WO2023102122A1

WO2023102122A1 - Sulfur cathode binders

Info

Publication number: WO2023102122A1
Application number: PCT/US2022/051544
Authority: WO
Inventors: Stephen Burkhardt
Original assignee: Conamix Inc.
Priority date: 2021-12-02
Filing date: 2022-12-01
Publication date: 2023-06-08

Abstract

Cathodes for secondary sulfur batteries include an ionically conductive polymer binder. In certain embodiments, the ionically conductive polymer binder includes a polymer, a dopant, and an ionic compound. In some embodiments, the doped polymer binder is polyphenylene sulfide.

Description

SULFUR CATHODE BINDERS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63/285,280, filed on December 02, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] This disclosure relates to cathodes for secondary batteries or other energy storage devices, and methods of making same. More specifically, this disclosure relates to cathodes including ionically conductive polymer binders.

BACKGROUND

[0003] A major objective in commercial development of next generation rechargeable batteries is to provide batteries with higher energy densities than currently available with state- of-the-art lithium ion batteries. One of the most promising approaches to this goal relies on using a sulfur cathode. Sulfur is attractive because it is inexpensive, abundant, and offers a theoretical discharge capacity that is an order of magnitude higher than conventional metal oxide-based intercalation cathodes used in current lithium ion cells. However, realization of a practical sulfur battery has been an elusive goal. Among the problems that plague sulfur cathodes, the most serious arise from the fact that both sulfur and lithium sulfide are insoluble and electrically insulating while the polysulfide intermediates formed during battery discharge are highly soluble in electrolytes and difficult to retain in the cathode. The first problem leads to high impedance and low sulfur utilization while the second feature leads to a so-called poly sulfide shuttle that decreases battery efficiency and leads to fouling of the anode.

[0004] Thus, although elemental sulfur has been under investigation as a battery cathode material for more than 50 years, these two fundamental challenges have yet to be sufficiently overcome. The first challenge is to enhance the conductivity of elemental sulfur. Unlike commercial lithium ion cathodes containing LiCoCh and other metal oxides which have electronic conductivity and do not require significant addition of conductive additives, sulfur is an insulator. Therefore, in order to prepare a viable and commercially useful battery based on an elemental sulfur cathode, the active material must be present in a structure that makes the sulfur electrochemically accessible. Numerous approaches to achieve this have been explored including nanoporous and mesoporous monoliths and engineered nanomaterials such as coreshell particles, nanotubes and laminates.

[0005] The second challenge is to control the diffusion and subsequent loss of polysulfide intermediates formed during cycling. During discharge, sulfur reduces in a stepwise manner by forming a series of polysulfide intermediates which are ionic in nature, dissolve readily in the electrolyte, and may be lost by migration to the anode causing mass loss of active material during cycling.

[0006] To date, the technical approaches taken to address and solve these two fundamental challenges have resulted in diminished discharge capacity in comparison to the theoretical value of sulfur.

[0007] Although incremental improvements in capacity and cycle lifetime have been made, significantly greater improvements in reduction of polysulfide shuttling is needed to produce commercially viable metal-sulfur batteries. Thus, there is a need for a sulfur active material that allows for complete utilization of sulfur while minimizing loss of poly sulfides.

[0008] An object of the present disclosure is to provide a cathode active material which is capable of providing good sulfur utilization while effectively containing soluble poly sulfides to prevent their loss or migration.

SUMMARY

[0009] The present disclosure provides, among other things, a sulfur-containing cathode that utilizes an ionically conductive binder. In certain embodiments, the binder includes a doped polymer and an ionic additive. [0010] In one aspect, the disclosure provides a battery comprising a lithium anode combined with a sulfur cathode including an ionically conductive polymer binder.

[0011] In certain embodiments, a sulfur cathode utilizes an ionically conductive polymer as the binder. In one embodiment, the binder includes a doped or undoped polymer as part of the cathode. In other preferred embodiments, the binder also includes at least one ionic compound.

[0012] In certain embodiments, an electrochemical energy storage device comprises an anode, a cathode comprising electroactive sulfur-based materials, a binder and an electrolyte, where the binder comprises a doped polymer including an ionic additive. In certain embodiments, the doped polymer comprises polyphenylene sulfide. In certain embodiments, the ionic additive comprises a lithium salt. In certain embodiments, the binder is about 2 to about 12 wt% of the cathode.

[0013] In certain embodiments, a powder for use in making an electrode comprises electroactive sulfur-based materials, electrically conductive particles and a binder, where the binder comprises a doped polymer including an ionic additive. In certain embodiments, the binder is about 2 to about 12 wt% of the cathode. In certain embodiments, the doped polymer comprises polyphenylene sulfide.

[0014] In certain embodiments, a cathode comprises electroactive sulfur-based materials and a binder, where the binder comprises a doped polymer including an ionic additive. In certain embodiments, the binder is about 2 to about 12 wt% of the cathode. In certain embodiments, the doped polymer comprises polyphenylene sulfide.

DEFINITIONS

[0015] In order for the present disclosure to be more readily understood, certain terms are first defined below. Additional definitions for the following terms and other terms are set forth throughout the specification.

[0016] In this application, unless otherwise clear from context, or otherwise explicitly stated, (i); the term “a” may be understood to mean “at least one”; (ii) the term “or” may be understood to mean “and/or”; (iii) the terms “comprising” and “including” may be understood to encompass itemized components or steps whether presented by themselves or together with one or more additional components or steps; (iv) the terms “about” and “approximately” may be understood to permit standard variation as would be understood by those of ordinary skill in the relevant art; and (v) where ranges are provided, endpoints are included.

[0017] About, Approximately, as used herein, the terms “about” and “approximately” are used as equivalents. Unless otherwise stated, the terms “about” and “approximately” may be understood to permit standard variation as would be understood by those of ordinary skill in the art. Where ranges are provided herein, the endpoints are included. Any numerals used in this application with or without about/approximately are meant to cover any normal fluctuations appreciated by one of ordinary skill in the relevant art. In some embodiments, the term “approximately” or “about” refers to a range of values that fall within 25 %, 20 %, 19 %, 18 %, 17 %, 16 %, 15 %, 14 %, 13 %, 12 %, 11 %, 10 %, 9 %, 8 %, 7 %, 6 %, 5 %, 4 %, 3 %, 2 %, 1 %, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100 % of a possible value).

[0018] Electroactive Substance'. As used herein, the term “electroactive substance” refers to a substance that changes its oxidation state, or partakes in a formation or breaking of chemical bonds, in a charge-transfer step of an electrochemical reaction.

[0019] Polymer'. As used herein, the term “polymer” generally refers to a substance that has a molecular structure consisting chiefly or entirely of repeated sub-units bonded together, such as synthetic organic materials used as plastics and resins.

[0020] Nanostructure, Nanomaterial', as used herein, these terms may be used interchangeably to denote a composition with sub-micrometer features. Such materials can have essentially any shape or configuration, such as a tube, a wire, a laminate, sheets, lattices, a box, a core and shell, or combinations thereof.

[0021] Nanoparticle', as used herein refers to a discrete particle with at least one dimension having sub-micron dimensions. [0022] Substantially. As used herein, the term “substantially” refers to the qualitative condition of exhibiting total or near-total extent or degree of a characteristic or property of interest.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Drawings are presented herein for illustration purposes, not for limitation. The foregoing and other objects, aspects, features, and advantages of the disclosure will become more apparent and may be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which:

[0024] FIG. l is a schematic representation of an electrochemical cell according to illustrative embodiments of the present disclosure;

[0025] FIG. 2 is a pictorial representation of an electrochemical cell, according to illustrative embodiments of the present disclosure;

[0026] FIG. 3 is a perspective representation of a cylindrical battery illustrative embodiments of the present disclosure;

[0027] FIG. 4 is a cross-sectional representation of a nanostructure according to illustrative embodiments of the present disclosure;

[0028] FIG. 5A-5C are perspective representations of nanostructures according to illustrative embodiments of present disclosure;

[0029] FIG. 6 is a perspective representation of a portion of an electrode comprising nanostructures according to illustrative embodiments of the present disclosure; and

[0030] FIG. 7 is a schematic representation of an electrical storage device during a discharging cycle according to illustrative embodiments of the present disclosure. DETAILED DESCRIPTION

[0031] The present disclosure provides, among other things, a sulfur cathode that utilizes an ionically conductive polymer as the binder. In certain embodiments, the binder includes a polymer, a dopant and an ionic compound, such as a salt.

