Battery cathode

Abstract

The present application relates to a lithium battery having a novel cathode comprising a current collector, at least one first active material layer comprising a conversion active material, and at least one second active material layer comprising a lithium ion intercalation active material. The present disclosure is also directed to a method of making and / or enhancing the performance of a lithium-sulfur battery comprising a current collector, at least one first active material layer comprising a conversion active material, and at least one second active material layer comprising a lithium ion intercalation active material, where the second active material layer is located between the current collector and the first active material layer.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 217,169, filed June 30, 2021, the disclosure of which is incorporated by reference in its entirety herein.

[0002] This application relates to cathodes for use in secondary batteries or other energy storage devices, and methods for making the same. [Background technology]

[0003] A major objective in the commercial development of next-generation rechargeable batteries is to provide batteries with higher energy density and lower cost than state of the art lithium-ion batteries. One of the most promising approaches to this goal is the use of sulfur cathodes combined with lithium metal anodes. Sulfur is cheap, abundant, and offers an order of magnitude higher theoretical energy capacity than the conventional metal oxide-based intercalation cathodes used in current lithium-ion cells. Similarly, metallic lithium-based anodes have substantially higher energy density than the lithium graphite anodes used in current lithium-ion cells. However, the fabrication of practical lithium-sulfur batteries has been an elusive goal. Among the many challenges that undermine sulfur cathodes, one of the more serious is the redistribution of sulfur inside the battery during operation, with the well-known phenomenon of polysulfide shuttles that cause soluble polysulfides to migrate toward and away from the anode, as well as the inappropriate precipitation of insoluble species such as sulfur, Li2S, and Li2S2 in places that become electrochemically inaccessible or cause other problems.

[0004] There remains a need to address these issues to enable the fabrication of practical sulfur batteries that exhibit high gravimetric energy density while providing discharge rates and cycle life capacities sufficient to function in critical applications such as electric vehicles. The present disclosure addresses these issues, and related challenges. Summary of the Invention

[0005] In particular, the present disclosure provides a cathode for a lithium battery comprising at least two active material layers, at least one of which comprises a conversion active material and at least one of which comprises a lithium ion intercalation active material. In some embodiments, the provided cathode is for a lithium-sulfur battery and comprises a current collector, at least one first active material layer comprising a conversion active material, and at least one second active material layer comprising a lithium ion intercalation active material, the second active material layer being located between the current collector and the first active material layer. In some embodiments, the provided cathode is characterized in that the intercalation / deintercalation potential (or discharge voltage) of the lithium ion intercalation active material overlaps with the potential of the conversion active material. In some embodiments, the conversion active material comprises electroactive sulfur. In certain embodiments, lithium-sulfur batteries using the provided cathodes have improved performance (e.g., cycle life, energy density, or active material utilization).

[0006] The present disclosure is also directed to a method of making and / or enhancing the performance of a lithium-sulfur battery comprising a current collector, at least one first active material layer comprising a conversion active material, and at least one second active material layer comprising a lithium ion intercalation active material, wherein the second active material layer is located between the current collector and the first active material layer.

[0007] definition In order that this disclosure may be more readily understood, certain terms are first defined below. Additional definitions of the following terms, as well as other terms, are set forth throughout the specification.

[0008] As used herein, unless otherwise clear from the context, the term "a" may be understood to mean "at least one." As used herein, the term "or" may be understood to mean "and / or." As used herein, the terms "comprising" and "including" may be understood to encompass an itemized component or step, whether presented by itself or together with one or more additional components or steps. As used herein, the term "comprise" and variations of terms such as "comprising" and "comprises" are not intended to exclude other additives, ingredients, integers or steps.

[0009] About, Approximately: As used herein, the terms "about" and "approximately" are used as equivalents. Unless otherwise stated, the terms "about" and "approximately" can be understood to allow for standard variations as understood by those of ordinary skill in the art. When numerical ranges are provided, the endpoints are included. Any numbers used herein with or without approximately / about are intended to encompass any normal variations that would be understood by one of ordinary skill in the art. In some embodiments, the term "about" or "approximately" refers to a range of values ​​that is included 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 both directions (greater or less than) the stated reference value, unless otherwise stated or otherwise clear from the context (except where such number exceeds 100% of the possible values).

[0010] Electroactive Sulfur: As used herein, the term "electroactive sulfur" refers to a sulfur-containing composition that contains one or more sulfur atoms that can change its oxidation state in a charge transfer step of an electrochemical reaction.

[0011] Polymer: As used herein, the term "polymer" generally refers to a substance having a molecular structure consisting primarily or entirely of repeating subunits bonded together, such as the synthetic organic materials used as plastics and resins.

[0012] Substantially: As used herein, the term "substantially" refers to the quantitative state of exhibiting a complete or near complete degree or degree of a desired feature or characteristic.

[0013] In the drawings, like reference numerals generally refer to the same parts throughout the different drawings. Also, the drawings are not necessarily to scale, and rather, emphasis is generally placed on illustrating the principles of the disclosed compositions and methods, and is not intended as being limiting. For clarity, not every component is labeled in every drawing. In the following description, various embodiments are described with reference to the following drawings: [Brief description of the drawings]

[0014] [Figure 1] 1 is a pictorial representation of a cross-section of an electrochemical cell according to one or more embodiments of the present disclosure.

[0015] [Diagram 2] 1 is a pictorial representation of a cross-section of an electrochemical cell according to one or more embodiments of the present disclosure.

[0016] [Diagram 3] 1 is a pictorial representation of a cylindrical battery embodying concepts of the present disclosure.

