CA2098686C

CA2098686C - Method of forming lead-acid battery electrode

Info

Publication number: CA2098686C
Application number: CA002098686A
Authority: CA
Inventors: Romeo R. Witherspoon; Gregory C. Garabedian
Original assignee: General Motors Corp
Current assignee: Motors Liquidation Co
Priority date: 1992-10-06
Filing date: 1993-06-17
Publication date: 1999-12-28
Anticipated expiration: 2013-06-17
Also published as: EP0592028B1; CA2098686A1; EP0592028A1; DE69301995T2; US5252105A; DE69301995D1

Abstract

In a preferred method, an electrode for a lead-acid battery is prepared in a new continuous process without the conventional curing step. The general procedure for preparing electrodes includes preparing a mixture (paste) comprising an active material precursor and an inhibitor. The active material precursor includes lead oxides having at least 10% by weight lead oxide in the form of Pb3O4 (red lead), and a BET surface area of at least about 0.8 m2/gram; desirably about 1.00 to 1.50 m2/gram and preferably about 1.0 to 1.25 m2/gram. The inhibitor prevents formation of tribasic lead sulfate and tetrabasic lead sulfate from the precursor material, except at elevated temperature. The paste is applied to electrode grids and reacted at elevated temperatures for between about 5 and about 30 minutes, to form the active material of the electrode for both positive and negative electrodes. Plates are then assembled into batteries and charged. Negative electrodes differ from the positive, mainly in the additives used.

Description

2~~~~~~

METHOD OF FORMING LEAD-ACID
BATTERY ELECTRODE
Field of the Invention This invention relates to electrodes of lead acid batteries and to a method of their manufacture.
Background of: the Invention Automotive type lead-acid batteries have interlaced positive and negative electrodes, also called plate... Each plate consists of special material, known as active material, supported on lead-alloy grids. The active material is formed from lead oxide pastes which are processed to a firm, porous form.
In the preparation of plates for a lead-acid battery, a mixture is formed containing oxides of lead, a significant: amount of metallic lead, sulfuric acid, water, and various additives. As a result of chemical reaction during mixing, a portion of the mixture is initially corwerted to lead sulfate (PbS04), providing an active material precursor paste which includes lead and its oxides and sulfates.
They precursor paste is applied to conductive lead grids and, using conventional methods, the freshly pasted platef~ are then typically cured to stabilize the precursor material and to enhance the strength of the plates. Both positive and negative plates are made by the same basic process except for the selection of additives.