[0032] Cathodes using an ionically conductive polymer binder are described herein. In certain embodiments, PPS is the polymer material that is used in the binder for a sulfur cathode. When appropriately doped and combined with lithium salts, the ionically conductive polymer forms compositions that are good lithium ion conductors. The use of ionically conductive binders in place of traditional polymer binders that do not have appreciable ionic conductivity is advantageous in that it increases the bulk ionic conductivity of the cathode film and in certain embodiments, thereby enables less liquid electrolyte to be used.

[0033] The sulfur active material in a cathode using an ionically conductive polymer binder can be a carbon sulfur blend, a core shell nanoparticle, a sulfur composite or a sulfur- containing polymer. Such a cathode is preferably combined with electrolytes. Ionically conductive polymer binders replace traditional inert binders with a material that contributes to the overall ion conductivity of the cathode.

[0034] Because some polymers (such as PPS) can be difficult to process, in certain embodiments, low molecular weight polyphenylene sulfide oligomers such as those formed by reaction of para dichloro benzene with sodium sulfide in NMP may be used. These low molecular weight oligomers are more soluble and can be post-cured according to procedures known in the art once the cathode composite has been applied to a current collector (e.g. thermal, or UV curing). If synthesized in the presence of electron deficient dopants (e.g. DDQ, TCNQ) in some embodiments, a charge transfer complex may result which imparts electronic conductivity to the polymer binder. Other polymers, such as polyaniline, polyphenyleneoxide, polythiophenes, polypyrroles and polyfurans and substituted derivatives, may alternatively or additionally be used.

[0035] The ionically conductive polymer binder may also be heat treated resulting in a vulcanized polymer where sulfur reacts with the phenyl rings in polymers with sulfur rings (such as PPS) to form covalent C-S bonds. This may also cross-link and rigidify the binder. [0036] Solid polymer electrolytes for lithium batteries are described in U.S. Patent No. 10,741,877, and PCT Publication No. WO 2019/126532, the entire disclosures of which are hereby incorporated by reference herein. Lithium sulfur cells are also described in U.S. Patent Publication No. 2015/0280218, the entire disclosure of which is hereby incorporated by reference herein.

[0037] The cathode composites optionally contain additional components (such as conductive additives) and can be used with liquid electrolytes or be combined with solid electrolytes (polymer or inorganic).

Electrochemical Cells

[0038] In some aspects, the present disclosure provides lithium sulfur batteries comprising a sulfur-containing cathode including an ionically conductive polymer binder and a lithium metal anode.

[0039] Generally, an electrochemical battery such as an Li/S battery comprises a stack of electrodes comprising a plurality of individual electrochemical cells.

[0040] In certain embodiments, secondary sulfur batteries comprise ionically conductive polymer binders as described herein. In certain embodiments, the ionically conductive polymer binder includes an ionically conductive polymer, a dopant, and an ionic additive.

[0041] For example, in certain embodiments, such batteries include a lithium-containing anode composition coupled to the provided cathode composition by a lithium conducting electrolyte. In some embodiments, such batteries also comprise additional components such as separators between the anode and cathode, anodic and cathodic current collectors, terminals by which a cell can be coupled to an external load, and packaging such as a flexible pouch or a rigid metal container. It is further contemplated that the present disclosure regarding secondary sulfur batteries can be adapted for use in sodium-sulfur batteries, and such batteries are also considered within the scope of certain embodiments of the present disclosure.

[0042] FIG. 1 shows a cross section through a representative electrochemical cell 600 that can be used in an Li/S battery. Cell 600 is formed with: a positive electrode comprising a cathode active layer 602 in contact with a cathode current collector 601 and a electrolyte 603; an anode comprising a lithium metal layer 606 having one surface in contact with an optional anode current collector 607 and the other surface in contact with an optional separator 604 disposed between the lithium metal layer 606 and the cathode. In certain embodiments, the cathode active layer 602 includes a conductive polymer binder comprising an ionically conductive polymer, a dopant, and an ionic additive. In certain embodiments, the electrolyte may be a liquid or a gel electrolyte. In certain embodiments, the electrolyte 603 is a liquid electrolyte. In certain embodiments, where a liquid electrolyte is used, it may be held in the pores of porous separator 604, as well as in pores in cathode 602. These cells 600 can be used for a variety of batteries or other electrochemical energy storage devices. The inventive cells disclosed herein can be substituted in place of, or used in conjunction with, conventional electrodes for lithium-sulfur batteries or other types of batteries. The number of cells 600 and their specific configurations can vary to suit a particular application.

[0043] FIG. 2 illustrates a cross section of a multilayer electrochemical cell 800 in accordance with exemplary embodiments of the disclosure. Electrochemical cell 800 includes a negative electrode 802, a positive electrode 804, a separator 806 interposed between negative electrode 802 and positive electrode 804, a container 810, and a fluid electrolyte 812 in contact with negative and positive electrodes 802, 804. Such cells optionally include additional layers of electrode and separators 802a, 802b, 804a, 804b, 806a, and 806b. In certain embodiments, the positive electrode layer 804 includes an ionically conductive polymer binder comprising an ionically conductive polymer, a dopant, and an ionic additive.

[0044] Negative electrode 802 (also sometimes referred to herein as an anode) comprises a negative electrode active material that can accept cations. Non-limiting examples of negative electrode active materials for lithium-based electrochemical cells include Li metal, Li alloys such as those of Si, Sn, Bi, In, and/or Al alloys, Li4TisOi2, hard carbon, graphitic carbon, metal chalcogenides, and/or amorphous carbon. In accordance with some embodiments of the disclosure, most (e.g., greater than 90 wt %) of an anode active material can be initially included in a discharged positive electrode 804 (also sometimes referred to herein as a cathode) when electrochemical cell 800 is initially made, so that an electrode active material forms part of first electrode 802 during a first charge of electrochemical cell 800. [0045] A technique for depositing electroactive material on a portion of negative electrode 802 is described in U.S. Patent Publication Nos. 2016/0172660 and 2016/0172661, in the name of Fischer et al., the contents of each of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure.

[0046] Positive electrode 804 (also referred to herein as cathode) comprises a cathode composition as described herein. In certain embodiments, the positive electrode comprises an ionically conductive polymer binder. In certain embodiments, the ionically conductive polymer binder includes an ionically conductive polymer, at least one dopant, and at least one ionic compound.

[0047] In certain embodiments, a cathode composite comprises about 30 to about 70 wt% electroactive sulfur. In certain embodiments, a cathode comprises at least about 70% of total sulfur present in an electrochemical cell. In certain embodiments, a cathode comprises at least about 80% of total sulfur present in an electrochemical cell. In certain embodiments, a cathode comprises at least about 90% of total sulfur present in an electrochemical cell. In certain embodiments, a cathode comprises at least about 95% of total sulfur present in an electrochemical cell. In certain embodiments, a cathode comprises at least about 99% of total sulfur present in an electrochemical cell. In certain embodiments, a cathode comprises essentially all of the total sulfur present in an electrochemical cell.

[0048] In certain embodiments, the amount of binder chosen is just enough to bridge and bind the particles. In certain embodiments, the cathode composite comprises between about 1 to about 20 wt% ionically conductive polymer binder. In certain embodiments, the cathode composite comprises between about 1 to about 5 wt% ionically conductive polymer binder, for example, about 1%, about 2%, about 3%, about 4%, or about 5%. In certain embodiments, the cathode composite comprises between about 5 to about 10 wt% ionically conductive polymer binder, for example, about 5%, about, about 7.5% or about 10%. In certain embodiments, the cathode composite comprises between about 10 to about 20 wt% ionically conductive polymer binder. In certain embodiments, the cathode composite comprises between about 2 to about 4 wt% ionically conducitve polymer binder. In certain embodiments, the cathode composite comprises between about 4 to about 8 wt% ionically conductive polymer binder. [0049] Negative electrode 802 and positive electrode 804 can further include one or more electrically conductive additives as described herein.

[0050] FIG. 3 illustrates an example of a battery according to various embodiments described below. A cylindrical battery is shown here for illustration purposes, but other types of arrangements, including prismatic or pouch (laminate-type) batteries, may also be used as desired. Example Li battery 901 includes a negative anode 902, a positive cathode 904, a separator 906 interposed between the anode 902 and the cathode 904, an electrolyte (not shown) impregnating the separator 906, a battery case 905, and a sealing member 908 sealing the battery case 905. In certain embodiments, the positive cathode 904 includes an ionically conductive polymer binder comprising an ionically conductive polymer, a dopant, and an ionic additive. It will be appreciated that example battery 901 may simultaneously embody multiple aspects of the present disclosure in various designs.

[0051] PCT Publication Nos. WO2015/003184, W02014/074150, and WO2013/040067, the entire disclosures of which are hereby incorporated by reference herein, described various methods of fabricating electrodes and electrochemical cells that are suitable to utilize materials of the present disclosure.

