U.S. patent application number 12/996691 was filed with the patent office on 2011-04-14 for electrode for lead-acid battery and method for producing such an electrode.
This patent application is currently assigned to COMMISSARIAT A L 'ENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES. Invention is credited to Angel Zhivkov Kirchev.
Application Number | 20110083966 12/996691 |
Document ID | / |
Family ID | 40377352 |
Filed Date | 2011-04-14 |
United States Patent
Application |
20110083966 |
Kind Code |
A1 |
Kirchev; Angel Zhivkov |
April 14, 2011 |
ELECTRODE FOR LEAD-ACID BATTERY AND METHOD FOR PRODUCING SUCH AN
ELECTRODE
Abstract
An electrode for lead-battery comprises a current collector
covered by an active layer of lead-containing paste. The current is
formed by a glassy carbon substrate on which is deposited an
intermediate layer. The glassy carbon substrate has preferably a
thickness comprised between 1 mm and 3 mm whereas the thickness of
the intermediate layer is advantageously comprised between 50 .mu.m
and 200 .mu.m. In a particular embodiment, the glassy carbon
substrate is in form of a comb.
Inventors: |
Kirchev; Angel Zhivkov;
(Aix-les-Bains, FR) |
Assignee: |
COMMISSARIAT A L 'ENERGIE ATOMIQUE
ET AUX ENERGIES ALTERNATIVES
Paris
FR
|
Family ID: |
40377352 |
Appl. No.: |
12/996691 |
Filed: |
June 9, 2008 |
PCT Filed: |
June 9, 2008 |
PCT NO: |
PCT/IB08/02468 |
371 Date: |
December 7, 2010 |
Current U.S.
Class: |
205/161 ;
205/162 |
Current CPC
Class: |
C04B 35/524 20130101;
Y02E 60/10 20130101; H01M 4/685 20130101; H01M 4/663 20130101; H01M
4/73 20130101; H01M 4/16 20130101; H01M 10/06 20130101; H01M 4/20
20130101; H01M 4/0452 20130101; H01M 4/0433 20130101 |
Class at
Publication: |
205/161 ;
205/162 |
International
Class: |
C25D 5/54 20060101
C25D005/54 |
Claims
1-9. (canceled)
10. A method for producing an electrode for lead-acid battery
comprising at least the following steps: formation of a glassy
carbon substrate by plastic molding of a thermosetting resin in a
predetermined shape followed by carbonizing the thermosetting resin
in inert atmosphere, formation of a compact intermediate layer made
from a lead-tin alloy with a percent of tin in the lead-tin alloy
of about 2.5% in weight on at least one part of a surface of the
glassy carbon substrate, by an operation of electroplating with an
electrolyte comprising Pb(II) salt of the 4-hydroxybenzensulfonic
acid, Sn(II) salt of the 4-hydroxybenzenesulfonic acid and
p-phenolsulfonic acid, and formation of an active layer of
lead-containing paste by covering the intermediate layer with the
lead-containing paste, wherein the glassy carbon substrate presents
an apparent volume and a volume of pores, the volume of pores of
the glassy carbon substrate being comprised between 0% and 10% of
its apparent volume.
11. The method according to claim 10, wherein formation of the
glassy carbon substrate is followed by a surface treatment step of
the glassy carbon substrate comprising a mechanical treatment, an
electrochemical etching and a water rinsing.
12. The method according to claim 10, wherein that the glassy
carbon substrate comprises a tab and wherein an electroplating
operation of the tab with copper is achieved before the formation
of the compact intermediate layer.
13. The method according to claim 10, wherein the volume of the
pores in the glassy carbon substrate is comprised between 1% and 6%
of its apparent volume.
14. The method according to claim 10, wherein the predetermined
shape of the glassy carbon substrate is a comb.
15. The method according to claim 14, wherein the glassy carbon
substrate comprises a plurality of branches, having a round,
rectangular, square or elliptic cross-section.
16. The method according to claim 10, wherein the glassy carbon
substrate has a thickness comprised between 1 mm and 3 mm.
