Electrode for super capacitor having metal oxide deposited on ultrafine carbon fiber and the fabrication method thereof

Abstract

The present invention discloses an improved electrode for a supercapacitor and a method of preparation thereof. The inventive electrode comprises a collector, a carbon substrate disposed on the collector comprising ultrafine carbon fibers having a specific surface area of at least 200 m 2 /g (BET) and a d 002 value of 0.36 nm or less, and a metal oxide thin layer formed on the carbon substrate. The electrode of the subject invention retains a high specific capacitance during high-speed charging and discharging cycles.

1 . A method of preparing an electrode for a supercapacitor which comprises the steps of:
 (a) forming ultrafine carbon fibers having a specific surface area of at least 200 m 2 /g (BET) and a d 002  value of 0.36 nm or less by electrospinning a melt or a solution of a carbon fiber-precursor polymer to obtain spun fibers and carbonizing the spun fibers;   (b) attaching a mat-type carbon substrate consisting of the ultrafine carbon fibers on a collector using a binder, or forming a carbon substrate by coating a mixture of a ground form of the ultrafine carbon fibers and a binder on a collector; and   (c) forming a metal oxide thin layer on the carbon substrate.   
     
     
         2 . The electrode according to  claim 1 , wherein the binder is selected from the group consisting of polyurethane and polyurethane copolymers comprising polyetherurethane; cellulose derivatives such as cellulose acetate, cellulose acetate butylate and cellulose acetate propionate; polymethylmethacrylate (PMMA); polymethylacrylate (PMA); polyacryl copolymers; polyvinylacetate and polyvinylacetate copolymers; polyvinylalcohol (PVA); polyperfurylalcohol (PPFA); polystyrene and polystyrene copolymers; polyethyleneoxide (PEO); polypropyleneoxide (PPO) and polyethyleneoxide copolymers; polypropyleneoxide copolymers; polycarbonate (PC), polyvinylchloride (PVC), polycaprolactone, polyvinylpyrrolidone (PVP), polyvinylfluoride, polyvinylidenefluoride and the copolymers thereof; and polyamide. 
     
     
         3 . The electrode according to  claim 1 , wherein the mixture used in step (b) further comprises a conducting material. 
     
     
         4 . The electrode according to  claim 1 , wherein the carbon substrate of step (b) is formed using a doctor-blade or electrospray method. 
     
     
         5 . The electrode according to  claim 1 , wherein the metal oxide thin layer of step (c) is deposited on the carbon substrate by a constant current or cyclic voltammetry method. 
     
     
         6 . The electrode according to  claim 1 , which further comprises the step of heat-treating the metal oxide thin layer after step (c). 
     
     
         7 . The electrode according to  claim 1 , wherein step (a) further comprises the step of heat-treating the spun fibers obtained after electrospinning at a temperature of 300° C. or less before the carbonizing step. 
     
     
         8 . The electrode according to  claim 1 , wherein step (a) further comprises the step of activating the ultrafine carbon fibers under an oxidative environment. 
     
     
         9 . The electrode according to  claim 1 , wherein the carbon fiber-precursor polymer is 1) petroleum pitch or coal pitch, 2) a polyacrylonitrile or polyacrylonitrile copolymer, 3) cellulose or a cellulose derivative or 4) a halogenated polymer, wherein the halogenated polymer is selected from the group consisting of i) homopolymers and copolymers of fluoropolymers comprising poly(vinylidene fluoride), poly(vinylidenefluoride-co-hexafluoropropylene), poly(vinylidenefluoride-co-tetrafluoroethylene), poly(vinylidenefluoride-co-trifluoroethylene) and perfluoropolymers; ii) homopolymers and copolymers of halogenated monomers comprising polyvinyl chloride), poly(vinylidene chloride), poly(vinylidenechloride-co-vinylchloride) and saran polymers; and iii) a mixture thereof. 
     
     
         10 . The electrode according to  claim 1 , wherein the carbonization in step (a) is conducted in the presence of a C 1 -C 10  hydrocarbon gas. 
     
     
         11 . The electrode according to  claim 1 , wherein the melt or the solution of the carbon fiber-precursor polymer contains a graphitization catalyst. 
     
     
         12 . The electrode according to  claim 11 , wherein the graphitization catalyst is particles of a metal selected from the group consisting of a transition metal, a non-transition metal, and a mixture thereof; or a compound of said metal which can form the corresponding metal particles during the carbonization step. 
     
     
         13 . The electrode according to  claim 12 , wherein the transition metal is Pt, Ru, Cu, Fe, Ni, Co, Pd, W, Ir, Rh, Sr, Ce, Pr, Nd, Sm, Re, or a mixture thereof; the non-transition metal is Mg, B, Al, or a mixture thereof; and the metal compound is selected from the group consisting of CuCl 2 , CoCl 2 , OsCl 3 , CrCl 2 , VCl 3 , TaCl 2 , TiCl 4 , (NH 3 ) 6 RuCl 3 , ZrCl 4 , HfCl 4 , MnCl 2 , ZnCl 2 , FeCl 3 , NiCl 2 , PdCl 2 , MgCl 2 , Pd(NO 3 ) 2 , (NH 3 ) 4 Pt(NO 3 ) 2 , Fe(NO 3 ) 3 , Ni(NO 3 ) 2 , Mg(NO 3 ) 2  and organometallic compound containing Fe, Pd, or Ni, and a mixture thereof. 
     
     
         14 . The electrode according to  claim 1 , wherein the melt or the solution of the carbon fiber-precursor polymer further comprises carbon black or carbon nanotubes dispersed uniformly therein.