artigo de baterias chumbo ácido

Journal of Power Sources 140 (2005) 168180

Pro ad-soak uen

. MaCentral nces, A

uly 200r 2004

Abstract

The soaki f leadformation so tion prpartial sulfa e strucprepared wit stigatesoaking the d thenphases decre f a hetesulfation of the corrosion layer has also been investigated. Batteries with plates prepared with 3BS paste and PbSnCa grids have considerablylonger cycle life, if soaked and formed in 1.06 s.g. H2SO4 solution as compared to those soaked and formed in 1.25 s.g. H2SO4 solution. 2004 Elsevier B.V. All rights reserved.

Keywords: Lpaste; Structu

1. Introdu

Duringand curedmation, sulpaste is sulproceeds inand sulfateadvances infated pastedecreases.of the plate

It has bthe plates dcentration opaste [46]conditions

CorrespoE-mail a

0378-7753/$doi:10.1016/jead-acid battery; Lead-acid battery technology; Soaking of lead-acid battery plates in H2SO4 solution; Sulfation of lead oxides; Sulfation of 3BSre of sulfated lead-acid battery paste

ction

the production of lead-acid batteries, when pastedplates are soaked in H2SO4 solution before for-furic acid reacts with the cured paste whereby thefated. The reaction between H2SO4 and the pastea reaction layer between the zones of cured paste

d paste. With the time of soaking, the reaction layerto the bulk of the cured paste, thus the zone of sul-grows in size, whereas the volume of cured pasteZone processes take place also during formations of lead-acid batteries [13].een established that the processes of sulfation ofuring soaking are influenced greatly by the con-f H2SO4 and the phase composition of the cured. Attempts have been made to find the optimumof soaking [7,8]. The processes during soaking of

nding author. Tel.: +359 271 8651; fax: +359 273 1552.ddress: [email protected] (D. Pavlov).

4BS plates have also been investigated as well as the sulfationof the bulk of 4BS crystals [912].

The aims of the present investigation are: (a) to disclosethe mechanism of the processes that take place in the 3BScured paste during plate soaking, (b) to find out how doesthe soaking process influence the macrostructure of the pasteand of the paste/grid interface and (c) to establish what is theeffect of the soaking process on battery cycle life.

2. Experimental

2.1. Plate preparation

The paste for the experimental plates was preparedthrough mixing commercial leady oxide (LO), water andH2SO4 (s.g. 1.40) in a ratio equal to 5% H2SO4/LO at 30 C.The paste had a density of 4.15 g/cm3 and was composedof 3BS, and -PbO, and Pb. Commercial grids cast fromPb1.2%Sn0.056%Ca0.002%Al alloy were pasted, set to

see front matter 2004 Elsevier B.V. All rights reserved..jpowsour.2004.08.006cesses taking place in the paste of leing prior to formation and their infl

M. Dimitrov, D. Pavlov, T. Rogachev, MLaboratory of Electrochemical Power Sources, Bulgarian Academy of Scie

Received 19 March 2004; received in revised form 29 JAvailable online 6 Octobe

ng procedure is a step in the technological process of production olution on open circuit (i.e. soaked) for 14 h and after that the forma

tion. The changes in chemical and phase composition as well as thh 3BS pastes and soaked in 1.06 or 1.25 s.g. H2SO4 solution are invelead oxides and basic lead sulfates in the paste are hydrated first anases in the inner parts of the plates. This results in the formation oacid battery plates duringce on battery performancetrakova, L. Bogdanovacad. G. Bonchev Street, Block 10, Soa 1113, Bulgaria4; accepted 16 August 2004

-acid battery plates. Cured plates are left to stay in theocess starts. During soaking, the cured paste undergoesture of the paste and the crystal morphology of platesd in the present work. It has been established that duringsulfated forming 1BS and PbSO4. The content of theserogeneous structure and composition of the paste. The

M. Dimitrov et al. / Journal of Power Sources 140 (2005) 168180 169

curing at 50 C and 98% RH for 18 h, and then dried at 60 Cand 60% RH for 5 h followed by another 4 h at 60 C and10% RH [13].

2.2. Invest

Three cu1.06 s.g. Htaken out fof soaking.

As theacross theplates wason the platner) sub-labetween thvarious ana

(a) chemicPbO an

(b) X-ray dsition o

(c) SEM oand the

(d) differengravimdration

(e) BET susurface

(f) pore voplate.

