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

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23.16 CHAPTER TWENTY-THREE

FIGURE 23.7c Preparation of sulfuric acid solutions of

any speciﬁc gravity from concentrated sulfuric acid.

(From G. W. Vinal, Storage Batteries, Wiley, New York,

1955, p. 129.)

The speciﬁc gravities for several types of lead-acid battery designs are given in Table

23.12; the change in speciﬁc gravity at different states of charge is shown in Table 23.6. A

comparison with freezing-point data will show that battery type A will freeze at

⫺30⬚C when

fully discharged while battery type D will freeze at about

⫺5⬚C, a factor which must be

considered in the design of the battery and the battery housing. The acid concentration for

most lead-acid batteries for use in temperate climates is usually between 1.26 and 1.28

speciﬁc gravity. Higher-concentration electrolytes tend to attack some separators and other

components; lower concentrations tend to be insufﬁciently conductive in a partially charged

cell and freeze at low temperatures. In high-temperature climates, a lower concentration is

used, and in stationary cells with larger proportional electrolyte volumes and no high-rate

demands, electrolytes with speciﬁc gravity as low as 1.21 are used (see Table 23.12).

Figure 23.7c indicates the method of preparing sulfuric acid solutions of any speciﬁc

gravity from concentrated sulfuric acid.

23.3 CONSTRUCTIONAL FEATURES, MATERIALS, AND

MANUFACTURING METHODS

Lead-acid batteries consist of several major components, as shown in a cutaway view of Fig.

23.8. This ﬁgure shows the construction of an automotive SLI battery. Batteries for other

applications have analogous components, as illustrated and described in Secs. 23.4–23.6.

The applications of the various cells and batteries dictate the design, size, quantities, and

types of materials that are used.

The active components of a typical lead-acid battery constitute less than one-half of its

total weight. A breakout of the weights of the components of several types of lead-acid

batteries is shown in Fig. 23.9.

The battery components are fabricated and processed as shown in the ﬂowsheets of Fig.

23.10. The major starting material is highly puriﬁed lead.

The lead is used for the produc-

tion of alloys (for subsequent conversion to grids) and for the production of lead oxides [for

subsequent conversion ﬁrst to paste and ultimately to the lead dioxide positive active material

(Fig. 23.10a) and the sponge lead negative active material].

LEAD-ACID BATTERIES 23.17

FIGURE 23.8 Maintenance-free lead-acid SLI battery. (Courtesy of Delphi Energy Systems.)

FIGURE 23.9 Weight analysis of typical lead-acid batteries. (a) SLI battery. (b) Tubular industrial

battery. (c) Flat-plate traction battery. (From Ref. 10.)

23.18 CHAPTER TWENTY-THREE

FIGURE 23.10 (a) Chemical compounds and process parameters in production of SLI

batteries. (b) Production ﬂow sheet for lead-acid batteries.

LEAD-ACID BATTERIES 23.19

Automotive lead-acid batteries (SLI) are produced mainly in high-volume plants with a

great deal of automation. Many modern factories are capable of producing quantities on the

order of 20,000 to 30,000 batteries per day. On average, an automated facility might require

less than 500 employees, including all stafﬁng levels. The automation has been prompted

by environmental, reliability, and cost considerations.

23.3.1 Alloy Production

Pure lead is generally too soft to be used as a grid material. Exceptions that use pure lead

plates are some special, very thick plate Plante´ or pasted-plate batteries, some small spiral

wound batteries, some valve regulated cells and batteries (see Fig. 23.12c) and a cylindrical

cell. The latter were developed by Bell Laboratories (now part of Lucent Technologies) (see

Fig. 23.36).

The pure lead has been hardened, traditionally, by the addition of antimony metal. The

amount of antimony has varied between 5 and 12% by weight, generally dependent on the

availability and cost of antimony. Typical modern alloys, especially for deep-cycling appli-

cations, contain 4 to 6% antimony. The trend in grid alloys is to go to even lower antimony

contents, in the range of 1.5 to 2% antimony, in order to reduce the maintenance (water

addition) that the battery will require. As the antimony content goes below 4%, the addition

of small amounts of other elements is necessary to prevent grid fabrication defects and grid

brittleness. These elements, such as sulfur, copper, arsenic, selenium, tellurium and various

combinations of these elements act as grain reﬁners to decrease the lead grain size.

