Abstract:
The specification discloses a method of making an ultracapacitor including the steps of forming a first electrode by adhering CNT on a porous first substrate; placing a non conductive separator over the first electrode, forming a second electrode by adhering a second layer of CNT to a second substrate and placing over the first substrate, attaching a conductive tab to each electrode, rolling the combined electrodes, inserting the rolled electrodes into a metal can, attaching one conductive tab to the bottom of the can, adding an electrolyte to the can, attaching the second conductive tab to a lid of the can, and placing an insulator between the lid and the can.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to and benefit of provisional application No. 60893564 entitled “Multifunctional Power Storage Device” filed Mar. 7, 2007 and which is incorporated herein by reference. This application also incorporates by reference the contents of the non provisional application entitled “Multifunctional Power Storage Device” filed the same date as this application. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract No. HQ0006-05-C-7220. 
     
    
     BACKGROUND OF INVENTION 
       [0003]    1. Field of Use 
         [0004]    The invention pertains to the method of manufacture and application of wound ultracapacitors, particularly ultracapacitors utilizing carbon nanotubes (“CNT”) 
         [0005]    2. Prior Art 
         [0006]    Methods of manufacturing some ultracapacitors are known in the prior art. For example reference is made to U.S. Pat. No. 7,095,603. 
       SUMMARY OF INVENTION 
       [0007]    Ultracapacitors are electrochemical capacitors with unusually high energy density when compared to common capacitors. One area of interest is use of the ultracapacitors for the storage of electrical power. They can be replacements or supplements to batteries. 
     
    
     
       SUMMARY OF DRAWINGS 
         [0008]      FIGS. 1A and 1B  illustrate the forming of two electrodes as taught by the invention. 
           [0009]      FIG. 2  illustrates a side view of the completed electrode. 
           [0010]      FIG. 3  illustrates the configuration of the rolled electrode and the can with the lid and seal/insulator. 
       
    
    
       [0011]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention. These drawings, together with the general description of the invention given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0012]    The above general description and the following detailed description are merely illustrative of the subject apparatus and method and additional modes, advantages and particulars of this invention will be readily suggested to those skilled in the art without departing from the spirit and scope of the invention. 
         [0013]    The specification discloses a novel method of manufacturing multi-walled Carbon Nanotubes (CNT). The specification also discloses a novel electrolyte that achieves unprecedented power when used in combination with the ultracapacitor electrode of at least one embodiment. The specification discloses placing the CNT and electrolyte into a metal can be dimensioned to the size of a D-cell battery and used as a power source. 
         [0014]    The device and method subject of this disclosure pertains in one embodiment to an ultracapacitor comprising carbon nanotubes manufactured from Nickel sintered on a metal substrate at 900° C. in argon (or Nitrogen) atmosphere and, after sintering is completed, growth of CNT by introducing hydrocarbon methane or ethylene. The substrate may comprise stainless steel or Nickel. 
         [0015]    In one embodiment, the process begins with a metal foil electrode of nickel or stainless steel. The electrode is coated with nickel chrome powder, stainless steel powder and a catalyst solution. In one embodiment, the Nickel substrate is coated with Nickel-Chrome powder. In another embodiment, a stainless steel substrate is coated with stainless steel powder. The next step is chemical vapor deposition (CVD) processing at 900° C. sintering for 30 minutes. Included is CNT growth processing within a temperature range of 600° C. to 1,200° C. with hydrogen and hydrocarbon precursors. This process achieves a CNT enhanced electrode. 
         [0016]    The manufacturing process may achieve distributions of carbon nanotubes (multi-wall and single-wall) bonded/physically interlocked onto the electrode material (Nickel or Stainless Steel) and, when combined with an electrolyte of KOH and/or Glacial ascetic acid acetate salt mixture. The combination demonstrates high specific capacitance and voltages between 1.2 to 18 volts of potential. 
         [0017]    Numerous carbon nanotubes were tested and evaluated. Initially commercially available CNT were evaluated. However the results were not deemed satisfactory. It was determined that efforts should be made by the inventors to fabricate their own supply of CNT. Various methods and materials were tried and evaluated. Methane and/or ethylene were used as the carbon sources in combination with substrates (ceramic powders, and metal). 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 CVD PROCESS RECIPIES 
               
             
          
