COMPOSITIONS COMPRISING CARBON NANOTUBE AND AT LEAST ONE POLYMER, AND CONTAINING LITTLE OR NO SOLVENT - Patent application

Abstract

The present invention relates to compositions of carbon nanotubes that can be used in solid form, i.e. without solvent. These compositions contain at least one polymer and are easily dispersible in formulations for the manufacture of electrodes for batteries, in particular lithium-ion batteries, by liquid or solid-state processes. The invention also relates to a method for obtaining these powders, their use in the manufacture of electrodes for batteries, and to the batteries containing them.

Description

[Technical field]

[0001] The present invention relates to compositions comprising carbon nanotubes in powder form, which compositions in powder form contain at least one polymer and are easily dispersible in solvent-containing or solvent-free formulations for the manufacture of electrodes for batteries, in particular lithium-ion batteries. [Background technology]

[0002] context Carbon nanotubes are made of rolled-up sheets of graphite. Nanotubes consist of a single sheet and are known as single-walled nanotubes (SWNTs). Nanotubes can also consist of multiple concentric sheets, in which case they are known as multi-walled nanotubes (MWNTs). Carbon nanotubes are therefore ideal candidates for a wide range of applications, particularly as additives to improve the electronic resistance of materials and devices such as battery electrodes, including the anodes and cathodes of lithium-ion batteries. Such improved battery performance is part of the development of electric vehicles and also in the fight against global warming.

[0003] Carbon nanotubes, as obtained by known synthesis processes, are in the form of entangled bundles or spheres and therefore cannot be directly blended with the components used in the construction of battery electrodes: their relative density is too low, usually less than 0.1, and the resulting blends do not show the improvement in electrical conductivity that would be expected from their presence.

[0004] Currently, to use them, they must be pre-dispersed in a liquid form containing a solvent, which can be water or an organic solvent. This dispersion in a liquid allows the carbon nanotubes to be de-entangled, but requires large amounts of solvent. The small amounts of carbon nanotubes present in these dispersions require the transportation of large amounts of material between the production sites of the carbon nanotubes and their dispersions and the production sites of the electrodes and batteries that use these dispersions, with a very unfavorable carbon footprint.

[0005] Therefore, a solution is needed to minimize the amount of solvent required for the production of these dispersions or to eliminate the solvent. Combining carbon nanotubes with other compounds and shipping them in a dry state with a high carbon nanotube content is the least carbon-intensive alternative. To date, EP 2550699 describes a composition combining carbon nanotubes with a solvent and a polymer that helps disperse the carbon nanotubes. This document describes the production of carbon nanotube / water / carboxymethylcellulose pellets. These pellets are dried in an oven and redispersed before the formation of the electrodes.

[0006] However, these pellets do not allow the same electrical performance during the manufacture of electrodes as is obtained with dispersions in solvents, obtained for example by ball milling, which are the methods currently used industrially. As a result, to date, no solution exists that allows the formation of electrodes containing carbon nanotubes under optimal conditions. The dry route of EP 2550699 does not provide optimal electrical performance qualities, and the solvent-based route requires the transportation of large amounts of carbon nanotubes that are formulated in the presence of a solvent.

[0007] Therefore, the applicant seeks a dry form other than pellets, which can be redispersed by the user at the electrode preparation stage, thus significantly reducing the amount of material to be transported.

[0008] Unexpectedly, the applicant has discovered that certain parameters of powder density and porosity allow obtaining carbon nanotube polymer compositions that are very well redispersed and provide performance qualities comparable to the liquid route. These powdered carbon nanotube polymer compositions can be appropriately reformulated into high performance electrodes for batteries. In particular, these powders can be combined with other components of the electrode by returning them to the solvent route for producing electrodes, depositing the mixture in liquid form and then drying the electrode, or depositing these powders in solid form together with the mixed electrode components and then depositing them in a suitable manner, such as electrostatic spraying followed by calendaring. Summary of the Invention

[0009] The present 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, the composition being between 0.11 and 0.5 g / cm 3 It is in the form of a powder with a loose bulk density of 50 to 350 m 2 / g and a solvent content of less than 10% by weight.

