Lead storage battery

A lead storage battery having electro-collecting boards of lead or lead alloys, and active material layers closely contacted with the electro-collecting boards. The active material layers are integrally formed with the electro-collecting boards by providing a mixture, in the form of slurry, of an active material powder and a liquid to the electro-collecting boards, and then drying the mixture.

BACKGROUND OF THE INVENTION 
The present invention relates to a lead storage battery and, more 
particularly to a thin and sealed typed lead storage battery wherein an 
electro-collecting board of lead or lead alloy is arranged within a 
battery casing and a cover thereof, and active material layers are formed 
closely adjacent to the electro-collecting boards, and the thus produced 
casing and cover with the plates for the anode and cathode are connected 
together with a separator therebetween. 
In a standard lead storage battery, a lead or lead alloy supporter; which 
is formed by a punching, a casting or an expanding method, is coated with 
active materials which are mixed with lead powder or lead monoxide powder 
and an aqueous solution of sulfuric acid and other additives, and then 
subjected to curing process in a vapor atmosphere, and to a drying process 
to form positive and negative electrodes. The thus produced electrodes are 
combined with a porous separator and then inserted into the casing made of 
synthetic resins, and followed by a sealing step of the casing to thereby 
complete the lead storage battery. 
The conventional lead storage battery as described has been extensively 
used for its reliability in quality and economic aspects. Along with the 
recent miniaturization of devices and instruments in various fields, the 
miniaturization of batteries, such as lead storage batteries, for power 
sources of such devices and instruments is of interest and is sought after 
enthusiastically. In order to comply with the requirement of the industry, 
an attempt has been made to use a synthetic net as a supporter in place of 
the conventional metal in the form of a lattice and a lead plate or lead 
alloy plate was used for an electrocollecting board so that pastelike 
active materials are disposed to the synthetic resin net to form 
electrodes. The thus formed electrodes are cut to a predetermined size and 
then closely contacted to the collector to thereby complete a thin and 
light-weighed lead storage battery. 
However, the lead storage battery in accordance with the above-mentioned 
attempt reveals some difficulties, which will be described hereinafter. 
The aforesaid electrodes attempt in producing is basically common to that 
of the conventional method, and more specifically, it is necessary that 
paste-like active materials be prepared and then provided onto the 
supporter for the synthetic resin net. Therefore, during the process of 
forming the active material, a noxious powder such as a lead powder is apt 
to be scattered in the air, resulting in an extreme deterioration of the 
active material. Further, it is difficult to make the density of the 
paste-like active material constant resulting in a scattering in the 
capacity of the electrodes. Particularly, since the quantity of the 
applied paste-like active material is limited in the thin-type battery, 
non-uniformity of the battery characteristics becomes much more serious in 
accordance with the uniformity of the electrodes in respect to the 
capacity thereof. Besides, in the production of the lead storage battery, 
troublesome assemblies and steps are necessary such as the preparation of 
paste-like active materials, coating of the active materials on the 
supporter, cutting it to a predetermined size, and assembling it to make 
it closely contacted with the electr-collecting board. 
In addition, such a thin-type lead storage battery, which is to be mounted 
within a device or an instrument, must be sealed, as described in Japanese 
Patent Publication No. 50-12092 or Japanese Unexamined Patent publication 
No. 57-176667. The basic structure thereof will be explained with 
reference to FIG. 1 of the drawings. In FIG. 1, reference numerals 1 and 2 
represent a battery casing of a synthetic resin and a battery cover 2 of a 
synthetic resin, respectively. Within the space 3 confined by the casing 1 
and the cover 2, a negative electrode 4 and a positive electrode 5 are 
positioned through a separator 6. In such a thin-type storage battery, the 
conventional method wherein an electrolyte is supplied through a small 
hole of the casing after the cover and the casing are adhered together is 
not applicable for miniaturizing the batteries and producing them in 
quantity. Thus, a method has been used in which the casing and cover are 
subject to ultrasonic welding after the electrolyte is secured by the 
electrodes 4, 5 and the separator 6. The battery has an outlet valve 7 on 
the inner wall of the casing, an outlet port 8, and a valve seat 9, as 
illustrated. 
