Compositions comprising carbon nanotube bundles and use thereof in battery cells

Abstract

Liquid compositions containing carbon nanotubes may be produced without de-agglomerating the carbon nanotubes prior to blending the carbon nanotubes with a solvent. The compositions may comprise a solvent, and a plurality of carbon nanotubes dispersed in the solvent, in which the carbon nanotubes comprise a plurality of carbon nanotube bundles, and the carbon nanotubes have a bulk density of about 0.5 g / cm3 or greater and an aspect ratio of about 1000 or greater. The carbon nanotubes may be produced by a floating catalyst chemical vapor deposition process. The compositions may be incorporated within a battery cell as a non-limiting example.

Description

COMPOSITIONS COMPRISING CARBON NANOTUBE BUNDLES AND USE THEREOF IN BATTERY CELLSFIELD

[0001] The present disclosure relates to batteries and battery cell materials and, more particularly, battery cells containing carbon nanotubes.BACKGROUND

[0002] Carbon nanotubes (CNTs), including single-walled carbon nanotubes (SWCNTs) and multi- walled carbon nanotubes (MWCNTs), are an allotrope of carbon comprising cylindrical nanoscale carbon structures having rounded ends. The sidewalls of carbon nanotubes are formed from fused 6-membered rings, whereas the rounded ends contain 5-membered rings surrounded by 6-membered rings.

[0003] Many applications have been proposed for carbon nanotubes due to their combination of excellent mechanical, electrical, and thermal properties. Costs of carbon nanotubes have dropped considerably in recent years, thereby rendering their incorporation in a diverse range of applications much more feasible. Among the numerous desirable mechanical properties of carbon nanotubes are high values for tensile strength, strain to failure, and tensile modulus. Additionally, carbon nanotubes are highly resistant to fatigue, radiation damage, and heat, thus facilitating their use under harsh conditions.

[0004] Carbon nanotubes (including carbon nanotube composites) have been explored for many applications in energy storage, including incorporation in batteries. Incorporating carbon nanotubes in batteries may increase battery performance, such as improving charging capacity and charging rate. Despite the potential benefits of incorporating carbon nanotubes into batteries, processing of carbon nanotubes remains difficult and performance gains approaching theoretical values have not yet been realized in many instances. Processing and performance difficulties may be due, at least in part, to the difficulty in dispersing carbon nanotubes in various media, including solvents and polymers. In addition, amorphous carbon impurities and inorganic impurities, such as metallic or mineral impurities (e.g, iron, manganese, chromium, cobalt, nickel, aluminum, molybdenum, vanadium, and silicon) may further degrade performance of battery cells in which carbon nanotubes are present. Such impurities may be present in carbon nanotubes in varying amounts depending on the specific process used to manufacture the carbon nanotubes. For example, carbon nanotubes prepared by many traditional synthesis processes may retain residual metallic catalysts, which are frequently difficult to remove.SUMMARY

[0005] In various aspects, the present disclosure provides compositions comprising: a solvent; and a plurality of carbon nanotubes dispersed in the solvent: wherein the carbon nanotubes comprise a plurality of carbon nanotube bundles, and the carbon nanotubes have a bulk density of about 0.5 g / cm3or greater and an aspect ratio of about 1000 or greater. In non-limiting examples, the compositions may be present in a battery cell.

[0006] In other various aspects, methods of the present disclosure comprise: providing a plurality of carbon nanotubes comprising a plurality of carbon nanotube bundles; wherein the carbon nanotubes have a bulk density of about 0.5 g / cm3or greater and an aspect ratio of about 1000 or greater; and dispersing the plurality of carbon nanotubes in a solvent to form a composition; wherein at least a portion of the carbon nanotubes remain bundled when dispersed in the solvent.

[0007] These and other features and attributes of the disclosed compositions and methods of the present disclosure and their advantageous applications and / or uses will be apparent from the detailed description which follows.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings. The following figures are included to illustrate certain aspects of the disclosure and should not be viewed as exclusive configurations. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

[0009] FIG. 1 is an illustrative TEM image of carbon nanotubes produced using a FCCVD process.

[0010] FIG. 2 is a graph of charging capacity as a function of cycles at various charging rates for experimental and comparative samples.

[0011] FIG. 3 is a graph of DC internal resistance for experimental and comparative samples.

[0012] FIG. 4 is a graph of discharge capacity ratio as a function of discharge rate for experimental and comparative samples.

[0013] FIG. 5 are electronic microscopic graphs of experimental and comparative samples coated.

[0014] FIG. 6 is a graph of charging capacity as a function of cycles at various charging rates for experimental and comparative samples.

[0015] FIG. 7 is a graph of DC internal resistance for experimental and comparative samples.

[0016] FIG. 8 is a graph of discharge capacity ratio as a function of discharge rate for experimental and comparative samples.DETAILED DESCRIPTION

[0017] The present disclosure relates to batteries and battery cell materials and, more particularly, battery cells containing carbon nanotubes.