2.3. Batter

Cells wein 3 mm thcell. The thfilled with 112 V/21 A hjected to sthe same solaboratory.replaced w1.28 s.g. finwere set todischarge dversus the

3. Experim

3.1. Changsoaking

Fig. 1solutions w

Fig. 1. Changes in H2SO4 concentration during plate soaking.

positive plates. The volume of electrolyte per g paste1.6 ml of 1.06 s.g. H2SO4 and 1.0 ml of 1.25 s.g.4.e higher the H2SO4 concentration the greater the

ges in acid concentration during soaking. When thes werges weeven a

ined uf sulf

ult oftures.

Zonalent su

g. 2 pr4 h ofree sued:

. A cross-section view of the plate after 4 h of soaking in 1.06 s.g.4 solution: (A) outer sub-layer; (B) intermediate sub-layer; (C) central) sub-layer.igation of the processes during plate soaking

red positive plates were placed in a cell box with2SO4 or 1.25 s.g. H2SO4 solution. One plate wasrom the box, washed and dried after 1, 2 and 4 h

process of sulfation affects the different zonesplate thickness to a different extent, each of thedivided in three sub-layers: (i) outer sub-layer

e surface contacting the solution, (ii) central (in-yer of the plate, and (iii) intermediate sub-layere above two. These three sub-layers were set tolysis as follows:

al analysis to determine the content of PbSO4,d Pb;iffraction analysis to determine the phase compo-f the paste;bservations to examine the structure of the pastemorphology of its crystals;tial scanning calorimetry (DSC) and thermo-

etric analysis (TGA) to measure the degree of hy-of the paste;rface measurements to determine the integral BETarea of the plate;lume distribution by pore radius throughout the

y cycle life tests

re assembled with two positive plates, envelopedick AGM separator, and three negative plates perus assembled cells (under 20% compression) were.06 or 1.25 s.g. H2SO4 solution. Six test batteries(20 h discharge rate) were assembled and sub-

oaking for 1, 2 or 4 h, and then to formation inlution employing an algorithm developed in thisAfter formation, the solution was poured out andith a fresh one of such a concentration as to obtainal H2SO4 concentration in the cells. The batteries

three capacity tests and then to cycling at 3 h rate ofown to 100% DOD followed by 115% overchargepreceding discharge cycle.

ental results and discussion

es in H2SO4 concentration during plate

shows the changes in H2SO4 concentration ofith 1.06 and 1.25 s.g. during soaking of the

threewas

H2SOTh

chanplatechanthat,rema

rate oa res

struc

3.2.differ

Fiafter

Thguish

Fig. 2H2SO(innere soaked in H2SO4 with 1.25 s.g., the greatestre observed within the first hour of soaking. Afterfter 4 h of soaking, substantial amounts of H2SO4nreacted. This means that after 1 h of soaking theation of the paste is slowed down substantially asdifficulties created by the newly formed sulfated

processes during plate soaking formingb-layers across the plate thickness

esents a micrograph of the cross-section of a platesoaking in 1.06 s.g. H2SO4 solution.b-layers (zones) of different colour can be distin-

170 M. Dimitrov et al. / Journal of Power Sources 140 (2005) 168180

Fig. 3. Conte ss after

A. outer sin colou

B. intermeC. central

lowish

3.3. Chemacross thes.g. H2SO4

Fig. 3 susamples frothe contentfree PbO in

The highsub-laye

At bothmost int

Fig. 4 shpaste afterobtained frthree sub-l

The degH2SO4 solusoaked in 1time of soa

Changg platnt of PbO and PbSO4 in the three sub-layers (AC) across the plate thickne

ub-layer: contacting the bulk solution, dark greyr, with compact structure;

3.4.durindiate sub-layer: grey with white spots;(inner) sub-layer: light grey in colour with yel-

tint and white spots.

ical composition of the three sub-layersthickness of the plates soaked in 1.06 and 1.25solution

mmarizes the results of the chemical analysis ofm the three sub-layers. Cured paste stands forof PbSO4 in 3BS as well as for PbO in 3BS andthe cured paste.

est degree of sulfation is established in the outerr (A).H2SO4 concentrations, sulfation of the paste is

ense within the first hour of soaking.

ows the average amount of PbSO4 formed in the1, 2 and 4 h of soaking. The average amount isom the sum of the PbSO4 quantities formed in theayers across the plate thickness divided in three.ree of sulfation of the pastes soaked in 1.06 s.g.tion for 4 h reaches up to 47%, whereas the pastes

.25 s.g. H2SO4 undergo 75% sulfation for the sameking.