Electroactive Compositions

[0052] The provided cathode compositions include an electroactive material. The electroactive material is preferably an electroactive sulfur-based material. In certain embodiments, the electroactive sulfur is present in the form of elemental sulfur. In certain embodiments, the electroactive sulfur material comprises Ss. In certain embodiments, the electroactive sulfur material comprises a composite of carbon and elemental sulfur. In certain embodiments, the electroactive sulfur material comprises a sulfur-containing polymer.

[0053] In certain embodiments, the electroactive sulfur is present as a metal sulfide. In certain embodiments, the metal sulfide comprises an alkali metal sulfide; in certain embodiments, the metal sulfide comprises lithium sulfide.

[0054] In certain embodiments, the electroactive sulfur material is present as a composite with another material. Such composites may include conductive additives such as graphite, graphene, carbon nanotubes, metals, metal sulfides, metal phosphides, metal oxides, or conductive polymers. In certain embodiments, the sulfur may be alloyed with other chalcogenides such as selenium, tellurium or arsenic.

[0055] The electroactive sulfur material in a cathode using an ionically conductive polymer binder can be a carbon sulfur blend, a core shell particle, a sulfur composite or a sulfur- containing polymer. Such a cathode is preferably combined with electrolytes.

[0056] In certain embodiments, provided sulfur-containing cathode compositions comprise nanostructured materials combining a sulfur-based electroactive material in combination with one or more additional materials. These nanostructured materials are not limited to any specific morphology. Provided nanostructured materials may take various forms, a few non-limiting examples of which are illustrated in FIGS. 4 and 5A-5C. In certain embodiments, the nanostructured materials comprise core-shell nanoparticles wherein a shell surrounds a core comprising an electroactive substance(s). In certain embodiments, the nanostructured materials comprise yolk-shell nanoparticles 10 where a shell 14 surrounds a volume 18 containing a void space and a smaller ‘yolk’ 12a comprising the electroactive substance(s) (FIG. 4). The shell may be made of polymers, carbon, inorganic materials, or any combination thereof. In certain embodiments, the nanostructured materials comprise a porous matrix of a conductive polymer wherein the electroactive substance is disposed within the pores of the matrix.

[0057] In certain embodiments, the nanostructured materials comprise nanowires (FIG. 5 A) wherein the shell comprises a substantially cylindrical structure 114 containing the electroactive substance(s) 112 within. In certain embodiments, the nanostructured materials comprise layered structures containing one or more layers of the electroactive substance(s) 312 alternating with one or more layers of the shell 314 (FIG. 5C). In certain embodiments, the nanostructured materials comprise complex structures containing one or more arcuate and/or polygonal shapes 214 containing the electroactive substance(s) 212 (FIG. 5B).

[0058] In certain embodiments, the nanostructures comprise one or more polymers. In certain embodiments, the nanostructures comprise a conductive polymer (e.g. as a shell in a core shell structure). Non-limiting examples of suitable conductive polymers that may be used include those based on heterocyclic monomers such as polypyrrole (PPy), polythiophene (PTh), poly dopamine, poly(3,4-ethylenedi oxythiophene) (PEDOT), poly(3,4-propylenedi oxythiophene) (ProDOT), poly(3,4-ethylenedi oxypyrrole) (PEDOP), poly(3,4-propylenedi oxypyrrole) (ProDOP), poly(3,4-ethylenedithiopyrrole) (PEDTP), poly(3,4-ethyleneoxyhiathiophene) (PEOTT), poly(3,4-ethylenedioxyselenophene) (PEDOSe). Other non-limiting examples of polymers that may be used include those based on hetero-substituted aromatic monomers such as: polyaniline (PAni), poly(o-methylaniline) (POTO), poly(o-methoxyaniline) (POAS), poly(2,5-dimethylaniline) (PDMA), poly(2, 5 -dimethoxy aniline) (PDOA), sulfonated polyaniline (SPAN), poly(l -aminonaphthalene) (PNA), poly(5-aminonaphthalene-2-sulfonic acid) and polyphenylene sulfide (PPS). In certain embodiments, the provided nanostructures may comprise copolymers, mixtures, or composites comprising two or more of the materials described above. In other embodiments, the nanostructures may be made of polymers, carbon, inorganic materials, or any combination thereof.

[0059] In any of these nanostructures, the portions of the structure comprising the conductive polymer (e.g. the shell, matrix, layer, etc.) may consist entirely of a single conductive polymer, or may comprise multiple conductive polymers and/or additional materials such as polymers, carbon or inorganic materials. Such additional materials may be present in various forms, for example: additional materials can be present as discrete layers contained within or disposed upon the conductive polymers (e.g. in a multilayer shell); the additional materials may be present as mixtures intimately mixed or compounded with the conductive polymer; or the additional materials may be present in composites with the conductive polymer. Suitable additional materials that may be present with the conductive polymers include other polymers, elemental carbon, metallic elements or their alloys, metal oxides, metal chalcogenides, metal salts, ceramics, glasses, clays, semiconductors, and the like, as described more fully in the embodiments and definitions provided herein.

[0060] In certain embodiments, the nanostructured materials comprise inorganic materials (e.g. as a shell in a core shell nanoparticle). In certain embodiments, provided nanostructured materials comprise metals, metal oxides, metal sulfides, metal phosphides and the like. In certain embodiments, the nanostructured materials comprise an elemental transition metal or alloy thereof. In certain embodiments, the nanostructured materials comprise transition metal oxides. In certain embodiments, the nanostructured materials comprise transition metal sulfides. In certain embodiments, the nanostructured materials comprise transition metal phosphides. In certain embodiments, the nanostructured materials comprise a mixture or composite of any two or more of these.

[0061] In certain embodiments, the nanostructured materials comprise elemental carbon. In certain embodiments, the nanostructured materials comprise amorphous carbon. In certain embodiments, the nanostructured materials comprise graphitic carbon. In certain embodiments, the nanostructured materials comprise graphene, carbon nanotubes, fullerenes or similar allotropes of carbon. In certain embodiments, the nanostructured materials comprise a mixture or composite of any two or more of these.

[0062] In certain embodiments, provided nanostructured materials are characterized in that the electroactive substance is in a form having nanometer dimensions. In certain embodiments, the electroactive substance is present in a form having at least one dimension with a length in the range of 5 to 1,000 nm. In certain embodiments, the electroactive substance is present in a form having at least one dimension with a length in the range of 10 to 50 nm, 30 to 100 nm, 100 to 500 nm, or 500 to 1,000 nm.

[0063] In certain embodiments, nanostructured materials are characterized in that features of the material (e.g. such as a shell in a core-shell nanostructured material) are present in a form having nanometer dimensions. In certain embodiments, the features are present in a form having at least one dimension with a length in the range of 5 to 1,000 nm. In certain embodiments, the features are present in a form having at least one dimension with a length in the range of 5 to 10 nm, 10 to 50 nm, 30 to 100 nm, 100 to 500 nm, or 500 to 1,000 nm. In certain embodiments, the features are present in a three-dimensional form characterized in that one dimension (i.e. the thickness) is substantially smaller than the other two dimensions, examples of these forms include, sheets, shells, platelets, tubes, coatings and the like. In certain embodiments, such compositions are characterized in that they have a smallest dimension (e.g. thickness) less than 50 nm. In certain embodiments, the features are present in a sheet-like form or a shell having a thickness between 1.5 and 5 nm, between 5 and 10 nm, between 5 and 25 nm, between 10 and 40 nm or between 25 and 50 nm. [0064] In certain embodiments, the present disclosure provides compositions comprising nanostructured materials with consistent morphological features. Such compositions are distinct from, and have performance advantages relative to, polydispersed mixtures that may randomly contain individual particles having the nanostructural features described herein. In certain embodiments, the present disclosure provides compositions comprising nanostructured particles with a narrow size distribution. In certain embodiments, the present disclosure provides compositions comprising nanostructured particles with a high level of morphological homogeneity. These characteristics can be assessed by direct observation (e.g., electron microscopy) or by measuring particle size distribution using light scattering or similar techniques known in the art.

[0065] In certain embodiments, the nanostructured materials of the present disclosure include core-shell nanoparticles. Such core-shell particles include an electroactive core surrounded by a shell. In certain embodiments, such core-shell particles are characterized in that the electroactive core occupies only a portion of the volume contained by the shell. Such architecture is sometimes referred to as “yolk-shell” and is valuable for electroactive materials that undergo substantial volume changes during charge and discharge. In certain such embodiments, nanostructured materials of the present disclosure comprise core-shell nanoparticles characterized in that an electroactive core occupies less than about 80% of the internal volume contained by the shell. In certain embodiments, such compositions are characterized in that the electroactive core occupies less than 75%, less than 60%, or less than 50% of the internal volume defined by the shell. In certain embodiments, nanostructured materials of the present disclosure comprise core-shell nanoparticles characterized in that an electroactive core occupies between about 30 and about 80% of the internal volume contained by the shell. In certain embodiments, such compositions are characterized in that the electroactive core occupies between 30 and 50%, between 40 and 65%, between 50 and 75% or between 60 and 80% of the internal volume defined by the shell.

