Pressure-equalized electrochemical battery system

A pack of ordinary, commercially-available batteries is provided with a con electrolyte-filled reservoir coupled to each battery by a small tube. The reservoir includes a compliant diaphragm which, when exposed to deep-sea pressure, applies the pressure to the reservoir electrolyte to force it into the battery. Forceful filling of the cells equalizes their internal and external pressures. Electrical discharge currents are reduced to a minimum by making the tubes as small as and as long as possible.

BACKGROUND OF THE INVENTION 
The present invention relates to electrochemical batteries and, in 
particular, to battery systems adapted for deep-sea operation. 
Batteries which are exposed to deep-ocean pressures can, of course, be 
easily crushed or damaged unless they are specially-designed or unless 
their pressure-compensating arrangements are provided. For example, a 
conventional practice has utilized special pressure vessels which, 
although they may be capable of, withstanding the ambient pressure 
nevertheless can become quite complex and expensive particularly when 
their cost is compared with that of ordinary commercially-available types. 
However, the usual commercial batteries, such as the lead-acid or Nicad 
battery types, unfortunately are formed with a relatively thin and 
flexible casing wall which yields readily to external pressures especially 
when the casing or cell is not completely filled with its electrolyte. As 
far as is known, the susceptability of these commercial type batteries to 
damage has prevented their use in deep-ocean operations in which they are 
exposed to the severe ambient pressures. 
It is therefore an object of the present invention to provide a battery 
system capable of utilizing relatively thin-walled, commercial-type 
batteries in deep-ocean applications. 
Another object is to provide such a pressure-equalizer system for use with 
the thin-walled commercial cells. 
A further object is to provide a pressure equalizing system in which any 
discharge current between the batteries is reduced to a minimum. 
Another object is to provide a pressure-equalized system which is simple, 
inexpensive and easily adapted for use with commercially-available 
batteries.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, the arrangement includes a pair of electrochemical 
battery cells 1 and 2, which, for descriptive purposes, can be considered 
as a battery pack having electrical interconnections 3, 4 and 5 coupling 
the positive and negative terminals of the two batteries one to another 
and also to other batteries of the pack which are not shown in the 
drawing. The battery cells are shown schematically since, as will become 
apparent, many types of commercially-available cells can be modified and 
used for the purposes of the invention. For descriptive purposes it can be 
considered that the illustrated cells are commercially-available lead-acid 
cells having a casing 6 filled with an electrolytic fluid 7. The 
electrolyte will be that ordinarily used in the particular cells. Thus, if 
the cell is an acid type (leadacid), it would be sulfuric acid. Alkaline 
cells, such as the familiar Nicad cells, use KOH or its equivalent. The 
casing is a relatively thin-walled, flexible member common to most 
commercial cells. Electrolyte 7 only partially fills each of the cells 
leaving an empty, unfilled volume 8 at the top. As will be appreciated, 
this empty volume exists in charged electrochemical battery cells due 
principally to the gassing which occurs on charging. Insofar as the 
present invention is concerned such empty portions will be considered as 
being normally present although their presence is not an operational 
requisite. 
A pressure-equalization arrangement obviously is needed if these cells are 
to withstand heavy ambient pressures such, for example, as pressures of a 
deep-ocean environment. Such pressures, of course, are capable of crushing 
the relatively light side walls of the cells. The present arrangement 
avoids the need for the heavy, specially-designed pressure vessel type of 
cell although such structures can be used if desired. 
To provide the pressure-equalization a common reservoir 9 is coupled by 
small, hollow tubes 11 and 12 coupling the reservoir to each of the cells. 
If, as is assumed in FIG. 1, the battery pack includes cells other than 
the illustrated pair, each of the other cells also will be connected to 
common reservoir 9 by a similar tube. The reservoir is a closed vessel 
formed with rigid side and upper wall portions 12 and 13 and, in 
particular, with a bottom wall formed of a compliant diaphragm 14. The 
small tubes, in turn, communicate the interior of the reservoir with each 
of the cells and, preferably, enter the cells at their upper portion to 
communicate directly with their empty or unfilled portions. The manner in 
which the tubes are coupled to the cells will depend somewhat upon the 
type of cell used although this coupling should present no particular 
difficulty. In fact, many of the commercially-available cells already are 
provided with fill openings into which the tubes can be inserted and 
sealed. Of particular importance, reservoir 9 is filled with a fluid 
electrolyte 16 which, in use, also fills the tubes. The type of 
electrolyte used in the reservoir normally will be the same as that used 
by the cells themselves or, in other words, if the cell electrolyte is a 
dilute sulfuric acid, the fluid in the reservoir will be the same. 
