Hierarchical network structure cathode material for lithium-sulfur batteries and method for producing the same

Abstract

A lithium-sulfur cathode that can be incorporated into a lithium-sulfur battery contains a sulfur host material configured to receive a sulfur electroactive material that circulates lithium ions. The sulfur host material contains a fibrous carbonaceous network, an electroactive metal in conjunction with the fibrous carbonaceous network, and a plurality of carbon nanotubes formed in the fibrous carbonaceous network. A method for producing the lithium cathode material may include forming a porous membrane from aramid nanofibers, contacting it with a salt containing an electroactive metal, contacting it with a plurality of zeolite-type imidazolate skeleton-67 particles, thermal decomposition to form a fibrous carbonaceous network having an electroactive metal, and then forming a plurality of carbon nanoparticles at multiple sites in the fibrous carbonaceous network.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 452,867, filed on March 17, 2023. The entire disclosure of the above application is incorporated herein by reference.

[0002] Government Support This invention was made with government support under Grant No. 1538180 awarded by the National Science Foundation. The government has certain rights in this invention.

[0003] Field This disclosure relates to a positive electrode material for a lithium - sulfur electrochemical cell comprising a hierarchical sulfur host material configured to accept a sulfur electroactive material that circulates lithium ions, and a method of making such a positive electrode.

Background Art

[0004] This section provides background information related to this disclosure which is not necessarily prior art.

[0005] Lithium - sulfur (Li - S) electrochemical cells or lithium - sulfur (Li - S) batteries are one of the most attractive platforms for energy storage in various technical fields due to their high energy density (2600 Wh / kg -1 ), large theoretical capacity (t1675 mAh / g<e -1 ), cost - effectiveness, and environmental friendliness. However, the practical implementation of Li - S batteries is still hindered by several difficult problems, mainly due to the low electrical conductivity of sulfur and its discharge products (Li2S2 / Li2S), the shuttle effect of soluble lithium polysulfides (LiPS: Li2S n , 4 ≤ n ≤ 8), and the large volume expansion of the sulfur electrode during the cycle period leading to capacity loss.

[0006] Recently, extensive research has been directed towards addressing these issues, including cathode structure optimization, multifunctional separators, new concepts for electrolyte assembly, and anode protection. For example, the design of positive electrodes or cathodes for Li-S batteries is central. The molecular, nanoscale, and microscale morphology of sulfur hosts in the cathode is crucial for highly efficient sulfur electrochemical reactions and enhanced battery performance. A wide range of sulfur host materials, such as porous carbon, conductive polymers, graphene, carbon nanotubes, metal-organic skeletons, metal oxides / sulfides, and their hybrids, have been used in attempts to improve the electrochemical performance of Li-S batteries. The design principles behind these studies include accelerated lithium ions (Li) for easy sulfur electrochemical redox reactions, as well as desired sulfur immobilization. + The objective is to provide a sulfur host equipped with diffusion and electron transport.

[0007] However, for non-polar porous carbon, due to the relatively weak interaction between sulfur and its Li intercalates, and also for inorganic polar materials due to their lower conductivity, there is still a significant room for improvement in the cycle life and overall performance of Li-S batteries, especially under long-term cycles and high sulfur loadings. On the other hand, the insufficient surface area and binding interaction sites for most of the designed sulfur host materials derived from irregular granules or flakes only bind the limited LiPS near the surface and are only effective for low sulfur loadings, which significantly impair the energy density of the Li-S system for such sulfur host materials, leading to the conclusion that these sulfur host materials are not suitable for practical applications. Therefore, it would be advantageous for the sulfur host materials to limit or minimize the shuttling of LiPS while providing efficient charge transport for the high loading of non-conductive sulfur. Further breakthroughs are still needed to meet the essential requirements for Li-S batteries that combine sufficient sulfur loading, highly reversible specific / areal capacity, high discharge rate capability, reduced shuttling of lithium polysulfides, and operational durability.

Summary of the Invention

[0008] This section provides a general overview of the present disclosure and is not a complete disclosure of the full scope of the present disclosure or all of the features of the present disclosure.

[0009] In certain aspects, the present disclosure relates to an electrode material for an electrochemical cell.

[0010] In one aspect, the electrode material may include a fibrous carbonaceous network. A metal such as an electroactive metal, such as a transition metal, may cooperate with the fibrous carbonaceous network, and a plurality of carbon nanotubes may be disposed in the fibrous carbonaceous network.

[0011] In one aspect, the plurality of carbon nanotubes may be nitrogen-doped.

[0012] In certain embodiments, the disclosure further relates to cathode materials for lithium-sulfur electrochemical cells.

[0013] In one embodiment, the cathode may include a sulfur host material configured to receive a sulfur electroactive substance that circulates lithium ions. The sulfur host may include a fibrous carbonaceous network structure. Cobalt (Co) may be associated with the fibrous carbonaceous network structure, and a plurality of carbon nanotubes may be arranged in the fibrous carbonaceous network structure.

[0014] In one embodiment, multiple carbon nanotubes may be nitrogen-doped.

[0015] In one embodiment, the positive electrode has a capacitance of approximately 17 mAhcm². -2 It may have the above area capacity.

[0016] In one embodiment, the positive electrode may further contain a sulfur electroactive substance. For example, the positive electrode may contain about 15 mg / cm³. 2 It may have a sulfur load greater than or equal to the above.

[0017] In certain embodiments, this disclosure relates to a lithium-sulfur electrochemical cell.

[0018] In one embodiment, the lithium-sulfur electrochemical cell may include a positive electrode. The positive electrode may include a sulfur host material configured to receive a sulfur electroactive substance that circulates lithium ions. The sulfur host material may include a fibrous carbonaceous network structure. Cobalt (Co) may be associated with the fibrous carbonaceous network structure, and a plurality of carbon nanotubes may be arranged in the fibrous carbonaceous network structure. The electrochemical cell may also further include a negative electrode. The negative electrode may contain lithium. The electrochemical cell may also further include a separator which may be placed between the positive and negative electrodes. The electrochemical cell may also further include an electrolyte which may be incorporated into at least one of the positive electrode, negative electrode, and separator.

[0019] In one embodiment, the positive electrode has a capacitance of approximately 17 mAhcm². -2 It may have the above area capacity.

[0020] In one embodiment, the positive electrode is approximately 15 mg / cm³ 2 It may have a sulfur load greater than or equal to the above.

[0021] In one embodiment, multiple carbon nanotubes may be nitrogen-doped.

[0022] In one embodiment, the lithium-sulfur electrochemical cell may have an electrolyte-to-sulfur ratio (E / S) of about 8:1 or less.

[0023] In certain embodiments, the disclosure further relates to a method for fabricating a cathode for a lithium-sulfur electrochemical cell.

[0024] In certain embodiments, a method for fabricating electrodes for a lithium-sulfur electrochemical cell may include thermal decomposition of a porous membrane formed from a plurality of aramid fibers or aramid nanofibers and a plurality of metal-organic skeleton nanoparticles to form a fibrous carbonaceous network. The method may further include incorporating a transition metal into the fibrous carbonaceous network and then forming a plurality of carbon nanotubes at multiple sites in the fibrous carbonaceous network that are coupled with the transition metal to form a sulfur host material configured to receive a lithium-sulfur electroactive substance that circulates lithium ions.

[0025] In one embodiment, the method further comprises forming the porous film by spin-coating the plurality of aramid nanofibers and incorporating the plurality of metal-organic skeleton nanoparticles therein.

[0026] In one embodiment, the metal-organic skeleton nanoparticles comprise a plurality of zeolite-type imidazolate skeleton-67 (ZIF-67) particles, and the transition metal comprises cobalt.

