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STORAGE BATTERIES
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Formation Temperature and Cold Cabacity
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THOMAS C. LYNES' AND FRANK HOVORKA
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Western Reserve University, Cleveland, Ohio
LELAND E. WELLS Willard Storage Battery Company, Cleveland, Ohio
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ACTORS affecting the initial cold capacity of containerformed SLI storage batteries have been investigated, a p e cially those causing variability in routine cold-discharge capacities. Length of standing on open circuit in charged and discharged condition was studied; length, rate, and temperature of charging; length, rate, and temperature of previous discharges; and conditions of discharging. I n battery preparation, charging temperature proved to be most significant; in testing, achieving correct mean temperature at start of cold discharges. Only two charging temperatures (SO" and 115' F.) were investigated. Regular production type, 80-100 ampere-hour SLI batteries were used throughout. Critical influence on cold capacity and other features of battery performance is exerted by the temperature at which unformed or discharged active material is transformed into charged active material. Formation at 80' F. provides much better negative performance from pasted SLI plates than formation at 115' F.e.g., 50% more cold capacity. On the other hand, the 80" F. formation produces somewhat poorer positive plates than formation a t 115' F. Marshall (8)indicates that fewer life cycles are obtained from batteries formed at the lower temperature; negatives formed at low temperature remain better through most of life test, though they drop below high-temperatureformed negatives toward the end. Likewise, shelf life is not so goad after the cool formation. But this shelf-life effect is largely reduced by cycling the batteries before they are placed on the shelf test; in any cme, it applies only during the first few weeks on that test (Figure 1). However, this relatively slight effect on life is, for most purposes, overshadowed by the large increase in cold capacity obtained by lowering the formation temperature. The influence of formation temperature applies specifically during actual charging of active material, but not during mere passage of charging current between fully charged plates. Thus the temperature of mix charge or overcharge has little or no influence on initial cold capacity; Hatfield (1)indicates that life test, as well as initial cold capacity performance, improves aa the formation temperature of negative plates is lowered. Both Marshall and Hatfield call attention to the increased formation input required as the formation temperature is lowered. Lowering the charging temperature improves the deep capacity only slightly.
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EFFECT OF CHANGING TEMPERATURE
Formation at temperatures as high as 115' F. effects a major reduction in cold capacity which is not appreciably recovered by a series of cycles with 80" F. recharges (Figure 2). The capacity
Figure 1. Influence of Formation Temperature on Specac Gravity of 80' F. Open-Circuit Shelf Test Ainwe, d d d ; below, after 8re initid aapaaity a7ale..
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776
Present addreas, National L e d Company, Brooklyn,
N. Y.
August, 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
PTZ
Charging SLI lead storage batteries at 80' F. results in much greater cold capacity than at 115' F. but decreases life somewhat. Controlled charging temperature materially reduces the cold-capacity variability.
of batteries formed at 80" F. is somewhat lower following 115' F. recharges, but much of this loss is recovered on return to the lower recharge temperature. In general, the influence on cold capacity of temperature during formation varies directly with the length of time at that temperature. However, if the formation period is divided into fourths, the relative effectiveness of temperature during these periods from greatest to least is second, first, third, and fourth. Tank-formed plates give better cold capacity than container-formed plates, apparently because of lower mean formation temperature. Likewise, the characteristically low cold capacity of the middle cells of container-formed batteries (e.g., 3.12 in comparison to 3.42 minutes for 90-ampere-hour O°F, type), resulta from the higher temperatures they CYCLF: NUMEER IT60 attain during formation. Also, the increase, 0 1$ 12 33 4 T after the first cold cycle, in the cold capacity of container-formed batteries with room-temperaFigure 2. Effect of Charging Temperature on Cold Capacity ture recharge indicates partial recovery of the (Successive Oo F., 100-Ampere Discharges) cold capacity lost as theresult of higher temperatures reached durine formation. In batteries formed at 80" and otherwise charged a t 115" F. there is a considerable drop in capacity after the first cycle. CAPACITIES OF W-1-80BATTERIES TABLE I. AVERAGE The effect of charging temperature on capacity may be illusAv. Capacity at Charging Temp. of: trated by Table I, which shows the capacities obtained from pairs Cycle 116' F. 80° F. batteries assembled from a single lot of materiala; one of W-1-80 I. bbour, 80° F. 4 72* 0 . 1 5 20) 4 . 6 7 * 0 . 1 7 (21) 11. Oo F.. 300-am 1:tTl-k 0 22 {17) 2 . 2 9 * 0.12 (19) battery from each pair was charged throughout at 116O and the III.20-hour, SO0 ?!I 1 9 , 7 2 6 0 61 20.26- 0 . 6 3 (21) other at 80" F. Capacity is expressed as arithmetic mean, vwiIV. Oo F 300-amp. 1 . 4 0 * 0 . 1 6 17) 2 . 4 1 * 0 . 2 3 (19) V. -Idd F., 300-amp. 0 . 9 6 * 0 . 1 2 20) 1 . 6 5 * 0 . 1 5 (21) ability as standard deviation; numbers in parentheses indicate P M S life ayclea 905* 86 (6) 831* 67 (6) the number of batteries involved in the computation.