However, the method by ultrasonic welding have revealed other difficulties. 
Namely, in the welding step of the casing and cover, the active materials 
positioned adjacent to the positive and negative electrodes 4, 5 are 
scattered due to vibration, and the scattered active material around the 
electrodes induces a short circuit of the positive and negative electrode. 
Similarly, the scattered active material is exhausted together with the 
electrode out of the casing 1 through the outlet port 8, and at this 
moment the scattered material is stuck to the position between the outlet 
valve 7 and the valve seat 9, resulting in a failure of the sealing at 
this part of the battery. In order to avoid such a short circuit, a 
separator having a larger areas than the electrodes is used to provide an 
electrical separation between the electrodes. Further, a sufficient space 
10 is formed between the electrodes and the outlet port 8 so that a longer 
passage is formed between these elements in order to minimize the quantity 
of the active material which is exhausted through the outlet port 8 and to 
minimize the sticking of the active material to the valve seat 9. However, 
the provision of the relative large space 10 and larger separator reduces 
a volume efficiency of the battery and results in a failure of 
miniaturization. 
A mechanism for permitting a gas, which is generated by an electrochemical 
reaction within the lead storage battery, to be exhausted by means of a 
safety valve or gas exhaustion hole is known in, for example, Japanese 
Utility Model Publication Nos. 40-31878, and 40-31879 and Japanese 
Unexamined Utility Model Publication No. 58-155763. In Japanese Utility 
Model Pub. No. 40-31878, as illustrated in FIGS. 2A-2C, the casing 11 has 
at its upper portion a cylindrical projection 12, an aperture 13 
communicated with the interior of the casing, and a rubber tube 14 fitted 
to the cylindrical projection to close or plug the aperture 13. A cover 
(not shown) prevents the rubber tube 14 from being dislocated from the 
cylindrical projection, wherein the cover has an aperture (not shown). In 
Japanese Utility Model Pub. No. 40-31878, as illustrated in FIGS. 3A-3C, a 
cylindrical projection 16 with an opening 17 is formed on top of the 
casing 15 and a rubber cap 18 is adapted to the projection to close the 
opening 17. The cap is held by a cover (not shown) so that it is not 
removed or dislocated, wherein the cover has an aperture (not shown). In 
Japanese Unexamined Utility Model Publication No. 58-155763 a casing is 
formed with a pair of synthetic resin members and a frame interposed 
therebetween, and a safety valve port is provided for communication 
between the interior and outside of the casing. 
However, the above-mentioned structure reveals the serious problems as 
described hereinafter. In the battery structure of Japanese Utility Model 
Pub. No. 40-31878, if it is applied to a thin-type lead storage battery, 
the cylindrical projection 10 must be formed on the side portion of the 
casing 9 so as to minimize the thickness of the casing, as shown in FIG. 
4. Such a casing 9 with a cylindrical projection 9 is unitarily formed by 
molds which are moved in the direction as shown by arrows A and B (FIG. 
4). The molds must have slidable rod for providing the cylindrical 
projection 10, and it is difficult to prepare such molds. By contrast the 
battery disclosed in Japanese Utility Model pub. No. 40-31879 permits a 
relatively easy production of the mold having a slidable rod, but is 
almost unapplicable to a battery which is not only small but also complex 
in shape since there is an inherent limitation of produceable shape and 
size due to working prevision of the molds, packing characteristics of 
resins and other factors such as shrinkage of the hardening resin. 
Japanese Unexamined Utility Model Pub. No. 58-155763 shows a structure in 
which circumferential portion of the safety valve is forcibly contacted 
with the frame and a pair of the resin members, and thus additional space 
for the valve chamber, resulting in an increase of the size in the 
longitudinal direction. Additionally, the safety valve must provisionally 
be fixed to the predetermined position within the valve chamber prior to 
setting of the resin members, and at this moment, the safety valve, which 
was provisionally press-fitted to the chamber, is displaced out of the 
chamber by its resilient recovery force. Thus, this structure presents 
difficulties in assembly operation. 
