Sulfur material containing quantum dot component, method for producing the sulfur material, electrode, and lithium-sulfur battery

Abstract

A material may include sulfur and a quantum dot component. The quantum dot component may be a quantum dot-nanotube composite, a quantum dot-graphene composite, carbon quantum dots consisting essentially of carbon, hybrid quantum dots comprising carbon and at least one metal oxide, or any combination. A method of making the material may involve making the quantum dot component by a sol-gel process and combining the quantum dot component with the sulfur. The material may serve as a cathode material for a battery, particularly a lithium-sulfur battery. The lithium-sulfur battery may overcome or partially overcome the shuttle effect.

Description

[0001] TITLE

[0002] SULFUR MATERIAL CONTAINING QUANTUM DOT COMPONENT, METHOD FOR PRODUCING THE SULFUR MATERIAL, ELECTRODE, AND LITHIUM- SULFUR BATTERY

[0003] BACKGROUND

[0004] Technical Field

[0005] The present disclosure relates to a material that includes sulfur and a quantum dot component. The material may be used in electrochemical energy storage devices, in particular as an electrode in batteries such as lithium-sulfur batteries. The present disclosure further relates to improvements in the composition and function of batteries such as lithium-sulfur batteries, with respect to mitigating the shuttle effect.

[0006] Background Art

[0007] Rechargeable lithium-sulfur batteries may have certain advantages in terms of cost-effectiveness, capacity, and relatively low weight resulting from lower density materials. Lithium-sulfur batteries have high theoretical capacity of about 1672 mAh / g, and high theoretical energy density of about 2600 Wh / kg. These advantages may render lithium-sulfur batteries more desirable in some respects than lithium-ion batteries. However, performance in lithium-sulfur batteries may suffer over time and / or after several charge-discharge cycles, due to the shuttle effect.

[0008] Lithium-sulfur batteries involve a metallic lithium anode and a sulfur (Ss) cathode. As the battery discharges, lithium from the lithium anode produces lithium ions and electrons. The lithium ions then react with the sulfur in the cathode to produce lithium sulfide (LiiS).

[0009] In the formation of the lithium sulfide during discharge, lithium poly sulfides (Li2Ss, Li2Se, Li2S4, Li2S2) form as intermediates. These polysulfides may be soluble in the electrolyte, which may move from the cathode into the electrolyte and to the lithium anode, where they may form shorter polysulfides. The shorter polysulfides may then move back to the cathode to again form longer poly sulfides. This movement and reaction of the poly sulfides between the anode and the cathode depletes the capacity of the battery. Such depletion of lithium-sulfur battery capacity by formation and movement of poly sulfides may be referred to as the “shuttle effect.”

[0010] Inclusion of nanostructures may have represented other attempts to mitigate the shuttle effect or to obtain other benefits in lithium sulfur batteries or in other batteries. However, inasmuch as such attempts have failed to include a quantum dot component as disclosed herein, they have accordingly failed to provide sufficient mitigation of the shuttle effect in a lithium sulfur battery. For example, the cathode may have incorporated nanotubes or nanoporous, microporous, or mesoporous carbon, (see Li et al., “Engineering Strategies for Suppressing the Shuttle Effect in Lithium-Sulfur Batteries” Nano-Micro Lett. (2024) 16:12, published online November 10, 2023, incorporated herein by reference). In CN109494346B, incorporated herein by reference, the cathode may have incorporated functionalized quantum dots such as polyethyleneimine- functionalized quantum dots, for an absorption effect of the polyethyleneimine on poly sulfide. CN108417893B, incorporated herein by reference, may have used carbon quantum dots containing nitrogen or oxygen elements with strong polarity or boron, sulfur, and phosphorous elements, in an attempt to provide a chemical adsorption effect on lithium in lithium polysulfide molecules. In CN11134200 IB, incorporated herein by reference, the cathode may have incorporated other functionalized carbon quantum dots or other nanomaterials entirely, nanometer oxide, nanometer carbide (for example tungsten carbide or titanium carbide), nanometer nitride (for example tungsten nitride), nanometer sulfide. CN10678485 IB, incorporated herein by reference, may have included graphene quantum dots, formed in a bottom-up fashion of stacking graphene layers, rather than a cohesive, bonded material as in a carbon quantum dot. KR101884870B1, incorporated herein by reference, may have included graphene quantum dots and / or carbon black particles, but not carbon quantum dots. In CN10678485 IB, incorporated herein by reference, the cathode may have incorporated titanium nitride and / or titanium di oxi de-titanium nitride quantum dots. In CN106784851B, incorporated herein by reference, the cathode may have incorporated zinc sulfide quantum dots with carbon nanotubes.

[0011] In still other possibilities, in an attempt to mitigate the shuttle effect, the electrolyte may have incorporated one or more additives, for example ammonia modified carbon quantum dots as in CN110518285B, incorporated herein by reference, or graphene quantum dots as in CN110504488B, incorporated herein by reference. In yet other possibilities, the lithium anode may have incorporated one or more additives, for example graphene quantum dots, as in CN110504451B, incorporated herein by reference.

[0012] Even with such measures for adding nanomaterials or other materials to the cathode or to the electrolyte, reduction or further reduction of the shuttle effect has still been needed. Furthermore, concerns with respect to environmental or toxicological hazards of some of the additives may further inhibit implementation or scaling of such measures. Accordingly, any of the above-noted additives or combinations thereof may be omitted. Such additives and combinations of additives could also be included to the extent that they would not act against the materials and batteries described herein.

[0013] BRIEF SUMMARY

[0014] Inclusion of a quantum dot component in a sulfur material may provide a material with improved properties and uses in the field of batteries, particularly for lithium-sulfur batteries. The resulting material may also represent a lower concern as to toxicity or environmental impact, especially with respect to materials that include other types of quantum dot-based components. The quantum dot component may consist essentially of carbon, or may further include at least one metal, for example in the form of an oxide. A battery, in particular a lithium-sulfur battery, may have such a sulfur material containing a quantum dot component as a cathode.

[0015] The inventors have surprisingly found that the inclusion of a quantum dot component in the sulfur cathode of a lithium-sulfur battery may result in increased battery capacity retention over several charge-discharge cycles, with respect to an otherwise-comparable lithium-sulfur battery lacking the quantum dot component. Without limiting the disclosure to any specific mechanism, explanation, or theory, the increased capacity retention may result from suppression of the shuttle effect.

[0016] Specifically, the inventors have discovered the material, the method of making the material, the electrode material, and the lithium-sulfur battery cell as follows.

[0017] (1) A material contains sulfur, and a quantum dot component, and the quantum dot component is at least one component selected from the group consisting of: a quantum dot- nanotube composite, a quantum dot-graphene composite, carbon quantum dots consisting essentially of carbon, and hybrid quantum dots comprising carbon and at least one metal oxide.

[0018] (2) In the material of (1), the quantum dot component may contain the quantum dot-nanotube composite.

[0019] (3) In the material of (2), the quantum dot-nanotube composite may contain a plurality of nanotube portions, and the quantum dot-nanotube composite further may contain a plurality of quantum dot portions along a length of each nanotube portion.

[0020] (4) In the material of (3), quantum dot portions of the plurality of quantum dot portions may have a number average particle diameter of from 5 to 40 nm.

[0021] (5) In the material of any one of (1) to (4), the quantum dot component may be obtained by subjecting a mixture to a sol-gel process, the mixture containing a carbon source, a solvent, optionally a metal oxide precursor, optionally nanotubes, and optionally graphene.

[0022] (6) In the material of (5), the mixture may contain an alkoxide of at least one metal as the metal oxide precursor.

[0023] (7) In the material of any one of (1) to (6), the sulfur may contain octasulfur Ss and / or elemental sulfur.

[0024] (8) In the material of any one of (1) to (7), the quantum dot-nanotube composite may consist essentially of carbon.

