Hybrid electrode for battery cell and production method thereof

Abstract

Carbon-based electrodes for battery cells. The carbon-based electrodes can be pure binder-free carbon electrodes. The electrodes can also include a carbon nanotube-based intermediate layer that contains about 1-30% oxidized carbon nanotubes, wherein the intermediate layer can be configured to serve as a secondary pathway to the current collector of the battery cell. Some formed cathodes can be used in battery cells that include a lithium-based anode and a separator formed between the cathode and the anode. An electrolyte solution can be utilized to expose the cathode to an activated sulfur material.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to U.S. Provisional Application No. 62 / 899,569, filed on September 12, 2019, and U.S. Provisional Application No. 62 / 899,612, filed on September 12, 2019. The disclosures of such applications are hereby incorporated by reference in their entireties and are considered part of the disclosure of this application. Technical field

[0003] The present invention generally relates to electrochemical cells and components therein. More specifically, the present invention relates to cathode compositions and methods of making the same, including hybrid cathode electrodes having a carbon interlayer for lithium - sulfur batteries, which are suitable for electric vehicle applications and industrial applications such as windmills and PV (photovoltaic) that require repeated rapid charging and discharging at intermediate states of charge, as well as grid storage. Background art

[0004] Battery performance can be evaluated in terms of both energy density and power density. The energy density of a battery is a measure of the amount of energy that the battery can store (e.g., per unit volume or mass of the battery). High - energy batteries can store a large amount of energy (e.g., relative to the volume or mass of the battery) and are more suitable for applications that require longer run - times (e.g., rechargeable or secondary batteries). At the same time, the power density of a battery indicates how quickly the battery can accept and / or deliver energy (e.g., the rate of energy transfer). Thus, batteries with high power density tend to charge and discharge quickly. Such batteries are suitable for applications that generate and / or consume rapid energy bursts (e.g., vehicle acceleration).

[0005] The optimal battery should have both high energy and high power. However, despite having high energy density, conventional batteries (e.g., lithium (Li) - ion) tend to have poor power density. This is because the electrodes in conventional batteries typically contain materials that limit the charging rate (e.g., graphitized carbon for lithium - ion batteries).

[0006] Conventional cathode fabrication can additionally rely on using a polymer binder to adhere the active material to a metallic current collector. Here, we describe a process for fabricating a pure - carbon cathode using conventional electrode coating techniques, resulting in a high (ionic and electronic) conductivity, binder - free, lightweight carbon cathode structure. Currently, using sulfur as a component of a battery electrode has many drawbacks, including low electrical conductivity of the sulfur active material, low power of the sulfur electrode, low surface area of the sulfur electrode, and sulfur dissolution and polysulfide shuttle effect.

[0007] Batteries typically consist of solid electrodes, separators, electrolytes, and auxiliary components (such as, for example, encapsulation, thermal management, cell balancing, current collectors, and / or other such components). Electrodes typically include active materials, conductive additives, binders, and other additives.

[0008] Some known methods for preparing batteries include: coating a metallic substrate (e.g., a current collector) with a slurry composed of an active material, a conductive additive, and a binder dissolved or dispersed in a solvent, evaporating the solvent, calendering the dried electrode to a specified thickness. The electrode is then cut with a die, encapsulated with other components, infiltrated with an electrolyte, and then sealed in a package.

[0009] Such known methods generally involve complex and expensive manufacturing steps, such as casting the electrode, and are only applicable to electrodes of limited thickness, e.g., less than 100 μm (final single-sided coating thickness). These known methods for producing electrodes of limited thickness result in batteries with lower capacity, lower energy density, and a high ratio of inactive components to active material. Also, the binders used in known electrode formulations increase tortuosity and reduce the ionic conductivity of the electrodes.

[0010] To increase the ratio of active material to inactive material, conventional electrochemical cells are generally formed by coating electrode active materials (i.e., anode formulation slurry and cathode formulation slurry) on both sides of a current collector. A separator is disposed between the electrodes, i.e., between the anode and the cathode, to form a conventional electrochemical cell. Multiple such electrochemical cells can be stacked on top of each other, generally with spacers disposed therebetween, to form an electrochemical cell stack.