[0027] In one embodiment, the method may include forming a porous membrane from aramid nanofibers, contacting the porous membrane with a cobalt-containing salt to incorporate cobalt, contacting a plurality of zeolite-type imidazolate skeleton-67 (ZIF-67) particles with the porous membrane, and thermally decomposing the porous membrane to form a fibrous carbonaceous network structure in which cobalt is interconnected. The method may further include forming a plurality of carbon nanoparticles at a plurality of sites in the fibrous carbonaceous network structure that form a sulfur host material configured to receive a sulfur electroactive substance that circulates lithium ions, for example, at a plurality of sites corresponding to cobalt.

[0028] In certain embodiments, this disclosure relates to electrode materials.

[0029] In one aspect, the electrode material may include a sulfur electroactive material and a sulfur host material configured to receive the sulfur electroactive material. The sulfur host material may include a fibrous carbonaceous network, an electroactive metal in cooperation with the fibrous carbonaceous network, and a plurality of carbon nanotubes formed in the fibrous carbon-based network.

[0030] In one aspect, the electroactive metal may include a transition metal.

[0031] In one aspect, the transition metal may include cobalt.

[0032] In one aspect, the electroactive material may be adsorbed on the surface of the fibrous carbonaceous network.

[0033] In one aspect, the electroactive material may be embedded in the fibrous carbonaceous network.

[0034] In one aspect, the electroactive material may be adsorbed on the surface of the fibrous carbonaceous network and embedded in the fibrous carbonaceous network.

[0035] In one aspect, the plurality of carbon nanotubes may be formed in the fibrous carbon-based network at the sites of the electroactive metal.

[0036] In one aspect, the plurality of carbon nanotubes may be nitrogen-doped.

[0037] In one aspect, the electrode material may have an areal capacity of about 17 mAh / cm -2 or more.

[0038] In one aspect, the electrode material may have a sulfur loading of about 15 mg / cm 2 or more.

[0039] In certain aspects, the present disclosure relates to a lithium-sulfur electrochemical cell.

[0040] In one embodiment, a lithium-sulfur electrochemical cell may include a positive electrode, a negative electrode, a separator positioned between the positive and negative electrodes, and an electrolyte incorporated in at least one of the positive electrode, the negative electrode, and the separator. The positive electrode may include a sulfur electroactive material and a sulfur host material configured to receive the sulfur electroactive material. The sulfur host material may include a fibrous carbonaceous network, an electroactive metal in conjunction with the fibrous carbonaceous network, and a plurality of carbon nanotubes formed in the fibrous carbonaceous network. The negative electrode may contain lithium.

[0041] In one embodiment, the electroactive metal may include a transition metal.

[0042] In one embodiment, the electroactive material may be adsorbed on the surface of the fibrous carbonaceous network, or embedded in the fibrous carbonaceous network, or the electroactive material may be adsorbed on the surface of the fibrous carbonaceous network and embedded in the fibrous carbonaceous network.

[0043] In one embodiment, the multiple carbon nanotubes may be formed in a fibrous carbon network structure at the electroactive metal sites.

[0044] In one embodiment, multiple carbon nanotubes may be nitrogen-doped.

[0045] In one embodiment, the positive electrode has a capacitance of approximately 17 mAhcm². -2 The above area volume, and approximately 15 mg / cm² 2 It may have a sulfur load greater than or equal to the above.

[0046] In one embodiment, the lithium-sulfur electrochemical cell may have an electrolyte-to-sulfur ratio (E / S) of about 8:1 or less.

[0047] In certain embodiments, the present disclosure relates to a method for fabricating electrodes for a lithium-sulfur electrochemical cell.

[0048] In one embodiment, the method may include contacting a salt containing an electroactive metal with a porous membrane, contacting an aerogel precursor with the porous membrane, thermally decomposing the porous membrane to form a fibrous carbonaceous network structure in which the electroactive metals are interconnected, and forming a plurality of carbon nanoparticles at a plurality of sites in the fibrous carbonaceous network structure to form a sulfur host material configured to receive a sulfur electroactive substance that circulates lithium ions.

[0049] In one embodiment, the method may further include forming the porous membrane. The porous membrane may contain aramid nanofibers.

[0050] In one embodiment, the aerogel precursor may contain a plurality of zeolite-type imidazolate skeleton-67 (ZIF-67) particles.

[0051] Further areas of applicability will become apparent from the descriptions provided herein. The descriptions and examples in this summary are for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0052] The drawings described herein are for illustrative purposes only of selected embodiments, not all possible embodiments, and are not intended to limit the scope of this disclosure. [Brief explanation of the drawing]

[0053] [Figure 1A]This is a schematic diagram illustrating an exemplary synthesis of a sulfur host material configured to accept a sulfur electroactive substance, in which the sulfur host material comprises a fibrous carbonaceous reticular structure formed from a reticular structure of aramid nanofibers (ANF) together with nanoparticles (NPs) of a metal-organic skeleton (e.g., a zeolite-type imidazolate skeleton (e.g., ZIF-67)) that can self-assemble on the surface of the ANF, together with an electroactive metal (e.g., cobalt) that is in conjunction with the fibrous carbonaceous reticular structure, and thus the sulfur host material forms multiple carbon nanotubes in a fibrous carbon-based reticular structure (NCZC) according to various embodiments of this disclosure. [Figure 1B] These are scanning electron microscope images of ANF aerogel films at a scale of 500 nm, prepared according to various aspects of this disclosure. [Figure 1C] These are scanning electron microscope images of ANF aerogel films at a scale of 200 nm, prepared according to various aspects of this disclosure. [Figure 1D] Scanning electron microscope images of ANF@ZIF-67 at a 500 nm scale, according to various aspects of this disclosure. [Figure 1E] Scanning electron microscope images of ANF@ZIF-67 at a 200 nm scale, according to various aspects of this disclosure. [Figure 1F] Scanning electron microscope images of NCZC at a 500 nm scale, according to various aspects of this disclosure. [Figure 1G] Scanning electron microscope images of NCZC at a 200 nm scale, according to various aspects of this disclosure.

[0054] [Figure 2A] These are transmission electron microscope images of NCZC composites according to various aspects of this disclosure, showing the growth of multilayer N-CNTs with highly graphite walls having inner and outer diameters, cobalt, and lattice spacing, at a scale of 500 nm. [Figure 2B]These are transmission electron microscope images of NCZC composites according to various aspects of this disclosure, showing the growth of multilayer N-CNTs with highly graphite walls having inner and outer diameters, cobalt, and lattice spacing, at a scale of 200 nm. [Figure 2C] These are transmission electron microscope images of NCZC composites according to various aspects of this disclosure, showing the growth of multilayer N-CNTs with highly graphite walls having inner and outer diameters, cobalt, and lattice spacing, on a 20 nm scale. [Figure 2D] These are transmission electron microscope images of NCZC composites according to various aspects of this disclosure, showing the growth of multilayer N-CNTs with highly graphite walls having inner and outer diameters, cobalt, and lattice spacing, at a scale of 5 nm. [Figure 2E] These are transmission electron microscope images of NCZC composites according to various aspects of this disclosure, showing the growth of multilayer N-CNTs with highly graphite walls, having inner and outer diameters, cobalt, and lattice spacing. The scale is 5 nm, with the circled areas showing more detail in the upper right and lower right. [Figure 2F] High-resolution X-ray photoelectron spectra of carbon (C1s) according to various aspects of this disclosure are shown (see Figure 2B). [Figure 2G] High-resolution X-ray photoelectron spectra of nitrogen (N1s) according to various aspects of this disclosure are shown (see Figure 2C). [Figure 2H] This is a high-resolution X-ray photoelectron spectrum of cobalt (Co2p) according to various aspects of this disclosure (see Figure 2D).

