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Method for producing anode paste for lithium-ion battery

20230246166 · 2023-08-03

    Inventors

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    Abstract

    The invention relates to electrotechnical industry, more particularly to lithium-ion batteries, and even more particularly to lithium-ion batteries with silicon-containing negative electrode (anode). The invention provides a method for producing an anode slurry (paste), an anode slurry (paste), a method for producing an anode for a lithium-ion battery, an anode for a lithium-ion battery, and a lithium-ion battery with a high initial specific capacity and a long cycle life with a large number of charge-discharge cycles over which the battery retains at least 80% of its initial capacity. This result becomes possible due to the presence in the anode material of bundles of single-walled and/or double-walled carbon nanotubes having a length of less than 5 μm, together with bundles of single-walled and/or double-walled carbon nanotubes having a diameter of more than 500 nm and a length of more than 10 μm.

    Claims

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    26. A method for producing an anode slurry for a lithium-ion battery, comprising the steps of: (1) introducing a composition (C) comprising an active component that includes a phase of silicon or phases of silicon oxides, SiO.sub.x, where x is a positive number less than or equal to 2, or a combination of such phases with a total atomic ratio of oxygen:silicon contents in the combination of the phases of more than 0 and less than 1.8, into a liquid-phase suspension (S) comprising 0.01 wt. % to 5 wt. % of carbon nanotubes, wherein more than 5 wt. % of carbon nanotubes of the total carbon nanotubes in the suspension (S) are bundled single-walled and/or double-walled carbon nanotubes with a bundle length of more than 10 μm, and wherein a mode of hydrodynamic diameter distribution of the number of bundles of carbon nanotubes in the suspension (S) is less than 500 nm, and (2) mixing the mixture of the composition (C) in the suspension (S) until a homogeneous anode slurry is obtained, wherein, after step (2), dry matter of the homogeneous anode slurry includes more than 50 wt. % and less than 99.9 wt. % of the active component, and wherein a total atomic ratio of oxygen:silicon contents in the dry matter of the homogeneous anode slurry is more than 0 and less than 1.8, and wherein the dry matter of the homogeneous anode slurry includes more than 0.1 wt. % and less than 20 wt. % of carbon nanotubes.

    27. The method of claim 26, wherein the hydrodynamic diameter distribution of a number of bundles of carbon nanotubes in the suspension (S) is bimodal.

    28. The method of claim 26, wherein graphite and/or binder additives and/or dispersant and/or solvent are introduced simultaneously with introducing the composition (C) into the suspension (S).

    29. The method of claim 26, further comprising introducing graphite and/or binder additives and/or dispersant and/or solvent into the suspension (S) or into the mixture of the composition (C) and the suspension (S).

    30. The method of claim 26, wherein the phases of silicon and silicon oxide in the composition (C) are agglomerated into joint agglomerates distributed by diameter with a distribution median of more than 5 μm.

    31. The method of claim 26, wherein sizes of X-ray coherent-scattering domains for the phases of silicon and silicon oxides are less than 10 nm.

    32. The method of claim 26, wherein the surface of agglomerates of silicon and silicon oxide is covered with carbon layer, and the mass C:Si ratio in the composition (C) is more than 0.01 and less than 0.1.

    33. The method of claim 26, wherein the carbon nanotubes in the suspension (S) have a ratio of Raman spectrum intensities of G/D bands of more than 5 at 532 nm.

    34. The method of claim 33, wherein the carbon nanotubes in the suspension (S) have a ratio of Raman spectrum intensities of G/D bands of more than 50 at 532 nm.

    35. The method of claim 26, wherein the carbon nanotubes in the composite material contain on their surface more than 0.1 wt. % of functional groups comprising elements with the Pauling electronegativity higher than that of carbon.

    36. The method of claim 35, wherein the carbon nanotubes in the composite material contain on their surface more than 0.1 wt. % of functional groups comprising at least one of the following elements: oxygen, fluorine or chlorine.

    37. The method of claim 35, wherein the carbon nanotubes contain more than 0.1 wt. % of carboxyl groups on their surface.

    38. The method of claims 26, wherein the suspension (S) is an aqueous suspension or a suspension in a polar organic solvent with a dipole moment of more than 1.5 D.

    39. The method of claim 38, wherein the suspension (S) is a suspension in N-methylpyrrolidone.

    40. An anode slurry for a lithium-ion battery, comprising: (1) an active component that includes a phase of silicon or phases of silicon oxides, SiO.sub.x, where x is a positive number less than or equal to 2, or a combination of such phases with a total atomic ratio of oxygen:silicon contents in the combination of the phases of more than 0 and less than 1.8, and (2) carbon nanotubes, wherein more than 5 wt. % of carbon nanotubes of the total carbon nanotubes in the anode slurry are bundled single-walled and/or double-walled carbon nanotubes with a bundle length of more than 10 μm, and wherein a mode of bundle length distribution of the number of bundles of carbon nanotubes in the anode slurry is less than 5 μm, and wherein the dry matter of the anode slurry includes more than 50 wt. % and less than 99.9 wt. % of the active component, wherein a total atomic ratio of oxygen:silicon contents in the dry matter of the anode slurry is more than 0 and less than 1.8, and wherein the dry matter of the anode slurry includes more than 0.1 wt. % and less than 20 wt. % of carbon nanotubes.

    41. The anode slurry of claim 40, wherein the anode slurry includes one or several binding polymer substances selected from: polyvinylidene fluoride, styrene-butadiene rubber, latex thereof, carboxymethyl cellulose, Na salt thereof, Li salt thereof, polyacrylic acid, Na salt thereof, Li salt thereof, fluoroelastomer, and latex thereof and/or one or several dispersants selected from: carboxymethyl cellulose, Na salt thereof, Li salt thereof, polyacrylic acid, Na salt thereof, Li salt thereof, and polyvinylpyrrolidone.

    42. The anode slurry of claim 40, wherein the anode slurry includes more than 0.1 wt. % of one or several electrically conductive additives differing in their composition and structure from carbon nanotubes, the additives being any of carbon black, graphite, metals of groups 8-11 of the periodic table.