In addition to the above, in the sealed type lead storage battery, a 
quantity of the electrolyte is generally restricted, and the concentration 
of the electrolyte is set to about 40 percent which is higher than that of 
a general storage battery for automobiles, wherein the electrolyte 
concentration at the time of charge is about 35 percent. The reason for 
the higher concentration of the electrolyte are as set forth below. 
(1) Repetition of discharge to an extent that the active material is used 
up will shorten a life time for the battery and thus quantity of sulfuric 
acid in the electrolyte is restricted to restrictively determine the 
electrode reaction, with unused active material being maintained as it is, 
whereas such a problem as above is not raised with reference to the 
automobile battery in which charge and discharge proceed at the same time. 
(2) For the purpose of obtaining higher energy density of the battery, 
unnecessary water is excluded as much as possible to provide higher volume 
efficiency and weight efficiency. Particularly, this requirement is 
remarkable for the thin type or small sized lead storage battery. 
(3) In a sealed structure, oxygen gas generated from the positive electrode 
during charge is chemically consumed by the negative electrode. In such a 
chemical reaction, three phases (Pb for solid phase; electrolyte for 
liquid phase; and O.sub.2 for gaseous phase) are necessary, and this 
chemical reaction is delayed if the quantity of the electrolyte is greater 
than the normal. Therefore, the electrolyte is restricted in its quantity. 
By the reasons described above, in the sealed type lead storage battery, 
the electrolyte thereof is set to have the highest concentration which is 
close to the upper limit of the allowed concentration for the lead storage 
batteries. 
In the conventional sealed-type lead storage battery, the casing and the 
cover are made of ABS resins from the viewpoints of mechanical strength, 
dimensional stability, surface appearance, ecconomical aspects, etc. 
However, such resins as ABS resins has a vapored water permeable property, 
and water in the electrolyte is vapored to penetrate the casing wall or 
cover wall to lead out of the battery. Consequently, the concentration of 
the electrolyte becomes higher than the aforementioned limitation, and 
such a high concentration of the electrolyte accelerates the corrosion 
speed of the electrodes plates resulting in the deterioration of the 
electrode plate capacity and the life of the battery. Up to the present, 
no specific countermeasure has been successfully made to alleviate the 
exceedingly high concentration of the electrolyte due to the 
abovementioned phenomena, presumably because the property level of the 
conventional batteries is rather low. Although an attempt was made to use 
a resin having a relatively low vapored water permeability such as a 
high-impact polystyrene, the above-mentioned problems have not yet been 
solved successfully. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a sealed type lead storage 
battery which permits a simple manufacturing step, an improvement in the 
working circumstances in respect to the deterioration of the battery as a 
result of the noxious or toxic powder. Also, an object of the present 
invention is to improve the reliability of the storage battery capacity. 
Another object of the present invention is to provide an improved sealed 
type lead storage battery which can be maufactured by relatively simple 
production facilities. 
Another object of the present invention is to provide a sealed type lead 
storage battery, which can prevent the active material from being 
scattered around the electrode plates when the battery casing and cover 
are welded together. 
A further object of the present invention is to provide a new sealed type 
lead storage battery which permits one to produce of a safety valve 
mechanism provided to a battery casing or a of a simple structure, and 
which can decrease the occupied volume of the valve mechanism in 
accordance with the miniaturization or thinning of the battery. 
An additional object of the present invention is to provide an improved 
sealed type lead storage battery which can prevent a concentration of the 
electrolyte from becoming excessively higher, and which provides improved 
properties and life time. 