[0055] [Figure 3A] This graph illustrates a voltage profile comparing the NCZC electrode of the present invention with a reduced graphene oxide (rGO) electrode and a Co-embedded porous carbon skeleton (CoCF) electrode at a rate of 0.2C (1C = 1675 mAg-1) with a controlled sulfur load of 3.84 mg cm-2, where the x-axis represents capacitance and the y-axis represents voltage. [Figure 3B]This graph illustrates the cycle performance of NCZC electrodes, rGO electrodes, and CoCF electrodes compared at a rate of 0.2C (1C = 1675 mAg-1) with a controlled sulfur load of 3.84 mg cm-2, according to various aspects of the present disclosure, where the x-axis represents the number of cycles, the y1-axis represents the capacity, and the y2-axis represents the Coulomb efficiency. [Figure 3C] This graph illustrates the rate performance of NCZC type Li-S batteries, rGO type Li-S batteries, and CoCF type Li-S batteries in a scanning rate range of 0.2C to 10C (1C = 1675mAg-1), according to various aspects of this disclosure, where the x-axis represents the number of cycles and the y-axis represents the capacity. [Figure 3D] This graph illustrates a constant current charge-discharge profile comparing NCZC type Li-S battery, rGO type Li-S battery, and CoCF type Li-S battery at scan rates ranging from 0.2C to 10C (1C = 1675mAg-1), according to various aspects of this disclosure, where the x-axis represents capacity and the y-axis represents voltage. [Figure 3E] This is a comparison of the electrochemical impedance spectra of NCZC electrodes, rGO electrodes, and CoCF electrodes according to various aspects of this disclosure. [Figure 3F] This graph illustrates the capacitance decay per cycle using carbon-based electrodes derived from various metal-organic framework (MOF) nanoparticles. [Figure 3G] This graph illustrates the long-term cycle performance of an NCZC electrode over 2500 cycles at a rate of 1.0C, according to various aspects of this disclosure, where the a-axis represents the number of cycles, the y1-axis represents the capacitance, and the y2-axis represents the Coulomb efficiency.

[0056] [Figure 4A] This is a schematic diagram showing an optimized configuration for the binding of Li2SX (1 ≤ x ≤ 8) to a C-Co-N NCZC sulfur host material according to various aspects of this disclosure. [Figure 4B]This is a graphical representation illustrating the binding energy (Eb) for Li2SX (1≦x≦8) in a comparative rGO electrode, a comparative N-doped carbon electrode, and an NCZC electrode of the present invention composed of C-Co-N prepared according to various embodiments of this disclosure. [Figure 4C] The graph illustrates the ultraviolet / visible absorption spectra of the Li2S4 solution before and after the addition of rGO and NCZC, and the inset photograph is an optical image of Li2S4 capture by rGO and NCZC after 24 hours. [Figure 4D] These are high-resolution XPS S2p spectra of Li2S4 before and after adsorption, according to various aspects of this disclosure, where the x-axis represents the binding energy and the y-axis represents the intensity. [Figure 4E] These are high-resolution XPS Li1s spectra before and after adsorption of Li2S4, according to various aspects of this disclosure, where the x-axis represents the binding energy and the y-axis represents the intensity.

[0057] [Figure 5A] This graph illustrates the area capacities of NCZC electrodes with various sulfur loads, prepared according to various embodiments of this disclosure, where the x-axis represents the number of cycles and the y-axis represents the area capacities. [Figure 5B] This graph illustrates a comparison between sulfur load and area capacity between an NCZC electrode and a typical high-sulfur load (e.g., greater than 5 mg cm⁻²) electrode, according to various aspects of the present disclosure, where the x-axis represents sulfur load and the y-axis represents area capacity. [Figure 5C] This graph illustrates the rate performance of NCZC electrodes prepared according to various embodiments of this disclosure at various rates from 0.2C to 5.0C with a high sulfur load of 15.4 mg cm⁻², where the x-axis represents the number of cycles, the y1-axis represents the volume, and the y2-axis represents the area volume. [Figure 5D] The graph illustrates the constant current charge / discharge profiles of NCZC electrodes at various rates from 0.2C to 5.0C with a high sulfur load of 15.4 mgcm-2, according to various aspects of this disclosure, where the x1 axis represents capacitance, the x2 axis represents area capacitance, and the y axis represents voltage. [Figure 5E] A graph illustrating the cycle stability and corresponding area capacity of an NCZC electrode with a high sulfur load of 15.4 mgcm-2 at a rate of 0.2C, according to various aspects of this disclosure, where the x-axis represents the number of cycles, the y1-axis represents the area capacity, the y2-axis represents the capacity, and the y3-axis represents the Coulomb efficiency.

[0058] [Figure 6] This graph illustrates the charge / discharge curves of an NCNC type lithium sulfur battery prepared according to various aspects of this disclosure for cycles 1 through 100, where the x-axis represents capacity and the y-axis represents voltage.

[0059] [Figure 7A] These are scanning electron microscope images at a 300 nm scale of ANF nanofibers after firing at 700°C in an N2 atmosphere according to various aspects of this disclosure. [Figure 7B] These are scanning electron microscope images at a 200 nm scale of ANF nanofibers after firing at 700°C in an N2 atmosphere according to various embodiments of this disclosure. [Figure 7C] These are transmission electron microscope images at a 100 nm scale of ANF nanofibers after firing at 700°C in an N2 atmosphere according to various aspects of this disclosure. [Figure 7D] These are transmission electron microscope images of ANF nanofibers at a scale of 10 nm after firing in an N2 atmosphere at 700°C according to various aspects of this disclosure.

[0060] [Figure 8] This schematic diagram shows an optimized configuration for the binding of lithium polysulfide (Li2SX (1≦x≦8)) to pyridine-based N NCZC HFN according to certain aspects of this disclosure, compared to the integration with comparative rGO. [Modes for carrying out the invention]

[0061] The corresponding reference numbers indicate the corresponding parts through several figures in the drawing.

[0062] Example embodiments are provided so that the disclosure may be complete and its scope may be fully conveyed to those skilled in the art. Numerous specific details, such as various examples of specific compositions, components, devices, and methods, are described to provide a complete understanding of the embodiments of the disclosure. It will be apparent to those skilled in the art that specific details are not necessary, that the example embodiments may be embodied in many different forms, and that neither should be construed as limiting the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known techniques are not described in detail.

[0063] The terms used herein are for the sole purpose of describing specific exemplary embodiments and are not intended to be limiting. Where used herein, the singular “a,” singular “an,” and singular “the” may also be intended to include the plural, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having” are inclusive and thus specify that the described features, elements, compositions, processes, completes, operations, and / or components exist, but do not exclude the existence or addition of one or more other features, completes, processes, operations, elements, components, and / or groups thereof. Although the open-ended term “comprising” is to be understood as a non-restrictive term used to describe and assert the various embodiments shown herein, in certain embodiments this term may instead be understood as a more restrictive and limiting term, such as “consisting of” or “consisting essentially of.” Accordingly, with respect to any given embodiment that enumerates compositions, materials, components, elements, features, completes, operations, and / or process steps, this disclosure also specifically includes embodiments that consist of, or essentially consist of, such enumerated compositions, materials, components, elements, features, completes, operations, and / or process steps.In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, completes, operations, and / or process steps, whereas in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, completes, operations, and / or process steps that substantially affect the basic and novel properties are excluded from such embodiment, but any additional compositions, materials, components, elements, features, completes, operations, and / or process steps that do not substantially affect the basic and novel properties may be included in such embodiment.

[0064] None of the methods, steps, processes, and operations described herein should be construed as necessarily requiring their performance in any particular order discussed or illustrated, unless specifically identified as such. It should also be understood that additional or alternative steps may be used, unless otherwise indicated.

