EP2115800A2

EP2115800A2 - Electrode for lead-acid batteries

Info

Publication number: EP2115800A2
Application number: EP08708520A
Authority: EP
Inventors: Joseph Cilia; George Schembri; Joseph Pule; Malcolm Tabone
Original assignee: Abertax Research and Development Ltd
Current assignee: Abertax Research and Development Ltd
Priority date: 2007-01-31
Filing date: 2008-01-31
Publication date: 2009-11-11
Also published as: WO2008092925A3; WO2008092925A2

Abstract

Conductive element in a lead acid battery made up of a series of lead or lead alloy wires held in a support structure comprising a lower bar used to position lower ends of said wires, the upper ends of which are bunched together forming a bundle. Lead acid battery electrode made up of least one wire, wherein the wire has a core being covered by a coating of lead or lead alloy and embedded in a lead dioxide mass, the core being at least partially made of a highly conductive or semi-conductive non-lead material, the core being centered in a textile gaunlet. Conductive element in a lead acid battery made up of at least one lead or lead alloy tube containing a flowing cooling medium.

Description

Electrode for Lead- Acid Batteries

Description

The present invention relates to an electrode forming a plate in a lead acid battery.

Up to now, electrodes for batteries made up of lead or lead alloy are formed as plates which are manufactured by casting or injection-casting of lead. However, this conventional process presents a large number of disadvantages including environmental problems, health problems and cost issues.

The actual use of the element lead (Pb) in any manufacturing process has to be carried out under severely controlled conditions. The specific process of casting lead presents much larger problems associated with health issues - in the sense that strict precautions have to be taken against the leaking of any fumes, dust and other impurities in the vicinity of operators. This carries with it the added disadvantage of cost.

Added to this the casting process involves melting of the lead which is continually forming a slag on the surface. This has to be scooped up very often and also presents additional costs to the process, plus the added disadvantage of loss of material. The slag cannot be disposed of easily due to environmental reasons, and added costs for its disposal are usually extremely high.

The casting process also necessitates the addition of certain elements like antimony, together with other trace elements which are needed to improve the cast ability of grids. The addition of these elements reduces the electrical conductivity of the plates, thus reducing the electrical properties of the battery cells. These add up to the disadvantages of lower current capability of the cells and more difficult charging and discharging of the plates.

The injection casting (or die casting) process presents further disadvantages in its limit to the maximum length of cast plates. This limits the length of the finished battery cells. Filling longer moulds with this method presents bigger process problems. Another disadvantage is that the existing process does not allow the flexibility of varying the conductivity of the electrodes to a required value due to the casting limitations.

During this die casting process there is a very high tendency to porosity, shrinkage and trapped gasses because of the turbulences in the melt during the high pressure casting process. All these defects in the finished plates have an adverse effect on the mechanical and corrosion resistance of the plates. These injection casting defects also have a very big influence on the extremely high reject rate with this method of production of battery grids.

A further disadvantage of the casting process is that it is very slow compared to other processes as time is required for the following phases:

• Pressure filling of the mould.

• Solidification of the melt.

• Removing of the cast pieces from the mould.

• Trimming of the casting gates.

• Trimming of unnecessary parts.

In general the pressure casting process is also very detrimental to the environment because of the production of the lead vapour and the use of certain special chemical sprays for the coating of the moulds to facilitate the release of cast pieces from the moulds. This has an added cost disadvantage in the use of special filters, suction etc.

It is an object of the invention to provide an electrode as set forth in the preamble of claim 1 in which the above mentioned problems are eliminated in total and to provide a possibility of varying the electrode conductivity already in its phase of production. The electrically positive electrode (anode) in a modern flooded and valve-regulated lead acid battery is made of lead dioxide as electro-chemically active matter and has a core of lead or lead alloy. Batteries require a maximised surface of active matter to enhance the electrochemical reaction and a good electric conductivity to allow high amperage charging and discharging.

A good capacity is achieved, for instance, by a high amount of active material placed in a textile tube and a solid lead or lead alloy core in the centre to achieve good conductivity. However, the relatively poor conductivity of lead makes it unavoidable to use a rather massive lead core which is heavy, voluminous and expensive.