[0010] Detailed Description: The composition of the invention has 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 present invention are in the form of a powder of spherical particles varying in diameter from a few microns to about 100 microns. [Brief description of the drawings]

[0012] [Figure 1] 1 shows a scanning electron microscope photograph of a typical powder of the present invention. [Diagram 2] 1 shows the particle surface morphology of a typical powder of the present invention.

[0013] These powders containing carbon nanotubes can be obtained under specific conditions of drying the dispersion, of which atomization (spray drying) is one of the possibilities exemplified by the applicant.

[0014] These dispersions are generally produced by subjecting carbon nanotubes, which have a relative density of less than 0.1, to high shear in the presence of a solvent and at least one polymer. During the preparation of these dispersions, other compounds can be mixed with these dispersions.

[0015] Other compounds that may be added to the composition of the present invention include carbon fibers, carbon nanofibers, graphene, or carbon black. Carbon black is preferred. When carbon black is included, the mass ratio of carbon nanotubes / carbon black may be in the range of 100 / 1 to 1 / 100, preferably 100 / 5 to 1 / 5.

[0016] The carbon nanotubes present in the composition of the invention may be single-walled or multi-walled carbon nanotubes. Multi-walled ones are preferred. They are in entangled form or in the form of bundles. They are preferably in entangled form. They can be purified, that is to say freed from residual impurities, especially metals, present at the end of the synthesis.

[0017] The polymers used within the context of the present invention may be homopolymers, random copolymers, block copolymers or gradient copolymers, and it is possible to combine these various polymers or use them alone. Preferably, the polymers have a weight average molecular weight, measured by size exclusion chromatography calibrated with polystyrene standards, of less than 150000 g / mol, preferably less than 120000 g / mol, and even more preferably less than 80000 g / mol.

[0018] The choice of polymer or combination of polymers is adapted to the solvent used to prepare the predispersion containing the carbon nanotubes: the polymer must be soluble in the solvent, i.e. it must show a homogeneous solution.

[0019] "Soluble" is understood to mean that at least 5 g of polymer per liter of solvent, preferably at least 20 g of polymer per liter of solvent, can be dissolved at temperatures between 5 and 80°C, preferably between 15 and 35°C, more preferably between 15 and 25°C.

[0020] Thus, any type of polymer and any type of solvent may be suitable in the context of the present invention, as long as the polymer-solvent pair meets the solubility requirements.

[0021] The solvent is selected from, but is not limited to, water, N-methylpyrrolidone, triethylphosphate, Cyrene™, dimethylsulfoxide, dimethylformamide, ketones, acetates, furans, alkyl carbonates, alcohols, and mixtures thereof. The solvent may be CO2 in a supercritical state. Water is a preferred solvent.

[0022] The polymer may be a copolymer comprising (meth)acrylic or styrene monomer entities, at least one of which has a functional group selected from hydroxy, acid, sulfonic acid, epoxy, amide, ether, ester and pyrrolidone. These functional or non-functional monomers include monomers such as methacrylic acid, acrylic acid, dimethylacrylamide, glycidyl methacrylate, hydroxyethyl acrylate, methyl methacrylate, methyl acrylate, more generally substituted or unsubstituted, cyclic or non-cyclic alkyl (meth)acrylates, but also substituted or unsubstituted styrene, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone. The polymer may also be selected from polysaccharides, modified polysaccharides, polyacrylamide homopolymers or copolymers, polyacrylic acid homopolymers or copolymers containing mainly acrylic acid, polyvinyl alcohol homopolymers or copolymers, polyvinylpyrrolidone homopolymers or copolymers, and mixtures of these polymers.