[0025] (9) In the material of any one of (1 ) to (8), the quantum dot component may contain the quantum dot-nanotube composite, the hybrid quantum dots, or both, and the quantum dot- nanotube composite, the hybrid quantum dots, or both may contain carbon and a metal oxide.

[0026] (10) In the material of (9), the metal oxide may contain at least one oxide of a transition metal. (11) In the material of (9), the metal oxide may contain an oxide of at least one metal or metalloid selected from the group consisting of tungsten, molybdenum, ruthenium, niobium, tantalum, germanium, iron, silver, manganese, titanium, tin, antimony, bismuth, gold, silicon, nickel, cobalt, chromium, zirconium, and vanadium.

[0027] (12) In the material of (9), the metal oxide may contain an oxide of tungsten or molybdenum.

[0028] (13) In the material of (9), the metal oxide may contain a tungsten oxide.

[0029] (14) In the material of any one of (9) to (13), the quantum dot component may contain the quantum dot-nanotube composite, and the quantum dot-nanotube composite may have a carbon content of from 90% to 99.9% by mass and a total content of the at least one metal oxide of from 0.1% to 2% by mass, based on a total mass of the quantum dot-nanotube composite.

[0030] (15) In the material of any one of (1) to (14), the sulfur may be mixed with the quantum dot component on a nanometer scale.

[0031] (16) In the material of any one of (1) to (15), a quantum dot component content may be from 5% to 40% by mass, based on a total mass of the material.

[0032] (17) In the material of any one of (2) to (16), nanotubes constituting the carbon dot-nanotube composite may be carbon nanotubes.

[0033] (18) In the material of any one of (2) to (17), nanotubes constituting the carbon dot-nanotube composite may be single wall carbon nanotubes.

[0034] (19) In the material of any one of (5) to (18), the mixture may contain from 0. 1 to 20% by mass of the carbon source, from 0.10% to 5.0% by mass of the nanotubes, from 60% to 95% by mass of the solvent, and from 0 to 20% by mass of the metal oxide precursor.

[0035] (20) In the material of any one of (1) to (19), further may contain carbon black. (21) In the material of (20), a carbon black content may be from 0.5% to 15.0% by mass, based on a total mass of the material.

[0036] (22) In the material of (20) or (21), the sulfur may be mixed with the quantum dot-nanotube composite and the carbon black on a nanometer scale.

[0037] (23) In a method of making the material of any one of (1) to (22), the method may contain subjecting a mixture to a sol-gel process, the mixture comprising a carbon source, a solvent, optionally a metal oxide precursor, optionally nanotubes, and optionally graphene, thereby obtaining the quantum dot component, combining the quantum dot component and the sulfur in a slurry, and applying the slurry to a substrate.

[0038] (24) An electrode material may contain the material of any one of (1) to (23), and a binder.

[0039] (25) In the electrode material of (24), the binder may be a polymer.

[0040] (26) In the electrode material of (24), the binder may be PVDF.

[0041] (27) A lithium-sulfur battery cell may contain an anode, comprising lithium, an electrolyte, a separator, and a cathode, comprising the electrode material of any one of (24) to (26).

[0042] (28) In the lithium-sulfur battery cell of (27), the electrolyte may be an organic liquid electrolyte.

[0043] (29) In the lithium-sulfur battery cell of (27) or (28), a capacity of the cell after 100 charge / discharge cycles may be at least 41% of the capacity of the cell before any charge / discharge cycles.

[0044] (30) In the lithium-sulfur battery cell of any one of (27) to (29), a capacity of the cell after 1000 charge / discharge cycles may be at least 55% of the capacity of the cell before any charge / discharge cycles. (31) In the lithium-sulfur battery cell of any one of (27) to (30), an initial capacity of the cell may be at least 1000 mAh / g.

[0045] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0046] FIG. l is a scanning electron microscope image of a quantum dot-nanotube composite as a quantum dot component at a first resolution.

[0047] FIG. 2 is a scanning electron microscope image of a quantum dot-nanotube composite at a second resolution.

[0048] FIG. 3 is a scanning electron microscope image of a quantum dot-nanotube composite at a third resolution.

[0049] FIG. 4 is a transmission electron microscope image of quantum dots of a type that may be present in a quantum dot-nanotube composite.

[0050] FIG. 5 is an absorbance spectrum of carbon quantum dots under photoexcitation.

[0051] FIG. 6 is an emission intensity spectrum of carbon quantum dots under photoexcitation from various wavelengths.

[0052] FIG. 7 shows emission counts over time for carbon quantum dots under photoexcitation.

[0053] FIG. 8 is an absorbance spectrum of carbon-tungsten hybrid quantum dots under photoexcitation.

[0054] FIG. 9 is an emission intensity spectrum of carbon-tungsten hybrid quantum dots under photoexcitation from various wavelengths.

[0055] FIG. 10 shows emission counts over time for carbon-tungsten hybrid quantum dots under photoexcitation.

[0056] FIG. 11 is a sectional view of one embodiment of a lithium-sulfur battery cell.

[0057] FIG. 12 is a graph showing charge and discharge curves for a first embodiment of a lithiumsulfur battery. FIG. 13 is a graph showing changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles for the first embodiment of a lithium-sulfur battery.

[0058] FIG. 14 is a graph showing charge and discharge curves for a second embodiment of a lithiumsulfur battery.

[0059] FIG. 15 is a graph showing changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles for the second embodiment of a lithium-sulfur battery.

[0060] FIG. 16 is a graph showing charge and discharge curves for a third embodiment of a lithiumsulfur battery.

[0061] FIG. 17 is a graph showing changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles for the third embodiment of a lithium-sulfur battery.

[0062] FIG. 18 is a graph showing charge and discharge curves for a fourth embodiment of a lithiumsulfur battery.

[0063] FIG. 19 is a graph showing changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles for the fourth embodiment of a lithium-sulfur battery.

[0064] FIG. 20 is a graph showing charge and discharge curves for a first comparative embodiment of a lithium-sulfur battery.

[0065] FIG. 21 is a graph showing changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles for the first comparative embodiment of a lithium-sulfur battery.

[0066] FIG. 22 is a graph showing charge and discharge curves for a second comparative embodiment of a lithium-sulfur battery.

[0067] FIG. 23 is a graph showing changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles for the second comparative embodiment of a lithium-sulfur battery. DETAILED DESCRIPTION

[0068] Quantum Dot Components

[0069] The quantum dot component may be a quantum dot-nanotube composite, a quantum dotgraphene composite, carbon quantum dots consisting essentially of carbon, hybrid quantum dots comprising carbon and at least one metal oxide, or any combination thereof.

[0070] Quantum Dot-Nanotube Composites

[0071] A quantum dot-nanotube composite may be obtained by a sol-gel process conducted with a mixture of a solvent, a carbon source, and optionally a metal oxide precursor.

[0072] The carbon source may be an organic and / or carbon-containing compound from which carbon dots may be obtained by a sol-gel process. The carbon source may preferably be a furan derivative, preferably furfural; phloroglucinol; resorcinol; or formaldehyde.

[0073] The sol-gel process may involve a single carbon source, or a combination of multiple carbon sources of similar or different types. One such combination may be a combination of a phenolic hydroxyl group-containing compound and an aldehyde group-containing compound in combination. The phenolic hydroxyl group-containing compound may be phloroglucinol, resorcinol, or any combination thereof. The aldehyde group-containing compound may be furfural, formaldehyde, or any combination thereof. Specific examples include a combination of phloroglucinol and furfural; a combination of resorcinol, phloroglucinol, and formaldehyde; a combination of resorcinol and formaldehyde; or a combination of phloroglucinol and furfural. The combination of phloroglucinol and furfural may be preferred.

