Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a nonaqueous electrolyte
cell having a positive electrode of a material with
the apparent volume thereof increased with the discharge
reaction.
There are materials with the apparent volume thereof
increased with the discharge reaction, e.g., carbon
fluorides, silver chromate and manganese dio~ide as
disclosed in Japanese Patent Publication 54-35,653 published
Nov. 5, 1979 and metal sulphides (such as F`eS, FeS2,
CuS, Cu2S) or copper oxide and bismuth oxide, as disclosed
in Japanese Laid-Open Patent Publication No. 57-174871,
published oct. 27, 1982. Where such materials are used
as positive electrode active material for a nonaqueous
electrolyte cell, the following problem arises.
As the separator for this type of cell, unwoven
~abric of polypropylene is generally used as disclosed
in the literatures described above. However, as the
volume of the positive electrode is increased with the
discharge reaction, the separator of polypropylene unwoven
fabric disposed between the positive and negative electrodes
is compressed to squeeze out the retained electrolyte
from the separator. Consequently, a local portion of
polypropylene unwoven fabric where there is substantially
no electrolyte contained therein is present between
the positive and negative electrodes, so that the internal
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resistance ls sharply increased, resulting in deterioration of
cell characteristics.
The present invention provides an improved non-aqueous
electrolyte cell ~hich has desirous discharge voltage character-
istics, without a sharp increase of the internal resistance.
The present invention also provides an improved non-
aqueous electrolyte cell which can suppress a sharp increase of
the internal reistance thereo~, the cell having a positive
electrode with the apparent volume thereof increase with the
discharge reaction in the process of discharge.
The present invention again affords a new non-aqueous
electrolyte cell ~hich provides improved cell characteristics
with a stable internal resistance and a discharge voltage.
According to the present invention, there is provided a
non aqueous elecrolyte cell, which comprises a negative electrode
containing as active material a light metal such as lithium or
sodium or an alloy of these light metals, and a positive elec-
trode consisting substantially
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of a material wi-th the apparent volume thereof increasing by a
discharge reaction. The cell has a separator formed substan-
tially of a microporous resin film on the surface of either elec-
trode facing the other electrode, and an electrolyte layer filled
in a space between the above-described other electrode and the
separator wherein said electrolyte layer is formed by filling
said space with liquid electrolyte.
In the non-aqueous electrolyte cell according to the
present invention, the apparent volume increase of the positive
electrode caused with the discharge reaction is substantially
absorbed by the electrolyte layer. In addition, since the sepa-
rator provided between the positive and negative electrodes is
formed of a very thin synthetic resin film or films, even if the
volume of the positive electrode is increased until the positive
and negative electrodes are in contact with the separator where
there is locally substantially no electrolyte present, the dis-
tance between the positlve and negative electrodes is very small,
and the internal resistance will never be sharply increased.
In one embodiment of the present invention said separa-
tor is disposed on the surface of said positive electrode and
said electrolyte layer is formed between said separator and sald
ne~ative electrode. Suitably said microporous resln film is a
polypropylene film. Desirably the polypropylene film has a
thickness of approximately 0.025 mm.
In another embodiment of the present invention said
separator comprises a first separator element of a polyethylene
film and a second separator element of a polypropylene film, and
wherein said first separator element is closely contacted with
said positive electrode and said second separator is closely con-
tacted with said electrolyte layer. Desirably the cell ~urther
comprises a third separator element of a polyethylene film
between said first separator element and said second separator
element in a closely contacted three-layer structure. Suitably
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said :Eirst separator element consisks of two polyethylene films
closely con-tacte~ together.
The present inven-tion also provides a non-aqueous elec-
trolyte cell comprising a negative electrode containlng an active
material of at least a single light metal or its alloy, an annu-
lar insulating gasket along an edge of said negative electrode, a
positive electrode composed of a material with an apparent volume
thereof increased with a discharge reaction, a separator having a
microporous polyethylene film disposed on a surface of said posl-
tive electrode, and an electrolyte layer filled in a space
between said separator and said negative electrode wherein said
separator is held at a circumferential end thereof be-tween said
positive electrode and said annular insulating gasket and wherein
said electrolyte layer is formed by filling said space with
liquid electrolyte such that said electrolyte layer is disposed
in the direction of stacking of said separator and the positive
and negative electrodes.
