CA2177618C

CA2177618C - Battery electrolyte circulation system

Info

Publication number: CA2177618C
Application number: CA002177618A
Authority: CA
Inventors: William B. Brecht
Original assignee: Trojan Battery Co LLC
Current assignee: Trojan Battery Co LLC
Priority date: 1993-12-01
Filing date: 1993-12-01
Publication date: 1999-07-06
Anticipated expiration: 2013-12-01
Also published as: AU6811894A; EP0737368A4; WO1995015586A1; JPH09505936A; AU675326B2; EP0737368A1; CA2177618A1

Abstract

A liquid electrolyte battery (10) comprises a number of electrolytic cells (12), an inlet port (22) extending into a first electrolytic cell (12-1), an electrolyte transport channel (30) residing within each electrolytic cell, a number of carry-over passages (40) hydraulically connecting adjacent electrolytic cells, an outlet port (50) extending from a last electrolytic cell (12-4), and a pump (58) for introducing an electrolyte solution or air into the electrolytic cells. The battery electrolyte is replenished by introducing an electrolyte solution (14) into the first electrolytic cell, causing the electrolyte level to rise and be hydraulically transported through the carry-over passages to fill each electrolytic cell. The electrolyte exiting the last electrolytic cell is collected and reintroduced back into the first electrolytic cell and circulated throughout the battery. The electrolyte exiting the battery may be collected in an electrolyte reservoir (72) and circulated through a temperature management device (78) to ensure a battery temperature within design parameters. The electrolyte level in each electrolytic cell is adjusted to a predetermined level by introducing air into the battery causing the hydraulic transport of an electrolyte volume residing above an inlet end (54) of the outlet port through the outlet port in the last electrolytic cell, and the electrolyte volume above an inlet end (42) of the carry-over passage through the carry-over passage in each other electrolytic cell. The air exiting the last electrolyte cell may be vented or treated for the removal of hazardous gases.

Description

Wo95/15586 2 1 776 1 8 PCT~593/11698 .

--I
BATTERY ELECTROLYTE CnRCULATION SYjTEM

r ~
This invention relates to the ~ of a flooded electrolyte storage battery that facilitatw the -ar~ ~ t, circulation, and '_ of the baKeq electrolyte amd also relatw to a procws for charging such baKeries.
r~ T
Although there has been '' '- effort spent ~ . wL~;4fl g alternative rl ~ I"J. a - ~1 systems, the flooded electrolyte lead-acid battery is still the baKery of choice for general purposw such as starting a vehicle, boat or airplane engine, emergency lighting, electric vehicle motive power, energy buffer storage for solar-electric energy, and field hardware, both industrial amd military.
These batteriw may be periodically charged from a generator or other source of suitable DC power.
Historically, the electric power for such applications has been provided by W..~w.iu..dl lead-acid baneries. The w.. ~ Iead-acid battery is a multi-cell structure, each cell generally comprising a set of vertical ~ li" ' monopolar positive and negative platw formed of lead or lead-alloy grids containing layers of el_,L-- ~ ~Iy active pastes or active materials. The paste on the positive electrode plate when charged comprisw lead dioxide (PbO~), which is the positive active material, and the negative plate contains a negative active material such as sponge lead. An acid electrolyte based on sulfuric acid is interposed between the positive amd negative plates. The acid electrolyte, in effect, is a third active material in each cell of a lead acid battery amd it, like the lead oxide anodic active material and the sponge lead cathodic active material, is reversibly changed during discharge of such a battery.
Bipolar batteriw have rec~w-tly gained attention and may serve to replace the use of the w ._.1~iU~lGi baKery in such applications due to their inherently decreased size and weight. Bipolar battery ( u -- ~ comprisw a seriew of electrode platw that each contain a negative active materlal on one side and a positive active material on the other side, hence the terms rbipolar" and ~biplate~ .
The biplates are serially arranged in such a fashion that the positive side of one plate ls dlrected toward the negative side of an adjacent plate. The bipolar baKery is made up of separate electrolytic cells that are defined by biplate surfacew of opposing polaritiw. The biplates must be impervious to electrolyte amd be electrically conductive to provide a serial electrical connection between cells.
Both ~ iul~al and bipolar lead acid baKeriw are ,~ ~ ;, .1 by a seriw of electrolytlc cells. During the charglng of these baKeries, as well as through normal discharge, the water component of the electrolyte contained in each electrolytic cell is converted by electrolysis to form ~ 35 hydrogen gas and oxygen. The ~ . l;- of some forms of these batteries permits the release of these gasw by venting them to the atmosphere. Other forms of thwe batteriw are vaive regulated and are constructed so as to facilitate both the ~ ~ ~ of the o~ygen gas and its ~ ~ into the electrolyte solution. The electrolysis of the electrolyte during the charging of a vented battery produce a loss in the water constituent of the acid electrolyte, thereby causing the of that acid and its specific gravity to increase and the liquid level to drop. Ideaiiy, the and specific gravity of a fully-charged flooded electrolyte lead-acid battery should be within a WO9S/15586 2 1 7 7 6 ~ 8 PCT/US93/11698 relatively narrow range of values for which the batteq has been designed. ~n acid electrolyte of too-low produces a decrease in battery p, r ~ while an acid electrolyte of too-high decreases the useful life of the battery and also reduces battery discharge p, Therefore, in batteries where water loss can occur, it is necessary to periodically add water to the electrolyte to replenish the volume of electrolyte in the battery and to bring the specific gravity of the electrolyte into the design range from a too-high value. In order to permit the volumetric ~' ' of the electrolyte, these batteries are typically constructed with a sealable opening at each cell which e~ctends to an outside top surface of the battery. Al ' _'y, the user can replenish the electrolyte volume in each cell by adding water tbrough each cell opening.
The technique of , ' ~ ' ~ a battery electrolyte by adding water to each individual cell can be a dangerous, messy, time consuming, and inaccurate operation. When the user removes the cap of each cell during the l~ . ' ' operation, the user is e cposed to both the battery electrolyte and the gases. The battery electrolyte is e~tremcly acidic, and may cause burns to slcin or permanent damage to clothmg and the like. Therefore, contact by the user is to be avoided. ,~ ' " "~" the gases produced during the chargmg or discharge of the battery is largely hydrogen which may be e~plosive under certain conditions.
During the ,' ' operation it is not uncommon for the water being used to fill the battery electrolytic cell, to spill onto the surface of the battery or onto the user. The dangers associated with coming into contact with acidtc battery electrolyte has already been described.
However, when water is used to replenish the electrolytic cell the spilled watcr will oftentimes combine with ' electrolyte on the surface to form an acidic solution. The clean up of this spilled water may place the user in contact with the acidic solution, posing a risk of injury to the wer.
Additionally, improper watering practices, such as adding water to the electrolytic cells in a discharged battery, may result in electrolyte ~flooding~, due to the imcrease in electrolyte volume associated with the charging of the battery, again posimg a risk to the user.
R ~ ' ' ,, each individual electrolytic cell with the proper amoumt of electrolyte is a matter of the user's judgement and requires that tbe user repeat the process of adding water and visually chec3~ing the level in each cell until the proper level is achieved. During the charging operation, the technique of visually checkmg the electrolyte level in each cell may pose a risk of electrolyte conUct to the user due to generation of effervescent electrolyte caused by the gassing or electrolysis reaction of the water component of the electrolyte.
The of ~ ._,.li~,~ and bipolar flooded electrolyte batteries also restricts the circulation and mi~cing of tbe banery electrolyte within each cell during the charging operation.
Mi~ing of the electrolyte is import;mt in order to ensure that each electrolytic cell comprises a 1~ volume of electrolyte having a uniform specific gravity. Specific gravity is a measure the ability of the desired electrolyte to participate in the il ' ' reaction. A~ , an electrolytic cell having a ~ O electrolyte of selected volume and specific gravity is desirable because it will necessarily render an optimal amount of electrical energy and power and assure long life.
In . ' and bipolar electrolyte batteries, the agiUtion and miking of electrolyte in each CA 02177618 lsss-03-ol wo 95/15586 PCTIUS93/l 1698 cell during the el~ g operation is accomplished by passing an amount of current usually measured as ampere-hours into the battery in e~ccess of that required to restore the voltage capacity of the particular battery. This u~hdion is referred to as ~overcharging~ the battery. During a normal charging opc~diùn, a current is passed into the battery for the purpose of ~ g the active m~Pri~lc within the battery. The applied current reverses the ele_hoc~ ;r~l reaction ,~onc~ e for the prod~lrtinn of electrihal energy during the pluc~ ;ug ~ ch~ge cycle, causing the ,~con~ n of the active .--~ c As the charging OpC,.diOII pluceeds, the active m -Priql will contimlP to be l~n~ d until the voltage and capaciq of the battery is fully re tored at which time the battery is said to be co~rletPIy charged.
The ~ l;l;on~l current passed into the battery after it has been fu11y charged and l~or~ n of the cell active materials (i.e., during the o.e.~ge operation) no longer causes the reversal of the de~ho~h~ reaction and rccQ~ ~ of the cell active In''-PriqlC~ but will instead cause the water cc.- ~~ 1 of the electrolyte to dectrolyze. The dc~,hul~ . of the de~hul~llte causes the gas plodu.
of that process ~dlog_~ and o~cygen) to migrate through the volume of electrolyte as free bubbles rising to the surface of each dectrolytic cdl. The l.. u.~e.~l of the ele. hul~i,is gas bubbles through the electrolyte volume serves to agitate and mLlc the cle~hul~le within each de.,l-ul~lic cell. As the u~ .L~,~, Opf ~ ;h-- a '-'1 ;~ C, the a6;~ of the cle~ llol~ s gas bubbles plU lu~.e~c a hu~-lGg~.~uS
volume of dectrolyte having a uniform specific gravity. An ele~ul~lè volume having a uniform specific gravity is ~ e because it serves to .---~ the de~l,;cal enerD storage pot~ l and life of each de~ul~Lic cdl. However, the operation of overcharging the battery in order to achieve a h~...og~ volume of de~,~ol~te generates heat and cûlluSiOn of the positive current c~llec~r which ~hol~ the life of the battery, i..~e&s~c the need for de~ulyte rep1~ -;Dl ---r ~1 h..~eases the time and e~e~ic-1 energy C4-- ~ in charging the battery, and is o;oAr~ 11y inPffirjPn-It is therefore seen that a need e~cists for a flooded ele~ te battery (~..~ , bipolar or otherwise) which is ~o~t~u~ to r ~~ the ~ ~r ~1 repl~ 1 of battery de~l~ul~le in a manner that is not d~g~u~, messy, or time consuming and perrnits the user to easily and ~
~len;~1 each ele~hul~c cell with the correct amount of de~llùl~le having the correct specific gravity.
A need e~ists for a flooded decl.ùl~t;c battery (conventional, bipolar or otherwise) which is co~LIu~.~d to f~~i1jt~-P the mi~ing and ~, ~geu~ ~;o ~ of the battery e~ ùl~te within each cell in a manner that avoids the need to u.~.ha~ge the battery, and thus e~ s the adverse affects ~ccoci~-ed with the u.~ h u6~ operation.