[0023] Preferably, the polymer used is selected from carboxymethylcellulose, polyvinylpyrrolidone homopolymer or copolymer, polyvinyl alcohol homopolymer or copolymer, polyacrylic acid homopolymer or copolymer containing mainly acrylic acid, more specifically carboxymethylcellulose (CMC), polyvinylpyrrolidone homopolymer or copolymer, more preferably polyvinylpyrrolidone homopolymer or copolymer. As for the polyvinylpyrrolidone homopolymer or copolymer, the weight average molecular weight is 10000 to 120000 g / mol, preferably 20000 to 60000 g / mol, more preferably 20000 to 40000 g / mol. The polymer having an acidic functional group (CMC, polyacrylic acid, etc.) is preferably substituted with an alkali metal salt (preferably Li + Or Na + ) can be used.

[0024] Additionally, halogenated polymers such as PVDF or non-halogenated elastomers may be present in addition to, in combination with, or otherwise coexisting with the polymers already present that are used in the composition of the electrode and may be added at this stage, prior to the final formulation of the electrode.

[0025] The present invention also relates to these compositions in which a halogenated polymer, such as PVDF, or a non-halogenated elastomer is present, alone or in combination.

[0026] As used herein, the term "PVDF" includes vinylidene fluoride (VDF) homopolymers or copolymers of VDF and at least one other comonomer, wherein VDF is present at least 50 mole %. Comonomers which can be polymerized with VDF include vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), or perfluoro(propyl vinyl) ether (PPVE), perfluoro(1,3-dioxazole), perfluoro(2,2-dimethyl-1,3-dioxazole) (PDD), products of the formula CF2=CFOCF2CF(CF3)OCF2CF2X, where X is SO2F, CO2H, CH2OH, CH2OCN, or CH2OPO3H, products of the formula CF2=CFOCF2CF2SO2F, products of the formula F(CF2) n Products of the formula CH2OCF=CF2 [n is 1, 2, 3, 4 or 5], R1CH2OCF=CF2 [R1 is hydrogen or F(CF2) z and z is 1, 2, 3 or 4], a product of the formula R3OCF=CH2 [R3 is F(CF2) zand z is 1, 2, 3 or 4; and perfluorobutylethylene (PFBE), fluorinated ethylene propylene (FEP), 3,3,3-trifluoropropene, 2-trifluoromethyl-3,3,3-trifluoro-1-propene, 2,3,3,3-tetrafluoropropene or HFO-1234yf, E-1,3,3,3-tetrafluoropropene or HFO-1234zeE, Z-1,3,3,3-tetrafluoropropene or HFO-1234zeZ, 1,1,2,3-tetrafluoropropene or HFO-1234yc, 1,2,3,3-tetrafluoropropene or HFO-1234ye, 1,1,3,3-tetrafluoropropene or HFO-1234zc, and chlorotetrafluoropropene or HCFO-1224. PVDF can be introduced into the composition of the invention in dissolved form or in the form of a latex in the particular case where the process for preparing the powdered composition of the invention is atomization.

[0027] The non-halogenated elastomers may be of the type natural or non-natural rubber, nitrile rubber, NBR (nitrile butadiene rubber), SBR (styrene butadiene rubber), substituted polyphosphazenes, acrylic polymers, or silicone polymers, optionally a combination of these elastomers.

[0028] According to one variant of the invention, the composition of the invention may also contain additives, in particular organic carbonates such as ethyl carbonate, propyl carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, alone or as a mixture, preferably ethyl carbonate, in a proportion of organic carbonate relative to the polymer of less than 60% by weight, and optionally 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 the form of an acid or a lithium salt, alone or as a mixture, in particular 4,5-dicyano-2-(trifluoromethyl)imidazole in the form of an acid or a lithium salt, in an amount of up to 50% by weight relative to the carbon nanotubes.

[0029] The present invention also relates to compositions in which these additives are present.

[0030] The powdered composition of the present invention can be produced by various methods, including precipitating the carbon nanotube / solvent / polymer composition with the aid of a non-solvent for the polymer, extruding the carbon nanotube / polymer composition with supercritical CO in a mass fraction between 25% and 1000% of the composition during the extrusion process, followed by degassing of the CO, or by other devices using supercritical CO, or by atomizing the carbon nanotube / solvent / polymer composition.

