Chemistry: electrical current producing apparatus – product – and – Process of cell operation
Patent
1980-09-26
1983-06-07
Skapars, Anthony
Chemistry: electrical current producing apparatus, product, and
Process of cell operation
429217, 429225, 429228, 75252, H01M 414
Patent
active
043871429
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a granular material consisting of microporous, substantially hollow granules of lead powder, which is a powdered mixture of lead and lead oxides, a method for the production of this granular material as well as the use thereof as an active substance in an electrode plate in a lead accumulator.
The lead accumulator despite its great weight and rather considerable self-discharge is still the type of accumulator of greatest importance and it is reasonable to presume it will stay this way even in a force-seeable future. Thus, it is essential to try to improve its construction and its capacity. Depending on the range of use a distinction is made between storage batteries, tractionary batteries and stationary batteries.
In a conventional lead accumulator the electrode plates are formed as lead grids, the spaces of which through lubrication have been filled with lead powder. During the first charge, the formation, the PbO and Pb in the lead powder are oxidized to PbO.sub.2 in the positive plate and PbO is reduced to Pb in the negative plate, whereafter the cell is ready to be used.
The electrode plate can also be of a tubular type, which is the case especially in tractionary and stationary batteries whereby a considerably improved life time is achieved. A tubular electrode plate consists of a conducting grid frame of lead connected to a number of parallel central conductors, which each is surrounded by an inert, perforated tube casing, being sealed at the bottom. Between the casing and the central conductors the active material is placed, which normally consists of a pulverous lead powder. The production of these tubular electrodes is involved with certain difficulties as the active material is very fine-grained. In order to achieve an acceptable filling with a dry powder the tubes must be vigorously shaken and special vibration devices must be used. Furthermore, this dry filling is directly unsuitable from an environmental point of view as the powder easily raises dust and due to its toxicity, thus, requires the personel to use protective clothing and breathing protections.
To avoid these problems the s.c. wet filling method has been introduced by which the lead powder is mixed with sulphuric acid and water to a homogenous paste which is pressed into the tubes. However, this method renders varying results and throughout a decrease of the capacity. Another disadvantage is high installation costs and a "sticky" work requiring an intensive supervision.
Through the production of granules of the lead powder the tubular electrodes can be filled by pouring without raiseing dust and without vibration. The obtained electrode filling also becomes very homogenous, i.e. the structural differences in the packed material which easily result from filling with powder are avoided. Furthermore, a much too dense packing making the electrolyte flow difficult is avoided. Thus, for a long time, one has tried to obtain granules of lead powder which could be used as an active material in electrode plates.
Different additives have been tested for the production of granules with a sufficient strength. SE PS No. 224,815, for example, discloses a method to produce particles of active material with the desired filling qualities wherein the material is wetted with a mixture of a sparingly volatile and a volatile substance and is thereafter pressed through a sieve. DE AS No. 1,013,273 also discloses a method to produce granules which method consists of adding 5-15% additive to the active material while stirring, heating the active material to 300.degree. C. and sieving.
In order to avoid deposits in the accumulator cell which decreases its life time one has also tried to produce granules without the addition of a binder of any kind. DE OS No. 1,817,966 discloses a method for the production of a PbO granulate free from binders according to which the active material is mixed with water and granulated in a known way in a granulator and dried. It is also known to mix the active material with sulphuric acid and wat
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Lindholm Alfons S. M.
Magnusson Rolf C. G.
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