[0065] When one component, element, or layer is referred to as “adjacent,” “engaged,” “connected,” or “linked” to another element or layer, that component, element, or layer may be directly adjacent, engaged, connected, or linked to the other component, element, or layer, or there may be an intervening element or layer. In contrast, when one element is referred to as “directly adjacent,” “directly engaged,” “directly connected,” or “directly linked” to another element or layer, there may be no intervening element or layer. Other words used to describe relationships between elements should be interpreted in a similar manner (e.g., “between” vs. “directly between,” “adjacent” vs. “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the related enumerated items.

[0066] Terms such as "first," "second," and "third" may be used herein to describe various processes, elements, components, areas, layers, and / or parts, but these processes, elements, components, areas, layers, and / or parts shall not be limited by these terms unless otherwise indicated. These terms may be used simply to distinguish one process, element, component, area, layer, or part from another. Terms such as "first," "second," and other numerical terms, when used herein, do not imply order or sequence unless clearly indicated by the context. Thus, the first process, element, component, area, layer, or part discussed below may be referred to as the second process, element, component, area, layer, or part without departing from the teaching of the exemplary embodiments.

[0067] Spatial or temporal relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and similar terms may be used herein to facilitate description of the relationship of one element or feature to another element or feature, as illustrated in the figures. Spatial or temporal relative terms may be intended to encompass various orientations of a device or system during use or operation, in addition to the orientation depicted in the figures.

[0068] Throughout this disclosure, numerical values ​​represent an approximate measure or limit to a range in order to encompass embodiments having a small deviation from a given value and approximately the value mentioned, as well as embodiments having the exact value mentioned. Unlike in the examples provided at the end of the detailed description, all numerical values ​​of parameters in this specification (e.g., all numerical values ​​of quantities or conditions), including in the appended claims, will be understood to be modified in all cases by the term “about,” whether or not “about” actually appears before the numerical value. “About” indicates that the numerical value stated is tolerant of some degree of inaccuracy (by some degree of approach to exactness in the value; approximately or reasonably close to the value; nearly). If the inaccuracy introduced by “about” is not understood as not being so in the Art in this ordinary sense, then “about,” as used herein, indicates at least variation that may result from the ordinary methods of measuring and using such parameters. For example, “about” may include variation of 5% or less, optionally 4% or less, optionally 3% or less, optionally 2% or less, optionally 1% or less, optionally 0.5% or less, and in certain embodiments optionally 0.1% or less.

[0069] In addition, the disclosure of a range includes the disclosure of all values ​​within the entire range and any further subdivided ranges, including the endpoints and subranges given for that range.

[0070] Next, an example embodiment will be described in more detail with reference to the attached drawings.

[0071] High-energy-density electrochemical cells, such as lithium-sulfur (LiS) batteries, can be used in a variety of applications. A typical lithium-sulfur battery includes at least one positive electrode or cathode, at least one negative electrode or anode, an electrolyte, and a separator. The lithium-sulfur battery operates by reversibly passing lithium ions between the negative and positive electrodes. The positive electrode typically contains a sulfur host material containing a sulfur / sulfur compound that reversibly reacts with lithium, while the negative electrode may be lithium metal. A separator, such as a polymer separator, may be placed between the negative and positive electrodes. A liquid or solid electrolyte is also placed between the positive and negative electrodes. For example, the liquid or solid electrolyte may be placed in the pores of the separator. Electrolytes suitable for transporting lithium ions between electrodes may be in solid form and / or liquid form and / or hybrids thereof. In the case of an all-solid-state battery, since the all-solid-state battery includes solid electrodes and a solid electrolyte (or solid separator), the solid electrolyte (or solid separator) may be physically separated from the electrodes so that a separate separator may not be required.

[0072] Lithium ions move between the cathode (positive electrode) and anode (negative electrode) in a first direction during battery charging and in the opposite direction during battery discharge. Each negative and positive electrode is connected to a current collector. Throughout the battery's lifespan, the current collector, in conjunction with these two electrodes, is connected by an external circuit that allows electron-generated current to pass between the electrodes to compensate for the transport of lithium ions.

[0073] Due to the low conductivity of sulfur and the small molecular size of lithium polysulfides, lithium-sulfur batteries face various fundamental difficulties in achieving cycleability, discharge rate, and Coulomb efficiency comparable to semiconductor metal oxides. Building on previous studies of charge, mass, and stress transport in permeable network structures, this disclosure addresses such challenges by providing novel cathode materials having sulfur host materials in a hierarchical structural manner.

[0074] In certain embodiments, a cathode material for a lithium-sulfur electrochemical cell is provided. The cathode may comprise a sulfur host material configured to receive a sulfur electroactive substance that circulates lithium ions. The hierarchical sulfur host material may comprise a fibrous carbonaceous network. The fibrous carbonaceous network may be formed by thermal decomposition of an aerogel precursor produced from aromatic polyamide nanofibers or aramid nanofibers (these are indicated herein as PAF or ANF). In certain modifications, the aerogel precursor having ANF fibers may also comprise a plurality of metal-organic framework (MOF) particles, such as zeolite-type imidazolate framework-67 (ZIF-67) particles, which are arranged on or mixed with the ANF fibers. Furthermore, the fibrous carbonaceous network comprises a cobalt (Co) metal that is associated with the fibrous carbonaceous network, for example, the cobalt may be adsorbed on the surface of the fibrous carbonaceous network or embedded in the fibrous carbonaceous network. Cobalt may be applied as nanoparticles, for example, as nanoparticles with an average diameter of about 20 nanometers in one deformation, to the surface of the fibrous carbonaceous network structure. In certain deformations, reagents or conditions during the thermal decomposition period may facilitate nitrogen (N) doping of the carbon-based material (produced by thermal decomposition of aramid fibers).

[0075] Following the thermal decomposition of the aerogel precursor, multiple carbon structures may be formed in the fibrous carbonaceous network by being grown from multiple sites in the fibrous carbonaceous network by a deposition process such as chemical vapor deposition (CVD). In certain embodiments, the carbon structures are carbon nanotubes formed in the fibrous carbonaceous network, such as multi-walled carbon nanotubes (MWCNTs), or in alternative embodiments, single-walled carbon nanotubes (SWCNTs). These sites may correspond to a portion of the cobalt present on the surface and act as catalysts for nanotube growth from there. In certain modifications, the carbon nanotubes grow in an environment that promotes nitrogen (N) doping to the carbon nanotubes.

[0076] In this hierarchical sulfur-host material, the high connectivity and conductivity of N-doped aramid carbide nanofibers containing cobalt (Co) nanoparticles (e.g., with an average diameter of less than approximately 20 nanometers) and N-doped carbon nanotubes (CNTs) results in a multiscale network structure that enables efficient charge transport, minimal dead volume, and strong bonding of lithium polysulfides. More specifically, the composite material may be formed having a multiscale structure that includes interconnected N-doped carbon nanofiber skeletons (NCNFs), cobalt-embedded porous carbon skeletons (CoCFs) derived from aramid nanofibers (ANFs), and N-doped carbon nanotubes (N-CNTs) anchored to or attached to the CoCFs. During the synthesis period, metal-organic skeleton nanoparticles such as ZIF-67 nanoparticles may be assembled on the surface of a fibrous aerogel skeleton formed from aramid nanofibers (ANFs) via electrostatic attraction and coordination bonds, while N-CNTs may subsequently be grown by chemical vapor deposition (CVD) to further entangle the nanofibers and form a highly interconnected, self-supporting conductive skeleton (see Figure 1A).

