Battery with rust preventive structure

A battery having a rust-preventive structure includes a battery cell, the side-wall and an outer peripheral region of the safety valve end of which are covered with heat-shrink tubing. A sealing plate is attached in a moisture-tight fashion to the heat-shrink tubing on the safety valve end via a pressure separating adhesive layer. Adhesive seals the region between a lead-tab connected to the battery terminal and the sealing plate.

BACKGROUND OF THE INVENTION 
This invention relates to batteries with rust-preventive structures 
primarily incorporated in electric-powered vehicles or in equipment used 
where moisture is likely to accumulate on the batteries. 
A single battery cell typically has an iron case with a nickel-plated 
surface. When moisture adheres to the surface of the metal case, the 
nickel plating peels off exposing the iron such that the iron may rust. 
Battery rusting causes poor electrical contact by increasing contact 
resistance, and also impedes proper operation of the safety valve. To 
alleviate these problems, battery packs used outdoors have a plurality of 
battery cells sealed within a moisture-tight case. 
Because the battery cells are protected in the moisture-tight case, they 
can be used outdoors with confidence. However, only small capacity 
batteries can be employed in this structure. This is because the battery 
cells cannot be effectively air-cooled for applications where high 
currents are extracted. Since battery packs used as power supplies for 
applications such as electric-powered vehicles output high currents and 
correspondingly large amount of heat, how efficiently that heat can be 
given off is extremely important. When a battery heats up and its 
temperature rises, battery performance drops drastically. High current 
batteries used for applications such as electric-powered vehicles have 
large battery capacities. In order to reduce the charging time of high 
capacity batteries, charging currents are increased and effective 
air-cooling during charging is also important. Consequently, high current 
batteries, even those used outdoors, cannot be waterproofed by configuring 
a plurality of battery cells inside a moisture-tight case. Therefore, 
prior art high current batteries have the drawback that effective cooling 
as well as a waterproof structure are difficult to achieve. 
A safety valve is provided to prevent a battery's external case from 
bursting. The safety valve opens when internal pressure rises abnormally. 
An open safety valve prevents external case rupture by exhausting gases 
within the battery. Provision of a safety valve makes it difficult to 
attain a moisture-tight seal for the battery. As discussed in Japanese 
Utility Model Publication No. 59-19301 issued Jun. 4, 1984 and Japanese 
Non-examined Utility Model Publication No. 62-59961 issued Apr. 14, 1987, 
this is because battery gases cannot be quickly discharged out of an 
opened safety valve. 
SUMMARY OF THE INVENTION 
This invention was developed for the purpose of correcting these and other 
drawbacks. It is thus a primary object of this invention to provide a 
battery with a rust-preventive structure which can be effectively 
air-cooled and which has a moisture-resistant configuration without 
offering an impediment to the safety valve operation. 
To achieve this object, the battery of the present invention includes a 
battery cell the outer sidewall of which is covered with heat-shrink 
tubing. The heat-shrink tubing that covers the sidewall also covers the 
outer peripheral portion of a battery terminal end provided with a safety 
valve. The heat-shrink tubing is longer than the total battery cell length 
so that it extends beyond the terminal ends. The portion of the tubing 
that extends beyond a terminal end is shrunk to form a ring covering the 
outer periphery of the terminal end. This portion of the heat-shrink 
tubing extending around the outer periphery of the safety valve terminal 
end is attached in a moisture-tight fashion to a sealing plate via a 
pressure separating adhesive layer. The sealing plate has an opening open 
to the battery terminal. The pressure separating adhesive layer allows the 
sealing plate to separate from the tubing when the battery cell safety 
valve opens and gas pressure is exerted against the sealing plate. When 
the separation occurs, an opening is created for gas to escape between the 
sealing plate and the heat-shrink tubing. A terminal lead-tab extends 
through the battery terminal opening in the sealing plate, and the end of 
the lead-tab connects with the terminal at the safety valve end of the 
battery. The area between the lead-tab and the sealing plate is filled 
with adhesive to prevent the ingress of moisture. The region of the 
battery terminal end opposite the safety valve end is also covered in a 
moisture-tight fashion. Since this terminal end has no safety valve, it 
can be made moisture-tight by applying adhesive between a sealing plate 
and the heat-shrink tubing. However, this sealing plate is attached to the 
heat-shrink tubing without a pressure separating adhesive layer but rather 
with an adhesive that does not fail even when pressure is applied to the 
sealing plate.