[0018] Advantageously, the present disclosure provides carbon nanotube compositions and methods for production thereof that may facilitate incorporation of the carbon nanotubes into battery cells, such as in a liquid composition. The compositions may provide battery cells having improved battery performance, including increased charging capacity and decreased resistance. In addition, the compositions may exhibit a relatively low impurity level, particularly a low level of metal impurities, which may further aid in improving battery performance. The foregoing feature may be realized without debundling as-produced carbon nanotubes, as described further herein. Surprisingly, the carbon nanotubes may be manipulated to form such compositions even when the carbon nanotubes have a high aspect ratio and are otherwise prone toward bundling and agglomeration.

[0019] Conventional methods for producing carbon nanotubes may retain significant quantities of impurities in the carbon nanotubes, including both carbonaceous and metal impurities, in amounts as high as about 20 wt%. Extensive purification may be needed to achieve a satisfactory impurity profile for use of the carbon nanotubes in battery applications. Such purification strategies may be time-consuming, increase processing expense, and degrade the conductivity performance of the carbon nanotubes in some cases.

[0020] To address the foregoing difficulty, the present disclosure utilizes a floating catalyst chemical vapor deposition (FCCVD) method for producing the carbon nanotubes. FCCVD methods may be tuned to afford a relatively low amount of impurities, particularly metal impurities, as well as produce the carbon nanotubes in a form from which they may be easily processed to promote effective dispersion in media such as polymers and solvents. Moreover, to the extent that further removal of metal impurities is needed, the present disclosure provides methods for removing at least a portion of such metal impurities with a mild acid. Preferably, the mild acid may comprise one or more organic acids, which may enhance metal dissolution through salt formation and / or complexation depending on structure of the organic acid.

[0021] In addition to the foregoing, the present disclosure may utilize carbon nanotubes in the form of a carbon nanotube powder that may further promote dispersion in various media. The carbon nanotube powder may be produced directly from FCCVD or by chopping or otherwise mechanically processing carbon nanotubes obtained from a carbon nanotube productionprocess, particularly FCCVD, to provide a low-density carbon nanotube construct. The carbon nanotubes within the carbon nanotube powder may comprise carbon nanotube bundles that are entangled with one another and optionally a variable fraction of individualized carbon nanotubes that are also mutually entangled, yet may undergo ready dispersion in a solvent in the disclosure herein. The term “bundle” refers to a structure where carbon nanotubes are tightly assembled wall-to-wall, and depending on the number and diameter of the carbon nanotubes, exhibit a bundle diameter up to about 200 nm. The entangled carbon nanotube bundles may undergo ready dispersion once processed with a solvent and incorporated within a battery cell. The carbon nanotube powders may retain the carbon nanotube bundles in a readily dispersible state even after treating with an organic acid, should a further reduction in the content of metal impurities be needed. Surprisingly, the carbon nanotube bundles need not be further debundled fully into individual carbon nanotubes in order to realize enhanced performance when utilized in the applications disclosed herein. Moreover, the bundles may remain present once the carbon nanotubes are dispersed in the solvent.

[0022] The compositions of the present disclosure, which may be suitable for incorporation in a battery cell, may include a solvent and a plurality of carbon nanotubes dispersed in the solvent. An anionic, cationic, or polymeric surfactant may also be present to facilitate the dispersion of the carbon nanotubes. The carbon nanotubes may be produced by FCCVD and be in the form of readily dispersible bundles, as discussed above. Optionally, a polymer such as polyvinylidene fluoride (PVDF) may also be dispersed in the solvent as well. The carbon nanotubes may be dissolved, dispersed as solids, or any combination thereof in the solvent. The carbon nanotubes may comprise a plurality of carbon nanotube bundles, optionally mutually entangled with individual carbon nanotubes, and the carbon nanotubes (combination of carbon nanotube bundles and individual carbon nanotubes) may have a bulk density of about 0.5 g / cm3or greater (preferably 0.7 g / cm3or greater) and an aspect ratio of about 1000 or greater. Additional properties of the carbon nanotubes are specified below. Suitable solvents and surfactants may be selected for their ability to effectively disperse the carbon nanotubes in the form of carbon nanotube bundles and for suitability of the solvents for use in battery half-cells. Preferably, the carbon nanotube bundles may further be in a form of a carbon nanotube powder prior to dispersion in the solvent.

[0023] The compositions of the present disclosure may have a carbon nanotube content, by mass of the composition, of about 0.01 wt% or above, such as ranging from about 0.05 wt% to about 10 wt%, or about 0.05 wt% to about 7 wt%. or about 0.05 wt% to about 6 wt%, or about 0.05 wt% to about 2.5 wt%, or about 0.05 wt% to about 1.5 wt%, or about 0.05 wt% to about0.75 wt%, or about 0.05 wt% to about 0.5 wt%, or about 0.05 wt% to about 0.1 wt%, or about 0.1 wt% to about 10 wt%, or about 0.1 wt% to about 7 wt%, or about 0.1 wt% to about 6 wt%, or about 0.1 wt% to about 2.5 wt%, or about 0.1 wt% to about 1.5 wt%, or about 0.1 wt% to about 0.75 wt%, or about 0.1 wt% to about 0.5 wt%, or about 1 wt% to about 5 wt%, or about 1 wt% to about 2.5 wt%, or about 1 wt% to about 1.5 wt%.

