WO1997030486A1

WO1997030486A1 - A compressed gelled electroylyte lead acid battery having pressure applying means and components therefor

Info

Publication number: WO1997030486A1
Application number: PCT/AU1997/000080
Authority: WO
Inventors: Russell Harvey Newnham; Anthony Frank Hollenkamp
Original assignee: Commonwealth Scientific And Industrial Research O Rganisation; International Lead Zinc Research Organization Inc.
Priority date: 1996-02-16
Filing date: 1997-02-14
Publication date: 1997-08-21
Also published as: AUPN808096A0

Abstract

A compressed gelled electrolyte lead acid battery (1) having adjustable pressure applying means (5) for applying pressure to plates contained within the battery and a separator (3) for separating positive plates (4) from negative plates (2), the separator (3) comprising at least one sheet of suitable material supported on a support body comprising two sheets of an acid resistant material separated one from the other by ribs that extend transversely from one sheet to the other, the support body having a number of through-holes therein to enable electrolyte to flow therethrough, the pressure applying means (5) being used to apply pressure to the plates (2, 3, 4) in a range from 10 to 100 kilopascals.

Description

ACOMPRESSEDGELLEDELECTROLYTELEADACIDBATTERYHAVINGPRESSUREAPPLYING MEANSANDCOMPONENTSTHEREFOR

The present invention relates to gelled electrolyte lead acid batteries especially for use at high rates.

Gelled electrolyte batteries hitherto have been used in 5 applications where generally high cyclability is required but a high rate of discharge is not. Separators used in gelled electrolyte batteries have normally been sheets of microporous materials, such as sintered polyethylene composites. A microporous separator greatly inhibits the

10 tendency for conducting lead dendrites to form bridges between adjacent plates. Such bridges constitute short circuits that cause rapid battery failure. Current microporous separators are also able to withstand moderate levels of plate compression within a gelled electrolyte

15 battery. This ensures generally acceptable, though often unremarkable, cycle life. Unfortunately, microporous materials also introduce an unwanted effect. They contribute adversely to the internal resistance of the battery and thereby reduce battery performance at high

20 rates of discharge. D Berndt has summarised this trade-off of properties in the following way: "The slightly higher internal resistance of batteries with gelled electrolyte is mainly because a conventional microporous separator has to be used with gel, otherwise lead dendrites can penetrate

25 the space between the electrodes". In order to raise the high rate performance of gelled electrolyte batteries, whilst at the same time maximising cyclability, it is necessary not only to reduce the resistance of the separator, but also to provide a means for:

30 (i) applying high levels of plate compression;

(ii) preventing adjacent plates from touching under the influence of compressive forces.

(iii) maintaining ease of gel filling during production.

The specifications of Japanese patent application Nos 12760/84, 170074/90, 325055/90 and 57930/93 all disclose compressed lead acid batteries. Each discloses a different means of applying pressure to the plates. For example the specification of patent application No 12760/84 discloses an "elastic compressive" body that encloses the plates and the electrolyte.

The specification of French patent application having publication No 2425733 discloses a flooded electrolyte battery in which the plates are compressed by means of an assembly of nuts, bolts and springs in which the pressure applied to the plates is increased to the desired level by tightening the nuts on the bolts and compressing the springs surrounding the bolts so that they bear against the outer plate of the battery assembly. Examples disclosed in the specification demonstrate that cycle life increases with increased pressure from 800 cycles at a pressure of .15 bar to 1500 cycles at a pressure of 1 bar.

The specification of Japanese patent application No 53184/83 discloses a lead acid battery containing an inflated bag that applies a pressure in the range from 5 to 20kg/dm² to the plates of a lead acid battery. Hence the maximum pressure contemplated in this specification is approximately five times lower than the optimum pressure contemplated in the specification of the French patent application referred to previously.

The specification of United States patent No 4664992 describes a separator that comprises two grids that compress a thin sheet of microporous material therebetween. In principle this separator should function reasonably well. However the volume occupied by the grid and microporous sheet is likely to exceed 25% and in addition the structure of the overall battery proposed in this specification appears totally impractical because of the low active material to total volume ratio.

An object of the present invention is to provide a gelled electrolyte lead/acid battery having high cyclability that is capable of operating at high rates of discharge.

