Accumulator with plastic casing

So that an accumulator having a gas-tight and liquid-tight, electrolyte-filled casing in which are arranged electrodes which are separated from each other by a separator and which are each electrically connected to pole contacts accessible from the outside of the casing can be produced in an advantageous manner from the point of view of the manufacturing procedure, wherein the accumulator is to have a durably and reliably sealed casing which is not restricted in terms of its shape, it is provided that in the region of the pole contacts the casing comprises a soft plastic material and a hard plastic material which are fixedly connected together, the soft plastic material forming a seal for the pole contacts and/or the feed-through ducting means of the pole contacts.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention concerns an accumulator with a gas-tight and liquid-tight 
electrolyte filled casing in which electrodes are separated from each 
other by a separator and are respectively electrically connected to pole 
contacts that are accessible from outside of the casing. 
2. Discussion of the Prior Art 
Accumulators of that kind are known with a large number of different casing 
shapes. A conventional alkaline accumulator has a cylindrical casing which 
comprises metal and forms a pot-shaped, electrolyte-filled container both 
for the electrodes and also for the separator. The cover which holds the 
positive pole contact is fitted into the opening of the pot configuration. 
In that case the flanged-over edge forms a holding arrangement which is 
both gas-tight and also liquid-tight. However, a metal casing of that kind 
is difficult to produce when dealing with non-round and in particular 
rectangular cells. 
The use of plastic casings is known for lead-acid accumulators and makes it 
possible to produce rectangular casings, while making good use of the 
available space. This construction however cannot be applied to all types 
of accumulators. The metal pole contacts which are cast into the plastic 
material casing or the metal feed-through ducting means thereof are of 
different coefficients of thermal expansion from the plastic material, but 
nonetheless may not became leaky upon an increase in temperature during 
charging or discharging at high current levels. It is necessary throughout 
the entire service life of the accumulator to ensure that neither gas nor 
electrolyte accidentally escapes. Accumulators with a very low internal 
resistance such as for example alkaline nickel-cadmium or nickel-metal 
hydride accumulators may build up greatly increased internal pressures 
under a high current loading, and such pressures should not result in 
leaks occurring in the region of the pole contacts. 
Seals which are fitted between the casing and the pole contact, such as for 
example the elastic round-cord rings which are referred to as O-rings 
require an additional production step in terms of inserting and correctly 
positioning the seal and therefore have an adverse effect on the 
production costs of the accumulator. Difficult electrolytes which, by 
virtue of a high capillary action, have a tendency to creep under seals, 
such as for example caustic potash solution, which additionally exhibits a 
migration movement in the direction of negative potential, can escape from 
the casing if the seal is not correctly inserted or if the seal is 
subsequently mechanically displaced, and they can subsequently give rise 
to damage. 
EP-A1-0 089 619 describes a gas-tight and liquid-tight pole sealing 
arrangement which is desired in particular for lead accumulators whose 
casing consists of plastic material. For sealing purposes, there is 
proposed therein a sealing system which comprises a plurality of layers of 
different materials and in which inter alia a free chamber is designed to 
surround the pole contact, and melt adhesives and further seals are 
arranged on that chamber. However that pole sealing arrangement can only 
be produced by a considerable number of production steps. 
U.S. Pat. No. 5 197 994 discloses thermal casing welding procedures in 
respect of battery casings which comprise plastic material. 
EP-A2-0 538 039 discloses an inserted cap which comprises a sealing means 
and which, in the case of a cylindrical battery, holds the central 
electrode and the pole contact relative to the casing and at the same time 
forms a seal for the battery casing to prevent fluid from escaping. 
SUMMARY OF THE INVENTION 
Consequently the object of the present invention is to provide an 
accumulator which is advantageous in terms of production from the 
manufacturing process point of view and which has a durably and reliably 
sealed casing which is not restricted in terms of its shape. 
That object is attained by an accumulator with a gas-tight and liquid-tight 
electrolyte filled casing in which electrodes are separated from each 
other by a separator and respectively electrically connected to pole 
contacts that are accessible from outside the casing, wherein in a region 
of the pole contacts the casing comprises a soft plastic material and a 
hard plastic material fixedly connected together and the soft plastic 
material forms a seal for the pole contacts and/or for a feed-through 
ducting means of the pole contacts. 
