Linden D., Reddy T.B. (eds.) Handbook of batteries

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23.26 CHAPTER TWENTY-THREE

The third major grid production method is circumferential continuous casting onto a mold

cut into the surface of a drum. Successful high-speed production of up to 150 grids per

minute has been reported. Continuous-cast grids are not symmetrical about a central planar

axis and need to be overpasted to hold the active material in place.

A fourth major grid production method, expansion from wrought or cast lead alloy strip,

is rapidly supplanting book-mold casting as the preferred method for the manufacture of SLI

battery grids. The advantages of this method are lower grid weight per unit of battery elec-

trical performance, the capability to manufacture a wide variety of sizes with a minimum

investment in tooling, a very high-rate production capability (up to 600 plates per minute),

and very uniform grid and plate sizes. Most development and commercialization have been

done on nonantimonial lead-calcium tin alloys (Fig. 23.14). Strip is produced from cast slabs

by a variety of proprietary metal-working processes, and the thin strip is slit to the width

speciﬁed by the battery manufacturer. The worked metal increases in strength as it decreases

in thickness during this processing.

FIGURE 23.14 Expanded wrought grid

for lead-acid batteries.

Machinery to produce grids from wrought strip has been developed and put into produc-

tion by several manufacturers. Four types of machinery are involved: progressive die expan-

sion, precision expansion, rotary expansion, and diagonal slit expansion. Progressive die

expansion has been the most extensively utilized of the four methods, but rotary expansion

is of increasing importance. Continuous drum casting of automotive grids is also challenging

the expansion processes as the dominant manufacturing method for calcium alloy grids used

in negative plates in automotive batteries. Positive-plate grids are most often produced of

low-antimony lead cast in book molds.

Whatever grid production method is used, there is often the need for small cast parts for

plate and cell interconnections and connection to external equipment. These parts have tra-

ditionally been cast in ﬁxed molds, sometimes with mold inserts to allow a variety of similar

parts to be made in each mold. Newer battery production methods often produce these

various interconnections automatically in the course of battery assembly.

LEAD-ACID BATTERIES 23.27

23.3.3 Lead Oxide Production

Lead is used to make the active materials as well as the grids. The lead must be highly

reﬁned (usually virgin or primary lead) to preclude contamination of the battery. It is de-

scribed as corroding-grade lead in ASTM speciﬁcation B29.

Lead is oxidized by either of

two processes—the Barton pot or the ball mill.

In the Barton pot process, a ﬁne stream of

molten lead is swept around inside a heated pot-shaped vessel, and oxygen from the air

reacts with ﬁne droplets or particles to produce an oxide coating around each droplet. Typical

Barton pot oxides contain 15 to 30% free lead, which usually exists as the core of each ﬁne

leady oxide spherically shaped particle. Barton pots are available in a variety of sizes up to

1000 kg /h output.

Ball milling describes a larger variety of processes. Lead pieces are put into a rotary

mechanical mill, and the attrition of the pieces causes ﬁne metallic ﬂakes to form. These are

oxidized by an airﬂow, and the airﬂow also serves to remove the leady oxide particles to

collection in a baghouse. The feedstock for ball mills can range from small cast slugs weigh-

ing less than 30 g to full pigs of lead weighing approximately 30 kg. Typical ball mill oxides

also contain 15 to 30% free lead in the shape of a ﬂattened platelet core surrounded by an

oxide coating.

Some battery positive plates use an additive of red lead (Pb

), which is more conductive

than PbO, to facilitate the electrochemical formation of PbO

, Red lead is produced from

leady oxide by roasting this material in an airﬂow until the desired conversion is complete.

Such processing reduces the free lead content and generally increases the oxide particle size.

A variety of other oxides and lead-containing materials have been used to produce battery

plates but are of only historical interest.

