Method for manufacturing vertically aligned carbon nanotubes, and electrochemical capacitors using these nanotubes as electrodes
A composite comprises vertically aligned carbon nanotubes (VACNT) on a substrate and additional disordered carbon deposited on the outer face of the nanotubes. This additional carbon is not amorphous but comprises graphitic domains. This composite can be prepared by a chemical vapor deposition (CVD) process in the presence of a catalyst on a metal substrate at atmospheric pressure. It can be used as an electrode in electronic and electrotechnical devices, such as supercapacitors.
1 . A method for preparing a composite that comprises vertically aligned carbon nanotubes (VACNTs) on a substrate and disorganized additional carbon with graphitic domains deposited on an external surface of the nanotubes, the method comprising chemical decomposition of a carbon-source gas in a reactor comprising a heated enclosure and growth of the VACNTs and graphitic domains on a substrate, in the presence of a catalyst, wherein:
a gaseous phase comprising the carbon source and catalyst precursor is injected continuously into the heated enclosure at a temperature of between 580° C. and 630° C. and at a pressure of between 0.5 bar and 1.5 bar,
the catalyst precursor comprises ferrocene,
the disorganized additional carbon comprises the graphitic domains and has a degree of semigraphitic organization in which a width ratio between band D and band G in a Raman spectrum of the VACNTs is greater than 2.0,
the gaseous phase injected into the enclosure comprises acetylene as a source of carbon, toluene as a carrier gas for the catalyst precursor, hydrogen, and argon as an inert gas, and
the growth of the VACNTs and the deposition of the disorganized additional carbon take place a single-step chemical vapor deposition process.
2 . The method according to claim 1 , wherein the gaseous phase injected into the enclosure consists essentially of acetylene as a source of carbon, hydrogen, ferrocene as a catalyst precursor, toluene as a carrier gas for the ferrocene, and argon as an inert gas.
3 . The method according to claim 1 , wherein the speed of passage of the gaseous phase is between 1 mm/s and 15 mm/s, and preferably between 3 mm/s and 10 mm/s.
4 . The method according to claim 1 , wherein the iron content based on the total carbon content in the gaseous phase is between 0.4% and 1.2%, preferably between 0.5% and 1.1%, and even more preferentially between 0.55% and 0.9% (as a percentage by mass).
5 . The method according to claim 1 , wherein
the total volume of acetylene is between 0.7 and 6 ml/mm 2 .
6 . A supercapacitor device comprising two electrodes,
wherein at least one of the two electrodes comprise the composite according to claim 1 .
7 . The supercapacitor device according to claim 6 , wherein the two electrodes are contained in an enclosure, separated by a separator, and the supercapacitor device comprises an electrolyte that comprises at least one anion, at least one cation, and optionally a solvent.
8 . The supercapacitor device according to claim 6 , wherein the supercapacitor device is capable of storing energy of at least 0.8 Wh/m 2 , preferably at least 1 Wh/m 2 , and even more preferentially at least 2 Wh/m 2 for a power of between 0.01 and 1 kW/m 2 .
9 . A method for manufacturing a supercapacitor device, the method comprising:
providing a pair of electrodes, each comprising a composite comprising: a substrate, vertically aligned carbon nanotubes (VACNTs) grown on the substrate, and disorganized additional carbon comprising graphitic domains deposited on an external surface of the VACNTs, separators, current collectors, electrolyte, and an enclosure, wherein the disorganized additional carbon comprises the graphitic domains and has a degree of semigraphitic organization, and wherein the VACNTs and the disorganized additional carbon are formed simultaneously in a single-step chemical vapor deposition process using a gaseous phase comprising acetylene, hydrogen, ferrocene, toluene, and an inert gas;
welding the current collectors on the electrodes;
assembling the electrodes and separators to obtain an electrode/separator assembly;
welding the current collectors of the electrodes to the terminals of the enclosure;
fitting the electrode/separator assembly in the enclosure;
adding and diffusing the electrolyte in the enclosure; and
sealing the enclosure.
10 . The method according to claim 9 , wherein the electrolyte is an ionic liquid containing a cation associated with an anion, or an electrolytic solution containing a salt dissolved in a solvent, the solvent being likely to be a protic solvent or an aprotic solvent or a mixture of at least one protic mixture of at least one aprotic solvent.
11 . The method according to claim 10 , wherein the aprotic solvent is chosen from halogenated alkanes such as dichloromethane; dimethylformamide (DMF); ketones such as acetone or 2 butanone; acetonitrile; tetrahydrofuran (THF); N-methylpyrrolidone (NMP); dimethyl sulfoxide (DMSO) and mixtures thereof; propylene carbonate; ethylene carbonate; dimethylcarbonate and mixtures thereof; and lactones such as γ-butyrolactone.