13–15

Some of the alloying elements, not previously described as grain reﬁners, fall into two

broad classes of elements that are beneﬁcial or detrimental to grid production or battery

performance. Beneﬁcial elements include tin, which operates synergistically with antimony

and arsenic to improve metal ﬂuidity and castability. Silver and cobalt are also thought to

improve corrosion resistance. Detrimental elements include iron, which increases drossing;

nickel, which affects battery operation; and manganese, which attacks paper separators. Cad-

mium has been used in grid alloys to enhance processability in antimonial alloys to minimize

the detrimental effects of antimony. Cadmium, however, is not popular because of its toxicity

and difﬁculty of removal during lead recovery (recycling) operations. Bismuth exists in many

lead ore feedstocks and has been reported to both increase and decrease grid corrosion rates.

A second class of lead alloys has been developed which uses calcium or other alkaline

earth elements for stiffening. These alloys were developed originally for telephone service

applications.

2,16

Antimony from the grids is dissolved during battery operation and migrates

to the negative plates where it redeposits, which results in increased hydrogen evolution and

water loss. For telephone applications, more stable battery operation and less frequent wa-

tering were desired. The composition of the alloy depends somewhat on the grid manufac-

turing process. Calcium is used in the range of 0.03 to 0.20% but for corrosion resistance

the preferred range is 0.03 to 0.05%. A variation has been to substitute strontium for calcium.

Barium has been investigated but is generally felt to be detrimental to performance. Tin has

been used to enhance the mechanical and corrosion-resistant properties of the Pb-Ca alloys

and is usually used in the range of 0.25 to 2.0% by weight. The trend in nonantimonial

alloy development is toward ternary alloys (Pb-Ca-Sn) containing a minimal amount of tin

because of the expense of this element. Some batteries are produced with a quaternary

alloy—the fourth element being aluminum—to stabilize the drossing loss of the alkaline

earth element (calcium or strontium) from the molten alloy. Grain reﬁning is done by the

alkaline earth metal, and no other elements (impurities) are desired. The properties of the

alloys are summarized in Table 23.8.

23.20

TABLE 23.8 Properties of Lead Alloys

Alloys of the 1970s

Property

Conventional

antimony

Low

antimony

Cast

lead-calcium-tin

0.1Ca

0.3Sn

0.1Ca

0.7Sn

Lead-

strontium

tin-

aluminum

Lead-

cadmium-

antimony

Wrought-lead-

calcium-tin

0.065Ca

0.7Sn

Ultimate tensile

strength, Pa

⫻ 10

⫺

38–46 33–40 40–43 47–50 53 33–40 60

Percent elongation 20–25 10–15 25–35 20–30 15 25 10–15

Property

Cast

conventional

antimony

Cast

low-

antimony

Cast lead-

calcium

Cast lead-

strontium

Cast

lead-cadmium

antimony

Wrought

lead-calcium-tin

(1st generation)

Ease of grid manufacture Good Fair Fair Fair to good Fair Good

Mechanical Good Fair Fair to good Fair to good Fair Good

Corrosion Fair Fair Good Good Fair Good

Battery performance Poor Fair Good Good Good Fair to good

Economics Good Good Fair Poor Fair Fair to good

23.21

Alloys of the 1980s and 1990s

Property

Cast alloys

Lead-

calcium-tin

0.1Ca

0.3Sn

Lead-

calcium

0.1Ca

Lead-

calcium-tin

with

aluminum

Lead-

calcium

with

aluminum

Wrought alloys

Lead-

calcium-tin

0.065Ca

0.3Sn

Lead-

calcium-tin

0.065Ca

0.5Sn

Lead-

calcium

0.075Ca

Low

antimony

2.5–3.0%

Cast and

wrought

Lead

0.01–1.5Sn

Ultimate tensile

strength, Pa

⫻ 10

⫺

40–43 37–39 40–43 37–39 43–47 47 43 37–40

Percent

elongation

25–35 30–45 25–35 30–45 15 15 25 25–40

Property

Cast alloys

Low

antimony Lead-calcium

Wrought alloys

Wrought

lead-calcium-tin

(2d generation)

Wrought

low antimony

Ease of grid manufacture Fair to good Good (aluminum) Good Good Conductivity

Mechanical Fair Fair to good Good Good and corrosion-

Corrosion Fair Good Good Fair to good equivalent to

Battery performance Fair to good Good Fair to good Fair pure lead

Economics Good Good (lower tin) Good Good

NOTE: Alloy constituents given in weight percent.

