Catalyst, Catalyst Precursor, Production Process, and Resulting High Purity and Controlled Morphology Carbon Nanotubes

Abstract

A catalyst, catalyst precursor, and carbon nanotubes grown using the catalyst. The catalyst includes a support comprising alumina and a cobalt species on a surface of the support, wherein cobalt is the sole active catalyst species for carbon nanotube growth. The support surface is iron-free.

Claims

1. A carbon nanotube (CNT)-based composition, comprising: at least about 99 weight % CNT; and no more than about 0.5 weight % metal catalyst; wherein the residual mass as determined by an ashes method is no more than about 0.80 weight %.

2. The CNT-based composition of claim 1, comprising at least about 99.7 weight % CNT.

3. The CNT-based composition of claim 1, comprising no more than about 0.3 weight % metal catalyst.

4. The CNT-based composition of claim 1, wherein the CNT comprise multi-wall CNTs.

5. The CNT-based composition of claim 1, wherein the CNT have a BET surface area of over 300 m.sup.2/g.

6. The CNT-based composition of claim 1, wherein the CNT have a pore volume of at least about 2 cc/g.

7. The CNT-based composition of claim 1, wherein the CNT have a bulk density of at least about 0.08 g/cc.

8. The CNT-based composition of claim 1, wherein the CNT have a diameter range of from about 8 nm to about 12 nm.

9. The CNT-based composition of claim 1, wherein the CNT have a G/D relative Raman intensity ratio of at least about 1 measured using a 638 nm laser source and at least about 0.9 measured using a 532 nm laser source.

10. The CNT-based composition of claim 1, wherein the CNT have lengths of at least about 10 microns.

11. The CNT-based composition of claim 1, wherein at least most of the CNT have a bulk density in the range of from about 0.06 to about 0.09 g/cc.

12. The CNT-based composition of claim 1, made in a fluidized bed reactor or a rotary tube reactor using a catalyst comprising an alumina support and cobalt on a surface of the support, wherein cobalt is the sole active catalyst species for CNT growth, and wherein the surface of the support is iron-free.

13. The CNT-based composition of claim 12, wherein a carbon source for the CNT is provided into the reactor, wherein the carbon source comprises one or more of CO, CH.sub.4, C.sub.2H.sub.2, C.sub.2H.sub.4, C.sub.3H.sub.6, C.sub.2H.sub.6, C.sub.3H.sub.8, and C.sub.4H.sub.10.

14. The CNT-based composition of claim 12, wherein the support further comprises an element from Group IIA of the periodic table.

15. The CNT-based composition of claim 14, wherein the element from Group IIA of the periodic table comprises magnesium.

16. The CNT-based composition of claim 12, wherein the cobalt is developed from a cobalt oxide.

17. The CNT-based composition of claim 12, wherein the cobalt comprises less than 15% by weight of the catalyst.

18. The CNT-based composition of claim 12, wherein the cobalt comprises about 10% by weight of the catalyst.

19. The CNT-based composition of claim 12, wherein the catalyst has a BET surface area of over 300 m.sup.2/g.

20. The CNT-based composition of claim 12, wherein the catalyst has a pore volume of at least about 0.25 cc/g.

21. The CNT-based composition of claim 12, wherein the catalyst is configured to yield at least about 85% CNT.

22. The CNT-based composition of claim 12, wherein the catalyst is configured to produce multi-wall CNTs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Various aspects of at least one example are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and examples, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the inventions. In the figures, identical or nearly identical components illustrated in various figures may be represented by a like reference character or numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

[0033] FIG. 1 is a schematic diagram of a prior art catalyst preparation procedure.

[0034] FIG. 2 is a schematic diagram of a catalyst preparation procedure of the present disclosure.

[0035] FIG. 3A is a Raman spectrum using 638 nm laser source for prior art CNT comprising 96.90% MWCNT.

[0036] FIGS. 3B and 3C are similar Raman spectra but for two examples of the inventive purified CNTs made using the Co/MgOAl.sub.2O.sub.3 based catalyst, at two different carbon purities, 99.70% and 99.17% MWCNT, respectively.

