NEGATIVE PLATE FOR LEAD ACID BATTERY
TECHNICAL FIELD
The present invention relates to a lead acid battery. In particular the invention relates to a negative plate for use in such batteries.
BACKGROUND
A lead acid battery of the prior art comprises multiple cells that are electrically connected together. A cell of a lead acid battery of the prior art is described in Fig. 1. The cell comprises; positive plates 301 of multiple lead or lead alloy spines 311 or grids 411; lead or lead alloy grid 341 for use as negative plate 381; intervening separators 351 between the positive and negative plates; positive and negative active material 321A and 321B applied to positive and negative plates respectively; electrolyte 371 which is normally sulphuric acid. The negative active material 321B normally comprises lead oxide, sulphuric acid, water and expanders such as lignosulfonate.
The positive active material 321A is normally in the form of soft paste, slurry or dry powder filled around each spine 311 of the positive plate 301 and supported in place by a porous tubular gauntlet tube 331 and a bottom bar 361. The negative active material 321B is normally in the form of soft paste and is pasted on to the grid 341. No gauntlet tube is used with the grid 341.
The reason for the above construction of the positive plate is that during operation of a lead acid battery the positive active material changes from PbO2 to PbSO4 resulting in volume expansion of the positive active material. During recharge, the reaction is reversed. In case the positive active material 321A is not supported in place around the spine by the tubular gauntlet tube 331, due to continuous volume expansion and reversal, the inter particle cohesion of positive active material 321A will be lost and contact between lead or lead alloy spines 311 or grid 411 will deteriorate, resulting in loss of electrical conductivity. Further, shedding of positive active material 321A results in build up of paste sediment at the bottom of the cell and sufficient sediment build up would contact the negative active material 321B, resulting in short circuit failure.
The negative active material 321B is in the form of sponge lead and, in typical deep cycle operation, the negative active material does not lose cohesion and shed easily and is readily retained by the underlying lead grid structure.
The above lead acid batteries of the prior art are of robust construction and suffice for most prior art applications. However, in applications where the batteries are not fully recharged and operate in partial state of charge, there is an accumulation of lead sulphate in the negative active material. Over prolonged usage, due to excessive build up of lead sulphate, the negative active material loses cohesion and tends to shed from the underlying grid structure. As with positive plate shedding, accumulation of negative material at the bottom of the cell would result in short circuit failure.
Further it has been found that lead acid batteries of the prior art are not suitable for certain emerging applications, particularly in applications involving operation of batteries in a partial state of charge. It has been found that the negative active material 321B of the prior art is unable to handle prolonged battery use in partial state of charge. In partial state of charge operation, it has been found that negative plate performance degrades. This degradation can be minimized through the addition of high conductivity materials to the negative active material. Such additives include purified natural flake graphite, purified expanded graphite, purified isotropic graphitic carbon, primary synthetic graphite, carbon black, activated carbon, titanium dioxide and materials similar to the foregoing. These materials are hereinafter collectively referred to as "conductive additives" and individually either by name or as "individual conductive additive". It may be noted that in this document the term conductive additives means the use of either any one, some or all of the individual conductive additives.
Such additives have poor bonding qualities and with high additive levels, negative active material 321B tends to lose inter particle cohesion and contact with grid 341.
There is therefore a need for lead acid batteries where the negative active material does not lose contact with the grid. There is also a need for lead acid batteries where the negative active material does not lose contact with the grid when high levels of additives are used.
SUMMARY
The present invention in one aspect relates to a cell of a lead acid battery. More particularly the present invention relates to a negative plate comprising multiple negative spines, negative active material, a top bar and a bottom bar for use with the negative plate and one or more negative gauntlet tubes. In another aspect the invention relates to a lead acid battery wherein the negative plate performance is improved in partial state of charge operation.
This summary is provided to explain the technical considerations and to introduce a selection of embodiments in a simplified form that are further described below in the detailed description. This summary is not intended to limit the scope of the claimed subject matter.
This invention in one embodiment relates to a cell of the lead acid battery, such cell comprising a positive plate comprising positive spines or positive grids, positive active material, a negative plate comprising multiple negative spines, negative active material, a top bar and a bottom bar for use with the negative plate, one or more negative gauntlet tubes, intervening separators between the positive plate and negative plate, electrolyte and electrical connectors.
The positive active material can be either dry filled or extruded as a wet paste into the positive gauntlet tubes or applied as a paste to the positive grid as in prior art.
The negative plate comprises multiple negative spines connected to a negative top bar. The negative top bar provides path for current and necessarily has to be of conductive material.
It would be noted that there is no practice in the art of using negative plates which comprise negative spines. The prior art teaches the use of grids that are pasted with negative active material.
The negative active material can be either dry filled or extruded as a wet paste into the negative gauntlet tube and the negative spines can be positioned into the negative gauntlet tube.
The negative gauntlet tube supports the negative active material applied to the negative plate. It would be clear to a person skilled in the art that the negative gauntlet tubes can be used to support the negative active material in more than one manner and this invention is not limited to the use of either a single negative gauntlet tube or individual negative gauntlet tube for each negative spine.