~~n~~~r"
e1 ;-~~ ,:.i 'v Typically, negative plates are cured for up to three days. in a highly humid and warm air atmosphere to oxidize the free lead. Positive plates are cured by steam at near 100°C for 3 hours. Plates are assembled in the battery and formed in a multi-stage process which involves charging at a relatively high rate in several stages, each lasting several hours.
The curing steps of current processes are time consuming and often_lead to irregular product quality because such curing often fails to fully oxidize lead. The achievement of being essentially lead-free (i.e. fully oxidized product) is a key feature of a high quality product.
Therefore, it is desirable to have a new process for preparing electrodes which produces a more consistent and lead-free product.
Summary of the Invention There is provided an electrode for a lead acid battery, formed in a continuous process without steaming and curing.
The general procedure for preparing electrodes includes preparing a mixture (paste) comprising an active material precursor, sulfate-containing acids, and an inhibitor. The active material precursor includes lead oxides having at least 10% by weight lead oxide in the form of Pb304 (red lead), and a ;BET surface area of at least about 0.80 m2/gram; desirably about 1.00 to about 1.50 m2/gram, and preferabl;Y about 1.0 to about 1.25 m2/gram. The inhibitor pre~~ents formation of tribasic lead sulfate and tetrabasi,c lead sulfate from the precursor material and sulfate-containing acids, except at elevated temperatures. The paste is applied to electrode grids and reacted apt elevated temperatures for between about 5 and about a0 minutes, to form the active material of the electrodes for both positive and negative electrodes. Plates are then assembled into batteries and charged. Negative electrodes differ from the positive, mainly in the additives used.
More specifically, the lead sulfates at non-elevated temperatures are predominantly monobasic lead sulfate, PbO..PbS04 (nPbO.PbS04,n=1). At moderately high temperatures, tribasic lead sulfate (3Pb0.PbS04) forms; and tE~trabasic lead sulfates (4Pb0.PbS04) forms with further processing at temperatures of about 80°C
to about 100"C. Typically, the tri-(n=3) and tetra-(n=4) basic J.ead sulfates form, rather than dibasic lead sulfate (n=2).
An important aspect of the invention is the use of a lead sulfate derived from red lead in which the surface area is maximized through control of acid stoichiometrJr and reaction conditions. The lead sulfate derived from red lead is actually a mixture of Pb02, PbO, acid PbO.PbS04. It has been found that the surface area is maximized where the stoichiometry is near the monobasic lead sulfate point (PbO.PbS04).
That is, a r~stio of Pb0/PbS04 of about 2, providing about one mo:Le equivalent sulfate (S04) for every two moles equivalent of lead (Pb). The maximum surface area at this same stoichiometry is obtained through the controlled reaction of 50% sulfuric acid with a red t -_ lead, preferably by absorbing the d on a diatomaceous earth material (Celit03) prior to adding the red lead. Good results arc obtained when at least a minimum amount of red lead, at least down to about 10 weight percent, is used.
Objects, features and advantages of this invention are an electrode for a lead-acid battery and method of making it which improves consistency of product, essentially eliminates hard-to-control curing steps, prevents blistering of plates, and enhances plate strength.
These and other objects, features and advantages will become apparent from the following description of the preferred embodiments, appended claims and accompanying drawings.
Brief Description of the Drawings Figure 1 is a schematic drawing of an electrode for a battery.
Figure 2 is a flow diagram showing some of the important steps of a process according to one aspect of the invention.
Figures 3(a), 3(b), 4, and 5 are flow diagrams showing some of the important steps of other alternative processes of the invention.
Figures 6(a) and (b) are flow diagrams showing some of the important steps of an alternative process of the invention for forming negative plates.
Figures 7, 8, 9, and 10 are diagrams of percent utilization as a function of battery cycles.

2~~~~
Detailed Description of the Preferred Embodiments Figure 1 shows a schematic drawing of an electrode 10 for use in a lead-acid battery. The electrode has. a lead-based alloy substrate 15 which is 5 in the form of a grid with recesses 20. The substrate grid 15 has surface oxides of lead. A coating 25, comprising an. active material 30, is applied to both sides of the grid 15. In Figure 1, only one side has active material. A tab 40 provides a terminal.
Electrodes 10 were made from standard production grids 15 available from Delco-Remy. These grids 15 are of a typical 1% tin alloy with a minor amount of calcium. A grid for a positive electrode 10 is of a 1% tin, 0.05% to 0.07% calcium lead-alloy, with a thickness of about 0.043" (0.109 cm). Electrode grids of about 11.6 cm2 were made. The active area of the grid consisted of about 12 diamond-shaped sections at the lower end of the test electrode. Larger, full-sized electrodes were 264 cm2. Smaller electrodes were used primarily for screening purposes.
The general procedure for preparing electrodes includes preparing a mixture (paste) comprising an active material precursor and an inhibitor. T:he active material precursor includes lead oxides having at least 10% by weight lead oxide in the form of Pb304 (red lead), and a surface area of at least about 0.8 m2/gram. Desirably, the red lead (Pb304) content of the lead oxide is about 5 to about weight per~~ent, and preferably about 7.5 to about 15 30 weight percent. Desirably, the BET surface area of the lead oxide, h~~ving the desired red lead content, is 2~~ ~~