Positive plates for the Lucent Technologies bat-

teries (formerly Bell Laboratories) were initially made with tetrabasic lead sulfate

(4PbO

PbSO

), which is a precursor for

␣

-PbO

. These plates now contain up to 25% red

lead (Pb

) in order to facilitate the electrochemical formation process.

23.3.4 Paste Production

Lead oxide is converted to a plastic doughlike material so that it can be afﬁxed to the grids.

Leady oxide is mixed with water and sulfuric acid in a mechanical mixer. Three types of

mixers are commonly used—the change can or pony mixer, the muller, and a vertical muller.

The pony mixer is the traditional unit. A preweighed amount of leady oxide is placed

into the mixing tub, and this is wetted ﬁrst with water and then with sulfuric acid solution.

Dry paste additives, if any, are premixed into the leady oxide before water addition. These

additives can be plastic ﬁbers to enhance the mechanical strength of the dried paste, ex-

panders to maintain negative-plate porosity in operation, and various other proprietary ad-

ditives which ease processing or are believed to improve battery performance. Muller mixers

are usually ﬁlled ﬁrst with the water component, then the oxide, then the acid.

As mixing proceeds, the paste viscosity increases, then decreases, as measured by the

amount of power consumed by the mixer motor. The paste becomes hot from the mechanical

mixing and from the reaction of H

with the leady oxide. Paste temperature is controlled

by cooling jackets on the mixer or by evaporation of water from the paste. The amounts of

water and acid for a given amount of oxide will be different for the two mixer types and

will also depend on the intended use of the plates: SLI plates are generally made at a low

PbO:H

ratio and deep-cycling plates at a high PbO:H

ratio. Sulfuric acid acts as a

bulking agent—the more acid used, the lower the plate density will be. The total amount of

liquids and the type of mixer used will affect ﬁnal paste consistency (viscosity). Paste mixing

is controlled by the measurement of paste density using a cup with a hemispherical cavity

and by the measurement of paste consistency with a penetrometer.

23.28 CHAPTER TWENTY-THREE

23.3.5 Pasting

Pasting is the process by which the paste is actually integrated with the grid to produce a

battery plate. This process is a form of extrusion, and the paste is pressed by hand trowel

or by machine into the grid interstices. Two types of pasting machines are used: a ﬁxed-

oriﬁce paster that pushes paste into both sides of the plate simultaneously and a belt paster

in which paste is pressed into the open side of a grid that is being conveyed past a paste

hopper on a porous belt. The amount of paste applied to a plate by a belt paster is regulated

by the spacing of the hopper above the grid on the belt and the type of troweling (roller or

rubber squeegee) used at the hopper exit. Using identical paste and grids, a trowel roller

machine packs the paste both thicker and more densely than a rubber squeegee machine. As

plates are pasted on either belt pasting machine, water is forced out of the paste, into the

belt, and ultimately to a sump on or near the machine. The sump material can be used in

place of some of the liquids for subsequent batches of negative paste.

Grids are automatically or manually placed onto the belt before being moved under the

paste hopper. Most smaller-sized plates are made as ‘‘doubles’’ joined at the feet (cast) or

at the tab edge (wrought expanded), or as panels of varying number of plates. Typically the

belt is 35 to 50 cm wide and can handle such doubles. Industrial stationary or traction plates

(being larger) are pasted by lengthwise feed into the machine or are hand-pasted.

After pasting, plates are racked or stacked for curing. Stacked plates contain enough

moisture to stick together, and so before stacking, the plate surfaces are dried somewhat by

a rapid passage through a high-temperature drier or over heated platens. Some carbon dioxide

from the combustion process might be absorbed on the surface such that the surface is made

‘‘harder.’’ The ﬂash drying process may also help start the curing reactions. Thicker plates

are usually placed the long edge upward in racks rather than being stacked horizontally on

pallets after ﬂash drying.

Wrought expanded plates and some cast plates are cut into discrete plate portions by a

slitter machine in the pasting line. Some manufacturers also have the plate lugs brushed

clean of paste and surface oxidation on the same machinery.

