Solvent-free compositions comprising carbon nanotubes

Abstract

The present invention relates to carbon nanotube compositions that can be implemented in solid form, i.e., in the absence of solvent. These compositions comprise at least one polymer and are readily dispersible in formulations for the manufacture of battery electrodes, and in particular Li-ion batteries, in liquid or solid processes. The invention also relates to the process for obtaining these powders, their use in the manufacture of battery electrodes, and the batteries comprising them.

Description

Title of the invention: Solvent-free compositions comprising carbon nanotubes FIELD OF THE INVENTION

[0001] The present invention relates to compositions comprising carbon nanotubes in powder form. These compositions in powder form comprise at least one polymer and are easily dispersible in solvent-based or non-solvent-based formulations for the manufacture of electrodes for batteries and in particular Li-ion batteries. CONTEXT

[0002] Carbon nanotubes are made of rolled graphite sheets. The nanotubes can be composed of a single sheet and are then called single-wall nanotubes (SWNT, commonly used abbreviation in English for "single-wall nanotubes"). The nanotubes can also be composed of several concentric sheets, and are then called multi-wall nanotubes (MWNT, commonly used abbreviation in English for "multi-wall nanotubes"). Carbon nanotubes are, therefore, ideal candidates for a wide range of applications, in particular as additives to improve the electronic resistance of materials and devices such as battery electrodes, including anodes and cathodes, especially in lithium-ion batteries. These improvements in battery performance are in line with the development of electric vehicles and therefore the fight against global warming.

[0003] Carbon nanotubes as can be obtained in known synthesis processes cannot be directly formulated with the components used in the composition of battery electrodes because they are in the form of tangled bundles or balls. Their density is too low, typically less than 0.1 and the formulations obtained do not exhibit the improvements in electrical conduction that can be expected due to their presence.

[0004] Today, their use requires a prior dispersion in liquid form comprising a solvent which can be water or an organic solvent. This dispersion in a liquid makes it possible to free the carbon nanotubes from their entanglements but requires significant quantities of solvent. Given the small quantities of carbon nanotubes present in these dispersions, it is therefore necessary to transport large quantities of material between production sites. of carbon nanotubes and their dispersion and the manufacturing sites of electrodes and batteries using these dispersions, generating a very unfavorable carbon footprint.

[0005] Solutions are therefore sought that minimize the quantities of solvent required for the manufacture of these dispersions, or even eliminate the solvent. Transporting the carbon nanotubes associated with other compounds in dry form with a high carbon nanotube content is an alternative that has the best carbon footprint. Until now, EP2550699 describes compositions comprising carbon nanotubes associated with a solvent and a polymer that helps disperse the carbon nanotubes. In this document, the manufacture of carbon nanotube / water / carboxy methyl cellulose granules is described. These granules can then be dried in an oven and redispersed before electrode formulation.

[0006] However, these granules do not allow, during the manufacture of an electrode, to achieve an electrical performance equivalent to that with a dispersion in a solvent obtained by ball milling for example, which constitutes the method currently used industrially. Consequently, there is currently no solution allowing the formulation of electrodes comprising carbon nanotubes under optimal conditions. Either the dry route of EP2550699 does not allow optimal electrical performance, or the route in the presence of solvent requires the transport of large quantities of carbon nanotubes formulated in the presence of solvent.

[0007] The applicant has therefore sought a dry form other than granules, this dry form being able to be redispersed at the user's premises in the electrode preparation step. In this way, the volumes of transported materials are considerably reduced.

[0008] Unexpectedly, the applicant discovered that with certain parameters of density and porosity of a powder, it is possible to obtain a composition of carbon nanotubes - polymer which can be very well redispersed and which provides performances equivalent to the liquid route. These compositions of carbon nanotubes - polymer in powder form can then be correctly reformulated in a high-performance electrode for batteries. In particular, these powders can be combined with the other components of the electrodes either by going back to the solvent route to manufacture the electrode, by depositing the mixture in liquid form and then drying the electrode, or by depositing these powders together with the components of the electrode mixed in solid form and then deposited by a suitable method such as electrostatic spraying and then calendering. Summary of the invention

[0009] The invention relates to a composition comprising carbon nanotubes and at least one polymer, in a carbon nanotube / polymer mass ratio of less than 100 / 5, said composition being in the form of a powder with an unpacked apparent density of between 0.11 and 0.5 g / cm3, having an apparent specific surface area of ​​between 50 and 350 m2 / g and a solvent content of less than 10% by mass. Description of the embodiments

[0010] The compositions of the invention have a carbon nanotube / polymer mass ratio of less than 100 / 5, preferably less than 10 / 1, preferably less than 4 / 1 but greater than 1 / 1.