about 0.80 to about 1.50 m2/gram, and preferably about 1.0 to about 1.25 m2/gram. The inhibitor prevents formation of tribasic lead sulfate and tetrabasic lead sulfate from the precursor material, except at elevated temperature, typically in excess of 80°C. The paste is applied to e:Lectrode grids and reacted at elevated temperatures in a range of about 80°C to about 100°C
for between <~bout 5 and about 30 minutes, to form the active material of the electrode for both positive and negative electrodes. Plates are then assembled into batteries anti charged. Negative electrodes differ from the positive,, mainly in the additives used.
The inhibitor facilitates a two-stage reaction pro~:ess. In a first stage, discreet lead sulfate or basic lead sulfate is prepared. These compounds mast be prepared from either lead oxide or red lead. The lead sulfate of the first stage is subsequently reacted with more lead oxide in the second stage to for~a the tribasic or tetrabasic sulfate in the electrode pl~~te. More specifically, the lead sulfates prepared in i:he first stage are predominantly the monobasic le~id sulfate, PbO.PbS04 (nPbO.PbS04,n=1).
This is then reacted in the second stage process to form tribasic lead sulfate (3Pb0.PbS04) at relatively moderate temperatures, or tetrabasic lead sulfates (4Pb0.PbS04), with further processing at temperatures of about 80°C to about 100°C. Typically, the tri-(n=3) and tetra-(n~~4) basic lead sulfates form, rather than dibasic lead sulfate (n=2).
It has been found that under certain conditions, :lead sulfate forms slowly from lead oxide and sulfuric acid. Thus, the monobasic sulfate is formed as thcr stable first stage material. Ordinarily, these reactions take place quite rapidly in conventional pasting procedures with sulfuric acid. in contrast, in the method of the invention, the transition from monobasic to tribasic lead sulfates is retarded by the presence of inhibitors which block the surface of th.e lead oxide until activated by heat.
This process permits the crystals of tribasic lead sulfate to develop in the pasted plate, rather than in the paste mixer, and to give better plate strength.
An important aspect of the invention is the use of a lead sulfate derived from red lead in which the surface area is maximized through control of acid stoichiometry and reaction conditions. The lead sulfate derived from red lead is actually a mixture of Pb02, PbO, and PbO.PbS04. It has been found that the surface area is maximized where the stoichiometry is near the monobasic lead sulfate point (PbO.PbS04).
That is, a ratio of Pb0/PbS04 of about 2, providing about one mole equivalent sulfate (S04) for every two moles equivalent of lead (Pb). The maximum surface area at this same stoichiometry is obtained through the controlled reaction of 50% sulfuric acid with a red lead, preferably by absorbing the acid on a diatomaceous earth material (Celite 503) prior to adding the red lead: Good results are obtained when at least a minimum amount of red lead, at least down to about 10 weig',ht percent, is used. As shown from the following examples, the use of red lead sulfate with maximized sur:Eace area, enhances formation of the 2~~~6~

positive plai:es and very probably eliminates blistering after the pl~~te is formed. The use of hydroxyl-containing organic or inorganic reaction inhibitors controls the course of the two-stage chemical reactions which take p7lace in the formation process (pasting process), anc~ gives better plate strength. Desirably, the hydroxyl--containing compound is a polyhydroxyl organic compound, and preferably is glucose, fructose or sorbitol.
ThE~ various lead oxides and reagents used are as shown in 9~able 1. The preferred active material formed from red lead is prepared by one of several preferred met:hods, as described in the examples. The active material precursor was applied to grids which were not pretreated to form surface oxides. If desired, oxidized grids could be used.
Example 1 Lead sulfate pastes were made by combining red lead (a lead oxide having 25% by weight Pb304) with 10% by weight. of J.T. Baker lead sulfate in a high speed blende=. The resulting dry powder was then mixed with the appropriate amount of Water along with the selected inhibitor, typically boric acid or sorbitol (see Table 1). The resulting paste was applied to the grids and heated in a humid atmosphere in unsealed metal foil envelopes for about 10 to about 15 minutes at about 100°C, removed from foils and dried. The plates were then assembled in a battery and charged.
The general~flow diagram for this process is shown in Figure 2.