[0011] There is a need for electrodes and electrochemical cells that have increased electrical conductivity of sulfur active materials, increased potential of sulfur electrodes, increased surface area of sulfur electrodes, and further minimize or inhibit the dissolution of sulfur and the polysulfide shuttle effect in current sulfur electrodes. SUMMARY OF THE INVENTION

[0012] In one aspect, the present disclosure relates to a method for manufacturing a carbon nanotube-based interlayer. Such an interlayer is formed on the surface of its electrodes and can be deposited as a coating (i.e., an interlayer) made of porous carbon having a high surface area.

[0013] In another aspect, the present disclosure relates to a carbon nanotube-based interlayer that contains 1-30 wt% of oxidized carbon nanotubes (Ox-CNT). The carbon interlayer has capacitor capacity and / or pseudocapacitor capacity properties, which can increase the power content of battery cells.

[0014] In yet another aspect, the present disclosure relates to a pure carbon, zero-binder, roll-to-roll processable cathode structure for batteries and a method for manufacturing the same.

[0015] In another aspect, the present disclosure relates to a cathode structure for a lithium-sulfur battery cell and a method of manufacturing the same.

[0016] In another aspect, the present disclosure relates to a cathode structure for a battery cell and a method of manufacturing the same.

[0017] In another aspect, the present disclosure relates to an extrusion method for forming a 3D cathode structure with or without a binder. In some aspects, the binder material for the extrusion process is a fibrous polymer, such as PTFE. In other aspects, a binder-free cathode is formed by extruding or winding carbon nanotubes (CNTs).

[0018] In yet another aspect, the present disclosure relates to an electrochemical cell that includes a 3D positive electrode formed using a carbon material that includes, but is not limited to, carbon nanotubes or graphene nanosheets having a high surface area and connected together to form a permeable 3D network with or without a binder. The carbon positive electrode may also contain an extremely high sulfur loading (mAh / cm 2 ) as an active material deposited after cathode formation or during manufacturing. The negative electrode may be made of lithium metal or a lithium alloy or any other anode material capable of matching the high capacity of the cathode. A separator may be disposed between the 3D positive electrode and the negative electrode. In some embodiments, such a separator system may be made of a solid electrolyte or include a solid electrolyte layer. At least one of the 3D positive electrode and the negative electrode may have a thickness of at least about 100 μm.

[0019] In yet another aspect, the present invention includes a method of forming such a cathode 3D microstructure with or without a binder and using a method including, but not limited to, extrusion, lamination, roll pressing, molding, casting, slot die coating methods, any one of any other methods of forming a thick film. In yet another aspect, the present invention relates to a cathode electrode comprising two carbon materials, a first carbon material such as conductive carbon black or graphene nanosheets and a second carbon material such as activated carbon or carbon nanotubes, having a capacitor capacity and / or a pseudocapacitor capacity, with or without a binder. Such a carbon electrode can provide a porous carbon permeable network (e.g., a nanographene permeable network, or an equivalent carbon network formed) with or without a binder and provide a sulfur active material filled in the pores or deposited on the electrode active surface area therein. The sulfur active material can contribute to the energy content of the cell. A coating (intermediate layer) made of porous carbon having a high surface area (e.g., a carbon nanotube intermediate layer) may be formed on the surface of the electrode, wherein such a layer helps to improve the performance and power content of the cell.

[0020] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, which are to be read in conjunction with the present invention content, specific embodiments, and any preferred and / or specific embodiments disclosed in detail or otherwise. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example only so that this disclosure is thorough and complete and will fully convey the full scope of the present invention to those skilled in the art. Description of the Drawings

[0021] Figure 1 is a side view of an exemplary embodiment of the carbon interlayer of the present disclosure.

[0022] Figure 2 is a top view of an exemplary embodiment of the carbon interlayer of the present disclosure.

[0023] Figure 3 is a schematic diagram of an exemplary embodiment of the process for coating an adhesive-free carbon interlayer of the present disclosure.

[0024] Figure 4A is a schematic diagram of an exemplary embodiment of how to construct a single cell (lithium-sulfur cell).

