GB2134699A

GB2134699A - An accumulator

Info

Publication number: GB2134699A
Application number: GB08401677A
Authority: GB
Inventors: Eric Pohlmann
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-02-01
Filing date: 1984-01-23
Publication date: 1984-08-15
Also published as: GB8401677D0; JPS59143267A; FR2540292A1; DE3303189C1

Abstract

An accumulator, more particularly a lead accumulator, consists of a casing (1) containing a set (2) of a plurality of positive pole plates (3) connected in parallel and a set (4) of a plurality of negative pole plates (5) connected in parallel, and two terminal posts (6, 7) for the sets (2 and 4) of positive and negative plates respectively, which posts protrude from the casing, on the underside. In this way, segregation in the electrolyte (8) is counteracted by utilising the heat generated in the pole plates (3, 5) during discharging. Each plate (3, 5) preferably has a woven lattice core of electrically high- conductivity material (copper or silver) coated with cast material (lead) and increasing the current-carrying cross- section towards the terminal posts. <IMAGE>

Description

SPECIFICATION An accumulator This invention relates to an accumulator, more particularly - but not exclusively - a lead accumulator, consisting of a casing containing a set of a plurality of positive pole plates connected in parallel and a set of a plurality of negative pole plates connected in parallel, and two terminal posts for the sets of positive and negative plates respectively, which posts protrude from the casing, the pole plates in the two sets preferably being interlocked in each other, and the casing being filled by a liquid electrolyte, more particularly aqueous sulphuric acid.

Accumulators have long been known in the widest variety (cf. of the review in "Lexikon der Physik", vol. 1, DTV, Munich 1970, pp.68 et seq.).

An accumulator provides an electro-chemical store of electrical energy, based on at least approximately reversible electrochemical processes, in the normal case on heterogeneous redox reactions. As in all electrochemical cells, the satisfactory functioning of an accumulator depends on the transfer of current from electrons or defect electrodes to ions at the boundary faces of the electrodes, which are known in accumulators as pole plates. Furthermore, the ion carrier, i.e., the electrolyte, must be free from electron conduction. Few systems have in fact being successful in practice; more particularly, one successful system is the lead accumulator, which was discovered in the mid-1 9th Century. Other practically successful systems include the nickel oxide accumulator, known as the steel accumulator, and the silver-zinc, zinc-air and nickel-cadmium accumulators.Although the present invention relates to all types of accumulators in general, the lead accumulator will be considered in the following account for the sake of simplicity.

The basic technical construction of an accumulator is described in detail in the publication referred to above, and the latter can be consulted on this point. However, it must be pointed out with reference to the pole plates that quite diverse constructions are known in the art, including lattice plates in which a pasty active mass is inserted into a supporting lattice of hard lead, large-area plates in which the active mass is developed electrolytically from a cast electrode of soft lead, and tube plates consisting of perforated plastics or hard rubber tubes into which the active mass is rammed around a lead or hard lead pin acting as the core and conduction electrode.

Because of the materials used, accumulators in general and lead accumulators in particular are relatively heavy; in other words, the storage capacity or specific efficiency per unit of weight is a problem that cannot be ignored. One important aspect of this problem is the electrical losses originating from the design of the accumulators, since electrical energy is converted to heat by the high resistances to current flow and so on.

Another specific problem arises from the so-called segregation phenomenon when an accumulator is discharged, the density d of the undiluted electrolyte in a fully charged accumulator being so much greater than that of the diluted electrolyte in the largely discharged accumulator (d = 1.2 1.3 against d = 1.03-1.1). As the accumulator is progressively discharged, the water layer in its top section extends further down, so that progressively larger areas of the pole plates cease to function, starting from the top downwards. This segregation is further stabilized by the fact that the pole plates are increasingly heated from the bottom upwards by the concrescing current density brought about by current integration.

Consequently, the overall resistance of the known accumulators when discharged is invariably higher than it should be in theory.

Attempts have been made to prevent this segregation, in very large accumulators particularly, by fitting an external circulation pump and continuously pumping electrolyte up from the bottom. This of course is not a very elegant solution to the problem.

On this basis of prior art, the object of the invention is to provide an accumulator in which the efficiency per unit of weight is improved.

According to the present invention, therefore, the terminal parts of an accumulator are disposed at the bottom of the casing. Thus the sets of pole plates are disposed so to speak "upside down" in the casing, and the current flows down to the terminal plugs rather than up to them as has hitherto been the case. The current similarly flows in the opposite direction when the accumulator is being charged.

The invention arises from the discovery that the heating of the pole plates by the passage of current through them to the terminal posts, which has already been referred to, can be utilised to counteract electrolyte segregation. Thus the pole plates are heated most strongly at the bottom, since the current density there is at a maximum.

This heat is transferred to the liquid electrolyte and promotes an upward flow. As a result, the electrolyte undergoes constant sponstaneous mixing and the pole plates remain active over their entire area under all circumstances.

Measurements have shown that the storage capacity of a lead accumulator of otherwise conventional construction but with the terminal posts on the underside can be increased by 6% in this way alone, by reducing the electrical losses and lowering the resistance during charging and discharging.

For complete disclosure, it should be stated at this point that the proposed disposition of the terminal posts is advantageous in accumulators of all types, and that the terminal posts are preferably located on the actual base of the casing; but, if more convenient, they can be located near the bottom of a sidewall of the casing.

