Electrode materials for lithium-sulfur batteries and methods for manufacturing the same

Abstract

The present invention provides electrodes for lithium-sulfur batteries with high capacity and a stable lifecycle, a lithium-sulfur battery, and a method for manufacturing the electrodes. [Solution] An electrode material is provided comprising a conductive powder obtained from nitrogen-rich MWCNTs by 15 to 30% of total weight, sulfur by 60 to 80% of total weight, and a binder by 5 to 10% of total weight, wherein the nitrogen-rich MWCNTs are prepared by treating a reduced form of catalyst with a compound selected from the group consisting of quinoline, quinoline heterocyclic compounds, mixtures of quinoline and aliphatic amines, mixtures of quinoline and naphtha, aliphatic acetonitrile, and combinations thereof. A lithium-sulfur battery manufactured using the above electrode material as the cathode and lithium metal foil as the anode exhibits good cycle stability and Coulomb efficiency.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries. More specifically, the present invention relates to an electrode material containing nitrogen-rich multi-walled carbon nanotubes (MWCNTs), and a method for preparing the electrode material from quinoline and acetonitrile compounds. Furthermore, the present invention relates to an electrode for a lithium-sulfur battery having a high capacity and a stable life cycle and a method for manufacturing the same.

Background Art

[0002] Lithium-sulfur batteries have received high attention in recent years because they have a much higher theoretical capacity than current lithium-ion batteries. Furthermore, sulfur is inexpensive and abundantly present on the earth, and is one of the purification wastes. However, there are significant problems in the development of advanced lithium-sulfur batteries. When elemental sulfur reacts with lithium ions, various polysulfide intermediates are generated during the discharge process, and these lithium polysulfide intermediates dissolve in most organic electrolyte solutions. The high solubility of this polysulfide may cause the loss of active material (sulfur) from the positive electrode during operation, which is the main factor causing a large capacity decrease during cycling.

[0003] Therefore, it is extremely important to recognize that the cycle life of lithium-sulfur batteries is limited by the combination of chemical degradation and mechanical degradation. To dramatically improve current technology lithium-sulfur batteries, both degradation mechanisms must be properly addressed. Due to the insulating property of sulfur, more conductive materials are required for the electrode, and the advantages of this technology are often offset by the large amount of carbon dead weight.

[0004] Korean Patent Publication No. 2019-0083397 relates to a method for manufacturing a porous carbon material doped with nitrogen and sulfur for a lithium-sulfur battery.

[0005] International Publication No. 2014 / 028218 relates to an electrochemical battery comprising an anode, a sulfur-containing cathode, a lithium-ion-containing electrolyte, and a porous carbon interlayer made of MWCNTs or microporous carbon paper.

[0006] The Journal of Power Sources 256:361-368 describes nitrogen-doped graphene / sulfur composites as cathode materials for high-capacity lithium-sulfur batteries.

[0007] Chinese Patent Application Publication No. 109449374 relates to a type of lithium-sulfur battery positive electrode, a battery, and a manufacturing method, which includes forming a lithium-sulfur battery positive electrode using nitride / carbon nanotubes as an intermediate layer, on a sulfur-containing anode, thereby constituting a lithium-sulfur battery positive electrode using nitride / carbon nanotubes as an intermediate layer.

[0008] The invention described in Chinese Patent No. 111362254 provides a method for preparing phosphorus-doped cobalt oxide composite materials filled with nitrogen-doped carbon nanotubes for lithium-sulfur batteries and their applications.

[0009] Chinese Patent Application Publication No. 104254938 discloses a sulfur-carbon nanotube composite comprising a carbon nanotube sheet and sulfur nucleated on the carbon nanotubes, and a method for synthesizing the same. In some embodiments, the sulfur-carbon composite further comprises the carbon nanotube sheet without a binder, eliminating the need for a binder and current collector. In other embodiments of the disclosure, a cathode comprising the sulfur-carbon nanotube composite is disclosed. In other embodiments of the disclosure, a battery may comprise the cathode described in the specification. These batteries can achieve fast charge-discharge performance.