According to the present invention, there is provided a lead storage 
battery in which an electro-collecting board made of lead or lead alloy is 
positioned in a casing and electrode plates are formed in a close contact 
with the collector. In the invention, a slurry-like mixture of an active 
material powder and liquid is applied to a surface of the 
electro-collecting board, and then dried to form a unitary structure of 
the electrode plates of the active material and the electro-collecting 
board. This structure is effective for decreasing the irregularity of the 
electrode plate capacity and for a desired production process without 
substantial labor and difficulty. In the invention, the mixture of an 
active material powder and a liquid such as an aqueous solution of 
sulfuric acid is prepared in the state of slurry which has a stronger 
Newtronian flow characteristic than when it is in the state of paste. This 
means that time and energy required for the mixture of a liquid and an 
active material powder are decreased. Further, a much simpler mixing 
device or tools such as a vessel with an agitator can desirably mix the 
liquid and the active material powder, without using a large-scaled and 
complex mixer such as a Banbury mixer or a kneader having a plurality of 
agitators. It is difficult to reliably control the density of the active 
material if it is in the state of paste since the density is largely 
dominated by air contained in the paste, and therefore it is necessary to 
conduct a measurement every time it is regulated. By contrast, a mixture 
in the form of slurry reveals a constant density of the mixture because 
the slurry does not substantially contain air and because the true density 
of the powder is unchanged even when apparent density thereof is changed 
in accordance with a production lot. The same is true of various factors 
which dominate the working properties, such as, for example, the viscosity 
and the volume change of the mixture which contains an active material 
powder. By preparing the mixture in the form of a slurry, displacement or 
transportation and measurement of the volume of the mixture can be 
achieved readily. Apparently, this is based upon the difference in the 
solid state properties between the paste and the slurry. Such an effective 
form of slurry as described above can be realized successfully by simply 
controlling the mixing ratio of the liquid and the powder, or in other 
words, by increasing the quantity of the liquid. 
In the present invention, a electro-collecting board is placed 
horizontarily and then a fixed volume of the mixture in the form of slurry 
is supplied to form a rectangular mixture layer on the electro-collecting 
board, utilizing the solid state properties of the Newtonian fluid of the 
slurry. Thereafter the mixture is dried to complete the electrodes. By 
forming the electrode plates on the electro-collecting board as described 
above, the following advantages are expected. 
Firstly, a manufacturing step or stage which causes an active material 
powder to be scattered in the air is not necessary at all, and any 
consideration or anxiety in regard to the working circumstances is not 
required. Secondly, the formed electrode plates can be used by 100% 
thereof without a material loss which is inherent in the conventional 
steps such as the cutting step. Thirdly, the volume of the liquid can be 
measured almost ten times as precisely as that of the conventional method 
in which the volume is measured by controlling the thickness, width and 
length to obtain a predetermined electrode plate capacity. This means that 
the active material in the battery can be controlled quite precisely, 
therefore no anxiety is necessary for providing the balanced capacity 
between the positive electrode and the negative electrode and the process 
described above provides advantages in both cost and quality. Besides, 
there is an advantage in that formation of the electrode plate and 
attachment of it to the electrocollecting board can be performed 
simultaneously. 
In a preferred embodiment of the invention, projections are formed in an 
opposed relation at the peripheral portion of the battery casing or the 
cover so that the projections hold the separator under pressure. This 
structure can prevent the active material from being scattered from the 
electrode plate at the time of ultrasonically welding the casing and the 
cover and then exhausted out the battery. 
In a further embodiment of the invention, a safety valve chamber is formed 
between the casting and the cover, and an outlet port which is 
communicated with the interior of the casing is opened at the inner wall 
of the casing. The casing has a gas exhaustion hole. Within the safety 
valve chamber is disposed a resilient, tubular safety valve which is 
located such that its ends are contacted with the casing and the cover. 
In a further embodiment of the invention, the casing and the cover are made 
of a synthetic resin which has a filler of a low water vapor permeability. 
