Coating for separator or cathode of a lithium-sulfur or silicon-sulfur battery

Abstract

A battery comprising a sulfur-containing cathode, an anode, and a separator between the cathode and the anode, wherein the cathode or the separator has a coating comprising a single lithium ion conductor, the single lithium ion conductor comprising a polymeric lithium salt, the polymeric lithium salt being a polymer having a polysulfone backbone with pendant lithium bis(trifluoromethanesulfonyl)imide groups.

Description

AREA

[0001] The present disclosure relates to batteries, in particular to batteries with sulfur cathodes and especially to separators and cathodes thereof. BACKGROUND

[0002] This section provides background information that is relevant to the present disclosure but is not necessarily prior art.

[0003] Electric vehicles or EVs (e.g., hybrid electric vehicles (HEVs), battery electric vehicles (BEVs), plug-in hybrid EVs, and extended-range electric vehicles (EREVs)) require efficient, cost-effective, and safe energy storage systems with high energy density and high power. Lithium-ion batteries can be used in many applications ranging from vehicles to portable electronic devices, such as laptop computers, mobile phones, and so on. EVs powered by current lithium cobalt or lithium iron phosphate batteries often have a range of less than 160 km (100 miles) per charge, while longer ranges are desirable.

[0004] A battery based on Li-S chemistry offers an attractive technology that solves the two most pressing problems for an electric vehicle: the need for low cost and high specific density. Such and comparable batteries are described, for example, in US 2013 / 0017441 A1, DE 10 2011 004 094A1, US 2011 / 0059367 A1, DE 10 2010 018 731 A1, US 2009 / 0061288 A1, EP 2 246 923 A1, and the following Schneider article. (Schneider article: SCHNEIDER, Holger, et al. Influence of different electrode compositions and binder materials on the performance of lithium-sulfur batteries, Journal of Power Sources, 2012, vol. 205, pp. 420-425)

[0005] Li-S battery technology has been the subject of intensive research and development in both academia and industry due to its high specific energy of 2600 Wh / kg and the low cost of sulfur. The theoretical capacity of sulfur through two-electron reduction (S + 2Li+ + 2e <-> Li2S) is 1672 mAh / g (elemental sulfur is converted to S). 2- -anion). The discharge process begins with a crown S8 molecule and proceeds by reduction to higher-order polysulfide anions (Li2S8, Li2S6) at a higher voltage level (2.3 to 2.3 V), followed by further reduction to lower-order polysulfides (Li2S4, Li2S2) at a lower voltage level (2.1 V), and ends with the Li2S product. During the charge process, Li2S is converted back to S8 by the intermediate polysulfide anions S x oxidized. The S produced at the cathode xPolysulfides are soluble in the electrolyte and can migrate to the anode, where they react parasitically with the lithium electrode to generate lower-order polysulfides that diffuse back to the cathode and regenerate the higher polysulfide forms. Y.V. Mikhaylik & J.R. Akridge, "Polysulfide Shuttle Study in the Li / S Battery System," J. Electrochem. Soc., 151, A1969-A1976 (2004) and J.R. Akridge, Y.V. Mikhaylik & N. White, "Li / S fundamental chemistry and application to high-performance rechargeable batteries," Solid State Ionics, 175, 243-245 (2004) describe this shuttle effect, which leads to reduced sulfur utilization, self-discharge, poor ability to cycle repeatedly through oxidation and reduction, and reduced Coulombic efficiency of the battery. The insulating nature of S and Li2S results in poor electrode rechargeability and limited discharge rate.In addition, an 80% volume expansion occurs during discharge. These factors preclude the commercialization of Li-S batteries for EVs.

[0006] The theoretical energy density of a Si-S battery is comparable to that of a Li-S battery. However, because a Si-S battery uses the same sulfur chemistry, it suffers from the same problem of polysulfide diffusion to the anode.