    43. A method of producing an anode for a lithium-ion battery, comprising: (1) introducing a composition (C) comprising an active component that includes a phase of silicon or phases of silicon oxides, SiO.sub.x, where x is a positive number less than or equal to 2, or a combination of such phases with a total atomic ratio of oxygen:silicon contents in the combination of the phases of more than 0 and less than 1.8, into a liquid-phase suspension (S) comprising 0.01 wt. % to 5 wt. % of carbon nanotubes, wherein more than 5 wt. % of carbon nanotubes of the total carbon nanotubes in the suspension (S) are bundled single-walled and/or double-walled carbon nanotubes with a bundle length of more than 10 μm, and wherein a mode of hydrodynamic diameter distribution of the number of bundles of carbon nanotubes in the suspension (S) is less than 500 nm, and (2) mixing the mixture of the composition (C) in the suspension (S) until a homogeneous anode slurry is obtained, wherein, after step (2), dry matter of the homogeneous anode slurry includes more than 50 wt. % and less than 99.9 wt. % of the active component, wherein a total atomic ratio of oxygen:silicon contents in the dry matter of the homogeneous anode slurry is more than 0 and less than 1.8, and wherein the dry matter of the homogeneous anode slurry includes more than 0.1 wt. % and less than 20 wt. % of carbon nanotubes, (3) applying the homogeneous anode slurry on a current collector of a lithium-ion battery; (4) drying the applied homogeneous anode slurry to form an anode of the lithium-ion battery; and (5) compacting the anode.

    44. An anode for a lithium-ion battery comprising: (1) a current collector; (2) an active component that includes a phase of silicon or phases of silicon oxides, SiO.sub.x, where x is a positive number less than or equal to 2, or a combination of such phases with a total atomic ratio of oxygen:silicon contents in the combination of the phases of more than 0 and less than 1.8, and (3) carbon nanotubes, wherein more than 5 wt. % of carbon nanotubes of the total carbon nanotubes in the anode are bundled single-walled and/or double-walled carbon nanotubes with a bundle length of more than 10 μm, wherein a mode of bundle length distribution of the number of bundles of carbon nanotubes in the anode is less than 5 μm, wherein the active component makes up more than 50 wt. % and less than 99.9 wt. % of the weight of the anode excluding current collector, wherein a total atomic ratio of oxygen:silicon contents in the anode is more than 0 and less than 1.8, and wherein the carbon nanotubes make up more than 0.1 wt. % and less than 20 wt. % of the weight of the anode excluding current collector.

    Description

    BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

    [0046] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

    [0047] In the drawings:

    [0048] FIG. 1 shows an X-ray diffraction pattern from composition (C) used in Example 1.

    [0049] FIG. 2 shows a microphotograph of the suspension (S) used in Examples 1, 3, and 8.

    [0050] FIG. 3 shows a microphotograph of the suspension (S) used in Examples 1, 3, and 8 after sedimentation of long bundles of nanotubes by centrifuging.

    [0051] FIG. 4 shows DLS data on the hydrodynamic diameter distribution of the number of particles (nanotubes and their bundles) in the suspension (S) used in Examples 1, 3, and 8 (circles), in the suspension (S) used in Example 2 (squares), and in the suspension (S) used in Example 9 (triangles).

    [0052] FIG. 5 shows dependence of the specific capacity of the anode of Example 1 on the number of charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g).

    [0053] FIG. 6 shows capacity of the lithium-ion battery of Example 1 referred to its initial capacity versus the number of charge-discharge cycles (charge and discharge currents 46 mA).

    [0054] FIG. 7 shows a microphotograph of the suspension (S) used in Example 2.

    [0055] FIG. 8 shows a microphotograph of the suspension (S) used in Example 2 after sedimentation of long bundles of nanotubes by centrifuging.

    [0056] FIG. 9 shows specific capacity of the anode of Example 2 versus the number of charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g).

    [0057] FIG. 10 shows an electronic microphotograph (TEM) of the dry residue of the suspension

    [0058] (S) used in Example 4.

    [0059] FIG. 11 shows an energy dispersion spectrum (EDS) of the dry residue of the suspension

    [0060] (S) used in Example 6.

    [0061] FIG. 12 shows a microphotograph of the suspension (S) used in Example 7.

    [0062] FIG. 13 shows specific capacity of the anode of Example 7 versus the number of charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g).

    [0063] FIG. 14 shows capacity of the lithium-ion battery of Example 7 referred to its initial capacity versus the number of charge-discharge cycles (charge and discharge currents 37.5 mA).

    [0064] FIG. 15 shows specific capacity of the anode of Example 8 versus the number of charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g).

    DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

    [0065] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

    [0066] For convenience, the information on the provided examples is also provided in the table below.

    EXAMPLES

    [0067]

    TABLE-US-00001 Composition of the suspension (S), wt. %; Specific capacity Fraction of CNT in of the anode, mA h/g the bundles having Composition of After After L > 10 μm, wt. %; anode material, 50 500 Example D.sub.hm, nm wt. % Initial cycles cycles 1 0.4% SWCNT 90% C—Si/SiO.sub.x 1296 1300 1050 0.6% Na—CMC 3% SWCNT, 99% water 4.5% Na—CMC 19% in the 2.5% SBR bundles > 10 μm D.sub.hm = 400 nm 2 0.4% SWCNT 90% C—Si/SiO.sub.x 1079 1116 868 0.8% BYK-LP N24710 3% SWCNT 98.8% NMP 6% BYK-LP 54% in the N24710 bundles > 10 μm 1% PVDF D.sub.hm = 370 nm 3 As in Example 1 86.3% C—Si/SiO.sub.x 1160 1115 970 5.3% SWCNT, 8.4% Na—CMC 4 0.05% SWCNT + 94.9% Si/SiO.sub.x 1481 1284 1193 DWCNT 0.73% SWCNT + 0.1% Li—CMC DWCNT, 99.95% water 1.47% Li—CMC 12% in the 2.9% SBR bundles > 10 μm D.sub.hm = 360 nm 5 0.4% SWCNT 80.8% C—Si/SiO.sub.x 963 928 795 3.0% MWCNT 12.1% CNT 1% PVP 3.6% PVP 95.6% NMP 3.6% Li—PA 6% in the bundles > 10 μm D.sub.hm = 450 nm 6 0.6% Cl, O— SWCNT 88.4% C—Si/SiO.sub.x 1122 1081 937 (0.47% Cl & 2.2% O) 8.2% Cl, O— 99.4% DMAA SWCNT, 28% in the 3.4% PVP bundles > 10 μm D.sub.hm = 420 nm 7 0.25% F, O— SWCNT 94.9% C—Si/SiO.sub.x 1257 1302 1117 (14% F & 7% O) 3.1% F, O— 99.75% NMP SWCNT, 9% in the 2.0% PVDF bundles > 10 μm D.sub.hm = 370 nm 8 As in Example 1 50.1% C—Si/SiO.sub.x 634 639 581 3% SWCNT, 40.1% graphite 4.5% Na—CMC 2.3% SBR 9 0.4% SWCNT 90% C—Si/SiO.sub.x 1241 1056 712 (comparative) 0.6% Na—CMC 3% SWCNT 99% water 4.5% Na—CMC <3% in the 2.5% SBR bundles > 10 μm D.sub.hm = 380 nm