[0066] Generally, the dimensions and shape of the electroactive sulfur-based material in the cathode composition may be varied to suit a particular application and/or may be dictated or a consequence of the morphology of the nanostructure comprising the shell composition. [0067] If nanostructured materials are used, they comprise a shell and an electroactive substance. In these embodiments, the electroactive substance is preferably in a form having nanometer dimensions. In certain embodiments, the electroactive substance is present in a form having at least one dimension with a length in the range of 5 to 1,000 nm. In certain embodiments, the electroactive substance is present in a form having at least one dimension with a length in the range of 10 to 50 nm, 30 to 100 nm, 100 to 500 nm or 500 to 1,000 nm. In certain embodiments, the electroactive substance is present in a form having at least one dimension with a length in the range of 400 to 1,000 nm.

[0068] In certain embodiments, provided nanostructured materials or other electroactive materials have utility as cathode compositions for sulfur batteries. In certain embodiments, such compositions comprise an electroactive sulfur-based material. Examples of suitable electroactive sulfur-based materials include elemental sulfur, sulfur composites, sulfur- containing organic molecules, sulfur-containing polymers, metal sulfides as well as combinations or composites of two or more of these.

[0069] In various embodiments, the electroactive sulfur-based material is present as a nanoparticle. In certain embodiments, such electroactive sulfur-based nanoparticles have a spherical or spheroid shape. In certain embodiments, nanostructured materials of the present disclosure comprise substantially spherical sulfur-containing particles with a diameter in the range of about 50 to about 1,200 nm. In certain embodiments, such particles have a diameter in the range of about 50 to about 250 nm, about 100 to about 500 nm, about 200 to about 600 nm, about 400 to about 800 nm or about 500 to about 1,000 nm.

[0070] In certain embodiments, such electroactive sulfur-based nanoparticles have a rhomboid or polyhedral shape. In certain embodiments, nanostructured materials of the present disclosure comprise substantially rhomboid or polyhedral particles with a major dimension in the range of about 50 to about 1,200 nm. In certain embodiments, such particles have a major dimension in the range of about 50 to about 250 nm, about 100 to about 500 nm, about 200 to about 600 nm, about 400 to about 800 nm or about 500 to about 1,000 nm.

[0071] In certain embodiments, the nanoparticles comprise cylindrical particles with a cross-sectional diameter in the range of about 10 to about 1000 nm. In certain embodiments, the cross-sectional diameter of such nanoparticles is less than about 100 nm — for example, provided cylindrical particles may have diameters of 10 to 40 nm; 25 to 50 nm; or 50 to 100 nm. In certain embodiments, the provided cylindrical particles have a cross-sectional diameter less than about 500 nm — for example, provided cylindrical particles may have diameters of 75 to 150 nm; 100 to 200 nm; 150 to 300 nm; 200 to 500 nm; or 300 to 500 nm. In certain embodiments, the provided nanoparticles comprise cylinders with a cross-sectional diameter less than about 1000 nm — for example, provided nanoparticles may have diameters of 200 to 600 nm; 500 to 800 nm; 600 to 800 nm; or 750 to 1000 nm. In certain embodiments, the provided nanoparticles comprise cylindrical particles with a diameter between about 100 and 400 nm. In certain embodiments, provided cylindrical particles have lengths greater than 1 pm. In certain embodiments, provided cylindrical nanoparticles have lengths greater than 5 pm, greater than 10 pm, greater than 20 pm, or greater than 50 pm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 1 pm to about 1 cm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 5 pm to about 1 cm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 10 pm to about 1 cm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 20 pm to about 1 cm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 50 pm to about 1 cm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 1 pm to about 1 mm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 5 pm to about 1 mm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 10 pm to about 1 mm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 20 pm to about 1 mm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 50 pm to about 1 mm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 1 pm to about 100 pm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 5 pm to about 100 pm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 10 pm to about 100 pm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 20 pm to about 100 pm. In certain embodiments, provided cylindrical nanoparticles have lengths of about 50 pm to about 100 pm. In certain embodiments, provided nanoparticles have an aspect ratio greater than 3, greater than 5, greater than 10, greater than 20. In certain embodiments, provided nanoparticles have an aspect ratio greater than 50, greater than 100, greater than 200, greater than 500, or greater than 1000.

[0072] Such electroactive sulfur-based nanoparticles may comprise a component of nanostructures that have various morphologies as described above. In certain embodiments, the electroactive sulfur-based material is present as the core of a core-shell particle, where it is surrounded by a shell. In certain embodiments, such core-shell particles may comprise yolkshell particles as described above.

[0073] Various methods of doping, de-doping and chemical cross-linking of conductive polymers are disclosed in “Polyaniline Membranes for Use in Organic Solvent Nanofiltration" by Xun Xing Loh, Dept, of Chemical Engineering and Chemical Technology Imperial College of London, April 2009, the entire disclosure of which is incorporated by reference herein.

[0074] FIG. 6 depicts one possible arrangement of nanoparticles to create an electrode 20, such as a cathode. Generally, the cathode 20 is made up of a plurality of nanoparticles 10 that may take the form of sheets or foils, wires, or other agglomerations of encapsulated structures combined with one or more suitable binders (see, for example, FIGS. 5A-5C). In certain embodiments, the binder(s) include an ionically conductive polymer.

[0075] FIG. 7 depicts one possible electro-chemical cell 22 that can be used to manufacture a battery in accordance with one or more embodiments of the disclosure. The cell 22 is depicted during a discharge operation. The cell 22 includes an anode 24 made up of a lithium-based material, a cathode 20 preferably made up of the inventive nanoparticles disclosed herein, a separator 26, and an electrolyte 16. During the discharge operation, the lithium-based material of the anode (a high potential energy state) is oxidized, generating an electron 28 and a lithium ion 30. The electron 28 performs work in an external circuit 32, while the lithium ion 30 passes through the separator 26 and recombines with the electron 28 in the cathode 20 (a lower potential energy state). The electrolyte 16 acts as a medium for the lithium ions 30 to move within the cell and to passivate the reactive anode surface (e.g. a protective “Solid Electrolyte Interphase” (SEI)). Although FIG. 7 describes a cathode including nanoparticles, the cathode may include any sulfur-based electroactive material as described herein. [0076] During charging, specifically recharging, the lithium ions 30 move back through the electrolyte 16 towards the anode 24, and the electrons 28 travel back through the external circuit 32. Typically, cathode active materials that have dissolved into the electrolyte, such as polysulfides, form insoluble solids that lead to anode and cathode fouling and reduced capacity and slower charging. Using the inventive nanoparticles described herein helps to retain the sulfur in the cathode to reduce or eliminate the migration of poly sulfides into the bulk electrolyte 16.

Cathode Compositions

[0077] In certain embodiments, the electroactive sulfur material is mixed with electrically conductive particles (e.g., conductive carbon, such as carbon black, graphene, etc.) and a binder. Binders are typically polymeric materials that help adhere individual particles composing a cathode mixture into a stable composite. In certain embodiments, the binder comprises an ionically conductive polymer binder. In certain embodiments, the ionically conductive polymer binder includes an ionically conductive polymer, a dopant, and an ionic additive. The ionically conductive polymer binder preferably replaces traditional inert binders with a material that contributes to the overall ion conductivity of the cathode.

[0078] In certain embodiments, the polymer in the ionically conductive polymer binder is polyphenylene sulfide (PPS). In certain embodiments, the binder may also or alternatively include one or more other polymers including, but not limited to, polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropene) (PVDF/HFP), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE), polyacrylates, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate ) (PMMA), copolymers of polyhexafluoropropylene and polyvinylidene fluoride, polyethyl acrylate, polyvinyl chloride (PVC), polyacrylonitrile (PAN), poly caprolactam, polyethylene terephthalate (PET), polybutadiene, polyisoprene or polyacrylic acid, or derivatives blends or copolymers thereof. In some embodiments, the ionically conductive polymer binder also includes sodium alginate or carrageenan. Generally, the binders hold the active materials together and are in intimate contact with a current collector (e.g., aluminum foil or copper foil, carbon paper or fabric). [0079] In certain embodiments, the present disclosure includes an ionically conductive polymer as a binder in a cathode. In some embodiments, the ionically conductive polymer is doped. In certain embodiments, the binder also includes at least one ionic compound.