[0074] Relative amounts of a phenolic hydroxyl group-containing compound and an aldehyde group- containing compound in combination as carbon source are not particularly limited. Some embodiments may use at least 100 parts by mass of the aldehyde group-containing compound for 100 parts by mass of the phenolic hydroxyl group-containing compound, more preferably at least 120 parts by mass, more preferably at least 150 parts by mass, and more preferably at least 160 parts by mass. Some embodiments may use up to 500 parts by mass of the aldehyde group- containing compound for 100 parts by mass of the phenolic hydroxyl group-containing compound, more preferably up to 340 parts by mass, more preferably up to 320 parts by mass, more preferably up to 310 parts by mass, more preferably up to 250 parts by mass, and more preferably 230 parts by mass. Some embodiments may use 100-500 parts by mass of the aldehyde group-containing compound for 100 parts by mass of the phenolic hydroxyl group- containing compound, more preferably 120-340 parts by mass, more preferably 150-320 parts by mass, more preferably 160-310 parts by mass, more preferably 150-310 parts by mass, more preferably 150-250 parts by mass, more preferably 160-230%, and more preferably 150-230 parts by mass.

[0075] The content of the carbon source in the sol-gel mixture may preferably be 0.1% by mass or more for example for controlling the specific surface area and / or particle size of resulting particles.

[0076] The content of the carbon source in the sol-gel mixture may more preferably be 0.5% by mass or more, and further preferably 1.0% by mass or more. The content of the carbon source in the solgel mixture may preferably be 20% by mass or less, more preferably 10% by mass or less, more preferably 8% by mass or less, and more preferably 5% by mass or less. For example, the content of the carbon source in the sol-gel mixture may preferably be 0.1% by mass or more and 20% by mass or less, more preferably 0.5% by mass or more and 10% by mass or less, still more preferably 1.0% by mass or more and 8% by mass or less, and most preferably 1.0% by mass or more and 5% by mass or less.

[0077] The solvent in the sol-gel mixture may include an organic solvent. Examples of the organic solvent include ethanol, isopropanol, methanol, acetone, and methyl ethyl ketone. Ethanol may be preferred in certain embodiments. A dehydrating solvent with a water content of 1% or less may be preferred in some embodiments, for example to control hydrolysis. The solvent may also contain water in addition to the organic solvent.

[0078] The sol-gel mixture may have enough solvent to give a solid content concentration of at least 1% by mass, more preferably at least 1.5% by mass, more preferably at least 2% by mass, even more preferably at least 4% by mass. The sol-gel mixture may have enough solvent to give a solid content concentration of up to 45% by mass, more preferably up to 30% by mass, more preferably up to 25% by mass, even more preferably up to 20% by mass. The sol-gel mixture may have enough solvent to give a solid content concentration of 1-45% by mass, more preferably 1.5-30% by mass, more preferably 2-25% by mass, even more preferably 4-20% by mass. The “solid content” may indicate all components other than the solvent, even if another component or components are in a liquid or dissolved state. Thus, the sol-gel mixture may have a solvent content of at least 55% mass, more preferably at least 60% by mass, more preferably at least 70% by mass, more preferably at least 75% by mass, even more preferably at least 80% by mass. The sol-gel mixture may have a solvent content of up to 95% mass, more preferably up to 98.5% by mass, more preferably up to 98% by mass, even more preferably up to 96% by mass. The sol-gel mixture may have a solvent content of 55-95% mass, more preferably 60%-95% by mass, more preferably 70-98.5% by mass, more preferably 75-98% by mass, even more preferably 80-96% by mass.

[0079] The nanotubes in the sol-gel mixture are not particularly limited. In some embodiments, the nanotubes may be carbon nanotubes, for example single-wall carbon nanotubes, double-wall carbon nanotubes, or other multi-wall carbon nanotubes.

[0080] Single-wall carbon nanotubes (SWCNTs) may be preferred in some embodiments. SWCNTs may have an armchair configuration, a zigzag configuration, or may represent a mixture of such configurations. In some embodiments, preferred SWCNTs may have a diameter of at least 0.4 and / or up to 2.0 nm, more preferably at least 0.8 and up to 2.0 nm. Exemplary SWCNTs may, for example, be TUB ALL™ products from OCSiAl, for example TUBALL™ BATT, having a diameter of 1.6 ± 0.4 nm and a length of at least about 5 pm.

[0081] In some embodiments, the nanotubes may be present in the sol-gel mixture in a content of at least 0.05% by mass, more preferably at least 0.10% by mass, more preferably at least 0.15% by mass, even more preferably at least 0.20% by mass. The nanotubes may be present in the sol-gel mixture in a content of up to 5.0 by mass, more preferably up to 4.0% by mass, more preferably up to 3.0% by mass, more preferably up to 2.0% by mass, even more preferably up to 1.0% by mass. The nanotubes may be present in the sol-gel mixture in a content of 0.05-5.0% by mass, more preferably 0.10-5.0% by mass, more preferably 0.10-4.0% by mass, more preferably 0.10- 3.0% by mass, more preferably 0.15-2.0% by mass, even more preferably 0.20-1.0% by mass.

[0082] In some embodiments, the sol-gel mixture may further include a metal oxide precursor. The metal oxide precursor may be any component that can provide a metal oxide content in the product of the sol-gel process.

[0083] The metal in the metal oxide precursor may be any metal that forms an oxide. Transition metals may be preferred in some embodiments, though in other embodiments, other metals or metalloids may also be preferred. In some embodiments, tungsten, molybdenum, ruthenium, niobium, tantalum, germanium, iron, silver, manganese, titanium, tin, antimony, bismuth, gold, silicon, nickel, cobalt, chromium, zirconium, vanadium, or any combination thereof may be preferred as the metal. Some embodiments may have a particular preference for tungsten, molybdenum, ruthenium, niobium, tantalum, or any combination thereof, more preferably tungsten and / or molybdenum, even more preferably tungsten.

[0084] The metal oxide precursor may include metal salts such as metal alkoxides, metal salts of carboxylic acids, metal sulfates, metal nitrates, or any combination thereof. Metal salts of carboxylic acids may include, for example, metal acetates. Only one type of metal oxide precursor may be used, or two or more types may be used in combination. Metal alkoxides may be preferred in some embodiments, and may include metal methoxide, metal ethoxide, metal propoxide, or metal butoxide. Metal ethoxide may be especially preferred in some embodiments.

[0085] As metal oxide precursors, tungsten alkoxide and / or molybdenum alkoxide may be preferred, and tungsten ethoxide and / or molybdenum ethoxide may be especially preferred.

[0086] In some embodiments, the metal oxide precursor, where present, may be present in the sol-gel mixture in a content of greater than 0% by mass, more preferably at least 1.0% by mass, more preferably at least 2.0% by mass, even more preferably at least 4.0% by mass. The metal oxide precursor may be present in the sol-gel mixture in a content of up to 20% by mass, more preferably up to 18% by mass, more preferably up to 15% by mass, even more preferably up to 14% by mass. The metal oxide precursor may be present in the sol-gel mixture in a content of 0- 20% by mass, more preferably 1.0-18% by mass, more preferably 2.0-15% by mass, even more preferably 4.0-14% by mass.

[0087] A molar content of the metal in the sol-gel mixture may be indicated as a molar ratio of the metal in the metal oxide precursor and the carbon in the carbon source:

[0088] (mass of metal in metal oxide precursor) / (atomic weight of metal) (mass of carbon in carbon source) / (atomic weight of carbon)

[0089] In some embodiments, this molar content may be preferably as high as 10000 / 1 and as low as 1 / 10000, more preferably as high as 10 / 1 and as low as 1 / 1000. More preferably, this quantity may be as high as 1 / 1 and as low as 1 / 100. When two or more metal oxide precursors are used, or when the metal oxide precursor includes two or more metals, the total number of moles of metal may be used to calculate the molar content. Further, when two or more carbon sources are used, the total number of moles of carbon may be used to calculate the molar content.

[0090] In other embodiments, the sol-gel mixture may not contain the metal oxide precursor, resulting in a quantum dot-nanotube composite that does not contain the metal oxide.