[0011] The compositions of the invention are in the form of a powder of spheroidal grains whose diameter varies from a few microns to around a hundred microns.

[0012] [Fig. 1] shows a scanning electron microscopy photograph of a typical powder of the invention.

[0013] [Fig.2] shows the surface morphology of a grain of a typical powder of the invention.

[0014] These powders comprising carbon nanotubes can be obtained under certain drying conditions of a dispersion, of which atomization (spray drying) is a possibility exemplified by the applicant.

[0015] These dispersions are manufactured from carbon nanotubes generally with a density of less than 0.1 treated under high shear in the presence of a solvent and at least one polymer. During the preparation of these dispersions, other compounds can be combined with these dispersions.

[0016] Among the other compounds that can be added to the compositions of the invention, mention may be made of carbon fibers, carbon nanofibers, graphene, or carbon black. Preferably, it is carbon black. When it is carbon black, the carbon nanotube / carbon black mass ratios can vary from 100 / 1 to 1 / 100, preferably from 100 / 5 to 1 / 5.

[0017] The carbon nanotubes present in the compositions of the invention may be single-walled or multi-walled carbon nanotubes. Preferably, they are multi-walled. They are in entangled form (called "entangled") or in bundle form (called "bundle"). Preferably, they are in entangled form. They may be purified, that is to say, freed from residual impurities present at the end of their synthesis, in particular metals.

[0018] The polymers used in the context of the invention may be homopolymers, random copolymers, block copolymers or even gradient copolymers, these different polymers being able to be combined or used alone. preferably the polymers have a molecular mass by weight of less than 150,000 g / mol, preferably less than 120,000 g / mol and more preferably less than 80,000 g / mol measured by size exclusion chromatography calibrated with polystyrene standards.

[0019] The choice of the polymer or combination of several polymers is adapted to the solvent used to prepare the preliminary dispersions comprising the carbon nanotubes. The polymers must be soluble in the solvent, that is to say present a homogeneous solution.

[0020] By soluble is meant the possibility of dissolving at least 5 g of polymer per liter of solvent and preferably at least 20 g per liter of solvent at a temperature between 5 and 80°C, preferably between 15 and 35°C, and more preferably between 15 and 25°C.

[0021] Thus, any type of polymer and any type of solvent may be suitable within the scope of the invention, provided that the polymer-solvent pair meets the solubility condition.

[0022] The solvents are chosen in a non-limiting manner from water, N-methyl pyrrolidone, triethyl phosphate, cyrene™, dimethyl sulfoxide, dimethylformamide, ketones, acetates, furans, alkyl carbonates, alcohols and their mixture. The solvent may be CO2 in supercritical state. Preferably the solvent is water.

[0023] The polymer may be a copolymer comprising (meth)acrylic or styrenic monomeric entities of which at least one entity has a functionality chosen from hydroxy, acid, sulfonic acid, epoxy, amide, ether, ester, and pyrolidone. Among these functional or non-functional monomers, mention may be made of monomers such as methacrylic acid, acrylic acid, dimethyl acrylamide, glycidyl methacrylate, hydroxyethyl acrylate, methyl methacrylate, methyl acrylate and more generally substituted or unsubstituted, cyclic or non-cyclic alkyl (meth)acrylates, but also substituted or unsubstituted styrenes, 2-acrylamido-2-methylpropane sulfonic acid, N-vinyl pyrrolidone.The polymer may also be chosen from polysaccharides, modified polysaccharides, polyacrylamides homopolymers or copolymers, polyacrylic acids homopolymers or copolymers comprising mainly acrylic acid, polyvinyl alcohols homopolymers or copolymers, polyvinyl pyrrolidone homopolymers or copolymers, as well as the mixture of these polymers.

