MASTERBATCH OF CARBON-BASED CONDUCTIVE FILLERS FOR
LIQUID FORMULATIONS, ESPECIALLY IN Li-ION BATTERIES
The present invention relates to a masterbatch
5 containing carbon-based conductive fillers, such as
carbon nanotubes, and also to its preparation method and
to the use of this masterbatch for the manufacture of
components of Li-ion batteries and of supercapacitors,
and more generally for integrating carbon nanotubes into
10 aqueous-based or organic-based liquid formulations.
An Li-ion battery comprises at least one negative
electrode, or anode coupled to a current collector made of
copper, one positive electrode or cathode coupled to a
15 current collector made of aluminum, a separator, and an
electrolyte. The electrolyte consists of a lithium salt,
generally lithium hexafluorophosphate, mixed with a
solvent, which is a mixture of organic carbonates chosen
to optimize the transport and the dissociation of the
20 ions. A high dielectric' constant is favorable to ion
dissociation, and therefore to the number of ions
available in a given volume, whereas a low viscosity is
favorable to ion diffusion which, among other parameters,
plays an essential role in the charge and discharge rates
25 of,-the electrochemical system.
An electrode generally comprises at least one
current collector on which is deposited a composite
material which consists of: a material that is said to be
30 active because it has an electrochemical activity with
respect to lithium, a polymer, which acts as binder and
is generally a vinylidene fluoride copolymer for the
positive electrode and aqueous-based binders, of
2
carboxymethyl cellulose or styrene-butadiene latex type,
for the negative electrode, plus an electronically
conductive additive, which is generally Super P carbon
black or acetylene black.
5
During charging, lithium is inserted into the
negative electrode (anode) active material and its
concentration in the solvent is kept constant by an
equivalent amount being extracted from the positive
10 electrode (cathode) active material. Insertion into the
negative electrode' results in lithium reduction and
therefore it is necessary to supply, via an external
circuit, electrons to this electrode going from the
positive electrode. During discharging the opposite
15 reactions take place.
It has been demonstrated in preceding studies that
replacing the carbon black or the acetylene black with
carbon nanotubes (CNTs),' or else adding CNTs to such
20 conductive additives, exhibits many advantages: increase
of the electrical conductivity, better integration around
particles of active material, good intrinsic mechanical
properties, ability to form an electrical network that is
better connected in the bulk of the electrode and between
25 the metallic collector and the active material, good
capacity retention during cycling in the electrode
composite, etc.
By way of example, K. Sheem et al. (J. Power
30 Sources, 158, (2006), 1425) show that CNTs at 5 wt%
relative to the electrode materials may provide a better
cycling performance than Super P carbon black, with
LiCoO2 as cathode material. As regards W. Guoping et al.
3
(Solid State Ionics 179 (2008) 263-268), they report a
better capacity performance during cycling and as a
function of the current density of an LiCoO2 cathode when
the electrode contains 3 wt% of CNTs instead of 3 wt% of
5 acetylene black or nanofibers.
However, the introduction of carbon nanotubes into
the formulations of the materials forming the electrodes
all the same still raises some negative points that need
10 to be improved.
When the dispersion of the CNTs is carried out
directly in the liquid formulations. (especially in
organic solvent bases), a high viscosification of the
15 dispersion and a low stability of such a dispersion are
witnessed. To overcome this drawback, use is made of ball
mixers and high-shear mills and mixers. However, the
content of CNTs capable of being introduced into the
liquid formulations remains limited to 1-2%. These
20 difficulties limit the practical use of CNTs in the
formulations of the materials constituting the electrodes
owing to the aggregation of the CNTs due to their highly
entangled structure.
25 Moreover, from a toxicological point of view, the
CNTs are generally in the form of agglomerated powder
grains, the average dimensions of which are of the order
of a few hundreds of microns. The differences in
dimensions, in form, and in physical properties mean that
30 the toxicological properties of the CNT powders are not
yet fully known. It would therefore be preferable to be
able to work with CNTs in agglomerated solid form of
macroscopic size.
4
In this respect, document US 2004/0160156 describes
a method of preparing an electrode for a battery from a
masterbatch, in the form of granules composed of CNTs and
5 of a resin that acts as binder, to which a suspension of
electrode active material is added.
In this document, the resin is present in a large
amount within the masterbatch, since the CNTs are present
10 in proportions ranging from 5 to 20 parts by weight per
100 parts by weight of resin. This high binder content is
problematic for the compounder of electrode materials who
wishes to use "universal" masterbatches in predefined
compositions without generating formulation constraints,
15 in particular without limiting the choice of the binder
used in these compositions.
This is why it would be advantageous for the
compounder to have available ready-to-use masterbatches
20 that can be used directly in a wide variety of
formulations for the manufacture of electrodes
(varnishes, inks, films, etc.) with a view to increasing
their electrical conductivity.
25 The Applicant has discovered that this requirement
could be met by preparing a masterbatch of carbon
nanotubes in agglomerated solid form containing a binder
content of the same order of magnitude as that of the
CNTs. The Applicant has also developed a process for
30 manufacturing this masterbatch, which allows an efficient
and homogeneous dispersion of the carbon nanotubes within
the masterbatch and around the electrode active material.
Finally, it has become apparent to the Applicant that
5
this masterbatch could be used for integrating carbon
nanotubes into other liquid formulations.
Document EP 2 081 244 describes a composition based
5 on carbon nanotubes, a solvent and a binder, but which is
not in an agglomerated solid form since it is intended to
be sprayed over a layer of electrode active material, and
not to be used as a masterbatch to be diluted in an
electrode composition.
10
It has furthermore become apparent to the Applicant
that this invention could also be applied to carbon-based
conductive fillers other than nanotubes and in particular
to carbon nanofibers and to carbon black, which are also
15 capable of posing safety problems owing to their
pulverulent nature and their ability to generate fines in
the production plants.
Carbon nanofibers are, like carbon nanotubes,
20 nanofilaments produced by chemical vapor deposition (or
CVD) starting from a carbon-based source which is
decomposed over a catalyst comprising a transition metal
(Fe, Ni, Co, Cu), in the presence of hydrogen, at
temperatures of 500 to 1200°C. However, these two carbon-
25 based fillers differ due to their structure (I. MARTINGULLON
et al., Carbon, 44 (2006), 1572-1580).
Specifically, the carbon nanotubes consist of one or more
sheets of graphene rolled up concentrically about the
axis of the fiber to form a cylinder having a diameter of
30 10 to 100 nm. Conversely, carbon nanofibers are made up
of relatively organized graphitic regions (or
turbostratic stacks), the planes of which are inclined at
various angles to the axis of the fiber. These stacks may
take the form of platelets, herringbones or stacked cups
in order to form structures that have a diameter ranging
generally from 100 nm to 500 nm or even more.