[0025] Figure 4B is a schematic diagram of an exemplary embodiment of how to construct a single supercapacitor.

[0026] Figure 4C is a schematic diagram of an exemplary embodiment of how to construct a hybrid sulfur cell.

[0027] Figure 5 is a cross-sectional view of an exemplary embodiment of the battery cell of the present disclosure.

[0028] Figure 6 is a graph showing the improved performance of an exemplary embodiment of the battery cell of the present disclosure compared to a conventional battery cell.

[0029] Figure 7 is a graph showing the improved performance of an exemplary embodiment of the battery cell of the present disclosure compared to a conventional battery cell.

[0030] Figure 8A is a schematic diagram of an exemplary embodiment of an adhesive-free carbon cathode including a separator during the first step of fabricating a cathode structure.

[0031] Figure 8B is a schematic diagram of an exemplary embodiment of an adhesive-free carbon cathode including a separator during the second step of fabricating a cathode structure.

[0032] Figure 8CSchematic diagram of an exemplary embodiment of a binderless carbon cathode including a separator during the third step of fabricating a cathode structure.

[0033] Figure 8D Schematic diagram of an exemplary embodiment of a binderless carbon cathode including a separator during the fourth step of fabricating a cathode structure.

[0034] Figure 9 Top view of an exemplary embodiment of a binderless carbon cathode including a separator during the second step of fabricating a cathode structure.

[0035] Figure 10 Graph showing the current density of a battery cell using the pure binderless carbon cathode of the present disclosure.

[0036] Figure 11 Graph showing the cycle life of a battery cell using the pure binderless carbon cathode of the present disclosure.

[0037] Figure 12A Cross-sectional view of an exemplary embodiment of a all-carbon electrode of the present disclosure having an enhanced microstructure and high surface area.

[0038] Figure 12B Top view of an exemplary embodiment of a all-carbon electrode of the present disclosure having an enhanced microstructure and high surface area. Detailed Description

[0039] The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. The embodiments, which are also referred to herein as "examples," are described in sufficient detail to enable those skilled in the art to practice the invention. Embodiments may be combined, other embodiments may be utilized, or structural and logical changes may be made without departing from the scope of the invention. Accordingly, the following detailed description should not be construed as limiting.

[0040] However, before describing the present invention of the present disclosure in such detail, it should be understood that the invention is not limited to the specific variations set forth and may of course vary. Various changes may be made to the described invention and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act or step to the objectives, spirit or scope of the present invention. All such modifications are intended to fall within the scope of the disclosure made herein.

[0041] Unless otherwise indicated, the words and phrases presented herein have their ordinary meaning to those skilled in the art. These ordinary meanings may be obtained by reference to their use in the art and reference to general and scientific dictionaries.

[0042] References to "one embodiment" in the specification mean that the described embodiment may include a particular feature, structure, or characteristic, but each embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, these phrases do not necessarily refer to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is contemplated that such feature, structure, or characteristic can be implemented in connection with other embodiments (whether or not explicitly described) within the knowledge of those skilled in the art.

[0043] The following explanations of certain terms are illustrative and not exhaustive. These terms have their ordinary meanings as given by usage in the art, and additionally include the following explanations.

[0044] As used herein, the term "and / or" means any one of the items associated with this term, any combination of the items, or all of the items.

[0045] As used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

[0046] As used herein, the terms "comprising", "such as", "for example", etc. are used illustratively and are not intended to limit the present invention.

[0047] As used herein, the terms "preferred" and "preferably" refer to embodiments of the present invention that may provide certain benefits in certain circumstances. However, in the same or other circumstances, other embodiments may also be preferred.

[0048] Moreover, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the present invention. As used herein, the term "coupled" means joining two components directly or indirectly to each other. Such joining can actually be immovable or can actually be movable. Such joining can be achieved by integrally forming two components or two components and any additional intermediate components as a single unit with each other or by attaching two components or two components and any additional intermediate components to each other. Such joining can actually be permanent, or can actually be removable or releasable. Similarly, coupling can refer to two components or elements being coupled interactively, where the two elements can be electronically coupled by various means such as wires, wireless networks, optical fibers, or other media and methods.