~Q~~~n~~

Example 2 In this example 75% red lead (75% Pb304) was reacted with sulfuric acid in the presence of sufficient water to form the desired paste consistency in the final stage when more lead oxide was added. The amount of sulfuric acid was varied from the stoichiometri.c point to slightly more than the amount needed to give monobasic lead sulfate (PbO.PbS04). For each lot of i'S% red lead it was necessary to titrate for the exact: analysis since it was found that the actual amount: of red lead in the lead oxide was closer to 71%, ratherr than the stated 75%. The acid-water-lead oxide mixture was heated to about 75°C to 80°C, with vigorous. stirring for a period of 2 hours, or until the pH rose above 5. The resulting product had a thick, cream~~ consistency and was light brown in color.
Electrodes were made by weighing the proper amount of the mixture s~o as to give a 10% by weight PbS04 paste when added to the selected lead oxide or red lead oxide and inhibitor, as shown in Figure 3(a). The inhibitor improved viscosity and retarded hardening of the pastes. The applied pastes were heated at a temperature c~f about 80°C to about 100°C, for about 20 minutes to at~out 25 minutes, in a humid (100% relative humidity) atmosphere as per Example l, and then assembled into a battery.
Example 3 A variation of the pasting process of Example 2 used a two-part paste in which 50% to 70% by weight to of the paste was tetrabasic lead sulfate for plate stability, acid the remainder was from the paste-mix described above and shown in Figure 3(a). This process is shown in Figure 3(b).
Comparative 9Pests In comparative tests, pastes made from 25%
red lead (25% Pb304) and lead sulfate pastes, rapidly turned to a c3rainy consistency with very poor plasticity, awaking it almost impossible to paste on grids. Increaasing the water content caused cracking of dried electrodes, as was seen in previous work. In contrast, then use of 1% boric acid or other inhibitors, preferably organic inhibitors, as in Examples 1 and 2, gave smooth pastes stable for a minimum of 30 minutes.
Small and large electrodes made by the method of the examples were tested. Small electrodes were evaluated eii:her against gassing lead counter electrodes with a lead sponge reference electrode, or in small triE~lectrode cells with two small Delco Remy negative counter electrodes. Most of the preliminary screening tef>ts were run with gassing counter electrodes iii a large excess of electrolyte. Normally, 1.280 acid (:37 w/o) was used as the electrolyte. Small electrodes were most commonly formed at the two hour rate with a 25% excess charge above the theoretical amount. Discharge was at the same current density as for formation. If small complete cells were used, the same procedure was used With the exception that the electrolyte contained Formax (phenolsulfonic acid) at 3 to 5 ml/gallon to help negative formation. Full-sized positives were always evaluated in polyethylene "baggy"
type cells against two Delco-Remy production negative electrodes retained by plexiglass plates. Daramic separators (s:ilica filled polyethylene) were used around the positive electrodes. In the present work, production De~lco-Remy negatives were preformed over a 16 hour period to about 25% of the theoretical capacity and then assembled into the test cell with the positives, formed as per the examples. The test cell was then form~,ed over a 5 hour period at constant current to 125% of the positive theoretical capacity.
The discharge was at a 2 hour rate to 1.75V. Normal charge during cycling was at a 5 hour rate With a voltage lid of 2.65V. In all cases, the full capacity of the electrodes was removed (100% depth of discharge). Cycling was normally terminated at 20% of theoretical.
Plates made with the inhibited paste, by the process of Examples 1 and 2, were strong and gave good cycling results, as seen in Figure 7. In contrast to conventional methods, the pastes of Examples 1 and 2 were applied and heated, only. There was _no conventional curing step. After heating, the plates were assemble~a into a battery and charged.

2~~~fi~6 c~~ 0 0 ov ao a~ o o v~ ar o H ~ O O 01 O ~I O O r~l N N N N
n . . . .
i~ ro r-1 e~ O ~i e-I v-1 M a~ 1l~ ,-~ 1p N
1r N
~ iJ