           
               
                 PROCESS 
                 Growth 
                 Ethylene 
                 Methane 
                 Hydrogen 
               
               
                 ID 
                 Temp C. 
                 (SLPM) 
                 (SLPM) 
                 (SPLM) 
               
               
                   
               
             
          
           
               
                 VT-CVD-1 
                 700 
                 0.7 
                   
                 −0.7 
               
               
                 VT-CVD-2 
                 750 
                 0.7 
                   
                 −0.7 
               
               
                 VT-CVD-3 
                 800 
                 0.7 
                   
                 −0.7 
               
               
                 VT-CVD-4 
                 900 
                 0.7 
                   
                 −2 
               
               
                 VT-CVD-5 
                 900 
                 0.5 
                   
                 −2 
               
               
                 VT-CVD-6 
                 900 
                 0.3 
                   
                 −2 
               
               
                 VT-CVD-7 
                 900 
                   
                 −2 
                 0.4 
               
               
                 VT-CVD-8 
                 900 
                   
                 −2 
                 0.2 
               
               
                   
               
             
          
         
       
     
         [0018]    Also catalytic solutions were used in the CVD process. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Catalyst Solution Constituents 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                 100 mesh 
                   
                 Cu(NO 3 ) 2   
               
               
                 CAT ID 
                 HNO 3   
                 Di-H 2 O 
                 MnO 2   
                 MgO 
                 Al 2 O 3   
                 Fe 
                 Fe(NO 3 ) 3   
                 2½H 2 O 
               
               
                   
               
               
                 VT-Cat-1 
                 X 
                 X 
                   
                   
                   
                   
                   
                   
               
               
                 VT-Cat-2 
                 X 
                 X 
                   
                   
                   
                 X 
               
               
                 VT-Cat-3 
                 X 
                 X 
                   
                   
                 X 
                   
                 X 
               
               
                 VT-Cat-4 
                 X 
                 X 
                   
                 X 
                   
                   
                 X 
               
               
                 VT-Cat-5 
                 X 
                 X 
                 X 
                 X 
                   
                 X 
                 X 
               
               
                 VT-Cat-6 
                 X 
                 X 
                 X 
                 X 
                 X 
                   
                 X 
               
               
                 VT-Cat-7 
                 X 
                 X 
                   
                   
                   
                   
                   
                 X 
               
               
                   
               
             
          
         
       
     
