U.S. patent application number 16/127913 was filed with the patent office on 2019-04-04 for method for forming an electrical connection to a conductive fibre electrode and electrode so formed.
The applicant listed for this patent is ArcActive Limited. Invention is credited to John Abrahamson, Shane Christie, Suzanne Furkert, Yoon San Wong.
Application Number | 20190103604 16/127913 |
Document ID | / |
Family ID | 50341742 |
Filed Date | 2019-04-04 |
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United States Patent
Application |
20190103604 |
Kind Code |
A1 |
Abrahamson; John ; et
al. |
April 4, 2019 |
Method for Forming an Electrical Connection to a Conductive Fibre
Electrode and Electrode So Formed
Abstract
A method for forming an electrical connection to a microscale
electrically conductive fibre material electrode element, such as a
carbon fibre electrode element of a Pb-acid battery, comprises
pressure impregnating into the fibre material an electrically
conductive lug material, such as molten Pb metal, to surround
and/or penetrate fibres and form an electrical connection to the
fibre material and provide a lug for external connection of the
electrode element. Other methods of forming a lug for external
connection are also disclosed.
Inventors: |
Abrahamson; John;
(Christchurch, NZ) ; Furkert; Suzanne;
(Christchurch, NZ) ; Christie; Shane;
(Christchurch, NZ) ; Wong; Yoon San;
(Christchurch, NZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ArcActive Limited |
Christchurch |
|
NZ |
|
|
Family ID: |
50341742 |
Appl. No.: |
16/127913 |
Filed: |
September 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14429973 |
Mar 20, 2015 |
10096819 |
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PCT/NZ2013/000174 |
Sep 20, 2013 |
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16127913 |
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61703442 |
Sep 20, 2012 |
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61857729 |
Jul 24, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/126 20130101;
C22C 47/066 20130101; Y02T 10/7016 20130101; H01M 2/266 20130101;
H01M 4/82 20130101; H01M 4/0433 20130101; H01M 4/22 20130101; Y02E
60/10 20130101; Y02T 10/70 20130101; H01M 4/747 20130101; H01M
10/12 20130101; H01M 2/28 20130101; H01M 2/30 20130101; H01M 4/0404
20130101; H01M 4/663 20130101; B22D 19/14 20130101; H01M 2220/20
20130101; B23K 20/002 20130101; B23K 20/02 20130101; H01M 10/06
20130101; C22C 47/12 20130101 |
International
Class: |
H01M 4/22 20060101
H01M004/22; H01M 4/04 20060101 H01M004/04; H01M 2/30 20060101
H01M002/30; B23K 20/02 20060101 B23K020/02; B23K 20/00 20060101
B23K020/00; C22C 47/12 20060101 C22C047/12; C22C 47/06 20060101
C22C047/06; H01M 10/12 20060101 H01M010/12; H01M 10/06 20060101
H01M010/06; H01M 4/82 20060101 H01M004/82; H01M 4/74 20060101
H01M004/74; H01M 4/66 20060101 H01M004/66; H01M 2/28 20060101
H01M002/28; H01M 2/26 20060101 H01M002/26; B22D 19/14 20060101
B22D019/14 |
Claims
1. A lead acid battery or cell including at least one electrode
comprising as a current collector a conductive fibre material
having an average interfibre spacing of less than 250 microns,
comprising an electrically conductive lug material pressure
impregnated into a lug zone part of the fibre material surrounding
and/or penetrating the fibres and forming an electrical connection
to the fibre material in said lug zone and providing a lug for
external connection of the electrode element, and comprising and an
active material in at least a part of the conductive fibre material
other than in said lug zone, and wherein a surface to volume ratio
of Pb particles in the active material is at least about 3 times
greater than a surface to volume ratio of lug material in the lug
zone.
2. A lead acid battery or cell according to claim 1 wherein the
surface to volume ratio of Pb particles in the active material is
at least about 10 times greater than a surface to volume ratio of
lug material in the lug zone.
3. A lead acid battery or cell according to claim 1 wherein the
surface to volume ratio of Pb particles in the active material is
greater than about 2 m.sup.2/cm.sup.3 and the surface to volume
ratio of lug material in the lug zone is less than about 0.5
m.sup.2/cm.sup.3.
4. A lead acid battery or cell according to claim 1 wherein the
surface to volume ratio of Pb particles in the active material is
greater than about 1 m.sup.2/cm.sup.3 and the surface to volume
ratio of lug material in the lug zone is less than about 0.5
m.sup.2/cm.sup.3.
5. A lead acid battery or cell according to claim 1 wherein the lug
material comprises a metal that is either Pb or a Pb alloy Zn or a
Zn alloy, or Cd or a Cd alloy.
6. A lead acid battery or cell according to claim 1 wherein the
active material contacts the lug where the conductive fibre
material enters the lug and electrically connects direct to the
lug.
7. A lead acid battery or cell according to claim 1 wherein the
electrically conductive lug material is impregnated between at
least 50% of the fibres in said lug zone part of the conductive
fibre material.
8. A lead acid battery or cell according to claim 1 wherein the
electrically conductive lug material is impregnated between at
least 70% of the fibres in said lug zone part of the conductive
fibre material.
9. A lead acid battery or cell according to claim 1 wherein the
conductive fibre material has an average interfibre spacing of less
than 100 microns.
10. A lead acid battery or cell according to claim 1 wherein active
material contacts the lug where the fibre material enters the lug,
and electrically connects direct to the lug.
11. A lead-acid battery or cell according to claim 1 in which the
electrical resistance of the electrical connection between the lug
material and the conductive fibre material in said lug zone is less
than the resistance of the active material by at least 10% when the
battery or cell is 10% charged.
12. A lead acid battery or cell including at least one electrode
comprising as a current collector a conductive fibre material
having an average interfibre spacing of less than 250 microns,
comprising an electrically conductive lug material in a lug zone
part of the conductive fibre material surrounding and/or
penetrating the conductive fibre material and forming an electrical
connection to the conductive fibre material in said lug zone part
of the conductive fibre material and providing a lug for external
connection of an electrode element, the electrically conductive lug
material impregnating between at least 30% of the fibres in said
lug zone part of the conductive fibre material, the electrode also
comprising an active material in an active area comprising at least
a part of the conductive fibre material other than in said lug
zone, the active material impregnating the conductive fibre
material in said active area, and wherein a surface to volume ratio
of Pb particles in the active material is at least about 3 times
greater than a surface to volume ratio of lug material in the lug
zone.
13. A lead acid battery or cell according to claim 12 wherein the
surface to volume ratio of Pb particles in the active material is
at least 10 times greater than a surface to volume ratio of lug
material in the lug zone.
14. A lead acid battery or cell according to claim 12 wherein the
surface to volume ratio of Pb particles in the active material is
greater than 2 m.sup.2/cm.sup.3 and the surface to volume ratio of
lug material in the lug zone is less than 0.5 m.sup.2/cm.sup.3.
15. A lead acid battery or cell according to claim 12 wherein the
surface to volume ratio of Pb particles in the active material is
greater than 1 m.sup.2/cm.sup.3 and the surface to volume ratio of
lug material in the lug zone is less than 0.5 m.sup.2/cm.sup.3.
16. A lead acid battery or cell according to claim 12 wherein the
lug material comprises a metal that is Pb or a Pb alloy, Zn or a Zn
alloy, or Cd or a Cd alloy.
17. A lead acid battery or cell according to claim 12 wherein the
electrically conductive lug material is impregnated between at
least 50% of the fibres in said lug zone part of the conductive
fibre material.
18. A lead acid battery or cell according to claim 12 wherein the
electrically conductive lug material is impregnated between at
least 70% of the fibres in said lug zone part of the conductive
fibre material.
19. A hybrid automotive vehicle comprising a battery according to
claim 1.
20. A hybrid automotive vehicle comprising a battery according to
claim 12.
Description
REFERENCE TO PRIOR APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 14/429,973, which was the National Stage of International
Application PCT/NZ2013/000174, filed on Sep. 20, 2013, which claims
benefit of U.S. provisional application Nos. 61/857,729, filed Jul.
24, 2013 and 61/703,442, filed Sep. 20, 2012, the entireties of
which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to an improved method for forming an
electrical connection to a conductive fibre electrode, such as
battery or cell conductive fibre electrode, and to an electrode so
formed.
BACKGROUND
[0003] In a lead-acid battery or cell comprising a carbon fibre
electrode or electrodes, a very low electrical resistance and
mechanically durable connection is required between the carbon
fibre electrode material and a connector or lug (herein generally
referred to as a lug) to the external circuit. This can be
difficult to achieve particularly when the carbon fibre electrode
material has an interfibre spacing of less than 100 microns, for
reasons that include that carbon strongly repels metal from its
surface and/or the need to overcome surface tension to enable lug
metal to penetrate between the carbon fibres (whether interfibre or
intrafibre i.e. the latter referring to between filaments of
individual fibres if the carbon fibres are multifilamentary).