Accordiliterature t3PbOPbSOcesses thatestablish wtake placesolution filhigh as thesub-layers,

Fig. 4. Averaand 1.06 s.g.1, 2 and 4 h of soaking in 1.06 and 1.25 s.g. H2SO4 solution.

es in H2O content in the paste particlese soaking in H2SO4 solutionng to the 3BS formula generally accepted in thehe basic sulfate contains one water molecule:

4H2O. In order to disclose the chemical pro-proceed between H2SO4 and 3BS, we have tohether or not some processes of paste hydrationon plate soaking. During soaking the pH of theling the paste pores in the central plate zone C isH2SO4 is consumed in the outer and intermediateand hence 3BS and PbO may undergo hydration.

ge PbSO4 content formed in the plate during soaking in 1.25H2SO4 solution.


Fig. 5. Differ eraturesub-layers aft

On heatingmetric (DTand the sam

Fig. 5 pferential wintermediaand 4 h of stively.

The foll

The DTGing featu

Fig. 6. WeighH2SO4 solutiential thermogravimmetric (DTG) curves of the weight losses with temper 1 and 4 h of soaking in 1.06 and 1.25 s.g. H2SO4 solution.the samples during the differential thermal gravi-G) measurements this hydrating water evaporatesple loses weight

resents the obtained DTG curves giving the dif-eight losses on temperature increase for the outer,te and central sub-layers of samples taken after 1oaking in H2SO4 with 1.06 and 1.25 s.g., respec-

owing conclusions can be drawn from this figure:

curve for the 3BS paste immediately after cur-res a great low-temperature (200300 C) and a

t losses for the three sub-layers of the plate (AC), determined through TGA meason.

small higWithin tclearly tindicativparticles

The chaDTG cufirst houof soaki3BS cryof soakiparticlesincrease for the outer (A), intermediate (B) and central (C)

urements after different times of soaking in 1.06 and 1.25 s.g.

h-temperature (300400 C) characteristic peaks.he former temperature interval we can distinguishwo peaks: at 240 and at 270 C. These peaks aree of different types of water bonding in the 3BSof the paste.racteristic peaks for 3BS disappear from therves for the A and B sub-layers within ther of soaking, and for the C sub-layer after 4 hng in 1.25 s.g. H2SO4 (Fig. 5a and b). Thestals disintegrate under acid attack. After 1 hng, the C sub-layer still contains some 3BS.


Fig. 7. Average weight losses for the samples, determined through TGAmeasurements, as a function of time of soaking in 1.06 and 1.25 s.g. H2SO4solution.

It is evident from Fig. 5c and d that during soaking in 1.06s.g. H2SO4 solution, the characteristic peaks for 3BS arepreserved, though less intensive, even after 4 h of soaking.3BS crystals remain not much affected by sulfation.

Fig. 6 shows the weight losses (as measured by thermalgravimmetry (TG)) for the three sub-layers on heating thesamples after different times of soaking. When the plates aresoaked in 1.06 s.g. H2SO4 solution (Fig. 6a), the weight lossesof sub-layersA andB decrease slightly. The weight loss of the

Fig. 8. DSC

central sub-layer C after 4 h of soaking is greater even thanthat of the cured paste. This indicates that some hydrationprocesses take place in the central sub-layer of the platesduring soaking. Probably, the PbO and 3PbOPbSO4H2Ophases undergo hydration.

Fig. 6b presents the weight losses for the three sub-layerson heating the samples soaked in 1.25 s.g. H2SO4 solution.After 4 h of soaking the weight losses for the three sub-layersare almost the same (0.4%). Despite the still high H2SO4concentration (1.105 s.g., Fig. 1), no sulfation of PbO pro-ceeds or, if any, it proceeds at a very low rate. Fig. 5 evidencesthat the characteristic endothermic peaks for 3BS disappearfrom the curves for the A and B sub-layers after 1 h of soak-ing in 1.25 s.g. H2SO4, i.e. in these layers the 3BS phasehas decomposed. The same effect is also observed in the Csub-layer after 4 h of soaking. On the other hand, Fig. 6 in-dicates that all three sub-layers contain H2O, though in verysmall amounts. Hence, the oxides and basic lead sulfates inthe soaked pastes have undergone hydration and have beenisolated from direct contact with the H2SO4 solution.

Fig. 7 presents the average weight losses of the samplesas a function of time of soaking. On comparing the curves inFigs. 7 and 4 it can be seen that they are opposite in profile.The more sulfated the paste (Fig. 4), the smaller the waterloss (Fig. 7), i.e. the lower the hydration of the oxides in thepaste.curves for samples taken from the three sub-layers across the plate thickness after 1 and 4 h of soaking in 1.06 and 1.25 s.g. H2SO4 solution.


