Reduced maintenance nickel-cadmium storage cell

Details Reduced maintenance nickel-cadmium storage cell Reduced maintenance nickel-cadmium storage cell

1991-01-15

1992-07-07

Kalafut, Stephen

Chemistry: electrical current producing apparatus, product, and

Means externally releasing internal gas pressure from closed...

429 61, 429206, H01M 1030

Patent

active

051282178

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a reduced maintenance nickel-cadmium storage cell intended, in particular, for applications requiring high powers for short durations, e.g. in aviation or in back-up power supplies for certain types of equipment.
A first so-called "vented" type of nickel-cadmium storage cell is known for these applications, comprising sintered negative electrodes and positive electrodes with the gap between two successive electrodes being in the range 0.15 mm to 0.4 mm. This gap is filled with a separator comprising felts associated with a cellophane membrane made of grafted polyethylene or of microporous polypropylene. The electrode assembly is enclosed in a case of plastic material containing a certain quantity of free electrolyte. The operating pressure lies in the range of 0.2 bars to 0.7 bars relative pressure, said pressure being controlled by a valve. In its application to aviation, each storage cell, when discharged in 15 seconds at 25.degree. C., presents a power density of 400 watts per kilogram (W/kg) to 700 W/kg.
Most remarkably, such a storage cell presents the following operating characteristic: when charged at constant voltage and limited current, its voltage increases very suddenly at the moment it becomes overcharged. This increase makes it possible for storage cell charging to be self-limiting. This operating characteristic occurs for constant voltage charging regardless of temperature in the range -20.degree. C. to +60.degree. C.
In addition, the storage cell is very reliable throughout its lifetime which may lie in the range 5000 hours (h) to 50,000 h of operation, depending on conditions of utilization. However, it suffers from the drawback of consuming a quantity of water proportional to the overcharge applied thereto. This water consumption must be compensated by periodically adding distilled water, which operation takes the battery out of service and requires human intervention. Water consumption is about 1 cm.sup.3 per 3 Ah of overcharge.
A second so-called "vented" type of storage battery is known having sintered positive electrodes and negative electrodes whose active mass is consolidated by a polymer. The negative electrodes are described, in particular, in French patent number FR-A-2 586 407. The gap between two successive electrodes is greater than 0.4 mm and may be as much as 1.5 mm, depending on the application and the desired power density. Power density may lie in the range 50 W/kg to 200 W/kg. The separator may be constituted either by felts associated with a membrane, as in a cell of the first type, or else by a spacer of plastic material, in particular for inter-electrode gaps in the range 0.8 mm to 1.5 mm. This storage cell does not operate under pressure. It has the same advantage as the first type of cell from the point of view charging, being self-limiting over a vast temperature range, and the same drawback from the point of view of water consumption. In addition, it does not meet the power characteristics required for aviation applications.
Sealed nickel-cadmium storage cells are also known having substantially zero water consumption throughout their lifetime. One such cell comprises sintered positive electrodes and negative electrodes consolidated by a polymer, the electrodes being separated by a gap in the range 0.1 mm to 0.2 mm. The separator is a felt of polyamide, polypropylene, polyethylene, or a mixture of these substances. The assembly is installed in a metal container provided with a valve, and operating pressure is usually 3 bars to 4 bars relative to pressure.
Although sealed nickel-cadmium storage cells do not suffer from the drawback of consuming water, as mentioned above, they do not have the very advantageous charging characteristic enabling charging to be self-limiting. Their utilization in the applications outlined above requires sophisticated charging systems in which charge monitoring is essential in order to verify that the pressure is not exceeded and that no electrolyte is lost: any such loss would quickly lead to cell failure

REFERENCES:
patent: 4650733 (1987-03-01), Cimino et al.
patent: 4883727 (1989-11-01), Liska
Journal of Power Sources, vol. 8, No. 4, Nov. 1982, pp. 403-408, Elsevier Sequoia, Lausanne, Switzerland; J. Mrha et al.: "On the Anomalous Behaviour of Deeply Discharged, Sealed Ni-Cd Cells".
Journal of Power Sources, vol. 19, No. 1, Jan. 1987, pp. 55-66; S. Petrovic et al.: "Oxygen Recombination on Plastic-Bonded Cadmium Electrodes Doped with Nickel (II) Hydroxide".
Journal of Power Source, vol. 14, No. 4, Apr. 1985, pp. 285-293, Elsevier Sequoia, Lausanne, Switzerland: V. Fiala: "Protection of Sealed Ni-Cd Cells from Cell Voltage Reversal".
Patent Abstracts of Japan, vol. 9, No. 302 (E-362) [2025], Nov. 29, 1985; & JP-A-60 140 661 (Shinkoube Denki K.K.).
J. Power Sources, vol. 22, Nos. 3-4, Mar./Apr. 1988, pp. 243-259; David F. Pickett et al., "Advanced Nickel-Cadmium Batteries for Geosynchronous Spacecraft".
Intelec '88, Oct. 30 to Nov. 2, 1988, pp. 522-527; Dr. Klaus Gutzeit: "Sealed Nickel-Cadmium Batteries with Fiber Structured Electrodes".

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