[0077] Figure 1A shows the first step in a method for fabricating a cathode for a lithium-sulfur electrochemical cell, which will be further described below. In Figure 1A, in the upper panel, a porous membrane is formed from aramid nanofibers, for example, by spin casting. This may be processed to form an aerogel porous membrane. Next, a plurality of zeolite-type imidazolate skeleton-67 (ZIF-67) particles are brought into contact with the porous aerogel membrane or grown in the porous aerogel membrane. The precursor may then be thermally decomposed to form a fibrous carbonaceous network structure.

[0078] In certain deformations, a self-supporting aramid nanofiber (ANF) film acting as a cathode substrate was prepared by spin coating (see Figures 1B and 1C). Subsequently, the ANF aerogel film may be immersed in a solution of Co(NO3)2·6H2O in methanol, in which case Co 2+ Ions adsorb to the nanofibers, thereby forming coordination bonds with the amide groups. Subsequently, nanoparticles (NPs) of the zeolite-type imidazolate skeleton-67 (ZIF-67) may self-assemble on the surface of ANF (ZIF@ANF), as shown by scanning electron microscopy (SEM) (see Figures 1D and 1E). The concentration of ZIF-67 on the ANF@ZIF precursor can be varied by immersion time (e.g., 1 hour, 2 hours, 3 hours, and 4 hours). As the immersion time was extended, cubic NPs also nucleated in the solution and formed in the gaps between the nanofibers (ANF@ZIF-4).

[0079] Multiscale reticular composites were obtained by catalytic CVD carbonization in a nitrogen (N2) atmosphere. In this process, ZIF@ANF may be thermally decomposed and converted into cobalt-containing / embedded porous carbon skeletons (CoCF) and interconnected N-doped carbon nanofiber skeletons (NCNF) (CoCF@NCNF). In certain embodiments, N-doped carbon aerogel@Co-embedded hierarchical carbon hybrid@CNT (indicated as HFN) composite electrode materials may be produced by using chemical vapor deposition (CVD) techniques that may involve thermal annealing of ANF@ZIF using melamine as a precursor without the use of any additional catalysts. As melamine begins to decompose, it is accompanied by the release of NH3 and H2. These gases contribute to the formation of active Co nanoparticles and promote the catalytic growth of N-CNTs on the surface from abundant carbon and nitrogen sources. CoCF acquired various forms resulting from the catalytic growth of N-CNTs (see Figures 1F and 1G). Unlike carbon nanofibers derived from ANF, which have a smooth surface, the fibers in NCZC have a rough surface with abundant bamboo-like N-CNT growth. The surface density of ZIF-67 NPs influences the morphology of the carbonized composite. For example, NCZC-4 is less uniform than NCZC-3 due to its higher ZIF-67 NP content. In the absence of melamine, the N-CNTs disappeared after annealing.

[0080] The sulfur-host materials produced by such processes and resulting from various aspects of this disclosure possess several structural features that are advantageous for integration into numerous transport requirements. For example, the highly 3D interconnected continuous carbon nanofiber reticular structure provides a uniform sulfur distribution, fast electron conduction, and a sufficient electrode / electrolyte interface for rapid ion transfer. Furthermore, the growth of porous carbon units, as well as N-CNTs, extends throughout the internal space of the fibrous reticular structure, providing more active sites for redox processes with sulfur, which is particularly useful for high-sulfur-loaded systems. Moreover, polar surfaces with uniformly distributed nitrogen (N) and cobalt (Co) doping facilitate the containment of lithium polysulfides (LiPS), which helps to minimize or prevent LiPS shuttles. Furthermore, the self-supporting electrode design has a large surface area, avoids insulating polymer binders, and thus further enhances the conductivity of the electrode, as well as accommodating sulfur species that counteract their volume changes during the battery cycle process.

[0081] In certain embodiments, lithium-sulfur batteries incorporating such cathodes exhibit high rate performance up to 10C, negligible capacity decay of 0.011% per cycle over very long cycle processes (e.g., over more than 2,500 charge / discharge cycles), and a low electrolyte-to-sulfur ratio (E / S) of approximately 8:1, with a capacity of approximately 15.4 mg / cm³. -2 17.0 mAhcm² under high sulfur load until it reaches this level. -2 The high area capacity demonstrated makes batteries incorporating these cathodes highly suitable for many practical applications. These electrochemical parameters are approximately 300% to 500% higher than those of major commercial batteries with metal oxide cathodes, and also 300% higher than the DOE target for electric vehicle batteries.

[0082] In various embodiments, the disclosure provides a lithium-sulfur electrochemical cell comprising a positive electrode containing a sulfur host material configured to receive a sulfur electroactive material that circulates lithium ions. The sulfur host material may comprise a fibrous carbonaceous network structure. Cobalt (Co), for example, cobalt nanoparticles, may be coupled with the fibrous carbonaceous network structure. Furthermore, the sulfur host material may comprise a plurality of carbon nanotubes formed in the fibrous carbonaceous network structure. The lithium-sulfur electrochemical cell may also comprise a lithium-containing negative electrode, a separator positioned between the positive and negative electrodes, and an electrolyte.

[0083] In one embodiment, a lithium sulfur electrochemical cell has a capacity of approximately 17.0 mAhcm³. -2 It may have a surface capacity greater than the above. In another embodiment, the lithium sulfur electrochemical cell has a concentration of approximately 15.3 mg / cm³. 2 The above sulfur load may be present. In yet another embodiment, the electrolyte-to-sulfur ratio (E / S) of the electrochemical cell may be approximately 8:1 or less.

[0084] Hierarchical network structure design based on graph-theoretic descriptions of nanofiber composites can also be extended to other materials for sustainable energy technologies that require high efficiency in charge transport and mechanical robustness.

[0085] It will be further understood that porous hierarchical electrode materials may be used in applications other than lithium-sulfur batteries. These may include, as non-limiting examples, other energy storage applications, such as supercapacitors, metal-ion batteries or metal-air batteries, and similar applications. In such applications, the electrodes may include a porous material configured to receive an electroactive material through which lithium ions circulate. The porous material may contain a fibrous carbonaceous network and may have one or more electroactive metals (e.g., transition metals such as cobalt (Co), manganese (Mn), nickel (Ni), and aluminum (Al)) in association with the fibrous carbonaceous network. Furthermore, the porous material may have multiple carbon nanotubes formed in the fibrous carbonaceous network. The multiple carbon nanotubes and / or the fibrous carbonaceous network may be doped with nitrogen (N).

[0086] Various embodiments of this disclosure are further illustrated by the following examples, which are not limited to this disclosure.

[0087] Example 1 Preparation of ANF hydrogel membranes. Aramid nanofiber (ANF) dispersions were prepared according to J. Zhu et al., “Branched aramid nanofibers,” Angew. Chemie Int. Ed., 56, 11744-11748 (2017) (the relevant parts thereof are incorporated herein). In this example, a 2 wt.% ANF dispersion was prepared by stirring KEVLAR® 69 (Thread Exchange) in dimethyl sulfoxide (DMSO, Sigma Aldrich, ≥99.9%) in the presence of potassium hydroxide (KOH, Sigma Aldrich) for one week until a dark red ANF solution was obtained. Subsequently, a spin coating method was used to prepare the ANF hydrogel membranes. Specifically, 2 mL of ANF (2 wt.%) dispersion was placed on a clean glass slide and spin-coated at approximately 1500 rpm for approximately 30 seconds. Subsequently, the glass slides were immersed in deionized water to remove DMSO, and then stored in methanol (Sigma Aldrich) solution for later use. It should be noted that prior to use, the glass slides were cleaned in piranha solution (3:1 H2SO4 / H2O2) for approximately 24 hours, followed by thorough rinsing with deionized water.