DETAILED DESCRIPTION OF THE INVENTION 
The outer sidewall 1A of the battery cell 1 of the battery is covered with 
heat-shrink tubing 2. The battery cell is shown in the figures as 
cylindrical. However, the present invention is not limited to a battery 
cell having the shape of a right cylinder. For example, the battery cell 
may also have the shape of a rectangular column or an elliptical column. 
As shown in FIG. 4, the battery cell has a built-in safety valve 47. The 
safety valve 47 opens when gas pressure within the battery rises 
abnormally. The safety valve 47 shown in FIG. 4 is built-in to the 
+terminal end of the battery cell 41. 
The heat-shrink tubing 2 covering the outer sidewall 1A of the battery cell 
1 shown in FIGS. 1 through 3 is a synthetic resin film that shrinks when 
heated. In its un-shrunken state, the heat-shrink tubing 2 has a 
cylindrical shape larger than that of the battery cell 1. The battery cell 
1 is inserted into the cylindrical heat-shrink tubing 2, and the tubing is 
heated and shrunk to adhere tightly to the outer sidewall 1A of the 
battery cell 1. As shown in FIGS. 1 and 3, the heat-shrink tubing 2 covers 
not only the battery cell sidewall 1A but also the outer peripheral region 
of the battery terminal end 1B. The width (W) of the heat-shrink tubing 2 
covering the outer peripheral region of the terminal end 1B is between 2mm 
and 20mm and preferably between 3mm and 10mm in order to facilitate the 
attachment of a sealing plate 4. The width (W) of the heat-shrink tubing 2 
covering the outer peripheral region of the end 1B can be set by selecting 
an appropriate overall length of the heat-shrink tubing 2. The width (W) 
of heat-shrink tubing 2 covering the end 1B is widened with increases in 
the overall length of the heat-shrink tubing 2. Since the heat-shrink 
tubing 2 shrinks when heated, it adheres tightly to the outer peripheral 
region of the terminal end 1B as shown in FIG. 3. The heat-shrink tubing 2 
bends through a 90.degree. angle between the battery cell sidewall 1A and 
the terminal end 1B tightly adhering to the surface of the battery cell 1. 
The battery has a sealing plate 4 attached to the outer peripheral region 
of the battery terminal end 1B. The sealing plate 4 is made from 
insulating sheet material that moisture does not penetrate such as 
plastic. The sealing plate 4 has essentially the same shape as that of the 
battery cell terminal end 1B in order to close it off. A battery terminal 
hole 4A is provided at the center of the sealing plate 4 to allow a 
lead-tab 5 to pass therethrough. A ring 8 is attached in a moisture-tight 
fashion to the sealing plate 4 at the terminal hole 4A. The ring 8 
prevents leakage of adhesive 6 applied in the vacancy at the terminal hole 
4A with the lead-tab 5 inserted. In other words, the sealing plate 4 with 
the ring 8 establishes a reliable moisture-tight seal between the lead-tab 
5 and the sealing plate 4 with a small amount of adhesive 6. This also 
gives the battery terminal 1B a good finished appearance. The sealing 
plate 4 is attached to the surface of the heat-shrink tubing 2 covering 
the outer peripheral region of the terminal end 1B via a pressure 
separating adhesive layer 3. 