[0024] Preferably the polymers used are chosen from carboxy methyl cellulose, polyvinyl pyrrolidone homopolymers or copolymers, polyvinyl alcohols homopolymers or copolymers, polyacrylic acids homopolymers or copolymers comprising mainly acrylic acid, and more particularly carboxy methyl cellulose (CMC), polyvinyl pyrrolidone homopolymers or copolymers and more preferably polyvinyl pyrrolidone homopolymers or copolymers. With regard to polyvinyl pyrrolidone homopolymers or copolymers, the weight-average molecular mass is between 10,000 and 120,000 g / mol, preferably between 20,000 and 60,000 g / mol and more preferably between 20,000 and 40,000 g / mol. Polymers having acid functional groups (CMC, polyacrylic acids, etc.) can be used in the form of their alkali salts, preferably Li+ or Na+).

[0025] In addition, halogenated polymers such as PVDF or non-halogenated elastomers, in combination or not, may be present together in addition to the polymers already present. These are polymers which are part of the composition of the electrodes and which may be added at this stage, i.e. before the final formulation of the electrode.

[0026] The invention also relates to these compositions in the presence of halogenated polymers such as PVDF or non-halogenated elastomers, alone or in combination.

[0027] The term "PVDF" as used herein includes homopolymers of vinylidene fluoride (VDF) or copolymers of VDF and at least one other comonomer in which VDF represents at least 50 mol%. The comonomers polymerizable with VDF are selected from vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers such as perfluoro(methylvinyl)ether (PMVE), perfluoro(ethylvinyl)ether (PEVE), perfluoro(propylvinyl)ether (PPVE), perfluoro(1,3-dioxozole); perfluoro(2,2dimethyl-1,3dioxozole) (PDD), the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH; CH2OCN or CH2OPO3H, the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1,2,3,4 or 5, the product of formula R1CH2OCF=CF2 in which RI is hydrogen or F(CF2)z and z is 1, 2, 3, or 4;the product of formula R3OCF=CH2 in which R3 is F(CF2)z and z is 1, 2, 3, or 4 or perfluorobutylethylene (PFBE), fluoroethylenepropylene (FEP), 3,3,3-trifluoropropene, 2 trifluoromethyl-3,3,3-trifluoro-l-propene, 2,3,3,3-tetrafluoropropene or HFO-1234yf, El,3,3,3-tetrafluoropropene or HFO-1234zeE, Zl,3,3,3-tetrafluoropropene or HFO-1234zeZ, 1,1,2,3-tetrafluoropropene or HFO-1234yc, lel,2,3,3-tetrafluoropropene or HFO-1234ye, 1,1,3,3-tetrafluoropropene or HFO-1234zc and chlorotetrafluoropropene or HCFO-1224. PVDF may be introduced into the compositions of the invention as; solubilized form or in the form of a latex in the particular case where the process for preparing the compositions of the invention in powder form is atomization.

[0028] The non-halogenated elastomers can be of the type of natural or non-natural rubbers, nitrile rubbers, NBR (nitrile butadiene rubber), SBR (styrene butadiene rubber), substituted polyphosphazenes, acrylic polymers, silicone polymers, possibly in combination of these elastomers.

[0029] According to a variant of the invention, the compositions of the invention may also be supplemented with additives and in particular organic carbonates such as ethyl carbonate, propyl carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate alone or as a mixture, and preferably ethyl carbonate with a proportion of organic carbonate less than 60% by mass relative to the polymer and optionally moisture absorbers such as lithium bis(trifluoromethane)sulfonimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium hexafluoroarsenate, and 4,5-dicyano-2-(trifluoromethyl)imidazole in acid form or lithium salt, alone or as a mixture and in particular 4,5-dicyano-2-trifluoromethylimidazole in acid form or lithium salt, in a maximum quantity 50% by mass compared to carbon nanotubes.

[0030] The invention also relates to these compositions in the presence of these additives.

[0031] The compositions of the inventions in powder form can be prepared by various processes, among which may be mentioned the process of precipitation of the compositions comprising carbon nanotubes / Solvent / Polymer using a non-solvent for the polymer, the process of lyophilization of the compositions comprising carbon nanotubes / Solvent / Polymer, the process comprising the steps of extrusion of the compositions comprising carbon nanotubes / Polymer with injection of supercritical CO2 during the extrusion step with a mass proportion of supercritical CO2 of between 25% and 1000% of the composition then followed by degassing of the CO2, or other device using supercritical CO2, or the process of atomization of the compositions comprising carbon nanotubes / Solvent / Polymer.

[0032] When preparing the compositions of the invention in powder form with either of the methods, the additives may be added together with the compositions comprising carbon nanotubes and at least one polymer. Powders are then obtained which may comprise carbon nanotubes, at least one polymer and one or more additives.