[0024] The compositions of the present disclosure may have a surfactant content, by mass of the composition, of about 0.01 wt% or above, such as ranging from about 0.05 wt% to about 10 wt%, or about 0.05 wt% to about 7 wt%, or about 0.05 wt% to about 6 wt%, or about 0.05 wt% to about 2.5 wt%, or about 0.05 wt% to about 1.5 wt%, or about 0.05 wt% to about 0.75 wt%, or about 0.05 wt% to about 0.5 wt%, or about 0.05 wt% to about 0.1 wt%, or about 0.1 wt% to about 10 wt%, or about 0.1 wt% to about 7 wt%, or about 0.1 wt% to about 6 wt%, or about 0.1 wt% to about 2.5 wt%, or about 0.1 wt% to about 1.5 wt%, or about 0.1 wt% to about 0.75 wt%, or about 0.1 wt% to about 0.5 wt%, or about 1 wt% to about 5 wt%, or about 1 wt% to about 2.5 wt%, or about 1 wt% to about 1.5 wt%.

[0025] Suitable surfactants may be cationic, anionic, non-ionic. or zwitterionic. Surfactants may include various polymeric surfactants. Suitable surfactants may include, for example, polyvinyl pyrollidone (PVP), poly vinylidene fluoride (PVDF), polybutryal, hydrogenated nitrile butadiene-based rubber (H-NBR), polyvinyl alcohol (PVA), polystyrene sulfonate) (PSS), poly(phenylacetylene) (PAA), poly(mela-phenylenevinylene) (PrnPV). polypyrrole (PPy), poly(p-phenylene benzobisoxazole) (PBO), natural polymers, vinyl polymers with a polar side group, aromatic polymers with a polar group, sodium dodecyl sulfate (SDS) and similar amphiphilic compounds, cyclic lipopeptide biosurfactants such as surfactin, water- soluble polymers, carboxymethyl cellulose, hydroxylethyl cellulose, polyoxyethylene, polyaciylic acid (PAA), polyvinyl chloride (PVC) and combinations thereof. The foregoing are illustrative in nature and numerous other surfactants may also be suitable for use in the disclosure herein

[0026] The compositions of the present disclosure may have a solvent content, by mass of the composition, of about 80 wt% or greater, or about 85 wt% or greater, or about 90 wt% or greater, or about 95 wt% or greater, or about 97 wt% or greater, or about 98 wt% or greater, or about 99 wt% or greater, such as within a range of about 90 wt% to about 99.99 wt%, or about 95 wt% to about 99.99 wt%, or about 96 wt% to about 99.99 wt%, or about 97 wt% to about 99.99 wt%, or about 98 wt% to about 99.99 wt%, or about 99 wt% to about 99.99 wt%.

[0027] The solvent used in the compositions of the present disclosure may comprise at least one dipolar aprotic solvent, at least one protic solvent, or any combination thereof. Suitableprotic solvents may be aqueous or non-aqueous in nature. Example protic solvents may include, for example, water, m-cresol, alcohols (e.g, methanol, ethanol, isopropanol, and the like), or any combination thereof. Example dipolar aprotic solvents suitable for use in compositions of the present disclosure may include, but are not limited to, N-methyl-2-pyrrolidone (NMP) and similar pyrrolidones, N, N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetone and similar ketone solvents, sulfolane, butyl acetate and similar ester solvents, quinolone or quinoline and similar heteroaromatic solvents, ethylene carbonate and similar carbonate solvents, toluene and similar aromatic solvents, cyrene (dihydrolevoglucosenone), or any combination thereof.

[0028] Any carbon nanotubes containing carbon nanotube bundles that may be used without de-agglomeration, optionally with further treatment using an organic acid or a vapor phase treatment to remove metal impurities, may be suitably used in the compositions disclosed herein. In more specific examples, the carbon nanotubes may be produced using a FCCVD process. Illustrative FCCVD processes are disclosed in more detail in U. S. Patent 8,999,285 and International Patent Application Publication WO 2005 / 007926. each of which is incorporated herein by reference. Illustrative FCCVD processes may synthesize carbon nanotubes from a vaporized carbon source in a heated chamber. Example carbon sources suitable for use in the present disclosure may include hydrocarbons such as, but not limited to, acetylene, ethylene, methane, the like, or any combination thereof. Alcohols such as methanol or ethanol may also suitably be used, optionally in combination with the foregoing hydrocarbons. The heated chamber utilized in FCCVD may have any suitable temperature under which carbon nanotube formation takes place such as, for example, a temperature from about 500°C to about 1500°C or about 600°C to about 1300°C. In some examples, the FCCVD process may take place at or near atmospheric pressure (1 bar at sea level).

[0029] Suitable FCCVD processes may take place in the presence of a catalyst effective to convert the carbon vapor into carbon nanotubes. The catalyst may be introduced to the carbon source within the heated chamber and / or prior to entry' of the carbon source into the heated chamber. Example catalysts suitable for use in the present disclosure may include, but are not limited, an iron-based catalyst, a cobalt-based catalyst, a nickel-based catalyst, a molybdenum-based catalyst, the like, or any combination thereof. One of ordinary' skill in the art will be able to implement an FCCVD system and suitable catalyst therefor for production of carbon nanotubes suitable for use herein.