[0004] Achieving high penetration between fibres to minimise
remaining voidage between the lug material and the fibres of the
lug connection is also important as one way of preventing battery
electrolyte from subsequently entering the lug to fibre connection
and deteriorating the connection.
[0005] U.S. Pat. No. 3,926,674 discloses a method for manufacturing
electrical connection elements on battery electrodes of glass fibre
by molten lead injection.
SUMMARY OF INVENTION
[0006] In broad terms in one aspect the invention comprises a
method for forming an electrical connection to an electrically
conductive fibre material electrode element having an average
interfibre spacing less than about 100 microns, which comprises
pressure impregnating into a lug zone part of the fibre material,
an electrically conductive lug material to surround and/or
penetrate fibres of the fibre material and form an electrical
connection to the fibre material in said lug zone and provide a lug
for external connection of the electrode element.
[0007] In broad terms in another aspect the invention comprises an
electrically conductive fibre material electrode element having an
average interfibre spacing less than about 100 microns, which
comprises an electrically conductive lug material pressure
impregnated into a lug zone part of the fibre material and
surrounding and/or penetrating the fibres and forming an electrical
connection to the fibre material in said lug zone and providing a
lug for external connection of the electrode element.
[0008] In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell, or a lead-acid battery or
cell comprising at least one electrode, comprising a conductive
fibre material having an average interfibre spacing less than about
100 microns, the electrode comprising an active area and a
conductive element in a lug zone as a connector to the electrode,
in which the electrical resistance of the connection when the
battery or cell is at about 10% charged/90% discharged is less than
the resistance of the active area (when fully charged) by at least
10%.
[0009] In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell, or a lead-acid battery or
cell comprising at least one electrode, comprising an electrically
conductive fibre material having an average interfibre spacing less
than about 100 microns, the electrode comprising an active area and
a conductive lug element in a lug zone as a connector to the
electrode, in which in the lug zone part of the fibre material, lug
material surrounds and/or penetrates and electrically connects to
the fibres.
[0010] In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell or a lead-acid battery or
cell comprising at least one electrode, comprising a 3-dimensional
matrix of electrically conductive material extending between an
active area of said electrode and a lug zone as a connector to the
electrode, in which in the lug zone part of the conductive
material, lug material surrounds and/or penetrates and electrically
connects to the conductive material and reduces voidage compared to
voidage in the active area.
[0011] In some embodiments the resistance of the lug connection
when the battery is fully discharged is at least 10% lower than the
resistance of the active area.
[0012] In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell or a lead-acid battery or
cell comprising at least one electrode, comprising a 3-dimensional
matrix of electrically conductive material extending between an
active area of said electrode and a lug zone as a connector to the
electrode, in which in the lug zone part of the conductive
material, lug material surrounds and/or penetrates and electrically
connects to the conductive material and reduces voidage compared to
voidage in the active area.
[0013] In some embodiments the collective resistance between the
conductive material and the lug is less than or about the same as
the resistance along the active area.
[0014] Typically the conductive fibre material is a non-metallic
conductive material such as a carbon fibre material, such as a
non-woven such as felted carbon fibre material, or a knitted or a
woven carbon fibre material. The material has an average interfibre
spacing less than about 100 microns and in some embodiments less
than about 50 microns, less than about 20 microns, or less than
about 10 microns.
[0015] In some embodiments the impregnating material impregnates
between at least about 30%, at least about 40%, at least about 50%,
at least about 70%, at least about 80%, or at least about 95% or at
least about 98%, or at least about 99% of the fibres.
[0016] In some embodiments the interfibre voidage in the fibre
material (being the fraction of the total volume defined by the
material outside dimensions not occupied by the fibres--in the
unimpregnated material) is reduced by at least about 50%, at least
about 70%, at least about 80%, or at least about 95%, or at least
about 98%, or at least about 99%.
[0017] In some embodiments the fibres of the conductive fibre
material are multifilament fibres and the impregnating lug material
also penetrates between filaments also reducing intrafibre voidage.
In some embodiments intrafibre voidage is also reduced to about
40%, to about 30%, to about 25%, to about 20%, or to about 10%, to
about 5%, to about 1% of the intrafibre voidage in the
unimpregnated fibre material.
[0018] In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell or a lead-acid battery or
cell comprising at least one electrode, comprising an electrically
conductive material comprising a matrix of electrically conductive
material extending between an active area of said electrode and a
lug zone as a connector to the electrode, in which in the lug zone
part of the conductive material lug material surrounds and/or
penetrates and electrically connects to the conductive material so
that the lug zone has voidage (being the fractional volume occupied
by the pores between the lead and conductive fibres) of less than
about 30% (over at least a major fraction of the electrode).
[0019] In broad terms in a further aspect the invention comprises a
lead acid battery or cell including at least one electrode
comprising as a current collector a conductive fibre material,
comprising an electrically conductive lug material in a lug zone
part of the fibre material surrounding and/or penetrating the
fibres and forming an electrical connection to the fibre material
in said lug zone and providing a lug for external connection of the
electrode element, and comprising an active material in at least a
part of the conductive fibre material other than in said lug zone,
and wherein a surface to volume ratio of Pb particles in the active
material is at least about 3 times greater than a surface to volume
ratio of lug material in the lug zone.
[0020] Preferably the surface to volume ratio of Pb particles in
the active material is at least about 5 times greater, or at least
about 10 times greater, at least about 20 times greater, than a
surface to volume ratio of lug material in the lug zone.
[0021] Preferably the surface to volume ratio of Pb particles in
the active material is greater than about 2 m.sup.2/cm.sup.3 and
the surface to volume ratio of lug material in the lug zone is less
than about 0.5 m.sup.2/cm.sup.3, or the surface to volume ratio of
Pb particles in the active material is greater than about 1
m.sup.2/cm.sup.3 and the surface to volume ratio of lug material in
the lug zone is less than about 0.5 m.sup.2/cm.sup.3.
[0022] In at least some embodiments of a cell or battery employing
an electrode of the invention a low surface to volume ratio of lug
material in the lug zone may be desirable in order to keep the lug
material, such as for example Pb, from being substantially reacted,
for example to PbSO4, during discharge.
[0023] In broad terms in a further aspect the invention comprises a
lead acid battery or cell including at least one electrode
comprising as a current collector a conductive fibre material,
comprising an electrically conductive lug material in a lug zone
part of the fibre material surrounding and/or penetrating the
fibres and forming an electrical connection to the fibre material
in said lug zone and providing a lug for external connection of the
electrode element, and comprising an active material in at least a
part of the conductive fibre material other than in said lug zone,
and wherein the active material contacts the lug where the fibre
enters the lug and electrically connects direct to the lug.
[0024] Preferably the active material contacts the lug where the
fibre enters the lug and electrically connects direct to the lug
through a thickness of the fibre material, and preferably also
along a major part of or substantially all the length of a boundary
between the lug material and the non-lug material impregnated fibre
material at this boundary.
Pressure Impregnation Lug Forming
[0025] In broad terms in another aspect the invention comprises a
method for forming an electrical connection to an electrically
conductive fibre material electrode element having an average
interfibre spacing less than about 250 microns, which comprises
pressure impregnating into a lug zone part of the fibre material,
an electrically conductive lug material to surround and/or
penetrate the fibres and form an electrical connection to the fibre
material in said lug zone.
[0026] In broad terms in another aspect the invention comprises an
electrically conductive fibre material electrode element having an
average interfibre spacing less than about 100 microns, which
comprises an electrically conductive lug material pressure
impregnated into a lug zone part of the fibre material and
surrounding and/or penetrating the fibres and forming an electrical
connection to the fibre material in said lug zone.
[0027] At least some embodiments comprise heating the lug material
and pressure impregnating it when molten into the fibre material.
At least some embodiments comprise surrounding or enclosing the lug
zone part of the fibre material in a die, pressure impregnating the
molten lug material into the fibre material in the lug zone in the
die, and allowing the lug material to cool and solidify around the
fibres. In at least some embodiments pressure impregnating the
molten lug material into the fibre material includes pressure
impregnating the molten lug material into the die. In other
embodiments the lug material may be a thermoplastic or thermoset or
reaction set conductive polymer that is then pressure impregnated
into the fibre material. The die may comprise die parts which are
brought together with the fibre material between, and a closing
pressure or force of the die parts against the fibre material is
less than a pressure impregnating the molten lug material into the
die. In other embodiments pressure impregnating the molten lug
material into the fibre material includes closing a die on the lug
material and fibre material in the die so that the die closing
force pressure impregnates the molten lug material into the fibre
material. In another embodiment on closing the die parts this holds
the fibre material in place to assist and/or enable the molten lug
material to pressure impregnate the fibre material.