Furthermore, carbon black is a colloidal carbon-based
5 material, manufactured industrially by incomplete
combustion of heavy petroleum products, which is in the
form of spheres of carbon and aggregates of these
spheres, the dimensions of which are generally between 10
and 1000 nm.
10
Japanese patent document JP 10 255844 describes the
manufacture of a battery, the positive electrode of which
is produced by means of a masterbatch containing a
conductive material chosen from furnace black, acetylene
15 black and graphite.
Document FR 1 307 346 describes the preparation of
masterbatches containing rubber, carbon black and
optionally a plasticizer or an extender oil. This
20 masterbatch is in liquid form and contains only a small
content of carbon black relative to the total weight of
the masterbatch. It is only used after the solvent has
been evaporated.
25 The present invention consequently relates,
according to a first aspect, to a masterbatch in
agglomerated solid form comprising:
30
a) carbon nanofibers and/or nanotubes and/or
carbon black, the content of which is between
15 wt% and 40 wt%, preferably between 20 wt%
and 35 wt%, relative to the total weight of the
masterbatch;
b) at least one solvent;
c) at least one polymer binder, which represents
from 1 wt% to 40 wt%, preferably from 2 wt% to
30 wt% relative to the total weight of the
masterbatch,
5
In the remainder of this description, for the sake
of simplicity, the expression "carbon-based conductive
filler" denotes a filler comprising at least one element
from the group formed of carbon nanotubes and nanofibers
10 and carbon black, or a mixture of these in any
proportions.
The binder/carbon-based conductive filler weight
ratio is preferably less than 2.
15
The carbon nanotubes that are incorporated into the
composition of the masterbatch according to the invention
may k of single-walled, double-walled or multiwalled
type. The double-walled nanotubes may especially be
20 prepared as described by FLAHAUT et al. in Chem. Com.
(2003), 1442. The multiwalled nanotubes may, for their
part, be prepared as described in document WO 03/02456.
Nanotubes customarily have an average diameter
25 ranging from 0.1 to 100 nm, preferably from 0.4 to 50 nm
and, better still, from 1 to 30 nm, or even from 10 to 15
nm, and advantageously a length from 0.1 to 10 pm. Their
length/diameter ratio is preferably greater than 10 and
usually greater than 100. Their specific surface area is
30 for example between 100 and 300 m2/g, advantageously
between 200 and 300 m2/g, and their bulk density may
especially be between 0.05 and 0.5 g/cm3 and more
preferably between 0.1 and 0.2 g/cm3. The multiwalled
nanotubes may for example comprise from 5 to 15 sheets
(or walls) and more preferably from 7 to 10 sheets. These
nanotubes may or may not be treated.
5 An example of raw carbon nanotubes is in particular
commercially available from the company Arkema under the
trade name Graphistrength® C100.
These nanotubes may be purified and/or treated (for
10 example oxidized) and/or milled and/or functionalized
before they are used in the process according to the
invention.
The milling of the nanotubes may especially be
15 carried out cold or hot using known processing techniques
in equipment such as ball mills, hammer mills, grinding
mills, knife or blade mills, gas jet mills or any other
milling system that can reduce the size of the entangled
network of nanotubes. It is preferable for this milling
20 step to be carried out using a gas jet milling technique,
in particular in an air jet mill.
The raw or milled nanotubes may be purified by
washing with a solution of sulfuric acid, so as to strip
25 them of any residual metallic or mineral impurities, such
as iron for example, resulting from their preparation
process. The weight ratio of nanotubes to sulfuric acid
may especially be between 1/2 and 1/3. The purifying
operation may furthermore be carried out at a temperature
30 ranging from 90 to 120°C, for example for a time of 5 to
10 hours. This operation may advantageously be followed
by steps in which the purified nanotubes are rinsed with
water and dried. Another way of purifying the nanotubes
consists in subjecting them to a heat treatment at high
temperature, typically above 1000°C.
Advantageously, the oxidation of the nanotubes is
5 carried out by bringing them into contact with a sodium
hypochlorite solution containing 0.5 to 15% NaOCl by
weight and preferably 1 to 10% NaOCl by weight, for
example in a` nanotube/sodium hypochlorite weight ratio
ranging from 1/0.1 to 1/1. Advantageously, the oxidation
10 is carried out at a temperature below 60°C and preferably
at room temperature, for a time ranging from a few
minutes to 24 hours. This oxidation operation may
advantageously be followed by steps in which the oxidized
nanotubes are filtered and/or suction-filtered, washed
15 and dried.
The nanotubes may be functionalized by grafting
reactive units such as vinyl monomers to the surface of
the nanotubes. The constituent material of the nanotubes
20 is used as a radical polymerization initiator after
having been subjected to a heat treatment at more than
900°C, in an anhydrous, oxygen-free medium, which is
intended to remove the oxygenated groups from, its
surface. It is thus possible to polymerize methyl
25 methacrylate or hydroxyethyl methacrylate at the surface
of carbon nanotubes with a view to facilitating, in
particular, their dispersion in PVDF or polyamides.
Use is preferably made, in the present invention, of
30 raw, optionally milled, nanotubes, that is to say of
nanotubes that are neither oxidized nor purified nor
functionalized and that have not undergone any other
chemical and/or heat treatment.
10
Furthermore, it is preferred to use carbon
nanofibers having a diameter of 100 to 200 nm, for
example of around 150 nm (VGCF® from SHOWA DENKO), and
5 advantageously a length of 100 to 200 pm.
The polymer binder used in the present invention is
advantageously chosen from the group consisting of
polysaccharides, modified polysaccharides, polyethers,
10 polyesters, acrylic polymers, polycarbonates, polyimines,
polyamides, polyacrylamides, polyurethanes, polyopoxides,
polyphosphazenes, polysulfones, halogenated polymers,
natural rubbers, functionalized or unfunctionalized
elastomers, especially elastomers based on styrene,
15 butadiene and/or isoprene, and mixtures thereof. These
polymer binders may be used in solid form or in the form
of a liquid solution or dispersion (latex type) or else
in the form of a supercritical solution. It is preferred
to use a polymer binder in the form of a solution.
