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Publication numberUS20060223701 A1
Publication typeApplication
Application numberUS 09/793,379
Publication dateOct 5, 2006
Filing dateFeb 26, 2001
Priority dateFeb 26, 2001
Also published asUS7119047, US7569514, US20070060476
Publication number09793379, 793379, US 2006/0223701 A1, US 2006/223701 A1, US 20060223701 A1, US 20060223701A1, US 2006223701 A1, US 2006223701A1, US-A1-20060223701, US-A1-2006223701, US2006/0223701A1, US2006/223701A1, US20060223701 A1, US20060223701A1, US2006223701 A1, US2006223701A1
InventorsMichail Adrianov, Vera Litvinskaya, Vitaly Popov, Natalia Zarutcheyskaya, Valentin Chebykin, Pavel Shmatko, Valery Carev
Original AssigneeAdrianov Michail N, Litvinskaya Vera V, Popov Vitaly P, Zarutcheyskaya Natalia M, Chebykin Valentin V, Shmatko Pavel A, Carev Valery A
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Modified activated carbon for capacitor electrodes and method of fabrication thereof
US 20060223701 A1
Abstract
A novel electrode and method of making the same. The electrode includes activated carbon that has been modified by treatment with an alkali solution and an acid, such as nitric acid, and then washed and dried. The carbon may then be annealed. The method of modifying the activated carbon helps produce an electrode with considerably higher electric capacity and stable electric characteristics. Additionally; the electrodes may be produced more quickly and inexpensively and, therefore, permits their production of electrodes that are used for superconductors.
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Claims(10)
1. (canceled)
2. A method according to claim 3, wherein after drying said carbon is annealed at 135-950 C.
3. A method of fabrication of modified activated carbon, comprising treatment of pristine carbon with nitric acid, subsequent washing, drying, and annealing, wherein prior to acid treatment said carbon is treated with alkali solution having concentration of 1.0 to 10.0%, while the nitric acid concentration ranges from 0.2 to 10.0%, and wherein washing of said carbon is performed using ammonia solution to pH 4-10.
4.-5. (canceled)
6. A method of fabrication of modified activated carbon, comprising
treatment of pristine carbon with nitric acid, subsequent washing, drying, and annealing,
wherein prior to acid treatment said carbon is treated with alkali solution having concentration of 1.0 to 10.0%, while the nitric acid concentration ranges from 0.2 to 10.0%,
wherein after drying said carbon is annealed at 135-950 C. and
wherein the carbon is annealed in an atmosphere comprising CO2.
7. A method according to claim 2, wherein the carbon is annealed in an atmosphere comprising argon.
8.-9. (canceled)
10. A method according to claim 6, wherein said annealing step is carried out at 400 C.
11. (canceled)
12. A method according to claim 7, wherein said annealing step is carried out at 600 C.
Description
    FIELD OF THE INVENTION
  • [0001]
    This invention relates generally to capacitors and other energy storage devices, and more particularly to electrodes for use in such devices.
  • DESCRIPTION OF THE PRIOR ART
  • [0002]
    Numerous ways to produce activated carbon materials for use in electric storage devices are known. Russian Patent 2,038,295 teaches the preparation of a granulated activated carbon for recuperation from hydrolysis processes residua modified using 0.75 to 1.5% (w/w) orthophosphoric acid. The row semicoke material, having total pore volume in the 0.20-0.40 cm3/g range, ash content of 1.5 to 4.0%, and phosphorous content from 0.6 to 1.2%, is ground, mixed with binder, granulated, dried, carbonized and steam-activated to achieve total pore volume of 0.60-0.75 cm3/g. The electric capacity of the activated carbon produced by this method is insufficient.
  • [0003]
    Russian Patent 2,031,837 describes method for preparation of activated carbon comprising: mixing of cellolignin or lignin with 0.3-1.0% (w/w) orthophosphoric acid, briquetting, drying, carbonization at heating rate of 20-50 C./h (?) up to 500-700 C., grinding and activation to total pore volume of 0.8-1.2 cm3/g. However, the activated carbon produced according to this method has unsatisfactory electric properties.