[0010] The publication ACS Appl. Energy Mater. 2023, 6, 9, 4511-4519 discloses self-supporting composite lithium sulfur cathodes based on multiwalled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) following a solution-based, scalable manufacturing process. The two types of CNTs work synergistically, with SWCNTs providing high conductivity, large surface area, and mechanical strength / flexibility, while the large pores of MWCNTs ensure easy ion diffusion and lithium polysulfide capture.

[0011] The paper Chem. Commun., 2012, 48, 8817-8819 describes a novel method for improving the cycle performance of rechargeable lithium-sulfur batteries by inserting a self-supporting MWCNT intermediate layer.

[0012] The reference Batterys 2021, 7(2), 26 describes a high-performance lithium-sulfur battery based on a multidimensional graphene-CNT-nanosulfur hybrid cathode.

[0013] LiteratureInternational Journal of Electrochemical Science, volume 18, issue The paper dated August 8, 2023 (100217) describes the improvement of lithium-sulfur battery cathode performance through compositional optimization using modified MWCNTs as the conductive material and poly(acrylic acid) as the binder.

[0014] The document *International Journal of Energy Research*, volume 43, issue 11, 2019, discusses the improvement of lithium-sulfur battery performance by a lignin-reinforced MWCNT protective layer.

[0015] The paper Nano Research, volume 16, pages 8433-8447 (2023) relates to current collectors based on multi-walled carbon nanotubes and multi-layered graphene for improving the conversion process in scalable lithium-sulfur batteries.

[0016] The document NPG Asia Materials, volume 13, Article number: 30 (2021) relates to a flexible, high-energy-density lithium-sulfur battery using a fibrous sulfur cathode and membrane separator embedded with nanocarbon.

[0017] LiteratureECS Meeting Abstracts, volume MA2019-01, A02-Lithium Ion Batteries "and Beyond, Yong-Hong Lai and Hsun-Yi Chen 2019 Meet. Abstr. MA2019-01 115" concerns a performance study of lithium-sulfur batteries using a self-supporting amide-MWCNT protective layer.

[0018] The paper Nano Research, 2023, 16(6): 8433-8447 relates to current collectors based on multi-walled carbon nanotubes and multi-layered graphene for improving the conversion process in scalable lithium-sulfur batteries.

[0019] However, nitrogen-doped MWCNTs prepared by other chemical methods are not commercially viable and increase the cost of sulfur cathodes for lithium-sulfur batteries. Furthermore, none of the prior art described above discloses quinoline / acetonitrile-derived nitrogen-rich MWCNT-based sulfur cathodes for lithium-sulfur batteries. [Overview of the project]

[0020] The main objective of this invention is to provide an electrode material. Another object of the present invention is to provide electrodes for lithium-sulfur batteries that have high capacity and a stable lifecycle.

[0021] Another object of the present invention is to provide an electrode material comprising nitrogen-rich multiwall carbon nanotubes (MWCNTs) derived from compounds selected from the group consisting of quinoline, quinoline heterocyclic compounds, mixtures of quinoline and aliphatic amines, mixtures of quinoline and naphtha, aliphatic acetonitrile, and combinations thereof.

[0022] Another object of the present invention is to provide a method for manufacturing electrodes from the above-mentioned electrode material. Another object of the present invention is to provide a method for preparing nitrogen-rich multiwall carbon nanotubes (MWCNTs) from compounds selected from the group consisting of quinoline, quinoline heterocyclic compounds, mixtures of quinoline and aliphatic amines, mixtures of quinoline and naphtha, aliphatic acetonitrile, and combinations thereof.

[0023] This summary is provided to introduce some of the concepts that will be further elaborated in the detailed description of the invention in a simplified form. This summary is not intended to identify any key or essential inventive concepts of the invention, nor is it intended to define the scope of the invention.

[0024] The present invention provides an electrode material comprising a conductive powder obtained from nitrogen-rich multiwalled carbon nanotubes (MWCNTs) by total weight, 60 to 80% sulfur by total weight, and 5 to 10% binder by total weight, wherein the nitrogen-rich multiwalled carbon nanotubes are prepared by treating a reduced form of catalyst with a compound selected from the group consisting of quinoline, quinoline heterocyclic compounds, mixtures of quinoline and aliphatic amines, mixtures of quinoline and naphtha, aliphatic acetonitrile, and combinations thereof.

