 
forming the terminal pole having the flange and a pole projecting from the 
flange, (b) a step of bonding chemically the sealing member to the upper 
surface of the flange, at a position enclosing the pole, (c) a step of 
penetrating the pole by forming a gap, in a direction from inside to 
outside of the container through the penetration hole, and opposing the 
upper surface of the flange bonding the sealing member against the inner 
surface of the cover member in the container, and (d) a step of fixing the 
terminal pole and the cover member, so that the upper surface of the 
sealing member may contact with the inner surface of the cover member as 
being compressed by a pressing force between the inner surface of the 
cover member and the flange. The sealing member can be deformed by an 
external force. 
In this constitution, electrolyte leak through the gap between the terminal 
pole and cover member is completely prevented, and the electrolyte of the 
closed secondary battery can be prevented for a long period. Moreover, 
since the shape of the terminal pole is simple, the manufacturing cost of 
the terminal pole is saved. Still more, since the shape of the sealing 
member does not require high precision, the manufacturing cost of the 
sealing member is also lowered.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the invention is described below while referring 
to the accompanying drawing. The embodiment is only a practical example of 
the invention, and is not intended to limit the technical scope of the 
invention whatsoever. 
A constitution near a terminal pole of a closed secondary battery according 
to an embodiment of the invention is shown in FIG. 1. In FIG. 1, a closed 
secondary battery 1 comprises a container 8, a functional member (not 
shown) such as electrolyte contained in the container 8, a cover member 4 
installed at an end of the container 8, and a terminal pole 2 installed by 
penetrating through the cover member 4. The terminal pole 2 integrally 
forms and comprises a pole 7 and a disk-shaped flange 5. The pole 7 
penetrates through the cover member from inside of the battery, and 
projects outside of the battery. The projecting pole 7 is fixed to the 
cover member 4 by the spring pressure of an annular spring 6. A flange 5 
is formed inside of the battery of the terminal pole 2. The cover member 4 
is made of, for example, synthetic resin or metal material. The container 
8 is made of, for example, synthetic resin or metal material. The terminal 
pole 2 is made of a metal material having conductivity or the like. The 
cover member 4 has a penetration hole in its center. The pole 7 of the 
terminal pole 2 penetrates through its penetration hole, and projects 
outside of the battery. In the penetration hole, a gap 9 is formed between 
the pole 7 and the cover member 4. A sealing member 3 is installed on the 
surface of the flange 5 in a ring form centered on the pole 7. That is, 
the surface of the flange 5 mounting the sealing member 3 and the inner 
surface of the cover member 4 are disposed oppositely to each other. The 
sealing member 3 is composed by using an elastic material which can be 
deformed as being compressed by an external pressure. The sealing member 3 
is made of, for example, rubber material, elastic material, or packing 
material. 
In the embodiment, this sealing member 3 is chemically bonded to the 
surface of the flange 5. More preferably, the sealing member 3 contains an 
element chemically adhering to the surface of the flange 5. As such 
sealing member 3, for example, butadiene rubber, ethylene propylene rubber 
or other rubber material is used. These rubber materials contain 
vulcanizing agent or crosslinking agent such as sulfur and peroxide in 
their material components, and such vulcanizing agent or crosslinking 
agent is chemically bonded with an oxygen atom on the surface of the 
flange 5 when curing the rubber materials, so that the rubber materials 
are firmly adhered and fixed to the surface of the flange 5. 
Incidentally, as the method of chemically bonding the sealing member 3 and 
flange 5, there is also a method of using a junction material that can be 
chemically joined to both sealing member 3 and flange 5. In this method, 
however, the effect is slightly smaller than the above case of using a 
rubber material containing vulcanizing agent or crosslinking agent, but 
the effect is superior to that of the prior art. 
An example of bonding and fixing the sealing member 3 to the flange 5 by 
using the rubber material such as butadiene rubber or ethylene propylene 
rubber is described below. First, the rubber material containing 
vulcanizing agent or crosslinking agent is pre-molded in a specified ring 
shape. In this case, the vulcanizing agent of crosslinking agent does not 
react, but remains in the rubber material. The pre-molded rubber material 
is put on the surface of the flange 5 of the terminal pole 2, and is 
heated while applying a light pressure. By this heating, the pre-molded 
rubber material is crosslinked and cured, while the sulfur or peroxide 
contained in the rubber material chemically react with oxygen on the 
surface of the flange 5 to be bonded, so that an elastic cured rubber 
material (that is, the sealing member 3) is formed, and is firmly bonded 
to the flange 5. 
Meanwhile, the rubber material containing vulcanizing agent or crosslinking 
agent that can react with oxygen is not limited to butadiene rubber or 
ethylene propylene rubber, but other rubber materials including synthetic 
rubber and natural rubber can be used. 
