WO2013150151A1

WO2013150151A1 - Hybrid electrode for a supercapacitor

Info

Publication number: WO2013150151A1
Application number: PCT/EP2013/057245
Authority: WO
Inventors: Pierre Le Barny; Laurent Divay; Christophe Galindo
Original assignee: Thales
Priority date: 2012-04-06
Filing date: 2013-04-05
Publication date: 2013-10-10
Also published as: FR2989215A1; FR2989215B1

Abstract

The invention relates to an electrode for a supercapacitor and its manufacturing process. The electrode comprises an electrically conductive first material and a macromolecular material. The macromolecular material is grafted onto the first material; said macromolecular material generates a graphitic structure by pyrolysis, thereby increasing the specific surface area of the electrodes. The first material is a metallic foam made of silver or gold or based on carbon.

Description

Hybrid electrode for supercapacitor

The invention lies in the field of energy storage and more particularly in the field of electrodes for supercapacitors.

A supercapacitor or electrochemical capacitor is a capacitor of particular technique for obtaining intermediate power and energy densities between batteries and conventional electrolytic capacitors. Most supercapacitors comprise two porous electrodes impregnated with electrolyte and separated by an insulating and porous membrane allowing the circulation of the ions contained in the electrolyte.

The basic principle of supercapacitors is based on the capacitive properties of the interface between the electrodes which are solid electrical conductors and the electrolyte which is a liquid ionic conductor. Energy storage is effected by the distribution of ions of the electrolyte in the vicinity of the surface of each electrode, under the influence of the potential difference applied between the two electrodes. It creates at the interfaces a space charge zone, called double electrochemical layer, of a thickness limited to a few nanometers. Supercapacitors are therefore capabilities in their own right. Energy storage is de facto electrostatic, not electrochemical as in the case of accumulators, which gives them a potentially high specific power.

One of the key parameters to achieve a high stored charge density is the geometry of the electrodes. Indeed, the capacitance C is proportional to the specific surface S of the electrode and inversely proportional to the thickness e of the double layer, according to the relation (i) where ε is the permittivity of the electrolyte: C = ε ( i).

The use of activated carbon as a supercapacitor electrode material is well known in the state of the art. However, since the electrical conductivity of the active carbons is very low, a metal electrode is necessary to collect the current, which reduces the performance of the supercapacitors that use this type of electrode.

It is also well known in the state of the art to use carbon nanotubes as electrode material for supercapacitors. Carbon nanotubes have higher electrical conductivity sometimes allowing them to be used as electrode material without the need for a current collector. This material implemented in the form of nanotube mattresses muiti walls, has a specific surface, of the order of 270 m ² .g ^-1 , much lower than activated carbons which have an activated surface of the order of 2000 to 3000 m ² g ^-1 .

Moreover, materials such as metal foams are also often used as electrode material for supercapacitors. Indeed, this type of material has a very good electrical conductivity and a specific surface of the order of 10 ² m ² . g ^"1 .

An object of the invention is to provide a hybrid electrode for a supercapacitor whose specific surface area is increased relative to the electrodes conventionally used such as metal foam electrodes, carbon nanotubes or activated carbon.

According to one aspect of the invention, there is provided a supercapacitor electrode comprising a first electrically conductive material and a macromolecular material. The macromolecular material is grafted onto the first material, the macromolecular material being able to generate a graphitic structure by pyrolysis. The first material is a metal foam of gold or silver or carbon-based.

In this case, the term "grafting" corresponds to the creation of a chemical bond between the first material and the macromolecular material.

Hybrid electrode material, according to one aspect of the invention allows the addition of a conductive graphite structure to the surface of the electrode which increases the specific surface area with respect to an electrode consisting solely of a material of electrode usually used.

Advantageously, the macromolecular material is polyacrylonitrile. Polyacrylonitrile makes it possible to increase the specific surface area of the first material and consequently to increase the interaction surface between the electrode and the electrolyte while limiting the increase in mass, which allows a cost saving.

According to another aspect of the invention, there is provided a method for producing an electrode as described above in which:

a macromolecular material capable of being graphitized and comprising a function capable of creating at least one covalent bond is synthesized, the macromolecular material is grafted onto said first material, and

the macromolecular material is graphitized.

Thus, producing the hybrid electrode according to one aspect of the invention allows a graphitization of the carbon precursor on the surface of the first material so as to increase its specific surface area. The graphite structure thus produced does not obstruct the pores of the first material. The distribution of the graphitic planes in the porous structure of the first material is homogeneous.

Advantageously, the grafting is carried out by heating.

Advantageously, the macromolecular material is polyacetonitrile.

In one embodiment, the first material is based on carbon and preferably carbon nanotubes.

Advantageously, the function is an azide or diazonium salt function.