[0025] Furthermore, the present invention provides an electrode comprising the electrode material defined above, wherein the electrode material is deposited on a substrate.

[0026] The present invention also provides a lithium-sulfur battery comprising a separator selected from a polypropylene cell guard polymer or a CNT-coated polypropylene cell guard polymer, and an electrolyte containing 0.5 to 2 M lithium bis(trifluoromethylsulfonyl)imide, an ionic liquid n-methyl-n-butylpyrrolidinium bis(trifluoromethanesulfonylimide), and an additive lithium nitrate in an organic solvent DME / DOI (dimethoxyethane / dioxolane), wherein a CR2032 coin-type battery is repeatedly charged and discharged between 1.5 and 2.8 V, and comprising an electrode containing the electrode material defined above.

[0027] The present invention also provides a method for manufacturing the electrode defined above, comprising: i. preparing nitrogen-rich multi-walled carbon nanotubes (MWCNTs); ii. pulverizing carbon together with the nitrogen-rich MWCNTs to obtain a powder; iii. heating the powder obtained in step ii); iv. mixing the powder obtained in step iii) with sulfur in an amount of 60 to 80% by total weight in an amount of 15 to 30% by total weight to obtain a sulfur / nitrogen-rich MWCNT mixture; v. adding a binder in an N-methyl-2-pyrrolidone (NMP) solution to the sulfur / nitrogen-rich MWCNT mixture to obtain a slurry; vi. coating the slurry on a substrate to obtain an electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] These and other features, aspects, and advantages of the present invention will be better understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, like reference numerals represent like parts throughout the drawings.

[0029] [Figure 1] FIG. showing a sulfur cathode containing 75% sulfur together with an ionic liquid. [Figure 2] This figure shows the stable lifecycle of a sulfur cathode containing 75% sulfur along with an ionic liquid. [Modes for carrying out the invention]

[0030] To facilitate understanding of the principles of the invention, specific linguistic embodiments illustrating them are referenced. However, this is not intended to limit the scope of the invention, and it should be understood that any changes and further modifications in the illustrated processes, and further applications of the principles of the invention shown herein, are within the realm of what a person skilled in the art to which the invention relates would ordinarily conceive. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as generally understood by a person of ordinary skill in the art to which the invention belongs. The compositions, methods, and examples described herein are illustrative and not intended to limit the scope.

[0031] The articles "one," "one," and "that" are used to refer to one or more (i.e., at least one) items that are the grammatical object of the article.

[0032] As used herein, the term “several” is defined as “none, one, more, or all.” Thus, the terms “none,” “one,” “one or more,” “one or more but not all,” and “all” are all included in the definition of “several.” The term “several embodiments” may mean no embodiments, one embodiment, more embodiments, or all embodiments. Thus, the term “several embodiments” is defined as meaning “no embodiments, one embodiment, more embodiments, or all embodiments.”

[0033] More specifically, the terms “including,” “equipped,” “possess,” “consist of,” and their grammatical variations as used herein are inclusive or open-ended and do not preclude any additional, undescribed elements or method steps. This specification is understood to also include embodiments having the transition phrases “consist of” or “essentially consist of” instead of the transition phrase “equipped of.” The transition phrase “consist of” excludes any elements, steps, or components (excluding any impurities associated therewith) that are not expressed in the claim. The transition phrase “essentially consist of” limits the scope of the claim to the identified material or step “and which does not substantially affect the basic and novel properties.”

[0034] Regardless of whether a particular feature or element is limited to a one-time use or not, it may be referred to as "one or more features" or "one or more elements" or "at least one feature" or "at least one element." Furthermore, the use of the terms "one or more" or "at least one" features or elements does not rule out the possibility that they do not exist at all, unless otherwise specified by a more restrictive expression such as "one or more must exist" or "one or more elements are required."