[0030] The carbon nanotubes used herein may comprise single-walled carbon nanotubes, multi-walled carbon nanotubes, or any combination thereof. Any of the carbon nanotubes maycontain a discontinuous wall structure along the carbon nanotube length, which may introduce discontinuities ranging from about 1 nm up to about 10 microns. 100 microns, or 1000 microns in length. When present, the discontinuous wall structure does not extend all the way around the circumference of the carbon nanotube, as this would result in the carbon nanotube being divided into two sections. Branched / bifurcated carbon nanotubes and bamboo-like carbon nanotubes are also possible and may be suitably used. The carbon nanotubes may be further characterized in terms of suitable dimensions and / or properties, as specified hereinafter. It should be noted that the dimensions and / or properties of the carbon nanotubes may be dependent on factors including, but not limited to, the desired carbon nanotube loading in the compositions, the type(s) of carbon nanotubes present, the desired battery cell performance, or any combination thereof.

[0031] In non-limiting examples, the carbon nanotubes may have a diameter of about 1 nanometer (nm) to about 500 nm, or about 5 nm to about 500 nm, or about 5 nm to about 100 nm, or about 1 nm to about 50 nm. The carbon nanotubes may have a length of about 0.001 millimeter (mm) (i.e., 1 micron) to about 20 mm, or about 0.001 mm to about 10 mm. The carbon nanotubes may have a density of about 0.7 g / cm3to about 2.5 g / cm3, or about 0.7 g / cm3to about 2.0 g / cm3, or about 0.7 g / cm3to about 1.9 g / cm3. The carbon nanotubes may have an aspect ratio of about 1000 to about 2000, or about 1000 to about 5000, or about 1000 to about 10,000. or about 10,000 to about 50,000, or even greater than 50,000. The carbon nanotubes may have a surface area, as measured by BET, of about 20 m2 / g to about 2000 m2 / g, or about 50 m2 / g to 1000 m2 / g, or about 25 m2 / g to 1500 m2 / g, or about 50 m2 / g to about 500 m2 / g, or about 500 m2 / g to about 1000 m2 / g. The carbon nanotubes may have a conductivity of about 10 S / m to about 10,000,000 S / m, or about 10 S / m to about 500 S / m. or about 100 S / m to about 1000 S / m, or about 1000 S / m to about 10.000 S / m, or about 10,000 S / m to about 50.000 S / m, or about 50,000 S / m to about 500,000 S / m, or about 500,000 S / m to about 5,000,000 S / m, or about 1,000,000 S / m to about 10,000,000 S / m. The carbon nanotubes may have a tensile strength of about 0.1 GPa to about 4.0 GPa, or about 0.2 GPa to about 3.2 GPa, or about 0.3 GPa to about 3 GPa, or about 0.3 GPa to about 2.8 GPa. The carbon nanotubes may have a have a specific strength of about 1800 kN m / kg to about 2900 kN m / kg, or about 2000 kN m / kg to about 2700 kN m / kg, or about 2200 kN m / kg to about 2600 kN m / kg. The carbon nanotubes may have a strength modulus of about 1 GPa to about 400 GPa, or about 5 GPa to about 300 GPa, or about 5 GPa to about 250 GPa, or about 5 GPa to about 150 GPa. The carbon nanotubes may have a strain to failure ratio of about 0.5% to about 20.0%, or about 0.5% to about 15.0%, or about 1.0% to about 20.0%, or about 1.0% to about 15.0%, or about 1.0% to about 10.0%,or about 1.0% to about 8.0%. It should be understood that carbon nanotube properties outside the aforementioned ranges are additionally contemplated and furthermore it should be understood that selected individual carbon nanotubes within a plurality of carbon nanotubes may fall outside the aforementioned ranges.

[0032] Carbon nanotubes of the present disclosure may be treated with an organic acid following synthesis thereof so as to remove all or at least a portion of any metal impurities that may be present within the plurality of carbon nanotubes. The level of metal impurities may be reduced to about 5 wt% or less, or about 2 wt% or less, or about 1 wt% or less, or about 0.5 wt% or less, or about 0.1 wt% or less, based on the total mass of the carbon nanotubes. Preferably, after treatment with the organic acid, the content of metal impurities may be about 200 ppm or below, or about 100 ppm or below, or about 50 ppm or below, or about 5 ppm or below. Any suitable organic acid may be used to promote purification including, but not limited to, glycolic acid, ascorbic acid, malonic acid, the like or any combination thereof. Stronger organic acids such as methanesulfonic acid, chlorosulfonic acid, and the like may also be suitably used. Inorganic acid such as hydrochloric acid may also be suitable. When used, the organic acid may be used neat or dissolved in water, an aqueous fluid, or an inert organic solvent at any suitable strength such as, for example, about 0.1 mol / L (M) to about 5 M, or about 0.1 M to about 1 M. The carbon nanotubes may be treated at room temperature or below with the acid or heated at any temperature up to reflux, preferably with mechanical agitation such as stirring or sonication, during the treatment process. A carbon nanotube powder may be formed before or after conducting purification with an acid.

