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• • H—ELECTRICITY
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  • C08J2201/00—Foams characterised by the foaming process
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  • C08J2201/00—Foams characterised by the foaming process
  • C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
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  • C08J2433/04—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers esters
  • C08J2433/14—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers esters of esters containing halogen, nitrogen, sulfur, or oxygen atoms in addition to the carboxy oxygen
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  • C08J2479/00—Characterised by the use of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen, or carbon only, not provided for in groups C08J2461/00 - C08J2477/00
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  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/13—Energy storage using capacitors

Definitions

• the present invention relates to a gelled, uncured and undried aqueous polymeric composition capable of forming a non-monolithic organic airgel by drying, this airgel, a non-monolithic porous carbon resulting from a pyrolysis of this airgel, an electrode based on this porous carbon. , and a process for preparing this composition and this airgel.
• the invention applies in particular to supercapacitors for example adapted to equip electric vehicles.
• Organic aerogels are very promising for use as thermal insulators, because they have thermal conductivities that can be only 0.012 Wm “1 K “ 1 , ie close to those obtained with silica aerogels (0.010 Wm -1 K “1 ). Indeed, they are highly porous (being both microporous and mesoporous) and have a specific surface area and a high pore volume.
• Organic high surface area aerogels are typically prepared from a resorcinol-formaldehyde resin (abbreviated RF). These resins are particularly interesting for obtaining these aerogels, because they are inexpensive, can be implemented in water and allow to obtain different porosities and densities depending on the conditions of preparation (ratios between reagents, choice of catalyst, etc.).
• the gel formed by such a resin is usually an irreversible chemical gel, obtained by polycondensation of the precursors and which can no longer be used. In addition, at high conversion, this gel becomes hydrophobic and precipitates, which induces mechanical stresses in the material and therefore greater fragility.
• Organic resorcinol-formaldehyde aerogels can be pyrolyzed at temperatures above 600 ° C under an inert atmosphere to obtain carbon aerogels (i.e., porous carbons). These carbon aerogels are interesting not only as stable thermic insulators at high temperatures, but also as electrodes active material for supercapacitors.
• supercapacitors are electrical energy storage systems particularly interesting for applications requiring the conveyance of high power electrical energy. Their ability to charge and discharge fast, their longer life compared to a high power battery make them promising candidates for many applications.
• Supercapacitors generally consist of the combination of two conductive porous electrodes with a high specific surface area, immersed in an ionic electrolyte and separated by an insulating membrane called "separator", which allows ionic conductivity and avoids electrical contact between the electrodes. Each electrode is in contact with a metal collector for the exchange of electric current with an external system.
• This article also adds on page 30 (left-hand column, first paragraph) that as an example "control” was prepared a gel in powder form with a molar ratio P / R ten times greater than that used for monolithic gel. Given the number average molecular weight of P equal to 4763 g / mol, it can be deduced that the mass ratios P / R used for the preparation of the monolithic and powder gels are respectively 0.69 and 6.91.
• the irreversible chemical monolithic gels presented in this article have the major drawbacks of having a very low viscosity which renders them totally incapable of being coated with a thickness of less than 2 mm and, in particular for high volumes of gels which are difficult to dry effectively, to require an intermediate step of transformation of the monolithic organic airgel into airgel powder (to be agglomerated with or without a binder to obtain the final electrode). Starting from a monolith, it is therefore necessary to go through a grinding step which is expensive and little controlled.
• a porous carbon into a supercapacitor electrode, it is particularly known from US-B2-6 356 432, US-A1 -2007/0146967 and US-B2-7,811,337 to disperse it in the form of microparticles in a binder. organic non-active and in a solvent, then coat the paste obtained on a current collector. It is then possible to obtain a deposited thickness of less than 200 ⁇ m and to wind the electrodes corresponding to form a cylindrical supercapacitor, since it is porous carbon in the form of microparticles.
• the latter method has the disadvantage of requiring an organic solvent before the drying step.
• the aerogels are obtained in the form of nanoparticles that can pose toxicity problems.
• the porosity of the material is indeterminate.
• An object of the present invention is to provide an aqueous gelled, non-dried, crosslinked polymeric composition capable of forming a non-monolithic organic airgel directly in the form of microparticles, which overcomes the aforementioned drawbacks by being obtained by a simple and inexpensive method and with fast drying that does not require the use of an organic solvent or supercritical drying.
• a gelled, uncured and undried aqueous composition according to the invention which is based on a resin derived at least in part from a polycondensation of polyhydroxybenzene (s) R and of formaldehyde (s) F and which comprises at least one polyelectrolyte
• the water-soluble cationic substance P is thus such that the composition is formed of an aqueous dispersion of microparticles of a rheofluidifying physical gel crosslinked in an aqueous medium.
