A method for making a high-density carbon material for high-density carbon electrodes

Abstract

The present invention is related with a method for making a high-density carbon material for high-density carbon electrodes by wet process free of organic solvents comprising the steps of pre-compaction of carbon/polymer composite in wet process, making a dry precursor from pre-compacted carbon/polymer composite in the form of slurry by evaporating aqueous solution from said carbon-polymer composite slurry and milling in non-destructive way a blended dry precursor thereafter into a carbon-polymer composite granulated powder and thereafter forming a carbon-polymer composite film from said carbon-polymer composite granulated powder.

Claims

1) A method for making a high-density carbon material for high-density carbon electrodes by wet process free of organic solvents, the method comprising the steps of: a) pre-compaction of carbon/polymer composite in wet process where i) applying an aqueous solution free of organic solvents to the carbon powder to form a creamy slurry of the carbon powder and an aqueous solution in which the nanopores of carbon powder are not penetrated by aqueous solution, ii) dispersing a non-soluble polymeric binding material into the creamy slurry of the carbon powder and the aqueous solution to form homogeneous mixture of carbon-polymer composite in the form of slurry; b) making a dry precursor from pre-compacted carbon/polymer composite in the form of slurry by evaporating aqueous solution from said carbon-polymer composite slurry, c) milling in non-destructive way a blended dry precursor thereafter into a carbon-polymer composite granulated powder and thereafter forming a carbon-polymer composite film from said carbon-polymer composite granulated powder.

2) The method according to claim 1 wherein in step a) i) before forming the creamy slurry of the carbon powder and the aqueous solution an ionic compound as a component of electrolyte is added to the aqueous solution.

3) The method according to claim 1 wherein in step i) before forming the creamy slurry of the carbon powder and the aqueous solution a water-soluble non-organic compounds are added to aqueous solution to modify the chemical-physical properties of high-density carbon electrode.

4) The method according to claim 1 wherein in step c) the blended dry precursor is compounded by high-shear treatment and thereafter the carbon-polymer composite is milled to the carbon-polymer granulated powder.

5) The method according to the claim 1 wherein in step d) the high-density carbon sheet is formed from the carbon-polymer granulated powder.

6) The method according to claim 1 wherein a non-soluble polymeric binding material is a polymeric fluoroalkyl compound.

7) The method according to claim 1, wherein the non-soluble polymeric binding material contains at least one fluorinated polymer.

8) The method according to claim 1, wherein the polymeric binding material is polytetrafluoroethylene.

9) The method according to claim 1, wherein the carbon powder consists of at least 70% of porous disordered carbon.

10) The method according to claim 9, wherein the porous disordered carbon is activated carbon.

11) The method according to claim 9, wherein the porous disordered carbon is carbide-derived carbon.

12) The method according to claim 4, wherein by high-shear treatment is achieved a simultaneous fibrillation and compaction of the carbon-polymer composite granulated powder.

13) A high-density carbon electrodes made from the high-density carbon material manufactured according to the method of claims 1-12.

14) The high-density carbon electrode according to claim 13 wherein the density of the carbon-polymer composite film is more than 0.67 g/cm.sup.3.

15) Use of the high-density electrodes according to claim 13 in energy storage devices, such as ultracapacitors or hybrid capacitors.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1. General sequence of procedures applied for the pre-compaction of the electrode material prior electrode formation.

[0028] FIG. 2. General sequence of procedures, including high-shear treatment, applied for the pre-compaction of the electrode material prior electrode formation.

BEST MODE FOR CARRYING OUT THE INVENTION

[0029] According to the present invention a method for making a high-density carbon material for high-density carbon electrodes by wet process free of organic solvents comprising the steps of:

[0030] a) pre-compaction of carbon/polymer composite in wet process where ii) applying an aqueous solution free of organic solvents to the carbon powder to form a creamy slurry of the carbon powder and an aqueous solution in which the nanopores of carbon powder are not penetrated by aqueous solution,

[0031] ii) dispersing a non-soluble polymeric binding material into the creamy slurry of the carbon powder and the aqueous solution to form homogeneous mixture of carbon-polymer composite in the form of slurry;

[0032] b) making a dry precursor from pre-compacted carbon/polymer composite in the form of slurry by evaporating aqueous solution from said carbon-polymer composite slurry,

[0033] c) milling in non-destructive way a blended dry precursor thereafter into a carbon-polymer composite granulated powder and thereafter forming a carbon-polymer composite film from said carbon-polymer composite granulated powder.

[0034] Before forming the creamy slurry of the carbon powder and the aqueous solution in step a) i) an ionic compound as a component of electrolyte is added to the aqueous solution.

[0035] Before forming the creamy slurry of the carbon powder and the aqueous solution in step i) a water-soluble non-organic compounds are added to aqueous solution to modify the chemical-physical properties of high-density carbon electrode.

[0036] In step c) the blended dry precursor is compounded by high-shear treatment and thereafter the carbon-polymer composite is milled to the carbon-polymer granulated powder.

[0037] In step d) the high-density carbon sheet is formed from the carbon-polymer granulated powder.

[0038] A non-soluble polymeric binding material is a polymeric fluoroalkyl compound or contains at least one fluorinated polymer or said polymeric binding material is polytetrafluoroethylene.

[0039] The carbon powder consists of at least 70% of porous disordered carbon which for example is activated carbon or carbide-derived carbon.

[0040] By high-shear treatment is achieved a simultaneous fibrillation and compaction of the carbon-polymer composite granulated powder.

[0041] A high-density carbon electrodes made from the high-density carbon material manufactured according to the present method described above.

