W illa rd S to ra g e B a tte r y C o m p a n y , C le v e la n d , O h io
F
A C TO R S affecting th e in itial cold c ap acity of container- form ed SL I storage b a tte rie s have been in v estig ated , especially those causing v a ria b ility in ro u tin e cold-discharge capaci
ties. L ength of stan d in g on open circuit in charged an d dis
charged condition was stu d ied ; length, ra te , a n d tem p eratu re of charging; length, ra te , an d tem p e ratu re of previous discharges;
and conditions of discharging. I n b a tte ry p rep aratio n , charging tem p eratu re proved to be m o st significant; in testin g , achieving correct m ean tem p eratu re a t s ta r t of cold discharges. Only two- charging tem p eratu res (80° an d 115° F .) w ere investigated.
R egular production ty p e, 80-100 am pere-hour S L I b a tte rie s were used throughout.
C ritical influence on cold cap acity an d o th er featu res of b attery perform ance is exerted b y th e tem p e ratu re a t w hich unform ed or discharged active m aterial is transform ed in to charged active m a
terial. F o rm atio n a t 80° F . provides m uch b e tte r n eg ativ e per
form ance from p asted SL I p lates th a n fo rm ation a t 115° F .—
e.g., 50% m ore cold capacity. On th e o th er h an d , th e 80° F.
form ation produces som ew hat poorer positive p lates th a n form a
tio n a t 115° F . M arshall {%) indicates t h a t few er life cycles are o btained from b atteries form ed a t th e low er tem p e ratu re; nega
tiv es form ed a t low tem p e ratu re rem ain b e tte r th ro u g h m o st of life test, tho u g h th ey drop below h igh-tem perature-form ed nega
tives to w ard th e end. Likewise, shelf life is n o t so good after th e cool form ation. B u t th is shelf-life effect is largely reduced by cycling th e b a tte rie s before th e y are placed on th e shelf te s t; in an y case, it applies only d uring th e first few weeks on t h a t tes t (Figure 1). H ow ever, th is relativ ely slig h t effect on life is, fo r m ost purposes, overshadow ed by th e large increase in cold capac
ity o b tain ed by lowering th e form ation tem p e ratu re. T h e in fluence of form ation tem p e ratu re applies specifically d uring a ctu al charging of active m aterial, b u t n o t during m ere passage of charg
ing cu rren t betw een fully charged plates. T h u s th e tem perature- of m ix charge or overcharge h a s little or no influence on initial cold cap acity ; H atfield (1) indicates th a t life te s t, as well as initial cold capacity perform ance, im proves as th e fo rm ation tem p era
tu re of negative p lates is lowered. B o th M arshall a n d H atfield call a tte n tio n to th e increased form ation in p u t req u ired as th e form ation tem p e ratu re is lowered. Low ering th e charging tem p e ratu re im proves th e deep capacity only slightly.
E F F E C T O F C H A N G IN G T E M P E R A T U R E
F orm ation a t tem p eratu res as high as 115° F . effects a m a jo r reduction in cold cap acity w hich is n o t appreciably recovered b y a series of cycles w ith 80° F . recharges (F igure 2). T h e capacity
1 P r e s e n t a ddress, N a t i o n a l L e a d C o m p a n y , B r o o k l y n , N . Y .
776
August, 1945 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Charging SLI lead storage batteries at 80° F. results in m uch greater cold capacity th a n a t 115° F. b u t decreases life some
w hat. Controlled charging tem perature m aterially reduces th e cold-capacity vari
ability.
4-.00
S-.60
B attery Formed Recharged 80°F. 116°F.
171 115°K 0---0---o
172 116°F. +---
1---173 115°F. A ---
A---174 116 F. tr---*
---176 80°F.