20
Preferably, for a use in the manufacture of an
electrode, the polymer binder is chosen from the group
consisting of halogenated polymers and more preferably
still from fluoropolymers defined, in particular, in the
25 following manner:
(i) those comprising at least 50 mo1% of at least
one monomer of formula (I):
CFX1=CX2X3 ( I )
where X1, X2 and X3 independently denote a hydrogen
30 atom or halogen atom (in particular a fluorine or
chlorine atom), such as polyvinylidene fluoride (PVDF),
preferably in a form, polytrifluoroethylene (PVF3),
polytetrafluoroethylene (PTFE), copolymers of vinylidene
11
fluoride with either hexafluoropropylene (HFP), or
trifluoroethvlene (VF3), or tetrafluoroethylene (TFE), or
chlorotrifluoroethylene (CTFE), fluoroethylene/propylene
(FEP) copolymers, copolymers of ethylene with either
5 fluoroethylene/propylene (FEP), or tetrafluoroethylene
(TFE), or chlorotrifluoroethylene (CTFE);
(ii) those comprising at least 50 mol% of at least
one monomer of formula (II)
R-O-CH-CH2 (II)
10 where R denotes a perhalogenated (in particular
perfluorinated) alkyl radical, such as perfluoropropyl
vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE) and
copolymers of ethylene with perfluoromethyl vinyl ether
(PMVE)a
15
When it is intended to be integrated into
formulations in an aqueous medium, the masterbatch
according to the invention advantageously contains, as
binder, at least one modified polysaccharide such as a
20 modified cellulose, in particular carboxymethyl
cellulose. This may be in the form of an aqueous solution
or in solid form or else in the form of a liquid
dispersion.
25 The solvent used in the present invention may be an
organic solvent or water or mixtures thereof in any
proportions. Among the organic solvents mention may be
made of N-methyl pyrrolidone (NMP), dimethyl sulfoxide
(DMSO), dimethylformamide (DMF), ketones, acetates,
30 furans, alkyl carbonates, alcohols and mixtures thereof.
NMP', DMSO and DMF are preferred for use in the present
invention.
12
The amount of solvent present in the masterbatch
ranges from 20 to 84 wt%, more preferably from 50 to 75
wt% and, better still, from 60 to 75 wt% relative to the
total weight of the masterbatch, as long as all of the
5 constituents of the masterbatch represent 100%.
The masterbatch according to the invention thus
advantageously contains: from 20 to 30 wt% of carbon
nanotubes, from 2 to 5 wt% of PVDF resin and from 65 to
10 75 wt% of NMP. One example of such a masterbatch is that
containing: 25 wt % of CNT, 4 wt % of PVDF and 71 wt % of
NMP, available in the form of granules, which is
especially sold by the company Arkema under the trade
name CM19-25.
15
20
According to a second aspect, the invention relates
to a process for preparing said masterbatch comprising:
(i) dissolving a powder of the polymer binder in
the solvent to form a solution;
(ii) mixing said solution with carbon nanofibers
and/or nanotubes and/or carbon black, in a compounding
device;
(iii) kneading said mixture.
25 The masterbatch is thus prepared in three successive
steps.
One embodiment of step i) consists in dissolving the
powder of the polymer binder in the solvent by stirring
30 the solution thus formed over a time period of between
30 minutes and 2 hours at a temperature between 0°C and
100°C, preferably between 20°C and 60°C.
13
One embodiment of step ii) consists in introducing,
into a kneader or compounding device, the carbon-based
conductive fillers and the polymer solution resulting
from step i) at an introduction temperature of between
5 10°C and 90°C.
The carbon-based conductive fillers and the polymer
solution may be mixed before being introduced into the
kneader. In this case, the carbon-based conductive
10 fillers and the polymer solution are introduced
simultaneously into the same feed zone of the kneader, in
particular BUSS® type kneader. In the case where the
carbon-based conductive fillers are mixed with the
polymer solution after being introduced into the kneader,
15 the carbon-based conductive fillers and the polymer
solution are introduced successively into the same feed
zone of the kneader or else into two separate feed zones.
One embodiment of step iii) consists in kneading the
20 mixture via a compounding route, advantageously using a
co-rotating or counter-rotating twin-screw extruder or
using a co-kneader (in particular of BUSS® type)
comprising a rotor provided with flights designed to
cooperate with teeth mounted on a stator. The kneading
25 may be carried out at a temperature preferably between
200C and 90°C.
;Compounding devices are well known to those skilled
in the art and generally include feed means, especially
30 at least one hopper for pulverulent materials and/or at
least one injection pump for liquid materials; high-shear
kneading means, for example a co-rotating or counterrotating
twin-screw extruder or a co-kneader, usually
14
comprising a feed screw placed in a heated barrel (or
tube); an output head, which gives the extrudate its
shape; and means for cooling the extrudate, either by air
cooling or by circulation of water. The extrudate is
5 generally in the form of rods continuously exiting the
device and able to be cut or formed into granules.
However, other forms may be obtained by fitting a die of
desired shape on the output die.
10 Examples of co-kneaders that can be used according
to the invention are BUSS® MDK 46 co-kneaders and those
of the BUSS® MKS or MX series, sold by the company BUSS
AG, which all consist of a screw shaft provided with
flights, placed in a heated barrel optionally made up of
15 several parts, and the internal wall of which is provided
with kneading teeth designed to cooperate with the
flights so as to shear the kneaded material. The shaft is
rotated, and given an oscillatory movement in the axial
direction, by a motor. These co-kneaders may be equipped,
20 with a granulation system, for example fitted at the exit
orifice of said co-kneaders, which may consist of an
extrusion screw.
The co-kneaders that can be used according to the
25 invention preferably have an L/D screw ratio ranging from
7 to 22, for example from 10 to 20, whereas co-rotating
extruders advantageously have an L/D ratio ranging from
15 to, 56, for example from 20 to 50.
30 The carbon-based conductive fillers are thus
dispersed efficiently and homogeneously. In addition, it
is possible to modify the surface of the carbon-based
conductive fillers, in particular of the CNTs, during the
15
compounding step with additives that promote the
integration of these fillers into the liquid
formulations.;
5 The masterbatch thus obtained may then optionally be
dried, by any known process (ventilated or vacuum oven,
infrared, induction, microwave, etc.), for the purpose,
in particular, of removing all or part of the solvent and
of thus obtaining a masterbatch that is more concentrated
10 in carbon-based conductive fillers, containing for
example from 20 to 98 wt%'. of these fillers, preferably
from 25 to 60%, or even from 40 to 60% in the case of an
aqueous solvent or from 60 to, 95% in the case of an
organic solvent, and advantageously having a
15 binder/carbon-based filler weight ratio of less than 2,
or even of less than 1.6. This embodiment is more
particularly suitable for the masterbatches intended to
be introduced into liquid formulations.
20 Therefore, the present invention also relates to a
concentrated masterbatch, characterized in that it is
obtained by removing all or part of the solvent from the
masterbatch described previously.