[0028] In at least some embodiments the die comprises a boundary or
periphery part which is more thermally conductive (alternatively
referred to as thermally dissipative) than a non-boundary or
periphery part of the die. In other embodiments the die comprises a
boundary or periphery part which is cooler than a non-boundary or
periphery part of the die. The impregnating material flows towards
the higher thermally conductive or cooler boundary part of the die.
At this boundary part, the impregnating material, including
impregnating material which has flowed/impregnated into the fibres,
cools and solidifies (`freezes`), to reduce or prevent flow of
further molten impregnating material beyond this (frozen) boundary
part. Because the solidified lug boundary part helps reduce the
further flow of molten lug material, less clamping pressure may be
required to contain the molten material in the lug zone of the
fibre material. The boundary or periphery part may be all or part
of the whole boundary or periphery of the lug zone. The die may
comprise two die parts which are brought together with the fibre
material between them and thus the closing pressure or force
applied to the area between the die parts and thus against the
fibre material may be less than an injection pressure of the
impregnating material into the die cavity or the fibre material
because in this embodiment the impregnated material is contained by
a combination of closing pressure of the die parts and such
boundary solidification. The closing pressure on the fibre material
between the die parts may thus be at a level which does not damage
or significantly damage for example structurally damage the fibre
material, by crushing. In some embodiments the die closing force
against the fibre material may result in a pressure against the
fibre material of less than about 240 Bar or about 120 Bar for
example for woven or knitted materials such as carbon woven
materials, or less than about 40 Bar or about 20 Bar when the fibre
material is a non-woven such as for a felt or carbon felt material
for example. In other embodiments die parts may not actually
contact the fibre material, so that there is no pressure (from the
die) on the fibre material during lug impregnation.
[0029] In some embodiments a die part on at least one side
comprises an area such as a centre area which has lower thermal
conductivity than the more thermally conductive (or dissipative) or
cooler boundary or periphery part. In some embodiments a die part
on at least one side comprises an area such as a centre area which
has a higher temperature, for example is heated, than the more
thermally conductive or cooler boundary part. In some embodiments
such a centre area of the die part is mounted on a piston or
similar, which is arranged to move to apply force to the molten lug
material after injection and whilst cooling, to increase
penetration of the lug material into the fibre material. The piston
arrangement may also eject the electrode from the die after
solidification of the lug.
[0030] In some embodiments a die system is arranged to cause the
molten lug material to enter the fibre material along an edge of
the fibre material. The die (at least when closed) may define a
transverse injection gap through which the molten lug material
enters the fibre material through said edge of the carbon fibre
material. The transverse injection gap may be defined between two
opposite die parts when closed together. In some embodiments the
die is open along a transverse opening opposite or above the
transverse injection gap in the direction of molten lug material
movement, and the fibre material beyond the lug zone extends
through said transverse opening during impregnation. Impregnating
the fibre material may be for a predetermined time and/or
predetermined volume of lug material, and then the injection
pressure is terminated and the lug material in the die allowed to
cool and solidify. In some embodiments a dimension across the die
cavity through a major plane of the carbon fibre material in use is
less than a transverse dimension of the die in the plane of the
carbon fibre material, such as approximately the same as the
thickness of the fibre material to form a thin lug of approximately
the same thickness as the fibre material.
[0031] In some embodiments the die is also arranged to form a lug
extension (of solid lug material) beyond an edge of the fibre
material.
[0032] In some embodiments remaining voidage if any between the lug
and the fibre material is reduced by impregnating after forming the
lug, a filler which is substantially inert to an electrolyte, or is
separated from bulk electrolyte by a barrier of a material
substantially inert to the electrolyte. In other embodiments the
lug material is substantially inert to an electrolyte eg
titanium.
Conductive Filler Lug Forming
[0033] In broad terms in another aspect the invention comprises a
method of forming a conductive lug to conductive fibre electrical
connection comprising applying a conductive paste, an encapsulating
material, or an adhesive to a lug zone of the fibre material and
forming a conductive region electrically connected to the fibre
material.
[0034] In broad terms in another aspect the invention comprises a
conductive lug to conductive fibre connection formed by applying a
conductive paste, an encapsulating material or an adhesive to a lug
zone of fibre material and causing electrical connection to and/or
into said fibre material with, if required, either heat and/or
pressure, to form a conductive fibre connection in said lug region
with reduced voidage relative to the bulk fibre material.
Electrochemical Lug Forming
[0035] In broad terms in another aspect the invention comprises a
method for forming a conductive lug to conductive fibre electrical
connection comprising: [0036] applying to the conductive fibre
material a paste which comprises a mixture of lead-based particles,
[0037] applying to at least part of a thus pasted part of the
conductive fibre material a metal element, and [0038] passing an
electric current through the metal element and through the paste
beneath and through the conductive fibre material beneath at a
suitable potential with respect to the acid electrolyte to form a
metal penetration into the conductive fibre material and connection
between the conductive fibre material and the metal element.
[0039] In broad terms in another aspect the invention comprises a
conductive lug to conductive fibre electrical connection formed by
applying a paste which comprises a mixture of lead-based particles
to the conductive fibre material, applying to at least a part of a
thus pasted part of the conductive fibre material the metal
element, and passing an electric current through the metal element
and through the paste beneath it and gradually to at least said
part of the conductive fibre material at a suitable potential with
respect to the acid electrolyte to form a metal penetration into
the conductive fibre material and connection between the conductive
fibre material and the metal element.
[0040] In some embodiments the paste comprises Pb-sulphate
particles, PbO particles, Pb particles, or a mixture of Pb-sulphate
particles, and/or PbO particles, and/or Pb particles, or a mixture
of zinc and zinc oxide particles, or Cd or Cd(OH)2 particles.
Circuit connections for the electro chemical paste conversion, may
be made to the metal element and a part of the fibre material for
example one edge of the fibre material, or to the metal element and
two or more parts of the fibre material for example two edges such
as two opposite edges of the fibre material. During the step of
passing an electric current through the metal element or connector
and at least said part of the conductive fibre material to connect
the conductive fibre material and the connector, the Pb-based
particles in the paste convert to lead first just beneath the
connector and gradually intimately between the fibres beneath the
connector and thus to connect or electrically connect the fibres
and the metal element or connector.
General
[0041] In all embodiments above the conductive fibre material may
be a non-woven material such as a felt material, a woven material
(comprising intersecting warp and weft fibres), or a knitted
material. The material may be a carbon fibre material, such as a
non-woven, knitted, or woven carbon fibre fabric, or alternatively
a glass fibre or silicon based fibrous material. The fibres, for
example, carbon fibres are typically multifilamentary but may be
monofilament. In some embodiments the fibre material has an average
interfibre spacing of less than about 250 microns, or less than
about 100 microns, less than about 50 microns, less than about 20
microns, or less than about 10 microns. The fibre diameter may be
in the range from about 1 micron to about 30 microns, from about 4
microns to about 20 micron, from about 5 microns to about 15
microns. The voidage in the (unimpregnated) material may be at
least about 80% or at least about 95% for example, to about 2% for
example.
[0042] In some embodiments the impregnating lug material is a
metal. In one embodiment the metal is Pb or a Pb alloy (herein both
referred to inclusively as Pb). In another embodiment the metal is
a Zn or a Zn alloy (herein both referred to inclusively as Zn). In
another embodiment the metal is Cd or a Cd alloy (herein both
referred to inclusively as Cd). Alternatively the impregnating lug
material may be a conductive polymer for example.
[0043] In some embodiments the conductive fibre material may be
carbon fibre material which has been treated by electric arc
discharge. The carbon fibre material may be electric arc treated by
moving the carbon fibre material within a reaction chamber either
through an electric arc in a gap between electrodes including
multiple adjacent electrodes on one side of the material, or past
multiple adjacent electrodes so that an electric arc exists between
each of the electrodes and the material. In other embodiments the
carbon fibre material for use as the electrode current collector
material may be thermally treated at an elevated temperature for
example in the range 1200 to 2800.degree. C. Such treatment may
increase electrical conductivity of the material.
[0044] In some embodiments the conductive fibre material has been
woven, or knitted, from multifilament carbon fibre which has been:
[0045] split from a higher filament count bundle of carbon fibres
(`tow`), into smaller tows, or [0046] 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 [0047] 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.
[0048] In a cell or battery, the positive electrode or electrodes,
the negative electrode or electrodes, or both, may be formed of one
or more layers of the conductive fibre material with a lug, in
accordance with the invention. The invention has been described
herein sometimes with reference to electrodes of Pb-acid batteries
but may also have application to other battery types such as Li-ion
batteries, and in other applications such as in electrodes in solar
cells, or in capacitors or supercapacitors, for example.