[0033] According to a preferred embodiment, the compositions in powder form are prepared by the process comprising the steps of extruding one of these compositions comprising carbon nanotubes and at least one polymer with injection of Supercritical CO2 during the extrusion step with a mass proportion of supercritical CO2 between 25% and 1000% of the composition comprising carbon nanotubes and at least one polymer then followed by degassing of the CO2 and recovery of powder.

[0034] Thus, the present invention also relates to a process for obtaining the compositions of the invention by extrusion of the compositions comprising carbon nanotubes and at least one polymer, with injection of supercritical CO2 during the extrusion step, with a mass proportion of supercritical CO2 of between 25% and 1000% of the composition, then followed by degassing of the CO2 and recovery of powder.

[0035] According to an even more preferred embodiment, the compositions in powder form are prepared by the atomization process.

[0036] In the case of atomization, the procedure is as follows:

[0037] The compositions of the invention are prepared in two stages:

[0038] A first step consists of dispersing the carbon nanotubes in the presence of at least one polymer and the solvent in a suitable tool chosen from deflocculators, ball mills, z-dispersion tools equipped with rotor / stator agitation, ultrasound or cavitators. These are tools that allow, under high shear, the dissociation of the carbon nanotube balls and their correct dispersion in the solvent. Preferably, these are deflocculators and ball mills, in a combined manner or not.

[0039] During this step, it is also possible to combine PVDF, and / or non-halogenated elastomers and / or additional compounds such as organic carbonates or moisture absorbers.

[0040] The operation is carried out in mass proportions of carbon nanotubes - polymer of between 3 and 20% and preferably between 5 and 10% in relation to the solvent. The dispersion thus obtained is then diluted in the solvent so that its viscosity is brought into Brookfield values ​​of between 50 and 10000 Centipoise and preferably between 100 and 1500 Centipoise. The viscosity values ​​relate to the dispersions measured at the end of their preparation. The viscosity of these dispersions may change slightly over time beyond 10000 Centipoise.

[0041] For the sake of good stability, it is advisable to operate under dispersion pH conditions of between 3 and 12 and preferably between 5 and 10.

[0042] In a second step, this latter dispersion is atomized by passing through a gas flow which may be air, an inert gas or a mixture of inert gases, or even air and inert gas, with a temperature of the gas entering the atomizer greater than 120°C, preferably between 120 and 240°C and even more preferably between 140 and 240°C, ideally between 200 and 240°C and the carbon nanotube / polymer powder is recovered. Post-atomization drying may be necessary to bring the solvent content below 0.5% by mass. Alternatively, and depending on the formulations used during the subsequent electrode manufacturing process, PVDF and / or non-halogenated elastomers in the form of a latex may be added to the compositions of the invention during the atomization phase.

[0043] Thus, the present invention also relates to a process for obtaining the compositions of the invention by atomization comprising the following steps:

[0044] -dispersion of carbon nanotubes in a solvent in the presence of at least one polymer.

[0045] -atomization of the dispersion by a gas heated to a temperature above 120°C then recovery of powder.

[0046] Preferably, the solvent used in the atomization process is water.

[0047] The compositions of the invention are in the form of powders of particles porous unit particles or aggregates of porous unit particles with preferably a particle size corresponding to Dv10 values ​​between 4 and 8 pm, Dv 50 between 15 and 30 pm and Dv 90 between 50 and 100 pm, Dv meaning the volume average diameter. The measurement is carried out using a Malvem type laser diffraction device (Mastersizer 3000). Powders with larger or smaller particle sizes would not be outside the scope of the invention.

[0048] The powder has an apparent specific surface area of ​​between 50 and 350 m2 / g and preferably between 90 and 200 m2 / g. The BET measurement is carried out using an AS AP 2460 device from microméritics.

[0049] The powder has an unpacked apparent density of between 0.11 and 0.5 g / cm3, preferably between 0.12 and 0.5 g / cm3, and more preferably between 0.15 and 0.5 g / cm3.

[0050] The powder has a residual solvent content by mass of less than 10%, preferably less than 6% and more preferably less than 5%.

[0051] The compositions of the invention in the form of powders are useful for the manufacture of battery electrodes and in particular for the manufacture of cathodes. For the manufacture of the electrodes, the compositions of the invention are mixed either in dispersed form in a solvent with the other compounds of the electrode, or as such with the other compounds of the electrode, i.e. in dry form in a suitable mixer.