It is therefore a further object of the invention to provide an electrode for a lead acid battery where at least the anode has less weight and volume as well as better high current properties than in comparable batteries of so far usual construction.

According to the invention, said problems are resolved by an electrode which is made up of at least one wire containing lead or lead alloy. Depending on the capacity required, the electrode may be made up of a series of such wires which may be placed in a parallel or a grid arrangement.

The wire or wires forming the plate of an anode or cathode in a battery may be prefabricated in any mechanical, chemical or electrochemical means excluding the conventional casting process. As an advantageous example, the wire or wires may be extruded or cold-formed. Such a process can be a continuous process allowing the production of lead or lead alloy wires in any desired length having not necessarily a round cross-section. The cross-section may be polygonal or star- shaped which increases the outer surface resulting in a better and quicker charging process of the battery.

An extrusion process for manufacturing the wires has the further advantage that each wire may contain a core, e. g. an inner tube or a core of highly conductive material like copper or silver. If a lower conductivity is sufficient, said core may be made up of a non-conductive or semi-conductive material like plastic or silicone steel which has the advantage to reduce the battery weight. The lead or lead alloy wire may also be produced by a cold drawing process giving the micro structure of the lead a better corrosion resistance and higher conductivity, due to the lower percentage of certain chemicals like antimony that can be used when prefabricating the wire. In that case the wire with improved conductivity may not need an inner core.

Further characteristic features and advantages will result from the claims and the following description of preferred embodiments illustrated in the drawings in which:

Figure 1 is a schematic section of an electrode according to the invention, figure 2 is a modification of figure 1 , figure 3 is a further modification, figure 4 shows a further embodiment, figure 5 shows the schematics of a battery cell, figure 6 shows an anode according to another embodiment of the invention, figure 7 shows a modified anode, figure 8 is a further embodiment of the invention, figure 9 illustrates an advantageous structure of an electrode and figure 10 is a modified embodiment of figure 9.

Figure 1 shows an electrode 10 of a battery which is made up of a series of wires 12 placed in a parallel arrangement 14 in a support structure 16. The support structure 16 is made up of an upper bar 18 and a lower bar 20.

According to the invention, the wires 12 may be extruded or cold- formed wires 12 of lead or lead alloy. They may have any cross-sectional shape and size and not necessarily a round cross-section. Thanks to the selected process for manufacturing said wires 12, there is no limit either in length or in composition which could be any lead alloy. The wires 12 may be prefabricated by any mechanical, chemical, physical or electric chemical process, excluding casting.

In the case of figure 1, the wires 12 can go right up in upper bar 18 to form part of it. Said bar 18 may be of lead or lead alloy or of any other material whether electrically conducting or not. The lead or lead alloy wires 12 may be embedded in the upper bar 18 by an insert molding injection process or any other process that would give the same end result. Some other possible ways of connecting the wires 12 to the upper bar 18 will be described on the embodiments shown in figures 3, 4, 9 and 10.

As further illustrated in figure 1, the wires 12 in the parallel arrangement 14 are covered by a textile gauntlet 22. In this case, the lead or lead alloy wires 12 may be provided with integral outer wings 24 for positioning the wires in the centre of said gauntlet 22. The extrusion manufacturing process of the lead or lead alloy wires 12 enable said side wings 24 to be an integral part of the wires 12, possibly throughout the whole length of the wires 12, or only at points where required along the wires. These could also be trimmed to provide the wings 24 at specific interval positions.

In figure 1 it is further illustrated that the lead or lead alloy wires 12 may have an inner core 26. Said core 26 may be made up of a variable conductive material. However, it is also possible to provide a core 26 made up of a hollow tube 28 (see figure 3), in which a cooling medium, possibly water, could be made to flow through the tubes 28 to assist in cooling of the electrode 10. As further illustrated in figure 3, the cooling circuit may be completed by a channel 30 provided in the lower bar 20 and connecting the lower ends of said tubes 28. In figure 2, the arrows 32 above a terminal 34 on top of the upper bar 18 are symbolics for the inlet and outlet of the cooling fluid.

