Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-11-19
2002-03-05
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S228000, C429S226000, C429S227000, C029S623100, C029S623500
Reexamination Certificate
active
06352795
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This application concerns a lead battery electrode and a method for its production.
The active components of a lead battery consist of porous PbO
2
(PAM, positive active material), porous Pb (NAM, negative active material) and sulphuric acid. As inactive material is considered vessels, separators, grids etc. Theoretically 4.463 g PbO
2
, 3.866 g Pb and 3.660 g H
2
SO
4
(concentrated) is needed to obtain 1 Ah. When utilization of PAM and NAM is inferior, the electrodes in the cells must be provided with considerably more of these components than what is calculated theoretically. Further, sulphuric acid may not be used effectively, on the one hand because it must be diluted with water to a density not exceeding 1.30-1.35 g/cm
3
, on the other hand because it cannot be located such in the battery that the whole amount is coming in close contact with the electrodes. It is true that PAM and NAM due to its porosity include part of the necessary acid amount, but more acid is located in areas between the electrodes (in the separator), beside the electrodes and above the electrode package. There is often acid also below the electrode package but this amount of acid may only take part in the discharges to a small degree. The location of sulphuric acid just described is with respect to cells having vertical electrodes, in particular if they are monopolar. Bipolar electrodes may also function well in a vertical position but often horizontally functioning bipolar electrodes are preferred.
The most characteristic difference between bipolar and monopolar electrodes is that on the former at one side of an electron-conducting wall
2
has been placed PAM
3
and at the other side NAM (FIG.
1
). The electron-conducting wall
2
is tight and separates the sulphuric acid from the adjacent cells. Another factor considered characteristic for bipolar electrodes is that the current at discharge is very evenly distributed over the electrodes which facilitate discharges with high currency. The inner resistance diminishes by the current between the cells going directly between the wall between PAM and NAM. Bipolar batteries are therefore used mainly for very high loads during short times, seconds down to milliseconds. A bipolar construction could be regarded as favourable also for its utilization of the so called oxygen gas recombination, by having a short distance between the electrodes in order to bring down the inner resistance of the cells. Oxygen recombination means that oxygen gas formed at the positive electrode during charge is transferred to the negative electrode and is reduced to water. This process is enhanced by a short electrode distance. In a monopolar construction having horizontal electrodes, the acid may as a contrast be allowed to freely circulate between the parallel coupled electrodes in one and the same cell.
Bipolar electrode may sometimes be called semi-bipolar depending on that each of the negative and the positive side respectively of the electrode is treated differently and is thereafter put together to a bipolar electrode.
Common for both kinds of electrodes is that between the positive and the negative electrode there must be a separator. In many cases this separator consists of a disc of a porous polymer having a porosity between about 60-80%. In other cases it may be comprised of microfine glass wool having a porosity of about 95%.
For the sake of the working life of these batteries, it is absolutely essential to have a relatively high pressure load on the electrode material. A suitable pressure may in the simplest way be brought about to horizontal electrodes and should be between 0.5 and 10 kg/cm
2
provided that the separators and the active material are not pressed so that they brake.
The capacity of a bipolar as well as a monopolar electrode is depending on the volume of acid which may be located at PAM, NAM and intermediate spaces. It is also possible to arrange spaces for extra acid outside the real electrode surface, that is the circumference of the cell is expanded without increasing the active electrode surface. The extra volume for acid being created will however be far away from the central parts of the electrode and thereby not only a long path has been obtained for transport of acid but also an uneven distribution of the current although the provisions for this are at hand in the bipolar construction as such. One could of course get larger space for the acid by increasing the distance between the electrodes, but because of the low conductivity of the electrolyte, the inner resistance will thereby increase and the oxygen gas recombination will suffer.
A usual and obvious way of increasing the provision of sulphuric acid in electrodes is to increase the porosity of PAM and NAM. This however brings about the risk of breaking the structure already after a rather small number of discharges.
Batteries having vertical electrodes have, as is mentioned, often a great part of the necessary acid volume placed above the electrodes. This acid is easily accessible since the difference in density in respect of that between the electrodes, after a time of discharge, is so great that convection currents will result. This has, however, a negative effect at charging. During the discharge, a large amount of acid has been bound in the electrode as lead sulphate. In the subsequent charge, this acid will be released, thereby, because of the difference in density with respect to the discharge outside the electrode, sinking downwards in the cell. Mixing of the electrolyte for example by circulation pumping or gas charging will then be necessary in order to level the resulted gradient and avoid stratifying.
SUMMARY OF THE INVENTION
This invention concerns reducing the problems of the known art and to provide a method of increasing the available amount of acid at PAM and NAM and still keep a short distance between the electrode surfaces.
This is achieved in a lead battery electrode by the features in that a great part of the amount of acid necessary for discharge is distributed into open space within or near the active material and that the spaces are given structure so that the structure comprise a mechanical support for the active material.
This way the accessibility of acid near the active material is ensured while maintaining support for this material which results in high strength and high mechanical resistibility.
The present invention defines preferred embodiments of the lead battery electrode, stating preferred constructions and arrangement of electrodes as such as well as of the porous particles which comprise support and acid reservoirs.
The invention also concerns a method of producing lead battery electrodes ensuring effective manufacture. Further the invention concerns a lead battery including electrodes. Further advantages of the invention will be apparent from the following.
The invention is describes with respect to bipolar electrodes, particularly such being constructed on a porous ceramic disc, which has been made electron-conducting by having the pores filled with lead (Sundberg, Nilsson U.S. Pat. No. 5,510,211) but is not limited to such electrodes but may be applied also in monopolar electrodes. The invention is further described in the
FIGS. 1-7
without these embodiments comprising limitations of the invention.
REFERENCES:
patent: 5468575 (1995-11-01), Holland et al.
patent: 5474863 (1995-12-01), Yamamoto
patent: 5582937 (1996-12-01), LaFollette
patent: 3532697 (1987-04-01), None
patent: 0630063 (1994-12-01), None
patent: WO85/05227 (1985-11-01), None
patent: WO95/26055 (1995-09-01), None
Patent Abstracts of Japan, vol. 8, No. 285, abstract of JP 59-151774 A (Shinkoube Denki K.K.), Aug. 30, 1984.
Nilsson Ove
Sundberg Erik
Brouillette Gabrielle
Martin Angela J.
Volvo Technology Transfer AB
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