[0035] The use of phrases and / or terms such as “first embodiment,” “further embodiment,” “alternative embodiment,” “one embodiment,” “one embodiment,” “multiple embodiments,” “several embodiments,” “other embodiments,” “further embodiments,” “further embodiments,” and “additional embodiments” (but not limited to these) does not necessarily refer to the same embodiment. Unless otherwise specified, one or more particular features and / or elements described in relation to one or more embodiments may be found in only one embodiment, present in multiple embodiments, present in all embodiments, or absent in any embodiment. One or more features and / or elements may be described herein in the context of only one embodiment, multiple embodiments, or even all embodiments, but these features and / or elements may instead be provided individually, in any suitable combination, or not provided at all. Conversely, features and / or elements described in the context of separate embodiments may be realized as present together in the context of a single embodiment.

[0036] The terms and constructs used herein are for the purpose of describing, teaching, and illustrating certain embodiments and their specific features and elements, and are not intended to limit, restrict, or diminish the spirit and scope of the invention.

[0037] The present invention provides an electrode material comprising a conductive powder obtained from nitrogen-rich multiwalled carbon nanotubes (MWCNTs) in an amount of 15 to 30% by total weight, sulfur in an amount of 60 to 80% by total weight, and a binder in an amount of 5 to 10% by total weight, wherein the nitrogen-rich multiwalled carbon nanotubes are prepared by treating a reduced form of catalyst with a compound selected from the group consisting of quinoline, quinoline heterocyclic compounds, mixtures of quinoline and aliphatic amines, mixtures of quinoline and naphtha, aliphatic acetonitrile, and combinations thereof.

[0038] In one embodiment of the present invention, the MWCNT contains 3 to 5% nitrogen.

[0039] In one embodiment of the present invention, the binder is selected from the group consisting of polyvinylidene fluoride (PVDF), carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), styrene-butadiene styrene (SBS), and polytetrafluoroethylene (PTFE).

[0040] In one embodiment of the present invention, the catalyst is a solid supported metal catalyst in which a metal selected from iron, cobalt, nickel, manganese, molybdenum, and combinations thereof is supported on a binary metal oxide consisting of boron, magnesium, aluminum, silicon, calcium, barium, and combinations thereof.

[0041] Furthermore, the present invention provides an electrode comprising the electrode material defined above, wherein the electrode material is deposited on a substrate.

[0042] In one embodiment of the present invention, the electrode has a thickness of 100 to 300 μm, and the substrate is aluminum foil.

[0043] In one embodiment of the present invention, the electrode is a cathode. In a more preferred embodiment of the present invention, a nitrogen-rich MWCNT-based sulfur cathode electrode derived from a quinoline heterocyclic compound or aliphatic acetonitrile is prepared for a lithium-sulfur battery.

[0044] Furthermore, the present invention provides a lithium sulfur battery comprising an electrode containing the electrode material defined above, which comprises a separator selected from polypropylene Celgard polymer (Celgard registered trademark), poly mV, and CNT-coated polypropylene Celgard polymer (Celgard registered trademark), and an electrolyte solution comprising an organic solvent DME / DOI (dimethoxyethane / dioxolane) containing 0.5 to 2 M lithium bis(trifluoromethylsulfonyl)imide, compounded with the ionic liquid n-methyl-n butylpyrrolidinium bis(trifluoromethanesulfonylimide) and lithium nitrate as an additive, allowing the CR2032 coin-type battery to be repeatedly charged and discharged between 1.5 and 2.8 V.

[0045] In yet another embodiment, the present invention provides the formation of a lithium-sulfur battery having high Coulomb efficiency, high capacity, and a stable lifecycle. The lithium-sulfur battery of the CR2032 coin cell type is manufactured using a high sulfur content (~75%) as the cathode active material and lithium metal foil as the anode, with a capacity of 1000 to 1200 mAhg at a 0.2C rate. -1 It exhibits a specific capacitance and, when repeated between 1.5 and 2.8V, shows good cycle stability and high Coulomb efficiency at the same rate.

[0046] According to one aspect of the present invention, a quinoline-derived nitrogen-rich MWCNT-based sulfur cathode electrode attracts polysulfides to itself, reducing the dissolution of polysulfides in the organic electrolyte, thereby providing a stable lifecycle and increasing the sulfur content in the cathode electrode to up to 75%.