3.5. Investigation of the dehydration phenomena in thepastes by differential scanning calorimetry (DSC)

On heating the samples at linearly increasing temperaturethe amount of evaporating water from the samples was mea-sured through determining the energy of dehydration. Fig. 8presents the DSC curves for samples taken from the threesub-layers of the plate after 1 and 4 h of soaking in 1.06 s.g.H2SO4 solution (Fig. 8a and b) or in 1.25 s.g. H2SO4 solution(Fig. 8c and d).

The basic endothermic peak of 3BS dehydration occursbetween 170 and 300 C and features two characteristic peaksat 240 and 270 C, respectively (Fig. 8ac, sub-layer C). Asharp peak appears at 330 C, which reflects the energy formelting the lead that has remained unoxidized during thecuring process. In the temperature region between 300 and400 C, two small endothermic peaks are observed with de-hydration efor the PbDTG curvesame phendrated oxid

Fig. 8c a3BS havesub-layers,instead. Thfrom the oxin the paste(see next p

The dehpaste werethe averagepresented imuch the slosses as de

Fig. 10from the Dtermined frchemicallytained depebeginning o

Fig. 9. Averafunction of tim

Fig. 10. Average dehydration energy (DSC measurement) versus averageweight loss (TGA measurement) on heating samples of pastes soaked in1.06 and 1.25 s.g. H2SO4 solution.

we have determined that the dehydration energy for the 3BSpaste is equal to 3.2 kJ/g (H2O) in the paste. Fig. 10 shows

that at high degrees of paste sulfation, when soaked ins.g. H2SO4 solution, the values for the dehydration en-lie below the straight line. The slope of the new linen through these points is steeper. This indicates that aer amof theBS crylated

ehydraan attarbone withset toatmosl scanydrocented ie DScarbos betw

1. DSC curves for: cured paste, cured paste after 1 month stay in air,paste after 3 h stay in humid CO2 atmosphere, hydrocerrusite.nergy lower than 1.5 J/g (Fig. 8a and b). Exceptpeak, the DSC curves (Fig. 8) are similar to thes (Fig. 5), which means that they both reflect theomena the evaporation of water form the hy-es and basic lead sulfates.nd d shows that after the characteristic peaks for

disappeared from the DSC curves for the threesome wide but shallow endothermic peaks appearey are due to the evaporation of the hydrating waterides and the hydrated PbOPbSO4 (1BS) formedas an intermediate product of the sulfation of 3BS

aragraph).ydration energies for the three sub-layers of thesummed up and divided by three in order to obtain

energy of dehydration. The obtained values aren Fig. 9. The energy curves in Fig. 9 look veryame as the curves in Fig. 7 reflecting the weighttermined through TGA analysis.presents the dehydration energy as determinedSC curves versus the water loss on heating as de-om the TGA curves. The dehydration energy forprepared 3BS is also given in the figure. The ob-ndence yields a straight line passing through thef the coordinate system. From the slope of this line

ge dehydration energy for the samples of soaked pastes as ae of soaking in 1.06 and 1.25 s.g. H2SO4 solution.

also1.25ergydrawgreattionthe 3capsuthe d

Intain ca platthenCO2entiathe hprese

Thof depeak

Fig. 1curedount of energy should be introduced for dehydra-highly sulfated paste after the disintegration ofstals. This may mean that the hydrated oxides arein PbSO4 and hence more energy is required fortion of these hydroxides.empt to determine whether the cured pastes con-ates and what is their influence on the DSC curves,cured 3BS paste was left in the air for 1 month andDSC analysis. Another plate was left in a humidphere for 3 h and then analyzed through differ-

ning calorimetry. And finally, the DSC profile ofrussite was plotted. The obtained DSC curves are

n Fig. 11.C curve for hydrocerussite features a basic peaknation between 300 and 420 C, and two smallereen 230 and 300 C. As the DSC curve for the


Fig. 12. Aver 4 solutcured paste.

cured pastethe temperis no proceand 380 Cpeak for hycured pasteis not the cin the air abonation pper temperfor 3BS as270 C intoatmosphere

3.6. Changplate soaki

The chaing soakingwere followcompositiointensities(d = 0.281PbOPbSOand Pb (d =of the charsus the sumage phase composition of the paste after soaking in 1.25 or 1.06 s.g. H2SOfeatures two very small peaks (below 2 J/g) inature range between 300 and 420 C, and theress leading to energy consumption between 360(where the maximum of the basic endothermic

drocerussite occurs), it can be concluded that thes used in our experiment are not carbonated. Thisase, however, after prolonged stay of the platesnd in CO2 atmosphere. Then a process of car-roceeds which is reflected in the increased up-ature limit of the characteristic endothermic peakwell as by the merger of the peaks at 240 anda single peak for the paste that had stayed in CO2.