[0088] Example 2 Preparation of ANF@ZIF-67 composite aerogel membrane. To prepare the ANF@ZIF-67 composite membrane, an ANF membrane (4 cm × 4 cm) was first immersed in 9 mL of 20.0 mM Co(NO3)2·6H2O (≧99.0%, Sigma Aldrich) / methanol solution for approximately 10 minutes. Subsequently, 15 mL of approximately 160.0 mM 2-methylimidazole (99.0%, Sigma Aldrich) / methanol was added to the above solution, combined with vigorous magnetic stirring for approximately 10 minutes. The ANF membrane was then kept in the purple solution at room temperature for various times (e.g., 1 hour, 2 hours, 3 hours, and 4 hours). The resulting ANF@ZIF samples (denoted as ANF@ZIF-1, ANF@ZIF-2, ANF@ZIF-3, and ANF@ZIF-4, respectively) from different reaction times were washed three times with methanol to remove excess ZIF-67 nanoparticles (NPs), and then dried by lyophilization. For comparison, ZIF-67 nanoparticles (NPs) were also prepared under the same conditions without the ANF film (held for approximately 3 hours).

[0089] Example 3 Preparation of HFN composites. HFN composites according to certain embodiments of this disclosure were prepared by chemical vapor deposition (CVD) technology via a thermal annealing process of ANF@ZIF using melamine as a precursor, without the use of any additional catalysts. An ANF@ZIF composite serving as a template was placed on a ceramic boat in combination with a certain amount of melamine (melamine / ANF@ZIF = 10:1 mass ratio) and subsequently carbonized at approximately 700°C for approximately 1 hour at a slow heating rate of 2°C min⁻¹ under an N₂ atmosphere (see Figures 7A to 7D).

[0090] Example 4 Material characterization. Scanning electron microscopy (SEM, FEI Nova Nanolab dual-beam FIB) and transmission electron microscopy (TEM, JEOL JEM-2010 operating at 200kV) were performed to observe the morphology of ANF, ANF@ZIF, and HFN. X-ray diffraction patterns (XRD, using CuKa radiation between approximately 5° and 60° at a scanning speed of 2° / min, D / Max-2550 PC rotating anode X-ray generator), Raman spectroscopy (using a 488nm laser under ambient conditions, WITEC Alpha 300S microRaman system), X-ray photoelectron spectroscopy (XPS, RBD's upgraded PHI-5000C ESCA, using monochromatic Al Ka ​​(1486.6eV) radiation), and thermogravimetric analysis (TGA, TA Instruments Discovery, in an air atmosphere, 30 mL min) were performed. -1 At the flow rate, 10℃ min -1 (A temperature gradient up to 500°C was used). The specific surface area of ​​HFN was measured using the nitrogen adsorption / desorption isotherm method (Micromeritics ASAP 2020 V3.00 H) with the Brunauer-Emmett-Teller (BET) theory. Ultraviolet-Vis absorption spectroscopy was performed to evaluate the polysulfide adsorption capacity of conventional rGO and the HFN example of the present invention. Approximately 4 milligrams each of rGO and HFN were placed in a sealed vial of Li2S4 solution (4 mL, 0.1 mmol L, respectively). -1 The solutions were placed separately in a container, and a pure Li2S4 solution was used as a reference. After absorption over 24 hours, the UV-Vis absorption spectra of these solutions were examined using an Evolution 300 UV-vis spectrophotometer with baseline correction. Li2S4 was prepared by synproportionation between Li2S (99.9%, Sigma Aldrich) and sulfur (99.5%, Sigma Aldrich) in a DOL / DME (v:v=1:1) solution at a molar ratio of 1:3.

[0091] Example 5 Electrochemical measurements. The electrolyte for the Li-S battery was prepared by dissolving lithium trifluoromethanesulfonate (LiCF3SO3, 98%, Sigma Aldrich, 1M) and LiNO3 (99%, Sigma Aldrich, 2wt.%) in DME (99%, Sigma Aldrich) and DOL (99.5%, Sigma Aldrich) (v:v=1:1). The cell (standard CR2032 coin cell) was prepared in an Ar-filled glove box. Before assembling the battery, the sulfur host of the HFN cathode was dried in a vacuum drying oven at 80°C for 12 hours. The HFN was formed into a plate with an area of ​​1.0 cm × 1.0 cm, which would act directly as the cathode.

[0092] Various sulfur cathodes were prepared by dropping a 0.5 M S / CS2 solution onto a prepared host substrate to obtain CoCF@S electrodes, rGO@S electrodes, and HFN@S electrodes, followed by drying at approximately 60°C for approximately 6 hours and heat treatment at approximately 155°C for approximately 12 hours. The area sulfur content for the standard electrodes was approximately 3.84 mg / cm². -2 It is controlled by 7.68 mg cm -2 , 11.52 mg / cm -2 , 15.35 mg cm -2 and 19.20 mg cm -2 Higher sulfur content was also produced by increasing the amount of S / CS2 solution. CELGARD® 2400 and pure lithium foil were used as separator and anode, respectively. The electrolyte contained 1 M LiTFSI in a DME / DOL (v:v=1:1) solution with 2 wt.% LiNO3 as an additive. The total electrolyte / sulfur ratio was 8:1 (μL mg). -1 The assembled coin cells were tested at room temperature using the LAND-CT2001A battery test apparatus at 1.7~2.8V (vs. Li / Li). + Measurements were taken in constant current mode with different currents within the voltage range of ( ). The set current rate was varied from 0.2C to 10C (1C = 1675mAg). -1EIS was performed in the range of 100kHz to 0.05Hz with a potential amplitude of 20mV.

[0093] Density functional theory (DFT) was performed to calculate the binding energy (Eb) between HFN and LiPS, which is defined by the following equation:

number

[0094] In the formula, E s+HFN , E s , and E HFN These are the energies for LiPS-HFN, LiPS, and HFN, respectively. The initial conformations of all molecules were obtained by molecular mechanics (MM) (Forcite module). DFT calculations were performed using the Dmol3 module in Accelrys Material Studio.

[0095] Transmission electron microscope (TEM) images (see Figures 2A-2E) revealed the growth of multilayer N-CNTs with highly graphite walls, having an outer diameter ranging from approximately 5 to 10 nanometers and an inner diameter of approximately 15 nanometers. Several randomly stacked carbon layers suggest a higher proportion of defects and edges in the N-CNTs (see Figure 2C, circled area). In particular, a large number of 20-nanometer NPs were detected between the N-CNTs. The lattice spacing of 0.20 nanometers indicates that these regions are Co originating from Co2+ in ZIF-67 at high temperatures, consistent with XRD and Raman characterization (see Figures 2D and 2E).

[0096] NCZC, based on Brunauer-Emmett-Teller (BET) analysis, is 653m 2 g -1It exhibits a large specific surface area and a large pore volume due to pore sizes that are mostly less than 10 nanometers, which may effectively enhance sulfur loading and electrolyte permeation along with LiPS confinement and conversion. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of Co and N in NCZC, as they have characteristic peaks at approximately 780 eV and 399 eV, respectively. The C1s spectrum of NCZC (see Figure 2F) confirms that the presence of CN bonds successfully dops the N atoms into graphite domains. N-doped carbon materials are known to have high electrical conductivity and a strong affinity for LiPS. The XPS peak of N1s reveals three types of N, including pyridine-based N (398.1 eV), graphite-based N (400.8 eV), and oxide-based N (404.9 eV) (see Figure 2G). Undoubtedly, these various N peaks originated from the ANF reticular structure, ZIF-67, and also from the degradation of melamine. The peak at 783.1 eV in Figure 2H is the Co-N peak commonly detected in Co-containing N-doped carbon composites. x It represents the species. NCZC's Co 2p Co in the spectrum 2p1 / 2 (796.1eV) and Co 2p3 / 2 The presence of (780.4 eV) indicates that the majority of Co exists in an oxidized state, primarily due to the oxidation of Co NPs in air. Thermogravimetric analysis (TGA) revealed that NCZC-3 contains approximately 25.3 wt.% Co. The abundant polar sites in this complex are expected to facilitate the redox kinetics of sulfur species within the porous carbon network structure, synergistically contributing to the inhibition of the shuttle of soluble LiPS away from the cathode.