Accordingly the present invention provides a compressed gelled electrolyte lead acid battery having adjustable pressure applying means for applying pressure to plates contained within the battery and a separator for separating positive plates from negative plates, the separator comprising at least one sheet of suitable material supported on a support body comprising two sheets of an acid resistant material separated one from the other by ribs that extend transversely from one sheet to the other, the support body having a number of through-holes therein to enable electrolyte to flow therethrough, the pressure applying means being used to apply pressure to the plates in a range from 20 to 100 kilopascals or more preferably from 10 to 100 kilopascals.

The adjustable pressure means may comprise an inflatable bag made from a flexible resilient acid resistant material provided with a means for measuring fluid pressure contained within the bag and a means of adding fluid to the bag or removing fluid from it in order to control the pressure within it. Butyl rubber and natural rubber are two materials from which the inflatable bag could be made.

Pressure inside the bag once filled can be monitored by means of a transducer. Changes in pressure, corrected for any change in temperature can be used to follow any expansion or contraction in the plates and make any desired changes in the pressure. Another method for maintaining the required level of compression in a gelled electrolyte lead acid battery is to replace the inflatable bag with an elastically compressible member for example a solid piece of an acid resistant rubber such as silicon rubber, closed pore polyethylene foam and certain natural rubbers. Alternatively the elastically compressible member may comprise a base supporting multiple protrusions each of which may be elastically deformed as pressure is applied to them. The multiple protrusions may comprise a series of ridges protruding transversely from a face of the base.

In general the adjustable pressure means may comprise any body that is capable of elastically adjusting the pressure applied to the plates as internal plate pressure changes. Such a body may comprise a band that is capable of being elastically stretched to surround the plates and squeeze them together.

The separator used in the battery of the present invention was designed to occupy a minimal volume as well as have a minimal effect on the rate of diffusion of electrolyte therethrough. In a preferred form of the separator it comprises a support body constructed from an acid resistant material for example polyethylene and a thin outer layer located on opposite sides of the main body. The thin outer layer may be for example a glass mat. The thin outer layer may also comprise a high performance microporous mat or a woven polyester sheet or any combination of glass mat, high performance microporous mat and/or woven polyester sheet.

Depending on the material and method of manufacture, the support body of the separator may be either one piece or consist of two halves that are bonded together. Normally the construction of the support body is such that the outer sheets are separated by a series of ribs that form a series of compartments. The ribs provide the support body with most of its mechanical strength. The thickness of both the outer sheets and ribs and the rib spacing are determined by the strength of the material used. A series of holes are formed, punched or drilled through the main body of the separator to allow for the movement of electrolyte. The holes may be round, diamond shaped or any other shape. The holes are located along the ribs to allow the diffusion of acid from one compartment to another. The location, shape and size of the holes, that is the hole pattern, depend upon the intended application of the battery and the required compression resistance of the whole separator.

The various aspects of the invention will now be explained with reference to the accompanying drawings in which Figure 1 represents a cross-sectional side elevation of the battery according to the invention, Figure 2 is an end elevation showing an embodiment of an adjustable pressure means, Figure 3 is a plan view of a separator according to the invention, Figure 4 is a cross-sectional view along line AB of Figure 3; Figure 5 is a cross-sectional side elevation of another embodiment of a battery according to the invention; and Figure 6 is a graph illustrating the differing capacities of gelled-electrode batteries constructed with high and low plate-group compression.

Figure 1 depicts a battery 1 having negative plates 2 separators 3 and positive plates 4 arranged in seven plate sets. The battery 1 is provided with an inflatable rubber bag 5 located at one end of the plate sets within the casing 6 but separated from the plate sets by spacer 7. As shown in Figure 2 the rubber bag 5 has a valve 8 connected to a pump 9. The inflatable rubber bag 5 is also provided with a pressure transducer 10 connected to pump controlling means 11.

After the plates and electrolyte have been inserted into the battery casing, gas is pumped into the rubber bag 5 though inlet 8 thereby inflating rubber bag 5 and causing it to bear against spacer 7 thereby transferring pressure evenly to the plate sets comprising battery 1. The pressure applied to the plate sets by the inflated rubber bag 5 can be adjusted in response to changes in the pressure of gas contained within the inflatable rubber bag 5 measured by the pressure transducer 10.