In the embodiment of figure 1 - and also of figure 3 - the upper ends of the wires 12 embedded in the upper bar 18 are bunched together to form a bundle 36 which is connected to said terminal 34 on the top of the upper bar 18. Such bundle 36 improves the rigidity of the wire electrode 10, particularly in the case of very thin wires 12. As shown in figure 1, in said terminal 34 the lead wires 12 have their ends with the inner cores 26' exposed. These inner cores 26' are grouped together or left near each other and covered or coated with a conductive material such as lead or possibly any other conductive material to act as said terminal 34 for the whole assembly.

Figure 2 shows a modified electrode 10 of a battery which is also made up of a series of wires 12 placed in a parallel arrangement 14 and bunched together by any mechanical, chemical, physical or electric chemical process to form a top bundle 36, however without an upper bar. The lower bar 20 of the support structure 16 is used at the lower end to ensure a consistent spacing of the wires 12 after the textile gauntlet 22 is inserted and filled up with an active mass 46 which will be described in detail in the embodiments of figures 5 to 8.

In the embodiment of figure 4, the upper bar 18, whether made of a conductive material such as lead or not, is provided with an inner conductor 38 embedded in the upper bar 18 to improve the electrical properties and conductivity. In this case, the inner conductor 38 connecting the upper ends of the lead or lead alloy wires 12 has an upper protrusion 40 which is connected to the terminal 34 on top of the upper bar 18. The upper bar 18 could be made in lead, lead alloy or any other material by a forging process or any other mechanical, chemical or electrochemical means.

In the embodiment of figure 4, the lead or lead alloy wires 12, whether with or without an internal core 26, could also be prefabricated and then connected and fixed to the upper bar 18 by glueing, welding, soldering or any other chemical, mechanical or electrochemical process.

Figure 5 illustrates a battery cell 42 which is filled with an electrolyte 44 like H₂SO₄ and contains two electrodes - the cathode 10c and the anode 10a - which may have the form of plates, grids, rods or tubes. The anode electro-chemically active material 46 is lead dioxide PbO₂.

According to this embodiment of the invention the anode 10a made of lead dioxide has a core 26 made of highly conductive material or a mixture of highly conductive components, preferably metals. As an example, metals used here can be copper or silver.

As illustrated in the examples of figures 5 and 6, the inner core 26 is covered by a coating 48 of lead or a lead alloy. In this way the core 26 is in contact with lead or lead alloy only and not with the electrolyte 44 thus excluding undesired reactions like corrosion.

A lead dioxide mass 46 is placed between the coating 50 of lead or lead alloy covering the core 26 and a textile shell or gauntlet 22 which permits direct contact between the electrolyte 44 and the electro-chemically active mass 46. Good electric contact between the lead dioxide mass 46 and the core 26, 48 results in good high current properties of the anode 10a. In a further development of the invention (see figure 5) centring elements 24 may be placed between the core 26, 48 and the gauntlet 22 to ensure the central position of the core 26, 48 in the mass 46. Such centring elements 24 can be made of electro-chemically inactive matter, like for instance plastic or metal-covered plastic, or of lead or lead alloy.

It is further possible to achieve the desired high conductivity of the core 26, 48 by using instead of a solid metal a bundle of low diameter highly conductive wires.

Figure 7 shows an alternative for the core 26 made of a rod 26' of non-conductive material which is covered with a highly conductive material 26" and separated by the lead or lead alloy coating 48 from the electro-chemically active mass 46.

As illustrated in figure 8, it is further possible to replace the highly conductive core 26, 48 by a cavity 50. The surrounding electro-chemically active mass 46 may covered on the hollow inside by a coating 48 of lead or lead alloy and some highly conductive material 26".

Figure 9 shows schematically an electrode structure which is made up of a series of wires 12 placed in a parallel arrangement 14 in a support structure 16. The support structure 16 is made up of an upper bar or crosshead 18 and a lower bar or crosshead 20. The wires 12 are electrically connected by soldering points 52 at least to the upper crosshead 18, which is provided with a vertical extension serving as battery terminal 34.

