GELLED AQUEOUS POLYMER COMPOSITION, PYROLYSED CARBONATED COMPOSITION PRODUCED THEREFROM FOR A SUPERCAPACITOR ELECTRODE, AND METHODS FOR THE PRODUCTION THEREOF

Abstract

The invention relates to a gelled aqueous polymer composition for forming, by means of drying then pyrolysis, a monolithic porous carbon, to a pyrolysed carbonated composition produced by the drying, followed by the pyrolysis, of said gelled composition, to a porous carbon electrode for a supercapacitor comprising said pyrolysed composition, and to methods for producing said respectively gelled and pyrolysed compositions. A gelled composition according to the invention, produced from the polycondensation of polyhydroxybenzene(s) and hexymethylenetetramine, is such that the hexymethylenetetramine comprised therein represents a mass fraction of between 7% and 15% inclusive. Said gelled composition is produced by a) polycondensation in an aqueous solvent of the polyhydroxybenzene(s) and hexymethylenetetramine, followed by b) gelling by heating of said polycondensate.

Claims

1. A gelled aqueous polymer composition capable of forming, by drying and then pyrolysis, a monolithic porous carbon, the composition comprising the product of a polycondensation reaction in an aqueous solvent W of polyhydroxybenzene(s) R and hexamethylenetetramine H, wherein the polycondensation reaction is performed such that an H/(R+H+W) fraction by weight is between 7% and 15% inclusive.

2. The gelled composition of claim 1, wherein the H/(R+H+W) fraction by weight is between 10% and 14% inclusive.

3. The gelled composition of claim 1, wherein the polycondensation reaction is performed such that an R/H molar ratio of the polyhydroxybenzene(s) R and the hexamethylenetetramine H is between 2 and 4 inclusive.

4. The gelled composition of claim 1, wherein the polycondensation reaction is performed such that an R/W ratio of the polyhydroxybenzene(s) R and the aqueous solvent W is between 0.07 and 1 inclusive.

5. The gelled composition of claim 1, wherein the composition is devoid of any amphiphilic polymer, any hydrophobic compound, or any mixture thereof.

6. The gelled composition of claim 1, wherein: the aqueous solvent W is water; and formaldehyde is not present in the polycondensation reaction.

7. A pyrolyzed carbon-based composition which is obtained by drying and then pyrolysis of the gelled composition of claim 1 and which forms a monolithic porous carbon with a specific surface of greater than 550 m.sup.2/g and with a pore volume of less than 0.50 cm.sup.3/g, wherein: the pore volume is microporous with diameters of pores of less than 2 nm according to a fraction by volume of greater than 50%; and the specific surface is microporous with diameters of pores also of less than 2 nm according to a fraction by surface equal to or greater than 80%, the pore volume and the specific surface being measured by nitrogen adsorption manometry at 77K.

8. The pyrolyzed composition of claim 7, wherein: the specific surface is equal to or greater than 580 m.sup.2/g;and the pore volume is less than or equal to 0.40 cm.sup.3/g.

9. The pyrolyzed composition of claim 7, wherein the pore volume is microporous according to a fraction by volume of greater than 55%.

10. The pyrolyzed composition of claim 9, wherein the pore volume is microporous according to a fraction by volume equal to or greater than 70%.

11. A porous carbon electrode adapted to function as an electrode in a supercapacitor cell, wherein the porous carbon electrode comprises, as active material, a pyrolyzed composition of claim 7.

12. A process for preparing the gelled composition of claim 1, the process comprising: a) performing a polycondensation reaction in an aqueous solvent W of polyhydroxybenzene(s) R and hexamethylenetetramine H in order to obtain a polycondensate in an aqueous medium; and then b) a gelling by heating the polycondensate, in order to obtain the gelled composition.

13. The process of claim 12, comprising: a1) dissolving the polyhydroxybenzene(s) R in a first portion of the aqueous solvent W, in order to obtain a first aqueous solution; a2) dissolving by heating the hexamethylenetetramine H in a second portion of the aqueous solvent, in order to obtain a second aqueous solution; and a3) contacting the first aqueous solution with the second aqueous solution, until a third homogeneous aqueous solution comprising the polycondensate is obtained.