[0049] In some embodiments the invention comprises a hybrid
automotive vehicle comprising a lead acid battery of the present
invention and/or made in accordance with the methods taught herein.
In other embodiments the hybrid automotive vehicle has stop-start
and/or regenerative braking functionality. In other embodiments the
battery can carry accessory loads when the vehicle engine is
off.
[0050] In this specification `lug` means any electrically
conductive element or connector which enables external connection
of the conductive fibre electrode, regardless of physical or
mechanical form.
[0051] In this specification `lug region` and `lug zone` are used
interchangeably and have the same meaning.
[0052] In this specification "matrix" in relation to the lug refers
to lug material encapsulating the conductive fibre material in the
lug zone in a 3-dimensional structure that has length, width and
depth.
[0053] In this specification "hybrid vehicle" refers to a vehicle
that incorporates any one of idle elimination (stop-start
functionality), regenerative braking, and any combination of an
internal combustion engine with an electric motor where one or the
other or both can provide a drive functionality, a hybrid vehicle
may also include a vehicle that may only be a partial hybrid
vehicle.
[0054] 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
[0055] Embodiments of the invention are further described with
reference to the accompanying figures by way of example
wherein:
[0056] FIG. 1 shows part of a carbon fibre material electrode with
a Pb lug formed by a first pressure impregnating embodiment of the
invention,
[0057] FIG. 2 is schematic cross-section of an electrode comprising
multiple layers of carbon fibre material and a lug,
[0058] FIG. 3 schematically shows a series of steps for forming a
lug on an electrode of fibre material according to the first
pressure impregnating embodiment of the invention,
[0059] FIGS. 4A and 4B are schematic views of the inside faces of
two opposite die parts of one embodiment of a die,
[0060] FIGS. 5A and 5B are schematic cross-section views along line
I-I of FIG. 4A and line II-II of FIG. 4B respectively of the back
and front plates of another embodiment of a die,
[0061] FIGS. 6A and 6B, 7A and 7B, and 8A and 8B are SEM images of
lugs formed by the first pressure impregnating embodiment of the
invention and as referred to further in the subsequent description
of experimental work,
[0062] FIG. 9 shows a carbon fibre material electrode with another
form of Pb lug formed by a second pressure impregnating embodiment
of the invention,
[0063] FIG. 10 is a view of the carbon fibre electrode of FIG. 9 in
the direction of arrow F thereof,
[0064] FIG. 11 is an expanded schematic cross-section view of a die
to form a lug of the form of FIGS. 9 and 10,
[0065] FIGS. 12A and 12B are schematic views of the inside faces of
two opposite die parts of the die of FIG. 11,
[0066] FIG. 13 is a schematic cross-section view along line III-III
of FIG. 11 but of one die part only (left hand part in FIG.
14),
[0067] FIG. 14 is a schematic cross-section view along line IV-IV
of FIG. 11 (both die parts),
[0068] FIG. 15 schematically shows a series of steps for forming a
lug on an electrode of fibre material according to the second
pressure impregnating embodiment of the invention,
[0069] FIG. 16 is a schematic cross-section of a die to form a lug
on an electrode of fibre material, according to a third pressure
impregnating embodiment of the invention,
[0070] FIG. 17 schematically illustrates steps of an embodiment for
electrochemically forming a lug on a fibre material electrode,
[0071] FIG. 18 is a perspective view of an electrode produced by
the method of FIG. 17,
[0072] FIGS. 19 and 20 are SEM images of lugs formed by the second
pressure impregnating embodiment of the invention and as referred
to further in the subsequent description of experimental work,
and
[0073] FIG. 21 shows results of CCA performance testing referred to
in the subsequent description of experimental work.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Pressure Impregnated Lugs
[0074] FIG. 1 shows a section of a conductive fibre electrode such
as of carbon fibre, for a Pb-acid cell or battery for example, with
one form of lug such as a Pb lug, formed on the fibre material by a
first pressure impregnating embodiment of the invention. The fibre
material is indicated at 1 and the lug at 2. The lug may have a
similar thickness (dimension through the plane of the material) to
the fibre material thickness or a greater thickness. FIG. 2 is a
schematic cross-section of a similar electrode comprising multiple
layers 1 of fibre material, and a lug 2. In both embodiments the
lug has a lug extension 3 beyond the edge of the fibre material,
comprising lug material only ie solid lug material such as Pb.
[0075] FIGS. 9 and 10 show a conductive fibre electrode such as of
carbon fibre, for a Pb-acid cell or battery for example, with
another form of lug such as a Pb lug, formed on the fibre material
by a second pressure impregnating embodiment of the invention. The
fibre material is again indicated at 1 and the lug at 2. The lug 2
comprises a portion 4 (the lug zone of the electrode) in which the
fibre material is impregnated by the lug material, and a lug
extension 3 beyond the edge of the fibre material, comprising lug
material only. In the embodiment shown the lug has a similar
thickness (dimension through the plane of the material) to the
fibre material thickness and the lug may be not thicker than the
carbon fibre material.
[0076] The lug is typically formed of metal such as Pb or a Pb
alloy, Zn or a Zn alloy, or Cd or a Cd alloy, but may alternatively
be formed of other lug material such as a conductive polymer for
example.
[0077] In the embodiment shown the lug extends along a single edge
of the electrode, which is a single upper edge, but alternatively
the lug may extend along two or more edges of the electrode, the
lug may be curved or arcuate in shape, and/or may be formed to
extend across a centre area of an electrode.
[0078] In some embodiments substantially all or at least a majority
of the fibres of the electrode material extend continuously across
the electrode to or through the lug.
[0079] The fibre material may be a non-woven such as felt, knitted,
or woven fibre fabric, in particular a non-woven such as felt,
knitted, or woven carbon fibre fabric. Alternatively the material
may be a glass fibre or silicon based fibrous material, which may
be coated with a conductive material typically metal, such as a Pb
film or coating. The fibres, for example carbon fibres, are
typically multifilamentary but may be monofilament. In at least
some embodiments the fibre material has an average interfibre
spacing of less than about 250 microns, less than about 100
microns, less than about 50 microns, less than about 20 microns, or
less than about 10 microns. In at least some embodiments the fibre
diameter is in the range from about 1 micron to about 30 microns,
from about 4 microns to about 20 micron, or from about 5 microns to
about 15 microns. The voidage in the (unimpregnated) material may
be in the range of from about 50% to at least about 1%, from about
40% to about 1%, or from about 30% to about 1%.
[0080] In some embodiments the impregnating material impregnates
between at least about 50%, at least about 70%, at least about 80%,
or at least about 95% of the fibres.
[0081] In some embodiments the interfibre voidage in the fibre
material (being the fraction of the total volume defined by the
material outside dimensions not occupied by the fibres--in the
unimpregnated material) is reduced by impregnation of the lug
material between into the interfibre voidage between the fibres, at
least about 50%, at least about 70%, at least about 80%, at least
about 95%, at least about 98%, or at least about 99%.
[0082] In some embodiments the fibres of the fibre material are
multifilament fibres and the impregnating lug material also
penetrates between filaments also reducing intrafibre voidage. In
some embodiments intrafibre voidage is also reduced to about 40%,
to about 30%, to about 25%, to about 20%, to about 10, to about 5%,
or to about 1% of the intrafibre voidage in the unimpregnated fibre
material.
[0083] A matrix of the lug material encapsulates the microscale
carbon fibre electrode material in the lug zone. A very low
electrical resistance connection is formed between the microscale
carbon fibre electrode material and lug. Also voidage between the
lug material and the fibres is minimised, preventing or minimising
battery electrolyte from subsequently entering the lug to fibre
connection and deteriorating the connection, so the connection is
more durable.
[0084] Optionally any remaining (open cell/porous) voidage between
the lug material and the fibres and/or filaments may be reduced by
filling with a material which is substantially inert to the
electrolyte, such as for example a non-conductive polymer such as
an epoxy.
[0085] Optionally the impregnating material (not inert to an
electrolyte) is protected from the bulk of the electrolyte by an
inert material barrier.
[0086] Optionally also the impregnating lug material may be a
material which is electrically conductive but substantially inert
to a battery electrolyte such as a Pb acid battery electrolyte such
as titanium.
[0087] The conductive or carbon fibre material may have a thickness
(transverse to a length and width or in plane dimensions of the
electrode) many times such as about 10, 20, 50, or 100 times less
than the or any in plane dimension of the electrode. The thickness
may be less than about 5 or less than about 3 mm or less than about
2 mm or about or less than about 1 mm or about 0.2 mm for example.
Each of the in plane length and width dimensions of the electrode
may be greater than about 50 or about 100 mm for example. Such
electrodes have a planar form with low thickness. 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 about 100 mm or less than about 70 mm, or
less than about 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.