[0007] To overcome these obstacles, extensive efforts have been devoted to the development of improved sulfur cathodes, primarily based on the infiltration or in situ growth of sulfur into or on conductive frameworks, such as conductive polymers (e.g., polythiophene, polypyrrole, and polyaniline) and porous carbons (e.g., activated carbons, mesoporous carbons, hollow carbon spheres, carbon fibers, and graphene). It has been found that, in general, the incorporation of sulfur into conductive polymers results in sulfur / polymer cathodes with improved capacity and cycling stability. The sulfur and the polymer can be cross-linked, resulting in electrodes with further improved cycling lifetime.Compared to polymer frameworks, carbon frameworks offer many advantages, such as better stability and conductivity, low cost, and tunable pore structure, making them more attractive candidates for sulfur cathodes. Polymers (e.g., poly(ethylene oxide) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)) can be coated onto the carbon / sulfur composites to further improve cycling life and Coulombic efficiency. Although extensive efforts have been made, current sulfur cathodes do not yet meet the requirements for high-performance Li / S batteries. Current sulfur cathodes do not sufficiently retard polysulfide migration to be able to extend cathode cycling life. During discharge of current sulfur / carbon cathodes, the cyclic S8 molecules are converted into polysulfides (Li2S). n, 2<n<8) umgewandelt. Angetrieben durch den Konzentrationsgradienten diffundieren die Polysulfide, die in dem Elektrolyt gelöst sind, unvermeidlich weg von den Kathoden, was ein schnelles Kapazitätsabklingen mit schlechter Zyklisierungslebensdauer verursacht. Nichtsdestotrotz benötigt eine funktionierende Kathode auch einen wirksamen Lithiumionentransport zwischen dem Elektrolyt und den Elektroden. Da Elektrolytmoleküle, Lithiumionen und die Polysulfide vergleichbare Diffusionskoeffizienten aufweisen, werden Kohlenstoffmaterialien, die fähig sind, die nach außen gehende Polysulfiddiffusion zu verzögern, auch den Transport von Elektrolyt und Lithiumionen verzögern, was in einem schlechten Leistungsgrad oder sogar einer Fehlfunktion der Kathode resultiert. Dieses grundsätzliche Dilemma hat bis jetzt verhindert, dass das Fachgebiet das große Potential von Li / S-Batterien verwirklicht.

[0008] Silicon-sulfur batteries also use a sulfur cathode and are therefore subject to the same problems of polysulfide migration. SUMMARY

[0009] This section provides a general summary and not necessarily a comprehensive disclosure of the invention and all of its features.

[0010] The present invention is based on the object of providing an improved battery comprising a sulfur-containing cathode, an anode and a separator between the cathode and the anode, and a method for improving the cycling stability of a battery.

[0011] This object is achieved by the subject matter of the independent patent claims. Advantageous embodiments of the present invention are described in the dependent claims.

[0012] Lithium-sulfur and silicon-sulfur batteries are disclosed, comprising a cathode or separator coated with a coating layer containing a single lithium ion conductor. The single lithium ion conductor comprises a polymeric lithium salt, wherein the polymeric lithium salt is a polymer having a polysulfone backbone with pendant lithium bis(trifluoromethanesulfonyl)imide groups.

[0013] In one aspect, a sulfur-containing electrode is coated with a coating layer containing a single lithium ion conductor. In another aspect, a separator for a battery is coated with a coating layer containing a single lithium ion conductor.

[0014] Also disclosed is a method of operating an electrical device that provides electricity to a device having a lithium-sulfur battery or a silicon-sulfur battery, wherein the battery has a cathode or separator with a coating layer comprising a single lithium ion conductor. The single lithium ion conductor comprises a polymeric lithium salt, wherein the polymeric lithium salt is a polymer having a polysulfone backbone with pendant lithium bis(trifluoromethanesulfonyl)imide groups. The single lithium ion conductor prevents or slows passage of polysulfide anions, resulting in improved cycling stability (capacity retention or charge maintenance during repeated cycles of discharge and recharge) for the battery.