[0017] [Figure 4] 1 is a pictorial representation of a coin cell assembly in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In some embodiments, the present disclosure is directed to novel cathodes for use in lithium-sulfur batteries, and associated methods for making and using such devices. In some embodiments, the present disclosure provides such lithium-sulfur batteries, where the cathode comprises an active material layer of at least one conversion active material and at least one lithium ion intercalation active material. Such active material layers provide improved electrochemical cycling characteristics at higher current densities and improved cycle life.

[0019] The present disclosure embraces the recognition that the accumulation of undesirable sulfur deposits in the cathode of a lithium-sulfur battery can result in "cathode shutdown," i.e., an increase in cell resistance, a decrease in cell voltage, and / or limitations to the rate capability of the cell. Such deposits can occur, for example, within the pore structure of the cathode and / or at the surface of the cathode. Without wishing to be bound by any particular theory, applicants propose that cathode shutdown may occur due to high concentrations of sulfides at the cathode / separator interface. Such high concentrations of sulfides may be due, for example, to soluble sulfides migrating toward the cathode and / or to polysulfides that are rapidly oxidized at the cathode / separator interface as they return from the anode side of the cell during a charge cycle. Thus, the present invention, in some embodiments, provides identification of a previously unknown cause of the problem.

[0020] In lithium-battery cells, sulfides move due to both migration and diffusion. Migration can occur because an electric field is created that can simultaneously generate high concentrations of lithium ions at the anode and high concentrations of sulfides at the cathode. Diffusion can occur because high concentrations of soluble sulfides are generated at the cathode, creating a concentration gradient. The present disclosure embraces the recognition that it may be desirable to have a uniform concentration of polysulfides in the cathode host for more optimal kinetics and cycle life.

[0021] The cathodes provided by the present disclosure promote conditions in which sulfides may migrate back toward the cathode current collector due to a high concentration of cations in close proximity to the cathode current collector. This may be accomplished in some embodiments by coating the current collector with a lithium ion intercalation compound (e.g., lithium ion intercalation active material). Without wishing to be bound by any particular theory, the lithium ion intercalation active material may deintercalate and release lithium ions to the cathode upon charging the battery, resulting in a local concentration of cations, followed by the migration of anions (e.g., sulfides) back toward the current collector. Applicants propose that additional charging may reoxidize the sulfides to sulfur, rebalancing the lithium concentration of the cell. Providing an additional source of lithium cations to the cathode as described by the present disclosure balances the concentration of lithium, thus counteracting the development of an anion concentration gradient within the battery cell. Therefore, this novel approach is designed to retain polysulfides inside the cathode and avoid or minimize the buildup of uncontrolled sulfur deposits on the cathode surface that could result in shutdown.

[0022] In certain embodiments, suitable lithium ion active materials exhibit an intercalation / deintercalation potential (or discharge voltage) that overlaps with the discharge voltage range of the conversion active material. For example, when sulfur is the conversion material, the voltage window of the intercalation / deintercalation material overlaps with the potential at which sulfur-lithium sulfide interconversion occurs. In some embodiments, a mixture of lithium ion intercalation compounds may be useful to maximize the overlap between the intercalation potential(s) (or discharge voltage(s)) of the mixture of lithium ion intercalation compounds and the intercalation potential of the conversion active material.

[0023] FIG. 1 illustrates a cross-section of an electrochemical cell 800 according to an exemplary embodiment of the present disclosure. The electrochemical cell 800 includes a negative electrode 802, a positive electrode 804, a separator 806 interposed between the negative electrode 802 and the positive electrode 804, a container 810, and a fluid electrolyte 812 in contact with the negative electrode 802 and the positive electrode 804, respectively. Such a cell optionally includes additional electrode and separator layers 802a, 802b, 804a, 804b, 806a, and 806b. FIG. 2 illustrates another view of a cross-section through a representative cell stack showing the negative electrode 802, the positive electrode 804, and the separator 806 interposed between the negative electrode 802 and the positive electrode 804, and FIG. 2 also illustrates the layers including the electrode 804. Specifically, the layers include a current collector 804-1, a cathode layer 804-2 including a lithium intercalation active material, and a cathode layer 804-3 including a conversion active material. As shown, the lithium intercalation active material 804-2 is interposed between the current collector 804-1 and the cathode layer 804-3.

[0024] The negative electrode 802 (sometimes referred to herein as the anode) comprises a negative electrode active material capable of accepting cations. Non-limiting examples of negative electrode active materials for lithium-based electrochemical cells include Li metal, Si, Sn, Bi, In, and / or Li alloys, such as Al alloys, Li4Ti5O 12 , hard carbon, graphitic carbon, metal chalcogenides, and / or amorphous carbon. According to some embodiments of the present disclosure, most (e.g., greater than 90% by weight) of the anode active material may be included in the positive electrode 804 (also sometimes referred to herein as the cathode), which is initially discharged when the electrochemical cell 800 is first fabricated, such that the electrode active material forms part of the first electrode 802 during the initial charging of the electrochemical cell 800.

[0025] Techniques for depositing an electroactive material onto a portion of the negative electrode 802 are described in U.S. Patent Application Publication No. 2016 / 0172660, and similarly U.S. Patent Application Publication No. 2016 / 0172661, the contents of each of which are incorporated by reference herein to the extent such content is not inconsistent with this disclosure.

[0026] The negative electrode 802 and the positive electrode 804 may further include one or more conductive additives herein. According to some embodiments of the present disclosure, the negative electrode 802 and / or the positive electrode 804 further include one or more polymer binders, as described below.

[0027] FIG. 3 shows an example of a battery according to various embodiments described below. A cylindrical battery is shown here for illustrative purposes, but other types of configurations including prismatic or pouch (laminated type) batteries may be used if desired. The 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. Of course, the example battery 901 may simultaneously embody multiple aspects of the present disclosure in various designs.