[0049] It should be understood that although the terms first, second, etc. are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the teachings of the present invention.

[0050] The present disclosure relates to a battery cell having an anode, a cathode, an outer coated intermediate layer surrounding the cathode, and a separator located between the anode and the cathode. Similarly, the present disclosure provides a carbon nanotube-based intermediate layer composition comprising about 1-30 wt% oxidized carbon nanotubes (Ox-CNT), which can be coated onto the surface of a dry electrode (including but not limited to the cathode). Any suitable method such as a doctor blade method can be used to coat the electrode. This layer may be referred to as an "intermediate layer" or a "secondary current collector". The intermediate layer can be located between the cathode and the separator 11 and can serve as a secondary path to the current collector for electrons to shuttle in and out of the cathode.

[0051] In some exemplary embodiments, the separator can be configured as a permeable membrane located between electrodes (e.g., the anode and the cathode), as Figure 5 shown. The separator can be electrically insulating and can operate to keep the electrodes separated, prevent physical contact between the electrodes, and mitigate electrical short circuits in the battery. The separator can also be permeable to allow ionic charge carriers (e.g., lithium ions) to transport therethrough, which completes the electrical circuit during current passage in an electrochemical cell. The separator is flexible while also providing sufficient mechanical strength (e.g., high resistance to in-plane puncture and in-plane tensile strength), dimensional stability, and resistance to thermal shrinkage. The separator can be made of any suitable material, including but not limited to cotton, nylon, polyester, glass, polyethylene, polypropylene, polytetrafluoroethylene, polyvinyl chloride, ceramics, rubber, asbestos, or wood. As Figures 6 - 7 shown, the intermediate layer can significantly improve the performance of the battery cell, including but not limited to electron conductivity, while also increasing the utilization rate of sulfur.

[0052] As Figure 1 and Figure 2 shown, exemplary embodiments of the present disclosure may include a cathode 3 having an intermediate layer 5 and a current collector 7. The cathode 3 can be made of any suitable material, including but not limited to pure carbon components, sulfur components, graphene components, or other suitable materials and combinations thereof. In some exemplary embodiments, the cathode is made of a sulfur-graphene composite material. The current collector can be made of any suitable material, such as a metal or other conductive material. In some exemplary embodiments, the current collector can be a carbon-coated aluminum current collector. Similarly, the intermediate layer can be made of any suitable material, including but not limited to carbon nanotubes.

[0053] In an exemplary embodiment, the intermediate layer can be formed by using oxidized CNTs, which can be synthesized by heat-treating CNTs with a diameter of about 20 - 60 nm at a temperature of about 500 - 600 °C for about 3 - 5 hours with an air flow rate between about 0.1 - 1 SCCM. The heat treatment can be carried out in a quartz tube furnace. In some exemplary embodiments, the intermediate layer can be a polarized porous host for sulfur deposition. Similarly, the intermediate layer 5 can be bonded to the current collector by van der Waals (VdW) forces / interactions without the need for an additional binder. In other exemplary embodiments, a binder can be used to assist in coupling the intermediate layer to the current collector 7. In embodiments comprising a binder, the binder can comprise styrene-butadiene copolymer (SBR) and polyvinylidene fluoride (PVDF).

[0054] In an exemplary embodiment, the intermediate layer can be composed of Ox-CNT. Additionally, in some exemplary embodiments, Ox-CNT can be mixed with pristine CNTs in a preferred weight percentage ratio between about 1:99 to about 99:1 (Ox-CNT:CNT). In an exemplary embodiment, the preferred weight percentage ratio can be about 20:80 (Ox-CNT:CNT). Typically, in some embodiments, the weight percentage of Ox-CNT ranges from about 1 - 30%. A higher Ox-CNT content can provide a high catalytic effect and a loss in electron conductivity. Above 30 wt% Ox-CNT, the binding becomes poor and the adhesion to the current collector can become poor. At about 1 - 30 wt% Ox-CNT, the intermediate layer can be cast in any thickness without cracking or delamination even without a binder. Zero polymer binder can be used in the exemplary embodiments of the present invention. In some exemplary embodiments, the length of the CNT can be between about 50 - 200 nm and the diameter can be between about 20 - 60 nm. Additionally, the length of Ox-CNT can be about 10 - 200 nm and is highly disordered due to oxygen etching.