In Europe, and less commonly in the United States, many of the heavy-duty battery

positive plates are made in porous tubular sheaths. The grid is cast or injection-molded of

lead, with long-ﬁnned spines attached to a header bar and a connection lug. Individual woven

ﬁberglass plastic sheaths or a multitube gauntlet are placed on the spines. These plates are

ﬁlled with powder or with a slurried paste until the tubes are full. A plastic cap plugs the

open sheath ends and becomes the bottom of the plate (Fig. 23.15).

LEAD-ACID BATTERIES 23.29

FIGURE 23.15 Tubular and gauntlet plates. (a) Tubular. (b) Gauntlet.

23.30 CHAPTER TWENTY-THREE

23.3.6 Curing

The curing process is used to make the paste into a cohesive, porous mass and to help

produce a bond between the paste and the grid. Several different curing processes are used

for lead oxides, depending on paste formulation and the intended use of the battery.

Typical cure for SLI plates is ‘‘hydroset,’’ at low temperature and low humidity for 24 to

72 h. The temperature is preferably between 25 and 40⬚C; the humidity is that contained in

the ﬂash-dried plates, typically 8 to 20% H

O by weight. The plates are usually covered by

canvas, plastic, or other materials to help retain both temperature and moisture. Some man-

ufacturers use enclosed rooms for the hydroset, and these rooms may be heated where

required by climatic conditions. As the plates cure, they reach a peak temperature, and

temperature and humidity decrease. Hydroset typically produces tribasic lead sulfate, which

gives high energy density.

More and more manufacturers are using curing ovens, where temperature and humidity

can be precisely controlled. This controls the peak temperature and makes sure that sufﬁcient

moisture is available to oxidize the remaining free lead in the paste. Peak temperatures in

the range of 65 to 90

⬚C are used; at higher temperatures or longer times, signiﬁcant amounts

of tetrabasic lead sulfate are produced in the plate, and the plates generally have lower energy

density. At the end of curing, the free lead content of the paste should be below 5%, pref-

erably as low as possible. (Insufﬁcient paste cure is observed as ‘‘soft,’’ easily broken pasted

plates, usually pale in color.) If the plates have not cured, they can be rewetted and reheated

to force the cure. Another process to force completion of curing is to dip the partially cured

plates into dilute sulfuric acid. This latter process (‘‘pickling’’) is also used for cure of

powder-ﬁlled tubular positive plates.

Cured plates are stored until use. Shelf life is not critical, but the high cost of inventory

usually makes storage time minimal.

23.3.7 Assembly

The simplest cell consists of one negative, one positive, and one separator between them.

Most practical cells contain about 3 to 30 plates with separators in between. Individual or

leaf separators are generally used. The use of ‘‘envelope’’ separators, which surround either

the positive or negative plate, or both, is becoming more popular in small, sealed cells, SLI,

motive power, and standby batteries to facilitate production and to control lead contamination

during manufacture.

Separators are used to electrically insulate each plate from its nearest counterelectrode

neighbors but must be porous enough to allow acid transport into or out of the plates. The

properties of typical separators are given in Table 23.10.

SLI batteries use either phenolic /cellulosic separators, sintered PVC separators or more

recently a trend toward microporous polyethylene in either ‘‘leaf’’ or ‘‘envelope’’ form. The

average pore diameters are in the 5 to 30-

␮

m range. Heavy-duty batteries usually have

microporous rubber or polyoleﬁn (mainly polyethylene) separators which have smaller pore

sizes and give longer life at a higher cost. Glass ﬁber scrim is added to some separator

materials to improve acid retention.

Industrial traction-pasted positive plates are usually wrapped with several layers of ﬁbrous

glass matting to help retain the active material during use. The inner layer consists of usually

very ﬁne parallel strands of ‘‘slyver’’ glass, and subsequent layers are randomly oriented

glass ﬁbers held together by a plastic (styrene or acrylic) binder. The matting is held in place

by a heat-sealed, perforated rubber retainer. In lieu of plate wrapping, many heavy-duty

batteries use a layer of glass matting on the ribs of the separator to help retain the positive

active material.