[0037] FIG. 4A is a Raman spectrum using 532 nm laser source for the prior art CNT comprising 96.90% MWCNT reported in FIG. 3A.

[0038] FIGS. 4B and 4C are similar Raman spectra but for the two examples of the inventive purified CNTs at two different carbon purities, 99.70% and 99.17% MWCNT, respectively, as reported in FIGS. 3B and 3C.

[0039] FIGS. 5A and 5B are Raman spectra using a 532 nm laser source and a 638 nm laser source, respectively, for examples of the inventive purified CNTs made using the CoAl.sub.2O.sub.3 based catalyst.

[0040] FIG. 6 includes nine SEM images. The top row is taken at 1 KX, the middle row at 5 KX and the bottom row at 25 KX. The leftmost column includes three images of CNTs of the present invention created based on a ten-minute reaction time, the middle column includes three images of CNTs of the present invention created based on a twenty-minute reaction time, and the rightmost column includes three images of CNTs of the present invention created based on a thirty-minute reaction time.

[0041] FIG. 7 is an SEM image taken at 10 KX magnification corresponding to the CNTs synthesized in the present invention and capturing the supported catalyst.

[0042] FIG. 8 is an SEM Image taken at 10 KX magnification corresponding to the CNT purified sample at 99.17 wt % carbon, details of which are provided in other drawings, as indicated herein.

[0043] FIG. 9 is an SEM image taken at 10 KX magnification for a purified CNT of the present invention made using the Co/Al.sub.2O.sub.3 catalyst.

[0044] FIG. 10 includes nine SEM images organized in the same manner as those of FIG. 6, but of prior art CNTs, wherein the top row is taken at 1 KX, the middle row at 5 KX and the bottom row at 25 KX. The leftmost column includes three images of prior art CNTs created based on a ten-minute reaction time, the middle column includes three images of prior art CNTs created based on a twenty-minute reaction time, and the rightmost column includes three images of prior art CNTs created based on a thirty-minute reaction time.

[0045] FIG. 11 illustrates the CNT length distribution in an aqueous dispersion of inventive CNTs.

DETAILED DESCRIPTION

[0046] Examples of the materials, systems, methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The materials, systems, methods and apparatuses are capable of implementation in other examples and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, functions, components, elements, and features discussed in connection with any one or more examples are not intended to be excluded from a similar role in any other examples.

[0047] Examples disclosed herein may be combined with other examples in any manner consistent with at least one of the principles disclosed herein, and references to an example, some examples, an alternate example, various examples, one example or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one example. The appearances of such terms herein are not necessarily all referring to the same example.

[0048] Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to examples, components, elements, acts, or functions of the computer program products, systems and methods herein referred to in the singular may also embrace embodiments including a plurality, and any references in plural to any example, component, element, act, or function herein may also embrace examples including only a singularity. Accordingly, references in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of including, comprising, having, containing, involving, and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to or may be construed as inclusive so that any terms described using or may indicate any of a single, more than one, and all of the described terms.

[0049] In this invention, the limitations presented above were solved by the preparation of a catalyst with a low Co loading supported on MgAl.sub.2O.sub.4, MgOAl.sub.2O.sub.3, and processes for the use of the catalyst for the production of CNTs having high purity and controlled morphology. These CNTs are useful in energy storage and other commercial applications that require or are advantaged by these features.

[0050] Unlike the prior art, in examples herein a solution containing either a Co salt alone, or Co and Mg salts in combination, is contacted with an alumina precursor (Al(OH).sub.3) to form a homogeneous paste in a mixing equipment. After a certain aging time, where the Co.sup.+2 and Mg.sup.+2 ions are exchanged with the OH.sup. groups of the Al(OH).sub.3, the paste is dried at different temperatures to control the thermal decomposition of the salts. The drying stage helps to prevent the exothermic decomposition of the active metal surface dispersion that can be caused if the removal of water and the reaction of the metal salts containing nitrates or acetates are carried out faster, such as in the reactor. This excessive heat produced by the exothermic decomposition reaction of nitrates or acetates can be controlled by using air diluted with N.sub.2 or N.sub.2 flow during the drying stage.