[0015] Also not described in the invention is a method for increasing the charge retention of Li / S and Si / S batteries by applying to or depositing on one of the sulfur cathode or separator a coating layer or a cation exchange membrane layer containing a single lithium ion conductor to prevent or reduce the diffusion of polysulfide ions to the anode.

[0016] In various embodiments, the single lithium ion conductor is a polymeric lithium salt or an inorganic sulfide, oxide or phosphate lithium ion conductor.

[0017] In the discussion of the disclosed electrodes and batteries, and methods of making and using the same, "a," "an," "the," "at least one," and "one or more" are used interchangeably to indicate that at least one of the items is present; a plurality of such items may be present unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having" are inclusive and therefore specify the presence of specified items but do not preclude the presence of other items. The term "or" includes any combination and all combinations of one or more of the associated listed items. When the terms first, second, third, etc. are used to distinguish various items from one another, these terms are for convenience and do not limit the items.

[0018] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are provided for purposes of illustration only and are not intended to limit the scope of the present disclosure. DRAWING

[0019] The drawing illustrates an embodiment of the disclosed technology. The figure is a schematic representation of a structure for a battery with a sulfur cathode. DETAILED DESCRIPTION

[0020] The following is a detailed description of exemplary, non-limiting embodiments.

[0021] The figure depicts a structure for a cell or battery 10 in which foils of an anode 12, which may be a lithium-containing or silicon-containing anode, and a sulfur-containing cathode 14, separated by a foil of a polymer separator 16, are wound together or alternately stacked inside a cell casing 18. The polymer separator 16 is electrically non-conductive and ion-permeable due to the electrolyte solution filling its open pores. The polymer separator 16 may, for example, be a microporous polypropylene or polyethylene film. The casing 18 contains a non-aqueous lithium salt electrolyte solution to conduct lithium ions between the electrodes. The anode is connected to an anode current collector 20; the sulfur-containing cathode is connected to a cathode current collector 22.The terminals may be connected in a circuit to either discharge the battery by connecting a load (not shown) into the circuit or to charge the battery by connecting an external power source (not shown).

[0022] The battery or cell 10 may be shaped and constructed for specific uses, as is known in the art. For example, the loads may be electric motors for automotive and aerospace applications, consumer electronics, such as laptop computers and cell phones, and other consumer goods, such as cordless power tools, to name a few. The load may also be a power-generating device that charges the battery 10 for energy storage purposes. For example, the tendency of windmills and solar panel displays to generate electricity variably and intermittently results in the need to store excess energy for later use.Batteries with sulfur-containing cathodes can be constructed in four general ways: (1) as small solid cylinders, for example, laptop computer batteries; (2) as large solid cylinders with screwed terminals; (3) as soft, flat pouches, for example, mobile phone batteries with flat terminals flush with the body of the battery; and (4) as plastic boxes with large terminals in the form of aluminum and copper foil, such as battery packs for automobiles.

[0023] The battery 10 may optionally include a wide range of other components known in the art for performance-related or other practical purposes, for example, sealing shims, gaskets, terminal caps, etc. The battery 10 may also be connected in a suitably designed combination of electrical circuits in series and parallel with other similar batteries to produce a greater voltage output and higher current when the load requires it.

[0024] The battery 10 with a sulfur-containing cathode 14 can generate reversible sulfur during battery discharge through reversible electrochemical reactions that occur when an external circuit connecting the anode 12 and the cathode 14 is closed at a time when the cathode contains reducible sulfur. The average chemical potential difference between the cathode 14 and the anode 12 directs the electrons produced by the oxidation of lithium at the anode 12 through an external circuit to the cathode 14. Simultaneously, lithium ions produced at the anode are carried by the electrolyte solution through the microporous polymer separator 16 and toward the cathode 14. At the same time as Li ions enter the solution at the anode, Li +Ions from the solution recombine with electrons at the interface between the electrolyte and the cathode, and the lithium concentration in the active material of the cathode increases. The electrons flowing through an external circuit reduce the sulfur in the cathode 14. The electric current traveling through the external circuit can be harnessed and directed through the load until the sulfur in the cathode 14 is completely reduced and the capacity or performance of the battery 10 is reduced below the usable level for the particular practical application at hand.