[0047] Furthermore, the present invention relates to a method for manufacturing the electrode defined above, i. A step of preparing nitrogen-rich multiwalled carbon nanotubes (MWCNTs), ii. A step of grinding nitrogen-rich MWCNTs and carbon to obtain a powder, iii. A step of heating the powder obtained in step ii), iv. A step of mixing 15 to 30% of the total weight of the powder obtained in step iii) with 60 to 80% of the total weight of sulfur to obtain a sulfur / nitrogen-rich MWCNT mixture, v. A step of obtaining a slurry by adding a binder in an N-methyl-2-pyrrolidone (NMP) solution to a sulfur / nitrogen-rich MWCNT mixture, vi. The step of applying slurry onto a substrate to obtain electrodes, The present invention provides a method for manufacturing electrodes.

[0048] In one embodiment of the present invention, carbon is selected from the group consisting of acetylene black, super P, and Ketzen black.

[0049] In one embodiment of the present invention, grinding is performed using a ball mill at a speed of 500 RPM at room temperature for 1 to 3 hours.

[0050] In one embodiment of the present invention, the powder is heated at a temperature of 200 to 250°C for 3 to 5 hours.

[0051] In one embodiment of the present invention, the mixing of the powder and sulfur is carried out using a mortar and pestle or a vacuum mixer for 15 to 60 minutes.

[0052] In one embodiment of the present invention, coating is performed by the doctor blade method, and the electrodes are dried at 60°C.

[0053] This invention discloses a method for preparing a nitrogen-rich MWCNT-based sulfur cathode derived from a quinoline heterocyclic compound, for use as a cathode in lithium-sulfur batteries.

[0054] The sulfur in this invention can be produced by any chemical method, refining waste, or any industrial waste.

[0055] In one embodiment of the present invention, the preparation of nitrogen-rich MWCNTs is i. The catalyst is treated in a vertical reactor, and a compound selected from the group consisting of quinoline, quinoline heterocyclic compounds, mixtures of quinoline and aliphatic amines, mixtures of quinoline and naphtha, aliphatic acetonitrile, and combinations thereof is supplied to the vertical reactor at a flow rate of 0.5 to 1 ml / min. ii. The step of passing hydrogen gas through a reactor to obtain a reduced catalyst, iii. A step of treating the reduced catalyst with the passing compound in a reactor at a flow rate of 25 to 35 ml / h for 7 to 10 hours in the presence of a nitrogen carrier gas, iv. The step of cooling the reactor under an inert atmosphere to obtain nitrogen-rich MWCNTs.

[0056] In one embodiment of the present invention, the catalyst is a solid supported metal catalyst in which a metal selected from iron, cobalt, nickel, manganese, molybdenum, and combinations thereof is supported on a binary metal oxide consisting of boron, magnesium, aluminum, silicon, calcium, barium, and combinations thereof.

[0057] In a preferred embodiment of the present invention, the vertical reactor is packed with 2 to 4 g of a solid-supported metal catalyst containing 5 wt% iron, 2 wt% cobalt, and 4 wt% nickel supported on alumina.

[0058] In one embodiment of the present invention, the vertical reactor is maintained at operating temperatures of 615 to 625°C, 640 to 650°C, and 665 to 675°C under 1 atmosphere.

[0059] In one embodiment of the present invention, hydrogen gas is passed through a vertical reactor at a flow rate of 90 to 120 sccm for 2 to 3 hours at the operating temperature. [Examples]

[0060] This disclosure, with reference to the attached examples, describes the present invention. However, those skilled in the art should understand that, in light of this disclosure, many modifications can be made to the specific embodiments disclosed, and similar or comparable results can be obtained without departing from the spirit and scope of the invention. The examples are provided solely for illustrative purposes and are not intended to limit the scope of the invention in any way.

[0061] (Example 1) Two to four g of alumina-supported catalysts consisting of 5 wt% iron, 2 wt% cobalt, and 4 wt% nickel were packed into a vertical reactor. The reactor operating temperature was maintained at three different temperature ranges: 620°C, 645°C, and 670°C ± 5°C, and at atmospheric pressure of 1 atm. The catalyst was initially reduced for two to three hours at an operating temperature of 650°C in the presence of hydrogen gas at a flow rate of 90 to 120 sccm. After the catalytic reduction was complete, acetonitrile was supplied to the reactor at a flow rate of 25 to 35 ml / h for seven to ten hours using a pump in the presence of nitrogen carrier gas. After the process was complete, the reactor was cooled in an inert atmosphere. The resulting carbon nanotubes (CNTs) were nitrogen-rich, and as confirmed by elemental analysis, the nitrogen content in the CNT matrix was 4.8%.