14. A process for preparing the pyrolyzed carbon-based composition of claim 7, the process comprising: a) performing a polycondensation reaction in an aqueous solvent W of polyhydroxybenzene(s) R and hexamethylenetetramine H in order to obtain a polycondensate in an aqueous medium; b) gelling by heating the polycondensate in order to obtain the gelled composition; c) drying of the gelled composition; and then d) performing a pyrolysis of the gelled and dried composition obtained in c), in order to obtain the porous carbon.

15. The process of claim 14, further comprising, after step d), a step e) of: (e) activating the porous carbon by impregnation of the porous carbon with a sulfur-comprising strong acid.

Description

EXAMPLES OF PREPARATION ACCORDING TO THE INVENTION OF GELLED AND PYROLYZED COMPOSITIONS, IN COMPARISON WITH A CONTROL EXAMPLE OF SUCH COMPOSITIONS

[0045] Two gelled aqueous polymer compositions G1 and G2 according to the invention, corresponding to examples 1 and 2 below, both resulting from the polycondensation of resorcinol R (from Acros Organics, 98% pure) and hexamethylenetetramine H (supplied by Sigma-Aldrich), and a control gelled aqueous polymer composition G0, resulting from the polycondensation of the same resorcinol R but with formaldehyde F (from Acros Organics, 37% pure) in place of hexamethylenetetramine, were prepared.

[0046] The formulations used for these three compositions G1, G2 and GO are described in detail in table 1 below, with:

[0047] R/H: resorcinol/hexamethylenetetramine molar ratio,

[0048] R/W: resorcinol/water ratio by weight, and

[0049] % H: fraction by weight of hexamethylenetetramine in each gelled composition G1 and G2.

TABLE-US-00001 TABLE 1 G1 G2 G0 Resorcinol R 175.21 g 175.21 g 175.21 g Hexamethylenetetramine H 74.36 g 74.36 g Formaldehyde F 258.30 g Distilled water 350.42 g 292.02 g 311.20 g R/H 3 3 R/W 0.5 0.6 0.4 % H 12.39 13.73

[0050] Preparation of Gelled Compositions G1, G2 and G0 and of Pyrolyzed Compositions C1, C2 and C0 Which Result Therefrom:

[0051] During a first step, the resorcinol was first dissolved in half of the distilled water with magnetic stirring. At the same time, the hexamethylenetetramine for the compositions G1 and G2 was dissolved in the remaining water half using a reactor immersed in an oil bath between 40 C. and 80 C. After complete dissolution of the hexamethylenetetramine for the purpose of preparing G1 and G2, the water/resorcinol mixture was added until a homogeneous solution was obtained (in order to prepare the composition G0, formaldehyde F was used in place of hexamethylenetetramine H).

[0052] During a second step, this polycondensate solution was poured into molds with a thickness of 2 mm made of steel covered with Teflon and then gelling was carried out at 90 C. for 24 hours. The organic gels thus formed were subsequently dried at 85 C. and 85% humidity for 6 hours. The carbon-based compositions C1, C2 and C0, respectively resulting from G1, G2 and G0, were subsequently obtained by pyrolysis at 800 C. under nitrogen in the form of monolithic porous carbons. The flat monoliths obtained were machined to a set thickness of 0.7 mm and were then characterized.

[0053] During a third optional step, the porous carbon C1 thus obtained was activated using a treatment with sulfuric acid (18M H.sub.2SO.sub.4), as described in the abovementioned document EP-B1-2 455 356.

[0054] Characterization of Each Pyrolyzed Composition C1, C2 and C0:

[0055] Each composition C1, C2 and C0 prepared by carrying out these first and second polycondensation and gelling, drying and pyrolysis steps was characterized by measuring the density of each porous carbon C1, C2 and C0 by the weight/volume ratio of the monolith. The results presented in table 2 below were obtained by nitrogen adsorption manometry at 77 K on an ASAP 2020 device from Micromeritics, namely the values thus measured of respectively total, microporous and mesoporous specific surfaces and of respectively total and microporous pore volumes.