[0055] In some exemplary embodiments, the binder-free intermediate layer can be mixed and cast under very specific conditions to exhibit high adhesion and zero cracking. Propylene glycol (PG) can be used as a solvent due to its high viscosity, safety, and non-toxicity. The high viscosity of PG is necessary to prevent CNT agglomeration and to keep the CNTs suspended even under storage conditions. The carbon concentration in the slurry can be about 20 g / L at room temperature. The concentration can range from about 18 - 22 g / L, yet similar results are obtained.

[0056] As a result of the high agglomeration tendency of CNTs, a high-shear mixer such as a homogenizer can be used to shear the CNTs. The interlayer slurry can be homogenized at about 3500 rpm for about 30 minutes. Thereafter, the slurry can be stirred at a low speed to keep the CNTs suspended, but simple low-speed stirring may not provide sufficient shear force to separate the CNTs from each other. Improper dispersion of carbon nanotubes can lead to agglomeration, poor adhesion, and cracking.

[0057] The interlayer loading on a typical cathode ranges from about 0.1 mg / cm 2 to about 1 mg / cm 2 and can depend on the sulfur loading of the underlying cathode. The interlayer coating can be applied about 1-2 mm wider than the cathode coating so that the interlayer can make direct contact with the carbon-coated aluminum current collector and form a strong bond. Figure 3 An exemplary embodiment of the coating process is shown. The cathode 3 can be coated with the interlayer 5 in a first direction. In one exemplary embodiment, carbon-coated aluminum foil can be used because of its ability to form a very strong bond with the binder-free interlayer. In other embodiments, the raw aluminum foil may not be preferred due to the formation of a weak bond between the Al and the interlayer. In some exemplary embodiments, the interlayer can be cast at about 20-40 °C, but preferably at about 30 °C. The cathode coated with the interlayer can then be dried at 70 °C by natural convection. The cathode can then be dried in a vacuum at about 65 °C for about 12 hours.

[0058] Figure 4A -C provides various exemplary configurations of the battery. As Figure 4A shown, a conventional battery cell can include an anode 9 and a separator 11 between the anode and the cathode 3. Additionally, as Figure 4B shown, a supercapacitor cell can include an anode 9 and a cathode 3, where the cathode is composed of carbon nanotubes and additionally has a separator 11 located between the anode 9 and the cathode 3. In one exemplary embodiment of the present disclosure, a battery cell can include an anode 9, a cathode 3, and a separator, where the separator 11 is located between the anode 9 and the cathode 3. Additionally, the cathode can include an interlayer.

[0059] As Figure 5As shown, an exemplary embodiment of the present disclosure may include a battery cell 1 having one or more anodes 9 and one or more cathodes 3, wherein the cathodes are electrically connected and the anodes are electrically connected in parallel or series. One or more separators 11 may surround the anode 9. Additionally, one or more cathodes 3 may include an intermediate layer 5 surrounding the cathode structure. Each individual electrode may additionally include a current collector 7, which may comprise any suitable material, such as a metal or other conductive material. In an exemplary embodiment, the current collector may comprise carbon-coated aluminum. The cathode may comprise any suitable material, including but not limited to sulfur, cobalt, nickel, graphene, or other metals and their composites. An exemplary embodiment of the present invention may include a cathode comprising a graphene / sulfur composite. Similarly, in some exemplary embodiments, the anode may comprise lithium or a lithium oxide material. In some embodiments, the cathode may comprise a graphene / sulfur material. And, the intermediate layer surrounding the cathode may comprise carbon nanotubes. In some exemplary embodiments, the intermediate layer may include a mixture of pristine carbon nanotubes and oxidized carbon nanotubes in a ratio between about 20:80 (Ox-CNT:CNT) to about 80:20 (Ox-CNT:CNT).

