WO2014042542A1

WO2014042542A1 - Method of manufacturing a carbon fibre electrode of a lead-acid battery or cell

Info

Publication number: WO2014042542A1
Application number: PCT/NZ2013/000167
Authority: WO
Inventors: John Abrahamson
Original assignee: Arcactive Limited
Priority date: 2012-09-11
Filing date: 2013-09-11
Publication date: 2014-03-20

Abstract

A method for manufacturing a carbon fibre electrode of a lead-acid battery or cell includes thermally treating a carbon fibre tow splitting the tow into two or more smaller tows or stretch breaking the tow, weaving or knitting the carbon fibre into a carbon fibre material, or forming a non-woven carbon fibre material from the carbon yarn, and manufacturing the carbon fibre electrode from the carbon fibre material.

Description

METHOD OF MANUFACTURING A CARBON FIBRE ELECTRODE OF A LEAD-ACID

BATTERY OR CELL

FIELD OF THE INVENTION

The invention relates to an improved method for manufacturing a carbon fibre electrode of a lead-acid battery or cell, and to a battery or cell electrode so formed.

BACKGROUND

International patent application publication WO2011/078707 discloses a lead-acid battery or cell and method for manufacturing same, including at least one electrode comprising as a current collector a conductive fibrous material carbon fibre material. SUMMARY OF INVENTION

In broad terms in one aspect the invention comprises a method for manufacturing a carbon fibre electrode of a lead-acid battery or cell, or a lead-acid battery or cell, which includes manufacturing at least one carbon fibre electrode from carbon fibre material which has been woven, or knitted, or formed as a non-woven carbon fibre material, from

multifilament carbon fibre which has been :

• split from a higher filament count bundle of carbon fibres ('tow'), into smaller tows, or

• stretch broken to break individual continuous filaments into shorter filaments and separate lengthwise the ends of filaments at each break, reducing the filament count of the carbon fibre tow, or

• split from a higher filament count bundle of carbon fibres ('tow'), into smaller tows, and then stretch broken to break individual continuous filaments into shorter filaments and separate lengthwise the ends of filaments at each break, further reducing the filament count of the carbon fibre tows.

The tow may have been thermally treated before splitting or stretch breaking, to carbonise same. The starting tow may comprise more than about 3000, more than about 4000, more than about 5000, more than about 8000, more than about 10,000, more than about 15,000, more than about 20,000 filaments, more than about 30,000 filaments, more than about 40,000 filaments, more than about 50,000 filaments, or more than about 55,000 filaments for example. The tow may be split and/or stretch broken to tows of less than 3000, less than 2000, less than 1500, or less than 1000 fibres or filaments for example. The step of splitting the tow may comprise splitting the tow to two, three, four, five, ten, or more smaller tows of carbon fibres, for example.

In broad terms in another aspect the invention comprises a method for manufacturing a carbon fibre electrode of a lead-acid battery or cell, or a lead-acid battery or cell, which includes:

• thermally treating a bundle of hydrocarbon-based filaments ('tow') to carbonise same,

• splitting the bundle of carbon filaments into two or more smaller bundles (tows of 'carbon fibre'), or stretch breaking the tow of carbon filaments to break individual continuous filaments into shorter filaments and separate lengthwise the ends of filaments at each break, reducing the filament count of the carbon fibre tow, or both,

• weaving or knitting the tows of carbon fibre into a carbon fibre material, or forming a non-woven carbon fibre material, and

· manufacturing at least one carbon fibre electrode from the carbon fibre material.

In broad terms in another aspect the invention comprises a carbon fibre electrode of a lead-acid battery or cell, or a lead-acid battery or cell comprising at least one carbon fibre electrode, produced by the method defined above.

