GB2351385A

GB2351385A - Separator

Info

Publication number: GB2351385A
Application number: GB9913884A
Authority: GB
Inventors: Thomas William Welch
Original assignee: Hawker Energy Products Ltd
Current assignee: Hawker Energy Products Ltd
Priority date: 1999-06-16
Filing date: 1999-06-16
Publication date: 2000-12-27
Also published as: GB9913884D0

Abstract

A separator (1) for interposing between the positive and negative electrode plates (5) in a battery cell comprises a rectangular sheet of material comprising glass and organic fibres having a region (3, 4)extending parallel to and adjacent at least one edge which is of increased hardness or toughness with respect to the remainder (2) of the separator. The region of increased hardness or toughness may include fibres bonded more closely together than those fibres in the remainder of the separator.

Description

2351385 SEPARATOR This Invention relates to a separator as used to

separate the positive and negative electrode plates in a battery cell.

Conventionally a battery cell comprises alternate positive and negative electrode plates, usually rectangular, separated from one another by interleaved separators, also usually in the form of a rectangular sheet. The simplest arrangement is a positive electrode plate, a negative electrode plate and, sandwiched between the two plates, a separator, Further separators may also be arranged outwardly of the two electrodes to space the assembly away from the walls of the cell box or chamber within which the assembly is positioned. The box or chamber is then filled with electrolyte. The separator being porous thus allows the electrolyte to contact the electrode plates but also prevents an electrical short occurring between the plates. Other arrangements are known, eg seven positive plates and six negative plates in a cell, depending on the battery performance required.

The separator is usually a piece of sheet material cut from a long length, the dimensions of each piece being slightly larger than the dimensions of the electrode plate. This protects the plate by reducing the likelihood of damage occurring to the edges of the plates and also prevents electrical shorts between the edge of one plate and the edge of the next adjacent plate of opposite polarity. However it has been found that the edges of the separators themselves are prone to damage so that the protective effect does not occur.

It is an object of the present invention to provide a separator which does not suffer from, or suffers less, from this disadvantage.

In accordance with the invention a separator comprises a rectangular sheet of material comprising glass and organic fibres having a region extending parallel to and adjacent at least one edge which is of increased hardness or toughness with respect to the remainder of the separator.

Preferably the region of increased hardness or toughness includes fibres bonded more closely together than those fibres in the remainder of the separator.

Preferably, the separator has two regions respectively adjacent two 2 opposite parallel edges of the sheet. The edges are those which extend longitudinally of a long length of separator material from which a piece has been cut to form the individual separator.

One example of the organic fibres is polyester fibres.

Within the separator glass and organic fibres are preferably non-woven, but may be woven, and in the said region the fibres are more closely positioned together, the number and size of spaces between the fibres being reduced compared to the number and size of the spaces between fibres in the remainder of the separator.

The region preferably has a thickness which is less than that of the remainder of the separator, said thickness being predetermined. The region is also preferably less compressible than the remainder of the separator.

In accordance with another aspect of the invention, a method of manufacturing a separator comprises forming a rectangular sheet of glass and organic fibres, and forming a region adjacent one edge of the sheet of increased hardness or toughness compared to the remainder of the separator.

The method preferably includes cuffing the rectangular sheet from a long length of material having two parallel edges, and forming the region either before or after the sheet is cut from the long length. Two regions may be formed, each one adjacent a respective one of the two parallel edges.

The method also preferably includes forming the or each region by causing the fibres therein to be more closely positioned together, so that the number and size of spaces between the fibres is reduced.

in one method according to the invention the or each region is subjected to a heating step causing local melting of the organic fibres and/or softening of the glass fibres, and subsequent increase in the number and size of bonds between the respective fibres with corresponding reduction in the number and size of spaces between fibres. The method may also include the step of compressing the or each region immediately before and/or after and/or during the heating step.

One embodiment of the invention will now be described by way of example only with reference to and as illustrated in the accompanying drawings 3 of which:- Figure I shows a perspective view of one end of part of the separator according to the invention; Figure 2 shows an end view of a stack of separators and electrode plates prior to being inserted into a battery cell box or chamber; Figure 3 shows a simplified diagrammatic side view of the manufacture of the separator shown in Figure 1; and Figure 4 shows a section on line IV-IV of Figure 3.

The separator I as shown in Figure 1 comprises a rectangular sheet of material of non-woven glass and polyester fibres. Two opposite edges are provided with adjacent regions 3, 4 which are of a predetermined thickness and less than the remaining central part 2 of the separator.