[0031] During the preparation of the composition of the present invention in powder form by any method, additives may be added together to the composition comprising carbon nanotubes and at least one polymer, resulting in a powder comprising carbon nanotubes, at least one polymer, and one or more additives.

[0032] According to a preferred embodiment, the composition in powder form is produced by a method comprising the step of extruding one of these compositions comprising carbon nanotubes and at least one polymer with supercritical CO2 in a mass proportion between 25% and 1000% of the composition comprising carbon nanotubes and at least one polymer during the extrusion step, while injecting supercritical CO2, followed by degassing the CO2 and recovering the powder.

[0033] The present invention therefore relates to a method for obtaining a composition according to the invention, by extruding a composition comprising carbon nanotubes and at least one polymer with supercritical CO in a mass proportion between 25% and 1000% of the composition comprising carbon nanotubes and at least one polymer during the extrusion step, while injecting supercritical CO, followed by degassing of the CO and recovery of the powder.

[0034] According to a further preferred embodiment, the composition in powder form is prepared by a spraying process.

[0035] In the case of atomization, the method is as follows. The compositions of the present invention are prepared in two steps. The first step mainly consists of dispersing the carbon nanotubes in the presence of at least one polymer and a solvent in a suitable device chosen from a deflocculator, a ball mill, a rotor / stator agitator, ultrasound, or a Z-disperser equipped with a cavitator. These are devices that allow the carbon nanotube balls to be dissociated under high shear and properly dispersed in the solvent. A combination of a deflocculator and a ball mill, or other methods, is preferred.

[0036] During this process, it is also possible to combine PVDF and / or non-halogenated elastomers and / or additional compounds such as organic carbonates and moisture absorbents.

[0037] The method is carried out with a carbon nanotube-polymer mass fraction of between 3% and 20%, preferably between 5% and 10%, relative to the solvent. The dispersion thus obtained is then diluted with the solvent so that its viscosity is between 50 and 10,000 centipoise, preferably between 100 and 1,500 centipoise, Brookfield value. The viscosity values ​​relate to values ​​measured at the end of the preparation of the dispersion. The viscosity of these dispersions may vary slightly over time above 10,000 centipoise.

[0038] To ensure good stability, it is recommended to operate under conditions of dispersion pH between 3 and 12, preferably between 5 and 10.

[0039] In a second step, the latter dispersion is atomized by passing it through a gas stream of air, inert gas, or a mixture of inert gas, or a mixture of air and inert gas, at a temperature of the gas entering the atomizer above 120°C, preferably between 120°C and 240°C, more preferably between 140°C and 240°C, and ideally between 200°C and 240°C, and the carbon nanotube / polymer powder is recovered. Drying after spraying may be required to reduce the solvent content to less than 0.5% by weight. Alternatively, PVDF in the form of a latex and / or a non-halogenated elastomer may be added to the composition of the present invention during the spraying stage, depending on the formulation used during the subsequent electrode manufacturing process.

[0040] The present invention therefore also relates to a process for obtaining a composition according to the invention by spraying, comprising the following steps: - dispersing the carbon nanotubes in a solvent in the presence of at least one polymer; - Atomization of the dispersion with a gas heated to a temperature above 120°C, followed by recovery of the powder.

[0041] Preferably, the solvent used in the spraying process is water.

[0042] The composition of the present invention is in the form of a powder of porous unit particles or an agglomerate of porous unit particles, preferably having a D of between 4 μm and 8 μm. v 10 values, D between 15μm and 30μm v 50 values, D between 50μm and 100μm v 90 value, and D v represents the volume average diameter. Measurements are performed using a Malvern laser diffraction instrument (Mastersizer 3000). Powders with larger or smaller particle sizes do not depart from the scope of the invention.

[0043] The powder is 50m 2 / g and 350m 2 / g, preferably 90m 2 / g and 200m 2 / g. BET measurements are performed using a Micromeritics ASAP 2460 instrument.

[0044] Powder is 0.11g / cm 3 and 0.5g / cm 3 between 0.12 g / cm and preferably 0.12 g / cm 3 and 0.5g / cm 3 and more preferably 0.15 g / cm 3 and 0.5g / cm 3 The loose bulk density is between .