[0091] The sol-gel mixture in various embodiments may include or exclude a catalyst, a surfactant, a pH adjuster, as other components in addition to the above-described carbon source, solvent, nanotubes, and optional metal oxide precursor. Examples of the catalyst include acid catalysts such as oxalic acid, nitric acid, citric acid, sulfuric acid, chloric acid, and acetic acid, with preference in some embodiments for oxalic acid or citric acid. In embodiments containing a catalyst, the content of the catalyst may preferably be 0.01-1% by mass with respect to the total mass of the sol-gel mixture.

[0092] The sol-gel mixture may be obtained by mixing the constituent components. The method and / or order of mixing is not particularly limited. Components may be added in any order, separately or together. However, in some embodiments, the nanotubes are first added to the solvent and mixed; then one or more carbon sources are added to the mixture of nanotubes and solvent while mixing; and finally, if present, one or more metal oxide precursors are added while mixing. One or more components may be dispersed or dissolved in a solvent in advance of addition to the mixture.

[0093] The sol-gel mixture may be subjected to a sol-gel process at room temperature or at an elevated temperature, for example 40-70°C. The sol-gel process involves gelling the sol-gel mixture, for example by stirring under heating. Stirring may occur in some embodiments for 1-72 hours under heating at 40-70°C, and may involve a known stirring device such as a magnetic stirrer or an overhead stirrer and a stirring rate of 200-800 rpm. After stirring, the composition may be allowed to stand under heating at 40-70°C for a time, for example 3-7 days.

[0094] The sol-gel product obtained by the sol-gel process includes metal compound nanoparticles such as polymers formed by carbon element precursors and metal hydroxides formed by metal element precursors. The product of the sol-gel process includes nanostructures comprising carbon. If the metal oxide precursor was used, then the product of the sol-gel process further includes the metal oxide precursor or one or more intermediates, such as metal hydroxides.

[0095] The sol-gel process may be followed by cleaning, involving washing the sol-gel product, preferably before any supercritical drying. In some embodiments, the solvent used for cleaning may include an alcohol-based solvent, a hydrocarbon-based solvent, a ketone-based solvent, water, or other solvent. An alcohol-based solvent may be preferable. Examples of the alcohol- based solvent include ethanol, methanol, isopropanol, butanol, with a preference in some embodiments for ethanol.

[0096] The cleaning can be performed, for example, by repeatedly adding a cleaning solvent to the solgel product and discharging the added cleaning solvent. The cleaning step is preferably performed until the cleaning solvent to be discharged becomes transparent.

[0097] Cleaning may use one type of cleaning solvent or two or more types of cleaning solvents. When two or more types of cleaning solvents are used, they may be used as a mixed solvent, and may be washed using another cleaning solvent after cleaning using one type of cleaning solvent.

[0098] After cleaning, the sol-gel product may be dried in a supercritical drying step to obtain an aerogel powder. For example, the sol-gel product may be placed in a sealed container, and supercritical CO2 may be introduced into the sealed container under a pressure of 1500 psi. The contents of the container may be maintained at 1500 psi and 45°C, for example for 1 hour, and then supercritical CO2 may be released emitted. One iteration or more than one iteration of such supercritical drying may be performed.

[0099] After the supercritical drying, a pyrolysis step may be used to treat the aerogel powder. In the pyrolysis step, the aerogel powder obtained may be heated, for example in a furnace at a heating rate, for example 0.8-1.2°C / min, in an inert gas atmosphere. The inert gas is not particularly limited, but for example, argon gas or nitrogen gas may be used. After the increase in temperature, the aerogel is thermally decomposed by maintaining an elevated temperature for 5- 60 minutes, more preferably 20-30 minutes.

[0100] In some embodiments, a crushing step may optionally follow pyrolysis. The crushing may resolve aggregation between particles after the pyrolysis step. In the crushing step, the heated hybrid quantum dots may be returned to room temperature, and the hybrid quantum dots may be crushed, for example by a mortar, a pestle, and a ball mill.

[0101] The resulting quantum dot-nanotube composite may contain carbon and optionally, if a metal oxide precursor was included in the sol-gel mixture, a metal oxide. The metal oxide may be a decomposed product of the metal oxide precursor. Aside from carbon and the optional metal oxide, the quantum dot-nanotube composite may or may not contain other components.

[0102] In some embodiments, the quantum dot-nanotube composite may have a carbon content of at least 90% by mass, more preferably at least 93% by mass, even more preferably at least 96% by mass, even more preferably at least 98% by mass, based on a total mass of the quantum dot- nanotube composite. The quantum dot-nanotube composite may have a carbon content of at most 99.95% by mass, more preferably at most 99.9% by mass, even more preferably at most 99.5% by mass, even more preferably at most 99.2% by mass, based on a total mass of the quantum dot- nanotube composite. The quantum dot-nanotube composite may have a carbon content of from 90% to 99.95% by mass, preferably 90% to 99.9% by mass, more preferably from 93% to 99.9% by mass, even more preferably from 96% to 99.5% by mass, even more preferably from 98% to 99.2% by mass, based on a total mass of the quantum dot-nanotube composite. In the same or other embodiments, the quantum dot-nanotube composite may have a total content of the at least one metal oxide of at least 0.05% by mass, more preferably at least 0.1% by mass, even more preferably at least 0.4% by mass, even more preferably at least 0.5% by mass, even more preferably at least 0.8% by mass, based on a total mass of the quantum dot-nanotube composite. The quantum dot-nanotube composite may have a total content of the at least one metal oxide of at most 10% by mass, more preferably at most 7% by mass, even more preferably at most 4% by mass, even more preferably at most 2% by mass, even more preferably at most 0.9% by mass, based on a total mass of the quantum dot-nanotube composite. The quantum dot-nanotube composite may have a total content of the at least one metal oxide of from 0.05% by mass to 10% by mass, more preferably from 0.1% to 7% by mass, even more preferably from 0.1% to 2% by mass, even more preferably from 0.4% to 0.9% by mass or may be more preferably from 0.5% to 4% by mass, or may be from 0.8% to 2% by mass, based on a total mass of the quantum dot-nanotube composite. Preferably, in some embodiments, the quantum dot-nanotube composite includes only carbon and optionally the one or more metal oxides, and does not include other components except for small amounts of inevitable impurities, for example in amounts of less than 1.0% by mass, more preferable less than 0.5% by mass, even more preferably less than 0.1% by mass, even more preferably less than 0.05% by mass.

[0103] In embodiments without the metal oxide, the quantum dot-nanotube composite may consist essentially of carbon, having a carbon content, for example, of at least 98%, preferably at least 99%, more preferably at least 99.5%, more preferably at least 99.9%, and even more preferably at least 99.95%. The quantum dot-nanotube composite in some embodiments may consist of carbon and inevitable impurities, which inevitable impurities may have a maximum content of 2%, preferably a maximum content of 1%, more preferably a maximum content of 0.5%, more preferably a maximum content of 0.1%, and even more preferably a maximum content of 0.05%.

[0104] The shape of particles within the quantum dot-nanotube composite may include quantum dot portions that resemble quantum dots and nanotube portions that resemble nanotubes. Particles of the quantum dot-nanotube composite may include one or more quantum dot portions on a surface of a nanotube portion. The quantum dot portions may be at one end of the nanotube portion, the opposite end of the nanotube portion, along the length of the nanotube portion, or any combination thereof. In some embodiments, each nanotube portion may have a plurality of quantum dot portions along a length of the nanotube portion, preferably on an outside surface of the length of the nanotube portion.