    Examples

    Example 1

    [0068] The anode slurry was produced using a powder of composition (C) comprising a phase of silicon and phases of silicon oxide covered with a layer of amorphous carbon. Particle size distribution analysis of a composition (C) yields the median for powder particle diameter of 6.2 μm. X-ray diffraction pattern for the composition is shown in FIG. 1. This data may suggest that the composition includes phases of Si (Powder Diffraction File 27-1402) with the size of the coherent-scattering domain 5.0 nm and amorphized SiO.sub.x (a broad maximum in the region of 20-23° is the most intense diffraction line for the structure of christobalite, SiO.sub.2) with the size of the coherent-scattering domain 1.5 nm. Data for changes in the weight of a sample of the composition (C) during temperature-programmed oxidation in the oxygen flow with rising temperature demonstrate that amorphous carbon accounts for 2.6 wt. % of the composition (weight loss at 700° C.), while oxygen deficit relative to stoichiometry SiO.sub.2 is 14 wt. % of the initial weight of the composition (C) (weight gain in the range of 200 to 1400° C.). Thus, the total atomic ratio of oxygen:silicon contents in the combination of phases is 1.55. Weight ratio C:Si in the composition (C) is 0.048.

    [0069] The anode slurry was produced using an aqueous suspension (S) of single-walled carbon nanotubes (SWCNT) TUBALL with a diameter of 1.2 to 2.1 nm and a mean diameter 1.6 nm (diameter was determined using TEM of the dry residue of the suspension, as well from the position of absorption bands S.sub.1-1 in the optical absorption spectrum of the suspension). Raman spectroscopy at wavelength 532 nm reveals a pronounced G band at 1580 cm.sup.−1 characteristic of single-walled carbon nanotubes, and D band at ca. 1330 cm.sup.−1 characteristic of other allotropic modifications of carbon and defects of single-walled carbon nanotubes. The ratio of intensities of G/D bands is 75. SWCNT concentration in the suspension is 0.4 wt. %. The suspension also comprises 0.6 wt. % of Na-carboxymethyl cellulose (CMC) as a dispersant.

    [0070] The fraction of carbon nanotubes contained in bundles with the length more than 10 μm was determined by comparing optical density at 500 nm of the suspension (S) and the suspension after removal of long bundles from it by sedimentation via centrifuging at 8000 g for 1 hour. A microphotograph of the suspension placed between glasses is shown in FIG. 2. The microphotograph clearly shows long bundles of carbon nanotubes with a thickness up to 2 μm and the length of 10 to 50 μm. To determine the optical density, the suspension was diluted with water down to the SWCNT concentration in suspension of 0.001 wt. % (400 times). Before sedimentation, the suspension was diluted with water to the SWCNT concentration in the suspension of 0.01 wt. % (40 times). A microphotograph of the suspension after sedimentation by centrifuging is shown in FIG. 3. The microphotograph shows no long bundles of carbon nanotubes. The optical density of the suspension (S) diluted 400 times at the optical path length 10 mm is 0.56, which corresponds to the SWCNT concentration in the suspension (S) of 0.38 wt. %. The optical density of the suspension (S) diluted 40 times, subjected to sedimentation, and then further diluted 10 times is 0.45, which corresponds to the SWCNT concentration in the suspension (S) of 0.31 wt. %. Thus, the fraction of carbon nanotubes in long bundles of carbon nanotubes with the length more than 10 μm is 19 wt. % of the total amount of carbon nanotubes in the suspension.

    [0071] The size distribution of the number of bundles of carbon nanotubes was determined by Dynamic Light Scattering (DLS) of the suspension (S) diluted to the SWCNT concentration of 0.001 wt. %. The hydrodynamic diameter distribution of the number of particles (nanotubes and their bundles) in the suspension (S) obtained by DLS using a Malvern Zetasizer ZS instrument is shown in FIG. 4 by a curve with circular markers. Based on the data of FIG. 4, the size distribution of the number of bundles of nanotubes is bimodal, with hydrodynamic diameters in the ranges of 100-700 nm and 4-6 μm. The second mode of distribution corresponds to bundles of nanotubes with the length more than 10 μm, whose weight fraction was determined as described above to be about 19 wt. %. The first maximum corresponds to bundles with the length certainly less than 7 μm (<10×700 nm). This maximum is described by a log-normal hydrodynamic diameter distribution of the number of bundles, with the mode at Dhm=400 nm, which, according to inequality (4), means 2 μm<L.sub.m<4 μm.