17. The method according to claim 10, wherein the compact
intermediate layer has a thickness comprised between 50 .mu.m and
200 .mu.m.
18. The method according to claim 10, wherein the electrolyte is
obtained by mixing: 140 g.L.sup.-1 of
Pb(p-C.sub.6H.sub.4OHSO.sub.3).sub.2, 40 g.L.sup.-1 of
p-C.sub.5H.sub.4OHSO.sub.3H, 4 g.L.sup.-1 of
Sn(p-C.sub.6H.sub.4OHSO.sub.3).sub.2, and 4 g.L.sup.-1 of gelatin.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to an electrode for lead-acid battery
comprising : [0002] a glassy carbon substrate [0003] an
intermediate layer deposited on the glassy carbon substrate [0004]
and an active layer of a lead-containing paste covering the
intermediate layer.
[0005] The invention also related to a method for producing such an
electrode.
STATE OF THE ART
[0006] Lead-acid battery is known to include at least one positive
current collector, at least one negative current collector and an
electrolytic solution. Usually, the negative and positive current
collectors are lead grids or lead plates of various configurations
(flat-plates, tubular-plates . . . ) and on which is disposed an
active material paste in order to form an electrode. Storage and
release of electrical energy in lead-acid batteries is enabled by
chemical reactions that occur in the paste.
[0007] However, the main drawback of the lead-acid batteries is
their low specific energy. Flat-plate lead-acid battery has a
specific energy about 30-35 Wh/kg whereas tubular-plate lead-acid
battery has a specific energy about 20-25 Wh/kg. These low values
of the specific energy result from the low utilization efficiency
of the active materials in conjunction with the heavy weight of the
lead current collectors.
[0008] In the past, it has been proposed to replace the lead of the
current collectors by an alternative material having low density
and high electrical conductivity in order to increase the specific
energy of lead-acid batteries.
[0009] L. A. Yolshina and al. in the article "A lead-film electrode
on an aluminium substrate to serve as a lead-acid battery plate"
(Journal of Power Sources, 78 (1999) 84-87) have proposed to
deposit compact lead layers on the surfaces of aluminium and
aluminium alloys and to use the lead-film electrode produce on
aluminium plate as positive electrode in a lead-acid battery.
However the deposition process of the lead layer on the surface of
aluminium and aluminium alloys is rather expensive and complicated.
Furthermore any unprotected aluminium surface resulted from cracks
or fissures of the lead layer will lead to accelerated grid
corrosion process, causing fast battery failure.
[0010] In the International application WO-A-2006/070405, it has
been proposed a corrosion resistant grid structure for use in a
lead-acid battery. The grid structure comprises: [0011] a substrate
material formed by acrylonitrile butadiene styrene (ABS) coated
with a metal layer of copper or nickel [0012] a lead/lead-based
alloy layer deposited on the metal layer, and [0013] an
electrically conductive and corrosion-resistant polyaniline layer
providing corrosion protection for the lead/lead-based alloy
layer.
[0014] Since the ABS is an insulator, the current collectors will
show much higher electrical resistance and the plastic substrate is
also unsuitable in a further cast on strap process also called COS
process.
[0015] Another alternative consists to use graphite electrode-plate
as mentioned in patent U.S. Pat. No. 5,512,390. In this patent, one
of the plates forms a cathode and has a surface layer of lead in
contact with the electrolyte whereas the other plate forms the
anode and has a surface layer of manganese dioxide in contact with
the electrolyte. Moreover, the article "Lead-acid cells with
lightweight, corrosion-protected, flexible-graphite grids" of B.
Hariprakash et al. (Journal of Power Sources, 173 (2007) 565-569)
proposes to use lightweight grids prepared from flexible graphite
sheets of mass density 1.1 g.cm.sup.-3. The grids are then coated
with a lead layer followed by a corrosion-resistant polyaniline
layer. The corrosion-protected grids are then pasted with active
materials.
[0016] Despite the low density and the high conductivity of the
graphite, the active material sheds easy from these grids or
plates. Indeed, the electroplated polyaniline layer used in the
article of B. Hariprakash et al. degrades fast under the high
potential of the operation of the positive plate. Moreover, the
graphite is a very soft material and its surface cannot withstand
the changes mechanical stress during the charge and the discharge
and the quality of the lead layer is poor, causing fast
peeling.
