Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1983-09-15
1985-11-26
Hearn, Brian E.
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429204, H01M 604
Patent
active
045554587
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electrolyte for a lead acid accumulator and to an accumulator using said electrolyte.
In conventional lead acid accumulators, it is well known that the electrolyte is an aqueous solution of sulphuric acid.
One known way of promoting deep discharges and of increasing the cycle lifetime of such batteries, is to add phosphoric acid to the electrolyte, and in particular to add orthophosphoric acid.
Such an electrolyte is described in French patent specification No. 642 145. The specification describes adding the phosphoric acid to the electrolyte in the form of orthophosphoric acid or in the form of substances which are transformed into orthophosphoric acid inside the accumulator, for example meta- or pyro-phosphoric acid.
It has nonetheless been observed that inserting such phosphoric acid can lead to various drawbacks. Thus accumulators using such an electrolyte provide lower energy density per unit mass than accumulators using an electrolyte which has no phosphoric acid. Further, forming such accumulators is difficult. Finally, during cycling, short ciruits can be set up by migration of the positive active material, thereby reducing the service lifetime.
Preferred embodiments of the present invention mitigate these drawbacks.
The present invention provides an electrolyte for a lead acid accumulator, in which the electrolyte comprises an aqueous solution of sulphuric acid and contains phosphoric acid, characterized in that the electrolyte includes 5 to 30 grams per liter of pyrophosphoric acid and 5 to 50 grams per liter of orthophosphoric acid, the total quantity of phosphoric acids contained in the electrolyte being equal to or less than 60 grams per liter.
The invention also provides lead acid accumulators including the above-defined electrolyte.
Thus the Applicant has discovered, surprisingly, that simultaneously adding both ortho- and pyro-phosphoric acid to the sulphuric acid avoids the above-mentioned drawbacks which are observed when only one of said phosphoric acids is added on its own.
This means that a greater energy density is obtained, and that forming is easier, giving a longer initial discharges and a longer lifetime.
Preferably the quantities of orthophosphoric acid and of pyrophosphoric acid present in the electrolyte are substantially equal.
Advantageously they are present at a concentration of about 10 grams per liter.
The advantages which result from applying the invention can be seen by examining the test results which appear in the following table and which are expressed as follows: number of cycles for which no short circuit (CC) was observed. phosphoric acid in the electrolyte.
The tests were performed on sealed lead acid accumulators having 6 negative plates and 5 positive plates each. There were 100 grams of positive active material and the total capacity was 10 Ah. The grids of the positive and the negative plates were made from a lead-calcium alloy having 0.09% calcium.
The electrolyte included 94 cm.sup.3 of H.sub.2 SO.sub.4 at a density of 1.26 before forming, and it impregnated a separator made of glass felt.
Discharging was performed at a constant current of 2 A.
______________________________________ Make up of phosphoric
acid in the electrolyte
and content in g/l
E D N
______________________________________
(1) ortho 5 + pyro 5
10.20 277 no SC after 65
cycles
(2) ortho 10 9.95 270 SC on 12th cycle
(3) pyro 10 9.95 270 SC on 65th cycle
(4) ortho 50 + pyro 5
12.04 260 SC on 12th cycle
(5) ortho 55 10.75 205 SC on 1st cycle
(6) pyro 55 10.97 200 SC on 1st cycle
(7) ortho 5 + pyro 30
11.88 275 SC on 1st cycle
(8) ortho 35 11.40 270 SC on 1st cycle
(9) pyro 35 11.08 270 SC on 1st cycle
(10) ortho 30 + pyro 30
12.47 245 SC on 12th cycle
(11) ortho 60 10.22 205 SC on 1st cycle
(12) pyro 60 10.32 200 SC on 1st cycle
(13) ortho 10 + pyro 10
11.83 290 no SC after 136
cycles
(14) ortho 20 11.77 270 SC on 1st cycle
(15) pyro 20 11.08 275 SC on 1st cycle
________________
REFERENCES:
patent: 1748485 (1930-02-01), Kugel
patent: 3011007 (1961-11-01), Evers et al.
patent: 3447969 (1969-06-01), Tudor et al.
patent: 3887488 (1975-06-01), Scott et al.
patent: 4049733 (1977-09-01), Martan
Chemical Abstracts: vol. 98, Nos. 163757, 162220, 134328, 62114; vol. 97, Nos. 146155, 19704; vol. 96, No. 11721; vol. 90, No. 96887; vol. 84, No. 77752.
Gindre Jean
Mirebeau Pierre
Compagnie Europeenne d'Accumulateurs S.A.
Hearn Brian E.
Kalafut Stephen J.
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