Other example of bonding and fixing the sealing member 3 to the flange 5 is 
described next. First, using a first rubber material, a ring-shaped 
sealing member 3 having an elasticity is prepared. Then, this ring-shaped 
sealing member 3 is adhered and fixed to the flange 5, by using an 
adhesive having a second rubber material containing a vulcanizing agent or 
crosslinking agent that can react with oxygen. In this case, the rubber 
material, vulcanizing agent, or crosslinking agent contained in the 
adhesive chemically reacts with the vulcanizing agent or crosslinking 
agent remaining in the first rubber material, or the rubber component that 
has not reacted yet, and is chemically joined to the sealing member 3. At 
the same time, the second rubber material (that is, the adhesive) is 
cured, and the sulfur or peroxide contained in the adhesive chemically 
reacts with the oxygen on the surface of the flange 5, and is joined 
firmly. In this way, the sealing member 3 is joined to the flange 5. This 
method is slightly inferior in the effect to the above method not using 
the adhesive, but has a better effect than the prior art. 
Below is described a method of fixing the terminal pole 2 to the cover 
member 4. The pole 7 of the terminal pole 2 is inserted into the 
penetration hole in the cover member 4 from inside of the battery. Then, 
with the terminal pole 2 having the sealing member 3 in the state of 
pulling up the flange 5 to outside of the battery, the annular spring 6 is 
press-fitted into the pole 7 of the terminal pole 2. In this way, the 
terminal pole 2 is fixed at a specified position, and the sealing member 3 
is pressed between the flange 5 and the inside of the cover member 4, and 
compressed and deformed. As a result, the gap 9 running from inside to 
outside of the battery is closed by the sealing member 3, thereby 
preventing leak of electrolyte contained in the battery. 
In the conventional constitution in FIG. 2, both the contact portion of the 
annular packing 25 and flange 23, and the contact portion of the annular 
packing 25 and cover 22 were possible to form a passage for electrolyte 
leak, but in the constitution of the invention, by contrast, since the 
sealing member 3 and flange 5 are completely bonded chemically, 
possibility of electrolyte leak is found only in the contact portion of 
the sealing member 3 and cover member 4. Therefore, the constitution of 
the embodiment is excellent in the effect of preventing electrolyte leak 
as compared with the prior art. Moreover, as other constitution, it is 
also possible to inject a sealing agent such as asphalt pitch in the 
contact portion of the sealing member 3 and cover member 4, and in this 
constitution, therefore, the electrolyte leak in the contact portion of 
the sealing member 3 and cover member 4 is decreased, so that the effect 
of preventing electrolyte leak is further enhanced. 
The effects of the embodiment are specifically described below. The closed 
secondary battery of the embodiment, and the closed secondary battery of 
the conventional constitution were comparatively experimented. Samples of 
five cells of the closed secondary battery of the embodiment and five 
cells of closed secondary battery of the conventional constitution were 
prepared. These samples were kept in an atmosphere of 45.degree. C. for 2 
years. Then the alkaline reaction on the surface of the cover members 4, 
22 was investigated to check for presence or absence of electrolyte leak. 
The results are shown in Table 1. 
TABLE 1 
______________________________________ 
Sample No. 
Electrolyte leak 
______________________________________ 
Closed secondary battery of 
1 Absent 
the embodiment 2 Absent 
3 Absent 
4 Absent 
5 Absent 
Closed secondary battery of 
6 Present 
the prior art 7 Present 
8 Present 
9 Present 
10 Present 
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As clear from Table 1, all samples of the closed secondary battery having 
the constitution of the embodiment (samples No. 1 through No. 5) were free 
from electrolyte leak. By contrast, electrolyte was detected in all 
samples of the closed secondary battery of the conventional constitution 
(samples No. 6 through No. 10). That is, the closed secondary battery 
having the constitution of the embodiment has an effect of preventing 
electrolyte leak for a long period. As a result, the closed secondary 
battery having an excellent long-term reliability is obtained. 
As clear from the comparison between FIG. 1 showing the embodiment and FIG. 
2 showing the prior art, the groove for disposing the sealing member 3 is 
not needed in the embodiment. Hence, the shape of the terminal pole 2 is 
simple. As a result, the manufacturing cost of the terminal pole 2 is 
lowered. Still more, the sealing member 3 does not require high precision 
in its shape. That is, the sealing member 3 is processed so that the 
ring-shaped sealing member 3 may be positioned on the outer circumference 
of the gap 9. Accordingly, the processing job of the sealing member 3 is 
easy, and the manufacturing costs of the sealing member is lowered. 
Moreover, it is possible to dispose by joining the sealing member 3 
directly to the flange 5 by using a rubber material containing a 
crosslinking agent, and therefore it does not require sealing member 3 
having a high surface precision. 
In this constitution, electrolyte through the gap between the terminal pole 
and cover member is completely prevented, and the electrolyte of the 
closed secondary battery is prevented for a long period. In addition, 
since the shape of the terminal pole is simplified, the manufacturing cost 
of the terminal pole is reduced. Further, since the shape of the sealing 
member does not require high precision, the manufacturing cost of the 
sealing member can be reduced.