[0080] In certain embodiments, the cathode composition comprises between about 2 to about 12 wt% ionically conductive polymer binder. The amount of binder chosen is just enough to bridge and bind the particles. In certain embodiments, the cathode composite comprises between about 4 to about 10 wt% ionically conductive polymer binder. In certain embodiments, the cathode composite comprises between about 6 to about 8 wt% ionically conductive polymer binder. In certain embodiments, the cathode composite comprises between about 2 to about 4 wt% ionically conductive polymer binder. In certain embodiments, the cathode composite comprises between about 4 to about 8 wt% ionically conductive polymer binder.

Ionically Active Polymer Binders

[0081] The present disclosure preferably includes an ionically conductive polymer as a binder in a cathode. In some embodiments, the ionically conductive polymer is doped. In certain embodiments, the binder also includes at least one ionic compound. In certain embodiments, the ionically conductive polymer is PPS.

[0082] The ionically conductive polymer binder has high ionic conductivity and in particular high ionic conductivity for lithium ions. In certain embodiments, such lithium ion conductive polymers have preferential conductivity of lithium ions — i.e. the polymers conduct lithium ions more readily than other non-lithium ions.

[0083] In certain embodiments, the binder comprises a polymer selected from the group consisting of: polyethers, polysulfides, polyether ketones, polyimides, polysulfones, polyamides, and polyheterocycles. In certain embodiments, the binder comprises a polyether. In certain embodiments, the binder comprises a polysulfide. In certain embodiments, the binder comprises a polyether ketone. In certain embodiments, the binder comprises a polyimide. In certain embodiments, the binder comprises a sulfone. In certain embodiments, the binder comprises an ethersulfone. In certain embodiments, the binder comprises a polyamide. In certain embodiments, the binder comprises a polyimide. In certain embodiments, the polymers comprise aromatic monomers.

[0084] In certain embodiments, the binder comprises polyphenylene sulfide. In certain embodiments, the binder comprises polyphenyl ether. In certain embodiments, the binder comprises polyphenylene oxide. In certain embodiments, the binder comprises polyphthalamide. In certain embodiments, the binder comprises polyphthalimide. In certain embodiments, the binder comprises an aromatic polyester. In certain embodiments, the binder comprises Vectran® (poly-(/?-phenylene-2,6-naphthalate)). In certain embodiments, the binder comprises poly-(/?- phenyleneteraphthalate). In certain embodiments, the binder comprises polysulfone. In certain embodiments, the binder comprises polyethersulfone.

[0085] In certain embodiments, the ionically conductive polymer comprises a polyheterocycle. In certain embodiments, the ionically conductive polymer comprises polypyrrole. In certain embodiments, the ionically conductive polymer comprises polyaniline.

[0086] Table 1 lists polymers suitable for certain embodiments of the present disclosure. In certain embodiments, the ionically conductive polymer binder comprises a doped polymer composition.

[0087] Polymers that are useful as reactants in the synthesis of the ionically conductive polymer material are electron donors or polymers which can be oxidized by electron acceptors. Semi-crystalline polymers with a crystallinity index greater than 30% or greater than 50% are suitable reactant polymers. In certain embodiments, totally crystalline polymer materials such as liquid crystal polymers (LCP) may also be useful as reactant polymers. LCPs are totally crystalline and therefore their crystallinity index is hereby defined as 100%. Undoped conjugated polymers and polymers such as polyphenylene sulfide (PPS) are also suitable polymer reactants.

[0088] Polymers are typically not electrically conductive. For example, virgin PPS has an electrical conductivity of 10-20 S/cm. Non-electrically conductive polymers are suitable reactant polymers.

[0089] Polymers useful as reactants may possess an aromatic or heterocyclic component in the backbone of each repeating monomer group, otherwise known as a monomer residue, and a heteroatom either incorporated in the heterocyclic ring or positioned along the backbone in a position adjacent the aromatic ring. The heteroatom can be located directly on the backbone or bonded to a carbon atom which is positioned directly on the backbone. In both cases where the heteroatom is located on the backbone or bonded to a carbon atom positioned on the backbone, the backbone atom is positioned on the backbone adjacent to an aromatic ring. In certain embodiments, polymers that may be used include, but are not limited to, poly (p-phenylene oxide) (PPO), polyether ether ketone (PEEK), polyphthalamide (PPA), polypyrrole, polyaniline, polysulfone, Xydar® LCP, other liquid crystal polymers, vectran poly-paraphenylene terephthalamide, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylene (PE) or polyphenylene sulfide (PPS). Copolymers including monomers or monomer residues of the listed polymers and mixtures of these polymers may also be used. For example, copolymers of p-hydroxybenzoic acid can be appropriate liquid crystal polymer base polymers. Combinations of two or more of these polymers may form the binder in some embodiments.

[0090] In certain embodiments, the ionically conductive polymer is polyphenylene sulfide (PPS):

[0091] Table 1 lists examples of reactant polymers useful in the synthesis of the ionically conductive polymer material along with monomer or monomer residue structures and some physical property information.

Table 1

[0092] As noted above, in certain embodiments, the ionically conductive polymer comprises a doped polymer. Dopants such as electron acceptors or oxidants are useful as reactants in the synthesis of the ionically conductive polymer material. Dopants which can be used in the present disclosure include, but are not limited to, quinones such as 2,3-dicyano-5,6- dichlorodicyanoquinone (C8CI2N2O2, DDQ) and tetrachloro-l,4-benzoquinone (CeChCh, chloranil), tetracyanoethylene (CeN4, TCNE), sulfur tri oxide (SO3), ozone (tri oxygen or O3), oxygen (O2, including air), transition metal oxides, for example manganese dioxide (MnCh), or any suitable electron acceptor, etc. and combinations thereof. Suitable dopants are those that are temperature stable at the temperatures of the synthesis heating step. Non limiting examples include quinones and other dopants which are both temperature stable and strong oxidizers.

[0093] Table 2 provides a listing of some suitable dopants, along with their chemical formulas and structures. Table 2

[0094] In certain embodiments, the ionically conductive polymer binder comprises ionic compounds (i.e. salts). In certain embodiments, the ionic compounds comprise lithium cations. These compounds release desired lithium ions during the synthesis of the ionically conductive polymer material. The ionic compound is distinct from the dopant, and both an ionic compound and a dopant are preferred. Ionic compounds that could be incorporated into the binder described herein include, but are not limited to, Li2O, LiOH, LiNCh, LiTFSI (LiC2FeNO4S2 or lithium bis- trifluoromethanesulfonimide), LiFSI (F2LiNO4S2 or Lithium bis(fluorosulfonyl)imide), LiBOB (Lithium bis(oxalato)borate or C4BLiOs), lithium triflate (LiCFsCLS or lithium trifluoromethane sulfonate), LiPFe, (lithium hexafluorophosphate), LiBF4 (lithium tetrafluorob orate), LiAsFe (lithium hexafluoroarsenate) and other lithium salts and combinations thereof. Hydrated forms (e.g. monohydride) of these compounds can be used to simplify handling of the compounds. Inorganic oxides, chlorides and hydroxide are suitable ionic compounds in that they dissociate during synthesis to create at least one anionic and/or cationic diffusing ion. Any such ionic compound that dissociates to create at least one anionic and/or cationic diffusing ion would similarly be suitable. Multiple ionic compounds may also be useful that result in multiple anionic and/or cationic diffusing ions can be preferred. The particular ionic compound included in the synthesis depends on the utility desired for the material. For example, when it is desirable to have a lithium cation, a lithium hydroxide or a lithium oxide convertible to a lithium and hydroxide ion may be appropriate. A lithium containing compound that releases both a lithium cathode and a diffusing anion may be used in the synthesis method. Non-limiting examples of these lithium ionic compounds includes those used as lithium salts in organic solvents.

[0095] In certain embodiments, the cathode including an ionically conductive polymer binder is combined with electrolytes. In certain embodiments, the ionically conductive polymer binder replaces inert binders with a material that contributes to the overall ion conductivity of the cathode.