         [0019]    A preferred preparation of the catalytic solution (VT-Cat-5) is composed of the following constituents: Magnesium, manganese, and iron dissolved in an aqueous bath of Nitric Acid and de-ionized water. The mass ratios of Mg:Mn:Fe:HNO 3  (15.5M):H 2 O is 8:2:1:20:20 respectively. The catalytic solution can be used on Nickel foam substrates and further processed using chemical vapor deposition. 
         [0020]    For the porous nickel substrate, 4 grams of catalytic solution were used per gram of nickel substrate. The same ratio was used for iron wool processing. 
         [0021]    The specification also teaches an embodiment for the fabrication of CNT beginning with the sintering of Nickel or Chromium powder at 900° in an argon or nitrogen atmosphere. The substrate may be stainless steel or Nickel. The process preferably utilizes stainless steel foil with stainless steel powder. A solution containing magnesium, manganese and iron is used with the metal. 
         [0022]    The electrolyte developed by the inventors comprises a saturated mixture of anhydrous ascetic acid (fluid) and potassium acetate salt (powder). Potassium acetate salt is added to the point of saturation. The liquid component is used as the electrolyte. 
         [0023]    The method of manufacturing carbon nanotubes described above was used in the supply of carbon nanotubes used as the wound electrode for the ultracapacitor configured into a battery D-cell assembly. 
         [0024]    In one embodiment, the electrodes comprise two porous Nickel plates (sintered as discussed above). Each plate is coated or pasted with a mat of carbon nanotubes. The plates are combined after a non-conductive separating material is inserted between the electrodes. In one embodiment, the separator is non woven micro-porous polypropylene (25 um thick). The sandwiched electrodes comprise a positive electrode and a negative electrode. 
         [0025]    The configuration of the electrode is a first layer comprising sintered porous metal, a layer of CNT pasted or placed on the metal surface, the layer of non woven polypropylene, a layer of CNT pasted or placed on a second sintered and porous metal. 
         [0026]    Prior to pasting, a conductive tab is attached to each nickel plate. The orientation of each tab is opposite to allow connection of each tab of the finished roll to be welded to the positive and negative ends of the can and cover respectively. When the electrode is combined in the final configuration as discussed above, one tab extends downward and the other tab extends upward. 
         [0027]      FIGS. 1A and 1B  illustrates the fabrication of the two electrodes. The material  10 ,  11  is porous metal such as nickel. A conductive, flexible tag  12 ,  13  is attached to the metal strip. CNT material  21  is pasted to the entire length of one side of each metal strip. Not shown in  FIG. 1A  or  FIG. 1B  is the insulating separator layer. 
         [0028]    Prior to winding, the flat electrode and non conductive separator are first cut to the appropriate width and length. They are then sized (calendared) to the correct thickness and wrapped in plastic as a preparation for winding. In one embodiment, the calendaring process reduced the thickness of the porous nickel and CNT from 0.060″ to 0.022″. This process physically intermeshes the CNT to the porous nickel and produces more intimate contact to reduce effective series resistance (ESR). The electrodes and separator are fed horizontally into the rollers and are then formed around the arbor. 
         [0029]    The preferred method to make a single wound cell uses an arbor and a pair of “rocking rollers” that form the electrodes as the arbor turns. Only two rollers are required. In one embodiment, the rollers maintain surface contact on the winding electrode by use of a pneumatic cylinder that pushes the rollers into the winding. Each roller can pivot in relation to the other. Therefore the first roller can rise up when encountering the start of the winding electrode. The second roller will pivot up when encountering the progressing start of the electrode. This mechanism allows for even layering, e.g., as the arbor containing the start of the winding passes under the first roller. At completion of the winding step, the arbor is removed, creating an annulus within the combined wound electrode. (See  FIG. 3 ) After winding, an electrical test may be performed to insure that the electrodes are not physically in contact. 
         [0030]      FIG. 2  is a side view of one embodiment of the assembled electrode  40 . Illustrated are one metal strip  10  and the CNT layer  21  coating the strip. Also illustrated is the non conductive separator material which may be non woven polypropylene  30 . Continuing there is a second layer of CNT material  22  coating a second metal strip  11 . The strips are combined into a single electrode with a positive side and a negative side. 
         [0031]    In one embodiment, the rolled electrode is inserted into an approximate 1.25 inch cylindrical shaped can. The can is dimensioned to the size of a D-cell battery. The negative tab attached to the negative electrode is placed in the center of the bottom of the can. A welding electrode can be inserted through the annulus and presses the tab to the bottom of the can. A second welding electrode of opposite charge is placed in contact with the can bottom and the negative tab is welded to the can bottom. The positive tab is welded to the can lid. The can is machined to create a groove or shelf within the interior of the can. The positive tab is then welded to the lid and the lid is fitted into the grooved can. A sealing ring (e.g., polypropylene) can be installed and the can top can be crimped over the lid. The sealing ring also acts as an insulator between the can and the lid. 
         [0032]    Prior to crimping of the can lid, a liquid dielectric is added to the can. In various embodiments, the electrolyte is KOH, acetonitrile base, and proprietary formulations designated VT and others proprietary electrolytes. 
         [0033]    A typical D-Cell ultracapacitor configuration may comprise a plate area of 8 sq. in.; nickel 8 grams; CNT plate 4 grams; plate mass 12 grams; and enclosure (can and lid) 20-30 grams. 
         [0034]      FIG. 3  illustrates the open can  50  receiving the rolled electrode  40 . Also shown is the annulus  41  created by the removal of the arbor. The conductive tab  12  is illustrated. This tab can be welded to the bottom of the can. Also shown is the second tab  13  which can be attached to the can lid  51 . This can be the positive side of the ultracapacitor. Also shown is the non conductive element  31  or sealing ring which separates the lid and the can. 
         [0035]    Ultracapacitors manufactured using the same methods and materials, i.e., sintering nickel, chrome or stainless steel powder on a metal substrate such as nickel or stainless steel with a catalyst comprising, for example magnesium, manganese, and iron dissolved in an aqueous bath of Nitric Acid and de-ionized water, and CNT growth processing within a temperature range of 600° C. to 1,200° C. with hydrogen and hydrocarbon precursors, etc., have demonstrated the following properties: 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Specific Energy 
                 20.4 
                 WH/Kg 
               
