Composition for an organic gel and the pyrolysate thereof, production method thereof, electrode formed by the pyrolysate and supercapacitor containing same

Abstract

The invention relates to a noncrosslinked gelled carbonaceous composition and a pyrolyzed composition respectively forming an aqueous polymer gel and the pyrolysate thereof in the form of porous carbon. The invention also relates to the production method thereof, to a porous carbon electrode formed by the pyrolyzed composition, and to a supercapacitor containing said electrodes. The gelled, noncrosslinked composition (G2) is based on a resin created at least partly from polyhydroxybenzene(s) R and formaldehyde(s) F and comprises at least one hydrosoluble cationic polyelectrolyte P. According to the invention, the composition forms a rheofluidifying physical gel. A pyrolyzed carbonaceous composition according to the invention, consisting of a carbon monolith, is the product of coating, crosslinking, drying and pyrolysis of the non-crosslinked gelled composition, the carbon monolith being predominantly microporous and able to form a supercapacitor electrode having a thickness of less than 1 mm.

1 . A process for preparing a non-crosslinked, gelled carbon-based composition (G2) forming an aqueous polymer gel, the composition being based on a resin derived at least partly from polyhydroxybenzene(s) R and from formaldehyde(s) F and comprising at least one water-soluble cationic polyelectrolyte P, the composition forming a shear-thinning physical gel, wherein the process comprises:
 a) dissolution in an aqueous solvent W of said polyhydroxybenzene(s) R and formaldehyde(s) F, in the presence of said at least one cationic polyelectrolyte P and of a catalyst C, in order to obtain an aqueous solution,   b) prepolymerization until precipitation of the solution obtained in a) in order to obtain a precipitated prepolymer forming said non-crosslinked gelled composition (G2), then   c) coating or molding of the precipitated prepolymer obtained in b) with a thickness of less than 2 mm.   
     
     
         2 . The process for preparing the non-crosslinked gelled composition (G2) as claimed in  claim 1 , wherein in step a):
 said at least one cationic polyelectrolyte P is used according to a mass fraction of between 0.5% and 5%; and/or   said at least one cationic polyelectrolyte P and said polyhydroxybenzene(s) R are used according to an R/P mass ratio of less than 50, and/or   said polyhydroxybenzene(s) R and said aqueous solvent W are used according to an R/W mass ratio of between 0.2 and 2,   wherein step a) is carried out:   a1) by dissolving said polyhydroxybenzene(s) R in said aqueous solvent W,   a2) by adding, to the solution obtained in a1), said formaldehyde(s) F, said acid or basic catalyst C and said at least one cationic polyelectrolyte P, then   a3) by stirring the mixture obtained and adjusting its pH,   and wherein step b) is carried out in a reactor.   
     
     
         3 . The process for preparing the non-crosslinked gelled composition (G2) as claimed in  claim 2 , wherein in step a):
 said at least one cationic polyelectrolyte P and said polyhydroxybenzene(s) R are used according to an R/P mass ratio of between 10 and 25, and/or   said polyhydroxybenzene(s) R and said aqueous solvent W are used according to an R/W mass ratio of between 0.3 and 1.3,   wherein step a1) is carried out by dissolving said polyhydroxybenzene(s) R in water,   and wherein step b) is carried out in the reactor immersed in an oil bath between 50 and 70° C.   
     
     
         4 . The process for preparing the non-crosslinked gelled composition (G2) as claimed in  claim 1 , wherein step b) comprises forming the precipitated prepolymer which forms the shear-thinning physical gel which has a viscosity, measured at 25° C. using a Brookfield viscometer, greater than 100 mPa s at a shear rate of 50 revolutions/minute and/or greater than 200 mPa·s at a shear rate of 20 revolutions/minute. 
     
     
         5 . The process for preparing the non-crosslinked gelled composition (G2) as claimed in  claim 1 , wherein said at least one water-soluble cationic polyelectrolyte P is an organic polymer chosen from the group made up of quaternary ammonium salts, poly(vinylpyridinium chloride), poly(ethyleneimine), poly(vinylpyridine), poly(allylamine hydrochloride), poly(trimethylammoniumethyl methacrylate chloride), poly(acrylamide-co-dimethylammonium chloride) and mixtures thereof. 
     
     
         6 . The process for preparing the non-crosslinked gelled composition (G2) as claimed in  claim 5 , wherein said at least one water-soluble cationic polyelectrolyte is a salt comprising units resulting from a quaternary ammonium chosen from poly(diallyldimethylammonium halides). 
     
     
         7 . A process for preparing a pyrolyzed carbon-based composition consisting of a carbon monolith, the pyrolyzed composition being the product of coating, crosslinking, drying then pyrolysis of a non-crosslinked gelled composition forming an aqueous polymer gel,
 the non-crosslinked gelled composition being based on a resin derived at least partly from polyhydroxybenzene(s) R and from formaldehyde(s) F and comprising at least one water-soluble cationic polyelectrolyte P, the non-crosslinked gelled composition forming a shear-thinning physical gel,   said carbon monolith being predominantly microporous and capable of forming a supercapacitor electrode having a thickness of less than 1 mm,   wherein the process comprises:   a) dissolution in an aqueous solvent W of said polyhydroxybenzene(s) R and formaldehyde(s) F, in the presence of said at least one cationic polyelectrolyte P and of a catalyst C, in order to obtain an aqueous solution,   b) prepolymerization until precipitation of the solution obtained in a) in order to obtain a precipitated prepolymer forming said non-crosslinked gelled composition (G2),   c) coating or molding of the precipitated prepolymer obtained in b) with a thickness of less than 2 mm,   d) crosslinking and drying of the gel coated or molded in c) in order to obtain the dried, crosslinked, gelled composition forming a porous xerogel, and   e) pyrolysis of the dried gel obtained in d), in order to obtain said pyrolyzed composition in the form of monolithic porous carbon.   
     
     
         8 . A pyrolyzed carbon-based composition consisting of a carbon monolith obtained by the process of  claim 7 . 
     
     
         9 . The pyrolyzed carbon-based composition as claimed in  claim 8 , wherein the pyrolyzed composition is the product of coating, crosslinking, drying then pyrolysis of the non-crosslinked gelled composition, said carbon monolith being predominantly microporous and having a thickness of less than 1 mm. 
     
     
         10 . The pyrolyzed carbon-based composition as claimed in  claim 9 , wherein said carbon monolith has a thickness of less than or equal to 0.5 mm. 
     
     
         11 . The pyrolyzed carbon-based composition as claimed in  claim 8 , wherein it has:
 a density of between 0.1 and 1.2, and/or   a specific surface area of greater than 400 m 2 /g, and/or   a pore volume of between 0.2 and 0.8 cm 3 /g.   
     
     
         12 . A porous carbon electrode which is usable for equipping a supercapacitor cell while being immersed in an aqueous ionic electrolyte, the electrode covering a metal current collector, wherein the electrode consists of a pyrolyzed carbon-based composition as claimed in  claim 8  and has a thickness of less than 1 mm. 
     
     
         13 . The porous carbon electrode as claimed in  claim 12 , wherein the electrode has a thickness of less than 0.5 mm. 
     
     
         14 . A supercapacitor comprising cells each comprising at least two porous electrodes, an electrically insulating membrane separating the two porous electrodes from one another and an ionic electrolyte in which the two porous electrodes are immersed, each cell comprising at least two current collectors respectively covered with the two porous electrodes, wherein at least one of the two porous electrodes is as defined in  claim 12 .