TABLE-US-00002 TABLE 2 C1 C2 C0 Density 0.89 0.96 0.68 (g .Math. cm.sup.3) Specific 600 589 800 surface 558 microporous 498 microporous 460 microporous (m.sup.2 .Math. g.sup.1) (i.e. 93%) (i.e. 84.6%) (i.e. 57.5%) 82 mesoporous 91 mesoporous 340 mesoporous (i.e. 7%) (i.e. 15.4%) (i.e. 42.5%) Pore 0.30 0.35 1.16 volume 0.22 microporous 0.20 microporous 0.20 microporous (cm.sup.3 .Math. g.sup.1) (i.e. 73.3%) (i.e. 57.1%) (i.e. 17.2%)

[0056] The porous carbons C1 and C2 according to the invention resulting from gels G1 and G2 based on hexamethylenetetramine according to a relatively high fraction by weight (in these examples, of between 10 and 14%) thus exhibit high specific surfaces (of the order of 600 m.sup.2.Math.g.sup.1) with low pore volumes (less than 0.40 cm.sup.3.Math.g.sup.1), in comparison with the pore volume, more than three times greater, which characterizes the control carbon C0 resulting from formaldehyde.

[0057] Furthermore, the micropore contribution in these two carbons C1 and C2 of the invention is very high, both for the specific surface (micropore fraction greater than 80%, indeed even 90% for the preferred carbon C1) and for the pore volume (micropore fraction greater than 50%, even greater than 70% for this carbon C1), in comparison with micropore fractions for the specific surface and the pore volume of the carbon C0, which are respectively less than 60% and than 20%.

[0058] It should be noted that carbon C0 exhibits a higher specific surface than those of the carbons C1 and C2 but a much higher pore volume, which implies that the amount of electrolyte for filling this carbon C0 is greater than for carbons C1 and C2 of the invention.

[0059] Electrochemical Tests with Porous Carbons C1 and C2:

[0060] Electrodes E1 and E2 were respectively prepared from porous carbons C1 and C2. For this, binders, conductive fillers, various additives and each porous carbon were mixed with water according to the method described in example 1 of the document FR-A1-2 985 598 on behalf of the applicant company. The formulation obtained was coated and then crosslinked on a metal collector. The capacitance of the electrodes E1 and E2 was measured electrochemically by using the following device and tests.

[0061] Two identical electrodes isolated by a separator were mounted in series within a supercapacitor measurement cell containing an aqueous electrolyte (1M H.sub.2SO.sub.4 in a first series of tests and 5M LiNO.sub.3 in a second series of tests) and controlled by a Bio-Logic VMP3 potentiostat/galvanostat via a three-electrode interface. The first carbon electrode corresponds to the working electrode, the second constitutes the counterelectrode, and the reference electrode used is the calomel reference electrode.

[0062] The capacitances of the electrodes were measured by subjecting the system to charging/discharging cycles at a constant current I of 0.125 A/g for the working electrode (positive electrode). As the potential changes linearly with the charge conveyed, the capacitance of each supercapacitive electrode was reduced from the slopes p in the charging and in the discharging (C=I/p). The mean specific capacitances thus measured for each electrode E1 and E2 can be seen:

[0063] in table 3, which gives the performances of these electrodes for a supercapacitor in an electrolyte based on 1M H.sub.2SO.sub.4, and

[0064] in table 4, for the performances of the electrodes of a supercapacitor comprising an electrolyte based on 5M LiNO.sub.3, before and after the activation post-treatment of the carbon C1 during the abovementioned third step.

TABLE-US-00003 TABLE 3 1M H.sub.2SO.sub.4 Electrolyte E1 E2 Specific capacity 170 175 positive electrode (F/g) Specific capacity 250 270 negative electrode (F/g)

TABLE-US-00004 TABLE 4 5M LiNO.sub.3 Electrolyte C1 before post- C1 after post- treatment treatment Specific capacity 115 125 positive electrode (F/g) Specific capacity 105 150 negative electrode (F/g)

[0065] These tables 3 and 4 show that the porous carbons C1 and C2 of the invention confer elevated electrochemical performances on electrodes incorporating them within a supercapacitor having an acidic or basic aqueous electrolyte, preferably with the implementation of an acid impregnation post-treatment of these porous carbons according to the invention which makes it possible to further improve the performance of these electrodes incorporating them.