               
                   
                 Specific Power 
                 14 
                 KW/kg 
               
               
                   
                 Energy Density 
                 30.8 
                 WH/L 
               
               
                   
                 Power Density 
                 22 
                 KW/L 
               
               
                   
                   
               
             
          
         
       
     
         [0036]    The above properties were measured from a double layer ultracapacitor (smaller than the D-cell configuration). This ultracapacitor demonstrated 3 times the specific power and over 20 times the specific energy of the commercially available NessCap ultracapcitor discussed below. 
         [0037]    The D-Cell configuration taught by this specification achieves an ultracapacitor that is dimensioned and shaped like a common battery. However the ultracapacitor offers high energy density and good mechanical stability. The cylindrical configuration can also withstand high internal pressures. 
         [0038]    The ultracapacitor was preliminarily tested and compared with a commercially available NessCap unit. A Nesscap unit is substantially larger than the D-cell sized ultracapacitor described by this specification. Nesscap products are available from 750-8, Gomae-Dong, Kiheung-Gu, Yongin, Kyonggi-Do, 449-901, Republic of Korea. 
         [0039]    Table 3 presents results of the testing. It should be appreciated that commercially available electrolytes were used and the test does not reflect the electrolyte comprised of a saturated mixture of anhydrous ascetic acid (fluid) and potassium acetate salt (powder) disclosed within this specification. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Summary of Ultracapacitor Test Results 
               
             
          
           
               
                   
                   
                   
                 V120303-2 
                 D-cell 
               
               
                   
                   
                 V120606-1 
                 5.5 V 
                 5.0 V 
               
               
                 VARIABLE 
                 NessCap 
                 KOH 
                 Phnx#1 
                 Phnx#2 
               
               
                   
               
             
          
           
               
                 CNT wt (g) 
                 unknown 
                 11.9 
                 6.6 
                 11 
               
               
                 Cell wt(g) 
                 985 
                 117.9 
                 112.6 
                 112.6 
               
               
                 Cell Vol (cc) 
                 758.74 
                 293.19 
                 205.92 
                 40.22 
               
               
                 Dielectric const, k 
                 unknown 
                 100 
                 20 
                 100 
               
               
                 Breakdown 
                 2.7 
                 1.4 
                 5 
                 1.4 
               
               
                 Voltage, V 
               
               
                 Capacitance (F) 
                 5951 
                 67.4 
                 67.4 
                 117 
               
               
                 Capacity (mAh) 
                 1350 
                 6 
                 11 
                 0.275 
               
               
                 Mid-Point- 
                 0.7 
                 0.5 
                 0.6 
                 0.22 
               
               
                 Voltage (MPV) 
               
               
                 CNT process 
                 unknown 
                 Mg/Mn/NiA 
                 Mg/Mn/Fe 
                 Mg/Mn/NiA 
               
               
                 Impregnation 
                 unknown 
                 pasted 
                 pasted 
                 pasted 
               
               
                 Wh 
                 0.945 
                 0.003 
                 0.0066 
                 0.0000605 
               
               
                 Wh/kg 
                 0.959 
                 0.025 
                 0.059 
                 0.001 
               
               
                 Cell F/g 
                 6.04 
                 0.57 
                 0.57 
                 1.04 
               
               
                 CNT F/g 
                 n/a 
                 5.66 
                 9.80 
                 10.64 
               
               
                 CNT mAh/g 
                 unknown 
                 0.50 
                 1.67 
                 0.03 
               
               
                 Cell mAh/g 
                 1.371 
                 0.051 
                 0.098 
                 0.002 
               
               
                   
               
             
          
         
       
     
         [0040]    This specification is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the manner of carrying out the invention. It is to be understood that the forms of the invention herein shown and described are to be taken as the presently preferred embodiments. As already stated, various changes may be made in the shape, size and arrangement of components or adjustments made in the steps of the method without departing from the scope of this invention. For example, equivalent elements may be substituted for those illustrated and described herein and certain features of the invention may be utilized independently of the use of other features, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. 
         [0041]    Further modifications and alternative embodiments of this invention will be apparent to those skilled in the art in view of this specification.