Chemistry: electrical current producing apparatus – product – and – Having specified venting – feeding or circulation structure
Reexamination Certificate
1998-09-02
2001-02-06
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having specified venting, feeding or circulation structure
C429S101000, C429S142000, C429S144000, C429S145000, C429S206000, C429S229000, C429S249000, C429S254000, C429S317000
Reexamination Certificate
active
06183900
ABSTRACT:
This invention relates to an alkaline storage battery with a negative zinc electrode comprising a membrane separating two electrolytes of different volume and composition, in particular an ion-exchange membrane.
The following description relates to an Ni-Zn storage battery but it can just as well relate to an Ag-Zn storage battery, the Ni being replaced by the Ag, or to an Air-Zinc storage battery, etc.
Much work has been done in the last twenty years with a view to perfecting an Ni-Zn storage battery with a satisfactory longevity in cycling.
Of late, it has been admitted that the poor cycling strength of the Ni-Zn storage battery was due to short-circuits caused by the formation of zinc dendrites on charging.
Now, the dendrites have a greater tendency to form, the greater the concentration of zincates in the electrolyte in contact with the negative electrode.
The most effective remedies consist therefore in reducing the solubility of the zinc in the alkaline solutions, either by reducing its basicity, or by incorporating additives such as CaO in the active mass of the negative electrode in order to form insoluble complexes with the ionised forms of zinc.
Finally, the addition to the electrolyte of metallic ions such as Pb
4+
or compounds capable of acting on the morphology of the zinc deposits has also been noted.
By combining these various means, Cairns noted (J. Electrochem. Soc., 1993, 140, 2, pp 289-293) that the problem of the dendrites was resolved but that on the other hand the longevity in cycling, of the order of 500 cycles, although considerably increased in relation to the best results in the past (200 cycles), was limited by the deficiency of positive nickel electrodes.
Work done by the applicant has led to the same conclusion as Cairns.
The object of the present invention is to alleviate in particular the above-mentioned drawbacks.
To this end, the invention relates to an alkaline storage battery, comprising at least one positive electrode and a negative zinc electrode in contact with an electrolyte via at least one electrolyte-impregnated separator, clamped against two respective bipolar screens supported by a sealing frame.
According to the invention, the positive electrode is in contact with a first electrolyte having a predetermined volume and composition via at least one first separator in that the negative electrode is in contact with a second electrolyte having a predetermined volume and composition different from those of the first electrolyte via at least one second separator. The first and second electrolytes are separated by a membrane forming a zincate and optionally aluminate filter, particular an anionically conductive membrane defining first and second compartments.
According to a characteristic of the present invention, the electrolyte in contact with the negative electrode is essentially contained in the porosity of the negative electrode and the second separator holding a volume of electrolyte of between 2 and 3 cm
3
per dm
2
of frontal surface.
The electrolyte in contact with the negative electrode is composed for example of an aqueous solution of KOH in an initial concentration of between 4 and 8 M in which has been dissolved between 70 and 100 g of aluminium, or in a concentration of between 3 and 4 M.
This solution of KOH in a concentration of between 3 and 4 M may comprise moreover a zinc sequestering agent, for example a lignosulphonate or stannates in a concentration of between 0.01 and 0.1 M.
According to one characteristic, the positive electrode is an Ni or Ag electrode.
According to this characteristic, the electrolyte in contact with the positive electrode is essentially contained in the porosity of the positive electrode and the first separator holding a volume of electrolyte of between 3 and 8 cm
3
per dm
2
of apparent surface.
The electrolyte in contact with the positive electrode is for example composed of a solution of KOH in a concentration of between 4 and 8 M, and may comprise moreover 1 M in LiOH.
The membrane has a given anionic conductivity for example of at least 90% of the through-current of OH
−
anions.
It is for example based on polyoxyethylene or polyoxymethylene modified by exchange groupings of the quaternary ammonium type.
According to one characteristic, the membrane is provided, in one free part, with at least one means allowing the passage of gases released by the electrodes between the first and second compartments.
According to another characteristic, the storage battery comprises respective first and second reserves of electrolyte at the bottoms of the first and second compartments; the storage battery being in a vertical position in use.
Finally, the positive electrode may also be an electrode porous to gas, fed by oxygen or air.
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Bronoel Guy
Millot Alain
Tassin Noelle
Crepeau Jonathan
Henderson & Sturm LLP
Kalafut Stephen
Laboratoires Sorapec
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