12 . The method according to claim 10 , wherein the ionic liquid is selected from the group consisting of:
ionic liquids containing quaternary ammonium ions, and in particular the ions of 1-ethyl-3-methyl imidazolium, 1-methyl-3-propyl imidazolium, 1-methyl-3-isopropyl imidazolium, 1-butyl-3-methyl imidazolium, 1-ethyl-2,3-dimethyl imidazolium, 1 ethyl-3,4-dimethyl imidazolium, N-propyl pyridinium, N-butyl pyridinium, N-tert-butyl pyridinium, N-tert-butanol-pentyl pyridinium, N-methyl-N-propylpyrrolidinium, N-butyl-N-methyl-pyrrolidinium, N-methyl-N-pentyl pyrrolidinium, N-propoxyethyl-N-methyl pyrrolidinium, N-methyl-N-propyl piperidinium, N-methyl-N-isopropyl piperidinium, N-butyl-N-methyl piperidinium, N—N-isobutylmethyl piperidinium, N-sec-butyl-N-methyl piperidinium, N-methoxy-N-ethylmethyl piperidinium, and N-ethoxyethyl-N-methyl piperidinium; and
ionic liquids containing ammonium ions such as the butyl-N—N-trimethyl ammonium, N-ethyl-N,N-dimethyl-N-ammonium and N,N,N-trimethyl ammonium ions, associated with any anion such as the tetrafluoroborate (BF 4 − ), hexafluorophosphate (PF 6 − ), bis(trifluoromethane-sulfonyl)amide (TFSI − ) or bis(fluorosulfonyl)amides (FSI) ions.
13 . The method according to claim 9 , wherein the electrolyte comprises an ionic liquid comprising:
at least one cation selected from the group consisting of the derivatives of pyridine, pyridazine, pyrimidine, pyrazine, imidazole, pyrazole, thiazole, oxazole, triazole, ammonium, pyrrolidine, pyrroline, pyrrole, and piperidine; and
at least one anion selected from the group consisting of F − , Cl − , Br − , I − , NO 3 − , N(CN) 2 − , BF 4 − , ClO 4 − , PF 6 − , RSO 3 − , RCOO − , where R is an alkyl or phenyl group, (CF 3 ) 2 PF 4 − , (CF 3 ) 3 PF 3 , (CF 3 ) 4 PF 2 − , (CF 3 ) 5 PF − , (CF 3 ) 6 P − , (CF 2 SO 3 − ) 2 , (CF 2 CF 2 SO 3 − ) 2 , (CF 3 SO 2 − ) 2 N − , (CF 3 CF 2 (CF 3 ) 2 CO − , (CF 3 SO 2 − ) 2 CH − , (SF 5 ) 3 C, (CF 3 SO 2 ) 3 C, [O(CF 3 ) 2 C 2 (CF 3 ) 2 O] 2 PO − , CF 3 (CF 2 ) 7 SO 3 − , 1-ethyl-3-methylimidazole, bis(trifluoro-methylsulfonyl)imide ([EMIM][Tf2M]).
14 . The method according to claim 10 , wherein the electrolytic solution comprises, in addition to a solvent, an electrolyte in the form of a salt dissolved in a solvent, knowing that:
an anion of this salt is advantageously chosen from:
inorganic ions such as F − , Br − , Cl − , I, HCO 3 − , H 2 PO 4 − , Cr 2 O 4 3− , BF 4− , PF 6 − , or N(CN) 2 − ;
organic anions, preferably selected from the group consisting of: RSO 3 − , RCOO − (where R is an alkyl or phenyl group, possibly substituted); (CF 3 ) 2 PF 4 , (CF 3 ) 3 PF 3 , (CF 3 ) 4 PF 2 − , (CF 3 ) 5 PF − , (CF 3 ) 6 P − , (CF 2 SO 3 − ) 2 , (CF 2 CF 2 SO 3 − ) 2 , (CF 3 SO 2 − ) 2 N − , (CF 3 CF 2 (CF 3 ) 2 CO − , (CF 3 SO 2 − ) 2 CH − , (SF 5 ) 3 C − , (CF 3 SO 2 SO 2 ) 3 C − , [O(CF 3 ) 2 C 2 (CF 3 ) 2 O] 2 PO, CF 3 (CF 2 )SO 3 − , bis(trifluoro-methanesulfonyl)amide, bis(fluorosulfonyl) amide;
polymeric anions; and
biological anions; and/or
the cation of this salt is a metallic cation, preferably selected from the group consisting of Li + , Na + , Mg 2+ , Cu 2+ , Zn 2+ and Al 3+ or organic cations.
15 . The method according to claim 1 , wherein the speed of passage of the flow of gases is between 1 mm/s and 15 mm/s.
16 . The method according to claim 1 , wherein the speed of passage of the flow of gases is between 3 mm/s and 10 mm/s.
17 . The method according to claim 9 , wherein the composite comprises between 30% and 65% disorganized additional carbon by mass, based on the mass of the VACNTs.