After the negative gauntlet tubes are in filled with negative active material the negative bottom bar is attached to the negative spines at the end of the negative spines away from the negative top bar.
The second embodiment of the invention further comprises the negative plate and the negative active material of the previous embodiment wherein the negative active material further comprises conductive additives.
It has now been found that using the negative plate of this invention and the negative gauntlet tubes as described in previous embodiment, it is possible to use negative active material comprising approximately 60% or even higher by weight of conductive additives in dry oxide.
The third embodiment of the invention comprises a tubular positive plate lead acid battery of this invention wherein the multiple cells are electrically connected together.
The third embodiment of the invention comprises a flat positive plate lead acid battery of this invention wherein the multiple cells are electrically connected together.
The above embodiments are intended to only exemplify the various manners in which the invention can be embodied. The embodiments are not intended to limit the scope of the invention. The invention, as would be evident to a person skilled in the art, can be exemplified in many other ways.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 describes a cell of a lead acid battery of the prior art.
Fig. 2A describes the cell 44 of lead acid battery 4 of the present invention.
Fig. 2B describes the negative plate 303 of the present invention.
Fig. 3A describes negative gauntlet tube 333 of the negative plate 303.
Fig. 3B describes individual negative gauntlet tubes 333 in accordance with one of the
embodiment of the present invention.
Fig. 3C describes the negative plate 303 in accordance with another embodiment of the
present invention.
Fig. 4 describes a tubular lead acid battery 4 of the present invention in accordance with
another embodiment of the present invention.
Fig. 5 describes a flat plate lead acid battery 4 of the present invention in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
The present invention is described with reference to the following embodiments. It will be evident to a person skilled in the art that the following embodiments are by way of example only and that the invention can be exemplified in many other ways. The embodiments are not intended to limit the scope of the invention and the invention can be exemplified in many other ways evident to a person skilled in the art.
The invention is general in nature and the battery of this invention can comprise any number of cells.
Embodiment 1
The first embodiment of the invention as described in Fig. 2A comprises a cell 44 of a lead acid battery 4 comprising:
1) positive plate 301 comprising positive spines 311 or positive grids 411;
2) positive active material 321A;
3) a negative plate 303 comprising multiple negative spines 313;
4) a top bar 315 and a bottom bar 317 for use with the negative plate 303;
5) one or more negative gauntlet tubes 333;
6) negative active material 321B;
7) intervening separators 351 between the positive plate 301 and negative plate 303;
8) electrolyte 371;
9) electrical connectors 345.
The positive plate 301 of this invention may comprise of positive spines 311 or positive grids 411 produced via casting, extrusion, punching or other processes.
The positive active material 321A of this embodiment can comprise lead oxide, sulphuric acid, water, additives or any other positive active material known to the art. The positive active material 321A can be either dry filled or extruded as a wet paste into the positive gauntlet tubes 335 or applied as a paste to the positive grid 411 as in prior art.
The negative plate 303 of this invention is described in Fig. 2B. The negative plate 303 comprises multiple negative spines 313 connected to a negative top bar 315. The negative top bar 315 provides path for current and necessarily has to be of conductive material. The conductive material can be lead, lead alloy or any other conductive material known to the art. The negative spines 313 are of the same material as negative top bar 315 and are often cast together with the negative top bar 315. The negative spines 313 can also be fabricated separately and joined to the negative top bar 315 by welding, riveting, use of adhesives or any other means known to the art.
It would be noted that there is no practice in the art of using negative plates 303 which comprise negative spines 313. The prior art teaches the use of grids that are pasted with negative active material.
The negative gauntlet tubes 333 of this embodiment can be woven and non woven tubes of material such as polyester or tubes made of porous acid resistant material such as ceramics or glass fiber.
The negative active material 321B of this embodiment can comprise lead oxide, sulphuric acid, water, expanders such as lignosulfonate, gels or any other negative active material known to the art. The negative active material can be either dry filled or extruded as a wet paste into the negative gauntlet tube 333 and the negative spines 313 can be positioned into the negative gauntlet tube 333.
There can be one or more negative gauntlet tubes 333 used with the negative plate 303. In case one negative gauntlet tube 333 is used the negative plate 303 can be inserted into the negative gauntlet tube 333 with the negative top bar 315 outside the negative gauntlet tube 333 as shown in Fig. 3A. In case individual negative gauntlet tubes 333 are used for each negative spine 313, individual negative spines 313 can be centered in each negative gauntlet tube 333 as shown in Fig. 3B.
The negative gauntlet tube 333 supports the negative active material 321B applied to the negative plate 303. It would be clear to a person skilled in the art that the negative gauntlet tubes 333 can be used to support the negative active material 321B in more than one manner and this invention is not limited to the use of either a single negative gauntlet tubes or individual negative gauntlet tube for each negative spine 311.