[0105] In some embodiments, the quantum dot portions may constitute at least 40% by mass of the quantum dot-nanotube composite, more preferably at least 50% by mass, more preferably at least 60% by mass, more preferably at least 70% by mass, more preferably at least 80% by mass, more preferably at least 85% by mass. The quantum dot portions may constitute up to 99.5% by mass of the quantum dot-nanotube composite, more preferably up to 99.0% by mass. For example, the quantum dot portions may preferably constitute at least 40% by mass and up to 99.5% by mass of the quantum dot-nanotube composite, more preferably at least 50% by mass and up to 99.5% by mass, still more preferably at least 60% by mass and up to 99.5% by mass, and most preferably at least 70% by mass and up to 99.0% by mass. The nanotube portions may constitute at least 0.1% by mass of the quantum dot-nanotube composite, more preferably at least 0.2% by mass, more preferably at least 0.3% by mass. The nanotube portions may constitute up to 60% by mass of the quantum dot-nanotube composite, more preferably up to 50% by mass, more preferably up to 40% by mass, more preferably up to 30% by mass, more preferably up to 20% by mass, more preferably up to 10% by mass. The nanotube portions may preferably constitute at least 0.1% by mass and up to 60% by mass of the quantum dot-nanotube composite, more preferably at least 0.2% by mass and up to 50% by mass, still more preferably at least 0.3% by mass and up to 40% by mass, even more preferably at least 0.3% by mass and up to 30% by mass, yet more preferably at least 0.3% by mass and up to 20% by mass, and most preferably at least 0.3% by mass and up to 10% by mass.

[0106] In the quantum dot-nanotube composite, the numeric ratio of quantum dot portions to nanotube portions may be as low as 0.8:1; more preferably as low as 1: 1; more preferably as low as 10:1. The ratio of quantum dot portions to nanotube portions may be as high as 10’: 1; more preferably as high as 104: 1 ; more preferably as high as 1000:1. The ratio of quantum dot portions to nanotube portions may be as low as 0.8: 1 and as high as 105: 1 ; more preferably the ratio of quantum dot portions to nanotube portions may be as low as 1 : 1 and as high as 104: 1 ; more preferably the ratio of quantum dot portions to nanotube portions may be as low as 10: 1 and as high as 1000:1.

[0107] In some embodiments, at least some quantum dot portions and nanotube portions may be connected in any manner, for example directly covalently bonded, or bonded via a linking group. In other embodiments, at least some quantum dot portions and nanotube portions may be unbonded, and may maintain contact for example through electrostatic force.

[0108] FIG. 1 is a scanning electron microscope image of an embodiment of a quantum dot-nanotube composite at a first resolution. FIG. 2 is a scanning electron microscope image of an embodiment of a quantum dot-nanotube composite at a second resolution. FIG. 3 is a scanning electron microscope image of an embodiment of a quantum dot-nanotube composite at a third resolution. FIG. 1, FIG. 2, and FIG. 3 show a plurality of nanotube portions, each having a lengthwise direction, with a plurality of quantum dot portions along the length of each nanotube portion.

[0109] Quantum dot portions of the quantum dot-nanotube composite may have a number average particle diameter at least 2 nm, more preferably at least 4 nm, more preferably at least 5 nm, and even more preferably at least 10 nm. Quantum dot portions of the quantum dot-nanotube composite may have a number average particle diameter of up to 50 nm, more preferably up to 40 nm, and even more preferably up to 20 nm. Quantum dot portions of the quantum dot- nanotube composite may have a number average particle diameter of 2-50 nm, more preferably 4-50 nm, more preferably 5-40 nm, and even more preferably 10-20 nm. The number average particle diameter can be measured by, for example, the average value of the diameter of the particles when observing 200 particles with an electron microscope such as a scanning electron microscope (SEM), transmission electron microscope (TEM), or scanning transmission electron microscope (STEM). The composition, structure, and size of the quantum dot portions can be easily adjusted by adjusting the type, amount, and conditions of the carbon source and the metal oxide precursor.

[0110] In some embodiments, the quantum dot portions of the quantum dot-nanotube composite may have a cohesively-bonded carbon shell, which in some embodiments may enclose a hollow interior region. In some embodiments, the quantum dot portions of the quantum dot-nanotube composite may not be or may not include graphene quantum dots, formed in a bottom-up fashion of stacking graphene layers, rather than a cohesive, bonded material. In some embodiments, the quantum dot-nanotube composite itself may be free or substantially free of graphene quantum dots, formed in a bottom-up fashion of stacking graphene layers, rather than a cohesive, bonded material.

[0111] In some embodiments, one or more quantum dot portions of the quantum dot-nanotube composite may contain a metal oxide obtained from the metal oxide precursor. Preferred embodiments may include the metal oxide in an interior region of some or substantially all of the quantum dot portions of the quantum dot-nanotube composite.

[0112] FIG. 4 shows an embodiment of quantum dots as in the quantum dot portions of the quantum dot-nanotube composite. In the embodiment shown in FIG. 4, the quantum dots generally have diameters in or near a range of 10-20 nm.

[0113] In some embodiments, quantum dot portions of the quantum dot-nanotube composite may have luminous properties. In such embodiments, the quantum dot portions may exhibit photoluminescence, for example fluorescence. Photoluminescence may occur with ultraviolet photoexcitation, visible-wavelength photoexcitation, or any combination thereof. Depending on the presence or absence of the metal oxide in the quantum dot portions as well as the type and amount of the metal oxide, the photoluminescence may vary in intensity, responsiveness to photoexcitation at different wavelengths, or both.

[0114] FIG. 5, FIG. 6, and FIG. 7 show photoluminescent properties for carbon quantum dots as an embodiment of the quantum dot portions of the quantum dot-nanotube composite. FIG. 5 shows an absorbance spectrum under photoexcitation, FIG. 6 shows an emission intensity spectrum under photoexcitation from various wavelengths, and FIG. 7 shows emission counts over time under photoexcitation.

[0115] FIG. 8, FIG. 9, and FIG. 10 show photoluminescent properties for carbon-tungsten hybrid quantum dots as an embodiment of the quantum dot portions of the quantum dot-nanotube composite. FIG. 8 shows an absorbance spectrum under photoexcitation, FIG. 9 shows an emission intensity spectrum under photoexcitation from various wavelengths, and FIG. 10 shows emission counts over time under photoexcitation. The photoluminescent properties are different from photoluminescent properties for carbon quantum dots without tungsten, for example in that the photoluminescent intensity under photoexcitation at 350 nm is higher for the carbon-tungsten hybrid quantum dots than for the carbon quantum dots without tungsten.

[0116] Nanotube portions of the quantum dot-nanotube composite may comprise SWCNT structures. In some embodiments, SWCNTs may have an armchair configuration, a zigzag configuration, or may represent a mixture of such configurations. In some embodiments, preferred SWCNTs may have a diameter of 0.4-2.0 nm, more preferably 0.8-2.0 nm. Exemplary SWCNTs may, for example, be alike in dimension to TUB ALL™ products from OCSiAl, for example TUB ALL™ BATT, having a diameter of 1.6 ± 0.4 nm and a length of at least about 5 pm. Nanotube portions of the quantum dot-nanotube composite may have the same diameter and configuration as in the nanotubes used in the sol-gel mixture. Nanotube portions of the quantum dot-nanotube composite may have substantially the same diameter or shorter diameter, relative to the nanotubes used in the sol-gel mixture.

[0117] Other Quantum Dot Components

[0118] A quantum dot-graphene composite may also serve as a quantum dot component. A quantum dotgraphene composite may be obtained using the methods and components described previously to obtain a quantum dot-nanotube composite, except that graphene is provided in place of nanotubes. A quantum dot-graphene composite may comprise quantum dot portions and graphene portions, wherein the quantum dot portions may have the composition, properties, and parameters described previously in describing a quantum dot-nanotube composite.

[0119] Carbon quantum dots consisting essentially of carbon may also serve as a quantum dot component. In addition or in the alternative, hybrid quantum dots comprising carbon and at least one metal oxide may also serve as a quantum dot component. Carbon quantum dots, hybrid quantum dots, or both may be obtained using the methods and components described previously to obtain quantum dot portions in a quantum dot-nanotube composite, except that nanotubes are not included. Carbon quantum dots consisting essentially of carbon may be obtained without the use of the aforementioned metal oxide precursor, while hybrid quantum dots comprising carbon and at least one metal oxide may be obtained by providing the aforementioned metal oxide precursor. Carbon quantum dots, hybrid quantum dots, or both may have the composition, properties, and parameters described previously in describing quantum dot portions of a quantum dot-nanotube composite.

