Methods for forming integrated spray-on aramid nanofiber separator-electrode components for high throughput battery production

Abstract

Methods of making an integrated electrode-separator component for a lithium-sulfur electrochemical cell are provided. A liquid dispersion comprising aramid nanofibers (ANF) is sprayed onto an active material layer comprising at least one electroactive material to form a sprayed layer that defines an integrated electrode-separator component having an interfacial resistance between the sprayed layer and the active material layer of less than or equal to about 10 Ω·cm2. An electrode-separator component and lithium-sulfur electrochemical cell are also provided.

Description

METHODS FOR FORMING INTEGRATED SPRAY-ON ARAMID NANOFIBER SEPARATOR-ELECTRODE COMPONENTS FOR HIGH THROUGHPUT BATTERYPRODUCTIONGOVERNMENT SUPPORT

[0001] This invention was made with government support under FA9550-20-1-0265 awarded by the U.S. Air Force Research Laboratory. The government has certain rights in the invention.CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 622,181, filed on January 18, 2024. The entire disclosure of the above application is incorporated herein by reference.FIELD

[0003] The present disclosure relates to integrated electrode- separator components for electrochemical cells, such as lithium- sulfur batteries, where the electrode- separator component comprises polymeric (e.g., aramid) nanofibers sprayed over an electroactive material layer and to methods for forming the same.BACKGROUND

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

[0005] Metal-sulfur and, especially, lithium-sulfur (LiS), sodium sulfur, potassiumsulfur and similar batteries are technologically attractive due to their high energy density and abundance of U.S. sources of sulfur. For example, lithium-sulfur (Li-S) electrochemical cells or batteries are an attractive energy storage option due to the high energy density (2,600 Wh / kg), large theoretical capacity (1,675 mAh / g), cost effectiveness, abundance of raw materials, and environmental friendliness. Due to their high-energy density, lithium-sulfur (LiS) batteries can be used in a variety of applications. Typical lithium- sulfur batteries comprise at least one positive electrode or cathode, at least one negative electrode or an anode, an electrolyte material, and a separator. Lithium- sulfur batteries operate by reversibly passing lithium ions between thenegative electrode and the positive electrode. The positive electrode typically includes a sulfur host material that contains sulfur / sulfur compounds that reversibly react with lithium, while the negative electrode may be a lithium metal. Each negative and positive electrode is connected to a current collector. A separator, such as a polymeric separator, may be disposed between the negative and positive electrodes. A liquid or solid electrolyte is also disposed between the positive and negative electrodes and may be disposed in pores of a separator. Electrolytes suitable for conducting lithium ions between the electrodes and may be in solid and / or liquid form and / or a hybrid thereof. In instances of solid-state batteries, which include solid-state electrodes and a solid-state electrolyte (or solid-state separator), the solid-state electrolyte (or solid-state separator) may physically separate the electrodes so that a distinct separator is not required. During battery usage, the current collectors associated with the two electrodes are connected by an external circuit that allows current generated by electrons to pass between the electrodes to compensate for transport of lithium ions.

[0006] However, Li-S batteries are still impeded by challenges, including low electrical conductivity of sulfur and its discharge product (Li2S2 / Li2S), the shuttle effect of the solubility lithium poly sulfides (LiPS: Li2Sn4 < n < 8), the large volumetric expansion of sulfur electrodes during cycling, which leads to loss of capacity. These issues create fundamental difficulties for lithium-sulfur batteries to attain cyclability, discharge rate, and Coulombic efficiency compared with other active materials. Generally, dendrite formation, poly sulfide shuttling, and manufacturing challenges have prevented widespread adoption of Li-S.

[0007] Advanced materials developed for cathodes and separators, which combine high strength, low thickness, and effective polysulfide screening, may address these problems. However, conventional materials have been too structurally complex, resulting in prohibitively high costs and unrealistic manufacturing conditions. It would be desirable to develop electrodes having integrated separators, especially those for Li-S batteries, which provide these benefits while being capable of being seamlessly integrated with the current roll-to-roll (R2R) battery processing, for example, being suitable for giga factories.SUMMARY

[0008] This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.

[0009] In certain aspects, the present disclosure relates to a method of making an integrated electrode- separator component for a lithium- sulfur electrochemical cell. The method may comprise spraying a liquid dispersion comprising aramid nanofibers (ANF) onto an activematerial layer comprising at least one electroactive material to form a sprayed layer that defines an integrated electrode- separator component. The integrated electrode-separator component has an interfacial resistance between the sprayed layer and the active material layer of less than or equal to about 10 Q-cm2.

[0010] In one aspect, the liquid dispersion comprises dimethyl sulfoxide (DMSO).

[0011] In one aspect, the liquid dispersion comprises a solvent selected from the group consisting of: dimethyl sulfoxide (DMSO), acetonitrile, isopropyl alcohol, diethyl ether, and combinations thereof.

[0012] In one aspect, the liquid dispersion comprises potassium hydroxide (KOH).

[0013] In one aspect, the aramid nanofibers (ANF) are present in the liquid dispersion at greater than or equal to about 0.05 weight % to less than or equal to about 3 weight %.

[0014] In one aspect, the method occurs on a roll-to-roll process and the active material layer is disposed on a first roll, so the method further comprises unrolling the active material layer from the first roll prior to the spraying and rolling the integrated electrode-separator component that is processed via the spraying onto a second roll.

[0015] In one aspect, the spraying is automated and occurs via a robotic arm.

[0016] In one aspect, the method further comprises applying one or more of heat, radiation, or reduced pressure to remove liquid from the liquid dispersion sprayed on the active material layer.

[0017] In one aspect, the sprayed layer has a thickness of less than or equal to about 1 micrometer and the active material layer has a thickness of less than or equal to about 25 micrometers.

[0018] In certain other aspects, the present disclosure relates to an integrated electrodeseparator component. The integrated electrode-separator component comprises an active material layer comprising at least one electroactive material. The integrated electrode- separator component also comprises a sprayed layer formed from aramid nanofibers (ANF) defining a separator, wherein an interfacial resistance between the sprayed layer and the active material layer is less than or equal to about 10 Q-cm2.

[0019] In one aspect, the sprayed layer has an ionic conductivity of greater than or equal to about 1 x 10'4S / cm.

[0020] In one aspect, the sprayed layer has a thickness of less than or equal to about 1 micrometers and the active material layer has a thickness of less than or equal to about 20 micrometers.

[0021] In one aspect, the integrated electrode-separator component further comprises a current collector disposed adjacent to the active material layer.

[0022] In one aspect, the active material layer is a porous composite having the at least one electroactive material distributed in a polymeric matrix.

[0023] In one aspect, the at least one electroactive material comprises at least one sulfur positive electroactive material that cycles lithium ions.

[0024] In yet other aspects, the present disclosure relates to a lithium-sulfur electrochemical cell comprising a positive electrode. The positive electrode comprises a positive electroactive material layer comprising at least one sulfur positive electroactive material that cycles lithium ions. The positive electrode further comprises a sprayed layer formed from aramid nanofibers (ANF) defining a separator. An interfacial resistance between the sprayed layer and the positive electroactive material layer is less than or equal to about 10 Q-cm2. The lithium-sulfur electrochemical cell further comprises a negative electrode comprising lithium and an electrolyte.

[0025] In one aspect, the positive electrode further comprises a current collector comprising a metal selected from the group consisting of: aluminum, and combinations thereof.

[0026] In one aspect, the positive electrode has an areal capacity of greater than or equal to about 10 mAh / cm2.

[0027] In one aspect, the positive electrode has a current density of greater than or equal to about 10 mA / cm2.

[0028] In one aspect, the positive electrode has a sulfur loading of greater than or equal to about 6 mg / cm2.

[0029] In one aspect, the lithium- sulfur electrochemical cell has an electrolyte-to-sulfur ratio (E / S) ratio of less than or equal to about 8:1.