[0062] (Example 2) Two to four g of alumina-supported catalysts consisting of 5 wt% iron, 2 wt% cobalt, and 4 wt% nickel were packed into a vertical reactor. The reactor operating temperature was maintained at three different temperature ranges: 620°C, 645°C, and 670°C ± 6°C, and at atmospheric pressure of 1 atm. The catalyst was initially reduced for two to three hours at an operating temperature of 650°C in the presence of hydrogen gas at a flow rate of 90 to 120 sccm. After the catalytic reduction was complete, a quinoline heterocycle was supplied to the reactor at a flow rate of 25 to 35 ml / h for seven to ten hours using a pump in the presence of nitrogen carrier gas. After the process was completed, the reactor was cooled in an inert atmosphere. The resulting carbon nanotubes (CNTs) were nitrogen-rich, and elemental analysis confirmed that the nitrogen content in the CNT matrix was 3.5%.

[0063] [Table 1]

[0064] (Example 3: Method for preparing a sulfur cathode for lithium-sulfur batteries) Nitrogen-rich MWCNTs derived from carbon and quinoline were ground together using a planetary ball mill at a rate of 500 RPM at room temperature for 1 to 3 hours. The resulting powder was held in an oven at 200 to 250°C for 3 to 5 hours.

[0065] The conductive powder prepared in the above steps was taken at a concentration of 15% by weight and mixed with 75% by weight of sulfur using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour to obtain a homogeneous sulfur / nitrogen-rich MWCNT mixture.

[0066] The homogeneous sulfur / nitrogen-rich MWCNT mixture prepared in the above steps, 90 to 95% by weight of its composition, was mixed with 5 to 10% by weight of a binder in an NMP solution, and stirred overnight with a magnetic stirrer to obtain a homogeneous cathode electrode slurry.

[0067] The cathode slurry prepared in the above steps was coated onto aluminum foil to a thickness of 150 to 160 μm using a doctor blade applicator. The cathode electrode was then dried overnight in a vacuum oven at 60°C.

[0068] (Example 4: Method for preparing sulfur cathode for lithium-sulfur batteries) Nitrogen-rich MWCNTs derived from carbon and quinoline were ground together using a planetary ball mill at room temperature at a speed of 500 RPM for 1 to 3 hours. The resulting powder was held in an oven at 200 to 250°C for 3 to 5 hours.

[0069] The conductive powder prepared in the above steps was taken at a concentration of 30% by weight and mixed with 60% by weight of sulfur using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour to obtain a homogeneous sulfur / nitrogen-rich MWCNT mixture.

[0070] The homogeneous sulfur / nitrogen-rich MWCNT mixture prepared in the above steps, 90 to 95% by weight of its composition, was mixed with 5 to 10% by weight of a binder in an NMP solution, and stirred overnight with a magnetic stirrer to obtain a homogeneous cathode electrode slurry.

[0071] The cathode slurry prepared in the above steps was coated onto aluminum foil to a thickness of 150 to 160 μm using a doctor blade applicator. The cathode electrode was then dried overnight in a vacuum oven at 60°C.

[0072] (Example 5: Method for preparing a sulfur cathode for lithium-sulfur batteries) Carbon and nitrogen-rich MWCNTs derived from acetonitrile were ground together using a planetary ball mill at a rate of 500 RPM at room temperature for 1 to 3 hours. The resulting powder was held in an oven at 200 to 250°C for 3 to 5 hours.

[0073] The conductive powder prepared in the above steps was taken at a concentration of 15% by weight and mixed with 75% by weight of sulfur using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour to obtain a homogeneous sulfur / nitrogen-rich MWCNT mixture.