  • [0004]
    Another method for preparation of activated carbon to be used as capacitor electrodes is described comprising treatment of the carbon with cyanides and subsequently with 1M phosphoric acid (see Carbon, Vol. 28, No. 2/3, pp. 301-309, 1990). A drawback of this method is that the modified active carbon contains complex insoluble iron compounds, which cause decrease in the micropore volume and thus, in the electric capacity of the carbon. Moreover, the use of highly toxic cyanides as modifiers requires additional safety means.
  • [0005]
    Closest to the present invention from technical point of view is the method developed by the I. A. Kuzin's group, comprising treatment of the carbon with concentrated nitric acid, washing and drying (see I. A. Tarkovskaya, “Oxidized Carbon”, Kiev, 1981 pp. 123-132 and 164, in Russian). This method is considered as a prototype of the invention hereafter. Some drawbacks of the prototype can be pointed out: its unstable electric properties and loses of electric capacity due to both changes in the pore structure and formation of considerable amount of soluble organic compounds in carbon bulk. Furthermore, high concentrations of nitric acid cause valuable destruction and loses of the carbonaceous material.
  • [0006]
    The goal of the present invention is to obtain activated carbon having high electric capacity and stable electric characteristics.
  • [0007]
    This goal is achieved by the method proposed, comprising treatment of the activated carbon with 1.0-10.0% alkali solution, followed by treatment with 0.2-10.0% nitric acid, washing and drying. After drying, the carbon can be annealed at 135-950 C. in inert or slightly oxidative medium or at 135-350 C. in air, steam or exhaust gases atmosphere. In addition, washing of the carbon following the acid treatment can be done using ammonia solution up to pH 4-10, and the annealing after drying is applied in inert or exhaust gases atmosphere up to 135-950 C.
  • [0008]
    The difference of the present invention from the prototype is in the alkali solution (1.0-10.0%) treatment prior to nitric acid one, while the preferred concentration of the nitric acid is 0.2-10.0%. Moreover, the carbon after drying can be annealed up to either 135-950 C. in inert or mildly oxidative atmosphere or 135-350 C. in air, steam or exhaust gases atmosphere. Acid treatment can be followed by washing in ammonia solution up to pH 4-10 and subsequent annealing up to 135-950 C. in inert or exhaust gases atmosphere.
  • [0009]
    To the best of the inventors' knowledge, no such method has been described so far in the literature for fabrication of electrodes for capacitors.
  • [0010]
    Employing the abovementioned features in accordance with the present invention provides considerable increase of the electric capacity and stable characteristics of the resulting carbon and, therefore, permits fabrication of electrodes for supercapacitors based on said carbon having maximum electric capacity and stable performance.
  • [0011]
    The present invention provides formation of the carbon surface, which renders it resistant to oxidation-reduction processes in the electrolyte if the electrode is employed in bipolar configuration for typical electric double-layer applications.
  • [0012]
    In another embodiment, when the electrode is employed in monopolar configuration, its electric capacity increases due to formation of ionic adduct of the electrolyte and the carbon matrix, and to formation of surface functional groups that can be protonated and deprotonated.
  • [0013]
    Numerous experiments led to conclusion that the determining factors to achieve the goal of the invention are the concentrations of both alkali and acid as well as proper choice of the heating conditions, namely atmosphere and temperature range.
  • [0014]
    It has been experimentally ascertain that the carbon precursor is to be treated with alkali solution with concentration ranging from 1.0 to 10.0%. The alkali concentration is determined by the need to dissolve phosphorus, aluminum, silicon, and iron while keeping the pH in the range that excludes possibility of hydrolysis of these elements, which reduce the electric capacity. Alkali concentration higher than 10% leads to unnecessary expenses, while dissolution using alkali with concentration lower than 1.0% is not complete.