. .....

CA 02l776l8 l999-03-Ol Summary of the Invention According to the invention, there is provided a flooded electrolyte seco~Ary storage battery which comprises: a plurality of cells having coplanar tops and coplanar bottoms; an electrolyte transport rhAnnel ext~n~ing substantially vertically in each cell from an upper end proximate the cell top to a lower end proximate the cell bottom; a gas and liquid inlet port into a top portion of a first one of the cells for discharging liquid introduced thereinto to an upper end of the transport ~hAn~el in that cell; fluid carry-over passages connecting the first cell, a last one of the cells and all ~ -ining cells of the plurality, each carry-over passage having an inlet end at a selected level in the cell in which the inlet is located and an outlet end in a different cell at a location selected for discharging liquid flowing through the outlet end to the transport rhAnnel in that different cell, each carry-over passage being in~p~n~nt of each other one and r lnicating between only two cells; and a gas and liquid outlet port to the exterior of the battery from the top portion of the last cell, the outlet port having an entry opening at a selected level in the last cell, the selected level in each cell being at or below the upper end of the transport ~hAnnel for that cell.

According to a further aspect of the invention, there is provided a system for replenishing and circulating electrolyte in a liquid electrolyte secondary battery, the system comprising: an electrolyte transport rhAn~e1 ext n~ing vertically in each of a plurality of electrolytic cells from an inlet end near a top of the cell to an outlet end near a bottom of the cell, the tops and bottoms of all cells being coplanar with one another; an inlet port exten~ing from a position outside a battery to a position within a first one of the electrolytic cells; an outlet port ext~n~ing from a position within a last one of the electrolytic cells to a position outside the battery; a fluid carry-over passage ext~n~ing between and hydraulically connecting the upper ends of each adjacent set of cells and providing a portion of a serial fluid flow path from the first cell to the last cell via all other cells, each transport ~hAnnel receiving CA 02177618 1999-03-ol electrolyte intro~llceA to its cell via the respective one of the inlet port and the carry-over passages, each carry-over passage being in~p~n~nt of each other carry-over passage and c ln;cating between only two cells; and means for intro~1lcing an electrolyte solution into the inlet port.

According to a further aspect of the invention, there is provided an electrolyte replenishing and circulation system comprising; an inlet port comprising a passage ext~n~ing from a location outside an electrolyte battery, through an upper cell boundary, and into a first electrolytic cell; an outlet port comprising a passage ext~ing from a position within a last electrolytic cell through the upper cell boundary, to a position outside of the battery; a plurality of transport ~h~nn~ls, each transport ~h~nnel exten~ing vertically in each electrolytic cell, each transport ch~nnel comprising a flared portion at one end near the top of the cell and a ~h~n~el op~ning near a bottom of the cell;
a plurality of carry-over passages, each carry-over passage having an inlet end and an outlet end, the inlet end and outlet end of each carry-over passage ext~n~ing through the upper cell boundary and into adjacent electrolytic cells to hydraulically connect each cell, each transport ~h~nn~l receiving electrolyte introduced to its cell via the respective one of the inlet port and the carry-over passages, the position of the inlet end of the carry-over passage within each electrolytic cell defining a working electrolyte level in the cell; and means for intro~l~cing an electrolyte solution into the electrolyte battery.

According to still yet a further aspect of the invention, there is provided a method for establishing working levels of liquid electrolyte in each of the cells of a multi-cell liquid electrolyte storage battery, the method comprising the steps of: providing in each cell a fluid flow passage exten~ing from an upper end above a working cell electrolyte level to an open lower end proximate a bottom of the cell; providing fluid flow interconnections between all of the cells each of which interconnections has an inlet at the working level in one of two cells interconnected by it and an outlet associated with the upper end of the flow passage in the other cell interconnected by it, each cell being gas-tight except for the flow interconnection from it;

~ . . . ~ . . ..

CA 02l776l8 l999-03-Ol pumping electrolyte into a first one of the cells to the flow passage in the first cell and from the first cell to a last cell via the flow interconnections and from the last cell through an outlet having an entrance op~ning at the working level in the last cell to fill each cell with electrolyte at least to the working level in each cell; and pumping air into the inlet and through the several cells to the outlet to adjust the electrolyte level in each cell to the working level in each cell.
According to still yet a further aspect of the invention, there is provided a method for replenishing and circulating electrolyte through electrolytic cells of a liquid electrolyte sero~Ary battery, the method comprising the steps of: introAllcing an electrolyte solution into a first electrolytic cell of the battery; hydraulically transporting the electrolyte solution through the first electrolytic cell via intercell flow passages to a plurality of hydraulically serially connected electrolytic cells that are coplanar with one another until each cell is filled;
circulating the electrolyte through the plurality of electrolytic cells; and adjusting the level of electrolyte solution in each electrolytic cell to a working level by circulating air through each of the electrolytic cells via the intercell flow passages.

According to yet a further aspect of the invention, there is provided a flooded electrolyte secondary battery which includes a plurality of cells each having a top and a bottom, and a substantially planar cover closing the tops of the cells, the battery comprising: an electrolyte transport rhAnne1 ext~n~ing substantially vertically in each cell from an upper end proximate the cover to a lower end proximate the cell bottom; a gas and liquid inlet port ext~n~ing from outside of the battery through the cover into a top portion of a first one of the cells for discharging liquid introduced thereinto to an upper end of the transport in that cell; carry-over passages connecting the first cell, a last one of the cells and all ,~ -ining cells of the plurality in series liquid flow relation, each carry-over passage having an inlet end at a selected level in the cell in which the inlet is located and an outlet end in a different cell, wherein the inlet end for each carry-over passage is below its outlet end, and wherein . , .

the outlet end of each carry-over passage is at a location selected for discharging liquid flowing through the outlet end to the transport ch~nn~l in that different cell; and a gas and liquid outlet port ext~nrli ng from outside of the battery through the cover to the top portion of the last cell, the outlet port having an entry opening at a selected level in the last cell, the selected level in each cell being at or below the upper end of the transport ch~nnel for that cell.

According to a further aspect of the invention, there is provided a method for charging a liquid electrolyte secondary battery, the method comprising the steps of:
introducing an electrical current into the battery;
circulating the electrolyte serially through electrolytic cells of the battery during at ]east during a terminal portion of the charging process, and equalizing the level of electrolyte in each electrolytic cell by serial air movement through the cells.

Brief Description of the Drawinqs The above-mentioned and other features of this invention are set forth in the i.ollowing detailed description of the presently preferred and other embodiments of the invention, which description is presented with reference to the accompanying drawings wherein:

FIGS. 1,5,6 and 7 are cross-sectional elevation views of a preferred embodiment of a ~Elooded electrolyte battery, constructed to facilitate the replenishment and circulation oi battery electrolyte, at successive stages in practice oi the procedural aspects of this invention; more specifical]y, FIG. 1 illustrates commencement of an electrolyte replenishment operation;
FIG. 2 is a cross-section view taken along line 2-2 in FIG l;
FIG. 3 is a cross-section view taken along line 3-3 in FIG. l;
FIG. 4 is a fragmentary cross-sectional elevation view of an exemplary bipolar balttery according to the present invention;
FIG. 5 illustrates the states of the electrolytic cells at the end of the electro:Lyte pumping phase of the procedure;
FIG. 6 shows an initial stage of the cell levelling phase of the procedure;
FIG. 7 shows the battery a:Eter the electrolyte in each electrolytic cell has been levelled;
FIG. 8 is a schematic diag:ram of an embodiment of a electrolyte conditioning, replenishment and circulation system;
FIG. 9 is a graph that describes the electrolyte condition in a test battery at ,~ifferent times during a charging operation where the el,ectrolyte is circulated according to principles of this invention; and FIG. 10 iS a schematic diagram of a charging apparatus useful to implement the procedural aspects of this invention.

Detailed Description The need to conserve resources and reduce pollution directs attention to the electrolyte battery as a desirable alternative to internal combustion engines and power source for an automobile. However for the public to adopt battery powered vehicles their use and maintenance must be at least as convenient as the hydrocarbon powered vehicles that they are replacing. For example apart from reducing air pollution there is little incentive for an automobile owner to give up a gasoline fuelled automobile in i-avour of a battery powered automobile when the battery powered automobile is less convenient and more costly to maintain.