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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 CHEMISTRY
AFTER RECHARGE
to-cycle variability, as standard deviation of individual batteries (regular factory production SW-1-92) from the battery's mean capacity, averages 0.23 minute; the standard deviation of all these batteries together from their mean is 0.42 minute. The corresponding values for laboratory-assembled batteries, the charging and discharging temperatures of which were carefully controlled, were 0.08 and 0.17. Careful laboratory control was employed to ensure that the electrolyte temperature a t the start of the cold discharges was uniform and correct. On 0 ' F. discharges immediately preceded by cold cycles, this control reduced the variability in cold capacity of individual batteries by 60%-from 0.20 t o 0.08 minute. Making the comparison in terms of groups of batteries assembled a t one time for one experiment, the control of discharge initial temperature by the laboratory reduced the standard deviation from the mean capacity of the group of batteries from 0.32 to 0.12 minute-a decrease in variability of over 60%.
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INITIAL
BATTERY
SPECIFIC
HW-1-100
1.286 1.260
Vol. 31, No. 8
COLD-CAPACITY VARIABILITY
y----K
In spite of the reduced capacity variability, cells (and hence batteries) have, a t the end of mix charge, an ingrained "personality" which cannot be eliminated by subsequent treatment. These innate differences are a property of the elements themselves, not of their environment, as indicated by interchanging the positions of weak and strong elements without affecting their performance. Cycling tends to decrease capacity variability. There still remains unexplained the relatively great variability in deep-capacity and life results, although the variability of both has been largely reduced by the control of formation temperature. Even with careful control we cannot eliminate all the cold-capacity variability of similarly prepared batteries, as Figure 2 shows. But in many cases we have been able to trace this variability t o differences between different lots of Figure 4. Effect of Open-circuit Standing on Specific Gravity and plates, though we do not know what causes this Cold Capacity, before and after 80' F. Shelf Test and Recharge difference. Cells and groups of batteries tested together usually change in the same direction between cycles and remain In routinelaberatory testing, the coefficient of variability (ratio in the same capacity order. A battery's performance represents of standard deviation to mean) of cold capacity of regular producan average of that of its cells, weighted by the weakest cell. tion batteries is 10 to 20% (somewhat less at 0" than at 10" F.). There is frequently considerable reserve capacity in a battery's To ascertain whether individual batteries tend to give coneiststrong cells, after a weak cell has limited the discharge. ently high or low capacities on the different test cycles, coefficients of correlation were obtained for 8W-1-95batteries between W-1-100
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various cold discharges; - that slight positive correlation exists between cold and deep discharges, and that the correlation between capacity and life tends to be negative. In other words, a given battery tends to give similar performance on similar cycles although there is considerablevariation from this principle; capacity on deep discharges is not closely related to that on cold discharges, and batteries giving good capacity performance usually do not last so long on life test as those giving poorer capacity. It would appear, then, that the larger the proportion of the plate taking part in the dischargerecharge cycle, the fewer cycles that plate can stand. With control of charging temperature and temperature a t the start of the cold dischargea, the coefficientof variability in initial cold-capacity resulte has been reduced to 8 or 4%. The cycle-
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Between 6-hour 6-hour 6-hour &hour 5-hour 1st Oo F., 300-amp. 1st 0' F 300-amp. 1st 00 F" amp. 1st 00 F" 300-amp. 1st 00 F::300-amp. 20410~1 20-hour 20-hour 20-hour 2nd Oo F 300-amp. 2nd Oo F:: 300-amp. 2nd 0" F 300-amp. IOo F.,'$OO-amp. -loo F., 300-amp.
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and 1st Oo F., 300-amp. 2O-hour 2nd 0 ' F., 300-amp. -loo F., 300-amp. K life c d e s P M S d e cycles 20-hour 2nd Oo F., 300-amp. -loo F., 300-amp. K life c des P M S 1iL cycles 2nd Oo F.. 300-amp. - 10" F., 300-amp. K lrfe c cles P M S d e cycles 10" F., 300-amp. K life c ole8 P M S liZ cycles K life c cles P M S 1iL cycles
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0 0 0 0
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0320 2662 0 1131 -0 0347 0.2783 0.6842 0 6697 0.0004 0 2032 0.4666 0 3417 -0.13a7 - 0 3968 0.8352 0.1664 -0.2680 - 0 1740 -0.1178
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INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1945
The electromotive force throughout the discharge, and not merely the position of the knee, is affected by cell strength and temperature of recharge. This is shown in Table I11 which gives the average voltage drop per cell from 5-second voltage during the cold discharge (W-D-90 batteries).