Making the casing in the region of the pole contacts from a soft and a hard 
plastic material which are fixedly connected together makes it possible to 
use the soft plastic material as a seal for the pole contacts and/or for 
the feed-through ducting means of the pole contacts. In that respect 
displacement of the seal due to external influences can be prevented by 
the mechanical connection between the two plastic materials. This design 
configuration also provides that there is essentially only one sealing 
surface, namely the sealing surface between the soft plastic material and 
the pole contact and/or the feed-through ducting means thereof. Therefore 
the electrolyte or the gas developed thereby can no longer escape along a 
second sealing surface between the seal and the casing. Furthermore, a 
sealing contact of the soft plastic material against the pole contact or 
the feedthrough ducting means thereof can be so designed that the sealing 
surface is greatly enlarged and fluid has to creep under long distances if 
it is to be escape. 
This design configuration is advantageous from the point of view of 
manufacturing procedure as, after the soft and the hard plastic materials 
are joined together, suitable openings for the pole contacts can be formed 
therein, for example by stamping, with a high degree of accuracy. 
Alternatively, a pole contact or its feed-through ducting means, which is 
already held in the hard plastic material, can be subsequently surrounded 
by the soft plastic material in a hot-in-hot injection welding process. 
That gives in each case a connection between the soft and the hard plastic 
materials, over the full surface area thereof. 
As both plastic materials essentially comprise the same thermoplastic 
elastomer and differ from each other in terms of their hardness either by 
a differing addition of plasticisers or by virtue of a different degree of 
cross-linking, there are no detrimental thermal stresses involved. The 
choice of the thermoplastic elastomer makes it possible to use chemically 
inert materials, such as for example modified polyamides, 
styrene-ethylene-butylene-styrene copolymers or polypropylenes which have 
excellent levels of resistance relative to the electrolyte. 
Highly developed production procedures which are available at the present 
time for shaped plastic members such as for example injection welding can 
be used without limitation, whereby the shape of the casing is no longer 
restricted. 
In a preferred embodiment the pole cap of the pole contact is connected to 
the feed-through ducting means thereof by spot welding and engages 
cup-like over a part of the soft plastic material. That increases the 
creep distance under the seal, by the area with which the soft plastic 
material bears against the pole cap. The pole cap is correctly positioned 
upon being subsequently fitted to the feed-through ducting means, by the 
soft plastic material. 
An alternative embodiment uses a pole contact which comprises a 
substantially cup-shaped rivet and the rearward end of which, in the 
manufacturing operation, is flanged over in such a way that it engages 
behind a part of the hard plastic material. In that situation, the front 
region of the pole contact is always securely held in sealing contact 
against the soft plastic material by the flanged-over part of the rivet. 
In that respect, in a manner which is advantageous from the point of view 
of the manufacturing procedure involved, the flanged-over part of the 
rivet may engage behind a conductive tongue which is inserted between the 
rivet and the casing and which makes the electrical contact with the 
respective electrode. In that way both the pole contact can be fitted in 
position and also the electrical connection thereof can be made in a 
single working step by riveting, in an inexpensive operating procedure. 
A further improvement in regard to manufacturing procedure is achieved if 
the casing of the accumulator includes between two casing portions a 
volume which extends therearound and which, in the operation of injection 
welding of the soft plastic material, can also be simultaneously filled. 
The soft plastic material within that volume advantageously serves as an 
additional casing seal but does not require any manufacturing step of its 
own. 
If both casing portions comprise a plastic material of approximately the 
same hardness, they can be securely and durably sealingly connected 
together by ultrasonic welding in an overlapping region. 
In an alternative configuration both casing portions are held together by 
retaining elements which are disposed in an overlapping region. In that 
way the casing portions can be securely joined together by being simply 
pressed together in an operation which is advantageous from the point of 
view of the manufacture procedure involved. If, after the two casing 
portions have been latched together, the soft plastic material is 
introduced into the volume extending around the casing, the soft plastic 
material and the hard plastic material of the two casing portions are 
sealingly joined together over their full areas by virtue of the welding 
operation in that region. If the two casing portions are latched together 
after the operation of injecting or spray welding the soft plastic 
material, the retaining elements guarantee that the hard plastic material 
of the one casing portion bears sealingly against the soft plastic 
material of the other casing portion. 