[0025] The lithium-sulfur or silicon-sulfur battery 10 can be recharged at any time by applying an external power source to the battery 10, reversing the electrochemical reactions that occur during battery discharge and feeding back electrical energy. Connecting an external power source to the battery 10 forces the otherwise nonspontaneous oxidation of the lithium polysulfides at the cathode 14 to produce electrons and lithium ions. The electrons, which flow back to the anode 12 through an external circuit, and the lithium ions, which are carried by the electrolyte through the polymer separator 16 back to the anode 12, combine at the anode 12 and replenish it with lithium for consumption during the next battery discharge cycle.

[0026] The anode 12 has a base electrode material, for example, lithium metal, which serves as the active anode material. The lithium metal may be in the form of, for example, a lithium metal foil or a thin lithium film deposited on the anode current collector. The lithium metal may also be in the form of a lithium alloy, for example, a lithium-tin alloy, a lithium-aluminum alloy, a lithium-magnesium alloy, a lithium-zinc alloy, a lithium-silicon alloy (which is used as an electrode in a sulfur-silicon battery), or a mixture thereof.

[0027] The anode 12 may alternatively comprise any lithium host material capable of sufficient lithium intercalation and deintercalation while functioning as the anode of the lithium-ion battery 10. Examples of host materials include electrically conductive carbonaceous materials, for example, carbon, graphite, carbon nanotubes, graphene, and petroleum coke. Mixtures of such host materials may also be used. Graphite is widely used to form the anode because it is inexpensive, has favorable lithium intercalation and deintercalation characteristics, is relatively non-reactive, and can store lithium in quantities that produce a relatively high energy density.Commercial forms of graphite that can be used to manufacture Anode 12 include those from Timcal Graphite & Carbon headquartered in Bodio, Switzerland, Lonza Group headquartered in Basel, Switzerland, Superior Graphite headquartered in Chicago, IL, USA, or Hitachi Chemical Company headquartered in Japan.

[0028] In silicon-sulfur batteries, the anode is a porous silicon anode containing a lithium-silicon alloy, which is manufactured, for example, with silicon nanoparticles consisting of high-purity silicon or with silicon nanowires, specifically with a carpet-brush type morphology.

[0029] The anode comprises a polymer binder material in sufficient quantity to structurally hold the lithium host material together. Non-limiting examples of suitable binder polymers include polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyethylene, polypropylene, polytetrafluoroethylene, polybutadiene, polystyrene, polyalkyl acrylates and methacrylates, ethylene-(propylene-diene monomer) copolymer (EPDM) rubber, copolymers of styrene and butadiene, and mixtures of such polymers. Carboxymethylcellulose is a preferred binder for silicon-containing anodes.

[0030] The anode current collector 20 may be formed of copper or any other suitable electrically conductive material known to those skilled in the art.

[0031] The cathode 14 is a porous sulfur-containing electrode. A porous sulfur-containing electrode generally has a porous conductive carbonaceous material or other host material, such as conductive polymers or metal oxides, for example, any of those already mentioned as usable in the electrode, infiltrated with sulfur, which in its elemental form is a crown S8 molecule. When the battery is discharged, the cyclic S8 is reduced by a series of lithium sulfide compounds of progressively smaller volume via two-electron reduction (from elemental sulfur through the series Li2S8, Li2S6, Li2S4, Li2S2). When the battery is charged, the sulfides are oxidized back to crown S8.The positive electrode materials, which comprise the active lithium transition metal compound and conductive carbon or other conductive host material, are held together by means of a binder, for example any of those already mentioned above.