[0120] Sulfur Material and Sulfur Electrode Material

[0121] The quantum dot component may be included with sulfur and other components in a sulfur material or sulfur electrode material. Other components may include carbon black, nanomaterials, and one or more binders.

[0122] The process for making the sulfur material or sulfur electrode material is not particularly limited. In an exemplary production process, the sulfur electrode material may be produced by milling sulfur and the quantum dot component, for example in a ball mill other suitable milling or grinding apparatus, to obtain a milled composition. The milled composition may be pressed, for example in a hydraulic press, for example at 3-5 tons or more preferably about 4 tons. The resulting composition may be treated in an autoclave, for example for 3-12 hours or more preferably 6 hours at 120-200°C or more preferably 160°C. The composition may then be ground with a mortar and pestle or other milling or grinding apparatus and formed into a slurry. The slurry may contain about 65-95% or more preferably about 85% in total of the sulfur and quantum dot component, about 0-10% or more preferably about 5% of carbon black, and about 5-20% or more preferably about 10% of a binder, such as polyvinylidene fluoride (PVDF). The slurry may then be coated, for example by spraying, onto a substrate, for example a foil and particularly an aluminum foil. The resulting material may be dried, for example in a vacuum furnace oven at 30-50°C or more preferably 40°C for 6-24 hours or more preferably 12 hours.

[0123] The sulfur material and sulfur electrode material includes sulfur. In some embodiments, the sulfur may be present as octasulfur (Ss), which may be present in the form of a cyclic sulfur molecule. The sulfur material may include elemental sulfur and / or one or more poly sulfides having two, three, four, five, six, or seven sulfur atoms. The content of the sulfur may be at least 40% by mass, more preferably at least 50% by mass, more preferably at least 55% by mass, more preferably at least 60% by mass, with respect to a total mass of an electrode material including sulfur, the quantum dot component, any components to provide conductivity or increase conductivity, and any binder. The content of the sulfur may be up to 95% by mass, more preferably up to 90% by mass, more preferably up to 80% by mass, more preferably up to 75% by mass. The content of the sulfur may be 40%-95% by mass, more preferably 50%-90% by mass, more preferably 55%-80% by mass, more preferably 60%-75% by mass, for example about 68% by mass.

[0124] The sulfur material and sulfur electrode material includes the quantum dot component. The content of the quantum dot component may be at least 1% by mass, more preferably at least 5% by mass, more preferably at least 10% by mass, more preferably at least 12% by mass, with respect to a total mass of an electrode material including sulfur, the quantum dot component, any components to provide conductivity or increase conductivity, and any binder. The content of the quantum dot component may be up to 50% by mass, more preferably up to 40% by mass, more preferably up to 30% by mass, more preferably up to 25% by mass. The content of the quantum dot component may be l%-50% by mass, more preferably 5%-40% by mass, more preferably 10%-30% by mass, more preferably 12%-25% by mass, for example about 17% by mass.

[0125] In the sulfur material and sulfur electrode material, the quantum dot component and the sulfur may be in a mixed state on a micrometer or nanometer scale. Areas of sulfur may include one or more particles of the quantum dot component at least every 10 pm, more preferably at least every 1.0 pm, more preferably at least every 100 nm, as observed in a linear path by with an electron microscope such as a scanning electron microscope (SEM), transmission electron microscope (TEM), or scanning transmission electron microscope (STEM). In some embodiments, at least a portion of the sulfur present in the sulfur material and sulfur electrode material may be contained in and / or capable of migrating into an interior portion of the quantum dot component. In such embodiments, the sulfur may migrate into an interior portion of the quantum dot component, for example into the interior portion of a quantum dot portion of the quantum dot-nanotube composite, or into the interior portion of a nanotube portion of the quantum dot-nanotube composite, or both. The sulfur may migrate into the interior portion in the form of octasulfur (Ss), elemental sulfur, and / or one or more polysulfides having two, three, four, five, six, or seven sulfur atoms. Sulfur may be contained in an interior portion of the quantum dot component upon the initial production of the quantum dot component, and / or capable of migrating into an interior portion of the quantum dot component after one or more chargedischarge cycles.

[0126] In some embodiments, the sulfur material and sulfur electrode material may include one or more components to provide conductivity or increase conductivity of the material as an electrode material. Such materials may for example be carbon-containing materials, such as carbon black, activated carbon, graphite, and carbon nanomaterials, with a preference in some embodiments for carbon black. Carbon nanomaterials may include graphene sheets, graphene quantum dots, carbon quantum dots, hybrid quantum dots containing carbon, carbon nanospheres, SWCNTs, and multi-wall carbon nanotubes. The content of the one or more components to provide conductivity or increase conductivity may be at least 0.5% by mass, more preferably at least 1% by mass, more preferably at least 2% by mass, more preferably at least 3% by mass, with respect to a total mass of an electrode material including sulfur, the quantum dot component, the one or more components to provide conductivity or increase conductivity, and any binder. The content of the one or more components to provide conductivity or increase conductivity may be up to 50% by mass, more preferably up to 40% by mass, more preferably up to 20% by mass, more preferably up to 15% by mass, more preferably up to 10% by mass. The content of the one or more components to provide conductivity or increase conductivity may be 0.5%-50% by mass, more preferably l%-40% by mass, more preferably 2%-20% by mass, more preferably 0.5%- 15% by mass, more preferably 3%-l 0% by mass, for example about 5% by mass.

[0127] In some embodiments, the sulfur electrode material may include one or more binders. The binder or binders may provide the electrode material with suitable mechanical properties. In some embodiments, the binder may be a polymer, for example a cellulose-derived polymer, a halogenated polymer, lithium polyacrylate, or polyethylene oxide. The cellulose-derived polymer may be carboxymethyl cellulose optionally with a styrene-butadiene rubber. The halogenated polymer may preferably be polyvinylidene fluoride (PVDF). In the same or other embodiments, the binder may include an electrically conductive material, and may further enhance other properties of the sulfur electrode material, such as the electrical conductivity of the sulfur electrode material.

[0128] The content of the one or more binders may be at least 0.5% by mass, more preferably at least 1% by mass, more preferably at least 5% by mass, with respect to a total mass of an electrode material including sulfur, the quantum dot component, the one or more components to provide conductivity or increase conductivity, and the binder. The content of the one or more binders may be up to 30% by mass, more preferably up to 20% by mass, more preferably up to 15% by mass. The content of the one or more binders may be 0.5%-30% by mass, more preferably l%-20% by mass, more preferably 5%-l 5% by mass, for example about 10% by mass.

[0129] Lithium- Sulfur Battery

[0130] The sulfur material or sulfur electrode material may advantageously serve as a cathode in a lithium-sulfur battery cell for a lithium-sulfur battery. The battery cell may further include an anode and an electrolyte.

[0131] In the lithium-sulfur battery cell, the anode includes lithium. At least some of the lithium is preferably in the form of metallic lithium. In some embodiments, the anode consists essentially of lithium or consists of lithium, preferably metallic lithium, for example in the form of a foil. In other embodiments, the lithium in the anode is present in the form of an alloy with another metal, for example with magnesium or aluminum. In these or other embodiments, the lithium may be present in the form of a foil, for example having a thickness of from 10 pm to 1000 pm, more preferably from 20 pm to 100 pm. In some embodiments, the anode may further include a coating or surface layer for formation of an advantageous solid electrolyte interphase (SEI).

[0132] The lithium-sulfur battery cell further includes an electrolyte, preferably a liquid electrolyte. The liquid electrolyte can contain a solvent or mixture of solvents, for example an organic solvent or mixture of organic solvents. In some embodiments, the solvent may include ethers such as cyclic ethers, short-chain ethers, and glycol ethers. Cyclic ethers may include dioxolane (DOL). Shortchain ethers may include dialkyl ethers, for example dimethyl ether (DME). In some embodiments, the solvent may comprise or consist of a combination of DOL and DME, for example in a DOL:DME volume ratio of as low as 10:90 and as high as 90:10, preferably as low as 30:70 and as high as 60:40, for example in a ratio of 50:50.