[0051] The dried solid is ground and sieved to the desired particle sizes, depending on the reactor to be employed for CNTs synthesis, and subsequently, calcined at moderate temperature (e.g., 450 C.) to control the textural properties (specific surface area, pore sizes distribution, pore volume) and surface properties (surface acidity, surface charge) of the catalyst support and to prevent the active metal from reacting with the alumina of the catalyst support to form the inactive CoAl.sub.2O.sub.4 phase. Depending on the type of aluminum hydroxide employed (boehmite, gibbsite or bayerite), different types of transition aluminas (-Al.sub.2O.sub.3, -Al.sub.2O.sub.3 or -Al.sub.2O.sub.3) can be produced after calcination at temperatures above 250 C. This is the importance of a well-controlled calcination process.

[0052] The synthesis of carbon nanotubes is carried out in a fluidized bed or rotating tube reactor at temperatures between 60 and 800 C. in the presence of a gaseous mixture of a carbon source (e.g., ethylene) and hydrogen. Ethane, propane, propylene and butane, and potentially other gaseous hydrocarbons, can also be used as carbon sources, either individually or in a desired combination. The residence time of the catalyst in the rotary tube reactor in some examples is 10 minutes compared to 30 minutes of reaction in a fluidized bed reactor in the prior art. Under these reaction conditions, carbon yields greater than 90% are obtained, conversion levels comparable to the prior art.

[0053] After removing the metals and support particles from the catalyst using inorganic acid solutions, a product whose carbon purity is greater than 99.8 wt % is obtained.

[0054] Examples include the following:

Example 1

[0055] In this example, and as depicted in FIG. 1, a prior-art CoMo/Al.sub.2O.sub.3 supported catalyst was prepared according to the method described in the prior art (e.g., the patent incorporated by reference herein). Aluminum hydroxide (Al(OH).sub.3) was calcined at 400 C. for 4 h to obtain alumina (Al.sub.2O.sub.3) catalyst support. The calcined material was subsequently impregnated with a solution containing cobalt nitrate and ammonium heptamolybdate (an active metal solution). The Co:Mo:Al.sub.2O.sub.3 molar ratio composition of the catalyst was 5:1:15, respectively. Citric acid was added to the solution to avoid cobalt molybdate precipitation. The impregnated material was subsequently aged with stirring in a thermostatic bath for 30 minutes at 60 C. and then the excess of water was removed from the solid under vacuum to form wet cake. The drying was completed at 120 C. and then the solid was calcined at 300 C. for 4 h. The catalyst was sieved to a grain size between 100 and 300 microns to create the final catalyst.

[0056] Two catalysts according to the invention were also prepared. One was based on Co/Al.sub.2O.sub.3 and the other on Co/MgOAl.sub.2O.sub.3. These catalysts were prepared according to the following procedure, outlined in FIG. 2. For the first catalyst, a solution containing cobalt nitrate was contacted with Al(OH).sub.3 in a mixer to form a paste. In the second catalyst, a magnesium nitrate salt was added to the cobalt nitrate solution. The Co, MgO and Al.sub.2O.sub.3 molar composition (Co:Al.sub.2O.sub.3 and Co:MgO:Al.sub.2O.sub.3) in the catalysts are 14:70 and 14:1:70, respectively. The impregnated materials were subsequently aged at room temperature for 2 hr., subsequently dried at 60 C. for 3 hours and finally at 120 C. for 2 hours in air flow. The dried solid particles were sieved to a grain size between 100 and 300 microns and calcined in air flow at 450 C. for 3 h to create the final catalyst.