W ..a O ef' rl ~' .a O ur .i.rp ~n U
M

ro ~ N ro N

V ~' x to O .C ~

W

-f 'C~'O dP ~ .~ iJ

~

-.~ U N N t~ ~ ~ r-1 ~ N c~

a~ ~ ro ro >. >~ ~ ~

U o 3 3 'o w ro N c o .~ ro ro O

~ O O

E11 .A .!ar-1r-I N rl O 'C U

N i~ 1~ illN

a 'O ~-1N w 'C3 'C .u ro ro w .L~ro O Gl C7 d O N la Ir d tr O

> E3 E3 ~ > > ~3 9 O yr vC er O O .,~.. ., O w w ., ~n ro Q

C7 d 1.11..1C~ ~ Q) .i rl rl Q~ .Ia x V1 M
rl rl U W W U U U .G U U U ro r-i O N O
'C

ro Ir C7 G7 1r 1r I U '~'~' G W 0 M .. ..
O U

r . O ~ ~ ~

Ea 'O 'O O O r f U .~

tJ!ro ro (!1H~ V! i.~ .Ll.17to U U M vD 2 '~7r' T4 ~ ~ ~ ~ v1 w a~ ~ ~ ~ x U ~- Z

.4 O

.G '~ N

a' O y W M w ro a~ O

O b ~
a.

.G W iC W
aP O W ro p4 ...O ~ CL r-1U
.-I

O .i r-i N 'O N I~ I~ M 01 ~ 'Cf N

~ ~

r~ d O O 'O 'O U7 U r~

ro tr O ~e ~ ro ro w N N ro O a ~o tr~ O d d ro ro d ~ r~
~

N ro ro d' 'n' r-1r-1 aJ U .-1(,"C

N f.,1r O 'O O E~ N N rl O .rl,Q

w w w ~1 ro ~ 'Cf'C C3 #'~~ ~ s.~~., O

ro ..iN ~ C7 G7 G) C) ro ro G1 ro O O
!.r a H w a o c~ x u~ v~ U v1 pp t/~
w O r-I N M C~ U~

.-iN M ~ tl1 10 f~ 00 01 v-1.-I rl ri .-i.-I

2~~~6~~

E ~ w w O

W

GD ~ C

O O O

'~ .~ w N

W d ro 'O U

., 'Jt r~ a rl Ir 0~ N O

I U N

O O ~ N

U U O +~

~--1 1~ Ir .~

b C ~' t 0 A ~ O. d fa N U U

N w a N .rc N '~ 'L7 r1 LI yJ N

U N 1~ b . y O ro sr ~n a oo, x roar O U .-~ ro C~

~ U ,~ ro _ U

'O \ C w ~~ G

xroro HO'Cf O W

'C!o fa C7 rl fir"r1 rl 47 U1 ~ h U O

~ ~ ~ w tT CO ro N

U .~ t Q N -1 N ~
fJ , M
b r-iO
~

C ~ O .C C -..i .
.u O

0 o a ~ ~n v w wo ro a U U~ C) C ~-1 .-i .i 01 N .C = da ro N 1 "G 'O

W .k~.-I r/ ~ N

~~ ro H

N N N rl N C: C C C ra 'b ro O

w ~ N w w U U

N O O O O I

o N tr www w x o a~ w a~ a~

ro .raw ro ro ro ro w ..~

d ..~o ..~ .., ..~

sr w a w N N sr ro C

a~ a~ a~ N a~ ro d rob ~

rooro.~

U N ~-t F~ F3 E~ ~ E~ N

ro r-141 O n1 x., w w w ~; w O ~

.-i V G1~d O O O O tsf O > ~-1 '~ ~ ~ ~ w d a~ a~ ro a~ a~ .ct N C1~.1~ U V U 1.r V y a~ w ~ ?, .~ H s.. s~ O s~ .., p .1.~ r-IN r-1N ,~~ '~ ",~ ~.," ,~~ .~ ri ro C O O O O O O d O Gl O