LEAD-ACID BATTERIES 23.31

TABLE 23.10 Comparison of Various Types of Battery Separator Materials

Type Rubber Cellulose PVC PE

Glass

ﬁber Microglass

Year available 1930 1945 1950 1970 1980 1985

Backweb, mils 20

⫹ 17–30 12–20 7–30 22–26 10–150

Porosity, % 60

 565 540⫹ 60  585 590⫹

Maximum pore ⬎535 25 ⬍1 45 15–30

size,

␮

Average pore 3 25 15

⬍0.1 80 10–15

size,

␮

Electrical 30–50 25–30 15–30 8–40 10

⬍5

resistance, (in acid)

⍀in

Purity Good Fair Good Good Good Excellent

Corrosion Good Fair Excellent Excellent Excellent Excellent

resistance

Flexibility Brittle Brittle Brittle Excellent Good Fair to good

Source: Battery Man. (Mar. 1993).

Plates and separators are stacked manually or by a stacking machine. Stacked elements

are staged on roller conveyors or carts as input to the interplate welding operations. Welding

is done by two general methods: melting of the lugs in a mold with the lugs facing upward,

or immersion of lugs facing downward into pools of molten lead alloy contained in a pre-

heated mold. The ﬁrst method is the traditional assembly method for lead-acid batteries. In

this method the plate lugs ﬁt up through slots in a mold ‘‘comb’’; the shape and the size of

the group strap are delineated by the ‘‘dam’’ and ‘‘back iron’’ portions of the tooling. Some

battery manufacturers use slotted ‘‘crowfoot’’ posts to ﬁt over the plate lugs to speed the

welding process. The second welding method is called the ‘‘cast-on strap’’ process and is

typically used for SLI cells. Stacked elements are loaded into slots of the cast-on machine.

A mold which has cutouts corresponding to the desired straps and posts is preheated and

ﬁlled with the appropriate molten lead alloy, making sure not to join lead or lead-calcium

alloys with antimony alloys. The mold and the stacked elements are moved until the plate

lugs are immersed in the strap cutouts. External cooling solidiﬁes the strap onto and around

each lug, and the elements are moved to a point where they can be dropped into a battery

case. Visual examination can differentiate between the two welding methods: ﬁxture-welded

plate straps are usually thicker and smoother than cast-on straps; cast-on straps also will

usually show a convex meniscus of metal between adjacent plate lugs on the underside of

the strap if the lug is properly cleaned of paste. A good weld is required between each plate

lug and the strap so that high-rate discharge performance is maximized. The resultant as-

semblage of plates and separators is known as an element, and the welded subelements are

known as groups. Electrical testing for short circuits is usually done on elements before

further assembly.

Cast-on battery elements are either continuously connected or made in discrete one-cell

modules. The ﬁrst method requires that long intercell connections be used, which travel over

the intercell partition and are seated in a slot in this partition; this is known as the loop-

over-partition design. In the second cast-on method, tabs on the ends of the plate straps are

positioned over holes that have been prepunched into the intercell partitions of a battery

case. These tabs are welded together manually with a very small torch or automatically by

a resistance welding machine. The latter also squeezes the tabs and the intercell partition to

provide a leak-proof seal.

23.32 CHAPTER TWENTY-THREE

Industrial traction cells and old-style SLI cells have been connected into batteries after

the cell cases and covers are sealed together. Traction batteries are needed in thousands of

different sizes for various applications, and the standard unit of construction is a cell, not a

quantity of plates and separators. A heavy steel tray is fabricated and coated with an acid-

resistant coating (urethane, epoxy, etc.). Traction cells are placed into the tray and shimmed

as necessary, and intercell connections are welded on. Heavy ﬂexible wires (made from

welding cable) are welded to the end cells for connection to the external circuit.