[0052] When manufacturing electrode formulations with the compositions of the invention, the mixing will preferably be carried out with an extruder. The applicant has in fact found that the extruder is the tool giving the best results of electrical conductivity in the formulations used for electrodes.

[0053] The invention therefore also relates to electrodes manufactured using these powders and preferably cathodes.

[0054] According to a first preference, the powders of the invention are thus mixed with an active material of the lithium oxide type NMC (Nickel, Manganese, Cobalt), LFP (Lithium, Iron, Phosphate), LMO (Lithium, Manganese Oxide) or LMNO (Lithium Manganese and Nickel Oxide) and a fluorinated polymer typically PVDF and / or non-halogenated elastomers when they are not already present in the compositions of the invention in a suitable mixer, for example a disc mixer or a planetary mixer, then a solvent is added. The mixture obtained is deposited on a conductive plate then the solvent is evaporated.

[0055] According to a second preference, and this constitutes another advantage of the invention, the powders of the invention can be used in solvent-free electrode formulation processes (known as "dry processes" in English), that is to say the direct formulation of the powders of the invention with powders of active material of the electrode and other compounds depending on whether the electrode is an anode or a cathode. Thus, all the ingredients which constitute an electrode in powder form can be directly mixed, without solvent, and the electrode can be shaped by calendering / hot lamination, electrospray (deposition of powder by electrostatic means) followed by hot lamination.

[0056] Other solvent-free technologies can therefore advantageously use the powder compositions of the invention in powder form, in the extrusion of the active materials of the cathodes or anodes formulated directly in the liquid or solid electrolyte and thus manufacture cathodes or anodes directly usable in the assembly of batteries.

[0057] The invention also relates to the use of the compositions of the invention for obtaining electrodes, cathodes or anodes, the electrodes, cathodes or anodes obtained using the compositions of the invention formulated by solvent route or in dry form and preferably cathodes, as well as the batteries obtained with these electrodes.

[0058] Examples.

[0059] The examples were carried out with Graphistrength® C100 carbon nanotubes (Arkema) having residual metal levels of less than 50 ppm.

[0060] Example 1. Liquid composition of reference carbon nanotubes. Comparison outside the invention.

[0061] In this example, a carbon nanotube composition typical of the practices used in industry to date is reproduced. The composition comprising carbon nanotubes is therefore a liquid composition with a low carbon nanotube content and a high solvent content. This composition is used in Example 2 for the manufacture of a reference electrode constituting the objective to be achieved with the compositions of the invention.

[0062] 100g of carbon nanotubes, 25g of PVP ((Poly Vinyl Pyrrolidone)) (molecular mass by weight of 24000g / mol) and 1000g of N-methyl pyrrolidone are introduced into a flocculator. This mixture is homogenized in a deflocculator and then treated in a horizontal ball mill, in order to disperse the carbon nanotube particles. The balls used have a diameter of 0.6 mm and the grinding time is 200-260 minutes. Additional N-methyl pyrrolidone (166g) is added so as to obtain a fluid and manipulable composition.

[0063] The viscosity of the dispersion called Dref obtained is measured on a Brookfield viscometer. The composition obtained Dref has a carbon nanotube content of 7.68% and the viscosity is measured at 600 Centipoise at 25°C.

[0064] Example 2: Fabrication of a reference electrode (Cathode).

[0065] The dispersion Dref obtained in Example 1 is introduced into a planetary mixer followed by the addition of 95 g of lithium nickel manganese cobalt oxide containing a ratio of Ni: Mg: Co 6: 2: 2, called NMC 622, of N-methyl pyrrolidone comprising PVDF (marketed by Arkema under the reference Kynar HSV 1810) for 30 minutes so as to obtain a paste with all the constituent compounds of a cathode. The formulation obtained expressed in dry form is as follows in mass percentage:

[0066] • 97.75% of NMC 622;

[0067] • 1% carbon nanotubes;

[0068] • 1% PVDF

[0069] • 0.25% PVP.

[0070] The dry matter content is 74%.

[0071] The electrode is prepared by coating using a Sheen type filmograph and an adjustable BYK-Gardner applicator. A 200 μm thick film is applied to a 25 μm thick aluminum foil on a polyethylene terephthalate (PET) sheet constituting an insulating support. Drying in a ventilated oven is carried out for 2 h at 120°C.