• this gelled composition according to the invention in the form of a dispersion of gelled microparticles makes it possible to avoid the step of grinding the gel which was required for satisfactory drying of the monolithic gels of the prior art, by leading directly to an airgel. powder by simple steaming.
• this aqueous dispersion advantageously makes it possible to obtain the gelled compositions according to the invention in a reduced time compared with the gelling processes of the aforementioned prior art implemented in a closed mold.
• gel in known manner the mixture of a colloidal material and a liquid, which is formed spontaneously or under the action of a catalyst by flocculation and coagulation of a colloidal solution.
• rheofluidifying gel means a gel with non-Newtonian and time-independent rheological behavior, sometimes also called pseudoplastic and which is characterized by the fact that its viscosity decreases when the gradient shear rate increases.
• water-soluble polymer is meant a polymer which can be solubilized in water without the addition of additives (surfactants in particular), unlike a water-dispersible polymer which is capable of forming a dispersion when it is mixed with some water.
• the composition according to the invention has the advantage, thanks to the reversible rheofluidifying gel, that it can be used in the form of a thin layer and have improved mechanical properties.
• the unmodified RF resins of the prior art formed directly from their precursors an irreversible chemical gel which could not be coated as a thin layer and which deformed to a small thickness during the pyrolysis of the gel.
• said cationic polyelectrolyte P has a coagulating effect and makes it possible to neutralize the charge of the phenolates of the polyhydroxybenzene R and thus to limit the repulsion between pre-polymer colloids, favoring the formation and agglomeration of polymeric nanoparticles. at low conversion of the polycondensation reaction.
• the precipitation occurring before the crosslinking of the composition according to the invention the mechanical stresses are lower at high conversion when the gel is formed.
• the gelled composition of the invention can be dried more easily and rapidly - by simple curing - than the aqueous gels of the prior art.
• This drying in an oven is indeed much simpler to implement and penalizes less the cost of production of the gel than the drying carried out by solvent exchange and supercritical CO 2 .
• said at least one polyelectrolyte P5 makes it possible to preserve the high porosity of the gel after drying in an oven and to give it a low density combined with a specific surface area and a high pore volume, it being specified that this gel according to The invention is mainly microporous which advantageously allows to have a specific energy and a high capacity for a supercapacitor o electrode consisting of this pyrolyzed gel.
• said microparticles may have a median particle size distribution, measured by a laser diffraction granulometer in a liquid medium, which is between 1 ⁇ m and 100 ⁇ m.
• microparticles are distinguished from the potentially toxic nanoparticles forming the airgel obtained in the aforementioned document US-A1-2012 / 0286217.
• the mass fraction of said gel in said aqueous dispersion which characterizes the dilution of the solution of said prepolymer o can be between 10% and 40% and preferably between 15% and 30%.
• the mass ratio P / R may be less than 0.5 and is preferably between 0.01 and 0.1.
• said gel may be a precipitated pre-polymer which is the product of a prepolymerization and precipitation reaction of an aqueous solution of polyhydroxybenzene (s) R, (s) formaldehyde (s) F, of said at least one cationic polyelectrolyte P and an acidic or basic catalyst C in an aqueous solvent W, the composition being free of any organic solvent.
• this product of the prepolymerization and precipitation reaction may comprise:
• said at least one cationic polyelectrolyte P in a mass fraction of between 0.2% and 3%, and / or
• Said at least one polyelectrolyte P that can be used in a composition according to the invention may be any cationic polyelectrolyte totally soluble in water and of low ionic strength.
• said at least one cationic polyelectrolyte P is an organic polymer selected from the group consisting of quaternary ammonium salts, polyvinylpyridinium chloride, polyethyleneimine, polyvinylpyridine, poly (allylamine hydrochloride), poly (trimethylammonium chloride ethyl methacrylate), poly (acrylamide-dimethylammonium chloride) and mixtures thereof.
• said at least one cationic polyelectrolyte P is a salt comprising units derived from a quaternary ammonium chosen from poly (diallyldimethylammonium halide), and is preferably poly (diallyldimethylammonium chloride) or poly (diallyldimethylammonium halide). diallyldimethylammonium bromide).
• polyhydroxybenzenes that may be used are preferably di- or tri-hydroxybenzenes, and advantageously resorcinol (1,3-dihydroxybenzene) or the mixture of resorcinol with another compound chosen from catechol, hydroquinone and phloroglucinol.
• polyhydroxybenzene (s) R and formaldehyde (s) F may be used in a molar ratio R F of between 0.3 and 0.7.
• said pre-polymer forming said rheofluidifying physical gel of the composition according to the invention may have in the uncrosslinked state a viscosity measured at 25 ° C. by a Brookfield viscometer which, at a shear rate of 50 rpm , is greater than 100 mPa.s and is preferably between 150 mPa.s and 10000 mPa.s, it being specified that at 20 rpm, this viscosity is greater than 200 mPa.s and preferably greater than 250 mPa.s .s.