    [0072] 75 g of the suspension (S) was placed into a 150 cm.sup.3 beaker, and then 9 g of the composition (C) was added and mixed using an overhead stirrer with a disk impeller at impeller rotation speed 2000 rpm for 2 hours, then 1.25 g of 20 wt. % of butadiene-styrene latex was added, and, after additional mixing in the same conditions for another 15 min, a homogeneous anode slurry was obtained. The dry residue of the obtained anode slurry comprises 90 wt. % of the active component, 3 wt. % of carbon nanotubes, 4.5 wt. % of CMC, and 2.5 wt. % of butadiene-styrene rubber. 19 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes are distributed by length bimodally, with a more intense mode at the length of 4 μm.

    [0073] To produce the anode, the obtained anode slurry was applied on copper foil using a doctor blade, dried at 40° C. for 1 hour, and compactified at a calender with a 5 t force to a density of the anode material of 1.2 g/cm.sup.3. The load of the active material on the anode is 2.2 mg/cm.sup.2.

    [0074] An anode with area 17.5 cm.sup.2 was cut from the foil with anode material, to which a nickel lead was welded. No carbon nanotubes other than those introduced with the anode slurry were introduced into the anode. Thus, 19 wt. % of carbon nanotubes in the anode are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes are distributed by length bimodally, with a more intense mode of distribution at a bundle length of less than 4 μm.

    [0075] To determine anode properties, a cell was assembled with a Li cathode and Li reference electrode and electrolyte using 1 M solution of LiPF.sub.6 in the solvent mixture of propylene carbonate:ethylmethyl carbonate:dimethyl carbonate in volume ratio 1:1:1 with addition of 5% v/v vinyl carbonate. The initial specific capacity of the anode at charge current 2 A/g of the anode material is 1296 mA.Math.h/g of the anode material. The specific capacity versus the number of charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g) is shown in FIG. 5. The anode does not lose its specific capacity within first 50 cycles (1318 mA.Math.h/g). After 500 cycles, the specific capacity of the anode is 1050 mA.Math.h/g, i.e., more than 80% of the initial specific capacity.

    [0076] A lithium-ion battery was assembled from the produced anode and a cathode having as the active material nickel-cobalt manganese oxide (NCM) with atomic ratio Ni:Co:Mn 6:2:2 at a load of 16 mg/cm.sup.2. A 10 μm lithium foil was placed on the anode to increase the coulombic efficiency of the first cycle. A 25 μm thick polypropylene separator was used. 1 M solution of LiPF.sub.6 in the solvent mixture propylene carbonate:ethylmethyl carbonate:dimethyl carbonate in volume ratio 1:1:1 with addition of 5% v/v vinyl carbonate was used as electrolyte. The initial capacity of the battery at discharge current 0.1 C was 46.5 mA.Math.h. The dependence of the capacity referred to the initial capacity on the number of charge-discharge cycles (charge current 46 mA, discharge current 46 mA) is shown in FIG. 6. The battery does not lose its capacity within first 50 cycles (99.6%). After 500 cycles, the capacity of the battery is 39 mA.Math.h, i.e., more than 83.5% of the initial capacity.

    Example 2

    [0077] The anode slurry was produced using the powder of the composition (C) as in Example 1. The anode slurry was produced using a suspension (S) of single-walled carbon nanotubes (SWCNT) TUBALL in N-methylpyrrolidone with dispersant BYK-LP N24710. The SWCNT diameter was distributed in the range of 1.2 to 2.1 nm with a mean diameter of 1.49 nm (the diameter was determined using TEM of the dry residue of the suspension, as well from the positions of absorption bands S.sub.1-1 in the optical absorption spectrum of the suspension). Raman spectroscopy at wavelength 532 nm reveals a pronounced G band at 1580 cm.sup.−1 characteristic of single-walled carbon nanotubes, and D band at ca. 1330 cm.sup.−1 characteristic of other allotropic modifications of carbon and defects of single-walled carbon nanotubes. The ratio of intensities of G/D bands is 64. SWCNT concentration in the suspension is 0.4 wt. %. The concentration of dispersant BYK-LP N24710 is 0.8 wt. %.

    [0078] The fraction of carbon nanotubes contained in bundles having the length more than 10 μm was determined by comparing optical density at 500 nm of the suspension (S) and suspension after removal of long bundles from it by sedimentation via centrifuging at 8000 g for 1 hour. A microphotograph of the suspension placed between glasses is shown in FIG. 7. The microphotograph clearly shows long bundles of carbon nanotubes with a thickness up to 2 μm and the length of 10 to 50 μm. To determine the optical density, the suspension was diluted with N-methylpyrrolidone down to the SWCNT concentration in suspension of 0.001 wt. % (diluted 400 times). Before sedimentation, the suspension was diluted with N-methylpyrrolidone to the SWCNT concentration in suspension of 0.01 wt. % (diluted 40 times). A microphotograph of the suspension after sedimentation by centrifuging is shown in FIG. 8. The microphotograph shows no long bundles of carbon nanotubes. The optical density of the suspension (S) diluted 400 times in a cuvette 10 mm thick is 0.56, which corresponds to the SWCNT concentration in the suspension (S) of 0.38 wt. %. The optical density of the suspension (S) diluted ×40, subjected to sedimentation, and then further diluted 10 times is 0.30, which corresponds to the SWCNT concentration in the suspension (S) of 0.21 wt. %. Thus, the fraction of carbon nanotubes in long bundles of carbon nanotubes with the length more than 10 μm is about 54 wt. % of the total amount of carbon nanotubes in the suspension.

    [0079] The size distribution of the number of bundles of carbon nanotubes was determined by Dynamic Light Scattering (DLS) of the suspension (S) diluted ×400. The hydrodynamic diameter distribution of the number of particles (nanotubes and their bundles) in the suspension (S) obtained by DLS using a Malvern Zetasizer ZS instrument is shown in FIG. 4 by a curve with square markers. Based on the data of FIG. 4, the size distribution of the number of bundles of nanotubes is bimodal, with hydrodynamic diameters in the ranges of 100-700 nm and 4-8 μm. The second mode of distribution corresponds to bundles of nanotubes with the length more than 10 μm, whose weight fraction was determined as described above to be about 54 wt. %. The first mode corresponds to bundles with length certainly less than 8 μm (<10×800 nm). This maximum is described by a log-normal hydrodynamic diameter distribution of the number of bundles, with the mode at D.sub.hm=370 nm, which, according to inequality (4), means 2.25 μm<L.sub.m<3.7 μm.