By embedding glass fibres in the plastic material, preferably in a 
proportion by volume of about 40%, it is possible markedly to improve the 
mechanical properties of the casing, such as its impact strength, its 
breaking load-carrying capacity and its flexural load-carrying capacity. 
With a rectangular accumulator casing in which the electrodes are arranged 
in superposed relationship in a layer-wise manner respectively separated 
by the separator, it is possible to eliminate unused volumes and it is 
possible to provide an accumulator of high capacity. 
In the case of gas-tight alkaline accumulators such as for example 
nickel-cadmium or nickel-metal hydride accumulators, a desired-rupture 
location can be disposed as a portion of reduced thickness, within the 
casing portion which comprises hard plastic material. That prevents the 
accumulator from exploding in the event of an abrupt rise in internal 
pressure by virtue of specific gas discharge by way of the desired-rupture 
location. 
Subsequent filling of the accumulator with the electrolyte is made possible 
by virtue of a closable filling opening. Arranging the filling opening 
closer to the positive pole contact than to the negative pole contact 
reduces the creep effect when using caustic potash solution as the 
electrolyte. 
In another embodiment the casing of the accumulator at the same time also 
forms a part of a casing of an electrical device. That makes it possible 
for example to simplify the construction of portable radiotelephones and 
to reduce the size of the accumulator, in spite of the accumulator being 
of high capacity.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In the Figures, the same or similar components of different embodiments are 
each denoted by the same references. 
Without limitation in respect of the large number of design configurations 
which are possible by virtue of the present invention, a rectangular 
gas-tight and liquid-tight alkaline accumulator is described hereinafter. 
In that respect, the term gas-tight and liquid-tight is used in relation 
to accumulators to denote accumulators which do not allow either gases or 
liquids to escape under normal operating conditions but which can 
intentionally form openings when predetermined conditions are attained, 
such as for example a predetermined increased pressure. 
The accumulator 1 has a casing which comprises two portions 2 and 3 and 
which surrounds the positive electrode 5 and the negative electrode 6. The 
electrodes 5 and 6 are separated from each other by the separator 4. In 
the condition in which it is ready for operation the accumulator 1 is 
filled in known manner with an electrolyte which is not shown in the 
Figures. 
In the region of the pole contacts 7, 8 the casing is in two layers, 
comprising a layer of a hard plastic material 24 and a layer of a soft 
plastic material 14. The soft plastic material 14 which is shown by 
crossed hatching in the Figures is welded over the entire surface area to 
the hard plastic material 24 which is shown by inclined-line hatching. 
With the hot-in-hot injection welding process which is used the welded 
surface is formed upon injection of the soft plastic material 14 along its 
contact surface relative to the hard plastic material 24. By virtue of the 
addition of plasticisers or by the choice of its degree of cross-linking, 
the soft plastic material 14 is of an adjustable hardness which is in the 
range of known sealing materials. The hardness of the hard plastic 
material is so adjusted that it reaches the usual levels of casing 
strength. 
The materials used are modified polyamides 
styrene-ethylene-butylene-styrene-copolymers and/or polypropylene. The 
portions of the casing 2, 3, which comprise plastic material, each have a 
peripherally extending overlapping region 9, 10 in which they are in 
contact with each other over a surface area. The portions 9, 10 are held 
together by an ultrasound welded seam 11 extending therearound. 
In a further configuration according to the invention, formed above the 
overlapping region 9 and enclosed by the region 10 is a volume 12 which 
extends around the periphery of the arrangement and which is connected by 
way of a passage 13 to the volume of the soft plastic material 14 in the 
region of the pole contacts 7, 8. That volume 12 is also simultaneously 
filled in the operation of injection welding of the soft plastic material 
14. The soft plastic material 14 within the volume 12 is thus formed 
integrally with the soft plastic material 14 in the region of the pole 
contacts 7, 8 and is also welded over its full area to the hard plastic 
material 24. 
