The present invention refers to the construction of hermetically
sealed lead acid bipolar batteries. More specifically, the invention relates to
a method of forming and assembling the seal components of the electrode stack
and sealing same by molding a final packaging frame thereon.
Description of prior art
Several prior art documents such as document EP-A-0 631 338 disclose
a typical bipolar battery arrangement. The electrode stack is formed by the union
of a number of frames of thermoplastic material, each of which is fitted with an
inside bipolar electrode plate and has surfaces extending beyond the plate. Said
extending surfaces provide coupling to adjacent frames.
The electrode stack is formed by stacking the single frames on one
another in a sequence so as to alternate electrodes having opposite polarities
and interposing glass microfiber separators therebetween.
Accordingly, the above cited frames act as spacer members between
the cells, as their coupling forms a cell unit comprising the negative electrode,
the separator and the positive electrode, as known in the art.
In some prior art cases, frames are provided with one or a number
of channels communicating with the inside of the cell. For example, in US Pat.
No. 4,900,643 each frame has a pair of grooves running along its longer side,
whereby coupling of two consecutive frames determines an inner double channel for
filling the cell and letting the gas out, respectively.
The main condition for ensuring correct operation of the bipolar
battery is the effectiveness of the sealing between the coupled frames. Sealing
action of each cell must be hermetical with respect to adjacent cells and the
In the past, prior art sealing was provided joining coupling frames
by heat welding. In US Pat. No. 5,035,045 this is accomplished by using an infrared
heater positioned in the space between the coupling surfaces of two frames. When
the surfaces begin to melt, the heating unit is withdrawn and the frames are moved
and into contact with each other and slightly pressed together to weld.
An alternative approach is disclosed in US. Pat. No. 4,164,068, which
makes provision of ultrasonic soldering.
The development of bipolar batteries has been hindered by inadequate
solutions being adopted for providing hermetical sealing to the cells. Among the
problems which are encountered more frequently there is that of deformation of
contacting surfaces due to high temperatures and relatively thin frames. This results
in inadequate welding in some points of the perimeter of the frame. This also
adversely affects operation of the communicating channels.
On the other hand, welding operations are excessively complicated
and costly, and are not adequate from an industrial point of view.
SUMMARY OF THE INVENTION
The present invention solves the sealing and packaging problems of
lead acid bipolar batteries by:
- a) using a different arrangement of the sealing members: the cell unit consists
of the coupling of a central spacer member and opposite frames of electrodes of
- b) using new modes of sealing cell sealing members by molding a side frame
which serves to form a housing for the electrode stack and forms seats for gas
The present invention represents an improvement with respect to prior
art sealing and packaging of bipolar batteries.
It is an object of the present invention to provide an original arrangement
of the hermetic sealing members, wherein the electrode frames are coupled to a
central spacer frame. Said members are stacked in series and sealed by molding
a final packaging frame.
It is another object of the present invention to provide an original
solution concerning modes of sealing and packaging the electrode stack of a lead
acid bipolar battery. Functionality of the system is made effective by:
- hermetic sealing of each cell with respect to the adjacent cells and the outside;
- uniform spacing between electrodes having the same polarity;
- regular dimensions of the active electrode surface;
- regular shape of cell inlet channels in order to:
- a) introduce the electrolyte easily and practically in a cell, independently
of the other cells, with a speed satisfying manufacture requests;
- b) allow, at a predetermined inner pressure, the outlet of gases which form
within the battery;
- contain the preloading required to gain good physical contact between the electrodes
and the glass microfiber separators.
The present invention provides a lead acid bipolar battery where
coupling of its components is simple. The assembly of the electrode stack is rendered
easy and gives a reliable and functional final product.
It is another object of the present invention to provide a method
of sealing the cells of a lead acid bipolar battery, simultaneously packaging the
battery so as to guarantee hermetical sealing and mechanical strength to the battery
In accordance with the invention, there is provided a method as claimed
in claim 1.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the present invention may be well understood there
will now be described a preferred embodiment thereof, given by way of example,
reference being made to the accompanying drawings, in which:
GENERAL DESCRIPTION OF THE METHOD OF THE INVENTION
- FIG. 1
- is a schematic front view of a battery constructed according to the present
- FIG. 2
- is a schematic sectional view, to an enlarged scale, taken along the line II-II
of FIG. 1;
- FIG. 3
- is a top view of the battery of FIG. 1;
- FIGS. 4 and 5
- are front and side views, respectively, of a spacer member being part of the
- FIGS. 6 and 7
- are plan views of the end plates of the battery;
- FIG. 9
- is a sectional view taken along line IX-IX of FIG. 7; and
- FIG. 10
- shows front and side views of a further detail mounted and detached.
- A plastic frame is molded on the electrode made of lead or other electrically
conductive material or polymeric material (such as polyaniline, polyparaphenylene,
polypirrole), or ceramic material (for example titanium carbide or molybdenum
silicide). The frame is for stiffening the electrode, provide a reference during
assembly, seal the edge of the electrode and eventually provide a reference for
applying the desired thickness of active compound.