[0057] These catalysts were used in the synthesis of carbon nanotubes carried out in a fluidized bed reactor (FBR) and in a rotary tube reactor (RR) under the following conditions:

[0058] For the fluidized bed reactor, the process gas contained 80 v % ethylene and 20 v % of H.sub.2, a space velocity (WHSV) of 180 L C.sub.2H.sub.4/g. catalyst hour, a reaction temperature of 675 C. and reaction time of 10, 20 and 30 minutes.

[0059] For the rotary tube reactor, the process gas contained 60 v % ethylene, 20 v % H.sub.2 and 20 v % N.sub.2, the catalyst residence time in the reaction zone was about 10 minutes and the ethylene flow/catalyst feed ratio was 3 liters/gram.

[0060] Table 1 includes the results of the synthesis of the CNTs carried out in a fluidized bed reactor (FBR) at different reaction times for the prior art catalyst and both Co/Al.sub.2O.sub.3 and Co/MgO-Al.sub.2O.sub.3 prepared catalysts, all as described above. It is observed that the ethylene conversion increases progressively with the reaction time. The catalysts prepared according to the method of the present invention show the highest MWCNT yield, despite the fact that the active phase composition is 5 wt % lower in the catalyst prepared in the present invention, as described below. The maximum MWCNT content reached for the catalyst of the present invention is 94.2 wt % for the Co/MgOAl.sub.2O.sub.3 catalyst and 96.4 wt % for the Co/Al.sub.2O.sub.3 catalyst, which corresponds to a CNT/catalyst productivity ratio of about 16.2 and 17.9, respectively.

[0061] The same Table reports the result of the MWCNT yield obtained after 10 minutes of reaction in the rotating tube reactor (RR) for the Co/MgOAl.sub.2O.sub.3 catalyst of the present invention. It is observed that the MWCNT yield obtained in rotary reactor is lower than that of fluidized bed reactor (88.4 wt % vs 92.0 wt %). This is mainly due to the existence of a better heat and mass transfer and an optimal contact between the ethylene molecules and the active surface of the catalyst in the fluidized bed reactor. However, this catalyst is much more active than that of the prior art. which showed a MWCNT yield of only 75.5 wt %.

TABLE-US-00001 TABLE 1 Effect of the reaction time on the MWCNT yield Catalyst 7 minutes 10 minutes 20 minutes 30 minutes Prior art (FBR) 75.5 wt % 78.2 wt % 81.1 wt % Present invention (FBR) Co/MgO- 89 wt % 92.0 wt % 93.4 wt % 94.2 wt % Al.sub.2O.sub.3 Present invention (RR) Co/MgO- 88.4 wt % Al.sub.2O.sub.3 Present invention (FBR) Co/Al.sub.2O.sub.3 96.4 wt %

Example 2: Properties of the Catalysts

[0062] In this example are compared the textural properties of the alumina support and the prepared cobalt supported catalysts (Table 2). The surface area of the aluminum hydroxide used for the synthesis of the alumina and the catalyst is about 5 m.sup.2/g. When the Al(OH).sub.3 was calcined at 400 C. to form Al.sub.2O.sub.3, the specific surface area increased to about 369 m.sup.2/g and the pore volume to about 0.29 cc/g. The average pore diameter was 27 A. For the prior art catalyst preparation, when the active metals were deposited on the Al.sub.2O.sub.3 surface, both specific surface area and pore volume decreased to about 267 m.sup.2/g and about 0.22 cc/g, respectively. However, the catalyst of the present invention shows a surface area and pore volume comparable to that of Al.sub.2O.sub.3 support (348 m.sup.2/g and 0.27 cc/g) and a lower cobalt content than the catalyst of the prior art (about 33% less cobalt). In spite of the lower active phase composition of the present invention catalyst its MWCNT yield is significantly higher.