[0074] The homogeneous sulfur / nitrogen-rich MWCNT mixture prepared above, at a concentration of 90 to 95% by weight, was mixed with 5 to 10% by weight of a binder and an NMP solution, and stirred overnight with a magnetic stirrer to obtain a homogeneous cathode electrode slurry.

[0075] The cathode slurry prepared in the above steps was coated onto aluminum foil to a thickness of 150 to 160 μm using a doctor blade applicator. The cathode electrode was then dried overnight in a vacuum oven at 60°C.

[0076] (Example 6: Method for preparing a sulfur cathode for lithium-sulfur batteries) Carbon and nitrogen-rich MWCNTs derived from acetonitrile were ground together using a planetary ball mill at a rate of 500 RPM at room temperature for 1 to 3 hours. The resulting powder was held in an oven at 200 to 250°C for 3 to 5 hours.

[0077] The conductive powder prepared in the above steps was taken at a concentration of 30% by weight and mixed with 60% by weight of sulfur using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour to obtain a homogeneous sulfur / nitrogen-rich MWCNT mixture.

[0078] The homogeneous sulfur / nitrogen-rich MWCNT mixture prepared above, at a concentration of 90 to 95% by weight, was mixed with a binder at a concentration of 5 to 10% by weight of the total composition in an NMP solution, and stirred overnight with a magnetic stirrer to obtain a homogeneous cathode electrode slurry.

[0079] The cathode slurry prepared in the above steps was coated onto aluminum foil to a thickness of 150 to 160 μm using a doctor blade applicator. The cathode electrode was then dried overnight in a vacuum oven at 60°C.

[0080] (Example 7: Fabrication of a lithium-sulfur 2032 coin-type battery) CR2032 coin-type batteries were assembled in an argon-filled glove box using lithium foil for the anode and nitrogen-rich MWCNT-based sulfur derived from quinoline / acetonitrile for the cathode, with a polypropylene Cellguard polymer separator or CNT-coated polypropylene Cellguard polymer separator, and an electrolyte consisting of 0.5 to 2 M lithium bis(trifluoromethylsulfonyl)imide in the organic solvent DME / DOI (dimethoxyethane / dioxolane), the ionic liquid n-methyl-n-butylpyrrolidinium bis(trifluoromethanesulfonylimide), and the additive lithium nitrate. The coin-type batteries underwent discharge / charge cycles between 1.5 and 2.8 V using a Biologic BCS805 battery charge / discharge unit, as shown in Figure 1. The manufactured CR2032 lithium-sulfur coin-type batteries were tested as shown in Tables 2 to 4 below. The stable lifecycle of the sulfur cathode containing 75% sulfur and the ionic liquid is shown in Figure 2.

[0081] [Table 2]

[0082] [Table 3]

[0083] [Table 4]

[0084] (Advantages of the present invention) Preparation of lithium-sulfur batteries with sulfur cathodes based on nitrogen-rich MWCNTs derived from quinoline heterocycles. Preparation of lithium-sulfur battery electrodes that are lower cost and have higher capacity than lithium-ion batteries. • Utilization of sulfur materials from refinery waste for battery applications • Achieved a high sulfur content of up to 75% in the cathode of lithium-sulfur batteries.

Claims

1. It comprises a conductive powder obtained from nitrogen-rich multi-walled carbon nanotubes (MWCNTs) by 15 to 30% of total weight, sulfur by 60 to 80% of total weight, and a binder by 5 to 10% of total weight. An electrode material wherein the nitrogen-rich multiwalled carbon nanotubes are prepared by treating a reduced form of catalyst with a compound selected from the group consisting of quinoline, quinoline heterocyclic compounds, mixtures of quinoline and aliphatic amines, mixtures of quinoline and naphtha, aliphatic acetonitrile, and combinations thereof.

2. The electrode material according to claim 1, wherein the MWCNT contains 3 to 5% nitrogen.

3. The electrode material according to claim 1, wherein the binder is selected from the group consisting of polyvinylidene fluoride (PVDF), carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), styrene-butadiene styrene (SBS), and polytetrafluoroethylene (PTFE).