The principal costs associated with owning a battery powered automobile apart from lthe initial purchase cost is the cost of recharging serv:icing and eventually replacing the battery or batter:ies. Electrolyte batteries conventional or bipo:Lar lead-acid or other all have a limited life that is dependent on the materials used within the battery and upon their ability to participate in the electrochemical reactions that produce electricity. To m~Yimize the useful life of electrolyte batteries the user must at the very least recharge the battery and replenish the batte:ry electrolyte that has been lost during the electrochemical reactions which produce and release electrical energy. Since the cost to replace the battery or batteries used in an electric automobile may be substantial it is highly desirable that the useful life of the electrolyte battery be ~-Yimized through improved charging and electrolyte replenishment procedures that can be conveniently carried out by the user.

This invention relates to methods and equipment for maximizing the useful life of an electrolyte battery conventional or bipolar that may be used in applications such as the automobile. The inventive methods permit a CA 02l776l8 l999-04-06 user to maximize the useful life of an electrolyte battery in a manner that is convenient, cost effective, and will remove the dangers and risks associated with battery maintenance.

FIGS. 1-3 and 5-7 illustral:e, in simplified form, a flooded electrolyte battery constructed according to principles of this invention, and which, for purposes of illustration and clarity, compr:ises four electrolytic cells. It is, therefore, to be understood that the principles of this invention apply to an electrolyte battery comprising any plural number of electrolytic cells. For purposes of reference, the uppermost portion of the battery will hereafter be referred to as the top of the battery and the bottommost portion of the battery will hereafter be referred to as the bottom of the battery.
For purposes of definition, a f;looded battery as referred to comprises any type of electrolyte battery that can be characterized as having a plurality of electrodes immersed in an electrolyte solution.

FIG. 1 shows a preferred embodiment of a flooded electrolyte battery 10 according to principles of this invention. Battery 10 comprises a number of electrolytic cells 12 which each may comprise a number of electrically conductive electrodes (not shown) and electrically non conductive separators (not shown) immersed in an electrolyte solution 14. The electrolyte solution may include any type of liquid capable of participating substantially with active materials disposed on each electrode in an electrochemical reaction for producing electricity. In lead-acid electrolyte batteries an electrolyte comprising an aqueous sulphuric acid solution is preferred. It is to be understood that the electrolyte battery according to this invention may comprise a conventional flooded monopolar battery, a flooded bipolar battery (see FIG. 4), or any other type of flooded electrolyte battery.

The electrolytic cells 12 of the battery are physically separated from adjoining cells by cell partitions 16 which extend vert:ically from the top of the battery to the bottom of the battery. Each electrolytic cell is bound on its top by a b.~ttery cover 18 which may extend to cover and form a gas and electrolyte tight seal across all of the cells in the ]battery. Each cell is bounded on its bottom by a base 20 which may extend to cover and form a seal across all of the cells at the bottom of the battery. The cell partitions 16 are spaced apart at preferably equidistant positions from each other throughout the battery to form the series of preferably equal volume cells 12.

An inlet port 22 extends from outside of the battery 12 through an inlet hole 24 in the battery cover 18 and into a first cell 12-1. The inlet port may comprise an L-shaped tube positioned with its horizontal portion located outside of the battery and its vertical portion ext~n~i ng into the battery. The inlet port comprises an inlet end 26 at an end outside of the battery, and an outlet end 28 at an opposite end within the first electrolytic cell 12-1. The location of the inlet hole 24 preferably causes the inlet port 22 to enter the cell 12-1 at a position near a battery wall 32.
An electrolyte transport channel 30 extends vertically along the battery wall 32 in the first electrolyte cell 12-1, and other such chAnn~ls extend vertically along a cell partition 16 or other cell wall in each other cell 12. Each channel opens to its cell adjacent the bottom of the cell. As shown in FIGS. 1 and 2, the transport rh~nnels 30 can be formed by a space between a ~.h~nnel partition 34 and the battery wall 32, in the first cell, and by spaces between a ch~nn~l partition 34 and a cell partition or wall in each other cell. In a preferred embodiment, the channel partitions 34 can each comprise a rectangular sheet (not shown) having a horizontal dimension equal to the width of each electrolytic cell parallel to w;~ll 32 and a vertical dimension slightly shorter than the height of each cell.
The ~h~nn~l partitions may be m;~de from electrically nonconductive materials that are chemically resistant to the effect of the electrolyte and may include polymeric materials such as polypropylene and the like.

Each channel partition 34 preferably has a flared upper end 36 which is positioned near the battery top within each electrolytic cell. The flared end 36 forms a wide inlet mouth in the ~hAnn~l 30 for directing into the chAnn~l the liquid electrolyte ~which can be introduced into the cell, as through the inlet port 22 or through a carry-over passage 40. As shown in FIG. 3, each channel partition defines a ~hAnnel outlet opening 38 at its bottom end near the cell bottom. The channel outlet op-~ni ng 38 may be formed either by a single slot op~n; ng or by plural openings adjacent the cell bottom. ChAnn~
30 provides a passage for the flow of electrolyte introduced into the top of the cell to an entry into the cell adjacent the bottom of the cell through opening 38.

The position of each rhAnnel partition in preferably parallel relation to either the battery wall or a cell partition can be maintained by a number of vertical ribs 37 which can extend from the wall or partitions, as shown in FIG. 2, or from the ~hAnn~l partition itself. If present, the ribs subdivide the chAnnel into a plurality of vertical electrolyte flow passages to the bottom of each cell.

As shown in FIGS. 2 and 3, in a preferred embodiment, each battery side wall enclosing the electrolytic cells comprises at least one pair of ridges 39 per each cell.
The ridges are arranged to accommodate the thickness of the ~hAnnel partition. Each partition is placed into position within its cell to form the transport chAnn~l 30 by inserting the partition so that its vertical edges lie between the ridges at each battery wall. Once in place, the ridges restrict the movement: of the channel partition and maintain its spaced paralle]L relationship with the battery wall or cell partition.

The battery can be manufacl:ured by placing the ~hAnn~l partitions within each electrolytic cell before the battery electrode plates are introduced. In order to permit the passage of the batte:ey electrodes past the flared portion of the rh~nnel paLrtition, the rh~nnel partition may be constructed having a live hinge near the flared portion to allow the flared portion to be moved aside and out of the way to facilitate the electrode plate installation. The flared portion can be an integral member of the battery, molded into a permanent battery element.

It is to be understood that the transport rhAnnel 30 can have a configuration other than that specifically described and illustrated. For example, instead of being formed between the ~h~nn~l partition and the battery wall or cell partition, the transport ~h~nn~l may comprise a tube that extends vertically from the battery cover into the cell to an open lower end near the cell floor; see, for example, FIG. 4 which illustrates the practice of this invention in the context of a bipolar battery.

Each electrolytic cell 12 is hydraulically connected at its upper end to the upper e!nd of an adjacent cell by an electrolyte carry-over passage 40 or by an equivalent duct in or in association with the upper boundary of the electrolytic cell within the battery. Each carry-over passage may comprise an inverted U-shaped tube having substantially parallel legs, an inlet end 42 and an outlet end 44. Each carry-over passage can extend from one cell to an adjacent cell through a pair of carry-over passage holes 46 located in the battery cover 18 as shown in Fig.
1. Alternatively, each carry-over passage may extend from one cell to an adjacent cell through a carry-over passage hole located in an upper portion of the cell partition 16.
The carry-over passage holes are located so that the outlet end 44 of each carry-over passage is aligned with the upper end of a transport ch:~nnel 30. In FIG. 1, the carry-over passages 40 are shown having their inlet ends 42 at greater distances be:Low the top of the cells than their outlet ends 44. As discussed in detail below, the location of the inlet end 4:2 from the highest part of the carry-over passage is signi:Eicant because it defines the electrolyte level in each e.lectrolytic cell 12 during a levelling operation performed according to methods of this invention. Additionally, the length of the outlet end 44 of each carry-over passage is also significant because it is desired that an air gap or headspace 48 be maintained between the outlet end and the adjacent transport rhAnnel opening. This air gap is important because it facilitates low pressure replenishing and levelling of the electrolyte in each cell according to methods of this invention. The smaller the air gap, i.e., the smaller the air space in the electrolytic cell, the lower the pressure associated with electrolyte replenishing. The air gap 48 or opening in the liquid flow path is not required but is preferred to reduce liquid and air back pressure associated with the electrolyte replenishment operation. This reduced back pressure translates into reduce!d pump requirements and simpler and safer acid transport.

An outlet port 50 extends vertically from a last electrolytic cell 12-4, through an outlet hole 52 in the battery cover 18. The outlet port may comprise an L-shaped tube having an inlet encl 54 within the last cell and an outlet end 56 outside oi. the battery. Like the inlet end 42 of each carry-over passage 18, the length of the inlet end of the outlet port 50 is important because it defines the electrolyte level in the last electrolytic cell during a levelling operation according to methods of this invention.

CA 02l776l8 l999-04-06 The electrolytic cells in l_he flooded electrolyte battery are completely sealed from the atmosphere except for the existence of the inlet ~nd outlet ports. The electrolytic cells 12 are completely sealed from each other except for the cross-over passages 40 hydraulically connecting them.

Bipolar batteries can also be constructed according to practice of this invention. FIG. 4 shows a sectional view of a bipolar battery 11 comprising several electrolytic cells 12-1 through 12-N each defined by a pair of bipolar electrode plates 19 or biplates . The top portion of each of the cells making up the bipolar battery is sealed from the atmosphere by a battery cover 18. The cover comprises at least one inlet port 22 ext~n~;~g through the cover frcm outside the battery into a first cell 12-1. The inlet port 22 empties into an electrolyte transport passage 31 positioned along an adjacent electrode plate 19 ancl ext~n-l; ng downwardly into the first cell. The transport passage 31 may comprise a hollow tube or the like made from the same type of electrically nonconductive and chemically inert materials previously described for the tr.ansport channel partitions 34 in the embodiment illustrated in FIG. 1. The transport passage comprises an air hole "7 near the top portion of the cell that serves the same i-unction as the air gap 48 previously described in the e~odiment illustrated in FIG.
1. Alternatively the carry-over passages and transport passage described in FIG. 4 may also be used in conventional flooded electrolyte batteries such as that described in FIGS. 1 5 6 and 7.

