Current-conducting electrode and corresponding
manufacturing process
The present invention relates to conductive electrodes
with current collectors, in particular used in energy
storage systems such as supercapacitors. More
specifically, the present invention relates to a
conductive electrode comprising a current collector
comprising at least one protective conductive layer and
also to the process for producing said current
collector.
Supercapacitors are electrical energy storage systems
that are particularly advantageous for applications
that necessitate conveying electrical energy at high
power. The possibilities of rapid charging and
discharging and the increased service life compared to
a high-power battery make supercapacitors promising
candidates for many applications.
Supercapacitors generally consist of the combination of
two conductive electrodes having a high specific
surface area, immersed in an ionic electrolyte and
separated by an insulating membrane referred to as a
"separator", which allows ionic conductivity and
prevents electrical contact between electrodes. Each
electrode is in contact with a metallic current
collector enabling the exchange of the electric current
with an outside system. Under the influence of a
potential difference applied between the two
electrodes, the ions present within an electrolyte are
attracted by the surface having an opposite charge thus
forming an electrochemical double layer at the
interface of each electrode. The electrical energy is
thus stored electrostatically by charge separation.
The expression of the capacitance of such
supercapacitors is identical to that of conventional
electrical capacitors, namely:
C = e.S/e
with: e: the permittivity of the medium,
S: the surface area occupied by the double
layer, and
e: the thickness of the double layer.
The capacitances that can be attained within
supercapacitors are much larger than those commonly
attained by conventional capacitors, due to the use of
porous electrodes having a high specific surface area
(maximization of the surface area) and due to the
extreme thinness of the electrochemical double layer (a
few nanometres).
The carbon-based electrodes used within supercapacitive
systems must inevitably be:
- conductive, in order to ensure the transport of the
electrical charges,
- porous, in order to ensure the transport of the ionic
charges and the formation of the electrical double
layer over a large surface area, and
- chemically inert, to prevent any energy-consuming
parasitic reactions.
The energy stored within the supercapacitor is defined
according to the conventional expression of capacitors,
namely:
E = 1/2.C.v2,
in which V is the electric potential of the
supercapacitor.
According to this expression, the capacitance and the
potential are two essential parameters that it is
necessary to optimize in order to favour the energy
performances. For example, for applications in
transport and especially for an electric vehicle,
having a high energy density is necessary in order to
limit the onboard mass of supercapacitors.
The potential depends mainly on the nature of the
electrolyte. Typically, various types of electrolyte
exist. One family is the family of organic
electrolytes, that is to say those comprising an
organic salt dispersed in an organic solvent. Some of
these electrolytes make it possible to attain an
operating potential of 2.7 V. On the other hand, these
electrolytes are expensive, inflammable, toxic and
potentially polluting. They thus pose safety problems
for use in a vehicle. Aqueous electrolytes are
inexpensive and nonflammable, they are therefore more
advantageous for this application. In an aqueous
medium, the applicable potential is 1.2 V. Various
aqueous electrolytes may be used, for example an
aqueous solution of sulphuric acid, or of potassium
chloride, or of potassium sulphate, or of other salts
in an acidic, basic or neutral medium.
In order to store a high energy density, it is
therefore necessary to have a high capacitance per unit
weight. The capacitance depends on the porous texture
actually accessible by the electrolyte, the potential
depends itself directly on the stability of the
electrolyte under the influence of the electric field.
In order to obtain a high capacitance per unit weight,
one known solution is to add active material to the
supercapacitors. Various possibilities exist for
incorporating the active material into a
supercapacitor. Document PCT/FR2009/000332 describes
the use of monolithic carbons in supercapacitors having
high capacitances per unit weight. In order to attain
high energy densities, it is therefore particularly
advantageous to incorporate the active material into
the system in monolith form. Specifically, in this
case, no inert binder is necessary for dispersing the
active material, which makes it possible, ipso f a c t o r
to increase the energy density that can be attained.