[0097] Driven by its highly networked structure, NCZC was tested as a sulfur host for Li-S batteries and compared to cells based on rGO aerogel or CoCF. All of these batteries exhibited typical two-discharge plateau curves consistent with the formation of higher-order and lower-order LiPS (see Figure 3A). Notably, NCZC enabled the lowest potential gap between the discharge and charge curves among these various cells, and at the same time, allowed for much sharper peaks and smaller electrochemical polarization in cyclic voltammetry (CV), suggesting easy redox kinetics in NCZC electrodes. The constant-current cycling performance of cells with different electrodes (see Figure 3B) showed that the NCZC cell had a higher initial capacity (1192 mAhg) than state-of-the-art rGO-type sulfur hosts. -1 ) exceeding 1351mAh -1 This indicates that it is delivering a high initial capacity. This initial capacity also indicates the capacity of the CoCF type cell (1296mAhg). -1 This exceeds ), which suggests significantly improved sulfur utilization resulting from the hierarchical multiscale design. 1205mAhg -1 High capacity retention and a Coulomb efficiency (CE) of nearly 99% for over 100 continuous cycles were also achieved for the NCZC cathode: this indicates that its operational durability is superior to that of other sulfur host designs (970mAhg for the CoCF electrode). -1 CE:97%; rGO electrode: 832mAhg -1This indicates that the CE:92% is higher. Impressively, the shape of the charge / discharge curve remained virtually unchanged from the 1st to the 100th cycle for NCZC type cells (see Figure 6), suggesting that the multiscale design effectively limits LiPS diffusion and stabilizes the sulfur redox reaction. The functional advantages of NCZC in its larger initial discharge capacity, lower potential gap, and longer operational endurance are thought to be due to its structure, namely the highly porous conductive network structure of ANF carbide supplemented by CNTs. The morphology of the NCZC electrode is further characterized to assess the structural stability of NCZC against the cycle process. The hierarchical nanofiber-based structural mode was retained without decomposition after 100 cycles, suggesting remarkable structural stability of NCZC throughout the battery cycle process.

[0098] Further tests at various rates and long-term cycle tests were conducted to investigate its rate performance and cycleability (see Figures 3C-3G). Even at high current densities up to 10C, the NCZC cell maintained approximately 600mAhg -1 It still delivers a very reversible capacity close to that, and when the current density returns to 0.5C it is approximately 1040mAhg -1 The cell recovers rapidly, indicating rapid charge transport, particularly rapid charge transport to sulfur. Despite the voltage plateau in the discharge curve decreasing at high current densities, the slope shape remains almost unchanged (see Figure 3D), further confirming the rapid sulfur redox conversion from the NCZC type cell. This conclusion can also be further demonstrated by a Nyquist plot (see Figure 3E), in which case the semicircle in the high-frequency region is much smaller for NCZC than for rGO and CoCF electrodes, due to lower charge transfer resistance. Conversely, rGO and CoCF type cells exhibit approximately 302 mAhg -1 and approximately 420mAhg -1It exhibits far inferior capacity at a high current density of 10C (see Figure 3C). Equally important, NCZC cells also demonstrate excellent cycle life exceeding 2500 cycles, along with a negligible capacity decay of 0.011% per cycle and consistently over 98% Coulomb efficiency (CE) at a current rate of 1.0C (see Figure 3G). It is noteworthy that the rate performance, cycle life, and capacity retention of NCZC-enabled batteries are superior to those of representative MOF-derived or carbon-based sulfur host electrodes previously reported (see Figure 3F, and in Tables 1 and 2), which strongly supports the advantages of NCZC as an improved sulfur host in cathodes for Li-S batteries.

[0099] [Table 1]

[0100] BHPC: Bicontinuous hierarchical porous carbon; CPZC: Tube with a hexahedral carbonaceous hybrid surface; HPTCF: Hollow carbon polyhedron embedded in the surface of a tubular carbon fabric; NDC: Nitrogen-doped carbon; N-ZDC: N-doped ZIF-8 derived carbon nanospheres; HPCN: Porous carbon nanoplate; AMCP: Activated mesoporous carbon polyhedron; ISCF: Self-supporting conductive skeleton; NSHPC: N, S co-doped hollow porous carbon shell; CHPCF: Crosslinked hierarchical porous carbon fiber; FMNCN: Flower-like microporous nitrogen-doped carbon nanosheet; FLHPC: French fry-like hierarchical porous carbon; MPCN: Micro / mesoporous carbon nanorod; rGO: Reduced graphene oxide; GO: Graphene oxide; CNT: Carbon nanotube; NS: Nanosheet; MWCNT: Multilayer carbon nanotube; Meso: Mesoporous; GC: Graphite-like carbon; PC: Porous carbon.

[0101] [Table 2-1] [Table 2-2]

[0102] The quantitative description of LiPS chemisorption by NCZC was evaluated using density functional theory (DFT) calculations (see Figures 4A and 4B). In contrast to the weak binding of higher-order LiPS (e.g., Li2S8, Li2S6, and Li2S4) to rGO, their binding to NCZC is much stronger (see Figures 4 and 4B and Table 3), which enables the chemical capture of LiPS that hinders their transport to the Li anode.

[0103] [Table 3]

[0104] For lower-order LiPS cells, such as Li2S2 and Li2S, the binding energy is even higher, which is important for preventing LiPS cross-conjugation and is an advantage over rGO. Theoretical predictions of NCZC's LiPS affinity were experimentally confirmed using LiPS colorimetric analysis. After approximately 24 hours of dispersion of rGO and NCZC in a Li2S4 solution, the NCZC test showed a much brighter color than rGO (see Figure 4C), which corresponds to the S4 observed in the UV-vis spectrum. 2- This is consistent with a much weaker peak at 415 nm (see Figure 4C). Chemical polysulfide adsorption is further evaluated by XPS analysis (see Figure 4D). Specifically, terminal sulfur (S T -1 ) and bridging sulfur (SB 0 These are attributed to the following, but the two pairs of typical bond energies located at approximately 161.5 eV and 162.8 eV are the S bonds of Li2S4. 2pObservable in the spectrum. After contact with NCZC, a slight shift of these peaks to a higher bond energy range is read, which illustrates the decrease in electron cloud density at the sulfur atom due to the formation of a chemical interaction between Li2S4 and NCZC. On the other hand, two new pairs of peaks appear in the higher bond energy range corresponding to sulfite and sulfate, which represents the interaction between the polysulfide and oxide species in NCZC. Another new peak appears at 160.5 eV, resulting from the Co-S bond, which suggests an interaction between the polysulfide and the Co moiety. Furthermore, Li 1s The spectrum shows a broadened peak after absorption by NCZC, which is consistent with the XPS analysis described above, but provides evidence of a new subpeak appearing at 55.7 eV resulting from the formation of a Li-N bond (see Figure 4E). These variations in the XPS spectrum together demonstrate the strong chemioadsorption capacity of NCZC to LiPS, which chemically enhances the confinement of electroactive materials in Li-S batteries.

[0105] To achieve a cathode material with high energy density and greater compatibility with scale-up commercial battery manufacturing processes, with a limiting E / S ratio of 8:1, a material of 7.68 mg / cm³ was used. -2 , 11.52 mg / cm -2 , 15.36 mg cm -2 , and 19.20 mg cm -2 A sulfur host of NCZC with a larger area sulfur loading was also prepared. 15.36 mg cm -2 A cell with a sulfur load produced 17.0 mAhcm² over 50 charge / discharge cycles. -2 It still provides a large reversible area capacity up to 1000 (see Figure 5A), which outperforms most state-of-the-art sulfur hosts specifically designed for high sulfur loads (see Figure 5B and Table 4), and also outperforms commercially available lithium-ion batteries.