The cover 18 also comprises a number of carry-over passages 40 which serves to hy~draulically interconnect adjacent bipolar cells. Each carry-over passage comprises an inlet end positioned near the top of each cell an outlet end which empties into a transport passage 31 in an adjacent cell, the outlet end having an air ho:Le 47 near the cover. The cover 18 also comprises at least one outlet port 50 extending from a position within a last cell 12-N, through the cover to a position outside the bipolar battery.

Like the embodiment described in FIG. 1, the inlet position for each carry-over passage 40 and the outlet port is important because it serves to define the electrolyte level in each electrolyte cell during a levelling operation according to methods of this invention. Additionally, the air hole 47 in each carry-over passage is important because it serves to permit the flow of air, during an air purge operation that will be described in detail below, to remove electrolyte from the carry-over passage. The remova.l of electrolyte from the carry-over passages is desirable because electrolyte rem~; n; ng inside the carry-over passages may cause the interconnecting electrolytic cells to electrically short circuit. Alternatively, instead of passing through the battery cover 18, the carry-over passages 40 may be configured to pass through a cell partition 16.

Although specifically described and illustrated in FIG. 4, it is to be understood that other bipolar battery configurations are within the ~;cope of this invention.
For example, the battery cover 18 may be configured so that the portion of the carry-over passage connecting its inlet end and outlet end compr:ises a ~h~nn~l along the top surface of the battery cover. In this embodiment, the carry-over passage may be formed by placing an appropriately sized and configured cover over the ch~nnel in the battery cover.

FIG. 1 shows a preferred embodiment of the electrolyte battery according to principles of this invention at a condition where the electrolyte level in each electrolytic cell is low and in need of replenishment, i.e., addition oE electrolyte to restore desired electrolyte levels in tlhe several cells. The electrolyte battery 10 constructed according to principles of this invention permits replenishment of the electrolyte in each of the cells to a predetermined or working level by methods according to this invention.

The electrolyte 14 can be replenished by introducing (as by use of pump 58 shown in FIG. 8) the desired electrolyte or water solution into the inlet end 26 of the inlet port 22, causing the electrolyte to flow through the inlet port and into the first e!lectrolytic cell 12-1 as shown in FIG. 1. The electroly~te exits the outlet end 28 of the inlet port 22 and empties into the electrolyte transport chAnnel 30. The elec:trolyte flows vertically down the depth of the transport: chAnn~l, out the chAn~el outlet opening 38 near the bot1:om portion of the cell and vertically upwards through the volume of the cell. The level in the Eirst electrolyte cell rises as the electrolyte is continuously introduced through the inlet port.

Referring now to FIG. 5, .~s the electrolyte continues to fill the first electrolytic cell 12-1, the electrolyte level will begin to approach the inlet end 42 of a first carry-over passage 40-1 which hydraulically connects the first cell with a second adjacent cell 12-2. When the electrolyte surface in cell 12-1 reaches the inlet end 42 of passage 40-1, the rising electrolyte surface begins to compress the gas in the gas-tight upper end of the cell.
However, the pressure in adjacent cell 12-2 remains substantially unchanged. The level of the electrolyte surface in the inlet leg of passage 40-1 becomes higher than the level of the electrolyte surface in cell 12-1 outside passage 40-1. As introduction of electrolyte into cell 12-1 continues, the liquid level in passage 40-1 becomes sufficiently high that .. , . , . ... ~

electrolyte begins to flow through passage 40-1 into cell 12-2. At that point, the level of electrolyte in cell 12-1 reaches a stable level between the upper end of transport channel 30 and the level of the lower end of the inlet leg of passage 40-1, and ~Eurther flow of electrolyte into the battery then causes the level of the electrolyte in cell 12-2 to rise. The process is repeated in sequence in each of cells 12-2, 12-3 and 12-4 to cause each of those cells to be filled to a s1able level in each cell at a point above the carry-over passage inlet or inlet opening to outlet port 50, as appropriate. Thereafter, continued introduction of electrolyte into the battery via inlet port 22 causes electrolyte to circulate through the battery and out of outlet port 50, as shown in FIG. 5.
The level of electrolyte in cell 12-1 r~-ins constant during filling of cell 12-2 until the level in cell 12-2 reaches the inlet end of carry-over passage 40-2. As the liquid level in cell 12-2 begins to rise to compress gas in the top of that cell, the liquid level in cell 12-1 also rises slightly. At the point where liquid flow through passage 40-2 begins into cell 12-3, the level in cell 12-2 will be at an elevation equal to the liquid level in cell 12-1 during initial filling of cell 12-2, and the level in cell 12-1 will be above that in cell 12-2; that is true if, as preferrecl, the inlet ends of tube 40 and of outlet port 50 are all at a common level in the battery. It will be seen, therefore, that upon filling of the battery to a point where electrolyte flows through outlet 50, the respective cell liquid levels in the several cells will be as shown i.n FIG. 5 where the levels are lower in the cells proceeding from first cell 12-1 to last cell 12-4. The difference in electrolyte ... .

- lOA -level for each cell is the inherent result of replenishing the battery electrolyte using hydraulic principles which depends upon a cumulative hydraulic pressure effect.

The pressure of electrolyte required at the inlet port to achieve filling of the several cells to the stable levels described above and shown in FIG. 5, is the sum of the effective electrolyte columns in the inlet legs of the several carry-over passages 40 and in the outlet port above the electrolyte levels in the cells from which they provide flow paths. That is a relatively low pressure which follows from the dimensions of the structures and arrangements present in the upper portions of the several cells.
The ability to transport the electrolyte between adjacent electrolytic cells by hydraulic principles through the carry-over passages avoids the need for using moving parts within each electrolytic cell, which effectively eliminates the potential for failure associated with such moving part:s.

The introduction of electrolyte into the first cell may be terminated once the elect:rolyte is observed to be exiting the battery through the outlet port 50 in the last cell 12-4. Alternatively, the electrolyte exiting the battery may be collected to permit its circulation and reintroduction back into the first electrolytic cell.

After the battery has been charged to a predetermined level and the electrolyte in the battery is completely homogeneous the electrolyte replenishment and circulation operation may be terminated. The electrolyte levels in the several cells can be equalized to a predeter~ined level by an air purge operation according to methods of this invention. As shown in FIG. 6 air at a suitable - lOB -pressure is introduced into port: 22 and into the first electrolytic cell 12-1. The air exits the outlet end 26 of the inlet port, and flows int:o the portion of cell 12-1 which is above the electrolyte surface in that cell. In such flow, the air enters the top of the cell via air gap 48 which exists between the outlet end of the inlet port and the top end of channel 30 in cell 12-1. The air does not flow down , . _ .

the rhAnnel and up through the electrolyte in the cell.
The air so introduced into cell 12-1 exerts pressure on the surface of the electrolyte. This air pressure causes the volume of electrolyte which lies above the inlet end 42 of carry-over passage 40-1 to be transported through the carry-over passage and into the second adjacent electrolytic cell 12-2. The electrolyte transport from the first to the second cell continues until the level of the electrolyte in the first cell drops to just below the inlet end 26 of the carry-over passage 40-1, at which time the air introduced into the first cell is transported through the carry-over passage and into the second cell 12-2.

The volume of electrolyte entering the second cell increases the head pressure of 1:he electrolyte in the second cell causing the transport of the electrolyte through the second carry-over passage 40-2 and into the third cell 12-3 according to the same principles previously described for the electrolyte replenishing operation. Once the electrolyte level in the first cell drops below the inlet end 26 of the carry-over passage 40-1 and air begins to enter the second cell, that air enters directly into the upper portion of the second cell and exerts its pressure onto the surface of the electrolyte in cell 12-2 causing the volume of electrolyte present above the inlet end 26 of the second carry-over passage 40-2 to continue to pass through the second carry-over passage and into the third electrolytic cel]L 12-3. As in the first cell, the electrolyte transport from the second to the third cell will continue until 1he level of the electrolyte in the second cell drops below the inlet end 26 of the second carry-over passage 40-2, at which time the air introduced into the first cell and communicated into the second cell is communicated through the second carry-over passage 40-2 and into the third cell 12-3.

- llA -The air pressure effects and events which occurred in the first and second cells are repeated in succession in third cell 12-3 and in last cel]. 12-4. Assuming, as is preferred, that the openings to the carry-over passages 40 and to the outlet port 50 are located at a common elevation in battery 10, the result of the air pumping process is the condition shown in FIG. 7 where the licIuid surfaces in the several cells are coplanar at that common elevation.
During this air pumping process the electrolyte moving through the several cells exits the battery through the outlet port 50 in the last c:ell. If desired this electrolyte can be collected ancl used for electrolyte replenishment according to this invention at a later date.

At the point where air is observed exiting the outlet port, the electrolyte in each electrolytic cell will have a level corresponding either to the location of the inlet end 42 of each carry-over passacle 40, or to the location of the inlet end 54 of the outlet port 50. Accordingly, the lengths of either the carry-over passage inlet ends or the outlet pipe inlet end may be varied according to the level of electrolyte desired in each cell. In a preferred embodiment, the length of the inlet end should yield an electrolyte level that results i.n the complete immersion of the electrodes within each cell in order to maximize each cell's production of electricity through its participation in the electrochemical reaction.

_ .

- llB -A consequence of the air-driven liquid level equalizing (or adjusting) process described above is that the head spaces in the upper encls of the cells are purged of undesired or hazardous gases.. Such gases can be vented to atmosphere or introduced to an air purification device such as a scrubber or the like clS they leave the battery.

Alternatively, the air purge operation according to methods of this invention may a]Lso be .