[0030] In one aspect, the positive electroactive material layer further comprises a polymeric binder that defines a porous composite having the at least one electroactive material distributed in a polymeric binder.

[0031] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.DRAWINGS

[0032] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0033] FIG. 1 is an illustration of an example of an electrochemical cell having an integrated positive electrode / sprayed on separator component comprising a plurality of aramid nanofibers prepared in accordance with certain aspects of the present disclosure.

[0034] FIG. 2 shows a manufacturing process according to certain aspects of the present disclosure for fabricating an integrated cathode and separator assembly for a lithium- sulfur (LiS) pouch cells. In the insets: (left) exemplary hardware realization of a roll-to-roll (R2R) process for pilot scale manufacturing and (right) a 3D surface profiler image of an ANF coating in a process of drying on commercial sulfur-carbon cathode.

[0035] FIG. 3 shows a spraying device for fabricating an integrated cathode and separator assembly according to certain aspects of the present disclosure.

[0036] FIGS. 4A-4D. FIGS. 4A-4C show SEM images of low porosity ANF coatings on sulfur-carbon cathode prepared in accordance with certain aspects of the present disclosure. FIG. 4C is a magnified section of the sample in FIG. 4A. FIG. 4C shows a schematic of a SCAN cathode. FIG. 4D is a scanning electron microscope (SEM) image of an integrated sulfur-carbon cathode produced in accordance with certain aspects of the present disclosure.

[0037] FIGS. 5A-5C. FIG. 5A shows Nyquist plots of cathodes with two inventive ANF-based and comparative CELGARD™ 2400 separators. FIG. 5B shows rate performance of batteries having an integrated positive electrode / sprayed on separator component comprising a plurality of aramid nanofibers prepared in accordance with certain aspects of the present disclosure at 0.1C to 3C and their comparison to conventional CELGARD™ 2400. FIG. 5C shows cycling performance of prototypes of batteries with spray-on ANF coating at 0.2 C rate.

[0038] FIGS. 6A-6C. FIGS. 6A-6B show a lithium poly sulfide (LPS) diffusion test for cycled sulfur cathode and an integrated positive electrode / sprayed on separator component comprising a plurality of aramid nanofibers prepared in accordance with certain aspects of the present disclosure. FIG. 6A is at the start and FIG. 6B is 96 hours later. FIG. 6C shows an SEM image of ANF coating on the surface of a cathode after 100 cycles. Note small pore size and uniform coating.

[0039] FIGS. 7A-7B are SEM images of a sprayed layer of ANFs that define a 3D network and thus a separator layer integrated with a cathode active material layer that together define an integrated cathode and separator assembly prepared according to certain aspects of thepresent disclosure. FIG. 7B is a magnified view of a portion of FIG. 7A. The scale in FIG. 7A is 3 micrometers and the scale in FIG. 7B is 500 nm.

[0040] FIGS. 8A-8D are SEM images showing contact angle for lithium-sulfur electrolytes, showing comparative contact angles for sprayed ANF (SCAN) coatings (FIG. 8A), a free-standing ANF separator layer (FIG. 8B), as compared to commercially available separators, including one from Celgard (FIG. 8C) and Entek (FIG. 8D).

[0041] FIG. 9 shows cycle performance for a pouch cell incorporating an integrated sulfur-based positive electrode / sprayed on separator component comprising a plurality of aramid nanofibers prepared in accordance with certain aspects of the present disclosure. FIG. 9 shows both Coulombic efficiency and rate performance at 0.1C to 2C over 500 cycles.

[0042] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.DETAILED DESCRIPTION

[0043] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth, such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0044] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, 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 claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of’ or “consisting essentially of.” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and / or process steps, the presentdisclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and / or process steps. In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and / or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and / or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and / or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.

[0045] Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.

[0046] When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0047] Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and / or sections, these steps, elements, components, regions, layers and / or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer or section discussed below could be termed a second step, element, component, region, layer or section without departing from the teachings of the example embodiments.

[0048] Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.

[0049] Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.

[0050] In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges.

[0051] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0052] As noted above, while metal-sulfur e.g., lithium- sulfur (LiS)) batteries have high energy density and are made from widely available raw materials, issues including dendrite formation, polysulfide shuttling, and difficulty in manufacturing suitable separators have prevented their widespread adoption. For example, ion-conducting membranes, also known as separators, electrically isolate battery electrodes, preventing short-circuits and fires while permitting ion diffusion. Additional requirements for separators include adequate mechanical properties, ionic conductivity, electrical insulation, thermal stability, and chemical stability. In the case of LiS batteries, separators also control lithium polysulfide (LPS) shuttling from cathodes and prevent growth of lithium dendrites on anodes.

[0053] Separators are currently supplied as stand-alone polymer rolls by companies. These sheets are inserted between cathode and anode in the battery assembly stage followed byelectrolyte wetting. Separators must be thin to reduce the volume of costly electrolytes used and the total mass of the battery. Separators must also be sufficiently strong to withstand stresses during manufacturing and to block dendrite growth on anodes during charge. Besides high specific energy density, thin separators are also support increased charging rates due to low impedance, which is particularly important for electric vehicles (EVs). Manufacturing problems related to current separators may occur during integration of separators with batteries, resulting in accidental tears and drastically enlarged pores. These faults may result in short circuits and increase risk of battery fires.

[0054] Thin, strong, uniform separators are needed for LiS batteries. Many advanced materials have been tested for their design including metal-organic framework (MOF), graphene oxide (GO), MoSe2 nanotubes, zeolites and other nanomaterials and polymers. Other separator technologies attracting attention include ceramics-based solid-state electrolytes. These materials have high Young’s modulus, but they are also brittle. Combined with low toughness and reduced electrode-separator contact, these properties lead to safety issues, especially for fastcharging EV batteries demanded by the consumers as discussed below. Also, solid state ceramic separators are typically quite thick, for example, from about 20 micrometers to 100 micrometers thick, decreasing cell and pack-level energy density. Advanced materials developed for cathodes and separators that combine high strength, low thickness, and effective polysulfide screening, in theory, address these problems. However, their chemical structure is often too complex or sophisticated, resulting in prohibitively high costs and unrealistic manufacturing conditions incompatible with markets for electrical vehicles (EVs), robotics, electronics, aviation, and other applications.

[0055] In accordance with various aspects of the present disclosure, methods of manufacturing an integrated electrode- separator component having an electroactive material (e.g., sulfur-containing positive electrode or cathode active material) with a sprayed-on separator made from high-strength polymeric nanofibers, such as aramid nanofibers, are contemplated. Such an integrated sprayed-on separator layer is strongly adhered and integrated to the electrode below, for example, where it is a porous composite electrode, and has a low interfacial resistance, as will be described further below. Such methods can be readily integrated with roll- to-roll (R2R) processing commonly used in battery manufacturing. Unlike current manufacturing of batteries (e.g., electric vehicle (EV) batteries) that involves a distinct suboptimal separator sheet(s) that are joined with separate electrode components, the present disclosure contemplates forming ion-conductive separator membranes by directly spraying high-strength polymeric nanofibers, such as aramid nanofibers (ANFs), onto the active material (e.g., porous sulfur-carbon layer) creating an integrated electrode / cathode unit.

[0056] A thickness of the separator layer comprising ANF can be adapted for specific manufacturing conditions and battery components. In certain variations, a thickness of the separator layer is ultrathin, for example, having a submicron thickness, as described below. The integrated electrode- separator units can serve as drop-in replacement for current cathodes in LiS and other batteries. Further, the ANF-containing separator layer can minimize or suppress metal dendrite formation and prevent lithium poly sulfide (LPS or LiPS: Li2Sn4 < n < 8) transport enabling breakthrough performance of LiS batteries. The technology of spray-on cathodes coated with aramid nanofibers (SCAN) provided by the present teachings is particularly suitable for R2R manufacturing of LiS pouch cells. As will be described further below, such LiS cells may have current densities greater than or equal to about 10 mA / cm2and an areal capacity of greater than or equal to about 10 mAh / cm2, thereby reducing EV charging time from current commercial batteries two-fold. Batteries made in accordance with certain aspects of the present disclosure are expected to reduce manufacturing energy consumption, for example by approximately 16%, and the cost of EV batteries, for example by approximately 30%. The manufacturing methods of the sprayed separator layer for the integrated electrode-separator component are highly controllable by adjusting the concentration, composition, and viscosity of a dispersion of fibers, as well as the flow rate, distance, and amount of the spraying material on various cathode chemistries, including but not limited to sulfur.