The material used in the experimental work described in WO2011/078707 was formed from carbon fibre which had not been split or stretch broken from higher filament tow(s) (and each comprising less than 3000 carbon filaments per fibre). This provides a certain battery performance. We have surprisingly found that similar performance can be obtained when the carbon fibre material is formed from carbon fibres which have been processed as a higher count tow and then the tow split into multiple fibre bundles of lower filament count than the tow, or stretch broken into a lower filament count fibre bundle, or both tow split and then stretch broken. This was contraindicated because it is known for other applications of carbon fibre materials that for example splitting a higher filament carbon fibre tow and then forming a carbon fibre material from the resulting 'splits' or fibres produces a weaker carbon fibre material probably because the mechanical splitting of the tow breaks and/or otherwise physically damages a proportion of the individual filaments, and the same could be expected for stretch breaking also, in which the longer continuous fibres are broken into shorter staple fibres. We have found that in a Pb acid battery or cell electrode application, where the electrode(s) is/are formed from a carbon fibre material produced from carbon fibres split or stretch broken from higher count tows, the mechanical damage is advantageous to the electrode performance and/or that any mechanical weakness is not disadvantageous, and also that a processing economy can simultaneously be achieved by thermal treatment of the higher tow fibre bundles.

The electrode carbon fibre material may comprise an average interfibre spacing of less than 200 or less than 100 or less than 50 or less than 20 microns. The electrode material may be a woven material (comprising intersecting warp and weft fibres), a knitted material, or a non-woven material such as a felted material.

The method for manufacturing a carbon fibre electrode of a lead-acid battery or cell, or a lead-acid battery or cell, may also include impregnating the carbon fibre material under pressure with a paste, such as a paste comprising a mixture of lead sulphate particles and dilute sulfuric acid. In some embodiments the paste comprises Pb-sulphate particles, PbO particles, Pb particles, or a mixture of Pb-sulphate particles, PbO particles, and/or Pb particles. In some embodiments lead sulphate paste is substantially the sole source of lead in the active material paste.

The method may also include forming a conductive connection ('lug') to the carbon fibre material or electrode.

The positive electrode or electrodes, the negative electrode or electrodes, or both, may be formed from the carbon fibre material.

By 'hydrocarbon-based' in relation to the filaments of the tow is meant any material able to be spun into filamentary fibres having a backbone of predominantly carbon and able to be formed into substantially solid carbon by processing, such as polyacrylonitrile (PAN), rayon, pitch, lignin, or polypropylene for example.

By 'carbonise' is meant processing typically thermal processing for example at 800C or more or 1100C or more, in an inert gas atmosphere, but which may be aided by chemical reaction in the liquid phase, to remove non-carbon elements.

By 'tow' is meant a filament bundle of carbon fibres. By 'tow splitting' is meant dividing a carbon fibre bundle into two or more carbon fibre bundles which each has a lower filament count and 'tow split' has a corresponding meaning. By 'stretch breaking' is meant subjecting a carbon fibre bundle to a tensile force to break individual continuous filaments into shorter filaments and lengthen and reduce the filament count of the carbon fibre tow per unit length and 'stretch broken' or 'stretch break' has a corresponding meaning. The term "comprising" as used in this specification means "consisting at least in part of". When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner. BRIEF DESCRIPTION OF THE FIGURES

The invention is further described with reference to the accompanying figures by way of example in which :

Figure 1 schematically illustrates steps in a manufacturing method of the invention utilising tow splitting, and

Figure 2 schematically illustrates steps in a manufacturing method of the invention utilising stretch breaking.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention relates to an improved battery construction and method for manufacturing lead-acid batteries.

In the traditional pasted-plate construction of a lead-acid battery each plate consists of a conductive grid initially filled with a paste comprising a mixture of leady oxide (Pb and

PbO) and dilute sulfuric acid. The acid in the paste reacts with the leady oxide inside the plate during cell formation. Alternatively, it is also known to form the conductive grid of the negative or positive or both electrodes of the cells of a Pb-acid battery of a carbon fibre material. WO2011/078707 discloses a lead-acid battery or cell in which the conductive grid is a carbon fibre material.