It is generally known that a filler is added to a resin so as to improve 
the solid state properties of the resin. However, no specific 
counter-measure has been found for improvement of the water vapor 
permeability by addition of a filler. The inventors of the present 
invention have found by various experiments that the resin, if mixed with 
a special filler, reveals an improved water vapor permeability. This 
filler itself hardly has a water vapor permeability if it is solely used, 
such as a flat shaped material, for example, a micrograss flake (CCF-048) 
developed by Nippon Garasu Co., Ltd. a corporation of Japan. In principle, 
since the fillers are of flat shape, the flat surfaces of the fillers are 
aligned in a continuous manner in accordance with a flow of the resin in 
the molding step, and a substantially unitary layer of the filler is 
formed. The filler covers the substantial surface of the casing and the 
cover, and prevents a transmission of water vapor through the casing and 
the cover since the filler has an extremely low permeability to water 
vapor.

DETAILED DESCRIPTION OF REFERRED EMBODIMENTS 
Embodiment 1 
A preferred embodiment of the invention will be described with reference to 
FIGS. 5 and FIG. 6 and FIGS. 7A to 7C. 75 weight part of lead monoxide 
powder, 25 weight part of trilead tetraoxide, 0.2 weight part of 
hydroxypropylcellulose (a thickening agent having a higher viscosity than 
polyethyleneoxide : HPC), and 24 weight part of water are mixed by an 
agitator for about 5 minutes to obtain a mixture in the form of slurry. By 
making the mixture in the form of slurry, the mixing time can be decreased 
to 1/6 relative to that of a mixture in the form of paste which generally 
contains water of about 10 part by weight and must be treated by a 
high-power mixer for about 30 minutes. The density of the mixture in the 
form of slurry is about 3.3 g/cc, whereas the conventional paste mixture 
generally has a density of about 4.4 g/cc. 
The mixture in the form of slurry is supplied into a battery casing 23 
which is made of a synthetic resin and is provided unitarily with an 
electro-collecting board 22, as illustrated in FIG. 5 and subject to 
drying to thereby form an electrode plate 21 on the collector 22. When the 
slurry is supplied, it flows on the surface of the electro-collecting 
board 22 and is diffused into a rectangular shape. This diffusion is 
facilitated if the casing 23 is vibrated slightly so that the rectangular 
shape of the slurry can be obtained in a shorter time. Lead weight (lead 
density) per a unit volume of the electrode plate at the time when the 
drying step is completed was 4.2g/cc, which is substantially equal to that 
of the conventional electrode which was made from the mixture in the form 
of paste. This is supposedly based upon the fact that the lead compound 
powder in the fact that the slurry mixture is spontaneously settled down 
in the drying step with the result that the density thereof is 
substantially equal to that of the mixture in the form of paste as used in 
the conventional process. 
A density of active material is readily controlled by simply adding a small 
amount of sulfuric acid to the mixture in the form of slurry. 
The foregoing is the explanation of forming the positive electrode, and the 
negative electrode can be manufactured in a substantially similar manner 
by selecting materials such as the active material and thickener and 
compounding ratio thereof, and utilizing the cover of the battery casing 
23. 
The thus produced casing for the positive electrode and the cover for 
negative electrode are fitted together, and an electrolyte is supplied, 
and thereafter the casing and the cover are welded by an ultrasonic 
welding method to completely seal the casing. Thus, a sealed, thin type 
lead storage battery can be made. 
Alternatively, as illustrated in FIG. 6, a frame 24 which has an area for a 
unit electrode plate is prepared and located on the electro-collecting 
plate 22, and then the mixture in the form of slurry is supplied into the 
frame 24. After the slurry is dried, the frame 24 is removed to form a 
unitary structure of the electro-collecting board and the electrode plate 
21. This unitary structure can be integrally formed in the casing 23 by an 
insert molding. 
As illustrated in FIG. 7A, a shoulder 25 can be formed at the position 
where the electro-collecting board 22 is enclosed by the casing wall, so 
that the boundary surface of the mixture in the form of slurry becomes 
more distinct as illustrated in FIG. 7B than the structure of FIG. 7C 
wherein no shoulder is formed. Thus, the shoulder 25 is effective for 
obtaining electrode plates 21 of a constant thickness. 