W W f!1 fJ~ V1 (7 V~ U N

W

1C f~ OD 01 Q

rl r-1rl e-1 ',T., r-1 N M e! Lf1 2~~6~~

In various tests, it was shown that the surface area of lead dioxide (Pb02), derived from red lead could bE~ maximized by controlling the amount of residual Pb0 in the lattice through treatment with nitric acid, rather than sulfuric acid as in Example 2.
The condition of red lead treated with either nitric acid or sulfturic acid was similar. Using sulfuric acid, good results were observed by controlling stoichiometry.
From Table 1, items 6-9 and 11, it is seen that the surface area of the acid treated red lead goes through a ma~:imum. Although not precisely determined, it appears that the highest surface area takes place at a Pb0/H2S04 ratio of 2.25 and slowly decreases thereafter. This coincides with conditions needed to maintain an initial composition near the monobasic sulfate. Then the remaining reaction to the tribasic will take place at a later stage when the electrodes have been pasted. The highest surface area was obtained in material #11, where the reaction was controlled by pre-absorbing the acid in Celite 503.
The surface area optimization effect is seen only with red leads containing more than 50% Pb304. It is important that each lot of red lead be analyzed to make sure the actual red lead content is matched to the proper amount of acid.
Another important factor is the order of addition of the reaction inhibitor. If the inhibitor is added to the red lead before the addition of the sulfuric acid, the surface area of the product may be reduced by as much as 50%. It is, therefore, important that the inhibitor always be added after the formation of the red lerad sulfate.
It should be noted that the treatment of plain lead oa:ide with sulfuric acid did not produce the same effect as did red lead, and surface area did not vary with stoichiometry. Thus, red lead is the preferred starting material.
A large number of plates, both negative and positive, have been made by the method of Example 2, as shown in Figure 3(a). Most of the electrodes made with this process used either a 1% boric acid inhibitor or a 0.25% sorbitol inhibitor. A major portion of the plates in this example were designed with 10% lead sulfate level., red lead content of 15% to 17%, and inhibitors selected from boric acid, sorbitol, fructose, glucose or other simple sugars. Positive plates made by this method gave good cycling results, as shown in figure 8, when compared with conventional positive plates.
Example 4 They method of Example 2 was used except that the 25% red lead was replaced with ordinary leady oxide. When not fully cured to remove the free lead, leady oxide normally gives blistered positive plates in conventional electrodes. The plates made by the method of Example 2 did not show this blistering, and the cycle life of plates made with pure 25% red lead or leady oxide a,re essentially the same.

2fl~8fl~6 Example 5 Plates were made by a modification of the process of Example 2, as shown in Figure 4. In this case, the acid was pre-absorbed by the Celite and then reacted with the red lead. The resulting plates appeared somewhat stronger than those of Example 2 (non-Celite plates), and showed comparable utilizations and life as shown in Figure 9. An additional benefit of the CelitE: was the lower loss of the positive active material at t:he end of battery life. Pasted plates without the (:elite showed 20 grams or more active material los:~ after 50, C/2 rate cycles, whereas the Celite-containing plates lost only 5 to 6 grams.
ThE~ amount of Celite which could be used in the plates to improve the plate properties was only up to about 3% by weight. Anything above this level tended to reduce the density of the plates too much or lower the strength of the plate. Another problem with the Celite iii any of its available forms is the iron content, i.e,. about 1% ferric oxide. Small amounts of iron are known to reduce both the hydrogen and oxygen over voltage~~ at the negative and positive electrodes, respectively., The iron could be removed by acid treatment wil:h HCl, but this would increase the cost significantl~t. There are other forms of porous ceramics available which have very high liquid z~bsorption v<~lues as alternatives to Celite.
Example 6 A i'inely powdered red lead sulfate was obtained by a modification of Example 5, in which the 2~v~C~;~' acid concentration was increased by restricting the amount of wai:er used prior to reaction with sulfuric acid. Although 50% acid gives a granular and essentially non-usable product, increasing the acid concentration to 75% gives a finely divided material which can be used to make electrodes with good physical and electrochemical properties. Lots of 200 grams Pb304 were treated with 40 grams of 75 w/o sulfuric acid in a mm:er at an acid addition rate such that the heat evolution was not excessive. The reaction was extremely rapid and completed within 5 minutes. The process is shown in Figure 5. The resulting product was stable and could be stored for long periods of time until it is reacted with lead oxide, water, and inhibitor to make the desired paste.
The typical cycling results for electrodes made by the concentrated acid method (Example 6, Figure 5) of preparing red lead sulfate are shown in Figure 10. The cycling results were similar to other data with the exception that the capacity was relatively flat for about 30 cycles, rather than reaching a maximum and then slowly decreasing. The initial utilization was quite good in spite of the fact that the surface area of the red lead sulfate made by the concentrated acid method was only in the 3 to 4 m2/gram range. It may well be that areas as high as the 6 to 7 m2/gram seen with the Celite methods are not necessary.
The most important factor to be considered in preparing the red lead sulfate is that there should be no agglomeration of the crystals which gives non-uniform electrodes with poor strength.