[0057] As background, a rechargeable battery operates by reversibly passing ions back and forth between the negative electrode and the positive electrode during charging and discharging. For example, ions may move from the positive electrode to the negative electrode during battery charging and in the opposite direction when discharging the battery. In a lithiumsulfur battery, energy is stored and transferred by reversible electrochemical reactions between lithium and sulfur, for example, where the respective electrodes are reversibly plated. For example, a representative rechargeable battery 20 prepared in accordance with certain aspects of the present disclosure is shown in FIG. 1. The battery 20 includes a positive electroactive material layer or as referred to herein, a positive electrode 22 (e.g., cathode) and a negative electroactive material layer or as referred to herein, a negative electrode 24 (e.g., anode). The positive electrode 22 may include a positive electroactive material. The positive electrode 22 may be a composite electrode that comprises a plurality of electroactive material particles distributed in a polymeric matrix (that may comprise an ionically conductive material),optionally further including electrically conductive particles distributed therein. The positive electroactive material may comprise sulfur, as will be described further below.

[0058] Thus, the positive electrode 22 may be formed from a sulfur-based or lithium- based electroactive material that can undergo lithium cycling (e.g., plating and depleting or intercalation and deintercalation) while functioning as the positive terminal of the battery 20. In certain aspects, the positive electrode 22 may include elemental sulfur or a sulfur-containing compound as an electroactive material. For example, lithium-sulfur cathode active materials can be formed by compounding sulfur or sulfur-containing compounds with host or matrix materials that can enhance electrochemical performance including specific capacity, cycle and rate performances, and conductivity.

[0059] In certain aspects, a positive electrode material for a lithium- sulfur electrochemical cell comprises a sulfur host material configured to receive a sulfur electroactive material that cycles lithium ions. Carbon-based materials are common sulfur carriers and thus can form suitable host materials for positive electroactive sulfur-based materials, as can metallic compounds, metal oxides, and other conductive materials, like conductive polymers. Thus, host materials for sulfur or sulfur compounds may include a variety of different materials, including by way of example, carbon nanotubes, hierarchical porous carbon, hollow structured carbon, graphene, reduced graphene oxide, manganese oxide (MnC ), titanium oxide (TiC ), iron oxide (Fe2O3), vanadium pentoxide (V2O5), cobalt sulfides (e.g., C0S2, CogSs), titanium sulfide (TiS), titanium carbide (Ti2C), and combinations thereof. In one non-limiting variation, a high surface area lithium- sulfur nanocapsule can be used. The sulfur cathode material can be fabricated or is commercially available from NEI Corp., by way of non-limiting example.

[0060] In other alternative aspects, the positive electrode 24 may be formed of a positive electroactive material 36 used for a traditional lithium-ion battery that is one of a layered-oxide cathode, a spinel cathode, or a polyanion cathode. Various conventional positive electrodes / cathodes may be made from lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel manganese cobalt oxides (NMC), lithium iron phosphate (LFP), lithium nickel cobalt aluminum oxide (NCA), lithium titanate (LTO), and the like. By way of nonlimiting example, such positive electroactive particles may comprise one or more positive electroactive materials selected from the group consisting of: LiM CU (LMO), LiNixMni.sO4, LiCoO2 (LCO), LiNixMnyCoi-x-yO2 (where 0 < x < 1 and 0 < y < 1, NMC), LiNixM .x02 (where 0 < x < 1), LiNiMnCoAlO2(NCA), Lii+XMO2(where 0 < x < 1), LiFePO4(LFP), LiVPO4, LiV2(PO4)3, Li2FePO4F, Li3Fe3(PO4)4, Li3V2(PO4)F3, LiFeSiO4, NaCoO2, NaNixMnyCoi-x.yO2(where 0 < x < 1 and 0 < y < 1), NaNixMni-xO2 (where 0 < x < 1), Nai+XMO2 (where 0 < x < 1),NaMi C , NaNixMni.504, NaFePCU, NaVPCU, NaV2(PO4)3, Na2FePO4F, Na3Fe3(PO4)4, Na3V2(PO4)F3, NaFeSiCU, equivalents and combinations thereof.

[0061] The positive electroactive materials may be powder compositions. The positive electroactive materials may be intermingled with an optional electrically-conductive material (e.g., electrically-conductive particles that provide an electron conduction path) and a polymeric binder. The polymeric binder may hold together the positive electroactive material particles, as well as providing ionic conductivity to the positive electrode 24. Thus, in certain variations, the positive electroactive particles may be optionally intermingled with one or more electrically conductive materials and / or a polymeric binder material as a matrix for the solid-state particles.

[0062] Electrically conductive materials may include, for example, carbon-based materials, nickel powder or other metal particles, or a conductive polymer. Examples of carbonbased particles may include, for example, graphite, acetylene black (such as KETCHEN™ black or DENKA™ black), graphene, carbon fibers and nanotubes, and the like. Examples of a conductive polymer may include polyaniline, polythiophene, polyacetylene, polypyrrole, and the like. In certain aspects, mixtures of the conductive materials may be used.

[0063] The polymeric binder materials may include polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), poly(vinyl alcohol) (PVA), ethylene propylene diene monomer (EPDM) rubber, nitrile butadiene rubber (NBR), poly(diallyldimethylammonium chloride) (PDDA), styrene-butadiene rubber (SBR), lithium polyacrylate (LiPAA), and / or sodium polyacrylate (NaPAA) binders, by way of example.

[0064] The positive electrode 22 may include greater than or equal to about 50 wt.% to less than or equal to about 95 wt.%, optionally greater than or equal to about 65 wt.% to less than or equal to about 90 wt.%, and in certain aspects, optionally greater than or equal to about 70 wt.% to less than or equal to about 90 wt.% of the electroactive materials. In certain aspects, the positive electrode 22 may have a relatively high active material loading of sulfur-based electroactive material, for example, optionally greater than or equal to about 50% to about 70% of sulfur, at greater than or equal to about 3 mg sulfur / cm2(or 2.8 mAh / cm2) up to about 15 mg sulfur / cm2(or 8.7 mAh / cm2, optionally greater than about 6 mg sulfur / cm2(or 5.9 mAh / cm2) or optionally greater than or equal to about 7.5 mg / cm2(or 6.7 mAh / cm2)), so that a specific capacity may be greater than or equal to about 900 mAh / g, optionally greater than or equal to about 1100 mAh / g, optionally greater than or equal to about 1200 mAh / g, optionally greater than or equal to about 1250 mAh / g, optionally greater than or equal to about 1300 mAh / g, and in certain aspects, optionally greater than or equal to about 1400 mAh / g.

[0065] The positive electrode 22 may include greater than or equal to about 0 wt.% to less than or equal to about 25 wt.%, optionally greater than or equal to about 0 wt.% to less than or equal to about 15 wt.%, and in certain aspects, optionally greater than or equal to about 0 wt.% to less than or equal to about 15 wt.% of the one or more electrically conductive additives 38 and greater than or equal to about 0 wt.% to less than or equal to about 20 wt.%, optionally greater than or equal to about 0 wt.% to less than or equal to about 15 wt.%, and in certain aspects, optionally greater than or equal to about 0 wt.% to less than or equal to about 15 wt.% of the one or more binders. In one example, an electroactive material may be present in the positive electrode 22 at about 70 wt.% with about 15 wt.% electrically conductive carbon particles, and about 15 wt.% binder.