CA 02l776l8 l999-04-06 carried out by reversing the flow of the air purge operation as previously described and introducing air into the outlet end 56 of the outlet port 50 and into the last electrolytic cell 12-4. This can be achieved by selecting a reversible pump to recirculate the electrolyte and by reversing the direction of the pump so that air is drawn through the electrolytic cells i-rom the outlet port 50.
In order to accommodate electro]Lyte level equilibration using this reverse air purge operation the length of each carry-over passage inlet and oul:let end as well as the outlet port inlet end, shown in FIGS. 1, 5,6 and 7, would have to be adjusted to both facilitate the hydraulic transport of the electrolyte during the replenishment and recirculation operations to establish the desired or working electrolyte level in each cell during the air purging operation. For example, in order to maximize the electrolyte level in each of the electrolytic cells 12 illustrated in FIGS. 1, 5,6 and .7, it would be desirable to construct battery having an outlet end 28 of the inlet port 22, an inlet end 42 of each carry-over passage 40, an outlet end 44 of each carry-over passage and an inlet end 54 of the outlet port extending the same distance, preferably a short depth, into each electrolytic cell.
Configured in this manner, each electrolytic cell would be filled completely, i.e., the electrolyte level would be near the battery cover 18, during the electrolyte replenishment operation. Conduc:ting the reverse air purge operation in this embodiment would not result in a significant degree of levelling. Rather, the air purge operation would operate to clear. the electrolyte solution from each of the carry-over passages 40 to eliminate any short circuit between adjoining electrolytic cells.
Alternatively, the electrolyte ]evel could be established at less than at m~Y;mllm level by varying the distance that the outlet end 44 of each carry--over passage extends from .. . .. . .....

the battery cover 18 into each electrolytic cell.
Additionally, by using the reverse air purge operation one can obtain a different electrolyte level in the several cells than that obt~ine~ by using the st~n~rd air purge operation, for a set carry-over passage configuration.

The reverse air purge operation can also be carried out in a bipolar battery configured according to FIG. 4 without changing the battery configuration. The placement of the inlet end 42 of the carry-over passage 40, the inlet end 54 of the outlet port 50, and the air hole 47 permits the complete filling of each electrolyte cell, i.e., the electrolyte level wou]Ld be near the battery cover 18, during the electrolyte replenishment operation.
Conducting the reverse air purge operation in this embodiment, like the previously discussed embodiment, would serve to clear any residual electrolyte from each carry-over passage 40 to eliminate any short circuit between adjoining electrolytic cells. In either embodiment, the reverse air purc~e operation may be effected by using the same pumping means used for introducing electrolyte during l:he electrolyte circulation operation by simply reversing i1:s operation and, thus eliminating the need for valving in the plumbing of the circulation system.

Collecting the electrolyte and circulating it back through the cells of the battery in the m~nner previously described is highly desirable when the battery is being charged to restore capacity. During the charging operation, a voltage is applied to the battery to induce current flow in the battery in a direction opposite to the direction in which current flows during discharge of the battery. That reverse current i--low reverses the electricity-producing electrochemical reactions and restores the condition of active materials within the CA 02l776l8 l999-04-06 battery. At the point where the active materials within the battery are restored to a condition where their participation in the electrochemical reactions produces a desired discharge capacity of the battery, the battery is said to be at 100 percent charge. Ideally, the charging operation should terminate after achieving 100 percent charge. However, in order to maximize each cell's ability to participate in the electrochemical reactions and to store electricity, it is currently common practice to continue the charging operation by up to 30 percent beyond 100 percent charge. "Overcharging" the battery, as it is referred to in the trade, is an operation used to ensure the agitation and ~iYi ng of the electrolyte (i.e., to homogenize the electrolyte) within each electrolytic cell after 100 percent charge has been attained.

The homogenization of the electrolyte within each cell as a part of a charging operation is desirable because, as the battery is charged, the electrolyte within the cell is restored to a specii-ic gravity indicating its ability to participate as desired in the electrochemical reaction productive of useful electrical energy. During the charging operation, localized "bodies" of electrolyte having either high or low specii.ic gravities may develop within the electrolyte in each c:ell. Generally speaking, the specific gravity of the elec:trolyte corresponds to the state of charge of the electrol~rtic cell, e.g., an electrolytic cell comprising electrolyte having a specific gravity value of 1.3 exhibits a higher state of charge than an electrolytic cell compri.sing electrolyte having a specific gravity of 1Ø A batt:ery exhibits maximum voltage capacity when each elect:rolytic cell is filled with a volume of homogeneous electrolyte, i.e., an electrolyte volume having a uniiorm specific gravity.
Stratification of the electrolyt:e within each cell is not desired because it serves to recluce the voltage capacity of the battery. Therefore, in order to maximize the electricity producing potential of each cell, it is desired that each cell comprise an electrolyte volume having a uniform specific gravily. During the overcharge operation, the current entering the battery causes electrolysis of the water constituent of the acid electrolyte. (Electrolysis is 1_he dissociation of water molecules into hydrogen and oxygen gas.) Electrolysis is intentionally produced by overcharging so that the hydrogen and oxygen which is formed on the electrodes in each cell will bubble up through the electrolyte volume and cause stirring and mixing oi- the electrolyte so that it becomes uniform throughout the cell.

Overcharging a battery is wasteful of energy and harmful to the battery, but is c:urrently accepted as a necessary evil and tradeoff upon performance of the battery. Overcharging causes the battery to become hot;
if overcharge current levels are high hazardous boiling-over of the electrolyte can occ:ur.

Heating of battery components beyond their designed temperature parameters effectively shortens the life of the battery. Also, during the overcharge operation, the positive electrode in a cell unclergoes corrosion which effectively limits, in a progressive manner the extent to which the battery can participat:e in the electrochemical reaction, and thus store electri.city. It is estimated that the need to overcharge the battery to achieve electrolyte mixing may decrease battery life by up to fifty percent. The overcharging operation also results in gassing due to electrolysis. The electrolysis of the electrolyte not only produces potentially explosive gasses such as hydrogen but operates to decrease the electrolyte replenishment interval m~ki ng t:he need to replenish electrolyte more frecIuent. The practice of applying more energy to achieve overcharge ancl electrolyte m; Y; ng iS
both costly, in terms of the adcled cost associated with the electricity needed for overcharging, and time consuming, in terms of the extral time spent both during the overcharge operation and during electrolyte replenishing.

CA 02l776l8 l999-04-06 Accordingly the advantages associated with eliminating the need to overcharge the battery during the charging operation are numerous. The life of a battery can be extended by both reducing the severe temperatures that adversely affect the battery s active materials and by eliminating the electrode corrosion associated with overcharging. Eliminating eleclrode corrosion can result in a weight savings since the battery electrodes are largely made of lead and would no longer have to be sized to accommodate the progressive effects of overcharge corrosion. The generation of potentially explosive gasses can be eliminated or greatly rec~uced and the electrolyte replenishment interval can be extended. Additionally eliminating the need to overcharge will result in both a cost and a time savings associa1:ed with the overcharging operation itself.

Although overcharging the battery during the charging operation is not desirable charging the battery a small amount beyond lO0 percent charge is oftentimes necessary to overcome inefficiencies inherent in the charging operation such as gassing which may occur before achieving lO0 percent charge. Therefore in order to restore the full reserve voltage capacity of a particular battery it may be necessary to charge the battery in the range of from lO0 to llO percent;. A preferred amount of charging being in the range of 102 to 103 percent. This amount of charge is far short oi. the 30 percent over lO0 percent charge that is known to be used to effect electrolyte agitation and cause the above mentioned undesirable side effects.

Recirculating the electrolyte through a battery in the ~nn~r described above during the charging operation avoids the need to overcharge. As shown in FIG. 5 as the electrolyte is continuously introduced into the first electrolytic cell 12-1 transported through each adjacent cell transported out the outlelt port 50 and circulated back into the first cell it is being uniformly distributed within each cell and ultimately within the battery. This circulation operation effectively eliminates the need to overcharge because it results in each electrolytic cell having an electrolyte volume of uniform specific gravity and thus maximizes the electricity producing potential of each cell. By eliminating the need to overcha~.ge the battery the circulation operation according to methods of this invention makes possible all of the previously mentioned advantages. The electrolyte circulation process may also include routing the electrolyte from the battery through a heat exchanger radiator or the like for purposes of thermal management. During the charging operation the current entering the battery causes the battery to heat.
As discussed previously heating the battery adversely affects the active materials in the battery and thus shortens the life of the battery. Accordingly the ability to remove heat from the electrolyte by circulating it through a heat exchanger or t:he like serves to keep the battery s temperature within its design parameters during the charging operation and thus m-Yimize the useful life of the battery.

Additionally it is well known that the performance .
of a battery is strongly influenced by ambient temperatures. Therefore it can be desirable to circulate a battery s electrolyte through a heat exchanger or the like before its operation to ensure that the temperature of the battery is within design parameters. For example when the ambient temperature is cold and below a battery s design parameters, the electrol~yte can be circulated through a heat exchanger or the like to raise the temperature of the battery to design parameters.
Conversely, when the ambient temperatures are hot and above design parameters, the electrolyte can be circulated through a heat exchanger or the like to lower the temperature of the battery to design parameters.