TABLE-US-00002 TABLE 2 Textural and active metal composition of the different catalysts BET Pore S.A volume Co Mo MgO Al.sub.2O.sub.3 Catalyst (m.sup.2/g) (cc/g) (wt %) (wt %) (wt %) (wt %) Al.sub.2O.sub.3 369 0.29 Catalyst prior art 267 0.22 15.3 5.0 79.7 Catalyst present 348 0.27 10.3 0.50 89.2 invention Catalyst present 10.0 90.0 invention

Example 3: Properties of the MWCNT Purified Materials

[0063] To compare the intrinsic properties of the carbon nanotubes syntheses, the CNTs samples obtained after 30 minutes reaction time were subjected to a chemical purification treatment. An acid solution containing 22.5% v of HF was used to digest the catalyst particles. This treatment was carried out overnight at room temperature under stirring. The solid was then separated from the HF acid solution by vacuum filtration. The purified CNTs were washed with abundant deionized water several times until reaching a neutral pH and subsequently dried using a freeze-dryer.

[0064] The characterization results of these purified carbon nanotubes samples are shown in Table 3. The CNT sample corresponding to the prior art has a carbon purity of approximately 96.84 wt % (i.e., a residual metal content of about 3.16 wt %), while the residual metal in the CNTs synthesized using the catalysts of the present invention was about one tenth of this, or between 0.30-0.35 wt %, which represent a significantly greater carbon purity of about 99.65-99.70 wt %. The specific surface area (BET S.A.) results obtained for the CNTs purified samples show slight differences vs. the values obtained for the catalysts used in the prior art and in the present invention (264 m.sup.2/g vs 267 m.sup.2/g and 337 m.sup.2/g vs 348 m.sup.2/g, respectively). However, the pore volume of the purified samples increased significantly vs. the values observed for their respective catalysts. The greatest increase in pore volume was observed for the CNT synthesized with the catalyst of the present invention (2.5 cc/g for the present invention vs 0.92 cc/g for the prior art). The tap bulk density value is lower for the prior art CNTs (0.056 g/cc). Scanning electron microscopy analyzes (SEM) revealed that both purified carbon nanotubes have external diameters between 10 and 14 nm for the prior art and between 8-12 nm for the present invention. The conductivity properties of the purified samples were determined via surface resistivity measurements using a 4-probe electrode. The results of Table 3 clearly show the higher conductivity of the CNTs synthesized with the catalyst of the present invention. It should be noted that the CNT content was kept the same during the sample preparation for surface resistivity measurements, since there are differences in carbon purity between both samples, the amounts of material used for their preparation have to be normalized.

TABLE-US-00003 TABLE 3 Characterization results of carbon nanotubes (after purification) Residual BET Pore Bulk Electrical metal S.A volume density CNT resistivity (wt %) (m.sup.2/g) (cc/g) (g/cc) Diameter (/) Prior art 3.16 264 0.92 0.056 10-14 1566 Present 0.30 337 2.5 0.087 8-12 1287 invention Co/MgO-Al.sub.2O.sub.3 Present 0.83 329 2.4 0.062 9-12 906 Invention Co/MgO-Al.sub.2O.sub.3 Present 0.35 339 2.4 0.066 8-12 1271 Invention Co/Al.sub.2O.sub.3

Raman Spectra:

[0065] Raman spectroscopy is a useful technique for carbon nanotube characterization which enable the determination of the purity of tubular carbon species and their number of structural defects through the G/D relative intensities determination. Analysis was conducted using both the 532 and 638 nm laser sources. The D-band located at approximately 1350 cm-1 is attributed to the presence of amorphous carbon and/or structural defects in the carbon nanotubes while the G-band, located at approximately 1585 cm-1, corresponds to tubular carbon. The G/D ratios values obtained using 532 nm laser source were lower compared to the values obtained using 638 nm laser source. FIGS. 3A-3C (using 638 nm laser source) and FIGS. 4A-4C (using 532 nm laser source) shows the Raman spectra corresponding to the CNTs purified samples of the prior art and that of the present invention obtained with the Co/MgOAl.sub.2O.sub.3 catalyst. It is clearly observed that the G/D ratio is higher in the sample of the present invention when analyzed by both the laser sources, which implies that the CNTs have higher purity in tubular carbon and/or fewer structural defects. FIGS. 5A and 5B illustrate the Raman spectra corresponding to a purified CNT sample obtained with the Co/Al.sub.2O.sub.3 catalyst. The G/D ratio value using the 532 nm laser is similar to those obtained CNTs obtained using the Co/MgOAl.sub.2O.sub.3 catalyst. Using the 638 nm laser, the obtained G/D ratio value is significantly higher than the CNTs purified product of prior art.