[0066] The negative electrode 24 may comprise a negative electroactive material, which may be in the form of a solid film or alternatively a composite electrode like that described above in the context of the positive electrode but comprising a plurality of negative electroactive material particles. In certain aspects, the negative electrode 24 may include lithium, and in certain variations, comprising only metallic lithium (e.g., > 99% lithium) in the form of a lithium metal electrode (LME). The negative electroactive material may be a material that comprises lithium or an alloy of lithium, for example.

[0067] In addition to lithium / lithium- alloys, other electrochemically active materials for forming an anode include lithium-graphite intercalation compounds, lithium-silicon alloying compounds, and lithium-tin alloying compounds. For example, graphite or other electroactive carbon-based active materials can be used, or silicon, silicon-containing alloys, tin-containing alloys, and combinations thereof. By way of example, electroactive material particles comprising silicon may include silicon, or silicon containing binary and ternary alloys and / or tin-containing alloys, such as Si-Sn, SiSnFe, SiSnAl, SiFeCo, SnCh, and the like. Another suitable anode material includes lithium titanate oxide (Li TiOa - LTO). Where the negative electroactive materials are provided in a composite negative electrode, they may be intermingled with a polymeric binder and optionally electrically conductive particles like those specified above in the context of the positive electrode.

[0068] In accordance with certain aspects of the present disclosure, a separator layer 26 is disposed between the positive electrode 22 and negative electrode 24. The separator layer 26 prevents physical contact and electrically isolates the positive electrode 22 and negative electrode 24 — and further is suitable for conducting ions (e.g., lithium ions). The separator layer 26 is sprayed onto and thus integrally formed onto the positive electrode 22 and comprises a plurality of polymeric nanofibers, such as ANF fibers. For example, such nano fibers maycomprise aromatic polyamide (aramid) nanofibers (ANFs). Suitable aromatic polyamide (aramid) nanofibers may be KEVLAR™ microfibers (generally formed by the copolymerization of benzene- 1,4-diamine and terephthaloyl dichloride). Kevlar™ is commercially available from DuPont and has exceptionally high strength and stiffness, for example, with a tensile strength of 3.6 GPa and Young’s modulus of approximately 90 GPa. Macroscale fibers of aramid also display a high tensile strength to weight ratio making these material particularly suitable for lightweight and safe batteries. Mechanical properties of ANF-based ion conductive membranes formed in accordance with certain aspects of the present disclosure are more favorable than those of cellulose nanofibers or carbon nanotubes.

[0069] Aramid nanofibers can be formed by controlled reaction of microfibers or precursors of microfibers at low temperatures for extended times in a carrier, such as an aprotic solvent, optionally in the presence of a base, at relatively low concentrations, relatively low temperature, or lower time than the conditions for formation of unbranched ANFs that represent the product of nearly full separation of microscale aramid fibers into fibrils. Aromatic polyamide (aramid) nanofibers used in certain variations may be made from KEVLAR™ microfibers (generally formed by the co-polymerization of benzene- 1,4-diamine and terephthaloyl dichloride) that may be formed by high-energy agitation in DMSO. In certain variations, the fiber may have an average diameter of greater than or equal to about 3 nm to less than or equal to about 50 nm, optionally greater than or equal to about 3 nm to less than or equal to about 30 nm, and in certain aspects, optionally greater than or equal to about 10 nm to less than or equal to about 15 nm. ANFs may have a relatively high aspect ratio (AR) = L / D, where L is the length of the longest axis (here a major longitudinal axis of the fiber) and D is the diameter of the fiber, for example, exceeding about 100:1.

[0070] Such ANFs may be formed by way of example, by dispersing a KEVLAR™ precursor, such as a thread or bulk KEVLAR™ pulp commercially available from DuPont Co. in an aprotic solvent, such as dimethyl sulphoxide (DMSO), and stirred at room temperature at high speeds. After 2 hours, the dispersion can be collected and placed in a centrifuge to spin, for example, at 10,000 rpm for 10 minutes. ANFs are thus formed and may be further washed.

[0071] Then, the prepared nanofibers 30 may be mixed with a liquid to form a dispersion. The liquid may be a polar aprotic solvent like dimethyl sulfoxide (DMSO), acetonitrile, low boiling point organic solvents, such as diethyl ether, low viscosity organic solvents, such as isopropyl alcohol, and combinations and equivalents thereof. In certain aspects, a base, such as potassium hydroxide (KOH), may be mixed in with the liquid and nanofibers. KOH provides OH ions to attack hydrogen (H) bonds and plays a key role in thedeprotonation of Kevlar™ / aramid fibers. As noted above, in certain aspects, the aramid nanofibers (ANF) may be branched aramid nano fibers. The aramid nano fibers (ANF) may be present in the liquid dispersion at greater than or equal to about 0.05 weight % to less than or equal to about 5 weight %, for example, at about 2 weight %. A suitable dynamic viscosity of ANF dispersion in DMSO and KOH may be as low as 2cP at room temperature (e.g., 21° C) the highest dilution.

[0072] The liquid mixture comprising the nanofibers is then sprayed onto a positive electrode 22. As noted above, the positive electrode 22 may be a porous composite so that the sprayed liquid may coat the surface and optionally infiltrate pores on the surface or even penetrate a distance into the positive electrode 22. This facilitates formation of a highly integrated interface between the positive electrode 22 and the sprayed separator layer 26 that exhibits low interfacial resistance. In one example, 2 grams of KEVLAR™ thread and 2 grams of potassium hydroxide (KOH) is mixed in 100 mL DMSO for 2 wt. % ANF dispersion. As noted above, by adding low boiling temperature organic solvents to the admixture, this can accelerate drying that is beneficial for the spray coating process. Further, certain solvents may be used to reduce viscosity of the admixture / dispersion with the nanofibers, such as isopropyl alcohol. Further, viscosity of the admixture may be reduced by reducing an aspect ratio or average thickness of the nanofibers. Thus, the process may further involve removing the liquids from the sprayed dispersion, for example, by applying heat, radiation, and / or reduced pressure (e.g., vacuum) to accelerate volatilization of the liquids and drying.

[0073] The spraying may be achieved by a sprayer device at a spray station where the liquid dispersion is drawn (e.g., pumped) into a spray head having a nozzle. The liquid dispersion may pass through the nozzle concurrently with a pressurized gas, such as air, to form an atomized spray that is deposited onto the target (active material layer). In certain variations, the spraying may be automated, for example, the spray head and nozzle may be robotic, for example, disposed on a robotic arm that may be controlled via a computer numerical controller (CNC) device.

[0074] The nanofibers 30 create a porous network with open pores that may be filled with the polymer matrix 32. Further, to enhance ion conducting properties of the separator 26, ion conductive materials, such as nanoceramic particles, can be introduced into the 3D network of nanofibers to introduce ion hopping paths within the structure.

[0075] Notably, the spraying and formation process in situ on a positive electrode described herein facilitates an enhanced bonding and reduced interfacial resistance as compared to two separately formed layers joined together via lamination, calendaring, or other adhering orbonding techniques commonly used in fabricating batteries. The separator layer 26 is different in composition from a conventional polymeric separator used in lithium-ion or lithium- sulfur batteries, for example, a polyolefin-based microporous separator. Conventional ion-conducting membranes compatible with rapidly expanding battery markets, like electric vehicles, are based on polyolefins and are commercially available from Celgard as CELGARD™ separators. Most commonly, triple layer CELGARD™ membranes, those with polypropylene sheets sandwiched between two sheets of polyethylene, are used because they are compatible with current manufacturing requirements of roll-to-roll (R2R) processing. However, these conventional polyolefin separators are suboptimal for LiS chemistry because of their large pore size, inability to repress LPS shuttling, and relatively large (e.g., 20 micrometers or greater thickness).