  • [0015]
    Nitric acid is applied with preferred concentration of 0.2 to 10.0%. The process of fabrication of activated carbon slows when concentrations below this range are used, higher amount of liquid and higher energy consumption are required, and the total process is not profitable. At concentration higher than 10.0%, the oxidation process is unstable for its electrochemical potential becomes higher than the permissible, thus the carbon is partially destroyed and capacity lost.
  • [0016]
    The annealing at 135-950 C. in inert or slightly oxidative atmosphere aims to improve the electric properties of the carbon. Annealing at temperature lower than 135 C. only dries the activated carbon and does not provide sufficient capacity, while temperatures above 950 C. completely destroy the active surface groups of the carbon, which leads to partial loss of capacity and substantial rise of energy consumption during the formation process.
  • [0017]
    If the annealing under air, steam or exhaust gases is performed at temperature lower than 135 C., no changes of the surface groups take place and, therefore, is impossible to obtain carbon with desirable properties. If it is performed at temperatures higher than 350 C., oxidative destruction causes loss of the acquired capacity.
  • [0018]
    Nitric acid treatment can be followed by neutralization with ammonia solution up to pH 4-10. Below pH 4, the neutralization does not achieve the desired effect since nitric acid is evolved at drying. Above pH 10, ammonia is evolved causing unnecessary high consumption and environmental pollution. In this case, the annealing is performed at 135-950 C. Ammonia surface compounds do not decompose below 135 C., therefore the resulting carbon cannot provide the desired capacity. Annealing at temperatures higher than 950 C. leads to complete destruction of the active groups on the carbon surface and thus to lower electric capacity.
  • [0019]
    According to the invention, the activated carbon is treated as follows: modified with 1.0-10.0% alkali solution, washed, placed into a column, leached with 1.0-10.0% nitric acid, washed from the free nitric acid and dried. After drying, the carbon can be annealed at 135-950 C. in inert or mildly oxidative atmosphere or at 200-350 C. under air, steam or exhaust gases. The acid treatment can be followed by neutralization with ammonia solution to pH 4-10 and subsequently by annealing at 135-950 C. under inert or exhaust gases.
  • EXAMPLES Example 1
  • [0020]
    1 kg of activated carbon is treated with 315% NaOH and washed with water. Then it is placed in a stationary layer column and treated with 2% solution of HNO3. The free nitric acid is washed off and the carbon dried, cooled and unloaded. During the formation process, an electrode employing the resulting carbon exhibits 5-7 times lower irreversible losses than an electrode employing a carbon made from the same precursor, which have been only de-ashed with HCl. In the former case, the irreversible capacity losses begin at 1.1 V, while in the latter at 0.8 V. On cycling between +0.9 and −0.1 V, the former electrode delivers integral capacity of 520-550 F/g and the latter 180-200 F/g. When cathodically polarized, the carbon obtained according to the invention exhibits two capacitance maxima in the ranges 0.7-0.5 V and 0.2-0.1 V.
  • Example 2
  • [0021]
    Carbon obtained in Example 1 is annealed under CO2 flow at 400 C.
  • Example 3
  • [0022]
    Carbon obtained in Example 1 is annealed in steam atmosphere at 275 C.
  • Example 4
  • [0023]
    Carbon obtained in Example 1 is annealed in argon atmosphere at 600 C.
  • Example 5
  • [0024]
    Carbon obtained in Example 1 is annealed in air atmosphere at 250 C.
  • Example 6
  • [0025]
    Carbon obtained in Example 1 is annealed in exhaust gases environment at 320 C.
  • [0026]
    On cycling between +0.9 and −0.1 V, electrodes made using carbons of Examples 2-6 exhibited integral capacity of 500-540 F/g. At cathodic polarization the carbon capacity displays a maximum in the +0.4−0.1 V range.
  • Example 7
  • [0027]
    1 kg of active carbon is treated with 315% NaOH and washed with water. Then it is placed in a stationary layer column and treated with 2% solution of HNO3. The carbon is subsequently neutralized with 1% solution of ammonia up to pH 9, dried at 105 C. and annealed at 380 C. in inert or exhaust gases atmosphere. On cycling in the same potential range, 500-550 F/g are achieved and the cathodic polarization maximum is situated between +0.5 and 0.0 V.