In another embodiment, the first material is a metal foam, preferably gold or silver.

Advantageously, the function is a thiol function.

The invention will be better understood from the study of some embodiments described by way of non-limiting examples, and illustrated by appended drawings in which:

FIG. 1 schematically represents the grafting of a macromolecular material on a substrate comprising carbon, according to one aspect of the invention, and

FIGS. 2a, 2b and 2c show an exemplary method of producing a hybrid electrode, according to one aspect of the invention.

FIG. 1 illustrates, on the one hand, the grafting of a macromolecular material 1 on a carbon nanotube 2 to form a functionalized carbon nanotube 3a. On the other hand, Figure 1 illustrates the electrochemical growth of the macromolecule from a carbon nanotube to lead to a functionalized carbon nanotube 3b.

The macromolecular material 1, in this case polyacrylonitrile, is capable of creating a graphitized structure by graphitization and comprises a function X capable of generating covalent bonds

Preferably, the macromolecular material 1 may be a functionalized polymer which comprises a first nitrile CN side chain capable of forming a graphitized structure by graphitization, and a group X capable of forming at least one covalent bond with the first material.

Advantageously, the function X may be an azide function N ₃ or a diazonium salt -N = N ⁺ .

In this case, Figure 1 shows the grafting of a macromolecular material 1 on a carbon nanotube 2.

However, the grafting of a macromolecular material 1 via azide or diazonium salt functions can be carried out on any carbon-based structure.

The grafting can be carried out chemically or electrochemically, according to an article by P. Petrov et al. Macromolecular Rapid Communications, 25, 987-990, (2004).

By chemical means, structure 3a is obtained in which the covalent bond is created between a carbon of the carbon-based structure 2 and an intermediate carbon of the main chain of macromolecule 1.

Electrochemically, structure 3b is then obtained. The covalent bond is created between a carbon of the carbon-based structure 2 and a terminal carbon of a main chain of the macromolecular material 1.

According to a variant of the invention, it is possible to graft a macromolecular material capable of creating a graphite structure by graphitization and which comprises a function X capable of generating a covalent bond on a metal structure, such as a gold metal foam or silver.

Advantageously, the function X can be a -SH thiol group

Figures 2a, 2b and 2c illustrate the steps of an exemplary method of producing a hybrid material, according to one aspect of the invention.

In this case, it is the grafting of a copolymer 4 comprising a methacrylate monomer functionalized with an azide function 5 copolymerized with acrylonitrile 6, on carbon nanotubes 2.

Figure 2a illustrates the various steps of synthesis of the methacrylate monomer functionalized with an azide function from 4-azidobenzoic acid.

In a 100 ml three-necked flask, 1.04 g (8 mmol) of hydroxyethyl methacrylate and 1.304 g (8 mmol) of 4-azidobenzoic acid are dissolved under a stream of argon in a mixture comprising 30 mL of tetrahydrofuran THF distilled on sodium and 15 mL of dichloromethane. Then 234 mg (0.8 mmol) of 4-dimethylamino pyridinium DPTS Paratoluene Sulfonate are added and the mixture is stirred for 30 minutes at room temperature and then 1.814 g (8.8 mmol) of dicyclohexyl carbodiimide DCCI are added. It is then stirred for 20 hours at room temperature.

Urea is formed and is separated by filtration.

The filtrate is evaporated to dryness and the crude product thus obtained is purified by chromatography on 120 g of silica. The eluent used for the chromatography is a 50/50 mixture of dichloromethane and hexane and then pure dichloromethane.

1. 62 g (5.88 mmol) of yellow methacrylate are obtained, ie a yield of 73.5%.

Methacrylate is characterized by infrared spectroscopy and nuclear magnetic resonance, we obtain the following results:

IR (NaCl window; cm ^"1 ): 2125 (s, elongation -N ₃ ), 1720 (s, elongation C = O), 1637 (w, C = C methacrylate) 1603 (s, C = C aromatic)

¹ H-NMR (CDCl 3, 300 MHz, δ ppm): 1.95 (s, 3H); 4.49 (m, 2H); 4.56 (m, 2H); 5.59 (m, 1H); 6.1 (m, 1H) 7.0 (d, 2H); 8.0 (d, 2H) 13.0.

Advantageously, 4-azidobenzoic acid is synthesized according to the process presented below.

In a 100 ml beaker, 4.1 l (0.03 mole) of 4-aminobenzoic acid is dissolved in an acidic solution obtained by diluting 6.6 ml of 25% hydrochloric acid in 72 ml of water.

A first solution is obtained and is cooled to a temperature of -10 ° C.

A solution of 12.13 g (0.038 mole) of sodium nitrite in 8 mL of water is added dropwise into the first solution. The reaction medium is en masse.