[0072] The dried electrode is then calendered to achieve a final film thickness of approximately 80 μm.

[0073] In order to calculate the specific resistance, the electrode supported by the PET is cut into 3x4 cm format. Silver lacquer is painted on the ends of the cutting. Once the lacquer is dry, the specific resistance (R) is measured at 25°C with an ohmmeter.

[0074] The value of the specific resistance R is a good indication of the performance of the effect of the carbon additive (carbon nanotubes in this case).

[0075] A resistance of 7 ohms is measured on this electrode. This value constitutes the reference and therefore the objective to be achieved within the framework of the invention.

[0076] Example 3: Composition in dry form of carbon nanotubes according to the known state of the art. Comparison 2 outside the invention.

[0077] In this example we operate according to EP 2550699.

[0078] 4 kg of carbon nanotubes are mixed with 200 g of PVP (molecular mass by weight of 24000 g / mol). After the addition of 14 L of demineralized water, the mixture is homogenized in a 60 L rotary mixer.

[0079] The mixture is then introduced into the hopper of a Clextral BC21 extruder by a gravimetric doser set at 15 kg / h and a granulation of the rod obtained adapted. The temperature control system of the extruder is set at 50°C. The rotation speed of the screws is 400 rpm. Cylindrical granules with a diameter of 4-5 mm and a length between 3-20 mm are obtained.

[0080] The granules are then dried in a ventilated oven at 140°C for 4 hours.

[0081] The apparent density of the granules is 1.2 g / cm3. These granules are ground in a gas jet mill to obtain a powder having a Dv90 < 100 pm. The unpacked apparent density of this powder after grinding was measured at 0.85 g / cm3. This powder obtained is called PO and has an apparent specific surface area measured by BET of 34 m2 / g. The BET measurement is carried out using an AS AP 2460 device from microméritics.

[0082] The untapped bulk density (UTBD) is defined by the ratio of the mass of powder to its volume after being untapped.

[0083] The measurement is carried out by measuring the maximum volume occupied by the powder in a closed graduated cylinder of mass T of 100 cm3 turned over slowly several times. The weighings are carried out using a precision balance to 0.1 g.

[0084] The test tube is filled to three-quarters then weighed to a mass ml, closed, then slowly turned over several times until the maximum volume occupied by the powder is obtained. The volume occupied is noted v in cm3.

[0085] The unpacked apparent density expressed in g / cm3 is calculated by the following formula:

[0086] MVNT = (ml-T) / v

[0087] Example 4. Composition of carbon nanotubes and PVP according to the invention.

[0088] The composition described in Example 1 is produced in an identical manner but replacing the N-methyl pyrrolidone with water.

[0089] The dry matter composition is as follows: 100 g of carbon nanotubes and 25 g of poly(vinyl pyrrolidone) (PVP) with a mass ratio of carbon nanotubes / PVP 4 / 1. This mixture is homogenized in a deflocculator with 1000 g of water, and then ground in a horizontal ball mill as described in Example 1. The additional quantities of water were added during grinding to adjust the viscosity.

[0090] At the end of grinding, the dry extract is 6% by mass and the proportion of carbon nanotubes is 4.8%. The final viscosity is 500 Centipoise.

[0091] The aqueous dispersion is then dried in an atomizer. The dispersion is sprayed in the presence of air flows preheated to different temperatures.

[0092] The solid compositions PI to P4 are collected in powder form at the outlet of the atomizer under the conditions given in Table 1.

[0093] [Tables 1] Table 1 T MVNT HSG PI 120 0.38 6 34 P2 160 0.32 3.84 92 6 / 19 / 63 P3 200 0.31 4.95 117 7 / 24 / 88 P4 240 0.28 1.95 158 6 / 19 / 65

[0094] T: Temperature of the preheated air entering the atomizer °C.

[0095] MVNT: Apparent unpacked density.

[0096] H: % by mass of residual moisture.

[0097] S: Apparent specific surface area, BET m2 / g.

[0098] G: Particle size distribution Dv10 / Dv50 / Dv90 in pm.

[0099] The 4 powder samples PI to P4 obtained after atomization are subsequently treated in a vacuum oven to eliminate residual moisture.

[0100] The formulations of this example in powder form are used directly in the NMC Cathode type electrode formulation, as described in Example 2.