Pressure Impregnation Lug Forming
[0088] FIG. 3 schematically shows a series of steps for pressure
impregnating a microscale fibre material to form a lug of the form
of FIGS. 1 and 2, FIG. 4A is a schematic view of the inside face of
the die part shown on the left in FIG. 3, and FIG. 4B is a
schematic view of the inside face of the die part shown on the
right in FIG. 3. The lug is formed by pressure impregnating lug
metal into a lug zone part of the fibre material to penetrate into
and form an electrical connection to the fibre material in the lug
zone. Referring to FIGS. 3 and 4A and 4B, in the embodiment shown
the die comprises two die parts 10 and 11 with internal cavities 12
and 13. The die parts 10 and 11 close together and open
reciprocally in operation in the direction of arrow A (see step 3-1
of FIG. 3). The die parts are brought together with the fibre
material, indicated at 1 in FIG. 3, between and extending through
the die cavity as shown. Step 3-1 of FIG. 3 shows the die open ie
the two die parts separated, and step 3-2 of FIG. 3 shows the two
die parts closed against the fibre material but before lug metal
injection. One (or both) of the die parts may comprise a peripheral
protrusion or wall 14 (boundary or periphery part of the die)
around the cavity which when the die parts close together contacts
the carbon fibre around a periphery or boundary part of the lug
zone of the fibre material. However the closing pressure or force
between the die parts and thus against the fibre may be at a level
which does not damage or significantly damage for example
structurally damage the fibre material, by crushing. The closing
pressure may be less than the injection pressure of the molten
metal into the die cavity. In some embodiments the pressure against
the fibre material may be (only) about 5 Bar, for example for woven
carbon fibre materials, or up to only 5 Bar for non-woven carbon
fibre material such as felt material for example. In one embodiment
the die parts may not touch the fibre material but may when the die
is closed be closely spaced for example less than 0.5 mm or less
than 0.25 mm from the surface of the fibre material. Such a gap may
allow the lug material to flow around the outside surfaces of the
fibre material, but should be sufficiently small that this lug
material will quickly cool and solidify (freeze) so that further
injected lug material is then pressure impregnated into the fibre
material. Alternatively the die parts may contact the fibre
material when closed but with no pressure/compression of the fibre
material.
[0089] Referring to step 3-3 of FIG. 3, lug metal 2a is heated and
impregnated into the die cavity through one or more ports and
preferably a port such as indicated at 15 which delivers molten lug
metal into a central area of the cavity as shown. The impregnating
pressure causes the molten metal to penetrate between the
microscale fibres in the lug zone, and is maintained at a level so
that molten metal will pass from the injection side 11 of the die
cavity, and between the fibres in the lug zone, to fill the cavity
between the two sides of the die cavity, so that a lug with metal
on both sides of the fibre material is formed and with metal
penetrating between the fibres ie at least partially filling the
interfibre voidage, and preferably also penetrating into the fibres
if the fibres are multifilamentary fibres ie filling at least
partially the intrafibre voidage. Alternatively metal may be
impregnated from both sides or from an edge of the die cavity.
[0090] When the penetrating metal reaches the boundary part 14 of
the die cavity or lug zone of the fibre material, the penetrating
molten metal at or adjacent and around the boundary part 14 cools
and solidifies ie freezes. This cooled and solidified boundary
metal of the forming lug prevents further penetration of molten lug
metal into the fibre material beyond boundary part 14, and
therefore the clamping pressure between the two die parts may be
less than the injection pressure of the impregnating material or
metal. The metal in the die cavity ie the formed lug 2, is then
allowed to cool and solidify as shown in steps 3-5 and 3-6 of FIG.
3 to form a complete (solid) lug as shown in step 3-6 of FIG. 3,
and the die is then opened as shown in step 3-6 of FIG. 3 to
release or eject the fibre material with a solidified metal lug
thereon.
[0091] In some embodiments cooling and solidification first of the
lug periphery is achieved by the boundary or periphery part of the
die, such as the protrusion or wall 14, being more thermally
conductive (or thermally dissipative) than a central area of the
die cavity. In other embodiments the boundary part is held at or
cooled to a lower temperature than a central area of the die cavity
by ducts in the die parts through which a cooling fluid is
circulated for example.
[0092] In the embodiment shown in FIG. 3, the die part 10 has a
cavity 12 opposite the injection port 15 which is held at or cooled
to a lower temperature lower than the melting temperature of the
lug material injected. The die part 10 also is provided with a
thermal insulating insert 17. The temperature of the other die part
11 with injecting port 15 is held closer to the melting point of
the lug metal to prevent the injected molten metal solidifying
prematurely. Referring to step 3-5 in FIG. 3, when molten metal
first flows into and begins filling the die cavity, in the centre
of the die cavity it contacts the insulating thermal insert 17
which prevents the molten metal from cooling and solidifying too
quickly in the centre of the die cavity. Thus the molten metal in
the centre of the die cavity continues to flow under the injection
pressure, outwardly toward the periphery of the die cavity, to fill
the entire die cavity and to penetrate the carbon fibre in the die
cavity (and freezes first at the boundary as described above).
Alternatively instead of providing the insulating thermal insert 17
the central area of the die cavity may be heated during the metal
injection relative to the boundary 14 of the die cavity.
[0093] FIG. 5A is a schematic side cross-section view of die back
plate part 10 along line I-I of FIG. 4A showing thermal insulating
material 17 in the centre of the die cavity mounted on a piston 18.
This piston can move in the direction of arrow A to compress the
molten impregnated material into the fibre material prior to
freezing, to further reduce voidage, and can also operate to eject
the formed lug once the die plates have opened.
[0094] FIG. 5B is a schematic side cross-section view of die front
plate part 11 along line II-II of FIG. 4B. In this embodiment
thermal insulating material 17a is provided in the centre of the
injection part side of the die and around injection port 15.
[0095] FIGS. 11 to 15 schematically show pressure impregnating by a
second embodiment to form a lug of the form of FIGS. 9 and 10.
FIGS. 11 to 14 are schematic cross-section views of a die system,
and FIG. 15 schematically shows a series of steps for forming a
lug.
[0096] Again the lug is formed by pressure impregnating into a lug
zone part of fibre material to form a conductive penetration into
and connection to the fibre material in the lug zone. The die
comprises two die parts 20 and 21 which close together and open
reciprocally in operation in the direction of arrow B. The die
comprises internal cavity 22. The die (when closed) comprises a
transverse flow conduit 23 (see step 15-2 in FIG. 15) below the
cavity 22 (below in the direction of molten material movement C--as
will be further described). The transverse flow conduit 23 is made
up of transverse cavities 23a and 23b in the opposite die parts.
Both die cavity 22 and flow conduit 23 extend transversely across
the die (see FIGS. 12A, 12B, and 14) and they are separated by a
transverse projection 25 in one die part 21 part way across the die
cavity 22. When the die parts 20 and 21 are brought together the
top of the die cavity is open at transverse slot 24.
[0097] In operation the die parts 20 and 21 are brought together
with an edge of fibre material 1 on which a lug is to be formed in
the die cavity as shown in FIG. 11 (though FIG. 11 shows the die
open with the lug formed thereon). The balance of the fibre
material 1 extends from the open transverse slot 24. Lug metal 2a
is heated and impregnated into the die cavity through injection
port 26 which delivers molten metal into flow conduit 23 extending
transversely across the die, which it fills. Molten metal then
exits flow conduit 23 transversely across the die moving in the
direction of arrow C in FIG. 11, and flows through a transverse
injection gap past transverse protrusion 25 also extending across
the die, and into the fibre material 1 along and through its edge,
thus impregnating the fibre material. The molten metal penetrates
the fibre material in the lug zone. Cooling ducts 28 are provided
in the die parts 20 and 21 through which cooling fluid is
circulated to cool the die above the lug zone of the fibre material
in use. The front of molten metal moving up the die cavity 22 and
into the fibre material 1 cools and solidifies ie freezes, and the
resulting transverse line of solid metal across the die prevents
further penetration of the metal into the fibre material and
defines the limit of the metal lug. After a predetermined time
period the injection pressure is terminated and the metal in the
flow conduit 23 and die cavity 22 allowed to cool and solidify, and
the die parts are then opened to release or eject the carbon fibre
material with a metal lug thereon.
[0098] Step 15-1 of FIG. 15 shows the die open ie the two die parts
20 and 21 separated, and step 15-2 of FIG. 15 shows the two die
parts closed against the fibre material 1 but before metal
injection. Step 15-3 of FIG. 15 shows hot metal 2a entering the die
cavity through port 26 and filling conduit 23 across the width of
the die. Step 15-4 of FIG. 15 shows molten metal entering die
cavity 22--and penetrating the carbon fibre. Step 15-5 of FIG. 15
shows the metal cooling to solidify the lug on the carbon fibre 1,
and step 15-6 of FIG. 15 shows the die opening to release the
carbon fibre material with a metal lug thereon.