In order to be able to achieve operation with high
powers, the resistance to the passage of the current in
the system (ESR) must be very low. Specifically, this
resistance leads to losses via the Joule effect, which
reduce the efficiency of the supercapacitor. This
resistance is the sum of the resistances of the various
components of the system, and especially the resistance
of the electrolyte, and the resistance of the current
collectors. In the case of an active material in
monolith form, a primary contribution is the resistance
of the interface between the current collector and the
active material. This resistance is dependent on the
quality and on the nature of the contact.
In order to limit the contribution of the resistances
of the current collectors, it is necessary to use
metals of high conductivities. Furthermore, in the
interest of economy and ease of use, the metals used
must be inexpensive and must be able to be easily
formed. Examples of metals that may be favourably used
are therefore typically copper and aluminium. The use
of these materials in an aqueous medium however poses
chemical and electrochemical stability problems.
Indeed, at a typical oxidation potential in an aqueous
medium of 1.2 V, most of the metals corrode.
It is therefore necessary both to protect the metallic
collector from corrosion and to have a good electrical
contact between the collector and the monolithic active
material.
For this, various strategies have been used. Document
EP 1 032064 describes a current collector of a positive
electrode constituted of a paste of active material
comprising a polymer layer comprising an oxalate and a
compound based on silicon, on phosphate or on chromium.
This solution makes it possible to protect the
collector during the deposition of the paste of active
material but has no effect on the characteristics of
the electrode in use. Furthermore, this strategy cannot
be used in the case of a monolith as active material.
It is therefore necessary to use an interface between
the metallic current collector and the monolithic
active mater'ial.
Using an interface of lower conductivity than the metal
of the collector between the latter and the active
material poses a problem since it is highly likely to
increase the resistance of the system and therefore to
disrupt the functioning with high electric powers.
Various interfaces have been tested between the
collector and the active material.
One solution consists in coating the collector with a
protective layer. Document FR 2824418 describes a
current collector covered with a layer of paint
comprising conductive particles, such as graphite or
carbon black. The paint is applied between the
collector and the active material, then is heated in
order to remove the solvent. The paint is an epoxybased
paint or a polyurethane-based paint. This layer
of paint makes it possible to protect the collector in
an organic medium, but no information is given on its
effectiveness for protecting the collector from an
aqueous electrolyte. Furthermore, these paints are
crosslinked, and are therefore not very deformable and
can not thus conform to the surface of the active
material when it is present in monolith form, which
increases the contact resistance and therefore prevents
optimal functioning of the supercapacitor.
Document WO 2007/036641 describes a method for
depositing a thin film of carbon by deposition of a
dispersion of carbon-based particles in a sol-gel
polymer followed by the removal of said sol-gel polymer
at a high temperature. This additional layer makes it
possible to improve the conduction properties at.the
contact. Nevertheless, no information is given on its
impermeability in an aqueous medium. Furthermore, the
carbon-based films obtained by this method are brittle
and are subject to abrasion during the assembling of
the electrodes.
One of the objectives of the invention is therefore to
propose a current collector and also the production
process thereof, having optimized conductivity and
longevity properties, especially in the use thereof
within an electrode containing monolithic active
material.
Thus, the present invent ion relates conductive
electrode for an electrical energy storage system
containing an aqueous electrolytic solution, said
electrode comprising a metallic current collector and
an active material, said metallic current collector
comprising a protective conductive layer placed between
said current collector and said active material, said
protective conductive layer comprising:
- between 30% and 85% in a proportion by weight of dry
matter of a copolymer matrix,
- between 70% and 15% in a proportion by weight of dry
matter of conductive fillers, in addition to the
proportion by weight of dry matter of copolymer in
order to achieve a total of 100%.
According to one aspect of the invention, the metallic
current collector comprises at least one additional
protective conductive layer placed on the protective
conductive layer.
According to another aspect of the invention, the
protective conductive layer comprises:
- between 50% and 65% in a proportion by weight of dry
matter of a copolymer matrix,
- between 50% and 35% in a proportion by weight of dry
matter of conductive fillers, in addition to the
proportion by weight of dry matter of copolymer in
order to achieve a total of 100%.
According to another aspect of the invention, the
copolymer comprises vinyl chloride units and/or vinyl
acetate units and/or carboxylic acid groups.