The battery electrolyte exiting the battery may also be stored in a reservoir or the like. During the normal discharge and charge cycles of an electrolyte battery the battery active material flakes away from the surface of the electrode forming particula1e matter that settles and collects along the bottom of eac:h cell. Particulate matter that accumulates at the bottom of the electrolytic cells is referred to as sediment in the trade, while that which accumulates near the top of the cell is referred to as moss and that which accumulates about the sides of the cell is referred to as tree shorts . This particulate matter is electrically conductive and thus may accumulate to a degree within the cell to bridge electrodes of opposite polarity thus causing a short circuit and shorten;ng the useful life of the battery.
It is therefore, preferrecl that an electrolyte reservoir be configured to accon~modate the physical separation of solid particulate matter from the electrolyte as the electrolyte i.s introduced into the reservoir, as in the course of c:irculating electrolyte through the battery. In a preferred arrangement the reservoir can be a container configured in the shape of an hourglass. The constricted port:ion of the contA;ner should be of sufficient diameter to permit the passage of particulate matter. The inlet t:o the reservoir may be located above the constricted portion and the outlet from the reservoir can also be locate!d above the constricted portion to ensure that the particulate matter accumulating below the constricted portion is not picked up and circulated back through the batt:ery. Alternatively, the particulate matter contained in the circulating CA 02l776l8 l999-04-06 electrolyte may be removed outs:ide of the reservoir by passing the electrolyte through a filter or the like.

In addition, a reservoir m2~y serve as the single location for conveniently AC1~1; ng make up water to the existing electrolyte and may comprise an indicator such as a fill line or the like that a user may conveniently refer to for determin;ng whether such make up water should be added. The reservoir may be located to within the battery powered device or may be locate(~ within a structure where the battery powered device is slored. For example, the reservoir may reside within a battery powered car at a location that would facilitate easy access for purposes of A~; ng water, such as locations currently occupied by automobile w;n~ch;eld washer ancl radiator reservoirs.

The electrolyte may be introduced to the battery during the electrolyte replenishment and circulation procedure according to this invention by using a fluid transport device such as a pump The pump may be centrifugal, peristaltic or the like, and must be capable of facilitating the fluid transport of acidic electrolyte solutions such as sulphuric acicl. In addition, the pump must be capable of handling the displacement of air as well as fluid during the air-powered electrolyte levelling and air purge procedures. The pump may be powered from the battery itself, or from an external power supply such as a battery charger or stAn~Arcl household voltage. The pump should be of sufficient capacity to provide a desired flow rate of electrolyte through the battery at a suitable pressure. Additionally, in order to accommodate the electrolyte level equilibration according to the alternative reverse air purge operation, it may be desirable that the fluid transport device be capable of inducing a vacuum through the battery by reversing its direction. A preferred fluid transport device is a peristaltic pump.

During the normal battery c:harging operation, some of the current introduced into the battery CA 02l776l8 l999-04-06 to restore the battery's discha~ge capacity results in the electrolysis of the water component of the battery electrolyte. This electrolysis results in the production of small amounts of hydrogen gas which may be explosive under certain conditions. It is desirable to remove this hydrogen gas from the battery in order to eliminate the potential for an explosion. The hydrogen gas, or any other gases produced during the charging operation, are purged from the battery by the air purge procedure which comprises transporting air through each of the electrolyte cells of the battery as described above. By using the air purge procedure to sweep unwanted gasses out of the battery the unwanted gasses can be collected and disposed of by appropriate means. In the case of hydrogen gas, the air exiting the battery may sim~)ly be collected and vented to the atmosphere. However, in the case of other gases which may be hazardous or toxic, the air exiting the battery may be routed through an air purification device such as a filter, scrubber or the like to ~ e the hazardous or toxic gases, routecl through a catalytic convertor to form water, or sim~)ly routed away from the working area and vented to the atmosphere.

FIG. 8 shows an exemplary and preferred embodiment of an electrolyte circulation system 57 according to the present invention. The circulat:ion system includes the electrolyte battery, as previously concerning FIG. 1, configured to accommodate both electrolyte replenishment by hydraulic means and electrol~te level equilibration by hydraulic and pneumatic means. A pump 58 of the type previously described is positioned at a location in a circulation loop between the inlet port 22 and the outlet port 50 of the battery 10. The pump is powered by a pump CA 02l776l8 l999-04-06 motor 59. A pump outlet 60 iS c:onnected by tubing and the like to the inlet end of a heat exchanger 78 of the type previously described. An outlet; end 80 of the heat exchanger is attached by tubing and the like to the inlet end of the inlet port 22. A pump inlet 62 iS attached to an inlet manifold 64 comprising an air inlet valve 66 and an electrolyte inlet valve 68. Alternatively, a single valve may be used that is capable of switching between electrolyte and air connections.

An inlet end of the electrolyte inlet valve 68 iS
connected through tubing and the like to an outlet 70 of an electrolyte reservoir 72 of t:he type previously described. The reservoir outlet: 70 iS below a minimum reservoir electrolyte level and above the constricted portion of the reservoir. A reservoir inlet 74 iS
positioned near the top of the reservoir and is connected by tubing and the like to the outlet end of an electrolyte outlet valve 82. The electrolyt:e outlet valve is connected to an outlet manifold 84. An inlet end of the air outlet valve 86 iS also attached to the outlet manifold. An outlet end of the air outlet valve 86 can be attached by tubing and the like to an air purification device. If desired, however, the outlet end of the air inlet valve may simply be ventecl to the atmosphere.
The outlet manifold 84 iS attached by tubing and the like to the battery outlet port 50.

Preferably as shown in FIG. 8, there is associated with the electrolyte reservoir 72 a water reservoir 90 which discharges to the electrol.yte reservoir via a valve 91, the operation of which is controlled by the output of a level sensor 92. The level sensor is mounted to the electrolyte reservoir to cause water to be added to the electrolyte, and to restore the electrolyte volume in the system to a desired volume, when the amount of electrolyte in reservoir 72 becomes too sma:Ll to accommodate system electrolyte volume loses due to evaporation and electrolysis of the water in the electrolyte.

In a preferred embodiment, the electrolyte replenishment and circulation procedure according to this invention can be initiated by closing the air inlet valve 66 and opening the electrolyte inlet valve 68 to permit the passage of electrolyte from the electrolyte reservoir 72 to the inlet of the pump 58. The pump is turned on to cause the transport of electrolyte through the heat exchanger 78. The electrolyte enters the heat exchanger 78 and is either cooled or heated dep~n~; ng on whether the battery is being charged or whether the electrolyte temperature is being adjusted to ensure m~Y~mllm performance at the prevailing ambient temperature.
The electrolyte is circulated through the heat eYchAnger 78 and is routed through the ba1tery inlet port 22 and into the first electrolyte cell of the battery lO. The pump continues to introduce electrolyte into the first cell causing the hydraulic transport of the electrolyte through the battery, filling each cell in the manner previously described.
After the last electrolytic cell is filled, the electrolyte exits the battery through the battery outlet port 50 and enters the outlet manifold 84. In the electrolyte circulation procedure the air outlet valve 86 is closed and the electrolyte outlet valve 82 is open to facilitate the transfer of elect;rolyte to the electrolyte reservoir 72 where any particulate matter contained in the entering electrolyte is allowed to settle out and pass through the constricted portion of the reservoir to the bottom of the reservoir where it: can not again be picked up and circulated back through t:he battery.

The electrolyte circulation process may be conducted throughout battery charging proc:edures to ensure that each electrolytic cell has a homogeneous electrolyte volume of CA 02l776l8 l999-04-06 - 172~ -the desired temperature and uni:Eorm specific gravity throughout each cell. If desired, the electrolyte may be circulated for a time beyond the charging period to ensure that the temperature of the battery is within the predetermin~d design parameters, and to ensure the removal of particulate matter entrained in the electrolyte.

The air pumping procedure used to equilibrate the electrolyte levels in the sever~l battery cells according to the present invention may be initiated by closing the electrolyte inlet valve 68 and opening the air inlet valve 66, thus causing air to pass through the pump 58, through the heat exchanger 7 8 and into l_he battery via the inlet port 22. As the air is introduced into the battery the electrolyte in each electrolytic cell will be levelled according to previously described principles of this invention. The electrolyte outlet valve 82 is closed and the air outlet valve 86 is opened to permit the flow of electrolyte and air exiting the battery to enter a suitable liquid/gas separation clevice 88 where the air exiting the battery can be separated and either vented or collected and treated.

The air purging operation may be conducted after each replenishment/circulation operat:ion to equilibrate the electrolyte level in each electrolyte cell. The duration of the air purge operation may c:ontinue beyond the point where air is observed exiting the outlet port 50 of the battery in order to sweep any hazardous gases out of the battery where they can be properly treated.

The electrolyte circulation system described permits the "conditioning" of the electrolyte. Electrolyte conditioning refers to the process of ~;x; ng the electrolyte within the battery -e;o that the battery comprises a homogeneous electrolyte volume of uniform specific gravity. Electrolyte conditioning also refers to the process of adding make up w.~ter to the existing battery electrolyte to adjust t]he specific gravity value of the electrolyte to a predetermined range representing optimal participation in the electrochemical reaction producing electricity.

It is to be understood that the electrolyte circulation system described above and illustrated in CA 02l776l8 l999-04-06 FIG. 8 iS only preferred embodiment according to the methods and principles of this invention. Other types of circulation systems may be used to carry out the practice of this invention. The circulation system need not comprise all of the devices illustrated in FIG. 8, and it need not comprise the devices in the same m~nner or order as illustrated in FIG. 8. For ~example, a circulation system comprising a pump, reservoir, and heat exchanger may combine these devices in an order other than that illustrated in FIG. 8.

Additionally, the electrolyte circulation system may be accomplished according to principles of this invention by, instead of pumping electrol~yte under positive pressure, using a vacuum to dra~w the electrolyte solution through each of the electrolytic cells within the battery In such an embodiment, the pump 5 8 in FIG. 8 could be positioned with its inlet 62 attached to the outlet port 50 and its outlet 60 configured to discharge into the reservoir 72. The reservoir ou-tlet 70 could be connected to the inlet port 22. Operating the pump would cause the vacuum circulation of electrolyte in the reservoir throughout each electrolytic ce:Ll. This method of vacuum electrolyte circulation may present certain advantages over using a positive pressure electrolyte circulation system, due mainly to eliminating the hazards that may be associated with an acid leak in a positive pressure acid transport system.

