Rechargeable batteries in general and lead-acid batteries in particular per se are well known in prior art so that supporting documents need not be cited at this point.
A battery of this generic type typically comprises a battery housing having electrodes arranged therein that are surrounded by a mostly liquid electrolyte when used as intended. The design of plate-shaped electrodes is rather popular. While the negative electrodes usually comprise an electrode plate having a grid-like design in which the grid meshes are filled with an active mass, the positive electrodes usually have a plurality of cores arranged on a common electrode bridge, each core being disposed inside a tube pocket tube filled with an active mass.
Said electrodes are arranged adjacent to each other inside the battery housing, wherein negative electrodes alternate with positive electrodes. To prevent shorting, a separator is respectively arranged between a negative electrode and a positive electrode, which electrically decouples these two electrodes from each other.
Different separator configurations are known in prior art. A typical type of construction is a separator, which is designed as a separator pocket. The same provides a receiving space for the electrode plate of the negative electrode. In the finally mounted state, said separator pocket surrounds the electrode plate of the negative electrode while receiving it like a wrapping.
Said separator pocket is composed of two single separator sheets bearing on each other. Along their longitudinal sides, said separator sheets are connected to each other, preferably by welding. Normally, said separator pocket is sealed along its lower outer edge, whereas the upper outer edge has an open configuration for being equipped with said electrode plate.
When a battery is used as intended, it cannot be avoided that particles stemming from the active mass and present in the electrolyte accumulate on the electrode plate of the negative electrode. These particles accumulate on the upper outer edge of the electrode plate as a result of the separator pocket being open on the upper side. Even if the battery is used as prescribed, these particles accumulating on the upper outer edge of the electrode plate of the negative electrode may form a shorting bridge to an adjacent positive electrode. This phenomenon is also called “mossing”.
To prevent the accumulation of electrically conducting particles on the electrode plate of the negative electrode leading to the formation of a shorting bridge, it has been proposed to seal the separator pocket of the negative electrode also on its upper outer edge. Such a construction is known for instance from U.S. Pat. No. 2,570,677 and U.S. Pat. No. 4,680,242.
Separator pockets sealed all around are problematic in that the separator pocket may swell as a result of gases released during normal usage. This may affect normal operation of the battery. However, the result of the accumulation of released gas within said separator pocket is above all a kind of gas occupation of the electrode so that the electrolyte can no longer or only partly reach the electrode. This may even result in a complete failure of the electrode.
To solve this problem, it has been proposed in U.S. Pat. No. 4,680,242 to make the recess in the separator pocket provided for the passage of a current-collecting lug disposed on the upper outer edge of the electrode plate slightly larger than said current-collecting lug. Gas that is released during operation can thus escape via said recess formed in said separator pocket for the current-collecting lug to pass through.
The construction known from U.S. Pat. No. 4,680,242 has the disadvantage that for the purpose of a degasification, said recess for the current-collecting lug must be dimensioned sufficiently large for allowing the floating particles from the electrolyte to flow into the separator pocket and to settle on the electrode plate, especially in the region of the current-collecting lug. Accordingly, this may cause undesired fouling of the electrode despite the sealed configuration of the separator pocket. With an advanced accumulation of particles, said recess for the current-collecting lug becomes clogged at least partially, so that sufficient degasification cannot take place any longer, and the risk of a battery failure as a result of a swelling phenomena of the separator pocket increases.