[0099] The dimension across the die cavity 22 between the two die
parts 20 and 21 may be approximately the same as the thickness of
the fibre material to form a thin lug of approximately the same
thickness as the fibre material, as described previously or greater
to form a thicker lug. Again, the closing pressure or force between
the die parts and thus against the fibre may be at a level which
does not damage or significantly damage for example structurally
damage the fibre material, by crushing. In some embodiments the
pressure against the fibre material may be (only) about 5 Bar, for
example for woven carbon fibre materials, or up to only 5 Bar for
non-woven carbon fibre material such as felt material for example.
In one embodiment the die parts may not touch the fibre material
but may when the die is closed be closely spaced for example less
than 0.5 mm or less than 0.25 mm from the surface of the fibre
material. Such a gap may allow the lug material to flow around the
outside surfaces of the fibre material, but should be sufficiently
small that this lug material will quickly cool and solidify
(freeze) so that further injected lug material is then pressure
impregnated into the fibre material. Alternatively the die parts
may contact the fibre material when closed but with no
pressure/compression of the fibre material.
[0100] FIG. 16 is a schematic cross-section of a die to form a lug
on an electrode of fibre material, according to a third pressure
impregnating embodiment of the invention. In this embodiment the
pressure which impregnates the molten lug material into the fibre
material is generated by closing a die on the lug material and
fibre material in the die. Referring to FIG. 16, die parts 80 and
81 move reciprocally as indicated by arrows D on a machine bed 82
(the figure shows the die open). Duct(s) 89 which carry cooling
fluid are provided along a distal part of each die part 80 and 81.
Alternatively the distal parts of the die parts 80 and 81 may be
formed of a material which dissipates heat more quickly for
example.
[0101] In operation the edge of fibre material 1 on which a lug is
to be formed is positioned in the die cavity between the die parts
80 and 81 as shown. The balance of the fibre material extends from
the open transverse slot 85. Lug metal is also pre-positioned in
the die cavity. For example in the figure two strips 84 of lug
material are shown interleaved between three fibre material layers
1. The die parts 80 and 81 are heated and are brought together to
close the die, heating the lug metal under pressure, which melts
and penetrates the fibre material 1 in the lug zone. Molten lug
metal moving through the fibre material in the direction of arrow E
cools and solidifies ie freezes adjacent the duct(s) 89, and the
resulting transverse line of solid metal in the fibre material
across the slot die opening prevents further penetration of the
metal into the carbon fibre material and defines the limit of the
metal lug. After a predetermined time period the injection pressure
is terminated and the metal in the die cavity allowed to cool and
solidify, and the die is then opened to release or eject the carbon
fibre material with a metal lug thereon.
[0102] In all embodiments above, to aid impregnation of the fibre
material by the lug metal under pressure, vibration or energy may
be applied to the molten lug metal via one or more die parts during
impregnation, for example at an ultrasound frequency such as a
frequency in the range about 15 to about 25 kHz.
Battery or Cell Construction
[0103] A lug formed on fibre material electrode as described above
may also comprise on one or both sides of the fibre material a
metal wire or tape electrically conductively attached to the
electrode material and to the lug, to provide an additional
macro-scale current collecting pathway from the carbon fibre to the
metal lug, in addition to the micro-scale pathways through the
carbon fibre material itself of the lug. The metal wire or tape may
be attached to the fibre material for example by stitching or
sewing with a thread that will not dissolve in battery electrolyte,
or other inert Pb acid battery binding material that will hold the
current collector in place, such as a resin, cement or potting mix.
The metal wire or tape may be pressed into the fibre material
during manufacture. Alternatively the wire or tape or similar may
be soldered to or printed on the fibre material. The metal wire or
tape(s) may be arranged in a sinuous shape on one or both sides of
the fibre material, extending continuously between the lug at one
edge of the electrode, at which edge the wire or tape is
conductively connected to the lug by being embedded in the lug, and
at or towards another spaced edge of the electrode. Alternatively
the wire or tape may extend between metal lugs along opposite edges
of the electrode or a frame around the electrode. Alternatively
again separate lengths of the wire or tape may extend from the lug
at one edge to or towards another edge of the electrode, or
alternatively again the wire or tape macro-conductor as described
may comprise a metal mesh attached on one or both sides of the
fibre material. The ends of the wire or tape or mesh may terminate
and be embedded in the lug. It is important that when the current
collector is on the outer surface of the electrode that acts as the
negative electrode the current collector is protected from anodic
oxidation from the positive electrode. Preferably the wire or tape
runs up and down the length of the electrode with equal spacing
across the width of the electrode without any cross over points, to
prevent local hotspots occurring or heat build up in particular
areas, and an even current collection across the electrode.
Preferably the volume of the wire or tape or mesh or similar
macro-scale current collecting system is less than about 15% of the
volume of the electrode (excluding the lug or surrounding metal
frame or similar).
[0104] Typically during battery or cell construction the microscale
current collector material is impregnated under pressure with a
paste, which in a preferred form comprises a mixture of Pb and PbO
particles of Pb and PbO and dilute sulfuric acid. Alternatively the
paste may comprise lead sulphate (PbSO.sub.4) particles and dilute
sulphuric acid. In some embodiments the paste at impregnation into
the electrode comprises dilute sulphuric acid comprising between
greater than 0% and about 5%, or between 0.25% and about 3%, or
between 0% and about 2%, or between 0.5 and 2.5% by weight of the
paste of sulphuric acid. The Pb-based particles may comprise milled
or chemically formed particles which may have a mean size of 10
microns or less, small enough to fit easily into spaces between the
fibres. The paste or active material may fill the carbon fibre
electrode up to the lug so that the active material contacts or
abuts the lug where the fibre enters the lug and electrically
connects direct to the lug, not only at the surface of the fibre
material on either side but also through the thickness of the fibre
material, and along a major part of or substantially all the length
of the boundary between the lug material and the non-lug material
impregnated fibre material at this boundary, or may stop short of
the lug so that there is a small gap between the paste and the lug
such as a gap of up to about 5 mm for example. In a preferred
embodiment the lug is formed so as to have protrusions of the lug
such as Pb protrusions, into the active material impregnated into
the carbon fibre material, as described above.
[0105] As stated preferably the surface to volume ratio of Pb
particles in the active material is at least about 3 times greater,
or preferably about 5 times greater, or preferably about 10 times
greater, or preferably about 20 times greater, than a surface to
volume ratio of lug material in the lug zone. Preferably the
surface to volume ratio of Pb particles in the active material is
greater than about 2 m.sup.2/cm.sup.3 or greater than about 1
m.sup.2/cm.sup.3 and the surface to volume ratio of lug material in
the lug zone is less than about 0.05 m.sup.2/cm.sup.3. The surface
associated with molten lug material that has been injected into
fibre layers, cooling as it enters, is likely to be similar to the
surface area of the fibres that it will cool around, or less. For
example, a carbon felt may have an area of the cylindrical surfaces
of the fibres equal to around 20 m.sup.2 per mm thickness for 1
m.sup.2 of superficial area, which is equivalent to 0.02 m.sup.2
per cm.sup.3 of felt total volume. Thus flowing molten lead around
this fibre network will form (by freezing onto the cold fibres
first) a lead structure with branches larger in diameter than the
diameter of the fibres ie. the diameter of the branches of this
lead-loaded felt may increase from 10 microns to around 15 to 20
microns with surface area perhaps 0.01 m.sup.2 per cm.sup.3 (for
higher volume fraction impregnation these branches will merge and
the surface will decrease even further). These surface areas can be
compared with those for the normal active material within a
negative electrode in a lead-acid cell. Lead-containing active mass
is divided into a lead skeleton that carries current (which is not
susceptible to electrochemical change during charge and discharge
cycles) and a much finer mass that is susceptible to change and in
fact produces the working electrical currents of the battery. The
much finer "energetic active material" may have around 0.3 micron
diameter branches. The skeleton may be very similar to the branches
formed by partial impregnation above, with negligible
electrochemical attack. However the surface area of the fine
electrochemically active material may have (20)/0.3)=70 times the
surface area per unit volume of lead, and so suffers almost all the
chemical attack. The division between fine material and coarse
skeleton material is around 50/50 in most negative electrodes.
Electrochemical Lug Forming
[0106] Referring to FIG. 17 in an embodiment of an electrochemical
lug forming method of the invention as applied to a Pb-acid battery
or cell electrode, a carbon or conductive fibre material element
such as an electrode element has applied thereto a paste which
comprises lead-based particles--in FIG. 17 the thus pasted element
61 is indicated at step 17-1. The paste may be impregnated into the
fibre material under pressure and/or with vibration such as
ultrasonic vibration to fully impregnate the paste between fibres.