[0106] [Table 4]

[0107] 19.2 mg cm -2 Further increases in sulfur loading result in limited capacity improvement, due to hindered electron / ion transfer. At a high current density of 5C, approximately 15.36 mgcm³ -2 NCZC cells with a high sulfur content produce approximately 9.9 mAhcm³ -2 (642.8mAhg -1 It achieves a highly reversible capacity (see Figures 5C and 5D). When the charge / discharge rate is returned to 0.5C, it has a capacity of approximately 15.8 mAhcm². -2 (1023.3mAhg -1 A rapid increase in capacity is observed. In the cycle performance test in Figure 5E, the NCZC electrode achieved approximately 10.2 mAhcm at 0.2C with a low capacity decay rate of 0.20% over 200 cycles. -2 (662.3mAhg -1 It has demonstrated a large reversible area capacity, which also indicates a significant increase in cycle stability and capacity retention compared to other sulfur hosts.

[0108] In certain deformations, a highly efficient sulfur hybrid host material is obtained through a hierarchical structural mode containing a carbon fibrous aerogel backbone, paired with abundant growth of N-doped carbon nanotubes and Co-embedded N-doped porous carbon. Benefiting from improved conductivity due to the N-doped carbon substrate, suppressed shuttle phenomena due to strong binding affinity between polysulfides and polar active sites, enhanced sulfur redox kinetics due to sufficient electrode / electrolyte interface, and greater tolerance of volume change due to the porous structure, the assembled sulfur host material exhibits exceptional rate performance up to 10C, remarkable cycle endurance over 2500 cycles with ultra-low volume decay of 0.011% per cycle, and a moderate electrolyte of 15.36 mg / cm³. -2 17.0 mAhcm² under high sulfur load -2This reveals a large, reversible specific capacity / area capacity, demonstrating the great potential of Li-S batteries.

[0109] In summary, this disclosure provides a novel porous network structure for high-performance Li-S battery cathodes by addressing many of the inherent problems faced by conventional sulfur-host materials. The clearly defined 3D hierarchical hybrid structural mode results in a hierarchically scaled conductive network structure with easy electron / ion transfer, while the highly porous structure with abundant active Co and N sites exposes interfaces for LiPS capture and easy sulfur redox kinetics. Furthermore, the growth of N-CNTs on the porous carbon surface not only provides additional nitrogen (N) polar sites for the chemical fixation of lithium polysulfide (LiPS), but also interconnects adjacent 3D nanofiber network structures to enhance structural integrity and result in fast charge transfer throughout the electrode. Thought to be due to these unique and synergistic advantages, assembled NCZC prepared according to certain aspects of this disclosure results in a sulfur host material for cathodes that has fast reaction kinetics, high sulfur utilization, excellent rate performance, and an ultra-long cycle life with very low capacity decay at both low and high sulfur loads, along with a modest electrolyte. This disclosure provides a novel method for designing cathode structures and active material chemical interactions toward the realization of high energy density and long-life Li-S batteries for practical applications, as well as in other energy storage, such as supercapacitors, metal-ion batteries or metal-air batteries, and similar devices.

[0110] The foregoing description of embodiments is provided for illustrative and explanatory purposes only. The description is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are not generally limited to that particular embodiment and, where applicable, are interchangeable and can be used with one another in selected embodiments, even if not specifically shown or described. They can also be modified in many ways. Such modifications will not be considered deviations from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

1. Electrode material, Sulfur electroactive substances; and A sulfur host substance configured to accept the aforementioned sulfur electroactive substance, Fibrous carbonaceous network structure; Electroactive metals that are in conjunction with the aforementioned fibrous carbonaceous network structure; and Multiple carbon nanotubes formed in the fibrous carbon network structure. sulfur host substances containing Electrode materials including

2. The electrode material according to claim 1, wherein the electroactive metal includes a transition metal.

3. The electrode material according to claim 2, wherein the electroactive metal includes cobalt.

4. The electrode material according to claim 1, wherein the electroactive substance is adsorbed on the surface of the fibrous carbonaceous network structure.

5. The electrode material according to claim 1, wherein the electroactive substance is embedded in the fibrous carbonaceous network structure.

6. The electrode material according to claim 1, wherein the electroactive substance is adsorbed onto the surface of the fibrous carbonaceous network structure and embedded in the fibrous carbonaceous network structure.

7. The electrode material according to claim 1, wherein the plurality of carbon nanotubes are formed in the fibrous carbon network structure at the electroactive metal sites.

8. The electrode material according to claim 1, wherein the plurality of carbon nanotubes are nitrogen-doped.

9. Approximately 17mAhcm －２ The electrode material according to claim 1, having the above area capacity.

10. Approximately 15mg / cm ２ The electrode material according to claim 1, having the above sulfur load.

11. A lithium sulfur electrochemical cell, It is the positive electrode, Sulfur electroactive substances; and Sulfur host substance configured to accept the aforementioned sulfur electroactive substance Includes, The aforementioned sulfur host substance, Fibrous carbonaceous network structure; Electroactive metals that are in conjunction with the aforementioned fibrous carbonaceous network structure; and Multiple carbon nanotubes formed in the fibrous carbon network structure. including, positive electrode; A negative electrode containing lithium; A separator disposed between the positive electrode and the negative electrode; and The electrolyte incorporated in at least one of the positive electrode, the negative electrode, and the separator. A lithium sulfur electrochemical cell containing a lithium sulfur cell.

12. The lithium sulfur electrochemical cell according to claim 11, wherein the electroactive metal includes a transition metal.

13. The lithium sulfur electrochemical cell according to claim 11, wherein the electroactive substance is adsorbed on the surface of the fibrous carbonaceous network structure, or the electroactive substance is embedded in the fibrous carbonaceous network structure, or the electroactive substance is adsorbed on the surface of the fibrous carbonaceous network structure and embedded in the fibrous carbonaceous network structure.

14. The lithium sulfur electrochemical cell according to claim 11, wherein the plurality of carbon nanotubes are formed in the fibrous carbon network structure at the electroactive metal sites.

15. The lithium sulfur electrochemical cell according to claim 11, wherein the plurality of carbon nanotubes are nitrogen-doped.

16. The positive electrode has approximately 17 mAh cm －２ The above area volume, and approximately 15 mg / cm² ２ The lithium sulfur electrochemical cell according to claim 11, having the above sulfur load.

17. The lithium sulfur electrochemical cell according to claim 11, having an electrolyte-to-sulfur ratio (E / S) of approximately 8:1 or less.

18. A method for fabricating electrodes for a lithium sulfur electrochemical cell, The thermal decomposition of a porous membrane formed from multiple aramid nanofibers and containing multiple metal-organic skeleton nanoparticles to form a fibrous carbonaceous network structure; Incorporating transition metals into the fibrous carbonaceous network structure; and Multiple carbon nanotubes are formed at multiple sites in the fibrous carbonaceous network structure that interact with the transition metal, in order to form a sulfur host material configured to accept a lithium-sulfur electroactive substance that circulates lithium ions. Methods that include...

19. The porous film is formed by spin-coating the plurality of aramid nanofibers and incorporating the plurality of metal-organic skeleton nanoparticles therein. The method according to claim 18, further comprising:

20. The method according to claim 18, wherein the metal-organic skeleton nanoparticles comprise a plurality of zeolite-type imidazolate skeleton-67 (ZIF-67) particles, and the transition metal comprises cobalt.

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