As described above, the mixture in the form of a slurry of the active 
material powder and the liquid is supplied to form a unitary structure of 
the electro-collecting board and the electrode plate of the active 
material. Accordingly, the process of forming the mixture and the assembly 
of the electrode plate can be greately simplified, and therefore the 
facilities can be simplified. Further, a step for cutting into a unit 
electrode plate is not required at all, and thus any devices and 
instruments for the cutting process is unnecessary. Besides, the 
production time according to the invention can be decreased to about 80 
percent relative to the time consumed by the conventional process which 
uses the mixture in the form of paste. In the present invention, 
preparation of the mixture in the form of slurry can be conducted within a 
sealed container, and there is no need to take care of working 
circumstances. In addition the, uniformity or variability in weight of the 
electrode plate can be greately improved to the value of .+-.0.7%, whereas 
the conventional process using the paste-like mixture had a value of 
.+-.6.5%. 
EMBODIMENT 2 
FIG. 8 shows another embodiment of the present invention, wherein reference 
numerals 31 and 32 are a casings of synthetic resins such as an ABS resin 
or AS resin, and a cover of similar synthetic resins, respectively. Within 
the interior space confirmed by the casing 31 and the cover 32, an 
positive electrode plate 35, a separator 36 and a negative electrode plate 
37 are interposed between electro-collecting board 33 for positive 
electrode and a electro-collecting board 34 for negative electrode, in a 
stratified configuration. The positive electrode plate 35 and the negative 
electrode plate 37 are formed by supplying the mixture in the form of 
slurry of the active material powder onto the electro-collecting board 33, 
34 to form a layer of a constant thickness, and drying the layer. The 
separator 36 is made of a suitable glass fiber to form a porous structure 
having a larger area than the positive and negative electrode plates 35, 
36, and an aqueous solution of sulfuric acid is impregnated thereto as an 
electrolyte. The casing 31 has a projection 38 at its circumferential 
portions and the cover 32 has a recess 40 for snugly receiving the 
projection 38 of the casing 31. The casing 31 has a valve seat 43 at its 
one end, and a safety valve 42 is fitted to the valve seat to generally 
close a gas exhaustion hole 44 formed in the casing 31 but function to 
permit the gas to flow out of the battery when a gas pressure within the 
casing 31 is elevated up to a predetermined value through the hole 44. 
The casing 31 in this embodiment has a shoulder 45 and the cover 32 has a 
shoulder 47 in an opposed or confronting relation as illustrated in FIG. 8 
so that the separator is forcibly secured from opposed sides by the 
shoulders 45 and 47. Thus, the interior of the battery which is confined 
by the casing 31 and the cover 32 is fully shielded from the outside. 
After the positive electrode plate 35 and the negative electrode plate 37 
are formed on the elecrtro-collecting board 33, 34 as described, the 
separator 36 is arranged between the positive and negative electrode 
plantes 35, 37 and the electrolyte is supplied into the separator 36. 
Thereafter, the safety valve is fitted to the valve seat of the casing 31, 
and the cover is attached to the casing and then welded together by an 
ultrasonic welding apparatus to complete a lead storage battery of the 
invention. Since the entire circumference of the separator is firmly held 
by the opposed shoulders 45, 47 in the welding process, the active 
material powder, which may appear on the surface of the plates 35, 37 
during the ultrasonic welding, is obstructed from flowing towards the gas 
exhaustion hole 44. However, it will be anticipated from the foregoing 
description that the gas generated within the casing and the electrolyte 
are movable, and therefore the structure as well as the process for making 
the battery as described above does not affect at all to the battery 
properties. 
The provision of the shoulders 45, 47 in a confronting relation provides an 
effective function for preventing the active material powder, which may be 
scattered during the welding step, from being scattered into the plate of 
opposite polarity. Therefore, the property deteriorations and short 
circuits due to such an undesirable flow of the powder can be avoided. 