[0096] Since some polymers (e.g.- PPS) can be difficult to process, in certain embodiments, low molecular weight polyphenylene sulfide oligomers such as those formed by reaction of para dichloro benzene with sodium sulfide in NMP may be used. These low MW oligomers are more soluble and can be post-cured according to known procedures once the cathode composite has been applied to a current collector (e.g. thermal, or UV curing). If synthesized in the presence of electron deficient dopants (e.g. DDQ, TCNQ), a charge transfer complex may result which imparts electronic conductivity to the polymer binder. In certain embodiments, one or more polymers including, but not limited to, polyphenylene sulfide, polyaniline, polyphenyleneoxide, polythiophenes, polypyrroles and polyfurans and substituted derivatives may be used, alone or in combination. The ionically conductive polymer binder may also be heat treated resulting in a vulcanized polymer where, in polymers with phenyl rings, sulfur reacts with the phenyl rings to form covalent C-S bonds. This may also cross-link and rigidify the binder. Anodes

[0097] The negative electrode (i.e., anode) contains the negative active material. The negative active material is one that can reversibly release lithium ions. Any lithium anode suitable for use in lithium-sulfur cells may be used. In certain embodiments, an anode of a secondary sulfur battery comprises a negative active material selected from materials in which lithium intercalation reversibly occurs, materials that react with lithium ions to form a lithium- containing compound, metallic lithium, lithium alloys, and combinations thereof. In certain embodiments, an anode comprises metallic lithium. In certain embodiments, lithium-containing anodic compositions comprise carbon-based compounds. In certain embodiments, a carbonbased compound is selected from the group consisting of crystalline carbon, amorphous carbon, graphite, graphene, carbon nanotubes, and combinations thereof. In certain embodiments, a material that reacts with lithium ions to form a lithium-containing compound is selected from the group consisting of tin oxide (SnCh), titanium nitrate, and silicon. In certain embodiments, a lithium alloy comprises an alloy of lithium with another alkali metal (e.g. sodium, potassium, rubidium or cesium). In certain embodiments, a lithium alloy comprises an alloy of lithium with a transition metal. In certain embodiments, lithium alloys include alloys of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, Sn, In, Zn, Sm, La, and combinations thereof. In certain embodiments, a lithium alloy comprises an alloy of lithium with indium. In certain embodiments, a lithium alloy comprises an alloy of lithium with aluminum. In certain embodiments, a lithium alloy comprises an alloy of lithium with zinc. In certain embodiments, an anode comprises a lithium-silicon alloy. Examples of suitable lithiumsilicon alloys include: Li isSi4, LinSi?, LizSis, Li i3Si4, and Li2iSis/Li22Si5. In certain embodiments, a lithium metal or lithium alloy is present as a composite with another material. In certain embodiments, such composites include materials such as graphite, graphene, metal sulfides or oxides, or conductive polymers. Typically, the negative electrode may also contain the negative active material disposed on a current collector, such as those described herein.

[0098] In some embodiments, an anode is protected against redox shuttling reactions and hazardous runaway reactions by any of the methodologies reported in the art, for example, by creating a protective layer on a surface of an anode by chemical passivation or by deposition or polymerization. For example, in certain embodiments, an anode comprises an inorganic protective layer, an organic protective layer, or a mixture thereof, on a surface of lithium metal. In certain embodiments, an inorganic protective layer comprises Mg, Al, B, Sn, Pb, Cd, Si, In, Ga, lithium silicate, lithium borate, lithium phosphate, lithium phosphoronitride, lithium silicosulfide, lithium borosulfide, lithium aluminosulfide, lithium phosphosulfide, lithium fluoride or combinations thereof. In certain embodiments, an organic protective layer includes a conductive monomer, oligomer, or polymer. In certain embodiments, such polymer is selected from poly(p-phenylene), polyacetylene, poly(p-phenylene vinylene), polyaniline, polypyrrole, polythiophene, poly(2,5-ethylene vinylene), acetylene, poly(perinaphthalene), polyacene, and poly(naphthalene-2,6-di-yl), or combinations thereof.

[0099] Moreover, in certain embodiments, inactive sulfur material, generated from an electroactive sulfur material of a cathode, during charging and discharging of a secondary sulfur battery, attaches to an anode surface. The term "inactive sulfur", as used herein, refers to sulfur that has no activity upon repeated electrochemical and chemical reactions, such that it cannot participate in an electrochemical reaction of a cathode. In certain embodiments, inactive sulfur on an anode surface acts as a protective layer on such electrode. In certain embodiments, inactive sulfur is lithium sulfide.

Electrolytes

[0100] In certain embodiments, a secondary sulfur battery comprises an electrolyte comprising an electrolytic salt. Examples of electrolytic salts include, for example, lithium trifluoromethane sulfonimide, lithium triflate, lithium perchlorate, LiPFe, LiBF4, tetraalkylammonium salts (e.g. tetrabutyl ammonium tetrafluorob orate, TBABF4), liquid state salts at room temperature (e.g. imidazolium salts, such as l-ethyl-3-methylimidazolium bis- (perfluoroethyl sulfonyl)imide, EMIBeti), and the like.

[0101] In certain embodiments, an electrolyte comprises one or more alkali metal salts. In certain embodiments, such salts comprise lithium salts, such as LiCFsSCh, LiCICU, LiNCh, LiPFe, LiBr, LiTDI, LiFSI, and LiTFSI, or combinations thereof. In certain embodiments, an electrolyte comprises ionic liquids, such as l-ethyl-3-methylimidzaolium-TFSI, N-butyl-N- methyl-piperidinium-TFSI, N-methyl-n-butyl pyrrolidinium-TFSI, and N-methyl-N- propylpiperidinium-TFSI, or combinations thereof. In certain embodiments, an electrolyte comprises superionic conductors, such as sulfides, oxides, and phosphates, for example, phosphorous pentasulfide, or combinations thereof.

[0102] In certain embodiments, an electrolyte is a liquid. For example, in certain embodiments, an electrolyte comprises an organic solvent. In certain embodiments, an electrolyte comprises only one organic solvent. In some embodiments, an electrolyte comprises a mixture of two or more organic solvents. In certain embodiments, a mixture of organic solvents comprising one or more weak polar solvents, strong polar solvents, and lithium protecting solvents.

[0103] The term "weak polar solvent", as used herein, is defined as a solvent that is capable of dissolving elemental sulfur and has a dielectric coefficient of less than 15. A weak polar solvent is selected from aryl compounds, bicyclic ethers, and acyclic carbonate compounds. Examples of weak polar solvents include xylene, dimethoxyethane, 2- methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme, tetraglyme, and the like. The term "strong polar solvent", as used herein, is defined as a solvent that is capable of dissolving lithium polysulfide and has a dielectric coefficient of more than 15. A strong polar solvent is selected from bicyclic carbonate compounds, sulfoxide compounds, lactone compounds, ketone compounds, ester compounds, sulfate compounds, and sulfite compounds. Examples of strong polar solvents include hexamethyl phosphoric triamide, y-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone, dimethyl formamide, sulfolane, dimethyl acetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, ethylene glycol sulfite, and the like. The term "lithium protection solvent", as used herein, is defined as a solvent that forms a good protective layer, i.e. a stable solid-electrolyte interface (SEI) layer, on a lithium surface, and which shows a cyclic efficiency of at least 50%. A lithium protection solvent is selected from saturated ether compounds, unsaturated ether compounds, and heterocyclic compounds including one or more heteroatoms selected from the group consisting of N, O, and/or S. Examples of lithium protection solvents include tetrahydrofuran, 1,3-dioxolane, 3,5-dimethylisoxazole, 2,5-dimethyl furan, furan, 2-methyl furan, 1,4-oxane, 4-m ethyldi oxolane, and the like. [0104] In certain embodiments, an electrolyte is a liquid (e.g., an organic solvent). In some embodiments, a liquid is selected from the group consisting of organocarb onates, ethers, sulfones, water, alcohols, fluorocarbons, or combinations of any of these. In certain embodiments, an electrolyte comprises an ethereal solvent.

[0105] In certain embodiments, an organic solvent comprises an ether. In certain embodiments, an organic solvent is selected from the group consisting of 1,3 -di oxolane, dimethoxyethane, diglyme, triglyme, y-butyrolactone, y-valerolactone, and combinations thereof. In certain embodiments, an organic solvent comprises a mixture of 1,3-dioxolane and dimethoxyethane. In certain embodiments, an organic solvent comprises a 1 : 1 v/v mixture of 1,3-dioxolane and dimethoxy ethane. In certain embodiments, an organic solvent is selected from the group consisting of: diglyme, triglyme, y-butyrolactone, y-valerolactone, and combinations thereof. In certain embodiments, an electrolyte comprises sulfolane, sulfolene, dimethyl sulfone, methyl ethyl sulfone, or a combination thereof. In some embodiments, an electrolyte comprises ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, or a combination thereof.

[0106] In certain embodiments, an electrolyte is a solid. In certain embodiments, a solid electrolyte comprises a polymer. In certain embodiments, a solid electrolyte comprises a glass, a ceramic, an inorganic composite, or combinations thereof. In certain embodiments, a solid electrolyte comprises a polymer composite with a glass, a ceramic, an inorganic composite, or combinations thereof. In certain embodiments, such solid electrolytes comprise one or more liquid components as plasticizers or to form a “gel electrolyte”.