The overall width of the separator is slightly greater than the width of the electrode plate 5 as seen in Figure 2, and the two regions 3, 4 are narrow compared with the overall width of the separator. The edge of each electrode lies immediately adjacent and parallel to a region of an adjacent separator, so the outer edge of the region lies beyond the edge of the electrode and the inner edge of the region lies inwardly of the edge of the electrode.

The edge regions of the separator have been formed by being locally heated and compressed, as will be described so that in the region the polyester fibres have melted and the glass fibres softened so that each sort of fibres bond together so that the number and size of spaces in the edge regions are reduced compared to the number and size of spaces in the remainder of the separator, This has the effect of hardening or toughening the edge regions, so that during battery manufacture and use, the side edges of the electrode plates are better protected, since the edges of the separators are less prone to damage. Further, when the stack of plates and separators are placed in a battery cell, compression of the separator takes place, Since the edge regions are harder and/or tougher, the amount of compression of the central region 2 is controlled and the final thickness of the central region is substantially equal to the thickness of each of the edge regions 3 and 4 which as been predetermined during manufacture.

4 As shown in Figures 3 and 4, to manufacture a separator in accordance with the invention, a roll 6 of conventional separator material in the form of a long strip is provided. Material 7 is fed from the roll 6 through pairs of heating platens 8 which heats the two regions immediately adjacent the two longitudinal parallel edges of the strip. This melts the polyester fibres and softens the glass fibres. The strip is then fed between a pair of rollers 9, 10 profiled as shown in Figure 4. As can be seen, the roller has two side parts 11, 12 which contact one another, two intermediate parts 13, 14 which receive and compress the side regions of the strip to the required predetermined thickness, and a central part 15 which allows the central region of the strip material 7 to pass through at its natural thickness. The side parts 11, 12, instead of being smooth may be formed with gear teeth which intermesh during rotation of the rollers 9,10.

Pieces 18 of the long length of separator material are then cut at 17 by a knife 16. The pieces 18 cut from the long length become the separators 1 which are subsequently used in the cell.

Claims

CLAIMS:

1 A separator comprising a rectangular sheet of material comprising glass and organic fibres having a region extending parallel to and adjacent at least one edge which is of increased hardness or toughness with respect to the remainder of the separator.

2 A separator according to Claim 1 wherein the region of increased hardness or toughness includes fibres bonded more closely together than those fibres in the remainder of he separator.

3 A separator according to either Claim 1 or Claim 2 having two regions respectively adjacent two opposite parallel edges of the sheet.

4 A separator according to any one of the preceding claims wherein the organic fibres are polyester fibres.

A separator according to any one of the preceding claims wherein the glass and organic fibres are non-woven.

6 A separator according to any one of Claims I to 4 wherein the glass and organic fibres are woven.

7 A separator according to Claim 5 or Claim 6 wherein in the said region the fibres are more closely positioned together, the number and size of spaces between the fibres being reduced compared to the number and size of the spaces between fibres in the remainder of the separator.

8 A separator according to any one of the preceding claims wherein the region has a thickness which is less than that of the reminder of the separator, said thickness being predetermined.

9 A separator according to any one of the preceding claims wherein the region is less compressible than the remainder of the separator.

A separator substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings.

11 A method of manufacturing a separator comprises forming a rectangular sheet of glass and organic fibres, and forming a region adjacent one edge of the sheet of increased hardness or toughness compared to the remainder of the separator.

12 The method according to Claim 11 comprising cuffing the rectangular 6 sheet from a long length of matedal having two parallel edges, and forming the region either before or after the sheet is cut from the long length.

13 The method according to Claim 12 wherein two regions are formed, each one adjacent a respective one of the two parallel edges.

14 The method according to any one of Claims 11, 12 or 13 including forming the or each region by causing the fibres therein to be more closely positioned together, so that the number and size of spaces between the fibres is reduced.

The method according to any of Claims 11 to 14 comprising subjecting the or each region to a heating step thus causing local melting of the organic fibres and/or softening of the glass fibres and subsequent increase in the number and size of bonds between the respective fibres with corresponding reduction in the number and size of spaces between the fibres.

16 The method according to Claim 15 including the step of compressing the or each region immediately before and/or after and/or during the heating step.

17 A method of manufacturing a separator substantially as described herein with reference to and as illustrated in Figures 3 and 4 of the accompanying drawings.

18 A battery cell comprising at least one separator according to any one of Claims 1 to 10.

19 A battery cell comprising at least one separator manufactured by a method according to any one of Claims 11 to 17.