25 As a variant, the masterbatch may be used as is, in
the form of granules or other agglomerated solid forms,
the conditioning of which facilitates the storage
thereof.
30 The masterbatch obtained at the end of this process
and that is optionally concentrated may be used for the
manufacture of electrodes for Li-ion batteries or
supercapacitors, for the manufacture of paints, inks,
16
adhesives, primary coatings, ceramic composites and
concretes, thermosetting composites, and compositions for
sizing fibers or for treating textiles, in particular.
5 Therefore, another subject of the present invention
is the use of the (optionally concentrated) masterbatch
as described previously for preparing liquid
formulations.'
10 According to one particular aspect, the invention
also relates to a process. for preparing an electrode,
comprising the following steps:
a) the preparation of a mixture by dispersion in a
dispersion solvent of the (optionally
15 concentrated) masterbatch described previously,
containing at least a first binder and
optionally at least a first solvent;
b) the preparation of a solution by dissolving at
least a second polymer binder in at least a
20 second solvent;
c) the addition of an electrode active material to
said solution;
d) the mixing of the products resulting from steps
a) and c);
25 e) the deposition of the composition thus obtained
on a substrate in order to form a film;
f) the drying of said film.
It is clearly understood that the above process may
30 comprise other preliminary, intermediate or subsequent
steps, as long as they do not adversely affect the
production of the desired electrode film. Thus, an
intermediate step may in particular be provided between
17
steps d) and e), comprising the addition of a portion of
the second binder, for example in solution in the first
solvent, by means, in particular, of a flocculator type
stirrer.
5
The expression "first binder" is understood to mean
the binder used during the preparation of the masterbatch
described previously. The expression "first solvent" is
understood to mean the solvent used during the
10 preparation of the masterbatch described previously.
During step (a), the masterbatch is dispersed in a
dispersion solvent which may correspond to the first
solvent or be different therefrom. The fact that the
15 masterbatch is in agglomerated solid form comprising a
high solvent content makes it possible to facilitate the
dispersion of the carbon-based conductive fillers, in
particular CNTs, in the medium. Similarly, when the
masterbatch is in dried form, the high porosity of the
20 "dry" solid makes it possible to facilitate the wetting
of the solid and therefore the dispersion of the carbonbased
conductive fillers in the medium.
During this step (a), the masterbatch containing the
25 carbon-based conductive fillers is dispersed using a
suitable mixer which may be either a propeller mixer,
with a marine propeller type spindle, or a mixerdisperser
of "flocculator" type or of "rotor-stator"
type.
30
The flocculator system corresponds to a stirrer
having a spindle that consists of a disk provided with
18
prongs perpendicular to the plane of the disk, which
makes it possible to obtain a high local shear.
The rotor-stator system generally comprises a rotor
5 driven by a motor and provided with fluid guiding systems
perpendicular to the rotor axis, such as paddles or
blades placed approximately radially, or a flat disk
provided with peripheral teeth, said rotor being
optionally provided with a ring gear, and a stator
10 arranged concentrically with respect to the rotor, and at
a short distance to the outside of the latter, said
stator being equipped, over at least a portion of its
circumference, with openings provided for example in a
grid or defining between them one or more rows of teeth,
15 which are suitable for passage of the fluid drawn into
the rotor and ejected by the guiding systems towards said
openings. One or more of the aforementioned teeth may be
provided with sharp edges. The fluid is thus subjected to
a high shear, both in the gap between the rotor and the
20 stator and through the openings provided in the stator.
One such rotor-stator system is in particular' sold
by the company SILVERSON under the trade name Silverson"
L4RT. Another type of rotor-stator system is sold by the
25 company IKA-WERKE under the trade name Ultra-Turrax©. Yet
other rotor-stator systems consist of colloid mills, and
high-shearmixers of the rotor-stator type, such as the
machines sold by the company IKA-WERKE or by the company
ADMIX.
30 According to the invention, the speed of the rotor
is preferably set at at least 1000 rpm and preferably at
least 3000 rpm or even at least 5000 rpm. Furthermore,
the width of the gap between the rotor and the stator is
19
preferably less than 1 mm, preferably less than 200 pm,
more preferably less than 100 pm and better still less
than 50 pm or even less than 40 pm. Moreover, the rotorstator
system used according to the invention
5 advantageously applies a shear rate ranging from 1000 to
109 s-1.
Step (b)' consists in dissolving a polymer binder,
which may correspond to the first binder used in the
10 preparation of the masterbatch or be different therefrom,
in a
used
solvent which may correspond to the first
in the
dispersion
preparation of the
solvent
masterbatch or to the
solvent or be
step, stirrers
different therefrom. During this
of "flocculator" type are preferred. It is
15 followed by the addition of an electrode active material,
which may be dispersed, while being stirred, in the form
of powder, in the mixture resulting from step (b).
The electrode active material introduced during step
20 (c) is chosen from the group consisting of:
i) transition metal oxides of spinel structure of
LiM2O4 type, where M represents a metal atom containing
at least one of the metal atoms chosen from the group
formed by Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti,
25 Al,, Si, B and Mo, said oxides preferably containing at
least one Mn and/or Ni atom;
ii) transition metal oxides of lamellar structure
of LiMO2 type, where M represents a metal atom containing
at least one of the metal atoms chosen from the group
30 formed by Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Be, Ti,
Al,' Si, B and Mo, said oxides preferably containing at
least one of the atoms chosen from the group formed by
Mn, Co and Ni;
20
iii) oxides having polyanionic frameworks of
LiMy(XO,)n type where:
o M represents a metal atom containing
at least one of the metal atoms chosen from the
5 group formed by Mn, Fe, Co, Ni, Cu, Mg, 7n, V,
Ca, Sr, Ba, Ti, Al, Si, B and Mo, and
o X represents one of the atoms chosen
from the group formed by P, Si, Ge, S and As,
preferably LiFePO4,
10 iv) vanadium-based oxides,
v) graphite,
vi) titanates.
The 'electrode active materials i) to iv) are more
suitable for the preparation of cathodes, whereas the
15 electrode active materials v) and vi) are more suitable for
the preparation of anodes.
The product resulting from step (c) is mixed with
that resulting from step (a) (step (d)), optionally after
20 mixing using the flocculator. The mixing may be carried
out using any mechanical means as long as they make it
possible to obtain a homogeneous dispersion.` The
expression "homogeneous dispersion" is preferably
understood, within the meaning of the present invention,
25 to--mean that the mixture of the dispersion resulting from
step (a) with the dispersion resulting from step (c),
observed using an electronic microscope after 30 minutes
of treatment, or even after 20 minutes of treatment, does
not reveal (in the case of CNTs) aggregates having a size
30 greater than 50 pm, preferably greater than 30 pm, or
even greater than 20 pm, measured along their longer
dimension.