[0033] In addition to carbon nanotubes, the compositions of the present disclosure may comprise additional additives. Additional additives may be added at a concentration within the compositions to perform an intended function. Additional additives may be added to the composition through any suitable means and at any suitable point during production of the compositions. One of ordinary skill in the art will be able to select and appropriately add additional additives to the compositions of the present disclosure. Examples of additional additives that may be suitable include, but are not limited to fillers, stabilizers, metals, electrolytes, the like, or any combination thereof. When used, suitable additives may be dissolved in the solvent or dispersed as solids in the composition.

[0034] Once suitable carbon nanotubes and optional additives have been provided according to the foregoing description, the carbon nanotubes and the optional additives may be dispersed in the solvent to form the composition. The carbon nanotubes comprising the plurality of carbon nanotube bundles may be produced using a FCCVD process. To further prepare thecarbon nanotubes for incorporation in the solvent, the methods of the present disclosure may further comprise dissociating and / or chopping the carbon nanotubes to form a carbon nanotube powder prior to formation of the compositions. Powder formation may take place by one or any combination of chopping (e.g., in a blender), grinding, milling, mulling, homogenizing in a high-pressure homogenizer or shear mixer, sonication, tensile dissociation, and the like. Some of the foregoing may also be suitable for dispersing carbon nanotubes in a solvent.

[0035] The compositions may subsequently be formed into a battery cell, either within the cathode or the anode half-cell of a battery, including a lithium-ion battery cell. In some examples, the compositions may be incorporated within the cathode of a lithium-ion battery cell.

[0036] In some examples, the cathode of a lithium-ion battery’ may comprise a composition of the present disclosure. The cathode may comprise a conventional cathode material such as, for example, nickel-manganese-cobalt (NMC), lithium iron phosphate (LFP), lithium nickel manganese spinel (LNMO), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), or lithium cobalt oxide (LCO), and the composition may be in contact with the cathode material or dried directly on the cathode material by removing the solvent. Preferably, the composition containing dispersed carbon nanotubes may be mixed with a slurry' of the cathode material, a polymeric binder, and a solvent. Carbon black may also be present in combination with the carbon nanotubes, such as in a carbon nanotube: carbon black mass ratio of about 1: 10 to about 1:1. The lithium-ion battery may comprise an anode of lithium metal. A separator permeable to lithium ions may separate the cathode from the anode. In some examples, the separator may comprise a glass separator or a polymeric separator. An electrolyte suitable to convey lithium ions from the cathode to the anode is also present in the lithium-ion batteries. In non-limiting examples, the electrolyte may include a salt (e.g.. a hexafluorophosphate salt) in a carbonate solvent, such as ethylene carbonate, propylene carbonate, diethylcarbonate, dimethylcarbonate, or any combination thereof. Other polar aprotic solvents may also be suitably present in the electrolyte, including the polar aprotic solvents that may be present within the compositions of the present disclosure.Additional Embodiments

[0037] The present disclosure is further directed to the following non-limiting embodiments.

[0038] Embodiment 1. A composition comprising: solvent; and a plurality of carbon nanotubes dispersed in the solvent; wherein the carbon nanotubes comprise a plurality of carbon nanotube bundles, and the carbon nanotubes have a bulk density of about 0.5 g / cm3or greater and an aspect ratio of about 500 or greater.

[0039] Embodiment 2. The composition of embodiment 1, wherein the composition comprises about 0.05 wt% to about 10 wt% carbon nanotubes and about 90 wt% or greater solvent, each based on a total mass of the composition.

[0040] Embodiment 3. The composition of any of embodiments 1-2, wherein the solvent comprises N-methyl-2-pyrrolidone.

[0041] Embodiment 4. The composition of any of embodiments 1-3, wherein the carbon nanotubes have a diameter of about 1 nm to about 500 nm.

[0042] Embodiment 5. The composition of any of embodiments 1-4, wherein the carbon nanotubes have a length of about 1 pm to about 2000 pm.

[0043] Embodiment 6. The composition of any of embodiments 1-5, wherein the carbon nanotubes have a density of about 0.5 g / cm3to about 2.5 g / cm3.

[0044] Embodiment 7. The composition of any of embodiments 1-6, wherein the carbon nanotubes have a metal impurity content of about 100 ppm or below.

[0045] Embodiment 8. The composition of any of embodiments 1-7, wherein the carbon nanotubes have a conductivity of about 10 S / m to about 10,000,000 S / m.

[0046] Embodiment 9. The composition of any of embodiments 1-8. wherein the carbon nanotubes have a surface area of about 25 m2 / g to 1500 m2 / g, as determined by BET.

[0047] Embodiment 10. The composition of any of embodiments 1-9, wherein the plurality of carbon nanotubes were produced by a floating catalyst chemical vapor deposition (FCCVD) process.

[0048] Embodiment 11. The composition of any of embodiments 1-10, wherein the plurality of carbon nanotubes were treated with an organic acid to remove at least some metal impurities therefrom, prior to dispersion of the carbon nanotubes in the solvent.

[0049] Embodiment 12. The composition of any of embodiments 1-11, wherein the organic acid comprises glycolic acid, ascorbic acid, malonic acid, hydrochloric acid, nitric acid, or any combination thereof.

[0050] Embodiment 13. The composition of any of embodiments 1-12, wherein the plurality of carbon nanotubes comprise temperature treated carbon nanotubes, having increased crystallinity and decreased impurities as compared to carbon nanotubes which are not temperature treated.