[0042] The high-density carbon electrode has density of the carbon-polymer composite film more than 0.67 g/cm.sup.3.

[0043] The high-density electrodes can be used in energy storage devices, such as ultracapacitors or hybrid capacitors.

[0044] Following examples explain in more details the inventive matter. However, it should be understood that this invention is certainly not limited by these examples.

EXAMPLE 1

[0045] The quantity of aqueous solution free of organic solvents is added to the carbon powder, such that the carbon and an aqueous solution form creamy carbon slurry. The exact amount of the aqueous solution depends on the porosity of carbon powder, but usually is 3 to 1 by weight relative to carbon. In one example, the aqueous solution free of organic solvents may be water (distilled water). In another example, this aqueous solution may comprise an ionic compound used as a component of electrolyte. Yet in the other example the aqueous solution may comprise a various water-soluble compounds used to modify the chemical-physical properties of high-surface carbon electrode.

[0046] After that a desired amount of the polymeric fluoroalkyl compound is dispersed in the creamy carbon slurry to form homogeneous slurry of carbon-polymer composite. In one example the fluoroalkyl compound may be polytetrafluoroethylene (PTFE). Yet in another example it may be any completely or partially fluorinated hydrocarbon polymer. The hydrocarbon polymer may be polyethylene (PE), polypropylene (PP), polystyrene (PS), polyacrylonitrile (PAN), polyacrylamide (PAA), RF-resin, polyisobutylene, poly-p-xylylene or ethylene.propylene co-polymers. The amount of PTFE, used to make the carbon-polymer composite, depends on the size of carbon particles and the final thickness of carbon tape, but usually ranges from 4% wt to 12% wt relative to the sum of dry components of carbon/PTFE composite.

[0047] In next step, the water is evaporated from a cake-like mixture of carbon powder and PTFE, that can be made at normal pressure at a temperature of 120-140° C. in extensively ventilated drying hood. After that the dried cake of carbon powder and PTFE is milled in the nondestructive milling mixer into the granules. The non-destructive milling, here, means that no knives can be used for milling, which could course the damage to polymer chains created in carbon agglomerates during pre-compaction treatment.

[0048] Then, in next step, the carbon/PTFE granules can be directly rolled into the thin carbon tape by using single or multi-step calendering. In another example, the carbon/PTFE powder is firstly extruded into the thick raw tape, wherein the extrusion, for example, can be done by using a roll-press equipped with a feeder for inserting the carbon/PTFE powder. In one example, the thickness of raw type may vary in between 200-400 micrometers.

[0049] In final stage the carbon/PTFE tape is compacted by calendering to reach the desired tape thickness that, for example, can be any thickness in between 30 to 200 micrometers.

EXAMPLE 2

[0050] Polarisable carbon electrodes were prepared as follows. The pre-compacted mixture of 87% (wt.) microporous carbon (YP-50F, Kuraray), 3% (wt.) carbon black (Super C60, Timcal) and 10% (wt.) polytetrafluoroethylene (PTFE, Aldrich, 60% suspension in water) was prepared according to the method of example 1 and rolled stepwise into the carbon film with a final thickness of 60 μm. The density of 0.74 g/cm3 was reached.

EXAMPLE 3

High Shear Compounding Process.

[0051] An amount of carbon electrode material prepared according to the method of example 1 was inserted into the high shear compounder. The compounder was equipped with a torque measuring device. The electrode material mixture was mixed until the mixing torque achieved desired or maximum value (depending on the type of high-shear compounder).

[0052] In the next step the resulting material, dense rubber like substance, underwent the non-destructive granulation/milling process to the size of 10-1000 mkm, depending on final electrode thickness required. Each individual granule retains the pre-compacted material density—hence less force is required for calendering process.

[0053] Examples collected in Table 2 present the major characteristics of carbon electrodes achieved according to this invention from the pre-compacted carbon/binder composite granules preliminary treated in high-shear compounder.

[0054] Table 1. Characteristics of the electrodes made with variable thicknesses from 3 different electrode compositions (No. 1-3).

TABLE-US-00001 TABLE 1 Electrode Geometric Thick- Com- Electrode density BET V(micro) V(total) ness position No. g/cm3 m2/g cm3/g cm3/g mkm 1#1 0.81 1126 0.46 0.55 62 90% 1#2 0.80 58-59 AC1 + 10% PTFE 1#3 0.80 65-66 90% 2#1 0.79 1064 0.44 0.52 58-59 AC1/AC2 (3/2) + 10% PTFE 2#2 0.79 67-68 87% 3#1 0.67 1219 0.49 0.61 65 AC2 + 3% CB + 10% PTFE 3#2 0.67 58-59 AC1 and AC2—activated carbons, CB—carbon black, PTFE—polytetrafluoroethylene

[0055] High-shear treatment during pre-compaction of the carbon-PTFE mixture enables to reduce the relative quantity of the binding material (Table 2) required for efficient binding of the carbon particles in the electrode that is beneficial for increasing the quantity of active materials (i.e. porous carbon) in the predetermined volume of the energy storage cell.

[0056] Table 2. Comparison of the densities achievable with different quantities of binding material in the pre-compacted electrode material made according to this invention.

TABLE-US-00002 TABLE 2 Bulk density of the compacted Composition high-shear experimental experimental Sample of the electrode treated electrode body body No mixture material, g/cm3 mass (g) hight (cm) #9 87% AC2 + 3% 0.664 0.53732 0.74 CB + 10% PTFE #16 92% AC2 + 3% 0.657 0.53245 0.741 CB + 5% PTFE