21
It is preferred according to the invention that the
mixing of step d) is carried out using a mixer of
"flocculator" type or using "rotor-stator" systems of
Silverson® type and/or using ball mills and/or planetary
5 mills.
The proportions of the various compounds used in the
above process are adjusted so that the film obtained
advantageously contains from 1 to 2 wt% of carbon-based
10 conductive fillers.
By virtue of the process according to the invention,
it is especially possible to distribute the carbon
nanofibers and nanotubes so that they form a mesh around
15 the particles of active material and thus play both a
conductive additive role and also a mechanical support
role, important for accommodating the volume changes
during charge-discharge steps. On the one hand, they
ensure the distribution of electrons to the particles of
20 active material and, on the other hand, owing to their
length and their flexibility, they form electrical
bridges between the particles of active material which
shift following their change in volume. When they are
used alone, standard conductive additives (SP carbon,
25 acetylene black and graphite), with their relatively low
aspect ratio, are less effective for ensuring the
maintenance, during the cycling, of the transport of
electrons from the current collector. Indeed, with
conductive additives of this type, the electrical
30 pathways are formed by the juxtaposition of grains and
the contacts between them are easily broken following the
volume expansion of the particles of active material.
22
During step (e) , the film obtained from the
suspension resulting from step (d) may be deposited on a
substrate by any conventional means, for example by
extrusion, by tape casting, by coating or by spray drying
5 followed by a drying step (step (f)).
The substrate may in particular be a current
collector. An electrode is thus obtained.
10 Another subject of the invention consequently
consists of a composite electrode, anode or cathode (in
particular a cathode), capable of being obtained as
described' above, from the masterbatch according to the
invention.
15
According to another aspect, the invention also
relates to a process for preparing a composite active
material for an electrode, comprising the following
steps:
20 a) the provision of an electrode active material in
the form of an aqueous solution or dispersion;
b) the addition and mixing of the (optionally
concentrated) masterbatch described previously, said
masterbatch containing a water-soluble or water-
25 dispersible binder, to the aqueous solution or dispersion
obtained in step (a);
c) the suction-filtering and drying of the mixture
obtained in step (b).
It is clearly understood that the above process may
30 comprise other preliminary, intermediate or subsequent
steps, as long as they do not adversely affect the
production of the desired composite material for an
electrode. Thus, one or more intermediate step(s) may in
23
particular be provided between steps (a) and (b) and/or
between steps (b) and (c), comprising washing, filtration
or any other step of purifying the mixture.
One electrode active material defined above is, for
5 example, that described in patent document FR 2 865 576.
Such a process is characterized by the reaction, under a
controlled atmosphere, of a precursor of the electrode
active material, for example Li2HPO4, with an iron (III)
complex. The electrode active material formed is then in
10 aqueous solution.
According to one embodiment, the electrode active
material then obtained may be used directly in step (a)
of the above process.
15
According to another embodiment, this electrode
active material may be recovered by filtration or
sedimentation, and optionally washed then dried. Step (a)
of the above process may then consist of the redispersion
20 or resolubilization of this electrode active material.
The redispersion or resolubilization may be carried out
using a suitable mixer which may be either a propeller
mixer, with a marine propeller type spindle, combined
with scrapers along the walls of the container, or a
25 mixer-disperser of "flocculator" type or of "rotorstator"
type.
Preferably, the electrode active material in the
form of an aqueous solution or dispersion is provided in
30 step (a) in a filter, advantageously equipped with a
stirrer.
24
During step (b), the masterbatch containing the
carbon-based conductive fillers is added and mixed with
the aqueous solution or dispersion of electrode active
material using a suitable mixer which may be either a
5 propeller mixer, with a marine propeller type spindle,
combined with scrapers along the walls of the container,
or a mixer-disperser of "flocculator" type or of "rotorstator"
type. Preferably, it is a "flocculator" type
mixer, as described above. This method of mixing makes it
10 possible, unlike milling processes, not to break the
carbon-based conductive fillers too much, in particular
when these are carbon nanotubes. The binder contained in
the masterbatch is water-soluble or water-dispersible.
Advantageously, said binder comprises at least one
15 modified polysaccharide such as a modified cellulose, in
particular carboxymethyl cellulose.
The composite active material for an electrode is
recovered after having been suction-filtered and dried
20 during step (c). The drying consists in removing all or
part of the water, preferably all of the water, so as to
obtain an anhydrous material. The drying is preferably
carried out according to the conventional heating
techniques or by spray drying (atomization).
25
This process for preparing a composite active
material for an electrode has the advantage of allowing
the addition of the masterbatch comprising the carbonbased
conductive fillers during the preparation of the
30 electrode active material, which is in an aqueous medium
during its synthesis, and therefore of simplifying the
process.
25
As a variant, step (b) of the process for preparing
a composite active material for an electrode described
above may be replaced by a step (b') consisting:
- in preparing a mixture by dispersion in water of
5 the (optionally concentrated) masterbatch described
previously, said masterbatch containing a water-soluble
or water-dispersible binder, and
in adding and mixing said solubilized or dispersed
masterbatch to the aqueous solution or dispersion of the
10 electrode active material obtained in step (a).
The proportions of the various compounds used in the
various variants of the above, process are adjusted so
that the composite active material for an electrode
15 obtained advantageously contains from 1 to 5 wt% of
carbon-based conductive fillers.
The composite active material for an electrode
obtained, comprising an electrode active material and a
20 carbon-based conductive filler, has^a morphology suitable
for the manufacture of electrodes. Moreover, since the
material has not been subjected to mechanical milling,
the particle size of the active material has not been
modified. In addition, the electrode manufacturing
25 process is simplified.
Another subject of the invention consequently
consists of a composite active material for an electrode,
anode or cathode (in particular a cathode), capahle of
30 being obtained as described above, from the masterbatch
according to the invention.
26
5
Another subject of the invention is the use of the
(optionally concentrated) masterbatch as described
previously for the preparation of liquid formulations
containing carbon-based conductive fillers.
The invention will now be illustrated by the
following examples, the purpose of which is not to limit
the scope of the invention, defined by the appended
claims. In these examples, reference is made to the
10 appended figures, in which:
- figures 1A and 1B illustrate, using SEM and at two
different working distances, the dispersion of the CNTs
within the masterbatch obtained in example 1;
- figures 2A and 2B illustrate, using SEM and at two
15 different working distances, the dispersion of the CNTs
within the masterbatch obtained in example 2;
- figure 3 illustrates the discharge capacity of a
battery containing a cathode obtained from the
masterbatch according to the invention, as a function of
20 the number of cycles; and
- figure 4 illustrates the electrochemical
performances of an electrode manufactured from the
25
masterbatch according to the invention.