[0028] In some embodiments, the lithium-sulfur battery of the present disclosure includes a lithium anode, a sulfur-based cathode, and an electrolyte that allows for ion transport between the anode and the cathode. In certain embodiments described herein, the anode portion of the battery includes the anode and a portion of the electrolyte with which it is in contact. Similarly, in certain embodiments described herein, the cathode portion of the battery includes the cathode and a portion of the electrolyte with which it is in contact. In certain embodiments, the battery includes a lithium-ion permeable separator that defines a boundary between the anode portion and the cathode portion. In certain embodiments, the battery includes a case that encapsulates both the anode portion and the cathode portion. In certain embodiments, the battery case includes a conductive anode end cover in electrical communication with the anode and a conductive cathode end cover in electrical communication with the cathode to facilitate charging and discharging via an external circuit.

[0029] A. Cathode The cathodes described herein have a multi-layer structure and include at least one first active material layer and at least one second active material layer. In certain embodiments, the first active material layer includes a conversion active material. In certain embodiments, the second active material layer includes a lithium ion intercalation active material. In some embodiments, the provided cathodes include at least one first active material layer including a conversion active material and at least one second active material layer including a lithium ion intercalation active material.

[0030] In certain embodiments, a cathode is provided that includes a current collector. In some embodiments, a cathode is provided that includes a current collector, at least one first active material layer that includes a conversion active material, and at least one second active material layer that includes a lithium ion intercalation active material. In certain embodiments, the second active material layer that includes the lithium ion intercalation active material is disposed between the current collector and the first active material layer that includes the conversion active material.

[0031] In certain embodiments, the current collector comprises a component selected from a metal foil, a metallized polymer film, and a carbon composition. In some embodiments, the current collector comprises aluminum foil, copper foil, nickel foil, stainless steel foil, titanium foil, zirconium foil, molybdenum foil, nickel foam, copper foam, carbon paper or fiber sheet, polymer substrate coated with a conductive metal, and / or combinations thereof. In certain embodiments, the current collector comprises a metal foil. In certain embodiments, the current collector comprises a metallized polymer film. In certain embodiments, the current collector comprises a carbon composition. In certain embodiments, the cathode comprises a conductive carbon coating between the current collector and a second active layer comprising a lithium ion intercalation active material.

[0032] In certain embodiments, both the first active material layer comprising the conversion active material and the second active material layer comprising the lithium ion intercalation active material are porous. In certain embodiments, the first active material layer comprising the conversion active material is porous. In certain embodiments, the second active material layer comprising the lithium ion intercalation active material is porous. In certain embodiments, the second active material layer comprising the lithium ion intercalation active material exhibits a lower porosity than the first active material layer comprising the conversion active material. In certain embodiments, the second active material layer comprising the lithium ion intercalation active material exhibits the same porosity as the first active material layer comprising the conversion active material. In certain embodiments, the second active material layer comprising the lithium ion intercalation active material exhibits a higher porosity than the first active material layer comprising the conversion active material.

[0033] In certain embodiments, the first active layer comprising the conversion active material comprises a porosity gradient. In certain embodiments, the first active layer comprising the conversion active material comprises a lower porosity toward the interface between the first active layer comprising the conversion active material and the second active layer comprising the lithium ion intercalation active material.

[0034] In certain embodiments, the discharge voltage range of the conversion active material and the discharge voltage range of the lithium ion intercalation active material substantially overlap. In certain embodiments, the discharge voltage range of the lithium ion intercalation active material is higher than the discharge voltage range of the conversion active material. In certain embodiments, the discharge voltage range of the lithium ion intercalation active material is equal to the discharge voltage range of the conversion active material. In certain embodiments, the discharge voltage range of the lithium ion intercalation active material is lower than the discharge voltage range of the conversion active material.

[0035] In certain embodiments, the lithium ion intercalation active material includes a discharge voltage (or potential) range of about 1 to about 3 volts. In certain embodiments, the lithium ion intercalation active material includes a discharge voltage range of about 1.5 to about 2.8 volts. In certain embodiments, the lithium ion intercalation active material includes a discharge voltage range of about 1.8 to about 2.8 volts. In certain embodiments, the lithium ion intercalation active material includes a discharge voltage range of about 2 to about 2.5 volts. In certain embodiments, the lithium ion intercalation active material includes a discharge voltage range of about 2 to about 2.2 volts. In certain embodiments, the lithium ion intercalation active material includes a discharge voltage of about 2, 2.1, or 2.2 volts.

[0036] In certain embodiments, the conversion active material includes a discharge voltage (or potential) range of about 1 to about 3 volts. In certain embodiments, the conversion active material includes a discharge voltage range of about 1.5 to about 2.8 volts. In certain embodiments, the conversion active material includes a discharge voltage range of about 1.8 to about 2.8 volts. In certain embodiments, the conversion active material includes a discharge voltage range of about 2 to about 2.5 volts. In certain embodiments, the conversion active material includes a discharge voltage range of about 2 to about 2.2 volts. In certain embodiments, the conversion active material includes discharge voltages of about 2, 2.1, and 2.2 volts.

[0037] In certain embodiments, the conversion active material comprises a theoretical total discharge capacity that is about 2 to about 5 times greater than the discharge capacity of the lithium ion intercalation material. In certain embodiments, the conversion active material comprises a theoretical total discharge capacity that is about 2 to about 4 times greater than the discharge capacity of the lithium ion intercalation active material. In certain embodiments, the conversion active material comprises a theoretical total discharge capacity that is about 3 to about 4 times greater than the discharge capacity of the lithium ion intercalation active material. In certain embodiments, the conversion active material comprises a theoretical total discharge capacity that is about 2, 3, 4, and 5 times greater than the discharge capacity of the lithium ion intercalation active material.