23.3.8 Case-to-Cover Seal

Four different processes have been used to seal battery cases and covers together. Enclosed

cells are necessary to minimize safety hazards related to the acidic electrolyte, to the poten-

tially explosive gases produced on overcharge, and to electrical shock. Most SLI batteries

and many modern traction cells are sealed with fusion of the case and cover. The fusion

comes from preheating each on a platen, then forcing the two together mechanically, or from

ultrasonic welding of the case and cover. Fusion-sealed batteries are virtually impossible to

repair. At best the elements can be salvaged, but the cover and usually the case are discarded

and replaced. A few SLI batteries are sealed using an epoxy cement which ﬁlls a groove in

the cover; the battery is inserted and positioned so that the case and intercell partition lips

ﬁt into the epoxy-ﬁlled groove. Heat is used to activate the catalyst to set the epoxy.

Some small deep-cycling batteries feature tar (asphalt)-sealed cases and individual cell

covers. Here the tar seal allows easy repair to the battery. Traditionally all batteries were

made this way before about 1960, but heat seals are typical for SLI batteries today. Molten

tar is dispensed from a heated kettle to ﬁll a groove between the cover and the case. The

tar must be hot enough to ﬂow easily but cool and viscous enough to solidify before running

down into the cell.

Stationary batteries in plastic cases are sealed with epoxy glues, with solvent cement, or

(for PVC copolymer cases and covers) with a thermal seal. Terminals are cast or welded on.

Some very large stationary and traction cells are made so that coolant can be circulated

through the terminals, and others are made with terminals with copper inserts for increased

conductivity and mechanical strength.

23.3.9 Tank Formation

Plates or assembled groups can be electrically formed or charged before assembly into the

case. When SLI plates are formed, these are usually formed as ‘‘doubles,’’ with two to ﬁve

panels stacked together in a slotted plastic formation tank, spaced an inch or less from stacks

of counterelectrode-pasted panels in adjacent slots. The stacks are arranged so that all positive

lugs protrude out of one side of the tank top and all negative lugs protrude out of the other

side of the tank top. All lugs with the same polarity are connected by welding to a heavy

lead bar, and the two bars are connected to a low-voltage, constant-current power supply.

The tank is ﬁlled with electrolyte, and current is passed until the plates have been formed:

the positives are converted to a deep brownish black and the negatives to a soft gray which

shows a bright metallic streak when scratched. Industrial plates are usually formed singly.

Sometimes these are also formed against dummy plates or grids. A variety of tank materials

have been used, but the most common are PVC, polyethylene, or lead. The tanks are arranged

so that the acid can be drained and reﬁlled because formation increases the electrolyte con-

centration.

A variety of formation conditions are used, with variations in electrolyte density, charging

rate (current), and temperature. Electrolyte is typically dilute, in the range of 1.050–1.150

speciﬁc gravity. The charging rate is usually ﬁxed, but some manufacturers use a sequence

of two or three different charging rates for different periods of time.

Tank-formed groups or plates are somewhat unstable (negatives will spontaneously oxi-

dize in air) and therefore are ‘‘dry charged’’ before use (see Sec. 23.3.11).

LEAD-ACID BATTERIES 23.33

TABLE 23.11 Formation Processes

One-shot Two-shot

Typical application SLI All others, some SLI

Electrolyte concentrations, sp gr.:

Initial

Final

1.200

1.280

1.005–1.150

1.150–1.230

Subsequent processing None Dump and reﬁll with 1.280–1.330

sp gr electrolyte; continue charge

for several hours

TABLE 23.12 Speciﬁc Gravity of Electrolytes at Full Charge at 25⬚C

Type of battery

Speciﬁc gravity

Temperate climates Tropical climates

SLI 1.260–1.290 1.210–1.230

Heavy duty 1.260–1.290 1.210–1.240

Golf cart 1.260–1.290 1.240–1.260

Golf cart (electric vehicle) 1.275–1.325 1.240–1.275

Traction 1.275–1.325 1.240–1.275

Stationary 1.210–1.225 1.200–1.220

Diesel starting (raiload) 1.250

Aircraft 1.260–1.285 1.260–1.285

Modern electronic chargers for formation are made to operate in a constant-current mode,

either by a saturable reactor control or by use of silicon controlled rectiﬁers (SCRs). The

most recent development in formation chargers is to control the current and time by use of

a microcomputer. Some formation schedules include charge at three or more different cur-

rents which start at low currents, go to higher currents, and then revert to lower currents.