EXAMPLES
EE2m le 1: Preparation of a CNT/P F/ P masterbatch
A 5 wt% solution of PVDF (Kynar® HSV 900 from
30 ARKEMA) was produced previously by dissolving the powder
of the polymer in N-methyl pyrrolidone (NMP); the
solution was stirred at 50°C for 60 min.
27
The CNTs (Graphistrength® C100 from ARKEMA) were
introduced into the first feed hopper of a BUSS® MDK 46
(L/D = 11) co-kneader, equipped with a discharge
extrusion screw and a granulation device. The 5% solution
5 of PVDF (Kynar® HSV 900) in N-methyl pyrrolidone (NMP)
was injected in liquid form at 80°C into the first zone
of the co-kneader. The temperature settings and the
throughput within the co-kneader were the following: zone
1: 80°C, zone 2: 80°C, screw: 60°C, throughput: 15 kg/h.
10
At the outlet of the die, the masterbatch was cut
into granules under dry conditions. The granules were
packaged in an airtight container to avoid loss of NMP
during storage. The composition of the final masterbatch
15 was the following: 30 wt% of carbon nanotubes, 3.5 wt% of
PVDF resin and 66.5 wt% of NMP.
Observations of the dried masterbatch using a
scanning electron microscope (SEM) showed that the carbon
20 nanotubes were well dispersed (figures 1A and 1B).
Eacample 2: Use of the CNT/P F'/ P masterbatch for
manufacturing an electrode
25 Step a) 20 g of masterbatch granules from example 1
were wetted with 160 g of NMP solvent. After 2 h of
static impregnation under ambient conditions, the
masterbatch granules were dispersed in the solvent using
a Silversori L4RT mixer at 6000 rpm for 15 minutes. A
30 significant temperature rise was observed during the
dispersion operation: the mixture containing the CNTs
reached a temperature of 67°C. The solution obtained was
denoted by "CNT premix".
28
Step b) 14.3 g of Kynar® HSV 900 were dissolved in
276 g of NMP solvent using a flocculator-type agitator
for 4 hours.
5
Step c) 279 g of LiFePO4/C (LFP) (grade P1 from
Phostech) powder were dispersed in the Kynar solution;
during this step, the LiFePO4 powder was added gradually
while stirring (600 rpm) The suspension obtained was
10 denoted by "LFP premix".
Step d) In order to obtain a good dispersion of the
CNTs around the active LFP material, the two CNT and LFP
premixes respectively obtained during steps a) and c)
15 were mixed for 10 minutes using a flocculator agitator at
600 rpm then using a Silverson® L4RT mixer for 15 minutes
at 6000 rpm and finally using a Retsch Minicer® ball mill
for 30 minutes at 2000 rpm using 0.7 to 0.9 mm ceramic
balls. The composition of the ink, as dry matter, was the
20 following: 2% of CNTs; 5% of Kynar® HSV 900 and 93% of
LiFePO4/C with a solids content of 40% in the NMP
solvent.
Step e) Using a Sheen film applicator and an
25 adjustable BYK-Gardner® applicator, un film with a
thickness of 100 pm was produced on a 25 pm aluminum
foil.
Step f) The film produced during step e) was dried
30 at 70°C for 4 h in a ventilated oven then compressed
under 200 bar.
29
SEM observations showed that the CNTs are well
dispersed around the micron-sized particles of LiFePO4/C
(figures 2A and 2B).
5 Example 3: Evaluation of the electrochemical
performances of an electrode according to the invention
The CEA/LITEN laboratories in Grenoble evaluated the
electrochemical performances of the positive electrode
10 (cathode) from example 2 by combining it with a graphite
anode.
The formulation of the cathode containing 2 wt% of
CNTs and 5 wt% of PVDF binder was compared to a standard
15 formulation containing, as conductive additive, 2.5 wt%
of Super P carbon black from Timcal (CB) and 2.5 wt% of
VGCF carbon fibers from Showa Denko (CF) with 5 wt% of
PVDF binder. This standard formulation is obtained by
mixing of powders, without going through the preparation,
20 then the dilution, of a masterbatch according to the
invention.
On an Li-ion battery having a capacity of 500:mAh,
the results obtained under various charge/discharge
25 regimes 1C, 2C, 3C, 5C and 10C (cf. figure 4) show that
greater capacities are obtained with the battery
containing 2 wt% of CNTs in the cathode compared to the
standard battery (CB+CF), even more so when the
charge/discharge regime is faster (10C).
30 This example therefore illustrates the better
electrochemical performances of the electrode obtained
from a masterbatch according to the invention.
30
Example 4: Preparation of a CNT/P F/ P masterbatch
A 5 wt% solution of PVDF (Kynar_o HSV 900 from
ARKEMA) was produced previously by dissolving the powder
5 of the polymer in N-methyl pyrrolidone (NMP); the
solution was stirred at 50°C for 60 min.
The CNTs (Graphistrength® C100 from ARKEMA) were
introduced into the first feed hopper of a BUSS MDK 46
10 (L/D = 11) co-kneader, equipped with a discharge
extrusion screw and a granulation device. The 5% solution
of PVDF (Kynar® HSV 900) in N-methyl pyrrolidone (NMP)
was injected in liquid form at80°C into the first zone
of the co-kneader. The temperature settings and the
15 throughput within the co-kneader were the following: zone
1: 80°C, zone 2: 80°C, screw: 60°C, throughput: 15 kg/h.
At the outlet of the die, the masterbatch was cut
into granules under dry conditions. The granules were
20 packaged in an airtight container to avoid loss of NMP
during storage. The composition of the final masterbatch
was the following: 25 wt% of carbon nanotubes, 4 wto of
PVDF resin and 71 wt% of NMP.
25 Observations of the dried masterbatch using a
scanning electron microscope (SEM) showed that the carbon
nanotubes were well dispersed.
30 Ex plc 5: Study of the stability of the batteries
obtained from the masterbatch according to the invention
31
The stability of the batteries was studied using, as
cathode conductive additive, "raw" CNTs that contain
between 2 and 3% of Fe. In order to do this, aging tests
at 55°C were carried out by the CEA/LITEN laboratories on
5 25 mAh "Pouch cell" batteries comprising a cathode with
93 wt% of the LiNil/3Col/3All/302(NCA) active material
with no iron and 2 wt % of "raw" CNTs and 5 wt % of PVDF
binder combined with a graphite anode. After 100 cycles
at 55°C with a charge/discharge rate of C/5, the
10 discharge capacity drops by 20% but ICP chemical analysis
of the anode does not show an increase in the iron
content which remains equal to 3 ppm. There is not
therefore any migration of the iron contained in the CNTs
of the cathode to the anode (cf. figure 3).