[0101] All the formulations obtained in this example have a much lower apparent density compared to the solid ground aggregates of Example 3 (PO). P2, P3 and P4 have apparent specific surfaces greater than PO and PL

[0102] Example 5: Production of inks for cathodes and evaluation of the cathodes with carbon nanotube powders PI to P4 and sample PO of example 3.

[0103] Two methods are used to make the cathode of the formulation described in Example 2.

[0104] Method 1: The formulation is identical to the method of Example 2, but using the powders PO to P4 instead of the dispersion Dref of Example 1.

[0105] NMC 622, PVDF Kynar HSV8010 and PO to P4 powders were pre-mixed dry in a planetary mixer and then in a disc mixer for 40 min at 50°C. N-methyl pyrrolidone was added gradually to maintain the viscosity of the obtained cathode inks in the values ​​6000-10000 Centipoise.

[0106] Method 2: With this method, the cathode paste is manufactured according to the original extrusion method from the dry products PO crushed granules, PI to P4 powder obtained by atomization as well as the active materials and the PVDF binder. In this case the liquid Dref cannot be used. The NMC 622, PVDF Kynar HSV8010 mixture is extruded successively with the PO to P4 powders using a micro-extruder marketed by the company DSM. NMP is introduced then the P powders together with the NMC 622, PVDF Kynar HSV8010 mixture. The NMP is added to the solid mixture and adjusted so as to obtain viscosities of the inks obtained between 6000 and 10000 Centipoise and are used for the production of the electrodes as described in example 2.

[0107] The following identical steps are followed for powders PO to P4:

[0108] - Introduction of 9.35 mL of NMP into the extruder, preheated to 50°C; a

[0109] Once the NMP is introduced, the screw speed is increased to 240 rpm;

[0110] - 42.6 g of P powders together with the mixture NMC 622, PVDF Kynar HSV8010 are introduced gradually for 30-60 seconds; the torque is continuously monitored, it is adjusted with NMP so as to remain in the range 1000 - 1400 Nm

[0111] - Once the torque has stabilized, 4.9 g of NMP are gradually introduced

[0112] for 30-60 seconds; the torque gradually decreases to 100

[0113] Nm

[0114] - The cathode ink is recovered at the outlet of the extruder. The dry mass is of 76-78%. 5 cathode inks are obtained with the 5 powders PO, PI, P2, P3 and P4 used for the production of the electrodes as described in example 2.

[0115] The cathodes produced as described in Example 2 from the inks obtained by the two methods have similar thicknesses, of the order of 78-82 μm and their resistances are given in Table 2. The value of the reference cathode produced according to the conventional method from a liquid dispersion will be found.

[0116] [T ableaux2] Example 2 Example 4 Example 4 Carbon nanotube source Reference Specific resistance Cathode Ohms cm Method 1 Specific resistance Cathode Ohms cm Method 2 Specific resistance Cathode Ohms cm PO 55+5 18+2 PI 12+1 8+1 P2 8+1 7+1 P3 9+1 7+1 P4 9+1 7+1 Dref 7+1

[0117] These results show that the cathodes obtained from the compositions of the invention show an electrical performance superior to those of the prior art such as the powders derived from the granules of EP 2550699 (PO) but give the same results in terms of electrical performance as the NMP-based carbon nanotube dispersion of example 1 (Dref). The lower density particles, resulting from atomization at an air flow temperature above 120°C, show results close to the reference. It can therefore be concluded that carbon nanotubes usable in such applications must have densities lower than 0.5.

[0118] The extrusion method (Method 2) gives the results closest to the reference of example 2. The use of PO powders from the granules of EP 2550699 gives results which always remain out of step with the products of the invention.

[0119] Example 6: measurement of absorbance.

[0120] The dry powders (PO and P4) were introduced into NMP at 6% by mass at room temperature.

[0121] After mixing at 600 rpm with the disk mixer for 30 min, the precise dry extract was evaluated with a thermo balance. Solutions with dilutions to 50 +-2 ppm were made.

[0122] Absorbance is measured using a HACH DR1900 spectrophotometer, at a light wavelength of 360 nm.

[0123] Absorbance (A), also called optical density (OD), is the amount of light absorbed by a dispersion. The higher the absorbance A, the better the particles are distributed in the dispersion volume (Table 3).

[0124] [Tables3] Table 3 Absorbance A Dispersion of example 1 Dref 3.2 - 3.4 Dispersion with PO 2.2 - 2.6 Dispersion with P 4 3-3.4

[0125] The dispersion produced from the P4 powder of the invention has an absorbance equivalent to that of example 1 Dref, much higher than that obtained from PO, demonstrating a good distribution of the carbon nanotubes from P4 in the solvent.