The pressure separating adhesive layer 3 allows at least a portion of the 
sealing plate 4 to separate from the heat-shrink tubing 2 when the battery 
cell's safety valve opens. The safety valve built-in to a nickel-cadmium 
battery is designed to open when internal pressure rises to about 
20Kg/cm.sup.2. Consequently, the pressure separating adhesive layer 3 has 
a design strength that will cause the sealing plate 4 to separate 
therefrom when the sealing plate 4 is pushed by gas discharged from the 
battery case through the open safety valve. For example, double-sided 
adhesive tape can be used as the pressure separating adhesive layer 3. The 
sealing plate 4 can be easily attached to the heat-shrink tubing 2 when 
double-sided tape is used. Adhesive can also be used for the pressure 
separating adhesive layer instead of double-sided tape. To attach the 
sealing plate to the heat-shrink tubing, adhesive can be applied to either 
the surface of the sealing late or the heat-shrink tubing or to both. 
Further, instead of adhesive, the pressure separating adhesive layer can 
be of any type of bonding means that allows separating of the sealing 
plate from the heat-shrink tubing when the sealing plate is pushed on by 
gas pressure. 
When the safety valve opens, the pressure separating adhesive layer 3 
causes the sealing plate 4 to separate from the heat-shrink tubing 2. 
Consequently, it is necessary for the sealing plate 4 at the safety valve 
terminal end 1B to be attached to the heat-shrink tubing 2 via a pressure 
separating adhesive layer 3. The reason for this is because gas which 
passes through the safety valve into the battery terminal must be 
exhausted between the sealing plate 4 and the heat-shrink tubing 2. 
After the sealing plate 4 is attached to the heat-shrink tubing 2 on the 
terminal end 1B, the lead-tab 5 is spot welded to the terminal of the 
battery cell 1. The end of the lead-tab 5 passes through the sealing plate 
4 and connects with the terminal of the battery cell 1. The lead-tab 5 is 
made of sheet metal and is bent as shown in FIG. 3 for easy passage 
through the ring 8 of the sealing plate 4. 
After the lead-tab 5 is connected to the battery terminal, the vacancy 
between the lead-tab 5 and the terminal hole 4A is plugged with the 
adhesive 6. Adhesive is applied within the ring 8 to effect a 
moisture-tight seal between the lead-tab 5 and the sealing plate 4. 
Adhesives such as those in the epoxy, urethane, phenol, and acrylic 
families can be used as the adhesive 6. 
The battery shown in FIG. 1 has both the +and -terminals sealed against 
moisture by the same structure. Although it is necessary to attach the 
sealing plate 4 to the heat-shrink tubing 2 via the pressure separating 
adhesive layer 3 to allow gas to be exhausted between the sealing plate 4 
and the heat-shrink tubing 2, the battery terminal end without the 
built-in safety valve (normally the - terminal end) can have an 
intrinsically moisture-tight structure. In other words, at this terminal 
end there is no demand for the ability to release gas that builds up 
pressure within the battery. Consequently, the sealing plate 4 at this 
terminal end can be attached to the heat-shrink tubing via a robust 
adhesive that does not separate due to internal gas pressure. Further, 
although not illustrated, the area of this terminal end can be nearly 
entirely covered by the heat-shrink tubing and the gap between the 
lead-tab and the heat-shrink tubing can be sealed against moisture by 
adhesive without using a sealing plate. 
A high capacity battery to which this type of moisture-tight sealing is 
applied is seldom used as a single unit. More often a plurality of battery 
cells are used as a battery pack by connecting them in series to establish 
the proper output voltage or in parallel to further increase the battery 
capacity. By connecting a plurality of batteries together in this fashion, 
the battery pack can be made to have a capacity and voltage optimally 
suited for applications such as a power source for electric-powered 
vehicles. 
When this is done, it is important to connect the battery cells together in 
a configuration that allows effective cooling. In particular, the total 
quantity of heat generated by a battery pack with many high capacity 
battery cells is large, and effective cooling to prevent an excessive 
temperature rise is extremely important. It is also important to make the 
battery pack compact enough to fit within a limited space. Compactness and 
effective heat dissipation are mutually exclusive characteristics that are 
very difficult to realize simultaneously. When a battery pack is assembled 
in a compact fashion, heat dissipation is difficult, battery temperature 
rises, and reduction in battery performance due to such a temperature rise 
becomes a problem. 