15
Ezeaxnle 6: Preparation of a CNT/CMC/water
ma s terbatch
A 10 wt% solution of low-weight carboxymethyl
20 cellulose (CMC) (Finnfix® 2 grade) was produced
previously by dissolving the powder of the CMC polymer in
demineralized water. The solution was stirred at ambient
temperature for 60 min.
25 The CNTs (Graphistrengtho C100 from ARKEMA) were
introduced into the first feed hopper of a BUSSOO MDK 46
(L/D = 11) co-kneader, equipped with a discharge
extrusion screw and a granulation device. The 10%
solution of CMC in demineralized water was injected in
30 liquid form at 30°C into the first zone of the cokneader.
The balance of the CMC (22 wt%) was introduced
in powder form into the first feed hopper. The
temperature settings and the throughput within the co32
kneader were the following: zone 1: 30°C, zone 2: 30°C,
screw: 30°C, throughput: 15 kg/h.
At the outlet of the die, the masterbatch was cut
5 into granules under dry conditions. The granules were
dried in an oven at 80°C for 6 hours to remove the water.
The composition of the final masterbatch was the
following: 40wto of carbon nanotubes, 60 wt% of CMC.
10 The granules were packaged in an airtight container
to avoid uptake of water during storage.
Exam le 7: Preparation of a CNT/CMC/water
masterbat.ch
15
A 10 wt% solution of low-weight carboxymethyl
cellulose (CMC) (Finnfix® 2 grade) was produced
previously by dissolving the powder of the CMC polymer in
demineralized water. The solution was stirred at ambient
20 temperature for 60 min.
20 kg of CNTs (Graphistrength® C100 from ARKEMA)
were introduced into the first feed hopper of a B'USSOO
MDK 46 (L/D = 11) co-kneader, equipped with a discharge
25 extrusion screw and a granulation device. 61.1 kg of 10%
solution of CMC in demineralized water were injected in
liquid form at 30°C into the first zone of the cokneader.
The balance of the CMC (18.9 kg) was introduced
in the form of powder into the first feed hopper. The
30 temperature settings and the throughput within the cokneader
were the following: zone 1: 30°C, zone 2: 30°C,
screw: 30°C, throughput: 15 kg/h.
33
The composition of the mixture exiting the die was
the following: 20% CNTs/25% CMC and 55% water.
At the outlet of the die, the masterbatch was cut
5 into granules under dry conditions. The granules were
dried in an oven at 80°C for 6 hours to remove the water.
The composition of the final masterbatch was the
following: 45 wt% of carbon nanotubes, 55 wt% of CMC.
10 The granules were packaged in an airtight container
to avoid uptake of water during storage.
EE mp9le 8: Dispersion of 'a CNT/CMC masterbatch in
water
15
The dried masterbatch obtained in example 7 is
introduced into hot water at 90°C with gentle stirring so
as to obtain a nanotube concentration of 2 wt%. The
stirring is continued for 1 hour, which results in a.
20 gradual cooling of the dispersion.
Under these conditions, an effective dispassion of
the nanotubes in water is obtained.
Such a dispersion may be used for example as an
25 aqueous formulation base for the manufacture of an
electrode or of paints.
Ens ple 9. Preparation of a masterbatch based on
carbon nanofibers
30
A 5 wt% solution of PVDF (Kynar® HSV 900 from
ARKEMA) was produced by dissolving the powder of the
34
polymer in N-methyl pyrrolidone (NMP); the solution was
stirred at 50°C for 60 min.
Carbon nanofibers (VGCF° from SHOWA DENKO) were
5 introduced into the first feed hopper of a BUSS® MDK 46
(L/D = 11) co-kneader, equipped with a discharge
extrusion screw and a granulation device. The 5% solution
of PVDF (Kynar° HSV 900) in N-methyl pyrrolidone (NMP)
was injected in liquid form at 80°C into the first zone
10 of the co-kneader. The temperature settings and the
throughput within the co-kneader were the following: zone
1: 80°C, zone 2: 80°C, screw: 60°C, throughput: 15 kg/h.
At the outlet of the die, the masterbatch was cut
15 into granules under dry conditions. The granules were
packaged in an airtight container to avoid loss of NMP
during storage. The composition of the final masterbatch
was the following: 25 wt% of nanofibers, 3.75 wt% of PVDF
resin and 71.25 wt% of NMP.
20
!xaanle 1®: Preparation of a masterbatch based on
carbon black
A 5 wt% solution of PVDF (Kynar® HSV 900 from
25 ARKEMA) was produced by dissolving the powder of the
polymer in N-methyl pyrrolidone (NMP) ; the solution was
stirred at 50°C for 60 min.
Carbon black (Super P® from TIMCAL) was introduced
30 into the first feed hopper of a BUSS® MDK 46 (L/D = 11)
co-kneader, equipped with a discharge extrusion screw and
a granulation device. The 5% solution of PVDF (Kynar® HSV
900) in N-methyl pyrrolidone (NMP) was injected in liquid
35
form at 80°C into the first zone of the co-kneader. The
temperature settings and the throughput within the cokneader
were the following: zone 1: 80°C, zone 2: 80°C,
screw: 60°C, throughput: 15 kg/h.
5
At the outlet of the die, the masterbatch was cut
into granules under dry conditions. The granules were
packaged in an airtight container to avoid loss of NMP
during storage. The composition of the final masterbatch
10 was the 'following: 25 wt % of carbon black, 3.75 wt % of
PVDF resin and 71.25 wt% of NMP.
Ex ple 11: use of the CNT/CHIC. masterbatch for
manufacturing a conductive material for electrodes
15
Preliminary step) The electrode active material
LiFePO4 was synthesized according to the procedure
described in the example 1 of patent FR 2 848 549. 5 g of
the iron (III) nitrilotriacetic complex were introduced
20 into an autoclave reactor in 800 ml of a 0.0256 mol/l
solution of lithium hydrogen phosphate, Li2HPO4. The
reaction was carried out at 200°C under an autogenous
pressure of 20 bar for 2 hours. The mixture was cooled
slowly, without stirring, via inertia of the reactor
25 (over around 12 hours). When the reactor had returned to
ambient temperature and to atmospheric pressure, the
autoclave, was opened and the powder recovered was
filtered over a Buchner flask. The cake obtained was
washed with deionized water, then suction-filtered.