According to a further feature of the invention, of special and even independent significance, the accumulator is preferably constructed as described above and modified so that the pole plates have a current-carrying cross-section that increases from the end remote from the terminal posts towards the terminal posts. This modification arises from the discovery that the pole plates in accumulators of the type in question, and as previously described, do not merely have an electrochemical function but also function as the current carriers for the charging and discharging currents. Irrespective of the detailed construction of the pole plates, the current-carrying cross-section of the pole plates advantageously increases in the direction of the terminal posts.In this way, the invention allows for the fact that current integration increases the current strength in the direction of the terminal posts. Thus the increasing current strength is matched by the current-carrying cross-section.

One can vary the full cross-section of the pole plates, but it is preferably to vary only the internal current-carrying cross-section of the pole plates.

In connection with the last-mentioned feature of the invention, another significant feature arises in that instead of increasing the current-carrying cross-section of the pole plates in the direction of the terminal posts one can provide a reduction in the specific electrical resistance of the pole plates.

This could be brought about for example by continuously varying the material composition in the direction of the terminal posts.

According to another feature of the invention of special and independent significance, the pole plates in an accumulator of the type in question have a core of high-conductivity material, more particularly copper but alternatively silver or the like. The core of high-conductivity material can be coated with the pole-plate material or surrounded by cast pole-plate material, and is preferably formed as a woven lattice. This feature of the invention arises from the discovery that the present unsatisfactory efficiency of the known accumulators per unit weight arises from the poor conductivity of the materials used for the pole plates. Thus the specific conductivity of copper for example is ten times the specific conductivity of lead.The invention now teaches the combination of materials necessarily used for electrochemical reasons for the pole plates with high-conductivity materials advantageous from the electrical viewpoint. In this way, the weight of a conventional lead accumulator can be reduced by about 14% without affecting the electrical properties and characteristics.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawing, which is a partly sectioned perspective view from below of an accumulator in accordance with the invention.

The accumulator shown in the drawing is a lead accumulator and consists of a casing 1 containing a set 2 of a plurality of postive pole plates 3 connected in parallel and a set 4 of a plurality of negative pole plates 5 connected in parallel, and two terminal posts 6 and 7 for the sets 2 and 4 of positive and negative plates respectively, which protrude from the casing. The pole plates 3, 5 in the two sets 2, 4 are interlocked in each other, and the casing 1 is filled with a liquid electrolyte 8, viz., aqueous sulphuric acid, indicatd by dots, through a filling cover 10 on the top face of the casing 1.

The drawing also shows lower prisms 9 and upper prisms 1 1 to locate the pole plates 3, 5 in the casing 1.

The drawing shows explicitly that the terminal parts 6, 7 are disposed on the underside of the casing 1. Though it is not apparent in the drawing, the pole plates 3, 5 preferably have a currentcarrying cross-section that increases from the end remote from the terminal posts towards the terminal posts. For this purpose, the pole plates 3, 5 preferably each have a core of high-conductivity material, viz., copper, the remainder of the material of the pole plates, viz., lead, being cast around the core of high-conductivity material, which is preferably formed as a woven lattice.

By virtue of the constructional features described above, the specific efficiency per unit weight of the accumulator shown in the drawing is about 20% higher than that of the long known accumulators of otherwise similar construction but with the terminal posts at the top.

Claims

1. An accumulator consisting of a casing containing a set of a plurality of positive pole plates connected in parallel and a set of a plurality of negative pole plates connected in parallel, and two terminal posts for the sets of positive and negative plates respectively, which posts protrude from the casing, which is filled with a liquid electrolyte, the terminal posts being disposed at the bottom of the casing.

2. An accumulator as in Claim 1, wherein the pole plates have a current-carrying cross-section that increases from the end remote from the terminal posts towards the terminal posts.

3. An accumulator as in Claim 1 or Claim 2, wherein the pole plates each have a core of electrically high-conductivity material.

4. An accumulator as in Claim 3 wherein, the electrically high-conductivity material is copper or silver.

5. An accumulator as in Claim 3 or Claim 4, wherein the core of high-conductivity material is coated with cast material.

6. An accumulator as in Claim 5, wherein the cast material is lead.

7. An accumulator as in any one of Claims 3 to 6, wherein the core of high-conductivity material is formed as a woven lattice.

8. An accumulator consisting of a casing containing a set of a plurality of positive pole plates connected in parallel and a set of a plurality of negative pole plates connected in parallel and two terminal posts for the sets of positive and negative plates respectively, which posts protrude from the casing, which is filled with a liquid electrolyte, the pole plates having a currentcarrying cross-section that increases from the end remote from the terminal posts towards the terminal posts.

9. An accumulator consisting of a casing containing a set of a plurality of positive pole plates connected in parallel and a set of a plurality of negative pole plates connected in parallel, and two terminal posts for the sets of positive and negative plates respectively, which posts protrude from the casing, which is filled with a liquid electrolyte, the pole plates each having a core of electrically high-conductivity material.

10. An accumulator as in Claim 9, wherein the electrically high-conductivity material is copper or silver.

1 1. An accumulator as in Claim 9 or Claim 10, wherein the core of high-conductivity material is coated with cast material.

12. An accumulator as in Claim 1 wherein the cast material is lead.

13. An accumulator as in any oen of Claims 9 to 12, wherein the core of high-conductivity material is formed as a woven lattice.

14. An accumulator substantially as hereinbefore described with reference to the accompanying drawing.