  • [0028]
    The following table compares cycling data for some carbons represented in the Russian Catalogue that have been treated with 1M H2SO4 and according to the present invention.
    TABLE
    Cycling results of some treated carbons.
    Starting carbon Carbon of example 1 Carbon of example 2 Carbon of example 3
    Carbon C, SD, SD, C, SD, SD, C, SD, SD, C, SD, SD,
    code F/g mV/h mV/h F/g mV/h mV/h F/g mV/h mV/h F/g mV/h mV/h
    AG-3 35-45 50-70 30-50 120-150 1.2 5.0-6.0 122 5.0 1.5 127 4.0 1.0
    MeKC 100-150 60-80 30-50 250-300 0.6 3.2 250-320 1.2 0.6 270 1.2 0.3
    ACB 250-300 30-40 20-30 450-620 0.2 1.3 470-650 1.0 0.1 450-650 1.0 0.25
    CKT 250-300  70-100 30-60 500-750 1.0-1.5 5.0-6.0 500-760 5.0 2.5 500-740 4.0 2.0

    C designates capacity, SD designates self-discharge (measured at potential of 0.8 V).
  • [0029]
    The table shows that the electric capacity of the carbons produced according to the present invention is considerably higher than that of the initial ones, the self-discharge is considerably lower, which testifies on their high electric stability.
  • [0030]
    The carbon fabricated using combination of treatment modes 1, 2, and 3 is a multipurpose material and can be used in preparation of composite electrodes for acidic and basic mono- and bipolar capacitors as well as for capacitors employing neutral and aprotic electrolyte.
  • [0031]
    The main advantage of the carbon fabricated according to the invention is realized in hybrid capacitor storage systems, for instance, carbon-lead.
Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4937223 *Feb 10, 1989Jun 26, 1990Mitsubishi Kasei CorporationProcess for preparing activated carbon
US4946663 *Oct 14, 1988Aug 7, 1990The British Petroleum Company, P.L.C.Production of high surface area carbon fibres
US6251822 *Jul 7, 1999Jun 26, 2001Corning IncorporatedMethod of making activated carbon derived from pitches
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7923151Sep 16, 2004Apr 12, 2011Commonwealth Scientific And Industrial Research OrganisationHigh performance energy storage devices
US8232006Mar 1, 2011Jul 31, 2012Commonwealth Scientific And Industrial Research OrganisationHigh performance energy storage devices
US9203116Dec 12, 2007Dec 1, 2015Commonwealth Scientific And Industrial Research OrganisationEnergy storage device
US20090117257 *Nov 19, 2008May 7, 2009University Of South CarolinaCatalysts for Fuel Cell Applications Using Electroless Deposition
US20090220682 *Sep 13, 2006Sep 3, 2009University Of South Carolinacatalysts for fuel cell applications using electroless deposition
Classifications
U.S. Classification502/416
International ClassificationC01B31/08
Cooperative ClassificationC01B31/083, H01G11/34, Y02E60/13, H01M4/583, H01G9/058
European ClassificationH01G11/34, H01M4/583, C01B31/08F, H01G9/058
Legal Events
DateCodeEventDescription
Sep 24, 2001ASAssignment
Owner name: C AND T COMPANY, INC., CANADA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:ADRIANOV, MICHAEL N.;LITVINSKAYA, VERA V.;POPOV, VITALY P.;AND OTHERS;REEL/FRAME:012190/0391
Effective date: 20010913
Mar 13, 2007ASAssignment
Owner name: AXION POWER INTERNATIONAL, INC., PENNSYLVANIA
Free format text: NUNC PRO TUNC ASSIGNMENT;ASSIGNOR:C AND T COMPANY, INC.;REEL/FRAME:019000/0281
Effective date: 20070205
Oct 22, 2009FPAYFee payment
Year of fee payment: 4
Apr 14, 2014FPAYFee payment
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Apr 14, 2014SULPSurcharge for late payment
Year of fee payment: 7