30
Step a) The suction-filtered cake comprising the
electrode active material LiFePO4 preliminarily prepared
36
was put into suspension in 100 ml of water in the filter
using a flocculator-type agitator.
Step b) 134 mg of the CNT/CMC concentrated
masterbatch obtained according to example 7 (consisting
5 of 45 wt% of carbon nanotubes and of 55 wt% of CMC) were
dispersed in the suspension prepared in step a).
Step C) After suction-filtering the cake, the
LiFePO4/CNT composite active material is dried at 60°C
under vacuum.
10
An LiFePO4/CNT conductive material for an electrode
containing 3 wt% of CNTs was obtained. It was observed
that the CNTs were advantageously well distributed at the
surface of the LiFePO4 particles. CMC is compatible with
15 applications in the batteries.
37
CLAIMS
1. A masterbatch in agglomerated solid form
comprising:
5 a) carbon nanofibers and/or nanotubes and/or carbon
black, the content of which is between 15 wt% and 40 wt%,
preferably between 20 wt% and 35 wt%, relative to the
total weight of the masterbatch;
b) at least one solvent;
10 c) at least one polymer binder, which represents
from 1 wt% to 40 wt%, preferably from 2 wt % to 30 wt%
relative to the total weight of the masterbatch.
2. The masterbatch as claimed in claim 1,
15 characterized in that said solvent is an organic solvent,
water or mixtures thereof in any proportions.
3. The masterbatch as claimed in claim 2,
characterized in that said organic solvent is chosen from
20 N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO),
dimethylformamide (DMF), ketones, acetates, furans, alkyl
carbonates, alcohols and mixtures thereof.
4. The masterbatch as claimed in one of claims 1
25 to..3, characterized in that said polymer binder is chosen
from the group consisting of polysaccharides, modified
polysaccharides, polyethers, polyesters, acrylic
polymers, polycarbonates, polyimines, polyamides,
polyacrylamides, polyurethanes, polyepoxides,
30 polyphosphazenes, polysulfones, halogenated polymers,
natural rubbers, functionalized or unfunctionalized
elastomers, especially elastomers based on styrene,
butadiene and/or isoprene, and mixtures thereof.
38
5. The masterbatch as claimed in claim 4,
characterized in that the polymer binder is chosen from
the group consisting of halogenated polymers and
5 preferably from fluoropolymers.
6. The masterbatch as claimed in claim 5,
characterized in that the fluoropolymer binder is chosen
from:
10 (i) those comprising at least 50 moi% of at least
one monomer of formula (I):
CFX1=CX2X3 (I)
where X1, X2 and X3 independently denote a hydrogen
15 atom or halogen atom (in particular a fluorine or
chlorine atom), such as polyvinylidene fluoride (PVDF),
preferably in a form, polytrifluoroethylene (PVF3),
polytetrafluoroethylene (PTFE), copolymers of vinylidene
fluoride with either hexafluoropropylene (HFP), or
20 trifluoroethylene (VF3), or tetrafluoroethylene (TFE), or
chlorotrifluoroethylene (CTFE), fluoroethylene/propylene
(FEP) copolymers, copolymers of ethylene with either
fluoroethylene/propylene (FEP), or tetrafluoroethylene
(TFE), or chlorotrifluoroethylene (CTFE);
25 (ii) those comprising at least 50 mol% of at least
one monomer of formula (II):
R-O-CH-CH2 (II)
where R denotes a perhalogenated (in particular
perfluorinated) alkyl radical, such as perfluoropropyl
30 vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE) and
copolymers of ethylene with perfluoromethyl vinyl ether
(PMVE).
39
7. The masterbatch as claimed in claim 4,
characterized in that the polymer binder is chosen from
the group consisting of modified polysaccharides and more
preferably from modified celluloses such as carboxymethyl
5 cellulose.
8. The masterbatch as claimed in any one of claims 1
to 6, characterized in that it contains: from 20 to 30 wt%
of carbon nanotubes, from 2 to 5 wt% of PVDF resin and from
10 65 to 75 wt% of NMP.
9. The use of the masterbatch as claimed in one of
claims 1 to 8 for manufacturing an electrode.
15 10. A process for preparing a masterbatch as
claimed in one of claims 1 to 8 comprising:
(a) dissolving a powder of the polymer binder in the
solvent to form a solution;
(b) mixing said solution with the carbon nanofibers
20 and/or nanotubes and/or the carbon black, in a
compounding device;
(c) kneading said mixture.
11. The process as claimed in claim 10,
25 characterized in that the kneading is carried out via a
compounding route using a co-rotating or counter-rotating
twin-screw extruder or using a co-kneader.
12. A concentrated masterbatch, characterized in
30 that it is obtained by removing all or part of the
solvent from the masterbatch as claimed in any one of
claims 1 to 8.
40
13. The concentrated masterbatch as claimed in
claim 12, characterized in that it contains from 20 to
98%, preferably from 25 to 60%, or even from 40 to 60% in
the case of an aqueous solvent or from 60 to 95% in the
5 case of an organic solvent, by weight of carbon-based
fillers, and advantageously a binder/carbon-based filler
weight ratio of less than 2, or even of less than 1.6.
14. A process for preparing an electrode,
10 comprising the following steps:
a) the preparation of, a mixture by dispersion in a
dispersion solvent of the masterbatch as claimed in one
of claims' 1 to 8 or 12 to 13, or obtained according to
the process as claimed in either of claims 10 and 11,
15 containing at least a first binder and optionally at
least a first solvent;
b) the preparation of a solution by dissolving at
least a second polymer binder in at least a second
solvent;
20 c) the addition of an electrode active material to
said solution;
d) the mixing of the products resulting from 'steps
a) and c);
e) the deposition of the composition thus obtained
25 on.,a substrate in order to form a film;
f) the drying of said film.
15. An electrode capable of being obtained
according to the process as claimed in claim 14.
30
16. A process for preparing a composite active
material for an electrode, comprising the following
steps:
41
a) the provision of an electrode active material in
the form of, an aqueous solution or dispersion;
b) the addition and mixing of the masterbatch as
claimed in one of claims 1 to 8 or 12 to 13, or obtained
5 according to the process as claimed in either of claims
10 and 11, said masterbatch"containing a water-soluble or
water-dispersible binder, to the aqueous solution or
dispersion obtained in step (a);
c) the suction-filtering and drying of the mixture
10 obtained in step (b).
17. A composite active material for an electrode
capable of being obtained according to the process as
claimed in claim 16.
15
18. The use of the masterbatch as claimed in any
one of claims 1 to 8, 12 and 13 for the preparation of
liquid formulations containing carbon nanofibers and/or
nanotubes and/or carbon black.