The present invention will be further illustrated by
way of -the accompanying drawings, in which:-
Figure 1 is a sectional view of a non-aqueous elec~
trolyte cell according to the present invention;
Figure 2 is a sectional view of a comparative cell
which is known in the art;
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Figure 3 is a graph showing cell voltage characteristics
and internal resistance characteristics plotted relative
to a discharge time, with respect to the inventive cell
of Figure 1 and the comparative cell of Figure 2; and
Figure 4 is a sectional view of a cell according
to another embodiment of the invention.
Referring to Figure 1 of the drawing, a cell has
a positive electrode 1, a negative electrode 2, a separator
3 and an electrolyte layer 4. The positive electrode
1 is obtained by adding 10 wt~ of graphite as electrical
conductor and 5 wt~ of fluorine resin powder as binder
to 85wt~ of iron disulfide (FeS2) as active material
press molding the mixture with a pressure of 2 tons/cm2
to produce pellets with a diameter of approximately
11.0 mm and a thickness of approximately 1.8 rnm, and
sintering the pellets at a temperature of 200 to 300C.
The negative electrode 2 is a stamped lithium sheet
with a diameter of approximately 7.5 mm and a thickness
of approximately 2.2 mm. The separator 3 is a stamped
microporous polypropylene film with a diameter of approximately
11.0 mm and a thickness of approximately 0.025 mm.
The electrolyte layer 4 is formed by filling the space
between the negati~e electrode 2 and the separator 3
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with liquid electrolyte. The microporous resin film
may be a polyethylene film instead of the polypropylene
film as in the above embodiment.
An assembly operation of the nonaqueous electrolyte
cell illustrated in Figure 1 will be explained. First,
the lithium negative electrode 2 is press bonded to
a negative electrode collector 7, which is secured to
the inner surface of a seal cap 6 also serving as a
negative electrode terminal with an annular insulating
gasket 5 provided along the edge by insert molding,
so that the lithium negative electrode 2 will not fall
when the cell is inverted. At this time, a space is
defined by the lithium negative electrode 2 and the
annular insulating gasket 5.
Meanwhile, the positive electrode 1 is held in
forced contact with a positive elec,rode collector 9
secured to the inner surface of a container 8 also serving
as a positive electrode terminal. Then, the separator
3 is placed in position on the positive electrode 1.
In this state, the seal cap 6 is fitted in the open
top of the container 8.
The battery thus assembled is then put in a sealed
vessel (not shown) and the sealed vessel is vacuumized.
Then it is immersed in an electrolyte which i9 obtained
by dissolving 1 mole/Q of lithium tetrafluoroborate in
a mixed solution of propylene carbonate and 1,2-dimethoxyethane
to fill the space described above with the electrolytej thus
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forming the electrolyte layer 4. Thereafter, the open
edge of the container 8 is sealed on the insulating
gasket 5 to complete the cell.
Figure 2 is a sectional view showing a comparative
cell which has a generally known structure. The cell
illustrated in Figure 2 has no electrolyte layer and
the separator 13 thereof is different from the separator
3 of the cell of the invention shown in Figure 1. The
separator 13 in the comparative cell consists of an
unwoven fabric of polypropylene with a thickness of
approximately 0.5 mm.
Figure 3 shows the voltage and internal resistance
of the cell of Figure 1, indicated at '`A" and the comparative
cell of Figure 2, indicated at "B" plotted relative
to the time of discharge under a constant load of 5.6
K~ at a temperature of 20C.
As is apparent from Figure 3, the cell "A" according
to the present invention provided a constant internal
resistance and no sharp increase in the internal resistance
was examined. Thus, desirable discharge voltage characteristics
were obtained. By contrast, the comparative "B" showed
that the internal resistance was abruptly and sharply
increased in a certain stage of ~he discharge and, therefore,
the cell "B'' has a "two-stage" discharge voltage characteristic
as shown.