[0051] Embodiment 14. The composition of any of embodiments 1-13, wherein the temperature treatment occurs above 2000°C.

[0052] Embodiment 15. The composition of any of embodiments 1-14, further comprising: a polymer dispersed in the solvent.

[0053] Embodiment 16. A method comprising: providing a plurality of carbon nanotubes comprising a plurality of carbon nanotube bundles; wherein the carbon nanotubes have a bulk density of about 0.5 g / cm3or greater and an aspect ratio of about 500 or greater; and dispersing the plurality of carbon nanotubes in a solvent to form a composition; wherein at least a portion of the carbon nanotubes remain bundled when dispersed in the solvent.

[0054] Embodiment 17. The method of embodiment 16, wherein the composition comprises about 0.05 wt% to about 10 wt% carbon nanotubes and about 90 wt% or greater solvent, each based on a total mass of the composition.

[0055] Embodiment 18. The method of any of embodiments 16-17, wherein the solvent comprises N-methyl-2-pyrrolidone.

[0056] Embodiment 19. The method of any of embodiments 16-18, further comprising: powdering the plurality of carbon nanotubes prior to forming the composition.

[0057] Embodiment 20. The method of any of embodiments 16-19, wherein the plurality' of carbon nanotubes were produced using a FCCVD process.

[0058] Embodiment 21. The method of any of embodiments 16-20, further comprising: treating the plurality of carbon nanotubes with an organic acid to remove at least some metal impurities therefrom, prior to dispersion of the carbon nanotubes in the solvent.

[0059] Embodiment 22. The method of any of embodiments 16-21, wherein the organic acid comprises glycolic acid, ascorbic acid, malonic acid, hydrochloric acid, nitric acid, or any combination thereof.

[0060] Embodiment 23. The method of any of embodiments 16-22, wherein the plurality of carbon nanotubes comprise temperature treated carbon nanotubes, having increased crystallinity' and decreased impurities as compared to carbon nanotubes which are not temperature treated.

[0061] Embodiment 24. The method of any of embodiments 16-23, wherein the temperature treatment occurs above 2000°C.

[0062] Embodiment 25. The method of any of embodiments 16-14, wherein the carbon nanotubes have one or more of the following properties: a diameter of about 1 nm to about 1000 nm. a length of about 1 pm to about 2000 pm, a density of about 0.5 g / cm3to about 2.5 g / cm3, a metal impurity content of about 100 ppm or below, a conductivity of about 10 S / m to about 10,000,000 S / m, or a surface area of about 50 m2 / g to 1000 m2 / g, as determined by BET.

[0063] Embodiment 26. A battery cell comprising the composition of embodiment 1.

[0064] To facilitate a better understanding of the embodiments of the present disclosure, the following examples of preferred or representative embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the invention.Example 1

[0065] Carbon nanotubes were produced according to a FCCVD process, such as that described in International Patent Application Publication WO 2005 / 007926. FIG. 1 is a transmission electron microscope (TEM) image of illustrative carbon nanotubes produced using a FCCVD process. The carbon nanotubes largely comprised bundles of carbon nanotubes having 2-8 walls and having a diameter ranging from 10-50 nm and a length of greater than 10 microns.

[0066] Half-cell cathodes were formed to lithium metal coin-cells (CR2023). The cathodes of experimental samples were prepared by casting a slurry that included 13.5 g of solids |95.5 wt% nickel manganese cobalt (NMC) 622, 1.5 wt% carbon nanotubes, and 3 wt% poly vinylidene difluoride (PVDF)] and 12.7 g NMP. The carbon nanotubes were added directly to the slurry without preparing a solvent dispersion of the carbon nanotubes first. Control samples were prepared similarly, except replacing the carbon nanotubes with an equivalent mass of C65 carbon black. The slurry was mixed for 5 minutes and cast into a 330 micron thick film on a 15 micron Al foil current collector. The cast cathode material and Al foil were then calendared together. In total, the cells included about 18 mg / cm2of active material. The materials were mixed for a time of 5 minutes. The electrolyte used comprised a 1: 1: 1 v / v ratio of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) containing 1 mol / L (M) lithium hexafluorophosphate (LiPF₆). The cells included a glass separator (Whatman 1820) between the cathode and the anode.

[0067] The experimental and control coin cells were subsequently tested for performance over a voltage window of 4.3 V to 2.7 V. A cycling protocol of CC-CV (C / 5 + C / 10Hold) / Discharge CC: C / 10 x 2 -> C / 5 x 5 -> C / 2 x 5 -> 1C x 5 -> 3C x 5 -> -> 5C x 5 -> C / 5 x 5 -> Pulse Section -> C / 5 x 30, where C=180 mA / g, was used. In the foregoing, 1C represents a normal charge rate; 2C, 3C, etc. represent a charge rate higher than the normal charge rate (e.g., twice or three times the normal charge rate); and C / 10, C / 5, C / 2, etc. represent a charge rate lower than the normal charge rate (e.g., one-tenth, one-fifth, or half the normal charge rate). The number following the “C” value represents the number of charging / discharging cycles. Results are shown in FIGS. 2-4. FIG. 2 is a graph of charging capacity as a function of cycles at various charging rates. As shown, samples including carbon nanotube bundles showed increased capacity compared to the comparative sample containing carbon black, especially at highcharging rates. FIG. 3 is a graph of DC internal resistance for the experimental and comparative samples. As shown, the experimental samples containing carbon nanotube bundles had a lower internal resistance compared to the comparative samples. FIG. 4 is a graph of discharge capacity ratio as a function of discharge rate. As shown, experimental samples including carbon nanotube bundles showed increased discharge capacity ratio at higher discharge rates as compared to the comparative samples. Thus, the data demonstrates that even bundles of carbon nanotubes may afford improved performance relative to carbon black in battery applications, even without performing an initial dispersion to produce individualized carbon nanotubes.Example 2