    [0080] 400 g of the suspension (S) in NMP were placed into a glass beaker with a volume of 800 ml, and 47.7 g of the composition (C) were added and mixed using an overhead stirrer with a disk impeller at impeller rotation speed 2000 rpm for 30 min. Then 0.53 g of polyvinylidene fluoride powder, mixed in the same conditions for another 2 hours, were added, and a homogeneous anode slurry was obtained. The dry matter of the obtained anode slurry comprises 90 wt. % of the active component, 3 wt. % of carbon nanotubes, 6 wt. % of dispersant BYK-LP N24710, and 1 wt. % of polyvinylidene fluoride. 60 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes are distributed by length bimodally, with the more intense mode at the length of less than 3.7 μm.

    [0081] To produce the anode, the obtained anode slurry was applied on copper foil using a doctor blade, dried at 110° C. for 1 hour, and compactified at a calender with a 5 t force to a density of the anode material of 1.3 g/cm.sup.3. The load of the active material on the anode is 2.4 mg/cm.sup.2. An anode with area 17.5 cm.sup.2 was cut from the foil with anode material, to which a nickel lead was welded. No carbon nanotubes other than those introduced with the anode slurry were introduced into the anode. Thus, 54 wt. % of carbon nanotubes in the anode are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes are distributed by length bimodally, with a more intense mode of the distribution at a bundle length of less than 3.7 μm.

    [0082] To determine anode properties, a cell was assembled with a Li cathode and Li reference electrode and electrolyte using 1 M solution of LiPF.sub.6 in the solvent mixture of propylene carbonate:ethylmethyl carbonate:dimethyl carbonate in volume ratio 1:1:1 with addition of 5% v/v vinyl carbonate. The initial specific capacity of the anode at charge current 2 A/g of anode material is 1079 mA.Math.h/g of anode material. The specific capacity vs the number of charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g) is shown in FIG. 9. The anode does not lose its specific capacity within first 50 cycles (1116 mA.Math.h/g). After 500 cycles, the specific capacity of the anode is 868 mA.Math.h/g, i.e., more than 80% of the initial specific capacity.

    Example 3

    [0083] The anode slurry was produced similarly to Example 1, however, as the composition (C) a dispersed silicon powder with dimension of CSR 60 nm and median of weight distribution of powder particles by diameter of 2.5 μm was used, and solvent, water, and Na-carboxymethyl cellulose dispersant were introduced into the suspension together with the composition (C). The composition (C) was wetted before introduction into the suspension (S) by a solution of Na-carboxymethyl cellulose to prevent fine silicon dust from getting into the workplace air. Based on the data for changes in the weight of a sample of the composition (C) in the course of temperature-programmed oxidation in the oxygen flow with rising temperature, the used silicon powder is partially oxidized and contains X-ray amorphous silicon oxide. Oxygen deficit relative to stoichiometry SiO.sub.2 is 10.4 wt. % of the initial weight of the composition (C) (weight gain in the temperature range of 200 to 1400° C.). Thus, the total atomic ratio of oxygen: silicon contents in the combination of phases is 0.09.

    [0084] 2.0 g of the powder (C) pre-wetted with 10 g of aqueous solution of Na-carboxymethyl cellulose with a concentration of 0.1 wt. % were introduced into 30 g of the suspension (S), and mixed until a homogeneous slurry was obtained. The dry matter of the obtained anode slurry comprises 86.3 wt. % of the active component, 8.3 wt. % of Na-carboxymethyl cellulose, and 5.3 wt. % of carbon nanotubes. 19 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes are distributed by the bundle length bimodally, with a more intense mode at a hydrodynamic diameter of 400 nm.

    [0085] The anode was produced from the obtained anode slurry similarly to Example 1. The initial specific capacity of the anode at charge current 2 A/g of the anode material is 1160 mA.Math.h/g of the anode material. After 50 charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g), the specific capacity of the anode is 1115 mA.Math.h/g. After 500 cycles, the specific capacity of the anode is 970 mA.Math.h/g, i.e., more than 83% of the initial specific capacity. 19 wt. % of carbon nanotubes in the anode are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes are distributed by length bimodally, with a more intense mode of distribution at a bundle length of less than 4 μm.

    [0086] A lithium-ion battery was manufactured using the produced anode similarly to Example 1. The initial capacity of the battery at discharge current 0.1 C was 44.8 mA.Math.h. Within first 50 charge-discharge cycles (charge current 45 mA, discharge current 45 mA), the battery does not lose its capacity (99.0%). After 500 cycles, the capacity of the battery is 37 mA.Math.h, i.e., more than 82.5% of the initial capacity.

    Example 4

    [0087] The anode slurry was produced similarly to Example 1, however, as the suspension (S) an aqueous suspension of a mixture of single-walled and double-walled carbon nanotubes with diameters of 1.2 to 2.8 nm and mean diameter of 1.8 nm (diameter was determined using TEM of the dry residue of the suspension, as well from the position of the breathing mode bands in the Raman spectra) was used, and after the step of introducing the composition (C) into the suspension (S), a latex of styrene-butadiene rubber was added to the mixture, and the resultant mixture was mixed to obtain a homogeneous slurry. The ratio of intensities of G/D bands in the Raman spectrum is 34. The presence of double-walled carbon nanotubes bundled together with single-walled carbon nanotubes is confirmed by electronic microphotographs shown in FIG. 10. The concentration of carbon nanotubes in the aqueous suspension (S) is 0.05 wt. %. The suspension also comprises 0.1 wt. % of Li-carboxymethyl cellulose (Li-CMC) as a dispersant.

    [0088] The fraction of carbon nanotubes in long bundles of carbon nanotubes with the length more than 10 μm is 12 wt. % of the total amount of carbon nanotubes in the suspension. Based on the DLS data, the bundles of nanotubes are distributed bimodally, with the modes at hydrodynamic diameters 360 nm and about 6 μm (the second maximum is very weak).