The temperature is brought back to 0 ° C. After stirring for 30 minutes at a temperature of 0 ° C., the solid obtained is removed by filtration.

A yellow filtrate comprising diazonium salt is placed in a 500 ml beaker and then cooled to a temperature of -10 ° C.

Under vigorous stirring, a solution obtained by dissolving 1.95 g (0.03 mol) of sodium azide in 8 ml of water is added dropwise to the diazonium salt solution. There is abundant formation of moss. Stirring is continued for 30 minutes at -10 ° C after the addition of sodium azide. The solid is separated by filtration, washed with water and then with petroleum ether. Finally, it is dried under vacuum at room temperature.

2.81 g (0.017 mol) of 4-azidobenzoic acid is obtained, a yield of 57.4%.

FIG. 2b illustrates the synthesis of the copolymer 4 from the methacrylate functionalized with an azide function 6 and acrylonitrile 5 according to the procedure presented hereinafter.

The acrylonitrile is dried over calcium hydride for several days and then distilled at atmospheric pressure under a stream of argon.

In a pre-sealed ampoule, 2.1 g (39.5 mmol) of acrylonitrile, 1.1 mg (0.4 mmol) of methacrylate in 20 mL of dry DMF and 65.6 mg (0.4 mmol) are introduced. ) azobisisobutyronitrile or AIBN.

The reaction medium is degassed three times under vacuum and then sealed under vacuum and the reaction medium is heated at 60 ° C. for 24 hours.

The copolymer is precipitated in 250 ml of methanol. The solid is separated by filtration and then dried under vacuum at room temperature. The product thus obtained is purified by dissolving in a mixture of 20 ml of THF and 20 ml of DMF followed by reprecipitation in 600 ml of methanol. The solid is separated by filtration and then dried under vacuum.

1.88 g of copolymer is obtained, a yield of 85%.

FIG. 2c illustrates the grafting reaction of the copolymer 4 on a carbon nanotube 2 according to the procedure described hereinafter.

40 mg of multi-layer carbon nanotubes are dispersed by ultrasonic treatment for 3 hours in 36 ml of 1,2-dichlorobenzene.

The dispersion of carbon nanotubes thus obtained is introduced into a three-necked flask of 100 ml.

Under argon flushing, a solution of 153 mg of copolymer 4 in 5 ml of dry DMF is added dropwise to the carbon nanotube dispersion.

The reaction medium is heated at a temperature of 135 ° C. under argon for 24 hours.

A black solid is separated by centrifugation at 3000 rpm.

The black solid is washed twice with DMF and then isolated by filtration on a Sartorius stedem filter (PTFE, 4,45 μιτι), washed with acetone and dried under vacuum at a temperature of 110 ° C. 0.167 g of solid is obtained, ie a yield of 86.5%.

The nanotubes modified with the polyacrylonitrile chains are then pyrolized at a temperature of 1000 ° C. for 3 hours in a neutral atmosphere.

The hybrid material of carbon nanotubes and graphite thus obtained can be used directly to prepare a supercapacitor electrode.

This hybrid material obtained by grafting a macromolecular material capable of forming a graphite structure makes it possible to increase the specific surface area of the electrodes conventionally used.

Claims

claims

1. Supercapacitor electrode comprising a first electrically conductive material (2) and a macromolecular material (1) characterized in that the macromolecular material (1) is grafted onto the first material (2), said macromolecular material (1) is capable of generating a graphitic structure by pyrolysis, the first material being a metal foam of gold or silver or carbon-based.

2. The electrode of claim 1 wherein the macromolecular material (1) is polyacrylonitrile.

3. Electrode according to one of claims 1 or 2 wherein said first material (2) comprises carbon nanotubes.

4. A method of producing an electrode according to one of the preceding claims characterized in that it comprises the steps in which:

the macromolecular material (1) capable of being graphitized and comprising a function (X) capable of creating covalent bonds, is synthesized,

the macromolecular material (1) is grafted onto said first material (1), and

the macromolecular material (1) is graphitized.

The method of claim 4 wherein the macromolecular material is polyacrylonitrile.

6. Method according to one of claims 4 or 5 wherein said first material (2) is carbon-based.

7. Method according to one of claims 4 to 6 wherein said first material (2) comprises carbon nanotubes.

8. Method according to one of claims 4 to 7 wherein the function (X) is an azide function (-N ₃ ) or a diazonium salt function (-N = N ⁺ ).

9. Method according to one of claims 4 or 5 wherein said first material (2) is a metal foam of gold or silver.

10. Method according to one of claims 4, 5 or 9 wherein the function (X) is a thiol function (-SH).

1 1. Process according to one of Claims 4 to 11, in which the grafting is carried out by ultrasonic treatment followed by heating at 135 ° C.