[0066] ICP (inductively coupled plasma) spectroscopy analysis is a useful technique for analyzing the chemical composition of the materials. Analysis was conducted on a sample that contained 99.70 wt % MWCNT and the results showed that total metal content was less than 2000 ppm, with almost 1814 ppm (approx. 90%) of this metal being Co. Table 4 provides a more complete description of metals observed in the sample:

TABLE-US-00004 TABLE 4 ICP results of the purified carbon nanotubes sample obtained with the Co/MgO-Al.sub.2O.sub.3 catalyst. Other metal Metal Al Co Mg impurities ppm 12 1814 2.31 105.3

Example 4: Morphology Properties of the CNTs

[0067] In this example, the CNTs synthesized with the Co/MgOAl.sub.2O.sub.3 catalyst at different reaction times in Example 1 were analyzed by the Scanning Electron Microscopy (SEM) technique in order to investigate their morphological properties. FIG. 6 includes the SEM images obtained at 1 KX, 5 KX, and 25 KX magnification corresponding to the CNTs obtained in the present invention, while FIG. 10 provides the same for CNTs obtained using the prior art catalyst described above. Differences in morphological properties of the CNTS are clearly observed. The carbon nanotubes of the present invention form long rods-like structures whose lengths are greater than 10 microns and the CNT diameter varies between 8 to 12 nm. As the reaction time increases from 10 minutes to 30 minutes these rods get longer but the diameter of the CNTs do not change (FIG. 6).

[0068] FIG. 7 shows an SEM image taken at 10 KX magnification of the CNTs synthesized in the present invention. It shows the growth of MWCNTs rods on a catalyst particle.

[0069] FIG. 8 shows SEM images corresponding to MWCNT purified samples where no residual catalyst particles are visible and the tubes preserve the same morphology before and after purification.

[0070] FIG. 9 shows an SEM image taken at 10 KX magnification of the inventive CNTs synthesized with the Co/Al.sub.2O.sub.3 catalyst. The morphology looked similar compared to the CNTs synthesized using the Co/MgO-Al.sub.2O.sub.3 catalyst.

[0071] The carbon nanotubes synthesized according to the prior art show agglomerated cotton ball-like structures (FIG. 10). The tubes are short (<10 microns) and their diameter varies between 10 and 14 nm. These differences in CNT morphology may influence the dispersibility and electrical conductivity properties that are important for the Li-ion battery electrode fabrication.

Example 5: Method for Dispersing Carbon Nanotubes

[0072] An aqueous dispersion of purified CNTs was prepared using polyvinylpyrrolidone (PVP), and N-methy-2-pyrrolidone (NMP) as dispersing agents and their composition is shown in Table 5.

TABLE-US-00005 TABLE 5 Composition of the CNT dispersion in the present invention Formulation CNTs PVP NMP Total Solids Composition 1.53 1.52 96.95 3.05 (wt %)

[0073] The procedure for preparing the CNT dispersion was as follows: [0074] 1) Weigh a desired quantity of purified CNTs and PVP stock (9.1 wt % PVP in NMP) solution in a cup, [0075] 2) Apply high speed mixer and mill, with paste composition being 6.26 wt % purified CNTs, 6.24 wt % PVP and 87.49% NMP, [0076] 3) Dilute further with NMP to obtain a final composition of 1.53 wt % purified CNTs, 1.52 wt % PVP and 96.95 wt % NMP, and [0077] 4) Sonicate the above solution using 8600 kJ/L energy.