According to another aspect of the invention, the
copolymer matrix additionally comprises additives.
According to another aspect of the invention, the
conductive fillers are chosen from carbon black and/or
graphite and/or carbon nanotubes.
According to another aspect of the invention, the
thickness of the protective conductive layer is between
5 and 50 micrometres.
According another aspect the invention, the
active material is a monolithic active material.
According to another aspect of the invention, the
monolithic active material is a carbon monolith.
The present invention also relates to a process for
producing a metallic current collector for an
electrical energy storage system, said metal-lic current
collector being intended to come into electrical
contact with an active material so as to form a
conductive electrode containing an aqueous electrolytic
solution, and comprising a protective conductive layer,
comprising the following steps:
- preparation of a composition comprising 30% to 85% of
a copolymer in a proportion by weight of dry matter
and 70% to 15% of conductive fillers in a proportion
by weight of dry matter, in addition to the
proportion by weight of dry matter of copolymer in
order to achieve a total of loo%, diluted in a
solvent in order to achieve a viscosity of 1000 mPa
to 10 000 mPa at 50 rpm,
- deposition of said composition on the current
collector,
- first heat treatment of the covered metallic current
collector at a temperature below the boiling point of
the solvent,
- second heat treatment of the covered metallic current
collector at a temperature above the glass transition
temperature of the copolymer and above the boiling
point of the solvent, said heat treatment temperature
being however below the degradation temperature of
the polymer.
According to another aspect of the production process,
said process further comprises, following the second
heat treatment step, the following steps for applying
at least one additional protective conductive layer:
- deposition of a composition comprising 30% to
85% of a copolymer in a proportion by weight of
dry matter and 70% to 15% of conductive fillers
in a proportion by weight of dry matter, in
addition to the proportion by weight of dry
matter of copolymer in order to achieve a total
of loo%, diluted in a solvent in order to
achieve a viscosity of 1000 mPa to 10 000 mPa at
50 rpm,
- heat treatment at a temperature below the
boiling point of the solvent,
- subsequent heat treatment at a temperature above
the glass transition temperature of the
copolymer and above the boiling point of the
solvent, said heat treatment temperature being
however below the degradation temperature of the
polymer.
According to another aspect of the production process,
the final viscosity of the composition is 7200 mPa at
50 rpm.
According to another aspect of the production process,
the composition comprises 50% to 65% of copolymer in a
proportion by weight of dry matter, 50% to 35% of
conductive fillers in a proportion by weight of dry
matter, in addition to the proportion by weight of dry
matter of copolymer in order to achieve a total of
100%.
According to another aspect of the production process,
the copolymer comprises vinyl chloride units and/or
vinyl acetate units and/or carboxylic acid groups.
According to another aspect of the production process,
the composition comprising 30% to 85% of a copolymer in
a proportion by weight of dry matter and 70% to 15% of
conductive fillers in a proportion by weight of dry
matter, additionally comprises additives.
According to another aspect of the production process,
the conductive fillers are chosen from carbon black
and/or graphite and/or carbon nanotubes.
According to another aspect of the production process,
the step of depositing the composition on the metallic
current collector is carried out using a film spreader.
According to another aspect of the production process,
the first and second heat treatment steps have a
duration of 30 minutes each.
Other features and advantages of the invention will
become more clearly apparent on reading the following
description, given by way of illustrative and
nonlimiting example, and from the appended drawings,
among which:
- Figure 1 shows a schematic representation of the
structure of a supercapacitor,
- Figure 2 shows a schematic representation of a test
structure made for measuring the contact resistances,
-Figure 3 shows a graph of the results of
electrochemical impedance spectroscopy measurements
of an example according to the invention.
Figure 1 shows a schematic representation of the
structure of a supercapacitor 1.
The supercapacitor 1 comprises two conductive
electrodes immersed in an ionic electrolyte (not
represented) and separated by an insulating membrane
referred to as a separator 9, which permits ionic
conductivity and prevents electrical contact between
the electrodes.