[0017] Another way to produce lightweight current collectors is the
use of high-porous carbons. The open porosity of these materials is
90-95% of their apparent volume. The high-porous carbon can be
carbon foam. For instance, patent U.S. Pat. No. 6,979,513 describes
a current collector formed from of a carbon foam material which may
include carbon or carbon-based material that exhibit some degree of
porosity. The positive and negative plates include then a current
collector made from carbon foam and packed or coated by a
chemically active material including, for example, an oxide or salt
of lead. The carbon foam material can be obtained by subjecting
various organic material to a carbonizing and/or graphitizing
process. More particularly, at least of portion of carbon foam
matrix is graphite.
[0018] However, the direct use of carbon foam as current collector
for the positive plates is strictly limited due to the anodic
degradation of the material in the potential domain of the oxygen
evolution and the anodic degradation causes fast capacity loss in
the first few cycles
[0019] As mentioned in the patent U.S. Pat. No. 7,060,391, the
high-porous carbon can also be reticulated vitreous carbon also
called RVC. Furthermore, in order to improve the performance,
especially the cycling performance, of lead-acid battery, patent
U.S. Pat. No. 7,060,391 proposes current collector structures based
on light-weight, porous, open pore, high specific surface area
substrates coated with lead or lead-tin alloy. The substrates can
be reticulated vitreous carbon. Lead or lead-tin alloy can be
deposited by electroplating method. Lead or lead-tin alloy covers
the surface of the substrates and also occupies the openings of the
reticulated substrates. Once the substrates have been coated, the
corresponding tab and frame made of lead or lead-alloy are formed
and the current collectors are subjected to pasting with any
variety of lead oxide and/or lead sulfate based pastes in order to
form electrodes. Such current collectors have the following
drawbacks: [0020] as the surface of the RVC substrate is
substantial, forming tab and frame can decrease substantially the
specific energy of the battery, [0021] the internal resistance of
the corresponding battery can be high due to the low ohmic
resistance of the reticulated vitreous carbon, [0022] the
reticulated vitreous carbon is brittle and the performance of the
battery can be disappointing during operation under vibrations and
other kinds of mechanical stress, [0023] the pasting operation with
a RVC substrate coated by lead or lead-tin alloy is markedly harder
than the pasting operation with other conventional grids, [0024]
applying compression of the active block is nearly impossible,
because the reticulated structure has poor elastic properties. The
absence of compression leads to fast softening and peeling of the
positive active material from the supporting grid at deep discharge
or high rate cycling and to decrease in capacity.
[0025] Alternatively, in the abstract of the document JP2158057, it
has been proposed to use a current collector consisting of a glassy
carbon plate coated by a conductive, oxidation resistant film
formed by SnO.sub.2 or Ti.sub.4O.sub.7.
[0026] Then, a cathode active material is pasting on the surface of
the film in order to form the corresponding electrode. Such a film
is strongly bonded on the surface of the glassy carbon plate and
does not separate from the plate even after long use. However, it
isn't stable at deep discharge conditions and in the absence of the
PbO.sub.2 corrosion layer generally formed from a metallic lead
support, the positive active material can easy loss the mechanical
and electrical connection with the carbon support.
OBJECT OF THE INVENTION
[0027] The object of the invention is to provide an electrode for
lead-battery and a method for producing such an electrode remedying
the shortcomings of the prior art.
[0028] More particularly, one object of the invention is to provide
an electrode for lead-acid battery comprising a glassy carbon
substrate, an intermediate layer deposited on the glassy carbon
substrate and an active layer of a lead-containing paste covering
the intermediate layer, having improved mechanical and electrical
connection between the lead-containing paste and the substrate and
a stabilized interface between the substrate and the intermediate
layer even if deep discharge conditions are applied.