23.22 CHAPTER TWENTY-THREE

23.3.2 Grid Production

Two general classes of grid production methods virtually describe all modern production,

but two other classes of production techniques might become widespread in the future. These

are listed in Table 23.9.

TABLE 23.9 Grid Production Methods

Book mold cast

Gravity cast

Injection molded (die cast)

Mechanically worked (Plante´, Manchester)

Continuous cast, drum cast

Continuous cast, wrought-expanded, cast-expended

Casting

Working

Expansion

Progressive die expansion

Precision expanded

Rotary expanded

Rotary expansion

Diagonal/ slit expansion

Punching

Composite

The purposes of the grid are to hold the active material mechanically and conduct elec-

tricity between the active material and the cell terminals. The mechanical support can be

provided by nonmetallic materials (polymer, ceramic, rubber, etc.) inside the plate, but these

are not electrically conductive. Additional mechanical support is sometimes gained by the

construction method or by various wrappings on the outside of the plate. Metals other than

lead alloys have been investigated to provide electrical conductivity, and some (copper, alu-

minum, silver) are more conductive than lead. These alternate conductors are not corrosion-

resistant in the sulfuric acid electrolyte and are often more expensive than lead alloys. Ti-

tanium has been evaluated as a grid material; it is not corroded after special surface

treatments but is very expensive. Copper grids are used in the negatives of some submarine

batteries.

The grid design is generally a rectangular framework with a tab or lug for connection to

the post strap. For cast grids, the framework features a heavy external frame and a lighter

internal structure of horizontal and vertical bars. In some grid designs the frame tapers with

the greater width near the lug; the internal bars may also be tapered. A recent advance in

grid design is the ‘‘radial’’ grid, with the vertical wires displaced along the frame, pointing

directly toward the tab area in order to increase grid conductivity (Fig. 23.11). The radial

design has been further reﬁned to a composite of lead alloy radial conductor arrangement

cast into a rectangular plastic frame. An example of this composite grid is shown in Fig.

23.12a. The grids used in the cylindrical-cell design (Fig. 23.12b) incorporate both concentric

and radial members. This system has been in commercial production since 1970, with most

of the original cells still in use. An example of a balanced positive grid design is shown in

Fig. 23.12c.

LEAD-ACID BATTERIES 23.23

FIGURE 23.11 Examples of lead-acid battery cast grids. (a) Conventional cast ﬂat grid. (b)

Radial-design grid.

FIGURE 23.12a Composite grid, radial conductor. Grid

combines diagonal conducting members with light robust

plastic frame.

‘‘Book-mold’’ casting historically accounted for most grid production. Permanent molds

are made from steel (Meehanite) blocks by machining grooves to form the grid frames and

internal lattice structure. The molds are ﬁlled when closed with an amount of lead sufﬁcient

to form the grid and leave an excess gate or sprue which is subsequently trimmed off by a

cutting or stamping operation. The grid alloy is put into the mold from a ladle in a recir-

culation lead alloy stream, from a metering valve in a nonrecirculation lead stream, or from

a hand-ﬁlled ladle. A variation on book-mold casting is injection molding or die casting of

battery grids. Here the lead alloy is forced into a clamped mold by high injection pressure.

Depending on the alloy characteristics, injection molding can be capable of very high pro-

duction rates.

Another method of grid manufacture is via mechanical treatment of a strip or slab of lead

alloy. The traditional procedures (Plante´-type plate) have been either to cut grooves into a

thick lead plate, thereby increasing its surface area, or to crimp and roll up lead strips into

rosettes which are inserted into round holes in a cast plate. The resultant plates are formed

electrolytically into positives in the classic Plante´ and Manchester designs (Fig. 23.13).

23.24 CHAPTER TWENTY-THREE

FIGURE 23.12b Balanced positive design

takes into account grid corrosion and

growth and promotes the maintenance of contact of the grid with the active material,

while maintaining the shape of the plate and its angle with the horizontal. This

concept has also been carried into the prismatic grid structure. (Courtesy of AT&T.)

FIGURE 23.12c Balanced rectangular positive grid

design. This design promotes active material contact

and accounts for grid corrosion and growth in a pris-

matic cell. (From Ref. 36.)

LEAD-ACID BATTERIES 23.25

FIGURE 23.13 Plante´ and Manchester plates. (a) Plante´. (b) Manchester.