• a non-monolithic organic airgel according to the invention is derived from a drying of said gelled, crosslinked and undried composition described above with reference to the invention, and this airgel is such that it is formed of a powder of said microparticles dried by heating in an oven, said dried microparticles having a median particle size distribution, measured by a laser diffraction granulometer in a liquid medium, which is between 10 pm and 80 pm.
• this particle size of the microparticles of the airgel is particularly well suited for obtaining optimized properties of supercapacitor electrodes incorporating a pyrolysate of this airgel, as indicated below.
• said airgel may have a specific surface area and a pore volume, both of which are predominantly microporous, preferably greater than 60%.
• this essentially microporous structure is defined by definition with pore diameters of less than 2 nm, unlike mesoporous structures such as those obtained in the aforementioned article by Mariano M. Bruno et al. which by definition are characterized by pore diameters inclusively between 2 nm and 50 nm.
• said airgel may have a thermal conductivity less than or equal to 40 mW.m -1 .K -1 (also unlike the aforementioned article), thus belonging to the family of super-insulating materials.
• a non-monolithic porous carbon according to the invention is derived from a pyrolysis of said organic airgel implemented at a temperature typically greater than 600 ° C., and this porous carbon is such that it is formed of a powder of microspheres having a median particle size distribution, measured by a laser diffraction granulometer in a liquid medium, between 10 ⁇ m and 80 ⁇ m and preferably between 10 ⁇ m and 20 ⁇ m.
• said porous carbon may have:
• a total surface area equal to or greater than 500 m 2 / g, with a microporous specific surface area greater than 400 m 2 / g and a mesoporous specific surface area of less than 200 m 2 / g (unlike the article cited above for the test leading to a gel in the form of powder), and / or
• a pore volume equal to or greater than 0.25 cm 3 / g, of which a microporous volume greater than 0.15 cm 3 / g.
• An electrode according to the invention can be used to equip a supercapacitor cell by being immersed in an aqueous ionic electrolyte, the electrode covering a metal current collector, and this electrode comprises said porous non-monolithic carbon as an active ingredient and has a thickness less than 200 ⁇ m.
• this electrode has a geometry wound around an axis, for example substantially cylindrical.
• the porous carbon microspheres according to the invention are incorporated directly into inks, and they are coated on a metal collector before being dried.
• a process for preparing said gelled, uncured and undried aqueous polymeric composition comprises successively:
• step a) said at least one cationic polyelectrolyte P and said polyhydroxybenzene (s) R are used in a mass ratio P / R of less than 0.5 and preferably of between 0. , 01 and 0.1.
• said at least one cationic polyelectrolyte P in a mass fraction of between 0.2% and 3%;
• catalyst usable in step a mention may be made for example of acidic catalysts such as aqueous solutions of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, phosphoric acid, trifluoroacetic acid, trifluoromethanesulfonic acid, perchloric acid, oxalic acid, toluenesulfonic acid or dichloroacetic acid, formic, or basic catalysts such as sodium carbonate, sodium hydrogencarbonate, potassium, ammonium carbonate, lithium carbonate, ammonia, potassium hydroxide and sodium hydroxide.
• acidic catalysts such as aqueous solutions of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, phosphoric acid, trifluoroacetic acid, trifluoromethanesulfonic acid, perchloric acid, oxalic acid, toluenesulfonic acid or dichloroacetic acid, formic, or basic catalysts such as sodium carbonate, sodium hydrogencarbon
• step d) is carried out at a temperature of between 10 ° C. and 30 ° C. and according to a mass fraction of said pre-polymer in said aqueous dispersion of between 10% and 40% and preferably comprised between 10% and 40%. between 15% and 30%.
• step e) is carried out under reflux, for at least 1 hour with stirring and at a temperature of between 80 ° C. and 110 ° C., to completely polymerize said gel.
• this process may comprise, after step e), a separation step f) applied to said aqueous dispersion of said crosslinked prepolymer comprising sedimentation and elimination of the supernatant water of the dispersion, or filtration of said dispersion.
• this process may advantageously be devoid of any use of an organic solvent and any step of obtaining and then grinding a monolithic gel.
• a method of preparation according to the invention of said non-monolithic organic airgel is such that said gelled, crosslinked and undried composition is dried by heating in an oven without solvent exchange or drying by a supercritical fluid.
• the following examples illustrate the preparation of three gelled compositions, crosslinked and undried G1 to G3 according to the invention, three aerogels AG1 to AG3 according to the invention in powder form which are respectively derived from drying and three porous carbons C1 to C3 according to the invention respectively obtained by pyrolysis of aerogels AG1 to AG3, in comparison with a gelled and crosslinked "control" GO composition, an airgel AGO also in powder form and a porous carbon C0 which in are from.