Additionally, instead of using positive air pressure to equilibrate the electrolyte levels in the several battery cells, the levelling operation can be performed by using a vacuum according to an alternative reverse air purge operation. As shown in FIG. 8, the reverse air purge operation can be initiated by reversing the direction of the pump 58, closing the electrolyte inlet valve 68, closing the air inlet valve 66, op~n; ng an air outlet valve 102, closing the electrolyte outlet valve 82, and opening the air outlet valve 86. As the air is drawn through the battery outlet port 50 into the battery the electrolyte in each electrolyti,: cell will be levelled according to previously described principles of this invention. Additionally, each carry-over passage will be purged of electrolyte and filled with air, eliminating the possibility of electrical short circuits between adjacent cells. The air leaving the battery travels through the battery inlet port 22, the heat exchanger 78, through the pump 58, through the air outlet valve 102, and into a suitable liquid/gas separation device 104 where the air exiting the battery can be separated and either vented or collected and treated.

Additionally, the electrolyte circulation system of the present invention may be configured to circulate the electrolyte throughout the eleclrolytic cells in a battery in a parallel-series manner in order to accommodate a large pressure drop associated with a battery having a large number of electrolytic cells. For example, in a large application calling for a battery having 250 electrolytic cells, the battery may be configured having 10 parallel circulation systems for circulating electrolyte through 25 electrolytic cells in serial fashion. In such an embodiment, each parallel circulation system would have it:s own pump that would pick up electrolyte from a common reservoir. The electrolyte . , exiting the final electrolytic cell in each parallel circulation system would be col:lected in the common reservoir and, thus facilitate the homogenization of the electrolyte solution throughout each of the electrolytic cells in the battery.

The methods of replenishin/~, circulating and adjusting the level of the battery electrolyte according to methods of this invention ha.s been specifically described and illustrated in the context of a lead-acid electrolytic battery of conventional construction comprising four el~ectrolytic cells for purposes of illustration and cl~rity. It is, therefore, to be understood that the metho~s according to this invention apply to liquid electrolyte batteries using other electrochemical materials or comprising any number of electrolytic cells. Also, as shown below with reference to FIG. 4, the structural and procedural aspects of this invention can be practiced to advantage with liquid electrolyte bipolar batteries.

A test was conducted using a lead-acid battery comprising three electrolytic c-311s, constructed according to principles of this invention, to determine the effectiveness of the circulation system in distributing the electrolyte through the electrolyte battery during a charging operation.

The useable voltage capacilty of the three cell battery was completely discharged and the battery was connected to a constant current charger. A tube was inserted into beaker cont~i ni ng fresh electrolyte solution having a specific gravity of approximately 1.28. The other end of the tube was connected to the inlet of a peristaltic pump. The outlet oiE the pump was connected to an inlet end of an inlet port oiE the battery constructed consistently with the foregoing description of battery 10 shown in FIGS. 1-3. Prior to commencing the charging operation, specific gravity mea-;urements were taken in each electrolytic cell and were measured to be approximately 1.16. The charging and the electrolyte replenishment and circulation operations were commenced concurrently, and specific gravity measurements were taken in each electrolytic cell at one hour intervals.
Measurements of the specific gravity of the electrolyte in ., . . . _ ..

- l9A -the beaker (reservoir) were madle more frequently.

As shown in FIG. 9 the specific gravity in each electrolytic cell began to rise as the electrolyte in the beaker circulated through the t~est battery and the battery began to charge. After approximately two hours of charging, specific gravity measurements made in each cell and in the beaker showed that the electrolyte specific gravity had become uniform throughout the system. The specific gravity of the electrolyte in each electrolytic cell continued to rise uniformly as the charging and circulation operations proceeded. After ten and one half hours the voltage capacity of t:he battery was restored (103 percent charging) and the charging and circulation operation was completed. Restoration of full charge to the battery was signalled when the electrolyte's specific gravity ceased to increase and reached a predet~r~; neA
full charge specific gravity value. Also, the ampere-hours of battery discharge before commencement of the test was known, and full charge existed when discharge and charge ampere-hours became equal.

In FIG. 9, curve 93 descri]bes the specific gravity of electrolyte in the beaker, the ,-urves grouped at 94 describe the specific gravity in the several battery cells, and curve 95 describes t]he charging energy (in ampere-hours) applied to the battery. Line 96 denotes the point at which the battery was restored to a condition of full charge.

The measurement of uniform specific gravity values in each electrolytic cell during t]he charging and circulation operation evidenced the effectiveness of the electrolyte circulation operation in distributing the electrolyte throughout the battery, thus el.iminating the need to . ~ _ , .. . .. . ..

- l9B -overcharge the battery to achieve electrolyte mi Yi ng and homogeneity.

In order to ensure charger cut off after the battery has achieved full charge, i.e., 103 percent charge, and prevent or guard against undesi:rable overcharge, i.e., greater than 110 percent charge, .. . .

CA 02l776l8 l999-04-06 - 20 ~
a control device can be incorporated into the charging system. FIG. 10 shows a schematic of such a charging system comprising a battery 10, a battery charger 98, and a charger controller 100 capable of shutting off the charger after full charge is detected. The controller may be of the type that measures the change in voltage as a function of time or measures the total amount of ampere hours charged.

A controller that measures the total ampere-hours discharged and charged can be programmed to shut off the charger after the charger puts into the battery the same amount of ampere-hours removed from the battery during discharge plus some small predet~rmined overcharge to compensate for any losses or inefficiencies, thus effectively protecting against overcharge.

A controller that measures the change of voltage as a function of time can be programmed to shut off the charger when it no longer senses a change in voltage as a function of time. At the point of 103 p,ercent charge, the voltage applied to the battery will no longer result in increasing the batteries discharge potential and the battery voltage will remain constant. Therefore, a controller programmed to sense a lack of voltage change with time and to shut off the charger will effectively prevent overcharge.

Alternatively, as shown in FIG.s 8 and 10, the charger controller 100 can be configured to deactivate the battery charger 98 dep~n~1;ng on the specific gravity value of the electrolyte in the reser~oir 72. A specific gravity sensor 106 can be posit:ioned within the reservoir and electrically connected to relay specific gravity information to the controller v.ia a lead 107. As shown in .. _ _. . , . , . . . _ .

CA 02l776l8 l999-04-06 - 20~ -FIG. 9, as the charging energy of the battery increases, so does the specific gravity of the battery electrolyte.
When the battery is restored to full charge 96 the change in specific gravity as a function of time is essentially zero. Accordingly, the controller can be designed to deactivate the charger a predetermined amount of time after the specific gravity of the battery electrolyte no longer increases as a function of time to ensure that the battery has achieved full charge, i.e., 103 percent charge, and prevent or guard against undesirable overcharge, i.e., greater than 110 percent charge. The controller 100 may also be configured to deactivate the pump motor 59 during the electrolyte charging and circulation operation when it senses that the specific gravity of the battery electrolyte no longer increases as a function of time.

The method of circulating the electrolyte according to principles of this invention has been specifically described as occurring concurrently with the charging operation. However, it is to be understood that the electrolyte circulation may be conducted at different times during the charging operation, or may be conducted independent from the charging operation, i.e., after the charging operation has concluded. Tests were conducted to determine whether the circulation operation could be conducted at a time after the commencement of the charging operation in order to minimize both the pump requirements and the energy consumed by circulating the electrolyte during the entire charging operation.

In one such test, it was discovered that initiating the circulation operation 1/4 of the way into the charging operation produced a homogeneous electrolyte volume throughout the battery having a specific gravity at the completion of the charging operation equal to that .... . . . . _ - 20E~ -realized when the circulation operation proceeded concurrently with the charging operation. In another such test, the electrolyte CA 02l776l8 l999-04-06 circulation was initiated 3/4 of the way into the charging operation. Like the previous test, it was discovered that initiating the electrolyte circulation 3/4 of the way into the charging operation produced a homogeneous electrolyte volume throughout the battery having a specific gravity equal to that realized when the circulation operation proceeded concurrently with the charging operation.
Theses test results provide evidence that the circulation operation of this invention need not be conducted during the entire charging operation in order to provide electrolyte homogenization; therefore, allowing a user to ~i n; m; ze the pump requirements and the energy consumed during the circulation operation.

The construction and procedural aspects of the battery and related electrolyte replenishing/conditioning system according to principles of this invention have numerous advantages which would help overcome any perceived inconveniences or financial encumbrances associated with replacing traditional hydrocarbon power sources with environmentally desirable battery powered sources in such applications as the automobile. Practice of this invention can: (1) permit the replenishment of the battery electrolyte to a desired electrolyte level in each cell without the use of moving parts within the battery and from a single convenient location; (2) increase the electrolyte replenishment frequ~ency due to the ability to circulate the electrolyte, eliminating the need to overcharge the battery, and thus reducing the amount of electrolyte lost due to water hydrolysis; (3) permit the removal of particulate active m,aterial from the electrolyte, eliminating the potential for electrical short circuit within the battery; (4) increase the life of the battery by circulating the ]battery electrolyte through a temperature management device to maintain internal battery temperatures within design temperature parameters CA 02l776l8 l999-04-06 - 21~- -both during the charging and prior to discharge of the battery; (5) increase the life of the battery by circulating the electrolyte during charging, eliminating the need to overcharge the battery, and thus eliminating corrosion which occurs at the positive electrode plate;
(6) save energy by eliminating the need to apply a voltage to the battery in excess of that needed to achieve 100 percent charge; (7) save time by eliminating the need to charge the battery beyond the time associated with achieving 100 percent charge; and (8) promote safety by, (a) permitting a user to replenish the battery electrolyte in a m~nner that would avoiding placing the user in contact with the acidic solution, (b) reducing the amount of potentially explosive gaseous hydrolysis products created during the charging process by replacing the need to overcharge with electrolyte circulation, and (c) removing potentially explosive gases from the battery by air purging during the charging operation.