[0032] In one process, a sulfur-containing cathode can be fabricated by using a high-pore-volume carbon framework, then infiltrating the framework with molten crown S8. Porous carbon particles can be synthesized using an aerosol or spray process. To control the pore structure, surfactants (e.g., surfactants that are block copolymers of ethylene oxide and propylene oxide, such as those sold by BASF under the registered trademark PLURONIC®), silicate clusters, and colloidal silica particles of various sizes can be used as porogens (matrices) to form pores. The pore volume can be controlled by adjusting the amount of porogens added. Carbonization conditions (e.g., temperature and time) are controlled to ensure high electrical conductivity.Carbon nanotube networks (CNTs) can also be added to the carbon particle precursor solutions to further improve conductivity and discharge rate. A high pore volume allows for high sulfur loading; however, this must be balanced against maintaining adequate electrical conductivity.

[0033] In a synthesis of highly porous carbon particles with a specific surface area of 1219.4 m 2 / g and a pore volume of 4.01 cm 3 / g, for example, 2-3 g of sucrose and 4 g of a colloidal silica solution (20-30 nm) were added to 10 ml of 0.1 M HCl until completely dissolved. The resulting solution was used as a precursor solution and was then passed through an aerosol atomizer (TSI Model 3076) to generate aerosol droplets, using 40 psi of nitrogen as the carrier gas. The resulting particles were heated to 900 °C at a rate of 3 °C / min and kept under a nitrogen stream for 4 h. Afterward, a black powder was collected and immersed in a 5 M NaOH solution and stirred for 48 h. The solution was then filtered, washed several times with deionized water, and dried in an oven at 100 °C. The porous conductive carbon or other host material (e.g.,conductive polymers or metal oxides) is infiltrated with molten sulfur and then mixed with a binder and optionally additives and formed into an electrode.

[0034] The cathode current collector 22 may be formed of aluminum or other suitable electrically conductive material.

[0035] An electrically insulating separator 16 is positioned between the electrodes, for example, in batteries constructed as shown in the figure. The separator must be permeable to the ions, particularly lithium ions, to ensure ion transport for lithium ions between the positive and negative electrodes. Non-limiting examples of suitable separator materials include polyolefins, which may be homopolymers or random or block copolymers, either linear or branched, including polyethylene, polypropylene, and blends and copolymers thereof;Polyethylene terephthalate, polyvinylidene fluoride, polyamides (nylon), polyurethanes, polycarbonates, polyesters, polyetheretherketones (PEEK), polyethersulfones (PES), polyimides (PI), polyamideimides, polyethers, polyoxymethylene (acetal), polybutylene terephthalate, polyethylene naphthenate, polybutene, acrylonitrile-butadiene-styrene copolymers (ABS), styrene copolymers, polymethyl methacrylate, polyvinyl chloride, polysiloxane polymers (for example, polydimethylsiloxane (PDMS)), polybenzimidazole, polybenzoxazole, polyphenylenes, polyarylene ether ketones, polyperfluorocyclobutanes, polytetrafluoroethylene (PTFE), polyvinylidene fluoride copolymers and terpolymers, polyvinylidene chloride, polyvinyl fluoride, liquid crystalline polymers, polyaramids, polyphenylene oxide and mixtures thereof.;