Each electrode comprises a metallic current collector
3, for example made of copper or aluminium, covered
with a protective conductive layer 5, for example
having a thickness between 5 and 50 micrometres, and
also a monolithic active material 7, for example made
of carbon, in contact with the separator 9.
The protective layer 5 is impermeable to the aqueous
electrolytes especially in an acid medium, for example
at a pH of less than or equal to 4, or else in a
neutral medium at a pH of 7. This impermeability thus
allows protection of the metallic current collector 3
against corrosion in aqueous media, thus preventing a
deterioration of the electrical contact between said
metallic current collector 3 and the monolithic active
material 7.
Furthermore, the protective conductive layer 5 also
allows an improvement of the electrical contact between
said metallic current collector 3 and the monolithic
active material 7.
The protective conductive layer 5 preferably comprises
between 30% and 85% in a proportion by weight of dry
matter of a copolymer matrix and between 70% and 15% in
a proportion by weight of dry matter of. conductive
fillers, in addition to the proportion by weight of dry
matter of copolymer in order to attain a total of 100%.
Using a copolymer enhances the flexibility of the one
protective conductive layer 5, which is favourable for
the purpose of reducing the contact resistance.
Moreover, a copolymer adheres more easily to a metallic
surface, removing the need to use additives which might
migrate into the electrolyte during the use of the
electrode, and might disrupt its operation.
The copolymer used preferably comprises vinyl chloride
units and/or vinyl acetate units and/or carboxylic acid
groups, such as for example Vinnol H15/45 M.
The copolymer matrix may additionally comprise
additives such as crosslinking agents, wetting agents,
dispersants or else stabilizers.
As for the conductive fillers, they are preferably
chosen from carbon black and/or graphite and/or carbon
nanotubes.
According to one alternative embodiment, the metallic
current collector 3 may comprise at least one
additional protective conductive layer (not shown)
placed on the protective conductive layer 5. The at
least one additional protective conductive layer may be
similar to the protective conductive layer 5 and may
therefore have features similar to that layer. The
addition of at least one additional protective
conductive layer on the protective layer 5 thus allows
the protection of the metallic current collector 3 to
be enhanced.
The process for producing the metallic current
collector 3 covered with the protective conductive
layer 5 is carried out in several steps.
The first step is a step of preparing a composition
comprising 30% to 85% of a copolymer in a proportion by
weight of dry matter and in addition 70% to 15% of
conductive fillers in a proportion by weight of dry
matter, in addition to the proportion by weight of dry
matter of copolymer in order to attain a total of 100%.
As stated previously, the copolymer used preferably
comprises vinyl chloride units and/or vinyl acetate
units and/or carboxylic acid groups, such as for
example Vinnol H15/45 M.
As for the conductive fillers, they are preferably
chosen from carbon block and/or graphite and/or carbon
nanotubes.
This composition is diluted in a solvent, for example
methyl isobutyl ketone (MIBK), in order to attain a
viscosity value between 1000 mPa and 10 000 mPa,
measured with a Brookfield viscometer.
This composition may additionally comprise additives
such as crosslinking agents, wetting agents,
dispersants or else stabilizers.
The second step is a step of applying a layer of the
composition on the metallic current collector 3, for
example by means of a film spreader.
The third step is a step of heat treatment of the
covered metallic current collector 3, at a temperature
that is below the boiling point of the solvent but that
is sufficient in order to have evaporation and
therefore a removal of a large part of the solvent from
the composition.
This heat treatment step thus makes it possible to
remove the solvent from the protective conductive layer
5 covering the metallic current collector 3, while
retaining the mechanical properties of the latter.
The fourth step is again a step of heat treatment of
the covered metallic current collector 3. This new heat
treatment takes place at a temperature above the glass
transition temperature (tg) of the copolymer and above
the boiling point of the solvent, said heat treatment
temperature being however below the degradation
temperature of the copolymer.
The expression "degradation temperature" is understood
to mean the temperature at which the copolymer is
destroyed and disappears from the protective conductive
layer 5.
The glass transition temperature (tg) of the copolymer
I
may for example be 75°C for Vinnol H15/45 M as measured
by differential scanning calorimetry (DSC) with a
reascendance rate of 10°C per minute.