es in phase composition of the pastes duringng

nges in phase composition of the cured pastes dur-in 1.06 or 1.25 s.g. H2SO4 solution for 1, 2 or 4 hed through X-ray diffraction analysis. The phase

n of the pastes was determined from the relativeof the characteristic diffraction lines for -PbOnm), -PbO (d = 0.308 nm), 3BS (d = 0.326 nm),4 (1BS) (d = 0.296 nm), PbSO4 (d = 0.380 nm)

0.285 nm). The relative intensity is the intensityacteristic diffraction line for a given phase ver-

of the intensities of the characteristic lines for

all phases ipaste comp3BS: 17.0%above com

Fig. 121, 2 and 4 hDuring plaand with 3H2SO4 conphase withsoaked in 1formed areof the 1BSformed inof the porecross-sectio

3.7. Changpaste durin

The resuAfter 4 h ofand the totradius beinvolume ofthe cured pthe total poion for 1, 2 or 4 h. CP is the phase composition of the initialn the sample. The phase composition of the curedrises the following crystal phases: -PbO: 66.1%,, -PbO: 14.0% and Pb: 2.3%. The paste with the

position was subjected to H2SO4 attack.presents the phase composition of the paste after

of soaking in 1.06 or 1.25 s.g. H2SO4 solution.te soaking H2SO4 reacts with -PbO and -PbO,BS forming mainly PbSO4 and 1BS. When thecentration is 1.25 s.g., PbSO4 is the predominantabout 15% of 1BS as well. When the plates are.06 s.g. H2SO4 solution, the quantities of PbSO4commensurable with those of 3BS and the amountphase is about 8%. As the above substances are

three different pH regions, it follows that the pHsolution in the different parts across the plate

n is different.

es in BET surface and porosity of the 3BSg soaking in 1.25 s.g. H2SO4 solution

lts of these investigations are presented in Fig. 13.soaking the BET surface area decreases by 35%,

al pore volume by almost 60%, the mean poreg reduced from 0.20 to 0.07m. As the molarPbSO4 is greater than that of the components ofaste, and especially of PbO, sulfation will reducere volume of the paste.


Fig. 13. (a) Pore volume distribution by pore radius for the cured pastes and after soaking in 1surface of pastes immediately after curing (CP), and after soaking in 1.25 s.g. H2SO4 solution fo

3.8. Structure of the paste after soaking

3.8.1. Structure of the outer zone of the plate aftersoaking

Fig. 14 shows the paste structure and the crystal morphol-ogy in the outer plate zones after 2 h of soaking in 1.25 s.g.

Fig. 14. SEMouter sub-laystructure of thtacting the bu

H2SO4 solture of the p(Fig. 14a) areacted pashave formesolution ofprocess of PObviously,tallization cpaste, whic

3.8.2. Strusoaking

SEM pis.g. H2SO4of the pastebut a procePbO particof the crysparticles ar

(Fig. 1

. Strug. 16 s, wherith w1BS

3.8.3Fi

zone

tals wmicrograph of the structure and crystal morphology of theer of a plate soaked in 1.25 s.g. H2SO4 solution for 2 h: (a)e outer plate sub-layer; (b) crystals on the plate surface con-

lk solution.

or long nepart) are foform a layePbSO4 crythus the prH2SO4 traably, this pthe paste opores onlyides and oof the cureby the PbSpores..25 s.g. H2SO4 solution for 1, 2 or 4 h. (b) Changes in BETr different periods of time.

ution. The picture in Fig. 14b features the struc-late surface. The outer sub-layer is more compactnd consists of PbSO4 crystals and remnants of un-te particles (Fig. 14b). The large PbSO4 crystalsd as a result of recrystallization processes: dis-the small crystals and growth of large ones. ThebSO4 recrystallization was discussed in Ref. [15].the processes of sulfation and of PbSO4 recrys-hange substantially the pore system of the soakedh is also evident from Fig. 13a.

cture of the central zone of the plate after

ctures of the central zone C after soaking in 1.25solution for 1 h are presented in Fig. 15. Mostparticles have remained unaffected by sulfation,

ss of rounding off and merging of the 3BS andles has started, which is probably due to hydrationtal surface (Fig. 15b). Besides, some needle-likee observed with crystal shape characteristic for5a and b).