[0076] Instead, in accordance with the present teachings, the separator layer 26 may comprise a plurality of nanofibers 30, such as aramid nanofibers (ANF) and optionally may further comprise a matrix of polymeric material 32. The polymeric material 32 may be selected from binders, like poly vinylidene difluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene oxide (PEG), poly (vinyl alcohol) (PVA), ethylene propylene diene monomer (EPDM) rubber, or carboxymethyl cellulose (CMC), a nitrile butadiene rubber (NBR), poly(diallyldimethylammonium chloride) (PDDA), styrene-butadiene rubber (SBR), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, and the like. The sprayed separator layer 26 may be relatively thin, for example, having a thickness of less than or equal to about 10 micrometers, optionally less than or equal to about 5 micrometers, optionally less than or equal to about 3 micrometers, optionally less than or equal to about 2 micrometers, an in certain variations, preferably less than or equal to about 1 micrometer. In certain further variations, the sprayed separator layer 26 may have a thickness of optionally less than or equal to about 900 nm, optionally less than or equal to about 800 nm, optionally less than or equal to about 700 nm, optionally less than or equal to about 600 nm, optionally less than or equal to about 500 nm, optionally less than or equal to about 400 nm, optionally less than or equal to about 300 nm, optionally less than or equal to about 200 nm, an in certain variations, optionally less than or equal to about 100 nm. In certain variations, a submicron thickness (e.g., < 1 micrometer) of the separator layer can enable a sulfur battery with a low an electrolyte-to-sulfur ratio (E / S) ratio (e.g., < 5 pl / mg) and high S loading (e.g., > 5 mg / cm2), resulting in high energy density batteries. Such sprayed separator layers at submicron thicknesses can also offer a competitive performance due to low interfacial resistance, high electrolyte wettability, and high ionic conductivity.

[0077] The sprayed separator layer 26 may have a relatively low porosity and have small pores sizes, for example, in the single nanometer range (e.g., less than 10 nm), which is smaller than the diameter of lithium dendrites. In certain aspects, the porosity of the sprayed separator layer 26 may be greater than or equal to about 1 vol.% to less than or equal to about 40 vol.%, and in certain aspects, optionally greater than or equal to about 5 vol. % to less than or equal to about 25 vol.%, for example, about 18 vol. %.

[0078] In this manner, an integrated electrode- separator component 34 is defined by the positive electrode 22 and the sprayed separator layer 26, for example, formed from aramid nanofibers (ANF). As will be described below, an interfacial resistance at an interface 36 between the sprayed layer / separator 26 and the active material layer / cathode 22 is low, for example, less than or equal to about 40 Q-cm2, optionally less than or equal to about 30 Q-cm2, optionally less than or equal to about 20 Q-cm2, and in certain variations, optionally less than or equal to about 10 Q-cm2. The sprayed-on separator layer 26 may have an ionic conductivity of greater than or equal to about 1 x IO"4S / cm, optionally greater than or about 5 x 10'4S / cm, and in certain variations, optionally greater than or equal to about 1 x 10'3S / cm, optionally having a resistance of less than or equal to about 10 Q-cm2and an electrical resistivity of greater than or equal to about 2.1 Q.

[0079] Both the positive electrode 22 and the separator layer 26 may be porous or have voids defined therein. The open pores may define a network through the separator 26. At least a portion of the pores of the separator layer 26, and optionally of the positive electrode 22, are filled with an electrolyte 28, which may be a liquid electrolyte or a solid state electrolyte particle, which helps to transport ions therethrough. Where the electrolyte is a solid electrolyte, it may be sprayed onto the positive electrode during formation of the separator layer 26. A liquid electrolyte may be imbibed into pores of the separator layer 26.

[0080] A composite electrode may be made by slurry casting, where the electrode active material, such as a sulfur-containing electroactive material, is formed into a slurry by combining it with a polymeric binder compound, a liquid, such as a non-aqueous solvent, optionally a plasticizer, and optionally electrically conductive particles. The slurry can be mixed and then cast, for example, by being thinly applied to a substrate e.g., via a doctor blade). The substrate can be a functional substrate, such as a current collector (such as a foil, metallic grid, or mesh layer) attached to one side of the electrode film. In one variation, heat, radiation, or negative pressure can be applied to evaporate the solvent from the electrode film, leaving a solid residue. The electrode film may be further consolidated, where heat and pressure are applied to the film to sinter and calendar it. In other variations, the film may be air-dried at moderate temperatures.In variations where the substrate is removable rather than functional, it is removed from the electrode film that is then further laminated to a current collector. With either type of substrate, it may be necessary to extract or remove the remaining plasticizer prior to incorporation into the battery cell.

[0081] In solid-state batteries, the solid-state electrolyte 28 may be solid state particles disposed between solid-state electrodes (positive electrode 22 and negative electrode 24), where the solid-state electrolyte 28 and separator 26 physically separates the respective electrodes and can thus serve as a separator and ionic conductor, so that a distinct conventional polymeric separator is not required. In other variations, the electrolyte 28 may be a non-aqueous liquid electrolyte solution that includes a salt, such as a lithium salt, dissolved in an organic solvent or a mixture of organic solvents. In certain variations, an electrolyte-to-sulfur ratio (E / S) ratio of a lithium-sulfur battery prepared according to certain aspects of the present disclosure may be less than or equal to about 8:1.

[0082] A positive electrode current collector 38 may be in electrical communication with the positive electrode 22 and thus positioned adjacent to or near the positive electrode 22. The positive electrode current collector 38 and the positive electroactive layer / positive electrode 22 together may be considered to form a positive electrode assembly. The positive electrode current collector 38 may be formed from aluminum (Al) or any other suitable electrically conductive material known to those of skill in the art.

[0083] Likewise, a negative electrode current collector 40 may be in electrical communication with the negative electrode 24 and thus positioned adjacent to or near the negative electrode 24. The negative current collector 40 may be formed of copper (Cu), nickel (Ni), alloys thereof, or any other suitable electrically conductive material known to those of skill in the art. The positive electrode current collector 38 and the negative electrode current collector 40 move free electrons to and from an external circuit 42 that may include a load device 44. For example, the battery 20 can generate an electric current during discharge when electrochemical reactions occur. The chemical potential difference between the positive electrode 22 and the negative electrode 24 drives electrons produced at the negative electrode 24 through the external circuit 42 towards the positive electrode 22.

[0084] The negative electrode current collector 40 and the negative electroactive layer / negative electrode 24 together may be considered to form a negative electrode assembly. The positive electrode current collector 38 and the positive electroactive layer / positive electrode 24 along with the separator layer 26 may all be considered to form a positive electrode assembly.

[0085] Ions, which are also produced at the negative electrode 24, are concurrently transferred through the separator 26 and electrolyte 28 towards the positive electrode 22. While in lithium-ion batteries, lithium intercalates and / or alloys in the electrode active materials, in a lithium-sulfur battery, instead of intercalating or alloying, the lithium dissolves from the negative electrode 24 and migrates to the positive electrode 22 where it reacts and / or plates during discharge, while during charging, lithium plates on the negative electrode 24. Electric current passing through the external circuit can be harnessed and directed to a device until the reaction in the negative electrode 24 is depleted or completed and the capacity of the battery is diminished.

[0086] When the battery 20 is rechargeable and is capable of undergoing reversible electrochemical reactions, the rechargeable battery can be charged or reenergized by connecting to an external power source (for example, a charging device) to reverse the electrochemical reactions that occur during battery discharge. The connection of the external power source to the battery 20 causes a reaction at the positive electrode 22 to produce electrons and ions. The electrons, which flow back towards the negative electrode 24 through the external circuit, and the ions, which move across the solid-state electrolyte 26 back towards the negative electrode 24 combine at the negative electrode 22 to replenish it for reaction during the next battery discharge cycle. Each discharge and charge event is considered to be a cycle in a rechargeable battery, where ions are cycled between the positive electrode 22 and the negative electrode 24.