[0038] In certain embodiments, the lithium ion intercalation active material comprises one or more components selected from the group consisting of metal oxides, metal sulfides, metal phosphates, metal selenides, mixtures, and / or combinations thereof. In certain embodiments, the lithium ion intercalation active material comprises one or more metal sulfides. In certain embodiments, the lithium ion intercalation active material comprises a metal sulfide. In certain embodiments, the metal sulfide is selected from the group consisting of vanadium sulfide (e.g., VS2), molybdenum sulfide (e.g., MoS2 and / or Mo6S8), and titanium sulfide (e.g., TiS2). In certain embodiments, the metal sulfide is selected from the group consisting of VS2, MoS2, Mo6S8, and TiS2. In certain embodiments, the metal sulfide is TiS2. In certain embodiments, the metal sulfide is Mo6S8.

[0039] In certain embodiments, the provided cathodes include three or more active material layers, each active material layer being selected from a conversion active material and a lithium ion intercalation active material. In certain embodiments, the provided cathodes include 3 to 12 active material layers. In certain embodiments, the provided cathodes include 4 to 12 active material layers. In certain embodiments, the provided cathodes include 4 to 8 active material layers. In certain embodiments, the provided cathodes include 4 to 6 active material layers. In certain embodiments, the provided cathodes include 3 to 6 active material layers. In certain embodiments, the provided cathodes include 6 to 12 active material layers. In certain embodiments, the provided cathodes include 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 active material layers. In certain embodiments, the provided cathodes include alternating layers of conversion active material and lithium ion intercalation active material. In certain embodiments, the active material layer closest to the current collector includes a lithium intercalation active material. In certain embodiments, the lithium ion intercalation active material can function as a current collector, such as a tri-layer cathode having lithium ion intercalation active material located between two layers of conversion active material, and a cathode tab is welded along the side of the cathode.

[0040] In certain embodiments, the lithium-sulfur battery includes a sulfur-based cathode. In certain embodiments, the lithium-sulfur battery cathode includes a positive electrode active material and a conductive material. In certain embodiments, the lithium-sulfur battery cathode includes a positive electrode active material, a conductive material, and a binder. In certain embodiments, the positive electrode active material is electroactive sulfur. In certain embodiments, the electroactive sulfur is selected from the group consisting of elemental sulfur (S8), a sulfur-based compound, a sulfur-containing polymer, or a combination thereof. In certain embodiments, the sulfur-based compound is Li2S n (n≧1), organic-sulfur compounds, and carbon-sulfur polymers (C2S x ) nwhere x=2.5-50 and n≧2. In certain embodiments, the electroactive sulfur in the lithium-sulfur battery comprises elemental sulfur. In certain embodiments, the electroactive sulfur in the lithium-sulfur battery comprises a sulfur-containing polymer.

[0041] In certain embodiments, the conductive material comprises a conductive material that facilitates the movement of electrons within the cathode. For example, in certain embodiments, the conductive material is selected from the group consisting of carbon-based materials, graphite-based materials, conductive polymers, and combinations thereof. In certain embodiments, the conductive material comprises a carbon-based material. In certain embodiments, the conductive material comprises a carbon-based material. For example, in certain embodiments, the conductive material is selected from the group consisting of conductive carbon powders such as carbon black, Super P®, C-NERGY™ SuperC65, Ensaco® black, Ketjenblack®, acetylene black, synthetic graphite such as Timrex® SFG-6, Timrex® SFG-15, Timrex® SFG-44, Timrex® KS-6, Timrex® KS-15, Timrex® KS-44, natural flake graphite, graphene, graphene oxide, carbon nanotubes, fullerenes, hard carbon, mesocarbon microbeads, and the like. In certain embodiments, the conductive material comprises one or more conductive polymers. For example, in certain embodiments, the conductive polymer is selected from the group consisting of polyaniline, polythiophene, polyacetylene, polypyrrole, and the like. In certain embodiments, the conductive material is used alone. In other embodiments, the conductive material is used as a mixture of two or more of the conductive materials mentioned above.

[0042] In certain embodiments, a binder is attached to the positive electrode active material of the current collector. Typical binders include polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropene) (PVDF / HFP), polytetrafluoroethylene (PTFE), Kynar Flex® 2801, Kynar® Powerflex LBG, Kynar® HSV 900, Teflon®, carboxymethylcellulose, styrene-butadiene rubber (SBR), polyethylene oxide, polypropylene oxide, polyethylene, polypropylene, polyacrylate, polyvinylpyrrolidone, poly(methyl methacrylate), polyethyl acrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polycaprolactam, polyethylene terephthalate, polybutadiene, polyisoprene, or polyacrylic acid, or any derivative, mixture, or copolymer thereof. In some embodiments, the binder is a water-soluble binder such as sodium alginate or carboxymethylcellulose. Generally, the binder holds the active materials together and in contact with the current collector (e.g., aluminum or copper foil). In certain embodiments, the binder is selected from the group consisting of poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), polyvinylidene fluoride, copolymers of polyhexafluoropropylene and polyvinylidene fluoride, polyethyl acrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polystyrene, and derivatives, mixtures, and copolymers thereof.