176 80°F. * .--- x ---X
177 80°F. a ----o ----a 178 80°F. * ---a----u
zr.oQ
Z.60
e-.oo
of b atteries form ed a t 80° F . is som ew hat lowerfollowing 115° F . recharges, b u t m uch of this loss is recovered on re tu rn to th e lower recharge tem p eratu re. In general, th e influence on cold capacity of tem p eratu re during form ation varies directly w ith th e length of tim e a t th a t tem perature. H ow ever, if th e form ation period is divided in to fourths, th e relative effectiveness of tem p eratu re during these periods from g reatest to least is second, first, th ird , and fo u rth . T ank-form ed p lates give b e tte r cold capacity th a n container-form ed plates, apparently because of lower m ean form a
tion tem perature. Likewise, th e characteristi
cally low cold capacity of th e m iddle cells of container-form ed b atteries (e.g., 3.12 in com
parison to 3.42 m inutes for 90-am pere-hour ty p e), results from th e higher tem peratures they a tta in during form ation. Also, th e increase, after th e first cold cycle, in th e cold capacity of container-form ed b atteries w ith room -tem pera- tu re recharge indicates p a rtia l recovery of the cold capacity lost as th e resu lt of higher tem pera
tures reached during form ation. In b atteries
formed a t 80° and otherw ise charged a t 115° F . th ere is a con
siderable drop in capacity a fte r th e first cycle.
T he effect of charging tem p eratu re on capacity m ay be illus
tra te d by T able I, which shows th e capacities obtained from pairs of W -l-80 batteries assembled from a single lot of m aterials; one b a tte ry from each p air was charged th ro u g h o u t a t 115° and th e other a t 80° F . C apacity is expressed as arithm etic m ean, vari
ability as stan d ard deviation; num bers in parentheses indicate th e num ber of batteries involved in th e com putation.
3 0 0
A
U P E R B S 0°F
t7«0
1 — 3____ 1
CYCLE NUMBER 1 ___ I____!_
Figure 2. Effect of Charging Tem perature on Cold Capacity (Successive 0° F., 300-Ampere Discharges)
Ta b l e I.
C y c le
Av e r a g e Ca p a c i t i e s o p W -l-80 Ba t t e r i e s A y . C a p a c i t y a t C h a rg in g T e m p , of :
I. 5-h ou r, 8 0 ° F . I I . 0 ° F . , 3 0 0 - a m p . I I I. 2 0 -h o u r , 8 0 “ F . IV . 0 ° F . , 3 0 0 - a m p . V. - 10° F . , 3 0 0 - a m p . P M S life c y c le s
1 1 5 ° F . 4 . 7 2 * 0 . 1 5 (20) 1 . 6 1 * 0 . 2 2 (17) 1 9 . 7 2 * 0 . 5 1 (20) 1 .4 0 = * 0 . 1 5 (17) 0 . 9 6 * 0 . 1 2 (20)
9 0 6 * 85 (5)
8 0 ° F . 4 . 6 7 * 0 . 1 7 (21) 2 . 2 9 * 0 . 1 2 (19) 2 0 . 2 5 * 0 . 5 3 (21) 2 . 4 1 * 0 . 2 3 (19) 1 . 5 5 * 0 . 1 6 (21)
831 * 6 7 (5)
2 ?
» a.
H
to •<
5“®
5 S'
l_l s
•a .
n
'S.'sj B i
>
5
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I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 37, No. 8
cients of correlation were o b tain ed for SW-1-95 b atteries betw een th e different cap acity cycles.
August, 1945 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y T h e electrom otive force th ro u g h o u t th e discharge, an d n o t
m erely th e position of th e knee, is affected by cell stren g th and tem p eratu re of recharge. T h is is show n in T able I I I w hich gives th e average voltage drop per cell from 5-second voltage during th e cold discharge (W -D-90 batteries).