Optimally a curing process may then be undertaken, where for
example the humidity and/or temperature is controlled.
[0107] The paste may comprise Pb-sulphate particles, PbO particles,
Pb particles, or a mixture of Pb-sulphate particles, PbO particles,
and/or Pb particles. In preferred embodiments this paste is
substantially the sole source of lead in the active material paste.
The particles may comprise milled or chemically formed particles
and at least a major fraction of and preferably at least 80% of the
particles may have an average size or diameter of 10 microns or
less. The paste may optionally also contain other additives such as
carbon black, barium sulphate and sulphonate.
[0108] The fibre surfaces of the material may be surface treated to
enhance attachment of the Pb-based particles by processing to
attach oxide particles or oxygen bearing chemical groups to the
fibres. Anodic oxidation of electric arc-treated carbon fibre
fabric also may convert it to a hydrophilic material. This may
assist an even distribution of the active particles through the
material and initial attraction of the Pb (covered with oxide
groups) to the carbon, by dipole-dipole attractions.
[0109] As indicated at FIG. 17 step 17-2, a metal or conductive
connector or connectors 62 comprising for example metal strips or
in any other suitable form are mechanically attached to the pasted
carbon fibre element 1 for example along at least one edge or
alternatively extending across the carbon fibre element. Thus an
area 63 of the pasted material is captured by the connectors 62.
The strips may for example be crimped to the material edge or
otherwise mechanically fixed to the material, with for example,
compression, heating such as by induction or resistive heating, as
indicated at step 17-3. Alternatively or additionally metal
strip(s) may be provided between each of two or more layers of
carbon fibre material forming the carbon fibre element 1.
Alternatively again metal fibres may be incorporated in the edge of
the carbon fibre element 1 for example by weaving into the carbon
fibre material at or near the edge.
[0110] As indicated at step 17-4 the pasted carbon fibre element 1
with connector(s) 62 is dipped into dilute sulphuric acid in a cell
64, to cover the top of the connector, and connected as the
negative electrode opposite another electrode polarised positively.
An electric current is passed through the connector(s) 62 and the
material 1 to electrically connect the fibres and the connector(s)
by electrochemically converting the paste in area 63 into a Pb
network. This forms Pb between the carbon fibres and overcomes the
surface tension problems between Pb and carbon fibres in methods
currently available. Alternatively in some embodiments the paste
comprises dilute sulphuric acid, or is contacted with dilute
sulphuric acid for example by spraying dilute sulphuric acid onto
the carbon fibre element material instead of dipping. The electric
current passing through the connector(s) and the carbon fibre
element material and the dilute sulphuric acid-wetted paste
between, causes the Pb-based particles in the paste to convert to
lead first just beneath the connector and gradually intimately
between the electrode material fibres in area 63, to connect or
electrically connect the fibres there with the connector. Typically
this step may be carried out at the start of initial electrode
formation (first charge and discharge cycle during which active
particle linkages form) before or after cell or battery
construction. Thus the same conduction-forming process occurring in
area 63 propagates to the remainder of the electrode. It may be
advantageous that during formation the charging current is pulsed
periodically.
[0111] In the embodiments described above the connector 62 is a
metal strip such as a Pb strip mechanically attached to the carbon
fibre element. In an alternative embodiment each of the connectors
62 is replaced by a mechanical fastening device for example a clamp
having leady surfaces of the same desired geometry as the connector
62. These opposing fastening devices may then be removed after
providing temporary contact with the area 63 during the formation
process. The required acid electrolyte diffuses into area 63 along
the fibre material from the edge or from the bulk of the
electrode.
[0112] After the electrochemical conversion, the carbon fibre
element at step 17-5 with resultant lug can then undergo a further
process step to remove any porosity in area 63, to prevent or
minimise or reduce electrolyte entering the pores in the Pb network
in 63 (as subsequent discharge of the cell would then cause
PbSO.sub.4 to form, reducing or eliminating the conductive property
of 63). Removal or reduction of porosity may be achieved by for
example: [0113] compression and/or heating area 63, for example, by
induction or resistive heating, [0114] the region 63 is further
dipped into a sealant solution that leaves the pores filled with a
polymer that does not dissolve in the electrolyte, such a sealant
solution includes for example a resin, and [0115] filling some of
the remaining pores in 63 by electrode deposition of Pb from a
strong solution of Pb ions.
[0116] To explain the electro deposition of Pb, an alternative
embodiment is illustrated in FIG. 18. One of the connectors 62 is
replaced by a mechanical fastening device comprising an internal
lengthwise conduit 67 and also supplied with sulphuric acid and
also having leady surfaces 66 arranged to physically contact the
carbon fibre element 1 on one side in the area 63 where paste
material has already been applied and a connection is desired. The
device may be fastened to an edge of the carbon fibre element or
extend across the carbon fibre element so long as the desired
pasted area 63 is captured by the leady surfaces 66 of the clamp. A
suitable positive electrode is installed in the (recirculating)
electrolyte flow entering and leaving 67 to complete a cell and
current flow may generate Pb within the inter-fibre space within
area 63, as carried out previously with a connector 62.
[0117] The leady surface 66 as shown in FIG. 18 may consist only of
a leady perimeter (ie otherwise open) or may be a porous leady
material, so that the electrolyte passing through the conduit 67
may permeate to the carbon fibre and paste.
[0118] After the above described formation process, a lead salt
solution (for example of PbNO3) may then be passed through the
conduit 67 so that the lead pores that are in front of the conduit
are filled with lead. A metered amount of solution may be injected
into the conduit. The voltage applied between the positive and
negative electrodes is then adjusted to achieve a suitable level so
that lead is evenly deposited in the pores of the lug zone. The
injection of the lead salt solution and the electrochemical
deposition process is repeated until the pores are close to being
filled with lead. Successive injections will be smaller and more
difficult to achieve until no more injection or deposition can be
achieved. Collapse procedures or resin injection may also be used
at this point to remove any small accessible porosity remaining.
This also may be carried out as an alternative to dipping as above,
but is more practical as a subsequent step.
[0119] In an embodiment for forming a carbon fibre electrode of a
Ni--Cd battery or cell the lug may be formed of Cd and the paste
comprise Cd such as CdOH particles.
General
[0120] In a battery typically a lead-acid battery, the positive
electrode or electrodes, the negative electrode or electrodes, or
both, may be formed with a lug in accordance with the method(s) of
the invention. Preferably the current collector material and the
fibres thereof are flexible, which will assist in accommodating
volume changes of the active material attached to the current
collector material during battery cycling, and the microscale
fibres may also reinforce the active material, both assisting to
reduce breaking off ("shedding") of active material from the
electrode in use.
[0121] In preferred embodiments the electrode fibres are inherently
conductive without requiring coating with a more conductive
material such as a metal to increase conductivity, and may be
carbon fibres which may in some embodiments be treated to increase
conductivity. In other embodiments the electrode fibres may be a
less conductive material, the fibres of which are coated with a
conductive or more conductive coating. In some embodiments the
fibres of the current collector material may be coated with Pb or a
Pb-based material. For example the negative electrode or electrodes
may be coated with Pb and the positive electrode(s) coated with Pb
and then thereon PbO.sub.2.
[0122] The current collector material may be a woven material, a
knitted material, or a non-woven material, such as a felt. The
material may comprise filaments extending in a major plane of the
material with each filament composed of multiple fibres, with
optionally connecting threads extending transversely across the
filaments to mechanically connect the filaments. The average depth
of the material may be at least 0.2 millimetres or at least 1
millimetre. At least a majority of the fibres have a mean fibre
diameter of less than about 15 microns, more preferably less than
or equal to about 6 to about 7 microns.
[0123] The fibre surfaces of the material may be surface treated to
enhance attachment of the Pb-based particles by processing to
attach oxide particles or oxygen bearing chemical groups to the
fibres. Anodic oxidation of electric arc-treated carbon fibre
fabric also may convert it to a hydrophilic material. This may
assist an even distribution of the active particles through the
material and initial attraction of the Pb (covered with oxide
groups) to the carbon, by dipole-dipole attractions.
[0124] In some embodiments the conductive fibre material may be
carbon fibre material which has been thermally treated at an
elevated temperature, for example in the range 1000 to 4000.degree.
C. In some embodiments the conductive fibre material may be carbon
fibre material which has been treated by electric arc discharge.
The carbon fibre material may be electric arc treated by moving the
carbon fibre material within a reaction chamber either through an
electric arc in a gap between electrodes including multiple
adjacent electrodes on one side of the material, or past multiple
adjacent electrodes so that an electric arc exists between each of
the electrodes and the material.