[0036] The microporous polymer separator 16 may be a woven or nonwoven single layer or a multi-layer laminate manufactured by either a dry process or a wet process. In a dry process, a polymer film is stretched to create lithium ion-permeable holes between crystalline regions. In a wet process, a material is dissolved or otherwise removed from the polymer film, leaving lithium ion-permeable holes. In one example, for example, the polymer separator may be a single layer of the polyolefin. In another example, it may be a single layer of one or a blend of any of the polymers from which the polymer separator 16 may be formed (e.g., the polyolefin or one or more of the other polymers listed above for the separator 16). In certain embodiments, a nonwoven fabric orNonwoven fabric is preferred due to its random fiber orientation. As another example, multiple separate layers of similar or different polyolefins or other polymers for the separator 16 may be assembled to fabricate the microporous polymer separator 16. In one example, a separate layer of one or more of the polymers may be coated onto a separate layer of the polyolefin for the separator 16. Further, the polyolefin (and / or other polymer) layer and any other optional polymer layers may be included in the porous polymer separator 16 as a fibrous layer to assist in providing the microporous polymer separator 16 with suitable structural and porosity characteristics. A more complete discussion of single and multi-layer lithium-ion battery separators and the dry and wet processes that may be used to fabricate them can be found in P. Arora and Z.Zhang, “Battery Separators,” Chem. Rev., 104, 4424-4427 (2004).

[0037] Typically, separators have a thickness of about 25 micrometers.

[0038] At least one of the separator and the cathode is coated with a cation exchange membrane layer or a coating layer containing a single lithium ion conductor. The single lithium ion conductor can be a polymeric lithium salt or an inorganic ceramic with lithium ion-sized ionic point defects.The single lithium ion conductors may be any polyanion-lithium cation material, including, as non-limiting examples, polymers with anionic acid groups, for example, carboxyl groups, sulfonic acid groups, phosphoric and phosphonic acid groups, and boric acid groups with associated lithium cations, polymers with ammonium groups and associated lithium cations, and polymers functionalized with lithium bis(trifluoromethanesulfonyl)imide groups or similar groups; or an inorganic ceramic with ionic point defects of lithium ion size, for example, sulfide compounds in crystalline, amorphous, and partially crystalline forms, for example, a Li2S-P2S5 glass or glass-ceramic, lithium ion-conducting sulfide crystals, garnet oxides based on Li5a3Ta2O. 12, and lithium ion-conducting inorganic phosphate compounds. According to the invention, the single lithium ion conductor comprises a polymeric lithium salt, wherein the polymeric lithium salt is a polymer having a polysulfone backbone with pendant lithium bis(trifluoromethanesulfonyl)imide groups.

[0039] Some examples of specific polymeric anions with associated lithium cations are: (i) the lithium salts of polymers and copolymers of ethylenically unsaturated acids, for example acrylic acid, methacrylic acid, crotonic acid, α-ethacrylic acid, vinylacetic acid, acryloxypropionic acid, maleic acid and its monoesters, itaconic acid and its monoesters, fumaric acid and its monoesters, mesaconic acid and its monoesters, citraconic acid and its monoesters, 4-vinylbenzoic acid and anhydrides thereof, sulfopropyl acrylate, sulfoethyl acrylate, sulfoethyl methacrylate, styrenesulfonic acid, vinylsulfonic acid, vinylphosphonic acid, phosphoethyl acrylate, phosphonoethyl acrylate, phosphopropyl acrylate, phosphonopropyl acrylate, phosphoethyl methacrylate, phosphonoethyl methacrylate, phosphopropyl methacrylate and phosphonopropyl methacrylate and the like, including polyacrylic acid, polymethacrylic acid, Poly[ethylene-co-(maleic acid)], Poly[styrene-co-(maleic acid)], Poly[styrene-co-(acrylic acid)], Poly[vinylpyridine-co-(methacrylic acid)], Poly[(vinylidene chloride)-co-ethylene-co-(acrylic acid)],Poly[(methyl vinyl ether)-co-(maleic acid)], polyvinylbenzoic acid and poly(perfluorosulfonic acid), poly[(vinyl chloride)-co-(vinyl acetate)-co-(maleic acid)], poly[ethylene-co-(acrylic acid)], poly[(ethylene-co-(methacrylic acid)];, (ii) the lithium salts of carboxylated polyvinyl chloride; (iii) the lithium salts of carboxymethylcelluloses and lithium alginates; (iv) the lithium salts of polyundecylenic acid and copolymers of olefins and undecylenic acid; (v) the lithium salts of polymers prepared by acidification of a polymer followed by neutralisation with lithium cations, for example the lithium salts of maleated or fumerated polymers and monoesters thereof, for example maleated polyolefins, for example maleated polypropylene and maleated polyethylene, maleated ethylene-vinyl acetate copolymers, maleated ethylene-methyl acrylate copolymers, maleated ethylene-propylene copolymers, maleated styrene-ethylene-butene-styrene triblock copolymers, maleated polybutadiene and maleated ethylene-propylene-diene copolymers; (vi) the lithium salts of novolak epoxy resins; (vii) lithium salts of perfluorinated polysulfonic acids, for example, sulfonated tetrafluoroethylene-based fluoropolymer copolymers commercially available under the brand name NAFION® from DuPont; (viii) a polymer having a polysulfone backbone with pendant lithium bis(trifluoromethanesulfonyl)imide groups, and mixtures thereof.