[0043] In certain embodiments, the cathode further comprises a coating layer. For example, in certain embodiments, the coating layer comprises a polymer, an inorganic material, or a mixture thereof. In certain such embodiments, the polymer is selected from the group consisting of polyvinylidene fluoride, copolymers of polyvinylidene fluoride and hexafluoropropylene, poly(vinyl acetate), poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), poly(methyl methacrylate-co-ethyl acrylate), polyacrylonitrile, polyvinyl chloride-co-vinyl acetate, polyvinyl alcohol, poly(1-vinyl pyrrolidone-co-vinyl acetate), cellulose acetate, polyvinyl pyrrolidone, polyacrylates, polymethacrylates, polyolefins, polyurethanes, polyvinyl ethers, acrylonitrile-butadiene rubber, styrene butadiene rubber, acrylonitrile-butadiene styrene, sulfonated styrene / ethylene-butylene / styrene triblock copolymers, polyethylene oxide, and derivatives, mixtures, and copolymers thereof. In certain such embodiments, the inorganic material includes, for example, colloidal silica, amorphous silica, surface-treated silica, colloidal alumina, amorphous alumina, tin oxide, titanium oxide, titanium sulfide (TiS2), vanadium oxide, zirconium oxide (ZrO2), iron oxide, iron sulfide (FeS), iron titanate (FeTiO3), barium titanate (BaTiO3), and combinations thereof. In certain embodiments, the organic material includes conductive carbon. In certain embodiments, the organic material includes graphene, graphene oxide.

[0044] In certain embodiments, the provided mixture can be formulated without a binder, which can be added during the manufacture of the electrode (e.g., dissolved in a solvent used to form a slurry from the provided mixture). In embodiments in which a binder is included in the provided mixture, the binder can be activated when slurried to manufacture the electrode.

[0045] Materials suitable for use in the cathode mixture include those disclosed in Cathode Materials for Lithium Sulfur Batteries: Design, Synthesis, and Electrochemical Performance, Lianfeng, et al., Interchopen.com, published June 1, 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 each of which are incorporated herein by reference.

[0046] B. Anode In certain embodiments, the lithium battery (e.g., lithium-sulfur battery) includes a lithium anode. Any lithium anode suitable for use in lithium-sulfur batteries can be used. In certain embodiments, the anode of the lithium-sulfur battery includes a negative electrode active material selected from a material in which lithium intercalation occurs reversibly, a material that reacts with lithium ions to form a lithium-containing compound, metallic lithium, a lithium alloy, and combinations thereof. In certain embodiments, the anode includes metallic lithium. In certain embodiments, the lithium-containing anode composition includes a carbon-based compound. In certain embodiments, the carbon-based compound is selected from the group consisting of crystalline carbon, amorphous carbon graphite, and mixtures thereof. In certain embodiments, the material that reacts with lithium ions to form a lithium-containing compound is selected from the group consisting of tin oxide (SnO2), titanium nitrate, and silicon. In certain embodiments, the lithium alloy includes an alloy of lithium with another alkali metal (e.g., sodium, potassium, rubidium, or cesium). In certain embodiments, the lithium alloy includes an alloy of lithium with a transition metal. In certain embodiments, the lithium alloy comprises an alloy of lithium with a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, Sn, and combinations thereof. In certain embodiments, the lithium alloy comprises an alloy of lithium with indium. In certain embodiments, the anode comprises a lithium-silicon alloy. An example of a suitable lithium-silicon alloy is Li 15 Si4, Li 12 Si7, Li7Si3, Li 13 Si4 and Li 21 Si5 / Li 22 In certain embodiments, the lithium metal or lithium alloy is present as a composite with another material. In certain embodiments, such a composite includes a material such as graphite, graphene, a metal sulfide or oxide, or a conductive polymer.

[0047] The anode may be protected from redox shuttling reactions and detrimental runaway reactions by any method reported in the art, for example, by chemical passivation or polymerization to create a protective layer on the surface of the anode. For example, in certain embodiments, the anode comprises an inorganic protective layer, an organic protective layer, or a mixture thereof, on the surface of the lithium metal. In certain embodiments, the inorganic protective layer comprises Mg, Al, B, Sn, Pb, Cd, Si, In, Ga, lithium silicate, lithium borate, lithium phosphate, lithium phosphate nitride, lithium silicate sulfide, lithium borosulfide, lithium aluminosulfide, lithium phosphosulfide, lithium fluoride, or a combination thereof. In certain embodiments, the organic protective layer comprises a conductive monomer, oligomer, or polymer selected from poly(p-phenylene), polyacetylene, poly(p-phenylenevinylene), polyaniline, polypyrrole, polythiophene, poly(2,5-ethylenevinylene), acetylene, poly(perinaphthalene), polyacene, and poly(naphthalene-2,6-di-yl), or combinations thereof.

[0048] Furthermore, in certain embodiments, during charging and discharging of a lithium-sulfur battery, inert sulfur material generated from the electroactive sulfur material of the cathode is deposited on the anode surface. As used herein, the term "inert sulfur" refers to sulfur that is not active in repeated electrochemical and chemical reactions and cannot participate in the electrochemical reactions of the cathode. In certain embodiments, the inert sulfur on the anode surface acts as a protective layer for such electrodes. In certain embodiments, the inert sulfur is lithium sulfide.

[0049] It is further contemplated that the present disclosure may be adapted for use in sodium-sulfur batteries, which include a sodium-based anode and are included within the scope of the present disclosure.

[0050] C. Electrode Preparation There are various methods for manufacturing electrodes for use in lithium batteries (e.g., lithium-sulfur batteries). One process, such as the "wet process," involves adding the positive electrode active material, binder, and conductive material (i.e., cathode mixture) to a liquid to prepare a slurry composition. These slurries are typically in the form of viscous liquids formulated to facilitate downstream coating operations. Thorough mixing of the slurry can be important for coating and drying operations, which affect the performance and quality of the electrode. Suitable mixing devices include ball mills, magnetic stirrers, ultrasonication, planetary mixers, high-speed mixers, homogenizers, universal mixers, and static mixers. The liquid used to make the slurry can be one that uniformly disperses the positive electrode active material, binder, conductive material, and any additives, and evaporates easily. Suitable slurry liquids include, for example, N-methylpyrrolidone, acetonitrile, methanol, ethanol, propanol, butanol, tetrahydrofuran, water, isopropyl alcohol, dimethylpyrrolidone, and the like.