2~

Example 7 Negative plate pastes were made by slight modificationf> to the positive plate procedures, primarily by addition of an expander. Plates were then reacted in open foil envelopes similar to the positives. 9Phese processes are shown in Figures 6(a) and 6(b). Af> shown in Figure 6(a), 25% red lead by weight, de~ri~red from 75% red lead, was added to the dry ingredients end processed. In another variation (Figure 6(b)), the rE'd lead was prereacted with the acid in a large lot followed by the addition of the lead oxide, expander, inhibitor, and polymer fibers. This method was used to make both positives and negatives from a single lot. Positives are made first, and to the remaining part of the mix, an expander is added for the negatives.
Tef~ts showed that the negatives made by the process of Figure 6(a) gave cycling results essentially the same as i:hose with conventional negatives.
Negatives made by the process shown in Figure 6(b) have also been shown to give good cycling properties. while process Figure 6(b) is more complicated then 6(a), 6(b) process is the preferred one because the electrodes are stronger.
Comparative 9Pests - Negative Plates Negatives were made using leady oxide and with all ingredients combined at the beginning. The sulfuric acid was added last and the paste applied to the grids. '.these did not form or cycle well. There were large areas of unconverted lead sulfate, and capacities were lower than that of plates made as shown in Figures 6~(a) and 6(b).
Thirty full-sized positive and negative plates, made according to the invention, were evaluated in full-sized 9 plate cells consisting of 5 positive and 4 negative plates. Positive plates were made by the method o:E Example 2 with leady oxide as the major component and with boric acid inhibitor. Negative plates were made by the process in Figure 6(a) also using leady oxide and a boric acid inhibitor. All cells were given a standard 130Ah/lb formation. The cell capacities were all within acceptable limits for the first 25A rate tests, but showed poor results when given a cold cranking test at 0°F. This was due to the effects of the boric acid inhibitor in the negative electrodes. When boric acid was replaced with sorbitol or one of the other simple sugars, good results were obtained.
The inhibitors used in the Examples have at least one hydroxyl group per carbon atom. Preferably, they are simple sugars and related compounds. Boric acid and ammonium bicarbonate were also used as inhibitors, ~~lthough the organic polyhydroxyl compounds are preferred. Best results were obtained using organic comp~~unds where most of the carbon atoms have hydroxyl gro~ips attached. Linear molecules are preferred. »andom ketone, aldehyde or carboxyl groups are acceptable, unless there is reaction to form acetic acid, which will ruin the positive electrode of the battery. Good results were obtained with sorbitol, 2~~~6~6 mannitol, fructose, glucose, and even sucrose. There are many other polyhydroxyl compounds which will work as well, including optical and geometrical isomers of simple sugars. and their acids. The simple sugars such 5 as glucose and fructose, as well as sorbitol, are preferred since they are low in cost. They are effective in the 0.05 to 0.50 w/o range, and in the preferred range of 0.10 to 0.25 w/o. While specifically added as a reaction inhibitor in positive 10 pastes, the polyhydroxyl~compounds appear to improve the negative electrode as well. The surface area of the lead on cycling is in the range of 1.0 to 1.34 m2/gram with the sorbitol and a maximum of only 0.79 m2/gram without sorbitol.
15 While this invention has been described in terms of certain embodiments thereof, it is not intended that it be limited to the above description, but rather only to the extent set forth in the following claims.
20 The embodiments of the invention in which an exclusive property or privilege is claimed are defined in the appended claims.