FIGS. 5 and 6 show an improved battery pack that can effectively dissipate 
heat and has an overall compact shape. This battery pack connects 
batteries together using a honeycomb core 59 that creates air cooling 
ducts 510 between each set of adjacent batteries. Both ends of the 
honeycomb core 59 are open to allow air to flow freely through the air 
cooling ducts 510 of the battery pack. Batteries with the above-described 
rust-preventive structure are inserted into the hexagonal cylinders of the 
honeycomb core 59 forming air cooling ducts 510 between adjacent 
batteries. 
Sheet material with the flexibility to deform and some resiliency is used 
for the honeycomb core 59. The honeycomb core 59 is sized to cause some 
outward expansion of the cylinders when the batteries are inserted. As 
shown in FIG. 6, when batteries are inserted into the honeycomb core's 
hexagonal cylinders, air cooling ducts 510 of identical shape are created 
between each set of adjacent batteries. 
The air cooling ducts 510 pass vertically through the battery pack allowing 
air to pass freely therethrough. Consequently, cooling air easily flows 
through the air cooling ducts 510 to effectively and uniformly cool the 
surface of each battery. In particular, the honeycomb core 59 does not 
attach to the entirety of the battery surfaces and uniform forced cooling 
of those battery surfaces is accomplished by air flowing through the air 
cooling ducts 510. Since the honeycomb core 59 does not cover the battery 
surfaces, battery surfaces exposed to the air cooling ducts 510 are in 
direct contact with the air and are cooled without intervention by the 
honeycomb core 59. The cooling ducts 510 are of course provided at the 
innermost part of the battery pack. The temperature can easily rise at the 
innermost part of the battery pack since it is difficult to dissipate heat 
there. Except for the portion of each battery that abuts the batteries 
adjacent thereto through the core 59, a relatively large battery surface 
area is exposed within the air cooling ducts 510. Consequently, a battery 
pack employing the honeycomb core has the advantage that many batteries 
can be cooled very effectively by passing cooling air through the ducts 
510. Further, since the honeycomb core 59 can neatly arrange the batteries 
in fixed positions, a compact overall shape can be obtained. 
The lead-tab that connects battery cell terminals together can also have 
the shape shown in FIG. 7. Both ends of the lead-tab 75 shown in this 
figure are bifurcated, i.e. divided in two. As shown in the side view of 
FIG. 8, the divided part of the lead-tab 75A is passed through the hole in 
the battery terminal sealing plate and welded to the battery terminal as 
facilitated by the end of the lead-tab 75 bent at an obtuse angle 
(.alpha.) to form a welding region 75B. As can be seen, the ends of the 
lead-tab 75 are each bent at obtuse angles at two points and the center 
portion of the lead-tab 75 is linear. However, although not illustrated, 
it is not necessary to bend each end of the lead-tab in two places next to 
the welding region 75B. For example, it is also possible to bend each tab 
once at each end at an obtuse angle to form the welding region 75B, and to 
then bend the remainder of the lead-tab into a slightly curved arch. The 
welding region 75B provided by bending each end of the lead-tab 75 is spot 
welded to a +or -terminal of a battery. 
A lead-tab 75 with bifurcated ends can be efficiently spot-welded. This is 
because when points A and B shown in FIG. 7 touch the terminal during spot 
welding, parasitic current I flowing through the circuit shown by a broken 
line is reduced and a large current can flow between the welding region 
75B and the battery cell terminal. 
Further, clad material that is a laminate of different metals can be used 
for the lead-tab 75 to reduce parasitic currents during spot welding. The 
clad material is copper with a metal of lower conductivity plated over the 
surface of the copper. FIG. 9 shows an enlarged cross-sectional view of an 
optimum clad material for the lead-tab 95. The clad material in this 
figure has layers of nickel as the lower conductivity metal laminated on 
both surfaces of copper. Nickel and copper are joined together by forming 
alloys at the interfaces. The clad material in this figure has the side 
with the thick nickel layer welded to the battery terminal. The thick 
nickel layer that is welded to the terminal is designed, for example, to 
be 0.1mm to 0.25mm thick and the thin layer on the opposite side is 
designed, for example, to be 0.02mm to 0.1mm thick. The center layer of 
copper is designed, for example, to be 0.1mm to 0.4mm thick. For a 
lead-tab carrying several tens of amperes of current, a copper thickness 
of 0.2mm, a thick nickel welding side thickness of 0.2mm, and a thin 
nickel side thickness of 0.05mm is desirable. The lead-tab 95 made of clad 
material with the cross-sectional structure of FIG. 9 can be spot-welded 
to make the center copper layer form alloys. When the lead-tab is 
spot-welded, heat from the welding fuses the nickel layer to form alloys 
and weld the copper to the battery terminal. 