This second heat treatment makes it possible to remove
the excess solvent and also to strengthen the
impermeability of the protective conductive layer 5.
The duration of each heat treatment of the third and
fourth steps may, for example, be 30 minutes in order
to be optimal.
In the alternative embodiment where the metallic
current collector 3 comprises at least one additional
protective conductive layer, the production process
further comprises additional steps for applying said
additional protective conductive layer. These steps are
carried out following the second heat treatment step,
and are as follows:
- deposition of a composition comprising 30% to
85% of a copolymer in a proportion by weight of
dry matter and 70% to 15% of conductive fillers
in a proportion by weight of dry matter, in
addition to the proportion by weight of dry
matter of copolymer in order to achieve a total
of loo%, diluted in a solvent in order to
achieve a viscosity of 1000 mPa to 10 000 mPa at
50 rpm, for example by means of a film spreader,
- heat treatment at a temperature below the
boiling point of the solvent,
- subsequent heat treatment at a temperature above
the glass transition temperature of the
copolymer and above the boiling point of the
solvent, said heat treatment temperature being
however below the degradation temperature of the
polymer.
These steps of applying additional protective
conductive layer may be repeated successively so as to
obtain the desired number of additional 'protective
conductive layers. In the same way as the heat
treatments of the protective conductive layer ( 5 ) , the
heat treatments may last 30 minutes, for example, for
optimum results;-
Illustrated below in Table 1 are examples ,of
compositions having a final viscosity of 7200 mPa at
50 rpm, used for producing a metallic current collector
3 covered with a protective conductive layer 5
according to the invention.
The compositions used in these examples all comprise
between 50% and 65% in a proportion by weight of dry
matter of a copolymer matrix and in addition between
50% and 35% in a proportion by weight of dry matter of
conductive fillers, in addition to the proportion by
weight of dry matter of copolymer in order to attain a
total of 100%.
Table 1: Composition formulation examples
1) Characterization of the electrical resistance of
covered metallic current collectors 3 and of the
conductivity of a protective conductive layer 5
obtained with one of the compositions of Examples 1
Formulation
First, a measurement of the electrical resistance is
carried out on a test structure illustrated by
Figure 2.
Example
1
100 g
0
8 g
0
0
4 9
Copolymer
Conductive
fillers
Initially, a layer 5 having a thickness of 100 microns
of these compositions is deposited on a copper current
collector 3 using a film spreader that enables a
homogeneous and controlled deposition.
Vinnol H
15/45 M 20%
in MIBK
ENSACO 260G
ENSACO 250P
ENSACO 350G
Nanocyl
3101
Graphite
After drying for 30 minutes at 5 0 " ~th~e covered copper
current collector 3 is then treated at 1 2 0 " ~ for
30 minutes.
Example
2
100 g
8 9
0
0
0
4 9
Example
3
100 g
12 9
0
0
0
6 g
Example
4
100 g
0
0
8 g
0
4 g
Example
5
100 g
8 9
0
0
0.5 g
2 9
The thickness of the protective conductive layer 5 is
measured using a micrometer, and is between 20 and
30 micrometres for each face.
The test structure illustrated by Figure 2 t-hen
comprises a monolithic carbon 3 having a surface area
of 2.5 x 2.5 cm and a thickness of 0.7 rnm placed
between two covered copper current collectors 3, and
put under pressure by a weight 11, for example 200 N,
which makes it possible to characterize the electrical
contacts. The measured resistance must be as low as
possible to allow a high-power operation of the
supercapacitor.
The resistance linked to the copper circuit was
measured at 8 mQ, and was substrated from the values
measured.
Subsequently, a protective conductive layer 5 is
deposited on glass according to the same method used
previously, in order to measure the conductivity of
said protective conductive layer 5. This measurement is
carried out by a conventional four-point conductivity
test.
The measured characteristics of the electrical
resistance of metallic current dollectors covered with
a protective conductive layer 5 obtained with one of
the compositions from Examples 1 to 5 and also of the
conductivity are listed in Table 2.