- Spacer frames are provided to be interposed between the electrodes and contain
electrolyte supporting material, for example glass microfiber layers. The spacer
frames are provided with electrolyte inlet bores and gas outlet bores.
- Stack end plates are provided.
- Bipolar electrodes are stacked between the end plates. The bipolar electrodes
have active compounds applied thereto and are alternately arranged with the electrolyte
support containing frames. The end electrodes are monopolar and the intermediate
ones bipolar. A preloading is applied to the stack.
- The stack is preloaded in a mold and a layer of polyolefin material is molded
over the stack to seal same and provide a housing for the battery. Gas outlet valves
are obtained at the electrolyte inlet bores.
To attain perfect sealing of the battery, the materials forming the
electrode frames, the spacer frames and the end plates are chemically compatible
therebetween and with the molding material so as to heat seal in the contact zones
DETAILED DESCRIPTION OF THE INVENTION
With reference to the enclosed drawings, the method of constructing
a battery according to the present invention comprises firstly the step of providing
a series of electrodes 10, of which the intermediate ones are bipolar while the
terminal electrodes are monopolar. Each electrode 10 consists of a substantially
rectangular plate of electrically conductive material. Securely and continuously
fixed to the outer edge of the plate is a peripheral frame of polyolefinic material
for stiffening the plate, sealing its the edge and providing a reference member
useful in applying the active compound to the faces of the plate. Preferably,
the frame is obtained by pressure molding and welding of two complementary plastic
half-frames separately obtained by injection molding in a separate mold. Advantageously,
the half-frames are of a polyolefin based material being modified with polar groups
adapted to bind chemically to the conductive substrate.
With reference to FIGS. 4 to 6, there is shown a spacer 13 according
to the present invention. The spacers are frame-like members having a shape corresponding
to that of the electrodes and alternately arranged therewith. Besides keeping
the predetermined distance between adjacent electrodes, each spacer acts as an
outer housing for a conventional porous layer 12 supporting the electrolyte. Typically,
glass microfiber layers are use for this purpose.
Preferably, the spacer is obtained through injection molding of polyolefin
based material chemically compatible with the plastic material constituting the
frames so as to solder thereto during molding. For example, talc added polypropylene
or glass added polypropylene are suitable for forming the spacers. The added materials
have to be chosen so as to provide greater stiffness and size accuracy with respect
to the electrode frames, provide the desired dimension of the assembled battery
stack and attain greater heat resistance during molding of the outer housing, as
will be apparent herein after.
The cross-section of spacers 13 (FIG. 6) is so shaped as to contain
the electrodes 10. Therefore, transverse seats 14 are obtained along the edge of
both of their sides. Seats 14 prevent the spacer and the electrode frame from
sliding relative to one another during manufacturing and also improve the sealing.
A vertical, preferably tapered bore 15 is formed in each spacer for filling the
assembled battery with electrolyte (FIG.2). Advantageously, each bore 15 is formed
by two pins (not shown) mounted to moving parts of the mold used for forming the
Referring to FIGS. 7 to 9, each battery is fitted with a pair of
flat end plates 16. The thickness of end plates 16 depends on the inner pressure
acting in the pre-loading initial stage and the following stages of forming and
loading. Also, the thickness depends on maximum yielding that is admissible in
the center of each plate. Advantageously, end plates 16 are of a thermoplastic
polymer material chemically compatible with the material forming the spacers,
so as to heat seal to the molding material during packaging.
Obtained in each end plate 16 on the side facing the inside of the
battery is a seat 17 for a terminal 18 welded to the end monopolar collector electrode
plate. On the outwardly facing side there is formed a thinner edge portion 21
to be filled with molding material during the final manufacturing step. Within
thinner edge portion 21 a channel 19 is formed constituting a seat for hooking
clips 20 adapted to keep the assembled stack firm (FIG. 10).
In assembling the components of the battery (end plates, monopolar
and bipolar electrode plates with active compound, spacers, etc.) a special press
(not shown) is used which provides stacking and centering of the components, and
successive pre-compression of same until the desired thickness is reached.
Said press comprises two faces, of which one is movable and one is
stationary with reference templates. Suitable pneumatic rams drive the movement
of the movable face and control the drawing system.
The assembled and pre-compressed stacks are kept in position by hooking
clips 20 fitted to the sides of the stacks in the special seats of end plates 16.
Referring to FIG. 2, sealing and final packaging of the battery stack
are accomplished by injection molding of a special plastic material 22, for example
suitably strengthened polypropylene.
Then, the assembled stack is positioned within the injection mold
with special means, for example plugs also serving to close the acid inlet bores,
seats in the end plates, bores in the terminal current collectors, templates retractable
after the closing of the mold, etc.