The foregoing description of presently preferred and other aspects of this invention has been presented by way of illustration and example. It does not present, nor is it intended to present, an exhaustive catalog of all structural and procedural forms by which the invention can be embodied. Variations upon and alterations of the described structures and procedures can be pursued without departing from the fair substance and scope of the invention consistent with the foregoing descriptions, and the following claims which are to be read and interpreted liberally in the context of the state of the art from which this invention has advanced.

.

Claims

WHAT IS CLAIMED IS:

1. A flooded electrolyte secondary storage battery which comprises:

a plurality of cells having coplanar tops and coplanar bottoms;

an electrolyte transport channel extending substantially vertically in each cell from an upper end proximate the cell top to a lower end proximate the cell bottom;

a gas and liquid inlet port into a top portion of a first one of the cells for discharging liquid introduced thereinto to an upper end of the transport channel in that cell;

fluid carry-over passages connecting the first cell, a last one of the cells and all remaining cells of the plurality, each carry-over passage having an inlet end at a selected level in the cell in which the inlet is located and an outlet end in a different cell at a location selected for discharging liquid flowing through the outlet end to the transport channel in that different cell, each carry-over passage being independent of each other one and communicating between only two cells; and a gas and liquid outlet port to the exterior of the battery from the top portion of the last cell, the outlet port having an entry opening at a selected level in the last cell, the selected level in each cell being at or below the upper end of the transport channel for that cell.

2. A flooded electrolyte storage battery as recited in claim 1 wherein the transport channels, inlet port, carry-over passages, and outlet port comprises no moving parts.

3. A system for replenishing and circulating electrolyte in a liquid electrolyte secondary battery, the system comprising:

an electrolyte transport channel extending vertically in each of a plurality of electrolytic cells from an inlet end near a top of the cell to an outlet end near a bottom of the cell, the tops and bottoms of all cells being coplanar with one another;

an inlet port extending from a position outside a battery to a position within a first one of the electrolytic cells;

an outlet port extending from a position within a last one of the electrolytic cells, to a position outside the battery;

a fluid carry-over passage extending between and hydraulically connecting the upper ends of each adjacent set of cells and providing a portion of a serial fluid flow path from the first cell to the last cell via all other cells, each transport channel receiving electrolyte introduced to its cell via the respective one of the inlet port and the carry-over passages, each carry-over passage being independent of each other carry-over passage and communicating between only two cells; and means for introducing an electrolyte solution into the inlet port.

4. An electrolyte replenishing and circulation system as recited in claim 3 wherein the inlet port comprises a passage extending through an upper cell boundary to a passage outlet end over the opening to the transport channel residing in the first electrolytic cell.

5. An electrolyte replenishing and circulation system as recited in claim 3 wherein each carry-over passage has an inlet end and an outlet end and extends through an upper cell boundary, the inlet end of each carry-over passage extending into a cell to a location corresponding to a working level of electrolyte in the cell.

6. An electrolyte replenishing and circulation system as recited in claim 3 wherein the means for introducing the electrolyte solution comprises a pump having an inlet and an outlet, the pump inlet being connected to the outlet port and the pump outlet end being connected to the inlet port.

7. An electrolyte replenishing and circulation system as recited in claim 6 wherein a heat management device is connected in series with the pump.

8. An electrolyte replenishing and circulating system as recited in claim 7 wherein the heat management device is connected between the outlet port and an electrolyte reservoir located upstream of the pump.

9. An electrolyte replenishing and circulation system comprising:

an inlet port comprising a passage extending from a location outside an electrolyte battery, through an upper cell boundary, and into a first electrolytic cell;

an outlet port comprising a passage extending from a position within a last electrolytic cell, through the upper cell boundary, to a position outside of the battery;

a plurality of transport channels, each transport channel extending vertically in each electrolytic cell, each transport channel comprising a flared portion at one end near the top of the cell and a channel opening near a bottom of the cell;

a plurality of carry-over passages each carry-over passage having an inlet end and an outlet end, the inlet end and outlet end of each carry-over passage extending through the upper cell boundary and into adjacent electrolytic cells to hydraulically connect each cell, each transport channel receiving electrolyte introduced to its cell via the respective one of the inlet port and the carry-over passages, the position of the inlet end of the carry-over passage within each electrolytic cell defining a working electrolyte level in the cell; and means for introducing an electrolyte solution into the electrolyte battery.

10. An electrolyte replenishing and circulation system as recited in claim 9 wherein an outlet end of the inlet port and the outlet end of each carry-over passage is positioned adjacent to the electrolyte transport channel within each electrolytic cell such that an air gap is formed between the two.

11. An electrolyte replenishing and circulation system as recited in claim 10 wherein the position of an inlet end of the outlet port defines the electrolyte level in the last electrolytic cell.

12. An electrolyte replenishing and circulation system as recited in claim 9 comprising means for cooling the electrolyte introduced into the electrolyte battery.

13. A method for establishing working levels of liquid electrolyte in each of the cells of a multi-cell liquid electrolyte storage battery, the method comprising the steps of:

providing in each cell a fluid flow passage extending from a upper end above a working cell electrolyte level to an open lower end proximate a bottom of the cell;

providing fluid flow interconnections between all of the cells each of which interconnections has an inlet at the working level in one of two cells interconnected by it and an outlet associated with the upper end of the flow passage in the other cell interconnected by it, each cell being gas-tight except for the flow interconnection from it;

pumping electrolyte into a first one of the cells to the flow passage in the first cell and from the first cell to a last cell via the flow interconnections and from the last cell through an outlet having an entrance opening at the working level in the last cell to fill each cell with electrolyte at least to the working level in each cell;
and pumping air into the inlet and through the several cells to the outlet to adjust the electrolyte level in each cell to the working level in each cell.

14. The method according to claim 13 including the further steps of charging the battery and of pumping electrolyte through the battery during performance of the charging step.

15. The method according to claim 13 including the further steps of charging the battery and commencing performance of the step of pumping electrolyte during a terminal portion of the battery charging operation and continuing the pumping of electrolyte at least until the end of the charging operation, and performing the step of pumping air after completion of the charging operation.

16. The method according to claim 13 including performing the steps of pumping electrolyte and of pumping air substantially upon completion of a further step of charging the battery.

17. The method according to claim 14 including the further step of terminating performance of the charging step substantially upon the battery attaining a state of full charge.

18. The method according to claim 17 including the step of terminating performance of the electrolyte pumping step substantially concurrently with terminating performance of the charging step.

19. A method for replenishing and circulating electrolyte through electrolytic cells of a liquid electrolyte secondary battery, the method comprising the steps of:

introducing an electrolyte solution into a first electrolytic cell of the battery;

hydraulically transporting the electrolyte solution through the first electrolytic cell via intercell flow passages to a plurality of hydraulically serially connected electrolytic cells that are coplanar with one another until each cell is filled:

circulating the electrolyte through the plurality of electrolytic cells; and adjusting the level of electrolyte solution in each electrolytic cell to a working level by circulating air through each of the electrolytic cells via the intercell flow passages.

20. The method as recited in claim 19 comprising the further step of charging the battery during the step of transporting the electrolyte through the plurality of cells.

21. The method as recited in claim 20 comprising the further step of thermally conditioning the circulated electrolyte.

22. The method as recited in claim 19 comprising the further steps of collecting the circulated electrolyte in a reservoir and removing particulate matter from the electrolyte.

23. The method as recited in claim 19 comprising circulating air through the path used for introducing electrolyte into each cell, the air being circulated through the battery in a direction which is the reverse of the electrolyte introduction into the first cell and of transport of the electrolyte between cells.

24. The method as recited in claim 23 comprising providing a pump for circulating electrolyte and circulating air through the battery, and operating the pump in one direction to pump electrolyte and in an opposite direction to pump air.

25. A flooded electrolyte secondary battery which includes a plurality of cells each having a top and a bottom, and a substantially planar cover closing the tops of the cells, the battery comprising:

an electrolytic transport channel extending substantially vertically in each cell from an upper end proximate the cover to a lower end proximate the cell bottom;

a gas and liquid inlet port extending from outside of the battery through the cover into a top portion of a first one of the cells for discharging liquid introduced thereinto to an upper end of the transport channel in that cell;

carry-over passages connecting the first cell, a last one of the cells and all remaining cells of the plurality in series liquid flow relation, each carry-over passage having an inlet end at a selected level in the cell in which the inlet is located and an outlet end in a different cell, wherein the inlet end for each carry-over passage is below its outlet end, and wherein the outlet end of each carry-over passage is at a location selected for discharging liquid flowing through the outlet end to the transport channel in that different cell; and a gas and liquid outlet port extending from outside of the battery through the cover to the top portion of the last cell, the outlet port having an entry opening at a selected level in the last cell, the selected level in each cell being at or below the upper end of the transport channel for that cell.

26. A flooded electrolyte secondary battery as recited in claim 25 wherein the carry-over passages extend above the cell tops between adjacent cells.

27. A flooded electrolyte secondary battery as recited in claim 25 wherein the inlet end of each carry-over passage and an inlet end of the liquid outlet port each extend into respective cells at equal levels to effect electrolyte levelling by the serial movement of air through the plurality of cells via those passages.

28. A method for charging a liquid electrolyte secondary battery, the method comprising the steps of:

introducing an electrical current into the battery;
circulating the electrolyte serially through electrolytic cells of the battery during at least during a terminal portion of the charging process; and equalizing the level of electrolyte in each electrolytic cell by serial air movement through the cells.

29. A method as recited in claim 28 wherein, during the step of circulating the electrolyte, the electrolyte is circulated in a manner which causes mixing of electrolyte to substantial homogeneity in each cell.

30. A method as recited in claim 28 further comprising the step of adjusting the temperature of the battery during the charging process.

31. A method as recited in claim 28 further comprising the step of purifying the electrolyte during the step of circulating the electrolyte.