cture of the intermediate plate zonehows pictures of the paste in the intermediate platee there are pores with large radii. PbSO4 crys-ell pronounced walls, edges and apexes (Fig. 16a)

edle-like crystals of 1BS (Fig. 16c, upper rightrmed on the pore walls. The PbSO4 crystals mayr over the pore walls. The distance between the

stals in this layer may reach membrane sizes andocess of sulfation may stop because of impedednsport through the membrane pores. Most prob-rocess is responsible for the slowed sulfation ofn soaking. Water passes through the membraneand the formation of hydrates of the lead ox-

f the basic lead sulfates occurs in those regionsd paste that are isolated from the H2SO4 solutionO4 membrane formed on the surface of the large


Fig. 15. StrucH2SO4 soluti

3.8.4. Struafter soaki

Fig. 17grid was stacross its th

The pasthe corrosithe grid durcorrosion lthe metal sat its interf

Fig. 18 shas reactedsection ofmetal grainindividuallization pro

Fig. 18cPbSO4 laywhich havesurface ofPbSO4 parof H2SO4 v

Fig. 19is small. Tture of the central plate zone after 1 of soaking in 1.25 s.g.on. The layer is but very slightly affected by sulfation.

cture of the paste/grid interface obtainedng of positive plates in H2SO4 solutionpresents pictures of the interface structure. Theretched to allow a better view of the sub-layersickness.

te/grid interface consists of the metal surface withon layer (CL) formed as a result of oxidation ofing plate curing and the paste layer adjacent to theayer. The CL comprises PbO at its interface withurface and a partly hydrated lead oxide sub-layerace with the paste [14].hows SEM pictures of the corrosion layer, whichwith H2SO4. The grid was stretched and the cross-the corrosion layer and its connection with thes can be seen in Fig. 18a and c. Fig. 18b featuresPbSO4 particles, formed as a result of recrystal-cesses, and small PbSO4 nuclei.and d shows a profile and en face views of the

er comprising large elongated shapeless particlesformed along the path of the H2SO4 flow on the

the CL. The formation of this particular type ofticles was found to occur when the concentrationersus Pb2+ is very high (or vice versa) [15].

illustrates the case when the thickness of the CLhe H2SO4 flow reacts with this thin CL over the

Fig. 16. SEMlarge pores. P

metal grainis composeof segregatto their boCa in thisonto whichtal shapes (in the intererns are foand the memicrograph of the intermediate plate sub-layer containingbSO4 crystals form a layer on the walls of the large pores.

s and the inter-grain layers. The inter-grain layerd of (Pb(1x)Snx)3Ca and is obtained as a resultion of Sn and Ca from the bulk of the metal grainsundaries [13,16]. The increased concentration oflayer facilitates the formation of CaSO4 nucleiPbSO4 is deposited and grows into regular crys-

Fig. 19a). When, however, Sn alone has segregated-grain layer, it dissolves during soaking and cav-rmed in the inter-grain space between the pastetal surface (Fig. 19b). These caverns impair the


Fig. 17. StrucCL for corros

contact pasbe conductof a thick cfully sulfatbe impededlow, the cofor the life

Fig. 20 pby a highlyPbSO4 crypicture of tent sizes. Ihydration apores are pbrane), thelayer (Fig.

3.9. Mechasoaking of

Liptay awith one atermined c

tained pastes until a stoichiometric ratio H2SO4/PbO = 1 wasreached. This ratio corresponds to the full consumption of

itial reagents for the reaction expressed by the follow-toichio

+ H2phasely aftented iositio4/PbO

g. 21s thatllowi

+ H

Pb2(Pb

PbSOmaximwherat H2letelythe ining s

PbO

ThediatepresecompH2SO

Fiversu

the fo

4PbO

3PbO

PbO

The33%,Evencompture of the grid/paste interface: M stands for the metal surface;ion layer; P for the paste that is partially sulfated.

te/grid. Hence, the process of plate curing shoulded under such conditions that allow the formationorrosion layer, which would prevent it from beinged and thus the access of H2SO4 to the metal will. As the rate of corrosion of PbSnCa grids is verynditions of curing of such plates play a key roleof the batteries.resents micrographs of an interface zone reacheddiluted H2SO4 flow. Only at some sites, small

stals have formed (Fig. 20a). Fig. 20b shows ahe paste layer contacting CL with pores of differ-n the zones with small pore radii the products ofnd sulfation fill up these small pores. When thelugged by the products of soaking (PbSO4 mem-interface looks like a continuous (uninterrupted)20b).

nism of the reactions that proceed during3BS pastes

nd Sors [14] mixed increasing amounts of H2SO4nd the same amount of leady oxide. They de-ontinuously the phase composition of the ob-

that take plThe cur

3BS, and wmass. The rof the PbOpores. TheFig. 21. Thplate, becaas a resultThe SEM pthe paste arates in theformation oof the paste