[0040] The polymeric lithium salt may be dissolved or dispersed in a suitable organic solvent, for example N-methylpyrrolidone, or dispersed in an aqueous medium to prepare a coating composition.

[0041] Non-limiting examples of inorganic ceramic materials with lithium ion-sized ionic point defects include sulfide compounds in crystalline, amorphous, and partially crystalline forms, for example, a Li2S-P2S5 glass or glass-ceramic, especially one with 20-30% P2S5; Li2S-SiS2, especially with the addition of lithium silicate; Li2S-Ga2S3-GeS2, and lithium ion-conducting sulfide crystals (Thio-LISICON), for example, crystalline Li 3,25 Ge 0,25 P 0,75 S4; oxides, for example perovskite (La 3y Li 2 / 3-yTiO3; garnet oxides based on Li 7-x La3Zr 2-x Ta x O 12 , for example Li5La3Ta2O 12 and similar oxides in which lanthanum is replaced by barium or strontium (barium- or strontium-doped garnets), and lithium ion-conducting phosphate compounds, for example Li 1+x Al x Ge 2-x (PO4)3 and Li 1+x+y Ti 2-x Al x Si y (PO4) 3-y Inorganic single-lithium ion conductors are preferably used in fiber form. The inorganic single-ion conductors can also be used in particulate form instead of or in addition to fiber form.

[0042] Any film-forming polymer that is stable in a battery environment and compatible with the inorganic single-ion conductor can be used as a binder in a coating composition containing an inorganic single-ion conductor. Non-limiting examples of suitable binders that can be used in coating compositions containing an inorganic single-ion conductor include polyolefins, polysulfones, polyimides, and polyamides. The binder can first be mixed with the inorganic single-ion conductor, after which an organic solvent can be added to the mixture to produce a coating composition that can be applied to the cathode or to one or both surfaces of the separator. Binders with low moisture absorption capacity are preferred. The binder can be a thermosetting binder.

[0043] In various embodiments, organic single-ion conductors are preferred because they can prevent polysulfide transport not only through size exclusion but also through charge repulsion between the anionic acid groups and the anionic polysulfide ions. For batteries that will be exposed to high temperatures, inorganic single-ion conductors are preferred due to their thermal stability. Inorganic single-ion conductors may also be preferred due to their stability in the electrolyte solution.

[0044] The sulfur cathode can be manufactured by applying cathode material, for example by slot die coating, in a layer on a cathode current conductor, for example an aluminum foil, then coating the sulfur cathode side with the coating composition, for example by slot die coating, curtain coating, brushing, roller coating, spray coating, doctor blade coating, etc., and forming a coating layer on the cathode.

[0045] The coating composition can be easily applied to one side of the separator by slot die coating, curtain coating, brushing, roller coating, spray coating, knife coating, etc., or to both sides of the separator by dip coating. In a preferred embodiment, the coating layer is applied to the cathode side of the separator. That is, a separator having a coating on one side is arranged in a battery with the coated side facing the cathode.