The wires 12, the battery terminal 34 and the upper crosshead 18 are made up of a core 26 of the above mentioned highly conductive non-lead material covered by said coating 48 of lead or lead alloy. In the example of figure 9, the lower crosshead 20 is of lead or lead alloy, but it may be as well of non-conductive material.

In the modified embodiment of figure 10 the wire 12, as in figure 9 made up of a core 26 with a coating 48 plus the outer electro-chemically active mass 46, is arranged in meanders in said support structure 16.

An important advantage of the invention shown in figure 5 to 8 is that the inner core 26 with its coating 48 of lead or lead alloy makes it possible to reduce the volume and weight of the battery; the production cost for the battery will also be lowered; in the absence of any lead melting the production is more environment friendly. A battery using the technology of the invention will have a better capacity/volume and weight ratio and greatly improved high current properties for its charging and discharging.

The invention covers also an electric lead acid battery cell in which other metal parts than the anode are made in application of the core technology set out in the above description and in the claims.

Claims

1. Electrode forming a conductive element in a lead acid battery, characterized in that it is made up of at least one wire (12) containing lead or lead alloy.

2. Electrode according to claim 1, wherein said element is a plate made up of a series of lead or lead alloy wires (12).

3. Electrode according to claim 1 or 2, wherein each wire (12) is electrically connected to a battery terminal (34).

4. Electrode according to claim 3, wherein said series of wires (12) is held in a support structure (16).

5. Electrode according to claim 4, wherein said support structure (16) comprises a lower bar (20) used to position the lower ends of said wires (12) the upper ends of which are bunched together forming a bundle (36).

6. Electrode according to any of the preceding claims, wherein each wire (12) is prefabricated by any mechanical, physical, chemical, electrochemical or any other process.

7. Electrode according to claim 6, wherein each wire (12) is an extruded or cold-formed wire.

8. Electrode according to any of the preceding claims, wherein each wire (12) is made of lead or lead alloy only.

9. Electrode according to any of claims 1 to 7, wherein in each of said wires (12) a core (26) is embedded.

10. Electrode according to claim 9, wherein said core (26) is made at least partially of a highly conductive or semi-conductive non-lead material such as copper or silver or silicone steel.

11. Electrode according to claim 10, wherein said core (26) is embedded in a lead dioxide mass (46) and is covered by a coating (48) of lead or lead alloy.

12. Electrode according to claim 10 or 11, wherein the core (26) is made of a highly conductive mixture of metallic or non-metallic materials.

13. Electrode according to claim 9, wherein said core (26) is made up of a non-conductive material like plastic.

14. Electrode according to any of claims 10 to 13, wherein the core (26) is made of a bundle of low-diameter wires.

15. Electrode according to claim 9, wherein the core (18) comprises a cavity (28) and wherein the surrounding active mass (46) is covered on its hollow inside by the coating (48) of lead or lead alloy and some highly conducting metallic or non-metallic material (26").

16. Electrode according to any of claims 9 to 15, wherein the core (26, 48) is centered in a textile gauntlet (22) by means of centring elements (24) made of electrolyte resistant material like plastic, lead, lead alloy or the like.

17. Electrode according to any of claims 9 to 16, wherein said core (26) is made up of a hollow tube (28) containing a flowing cooling medium.

18. Electrode according to any of the preceding claims, wherein a series of rods or wires (12) are placed in a parallel or grid or meander arrangement (14) connected to a lower bar (20) and an upper bar (18), both forming said support structure (16).

19. Electrode according to claim 18, wherein the upper ends of said wires (12) are bunched together to form a bundle (36) connected to a terminal (34) on top of said upper bar (18).

20. Electrode according to claim 18, wherein in said upper bar (18) an inner conductor (38) is embedded connecting the upper ends of the wires (12) and having an upper protrusion (40) connected to a terminal (34) on top of said upper bar (18).

21. Electrode according to any of the preceding claims 17 to 20, wherein the hollow tubes (28) of said wires (12) are connected to a common channel (30) provided in the lower bar (20) of said support structure (16).

22. Electrode according to any of the preceding claims, wherein said wires (12) are prefabricated by extrusion.