A process is provided for stabilizing a primary electrochemical generator comprising at least one reactive anode made from a metal chosen from the group comprising zinc, aluminum and magnesium, characterized in that to said electrode is added a percentage of 0.01% to 1% by weight with respect to the metal, of at least one perfluorated polyfluorated organic compound of the ethoxylated fluoroalcohol type. It also relates to an anode obtained by the above mentioned process and a primary electrochemical generator, with alkaline or saline electrolyte, comprising an anode of this type.
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1. Process for stabilizing a primary electrochemical generator comprising at least one reactive anode made from a metal taken from the group consisting of zinc, aluminium and magnesium, characterized in that there is added to said electrode a percentage of 0.01% to 1% by weight with respect to the metal of at least one perfluorated polyfluorated organic compound of the ethoxylated fluoroalcohol type.
2. The stabilization process according to
3. The stabilization process according to
Cn F2n+1 --(CH2)p --(CH2 CH2 O)q --OH (1) in which: n is between 4 and 20, preferably between 6 and 8; p is between 1 and 10 g and is preferably close to 2,; and q is between 3 and 40, preferably between 10 and 12. 4. The stabilization process according to
C6 F13 C2 H4 (C2 H4 O)q OH (3) in which q is close to 12. 5. The stabilization process according to
6. The stabilization process according to
C6 F13 C2 H4 (C2 H4 O)14 OH (4) and C10 F21 C2 H4 (C2 H4 O)14 OH with a mean molecular mass corresponding to the compound: C6 F15 C2 H4 (C2 H4 O)14 OH. 7. The stabilization process according to
Cn F2n-1 --(CH2)p --(CH2 CH2 O)q --OH (2) in which: n is between 4 and 20 , preferably 6 and 8; p is between 1 and 10 and is close to 2; and is between and 3 and 40 , preferably between .Badd.10 and 12.Baddend.. 8. The stabilization process according to
9. An anode for a primary electrochemical generator obtained by the process according to any one of the preceding claims.
10. A primary electrochemical generator with alkaline electrolyte, characterized in that it comprises an anode according to
11. A primary electrochemical generator with saline electrolyte, characterized in that it comprises an
anode according to 12. 14. An anode for a primary electrochemical generator comprising a metal taken from the group consisting of zinc, aluminum and magnesium and a percentage from 0.01% to 1.0% of at least one polyfluorated organic compound of the ethoxylated fluoroalcohol type. 15. An anode for a primary electrochemical generator according to claim 14, wherein the metal is zinc and further comprising mercury in an amount less than 2% by weight with respect to zinc. 16. An anode for a primary electrochemical generator according to claim 14, wherein the polyfluorated compound has the formula: Cn F2n+1 --(CH2)p --(CH2 CH2 O)q --OH in which: n is between 4 and 20, p is between 1 and 10, and q is between 3 and 40. 17. An anode for a primary electrochemical generator according to claim 16, wherein the polyfluorated organic compound has the formula: C6 F13 C2 H4 (C2 H4 O)q OH in which q is close to 12. 18. An anode for a primary electrochemical generator according to claim 16, comprising two or more of the polyfluorated compounds. 19. An anode for a primary electrochemical generator according to claim 18, comprising C6 F13 C2 H4 (C2 H4 O)14 OH and C10 F21 C2 H4 (C2 H4 O)14 OH in amounts such that the polyfluorated component has a mean molecular mass corresponding to the compound: C7 F15 C2 H4 (C2 H4 O)14 OH. 20. An anode for a primary electrochemical generator according to claim 14 wherein the polyfluorated organic compound has the formula: Cn F2n-1 --(CH2)p --(CH2 CH2 O)q --OH in which: n is between 4 and 20, p is between 1 and 10, and q is between 3 and 40. 21. An anode for a primary electrochemical generator according to claim 20, wherein the polyfluorated compound has the formula: ##STR4## 22. A primary electrochemical generator with alkaline electrolyte, characterized in that it comprises an anode according to claims 14 to 21. 23. A primary electrochemical generator with saline electrolyte, characterized in that it comprises an anode according to claims 14 to 21. |
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The invention relates to primary electrochemical generators, or electric cells, comprising very reactive anodes made from zinc, aluminium or magnesium, more especially of the (such as ethyl alcohol or acetone) which is then evaporated, or by mixing the inhibitor with the potash solution.
The anode mass thus obtained is tested in a 10 N potash solution at 45°C and the corrosion rate is measured in μl/g/day (microliter of CTPN hydrogen per gram of zinc and per day). A rate higher than 10 μl/g/day is unacceptable in an electrochemical generator. It is in fact known that the corrosion rate (determined by the volume of hydrogen freed per gram of sample and per day, when this sample is immersed in the electrolyte in question is widely used for testing amalgamated samples and shows a very good correlation with the effective conservation of electrochemical generators. For accelerating the test, it is generally carried out at 45°C
By way of comparison, a non amalgamated zinc powder has a corrosion rate considerably higher than 10 μl/g/day (of the order of 2000 μl/g/day); amalgamated at 0.2% it has a corrosion rate of the order of 2000 μl/g/day, at 1% a corrosion rate of the order of 20 μl/g/day, so still greater than 10 μl/g/day; amalgamated at 5% gives a corrosion rate of about 1.5 μl/g/day, this latter being acceptable in most generators.
The inhibitor is formed by the perfluorated polyfluorated organic compound of formula:
C6 F13 C2 H4 (C2 H4 O)q OH (3)
in which q is close to 12.