The DSthat somethe paste. Pand the obexample th

3PbO Pb 3Pb

3Pb(OH)2 2Pb

Part of the

Pb(OH)2 metric equation:

SO4 = PbSO4 + H2O (1)composition of the paste was determined imme-r its preparation and 24 h later. Based on the datan Ref. [14] we plotted the dependence of phasen of the paste as a function of the increasing

ratio from 3 to 100% (Fig. 21).indicates that on increasing the amount of H2SO4of PbO, the successive reactions represented by

ng general chemical equations proceed:

2SO4 3PbO PbSO4 H2O (2)

SO4 H2O + H2SO4O PbSO4) + H2O (3)

4 + H2SO4 2PbSO4 + H2O (4)um amount of 3BS is formed at H2SO4/PbO =

eas at H2SO4/PbO = 75% mostly 1BS is formed.SO4/PbO = 100%, the paste does not transformto PbSO4. Such is the picture of the processes

ace during paste preparation.ed paste is a porous mass composed of PbO and

hen soaked, H2SO4 gets into the pores of thiseactions of sulfation proceed between the surfaceand 3BS particles, and the H2SO4 in the paste

se processes are similar to the ones presented ine H2SO4/PbO ratio decreases in the depth of theuse part of the H2SO4 reacts and water is formedof the sulfation of the PbO, 3BS and 1BS phases.ictures evidence that the processes of sulfation of

nd of the paste/grid interface proceed at differentdifferent parts of the plate volume, and lead to thef different phases in the different micro-regions.

C, TGA and DTG curves in Figs. 5, 6 and 8 showhydration processes proceed during sulfation ofrobably, PbO, 3BS and 1BS are hydrated first,

tained hydrated products undergo sulfation, forrough the following reactions:

SO4 H2O + 3H2O(OH)2 PbSO4 H2O (5)

PbSO4 H2O + H2SO4(OH)2 PbSO4) + 3H2O (6)Pb(OH)2PbSO4 is dehydratedPbSO4 PbO PbSO4 + H2O (7)


Fig The gr

the 1BS phother part i

Pb(OH)2 The great aafter soakinreaction ofthe reaction

The ratiand sulfatiodepend onis smaller tH2SO4 indration wilHence, micfates will bpores havepores willtion of theof the hydrthese microface (Figs.

On commediatelyin Fig. 21)processes tcontent of

allizats.. 18. SEM micrographs of the corrosion layer that has undergone sulfation.

ase being registered by X-ray diffraction, and an-s sulfated further:

crystplatePbSO4 + H2SO4 2PbSO4 + H2O (8)mount of PbSO4 in the A and B sub-layers eveng in 1.06 s.g. H2SO4 solution, indicates that thesulfation of Pb(OH)2PbSO4 proceeds faster thanof dehydration.

o between the rates of the reactions of hydrationn of the lead oxide and of the basic sulfates will

the radii of the paste pores. If the mean pore radiushan a certain critical value, the diffusion flow ofthe pores is very small and the reactions of hy-l proceed at a higher rate than those of sulfation.ro-volumes of hydrated oxides and basic lead sul-e formed (Fig. 20b). On the contrary, when thelarge radii, the diffusion flow of H2SO4 in thebe large and the rate of the reactions of sulfa-various hydrates will be much higher than thatation reactions, and mostly PbSO4 will form in-regions of the paste and of the paste/grid inter-14, 16 and 18).paring the phase compositions of the paste im-after curing and after 24 h of soaking (presented, it becomes evident that some recrystallizationake place in the paste, as a result of which thecrystal PbSO4 increases from 8 to 42%. Such re-

3.10. Inulife perform

Three ccharge. Allcalculatedpresents ththe batterie

The conand formatof soaking.have longeThe time obasic proceDuring thisformed.

3.11. Inuoperation m

In a prepastes we1.15 or 1.2the batterie[6]. In the pid has been stretched to tear off the corrosion layer.

ion processes proceed also during soaking of theence of the soaking processes on battery cycleance

apacity tests were performed at 20 h rate of dis-batteries exhibited over 100% of the rated capacityat 50% utilization of the PbO2 active mass. Fig. 22e capacity versus cycle number dependencies fors under test.centration of the H2SO4 solution during soakingion exerts a stronger influence than the durationThe batteries soaked in 1.06 s.g. H2SO4 solution

r cycle life than those soaked in 1.25 s.g. H2SO4.f soaking has a weaker effect on battery life as thesses are completed within the first hour of soaking.time the three zones across the plate thickness are

ence of grid alloy, soaking conditions andode on battery cycle life

vious investigation of ours on soaking of 3BSestablished that the cells soaked and formed in5 s.g. H2SO4 solutions have longer cycle life thans soaked and formed in 1.05 s.g. H2SO4 solutionresent investigation, we have established that the


Fig. 19. Structhin: (a) H2Sforming PbSOthe paste at so

batteries socle life thasolution.