In the manufacturing method of the invention the carbon fibre electrode(s) is/are formed from carbon fibre material which has been woven, knitted, or formed as a non-woven material such as a felt material, from carbon fibre which has been in turn been split or stretch broken or both from higher filament count bundles, which have been previously thermally treated to carbonise the filaments ie the higher tow bundles which are thermally treated comprise a higher filament count than the subsequently divided fibres. This was contraindicated because it is known for other applications of carbon fibre materials that splitting or stretch breaking a higher filament carbon filament tow and then forming a carbon fibre material from the resulting fibres produces a weaker carbon fibre material probably because the mechanical splitting or breaking of the tow breaks and/or otherwise physically damages a proportion or all of the individual filaments.

However we have found that in a Pb acid battery or cell electrode application, where the electrode(s) is/are formed from a carbon fibre material produced from carbon fibre or stretch broken split from higher filament count tows, the mechanical damage is

advantageous to the electrode performance and/or that any mechanical weakness is not disadvantageous, and also that a thermal processing economy can simultaneously be achieved, and battery performance is not substantially adversely affected.

Manufacturing method steps of a tow splitting embodiment of the invention are illustrated in figure 1, and comprise first thermally treating a higher filamentary count tow, such as for example a tow of more than about 3000, about 4000, about 5000, about 8000, about 10,000, about 15,000, about 20,000, about 30,000, about 40,000, about 50,000, or about 55,000 carbon fibres, by moving the tow through an oven. The carbon containing fibres may be for example polyacrylonitrite (PAN) based carbon fibres. The thermal treatment may be carried out in a tube oven through which the tow is drawn.

Then the thermally treated tow is split into multiple lower filament count carbon fibres. The tow may be split to into two, three, four, five, ten, or more carbon fibres, each of less than about 2500, less than about 2000, less than about 1500, or less than about 1000 filaments for example.

Then the carbon fibre material is produced by weaving or knitting the carbon fibres, or forming a non-woven carbon fibre material such as a felt material. The average depth of the material may be at least about 0.2 millimetres or at least about 1 millimetre. At least a majority of the fibres may have a mean fibre diameter of less than about 15 microns, more preferably less than about 12 microns, more preferably less than about 10 microns, more preferably less than about 9 microns, more preferably less than about 8 microns, more preferably less than or equal to about 6 to about 7 microns, more preferably equal to about 4 to about 5 microns, more preferably equal to about 3 microns, more preferably equal to about 3 microns, more preferably equal to about 2 microns, more preferably equal to about 1 micron. The carbon fibre material may comprise filaments comprising fibres with an average inter fibre spacing of less than about 200 or less than about 100 or less than about 50 or less than about 20 microns.

Then the carbon fibre electrodes are manufactured from the carbon fibre material. The positive electrode or electrodes, the negative electrode or electrodes, or both, may be formed of one or more layers of the conductive fibrous material. The carbon fibre electrodes will be impregnated under pressure with a paste, such as a paste comprising a mixture of lead sulphate particles and dilute sulfuric acid. In some embodiments the paste comprises Pb-sulphate particles, PbO particles, Pb particles, or a mixture of Pb-sulphate particles, PbO particles, and/or Pb particles. In some embodiments lead sulphate paste is substantially the sole source of lead in the active material paste. A conductive connection ('lug') to the carbon fibre material or electrode is also formed. The positive electrode or electrodes, the negative electrode or electrodes, or both, may be formed from the carbon fibre material.

Optionally after the carbon fibre material is produced by weaving or knitting the carbon yarn into a carbon fibre material, or forming a non-woven carbon fibre material such as a felt material, the carbon fibre material may be further heat treated to a sufficient temperature to increase its electrical conductivity. In certain embodiments carbon fibre material may be treated by arc discharge by moving the carbon fibre material within a reaction chamber either through an electric arc in a gap between two electrodes or past an electrode so that an electric arc exists between the electrode and the material at a temperature effective to graphitise the carbon fibre material. Arc treatment may increase electrical conductivity, may also evaporate off some non-graphitic carbon from the material, and /or may have other benefits. The arc treatment may be carried out in a reactor chamber in which the discharge arc is created and through which the carbon fibre material is drawn. The electric current should not trigger a destructive localised arc attachment mode, and may suitably be between about 10 A and about 20 A. A mechanism is provided to feed the material through the reactor chamber. An inert gas such as nitrogen, argon or helium for example may be flushed through the reactor. The method may be carried out in the presence of an introduced metal additive. Suitable additives may be Ni-Co, Co-Y, Ni-Y or alternatively lower cost additives such as Fe or B additive for example or a Pb additive.