TABLE 111. DISCHARGE VOLTAQE DROP From 6-See. Voltage to That at: 30 BEC. 60 see. 90 4ec.
120 m e . 160 see.
180 seo.
Stronger Cells Room-temp. Warm reaharge recharge 0.02 0.08 0 06 0.08 0.08 0.13 0.11 0.17 0.15
0.244-
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Weaker Cells Room-temp. Warm reaharge recharge 0.03 0.04 008 0.08 0.10 0.14 0.18 0.1840.2140.8740.35+ Out
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-BATTERY TYEa
INITIAL SPECIFIC
GRAVITY
1.286 1.286 B 1.260 4
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T During cold dischargea, the positive and negative plate groups reflect intercell differences in dissimilar fashion. The positive voltages differ considerably (0.20 volt or more) but remain parallel; voltages of the negative plates (which almost invariably limit the cold discharges) are together a t the start of the discharge, but diverge and reach the discharge knee at different times. A positive cadmium voltage increase just before the discharge knee is observed following 115' F. charge, and is usually more pronounced in the stronger cells. Such a hump (shown on typical discharge curves in Figure 3) is absent Or very small after 80' F. recharge. The tendency to "hump" is present, though less pronounced, on the 20-hour discharge following 115' F. charge. If there is good capacity balance between positive and negative groups formed a t 115' F., the positive groups of similar batteries formed at 80' F. would limit the deep capacity. At 80' F. the formation voltage is distinctly higher (and increasingly so) than at 115' F. The open-circuit voltage a t 0' F. is higher after an immediately preceding recharge at 80' F. than after one at 115' F. The open-circuit voltage increases with cycling, especially with deep cycling. The positive cadmium voltage during a cold discharge is u n d e c t e d or slightly improved by increasing the temperature of formation and recharges; the negative cadmium voltage i s not changed during the early part of the discharge but reaches the discharge knee sooxier. High 5second voltage tends to be associated with high cold capacity and vice versa, especially for cycle-to-cycle changes. MISCELLANEOUS OBSERVATIONS
Electrolyte temperature above the plates gives a fair indication of mean cell temperature during cooling, but is not representative when the cell is being heated externally or by discharge. One deep cycle raises cold capacity, but a series of deep cycles lowers both deep and cold capacity. Shallow cycling before mix charge exerts slight influence on subsequent performance, but longer reversals during the latter part of formation do improve capacity, Lowered formation rates decrease capacity; higher rates increase cold and deep capacity somewhat, but lower cycling life. Cold capacity is not appreciably affected by differences in recharge from 110 t o 200% ampere-houm removed. Formation a t regular rates in finish gravity acid lowers capacity. ~~
BATTERIES WITH H~LRDENED TABLE IV. RECHARQING NEQATIVW Number Batteries Treatment 4 Cold cyde, recharged in orignal acid at finish rate 2 T w o oold cyolea. recharged in original acid a t 5nish rate 2 Cold oyole, triokle-aharged in water, doped
Time Min.' 4.01 4.28 4.60
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Figule 5. Effect on Cold Capacity of Decrease in Specifio Gravity Resulting from Open-Circuit Standing at 80' F.