What wtery tests inence the ba

Fig. 21. PhasThe curves arture of the grid/paste interface when the corrosion layer is veryO4 reacts with the inter-metalgrain layer of (Pb(1x)Snx)3Ca

4 crystals; (b) caverns form between the corrosion layer andme sites.

aked in 1.06 s.g. H2SO4 solution has longer cy-n those soaked and formed in 1.25 s.g. H2SO4

ere the conditions of plate production and of bat-the above investigations and how did they influ-

ttery cycle life performance?

e composition of pastes prepared with different amounts of H2SO4 vs. PbO. The vae plotted using data reported in Ref. [14].

Fig. 20. Struc(a) the grid hacorrosion laycontaining po

(a) In thegrids aPbSnCthe strulayer/plues 100% on the abscissa corresponds to H2SO4:PbO = 1:1.

ture of the interface accessed by a highly diluted H2SO4 flow:s been stretched before the SEM observations to tear off the

er; (b) structure of the interface grid/pate of a soaked plateres with radii of different sizes.

study reported in Ref. [6] we used PbSbSnAsnd in the present investigation the grids are ofaAl alloy. The different grid alloys used influencecture and properties of the interface grid/corrosionaste. The corrosion layer formed during curing on


Fig. 22. Battery capacity vs. number of chargedischarge cycles for batteriessoaked and formed in 1.06 or 1.25 s.g. H2SO4 solution.

the PbSnCa grids is thinner than that on the PbSbSn grids.The former CL is more easily sulfated during soaking.This affects the structure of the interface, which may limitthe cyc

(b) In ourfated pthan thwas ducompothe struThe PAmine thtoo.

(c) The tewere c

DIN43end-of-with cubatterieprogramchargelife critof their

The above comparison of the results indicates that theH2SO4 concentration for plate soaking and battery forma-tion should be selected taking into account the grid alloy andthe type and application of the batteries in order to ensureoptimum cycle life performance.

Acknowledgements

The present research was sponsored by the Advanced LeadAcid Battery Consortium (ALABC), a program of the In-ternational Lead Zinc Research Organization, Inc. (ILZRO).The authors want to extend their special thanks to both orga-nizations as well as to Dr. P. Moseley for his support for thepresent work.

References

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. Pavlo

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1997) 8. Pavlources. Lipta. Pavlo. Bourdle life of the battery.earlier investigation [6] the percent share of sul-aste after 1, 2 and 4 h of soaking was smallerat of the sulfated paste in the present work. Thise to the different H2SO4/paste ratio. The phasesition of the paste during plate formation affectscture of the lead dioxide active mass obtained.M structure is one of the factors that deter-e capacity of the battery and thus its cycle life,

sts of the batteries in our previous work [6]onducted according to the SLI test protocol539/2, cycling was performed at 40 C and thelife was determined through a CCA test at18 Crrent I = 5 C20 A. In the present investigation thes were cycled according to the traction battery test

at 25 C, 3 h rate of discharge and 115% over-versus the preceding discharge cycle. The end-of-erion was when the batteries failed to deliver 75%rated capacity.

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Processes taking place in the paste of lead-acid battery plates during soaking prior to formation and their influence on battery performanceIntroductionExperimentalPlate preparationInvestigation of the processes during plate soakingBattery cycle life tests

Experimental results and discussionChanges in H2SO4 concentration during plate soakingZonal processes during plate soaking forming different sub-layers across the plate thicknessChemical composition of the three sub-layers across the thickness of the plates soaked in 1.06 and 1.25 s.g. H2SO4 solutionChanges in H2O content in the paste particles during plate soaking in H2SO4 solutionInvestigation of the dehydration phenomena in the pastes by differential scanning calorimetry (DSC)Changes in phase composition of the pastes during plate soakingChanges in BET surface and porosity of the 3BS paste during soaking in 1.25 s.g. H2SO4 solutionStructure of the paste after soakingStructure of the outer zone of the plate after soakingStructure of the central zone of the plate after soakingStructure of the intermediate plate zoneStructure of the paste/grid interface obtained after soaking of positive plates in H2SO4 solution

Mechanism of the reactions that proceed during soaking of 3BS pastesInfluence of the soaking processes on battery cycle life performanceInfluence of grid alloy, soaking conditions and operation mode on battery cycle life

AcknowledgementsReferences

artigo de baterias chumbo ácido

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