Current adjustment during formation minimizes damage to the cells by high temperatures

and the need for cell cooling by water spray or forced air.

23.3.10 Case Formation

The more usual method of formation is to completely assemble the battery, ﬁll it with

electrolyte, and then apply the formation charge. This method is used for SLI and most

stationary and traction batteries. A variety of formation conditions are used, similar to those

for tank formation. The two major formation processes are the two-shot formation process

(used for stationary and traction batteries) and the one-shot formation process (used for most

SLI batteries). In the two-shot formation, the electrolyte is dumped to remove the low-density

initial electrolyte and reﬁlled with more concentrated electrolyte, chosen so that when this

is mixed with the dilute initial acid residue which is absorbed in the elements or trapped in

the case, the cell electrolyte will equilibrate at the desired density (Table 23.11). Typical

values of the electrolyte speciﬁc gravity at full charge after formation are given in Table

23.12.

23.34 CHAPTER TWENTY-THREE

23.3.11 Dry Charge

The performance of wet batteries degrades with long periods of inactivity, especially when

stored at warm temperatures. A loss of 1 to 3% of capacity each day is possible with SLI

batteries that contain antimonial lead grids. The loss on stand can be much lower for main-

tenance-free batteries (0.1 to 3%/day). When lead-acid batteries must be stored for a long

time, especially in high ambient temperatures, or when batteries are shipped for export, their

performance can be stabilized by removal of the electrolyte by one of several methods.

When the electrolyte is removed, the battery is termed ‘‘dry-charged’’ (that is, charged

and dry) or ‘‘charged and moist.’’ The ﬁrst process is done before the battery elements are

assembled inside the case and cover. The plates can be tank-formed, water-washed, then

dried in an inert gas before the element-welding portion of assembly. Alternately the welded

element can be tank-formed, washed, and then dried in an inert gas. The latter process is

simpler to carry out, but it is necessary that the separators can be rewetted easily after being

washed and dried. The assembly (case, elements, cover) is completed and the battery is

sealed. The battery can be stored in this dry-charged state for up to several years before

reactivation and use.

Several processing innovations have been commercialized in the past 10 years to convert

wet-charged batteries into moist or semidry batteries. In one process, most of the electrolyte

is removed by centrifugation. Another process uses an inorganic salt (sodium sulfate) in the

electrolyte, which minimizes degradation during storage and assists in an eventual reacti-

vation. A battery is formed, dumped, reﬁlled with electrolyte which contains the additive,

high-rate-discharge tested, and then ﬁnally dumped. The high-rate electrical discharge (to

simulate engine cranking) allows testing of an assembled ‘‘damp-dry’’ battery, but this also

probably blocks the plate surfaces with a thin layer of small lead sulfate crystals. These

crystals then minimize plate or separator degradation during storage when the battery is

sealed.

23.3.12 Testing and Finishing

Electrical tests are used to check the performance of batteries before they are sold and often

before they are put into use. The type of test employed depends on the intended use for the

battery. SLI batteries are tested by brief discharges at very high currents (200 to 1500 A) to

simulate engine-cranking performance. Stationary and traction cells are discharged at a rate

speciﬁed by the user, usually in the range of 1 to 10 h if stationary and 4 to 8 h for traction.

The discharge for SLI batteries is usually done by dissipation through a ﬁxed low-value

resistor or by a brief, high-rate electrical discharge driven by a power supply. Heavy-duty

batteries are discharged through a resistor, a transistorized load, or an inverter.