[0029] According to the invention, this object is achieved by the
appended claims and more particularly by the fact that the
intermediate layer is a compact layer of lead or lead-based alloy
and by the fact that the volume of the pores in the glassy carbon
substrate is comprised between 0% and 10% of its apparent
volume.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Other advantages and features will become more clearly
apparent from the following description of particular embodiments
of the invention given as non-restrictive examples only and
represented in the accompanying drawings, in which:
[0031] FIG. 1 represents a particular embodiment of an electrode
according to the invention in cross section.
[0032] FIG. 2 schematically represents a glassy carbon substrate in
the form of a comb in front view.
[0033] FIGS. 3 and 4 schematically represent a current collector
consisting in the glassy carbon substrate according to FIG. 2
covering by an intermediate layer, respectively in front view and
in cross section along A-A.
[0034] FIG. 5 schematically represents, in cross-section, an
alternative embodiment of the current collector according to FIGS.
3 and 4.
[0035] FIG. 6 represents cyclic voltammograms of an electrode
consisting in glassy carbon substrate in the form of a rod covered
by an intermediary layer of pure lead, immersed in sulfuric acid
solution at 40.degree. C., respectively at 100 and 1700 voltametric
cycles.
[0036] FIG. 7 represents an optical micrograph of a glassy carbon
substrate in the form of a rod electroplated by pure lead, after a
corrosion test at 40.degree. C. during 16 h.
[0037] FIGS. 8 and 9 represent the evolution of charge-discharge
current and potential of tubular-plate electrodes, respectively
assembled with lead-tin electroplated glassy carbon substrate in
the form of a rod and with cast lead-2.8% wt antimony material in
the form of a rod.
DESCRIPTION OF PARTICULAR EMBODIMENTS
[0038] As represented in FIG. 1, an electrode 1 for lead-battery
comprises a current collector 2 covered by an active layer 3 of
lead-containing paste. The current collector 2 is formed by a
glassy carbon substrate 4 on which is deposited an intermediate
layer 5. The glassy carbon substrate 4 has preferably a thickness
comprised between 1 mm and 3 mm whereas the thickness of the
intermediate layer 5 is advantageously comprised between 50 .mu.m
and 200 .mu.m.
[0039] The glassy carbon material is also called vitreous carbon,
glassy polymeric carbon or vitreous polymeric carbon. The glassy
carbon is a special form of carbon. It is a low-porous carbon.
Thus, the glassy carbon substrate 4 comprises pores but the volume
of these pores only represent between 0% and 10% of the apparent
volume of the substrate. More particularly, the ratio between the
volume of pores and the apparent volume is comprised between 1% and
6%. In addition, the glassy carbon material presents high electric
conductivity property and mechanical properties similar to those of
the glasses (hardness, capacity to polish the surface, etc). It has
also a very high chemical resistance and it is electrochemically
stable in a wide range of polarization potentials. Recycling of
lead-acid batteries that comprise a glassy carbon substrate can be
done by all existing technologies used for recycling of traditional
lead-acid batteries. The glassy carbon substrate can be separated
and used in other applications in the form of powder or subjected
to incineration together with the rest of the plastic components of
the battery (boxes, separators, etc).
[0040] The document JP2158057 cited in the state of the art has
already proposed an electrode for a bipolar lead-storage battery
comprising a glassy carbon plate. However the surface of the glassy
carbon plate is covered by a layer of SnO.sub.2 or by a layer of
Ti.sub.4O.sub.7 presenting some major drawbacks.
[0041] It has been surprisingly found that covering the glassy
carbon substrate 4 by an intermediate layer 5 made by lead or by a
lead-based alloy allows remedying to the drawbacks of the document
JP2158057. In addition, the intermediate layer 5 must be a compact
layer, i.e. a non-porous layer. The preferred lead-based alloy is
an alloy consisting in lead and tin and more particularly a
lead-tin alloy comprising 2.5 weight percents in total weight of
the elements containing in the intermediate layer.