Claims

1. A method of forming an electrode plate for a lead-acid battery comprising:
a) forming an oxide of lead having at least 10% by weight lead oxide in the form of Pb3O4 (red lead);
b) forming a wet mixture containing basic lead sulfate (nPbO.PbSO4) predominantly in the monobasic form PbO.PbSO4) by reacting the oxide of step (a) with one or more acids containing a sulfate group in an amount sufficient to provide at least one mole equivalent of sulfate (SO4) for every two moles equivalent of lead (Pb) in the oxide of step (a);
c) forming an oxide of lead having less than 1 % by weight lead in the form of free lead;
d) intermingling the mixture formed in step (b), the oxide of step (c), and an inhibitor for preventing formation of tribasic and tetrabasic lead sulfate except at elevated temperatures, said inhibitor having at least one hydroxyl group;
e) applying the product of step (d) to grids; and f) heating the applied product for a time and at a temperature and at a humidity sufficient to react the monobasic lead sulfate to form at least one of tribasic lead sulfate (3PbO.PbSO4) and tetrabasic lead sulfate (4PbO.PbSO4).

2. The method according to claim 1, wherein the temperature is 80°C to about 100°C.

3. The method according to claim 1, wherein the time is less than 5 minutes for a negative electrode and between about 10 and 15 minutes for positive electrodes.

4. The method according to claim 1, wherein the heating takes place in an atmosphere essentially saturated with water (100% relative humidity).

5. The method according to claim 1, wherein the acid is selected from the group consisting of sulfuric acid and ammonium sulfate.

6. The method according to claim 1, wherein step (d) is accomplished by first intermingling the oxide of step (c) and the inhibitor and then including the mixture formed in step (b).

7. The method according to claim 1, wherein the inhibitor is selected from the group consisting of hydroxyl-containing organic and inorganic compounds.

8. The method according to claim 1, wherein the inhibitor is selected from the group consisting of glucose, fructose and sorbitol.

9. The method according to claim 1, wherein the lead oxide of step (a) has a surface area of at least about 1.0 m2/gram.

10. The method according to claim 1, wherein step (b) is conducted by causing the acid to be absorbed by ceramic particles and then mixing the ceramic particles with the oxides of step (a), whereby the acid reacts with the oxide.

11. A method of forming an electrode plate for a lead-acid battery comprising:
a) forming a wet mixture comprising basic lead sulfate (nPbO.PbSO4) predominantly in the monobasic form (PbO.PbSO4), at least one oxide of lead and an inhibitor having at least one hydroxyl group for preventing formation of tribasic and tetrabasic lead sulfate except at elevated temperatures;
b) applying the mixture of step (a) to a support substrate; and c) heating the applied mixture for a time and at a temperature and at a humidity sufficient to react the monobasic lead sulfate to form at least one of tribasic lead sulfate and tetrabasic lead sulfate.

12. The method according to claim 11, wherein before step (a) the basic lead sulfate is formed by reacting an oxide of lead having at least 10% by weight lead oxide in the form of Pb3O4 (red lead) with one or more acids containing a sulfate group in an amount sufficient to provide at least one mole equivalent of sulfate (SO4) for every two moles equivalent of lead (Pb).

13. The method according to claim 12, wherein the oxide of lead having at least 10% by weight lead oxide in the form of Pb3O4 has a surface area of at least about 1.0 m2/gram.

14. The method according to claim 12 and further comprising causing the acid to be absorbed by ceramic particles and then mixing the ceramic particles with the oxide, whereby the acid reacts with the oxide.

15. The method according to claim 12, wherein the acid is selected from the group consisting of sulfuric acid and ammonium sulfate.

16. The method according to claim 11, wherein at least one oxide of lead is selected from the group consisting of leady oxide (PbO/Pb), lead oxide (PbO), and an oxide of lead having at least 10% by weight lead oxide in the form of Pb3O4 (red lead).

17. The method according to claim 11, wherein the temperature is 80°C to about 100°C.

18. The method according to claim 11, wherein the heating takes place in an atmosphere essentially saturated with water (100% relative humidity).

19. The method according to claim 11, wherein before step (a) the basic lead sulfate is formed by reacting lead sulfate (PbSO4) with an oxide of lead having at least 25 % by weight lead oxide in the form of Pb3O4 (red lead).

20. The method according to claim 19, wherein the oxide of lead having at least 25 % by weight lead oxide in the form of Pb3O4 has a surface area of at least about 1.0 m2/gram.

21. The method according to claim 11, wherein the inhibitor is selected from the group consisting of glucose, fructose, and sorbitol.