[0068] The experimental samples were prepared by casting a slurry with active cathode materials inside that included 13.5 g of solids [95 wt% nickel manganese cobalt (NMC) 532, 2 wt% carbon nanotubes, and 3 wt% polyvinylidene difluoride (PVDF)] and 13.5 g NMP. The carbon nanotubes were added directly to the slurry without preparing a solvent dispersion of the carbon nanotubes first. Control samples were prepared similarly, except adding 1 wt% carbon nanotubes which is produced from fluidized bed chemical vapor deposition (FBCVD) in an NMP-based pre-dispersion. The slurry was mixed for 5 minutes and cast into a 330 micron thick film on a 15 micron Al foil current collector. FIG. 5 is electronic microscopic graphs of experimental and comparative samples coated on NMC532 particles. As shown, experimental samples have aligned carbon nanotube bundles, and comparative samples were individualized carbon nanotubes coated on cathode particles. The cast cathode material and Al foil were then calendared together. In total, the cells included about 18 mg / cm2of active material. The materials were mixed for a time of 5 minutes. The electrolyte used comprised a 1:1:1 v / v ratio of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) containing 1 mol / L (M) lithium hexafluorophosphate (LiPF₆). The cells included a glass separator (Whatman 1820) between the cathode and the anode sheets.

[0069] The experimental and control coin cells were subsequently tested for performance over a voltage window' of 4.25 V to 2.7 V. A cycling protocol of CC-CV (C / 10 + C / 20 Hold) / Discharge CC: C / 10 x 3 -> C / 5 x 5 -> C / 2 x 5 -> 1C x 5 -> 2C x 5 -> -> 5C x 5 -> C / 10 x 4, where C=150 mA / g, was used. FIG. 6 is a graph of charging capacity as a function of cycles at various charging rates. As shown, samples including carbon nanotube bundles showed increased capacity compared to the comparative sample containing pre-dispersed carbon nanotube, especially at high charging rates as 2C and 5C. FIG. 7 is a graph of DC internal resistance for the experimental and comparative samples. As shown, the experimental samples containing carbon nanotube bundles had a lower internal resistance at both 20% and 80% state-of-charge (SOC) compared to the comparative samples suggesting a better conductive network inside the coin cell has formed with our experimental samples. FIG. 8 is a graph of discharge capacity ratio as a function of discharge rate. As shown, experimental samples including carbon nanotube bundles showed increased discharge capacity ratio at higher discharge rates, 2C and 5C as compared to the comparative samples. Thus, the data demonstrate that even bundles of carbon nanotubes may afford improved performance in battery applications, even without performing a pre-dispersion which helps debundle to produce individualized carbon nanotubes before making the cathode slurry.Example 3

[0070] The experimental samples were prepared by casting a slurry with NMC532 materials inside with different solid contents of 45%, 60%, 70% in which the composites consist of 95 wt% nickel manganese cobalt (NMC) 532, 2 wt% carbon nanotubes, and 3 wt% polyvinylidene difluoride (PVDF). The carbon nanotubes were added directly to the slurry without preparing a solvent dispersion of the carbon nanotubes first. Control samples were prepared similarly, except adding 1 wt% carbon nanotubes which is also produced from FCCVD in an NMP-based pre-dispersion. The slurry was mixed for 5 minutes and cast into a 330 micron thick film on a 15 micron Al foil current collector. The cast cathode materials and Al foils were then calendared together. In total, the cells included about 18 mg / cm2of active material. The materials were mixed for a time of 5 minutes. The electrolyte used comprised a 1:1:1 v / v ratio of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) containing 1 mol / L (M) lithium hexafluorophosphate (LiPF₆). The cells included a glass separator (Whatman 1820) between the cathode and the anode sheets.

[0071] The experimental and control coin cells were subsequently tested for performance over a voltage window of 4.25 V to 2.7 V. An activation protocol of CC-CV (C / 10 + C / 20 Hold) / Discharge CC: C / 10, where C=150 mA / g, was used. The capacity and initial coulombic efficiency (ICE) data are summarized in Table 1. As shown, the experimental samples were optimized to have 60% as solid content in cathode slurry since both the capacity and ICE are at the highest among others including the comparative samples. Thus, even the carbon nanotube bundles can form as good conductive network in the cathode composites as without performing a pre-dispersion.Table.1Sample Capacity / mAh.g’1ICE / % Experimental -45% 134 82Experimental-60% 145 85Experimental-70% 133 78Comparative 144 81

[0072] All documents described herein are incorporated by reference herein for purposes of all jurisdictions where such practice is allowed, including any priority documents and / or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. For example, the compositions described herein may be free of any component, or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein. Likewise, the term '‘comprising” is considered synonymous with the term “including.” Whenever a method, composition, element or group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “is” preceding the recitation of the composition, element, or elements and vice versa.