Further, in the battery of the type having a gas exhaustion hole, the 
powder, if produced during welding, does not stick to the portions around 
the gas exhaustion hole. Additionally, no additional space is required in 
the battery structure of the present invention, and a volume efficiency of 
the battery can be improved. 
EMBODIMENT 3 
FIGS. 9 to 12 show a further embodiment of the present invention, wherein 
reference numeral 51 represents a casing of high-impact polystyrene which 
has a space 52 for containing therein, though not shown, a pair of 
electrocollecting board of lead or lead alloys, electrode plates of an 
active material fitted to the electro-collecting boards, a glass fiber 
separator interposed between the electrode plates and electrolyte 
impregnated in the separator. A cover 53 which is made of the same 
material as that of the casing 51 is fixed to the casing 51 by an 
ultrasonic welding apparatus. The casing 51 has an oval chamber 54 for 
securing a safety valve (not shown) a gas exhaustion hole 55 which 
connects the chamber 54 and the space 52 of the casing 51, and a gas hole 
56 open to the outside of the battery. Reference numeral 57 is a tubular 
safety valve made of a suitable resilient material, which has ends 57a, 
57b and a circumferential outer surface 57c as shown in FIG. 10. The 
safety valve 57 is forcibly secured in position within the chamber 54 such 
that the ends 57a, 57b contact the base of the chamber 54 and the inner 
wall of the cover 53, respectively, against a resilient force of the valve 
57 itself. Thus, the valve 57 which is round shaped in cross section as 
shown in FIG. 10 is deformed into an oval shape and then closely and 
forcibly contacted with the substantially entire circumferential surface, 
or inner wall, of the chamber 54 by a recovery force of the valve 
material. Thus, the tubular safety valve 57 is provisionally fixed within 
the chamber 54 until the cover 53 is fixed to the casing 51. In FIG. 9 of 
the drawing, reference numeral 58 and 59 represent a terminal which is 
connected to the components in the space 52 of the casing, and a port for 
receiving the other terminal (not shown). 
The gas exhaustion hole 55 and the gas hole 56 can be formed relatively 
simply by utilizing a mold 61 having a rod 60 such that the rod 60 is 
inserted into an aperture (not shown) of an upper mold for forming the 
chamber 54, and then supplying the predetermined resin thereto. It is 
preferred that the safety valve have a circumferential length 
substantially equal to, or slightly larger than, the circumferential wall 
length of the chamber 54, but a valve having a slightly smaller 
circumferential length than the chamber may be applied. It will be 
anticipated that the shape of the chamber can be modified to a rectangular 
shape, for example, instead of the oval shape. 
Embodiment 4 
A further embodiment of the present invention will be described with 
reference to FIGS. 13, and 14, wherein a casing 61 has a space 62 for 
containing therein the battery components such as electro-collecting 
boards, electrode plates of the active material, a separator and 
electrolyte, as similar as the previous embodiment of FIGS. 9-12, and a 
similarly formed cover 63 is ultrasonicwelded to the casing 61. The casing 
61 has an oval or elliptical chamber 64 for securing therein a safety 
valve 57 (FIG. 10). Similar to the previous embodiment of FIGS. 9-12, the 
safety valve 57 is provisionally fixed until the cover 63 is fixed to the 
casing 61. The cover 63 has a tab 70 and the casing 61 has a recess 67 at 
the valve chamber 64 for receiving the tab 70 when the cover 63 is fixed 
to the casing 61. Further, the cover has a protrusion 71 which is to be 
engaged with the terminal port 69. It is to be noted that a slight space 
is formed between the tab 70 and the recess 67 for functioning a gas 
exhaustion. The gas exhaustion hole 65 can be simply formed by utilizing a 
mold 73 having a rod 72, as similar as previously described with reference 
to FIG. 12. In this embodiment of FIG. 13 the tab 70 extending downwardly 
functions as a safety valve, and it is modified, if desired, to other 
forms such as a tubular shape as the embodiment of FIGS. 9-12. 