[0042] Such an intermediate layer 5 improves the adhesion of the
active material paste on the current collector 2. The electrode is
also more stable when deep discharge conditions are applied. In
addition, the fact that the intermediate layer 5 contains tin is
advantageous because tin prevents the electrode from the
Predominant Capacity Loss (PCL) effect due to formation of highly
resistive layer of PbO and PbO.sub.n with 1<n<2 in the
corrosion layer. In fact, Sn(II) and Sn(IV) ions act as doping
agents in the crystal lattice of PbO and PbO.sub.n with 1<n<2
and they decrease substantially the ohmic resistance of these two
lead oxides that correspond to the compounds of the corrosion layer
formed on the surface of the positive current collector during the
implementation of the lead-acid battery. The presence of tin in the
intermediate layer 5 also improves its mechanical resistance.
However, the tin content in the intermediate layer 5 is preferably
limited to 2.5 weight % because when the tin content in a
lead-based alloy is more than 2.5%, its anodic corrosion rate
increases markedly.
[0043] The following steps preferably produce such an electrode:
[0044] formation of the glassy carbon substrate 4 by plastic
molding of a thermosetting resin in a predetermined shape followed
by carbonizing the thermosetting resin in inert atmosphere, [0045]
formation of the intermediate layer 5 by electroplating of the
whole of the surface of the glassy carbon substrate 4 with lead or
lead-based alloy [0046] and formation of the active layer 3 by
covering the intermediate layer 5 with a lead-containing paste.
[0047] The thermosetting resin can be a phenol-formaldehyde resin,
a furfural alcohol resin, a polyester resin, an epoxy resin or a
mixture of them. Carbonizing the thermosetting resin is achieved by
heat treatment.
[0048] More particularly, the formation of the glassy carbon
substrate 4 is followed by a surface treatment step of the glassy
carbon substrate 4. The surface treatment step comprises: [0049] a
mechanical treatment, for instance a sandblasting or a similar
treatment in order to roughen the surface of substrate 4. In fact,
the quality of the intermediate layer 5 is partly defined by the
mechanical treatment. [0050] an electrochemical anodic etching of
the glassy carbon surface. For instance, the etching conditions are
the followings: Use of an alkaline solution of 1M NaOH, with an
operation time of 10 min and an anodic current density of 20
mA/cm.sup.2. During this operation, the glassy carbon substrate is
cleaned and additionally roughened at sub-microlevel. [0051] and a
water rinsing to remove the alkaline solution.
[0052] In addition, the tab of the glassy carbon substrate 4, used
as connection element, is advantageously electroplated with copper.
Electroplating the tab with copper ensures the quality of the cast
on strap connection. In fact, the glassy carbon substrate cannot be
wetted in liquid metals and copper has a melting temperature much
higher than the lead and is nearly insoluble in it. Suitable
conditions for the copper electroplating operation can be the
following: [0053] an electrolyte bath comprising 250 g.L.sup.-1 of
CuSO.sub.4.5H.sub.2O and 70 g.L.sup.-1 of H.sub.2SO.sub.4, [0054] a
cathodic current density of 40 mA/cm.sup.2, [0055] a temperature
comprised between 20.degree. C. and 25.degree. C.
[0056] Moreover, the application of pulse current improves the
quality of the copper layer. Suitable pulse current regime is for
instance obtain by applying a cathodic current with a density of 60
mA/cm.sup.2 during 6 s and then an anodic current with a density of
60 mA/cm.sup.2 applied during 1 s.
[0057] An operation time of 30 min allows obtaining a copper layer
deposited on the tab having a thickness of about 25 .mu.m. The tab
electroplated by copper is then rinsed with water.
