Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Patent
1987-04-29
1988-11-29
Hearn, Brian E.
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
429140, 429234, 429245, H01M 462, H01M 472
Patent
active
047881143
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electrode for an electrochemical cell and to such a cell having at least one such electrode.
As is well known in connection with electrochemical cells, the power of the cell increases with an increase in the contact surface between the electrolyte and the electrode. One step towards such a power increase has been the development of particulate active materials (paste), e.g. in lead-acid cells. In e.g. plate electrodes, the contact surface of the compact frame and current collector supporting the active material has been increased by means of grooves provided therein for such power-increasing purposes. Such electrodes provided with a compact frame are necessarily heavy. It has been possible to reduce the weight by using a grid or expanded mesh as carrier for the active material and as current collector. However, also such a grid will considerably add to the weight of the cell. Further, such plate electrodes require special separators and have a tendency to crumble, i.e. release particles of active material. This has been counteracted by designing the electrode separator as a pocket for the electrode plate. In so-called tubular electrodes, the active material is contained in macroporous tubes or hoses of e.g. braided glass or synthetic fibres, cf. e.g. U.S. patent application No. 4,537,842.
Such tubes or hoses can be manufactured with an inner diameter of only down to about 4 mm. Further, by the macroporosity of the hoses, portions of enclosed active material may leave the hose especially when the active material is swelling during charge/discharge. Also, the hoses often burst during such swelling.
According to the invention, the solid active electrode material is enclosed in hollow fibres which have microporous peripheral walls permeable to electrolyte (ions) and which both support the active material and serve as electrode separator. Several thousands of such hollow fibres may exist in one electrode. Suitable hollow fibres consist of thermoplastic and are known from the ultrafiltration technique. Such plastic hollow fibres have the advantage of being light and elastic or at least yieldable, which means that the fibres can yield to the swelling of active material and be formed into any desired configuration. If the hollow fibre material is elastic, this affords the advantage that the hollow fibre follows any volumetric variation of the active material during charge/discharge and, in this manner, holds the particles in the active material together.
The invention is applicable to both negative and positive electrodes with solid active electrode material and to all types of electrochemical cells operating at moderate temperatures, both primary and secondary cells, such as lithium, lead-acid and alkaline nickel cells. The hollow fibre material is so selected that it is resistant to the electrolyte (e.g. polysulfone for acid electrolyte and polyamide for alkaline electrolyte). The other characteristics of the hollow fibres, such as inner diameter, wall thickness, pore diameter and porosity, can easily be adapted by the expert to the active material to be enclosed in the hollow fibres and to the reaction environment in the cell. It is contemplated that the diameter suitably is <3 mm, the wall thickness suitably <300 .mu.m, the pore diameter <20 .mu.m, and the porosity >50%. The hollow fibres may have a cross-sectional shape other than circular.
One embodiment of the invention will now be described in greater detail with reference to the accompanying principle drawing. This embodiment relates to a lead-acid cell.
One electrode comprises a bundle A of a plurality of hollow fibres 1 filled with lead dioxide powder. Another electrode comprises another bundle B of a plurality of elastic hollow fibres 2 which are permeable to electrolyte (sulfuric acid) and filled with spongy lead. One end 1' of the hollow fibres 1 is sealed, like one end 2' of the fibres 2. The bundles A and B are so assembled that their hollow fibres engage in between each other with the ends 1' and 2'
REFERENCES:
patent: 3011007 (1961-11-01), Evers et al.
patent: 3647557 (1972-03-01), Kegelman
patent: 3920479 (1975-11-01), Westberg et al.
patent: 4310607 (1982-01-01), Shay
Hearn Brian E.
Inclusion AB
Kalafut Stephen J.
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