[0125] In some embodiments the conductive fibre material may be
felt or other non-woven planar electrode material produced to very
low thickness such as for example 2.5 mm or less thickness by
dividing thicker material in plane. That is, the material may be
cut in its plane one or more times to divide a thicker non-woven
material into multiple sheets of similar length and width but
reduces thickness to the starting sheet.
[0126] In some embodiments the conductive fibre material may be
woven carbon fibre material may be woven from carbon fibre tows
which have been `stretch broken` ie a tow (bundle) of a larger
number of continuous carbon fibre filaments is stretched after
manufacture to break individual continuous filaments into shorter
filaments and separate lengthwise the ends of filaments at each
break, which has the effect of reducing the filament count of the
carbon fibre tow. The resulting 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. In some embodiments the conductive
fibre material may be carbon fibre material formed from carbon
fibre tows which have been `tow split` ie split from a higher
filament count bundle of carbon fibres (`tow`), into smaller tows.
In some embodiments the conductive fibre material may be carbon
fibre material formed from carbon fibre tows both split from a
higher filament count bundle of carbon fibres 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.
EXPERIMENTAL
Example 1--Lug Formation
[0127] In experimental work Pb lugs were formed on carbon fibre
material generally by the method described above with reference to
FIG. 5.
[0128] To obtain Scanning Electron Microscope (SEM) images of the
insides of the lug region, the lugs were dipped in liquid Nitrogen
and cleaved post formation. FIGS. 6A and 6B are a set of SEM images
from a lug on a woven material with lead injected at a pressure of
10 bar. FIGS. 7A and 7B are another set of SEM images from a lug on
a felted material with lead injected again at a pressure of 10 bar.
Similarly FIGS. 8A and 8B are a set of SEM images from a lug on
woven material with lead injected at a pressure of 10 bar with an
epoxy applied to the top of the lug. FIGS. 6B, 7B, and 8B are at
higher magnification than FIGS. 6A, 7A, and 8A. In all of FIGS. 6A,
6B, 7A, 7B, 8A and 8B the pale grey material is the lead and the
long fibres are carbon fibres. The highest lead penetration of the
material was achieved with a carbon felt material, which is shown
in the series of SEM images of FIG. 7--lead clearly surrounding
each fibre with very minimal presence of voids. FIG. 7A shows full
width or cross section of the lug, and FIG. 7B shows a close up
(higher magnification) of the carbon fibres in the Pb (the holes
are where fibres have been pulled out during cleaving of the
lug).
[0129] In certain embodiments to reduce electrolyte penetration
into voids in the lug, potentially leading to lead conversion to
lead sulphate and so a loss of conductivity, epoxy was applied to
the top of the lug, to wick into the lug and prevent acid
penetration. FIG. 8 shows the lug region with excellent epoxy
penetration and minimal voids.
Example 2--Lug Formation
[0130] The following two samples of lugs were attached to carbon
felt by edge impregnation of molten lead in the major plane of the
felt generally by the method described above with reference to FIG.
15.
[0131] The first sample was on carbon felt from Heilong Jiang in
China with solid volume fraction 7.2%, thickness 1.5 mm and mean
diameter of fibres 13.9 .mu.m and arc treated as described above.
This lug was made of two regions that lay next to each other--first
a strip of lead in a cavity along the edge of the felt and second a
lead matrix around the carbon fibres of the felt at its edge. By
cutting off the second area and carefully measuring its dimensions
and mass, together with determining the mass of a measured area of
the felt, one can calculate the voidage fraction within the matrix
(see below). This voidage was 22.5%. The resistivity of the matrix
was also determined by resistance measurement with a resistance
meter over a measured volume of the matrix. This resistivity was
0.32 mOhmmm, or 0.32/0.208=1.54, or 54% higher than that of pure
lead at room temperature.
[0132] FIG. 19 is an SEM image of this sample, showing holes where
fibres have been pulled out during brittle fracture using cryogenic
conditions, but otherwise shows lead surrounding most fibres. Two
parts show some localised lack of lead, where fibres were drawn
together.
[0133] FIG. 20 is an SEM image of a second lug sample produced in
the same way but on carbon felt from SGL in Germany with solid
volume fraction of 4.6%, 2.5 mm thick and mean fibre diameter of
9.1 .mu.m also arc treated. This was infiltrated as with the first
sample yielding a higher voidage fraction of 41% and resistivity of
0.61 mOhmmm, or almost 3 times that of pure lead. The fracture
surface shows large areas of fibres that are not contacting
lead.
[0134] The connection resistances of both samples were <50
mOhms.
[0135] The methods of measurement used were as follows:
Resistivity: Strips of the connector where carbon felt were
surrounded by lead, were cut off with a guillotine, and the ends
were held by the clamps of a resistance meter. The length l between
the clamps and the observed cross-sectional area A were used in the
expression
Resistivity=(Resistance)(Area)/(length) to calculate the
resistivity.
Voidage: The strips were weighed and the mass divided by the area
to get an overall mass density. The same was done for samples of
the carbon felt to obtain a carbon density, and this was subtracted
from the first to obtain the lead density. Dividing this by the
density of pure lead and by the thickness of the felt yielded the
volume fraction of lead in the composite strips. Thus the voidage
was obtained by subtracting both the lead volume fraction and the
carbon volume fraction from 1.0, the total volume fraction.
Resistance: Aluminium bars 8 mm square were used for contacts onto
the carbon felt, one each side of the felt, with a standard contact
force provided by the clamps of the resistance meter. Two pairs of
such contacts were spaced at difference distances (10 to 80 mm) and
5 resistances were recorded at different distances over this range.
The closely linear plot of resistance versus distance provided a
slope (which yielded the resistivity of the felt when multiplied by
the cross-sectional area) and an intercept, which was twice the
contact/felt resistance. Then one set of contacts were used on an
electrode with a connector on one end, with again different
placings of the contacts along the electrode, and the other meter
clamp attached to the lead tab at one end of the connector. A plot
of resistance versus distance again gave a linear plot, with
intercept equal to the sum of one contact/felt resistance plus the
electrode connector resistance we require. Thus the latter was
obtained by subtraction of the contact/felt resistance.
Example 3--Pb-Acid Cell CCA Performance with Electrode Comprising
Lug
[0136] Electrode & cell construction: An electrode was
constructed from arc-treated carbon fibre felt having a specific
weight of 238 g/m.sup.2, a thickness of 2.93 mm, and a carbon
volume fraction 5.8%. After arc-treatment the felt had a specific
weight of 204 g/m.sup.2, was 2.5 mm thick, and had a carbon volume
fraction .about.5.7%. The carbon felt section was rectangular in
shape and had previously had a Pb lug formed along one edge by edge
impregnation of molten lead in the major plane of the felt
generally by the method described above with reference to FIG. 15,
so that Pb material of the lug penetrated fully through the lug
zone of the carbon felt material from one side to the other.
[0137] Paste was prepared with 19.5 g of leady oxide having
.about.5.1% Pb content, 3.36 g of diluted sulphuric acid, 2.24 g of
Vanisperse A as an expander and water solution to achieve 0.10 wt %
of expander in the prepared paste, and 0.16 g of Barium Sulphate.
The paste was mixed in a bath for 2 minutes with ultrasound at a
frequency of 54 kHz.
[0138] The electrode was pasted with an even distribution of paste,
also under ultrasound vibration on for .about.1 min, via an
ultra-sound vibrating plate until a majority of the paste had
penetrated into the felt. The paste was applied to the electrode so
that it contacted the lug Pb along the length of the boundary
between the lug Pb and the non-lug Pb impregnated carbon felt (not
only at the surface on either side but also through the thickness
of the carbon felt material at this boundary). The total amount of
mass loaded into the carbon felt was 18.15 g where the achieved
capacity (low current discharge) was 2.52 Ah (i.e. 68.2%) of the
theoretical capacity. The pasted electrode active area (excluding
the lug) had dimensions: length of 60.6 mm, width of 43.3 mm, and
thickness of 2.52 mm. Therefore the achieved lead loading per
volume (pasted density of the electrode based on the mass loaded on
to the electrode) was about 2.62 g/cm.sup.3. The electrode was then
built into a test cell, as a negative was sandwiched between two
(one on each side) traditional positive plates of comparable size
and subjected to formation charging.
Testing & results: The cell was subjected to SAE -18.degree. C.
CCA (cold cranking amps) tests. In particular an automotive battery
should be able to deliver high current for engine starting, at low
temperature, and a CCA test tests the ability of a battery to do
so. Test currents were 310 mA/cm2 opposed electrode area,
respectively. Having successfully passed the 310 mA/cm2 test, the
electrode pasted right up to the lug was further tested at
successively higher currents, eventually achieving a rating of 390
mA/cm2. FIG. 21 shows the result of the CCA performance test and
shows that the electrode had very good CCA performance.
[0139] 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.
* * * * *