Figures 3 and 4 depict a separator that can be usefully employed in a high rate, compressed, gelled electrolyte battery. The separator 12 comprises a first sheet of material 13 separated from a second sheet of material 14 by ribs 15. Holes 16 are formed in the separator body 12 along the line of each of the ribs 15. The surfaces of the sheets 13 and 14 are covered with a thin sheet of a microporous material such as polyethylene, or a thin glass mat to complete the separator.

Figure 5 depicts a battery 17 having sets of negative plates 18 and positive plates 19 arranged alternatively and confined within a rigid spacer 20. A compression plate 21 bears against the spacer, transferring pressure evenly to the sets of negative and positive plates. The compression plate comprises a base member supporting multiple protrusions, each of which may be elastically deformed as pressure is applied to them, thus varying the pressure applied to the rigid spacer.

Figure 6 illustrates the performance of two gelled- electrode batteries as expressed in terms of their capacity (C₃/3 rate, 100% depth-of-discharge) against number of cycles. The batteries were identical apart from the separator systems used to separate the plates. One cell was constructed with a traditional separator and low plate- group compression (< 2kPa) . The other cell was assembled with the new high-compression separators, an elastically compressable member such as novel compression plate and a high level of plate-group compression (40 kPa) .

From the graph it is apparent that the low compression cell failed after - 60 cycles, whereas the high-compression variant is still operating at close to 100% of its nominal capacity after 160 cycles. The results clearly illustrate that incorporating high plate-group compression into gelled-electrolyte batteries can improve their cycle-life markedly, compared with low compression versions.

The invention will be further described with reference to the following non-limiting Example;

EXAMPLE

Two gelled-electrolyte cells were assembled with moderate compression. The cells were identical except for the separators used to isolate the positive and negative plates - one was fitted with standard gelled-electrolyte battery separators, the other had the new high-compression separators. The cells were discharged to 100% depth-of- discharge at several different discharge rates, i.e. C₃/3 (3h), C_j/l (1 h), C_{0 17}/0.17 (10 min) and C_{0 03}/0.03 (2 min). The results are given in Table 1. Each capacity value is the average of three discharges. It can be seen that C₃/3 capacity for the cell with the new separator is 13% higher than that of the cell with a standard separator. The performance advantage associated with the new separator increases to 400% at the highest discharge rate

(C_{0 03}/0.03). This leaves the separator system ideally placed for use in EV gelled-electrolyte batteries, as such duty requires excellent high-rate performance. TABLE 1

While the invention has been explained in relation to its preferred embodiments it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.

Claims

CLAIMS :

1. A compressed gelled electrolyte lead acid battery having adjustable pressure applying means for applying pressure to plates contained within the battery and a separator for separating positive plates from negative plates, the separator comprising at least one sheet of suitable material supported on a support body comprising two sheets of an acid resistant material separated one from the other by ribs that extend transversely from one sheet to the other, the support body having a number of through¬ holes therein to enable electrolyte to flow therethrough, the pressure applying means being used to apply pressure to the plates in a range from 10 to 100 kilopascals.

2. A compressed gelled electrolyte lead acid battery according to claim 1 wherein the pressure applied to the plates is in the range from 20 to 100 kilopascals.

3. A compressed gelled electrolyte lead acid battery according to claim 1 or claim 2 wherein the adjustable pressure applying means is an elastically compressible member.

. A compressed gelled electrolyte lead acid battery according to claim 3 wherein the elastically compressible member comprises a solid piece of an acid resistant rubber or closed pore polyethylene foam.

5. A compressed gelled electrolyte lead acid battery according to claim 3 wherein the elastically compressible member comprises a base supporting multiple protrusions each of which is elastically deformable.

6. A compressed gelled electrolyte lead acid battery according to claim 5 wherein the multiple protrusions comprise a series of ridges protruding transversely from a face of the base.

7. A compressed gelled electrolyte lead acid battery according to claim 1 or claim 2 wherein the adjustable pressure applying means comprises a band that is capable of being elastically stretched to surround the plates and squeeze them together.

8. A compressed gelled electrolyte lead acid battery according to claim 1 or claim 2 wherein the sheet of suitable material is a glass mat or a high performance microporous mat or a woven polyester sheet or any combination thereof.

9. A compressed gelled electrolyte lead battery according to claim 1 or claim 2 wherein the pressure applying means comprises an inflatable bag and pressure adjusting means for adjusting fluid pressure in the inflatable bag in response to changes in internal plate group pressure.