After the negative gauntlet tubes 333 are in place the negative bottom bar 317 is attached to the negative spines 313 at the end of the negative spines 313 away from the negative top bar 315 as shown in Fig. 3C. The negative bottom bar 315 can be of any non conductive material such as acid resistant plastic. The negative bottom bar 315 can be attached to the negative spines 313 by interference fit or using an acid resistant adhesive or by riveting or by any other means known to the art.
The intervening separators 351 can be of any porous acid resistant non conductive, microporous material such as glass fiber. The intervening separators 351 are placed between the positive plate 301 and the negative plate 303.
Embodiment 2
The second embodiment of this invention relates to the carbon and other additives comprised in the negative active material 321B. Studies indicate that while conductivity Increases, with consequent improvement in battery performance, with the use of carbon additives in the negative active material 321B, the negative active material 321B tends to lose contact with the negative plate 303 as the percentage of the carbon and other additives rises.
Presently it is difficult to use more than 5% by weight of conductive additives in negative active material 321B to produce a paste which can be applied to negative grids and held in place through battery assembly. It may be noted that the percentage weight of conductive additives in this document is calculated by ascertaining the dry weight of the additives as a percentage of the total dry weight of the negative active material 321B comprising the additives.
It has now been found that using the negative plate 303 of this invention and the gauntlet tubes 333 as described in Embodiments 1 and 2 permits use of negative active material 321B comprising approximately 60% or even higher by weight of dry oxide.
The individual conductive additive viz. purified natural flake graphite of this invention means purified natural flake graphite that has a mean particle size between approximately 7µm and approximately 12µm and BET specific surface area between approximately 5 m2g-1 and approximately 10 m2g-1.
The individual conductive additive viz. purified expanded graphite of this invention means purified expanded graphite that has a mean particle size between approximately 7µm and approximately 12µm and BET specific surface area between approximately 15 m2g-1 and approximately 40 m2g-1.
The individual conductive additive viz. purified isotropic graphitic carbon of this invention means purified isotropic graphitic carbon that has a mean particle size between approximately 12µm and approximately 30µm and BET specific surface area between approximately 10m2g-1 and approximately 20m2g-1.
The individual conductive additive viz. primary synthetic graphite of this invention means primary synthetic graphite that has a mean particle size between approximately 6µm and approximately 12µm and BET specific surface area between approximately 8m2g-1 and approximately 12m2g-1.
The individual conductive additive viz. carbon black of this invention means carbon black that has a mean particle size between approximately 12µm and approximately 24µm and BET specific surface area between approximately 100m2g-1 and approximately 200m2g-1.
The individual conductive additive viz. activated carbon of this invention means activated carbon that has a mean particle size between approximately 30µm and approximately 50µm and BET specific surface area between approximately 500m2g-1 and approximately 3000m2g-1
The conductive additives can be incorporated in the negative active material 321B by dry blending or mixing into a paste, slurry or any of the means known to the art.
Embodiment 3
Fig. 4 describes a tubular plate lead acid battery 4 of the present invention. The tubular plate lead acid battery 4 of this invention comprises multiple cells 44 of the previous embodiments that are electrically connected together as described in Fig. 4.

Embodiment 4
Fig. 5 describes a flat plate lead acid battery 4 of the present invention. The flat plate lead acid battery 4 of this invention comprises multiple cells 44 of the previous embodiments that are electrically connected together as described in Fig. 5.

We Claim:
1. A cell 44 of a lead acid battery 4 comprising:
a positive plate 301;
a tubular negative plate 303;
an intervening separator 351; and
an electrolyte 371, wherein said intervening separators 351 are placed between the positive plates 301 and negative plates 303.
2. A cell 44 of claim 1 wherein the positive plate 301 comprises multiple positive spines 311 or positive grid 411.
3. A cell 44 of claim 1 wherein the negative plate 303 comprises multiple negative spines 313.
4. A cell 44 of claim 1 which further comprises negative gauntlet tube 333, negative active material 321B applied to the negative plate 303 where such negative active material 321B is supported in place by one or more negative gauntlet tubes 333.
5. A cell 44 of claim 4 which comprises one negative gauntlet tube 333.
6. A cell 44 of claim 4 which comprises one negative gauntlet tube 333 for each negative spine 313.
7. A cell 44 of claim 4 which comprises a plurality of negative gauntlet tubes 333.
8. A cell 44 of claim 4 to claim 7 wherein the negative active material 321B comprises conductive additives or individual conductive additive.
9. A cell 44 of claim 8 wherein the negative active material 321B comprises at least 5% by weight of conductive additives.
10. A cell 44 of claim 8 wherein the negative active material 321B comprises at least 10% by weight of conductive additives.
11. A cell 44 of claim 8 wherein the negative active material 321B comprises at least 15% by weight of conductive additives.
12. A cell 44 of claim 8 wherein the negative active material 321B comprises at least 20% by weight of conductive additives.
13. A cell 44 of claim 8 wherein the negative active material 321B comprises at least 50% by weight of conductive additives.
14. A lead acid battery 4 comprising cells 44, positive plate 301, tubular negative plate 303 and conductive additives of any of the previous claims.