    [0089] 2.0 g of the composition (C) and simultaneously 0.3 g of 20 wt. % latex of butadiene-styrene rubber were added to 30 g of the suspension (S), and mixed until a homogeneous slurry was obtained. The dry matter of the obtained anode slurry comprises 94.9 wt. % of the active component, 2.9% of styrene-butadiene rubber of carbon nanotubes, 1.47% of Li-carboxymethyl cellulose, and 0.73 wt. % of carbon nanotubes. 12 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled and double-walled carbon nanotubes with the bundle length of more than 10 μtm. The bundles of single-walled and double-walled carbon nanotubes are distributed by the bundle length bimodally, with the more intense mode at the length of 3.6 μm.

    [0090] The anode was produced from the obtained anode slurry similarly to Example 1. The initial specific capacity of the anode at charge current 2 A/g of the anode material is 1481 mA.Math.h/g of the anode material. After 50 charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g), the specific capacity of the anode is 1284 mA.Math.h/g. After 500 cycles, the specific capacity of the anode is 1193 mA.Math.h/g, i.e., less than 80% of the initial specific capacity. 12 wt. % of carbon nanotubes in the anode are bundled single-walled and double-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled and double-walled carbon nanotubes are distributed by the bundle length bimodally, with a more intense distribution mode at the length of 3.6 μm.

    Example 5

    [0091] The anode slurry was produced similarly to Example 2, however, a suspension of a mixture of single-walled and multi-walled carbon nanotubes in N-methylpyrrolidone (NMP) was used as the suspension (S), and a solution of Li salt of polyacrylic acid in NMP was added to it simultaneously with introduction of the composition (C) into the suspension (S), and the obtained mixture was mixed to obtain a homogeneous slurry. The concentration of single-walled carbon nanotubes in the suspension (S) is 0.4 wt. %, the concentration of multi-walled carbon nanotubes is 3.0 wt. %. The mean diameter of single-walled carbon nanotubes is 1.6 nm, the mean diameter of multi-walled carbon nanotubes is 10 nm (the diameter was determined using TEM of the dry residue of the suspension, and for single wall carbon nanotubes also from the position of the radial breathing mode (RBM) bands in the Raman spectra). The ratio of intensities of G/D bands in the Raman spectrum of the suspension dry residue is 7. The suspension also contains 1.0 wt. % of polyvinylpyrrolidone (PVP) as a dispersant.

    [0092] The fraction of single-walled carbon nanotubes in long bundles of carbon nanotubes having the length more than 10 μm determined by comparing optical density at 500 nm of the suspension (S), and the suspension after removal of long bundles from it by sedimentation via centrifuging, is 6 wt. % of the total amount of carbon nanotubes in the suspension. Based on the DLS data, the particles in the suspension have a broad asymmetric unimodal distribution with the mode at hydrodynamic diameter 300 nm.

    [0093] 7.0 g of the composition (C) and simultaneously 10.0 g of 3 wt. % solution of Li salt of polyacrylic acid (Li-PA) in NMP were added to 30 g of the suspension (S), and the mixture was mixed to obtain a homogeneous slurry. The dry matter of the obtained homogeneous anode slurry comprises 80.8 wt. % of the active component and 12.1 wt. % of carbon nanotubes. 6 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of carbon nanotubes in the anode slurry are distributed by length, with the mode at bundle length of less than 3 μm.

    [0094] The anode was produced from the obtained anode slurry similarly to Example 2. The initial specific capacity of the anode at charge current 2 A/g of the anode material is 963 mA.Math.h/g of the anode material. After 50 charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g), the specific capacity of the anode is 928 mA.Math.h/g. After 500 cycles, the specific capacity of the anode is 795 mA.Math.h/g, i.e., less than 82% of the initial specific capacity. 6 wt. % of carbon nanotubes in the anode are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of carbon nanotubes in the anode are distributed by length, with the mode at a bundle length of less than 3μm.

    Example 6

    [0095] The anode slurry was produced similarly to Example 2, however, a suspension of single-walled carbon nanotubes comprising on their surface functional groups containing chlorine and functional groups containing oxygen in dimethylacetamide (DMAA) was used as the suspension (S), and after the step of introducing the composition (C) into the suspension (S), dispersant polyvinylpyrrolidone was added to the obtained mixture, and then the obtained mixture was mixed to produce a homogeneous slurry. The suspension contains 0.6 wt. % of single-walled carbon nanotubes in N-methylpyrrolidone. According to the results of elemental analysis by energy dispersive spectroscopy (EDS), the dry residue of the suspension comprises 97.1 wt. % of carbon; 2.2 wt. % of oxygen; 0.27 wt. % of iron, and 0.47 wt. % of chlorine. The EDS spectrum of the modified material is provided in FIG. 11. Thus, the carbon nanotubes in the suspension (S) comprise on their surface more than 0.47 wt. % of functional groups containing chlorine and more than 2.2 wt. % of functional groups containing oxygen.

    [0096] According to Raman spectroscopy results for light wavelength 532 nm, the ratio of integral intensities of the G mode and D mode is 97. Single-walled carbon nanotubes are distributed by diameter in the range of 1.2 to 2.8 nm with a mean diameter of 1.6 nm (the diameter was determined using TEM of the dry residue of the suspension, as well as from the positions of the breathing mode bands in the Raman spectra).

    [0097] The fraction of carbon nanotubes in long bundles of carbon nanotubes with the length more than 10 μm determined by comparing optical density at 500 nm of the suspension (S), and the suspension after removal of long bundles from it by sedimentation via centrifuging, is 28 wt. % of the total amount of carbon nanotubes in the suspension. Based on the DLS data, bundles of carbon nanotubes are distributed by hydrodynamic diameters bimodally, with modes at 420 nm (more intense one) and 6.5 μm (less intense one).

    [0098] 2.0 g of the composition (C) was added to 30 g of the suspension (S) and mixed, and then 1.5 g of 5 wt. % solution of polyvinylpyrrolidone in DMAA was added to the mixture, and mixed until a homogeneous slurry was obtained. The dry matter of the obtained anode slurry comprises 88.4 wt. % of the active component, 3.4 wt. % of polyvinylpyrrolidone, and 8.2 wt. % of single-walled carbon nanotubes. 28 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes in the anode slurry are distributed by length bimodally, with a more intense mode at the length of less than 4.2 μm.