[0060] The present disclosure further provides a means of using graphene or other suitable carbon materials to create a percolation network throughout the sulfur active material. The sulfur active material may be deposited on various suitable carbon substrates, including but not limited to graphene substrates or CNTs with high electrical conductivity and surface area, or other high-capacitance carbons with high surface area and high electrical conductivity. Using these different carbon substrates with sulfur reduces the electrode overpotential during charging at lower voltages and improves the charging efficiency. Additionally, by altering the electrode microstructure to have a uniform distribution of sulfur active material over the carbon active surface area, increased sulfur utilization is achieved.

[0061] In some exemplary embodiments, the cathode may comprise one or more carbon materials, including a first carbon material such as conductive carbon black or graphene nanosheets and a second carbon material such as activated carbon or carbon nanotubes, having capacitor capacitance and / or pseudocapacitor capacitance, with or without a binder. Such a carbon electrode may include a porous carbon percolation network (e.g., a nanographene percolation network, or an equivalent carbon network) formed with or without a binder. In some exemplary embodiments, one or more electrodes may include sulfur active material filled in the pores or deposited on the electrode active surface area therein, such materials contributing to the energy content of the cell. Additionally, a coating (intermediate layer) made of porous carbon with a high surface area is formed on its electrode surface (e.g., a carbon nanotube intermediate layer), such a layer contributing to the power content of the cell. Similarly, the intermediate layer may be composed of one or more carbon materials, such as pristine carbon nanotubes and oxidized carbon nanotubes. Other porous carbon compositions may be similarly used for the intermediate layer composition.

[0062] In addition, in some exemplary embodiments, the cathodes of the present disclosure can be pure carbon, binder-free, roll-to-roll processable cathode structures. The present disclosure provides a structure and method for obtaining a high (ionic and electrical) conductivity, binder-free, and lightweight carbon cathode structure. The cathode structure can be mainly used in battery cell construction and further optionally includes an intermediate layer.

[0063] In some exemplary embodiments, the carbon component of the pure carbon binder-free cathode can include, but is not limited to, carbon nanotubes, carbon nanofibers, Ketjen black, acetylene black, which can be dispersed in an organic solvent, including but not limited to propylene glycol, and mixed using high shear force. Shear force mixing can produce a stable carbon dispersion with a size between about 8 nm and 50 nm in diameter and between about 10 and 200 µm in length. In some exemplary embodiments, propylene glycol can be used in a ratio of 10 - 30 g of carbon material per 0.5 - 1.5 liters of propylene glycol. In one exemplary embodiment, the ratio can be 20 grams of carbon material per 1 liter of propylene glycol.

[0064] The resulting carbon dispersion can then be coated onto a conductive material / substrate, including but not limited to carbon-coated aluminum foil, copper foil, woven metal mesh, expanded metal mesh, aluminum foam, perforated foil, and other suitable conductive non-solid metal substrates. Any suitable method can be used to apply the carbon dispersion, including but not limited to the doctor blade method. The carbon loading on the conductive material can be about 0.1 - 5 mg / cm 2 of density. In some exemplary embodiments, the carbon cathode can then be wound into a bend radius between about 1 mm and 1 cm, depending on the carbon loading density. In one exemplary embodiment, the carbon loading is about 5 mg / cm 2 and has a bend radius of about 1 cm, mainly due to the flexibility of the cathode structure. The cathode structure can then be dried using any suitable method under forced dry air at about 60 - 150 °C, but typically about 60 - 80 °C, and in one exemplary embodiment at about 70 °C. In one exemplary embodiment without using a binder, only a cathode structure comprising 100% conductive material is used.

[0065] In another exemplary embodiment, the carbon dispersion 13 can also be directly coated onto the separator 5, such as a polypropylene separator, and used with or without a conventional metal current collector, as Figure 8A shown. The carbon dispersion can be coated onto the polypropylene separator 11a and the conductive foil strips 7, which include but are not limited to aluminum or copper foil, and can be intermittently embedded across the width of the cathode 3, as Figure 8B shown. As Figure 8C shown, a second coating of the carbon dispersion 13b can be applied to the cathode 3. In addition, as Figure 8DAs shown, the second separator 11b can be applied on top of the wet carbon dispersion 3b. As Figure 9 shown, the cathode structure can be produced in a first coating direction.