[0058] The intermediate layer 5 is then formed by electroplating at
least the whole of the surface of the glassy carbon substrate 4
with lead or lead-based alloy. This step is the most critical
operation of the process. It is in particular necessary to choose
an electrolyte enabling the highest adhesion strength of the
intermediate layer 5 to the glassy carbon substrate 4 and a
constant thickness of the intermediate layer 5 to be obtained. An
intermediate layer 5 made of 2.5% Sn--Pb alloy can be formed by
using an electrolyte comprising Pb(II) salt of the
4-hydroxybenzenesulfonic acid
(Pb(p-C.sub.6H.sub.4OHSO.sub.3).sub.2) and Sn (II) salt of the
4-hydroxybenzenesulfonic acid
(Sn(p-C.sub.6H.sub.4OHSO.sub.3).sub.2) and p-phenolsulfonic acid
(p-C.sub.6H.sub.4OHSO.sub.3H). The weight percent of the tin is
about 2.5% of the total weight of metals containing in the
electrolyte in the electrolyte. In a particular embodiment, the
electrolyte can be obtained by mixing: [0059] 140 g.L.sup.-1 of
Pb(p-C.sub.6H.sub.4OHSO.sub.3).sub.2, [0060] 40 g.L:.sup.-1 of
p-C.sub.6H.sub.4OHSO.sub.3H [0061] 4 g.L.sup.-1 of
Sn(p-C.sub.6H.sub.4OHSO.sub.3).sub.2 [0062] and 4 g.L.sup.-1 of
gelatin.
[0063] The electroplating step can be performed with: [0064] a
cathodic current density of 10 mA/cm.sup.2, [0065] a temperature of
20-30.degree. C. [0066] and an operation time of 85 or 190
minutes.
[0067] Moreover, the application of a pulse current during the
electroplating step improves additionally the homogeneity of the
layer. The pulse current characteristics can be as follows: [0068]
cathodic current amplitude=20 mA/cm.sup.2, [0069] t.sub.on=1 s
[0070] and t.sub.off=1 s.
[0071] For instance, with an electroplating step performing during
85 minutes, the intermediate layer 5 has a thickness about 50 .mu.m
(+/-2%). This thickness is sufficient for a current collector used
in a negative electrode. For a current collector used in a positive
electrode, the operation time can be doubled in order to deposit an
intermediate layer 5 having a thickness between about 100 .mu.m and
200 .mu.m (+/-2%).
[0072] Once the intermediate layer 5 is formed, the current
collector is rinsed with water and dried on air flow. Then, the
active layer 3 can be formed on the intermediate layer 5 by
depositing the lead-containing paste in order to form the
electrode. The lead-containing paste can be obtained by mixing PbO
(75%) with H.sub.2O (15%) and H2SO.sub.4 (10%).
[0073] Such a process presents the advantage to provide an
electrode having improved mechanical and electrical connection
between the lead-containing paste and the substrate. The interface
between the substrate and the intermediate layer is also stabilized
even if deep discharge conditions are applied.
[0074] Moreover, the electrodes for lead-acid battery can have any
known shape. For instance, the glassy carbon substrate can be in
the form of grid or comb, in order to obtain electrodes in the form
of flat plates or of tubular plates.
[0075] FIG. 2 represents more particularly a glassy carbon
substrate 4 in the form of a comb designed to be used to obtain a
tubular-plate electrode. The glassy carbon substrate 4 comprises a
plurality of parallel branches 4a connected together by a base 4b.
The base 4b also comprises a tab 6 equipped with an opening 7.
FIGS. 3 and 4 represent the glassy carbon substrate 4 covered by
the intermediate layer 5. In addition, copper 8 has filled the
opening 7 before the intermediate layer 5 is formed. The typical
diameter of the opening 7 is about 2-3 mm.
[0076] Moreover, the branches 4a of the glassy carbon substrate 4
have a round cross-section as represented on FIG. 4. This is the
traditional design of a current collector used for a tubular-plate
electrode.
[0077] However, the cross-section of the branches 4a can be of any
type of form. The branches 4a can also have a rectangular
cross-section as represented on FIG. 5 or a square cross-section or
elliptic square cross-section. The form of current collector
represented on FIG. 5 is also called Strap Grid Tubular Plates
(SGTP). This form is advantageous because it increases
substantially the performance of the corresponding lead-acid
battery in comparison with the traditional design (round
cross-section): The load factor of the active material is much
higher and the internal resistance is decreased. In addition,
manufacturing the SGTP current collectors from glassy carbon
substrate as represented in FIG. 5 is also much cheaper than the
corresponding traditional current collectors from glassy carbon
substrate as represented in FIG. 4. This great difference comes
from the difference in the characteristic thickness of both types
of branches. In FIG. 5 (SGTP design), the diameter d of a branch 4a
is about 1 mm or 1.5 mm and the diameter D of the branch 4a covered
by the intermediate layer 5 is about 3 mm or 4 mm. In FIG. 4
(traditional design), the corresponding values are more than twice
higher: d is about 3 mm and D is about 9 mm. The decreased
thickness at the SGTP design reduces greatly the time of
carbonization and hence the production cost.