Manufacturing method steps of a stretch breaking embodiment of the invention are illustrated in Figure 2, and comprise as before first thermally treating a higher filamentary count tow, such as for example a tow of more than about 3000, about 4000, about 5000, about 8000, about 10,000, about 15,000, about 20,000, about 50,000, or about 60,000 carbon fibres, by moving the tow through an oven. The carbon containing fibres may be for example polyacrylonitrite (PAN) based carbon fibres. The thermal treatment may be carried out in a tube oven through which the tow is drawn.

Then the thermally treated tow is stretched to break individual continuous filaments into shorter staple filaments and separate lengthwise the ends of filaments at each break, which has the effect of lengthening and reducing the filament count of the carbon fibre tow. The resulting longer reduced filament count tow is twisted (like a rope) to maintain tow integrity. For example a tow of 50,000 continuous filaments may be stretch broken to produce a much longer tow composed of 600 shorter individual filaments which is then twisted, for example. The tow may be stretch broken into a tow of less than about 2500, less than about 2000, less than about 1500, or less than about 1000 filaments for example.

Preferably the tow after stretch breaking comprises filaments of average length in the range or about 1 to about 300 mm, or about 1 to about 200 mm, or about 1 to about 100mm, or about 1 to 50 mm, or about 2 to about 45 mm, or about 4 to about 40 mm, or about 5 to about 35 mm, or about 6-8 to about 30 mm, or about 10 to 25 mm, or about 12-15 to about 20 mm.

Then the carbon fibre material is produced by weaving or knitting the carbon fibres, or forming a non-woven carbon fibre material such as a felt material, as described above, and the carbon fibre electrodes are manufactured from the carbon fibre material, also as described above. In some embodiments the electrodes may have a thickness (transverse to a length and width or in plane dimensions of the electrode) many times such as 10, 20, 50, or 100 times less than the or any in plane dimension of the electrode. The electrode thickness may be less than 5 or less than 3 mm for example. Each of the in plane length and width dimensions of the electrode may be greater than 50 or 100 mm for example.

Such electrodes have a planar form with low thickness. One form of composite electrode of the invention may comprise a metal grid of thickness about 3.5mm mm or less such as about 0,5mm mm thick, with a carbon fibre layer of thickness about 2 mm or less such as about 0.3 mm thick on either side. In preferred forms the electrode is substantially planar and has a dimension from a metal lug for external connection along at least one edge of the electrode less than 100 mm or less than 70 mm, or less than 50 mm, or about 30 mm or less for example (with or without a macro-scale current collector). Alternatively such a planar form may be formed into a cylindrical electrode for example. Optionally after the carbon fibre material is produced by weaving or knitting the carbon yarn into a carbon fibre material, or forming a non-woven carbon fibre material such as a felt material, the carbon fibre material may be further heat treated to a sufficient temperature such as arc treated to increase its electrical conductivity. The thermal treatment may be by electric arc discharge, by for example moving the carbon fibre material within a reaction chamber either through an electric arc in a gap between two electrodes or past an electrode so that an electric arc exists between the electrode and the material at a temperature effective to activate the material.

The foregoing describes the invention including preferred forms thereof and alterations and modifications as will be obvious to one skilled in the art are intended to be incorporated in the scope thereof as defined in the accompanying claims.

Claims

1. A method for manufacturing a carbon fibre electrode of a lead-acid battery or cell, or a lead-acid battery or cell, which includes manufacturing at least one carbon fibre electrode from carbon fibre material which has been woven, knitted, or formed as a non- woven material, from multifilament carbon fibre which has been:

• split from a higher filament count bundle of carbon fibres ('tow'),

• split from a higher filament count bundle of carbon fibres ('tow'), and then

stretch broken to break individual continuous filaments into shorter filaments and separate lengthwise the ends of filaments at each break, reducing the filament count of the carbon fibre tow.