[0087] In many of the configurations of the battery 20, each of the negative electrode current collector 40, the negative electrode 24, the separator 26, the electrolyte 28, the positive electrode 22, and the positive electrode current collector 38 are prepared as thin layers (for example, from several microns to a millimeter or less in thickness) and assembled in layers electrically connected in parallel or series arrangements (e.g., in a stack) to provide greater voltage output, energy, or power as required. The battery 20 may include a variety of other components not shown in FIG. 1, such as gaskets, casings, terminal caps, and any other conventional components or materials that may be situated within the battery 20. The battery 20 can be used to provide electrical energy to a variety of known electrically-powered devices, including by way of non-limiting example, robots, drones, satellites, prosthetic devices, vehicles, consumer products (e.g., wearable electronics, laptops, mobile devices, cellular phones), power tools, appliances, and the like.

[0088] As background, technical parameters required for electric vehicle (EV) batteries established by US American Battery Consortium (USABC) are outlined in Table 1.

[0089] TABLE 1

[0090] While electric vehicles (EVs) represent an essential part of a future world economy, such technical requirements for EV batteries are demanding. For example, they need to charge to more than 80% in less than 15 minutes and last for more than 500 cycles (Table 1). Lithium-ion chemistries with transition metal oxide cathodes dominate the current market, owing to their high energy density. Nickel and cobalt are costly and frequently mined in unsafe conditions and imported into the U.S. Therefore, manufacturer-friendly batteries chemistries reducing the dependence on problematically sourced transition metals are needed for energy storage and transportation technologies. As noted above, lithium-sulfur (LiS) batteries represent a technologically attractive alternative to metal oxide-based energy storage.

[0091] In various aspects, aramid nanofibers (ANFs) are made from readily available KEVLAR™ thread in a one-pot process of dissolution in basic DMSO, as described previously above. By way of example, ANF dispersions can be formed by mixing KEVLAR™ thread, a base, like KOH, and DMSO together. ANFs having a small diameter, for example, an average diameter of individual ANF nanofibers with greater than or equal to about 3 nm to less than or equal to about 30 nm as well as their high aspect ratio, exceeding 100: 1, and high flexibility makes this easily accessible nanomaterial easily dispersible in a variety of solvents. The same properties also make ANFs easily processable into thin films by spraying. Their unique branched morphology results in tightly interconnected network of nanofibers for which porosity can be controlled. Low porosity states of ANF ion-conducting membranes possess pore sizes in the single nanometer range, which is smaller than the diameter of dendrites. Combined with high strength and toughness, these unique characteristics makes ANF particularly attractive for high-performance separators. Spray deposition of ANFs can be easily implemented in current production lines of mega- and giga-scale battery factories. ANF-based separators incorporatedinto an LiS battery in accordance with certain aspects of the present disclosure produces excellent battery performance, as shown in Table 2.

[0092] Table 2

[0093] Additional comparison can be made based on data. ANF-based separators display some of the lowest capacity decay rates due to their nanometer-scale pore size and ability to reject diffusion of LPS species. In sum, ANF-based separators prepared in accordance with certain aspect of the present disclosure address LiS battery challenges and are compatible with large-scale manufacturing, for example, manufacturing at gigafactories.

[0094] In various aspects, the present disclosure contemplates spray-coating of ANFs onto cathodes, such as sulfur cathodes, in an R2R process. Resulting integrated electrodeseparator components (e.g., cathode units) formed in this manner serve as drop-in replacements for separate cathode and separator sheets in conventional batteries. This streamlines the manufacturing of top-performing, reliable and affordable LiS batteries. It is expected that pressurized pouch cells will demonstrate energy density > 500 Wh / kg, capacity of >250 Wh / kg, and cycle life >1,000 with 80% capacity retention, meeting the US American Battery Consortium (USABC) targets (see e.g., Table 1). Further, the integrated electrode- separator component may be used with LiS chemistry for EVs by assembling and testing a functional battery pack. It is estimated that this battery pack will result in an approximate 31 % cost and 19.4% mass savings as compared to an NMC battery of comparable capacity.

[0095] Examples

[0096] Spray coating in accordance with certain aspects of the present disclosure is readily integrated into current commercial R2R production lines. In this example, ANFs are directly sprayed on cathode substrates obtained after the deposition and drying of the carbonsulfur slurries, as shown in FIG. 2. This process creates integrated cathode and separator rolls (SCAN rolls) that can be sold to battery manufacturers and converted into pouch cells. ANF separators together with film of sulfur-carbon materials can be continuously quality controlled using laser profilometers.

[0097] An ANF dispersion is prepared as follows in an adapted process of the Yang- Kotov method described in Yang, et al., Dispersions of Aramid Nanofibers: A New Nanoscale Building Block, ACS Nano, Vol. 5, No. 9, pp. 6945-6954 (2011), the relevant portions of which are incorporated by reference herein. Briefly, 2 g of KEVLAR™ thread and 2 g of potassium hydroxide (KOH) is mixed in 100 mL DMSO for 2 wt. % ANF dispersion. This method may be modified by adding low boiling temperature organic solvents to accelerate drying that is beneficial for spray coatings.

[0098] The sulfur-carbon cathode film with variable sulfur loading is fabricated using standard melt-diffusion methodology. Super P carbon black powder and sulfur (S) powder are mixed by milling, for example, at a mass ratio of about 3:6. The mixture may be placed in a stir tank at 155 °C for 10 hours to incorporate sulfur into the carbonaceous matrix. The cathode slurry is then prepared by mixing 90 wt. % sulfur / carbon composite and 10 wt. % poly(vinylidene fluoride) binder in N-methylpyrrolidone (NMP) solvent. The cathode is formed by coating the slurry on aluminum foil and drying, as shown in FIG. 2. More specifically, the process is a roll-to-roll (R2R) process that beings with cathode slurry coating on a current collector roll that enters an oven for drying, followed by calendaring between rolls, where the roll then enters a spraying station where the ANF separator layer is sprayed on, followed by entering a second oven for drying, with a quality control station with a laser, and then a collection station where the integrated electrode- separator component (SCAN) may be rolled. The sulfur loading in the cathode can be varied, for example, from between about 3 to about 6 mg / cm2by adjusting coating thickness, in certain aspects.

[0099] A spraying system using a spray device 50 (a partial sectional view is shown in FIG. 3) can deposit ANFs from a liquid dispersion or suspension on a cathode substrate 54. Initially, one or more spray nozzles 60 (B1 / 4J Spraying Systems) are connected to a liquid pump (M50, Valeo Instruments Co.) and an air flowmeter (Red-Y, Vbgtlin Instruments GmbH). The spray device 50 includes the nozzle 60, along with a liquid feed line 62, and a pressurized gas / air feed 64. The liquid feed line 62 combines with the pressurized gas / air at the outlet 66 of the spray device to form atomized spray droplets 68 including the ANF fibers. These atomized spray droplets 68 are directed towards the cathode substrate 54, where they are deposited. More specifically, an ANF suspension (e.g., 0.5% in DMSO) is transferred to the nozzle 54 via the liquid feed line 62 by the liquid pump (not shown) at a controlled flow rate (e.g., about 5 mL / min). Compressed air, for example, at a flow rate of 10 L / min regulated by the flowmeter can be simultaneously injected to the nozzle 60 via the pressurized gas / air feed 64, creating an atomized cloud of the ANF suspension as the atomized spray droplets 68. The suspension can besprayed onto the substrate 54 (positive electrode) at a distance, for example, of approximately 10 cm. The films are dried, for example, in an environment having a temperature of about 70°C for an optimal length of time, so that the spraying process is integrated into existing R2R hardware, for example. The distance, flow rates, air pressures and the hardware can be adjusted depending on the scale and the required rate of the deposition.

[0100] FIGS. 7A-7B show SEM images after spraying of ANFs as described above as a 3D network that defines an integrated porous layer with the underlying electrode active material.