[0051] In some embodiments, the prepared composition is coated onto a current collector and dried to form an electrode. Specifically, the slurry is used to coat a conductor and form an electrode by uniformly spreading the slurry on the conductor, which in certain embodiments is then roll pressed (e.g., calendered) and heated as known in the art. In general, the matrix of positive electrode active material and conductive material is held together on the conductor by a binder. In certain embodiments, the matrix includes a lithium conductive polymer binder, such as polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropene) (PVDF / HFP), polytetrafluoroethylene (PTFE), Kynar Flex® 2801, Kynar® Powerflex LBG, Kynar® HSV 900, Teflon®, styrene butadiene rubber (SBR), polyethylene oxide (PEO), or polytetrafluoroethylene (PTFE). In certain embodiments, additional carbon particles, carbon nanofibers, carbon nanotubes are dispersed in the matrix to improve electrical conductivity. Alternatively or additionally, in certain embodiments, lithium ions are dispersed in the matrix to improve lithium conductivity.

[0052] In certain embodiments, the current collector is 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, carbon paper or fiber sheet, polymer substrate coated with a conductive metal, and / or combinations thereof.

[0053] PCT Publication Nos. WO2015 / 003184, WO2014 / 074150, and WO2013 / 040067, the disclosures of which are incorporated herein by reference in their entireties, describe various methods of manufacturing electrodes and electrochemical cells.

[0054] D. Separator In certain embodiments, the lithium-sulfur battery includes a separator that separates the anode and the cathode. In certain embodiments, the separator is an impermeable material that is substantially or completely impermeable to the electrolyte. In certain embodiments, the separator is impermeable to polysulfide ions dissolved in the electrolyte. In certain embodiments, the separator is generally impermeable to the electrolyte such that the passage of electrolyte-soluble sulfides is prevented. In some embodiments, ionic conductivity throughout the separator is provided, for example, through openings in such a separator. In certain such embodiments, the separator as a whole inhibits or limits the passage of electrolyte-soluble sulfides between the anode and cathode portions of the battery as a result of its impermeability. In certain embodiments, the impermeable material separator is configured to allow lithium ion transport between the anode and cathode of the battery during charging and discharging of the cell. In some such embodiments, the separator does not completely separate the anode and cathode from one another. To allow sufficient lithium ion flow between the anode and cathode portions of the battery, one or more electrolyte permeable channels must be provided that bypass or penetrate the impermeable surface of the separator. In some embodiments, where the separator itself is completely impermeable, the channels are provided through an annulus between the periphery of the separator and the wall of the battery case.

[0055] It will be understood by those skilled in the art that the optimum dimensions of the separator must balance competing demands, namely maximum impedance to polysulfide migration while enabling sufficient lithium ion flux. Beyond this consideration, the shape and orientation of the separator is not particularly limited and will depend in part on the configuration of the battery. For example, the separator may be substantially circular for coin type cells and substantially rectangular for pouch type cells. As described herein, the surface of the separator may be devoid of openings, so that lithium ion flux occurs exclusively around the edges of the impermeable sheet. However, certain embodiments are contemplated in which some or all of the required lithium ion flux is provided through the openings in the separator. In some embodiments, the separator is substantially flat. However, it is not excluded that curved or other non-flat configurations may be used.

[0056] The separator can be of any suitable thickness. To maximize the energy density of the battery, it is generally preferred that the separator be as thin and lightweight as possible. However, the separator should be thick enough to provide sufficient mechanical robustness and ensure adequate impermeability. In certain embodiments, the separator has a thickness of about 1 micron to about 200 microns, preferably about 5 microns to about 100 microns, and more preferably about 10 microns to about 30 microns.

[0057] E. Electrolyte In certain embodiments, the lithium-sulfur battery includes an electrolyte that includes an electrolyte salt, such as lithium trifluoromethanesulfonimide, lithium triflate, lithium perchlorate, LiPF6, LiBF4, tetraalkylammonium salts (e.g., tetrabutylammonium tetrafluoroborate, TBABF4), and salts that are liquid at room temperature (e.g., imidazolium salts, such as 1-ethyl-3-methylimidazolium bis-(perfluoroethylsulfonyl)imide, EMIBeti).

[0058] In certain embodiments, the electrolyte comprises one or more alkali metal salts. In certain embodiments, such salts include lithium salts, such as LiCF3SO3, LiClO4, LiNO3, LiPF6, and LiTFSI, or combinations thereof. In certain embodiments, the electrolyte comprises an ionic liquid, such as 1-ethyl-3-methylimidazolium-TFSI, N-butyl-N-methyl-piperidinium-TFSI, N-methyl-n-butylpyrrolidinium-TFSI, and N-methyl-N-propylpiperidinium TFSI, or combinations thereof. In certain embodiments, the electrolyte comprises a superionic conductor, such as a sulfide, oxide, and phosphate, e.g., phosphorus pentasulfide, or combinations thereof.

[0059] In certain embodiments, the electrolyte is a liquid. For example, in certain embodiments, the electrolyte comprises an organic solvent. In certain embodiments, the electrolyte comprises only one organic solvent. In some embodiments, the electrolyte comprises a mixture of two or more organic solvents. In certain embodiments, the mixture of organic solvents comprises organic solvents from at least two groups selected from a weakly polar solvent group, a strongly polar solvent group, and a lithium-protected solvent.