4. The electrode material according to claim 1, wherein the catalyst is a solid supported metal catalyst in which a metal selected from iron, cobalt, nickel, manganese, molybdenum and combinations thereof is supported on a binary metal oxide consisting of boron, magnesium, aluminum, silicon, calcium, barium and combinations thereof.

5. An electrode comprising an electrode material according to any one of claims 1 to 4, wherein the electrode material is deposited on a substrate.

6. The electrode according to claim 5, wherein the electrode has a thickness of 100 to 300 μm and the substrate is aluminum foil.

7. The device comprises a separator selected from polypropylene cellguard polymer or CNT-coated polypropylene cellguard polymer, and an electrolyte consisting of 0.5 to 2 M lithium bis(trifluoromethylsulfonyl)imide in an organic solvent DME / DOI (dimethoxyethane / dioxolane), an ionic liquid n-methyl-n butylpyrrolidinium bis(trifluoromethanesulfonylimide), and an additive lithium nitrate. A lithium-sulfur battery comprising electrodes made of the electrode material described in any one of claims 1 to 6, wherein a CR2032 coin-type battery is repeatedly charged and discharged between 1.5 and 2.8V.

8. A method for manufacturing an electrode according to claim 5, i. A step of preparing nitrogen-rich multi-walled carbon nanotubes (MWCNTs), ii. A step of grinding carbon together with the nitrogen-rich multiwalled carbon nanotubes (MWCNTs) to obtain a powder, iii. A step of heating the powder obtained from step iii), iv. A step of mixing the powder obtained from step iii) in an amount of 15 to 30% of the total weight with sulfur in an amount of 60 to 80% of the total weight to obtain a sulfur / nitrogen-rich MWCNT mixture, v. The step of adding a binder in an N-methyl-2-pyrrolidone (NMP) solution to the sulfur / nitrogen-rich MWCNT mixture to obtain a slurry, vi. The step of applying the slurry onto a substrate to obtain an electrode, Methods that include...

9. The method according to claim 8, wherein the carbon is selected from the group consisting of acetylene black, Super P, and Ketzen black.

10. The method according to claim 8, wherein the grinding step is carried out using a ball mill at room temperature at a speed of 500 RPM for 1 to 3 hours.

11. The method according to claim 8, wherein the powder is heated at a temperature of 200 to 250°C for 3 to 5 hours.

12. The method according to claim 8, wherein the step of mixing the powder with sulfur is carried out in a mortar or vacuum mixer for 15 to 60 minutes.

13. The method according to claim 8, wherein the coating step is performed by the doctor blade method and the electrode is dried at 60°C.

14. The step of preparing the nitrogen-rich multi-walled carbon nanotubes (MWCNTs) is: i. A step of treating the catalyst in a vertical reactor and supplying a compound selected from the group consisting of quinoline, quinoline heterocyclic compounds, mixtures of quinoline and aliphatic amines, mixtures of quinoline and naphtha, aliphatic acetonitrile, and combinations thereof, to the vertical reactor at a flow rate of 0.5 to 1 ml / min, ii. The step of passing hydrogen gas through the reactor to obtain a reduced catalyst, iii. A step of treating the reduced catalyst with a compound that passes through the reactor at a flow rate of 25 to 35 ml / h for 7 to 10 hours in the presence of a nitrogen carrier gas, iv. The method according to claim 8, comprising the step of cooling the reactor under an inert atmosphere to obtain the nitrogen-rich MWCNT.

15. The method according to claim 14, wherein the catalyst is a solid supported metal in which a metal selected from iron, cobalt, nickel, manganese, molybdenum and combinations thereof is supported on a binary metal oxide consisting of boron, magnesium, aluminum, silicon, calcium, barium and combinations thereof.

16. The method according to claim 15, wherein the vertical reactor is packed with 2 to 4 g of a solid-supported metal catalyst containing a 5 wt% iron, 2 wt% cobalt, and 4 wt% nickel catalyst supported on alumina.

17. The method according to claim 14, wherein the vertical reactor is maintained at operating temperatures of 615 to 625°C, 640 to 650°C, and 665 to 675°C at 1 atmosphere.

18. The method according to claim 14, wherein the hydrogen gas is passed through the vertical reactor for 2 to 3 hours at the operating temperature at a flow rate of 90 to 120 sccm.

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