[0046] Other coating components that may be included in the coating composition depend on the selected coating process. For example, in various embodiments, it may be desirable to include one or more co-solvents, dispersants, flow additives, or other additives to assist in dispersion, coating application, and film formation of the applied coating composition.

[0047] After application, the applied coating layer may be heated to assist evaporation of water or organic solvent, to promote film coalescence, or, in the case of a thermosetting binder, to cure the coating layer, as long as the separator or cathode is stable at the temperature to which it is heated, or a vacuum may be applied to promote evaporation of volatile compounds.

[0048] The coating layer, whether applied to the cathode or to the separator, can have a thickness of about 1 nanometer to about 15 micrometers. In various embodiments, the coating layer preferably has a thickness of about 10 nanometers, or about 15 nanometers, to about 1 micrometer, or to about 0.5 micrometers. If the coating layer is too thin, it will not sufficiently block the transmission of polysulfides through the coating layer. If the coating layer is too thick, it will adversely affect the conductivity of lithium ions.

[0049] The coating layer should be flexible enough so that it does not crack during assembly of the battery or during use in the battery.

[0050] Suitable electrolytes for lithium-sulfur or silicon-sulfur batteries include non-aqueous solutions of lithium salts. Non-limiting examples of suitable lithium salts include lithium bis(trifluoromethanesulfon)imide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(trifluorosulfonylimide), lithium trifluoromethanesulfonate, lithium fluoroalkylsulfonimides, lithium fluoroarylsulfonimides, lithium bis(oxalate borate), lithium tris(trifluoromethylsulfonimide)methide, lithium tetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate, lithium chloride, and mixtures thereof.

[0051] The lithium salt is dissolved in a non-aqueous solvent which can be selected from: ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, dipropyl carbonate, cyclopentanone, sulfolane, dimethyl sulfoxide, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, 1,2-diethoxymethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxyethane, methyl acetate, ethyl acetate, nitromethane, 1,3-propanesultone, γ-valerolactone, methyl isobutyryl acetate, 2-methoxyethyl acetate, 2-ethoxyethyl acetate, diethyl oxalate or an ionic liquid and mixtures of two or more of these solvents.

[0052] The electrolyte may further comprise one or more suitable additives, for example any of those disclosed in S. S. Zhang, "J. Power Sources", 162 (2006), 1379-1394 (available at www.sciencedirect.com), for example additives to increase the mobility of lithium ions.

[0053] When the lithium-sulfur or silicon-sulfur battery discharges, the coating layer containing the single-ion conductor slows, prevents, or at least partially prevents the diffusion of polysulfide compounds from the cathode to the outside when the coating layer is on the cathode, or the movement of polysulfide anions through the separator when the coating is on the separator. This results in improved cycling stability (capacity retention during repeated cycles of battery discharge and recharge). The coating with the single-ion conductor allows lithium ions to migrate through the separator and into the cathode, ensuring sustained satisfactory battery operation.

Claims

[1] A battery comprising a sulfur-containing cathode, an anode, and a separator between the cathode and the anode, wherein the cathode or the separator has a coating comprising a single lithium ion conductor, the single lithium ion conductor comprising a polymeric lithium salt, the polymeric lithium salt being a polymer having a polysulfone backbone with pendant lithium bis(trifluoromethanesulfonyl)imide groups. [2] The battery of claim 1, wherein the battery has a lithium-containing anode or a silicon-containing anode. [3] A device comprising a battery according to claim 1. [4] A method for improving the cycling stability of a battery having a sulfur-containing cathode, an anode, and a separator between the cathode and the anode, comprising applying a coating comprising a single lithium ion conductor to at least one of the cathode or the separator, wherein the single lithium ion conductor comprises a polymeric lithium salt, wherein the polymeric lithium salt is a polymer having a polysulfone backbone with pendant lithium bis(trifluoromethanesulfonyl)imide groups.

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