[0060] As used herein, the term "weakly polar solvent" is defined as a solvent capable of dissolving elemental sulfur and having a dielectric coefficient less than 15. In some embodiments, the weakly polar solvent is selected from aryl compounds, bicyclic ethers, and acyclic carbonate compounds. Non-limiting examples of weakly polar solvents include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme, tetraglyme, and the like. As used herein, the term "strongly polar solvent" is defined as a solvent capable of dissolving lithium polysulfide and having a dielectric coefficient greater than 15. In some embodiments, the strong polar solvent is selected from bicyclic carbonate compounds, sulfoxide compounds, lactone compounds, ketone compounds, ester compounds, sulfate compounds, and sulfite compounds. Non-limiting examples of strong polar solvents include hexamethylphosphoric triamide, γ-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone, dimethylformamide, sulfolane, dimethylacetamide, dimethylsulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, ethylene glycol sulfite, etc. As used herein, the term "lithium protective solvent" is defined as a solvent that forms a good protective layer on the lithium surface, i.e., a stable solid electrolyte interface (SEI) layer, and exhibits a cycling efficiency of at least 50%. In some embodiments, the lithium protective solvent is selected from saturated ether compounds, unsaturated ether compounds, and heterocyclic compounds containing one or more heteroatoms selected from the group consisting of N, O, and / or S. Non-limiting examples of lithium protective solvents include tetrahydrofuran, 1,3-dioxolane, 3,5-dimethylisoxazole, 2,5-dimethylfuran, furan, 2-methylfuran, 1,4-oxane, 4-methyldioxolane, and the like.

[0061] In certain embodiments, the electrolyte is a liquid (e.g., an organic solvent). In some embodiments, the liquid is selected from the group consisting of an organic carbonate, an ether, a sulfone, water, an alcohol, a fluorocarbon, or any combination thereof. In certain embodiments, the electrolyte comprises an ether-based solvent.

[0062] In certain embodiments, the organic solvent comprises an ether. In certain embodiments, the organic solvent is selected from the group consisting of 1,3-dioxolane, dimethoxyethane, diglyme, triglyme, gamma-butyrolactone, gamma-valerolactone, and combinations thereof. In certain embodiments, the organic solvent comprises a mixture of 1,3-dioxolane and dimethoxyethane. In certain embodiments, the organic solvent comprises a 1:1 v / v mixture of 1,3-dioxolane and dimethoxyethane. In certain embodiments, the organic solvent is selected from the group consisting of diglyme, triglyme, gamma-butyrolactone, gamma-valerolactone, and combinations thereof. In certain embodiments, the electrolyte comprises sulfolane, sulfolene, dimethyl sulfone, or methyl ethyl sulfone. In some embodiments, the electrolyte comprises ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate.

[0063] In certain embodiments, the electrolyte comprises a liquid (e.g., an organic solvent). In some embodiments, the liquid is selected from the group consisting of organic carbonates, ethers, sulfones, water, alcohols, fluorocarbons, or any combination thereof. In certain embodiments, the electrolyte comprises an ether-based solvent. In certain embodiments, the electrolyte comprises a liquid selected from the group consisting of sulfolane, sulfolene, dimethyl sulfone, and methyl ethyl sulfone. In certain embodiments, the electrolyte comprises a liquid selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0064] In certain embodiments, the electrolyte is solid. In certain embodiments, the solid electrolyte comprises a polymer. In certain embodiments, the solid electrolyte comprises a glass, a ceramic, an inorganic composite, or a combination thereof. In certain embodiments, the solid electrolyte comprises a polymer composite comprising a glass, a ceramic, an inorganic composite, or a combination thereof. In certain embodiments, such solid electrolytes include one or more liquid components as plasticizers or to form a "gel electrolyte."

[0065] F. Lithium-sulfur battery In one aspect, the present invention provides a sulfur secondary battery comprising the above-mentioned cathode composition. In certain embodiments, such a battery comprises a lithium-containing anode composition combined with a cathode composition provided by a lithium conductive electrolyte. In some embodiments, such a battery also comprises additional components such as a separator between the anode and the cathode, anode and cathode current collectors, terminals capable of connecting the cell to an external load, and packaging such as a flexible pouch or rigid metal container. In some embodiments, the present disclosure is directed to a lithium-sulfur battery comprising a sulfur-containing cathode, a lithium-containing anode, and an electrolyte ionically bonding the anode and the cathode. It is further contemplated that the present disclosure regarding sulfur secondary batteries may be adapted for use in sodium-sulfur batteries, and such batteries are also considered to be within the scope of certain embodiments of the present disclosure. EXAMPLES

[0066] G. Working Example The following examples embody certain compositions and methods of the present disclosure and demonstrate the fabrication of lithium-sulfur batteries according to certain embodiments herein. Additionally, the following examples are included to demonstrate the principles of the disclosed compositions and methods and are not intended as limitations.

[0067] Example 1: Construction of a cell with a bilayer cathode containing a TiS2 layer and a carbon-sulfur composite layer Example 1 describes a cathode according to a particular embodiment of the invention in which a layer of TiS2 (i.e., the lithium ion intercalation active material) is interposed between an aluminum current collector and a layer of a carbon-sulfur composite (i.e., the conversion active material).

[0068] Cathode preparation. A slurry was made by combining TiS2 powder (350 g), conductive carbon (SuperC65™ 100 mg), and PVDF (50 mg) as a polymeric binder with sufficient NMP to obtain a castable slurry composition. This slurry was applied to an aluminum current collector with a doctor blade at a thickness of 0.2-0.4 mm and dried at 65°C under vacuum. A second slurry was prepared by mixing a sulfur-carbon composite (7:3 S:C ratio) containing sulfur melt dispersed in a porous carbon host with polyacrylic acid (partial sodium salt) and conductive carbon (superC65™) at a weight ratio of 77:9:14 with sufficient ethanol to form a castable slurry. This slurry was applied on a TiS2-coated current collector at a thickness of 0.2-0.4 mm, and the cathode was again dried at 65°C. The resulting cathodes had a total thickness of 175–185 micrometers and a concentration of 4.0–4.5 mg S and 2.4 mg TiS / cm. 2 had an area loading of .