Separators

[0107] In certain embodiments, a secondary sulfur battery comprises a separator, which divides the anode and cathode and prevents direct electron conduction between them. In certain embodiments, the separator has a high lithium ion permeability. In certain embodiments, a separator is relatively less permeable to polysulfide ions dissolved in electrolyte. In certain such embodiments, a separator as a whole inhibits or restricts passage of electrolyte-soluble sulfides between anodic and cathodic portions of a battery. In certain embodiments, a separator of impermeable material is configured to allow lithium ion transport between anode and cathode of a battery during charging and discharging of a cell. In some such embodiments, a separator is porous. One or more electrolyte-permeable channels bypassing, or penetrating through apertures in, an impermeable face of a separator can be provided to allow sufficient lithium ion flux between anodic and cathodic portions of a battery.

[0108] It will be appreciated by a person skilled in the art that optimal dimensions of a separator must balance competing imperatives: maximum impedance to poly sulfide migration while allowing sufficient lithium ion flux. Aside from this consideration, shape and orientation of a separator is not particularly limited, and depends in part on battery configuration. For example, in some embodiments, a separator is substantially circular in a coin-type cell, and substantially rectangular in a pouch-type cell. In some embodiments, a separator is substantially flat. However, it is not excluded that curved or other non-planar configurations may be used.

[0109] A separator may be of any suitable thickness. In order to maximize energy density of a battery, it is generally preferred that a separator is as thin and light as possible. However, a separator should be thick enough to provide sufficient mechanical robustness and to ensure suitable electrical separation of the electrodes. In certain embodiments, a separator has a thickness of from about 1 pm to about 200 pm, preferably from about 5 pm to about 100 pm, more preferably from about 10 pm to about 30 pm.

Methods

[0110] In certain embodiments, an anode and a cathode with an ionically conductive polymer binder are combined with an electrolyte to form an electrochemical cell. In certain embodiments, the ionically conductive polymer binder includes a polymer, a dopant, and an ionic additive.

Forming the Ionically Conductive Polymer Binder

[OHl] A method synthesizes an ionically conductive polymer binder, where the ionically conductive polymer binder has at least three distinct components: a base polymer, a dopant and an ionic additive. In certain embodiments, the base polymer is an ionically conductive polymer. In certain embodiments, the base polymer comprises PPS. [0112] Methods of adding the dopant are known to those skilled in the art and can include vapor doping of a film containing the base polymer and other doping methods known to those skilled in the art. Upon doping, the polymer material becomes ionically conductive. Without being bound by theory, it is believed that the doping acts to activate the ionic components of the polymer material, so they are able to diffuse ions.

[0113] The components and method of synthesis are chosen for the particular application of the material. The selection of the base polymer, dopant and ionic additive may also vary depending on the desired performance of the material. In certain embodiments, the components and method of synthesis may be determined by optimization of a desired physical characteristic (e.g. ionic conductivity). The particular components and the desired form of the end material (for example, film or particulate) may also influence the method of synthesis.

[0114] In certain embodiments, the method includes the basic steps of mixing at least two of the polymer binder components initially, adding the third component in an optional second mixing step, and heating the components/reactants to synthesis the ionically conductive polymer material in a heating step. In certain embodiments, the resulting mixture is formed into a film of a desired size. If the dopant is not present in the mixture produced in the first step, then it can be subsequently added to the mixture while heat and optionally pressure (positive pressure or vacuum) are applied. In certain embodiments, all three components are present and mixed and heated to complete the synthesis of the polymer binder in a single step. In certain embodiments, the heating step may be done either in a separate step from the mixing step or concurrently with the mixing step. In certain embodiments, the heating step is performed regardless of the form (e.g.- film, particulate, etc.) of the mixture. In certain embodiments, all three components are mixed and then extruded into a film, which is heated to complete the synthesis.

[0115] In certain embodiments, a synthesis method includes a step of mixing the base polymer, ionic additive and dopant together, followed by heating the mixture. In certain embodiments, the heating step is performed in the presence of the dopant where the dopant can be in the gas phase. In certain embodiments, the mixing step is performed in an extruder, blender, mill or other equipment typical of plastic processing. In certain embodiments, the heating step can last several hours (e.g. twenty-four hours) and a color change is a reliable indication that synthesis is partially or fully complete. [0116] In certain embodiments, the base polymer and ionic additive are mixed first. The dopant is then mixed with the polymer-ionic compound mixture and heated. In certain embodiments, the heating is applied to the mixture during the mixture step. In certain other embodiments, the heating is applied to the mixture subsequent to the mixing step.

[0117] In certain embodiments, the base polymer and the dopant are first mixed and then heated. In certain embodiments, the heating is applied to the mixture during the mixture step. In certain other embodiments, the heating is applied to the mixture subsequent to the mixing step. Heating produces a color change indicating the formation of charge transfer complexes and a reaction between the dopant and the base polymer. In certain embodiments, the ionic additive is then mixed with the reacted polymer dopant material to complete the formation of the ionically conductive polymer binder.

[0118] The particular ionic compound included in the synthesis depends on the utility desired for the material. For example, when it is desirable to have a lithium cation, a lithium hydroxide or a lithium oxide convertible to a lithium and hydroxide ion may be appropriate. A lithium containing compound that releases both a lithium cathode and a diffusing anion may be used in the synthesis method. Non-limiting examples of these lithium ionic compounds includes those used as lithium salts in organic solvents.

[0119] In certain embodiments, other non-reactive components can be added to the polymer, dopants, and ionic compounds during the initial mixing steps, secondary mixing steps or mixing steps subsequent to heating. Such other components include, but are not limited to, depolarizers or electrochemically active materials such as anode or cathode active materials, electrically conductive materials such as carbons, rheological agents such as binders or extrusion aids (e.g. ethylene propylene diene monomer, EPDM), catalysts and other components useful to achieve the desired physical properties of the mixture.

[0120] In certain embodiments, the ionically conductive polymer binder is formed as a film, and then pressed onto the cathode. In certain other embodiments, the ionically conductive polymer binder is directly polymerized onto the cathode. In certain other embodiments, the ionically conductive polymer binder is formed in solution, and the solution coats the cathode. [0121] In certain embodiments, the synthesized polymer binder has a thickness between 2 microns and several 100 microns. In certain embodiments, the synthesized polymer binder has a thickness between 5 microns and 100 microns. In certain embodiments, the synthesized polymer binder has a thickness of less than 10 microns. In certain embodiments, the synthesized polymer binder has a thickness of more than 100 microns. In certain embodiments, the synthesized polymer binder has a thickness between 10 and 100 microns. In certain embodiments, an extruded polymer binder film has a thickness between .0003” and .005”.

Cathode Production

[0122] Cathode production typically involves applying a uniform layer of a cathode mixture onto a current conductor such as a metal foil or conductive carbon sheet. In certain embodiments, the present disclosure provides cathode mixtures that are useful for producing and manufacturing cathodes for batteries or other electrochemical devices. In some embodiments, the electroactive material is an electroactive sulfur-based material.

[0123] In certain embodiments, the electroactive sulfur material is mixed with electrically conductive particles (e.g., conductive carbon, such as carbon black, graphene, etc.) and a binder. Binders are typically polymeric materials that help adhere individual particles composing a cathode mixture into a stable composite. Generally, the binders hold the active materials together and are in intimate contact with a current collector (e.g., aluminum foil or copper foil, carbon paper or fabric).

[0124] In certain embodiments, the binder comprises an ionically conductive polymer binder. In certain embodiments, the ionically conductive polymer binder includes an ionically conductive polymer, a dopant, and an ionic additive. The ionically conductive polymer binder preferably replaces traditional inert binders with a material that contributes to the overall ion conductivity of the cathode.

[0125] In certain embodiments, the sulfur active material may be a carbon sulfur blend, a sulfur composition, or a sulfur-containing polymer.

[0126] There are a variety of methods for manufacturing the electrodes for use in a Li S battery. One such process, referred to as a “wet process,” involves adding a positive active material, a binder and a conducting material (i.e., the cathode composition) to a liquid to prepare a slurry. The compositions are typically formulated into a viscous slurry in order to facilitate a downstream coating operation. A thorough mixing of the slurry can be critical for the coating and drying operations, which will eventually affect the performance and quality of the electrodes. Appropriate slurry mixing devices include ball mills, magnetic stirrers, sonication, planetary mixers, high speed mixers, homogenizers, universal type mixers and static mixers. The liquid may be any that can effectively disperse the positive active material, the binder, the conducting material, and any additives homogeneously, and can be easily evaporated. Possible slurrying liquids include, for example, N-methylpyrrolidone, acetonitrile, methanol, ethanol, propanol, butanol, tetrahydrofuran, water, isopropyl alcohol, dimethylpyrrolidone and the like.