2) Characterization of the impermeability of a
protective conductive layer 5 obtained with one of
the compositions from Examples 1 to 5, covering a
metallic current collector 3.
The impermeability of the protective conductive layer 5
is characterized by electrochemical impedance
spectroscopy (EIS) of model cells operating under a
voltage of 1 V, before and after 1000 galvanostatic
cycles at 0.125 A/g.
These model cells, identical to the structure of a
supercapacitor 1 represented by Figure 1, are obtained
by assembling two monolithic carbons 7 having a
thickness of 0.7 mrn to two coated copper current
collectors 3 between which a separator 5 is placed. The
assembly is filled with electrolyte diluted in water
and packaged between two plastic films. A first series
of tests is carried out in an acid medium with a 1M
sulphuric acid (H2SO4) electrolyte and a second series
of tests is carried out in a neutral medium with a 5M
sodium perchlorate (NaC104) electrolyte.
EIS makes it possible to demonstrate the existence of
parasitic faradic phenomena. These reactions take place
whkn the copper is exposed to the electrolyte. In this
case, during the cycling, the metal is degraded and the
device can no longer function.
An EIS of a copper coated with a protective conductive
layer 5 obtained with the composition from Example 4 is
represented in Figure 3 before and after cycling. In
these cases, the behaviour observed is purely
capacitive, the impermeability test is therefore
considered to be successful.
The protective conductive layer 5 obtained with the
composition from Example 4 from Example 4 was then
scratched using a scalpel blade in order to reveal the
copper. In this case, the behaviour observed
demonstrates faradic phenomena linked to the oxidation
of the copper, the impermeability test is considered as
having failed.
The impermeability characteristics of coppers covered
with a protective conductive layer 5 obtained with one
of the compositions from Examples 1 to 5 are also
listed in Table 2.
3 ) Results
Table 2: Ex~erimental results
Legend:
+: EIS impermeability test successful,
-: EIS impermeability test failed
Formulation
Electron
conductivity
of the
protective
conductive
layer (S/cm)
Resistance at
200 N
according to
Figure 2 (mQ)
Impermeability
test (EIS)
wlth 1M H2SO4
Impermeability
test after
1000 cycles
(EIS) with 1M
H2S04
Impermeability
test (EIS)
with 5M NaC104
Impermeability
test after
1000 cycles
(EIS) with 5M
NaC104
Ex 1
1
6 0
+
+
+
+
Ex 2
2
7 1
+
+
t
+
Ex 3
5
3 8
+
+
+
+
Ex 4
0.4
9 3
+
+
+
+
Ex 5
9
Measurement
too low
+
+
+
+
N 0
coaking
107
> 200
-
-
-
-
Thus, as shown in experimental results Table 2, the
protective conductive layer 5 described in Examples 1
' to 5 makes it possible not only to protect the metallic
collector from the degradation linked to oxidation in
the presence of electrolyte, but also, surprisingly, to
improve the electrical contact between the collector
and the monolithic active material compared to a
collector without a coating.

CLAIMS
Conductive electrode for an electrical energy
storage system (1) containing an aqueous
electrolytic solution, said electrode comprising a
metallic current collector (3) and an active
material ( 7 ) , said current collector (3)
comprising a protective conductive layer (5)
placed between said metallic current collector (3)
and said active material (7), characterized in
that said protective conductive layer (5)
comprises:
- between 30% and 85% in a proportion by weight of
dry matter of a copolymer matrix,
- between 70% and 15% in a proportion by weight of
dry matter of conductive fillers, in addition to
the proportion by weight of dry matter of
copolymer in order to achieve a total of 100%.
2. Conductive electrode according to the preceding
claim, characterized in that the metallic current
collector (3) comprises at least one additional
protective conductive layer placed on the
protective conductive layer (5).
Conductive electrode according to either of the
preceding claims, characterized in that the
protective conductive layer (5) comprises:
- between 50% and 65% in a proportion by weight of
dry matter of a copolymer matrix,
- between 50% and 35% in a proportion by weight of
dry matter of conductive fillers, in addition to
the proportion by weight of dry matter of
copolymer in order to achieve a total of 100%.