[0045] The powder has a residual solvent content by mass of less than 10%, preferably less than 6% and even more preferably less than 5%.

[0046] The composition of the present invention in powder form is useful for the manufacture of battery electrodes, in particular cathodes. To manufacture the electrode, the composition of the present invention is mixed with the other components of the electrode either in the form dispersed in a solvent or as such, i.e. in the dry state in a suitable mixer.

[0047] During the manufacture of electrode formulations using the compositions of the present invention, mixing is preferably carried out in an extruder, as applicants have discovered that this is the device that provides the best electrical conductivity results for formulations used in electrodes.

[0048] The present invention therefore also relates to electrodes manufactured using these powders, preferably cathodes.

[0049] According to a first preferred embodiment, the powder of the invention is mixed with an active material of the lithium NMC (nickel manganese cobalt) oxide, LFP (lithium iron phosphate), LMO (lithium manganese oxide) or LMNO (lithium manganese nickel oxide) type and a fluoropolymer and / or a non-halogenated elastomer, typically PVDF, if they are not already present in the composition of the invention, in a suitable mixer, for example a disk mixer or a planetary mixer, and then a solvent is added. The mixture obtained is deposited on a conductive plate, after which the solvent is evaporated.

[0050] According to a second preferred method, which constitutes another advantage of the present invention, it is possible to use the powder of the present invention in a solvent-free electrode compounding process (known as the "dry process"), i.e. depending on whether the electrode is an anode or a cathode, the powder of the present invention can be directly compounded with the powder of the active substance and other compounds of the electrode. Thus, all the components constituting the electrode can be directly mixed in powder form without the use of solvents, and the electrode can be shaped by hot lamination / calendering, electrospraying (electrostatic powder deposition) followed by hot lamination.

[0051] Thus, in an otherwise solventless technique, the compositions of the present invention in powder form can be advantageously used in the extrusion of cathode or anode active materials directly incorporated into a liquid or solid electrolyte, thereby producing cathodes or anodes that can be directly used in the assembly of batteries.

[0052] The present invention also relates to the use of the compositions of the invention for obtaining electrodes, cathodes or anodes, to electrodes, cathodes or anodes, preferably cathodes, obtained using the compositions of the invention formulated by the solvent route or in dry form, and to batteries obtained using these electrodes. EXAMPLES

[0053] These examples were carried out using Graphistrength® C100 carbon nanotubes (Arkema) which have a residual metal content of less than 50 ppm.

[0054] Example 1: Reference carbon nanotube liquid composition. Comparative, outside the scope of the invention.

[0055] In this example, a typical practical carbon nanotube composition that has been used in the industry is reproduced. Thus, the carbon nanotube-containing composition is 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, which constitutes the objective achieved by the composition of the present invention.

[0056] 100 g of carbon nanotubes, 25 g of PVP (polyvinylpyrrolidone) (weight average molecular weight 24000 g / mol) and 1000 g of N-methylpyrrolidone are introduced into a deflocculator. The mixture is homogenized in the deflocculator and then processed in a horizontal ball mill so that the particles of carbon nanotubes are dispersed. The balls used have a diameter of 0.6 mm and the milling time is 200-260 min. Additional N-methylpyrrolidone (166 g) is added so that a flowable and easy-to-handle composition is obtained.

[0057] The viscosity of the dispersion obtained, denoted Dref, is measured with a Brookfield viscometer. The composition obtained, Dref, has a carbon nanotube content of 7.68% and a viscosity of 600 centipoise at 25° C.

[0058] Example 2: Preparation of the reference electrode (cathode). 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, called NMC 622, containing a Ni:Mg:Co ratio of 6:2:2, and PVDF with N-methylpyrrolidone (sold by Arkema under the name Kynar HSV 1810), for 30 minutes, to obtain a paste containing all the constituent compounds of the cathode. The formulation obtained, expressed in dry form, has the following mass percentages: · 97.75% NMC 622; · 1% carbon nanotubes; 1% PVDF; 0.25% PVP.