[0073] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by one or more embodiments described herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0074] Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “fromapproximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces.

[0075] One or more illustrative embodiments are presented herein. Not all features of a physical implementation are described or shown in this application for the sake of clarity. It is understood that in the development of a physical embodiment of the present disclosure, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related and other constraints, which vary by implementation and from time to time. While a developer's efforts might be time-consuming, such efforts would be, nevertheless, a routine undertaking for one of ordinary skill in the art and having benefit of this disclosure.

[0076] Therefore, the present disclosure is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to one having ordinary skill in the art and having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present disclosure. The embodiments illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and / or any optional element disclosed herein.

Claims

CLAIMSThe invention claimed is:

1. A composition comprising:a solvent; anda plurality of carbon nanotubes dispersed in the solvent;wherein the carbon nanotubes comprise a plurality’ of carbon nanotube bundles, and the carbon nanotubes have a bulk density of about 0.5 g / cm3or greater and an aspect ratio of about 500 or greater.

2. The composition of claim 1, wherein the composition comprises about 0.05 wt% to about 10 wt% carbon nanotubes and about 90 wt% or greater solvent, each based on a total mass of the composition.

3. The composition of any of claims 1-2, wherein the solvent comprises N-methyl-2-pyrrolidone.

4. The composition of any of claims 1-3. wherein the carbon nanotubes have a diameter of about 1 nm to about 500 nm.

5. The composition of any of claims 1-4. wherein the carbon nanotubes have a length of about 1 pm to about 2000 pm.

6. The composition of any of claims 1-5. wherein the carbon nanotubes have a density of about 0.5 g / cm3to about 2.5 g / cm3.

7. The composition of any of claims 1-6. wherein the carbon nanotubes have a metal impurity content of about 100 ppm or below.

8. The composition of any of claims 1-7, wherein the carbon nanotubes have a conductivity of about 10 S / mto about 10.000.000 S / m.

9. The composition of any of claims 1-8, wherein the carbon nanotubes have a surface area of about 25 m2 / g to 1500 m2 / g, as determined by BET.

10. The composition of any of claims 1-9, wherein the plurality of carbon nanotubes were produced by a floating catalyst chemical vapor deposition (FCCVD) process.

11. The composition of any of claims 1-10, wherein the plurality of carbon nanotubes were treated with an organic acid to remove at least some metal impurities therefrom, prior to dispersion of the carbon nanotubes in the solvent.

12. The composition of claim 11, wherein the organic acid comprises glycolic acid, ascorbic acid, malonic acid, hydrochloric acid, nitric acid, or any combination thereof.

13. The composition of any of claims 1-12, wherein the plurality of carbon nanotubes comprise temperature treated carbon nanotubes, having increased crystallinity and decreased impurities as compared to carbon nanotubes which are not temperature treated.

14. The composition of claim 13, wherein the temperature treatment occurs above 2000°C.

15. The composition of claim 1, further comprising:a polymer dispersed in the solvent.

16. A method comprising:providing a plurality of carbon nanotubes comprising a plurality' of carbon nanotube bundles;wherein the carbon nanotubes have a bulk density of about 0.5 g / cm3or greater and an aspect ratio of about 500 or greater; anddispersing the plurality of carbon nanotubes in a solvent to form a composition;wherein at least a portion of the carbon nanotubes remain bundled when dispersed in the solvent.

17. The method of claim 16, wherein the composition comprises about 0.05 wt% to about 10 wt% carbon nanotubes and about 90 wt% or greater solvent, each based on a total mass of the composition.

18. The method of any of claims 16-17, wherein the solvent comprises N-methyl-2-pyrrolidone.

19. The method of any of claims 16-18, further comprising:powdering the plurality of carbon nanotubes prior to forming the composition.

20. The method of any of claims 16-19, wherein the plurality of carbon nano tubes were produced using a FCCVD process.

21. The method of any of claims 16-20, further comprising:treating the plurality of carbon nanotubes with an organic acid to remove at least some metal impurities therefrom, prior to dispersion of the carbon nanotubes in the solvent.

22. The method of claim 21, wherein the organic acid comprises glycolic acid, ascorbic acid, malonic acid, hydrochloric acid, nitric acid, or any combination thereof.

23. The method of any of claims 16-22, wherein the plurality’ of carbon nanotubes comprise temperature treated carbon nanotubes, having increased crystallinity and decreased impurities as compared to carbon nanotubes which are not temperature treated.

24. The method of claim 23. wherein the temperature treatment occurs above 2000°C.

25. The method of any of claims 16-24, wherein the carbon nanotubes have one or more of the following properties:a diameter of about 1 nm to about 1000 nm,a length of about 1 pm to about 2000 pm,a density of about 0.5 g / cm3to about 2.5 g / cm3,a metal impurity content of about 100 ppm or below,a conductivity of about 10 S / m to about 10,000,000 S / m, ora surface area of about 50 m2 / g to 1000 m2 / g, as determined by BET.

26. A battery cell comprising the composition of claim 1.

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