Chemistry: electrical current producing apparatus – product – and – Process of cell operation – Electrolyte circulation
Reexamination Certificate
1999-10-08
2002-05-14
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Process of cell operation
Electrolyte circulation
C429S081000, C429S094000
Reexamination Certificate
active
06387561
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
This invention relates to a method for filling an electrolyte solution into a lithium secondary battery; said method capable of filling electrolyte solution into a case and extracting an excessive electrolyte solution therefrom, and sealing easily a battery, thereby the simplification of fabrication process, the reduction in the production cost, and the improvement in compaction of energy density can be achieved, and a battery structure of the lithium secondary battery; said battery having a reduced current collection resistance from positive electrodes and negative electrodes, and a narrowed deviation in the fluctuation in the resistances among the tabs engaged in current collection as well, and having a simple structure as a battery so as to enable easier assembly of the battery and to effectuate the aforementioned method for filling an electrolyte solution into the case easily.
In recent years, the lithium secondary battery has been widely used as a power battery for handy electronic appliances such as personal handy phone systems, video tape recorders, notebook-type computers, or the like. Additionally, in the case of a lithium secondary battery, a single battery can generate a voltage of approximately 4 V, and this level of voltage is higher than that of conventional secondary batteries such as a lead battery, or the like, and its energy density is also high. Thus, much attention has been paid to it not only as a power source for the aforementioned handy electronic appliances, but also as a motor driving power source for an electric vehicle (EV) or a hybrid electric vehicle (HEV), of which penetration among the general public is being earnestly planned as a low-pollution vehicle due to the recent development in the environmental problems.
In a lithium secondary battery, in general, a lithium-transition metal compound oxide as a positive active material, a carbon material as a negative active material, and an organic electrolyte solution obtained by dissolving a Li-ion forming electrolyte in an organic solvent as an electrolyte solution are used. And, for an internal electrode body as a portion where battery reaction is carried out, various types are available.
For example, in a coin-shaped battery with a small capacity, a sandwiched-type internal electrode body in which a separator is sandwiched between a positive electrode and a negative electrode is used. Here, as the positive electrode and the negative electrode, those that are formed in a disk like shape, or in a coin like shape by subjecting positive material and negative material to press-forming processing or the like, respectively are suitably used.
As one example of preferable structures of internal electrode bodies to be used for a lithium secondary battery with a comparatively large capacity usable for an EV, or the like, as is shown in FIG.
18
,there is given a wound-type internal electrode body
1
being formed by winding around the outer periphery of a hollow cylinder-shaped core
6
a positive electrode
2
having one or more tabs
5
for current collection and a negative electrode
3
having one or more tabs
5
for current collection, in such a manner that the positive electrode
2
and negative electrode
3
are not brought into direct contact with each other, by sandwiching a separator
4
between the positive electrode
2
and the negative electrode
3
. Here, in general, the length of the core
6
is set equal to the width of the positive electrode
2
and that of the negative electrode
3
. Incidentally, there is also proposed a battery using a laminate-type internal electrode body formed by laminating alternately via separators
4
a plurality of positive electrodes
2
and negative electrodes
3
having been prepared by cutting the above-mentioned positive and negative electrodes, respectively into those with small areas.
Now, in any case where any of the above-described structures is adopted as an internal electrode body, it is necessary to soak the internal electrode body in an electrolyte solution. Here, as an electrolyte solution, a non-aqueous electrolyte solution (hereinafter to be referred to as an “electrolyte solution”), which is obtained by dissolving a lithium electrolyte in an organic solvent, is used. In the case of a coin-shaped battery, for example, there is employed such a technique that a predetermined quantity of an electrolyte solution is injected by using a metering pump, or the like, under a reduced atmosphere and the battery case is sealed so as to fill the case with the electrolyte solution, after the internal electrode body is mounted inside a battery case. In addition, even in the case where a wound-type internal electrode body is used, a similar technique is used as long as a small capacity battery such as a common 18650 (with a diameter of 18 mm&phgr; and a length of 65 mm) cylinder-type battery is produced. In such a method, an excessive amount of electrolyte solution that is not actually required is liable to be filled therein,
Since electrolyte solution is generally expensive, the percentage of battery costs attributable to electrolyte solution is not small. Nevertheless, in the case of those batteries having a small capacity, the reasons why the aforementioned method for filling an electrolyte solution is adopted are considered that:
the space where excessive electrolyte solution (hereinafter to be referred to as a “excessive electrolyte solution”) is filled in is small in the absolute value, the cost for the electrolyte solution used for filling such a small space is considered not to be so high since the internal electrode body does not occupy much space in the interior of the battery in a small capacity battery;
a desired battery performance is obtainable if a minimum required quantity of an electrolyte solution is filled in a case since the area of reaction in the battery is small; and
an introduction of a step for recovering excessive electrolyte solution results in raising production costs unintentionally, etc.
On the contrary, in the case of a battery having a relatively large capacity (hereinafter to be referred to as a “large capacity battery”) to be applied to an EV, or the like, the size of a battery itself will necessarily become large. In such a case, the use of the wound-type internal electrode body
1
shown in
FIG. 18
requires a larger space for housing the current collection tabs
5
at both ends or one end of the case for the battery. Additionally, since a hollow cylinder-shaped type core is generally used for the core
6
, the absolute volume to be occupied by these spaces inside the case for the battery becomes large.
Accordingly, if an electrolyte solution is filled into a case for a large capacity battery by using a technique similar to that for the above-described small capacity battery, an expensive electrolyte solution is used not in an economic manner. This would bring about an increase in the production cost and a reduction in the energy density of the battery, as well. Furthermore, it is not preferable, from the viewpoint of durability, for metal members other than the internal electrode body, sealing members of the battery case, and the like, to be always in contact with the electrolyte solution since it causes often the leakage of the electrolyte solution, the corrosion of said members, or the like.
On the other hand, the electrolyte solution is required to fill in an amount sufficient to impregnate the internal electrode body properly even in the case of a large internal electrode body having a large battery area. And in the case where this is not fulfilled, not only the desired battery performance cannot be attained, but also the fluctuation in the performance of respective batteries will take place. Accordingly, in the case of a large capacity battery, it is preferable to impregnate the internal electrode body thoroughly in an excessive amount of an electrolyte solution under a reduced atmosphere, and thereafter the excessive electrolyte solution is removed.
Therefore, in a larg
Enomoto Akio
Kitoh Kenshin
Nemoto Hiroshi
Burr & Brown
Kalafut Stephen
Mercado Julian A.
NGK Insulators Ltd.
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