[0059] The solids content is 74%.

[0060] The electrodes are prepared by coating using a scene film applicator 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 that constitutes the insulating support. Drying in a ventilated oven is carried out for 2 h at 120 °C.

[0061] The dried electrode is then calendered to achieve a final film thickness of about 80 μm.

[0062] To calculate the resistivity, the PET-supported electrodes are cut into 3 x 4 cm moulds. The edges of the moulds are coated with silver lacquer. Once the lacquer has dried, the resistivity (R) is measured with an ohmmeter at 25°C.

[0063] The value of resistivity R is a good indicator of the performance of the carbon-based additive (in this case carbon nanotubes).

[0064] A resistance of 7 ohms is measured on this electrode, this value constituting the benchmark and therefore the target value to be achieved within the context of the present invention.

[0065] Example 3: Dry form composition of carbon nanotubes according to known prior art. Comparative Example 2, outside the invention.

[0066] This embodiment is carried out according to EP 2 550 699.

[0067] 4 kg of carbon nanotubes are mixed with 200 g of PVP (weight average molecular weight 24000 g / mol). After adding 14 L of demineralized water, the mixture is homogenized in a 60 L rotary mixer.

[0068] The mixture is then introduced into the hopper of a Clextral BC21 extruder by a gravimetric metering device set at 15 kg / h, and the resulting strands are subsequently pelletized appropriately. The temperature control system of the extruder is set at 50°C. The rotation speed of the screw is 400 rpm. Cylindrical pellets with a diameter of 4-5 mm and a length of 3-20 mm are obtained.

[0069] The pellets are then dried in a ventilated oven at 140° C. for 4 hours.

[0070] The bulk density of the pellets is 1.2 g / cm 3 These pellets were pulverized in a gas jet mill to obtain D v A powder with a particle size of 90<100 μm is obtained, which after grinding has a loose bulk density of 0.85 g / cm 3 The resulting powder was designated P0 and had an apparent specific surface area of ​​34 m2 as measured by BET. 2 / g. BET measurements are performed using a Micromeritics ASAP 2460 instrument.

[0071] The loose bulk density (LBD) is defined as the ratio of the mass of a powder to its volume after it has been loosened.

[0072] The measurement is taken at 100 cm of mass T. 3 This is done by slowly rotating a closed graduated cylinder several times and measuring the maximum volume occupied by the powder in it. Weighing is done using a balance with an accuracy of 0.1 g.

[0073] The cylinder is filled to three-quarters full, then weighed to mass m1, closed and slowly rotated several times until the maximum volume occupied by the powder is obtained. The occupied volume is cm 3 The unit is displayed as v.

[0074] g / cm 3 The loose bulk density, expressed as: LBD=(m1-T) / v

[0075] Example 4: Composition of carbon nanotubes and PVP according to the present invention.

[0076] The composition described in Example 1 is prepared in an identical manner except that N-methylpyrrolidone is replaced with water.

[0077] The composition of the solid component is as follows: 100 g carbon nanotubes and 25 g polyvinylpyrrolidone (PVP), with a carbon nanotube / PVP mass ratio of 4 / 1. The mixture is homogenized with 1000 g water in a deflocculator and then ground in a horizontal ball mill as described in Example 1. Additional water was added during grinding to adjust the viscosity.

[0078] At the end of the grinding, the solids content is 6% by weight and the proportion of carbon nanotubes is 4.8%. The final viscosity is 500 centipoise.

[0079] The aqueous dispersion is then dried in an atomizer: the dispersion is atomized in the presence of a stream of air preheated to various temperatures.

[0080] The solid compositions P1 to P4 are collected in powder form at the outlet of the atomizer under the conditions shown in Table 1. [Table 1] TIFF2025515077000001.tif41170T: Temperature of preheated air entering the atomizer in °C. LBD: Loose bulk density. H: Residual moisture in mass%. S: apparent specific surface area, BETm 2 / g. G: Particle size distribution, D in μm v 10 / D v 50 / D v 90.