The lead-tab 75 of FIG. 7 is also provided with adhesive bond insertion 
holes 712 between the bent portions of the lead-tab ends. The purpose of 
an adhesive bond insertion hole 712 is for allowing adhesive to be 
injected to the back side of the lead-tab 75. Without an adhesive bond 
insertion hole 712, the application of adhesive to the back side of a 
lead-tab 75 spot-welded to a battery terminal cannot be verified. As shown 
in FIG. 10, it is necessary to inject adhesive to the back side of the 
lead-tab 75 without creating voids. This is so that the surface of the 
lead-tab 105 can be completely covered to shut out air. It is a laborious 
process to fill the backside of the lead-tab 105 with adhesive without 
creating voids when an adhesive bond insertion hole is not provided. It is 
also difficult to determine whether voids have been left. After injected 
adhesive has filled all voids on the back side of the lead-tab 105 it 
leaks out from both sides to cover the lead-tab 105. In other words, when 
adhesive leaks out from the back side of the lead-tab 105, the back side 
of the lead-tab 105 has been filled without any voids having been left. 
The adhesive bond insertion hole 712 is defined between the bends in the 
lead-tab 75 shown in FIG. 7. This configuration has the advantage that the 
strength of the bent portions of the lead-tab 75 is not reduced by the 
adhesive bond insertion hole 712. The bent portions of the lead-tab 75 are 
easily damaged by vibration. The strength of the bent portions with 
respect to vibration is also ensured by making the angle (.alpha.) an 
obtuse angle as shown in FIG. 8. A lead-tab with right angle bends will 
exhibit large stress concentrations at the bent portions that reduce 
strength with respect to vibrations. The lead-tab 75 bent at obtuse angles 
as shown in FIG. 8 has little internal stress and is strong with respect 
to vibrations. 
Further, the lead-tab 75 shown in FIG. 8 is covered by tubular covering 
711. The tubular covering 711 covers the central portion of the lead-tab 
75. End portions of the lead-tab 75 not covered by tubular covering 711 
are covered by adhesive. The entire surface of the lead-tab 75 is covered 
in a completely moisture-tight fashion by the tubular covering 711 and the 
adhesive. Although any tubing that shuts out outside air from the lead-tab 
75 can be used as the tubular covering 711, heat-shrink tubing is most 
suitable. The lead-tab 75 is inserted into heat-shrink tubing, then heat 
is applied to tightly attach the heat-shrink tubing to the surface of the 
lead-tab 75. The lead-tab 75 shown in FIG. 8 has part of its ends covered 
but the regions where the adhesive bond insertion holes are located are 
not covered. 
FIGS. 10 and 11 show the structure of the +terminal region of the battery 
cell where the lead-tab 75 shown in FIG. 8 is spot-welded, and FIGS. 12 
and 13 show the structure of the terminal. In these and other figures, a 
casing 1013 extends over the sealing plate 104. A plan view of the casing 
1013 is shown in FIG. 14. The casing 1013 shown in this figure is of 
plastic and includes 12 disks 1013A connected in a manner creating 
openings. The disks 1013A are circular and slightly larger than the 
outside diameters of the batteries. Cylinders 1013B for receiving battery 
cells, respectively, are formed under the disks 1013A as one piece 
therewith. The bases of the cylinders 1013B are open to allow the battery 
cells to be inserted thereinto. 