This formula corresponds substantially to the product FORAFAC 1110 commercialized by the form Atochem.
The proportion of inhibitor used is 0.01% by weight with respect to the zinc.
The corrosion rate is measured and 0.7 μl/g/day was found.
Example 1 was repeated but with a zinc electrode amalgamated to 0.2% and non amalgamated zinc.
The table hereafter gives a comparison of corrosion rate measurements, without inhibitor, in accordance with the invention and with the inhibitor of formula (3) at 0.1%, with the zinc electrodes having different amalgamation rates and a non amalgamated zinc electrode.
| ______________________________________ |
| Amalgamation Rate |
| % by weight of Hg |
| Corrosion rate |
| ul/g/day |
| with respect to the |
| without inhibitor |
| with inhibitor |
| zinc of formula (3) |
| of formula (3) |
| ______________________________________ |
| 5% 1.5 -- |
| 1% 20 0.7 |
| 0.2% 200 5 |
| 0 2000 20 |
| ______________________________________ |
Example 1 was repeated by replacing compound (3) by the following mixture:
C6 F13 C2 H4 (C2 H4 O)14 OH (4)
and
C10 F21 C2 H4 (C2 H4 O)14 OH
with a mean molecular mass corresponding to the compound
C7 F15 C2 H4 (C2 H4 O)14 OH
the corrosion rate measured in accordance with the above defined method was 0.8 μl/g/day for a proportion of 0.1% of the above mixture (4).
Example 1 was repeated and using, in place of the compound (3), 0.01% of the non saturated perfluorated polyfluorated compound: ##STR1##
The corrosion rate measured in accordance with the above described method was 1.9 μl/g/day.
Primary generators, such as described in French Pat. No. 2 503 935 of the applicant, have been mounted in two series:
one comprising an anode mass formed of zinc powder amalgamated to 5%, an electrolyte formed by a 40% potash solution and a gelling agent (carboxymethylcellulose), the proportions being 300 ml of potash solution and 25 g of carboxymethylcellulose per kilo of amalgamated zinc;
the other comprising, in the same electrolyte and the same gelling agent, an anode mass whose zinc powder is only amalgamated to 1%, but in which, during mixing with the electrolyte and the same gelling agent, the above mentioned FORAFAX 1110 was introduced in a proportion of 0.1% by weight with respect to the zinc.
The two series were stored for three months at 45°C After this storage period, observation showed no sweating on the outside of the cells due to a possible overpressure. On dismantling the cells no expansions of the anode gel was discovered.
Finally the elements of these two series, the modulus R20, discharged across 3.9 ohms under continuous operating conditions, present the same dispersion in the discharge duration 59 h±1h, that is to say that there is no loss of capacity of the cells of the second series with respect to those of the first. B. Zinc electrode for so called "saline" cells with saline electrolyte.
It is well known that cells of the manganese dioxide/zinc type, so called "saline cells", use an electrolyte formed from an aqueous solution of zinc chloride and ammonium chloride, in which the zinc electrode tends to corrode and form hydrogen, which results in causing leaks of electrolyte by perforating the zinc case, and losses of capacity during storage.
The zinc electrode of these cells is formed from metal foil, so less reactive than the divided powder of a alkaline generators. This zinc foil is only amalgamated on the surface, the weight of mercury per cell is consequently 1000 times smaller than that required for so called "alkaline" cells with alkaline electrolyte.
The inhibitor effect of the compound of the invention is shown by the corrosion test carried out at 45°C in a saline solution comprising 25% by weight of Cl2 Zn, 25% by weight of NH4 Cl and the complement made up with water.
The use of powdered zinc test pieces has the advantage of giving a rapid and statistically more homogeneous response. In fact, the tongues cut out from cell case have great structural heterogeneity because of the extrusion lines of the tube, and consequently a great dispersion in the responses to the corrosion test.
The ratio of the active surfaces and consequently of the corrosion rates between the powder and the foil is close to 5000.
| ______________________________________ |
| The following corrosion rates were obtained: |
| ______________________________________ |
| reference electrode without mercury and |
| 2000 μl/g/day |
| without inhibitor according to the invention |
| electrode with 0.01% by weight of the above |
| 340 μl/g/day |
| compound (3) |
| electrode with 5% by weight of |
| 175 μl/g/day |
| mercury |
| ______________________________________ |
The inhibiting effect of the perfluorated polyfluorated compound of the ethoxylated fluoroalcohol type is very clear, even in a saline environment.
As is evident and as it follows moreover already from what has gone before, the invention is in no wise limited to those of its modes of application and embodiments which have been more especially considered; it embraces, on the contrary, all variants thereof.
It should be noted that, if U.S. Pat. No. 4,040,916 discloses a "method for forming a non-dendritic zinc layer which comprises providing a deposition solution containing a zinc compound and from 0.001 to 10 weight percent of a non-ionic surfactant additive which has the formula: ##STR2## where m is a number from 3 to 15, R is alkyl radical having from 1 to 10 carbon atoms, R' is a member of a group consisting of hydrogen and methyl radical, n is a number for the group from 0 to 30, and the surfactant additive has a molecular weight range of approximately 550-1500; positioning a pair of spaced apart electrodes within the deposition solution, applying an electric current to the electrodes, and depositing a non dendritic zinc layer on the negative electrode (claim 1), the additive and the function thereof are different in said U.S. patent and in the present patent application.
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