[0081] The four powder samples P1-P4 obtained upon completion of spraying are then treated in a vacuum oven to remove any residual moisture.

[0082] The powder formulation of this example is used directly in the formulation of an NMC cathode type electrode, as described in Example 2.

[0083] All the formulations obtained in this example have a much lower bulk density compared to the solid ground agglomerate of Example 3 (P0). The apparent specific surface area of ​​P2, P3, P4 is higher than that of P0 and P1.

[0084] Example 5: Production of cathode ink using carbon nanotube powders P1 to P4 and sample P0 of Example 3, and evaluation of the cathode.

[0085] To prepare cathodes of the formulation described in Example 2, two methods are used.

[0086] Method 1: The formulation is identical to that of Example 2, but powders P0 to P4 are used instead of dispersion Dref of Example 1.

[0087] NMC 622, PVDF Kynar HSV8010, and powders P0-P4 were dry premixed in a planetary mixer and then mixed in a disc mixer for 40 min at 50 °C. N-methylpyrrolidone was gradually added to maintain the viscosity of the resulting cathode ink within 6000-10000 centipoise.

[0088] Method 2: In this method, the cathode paste is produced from the ground pellet dried product P0, P1-P4 powders obtained by atomization, the active material and the PVDF binder according to a proprietary extrusion method. In this case, the liquid Dref cannot be used. A mixture of NMC 622 and PVDF Kynar HSV8010 is extruded successively with the powders P0-P4 using a micro-extruder sold by DSM. NMP and then powder P are introduced together with the mixture of NMC 622 and PVDF Kynar HSV8010. NMP is added to the solid mixture and adjusted so that the viscosity of the resulting ink is between 6000 and 10000 centipoise and used to produce the electrodes as described in example 2.

[0089] The following identical steps are carried out for the powders P0 to P4. - introduction of 9.35 ml of NMP into an extruder preheated to 50°C; - Once NMP is introduced, increase screw speed to 240 rpm; - 42.6 g of powder P is gradually introduced over 30-60 seconds together with a mixture of NMC 622 and PVDF Kynar HSV8010; the torque is continuously monitored; it is adjusted to maintain it in the range of 1000-1400 N.m in NMP. - Once the torque has stabilized, 4.9g of NMP is gradually introduced over 30-60 seconds; the torque is gradually reduced to 100N.m. - The cathode ink is collected at the extruder outlet. The solid content is 76-78%. Five cathode inks are obtained using the five powders P0, P1, P2, P3, and P4 used to manufacture the electrodes as described in Example 2.

[0090] The cathodes produced as described in Example 2 from the inks obtained by the two methods have similar thicknesses, on the order of 78-82 μm, and their resistances are shown in Table 2. The values ​​of a reference cathode produced by the conventional method from a liquid dispersion can be seen. [Table 2] TIFF2025515077000002.tif61170

[0091] These results show that the cathodes obtained from the compositions of the invention show better electrical performance than those of the prior art, such as the powder obtained from pellets of EP 2550699 (P0), but give the same results in terms of electrical performance as the NMP-based carbon nanotube dispersion of Example 1 (Dref). As a result of atomization at airflow temperatures above 120°C, particles with lower relative density show results closer to the standard. It can therefore be concluded that carbon nanotubes that can be used for such applications must have a relative density of less than 0.5.

[0092] The extrusion method (method 2) gives results that are closest to the criteria of example 2. The use of powder P0 obtained from the pellets of EP 2 550 699 gives results that always deviate compared to the product of the invention.

[0093] Example 6: Absorbance measurements.

[0094] The dry powders (P0 and P4) were introduced in NMP at 6% by weight at ambient temperature.

[0095] After mixing for 30 minutes at 600 rpm in a disc mixer, the exact solids content was evaluated on a thermobalance. A diluted solution of 50±2 ppm was prepared.

[0096] The absorbance is measured using a HACH DR1900 spectrophotometer at a light wavelength of 360 nm.