The centers of the disks 1013A of the casing 1013 define filling holes 1014 
filed with adhesive 106. The perimeters of the filling holes 1014 are 
defined by guide walls 1015. However, the guide walls 1015 are only 
provided in regions other than underneath the lad-tabs 105. The guide 
walls 1015 extend to the adhesive bond filling hole 1014 of an adjacent 
disk 1013A to hold the lead-tab 105 in place. The guide walls 1015 not 
only facilitate alignment of the lead-tabs 105 but also prevent the 
lead-tabs 105 from moving out of position. 
The casing 1013 has portions at both ends of the battery cells 101 to 
connect 12 battery cells 101 together in fixed positions. Connecting rods 
1016 are formed as a single unit with and are located between the disks 
1013A to connect the above-mentioned portions of the casing 1013 together. 
The cylinders 1013B of the casing 1013 inserted are also thereby connected 
together. 
The bent region of the lead-tab 105 extends through the adhesive bond 
filling hole 1014 of the casing 1013 and the battery terminal hole 104A of 
the sealing plate 104, and the welding region 105B is spot-welded to the 
+terminal of the battery cell. The end of the lead-tab 105 which is not 
covered by tubular covering 1011 is covered by adhesive 106 occupying both 
the adhesive bond filling hole 1014 and the battery terminal hole 104A. 
The adhesive is applied to on the underside of the lead-tab 105 through 
the adhesive bond insertion hole 1012. The adhesive 106 also covers the 
upper surface of the lead-tab 105. The adhesive bond filling hole 1014 and 
the battery terminal hole 104A are filled with the adhesive 106 so that 
adhesive covers the entire portion of the lead-tab 105 protruding from the 
tubular covering 1011. 
The battery shown in FIG. 1 has both the +and -terminal ends sealed with 
the same structure, namely the heat-shrink tubing. The +end of this 
battery is provided with a safety valve. For this reason the -end with no 
safety valve does not necessarily require the sealing plate to be attached 
to the heat-shrink tubing via a pressure separating adhesive layer. The 
sealing late at the -end can be attached to the tubing via adhesive that 
will not allow separation even if pressure acts on the sealing plate. 
However, if the sealing plate is attached to both the +and -terminal ends 
via a pressure separating adhesive layer, the battery can be efficiently 
manufactured in large quantities because the same structure is used at 
both ends of the battery. 
As described above, by covering each battery cell with heat-shrink tubing, 
sealing plates, and adhesive, each battery cell has a structure that 
prevents the ingress of moisture. This allows the battery cell surface to 
be cooled with outside air, and yet the battery cell is protected against 
moisture. A battery pack protected against moisture with each individual 
battery cell in a configuration that allows direct air cooling can be very 
efficiently cooled compared with prior art battery packs having a 
plurality of battery cells tightly sealed together within a case. This is 
because the actual air cooling area per unit battery capacity is 
substantial, and because the surface of a battery cell can be directly air 
cooled. The battery pack of this invention, which has a waterproof 
structure and can be efficiently air cooled, has the feature that it can 
be discharged or charged with large current while suppressing a 
temperature rise and preventing performance degradation due to such a 
temperature rise. Further, since each individual battery has a waterproof 
structure, corrosion due to the ingress of moisture to the battery cell is 
drastically reduced. 
Still further, the battery having the above-described structure has the 
feature that even though the battery cell is completely covered in a 
waterproof manner, internal battery gas can be exhausted when the safety 
valve opens. The reason for this is as follows. The battery of the present 
invention has heat-shrink tubing that covers the sidewall of the battery 
cell and extends over the outer peripheral region of the safety valve 
terminal end. A sealing plate is attached to the surface of heat-shrink 
tubing on the outer periphery of the safety valve terminal end via a 
pressure separating adhesive layer. When the safety valve opens and gas 
pressure between the battery cell and the sealing plate builds up, the 
pressure separating adhesive layer fails creating an opening between the 
sealing plate and the heat-shrink tubing through which gas within the 
battery terminal can escape. Consequently, the present invention provides 
a waterproof battery cell that can be effectively air cooled and yet 
provides no impediment to the operation of the safety valve.