    [0099] The anode was produced from the obtained anode slurry similarly to Example 2. The initial specific capacity of the anode at charge current 2 A/g of the anode material is 1122 mA.Math.h/g of the anode material. After 50 charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g), the specific capacity of the anode is 1081 mA.Math.h/g. After 500 cycles, the specific capacity of the anode is 931 mA.Math.h/g, i.e., less than 83% of the initial specific capacity. 28 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes in the anode are distributed by length bimodally, with a more intense mode at a length of less than 4.2 μm.

    Example 7

    [0100] The anode slurry was produced similarly to Example 2, however, a suspension of 0.25 wt. % of single-walled carbon nanotubes modified with fluorine in N-methylpyrrolidone was used as the suspension (S), and after mixing (S) with the composition (C), a powder of polyvinylidene fluoride (PVDF) was added to the mixture. Single-walled carbon nanotubes in the suspension were modified with fluorine. Based on the TEM data, carbon nanotubes in the suspension are single-walled with mean diameter 1.5 nm, which is also confirmed by data on the position of absorption bands S.sub.1-1 in the optical absorption spectrum. Based on the data of X-Ray Photoemission Spectroscopy (XPS), the weight fraction of fluorine in carbon nanotubes is 14%, the weight fraction of oxygen is 7%, and carbon to balance. The G/D ratio in the Raman spectrum at wavelength 532 nm is 2.4. Such a low G/D value also confirms a high degree of functionalization of the SWCNT surface with fluorine-containing functional groups.

    [0101] A microphotograph of the suspension (S) is provided in FIG. 12. The fraction of carbon nanotubes in long bundles of carbon nanotubes with the length more than 10 μm determined by comparing optical density at wavelength 500 nm of the suspension (S), and the suspension after removal of long bundles from it by sedimentation via centrifuging, is 9 wt. % of the total amount of carbon nanotubes in the suspension. Based on the DLS data, bundles of carbon nanotubes are distributed by hydrodynamic diameters bimodally, with modes at 370 nm (more intense one) and 4.8 μm (less intense one).

    [0102] 30 g of the suspension (S) was placed into a 100 cm.sup.3 beaker, and then 2.375 g of the composition (C) was added, and mixed using an overhead stirrer with a disk impeller at impeller rotation speed 2000 rpm for 0.5 hours, then 50 mg of polyvinylidene fluoride powder was added, and mixed under the same conditions for another 2 hours until a homogeneous slurry was obtained. The dry matter of the obtained anode slurry comprises 95 wt. % of the active component, 3 wt. % of carbon nanotubes, 2 wt. % of polyvinylidene fluoride. 9 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes are distributed by the bundle length bimodally, with a lesser mode at a bundle length of less than 3.7 μm.

    [0103] The anode was produced from the obtained anode slurry similarly to Example 2. The load of the active material on the anode is 2.4 mg/cm.sup.2. An anode with area 17.5 cm.sup.2 was cut from the foil with anode material, to which a nickel lead was welded. No carbon nanotubes other than those introduced with the anode slurry were introduced into the anode. Thus, 9 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes are distributed by the bundle length bimodally, with a lesser mode at a bundle length of less than 3.7 μm.

    [0104] To determine anode properties, a cell was assembled with a Li cathode and Li reference electrode and electrolyte using 1 M solution of LiPF.sub.6 in the solvent mixture propylene carbonate:ethylmethyl carbonate:dimethyl carbonate in volume ratio 1:1:1 with addition of 5% v/v fluoroethylene carbonate. The initial specific capacity of the anode at charge current 2 A/g of the anode material is 1257 mA.Math.h/g of the anode material. The specific capacity vs the number of charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g) is shown in FIG. 13. Within first 50 cycles, the specific capacity of the anode grows from 1257 to 1302 mA.Math.h/g. After 500 cycles, the specific capacity of the anode is 1117 mA.Math.h/g, i.e., less than 88% of the initial specific capacity.

    [0105] A lithium-ion battery was assembled from the obtained anode and a cathode having lithium-iron-phosphate, LiFePO.sub.4 (LFP), as the active material at a load of 14 mg/cm.sup.2. A 10 μm lithium foil was placed on the anode to increase the coulombic efficiency of the first cycle. A 25 μm thick polypropylene separator was used. 1 M solution of LiPF.sub.6 in the solvent mixture propylene carbonate:ethylmethyl carbonate:dimethyl carbonate in volume ratio 1:1:1 with addition of 5% v/v fluoroethylene carbonate was used as an electrolyte. The initial capacity of the battery at discharge current 0.1 C was 37.5 mA.Math.h. The capacity referred to the initial capacity versus the number of charge-discharge cycles (charge and discharge currents 37.5 mA) is shown in FIG. 14. Within first 200 cycles, the battery somewhat increases its capacity. After 500 cycles, the capacity of the battery is 37.5 mA.Math.h, i.e., 100% of the initial capacity.

    Example 8

    [0106] The anode slurry was produced similarly to Example 1, however, after adding the composition (C) to the suspension (S) and mixing, graphite was additionally introduced, mixed, and styrene-butadiene latex was further added, after which it was mixed to until a homogeneous slurry was obtained.

    [0107] 225 g of the suspension (S) was placed into a 400 cm.sup.3 beaker, to which then 13.5 g of the composition (C) was added and mixed using an overhead stirrer with a disk impeller at impeller rotation speed 2000 rpm for 0.5 hours; then 13.5 g of graphite with the BET specific surface of 3 m.sup.2/g was added, and mixed for 2 hours; then 3.5 g of 20 wt. % of styrene-butadiene latex were added, and mixed under the same conditions for another 2 hours until a homogeneous slurry was obtained. The dry matter of the obtained anode slurry comprises 50.1 wt. % of the composition (C), 3 wt. % of carbon nanotubes, 40 wt. % of graphite, 4.5 wt. % of carboxymethyl cellulose, and 2.3 wt. % of styrene-butadiene rubber. 19 wt. % of carbon nanotubes in the resultant slurry are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes are distributed by length bimodally, with the more intense mode at the length of less than 4μm.