In the embodiments of FIGS. 9 through 12 a gas exhaustion hole is formed at 
the portion of the valve chamber (54, 64) and a tubular safety valve of a 
resilient material is provided in the chamber such that the ends of the 
valve are contacted with the casing and the cover. Thus it is possible to 
make it smaller the safety valve mechanism without substantial difficulty 
or labor. Further, this structure permits a thinner structure of the 
battery since the valve is secured in contact with the casing and cover, 
and if necessary the valve chamber can be made larger in the longitudinal 
direction thereof without sacrificing the requirement of thinner 
structure. Additionally, the safety valve in the form of a tube can be 
obtained readiy and reliably. 
In the structure of the embodiment of FIGS. 13 and 14 wherein the gas 
exhaustion is effected by a slight gap formed between the casing and the 
cover, an appearance of the battery is not deteriorated since there is no 
need for providing a hole on the outer surface of the battery. Further, 
the safety valve in the form of a tab 70 is snugly fitted to the recess of 
the casing so that its provisionally engagement is made stable. 
Additionally, a shorter rod 72 of the mold 73 can form a single hole, 
which is the gas exhaustion hole 65, and there is little danger of injury 
or breaking of a long rod. 
EXAMPLE 1 
An ABS resin or high-impact polystyrene is homogeneously mixed with flat 
glass flakes of about 20% by volume, wherein the flat glass flakes having 
a thickness of about 3 microns and particle size of several hundred 
microns, and the mixture is heated to 60.degree. C. within an isothermal 
vessel for 4 hours, and heated up to a resin temperature of 250.degree. C. 
for injection molding of a casing. A predetermined volume of water is 
supplied into the casing in correspondence with the volume of a practical 
use, and subject to ultrasonic welding to provide a complete sealing. The 
thus prepared casing was left to stand in the atmosphere of 40.degree. C. 
for 4 days and its weight change was measured, as set forth in Table 1 
below. 
In Table 1, GFI represents glass fibers and GFL glass flakes. 
The weight loss ratio (%) is calculated by the following formula. 
TABLE 1 
______________________________________ 
Resin 
High 
ABS resin impact styrene 
GFI & 
Fillers GFI GFL mica GFL mica 
______________________________________ 
Volume ratio 
0 20 5 . . . GFL 
20 0 20 20 
of Filler 20 . . . GFL 
Weight loss 
100 100 24 24 59 14.7 18 
ratio (%) 
______________________________________ 
EXAMPLE 2 
Glass flakes of 20% by volume and glass fibers of 5% by volume are 
homogeneously mixed with ABS resin, and subject to a heat treatment for 
injection molding to form a casing. A the weight loss ratio of the casing 
was 24% is shown in Table 1, which suggests an effective restriction of 
water vapor permeation. It is understood further that the shock resistance 
of the casing has been improved by the addition of glass fibers. 
Table 2 shows the result of deterioration of the battery properties 
(capacity) due to a concentration of the electrolyte in response to the 
volume loss of the electrolyte by water vapor permeation only. 
TABLE 2 
______________________________________ 
ABS resin 
Filler GFL 
______________________________________ 
Volume ratio of 0 20 
Filler 
Time (month) until 6 24 
property deterioration 
was found. 
______________________________________ 
Note: 
The products were left to stand in the atmosphere at 40.degree. C. in the 
condition of a charge. 
Table 2 apparently shows that a prolongation of the predetermined battery 
properties was achieved. Further, the filler added in the resins has 
proved that it can improve the heat resistance property to about 
10.degree. C. higher than that of a conventional battery casing without 
the filler. This is useful for an extended use of the battery under a 
severer condition of elevated temperature. 
Although the present invention has been described with reference to the 
preferred embodiments, many modifications and alternations can be made 
within the spirit of the invention.