[0069] Coin Cell Construction. Working in an inert atmosphere glove box, a 12.7 mm diameter punch obtained from the prepared bilayer cathode film was placed inside a CR2032 coin cell base and wetted with electrolyte (DME / DOL mixture containing LiTFSI and LiNO3), a polymer separator (Celgard™) was placed on top of the wet cathode and wetted with additional electrolyte, and a 14.3 mm diameter lithium foil disk was placed on top of the separator. The assembly was completed by placing a spacer, spring, and lid on top and crimping the cell closed. Each coin cell contained a total of 26-28 μL of electrolyte, resulting in an E / S ratio of approximately 5:1.

[0070] Comparative Example 2: Construction of a comparative cell having a single layer cathode containing a homogeneous mixture of TiS2 and carbon-sulfur composite

[0071] A slurry was prepared by mixing TiS2 powder (40 mg), 80% sulfur / carbon composite (360 mg), conductive carbon (55 mg), and polyacrylic acid (partial sodium salt) (45 mg) as the polymer binder with an appropriate amount of ethanol to form a castable slurry. This slurry was applied to an aluminum current collector using a doctor blade and dried at 65 °C for 12-24 hours. The resulting cathodes had a total thickness of 110-135 micrometers and areal loadings of 3.1-3.5 mg S and 0.4 mg TiS2 / cm2. A punch from this cathode was used to construct coin cells as described above in Example 1.

[0072] Example 3: Performance evaluation of the batteries of Examples 1 and 2. A set of five cells constructed according to the procedures of Examples 1 and 2 were evaluated using the following galvanostatic cycling protocol: a 5.5 formation cycle including an initial C / 10 discharge, followed by a C / 5 charge, a C / 10 discharge, a C / 5 charge and discharge, two C / 3 cycles, a C / 5 charge and a C / 10 discharge. Formation is followed by a loop of 19 C / 3 cycles followed by a C / 5 charge and a C / 10 discharge, which is repeated for at least 100 total cycles. 1C is fixed at 4.5mA for the cycling protocol, with each charge pulse at 2.8V and each discharge pulse at 1.8V, with a 10 minute rest step between each galvanostatic pulse.

[0073] The average cycle 6 volumes of coin cells constructed according to Examples 1 and 2 are summarized in Table 1. [Table 1] The data in Table 1 show that in the homogenous mixture, increasing the TiS2 content from 8% to 12% leads to a decrease in volume (199.2 -> 138.3 mAh / cc). In contrast, in the bilayer structure, the even higher TiS2 content unexpectedly shows a significantly improved volume (223.1 mAh / cc).

Claims

1. A cathode for a lithium battery, wherein the cathode comprises at least one first active material layer containing a conversion active material, and at least one second active material layer containing a lithium-ion intercalation active material.

2. The cathode comprises a current collector, a first active material layer containing a conversion active material, and a second active material layer containing a lithium-ion intercalation active material, wherein the second active material layer is located between the current collector and the first active material layer. The cathode according to claim 1.

3. The cathode according to claim 1, wherein the conversion active material contains an electroactive sulfur composition.

4. The cathode according to claim 3, wherein the electroactive sulfur composition is selected from sulfur element, lithium sulfide, lithium polysulfide, polythionate, sulfur-containing organic molecules, sulfur-containing polymers, sulfur-containing carbon compositions, and any combination of two or more thereof.

5. The cathode according to claim 1, wherein the discharge voltage range of the conversion active material and the discharge voltage range of the lithium-ion intercalation active material substantially overlap.

6. The cathode according to claim 1, wherein the lithium-ion intercalation active material exhibits a higher average discharge voltage than the conversion active material.

7. The cathode according to claim 1, wherein the lithium-ion intercalation active material exhibits a lower average discharge voltage than the conversion active material.

8. The cathode according to claim 1, wherein both the conversion active material and the lithium-ion intercalation active material have a discharge voltage in the range of 1.8 to 2.8 V.

9. The cathode according to claim 1, wherein the theoretically total discharge capacity of the conversion active material is between 2 and 5 times the discharge capacity of the lithium-ion intercalation active material.

10. The cathode according to claim 1, wherein the lithium-ion intercalation active material is selected from metal oxides, metal sulfides, metal phosphates, metal selenides, and any combination of two or more thereof.

11. The cathode according to claim 1, wherein the lithium-ion intercalation active material contains a metal sulfide.

12. The cathode according to claim 11, wherein the metal sulfide is selected from vanadium sulfide, molybdenum sulfide, and titanium sulfide.

13. wherein the metal sulfide is VS ２ , MoS ２ , Mo ６ S ８ , and TiS ２ The cathode according to claim 11, selected from

14. wherein the metal sulfide is TiS ２ The cathode according to claim 11, comprising ２ .

15. The cathode according to claim 1, wherein both the first and second active material layers are porous.

16. The cathode according to claim 1, wherein the second active material layer has a lower porosity than the first active material layer.

17. The cathode according to claim 1, wherein the first active layer has a porosity gradient and the first active layer has a lower porosity toward the interface with the second active layer.

18. The cathode according to claim 1, further comprising a conductive carbon coating between the current collector and the second active material layer.

19. The cathode according to claim 2, wherein the current collector comprises a component selected from the group consisting of a metal foil, a metallized polymer film, and a carbon composition.

20. A lithium battery comprising the cathode according to claim 1.

21. A method of manufacturing a lithium battery comprising the cathode according to claim 1.

22. A method of improving the performance of a lithium battery using the cathode according to claim 1.

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