[0066] In some exemplary embodiments, the sulfur active material can be introduced into the carbon cathode in any suitable manner. In one exemplary embodiment, the sulfur active material is introduced by immersing the cathode in a polysulfide solution comprising dimethoxyethane (DME) and a polysulfide substance, the polysulfide substance including but not limited to Li2S4, Li2S5, Li2S6, Li2S7, Li2S8, Li2S9. In some embodiments, Li2S6 can be the main sulfur active material. In some exemplary embodiments, the polysulfide electrolyte solution is a polysulfide solution between 0.5 and 2 moles, including but not limited to a lithium polysulfide solution such as Li2S6. Also, some embodiments can utilize an ether-based electrolyte solution. The electrolyte solution can be an ether-based polysulfide solution with a concentration between 0.5 - 2M, and the battery cell of the present disclosure with a pure carbon cathode has a greater than 400 Wh / kg in the form of a cell or similarly greater than >400 Wh / L in the form of a cell. Figure 11 - 1 2 provides a graphical illustration of the improved performance of a battery cell with a pure carbon binder-free cathode structure using a pre-existing manufacturing process.

[0067] In another exemplary embodiment, a polysulfide-rich electrolyte can be used at the cell assembly to introduce the sulfur active material to uniformly introduce the sulfur active material into the cathode. A suitable polysulfide substance can be used to introduce sulfur, the polysulfide substance including but not limited to Li2S4, Li2S5, Li2S6, Li2S7, Li2S8, Li2S9. In some embodiments, Li2S6 can be the main sulfur active material.

[0068] Furthermore, the present disclosure provides a self-supporting tape of a binder-free cathode. According to the method of manufacturing the cathode, the cathode can be configured to have a highly conductive microstructure. Such a microstructure can similarly be produced in other methods, resulting in enhanced battery cell performance of more than 400 Wh / L or 400 Wh / kg. Figure 12A -B shows an exemplary microstructure of the pure carbon electrode of the present disclosure, where the electrode has an increased surface area and the desired characteristics for use as a high energy density cathode electrode.

[0069] In some exemplary embodiments, the battery cell of the present disclosure can comprise by using a density of about 0.1 - 5 mg / cm 2A pure binder-free carbon cathode formed by coating a carbon dispersion on a substrate. In some exemplary embodiments, the carbon dispersion can be coated onto the polypropylene separator 11a and one or more conductive foils 7. The battery cell can further include an anode such as a lithium anode and an electrolyte solution. The battery cell can optionally include an intermediate layer. In some exemplary embodiments, the intermediate layer can include a first carbon source and a second carbon source. The first carbon source can include oxidized nanotubes, and the second carbon source can include pristine nanotubes. The intermediate layer can include Ox-CNT accounting for about 1-30% by weight of the intermediate layer composition. Additionally, an electrolyte solution can be used to introduce sulfur active materials by immersing the cathode in a polysulfide electrolyte solution containing dimethoxyethane (DME) and a polysulfide substance, the polysulfide substance including but not limited to Li2S4, Li2S5, Li2S6, Li2S7, Li2S8, Li2S9. In some embodiments, Li2S6 can be the main sulfur active material. In some exemplary embodiments, the polysulfide electrolyte solution is a polysulfide solution between 0.5-2 moles, including but not limited to polysulfide lithium solutions such as Li2S6. In some embodiments, the resulting battery cell can achieve a performance greater than 400 Wh / kg and / or greater than >400 Wh / L.

[0070] Although the present invention has been described above according to specific embodiments, it should be understood that the present invention is not limited to these disclosed embodiments. After reading the teachings of the present disclosure, those skilled in the art to which the present invention pertains will envision many variations and other embodiments of the present invention, and both the present disclosure and the appended claims are intended to cover these variations and other embodiments. As those skilled in the art will understand from the disclosure in this specification and the drawings, the scope of the present invention is indeed intended to be determined by a proper interpretation and description of the appended claims and their legal equivalents.