[0127] The prepared composition is coated on the current collector and dried to form the positive electrode. Specifically, the slurry is used to coat an electrical conductor to form the electrode by evenly spreading the slurry on to the conductor, which may then optionally be roll- pressed, calendared and heated as is known in the art. Generally, the dried slurry forms a matrix held together and adhered to the conductor by a polymeric binder included in the cathode mixture.

[0128] The matrix preferably comprises a polymer binder. In some embodiments, the ionically conductive polymer is doped. In certain embodiments, the binder also includes at least one ionic compound. In some of these embodiments, lithium salts are dispersed in the matrix to improve lithium conductivity. Additional carbon particles, carbon nanofibers, carbon nanotubes, etc. may also be dispersed in the matrix to improve electrical conductivity. In certain embodiments, the ionically conductive polymer in the binder is PPS.

[0129] The current collector may be selected from the group consisting of: aluminum foil, copper foil, nickel foil, stainless steel foil, titanium foil, zirconium foil, molybdenum foil, nickel foam, copper foam, conductive carbon papers, sheets, or fabrics, polymer substrates coated with conductive metal, and/or combinations thereof.

[0130] The thickness of the matrix may range from a few microns to hundreds of microns (e.g., 2-200 microns). In one embodiment, the matrix has a thickness of 10-50 microns.

Generally, increasing the thickness of the matrix increases the percentage of active materials to other cell constituents by weight, and may increase the cell capacity. However, diminishing returns may be exhibited beyond certain thicknesses. In one embodiment, the matrix has a thickness of between 5 and 200 microns. In a further embodiment, the matrix has a thickness of between 10 and 100 microns.

[0131] In other embodiments, provided cathode mixtures include nanostructured materials according to the embodiments and examples herein (e.g., nanowires, core-shell particles, etc.) optionally mixed with additional materials such as electrically conductive additives, binders, surfactants, stabilizers, wetting agents and the like. In certain embodiments, the binder includes an ionically conductive polymer.

[0132] Such mixtures are typically provided in the form of fine powders that can applied by techniques such as slurry coating or roll-to-roll processing. Cathode mixtures typically comprise relatively larger quantities of materials than materials made for experimental evaluation and it can be non-trivial to produce nanostructured materials with consistent characteristics in large batches. In certain embodiments, the cathode mixtures of the present disclosure are characterized in that they are comprise a homogenous sample with a quantity greater than 100 grams (g), greater than 1 kilogram (kg), greater than 10kg, greater than 100kg, or greater than 1 ton.

[0133] Nanostructures may contain electroactive sulfur in the cathode, for example by constructing nanoparticles with core-shell and yolk-shell structures. Such particles mitigate sulfide shuttling between the cathode and anode by physically containing electroactive sulfur inside of an impermeable shell. Yolk-shell structures comprise a hollow shell with an inner core, surrounded by a void space.

[0134] Generally, the various nanostructures disclosed herein can be used to produce cathodes. The yolk shell nanoparticle compositions described herein are preferably used to form a cathode composite for a lithium sulfur battery. The cathode composites optionally contain additional components (such as additives and binders) and can be used with liquid electrolytes or be comingled with solid electrolytes (polymer or inorganic). If polymers are used to form the nanostructure, the conductive polymer may be synthesized in the presence of sulfur (or IJ2S) nanoparticles to impart a coating. Or, the polymer may be formed around a removable template to make hollow particles that can be infused with sulfur.

[0135] In methods coating sulfur particles with a shell, a subsequent step of removing a portion of the sulfur from the core shell particle to create void space may be included to form yolk-shell structures. In the case of coated I 2S, the void space will form when the battery is charged and the I 2S is converted to a smaller volume of sulfur. The coated particles may also be heat treated, resulting in a vulcanized shell where, with conductive polymers including phenyl rings, the sulfur reacts with the phenyl rings to form covalent C-S bonds. This may also crosslink and rigidify the polymer shell.

[0136] In various embodiments that include nanoparticles, additional materials may be included with the nanostructured materials to alter or otherwise enhance the provided cathode mixtures produced from the mixture. Generally, the provided cathode mixtures will contain nanoparticles in a proportion ranging from about 50 wt% to about 98 wt%, preferably about 60 wt% to about 95 wt%, and more preferably about 75 wt% to about 95 wt% of the total cathode mixture.

[0137] In certain embodiments, cathode mixtures comprising the provided nanoparticles contain at least 50 wt% sulfur relative to all components in the cathode mixture. In certain embodiments, provided cathode mixtures are characterized in that they have a high sulfur content. In certain embodiments, provided cathode mixtures are characterized in that they contain above 60 wt%, above 65 wt%, above 70 wt%, above 75 wt%, above 80 wt%, above 85 wt%, or above 90 wt% sulfur relative to the total cathode mixture.

[0138] In various embodiments, the cathode mixture is ground, powdered or mixed to control the properties of the powder (e.g. particle size) and to thoroughly mix ingredients. Such mixing can be performed by any means known in the art including but not limited to pin milling, hammer milling, jet milling, ball milling, air classifying, and combinations of these. The specific means used for mixing the powder will vary to suit a particular application, such as large scale production of cathode mixtures (e.g., production of drum quantities of powder for sale to cathode manufacturers). [0139] In certain embodiments, cathode powder mixtures can be provided without a binder, which can be added during a manufacturing process to produce electrodes (e.g., as a solution or dispersion in water or a suitable carrier). In these embodiments, the binders that are added later preferably include an ionically conductive polymer, at least one dopant, and at least one ionic additive.

[0140] Various materials for use in cathode mixtures are disclosed in Cathode Materials for Lithium Sulfur Batteries: Design, Synthesis, and Electrochemical Performance, Lianfeng, et al., Interchopen.com, Published June 1st 2016 and The strategies of advanced cathode composites for lithium-sulfur batteries, Zhou et al., SCIENCE CHINA Technological Sciences, Volume 60, Issue 2: 175-185(2017), the entire disclosures of which are hereby incorporated by reference herein.

[0141] It is contemplated that compositions, systems, devices, methods, and processes of the present application encompass variations and adaptations developed using information from the embodiments described in the present disclosure. Adaptation or modification of the methods and processes described in this specification may be performed by those of ordinary skill in the relevant art.

[0142] Throughout the description, where compositions, compounds, or products are described as having, including, or comprising specific components, or where processes and methods are described as having, including, or comprising specific steps, it is contemplated that, additionally, there are articles, devices, and systems of the present application that consist essentially of, or consist of, the recited components, and that there are processes and methods according to the present application that consist essentially of, or consist of, the recited processing steps.

[0143] It should be understood that the order of steps or order for performing certain action is immaterial so long as the described method remains operable. Moreover, two or more steps or actions may be conducted simultaneously.

Claims

CLAIMS What is claimed is:

1. An electrochemical energy storage device comprising: an anode; a cathode comprising electroactive sulfur-based materials; a binder; and an electrolyte; wherein the binder comprises a doped polymer including an ionic additive.

2. The electrochemical energy storage device of claim 1, wherein the doped polymer comprises polyphenylene sulfide.

3. The electrochemical energy storage device of claim 1 or claim 2, wherein the ionic additive comprises a lithium salt.

4. The electrochemical energy storage device of any of the preceding claims, wherein the binder is about 2 to about 12 wt% of the cathode.

5. The electrochemical energy storage device of any of the preceding claims, wherein the cathode comprises a plurality of nanoparticles comprising a shell and the electroactive sulfurbased materials disposed within the shell.

6. The electrochemical energy storage device of any of the preceding claims, further comprising a separator that separates the cathode and the anode.

7. The electrochemical energy storage device of any of the preceding claims, wherein the electrolyte is a liquid electrolyte.

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8. The electrochemical energy storage device of any of the preceding claims, wherein the electrochemical energy storage device is a lithium sulfur battery.

9. A powder for use in making an electrode, the powder comprising: electroactive sulfur-based materials; electrically conductive particles; and a binder; wherein the binder comprises a doped polymer including an ionic additive.

10. The powder of claim 9, wherein the binder is about 2 to about 12 wt% of the cathode.

11. The powder of claims 9 or 10, wherein the doped polymer comprises polyphenylene sulfide.

12. A cathode comprising electroactive sulfur-based materials and a binder, wherein the binder comprises a doped polymer including an ionic additive.

13. The cathode of claim 12, wherein the binder is about 2 to about 12 wt% of the cathode.

14. The cathode of claim 12 or claim 13, wherein the doped polymer comprises polyphenylene sulfide.

15. The cathode of any one of claims 12 through 14, wherein the cathode comprises a plurality of nanoparticles comprises a plurality of nanoparticles comprising a shell and the electroactive sulfur-based materials disposed within the shell.

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