[0097] Absorbance (A), also known as optical density (OD), is the amount of light absorbed by the dispersion. A higher absorbance A indicates that the particles are better dispersed within the dispersion volume (Table 3). [Table 3] TIFF2025515077000003.tif24170

[0098] The dispersion prepared from powder P4 of the present invention has an absorbance equivalent to that of Dref in Example 1 and much higher than that obtained from P0, indicating that the carbon nanotubes obtained from P4 are well dispersed in the solvent.

[0099] Example 7: This example evaluates the synergistic effect of the combination of carbon black and carbon nanotubes in electrodes made using the composition of the present invention compared to prior art compositions (the solvent-based route of Example 1, using pellets obtained from P0 of EP 2550699, mixing P2 with carbon black and drying).

[0100] Best results are obtained in combination with carbon black during the spraying process (Table 5).

[0101] The electrodes are prepared according to the ingredient ratio recipe in Table 4. [Table 4] TIFF2025515077000004.tif32170

[0102] Table 5 shows the measured resistance of cathodes made by mixing carbon nanotubes and carbon black in four different ways. The mixtures made before spraying according to the composition of the present invention have the best properties when formulated as electrodes. The synergistic effect of carbon nanotubes and carbon black is maximized using the procedure and composition of the present invention. [Table 5] TIFF2025515077000005.tif31170

Claims

1. A composition comprising carbon nanotubes and at least one polymer in a carbon nanotube / polymer mass ratio of less than 100 / 5, the composition having a mass ratio between 0.11 and 0.5 g / cm ３ It is in the form of a powder with a loose bulk density between 50 and 350 mm, measured with the aid of a Micromeritics ASAP 2460 instrument. ２ / g and a mass content of solvent of less than 10%, the polymer being selected from modified polysaccharides, polyvinylpyrrolidone homopolymers or copolymers, the loose bulk density (LBD) being defined as the ratio of the mass of the powder to its volume after loosening, the measurement being carried out at 100 cm ３ This is done by slowly rotating a closed female cylinder several times to measure the maximum volume occupied by the powder of mass T therein. The weighing is done using a balance with an accuracy of 0.1 g, filling the cylinder to three-quarters, then weighing to mass m1, closing it, and then measuring v (cm ３ ) is obtained, resulting in a maximum volume occupied by the powder, indicated as g / cm ３ and has a loose bulk density calculated by the following formula: LBD=(m1-T) / v.

2. 2. The composition of claim 1, wherein the polymer is selected from polyvinylpyrrolidone homopolymers or copolymers having a molecular weight between 20,000 and 60,000 g / mol.

3. 3. The composition of claim 1 or 2, further comprising carbon black in a weight ratio of carbon nanotubes / carbon black in the range of 100 / 1 to 1 / 100.

4. 4. The composition of any one of claims 1 to 3, further comprising at least one organic carbonate, such as ethyl carbonate, propyl carbonate, diethyl carbonate, dimethyl carbonate and fluoroethylene carbonate, alone or in admixture.

5. 5. The composition according to any one of claims 1 to 4, further comprising at least one compound, alone or in admixture, 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 the form of an acid or a lithium salt, in particular 4,5-dicyano-2-(trifluoromethyl)imidazole in the form of an acid or a lithium salt.

6. 6. The composition of claim 1, further comprising PVDF, a homopolymer or copolymer and / or a non-halogenated elastomer.

7. A method for preparing a composition according to any one of claims 1 to 6 using an atomizer, comprising the steps of: - preparing a composition according to any 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 containing carbon nanotubes; atomizing the dispersion with a gas heated to a temperature above 120° C. and recovering the powder; The method includes:

8. A method for producing the composition according to any one of claims 1 to 6, comprising the step of: adding supercritical CO in a mass proportion of 25% to 1000% of the composition; ２ during the extrusion process to extrude the composition, thereafter degassing the CO2, and recovering the powder.

9. 7. Use of a composition according to any one of claims 1 to 6 for the manufacture of a solvent-based or solvent-free electrode.

10. 10. An electrode obtained according to the use according to claim 9.

11. A battery comprising at least one electrode according to claim 10.

Images