The ﬁnal manufacturing steps consist of improving the battery appearance by washing,

drying, painting, installing vent plugs, and labeling as desired. Rubber-case batteries are

usually painted; plastic-case batteries are not. A large variety of plaques and labels are

available which can describe the battery, its performance, and use. Product liability require-

ments in many countries mandate that the user be warned of the hazardous nature of the

battery, especially that the electrolyte is corrosive and that gases are formed which can be

explosive.

Traction batteries are physically sized to ﬁt a myriad of different forklift trucks, and so

the ﬁnal assembly for a traction battery consists of inserting preformed and pretested cells

into a sturdy metal box (tray), making intercell connections, making cable connections, and

sometimes adding a tar or plastic (urethane) material in the spaces between cell covers.

LEAD-ACID BATTERIES 23.35

23.3.13 Shipping

Small batteries (SLI and golf-cart types) are palletized several layers high for long-distance

shipment. The batteries are cushioned by ﬁve-sided (slipover) or six-sided cardboard boxes

with cardboard or wood sheet between layers. The batteries are held laterally by banding or

by plastic sheet which is shrink- or stretch-wrapped around a full pallet. Pallets need to be

very sturdy to withstand the battery weight and handling abuse. Large batteries are palletized,

banded, and cushioned as appropriate.

Batteries have traditionally been shipped only minimal distances because of their fragile

nature, their weight, and their corrosive contents. The latter cause common carriers to charge

a signiﬁcant premium for battery shipment and usually preclude shipment by air. As the

number of small, localized-sales battery manufacturers continues to decrease in the United

States, the remaining large manufacturers now usually ship to their distribution chain on

their own trucks.

23.3.14 Activation of Dry-Charged Batteries

When batteries have been dry-charged, they have to be reactivated before use. Activation

consists of unpacking the battery, ﬁlling the cells with electrolyte (which sometimes is

shipped with the battery in a separate package), charging the battery (if time is available),

and testing the battery performance. When dry-charged batteries are activated, the materials

which had been used to seal the vent holes must be removed and discarded.

23.4 SLI (AUTOMOTIVE) BATTERIES: CONSTRUCTION AND

PERFORMANCE

23.4.1 General Characteristics

The design of lead-acid batteries is varied in order to maximize the desired type of perform-

ance. Tradeoffs exist for optimization among such parameters as power density, energy den-

sity, cycle life, ‘‘ﬂoat-service’’ life, and cost.

High power density requires that the internal resistance of the battery be minimal. This

affects grid design, the porosity, thickness, and type of separator, and the method of intercell

connection. High power and energy densities also require that plates and separators be thin

and very porous and, usually, that paste density be very low. High cycle life requires premium

separators, high paste density, the presence of

␣

-PbO

or another bonding agent, modest

depth of discharge, good maintenance, and, usually, the use of high-antimony (5 to 7% Sb)

grid alloy. Low cost requires both minimum ﬁxed and variable costs, high-speed automated

processing, and no premium materials for the grid, paste, separator, and other cell and battery

components.

1,14,18–20

The automotive industry is planning to introduce a 36 /42 volt battery system in the ﬁrst

decade of the new millennium (see Sec. 23.9.1).

23.4.2 Construction

An SLI battery whose main function is to start an internal combustion engine, discharges

brieﬂy but at a high current. Once the engine is running, a generator or alternator system

recharges the battery and then maintains it on ‘‘ﬂoat’’ at full charge or slight overcharge. In

recent automobile designs the parasitic electrical load of lights, motors, and electronics

causes a gradual discharge of the battery when the engine is not in operation. This factor,

coupled with normal self-discharge, introduces a signiﬁcant cycling component into the nor-

mal cranking /ﬂoating duty cycles. Studies of SLI battery life and failure modes are presented

in Secs. 23.4.3 and 23.8.4.