Standing in charged or discharged condition up t o one month, followed by recharge, does not greatly d e c t the cold capacity; longer standing gradually lowers the subsequent cold capacity (Figures 4 and 5). Wood-insulated and rubber-insulated batteries self-discharge at first at about the same rate, but the rate of self-discharge decreases much more rapidly in the case of the wood-separator batteries, especially the negative plates of the latter. The slowest t o be affected by self-discharge, the woodinsulated batteries also offer mmt resistance to high-rate recharge; they gas more and reach higher temperature. The resistance to self-discharge is slightly greater in 1.260 than in 1.286 specific gravity electrolyte. The hardening of negatives, resulting from long open-circuit standing, yields t o reoharging in water or sodium sulfate more readily than to recharging in the battery's electrolyte (Table IV). Slight variations in initial electrolyte specific gravity have little effect on cold capacity. However, the cold capacity of a battery drops rapidly as the cells become partially discharged, whether by external or self-discharge (Figures 4 and 5). Here the relation between cold capacity and specific gravity is approximately
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INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
linear; about one fourth of the capacity loss is due to discharged plate condition and three fourths to reduction in available electrolyte. Elimination of liners improves cold capacity slightly. Preformation standing for more than a few minutes lowers initial capacity, Low cold-discharge 5-second voltages usually indicate low cold capacity. The final temperature after a cold discharge is merely the result of P R T losses during discharge. High-rate discharges involve the plate surfaces principally. True battery resistance cannot be calculated directly from voltage drop during discharge or from discharge thermal energy changes. Cadmium voltage readings during discharge have been found reliable and reproducible. The formation temperature affects the structure of the plate active material. The sponge-lead surfaces through the negative plates after 80" F. formation are covered with fine lead hairs; after 115" F. formation, however, these surfaces are coated with much larger, rounded particles of lead. The latter are stronger and more resistant to changes in plate shape with cycling and to abrasion by gassing than the finer particles formed at low temperature, but offer much less surface t o the acid during high-rate discharges. The difference in appearance, under the microscope, of the plate surface effected by the temperature of formation persists after several cycles with recharges at either high or low temperatures. Greatly improved cold capacity with only minor decreases in
Vol. 37, No. 8
life may be obtained by keeping the plates cool during formation, especially in the first half of the forming period. I n tank formation, this may be accomplished with circulating electrolyte and lead cooling coils. Although water sprays, spacing of batteries during charging, and air cooling with fans are helpful in container formation, the best procedure for increasing cold capacity involves immersing the batteries nearly to the top of the container throughout the formation period in a circulating cold water bath. This also eliminates the need for a rest period or low-rate charging period during formation to keep the batteries from becoming overheated and permits increased formation rates. ACKNOWLEDGMENT
The contributions of C. C. Rose and A. C. Zachlin, of the Willard Storage Battery Company, t o the work reported here is gratefully acknowledged. LITERATURE CITED
(1) Hatfield, J. E.,and Brown, 0. W., Tram. Electrochem. SOC.,72, 361-87 (1937). (2) Marshall, E.G.,Part 11, unpub. doctor's dissertation, Indiana Univ., 1932. BASBDon part of a diasertation submitted by T. C. Lynu, to the Graduate Sohool of Western Reserve University in partial fulfillment of the requirements for the Ph.D. degree.
Noncatalvtic Esterification of Octvl Alcohol and Polvbasic Acids PHILIP L. GORDON AND RUTH ARONOWITZ Capitol Paint and Varnish Works, 47 Rodney Street, Brooklyn, N. Y .
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HE advent of synthetic rubber and high polymers has led to a widespread interest in higher boiling esters as plasticizers and as copolymerizing modifiers in the case of the unsaturated compounds. A well-known example of the plasticizing type of ester is dioctyl phthalate, which is widely accepted as a softener for polyvinyl resins and other high polymers. Esters of unsaturated acids have been used as copolymers with vinyl acetate, vinyl chloride, styrene, etc., to yield valuable end products (9).
The conventional method for preparation of these esters is the reaction of the acid with a n excess of alcohol in the presence of an acid catalyst, with subsequent purification of the ester by vacuum distillation. Since the most important factor in influencing the direction of esterification reactions is the removal of water of reaction, a number of specialized procedures have been evolved to
A method for the esterificationof octyl alcohol with polybasic acids under a column of desiccant material is described. Comparisons are made with sulfuric-acid-catalyeed esterifications, and the noncatalytic method is found to have the advantages of slightly better yields and better color on the final product. The important factor in operating under this method is found to be a careful control of the reacting temperature. This procedure was satisfactory for the synthesis of decyl maleate, but an attempt to esterify butyl alcohol with phthalic anhydride in this manner proved unsuccessful.
accomplish this. Gilman ( 4 ) referred to a synthesis of ethyl oxalate, reported by Frankland and Astor, where the water was removed from the reaction by passing the condensed vapors through a flask containing fused potarrsium carbonate and returning the dried ethyl alcohol vapors to the reaction chamber. A similar method of producing diethyl tartrate was described by Cumming, Hopper, and Wheeler @). I n this case quicklime was used as the water absorbent, and benzene was added to the reacting materials to facilitate the removal of the water. A special apparatus for the removal of water in esterification was designed by Strumnikov (6) who used a n added inert liquid, such as benzene, to remove the water. Carney ( 1 ) patented a method for esterification in a rectifying column with one reactant in the vapor phase and the other in the liquid phase. I n this investigation the possibilities of synthesizing octyi esters of polybasic acids, using an overhead column filled with desiccant material, have been explored, with the object of finding a simple and efficient method for making these esters. PROCEDURE FOR OCTY L ACONITATE
The apparatus consisted of a single-neck 250-cc. flask with a thermometer well, attached to a 20-mm. column and water condenser as shown in Figure 1. The first esterification attempted was octyl alcohol and aconitic acid. The octyl alcohol was a technical grade of 2-ethylhexanol and the aconitic acid was also a commercial grade. The flask was loaded with 85.8 grams of octyl alcohol and 35 grams of aconitic acid, representing a lOyo excess of alcohol. The column was charged with 55 grams of