In an alternative configuration the mechanical connection between the two 
casing portions 2, 3 is provided by retaining elements 30, 31 arranged in 
the overlapping region 9, 10. In that case, in the latched condition, a 
peripherally extending retaining projection 31 on the one casing portion 3 
engages behind a peripherally extending groove 2 in the respective other 
casing portion 2. Assembly of the two portions 2, 3 is made easier by 
virtue of the retaining projection 31 having an inclined run-on surface 
32. Within the volume 12 the soft plastic material 14 is either connected 
over the full surface area by injection welding to both regions 9, 10 or 
it is only connected by injection welding to the region 10 and the 
retaining elements 30, 31 hold the region 9 in contact against the soft 
plastic material 14, with a sealing effect at the end. 
Glass fibres or other known inert fibres are optionally embedded into the 
hard plastic material 24. In that case a proportion by volume of glass 
fibres of about 40% is preferred. 
A desired-rupture location 15 in the form of a portion of reduced thickness 
is arranged within the casing portion 2, 3 which comprises hard plastic 
material 24. The desired-rupture location 15 is of a defined area and 
thickness, which are so adjusted that, as from a given increased pressure 
within the accumulator casing, an opening is formed, which results in the 
pressure being reduced. 
In the case of accumulators which are filled with caustic potash solution 
as the electrolyte, a through opening 16 is preferably arranged in the 
vicinity of the positive pole contact 7 and is of a substantially T-shaped 
profile. That opening 16 is closed by a T-shaped plug 17 after the filling 
operation. 
A first embodiment includes pole contacts 7, 8 with a frustoconical 
feed-through ducting means 18, over which engages a cup-shaped pole cap 
21. The frustoconical feed-through ducting means 18 bears with its 
laterally enlarged edge portion against the hard plastic material 24 in 
surface contact therewith and is held in a self-centred condition in a 
through opening 20 which is also frustoconical. The cup-shaped pole cap 19 
is connected to the feed-through ducting means 18 by spot welding and 
engages over the soft plastic material 14 in sealing contact thereagainst. 
One or more spot welds 21 can be produced both prior to injection of the 
soft plastic material 14 and also thereafter. In the latter case, in known 
manner, the heat energy introduced in the welding operation is so selected 
that plastic deformation of the soft plastic material 14 and the hard 
plastic material 24 which forms the through opening 20 is prevented. 
In an alternative embodiment the pole contacts 7, 8 are of a substantially 
T-shaped cross-section whose radially enlarged region represents the pole 
caps 19 and forms an integral transition into the feed-through ducting 
means 18. The ducting means 18 has an internal space 22 which is 
cylindrically hollowed out and which forms a cup-like rivet and which 
permits the end 23 to be flanged over. The flanged-over end 23 engages 
behind a part of the hard plastic material 24 in the region of the pole 
contacts 7, 8. In that way the pole cap 19 is durably pressed in sealing 
contact into the soft plastic material 14. 
In a further embodiment, inserted between the flanged-over end 23 and the 
hard plastic material 24 is an electrically conductive tongue 25 which 
consists of metal and which makes a respective connection to each of the 
electrodes 5 and 6. The tongue 25 is connected by a spot weld 26 to 
connecting lugs 27, 28 which laterally project from the electrodes. The 
electrodes 5, 6 are arranged in the casing 2, 3 of the accumulator 1 in 
superposed relationship in a layer-like arrangement, as shown in FIGS. 2 
and 3. Alternatively the electrodes 5, 6 are folded one over the other in 
a meander-like configuration, with the interposition of the separator 4, 
as shown in FIG. 6. 
In this embodiment which preferably includes a respective pole contact 7, 8 
at each of oppositely disposed sides of the casing, the electrode carrier 
of the positive electrode 5 is directly connected to the feed-through 
ducting means 18 while the feed-through ducting means 18 of the negative 
pole contact 8 is connected directly to the negative electrode 6 or to a 
strip 29 which is in contact with the negative electrode 6. 
By virtue of the two-part casing structure, the electrodes 5, 6 can 
initially be fixed during manufacture to the pole contacts 7, 8 and a 
casing portion 3, by means of the connecting lugs 27, 28 of the electrodes 
5, 6. Such an accumulator structural group is shown in FIG. 5, wherein the 
pole contacts 7, 8 are already sealingly held within the soft plastic 
material 14 and the hard plastic material 24. 
Such a structural group can both be connected to the casing portion 2 shown 
in the Figures, and also fitted into a corresponding casing of an item of 
electrical equipment. The accumulator 1, with its casing, then forms a 
part of the casing of the item of electrical equipment.