2. A method for manufacturing a carbon fibre electrode of a lead-acid battery or cell, or a lead-acid battery or cell, which includes manufacturing at least one carbon fibre electrode from carbon fibre material which has been woven, knitted, or formed as a non- woven material, from multifilament carbon fibre which has been split from a higher filament count bundle of carbon fibres ('tow').

3. A method according to either claim 1 or claim 2 wherein the tow has been thermally treated before splitting or stretch breaking, to carbonise same.

4. A method for manufacturing a carbon fibre electrode of a lead-acid battery or cell, or a lead-acid battery or cell, which includes:

• splitting the bundle of carbon filaments into two or more smaller bundles

('carbon fibre or yarn'), or stretch breaking the bundle of carbon filaments to break individual continuous filaments into shorter filaments and separate lengthwise the ends of filaments at each break, reducing the filament count of the carbon fibre tow, or both,

• weaving or knitting the carbon fibre into a carbon fibre material, or forming a non-woven carbon fibre material from the carbon yarn, and

• manufacturing at least one carbon fibre electrode from the carbon fibre

material.

5. A method for manufacturing a carbon fibre electrode of a lead-acid battery or cell, or a lead-acid battery or cell, which includes:

• splitting the bundle of carbon filaments into two or more smaller bundles

('carbon fibre or yarn'),

· manufacturing at least one carbon fibre electrode from the carbon fibre

material.

6. A method according to any one of claims 1 to 5 including forming a carbon fibre felt from the carbon yarn.

7. A method according to any one of claims 1 to 6 wherein the starting tow comprises more than 5000 filaments.

8. A method according to any one of claims 1 to 6 wherein the starting tow comprises more than 10,000 filaments.

9. A method according to any one of claims 1 to 6 wherein the starting tow comprises more than 20,000 filaments.

10. A method according to any one of claims 1 to 6 wherein the starting tow comprises more than 40,000 filaments.

11. A method according to any one of claims 1 to 10 wherein the tow is split and/or stretch broken to tows of less than 3000 fibres or filaments.

12. A method according to any one of claims 1 to 10 wherein the tow is split and/or stretch broken to tows of less than 1000 fibres or filaments.

13. A method according to any one of claims 1 to 10 wherein the step of splitting the tow comprises splitting the tow to two or more smaller tows of carbon fibres.

14. A method according to any one of claims 1 to 10 wherein the step of splitting the tow comprises splitting the tow to four or more smaller tows of carbon fibres.

15. A method according to any one of claims 1 to 14 wherein the electrode carbon fibre material comprises an average interfibre spacing of less than 200 microns.

16. A method according to any one of claims 1 to 14 wherein the electrode carbon fibre material comprises an average interfibre spacing of less than 100 microns.

17. A method according to any one of claims 1 to 16 wherein a majority of the fibres have a mean fibre diameter of less than 15 microns after tow splitting and/or tow stretching.

18. A method according to any one of claims 1 to 17 also including forming a conductive connection to the carbon fibre material or electrode.

19. A method according to any one of claims 1 to 18 also including impregnating the carbon fibre material with a paste comprising Pb-based particles and passing a formation current through the electrode.

20. A method according to any one of claims 1 to 19 also including been thermally treating the carbon fibre material by electric arc discharge.

21. A carbon fibre electrode of a lead-acid battery or cell, or a lead-acid battery or cell comprising at least one carbon fibre electrode, produced by the method of any of claims 1 to 20.

22. A lead-acid battery or cell according to claim 21 wherein the electrode has a thickness (transverse to a length and width or in plane dimensions of the electrode) l/50th or less than the or any in plane dimension of the electrode.

23. A lead-acid battery or cell according to either claim 21 or claim 22 wherein the electrode has a thickness (transverse to a length and width or in plane dimensions of the electrode) less than 5 mm.

24. A lead-acid battery or cell according to any one of claims 21 to 23 wherein the electrode is substantially planar and has a length and/or width in the range 50 to 500mm.