[0078] The viscosity of the prepared CNT dispersion is about 3800 cps. Testing of the prepared CNT dispersion using a Hegman gauge indicates a uniform particle size distribution.

[0079] SEM analysis was employed to determine the CNT morphology properties in the dispersion. The CNT dispersion was diluted with DI water to analyze individual CNTs and then this diluted sample was vacuum filtered on a polycarbonate or alumina filter and rinsed several times with water and alcohol to remove residual dispersing agents. A total of about 50 measurements were made at several spots on the filter for determining the length of dispersed CNTs. The results of the length distribution analysis are shown in FIG. 11 and described below.

[0080] As the SEM images of FIGS. 6 and 7 (as produced) and FIG. 8 (purified) show, the length of the tubes after synthesis and purification is longer than 10 microns. However, SEM images of the CNTs after dispersion preparation shows length distribution almost entirely in the 1 to 5 microns range.

[0081] During dispersion, the CNTs are disentangled, which can result in breakage. If the tubes are long enough to begin with (as is the case here) and disentangled enough to begin with (as is the case here), then it is possible to make a dispersion comprising individualized CNTs that have an average length of at least about 1 micron (such as here, where the lengths are about 2 microns on average). Note that, assuming the CNTs are well-dispersed, that longer average length is desired, as this lowers the percolation threshold for the CNT electrically conductive network (i.e., it takes a lower loading of CNTs to achieve a low electrical resistivity network). Note also, however, that it may be best to ensure that there are relatively few CNTs in the dispersion that are greater than about 5 microns in length. The reason for this is to minimize toxicity of the CNTs. In the unlikely event that CNTs were inhaled into the lungs, then CNTs with length greater than about 5 microns are not easily ingested by macrophages that clear debris out of lungs. The present example clearly shows a dispersion with average length greater than about 1 micron, with negligible fraction being greater than about 5 microns.

[0082] The CNT produced using the catalysts of this disclosure are well suited for use in LiB. For one, the CNT are iron-free. Iron is the source of many problems in LiB. Battery producers prefer conductive carbon materials without iron. Also the metal loading levels of the purified CNT (primarily Co, or Co and Mg) is extremely low, in the range of 2,000 ppm (see Table 4), most of which is Co (1814 ppm).

[0083] Typically, as produced CNT products contain about 90 wt % carbon and about 10% supported catalyst. The present catalyst support is typically comprised of either alumina or magnesium oxide/alumina. Typically, the catalyst support represents more than 90 wt % of the supported catalyst, so the cobalt metal represents less than 10 wt % of the supported catalyst and less than 1 wt % of the as-produced products. Importantly, the overwhelming majority of the cobalt metal ends up being an active catalyst site. Any active sites end up nucleating the growth of CNTs and get fully encapsulated by carbon during CNT synthesis. Based on the high CNT yield and amount of cobalt in the catalyst composition, it is expected that at least 80% of the cobalt metal ends up being an active catalyst site. Thus, less than about 20 wt % of the cobalt ends up not being encapsulated by carbon. During chemical purification, essentially 100% of the catalyst support is removed, leaving a purified CNT products composition with greater than about 99.5 wt % carbon. Consistent with this, ICP analysis shows that cobalt content in purified CNT products is about 1814 ppm or 0.18 wt %. If only 20 wt % of this cobalt was inactive and therefore was not encapsulated by carbon, then this represents 0.036 wt %. Typical conductive CNT additive loadings in cathodes or anodes of LiB are expected to be about 0.5 wt % or less. Thus, the cobalt impurity that is not encapsulated by carbon will be less than about (0.036%0.5%)=0.00018 wt % or less than about 1.8 ppm of the electrode weight. This level of non-encapsulated cobalt impurity is not expected to be of concern to battery cell producers and battery industry experts. Also, Co is already present in LiBs, and so is generally a benign element present in conductive carbon (CNT) used in cathodes and anodes.

[0084] Having described above several aspects of at least one example, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only, and the scope of the invention should be determined from proper construction of the appended claims, and their equivalents.