[0133] The liquid electrolyte may contain a lithium salt. In some embodiments, the salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The concentration of the salt, particularly of LiTFSI may be from 0.1 to 3 M, preferably from 0.5 to 1.5 M, for example 1.0 M. LiTFSI may enable formation of an advantageous SEI on the lithium anode, potentially further mitigating the shuttle effect in some embodiments. In these or other embodiments, the liquid electrolyte may further contain other lithium salts, for example LiNOs. Li NO may be present in a content of from 0.2-3.5%, preferably 0.5-3.0%, more preferably 0.8-2.5% by mass. LiNO.3 may be present for example in an amount sufficient to passivate a surface of the lithium anode for further mitigation of the shuttle effect.

[0134] In some embodiments, the lithium-sulfur battery cell further includes a separator between the anode and the cathode. The separator is not particularly limited, and may be a porous material. In some embodiments, the separator is made of a polymer, preferably a polyolefin, more preferably polypropylene or polyethylene. In some embodiments, a coating on the separator, in particular a functional coating, may mitigate the shuttle effect by inhibiting polysulfide transit between the anode and the cathode.

[0135] FIG. 11 shows an exemplary embodiment of a lithium-sulfur battery cell 1. In this embodiment, lithium-sulfur battery cell 1 includes cathode 2 containing sulfur and a quantum dot component, separator 3, and anode 4, containing lithium. Separator 3 is between cathode 2 and anode 4. Electrical load 5 connects cathode 2 and anode 4, drawing electrical power from lithium-sulfur battery cell 1. Also between cathode 2 and anode 4, on either side and throughout separator 3 is electrolyte 6. Within electrolyte 6 are lithium ions 7a, 7b, 7c, and 7d, moving from anode 4 to cathode 2. Also within electrolyte 6 are lithium polysulfides 8a and 8b. In this embodiment, however, the inclusion of a quantum dot component in cathode 2 results in fewer lithium polysulfides 8a and 8b in the electrolyte. The lithium-sulfur battery cell may be included in a lithium-sulfur battery. In some embodiments, the lithium-sulfur battery may include one lithium-sulfur battery cell. In other embodiments, the lithium-sulfur battery may include a plurality of lithium-sulfur battery cells arranged in series, in parallel, or in a combination of series and parallel arrangements. Preferably, at least some lithium-sulfur battery cells in the lithium-sulfur battery are arranged in series, for example in order to provide a higher voltage battery than the voltage of one lithium-sulfur battery cell.

[0136] The lithium-sulfur battery may further include an enclosure. The enclosure may include a metal and / or a metal alloy. In some embodiments, the enclosure includes aluminum, and aluminum alloy, or steel. The enclosure may further include a lining in some embodiments. The enclosure of the lithium-sulfur battery may further include one or more terminals, preferably two or more terminals, even more preferably exactly two terminals, for example one positive terminal and one negative terminal.

[0137] The lithium-sulfur battery cell or the lithium-sulfur battery may exhibit improved properties and / or functionality as compared to an otherwise-identical or otherwise-comparable lithiumsulfur battery cell or lithium-sulfur battery that lacks the quantum dot component. In some embodiments, the initial capacity of a lithium-sulfur battery cell may be at least 300 mAh / g, more preferably at least 400 mAh / g, more preferably at least 500 mAh / g, more preferably at least 600 mAh / g, more preferably at least 700 mAh / g, more preferably at least 800 mAh / g, more preferably at least 900 mAh / g, more preferably at least 1000 mAh / g, and as high as 1010 mAh / g or higher. In some embodiments, after 100 charge-discharge cycles, the lithium-sulfur battery cell or the lithium-sulfur battery may retain a percentage of its initial capacity, for example greater than 35%, more preferably at least 40%, more preferably at least 41%, more preferably at least 45%, more preferably at least 50%, more preferably at least 55%, more preferably at least 60%, more preferably at least 65%, more preferably at least 70%, more preferably at least 75%, more preferably at least 80%, more preferably at least 85%, more preferably at least 90%, and as high as 94% or higher. In some embodiments, after 100 charge-discharge cycles, the lithiumsulfur battery cell or the lithium-sulfur battery may have a coulombic efficiency of at least 80%, more preferably at least 85%, more preferably at least 90%, more preferably at least 95%, and as high as 98.5%, 99.0%, 99.5% or higher. In some embodiments, the lithium-sulfur battery cell or the lithium-sulfur battery may be able to withstand a number of charge-discharge cycles, for example 200, more preferably 300, more preferably 400, more preferably 500, more preferably 600, more preferably 700, more preferably 800, more preferably 900, more preferably 1000 charge-discharge cycles, while retaining at least a minimum percentage of its initial capacity, for example at least 20%, more preferably at least 30%, more preferably at least 40%, more preferably at least 50%, and as high as 55% or higher.

[0138] Without limiting the disclosure of the lithium-sulfur battery cell and the lithium-sulfur battery to any specific mechanism, explanation, or theory, the increased capacity retention and / or other advantageous characteristics, properties, or results in some embodiments may relate to presence of sulfur within the cathode in an interior portion of the quantum dot component, for example in an interior portion of quantum dot portions of the quantum dot-nanotube composite, either initially before any charge-discharge cycles or by migration after a number of charge-discharge cycles. Such presence of sulfur in an interior portion of the quantum dot portions may mitigate the shuttle effect. In some embodiments that include a metal oxide in the quantum dot component, further beneficial characteristics, properties, or results may result in the presence of a metal oxide in an interior portion of the quantum dot component and / or to interactions between the metal oxide and the sulfur. Such interactions may further mitigate the shuttle effect.

[0139] Any reference in this specification to an “embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. The features of any one embodiment may be combined with features of one or more other embodiments described herein to form additional embodiments.

[0140] Although the present disclosure is provided with reference to a number of illustrative embodiments and to the examples provided below, other modifications and embodiments can be devised by those skilled in the art, within the spirit and scope of the principles of this disclosure. More particularly, reasonable variations and modifications are possible in the component parts and / or arrangements of the subject combination arrangement within the scope of the foregoing disclosure, the drawings, and the appended claims, without departing from the spirit of the disclosure overall. In addition to variations and modifications in the component parts and / or arrangements, alternative uses will also be apparent to those skilled in the art.

[0141] EXAMPLES

[0142] To provide exemplary embodiments of the sulfur material containing quantum dot-nanotube composites as the quantum dot component, sol-gel mixtures were prepared by adding dried SWCNTs or TUBALL™-BATT to isopropanol or ethanol as a solvent. Phloroglucinol as a carbon source was then added, followed by furfural as a second carbon source. Where indicated, molybdenum ethoxide or tungsten ethoxide were then further added. The compositions of the resulting mixtures are shown in Table 1.

[0143] Table 1 : Sol-Gel Mixtures for Quantum Dot-Nanotube Composites

[0144] Quantum dot-nanotube composite precursors were then prepared from the sol-gel mixtures by stirring the mixtures and then allowing them to stand under heating. The resulting products were washed and then dried with supercritical CO2 at 1500 psi at 45°C for 1 hour. Following pyrolysis, the quantum dot-nanotube composites listed in Table 2 were obtained. Table 2: Quantum Dot-Nanotube Composites

[0145] Sulfur electrode materials were produced from quantum dot-nanotube composites QN1, QN2, QN3, and QN4 by milling sulfur and the respective quantum dot-nanotube composite in a ball mill, to obtain a milled composition. The milled composition was pressed in a hydraulic press with a force of 4 tons. The resulting composition was treated in an autoclave for 6 hours at 160°C, ground in a mortar and pestle, and then formed into a slurry containing 85% in total of the sulfur and quantum-dot nanotube composition, 5% of carbon black, and 10% of PVDF as a binder. The resulting slurry was applied to an aluminum foil substrate and dried in a vacuum furnace oven 40°C for 12 hours to obtain the sulfur cathode material Ml, M2, M3, and M4 in Table 3.