4. Conductive electrode according to the preceding
claim, characterized in that the copolymer
comprises vinyl chloride units and/or vinyl
acetate units and/or carboxylic acid groups.
5. Conductive electrode according to one of the
preceding claims, characterized in that the
copolymer matrix additionally comprises additives.
6. Conductive electrode according to one of the
preceding claims, characterized in that the
conductive fillers are chosen from carbon black
and/or graphite and/or carbon nanotubes.
7. Conductive electrode according to one of the
preceding claims, characterized in that the
thickness of the protective conductive layer (5)
is between 5 and 50 micrometres.
8. Conductive electrode according to one of the
preceding claims, characterized in that the active
material is a monolithic active material (7).
9. Conductive electrode according to the preceding
- claim, characterized in that the monolithic active
material is a carbon monolith (7).
10. Process for producing a metallic current collector
(3) for an electrical energy storage system (I),
said metallic current collector (3) being intended
to come into electrical contact with an active
material (7) so as to form a conductive electrode
containing an aqueous electrolytic solution, and
comprising a protective conductive layer (5),
comprising the following steps:
- preparation of a composition comprising 30% to
85% of a copolymer in a proportion by weight of
dry matter and 70% to 15% of conductive fillers
in a proportion by weight of dry matter, in
addition to the proportion by weight of dry
matter of copolymer in order to achieve a total
of loo%, diluted in a solvent in order to
achieve a viscosity of 1000 mPa to 10 000 mPa at
50 rpm,
- deposition of said composition on the metallic
current collector (3),
- first heat treatment of the covered metallic
current collector (3) at a temperature below the
boiling point of the solvent,
- second heat treatment of the covered metallic
current collector (3) at a temperature above the
glass transition temperature of the copolymer
and above the boiling point of the solvent, said
heat treatment temperature being however below
the degradation temperature of the polymer.
Production process according to the preceding
claim, characterized in that it further comprises,
following the second heat treatment step, the
following steps for applying at least one
additional protective conductive layer:
- deposition of a composition comprising 30% to
85% of a copolymer in a proportion by weight of
dry matter and 70% to 15% of conductive fillers
in a proportion by weight of dry matter, in
addition to the proportion by weight of dry
matter of copolymer in order to achieve a total
of loo%, diluted in a solvent in order to
achieve a viscosity of 1000 mPa to 10 000 mPa at
50 rpm,
-heat treatment at a temperature below the
boiling point of the solvent,
- subsequent heat treatment at a temperature above
the glass transition temperature of the
copolymer and above the boiling point of the
solvent, said heat treatment temperature being
however below the degradation temperature of the
polymer.
12. Production process according to the preceding
claim, characterized in that the final viscosity
of the composition is 7200 mPa at 50 rpm.
13. Production process according to one of Claims 10
to 12, characterized in that the composition
comprises 50% to 65% of copolymer in a proportion
by weight of dry matter, 50% to 35% of conductive
fillers in a proportion by weight of dry matter,
in addition to the proportion by weight of dry
matter of copolymer in order to achieve a total of
100%.
14. Production process according to one of Claims 10
to 13, characterized in that the copolymer
comprises vinyl chloride units and/or vinyl
acetate units and/or carboxylic acid groups.
15. Production process according to one of Claims 10
to 14, characterized in that the composition
comprising 30% to 85% of a copolymer in a
proportion by weight of dry matter and 70% to 15%
of conductive fillers in a proportion by weight of
dry matter, additionally comprises additives.
16. Production process according to one of Claims 10
to 15, characterized in that the conductive
fillers are chosen from carbon black and/or
graphite and/or carbon nanotubes.
17. Production process according to one of Claims 10
to 16, characterized in that the step of
depositing the composition on the current
collector (3) is carried out using a film
spreader.
18. Production process according to one of Claims 10
to 17, characterized in that the first and second
heat treatment steps have a duration of 30 minutes
each.
Dated this 20.12.2013
NHA SNVASTAVA]
OF REMFRY & SAGAR
ATTORNEY FOR THE APPLICANT[S]