Ta b l e I I I . Di s c h a r g e Vo l t a g e Dr o p F r o m 5 -S e o . S tr o n g e r C e lls W e a k e r C e lls
V o l t a g e t o R o o m - t e m p . W a r m R o o m - t e m p . W a r m
T h a t a t: reo ha rg e r eoharge r e o h a rg e r e c h a r g e
3 0 s e c . 0 . 0 2 0 . 0 3 0 . 0 3 0 . 0 4
6 0 s e c . 0 0 5 0 . 0 8 0 06 0 . 0 8
9 0 se c. 0 . 0 8 0 . 1 3 0 . 1 0 0 . 1 4
1 2 0 s e c . 0 , 1 1 0 . 1 7 0 . 1 3 0 . 1 8 +
1 6 0 seo. 0 . 1 0 0 . 2 1 + 0 . 2 1 + 0 . 3 7 +
1 80 seo. 0 . 2 4 + O u t 0 . 3 6 + O u t
D uring cold discharges, th e positive a n d negative p late groups reflect intercell differences in dissim ilar fashion. T h e positive voltages differ considerably (0.20 v o lt o r more) b u t rem ain parallel; voltages of th e negative plates (which alm ost invariably lim it th e cold discharges) are to g eth er a t th e s ta r t of th e dis
charge, b u t diverge and reach th e discharge knee a t different tim es. A positive cadm ium voltage increase ju s t before th e dis
charge knee is observed following 115° F . charge, an d is usually more pronounced in th e stro n g er cells. Such a hum p (shown on typical discharge curves in Figure 3) is absent or very sm all after 80° F . recharge. T h e tendency to “h u m p ” is present, though less pronounced, on th e 20-hour discharge following 115° F . charge.
If there is good capacity balance betw een positive and negative groups form ed a t 115° F ., th e positive groups of sim ilar b atteries formed a t 80° F . would lim it th e deep capacity.
A t 80° F . th e form ation voltage is d istin ctly higher (an d in
creasingly so) th a n a t 115° F . T h e open-circuit voltage a t 0° F . is higher after an im m ediately preceding recharge a t 80° F . th a n after one a t 115° F . T he open-circuit voltage increases w ith cycling, especially w ith deep cycling. T h e positive cadm ium voltage during a cold discharge is unaffected or slightly im proved by increasing th e tem p eratu re of form ation an d recharges; th e negative cadm ium voltage is n o t changed during th e early p a rt of th e discharge b u t reaches th e discharge knee sooner. H igh 5- second voltage ten d s to b e associated w ith high cold capacity an d vice versa, especially for cycle-to-cycle changes.
M IS C E L L A N E O U S O B S E R V A T IO N S
E lectrolyte tem p eratu re above th e p lates gives a fair indication of m ean cell tem p eratu re during cooling, b u t is n o t representative when th e cell is being heated externally o r by discharge. One deep cycle raises cold capacity, b u t a series of deep cycles lowers bo th deep an d cold capacity. Shallow cycling before mix charge exerts slight influence on subsequent perform ance, b u t longer re
versals during th e la tte r p a rt of form ation do im prove capacity.
Lowered form ation rates decrease capacity; higher ra te s increase cold and deep capacity som ew hat, b u t lower cycling life. Cold capacity is n o t appreciably affected by differences in recharge from 110 to 200% am pere-hours rem oved. F o rm atio n a t regu
lar rates in finish g rav ity acid lowers capacity.
Ta b l e IV . Re c h a r g i n g Ba t t e r i e sw i t h Ha r d e n e d Ne g a t i v e s
N u m b e r T im e ,
B a t t e r i e s T r e a t m e n t M in .
4 C o ld c y c le , r e cha rg ed in o rig in a l a c id a t finish r a te 4 . 0 1 2 'I'w° oold c y c le s , re c h a r g ed in o rig in a l a c id a t fin ish r a te 4 . 2 8 2 C o ld c y c le , trio k le -c h a r g e d in w a te r , d o p e d 4 . 6 0
Figure 5. Effect on Cold Capacity of Decrease in Specific Gravity Resulting from Open-Circuit
Standing a t 80° F.