However, as long as the electrolyte fluid of the reservoir is capable of 
being used in the cells, the conditions of the present invention are 
satisfied. 
Operationally considered, when such a battery pack is deployed at a 
deep-ocean depth to power, for example, a sonobuoy or other oceanographic 
devices, the ambient water pressure compresses compliant diaphragm 14 to 
apply the ambient water pressure through tubes 11 and 12 for the purpose 
of completely filling cell casing 6. Pressure is equalized since the 
filling of the cells produces the same internal pressure as that to which 
the diaphragm is subjected. It will be noted that the capacity of 
reservoir 9 should be at least as great as the sum of the empty volumes 8 
of the cells themselves. For this reason, depending upon the number of 
cells that are desired for any particular application and also dependent 
upon the volume represented by unfilled portions 8 of the cell, it may be 
desirable to provide a common reservoir 9 for a certain plurality of 
cells. In other words, for practical reasons, it may become desirable to 
employ a common reservoir for a fixed number of batteries. This factor 
will become more apparent in the description of the implementation shown 
in FIG. 3. 
One other factor to be considered is that because electrolytic fluids are 
conductive, there will be an electrically-conductive path formed from one 
of the cells through its tube 11 and on through reservoir 9 and tube 12 to 
the other cell. Since the cells are electrically interconnected, this path 
is capable of permitting an undesirable electric discharge current to flow 
between the cells. To avoid this discharge current, tubes 11 and 12 should 
be formed with an internal diameter that is as small as possible and also 
they should have a length which is as large as possible. The purpose in 
these criteria is to impose in the conductor path a resistance that is 
sufficient to counteract the discharge current. In a particular 
implementation, the tubes have an ID of about 0.25 inches and a length of 
about 6 to 7 inches. Such dimensions provide a resistance of approximately 
10 Kohms per tube which is a sufficient resistance to reduce the discharge 
current to a point permitting submerged operation for relatively long 
periods of time. If the operational life of the system is to extend for 
excessive periods, it may be desirable to utilize the special gas bubble 
arrangement illustrated in FIG. 2. In this arrangement, each of the tubes, 
such as tube 11, is formed with a reverse bend or crimp 17 in which, 
during operation, a bubble of gas 18 becomes firmly lodged. The gas bubble 
is derived from the cell operation and its function is to break or disrupt 
the discharge current path which may be flowing within tube 11. 
FIG. 3 illustrates a special arrangement in which a large number of 
batteries are needed to supply the power for a particular underwater 
operation. This or other comparable arrangements are used when the number 
of batteries is so large that it becomes impractical to provide a common 
reservoir for the entire number. Instead, the batteries are arranged in 
separate packs each having its own reservoir 21. More specifically, a 
plurality of battery packs 22 are disposed in a stacked arrangement and 
held in this arrangement by a casing 23. Instead of using a special 
casing, it will be appreciated that other arrangements are equally 
suitable. For example, each of the battery packs can be interconnected and 
then potted as a unit and, in this case, the packs themselves simply would 
be held together by several vertical rods. In a manner similar to that 
shown in FIG. 1, each of the reservoirs 21 is communicated with the cells 
by small tubes 23 that, again, are as small as and as long as possible to 
minimize discharge current. Further, each of the reservoirs is provided 
with a compliant diaphragm 24 similar in all respects to the diaphragm 
shown in FIG. 1. To expose the diaphragm to ambient pressures, casing 19 
is formed with openings 26 through which sea-water obviously can enter. 
Sea-water pressure compresses compliant diaphragm 24 to force an 
electrolyte 27 carried by the reservoir into the battery cells to equalize 
the ambient pressure. It should be noted at this point that the use of a 
compliant diaphragm also is a matter of choice. Other compliant 
arrangements which yield to ambient pressure can be used. For example, a 
plunger type mechanism can be substituted. The plunger would yield to 
pressure to compress the electrolyte in the reservoir. If desired, the 
reservoir can be formed of a completely compliant casing. In the 
particular implementation shown in FIG. 3, each of battery packs 22 
included twenty cells with six of these packs stacked to provide the 
desired battery power. 
The operation of the system should be quite apparent from the foregoing 
description. Its advantages include its relative simplicity and economy in 
that the battery cells used can be ordinary, commercially-available cells. 
These cells clearly are simpler and less expensive than the special 
pressure vessels or other specially-designed sea-water types of batteries. 
Commercial cells purchased on the open market require only very simple 
modification to adapt them for present use. Even so, a unit such as that 
shown in FIG. 3, has been found suitable for operation at pressures up to 
10,000 psi. 
Obviously many modifications and variations of the present invention are 
possible in the light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described.