[0101] Unlike current technologies, separator layer thickness prepared in accordance with various aspects of the present disclosure is not constrained by requirements of folding, packaging, transportation, and the like. Direct spraying allows uniform coating, control of thickness, formation of uniform defect-free layers, and deposition to thicknesses as low as 200 nm, although thicknesses may be larger, for example, between about 2 micrometers to 10 micrometers. The integrated electrode- separator component provided by the methods described herein also allows fine control of separator porosity to maximize performance at a wide range of current rates during battery operation.

[0102] In certain aspects, quality control can be conducted as follows. Laser 3D surface profilometers are implemented as rapid, in-line noninvasive quality control tool for high scale manufacturing of integrated electrode- separator component (SCAN) rolls formed according to certain aspects of the present teachings. Laser profilometers afford rapid assessment of the thickness and roughness of multiple layers on the surface. The quality exemplified by the 3D surface profiler image of ANE coating (at an approximate 800 nm thickness) in the process of drying on commercial sulfur-carbon cathode is shown in the inset on the right of EIG. 2.

[0103] Eabrication and testing of coin and pouch cells, for example having 400 mAh cells, incorporating an integrated sprayed on separator-cathode component can be conducted. A pouch cell is assembled and tested. Imported commercially available pouch cells, such as LG Chem E66A (dimensions: 350 mm x 104 mm x 11.7 mm) are used in EV modules. Similar size pouch cells may be fabricated by assembling all the components, including the integrated separator-cathode component (SCAN), lithium metal anode, and separator stack, leading to the housing, covering, sealing of the pouch cells as well as adding insulation and the safety valves. The pouch cells are tested through a qualified end of life (EOL) testing to ensure the quality of the pouch cells. 400 mAh, lAh, and eventually lOAh cells are contemplated. Performance of assembled cells may be evaluated with the following tests.

[0104] Battery capacity and cyclic stability of the assembled cells may be tested within a voltage window of 1.7 V to 2.8 V using the MACCOR battery-testing instrument. The capacities can be calculated based on the mass of sulfur in the cathode.

[0105] Both Electrical Impedance Spectroscopy (EIS) and cyclic voltammetry (CV) can be performed on a Metrohm Autolab Potentiostat: EIS can be carried out in the range from 100 kHz to 0.05 Hz with a potential amplitude of 20 mV. The resulting Nyquist plots may be fitted to an equivalent circuit where ionic conductivity is then calculated from the equation: G= L / RbA, where L is the thickness of the film, Rb is the bulk resistance, and A is the contact area of the coated layer. CV is scanned at a rate range of 0.10 to 0.50 mV / s.

[0106] Abuse or battery safety tests, including nail penetration, may also be performed to ensure safety of assembled pouch cells.

[0107] Assembly and testing of a battery pack module is as follows. First, cells are stacked in module housing and the pouch cells are connected via a bus bar and then tested for an open circuit voltage (OCV) and GCD tests. A dedicated and computer-controlled cooling system, as well as the battery management system (BMS), will be installed with the battery modules. 200 x 10 Ah pouch cells will be assembled to make 4kWh commercial battery module. The module can be tested for its capacity and cyclic stability. Module running time, as well as the temperature, can also be continuously monitored with integrated thermal probes.

[0108] Safety and module management testing can also be performed. This involves continuous monitoring and balancing of the assembled cells, the safety control during the charge / discharge, and the communication of the module and battery pack with the external units. As the system involves several cells that are connected in series / parallel to deliver a high energy and power density, safety testing may be conducted.

[0109] Assembly and testing of functional commercial battery pack. A commercial vehicle model has 65 kWh battery with 288 pouch cells. This can be replaced with 12 modules of the integrated electrode- separator component (SCAN) pouch cells prepared in accordance with the present disclosure. Following battery assembly, the pack can be integrated into the vehicle for on road battery performance tests.

[0110] A series of the following tests and technology proof-of-concept demonstrations indicate feasibility of the integrated electrode-separator component (SCAN) technology and its scalability to R2R process. The tests include all key elements of the workflow described in FIG. 2, namely scalable preparation of ANF dispersion, preparation of sulfur-carbon cathode substrates; preparation of ANF layer on them by spraying from DMSO dispersions; testing of their performance in cells and their comparison with the state-of-the-art separators.

[0111] The preparation of ANF dispersions may be scaled up as follows. The Yang- Kotov method discussed above was adapted for a stir- tank reaction and can produce 1000 kg scale dispersions. One batch of ANF dispersions can be prepared rapidly over the course of 20 minutes by taking advantage of uniquely efficient delamination of polymer nanofibrils containing KEVLAR™ macrofibers by adding a co- solvent. Simultaneously their concentration can be increased 10 times, which can be useful for solvent replacement.

[0112] ANF Layers are formed on LiS Cathodes as follows. Spray-on coating of separator layers comprising ANF deposited directly onto cathode surfaces is shown in FIGS. 4A-4D. Commercial cathodes and those made in accordance with certain aspects of the present disclosure described above were utilized in these tests. ANFs were sprayed from DMSO dispersions with KOH forming a uniform layer with a continuous defect- free thickness of approximately 210 nm, as shown in FIGS. 4A-4B. Such spraying conditions provide a defect free layer of ANF coating as shown in FIG. 4C, without damaging sulfur cathode active material as shown in FIG. 4D.

[0113] Tunability of pore size of ANF layers enables dendrite suppression, high sulfur loading, and increased energy density. The ability to adjust pore size provides the flexibility for LiS batteries to meet the needs of specific EV models and enables scalable R2R-manufacturing of SCAN rolls for a wide array of battery applications, including but not limited, lithium iron phosphate (LFP) and other cathodes.

[0114] Charge storage performance of integrated electrode-separator component (SCAN) cell prototypes. The spray-on ANF layer made by SCAN technology was demonstrated to dramatically decreases ionic impedance (FIG. 5A) and enhance cycling performance of LiS batteries. For example, up to 1453 mAh g'1discharge capacity is obtained at 0.1C (FIG. 5B) meeting FOA requirements as set forth in Table 3. It is expected that current densities will exceed 10 mA / cm2and areal capacities will exceed 10 mAh / cm2, thereby reducing EV charging time by at least a factor of two. It was found that the ANF separator layer also effectively screens and captures LPS as shown in FIGS. 6A-6C, preventing their diffusion to anode, which is known to cause rapid decay of capacity in LiS batteries. FIGS. 6A-6B show comparative LPS diffusion test for cycled sulfur cathode and integrated electrode- separator component (SCAN) cathode at a start in FIG. 6A and 96 cycles later in FIG. 6B. FIG. 6C is an SEM image of ANF coating on the surface of SCAN cathode after 100 cycles, which has a small pore size and uniform coating.

[0115] It is noted that an important commercial and manufacturing advantage of the present technology with an integrated electrode- separator component (SCAN) compared toconventional polyolefin based CELGARD™ and other advanced separators is that the ANF coating forms a protective layer on the surface of cathode active materials and keeps it from degrading.

[0116] The ability of the ANF-based integrated electrode- separator component (SCAN) technology to successfully address challenges of EiS batteries has also been demonstrated for free-standing ANF separators (for example, having an approximate 5 micrometer thickness) in low-porosity state similar to the one in FIG. 5C. It is found that they exhibit a capacity of 1268 mAh g'1at 0.1C at 1.2 mg cm'2S loading. This battery can reach up to 500 cycles at 0.2 C at 5.8 mg cm'2sulfur loading and more than 3500 cycles at 3C at 1.2 mg cm'2sulfur loading. This approaches the theoretical limit for EiS batteries and exceeds the performance of many other cells. ANF-based separators also allow better high temperature performance as compared to conventional CEEGARD™ polyolefin separators. Furthermore, at a high sulfur loading level, for example, about 5.8 mg / cm needed for EVs, capacity retention is very low due to enhanced electronic and ionic impedance proportionally with the increased thickness for such conventional separators.

[0117] Cell-level performance of integrated electrode- separator component (SCAN) batteries and FOA Technical Performance Targets are shown in Table 3.

[0118] Table 3

[0119] In certain variations, examples of electrode and separator parameters are shown in Tables 4 and 5, respectively.