[0078] In the tubular-plate design, the active material paste is
encapsulated around each branch 4a covered by an intermediate layer
5, by means of a woven or non-woven textile tube. This tube
maintains a constant pressure on the active material and prevents
its softening or its non-cohesion from the current collector.
[0079] In a particular embodiment, a current collector formed by a
glassy carbon rod (or branch or spine) having a diameter d of 3 mm
and by an intermediate layer of pure lead having a thickness of 150
.mu.m is immersed in sulfuric acid solution, H.sub.2SO.sub.4, at
40.degree. C. with a density of 1.28 g/ml. It's testing in the
0.7V-1.6V potential interval vs. the potential of
Ag/Ag.sub.2SO.sub.4. FIG. 6 shows the corresponding cyclic
voltammetry curves A and B, for 100 cycles and 1700 cycles. The
curves A and B do not differ from the corresponding curves of a
cast lead electrode used in the state of the art.
[0080] During this test, the intermediate layer of pure lead is
subjected both to cathodic dissolution and anodic corrosion attack
at elevated temperature. After 1700 cycles, which correspond to a
test period of 16 hours, the current collector is washed, dried and
embedded in an epoxy resin 9. Its cross-section is polished and
subjected to a metallographic observation as represented in FIG. 7.
It can be seen that the intermediate layer 5 is homogeneous and
intact. The thickness of the corrosion layer 10 is also homogeneous
and there aren't cracks and pits.
[0081] In another embodiment, glassy carbon branches covered by an
intermediate layer of lead-tin having a thickness of 50 .mu.m, with
a diameter D of about 3 mm, were used to form a tubular-plate
electrode having a diameter of about 6 mm and a theoretical
capacity about 300 mA at 50% load factor of the active material. A
same type of electrode is assembled by using spines cut off from
commercial tubular-grids with a Pb-2.8 wt Sb alloy.
[0082] FIGS. 8 and 9 show the evolution of the current and of the
positive plate potential (measured vs. Ag/Ag.sub.2SO.sub.4
reference electrode) during the 28.sup.th charge/discharge cycle.
It can be seen that the electrochemical performance of the lead
electroplated glassy-carbon tubular electrode is identical with the
one of the lead-antimony cast spine.
[0083] The invention is not limited to the embodiments described
above. More particularly, the current collector can have the form
of: [0084] a grid suitable for a flat negative or positive plate
electrode. With a glassy carbon substrate having a thickness of 1
mm, the production costs of the glassy carbon substrate are
minimal. After the electroplating operation, the thickness of the
grid increases for instance to 1.1 mm. The manufacturing of
lead-acid battery plates with such thickness results in increased
battery power and active materials utilization. [0085] a plate used
in a bipolar lead-acid battery. For instance, a glassy carbon plate
having a thickness of 1-1.5 mm can be completely electroplated with
a lead-tin layer having a thickness of 50 .mu.m. The plate
comprises a plurality of ribs with a length of 2 mm and a typical
inter-ribs dimension of 10 mm. [0086] a flexible foil used in a
spiral-wound lead-acid battery with ultra-thin plates. For
instance, the flexible foil can have a thickness of 60-180 .mu.m
and the optimal thickness of the intermediate layer is 30 .mu.m.
Further the electroplated glassy carbon foil is double side pasted
with 200-250 .mu.m layers of basic lead sulphates and water mixture
(so called "paste").
[0087] In addition, the glassy carbon material forming the
substrate of an electrode according to the invention must not be
confused with reticulated vitreous carbon (RVC) as disclosed in
U.S. Pat. No. 7,060,391. In fact, reticulated vitreous carbon is a
high-porous carbon, in which the open porosity is about 90%-95% of
its apparent volume.
* * * * *