S tanding in charged or discharged condition up to one m onth, followed by recharge, does n o t greatly affect th e cold capacity;
longer stan d in g gradually lowers th e subsequent cold capacity (Figures 4 an d 5). W ood-insulated an d rubber-insulated b a tte r
ies self-discharge a t first a t ab o u t th e sam e rate, b u t th e ra te of self-discharge decreases m uch m ore rapidly in th e case of th e w ood-separator b atteries, especially th e negative plates of th e la tte r. T h e slowest to be affected by self-discharge, th e wood- in su lated b atteries also offer m ost resistance to high-rate re
charge; th ey gas m ore and reach higher tem perature. T he re
sistance to self-discharge is slightly g reater in 1.250 th an in 1.285 specific g rav ity electrolyte. T he hardening of negatives, result
ing from long open-circuit standing, yields to recharging in w ater or sodium sulfate m ore readily th a n to recharging in th e b a tte ry ’s electrolyte (T able IV ).
Slight variatio n s in in itial electrolyte specific g rav ity have little effect on cold capacity. However, th e cold capacity of a b attery drops rapidly as th e cells become p artially discharged, w hether by external or self-discharge (Figures 4 an d 5). H ere th e relation betw een cold capacity and specific grav ity is approxim ately
linear; ab o u t one fourth of th e cap acity loss is due to discharged p late condition an d th ree fourths to reduction in available elec
tro ly te. E lim ination of liners im proves cold cap acity slightly.
P reform ation stan d in g for m ore th a n a few m inutes lowers in itial cap acity . Low cold-discharge 5-second voltages usually indicate low cold capacity. T h e final tem p eratu re a fte r a cold discharge is m erely th e resu lt of I 2R T losses during discharge. H igh-rate discharges involve th e p late surfaces principally. T ru e b a tte ry resistance cannot be calculated directly from voltage drop during discharge or from discharge therm al energy changes. C adm ium voltage readings during discharge have been found reliable and reproducible.
T h e form ation tem p eratu re affects th e stru c tu re of th e p late active m aterial. T h e sponge-lead surfaces th rough th e negative plates a fte r 80° F . form ation are covered w ith fine lead hairs;
after 115° F . form ation, however, these surfaces are coated w ith m uch larger, rounded particles of lead. T h e la tte r are stronger an d m ore resistan t to changes in p late shape w ith cycling and to abrasion b y gassing th a n th e finer particles form ed a t low tem p erature, b u t offer m uch less surface to th e acid during high-rate discharges. T he difference in appearance, under th e microscope, of th e p late surface effected by th e tem p eratu re of form ation per
sists a fte r several cycles w ith recharges a t eith er high or low tem peratures.
G reatly im proved cold capacity w ith only m inor decreases in
life m ay be obtained by keeping th e p lates cool' d uring form ation, especially in th e first half of th e form ing period. In ta n k form a
tion, th is m ay be accom plished w ith circulating electrolyte an d lead cooling coils. A lthough w ater sprays, spacing of b a tte rie s during charging, and air cooling w ith fans are helpful in container form ation, th e best procedure for increasing cold cap acity in
volves im m ersing th e b atteries nearly to th e to p of th e container th ro u g h o u t th e form ation period in a circulating cold w a ter b ath . T h is also elim inates th e need for a re st period or low -rate charging period during form ation to keep th e b a tte rie s from becom ing o verh eated a n d perm its increased form ation rates.
A CK NO W L E D G M E N T
T he co n trib u tio n s of C. C. R ose a n d A. C. Zachlin, of th e Wil
lard Storage B a tte ry C om pany, to th e w ork rep o rted here is gratefully acknow ledged.
L IT E R A T U R E C IT E D
(1) H atfield, J . E ., an d B row n, O. W., Trans. Electrochem. Soc., 72, 361-87 (1937).
(2) M arshall, E . G ., P a r t I I , u n p u b . d o c to r’s d issertatio n , In d ian a U niv., 1932.
Ba s e d on part of a dissertation su b m itted b y T . C. L yn es to th e Graduate School of W estern R eserve U niv ersity in partial fulfillm ent of th e require
m ents for th e P h .D . degree.