Claims

1. A battery cell, comprising: An anode; A carbon-based cathode, which includes a current collector; An intermediate layer coated on the outer surface of the cathode, wherein the intermediate layer is configured to serve as a secondary path to the current collector; And A separator located between the anode and the cathode, Wherein the intermediate layer contains carbon nanotubes, Wherein the intermediate layer contains 1-30 wt% of oxidized carbon nanotubes, Wherein the cathode contains a first carbon material, a second carbon material, and a sulfur component.

2. The battery cell according to claim 1, wherein, The intermediate layer is disposed on the cathode by atomic layer deposition.

3. The battery cell according to claim 1, wherein, The first carbon material is selected from conductive carbon black or graphene nanosheets.

4. The battery cell according to claim 3, wherein, The second carbon material is selected from activated carbon or carbon nanotubes.

5. The battery cell according to claim 4, wherein, The sulfur component is a sulfur active material, which is configured to fill a plurality of pores or deposit on the electrode active surface region of the cathode.

6. The battery cell according to claim 5, wherein, The anode contains lithium and the cathode contains pure binder-free carbon.

7. The battery cell according to claim 6, wherein, The separator is selected from at least one of the following: cotton, nylon, polyester, glass, polyethylene, polypropylene, polytetrafluoroethylene, polyvinyl chloride, ceramic, rubber, asbestos, or wood.

8. The battery cell according to claim 7, wherein, Pure binder-free carbon is introduced into the sulfur active material to the carbon cathode by immersing the cathode in a polysulfide electrolyte solution containing dimethoxyethane (DME) and a polysulfide substance, and the polysulfide substance is selected from at least one of the following: Li2S4, Li2S5, Li2S6, Li2S7, Li2S8, Li2S9.

9. The battery cell according to claim 8, wherein, The intermediate layer contains pristine carbon nanotubes.

10. The battery cell according to claim 9, wherein, The weight ratio of oxidized carbon nanotubes to pristine carbon nanotubes is 20:

80.

11. An intermediate layer composition for coating the cathode of a battery cell according to any one of claims 1-10, comprising: A first carbon source and a second carbon source, wherein, The first carbon source is pristine carbon nanotubes and the second carbon source is oxidized carbon nanotubes, Wherein the intermediate layer contains 1-30 wt% of oxidized carbon nanotubes.

12. The intermediate layer composition according to claim 11 further comprises an adhesive, wherein, The binder is selected from at least one of the following: styrene-butadiene copolymer (SBR) and polyvinylidene fluoride (PVDF).

13. The intermediate layer composition according to claim 11, wherein, The weight ratio of oxidized carbon nanotubes to pristine carbon nanotubes is 20:

80.

14. A method for manufacturing a pure binder-free carbon cathode for use in an electrochemical cell, comprising: Providing a carbon dispersion by using high-shear mixing, wherein the carbon dispersion has a scale between 8 nm and 50 nm in diameter and between 10 and 200 µm in length; Directly applying a first coating of the carbon dispersion to a separator and one or more conductive strips, wherein the conductive strips are intermittently embedded across the width of the cathode; then Introducing a sulfur active material into the carbon cathode by immersing the cathode in a polysulfide electrolyte solution containing dimethoxyethane (DME) and a polysulfide substance, and the polysulfide substance is selected from at least one of the following: Li2S4, Li2S5, Li2S6, Li2S7, Li2S8, Li2S9; then Applying a second coating of the carbon dispersion to the cathode, which contains 1-30 wt% of oxidized carbon nanotubes; and Applying a second separator on top of the second coating of the carbon dispersion.

15. The method according to claim 14, wherein, The polysulfide electrolyte solution has a concentration between 0.5 and 2 M and, when used in an electrochemical cell with a pure binder-free carbon cathode, achieves greater than 400 Wh / kg.

16. The method according to claim 14, wherein The polysulfide electrolyte solution has a concentration between 0.5 and 2 M and, when used in an electrochemical cell with a pure binder-free carbon cathode, achieves greater than 400 Wh / L.

Images