The "two~stage" characteristic of the comparative
cell "B" is considered to stem from the following ground.
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With the process of the discharge, the electrolyte that
has been held by the polypropylene unwoven fabric as
separator is squeezed out and, consequently, the separator
has a portion or portions which include substantially
no electrolyte between the positive and negative electrodes.
This portion f the polypropylene unwoven fabric, which
has a considerable thickness, will function as a sort
of insulator to sharply increase the internal resistance.
As the discharge proceeds further, however, the thickness
of the polypropylene unwoven fabric is reduced, so that
the internal resistance increase curve becomes much
gentler and the dlscharge proceeds with a low cell voltage.
With the cell "A" according to the invention, which
uses the thin microporous film as separator, even when
the volume of the positive electrode is increased, the
distance between the positive and negative electrodes
is small, so that the internal resistance is not increased
rapidly. Further , although the microporous polypropylene
film has less liquid holdlny capacity compared to the
polypropylene unwoven fabric, this gives rise to no
--problem with the cell "A" since the electrolyte layer
consisting of the electrolyte only is formed between
the separator and the negative electrode.
Figure 4 shows a modified structure of the nonaqueous
electrolyte cell according to the present invention.
In the embodiment of Figure 4, the separator 3 has three
separator elements and the positive electrode 1 has
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a conductive ring 10 therearound. A first or lower separa-tor
element 3A, which is placed on the positive electrode 1 with the
ring 10 is made of a microporous polyethylene film having a
thickness of 0.05 mm. A desired microporous poyethylene film for
the separator element 3A is "HIPORE 3050" produced by Asahi Kasei
Co., Ltd., Tokyo, Japan, which has desired characte~istics for
holding the electrolyte, that is, 500~ and more, and provides
e~cellent extensibility toward the negative electrode 2 when the
volume of the positive electrode 1 is increased. Although the
first separator element 3A has two "HIPORE 3050" ( a trademark)
films simply superposed in the illustrated embodiment, these
films can be laminated together.
Above the first separator element 3A is disposed a sec-
ond or upper separator element 3B contacted with a lower surface
of the electrolyte layer 4 with a spac0 therebetween. The second
separator element 3B is a microporous polypropylene film having a
thickness of 0.03 mm, and for this purpose "DURAGAR~ 2400" (a
trademark) produced by Celanese Corp. is found to be desirable.
The second separator element 3B of "DURAGARD 2400", which pro-
vides lower property for holding the electrolyte but has smaller
pore opening than the first separator element 3A of "HIPORE
3050", can prevent the positive electrode powder from adhering to
the lithium surEace of the negative electrode 2, and consequently
C~ll characteristics are improved.
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A third or middle separator element 3C is disposed
in the space confined between the first or lower separator
element 3A and the second or upper separator element
3B in a closely contacted relation to form a three-
layered separator 3. The third separator element 3C
is a micropor~us polyethylene film having a thickness
of 0.1 rnm, and for this purpose "HIPORE 2100" produced
by Asahi Kasei Co., Ltd. is desirable. The third separator
element 3C of "HIPORE 2100" has an excellent property
of holding the electrolyte, but may be omitted if necessary.
Other elements and structure may be considered
to be substantially similar to those of the embodiment
of figure 1, and a detailed description is omitted.
The cell according to the present invention has
a separator of a microporous resin film or films and
an electrolyte layer consisting of an electrolyte only
between the separator and either electrode, while the
positive electrode consists of a material with the apparent
volume thereof increased by the discharge reaction.
Thus, it is possible to suppress a sharp increase of
the internal resistance with the progress of the discharge
and provide a flat or constant discharge voltage characteristic,
which is remarkablybeneficial in industries.
The aforementioned Japanese Laid-Open Patent Publication
No. 57-174871 discloses formation of an electrolyte
layer between a separator and a negative electrode.
In this case, however, the separator consists of an
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unwoven fabric of polypropylene. Therefore, the internal
resistance will increase sharply like the co~parative
cell which has been described above with reference to
Figure 2.