[0120] Table 4

[0121] Table 5

[0122] In certain aspects, the present disclosure contemplates spray-deposition of ANF- based ion conductor layers onto sulfur cathodes, providing high cycle stability, current density, and cycle life. Such spray deposition can integrated into R2R manufacturing of separator- integrated sulfur-based cathodes. Sulfur-based cathodes can be integrated and adapted for different LiS cell designs.

[0123] FIGS. 8A-8D show comparative contact angles representing wettability for lithium-sulfur electrolytes. FIG. 8 A shows a spray-deposited cathode with aramid nanofibers (SCAN) integrated electrode-separator component prepared in accordance with certain aspects of the present disclosure, having a contact angle of about 9°. FIG. 8B shows a free-standing ANF separator layer (FIG. 8B) having a contact angle of about 11°. FIG. 8C shows a contact angle for a commercially available Celgard separator as being about 42°, while the Entek separator in FIG. 8D has a contact angle of about 34°. This data demonstrates that the ANF and SCAN coating exhibit high wettability and affinity with lithium-sulfur electrolytes compared to commercial separators such as those sold by Celgard and Entek.

[0124] In another example, a pouch cell having an integrated sulfur-based positive electrode / sprayed on separator component comprising a plurality of aramid nanofibers (SCAN) prepared in accordance with certain aspects of the present disclosure is prepared as follows and then tested over 500 cycles to test performance.

[0125] A sulfur cathode was fabricated using a traditional melt-diffusion method. In brief, carbon black and sulfur powder were mixed in a 1:2 ratio. The mixture was heated to 155°C for 10 hours in vacuum-sealed glassware. This process enables the sulfur to melt and diffuse into the carbon structures. A composite slurry was formulated by dispersing sulfur (60 wt.%) and carbon black (30 wt.%) into a PVDF solution (10 wt.%) using N-methyl-2- pyrrolidone (NMP) as the solvent. This slurry was uniformly coated onto an aluminum current collector using a doctor's blade. The sulfur loading was approximately 3.95 mg / cm2for the pouch cell test. A lithium-coated copper anode (MSE PRO Lithium (40 micrometers) and Copper (11 micrometers) Single Side Laminated Foil) is used and commercially available from MSE supplies.

[0126] The electrolyte comprises 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a 1:1 v / v mixture of 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) with 1wt.% lithium nitrate (LiNOs) as an additive to enhance the cycling stability by passivating the lithium surface.

[0127] All assembly steps were performed in a dry room with a dew point below -40 °C to minimize moisture contamination. Components were weighed and handled under anhydrous conditions to prevent parasitic reactions with lithium metal. The pouch cell design incorporated a single-layer configuration, with an SCAN-integrated cathode prepared in accordance with certain aspects of the present disclosure and the lithium coated anode.

[0128] The electrodes (anode 56 mm x 43 mm; cathode 58 mm x 45 mm) were enclosed in a pre-cut aluminum laminate pouch, and electrolyte was introduced using a syringe. The pouch was then sealed using a vacuum- sealing device to remove trapped air and ensure tight encapsulation.

[0129] Electrochemical Characterization of the assemble pouch is conducted as follows with results shown in FIG. 9. The assembled pouch cell underwent an initial formation cycle at a constant current density of 0.05 coulombs (C) to stabilize the electrode / electrolyte interfaces. Subsequent cycles were conducted at different rates, namely at 0.1 C, 0.2 C, 0.5 C, 1 C, and 2 C, to evaluate capacity retention and rate performance. The pouch cell, rated at 0.1 Ah, can stably cycle over 500 times with an initial maximum capacity of 1352 mAh / g at 0.1 C with an average Coulombic Efficiency of greater than about 99% over 500 cycles. The ion conductor integration into the cathode design fundamentally improves the long-term cycling stability of Li-S pouch cells and can be used for other lithium metal chemistries, including but not limited to, NMC and LFP.

[0130] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

CLAIMSWhat is claimed is:

1. A method of making an integrated electrode-separator component for a lithiumsulfur electrochemical cell, the method comprising: spraying a liquid dispersion comprising aramid nanofibers (ANF) onto an active material layer comprising at least one electroactive material to form a sprayed layer that defines an integrated electrode- separator component having an interfacial resistance between the sprayed layer and the active material layer of less than or equal to about 10 Q-cm2.

2. The method of claim 1, wherein the liquid dispersion comprises dimethyl sulfoxide (DMSO).

3. The method of claim 1, wherein the liquid dispersion comprises a solvent selected from the group consisting of: dimethyl sulfoxide (DMSO), acetonitrile, isopropyl alcohol, diethyl ether, and combinations thereof.

4. The method of claim 1, wherein the liquid dispersion comprises potassium hydroxide (KOH).

5. The method of claim 1, wherein the aramid nanofibers (ANF) are present in the liquid dispersion at greater than or equal to about 0.05 weight % to less than or equal to about 3 weight %.

6. The method of claim 1, wherein the method occurs on a roll-to-roll process and the active material layer is disposed on a first roll, so the method further comprises unrolling the active material layer from the first roll prior to the spraying and rolling the integrated electrodeseparator component that is processed via the spraying onto a second roll.

7. The method of claim 1, wherein the spraying is automated and occurs via a robotic arm.

8. The method of claim 1, further comprising applying one or more of heat, radiation, or reduced pressure to remove liquid from the liquid dispersion sprayed on the active material layer.

9. The method of claim 1, wherein the sprayed layer has a thickness of less than about 1 micrometer.

10. The method of claim 1, wherein the active material layer has a thickness of less than or equal to about 25 micrometers.

11. An integrated electrode- separator component comprising: an active material layer comprising at least one electroactive material; and a sprayed layer formed from aramid nanofibers (ANF) defining a separator, wherein an interfacial resistance between the sprayed layer and the active material layer is less than or equal to about 10 -cm2.The integrated electrode- separator component of claim 11, wherein the sprayed layer has an ionic conductivity of greater than or equal to about 1 x 10'4S / cm.

13. The integrated electrode- separator component of claim 11, wherein the sprayed layer has a thickness of less than or equal to about 1 micrometers and the active material layer has a thickness of less than or equal to about 20 micrometers.

14. The integrated electrode-separator component of claim 11 further comprising a current collector disposed adjacent to the active material layer.

15. The integrated cathode- separator component of claim 11, wherein the active material layer is a porous composite having the at least one electroactive material distributed in a polymeric matrix.

16. The integrated cathode- separator component of claim 11, wherein the at least one electroactive material comprises at least one sulfur positive electroactive material that cycles lithium ions.

17. A lithium- sulfur electrochemical cell comprising: a positive electrode comprising:a positive electroactive material layer comprising at least one sulfur positive electroactive material that cycles lithium ions; and a sprayed layer formed from aramid nanofibers (ANF) defining a separator, wherein an interfacial resistance between the sprayed layer and the positive electroactive material layer is less than or equal to about 10 Q-cm2; a negative electrode comprising lithium; and an electrolyte.

18. The lithium-sulfur electrochemical cell of claim 17, wherein the positive electrode further comprises a current collector comprising a metal selected from the group consisting of: aluminum, and combinations thereof.

19. The lithium-sulfur electrochemical cell of claim 17, wherein the positive electrode has an areal capacity of greater than or equal to about 10 mAh / cm2.

20. The lithium-sulfur electrochemical cell of claim 17, wherein the positive electrode has a current density of greater than or equal to about 10 mA / cm2.

21. The lithium-sulfur electrochemical cell of claim 17, wherein the positive electrode has a sulfur loading of greater than or equal to about 6 mg / cm2.

22. The lithium- sulfur electrochemical cell of claim 17 having an electrolyte-to- sulfur ratio (E / S) ratio of less than or equal to about 8:1.

23. The lithium-sulfur electrochemical cell of claim 17, wherein the positive electroactive material layer further comprises a polymeric binder that defines a porous composite having the at least one electroactive material distributed in a polymeric binder.

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