[0126] Example 7:

[0127] In this example, the synergy of the combination of carbon black with carbon nanotubes in the electrodes manufactured using the compositions of the invention is evaluated compared to those of the compositions of the known art (solvent type route of example 1, route of granules from EP 2550699 PO and dry by mixing P2 with carbon black).

[0128] The combination with carbon black during the atomization step gives the best results. (Table 5)

[0129] The electrodes are formulated according to a recipe in the proportions of the components in Table 4:

[0130] [Tables4] Table 4 % by mass Active charge NMC622 (UMICORE) 96.38 Carbon Black C65 (Imerys) 1.5 carbon nanotubes 0.5 PVDF Kynar® 1810 (Arkema) 1.5 PVP K25 (Aldrich) 0.12

[0131] Table 5 shows the resistances measured on the cathodes made from 4 mixing methods of carbon nanotubes and carbon black. The mixture made prior to atomization according to the compositions of the invention has the best characteristics once formulated into an electrode. The carbon nanotube / carbon black synergy is maximum using the operating method and compositions of the invention.

[0132] [Tables5] Specific R Ohms cm Solvent cathode Dry mix with P2 15+1 Mixture in the dispersion of example 1 13+1 Mixture before atomization according to the invention 10+1 Dry mixture with PO powder 21+1

Claims

Claims

1. Composition comprising Carbon Nanotubes and at least one polymer, in a carbon nanotube / polymer mass ratio of less than 100 / 5, said composition being in the form of a powder with an unpacked bulk density of between 0.11 and 0.5 g / cm3, having an apparent specific surface area of ​​between 50 and 350 m2 / g measured using an AS AP 2460 device from micromeritics and a solvent mass content of less than 10% in which the polymer is chosen from modified polysaccharides, polyvinyl pyrrolidone homopolymers or copolymers, the unpacked bulk density (UBD) being defined by the ratio of the mass of powder to its volume after being unpacked, the measurement being carried out by measuring the maximum volume occupied by the powder in a closed graduated cylinder of mass T of 100 cm3 turned upside down. several times slowly with the weighings carried out using a precision balance at 0,1 g and filling three-quarters of the test tube then weighed in a mass ml, closed, then slowly turned over several times until obtaining the maximum volume occupied by the powder noted v in cm3 leading to an apparent unpacked density expressed in g / cm3 calculated by the following formula MVNT = (ml-T) / v.,

2. Composition according to claim 1 in which the polymer is chosen from polyvinyl pyrrolidone homopolymers or copolymers with a molecular mass of between 20,000 and 60,000 g / mol.

3. Composition according to claim 1 to 2 further comprising carbon black in carbon nanotube / carbon black mass ratios varying from 100 / 1 to 1 / 100.

4. Composition according to claims 1 to 3 additionally comprising at least one organic carbonate such as ethyl carbonate, propyl carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate alone or as a mixture.

5. Compositions according to claims 1 to 4 further comprising at least one compound selected from lithium bis(trifluoromethane)sulfonimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium hexafluoroarsenate, and 4,5-dicyano- 2-(trifluoromethyl) imidazole in acid or lithium salt form, alone or in mixture and in particular 4,5-dicyano-2-trifluoromethyl imidazole in acid or lithium salt form.

6. Composition according to claims 1 to 5 comprising in addition to PVDF, homopolymer or copolymer and / or a non-halogenated elastomer.

7. Process for preparing a composition according to one of claims 1 to 6 using an atomizer and comprising the following steps: -Preparation of a composition according to one of claims 1 to 6 in the presence of a solvent in a deflocculator, at a temperature between 5 and 80°C to obtain a dispersion comprising carbon nanotubes. -Atomization of the dispersion by a gas heated to a temperature above 120°C and recovery of the powder.

8. Process for preparing a composition according to one of claims 1 to 6 comprising the steps of extruding the composition with injection of supercritical CO2 during the extrusion step with a mass proportion of supercritical CO2 of between 25% and 1000% of the composition then followed by degassing of the CO2 and recovery of powder

9. Use of a composition according to one of claims 1 to 6 for the manufacture of electrodes with or without solvent.

10.

11. Electrode obtained according to the use of claim 9. Battery comprising at least one electrode according to claim 10.

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