    [0108] To produce the anode, the obtained anode slurry was applied on copper foil using a doctor blade, dried at 50° C. for 1 hour, and compactified at a calender with a 7 t force to a density of the anode material of 1.4 g/cm.sup.3. The load of the active material on the anode is 3.2 mg/cm.sup.2. An anode with area 17.5 cm.sup.2 was cut from the foil with anode material, to which a nickel lead was welded. No carbon nanotubes other than those introduced with the anode slurry were introduced into the anode. Thus, 19 wt. % of carbon nanotubes in the anode are bundled single-walled carbon nanotubes with the bundle length of more than 10 μm. The bundles of single-walled carbon nanotubes in the anode are distributed by length bimodally, with a more intense mode at the length of less than 4 μm.

    [0109] To determine anode properties, a cell was assembled with a Li cathode and Li reference electrode and electrolyte using 1 M solution of LiPF.sub.6 in the solvent mixture of propylene carbonate:ethylmethyl carbonate:dimethyl carbonate in volume ratio 1:1:1 with addition of 3% v/v vinyl carbonate. The initial specific capacity of the anode at charge current 2 A/g of the anode material is 634 mA.Math.h/g of the anode material. The specific capacity vs the number of charge-discharge cycles (charge current 2 A/g, discharge current 1 A/g) is shown in FIG. 15. Within the first 300 cycles, the specific capacity of the anode grows up to 670-690 mA.Math.h/g.

    [0110] After 500 cycles, the specific capacity of the anode is 581 mA.Math.h/g, i.e., less than 91% of the initial specific capacity.

    Example 9 (Comparative)

    [0111] The anode slurry was produced similarly to Example 1, however, using an aqueous suspension (S) of single-walled carbon nanotubes (SWCNT) TUBALL containing almost no long bundles of single-walled carbon nanotubes with the length more than 10 μm. The absence of any significant amount of such bundles is confirmed by the optical microscopy data, which show no fibrous particles visible in an optical microscope, as well as the DLS data, which show no particles with hydrodynamic diameter more than 800 nm: based on the DLS data, a bimodal particle distribution with modes in the range of hydrodynamic diameters about 90 nm and 380 nm is observed in the suspension, the lesser mode probably corresponding to an individual carbon nanotube and very thin bundles, while the second mode corresponding to the bundles of carbon nanotubes with the length less than 6 μm. The larger mode of the length distribution of bundles of carbon nanotubes is less than 3.8 μm. The DLS curves for the suspension (S) are provided in FIG. 1 by a curve with triangular markers.

    [0112] The fraction of carbon nanotubes contained in bundles with the length more than 10 μm was determined by comparing optical density at 500 nm of the suspension (S), and the suspension after removal of long bundles from it by sedimentation via centrifuging similarly to Example 1. The optical density of the suspension (S) diluted 400 times at the optical path length 10 mm is 0.58, which corresponds to the SWCNT concentration in the suspension (S) of 0.39 wt. %. The optical density of the suspension (S) diluted 400 times and subjected to sedimentation is 0.56, which corresponds to the SWCNT concentration in the suspension (S) of 0.38 wt. %. Thus, the fraction of carbon nanotubes in long bundles of carbon nanotubes with the length more than 10 μm is less than 3 wt. % of the total amount of carbon nanotubes in the suspension.

    [0113] The ratio of intensities of G/D bands for the dry residue of this suspension (S) is 87. As in

    [0114] Example 1, the SWCNT concentration in the suspension is 0.4 wt. %, and the suspension also contains 0.6 wt. % of Na-carboxymethyl cellulose (CMC) as a dispersant.

    [0115] As in Example 1, the dry matter of the obtained anode slurry comprises 90 wt. % of the active component, 3 wt. % of carbon nanotubes, 4.5 wt. % of Na-CMC, and 2.5 wt. % of butadiene-styrene rubber.

    [0116] The procedures of anode manufacture and cell assembly for its testing were similar to Example 1. The initial specific capacity of the anode at charge current 2 A/g of the anode material is 1241 mA.Math.h/g of the anode material, which is very close to the anode capacity according to Example 1. However, already by cycle 50 (charge current 2 A/g, discharge current 1 A/g), the specific capacity of the anode drops down to 1056 mA.Math.h/g. After 500 cycles, the specific capacity of the anode is 712 mA.Math.h/g, i.e., less than 58% of the initial specific capacity. Thus, the absence of long bundles of carbon nanotubes in the suspension (S) negatively affects the number of cycles that the anode supports until loosing 20% of its initial capacity. The presence of bundles of carbon nanotubes with the length more than 10 μm in the suspension (S) is required to achieve the claimed technical result.

    Industrial Applicability

    [0117] The present invention can be used in electrotechnical industry, more particularly in the production of lithium-ion batteries, lithium-ion batteries with silicon-containing negative electrodes (anodes), as well as in the production of anodes for lithium-ion batteries.

    [0118] Having thus described a preferred embodiment, it should be apparent to those skilled in the art that certain advantages of the described method and apparatus have been achieved. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention.

    List of Cited References (All Incorporated Herein by Reference in Their Entirety)

    Patent Literature

    [0119] Patent Literature 1: U.S. Pat. No. 8,263,265

    [0120] Patent Literature 2: U.S. Pat. No. 8,617,746

    [0121] Patent Literature 3: Patent EP 2755263 B1

    [0122] Patent Literature 4: U.S. Pat. No. 8697286

    [0123] Patent Literature 5: Patent RU 2717516 C2

    Non-Patent Literature

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    [0125] Non-Patent Literature 2: J. Gigault, I. Le Hécho, S. Dubascoux, M. Potin-Gautier, G. Lespes, Single-walled carbon nanotube length determination by asymmetrical-flow field-flow fractionation hyphenated to multi-angle laser-light scattering, J. Chromatogr. A, 2010, Vol. 1217, pp. 7891-7897