• the Applicant has prepared the GO gel, the AGO airgel and the C0 porous carbon under the conditions set forth in the "control" example on page 30 of the aforementioned article by Mariano M. Bruno et al., Who mentioned as a comparative test the preparation of a non-monolithic gel.
• a catalyst (C) consisting of sodium carbonate or hydrochloric acid
• R / C molar ratio between resorcinol and catalyst
• the non-viscous mixture was prepolymerized in a reactor immersed in an oil bath at 70 ° C. for 30 minutes.
• the prepolymer formed was then cooled to 15 ° C. and then diluted 25% in water at 25 ° C.
• the resulting mixture was refluxed to allow complete polymerization (crosslinking) of the gel.
• RF An aqueous dispersion of microparticles of the crosslinked G1 gel was then obtained.
• the dilution and refluxing conditions are shown in Table 2 below.
• the airgel AG1 was pyrolyzed under nitrogen at 800 ° C. to obtain microspheres.
• the non-viscous mixture was prepolymerized in a reactor immersed in an oil bath at 45.degree. 45 minutes. The formed mixture was then placed in a refrigerator at 4 ° C for 24 hours. The prepolymer formed was then diluted with water. The resulting mixture was then heated to reflux to allow complete polymerization (crosslinking) of the RF gel. An aqueous dispersion of microparticles of the crosslinked G2 gel was then obtained. Dilution and refluxing conditions are listed in Table 2.
• the airgel AG2 was pyrolyzed under nitrogen at 800 ° C. to obtain microspheres.
• the non-viscous mixture was prepolymerized in a reactor immersed in an oil bath at 70 ° C. for 45 minutes. The formed mixture was then placed in a refrigerator at 4 ° C for 24 hours. The prepolymer formed was then diluted with water. The resulting mixture was then heated to reflux to allow complete polymerization (crosslinking) of the RF gel. An aqueous dispersion of microparticles of the crosslinked G3 gel was then obtained. Dilution and refluxing conditions are listed in Table 2.
• the airgel AG3 was pyrolyzed under nitrogen at 800 ° C. to obtain microspheres.
• aerogels AG1 and AG3 and the porous carbons C1 and C2 according to the invention are in the form of microparticles of average size in volume between 50 pm and 70 pm.
• each organic airgel AG0-AG3 and each porous carbon C0-C3 obtained by the nitrogen adsorption manometry technique at 77 K were characterized by means of devices TRISTAR 3020 and ASAP 2020 from Micromeritics.
• the results of specific surfaces (respectively total, microporous and mesoporous) and of pore volumes (respectively total and microporous) are presented in Table 4 below. Table 4:
• the organic aerogels AG1-AG3 and the porous C1-C3 carbons according to the invention each have, in spite of the aqueous dispersion used, a specific surface area (greater than 500, or even 600 m 2 / g) and a porous volume sufficiently high to be incorporated in supercapacitor electrodes, with a microporous fraction greater than 80%, or even 90% for this specific surface area and greater than 60%, or even 80% for this pore volume.
• the Applicant has verified that the porous carbon C0 according to the "control" test of said article has a specific surface much too low to be used as an active material of a supercapacitor electrode.
• Carbon electrodes E1, E2, E3 are also produced respectively from the porous carbons C1, C2, C3.
• binders, conductive fillers, various additives and microspheres of each porous carbon were mixed with water according to the method described in Example 1 of FR-A1-2 985 598 in the name of the Applicant. .
• the resulting formulation was coated and cross-linked on a metal collector. We have measured the capacitance of electrode E2 electrochemically using the device and the following tests.
• Electrodes isolated by a separator were mounted in series in a supercapacitor measuring cell containing the aqueous electrolyte (LiNO 3, 5M) and driven by a "Bio-Logic VMP3" potentiostat / galvanostat via a three-way interface. electrodes.
• the first electrode corresponds to the working electrode, the second form the counter electrode and the reference electrode is calomel.
• This capacity was measured by subjecting the system to charge-discharge cycles at a constant current I of 1 A g. Since the potential evolves linearly with the load conveyed, the capacity of the supercapacitive system of the slopes p has been deduced from the load and the discharge. The specific capacity of the electrode E2 thus measured was 90 F / g.
• the thermal conductivity of the pulverulent airgel AG3 obtained according to the invention was measured at 22 ° C. with a Neotim conductivity meter according to the hot wire technique, and this conductivity thus measured was 30 mW.m -1 .K " 1 .

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• 2014
  • 2014-04-07 WO PCT/FR2014/050827 patent/WO2015155419A1/fr active Application Filing
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