[0146] Comparative sulfur cathode materials were prepared in the same manner except without any quantum dot-nanotube composite, and with carbon black and / or SWCNTs. The resulting comparative cathode materials M5 and M6 are shown in Table 3.

[0147] Table 3: Cathode Materials

[0148] Lithium-sulfur battery cells were then produced using the above cathode materials. The lithiumsulfur battery cells used IM LiTFSI and 2% by mass LiNCh as electrolyte, with an E / S (electrolyte-to-sulfur) ratio of 13 pl / mg.

[0149] Each lithium-sulfur battery cell was then subjected to at least 100 charge-discharge cycles, and capacity was measured for each cycle. The results are shown in Table 4, below.

[0150] Table 4: Coulombic Retention Results

[0151] For cell example El, FIG. 12 shows charge and discharge curves, and FIG. 13 shows changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles. For cell example E2, FIG. 14 shows charge and discharge curves, and FIG. 15 shows changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles.

[0152] For cell example E3, FIG. 16 shows charge and discharge curves, and FIG. 17 shows changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles.

[0153] For cell example E4, FIG. 18 shows charge and discharge curves, and FIG. 19 shows changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles.

[0154] For comparative cell example CE5, FIG. 20 shows charge and discharge curves, and FIG. 21 shows changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles.

[0155] For comparative cell example CE6, FIG. 22 shows charge and discharge curves, and FIG. 23 shows changes in charging and discharging capacity and coulombic efficiency over the course of multiple charge / discharge cycles.

[0156] Cell examples El, E2, E3, and E4 contain quantum dot-nanotube composites in their cathode materials, and surprisingly show improved capacity retention after 100 charge-discharge cycles, as compared to not only comparative cell example CE6, having carbon black in its cathode material, but also as compared to comparative cell example CE5, having carbon black and a SWCNT component in its cathode material. Thus, the quantum dot-nanotube composites provide for improved lithium-sulfur battery cells with improved capacity retention after 100 chargedischarge cycles.

[0157] Cell example El contains molybdenum oxide in its quantum dot-nanotube composite in its cathode material, and surprisingly shows improved initial capacity and comparable capacity after 100 charge-discharge cycles, over cell example E2, which does not have a metal oxide in its quantum dot-nanotube composite in its cathode material.

[0158] Cell examples E3 and E4 contain differing amounts of tungsten oxide in their quantum dot- nanotube composites in their cathode materials, and surprisingly show different balances of capacity and capacity retention. Cell example E4 surprisingly has a higher percentage of capacity retention after 100 charge-discharge cycles as compared to any of cell examples El, E2, E3, CE5, and CE6, showing advantages of such a content of tungsten oxide. Cell example E3 surprisingly has a higher initial capacity and a higher capacity after 100 charge-discharge cycles as compared to any of cell examples El, E2, E4, CE5, and CE6, showing advantages of such a content of tungsten oxide.

Claims

CLAIMSWhat is claimed is:

1. A material, comprising: sulfur, and a quantum dot component, wherein the quantum dot component is at least one component selected from the group consisting of: a quantum dot-nanotube composite, a quantum dot-graphene composite, carbon quantum dots consisting essentially of carbon, and hybrid quantum dots comprising carbon and at least one metal oxide.

2. The material of claim 1, wherein the quantum dot component comprises the quantum dot-nanotube composite.

3. The material of claim 2, wherein the quantum dot-nanotube composite comprises a plurality of nanotube portions, and wherein the quantum dot-nanotube composite further comprises a plurality of quantum dot portions along a length of each nanotube portion.

4. The material of claim 3, wherein quantum dot portions of the plurality of quantum dot portions have a number average particle diameter of from 5 to 40 nm.

5. The material of claim 1 , wherein the quantum dot component is obtained by subjecting a mixture to a sol-gel process, the mixture comprising a carbon source, a solvent, optionally a metal oxide precursor, optionally nanotubes, and optionally graphene.

6. The material of claim 5, wherein the mixture comprises an alkoxide of at least one metal as the metal oxide precursor.

7. The material of claim 1, wherein the sulfur comprises octasulfur Sx and / or elemental sulfur.

8. The material of claim 2, wherein the quantum dot-nanotube composite consists essentially of carbon.

9. The material of claim 1, wherein the quantum dot component comprises the quantum dot-nanotube composite, the hybrid quantum dots, or both, and wherein the quantum dot-nanotube composite, the hybrid quantum dots, or both comprise carbon and a metal oxide.

10. The material of claim 9, wherein the metal oxide comprises at least one oxide of a transition metal.

11. The material of claim 9, wherein the metal oxide comprises an oxide of at least one metal or metalloid selected from the group consisting of tungsten, molybdenum, ruthenium,niobium, tantalum, germanium, iron, silver, manganese, titanium, tin, antimony, bismuth, gold, silicon, nickel, cobalt, chromium, zirconium, and vanadium.

12. The material of claim 9, wherein the metal oxide comprises an oxide of tungsten or molybdenum.

13. The material of claim 9, wherein the metal oxide comprises a tungsten oxide.

14. The material of claim 9, wherein the quantum dot component comprises the quantum dot-nanotube composite, and wherein the quantum dot-nanotube composite has a carbon content of from 90% to 99.9% by mass and a total content of the at least one metal oxide of from 0.1% to 2% by mass, based on a total mass of the quantum dot-nanotube composite.

15. The material of claim 1, wherein the sulfur is mixed with the quantum dot component on a nanometer scale.

16. The material of claim 1, wherein a quantum dot component content is from 5% to 40% by mass, based on a total mass of the material.

17. The material of claim 2, wherein nanotubes constituting the carbon dot-nanotube composite are carbon nanotubes.

18. The material of claim 2, wherein nanotubes constituting the carbon dot-nanotube composite are single wall carbon nanotubes.

19. The material of claim 5, wherein the mixture comprises from 0.1 to 20% by mass of the carbon source, from 0.10% to 5.0% by mass of the nanotubes, from 60% to 95% by mass of the solvent, and from 0 to 20% by mass of the metal oxide precursor.

20. The material of claim 1, further comprising carbon black.

21. The material of claim 20, wherein a carbon black content is from 0.5% to 15.0% by mass, based on a total mass of the material.

22. The material of claim 20, wherein the sulfur is mixed with the quantum dot- nanotube composite and the carbon black on a nanometer scale.

23. A method of making the material of claim 1, the method comprising: subjecting a mixture to a sol-gel process, the mixture comprising a carbon source, a solvent, optionally a metal oxide precursor, optionally nanotubes, and optionally graphene, thereby obtaining the quantum dot component, combining the quantum dot component and the sulfur in a slurry, and applying the slurry to a substrate.

24. An electrode material, comprising:the material of claim 1, and a binder.

25. The electrode material of claim 24, wherein the binder is a polymer.

26. The electrode material of claim 24, wherein the binder is PVDF.

27. A lithium-sulfur battery cell, comprising: an anode, comprising lithium, an electrolyte, a separator, and a cathode, comprising the electrode material of claim 24.

28. The lithium-sulfur battery cell of claim 27, wherein the electrolyte is an organic liquid electrolyte.

29. The lithium-sulfur battery cell of claim 27, wherein a capacity of the cell after 100 charge / discharge cycles is at least 41% of the capacity of the cell before any charge / discharge cycles.

30. The lithium-sulfur battery cell of claim 27, wherein a capacity of the cell after 1000 charge / discharge cycles is at least 55% of the capacity of the cell before any charge / discharge cycles.

31. The lithium-sulfur battery cell of claim 27, wherein an initial capacity of the cell is at least 1000 mAh / g.

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